Crowder Environmental Associates, inc.
2905 Province Place, Piano, Texas 75075
TEL: 214/964-7661 FAX: 214/867-3617
Inspection Workshop
for
Volatile Organic Air Pollutants
Selected Readings
Prepared for:
USEPA, Region VIII
99918th Street, Suite 1300
Denver, Colorado 80202
February 1991
-------
Inspection Workshop
for
Volatile Organic Air Pollutants
Selected Readings
Prepared by:
Crowder Environmental Associates, Inc.
2905 Province Place
Piano, Texas 75075
Prepared for:
USEPA, Region VIII
99918th Street, Suite 1300
Denver, Colorado 80202
February 1991
-------
TABLE 1. RESPONSE FACTORS FOR TECO MODEL 580
PHOTOIONIZATION TYPE ORGANIC VAPOR ANALYZERS
10.0 ev Lamp
Compound lonization Potential Response Factor
-------
Table 2. RESPONSE FACTORS FOR THE HUN SYSTEMS, INC.
MODEL ISPI-101 PHOTOIONIZATION ANALYZER
Compound
Cc
Acetal
Carbon Disulfide
Carbon tetrachloride
Chloroform
Diketene
Perchloromethyl mercaptan
Toluene
Tetrachloroethane,1,1,2,2-
Trichloroethane,1,1,
Trichlorotr i fluoroethane
1,1,2-
ctual
entration
1000
5000
10000
1000
10000
500
1000
10000
1000
5000
10000
1000
5000
10000
5000
1000
1000
5000
10000
1000
5000
10000
5000
10000
Instrument
Concentration
925
7200
13200
1990
12900
784
1070
6070
756
2550
5250
148
318
460
103
1180
736
1170
1880
1020
6170
9430
155
430
Response
Factor
1.1
0.69
0.76
0.50
0.78
0.64
0.94
1.6
1.3
2.0
1.9
6.8
16.0
22.0
48.0
0.85
1.4
4.3
5.3
0.98
0.81
1.1
32.0
23.0
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Table 3. RESPONSE FACTORS FOR FOXBORO OVA-108 AND
BACHARACH TLV SNIFFER AT 10,000 ppmv RESPONSE
Compound
Acetic acid
Acetic ahydride
Acetone
Acetonitrile
Acetyl chloride
Acetylene
Acrylic acid
Acrylonitrile
Allene
Allyl alcohol
Amylene
Anisole
Benzene
Bromobenzene
Butadiene, 1,3-
Butane, N
Butanol, sec-
Butanol, tert
Butene, 1-
Butyl acetate
Butyl acrylate, N-
Butyl ether, N
Butyl ether, sec
Butylamine, N
Butylamine, sec
Butylamine, tert-
Butyrandehyde, N-
Butyronitrile
Carbon disulfide
Chloroacetaldehyde
Chlorobenzene
Chloroethane
Chloroform
Chloropropene, 1-
Chloropropene, 3-
Chlorotoluene, M-
Chlorotoluene, 0-
Response Factor
OVA-108
1.64
1.39
0.80
0.95
2.04
0.39
4.59
0.97
0.64
0.96
0.44
0.92
0.29
0.40
0.57
1.44 I
0.76
0.53
0.56
0.66
0.70
2.60
0.35
0.69
0.70
0.63
1.29
0.52
B
9.10
0.38
38
5
9
28
0.67
0.80
0.48
0.48
Response Factor
TLV Sniffer
15.60
5.88
1.22
1.18
2.72
B
B
3.49 I
15.00
X
1.03
3.91
1.07
1.19
10.90
4.11
1.25
2.17
5.84
1.38
2.57 I
3.58 I
1.15
2.02
1.56
1.95
2.30
1.47 I
3.92
5.07
0.88
3.90 P
B
0.87
1.24
0.91
1.06
Chlorotoluene, P-
0.56
1.17 I
-------
Table 3. RESPONSE FACTORS FOR FOXBORO OVA-108 AND
BACHARACH TLV SNIFFER AT 10,000 ppmv RESPONSE
Compound Response Factor Response Factor
OVA-108 TLV Sniffer
Crotonaldehyde 1.25 B
Cumene 1.87 B
Cyclohexane 0,47 0.70
Cyclohexanone 1.50 7.04
Cyclohexene 0.49 2.17
Cyclohexylamine 0.57 1.38
Diacetyl 1.54 3.28
Dichloro-l-propene,2,3- 0.75 1,75
Dichloroethane,!,!- 0.78 1,86
Dichloroethane,l,2- 0.95 2.15
Dichloroethylene,cisl,2- 1.27 1.63
Dichloroethylene,transl,2- 1.11 1.66
Dichloromethane 2.81 3.85
Dichloropropane,1,2- 1.03 1.54
Diisobutylene 0.35 1.41
Dimethoxy ethane,1,2- 1.22 1.52
Dimethylformamide,N,N- 4.19 5.29
Dimethylhydrazine 1,1- 1.03 2.70
Dioxane 1.48 1.31
Epichlorohydrin 1.69 2.03
Ethane 0.65 0.69 I
Ethanol 1.78 X
Ethoxy ethanol, 2- 1.55 1.82
Ethyl acetate 0.86 1.43
Ethyl acrylate 0.77 X
Ethyl chloroacetate 1.99 1.59
Ethyl ether 0.97 1.14
Ethylbenzene 0.73 4.74 D
Ethylene 0.71 1.56
Ethylene oxide 2.46 2.40
Ethylenediamine 1.73 3.26
Formic acid 14.20 B
Glycidol 6.88 5.55
Heptane 0.41 I 0-73
Hexane,N- 0.41 0.69
Hexene,!- 0.49 4.69 D
Hydroxyacetone 6.90 15.20
Isobutane 0.41 0.55
-------
Table 3. RESPONSE FACTORS FOR FOXBORO OVA-108 AND
BACHARACH TLV SNIFFER AT 10,000 ppmv RESPONSE
Compound Response Factor Response Factor
OVA-108 TLV Sniffer
Isobutylene 3.13 B
Isoprene 0.59 X
Isopropanol 0.91 1.39
Isopropyl acetate 0.71 1.31
Isopropyl chloride 0.68 0.98
Isovaleraldehyde 0.64 2.19 D
Mesityl oxide 1.09 3.14
Methacrolein 1.20 3.49 D
Methanol 4.39 P 2.01
Methoxy-ethano1,2- 2.25 3.13
Methyl acetate 1.74 1.85
Methyl acetylene 0.61 6.79
Methyl chloride 1.44 1.84
Methyl ethyl ketone 0.64 1.12
Methyl formate 3.11 1.94
Methyl methacrylate 0.99 2.42
Methyl-2-pentanol,4- 1.66 2.00
Methyl-2-pentone,4- 0.56 1.63
Methyl-3-butyn-2-ol,2 0.59 X
Methylcyclohexane 0.48 0.84
Methylcyclohexene 0.44 2.79
Methylstyrene,a- 13.90 B
Nitroethane 1.40 3.45
Nitromethane 3.52 7.60
Nitroopropane 1.05 2.02
Nonane-n 1.54 11.10
Octane 1.03 2.11
Pentane 0.52 0.83
Picoline,2- 0.43 1.18
Propane 0.55 I 0.60 P
Propionaldehyde 1.14 1.71
Proponic acid 1.30 5.08 D
Propyl alcohol 0.93 1.74
Propylbenzene,n- 0.51 B
Propylene 0.77 1.74 I
Propylene oxide 0.83 1.15
Pyridine 0.47 1.16
Styrene 4.22 B
-------
Table 3. RESPONSE FACTORS FOR FOXBORO OVA-108 AND
BACHARACH TLV SNIFFER AT 10,000 ppmv RESPONSE
Compound
Response Factor
OVA-108
Response Factor
TLV Sniffer
Tetrachloroethane,1,1,1,2
Tetrachloroethane,1,1,2,2
Tetrachloroethylene
Toluene
Trichloroethane,1,1,1-
Trichloroethane,1,1,2-
Trichloroethylene
Trichloropropane,1,2,3-
Triethylamine
Vinyl chloride
Vinylidene chloride
Xylene, p-
Xylene, m-
Xylene, 0-
4.83 D
7.89
2.97
0.39
0.80
1.25
0.95
0.96
0.51
0.84
1.12
2.12
0.40
0.43
6.91
25.40
B
2.68 D
2.40
3.69
3.93
99
48
06
2.41
7.87
5.87 D
1.40
1.
1.
1,
I Inverse Estimation Method
D Possible Outliers in Data
N Narrow Range of Data
X No Data Available
B 10,000 ppvm Response Unachievable
P Suspect Points Eliminated
-------
FUGITIVE VOC REGULATIONS
SIGNIFICANCE OF LEAKS
Fugitive emissions from thousands of individual components
in refineries and chemical plants are collectively significant.
TYPES OF REGULATIONS
Several sets of regulations have been Promulgated.
o NSPS Regulations
Subpart W - Synthetic Chemical Plants
Subpart GGG - Refineries
Subpart KKK - On-Shore Natural Gas
Subpart ODD - Polymer Plants
o NESHAPS Regulations
Subpart V - Fugitive Leaks
Subpart F - Vinyl Chloride
Subpart J - Benzene
TYPES OF REQUIREMENTS
Each NSPS and NESHAPS regulations has several types of requirements.
o Work Practice Standards
o Equipment Design
o Performance Limits
LEAK DETECTION AND REPAIR PROGRAMS
These are the main type of work practice standards and they
involve frequent monitoring of components with portable VOC
analyzers and other visual checks.
The portable VOC analyzers simply determine if there is or is
not a leak as defined in the regulations.
Due to compound-by-compound differences in instrument response
factors, the instrument reading is not a direct indication of
concentrat ion.
COMPARISON OF NSPS AND NESHAPS REGULATIONS
SIMILARITIES
o Leak Definition
o Screening Method
o Repair/Retest Procedures
o Recordkeeping and Reporting
o Components Subject to Regulations
DIFFERENCES
o Types of Exemptions
o Definition of Light and Heavy Liquids
o Component Labeling Requirements
-------
TYPES OF STANDARDS
WORK PRACTICE
o Leak Detection and Repair Programs
EQUIPMENT STANDARDS
o Equipment Specifications
o Design Specifications
PERFORMANCE STANDARDS
o No Detectable Emission Limits
VALVE SCREENING FREQUENCIES
GENERAL
o Monitor Monthly
o Skip to Quarterly Monitoring for EACH VALVE Not
Leaking for 2 Successive Months
ALTERNATIVE 1
o Notify Administrator
o Conduct Performance Test
o Screen All Valves Annually in a 1 Week Period
o >2% Valves Leaking is a Violation
ALTERNATIVE 2
o Notify Administrator
o Conduct Monthly Tests
o Option 1 - After 2 Successive Quarters with < 2% Leaking
Skip to Semi-Annual Monitoring
o Option 2 - After 5 Successive Quarters with < 2% Leaking
Skip to Annual Monitoring
o Revert to Monthly Monitoring When >2% of Valves Leaking
-------
INVENTORIES
CLOSED VENT SYSTEM AND CONTROL DEVICE DATA
COMPONENT DATA
o List of Identification Numbers
o List of Components Subject to the No Detectable Limit
o Dates of Compliance Tests
o Instrument Readings
o List of Equipment in Vacuum Service
o List of Difficult-to-Monitor Valves
o List of Unsafe-to-Monitor Valves
FACILITY DATA
o Design Capacity
o Equipment Not in VOC Service
RECORDKEEPING
TAG LEAKS
MAINTAIN LOGS FOR 2 YEARS
o Component's Identification Number
o Operator's Identification Number
o Instrument's Identification Number
o Dates Leak Detected
o Dates Repair Attempted
o Date of Successful Repair
o Expected Date of Repair is >15 Days
o Dates of Outages While Component Remained Unrepaired
o Repair Method Used
o Reason Repair Delayed
o >10,000 ppm Instrument Reading After Unsuccessful Repair
-------
OTHER RECORDS
CLOSED VENT SYSTEMS AND CONTROL DEVICES
o Schematics
o Specifications
o Piping and Instrumentation Drawings
o Monitoring Plan
o Non-operational Periods
o Start-up/Shut-down Dates
VALVES, UNSAFE-TO-MONITOR
o Identification Numbers
o Reasons Why Classified as Unsafe
o Monitoring Plan
VALVES, DIFFICULT-TO-MONITOR
o Identification Numbers
o Reasons Why Classified as Difficult-to-Monitor
o Monitoring Plan
EXEMPTIONS
o Design Capacities
o Feed Material Analyses
o Not-in-VOC Service Support Data
-------
NSPS INITIAL REPORTS
PROCESS UNIT "A"
o Number of Valves in Gas/Vapor or Light Liquid Service
o Number of Pumps in Light Liquid Service
o Number of Compressors
PROCESS UNITS "B" . . . "N"
o Number of Valves in Gas/Vapor or Light Liquid Service
o Number of Pumps in Light Liquid Service
o Number of Compressors
BENZENE/VINYL CHLORIDE INITIAL REPORTS
STATEMENT OF INTENT
PROCESS UNIT "A"
o Equipment Identification
o Equipment Type
o Percent VHAP
o State of VHAP
o Method of Compliance
PROCESS UNIT "B"..."N"
o Equipment Identification
o Equipment Type
o Percent VHAP
o State of VHAP
o Method of Compliance
SUBMISSION DATES
BENZENE/VINYL CHLORIDE REPORTING
INITIAL
SEMI-ANNUAL, Process Unit "A" . . . "N" (List for Each)
o Number of Valves Leaking
o Number of Valves Leaking That Were Not Repaired
o Number of Pumps Leaking
o Number of Pumps Leaking That Were Not Repaired
o Number of Compressors Leaking
o Number of Compressors Leaking That Were Not Repaired
o Shut-down Infeasibility Support Information
o Dates of Shut-downs
o Inventory Revision/Update
-------
INSPECTION PROCEDURES and TIME REQUIREMENTS
PRE-INSPECTION REVIEW (0.5 to 2.0 Hours)
o Initial Reports
o Semi-Annual Reports
o Notifications
o Previous Inspection Reports
o Plant Safety Equipment Guidelines
o Portable VOC Instrument Prechecks and
Calibration (Level 3 Inspections Only)
TRAVEL TO INSPECTION SITE (1 to 4 Hours)
PRE-INSPECTION MEETING (0.5 Hours)
o Inspection Scope
o Inspection Agenda
o Data and Information Considered Confidential by Source
o Semi-Annual Reports Received from Source
o Notifications Received from Source
REVIEW OF RECORDS (1-2 Hours)
o Monitoring Frequencies
o Extent of Time Repair
o Reasons for Delay of Repair
o Portable Instrument Calibrations, Calibration Precision
Tests, and Response Time Tests
OBSERVE COMPONENT SCREENING PROCEDURES (2-3 Hours)
o Observe Instrument Check-out/Start-up and Calibration
o Observe Screening of 20 to 50 Components
o Observe Several Difficult-to-Monitor Valve Locations
o Observe Several Unsafe-to-Monitor Valve Locations
o Confirm Proper Tagging
o Conduct Independent Screening Tests
(Level 3 Inspection Only)
CHECK COMPLIANCE WITH EQUIPMENT STANDARDS (0.5 to 1 Hour)
o Closed Sampling Lines
o Alarms
o Control Device Operating Conditions
POST-INSPECTION MEETING (0.5 Hours)
TRAVEL BACK TO AGENCY OFFICE (1 to 4 Hours)
EQUIPMENT MAINTENANCE (0.25 to 0.5 Hour)
o Clean and Store Safety Equipment
o Recharge and Store VOC Analyzers
(Level 3 Inspection Only)
-------
PORTABLE VOC INSTRUMENT PROBLEMS
WEAK BATTERIES
AIR INFILTRATION
CONTAMINATION AND GAS FLOW BLOCKAGE
POOR LEAK PLUME CAPTURE
GROSS CONTAMINATION
o Flame lonization Detectors - Flameout
o Photoionization Detectors - Optical Surface Deposits
o Catalytic Detectors - Sensor Volatilization
NOTE: ESSENTIALLY ALL INSTRUMENT PROBLEMS RESULTS
IN UNDETECTED LEAKS
PORTABLE VOC EQUIPMENT LIST
FLAME IONIZATION DETECTOR
with,
o Spare Battery
o Spare Charger
o Spare Probe
o Particulate Filters
o Precision Rotameter
o 5-Liter Tedlar Bag
o Calibration Gas Kit
o Cylinder Mounting Equipment
PHOTOIONIZATION ANALYZER
with,
o Spare Lamp
o Spare Intrinsically Safe Battery
o Spare Charger
o Soap Bubble Flow Meter
o 5-Liter Tedlar Bags
o Calibration Gas Kit
o Lamp Cleaning Compound
o Lamp Cleaning Cloth
CATALYTIC COMBUSTION ANALYZER
with,
o Spare Sensor
o Spare Intrinsically Safe Battery
o Spare Recharger
o Spare Particulate Filters
o Spare Rotameter
LABORATORY/SHOP FACILITIES
o Ventilated Hoods
o Cylinder Racks
o Bench Space
-------
SAFETY EQUIPMENT - VOC INSPECTIONS
(OTHER EQUIPMENT MAY ALSO BE NEEDED
IN SPECIAL CIRCUMSTANCES)
TRIPLE GAS DOSIMETER
RESPIRATORS
o Full- and Half-Face Respirators
(Check with Agency Safety Officer)
o Respirator Carrying Pouches
o Spare Cartridges or Canisters
o Emergency Respirators
EYEWEAR
SAFETY SHOES
(Several Types of Shoes May be Required)
EXPLOSION PROOF FLASHLIGHT
EAR PROTECTION
PROTECTIVE CLOTHING
-------
Note from the Editor
The information contained in this document has been
assembled solely for the purpose of general instruction in
the emissions, control and inspection of VOC sources.
Nothing in this document should be construed as
representing official policy or guidance. Readers are
advised to contact either their state agency or the USEPA
regional office for official policies and rules and their
interpretation.
-------
Table of Contents
Page
VOC Properties 1
Emission Measuring Techniques 35
Emission Inventories 79
Concepts of VOC Control 95
Control by Incineration 115
Control by Adsorption 149
Control by Condensation 189
Surface Coating Fundamentals 199
Surface Coating Calculations 233
Dry Cleaning 249
Degreasing 271
Petroleum Refining 325
Petroleum Product Storage and Distribution 357
-------
voc
Properties
001
-------
Organic Chemistry Review
Lesson Goal and Objectives
Goal
To familiarize you with the concepts and terminology of organic chemistry that will
prepare you for the technical literature associated with the measurement of organic
compounds.
Objectives
Upon completing this lesson, you should be able to:
1. classify organic compounds into the following groups:
a. aliphatic hydrocarbons (alkanes, alkenes, alkynes)
b. aromatic hydrocarbons
c. oxygenated compounds (ethanols, ethers, ketones, aldehydes, esters, acids)
d. amines, mercaptans
2. describe the difference between a straight chain hydrocarbon compound and
an aromatic hydrocarbon compound.
3. recognize the structure of problem organic pollutants, such as dioxin, benzo
alpha-pyrene, and polychlorinated biphenyls, that are frequently discussed in
the popular and technical literature.
4. identify the importance of chemical properties of organic compounds, such as
reactivity, for developing air pollution control regulations.
Introduction
Organic chemistry is the study of carbon compounds. Carbon has the property of
being able to bind with itself to form long chains, rings, and other chemical struc-
tures. Carbon can also bind with other elements to yield an almost endless number
of compounds. This combining power, and the number of compounds produced as
a result, makes organic chemistry so important to modem society.
Although many organic compounds occur hi natural products, others have been
made solely in the laboratory. Modem technology can produce large quantities of
naturally occuring compounds and new, synthesized compounds for a large number
of useful purposes. This has resulted hi the introduction of materials into the
environment which may sometimes have other than beneficial effects. The inability
2-1
002
-------
of the environment to accommodate large quantities of organic compounds in the
atmosphere can result in the production of smog. Also, a simple compound pro-
duced in quantity for plastics manufacturing may be discovered to cause toxic
effects in the people handling it.
The importance of measuring organic compound emissions to the environment
has become clear over the past decade. A better understanding of their role in
photochemical oxidant generation and an increasing awareness of their direct
effects on human health has necessitated the improvement and standardization of
monitoring techniques. Because of the large number of different organic species,
finding a "best" measurement method has been difficult; some methods work better
for one class of compounds than for another. To understand the applicability and
limitations of the various measurement techniques, we must first review some of the
basic terminology of organic chemistry. This lesson will review the classification
schemes of this field and will discuss some important chemical concepts associated
with it.
The Combining Power of Carbon
Elements combine with other elements to form compounds. The compounds pro-
duced depend principally on the electronic configurations of the elements. Carbon,
for example, is composed of a positively charged central nucleus and twelve
negatively charged electrons outside of it. Four of these electrons are available in
carbon to form chemical bonds. Let us take an example of one of the simplest
organic compounds, methane, which is composed of one carbon and four hydrogen
atoms and is given the symbol, CH*. The left side of Figure 2-1, gives a representa-
tion of the carbon atom, and its four available electrons. Hydrogen, also shown in
the figure, differs from carbon since it has only one electron available for bonding.
Electrons
available
for
bonding
Nucleus /£
Figure 2-1. Carbon and hydrogen atoms.
To form the chemical bonds necessary to make methane, the hydrogen atoms must
first come close to the carbon atom. When this happens, the hydrogen nuclei and
the carbon nucleus will share electrons between each other. This is shown for
2-2
003
-------
methane schematically in Figure 2-2a. The bonds, called covalent bonds, are
actually an electronic arrangement between the two types of elements. The positive
charge of a hydrogen nucleus would normally be repelled by a positive charge in a
carbon nucleus. However, the two negatively charged electrons, one from the
hydrogen and one from the carbon, mediate between the two nuclei to contribute
to the glue of the chemical bond. The negative charge of the shared electron pair
attracts both nuclei and holds them together in a bond (Figure 2-2b).
Positive
charge
Negative
charges
a. Electron sharing
b. Balancing of charges
Figure 2-2. Methane.
Methane can be represented in a number of ways, as can all organic compounds.
Figure 2-3 shows the common symbol, the electron-dot formula, a figure with stick
bonds representing the electron pair, and the actual three-dimensional structure of
methane.
CH4
Common
symbol
H
H2C2H
0«
H
Electron
dot formula
H
H-C-H
H
Stick
bonds
Three-dimensional representation
Figure 2-3. Representations for methane.
2-3
004
-------
Straight Chain Hydrocarbons
One of the most important properties of carbon is it's ability to form covalent
bonds with other carbon atoms. As a result, chains of carbon can be produced.
These chains can be either straight or branched, as shown in Figure 2-4 for a
number of hydrocarbons (compounds composed of just carbon and hydrogen).
Isooctane is a branched form of the straight octane chain shown.
H H
I I
H—C —C —H Ethane
I I
H H
H H
• o «o
HSC:CSH
o«I o» V
Hi H \ shar
I P«
Shared electron
pair between two
carbon atoms
Shared electron
pair between
carbon atom and
hydrogen atom
H
H
H-C-H H-C-H
v
1
Z— — C— (
1
H
i
: — C-H
.H H I
i
H H H
I I I
H — C — C — C — H Propane
III
H H H
ti
I
HHHHHHHH H-C
1 I I I I I I I I
H-C-C-C-C-C-C-C-C-H Octane H
I I I I I I I I H-C-H
HHHHHHHH j
H
Isooctane (branched chain)
Figure 2-4. Bonding between carbon atoms—straight and branched chains.
The number of possibilities associated with branching results in different com-
pounds with identical elements, but with different structures. These compounds are
called isomers of each other. In Figure 2-4, octane and isooctane are isomers. A
simpler example is that of the isomers of butane, C4H10 (Figure 2-5).
H H H H
till
H-C-C-C-C-H
I I I I
H H H H
H
H-C-H
H
H
H-C C — C-H
H
H
H
Normal butane
Isobutane
Figure 2-5. Isomers of butane.
2-4
005
-------
Another special property of carbon is that it can share more than one electron
with another element. In other words, a carbon can form either single or multiple
bonds. The simplest example is that of the double-bonded compound, ethylene,
(Figure 2-6).
H H
HSC::C:H
Ethylene
t
Electron dot
representation
of a double bond
H
H
H
\
H
Stick bond
representation
of a double bond
Figure 2-6. The double bond of ethylene.
Acetylene, H—C>*C—H, is an example of a triple-bonded hydrocarbon. Carbon
can also form multiple bonds with other elements such as oxygen, sulfur, and
nitrogen. Double-bonded compounds are quite important reactants in the genera-
tion sequences for photochemical oxidants. The double bond provides a reactive
site where the molecule can be broken apart or formed into other species.
Ring Structures
Another special property of carbon is the ability of carbon chains to turn back on
themselves to form rings. Rings may be either singly or multiply-bonded. For
example, consider the ring structures of cyclohexane and benzene (Figure 2-7).
H H
a. Cyclohexane
b. Benzene
H
H
c. Schematic of
delocalized
electron
Figure 2-7. Ring structures.
Cyclohexane contains two less hydrogen atoms than its corresponding straight chain
hydrocarbon containing the same number of carbon atoms. Benzene, on the other
hand, contains three double bonds and even fewer hydrogens. As shown in the
figure, the double bonds can be thought of as shifting between different carbon
2-5
006
-------
atoms. In actuality, the electrons associated with the bonds are spread evenly
around the ring as shown in Figure 2-7c. This "delocalization" of electrons creates
a very stable structure with very special properties. Ring compounds containing
delocalized electrons are classified in a group known as aromatic compounds
because many of them have a pronounced odor. The properties of aromatic com-
pounds can vary quite considerably. For example, because benzene has been found
to be carcinogenic, NESHAPs are currently being developed for its control. On the
other hand, toluene, which has the structure in Figure 2-8
CH,
Figure 2-8. Toluene.
has been found not to be a toxic material and will not be regulated under
NESHAPs. The xylencs (Figure 2-9) are, however, still being evaluated.
CH,
CH,
H'
H
Onho-xylene
Para-xylcne
Figure 2-9. Xylene.
Benzene rings can also be combined to each other. One way of doing this is to
join two carbons of two benzene rings by a single bond to obtain a biphenyl
(Figure 2-10). (The term phenyl is often used to refer to benzene rings.)
H
Figure 2-10. Biphenyl.
2-6
007
-------
Another way to combine benzene rings is to produce networks of ring structures
such as that shown in Figure 2-11.
Figure 2-11. Benzofelpyrene (BaP).
(Note: It is common practice not to show the hydrogen atoms in the aromatic
structures.) These are called polynuclear aromatics (PNA—an older acronym), or
polycyclic aromatic hydrocarbons (PAHs—acronym currently popular). The elec-
trons in such structures are delocalized as they are in benzene. Some of these com-
pounds can contribute to the formation of cancer.
Hydrocarbons are commonly divided into two major groups, aliphatic hydro-
carbons and aromatic hydrocarbons. Compounds having an open-chain structure
are known as aliphatic compounds and are further subdivided into alkanes or par-
affinic hydrocarbons (single-bonded carbon compounds), alkenes or olefins
(hydrocarbons containing a double bond between two carbons), and the alkynes or
acetylenes (hydrocarbons containing a carbon-carbon triple bond). These classifica-
tions are summarized in Figure 2-12.
1
Alkanes
CH«
(methane)
Hydrocarbons
I
1
Aliphatic
1 1
Alkenes Alkynes
H « H-C-C-H
Nc-c^
„/ '\,
1
Aromati
H
T^
H
H
Benzene
Ethylene
Figure 2-12. Classification of hydrocarbons with examples.
2-7
008
-------
Ring compounds such as cyclohexane are classified in a different category known as
alicyclics.
The nomenclature associated with aliphatic compounds forms the basis for
naming more complicated materials. For example, prefixes have been established
for aliphatics, based on the number of carbon atoms they contain (Table 2-1).
Table 2-1. Prefixes for aliphatics.
Prefix
mcth-
eth-
prop-
but-
pent-
hex-
hepc-
oct-
Number of carbon atoms
1
2
3
4
5
6
7
8
Examples
methane
ethylene
propane
butane
pentyne
cyclohexane
heptane
octane
For further information on standard nomenclature systems for organic compounds,
see IUPAC 1960.
Air pollution programs that address the control and measurement of organic
compounds have also developed a number of terms and acronyms which appear in
the literature. Among these are:
HC Hydrocarbon
THC Total Hydrocarbon—A term applied to measurements that report the
total amount of hydrocarbons in the sample.
NMHC Nonmethane Hydrocarbons—A term applied to measurements that
report the amount of hydrocarbons, excluding methane. This acronym
has been popular since methane is not regarded as a precursor to the
generation of photochemical smog.
Unfortunately, many documents and publications have misapplied these defini-
tions. For example, one such document has stated: "for the purposes of this report,
the term hydrocarbon sometimes refers to other organic materials also." This is
clearly incorrect in terms of scientific practice and a more concerted effort has
been made in current programs to correctly identify the larger class of organic
compounds which are regulated. This has led to another set of definitions and
acronyms including:
TGNMO Total Gaseous Nonmethane Organics—The total measure of gaseous
organic compounds in a sample, excluding methane.
NMOC Nonmethane Organic Compound—A measure of organic compounds
in a sample, excluding methane.
VOC Volatile Organic Compound—Any organic compound that, when
released into the atmosphere, can remain long enough to participate
in photochemical reactions. Almost all organics that can be con-
sidered VOCs have vapor pressures greater than 0.1 mm Hg at 20 °C
and 760 mm Hg; a typical regulatory definition.
2-8
009
-------
The Classification of Organic Compounds
The study of organic chemistry would be simple indeed if it incorporated only com-
pounds composed of carbon and hydrogen. Instead, other elements and groups of
elements can be attached to hydrocarbon chains and rings to provide wide-ranging
types of compounds. Organic chemists talk about these compounds by using a
short-hand notation.
First, hydrocarbons that join to other elements or groups of elements are often
called radicals. For example, when a group consisting of oxygen and hydrogen
attaches to a single carbon atom to form methyl alcohol, CHS —OH. Figure 2-13
represents the methyl radical.
H
I
H —C— or CHS— is the methyl radical
H
Figure 2-13. Methyl radicals.
(The dash, —, corresponds to the covalent bond of the stick figures.) In ethyl
alcohol, CHsCHt—OH. the hydrocarbon group CH,CHS— is called the ethyl
radical.
Secondly, the elements or groups of elements attached to the hydrocarbon
radicals are known as functional groups. Some examples of functional groups are
the —OH group which is characteristic of organic alcohols, the — NHS group for
amines, the —SH group for mercaptans, and — Cl for organic chlorides. The func-
tional groups located on a hydrocarbon chain or ring determine the principle
chemical properties of the molecule. For this reason the study of organic chemistry
is often divided into a series of studies of compounds classified by their functional
group. When a discussion centers around the properties of the functional group
and not of the hydrocarbon radical, the radical is often merely represented by the
symbol R— (the dash again stands for a bond). The symbol R—OH or ROH, thus
stands as a general expression for alcohols.
We will discuss a number of these classes in this lesson. Of primary importance
to the environmental scientist are the classes associated with compounds that con-
tain oxygen, chlorine, nitrogen, or sulfur.
2-10
010
-------
Organic Compounds Containing Oxygen
Let us examine first, the functional groups associated with the oxygen molecule.
These are:
Group Compound class
-O-H Alcohols
— O— Ethers
O
| Aldehydes
-C-H
O
| Ketones
-C-
O
| Organic acids
_C-0-H
9 Esters
-C-O-
Oxygen has the property of being able to share two electrons with other elements.
(From the first part of this lesson, we have seen that carbon will share four elec-
trons and hydrogen shares one electron.) Alcohols are composed of an —OH
group, where one electron is shared with a hydrogen and the other with a carbon.
Common alcohols are shown in Figure 2-14.
H
H » H O
H:C:OSH H-C-C-O-H CH,-C-CH, CHS-CH,-CH,-O-H
H i i H
Methyl alcohol Ethyl alcohol Isopropyl alcohol n propyl alcohol
(isopropanol)
Figure 2-14. Common alcohols.
2-11
Oil
-------
Aromatic alcohols can also be made, and are called phenols (Figure 2-15). Phenols
tend to behave more like acids than alcohols because of the properties of the
benzene ring.
OH
OH
CH,
H
CH,
Phenol
Ortho-cresol
(o-cresol)
Meta-crcsol
(m-cresol)
Figure 2-15. Phenol*.
Ethers form a class of compounds where the oxygen atom shares each of its elec-
trons with a different carbon atom. They have the general formula R—O—R,
where the radicals, R, may be different. Diethyl ether, CH,CH,—O-CH,CH,, is
an ether well known as an anesthetic. A special group of ethers known as cyclic
ethers are important in the plastics industry for making epoxides and other com-
pounds. Two compounds representative of this group are ethylene oxide and
propylene oxide (Figure 2-16).
GHt-CHt
O
Ethylene oxide
CHs-CH-CHt
Propylene oxide
Figure 2-16. Cyclic ethers.
Aldehydes compose a group of compounds that contribute significantly to the
generation of photochemical oxidants. By being either emitted into the atmosphere
or produced in the oxidant reaction sequences, aldehydes provide numerous
reaction pathways for the generation of photochemical oxidants. The aldehyde
group is composed of an oxygen atom sharing two electrons hi a double bond with
a carbon atom, with a hydrogen atom sharing an additional electron.
O O
R:CSH or R-C-H
2-12
012
-------
o
The simplest aldehyde is formaldehyde, H—C—H, a compound which has caused
some problem in urea-formaldehyde foam insulation products. A methyl radical
attached to the aldehyde functional group gives acetaldehyde or ethanol
(Figure 2-17). A more complicated aldehyde, acrolein, is found in photochemical
smog and is quite reactive.
O H H O
I \ I I
H,C-C-H C = C-C-H
H
Acetaldehyde Acrolein
Figure 2-17. Acetaldehyde and acrolein.
Ketones are widely used as solvents in industry. Acetone, the simplest ketone,
characterizes this classification, where a carbon double-bonded to an oxygen atom
is bonded with two other carbons (Figure 2-18).
O O O
I I I
R-C-R CH,-C-CHS CH,-C-CH,-CH,
Ketone representation Acetone Methyl ethyl ketone
(MEK)
Figure 2-18. Ketones.
Methyl ethyl ketone is widely used as a solvent in the coatings industry and is
popularly known as MEK. The ketones differ from the aldehydes by the replace-
ment of the aldehyde hydrogen with a carbon group. Ketones are also reactive and
contribute to smog generation.
Some other oxygen-containing compounds are the organic acids, esters, and acid
anhydrides. Acids have the structure shown in Figure 2-19a and are often
represented by the form RCOOH. Acetic acid, found in vinegar, has the structure
shown in 2-19b. Another type of acid, the peroxyatids, have an extra oxygen to
give the form in 2-19c. The peroxyacids are generated in photochemical smog and
are extremely reactive, being able to break apart and initiate chain reactions.
O O O
I 1 I
R-C-O-H CH,-C-OH R_c-O-O-H
a. Acids b. Acetic acid c. Peroxyacids
Figure 2-19. Acids.
2-13
013
-------
Acid anhydrides are derivatives of organic acids. Basically, they are a combina-
tion of two acids with the removal of a water molecule (hence the term anhydride).
They have the structure shown in Figure 2-20a.
O O O
\/\/
O O C C
II II
R-C-O—C-R C—C
I I
H H
a. Representation of an b. Maleic anhydride
acid anhydride
Figure 2-20. Acid anhydrides.
Maleic anhydride (Figure 2-20b) is the special case of a cyclic anhydride used in
the production of chemicals and plastics. It may have toxic effects.
Lastly, another type of derivative of organic acids is the ester (Figure 2-21) often
represented by RCOOR.
Here the hydrogen of the acid is replaced by a hydrocarbon radical. These com-
pounds are generally sweet smelling. They are generally formed by reacting acids
with alcohols.
O
R_C-O-R
Figure 2-21. Ester.
2-14
014
-------
Organic Compounds Containing Chlorine
Organic compounds containing chlorine are used widely in industry as solvents and
as starting compounds for producing other chemicals. Unfortunately, many of
them may cause serious environmental problems. In addition to contributing to
lexicological problems, some compounds in this class have been implicated in the
problem of the depletion of the stratospheric ozone layer. Although many of the
compounds do not react in the photochemical oxidant cycles, the Environmental
Protection Agency recommends that emissions of these compounds be reduced
because of their possible toxic effects. Figure 2-21 illustrates some of the organic
chlorides which are currently of concern to the EPA.
H
C1-C-C1
H
Methylene
chloride
H H
Chlorides of methane and ethane
H Cl
Cl- C -Cl
Cl
Chloroform
Cl- C -Cl
Cl
Carbon
tetrachloride
H Cl
I I
H-C-C-C1
I I
H Cl
Methyl chloroform
(1.1,1 • crichloroethane)
H Cl
Chlorides of ethylene
Cl Cl
H Cl
Cl Cl
H-C = C-C1 H-C=C-C1 H-C = C-H C1-C=C-C1 C1-C = C-C1
Trichloroethylene Perchloroethylene
Vinyl chloride
(chloroethene)
Vinylidene
chloride
Ethylene
dichloridc
Other double-bonded chlorides
H H H H Cl H
III III
H-C=C-C-Cl H-C = C-C = C
H
Allyl chloride CKloroprene
Chlorides of benzene
CH,-C1 Cl
Cl H H Cl
H
Chloro benzene
H
H Cl
Benzylchloride p-dichlorobenzene
Cl H H Cl
Example of a
polychlorinated biphenyl
(PCB)
Figure 2-21. Organic chlorides or chlorocarbon.
2-16
015
-------
Compounds that contain combinations of carbon, hydrogen, oxygen, and
chlorine can also be prepared. Figure 2-22 presents examples of some which are of
serious concern.
O
I
C1-C-C1
Phosgene
CH,-CH-CHt-Cl
O
Epichiorohydrin
Example of a
dioxin (TCDD)
2.3.7,8 tetrachlorodibenzo-p-dioxin
figure 2-22. Compounds containing both oxygen and chlorine.
Organic Compounds Containing Nitrogen
Organic compounds that contain nitrogen constitute another important class of
substances for the environmental scientist. The organic nitrates are end products in
the photochemical oxidant reaction sequences. Amines are odorous materials and
have often been the subject of nuisance complaints. Other combinations of
nitrogen with carbon, oxygen, and hydrocarbon result in chemicals which may be
toxic.
Nitrogen has the capability of sharing either three or five electrons with other
atoms. The simplest nitrogen compounds are the amines. These compounds share
three electrons with either carbon or hydrogen, having the general structures
illustrated in Figure 2-23.
H
R_N-H
Primary
amine
R
R_N_H or
Secondary
amine
Figure 2-23. Amines.
R
R-N-R
Tertiary
amine
Methyl amine, CHS —NH, is an example of a primary amine. The organic nitrites
also have a nitrogen that shares three electrons, but these are shared with oxygen
atoms instead of carbon and hydrogen: R—O—N = O.
The more complicated nitrogen compounds are those where the nitrogen atom
shares five electrons with other atoms. The organic nitro compounds are an
example here: R —NO,. Other compounds in this group are the nitrates:
R-ONO,. Nitroethane, CH5—CH,—NO, and ethyl nitrate, CH,-CH, —ONO,
2-17
016
-------
are materials formed in photochemical smog. One quite active group of compound
O
i
called peroxyacteyl nitrates (PAN), R,— C — O —ONOj, is responsible for many of
the adverse effects of photochemical smog.
Organic Compounds Containing Sulfur
Kraft pulp mills produce a large number of by-product chemicals in the paper-
making process. The sodium sulfide used in these operations reacts with the
organic matter in wood chips to produce organic compounds that contain sulfur.
One group of these, the mercaptans, have the structure R—SH, which is similar to
that of alcohols. Methyl mercaptan, CHS—SH, has a distinctive, unpleasant odor
at very low concentration levels. Dimethyl sulfide CHS—S—CHS also is a
malodorous product of this process. These compounds cause more of a nuisance
problem than a problem to public health.
Organic Chemistry—Reactivity
Organic compounds exhibit large differences in their ability to react with other
chemicals. For example, the double-bonded hydrocarbons will be more reactive
than the single-bonded hydrocarbons. Aldehydes will readily participate in the
photochemical oxidant sequences; aromatic hydrocarbons will not. However,
reactivity in the atmosphere is not the only concern of the environmental scientist.
The toxic effects of organic chemicals or the nuisance problem of odorous
materials also call for control of atmospheric emissions.
An early policy for emission control of organic compounds was that developed by
the State of California, known as Rule 66. This was based on the differences of
reactivity of compounds with sunlight. In these so-called "photochemical
reactions," light energy interacts with a molecule to cause it to dissociate and pro-
duce free radicals. Look at this example of an aldehyde (Figure 2-24).
O O
I I
R-CH + light - R-+-CH
Figure 2-24. Free radical generation.
2-18
017
-------
Note that the products of this reaction have unshared electrons. These materials
are known as free radicals. They are extremely.reactive and will attack other com-
pounds so that they can share their electrons again. Complicated sequences of
reactions involving free radicals are involved in the development of photochemical
smog. Rule 66 attempted to control the emission of compounds that react readily
in this process. The rule essentially required industry to replace reactive compounds
with less reactive compounds.
Although Rule 66 had some validity, it was not very effective in reducing
ambient oxidant levels. The replacement compounds may not have been as
reactive, but they were found to react with sunlight nevertheless; at a later time
and at a location more distant from the area of the emission. In addition to this,
EPA viewed the increased emissions of "nonreacrive" chlorinated hydrocarbons used
as replacement materials, as a threat to the stratospheric ozone. Other compounds
with less reactivity were also suspected of having carcinogenic, mutagenic, or
teratogenic effects on humans.
As a result of these problems, EPA adopted a policy of "positive emissions reduc-
tion." This EPA reactivity policy expressed in the Federal Register of July 8, 1977,
40 FR S5314, called for the reduction of organic emissions by the use of new
technological processes or the application of control equipment. This policy has
been incorporated in State Implementation Plans designed to bring ozone non-
attainment areas into attainment status and has been extended to the New Source
Performance Standards established for emission sources of organic compounds.
The policy of emissions reduction necessitates emissions monitoring. Progress in
controlling toxic emissions or precursors to ozone formation is monitored by a
variety of analytical methods. Because of the large difference in organic chemicals,
methods often have to be designed for specific groups of compounds. Some
methods, such as gas chromatography, can give the general information necessary
for monitoring overall emissions. In subsequent lessons we will be examining a
number of monitoring techniques and their application to the many groups of
organic chemicals discussed here.
2-19
018
-------
PHOTOCHEMICAL
OXIDANTS
Ozone
•» ,
o+
. ,..
•0. :Q: _:0. ,0
Peroxyacylnitrates
PAN PBzN
0 0
It
CH3COON02
fJTCOON02
IIIIIIIIIIIIIIIIIIIIIilllllllllllllllllllllllllllllllllllllllllllllllllllE
FORMALDEHYDE
H
H
C=0
• ACROLEIN
CH2CHCHO
IlilllllllHIIIllllllllllllllllllllllllllllllllIlllllllllllIlllllllllIH!!
3000 A
5000 A
A____
1
7000 A
019
-------
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
"PHOTOSTATIONARY STATE"
• NO + 03 - >N02 + 02 (4)
• NO2 + hv - ^NO + ()• (5)
" 0- + 02+ M-M>3 + M (6)
Illllllllllllllllllillllllllllllllllllllllllllllllllllilllllllllilllllll
o
2900 - 3500 A (5a)
NO2+ Kv— >NO2* - ^NO + (V D,
Singlet
Oxygen
3500 - 4300 A (5b)
NO2+ hv— >NO2* - >NO + O(3p)
Triplet
Oxygen
22Kcal>O(3p)
020
-------
(6)
N-'H
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIE!
IlllllUllllimillllllllllllllllllllllllllllllllllllllllllllllllllllllimi
(7)
New
• NO + Organic > Organic + NO2
021
-------
NET [03]
INCREASED
Ozone not destroyed
NO + 03J^N02 + 02
• New organic species are formed
which continue to reduce [NO]
illlllllllllllllllllllllllllllllllllllllllllllllllllllllHIIIIIIIIIIIIIIIH
PEROXY RADICALS
R02*
(7a)
• NO + RO2» - >RO»+ NO2
IIJIIIIIIIIIIIIIIIIIIIIillllllllllllllllllllllllllllHIIIIIIIIIIIIIIIIIIIII
PEROXY RADICAL FORMATION
STEP 1: Hydroxyl Radical Formation
O«+H2O - >2OH» (8)
or
R0«+02 - >H02« RCHO (9)
HO2»+NO - ^NO2 +OH- (10)
022
-------
PEROXY RADICAL FORMATION
STEP 2: Radical Formation
• RH + OH- + O.
R'O.
RCHO + O2
(11)
R"CHO
(12)
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII1IIIIIIIIU1
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiimiiiiiiiiiiiiiiiiiiiiiiiniiiimiii
(4) O« + 0
(2) NO + Organic + O3—>NO2
023
-------
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiii
OLEFINS
/\
AROMATICS
PARAFFINS
^
ACETYLENES
Least
Reactive
'lllllllllllllllllimilllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
WITH ATOMIC OXYGEN
Paraffins
RH + o-
Aromatics
\S\ + 0;
.R
[of + o-
R. •«- OH*
f Peroxides
.Acids
k Alcohols
> Attack either rinc or chain
024
-------
WITH ATOMIC OXYGEN
Olefin
R2
which yields
R.-C» and R4-o
4 '
etc-
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIHIIH:
l^nWITHOH* RADICALS
Paraffins
RH + OH- ^ R-+ H20
Aromatics
t*U f*U f*Uf*U
,cn2CH3 ^-tm.n3
+ OH-—^^ + H20
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIH
Rxn WITH OH« RADICAL
Olefins
CH3CH = CH2 + OH-
or
CH3CHCH2
OH
025
-------
mimimmiiiiiiimiiiiiiiiimiiiiimimiiiiiiiiiiimiiimmiii!
• NBS SPECIAL PUBLICATION 513
"Reaction Rate and Photochemical Data
for Atmospheric Chemistry -1977"
• EPA - 600/3-77-110, October 1977
"Measurement off Rate Constants of
Importance in Smog"
• John H. Seinfeld. Air Pollution - Physical
and Chemical Fundamentals.
McGraw-Hill, 1975.
lillllllllllllllllllllllllllllllllllllllllllllllllllllllllimiilllllllllH
ENVIRONMENTAL
RESEARCH LABORATORY
026
-------
HYDROCARBON COMPONENTS
OF ATMOSPHERE
Paraffins
Aromatics
Olefins
Acetylenes
Los Angeles
53%
20%
16%
10%
Kenosha, Wise.
60%
30%
10%
neg
iiiiiiiiimiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiimi^
MOBILE SOURCE CONTRIBUTION
Leaded Gas Unleaded Gas
38% 36% Paraffins
13% 21% Aromatics
36% 31% Olefins
13% 1O% Acetylenes
miiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiimiiiiiiiiiiiiiii
• EPA-600/3-77-109 a & b
"Effect of Hydrocarbon
Composition on Oxidant-
Hydrocarbon Relationships"
PHASE I - Mobile Sources
PHASE II - Mobile and
Stationary Sources
027
-------
OZONE PRODUCTION
DEPENDS ON:
Organics involved
Light intensity and duration
Temperature
minium
• 6 HR IRRADIATION
Max [O3] results at -^
between 12. to
10 HR IRRADIATION
HC
ratio
Max |O31 results at ~~ ratio
028
-------
OZONE VS INITIAL PRECURSOR LCVCU - MODELED RESULTS
11
.24-
.22-
.20-
.14-
.12-
.10-
.06-
.04-
.02-
DWrnat L((M Ut««»lt»
(0700-X«00)
0.2 0.4 0.«
OJ 1.0 1.2 1.4 1.6 l.»
NMHC, ppmC
Vt)C
iiiimiuinimiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiuiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiuitiii!
EKMA DOCUMENTS
EPA- 450/2-774)21 a & b
November 1977
"Use, Limitations, and Technical
Basis of Procedures for
Quantifying Relationships between
Photochemical Oxidants and
Precursors"
i EPA-450/3-77-022 a, b, c
"Relation of Oxidant Levels to
Precursor Emissions and
Meteorological Features'*
VOL. I: Analysis and Findings
VOL. II: Review of Available
Research Results and
Monitoring Data
VOL. Ill: Appendices
029
-------
• EPA 600/3-77- 001 a & b
"International Conference
on Photochemical
Pollution and Its Control"
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiimiiiiiiiiiiiiiiiiiiiiiimiimiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii minimi mi;
principal
bratoback to modeling;
is tlje po^ible inaccuracy
in representing; reality
PHOTOCHEMICAL MODEL TYPES
(i.)
Rollback,
according to
Appendix J
BASIC MODEL
(2.)
Kinetics
Models
Chemical ~J(~)-
Reactions-" / \ ^
•$%t? Ozone
MODIFIED n (Wind)
Parcel
Emissions
(3.) Trajectory Models
(4.) Grid Models
030
-------
AVAILABLE OXIDANT MODELS
MODEL TYPE
ROLLBACK
BOX
KINETICS
TRAJECTORY
GRID
MODEL NAME AND/OR DEVELOPER
• Rollback/Appendix J
• Hanna and Gift ord
• EPA Box Model
• Model for EKMA(EPA)
• OHkin* (Environmental Research &
Technological Technology)
• REM (Pacific Environmental Services)
• "SAI Model" (Systems Applications Inc.)
• URAQ (Lawrence Livermore Labs)
iiHiuniiinHinuiiinniiHiiiiiiiiiiiHiiiiHiiiiiiiiiuiuiiniiiiiniiiii
ROLLBACK
DATA REQUIREMENTS:
• Present Ox
Concentration
• Area-wide Emissions
iiiiiniiiiimHiiiHiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiiiiiiiimiiiiiiiiiiiiiiiiiiiimiiiiiiiiiiiiiiiiiiiiiiiiiiiii mini
iiiiiiiujir
REQUIRED HYDROCARBON EMISSION CONTROL
AS A FUNCTION OF PHOTOCHEMICAL OXIDANT CONCENTRATION
MuilRium M*MW*4 1 boar
Photochtmtcsl OildMit C«nc«ntr«tton, ppm
0.10
aiS
0.20
0-2S
0.30
to
CO
I;' »
511
KM wit -
ISO 200 HO 300 HO 400 4SO SOO SSO
Mubwtm M««Mir*4l 1 Iram ,
031
-------
KINETICS MODEL
BASIC
Present Ox Concentration Morning
HC/NOX Ratio Area-wide Emissions
KINETICS MODEL
MODIFIED
• Estimates are also required for
• light intensity parameters
• morning and afternoon mixing heights
• appropriate spatial emissions distribution
• transported ozone concentration, if possible
IIIIIIIUIIinilllllllUIHIIHIIIUIIIIHIIIIIIIIIIHIIIIIIIIIMIIIIIIIMIIIMIIIIIlllllllllllllllllllllllUllllllllllinillllllllllllMIIIII!
• EPA600/8-78-014a
July, 1978
"User's Manual for Kinetics
Model and Ozone Isopleth
Plotting Package"
032
-------
TRAJECTORY MODEL
• Sufficient wind data
(possibly Including upper
air data) to determine
trajectories
• Initial concentrations In
air parcels
• Hourly mixing heights
• Insolation
• Emission rates for the
areas traversed by the air
parcel
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GRID MODEL DATA REQUIREMENTS
TYPICAL RESOLUTION
• SPATIAL: (afew miles)2
e.g. 2 miles x 2 miles
• TEMPORAL: Hourly
• SPECIES: 4 Classes of HC-
ParaHins, Oleflns,
Aromatics, Aldehydes
Also NO, NO2. O3, CO, etc.
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GUIDELINE ON
AIR QUALITY MODELS
APRIL 1978
033
-------
034
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Emission
Measuring
Techniques
035
-------
SAMPLING
APPARATUS
'
ACTIVATED CARBON ADSORPTION
Filtw
I
Activated Carbon Section
Pump
UNIVERSAL COLLECTOR
MMPICMJ
OUTUT ',^<^—
ACT. CH«*CO«*.
SAMPLE COLLECTION
UNIVERSAL COLLECTOR
ACT. CHARCOAL
SAMPLE RECOVERY
4-2
036
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I PURGE FLASK
AND
SYRINGE SAMPLE
BAG SAMPLE
FLOWMETU
cr
*****""" •^!!^^B^*":I"»
-------
The strengths and weaknesses for the allowed
sampling techniques are as follows:
Direct Interface or Dilution Interface
Strengths: 1. Samples collected are in a form that approximates the form in stack
emissions.
2. No loss or alteration in compounds due to sampling since a sample
collection media (bag or adsorbent) is not used.
3. Method of choice for steady state sources when duct temperature is
below 100°C and organic concentrations are suitable for the GC
detector.
Weaknesses: 1. GC must be located at the sampling site.
2. GC cannot be operated at a sampling site if the presence of the H2
flame will be hazardous.
3. Cannot sample proportionally or obtain a time integrated sample.
4. Results represent only grab samples and should not be used for non
steady state processes.
Tedlar Bag
Strengths: 1. Samples collected are in a form that approximates the form in stack
emissions.
2. Samples may be returned to the laboratory for GC analysis.
3. Multiple analyses, if necessary, may be performed on each collected
sample.
4. Samples can be collected proportionally.
Weaknesses: 1. Unless protected, Tedlar bags are awkward and bulky for shipping back
to the laboratory. Caution must be taken to prevent bag leaks.
2. Stability of compound(s) of interest in Tedlar bags must be known and
sample storage time is generally less than 24 hours.
3. Polar compounds should not be collected due to bag absorption. Direct
interface or dilution interface is the method of choice for polar
compounds.
Adsorbent Tubes
Strengths: 1. Samples collected are compact and easy to return to the laboratory for
analysis.
2. Samples may be returned to the laboratory for GC analysis.
3. Sample storage time generally can be extended to a week by keeping
samples at O°C.
Weaknesses: 1. Quantitative recovery of organic compounds from the adsorbent material
must be known.
2. Breakthrough sample gas volume for organic compounds for the
adsorbent material must be known.
3. Any effect of moisture (in the stack gas) on the adsorbent material
collection capacity must be known. Moisture in the sample above 2 to 3
percent may severely reduce the adsorptive capacity.
4. Generally, samples are collected at a constant rate.
038
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Review of Analytical Methods for
Identifying Organic Compounds
Lesson Goal and Objectives
Goal
To provide a background in gas chromatography sufficient for understanding the
EPA measurement methods for organic compounds.
Objectives
Upon completing this lesson, you should be able to:
1. illustrate the separation of gaseous mixtures by the partitioning process of a
chromatograph column.
2. identify the components of a gas chromatograph,
3. list at least three techniques used to introduce samples into the gas
chromatograph. and
4. list and describe two types of chromatograph detectors.
Introduction
The measurement of organic compound emissions is not as straightforward a
procedure as the measurement of inorganic gases such as SOj and NO. Because of
the wide variation of properties associated with the different classes of organic
materials, developing one single analytical method for this category of pollutant
has been difficult. Instead, analytical approaches vary from the relatively simple
measurement of materials evaporated from a painted plate to sophisticated mass
spectroscopic techniques.
The degree of complexity in the sampling and analytical procedures also depends
on what the information is needed for. Testing for leaky valves at a petroleum
refinery is much simpler than identifying and quantifying the emissions of toxic
materials from a hazardous waste incinerator. However, what is required in any
sampling and analytical procedure for organic compounds, is a knowledge of the
limitations of the procedure and careful attention to experimental details.
One technique does stand out as being common to many of the field methods
used for characterizing organic compounds. That technique is gas chromatography.
The detectors used in gas chromatographs are also used in the small, portable leak
3-1
039
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checkers. Chromatographic separation principles are used in EPA Reference
Method 25 for measurement of Total Gaseous Nonmethane Organics (TGNMO)
and a detailed gas chromatographic procedure is specified in EPA Method 106 for
vinyl chloride. Ultimately in the analytical laboratory, a gas chromatographic
system tied in with a mass spectrometer, provides a powerful tool for identifying
organic species.
This lesson will provide a review of the chromatographic method. It will discuss
types of columns, detectors, and special techniques used for identifying organic air
pollutants. The lesson will provide a basis for our further study in this course on
the EPA reference methods for organic compounds.
Chromatography—Definition
Chromatography is used to isolate the individual components of a mixture of
organic compounds from each other for subsequent identification and quantitative
analysis. The term, Chromatography (color-writing) derives from an earlier tech-
nique used to separate colored compounds found in plants. It has since been
applied to a variety of techniques, the two most important today being gas
Chromatography and liquid Chromatography.
All types of Chromatography are based on the selective distribution of com-
pounds between a stationary material and a moving material. Figure 3-1 shows
such a distribution, or partitioning, for the example of gas Chromatography.
Gas molecules
Carrier gas
Separation
Stationary material
Figure 3-1. Partitioning in gas cnromatography.
Here, the moving gas phase passes over a stationary material which is chosen to
either absorb or adsorb the organic molecules contained hi the gas. In gas
cnromatography, the stationary material or phase can be either a liquid or a solid.
A phase is defined as a part of the system which is marked off by a boundary at
which physical properties (e.g.. gas phase and liquid phase) suddenly change. If
the stationary phase is a liquid, the technique is called gas-liquid cnromatography
(GLC); if a solid, it is called gas-solid Chromatography (GSC). Liquids are chosen
hi the GLC method for their ability to dissolve (absorb) the organic molecules to be
3-2
040
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separated. In liquid chroma tography, the moving phase is a liquid and the
stationary phase is either a liquid or a solid. Adsorption, the attraction of
molecules to the surface of a solid, is the predominant effect in the GSC technique.
These types of chromatographic techniques are summarized in Figure 3-2.
CHROMATOGRAPHIC METHODS
. _ \ _ ,
I I
Gas chromatography Liquid chromatography
Gas-liquid Gas-solid Liquid-liquid Liquid-solid
Figure 3-2. Types of chromatographic method).
Physical Basis of Gas-Liquid Chromatography
When a gas dissolves in a liquid, a certain equilibrium occurs. Some of the gas
molecules will not stay dissolved, but will evaporate to escape the surface of this
liquid. They may reenter the liquid again, but at constant temperature and
pressure, a steady-state condition results in the number of gas molecules entering
equaling the number leaving the liquid (Figure 3-3).
Gas phase
**•
* * * _ Liquid phase
Figure 3-3. Equilibrium condition, for a gai absorbed in a liquid.
The organic molecules will have a different concentration in the liquid, Q, than in
the gas (Ct). By definition, the ratio of the quantity of the material dissolved in
I ml liquid to the quantity in 1 ml of carrier gas is known as the partition coeffi-
cient K, shown in Equation 3-1.
(Eq.3-1) K=7T
vr
Different organic compounds have different solubilities in a given liquid. High
solubility means that the molecules stay longer in the liquid phase. At equilibrium,
the rate of the molecules entering, and leaving the liquid are equal. However, if the
compound is not very soluble in the liquid, that rate is small and most of the
3-3
041
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molecules will remain in the gas phase. If the compound is highly soluble, the rate
will be higher and at any given instant, more molecules will be found dissolved in
the liquid. So Q and K. would be larger than the corresponding values for the
poorly dissolving substance (Figure 3-4).
A! A**
&M
igh solubility
compound A
Low solubility
compound B
Cf (compound A) >Q (compound B)
Figure 3-4. Differences in solubility.
This difference in partition coefficients causes the separation of compounds in
chromatography. Let us see how the chromatographic method does this.
A simple gas-liquid chromatograph system is composed of the following:
• carrier gas,
• injection area,
• column, and
• detector.
A carrier gas, such as helium or nitrogen, sweeps a sample from the injection
area into the heart of the system, the column. The column is a tube which contains
the absorbing liquid. The liquid may be coated on a solid support such as
powdered firebrick packed in the tube as shown in Figure 3-5a, or it may coat a
support attached to the wall of the tube as shown in Figure 3-5b.
Liquid
Solid suppon
material ./
JL-
wajj
Column wall
Support for liquid ^ Liquid phase
Figure 3-5a. Packed GLC column. Figure 3-5b. Open-tubular GLC column (capillary).
3-4
042
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A detector located at the end of the column is designed to sense the organic
molecules in the sample when the carrier gas sweeps them to that point.
To understand the separation process, let us first divide the column into a
number of imaginary segments. Then suppose that the sample contains two types
of organic molecules, molecules A and molecules B. Let us assume that the
A molecules are equally soluble in both the gas and liquid. Let us also assume that
the B molecules are insoluble in the liquid. The sample containing organic
molecules is injected and the carrier gas sweeps it into the first segment
(Figure 3-6).
Sample
injection"
Column Gas phase
Sample
Liquid phase
Figure 3-6. GLC separation process—injection.
After a short period of time, an equilibrium will be reached over the first segment.
Since the A molecules have equal solubility in both phases, half will remain in the
gas phase and the other half will dissolve in the liquid. The B molecules will not
enter the liquid. The equilibrium result will be as shown hi Figure 3-7.
Molecules
A B
Injection
Step 1
Equilibrium
Figure 3-7. The GLC separation process—equilibrium
at the first segment.
3-5
043
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The carrier gas, however, will then propel the molecules in the gas phase on to the
next segments. All of the B molecules will be transported there, but half of the
A molecules will remain in the liquid since they only travel down the column when
they are in the gas phase (Figure 3-8).
Travel
figure 3-8. Travel of gas to the second segment and
equilibrium in first and second segments.
A new equilibrium will then be established. The molecules of A equilibrate both
the first and second section as shown in Figure 3-9.
Travel
Figure 3-9. Travel to the third segment and equilibrium
in first through third segments.
3-6
044
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This process of gas travel and equilibrium will proceed down the column at each
segment. Note the equilibrium of the A molecules down the column for its remain-
ing segments (Figure 3-10).
Concentration in the gas phase
for molecules A and B
figure 3-10. Travel and equilibrium continuing
through column.
At the fourth step we can see that the A molecules have almost separated from the
B molecules. Similarly, another organic compound with a different solubility and
partition coefficient will move through the column at a different rate and likewise
be separated from the other two. This constant movement between the gas and
liquid phase is the fundamental mechanism of the gas chromatographic process.
3-7
045
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The Chromatogram
Organic compounds swept to the chromatograph detector produce an electrical
signal proportional to the quantity of molecules present. Also, compounds
separated before they reach the detector produce signals at different times. Because
of the nature of the equilibrium processes just described and because of various
random diffusion processes that occur in the column, all molecules of a given
liquid will not arrive at the same time. This will give a distribution of signals at the
detector. This distribution corresponds to a normal probability curve and is shown
in what is called a chromatogram for our two compounds, A and B in Figure 3-11.
Compound B
Compound A
Signal
strength
Figure 3-11. Chromatogram for two organic
compounds, A and B.
By operating the chromatograph, data are obtained hi the form of chromatograms.
Peaks in the chromatogram give information about the identity of the compounds
in the injected sample and also provide information about their concentration. The
time taken for a compound to travel to the detector after the sample has been
injected is known as the retention time, tx. This time depends on the type of
column, the temperature of the column, the carrier gas velocity, and the properties
of the molecules themselves. The determination of retention times is used to iden-
tify the organic species present hi a sample. Different compounds are separated by
choosing a set of experimental conditions that will produce non-overlapping elution
curves with different retention times. In terms of the partition coefficient for each
compound, a large relative retention is desired for good separations (Equation 3-2).
(Eq. 3-2)
t«(A)-t.
t«(B)-t.
where t. is the sample injection time (usually determined by a small peak due to air
injected with the sample). The resolution of compounds into separate peaks is one
of the most important problems hi chromatography. This will be discussed further
in this lesson hi the section on chromatographic columns.
3-8
046
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Once separate peaks are obtained for the components of a sample mixture, their
identity can be determined by running known standards through the column under
the same set of experimental conditions. The object is to inject known compounds
that will produce retention times corresponding to those of the unknown com-
ponents in the sample. Matching known standards with unknowns then assists in
the sample identification. However, a rigorous identification of an unknown cannot
be made by a comparison of retention times since other materials may elute
similarly. Experience and the wealth of scientific literature on chromatography can
also assist in these efforts. Retention times for specific columns, compounds, and
experimental conditions are documented in a large volume of literature for this
purpose. Lastly, where standards or literature are not available, the compounds
corresponding to each peak can be collected or further analyzed for identification.
The coupling of mass-spectrometer systems to gas chromatographs is the principle
example of this identification technique.
The concentration of each component in a mixture can be determined from the
area defined by the elution curve. The area of each peak is compared to the total
area of all the peaks to obtain the relative proportion of each component in the
sample. This can be done crudely by manually measuring the areas, but today
microprocessor techniques have been applied to perform this operation
automatically.
047
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Gas Chromatograph—Components
Gas-chromatographic instrumentation may be simple or quite complex. Basic early
systems have led to today's microprocesser controlled units that provide the
analytical chemist with powerful tools for sample separation and identification.
Behind even the most complex systems, however, lie the basic components required
for gas chromatography (Figure 3-12).
Recorder
Figure 3-12. Block diagram.
A source of high pressure gas, such as a cylinder of nitrogen, helium, or argon
provides the moving gas phase. Gas regulators on these cylinders generally provide
a pressure ranging from 30 to 100 psi (200-700 kPa) for the carrier gas in the
chromatograph. The sample is introduced to the system by the injection system.
For gas samples, this system may consist of specially designed valves that allow
carefully measured amounts of the sample gas to enter the column. Liquid samples
are normally injected by a syringe into a heated chamber. The liquid sample is
vaporized in the chamber to be subsequently carried into the column.
The gas stream containing the sample introduced by the injection system is
carried to the column, which is housed in an oven. As discussed earlier, the
primary purpose of the column is to separate the individual components of the
sample. To choose a column, the analytical chemist must consider the following
variables:
• column: packed or open-tubular (capillary),
• column length and diameter,
• solid support material,
• liquid phase, and
• column operating temperature.
3-12
048
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For completely unknown samples, experience in chromatography and experimental
technique are needed to resolve the individual components. In industries, where a
compound such as benzene or vinyl chloride is to be monitored, sufficient
experience has been attained to specify column types in EPA reference method
procedures. This, for example, has been done in EPA Reference Method 106, for
vinyl chloride which gives two types of columns for the analysis:
Column A: Stainless steel, 2.0 m by 3.2 mm, containing 80/100-mesh
Chromasorb 102® at column temperature of 100°C
Column B: Stainless steel, 2.0 m by 3.2 mm, containing 20% GE SF-96 on
60/80-mesh at column temperature 100 °C
Chromasorb P-AW (to be used when acetaldehyde is present)
The column operating temperature is chosen so that all of the components in the
sample mixture will remain vaporized. If the retention times of the components
differ greatly, the column temperature may be varied or "programmed" by
progressive increases. Compounds of low volatility can be eluted faster by this
technique, therefore reducing the analysis time.
Sample components eluted from the column are subsequently sensed at the
detector. Many detectors are available today, but the two most widely used are the
flame ionization detector (FID) and the electron capture detector (ECD). The
sensitivity of a detector generally depends on the characteristics of the molecules
being measured. For example, the ECD is highly selective and sensitive to
halogenated compounds. The FID, on the other hand, has a relatively constant
response for different compounds, but is not as sensitive as the ECD. Other
detectors especially sensitive to nitrogen compounds or sulfur containing com-
pounds have been designed. These are often used in special studies and in some
experimental programs; two or even three types of detectors have been combined
for the analysis of complex environmental mixtures.
The recorder, of course, documents the results of the analysis in the form of
chromatograms. Modern microprocessor systems are used to provide additional
information on integrated peak areas, and hence provide the concentration of the
individual components.
This part of Lesson 3 will examine the components of the gas chromatograph in
more detail. The options available for injection systems, columns, and detectors
will be provided along with a discussion of the principles of operation and per-
formance for a number of the systems.
Sample Collection and Injection Systems
The GC injection method used for organic air pollutant samples depends on the
manner in which the sample is collected. A number of collection techniques are
common to both ambient and source sampling. Among these are:
• collection of whole air samples,
• condensation in cryogenic (low temperature) traps,
• adsorption on resin or charcoal columns, and
• absorption in liquids.
3-13
049
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Whole air samples are collected by using either evacuated flasks or gas sampling
bags. By first evacuating a flask and then opening it into the atmosphere being
tested, samples can be obtained at the site for subsequent analysis in the
laboratory. Tedlar® bags or their equivalent are similarly evacuated, but the air is
pumped into the bag to obtain a sample integrated over longer time periods.
Several methods are used to inject such whole air samples into the chromatograph.
One of the simplest methods is to use a gas-tight syringe. An example of a familiar
design is shown in Figure 3-13.
Figure 3-13. Gai syringe.
The sample withdrawn from the flask or bag is then injected into the gas
chromatograph through a rubber septum. The gas is expelled into the carrier gas
stream and the needle withdrawn from the rubber cap, which seals itself off again
(Figure 3-14).
Syringe.
Rubber
septum
Heated block
Column
Sample
Packing
Figure 3-14. Sample injection using syringe.
3-14
050
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Such gas syringes can have volumes of 0.1 /il to 50 ccs. The accuracy of such injec-
tions is about 1% for the volume.
Another method of injecting whole air samples is to use special sampling valves.
A pump draws the gas from the flask or bag into a sample valve containing a
sample loop of known volume. The loop is closed off and carrier gas then sweeps
the gas in the loop into the column. Two basic designs of gas-sampling valves are
the rotary and linear valves.
The rotary valve shown in Figure 3-15 determines the size of the gas sample as it
passes through ports in the valve to a loop of tubing with a known volume. The
loop serves as a reservoir for the sample until the valve is turned to the inject posi-
tion where the internal valve passages A, B, and C are rotated 45 ° to align with a
new set of ports. As a result, the carrier gas pushes the sample out of the loop and
into the column.
Sample loop
To column
Flow through position
(sample in loop)
Sample loop
Carrier gas
To column
Inject position
(carrier gas sweeps sample
into column)
Figure 3-15. Rotary valve.
3-15
051
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In the linear valve shown in Figure 3-16, sample gas passes through a loop of
known volume as carrier gas passes through another port to enter the column. By
pushing the valve into the inject position, the gas flow is changed by cutting off the
sample gas and sweeping the known amount in the loop on into the column.
Unlike the syringe method, systems with sampling valves can be automated to
provide a semi-continuous analysis. They can be designed to pull in a sample using
vacuum methods or can accept it under pressure.
Sample loop
Flow through
position Sample
Vent to atmosphere
Inject position
Carrier gas
Figure 3-16. Linear valve.
In many field studies, the concentration levels of organic compounds hi whole air
samples are too low to be conveniently analyzed. This is particularly true in
ambient air sampling, although the problem is still an important one when looking
for trace levels of pollutants in industrial source emissions. Many preconcentration
techniques have been developed to overcome this problem. The two most common
techniques are cryogenic trapping and adsorption.
In cryogenic trapping the sample gas is passed through a system, such as stainless
steel U-tube filled with glass beads, which is cooled with liquid oxygen or liquid
argon. Liquid nitrogen is generally not used for this purpose since it will liquefy
oxygen and make the chromatographic analysis more difficult. After the sample is
collected, the U-tube can be attached directly to the chromatograph. The tube can
then be flash heated and the sample subsequently injected into the column using
an appropriate sampling-valve system.
Another method of collecting a concentrated sample is by using a solid adsor-
bent. Tubes packed with solid adsorbents such as Tenax-GC? silica gel, or
3-16
052
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activated charcoal are often used for this purpose. Tenax-GC® is a polydiphenyl
ether having the structure shown in Figure 3^17.
(Where: n » number of units in the chain)
_J n
Figure 3-17. Tenax-GC*
Sample gas is pulled through a tube or specially designed cartridge containing the
adsorbent. After a sufficient period of time, the tube is capped and stored for
laboratory analysis. Various techniques have been developed to desorb such
sampling tubes. A common technique is to heat the tubes and collect the desorbed
materials in a cryogenic trap. The concentrated sample is then flash evaporated to
provide a sample for the chromatograph.
Problems do exist in using such adsorbents because their affinities for different
classes of organic compounds vary. For example, Tenax-GC® has poor adsorptive
capability for low molecular weight compounds. Tubes containing activated char-
coal, which does attract the lower molecular weight compounds, are often com-
bined in series as a back-up for Tenax-GC? Ambersorb® is another material com-
monly used for this purpose. Much research is presently being conducted on the
adsorption characteristics of solid adsorbents. New adsorbents are also being
developed which avoid some of the problems associated with those now in use.
Lastly, organic compounds may be collected by bubbling the sample gas through
liquids which either absorb or react with them. A liquid syringe can then be used
to inject the sample into the chromatograph.
We have seen great differences between the methods for the introduction of
gaseous samples. The method chosen depends on how the sample was acquired and
the concentration levels of the components being measured. In all cases, however,
three conditions must be fulfilled when a substance is introduced.
1. Gas or liquid samples should reach the column as a vapor. After introduc-
tion, the sample should be carried by the carrier gas to the column in as short
a time as possible. This is to minimize diffusion of the sample which may
excessively broaden the peak.
2. The volume of sample injected should not overload the capacity of the
column or change its temperature.
3. Both the quantity of substance introduced and the manner in which it is
introduced must be reproducible with a high degree of precision.
3-17
053
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In short, the type and manner of sample injection influence the gas
chromatographic result. For quantitative analysis the injection conditions must be
reproducible if a high degree of accuracy is required.
Columns
The column is the central component of the chromatograph. The actual separation
of the organic compounds is achieved here, so the choice of column type and
column materials are important to any analysis. Two types of GC columns are
widely used, the packed column and the open-tubular, or capillary column. As
discussed in the first pan of this lesson, packed columns consist of a tube contain-
ing near-spherically shaped particles coated with a liquid. The open-tubular
columns are open tubes of small diameter with a thin liquid film on the wall or on
a solid support coated on the wall. Packed columns are easier to prepare and have
a higher capacity than the capillary columns. However, capillary columns offer less
resistance to gas flow and can resolve complex mixtures using very small samples.
Choosing between these two types of columns will generally influence the design of
the other chromatograph components if optimum performance is to be achieved.
The small samples associated with capillary columns may require both special
injection and detection methods.
Packed columns can vary from less than 1 meter hi length to over 20 meters hi
length with diameters varying from 1.5 mm to 2 mm. Capillary columns can vary
from 0.25 mm to 1.25 mm hi diameter, with lengths ranging beyond 100 meters.
The column tubes can be stainless steel, glass, aluminum, or copper and are either
U-shaped or wound hi coils to fit hi the chromatograph oven.
Several types of columns have been suggested by EPA for use in the agency
source assessment program (Harris, 1979). These recommendations include
specifications for column material, column length and diameter, and the materials
to be used for the liquid phase and solid support material. These are given in
Table 3-1.
Table 3-1. Suggested columns for environmental source assessment activities.
Column (liquid/solid phases)
Oxypropionitrile/Porasil C on
2 mm x 2 m glass column
Methyl phenyl silicone (SP 2250 or
OV-17)/Supelcopoit 2 mm x 2 m
glass column
Dexsil 400/Supdcoport (2 mm x 2 m
glass column)
Carbowax 20M (SP 1000)/Supelcoport
(2 m X 2 m glass on stainless steel)
Applications
Hydrocarbons boiling between - 161 °C
and68°C
For compounds of moderate volatility
(can be used up to 375 °C)
For high boiling compounds, good for
polycyclic aromatic hydrocarbons
Ethers, carbonyls, alcohols— other
moderately volatile compounds
3-18
054
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Solid Supports
The purpose of the solid phase is to provide a support for the liquid film. (Note: In
gas-solid chromatography, solid materials are used to partition the sample pri-
marily by adsorption processes.) Solids used for packed columns should have a
large specific surface area, a pore structure with uniform pore diameter, thermal
stability, mechanical strength, uniformly shaped particles, and an inertness to the
sample being measured. They, of course, should be wettable by the liquid phase so
that uniform film can coat the surface.
Diatomaceous earth is commonly used as a support and is available in many
forms under a variety of commercial trade-names. The Chromasorb® series is
widely used and has been applied to solve numerous analytical problems.
Chromasorb-W* is a white support treated with sodium carbonate. Chroma-
sorb- P* is a pink material obtained from crushed diatomaceous earth firebrick.
Glass beads, Teflon® Fluoropak® Chromosorb-T® and metals tend to be more inert
than the diatomaceous earth supports, but they are more difficult to wet.
The Liquid Phase
The liquid phase is chosen to match the compounds being separated and
measured. The choice of a proper liquid phase or liquid phase/solid support com-
bination may be a trial and error procedure in the case of complex unknown
samples. The most important characteristic of a good liquid phase is that the parti-
tion coefficient (the K value) be appropriate for the components in the sample; it
should be neither too small nor too large. In other words, the liquid should be a
good solvent for the sample components, but it should not hold them so tightly
that they can't get back into the gas stream. The components should also have
varying solubilities in the liquid so that they can be correspondingly separated on
the column. The liquid should also be nonvolatile, thermally stable at column
temperatures, and should not react with the sample. Some commonly used liquid
phases used in ambient air monitoring and then- applications are given in
Table 3-2 (EPA, 1983).
Table 3-2. Commonly used GC liquid phases in ambient monitoring.
Liquid phase
SE-30, OV-1 (methyl silicones)
OV-17. SE-54 (methyl/phenyl silicones)
Carbowax 20M (polyethylene glycol)
FFAP. SP-1000 (polyethylene glycol
terephtalate)
Applications
Hydrocarbons, chlorinated hydrocarbons
PAHs. chlorinated pesticides, hydrocarbons
Polar compounds: esters, alcohols, etc.
Phenols, volatile acids
Several methods are used for coating the solid support with the liquid. In
general, the liquid is dissolved in a solvent and the solid particles are mixed in with
the solution. The solvent is then allowed to evaporate either under vacuum or by
adding heat. The amount of liquid used must be carefully calculated so that a thin
film will coat the particles without creating excess pools of liquid.
3-19
055
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Packing columns is a process which must be carefully done, but is still more of
an art than a technically defined procedure. For good column efficiency and
reproducibility, air pockets and channels need to be avoided. It is often convenient
to purchase prepared columns from vendors who are able to exercise quality con-
trol methods in their production.
Column Performance
The ability of a column to separate the components of a sample depends on many
variables. The choices of liquid and solid phases, column material and dimensions,
column temperatures, and flow rates, provide a wide range of possibilities when
approaching an analysis problem. To help the analytical chemist, several
mathematical methods have been developed that can be used to compare the effec-
tiveness of one column over another. In your reading of the literature associated
with gas chromatography, you will see a number of expressions characterizing
column performance. In the first part of this lesson, we discussed the partition
coefficient, K, and the relative retention, a. Here, we will introduce the concept of
plate number and plate height.
Earlier, we divided up an example column and showed how two types of
molecules behaved as they traveled along its length. The soluble molecules became
distributed in each segment, or were "partitioned" between the gas and liquid
phases at each segment under equilibrium conditions. As a result of this process,
we could visualize how two components could separate and produce signal peaks at
the detector. In a similar fashion, a theory, called plate theory, has been developed
to help explain the factors that influence the operation of a column.
Plate theory imagines that a column can be divided into a finite number of iden-
tical segments, n, each with a plate height, H, where H —.L/n, and L is the length
of the column (Figure 3-18).
Column
H
Figure 3-18. Plate height.
3-20
056
-------
The characteristic feature of each segment of "height H," is that the sample com-
ponent studied will need that amount of column in order to come into equilibrium
with the system. For example in Figure 3-19,
System B
B
Figure 3-19. Molecules exhibiting different plate heights.
the peak shown for system A requires a longer length of column before it resolves
into an equilibrium distribution than does system B. As a result, the peak observed
for system B will be sharper than that for system A.
The number of plates, n, can be calculated from the chromatogram by using the
formula shown in Figure 3-20.
Response
Tangent to point
of inflection
t«
At
retention time
width of peak at base
Figure 3-20. Schematic chromatogram.
This expression is derived from statistical consideration of the chromatogram curve
(see Nogare, 1966 for the best discussion). A high number of plates for a given
length of column implies high efficiency, or sharp peaks. The number of plates can
be increased by lengthening the column or by improving the column without
changing its length. The expression is useful when comparing similar columns or
setting standards for packing techniques.
The plate height, H, is also useful for characterizing columns. It is a better term
to use than the plate number when comparing columns of different length. The
plate height is also called the Height Equivalent to a Theoretical Plate (HETP),
since the plates themselves are imaginary, theoretical constructs.
3-21
057
-------
"This means that one HETP is the length of column in which the
equivalent of one simple equilibration step occurs. Thus the length of
column divided by the HETP is the effective number of partitions a com-
pound undergoes in its passage through the column" (Moore, 1971).
Plate theory does not address the experimental factors that determine the HETP; it
only tells how to calculate it after you have obtained a chromatogram. However,
another theory has been developed that relates column conditions to the HETP.
The HETP can be calculated from the "rate theory" for column performance. A
theoretical expression derived from basic principles expresses the plate height as
depending on three primary factors: 1) The path the gas must take when traveling
through the packing, 2) the diffusion of the organic components in the carrier gas,
and 3) the time it takes the molecules to reach equilibrium between the gas and
liquid phases. An abbreviated form of this expression is given in the Van Deemter
Equation, Equation 3-3.
(Eq. 3-3) HETP=A + — + Cu
u
Here, A, B, and C are constant and u is the carrier gas velocity. The A term is
called the eddy diffusion term, related to the path of the gas; B is the longitudinal
diffusion term; and C is the mass transfer term which expresses the equilibrium
characteristics of the column. The carrier gas velocity is the independent variable
in this simplified expression since it is the experimental parameter most easily
varied after the column is constructed. If the velocity is increased, there will be less
time for a band of adsorbing molecules to spread hi the column (i.e., At would
decrease). This is reflected hi the reciprocal form of the second term, B/u, so the
HETP would decrease.
However, if the velocity is increased, the carrier gas will rush the molecules
through the column at a faster rate and there will be less time available for them
to reach equilibrium with the adsorbent. You would therefore need a longer length
of column for the molecules to come into equilibrium with the adsorbent and the
HETP would increase. This is reflected in the third term Cu, which will increase
as the carrier gas velocity increases. The last two terms compete against each other
since the HETP decreases as the diffusion term decreases, but increases when the
third term increases. This is shown graphically hi what is known as a Van Deemter
3-22
058
-------
plot (Figure 3-21). The figure illustrates the effect on the HETP for each term in
the Van Deemter expression. Each of the terms is plotted separately against the
velocity of the carrier gas. The sum of the three terms at any velocity gives the
HETP.
HETP
phase, B> 11 Equilibrium between phases, C
j} Path in packing, A
u (gas velocity)
Figure 3-21. Plot of HETP against gas velocity.
Columns can be characterized for their effectiveness in separating an organic
compound by specifying a number of terms. These are t«, the retention time; the
plate number, n; and the plate height, H or HETP. When comparing how well
two different compounds are separated by the liquid phase, one can use the
relative retention, or, discussed earlier.
The choice of a column is essentially a problem in optimizing the values for n,
H, and a. In the.complex mixtures involved in environmental monitoring, the
selection of the proper column is important if all of the components are to be ade-
quately resolved. The scientific literature is well-documented with various
approaches taken towards the analysis of specific environmental samples. A study
of this extensive literature should precede the development of new monitoring
programs.
Detectors
The separation performed in the column must in some way be sensed and
recorded. The sample components will generally be eluted at very low concentra-
tions and will pass through the detector at a rapid rate depending on the velocity
of the carrier gas. Any detector designed for use in a gas chromatograph system
must have a high sensitivity for low concentration of organic molecules and a rapid
response time. Many detectors are available which meet these requirements; the
two most commonly used hi environmental analysis are the Flame lonization
Detector (FID) and the Electron Capture Detector (ECD).
Flame lonization Detector
lonization refers to the process where charged atoms or molecules (ions) are formed
from an electrically neutral compound. lonization detectors supply energy to the
sample to ionize the organic compounds contained in it. The number of ions
3-23
059
-------
produced by this process are then counted through a measurement of their electric
charge. Electronic circuitry can then convert this measurement to produce the
chromatogram.
The flame ionization detector provides energy to the gases eluted from the
column by burning hydrogen in the presence of oxygen (Figure 3-22).
Exhaust
Measuring
circuit
k Sample
and
hydrogen
Figure 3-22. Flame ionization detector.
The hydrogen flame produced in turn burns the organic vapors in the eluted gas.
In doing this, both positively and negatively charged ions are formed. These ions
make the gap between the two electrodes (anode and cathode) conductive. An elec-
tric current can then flow through this pan of the circuit. The current is approx-
imately proportional to the number of carbon atoms entering the flame. The
response of the detector is, however, slightly different for different types of oganic
compounds. As a result, the detector must be calibrated for the compounds being
studied if accurate results are to be obtained.
The flame ionization detector is convenient to use in many source sampling
situations since it does not respond appreciably to gases such as O», N,, H,O, CO,
SOt, and NO. Performance depends on the carrier gas flow rate, but the FID is
still one of the most sensitive detectors available.
Electron Capture Detector
The electron capture detector is selective towards certain groups of organic com-
pounds such as those containing halogen atoms or nitro groups. In this method, a
carrier gas such as nitrogen is ionized by a radioactive material such as Ni" or
tritium (H3) to produce a large number of free electrons. These electrons move to a
3-24
060
-------
positively charged anode as shown in Figure 3-23 to generate a current through the
system.
Electron travel
Radioactive
source
Carrier gas
and sample
Figure 3-23. Electron capture detector.
When the nitrogen carrier gas contains electron-absorbing molecules such as
halocarbons, the electric current will be reduced since the flow of free electrons is
reduced. The ECD is more sensitive for specific groups of compounds than is the
FID, but the response can vary from compound to compound.
Other Detectors
Other types of detectors are used in chromatographs applied to environmental
monitoring. Many of these are species selective like the ECD. Among these are the
Hall Electrolytic Conductivity Detector (HECD) used for halogen, sulfur, or
nitrogen compounds; the Flame Photometric Detector (FPD) used for sulfur or
phosphorous compounds; and the Alkalai Flame Detector (AFD), used for nitrogen
and phosphorous compounds. Systems that will detect a range of organic com-
pounds are the thermal conductivity detector (TCD), and the Mass Spectrom-
eter (MS). Thermal conductivity was a technique used in early chromatographs but
it has less sensitivity than does the flame ionization method. It is, consequently, not
widely used for trace level analysis of environmental samples. The photoionization
detector (PID) uses high energy UV radiation to ionize organic molecules. This
highly sensitive detector is becoming popular in both field and laboratory
applications.
With the increasing demands for the analysis of trace levels of toxic materials,
unique approaches are being taken to increase the resolving power and sensitivity
of chromatographic systems. Dual detector systems such as the combination of
PID/ECD, HECD/FID, and even FID/ECD/MS have been used for a variety of
applications (EPA, 1983) (Fox, 1983). Combining the gas chromatograph with the
mass spectrometer is useful in many applications where identifying the sample com-
ponents is paramount. This GC/MS combination has become very popular for such
analyses and is in widespread use in industry and university laboratories.
3-25
061
-------
Page
40 CFR PART 60 - APPENDIX A - REFERENCE TEST METHODS
Method 1A. Sample and Velocity Traverses for Stationary
Sources with Small Stacks or Ducts (proposed 48 FR 48955,
10-21-83) 1A-1
Method 2A. Direct Measurement of Gas Volume Through Pipes
and Small Ducts (promulgated 48 FR 37592, 8-18-83) 2A-1
Method 2B. Determination of Exhaust Gas Volume Flow Rate
from Gasoline Vapor Incinerators (promulgated 48 FR 37594,
8-18-83) 2B-1
Method 2C. Determination of Stack Gas Velocity and Volumetric
Flow Rate from Small Stacks and Ducts—Standard Pi tot Tube
(proposed 48 FR 48956, 10-21-83) - 2C-1
Method 18. Measurement of Gaseous Organic Compound Emissions
by Gas Chromatography (promulgated 48 FR 48344, 10-18-83) 18-1
Method 21. Determination of Volatile Organic Compound Leaks
(promulgated 48 FR 37598, 8-18-83) 21-1
Method 23. Determination of Halogenated Organics from
Stationary Sources (proposed 45 FR 38766, 6-11-80) 23-1
Method 24. Determination of Volatile Matter Content, Water
Content, Density, Volume Solids, and Weight Solids of
Surface Coatings (promulgated 45 FR 65958, 10-3-80) 24-1
Method 24A. Determination of Volatile Matter Content and
Density of Printing Inks and Related Coatings (promulgated
47 FR 50655, 11-8-82) 24A-1
Method 25. Determination of Total Gaseous Nonmethane Organic
Emissions as Carbon (promulgated 45 FR 65959, 10-3-80) 25-1
Method 25A. Determination of Total Gaseous Organic Concen-
tration Using a Flame lonization Analyzer (promulgated
48 FR 37595, 8-18-83) 25A-1
Method 25B. Determination of Total Gaseous Organic Concen-
tration Using a Nondispersive Infrared Analyzer (promul-
gated 48 FR 37597, 8-18-83) 25B-1
Method 27. Determination of Vapor Tightness of Gasoline
Delivery Tank Using Pressure-Vacuum Test (promulgated
48 FR 37597, 8-18-83)' 27-1
iii
062
-------
Page
40 CFR PART 61 - Appendix B - REFERENCE TEST METHODS
Method 106. Determination of Vinyl Chloride from
Stationary Sources (promulgated 47 FR 39170, 9-7-82) 106-1
Method 107. Determination of Vinyl Chloride Content of
Inprocess Wastewater- Samples and Vinyl Chloride Content
of Polyvinyl Chloride Resin, Slurry, Wet Cake, and Latex
Samples (promulgated 47 FR 39174, 9-7-82) 107-1
Method 110. Determination of Benzene from Stationary
Sources (proposed 45 FR 26660, 4-18-80; updated 7-23-82) 110-1
40 CFR PART 61 - APPENDIX C - QUALITY ASSURANCE PROCEDURES
Procedure 1. Determination of Adequate Chromatographic Peak
Resolution (promulgated 47 FR 39176, 9-7-82) Pl-1
Procedure 2. Procedure for Field Auditing GC Analysis
(promulgated 47 FR 39179, 9-7-82) P2-1
APPLICABLE STANDARDS TEST METHODS
ASTM-D1475-60. Density of Paint, Varnish, Lacquer, and
Related Products D1475-1
ASTM-D2369-81. Volatile Content of Coatings D2369-1
ASTM-D3792-79. Water Content of Water-Reducible Paints
by Direct Injection into a Gas Chromatograph D3792-1
ASTM-D4017-81. Water in Paints and Paint Materials by
the Karl Fischer Method D4017-1
IV
063
-------
METHOD 18. MEASUREMENT OF GASEOUS ORGANIC
COMPOUND EMISSIONS BY GAS CHROMATOGRAPHY
INTRODUCTION
[This method should not be attempted by persons unfamiliar with the
performance characteristics of gas chromatography, nor by those persons
who are unfamiliar with source sampling. Particular care should be
exercised in the area of safety concerning choice of equipment and
operation in potentially explosive atmospheres.]
1. Applicability and Principle
1.1 Applicability. This method applies to approximately 90 percent
of the total gaseous organics emitted from an industrial source. It
does not include techniques to identify and measure trace amounts of
organic compounds, such as those found in building air and fugitive
emission sources.
This method will not determine compounds that (1) are polymeric
(high molecular weight), (2) can polymerize before analysis, or (3) have
very low vapor pressures at stack or instrument conditions.
1.2 Principle. This method is based on separating the major
components of a gas mixture with a gas chromatograph (GC) and measuring
the separated components with a suitable detector.
The retention times of each separated component are compared with
those of known compounds under identical conditions. Therefore, the
analyst confirms the identity and approximate concentrations of the
organic emission components beforehand. With this information, the
analyst then prepares or purchases commercially available standard
mixtures to calibrate the GC under conditions identical to those of the
samples. The analyst also determines the need for sample dilution to
avoid detector saturation, gas stream filtration to eliminate particulate
matter, and prevention of moisture condensation.
18&64
-------
2. Range and Sensitivity
2.1 Range. The range of this method is from about 1 part per
million (ppm) to the upper limit governed by GC detector saturation or
column overloading. The upper limit can be extended by diluting the
stack gases with an inert gas or by using smaller gas sampling loops.
2.2 Sensitivity. The sensitivity limit for a compound is defined
as the mininun detectable concentration of that compound, or the
concentration that produces a signal-to-noise ratio of three to one.
The minimum detectable concentration is determined during the presurvey
calibration for each compound.
3. Precision and Accuracy
Gas chromatography techniques typically provide a precision of 5 to
10 percent relative standard deviation (RSD), but an experienced GC
operator with a reliable instrument can readily achieve 5 percent RSO.
For this method, the following combined GC/operator values are required.
(a) Precision. Duplicate analyses are within 5 percent of their
mean value.
(b) Accuracy. Analysis results of prepared audit samples are
within 10 percent of preparation values.
065
-------
40 CFR ?art 60, Appendix A
Final, promulgated
METHOD 21. DETERMINATION OF VOLATILE
ORGANIC COMPOUND LEAKS
1. Applicability and Principle
1.1 Applicability. This method applies to the determination of
volatile organic compound (VOC) leaks from process equipment. These
sources include, but are not limited to, valves, flanges and other
connections, pumps and compressors, pressure relief devices, process
drains, open-ended valves, pump and compressor seal system degassing
vents, accumulator vessel vents, agitator seals, and access door
seals.
1.2 Principle. A portable instrument is used to detect VOC
leaks from individual sources. The instrument detector type is not
specified, but it must meet the specifications and performance criteria
contained in Section 3. A leak definition concentration based on a
reference compound is specified in each applicable regulation. This
procedure is intended to locate and classify leaks only, and is not to
be used as a direct measure of mass emission rates from individual
sources.
066
-------
40 CFR Part 60, Appendix /U^ .,,*..- JT. ,1?
6/H/80 uO NOT QUOTE OR CITE
METHOD 23. DETERMINATION OF HALOGENATED
ORGANICS FROM STATIONARY SOURCES
INTRODUCTION
Performance of this method should not be attempted
by persons unfamiliar with the operation of a gas
chromatograph, nor by those who are unfamiliar with
source sampling because knowledge beyond the scope
of this presentation is required. Care must be
exercised to prevent exposure of sampling
personnel to hazardous emissions.
1. Applicability and Principle
1.1 Applicability. This method applies to the
measurement of halogenated organics such as carbon tetra-
chloride, ethylene dichloride, perch!oroethylene,
trichloroethylene, methylene chloride, 1,1,1-trichloroethane,
and trichlorotrifluoroethane 1n stack gases from sources as
specified in the regulations. The method does not measure
halogenated organics contained in particulate matter.
1.2 Principle. An integrated bag sample of stack gas
containing one or more halogenated organics is subjected
to gas chromatographic (GC) analysis, using a flame
ionization detector (FID).
2. Range and Sensitivity
The range of this method is 0.1 to 200 ppm. The upper
limit may be extended by extending the calibration range or
by diluting the sample.
23-1
067
-------
40 CFR Part 60 Appendix A
Final, promulgated 10/3/80
45 FR 65958
Revised 1/27/83
METHOD 24—DETERMINATION OF VOLATILE MATTER CONTENT, WATER
CONTENT, DENSITY, VOLUME SOLIDS, AND WEIGHT SOLIDS OF SURFACE COATINGS
1. Applicability and Principle
1.1 Applicability. This method applies to the determination of volatile
matter content, water content, density, volume solids, and weight solids of
paint, varnish, lacquer, or related surface coatings.
1.2 Principle. Standard methods are used to determine the volatile
matter content, water content, density, volume solids, and weight solids of
the paint, varnish, lacquer, or related surface coatings.
2. Applicable Standard Methods
Use the apparatus, reagents, and procedures specified in the standard
methods below:
2.1 ASTM D 1475-60 (Reapproved 1980). Standard Test Method for Density
of Paint, Lacquer, and Related Products (incorporated by reference - see §60.17)
2.2 ASTM D 2369-81. Standard Test Method for Volatile Content of Paints
(incorporated by reference - see §60.17).
2.3 ASTM D 3792-79. Standard Test Method for Water Content in Water
Reducible Paint by Direct Injection into a Gas Chromatograph (incorporated by
reference - see §60.17).
2.4 ASTM D 4017-81. Standard Test Method for Water in Paints or Paint
Materials by the Karl Fischer Titration Method (incorporated by reference -
see §60.17).
24-1
068
-------
40 CFR Part 60, Appendix A
Final, Promulgated
METHOD 24A—DETERMINATION OF VOLATILE MATTER CONTENT
AND DENSITY OF PRINTING INKS AND RELATED COATINGS
1. Applicability and Principle
1.1 Applicability. This method applies to the determination of
the volatile organic compound (VOC) content and density of solvent-borne
(solvent reducible) printing inks or related coatings.
1.2 Principle. Separate procedures are used to determine the VOC
weight fraction and density of the coating and the density of the solvent
in the coating. The VOC weight fraction is determined by measuring the
weight loss of a known sample quantity which has been heated for a
specified length of time at a specified temperature. The density of
both the coating and solvent are measured by a standard procedure. From
this information, the VOC volume fraction is calculated.
069
-------
40 CFR Part 60, Appendix A
Final, Promulgated
METHOD 25 - DETERMINATION OF TOTAL GASEOUS MONMETHANE
ORGANIC EMISSIONS AS CARBON
1. Applicability and Principle
1.1 Applicability. This method applies to the measurement of
volatile organic compounds (VOC) as total gaseous nonmethane
organics (TGNMO) as carbon in source emissions. Organic participate
matter will interfere with the analysis and therefore, in some cases,
an in-stack participate filter is required. This method is not the
only method that applies to the measurement of TGNMO. Costs,
logistics, and other practicalities of source testing may make other
test methods more desirable for measuring VOC of certain effluent
streams. Proper judgment is required in determining the most
applicable VOC test method. For example, depending upon the molecular
weight of the organics in the effluent stream, a totally automated
semi-continuous nonmethane organic (NMO) analyzer interfaced directly
to the source may yield accurate results. This approach has the
advantage of providing emission data semi-continuously over an
extended time period.
Direct measurement of an effluent with a flame ionization
detector (FID) analyzer may be appropriate with prior
characterization of the gas stream and knowledge that the
25-1
070
-------
detector responds predictably to the organic compounds in the stream.
If present, methane will, of course, also be measured. In practice,
the FID can be applied to the determination of the mass concentration
of the total molecular structure of the organic emissions under the
following limited conditions: (1) where only one compound is
known to exist; (2) when the organic compounds consist of only
hydrogen and carbon; (3) where the relative percentage of the
compounds is known or can be determined, and the FID response to the
compounds is known; (4) where a consistent mixture of compounds exists
before and after emission control and only the relative concentrations
are to be assessed; or (5) where the FID can be calibrated against
mass standards of the compounds emitted (solvent emissions, for
example).
Another example of the use of a direct FID is as a screening method.
If there is enough information available to provide a rough estimate
of the analyzer accuracy, the FID analyzer can be used to determine the
VOC content of an uncharacterized gas stream. With a sufficient buffer
to account for possible inaccuracies, the direct FID can be a useful
tool to obtain the desired results without costly exact determination.
In situations where a qualitative/quantitative analysis of an
effluent stream is desired or required, a gas chromatographic FID
system may apply. However, for sources emitting numerous organics,
the time and expense of this approach will be formidable.
25-2
071
-------
1.2 Principle. An emission sample is withdrawn from the stack
at a constant rate through a chilled condensate trap by means of an
evacuated sample tank. TGNMO are determined by combining the
analytical results obtained from independent analyses of the condensate
trap and sample tank fractions. After sampling is completed, the
organic contents of the condensate trap are oxidized to carbon
dioxide (COp) which is quantitatively collected in an evacuated
vessel; then a portion of the C02 is reduced to methane (CH.) and
measured by a FID. The organic content of the sample fraction
collected in the sampling tank is measured by injecting a portion into
a gas chromatographic (GC) column to achieve separation of the
nonmethane organics from carbon monoxide (CO), C02 and CH.; the
nonmethane organics (NMO) are oxidized to CCL, reduced to CH., and
measured by a FID. In this manner, the variable response of the FID
associated with different types of organics is eliminated.
072
-------
40 CFR Part 60, Appendix A
Final, promulgated
METHOD 25A - DETERMINATION OF TOTAL GASEOUS ORGANIC
CONCENTRATION USING A FLAME IONIZATION ANALYZER
1. Applicability and Principle
1.1 Applicability. This method applies to the measurement of
total gaseous organic concentration of vapors consisting primarily of
alkanes, alkenes, and/or arenes (aromatic hydrocarbons). The concentration
is expressed in terras of propane (or other appropriate organic calibration
gas) or in terms of carbon.
1.2 Principle. A gas sample is extracted from the source
through a heated sample line, if necessary, and glass fiber filter to
a flame ionization analyzer (FIA). Results are reported as volume
concentration equivalents of the calibration gas or as carbon equivalents.
073
-------
40 CFR Part 60, Appendix A
Final, promulgated
METHOD 25B DETERMINATION OF TOTAL GASEOUS ORGANIC
CONCENTRATION USING A NONDISPERSIVE INFRARED ANALYZER
1. Applicability and Principle
1.1 Applicability. This method applies to the measurement of
total gaseous organic concentration of vapors consisting primarily of
alkanes. (Other organic materials may be measured using the general
procedure in this method, the appropriate calibration gas, and an
analyzer set to the appropriate absorption band.) The concentration
is expressed in terms of propane (or other appropriate organic calibration
gas) or in terms of carbon.
1.2 Principle. A gas sample is extracted from the source through
a heated sample line, if necessary, and glass fiber filter to a nondispersive
infrared analyzer (NDIR). Results are reported as volume concentration
equivalents of the calibration gas or as carbon equivalents.
074
-------
40 CFR Part 60, Appendix A
Final, promulgated
METHOD 27-DETERMINATION OF VAPOR TIGHTNESS OF GASOLINE
DELIVERY TANK USING-PRESSURE-VACUUM TEST
1. Applicability and Principle
1.1 Applicability. This method Is applicable for the determination
of vapor tightness of a gasoline delivery tank which is equipped with
vapor collection equipment.
1.2 Principle. Pressure and vacuum are applied alternately to
the compartments of a gasoline delivery tank and the change 1n pressure
or vacuum is recorded after a specified period of time.
075
-------
40 CFR Part 61, Appendix B
Final, promulgated
METHOD 106—DETERMINATION OF VINYL CHLORIDE
FROM STATIONARY SOURCES
Introduction
Performance of this method should not be attempted by persons
unfamiliar with the operation of a gas chromatograph (GC) nor by those
who are unfamiliar with source sampling, because knowledge beyond
the scope of this presentation is required. Care must be exercised
to prevent exposure of sampling personnel to vinyl chloride, a
carcinogen.
1. Applicability and Principle
1.1 Applicability. The method is applicable to the measurement
of vinyl chloride in stack gases from ethylene dichloride, vinyl
chloride, and polyvinyl chloride manufacturing, processes. The method
does not measure vinyl chloride contained in particulate matter.
1.2 Principle. An integrated bag sample of stack gas containing
vinyl chloride (chloroethene) is subjected to GC analysis using a flame
ionization detector (FID).
2. Range and Sensitivity
This method is designed for the 0.1 to 50 ppm range. However,
common GC instruments are capable of detecting 0.02 ppm vinyl chloride.
With proper calibration, the upper limit may be extended as needed.
106-1
076
-------
DRAFT
40 CFR Part 61, Appendix B DO NOT QUOTE OR CITE
Proposed 4/18/80
45 FR 26660 (may be start of standard)
Updated draft 7/23/82
METHOD 110. DETERMINATION OF BENZENE
FROM STATIONARY SOURCES
Introduction
Performance of this method should not be attempted by
persons unfamiliar with the operation of a gas chroma^-
tograph, nor by those who are unfamiliar with source
sampling, because knowledge beyond the scope of this
presentation is required. Care must be exercised to
prevent exposure of sampling personnel to benzene,
a carcinogen.
1. Applicability and Principle
1.1 Applicability. This method applies to the measure-
ment of benzene in stack gases from processes as specified
in the regulations. The method does not measure benzene
contained in particulate matter.
1.2 Principle. An integrated bag sample of stack gas
containing benzene and other organics is subjected to gas
chromatographic (GC) analysis, using a flame ionization
detector (FID).
2. Range and Sensitivity
The range of this method is 0.1 to 70 ppm. The upper
limit may be extended by extending the calibration range or
by diluting the sample.
077
110-1
-------
078
-------
Emission
Inventories
079
-------
Emission Inventories For Volatile Organic Compounds
1. Introduction: (482-5-1) (482-5-lA)
Organic compounds are found or produced in nature, but many more have
been synthetically produced by man. Gasoline obtained from oil is a
natural product, but the plastic produced from oil do not occur in
nature. Over 30,000 new compounds are synthesized each year, adding
to a list exceeding 1,000,000 that are registered. Two important
facts are known about the environmental effects of these organic
materials: (462-5-2)
1. Organic compounds volatile enough to be emitted into the
atmosphere can contribute to the generation of photochemical
oxidants (smog). (482-5-2A)
2. Organic compounds can have toxic effects on plants and animals.
In dealing with the problem of photochemical oxidant generation,
control programs have been established to limit the emission of
organic compounds into the atmosphere.
Regulation of toxic organic compounds are Just now beginning to
characterize what compounds are toxic and to what degree they pose
a threat to public health and welfare when emitted into the
atmosphere.
National emissions of volatile organic compounds (VOC) are shown
in Table 5-1, classified by source category from the years 1970,
1975, and 1980. During the past 10 years the total amount of
VOC's emitted from industrial processes has remained relatively
constant VOC emissions from some individual Industrial categories
have increase slightly but have decreased slightly in others. .
(482-5-3) (482-5-3A) (482-5-3B)
2. Overview Of Inventory Procedures (482-5-4)
Four basic steps are involved in the preparation of a VOC emission
inventory. The first is planning. The agency should define the
need for the VOC inventory as well as the constraints that limit
the ability of the agency to produce it. The various planning
aspects discussed in the following sections of this chapter should
all be considered prior to initiation of the actual data gathering
phases of the inventory effort. All proposed procedures and data
sources should be documented at the outset and be subjected to
review by all potential users of the final inventory, including
the management and technical staff of the inventory agency.
The second basic step is data collection. A major distinction
involves which sources should be considered point sources in the
inventory and which should be considered area sources.
Fundamentally different data collection procedures are used for
these two source types. Individual plant contacts are used to
collect point source data, whereas collective information is
generally used to estimate area source activity. Much more
5-2
080
-------
Source Category
Transportation
Highway vehicles
Aircraft
Railroads
Vessels
Other off -highway vehicles
Transportation total
Stationary Source Fuel Combustion
Electric utilities
Industrial
Commercial- institutional
Residential
Fuel combustion total
Industrial nrocesses
Solid waste disposal
Incineration
Open burning
Solid waste total
Miscellaneous
Forest fires
Other burning
Miscellaneous organic solvent
Miscellaneous total
Total
12
Teragrams(10 )
1970 1975
10.5
0.2
0.2
0.4
0.5
11.8
0.0
0.1
0.0
0.5
0.6
9.8
0.3
1.3
1.8
0.7
0.3
2.2
3.2
27.2
8.8
0.2
0.2
0.4
0.5
10.1
0.0
0.1
0.0
0.5
0.6
9.3
0.4
0.5
0.9
0.5
0.1
1.7
2,3
23.2
vi ^m^.»aj.w..»
per year
1980
6.8
0.2
0.2
0.5
0.5
8.2
0.0
0.1
0.0
0.8
0.9
10.7
0.3
0.3
0.6
0.9
0.1
1.6
2,6
23.0
5 -3
081
-------
The third basic step in the inventory compilation effort involves an
analysis of data collected and the development of emission estimates
for each source. Emissions will be determined individually for each
point source, whereas emissions will generally be determined
collectively for each ares source category. Source test data,
material balances, and emission factors are all used to make these
estimates. Adjustments are required to exclude nonreactive VOC and to
make the resulting emission totals representative of the ozone season.
A special adjustment called "scaling up" is necessary in some cases to
account for sources not covered in the point source inventory.
Estimates of projected emissions must also be made as part of this
step.
The fourth step is reporting. Basically, reporting involves
presenting the inventory data in a format that serves the agency in
the development and implementation of an ozone control program or
other regulatory effort. Depending on the capabilities of the
inventory data handling system many kinds of reports can be developed
that will be useful in numerous facets of the agency's ozone control
effort.
An important consideration affecting emission accuracy is whether the
agency has included all sources of VOC in its inventory. Table 5-2
presents those major sources of VOC that, at a minimum, should be
considered in the inventory. Some sources in this table are generally
considered point sources, some are generally handled collectively as
area sources, while others, such as drycleaners, can be either point
or area sources, depending on the size of each operation and the
particular cutoff made between point and area sources. (482-5-5)
(482-5-6) (482-5-7) (482-5-8) (482-5-9) (482-5-10) (482-5-11)
The entries in Table 5-2 describe general source categories and do not
list all of the emitting points that may be associated with any of the
particular source categories. For example, petroleum refining
operations actually include many emitting points ranging from process
heaters to individuals seals and pumps.
Those stationary sources of VOC for which EPA has published or will
publish Control Techniques Guidelines (CTG) are included in the
categories listed in Table 5-2.
Table 5-3 shows industrial source category's VOC atmospheric emissions
by amounts and percentage for all of the industries listed on Table 5-
1. (482-5-12)
Point/Area Source Distinctions (482-5-13)
A manor distinction typically made in inventories is between point and
area sources. Point sources are those facilities/plants/activities
for individual source records are maintained in the inventory. Under
ideal circumstances, all sources would be considered point sources.
In practical applications, only sources that emit (or have the
potential to emit) more than some specified cutoff level of VOC are
considered point sources.
5 -
082
-------
Table 5.2 VOLATILE ORGANIC COMPOUND (VOC) EMISSION SOURCES
STORAGE, TRANSPORTATION AND MARKETING OF VOC
Oil and Gas Production & Processing
Gasoline and Crude Oil Storage
Synthetic Organic Chemical Storage & Transfer
Ship and Barge Transfer of VOC
Barge and Tanker Cleaning
Bulk Gasoline Terminals
Gasoline Bulk Plants
Service Station Loading (Stage I)
Service Station Unloading (Stage II)
Others
INDUSTRIAL PROCESSES
Petroleum Refineries
Lube Oil Manufacture
Organic Chemical Manufacture
Inorganic Chemical Manufacture
Fermentation Processes
Vegetable Oil Processing
Pharmaceutical Manufacture
Rubber Tire Manufacture
Plastic Products Manufacture
SBR Rubber Manufacture
Textile Polymers & Resin Manufacture
Synthetic Fiber Manufacture
Iron and Steel Manufacture
Others
INDUSTRIAL SURFACE COATING
Large Appliances
Magnet Wire
Automobiles
Cans
Metal Coils
Paper
Fabric
Metal Wood Products
Miscellaneous Metal Products
Plastic Parts Painting
Large Ships
Large Aircraft
Others
NON-INDUSTRIAL SURFACE COATING
Architectural Coatings
Auto Refinishing
Others
5-5
083
-------
Table 5.2 (cont^
OTHER SOLVENT USE
Degreasing
Dry Cleaning
Graphic Arts
Adhesives
Cutback Asphalt
Solvent Extraction processes
Consumer/Commercial Solvent Use
Other .
OTHER MISCELLANEOUS SOURCES
Fuel Combustion
Solid Waste Disposal
Forest, Agricultural, and Other Open Burning
Pesticide Application
Waste Solvent Recovery Processes
Stationary Internal Combustion
Engines
MOBILE SOURCES
Highway Vehicles
a. Light duty automobiles
b. Light duty trucks
c. Heavy duty gasoline trucks
d. Heavy duty diesel trucks
e. Motorcycles
OFF HIGHWAY VEHICLES
Rail
Aircraft
Vessels
5-6
084
-------
Industrial Source Category
Crude Oil Production, Storage,
transfer (1311,4463)
Food and beverage (20)
Textiles (22)
Graphic arts (27)
Plastics (2821,3079)
Organic chemicals (286)
Other chemicals (28)
Petroleum refining (2911)
Rubber tires (3011)
Glass (321,322)
Iron and steel (3312)
Petroleum produce storage and
transfer (5171,5541)
Dry cleaning (721)
Adhesives
Degreasing
Solvent extraction processes
Surface coating
Jther organic solvent use
Total
1970
and
550
120
180
280
400
570
520
720
100
50
110
1,570
280
460
560
230
1,730
1.370
9.790
Gieaerams
1975
530
130
170
240
390
690
330
880
90
50
90
1,740
250
400
400
190
1,470
1.210
9.250
per year
1980
560
150
190
330
550
710
370
970
80
60
80
1,500
320
540
440
250
2,070
1.560
10,730
1981
540
150
170
250
490
760
380
950
90
60
70
1,450
240
420
350
200
1,800
1.460
9.770
Percent of Total
for 1981
5.5
1.5
1.7
2.6
5.0
7.8
3.9
9.7
0.9
0.6
0.7
14.9
2.5
4.3
3.6
2.1
18.4
14.9
The Standard Industrial Classification (SIC) code is given in the parenthesis where
appropriate.
This is a general category which includes process emissions from organic solvent use in a
wide variety of industries. Thus no specific SIC is given.
NOTE: One Gigagram equal 109grams of*10 metric tons (1.1 x 10 short tons).
total may differ slightly from sum of source category totals due to
independent founding of data.
5-7
085
-------
Depending on the needs of and resources available to the agency, this
cutoff level will vary. Area sources, in contrast, are those
activities for which aggregated source and emission information is
maintained for entire source categories rather than for each source
therein. Sources that are not treated as point sources must be
included as area sources. The cutoff level distinction is especially
important in the VOC inventory because there are so many more small
sources of VOC than of most other pollutants.
If too high a cutoff level is chosen, many facilities will not be
considered individually as point sources, and if care is not taken,
emissions from these sources may not be included in the inventory at
all.
If too low a cutoff level is chosen, the result will be a significant
increase (1) in the number of plant contacts of various sorts that
must be made and (2) in the size of the point source file that must be
maintained. While a low cutoff level may increase the accuracy of the
inventory, the tradeoff is that many more resources are needed to
compile and maintain the inventory.
The choice of a point source cutoff level will not only determine how
many point sources will be contained in the inventory, but also will
impact on the kinds of sources included. As a rule, the lower this
cutoff is (1) the greater the cost of the inventory, (2) the more
confidence users will have in the source and emissions data, and (3)
the more applications that can be made of the inventory. At a
minimum, all facilities exceeding 100 tons of VOC per year should be
inventoried as point sources and each process emission point should be
identified. If possible, a point source cutoff level of less than 100
tons per year should be selected to avoid handling the myriad of
medium size VOC emitters found in most urban areas as a area sources.
In some cases, the agency may decide to pursue lower cutoff levels or
to simply include all of a certain type of source in the point source
inventory, regardless of size. This may be desirable, for example, if
all sources in a certain category and subject to control regulations
such as RACT
At a minimum, every source category shown in Table 5.2 should be
considered for inclusion, with an emphasis on those RACT categories
for which controls are anticipated in the ozone control program.
A. Exclusion of Nonreactive Compounds and Consideration of Species
Information (482-5-14)
While most volatile organic compounds ultimately engage in
photochemical reactions, some are considered nonreactive under
atmospheric conditions. Therefore, controls on the emissions of these
nonreactive compounds do not contribute to the attainment and
maintenance of the national ambient air quality standard for ozone.
These nonreactive compounds are listed below:
Methane
1,1,1-Trichloroethane (Methyl Chloroform)
Methylene Chloride
5-8
086
-------
Dichlorodifluoromethane (CFC 12)
Chlorodifluoromethane (CFC 22)
Trifluoromethane (FC 23)
Trichlorotrifluoroethane (CFC 113)
Dichlorotetrafluoroethane (CFC 114)
Chloropentafluoroethane (CFC 115)
These compounds should be excluded from emission inventories used
for ozone control strategy purposes. Because this list may change
as additional information becomes available, the inventory agency
should remain aware of EPA policy on reactivity considerations.
5. Emission Calculations (482-5-15)
After planning and data collection, the third basic step in the
inventory is the calculation of emissions. This involves (1) an
analysis of the point and area source data collected by the
procedures outlined in the proceeding two chapters and (2) the
development of emissions estimates for each source. In some
cases, test data.will be supplied by the source. However, in most
instances the agency will have to compute emissions using emission
factors or material balance considerations. The following three
sections discuss the making of emission estimates based on source
test data, material balances, and emission factors.
a. Source Test Data (482-5-15A)
In many cases, the most accurate method of estimating a source's
emissions is to use test data obtained by the agency or supplied
by the plant itself. The use of source test data reduces the
number of assumptions that need be made by the agency regarding
the applicability of generalized emission factors, control device
efficiencies, equipment variations, or fuel characteristics. A
single source test or series of tests, taken over a sufficiently
long time to produce results representative of conditions that
would prevail during the time period inventoried, will normally
account for most of these variables. The most nearly complete
type of source testing is continuous monitoring.
Most source test reports summarize emissions for each pollutant by
expressing them in terms of (1) a mass loading rate (weight of
pollutant emitted per unit time), (2) an emission factor (weight
of pollutant emitted per unit of process activity), or (3) in
terms of a flue gas concentration (weight or number of moles of
pollutant per some weight or volume of flue gas). Generally, when
a mass loading rate or emission factor is provided, the resulting
emission estimates can be easily calculated. For example, if the
average VOC emission rate for the time period tested was 12
Ibs/hr, and the source operated for 16 hrs/day, 350 days/year,
daily* emission would be 12 x 16, or 192 Ibs, and the annual
emission would be 192 x 350, or 67,200 Ibs (34 tons). Or, is an
emission factor of 5 Ibs. of VOC per ton of product was given and
the plant produced 160 tons of product per day for 200 days per
year, annual emission would be 5 x 1600 x 200, or 160,000 Ibs
(80 tons).
5-9
087
-------
If the source test results are expressed in terms of VOC
concentrations the emission calculations are more detailed. As an
example, assume that volatile organic compound emissions are
expressed as parts per million, as shown in Table 5.3. in this
case, the concentration measurements and the flow rate
measurements are used to obtain mass loading rates. (A formula
for determining mass loading rates is shown as part of the
calculations in Table 5-4. Note that in this example, the results
are expressed as methane, and molecular weight of 16 Ibs/lb -mole
is used in the mass loading rate formula. If the concentration
was expressed in terms of another organic reference compound, the
appropriate molecular weight would be used. Upon determining the
mass loading rate 0.3 Ibs/hr, in this example), this rate can be
divided by the production rate at the time of testing to yield an
emission factor of 0.1 Ibs VOC emitted per ton of production.
After averaging the individual mass loading rates and emission
factors determined for all runs of the source test, the resulting
average mass loading rate or emission factor can be multiplied by
the annual operating time or annual production, respectively, to
determine annual emissions. Emissions can be calculated similarly
for other time periods. (482-5-16) (482-5-17)
Two points should be noted when using source test data to
calculate emissions. First, because source tests are generally
only conducted over several hours or days, at most, caution is
urged when using these data to estimate emissions over longer time
intervals or for conditions different from those under which the
tests were performed. Adjustments may be needed to account for
differing conditions. Second, a source test supplied by a plant
may not adequately describe a given facility's annual or seasonal
operating pattern. In cases where such data are not included in
the test reports, an operating rate will have to be obtained in
order to make reliable annual or seasonal emission estimates.
This is best done by contracting the plant and obtaining operating
information for the period the test was conducted. Such
information could be obtained from questionnaire data but may not
be as accurate.
5-10
088
-------
Table 5-4 EXAMPLE SOURCE TEST DATA AND EMISSION CALCULATIONS
SOURCE TEST RESULTS
RUN NUMBER
Date
Stack flow rate
t Excess air
CO Emissions (ppm, by volume)
1
8-5-71
9840
225
2.5
2
8-6-71
8510
227
6.4
3
8-7-71
10290
366
4.6
VOC Emission
(ppm by volume, as CH )
4
Process Conditions
Production rate (tons/hour)
11.9
3.0
6.8
3.2
10.9
3.1
CALCOLATIOH OF VOC EMISSIONS
CONVERSION FORMULA:
CALCULATION FOR RUN 1:
LB VOC/HR - 1.58 x M x 10'7 x ppa x SCFM
where M - Molecular weight of reference VOC
Mass Loading Rate - 1.58 x 16 x 10'7 x 11.9 x 9840 - 0.3
Ib/hr
Emission Factor - 0.3 Ib/hr x 1 hr/3 tons production
- 0.1 Ib/VOC/TON Production
5-11
089
-------
MATERIAL BALANCE (482-5-18)
If source test results are not available, the agency can, in some
cases, use material balance considerations to estimate emissions. In
fact, for some sources, a material balance is the only practical
method to estimate VOC emissions accurately. Source testing of low
level, intermittent,or fugitive VOC exhaust streams can be very
difficult and costly in many instances. Emissions from solvent
evaporation sources are most commonly determined by the use of
material balances.
Use of a material balance involves the examination of a process to
determine if emission can be estimated solely on knowledge of specific
operating parameters and material compositions. Although the material
balance is a valuable tool in estimating emissions from many sources,
its use requires that a measure of the material being "balanced" be
known at each point throughout the process. If such knowledge is not
available, and is therefore assumed, serious errors may result.
In the VOC emission inventory, a material balance is generally used to
estimate emissions from solvent evaporation sources. This technique
is equally applicable to both point and area sources. The simplest
form of material balance is to assume that all solvent consumed by a
source process will be evaporated during that process. For instance,
the assumption is reasonable that, during many surface coating
operations, all of the solvent in the coating evaporates to the
atmosphere during the drying process. In such cases, emissions simply
are equal to the amount of solvent applied in the surface coating (and
added thinners) as a function of time. As another example, consider a
dry cleaning plant that uses Stoddard solvent as the cleaning agent.
To estimate emissions, the agency needs only to elicit from each plant
the amount of solvent purchased during the time interval of concern,
because emissions are assumed equal to the quantity of solvent
purchased.
Several other situations can complicate the material balance. First,
not all of the solvent losses from certain operations such as
drycleaning or degreasing occur at the plant site. Significant
quantities of solvent may be evaporated, instead, from the waste
solvent disposal site, unless the waste solvent is incinerated or
disposed of in a manner, such as deep well injection, that precludes
subsequent evaporation to the atmosphere. Generally, one can assume
that much of the solvent sent to disposal sites will evaporate. The
fact that some solvent associated with various operations evaporates
at the point of disposal rather than at the point of use should be
determined, as these losses may occur outside of the area covered by
the inventory.
Material balances cannot be employed in some evaporation processes
because the amount of material lost is too small to be determined
accurately by conventional measurement procedures. As an example,
applying material balances to petroleum product storage tanks is not
generally feasible, because the breathing and working losses are
small, relative to the total average capacity or throughout, to be
determined readily from changes in the amount of material stored in
each tank. In these cases, AP-42 emission factors developed by
5 -12
090
-------
special procedures, will have to be applied.
7. EMISSION FACTORS (482-5-19)
One of the most useful tools available for estimating emissions from
both point, and area sources is the emission factor. An emission
factor is an estimate of the quantity of pollutant released to the
atmosphere as a result of some activity, such as combustion or
industrial production, divided by level of that activity. In most
cases emission factors are expressed simply as a single number, with
the underlying assumption being that a linear relationship exists
between emissions and the specified activity level over the probable
range of application. Empirical formulas have been developed for
several source categories that allow the agency to base its emission
estimates on a number of variables instead of just one. The most
important VOC emitters for which a number of variables are needed to
calculate emissions are highway vehicles and petroleum product storage
and handling operations. As a rule, the most reliable emission
factors are those based on numerous and representative source tests or
on accurate material balances.
The use of an emission factor to estimate VOC emissions from a source
necessitates that the agency have complete source and control device
information.
Tables 5-5 and 5-6 are examples of metal furniture surface coating for
determining VOC emissions from a surface coating operation, using AP-
42 emission factors. (482-5-20) (482-5-21)
8. Reporting Formats (482-5-21A)
In addition to required reporting formats, wide variety of tables and
graphic displays can be employed to present inventory data via
personal computer programs. Pie charts, tables and graphs can
quickly convey to the reader emission breakdowns by industries,
geographical areas, or source size. Emission trends and the effects
of control programs can also be tabulated or graphed. Several
examples of tables and graphs are included here to provide some ideas
on how date can be presented. (482-5-22) (482-5-23)
5 -13
091
-------
Plant
•size
Small
Medium
Large
Operating
Schedule
(hr/yr)
2,000
2,000
2,000
Number of lines
1
( 1 spray booth )
2
( 3 booths/line )
10
( 3 booths/line )
Line speed
(o/mln)
2.5
2. A
4.6
Surface area
coated/yr
(»2>
45,000
780,000
4,000.000
Liters o]
coating usi
5,000
87,100
446,600
Line speed is not used to calculate emissions, only to characterize plant operations.
Using 35 volume & solids coating, applied by electrostatic spray at 65 % transfer
efficiency.
Table 5-6 EMISSION FACTORS FOR VOC FROM SURFACE COATING OPERATIONS
Plant Size and Control Techniques
Small
Uncontrolled emissions
65 Volume % high solids coating
Waterborne coating
Medium
Uncontrolled emissions
65 Volume % high solids coating
Waterborne coating
Large
Uncontrolled emissions
65 Volume % high solids coating
Vaterborne coating
VOC
ke/m coated
.064
.019
.012
.064
.019
.012
.064
.019
.012
Emissions
kc/vear
2,875
835
520
49,815
14,445
8,970
225,450
74,080
46,000
ke/hov
1.4*
.41
.2<
24.9i
7.2
4.4
127.7
37.0
23.0
Calculated using the parameters given in Table 4.2.2.12-2 and the following equation.
Values have been rounded off.
5-14
092
-------
How the inventory data can most efficiently be summarized will depend on time and
manpower available to assemble a report. Tabular reports are the most common
kind of report, as they can be readily generated from computerized inventory
systems.
093
-------
094
-------
Concepts
VOC Control
095
-------
Organic Compounds and Air Pollution
Regulations
Lesson Goal and Objectives
Goal
To review air pollution control programs that address the emission of organic com-
pounds from industrial sources.
Objectives
Upon completing this lesson, you should be able to:
1. state two reasons for developing emission control programs for organic
compounds,
2. identify common acronyms used in the regulatory documents associated with
the control of organic compounds,
3. describe control options for volatile organic compounds and control options
associated with trading policies, and
4. define air toxics and state the rationale behind regulatory programs for their
control.
Introduction
Organic compounds constitute the largest class of chemicals described hi the field
of chemistry. Organic compounds are composed of carbon and other elements such
as hydrogen, oxygen, chlorine, and nitrogen, and exist as solids, liquids, or gases.
As a result of their wide diversity, they are the products and waste products from
many of today's industries.
Organic compounds are found or produced hi nature, but many more have been
synthetically developed to serve some need, whether practical or out of scientific
curiosity. Gasoline obtained from oil is a natural product, but the plastics pro-
duced from oil do not occur hi nature. Over 30,000 new compounds are synthe-
sized each year, adding to a list exceeding over 1,000,000 that are registered
(Ref. 1983). The environmental effects of these materials are difficult to assess, but two
important facts are known.
1. Organic compounds volatile enough to be emitted into the atmosphere can
contribute to the generation of photochemical oxidants (smog).
2. Organic compounds can have toxic effects on plants and animals.
1-1
096
-------
The U.S. Environmental Protection Agency (EPA), under the requirements of
the Clean Air Act, is responsible for protecting and enhancing air quality. In deal-
ing with the problem of photochemical oxidant generation, control programs have
been established to limit the emission of organic compounds into the atmosphere.
In the regulation of toxic organic compounds, programs are just now beginning to
characterize what compounds are toxic and to what degree they pose a threat to
public health and welfare when emitted into the atmosphere.
This lesson will review the programs developed by the Federal government and
individual States to limit the emission of organic compounds. The lesson will
provide a rationale for characterizing these materials and for monitoring them.
The Photochemical Oxidant Problem*
Photochemical oxidants are contained in the atmospheric chemical mix known as
smog. A principal photochemical oxidant hi this mix is ozone. Ozone is defined a
criteria pollutant, and a National Ambient Air Quality Standard (NAAQS) has
been set for it of 0.12 ppm (235 /tg/m3). Volatile organic compounds (VOCs)
emitted into the atmosphere have been found to contribute to the formation of
ozone. Through a series of complex chemical reactions involving nitrogen oxides
and light, organic compounds lead to buildups of photochemical oxidants. As a
result of this, control strategies for ozone emphasize the control of these emissions.
Hopefully, by controlling these reaction precursors, the oxidant levels will in turn
be controlled.
Typical sources of volatile organic compounds are highway vehicles and
industrial sources associated with
• petroleum refining, distribution, and marketing,
• fuel combustion and solid waste incineration,
• evaporation of organic solvents,
• chemical manufacturing, and
• miscellaneous industrial processes.
Emissions of these compounds have ranged to about 25 million metric tons per
year. National estimates for these are given in Table 1-1.
•This section has been adapted from G. T. Joseph, D. S. Beachler, and W. F. Dimmick 1983.
VOC Emission Regulations Promulgated and Proposed. Paper presented at AICHE Meeting,
Houston, Texas March 1983.
1-2
097
-------
Table 1-1. National estimates of volatile organic compound (VOO emissions.
Source category
Transportation
Highway vehicles
Aircraft
Railroads
Vessels
Other off-highway vehicles
Transportation total
Stationary source fuel combustion
Electric utilities
Industrial
Commercial-institutional
Residential
Fuel combustion total
Industrial processes
Solid waste disposal
Incineration
Open, burning
Solid waste total
Miscellaneous
Forest fires
Other burning
Miscellaneous organic solvent
Miscellaneous total
Total
Teragrams (10") per year
1970
10.5
0.2
0.2
0.4
0.5
11.8
0.0
0.1
0.0
0.5
0.6
9.3
0.5
1.3
1.8
0.7
0.3
2.2
3.2
27.2
1975
8.8
0.2
0.2
0.4
0.5
10.1
0.0
0.1
0.0
0.5
0.6
9.3
0.4
0.5
0.9
0.5
0.1
1.7
2.3
23.2
1980
6.8
0.2
0.2
0.5
0.5
8.2
0.0
0.1
0.0
0.8
0.9
10.7
0.3
0.3
0.6
0.9
0.1
1.6
2.6
23.0
Source: Joseph et al. 1983.
During the past 10 years the total amount of VOCs emitted from industrial
processes has remained relatively constant. VOC emissions from some individual
industrial source categories have increased slightly, but have decreased slightly from
other source categories (Table 1-2). Therefore, in order to meet the ambient ozone
standards, industrial source emission standards have been adopted.
1-3
098
-------
Table 1-2. Volatile organic compound emissions from industrial processes.
Industrial source category
Crude oil production, storage, and
. transfer (1311.4463)
Food and beverages (20)
Textiles (22)
Graphic arts (27)
Plastics (2821,3079)
Organic chemicals (286)
Other chemicals (28)
Petroleum refining (2911)
Rubber tires (3011)
Glass (321,322)
Iron and steel (3312)
Petroleum product storage and
transfer (5171.5541)
Dry cleaning (721)
Adhesives
Degreasing
Solvent extraction processes
Surface coating
Other organic solvent use*
Total
Gigagraxns per year
1970
550
120
180
280
400
570
520
720
100
50
110
1.570
280
460
560
230
1.730
1,370
9,790
1975
530
130
170
240
390
690
330
880
90
50
90
1.740
250
400
400
190
1.470
1,210
9,250
1980
560
150
190
330
550
710
370
970
80
60
80
1,500
320
540
440
250
2,070
1,560
10,730
1981
540
150
170
250
490
760
380
950
90
60
70
1,460
240
420
350
200
1.800
1,460
9,770
The Standard Industrial Classification (SIC) code is given in the
parenthesis where appropriate.
•This is a general category which includes process emissions from
organic solvent use in a wide variety of industries. Thus no specific
SIC is given.
Note: One gigagram equals 10* grams or 10* metric tons
.(1.1 x 101 short tons). Total may differ slightly from sum of
source category totals due to independent rounding of data.
Source: Joseph et al. 1983.
States must set regulations, as required by the Clean Air Act, to limit the
amount of VOCs that can be emitted by sources of VOCs. The U.S. Environmental
Protection Agency (EPA) must set New Source Performance Standards (NSPS), as
required by the Clean Air Act, for major sources of pollutants such as VOCs.
In order to understand source emission standards, it is necessary to become
familiar with a few regulatory terms. The following definitions are from the
U.S. Code of Federal Regulations:
A new source is one which is contracted and installed at a facility after the date
emission standards are proposed for that industry.
Modification is any physical change or operational change of an existing facility
that increases the amount of an air pollutant emitted, or results in the emission of
an air pollutant not previously emitted into the atmosphere to which a standard
applies.
Existing source refers to an air pollution source constructed before the proposal
date of the emission standard.
1-4
099
-------
An attainment area is an air quality control region that actually meets
the NAAQS.
A nonattainment area is an area or region where the NAAQS for a particular
pollutant is being violated.
The Clean Air Act, as amended in 1977, mandates that all States develop
control plans, referred to as State Implementation Plans (SIFs), describing their
enforcement strategy for meeting and maintaining the NAAQS. The SIPs, which
must be approved by the EPA, list the State regulations aimed at
1. bringing nonattainment areas into attainment status, and
2. ensuring that clean air in" attainment areas will be maintained. (Prevention of
Significant Deterioration—PSD)
The Clean Air Act, as amended in 1977, also defines three classes of control
technology aimed at reducing emissions from both existing sources and new or
modified sources. These are Reasonably Available Control Technology (RACT),
Best Available Control Technology (BACT), and controls that reflect the Lowest
Achievable Emission Rate (LAER). Each of these classes describes technological
methods that are applied to industrial sources to reduce air pollution emissions.
RACT is generally defined as the lowest emission limit that an existing source is
capable of meeting by applying control technology that is reasonably available.
RACT considers both availability and economic feasibility of the control methods.
The section of a SIP covering VOC emission control must contain regulations for
industrial categories identified as major VOC sources. Regulations aimed at
existing sources in nonattainment areas (for ozone) must reflect the application of
RACT. In order to give the States guidance in setting RACT emission standards,
EPA has published and is continuing to develop a series of documents referred to
as Control Technique Guidelines (CTG). The guideline documents are not regula-
tions, but only serve as an information base from which State and local agencies
can develop their own regulations.
EPA has prepared CTG documents for many of the major sources of VOC emis-
sions. For each source, a CTG describes the source or industry, identifies the VOC
emission points, discusses the applicable control methods, analyzes the costs
required to implement the control methods, and recommends an emission limit.
Tables 1-3 through 1-5 list the stationary source categories for which a CTG has
been or is currently being developed. Table 1-3 lists the 11 CTG documents
published prior to January 1978. This first group of CTG documents is referred to
as Group I. Table 1-4 lists the 10 CTG documents (called Group II) that were
published hi 1978. Table 1-5 lists the Group III CTG documents that are currently
being developed. The NTIS ordering number is given in the table.
1-5
100
-------
Table 1-3. Group I—Control Technique Guideline documents.
Source category
Surface coating of cans, coils, paper,
fabric, automobiles, and light-duty
trucks
Surface coating of metal furniture
Surface coating for insulation of
magnetic wire
Surface coating of large appliances
Storage of petroleum liquids in fixed
roof tanks
Bulk gasoline plants
Solvent metal cleaning
Use of cutback asphalt
Refinery vacuum producing systems.
wastewater separators, and process
unit turnarounds
Hydrocarbons from tank truck
gasoline loading terminals
Design criteria for stage I vapor
control systems, gasoline service
stations. U.S. EPA. OAQPS.
November 1975
EPA reference number
EPA 450/2-77-008
EPA 450/2-77-032
EPA 450/2-77-033
EPA 450/2-77-034
EPA 450/2-77-036
EPA 450/2-77-035
EPA 450/2-77-022
EPA 450/2-77-037
EPA 450/2-77-025
EPA 450/2-77-026
—
NTIS number*
PB 272 445/8BE
PB 278 257/1BE
PB 278 258/9BE
PB 278 259/7BE
PB 276 749/9BE
PB 276 722/6BE
PB 274 557/8BE
PB 278 185/4BE
PB 275 662/5BE
PB 275 060/2BE
—
* Documents can be ordered from National Technical Information Service. 5285 Port
Royal Road. Springfield. VA 22161.
Source: Joseph et al. 1983.
Table 1-4. Group n—Control Technique Guideline documents.
Source category
Leaks from petroleum refinery
equipment
Surface coating of miscellaneous
metal pans and products
Manufacture of vegetable oil
Surface coating of flat wood
paneling
Manufacture of synthesized
pharmaceutical products
Manufacture of pneumatic
rubber tires
Graphic arts— rotogravure and
flexography
Petroleum liquid storage in
external floating roof tanks
Perchloroethylene dry cleaning
systems
Leaks from gasoline tank trucks
and vapor collection systems
EPA reference number
EPA 450/2-78-036
EPA 450/2-78-015
EPA 450/2-78-035
EPA 450/2-78-032
EPA 450/2-78-029
EPA 450/2-78-030
EPA 450/2-78-033
EPA 450/2-78-047
EPA 450/2-78-050
EPA 450/2-78-051
NTIS number
PB 286 158/1BE
PB 286 157/3BE
PB 286 307/4BE
PB 286 199/5BE
PB 290 580/OBE
PB 290 557/8BE
PB 292 490/OBE
PB 290 579/2BE
PB 290 613/9BE
PB 290 568/5BE
Source: Joseph et al. 1983.
1-6
101
-------
Table 1-5. Group ni—Control Technique Guideline documents.
Source category
Control of volatile organic compound emissions from the .
manufacture of high-density polyethylene, polypropylene,
and polystyrene resins
Control of volatile organic compound emissions from volatile
organic liquid storage and floating and fixed roof tanks
Control of VOC fugitive emissions from synthetic organic
chemical, polymer, and resin manufacturing equipment
Control of volatile organic emissions from large petroleum dry
cleaners
Control of volatile organic compound emissions from air
oxidation processes— synthetic organic chemical
manufacturing industry
Control of volatile organic compound equipment leaks from
natural gas/gasoline processing plants
Status
Draft, May 1982
Draft. August 1961
Draft. August 1981
Finalized
EPA 450/3-82-009
Draft. July 1981
Draft, December 1981
Source: Joseph et al. 1983.
The States are required to apply other control strategies in order to bring non-
attainment areas into attainment status. As a consequence of the Clean Air Act
amendments of 1977, they are required to institute a permit system for industrial
construction in either attainment or nonattainment areas. The States were also
required to develop a Reasonable Further Progress (RFP) schedule to provide a
timetable of activities for nonattainment areas leading to attainment status by
1982. The amendments gave the option, however, that an extension to 1987 could
be granted in meeting ambient air standards if (among other requirements) an
Inspection/Maintenance (I/M) program for motor vehicles were instituted for those
areas exceeding the standards. Failure to reach attainment by 1982 and to institute
such an I/M program could result hi the application of sanctions to that
area—withholding of Federal highway and other grant funds and the prohibition
of new industrial construction.
A flexible policy of "controlled trading" has also been established as a method
for VOC control. Controlled trading incorporates essentially three types of policies:
• offset,
• bubble, and
• banking.
The offset policy allows the trade-off of emissions between different sources so
that a new source can be allowed to locate in a nonattainment area. For example,
if an auto assembly plant is to be constructed in a nonattainment area, the
manufacturer might only be allowed to do so if a petroleum refinery or some other
industry in the area is willing to reduce their emissions to a level that will compen-
sate for the new emissions from the auto plant.
The bubble policy applies to existing sources in nonattainment areas. The policy
treats a plant as if an imaginary bubble were placed over it. Changes can be made
in different plant operations so long as overall VOC emissions from the bubble are
reduced. For example, a can coating operation may wish to increase emission con-
trols on two coating lines so that controls need not be placed on an older line.
1-7
102
-------
Banking policies allow sources to reduce emissions and bank the reductions for
future expansion in attainment or nonattainment areas.
All of these policies are used by the States to limit the emission of volatile
organic compounds into the atmosphere. Figure 1-1 provides a summary of these
existing source policies.
Existing source policies
(for unmodified sources)
Attainment area
Figure 1-1. Direct impact of Federal policies on stationary sources.
The large circle represents a nonattainment area and the space outside of it, an
attainment area. The smaller circles illustrate how the different control policies
apply and overlap between the two areas. For example, an existing source located
in a nonattainment area must apply RACT so that the area can reach attainment
status according to the RFP schedule developed in the State program. By reducing
emissions more than required, an existing source may provide an offset for a new
source wishing to locate in a nonattainment area, or it may bank them for future
expansion.
1-8
103
-------
New Source Performance Standards for VOC Sources
In addition to State regulations, direct Federal regulations also affect industrial
sources. Section 111 of the Clean Air Act provides the regulatory authority for
establishing New Source Performance Standards (NSPS). NSPS apply to all new or
modified sources that are constructed after the standards have been proposed.
NSPS are set for a number of industrial source categories and specify emission
limits, emission monitoring requirements, and occasionally the type of control
equipment that must be installed on various industrial sources.
Categories of major sources of.emissions which may affect public health and
welfare have been identified and placed on a priority list. EPA is required to per-
form an analysis for each source category on the list. Based on this analysis, EPA
may then set an NSPS for that source category. Presently, there are six NSPS for
VOC emission sources. Table 1-6 lists the stationary source categories for which
NSPS have been promulgated. Table 1-7 lists the source categories for which an
NSPS has been proposed in the Federal Register.
Table .1-6. Promulgated NSPS for VOC sources.
Affected facility
Petroleum liquid storage vessels
(40,000 gallons or larger)
Industrial surface coating:
• automotive and light duty trucks
• metal furniture
• large appliances
• metal coils
Rotogravure printing
Proposed
date
6/11/73
5/11/78
10/05/79
11/20/80
12/24/80
1/05/81
10/28/80
Promulgated
date
3/08/74
4/04/80
12/24/80
10/29/82
10/27/82
11/01/82
11/08/82
Background information
document number
APTD-1352 A. B & C
EPA 450/2-74-003
EPA 450/3-79-030 A & B
EPA 450/3-80-007 A & B
EPA 450/3-80-037 A & B
EPA 450/3-80-035 A & B
EPA 450/3-80-031 A & B
Proposed date: All sources whose construction "commenced" after this date are subject to
the NSPS.
Promulgated: Date the final rule appeared in the Federal Register.
Source: Joseph et al. 1983.
1-9
104
-------
Table 1-7. Recommended and proposed NSPS for VOC sources.
Affected facility
Organic solvent cleaners (metal cleaning
and degreasing)
Perchloroethylene dry cleaning
Industrial surface coating:
pressure sensitive tapes and labels
cans
vinyl coating and printing
metal furniture
metal coil
automobile and light duty truck
large appliances
Synthetic organic chemical manufacturing:
fugitive emissions
air oxidation processes
Bulk gasoline terminals
Volatile organic liquid storage
(40,000 gallons or more)
Rubber products industry—
tire manufacturing
Refining fugitive emissions
Synthetic fibers (solvent spinning)
Petroleum solvent dry cleaning
Solvent degreasing
On shore production (natural gas/ gasoline)
Distillation operations (for both refineries
and chemical manufacturing)
Polymer and resins manufacturing
Graphic arts rotogravure
Proposed
date
6/11/80
11/25/80
12/30/80
11/26/80
11/18/83
11/28/80
1/15/81
10/05/79
12/24/80
1/05/81
12/82*
12/17/80
Undetermined
1/20/83
1/04/83
12/82*
12/82*
Undetermined
10/82*
2/83*
9/83*
10/28/80
Date of
final rule
Undetermined
12/82*
10/18/83
8/25/83
9/83*
10/29/82
11/01/82
12/24/80
10/27/82
10/18/83
12/83*
8/18/83
Undetermined
Undetermined
12/83*
12/83*
12/83*
Undetermined
12/83*
9/83*
9/84*
11/08/82
•Estimated
The control policies for new and modified sources are generally more stringent
than for existing sources. In order to maintain and improve air quality, the PSD
program, BACT, and NSPS are applied to the attainment areas. All of this is over-
seen by the New Source Review (NSR) program. New sources wishing to locate in
nonattainment areas are affected by even more stringent policies such as LAER
and the requirement to obtain offsets. The application of these .policies is sum-
marized in Figure 1-2.
1-10
105
-------
New and modified source policies
NSR
Attainment area
Figure 1-2. Direct impact of Federal policies on stationary sources.
For example, a new source locating in an attainment area must comply with
PSD regulations, apply BACT, and meet NSPS. If it wishes to locate in a non-
attainment area, it must meet LAER, fit in with the RFP schedule, and obtain
offsets.
106
-------
Table 6-2
Group I CTGs Limits, Control Options & Affected Facilities
Industry
CTG
Emission
Llimit
Applicable
Control Options
Number
of
Affected
Facilities
SURFACE COATING OF
CANS
The
are
recommended voc emission limits
•
Sheet coating, two-piece exterior
0.34 Kgl (2.8 Lb/gal)*
Two- and three-piece interior
0.51 Kg/1 (4.2 Lb/gal)*
Two-piece end exterior 0.51 Kg/1
(4.2 Lb/gal)*
Three-piece side seam 0.66 Kg/1
(5.5 Lb/gal)*
End seal compound 0.44 Kg/1
(3.7 Lb/gal)*
Low solvent
Coatings
460
Add-on
Controls
RFACE COATING
METAL COILS
The recommended voc emission limit
is 0.31 Kg per liter of coating
minus water (2.6 Lb/gal).
Low solvent
Coatings
Add oh Controls
180
SURFACE COATING
OF FABRICS
The recommend voc emission limits
are:
a. Fabric coating 0.35 Kg per
liter of coating minus water
(2.9 Lb/gal).
b. Vinyl coating 0.45 Kg per liter
of coating minus water
(3.8 Lb/gal).
Low solvent
Coatings
Add on
Controls
130
SURFACE COATING
OF PAPER PRODUCTS
The recommended voc emission limit
is 0.34 Kg per liter of coating
minus water (2.9 Lb/gal).
Low Solvent
Coatings
Add on
Controls
290
107
-------
Table 6-2 (cont)
GROUP I CTGS LIMITS, CONTROL OPTIONS & AFFECTED FACILITIES
TANK TRUCK GASOLINE
LOADING TERMINALS
The recommended emission limit is
80 mg/liter (0.67 Lb/1,000 gal)
of gasoline loaded. This limit is
based on submerged fill and vapor
recovery/control systems. No leaks
in the vapor collection system
during operation is a requirement.
Add on
Controls
600
BULK GASOLINE PLANTS
Alternative 1 - submerged filling of
of tank trucks.
Alternative 2 - alternative 1 plus
a vapor balance (displacement)
system to control voc emissions from
filling of bulk plant storage tanks.
The vapors displaced from the storage
tank are transferred to the tank
truck being unloaded. Ultimately,
'the vapors are recovered when the
tank truck returns to the terminal.
Alternative 3 - alternative 2 plus a
vapor balance system to control voc
emissions from filling of account
tank truck are transferred to the
storage tank.
1800
Vapor Balance
System Equip-
ment Specifica-
Tions and Opera-
ting Procedures
GASOLINE SERVICE
STATIONS-STAGE I
Emission limits recommended in terms of
specifications. Recommended controls
are submerged fill of storage tanks, vapor
balance between truck and tank, and a leak
between truck and tank, and a leak free
truck and vapor transfer system.
Equipment
Specification
and Operating
Procedures
Vapor Balance
System
340000
FIXED-ROOF PETROLEUM
STORAGE TANKS
Emission limits recommended in terms of
equipment specifications: installation
of internal floating roofs or alternative
controls are not specified in the CTG
document.
Equipment Speci-
fications and
Maintenance
Requirements
Internal 5
Floating Roof
300
108
-------
Tablt 6-2 (cont)
GROUP I CTGS LIMITS, CONTROL OPTIONS & AFFECTED FACILITIES
PETROLEUM REFINERY
PROCESSES
CUTBACK ASPHALT
Emission limits recommend
a. VPS - incineration of VOC
emissions from con-
densers
b. ws - covering separator
forebays
c. PUT - combustion of vapor
Vented from vessels
Substitute water and non-
volatile emulsifier for
petroleum distillate
blending stock.
Various Equipment 285
Specification and
Operating Procedures
Water Emission
Emulsion Solvent
Content
n/a
SOLVENT METAL
CLEANING
The VOC emission limit is
recommended in terms of
equipment specifications and
operation procedures. Required
control equipment can be adsorp-
tion system depending on the type,
size, and design of the degreaser.
Equipment
Specifications
and Operating
Procedures
Add-on Carbon
Absorber
1,245,000
109
-------
Table 6-3
Group II CTGS Limits, Control Options
INDUSTRY
CTG EMISSION LIMIT
APPLICABLE
CONTROL OPTIONS
NUMBER OF
AFFTECTED
FACILITIES
Petroleum refinery
Fugitive emission*
(Leaks)
If a leaking component has a voc
concentration of over 10,000 ppm
at the potential leak source, it
should be scheduled for main-
tenance and repaired within 15 days.
Inspection monitor-
ing maintenance
311
Surface Coating
Miscellaneous
Metal Parts
FACTORY SURFACE
COATING FLATVOOD
Coating method
a. Air or forced
dried items
b. Clear cost
c. No or infrequent
color change or
s'mall number of
color applied
1. Powder coatings
2. Other
Recommended limitation wt. VOC
vol. Coating
0.42 Kg/1 (3.5 Lb/gal)
0.52 Kg/1 (4.3 Lb/gal)
0.05 Kg/1 (0.4 Ib/gal)
0.36. Kg/1 (3.0 Ib/gal)
d. Outdoor, harsh 0142 Kg/1 (1.5 Lb/gal)
exposure or extreme
performance
characteristics
0.36 Kg/1 (3.0 Lb/gal)
Frequent color
change, large
number of colors
applied, or first
cost on untreated
ferrous substrate
Recommended limitation
2
Printed hardwood plywood 2.9 Kg VOC/100 m 2
and partteleboard
Natural finish hardwood
Clean II Finishes for
boarding paneling
(6.0 Lb VOC/1000 ft
2
5.8 Kg VOC/100 m
2
(12.0 Ib VOC/1000 ft )
2
4.8 Kg VOC/100 m
2
(10.0 Ib VOC/100 ft
low solvent 9600
coatings
add on
Low Solvent 300
COATING
Add on
110
-------
Table 6.3 (cont)
NUMBE.
OF
CTG EMISSION APPLICABLE AFFTECTE[
INDUSTRY LIMIT CONTROL OPTIONS FACILITY
»
1. a. Surface condensers or equivalent Maintenance
control on vents from reactors, and Operation 800
harmaceutical Manufacture distillation operations, crystal-
lizers, centrifuges, and vacuum
dryers that emit 6.8 Kg/day
(15 Ib/day) or more voc.
b. Surface condensers must meet Add- on
certain temperature versus VOC
vapor pressure criteria.
2. Additional specific emission re-
ductions are required for air
dryers, production equipment ex-
haust system, and storage and
transfer of VOC.
3. Enclosures or covers are recommended
for rotary vacuum filters, processing
liquid containing VOC and in-process
tanks.
4. Repair of components leaking liquids
containing VOC.
IDBBER TIRE MANUFACTURE VOC emissions reduction from the affected
operations is recommended through Add-on 62
use of carbon adsorption of
incineration. Water-based coatings
may be sued for green tire spraying.
3RAPHIC ARTS ROTOGRAVURE Of vater-bome or high solids inks meeting
UJD FLEXOGRAPHY certain composition eria or the use of Low Sol- 53001
capture and control equipment which vent Inks, unit:
provides:
a. 75 Percent overall voc reduction
where a publication rotogravure
process is employed;
b. 65 Percent overall voc reduction where add-on
a packaging rotogravure process is
employed; or,
c. 60 Percent overall voc reduction where
a flexographic printing process is
employed.
Ill
-------
Table 6.3 (cont)
INDUSTRY
CTG EMISSION LIMIT
APPLICABLE
CONTROL OPTIONS
NUMBER
OF
AFFECTED
FACILITIES
External Floating
Roof Tanks
A continuous secondary seal or
equivalent closure on all
affected storage tanks, plus
certain inspection and record-
keeping requirements.
Inspection Mainte-
nance Monitoring
13,800
*Drycleaning
Perchloroethylene
Casoline Tank
Trucks
a. Reduction of dryer outlet
concentration to less than
100 ppm voc, by means of
carbon adsorption.
(Facilities with inadequate
space or steam capacity for
adsorbers are excluded.)
B. Reduction of voc emissions
from filter and distillation
wastes.
C. Eliminate liquid and vapor
leaks.
Operation and
Maintenance
60,000
Add*on Carbon
Adsorption
The control approach is a com-
bination of testing, monitoring,
and equipment design to ensure
that good maintenance practices
are employed to prevent leaks from
truck tanks or tank compartments
and vapor collection systems during
gasoline transfer at bulk plants,
bulk terminals, and service stations
A leak is a reading greater than or
equal to 100 percent of the lei at
2.5 Co from a potential leak source
as detected by a combustible gas
detector.
Pressure-Vacuum
Test
N/A
Inspection, Moni-
toring, Maintenance
Manufacture of
Vegetable Oil
Recommended VOC emission limits:
a. Limit extractor vent exhaust to
9000 ppm
Add-on
Inspection, Moni-
toring and Maintenance
N/A
b. Limit desolventizer, dryer cooler
and pneumatic conveyer emission
to 207 Ib/ton of flake
112
-------
Table 6-4. GROUP III GTC'S LIMITS AND CONTROL OPTIONS
INDUSTRY
CTG
DOCUMENT NUMBER
APPLICABLE
CONTROL OPTIONS
CTG
EMISSION
LIMIT
Large Petroleum
Dry Cleaners
EPA-450/3-82-009
Operation and Main-
nance
Solvent recover
dryer to reduce
emissions by 81%,
a cartridge filtration
system in place of
existing diatomite
filtration system and
improved operation of
stills with leak detect
ion and repair program
Natural Gas/
Gasoline
Processing
Plants
EPA-450/3-83-007
Inspection
Monitoring
Maintenance
SOCHI-Fugitive
EPA-450/3-83-006
Inspection Moni-
toring Maintenance
Weekly visual inspection
of pumps and quarterly
instrument monitoring of
pumps, valves, compres-
sors and relief valves.
Leaking components
>10,000 ppm should be
repaired within fifteen
(15) days.
Same as CTG for natural
gas/gasoline processing
plant except process
streams must be >10% VOC
and no small plant ex-
ception
Manufacture of
High Density Poly-
ethylene Polypropy-
styrene
EPA-450/3-83-008
Add-On
VOL STORAGE
SOCMI Air
Oxidation
CTG not issued as of
9/1/84
EPA-450/3-84-015
Reduction to 20 ppm for
continuous voc emissions
is recommended or a 98%
reduction for poly
propylene plants and an
emissions limit of 0.12
Kg voc/1000 kg product
for polystyrene plants
Recommended RACT requires
affected facilities to
reduce VOC emission by
98% or to 20 ppm which is
even less stringent.
113
-------
Pollutants, airflows, and, to a limited
extent, pollutant concentrations in the
atmospheric discharge are described.
The reports also identify emission con-
trols for each site and provides cost
estimates for carbon adsorption and
catalytic incineration for VOC control.
Call the CTC HOTLINE to order
these reports or to obtain additional
information.
El
W VOC CTG's, ACT'S
and RULES
By Bob Blaszczak
CCchcbaiL
U.S. EPA. OAQPS
The EPA has recently begun, or is
about to begin, work on 15 new VOC
control techniques guidelines (CTG'S),
alternative control techniques docu-
ments (ACTs), or rules. The following
source categories are included in this
new effort:
1. Synthetic Organic Chemical
Manufacturing Industry
(SOCMI) Distillation Processes
2. SOCMI Reactor Processes
3. SOCMI Batch Processes
4. Wood Furniture Manufacturing
5. Coating of Plastic Parts -
Business Machines
6. Coaling of Plastic Parts - Other
jng
7. Web Offset Lithography
8. Autobody Refinishing
9. Clean-up Solvents
10. Industrial Adhesives
11. Pesticides Application
12. Petroleum Wastewater
13. Consumer & Commercial
Products
14. Architectural & Industrial
Coatings
15. Marine Vessel Loading and
Unloading
If you have any questions concern-
ing the status or schedule for develop-
CTG's/ACT's/rules for any of these
itegories, call the CTC HOTLINE.
INDUSTRIAL
WASTEWATER
TREATMENT EMISSIONS
By Bob Blaszczak,
CTC Co-chair
and Penny Lassiter,
U.S. EPA. OAQPS
The CTC recently completed its
report on industrial wastewater treat-
ment emissions and controls. This
document, "Industrial Wastewater
Volatile Organic Compound Emissions
- Background Information For BACT/
LAER Determinations," provides tech-
nical information on 1) estimating emis-
sions of VOC from the collection and
treatment of industrial wastewater, and
2) determining the control technology
for VOC emissions from this category.
The document applies to four types
of industries: the organic chemicals,
plastics, and synthetic fibers industry;
the pesticides industry; the pharmaceu-
tical industry; and the hazardous waste
treatment, storage, disposal facilities
industry. This list, however, could be
expanded to include additional indus-
tries as new information becomes avail-
able. Sources within the four listed cate-
gories have the potential to generate
wastewater containing high concentra-
tions of volatile organic compounds.
Wastewater typically passes through a
series of collection and treatment units
prior to its discharge. Many of these
collection and treatment units are open
to the atmosphere. This allows organic-
containing wastewater to contact ambi-
ent air which results in significant VOC
emissions from the wastewater.
Three different control strategies
are available for the reduction of VOC
emissions. The most effective strategy
involves the implementation of pollution
prevention or waste minimization tech-
niques to reduce or eliminate the gen-
eration of wastewater or to reduce the
organic concentration of the wastewa-
ter. The second control strategy in-
volves the identification of potentially
significant VOC-emitting wastewater
streams, management of these
(continued page 4)
CTC ASSISTANCE
. No-cost assistance to staff of State and local agencies
and EPA Regional Offices on air pollution control technology
issues.
CTC HOTLINE: CALL (919) 541-0800 or (FTS) 629-
0800 to access EPA expert staff for consultations, refer-
ences to pertinent literature, or access to EPA technical data
and analyses. No question is too simple!
ENGINEERING ASSISTANCE PROJECTS: If you
need in-depth assistance concerning a specific control tech-
nology problem, call the HOTLINE or write the CTC. The
EPA staff and contractors are available for short-term proj-
ects such as review of proposed or existing control technol-
ogy applications. Projects are subject to CTC Steering Com-
mittee approval.
TECHNICAL GUIDANCE PROJECTS: If the CTC re-
ceives several similar HOTLINE calls or a joint request from
a group of agencies, the CTC Steering Committee may
undertake broad, long-term projects of national or regional
interest. The result may be a control technology document
for a particular type of source, microcomputer software, or
seminars and workshops.
CTC News page 3
114
-------
Control
by
Incineration
115
-------
Chapter 3
Combustion
Introduction
The process of combustion is most often used to control the emissions of volatile
organic compounds from process industries. At a sufficiently high temperature and
adequate residence time, any organic vapor can be oxidized to carbon dioxide and
water by the combustion process. Combustion systems are often relatively simple
devices capable of achieving very high removal efficiencies. They consist of:
burners, which ignite the fuel and organic vapors; and a chamber, which provides
appropriate residence time for the oxidation process. Due to the high cost and
decreasing supply of fuels, combustion systems are designed to include some type of
heat recovery. If heat recovery can be used, combustion can be a very effective
control technique. Eor example, pollutant emissions from paint bake ovens can be
reduced by 99.9+ % using incineration while heat recovered from the incinerator
flue gases can be fed back to the oven. Combustion can also be used for serious
emission problems which require high destruction efficiencies, such as odor
problems or the emission of toxic gases.
There are, however, some problems that may occur when using combustion to
control gaseous pollutants. Incomplete combustion of many organic compounds
results in the formation of aldehydes and organic acids which may create an addi-
tional pollution problem. Oxidizing organic compounds containing sulfur or
halogens produce unwanted pollutants such as sulfur dioxide, hydrochloric acid,
hydrofluoric acid or phosgene. If present, these pollutants would require a scrubber
to remove them prior to release into the atmosphere.
Four basic combustion systems can be used to control combustible gaseous emis-
sions. They are flares, thermal oxidizers, catalytic oxidizers, and process boilers.
Although these devices are physically similar, the parameters under which they
operate are markedly different. Choosing the proper device depends on many fac-
tors including: concentration of combustibles in the gas stream, process flow rate,
control requirements, presence of contaminants in the waste stream, and an
economic evaluation. This chapter will examine the principles of combustion, sim-
ple combustion calculations, and the design and operating parameters of each
combustion device.
Combustion Principles
Combustion is a chemical process occurring from the rapid combination of oxygen
with various elements or chemical compounds, resulting in the release of heat. The
process of combustion is also referred to as oxidation. Most fuels used for combus-
3-1
116
-------
tion are composed essentially of carbon and hydrogen, but can include other
elements such as sulfur. Simplified reactions for the oxidation of carbon and
hydrogen are given as:
(Eq. 3-1) C + Ot — CO2 + energy
(Eq. 3-2) 2H, + O2 — 2HtO + energy
Equations 3-1 and 3-2 show that the final products of combustion from an
organic fuel are carbon dioxide and water vapor. Although combustion seems to be
a very simple process that is well understood, in reality it is not. The exact manner
in which a fuel is oxidized does not occur exactly as given in the above equations,
but rather in a series of complex, free radical chain reactions. The precise set of
reactions by which combustion occurs is termed the mechanism of combustion. By
analyzing the mechanism of combustion, the rate at which the reaction proceeds
and the variables affecting the rate can be predicted. For most combustion devices,
the rate of reaction proceeds extremely fast compared to the mechanical operation
of the device. Maintaining efficient and complete combustion is somewhat of an art
rather than a science, as anyone who has built a campfire can attest to. Therefore,
this chapter will focus on the factors which influence the completeness of combus-
tion, rather than analyzing the mechanisms involved.
To achieve complete combustion once the air (oxygen) and fuel have been
brought into contact, the following conditions must be provided: a temperature
high enough to ignite the air and fuel mixture; turbulent mixing of the air and
fuel; and sufficient residence time for the reaction to occur. These three conditions
are referred to as the "three T's of combustion". Time, temperature, and tur-
bulence govern the speed and completeness of reaction. They are not independent
variables since changing one affects the other two.
Temperature
The rate at which a combustible compound is oxidized is greatly affected by
temperature. The higher the temperature, the faster the oxidation reaction will
proceed. The chemical reactions involved in the combination of a fuel and oxygen
can occur even at room temperature, but very slowly. For this reason, a pile of oily
rags can be a fire hazard. Small amounts of heat are liberated by the slow oxida-
tion of the oils. This in turn raises the temperature of the rags and increases the
oxidation rate, liberating more heat. Eventually a full-fledged fire can break out.
For combustion processes, ignition is accomplished by adding heat to speed up
the oxidation process. Heat is needed to combust any mixture of air and fuel until
the ignition temperature of the mixture is reached. By gradually heating a mixture
of fuel and air, the rate of reaction and energy released will gradually increase
until the reaction no longer depends on the outside heat source. More heat is being
generated than is lost to the surroundings. The ignition temperature must be
reached or exceeded to ensure complete combustion.
3-2
117
-------
The ignition temperature of various fuels and compounds can be found in com-
bustion handbooks such as the North American Combustion Handbook (1965).
These temperatures are dependent on combustion conditions and therefore should
be used only as a guide. Ignition depends on (EPA, 1972):
1. concentration of combustibles in the waste stream
2. inlet temperature of the waste stream
3. rate of heat loss from combustion chamber
4. residence time and flow pattern of the waste stream
5. combustion chamber geometry and materials of construction.
Most incinerators operate at higher temperatures than the ignition temperature
which is a minimum temperature. Thermal destruction of most organic compounds
occurs between 590 and 650 °C (1100 and 1200°F). However, most incinerators are
operated at 700 to 820 °C (1300 to 1500°F) to convert CO to CO2; which occurs
only at these higher temperatures.
Time
Time and temperature affect combustion in much the same manner as
temperature and pressure affect the volume of a gas. When one variable is
increased, the other may be decreased with the same end result. With a higher
temperature, a shorter residence time can achieve the same degree of oxidation.
The reverse is also true, a higher residence time allows the use of a lower
temperature. In describing incinerator operation, these two terms are always men-
tioned together. One has little meaning without specifying the other.
The choice between higher temperature or longer residence time is based on
economic considerations. Increasing residence time involves using a larger combus-
tion chamber resulting in a higher capital cost. Raising the operating temperature
increases fuel usage which also adds to the operating costs. Fuel costs are the major
operating expense for most incinerators. Within certain limits, lowering the
temperature and adding volume to increase residence time can be a cost effective
alternative method of operation.
The residence time of gases in the combustion chamber may be calculated from:
(Eq. 3-3) 0= —
Where: 0 = residence time, s
V = chamber volume, ms
Q_= gas volumetric flow rate at combustion conditions, mVs
O_ is the total flow of hot gases in the combustion chamber. Adjustments to the
flow rate must include any outside air added for combustion. Example 3-1 shows
the determination of residence time from the volumetric flow rate of gases.
3-3
118
-------
Turbulence
Proper mixing is important in combustion processes for two reasons. First, for com-
plete combustion to occur, every particle of fuel must come in contact with air
(oxygen). If not, unreacted fuel will be exhausted from the stack. Second, not all
of the fuel or waste gas stream it able to be in direct contact with the burner
flame. In most incinerators a portion of the waste stream bypasses the flame
and is mixed at some point downstream of the burner with the hot products of
combustion. If the two streams are not completely mixed, a portion of the waste
stream will not react at the required temperature and incomplete combustion will
occur.
A number of methods are available to improve mixing the air and combustion
streams. Some of these include the use of refractory baffles, swirl fired burners,
and baffle plates. These devices are discussed in more detail in the equipment sec-
tion of this chapter. The problem of obtaining complete mixing is not easily solved.
Unless properly designed, many of these mixing devices may create "dead spots"
and reduce operating temperatures. Merely inserting obstructions to increase tur-
bulence is not the answer. According to one study of afterburner systems, "the
process of mixing flame and fume stream to obtain a uniform temperature for
decomposition of pollutants is the most difficult part in the design of the after-
burner" (EPA, 1972).
Oxygen Requirements
Oxygen is necessary for combustion to occur. To achieve complete combustion of a
compound, a sufficient supply of oxygen must be present to convert all of the car-
bon to CO2. This quantity of oxygen is referred to as the stoichiometric or
theoretical amount. The stoichiometric amount of oxygen is determined from a
balanced chemical equation summarizing the oxidation reactions. For example,
from Equation 3-4, I mole of methane requires 2 moles o'f oxygen for complete
combustion.
(Eq. 3-4) CH* -I- 2O2 - CO2 + 2H,O
If an insufficient amount of oxygen is supplied, the mixture is referred to as rich.
There is not enough oxygen to combine with all the fuel so that incomplete com-
bustion occurs. This condition results in black smoke being exhausted. If more
than the stoichiometric amount of oxygen is supplied, the mixture is referred to as
lean. The added oxygen plays no part in the oxidation reaction and passes through
the incinerator.
Oxygen for combustion processes is supplied by using air. Since air is essentially
79% nitrogen and 21% oxygen, a larger volume of air is required than if pure
oxygen were used. To balance Equation 3-4, 9.53 moles of air would be required
to completely combust the 1 mole of methane. The stoichiometric calculations for
this are presented in Appendix D. A listing of theoretical air requirements is given
in Table 3-1.
3-4
119
-------
Table 3-1. Combustion constants and approximate limits of flammabilityf
of gases and vapors in air.
Substance
Carbon, C'
Hydrogen, H,
Oxygen, O|
Nitrogen (atm), Nt
Carbon monoxide, CO
Carbon dioxide, COi
Paraffin series
Methane, CH,
Ethane, C,H,
Propane, C,H,
n-Butane, C4H,«
Isobutane, C.Hu
n-Pentane, C,Hn
Isopemanc, C,H,i
Neopentane, CtH,,
n-Hexane, C,H,,
Olefm series
Ethylene, C,H»
Propylene, C,H,
n-Butene, C.H,
Isobutene, C.H,
n-Pemene. C,H,0
Aromatic series
Benzene, C,H,
Toluene, CtH,
Xylene, C,H10
Miscellaneous gases
Acetylene, C,H,
Napthalene, C|0H,
Methyl alcohol, CH.OH
Ethyl alcohol. C.H.OH
Ammonia, NH,
Sulfur, S* i
Hydrogen sulfide, H|S i
Sulfur dioxide, SOf ;
Water vapor, H,O
A :_
Air
Gasoline
Lb/ft«
0.0053
0.0846
0.0744
0.07401
0.1170
0.0424
0.0803
0.1196
0.1582
0.1582
0.1904
0.1904
0.1904
0.2274;
0.0746
0.1110
0.1480
0.1480;
0.1852.
0.2060
0.243L
0.2803
0.0697
0.3384
0.0846
0.1216
0.0456.
_
0.0911
0.1733.
0 {\A1ti
,U4/0
0.0766
Ft'/lb
187.723
Hfil O
.Ola
13.443
13.506
8.548
23.565
12.455
8.365
6.321
6.321
5.252
5.252
5.252
4.398
13.412
9.007
6.756
6.756
5.400
4.852
4.113
3.567
14.344
2.955
11.820
8.221
21.914
—
10.979
5.770
ni A1 7
21 .Ul /
13.063
Heat of combustion
(Btu/ft1)
Gross'
(high):
325
322
1013
1792
2590
3370
3363
4016
4008
3993
4762
1614
2336
3084
3068
3836
3751
4484
5230
1499
5854
868
1600
441
—
647
Net,
(low)
275
322
913
1641
2385
3113
3105
3709
3716
3693
4412
1513
2186
2885
2869
3586
3601
4284
4980
1448
5654
768
1451
365
596
(Btu/lb)
Gross
(high)
14.093
61.100
4,547;
23,879
22,320
21,661
21,308
21,257
21,091
21,052
20,970
20,940
21.644
21,041
20,840
20,730
20,712
18,210
18,440
18,650
21,500
17,298
10,259
13.161
9,668
3,983
7,100
Net
(low)
14.093
51,623
4,347
21.520
20,432
19,944
19.680
19.629
19.517
19,478
19.396
19,403
20.295
19.691
19.496
19.382
19,363
17.480
17.620
17.760
20.776
16.708
9.078
11.929
8.001
3.983
6.545
For 100% tout air •
(mol/mol of combustible).
(ft'/ft' of combustible)
Required
for combustion
0,
i.o :
0.5 :
0.5
2.0
3.5
5.0
6.5
6.5
8.0
8.0
8.0
9.5
3.0
4.5
6.0
6.0
7.5
7.5
9.0
10.5
2.5
12.0
1.5
3.0
0.75
1.0
1.5
N,
3.76!
1.88J
1
1.68
7.53
13.18
18.82
24.47
24.47
30.11
30.11
30.11
35.76
11.29
16.94
22.59
22.59
28.23
28.23
33.88
39.52
9.41
45.17
5.65
11.29
2.82
3.76
5.65
Air ;
4.76!
2.38;
2.38
9.53
16.68
23.82
30.97
30.97
38.11
38.11
38.11
45.26
14.29
21.44
28.59
28.59
35.73
35.73
42.88
50.02
11.91
57.17
7.15
14.29
3.57
4.76
7.15
Flue products
CO,,
1.0;
- i
1.0
1.0
2.0
3.0
4.0
4.0
5.0
5.0
5.0
6.0
2.0
3.0
4.0
4.0
5.0
6.0
7.0
8.0
2.0
10.0
1.0
2.0
-
SO,
1.0
1.0
H,O
—
1.0 ,
-
2.0
3.0
4.0
5.0
5.0
6.0
6.0
6.0
7.0
2.0
3.0
4.0
4.0
5.0
3.0
4.0
5.0
1.0
4.0
2.0
3.0
1.5
_
1.0
N,
3.76:
1.88
1.88
M
7.53
13.18
18.82
24.47
24.47
30.11
30.11
30.11
35.76
11.29
16.94
22.59
22.59
28.23
28.23
33.88
39.52
9.41
45.17
5.65
11.29
3.32
3.76
5.65
For 10096 total air
(lb/lb of combustible)
Required
for combustion
O,
2.66;
7.94:
0.57
3.99
3.73
3.63
3.58
3.58
3.55
3.55
3.55
3.53
3.42
3.42
3.42
3.42
3.42
3.07
3.13
3.17
3.07
3.00
1.50
2.08
1.41
1.00
1.41
N,
8.86|
26.41;
1.90
13.28
12.39
12.07
11.91
11.91
11.81
11.81
11.81
11.74
11.39
11.39
11.39
11.39
11.39
10.22
10.40
10.53
10.22
9.97
4.98
6.93
4.69
3.29
4.69
Air
11.53
34.S4J
;
2.47:
17.27
16.12
15.70
15.49
15.49
15.35
15.35
15.35
15.27
14.81'
14.81
14.81
14.81
14.81
13.30
13.53
13.70
13.30
12.96
6.48
9.02
6.10
4.29
6.10
Flue products
CO,
3.66
— ,
1.57
2.74
2.93
2.99
3.03
3.03
3.05
3.05
3.05
3.06
3.14
3.14
3.14
3.14
3.14
3.38
3.34
3.32
3.38
3.43
1.37
1.92
-
SO,
2.00
1.88
H.O
— ;
8.94;
2.25
1.80
1.68
1.55
1.55
1.50
1.50
1.50
1.46
1.29
1.29
1.29
1.29
1.29
0.69
0.78
0.85
0.69
0.56
1.13
1.17
1.59
—
0.53
N,
8.86;
26.41;
i
1.90;
13.28
12.39
12.07
11.91
11.91
11.81
11.81
11.81
11.74;
11.39
11.39
11.39
11.39
11.39
10.22
10.40
10.53
10.22
9.97
4.98
6.93.
5.51,
3.29
4.69
Flammability
limit!
(% by volume)!
Lower,
— i
4.00
12.50
5.00
3.00
2.12
1.86
1.80
—
—
—
1.18
2.75
2.00
1.75
—
—
1.40
1.27
1.00
—
—
6.72
3.28
15.50
—
4.30
1.40
Upper
—
74.20
74.20
15.00
12.50
9.35
8.41
8.44
—
—
—
7.40
28.60
11.10
9.70
—
—
7.10
6.75
6.00
—
—
36.50
18.95
27.00
—
45.50
-
7.60
OS
•Carbon and sulfur are considered as gases for molal calculations only.
Sources: Adapted from Fuel Flue Gases, American Gas Association.
Combustion Flame and Explosions of Gases, 1951.
-------
In industrial applications, more than the stoichiometric amount of air is used to
ensure complete combustion. This extra volume is referred to as excess air. If ideal
mixing were achievable, no excess air would be necessary. However, most combus-
tion devices are not capable of achieving ideal mixing of the fuel and air streams.
The amount of excess air is held to a minimum in order to reduce heat losses.
Excess air takes no part in the reaction but does absorb some of the heat produced.
To raise the excess air to the combustion temperature, additional fuel must be used
to make up for this loss of heat. Operating at a high volume of excess air can be
very costly in terms of the added fuel required. Equations to calculate excess air
are also listed in Appendix D.
In addition to the theoretical air required, Table 3-1 also lists the volume of
combustion products produced from oxidizing a substance. This is an important
term used to determine the size of the combustion chamber. Example 3-1 illustrates
how these values are used. The values in Table 3-1 are given in volume percent
and weight percent. Volume percent is the more important term for combustion of
gaseous substances since gas flows are measured in cubic meters per second instead
of weight units. For example, from Table 3-1, when 1 m3 of methane is combusted
with the theoretical amount of air, 10.53 ms of flue gas is produced. Table 3-1 is
given in English units. Since these are volume ratios (ftVft3), metric units and
English units are interchangeable.
Natural gas is not listed in Table 3-1 since its chemical composition can vary.
When 1 m3 of natural gas is burned with a stoichiometric amount of air, it pro-
duces approximately 11.5 m3 (average value) of flue gas.
Combustion Limits
Not all mixtures of fuel and air are able to support combustion. The flammable or
explosive limits for a mixture are the maximum and minimum concentrations of
fuel in air that will support combustion. The upper explosive limit (UEL) is
defined as the concentration of fuel which produces a nonburning mixture due to a
lack of oxygen. The lower explosive limit (LEL) is defined as the concentration of
fuel below which combustion will not be self-sustaining. Table 3-1 lists the
flammability limits (LEL and UEL) for common fuels and solvents.
For example, consider that a mixture of gasoline vapors and air is at
atmospheric conditions. From Table 3-1 the LEL is 1.4% by volume of gasoline
vapors and the UEL is 7.6%. Any concentration of gasoline in air within these
limits will support combustion. That is, once a flame has been ignited it will con-
tinue to burn. Concentrations of gasoline in air below or above these limits will not
burn and can quench the flame. The lower explosive limit is the more important of
the two terms in describing gas streams with combustible contaminants. Industrial
processes which handle combustible vapors, such as paint or solvent vapors, are
usually required by insurance companies to operate at less than 25% of the LEL of
the vapor in the ducts to minimize fire hazards. By using gas analyzers and an
alarm system, the concentration of vapor may be allowed to be as high as 50% of
the LEL by an insurance company covering the plant.
Flammability limits are not absolute values, but are affected by temperature,
3-6
121
-------
pressure, geometry of the chamber, and presence of other contaminants. The
higher the temperature, the greater the activation energy of combustion is. Thus,
there is a greater probability that the flame will propagate. At high enough
temperatures even vapor concentrations within 25% of their LEL can propagate a
flame. This high degree of flammability limits the temperature to which some
waste streams can be preheated prior to oxidation. Pressure also changes vapor
flammability by its effect on gas densities. The higher the pressure, the closer the
gas molecules are to one another. This decreases the distance a flame or spark
must jump from one combustible point to another (Bethea, 1978).
The size and geometry of the combustion chamber also affect the flammability
limits. The smaller the diameter of the chamber, the narrower the flammability
range will become. Increased surface-to-volume ratio promotes rapid cooling and
flame quenching, limiting flammability. Some flame arresters are designed on this
principle of large surface-to-air volume ratio to eliminate fire hazards. The
presence of other compounds can also affect flammability limits. The flammability
range of a mixture can be either increased or decreased depending on the proper-
ties of the contaminant.
Flame Combustion
When mixing fuel and air, two different mechanisms of combustion can occur. A
luminous (yellow) flame results when air and fuel flowing through separate ports
are ignited at the burner nozzle. The yellow flame results from thermal cracking of
the fuel. Cracking occurs when hydrocarbons are intensely heated before they have
a chance to combine with oxygen. The cracking releases both hydrogen and carbon
which diffuse to the flame to form CO2 and H,O. The carbon particles give the
flame the yellow appearance. If incomplete combustion occurs from flame tempera-
ture cooling or if there is insufficient oxygen, soot and black smoke will form.
Blue flame combustion occurs when the fuel and air are premixed in front of the
burner nozzle. This produces a short, intense, blue flame. The reason for the dif-
ferent flame is that the fuel-air mixture is gradually heated. The hydrocarbon
molecules are slowly oxidized, going from aldehydes and ketones to CO2 and H2O.
No cracking occurs and no carbon particles are formed. Incomplete combustion
results in the release of the intermediate, partially oxidized compounds. Blue haze
and odors are emitted from the stack.
122
-------
Combustion Equipment Used for Control
of Gaseous Emissions
Introduction
Afterburning, incineration, or thermal oxidation are interchangeable terms used to
describe the combustion process used to control gaseous emissions. Although not
technically correct, this nomenclature is generally accepted. Afterburners and
incinerators perform different functions even though both are forms of thermal
oxidation. The term afterburner is appropriate only to describe a thermal oxidizer
used to control gases coming from a process where combustion was not complete
(Ross, 1977). An example of an afterburner in use would be an application on a
copper wire reclaiming source which incompletely burns off the rubber coating.
Incineration or thermal oxidation are not necessarily afterburning. Each is a
primary burning process that is installed to control effluent pollutants which are
combustible. Incinerators are used to combust solid, liquid and gaseous materials.
When used in this manual, the term incinerator will refer to controlling gaseous
emissions of organic vapors. Examples of sources using incineration are curing and
drying ovens, chemical processes, petroleum refining processes, and food processing
plants. In this chapter the terms incinerator and thermal oxidizer will be used
interchangably.
Equipment used to control waste gases by combustion can be divided into three
categories: direct combustion or flaring, thermal oxidation, and catalytic oxida-
tion. A direct combustor or flare is a device in which air and all the combustible
waste gases react at the burner. Complete combustion must occur instantaneously
since there is no residence chamber. Therefore, the flame temperature is the most
important variable in flaring waste gases. In contrast, in thermal oxidation, the
combustible waste gases pass over or around a burner flame into a residence
chamber where oxidation of the waste gases is completed. Catalytic oxidation is
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very similar to thermal oxidation. The main difference is that after passing through
the flame area, the gases pass over a catalyst bed which promotes oxidation at a
lower temperature than does thermal oxidation.
Direct Combustion or Flaring
Direct combustion or flaring is used for the disposal of intermittent or emergency
emissions of combustible gases from industrial sources. Safety and health hazards at
or near the plant can be eliminated by using flares to prevent the direct venting of
these emissions. Flares have been used mainly at oil refineries and chemical plants
which handle large volumes of combustible gases.
Flares are simply burners that have been designed to handle varying rates of fuel
while burning smokelessly. In general, flares can be classified as either elevated or
ground level. The reason for elevating a flare is to eliminate any potential fire
hazard at ground level. Ground level flares must be completely enclosed to conceal
the flame. Either type of flare must be capable of operating over a wide range of
flow rates in order to handle all plant emergencies. The range of waste gas flows
within which a flare can operate and still burn efficiently is referred to as the turn-
down ratio. Flares are expected to handle turndown ratios of 1000:1, while most
industrial boilers seldom handle more than a 10:1 turndown ratio (Gottschlich,
1977). For example, a flare should be capable of maintaining complete combustion
for waste gas flow rates ranging from 20,000 mVh to 20 mVh.
Although the flare is designed to eliminate waste gas stream disposal problems, it
can present safety and operational problems of its own. Some of the problems
associated with operation of a flare system are:
1. Thermal radiation: Heat given off to the surrounding area may be
unacceptable.
2. Light: Luminescence from the flame may be a nuisance if the plant is located
in an urban area. '
3. Noise: Mixing at the flare tip is done by'jet Venturis which can cause excess
noise levels in nearby neighborhoods.
4. Smoke: Incomplete combustion can result in toxic or obnoxious emissions.
5. Energy consumption: Flares waste energy in two ways. First by keeping the
pilot flame constantly lit and secondly, by the potential recovery value of the
waste gas being flared.
For flaring to be economically feasible, the waste gas usually must supply at least
50% of the fuel value to combust the mixture. When the heat content of the waste
gas is below 4.28 X 10s kj/ms (115 Btu/ft3), injecting an additional gas with a
higher heating value is necessary to achieve complete combustion. This type of
system is referred to as a fired or endothermic flare. The cost of the additional fuel
for endothermic flaring can be considerable. To conserve energy, some companies
have used other waste gases in place of conventional fuels.
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Elevated Flares
A typical elevated flare is composed of a system which first collects the waste gases
and passes them through a knockout drum to remove any liquids. Water seals or
other safety devices are placed between the knockout drum and the flare stack to
prevent a flashback of flames into the collection system. The flare stack is essen-
tially a hollow pipe thai may extend to .1 height of 100 ineleis or more. Tlit-
diameter of the flare stack determines the volume of waste gases that can be
handled. At the top of the stack is the flare tip which is comprised of the burners
and a system to mix the air and fuel.
Smokeless combustion is accomplished by proper design of the flare tip.
Smokeless flares require a system allowing for intimate mixing of waste gases and
air. A number of flare tip designs provide good mixing characteristics over a wide
range of waste gas flow values and still have excellent flame holding capabilities.
Steam jets have proved to be one of the most effective ways to mix air and waste
gases. An example of a flare tip designed for steam injection is illustrated in Figure
3-4. In addition to increasing turbulence, steam injection reduces the partial
pressure of the waste gas, thus reducing polymerization reactions. The steam also
reacts with the gases to produce oxygenated compounds which readily burn at
lower temperatures. Other devices used to reduce smoke are high pressure fuel
gases, water sprays, high velocity swirl fired burners, and electric air blowers
(Straitz, 1980). In addition to these devices, shields are also used on elevated flares
to protect the flame zone from atmospheric conditions. This shield also helps
reduce noise and visibility problems associated with flares.
Steam injection point
Waste gas
retention ring
Steam distribution
ring
Flare stack
Pilot assembly
Figure 3-4. Smokeless flare tip.
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As previously mentioned, steam reacts with intermediate combustion products to
form compounds that burn readily at lower temperatures. One of the main reac-
tions taking place is a hydrolysis reaction referred to as the water-gas reaction. This
reaction produces hydrogen gas which helps flare operation. The simplified water-
gas shift can be written as:
Steam-to-hydrocarbon mass ratios are usually determined by the molecular weight
and concentration of the unsaturated organic compounds (alkenes and alkynes) in
the waste gas. Steam requirements generally range between 0.05 and 0.30 kg of
steam per kg of waste gas (Gottschlich, 1977). The steam is automatically injected
proportionally to the flow rate of the waste gases.
Enclosed Ground Flares
Manufacturers design a number of different ground flares. Most ground flares con-
sist of multiple burners enclosed within a refractory shell. The shell encloses the
flame to eliminate noise, luminescence, and safety hazards. The waste gas is
introduced through a jet or venturi to provide turbulent mixing. The term ground
flare refers to locating the flare tip at ground level. The flare system still requires a
stack for proper release of the effluent gases. Figure 3-5 shows a ground flare
installed at Nippon Steel Company in Oita City, Japan (Straitz, 1980). The flare is
composed of two chambers designed to combust eight different gases and a liquid-
waste stream.
Burners
Accoustical insulation
Liquid-waste
atomizing injectors
Source: Straitz, 1980.
Figure 3-5. Ground flare.
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Ground level flares normally have a much higher capital cost than elevated
flares. The cost of a ground flare depends on the size of the enclosure. The size of
a ground flare is directly proportional to the volume of vapors it must handle.
Ground flares can be designed for efficient combustion without steam injection.
Eliminating the use of steam injection can significantly lower operating costs as
compared to elevated systems (Straitz, 1980). Some plants have incorporated both
designs. A ground Hare is used lor normal or intermittent operation and a large
elevated flare is only used to control emergency releases of large quantities of gases.
Incinerators
Thermal oxidizers or organic vapor incinerators refer to any device that uses a
flame (temperature) combined with a chamber (time and turbulence) to convert
combustible material to carbon dioxide and water. An incinerator usually consists
of a refractory-lined chamber that is equipped with one or more sets of burners. A
typical incinerator is depicted in Figure 3-6. The contaminant-laden stream is
passed through the burners where it is heated above its ignition temperature. The
hot gases then pass through one or more residence chambers where they are held
for a certain length of time to ensure complete combustion. Depending on the par-
ticular needs of the'system, additional fuel and/or excess air can be added through
the burners. Also, since the flue gases are discharged at elevated temperatures, a
system to recover the heat may be included. With the rising costs of fuel and
solvents, heat recovery devices are becoming an integral part of many incineration
systems.
Plenum
Figure 3-6. Typical thermal incinerator (UOP raw gas burner).
Incinerators on industrial processes are most often used to control gas streams
with a low concentration of organic vapors. The concentration of vapors delivered
to an incinerator through process ductwork is limited by the LEL of the mixture.
Safety codes usually limit combustible vapor concentrations in ducts to a maximum
of 25% of the LEL. By using process control monitors and alarm systems, some
plants have been allowed to go up to 50% of the LEL. Supplemental fuel is
required to ignite the waste gas stream and bring it up to the proper operating
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temperature. The amount of fuel is then decreased proportionally to the heating
value supplied by the waste gas stream. Ideally, after initial startup, little or no
auxiliary fuel would be needed.
Incinerators operate at temperatures between 700 and 800°C (1300 and 1500°F)
with a residence time of 0.1 to 0.5 seconds. The residence time is determined by
the size of the combustion chamber and is measured after the required
temperature has been reached. Typical operating temperatures of thermal oxidizers
for various processes are listed in Table 3-3 (EPA, 1972). As noted previously,
temperature and residence must be discussed together since changing one affects
the other. By raising the temperature, the residence time for complete combustion
is reduced and vice versa. However, temperature is the more important process
variable. Figure 3-7 illustrates the effect of both temperature and residence time on
the percent destruction of pollutants (oxidation rate). Depending on the initial
temperature, small increases in temperature can bring dramatic increases in pollu-
tant destruction. For example, for a 0.01 second residence time increasing the
temperature from 1200 to 1400°F, the percent destruction is doubled from approx-
imately 50 to 100%. At 1200°F, the residence time must be increased ten times
(from 0.01 second to over 0.1 second) for the same increase in percent pollutant
destruction.
Table 3-3. Typical waste gas incinerators' operating temperatures (°F).
Industry
Asphalt blowing
Biological control, fermentation
Carpet laminating
Coffee roasting
Coil coating, sheet coating, metal decorating
Core ovens, foundry
Coating, engraving
Cloth carbonization
Deep fat fryers
Gum label drying oven
Mineral wool, fiberglass curing
Odor control (general) sludge off -gas
Hardboard tempering
Oil and grease smoke (metal chip recovery, heat
quench baths, tempering)
Paint bake ov?ns
Paper manufacture— sulfite digester off-gas
Pipe wrapping
Rendering plants
Rubber products
Petroleum refining and products
Printing, lithographing
Smelting, refining, metal recovery, wire bumoff
Smokehouse opriiuon
Solvent control
Varnish cookeis. resin kettles
Vinyl plaslisol curing
Wood milling
Wire enameling
Phthalir anhdyridc
Textile drying oven
LAAPCD**
recommendation
_
—
1200-1400
—
—
1400
—
1800
1200
—
—
1300-1500
—
1200-1400
1200-1500
—
1400
1200
—
-
—
—
1200
1500 1500
1200
1200-1400
—
-
—
—
Survey data
1000-2000
110-1250
-
1200-1500
1200-1500
2000
1000*- 1450
—
—
—
1000*
1100-1250
1200
900*- 1600
1100-1500
-
—
1200-1300
1300-1400
1300-2000
1300-1500
1300 1650
800*- 1200
—
1000M500
1200
—
-
1250-1440
1350
Literature
_
—
--
1050
1300
—
—
—
—
1250
1310
1300-1425
1200
--
1240
1350
—
1200
1300
—
—
—
—
—
1200-1400
900*
1200
1300-1350, 1400
-
-
*Low temperature generally for odor, smoke control, not true organic vapor destruction.
**LAAPCD is the Los Angeles Air Pollution Control District.
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100
.2
4-1
£>
"S
.a
•a
w
e
(4
£
20 —
600 800
Source: Rolke, 1972.
1000 ,1200/^ 1400
^Temperature,
1600 1800
Figure 3-7. Effects of temperature and residence time
on rate of pollutant oxidation.
Besides temperature and residence time, the concentration of the pollutant in
die waste gas stream also affects operation of the incinerator. First, the concentra-
tion of the contaminant dictates the amount of supplemental fuel required.
Initially, supplemental fuel must be added to start the oxidation reaction. As the
temperature rises, the rate of oxidation of the contaminant increases until the reac-
tion becomes self-sustaining. The amount of fuel can then be decreased. A certain
amount of fuel is normally burned to ensure stable operation. Secondly, there is a
problem of flame quenching. To avoid noncombustible mixtures, the entire
amount of waste gas and fuel cannot usually be mixed at the burner. It would
require an inordinate amount of fuel to bring the entire waste gas stream within
combustible limits. Only part (about one-half) of the waste gas stream is mixed
with the fuel at the burner. The remainder of the waste gas stream must be mixed
with the hot products of combustion downstream of the flame to avoid quenching
the flame. Unless adequate mixing of the waste gas stream and hot products of
combustion is accomplished, incomplete combustion products will be exhausted.
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Types of Burner Arrangements
The design of an incinerator must allow adequate mixing of the fuel and waste gas
streams. A number of different burner designs provide the required mixing without
quenching the flame. Burners are classified as either discrete or distributed (EPA,
1973). The main distinction between the two types of burners is the number and
size of flames in each type. The discrete burner produces a single large flame
plume into which the waste gas stream must be blended. The distributed burner
system produces an array of smaller flames. The waste gas stream is divided and
then flows around these flames. In distributed burners more of the waste gas
stream is passed over or around the flame. This allows distributed burners to com-
plete mixing of the waste gases and hot products of combustion in shorter distances
than in discrete burners. Distributed burners also utilize the oxygen in the waste
gas stream more efficiently, reducing the amount of oxygen supplied through the
burner. This in turn reduces the need for additional fuel to heat the air/waste gas
mixture to the required oxidation temperature.
Three types of distributed burner systems are the line burner, the multtjet, and
the grid burner. All three of these systems are comprised of a manifold system, to
inject the fuel, and a mixing or profile plate which regulates air flow to the flame
area. Fuel (usually natural gas) enters the burner area of the line burner (Figure
3-8) through holes in manifold pipes. The pipes are placed across the duct at 0.3
meters (1.0 foot) intervals (EPA, 1972). Waste gas enters the burner area through
holes in the profile plate. The plate allows only a portion of the waste gas, usually
50%, to directly contact the flame. The remaining portion of the gas bypasses the
flame area and is mixed with the hot combustion gases downstream of the flame.
Figure 3-9 illustrates an example of one type of mixing plate. The plate is attached
to the manifold pipes and forms a "v" shaped trough; part of the waste gas enters
the flame area through the holes, while the remaining portion of waste gas passes
around the plate.
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Fuel
Waste gas and air
Figure 3-8. Distributed (line) burner.
Burners
Burners
Fuel
Figure 3-9. Mixing plate for waste gas and hot combustion products.
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Multijet burners are very similar to line burners. Multijet burners have a single
fuel inlet which is manifolded to produce numerous individual flames. Figure 3-10
shows the Hirt multijet burner system. In this system, waste gases flowing to the
flame area are controlled by a profile or mixing plate. The profile plate allows a
portion of the waste gas stream to flow behind it and mix with the fuel to supply
the combustion area. The remaining gases must pass around in front of the profile
plate. Air flow to the burner flame area is adjusted by moving the profile plate
either closer or further away from the burners. Adjusting the profile plate on the
multijet system is relatively simple and can be accomplished while the unit is still in
service. Adjusting the mixing plate on the line burner is not as simple, because the
unit must be taken off line. The line burner, however, has the advantage of being
much smaller. The line burner accomplishes mixing over a relatively short
distance, a few inches, as compared to the multijet which requires several feet.
Adjustable gap
Mixing plate
Multijet burners
Fuel
Figure 3-10. Multijet burner.
The grid burner also uses a manifold system to introduce the fuel. Mixing is
accomplished by passing the waste gas stream through a slotted grid as shown in
Figure 3-11. The slots are approximately 2.5 by 7.5 cm (1 by 3 in.) (EPA, 1972).
The grid allows foj extremely fast mixing of the fuel and waste gas. There is,
however, very little control to allow for adjusting flow rates since the grid is sta-
tionary. Grid burners are best suited for applications where waste gas flow ratios
are relatively constant.
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Fuel
Flame area
Waste gas
Figure 3-11. North American flame grid burner.
Problems can arise using any of the three types of distributed systems. Some of
these are:
1. Natural gas is the only fuel source that can be used. If solid or liquid par-
ticles are present or formed during combustion, they can plug the tiny holes
in the fuel manifold system. This is known as burner fouling.
2. The oxygen content of the waste gas stream must be at least 16%. Oxygen for
combustion is supplied by the waste gas stream. If the oxygen content is not
16% or greater, incomplete combustion can occur.
3. Mixing, profile, and grid plates must be able to withstand high temperatures.
This adds to the capital equipment costs.
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To avoid some of the problems associated with distributed burners, especially
fouling, discrete burners are sometimes used. The discrete burner is simply one
large burner (Figure 3-12). Many other burner arrangements are classified as
discrete burners. They can range from a simple gas ring, comparable to those used
on home stoves, to a torch burner (Figure 3-6). In this illustration, mixing the pro-
cess waste gas and hot products of combustion is accomplished by using a conical
mixing plate.
Waste gas
Fuel and air
Conical mixing plate
Figure 3-12. Discrete burner.
In most discrete burners, mixing must usually be provided downstream of the
flame. Baffles are most commonly used to provide the required turbulence.
However, baffles increase the pressure drop across the incinerator. Unless installed
correctly, baffles can cause dead zones which actually decrease the degree of
mixing. Two main types used in incinerators are the bridge wall baffle and the
ring and disc baffle illustrated in Figure 3-13 and Figure 3-14. The bridge wall
baffle is a wall placed across the combustion chamber. The bridge wall technique
is most effective when pairs of baffles are used. The ring and disc baffles consist of
a series of rings inserted in the middle along with discs on the side walls of the
chamber.
Figure 3-13. Bridge wall baffle.
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Figure 3-14. Ring and disc baffle.
Catalytic Oxidation
A catalyst is a substance which causes or speeds a chemical reaction without itself
undergoing a change. In catalytic incineration, a waste gas is passed through a
layer of catalyst known as the catalyst bed. The catalyst causes the oxidation reac-
tion to proceed at a faster rate and lower temperature than is capable in thermal
oxidation. Catalytic incinerators operating in a 370 to 480 °C (700 to 900 °F) range
can achieve the same efficiency as a thermal incinerator operating between 700 and
820°C (1300 and 1500°F). This can result in a 40 to 60% fuel savings.
Catalytic reactions can be classified as either homogeneous or heterogeneous.
Homogeneous reactions occur throughout the bulk of the catalyst, while
heterogeneous reactions occur only on the surface of the catalytic material. In air
pollution control applications, all reactions are heterogeneous. The oxidation reac-
tion of the organic vapors occurs only on the surface of the catalyst. It should be
noted that catalytic reactions produce the same end products (CO2 and H2O) and
liberate the same heat of combustion as does thermal incineration.
A heterogeneous catalyst reaction proceeds through a series of five basic steps:
1. Organic compounds in the waste gas must first diffuse from the bulk of the
vapor to the surface of the catalyst.
2. Organic compounds then adsorb onto the surface of the catalyst.
3. Organic compounds then react (oxidize).
4. New compounds then desorb after reacting.
5. New compounds then diffuse and mix back into the bulk of the exhaust air
stream.
The most effective and commonly used catalysts for oxidation reactions come
from the noble metals group. Platinum either alone or in combination with other
noble metals is by far the most commonly used. Desirable characteristics of
platinum are that it gives a high oxidation activity at low temperatures, is stable at
high temperatures, and is chemically inert. Palladium is another noble metal which
exhibits these properties and is sometimes used in catalytic incinerators.
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Since catalytic oxidation is a surface reaction, the noble metal is coated onto the
surface of a cheaper support material. The support material can be made of a
ceramic or a metal such as alumina, silica-alumina or nickel-chromium. The sup-
port material is arranged in a matrix shape to provide: high geometric surface
area; low pressure drop; uniform flow of the waste gas through the catalyst bed;
and a structurally stable surface (EPA, 1972). Structures which provide these
characteristics are pellets, a honeycomb matrix, or a mesh matrix. Figure 3-15
shows a typical honeycomb catalyst module which is the most common. The sup-
port material for these is usually ceramic, but can be metal.
Figure 3-15. Typical honeycomb catalysts (metallic or ceramic).
A schematic of a catalytic incinerator is shown in Figure 3-16. Catalytic
incinerators consist of a preheat section (burner area), where part of the waste gas
is raised to operating temperature. The burners are the same as those used for
thermal incineration, with the majority being distributed burners. The remaining
portion of the waste gas is mixed with the hot products of combustion before
passing over the catalyst bed. This ensures a homogenous waste gas and
temperature mixture as it passes over the bed. After passing over the bed, the hot
flue gases may be sent to a heat recovery system.
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Heat exchanger tubes
Catalyst
Figure 3-16. Catalytic incinerator.
Catalyst bed depth controls the pressure drop across the incinerator. Typically,
the volume of catalyst required for 85 to 95% conversion of all organic compounds
in 0.01 to 0.05 seconds is between 0.03 to 0.14 m3 of catalyst per 1000 m/s of
waste gas (0.5 to 2.0 ft3 of catalyst per 1000 cfm of waste gas). As a general rule,
the higher the molecular weight of the compound, the more readily it is oxidized.
Normal pressure drops through catalytic incinerators are between 62 and 125 Pa
(0.25 and 0.5 in. H2O). If the exhaust does not have sufficient draft to overcome
this pressure drop, a blower may have to be installed.
To ensure proper operation, the inlet and outlet temperatures to the catalyst sec-
tion are monitored. This verifies that the temperature is sufficient to achieve the
required conversion and also ensures protection of the catalyst from excessive
temperatures. Since catalytic incinerators operate at lower temperatures than ther-
mal units, less refractory brick and small chamber volumes can be used. This
reduction in size of the device reduces installation costs.
Operating Limitations of Catalytic Incinerators
Catalytic incinerators usually cannot be used effectively on waste gas streams which
contain particulate matter. Particulate matter that deposits on the surface of the
catalyst prohibits the organic compounds from being adsorbed. Coating of the
catalyst surface in this manner is referred to as fouling of the catalyst. Oil droplets
can also foul the catalyst bed unless they are vaporized in the preheat section. By
periodically cleaning and washing the catalyst, 90% of its activity can be restored
^EPA, 1972). Maintenance of this type, however, adds significantly to the cost of
operating the unit.
Certain metals can chemically combine with or alloy to the catalyst, thereby
making it useless. Deactivation in this manner is called catalyst poisoning. Catalyst
poisons can be divided into two categories: fast acting poisons which include
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phosphorus, bismuth, arsenic, antimony, and mercury, and slow acting poisons
which include zinc, lead and tin. Catalysts are more tolerant of the slow acting
poisons, particularly at temperatures below 540°C (1000°F). At sufficiently high
temperatures (>590°C), even copper and iron are capable of alloying to platinum,
reducing its activity.
Sulfur and halogen compounds act as poisons, but not to the extent of the
metals. They are essentially reaction inhibitors called suppressants. Their chemical
interaction with the catalyst is reversible. Once the halogen or sulfur compound is
removed, catalyst activity is restored to normal.
All catalysts deteriorate with normal use. Gradual loss of the catalyst material
can occur from erosion, attrition, and vaporization. High temperatures can also
accelerate catalyst deactivation. Loss of catalyst activity due to high temperature is
known as thermal aging, and causes very rapid catalyst deterioration. Even short
term temperatures above 820°C (1500°F) can cause a near total loss of catalyst
activity. With proper monitoring of operating temperatures, a catalyst bed can be
expected to last from three to five years before it must be replaced. The percent
destruction of pollutants decreases with increasing thermal aging. Adjustment to
operating conditions (temperature, residence time, etc.) may need to be made to
ensure that the exhaust continues to meet emission limits.
Comparison of Thermal vs. Catalytic Incinerators
The major difference between thermal and catalytic incinerators is that complete
combustion can be achieved at much lower temperatures in a catalytic incinerator.
The reduced temperatures rut the cost of fuel usage by 40 to 60%. Operation at
lower temperatures also decreases the construction costs. Lighter materials of con-
struction can be used in catalytic units. This also makes installation easier and less
costly. In terms of overall equipment costs, for small capacity units, up to 4.7 or
5.7 mVs (10,000 or 12,000 cfm), the purchase costs for either unit is essentially
equal (EPA, 1972). For larger units that must be custom designed, thermal
incinerators are usually less expensive, but this depends on the type of heat
recovery system.
The main problem in catalytic incineration is the reduction or loss of catalyst
activity. Loss of catalyst activity occurs due to fouling by particulate matter or sup-
pression or poisoning due to other contaminants in the waste gas stream. In order
to effectively use catalytic incineration, these contaminants must be removed from
the waste gas stream. Removing these contaminants would require additional
equipment which adds greatly to the cost of the system. Finally, all catalysts must
periodically be replaced due to thermal aging.
Process Boilers Used as Incinerators
An alternative to installing a thermal or catalytic incinerator would be to combust
the waste gases in an existing plant or process boiler. This would avoid the capital
cost of new equipment and may help to reduce present fuel consumption. Process
and plant boilers are normally designed to operate in excess of 980 °C (1800°F)
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with a flue gas residence time of 0.5 to 3.0 seconds. These conditions exceed those
recommended for thermal incinerators. However, a number of additional condi-
tions must be satisfied before waste gases can be properly disposed of in this
manner.
The following criteria must be considered before a process boiler can be used as
an incinerator (EPA, 1977):
1. The waste gases must be almost completely combustible. If solid particles
are present in the waste gases, or formed by incomplete combustion, they can
foul heat exchanger surfaces in the boiler, thus reducing boiler efficiency.
Particulate matter may also cause boiler emissions to exceed applicable emis-
sion regulations. The costs of increased maintenance of the boiler and/or con-
trol of paniculate matter may well exceed the purchase price of an
incinerator.
2. The waste gas should, preferably, constitute only a small fraction of the air
requirements of the boiler. If the volume of the waste gas is large, special
attention must be paid to the oxygen balance, mixing, and continuation of
the air flow in the boiler when the process is shut down.
3. The oxygen concentration of the contaminated gas stream should be close to
that of air to ayoid incomplete combustion. Incomplete combustion produces
tars that coat heat exchanger surfaces, reducing boiler efficiency.
4. The boiler must operate at all times when incineration is required.
5. The waste gas must be free of compounds, such as halogenated hydrocarbons,
that accelerate corrosion of the boiler.
6. Baffling may be required in the combustion chamber to ensure adequate
mixing and combustion of the waste gas.
7. If the boiler-firing rate varies greatly, it may be necessary to install a small
auxiliary boiler that will operate under steady load conditions.
To date, not many industries have been successful in using plant or process
boilers as incinerators. Petroleum refineries, which have numerous waste gas
streams and process boilers, are one of the few industries which have been able to
incinerate waste gases in process boilers.
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THERMAL AND CATALYTIC INCINERATORS
Inspection Summaries
7.3 Inspection Summaries
7.3.1 Level 1 Inspections - Not Applicable
7.3.2 Level 2 Inspections
Basic Inspection Points
Stack ° Visible emissions
Bypass Stack
Incinerator
Vapor refraction lines
Heat recovery outlet gas temperature
Incinerator outlet temperature
Temperature rise across catalyst bed
Audible air infiltration
Obvious corrosion
Process Equipment
0 Process operating rate
Follow-up
Incinerator
0 Fan motor current
0 Hood static pressure
7.3.3 Level 3 Inspections
Stack ° All elements of a Level 2 Inspection
Incinerator
All elements of a Level 2 Inspection
Inlet gas temperature
Inlet VOC concentration
Outlet VOC concentration
Process
All elements of a Level 2 Inspection
Coatings compositions
147
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Inspection Summaries
7.3.4 Level 4 Inspections
Stack
0 All elements of a Level 3 inspection
Incinerator
0 All elements of a Level 3 inspection
0 Locations for measurement ports
0 Potential inspection safety problems
Process Equipment
0 All elements of a Level 3 inspection
0 Basic flowchart of process
0 Potential inspection safety problems
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THERMAL AND CATALYTIC INCINERATORS
Inspection Procedures
7.4. Inspection Procedures
The inspection procedures for incinerators can be classi-
fied as Level 2 and Level 3 inspections. The Level 2 inspec-
tion is a detailed walkthrough inspection utilizing the on-site
incinerator and process instrumentation. The Level 3 inspec-
tion includes all of the Level 2 steps and also includes the
limited use of portable instruments to verify incinerator per-
formance. The instruments generally used are the portable VOC
detectors and portable thermocouple thermometers. Instrument
measurement procedures and safety considerations are discussed
in another section of this notebook.
7.4.1 Basic Level 2 Inspections
Observe the Incinerator Exhaust.
There should be no visible soot or particulate emissions
from the exhaust. Visible emissions are generally due to
improper burner operation or condensation of unburned organic
compounds.
Observe the incinerator bypass stack.
Incinerators generally must have bypass stacks so that the
process equipment can be safely vented in the event of inciner-
ator malfunction. However, during routine operation, there
should be no significant leakage of VOC contaminated gas
through the bypass stack dampers. The leakage of high VOC
concentration gas can often be identified by the wavy light
refraction lines at the stack mouth.
Record the incinerator operating temperature.
For thermal incinerators, the combustion chamber exhaust
gas temperature should be recorded. This is generally monitored
by a thermocouple that is used to adjust the main burner firing
rate. A reduction in the operating temperature could result in
a reduced VOC oxidation efficiency.
For catalytic incinerators, the inlet and outlet gas tem-
peratures to the catalyst bed should be recorded. The inlet gas
temperature is the temperature after the preheat burner and
immediately ahead of the catalyst bed. The bed
149
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Basic Level 2 Inspection Procedures
Record the incinerator operating temperature.(Continued)
outlet temperature is the temperature before the gas stream
enters any of the heat recovery equipment. Smaller than normal
temperature increases across the catalyst bed are due to either
catalyst inhibition or to a reduced VOC concentration in the
inlet gas stream.
Listen for air infiltration into the incinerator system.
Air infiltration into incinerators under negative pressure
(fan downstream of the incinerator) can lead to localized
cooling of the gas stream. Incomplete VOC oxidation can occur
in these areas. Severe air infiltration into the inlet duct
could prevent proper incinerator operating temperatures since
this reduces the sensible heat and the heating value of the
inlet gas stream. Infiltration also reduces the VOC capture
effectiveness at the process source.
Check the incinerator shell, outlet ductwork, and stack for
obvious corrosion.
Hydrochloric acid vapor can be formed in incinerators due
to the oxidation of chlorinated hydrocarbons. This can lead to
corrosion of the incinerator shell and downstream gas handling
equipment.
Review the process operating records.
Confirm that the incinerator was operated whenever high-
solvent materials were being used.
7.4.2 Follow-up Level 2 Inspection Steps
Evaluate the fan motor current.
A decrease in the fan motor current as compared to the
baseline levels indicates a decrease in the total gas flow from
the process equipment. A flow rate decrease could be due to a
decrease in the process operating rate or a change in the process
operating conditions. Fugitive emissions should'be evaluated to
the extent possible when there has been a significant decrease in
the fan motor currents without process operating changes.
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Follow-up Level 2 Inspection Procedures
Measure the hood static pressure.
The hood static pressure provides a general indication of
the gas flow rate from the process equipment. This data is
useful to confirm that there are no significant fugitive VOC
emissions.
7.4.3 Level 3 Inspections
Measure the VOC outlet concentration.
The effluent gas concentration should be measured if there
is safe and convenient access to the effluent gas duct. The port
should be located downstream of the heat recovery equipment so
that the gas temperature is as low as possible. A glass-lined
probe is usually advisable to minimize losses of organic vapor to
the surfaces of the probe. If the gas temperature is greater
than 300 °F, it will probably be necessary to include a condensor
and knock-out trap in the sample line in order to protect the VOC
detectors.
The VOC detector (and its portable recorder, if any) should
be certified as intrinsically safe for the type of hazardous
location prevailing in the vicinity of the incinerator. No
electrically powered equipment should be used that could ignite
fugitive VOC vapors.
The observed concentration should be less than 5 to 10% of
the inlet concentration if the incinerator is operating properly.
Measure the inlet VOC concentration.
The inlet gas stream VOC concentration can usually be
measured using the same VOC instrument used for the outlet port.
A dilution probe will often be necessary for photoionization
instruments and flame ionization instruments limited to 1000 to
2000 ppm. The condensor and knock-out trap are rarely necessary
since the gas stream temperatures are normally less than 250 °F.
As in the case with the outlet measurements, the measurement of
the inlet concentration should be done only when all safety
requirements are satisfied.
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Level 3 Inspection Procedures
Measure the incinerator outlet temperature.
The measurement of the incinerator outlet temperature is
attempted whenever the on-site gauge does not appear to be
providing accurate data. However, measurement of the outlet
temperature using portable gauges is subject to a number of
significant possible errors. These include the following.
0 Higher than actual values due to exposure of
the probe to radiant energy from the burner.
0 Lower than actual values due to shielding of
the probe behind refractory baffles in the
combustion chamber.
0 Non-representative values due to spatial
variations of gas temperature immediately
downstream of the incinerator.
For these reasons, the independent measurement of the
incinerator outlet temperature is rarely done by regulatory
agency inspectors. Also, battery powered thermocouple ther-
mometers are not intrinsically safe and can therefore not be
used in certain areas.
Measure the hood static pressure.
The hood static pressure provides a general indication
of the gas flow rate from the process equipment. This data
is useful to confirm that there are no significant fugitive
VOC emissions.
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Level A Inspection Procedures
7.4.A Level A Inspection Procedures
The Level A inspection includes many inspection steps per-
formed during Level 2 and 3 inspections. These are described
in earlier sections. The unique inspection steps of Level A
inspections are described below.
Evaluate locations for measurement ports.
Many existing fabric filters do not have convenient and
safe ports that can be used for static pressure, gas temperature,
and gas oxygen measurements. One purpose of Level A inspections
is to select (with the assistance of plant personnel) locations
for ports to be installed at a later date to facilitate Level 3
inspections.
Evaluate potential safety problems.
Agency management personnel and/or senior inspectors should
identify any potential safety problems involved in standard Level
2 or Level 3 inspections at this site. To the extent possible,
the system owner/operators should eliminate these hazards. For
those hazards that can not be eliminated, agency personnel should
prepare notes on how future inspections should be limited and
should prepare a list of the necessary personal safety equipment.
A partial list of common health and safety hazards includes the
following.
0 Hot exhaust duct surfaces
0 Inhalation hazards due to low stack discharge points
0 Weak catwalk and ladder supports
0 Fugitive emissions from process equipment
0 Inhalation hazards from adjacent stacks and vents
0 Weak roofs or catwalks
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Level 4 Inspection Procedures
Prepare a_ system flowchart.
A relatively simple flowchart is very helpful in conducting
a complete and effective Level 2 or Level 3 inspection. This
should be prepared by agency management personnel or senior
inspectors during a Level 4 inspection. This should consist of
a simple block diagram that includes the following elements.
0 Source(s) of emissions controlled by a single
incinerator
0 Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures)
0 Locations of any main stacks and bypass stacks
Location of incinerator
Locations of major instruments (static pressure
gauges, thermocouples)
Evaluate potential safety problems in the process area.
The agency management personnel and/or senior inspectors
should evaluate potential safety problems in the areas which
may be visited by agency inspectors during Level 2 and/or Level
3 inspections. They should prepare a list of the activities
that should not be performed and locations to which an inspec-
tor should not go as part of these inspections. The purpose of
this review is to minimize inspector risk and to minimize the
liability concerns of plant personnel.
o
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148
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Control
by
Adsorption
149
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Chapter 5
Adsorption
Introduction
During adsorption, one or more gaseous components are removed from an effluent
gas stream by adhering to the surface of a solid. The gas molecules being removed
are referred to as the adsorbate, while the solid doing the adsorbing is called the
adsorbent. Adsorbents are highly porous particles. Adsorption occurs on the inter-
nal surfaces of the particles as illustrated in Figure 5-1.
Adsorbent
Adsorbate
Figure 5-1. Vapor adsorbed into pores of activated carbon.
The attractive forces which hold the gas to the surface of the solid are the same
that cause vapors to condense (van der Waals' forces). All gas-solid interfaces
exhibit this attraction, some more than others. Adsorption systems use materials
which are highly attracted to each other to separate these gases from the non-
adsorbing components of an air stream. For air pollution control purposes, adsorp-
tion is not a final control process. The contaminant gas is merely stored on the sur-
face of the adsorbent. After it becomes saturated with adsorbate, the adsorbent
must either be disposed of and replaced, or the vapors must be desorbed. Desorbed
vapors are highly concentrated and may be recovered more easily and more
economically than before the adsorption step.
Traditionally, adsorption has been used for air purification and solvent
recovery. Air purification processes are those in which the contaminant is present
n trace quantities (less than 1.0 ppm) but is highly odorous or toxic. Systems used
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for air purification arc small thin bed adsorbers. When the bed becomes saturated
with contaminant, it is taken out and replaced. Solvent recovery processes require
much larger systems and are usually designed to control organic emissions whose
concentrations are greater than 1000 ppm. This has been the point where the
recovery value of the solvent could justify the expense of the large adsorption-
desorption system. Currently, adsorption is used as a method of recovering valuable
organic vapors from flue gases at all concentration levels. This is due to present
regulations limiting volatile organic emissions and the higher costs of solvents.
Theory of Adsorption
Mechanism of Adsorption
Adsorption occurs by a series of three steps. In the first step, the contaminant dif-
fuses from the major body of the air stream to the external surface of the adsor-
bent particle. In the second step, the contaminant molecule migrates from the
relatively small area of the external surface (a few m2/g) to the pores within each
adsorbent particle. The bulk of adsorption occurs in these pores because the
majority of available surface area is there (hundreds of mVg). In the third step,
the contaminant molecule adheres to the surface in the pore. Figure 5-2 illustrates
this overall diffusion and adsorption process.
Step 1: diffusion to
adsorbent surface
Step 2: migration into
pores of adsorbent
Contaminant molecules
Step 3: monolayer
buildup of adsorbate
1 X.
. .T. *. /.r..^./V.V.vNA • :T- .*.• .''7.^•'.'^'\:
Figure 5-2. Mechanism of adsorption.
5-2
151
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The purpose of analyzing the mechanism of adsorption is to determine which
step controls the overall process. By describing this step mathematically, adsorber
performance can be predicted from physical data. The actual adsorption of a
molecule, step 3, proceeds relatively quickly compared to steps 1 or 2. Therefore,
step 3 can be ignored when developing design equations. Steps 1 and 2 are both
diffusional processes. They involve the transport of the adsorbate through a carrier
gas phase to an adsorption site. In the first step, diffusion occurs because of a con-
centration difference. The rate of mass transferred by this type of diffusion can be
predicted from Equation 5-1.
Equation 5-1 is based on a film resistance theory of bulk diffusion as presented
in Chapter 4 on absorption. Bulk diffusion assumes that the only resistance a gas
molecule encounters in movement through the carrier gas stream occurs during col-
lisions with other gas molecules.
(Eq.5-1)
QB
Where: NA = rate of mass transfer, kg mol/s
kg = local mass transfer coefficient, kg mol/s«m2«Pa
j8 = void area between adsorbent granules, mVm3
A = surface area of adsorbent, mVkg
p= partial pressure of adsorbate in gas phase, Pa
p.- = partial pressure of adsorbate at the gas-solid interface, Pa
Qa= bulk density of adsorbent, kg/m3
The mass transfer coefficient (kj is a function of the velocity, viscosity, and density
of the carrier gas stream; the diffusivity of the gas molecule that is being adsorbed;
and the diameter of the adsorbent. Equations to estimate the transfer coefficient
based on these parameters can be found in Perry (1973).
Once the gas molecule has reached the external surface of the adsorbent, it must
diffuse (move) into the pores. Diffusion in the pores of the adsorbent can occur by
a number of different diffusion mechanisms depending on the size of the pore.
When the pores are large, bulk diffusion predominates. As the pores begin to nar-
row, collisions with the wall of the adsorbate become more likely than inter-
molecular collisions. The gas molecules strike the wall, remain for a short time,
then return to the gas phase. This is termed Knudson (or molecular) diffusion and
occurs much more slowly than does bulk diffusion for a given pore length. Finally,
in the smallest pores, surface diffusion is the predominant mechanism of gas
transport. Gas molecules can either migrate along the surface of the solid or jump
between adsorption sites.
Due to these varied mechanisms by which diffusion occurs, mass transfer rates in
the pores are extremely difficult to predict. Unless extensive data are available con-
cerning the specific adsorption application, determining the rate-controlling step
(step 1 or step 2) is impossible.
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One approach to determining the mass transfer rate is to rewrite Equation 5-1 in
terms of an overall mass transfer coefficient.
5-2) Ny4
Where: a = external adsorbent area, mVm3
p* = partial pressure in equilibrium with the surface concentration
of adsorbate, Pa
p = partial pressure of adsorbate in the gas phase, Pa
Koc = overall mass transfer coefficient, kg mol/h»m2«Pa
The overall mass transfer coefficient represents the resistance to molecular motion
encountered both outside and inside the pore.
(Eq. 5-3) —— = — + —
Koc K, k,
Where: 1^ = local mass transfer coefficient for combined surface migration and
pore diffusion, kg mol/h»m2»Pa
The local mass transfer coefficient cannot be satisfactorily predicted from basic
theory at the present time. However, it (and therefore K0c) can be determined with
some certainty from experimental data. Therefore, Equation 5-2 still does not give
a simple and accurate means of predicting adsorber performance from physical
data. What Equation 5-2 does show is that the equilibrium partial pressure of the
adsorbate (p*) determines the theoretical minimum adsorber bed size. Empirical
design procedures based on adsorption equilibrium conditions are the easiest and
most common methods used to predict adsorber size and performance. These
methods will be discussed later.
Adsorption Forces—Physical and Chemical
The adsorption process is classified as either physical or chemical. The basic dif-
ference between physical and chemical adsorption is the manner in which the gas
molecule is bonded to the adsorbent. In physical adsorption the gas molecule is
bonded to the solid surface by weak forces of intermolecular cohesion. The
chemical nature of the adsorbed gas remains unchanged; therefore, physical
adsorption is a readily reversible process. In chemical adsorption a much stronger
bond is formed between the gas molecule and adsorbent. A sharing or exchange of
electrons takes place —as happens in a chemical bond. Chemical adsorption is not
easily reversible.
The forces active in physical adsorption are electrostatic in nature. These forces
are present in all states of matter: gas, liquid, and solid. They are the same forces
of attraction which cause gases to condense and real gases to deviate from ideal
behavior. This electrostatic force can be measured by the constant "a" in van der
Waals' equation describing nonideal gas behavior. Physical adsorption is sometimes
also referred to as van der Waals' adsorption. The electrostatic effect which pro-
duces the van der Waals' forces depends on the polarity of both the gas and solid
molecules. Molecules in any state are either polar or nonpolar depending on their
5-4
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chemical structure. Polar substances are those which exhibit a separation of
positive and negative charges within the compound. This separation of positive and
negative charges is referred to as a permanent dipole. Water is a prime example of
a polar substance. Nonpolar substances have both their positive and negative
charges in one center so they have no permanent dipole. Most organic compounds,
because of their symmetry, are nonpolar.
Physical, or van der Waals' adsorption can occur from three different effects: an
orientation effect, dispersion effects, or induction effects (Figure 5-3). For polar
molecules, attraction to each other occurs because of the orientation effect. The
orientation effect describes the attraction which occurs between the dipoles of two
polar molecules. The negative area of one is attracted to the positive area of the
other. An example of this type of adsorption would be the removal of water vapor
(polar) from an exhaust stream by using silica gel (polar).
Polar —Polar
Nonpolar—Nonpolar
•4/W\A>
Polar—Nonpolar
Figure 5-3. Physical forces causing adsorption.
The adsorption of a nonpolar gas molecule onto a nonpolar surface is accounted
for by the dispersion effect. The dispersion effect is based on the fact that although
nonpolar substances do not possess a permanent dipole, they do have a fluctuating
or oscillating dipole. Fluctuating dipoles are a result of momentary changes in elec-
tron distribution around the atomic nuclei. In a nonpolar substance, when two
iluctuating dipoles come close to one another, their total energy decreases, and
ihey fluctuate in phase with each other. Oscillating dipoles disperse light.
Consequently, this is where the name dispersion effect comes from. The adsorption
of organic vapors onto activated carbon is an example of nonpolar molecular
attraction.
5-5
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The attraction between a molecule with a permanent dipole (polar molecule)
and a nonpolar molecule is caused by the induction effect. A molecule with a per-
manent dipole can induce or polarize a nonpolar molecule when they come in close
contact. The energy of this effect is determined by the polarizability of the non-
polar molecules. The induction effect is, however, very small when compared to
the orientation or dispersion effects. Therefore, adsorption systems use polar
adsorbents to remove polar contaminants and nonpolar adsorbents to remove non-
polar contaminants. This ensures that the intermolecular forces of attraction
between the gas and solid will be greater than those between similar molecules in
the gas phase.
Chemical adsorption or chemisorption results from the chemical interaction
between the gas and the solid. The gas is held to the surface of the adsorbate by
the formation of a chemical bond. Adsorbents used in chemisorplion can be either
pure substances or chemicals deposited on an inert carrier material. One example
is using pure iron oxide chips to adsorb H2S gases. Another example is using
activated carbon which has been impregnated with sulfur to remove mercury
vapors.
All adsorption processes are exothermic, whether adsorption occurs from
chemical or physical forces. In adsorption, molecules are transferred from the gas
to the surface of a solid. The fast-moving gas molecules lose their kinetic energy of
motion to the adsorbent in the form of heat.
In chemisorplion, the heat of adsorption is comparable to the heat evolved from
a chemical reaction, usually over 10 kcal/mol. The heat given off by physical
adsorption is much lower, approximately 100 cal/mol, which is comparable to the
heat of condensation. Some additional general differences between physical
adsorption and chemisorption which make physical adsorption more desirable for
air pollution control are:
1. Molecules that are adsorbed by chemisorption are very difficult (and in some
cases, impossible) to remove from the adsorbent bed. Physically adsorbed
molecules can usually be removed by either increasing the operating
temperature or reducing the pressure of the adsorbent bed.
2. Chemisorption is a highly selective process. A gas molecule must be capable
of forming a chemical bond with the adsorbent surface for chemisorption to
occur. Physical adsorption occurs under suitable conditions in most gas-solid
systems. For industrial purposes specific solids are chosen which enhance the
rate of adsorption.
3. Chemisorption stops when all the reactive sites on the surface of the adsorbent
have reacted. Chemisorption forms only a monolayer of adsorbate molecules
on the surface. Because of van der Waals' forces, physical adsorption can
form multilayers of adsorbate molecules —one atop another.
4. The chtmisorptioM rate increases with increasing temperature. For physical
adsorption the exact opposite is true: the rate decreases with increasing
temperature.
For these and other reasons, chemisorption is not used extensively in air pollution
control systems. A summary of the characteristics of physical versus chemical
adsorption is presented in Table 5-1.
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Table 5-1. Summary of characteristics of chcmisorpiion and physical adsorption.
Chemisorption
Releases high heat
10,000 cal/mol
Forms a chemical compound
Desorption is difficult
Impossible adsorbate recovery
Physical adsorption
Releases low energy
100 cal/mol
Dipolar interaction
Desorption is easy
Easy adsorbate recovery
Adsorbent Materials
Several materials are used effectively as adsorbing agents. The most common
adsorbents used industrially arc activated carbon, silica gel, activated alumina
(alumina oxide), and zeolites (molecular sieves). Adsorbents are characterized by
their chemical nature, extent of their surface area, pore size distribution, and par-
ticle size. In physical adsorption the most important characteristic in distinguishing
between adsorbents is their surface polarity. As discussed previously, the surface
polarity determines the type of vapors a particular adsorbent will have the greatest
affinity for. Of the above adsorbents, activated carbon is the primary nonpolar
adsorbent. It is possible to manufacture other adsorbing material having nonpolar
surfaces. Since their surface area is much less than that of activated carbon, they
are not used commercially. Polar adsorbents will preferentially adsorb any water
vapor that may be present in a gas stream. Since moisture is present in most pollu-
tant air streams, the use of polar adsorbents is severely limited for an air pollution
system. Therefore, in further discussion, the emphasis is placed on the use of
activated carbon, although some of the information is applicable to polar adsorp-
tion systems.
Activated Carbon
Activated carbon can be produced from a variety of feedstocks such as wood, coal,
coconut, nutshells, and petroleum-based products. The activation process takes
place in two steps. First, the feedstock is carbonized. Carbonization involves heating
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msually in the absence of air) the material to a temperature high enough (600°C)
to drive off all volatile material. Thus, carbon is essentially all that is left. To
increase the surface area, the carbon is then "activated" by using steam, air, or
carbon dioxide at higher temperatures. These gases attack the carbon and increase
the pore structure. The temperatures involved, the amount of oxygen present, and
the type of feedstock, all greatly affect the adsorption qualities of the carbon.
Manufacturers vary these parameters to produce activated carbons suitable for
specific purposes. In sales literature, the activity and retentivity of carbons are
based on their ability to adsorb a standard solvent, such as carbon tetrachloride
(ecu).
Because of its nonpolar surface, activated carbon is used to control emission of
organic solvents, odors, toxic gases, and gasoline vapors. Carbons used in gas phase
adsorption systems are manufactured in granular form, usually between 4x 6 to
4X 20 mesh in size. Bulk density of the packed bed can range from 0.08 to 0.5
g/cm* (5 to 30 lb/ft3) depending on the internal porosity of the carbon. Surface
area of the carbon can range from 600 to 1600 mVg (2.9 X 106 to 7.8 x 10s ftVlb).
This is equivalent to having the surface area of 2 to 5 football fields in one gram of
carbon.
Silica Gel
Silica gels are made from sodium silicate. Sodium silicate is mixed with sulfuric
'acid, resulting in a jellylike precipitant from where the "gel" name comes. The
precipitant is then dried and roasted. Depending on the processes used in manufac-
turing the gel, different grades varying in activity can be produced. Silica gels have
surface areas of approximately 750 mVg (3.7X 10s ftVlb). Silica gels are used
primarily to remove moisture from exhaust streams, but are ineffective at
temperatures above 260°C (500°F).
Molecular Sieves
Unlike the other adsorbents, which are amorphous (not crystalline) in nature,
molecular sieves have a crystalline structure. The pores are, therefore, uniform in
diameter. Molecular sieves can be used to capture or separate gases on the basis of
molecular size and shape. An example of this are refining processes which
sometimes use molecular sieves to separate straight chained paraffins from branched
and cyclic compounds. However, the main use of molecular sieves is in the removal
of moisture from exhaust streams. The surface area of molecular sieves range from
600 to 700 mVg (2.9 x 106 to 3.4 x 10s ftVlb).
Aluminum Oxide (Activated Alumina)
Aluminum oxides are manufactured by thermally activated alumina or bauxite.
This is accomplished by heating the alumina in an inert atmosphere to produce a
porous aluminum oxide pellet. Aluminum oxides are not commonly used in air
pollution applications. They are primarily used for the drying of gases, especially
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under high pressures, and as support material in catalytic reactions. A prime
example is the impregnating of the alumina with platinum or palladium for use in
catalytic incineration. Activated alumina's surface areas can range from 200 to
300 mVg (0.98 X 10s to 1.5 x 10s ftVlb).
Pore Size Distribution
The physical properties of the adsorbent affect the adsorption capacity, rate, and
pressure drop across the adsorber bed. Table 5-2 summarizes these properties for
the above adsorbents. Since adsorption occurs at the gas-solid interface, the surface
area available to the vapor molecules determines the effectiveness of the adsorbent.
Generally, the larger the surface area, the higher the adsorbent's capacity.
However, the surface area must be available in certain pore sizes if it is to bo effec-
tive as a vapor adsorber. Dubinin (1936) classified the pores in activated carbon as
micropores, transitional gores, or macropores. Micropores are openings whose radii
are 200 nanometers (20 A) or less. Pores larger than 2000 nanometers (200 A) are
macropores. Transitional pores are those with radii between 200 and 2000
nanometers.
Table 5-2. Physical properties of major types of adsorbents.
Adsorbent
Activated carbon
Activated alumina
Molecular sieves
Silica gel
Internal
porosity
(%)
55-75
30-40
40-55
70
Surface
area
(m'/g)
600-1600
200-300
600-700
750
Pore
volume
(cm'/g)
0.80-1.20
0.29-0.37
0.27-0.38
0.40
Bulk dry
densitv
(g/cm')
0.35-0.50
0.90-1.00
0.80
0.70
Mean pore
diameter
(nm)
150-200
180-200*
30-90
220
*The 150-200 nanometer average is for the micropores only; since 95% ot the surface area is
associated with them.
Most gaseous air pollutant molecules are in the 40 to 90 nanometer size range. If
a large portion of an adsorbent's surface area is in pores smaller than
40 nanometers, many contaminant molecules will be unable to reach these active
sites. Figure 5-7 illustrates molecule movement in the pores. In addition, the larger
pore sizes (macro and transitional) contribute little to molecule capture. The vapor
pressure of the contaminant in these larger areas is too low to be effectively
removed. These larger pores serve mainly as passageways to the smaller micropore
area where the adsorption forces are strongest. Adsorption forces are strongest in
pores that are not more than approximately twice the size of the contaminant
molecule. These strong adsorption forces result from the overlapping attraction of
the closely spaced walls.
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Macropore
Molecule
blocking pore
Area unavailable
for adsorption
Figure 5-7. Molecular screening in pores of activated carbon.
Another phenomenon, capillary condensation usually only occurs in the
micropores. Capillary condensation occurs when multilayers of adsorbed contami-
nant molecules build up from both sides of the pore wall, totally packing the pore
and condensing in the pore. The amount of contaminant that is removed increases
since additional molecules condense on the surface of the liquid which has formed.
Contaminant molecules can also be removed at lower vapor pressures (more dilute
concentrations) since capture forces are now acting from three sides instead of just
one. However, desorption is not as complete if capillary condensation occurs, since
the forces that hold a liquid together are much stronger than the physical adsorp-
tion forces.
Air pollution control involves removing contaminant vapors at low partial
pressures. Therefore, the micropore structure of an adsorbent plays an important
role in determining the overall efficiency. Another reason for the wide use of
activated carbon is that 90 to 95% of its surface area is in the micropore size
range.
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Dynamic Adsorption Process
The movement of vapors through an adsorbent bed is often referred to as a
dynamic process. The term dynamic refers to motion both in the movement of air
through the adsorbent bed and change in vapor concentration as it moves through
the bed. There are a variety of configurations in which the contaminant air stream
and adsorbent are brought into contact. The most common configuration is to pass
the air stream down through a fixed volume or bed of adsorbent. Figure 5-8
illustrates how adsorption (mass transfer) occurs as vapors pass down through the
bed.
Mass transfer
zone
Saturated
bed
T^j^aa-iaawjf ^^^--:^^tf ^a^aar^f
TTT
S c
II
o ^C
a-s
3
"5
-*• Breakpoint
Volume of effluent treated (lime)
Figure 5-8. Breakthrough curve.
The gas stream containing the pollutant, at an initial concentration, c,, is passed
down through a deep bed of adsorbent material which is free of any contaminant.
Most of the contaminant is readily adsorbed by the top portion of the bed. The
small amount of contaminant that is left is easily adsorbed in the remaining section
of the bed. The effluent from the bottom of the bed is essentially pollutant free,
denoted at Ci.
After a period of lime the top layer of the adsorbent bed becomes saturated with
contaminant. The majority of adsorption (approximately 95%) now occurs in a
narrow portion of the bed directly below this saturated section. The narrow zone of
adsorption is referred to as the mass transfer zone (MTZ). As additional contami-
nant vapors pass through the bed, the saturated section of the bed becomes larger
and the MTZ moves further down the length of the adsorber. The actual length of
5-16
160
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the MTZ remains fairly constant as it travels through the adsorbent bed. Addi-
tional adsorption occurs as the vapors pass through the "unused" portion of the
bed. The effluent concentration at cz is essentially still zero since there is still an
unsaturated section of the bed.
Finally, when the lower portion of the MTZ reaches the bottom of the bed, the
concentration of contaminant in the effluent suddenly begins to rise. This is
icferred to as the breakthrough point —-where untreated vapors are being exhausted
»'rom the adsorber. If the contaminated air stream is not switched to a fresh bed,
the concentration of contaminant in the outlet will quickly rise until it equals the
initial concentration, illustrated at point c«.
In most air pollution control systems even trace amounts of contaminants in the
effluent stream are undesirable. To achieve continuous operation, adsorbers must
be either replaced or cycled from adsorption to desorption before breakthrough
occurs. In desorption or regeneration, the contaminant vapors are removed from
the used bed in preparation for the next cycle. Most commercial adsorption systems
are the regenerable type.
In regard to regenerable adsorption systems, three important terms are used to
describe the capacity of the adsorbent bed. All the capacities are measured in Ib of
vapor per Ib of adsorbent. First, the breakthrough capacity is defined as the
capacity of the bed at which unreacted vapors begin to be exhausted. The satura-
tion capacity is the maximum amount of vapors that can be adsorbed per unit
weight of carbon. (This is the capacity read from the adsorption isotherm). The
working capacity is the actual amount of adsorbent used in an adsorber. The
working capacity is a certain fraction of the saturation capacity. Working
capacities can range from 0.1 to 0.5 of the saturation capacity. (Note: a smaller
capacity increases the amount of carbon required.) This fraction is set by the
designer for individual systems by balancing the cost of carbon and adsorber opera-
tion versus preventing breakthrough allowing for an adequate cycle time.
Another factor in determining the working capacity is that it is uneconomical to
desorb all the vapors from the adsorber bed. The small amount of residual vapors
left on the bed is referred to as the heel. This heel accounts for a large portion of
the difference between the saturation and the working capacity. In some cases the
working capacity can be estimated by assuming it is equal to the saturation capa-
city minus the heel (Turk, 1977). The following example illustrates one method of
estimating the working capacity. In all the examples in this manual and the
accompanying workbook, a design factor of 0.5 of the saturation capacity is used.
This is the same as assuming the working amount of carbon is twice the amount
required at saturation.
5U16i
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Factors Affecting Adsorption
A number of factors or system variables influence the performance of an adsorp-
tion system. These variables and their effects on the adsorption process are dis-
cussed in the following section.
Temperature
For physical adsorption processes, the capacity of an adsorbent decreases as the
temperature of the system increases. Figure 5-9 illustrates this concept. As the
temperature increases the vapor pressure of the adsorbate increases, raising the
energy level of the adsorbed molecules. Adsorbed molecules now have sufficient
energy to overcome the van der Waals' attraction and migrate back to the gas
phase. Molecules already in the gas phase tend to stay there due to their high
5-18
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vapor pressure. As a general rule, adsorber temperatures are kepi below t>5°C
(130°F) to ensure adequate bed capacities. Temperatures above this limit can be
avoided by cooling the exhaust stream that is to be treated.
Cu
o
I
a
O
Temperature
Figure 5-9. Carbon capacity vs. temperature.
Adsorption is an exothermic process with the heat released for physical adsorp-
tion approximately equal to the heat of condensation. At low concentrations (below
100 ppm) the heat release is minimal and is quickly dissipated by the air flow
through the bed. At higher concentrations (approximately 5000 ppm) considerable
heating of the bed can occur, which if not removed can cause the adsorber effi-
ciency to rapidly decrease. In addition, granular carbon is a good insulator, which
Inhibits heat dissipation from the interior of the bed. In some cases, especially
'letone recovery, the temperature rise can cause auto-ignition of the carbon bed.
Monitoring of bed temperatures and leaving the bed slightly wet after steam
regeneration are techniques used to avoid bed fires.
Pressure
Adsorption capacity increases with an increase in the partial pressure of the vapor.
The partial pressure of a vapor is proportional to the total pressure of the system.
Any increase in pressure will increase the adsorption capacity of a system (see
Figure 5-4). The increase in capacity occurs because of a decrease in the mean free
path of vapors at higher pressures. Simply, the molecules are packed more tightly
together. More molecules have a chance to "hit" the available adsorption sites,
increasing the number of molecules adsorbed.
5-19
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Gay Velocity
The contact or residence time between the contaminant stream and adsorbent is
determined by the gas velocity through the adsorber. The residence time directly
affects capture efficiency. The slower the contaminant stream flows through the
adsorbent bed, the greater the probability of a contaminant molecule hitting an
available site. Once a molecule has been captured it will stay on the surface until
the physical conditions of the system are changed. To achieve 90% + capture
efficiency most carbon adsorption systems are designed for a maximum air flow
velocity of 30 m/min (100 ft/min) through the adsorber. A lower limit of at least
6 m/min (20 ft/min) is maintained to avoid flow distribution problems, such as
channeling.
Gas velocity through the adsorber is a function of the diameter of the adsorber
for a given volume of contaminant gas. By specifying a maximum velocity through
the adsorber, the minimum diameter is also specified. For example, if 300 mVmin
of contaminant gas is to be treated, and the maximum velocity through the
adsorber is to be 30 m/min, then the adsorber must have a cross sectional area of
at least 10 m2.
The gas flow rate through the adsorber also affects the pressure drop. Increasing
the flow rate increases the pressure drop. Within the above stated maximum and
minimum flow rates, the allowable pressure drop usually dictates the required
tower diameter and flow rate. The pressure drop across the bed also depends on
the depth of adsorbent. This will be discussed in the following section.
Bed Depth - (xjlcA^ OKV^lj/S- '\r$
. . . ^ ' ^ ' . . ' ^
Providing a sufficient depth of adsorbent is very important in achieving efficient
gas removal. If the adsorber bed depth is shorter than the required mass transfer
zone, breakthrough will immediately occur rendering the system ineffective. Com-
puting the length of the MTZ is very difficult since it depends Upon six factors: the
adsorbent particle size, gas velocity, adsorbate concentration, fluid properties of the
gas stream, temperature, and pressure of the system. The MTZ can be estimated
from experimental data using Equation 5-6 (Kovach, 1978). To obtain the
necessary data, vendors will usually test a small portion of the exhaust stream on a
pilot adsorber column.
1 / r '
= — -±— D 1 - ^
1 — Xj \ <-s
(Eq. 5-6) MTZ
Where: D = bed depth, m
C» = breakthrough capacity, %
Cs = saturation capacity, %
Xj= degree of saturation in the MTZ, % (usually assumed to be 50%)
MTZ = length of MTZ, m
The above equation is used mainly as a check to ensure that the proposed bed
depth is longer than the MTZ. Actual bed depths are usually many times longer
than the length of the MTZ. The additional bed depth allows for adequate cycle
times. Equation 5-6 can be rearranged to solve for the breakthrough capacity:
5-20
164
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(Eq. 5-7)
cfl =
+ CS(D - MTZ)
D
• The total amount of adsorbent required is usually determined from the adsorp-
tion isotherm, as illustrated in Example 5-2. Once this has been set, the bed depth
can then be estimated by knowing the tower diameter and density of the adsorbent.
Example 5-3 illustrates how this is done. Generally, the adsorbent bed is sized to
the maximum length allowed by the pressure drop across the bed. Data on the
pressure drop per meter of bed depth for typical carbons is presented in Figure
5-10 (Turk, 1977). The pressure drop per meter of bed depth is plotted versus the
gas flow rate, with the carbon mesh size as a parameter. From the figure, an
adsorber with a flow rate of 40 cm/s (80 ft/min) using 4x 10 mesh carbon will
have a pressure drop of approximately 5 kPa per meter (6 in. H2O per foot) of bed
depth. Therefore, if the pressure drop across the bed is limited to 4.5 kPa (18 in.
H2O) then the total bed depth should not exceed 0.9 meters (3 ft).
Linear velocity, cm/s
10 20
100 FT
O
M
X
c
•5 10 -
Q.
u
•O
o
I
§.
a.
I
K
I
a,
0.
10
20 30 40 50
Linear velocity, ft/min
Source l-mm Air Pollution, 3rd .-.I.. V«l IV, Kn^-cring tt-mml ,,l Air IV.Ihuion
Chapter 8 -Adsorption by Ames Turk, A.C. Stern cdiicir. fc,!
-------
Humidity
As stated previously activated carbon will preferentially adsorb nonpolar hydro-
carbons over polar water vapor. The water vapor molecules in the exhaust stream
exhibit strong attractions for each other rather than the adsorbent. At high relative
humidities, over 50%, the number of water molecules increases such that they
begin to compete with the hydrocarbon molecules for active adsorption sites. This
reduces the capacity and the efficiency of the adsorption system. Exhaust streams
with humidities greater than 50% may require installation of additional equipment
to remove some of the moisture. Coolers to remove the water are one solution.
Dilution air with significantly less moisture in it than the process stream has also
been used. Also, the contaminant stream may be heated to reduce the humidity as
long as the increase in temperature does not greatly affect adsorption efficiency.
Contaminants
In addition to humidity; paniculate matter, entrained liquid droplets, and organic
compounds which have high boiling points can also reduce adsorber efficiency if
present in the air stream. Any micron-sized particle of dust or lint which is not
filtered can cover the surface of the adsorbent. This greatly reduces the surface
area of the adsorbent available to the gas molecule for adsorption. Covering of
active adsorption sites by an inert material is referred to as blinding or
deactivation. To avoid this situation almost all industrial adsorption systems are
equipped with some type of paniculate matter removal device.
Entrained liquid droplets can also cause operational problems. Liquid droplets
that are nonadsorbing act the same as particulate matter. The liquid covers the
surface, blinding the bed. If the liquid is the same as the adsorbate, high heats of
adsorption occur. This is especially a problem in activated carbon systems where
liquid organic droplets carried over from the process can causeyed fires from the
heat released. Some type of entrainment separator may be required when liquid
droplets are present.
For activated carbon systems, other contaminants are high boiling point organic
compounds, usually in excess of 260 °C (500°F). High boiling point (high molecular
weight) compounds have such an affinity for the carbon that it is extremely dif-
ficult to remove them by standard desorption practices. These compounds also tend
to react chemically on the carbon surface forming solids or polymerization products
which are extremely difficult to desorb. Loss of carbon activity in this manner is
called chemical deactivation.
Adsorbent Regeneration Methods
Periodic replacement or regeneration of the adsorbent bed is mandatory in order to
maintain continuous operation. When the adsorbate concentration is high and/or
cycle time is short (less than 12 hours) replacement of the adsorbent is not feasible
5-22
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and in-situ regeneration is required. Regeneration is accomplished by reversing the
adsorption process, usually by increasing the temperature or decreasing the
pressure. Commercially, four methods are used in regeneration:
Thermal swing: The bed is heated so that the adsorption capacity is reduced to a
ower level. The adsorbate leaves the surface of the carbon and is removed from
the vessel by a stream of purge gas. Cooling must be provided before the sub-
sequent adsorption cycle begins. Steam regeneration is an example of thermal
swing regeneration.
Pressure swing: The pressure is lowered at a constant temperature to reduce the
adsorbent capacity.
Inert purge gas stripping: The stripping action is caused by an inert gas that
reduces the partial pressure of the contaminant in the gas phase, reversing the con-
centration gradient. Molecules migrate from the surface into the gas stream.
Displacement cycle: The adsorbates are displaced by some preferentially
adsorbed material. This method is usually a last resort for situations in which the
adsorbate is both valuable and is heat sensitive, and for which pressure swing -
regeneration is ineffective (Bethea, 1978).
Table 5-3 compares the effectiveness of the various regeneration methods (Wood,
1964). As can be seen 'from this table, steam regeneration was most effective for the
test conditions. This is also true for most industrial applications.
Table 5-3. Regeneration of one pound of activated carbon loaded with 20% ether.
Regeneration method
Thermal swing
Pressure swing
Combination
Thermal swing
Regeneration conditions
Heating at 100°C (212°F) for 20 min
Vacuum of 50 mm Hg at 20°C (68°F) for 20 min
Gas circulation at I3()°C (266 °F) for 20 min
Direct steam at 100°C (212°F) for 20 min
Expelled ether
15
25
45
98
are:
Thermal Swing—Steam Stripping
Because it is simple and relatively inexpensive, steam stripping is the most common
desorption technique. Several additional advantages to using steam for desorption
At high pressure, the steam's temperature (100°C) is high enough to desorb
most solvents of interest without damaging the carbon or the desorbed vapors.
Desorbed vapors can be polymerized or cracked, sometimes forming
undesirable compounds.
Steam readily condenses in the adsorber bed releasing its (the steam) heat of
condensation, aiding in desorption.
Many organic compounds can be easily separated and recovered from the
effluent stream by condensation or distillation.
5-23
167
-------
• Residual moisture in the bed is removed easily by a stream of cool dry air
(either pure or process effluent).
• Steam is a more concentrated source of heat than hot air so it is very effective
in raising the temperature of the adsorber bed very quickly.
The amount of steam required for regeneration depends on the adsorbate
loading of the bed. The longer a carbon bed is steamed, the more adsorbate will
be desorbed. It is usually not cost effective to try to desorb all of the adsorbed
vapors from the bed. Acceptable working capacities can be achieved by using less
steam and leaving a small portion of adsorbate in the bed. During the initial
heating period no vapors are desorbed. This is because a fixed amount of steam is
first required to raise the temperature of the cold bed to the desorption
temperature. After this initial period a substantial amount of adsorbate vapor is
released, until a plateau is reached. The plateau represents the optimum steam
requirement, usually in the range 0.25 to 0.35 kg of steam/kg of carbon (Parmele,
1979). In these systems, steam is usually supplied at pressures ranging from 21 to
103 kPa (3 to 15 psig).
A typical two bed adsorption system is shown in Figure 5-11. Regeneration steam
usually passes up through the bed countercurrent to the flow of solvent laden
vapors. Since the bed is switched to the desorption mode before breakthrough, the
outlet end of the bed remains adsorbate free, providing a safety margin for sub-
sequent cycles. The steam usage can range anywhere from 0.3 to 10 kg of steam
per kg of solvent removed.
Some disadvantages are associated with steam regeneration. Problems arising
are:
• The effluent from the condenser could pose a water pollution problem unless
the condensate is sent to a waste water treatment facility.
• Some organic compounds are subject to hydrolysis and/or other reactions with
water which may produce corrosive substances. Corrosive substances can
greatly reduce the life of the adsorption equipment unless* expensive corrosive
resistant materials are used.
• A hot wet carbon bed will not effectively remove organic vapors. Cooling and
drying of the bed may be needed to ensure adequate removal efficiencies at
the beginning of a subsequent cycle.
5-24
168
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Vapor inlet
Bed "A"
(a) Bod "A" idle,
Bed "B" adsorbing.
Vapor inlet
Bed "A"
(b) Bed "A" adsorbing,
Bed "B" regenerating.
Figure 5-11. Two bed adsorption system.
5-25
169
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Pressure Swing—Vacuum Desorption
Pressure swing or vacuum desorption has one primary advantage over thermal
desorption. Desorption is accomplished by a change in pressure rather than
temperature so no time is required to initially heat up or cool the carbon bed. This
adiabatic (no change in temperature) pressure swing allows the bed to be in the
adsorbing cycle longer. Units may also be sized smaller since there is no increase in
air volume due to heating of the bed. Both of these conditions allow for higher
throughputs or smaller adsorber designs than can be accommodated by thermal
swing desorption systems. In addition, the desorbed vapors may be recovered
directly without the need for additional downstream processing equipment.
The principle disadvantages of a pure pressure swing cycle are the high
operating and construction costs. In pressure/vacuum systems the adsorber vessel
and valving must be constructed of materials capable of withstanding vacuums of
9.5 kPa (28 in. Hg). Unless the adsorber is initially operated at elevated pressures
(so that the pressure swing can be accomplished by reducing the vessel to
atmospheric pressures) a vacuum producing system is required. Vacuum systems
that operate cyclically may require more operating attention than other regenera-
tion systems. To be effective, pressure regeneration systems must be designed so
that a small decrease in pressure will result in a drastic shift in the direction of
mass transfer.
Adsorption Control Systems
Adsorption control systems can be classified as either regenerable or non-
regenerable. Nonregenerable systems are normally used to control exhaust streams
with low pollutant concentrations, below 1.0 ppm. Generally these pollutants are
highly odorous or to some degree toxic. When these systems reach the
breakthrough point the bed is taken off stream and replaced with a fresh bed. The
used carbon can then be sent back to the manufacturer for reactivation.
Regenerable systems are used for higher pollutant concentrations such as in solvent
recovery operations. Once the bed reaches the breakthrough point in a regenerable
system, the pollutant vapors are directed to a second bed while the first has the
vapors desorbed.
Nonregenerable Adsorption Systems
Nonregenerable adsorption systems are manufactured in a variety of configura-
tions. Bed areas are sized to control the air flow through them at between 6.0 to 18
m/min (20 to 60 ft/min). They usually consist of thin adsorbent bed depth,
ranging in thickness from 1.25 to 10.0 cm (0.5 to 4.0 inches). These thin beds have
a low pressure drop, normally below 62 Pa (0.25 in. HZO) dependent on the bed
thickness, gas velocity, and particle size of the adsorbent. Service time for these
units can range from 6 months for "heavy" odor concentrations to up to 2 years for
5-26
170
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trace concentrations or intermittent operations (EPA, 1973). They are used mainly
as air purification devices for small air flows in offices, laboratory exhaust, and
other small exhaust streams.
The shapes of these thin bed adsorbers are flat, cylindrical, or pleated. The
granules of activated carbon are retained by porous support material, usually per-
forated sheet metal. An adsorber system usually consists of a number of retainers or
panels placed in one frame. Figure 5-12 shows a nine panel thin bed adsorber. The
panels are similar to home air filters except that instead of containing steel wool
;hey contain activated carbon as the filter. Figure 5-13 illustrates a pleated cell
adsorber. The pleated cell is one continuous retainer of activated carbon, rather
than individual panels. The cylindrical canisters (Figure 5-14) are usually small
units designed to handle low flow rates of approximately 0.12 m/s (25 cfm). Cylin-
drical canisters are made of the same materials as the panel and pleated adsorbers
except their shape is round rather than square. Panel and pleated beds are dimen-
sionally about the same size, normally 0.6 meters square (2 ft by 2 ft) with the car-
bon depth ranging from 0.2 to 0.6 m (8 in. to 2 ft). Flat panel beds are sized to
handle higher exhaust flow rates, approximately 9.4 m/s (2000 cfm), while pleated
beds are limited to flow rates of 4.7 m/s (1000 cfm). Typical flow rate values are
listed in Table 5-4. ,
Carbon
panel
Figure 5-12. Thin bed adsorber: nine cell system.
5-27
171
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Activated carbon
Figure 5-13. Pleated thin bed.
Figure 5-14. Canister.
Table 5-4. Adsorption filters.
Filter shape
Multiple panel cell
Pleated cell
Cylindrical canister
Size
-0.6 m2
~0.6ml
-0.002 m diameter
- 0.005 m length
Flow rate
9.4 m/s
4.7 m/s
0.12 m/s
5-28
172
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In addition to thin bed systems, thick bed nonrcgcnerable systems are also
ivailable. One system that can be used is essentially just a 55-gallon drum. The
oottom of the drum is filled with gravel to support a bed of activated carbon
weighing approximately 330 kg (150 Ib). A typical unit is shown in Figure 5-15.
These units are used to treat small flow rates (0.5 m/s or 100 cfm) from laboratory
hoods, chemical storage tank vents, and chemical reactors.
Activated carbon
Support material
Figure 5-15. Canister.
Regenerable Adsorption Systems
A large regenerable adsorption system can be categorized as a fixed, moving or
fluidized bed. The name refers to the manner in which the vapor stream and
adsorbent are brought into contact. The choice of a particular system depends on
the pollutants to be controlled and the recovery requirements. The most common
adsorption system for controlling air pollutants is the fixed carbon bed. These
systems are used to control a variety of organic vapors and are usually regenerated
by direct steaming of the bed. The organic compounds may be recovered by con-
densing the exhaust from the regeneration step and separating out the water and
solvent.
5-29
173
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Fixed Bed Adsorbers
Fixed bed adsorption systems generally involve multiple beds. One or more beds
treat the process exhaust while the other beds are either being regenerated or
cooled. A typical three bed adsorption system is shown in Figure 5-16. The solvent-
laden air stream is first pretreated to remove any solid or liquid particles which
could blind the carbon bed and decrease its efficiency. The solvent-laden air
stream then usually passes down through the fixed carbon bed. Upward flow
through the bed is usually avoided (unless flow rates are low (<500 cfm) to
eliminate the risk of entraining carbon particles in the exhaust stream).
Pretreatment
Outlet
Condenser
Regenerating
steam
Figure 5-16. Three bed system.
Atler a predetermined length of time, referred to as the cycle time, the solvent-
laden air stream is directed to the second adsorber by a series of valves. Steam is
then injected into the first bed to remove the adsorbed vapors. The steam and
desorbed vapors are then usually sent to a recovery system. If the solvents are
immiscible in water, they can be separated by condensing the exhaust and
decanting off the solvent. If the solvents are miscible in water, distillation may be
required. Before the first adsorber is returned to service, cooling and drying of the
carbon should be provided. This will ensure against immediate breakthrough
occurring from the "hot, wet" carbon bed. This can be accomplished by venting
the solvent-laden air stream through the hot, wet adsorber, then to the on-line
adsorber to maintain a high removal efficiency.
Regenerable fixed carbon beds are usually between 0.3 and 1.2 m (1 to 4 ft)
thick. The maximum adsorbent depth of 1.2 m is based on pressure drop
considerations (Vic Mfg. Co.). Superficial gas velocities through the adsorber range
from 6.0 to 30.0 m/min (20 to 100 ft/min) with 30.0 m/min being a maximum
5-30
174
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permissible flow rate. Pressure drops normally range from 750 to 3730 Pa (3 to 15
in. H2O) depending on the gas velocity, bed depth and carbon particle size
(Bethea, 1978). For specific applications, graphs similar to that in Figure 5-11 are
supplied by the carbon manufacturer to compute the pressure drop.
The two types of fixed bed adsorbers are distinguished by bed orientation in
relation to air flow. The first is referred to as a vertical flow adsorber. The bed
length is vertical as is the direction of air flow. The air stream usually flows
downward. This system is shown in Figure 5-16. These units are suited to handle
flows up to 1.4 to 2.0 mVs (3000 to 4000 cfm) per adsorber. Figure 5-17 shows a
three bed vertical system used to recover 34 kg/m (75 Ibs/hr) of trichloroethylene
from a vapor degreasing operation. Each vessel is 1.2 m (48 in.) in diameter,
contains 255 kg (560 Ibs) of carbon approximately 10 cm (4 in.) deep and handles
1.7 nWs (3500 scfm) air flow. One vessel is being desorbed each hour using 102 kg
(225 Ibs) of steam at 103 kPa (15 psig). The pressure drop across the system is
approximately 3 kPa (12 in. H2O) (Vic Mfg. Co. with permission).
Figure 5-17. Three bed vertical system.
5-31 175
-------
For larger flow rates, horizontal flow adsorbers are used. Structurally they are
more suited to handle the larger air volumes. In horizontal flow units, the bed
length is horizontal as is the direction of the incoming air stream. The air stream
flows across the bed and down. This system is illustrated in Figure 5-18. Adsorbers
of this type are manufactured as a package system capable of handling flow rates
up to 1150 m'/s (40,000 cfm). Larger units must be engineered and fabricated for
the specific application. Figure 5-19 shows a three bed horizontal system used to
recover 1180 kg/hr (2600 Ib/hr) of toluene from a rotogravure operation. Each
vessel is 7 m (22 ft) long and 3 m (10 ft) in diameter and contains 9000 kg (20,000
Ibs) of carbon packed to a 1 m (3 ft) bed depth. The system handles 21 m'/s
(44,000 scfm) air flow with a pressure drop of 6 kPa (24 in. H2O). One vessel is
desorbed each 45 minutes using 3600 kg/hr (8000 Ibs/hr) of steam at 103 kPa
(15 psig) pressure (Vic Mfg. Co. with permission).
Steam and
vapor outlet
Carbon bed
Steam inlet
Figure 5-18. Horizontal bed.
5-32
176
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Figure 5-19. Three bed horizontal system.
Moving Bed Adsorbers
Moving bed systems can also be used to obtain a higher degree of utilization of the
carbon bed than is possible with a fixed bed. In moving bed systems, the solvent-
laden vapor stream passes only through the unsaturated portion of the carbon bed.
This reduces the distance (thus pressure drop) the air stream travels through the
bed.
One design of a moving (rotary) bed system is illustrated in Figure 5-20 (Sutcliffe
Speakman Co., 1963). The device consists of four cylinders which are in constant
rotation. The granular carbon is held in place between two cylinders made of steel
screening or perforated sheet metal. This bed is placed between inner and outer
cylinders which are impervious to air flow except at slots near their ends.
The slots on the outer cylinder act as solvent-laden inlets. They permit the air
stream to pass into the annular section where the carbon is located. The solvent-
laden air stream passes through the carbon bed and purified air exits out the inner
slots. The carbon bed is broken into sections. The cylinders rotate such that when
the proper degree of saturation is reached the bed is desorbed. Desorption occurs
by injecting steam in through the slots on the inner cylinder. Steam and desorbed
vapors exit through the slots on the outer cylinder. During each rotation of the
cylinder, each segment of the carbon bed undergoes both an adsorption and
desorption cycle.
Because of the continuous adsorbing and desorbing process, bed utilization is
improved. The air stream is no longer required to pass through the top, saturated
portion; or the bottom, idle portion of the bed. The air stream passes only through
che active, mass transfer portion of the bed. Therefore, shorter and more compact
beds may be used which reduce the pressure drop. The disadvantages are wear on
moving parts and maintaining air tight seals on moving parts.
5-33
177
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Outer shell
Outer screen —
Inner screen
Inner shell -~
Regenerative steam
inlet -
Activated carbon
7
Interior
outlets
Steam and
vapor outlet
Vapor
inlets
Steam and
vapor outlet
y
Figure 5-20. Rotary bed system.
Fluidized Bed Adsorbers
A fluidized bed adsorption system operates in the same physical manner as a tray
scrubber. Instead of liquid flowing down the column from tray to tray, granular
activated carbon is used. Figure 5-21 shows one recently developed fluidized bed
system which is being marketed by Union Carbide. The solvent-laden air stream is
introduced at the middle of the tower. Then it passes up through the tower
fluidizing the activated carbon in a series of trays. The carbon then flows down
through the vessel from tray to tray until it reaches the desorption section.
Regeneration is accomplished in the bottom half of the vessel and the activated
carbon is air conveyed back to the top of the tower.
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178
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Air lift
blower
Clean air out
Perforated trays
Nitrogen recycle
blower
Recovered
solvent
Figure 5-21. Fluidized bed adsorber.
As with the moving bed, the fluidized bed also provides continuous operation
and more efficient utilization of the adsorbent. The need for multiple vessels is
eliminated, which can greatly reduce the cost of the system. Gas velocities around
! m/s (196 ft/min) are needed to fluidize the bed. These are 2 to 4 times the
\elocities achieved in fixed bed systems. This allows for use of a much smaller
vessel for comparable air flow and helps to achieve uniform gas distribution.
5-35
179
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The main disadvantage with fluidized bed adsorption systems is the high attrition
(wear) losses of the granular activated carbon. Recently a new "beaded" activated
carbon was developed in Japan. The beaded shape is inherently stronger and has
better fluidity properties than granular carbon. The beaded carbon has been used
in a number of installations (mostly in Japan) and is reported to reduce the attri-
tion losses to 2 to 5% per year as compared to 10% for fluidized granular carbon
(Union Carbide).
The following example illustrates the use of the principles and general rules of
practice discussed in this chapter in designing an adsorption system.
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INSPECTION OF CARBON BED ADSORBERS
Inspection Summaries
6.3 Inspection Summaries
6.3.1 Level 1 Inspections - No Inspection Steps
6.3.2 Level 2 Inspections
Basic Level 2 Inspection Steps
Stack/Exhaust
0 Exhaust VOC concentration for 10 - 15 minutes
near the end of the adsorption cycle*
Carbon Bed Adsorber
0 Obvious corrosion on the adsorber shell
0 Adsorption/desorption cycle times V
0 Steam pressure and temperature during/
desorption
Process Equipment
0 Obvious fugitive emissions*
Follow-up Level 2 Inspection Steps
Carbon Bed Adsorber
0 Inlet gas temperature
0 Inlet and outlet static pressures
0 Outlet detector calibration and maintenance
0 Quantity of solvent in recovered solvent
tank
Process Equipment
0 Maximum production rate during the last
6 months
0 Average production rate during the
last 12 months
0 Types of solvents used
0 Quantities of solvents purchased
Quantities of solvents sold/discarded
131
o
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INSPECTION OF CARBON BED ADSORBERS
Inspection Summaries
6.3.3 Level 3 Inspections
Stack/Exhaust
0 Exhaust VOC concentration for 10-15 minutes
near the end of the adsorption cycle*
0 Outlet gas temperature*
Carbon Bed Adsorber
0 Inlet gas temperature *
0 Obvious corrosion on the adsorber shell*
0 Adsorption/desorption cycle times*
0 Inlet and outlet static pressures*
i ° Outlet detector calibration and maintenance*
^t^ ° Quantity of solvent in recovered solvent tank*
A P r^ ^° Measure the outlet VOC concentration
\ |n&r U ° Measure the inlet gas temperature
£ r\0y ° Measure the static pressure drop
:v
Process Equipment
0 Obvious fugitive emissions*
0 Maximum production rate for last 6 months*
0 Average production rate for last 12 months*
0 Types of solvents used*
0 Quantities of solvents purchased*
0 Quantities of solvents sold/discarded*
0 Hood static pressure
6.3.4 Level 4 Inspection Procedures
Exhaust Stack
0 All elements of a Level 3 inspectibn
Carbon Adsorber
0 All elements of a Level 3 inspection
0 Locations for measurement ports
0 Potential inspection safety problems
Process Equipment
0 All elements of a Level 3 inspection
0 Basic flowchart of process
0 Potential inspection safety problems
* Refer to Level 2 Inspection Procedures
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182
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INSPECTION OF CARBON BED ADSORBERS
Basic Level 2 Inspection Procedures
6.4 Inspection Procedures
Techniques for the inspection of carbon bed adsorbers can
be classified as Level 2 or Level 3. The Level 2 inspections
primarily involve a walkthrough evaluation of the carbon bed
adsorber system and process equipment using on-site gauges.
The Level 3 inspection incorporates all of the inspection
points of the Level 2 inspection and includes independent
measurements of the adsorber operating conditions.
6.A.I Basic Level 2 Inspections
Evaluate the VOC outlet detector.
The VOC detectors often used at the outlet of the carbon
bed systems are relatively sophisticated instruments which
require frequent maintenance. Confirm that they are working
properly by reviewing the calibration records since the previous
inspection. Maintenance work orders should also be briefly
reviewed to determine if the instruments have been operational
most of the time.
Check carbon bed shell for obvious corrosion.
Some organic compounds collected in carbon bed systems can
react during steam regeneration. This leads to severe corrosion
of the screens retaining the carbon beds and of the unit shell.
Observe the adsorption/desorption cycles.
Determine the time interval between bed regenerations and
compare this with previously observed values. An increase in
this time interval could mean that breakthrough is occurring if
the quantities of organic vapor entering the carbon bed have
remained unchanged. Systems in which the cycle frequency is
controlled by a timer rather than an outlet organic vapor detec-
tor 'are especially prone to emission problems due to longer than
desirable cycle tijnes.
Check the regeneration steam line pressure.
Any decrease in the steam line pressure from previously
recorded levels could indicate less than necessary steam flow
for regeneration of the carbon beds.
133
183
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INSPECTION OF CARBON BED ADSORBERS
Follow-up Level 2 Inspection Procedures
6.A.2 Follow-up Level 2 Inspection Procedures
Evaluate carbon bed system static pressure drop.
If there are on-site gauges, evaluate any changes in the
static pressure drop. A decrease could mean deterioration of
the carbon bed to the point that channeling of the gas stream
is affecting gas-solid contact. Higher than normal static
pressure could mean partial pluggage of the carbon bed due to
fines formation or due to material entering with the gas stream.
However, gas flow changes could also be responsible for changes
in the static pressure drop.
Prepare solvent material balances.
For some processes, the effectiveness of the carbon bed
system can be evaluated by preparing a solvent material balance
around the facility for a period of several weeks to a month.
The information needed for the calculations includes solvent
quantities purchased, changes in solvent storage tank levels,
and solvent quantities transferred from the system.
Evaluate ventilation system.
To the extent safely possible, gas flow rates from process
equipment to the carbon bed system should be evaluated. Record
hood static pressures (if monitored) and look for any holes or
gaps in the ductwork.
6.4.3 Level 3 Inspections
Measure the VOC outlet concentrations.
The effluent concentration from each bed should be measured
if there is safe and convenient access to the effluent ductwork.
The measurements should be made with an organic vapor analyzer
that is calibrated for 50 to 2000 ppm.
The instrument (and its portable recorder, if any) should
be certified as intrinsically safe for Class I, Group C and D
locations. This means simply that the instrument is incapable
of initiating an explosion when used properly. A small port is
adequate to draw a 0.5 to 3.0 liter per minute sample into the
instrument. An observed VOC concentration greater than 500 ppm
(v/v) is a sign that the bed is not performing properly.
134
184
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INSPECTION OF CARBON BED ADSORBERS
Level 3 Inspection Procedures
Measure the VOC outlet concentration (continued).
It is important to determine the approximate desorption
cycle of multi-bed systems. Outlet VOC measurements conducted
earlier in the adsorption cycle of a bed may appear adequate
even when the bed activity is severely reduced. Breakthrough
usually does not occur until late in the operating cycle unless
the condition of the carbon is extremely poor. Therefore, an
effort should be made to measure the outlet VOC concentration
of each bed at a time when it is approaching the end of the
adsorption mode. The adsorption/desorption cycle is normally
controlled by a timer and this can be used to determine the
approximate status of each bed.
In some commercial multi-bed units there is only poor acces-
sibility to the effluent ducts from each unit. In this case,
the VOC concentration in the combined duct should be measured
at the exhaust point. Obviously, this measurement should be
attempted only when there is safe and convenient access to the
exhaust. It is especially important to avoid areas where high
VOC concentrations could accumulate.
Measure the inlet gas temperature.
Adsorption is inversely related to the gas temperature
entering the carbon bed adsorbers. An increase in the gas
temperature from the baseline period could result in a decreased
capacity for organic vapors. The gas temperature should be
measured in the inlet ductwork, immediately ahead of the carbon
bed.
Measure the static pressure drop.
A change in the static pressure drop since the baseline
period is usually due to either a change in the gas flow rate
through the carbon bed or due to the physical deterioration of
the bed itself.
135
185
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INSPECTION OF CARBON BED ADSORBERS
Level 3 Inspection Procedures
Measure the static pressure drop (continued).
Measurement taps on the adsorber shell should be used,
if available. Alternatively, the static pressure drop can be
measured using ports in the inlet ductwork to the adsorber
system and the outlet duct from the adsorber. Obviously, the
static pressure drop should be determined while the adsorber
is on-line.
Check/measure the hood static pressure.
At the hood, the gas stream is accelerated to the velocity
of 1200 to 2000 feet per minute. The static pressure in the
hood is a useful indicator of the total gas flow rate. A drop
in the hood static pressure from previously recorded levels
means that the gas flow has decreased.
The relationship between gas flow rate and hood static
pressure is indicated below. The equation simply illustrates
that the gas flow rate is proportional to the square root of
the hood static pressure. If the hood static pressure decreases
by a factor of 2, the gas flow rate has decreased by approxi-
mately a factor of 1.41.
Where: G » Gas flow rate, ACFM
C - Proportionality constant, ACPM/(Inches W.C.)
Sph » Hood static pressure
136
186
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INSPECTION OF CARBON BED ADSORBERS
Level 4 Inspection Procedures
6.4.A Level 4 Inspection Procedures
The Level 4 inspection includes many inspection steps
performed during Level 2 and Level 3 inspections. These are
described in earlier sections. The unique inspection steps of
Level 4 inspections are described below.
Evaluate locations for measurement ports.
Many existing carbon bed adsorbers do not have safe and
convenient ports that can be used for volatile organic compound
concentration, static pressure, and gas temperature measurements.
One purpose of the Level 4 inspection is to select (with the
assistance of plant personnel) locations for ports to be
installed at a later date to facilitate Level 3 inspections.
Evaluate potential safety problems.
Agency management personnel and/or senior inspectors should
identify any potential safety problems involved in standard
Level 2 or Level 3 inspections at this site. To the extent
possible, the system owner/operators should eliminate these
hazards. For those hazards that can not be eliminated, agency
personnel should prepare notes on how future inspections should
be limited and should prepare a list of the necessary personnel
safety equipment. A partial list of common health and safety
hazards includes the following.
0 Inhalation hazards due to low stack discharge points
0 Fugitive emissions from process equipment system
0 Inhalation hazards from adjacent stacks and vents
0 Access to system components only available by means
of weak roofs or catwalks
137
187
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INSPECTION OF CARBON BED ADSORBERS
Level 4 Inspection Procedures
Prepare «i system flowchart.
A relatively simple flowchart is very helpful in conducting
a complete and effective Level 2 or Level 3 inspection. This
should be prepared by agency management personnel or senior
inspectors during a Level A inspection. It should consist of a
simple block diagram that includes the following elements.
0 Source(s) of emissions controlled by a single
carbon bed adsorber
0 Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures)
0 Locations of any main stacks and bypass stacks
0 Location of any prefilters for particulate removal
0 Location of carbon bed adsorbers
0 Locations of major instruments (VOC concentration,
static pressure gauges, thermocouples)
Evaluate potential safety problems in the process area.
The agency management personnel and/or senior inspectors
should evaluate potential safety problems in the areas that may
be visited by agency inspectors during Level 2 and/or Level 3
inspections. They should prepare a list of the activities that
should not be performed and locations to which an inspector
should not go as part of these inspections. The purpose of
this review is to minimize inspector risk and to minimize the
liability concerns of plant personnel.
138
188
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Control
by
Condensation
189
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Chapter 6
Condensation
Introduction
Condensation is the process of reducing a gas or vapor to a liquid. Any gas can be
reduced to a liquid by lowering its temperature and/or increasing its pressure. The
most common approach is to reduce the temperature of the gas stream, since
increasing the pressure of a gas is very costly (EPA, 1973).
Condensers are simple, relatively inexpensive devices that normally use water or
air to cool and condense a vapor stream. Since these devices are usually not
capable of reaching low temperatures (below 80 °F), high removal efficiencies of
most gaseous pollutants are not obtained unless the vapors will condense at high
temperatures. Condensers are typically used as pretreatment devices. They are used
ahead of incinerators, absorbers, or adsorbers to reduce the total gas volume to be
treated by more expensive control equipment. Used in this manner, they help
reduce the overall cost of the control system.
Condensation Principles
When a hot vapor stream contacts a cooler surface, heat is transferred from the
hot gases to the cooler surface. As the temperature of the vapor stream is cooled,
the average kinetic energy of the gas molecules is reduced. Also, the volume that
these vapors occupy is reduced. Ultimately the gas molecules are slowed down and
crowded together so closely that the attractive forces (van de Waals' forces)
between the molecules cause them to condense to a liquid.
The two conditions which aid condensation are: low temperatures so that the
kinetic energy of the gas molecules are low; and high pressures so that the
molecules are brought close together. The actual conditions at which a particular
gas molecule will condense depends on its physical and chemical properties.
Condensation occurs when the partial pressure of the pollutant in the gas stream
equals its vapor pressure as a pure substance at operating conditions.
Condensation of a gas can occur in three ways: first, at a given temperature, the
system pressure is increased (compressing the gas volume) until the partial pressure
of the gas equals its vapor pressure; second, at a fixed pressure, the gas is cooled
until the partial pressure equals its vapor pressure; or third, by using a combina-
61 190
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tion of compression and cooling of the gas until its partial pressure equals its vapor
pressure. These processes are illustrated in Figure 6-1, a typical vapor pressure
diagram for a pure substance.
Solid
phase
Critical
point
Cool
Temperature
Figure 6-1. Typical vapor pressure curve.
In Figure 6-1, point I is the initial temperature and pressure of a gas. The
dotted lines indicate the paths a quantity of gas would follow to reach the vapor
pressure curve. Points on the vapor pressure curve are also referred to as dew
points. The dew point is defined as the condition at which gas is ready to condense
into the first drop of liquid.
Also on Figure 6-1, the critical point is plotted. Each substance has a critical
temperature and critical pressure. The critical temperature is important in that it
is a maximum temperature above which the gas will not condense, no matter how
great a pressure is applied. The pressure required to liquify a gas at its critical
temperature is the critical pressure.
Once the gas conditions (temperature, pressure, and volume) equal those on the
vapor pressure line, liquid begins to condense. From this point on, the gas-liquid
mixture follows the vapor pressure line. If the mixture is cooled continuously, the
partial pressure of the remaining gas will always equal the vapor pressure. This is
6-2
191
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important since even though the contaminated gas is being condensed, it still has a
certain partial pressure indicating that uncontrolled vapors are being emitted from
the condenser. For most practical applications, the vapor-liquid equilibrium
restricts the use of condensers as primary air pollution control devices. Unless very
low temperatures or high pressures are attained, condensers are not capable of
reducing the pollutant concentration to within acceptable emission limits.
Practically, temperature is the only process variable which governs the effec-
tiveness of a condenser. In industrial applications, increasing the system pressure is
very costly and therefore rarely used for condensation. At the operating pressure of
the system, the outlet temperature from the condenser determines the maximum
removal efficiency. Therefore, condensers cannot be used in the same manner as
other gaseous pollutant control devices. For example, condensers cannot be used in
series like adsorbers or absorbers to further reduce outlet concentration unless the
outlet temperature of the second condenser is lower than the previous one.
Increasing gas residence time or decreasing flow rates in the condenser does not
add to the theoretical achievable efficiency as these operations do in incinerators,
adsorbers, and absorbers.
Condensers
Condensers fall into two basic categories; contact and surface condensers. In a con-
tact condenser the coolant and vapor stream are physically mixed. They leave the
condenser as a single exhaust stream. In a surface condenser, the coolant is
separated from the vapors by tubular heat transfer surfaces. The coolant and con-
densed vapors leave the device by separate exits. Surface condensers are commonly
called shell-and-tube heat exchangers. The temperature of the coolant is increased,
so these devices also act as heaters.
6-3
192
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Direct Contact Condensers
Contact condensers are simple devices such as spray towers, steam or water jet
ejectors, and barometric condensers. These devices bring the coolant, usually
water, into direct contact with the vapors as illustrated in Figure 6-2. The liquid
stream leaving the condenser contains the coolant plus the condensed vapors. If the
vapor is soluble in the coolant then absorption also occurs. Absorption increases the
amount of contaminant that can be removed at the given conditions.
(a) spray contact condenser
Mist eliminator
Spray nozzles
Figure 6-2. Direct contact condensers:
(a) spray, (b) jet ejector, and (c) barometric.
6-4
193
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(b) jet ejector condenser
(c) barometric condenser
Spray
nozzle
Water
inlet -
Water
inlet -
Discharge
©
^
Discharge
Spray tower condensers (Figure 6-2a) are normally the same as the spray
absorbers discussed in Chapter 4. The vapors enter the bottom of the tower while
coolant is sprayed down over them. Baffles are usually added to ensure adequate
contact between coolant and vapors. Ejectors (Figure 6-2b) and barometric con-
densers (Figure 6-2c) operate in a similar manner. The difference being that they
use liquid sprays to move the vapor stream. In both of these devices the coolant is
sprayed into a venturi throat creating a vacuum which moves the vapor stream
through the condenser.
6-5
194
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Surface Condensers
Surface condensers are usually in the form of shell-and-tube heat exchangers
(Figure 6-3). The device consists of a circular or oval cylindrical shell into which
the vapor stream flows. Inside the shell are numerous small tubes through which
the coolant flows. Vapors contact the cool surface of the tubes, condense, and are
collected, while noncondcnsed vapors are sent for further treatment.
Removable
Reversing i K.inriel
Inlet
channel
Figure 6-3. Single-pass condenser.
Removal
-------
Figure 6-4 illustrates two types of multipass heat exchangers, referred to as 1-2
and 2-4 heat exchangers. The first digit refers to the number of passes the vapor
makes on the shell side, while the second digit indicates the number of tube side
passes. Both of these designs give improved performance over the single-pass
exchanger. The 2-4 heat exchanger is capable of higher gas velocities and better
heat transfer than the 1-2 heat exchanger. Adding more passes does have disadvan-
tages however. These disadvantages are: the exchanger construction is more com-
plicated; friction losses are increased due to the higher velocities; and exit and
entrance losses are multiplied.
1-2 parallel flow exchanger
Coolant
inlet
Noncondensing
vapor outlet
Reversing
channel
Coolant
outlet
Inlet
channel
Condensate
outlet
2-4 exchanger
Vapor
Coolant
inlet
inlet
Inlet
channel
1 '^±1±1L-'1.-. .'..I.! -tt' ' ""••jf-'j . i i uy .... . ^i....^^^i^a^n-i_My
Coolant
outlet
fCondensate
outlet
MO.U ing
head
Figure 6-4. Simplified air flow in multipass exchangers.
6-7
196
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Condensation applications normally require large temperature differentials
between vapor and coolant. These temperature variances can cause the tubes to
expand or contract. This expansion stress can eventually cause the tubes to buckle
or pull loose from the shell, destroying the condenser. Floating head construction is
commonly used to avoid condenser expansion stress damage. In a floating head,
one end of the tube bundle is mounted so that it is structurally independent from
the shell as shown in Figure 6-4. This allows the tubes to expand and contract
wilhin the shell.
Water is gent-rally the coolant used in condensers. However, short supply and
expense to treat water make it an uneconomical choice in some cases. In these
cases, air-coolers are used. The specific heat of air is only about 0.25 Btu/lb«°F,
approximately one-fourth that of water. Therefore, air condensers must be very
large compared to water condensers.
To conserve space and reduce the cost of equipment in these cases, heat
exchangers with extended surfaces can be used. In these devices, the outside area
of the tube is multiplied or extended by adding fins or disks. Figure 6-5 illustrates
two types of finned tubes. In extended surface condensers, the vapor is condensed
inside the tube while air flows around the outside contacting the extended surfaces.
Transverse fins
Longitudinal fins
Figure 6-5. Extended surface tubes.
Comparison of Contact and Surface Condensers
Since in contact condensers coolant is merely sprayed on the vapors, these systems
are simpler in design, less expensive, and more flexible in application than surface
condensers. However, contact condensers require more coolant, and due to direct
mixing, produce 10 to 20 times the amount of wastewater (condensate) than sur-
face condensers. Since '.he wastewater from a contact condenser is contaminated
with vapors, it cannot be reused posing a water disposal problem. If the condensed
vapors have a recovery value, surface condensers are usually used since the conden-
sate can be recovered directly.
6-8
197
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Condensers
Condensers remove vaporous contaminants from a gas stream by cooling it and
converting the vapor into a liquid. In some instances, control of volatile contaminants
am be satisfactorily achieved entirely by condensation. However, most applications
require additional control methods. In such cases, the use of a condenser reduces the
concentration load on downstream control equipment. The two most common types of
condensers are:
a. Contact or barometric condensers, where a direct spray contacts
the vapors to cause condensation (see Figure 13-15). The liquid
leaving the condenser contains the coolant plus the condensed
vapors.
b. Surface condensers, such as the shell-and-tube heat exchanger (see
Figure 13-16). This device consists of a shell into which the vapor
stream flows. Inside the shell are numerous small tubes through
which the coolant flows. Vapors contact the cool surface of the
tubes, condense and are collected without contamination by the
coolant.
Basic Level 2 Inspection Points
a. Physical condition: indications of corrosion or physical damage.
b. Outlet temperature: increased temperature may mean reduced
condensation efficiency.
c. Inlet liquid pressure: provides an indirect indication of the liquid
flow rate and nozzle condition; increases may indicate nozzle
pluggage and lower coolant flow rates; decreases may indicate
nozzle erosion and higher flow rates (contact-type only).
d. Liquid turbidity and settling rate: high settling rate indicates coarse
solids that could plug nozzles (contact-type only).
e. Droplet re-entrainment: droplet rainout or a mud-lip on the stack
indicates a significant demister problem.
198
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Surface
Coating
Fundamentals
199
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SECTION 1
OVERVIEW
1.0 Scope and Objective
This manual was developed to assist compliance officers with determining the
compliance status of surface coating and graphic arts operations with volatile organic carbon
(VOC) regulations. It is designed as an advanced level manual where the user has already
had some exposure to pertinent regulation terminology and process configurations. The
material presented will focus on (1) determinations of coating formulations, (2) compliance
determination calculations, and (3) process and add-on control equipment evaluations. The
information presented here is in a condensed form; more detail on these industries can be
found through other sources (4,5,6). A complete listing of reference materials used to develop
this manual is given in Section 6.
Examples and case studies are presented for typical industries. This manual should
assist inspectors to thoroughly evaluate a source and to assess its compliance with Federal,
State, and Local regulations.
1.1 Terminology
Many of the terms used to describe materials, processes, emissions and controls in the
surface coating and graphic arts facilities have been defined in the EPA glossary document
entitled, Glossary for Air Pollution Control of Industrial Coating Operations. Second Edition
(With Graphical Aids for Rapid Estimation of Acceptable Compliance Alternatives). EPA-450/3-
83-013R, December 1983. This glossary can be found in Appendix A and defines the most
common terms, both technical and regulatory, needed to be effective in carrying out VOC
regulatory compliance activities for surface coating and graphic arts operations.
1.2 Surface Coating Operations - Overview
Surface coating operations involve the application of paint, primer, varnish, and a
variety of other coatings to surfaces for both protection and decoration. Application methods
incluoe brushing, rolling, spraying, dipping and flow coating. Coatings are air or heat dried to
drive off volatile solvents and produce a hard surface film. Industrial surface coating
operations generally are categorized by the type of product coated because specific coatings,
application and control methods, etc., will vary somewhat with product category. The
categories addressed here are as follows:
* Can coating * Flat wood interior panel
* Metal coil * Paper coating
* Magnet wire * Fabric coating
* Large appliance * Vinyl and urethane
* Metal furniture * Auto/Light-duty truck
* Miscellaneous metal * Large aircraft
A more detailed description is given for each category in Section 2.
200
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1.2.1 Coating Operations
There are both "toll" (independent) and "captive" surface coating operations. Toll
operations fill orders to various manufacturer specifications, and thus change coating and
solvent conditions frequently. Captive companies fabricate and coat products within a single
facility, and might operate continuously with the same coatings.
Although the details of coating operations vary among companies and for the different
product categories, the typical components of a coating line can be described as follows.
Fabricated parts are first cleaned to remove grease, dust and other contamination. The most
common coating application methods are spray, dip and flow coating, usually in some type of
booth or enclosure to contain overspray and evaporated solvents. Parts are either air or oven
dried. Parts may be conveyed to a "flashoff zone" before entering a bake oven so that some
of the solvent can evaporate before the 120 to 230° C (250 to 45CPF) oven heat is applied.
Ovens are either single or multipass.
Depending on product requirements and the material being coated, a surface may
have one or more layers of coating applied. The first coat (primer) is applied to provide
corrosion protection, cover surface imperfections and/or assure adhesion of subsequent
coats. The intermediate coats usually provide the required color, texture or print, and a clear
protective topcoat is often added.
1.2.2 Costing Formulations
Coatings consist of finely divided solid materials (pigments and binders) dispersed in a
liquid medium (the volatile portion). The volatiles generally consist of a mixture of organic
solvents, and may also contain water. The organic solvent mixture may contain both
regulated (VOC) and exempt solvents, but the great majority of solvents used are considered
VOC's. Conventional (solvent borne) coatings contain at least 30 percent by volume of
solvents to permit easy handling and application, but can contain up to 70 to 85 volume
percent solvents. Typical paint solvents are acetone, methyl ethyl ketone, cellosolves,
toluene, xylene and mineral spirits. Coatings with 30 volume percent or less of solvent are
referred to as low solvent, or high solids, coatings (solids contents are greater than 70 volume
percent).
Waterborne coatings, whose use is continually increasing, are of several types: water
emulsions, water soluble and colloidal dispersion, and electrocoat. Common ratios of water
to solvent organics in emulsion and dispersion coatings are 80/20 and 70/30.
Two-part catalyzed coatings, powder coatings, hot melts, and radiation cured
(electromagnetic and electron beam) coatings contain essentially no VOC, although some
monpmers and other lower molecular weight organics may volatilize during curing (cure
volatiies).
1.2.3 Application Methods
Spray methods may consist of conventional air spray, airless, air-assisted airless, or
high volume-low pressure (HVLP) spraying. Electrostatic assist is sometimes added to
improve the transfer efficiency r. Air spray is versatile and can produce a very high quality
finish, but consumes a large amount (8 to 30 scfm) of high pressure airand suffers from low
transfer efficiency. Airless spray uses hydrostatic pressure (about 2,000 psi) to atomize the
1 Ratio of solids applied to solids used. This concept is discussed in more detail in Section 3.
201
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coating into slightly larger particles. Air-assisted airless technology combines these two
techniques, but can use lower pressures and air and fluid rates, and is more manageable for
an operator.
In hot airless spray, warm pressurized paint is forced through an atomizing nozzle.
Volumetric flow is less, and so overspray is reduced. Also, less solvent is required to maintain
viscosity, thus reducing VOC emissions. Electrostatic spray, in which charged paint particles
are attracted to an oppositely charged surface, is most efficient for low viscosity paints. Spray
guns, spinning discs or bell shaped atomizers can be used to atomize the paint.
Roller coating is used to apply coatings and inks to flat surfaces. If the cylindrical
rollers move in the same direction as the surface to be coated, the system is called a direct roll
coater. If they rotate in the opposite direction, the system is a reverse roll coater. Cpatings
can be applied to any flat surface efficiently and uniformly, and at high speeds. Printing and
decorative graining are applied with direct rollers. Reverse rollers are used to apply fillers to
porous or imperfect substrates, including papers and fabrics, to give a smooth, uniform
surface.
Brush coating is best suited for application of slow-drying coatings to uneven surfaces,
such a rough fiber panels. Brush coating machines have been largely replaced by air-knife
coalers.
Knife coating is relatively inexpensive, but it is not appropriate for coating unstable
materials, such as some knit goods, or when a high degree of accuracy in the coating
thickness is required.
Dip coating requires that the object be immersed in a bath of paint. Dipping is effective
for coating irregularly shaped or bulky items, and for priming. All surfaces are covered, but
coating thickness varies, edge blistering can occur, and a good appearance is not always
achieved.
In flow coating, materials to be coated are conveyed through a flow, or stream, of paint.
Paint flow is directed, without atomization, toward the surface through multiple nozzles, then is
caught in a trough and recycled. For flat surfaces, close control of film thickness can be
maintained by passing the surface through a constantly flowing curtain of paint at a controlled
rate.
1.3 Graphic Arts Operations • Overview
The term 'graphic arts" has come to encompass the various sectors of the printing and
publishing industry, including the production of books, newspapers, magazines and other
reading materials, as well as packaging and many types of specialty items. The four basic
printing processes are web offset lithography, web letterpress, gravure printing and
flexography. These four high volume processes are similar in that the image to be printed is
placed on a cylinder that rotates in contact with a paper "web", or continuous roll. Gravure
printing performed this way is termed "rotogravure." Other, lower production processes using
more manual (such as sheet fed) techniques often are used by smaller firms. The discussion
here is limited to the three graphic arts source categories covered by the Control Technology
Guidelines (5,6):
1. Publication rotogravure
2. Packaging rotogravure
3. Flexography
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Printing can be performed on coated or uncoated paper, and also on other substrates
such as metals, plastics and fabrics. Printing operations involve the transfer of an image,
using a transfer device that maintains a fixed position with respect to the substrate as contact-
is made. Coating operations, on the other hand, strive for uniform total coverage with the
coating material. From an emissions standpoint, however, printing and coating are very
similar.
Printing inks vary widely in composition, but all of them consist of three major
components. Pigments, which provide the ink's color, are composed of finely divided organic
and inorganic materials. Binders, which lock the pigments to the substrate, are composed of
organic resins and polymers or oils and resins. Solvents dissolve and disperse the solids, and
usually consist of volatile organic liquids. As in coatings, the volatile portion evaporates and
leaves the visible solids behind in the form of the desired image.
Both rotogravure and flexographic printing use very fluid inks of about 75 volume
percent organic solvent. Rotogravure solvents include alcohols, aliphatic naphthas, aromatic
hydrocarbons, esters, glycol ethers, ketones and nitroparaffins. Flexography solvents include
glycqls, ketones and ethers. Water base inks generally are used only in certain packaging or
specialty applications. A more detailed discussion of the individual printing categories is
presented in Section 2 of this manual.
1.4 Control Techniques • Overview
Most of these regulations of the surface coating and graphic arts industries have been
aimed at limiting the amount of VOC that is released in order to limit the formation of ozone in
the ambient air. It usually is assumed that all of the VOC content of a coating evaporates after
application to become potential emissions. Control strategies at reducing VOC content are
threefold: 1) reformulation to reduce the amount of VOC in the coatings, 2) improved
application methods, and the use of add-on controls to remove the VOC before emissions are
vented to the atmosphere. All of the evaporated solvent that is not in turn recovered or
destroyed in control equipment becomes actual emissions. This section provides an overview
of the principal control techniques used to limit VOC emissions from surface coating facilities.
1.4.1 Coating Formulation and Application
In cases where it is technically feasible, the substitution of exempt solvents (solvents
which have been determined to have negligible photoreactivity^) for VOC solvents in a coating
can be used to reduce emissions. The degree of reduction is equal to the percentage of the
VOC solvent that is replaced. Exempt solvents appear to have limited application in the
surface coating and printing industries, although 1,1,1-trichloroethane has been used as a
principal solvent in various applications ranging from specialty coatings for aerospace parts to
lacquers for wood furniture and two-component urethanes for coating plastics.
High solids coatings generally contain at least 70 weight percent of solids, and so the
solvent fraction, and VOC emissions, are dramatically reduced. Since the viscosity of such
coatings is higher than that of conventional coatings, handling problems with high solids
2. Negligible photoreactive compounds include methane, ethane, 1,1,1-trichloroethane
(Methyl chloroform), Methylene chloride, Trichlorotrifluoroethane (CFC-113),
Trichlorofluoromethane (CFC 11), Dichlorodifluoromethane (CFC-12), Chlorodifluoromethane
(CFC-22), Trifluoromethane (CFC-23), Dichlorotetrafluoroethane (CFC-114), and
Chloropentafluoroethane (CFC-115).
203
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principal solvent in various applications ranging from specialty coatings for aerospace parts to
lacquers for wood furniture and two-component urethanes for coating plastics.
High solids coatings generally contain at least 70 weight percent of solids, and so the
solvent fraction, and VOC emissions, are dramatically reduced. Since the viscosity of such
coatings is higher than that of conventional coatings, handling problems with high solids
coatings have been common. The resin binder component and solvents must be carefully
selected or developed specifically for a given application to create acceptable handling and
finish quality. A solvent-based coating containing 30 volume percent solids that was switched
to 75 volume percent solids would have a reduction in its VOC emission potential of 87
percent.
Waterborne coatings enlist water as the principal solids carrier in order to reduce the
VOC content. Most such coatings contain some organic solvent to provide desired properties
such as solubility, evaporation rate and film coalescence. Applications for these coatings are
growing, particularly in the aircraft, appliance, metal coil and wood panel categories. A 75/25
ratio of water to organic solvent is common. Waterborne inks have not received wide
acceptance in the printing industry.
Powder coatings represent perhaps the greatest potential for emissions reduction of
any type of coating reformulation. A powder coating is a collection of resin, pigments and •
various additives that has been thoroughly mixed and broken down into a fine powder. These
coatings usually are applied by electrostatic spray or fluidized bed dipping (electrocoating).
The application of heat fuses the powder coating into a hard film. Only very small amounts of
volatile organics are emitted during curing, and thus the emission reduction achievable by
switching to a powder coating can approach 100 percent. Powder coatings can be used in
can coating operations without cemented seams.(4)
A high transfer efficiency helps to limit VOC emissions by reducing the amount of
coating that must be used (all of the coating used will emit its total volatile content whether it
coats the part or is wasted as oyerspray). Electrostatic coating is very efficient because paint
particles are attracted preferentially to a part maintained at a different electric potential. This
method is used widely in conjunction with various types of spraying techniques, including
powder application. When electrostatic methods are used in conjunction with dip coating, it is
usually termed electrocoating.
1.4.2 Add-on Controls
In addition to changes to the materials in surface coating and printing, various types of
control equipment are used to limit VOC emissions from these facilities. In these systems, the
generated vapors are delivered to the control device using a system that captures them near
the points of origin. The capture system may consist of hoods, partial enclosures and/or total
enclosures which are adjacent to, or enclose, the process equipment, and pull vapor-laden air
into ducting using one or more fans. The overall control efficiency is a function of the capture
efficiency and the efficiency of add-on controls.
There are three basic types of Add-on controls; incinerators, carbon absorbers and
refrigeration systems. Incinerators oxidize organic vapors into nonphotoreactive compounds
by thermal or catalytic combustion. The catalytic incinerator system utilizes a catalyst, such as
platinum or cobalt, to oxidize at a lower temperature (600 to 1,200° F) than is required for
thermal incineration (about 1,500°F). High destruction efficiencies (over 95 percent) are
possible if adequate combustion temperatures are maintained in the system.
204
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Incinerators generally have been applied in most coating categories where the VOC
concentrations were sufficient to support combustion without using excessive amounts of
auxiliary fuel. Heat recovery, using combustion heat to pre-heat incoming vapors, is used to
reduce auxiliary fuel requirements. Incineration is used to some extent in the graphic arts
industry, but solvent recovery is the preferred approach in most applications.
Carbon adsorption systems exploit the high adsorptivity of organics onto activated
carbon to collect and recover volatile solvents in exhaust gas streams. Carbon beds are
exposed to organic vapors until the beds are nearly saturated, and then the organics are
desorbed by steam heat or vacuum and the solvents recovered. Systems contain two or
more beds to that one bed can be adsorbing vapors while another is being desorbed, in a
continuous adsorption/desorption cycle. Carbon beds are either fixed, moving or fluidized.
Solvents and water are collected after desorption and separated by gravity decantation or
distillation, or the mixture may be incinerated. These systems are subject to operating
problems due to the presence of certain organics in the inlet stream. High boiling point
compounds can be difficult to remove from the carbon, reducing the available surface area for
adsorption and lowering the control efficiency. Some other organics may be difficult to collect
or may have high heats of adsorption, raising the bed temperature excessively.
Carbon-adsorption systems are widely used in several surface coating and printing
categories where it is economical to recover solvents or where VOC concentrations are too
low to justify incineration. In painting operations, exhaust containing sticky particulate must be
filtered before entering the control system. Carbon systems are widely applied in the
publication printing categories, and less so in smaller specialty printing operations (6). A more
detailed discussion of control techniques and equipment is presented in Section 3.
1.5 Inspection Procedures
Finally, an on-site inspection is often required in order to determine and verify
compliance. The primary activity of an on-site inspection is the compilation and verification of
coating/ink composition data and then the calculation of emissions. Section 5 contains a
description of the steps that are necessary to conduct a thorough on-site inspection.
Although the surface coating and graphic arts industry is quite diverse there are areas
and operations that are common between them. Determining compliance through calculation
can also be complex. Compliance Calculation examples are given in Section 4. It is hoped
that the material contained in this manual will allow the compliance officer to work within this
complexity and provide him/her with the necessary understanding to conduct a compliance
determination.
205
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SECTION 2
INDIVIDUAL PROCESS DESCRIPTIONS
2.0 Summary
In this section a brief description of each surface coating and graphic arts process is
given. Process flow sheets are also given. These descriptions have been developed from the
EPA Guideline Series for the surface coating and graphic arts industries. (4,5,6)
2.1 Can Coating
Cans may be made from a rectangular sheet (body blank) and two circular ends (three
piece cans), or they can be drawn and wall ironed from a shallow cup to which an end is
attached after the can is filled (two piece cans). There are major differences in coating
practices, depending on the type of can and the product packaged in it. Figure 2.1 depicts a
three piece can sheet printing operation.
There are both "toll" and "captive" can coating operations. The former fill orders to
customer specifications, and the latter coat the metal for products fabricated within one
facility. Some can coating operations do both toll and captive work, and some plants fabricate
just can ends.
Three piece can manufacturing involves sheet coating and can fabricating. Sheet
coating includes base coating and printing or lithographing, followed by curing at
temperatures of up to 220° C (425° F). When the sheets have been formed into cylinders, the
seam is sprayed, usually with a lacquer, to protect the exposed metal. If they are to contain
an edible product, the interiors are spray coated, and the cans are baked at up to 220° C.
Two piece cans are used largely by beer and other beverage industries. The exteriors
may be reverse roll coated in white and cured at 170 to 200°C (325 to 400°F). Several colors
of ink are then transferred (sometimes by lithographic printing) to the cans as they rotate on a
mandrel. A protective varnish may be roll coated over the inks. The coating is then cured in a
single or multipass oven at temperatures of 180 to 200°C (350 to 400° F). The cans are spray
coated on the interior and spray and/or roll coated on the exterior of the bottom end. A final
baking at 110 to 200° C (225 to 400° F) completes the process.
2.2 Metal Coil
Metal coil surface coating (coil coating) is the linear process by which protective or
decorative organic coatings are applied to flat metal sheet or strip packaged in rolls or coils.
Although the physical configurations of coil coating lines differ from one installation to another,
the operations generally follow a set pattern. Metal strip is uncoiled at the entry to a coating
line and is passed through a wet sections, where the metal is thproughly cleaned and given a
chemical treatment to inhibit rust and to promote coating adhesion to the metal surface. In
some installations, the wet section contains an electrogalvanizing operation. Then the metal
strip is dried and sent through a coating application station, where rollers coat one or both
sides of the metal strip. The strip then passes through an oven where the coatings are dried
and cured. As the strip exits the oven, it is cooled by a water spray in a quench chamber and
206
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BLANKET
CYLINDER
INK
• APPLICATORS
VARNISH
TRAY
ro
o
SHEET (PLATE)
FEEDER
UTHOGRAPH
COATER
OVER-VARNISHED
COATER
WICKET
OVEN
SHEET (PLATE)
FEEDER
Figure 2.1 Three piece can sheet coating operation
-------
again dried. If the line is a tandem line, there is first the application of a prime coat, followed
by another of top or finish coat. The second coat is also dried and cured in an oven, and the
strip is again cooled and dried before being rewound into a coil and packaged for shipment o?
further processing. Most coil coating lines have accumulators at the entry and exit that permit
continuous metal strip movement through the coating process while a new coil is mounted at
the entry or a full coil removed at the exit. Figure 2.2 is a flow diagram of a coil coating line.
Coil coating lines process metal in widths ranging from a few centimeters to 183
centimeters (72 inches), and in thickness of from 0.018 to 0.229 centimeter (0.007 to 0.090
inch). The speed of the metal strip through the line is as high as 3.6 meters per second (700
feet per minute) on some of the newer lines.
A wide variety of coating formulations is used by the coil coating industry. The more
prevalent coating types include polyesters, acrylics, polyfluorocarbons, alkyds, vinyls and
plastisols. About 85 percent of the coatings used are organic solvent base and have solvent
contents ranging from near 0 to 80 volume percent, with the prevalent range being 40 to 60
volume percent. Most of the remaining 15 percent of coatings are waterborne, but they
contain organic solvent in the range of 2 to 15 volume percent. High solids coatings, in the
form of plastisols, organosols and powders, also are used to some extent by the industry, but
the hardware is different for powder applications.
a
The solvents most often used in the coil coating industry include xylene, toluene,.
methyl ethyl ketone, Cellosolve Acetate (TM), butanol, diacetone alcohol, Cellosolve (TM),
Butyl Cellosolve (TM), Solvesso 100 and 150 (TM), isophorone, butyl carbinol, mineral spirits,
ethanol, nitropropane, tetrahydrofuran, Panasolve (TM), methyl isobutyl ketone, Hisol 100
(TM), Tenneco T-125 (TM), isopropanol, and diisoamyl ketone.
There are both toll and captive coil coating operations. Toll coaters normally use
mostly organic-solvent base coatings. Major markets for toll coating operations include the
transportation and construction industries, and appliance, furniture and container
manufacturers. The captive coater is normally one operation in a manufacturing process.
Many steel and aluminum companies have their own coil coating operations, where the metal
they produce is coated and then formed into end products. Captive coaters are much more
likely to use water-base coatings because the metal coated is often used for only a few end
products. Building products such as aluminum siding are one of the more important uses for
waterborne metal coatings.
208
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PRIME
COATER
ACCUMULATOR
SPLICER
O
CC
METAL
CLEANNG PRETREATMENT
UNCOtED
METAL
TOPCOAT
COATER
PRIME "WE
OVEN QUENCH
ACCUMULATOR
SHEAR
TOPCOAT TOPCOAT
OVEN QUENCH
RECOLNG
METAL
Figure 2.2 Metal coil coating line
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2.4 Large Appliance
Large appliance surface coating is the application of protective or decorative organic
coatings to preformed large appliance parts. For this discussion, large appliances are defined
as any metal range, oven, microwave oven, refrigerator, freezer, washing machine, dryer,
dishwasher, water heater or trash compactor.
Regardless of the appliance, similar manufacturing operations are involved. Coiled or
sheet metal is cut and stamped into the proper shapes, and the major parts welded together.
The welded parts are cleaned with organic degreasers or a caustic detergent (or both) to
remove grease and mill scale accumulated during handling, and the parts are then rinsed in
one or more water rinses. This is often followed by a process to improve the grain of the
metal before treatment in a phosphate bath. Iron or zinc phosphate is commonly used to
deposit a microscopic matrix of crystalline phosphate on the surface of the metal. This
process provides corrosion resistance and increases the surface area of the part, thereby
allowing superior coating adhesion. Often the highly reactive metal is protected with a rust
inhibitor to prevent rusting prior to painting.
Two separate coatings have traditionally been applied to these prepared appliance
parts; a protective prime coating that also covers surface imperfections and contributes to
total coating thickness, and a final, decorative top coat. Single coat systems, where only a
prime coat or only a top coat is applied, are becoming more common. For parts not exposed
to customer view, a prime coat alone may suffice. For exposed parts, a protective coating
may be formulated and applied so as to act as the top coat. There are many different
application techniques in the large appliance industry, including manual, automatic and
electrostatic spray operations, and several dipping methods. Selection of a particular method
depends largely upon the geometry and use of the part, the production rate, and the type of
coating being used. Typical application of these coating methods is shown in Figure 2.4.
A wide variety of coating formulations is used by the large appliance industry. The
prevalent coating types include epoxies, epoxy/acrylics, acrylics and polyester enamels.
Liquid coatings may use either an organic solvent or water as the main carrier for the paint
solids.
Waterbome coatings are of three major classes, water solution, water emulsions and
water dispersions. All of the waterborne coatings, however, contain a small amount (up to 20
volume percent) of organic solvent that acts as a stabilizing, dispersion or emulsifying agent.
Waterborne systems offer some advantages over organic solvent systems. They do no
exhibit as great an increase in viscosity with increasing molecular weight of solids, they are
nonflammable, and they have limited toxicrty. However, because of the relatively slow
evaporation rate of water, it is difficult to achieve a smooth finish with waterborne coatings. A
bumpy "orange peel" surface often results. For this reason, their main use in the large
appliance industry is as prime coats.
While conventional organic solventborne coatings also are used for prime coats, they
predominate as top coats. This is due in large part to the controllability of the finish and the
amenability of these materials to application by electrostatic spray techniques. The most
common organic solvents are ketones, esters, ethers, aromatics and alcohols. To obtain or
maintain certain application characteristics, solvents often are added to coatings at the plant.
The use of powder coatings for top coats is gaining acceptance in the industry. These
coatings, which are applied as a dry powder and then fused into a continuous coating film
through the use of heat, yield negligible emissions.
210
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Direct-To-Metal Top Coal
Exterior
Parts
NAOC
Spray
Cleansing and
Pretreatment
Section
Or/off
oven
t
Powder
Electro-
Deposition
Interior
Parts
From Sheet Metal Manufacturing
VDC
Flowcoat
or
Dip Coat
VDC
(llasholl)
t
Soray
t
i
f
,
1
j
k
Oven
Oven
Prime Coat
Top Coat
-H
To Assembly
Figure 2.4 Typical large appliance coating methods
-------
2.8 Paper Coating
Paper is coated for various decorative and functional purposes with waterborne,
organic solventborne, or solvent free extruded materials. Paper coating differs from printing in
that coating involves the application of a uniform layer of coating material across the paper,
whereas printing involves the transfer of an illustration, design or script in a contrasting color
on the paper.
Waterborne coatings improve printability and gloss but cannot compete with organic
solventborne coatings in resistance to weather, scuff and chemicals. Solventborne coatings,
as an added advantage, permit a wide range of surface textures. Most solvent borne coating
is done by paper converting companies that buy paper from mills and apply coatings to
produce a final product. Among the many products that are coated with solvent borne
materials are adhesive tapes and labels, decorated paper, book covers, zinc oxide coated
office copier paper, carbon paper, typewriter ribbons and photographic film.
Organic solvent formulations generally used are made up of film forming materials,
plasticizers, pigments and solvents. The main classes of film formers used in paper coating
are cellulose derivatives'(usually nitrocellulose) and vinyl resins (usually the copolymer of vinyl
chloride and vinyl acetate). Three common plasticizers are dioctyl phthalate, tricresyl
phosphate and castor oil. The major solvents used are toluene, xyiene, methyl ethyl ketone,
isopropyl alcohol, methanol, acetone and ethanol. Although a single solvent is frequently
used, a mixture is often necessary to obtain the optimum drying rate, flexibility, toughness and
abrasion resistance.
A variety of low solvent coatings, with negligible emissions, has been developed for
some uses to form organic resin films equal to those of conventional solventborne coatings.
They can be applied up to 1 /8-inch thick (usually by reverse roller coating) to products like
artificial leather goods, book covers and carbon paper. Smooth hot melt finishes can be
applied over rough textured paper by heated gravure or roll coaters at temperatures from 65
to 230° C (150 to 450° F).
Plastic extrusion coating is a type of hot-melt coating in which a molten thermoplastic
sheet (usually low or medium density polyethylene) is extruded from a slotted die at
temperature up to 315° C (600° F). The substrate and the molten plastic coat are united by
pressure between a rubber roll and a chill roll which solidifies the plastic. Many products,
such as the polyethylene coated milk carton, are coated with solvent-free extrusion coatings.
Figure 2.8 shows a typical paper coating line that uses organic solventborne
formulations. The application device is usually a reverse roller, a knife or a rotogravure printer.
Knife coaters can apply solutions of much higher viscosity than roll coaters can, thus emitting
less solvent per pound of solids applied. The gravure printer can print patterns or coat a solid
sheet of color on a paper web.
Ovens may be divided into from two to five temperature zones. The first zone is usually
at about 43°C (110°F), and other zones have progressively higher temperatures to cure the
coating after most solvent has evaporated. The typical curing temperature is 120°C (250°F),
and ovens are generally limited to 200° C (400° F) to avoid damage to the paper. Natural gas
is the fuel most often used in direct fired ovens, but fuel oil is sometimes used. Some of the
heavier grades of fuel oil can create problems, because sulfur oxides and particulate may
contaminate the paper coating. Distillate fuel oil usually can be used satisfactorily. Steam
produced from burning solvent retrieved from an absorber or vented to an incinerator may
also be used to curing ovens.
212
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CO
KNIFE COATER
REVERSE ROLLCOATER
ROTOGRAVURE PRINTER
PICKUPV /
ROLL X^^/
^ WEB Q
HEATED AR FROM
BURNER BOILER, OR
HEAT RECOVERY
APPLICATION
DEVICE
\
ZONE1
EXHAUST
(MAJOR
EMISSION
POINT)
ZONE 2
EXHAUST
HOT AIR MANIFOLD
u u u u u u
ION ROLLS
UNWND
REWIND
Figure 2.8 Paper coating tine
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2.13 Publication Gravure Printing
Publication gravure printing is the printing by the rotogravure process of a variety of
paper products such as magazines, catalogs, newspaper supplements and preprinted inserts,
and advertisements. Publication printing is the largest sector involved in gravure printing,
representing over 37 percent of the total gravure product sales value in a 1976 study.
214
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The rotogravure press is designed to operate as a continuous printing facility.
However, normal press operation experiences numerous shutdowns caused by web breaks
and mechanical problems. Each rotogravure press generally consists of 8 to 16 individual
printing units, with an 8 unit press the most common. In publication printing, only four colors
of ink are used: yellow, red, blue and black. Each unit prints one ink color on one side of the
web, and colors other than these four are produced by printing one color over another.
In the rotogravure printing process, a web from a continuous roll is passed over the
image surface of a revolving gravure cylinder. For publication printing, only paper webs are
used, the printing images are formed by many tiny recesses or cells etched or engraved into
the surface of the gravure cylinder. The cylinder is about one-fourth submerged in a fountain
of low viscosity mixed ink. Raw ink is solvent diluted at the press and is sometimes mixed with
related coatings, usually referred to as extenders or varnishes. The ink, as applied, is a
mixture of pigments, binders, varnish and solvent. The mixed ink is picked up by the cells on
the revolving cylinder surface and is continuously applied to the paper web. After the
impression is made, the web travels through an enclosed heated air dryer to evaporate the
volatile solvent. The web is then guided along a series of rollers to the next printing unit.
Figure 2.12 illustrates this printing process by an end (or side) view of a single printing unit.
At present, only solventborne inks are used on a large scale for publication printing.
Waterborne inks are still in research and development states, but some are now being used in
a few limited cases. Pigments, binders and varnishes are the nonvolatile solid components of
the mixed ink. For publication printing, only aliphatic and aromatic organic liquids are used as
solvents. Presently, two basic types of solvents, toluene and a toluene-xylene-naphtha
mixture, are used. The naphtha base solvent is the more common. Benzene is present in
both solvent types as an impurity, in concentrations up to about 0.3 volume percent. Raw
inks, as purchased, have 40 to 60 volume percent solvent, and the related coatings typically
contain about 60 to 80 volume percent solvent. The applied mixed ink consists of 75 to 80
volume percent solvent, required to achieve the proper fluidity for rotogravure printing.
2.14 Packaging and Specialty Rotogravure
In addition to the publishing rotogravure industry, which prints newspapers and
supplements, magazines, catalogs and advertisements, the remaining segment of gravure
printing produces packaging products and a miscellaneous group of "specialty" products, the
packaging products include cigarette cartons and labels, can labels, and detergent and many
other folding cartons. In the specialty field, gravure is used for wall coverings and decorative
household paper products such as towels, tissue and shelf paper. Other products include
floor coverings, vinyl upholstery and items with woodgrain effects.
While the basic rotogravure printing process is very similar for publications, packaging
and specialties, packaging and specialty plants are generally much smaller and there are
many more of them than there are publication facilities.
2.15 Flexographic Printing
In flexographic printing, the image area is above the surface of the plate, as opposed to
the etched image used in rotogravure. Flexography uses a rubber image carrier and alcohol-
base inks. The process is usually web fed and is employed for medium or long multicolor
runs on a variety of substrates, including heavy paper, fjberboard, and metal and plastic foil.
The major categories of the flexography market are flexible packaging and laminates, multiwall
bags, milk cartons, gift wrap, folding cartons, corrugated paperboard (which is sheet fed),
paper cups and plates, labels, tapes and envelopes. Almost all milk cartons and multiwall
bags, and half of all flexible packaging are printed by this process.
215
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TO NEXT UNIT
(O
PAPER WEB
ADJUSTABLE
COMPENSATING
ROLLER
DRYER EXIT AIR FLOW
RECIRCULATION
FAN
DRYER INLET
AIRFLOW
CIRCULATION PUMP
TO DRYER
EXHAUST
HEADER
EXTENDER/VARNISH
INK
SOLVENT
M LIQUID VOLUME METERS
Figure 2.12 Schematic of rotogravure printing unit
-------
Steam set inks, employed in the "water flexo" or "steam set flexo" process, are low
viscosity inks of a paste consistency that are gelled by water or steam. Steam set inks are
used for paper bag printing, and they product no significant emissions. Water-base inks,
usually pigmented suspensions in water, also are available for some flexographic operations,
such as the printing of multiwail bags.
Solvent base inks are used primarily in publication printing (see Figure 2.13). As with
rotogravure, flexography publication printing uses very fluid inks of about 75 volume percent
organic solvent. The solvent, which must be rubber compatible, is straight alcohol or alcohol
mixed with an aliphatic hydrocarbon or ester. Typical solvents also include glycols, ketones
and ethers. The inks dry by solvent absorption into the web and by evaporation, usually in
high velocity steam drum or hot air dryers, at temperatures below 120°C (250° F). As in
rotogravure publishing, the web is printed on only one side at a time, but passes over chill rolls
after drying.
217
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HOT WATER
(SPHERE
L
TRACES OF
WATER
AND
SOLVENT
f
4
...A
• i
• i
^CONDENSER1 ^J DECANTER
^ COOLWATER
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X ACTIVATED CAHBON ! ™
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ACTIVATED CARBON '"^
ADSORBER .
v (REGENERATOR) !
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• i
« ^ »
-'WABM ' ^ WATER
WATER
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^
.
.. GAS 1
WATER
INK
SOLVENT LADEN AIR
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INK
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PRESS
(ONE UNIT)
^
\
STEAM DRUM OR
HOT AIR DRYER
*
t
CHILL
ROLLS
AIR
PRINTED
WEB
AIR
AIR HEAT COOL
FROM STEAM. WATER
HOT WATER.
OR HOT AIR
Figure 2.13 Flexography printing line VOC emissions points
218
2-24
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SECTION 3.0
EMISSION CONTROL STRATEGIES
3.0 Introduction
It is generally assumed that the entire VOC content of a coating evaporates after
application to become potential emissions. That portion of the evaporated solvent which
is not subsequently recovered or destroyed in control equipment becomes actual
emissions. The VOC content of all coatings applied, together with capture and control
efficiencies for the vapor-control system, determines the net VOC emissions from the
process.
The VOC emissions at a facility can also result from on-site dilution of coatings
with solvents, from makeup solvents, and from solvents used for cleanup. Makeup
solvents may be added to a coating to compensate for standing losses and to restore
the working specifications of the coating. These types of solvent emissions should be
added to VOC emissions from coatings to get total emissions from a facility. Note that
improved housekeeping efforts can help prevent VOC emissions by minimizing the
exposure of solvents to the air.
In Section 3.1, probable sources of VOC emissions from surface coating
processes are examined. Section 3.2 then discusses the principal methods used in the
coating industry to limit VOC emissions from surface coating facilities. A detailed
description of several representative coating processes was presented earlier in Section
2.0 of this Manual.
3.1 Process Emissions
Each plant has its own unique combination of coating formulations, application
equipment, and operating parameters. The emission points discussed, however, are
fairly typical of coating and graphic arts operations. Process emissions points include
the application area, floor grates, ovens, hoods and enclosures. The process examples
and data given herein have been developed from the EPA Control Technology Guideline
Series.(2,4,5,6) Plant-specific data should be used for emission estimates whenever
possible.
Emissions from coating operations depend on the composition of the coating, the
coated area, the coating thickness, and the efficiency of application. Post-application
chemical changes, and nonsolvent contaminants such as oven fuel combustion
products, can also affect the composition of emissions. All solvent used and not
recovered is considered to be potential emissions.
In can-coating processes, sources of VOC emissions include the coating area
and the oven area of the sheet base and lithographic coating lines, the three piece can
side seam and interior spray coating processes, and the two piece can coating and end
sealing compound lines. Emission rates vary with line speed, can or sheet size, and
coating type. On sheet coating lines, where the coating is applied by rollers, most
solvent evaporates in the oven. For other coating processes, the coating operation itself
is the major source.
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In metal coil surface-coating operations, VOC are emitted from the coating
application station, the curing oven, and the quench area. VOC emissions result from
the evaporation of organic solvents in the coating. The percentage of total VOC
emissions given off at each emission point varies from one installation to another, but on
the average, about 8 percent is given off at the coating application station, 90 percent at
the oven, and 2 percent at the quench area. On most coating lines, the coating
application station is enclosed or hooded to capture fugitive emissions and direct them
into the oven. The quench area is an enclosed operation located immediately adjacent
to the oven exit so that a large fraction of the quench emissions are drawn into the oven
by the oven ventilating air. In operations such as these, approximately 95 percent of the
total emissions is exhausted by the oven, and the remaining 5 percent escapes as
fugitive emissions.
The oven exhaust is also the most important source of solvent emissions in wire-
coating plants. Emissions from the applicator are comparatively low, because a dip
coating technique is used.
In surface coating of large appliances, VOC from evaporation of organic solvents
in the coating are emitted in the application station and flashoff area (80 percent), and
from the oven (20 percent).
Surface coatinc/of metal furniture results in the evaporation of organic solvents as
VOC emissions. Specific operations that emit VOC are the coating application process,
the flashoff area, and the baking oven. The percentage of total VOC emissions given off
at each emission point varies from one installation to another, but on the average spray
coating line, about 40 percent is given off at the application station, 30 percent in the
flashoff area, and 30 percent in the baking oven.
Emissions of VOC at flat-wood coating plants occur primarily from reverse roll
coating of filler, direct roll coating of sealer and basecoat, printing of wood-grain
patterns, direct roll or curtain coating of topcoat(s), and oven drying after one or more of
these operations.
The main emission points from paper coating lines are the coating applicator and
the oven. In a typical paper coating plant, about 70 percent of solvent emissions come
from the coating lines, chiefly from the first zone of the oven. The remaining 30 percent
of the emissions result from solvent transfer, storage, and mixing operations. A
negligible amount of the solvent used (i.e., less than 5 percent) is typically retained in the
product.
The VOC emissions in a fabric coating plant originate at the mixer, the coating
applicator, and the oven. Emissions from these three areas are from 10 to 25 percent,
20 to 30 percent, and 40 to 65 percent, respectively. Fugitive losses, amounting to a few
percent, escape during solvent transfer, storage tank breathing, agitation of mixing
tanks, waste solvent disposal, various stages of cleanup, and evaporation from the
coated fabric after it leaves the line.
In auto surface coating operations, the application and curing of the prime coat,
guide coat, and top coat account for 50 to 80 percent of the VOC emitted from assembly
plants. Final topcoat repair, cleanup, and miscellaneous sources such as the coating of
small component parts and application of sealants, account for the remaining 20
percent. Approximately 75 to 90 percent of the VOC emitted during the application and
curing process is emitted from the spray booth and flashoff area, and 10 to 25 percent
from the bake oven.
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In printing operations, VOC solvent and traces of aerosol emissions occur at
several points in the finishing steps. Most of the emissions occur when the wet web is
heated in the drying ovens. Approximately 80 percent of the solvent entering a print
station is evaporated in the associated oven. The balance of the solvent is emitted as
fugitive emissions in the area of the cylinders and coating reservoirs.
In publication rotogravure printing, the sources of VOC emissions are the solvent
components in the raw inks, the coatings used at the printing presses, and the solvent
added for dilution and press cleaning. In uncontrolled presses, emissions occur from
the dryer exhaust vents and the evaporation of solvent retained in the printed product.
About 75 to 90 percent of the VOC emissions occur from the dryer exhausts, depending
on press operating speed, press shutdown frequency, ink and solvent composition,
product printed, and dryer design. The amount of solvent retained by the various
rotogravure printed products is about 3 to 4 percent of the total solvent in the ink. The
retained solvent eventually evaporates after the printed product leaves the press.
There are numerous points around a printing press from which fugitive emissions
occur. Most of the fugitive vapors result from solvent evaporation in the ink fountain,
exposed parts of the gravure cylinder, the paper path at the dryer inlet, and the paper
web after exiting the dryers between printing units.
3.2 Process Control Techniques
In this section, techniques are presented for lowering VOC emissions:
(1) coating reformulations;
(2) improved application methods; and
(3) add-on control devices such as incineration and carbon adsorption.
The emission reduction potential of some of the strategies discussed in this
section are given below:
Table 3.1. Control Efficiencies for Surface Coating Operations
Reduction3
Control Option (%)
Substitute waterborne coatings 60-95
Substitute low solvent coatings 40-80
Substitute powder coatings. 92-98
Add afterburner/incinerator0 95-98
Add carbon adsorber3 95
f| Expressed as % of total uncontrolled VOC load.
D Reduction efficiency applies to control device only.
3.2.1 Coating Reformulations
Conventional coatings consist of finely divided solid materials (pigments and
binders) dispersed in a liquid medium (the volatile portion). The volatiles generally
consist of a mixture of organic solvents, and can also contain water. The organic solvent
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mixture may contain both regulated (VOC) and exempt solvents, but the great majority of
solvents are VOC. Solventborne coatings contain at least 30 percent by volume of
solvents to permit easy handling and application, and can contain up to 85 volume
percent solvents.
Most emission reduction efforts in the cpating industry today are focused on
lowering the VOC content of coatings. Four principal methods are available: solvent
substitution, high solids (low solvent) conventional coatings, waterborne coatings, and
powder coatings. Some Ipw-VOC coating formulations, when introduced as
replacements for conventional coatings, may eliminate the need for capture and control
devices in some situations. Table 3.2 shows recent trends in the use of some coating
formulations:
In cases where it is technically feasible, the substitution of exempt solvents for
VOC solvents can, in principle, be used to reduce coating emissions. Exempt solvents,
however, appear to have limited application in the surface coating and printing
industries. An example of solvent replacement is the use of 1,1,1-trichloroethane as a
primary solvent in specialty coatings for aerospace parts and in lacquers for wood
furniture.
Table 3.2. Percent Usage of Various Coating Formulations
Coating Type
Conventional solventborne
High solids
Waterborne
Powder
Two-component
Radiation cure
Other
Year
1985(%)
57.4
12.9
9.8
8.3
4.5
1.3
5.8
1988(%)
41.5
17.6
14.4
14.5
4.4
1.5
6.1
High-solids coatings generally contain at least 70 weight percent solids, which
dramatically reduces the solvent fraction and the VOC emissions. For example, if a
conventional solvent-based coating containing 30 volume percent solids is reformulated
to contain 75 volume percent solids, it will exhibit a 64 percent reduction in its VOC
emission potential. Because the viscosity of high-solids coatings is higher than that of
conventional coatings, handling problems are common. The resin binder component
and solvents must be selected carefully to create acceptable handling characteristics
and product quality.
Waterborne coatings use water as the principal solids carrier (e.g., solvent) to
reduce the VOC content. Most coatings of this type still contain some organic solvent to
provide desired properties such as solubility, evaporation rate, and film coalescence. A
75/25 ratio of water to organic solvent is typical. For example using this water-to-solvent
ratio, a conventional solvent-based coating originally containing 30 volume percent
solids (and 70 percent solvent) will exhibit a 75 percent reduction in its VOC emission
potential. Applications for waterborne coatings are growing, particularly in the aircraft,
appliance, metal coil, and wood panel categories. Waterborne inks, however, have not
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received wide acceptance in the printing industry due to slower drying and lower product
quality in some applications.
Powder coatings, which contain almost no VOC, represent perhaps the greatest
potential for emissions reduction of any type of coating reformulation. A powder coating
is a collection of resin, pigments, and various additives that has been thoroughly mixed
into a fine powder. These coatings are usually applied manually, by electrostatic spray,
or fluidized bed dipping (electrocoating). The application of heat then fuses the powder
coating into a hard film. Only very small amounts of volatile organics are emitted during
curing, enabling the emission reduction achievable by switching to a powder coating to
approach 100 percent.
Powder coatings are applied as single coats on some large appliance interior
parts and as topcoat for kitchen ranges. They are also used on metal bed and chair
frames, shelving, and stadium seating. Other single coat applications include small
appliances, small farm machinery, fabricated metal product parts, and industrial
machinery components (4).
3.2.1 Coating Application / Transfer Efficiency
The transfer efficiency is defined as the fraction of solids in the total consumed
coating that remains dn the product, and it varies with the type of application technique.
A high transfer efficiency helps to limit VOC emissions by reducing the amount of coating
that must be used to achieve a given film thickness (or to cover a given surface area).
Spraying equipment produces a mist of overspray with a large surface area for solvent
evaporation. A transfer efficiency of 60 percent means that 60 percent of the coating
solids consumed is deposited usefully onto the product. The other 40 percent is wasted
overspray. Because not every application method can be used with all parts and types
of coating, transfer efficiencies in the surface coating industry range widely.
Note that the total volatile content of a coating is emitted whether the part is
coated or the coating is wasted as overspray. By using !ow-VOC coatings and an
application system with a high transfer efficiency {such as electrostatic spraying), VOC
emission reductions can approach those achieved with control devices.
Powder coating systems are designed to capture and recirculate overspray
material, and are characterized in terms of a "utilization rate" rather than a transfer
efficiency. Most facilities achieve a powder utilization rate of 90 to 95 percent.
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SECTION 5
INSPECTION PROCEDURES
5.0 Summary
The primary focus of this section is on-stte inspection procedures. The purpose of
an inspection is to confirm that the coatings and solvents used are in compliance with
regulatory requirements. Procedures are presented which inform inspectors as to why,
where, how, and what to look for so a thorough inspection of a source can be
conducted. A description of some basic, often encountered equipment and instruments
is presented. Checklists are provided in the text for field use to guide and aid the
inspector in observing and noting the condition and operation of the capture and control
systems. This section also provides guidance on preparing for an inspection, and
procedures for conducting general plant inspections and inspections of surface coating
process operations.
. The material presented herein has been purposely written in a simple and general
manner that might mask the true complexity of VOC capture and control at surface
coating operations. Therefore, throughout this guide, references are made to
documents that provide further technical data.
5.1 Preparation
A certain amount of preparation prior to an inspection is always advisable. The
preinspection procedures suggested here are intended as general guidelines on how to
prepare for and begin the inspection of a surface coating operation. However, the
procedures are only suggestions; the inspector must become familiar with and follow the
procedures established by the regulatory agency at all times.
These procedures are for continuing compliance inspections; inspections of
sources which have previously proved initial compliance with regulatory emission limits
by installing air pollution control systems and/or modifying processes. A properly
conducted continuing compliance inspection will, at a minimum, allow a qualitative
comparison of present equipment operation and condition to the initially permitted
conditions.
5.1.1 File Review
The first step in preparing for an inspection is a review of all information available
in the regulatory agency's files on the operation that will be inspected. Efforts invested in
reviewing the available information will reduce onsite field time because the information
that must be collected and verified will be known.
Rrst, a general review of the documents on file should be conducted. The file
review should include items such as permit applications, approved permits, reports of
violations or enforcement actions, and annual coating or emissions inventory. Records
of citizen complaints, previous inspection reports, and equipment malfunctions should
also be noted. Plot plans showing the layout of the source, the location of equipment,
and identification of emission points should be examined. Documents should be
available that provide specific design and operational data for processes and control
equipment.
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During the review of the source file, the control strategy should be examined.
Specific references to regulations that apply to the emission points at the source may be
incprporated. These regulations should be reviewed thoroughly and the type of
emission limitation noted. For each emission point, the source should have either done
something (process modification, control equipment installation) or submitted something
(stack test/coating/ink composition data) that would establish initial compliance with
emission limits. In addition to regulations that establish emission limits, there are also
requirements for certain operation, maintenance, recordkeeping, or reporting activities
(See Section 4.4).
In addition, some sources may have a non-standard compliance method
incorporated as a source specific SIP revision. This is true for sources with approved
bubbles or alternate control strategy. The inspector should note any deviations from the
standard compliance procedures and become familiar with any such methods prior to
the on-site inspection. The type of data to be obtained in order to verify compliance with
these requirements will be discussed in Section 5.3.
Finally, the regulatory agency may have negotiated certain legally-binding
agreements with the subject source. These agreements are likely to be in regard to
issues unique to the activities at the source. They may allow the source some leniency
from the strict interpretation of a regulation, or they may have established requirements
more stringent than a regulation. These agreements are sometimes called variances,:
consent decrees, or compliance schedules. It is important to fully understand any such
agreements before the inspection.
The documentation that the source submitted to support its claim of compliance
along with records the source is required to maintain related to compliance should
contain the detailed information needed to become familiar with the process and control
equipment. It may be helpful to summarize some of the data or previous inspection
information so that it will be available during the inspection. Examples of inspection
forms/checklists are provided in Section 5.3..
At the end of the file review, the inspector should be aware of the following
information.
1. The emission points and the relative magnitude of their emissions.
2. The specific steps the source has taken at each emission point to comply with
emission limits.
3. The key parameters that affect emissions from each emission point.
4. The processes or process areas at the source.
5. The results, recommendations, or conclusions of previous inspections.
6. The history of citizen complaints against the source.
7. The history of process or control-equipment malfunctions that have caused
increased emissions.
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An outline of detailed information is presented in Table 5.1. If any of these items
of information are not available from the file, an effort should made to obtain them during
the inspection.
5.1.2 Preliminary Dafa Verification
As mentioned in Section 4.4, each source is required to maintain records of
coatings and process variables. Occasionally these records will be reviewed to verify
their accuracy as part of determining compliance or developing a case for enforcement
action. The review and verification for enforcement purposes will be fairly extensive but a
spot check of this recordkeeping data is recommended for compliance review also. This
is a way for the inspector to become familiar with the compliance methods and
calculations for the specific source and potentially uncover areas to focus the on-site
inspection.
5.2. Plant Inspection
Due to the variety and complexity of surface coating processes, a detailed
description of the inspection methods that would provide a basis for quantifying emission
rate changes that would result from process changes is beyond the scope of this
manual. However, some basic guidelines are presented below.
5.2.1 Field Inspection
The inspection can (and should) begin before entering the plant. The
observations outlined here can also be conducted after the in-plant inspection.
The perimeter of the plant should be circumnavigated, being careful not to
trespass on either the company's or other people's property. Visible emissions from
stacks in the plant, and fugitive emissions and odors leaving the plant property can
legally be read without obtaining permission from the company as long as they are not
done on the company's property. The noise levels around the plant boundary should be
noted as well as the proximity of homes, schools, and businesses to the plant property
line.
5.2.2 On-site Inspection
A brief meeting with plant personnel should be conducted before the actual
inspection is begun unless the inspector has good reason to suspect that violations will
be corrected during the meeting. The following topics are suggested for discussion
during this meeting.
1. The purpose of the inspection, the equipment to be inspected, the data and
samples desired.
2. The confidentially requirements and procedures of the company as they will
apply to the data collection or inspection needs.
3. The process and control equipment plot plans and flow sheets to confirm the
understanding of current operational equipment and to identify any changes or
modifications in plant operations since the last inspection.
4. The safety procedures, required safety equipment, and hazard potential of
areas covered in the inspection.
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TABLE 5.1
SPECIFIC DATA FROM FILE REVIEW
I. GENERAL
A. Number of coating lines at plant
B. Number of control systems at plant
C. Major noncoating line-related emission sources at plant
II. SURFACE COATING PROCESS
A. Material being coated
B. Production rate
C. Coating applied
D. Coating application method
E. Coating application rate
F. Drying/curing method
G. Drying/curing temperature
III. REGULATIONS
A. Emission Limitation and Expression
B. Control Strategy Description
C. Permit Conditions
D. Variances
IV. CAPTURE SYSTEM
A. Total number of hoods in each system
B. Type of hoods
C. Distance of each hood from source
D. Design capture/face velocity at each hood
E. Location of filters
F. Location of dampers
G. Type and location of fan(s) in system
H. Type of fan drive (direct, belt)
I. Design flow rate of system
V. CONTROL DEVICE
A. Type of control device
B. Inlet pollutant concentration
C. Outlet pollutant concentration
D. Air flow through device
E. Design efficiency
F. Disposal or recovery procedure for pollutant removed
from control device.
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In addition to these topics, the inspector should be prepared to discuss areas of
concern with the plant management, such as:
1. The agency's authority to conduct the inspection.
2. The specific applicability of regulatory requirements to the source.
3. The purpose of uses for information collected during the inspection.
Any noise, odor, or fugitive emission problems noted during the pre-inspection
circumnavigation of the source should be investigated. The inspector should note the
location of the raw material and finished product storage areas, noise-producing
processes or operations, their proximity to the source property line, the potential for the
noise to reach the nearest off-site receptor, operations that are odorous or dust-
producing and that have the potential for odors or dust from these sources to leave the
plant property should be evaluated.
If the plant operates a boiler, it should be inspected for obvious signs of improper
operation or malfunction. Other guidance documents are available that provide detailed
inspection procedures. However, obvious signs of boiler problems are a smoky stack or
erratic boiler temperature. Finally, if during the preinspection file review, a recurring
emission problem or citizen complaint was noticed, that equipment should be inspected
and note if the plant is taking steps to eliminate recurrence of the past problems.
5.3 Process Inspection
Changes in emission rates can result from changes in the surface coating
process operation. Changes that can affect emission rate are:
changes in coating compositions
changes in coating application methods
changes in coating application rates
changes in coating drying/curing methods or rates
changes in the material being coated.
5.3.1 Coating Formulation
The inspection of the surface coating process begins at the point where the
coating is prepared for application. The company escort can be questioned about the
composition, preparation and application methods. Does the coating require cut or
diluent solvents? Is it necessary to clean the preparation or application area with
solvents? Do they change the types of coatings applied by the applicator? How often
are they changed? What are the differences between coatings? Do they buy the
coatings from various suppliers? How is coating consumption tracked?
Regulatory requirements often dictate that coating/ink composition data be
maintained by the source and submitted to the State agency on a quarterly or
semiannual basis. These data records should, at a minimum, include the following for all
coatings used in the process during the previous year's time:
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volume percent solids
weight percent solvent
weight percent water
coating density (pounds per gallon)
solvent density (pounds per gallon)
5.3.2 Sample Qoatings
During the walk through inspection of the plant, the inspector may collect samples
of the individual "as applied" coatings being used at that time for EPA Reference Method
24 analysis. The inspector may choose to sample coatings which may not be compliant
based on the file and recordkeeping review or to sample coatings to verify the claim that
they are compliant. The samples should be handled in a consistent manner with a
chain- of- custody record. Duplicate samples should also be taken for analysis by an
EPA laboratory or EPA consultant laboratory and by the source. It is the responsibility
of the field inspector to determine the following when attempting to obtain a sample of
the coating or ink:
1. Can the sample be obtained safely?
2. Can the sample be handled and shipped safely?
3. Is the sample representative of the coating at the sample location or do non-
homogeneous conditions introduce significant error?
4. Is the sample representative of the coating(s).used at the source or does
normal process variability introduce significant error?
5.3.3 Sampling Location
To the extent possible, the sample should be obtained at the point of coating
application. In this way, the sample will adequately represent the "As Applied" coating
which may have been diluted by volatile organic solvents. However, it should be noted
that there can be numerous significant safety hazards involved in sampling coatings and
inks near the applicators. It is often impossible to obtain samples at the point of
application. In this case, inspectors should determine if it is possible to obtain
meaningful "As Supplied" samples from a storage or mixing vessel. Sampling safety is
also important when obtaining these samples.
Regulatory agency personnel should not attempt to take samples themselves.
This should be done only by plant personnel. The inspectors should note how the
sample was obtained and record on the data label the following information:
Sample identification number
Date and time
Source name
Sampling location
Type of coating (color, generic type)
Inspector's signature
Plant representative signature
Availability of "As Applied" formulation (yes or no)
Availability of "As Supplied" formulation (yes or no).
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A VOC sampling checklist should be completed for each sample. It should supply
pertinent information regarding sampling location and type of coating.
Coating equipment is generally cleaned using a VOC solvent. These solvents and
waste coatings are generally collected in 55-gallon drums for off-site disposal. If waste
coatings are disposed of as hazardous waste and the source is claiming the right to
subtract significant amounts of VOCs contained in the waste coatings from its emissions
estimates, samples of the waste coatings should be obtained for Reference Method 24
analysis.
5.3.4 Type of Sampling Container
All field inspectors should carefully consider the type of container to be used
before attempting to obtain any samples of coatings or inks. Metal cans with a bonding
cable back to the source of sample are generally preferred since they can be properly
grounded while obtaining the sample. Also, the main coating or ink source should be
properly grounded.
Another advantage of metal cans is that they usually will not break when dropped.
Slight contamination of the sample due to the soldered joint in the metal can is usually
not a problem because the analytical methods are all gravimetric.
Glass sample containers are not recommended because they break while being
carried or during shipping back to the agency laboratory. Metal and plastic containers
are virtually immune to breakage, but are especially prone to static charge accumulation.
5.4 Coating Processes.
The coating application method (spray, flow, dip, etc.) and the shape of the
material being coated (chairs, fenders, discs, springs, etc.) should be observed. Plant
personnel can be questioned if they have made any changes to the application method
recently. Have they changed the rate at which they apply the coating? Can they coat
other shapes on the same line? Do they change shapes often? Do they change the
application rate for different shapes? What adjustments do they make to the applicator
when they change shapes? Do they adjust the control system when they make
adjustments to the applicator?
Next, the drying/curing area of the line should be observed and the way the
coating is dryed/cured onto the material (gas-fired oven, infrared heaters, stacked in
room) noted. Many ovens operate continuously with material moved through them on
some type of conveyor system. Can the conveyor speed be changed? What
circumstances cause it to be changed? Is the temperature of the drying/curing
operation monitored? Is it necessary to vary the temperature frequently? The physical
integrity of the ovens should be checked. When ovens are totally enclosed, the capture
system will often evacuate them directly. Thus, they should be under negative pressure
and fumes should not be observed leaking from the entrance or exit of the ovens.
However, a crack or space between oven panels may allow too much air into the oven
and overload the capture system. The drying/curing process is important to the quality
of the coating and, therefore, the drying/curing equipment is likely to be well
maintained.
Due to of the diversity of coating process equipment, a suggested checklist is not
presented-one that would cover all possibilities would be too cumbersome and a
general one would be of little practical value. Instead, the preceding discussion is
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intended to inform you of the changes to the surface coating process that can be made
and the fact that these changes can influence the control system's ability to perform as
originally designed. Plant personnel may, in some cases, be genuinely unaware of the
influence that process changes can have on the control system. By asking about
process changes, potential changes in emission rates may be identified when the
inspection information is compared to the original permit conditions.
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5.7 Post Inspection Procedures
After an on-site inspection, the inspector may find that the data collected and
contained in the file is not sufficient. Deficiencies could include:
1. Additional data on coatings if the recordkeeping data do
not include all coatings or diluents.
2. Destruction or removal efficiency test results especially
if there is reason to believe that the control equipment
has deteriorated.
3. Capture efficiency test results.
4. EPA Reference Method test results for "as applied"
coatings or coatings in which the data are suspect.
The inspector may choose to initiate procedures under Section 114 which allows
the regulatory agency to request information for use in determining compliance or
to request a new performance tests for the control and capture systems.
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Surface
Coating
Calculations
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SECTION 4
COMPLIANCE DETERMINATION CALCULATIONS
4.0 Summary
Basic calculations for determining compliance with surface coating and graphic arts
regulations require four types of information. First the form of the emission limitation must be
known. The second is data on the physical and chemical properties and compositions of the
coatings or inks. Performance specifications for add-on controls and finally production rates
and usages must also be known. In this section, the regulatory basis for emission limitations
is presented along with a description of the sources of data necessary for compliance
determinations. Equations and methods for calculating emissions including example
calculations are also provided.
4.1 Expressions of Emission Limitations
The first piece of information that is needed to determine the compliance status of a
source in the surface coating or graphic arts industry is the emission limitation or limitations
which the source is required to meet. A number of Federal programs, such as Reasonably
available control technology, new source performance standards among others, apply to
surface coating and graphic arts industries, and States have a certain latitude in developing
specific control programs to reduce VOC emissions. It is beyond the scope of this manual to
present a complete description of the various regulatory programs that apply to these
industries. The brief description is designed to provide the reader with sufficient
understanding of the regulatory bases to interpret emission limitations. It is not meant as a
guide for determining emission limitations for sources.
The form in which the emission limit is expressed depends in part on the establishing
regulatory program. Common forms of emission limitations expressions for the surface
coating industry are (7):
• Weight VOC per volume of coating minus water,
* Weight VOC per square foot (flat wood coating) or
* Weight VOC per volume solids content
• Weight VOC per volume solids, as applied.
Emission limitations for graphic arts industry are on a different basis and common ones
are (3):
• Volume % VOC in volatile fraction for waterbome ink,
* Volume % Water in volatile fraction for waterborne ink,
• Volume % Solids in ink.
The regulatory basis for many of the emissions units is the reasonably available control
technologies (RACT) as issued by EPA and defined in the Control Techniques Guidelines
(CTG). Many States have adopted these limits into their SIP'S. Appendix B contains a copy of
the CTG limits for surface coating and graphic arts. Emission limits developed from New
Source Performance Standards (NSPS) are also listed in Appendix B, and they are typically
expressed on a solids basis.
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The SIP's generally require continuous compliance on a line-by-line over some period
of time, either a daily or hourly rate. Water and exempt solvents are not included in the basis-
or unit of the emission limitation. The emission limits may also be set "as applied," as actually
used in the process which would be calculated from the "as supplied" by the manufacturer
plus any diluent solvents or cutting solvents.
Compliance determination calculations are typically done in the units or basis of the
emission limitation. Calculations for sources which are complying by reformulating the
coatings, compliant coatings, are typically done on a weight of VOC per gallon of coating. It
may be necessary to convert the coatings "as supplied," as received from the manufacturer, to
"as applied" in the compliance determinations.
It is sometimes necessary to compare compliant coatings with other forms of emission
limitations. These types of calculations are called Equivalency calculations and are done on a
solids basis. The reason for this is the amount of solids it takes to coat a surface to a
particular film thickness is the same regardless of coating formulation or application method.
Solids basis or Solids applied basis are used when add-on controls or improved
transfer efficiencies are used for the same reasons as equivalency calculations. Occasionally,
a source may wish to use a combination of over-compliant and non-compliant coatings and
add-on controls on a plant wide basis. This is termed an alternative control strategy or
"Bubble". In these cases the emission limits are expressed on a solids basis. Bubbles must
provide an additional 20% emissions reduction, be approved by the State and EPA, and must
specify the method used to determine compliance.
Equations for determining compliance are given in Section 4.5 for each emission
limitation expression. Samples of each type of calculations are also provided in Section 4.6
4.2 Physical and Chemical Data Sources
The second set of information that is needed to conduct a compliance determination
calculation is physical and chemical data including densities, VOC contents, and solids
content, for the coating. Common methods and sources for obtaining the necessary data are
presented below. The sample calculations in Section 4.6 use data from these sources.
4.2.1 Standard Methods
The EPA has promulgated standard methods (Reference Methods 24 and 24A) for
determining the VOC content and densities of coatings and inks. Method 24 is used to
determine:
the volatile matter content (weight fraction or weight %),
water content (weight fraction or weight %),
coating density (kg per Liter), and
solids content (volume fraction).
of paint, varnish, lacquer, or related surface coatings. Although Method 24 is suitable for most
coatings, Method 24A is more applicable to publication rotogravure printing inks which
contain high volatile fraction inks. Method 24A specifies a gravimetric procedure to determine:
f 1) the VOC weight fraction of the coating,
(2) coating density, and.
(3) solvent densities.
235
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Both methods rely on American Society of Testing Materials (ASTM) procedures, and are
presented in Appendix C. Other methods may be used only if approved by the State and
EPA.
4.2.2. Data Sheets
In an attempt to simplify the process for determining compliant coatings, EPA prepared
a manual, Recordkeepino Guidance Document for Surface Coating Operations and the
Graphic Arts Industry (10) which identifies the data to be maintained by coating
manufacturers and users and suggests a format in which the data be presented. Other
formats may also be used. (8) Example data sheets are illustrated in Appendix D.
4.2.3 Materials Data Sheets
Materials Safety Data Sheets (MSDS) may also be used to supplement physical or
chemical data from the data sheets. MSDS are supplied by the manufacturer and contain
physical and chemical properties such as densities and composition of the manufacturer's
product. This may not be sufficient information to determine the VOC content of a coating in
a process setting. The MSDS data sheets however can be especially useful as a source of
data on diluents or cut solvents.
4.3 Transfer Efficiencies
The third piece of information that is necessary to determine the compliance status of a
specific source is the degree of emission reduction which can be expected of certain add-on
or alternative controls.
Certain minimum or baseline transfer efficiencies have been established in the CTG's
for the following four surface coating applications:
• spray applications in automotive assembly plants,
• surface coating of large appliances, and
• surface coating of metal furniture.
Transfer efficiencies have also been established in certain NSPS. These values can be
used in compliance determination calculations for NSPS sources. Many sources, however,
can take advantage of improved or enhanced transfer efficiencies (greater than baseline).(9)
The enhanced transfer efficiency is established under plant conditions and included in the SIP
along with the baseline transfer efficiency. When enhanced transfer efficiency is used,
compliance is determined by comparing the VOC emission from a baseline case and
enhanced transfer efficiency case. Example 4.7 is an example of the use of enhanced transfer
efficiencies.
Minimum performance criteria may be specified in the regulations for add-on control
equipment. The efficiency of capture and control equipment is determined by a performance
test for a specific source. EPA recommends that sources keep records of performance data
as part of recordkeeping requirements.
4.4 Recordkeeping Requirements
The fourth piece of information that is necessary for compliance determinations is
information on coating usage and process conditions. Most SIP's require sources to maintain
236
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a record of coatings used and other process data. Although recordkeeping requirements can
vary from State to State, generally the minimum information that must be maintained is:
• Coating formulation and analytical data,
* Coating consumption data,
* Capture and control equipment performance data,
• Spray applicator transfer efficiency data, and
* Process information.
Sources are only required to submit data applicable to their operation. For instance, if
a source uses only compliant coatings to meet emissions limitations, it need not maintain
records related to transfer efficiencies or control equipment performance. Sources subject to
NSPS or construction or operating permits may have other recordkeeping requirements
specific to those programs.
Sources are required to maintain records in a format consistent with the emission
limitations and time frame. Information on the method for determining compliance must also
be maintained if the source is subject to a bubble.
Examples of standard forms for recordkeeping purposes were illustrated in Section 4.2
above. Sources are not required to use these specific forms but they must provide the same
data. These recordkeeping forms should contain all the information that is necessary to
determine the compliance status of a source.
4.5 Compliance Calculations
As seen in Section 4.2, the regulations are expressed in different basis units and
different data can be required. A summary of applicable surface coating or graphic arts
regulations and corresponding data requirements are summarized in Table 4.1. On first
inspection, it appears to be a formidable task to calculate compliance. It is not as difficult as it
may seem if one keeps in mind some basic facts. Equations for determining compliance are
provided below.
Examples of basic calculations for determining compliance with regulations are
presented in the following material beginning with volume and weight percent conversions.
Up to this point, emissions limits have been discussed in terms of weight per volume. Most
emissions limitations will be codified in English units, i.e., pounds, gallons rather than metric,
kilograms, Liters. The examples are all presented in English units.
237
-------
TABLE 4.1
BASIC DATA REQUIREMENTS FOR COMPLIANCE DETERMINATIONS
Emission Source
Limitation Expression
Basic Data Required
SURFACE COATING
la. Ibs VOC/gal coating
(less water) as supplied
I
a. coating density (Ibs coating/gal coating)
b. weight % volatiles (Ibs volatiles/lb coating)
c. weight % water (Ibs water/lb coating2)
or
d. coating density (Ibs coating/gallon coating)
e. VOC density (Ibs VOC/gallon VOC)
f. volume % volatiles
g. volume % water
Ib. Ibs VOC/gal coating
(less water) as applied
h. a through c (or d through g) above
i. cut solvent density (Ibs VOC/gallon VOC)
j. ratio of cut solvent to coating (gallon of
cut solvent per gallon of coating as supplied)
2. Ibs VOC/gal solids as
applied
k. coating density (Ibs coating/gallon coating)
I. weight % VOC (Ibs VOC/lb coating)
m. volume % solids (gal solids/gal coating)
n. transfer efficiency (amount of solids
applied /amount of solids used)
-------
TABLE 4.1 (continued)
BASIC DATA REQUIREMENTS FOR COMPLIANCE DETERMINATIONS
Emission Source
Limitation Expression
Basic Data Required
SURFACE COATING (continued)
3. Ibs VOC/1,000 fr flatwood
o. coating usage rate
(gallons of coating applied/unit of time)
p. weight % VOC (Ib VOC/lb gal as applied)
q. flat wood production rate (1,000 ft /unit of
time)
GRAPHIC ARTS
4. gal VOC/(gal VOC + gal water)
and
gal water/(gal VOC + gal water)
r. ink density (Ibs ink/gal ink)
s. weight % VOC (Ibs VOC/lb ink)
t. weight % water (Ibs water/lb ink)
u. volume % solids (gal solids/gal ink)
v. ratio of ink as supplied to cut solvent
added (gal ink suppliedigal cut solvent added)
w. cut solvent density (Ibs VOC/gal VOC)
5. gal solids/gal ink as applied
x. volume % solids (gal solids/gal ink)
y. ratio of ink as supplied to cut solvent added
(gal ink supplied: gal cut solvent added)
z. volume % water (gal water/gal ink)
-------
TABLE 4.1 (conclusion)
BASIC DATA REQUIREMENTS FOR COMPLIANCE DETERMINATIONS
Emission Source
Limitation Expression
Basic Data Required
GRAPHIC ARTS (continued)
6. Overall capture and abatement
reduction percentage
aa. capture efficiency (Ib VOC captured/lbs VOC
released)
bb. destruction efficiency
(Ib VOC destroyed/lb VOC entering control device)
The composition and characteristics of these coatings and inks just delivered from the manufacturer and before the user opens the
containers are termed "as supplied". Before a coating or ink is applied to a substrate, the user may add dilution of "cut" solvent to
the coating in order to obtain desired characteristics (e.g., lower viscosity) or otherwise alter the coating after delivery. The
composition and characteristics of the coating or ink that is actually applied to the substrate are termed "as applied".
Once weight % water is known, the volume % water can be calculated by dividing the weight % water by the density of water,
which can be considered a constant (* 8.33 Ib/gal water).
The ratio of the amount of solids applied to the amount of solids used represents the transfer efficiency of the application
technique. For example, if 8 Ibs of solids are applied but 10 Ibs of solids are used (vis., sprayed), the ratio is 8:10 or 0.8, and the
application technique is said to have a transfer efficiency of 80%.
The solid portion of a coating that lands on and sticks to the substrate is the "solids applied". The amount of solids applied,
however, will most likely not be the same as the amount of "solids used". That is, in most cases, some portion of the solids in the
coating will not end up on the substrate, but will either miss it altogether or bounce off it.
-------
CTG Compliant Coating Equations
If the emission limitation is expressed as IBS PER GALLON OF COATING (LESS WATER) , then the
following equations can be used. Note that Volume and Weight %'s are used in these equations. If
Volume and Weight fraction are used substitute 1 for 100.
EQUATION 4.1
LBS VOC COATING DENSITY X (WEIGHT % VOLATILES - WEIGHT % WATER)
GAL COATING LESS WATER " (100 - VOLUME % WATER)
EQUATION 4.2
LBS VOC (VOC DENSITY X (VOLUME % VOLATILES - VOLUME % WATER))
GAL COATING LESS WATER = (100 % - VOLUME % WATER)
If there is no. water in the coating, % Volatiles = % VOC and both Weight % Water, and Volume
% water become 0, the equations reduce to the following:
EQUATION 4.1 (A)
LBS VOC WEIGHT % VOC
GAL COATING LESS WATER a COATING DENSITY X 100 %
EQUATION 4.2(A)
LBS VOC VOLUME %
GAL COATING LESS WATER = VOC DENSITY X 100 %
-------
CTG Compliant Coating Equations - As Applied
If the coating limit Is expressed as - - Ibs VOC per gallon of coating (less water) as applied.
then the addition of cut solvent has to be taken into account during calculations. Solvent
densities may be obtained from Manufacturer's Data Sheets or EPA Data Sheets.
If Method 24 data is available use Equation 4.3:
EQUATION 4.3
GAL COATING SUPPLIED.
( COATING DENSITY AS SUPPLIED X WT FRACTION VOC X QAL COATING APPLIED )
LBSVOC
GAL COATING
GAL SOLVENT
SOLVENT DENSITY X QAL COATING APPUED
(1 - VOL FRACTION WATER AS APPLIED)
ro
Note that if the volume fraction of water is given "as supplied", the denominator for the second term
of the equation becomes:
EQUATION 4.3 (A)
,, . GAL COATING SUPPLIED.
((1 - VOLUME FRACTION WATER AS SUPPLIED) X GAL COATING APPLIED )
-------
CTG Compliant Coating Equations - As Applied Continued
If Method 24 data is not available, Equation 4.4 may serve as an alternative. If the volume % of
water is given "as supplied" the denominator must be adjusted as in Equation 4.3 (A).
EQUATION 4.4
IBS VOC GAL COATING AS SUPPLIED .
GAL COATING LESS WATER AS APPLIED =
GAL CUT SOLVENT
DENSITY OF CUT SOLVENT X GAL COATING AS APPLIED
+ { 100 % - VOLUME % WATER AS APPLIED)
CO
-------
CTG Compliant Coating Equations: Solids Basis
If the coating limit is expressed in terms of solids, such-as - Ib VOC per gallon of solids
applied, use Equation 4.5 or Equation 4.6. Note that the data may need to be converted into the
variables used in these equations.
When the VOC content of a coating less water is known Equation 4.5 is appropriate:
EQUATION 4.5
LB VOC VOC CONTENT OF COATING LESS WATER
GAL SOUDS = VOLUME % SOLIDS
(100 - VOLUME % WATER)
When the VOC content of a coating with water is known or when no water is present, Equation 4.5
reduces to:
EQUATION 4.5 (A)
LBVOC VOC CONTENT OF COATING X 100%
GAL SOLIDS = VOLUME % SOUDS
Equation 4.6 may also be used when the data is presented as follows:
EQUATION 4.6
LBVOC _ COATING DENSITY X WEIGHT % VOC
GAL SOUDS - VOLUME % SOLIDS
-------
Graphic Arts Compliance Equations
If the graphic arts limitation is expressed as --VOC solvent volume % of the volatile fraction
Equation 4.7 applies:
EQUATION 4.7
QAL INK AS SUPPLED GAL SOLVENT
GAL VOC *VOL % VOC AS SUPPLIED x QAL INK AS APPLIED' * GAL INK APPLIED
GAL VOLATILE FRACTION AS APPLIED ~ GAL SOLIDS GAL INK SUPPLIED GAL SOLVENT
" " GAL INK AS APPLIED' X GAL INK APPLIED * GAL INK APPLIED
When there is no diluent or cut solvent added the equation reduces to Equation 4.7 (A):
EQUATION 4.7 (A)
Ol
GAL VOC VOL % VOC
GAL VOLATILE FRACTION AS APPLIED " (100 - VOL % SOLIDS)
If the graphic arts limitation is expressed as - water volume % of the volatile fraction
Equation 4.8 applies:
EQUATION 4.8
GAL INK AS SUPPLIED GAL SOLVENT
GAL WATER (VOL% WATER IN INK AS SUPPLIED X QAL INK AS APPLIED ' + GAL INK APPLIED
GAL VOLATILE FRACTION AS APPLIED ~ GAL SOLIDS GAL INK SUPPLIED GAL SOLVENT
' " " GAL INK AS APPLIED' X GAL INK APPLIED '+ GAL INK APPLIED
-------
Graphic Arts Compliance Equations Cont.
When no diluent or cut solvent is used Equation 4.8 reduces to Equation 4.8 (A) as below:
EQUATION 4.8 (A)
GAL WATER VOLUME % WATER IN INK
GAL VOLATILE FRACTION AS APPLIED = (100 % - VOLUME % SOLIDS)
If the graphic arts regulation is expressed as- volume % of nonvolatiles (i.e., gallons of solids
per gallons of ink) less water, as applied: use the Equation 4.9:
EQUATION 4.9
VOLUME % SOLIDS
VOLUME % SOLIDS IN INK, = GAL OF DILUTION SOLVENT GAL OF WATER
I ' + GAL OF INK AS SUPPLIED " GAL OF INK AS SUPPLIED*
Volume % have been used in all of the above equations for ease of presentation. If the data
is presented in Weight % it must be converted to Volume %. Example 4.1 illustrates the conversions
between weight and volume percent calculations. Note that the diluent solvent is assumed to be 100
% VOC. This is not always the case. If the diluent solvent contains water it must be subtracted out.
Example 4.11 shows how the calculation is completed.
-------
Graphic Arts Compliance Equations
Add- On Controls
If the graphic arts regulation requires calculation of - overall VOC capture and abatement reduction.
use Equations 4.10, through 4.12:
EQUATION 4.10
% OVERALL VOC CONTROL EFFICIENCY = CAPTURE EFFICIENCY(%) X DESTRUCTION EFFICIENCY(%)
where:
EQUATION 4.11
IB OF VOC DUCTED TO CONTROL DEVICE „
CAPTURE EFFICIENCY = LB OF VOC EMITTED DURING OPERATION X 10° %
EQUATION 4.12
LB OF VOC DUCTED TO CONTROL DEVICE - LB OF VOC EMITTED TO ATMOSPHERE
DESTRUCTION EFFICIENCY = LB OF VOC DUCTED TO CONTROL DEVICE * 10° %
-------
248
-------
Dry Cleaning
249
-------
INTRODUCTION
Dry cleaning is the pro-ess of cleaning fabric by washing in a substantially
noi. jqueow solvent. Two classes of organic solvents are used nost frequently by
tht cry cleaning industry. One class includes petroleum solvents, which are
clxtures cf paraffins and aromatic hydrocarbons. The other class includes
chlorinated hydrocarbon solvents, called "synthetic solvents" in the industry,
consisting almost exclusively of perchloroethylene, also known as
tetrachlorccthylene.
The Dry Cleaing Industry
The dry cleaning industry is divided into 3 segments based on the types of
servi.-es cfi'ered. The 3 categories are coin operated systems, commercial
systems, a;.d Industrial systems. Ccin operated dry cleaning facilities are
usual.y part by a laundromat and generally process about 16,000 pounds of clothes
per year pec stone. Commercial facilities include neighborhood dry cleaning
shops and specialty cleaners. A typical commercial facility processes
appr: > ioat«2y 60,000 pounds of clothes per year. Industrial craning plants
250
-------
typically supply uniform cleaning and rental services and process fren 600.000 to
1,500,000 pounds of clothes annually.
Nationwide perc emissions are 21,400 metric tons for coin-op,. 123,000 metric
tons for commercial and 13,600 metric tons for industry dry cleaners. The major
use of perchloroethylene dry cleaning machine is in commercial dry cleaning
establishments.
The Dry Cleaning Process
Figure I is a diagram of a typical perchloroethylene dry cleaning plant.
Cloches and perchloroethylene are loaded into a washer and agitated by the
turning motion of a paddle or wheel. After washing, the solvent is extracted
from the clothes by spinning as in a conventional washer spin cycle. After
extraction the used solvent is filtered and distilled to remove impurities and is
then returned to the system for reuse. The filtered solids, or "muck", contain
solvent which is usually removed by heating and condensed- for reuse Drying may
occur in the same unit as did the washing (a dry-to-dry machine) or it may occur
in a different machine (transfer machine system). During the drying cycle, the
perchloroethylene recovery dryer operates through a closed loop system with ouch
of the evaporated solvent recovered and Is then returned to the system through a
water cooled condenser. A final process called aeration or deodorization reduces
the amount of any solvent remaining in the clothes. This IB done by venting
ambient air through the clothes in the dryer and then sending the exhaust to the
atmosphere.
251
-------
WATER-
—
WASHER/EXTRACTOR
CHARGED
SOLVENT
TANK
DETERGENT
FILTER
FILTERED
SOLVENT
PURE
SOLVENT
TANK
MUCK
OASES
SOLVENT
EMISSIONS
HEAT
HEATED
Ain
,_•__>»•
I
I
DRYER
CONDENSER
-rrv
SOLVENT
SEPARATOR
SEPARATOR
CONDENSER
WATER
HEAT 1
(DESORPTION)
CARBON
ADSORBER
•
•
4"—. ii i •
DISTILLATION
T
DESORBED SOLVENT
, AND STEAM .
MUCK
COOKER
HEAT
DISTILLATION
BOTTOMS
STILL
RESIDUE
STORAGE
MUCXl
I
CONDENSER
FILTER
MUCX
STORAGE
SOLVENT
SEPARATOR
DISPOSAL
DISPOSAL
-»- WATER
Figure 1. Perchloroethylene dry cleaning plant flow diagram.
-------
Solvent Characteristics
Although other chlorinated hydrocarbon solvents have been used for dry
cleaning in the United States, perchloroethylene is the only chlorinated solvent
seeing significant use at this time. An estimated 346 Billion pounds of perc are
used annually for dry cleaning purposes. The solvent may be generally
characterized as follows: non flammable, very high vapor density and high cost.
Table I lists the properties of dry cleaning solvents.
Emission Sources
The primary source of perchloroethylene emissions from a dry .cleaning plant
is the dryer exhaust during the aeration cycle. After washing and extraction,
dry-cleaned goods still contain approximately 20-25 kg of solvent per 100 kg of
clothes. During the drying cycle, this solvent is vented to a water condenser
which typically reduces these potential losses to 3-6 kg per 100 kg of clothes.
In the absence of additional abatement equipment, this un-extracted per
chloroethylene is vented to the atmosphere.
A second significant source of perchloroethylene emissions from dry cleaning
plants is associated with solvent contained in disposed filtrate. This waste
solvent is generated in the form of distillation bottoms end filter muck. As
previously discussed, solvent extracted from the clothes is filtered and then
distilled for reuse. For the distillation unit, the EPA recommends that the
residue from the solvent still contain not more than 60 kg of solvent per 100 kg
of wet waste material. This Is to be considered a state-of-the-art operating
253
-------
- PROPERTIES OF DRY CLEANING SOLVENTS
Property
Flash point (TCC). «>F
Initial boiling point. °F
Dry end point. °F
API gravity
Specific gravity at 60 °F
Weight. Ib/gal
Paraffins, volume %
Aromatics. volume 7»
Naphthenes, volume 7*
Olefins, volume 7«
Toluene /ethylbenzene,
volume %
Corrosiveness
Caution
Odor
Color
Cost (average size
plant). S/gal
1-40-F
138. 2
3S7. 8
396
47.9
0.789
6. 57' ?
45.7
12.1
42.2
None
Flammable
Mild
Water white
0.29
Typical
140-F.
R 66
143
366
400
44.0
0.8063
6.604
82.5
7.0
0.5
None
Flammable
Mild
Water white
0.30
Stoddard
100
305
350
50.1
0.779
6.49
46.5
11.6
•41.9
None
Flammable
Sweet
Water white
0. 2fl
Typical
Stoddard,
R 66
108
316
356
48.1
0.788
6.56
88.3
5.9
0.8
5.0
None
Flammable
Sweet
Water white
0.29
Perchlc
ethylc
Extingui
fire
250
254
1.6:
13.5!
Slight on n
Toxic
Ether li
Colorlc
2.05
254
-------
procedure. During extraction, sclvent is filtered with either regenerable filter
materials (usually dlatomaceous earth) or paper cartridge filters. RACT (reason-
ably available control technology) is defined in the CTG as "the residue from any
diatooaceous earth filter shall be cooked or treated so that wastes shall not
contain more than 25 kg of solvent per 100 kg of wet waste material". For
filtration cartridges, RACT was defined as follows: "Filtration cartridges mist
be drained in the filter housing for at least 24 hours before being discarded.
The drained cartridges should be dries in the dryer tumbler If at all possible".
A third source of solvent emissions Is associated with liquid and vapor
leakage from various components of the dry cleaning system.
Types of Control Devices
Carbon Adsorption System
A typical carbon adsorption system used in a commercial dry cleaning
facility consists of one carbon canister which is usually des^obed with steam
once a day. Large industrial units, however, usually consist of
multiple canisters so that one can be used to control emissions while the others
Is being regenerated. In aany plants, other sources in addition to the dryer are
vented to the carbon adsorption unit. A current of fresh air is often required
at the operator's face when loading & unloading the washer or dryer for occu-
pational health reasons. An Internal fan, activated by opening the door, draws
air through a duct at the machine door lip. This air containing perchloroethy-
lene vapor should, if at all possible, be vented to the adsorber rather than
255
-------
directly to the atmosphere. Floor vents installed to control fugitive vapors
around the machines and to remove vapors from solvent spills nay also be ducted
to the adsorber. Additionally, vents from the distillation unit, muck treating
units, perchloroethylene separators, and storage tanks may also be controlled by
the adsorber.
Government supervised tests show over 99 Z removal efficiency and average
emission is less than 0.1 pounds per hour.
Carbon should be changed every 6-12 months.
Solvation System
The solvation process is azeotropic, and it replaces the aeration cycle of a
conventional dry cleaning system. In the solvation process, the warm dryer air
laden with perc is passed through water, where it is cooled due to evaporation of
the water. The resulting gas stream, saturated with water vapor, is returned to
the dryer as a low boiling, perchloroethylene-water azeotrope. Perc has a normal
b'oiling point of 189*F. In this vay, more perc Is vaporized at a lower tempera-
ture and ultimately recovered. Perc recovery is also enhanced due to the fact
that the materials dry cleaned have a greater affinity for water than perc. At
the end of the drying cycle, materials still contain a residual amount of perc.
When the air conditioned, humidified stream passes through the aaterials, they
absorb humidity which displaces the residual perc, thus allowing the perc
previously absorbed into the materials to be recovered. Figure 3 presents an
flow diagram of a solvation system. Government supervised test chow 99.982
removal efficiency and only 12 ppm average emissions.
256
-------
*PERC VAPORS
CONDENSED
RECOVERYj
CC'.DFNSER
tRECOVERY UNIT FAN MOTOR M
IS TURNED Of-F AUTOMATICALLY .£
DURING THE SOLVATION CYCLE L
PERC
ViPORS
LEAVE
THEDI
AZEOTRCP'C -'H IS QiH*C'tO I
AZEOTROPtC AIR r !
PASSES THROUGH GARMENTS IN THE DRUM
AND CAUSES PERC iLEFJ IN GARMENTS AT THE EM)
OF THE RECOVERY CYCLE I TO BE VAPORIZED
THE SOLVATION RECOVERY;!*
CYCLE OPERATES -".FOR J-Z
-"*/
ABOUT 4 MINUTES.
ING THE AERATION CYCLE. .•:*.
-AND CONTINUOUSLY VAPOR- '.''-V
EING PERC FROM THE GAR- :-
•MENTS. THE PERC VAPORS £?
ARE CONDENSED -.OVER . :*
THE RECOVERY UNITS CON-'X^
DENSER THE RECOVERED •:.'•
PERC IS SENT TO ITS USUAL •.,
STORAGE PLACE. -THE SOL
VATiON CYCLE REQUIRES NO
.ADDITIONAL TIME. NO LABOR
TANK
AZEOTROPiC CONOITION'l
AKES PLACE HERE
- SPECIFICATIONS
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• i Ov-io-D'v a-io i R«cn-T-ti and i Wasnet
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! ? =--raimcr* and 2 Wasners
3 f-:-c-:..-'f".
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1 3 r,*-ciaim«f$ «nd 2 Washers
1 2 C- , -lo Dry 1 Reclaimer and 1 Was*C»
1 2 ^ecainiefs ma 1 Dry-io-D'y ana 2 w.isne's
. v.vi:a' Drv-io-0»v Unit Caoncny 10 2^0 Lbs
SOLVATIO^' MODEL
1022-A
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426-F3A
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-------
Refrigeration System
The vapor condenser operates by modification of the dry cleaning process to
reduce solvent emissions. A dry cleaning device modified with a vapor condenser
does not include an aeration cycle.
The vapor condenser principle of operation can b« summarized in the follow-
ing way. The vapor condenser is placed into the air stream in conjunction with
the water cooled condenser near the end of the drying cycle. This effectively
reduces the air stream temperatures, thereby condensing the solvent vapors.
Under normal conditions, the temperature of recirculated air is approximately
100'F. However, with the vapor condenser, this recirculated air temperature is
reduced to approximately 45*F.
The vapor condensers are 95Z efficient in reducing dryer emis-
t
sions, as compared to a normally operated dryer. This efficiency is dependent
on:
1. The dryer/condenser system nusc not vent to Che atmosphere until the
air-vapor stream temperature on the outlet side of the refrigerated
condenser is equal to or less than A5*F.
2. The dryer/condenser system oust be closed to the atmosphere at all
times except vhen articles are being loaded or unloaded through the
door of the machine. The refrigerated condenser will be bypassed vhen
258
-------
the dryer door is open because perchloroethylene iray be evaporated from
the frozen coils resulting in increased emissions.
259
-------
4. ENVIRONMENTAL ANALYSIS OF RACT
The Installation of RACT equipment and the implementation of RACT
procedures in a typical dry cleaning plant involve the replacement of
existing dryers with recovery dryers, the replacement of existing diatomite
filtration systems with a cartridge filtration system, and improved
operating and maintenance procedures to identify and repair liquid and
vapor leaks.
The environmental impacts of RACT implementation on air, water, and
solid-waste disposal are discussed in this section. In addition, the
effects of RACT equipment operation on overall energy consumption are
detailed, based on the two model plants that were discussed in Chapter
2, and these values are compared with those of uncontrolled model plants.
Finally, beneficial and adverse effects from the installation of RACT
equipment are assessed in relation to emissions and energy consumption
in these model plants.
4.1 AIR POLLUTION
Table 4-1 lists the estimated uncontrolled VOC emissions for each
emission point and indicates the range (or nominal value) of controlled
emissions per 100 kg of articles cleaned. Because the uncontrolled
dryer provides from 60 to 80 percent of the total emissions, effective
control and reduction (81 percent) of VOC emissions from this source
provides the greatest direct impact on overall plant emissions.
Filtration system VOC emissions in dry cleaning facilities with
existing non-RACT diatomite filters account for about 25 percent of the
total uncontrolled emissions. Filtration emissions in these facilities
will be reduced by as much as 88 percent as a direct result of cartridge
filter installation. However, RACT will provide no reduction in filtration
system VOC emissions in facilities that have existing settling tanks or
280
-------
Table 4-1. NOMINAL EMISSIONS FACTORS FOR EXISTING AND RACT EQUIPMENT
(In kg VOC emitted per 100 kg dry weight of articles cleaned)
Source
Dryer
Filter
Diatomite
Cartridge
Still
Fugitive sources
Total
Existing
equipment
emissions
18
8
1
3
JL_
22-30
RACT
equipment
emissions
3.5
1
1
3
1_
7.5-8.5
VOC emission
reduction
14.5
7
0
0
b
14.5-21.5
Percent
reduction
81
88
0
0
b
Existing equipment emission estimates are based on industry association
data and EPA plant tests, and represent approximate midrange for most
sources. See Section 2.0 for complete explanations of controlled
emissions sources and levels.
Indeterminate quantity.
261
4-2
-------
cartridge filters. In addition, the VOC emissions resulting from fugitive
sources could be directly reduced by improvements in maintenance and
operating procedures. Thus, RACT equipment and procedures would produce
average VOC emissions reductions ranging from 66 to 72 percent.
Table 4-2 illustrates the VOC emissions reductions that result from
the Installation of RACT equipment and the adoption of RACT operating
and maintenance procedures in two model plants. Based on three uncon-
trolled emissions rates representing the three filtration alternatives
in model plant I and two RACT emissions rates, the model plants show a
66 to 70 percent reduction in model plant I and a 66 percent reduction
in VOC emissions in the model plant II. The specific reductions in VOC
emissions range from 26 Mg to 39 Mg per year in a model plant I and
approximately 92 Mg per year in a large model plant.
4.2 WATER POLLUTION
Increases in water pollution, due to RACT implementation in petroleum
dry cleaning plants, would result primarily from inefficient separation
of condensed solvent and water. Recovery dryers employ gravimetric
separators to remove water from the reclaimed solvent. This unit uses
the difference in density between petroleum solvent and water to separate
and divert them. Typically, water collected in this manner 1s dumped
into a sewer. The leveling of the separator is critical to the
optimization of its performance. If it is not level at installation or
is bumped during maintenance, the quantity of solvent in the sewered
water could increase to the point of becoming a significant source of
water pollution.
Insufficient drainage of RACT filter cartridges could prove to be a
source of groundwater pollution, especially if the cartridges were
buried in an improperly located or maintained landfill or dump. RACT
procedures for cartridge drainage would decrease the overall volume of
solvent exposed to groundwater and would, therefore, reduce water
pollution by petroleum solvent. Furthermore, based on a maximum
solubility of 100 kg (Saary, 1981) of petroleum solvent in 1,000,000 kg
of recovered water and an average recovery dryer water recovery rate
of 3.4 kg water per 100 kg of articles dried (Plaisance et al., 1981),
4-3 262
-------
Table 4-2. NOMINAL ANNUAL VOC EMISSIONS FOR TVO MODEL HANTS
EMPLOYING EXISTING AND RACT EQUIPMENT. AND PROCEDURES
(O
O
OJ
Type
of plant
Model plant I
with existing:
Dlatomlte filter
Cartridge filter
Settling tank
Model plant II
Plant
throughput,
kg/yr
(Ib/yr)
182,000
(400,000)
635,000
(1.400,000)
Nominal emission factors
In kg VOC emitted
per 100 kg dry weight
of articles cleaned
Existing
equipment
30
23
22
22
RACT
equipment
8.5
8.5
7.5
7.5
Nominal VOC emissions,
meo;agrams/yr (tons/yr)
Existing
equipment
55
(60)
42
(46)
41
(45)
140
(154)
RACT
equipment
16
(17)
16
(17)
14
(15)
48
(53)
Nominal annual VOC
emission reductions
resulting from
RACT Implementation,
megagrams/yr (tons/yr)
39
(43)
26
(29)
27
(30)
92
(101)
-------
model plant I and model plant II would lose about 0.5 kg and 1.5 kg per
year, respectively, from solvent dissolved in the recovered water.
4.3 SOLID-WASTE DISPOSAL
Implementation of RACT in existing petroleum dry cleaning facilities
would result in a net reduction in both the mass and solvent content of
solid wastes. Installation of RACT cartridge filters would produce a
dramatic decrease in emissions from solid wastes in petroleum dry cleaning
plants. Cartridge filters, when compared with diatomite filters, have
been shown to reduce solvent content of disposed filter wastes by 80 to
90 percent (Plaisance, 1981), thereby decreasing the overall quantity of
solvent-laden solids introduced to the environment. In addition, the
replacement of diatomite with cartridge filters will reduce the mass of
solid waste generated by 60 percent, based on an average industry estimate
of 3.57 kg of waste generated per 100 kg of throughput with a diatomite
filter (Fisher, 1975) and 1.47 kg solid waste per 100 kg of throughput
for a cartridge filter (Plaisance, 1981).
4.4 ENERGY
Energy savings result from the implementation of RACT guidelines in
both model plants. With the installation of RACT recovery dryers and
cartridge filters in the model plants, annual expenditures for both
steam and electricity are reduced by a combined average of 70 percent
over utility costs for existing standard dryers and diatomite filters
(see Section 5.2 and 5.3).
The energy value of recovered solvent is included in the overall
analysis of petroleum dry cleaning plant energy consumption. One approach
to this analysis that would be meaningful to the dry cleaning industry
is to assume that all recovered solvent is resold at its current market
value ($0.53 per kg) and that the proceeds are used to purchase electricity
at Us current market value of $0.0603 per kilowatt-hour (Vatavuk,
1980). This approach to energy conservation by solvent recovery
illustrates a savings of energy accrued directly to the individual
petroleum dry cleaning plant.
Table 4-3 delineates the impact of RACT implementation on model
plant energy consumption per year based on the previously discussed
4-5
264
-------
Table 4-3. ENERGY IMPACT OF EXISTING AND RACT EQUIPMENT3
(in Gigajoules per year)
Model plant
Model plant I
Model plant II
Existing
equipment
1,665
6,070
RACT
equipment
(660)b
(1,040)
Percent
reduction
135
120
aBased on 0.00314 GJ/kg steam and 0.0036 GJ/kWh electricity
(Baumeister et al., 1978), and utility consumption and solvent recovery
values calculated in Chapter 5.
Numbers in parenthesis represent overall energy savings, based on
savings from solvent recovery (at $0.53 per kg) to purchase electricity
at a cost of $0.0603 per kWh.
265
4-6
-------
approach. Considerable energy savings (over 140 percent for both model
plants) arise from the installation of RACT equipment. A maximum annual
energy savings of 6,260 GJ takes place in the model plant II, where
solvent recovery in the dryers is optimized by the plant's high
throughput without the additional solvent recovery due to the
installation of cartridge filters. Model plant I shows an annual energy
savings of 2,460 GJ, due to the combined effects of solvent recovery on
energy consumption.
4.5 REFERENCES FOR CHAPTER 4
Chevron Oil Co., 1980. Sales Brochure: Chevron Thinners and Solvents.
EL Segundo, California.
Fisher, W. 1975. ABC's of Solvent Mileage, Part 1. International
Fabricare Institute. Joliet, Illinois. IFI Special Report Vol. 3,
No. 4.
Baumeister, T., E. Avallone, and T. Baumeister, III. 1978. Marks'
Standard Handbook for Mechanical Engineers. McGraw-Hill. New
York, New York.
Plaisance, S. 1981. A Study of Solvent Drainage and Retention in
Discarded Petroleum Dry Cleaning Cartridge Filter Elements. TRW
Inc., Research Triangle Park, North Carolina (EPA Contract No.
68-02-3063).
Plaisance, S., J. Jernigan, G. May, and C. Chatlynne. 1981. TRW Inc.
Evaluation of petroleum solvent concentrations, emissions, and
recovery in a solvent recovery dryer (EPA Contract No. 68-02-3063).
Saary, Z. 1981. Chevron Research Laboratory, Telecon with S. Plaisance,
TRW Inc., July 20. Maximum solubility of Chevron petroleum solvent
in water.
Vatavuk, W. 1980. Factors for Developing CTG Costs. Cost and Energy
Analysis Section, Economic Analysis Branch. EPA/OAQPS. Research
Triangle. Park, North Carolina (Draft Document).
266
4-7
-------
£. Determining compliance (482-18-35)
1. Visual inspection
2. VOC detector
3. EPA Method 25 or 25A
4. Alternatives
F. Visual Inspection points (482-18-36)
1. Hose connections, unions, couplings, and valves
2. Machine door gaskets and seatings
3. Filter head gaskets and seatings
4. Pumps
5. Base tanks and storage containers
6. Water separators
7. Filter sludge recovery
8. Distillation unit
9. Diverter valves
10. Cartridge filters
11. Saturated lint and basket
G. Information to be gathered for each dry cleaning establishment
visted (482-18-37)
1. Dry cleaning equipment:
o Types (dry-to-dry, transfer)
o Capacity
2. Flow diagram for perc liquid/vapors
3. Pounds of clothes cleaned per load, day, month
4. Amount of solvent used per day, week, month (482-18-38)
267
18-7
-------
5. Carbon adsorption/condensing (refrigeratlon)/scrubber
equipment:
o Manufacturer
o Model number
o Year of installation
o New/retrofit
6. Frequency and time of steam out (carbon adsorbers)
7. Is the steamed carbon bed allowed to dry out (carbon
adsorbers)? (482-18-39)
8. How much perc is recovered per steam out (carbon adsorbers)?
9. Does the amount of recovered perc vary? (are records
available?)
10. Frequency of use of perc removal system (during dryer aeration
cycle only, continuously, etc.) (482-18-40)
11. Sources at dry cleaning facility that are vented through the
perc removal system
12. Cooling water temperature into and out of condenser (used
during drying)
13. System operating (manpower) requirements.
14. Steam pressure to adsorber (carbon adsorbers) (482-18-41)
)t 15. Has the carbon ever been replaced?
16. Describe any problems.
17. Is muck cooked properly? (482-18-42)
18. How long are cartridge drained?
19. Are cartridges dried?
H. Inspection items for dry cleaning facilities with perc removal
equipment (482-18-43)
1. Inspect following for vapor leaks:
o Ductwork
o Improper gasket seating
o Other
268
18-8
-------
2. Inspect following for liquid perc leaks:
o Hose connections, unions, couplings, and valves
o Machine door gaskets and seatings
o Filter head gasket and seating (482-18-44)
o pumps
o Base tanks and storage containers
o Water separators
o Filter sludge recovery
o Distillation unit
o Diverter valves
o Saturated lint from lint "basket
o Cartridge filters
3. Observe location of control system vent
4. Observe the following equipment to see where vented
(482-18-45)
o Perc removal system
o Still
o Muck cooler
o Separators
o Dry cleaning machine(s)
o Other sources vented through perc removal system
5. Inspect perc removal system for lint buildup and corrosion
problems (482-18-46)
6. Inspect floor pickup points for proper operation and for lint
accumulation
7. Obtain samples of muck cooker and still bottoms if possible
8. Observe general housekeeping
269
-------
270
-------
Degreasing
271
-------
1.2 EPA's POLICY ON RACT REGULATIONS FOR DEGREASERS
EPA's guidelines for RACT as applied to degreasers are contained in
Appendix B to this manual. Separate guidelines were Issued for cold cleaners,
open top vapor degreasers, and conveyorized degreasers. Each guideline is
divided into two levels of control. Control System A consists of operating
practices and simple, inexpensive control equipment. Control System B con-
sists of System A plus additional requirements to improve the effectiveness
of control.
1.2.1 Application of Control Systems A and B
An approvable State Implementation Plan (SIP) must require the
application of Control System B throughout urban nonattainment areas
(>200,000 population) seeking an extension and'to all facilities emitting
VOC's in excess of 100 tons per year in other nonattainment areas. Facil-
ities emitting 100 tons per year or less of VOC's in other nonattainment
areas must apply Control System A as a minimum. However, EPA encourages
states to control all degreasers in nonattainment areas to the Control
System B level.
1.2.2 EPA's Policy on Exemptions
The CTG recommends two exemptions for solvent metal cleaning processes.
First, conveyorized degreasers with an air/vapor interface of less than
2.0 square meters should be exempted from the requirement fot a major
control device. Requirements for controlling these smaller units would
not be cost effective and would tend to move the small conveyorized degreaser
users to open top vapor degreasers which emit more solvent per unit of work.
Second, open top vapor degreasers with an open area of less than 1.0 square
meter of open area should be exempt from the application of refrigerated
chillers and carbon adsorbers since these controls would not be cost effec-
tive. These two exemptions are the only ones EPA will approve in urban
nonattainment areas. Blanket exemptions such as a 3 pound per day cutoff
or exemptions for cold cleaners will not be approved.
In rural nonattainment areas EPA will approve exemptions for sources
emitting less than 100 tons per year of VOC's. This would allow a blanket
exemption for cold cleaners since a typical cold cleaner emits approximately
0.3 tons per year. However, SIP's will not be approved that exempt all
open top vapor degreasers and conveyorized degreasers that individually emit
-------
less than 100 tons per year in rural nonattainment areas because large scale
users may have over 100 separate degreasing operations at one plant location.
If a State chooses to exempt open top or conveyorized degreasing operations
in rural nonattainment areas, the limitation should be 100 tons or less on
a facility-wide basis based on annual solvent purchase records. Further,
any exemption which distinguishes between open top vapor degreasers and con-
veyorized degreasers will not be approved because of the potential of switching
between equipment types. Although conveyorized degreasers are larger emitters,
they emit significantly less solvent than do open top vapor degreasers for an
equivalent workload. Thus, it would not be advantageous to encourage
degreaser operators to choose open top vapor degreasers in order to avoid
regulations on conveyorized degreasers.
1.2-2
273
-------
1.3 DECREASING SOLVENTS
Degreasing solvents are organic chemicals derived principally from
petroleum. They commonly include (i) petroleum distillates such as Stoddard,
kerosene, heptane and cyclohexane, (ii) halogenated hydrocarbons such as
methylene chloride, perchloroethylene, 1,1,1-trichloroethane, trichloroethy-
lene and trichlorotrifluoroethane (FC-113), (iv) oxygenated organics such as
acetone, methyl ethyl ketone, isopropyl alcohol and ethers, and (v) aromatics
such as toluene, turpentine and xylene. Table 1-1 summarizes some of the
important properties of common metal cleaning solvents.
Selection of a solvent for a particular application depends on the
type of cleaning to be done (cold or vapor), the nature of the grease and
other soil to be removed, and the level of cleanliness required. The pur-
pose of the solvent is to dissolve oils, grease, waxes, tars, and in some
cases, water. When these materials have been removed from Lhe work,
insoluble material such as sand, metal chips, buffing abrasives and so
forth are flushed away at the same time. Consideration must be given to
nonmetallic portions of the work to be cleaned. For example plastic may
be dissolved or otherwise deteriorated by certain solvents. Other materials
may not be able to stand the heat necessary to boil high boiling solvents
in vapor degreasers.
Halogenated hydrocarbons are used universally in vapor degreasers
for two reasons. A very important consideration in solvent selection is
its flammability especially if the solvent must be heated to create a
vapor zone. The halogenated hydrocarbons used commonly in vapor degreasers
are nonflammable. Second, the vapors of halogenated hydrocarbons are
approximately four times more dense than air. This property enhances the
stability of the solvent vapor zone and thus reduces diffusion and convection
losses. Petroleum solvents are among the most widely used in cold cleaners,
especially in maintenance cleaners. If petroleum solvents are not adequate
for a particular cleaning application, the operator may turn to any of the
various alcohols, ketones, aromatics or halogenated hydrocarbons that are
capable of doing the job.
-------
TABLE 1-1
01
COMMON METAL CLEANING SOLVENTS****
Solvency for
Type of Solvent/ Metal Working
Alcohols
Solvent
Bthanol (95Z)
Isopropsnol
Methanol
Aliphatic Hydrocarbons
Heptane
Kerosene
Stoddard
Mineral Spirits 66
Soils
poor
poor
poor
good
good
good
good
TLV
(PP»)
1000*
400*
200*
500*
500
200
200
Flash
Point
60°F
55°F
58°?
<20°F
149°F
105°F
107°F
Evaporation
Rate**
'24.7
19
45
26
0.63
2.2
1.5
Aromatic Hydrocarbons
Chlorinated
Fluorinated
Xe tones
Benzene***
SC 150
Toluene
Turpentine
Xylene
Solvents
Carbon Tetrachloride***
Methylene Chloride
Perchloroethylene
1,1,1-Trichloroe thane
Trichloroethylene
Solvents
Trlchlorotrifluoro-
ethane (FC-113)
Acetone
Methyl ethyl ketone
good
good
good
good
good
excellent
excellent
excellent
excellent
excellent
good
good
good
10*
200
200*
100*
100*
10*
500*
100*
350*
100*
1000*
1000*
200*
10°F
151°F
45°F
91°F
81°F
none
none
none
none
none
none
<0°F
28°F
132
0.48
17
2.9
4.7
111
363
16
103
62.4
439
122
45
Water
Solubility Boiling Point
(Z wt.) (Range)
oo 165-176°F
oo 179-181°F
oo 147-149°F
<0.1 201-207°F
<0.1 354-525°F
<0.1 313-380°F
<0.1 318-382°F
<0.1 176-177°F
<0.1 370-410°F
<0.1 230-232°F
<0.1 314-327°F
<0.1 281-284°F
<0.1 170-172°F
0.2 104-105. 5°F
<0.1 250-254 °F
<0.1 165-194°F
<0.1 188-190°F
<0.1 117°F
oo 132-134°F
27 174-176°F
Pounds
Per Gal.
6.76
6.55
6.60
5.79
6.74
6.38
6.40
7.36
7.42
7.26
7.17
7.23
13.22
10.98
13.47
10.97
12.14
13.16
6.59
6.71
Price
Per Gal.
$ 1.59
$ 1.26
$ 1.11
$ 0.86
$ 0.66
$ 0.62
$ 06.2
—
$ 1.06
$ 0.90
$ 2.40
$ 0.96
$ 3.70
$ 2.83
$ 3.33
$ 2.78
$ 3.13
$ 7.84
$ 1.45
$ 1.74
•Federal Register. June 27, 1974, Vol. 39, No. 125. jt
**Evaporation Rate determined by weight loss of 50 mis in a 125 ml beaker on an analytical balance, (ml/dm/min) (Dow Chemical Co., method).
***Not recommended or sold for metal cleaning (formerly standards in industry).
****Frinary source from The Solvents and Chemicals Companies "Physical Properties of Common Organic Solvents" and Price List
(July 1, 1975).
-------
CHAPTER 2
COLD CLEANERS
2.1 PROCESS DESCRIPTION
2.1.1 Unit Operation
Manually operated cold cleaners provide solvent degreasing for low
volume workloads of small, variably shaped automotive and general plant
maintenance parts, and for fabricated metal products. The basic steps
involved in degreasing with a cold cleaner include soaking with solvent
in the dip tank, and drying the work of solvent after cleaning.
The solvent dissolves the dirt/grease on the part to be cleaned
as it is immersed. The part is usually lowered into the solvent bath
in a metal basket. The cleaning action is often enhanced by agitation
of the solvent and by spraying solvent on the part. After cleaning
the part is dried by allowing evaporation and drainage of the solvent
on drying racks which are located inside the cleaner or on external racks
which route the drainage back into the cleaner.
Many cold cleaners which are equipped with sprayers or pump agitation
utilize filters in the pump piping system to remove sludge and dirt thus
extending the useful life of the solvent.
2.1.2 Types of Cold Cleaner Degreasers
Cold cleaners can be generally classified as maintenance and manu-
facturing degreasers. Maintenance cold cleaners are by far more common
and are used for automotive and plant maintenance cleaning. Maintenance
cold cleaners are usually smaller, simpler and less expensive than manu-
facturing cleaners. A typical size of maintenance cold cleaners is
approximately 0.4 m2 (4 ft2) of opening and 0.1 m3 (30 gallon) solvent
capacity.
Manufacturing cold cleaners are employed in applications where a
larger volume workload, a higher degree of cleaning and larger parts to
be cleaned dictate the use of larger more specialized degreasers. Manu-
facturing cold cleaners are usually found in metal fabrication facilities.
The larger size, greater workload and higher solvency needed to achieve
the degree of cleaning required of manufacturing cold cleaners result in
more solvent emissions than is usually released by maintenance cold cleaners.
2.1
276
-------
The variety of specific applications for cold cleaners offers a
method for more accurately classifying cold cleaners by agitation techni-
que and tank design.
The two basic designs are the dip tank and the spray sink, although
many cold cleaners employ both cleaning methods. Dip tank cleaners (Figure
2-1) allow for more thorough cleaning by providing for soaking dirty parts
in the liquid solvent bath. The spray sink (Figure 2-2) is simple, inexpen-
sive and used when a relatively low degree of cleanliness is required. As
can be seen from Figure 2-2, the liquid solvent tank is not accessible
for soaking parts; however, solvent losses due to bath evaporation are
insignificant with this arrangement.
2.1.3 Operation of Degreaser Components
Agitation of the liquid solvent in dip tanks further improves clean-
ing efficiency and can be provided by pumping, compressed air, vertical
motion or ultrasonic vibration. Pump agitation rapidly circulates solvent
through the tank. Compressed air is dispersed from the bottom of the tank
in air agitation. The rising bubbles scrub the surface of the work. Ver-
tically agitated cold cleaners vibrate the dirty parts up and down in the
tank with a motor driven, cam actuated device usually operated at 60-70
cycles per minute. Ultrasonic agitation vibrates the solvent with high
frequency sound waves. This vibration causes cavitation, the implosion
of bubbles of vaporized solvent on the surface of the partsf which breaks
down the dirt film. To optimize cavitation, the solvent is usually heated
to a specific temperature.
Other degreaser components that are discussed in this chapter
include the cover, spray pump and hose, internal and external drain
boards and the parts basket.
277
2.1-2
-------
TOP
BASKET
SOLVENT
CLEANER
PUMP
Figure 2-1. Cold Cleaner
278
2.1-3
-------
Figure 2-2
SPRAY SINK
^ - . v- ""-,--" •'-,- -* -• . -11
(Safety-Kleen, New Berlin, Wisconsin)
2.1-4
279
-------
2.2 ATMOSPHERIC EMISSIONS
2.2.1 Emission Points
Solvent evaporation is the basic emission mechanism for cold cleaners
and the emission rates vary with size, frequency of use, and manner of their
operation. Based on national consumption data, cold cleaners each emit an
average of 0.3 metric tons of solvent vapor per year. Maintenance cold
cleaners emit an average of 0.25 metric tons per year and manufacturing cold
cleaners emit an average of 0.5 metric tons per year. Emissions from manu-
facturing cleaners are larger primarily because their units are used more
steadily in the course of a work day than maintenance clpaners.
There are several means by which organic solvent vapors can be
emitted to the atmosphere from a cold cleaner. These are illustrated
in Figure 2-3. Cold cleaners are very rarely hooded or vented to the
outside. Thus, an obvious emission point is the direct evaporation of
solvent from the tank to the atmosphere (Location 1). Carry out emissions
(Location 2) result from liquid solvent that is physically carried out
of the degreaser on the cleaned parts and subsequently evaporates. Mechan-
ical agitation of the solvent bath (Location 3) increases evaporative losses.
Turbulence from spraying (Location 4) increases emissions as does overspray-
ing (spraying outside the tank), and excessive spray velocity. Finally,
the emissions from the disposal of waste solvent (Location 5) can vary
«
significantly, depending on the techniques employed.
2.2.2 Parameters Affecting Rate of VOC Emissions
Bath evaporation occurs whenever the degreaser's hood is open but
is Increased by air movement such as drafts or ventilation and is directly
related to the evaporation rate of the solvent used. The solvents most
commonly used by cold cleaners are Stoddard solvents, safety solvents
(blends of chlorinated hydrocarbons and petroleum solvents), ketones and
fluorinated solvents.
Bath evaporation can be minimized during operation when adequate
freeboard height (distance from solvent level to top of the cold cleaner)
is employed. Freeboard height requirements are often expressed as free-
board ratio, which is the ratio of freeboard height to the width of the
degreaser.
2.2-1
280
-------
Bath evaporation emissions can be further reduced by keeping the
degreaser cover closed during degreasing operations except when parts are
removed from or added to the degreaser. Various types of covers are
available. Sliding plastic covers which roll up on a rotating shaft at
one end of the degreaser when not in use are the most simple and easy to
use. Some large degreaser covers use counterweights. Electrically or
pneumatically powered covers are also used. Guillotine covers are another
easily operated type found on many degreasers. Generally, the amount of
effort required will dictate the frequency of use of the cover and therefore
dictate the amount of bath evaporation. Hatch type covers such as the one
shown in Figure 2-3 usually have a fusible link support arm so that they
will slam shut in the event that a fire breaks out. Local fire and safety
codes often require such devices.
Air flow into the tank also influences solvent evaporation. The
degreaser should be located to minimize evaporative losses due to work
fans and ventilation ducts. Partitions, curtains or baffles help create
a still air zone around the degreaser and can reduce bath evaporation
emissions.
Control devices are required for cold cleaners with heated (>50°C)
or highly volatile (volatility >4.3 Kpa measured at 38°C) solvent. (The
term "cold cleaner" applies even if the solvent is heated, as long as the
objective is not to create a vapor zone.) The control devices which comply
with the FACT guidelines are refrigerated chillers, freeboard ratios >0.7,
carbon adsorption and water blankets. If properly applied, maintained and
operated, these control devices can significantly reduce solvent emissions.
Refrigerated chillers are condensing coils located peripherally
along the freeboard, which condense the solvent vapor before escaping
from the degreaser. Carbon adsorption is a device which reclaims solvent
from the air/vapor mixture escaping the cleaner. These are rarely used
on cold cleaners.
A water blanket is a layer of water in the dip tank on top of the
solvent which provides a vapor barrier between the solvent and the atmos-
phere. The solvent must be heavier than and insoluble in water.
Carry-out emissions occur when wet parts are removed from the
degreaser and are influenced by: drying procedure, location and type of
drying racks, size of the parts being cleaned, and the volume of the work-
load.
2.2-2
281
-------
BATH EVAPORATION
^-HL)--;^5*&k-\
*C^ AGITATIONS -fr?r-l»gv'«*
^i7^T~r^
\
'!
.\,'
\V -ii
\\ *' ]l,
^FREEBOARD 'i^W X ^
n T » ll I ///'
' I \ /' 1 ' / '
^Jcfrh'/'
\ i\~/y/ /
V, j,;^
(T) CARRY-OUT
:COMPRESSED AIR
5 ) WASTE SOLVENT
Figure 2-3. Cold Cleaner Emission Points
282
2.2-3
-------
Drainage of any solvent entrained in crevices or depressions in
the parts prior to moving them to external drying racks, and closing the
hood during drying if internal racks are used, minimizes carry-out emissions.
If external racks are employed, drains which return the carried-out solvent
to the degreaser tank reduce solvent loss. As recommended from ASTM D-26,
cleaned parts should be drained for 15 seconds.
The surface area of the parts workload affects carry-out since the
mass-transfer of solvent by evaporation is directly proportional to the
amount of solvent-laden surface area.
Agitation increases emissions. Agitation intensity, amount of heat
input, if any, and solvent volatility all affect VOC emissions from cold
cleaners. Proper operating procedures can minimize emission during agita-
tion. Emissions are insignificant if the cover is closed during agitation
and the bath should be agitated only during cleaning. If air or pump
agitation is used, the flow rate should be adjusted to the minimum amount
required to achieve the desired degree of cleaning. Air flow rate should
o
not exceed 0.01 to 0.03 m per minute per square meter of opening.
Evaporation from spraying will vary with spray pressure, spray
droplet size and distribution, amount of overspray which splashes from
the sink, solvent volatility and amount of time the spray is in use.
Spray operating techniques can lower emissions. Care to eliminate
t
overspray, adjusting spray to a solid fluid stream and limiting spray fluid
pressure to a maximum of 10 psig will reduce solvent losses by evaporation.
Waste solvent evaporation is the single largest mechanism for solvent
emissions from cold cleaning. The amount of solvent disposed by a single
degreaser is dependent upon the degreaser size, frequency of operation,
degree of cleanliness required and amount of oil and dirt to be removed.
If a cold cleaner spray system is equipped with a filter, the frequency of
disposal is reduced.
Leaks in spray lines and agitation pump discharge lines which are
under pressure can cause significant solvent emissions. Pipe flanges,
drain valves, corroded tanks (especially when using an acidic solvent or
if water is present in the solvent) can also leak if not properly maintained.
283
2.2-4
-------
Acceptable methods of disposal Include recycling by distillation,
proper incineration, distillation (recovery of solvent for re-use) and
chemical landfilling if waste is enclosed in sealed containers and surrounded
by impermeable soil.
Disposal by flushing solvent into sewers, spreading solvent for dust
control and landfilling without proper containers or prevention of leaching
all result in complete evaporative emissions of waste solvent to the atmos-
phere.
Solvent emissions are greatly influenced by the type of solvent.
Obviously volatility and operating temperatures are significant parameters
affecting emissions. Highly toxic solvents are more conscientiously
controlled to protect workers and comply with OSHA regulations. Solvent
costs often determine the care with which degreasers are operated. More
expensive solvents are usually conserved by the same procedures which
reduce emissions and are more likely to be recycled.
284
2.2-5
-------
2.3 EMISSION CONTROL METHODS
The EPA Control Technology Guideline (CTG) document for solvent metal
cleaning identifies a number of control strategies for reducing volatile
organic emissions from cold cleaning degreaser operations. These form the
basis of defining RACT for the cold cleaning degreasers and should therefore
be the focal point of a field inspection. The CTG suggests two levels of
control. (See Table 2-1). Level A could reduce cold cleaning emissions by
50% (+20%) and Level B may achieve a reduction of 53% (+20%). The range
represents the limits of reduction for poor operating procedure (-20%) and
good operating procedure (+20%). The estimated benefit from Level B only
slightly exceeds that from Level .A, assuming low volatility solvents. This
is because the additional devices required in Level B generally control only
bath evaporation which represents only 20% to 30% of the total emissions
from an average cold cleaner. For cold cleaners using highly volatile
solvents, bath evaporation may constitute 50% of the total emissions, and
it is estimated that Level B would then achieve an emissions reduction of
69% (+20%) and a 55% (+20%) reduction for Level A.
The preceding discussion on the parameters affecting the rate of
VOC emissions (Section 2.2.2) explicitly identifies the equipment and
operating procedures necessary to implement the RACT control strategies
except for the disposal of waste solvent. Dirt, grease, oil, metal chips
and the like slowly build up in the liquid solvent over a period of time
and eventually severely affects its ability as a cleaning agent. This
usually occurs when the solvent contamination level reaches about 10
percent by volume. It is fairly common for the small operator to secure
a service contract that provides for reclaiming the spent solvent. The
contractor distills the spent solvent and returns it to users for a fee.
One organization rents the cold cleaner and provides the solvent reclama-
tion service as a package deal. Large operations that use scores of
manufacturing cold cleaners sometimes operate stills on-site to reclaim the
solvent. Distillation, proper landfilling, and incineration (which is
not commonly used) will meet the RACT operating requirements ("not greater
than 20 percent can evaporate into the atmosphere"). Disposal of the
waste solvent (and still bottoms) at landfills may be subject to hazardous
waste disposal regulations. EPA has proposed regulations governing the
disposal of such material in the Federal Register at 43FR58946 (December 18,
1978).
285
2.3-1
-------
TABLE 2-1
CONTROL SYSTEMS FOR COLD CLEANING
Control System A
Control Equipment
1. Cover
2. Facility for draining cleaned parts
3. Permanent, conspicuous label, summarizing the operating requirements
Operating Requirements:
1. Do not dispose of waste solvent or transfer it to another party,
such that greater than 20 percent of the waste (by weight) can evaporate
Into the atmosphere.* Store waste solvent only in covered containers.
2. Close degreaser cover whenever not handling p.arts in the cleaner.
3. Drain cleaned parts for at least IS seconds or until dripping ceases.
Coatrol System B
Control Equipment:
1. Cover: Same as in System A, except if (a) solvent volatility is
greater than 2 kPa (15 mm Hg or 0.3 psi) measured at 38°C (100°F),**
(b) solvent is agitated, or (c) solvent is heated, then the cover must
be designed so that it can be easily operated with one hand. (Covers for
larger degreasers may require mechanical assistance, by spring loading.
counterwelghtlng or powered systems.\
2. Drainage facility: Same as in System A, except that if solvent
volatility is greater than about 4.3 kPa (32 mm Hg or 0.6 psi) measured at
38°C (100°?), then the drainage facility must be internal, so that parts are
enclosed under the cover while draining. The drainage facility may be
external for applications where an Internal type cannot fit Into the cleaning
system.
3. Label: Same aa in System A
4. If used, the solvent spray must be a solid,'fluid stream (not a
fine, atomized or shower type spray) and at a pressure which does not cause
excessive splashing.
S. Major control device for highly volatile solvents: If the solvent
volatility is > 4.3 kPa (33 mm Hg or 0.6 psi) measured at 38°C (100°F), or
if solvent is heated above 50°C (120°?), then oqe of the following control
devices must be used:
a. Freeboard that gives a freeboard ratio*** ^ 0.7
b. Water cover (solvent must be insoluble in and heavier than water)
c. Other systems of equivalent control, such as a refrigerated chiller
or carbon adsorption.
Operating Requirements:
Saaa as in System A
*Water and solid waste regulations must also be compiled with.
"Generally solvents consisting primarily of mineral spirits (Stoddard) have
volatilities - 2 kPa.
***Freeboard ratio is defined aa the freeboard height divided by the width
of the degreaaer.
286
2.3-2
-------
FIGURE 2-4
EXAMPLE WORKSHEET FOR FIELD INSPECTION OF
COLD CLEANERS
1. BUSINESS LICENSE NAME OF CORPORATION, COMPANY, OR INDIVIDUAL OWNER OR GOVERNMENTAL AGENCY:
2a. MAILING ADDRESS:
2b. PLANT ADDRESS WHERE THIS DEGREASER IS LOCATED:
3. SOURCE NO. (PERMIT NUMBER, NEDS ID, ETC.):
4. NAME AND TITLE OF COMPANY REPRESENTATIVE:
5. TELEPHONE NO.:
6. NAME OF OFFICIAL CONDUCTING INSPECTION:
7. DEGREASER
MANUFACTURER:
INSIDE DIMENSIONS OF TANK (FT.):
TYPE OF DEGREASER: SPRAY SINK [ ) DIP TANK | |
MODEL NO.
SERIAL NO.
WIDE X
LONG X
8. TITLE AND CODE NUMBERS OF DRAWINGS, SPECIFICATIONS, STANDARDS, CODES, PROCEDURES AND DOCUMENTS USED WITH THE
INSPECTION
9. TYPE OF SOLVENT IN USE (SPECIFIC NAME AND MANUFACTURER):
INSPECTION OBSERVATIONS
RACT REQUIREMENT
SUGGESTED INSPECTION
PROCEDURE
FIELD
OBSERVATION
CONTROL EQUIPMENT
1. Cover
Observe if a cover Is Installed
and if it is closed when parts
are not being handled in the
degreaser.
2. Cover oust be easily
operated with one hand
if:
- Solvent volatility
>2 kPa (measured at
38«C)
- Solvent is agitated
- Solvent is heated
Observe if cover can be operated
with one hand. Observe if solvent
is heated or agitated. If degreaser
cover is large, check for mechani-
cal assistance for operation. Deter-
mine the solvent type and Its vola-
tility. Vapor pressures for COBBOU
solvents can be found In Chapter 1
of this manual.
3. Drainage Facility
Observe if drainage racks are
provided. If drainage racks are
external to the degreaser, observe
if drainage la routed to the solvent
bath.
4. Internal drainage
facility is required
if:
- Solvent volatility
^4.6 kPa (measured
at 38°C)
Observe if drainage racks are
internal. Determine solvent
volatility.
2.4-2
287
-------
FIGURE 2-4
(Continued)
RACT REQUIREMENT
S. Solvent spray must be
a solid fluid stream
and at a pressure that
does not cause splash-
ing.
6. Permanent conspicuous
label summarizing
operating require-
ments.
7. If solvent volatility
>4.3 kPa measured at
38°C, or solvent temp-
erature is > 50°C then
one of the following
control measures must
be used.
a. Freeboard Ratio
>_ 0.7
b. Water Cover
c. Other systems of
equivalent control
such as chiller
or carbon adsorb-
tion
OPERATING REQUIREMENTS
1. Do not dispose of
waste solvent or trans-
fer it to another party
such that greater than
20Z (by weight) can
evaporate to the atmos-
phere. Store waste
solvent only in covered
containers.
2. Close degreaser cover
whenever not handling
parts in the cleaner.
3. Drain parts for at
least IS seconds or
until parts are dry.
SUGGESTED INSPECTION
PROCEDURE
o Observe if spray forms a' mist
or shower type consistency. Check
for splashing above degreaser free-
board
o Observe if label is clearly displayed,
complete and permanently fastened to
degreaser
o Determine if requirement is appli-
cable
o Measure solvent temperature
(If heated) with thermometer
o Calculate from degreaser
dimensions. Freeboard ratio •
Freeboard
Width
o Observe if the solvent
la covered with water.
o Determine if appropriate device is
Installed and operational
o Determine if source has inhouse
reclamation facility (I.e. still)
or a service contract with a
solvent reclamation firm.
o Confirm that storage la done
with covered containers. Note
whether containers leak.
o Observe the operation
o Observe this operation. Time If
necessary, or determine if parts
are dry when removed from drying
rack.
FIELD
OBSERVATION
288
2.4-3
-------
CHAPTER 3
OPEN TOP VAPOR DEGREASERS
3.1 PROCESS DESCRIPTION
3.1.1 Unit Operation
Open top vapor degreasers provide an efficient and economical method for
preparing clean, dry articles for subsequent finishing or fabricating. There
are several configurations in use for open top degreasers; all are similar in
basic design. In the simple vapor method, cleaning results from the condensa-
tion of solvent vapors on the cool surface of the article; the dissolving and
flushing action of the condensate removes the soil. When the article reaches
the temperature of the solvent vapor, no more condensation (or cleansing)
occurs and the article is removed from the vapor zone. Other cleaning methods
involve various combinations of the simple vapor method with immersion and spray-
ind with liquid solvent.
Open top vapor degreasers utilize nonflammable solvent contained in the
lower area of the degreaser, referred to as the boiling sump. The solvent is
boiled to produce a vapor zone, the height of which is controlled by cooling
coils installed above the vapor zone. The "cold work" introduced into the
vapor space of the degreaser must be at a temperature lower than the vapor zone
in order to cause the solvent vapors to condense on the work surfaces and flush
the oil and other foreign matter off with the liquid condensate. The removed
material accumulates in the boiling sump and only the pure vapor comes in con-
tact with the work load. In either case, flushing is often followed by pure
solvent spray and/or liquid immersion. The cool, pure liquid solvent reduces
the temperature of the work surface below the vapor temperature, producing a
second vapor condensation flushing action on the work surfaces. When the work
pieces are removed from the degreaser, they should be clean, dry, and ready for
further processing.
3.1.2 Types of Open Top Vapor Degreasers
Open top vapor degreasers are most suitable in situations where the
work flow is variable or intermittent. Otherwise, a conveyorized degreaser
might be the equipment preferred. Essentially, there are three variations of
vapor degreasing: (1) straight vapor, (2) liquid immersion-vapor, and
(3) vapor-spray-vapor degreasing.
3.1-
-------
o Straight Vapor; In this unit, the article to be cleaned is lowered
into the vapor zone and held there until it reaches the vapor temp-
erature, at which point vapors cease condensing on the article. It
is gently agitated to enhance drainage of trapped liquid solvent.
Then, it is brought into the freeboard area and allowed to dry for
a moment before being removed from the degreaser. Figure 3-1 is
a cut away sketch of a straight vapor degreaser. As with any open
top arrangement, the work to be cleaned may be lowered manually
or with an overhead hoist with hooks or long handle baskets. Hands
should never be placed below the vapor line.
o Liquid Immersion - Vapor: Immersion of the work in the hot or
boiling solvent is preferred; (i) for closely nested work, (ii) for
excessive soil levels (iii) for light gauge work, (iv) when ultra-
sonics is necessary, and (v) for parts with intricate patterns.
Figures 3-2.to 3-4 show various equipment configurations for this
technique. Typically, the work is lowered into the vapor zone for
a straight vapor rinse, then lowered into the liquid immersion
chamber to be rinsed. This will cool the work slightly. Then,
the work is raised into the vapor zone for a second vapor rinse.
The 2-compartment unit shown in Figure 3-3 may be operated in this
fashion or, if necessary for proper cleaning, the work may be
lowered directly into the boiling sump, then rinsed in the con-
densate reservoir. (Care should be taken not to drag dirty solvent
. from the boiling liquid tank to the rinse tank). After the liquid
rinse the work is given a vapor rinse above the condensate reser-
voir. The reservoir is often heated to ensure that the liquid
rinse is warm. Similarly, the 3-compartment unit depicted in
Figure 3-4 may be outfitted to operate with two or three liquid
immersions.
o Vapor - Spray - Vapor: This is similar to straight vapor degreasing
except that as soon as the work is below the vapor level, it is
sprayed with cool condensate. After spraying is complete the work
should remain in the vapor zone until it reaches the vapor tempera-
ture and condensation has stopped. Figure 3-5 is a schematic of
a spray unit with an offset condenser. Spraying should be done
as far below the top of the vapor line as possible so that evapora-
tive losses due to spraying are minimized.
Some units, especially larger ones, are equipped with a lip exhaust. A
lip exhaust draws air laterally across the top of the degreaser and vents the
air directly to the roof or to a carbon adsorption unit. Figure 3-6 is a
schematic of one of these units. The primary purpose of a lip exhaust is to
limit worker exposure to solvent vapors.
290
-------
CONDENSING COILS
WATER SEPARATOR
DISTILLATE
HEAT EXCHANGER
CLEANOUT
DOOR
SOLVENT LEVEL
SIGHT GLASS
SAFETY
THERMOSTAT
FREEBOARD
WATER
JACKET
h- CONDENSATE
TROUGH
HEATING
ELEMENTS
WORK REST AND
PROTECTIVE GRATE
^TEMPERATURE
INDICATOR
Figure 3-1. Single Compartment Vapor Degreaser
291
3.1-3
-------
FREE BOARD
CONDENSING COILSv
CONDENSATE TROUGH-
/WATER JACKET
.-.;•:•:.;•;-:•;•:•;•;-:•:•:-; -.;,;.;.;.;.;.;.;.•.;,-,;..;.;.;.; >;.:•:.:.:-:-:-:•:.;.;.:•:•:.;.:.:-:-:.:-:•
.WATER
SEPARATOR
CONDENSATE RETURN
LIQUID IMMERSION
CHAMBER
STEAM/
•BOILING SUMP
Figure 3-2. Liquid-Vapor Degreaser
292
3.1-4
-------
FREE BOARD
BOILING SUMP
CONDENSING COILS
WATER JACKET
CONDENSATE TROUGH
WATER SEPARATOR
CONDENSATE RESERVOIR
STEAM
Figure 3-3. Liquid-Liquid-Vapor Degreaser 2 Compartment
WORK FLOW
CONDENSING COILS
CONDENSATE TROUGH
HOT SOLVENT
RESERVOIR
WATER JACKET
WATER
SEPARATOR
CONDENSATE RETURN
BOILING SUMP
STEAM
OVERFLOW
WARM RINSE'
Figure 3-4. Liquid-Liquid-Vapor Degreaser 3 Compartment
3.1-5
293
-------
FREE
BOARD
SPRAY LANCE
VAPOR LEVEL
s^is^£
*'>*"vI-x*'.- fs^- ^»* ^>,•:* ->^^ / ^ f, * v. •"" >
STEAM
CONDENSING
COIL
CONDENSATE
TROUGH
WATER
SEPARATOR
CONDENSATE
RESERVOIR
SPRAY
PUMP
BOILING SUMP
Figure 3-5. Offset Condenser Vapor-Spray-Vapor Degreaser
TO ATMOSPHERE
OR ADSORBER BLOWER
EXHAUST INLET
EXHAUST DUCT
CONDENSING UNIT
Figure 3-6. Degreaser with Lip Exhaust
3.1-6
294
-------
3.2 ATMOSPHERIC EMISSIONS
3.2.1 Emission Points
There are several means by which organic solvent vapors can be emitted
to the atmosphere in an open top vapor degreaser. These are identified in
Figure 3-10. In general, open top units are not hooded or vented to the out-
side. Thus, an obvious emission point is the direct diffusion and convection
of vapors from the vapor zone to the atmosphere (Location 1). If a lip
exhaust is installed some of these vapors can be directed to a roof vent
(Location 2). If not properly designed, these systems can actually increase
solvent evaporation, especially if the exhaust rate is excessive, causing
disruption of the air/vapor interface. The use of lip (or lateral) exhausts
is usually limited to larger than average degreasers where the primary objec-
tive is to limit worker exposure to solvent vapors. A rule of thumb used by
degreaser and control systems manufacturers is to set the exhaust rate at 50
cubic feet per minute per square foot of degreaser opening. If this exhaust
rate is not adequate to protect the workers, higher rates may be encountered.
Carry-out emissions result from solvent that has condensed on the work
and has not fully evaporated before being removed from the degreaser (Loca-
tion 3). Also, solvent vapors may be entrained by the motion of removing
the work from the vapor zone or by convection due to the hot work heating
the solvent laden air as it is removed from the vapor zone. Porous or
adsorbant materials such as cloth, leather, wood or rope will adsorb and
trap condensed solvent and thus such materials should never enter a degreaser.
As the solvent material is spent and itself becomes contaminated with
impurities its usefulness decreases. To reduce the volume of waste material
some degreasers are used as a simple still during downtime where the solvent
in the sump is boiled off as much as feasible and the pure condensed vapors
are piped off to a storage tank, rather than back to the sump. Other
degreasers, especially the larger ones, may be used with an external still
that may run on a continuous or batch basis. Nevertheless, a significant
volume of waste material will remain to be disposed of and depending on the
method of disposal, waste solvents may enter the atmosphere (Location 4).
Fugitive emissions can occur at any of the piping connection or pump
seals that may have loosened, or become worn or corroded (Location 5).
These emission points are usually eliminated fairly quickly because they are
detectable by visual observation and represent a correctable loss of valuable
material, and create a potentially unhealthy work environment.
3.2-1
295
-------
POTENTIAL
ADSORBER
LIP TOP
EXHAUST
DIFFUSION AND
CONVECTION
CONDENSER
COILS
Figure 3-10. Open Top Degreaser Emission Points
-------
3.2.2 Parameters Affecting Rate of VOC Emissions
The rate of vapor emissions emanating from the various points pre-
viously discussed is dependent on a variety of operating and design para-
meters. Emissions can be minimized by attempting to achieve certain optimum
conditions; however, it is important to understand the cause and effect
relationsiip. The following parameters significantly affect VOC emissions
from open top vapor degreasers:
o Freeboard Ratio - The freeboard ratio is the ratio of the freeboard
height to the width (not the length) of the degreaser. Manufacturers
of degreasers generally size the equipment so that this ratio is at
least 0.5 for the higher boiling solvents. For solvents with lower
boiling points, such as methylene chloride and trichlorotrifluoroe-
thane, this ratio should be at least 0.75.
o Drafts - A fan or other air moving devices located in the work area
near the degreaser can cause a draft to enter the freeboard area of
the degreaser housing, thereby upsetting the interface and drawing
vapors into the ambient air.
o Type of Work Load - Atmospheric emissions increase when the parts
being processed in the degreaser contain numerous pockets or liquid
traps that allow liquids to be carried from the degreaser chamber.
o Size of Work Load - If the cross-sectional area of the work is sub-
stantial compared to the cross-sectional area of the vapor chamber,
moving the work in and out of the degreaser will have a piston
effect on the surrounding vapors; the resulting turbulence will
cause excessive emissions.
o Mass of Work Load - If the work load is especially massive the heat
required to bring the work to vapor temperature will be excessive.
This will cause the vapor zone to collapse resulting in turbulence
that will increase emissions.
o Solvent Heat Input - Once the solvent's boiling temperature has been
achieved, increasing the heat input to the solvent will increase
the rate of solvent vaporization. If continued, the cool air
blanket generated by the condenser coils may not be sufficient to
retain the increased vapors and breakthrough could occur, resulting
in greater emissions.
o Temperature and Flow Rate of the Cooling Water - The function of a
condensing coil is to limit the upper level of the vapor zone. A
condenser consisting of a coil of pipe through which cooling water
flows, creates a blanket of cool air. The flow rate and temperature
of the water affect the efficiency of a given set of coils with a
given heat input rate. Increasing flow increases efficiency.
Decreasing the temperature of the water will also increase the
efficiency of the coils in supporting the vapor layer.
3.2-3 297
-------
Work Rate - Moving the work into and out of the degreaser creates
turbulence that will result in the emission of vapors. Turbulence
and the resulting emissions increase as the speed of the work in-
creases.
Location of Spraying - If spraying is conducted in a manner that
disrupts the vapor/air interface, emissions will increase. Spray-
ing should be done below the vapor line; the spray should never
be pointed to allow liquid to be sprayed above the vapor line.
Water in the Solvent - If water is allowed to accumulate in the boil-
ing sump emissions may be increased in three ways: (i) the water/
solvent vapor mixture has a lower density than pure solvent vapor and
thus has a greater tendency to be lost by diffusion, (ii) water com-
bines with the solvent to form a low boiling azeotrope that results
in a higher vaporization rate, and (iii) water is corrosive to de-
greaser surfaces and piping, thus making leaks a serious problem.
Water has a tendency to form acidic by-products with certain solvents,
especially 1,1,1 - trichloroethane and methylene chloride, further
exacerbating the corrosion problem.
Covers - The use of a cover during idle and down time virtually
eliminates diffusion losses during these periods.
Drying Time - After the work has been removed from the vapor zone
it may carry some condensed solvent out of the degreaser. To
minimize these emissions the work should be allowed to dry for a
brief time (about 15 seconds) in the freeboard area. Note, however,
that when the hot part rests just above the vapor level, it will
cause solvent laden air to heat up and rise, so the drying time
should not become excessive.
Lip Exhaust - If the degreaser is equipped with a lip exhaust, the
ventilation rate should not be excessive; otherwise, the exhaust
system may disrupt the air/vapor interface and actually increase
emissions.
298
3.2-4
-------
3.3 EMISSION CONTROL METHODS
The EPA Control Technology Guideline document for solvent metal cleaning
identifies a number of control strategies for reducing volatile organic emis-
sions from open top vapor degreasers. These form the basis for defining RACT
for these degreasers and should therefore be the focal point of a field inves-
tigation. The CTG document suggests two alternative control schemes. Level A
represents a relatively low efficiency system consisting primarily of operating
procedures and has an estimated efficiency of 45 (+15) percent. Level B
consists of Level A plus additional control and has a control efficiency es-
timated at 60 (+15) percent. These control methods are presented in Table 3-1.
EPA's policy regarding the application of these control levels is discussed in
Chapter 1. EPA suggests that open top vapor degreasers with an open area
of less than one square meter be exempt from the application of refrigerated
chillers or carbon adsorbers because these devices would not be cost effective
on such small units.
The safety switches and thermostat recommended in Control System B are
the spray safety switch, the condenser flow switch and thermostat. The vapor
level thermostat is not included because it is already required by OSHA on
"open surface vapor degreasing tanks". The sump thermostat and solvent level
control discussed in Section 3.1.3 are used primarily to prevent solvent degra-
dation and protection of the equipment rather than to prevent solvent emissions.
Refrigerated chillers should not be confused with the condenser coils
or water jacket; rather, the chillers are an optional, additional control device
designed to minimize solvent losses. The refrigerated chiller consists of a
second set of condenser coils located slightly above the primary coils.
Figure 3-11 depicts a unit with finned chiller coils. The function of the
primary coils remains as in units without freeboard chillers, i.e. to control
the upper limit of the vapor zone. The refrigerated freeboard chiller creates
a sharper temperature gradient than would otherwise exist. The resulting cold
air blanket reduces diffusion losses and the stable inversion layer created
by the increased temperature gradient decreases upward convection of solvent
laden air.
Two types of chiller designs are commercially available; one that operates
below 0°C and one that operates above that temperature. Most manufacturers of
degreasing equipment offer both types, although there is a patent* on the sub-
zero design.
*U
.S. Patent 3,375,177 issued to Autosonics, Inc., March 26, 1968
-------
TABLE 3-1
COMPLETE CONTROL SYSTEMS FOR OPEN TOP VAPOR DEGREASERS
Control System A
Control Equipment:
1. Cover that can be opened and closed easily without disturbing the vapor zone.
Operating Requirements:
1. Keep cover closed at all times except when processing work loads through
the degreaser.
2. Minimize solvent carry-out by the following measures:
a. Rack parts to allow full drainage.
b. Move parts in and out of the degreaser at less than 3.3 m/sec.(ll ft/Bin).
c. Degrease the work load In the vapor zone at least 30 sec. or until
condensation ceases.
d. Tip out any pools of solvent on the cleaned parts before removal.
e. Allow parts to dry within the degreaser for at least IS sec. or until
visually dry.
3. Do not degrease porous or absorbent materials, such as cloth, leather, wood
or rope.
4. Work loads should not occupy more than half of the degreaser's open top area.
5. The vapor level should not drop more than 10 cm (4 in.) when the work load
enters the vapor zone.
6. Never spray above the vapor level.
7. Repair solvent leaks immediately, or shutdown the degreaser.
8. Do not dispose of waste solvent or transfer it to another party such that
greater than 20 percent of the waste (by weight) will evaporate into the
atmosphere. Store waste solvent only in closed containers.
9. Exhaust ventilation should not exceed 20 m3/min. per m (65 cfm per ft )
of degreaser open area, unless necessary to meet OSHA requirements. Ventilation
fans should not be used near the degreaser opening.
10. Water should not be visually detectable in solvent exiting the water separator.
Control System B
Control Equipment:
1. Cover (same as in system A).
2. Safety switches.
a. Condenser flow switch and thermostat - (shuts off sump neat if condenser
coolant la either not circulating or too warm).
b. Spray safety switch - (shuts off spray pump if the vapor level drops
excessively, about 10 cm (4 in).
3. Major Control Device:
Either: a. Freeboard ratio greater than or equal to 0.75, and if the degreaser
opening is >lm (10 ft ), the cover must be powered,
b. Refrigerated chiller,
c. Enclosed design (cover or door opens only when the dry part is
actually entering or exiting the degreaser), .
d. Carbon adsorption system, with ventilation >15 m3/min per m
(50 cfm/ft2) of air/vapor area (when cover is open), and exhausting
<25 ppm solvent averaged over one complete adsorption cycle, or
e. Control system, demonstrated to have control efficiency, equiva-
lent to or better than any of the above.
4. Permanent, conspicuous label, summarizing operating procedures fl to 16.
Operating Requirements:
Same as in System A
3-3-2 300
-------
The recommended operating temperature for below freezing chillers is
-30 to -25°C. The cold coils attract moisture as does a dehumidifier. There-
fore, the designs include a defrost cycle to remove frost from the coils and
restore heat exchange efficiency. The defrost cycle operates approximately
hourly, requiring only a few minutes to melt the accumulated ice and slush,
which is collected in the condensate trough and poured through the water
separator. Water contamination of the solvent can have an adverse affect on
water soluable stabilizer systems and can contribute to equipment corrosion.
Therefore, on some units, the material condensed from the chiller coils may
be diverted to a different water separator.
The operating temperature of above freezing chillers should not exceed
5°C. These units are normally designed to achieve a minimum of 500 Btu/hr
cooling capacity per foot of air/vapor interface perimeter. The sub-freezing
units are normally designed in the range of 200-600 Btu/hr per foot of peri-
meter, depending on the width of the degreaser.
301
3.3-3
-------
CHILLER
PRIMARY COILS
FREEBOARD
WATER JACKET
Figure 3-11. Refrigerated Freeboard Chiller
302
3.3-4
-------
FIGURE 3-12
EXAMPLE WORKSHEET FOR FIELD INSPECTION OF
OPEN TOP VAPOR DEGREASERS
BUSINESS LICENSE NAME OF CORPORATION, COMPANY, OR INDIVIDUAL OWNER OR GOVERNMENTAL AGENCY:
2a. MAILING ADDRESS:
2b. PLANT ADDRESS WHERE THIS DEGREASER IS LOCATED:
3. SOURCE NO. (PERMIT NUMBER. NEDS ID, ETC.)
NAME AND TITLE OF COMPANY REPRESENTATIVE:
5. TELEPHONE NO.:
NAME OF OFFICIAL CONDUCTING INSPECTION:
7. DEGREASER
MANUFACTURER:
MODEL NO.
INSIDE DIMENSIONS OF TANK (FT.):
WIDE X
SERIAL NO.
"LONG x "
DEEP
8. TITLE AND CODE NUMBERS OF DRAWINGS, SPECIFICATIONS, STANDARDS, CODES, PROCEDURES AND DOCUMENTS USED WITH
THE INSPECTION
9. TYPE OF SOLVENTS IN USE (SPECIFIC NAME AND MANUFACTURER):
INSPECTION OBSERVATIONS
RACT REQUIREMENTS
•SUGGESTED INSPECTION
PROCEDURE
FIELD
OBSERVATIONS
CONTROL EQUIPMENT
1. Lid
Observe if a lid is in-
stalled and if it is used
during idling and downtime.
Observe if opening and
closing the lid disturbs
the vapor zone.
2. Safety Switches
a. Condenser flow
switch 6 thermo-
stat
Confirm that the switch
and thermostat have been
installed.
If available, check read-
Ings of flow and tempera-
ture indicators. For high
boiling solvents, the temp-
erature should be about 8°
to 11°C (15° to 20°F) above
dewpoint of surrounding
atmosphere or 32° to 46°C
(90° to 115°F). For low
boiling solvents (methy-
lene chloride and fluoro-
carbon 113) the exit temp-
erature should be less than
29°C (85°F). Many installa-
tions may not have a temper-
ature indicator at the cool-
Ing coll exit. A rough es-
timate of the temperature
may be made if a bleed valve
is available at the exit end
of the colls. Bleed a sample
of coolant into a small vessel
and measure the temperature
with a portable thermometer.
If plant is agreeable,
Interrupt flow of coolant
and determine if switch is
tripped.
3.4-2 303
-------
FIGURE 3-12
(Continued)
FACT REQUIREMENTS
SUGGESTED INSPECTION
PROCEDURE
FIELD
OBSERVATIONS
b.
Spray safety
switch
Confirm that the switch
has been installed.
3. Major Control Devices
a. Freeboard ratio
greater than 0.75.
b. If the degreaser
area is greater
than 1.0m2 the
cover must be
powered.
c. Refrigerated
Chiller
d. Enclosed Design
Measure the height of the
freeboard and the width of
the tank; calculate the
ratio.
(Measurements usually can
be made externally to
avoid creating emissions
and breathing solvent
vapors. Otherwise, obtain
the measurements from
shop drawings). Measure
the length of the tank and
calculate the degreaser
area. Observe if the
cover is powered.
Unless observed during
the defrost cycle, sub-
zero chillers should be
coated with frost or
slush. The indicated
temperature of the coolant
should not exceed -25°C
(-13°F). Do not attempt
to extract a sample of
coolant from a refrigerated
chiller.
For above freezing chillers
the coolant temperature
should not exceed 5°C
(40°F).
Determine the cooling capacity
from the design specifications.
oo For subzero
chillers the
mln-limim cooling
capacity should be
as follows for each
degreaser width:
(The cooling units
are Btu's per hour
per foot of perimeter.)
<3.5 ft - 200
>3.5 ft - 300
>6 ft - 400
>8 ft - 500
>10 ft - 600
oo For above freezing
chillers the cooling
capacity should be
at least 500 Btu/hr
per foot of perimeter.
Observe that the cover or
doors are open only when
the dry part Is entering
or exiting the degreaser.
3.4-3
304
-------
FIGURE 3-12
(Continued)
RACT REQUIREMENTS
SUGGESTED INSPECTION
PROCEDURE
FIELD
OBSERVATIONS
Carbon Adsorber
If the degreaser is equipped
with an adsorber solvent odors
should not be detectable on
the roof downwind from the
stack.
See the source testing
section in this manual.
OPERATING REQUIREMENTS
1. Keep cover closed
except while process-
ing work loads.
o Observe the operation.
2. Minimize solvent carry-
out by the following
measures:
a. Rack parts to
allow full drain-
age.
b. Move parts in
and out of de-
greaser at lesa
than 3.3 m/sec
(11 ft/min).
c. Degrease parts for
at least 30
seconds or until
condensation stops.
d. Tip out pools of
solvent on the
cleaned parts be-
fore removal.
e. Allow parts to
dry within the
degreaser for at
least 15 seconds
or until visually
dry.
o Observe how the parts are
racked.
o Using a stopwatch, time
the vertical movement of
parts over a measured
distance.
o Observe this operation
and time it if necessary.
o Observe this operation.
o Observe this operation,
tlae It if necessary.
3.
Do not degrease porous
or absorbant materials.
Note the nature of the
materials being cleaned.
Baskets should not have
rope or leather handles.
4. Work loads should not
occupy more than half
of the degreasers open
top area.
o Observe the size of the
work load. Measure it if
necessary and compare it
to the open top area.
5. The vapor level should
not drop more than 10 cm
(4 Inches) when the
work load enters the
vapor zone.
Observe this operation and
estimate the drop In the
vapor level.
6. Never spray above the
vapor line.
0 Observe this operation.
7. Repair solvent leaks
immediately or shut
down the operation.
Look for leaks around the
degreaser. Note especially
the solvent spray pump and
line, piping, the external
sump drain valve (if so
equipped) and the water
separator.
3.4-4
-A 30 5
-------
FIGURE 3-12
(Continued)
RACT REQUIREMENTS
8. Do not dispose of
waste solvent or
transfer it to
another party such
that greater than
20 percent of the
waste (by weight)
can evaporate
into atmosphere.
Store waste solvent
only in covered con-
tainers.
9. a. Exhaust ventilation
should not exceed
20m3/mln per m2
(65 cfn per ft2) of
degreaser open area
unless necessary to
meet OSHA requirements .
b. Ventilation fans
should not be
used near degreaser
opening.
10. Water should not be
visually detectable
in solvent exiting
the water separator.
11. Permanent, conspicuous
label, summarizing
operating procedures
fl to 16 above.
SUGGESTED INSPECTION
PROCEDURE
° Determine If source has
inhouse reclamation
facilities (i.e. still)
or a service contract
with a solvent reclamation
firm.
o Confirm that storage is
done with covered con-
tainers by visual inspec-
tion. Note whether con-
tainers leak.
° Determine the air handling
capacity of the fan,
-or-
If sampling ports are
available, the velocity of
the exhaust gases may be
measured with a swinging
vane velocity meter. Also
determine the cross-sectional
area of the duct, then cal-
culate the cfm.
o After the air volume is
determined from either of
the above methods, obtain
the area of the degreaser
opening and calculate the
cfm per square foot of
degreaser opening.
o Note the location of ven-
tilation fans near the
degreaser.
o This solvent is normally
returned to the degreaser
sump, or if so equipped,
to the warn rinse tank.
This solvent should be clear.
o Confirm the presence of
this label.
FIELD
OBSERVATIONS
306
3.A-5
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CHAPTER 4
CONVEYORIZED DEGREASERS
4.1 PROCESS DESCRIPTION
4.1.1 Unit Operation
Conveyor operated solvent degreasers provide an efficient and econo-
mical method for preparing clean, dry articles for subsequent finishing or
fabricating. There are several types of conveyorized degreasers and each can
operate with either cold or vaporized solvents. The basic steps found in the
typical conveyorized vapor degreaser include a vapor rinse upon entry to the
degreaser vapor space section, liquid immersion, liquid spray, vapor rinse,
and, finally, a slow withdrawal through a cold air space drying area.
A nonflammable solvent contained in the lower area of the de-
greaser, referred to as the boiling sump, is boiled to produce a vapor zone,
the height of which is controlled by cooling coils installed above the vapor
zone. The "cold work" introduced into the vapor space of the degreaser must
be at a temperature lower than the vapor zone, in order to cause the solvent
vapors to condense on the work surfaces and flush the oil and other foreign
matter off with the liquid condensate. The removed material accumulates in
the boiling sump and only the pure vapor comes in contact with the work load.
Vapor flushing is followed by pure solvent spray and/or liquid immersion.
The cool, pure solvent reduces the temperature of the wqrk surface below the
vapor temperature, producing a second vapor condensation flushing action on
the work surfaces. When the work pieces are removed from the vapor zone,
they should be clean, dry, and ready for further processing.
A well-operated conveyorized vapor degreaser should provide the re-
quired cleansing action and confine the solvent and solvent vapors, thereby
maintaining a healthful working environment.
4.1.2 Types of Conveyorized Degreasers
Conveyorized degreasers are generally large, automatic units de-
signed to handle a high volume of work in either a straight-through process
or a return type process in which the work pieces enter and leave the
degreaser unit from the same end. Their use minimizes the human element and
produces consistently high quality cleaning with minimum solvent losses. As
indicated earlier, there are several basic designs which are termed conveyor-
ized degreasers: gyro, vibra, monorail, cross-rod, mesh belt and strip
cleaners. Figures 4-1 to 4-4 present a sketch of each design (with the excep-
-------
WORK BASKET
GEAR TO
TUMBLE BASKETS
BOILING CHAMBER
Figure 4-la. Gyro Degreaser
WORKLOAD
DISCHARGER
CHUTE
ASCENDING
VIBRATING
TROUGH
WORKLOAD
ENTRY CHUTE
DISTILLATE
RETURN FOR
COUNTERFLOW WASH
Figure 4-1b. Vibra Degreaser
4.1-2
308
-------
CONVEYOR
PATH
o
SPRAY
PUMP
WATER
JACKET
Figure 4-2. Monorail Degreaser
-------
CROSS-RODS
i. °
CONVEYOR
PATH
CHAIN
SUPPORTS
WORK
BASKET
WATER
JACKET
BOILING CHAMBER
Figure 4-3. Cross-Rod Degreaser
-------
CONVEYOR
PATH
I
IJ,
MESH
BELT
BOILING
CHAMBER
Figure 4-4. Mesh Belt Conveyorized Degreaser
-------
tion of the strip cleaner type). A brief discussion of the rationale for
each system follows:
o Gyro (ferris wheel) type degreasers permit the operator to load
and unload the baskets from one work station. The design is simi-
lar to the cross-rod degreaser. It is one of the smallest con-
veyorized degreasers available.
o Vibra type degreasers are used for high production rate applica-
tions where the work pieces are small. The work piece is dipped
into solvent, and rises on a spiral vibrating elevator through a
counter-flow rinsing action of clean solvent vapor. Cleaning
action is accomplished by the combination of vibration, solvent
dip, and solvent vapor condensation.
o Monorail conveyor systems are used for high production of stan-
dardized work pieces and are generally found in facilities that
use monorail systems to transport materials within the plant.
The monorail can be a straight through type, carrying parts in
one side and out the other, or can turn 180° and exit the material
through a duct that is parallel and adjacent to the entrance.
o Cross-rod conveyorized units are generally used for processing
small or irregular parts. A rod placed between two power-driven
chains carries parts within suspended pendant baskets or per-
forated cylinders. The cylinders are rotated to provide the
tumbling action required to clean and drain the crevices in
the work pieces. The pendant baskets do not rotate and are
used to carry small parts that do not require this action for
cleaning and draining.
o Mesh belt and strip cleaner degreasers are similar in design;
however, the mesh belt degreaser carries the material to be
cleaned while the other draws the material through. The latter
design is used for sheet metal products. A continuous strip of
material is drawn through tha unit for cleaning prior to coating
or fabrication processes. Mesh belt degreasers are used for
smaller parts and allow for rapid loading and unloading of
material.
312
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4.2 ATMOSPHERIC EMISSIONS
4.2.1 Emission Points
There are several locations in a.conveyorized degreaser that may
allow organic liquid or vapor to escape to the atmosphere. These are iden-
tified in Figure 4-6. In general, conveyorized degreasers are hooded and
vented to the outside. Therefore, an emission point is the vent line and
subsequent exhaust. In most instances, a control device such as a carbon
adsorption system is placed in the line to remove organic vapors. Although
constant ventilation of the hood should create a negative pressure and pre-
vent vapors from escaping from the work openings, ventilation rates are kept
o
to a minimum level (< 65 cfm per ft of degreaser opening) to prevent dis-
ruption of the vapor-level boundary and corresponding increased emissions.
However, in minimizing the ventilation rate, the opportunity for vapors to
escape from the work openings increases at the inlet (Location 2) and exit
(Location 3) of the degreaser. In addition, at the exit of the unit the cleaned
material may be carrying out liquid organic material which condensed on its
surface but did not totally dry or drip off while in the degreaser.
As the solvent material is spent and itself becomes contaminated with
impurities, its usefullness decreases. Most conveyorized degreasers are designed
to distill and recycle this material on a continuous basis through the use of
external stills. However, these stills will eventually accumulate wastes and,
depending on the method of disposal, waste solvents may enter the atmosphere
at this point.
Fugitive emissions can occur at any of the piping connections or sump
seals that may have loosened or become worn because of continuous operation.
Where good housekeeping practices are followed, these emission points are elimi-
nated fairly quickly because they are detectable by visual observation, repre-
sent a correctable loss of valuable material, and create a potentially unhealth-
ful work environment.
313
4.2-1
-------
TO ADSORPTION DEVICE
OR ATMOSPHERE
*~*. i umici_ — — v
—* "*^
/J I
SOLVENT
SPRAY PUMP
x DECREASED! \
/ PART \j
CONDENSING
COIL
WATER JACKET
CONDENSATE
TROUGH
STEAM
SOLVENT SPRAY
RESERVOIR
Figure 4-6. Typical Emission Points
4.1-
-------
4.2.2 Parameters Affecting Rate of VOC Emissions
The rate of vapor emissions emanating from the various points pre-
viously discussed is dependent on a variety of operating and design para-
meters. Emissions can be minimized by attempting to achieve certain optimum
conditions; however, it is important to understand the cause and effect
relationship. The following parameters significantly affect VOC emissions
from conveyorized degreasers:
o Drafts .- A fan or other air-moving devices located in the work
area near the degreaser can cause a draft to enter the freeboard
area of the degreaser housing, thereby upsetting the balance of
the air/vapor interface.
o Size of Work Opening - Although conveyorized degreasers are
generally covered, the size of the opening allowing work loads
to enter and exit should be kept to a minimum to reduce the
opportunity for vapors to escape. The term "average silhouette
clearance" is used to define the distance from the edge of the
degreaser opening to the part or the basket or cage conveying
the part. Where hoods are exhausted, the smaller the opening
the greater the capture velocity of the room air traveling
through the area and the greater the control of vapors escaping
at this point.
o Exhaust Rate - The greater the exhaust rate, the greater the
control of vapor escaping- from the work openings; however, an
excessive exhaust rate also produces greater emissions because
it disturbs the vapor and air interface within the degreaser,
thereby exhausting high concentrations of organic vapors into
the exhaust gas stream. To achieve both goals the exhaust rate
should not exceed 20 m3/min per m2 (65 cfm per ft2) of degreaser
opening.
o Conveyor Speed - As the conveyor speed increases, emissions in-
crease. Increased speeds represent less time for the material
to dry. Therefore, evaporation of the liquid droplets that ori-
ginally condensed on the cold material will take place outside
the hooded portion of the degreaser and will increase emissions.
Too rapid a conveyor speed may also induce drafts that will
create vapor loss at the outlet work opening. Conveyor speeds
must be maintained below 3.3 m/min (11 ft/min) to minimize
losses.
o Type and Magnitude of Load - Atmospheric emissions increase when
the parts being processed in the conveyorized degreaser contain
numerous pockets or liquid traps that allow liquids to be carried
from the degreaser chamber. Liquid trapped in pockets can be re-
moved by placing the working pieces in baskets which are rotated
and tumbled as they move through the degreaser so that they drain
liquid solvent back to the sump. Increases in the magnitude of
the work load will cool the vapor area. A massive load may cause
a collapse of the vapor space and increase emissions. When the
vapor space collapses two situations arise, (1) the vapor/air
4.
-------
layers mix and organic vapors escape and (2) the working pieces
spend less time within the collapsed vapor space and therefore
have less time to evaporate the condensed solvent, resulting
in greater carry out and subsequent emissions.
Solvent Heat Input - Once the solvent's boiling temperature
has been achieved, increasing the heat input to the solvent
will increase the rate of solvent vaporization. If continued,
the cool air blanket generated by the condenser coils may not
be sufficient to retain the increased vapors and breakthrough
could occur, resulting in greater emissions.
Temperature and Flow Rate of the Condensing Coils - The function
of a condensing coil is to limit the upper level of the vapor
zone. A condenser consisting of a coil of pipe through which
cooling water flows, creates a blanket of cool air. The flow
rate and temperature of the water affect the efficiency of a
given set of coils with a given heat input rate. Increasing
flow increases efficiency. Decreasing the temperature of the
water will also increase the efficiency of the coils in support-
ing the vapor layer.
4.2
-------
4.3 EMISSION CONTROL METHODS
The EPA Control Technology Guideline (CTG) document for solvent
metal cleaning identifies a number of control strategies for reducing volatile
organic emissions from conveyorized degreasing operation. These form the
basis of defining RACT for the conveyorized degreaser and should therefore
be the focal point of a field inspection. The CTG document suggests two
levels of control. EPA's policy regarding the application of these control
levels is discussed in Chapter 1. Level A represents a relatively low effi-
ciency system, estimated at 25 + 5 percent. Level B, consisting of Level A
plus additional requirements represents a higher efficiency system, estimated
at 60 + 10 percent. The following discussion will address these and other
control measures found in the CTG document. However, the organization is
slightly different. It is divided into three areas: process equipment de-
sign, operating requirements, and control equipment requirements. In addi-
tion, a second series of suggested controls is offered which do not appear in
the CTG document. These controls should be considered by the inspector as
additional means of reducing emissions.
It should be noted that a given control strategy will not provide
equal results for similar degreasers or degreasers used in different appli-
cations. Therefore, each degreaser should be evaluated individually.
4.3.1 RACT Controls
o Process Equipment Design
oo Minimum entrance and exit openings should be pro-
vided by silhouetting the work load. The average
silhouette clearance (distance between the edge
of the openings and the part) should be < 10
percent of the opening width.
oo Safety switches should be included in the design
to prevent emissions during malfunctions and ab-
normal operation.
a. Condenser flow switch and thermostat shut
off sump heat if coolant is either not
circulating or becomes too hot.
b. Spray safety switch shuts off spray pump
or conveyor if vapor level drops excessively.
c. Vapor level control thermostat shuts off sump
heat when vapor level rises too high.
4.3
317
-------
o Operating Requirements
oo Conveyor speed should be < 3.3 m/min (11 ft/min)
to minimize solvent carry-out emissions.
oo Exhaust ventilation should not exceed 20 m/min
per m (65 cfm per ft ) of degreaser opening
unless necessary to meet Occupational Safety and
Health Administration (OSHA) requirements or the
degreaser is vented to a carbon adsorber.
oo Work place fans should not be used near the
degreaser opening because they will induce
mixing of the air/vapor layer, thereby in-
creasing emissions.
oo Solvent leaks should be repaired immediately,
or the degreaser should be shut down, until
repairs can be made.
oo Water should not be visibly detected in the
solvent exiting the water separator. For
chlorinated solvents, water contributes to
vapor loss because the mixture of water and
solvent has a lower density than that of dry
solvent. In addition, water contributes to
corrosion and creates a low boiling azeotrope
with the solvent in the boiling sump.
oo Down-time covers must be placed over entrances
and exits of conveyorized degreasers immediately
after the conveyor and exhaust are shut down and
removed just before they are started.
oo Disposal or transfer of waste solvents sh'ould be
performed in a manner that will not allow greater
than 20 percent of the waste (by weight) to evapor-
ate to the atmosphere. Waste solvents should be
stored in covered containers.
oo Racking parts to allow maximum drainage should
be implemented to minimize carry-out emissions.
o Control Equipment Requirements
oo Rotating baskets, trays, etc., and/or a
drying tunnel should be provided to
prevent solvent drag-out. Such carry-
out is most likely to occur from solvent
hold up in recesses or pockets in the work
being degreased.
oo Covers must be provided for the entrance and
exit in order to close these openings immediately
after shutting down the degreaser. These covers
should close off at least 80 to 90 percent of
the opening to effectively prevent solvent emissions.
-------
oo Refrigerated chillers can be used to control
the upper limit of the vapor zone; or
carbon adsorption systems should be used to
control emissions in the exhaust line of the
degreaser. The ventilation rate (when down-
time covers are open) should be >_ 15 m /min
per m (50 cfm/ft ) of air /vapor area for adsorbers.
oo The exhaust gas from the adsorption system
must contain < 25 ppm solvent by volume
averaged over a complete adsorption cycle.
oo Alternate control systems may be used if they
demonstrate control efficiencies equal to or
greater than the refrigerated chiller or carbon
adsorption units.
4.3.2 Other Controls
Several control techniques are discussed in the literature that
deserve mention although they are not recommended by EPA as RACT requirements.
o The unit is capable of being hooded or covered without
affecting its operation. The enclosure of a degreaser
diminishes solvent losses from the system that result
from the movement of air within the plant.
o Sprays should be designed or adjusted so they do not
cause turbulence at the air/vapor interface; spraying
must be conducted below the vapor line. Spray pressure
should be the minimum necessary for adequate cleansing.
o Overloading work baskets may reduce the vapor temperature
and collapse the vapor zone, thereby increasing the air/
vapor mixing and subsequent emissions. This situation
can be avoided by following equipment specifications for
the allowable work load as determined by a system heat
balance.
o A solvent reclaimer-still to recycle and return a purified
solvent to the solvent sump. This will tend to stabilize
vaporization rates and eliminate emission due to improper
waste disposal methods.
o Where work being degreased contains acidic cutting oils or
other acidic products, acid acceptance and pH determination
should be made to determine the quality of the solvent.
o Absorbent materials such as wood and fabric materials should
not be degreased or used in the basket construction.
o A "good housekeeping" and maintenance program should be in
effect. Clean out doors, line connections, pumps, water
separator, etc., should be checked frequently.
o For large users of solvent, bulk storage may prove more
economical than purchases by individual drums. Where bulk
storage is used, a submerged fill pipe from the top of the
tank should be included in the design of the storage tank.
Alternate controls such as a return vent line to a recovery
still should be investigated.
4.3-3
319
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Figure A-7. Example Worksheet for Field Inspection of
Conveyorized Degreasers
1. BUSINESS LICENSE NAME OF CORPORATION, COMPANY. OR INDIVIDUAL OWNER OR GOVERNMENTAL
AGENCY:
2a. MAILING ADDRESS: 2b. PLANT ADDRESS WHERE THIS DEGREASER IS
LOCATED:
3. SOURCE NO. (PERMIT NUMBER, NEDS ID, ETC.)
4. NAME AND TITLE OF COMPANY REPRESENTATIVE:
5. TELEPHONE NO. :
6. NAME OF OFFICIAL CONDUCTING INSPECTION:
7. DEGREASER
MANUFACTURER: MODEL NO. SERIAL NO.
INSIDE DIMENSIONS OF TANK (FT.): WIDE X LONG X DEEP
TYPE OF DEGREASING:
TYPE OF CONVEYOR
COLD SOLVENT CLEANING ( 1 VAPOR DEGREASING i j
8. TITLE AND CODE NUMBERS OF DRAWINGS, SPECIFICATIONS, STANDARDS, CODES, PROCEDURES AND
DOCUMENTS USED WITH THE INSPECTION
9. TYPE OF SOLVENT IN USE (SPECIFIC NAME AND MANUFACTURER) :
INSPECTION OBSERVATIONS
RACT REQUIREMENTS
CONTROL EQUIPMENT
1. Safety Switches
a. Condenser flow
switch 6 thermo-
stat
SUGGESTED INSPECTION
PROCEDURE
o Confirm that the switch
and thermostat have been
installed.
o If available, check read-
ings of flow and tempera-
ture Indicators. For high
boiling solvents, the temp-
erature should be about 8°
to 11°C (15° to 20°F) above
dewpolnt of surrounding
atmosphere or 32° to 46°C
(90° to 115°F). For low
boiling solvents (raethy-
lene chloride and f luoro—
carbon 113) the exit temp-
erature should be less than
29°C (85°F). Many installa-
tions may not have a temper-
ature Indicator at the cool-
Ing coll exit. A rough es-
timate of the temperature
may be made if a bleed valve
Is available at the exit end
of the coila. Bleed a sample
of coolant into a small vessel
and measure the temperature
with a portable thermometer.
FIELD
OBSERVATIONS
4.4-2
320
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FIGURE 4-7
(Continued)
FACT REQUIREMENTS
SUGGESTED INSPECTION
PROCEDURE
FIELD
OBSERVATIONS
1. (continued)
b. Spray Safety
Switch
c. Vapor level
control thermo-
stats
o If plant is agreeable.
interrupt flow of coolant
and determine if switch la
tripped.
o Confirm that the switch
has been Installed.
o Confirm that vapor
level control thermostat
la located just above
cooling coll or jacket.
o Suggested thermostat
settings for four types
of solvents:
-Ferchlorethylene
82°C (180°F)
-Trlchlorethylene -
68°C (155°F)
-1,1,1-Trichloroethane
60°C (UO°F)
-Methylene Chloride
32°C (90°F) or
about 6°C (loop) lower
than boiling point of
solvent-water azeotrope
o Read temp, on indicators
2. Minimised openings at
entrance and exit of
conveyor
Determine with a tape
measure that the average
silhouette is less than
10 cm (4 in.) or less than
10 percent of the width
of the opening.
3. Drying tunnel or
rotating baskets
Observe whether the degreaser
is equipped with either of
these devices. Observe
whether parts are wet or
have liquid In crevices
when exiting the degreaser.
4. Refrigerated chiller
Observe indicated coolant
temperature.
oo For subzero chillers
the temperature
should not exceed
-25°C <-1
oo For above freezing
chillers the temperature
should not exceed 5°C
(40°F).
oo Do not attempt to extract
a sample of coolant from
a refrigerated chiller.
Determine the cooling capacity
from the design specifications.
4.4-3
321
-------
FIGURE 4-7
(Continued)
RACT REQUIREMENTS
SUGGESTED INSPECTION
PROCEDURE
FIELD
OBSERVATIONS
For subzero
chillers Che
minimum cooling
capacity should be
as follows for each
degreaser width:
(The cooling units
are Btu'a per hour
per foot of perimeter.)
<3.5 ft - 200
>3.5 ft - 300
>6 ft - 400
>8 ft -.500
>10 ft - 600
For above freezing
chillers the cooling
capacity should be
at least 500 Btu/hr
per foot of perimeter.
Carbon adsorption
system with ventilation
J>15 m3/nln per m2
(50 cfm/ft2) of air/
vapor area.
Solvent odors should not be
detectable on the roof down-
wind from the stack.
o Determine the air handling
capacity of the fan,
-or-
If sampling ports are available,
the velocity of the exhaust
gases may be measured with a
swinging vane velocity meter.
Also determine the cross-
sectional area of the duct,
then calculate the cfm.
o After the air volume is
determined from either of the
above methods, obtain the
area of the air/vapor opening
and calculate the cfm per
square foot of opening.
o See the source testing chapter
of this manual.
OPERATING REQUIREMENTS
1. a. Exhaust ventila-
tion should not
exceed 20m3/min
per a2 (65 cfm
per ft2) of de-
greaser open
area unless
necessary to
meet OSHA re-
quirements.
(This ventila-
tion rate is app-
licable If a
carbon adsorber
is not installed.)
b. Work place fans
should not be
used near degreaser
opening.
Determine the air handling
capacity of the fan,
-or-
If sampling ports are available,
the velocity of the exhaust gases
may be measured with a swinging
vane velocity meter. Also
determine the cross-sectional
area of the duct, then calculate
the cfm.
After the air volume is
determined from either of
the above methods, obtain
the area of the degreaser
opening and calculate the
cfm per square foot of
degreaser opening.
Note the location of ventilation
fans near the degreaser.
4.4-4
322
-------
FIGURE 4-7
(Continued)
RACT REQUIREMENTS
SUGGESTED INSPECTION
PROCEDURE
FIELD
OBSERVATIONS
2. Water should not
be visually detectable
in solvent exiting
the water separator.
Observe any water present
in the sight glass on the
separator.
Conveyor speed should
not exceed 3.3 a/min.
(11 ft/ain).
Check conveyor speed
with stop watch.
Rack parts for best
drainage.
Observe whether parts
are racked in a manner
that allows liquid solvent
to collect in pockets and
crevices.
5. Repair solvent leaks
Immediately.
Inspect for wetted areas
around pump seals, sight
glass, pipes, etc.
6. Downtime covers
If the unit is not in
operation, observe whether
they are in place.
7. a. Do not dispose of
waste solvent or
transfer it to
another party such
that greater than
20 percent of the
waste (by weight)
can evaporate
into atmosphere.
br Store water sol-
vent only In
covered containers.
Determine if source has
inhouse reclamation
facilities (i.e. still)
or a service contract
with a solvent reclama-
tion firm.
o Confirm that storage is
done with covered con-
tainers by visual inspec-
tion.
o Check for container leakage.
4.4-5
323
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324
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Petroleum
Refining
325
-------
SECTION 2
PETROLEUM REFINING - OVERVIEW
2.1 INTRODUCTION
2.1.1 Petroleum
Petroleum, usually called crude oil, is a complex mixture of
hydrocarbons, with small amounts of other substances, that occurs
as an oily liquid in many places in the upper strata of the
earth. Many crude oils, such as those from Arabia and Iraq, have
a strong odor of hydrogen sulfide and sulfur compounds; others,
such as those from Nigeria and Indonesia, contain "very little
sulfur and do not have any unpleasant odor. The color of crude
oil ranges from clear to black.
Crude oil in the ground is associated with hydrocarbon
gases, of which substantial quantities are dissolved in the oil
under pressure. Methane and ethane constitute by far the'great-
est proportion of the gases associated with crude oil.
It has been estimated that crude oil contains over 3000
different chemical compounds, and the chemical composition varies
with the source. Hydrocarbons are the predominant components;
the remainder consists chiefly of organic compounds containing
oxygen, nitrogen, sulfur, and traces of inorganic compounds
containing iron, nickel, vanadium, and arsenic.
The molecular weight of the hydrocarbons in crude oil varies
widely because they contain different numbers of carbon atoms per
molecule. The chemical structure of these hydrocarbons also dif-
fers greatly. The types of hydrocarbons present in crude oil are
paraffins (alkanes), naphthenes (cycloparaffins), and aromatics.
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Crude oil is separated by distillation into fractions desig-
nated as (1) light ends; (2) straight-run gasolines, with boiling
points that range up to about 204°C (400°F); (3) middle distil-
lates, boiling at about 185° to 343°C (365° to 650°F), from which
are obtained kerosene, heating oils, and fuels for diesel, jet,
rocket, and gas turbine engines; (4) wide-cut gas oil, boiling at
343° to 538°C (650° to 1000°F), from which are obtained waxes,
lubricating oils, and feedstock for catalytic cracking operations
that produce gasoline; and (5) residual oil, from which asphalt,
coke, and tar may be obtained.
2.1.2 Petroleum Refining
The refining sector of the petroleum industry converts crude
oils, various semifinished petroleum fractions, and hydrocarbon
gases into useful products. These products are refined by vari-
ous physical, thermal, catalytic, and chemical processes, into
the wide range of products mentioned earlier. Refinery products
generally are not pure chemical compunds but are mixtures of
chemical compounds. Table 2-1 characterizes many of these prod-
ucts. In each case the boiling range, rather than a single boil-
ing point, is due to the fractions being a mixture of chemical
compounds.
Because refining processes are complex and are specific to
each refinery, intermediate storage may be needed for certain
fractions that will be returned to various units for further
processing. Since each refinery is designed, engineered, and
constructed to handle specific crude oils and to produce specific
refined or semirefined products, there is no "typical" refinery.
Additionally, the processing parameters change with the type of
crude oil to be refined. For example, an increase in the refin-
ing of Alaska's North Slope crude has led to expanded use of
catalytic reformers and fluid-bed catalytic cracking units.
Even though there is no typical refinery, most U.S. refiner-
ies are designed to maximize the production of light distillates,
i.e., gasoline. The following operations (Figure 2-1) are basic:
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TABLE 2-1. CHARACTERIZATION OF FRACTIONS OBTAINED FROM CRUDE OIL
Fraction
Gas
Gasoline
Jet fuel
Gas oil
Lube oil
Residuum
Carbon
atoms
1 to 4
5 to 12
10 to 16
15 to 22
19 to 35
36 to 90
Molecular
weight
16 to 58
72 to 170
156 to 226
212 to 294
268 to 492
492 to 1262
API
gravity
58 to 62
40 to 46
34 to 38
24 to 30
8 to 18
Boiling,
O r <*
range, F
-259 to 31
31 to 400
356 to 525
500 to 700
640 to 875
875+
ioF = 5/9 (°C) + 32
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00.
O I .
o
O
H>
H-
0
n
h
w
H,
o
n
o
(D
n>
rt
£ Vs
ro i ("
CD ^g
(u
TO HYDROTREATERS
AND
HYDROCRACKER GAS
••GAS
GASOLINE
LUBES
•AND
WAXES
COKE
ASPHALT
I
Figure 2-1. Typical processing steps in a petroleum refinery.
H-
(D
-------
(1) separation processes, separating the crude oils to isolate
the desired products (e.g., distillation); (2) decomposition
processes, breaking large hydrocarbon chains into smaller ones by
cracking (e.g.> catalytic cracking, coking); (3) formation pro-
cesses, building the products by chemical reaction (e.g., reform-
ing, alkylation, isomerization); (4) treating processes, removing
impurities or compounds that are detrimental to operation of the
refinery; (5) recovery operations (e.g., sulfur recovery, fuel
gas recovery); (6) storage; and (7) auxiliary facilities. Figure
2-1 shows the interrelationships of these processes, which are
described in the following subsections.
2.2 SEPARATION PROCESSES
2.2.1 Desalting
Crude oil is a mixture of hydrocarbon compounds contaminated
by water, salt, and sand. Although most of the water and sand
settle out and separate during storage, the crude is saturated
with water, dissolved salts, and minerals. Crude oil desalting
is a combination separation/reaction operation, in which an
impressed electrical current field and/or chemical additives are
used to coalesce the salt particles, which are theji washed away
with water.
Electrical desalting, the most common technique, involves
the addition of water to crude under pressure and at 71° to 149°C
(160° to 300°F). This mixture is emulsified and introduced into
a high-potential electrostatic field, which causes the impurities
to associate with the water phase and at the same time causes the
water phase to agglomerate so that it can be removed. The de-
salted crude proceeds to the distillation units.
Chemical desalting of crude is accomplished by adding water
to the heated [93° to 149°C (200° to 300°F)] and pressurized oil.
The pressure must be high enough to prevent vaporization of the
water. The mixture is emulsified, and the salt enters the water
phase. Chemical additives may be used to break the emulsion and
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allow the water phase to settle. The water containing the salt
is discharged from the system.
2.2.2 Crude Distillation
The first major separation operation in refining is crude
oil distillation. In distillation towers (columns) various
constant-boiling-range fractions are separated, the lowest boil-
ing fraction leaving the top of the tower and the highest boiling
fraction leaving the bottom. Products may be withdrawn as side-
streams at appropriate points on the tower. The sidestreams are
further processed in small towers called strippers, in which
steam is used to free the sidestream (cut) from its more volatile
components so that the boiling point of the product can be ad-
justed to a specified value. There are three major types of
distillation systems: single-stage, two-stage, and two-stage
with a vacuum tower.
Single-stage Distillation—
The crude feed is preheated by outgoing streams before
entering a direct-fired, furnace-type heater, from which it goes
to a distillation column for separation into gas, gasoline,
naphtha, kerosene, gas oil, fuel oil, and residuum. These side-
streams are steam-stripped and then routed to storage. Topping
plants use single-stage distillation, usually separating the
crude into five or six sidestreams. Very little additional
treating is performed at these plants. The number and type of
fractions that result from distillation depend on the crude base
and on operating conditions.
Two-Stage Distillation—
Two-stage distillation provides more cuts than the single-
stage system. The process includes a primary tower (preflash
tower), which operates at above atmospheric pressure, and a sec-
ondary tower (atmospheric tower), which operates at atmospheric
pressure. These units, together with a stabilizer (stabilizing
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tower), are used to separate the crude into light ends, depropa-
nized light gasoline, light kerosene, naphtha, kerosene, light
diesel, heavy diesel, and residuum.
The preflash overhead is fed to the stabilizer for removal
of the lighter hydrocarbons (usually dissolved gaseous hydrocar-
bons such as propane). In the stabilizer, the light hydrocarbons
are removed overhead, and the stabilized product is removed at
the bottom.
The preflash bottoms feed the atmospheric tower, where again
side cuts are taken and steam stripped to remove the light ends.
Two-Stage Distillation with Vacuum Tower—
This system incorporates the two-stage arrangement and adds
to it a vacuum tower. The bottoms from the atmospheric tower
feed the vacuum distillation tower, which operates at below
atmospheric pressure. Operation under a vacuum allows the reduc-
tion of operating temperatures and thus prevents coking in the
heater tubes or on trays and thermal degradation, which may occur
in high-temperature operations.
The petroleum refinery uses vacuum distillation to produce
light and heavy gas oils, heavy fuel oil, vacuum gas oil, lubri-
cating oil fractions, and vacuum bottoms. A refinery that prod-
c
uces lubricating oils may use two separate vacuum towers, one
especially designed to recover lube oil fractions and the other
designed for fuel oil fractions.
Although steam is not usually injected into the vacuum unit,
in some wet vacuum units steam is added to the distillation
column operating under a vacuum. The dry vacuum process has the
advantage of using smaller towers and smaller condensing equip-
ment for a given throughput and also is more economical and
energy efficient than the wet process.
A vacuum is usually created by steam jet ejectors discharg-
ing to surface condensers (shell and tube), which limits air
pollution. Alternatively, direct contact condensers are .used, in
which case, water, steam, and hydrocarbon vapors are mixed. This
type of condenser can generate air pollutants; however, the
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noncondensables from these units usually are vented to the re-
finery flare system as a means of controlling hydrocarbon emis-
sions.
Appendix C provides more details of the principles of frac-
tionation. Literature references and definition of terms are
given in the Bibliography and Glossary at the end of this manual.
2.2.3 Deasphalting
Deasphalting separates asphalts or resins from more viscous
fractions. Refineries and chemical plants commonly accomplish
such separation by liquid-liquid extraction. In this operation,
a mixture is separated into two components by means of a selec-
tive solvent, the separation being due to differences in solu-
bility. For ease of separation, the solvent must yield a two-
phase mixture with appreciable difference in densities of the two
phases.
In deasphalting, residuum from the vacuum tower and liquid
propane are heated to a controlled temperature and mixed at a
controlled ratio as feed to the deasphalting tower. The two
phases that result are separated, and propane is removed from the
deasphalted oil phase by a two-stage evaporation process and
steam stripping. The asphalt phase is heated and' steam stripped
for removal of residual propane. The propane is then condensed
and recycled. Overhead from both strippers is water washed, com-
pressed, and condensed before being recycled as propane extract-
ant.
2.3 DECOMPOSITION PROCESSES
2.3.1 Catalytic Cracking
Catalytic cracking is a relatively inexpensive method of
breaking down heavier distillate fractions into lighter gasoline
material and thus increasing the overall gasoline yield from
crude oil. The variety of catalysts and system designs provide a
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wide range of operating flexibility for the catalytic cracking
process.
Two well-known catalytic processes are in use today—the
fluid catalytic cracker (FCC) and the Thermofor catalytic cracker
(TCC). The FCC uses a powdered catalyst and the TCC or Houdri-
flow, no longer generally manufactured, uses a bead catalyst.
In the FCC, finely powdered catalyst is lifted into the
reaction zone by the incoming oil, which vaporizes immediately
upon contact with the hot catalyst. When the reaction is com-
plete, the product and catalyst are lifted into a regeneration
zone by air. In the reaction and regeneration zones, the cata-
lyst powder is held in a suspended state by the passage of gases
through it, and a small amount of catalyst is moved from the
reactor to the regenerator and vice versa. Oil tends to saturate
the enormous volume of pulverized catalyst in the reactor, and
hence the catalyst must be steam stripped before it enters the
regenerator.
The TCC is a moving-bed system with catalyst in the form of
beads or pellets. The catalyst is lifted by air, or in old
plants by bucket elevators, to a high position so that it can
flow downward by the force of gravity. It moves through the oil
zone, causing reaction, and then through a regeneration zone.
In both the FCC and TCC processes the catalyst must be re-
generated. Coke that forms on the catalyst particles during the
reaction must be continuously removed to maintain catalyst acti-
vity. In the regenerator, a controlled stream of air is added to
burn off the coke. The resulting combustion gases flow through a
series of cyclones for removal of the entrained catalyst. The
regenerator gases (often rich in carbon monoxide, CO) may be
burned as fuel in a CO boiler to generate refinery steam and
eliminate CO emissions.
Reactor products are condensed and stabilized in a large
distillation tower, where several streams are taken off. The
lightest streams are sent to a gas recovery unit, and the heavi-
est streams are recycled to the catalytic cracker. The recycle
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ratio and the ratio of catalyst to oil depend on the type of
feedstock and the desired product.
More detailed explanations of the fluid unit are given in
Section 4.2 and Appendix B.
2.3.2 Hydrocracking
Hydrocracking units perform both cracking and hydrogenation.
Products from hydrocracking are essentially saturated materials
with high concentrations of isoparaffins and naphthenes.
The hydrocracker functions in a manner similar to the cata-
lytic cracker but operates over a wider range of feedstock boil-
ing points. Because of their great flexibility, hydrocracking
processes may be operated to produce high-quality motor gasoline,
petrochemical naphtha, jet fuel, and diesel oils. With the new
catalysts available, a single hydrocracking unit can be used to
convert feedstocks as heavy as vacuum gas oils into either naph-
tha or high yields of middle distillates, simply by regulation of
the fractionation cut points and reactor temperatures. Hydro-
cracking is also used to desulfurize high-sulfur crude oils while
upgrading the heavier fractions into lighter fuel oils. The
inherent flexibility of the process will allow a gradual increase
in yield of motor gasoline to meet current markett demand.
The fixed-bed hydrocracking catalysts maintain high activity
in the presence of nitrogen and sulfur compounds. Various pro-
cess configurations and catalyst systems can be combined to yield
the optimum product spectrum for a particular feedstock.
The feedstock undergoes heat exchange with the second reac-
tor product, combined with preheated recycle and makeup hydrogen,
and introduced into the first reactor. The first reactor product
is combined with preheated recycle and additional liquid recycle
and introduced into the second reactor. The product is exchanged
with feedstock, condensed, and separated to recover recycle
hydrogen. A second flash stage removes gases, and the liquid
product enters the fractionator, from which various product
streams are taken for blending or further processing. The bottom
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product is recycled to the second reactor. Because this process
consumes hydrogen (200 to 350 volumes of hydrogen per volume of
feedstock), refineries often operate a hydrogen production facil-
ity onsite.
In the United States, about one-third of the hydrocracking
capacity is on the West Coast, where it is used to upgrade heavy
fuels to motor gasoline and jet fuel. Another one-third is on
the Gulf Coast, where it is used to alternate production of motor
gasoline and light distillates according to market demands.
2.3.3 Coking
Coking is a severe form of thermal cracking; it is an ulti-
mate-yield destructive distillation process that produces gas,
distillate, and coke from residuals that may resist cracking by
other methods. Although coke was earlier considered a low-value
byproduct, it is now used in electrode manufacture when sulfur
and metals contents are low enough. Coke with intermediate-range
sulfur content may be used as fuel for steam generator boilers.
There are two principal coking processes, delayed and fluid.
Delayed coking is the more widely used, and very few fluid coking
units are in service.
In the delayed coking process, the feedstock goes directly
to the fractionator. The lighter material is vaporized and
leaves the fractionator overhead. It is cooled and separated,
and the vapor phase is sent to the refinery fuel gas system.
Various sidestreams from the fractionator include naphtha and
light and heavy gas oils, which may be further processed. The
bottoms from the fractionator are pumped through a furnace to the
coking drums. Overhead from the coking drums flows back to the
fractionator and is recycled.
Coke forms on the coking drum walls and eventually fills the
drum. After a purging with steam, the drum is isolated and
opened; coke is broken free by high-pressure water jets. At
least two coking drums are provided so that one may be mechani-
cally or hydraulically decoked while the other is filling. These
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drums are usually sized so that they can be decoked and returned
to service during one work shift. The coke particles are washed
out with water and separated from the water on vibrating screens.
In the fluid coking process, the feedstock enters the reac-
tor, where it is mixed with a fluidized bed of preheated recycled
coke particles. The hydrocarbons in the liquid feed crack and
vaporize, while the nonvolatile material is deposited on the
suspended coke particles. The coke particles thus grow larger,
sink to the bottom of the reactor, and flow to the burner. In the
burner, the particles are fluidized with air, partially burned,
and recycled to the reactor. A portion of the coke produced in
the reactor is withdrawn as product. The overhead vapor can be
desulfurized to yield fuel gas suitable for process heaters or
steam/power generation.
2.3.4 Visbreaking
Viscosity breaking, or "visbreaking," is a milder form of
thermal cracking than coking; it is used to reduce the viscosity
of some residual fractions so that they may be blended into fuel
oils. It is applied when the demand for middle distillates ex-
ceeds that for motor gasoline.
The atmospheric or vacuum-reduced crude is preheated by heat
exchange with visbroken fuel oil and fed to a furnace. Mild
cracking in furnace tubes produces a mixture of residual oil,
naphtha, and gas. The reaction products are quenched with a
recycle stream and sent to a fractionator, in which the vis-
breaker bottoms accumulate in the lower portion. A simple pump
system in the tower allows fractionation of the flashed vapors
into gas, gasoline, and light and heavy gas oils. The gas oil
sidestream normally flows through a steam-stripping tower for
separation of the motor gasoline fraction.
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2.4 FORMATION PROCESSES
2.4.1 Catalytic Reforming
Catalytic reforming is used to alter the structure of satu-
rated straight-chain paraffins, which have very low octane num-
bers, to yield a different kind of molecule with much higher
octane characteristics. The process converts straight-carbon-
chain naphtha to a ring or branch-structured gasoline. Catalytic
reforming is also called platforming (when a platinum catalyst is
used), ultraforming, or magnaforming.
Catalytic reforming is a high-temperature, low-pressure,
fixed-bed process using a bimetallic catalyst. The most impor-
tant property of the catalyst is that which causes ring formation
and permits ring preservation in molecules that have just under-
gone partial dehydrogenation (aromatization). As would be ex-
pected with a substance as complex as crude oil, the process
reactions are numerous and complex. (A basic organic chemistry
text will explain these reactions in detail.) Table 2-2 presents
the major types of reactions that occur in catalytic reforming
units. Naphthene dehydrogenation, naphthene dehydroisomeriza-
tion, and paraffin isomerization are the predominant reactions.
The other reactions may become significant at high temperatures,
high pressures, and low-space velocities. Avoidance of hydro-
cracking is particularly important since it can lead to excessive
coke deposition, which deactivates the catalyst.
Compared with the feed, the final product contains a high
percentage of aromatic compounds and a small quantity of ali-
phatic hydrocarbons. Some of the aromatics (benzene, toluene,
and xylenes) may be isolated to become petrochemical feedstock,
but the major portion becomes motor gasoline blending stock.
Catalytic reforming units are regenerative or nonregenera-
tive. Regenerative reformers are the most common since they
operate at the low pressures that produce larger yields of high-
octane gasoline and also produce more hydrogen.
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TABLE 2-2. MAJOR REACTIONS OCCURRING IN CATALYTIC REFORMING
NAPHTHENE DEHYDROGENATION
1
H
H
2 T "2
H,
H
CYCLOHEXANE
NAPHTHENE DEHYDROISOMERIZATION
. H CH^
H
CH,~
H
BENZENE
H CH,
3H-
H
1,2-DIMETHYLCYCLOPENTANE METHYLCYCLOHEXANE TOLUENE
3H,
PARAFFIN ISOMERIZATION
n-HEXANE
CH3
CH,
-»• CH,-CH-CH-CH, + CH--C-CH,-CH..
0 i J J i t J
CH,
CH,
2,3-DlMETHYLBUTANE NEOHEXANE
(2,2-DIMETHYLBUTANE)
PARAFFIN DEHYDROCYCLIZATION
CH3-CH2-CH2-CH2-CH2-CH3
n-HEXANE
H
BENZENE
4H-
PARAFFIN HYDROCRACKING
C10H22 + H2
n-DECANE
OLEFIN HYDROGENATION
C5H10
PENTENE
CH3-CH2-CH2-CH2-CH3
PENTANE
C5H12
PENTANE
CH,
ISOPENTANE
HYDRODESULFURIZATION
HC -
HC
CH
II
CH
4H-
THIOPHENE
BUTANE
H2S
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Before entering the reforming unit, the naphtha feed is
hydrotreated to remove elements that may poison the reforming
catalyst. The hydrotreated naphtha is mixed with hydrogen from
the reformate stabilizer, exchanged with product streams, and
heated in a- furnace. This feed mixture then passes through
several reactors. The charge is heated before entering each
reactor to compensate for the endothermic reactions that occur.
The final reactor effluent is cooled, and the gases are separated
from the liquid products. The gases may be recycled, sent to the
hydrogen recovery system, or sent to the plant fuel system.
The liquid products are sent to a stabilizer (tower). The
noncondensable overhead from the stabilizer goes to the fuel gas
system, and the condensable liquids are treated for recovery of
light ends. Bottoms from the stabilizer are the reformate prod-
uct, which is usually sent to gasoline blending.
So that a reactor may be regenerated, most reforming units
contain a spare ("swing") reactor, which is periodically placed
in service during the regeneration cycle. During regeneration,
the coke deposited on the catalyst is burned off by a carefully
controlled stream of inert gases and a limited amount of air.
The nonregenerative systems do not have a spare reactor;
instead, the unit is shut down when the catalyst is deactivated,
and the catalyst is replaced. In other respects operation of
these units is similar to that of regenerative reformers.
2.4.2 Alkylation
The alkylation process for production of high-octane gaso-
line resulted from the discovery that isoparaffin hydrocarbons
unite with olefins in the presence of a catalyst. The process
may involve isobutane and olefins, which produce high-octane
dimers or trimers. Table 2-3 summarizes some of the alkylation
reactions.
Sulfuric acids or hydrofluoric acid is used to catalyze the
alkylation reaction. The reactants are combined with rapid and
violent mixing into refrigerated liquid acid. The resultant
vapors are separated from the acid mixture, caustic washed, water
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TABLE 2-3. SUMMARY OF REACTIONS OCCURRING IN ALKYLATION
CH3-CH-CH3
ETHYLENE ISOBUTANE
CH,-C-CH,-CH,
3 i Z 3
CH,
CH3-CH-CH-CH3
CH,
'3 ""3
NEOHEXANE 2,3-DIMETHYLBUTANE
(2.2-DIMETHYLBUTANE)
CH3-CH=CH-CH3
CH3
CH3-CH-CH3
CH, CH,
i o
-*• CH,-C-CH,-CH-CH,
J i i 3
CH,
2-BUTENE ISOBUTANE 2,2,4-TRIMETHYLPENTANE
(sym-DIMETHYLETHYLENE)
1-BUTENE
(ETHYLETHYLENE)
CH3
CH3-CH-CH3
ISOBUTANE
CH3 CH3
CH,-C-CH,-CH-CH,
J i i J
CH3
2,2,4-TRIMETHYLPENTANE
CH3-CH=CH2
PROPYLENE
H
H
BENZENE
CH3-CH-CH3
CUMENE
(ISOPROPYLBENZENE)
ETHYLENE
H
BENZENE
H
ETHYLBENZENE
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washed, and stabilized in a fractionation tower (debutanizer).
The tower bottoms are taken as alkylate, and the overhead vapors
are condensed and recycled. The tower also yields a normal
butane fraction.
2.4.3 Isomerization
As in catalytic reforming, the isomerization processes
rearrange the molecular structure of the feedstock while reducing
losses that normally occur in cracking or condensation reactions.
In the isomerization reactions nothing is added to or taken away
from the material. Formation of branched-chain compounds from
straight-chain compounds increases the octane number. The main
types of isomerization are butane, pentane, hexane, and xylene
isomerization.
Butane isomerization is closely linked with alkylation when
alkylate is required and isobutane is in short supply. Isobutane
is produced to provide feedstock for the alkylation unit. Build-
ing alkylation and isomerization units together permits sharing
of common distillation equipment. Isomerization of butanes is
increasing as a means of supplying petrochemical feedstock.
Isomerization of pentane and hexane yields products more suited
for motor gasoline blending stocks because they have desirable
antiknock properties. If a refinery is extracting paraxylene
from the catalytic reformate, the remaining orthoxylene and
metaxylene may be fed to an isomerization unit to produce para-
xylene. (Details of this type of isomerization are given in
Reference 2).
The butane isomerization process converts normal butane into
isobutane over a catalyst in the presence of hydrogen. A mixed
butane feedstock is fed into the deisobutanizer tower (distilla-
tion tower) from which isobutane product is taken overhead. The
bottoms undergo heat exchange with the reactor product after
recycle, and makeup hydrogen is added. The mixture is heated to
the reaction temperature in a furnace. Vaporized butanes enter
the fixed-bed catalytic reactor, undergo heat exchange with the
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reactor feed, and are condensed; the reactor effluent flows to
the separator for recovery of recycle hydrogen. Separator liquid
is sent to the stabilizer, where overheads are condensed and
noncondensables flow to the refinery gas system. Stabilizer
bottoms go to the deisobutanizer, where the overhead is the
product isobutane.
2.4.4 Polymerization
Polymerization is the combining of monomers. In a refinery
operation, propylene (olefin; monomer) would be polymerized to
yield dimer (2-propylenes), trimer (3-propylenes), tetramer (4-
propylenes) and perhaps higher order polymers.
This process is used very rarely in refineries today. It
was first introduced to provide a motor gasoline blending stock
when octane levels were very low. The octane gain from blending
of polymer (poly) gasoline was soon replaced by blending of
alkylate from alkylation units. Polymers are valuable in some
applications, however, such as additives for motor oil.
A refinery stream of propylene and butylenes is mixed with
recycle propane and water, subjected to heat exchange with reac-
tor product, preheated, and introduced into the top of a multi-
ple-fixed-bed reactor. Solid phosphoric acid deposited on an
inert carrier is the catalyst. Water is injected between the
several fixed beds for temperature control. The reactor product
is cooled by heat exchange with feed and sent to the depropanizer
(distillation tower). The overhead product is recycled to the
reactor feed. Bottom material is debutanized in a distillation
tower, from which butane goes overhead and polymer gasoline is
taken as bottoms.
2.5 TREATING PROCESSES
The objective of all petroleum refinery treatment of inter-
mediate fractions or products is to remove or render inactive
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compounds that would otherwise reduce the quality of these frac-
tions or products. Treating is particularly important for remov-
ing sulfur, nitrogen, and metal compounds from feed for a cata-
lytic cracker or catalytic reformer. If these compounds were not
removed, they would attack the catalyst. Therefore, this treat-
ment both improves performance and lengthens catalyst life.
Refinery treating processes can be classified as catalytic
or chemical. Several processes can be applied, depending upon
the content of undesirable compounds and the required severity of
the treatment. The vent or waste gas streams from the treating
processes usually contain the hydrogenated form of the undesir-
able compound. These streams can be sent to the sulfur recovery
process or the refinery fuel system.
2.5.1 Catalytic Treating
Hydrotreating is the most widely used process for all types
of petroleum products. With the appropriate catalyst and operat-
ing conditions, hydrotreating can desulfurize, eliminate other
impurities such as nitrogen and oxygen, decolorize and stabilize,
and correct odor problems and many other product deficiencies.
Hydrodesulfurization processes convert the sulfur in sulfur
compounds into more easily removed hydrogen sulfide (H2S) by use
of rugged catalysts and hydrogen. The processes also convert
some nitrogen compounds into ammonia.
Other hydrogenation or hydrotreating processes (not intended
primarily to attack sulfur) saturate olefinic materials, which
are undesirable in many refinery products. For example, certain
cracked gasoline stocks contain hydrocarbons that tend to poly-
merize (form gums) upon exposure to air. These can be stabilized
by a mild catalytic hydrotreating process.
2.5.2 Chemical Processes
Chemical treating processes scrub fractions with inorganic
acids such as sulfuric acid (H2S04) and bases such as sodium
hydroxide (NaOH) to remove undesirable acids and sulfur com-
pounds. Certain chemical treating processes use proprietary
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chemicals to remove specific impurities and improve the quality
and/or performance of petroleum products.
Acid gas removal processes bring feed streams into contact
with a selective solvent or absorbent. These materials absorb
the acid gases (normally hydrogen sulfide); they are regenerated
by stripping and then recycled. The stripped acid gases are
disposed of either in the sulfur recovery unit or by incinera-
tion. The sulfur recovery process (Glaus unit) is preferred
because it minimizes emissions.
Many processes are commercially available to perform all
types of treating operations. The Bibliography gives literature
references in the categories of acid gas removal, chemical sweet-
ening, hydrotreating, and hydrodesulfurization processes.
2.6 RECOVERY OPERATIONS
2.6.1 Sulfur Recovery
Sulfur compounds in petroleum fractions are converted into
H2S by treating processes. This H,,S is collected and sent to the
sulfur recovery plant (Glaus unit).
In the Glaus unit, H2S is burned with air to form elemental
sulfur. The overall chemical reaction is:
2H2S + 02 -» 2S + 2H20
The reaction is normally conducted in stages in which part of the
H2S is oxidized with air to form S02/ as follows:
H2S + 3/2 02 -» S02 + H20
This S00 is combined with the remaining H9S over a fixed-bed
£ £•
catalyst to complete the reaction:
S02 + 2H2S -> 3S + 2H20
A number of catalytic stages can be used to increase the sulfur
recovery and reduce S02 emissions.
Final exhaust gases may contain sulfur carbonyls, carbon
disulfide (CS2), H2S, and some elemental sulfur. These are
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normally incinerated at high temperature in a tail gas unit, and
the exhaust gas contains only small quantities of SO-.
2.6.2 Fuel Gas Recovery
The fuel gas plant- incorporates a system of operations for
recovering- useful hydrocarbon vapor mixtures from the crude oil
distillation unit and other refinery processes. While adding
value to the overall refinery process, the recovery process also
prevents hydrocarbon losses and emissions. A well-operated gas
recovery system is essential to the overall economics of petro-
leum refining.
Vapors (noncondensable gases) from the crude distillation
towers, the reformers, and the catalytic cracking units are
collected and sent to the gas processing unit for light-ends
recovery. The gases are compressed, condensed, and distilled
(separated) into various mixtures having constant vapor pressure.
These mixtures may be used as refinery fuel (burned in fired
heaters and boilers), sold as liquefied petroluem gases, used as
feedstock for hydrogen production, used as alkylation feedstock,
or sold as petrochemical feedstock.
2.7 STORAGE
All refineries use tanks and vessels for storage of feed-
stocks (crude oil, pressurized liquid hydrocarbons, etc.) and of
intermediate products awaiting further processing and/or blend-
ing. A certain amount of lower volume storage within the pro-
cessing area is referred to as "rundown tankage." Tankage is
also provided for finished products awaiting shipment and for use
in loading and unloading operations.
2.8 AUXILIARY FACILITIES
A refinery requires many auxiliary facilities, which can
include those for steam generation, production of electrical
power, wastewater treatment, and hydrogen production, as well as
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cooling towers and blowdown systems (including flares and liquid
incineration).
Many large refineries now generate some of their own elec-
trical power. Steam leaving turbines goes into refinery steam
systems at various pressure levels.
Wastewater treatment systems can range from a simple API
separator to very elaborate biological treatment systems. All
water streams are treated to meet environmental standards as wel]
as to recover various products.
Process water is recirculated and cooled to the specified
temperatures in cooling towers. Air coolers are being used with
increasing frequency to reduce requirements for cooling water.
Because product treating processes require hydrogen, the
hydrogen production facilities are often considered as auxiliary
or utility systems.
Blowdown systems receive releases of liquid and gaseous
streams from emergency vents and safety valves. These systems
entail collection, separation, and disposition by a flare or
incinerator.
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SECTION 5
ENFORCEMENT PROCEDURES
Each petroleum refinery is designed, engineered, construct-
ed, and operated to process specific crude oils and produce
specific products. This results in each petroleum refinery being
unique in the complexity and number of processes employed. Since
there is no typical refinery, a standard procedure for conducting
the inspection does not exist. This section describes approaches
to conducting an inspection rather than describing a standard
procedure for the inspector to follow.
5.1 INTRODUCTION
This section describes the various levels of enforcement in-
spections and lists the process units and other emission sources
that are to be inspected on those levels.
A thorough search should be conducted of the file for the
refinery to be inspected to determine what process units are
there, to note compliance history and trends, and to collect
other pertinent data. The inspection checklists (which are given
in Appendixes J through M) should be filled out as much as possi-
ble from file data. The data can then be verified and additional
data collected during the inspection. The checklists are merely
a means of organizing data; they are not official forms.
The inspector should be as informed as possible before
entering the refinery, and one way to accomplish this is to
review the descriptions of the various refining processes (Sec-
tion 4). The inspector should review the subsections pertaining
to those units that will be inspected. Appendix B and Appendix C
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provide additional background on the chemical engineering princi-
ples applicable to petroleum refining. The more an inspector
knows about an industry he is inspecting, the better he will be
able to communicate with plant personnel and the better the
inspection will be. The inspector is cautioned not to appear to
possess more knowledge of a subject than he actually has; by
doing so, he may miss getting important information or discredit
himself if plant personnel detect an area of ignorance. An
honest, questioning approach is generally the most effective.
It is important that the inspector be assertive in order to
assess compliance. The inspector should guide the course of the
inspection and be persistent in getting and verifying important
data. For example, the inspector may have a list of process
units and their feed rates. Rather than accepting the word of
the plant personnel aiding in the inspection, the inspector
should ask to see production sheets or a logbook that will verify
these data. An inspector should be confident that correct data
are collected. This approach, although time consuming, is effec-
tive in uncovering additional compliance problems.
The following subsections describe three levels of inspec-
tion, which increase in degree of intensity and follow different
time schedules. The Level I inspection is aimed at obtaining
continuing compliance of a limited number of units. These units
are the most likely to cause emission problems. The purpose of a
Level II inspection is to obtain compliance with particulate,
sulfur oxide, nitrous oxide, and some hydrocarbon emission regu-
lations. In a Level II inspection more units are investigated
than on a Level I inspection. The Level III inspection is aimed
at obtaining strict compliance with hydrocarbon emission regula-
tions. The number of fugitive emission sources monitored on a
Level III inspection is much greater than the number monitored on
a Level II inspection. Level II and III inspections are similar
in the number of sources investigated for compliance with parti-
culate, sulfur oxide, and nitrous oxide emission regulations. In
the future, a fourth or very detailed inspection may be added.
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This manual does not rule out that possibility, which would
result from new state and Federal policies.
5.2 LEVEL I INSPECTION
It is recommended that a Level I inspection be performed
once every 2 to 4 months. The actual frequency depends on the
workload and manpower available at local, state and Federal
offices. The duration of the inspection depends on the size of
the refinery and the number of inspectors. A two-man inspection
team can investigate a 30,000 barrel per day refinery in 2 to 3
hours.
Note the overall condition of the refinery during this
inspection. Dust from the unpaved roads is a source of particu-
late emissions, and pools of oily water are a source of hydrocar-
bon emissions. Observe all heater and boiler stacks to monitor
opacity. When a heater or a boiler stack is out of compliance
with the state visible emission standard, complete the the visi-
ble emission observation form.
Review and investigate the following units:
Unit Pollutant
Fluid catalytic cracking Particulates; sulfur dioxide
Sulfur recovery Sulfur dioxide
The pollution control equipment that may be present at the
Fluid Catalytic Cracking (FCC) unit includes a CO boiler, an
electrostatic precipitator (ESP), and internal and external
cyclones. Note the type of control equipment that is used and
also note whether the CO boiler or ESP is bypassed during the
inspection. (A refinery that does not have a flare, bypasses the
CO boiler to the FCC sump stack.)
Sulfur dioxide emissions from a sulfur plant are continu-
ously monitored at incinerator stacks by recording the incinera-
tor temperature. The usual incinerator temperature is about
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1204°C (2200°F). This temperature increases, however, to about
1427°C (2600°F) when the acid gas feed bypasses the Glaus and
tail gas unit and is routed directly to the incinerator, thus
increasing S02 emissions at the stack. The incinerator tempera-
ture is a good indicator of the amount of acid gas being bypass-
ed.
Completion of the Level I checklist is further discussed in
Section 5.7.
5.3 LEVEL II INSPECTION
It is recommended that a Level II inspection be performed
once every 6 to 9 months. The actual frequency depends on the
workload and manpower available at the agency. The duration of
the inspection depends on the size of the refinery and the number
of inspectors. It takes a two-man team 1 to 2 days to inspect a
30,000 barrel per day integrated refinery. Before the inspec-
tion, obtain the data listed below for the units being inspected;
during the inspection, review the data with refinery personnel.
Process flow diagram
Process information
Heater and boiler data (type of fuel, heater ,duty, exit
temperature, and stack data)
Storage tank data
Wastewater separator data (type of separator, type of cover,
condition of cover)
Some fugitive emissions are monitored by a hydrocarbon detector,
in addition to the monitoring of particulates and SG>2 emissions.
Review and investigate the following units:
Unit Pollutant
Fluid catalytic cracking Hydrocarbon vapors; particu-
lates; sulfur dioxide
Sulfur recovery Sulfur dioxide
Watewater treatment Hydrocarbon vapors
(continued)
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Unit Pollutant
Isomerization Hydrocarbon vapors, particu-
lates
Alkylation Hydrocarbon vapors, particu-
lates
Storage Hydrocarbon vapors
Loading Hydrocarbon vapors
Light-ends/gas processing Hydrocarbon vapors
The survey of oil refineries by the California Air Resources
Board in April 1978 showed that isomerization, alkylation, stor-
age, loading, light ends/gas processing, and FCC units accounted
for about 40 percent of the fugitive hydrocarbon emissions. The
CARB study also identified the items that contributed most to
fugitive emissions: valves, pump seals, and compressor seals.
For each process unit listed, use a hydrocarbon detector to in-
spect a certain number of the key emission contributors (Table
5-1). A screening procedure for monitoring fugitive emissions is
provided in Appendix H. Appendix G contains operating instruc-
tions for a Century Organic Vapor Analyzer, hydrocarbon detector.
5.4 LEVEL III INSPECTION
It is recommended that a Level III inspection be performed
once every 12 to 18 months. The frequency and duration depends
on the workload and manpower available at the agency. The dura-
tion of the inspection depends on the size and complexity of the
refinery. It takes a four-man team about one week to inspect a
30,000 barrel per day integrated refinery. It is a very detailed
inspection of the following units:
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TABLE 5-1. LEVEL II LEAK DETECTION PROGRAM
Process unit
Isomerization
Alkylation
Storage
Loading
Gas processing
FCC
Valves (in gas service)
Sample
size
20
20
20
20
20
8
Accept
No.*
5
5
5
5
5
2
Pump seals
Sample
size
5
8
8
8
5
Accept
No.*
1
2
2
2
. 1
Compressor seals
Sample
size
2
2
2
Accept
No.*
1
1
1
*The accept number is the maximum number of leaks detected in the sample size
that results in statistically approving the sample. This number is based on
varying quality levels and statistics. Appendix E explains the derivation of
these numbers.
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Unit
Fluid catalytic cracking
Sulfur recovery
Wastewater treatment
Distillation: Vacuum
Distillation: Atmospheric
Isomerization
Alkylation
Storage
Loading
Light-ends/gas processing
Hydrocracking
Reforming
Visbreaking
Hydrotreating (Hydrodesul-
furization, or HDS)
Pollutant
Hydrocarbon vapors; particu-
lates, sulfur dioxide
Sulfur dioxide
Hydrocarbon vapors
Hydrocarbon vapors; particu-
lates
Hydrocarbon
lates
Hydrocarbon
lates
Hydrocarbon
lates
Hydrocarbon
Hydrocarbon
Hydrocarbon
Hydrocarbon
lates
Hydrocarbon
lates
Hydrocarbon
Hydrocarbon
parti cu-
particu-
particu-
vapors;
vapors;
vapors;
vapors
vapors
vapors
vapors; particu-
vapors; particu-
vapors
vapors
Again, the CARB study determined that the process units listed
above comprise about 52 percent of the fugitive hydrocarbon
emissions. For each process unit listed, use a hydrocarbon
sniffer to inspect a certain number of the key emission contri-
butors (Table 5-2). The operating instructions for using a
Century Organic Vapor Analyzer to monitor fugitive emissions is
provided in Appendix G. Appendix H contains a screening proced-
ure for monitoring fugitive emissions.
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TABLE 5-2 LEVEL III LEAK DETECTION PROGRAM
Process unit
Isomerization
Alkylation
Storage
Loading
Gas Processing
FCC
Vi screaking
Hydrotreati ng*
(HDS)
Hydrocracking
Reformer
Distillation:
Atmospheric
Distillation:
Vacuum
Valves (in g
Sample
size
20
50
50
50
50
20
20
20
20
20
20
20
as service)
Accept
No.
2
5
5
5
5
2
2
2
2
2
2
2
Pump seals
Sample
size
8
20
20
20
8
8
8
8
8
8
8
Accept
No.
1
2
2
2
1
1
1
1
1
1
1
Compressor seals
Sample
size
3
3
3
3
3
3
t
3
Accept
No.
0
0
0
0
0
0
0
*A refinery has hydrotreating units for several feedstreams, some of which are
listed below:
HDS--reformer feed
HDS--light gas oil
HDS--heavy gas oil
Vacuum--(Residue) gas oil
Coker--Naphtha
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Petroleum Product
Storage
ana
Distribution
357
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4.3 STORAGE OF ORGANIC LIQUIDS
4.3.1 Process Description
Storage vessels containing organic liquids can be found in many
industries, including (1) petroleum producing and refining, (2) petro-
chemical and chemical manufacturing, (3) bulk storage and transfer
operations., and (4) other industries consuming or producing organic liquids.
Organic liquids in the petroleum industry, usually called petroleum liquids,
generally are mixtures of hydrocarbons having dissimilar true vapor pressures
(for example, gasoline and crude oil). Organic liquids in the chemical
industry, usually called volatile organic liquids, are composed of pure
chemicals or mixtures of chemicals with similar true vapor pressures (for
example, benzene or a mixture of isopropyl and butyl alcohols).
Five basic tank designs are used for organic liquid storage vessels,
fixed roof, external floating roof, internal floating roof, variable vapor
space, and pressure (low and high).
Fixed Roof Tanks - A typical fixed roof tank is shown in Figure 4.3-1.
This type of tank consists of a cylindrical steel shell with a permanently
affixed roof, which may vary in design from cone or dome shaped to flat.
Fixed roof tanks are commonly equipped with a pressure/vacuum vent
that allows them to operate at a slight internal pressure or vacuum to
prevent the release of vapors during very small changes in temperature,
pressure or liquid level. Of current tank designs, the fixed roof tank is
the least expensive to construct and is generally considered the minimum
acceptable equipment for storage of organic liquids.
JUohoU
Nozzlt (For
ubMTgcd fill
or draln*g<)
9/85
Figure 4.3-1. Typical fixed roof tank.1
Evaporation Loss Sources
4.3-1
358
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External Floating Roof Tanks - A typical external floating roof tank is
shown in Figure 4.3-2. This type of tank consists of a cylindrical steel
shell equipped with a roof which floats on the surface of the stored liquid,
rising and falling with the liquid level. The liquid surface is completely
covered by the floating roof, except at the small annular space between the
roof and the tank wall. A seal (or seal system) attached to the roof
contacts the tank wall (with small gaps, in some cases) and covers the
annular space. The seal slides against the tank wall as the roof is raised
or lowered. The purpose of the floating roof and the seal (or seal system)
is to reduce the evaporation loss of the stored liquid.
Internal Floating Roof Tanks - An internal floating roof tank has both a
permanent fixed roof and a deck inside. The deck rises and falls with the
liquid level and either floats directly on the liquid surface (contact
deck) or rests on pontoons several inches above the liquid surface (non-
contact deck). The terms "deck" and "floating roof" can be used
interchangeably in reference to the structure floating on the liquid inside
the tank. There are two basic types of internal floating roof tanks, tanks
in which the fixed roof is supported by vertical columns within the tank,
and tanks with a self-supporting fixed roof and no internal support columns.
Fixed roof tanks that have been retrofitted to employ a floating deck are
typically of the first type, while external floating roof tanks typically
.have a self-supporting roof when converted to an internal floating roof
tank. Tanks initially constructed with both a fixed roof and a floating
deck may be of either type.
The deck serves to restrict evaporation of the organic liquid stock.
Evaporation losses from decks may come from deck fittings, nonwelded deck
seams, and the annular space between the deck and tank wall. Typical
contact deck and noncontact deck internal floating roof tanks are shown in
4.3-2
Figure 4.3-2. External floating roof tank.1
EMISSION FACTORS
9/85
359
-------
Figure 4.3-3. Contact decks can be aluminum sandwich panels with a honey-
comb aluminum core floating in contact with the liquid, or pan steel decks
floating in contact-with the liquid, with or without pontoons. Typical
noncontact decks have an aluminum deck or an aluminum grid framework
supported above the liquid surface by tubular aluminum pontoons or other
bouyant structures. Both types of deck incorporate rim seals, which slide
against the tank wall as the deck moves up and down. In addition, these
tanks are freely vented by circulation vents at the top of the fixed roof.
The vents minimize the possibility of organic vapor accumulation in con-
centrations approaching the flammable range. An internal floating roof
tank not freely vented is considered a pressure tank.
Pressure Tanks - There are two classes of pressure tanks in general use,
low pressure (2.5 to 15 psig) and high pressure (higher than 15 psig).
Pressure tanks generally are used for storage of organic liquids and gases
with high vapor pressures and are found in many sizes and shapes, depending
on the operating pressure of the tank. Pressure tanks are equipped with a
pressure/vacuum vent that is set to prevent venting loss from boiling and
breathing loss from daily temperature or barometric pressure changes. High
pressure storage tanks can be operated so that virtually no evaporative or
working losses occur. In low pressure tanks, working losses can occur with
atmospheric venting of the tank during filling operations.
Variable Vapor Space Tanks - Variable vapor space tanks are equipped with
expandable vapor reservoirs to accomodate vapor volume fluctuations attribut-
able to temperature and barometric pressure changes. Although variable
vapor space tanks are sometimes used independently, they are normally
connected to the vapor spaces of one or more fixed roof tanks. The two
most common types of variable vapor space tanks are lifter roof tanks and
flexible diaphragm tanks.
Lifter roof tanks have a telescoping roof that fits loosely around the
outside of the main tank wall. The space between the roof and the wall is
closed by either a wet seal, which is a trough filled with liquid, or a dry
seal, which uses a flexible coated fabric.
Flexible diaphragm tanks use flexible membranes to provide expandable
volume. They may be either separate gasholder units or integral units
mounted atop fixed roof tanks.
4.3.2 Emissions And Controls
Emission sources from organic liquids in storage depend upon the tank
type. Fixed roof tank emission sources are breathing loss and working
loss. External or internal floating roof tank emission sources are standing
storage loss and withdrawal loss. Standing storage loss includes rim seal
loss, deck fitting loss and deck seam loss. Pressure tanks and variable
vapor space tanks are also emission sources.
Fixed Roof Tanks - Two significant types of emissions from fixed roof tanks
are breathing loss and working loss. Breathing loss is the expulsion of
vapor from a tank through vapor expansion and contraction, which are the
results of changes in temperature and barometric pressure. This loss
occurs without any liquid level change in the tank.
9/85 Evaporation Loss Sources 4.3-3
360.
-------
Ccnctr 7«nt
V«nt —.
Maahol*
Tank Support Colin
with Column W«U
Contact Deck Type
Cater Vent
7«ne
V«por Spa
Noncontact Deck Type
4.3-4
Figure 4.3-3. Internal floating roof tanks.1
EMISSION FACTORS
9/85
361
-------
The combined loss from filling and emptying is called working loss.
Filling loss comes with an increase of the liquid level in the tank, when
the pressure inside the tank exceeds the relief pressure and vapors are
expelled from the tank. Emptying loss occurs when air drawn into the tank
during liquid removal becomes saturated with organic vapor and expands,
thus exceeding the capacity of the vapor space.
The following equations, provided to estimate emissions, are applicable
to tanks with vertical cylindrical shells and fixed roofs. These tanks
must be substantially liquid and vapor tight and must operate approximately
at atmospheric pressure. Fixed roof tank breathing losses can be estimated
from2:
/
(
V
= 2.26 x lO-'M p p ] Dl-73H0-51AT°-50FpCXc (1)
A
where:
Lr. = fixed roof breathing loss (Ib/yr)
M.. = molecular weight of vapor in storage tank (Ib/lb mole), see
Note 1
P. = average atmospheric pressure at tank location (psia)
A
P = true vapor pressure at bulk liquid conditions (psia), see Note 2
D = tank diameter (ft)
H = average vapor space height, including roof volume correction
(ft), see Note 3
AT = average ambient diurnal temperature change (°F)
Fp = paint factor (dimensionless) , see Table 4.3-1 '
C = adjustment factor for small diameter tanks (dimensionless), see
Figure 4.3-4
Kr = product factor (dimensionless) , see Note 4
i»
Notes: (1) The molecular weight of the vapor, M,., can be determined by
Table 4.3-2. for selected petroleum liquids and volatile
organic liquids or by analysis of vapor samples. Where
mixtures of organic liquids are stored in a tank, My can be
estimated from the liquid composition. As an example of the
latter calculation, consider a liquid known to be composed
of components A and B with mole fractions in the liquid X
and X, , respectively. Given the vapor pressures of the pure
9/85 ' Evaporation Loss Sources 4.3-5
362
-------
TABLE 4.3-1. PAINT FACTORS FOR FIXED ROOF TANKS3
Paint factors (Fp)
Tank color
Roof
White
Aluminum (specular)
White
Aluminum (specular)
White
Aluminum (diffuse)
White
Light gray
Medium gray
Shell
White
White
Aluminum (specular)
Aluminum (specular)
Aluminum (diffuse)
Aluminum (diffuse)
Gray
Light gray
Medium gray
Paint
Good
1.00
1.04
1.16
1.20
1.30
1.39
1.30
1.33
1.40
condition
Poor
1.15
1.18
1.24
1.29
1.38
1.46
1.38
1.44b
1.58b
Reference 2.
^Estimated from the ratios of the seven preceding paint factors.
ADJUSTMENT FACTOR, C
o o o o •-
• • • •
O K» ** O» 0»
X
/
/
/
/
7
/
7
^
^
^
*r*
— • "
^m
10 20 31
TANK DIAMETER, ft
Figure 4.3-4. Adjustment factor (C) for small diameter tanks.2
4.3-6 EMISSION FACTORS 9/85
*•»
-------
oo
Ln
TABLE 4.3-2. PHYSICAL PROPERTIES OF TYPICAL ORGANIC LIQUIDS'1
CO
C73
en
to
•a
o
«i
CD
tr>
O
Co
O
c
•1
o
re
M
Condensed
Vapor Product vapor
Organic liquid
Petroleum Liquid*0
Gasoline RVP 13
Gasoline RVP 10
Gasoline RVP 7
Crude oil RVP 5
Jel naphtha (JP-4)
Jet kerosene
Distillate fuel no. 2
Residual oil no. 6
Volatile Organic Liquids
Acetone
Acrylonitrile
Benzene
Carbon disullide
Carbon letrachloride
Chloroform
Cyrlohexane
1,2-Dichloroethane
Ethylacetate
Ethyl alcohol
Isopropyl alcohol
Methyl alcohol
Hethylene chloride
Hethyletnyl ketone
Hethylnethacrylate
1 , 1 , 1-Trichloroethane
Trichloroethylene
Toluene
Vinylacetate
weight
£ 60°F
62
66
68
50
ao
130
130
190
58
S3
78
76
154
119
84
99
88
46
60
32
85
72
100
133
131 .
92
86
— _..W»~J ^ — f |
Ib/gal
9 60*F
5.6
5.6
5.6
7.1
6.4
7.0
7.1
7.9
6.6
6.8
7.4
10.6
13.4
12.5
6.5
10. 5
7.6
6.6
6.6
6.6
II. 1
6.7,
7.9
11.2
12.3
7.3
7.8
) ——«—•»/ \— f \
Ib/gal
0 60°F
4.
5.
5.
4.
5.
6.
6.
6.
6.
6.
7.
10.
13.
12.
6.
10.
7.
6.
6.
6.
II.
6.
7.
II.
12.
7.
7.
9
1
2
5
4
1
1
4
6
8
4
6
4
5
5
5
6
6
6
6
1
7
9
2
3
3
8
True vapor pressure
40"F
4.7
3.4
2.3
1.8
0.8
0.0041
0.0031
0.00002
1.7
0.8
0.6
3.0
0.8
1.5
0.7
0.6
0.6
0.2
0.2
0.7
3.1
0.7
O.I
0.9
0.5
0.2
0.7
SOT
5.7
4.2
2.9
2.3
1.0
0.0060
0.0045
0.00003
2.2
1.0
0.9
3.9
I.I
1.9
0.9
0.8
0.8
0.4
0.3
1.0
4.3
0.9
0.2
1.2
0.7
0.2
1.0
60"F
6.9
5.2
3.5
2.8
1.3
0.0085
0.0074
0.00004
2.9
1.4
1.2
4.8
1.4
2.5
1.2
1.0
I.I
0.6
0.6
1.4
5.4
1.2
0.3
1.6
0.9
0.3
1.3
70°F
8.3
6.2
4.3
3.4
1.6
0.011
0.0090
0.00006
3.7
1.8
1.5
6.0
1.8
3.2
1.6
1.4
1.5
0.9
0.7
2.0
6.8
1.5
0.6
2.0
1.2
0.4
1.7
in p«ia at:
80"F
9.9
7.4
5.2
4.0
1.9
0.015
0.012
0.00009
4.7
2.4
2.0
7.4
2.3
4.1
2.1
1.7
1.9
1.2
0.9
2.6
8.7
2.1
0.8
2.6
1.5
0.6
2.3
90°F
11.7
8.8
6.2
4.8
2.4
0.021
0.016
0.00013
5.9
3.1
2.6
9.2
3.0
5.2
2.6
2.2
2.5
1.7
1.3
3.5
10.3
2.7
I.I
3.3
2.0
0.8
3.1
IOO°K
13.8
10. 5
7.4
5.7
2.7
0.029
0.022
6.00019
7.3
4.0
3.3
11.2
3.8
6.3
3.2
2.8
3.2
2.3
1.8
4.5
13.3
3.3
1.4
4.2
2.0
1.0
4.0
.References 3-4.
cFor a more comprehensive listing of volatile organic liquids, see Referrmr 3.
RVP = Reid vapor pressure in psia.
I
—4
-------
components, P and P, , and the molecular weights of the pure
components, Mfl and Mb> My is calculated:
where: P , by Raoult's law, is:
P " PX +
a a
(2) True vapor pressures for organic liquids can be determined
from Figures 4.3-5 or 4.3-6, or Table 4.3-2. In order to
use Figures 4.3-5 or 4.3-6, the stored liquid temperature, T_,
must be determined in degrees Fahrenheit. T,, is deter-
mined from Table 4.3-3, given the average annual ambient
temperature, TA, in degrees Fahrenheit. True vapor pressure
is the equilibrium partial pressure exerted by a volatile
organic liquid, as defined by ASTM-D-2879 or as obtained
from standard reference texts. Reid vapor pressure is the
absolute vapor pressure of volatile crude oil and volatile
nonviscous petroleum liquids, except liquified petroleum
gases, as determined by ASTM-D-323.
(3) The vapor space in a cone roof is equal in volume to a
cylinder, which has the same base diameter as the cone and is
one third the height of the cone. If information is not
available, assume H equals one half tank height.
(4) For crude oil, K_ = 0.65. For all other organic liquids,
KC = i.o. u
Fixed roof tank working losses can be estimated from2:
T - 9 LCl v 1CI-S M PVMV V O\
-L»j — z . **u A iu n«.ir vrir^TjAp v.*7
where:
L^. = fixed roof working loss (Ib/year)
M.. = molecular weight of vapor in storage tank (Ib/lb mole), see Note 1
to Equation 1
P = true vapor pressure at bulk liquid temperature (psia), see Note 2
to Equation 1
V = tank capacity (gal)
N = number of turnovers per year (dimensionless)
,. _ Total throughput per year (gal)
Tank capacity, V (gal)
4 .'; -'',' EM ISSI ON FACTOKS 9/85
365
-------
t«0
•
7
•10
• It
• 12
13
> 14
• IS
I
in
I
.— 2
— 3
_ 4
— 5
-10
I—IS
130 — 5
~3
120 —3
110 — §
-3
100 — =
I 5
90 — = K.-
— cc
• -1 I
70
= 0
6" —3 O
—
—
•^3
so -I
—
— C
3 Q
20 —z
10 —=
0 —=
Ki«ure 4.3-5. True vapor pressure (P) of crude oils (2-15 psi RVP).1
9/85
Evaporation Loss Sources
4.3-9
366
-------
— 0.20
— 0.30
'< — 0.50
p- 0.60
P- 0.70
h— 080
£- 0.90
— voo
i r 1-50
s. I
- 2.00
1/1 ~
1/1 ~
— 2.50
I E- 30°
5 E- 15°
=- 4.00
I-
5.00
£
'-
120 —
110
100-
90-
BO-
., - S.
70— a
- ^«
-: z
- I
- Q
«^ §
: a
— Ul
E §
Z. 6.00
E_ 7.00
30-E
=
r
|
^
9.00
10.0
n.o
liO
13.0
14.0
16.0
P-17.0
^-18.0
^-19.0
E-20.0
£-21.0
t-22.0
P-23.0
S - SLOPE OF TH6 ASTM DISTILLATION
CURVE AT 10 PERCENT EVAPORATED
PEG f AT 15 PERCENT MINUS PEG F AT 5 PERCENT
10
IN THE ABSENCE OF DISTILLATION DATA
THE FOLLOWING AVERAGE VALUE OF S MAY BE USED:
MOTOR GASOLINE
AVIATION GASOLINE
LIGHT NAPHTHA 19-1* LB RVP1
NAPHTHA (2-8 LB RVP) 2.5
t —
«
10 —
Ntiri Da»l»cJ line illu»iraie» sample problem (of RVP - III pound* per square inch. jtaxMine
SOL'Rl'E N,.rmi«rjph drawn from Ihe data of the National Bureau of Standard*
(5
|. anJ
Figure 4.3-0. True vapor presure (P) of refined petroleum liquids
like gasoline and napththas (1-20 psi RVP).6
4.3-10
EMISSION FACTORS
9/85
367
-------
K,, =
c
Note:
= turnover factor (dimensionless), see Figure 4.3-7
product factor (dimensionless), see Note 1
(1) For crude oil, Kr = 0.84. For all other organic liquids,
K,, = 1.0.
TABLE 4.3-3. AVERAGE STORAGE TEMPERATURE (T>)
AS A FUNCTION OF TANK PAINT COLOR3
Tank color
Average storage temperature,
TS
White
Aluminum
Gray
Black
TAb + °
TA + 2.5
TA + 3.5
TA + 5.0
3
Reference 5.
3T. is the average annual ambient temperature in
degrees Fahrenheit.
1.0
0.8
0.6
I
i 0.4
0.2
0 100
TURNOVERS PER TEAR -
200 300 400
ANNUAL THROUGHPUT
TANK CAPACITY
Note: For 36 turnovers per year or less, KN - 1.0
Figure 4.3-7. Turnover factor (KN) for fixed roof tanks.
9/85 Evaporation Loss Sources 4.3-11
3G8
-------
Several methods are used to control emissions from fixed roof tanks.
Emissions from fixed roof tanks can be controlled by the installation of an
internal floating roof and seals to minimize evaporation of the product
being stored. The control efficiency of this method ranges from 60 to
99 percent, depending on the type of roof and seals installed and on the
type of organic liquid stored.
The vapor recovery system collects emissions from storage vessels and
converts them to liquid product. Several vapor recovery procedures may be
used, including vapor/liquid absorption, vapor compression, vapor cooling,
vapor/solid adsorption, or a combination of these. The overall control
efficiencies of vapor recovery systems are as high as 90 to 98 percent,
depending on the method used, the design of the unit, the composition of
vapors recovered, and the mechanical condition of the system.
Another method of emission control on fixed roof tanks is thermal
oxidation. In a typical thermal oxidation system, the air/vapor mixture is
injected through a burner manifold into the combustion area of an incin-
erator. Control efficiencies for this system can range from 96 to
99 percent.
External And Internal Floating Roof Tanks - Total emissions from floating
roof tanks are the sum of standing storage losses and withdrawal losses.
Standing storage loss from internal floating roof tanks includes rim seal,
deck fitting, and deck seam losses. Standing storage loss from external
floating roof tanks, as discussed here, includes only rim seal loss, since
deck fitting loss equations have not been developed. There is no deck seam
loss, because the decks have welded sections.
Standing storage loss from external floating roof tanks, the major
element of evaporative loss, results from wind induced mechanisms as air
flows across the top of an external floating roof tank. These mechanisms
may vary, depending upon the type of seals used to close the annular vapor
space between the floating roof and the tank wall. Standing storage emis-
sions from external floating roof tanks are controlled by one or1 two separate
seals. The first seal is called the primary seal, and the other, mounted
above the primary seal, is called the secondary seal. There are three basic
types of primary seals used on external floating roofs, mechanical (metallic
shoe), resilient (nonraetallic), and flexible wiper. The resilient seal can
be mounted to eliminate the vapor space between the seal and liquid surface
(liquid mounted), or to allow a vapor space between the seal and .liquid
surface (vapor mounted). A primary seal serves as a vapor conservation
device by closing the annular space between the edge of the floating roof
and the tank wall. Some primary seals are protected by a metallic weather
shield. Additional evaporative loss may be controlled by a secondary seal.
Secondary seals can be either flexible wiper seals or resilient filled
seals. Two configurations of secondary seal are currently available, shoe
mounted and rim mounted. Although there are other seal system designs, the
systems described here compose the majority in use today. See Figure 4.3-8
for examples of primary and secondary seal configurations.
Typical internal floating roofs generally incorporate two types of
primary seals, resilient foam filled seals and wipers. Similar in design
4.3-12 EMISSION FACTORS 9/85
369
-------
TANK
WALL
1ETALLIC 'WEATHER
SHIELD
* FLOATING ROOF
SEAL FABRIC
RESILIENT FOAM
a. Liquid mounted seal with
weather shield.
RIM-MOUNTED
'SECONDARY SEAL
c. Vapor mounted seal with
rim mounted secondary seal.
ELASTOMERIC WIPER SEAL
I
SONCONTACT INTERNAL
FLOATING ROOF
• TANX WALL
b. Elastomeric wiper seal.
TANK
d. Metallic shoe seal with shoe
mounted secondary seal.
Figure 4.3-8. Primary and secondary seal configurations.1
9/85 Evaporation Loss Sources 4.3-13
370
-------
to those in external floating roof tanks, these seals close the annular
vapor space between the edge of the floating roof and the tank wall.
Secondary seals are not commonly used with internal floating roof tanks.
Deck fitting loss emissions from internal floating roof tanks result
from penetrations in the roof by deck fittings, fixed roof column supports
or other openings. There are no procedures for estimating emissions from
external roof tank deck fittings. The most common fittings with relevance
to controllable vapor losses are described as follows:1
1. Access Hatch. An access hatch is an opening in the deck with a
peripheral vertical well that is large enough to provide passage of workers
and materials through the deck for construction or servicing. Attached to
the opening is a removable cover which may be bolted and/or gasketed to
reduce evaporative loss. On noncontact decks, the well should extend down
into the liquid to seal off the vapor space below the deck.
2. Automatic Gauge Float Well. A gauge float is used to indicate the
level of liquid within the tank. The float rests on the liquid surface,
inside a well that is closed by a cover. The cover may be bolted and/or
gasketed to reduce evaporation loss. As with other similar deck penetra-
tions, the well extends fixed into the liquid on noncontact decks.
3. Column Well. For fixed roofs that are column-supported, the
columns pass through deck openings with peripheral vertical wells. On
noncontact decks, the well should extend down into the liquid. The wells
are equipped with closure devices to reduce evaporative loss and may be
gasketed or ungasketed to further reduce the loss. Closure devices are
typically sliding covers or flexible fabric sleeve seals.
4. Ladder Well. Some tanks are equipped with internal ladders that
extend from a manhole in the fixed roof to the tank bottom. The deck
opening through which the ladder passes has a peripheral vertical well. On
noncontact decks, the well should extend down into the liquid. The wells
are typically covered with a gasketed or ungasketed sliding cover.
5. Roof Leg or Hanger Well. To prevent damage to fittings underneath
the deck and to allow for tank cleaning or repair, supports are provided to
hold the deck a predetermined distance off the tank bottom. These supports
consist of adjustable or fixed legs attached to the floating deck or hangers
suspended from the fixed roof. For adjustable legs or hangers, the load-
carrying element passes through a well or sleeve into the deck. With
noncontact decks, the well should extend into the liquid.
6. Sample Pipe or Well. A funnel-shaped sample well may be provided
to allow for sampling of the liquid with a sample thief. A closure is
typically located at the lower end of the funnel and frequently consists of
a horizontal piece of fabric slit radially to allow thief entry. The well
should extend into the liquid on noncontact decks. Alternatively, a sample
well may consist of a slottled pipe extending into the liquid, equipped
with a gasketed or ungasketed sliding cover.
4.3-14
EMISSION FACTORS 9/85
371
-------
7. Vacuum Breaker. A vacuum breaker equalizes the pressure of the
vapor space across the deck as the deck is either being landed on or floated
off its legs.: The vacuum breaker consists of a well with a cover. Attached
to the underside of the cover is a guided leg of such length that it contacts
the tank bottom as the internal floating deck approaches. When in contact
with the tank bottom, the guided leg mechanically opens the breaker by
lifting the cover off the well; otherwise, the cover closes the well. The
closure may be gasketed or ungasketed. Because the purpose of the vacuum
breaker is to allow the free exchange of air and/or vapor, the well does
not extend appreciably below the deck.
The decks of internal floating roofs typically are made by joining
several sections of deck material, resulting in seams in the deck. To the
extent that these seams are not completely vapor tight, they become a
source of emissions. It should be noted that external floating roof tanks
and welded internal floating roofs do not have deck seam losses.
Withdrawal loss is another source of emissions from floating roof
tanks. This loss is the vaporization of liquid that clings to the tank
wall and is exposed to the atmosphere when a floating roof is lowered by
withdrawal of liquid. There is also clingage of liquid to columns in
internal floating roof tanks which have a column supported fixed roof.
Total Losses From Floating Roof Tanks - Total floating roof tank emissions
are the sum of rim seal, withdrawal, deck fitting, and deck seam losses.
It should be noted that external floating roof tanks and welded internal
floating roofs do not have deck seam losses. Also, there are no procedures
for estimating emissions from external floating roof tank deck fittings.
The equations provided in this Section are applicable only to freely vented
internal floating roof tanks or external floating roof tanks. The equations
are not intended to be used in the following applications: to estimate
losses from closed internal floating roof tanks (tanks vented only through
a pressure-vacuum vent); to estimate losses from unstabilized or boiling
stocks or from mixtures of hydrocarbons or petrochemicals for which the
vapor pressure is not known or cannot be readily predicted; or to estimate
losses from tanks in which the materials used in the seal system and/or
deck construction are either deteriorated or significantly permeated by the
stored liquid.6 Total losses may be written as:
where:
L_ = total loss (Ib/yr)
Lj, = rim seal loss (see Equation 4)
L,, = withdrawal loss (see Equation 5)
L_ = deck fitting loss (see Equation 6)
L-. = deck seam loss (see Equation 7)
9/85 Evaporation Loss Sources 4.3-15
372
-------
Rim Seal Loss - Rim seal loss from floating roof tanks can be estimated
by the following equation5-6:
(4)
where:
Lp = rim seal loss (Ib/yr)
Kg = seal factor (lb-mole/(ft (mi/hr)n yr)), see Table 4.3-4
V = average wind speed at tank site (rai/hr) , see Note 1
a = seal related wind speed exponent (dimensionless), see Table 4.3-4
P* = vapor pressure function (dimensionless), see Note 2
_P
P*= P
where:
P = true vapor pressure at average actual liquid storage
temperature (psia), see Note 2 to Equation 1
P. = average atmospheric pressure at tank location (psia)
A
D = tank diameter (ft)
tty = average-vapor molecular weight (Ib/lb-mole), see Note 1 to
Equation 1
Kp = product factor (dimensionless), see Note 3
W
Notes: (1) If the wind speed at the tank site is not available, wind
speed data from the nearest local weather station may be
used as an approximation.
(2) P* can be calculated or read directly from Figure 4.3-9.
(3) For all organic liquids except crude oil, KC * 1.0. For
crude oil, K.. = 0.4.
Withdrawal Loss - The withdrawal loss from floating roof storage tanks
can be estimated using Equation 5.5-6
(0.943)QCWT , , , .
•C-*)
4.3-16 EMISSION FACTORS 9/85
373
-------
TABLE 4.3-4. SEAL RELATED FACTORS FOR FLOATING ROOF TANKS3
Welded Tank Riveted Tank
Tank and seal type Kg n K
S
External floating roof tanks
Metallic shoe seal
Primary seal only 1.2 1.5 1.3 1.5
With shoe mounted secondary seal 0.8 1.2 1.4 1.2
With rim mounted secondary seal 0.2 1.0 0.2 1.6
Liquid mounted resilient seal
Primary seal only 1.1 1.0 NA NA
With weather shield 0.8 0.9 NA NA
With rim mounted secondary seal 0.7 0.4 NA NA
Vapor mounted resilient seal
Primary seal only 1.2 2.3 NA NA
With weather shield 0.9 2.2 NA NA
With rim mounted secondary seal 0.2 2.6 NA NA
Internal floating, roof tanks
Liquid mounted resilient seal
Primary seal only 3.0 0 NA NA
With rim mounted secondary seal 1.6 0 NA NA
Vapor mounted resilient seal
Primary seal only 6.7 0 NA NA
With rim mounted secondary seal 2.5 0 NA NA
aBased on emissions from tank seal systems in reasonably good working
condition, no visible holes, tears, or unusually large gaps between
the seals and the tank wall. The applicability of K decreases in
cases where the actual gaps exceed the gaps assumed during develop-
.ment of the correlation.
Reference 5.
5|A = Not Applicable.
Reference 6.
elf tank specific information is not available about the secondary
seal on an internal floating roof tank, then assume only a primary
seal ..is present.
9/85 Evaporation Loss Sources 4.3-17
374
-------
L
2
-
9
8
.7
6
5
3
.2
0.1
.09
M
07
001
^—
^
!/
I/
-
rj
/
/
i
/
/
i
.
/
/
i
^
X
I
j.
•
/
Whtrt:
Atmospheric press
1
ill 1
X
Of
f
1 - •
«
ure • 1
1
X
X
/
/
)
py
14.7J
4.7 pour
1
\
r)
ds per v
1
L
/-
/ -
/ -
-
-
1
5
-
-
—
—
^uare in
1
c
ch absol
1
ute. —
•»
;
7
5
5
.
:
2
:; •
09
08
07
06
05
04
03
02
00'
1 2 3 4 5 S 89 10 11
TRUE VAPOR PRESSURE. P (owl
NOTE. Duhed line illustrates sample problem for f - 54 pounds per square inch absolute.
12 13 14
4.3-18
Figure 4.3-9. Vapor pressure function (P*)-5
EMISSION FACTORS
9/85
373
-------
where:
L, = withdrawal loss (Ib/yr) •
Q = throughput (bbl/year) (tank capacity [bbl] times annual turnover
rate)
C = shell clingage factor (bbl/1,000 ft2), see Table 4.3-5
W = average organic liquid density (Ib/gal), see Note 1
u
D = tank diameter (ft)
N- - number of columns (dimensionless), see Note 3
\*
F = effective column diameter (ft) [column perimeter (ft)/7l], see
C Note 4
Notes: (1) If WL is not known, an average value of 5.6 Ib/gallon can be
assumed for gasoline. An average value cannot be assumed
for crude oil, since densities are highly variable.
(2) The constant, 0.943, has dimensions of (1,000 ft3 x gal/bbl2).
(3) For self-supporting fixed roof or an external floating roof
tank:
NC = o.
For column supported fixed, roof:
Nr = use tank specific information, or see Table 4.3-6.
(4) Use tank specific effective column diameter; or
FC = 1.1 for 9 inch by 7 inch builtup columns,
0.7 for 8 inch diameter pipe columns, and
1.0 if column construction details are not
known.
Deck Fitting Loss - Deck fitting loss estimation procedures for external
floating roof tanks are not available. Therefore, the following procedure
applies only to internal floating roof tanks.
Fitting losses from internal floating roof tanks can be estimated by
the following equation6:
(6)
9/85 Evaporation Loss Sources 4.3-19
376
-------
TABLE 4.3-5. AVERAGE CLINGAGE FACTORS (C) (bbl/1,000 ft2)3
Liquid
Gasoline
Single component
, Light rust
0.0015
0.0015
Shell condition
Dense rust
0.0075
0.0075
Gunite lined
0.15
0.15
stocks
Crude oil 0.0060 0.030 0.60
.Reference 5.
If no specific information is available, these values can be assumed
to represent the most common condition of tanks currently in use.
TABLE 4.3-6. TYPICAL NUMBER OF COLUMNS AS A
FUNCTION OF TANK DIAMETER FOR INTERNAL FLOATING
ROOF TANKS WITH COLUMN SUPPORTED FIXED ROOFSa
Tank diameter range Typical number
D (ft) of columns, Nr
0 < D £ 85
85 < D $ 100
100 < D $ 120
120 < D S 135
135 < D £ 150
150 < D $ 170
170 < D S 190
190 < D £ 220
220 < D $ 235
235 < D £ 270
270 < D 5 275
275 < D S 290
290 < D 5 330
330 < D £ 360
360 < D 5 400
1
6
7
8
9
16
19
22
31
37
43
49
61
71
81
Reference 1. This table was derived from a survey
of users and manufacturers. The actual number of
columns in a particular tank may vary greatly with
age, fixed roof style, loading specifications,
and manufacturing perogatives. Data in this table
should not supersede information on actual tanks.
4.3-20 EMISSION FACTORS 9/85
377
-------
where :
L_ = the fitting loss in pounds per year
FF = total deck fitting loss factor (Ib-mole/yr)
= UN L ) + N K- )+...+ (N, IL. )]
Fl Tl F* T* Fn Tn
where:
N_ = number of deck fittings of a particular type
i (i = 0,1,2,..., n) (dimensionsless)
K_ = deck fitting loss factor for a particular type fitting
i (i = 0,l,2,...,n) (Ib-mole/yr)
n = total number of different types of fittings
(dimensionless)
P*, M.., KC = as defined for Equation 4
The value of F_ may be calculated by using actual tank specific data
for the number of each fitting type (N,, ) and then multiplying by the
fitting loss factor for each fitting (1C ).* Values of fitting loss factors
and typical number of fittings are presented in Table 4.3-7. Where tank
specific data for the number and kind of deck fittings are unavailable,
then FF can be approximated according to tank diameter. Figures 4.3-10 and
4.3-11 present F_ plotted against tank diameter for column supported fixed
roofs and self-supporting fixed roofs, respectively.
Deck Seam Loss - Deck seam loss applies only to internal floating roof
tanks with bolted decks. External floating roofs have welded decks and,
therefore, no deck seam loss. Deck seam loss can be estimated by the
following equation:6
(7)
where
LJJ = deck seam losses (Ib/yr)
K_ = deck seam loss per unit seam length factor (Ib-mole/ft yr)
= 0.0 for welded deck and external floating roof tanks,
0.34 for bolted deck
SD = deck seam length factor (ft/ft2)
seam
9/85 Evaporation Loss Sources 4.3-21
378
-------
TABLE 4.3-7. SUMMARY OF INTERNAL FLOATING DECK FITTING LOSS
FACTORS (Kp) AND TYPICAL NUMBER OF FITTINGS (Np)a
Deck fitting type
Deck
fitting loss
factor, IL,
(Ib-mole/yr)
Typical number
of fittings,
N,,
Access hatch
Bolted cover, gasketed
Unbolted cover, gasketed
Unbolted cover, ungasketed
Automatic gauge float well
Bolted cover, gasketed
Unbolted cover, gasketed
Unbolted cover, ungasketed
Column well
Builtup column-sliding cover, gasketed
Builtup column-sliding cover, ungasketed
Pipe column-flexible fabric sleeve seal
Pipe column-sliding cover, gasketed
Pipe column-sliding cover, ungasketed
Ladder well
Sliding cover, gasketed
Sliding cover, ungasketed
Roof leg or hanger well
Adjustable
Fixed
Sample pipe or well
Slotted pipe-sliding cover, gasketed
Slotted pipe-sliding cover, ungasketed
Sample well-slit fabric seal,
10% open area
Stub drain, 1 inch diameter
Vacuum breaker
Weighted mechanical actuation, gasketed
Weighted mechanical actuation, ungasketed
1.6
25b
5.1
15.
28b
47
10
19
32
76°
7.9b
0
44
12b
1.2
0.71
0.9
(see Table 4.3-6)
(5 * -
10 600
D2 c
—)
125
.Reference 1.
If no specific information is available, this value can be assumed to
represent the most common/typical deck fittings currently used.
jD = tank diameter (ft).
Not used on welded contact internal floating decks.
4.3-22
EMISSION FACTORS
9/85
379
-------
8800
aooo
7500
7000
ssoo
5500
5000
4500
4000
3500
3000
2500
2000
1900
1000
500
BOLTED OKX. (S»« NOW)
f, - (0.04*1) 0* * (1.382)0 * 134.2
L/
WELDED DECK
, - (0.0385) O* » (1.382) 0 * 134.2
SO 100 ISO 200 250
TANK DIAMETER. 0 (HI
300
350
*00
BASIS: Finings include: (1) access hatch, with ungaiketed. unbolted cover (2) built-up column wells, with
uagasketed. sliding cover: (3) adjustable deck legs: (4) giuge float well, with ungasketed. unbolted cover. (5)
ladder well, with ungasketed sliding cover. (6) sample well, with slit fabric seal (10 percent open area): (7) I-
inch diameter stub drains (only on bolted deck): and (8) vacuum breaker, with gasketed weighted mechanical
actuation. This basis was derived from a survey of users and manufacturers. Other finings may be typically used
within particular companies or organizations to reflect standards and/or «pec ificai ions of (tut group. This figure
should not supersede information based on actual tank data.
NOTE If no specific information is available, assume bolted decks are [he most common/typical type currently in
use in tanks with column-supported fixed roofs.
Figure 4.3-10. Approximated total deck fitting loss factors V.F-) for
typical fittings in tanks with column supported fixed roofs and either a
bolted deck or a welded deck.6 This figure is to be used only when tank
specific data on the number and kind of deck fittings are unavailable.
9/85
Evaporation Loss Sources
4.3-23
380
-------
4500
«ooo
3500
3000
2500
2000
1SOO
1000
500
BOLTED DECK
F, - (0.0228) D* * (0.79) 0 • 105.2
V
/
WELDED DECK {SM Now)
F, - (0.0132) & - (0.79) 0 * 105.2
too
190
200 250
TANK DIAMETER. 0 (ID
300
ISO
400
BASIS: Finings include: (1) access hatch, with ungasketed. unbolted cover. (2) adjustable deck legs: (3) gauge
float well, with ungaskewd, unbolted cover. (•*) sample well, with slit fabric seal < 10 percent open area): (5) I-
inch diameter stub drains (only on bolted deck): and (6) vacuum breaker, with gasketed weighted mechanical
actuation. This basis was derived from a survey of users and manufacturers. Other finings may be typically used
within particular companies or organizations to reflect standards and/or specifications of thai group. This figure
should not supersede information based on actual tank dau.
NOTES: If no specific information is available, assume welded decks are the most common/typical type currently
in use in tanks with self-supporting fixed roofs.
Figure 4.3-11. Approximated total deck fitting loss factors (.Ff) for
typical deck fittings in tanks with self-supporting fixed roofs and
either a bolted deck or a welded deck.6 This figure is to be used only
when tank specific data on the number and kind of deck fittings are
unavailable.
4.3-24
EMISSION"FACTORS
9/85
381
-------
where:
L = total length of deck seams (ft)
seam
Adeck = area °f deck
D, P*, MV, KC = as defined for Equation 4
If the total length of the deck seam is not known, Table 4.3-8 can be
used to determine S-. Where tank specific data concerning width of deck
sheets or size of deck panels are unavailable, a default value for S~ can
be assigned. A value of 0.20 (ft/ft2) can be assumed to represent the most
common bolted decks currently in use.
TABLE 4.3-8. DECK SEAM LENGTH FACTORS (Sp) FOR TYPICAL
DECK CONSTRUCTIONS FOR INTERNAL FLOATING ROOF TANKS3
Typical deck seam
length factor,
Deck construction SD (ft/ft2)
Continuous sheet construction
5 ft wide 0.20C
6 ft wide 0.17
7 ft wide 0.14
Panel construction
5 x 7.5 ft rectangular 0.33
5 x 12 ft rectangular 0.28
Reference 6. Deck seam loss applies to bolted .decks only.
b .
Sn - -, where W = sheet width (ft)
u W
CIf no specific information is available, these
factors can be assumed to represent the most common bolted
decks currently in use.
» «b-«e W = panel width (ft) and L = panel
length (ft)
382
-------
4.5.4 STORAGE TANK INSPECTION
A storage tank inspection form is shown in Table 4-20. The RACT
for fixed roof tanks is an internal floating cover, but other
equivalent technology may be used on approval. Except for special
installations where vapor recovery or incineration is used, only
inspections at Levels 1 and 2are required for storage tanks.
Special systems may require a Level 3 inspection analogous to the
one for loading terminals described in Appendix D. The RACT require-
ments apply to storage tanks of capacities greater than 150,000
liters (39,600 gal) storing liquids whose true vapor pressure is
greater than 10.5 kiloPascals (1.5 psia).
Once every year or two, when they are empty, most storage
tanks are checked by their owners for corrosion, malfunctioning
seals, and so on. It is also recommended that they be examined
4-55 383
-------
Table 4-17. STORAGE TANK INSPECTION FORM
f CO
en CO
f*C fifty IUA>/£nflpjny -
Fulllty Addrisi — —
Conpiny Contact HIM HIU
Hill LUnit —
Phon.
IriMCtcr Rtprinntlno Phont
(u|uct1« Qit. !!•• 1wp«r»t«t roof tint optnfn^i covtrtd
Sul d*fKU. locttlon
CloctirfW from I«h)
-------
visually as part of Level 2 terminal and bulk plant in-
spections (refer to Sections 4.5.1 and 4.5.2). The following
guidelines summarize the procedures to be followed and may dupli-
cate portions of those sections.
4.5.4.1 Storage Tank Inspection. Level 1
Table 4-18 shows a Level 1 storage tank inspection checklist.
Equipment maintenance and product records should be checked to
learn whether they are adequately kept and whether the required
visual and internal inspections have been performed by the owners.
Visual examination of a selected tank through the roof hatch may be
desirable if jplant records are not adequate (refer to Section
4.5.4.2 for the method).
To ascertain whether or not the control device installed to
meet RACT requirements maintains its control efficiency, records
must be kept by the facility management and made available upon
request to EPA representatives. Records should be kept of the
inspections through roof hatches, recording evidence of any mal-
function. These roof hatch inspections should be performed at
intervals of 6 months or less. If the tank is emptied for mainte-
nance, or for other nonoperational reasons, records of a complete
inspection of the cover and seal must be maintained. The juris-
dictional control agency (EPA, state, or local) should be notified
prior to a complete inspection so that inspectors from that agency
may be present.
A record of the average monthly storage temperature and true
vapor pressure of the petroleum liquid stored should be maintained
if the product has a stored vapor pressure greater than 7.0 kPa
(1.0 psia) and is stored in a fixed roof tank not equipped with an
internal floating roof or alternative equivalent control device.
385
4-57
-------
Table 4-18. STORAGE TANK INSPECTION CHECKLIST, LEVEL 1
[For Tanks Larger Than 150,000 Liters (40,000 gal) Storing
Liquids With True Vapor Pressure Greater Than 10.5 kPa]
Key
1
Inspection Point
Records
RACT Requirements
Inspection through roof
hatches at least twice
yearly.
Whenever tank empty for
maintenance or other non-
operational reason, make
Internal Inspection of
cover and seal .
If no vapor control, main-
tain record of average
monthly storage temperature
and true vapor pressure,
If latter Is greater than
7.0 kPa.
Inspection Procedure
Examine records
Examine records
Examine records
Quick Key
TANK ID
RECORDS
Inspection Findings
en
CO
CO
CO
-------
The true vapor pressure may be determined by the typical Reid vapor
pressure of the stored product, using the average monthly storage
temperature and standard tables, nomographs, or equations.
Each of these records should be kept by the facility manage-
ment and made available upon request of the inspector. If a question
arises on the values reported for a product, analytical data may be
requested of the facility.
If other equivalent means of control are used, such as vapor
recovery, it may be necessary to record the amount of vapor captured,
flow rates, and operating parameters (such as temperatures and
pressures) to establish the day-to-day operating efficiencies. It
should not be, anticipated that this type of information on vapor
recovery systems will be available on the facility's first inspec-
tion.
4.5.4.2 Storage Tank Inspection, Level 2
In addition to the record check performed for Level 1, each
fixed roof tank should be inspected and the checklist given in
Table 4-19 should be completed. Inspectors should, if possible,
climb to the tank roof and visually inspect the roof seals and note
any vents. Under no circumstances should the inspector make such
a climb or perform any other act if plant personnel believe it to
be unsafe or if instrument readings indicate dangerously high
levels of organic vapors or hydrogen sulfide. Concentrations at
vents, flanges, valves, pumps, and relief valves in the tank may
be measured with instruments. Locations with significant concen-
trations should be recorded.
If the tank has an internal floating cover, the seal should
be visually inspected from the roof hatch to identify any obvious
387
4-59
-------
Table 4-19. STORAGE TANK INSPECTION CHECKLIST, LEVEL 2
[For Tanks Larger Than 150,000 Liters (40,000 gal) Storing
Liquids With True Vapor Pressure Greater Than 10.5 kPa]
Key
1
2
3
1
Inspection Point
Records
Internal
floating roof
Floating roof
seal
Openings in
floating roof
RACT Requirements
Inspection through roof
hatches at least twice yearly
Whenever tank empty for main-
tenance or other non-opera-
tional reason, make Internal
Inspection of cover and seal.
If no vapor control, maintain
record of average monthly
storage temperature and true
vapor pressure, if latter is
greater than 7.0 kPa.
Internal floating roof with
a closure seal , or approved
alternate control .
Roof uniformly floating on or
above liquid.
No visible gaps in seal; no
liquid on cover
All openings except stub
drain equipped with lids.
Lids closed except when roof
1s floated off or landed on
leg supports.
Inspection Procedure
Examine records
Examine records
Examine records
Brief visual examination
through* roof hatches
Brief visual examination
through roof hatches
Brief visual examination
through roof hatches for
obvious damage or malfunc-
tion.
Brief, visual examination
through roof hatches
Brief visual examination
through roof hatches
Quick Key
TANK ID
RECORDS
FLOATING ROOF
SEAL
VENTS
Inspection Findings
I
cr>
o
CO
CO
CO
-------
damage such as gaps, tears, or other openings that have a potential
for emission. The inspector should visually inspect whether the
internal roof is floating on or above the liquid and whether there
are visible defects in the surface of the roof or liquid accumu-
lated on it. The seal should be inspected along the entire circum-
ference to assure that it fits tightly to the tank wall and that
no gaps are visible. Conditions of the roof and seal should be
recorded.
389
4-61
-------
2. PROCESS DESCRIPTION
2.1 BULK GASOLINE TERMINAL DEFINITION
The distribution of gasoline and other petroleum liquids is
accomplished by a network of pipelines and tank vehicle transfer routes
that transport these products from refineries to consumer outlets.
Intermediate storage locations are used to transfer the gasoline to
progressively smaller points of distribution. Bulk terminals are
wholesale marketing facilities that receive gasoline from refineries by
pipeline, ship, or barge; store it in large aboveground tanks; and load
it into tank trucks for delivery to bulk plants or retail accounts.
Terminals handle several petroleum products in addition to gasoline,
including diesel fuel, kerosene, and heating oil. Figure 2.1 depicts
the marketing network.
Bulk terminals are distinguished from bulk plants largely by their
higher gasoline throughputs (greater than 20,000 gallons, or 75,700
liters, per day) and storage capacities. Another difference is that
incoming product at a bulk plant generally is delivered by means of tank
vehicles from refineries or bulk terminals.
2.2 LOADING RACKS
Loading racks consist of the equipment necessary to meter and
deliver the various liquid products into delivery tank trucks. A
typical loading rack contains fuel loading arms, pumps, meters, shutoff
valves, relief valves, check valves, electrical grounding, and lighting.
Terminals generally utilize two to four rack positions (loading lanes)
for gasoline, each having one to four loading arms. Gasoline is loaded
through an arm at about 600 gallons (2,270 liters) per minute.
Tank truck loading is performed using either top splash, top
submerged, or bottom loading, although essentially all NSPS terminals
use bottom loading. Top loading is divided into top splash loading,
with or without vapor collection, top submerged, and top tight submerged
390
2-1
-------
Imported
Gasoline
Imported
or
Domestic
Crude
Wholesale
Distribution
Level
Commercial,
Rural
Consumer
II • Storage
= Transport
Figure 2.1 Gasoline distribution in the U.S.
391
2-2
-------
loading (top submerged with vapor collection). Top loading involves
loading of products into the tank via the hatchway located at the top of
each compartment. Gasoline is loaded directly into the compartment
through a top loading fill pipe (splash fill). Attachment of a fixed or
extensible downspout to the fill pipe provides a means of introducing
the product near the bottom of the tank (submerged fill), creating less
turbulence and vapor mist generation than splash filling. Top loading
can also be designed for vapor collection, but a bulk terminal required
to comply with the NSPS is not likely to install (or retain) top loading
equipment.
Bottom loading refers simply to the loading of products into the
cargo tank through adapters located at the bottom. Submerged loading
occurs naturally using this method and turbulence is again held to a
minimum. Some of the advantages of bottom loading include: (1)
improved safety, (2) faster loading, and (3) better emission control
(because of the leakage often associated with top loading systems). The
loading arms are attached to each compartment's loading adapter using
dry-break couplers so that liquid loss is minimized during connecting
and disconnecting. For vapor collection, a flexible hose or swing-type
arm is connected to a vapor collection line on the truck. This line
routes gasoline vapors displaced during the loading operation to vapor
collection and processing systems. Figure 2.2 depicts the three basic
types of tank truck loading described above.
2.3 TANK TRUCKS
Oil companies operating bulk terminals typically operate from 3 to
20 "branded" gasoline tank trucks out of one or more terminals, although
many terminals are served exclusively by "for-hire" tank trucks operated
by other companies. These tank trucks range in size from 4,000 to
10,000 gallons (15,140 to 37,850 liters), averaging about 8,500 gallons
(32,170 liters) capacity. They are divided into four or five individual
compartments, allowing various products (leaded and unleaded gasolines,
diesel, etc.) to be transported in the same cargo tank.
During a bottom loading operation, an internal valve is opened to
allow product flow, and tank vents open to permit the exit of vapors
which are displaced by the incoming product. Vapor collection systems
on tank trucks incorporating bottom loading equipment collect vapors
2-3 392
-------
VAPOR EMISSIONS
GASOLINE . j,
VAPORS / •
i GASOLINE
FILL PIPE
HATCH COVER
VAPORS
TANK TRUCK
COMPARTMENT
CASE 1. SPLASH LOADING
VAPOR EMISSIONS
\
VAPORS Jf
Ul
1
1
FILL PIPE
^^ HATCH COVER
- Dpnnurr -5^ 1 ^ =
TANK TRUC
COMPARTMEh
CASE 2. SUBMERGED FILL
VAPOR VENT
TO RECOVERY
OR ATMOSPHERE
HATCH CLOSED
VAPORS
CASE 3. BOTTOM LOADING
TANK TRUCK
COMPARTMENT
GASOLINE
Figure 2.2 Basic types of tank truck loading.
393 2-4
-------
from the compartment vents through a common vapor manifold, which is
usually one of the two overturn rails running along the top of the tank.
This vapor line terminates at an adapter at the rear (and also sometimes
on the side center) of the tank truck. This adapter allows the driver
to hook up vapor recovery as part of the loading procedure while
standing on the ground. A coupler on the terminal's vapor return line
is compatible with and connects tightly to the truck's vapor fitting.
In order to measure the quantity of gasoline delivered during
bottom loading and to provide protection against overfilling, set-stop
meters are used to shut off the flow of gasoline when a preset amount
has been delivered. Liquid level sensing devices, electrically
connected to close flow control valves and shut off the delivery pumps
if the level approaches the top of the tank, are also commonly used to
provide secondary control in the event of a malfunction or human error.
This overfill protection may consist of fiber optics systems, electric
probe, or float switches.
It was mentioned earlier (Section 2.1) that bulk gasoline
terminals may also handle liquid petroleum products other than gasoline.
VOC emissions from the dedicated loading of fuel oil, diesel, and jet
fuel are essentially negligible compared to emissions from gasoline,
because of the lower volatilities of these products. At many terminals,
"switch loading" of delivery tank trucks is practiced. Switch loading
involves the transport, in a single tank compartment on successive
deliveries, of one or more other products in addition to gasoline.
Gasoline vapors can be displaced from the delivery tank either by
incoming gasoline or by any other liquid product when vapors from a
previous load of gasoline are left in the tank. Thus, VOC emissions can
occur at gasoline loading racks or at product loading racks that switch
load into tank trucks that transport gasoline.
The effectiveness of vapor control systems at bulk terminals is
dependent upon the minimization of leaks in the vapor-containing
equipment. Some gasoline delivery tank trucks have been demonstrated to
be major sources of fugitive vapor leakage during loading operations.
Tank trucks in areas having no tank vapor tightness requirements have
been found to leak approximately 30 percent of the displaced vapors to
the atmosphere, and some of these tanks may lose essentially all of the
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displaced vapors due to leakage. In contrast, the average leakage in
areas requiring vapor tightness certification averages about 10
percent.2 Sources of leakage include hatch covers and gaskets,
pressure-vacuum (P-V) vents, and other components of the tank truck's
vapor collection system. Figure 2.3 shows some common vapor leakage
points on a tank truck.
2.4 VAPOR COLLECTION SYSTEM
The flexible hoses or swing-type arms at the loading racks, which
collect air-vapor mixture from loading tank trucks, are manifolded
together and all of the collected vapors are piped to a single vapor
processor (or, occasionally, to a main processor plus add-on device).
In the case where two tank trucks are loading simultaneously at
different racks, it is possible for the vapors displaced from one tank
truck to pass through the manifold and escape through the other tank.
To avoid this problem, terminals often install check valves to isolate
individual lines and ensure that vapors are routed to the processor.
There are three types of equipment often used in the collection
system between the loading racks and the vapor processor: liquid
knockout tank, saturator tank, and vapor holder. The liquid knockout
tank removes any liquid gasoline that may have entered the vapor line
due to overfilling, condensation, etc. Saturator tanks contain gasoline
spray nozzles to raise the vapor concentration above the explosive
range, and sometimes serve as a preconditioner for certain less-used
types of processors. Vapor holders store air-vapor mixture until some
preset capacity is reached, and then release it to the control system
for processing. This intermittent form of processing minimizes
fluctuations in the vapor load and allows some processors to operate
more efficiently. Generally, a vapor holder consists of a large tank
containing a flexible bladder or lifter roof.
2.5 VAPOR CONTROL SYSTEM
The function of the vapor control system (VCS) is to receive air-
vapor mixture from the collection system and process it in some way so
that emissions to the atmosphere are reduced. These systems are often
referred to as vapor recovery units (VRU) or vapor processors. Systems
395
2-6
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OVERTURN
(VAPOR RETURN)
RAIL1
RUBBER BOOT
OR
ETAL COVER
VENT
VALVE
OVERFILL SENSOR
DOME LID SEAL
BASE RING GASKET
HATCHWAY
TANK SHELL
Figure 2.3 Vapor leakage points on a tank truck compartment
(bottom loading only).
-.7396
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that process vapors into recoverable liquid product include carbon
adsorption and refrigeration systems, as well as various hybrid systems
that operate on the principles of compression and absorption. Thermal
oxidation, or combustion, systems are also in widespread use. These
systems, in the form of either incinerators or flares, do not recover
any product from the vapors. Processor types are described in detail in
Section 4. Figure 2.4 demonstrates the recovery of vapors during tank
truck loading.
2.6 EMISSION POINTS
At a bulk terminal without vapor collection and control systems,
hydrocarbon vapors are displaced directly to the atmosphere during
product loading, the emission rate being determined largely by the type
of loading. Top splash loading creates a turbulent liquid surface that
causes the entrainment of gasoline mist and droplets into the vapor
space. In submerged fill or bottom loading, there is much less
turbulence and entrainment, and emissions are reduced. In response to
State regulations, tank trucks are often unloaded at bulk plants and
service stations using a closed piping system to contain the storage
tank's vapors and transfer them to the tank truck as it is emptied of
liquid product. Using this system, the VOC vapors that would otherwise
have been emitted are "balanced" into the tank truck. Tank trucks
practicing vapor balance (also termed Stage I control) return to the
terminal with a high concentration of vapors that can approach
saturation, which increases the emission rate over that without vapor
balance. Bulk terminal vapor control and Stage I are generally used
together in the same area to form a complete emission control program.
The emissions from controlled loading operations depend on the
control efficiency of the vapor processor and on the amount of leakage
(fugitive losses) from the vapor collection system. Fugitive leakage
from tank trucks during loading was discussed earlier (Section 2.3).
Such leaks can occur from any of the vapor-containing components
installed at the top of each compartment, including hatch covers and
vent valve covers. Another source of leakage is the interface between
the tank truck's vapor adapter and the terminal's vapor return line
coupler.
3972-8
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VAPOR RETURN LINE
03
to
00
VAPOR-FREE
AIR VENTED
TO
ATMOSPHERE
VAPOR
RECOVERY
UNIT
RECOVERED PRODUCT
TO STORAGE
PRODUCT FROM
LOADING TERMINAL
STORAGE TANK
Figure 2.4 Tank truck loading with vapor collection and recovery,
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In top loading vapor collection systems, a significant potential
source of leakage is the interface between the top loading vapor head
and the tank truck hatch. The vapor heads are designed to seal at the
hatch through the compression of a cone-shaped rubber ring. However,
these seals can develop flaws and a complete seal is often difficult to
achieve. The terminal's flexible vapor return lines may develop leaks
through damage or gradual wear, or can leak at the clamps that attach
them to the vapor manifold line. P-V vents on knockout (condensate)
tanks and vapor holders are leakage sources if they do not close fully
due to dirt or damage. The bladder in a vapor holder may eventually
crack or tear and can become a serious source of leakage.
The vapor processor itself is not often a source of fugitive
leakage emissions. However, any piping joint in the collection system,
including flanges where the processor is connected, can leak due to
improper installation or a damaged gasket. Process emissions consist of
the control system exhaust emission rate as measured in the most recent
performance test, although for calculation purposes it is often assumed
to be the applicable regulatory limit of either 80 or 35 milligrams of
total organic compounds (or of VOC) per liter of gasoline loaded (see.
Section 3.3)
The EPA's Office of Air Quality Planning and Standards (OAQPS) has
prepared two Control Techniques Guidelines (CTG) documents3'4, which
discuss reasonably available control technology (RACT) for bulk terminal
process emissions and for tank trucks and vapor collection systems. The
bulk terminal CTG prescribes a vapor processor that will achieve
emissions of 80 mg/liter. The tank truck CTG restricts the amount of
fugitive vapor and liquid leakage allowable from tank trucks and
collection systems, as indicated by a tank truck pressure/vacuum test
and monitoring of potential leak sources using a combustible gas
detector.
The bulk terminal NSPS uses the CTG recommendations as a starting
point, and then builds on them to create a scheme that employs the best
controls available, considering all other impacts. Therefore, many of
the NSPS requirements are very similar to those contained in State
regulations, and the NSPS inspection will parallel the inspections
traditionally performed by State and local agency personnel to enforce
the RACT-based rules.
3992-10
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INSPECTION OF GASOLINE TERMINALS AND BULK PLANTS
Baseline and Diagnostic Data
3.2. Baseline and Diagnostic Inspection Data
3.2.1 General Information
0 Method of refueling facility (e.g. pipeline, truck)
0 Gasoline throughput, annual total and daily maximum
0 Number of loading racks and loading arms
0 Types of loading arms
0 Average number of trucks loaded per day
0 Fraction of trucks returning with vapor
0 Types and capacities of storage tanks
0 Presence of vapor holding tank
3.2.2 Carbon Bed Vapor Recovery System
0 Maximum vacumn
0 On-line carbon bed temperatures
0 Gasoline supply temperature
0 Absorption gasoline supply pump pressure
0 Absorption gasoline return pump pressure
0 Carbon bed cycle times
0 Carbon bed outlet VCC concentrations
3.2.3 Refrigeration Vapor Recovery Systems
0 Second stage chamber temperature
0 Brine, coolant, and defrost pump pressures
3.2.4 Thermal Incinerator Vapor Recovery Systems
0 Outlet gas temperature
0 Presence of visible emissions
32
400
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INSPECTION OF GASOLINE TERMINALS AND BULK PLANTS
Routine Inspection Data
3.3 Routine Inspection Data
3.3.1 General Information
0 Type of products being handled
0 Fill rates
0 Vapor recovery system outages since last inspection
3.3.2 Level 2 Inspections
Fugitive Leaks (during loading of one or more trucks)
0 Presence of any visible, odorous, or audible
vapor leaks or spills
0 Vapor line is connected to truck during loading,
0 Unconnected vapor lines at other loading
not in service are closed
0 Truck relief valves do not open during loading
0 Top-loading nozzle grommet in good physical condition
and is seated properly against filling port
0 Top seal remains tight during loading and truck settling
0 Truck tank fill sensor is connected to automatic shutoff
0 Loading of distillate fuels into trucks previously
containing gasoline is not being done at loading racks
not connected to vapor recovery system.
Inspection of Vapor Recovery Systems - General
0 Confirm that vapor recovery system is operating
during truck loading or when vapor accumulator is full
0 Confirm that accumulator pressure relief valve is not
stuck open and emitting VOC materials
8 Confirm that level indicator is rising during truck
loading, if the vapor recovery system is not operating.
Carbon Bed Vapor Recovery Systems
0 Maximum vacumn during operation of each bed
0 On-line carbon bed temperatures
0 Absorption gasoline supply pump pressure
0 Absorption gasoline return pump pressure
0 Gasoline supply temperature
0 Verify that unit operates during truck loading or
when vapor accumulator is full
33
401
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INSPECTION OF GASOLINE TERMINALS AND BULK PLANTS
Routine Inspection Data (Continued)
Thermal Incinerator Vapor Recovery Systems
0 Outlet gas temperatures
0 Verify that unit operates during truck loading or
when holding tank is full
Refrigeration Vapor Recovery Systems
0 Temperature readings for second stage chamber*
0 Brine, coolant, and defrost pump pressures
Storage Tanks (Inspect one or more)
0 Examine internal floating roofs through roof hatch
to determine obvious damage or malfunctions.
3.3.3 Level 3 Inspections
Fugitive Leaks (during loading of one or more trucks)
0 All inspection points listed under, ,Section 3.3.2
0 Measure VOC concentrations near (1 (MB.) top-loading
seal and loading arm joints
0 Measure VOC concentration near (I'-em.) vapor line
connections. ,
0 Measure VOC concentration near (1'es.) near truck
pressure-relief valve
0 Measure VOC concentration near (lea.) all truck
top hatches
Vapor Recovery System - General
0 All inspection points listed in Section 3.3.2
0 Measure VOC concentration near (1 cm.) accumulator
pressure relief valve
0 Measure VOC concentration near (1 cm.) all flanges
and joints in vapor line to accumulator and to
vapor recovery system
Carbon Bed Adsorber Vapor Recovery Systems
0 All inspection points listed in Section 3.3.2
0 Measure VOC concentration (1 to 2 cm.) at outlet of
each bed near the end of the adsorption cycle
Refrigeration Systems and Thermal Incinerator Vapor
Recovery Systems
0 All inspection points listed in Section 3.3.2.
34
402
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INSPECTION OF GASOLINE TERMINALS AND BULK PLANTS
Inspection Procedures
3.4. Inspection Procedures
There are two levels of inspection for Gasoline distribution
terminals and bulk plants. A Level 2 inspection consists
primarily of a walk through inspection to confirm that all
engineering controls necessary to minimize visible emissions
are being used'. Also, an evaluation of the vapor recovery
systems is performed using on-site gauges. The Level 3
inspection involves the use of portable VOC monitoring
instruments to determine if there are any measureable fugitive
emissions and if the VOC emissions from the vapor recovery
systems are the within normal range.
3.4.1 General Information
Review the facilities operating records.
0 Determine the types of products being loaded into trucks
during the inspection. Compare this with the types of
products loaded since the last inspection to confirm that
operating conditions during the inspection are actually
representative of normal conditions.
0 Determine the peak loading rates to determine if the
vapor recovery system is potentially being overloaded.
0 Examine operating logs and maintenance records to
determine the extent of vapor recovery system downtime
since the last inspection. All organic vapors are emitted
when the vapor recovery system is not operated.
Check for any facility modifications.
0 Check for modifications to loading racks
0 Check for modifications to storage tanks
3.4.2 Level 2 Inspections
Fugitive Emissions from Trucks and Loading Racks
Check vapor return line connections
Inspect and verify the presence of a vapor collection line
at the account truck vapor port, the connection pipe at the
loading rack, and the inlet lines to stationary storage
tanks.
35
403
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INSPECTION OF GASOLINE TERMINALS AND BULK PLANTS
Inspection Procedures
Note any potential gasoline vapors leak sources.
Carefully observe one or more truck loadings to determine
if there are any potential leak sources. The most common
sources include:
(1) unconnected vapor return lines from trucks
(2) open vapor lines at other loading racks
(3) open truck pressure-relief lines
(4) poor top-loading truck nozzle seals
(5) pooc truck hatch covers
Leaks at any of these locations when allow gasoline vapor
to escape to the atmosphere rather than being pushed to the
vapor recovery system. Since the static pressures through-
out the vapor balance system is 2 to 16 inches W.C., even
small leaks can result in substantial emissions. Note all
odors, visual leaks, and audible leaks.
Check top-loading fill pipe extension.
Verify that the discharge is is within 6 inches o'f the bottom.
Check diameter of vapor return line to recovery system.
Locate and observe the use of an adequately sized vapor
return line. 'This should be properly sized properly for the
number of trucks loaded at peak periods.
Vapor Recovery System - General
Check the operation of the vapor accumulator (if present).
The level indicator should increase whenever the vapor
recovery system is not operating and one or more trucks are
being loaded.
Check the pressure-relief valve the accumulator.
Look for any visible emissions (vapor light refraction
lines) which indicate that this valve is stuck in the open
position. The presence of emissions also indicates that
there is leakage through the diaphragm of the accumulator.
Check for visible symptoms of emissions
Check for vapors light refraction lines from emergency
vent stacks and from holding/knockout tank vent.
36
404
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INSPECTION OF GASOLINE TERMINALS AND BULK PLANTS
Inspection Procedurs
Carbon Bed Vapor Recovery System
Check for system activation during truck loading.
For facilities without vapor accumulators (hold tanks),
the carbon bed system should be running during gasoline
transfer operations. For facilities with the accumulators,
the carbon bed system should run "whenever the tank level
is within a preset range.
Check for visible symptoms of vapor emission.
Observe the exhaust ports from both beds during the end
of the absorption cycle (usually 15 to 20 minutes duration).
Visible light refraction lines suggest higher than
normal VOC emissions and carbon bed operating problems.
Verify regeneration vacuum of_ 27_ ££ 2§. inches of mercury.
The regeneration vacuum should gradually reach 27 to 28
inches of mercury during desorption of each bed. Lower
levels of vacuum indicate that less than the necessary
amount of the adsorbed gasoline is being removed from the
bed. During the next adsoption cycle, there may be
insufficient active sites available to adequately remove
organic vapors.
Check carbon bed operating temperatures during adsorption.
Record dial-type thermometer readings near the end of each
adsorption cycle and during the air stripping of the carbon
beds during regeneration. If the bed temperatures during
adsorption are low (very close to ambient temperatures),
there is probably very little removal of organic vapor.
Adsorption is an exothermic process and is indicated by
slightly increased temperature.
Check gasoline supply temperature to absorber tower.
Verify that the gasoline supply temperature to the absorp-
tion tower is less than 100 °F. This is necessary to ensure
adequate absorption of the gasoline vapors stream removed
from the carbon beds.
37
405
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INSPECTION OF GASOLINE TERMINALS AND BULK PLANTS
Inspection Procedures
Verify that the gasoline absorption cycle is operational.
Verify operation of the gasoline absorption cycle by
recording the gasoline supply pump and gasoline return
pump pressures. Measurable pressures indicate that the
absorption cycle is working. The flow of gasoline to the
absorption tower is inversely related to the pressure for
a given pump.
Note any system warning lights.
All warning lights should be noted since these indicate
system malfunction. Ask the facility manager to explain
the possible impact of the indicated malfunction on the
system VCC collection efficiency.
Record Clock meter readings.
The total operating time of the vapor"recovery system
should be compared with previously recorded values
observed in earlier inspections. This data is used to
determine if the system has had excessive downtime.
Refrigeration Vapor Recovery Systems
Check the present operating temperature of the system.
This is checked using the system temperature recorder.. If
the unit is operating in the previously observed temperature
range (usually -90 to -120 °F), then other refrigeration
system components are probably operating properly. The
removal of VOC materials is directly proportional to the
operating temperature - the colder the better.
Evaluate temperature strip charts.
These are evaluated to identify any chronic high temper-
ature conditions. Ask the facility manager to explain
any problems which are preventing proper operating
temperatures in the refrigeration system.
Evaluate defrosting practices.
Confirm that the units are being defrosted on at least a
daily basis. All refrigeration units are subject to frost
problems which can ultimately have an adverse impact on
the VOC removal efficiency and the system availability.
38
406
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INSPECTION OF GASOLINE MARKETING AND BULK PLANTS
Inspection Procedures
Note any system warning lights.
These are indications of system malfunctions and should
be carefully noted. Ask the facility manager to explain
the potential impact of the indicated problem on system
efficiency and downtime.
Thermal Incinerators
Check system activation.
Confirm that the burner is ignited whenever the accumulator
is full and/or a truck is being loaded.
Check the outlet temperature.
The outlet temperature is generally 1400 °F. This can be
confirmed by use of the thermocouple installed either in the
stack or in the combustion chamber. Low outlet temperatures
indicate low efficiency combustion or flame out of the burner,
Check for visiblg emissions.
Black smoke indicates severe burner maladjustment or
fouling. Poor VOC destruction and objectionable smoke
result from the poor burner maintenance.
Storage Tanks
Examine Internal floatina roofs.
Examine internal floating roof in one or more fixed roof
storage tanks to determine the the presence of any physical
damage or malfunctions. It is important that inspectors
avoid inhalation of high concentrations of organic vapor
during this step.
Examine pressure-relief valves and vents.
Note any visible symptoms of VCC emission from these vents.
3.4.2 Level 3 Inspections
Level 3 inspections include all of the inspection described
above for Level 2 inspections. In addition, portable VOC
monitors are used to evaluate fugitive emissions and to
evaluate the performance of vapor recovery systems.
39
407
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INSPECTION OF GASOLINE TERMINALS AND BULK PLANTS
Inspection Procedures
The types of instruments generally used at gasoline
terminals and bulk plants include: (1) explosimeters,
(2) catalytic combustion instruments, and (3) flame ionization
detectors. Since these have different VOC concentration units,
care is necessary in determining what is and is not a leak in
accordance with the applicable regulation.
Instrument Check-out
Check-out Instrument(s) Before Leaving for Inspection Site.
All VOC detectors to be used during the inspection should
be fully checked before arriving at the facility. The
checks include:
0 Batteries or battery packs are fully charged
0 All probe assemblies are complete
8 All flame arrestors are present and in
good physical condition
0 All instruments are intrinsically safe
0 All necessary spare parts are packed
Calibrate instruments.
VOC detectors used for gasoline terminals and bulk plants
are generally calibrated using propane or butane. These
are most similar to the compounds emitted.
Evaluation of Fugitive Emissions
Measure VOC concentrations of potential truck leaks.
Measure VOC concentrations near (1 cm.) all truck pressure-
relief valves, vapor line connections, top-loading hatch
seals (if present), bottom-loading connections (if present),
and truck hatches. Measure emissions from pressure-relief
valves in the approximate center of the valve outlet. All
hatch and connection measurements should be made by travers-
ing the entire circumference. Complete all measurements
before each compartment of the truck is filled in case the
automatic shutoff is not working properly.
Measure VOC concentration cm loading racks.
Measure VOC concentrations near (1 cm.) all loading rack
line joints/connections and on all vapor return line
joints/connections.
403
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INSPECTION OF GASOLINE TERMINALS AND BULK PLANTS
Inspection Procedures
Evaluation of Vapor Recovery Systems - General
Measure the VOC concentrations from potential leak sources
on the vapor accumulator.
Measure the VOC concentrations from all pressure-relief
valves and vents on the vapor accumulator.
Evaluate Carbon Bed Adsorber System Performance
Measure the VOC concentration from each bed.
The VOC concentration of the exhaust from each bed
should be less than 1000 ppm (explosimeter: 0.05 to 0.10)
Higher concentrations indicate that the bed(s) is not
removing organic vapors at the efficiency intended.
Possible problems include inadequate regeneration and/or
gradual accumulation of high molecular weight materials
which can not be desorbed.
Evaluation of Refrigeration System Performance
VOC instruments are generally not applicable.
The VOC concentrations from refrigeration systems are
usually in the range of 10,000 ppm to 30,000 ppm which
is equivalent to approximately 90 to 95% control
efficiency. These concentrations are above the normal
operating range of VOC detectors.
Evaluation of Thermal Incinerator Performance
VOC instruments are generally not applicable.
The exhaust temperatures from incinerators are
several hundred degrees Fahrenheit above the allowable
maximum temperatures for the VOC instrument probes.
41
409
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