PB88-165683
A SELECTION GUIDE FOR VOLATILIZATION
TECHNOLOGIES FOR WATER TREATMENT
IT Corporation
Knoxville, TN
Feb 88
, U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
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PB08-16568J
EPA/600/2-88/014
February 1988
A SELECTION GUIDE FOR VOLATILIZATION
TECHNOLOGIES FOR WATER TREATMENT
By
Jeffrey L. Fleming
IT Corporation
Knoxville, Tennessee 37923
EPA Contract No.
68-03-3069
Project Officer
Michael D. Royer
Hazardous Waste Engineering Research Laboratory
Releases Control Branch
Edison, New Jersey 08837
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA/600/2-88/014
TITLE AND SUBTITLE
A Selection Guide for Volatilization
Technologies for Water Treatment
5. REPORT DATE
February 1988
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO,
Jeffrey L. Fleming
PERFORMING ORGANIZATION NAME AND ADDRESS
IT Corporation
312 Directors Drive
Knoxville TN 37923
10. PROGRAM ELEMENT NO.
11. CON
RANT NO.
68-03-3069
2. SPONSORING AGENCY NAME AND ADDRESS
Hazardous Waste Engineering Research Laboratory
Office of Research and Development
US Environmental Protection Agency
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final 2/84-6/84
14. SPONSORING AGENCY CODE
EPA/600/12
5 SUPPLEMENTARY NOTES
Project Officer:
Michael Royer
201-321-6633
6. ABSTRACT
Thie guide presents a methodology for evaluating applicability of volatilization technologies for removing volatile
organics from water. The volatilization technologies assessed in this study include: surface sprayers, surface aerators.
bubble columns, cooling towers, steam strippers, unaided evaporation from an impoundment, spray columns, and packed air
stripping columns. The guide enables users to assess performance and cost under a variety of operating conditions (e.g..
temperature, influent concentration, allowable liquid and gas effluent concentration, and flow rates) for representative
equipment designs that could be transported on a trailer 2.4 m wide, 13.7 m long, with a maximum height of 4.1 m. The
designs are used as a basis to calculate representative contaminant removal efficiency, treatment rates, air emissions, and
treatment costs of each technology. A key parameter used in assessing these technologies is the Henry's Law constant (H).
tabulation of available values of H is provided for volatiles designated as hazardous by the Comprehensive Environmental
Response. Compensation, and Liability Act (CERCLA). Methods for estimating H are also described. Qualitative guidance is
provided on other factors that should be considered during site-specific assessments of the technical and economic feasibility
of volatilization technologies. Offgas treatment is not described. An example problem is solved to demonstrate the methodology
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
18. DISTRIBUTION STATEMENT
Release to public
IB. SECURITY CLASS (THIS Report)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS
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NOTICE
The information in this document has been funded wholly or in part by
the United States Environmental Protection Agency under Contract No.
68-03-3069 to IT Corporation. It has been subjected to the Agency's peer
and administrative review, and it has been approved for publication as an
EPA document.
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
ii
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ABSTRACT
This guide presents a methodology for evaluating applicability of
volatilization technologies for removing volatile organics from water.
The volatilization technologies assessed in this study include: surface
sprayers, surface aerators, bubble columns, cooling towers, steam
strippers, unaided evaporation from an impoundment, spray columns, and
packed air-stripping columns. The guide enables users to assess
performance and cost under a variety of operating conditions (e.g.,
temperature, influent concentration, allowable liquid and gas effluent
concentration, and flow rates) for representative equipment designs that
could be transported on a trailer 2.4 m wide, 13.7 m long, and with a
maximum height of 4.1 m. The designs are used as a basis to calculate
representative contaminant removal efficiency, treatment rates, air
emissions, and treatment costs of each technology. A key parameter used
in assessing these technologies is the Henry's Law constant (H). A
tabulation of available values of H is provided for volatiles designated
as hazardous by the Comprehensive Environmental Response, Compensation,
and Liability Act (CERCLA). Methods for estimating H are also described.
Qualitative guidance is provided on other factors that should be
considered during site-specific assessment of the technical and economic
feasibility of volatilization technologies. Offgas treatment is not
described. An example problem is solved to demonstrate the methodology.
This document is submitted in fulfillment of EPA Contract No. 68-03-3069
(MOD-29) by IT Corporation under the sponsorship of the U.S. Environmental
Protection Agency. This report covers the period of February 1, 1984 to
June 29, 1984. Work was completed as of June 29, 1984. The document was
edited in partial fulfillment of EPA contract No. 68-03-3255 by
Enviresponse, Inc. under the sponsorship of the U.S. Environmental
Protection Agency.
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FOREWORD
Today's rapidly developing and changing technologies and industrial
practices frequently carry with them the increased generation of solid and
hazardous wastes. These materials, if improperly dealt with, can threaten
both the public health and the environment. Abandoned waste sites and
accidental releases of toxic and hazardous substances also have important
health and environmental implications. The Hazardous Waste Engineering
Research Laboratory assists in providing an authoritative and defensible
engineering basis for assessing and solving these problems. Its products
support the policies, programs, and regulations of the Agency; the
permitting and other responsibilities of the state and local government;
and the needs of both large and small businesses in handling their wastes
responsibly and economically.
This document describes methods for evaluating the applicability of
various volatilization technologies for removing organic chemicals from
contaminated water. The information generated from this program will be
useful to both government officials and industry members concerned with
this aspect of water pollution control.
For further information, please contact the Land Pollution Control
Division of the Hazardous Waste Engineering Research Laboratory.
Thomas R. Hauser, Director
Hazardous Waste Engineering Research Laboratory
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CONTENTS
Notice ii
Abstract iii
Foreword iv
Figures vi
Tables viii
Symbols ix
Conversion Factors x
1. Introduction 1
How to use this guide 1
Limitations of the guide 4
Volatilization of organic compounds from water: A review ... 5
2. Site Characterization 10
Instructions and explanations 10
3. Material Properties and Estimation Methods 13
Estimation methods 13
4. Technology Evaluation 17
Organic removals 17
Time requirements for removal 26
System emissions 40
Cost data 40
5. Design Bases 50
Volatilization from surface impoundments 50
Description of model impoundment and
volatilization enhancement systems 51
Air-stripping columns 60
Considerations for air-stripping equipment evaluation 90
Distillation systems 91
Description of model system 94
Considerations for steam-stripping equipment evaluation ... 102
6. Factors Affecting Evaluation 103
Material-specific factors 103
Site-specific factors 105
References 107
Appendices
A. Example 109
B. Material Properties Ill
C. Lower Flammability Limits 117
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FIGURES
Number Page
1 Decision tree for volatilization process selection 3
2 Bubble column design basis, organic removal, parallel
operation 18
3 Bubble column design basis, organic removal, series
operation (4 columns) 19
4 Spray column design basis, organic removal, parallel
operation 20
5 Spray column design basis, organic removal, series
operation (4 columns) 21
6 Packed air-stripping column design basis, organic removal,
single column operation 22
7 Cooling tower design basis, organic removal, parallel
operation 23
8 Cooling tower design basis, organic removal, series
operation (4 columns) 24
9 Packed column steam stripper design basis, organic
removal 25
10 Half-life in model impoundment, batch systems 27
11 Number of half-lives required to obtain removals 28
12 Half-life in model impoundment, bubble column design
basis, parallel operation 30
13 Half-life in model impoundment, bubble column design
basis, series operation 31
14 Half-life in model impoundment, spray column design
basis, parallel operation 32
15 Half-life in model impoundment, spray column design
basis, series operation 33
16 Half-life in model impoundment, packed column air
stripper, design basis 34
17 Half-life in model impoundment, cooling tower design
basis, parallel operation 35
vi
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18 Half-life in model impoundment, cooling tower design
basis, series operation . 36
19 Half-life in model impoundment, steam stripper design basis .... 37
20 Impoundment batch volatilization systems 52
21 Typical configuration for a surface spray unit. 54
22 Typical configuration for a floating high-speed surface
aeration unit 57
23 Psychrometric chart 62
24 Bubble column design, schematic 65
25 Bubble column design basis, process flow diagram 66
26 Bubble column design basis, side, top, and rear views 67
27 Spray column design basis, schematic 71
28 Spray column design basis, process flow diagram 72
29 Spray column design basis, side, top, and rear views 74
30 Packed-column air stripper, design basis schematic 78
31 Packed-column air stripper, design basis, process flow diagram. . . 79
32 Packed-column air stripper, design basis, side, top,
and on-road views 80
33 Cooling tower design basis, schematic 84
34 Cooling tower design basis, side view 85
35 Steam stripper design basis, process flow diagram 95
36 Steam stripper design basis, plan view 97
37 Flooding in a packed tower steam stripper 98
vii
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TABLES
Number Paqe
1 Henry's Law constant conversion factors 8
2 Checklist for site evaluation 11
3 Time required for treatment of model impoundment, recycle
discharge to pond 38
4 Time required for treatment of model impoundment, off-site
discharge available 39
5 Emissions from air stripping processes 41
6 Air emission rate from model steam stripper 42
7 Mechanical agitator capital costs 42
8 Air stripper capital costs 44
9 Steam stripper capital costs 46
10 Mobilization and demobilization costs 47
11 Operating costs 48
12 Characteristics of technologies for batch treatment
of an impoundment 59
13 Bubble column design case operating conditions 68
14 Spray column design case operating conditions 75
15 Packed air stripping column design case operating conditions ... 81
16 Cooling tower design case operating conditions 86
viii
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LIST OF SYMBOLS*
C -- concentration (mole fraction/mole fraction, wt % or
gmol/m3)
f -- fraction remaining (mole fraction/mole fraction)
G -- gas flow rate (cfm or moles/hour)
h -- humidity
H -- Henry's Law constant (mole fraction/mole fraction)
AHv -- heat of vaporization
i -- component in solution
KL overall mass transfer coefficient (m/hr)
k-j -- liquid phase mass transfer coefficient (m/hr)
kg -- gas phase mass transfer coefficient (m/hr)
L -- liquid flow rate (gpm or moles/hr)
N -- number of stages in a column
P -- pressure (atm, mm Hg, in water)
Pj -- partial pressure of component in vapor (atm, mm Hg,
in water)
Pj -- total pressure (atm, iron Hg, in water)
R -- universal gas constant (1.987 cal/gmol °K, 0.7302
(atm-ft3)/(lbmol °R), 8.2 X 10-5m3atm/gmol °K)
S -- stripping factor (HG/L)
t -- time (hours, minutes, days)
T -- temperature (°F, °C, °K, °R)
th -- half-life (hours)
V -- volume (gallons, liters, nr, ftj)
X^ -- mole fraction of component i in liquid phase
YJ -- mole fraction of component i in vapor phase
Mw -- molecular weight . .
s -- specific surface area of liquid phase (nr/nr)
al,2 -- relative volatilities of components 1 and 2
* These symbols are the author's and not necessarily standard symbols.
ix
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CONVERSION FACTORS
Metric to U.S. Customary
Metric
Name
centimeter (s)
centimeter (s) per hour
cubic meter
cubic meters per day
cubic meters per hectare
cubic meters per second
degrees Celsius
gram(s)
hectare
Joule
kilograin(s)
kilograms per hectare
kilograms per hectare
per day
kilograms per square
centimeter
kilometer
kilowatt
liter
liters per hectare per day
liters per second
megagram (metric tonne)
megagrams per hectare
mega^oule
megaliters (liters x 10 )
meters (s)
meters per second
micrograms per liter
milligrams per liter
nanograms per liter
Newtons per square
centimeter
square centimeter
square kilometer
square meter
Symbol
cm
cm/h
n,3
m3/d
m3/h»
mVs
c
g
ha
J
*9
kg/ha
kg/ha -d
kg/cm2
km
kW
L
L/ha d
L/s
Mg(or t)
rag/ha
MJ
ML
m
m/s
ug/L
mg/L
ng/L
N/cm2
cm2
km2
m2
Multiplier
0.3937
0.3937
8.1071 x 10-*
35.3147
264.25
2.6417 x 10"*
1.069 x 10'4
22.82
1.8CC) + 32
0.0022
2.4711
0.004
9.48 x 10~4
2.205
0.0004
0.893
14.49
0.6214
1.34
0.0353
0.264
0.11
0.035
22.826
15.85
0.023
1.10
0.446
0.278
0.264
3.2808
2.237
1.0
1.0
1.0
1.45
0.155
0.386
10.76
U.S.
customary
Abbreviation
in.
in./h
acre- ft
ft3
Mgal
Hgal/d
Hga I/acre
Hgal/d
P
Ib
acre
mi2
Btu
Ib
tons/acre
lb/acre-d
lb/in.2
mi
hp
ft3
gal
gal/acre-d
ft3/s
gal/d
gal/min
Hgal/d
ton (short)
tons/acre
kWh
Mgal
ft
mi/h
ppb
ppm
ppt
lb/in.2
in.2
mi2
ft2
unit
Name
inches
inches per hour
acre- foot
cubic foot
million gallons
million gallons
per day
million gallons
per acre
million gallons
per day
. degrees Fahrenheit
pound (s)
acre
square miles
British thermal unit
pound (s)
tons per acre
pounds per acre per day
pounds per square inch
mile
horsepower
cubic foot
gallon (s)
gallons per acre per day
cubic feet per second
gallons per day
gallons per minute
million gallons per day
ton (short)
tons per acre
kilowatt hour
million gallons
foot (feet)
miles per hour
parts per billion
parts per million
parts per trillion
pounds per square inch
square inch
square mile
square foot
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SECTION 1
INTRODUCTION
The purpose of this guide Is to aid In determining whether a
particular volatilization technology can successfully remove organic
contaminants from water. It describes the performance evaluation of
common volatilization technologies and provides an approach for selecting
the appropriate technology for a given situation. Data necessary for the
evaluation are described and, whenever possible, background data are given
for selected hazardous organics. In addition to being useful for
equipment selection, it can be used as an educational tool for background
data on volatilization technologies or as a decision-making tool for
purchasing a mobile technology.
The impetus for developing a guide stems from involvement of the
Hazardous Waste Engineering Research Laboratory's Releases Control Branch
in technical assistance activities that require assessment of the
feasibility and cost of various treatment options. It was recognized that
EPA On-Scene Coordinators (OSC) and their technical support personnel are
often faced with changing or uncertain conditions that could affect the
cost and feasibility of removing volatile substances from water. As
conditions change or as some of the uncertainties are resolved, the OSC's
technical support personnel are called upon to revise their estimates
accordingly. It was recognized that the OSC and their technical support
staffs did not have a concise guide on the subject of volatilization
technologies and their application to spill cleanup operations.
People with some technical training in chemistry and thermodynamics,
but limited experience in participating or coordinating cleanup activities
at uncontrolled hazardous waste sites will find the guide useful. (A
review of volatilization is provided for those with little experience in
this area or who may need a refresher.) OSC can use this guide to reduce
duplication of effort, accelerate the production of cost and performance
estimates for decision-makers, and promote consistency in estimation
procedures. Technical personnel who support the OSC by developing cost
and performance estimates for water treatment options are the principal
target audience for this guide.
HOW TO USE THIS GUIDE
This guide assists the reader to apply a five-phase process for
evaluating the applicability of a volatilization technology:
Phase 1. Preliminary assessment of the feasibility of volatilization
Phase 2. Site characterization
Phase 3. Calculation of basic material properties
Phase 4. Technology evaluation
Phase 5. Equipment selection
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The flow chart in Figure 1 shows the technology selection process In
greater detail and Indicates the pertinent sections of the guide for each
step of the selection process.
Phase 1 Is a preliminary assessment to determine the feasibility of
utilizing volatilization technologies for water pollution control.
Normally, volatilization Is only considered for removing low
concentrations of volatile materials. Water with a high percentage of
organics should be disposed of In some other manner. Further, compounds
that will volatilize at a rate close to or below the evaporation rate of
water are not likely candidates for volatilization.
Phase 2, site characterization (Section 2), requires a complete
evaluation of the site as a necessary part of the selection process. A
checklist of important site data for the evaluation is provided.
Phase 3, calculation of basic material properties (Section 3),
involves determining the properties of the spilled material. Several
properties of selected compounds are provided; however, for a variety of
different organics, other sources must be used to determine the properties
of the spilled material. Some of these sources are provided in the
references; readers are advised to contact the chemical manufacturer if
data are not available.
The technology evaluation phase (Phase 4, found in Section 4) is
designed to eliminate technologies from consideration at each evaluation
step, thus avoiding additional work on technologies that are not suitable
for the application. The technology evaluation process eliminates systems
based on a sequential evaluation of:
1. Removal ranges
2. Flowrate and time requirements for treatment
3. Emissions generated by treatment
Technologies still under consideration after the evaluation of these
parameters should then be examined on the basis of their costs. Costs for
pretreatment, disposal of treated water, emission controls, and water
polishing units (not addressed in this guide) should be added to costs for
treatment by volatilization as given in Section 4. Based on the problems
inherent in providing accurate cost estimates, it is recommended that cost
differences exceed a factor of two before eliminating a technology.
Phase 5, equipment selection (Sections 5 and 6), is the final step in
selecting a treatment unit for use at a site. This is a complex decision
for which no summary method is possible. Data in these sections are
designed to provide background information on the available technologies
in order to help the on-site field worker make an intelligent selection.
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PRELIMINARY ASSESSMENT
I PHASE I
DETERMINE APPLICABILITY OF VOLATILIZATION I
SECTIONS 1 AND 2 j
ITS CHARACTERIZATION
PHASE 2
~| COLLECT DATA ON THE SITE
SECTION 2
DEVELOP REQUIREMENTS FOR THE TREATMENT SYSTEM |
SECTION 1 |
CALCULATION OF MATERIAL PROPERTIES
I PHASE 3
ECHNOLOGY EVALUATION
PHASE 4
EQUIPMENT SELECTION
PHASE 9
CALCULATE MATERIAL PROPERTIES
SECTION 1
CALCULATE MATERIAL REMOVALS
SECTION 4
| SELECT TECHNOLOGIES THAT GIVE THE i
I DESIRED REMOVALS
CALCULATE TI-E 2EQUIPSHEHTS
SECTION <
SELECT TECHNOLOGIES GIVING DESIRED
TREATMENT TIMES AIID/OR FLOURATES
CALCULATE EMISSIONS
SECTION 4
I DETERMINE AVAILABLE
I EMISSION CONTPOLb
SELECT TECHNOLOGIES THAT APE |
UITHIII DESIRED EMISSION CRITERIA u.
CALCULATE COSTS
SECTION 4
I COMPARE COSTS FO> I
| TIEATME'IT OPTIONS L.
-I IDENTIFY AVAILABLE EQUIPMENT i
FOR COST-EFFECTIVE OPTIONS I
IE
| COMPARE AVAILABLE EQUIPMENT TO
DESIGN CASE SYSTEMS
SECTION S
'
ELIMINATE INAPPROPRIATE |
TECHNOLOGIES I
ELIMINATE INAPPROPRIATE
TECHNOLOGIES
ELIMINATE INAPPROPRIATE
TECHNOLOGIES
ELIMINATE OPTIONS WITH
MUCH GREATER COs'l
ESTIMATE PERFO7MANCE AND COSTS OF I
AVAILABLE EQUIPMENT UNDER FIELD CONDITIONS |
SECTIONS 5 AND 6 ALONG WITH VENDOR DATA I
.I SELECT EQUIPMENT I
Figure 1. Decision tree for volatilization process selection
3
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Of particular note, Section 5 presents more details for the various
technologies in preceding sections. Section 5 may be too lengthy for many
readers who can obtain a rapid evaluation using Sections 2, 3, and 4
without additional details on how the data were obtained. An example
application of this guide is given in Appendix A.
LIMITATIONS OF THE GUIDE
The guide is, of necessity, written about "representative" types of
equipment and about selected situations. Although the final selection of
equipment should take into account the factors cited in the guide, it will
be necessary to consider the individual characteristics of the equipment
and the situation in which it will be applied.
A variety of other technologies, such as cross-flow air stripping and
a proprietary activated carbon/stripping hybrid technology, are not
included because of their similarity to other technologies or because
systems are not available for widespread use. The guide does not address
mobile or readily transportable technologies for treating the offgases
from the described volatilization technologies.
In addition, the guide is not designed to be the sole reference for
making the final selection of a treatment system. There are
situation-specific considerations that are beyond its scope. As examples
the problems caused by poor water quality (e.g., salts, solids, biological
material); evaluating the significance of differences between equipment of
the same type; or performing pilot tests, cannot be adequately addressed
in this guide.
Pilot Testing
Estimates made in accordance with this guide's method, along with
variations between units of the same type, will normally be within a
factor of 2 to 3 of actual system performance. However, much of the
available data on Henry's Law are only accurate within an order of
magnitude, which reduces the accuracy of performance evaluations,
particularly for low Henry's Law constant. Also, when the equipment is
significantly different from design case assumptions, or when treatment
conditions are far from normal, estimates made using this manual may not
be valid. In cases where it is important to obtain a better estimate for
equivalent performance, pilot testing is recommended if time is available.
Pilot testing proves cost effective when the test cost is outweighed
by the resultant savings during operation. This is true when long-term
treatment is expected, the scale of treatment units is much larger than
available pilot units, and the pilot test is designed to give information
that can alter equipment selection for treatment. Normally, preliminary
performance estimates on the candidate full-scale units should be
completed before pilot testing; the test should then be designed to
demonstrate specific points. The manner in which the pilot test could
reduce costs should be known before testing begins.
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Much equipment available for mobile treatment is considered pilot
scale for use in demonstrations leading to large permanent- installations.
Often, this equipment scale is all that is necessary for a temporary
application requiring a mobile unit. In this case, it is advisable to try
the equipment rather than devise a bench-scale test, particularly if the
test is not to be run on-site with the actual water to be treated.
VOLATILIZATION OF ORGANIC COMPOUNDS FROM WATER: A REVIEW
This section is provided as a brief review of the principles of
volatilization. It also introduces the terminology used throughout the
guide.
Treatment technologies addressed herein involve volatilization of
organic solutes, which requires transfer of the organic from the liquid to
the gas phase. The extent to which these solutes are distributed between
the phases is dictated by the approach to thermodynamic equilibrium that
is achieved.
Equilibrium is attained when the net transfer of a solute between
phases ceases at the prevailing conditions of temperature and pressure. A
complete discussion may be found in many texts on the subject of
equilibrium (1-4).
The rate of mass transfer is dependent on a number of factors
including the departure of the system from equilibrium: The further the
two phases are from equilibrium, the faster the rate of mass transfer.
Also, the rate of mass transfer is directly dependent on the surface area
of the interface between the phases, the resistance to mass transfer at
the interface, and the degree of mixing in each phase. The nature and
degree of dispersion of the phases is of prime importance.
Equipment used for gas-liquid operations should provide intimate
contact between the two phases in order to reduce mass transfer resistance
and to permit increased interphase transfer of the constituents. The
degree of contact can be increased using a variety of devices, but greater
phase contacting generally requires more sophisticated equipment.
Heat and mechanical energies are required to increase the rate of
volatilization. Heat is necessary to increase the system temperature so
that a more favorable equilibrium is reached and to provide the energy
required for vaporization of a liquid. Mechanical energy is required for
dispersing liquids and gases. In air stripping, the energy comes from
cooling water and air; in steam stripping, energy comes from condensation
of steam.
The thermodynamic equilibrium between phases can be represented by the
relative volatility, described mathematically as
1,2 =
Y2/X2 (1)
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where:
a 1,2 = relative volatilities of components 1 and 2,
Y-j = mole fraction of component 1 in vapor phase,
Y2 = mole fraction of component 2 in vapor phase,
X^ = mole fraction of component 1 in liquid phase.
X2 = mole fraction of component 2 in liquid phase.
Relative volatility is concentration-dependent, which is a greater
factor at high concentrations.
For dilute solutions of organics in water, the equilibrium between
vapor and liquid phases can also be described by the Henry's Law constant
(H). This constant relates vapor-phase concentration to liquid-phase
concentration mathematically as
(2)
where:
H = Henry's Law constant,
Y^ = mole fraction of solute in the vapor phase at equilibrium,
Xi = mole fraction of solute in the liquid phase at equilibrium,
and Henry's Law constant is assumed to be constant at low organic
concentrations in water.
The use of Henry's Law in air stripping ignores the volatilization of
water. This assumption holds for compounds with a Henry's Law constant
much greater than that of water (H water 0.03 at 25°C).
Henry's Law constants are an area of confusion and misunderstanding in
some literature discussions. When using these constants, certain
assumptions are implied about the vapor-liquid equilibrium relationship.
The two most important assumptions are:
1. that the vapor behaves like an ideal gas (valid when
total pressure <100 psig), and
2. that the solution is very dilute.
For systems in which the organic has limited solubility* in water, the
* "Limited Solubility" is an area of considerable debate and cannot be
adequately defined. This limit will vary by compounds, temperature, etc.
However, the author suggest that a rough estimate for this limit could be
between 100 ppm (0.001%) and 10,000 ppm (1%).
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linear relationship represented by Henry's Law will hold within certain
limits. This limit is system-specific and requires experimental data to
be predicted. In most cases for organics with low solubilities, Henry's
Law constant will approximate the vapor-liquid equilibrium of a system up
to the solubility of the organic in water. The use of Henry's Law
constants can, therefore, be a powerful tool for designing volatilization
equipment.
Another source of confusion about Henry's Law constants arises over
units. A Henry's Law constant may be defined in many combinations of
units. In this guide, Henry's Law constants are defined as:
Mole fraction of component i in vapor = Yj
Mole fraction of component i in liquid Xf
This constant is independent of the solute or solvent, and is a
unitless number. All other Henry's Law constants are condition- or
compound-specific. Some other forms of the constant are also unitless,
but are not consistent with the previous definition. For example, one can
define a Henry's Law constant as:
Concentration in vapor (g/cm3)
Concentration in liquid (g/cm3)
This definition gives a unitless number. However, it is not
equivalent to a Henry's Law constant defined in mole fractions
(Yi/Xj), and is dependent on the molecular weight of the compound.
This constant is not equal to Yi/X1 because, although both numbers are
unitless, they are not dimensionless. The units used to describe a
unitless constant must be known to use the constant correctly. Another
example of this problem is the unitless constant of parts per million
(ppm): It must be known whether the concentration is expressed in volume
percent or weight percent in order to utilize the data. Similarly, before
a unitless Henry's Law constant can be used correctly for the purposes of
this manual, the units employed in its calculation must be known. Table 1
shows some conversion factors of common Henry's Law constant found in the
literature.
All Henry's Law constants must be determined experimentally However,
very little experimental data exist for dilute, low-solubility organic
contaminants in water. Instead, methods for estimating Henry's Law
constants from pure component physical properties or compound structures
are routinely used. Some of these procedures are described in Section 3.
For distillation systems, relative volatility (mathematically
described in Eq. 1) is normally used to describe the vapor-liquid
equilibrium.
-------
TABLE 1. HENRY'S LAW CONSTANT CONVERSION FACTORS*
Multiply By (Units) To obtain
Hi 1/PT (1/atm) H
HA 55,556/PT gmol/(m3-atm) H
m3-atm
HB 4.559(T/PT) (unitless) H
Hc 1343 (unitless) H
*A11 conversion factors assume dilute solutions in water and air taken at
standard conditions of 1 atm pressure and 25°C temperature.
Legend:
H = Henry's Law constant (Y^/X^, unitless)
H^ = Henry's Law constant (Pj/X^, atm)
HA = Henry's Law constant Pj/C, [(atnTm3)/gmol]
HB = Henry's Law constant (P^/CRT, unitless)
= Henry's Law constant C/C, g(cm"3)/g(cm"3) or
^"3) unitless
PT = total pressure (atm)
P^ = partial pressure of organic in vapor
T = temperature (°K)
MW = molecular weight of the organic
C = concentration
YJ = mole fraction of component i in vapor
Xj = mole fraction of component i in liquid
R = universal gas constant
8
-------
Conventionally, the more volatile component Is numbered 1 so the
relative volatility is always greater than-or equal to 1. At 1 atmosphere
pressure and 100°C the relative volatility of a dilute, low-solubility
organic in water is equal to the Henry's Law constant at 100°C. Because
these are the conditions at which a distillation column or steam stripper
normally operates, Henry's Law constant can be used to describe
vapor-liquid equilibrium behavior in both distillation and steam-stripping
systems.
-------
SECTION 2
SITE CHARACTERIZATION
Site characterization defines the treatment requirement and as such,
Is the first phase In selecting a treatment method. Many factors must be
evaluated, ranging from the nature and concentration of the contaminant to
local ordinances (Table 2). It Is Important that each Item In Table 2 be
considered so that the most suitable system can be selected.
INSTRUCTIONS AND EXPLANATIONS
This checklist Is provided to ensure that all Information necessary to
assess the site and Its treatment Is obtained. Some of the Items are
self-explanatory; others are discussed below.
Extent of Treatment Needed
If phases are evident, that is, if a film or layer of organic is
present above or below the water layer, then a phase separation should be
performed by skimming in a pond, pumping from multiple levels in a well,
or using a separation tank. The organic phase should be disposed of
separately, normally by proper packaging and shipment to an approved
disposal facility. Then, if desired, the aqueous phase can be treated on
site.
Effluent Requirements
Discharge options could include discharge into public sewer systems,
in-plant water treatment system, a permitted NPDES discharge point,
transferred off-site for disposal in an approved manner, or recharged into
an aquifer. Restrictions and limitations on these options should be
determined before a decision is reached.
Properties of Spilled Material
Henry's Law constant must be determined as outlined in Section 3. To
calculate Henry's Law constant, the operating temperature of each system
is required. Methods to obtain this temperature are provided in Section
3
Data on the basic properties of the contaminants must be gathered
before selecting a technology. Solubility may be used to estimate the
maximum concentration in the water to be treated, and to determine reflux
concentrations for steam stripping. Toxicity and f1ammabi1ity are
necessary to determine any emission limits. The reactivity and other fate
properties of the material are important to calculate material
disappearance and for safety considerations. Safe handling requirements
are necessary for selecting the proper equipment.
10
-------
TABLE 2. CHECKLIST FOR SITE EVALUATION
Influent characterization
Contaminant identity
Contaminant concentration (mole fraction) in water
Total quantity of water to be treated
Number, type, and thickness of nonaqueous layers
Influent flowrate
Effluent requirements
Available discharge options
Available discharge capacity
Discharge concentration limits
Discharge flow requirements
Properties of spilled material (see Section 3)
Henry's Law constant (mole fraction)
Solubility
Toxicity
Sorptive properties
Reactivity (hydrolysis, photolysis, biodegradation)
Flammability of vapor
Handling requirements (safety)
Disposal requirements for concentrated material
Other contaminants in water
Climate
Season during which water treatment is anticipated
Average ambient air temperature
Average precipitation
Solar radiation
Wind
Relative humidity
Site-specific considerations
Water temperature
Site accessibility
Water location (surface/groundwater)
Response time requirements
.Volatile emissions limits
Altitude
Integration with other treatment options
Relationship with other water treatment technologies at the
site
Emission control devices
Environmental considerations
Residential characteristics
Ambient air quality
OSHA requirements
Municipal requirements
11
-------
If concentrated organic compounds are to be generated by phase
separation or steam stripping, disposal requirements for this material
must also be considered before selecting a treatment option. Finally,
other contaminants In the water should be determined to assess any
pretreatment that might be necessary to prevent fouling, corrosion, etc.
Climate
The most important climatic consideration is the ambient temperature.
An average daily temperature must be used in calculation of Henry's Law
constants. If treatment is expected to continue over a long period of
time, calculations should be made for average temperature during each
month of the treatment. Average precipitation, solar radiation, relative
humidity, and wind speed (available from a variety of sources, including
local airports) also affect the evaluation, particularly in sites
consisting of open bodies of water. To account for these effects at least
partially, use measured water temperatures for the operational temperature
of supplied water.
Site-Specific Considerations
Selecting the proper technology and support equipment depends upon the
accessibility of the site, location of water (groundwater vs. surface
water), and the necessary response time.
Emission limits at the site are affected by land usage in the area
around it. The altitude of the site does not generally alter the outcome
of the evaluation, but the effects of lower boiling temperatures and air
densities can affect material removal rates. If the site is at a high
altitude, data in this manual can be recalculated for these effects (see
Section 3).
Integration with Other Treatment Systems
Careful evaluation of the site characteristics, as outlined
previously, define the treatment requirements; the need for an integrated
water treatment system often becomes apparent from this exercise. The
requirements for each unit operation in the integrated system must then be
defined and each unit selected based on available selection criteria.
Often, a single type of treatment unit is inadequate to meet
operational and removal requirements. Several units may then be used in
series. A common example is using sand filtration for solids removal,
then air or steam stripping to remove a large portion of a volatile
organic, followed by carbon adsorption to polish the effluent to meet a
low discharge standard.
Air emission standards are a critical consideration at many treatment
sites. Options for emission control technologies must be considered,
along with water treatment technologies, to yield total treatment costs.
This cost can then be compared to the cost of other technologies, such as
carbon adsorption, that generate lower emissions.
12
-------
SECTION 3
MATERIAL PROPERTIES AND ESTIMATION METHODS
To aid In estimating material properties, Appendix B lists common
physical properties and Henry's Law constants for volatile organic
compounds that are designated as hazardous substances under the
Comprehensive Environmental Response Compensation and Liability Act
(CERCLA). Synonyms and chemical formulas are listed for some compounds,
followed by solubility, vapor pressure and Henry's Law constant
Information. If the compound either reacts with water (hydrolyzes) or
decomposes In water by some other mechanism, then this Information is
listed with the solubility data.
Care should be exercised while using the data presented in Appendix
B. Although these data are the best available at the time of writing,
some experimental data were not available for certain compounds. For this
reason, the appendix gives both theoretical and experimental data
available for the listed compounds. These data are satisfactory for
making preliminary engineering evaluations of the technologies. However,
for design and construction purposes, experimental data collected at the
actual operating temperature should be used.
ESTIMATION METHODS
Henry's Law constants are very sensitive to temperature variation, so
experimental data taken at one temperature requires correction for use at
another. In this section, methods are given for predicting the variation
of Henry's Law constants with temperature and pressure, as well as for
predicting Henry's Law constants from other physical properties.
Estimation of Henry's Law Constants from Vapor
Pressure and Solubility Data
Case I: Vapor Pressure and Solubility at the Same Temperature--
The most common method for estimating Henry's Law constants is to
divide the pure compound vapor pressure by its solubility limit in water.
For compounds with low solubilities, this method is theoretically sound.
Attempts at making this type of prediction are a source of confusion in
the area of vapor-liquid equilibrium because of neglecting certain terms,
such as molecular weight. However, if careful attention is given to the
units and calculation procedures, this method can yield useful results
from readily available data.
Vapor pressure and solubility data used to calculate Henry's Law
constants must be taken at the same temperature and expressed in
consistent units. Qualitative solubility data, such as slightly soluble,
insoluble, very soluble, etc., are not useful for estimating Henry's Law
constant. Data must be expressed quantitatively, such as grams per liter,
at a given temperature. Pure compound vapor pressure can be taken from
vapor pressure or boiling point data, the boiling point being the
temperature at which the vapor pressure is 1 atm (or other pressure as
specified).
13
-------
Case II: Vapor Pressure and Solubility Data at Different Temperatures --
If vapor pressure and solubility data are available, but were taken at
different temperatures, the vapor pressure must be adjusted to conform to
the solubility data, since prediction of the temperature effect on
compound solubility is not as accurate and should be avoided. Vapor
pressure is adjusted for the temperature of interest using the
Clausius-Clapeyron equation:
dP_ PAHv (3)
dT RT2
where:
P = vapor pressure (atm),
T = temperature (°K),
AHV = heat of vaporization of the organic
(cal/gmol ) ,
R = universal gas constant,
= 1.987 (cal)/(gmol) (°K), and
= 0.7302 (atm)(ft3)/(lb-mol)(°R)
This equation is useful at atmospheric pressure, when the ideal gas
law may be assumed. The integrated form of Equation 3, assuming AH is
independent of temperature, is as follows:
m_L - A_Hy_ - *A. (4)
P0 RT0 RT
where:
PQ = vapor pressure of known data at temperature To, and
P = calculated vapor pressure at temperature of interest, T.
If two or more data points for compound vapor pressure are known,
interpolation techniques may be used to obtain vapor pressures at various
temperatures. In addition, equations are available in published
literature (5) to calculate vapor pressures for certain temperature
ranges.
Once vapor pressure and solubility data are known, Henry's Law
constant can be calculated by the following equation:
P/PT (5)
H o - ! -
C 0.18 C/MW
14
-------
where:
C = weight percent (wt %) organic at maximum solubility (%),
MW = molecular weight of organic (g/gmol)
H = unltless Henry's Law constant (mole fraction/mole fraction)
P = vapor pressure of pure organic (atm), and
PT = total pressure (atm).
0.18 = MW of water/100
This equation assumes a low concentration of the organic.
Estimation of Henry's Law Constants for Various Temperatures
Often the desired operating temperature differs from published data on
Henry's Law constants. In this case, the Henry's Law constant must be
adjusted to the system's operating temperature. When Henry's Law
constants are known for several temperatures, a linear Interpolation must
be used to find the Henry's Law constant of Interest. This method should
prove accurate enough for preliminary performance estimates If the desired
temperature Is bounded by data on both higher and lower temperatures.
Methods are available to express Henry's Law as a function of
temperature, thereby permitting calculation at any temperature. These
methods require experimental determination at several temperatures to
determine values of various constants given in the equation. Goldstein
(6) gives a good treatment of this topic and provides calculated values
for Henry's Law constants for a variety of organic compounds at several
temperatures.
Estimation of Henry's Law Constants for Various Pressures
Vapor pressure is a function of total pressure, although this
dependency can be ignored under the range of conditions normally found in
the field. The definition of Henry's Law in this manual assumes a total
pressure of one atmosphere.
To adjust Henry's Law constants for pressure, multiply the value given
in mole fraction/mole fraction by atmospheric pressure at sea level and
then divide by the operating pressure in the same units. For Henry's Law
constants presented in units of pressure, division by the ambient pressure
will normally give the unitless Henry's Law constant as used in this
manual. (See Table 1 for a summary of such conversions.)
Estimation for Compounds with High Solubilities In Water
If an organic is miscible with water, Equation 5 for Henry's Law
constant reduces to:
H - _P_ (6)
15
-------
where:
P = vapor pressure of pure organic, and
Pj = total pressure.
Equation 6 uses
H = P + 1 + MU(100 - C) (7)
Fj~ 18C
where:
MW = molecular weight of organic, and
C = weight percent (wt %) of organic at Its
solubility limit.
16
-------
SECTION 4
TECHNOLOGY EVALUATION
Performance and cost data for the representative equipment designs
discussed In Section 5 are covered 1n this section. These data are
estimated to be within an error factor of 2 to 3 of the actual performance
and cost that were found for similar systems in actual use. However,
available field systems may differ widely from the design assumptions used
in developing these data.
This section should only be used to obtain a rough estimate of the
relative merits of the technologies presented. Data in Section 5 should
then be used to compare the performance of available equipment to the
estimated performance and cost.
The process of system evaluation is divided into four major steps:
(1) the organic removal obtained using each continuous flow unit; (2) the
time required for treatment; (3) the emissions resulting from operation;
and (4) the cost of the units, their mobilization, and operation. The
evaluation process is intended to eliminate technologies based on
performance and then permit the selection of the best remaining technology
based on cost.
ORGANIC REMOVALS
Figures 2 through 9 give organic removals for technologies that allow
continuous operation. These are the bubble column (Figures 2 and 3);
spray column (Figures 4 and 5); packed-column air stripper (Figure 6);
cooling tower (Figures 7 and 8); and packed-column steam stripper (Figure
9). The figures have material removals plotted for each of four operating
modes. For all technologies, the selected cases represent approximate
operating ranges for gas and liquid flow for a clean water and organic
feed. Detailed operating modes are described in Section 5.
During actual treatment, the operating range can be limited by a
variety of factors (Section 6) that will reduce maximum gas and liquid
throughput. The removal is dependent on the ratio of gas and liquid flow
rates: If site factors limit one flowrate, the other may be reduced by
the same percentage to obtain the organic removals shown in the figures.
Figures 2 through 9 are calculated based on Henry's Law constants,
number of stages, and gas-to-liquid ratios. As such, they are theoretical
calculations that assume ideal column operation. Departures from the
ideal will occur in all real systems, although the magnitude of these
17
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Figure 3. Bubble column design basis, organic removal, series operation
(4 columns)
19
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20
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21
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23
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(4 columns)
24
-------
100
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Figure 9. Packed column steam stripper design basis, organic removal
25
-------
departures can vary greatly from system to system. The departures are
caused by: (1) gas and liquid short-circuiting, (2) adsorption and -
absorption of the organic onto impurities in the water, and (3) improper
placement of packings, distributors, and other column internals.
In any real operating system, the removal curves begin to level off at
high removal percentages. It is impossible to predict exactly where the
limit is; the specific column must be operated as it will be used. A
reasonable estimate of a single-column maximum removal would be between 99%
and 99.9%, although no data exist that allow this generalization. It
should be noted that this limitation is partially due to the limits of
single-column operation. We suggest that when high removals are necessary,
multiple columns should be used in series.
Removal calculations for designs with multiple units presented in Section 5
on trailers (i.e., bubble column, spray column, cooling tower) were
developed for both series and parallel operation of the units.
TIME REQUIREMENTS FOR REMOVAL
The batch systems of unaided evaporation, surface sprayers, and surface
aerators are best evaluated by comparing the half-lives of organics in
model impoundments employing the three systems. (A half-life is the time
required to volatilize one-half of the organic from the impoundment.)
For this comparison, the model impoundment is a square, steep-sided
basin 100 ft long x 100 ft wide x 10 ft deep. Figure 10 is a plot of the
half-lives of the volatile organic using the three batch systems against
the contaminant's Henry's Law constant. For both surface spraying and
aeration, results are plotted for two sizes of commercially available
units, representing the design cases in Section 5. These units are
transportable and proportional to the model impoundment size.
No attempt is made to quantify effects of other incidental variables
such as climatic conditions (wind and temperature), differences in a
particular equipment design, and quality of the contaminated water.
Instead, reasonable average values for the key variables are estimated
based on probable field conditions, as explained in Section 5. As a rule
of thumb, results obtained in the field should generally agree with the
plotted values by a factor of 2 to 3, but there are exceptions.
To evaluate the time necessary to obtain a desired organic removal
efficiency, refer to Figure 11 for the required number of half-lives. Then
multiply by the hours per half-life from Figure 10 to obtain the required
treatment time.
26
-------
10,000
1,000
I
100
10
0.1
0.1
10 100
HENRY'S LAW CONSTANT (mote/moK)
1.000
1. 100 HP SURFACE AERATOR
2. 50 HP SURFACE AERATOR
3. 50 HP SURFACE SPRAYER
4. 25 HP SURFACE SPRAYER
5. IMPOUNDMENT WO AGITATION
10,000
Figure 10. Half-life in model impoundment, batch systems
27
-------
10
1
i
<
J*
0.1
0.01
0-001
\
X
\
s,
\
V
\
V
\
V
\
\
\
X
\
~\~~~
\
\
\
^
\
s
s
5
^~
\
0
90
99
_J
<
>
O
111
999
99.99
9994
4 5 « 7 » 9 10 11 12 13 14
HALFLIFES
Figure 11. Number of half-lives required to obtain removals
28
-------
The continuous systems of air or steam stripping can be used to
augment volatilization from an impoundment. The discharge from the
treatment system could either be placed back into the impoundment or sent
to off-site disposal. Where the discharge is placed back into the
impoundment, the half-life in the pond will be governed by the equation:
th = 0.693 V (8)
L(l-f)
where:
tn= half-life of organic in the impoundment,
V = volume of the impoundment,
L = liquid flowrate of the treatment unit, and
f = organic fraction remaining after treatment,
based on the Kremser equation (4).
Results of this equation are plotted in Figures 12-19 for the design
case systems and operating modes in treating the model impoundment. The
same data are also presented in Table 3, along with batch system data.
These figures and table neglect the volatilization occurring naturally
from the impoundment. The actual half-life, including this or any other
competing removal mechanism, can be obtained using the following equation:
(9)
*h thl Ih2
where:
t|, = half-life of the organic in the impoundment, and tnx =
half-life of the organic, considering mechanism x.
The half-life thus obtained can then be used with Figure 11 to
calculate the time requirement for any removal percentage.
Examination of the half-life figures shows that surface aerators will
normally be the best option to augment volatilization from an
impoundment. However, operational constraints of surface aeration, the
desire to control organic emissions, or the unavailability of a surface
aerator may require the use of one of the other units for this service.
Table 4 compares the design case continuous treatment units, assuming
off-site discharge is available. In this case, the treatment time is
purely a function of liquid flowrate. For convenience, the percent
removals for each of four Henry's Law constants also appear.
29
-------
U)
-s
fD
ro
a a:
v v
-5
ta -h
n> -
'-h
IB
O
T3 ->
a> =>
-5
cu 3
c-f O
_1. Q.
O 05
-a
o
Q.
3
fD
a-
CT
fD
O
O
Q-
00
»i«
UD
3
CT
OJ
100 1000
HENRV'S LAW CONSTANT imou i.i
10.000
100.000
-------
1
ro
CO
t/> a:
(D fi)
-j
- -«>
m i
to i
_*.
o -»>
a (o
n>
T -*
(U 3
o o
3 O.
IP
XJ
o
Q.
3
cr
c
cr
cr
(D
o
o
Q.
CD
01
210
260
MO
220
ZOO
110
160
140
too
10
to
40
20
CASE1
L»MOgpm
t_
t
s
x
\
^_
ss
"^
\
V
.
kk
V^,
L
CASE 2 CASES CASE 4
SOflpm L = 300gpm L = 60gpm
C
L
ASE3
ASE4
(
:ASE
CAS
i
:2 - -
too
HENRY'S LAW CONSTANT ^o* m<11.>
10.000
100.000
cr
w
(A
-------
CQ
C
-j
CO
CO
ro
-J
eu
(D
O
T3 -
(D 3
-J
a, 3
H- O
Q.
O (D
TO
O
Q.
3
o>
n
o
3
a.
ro
too 1000
HENRY'S LAW CONSTANT (manmou)
100,000
cr
QJ
-------
CASE1
= 60gpm
CASE 2
L = 30gpm
CASE 3
= 60gpm
CASE 4
L = 30gpm
390
360
350
3*0
CASES
CASE 4
\
CASE 1
CASE 2
100 1000
HENRY'S LAW CONSTANT imour
Figure 15.
Half-life in model impoundment, spray column design basis,
series operation
33
-------
100.000
HENRY'S LAW CONSTANT
Figure 16. Half-life in model impoundment, packed column air stripper,
design basis
-------
CASE1
L = 240 gpm
CASE 2
L = 120gpm
CASE 3
L = 240 gpm
CASE 4
L = 120gpm
(D
140
130
OJ
1
tu
a
-s
(u 3
ft- O
_i. o.
o n>
3
U)
en
3
T3
O
c
3
Q.
O
O
O
3
in
ro
j
Q.
(D
3
CT
10
100
HENRY'S LAW CONSTANT (mota/
10,
100,000
-------
(D
^>
CO
0)
to i
o -h
T3 fD
ID
-$ -
CU 3
r+
O O
3 CL
ID
cr>
0)
13
r-f
O
O
o
-J
CL
0)
CASE1
= SOOgpm
CASE 2
L - SOgptt
CASE 3
L = 300 gpm
CASE 4
L = 60 gpm
CASE 3
CASE 1
CASE 2
CASE 4
100 IBM
HENBVS LAW CONSTANT (moi. note)
1(0.000
CQ
CT
01
-------
100,000
1,000
100
HALFLIFE (h,,
a
1
O.t
*
s
VN
s O
N \
\ \
" ' V
*,\
v
rt -
v-» S
> ».
<5 = DOTTED LINES
: >5 - SOLID LINES -
' S\
'>ikX
is
BOIL-UP
S 30%
El 5%
: 3%
1 10 100 1,000
HENRY'S LAW CONSTANT (moi./moi«)
10,000
Figure 19. Half-life in model impoundment, steam stripper design basis
37
-------
TABLE 3. TIME REQUIRED FOR TREATMENT OF MODEL IMPOUNDMENT, RECYCLE DISCHARGE TO POND
Operating Case
Case Operating Liquid Plot
Technology Number Mode Rate(gpm)
Pond, unagitated
Pond, surface
sprayer
Pond, surface
aerator
Bubble column
Spray column
CO
Packed air strip-
ping column
Cooling tower
Steam stripper
1
1
2
1
2
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
25 lip
50 hp
50 hp
100 hp
Parallel
Series
Parallel
Series
Single column
Parallel
Series
3% Boil -up
5S Boil -up
10% Boil -up
30X Boil -up
4000
200
4000
200
1000
50
1000
50
240
120
240
120
60
30
60
30
500
50
500
50
2000
200
1200
240
500
50
300
60
96
74
50
24
»
H=b
197
46
23
5
0.9
82
124
243
284
86
211
246
358
54
126
51
121
146
299
148
297
32
173
64
173
9
44
16
40
19
173
32
183
601
468
347
362
50%
H=25
107
18
9
1.4
0.3
18
59
50
91
22
174
54
188
40
92
40
84
144
289
144
289
17
173
17
173
5
43
8
36
17
173
29
176
121
119
173
361
Removal
H=200
87
12
6
0.6
0.2
4
45
8
49
9
173
12
173
37
78
36
74
144
289
144
289
17
173
17
173
4
43
7
36
17
173
29
144
90
117
173
361
H=5000
84
12
6
0.5
0.2
2
43
2
44
9
173
9
173
36
73
36
72
144
289
144
289
17
173
17
173
4
43
7
36
17
173
29
144
90
117
173
361
H=5
656
152
76
17
2.8
272
408
801
937
283
695
812
1181
179
417
420
399
482
986
489
979
107
572
212
572
30
145
53
131
62
572
105
605
1996
1555
1153
1203
90S
H=25
356
61
31
5
1.1
60
196
166
302
72
575
177
619
131
303
128
279
476
955
476
953
57
572
57
572
15
143
26
120
57
572
95
580
402
395
575
1199
Treatment Time Required(hr)
Removal
H=200
290
41
21
2
0.8
14
150
27
163
30
572
40
572
121
259
120
246
476
953
476
953
57
572
57
572
14
143
24
119
57
572
95
476
299
389
575
1199
H=5000
281
30
19
2
0.7
7
143
8
144
29
572
29
572
119
242
119
239
476
953
476
953
57
572
57
572
14
143
24
119
57
572
95
476
299
389
575
1199
H=b
1312
304
152
34
5.7
544
815
1602
1874
566
1391
1624
2361
357
834
840
798
965
1972
978
1957
214
1143
424
1143
61
290
106
262
124
1143
210
1210
3993
3109
2305
2405
99X
H=25
712
122
61
10
2.3
120
392
332
603
144
1150
354
1238
262
607
257
557
953
1910
953
1907
114
1143
115
1143
30
286
52
239
114
1143
191
1160
804
791
1149
2398
Removal
H=200
581
83
41
4
1.5
28
299
54
326
60
1143
81
1144
241
517
239
491
953
9106
953
1906
114
1143
114
1143
29
286
48
238
114
1143
191
953
598
777
1149
2398
H=5000
563
77
39
3
1.4
15
286
16
287
57
1143
57
1143
238
484
238
478
953
1906
953
1906
114
572
114
1143
29
286
48
238
114
1143
191
953
598
777
1149
2398
H=b
1967
457
228
51
8.5
824
1235
2428
2839
857
2107
2461
3578
541
1263
1259
1209
1462
2988
1482
2966
324
1733
642
1733
92
440
160
398
188
1733
318
1834
5989
4664
3458
3608
99.9%
H=25
1068
184
91
14
3.4
182
594
503
914
218
1742
537
1876
397
919
389
844
1444
2894
1444
2889
173
1733
174
1733
.46
433
,80
363
173
1733
289
1757
1206
1186
1724
3598
Removal
H=200
871
124
62
6
2.3
42
453
82
493
92
1733
122
1734
365
783
362
744
1444
2888
1444
2888
173
1733
173
1733
43
433
72
361
173
1733
289
1444
897
1166
1724
3598
H=5000
844
lift
58
5
21
?2
434
24
136
87
1733
87
1733
363
733
361
724
1444
2888
1444
2888
173
1733
173
1733
43
433
72
361
173
1733
289
1444
897
1166
1724
3598
-------
TABLE 4. TIME REQUIRED FOR TREATMENT OF MODEL IMPOUNDMENT, OFFSITE DISCHARGE AVAILABLE
CO
us
Technology
Bubble column
Spray column
Packed air
stripping
column
Cooling tower
Steam stripper
Case
Number
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Operating Case
Operating
Mode
Parallel
ii
H
H
Series
H
n
H
Parallel
n
n
n
Series
n
n
n
Single column
n
n
n
Parallel
n
n
n
Series
n
n
ii
3% boil -up
5% boil -up
10% boil -up
30% boil -up
T
Liquid
FlowRate
4000
200
4000
200
1000
50
1000
50
240
120
240
120
60
30
60
30
500
50
500
50
2000
200
1200
240
500
50
300
60
96
74
50
24
reatment
Time
(hr)
3
63
3
63
13
250
13
250
52
104
52
104
208
417
208
417
25
250
25
250
6
63
6
63
25
250
25
250
130
170
250
520
H=5
2.63
35.06
0.89
15.25
10.11
82.22
3.52
48.42
66.67
57.14
60.00
59.71
98.77
96.63
97.44
97.37
53.50
99.99
27.0
99.99
47.21
98.55
45.09
90.79
92.23
99.99
90.91
99.99
15.00
25.00
50.00
99.79
Percent
H=25
11.89
72.97
4.31
47.37
39.74
99.47
16.14
92.33
90.91
78.52
92.71
85.51
99.99
99.79
99.99
99.96
99.99
99.99
99.71
99.99
93.88
99.96
90.77
99.48
99.99
99.99
99.99
99.99
74.47
98.71
99.99
99.99
Removal
H=200
51.92
95.58
26.47
87.80
94.66
99.99
70.77
99.98
98.77
92.14
99.61
97.03
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.94
99.99
99.79
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
H=5000
96.43
99.81
90.00
99.45
99.99
99.99
99.99
99.99
99.95
98.42
99.99
99.77
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
99.99
-------
SYSTEM EMISSIONS
All processes that remove volatile organics from water will generate
some uncontrolled air emissions. However, there is a difference of many
orders of magnitude in the emissions from an uncontrolled technology and
one designed with emission control in mind. This section presents
approximations of emissions from volatilization technologies.
Emissions from an open body of water, such as an impoundment, are
extremely difficult to quantify or control adequately. The total quantity
of emitted volatiles is obtained directly from estimates of the quantity
removed. The concentration of these compounds in the air around the
impoundment is difficult, if not impossible, to quantify unless accurate
data on wind speeds, directions, and mixing rates are known. In general,
the concentration in air around the impoundment increases as the removal
rate is increased. Therefore, it is not advisable to augment
volatilization using an uncontrolled process if there are any potential
problems with air emissions from either a safety or air pollution
standpoint.
Air-stripping units generate an air stream containing organics that
potentially could be treated. The organic concentration is very important
since some air treatment technologies, such as condensers, are
concentration dependent. Table 5 gives the air flowrates and organic
concentrations in air exiting each of the design case systems. It
includes emissions for operating each system with each design case
operating mode and for both parallel and series operation if multiple
columns are available.
Emission concentrations given for series operation represent the
average based on a unit concentration in the influent water of 1
mg/liter. The emissions given can be multiplied by the aqueous
concentration in milligrams per liter to predict emission concentrations
in parts per million (wt/wt).
Steam stripping has much lower emissions than other volatilization
technologies by virtue of the collection and disposal of a concentrated
organic stream. Organic is emitted to the atmosphere using steam
stripping in the form of fugitive emissions.
The air emission rate from the model steam stripper is estimated and
summarized in Table 6. It is a function of molecular weight, the size of
the decanter, and the vapor pressure of the organic at operating
conditions. These estimates represent working losses from the decanter
during continuous operation. Other sources, such as startup losses, are
not expected to be significant.
COST DATA
Capital costs for the design case surface sprayers and surface
aerators, given in Table 7, are based on similar equipment (7).
40
-------
TABLE 5. EMISSIONS FROM AIR STRIPPING PROCESSES
Volatile Emission
Case Operating
technology number mode L (gpm) 6 (cfm) H-5 H=25 H=200 H=5000
Bubble Column
Spray Column
Packed Air
Stripping Column
Cooling Tower
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Parallel
Series
Parallel
Series
Single
Col umn
Parallel
Series
4,000
200
4,000
200
1,000
50
1,000
50
240
120
240
120
60
30
60
30
500
50
500
50
2,000
200
1,200
240
500
50
300
60
3,600
3,600
1,200
1,200
3,600
3,600
1,200
1,200
16,000
16,000
8,000
8,000
16,000
16,000
8,000
8,000
9,800
9,800
4,900
4,900
39,200
39,200
24,000
24,000
39,200
39,200
24,000
24,000
3.2
2.1
3.2
2.7
3.1
1.2
3.2
2.2
1.1
0.47
2.0
0.98
0.40
0.20
0.80
0.40
3.0
0.56
3.0
1.1
2.6
0.55
2.5
0.99
1.3
0.14
1.2
0.27
14
4.4
16
8.6
12
1.5
15
4.2
1.5
0.64
3.0
1.4
0.41
0.20
0.82
0.41
5.6
0.56
11
1.1
5.2
0.56
4.9
1.1
1.4
0.14
1.4
0.27
63
5.8
96
16
29
1.5
64
4.5
1.6
0.75
3.3
1.6
0.41
0.20
0.82
0.41
5.6
0.56
11
1.1
5.6
0.56
5.4
1.1
1.4
0.14
1.4
0.27
117
6.0
327
18
30
1.5
91
4.5
1.6
0.80
3.3
1.6
0.41
0.20
0.82
0.41
5.6
0.56
11
1.1
5.6
0.56
5.5
1.1
1.4
0.14
1.4
0.27
All concentrations are expressed as concentration in air (Ca) divided by
concentration in water (Cw). To calculate the concentration in air in ppm wt/wt,
multiply by concentration in water in mg/liter.
41
-------
TABLE 6.- AIR EMISSION RATE FROM MODEL STEAM STRIPPER*
Vaoor Pressure (mm Ha)
Molecular Wt
Ib/lb-mol 10-7
25 4 X 10-10
50 8 X 10-10
100 2 X 10-9
150 3 X 10-9
200 3 X 10-9
*Enrissions (Ib/day)
TABLE 7.
Unit
Surface sprayer, 25 hp
Surface sprayer, 50 hp
Surface aerator, 50 hp
Surface aerator, 100 hp
10-5 10-3 0.1 10
4 X 10-8 4 X 10-6 0.0004 0.04
8 X 10-8 8 X 10-6 0.0008 0.08
2 X 10-7 2 X 10-5 0.002 0.2
3 X 10-7 3 X 10-5 0.003 0.3
3 X 10-7 3 X 10-5 0.003 0.3
MECHANICAL AGITATOR CAPITAL COSTS*
Wt(lb)
4,000
5,000
4,000
5,000
1000
4.2
8.3
16.7
25.0
33.3
Delivered
($)
30,000
45,000
30,000
40,000
*A11 costs are based on delivered costs given in Richardson (7) and are
given in 1984 dollars.
42
-------
Capital costs for the bubble column, spray column, packed air
stripping column, and cooling tower air strippers are in -Table 8. All
equipment line items are based on installed costs to account for
engineering, contractors' fees, freight, contingencies, and tax.
Table 9 give the capital costs for the steam stripper. Because of
the complexity of this system, equipment purchase costs were used. A
factor was then applied to derive total installed costs. Individual
factors, totalling 52%, were applied to the installled cost to account for
tax, freight, contractors' fees, engineering, and contingencies.
All capital costs, given in mid-1984 dollars, are preliminary
estimates based on conceptual design. Costs are calculated to be within +
50% of actual purchase costs. This variability is the result of the
preliminary nature of the designs and differences in costs of similar
systems from various manufacturers.
Table 10 shows approximate mobilization and demobilization costs for
design case trailers. All costs include transporation; site preparation;
trailer and auxiliary equipment rental during setup and takedown; labor
for equipment assembly, hookup, and disassembly; and materials for
assembly, startup, and cleanup. These costs may vary significantly from
those found in the field.
In general, the design case systems are configured to minimize field
assembly. Mobilization costs should, therefore, be considered as minimum
numbers. If the equipment used is not designed for easy field setup,
mobilization may require a much higher cost.
Table 11 give the operating costs in dollars per day and dollars per
1,000 gallons treated for each of the design case systems and operating
modes. Cost-per-gallon give the best basis for comparing the technologies
since it accounts for varying flowrates. Operating cost also includes
captial recovery costs at a rate of 0.185% per day to allow comparison of
the treatment costs for each technology, both daily and adjusted for
flowrate. However, it must be noted that several of the technologies
benefit from economy of scale. If a low flowrate is required, the
cost-per-gallon using these technologies will increase significantly.
43
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TABLE 8. AIR STRIPPER-CAPITAL COSTS*
Installed cost
Item (thousands of dollars)
Bubble column
Flat-bed trailer 20.0
Columns (4) 40.0
Plumbing 23.8
Blower 9.0
Diesel engine 10.0
Demister (4) 5.2
Air diffuser (4) 2.0
Instrumentation 5.0
Railings, supports, gratings 5.0
Subtotal 120.0
Engineering, contingencies, freight, contractors' 64.8
fees, and tax (54%)
Total 184.8
Spray column
Flat-bed trailer 20.0
Columns (4) 40.0
Pumps (4) 6.2
Plumbing 10.7
Blowers (4) 4.2
Demisters (4) 5.2
Motors (8) 4.6
Electrical 7.4
Railings, supports, and gratings 5.0
Instrumentation 5.0
Subtotal 108.3
Engineering, contingencies, freight, contractors' 58.7
fees, and tax (54%)
Total 167.0
44
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TABLE 8. (CONTINUED)
Installed cost
(thousands of dollars)
Packed air-stripping column
Column 30.0
Frame 25.0
Plumbing 3.0
Electrical 3.0
Blower 2.9
Motor (50 hp) 3.4
Demister 1.3
Packing and Liquid distributer 60.0
Sump 2.8
Instrumentation 3.0
Subtotal 134.4
Engineering, contingencies, freight, contractors 72.6
fees, and tax (54%)
Total 207.0
Cooling tower
Flat-bed trailer 20.0
Package towers 84.0
Pumps 8.1
Motors 4.6
Electrical 8.0
Plumbing 13.3
Railings, supports, and gratings 5.0
Instrumentation 5.0
Subtotal 148.0
Engineering, contingencies, freight, contractors 79.9
fees, and tax (54%)
Total 227.9
*A11 costs are based on installed cost obtained primarily from Richardson (7)
and are given in 1984 dollars.
45
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TABLE 9. STEAM STRIPPER CAPITAL COSTS3
Purchase
(thousands of dollars)
1 - Column, 1.5' X 35', steel 17.0
45 ft3 - Packing, pall rings, 1 1/2", steel 2.0
1 - Condenser, BEU, 10" X 6', 75 ft2, steel 5.0
1 - Exchanger, BEM, 25" X 12', 850 ft2, steel 10.0
3 - Condenser, air, 1' X 7.5' X 7.5', 15 hp, steel 22.0
2 - Reboiler, electric, 225 kW, 240V, 3, steel 25.0
1 - Decanter, 2' X 6', 150 gal, steel 1.1
2 - Accumulator, 18" X 24" X 40", steel 1.1
2 - Reflux/product pump, 10 gpm 4.0
1 - Feed pump, 125 gpm 3.0
1 - Bottoms pump, 125 gpm 3.0
1 - Trailer, hydraulic lift and stabilizers 52.0
Subtotal 145.2
Allowance - for other undefined equipment and quote precision (20) 29.0
Total estimated equipment purchase cost 174.2
Installation costs (95%)b 165.5
Base cost 339.7
Sales tax and freight 13.1
Contractor's fees 49.7
Toll contract 402.5
Engineering 52.0
Contingencies 60.4
Total 514.9
* Given in 1984 dollars.
° Includes structures, equipment erection, piping, insulation, paint, fire
protection, instruments, and electrical work.
46
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TABLE 10. MOBILIZATION AND DEMOBILIZATION COSTS
Design case Cost
equipment ($)
Surface sprayer, 25 hp 5,400
Surface sprayer, 50 hp 6,000
Surface aerator, 50 hp 7,000
Surface aerator, 100 hp 8,000
Bubble column6 4,200
Spray columnb 4,100
Packed air stripperbc 8,400
Cooling towerb 4,400
Steam stripperbc 11,800
All costs include transportation to and from site, assumed as 500
miles at 40 miles/hour with a $52/hour cost for truck and driver,
plus a $0.20 per mile fuel cost. Total transportation cost =
$1,500. Costs are given in 1984 dollars.
Cost includes site preparation of leveling and graveling at $700.
Cost includes site preparation of placing poured footings for
guy-wires at $500.
47
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TABLE 11. OPERATING COSTS
Operating case
Technology
Pond, unag Hated
Pond, surface sprayer
Pond, surface aerator
Bubble column
Spray column
Case Operating
number mode
1
1 25 hp
2 50 hp
1 50 hp
2 100 hp
1 Parallel
2
3
4
1 Series
2
3
4
1 Parallel
2
3
4
1 Series
2
3
4
Liq. flow
rate (gpm)
NAb
NA
NA
NA
NA
4000
200
4000
200
1000
50
1000
50
240
120
240
120
60
30
60
30
Operating costs3
Total
(dollars/day)
0
170C
235C
235C
370C
1439d
1369d
1389d
1319d
1390d
1364d
1340d
1314d
1239d
1239d
1219d
1219d
1239d
1239d
1219d
1219d
Dollars/
1,000 gal
NA
NA
NA
NA
NA
0.25
4.75
0.24
4.82
0.97
18.94
0.93
18.25
3.59
7.17
3.54
7.05
14.34
28.68
14.11
28.22
48
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TABLE 11. (CONTINUED)
Technology
Packed air-stripping
col umn
Cooling tower
Steam stripper
Operating case
Operating costs3
Case Operating Liq. flow
number mode rate (gpm)
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Single
column
Parallel
Series
3% Boil up
5% Boil up
10% Boil up
30% Boil up
500
50
500
50
2000
200
1200
240
500
50
300
60
96
74
50
24
Total
(dollars/day)
1514d
1367d
1415d
1283d
1476d
1449d
1333d
1323d
1476d
1449d
1333d
1323d
3084c'd'e
2739c'd'e
2699c'd'e
2830c'd'e
Dollars/
1,000 gal
2.10
18.99
1.97
17.82
0.51
5.03
0.77
3.83
2.05
20.13
3.09
15.31
23.31
25.70
37.49
81.89
a All costs include pump rental if pump is not supplied on trailer. Fuel
costs are taken as $1.50/gal. Costs include equipment rental based on
purchase cost divided by 540 days (18 months). Costs for rental of
auxiliary equipment are based on standard weekly rental rates. All costs
are given in 1984 dollars.
b NA = not applicable.
c Costs include operator at 4 hr/day and $25/hr.
d Costs include operator at 24 hr/day and $25/hr.
e Costs include disposal costs assumed as $120/drum for 55-gal drums.
49
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SECTION 5
DESIGN BASES
This section provides specific background information on the
volatilization technologies. The equipment designs that form the basis
for the data presented in the tables and graphs in-Section 4 are also
described. Finally, important considerations for the evaluation of
available equipment are given to aid in the selection process for each
technology.
VOLATILIZATION FROM SURFACE IMPOUNDMENTS
Volatile organic compounds naturally volatilize from a body of water,
such as an impoundment. Volatilization rates can be increased by using
mechanical agitation to enhance liquid-air contact. Three methods for
removing volatile organics from an impoundment of contaminated water are:
o Exposing the water to the outdoor environment without any
mechanical agitation,
o Spraying the water on the impoundment surface, and
o Agitating the water surface with a high-speed mechanical
surface aerator.
Principle of Volatilization from an Impoundment
The mass transfer of volatile organics from an impoundment is
expressed by the normal rate equation:
dC/dt = - KLsC (10)
where:
C = bulk average organic concentration,
t = time (hr),
KL = the overall mass transfer rate coefficient (m/hr), and
s = the specific surface area of the liquid phase (nrVm3).
Integrating this equation gives:
-In C/Co = KLs(t - t0) (11)
where:
C and C0 are the volatile organic concentrations at times t and
t0, respectively. For the condition where C 1/2 C0, t is the
half-life and Equation 11 becomes:
50
-------
th = 0.693/(KLs) (12)
The mass transfer constant, KLs, Is affected by both the liquid-and
gas-phase resistance and can be estimated using the two-film concept for
estimating the flux of volatiles across the air-water Interface as
fol1ows:
1/KL = 1/k! + (5.56 X 104)RT/Hkg (13)
where:
k-j = liquid phase mass transfer coefficient (m/hr),
kg = gas phase mass transfer coefficient (m/hr),
R = universal gas constant [(m3-atm/mol)(°K)(8.2 X 10'5)],
T = absolute temperatures °K (Note: 20°C = 293°K), and
H = Henry's Law constant (mole fraction volatile in gas phase/mole
fraction volatile in liquid phase at 1 atm).
In this equation, 1/KL can be thought of as the total resistance to
the transfer of a volatile from water to air, with l/k-| and RT/Hkg
being the individual resistances across the liquid film and gas film,
respectively, at the liquid-gas interface. Smith, et al. (8) presents a
more thorough discussion of the volatilization of organic chemicals from
water bodies and typical values for mass transfer coefficient.
DESCRIPTION OF MODEL IMPOUNDMENT AND VOLATILIZATION ENHANCEMENT SYSTEMS
A model impoundment with a 100-ft2 surface area and 10-ft depth
(750,000 gal) is used to evaluate the volatilization of organic from
contaminated water for the described systems. The model does not have a
flow into or out of the impoundment during the treatment period (this is a
batch system). The model (representative of a typical body of
contaminated water) is adequate in size to accommodate available
commercial mechanical agitation equipment.
The following three volatilization systems (Figure 20) are considered
in this guide:
o Impoundment without mechanical agitation
o Impoundment with surface spraying
- 25 hp unit
- 50 hp unit
o Impoundment with high-speed surface aerator
- 50 hp unit
- 100 hp unit
51
-------
IMPOUNDMENT WITHOUT AGITATION
APPROX
12'
IMPOUNDMENT WITH SURFACE SPRAYER
APPROX 35'-55'
IMPOUNDMENT WITH SURFACE AERATOR
Figure 20. Impoundment batch volatilization systems
52
-------
To evaluate the systems, the organic half-life in the model
impoundment is calculated for .various Henry's Law constants using
equations 10-13. The mass transfer rate constant, KL, is calculated
using estimates for the liquid-phase mass transfer coefficient, k-|, the
gas-phase mass transfer coefficient, kg, and the specific surface area,
s, that are characteristic for the specific system and unit size (the
bases for these estimates are discussed below). These are estimated
values that should be typical, of .field.conditions,..but actual conditions
encountered could give half-life results that vary by a factor of 2 to 3.
(See Section 4 for the results of half-life calculations.)
Conditions that could cause variations in half-lives are:
1. Climatic (temperature, wind, rainfall, etc.),
2. Equipment design (spray-nozzle efficiency, pump
efficiency, etc.), and
3. Contaminated water conditions (presence of surfactants,
other soluble contaminants, solids, etc.).
Impoundment Without Mechanical Agitation
Mass transfer coefficients for stagnant impoundments without
mechanical agitation are a function of the wind conditions. The estimated
value used for ki is 0.025 m/hr and for kq is 5 m/hr. These are
selected from literature values representative of mild wind conditions,
i.e., less than 2 to 3 m/sec. If field conditions have consistently
higher winds, Lyman, Reehl, and Rosenblatt (9) provide more accurate
estimates. The specific surface area, s, is the total surface area
divided by the total volume, which is equal to I/depth. For the model
this is 0.33 nr/m This relationship makes the organic half-life
directly proportional to the impoundment depth. That is, an -impoundment
twice as deep as another would have twice the half-life regardless of its
surface area.
In evaluating organic volatilization from an unagitated impoundment,
the effect of local climatic conditions must be evaluated. Half-lives are
long for volatiles with low Henry's Law constants. Such conditions as the
long-term ambient temperature and the net evaporation (evaporation less
rainfall) could have a significant effect. Temperature effects can be
accounted for by adjusting Henry's Law constant. Water evaporation will
cause the organic to be concentrated.
Impoundment with a Surface Spraying System
Surface spraying systems have been developed to transfer heat from hot
water sources, such as cooling water that is recycled in power plants. A
typical surface spraying unit is shown in Figure 21. Heat is transferred
mainly by the mass transfer of water (evaporation) to the surrounding
air. The units have a large surface area, yet not so small that excessive
drift loss outside of the spray pattern area can be a problem. The spray
is directed up and allowed to fall back to the pond surface. This gives a
large (but undefinable) gas-to-liquid contact ratio, which is a
requirement for water transfer that is gas-phase (kn) controlled.
53 9
-------
AcI«G EYES FOR HANDLING
ASSEMBLED UNIT
FLOAT
MOORING
WATER LEVEL
PUMP
Figure 21. Typical configuration for a surface spray unit
54
-------
A surface spraying system is not as efficient as surface aeration for
the same power input. The energy consumed in generating the spray
droplets and projecting them into the air is not as efficiently used to
stimulate mass transfer of the volatile organic.
The value estimated for kj is 0.2 m/hr and kQ is 18 m/hr for the
design case surface sprayer. These are representative for small liquid
droplets being sprayed up and then falling through the air. The
liquid-specific surface area in contact with the air is directly
proportional to the spray drop air residence time and the spray system
pumping rate. It is inversely proportional to the spray droplet diameter
and the impoundment volume.
The spray droplet size produced by typical spray pond nozzles is
smaller than 1/4-in in diameter and averages 1/8-in in diameter. The
estimated droplet air residence time is 2 sec, which is probably typical
for a 12-ft high spray pattern. The pumping rate used is 3,500 gpm for a
25-hp spraying system and 7,250 gpm for a 50-hp system. The estimated
specific surface areas, for the model impoundment using these factors is
0.3 irrynr for the 25-hp system and 0.6 mz/nr for the 50 hp system.
The proportion of organic that volatilizes from the impoundment
surface area not directly involved in the spray pattern is normally a
small percentage of that volatilized from the spray droplets, so it can be
disregarded in the estimated specific surface areas.
In evaluating organic volatilization from an impoundment with a
surface spraying system, the effects of local climatic conditions must be
evaluated. There are three potential effects to be considered:
o A cooling effect is encountered because the mass tranfer of water
is enhanced; the impoundment water temperature probably will
approach the average climatic wet-bulb temperature. This
temperature should be used when calculating Henry's Law constant.
o Because of the greater gas-to-liquid contact, the amount of water
evaporated from the impoundment could be up to an estimated 20%
more than from an unagitated pond subjected to the same climatic
conditions.
o The half-life is considerably lower than the half-life from an
unagitated impoundment and therefore not subject to seasonal
climatic conditions for as long a time.
Impoundment with a High-Speed Surface Aeration System
High-speed surface aeration systems were developed to transfer oxygen
from air to water for biological treatment processes. A typical surface
aeration unit appears in Figure 22. The units have integral low-head,
55
-------
high-volume pumps to circulate large quantities of water designed to
cause vigorous contact of this water with air. Oxygen transfer from air
to water is liquid-phase (kj) controlled, and the vigorous generation of
a large liquid surface enhances this transfer.
A high-speed surface aerator is more efficient for organic
volatilization than surface spraying for the same power input because it
is designed to generate a large liquid surface area with an adequate
gas-to-liquid ratio.
The value estimated for ki is 0.2 m/hr and for kg is 18 m/hr.
These are considered representative for the type of Yiquid-gas contacts
generated by high-speed surface aerators. The specific surface area, s,
is estimated based on published performance testing for commercial-sized
surface aerators designed to transfer oxygen from air to water (10). The
relationship used to describe oxygen and organic mass transfer is:
K°rs _ 0.6 K°s (14)
where:
K^r = organic mass transfer coefficient
K^ = oxygen mass transfer coefficient
This equation holds for systems with relatively clean water and highly
volatile compounds, but not for dirty suspensions and waste waters.
The estimated specific surface area, s, for the model impoundment is
6.8 nr/m for the 50-hp surface aeration system and 16.0 mz/nr for
the 100-hp system. The proportions of organic that would volatilize from
the impoundment surface area not directly involved in the surface aeration
action is small and was disregarded in this surface area estimate. As in
the surface spraying system, the specific surface area for surface
aeration is a direct function of the aeration equipment horsepower, and an
inverse function of the volume of contaminated water in the impoundment.
In evaluating organic volatilization from an impoundment with a
high-speed surface aerator, the possible effect of the local climate must
be evaluated. Differences of the high speed surface aerator and surface
spraying system include:
o The specific surface area for a high-speed surface aerator is
considerably larger than for a surface sprayer, even though the
effective gas-to-liquid ratio may be lower for a surface aeration
unit. Therefore, the impoundment water temperatures will most
likely approach the average climatic wet-bulb temperatures, but
56
-------
LIFTING EYES FOR HANDLING
ASSEMBLED UNIT
MOTOR
CONDUIT BOX
MOORING CABLE
DEFLECTOR
FLOAT
X>*IS WATER LEVEL
Figure 22. Typical configuration for a floating high-speed surface
aeration unit
57
-------
possibly not as close as a surface spraying unit. It is suggested that an
average of the water temperature before .treatment and the wet-bulb
temperature be used to evaluate Henry's Law constant.
o The additional water evaporated over an unagitated pond is less for a
surface aerator than a surface spray unit.
o The organic half-life using aeration is considerably less than the
half-life using a surface spray unit system, and thus is less subject to
seasonal climatic condition variations.
o Spray drift problems for surface aeration are less than for surface
spraying units.
Applicability of Surface Impoundment Volatilization Technologies
Table 12 lists the characteristics of the impoundment systems discussed
in this section. In considering the applicability of these or similar
systems to a potential field situation, the following must be taken into
account:
o A suitable impoundment should be available. It would not be cost
effective to build an impoundment just for this purpose.
o The impoundment must be large enough to contain potential spray drift,
to allow adequate gas-liquid contact, and to provide adequate equipment
draft for proper operation.
o The shape of the impoundment should allow adequate mixing of the
contaminated water during treatment.
o These model systems are batch. An inflow (steady or batch) of
contaminated water to the impoundment would constitute a continuous
system, and the equipment described would probably not be as efficient in
treating the contaminated water as other systems discussed in this guide.
o These systems disseminate the volatile organic in the contaminated
water to the surrounding air.
o Surface spraying and surface aeration units are relatively large and
can transfer energy at a high rate to enhance organic volatilization from
contaminated water. Even though these batch systems are not as efficient
as a continuous system in removing volatile organics because of their
size, they can require less time to treat a given contaminated water
source and could be more cost effective in some situations.
58
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TABLE 12. CHARACTERISTICS OF TECHNOLOGIES FOR BATCH TREATMENT OF AN IMPOUNDMENT
en
vo
Purchase3 »° Setup/
Rating Pumping rate Weight cost takedown time
Unit type (hp) (gpm) (Ib) ($) (man-hours)
Impoundment NAC NA NA
without agitation
Surface sprayer 25 3,500 4,000 30,000 140
Surface sprayer 50 7,250 5,000 45,000 160
High-speed 50 19,000
-------
AIR-STRIPPING COLUMNS
Principle of Air Stripping
Air stripping is the controlled contact of a liquid phase containing
volatile contaminants with a clean air stream. The volatile component
transfer from the liquid to the vapor phase. Liquid-vapor contactors may
be designed to operate with a continuous vapor phase, as is found in a
spray column or packed column, or with a continuous liquid phase, as in a
bubble column. In either case, mass transfer is controlled by the
equilibrium partitioning of the compound between water and air, which is
represented by Henry's Law constant of that compound.
The removal efficiencies of air-stripping columns can vary widely,
depending on theoretical stages in the column, air flow rate, and liquid
flow rate. The height of a theoretical stage represents the height of a
column required to reach equilibrium between the liquid and vapor phases.
A theoretical stage is also known as an equilibrium stage, or a
theoretical plate.
The effect of the air flow rate, liquid flow rate, Henry's Law
constant, and number of theoretical stages on material removal is
described mathematically for a continuous isothermal stripper in the
Kremser equation (4):
f = 1 - (G/LHH1 (15)
1 - [(G/L)H]( N + 1 )
where:
f = fraction of material left in liquid phase,
G = molar flow rate of gas (in moles/min, for air: G = 0.0026 X cfm),
L = molar flow rate of liquid (in moles/min, for water: L = 0.46 X
gpm),
H = Henry's Law constant of strippable component (mole fraction/mole
fraction), and
N = number of stages in column.
For the derivation of this equation, the reader is referred to Smith
(4). It should be noted when (G/L)(H) = 1 this equation takes on the
indeterminate form, 0/0. To find f at (G/L)(H) = 1, the numerator and
denominator should be differentiated and the new fraction used for
evaluation.
f = 1/(N + 1), when (G/L)(H)= 1 (16)
An important consideration in evaluating the performance of any
air-stripping column is its operating temperature. This temperature
60
-------
determines the Henry's Law constant of the strippable compound and thereby
the amount of organic removed. Evaporation..during, normal operations
causes the operating temperature to be lower than the ambient water
temperature. The system operates at the influent water temperature when
water enters the air stripper at the wet-bulb temperature of the ambient
air, as in the case of an isothermal stripper.
In some cases, ambient air may heat cold..influent water. An
air-stripping column theoretically can be operated isothermally by adding
steam to the dry air stream, thereby increasing the wet-bulb temperature.
This method is recommended to permit control of an air stripper under a
variety of seasonal conditions.
If the air-stripping column is not operated isothermally, organic
removal is calculated using the air and water temperature in each stage,
based on water evaporation at that point of the column. The removal
achieved in each stage may then be calculated based on the Henry's Law
constant at the calculated temperature. Although this can easily be done
on a computer with the proper software, it is very tedious to do by hand.
Isothermal stripping can be assumed to occur at a temperature that is the
arithmetic mean of the feed water and the wet-bulb temperature (6)
adjusted for relative mass flow and heat capacities of the air and water.
This method should yield satisfactory results when the temperature
difference is small (20°C). Reference (6) also gives an excellent
treatment of the proper method for calculating adiabatic air stripping,
giving the method for calculation of temperature drop in each stage.
The wet-bulb temperature is attainable by using the psychrometric
chart in Figure 23. Relative humidity and ambient air temperature need to
be assumed to obtain the wet-bulb temperature to be used in performance
calculations; conservative values should represent close to the minimum
wet-bulb temperature for the particular location and season.
The number of stages in a column depends on numerous factors, such as
column geometry, contacting surface, liquid-surface tension with the
packing, liquid and vapor dispersion and mixing, and resistance to mass
transfer in both the liquid and vapor phases. Many of these factors are
dependent on the specific column used, mass flow, and properties of the
air/water system.
The prediction of column performance is a complex, time-consuming
process. However, for quick estimation of column performance, a
conservative value can be estimated for a number of stages in a particular
column. For further discussion of this field, the reader is referred to
many references on the subject (1,4,6,9).
For a cocurrent column, the maximum number of theoretical stages is
one. As long as a cocurrent column is at least one theoretical stage in
height, adding additional height does not increase compound removal. In a
countercurrent column, additional column height almost always increases
the number of stages, and hence, the amount of compound removal. However,
a point of diminishing returns is reached when column height is added to
an already-tall column.
61
-------
Reproduced from
best available copy.
9 ,/> '^ tMMpy - «
f /
W.I Mb.
D*« point ai
Figure 23. Psychrometric chart (reproduced courtesy of Carrie:
Corporati on)
-------
The presence of surfactant, salts, oils, and biomass alter the
stripping rate and vapor-liquid equilibrium. Recent proprietary studies
have demonstrated that this effect will vary the stripping rate no more
than + 50% when compared with pure water. Conservative estimation of
height per theoretical stage should allow these factors to be ignored
during preliminary performance estimates.
Description of Model Air-Stripping Systems
Four types of model systems representing the broad field of
air-stripping systems are discussed: cocurrent bubble column,
countercooling spray column, countercurrent packed column, and
countercurrent cooling tower.
Cocurrent Bubble Column--
A bubble column operates with a continuous liquid and discontinuous
vapor phase. As the name implies, air is bubbled through water by means
of a diffuser at the bottom of the column. Mass transfer is a function of
bubble size, and bubble size in the column is primarily controlled by mass
flow rates. Initial distribution of bubble sizes from the diffuser has
little to do with mass transfer rate, as long as the bubbles are evenly
distributed and within an order of magnitude of the steady-state size
distribution. Bubbles of a size distribution other than steady state will
rapidly coalesce or break apart to reach the steady-state size
distribution.
Bubble columns may be run in a cocurrent or countercurrent fashion.
Cocurrent devices are limited to one stage . Countercurrent devices may
have more than one stage, but back- mixing prevents good stage efficiency.
Most countercurrent columns operate as single-stage devices. A
theoretical stage is reached rapidly in cocurrent bubble columns. Recent
experimentation (11) has demonstrated that a contact height of 5 ft or
less is, in most cases, sufficient to achieve a single stage.
Maximum air-flow rates in bubble columns are limited by the mass flow
required to achieve the bubble flow pattern. As air flow is increased,
the column will enter the regime of a slug-flow pattern and, eventually, a
froth-flow pattern. Calculation of maximum flow rates is further
complicated by the uncertainty of the vapor-to-liquid ratio of the mixture
actually in motion.
The mixture differs from that admitted to the column due to slip,
known as holdup. In general, the gas phase tends to slip past the liquid
phase, reducing the gas-to-liquid ratio in the column over that of the
entering or exiting mixtures. For further information on flow in bubble
columns, the reader is referred to many sources (2,12,13,14).
Since flow is unrestricted by column internals, the theoretically
allowable water-flow in a bubble column is relatively great, particularly
for cocurrent systems. For large-diameter columns ( 4 ft), practical
63
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limitations in water- handling systems become more important than flow
considerations in the column. For cocurrent systems; the-most practical
consideration for large columns is the method for air-water separation at
the top of the column. The presence of surfactants in water causes
foaming in air space over the column. This limits the ability of the
demister to prevent spray from being emitted with exiting air. Water flow
is limited by the size of the weir over which the water must travel. To a
lesser extent, flow may be limited by piping, blower, or pumping
limitations.
Minimum air-flow rates in bubble columns are limited by the ability of
the air diffuser to distribute low air flows evenly. This should not be a
problem in a properly designed system. The turndown requirement (i.e.,
the minimum capacity of the system that can be used efficiently) for air
flow are dictated by the presence of surfactants in the water. It is not
expected that a turndown of greater than 10:1 would ever be necessary;
properly designed diffusers should be able to provide turndown in this
range. There are no limitations on turndown for liquid flow, so this
enables column operation with a wide range of gas-to-liquid ratios.
Cocurrent Bubble Column Design Basis--
The design basis selected for a bubble column is a cocurrent upflow
device with a single stage. A cocurrent device was selected over a
countercurrent device because columns may be operated in series without
pumps between the columns. This is possible since the density of the
air-water mixture in the columns is less than the water in lines running
between columns. Also, cocurrent columns have a slightly greater
throughput since gas holdup is less than in a countercurrent column.
Figure 24 shows the schematic of the design case column. The water
enters at the base of the 6-ft column. The air diffuser is positioned at
the lowest practical point in the column to maximize the contact volume.
Water exits the column by means of an overflow weir which breaks up any
fro# formed by the bubbling action. A demister section (as large as the
column to maximize its ability to break any foam) at the top of the column
breaks foam and surface bubbles and eliminates mist from the exiting air.
Figure 25 is a process flow diagram (PFD) of the design case system,
including valving. A single-turbine blower (B-1001) supplies air to all
four columns. This high-pressure blower (5 psig) requires a 150-hp
motor. The four columns (T-1001, T-1002, T-1003, T-1004) are arranged so
that they can be operated in parallel, two in series, or four in series.
Figure 26 gives the side, top, and rear views of the design case
system. The four columns, which must be drained when transporting, are
mounted on a 45-ft long, 13 1/2-ft high, and 8-ft wide low-boy trailer.
The blower, mounted on the front of the trailer, is powered by a 150-hp
diesel motor. Water must be pumped to the trailer using a pump rented for
that purpose.
Design case operating conditions are in Table 13. The water flow rate
of 1,000 gpm is the maximum able to exit the column over the weir,
64
-------
DEMISTER
OVERFLOW
WEIR
DRAIN
PIPE-
AIR DIFFUSER
l > ) WATER
V C INLET
Figure 24. Bubble column design, schematic
65
-------
Ol
Ol
-------
Figure 26. Bubble column design basis, side, top, and rear views
-------
TABLE 13. BUBBLE COLUMN DESIGN CASE OPERATING CONDITIONS
Gas flow Liquid flow G/L Column
Case No. moles/hr (cfm) moles/hr (gpm) moles/mole Stages
1 150 (900) 28,000 (1,000) 0.0054 1
2 150 (900) 1,400 (50) 0.108 1
3 50 (300) 28,000 (1,000) 0.0018 1
4 60 (300) 1,400 (50) 0.036 1
68
-------
assuming an 8-in head for the air-water mixture and no surfactants in the
water. The 900-cfm airflow represents an estimate of the maximum flow
rate that could be sent through a demister, considering the potential for
foaming in a clean water stream.
The selected airflow is about 30% of the maximum possible airflow rate
for a bubble flow pattern to be maintained in the column with a 1,000-gpm
water flow. The 50-gpm water flow was chosen to demonstrate the turndown
potential of a bubble column. Water flow could be further reduced for a
more advantageous G/L ratio. The lower airflow rate of 300 cfm represents
the estimate at a practical operating flow using water containing some
surfactants. Water flows of 1,000 and 50 gpm were used as they were with
the 900 cfm air flow.
Spray Column--
A spray column, which sprays water into air through spray nozzles,
operates with a continuous vapor phase and discontinuous liquid phase.
Mass transfer is a function of the droplet size, turbulence in the column,
and distribution of water in the column. Droplet size is, in turn, a
function of liquid flow rate.
It has been suggested that the number of stages in a spray tower is
approximately proportional to the liquid flow rate (2,15). This is true
for a limited flow regime and is dependent on the material being stripped
and the nozzle used. The same sources suggest that the number of column
stages decreases approximately as the square root of the gas velocity.
Well-designed spray columns generally have between 0.5 to 3 stages,
depending on the size of the column, mass flow rate, and spray nozzles
used. Theoretical stages are not proportional to column height because of
backmixing of the spray, less-efficient droplet distribution in a taller
column, and a greater influence of spray collection on the walls. Columns
taller than about 10 ft should have spray redistributed at an intermediate
point.
Generally, two types of spray towers are used: countercurrent and
cyclone. Cocurrent columns have also been designed for certain
applications, but are less efficient than the other types. Countercurrent
spray columns are arranged with nozzles at the top and a collection sump
at the bottom. Air enters at the bottom and exits through a demister at
the top.
Cyclone columns have a tangential air inlet at the side along its
base. Air travels in a spiral ing motion up the column and exits at the
top. Water, introduced via a manifold running about half-way up the
center of the column, collects at the bottom and exits out a drain.
The type of spray nozzles is an important consideration in spray
column design since the nozzle will affect turndown potential, droplet
size, horsepower requirement, potential for fouling, and spatial pattern
of the spray.
Droplet size and spatial pattern, in turn, affect the column's mass
transfer characteristics. For a discussion of different nozzle types,
refer to Perry (2).
69
-------
The maximum gas flow rate in a spray tower is limited by the
entrainment of liquid droplets. An accepted maximum flow rate is 800
Ib/hr ft', which may be converted to 106 cfm per ftz of column area
(2,15). A second consideration when choosing gas flow rates is the
decrease in number of stages as the gas rate is increased. Increasing the
gas flow rate will therefore not give as great an improvement in compound
removal as might be expected, although some increase in removal should
occur. Liquid flow is limited by the characteristics of the spray
nozzles. The spray must be distributed evenly throughout the column, with
a minimum of spray striking the walls of the column. The nozzles must
also maintain proper distribution of droplet sizes at the maximum
flowrate. The maximum liquid flow should be in the range of 1 to 3
gpm/ft'. The actual value will depend on column size, nozzle type, and
gas flow rate.
There is no minimum air flowrate for spray towers, although there is
little reason to run at low air flows for stripping, unless a greater
organic concentration in the exiting gas is desired. Minimum liquid flow
is determined by the spray nozzle used. The technology is limited in this
respect since turndown ratios of 5:1 are considered good and turndown
ratios of 3:1 are not uncommon for many nozzles. However, the column will
operate most efficiently at maximum nozzle flow. Turndown of the liquid
flow will not give a great increase in organic removal. Nozzles with
greater turndown ratios are available, but are of limited utility due to
the droplet sizes and spatial distributions possible with these nozzles.
However, nozzles can be successfully substituted into a spray column to
operate in different liquid-flow regimes.
Spray Column Design Basis--
A countercurrent spray column was selected over a cyclone column since
it will allow more than one stage, whereas the cyclone column is limited
to one stage. Also, a countercurrent column requires less maintenance and
a smaller area-per-liquid flow than the cyclone. The columns may be
operated in series for improved organic removal or parallel for higher
liquid flow. The trailer was designed with four short columns transported
upright.
Figure 27 gives the schematic for the design case column. Water is
pumped to spray nozzles through a dedicated pump (5-hp electric motor)
that can supply a relatively high-pressure (40 psi) stream. Water
collects in the sump at the column's base.
A main drain controls the water level and an overflow drain protects the
blower from process upset conditions. Each column has its own blower
requiring a 5-hp motor. Air enters the column through a duct, is directed
downward to allow even flow, and exits through a demister at the top.
Figure 28 gives the PFD for the design case trailer, including the
valving arrangement. The four columns (T-1001, T-1002, T-1003, T-1004)
may be run in parallel, or two or four in series. Four pumps (P1001,
P1002, P1003, P1004) supply water to the columns, which have individual
blowers (B-1001, B-1002, B-1003, B-1004) to supply air.
70
-------
DEMISTER
SPRAY NOZZLES
-BLOWER
WATER
INLET
PUMP
Figure 27. Spray column design basis, schematic
-------
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ro
IQ
c
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m
ro
00
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n
o
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m
IO
or
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-J
O
O
ro
10
-------
A side, top, and rear view of the trailer are shown in Figure 29.
Pumps on the tratier-are -sized to handle design-flows for pumping between
columns, or from a source directly beside the trailer. The four columns,
each 6 ft in diameter, 9-1/2 ft high, are mounted on a 45-ft long trailer
with a 4-ft bed height. Overall height of the trailer is 13-1/2 ft and it
is 8 ft wide.
Design case operating-conditions for a spray column are given in Table
14 along with column stages calculated for each flowrate. Water flow of 60
gpm (1,060 Ib/hr ft*) represents an estimate of the maximum flow for
good distribution through 40 psi nozzles in a 6-ft diameter column.
Maximum design air flow of 4,000 cfm represents the maximum that could be
used before excessive entrainment occurs. The maximum air and liquid
flows were halved to demonstrate the effect on column stages and removal
efficiencies.
Packed Column Air Stripper--
A packed air-stripping column operates with a continuous vapor phase
and discontinuous liquid phase. Packing in the column is designed to
expose liquid surface area, limit backmixing, and allow an even
distribution of liquid and vapor over its cross section. The
characteristics of the packing, the most important consideration in column
design, will determine overall performance.
Countercurrent columns can have either packing or trays. Packed
columns yield a lower pressure drop per stage and have a lower liquid
holdup. This gives them lower operating costs and sharp separation
between water and organics.
Packings are able to operate over a wider range of gas-to-liquid
ratios than trays, and perform better than trays when surfactants are
present because they are more resistant to entrainment.
Trays are generally made of metal and are subject to corrosion, while
packings can be made from metal, plastics, or ceramics. However, trays
are generally better for handling streams with high solids contents. They
also lend support to the column and are not subject to loss of efficiency
in transport as are many packings.
Column packings, which come in a myriad of materials, forms, and
sizes, are of three basic types: random dump, structured grid, and high
efficiency mesh. Random dump packing, normally 0.5-3-in in diameter, may
be shaped in a ring, saddle, or other configuration. As their name
implies, random dump packings are loaded into a column in a random
fashion. They are generally aceptable for mobile air stripping, although
they may settle during transport, reducing column perfomrance. It is
advisable to load random dump packings into the column on site to avoid
this problem.
Structured packings consist of a solid latticework of either metal or
plastic. Designs vary according to the size of slats in the lattice,
perforations and crimpings in the slats, and geometric arrangement of the
73
-------
Figure 29. Spray column design basis, side, top, and rear views
74
-------
TABLE 14. SPRAY COLUMN DESIGN CASE OPERATING CONDITIONS
Gas flow Liquid flow G/L Column
Case No. moles/hr (cfm) moles/hr (gpm) moles/mole Stages
1 660 (4,000) 1,660 (60) 0.40 1.0
2 660 (4,000) 830 (30) 0.80 0.5
3 330 (2,000) 1,660 (60) 0.20 1.5
4 330 (2,000) 830 (30) 0.40 0.8
75
-------
lattice. The surface area in the lattice will vary from 40 to 200 ft3
per ft' of packing. As the surface area is increased, the volume of
holdup, pressure drop, and number of stages per foot of column height
increase, thus sacrificing mass. High surface area packings sacrifice
mass flow for staging in a column. Structured packings are ideal for
mobile systems, for they maintain their shape during transport. They also
give high removal efficiencies with reasonably low pressure drop.
High-efficiency packings, made of metal wound into a tight mesh, are
extremely efficient in many industrial applications requiring difficult
separations. They have very small heights per theoretical stage and,
although they tend to have a higher pressure drop per foot than do random
dump or structured beds, often have a lower pressure drop per stage.
However, these packings are of limited utility in mobile applications due
to their: (1) startup problems, (2) potential for fouling, and (3)
sensitivity to placement in the column. In addition, high-efficiency
packings cost more than random dump or structured packings.
Evaluation of packings is an engineering field unto itself, and cannot
be sufficiently covered in this manual. For further information on
packings, consult packing manufacturers or the literature (2,16,17).
In order for a packing to perform properly, the liquid must be evenly
distributed over the column's area. Often, when a column fails to perform
as expected, the problem stems from problems with liquid distribution. A
variety of distributors are available, each with its own advantages and
disadvantages.
A "V"-notched distributor has a high potential turndown, low fouling
potential, and high maximum flow rate. Water is distributed by means of
troughs with "V" notches along their sides. The "V"-notched distributor
is suitable for columns with a diameter of 3 ft or greater. For
smaller-diameter columns, an orifice distributor is preferred, although
turndown is normally limited to about 4:1. Liquid is distributed through
orifices set either in a pan holding vapor risers, or in an array of
pipes. Both "V"-notched -and orifice distributors operate by gravity flow
and are very sensitive to level ness.
A mobile column containing these distributors must be perfectly
leveled before operation to perform properly. To avoid the leveling
problem, liquid distribution can be accomplished by means of spray
nozzles. However, spray nozzles are often subject to fouling, have low
turndown ratios, low maximum flowrates, and high pressure drop in the
nozzles.
Several sources can provide more information on liquid distributors
(e.g., 1,3,16). Liquid distributors are not perfectly efficient.
Therefore, some packing height is necessary to distribute liquid
throughout the column. A rule of thumb is to have approximately one
column diameter in packing height over and above the packing heights
estimated by the methods in this guide.
76
-------
Air distribution may also be a factor in an improperly operating
column. 'The most common problem is air bypassing the packing by flowing
between the packing and column wall. This is a particular problem with
structured packings, and can be prevented by using tabs to reduce flow up
the walls of the column.
Packed Column Air Stripper Design Basis--
The design basis selected-for a packed column is a 6-ft diameter
column with 25 ft of packing height. A structured grid packing with a
surface area of 120 ftyft* was selected. Liquid distribution is with
a "V"-notched distributor. In our opinion, this type of design should
give the best overall performance in a variety of mobile applications.
Figure 30 gives the schematic for the design case packed air-stripping
column. Water is pumped to the top of the column by an external pump,
rented for the flow needed. The liquid distributor sits at the top of the
column. Additional "wall wiper" distributors are placed along the sides
of the packing to redistribute flow running down and air up the walls of
the column. Water collects in a sump positioned below the packing and
exits out a drain. A blower sits at the base of the column. Air enters
the column through a duct and is directed downward to improve its
distribution. Air travels upward through the packing and exits through a
demister at the top of the column.
Figure 31 is the process flow diagram (PFD) for the system. It shows
the blower (B-1001) supplying air to the countercurrent packed column
(T-1001). The blower may be controlled by alteration of pulley
arrangement, reduction in amperage, or by means of a damper in the
ductwork.
Side view of the column during transport, and side and top views
during operation are shown in Figure 32. The high-density polyethylene
column rests in a metal framework 8 ft wide, 9-1/2 ft deep and 36 ft
high. The frame is moved by crane during setup. The column is secured
with four guy wires coming from each top corner of the frame. The 6-ft
diameter column rests on a 7-ft by 8-1/2 ft sump. The blower rests on top
of the sump, supported by the metal frame, and directs air flow downward
into the sump.
A 50-hp electric motor powers the blower. A fuse block and control
box are mounted on the side of the sump for ease of setup. The 36-ft
height permits room on the trailer for support supplies, such as hoses,
guy-wires, tools, and spare motor pulleys.
The design case operating conditions are given in Table 15. Flow is
limited by increased pressure drop caused by liquid holdup. Data on
structured packings were used to determine the maximum C factor for this
column of 0.2 ft/sec. The C factor is defined as Vs[Dv/(Di -
Dv)]u (Vs is the superficial vapor velocity taken as the
velocity of air flow in a column without packing or liquid flow.) Dv and
D-| are the vapor and liquid densities, respectively. This equals 0.0343
Vs for an air/water system at standard temperature and pressure. A C
factor of 0.2 corresponds to an air flow of 9,800 cfm in the design case
column.
77
-------
DEMISTER
LIQUID DISTRIBUTOR
HOLD DOWN GRID
STRUCTURED PACKING
WALL WIPER LIQUID
REDISTRIBUTOR
WATER INLET
BLOWER
WATER OUTLET
SUPPORT GRID
Figure 30. Packed-column air stripper, design basis schematic
78
-------
AIR
B-IOOI
WATERX
DISCHARGE /
T-IOOI
COUNTER-CURRENT
PACKED COLUMN
B-IOOI
BLOWER
Figure 31.
a1r striPPer' desi9n basis, process flow
79
-------
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-j yr
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£ 3
to 3
r*
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to
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-------
TABLE IS. PACKED AIR STRIPPING COLUMN DESIGN CASF OPERATING CONDITIONS
00
Case
Number
1
2
3
4
C
Factor
0.20
0.20
0.10
0.10
Stages
15
15
15
15
Superficial
Vapor
Velocity
(ft/sec)
5.8
5.8
2.9
2.9
Superficial
Liquid
Velocity
(ft/sec)
0.045
0.0045
0.045
0.0045
Gas Flow (G)
(moles/hr)
(cfm)
1,500 (9,800)
1,500 (9,800)
750 (4,900)
750 (4,900)
Liquid Flow (L)
(moles/hr)
(gpm)
14,000 (500)
1,400 (50)
14,000 (500)
1,400 (50)
G/L
(mole)
(mole)
0.107
1.071
0.054
0.536
Pressure Drop
(in water)
(ft packing)
0.41
0.18
0.12
0.056
Pressure Drop
Total
(in water)
12.25
0.5
4.2
2.4
Volume
Hold-up
(«)
8.0
6.6
2
2
-------
The maximum liquid flow, which was obtained by reviewing pressure drop
curves for structured packing, corresponds to a value close-to flooding....
Air flow was halved and water flow was reduced by a factor of 10 to yield
three other design cases to demonstrate the effect of varying mass flow.
The number of stages given represents a conservative estimate based on
packing efficiency found for other organics. The column may operate with
more stages in actual field situations. --
Cooling Tower--
Design and function of cooling towers for air stripping closely
parallels packed columns. As of this writing, fabricators of cooling
towers are generally new in the field of air stripping. As cooling tower
manufacturers become more sophisticated in the application of their units
to air stripping, the packings, column geometries, and column internals
they build for cooling towers are becoming like those used for packed
columns. These manufacturers have a number of advantages for building
mobile air-stripping units. The use of plastics in their designs,
experience with manufacturing transportable "turnkey" systems, and
facilities for inexpensive production of small units may give cooling
tower manufacturers a competitive edge in production of mobile systems.
At present, most manufacturers use a structured packing similar to
that for the packed column design. However, packing supplied by cooling
tower manufacturers will not be as efficient as that of packings
manufacturers. In the future, these manufacturers will probably continue
to gain understanding of the subtleties of mass transfer and may equal
traditional packing manufacturers in this respect.
Cooling Tower Design Basis--
We have selected two types of packing and liquid distribution
systems. The first is the same packing and liquid distribution system as
for the design case of packed columns. The second is a system found in
cooling towers. The packing supplied by packed column manufacturers is
slightly more efficient than that produced by cooling tower manufacturers
in our survey.
The cooling tower design case gives an interesting contrast to the
packed tower design, since it compares four short columns to one tall
column. The design case cooling tower system uses a column arrangement
common to several manufacturers. Four 6-ft diameter columns with 4 ft of
packing are transported vertically on a 45-ft trailer. Blowers are placed
directly on the side of each column.
For the first two design cases, liquid distribution is accomplished by
a "V"-notch distributor. The second two design cases employ spray nozzles
common to many cooling towers. This was done to demonstrate the greater
maximum liquid flow and greater turndown allowed by the "V" notch
distributor.
82
-------
Figure 33 gives the schematic for the cooling tower design basis.
Water is pumped to the top of the column with a 1.0-hp pump mounted on the
trailer. Pumps are sized to pump water between columns or from a source
beside the trailer. For pumping from any significant distance, an
external pump would be necessary. Water flows from the distributor, down
through 4 ft of packing and then collects in a sump. The distributor
pictured is a "V"-notch distributor, and is used in the first and second
desired cases. The water outlet may be directed to the next column or
discharged to the sewer. Figure 34 is a design sketch of the cooling
tower unit.
If the normal outlet becomes blocked, an overflow drain is provided to
protect the blower. Air is blown into the column with a 25-hp blower and
directed downward via ducting. Exiting air passes through a demister at
the top. The valving is arranged so that the columns can operate in
parallel, or two or four in a series. Discharge is directed to a common
drain line that also takes water from the overflow drain. Four blowers
supply air to the columns.
The four columns each have a 6-ft diameter and 9-1/2 ft overall
height. With a 4 ft high trailer bed, the overall trailer height is
13-1/2 ft. The trailer is 45 ft long and 8 ft wide. All blowers and
pumps are controlled from a panel mounted at the front of the trailer.
The design case operating conditions are shown in Table 16. The first
two operating conditions are the same as two of the conditions used in the
packed column. The second two operating conditions are for the less
efficient packing. Use of the spray nozzles reduces the maximum air flow
to 6,000 cfm due to entrainment of the liquid droplet.
Applicability of Air Stripping
Air-stripping columns are for treatment of water containing low- to
medium-hazard materials. Potential emissions from air stripping limit its
application. Control devices can be placed on the exiting air to reduce
emissions; however, the added cost of an air control device may make air
stripping less cost effective than other water treatment options, such as
steam stripping or aqueous-phase carbon adsorption.
The potential for fugitive emissions may require additional design
considerations for an air stripper to be used for removal of extremely
hazardous substances, regardless of the emission control device used.
Limitations on the applicable concentration ranges for air stripping
are extremely variable. At low organic concentrations, adsorption and
absorption of the organic onto oils, biological material, and suspended
solids present in natural waters may begin to limit the ability of an air
83
-------
oo
LIQUID
DISTRIBUTOR
SUPPORT
PLATE
111 iiMI i i
BLOWER
PUMP
Figure 33. Cooling tower design basis, schematic
-------
oo
en
CIOII-IFTIHG ^fS*;
MCCHKNI6M
Figure 34. Cooling tower design basis, side view
-------
TABLE 16. COOLING TOWER UESIGN CASE OPERATING CONDITIONS
00
at
Case
Number
1
2
3
4
C
Factor
0.20
0.20
0.12
0.12
Stages
2.4
2.4
2.0
2.0
Superficial
Vapor
Velocity
(ft/sec)
5.8
5.8
3.6
3.6
Superficial
Liquid Gas Flow (G)
Velocity
(ft/sec)
0.045
0.0045
0.027
0.0054
(moles/hr)
(cfm)
1,500 (9,800)
1,500 (9,800)
900 (6,000)
900 (6,000)
Liquid Flow (L) G/L
(moles/hr)
(gpm)
14,000 (500)
1,400 (50)
8,400 (300)
1,680 (60)
(mole)
(mole)
0.107
1.071
0.107
0.536
Pressure Drop
(in water)
(ft packing)
0.41
0.18
0.09
0.07
Pressure Drop
Total
(in water)
3.0
2.2
1.4
1.3
Volume
Hold-up
(X)
8.0
6.6
2.5
2
Packing
a
a
b
b
a Structured packing typical of packed towers.
D Structured packing typical of cooling towers.
-------
stripper to volatilize the organic. However, this is an extremely
variable concentration limit, depending on the organic to be stripped,
contaminants present in the water, and organic removal desired. At high
concentrations of organic, the air emissions or safety considerations
begin to limit the use of air stripping. This is also extremely variable
and is dependent on toxicities, flammabilities, and stripping rates.
The primary safety consideration for air stripping is the treatment of
flammable organics since a combustible mixture could be formed in the air
exiting the stripper. This is likely with flammable organics having a
high Henry's Law constant. Aqueous phase organic concentrations in the
range of 100 ppm can often result in air concentrations above the lower
flammability limit (LFL).
Whenever air-stripping is used, anticipated air emissions should be
calculated and compared with data on the LFL. Organic concentration in
air must be maintained below 25% of the LFL to meet the safety standards
in the EPA Standard Operating Safety Guidelines. Explosion-proof
equipment is required on all air stripping units used with any flammable
materials. A table of LFL values for various organics is given in
Appendix C as a reference.
In addition to general considerations on the applicability of air
stripping, each type of stripping column has its own applications, as
discussed below.
Applicability of Bubble Columns
Generally bubble columns are best applied to situations requiring high
liquid throughput with a relatively low requirement for material removal.
They are ideal for situations where there are solids in the water that
might cause fouling, but do not adapt well to situations requiring
difficult separations or treatment of water with high surfactant
concentrations. Mobile units can have a very simple design requiring a
short setup time.
The advantages of bubble columns include:
- High potential liquid throughput
- High liquid turndown ratio
- Wide range of G/L ratios
- Low potential for fouling
- Short columns, may be transported vertically
- Low liquid pressure drop
- Simple device, low maintenance
87
-------
- Adaptability to field situations
- Short setup time
- Design adaptable to available tankage and equipment
The disadvantages include:
- Surfactants in water limit flow rate
- Single-stage device, low removal percentage
- High gas-pressure drop requires high-horsepower blower
Applicability of Spray Columns
Of the air-stripping columns covered in this manual, spray columns are
the most limited in range of application. The only relative advantage
spray columns have over other air-stripping devices is a low pressure drop
for the gas which reduces blower horsepower requirements. In certain low
pressure distillations, this advantage justifies their use, although it is
not as important in air stripping.
Spray columns, which are not as efficient as packed columns, have
limited throughput and turndown potential, and can be prone to fouling at
the nozzles.
The advantages of spray columns include:
- Low pressure drop for gas
- Simple operation
- No packing, reduced potential for fouling and channeling
- Short setup time
- Design adaptable to available tankage and equipment
The disadvantages include:
- High pressure drop for liquid
- Gas flow limited by liquid entrainment
- Limited number of stages, low removal percentage
- Number of stages not proportional to column height
- Possibility of fouling in nozzles
- Low turndown ratio (unless nozzles are changed)
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Applicability of Packed Air-Stripping Columns
A packed air-stripping column, as described for the design case, is
useful for difficult separations requiring a high percentage removal.
However, the treatment potential in this column may not be required for
removal of many organics, particularly those having a high Henry's Law
constant or in situations where high percentage removal is not required.
In many cases, a shorter column gives adequate treatment for a lower
operating cost.
A major advantage is the extremely high removal allowed in a tall
packed bed. The disadvantages presented are a function of column design,
packing, and mass flow.
The potential for fouling should normally not be a problem with proper
packing selection. Fouling problems may also be eliminated by
pretreatment of wastewater with a sand filter or other device. Column
setup requirements will vary, but a tall column will either be transported
horizontally or in sections, thus requiring greater field setup time.
Other advantages of a packed air-stripping column include:
- Excellent removal efficiency (multistage device)
- High rate mass flow
- High turndown potential
- Large range of G/L ratios
- Low liquid pressure drop
The disadvantages include:
- Potential for fouling (depends on column internals)
- Difficult to transport and set up
- Significant gas pressure drop
- Difficult to adapt to available tankage and equipment
Applicability of Cooling Towers
Applications for this device are similar to those for the taller
packed column. Shorter columns are a better choice than tall columns if
they can give the desired treatment for they require a lower-horsepower
blower than a tall column for the same mass flows, thus reducing operating
costs.
Also, short multiple columns (four per trailer) can be transported
vertically, thus reducing setup time and permitting a higher treatment
rate. Operated in series, the four columns would give treatment at least
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as good as the tall column, although the tall column will have a lower
operating cost than four short columns. In addition, a trailer with
multiple short columns is more versatile than a single tall column, since
both series and parallel operation are possible.
The advantages of short columns, such as cooling towers, include:
- High rate of mass flow
- High turndown potential
- Large range of 6/L ratios
- Low liquid pressure drop
- Compact device - easily transported
- Short setup time
- Low gas pressure drop
The disadvantages include:
- Potential for fouling (depends on column internals)
- Relatively new application by manufacturers
- Two- or three-stage device, may not give enough removal
- Difficult to adapt to available tankage and equipment
CONSIDERATIONS FOR AIR-STRIPPING EQUIPMENT EVALUATION
Considerations for selecting a particular piece of air-stripping
equipment are: Number of stages in the column, mass flow rates, utility
requirements, and setup requirements.
The number of stages in a column is determined by the packing in the
column, and, to a lesser extent, the air and water flow rates and Henry's
Law constant of the organic. The vendor should be questioned on column
performance at various air and water flowrates. The vendor should be able
to give data on the packing in his column, including ranges of height per
theoretical stage, pressure drop for various flowrates, and liquid holdup
for various flowrates. A conservative estimate of height per theoretical
stage for use during preliminary performance calculations should be taken
as the upper end of the range given by the vendor.
Bubble columns should be treated as having a single stage. The number
of stages in a spray column is difficult to obtain, but may be assumed to
be one for preliminary estimates.
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The type of packing and column diameter determine mass flow rates.
The vendor should be able to provide a flooding curve (which defines the
limits at which the column can no longer support a discontinuous liquid
phase due to the mass flow) for the column. To estimate maximum column
performance, mass flows that represent 80% of flooding should be used.
The Kremser equation (Eq. 5), can be used to estimate material removal
at several flowrates. Pressure drop data should be used to determine
blower horsepower requirements. The blower provided with the column
should be examined to determine whether it will perform as required. New
pulley arrangements, different horsepower motors, and adjustment of
amperage will allow a range of performance from the same blower.
The design case systems assume columns of the maximum diameter
transportable on one trailer. Smaller columns of the same height and
packing will have lower maximum mass flows. To estimate the mass flow in
a smaller diameter column, multiply the mass flow by the square of the
smaller diameter, and divide the result by the square of the design case
diameter.
DISTILLATION SYSTEMS
Principle of Distillation
Distillation is a method of separating the components of a liquid
solution and depends on the distribution of the substances between a vapor
and a liquid phase. Instead of introducing a new substance into the
mixture in order to form the second phase, as is done in air stripping,
the new phase is created from the original solution by vaporization (1).
Distillation columns are divided into stripping and rectification
sections. Stripping sections operate at a higher concentration of the
lower-volatility component. Rectification sections operate at a higher
concentration of the higher- volatility component. Generally, water
columns have only a stripping column with no rectification section.
The vapor and liquid phases in contact in a distillation column are at
essentially the same temperature and pressure. Various kinds of devices
(plates, trays, or packings) are used to bring the two phases into
intimate contact. Trays or packings are stacked and enclosed in a
cylindrical shell to form a column. Feed material is introduced at one or
more points along the column shell. Because of the difference in specific
gravity between the vapor and liquid phases, the liquid runs down the
column, cascading from tray to tray, while the vapor goes up the column,
contacting the liquid at each tray.
The liquid reaching the bottom of the column is partially vaporized in
a heated reboiler to provide reboil vapor which is sent back up the
column. The remainder of the bottom liquid is withdrawn as the bottom
product. The vapor reaching the top of the column is cooled and condensed
to a liquid in the overhead condenser. Part of this liquid is returned to
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the column as reflux. The remainder of the overhead stream is withdrawn
as the overhead or distillate product. In some instances, the distillate
product consists of an organic-rich phase that is separated from the
aqueous phase. The overall flow pattern in a distillation column provides
countercurrent contacting of vapor and liquid streams throughout the
column.
The lighter (lower boiling) components tend to concentrate in the
vapor phase, while the heavier (higher boiling) components tend toward the
liquid phase. The result is a vapor phase that becomes richer in the
lighter components as it passes up the column, and a liquid phase that
becomes richer in the heavy components as it cascades downward. If the
feed is introduced at one point along the column shell, the column is
divided into an upper section, called the rectifying section, and a lower
section, referred to as the stripping section.
The overall separation achieved between the overhead product and the
bottom product depends primarily on the:
1. Relative volatilities of the components
2. Number of contacting trays or stages
3. Ratio of the liquid-phase rate to the vapor-phase rate
By appropriate manipulation of the two phases, repeated vaporizations
or condensations, or variation in column height, it is possible to make as
complete a separation as desired by using distillation (except for
azeotropes, see below). Both components of a two-component mixture can
then be recovered in as pure a state as desired.
Distillation is an energy-intensive separation process (1,2). In a
mobile system the limitations imposed by energy requirements are the
primary limitations on removals and flowrates. Limits on column height
may also be important in some cases.
Treatment of Aqueous Organic Solutions by Distillation
Application of distillation to dilute aqueous organic solutions of
limited solubility is confined to steam stripping. (Steam stripping uses
steam as a heat source instead of a reboiler and is in contact with the
waste liquid.) Because we are interested only in purifying the water
stream and not the organic stream, the desired distillation should contain
only a stripping section to remove the more volatile organic from the
water. Descriptions of theory for the removal of volatile organics from
wastewaters is contained in other sources (6,18,19).
The application of other distillation techniques, such as
multicomponent, azeotropic, extractive, vacuum, fractionation, and
molecular distillation, are applicable to specific systems where
vapor-liquid equilibrium data are experimentally determined or known, and
specific equipment and methods are needed to obtain a specific product.
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These applications are therefore beyond the scope of a generally
applicable distillation technique..for the..removal, of.many volatile organic
compounds from wastewater.
Relative Volatility
Relative volatility in a binary system is a measure of the degree to
which the more volatile component .concentrates .in the vapor phase and the
less volatile component concentrates in the liquid phase. Also, relative
volatility is the ratio of vapor to liquid composition for the two
components under consideration.
For steam stripping of a single volatile organic from water, the
relative volatility can be related to the Henry's Law constant after
making some simplifying assumptions. Henry's Law constant is used
exclusively throughout the manual for steam stripping. For further
information on the relationship between the relative volatility and
Henry's Law constant, see Section 1.
Azeotrooes
In a binary system, an azeotrope is a system in which the organic
concentration is the same in the vapor as in the liquid. An azeotrope
represents a limit to which a separation can be conducted. In general,
when dealing with dilute insoluble organics in water, azeotropic formation
will not affect the separation. If, however, the organic is soluble in
water and requires rectification, then an azeotrope will be more likely to
affect the degree of separation in a particular system. The exact effect
depends on the materials being separated and the operating conditions.
Each system should be evaluated for the possibility of azeotropic
formation before a full-scale system is designed or operated.
Azeotropic data are available; (20) these data should be used to
verify the existence of the azeotrope, and a design engineer should do a
final calculation. If azeotropic data are not found, it will be necessary
to attain vapor-liquid equilibrium data for
the system before a design is initiated. Structure-activity methods for
the prediction of azeotropes are available, but their accuracy will vary
depending on the system of interest. Data should be obtained from
published experimental data, if available, or from laboratory distillation
of the specific compound(s) of interest.
Steam-to-Feed Ratio
Distillation is an energy-intensive separation process. A major
portion of the operating cost of a steam stripper is the energy necessary
to make steam. For a given column with a fixed column height and packing
to produce a given separation, the steam-to-feed ratio (also called gas to
liquid ratio, 6/L, boilup, or percentage boilup) is fixed by Henry's Law
constant. The degree of separation is increased by selecting a higher
steam-to-feed ratio. The steam- to-feed ratio can be raised and lowered
in a given column, within limitations. The range used for this manual is
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a minimum steam-to-feed ratio of 0.03 and a maximum of 0.30. These limits
are imposed because of-equipment limitations, and should-be-generally
applicable to mobile steam-stripping systems.
Mass Transfer Equations and Estimation Procedures
As in air stripping, the performance of a steam stripper can be
described mathematically by the Kremser equation (Eq. 15). It should also
be noted that this equation assumes dilute isothermal solutions. The
Henry's Law constant used should be evaluated at 100°C. All other terms
have identical meaning and application as those stated for air stripping.
In cases where Henry's Law does not apply, the Kremser equation yields
an estimate, but the detailed methods of McCabe-Thiele or Ponchon-Savarit
should be used if a better estimate is desired for design purposes. These
methods, requiring specific vapor-liquid equilibrium data on the specific
compounds being separated, are described in various texts (1,2). The
reader should also use caution when applying the Kremser equation for more
soluble compounds.
DESCRIPTION OF MODEL SYSTEM
A process flow of the model steam stripping system is shown in Figure
35. It also includes major control instrumentation for clarity. A plan
view is shown in Figure 36.
The steam-stripping system consists of a packed column with two
packing sections. Feed inlets are located above each of the sections.
These sections have -5 ft of packing in the upper section and -20 ft of
packing in the lower section. A multistage operation is required to
provide an overhead organic concentration higher than the organic's
concentration in water. The rectification section provides for column
operation at organic concentrations higher than the feed organic
concentrations. In general, rectification will be necessary only if the
ratio of the organic solubility and the feed concentration is greater than
the Henry's Law constant evaluated at 100°C, assuming dilute solutions.
Or:
05
>H100°C
where:
Cos = Concentration of organic in water at solubility,
C0f = Concentration of organic in the feed water, and
HJOO°C = Henry's Law constant at 100°C.
(17)
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to
FEED |Q| (-0
AIR
Jgfas? 0
?
P-102 C-101 E-104
AB
PRODUCT
STORAGE
T-10IB
P-103A
DRAIN
Figure 35. Steam stripper design basis, process flow diagram
-------
If rectification is necessary, the final design or application should
be determined by a design engineer. In most instances a dilute, insoluble
organic will enter the top of the column and will not require a
rectification section.
The column diameter of the model system is limited by the physical
size and weight of the auxiliary system equipment required to operate the
column. This was apparent in the sizes of required heat exchangers
diagrammed in Figure 36. The largest standard column diameter (determined
by the maximum heat duty) that can be placed on a packed trailer is 1.5
ft. The packing used is 1.5-in metal pall rings. Random dumped packing
was chosen over trays because of easier cleaning, and over rigid packing
because of availability. The height of packing was chosen to be 25 ft.
This was due to the overall size of the column shell of 35 ft, which is a
realistic size for a single flatbed trailer.
The feed is pumped from the waste location, through a strainer, and
used as cooling water for the overhead condenser. From there the feed
exchanges heat in the bottoms heat exchanger with clean water from the
bottom of the column. The preheated feed enters the top of the
distillation column. Preheating the feed reduces energy input required to
operate the column. The total energy required can be estimated as the
differences in enthalpy between the feed in and the bottoms out (the
project out will usually be a small fraction of the feed). Another
advantage of preheating is that cooling water for condensation may not be
available, so some of this heat duty can be handled by the feed stream,
thus reducing the size of air condensers required on the trailer.
The practical liquid and gas flowrates are fixed by the column
diameter due to the limits of flooding. Flooding in a packed tower is an
unstable operating region in which the vapor rising up the column
interferes with the liquid traveling down the column, causing a sharply
increased pressure drop over the column. Flooding causes a reduction in
mass transfer resulting in lower effluent quality. The flooding flowrates
for the design case steam stripper removing dilute organic compounds from
a wastewater stream are shown in Figure 37. In this figure, column
diameter is plotted against flooding liquid rates for different boil-ups
(gas-to-liquid ratios). Different sizes of metal pall rings are used in a
range of diameters to conform with standard rules-of-thumb used in
industry. Standard practice is to operate at 80% of flooding.
Therefore, the operating conditions for a 1.5-ft diameter column are as
follows:
Boil-Up (G/L) Maximum Liquid Rate (qpm)
3% or 0.03 96
5% or 0.05 74
10% or 0.10 50
30% or 0.30 24
These rates will yield pressure drops in the column of 0.75 to 1.75 in of
water per foot of packing or -1.5 psi maximum over the entire column.
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GUV
vo
OUTRIGGER
Figure 36. Steam stripper design basis, plan view
-------
1,000 r
METAL PALL RING SIZE
BOIL
-4©%-
100
30%
-5'.4 J ..' ,^ - -_ : j ; JT
10
-'~- ' '- \ ': -'-
,-
0.5
1.5
DIAMETER I FT I
Figure 37. Flooding in a packed tower stream stripper
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The four heat transfer surfaces were sized to reduce the energy
consumption of the system over the entire range of operating conditions.
The range of heat duty for the reboiler and condensers is as follows:
Boil-Up (G/L) (%) Heat Duty (106Btu)/hr)
3 1.4
5 1.8
10 2.4
30 3.5
This range represents practical operating limits and operation should
not deviate from these ranges.
The reboiler consists of two 225-kW electric steam generators. This
will yield -1.4 X 106 Btu/hr of low-pressure steam for boil up of 3%. For
larger boil up the system operator could rent a portable diesel-powered
steam generator to hock into the bottom of the column. A combination of
the boil-up required and the standard size of available equipment in the
area would determine the size of boiler rented. When using the electric
steam generators supplied with the design case system, the operator would
select a rental electric generator based on the electric demand of the
reboiler.
The bottoms exchanger is sized such that the temperatures of the feed
on either side of it are similar in order to reduce boiler requirement and
minimize the heat released if the bottoms were returned to the
environment. A hot stream returned to a lagoon, for example, would
release more organic material to the atmosphere. This exchanger has a
heat transfer area of 850 ftz.
The overhead condenser is sized based on a 3% boil up, and has a heat
transfer area of 75 ft2. If a higher boilup is selected, then the
additional heat duty would be taken by the extended surface air
condenser. This is sized based on using 85°F air to condense 3.5 x
10° Btu/hr of atmospheric steam and has a total heat transfer area based
on a bare tube area of 385 ft . For some operating conditions, the
condensers provide some subcooling of the liquids. The temperature is a
function of boilup, organic concentration, and vapor-liquid equilibrium.
Some degree of subcooling of the organic is required to reduce vent
losses. The water phase returned to the top of the column should be as
close as possible to boiling to reduce energy costs of the reboiler. The
design case heat transfer system represents a compromise over the range of
operating conditions.
Four different operating regions were envisaged that would influence
the design of the product storage/reflux area. These are summarized as
follows:
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Number of Phases Formed
in the Decanter Liquid Organic Reflux
2 More dense than H20 All of the H20
2 Less dense than H20 All of the H20
1 Miscible with H20 None if stripping
only
1 Miscible with H20 A fraction of the
H20 if stripping
and rectifying
The first two operating modes cover most of the organic systems
encountered. Condensate from both condensers flows by gravity to the
accumulator/gravity separator. Separation occurs by allowing a minimum of
0.5 hr residence time in the accumulator (150 gal). A light and heavy
liquid stream are drawn off with a movable standpipe, which permits the
two-phase interface to be adjusted inside the accumulator. Both streams
then flow by gravity to individual levee control tanks. These allow
15-min residence time (75 gal). Individual reflux/product pumps are used
to return the water stream to the top of the column or to send organic
product to a storage location. This tank would be rented at the site.
Fifty-five gallon drums may also be used for product storage. Ultimately,
the choice will depend on the available organic disposal.
In the case of a single phase forming in the decanter, a single-level
control tank and pump is used to send part of the organic-rich stream back
to the column as reflux and part to an organic-rich storage tank. The
flowrate of this organic-rich stream is the product of boilup and the feed
flowrate divided by the reflux ratio. The product-rich storage tank
should be sized with this flowrate in mind. The column is transported in
a horizontal position with packing in place. At the treatment site the
column is raised by means of a hydraulic arm to an upright, vertical
position. The column is then interconnected with the rest of the system.
The trailer is also equipped with hydraulic stabilizer feet to form a base
of support for the column. Finally, the column is secured with four
guy-wires for added wind stability.
As designed, the model system is primarily a steam-stripping unit.
Provisions were made to operate the unit with rectification to provide
some flexibility to operate the system as a distillation unit. However,
it is anticipated that most field situations will involve organic
contaminants that will only require stripping to remove them from a
wastewater stream. The system represents a compromise so that as many
compounds as possible can be treated with the mobile steam-stripping
system.
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Applicability of Distillation Systems
In industry, steam stripping is used to remove compounds from water in
the concentration range of 1 - 10%. The application of steam stripping to
lower level of organic compounds has been proposed (6,19). Generally, at
concentrations below 100 ppm organic, other treatment alternatives become
more economically attractive, such as carbon adsorption (21). The lower
treatment concentration limit depends on the specific design of the
steam-stripping equipment, including such equipment details as liquid and
vapor distributors, wall effects, and gas-liquid contacting. Treatment
levels for some compounds were proposed down to 1 ppb (5).
Steam stripping is not generally applicable to certain classes of
compounds such as glycols, amides, acids, phenols, and glycol ethers
because they are the less volatile compounds. However, certain individual
compounds within those classes might be treatable by steam stripping.
If air emissions are not acceptable, steam stripping allows the
organic to be removed from water and discharged as a liquid phase, with
appropriate vent controls, air emission could be greatly reduced over
treatment technologies, such as air stripping, that discharge the organic
directly to the air. However, a concentrated organic stream may become a
disadvantage from a flammability and health standpoint. These factors
must be considered when a steam stripper will generate an extremely
flammable liquid or extremely toxic concentrated organic. Each situation
will have unique requirements that must be evaluated individually.
Compared with other systems in this manual, the advantages of steam
strippers include:
- Recovery of a concentrated organic (reduced disposal volume)
- Air emissions from tank vents only
- Availability of many equilibrium stages
The disadvantages of steam strippers include:
- Low 6/L ratio
- High energy consumption, high operating costs
- Not easily adapted outside of industrial plants
- Moderately complicated device, high maintenance
- Extended setup time
- High potential for fouling
- Low treatment rates
- Recovery of a concentrated organic (health and safety exposure)
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- Difficult to adapt to available tankage and equipment
In general, steam stripping is applied to situations requiring high
removal efficiencies with mandatory recovery of organic (low air
emissions).
Utility requirements are the principal factors limiting possible
treatment rates in a steam-stripping system. This is demonstrated in the
design case system by the relative sizes of equipment on the trailer. The
physical sizes of heat transfer equipment and associated heat duty are the
primary factors influencing the treatment rates through the system. If
cooling water is available from other sources, then a larger system could
be designed to fit a single flatbed trailer.
The model system previously described was designed to be a quick
response/emergency treatment system. Before operating this type of unit,
some study of available equilibrium data is required to evaluate whether
treatment criteria will be met. Certain design modifications may need to
be implemented in each specific case, such as vent controls, fire
proofing, special holding tanks, or high-hazard training courses for
operators and others. Also, a steam stripping unit requires evaluation
and extra setup time as compared with the other treatment technologies
covered in the manual.
CONSIDERATIONS FOR STEAM-STRIPPING EQUIPMENT EVALUATION
Equipment associated with a steam-stripping system is standard
chemical processing equipment. Although most of it is custom fabricated,
the specifications are standard designs used throughout the chemical
industry. In some cases, a vessel fabrication and packing manufacturer
may be able to build the entire system. Several package distillation
systems are available in the marketplace. However, it is generally not
practical to configure a steam-stripping system from available equipment.
For heat transfer equipment, most reputable manufacturers follow
standard design practices. Any heat exchanger can be designed using any
standard text (22). Pumps are standard designs available from vendors and
suitable for the required service. All packing manufacturers have
literature on the performance and specifications of their packing;
however, such data from vendors tend to be optimistic.
The design case system assumes a column of the maximum diameter
transportable on a trailer with all associated equipment. A
smaller-diameter column of the same height and packing has a
correspondingly lower treatment rate. However, smaller columns that were
designed to be pilot plants for demonstration purposes may be available.
These columns may have flows in the 1-10 gpm range. If this flow rate is
acceptable, these systems could provide an attractive option for water
treatment.
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SECTION 6
FACTORS AFFECTING EVALUATION
A variety of factors affect the performance of treatment systems under
actual field conditions. Many of these factors have effects that are
difficult to quantify on a theoretical basis. Further data to apply the
theory may often be difficult or impossible to gather in the field.
Normally, these factors taken together will not influence system
performance by more than a factor of 2 to 3. Therefore, they generally
fall within the accuracy of the predictive methods outlined in this guide
and can be ignored during preliminary evaluations. This section describes
some of these factors and qualitatively predicts their effects.
MATERIAL-SPECIFIC FACTORS
Multicomponent Mixtures
Effects of multicomponent mixtures become more profound as the organic
concentration is increased. The presence of organic contaminants affect
the volatilization of the compound(s) of interest by introducing
competitive interactions into the vapor-liquid equilibrium. These effects
are extremely complex and normally cannot be predicted accurately without
specific experimental data.
The volatilization technology most affected by multicomponent mixtures
is steam-stripping due to the concentration effect of rectification in a
steam stripping column. Air in an air-stripping unit normally will not
become saturated with organic, resulting in reduced interaction between
organic components in that technology.
We estimate the effect of multicomponent mixtures can be ignored for a
routine evaluation of performance, particularly when organic
concentrations are low. Volatilization of each organic component should
be estimated independently, as if it were the only organic present. This
gives a very rough estimate if no supporting data are available. The
effects of multicomponent mixtures are system specific, however, and may
be very significant, particularly at high concentrations of organics.
Safety Considerations
Two important safety considerations are the flammability and toxicity
of organic contaminants. By nature, air stripping creates a mixture of
air and organic vapor that could be explosive. Additionally, emissions
from airstripping devices may be difficult to treat to low
concentrations. Emission controls may not prevent a hazardous atmosphere
in the area around an airstripping operation, particularly if the process
involves very toxic organics or flammable organics that tend to collect in
low-lying areas. Generally, safety and emission restraints limit the
applicability of air-stripping devices, including surface aerators and
surface sprayers placed in a pond.
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Although steam stripping does not necessarily create a potentially
explosive or toxic mixture of air and organic vapors, these mixtures may
occur if precautions are not taken. Strict handling procedures must be
followed when handling potentially toxic or flammable materials. The
potential for unsafe conditions is increased by the elevated operating
temperatures of steam stripping and the formation of a concentrated
organic stream for disposal.
Safety practices must include: Vent condensers, LFL monitoring,
special fire suppression systems, operator respiratory protection, and
protective clothing.
Whenever evaluating treatment technologies for potentially hazardous
materials, a qualified industrial hygienist should determine if the
process can be run safely, draft safety precautions for operating the
process, and develop cost estimates for the safety program. Regardless of
the urgency of the cleanup process, there is no substitute for appropriate
safety planning and determination of the limitations of the equipment and
technology.
Absorption and Adsorption
Absorption is the dissolution of a material into another material. In
natural water, oils associated with solids or freely floating oils form a
separate nonpolar phase. The measure of the equilibrium partitioning
between water and a nonpolar phase is the octanol-water partition
coefficient. A relatively small amount of oils in natural water can
greatly influence the behavior of an organic with a high octanol-water
partition coefficient.
Adsorption is the binding of a material to the surface of a solid.
The tendency of organics to adsorb is greater for low-molecular-weight
organics and organics with low aqueous solubilities.
The absorption and adsorption of a compound on suspended solids,
sediments, oils, and biological tissue can reduce the stripping rate,
particularly for organics with low solubilities. This effect is the
result of the equilibrium and kinetics of organic transfer between water
and solid materials.
Decomposition in Water
Many organics will decompose in water by such mechanisms as
hydrolysis, photolysis, reaction with other substances in the water, and
biological degradation. These factors will compete with volatilization
for the disappearance of the organic from water. In some cases,
decomposition will yield products that are relatively innocuous. In other
cases, the decomposition product(s) may be hazardous in their own right
and require treatment.
The scope of this manual does not include the decomposition of
organics. However, Appendix B lists some compounds suspected to hydrolyze
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or photolyze in water. If decomposition by any means is suspected, the
mechanism should be studied, to.jdetermine, the .competing rate. The
properties of decomposition products should then be analyzed to determine
if their removal should be considered in the evaluation of treatment
alternatives.
SITE-SPECIFIC FACTORS
Season
Season mainly influences the operating temperatures of the treatment
system. For air stripping and volatilization from a pond, the
volatilization rate will decrease as ambient temperature decreases. For
stream stripping, the ambient temperature mostly affects the size of air
condensers and heat exchangers necessary to operate the column. If proper
insulation is not used, very cold ambient temperatures can cause freezing
in lines and excessive heat loss from a steam stripper.
For volatilization from a pond, seasonal effects other than
temperature can be important. For a pond without agitation, increased
wind speeds increase the volatilization rate. Incident radiation affects
pond temperature, thus increasing volatilization rates. Precipitation, or
lack of it, affects the concentration of the organic in the water,
although it may not affect the actual amount in it. The effects of
precipitation are not due just to rainfall, but also include runoff.
Expected seasonal variation must be considered as part of the initial
technology evaluation. If a unit is to be run in the winter, provisions
for insulation, steam injection into air strippers, and protection of
equipment and work areas from excessive condensation and ice formation
must be implemented.
Water Quality
Water quality can affect system performance through reduction of
volatilization rate, limitation of gas and liquid flow rates, and fouling
of equipment. Reduction in rates influences compound removal. Adsorption
and absorption are primary causes of reduction of volatilization rates.
The presence of surfactant can limit the gas and liquid flowrates
possible for proper operating of treatment systems. Agitation, a primary
characteristic of all methods, increases volatilization. If surfactants
are present, foaming can become a problem in agitated systems. Flow rates
must then be reduced to limit foaming. To overcome this problem,
additives can be used to help prevent foaming.
Fouling can be caused by suspended solids, biological material or
growth, or water hardness. It can reduce the effective surface area of
packing, diminish the effectiveness of spray nozzles, and increase
pressure drop in columns. It is difficult to predict the potential for
fouling in heating natural water. Use common sense to determine the
potential for fouling in specific situations. If any of these factors are
105
-------
present In abundance, the potential for fouling must be considered before
using any system that might be-prone-to-foul.
In many Instances, pretreatment will be necessary before application
of air- or steam-stripping columns. Warning signs are the presence of
solids, algae, or salts in the water to be treated, or any application
using water contaminated with an organic that will support bilogical
growth. Pretreatment methods could include sand filtration, treatment
with an oil absorbent, addition of additives to prevent growth, and
flocculation followed by sedimentation.
106
-------
REFERENCES
1. Treybal, R. E. Mass Transfer Operations, 2nd ed. McGraw-Hill, New
York (1955).
2. Perry, R. H., and C. H. Chilton. Chemical Engineers Handbook, 5th
ed. McGraw-Hill, New York {1973)-.
3. Smith, J. M., and H. C. Van Ness. Introduction to Chemical
Engineering Thermodynamics, 3rd ed. McGraw-Hill, New York (1975).
4. Smith, B. Design of Equilibrium Stage Processes. McGraw-Hill, New
York, (1963).
5. Dean, J. A. Lange's Handbook of Chemistry, 12th ed. McGraw-Hill, New
York (1979).
6. Goldstein, D. J. Air and Steam Stripping of Toxic Pollutant, Vols. 1
and 2. EPA Report Number 68-03-002 (May 1982).
7. Richardson Engineering Services, Inc. Process Plant Construction
Estimating Standards, Vols. 1-4 (1984).
8. Smith, J. H. et al. "Prediction of the Volatilization Rates of
High-Volatility Chemicals from Natural Water Bodies," Environmental
Science and Technology 14(11): 1332-1337 (1980).
9. Lyman, W. J., W. F. Reehl, and D. H. Rosenblatt. Handbook of Chemical
Property Estimation Methods. McGraw-Hill, New York (1982).
10. Published Literature of Ashbrook - Hartley Co., Houston, Texas.
11. Blackburn, J. W., et al. "Prediction of the Fates of Organic
Chemicals in Activated Sludge Wastewater Treatment Processes." EPA
draft report, Contracts 68-03-3027 and 68-03-3074 (November 1983).
12. Govier, G. W., B. A. Radford, and J. S. C. Dunn. "The Upwards
Vertical flow of Air-Water mixtures, I. Effect of Air- and
Water-Rates on flow Pattern, Holdup, and Pressure Drop." The Canadian
Journal of Chemical Engineering, pp. 58-70 (August 1957).
13. Reith, T., S. Renken, and B. A. Israel. "Gas Hold-Up and Axial Mixing
in the Fluid Phase of Bubble Columns." Chemical Engineering Science
23: 619-629 (1968).
14. Fair, J. R., A. J. Lambright, and J. W. Andersen. "Heat Transfer and
Gas Holdup in a Sparged Contractor." I and EC Process Design and
Development (1)1: 33-36 (1962).
15. Pigford, R. L. and C. Pyle. "Performance Characteristics of
Spray-Type Equipment." Industrial and Engineering Chemistry (43) 7:
1649-1662 (1950).
107
-------
16. Chen, G. K. "Packed Column Internals." Chemical Engineering (91)5:
40-51 (March 5, 1984).
17. Eckert, J. S. "How Tower Packings Behave." Chemical Egineering
(82)8: 70-76 (April 14, 1975).
18. Shukla, H. M. and R. E. Hicks. Process Design Manual for Stripping of
Organics." US EPA, IERL Cincinnati, Ohio. (1983).. .
19. Hwang, S. T. and P. Rahrenthold. "Treatability of the Organic
Priority Pollutants by Steam Stripping." Presented at AICHE meeting,
August 1979, Boston, MA. Organic Chemicals Branch, Effluent
Guidelines Division, USEPA.
20. Horsley, L. H. "Azeotropic Data." Advances in Chemistry Series, 116.
American Chemical Society, Washington, D.C. (1979).
21. Proprietary Data Base. IT Enviroscience. Knoxville, Tenn.
22. Kern, D. Q. Process Heat Transfer. McGraw-Hill, New York (1950).
108
-------
APPENDIX A
EXAMPLE
STATEMENT OF PROBLEM
A city drinking water field is contaminated with trichloroethylene
(TCE), with levels from the well field as high as 15 ppb. A contamination
assessment was performed around a manufacturing site 2 miles from the well
field. This assessment showed the presence of contaminated groundwater
migrating beyond the extent of monitoring wells at levels as high as 250
ppb. A temporary system is needed for approximately 1 year until new
water supply wells are installed into a deeper uncontaminated aquifer.
The flow rate from this well field is 1 mgd (700 gpm). The drinking water
standard for TCE is 5 ppb. The water temperature is 20°C.
EVALUATION
Figure 1 of this guide is used to direct the selection process. As
described in Phase 1 (Section 1, Introduction), volatilization is an
appropriate technology because the contaminant level is low and TCE
volatilizes faster than water evaporates. The second phase is the site
characterization (Section 2, Site Characterization), using the checklist
in Table 2. The extent of treatment needed and the treatment requirements
are defined in the statement of the problem. The maximum concentration
(250 ppb) found in the contamination assessment is used as the basis for
groundwater contamination. This will ensure that the system will operate
adequately if levels increase to the higher concentration.
The properties of the spilled material are then obtained from Section
3, Material Properties and Estimation Methods, and the appendices. The
Henry's Law constant and solubility of TCE are obtained in Appendix B;
they are 490 and 1110 ppm, respectively. The lower flammability limit of
12% is obtained from Appendix C. An azeotrope for TCE at 5.4% water is
obtainable (20). The fact that TCE solubility is much greater (an order
of magnitude) than the Henry's Law constant indicates that a column can
run very efficiently. Because the level of contamination is in the ppb
range, the lower flammability limit of 12% will not be reached; so an air
stripping column is also feasible. Finally, the azeotrope at 5.4% water
indicates a reasonably pure product. Based on these facts, no technology
is eliminated.
The water temperature of 20°C is confirmed with the well operators,
who confirm that this temperature remains fairly constant throughout the
year. The site is accessible and has utilities.
The calculation of material properties as listed in Figure 1 is
unnecessary for this example because all essential information is
available in the guide. If this step were necessary, explanations are
provided in Section 1.
The required removal is 98%, obtained from influent and effluent
criteria of 250 ppb and 5 ppb, respectively (1 - 5/250 = 0.98).
109
-------
Inspection of Figures 2-9 (Section 3) reveals that all technologies except
bubble columns and spray columns operated in parallel are applicable.
Bubble columns and spray columns are batch systems, and the requirement is
for a continuous system. Impoundments are not practical for a city water
supply. This preliminary evaluation is based on the Henry's Law constant
of TCE and the lowest removal rate plotted in the figures.
The flow rates are then compared for the model systems.. It is seen
from this comparison that to obtain a 700 gpm flow, two model packed air
stripping towers or one cooling tower system would be needed. Although
larger systems could be constructed on site, spray tower and steam
stripping systems have flow rates too low to be applicable for this
service. They are therefore dropped from consideration, leaving only the
packed air stripping column and cooling tower systems.
Air emissions are obtained from Table 5 (Section 4, Technology
Evaluation) for the two remaining technologies. Putting the two systems
on the same basis of pounds of TCE per hour, the emissions from the two
systems are very similar. This similarity should be expected because both
the packed air stripping column and cooling tower system provide greater
than 98% removal. To obtain the total emission rate, it is assumed that
all of the TCE in water is emitted. The daily TCE emission is then:
(106 gpd) (8.2 Ib water/gal) [(250 X 10'9 Ib TCE) /lb water] =
2 lb TCE/day.
This rate is permissible in some states for an air stripper. The
concentration of TCE in air emissions is calculated from Table 5 for the
packed air stripper column as 2.75 ppm (wt/wt) or 0.6 ppm (mole/mole).
These values would be compared to any applicable air quality criteria to
determine if these air emissions are acceptable. For the purposes of our
example, it is assumed that these emission rates are acceptable.
The final criterion for selection is cost (Section 4). Costs of the
air stripping column and cooling tower systems are compared on the basis
of dollars per 1000 gallons of water treated. Cost for packed air
stripping columns range from $1.97 to $18.99 per 1000 gallons, while
cooling tower prices in parallel operation range from $0.51 to $5.03 per
1000 gallons.
CONCLUSION
Either a packed tower air stripper or cooling tower should be selected
for this service. The height, diameter, and packing will need to be
evaluated in detail as a part of the vendor selection process.
110
-------
APPENDIX B miCMIAI PROPERTIES
CERCLA Chemical
Compound Formula
(Synonym)
Acetic acid CHiCOOH
(ethanolc acid)
Acetic acid, ethyl ester.
CH}COOC2Hj
(ethyl acetate)
Acetic anhydride
(CH3CO)20
Acetone CI^COCHj
(propanone)
Acetone cyanohydrln
(CH3)2C(OII)-CN
Acrylic acid CM, CHCOOH
(propenolc acid)
Aniline CgHjNH?
(imlnobeniene)
Benial chloride CKHjCHCI;
(beniylldene chloride)
Benienethlol CgHjSH
(mercaptobeniene)
Bentonltrlle CcHcCN
(phenyl cyanide)
Beniotrlchlorlde
(phenyl chloroform)
Benioyl chloride
C6H5COCI
2.2-Bioilrane CaHcO;
([rythntol Anhydride)
11.2 3.4-diepoiybutanel
CERCLA
Class
III
V
III
III
III
III
VI
VI
VI
III
Ml
1
III
Solubility
in H2o Temperature
(PP») ("0
-
89,800 25
Hydrolyies
(forms acetic
acid)
.
V S
Hydrolyies
(forms hydrogen
cyanide)
-
34,000
60,000 100
(Hydrolyiesl
1
10,000 100
Hydro lyies to
benioic and
hydroch lor ic
acid
Decompos
S
Hydrolyies to
Erythntol
Vapor Pressure
oa Hg Pure
Source Solute
23 760
10
24 760
95
23 760
214
5.3
5 760
227.1
200
24 IS
760
5 760
200
40
5
24 50
24 760
760
1.05
24 760
87 8
15.0
5 760
100
10
1
24 760
60
25
10
5 760
35
3
23 760
23
Temperature
118
17
77
25
139
100
25
56
25
25
81
95
142
103
66
27
102
184
205
35
169
100
60
191
124
89
28
221
129
105
89
192
100
49
144
51
Henry's Lan
Constant
Theoretical
Source (at 1 Atn) Units
23 1.29 N U
23 0.01 N U
24 63 N U
5
24
5
S
5 0.28 N.U
25 6 B < 10-6 b
26
24
24
5 0 01 N.U.
24
24
24
5 1.8 Atm
3 07 i 10-6 b
5 4 N.U.
23 1 70 I 10-4 b
25
22 3.10 « 10-4 b
5
5
24 30 N U
24
24
24
23 1 12 < 10-4 b
24
24
24
24
24
24
23
24
Henry's Lax
Constant
Temperature Experimental
(°C> Source (at 1 Atm)
100 6 0.73
17 Calc
25 Calc.
25 Calc. IS 5
25 26
27 Calc. 1.0
75 27
25 26
101 Calc.
25 26
25 26
100 Calc.
25 26
Temperature
Units (°C) Source
N U 100 28
N.U. 100 29
N U 100 30
-------
CERCIA Chemical
Compound Formula
(Synonym)
B1s(2-chloroethyl ) ether
C1C2H5OC2H5CI (2.'2'-
dlcfilorodlethyl ether)
B1s(2-chlorolsopropyl)
ether [C1CH2CH(C«3))20
(2,B-dlchlorod11sopropyl
ether)
Bls(chloromethyl) ether
(CH2CI)20 (l.r-dlchloro-
dlmethyl ether)
Bromoacetone BrCH2COCH3
Bromomethane CHiBr
(methyl bromide)
l-8utanol CiHlCHlCHlOH
(n-butyl alcohol)
2-Butanol peroxide
C2HSCH(OOH)CH1
(tec-butyl hydroperoilde)
Butyric acid C2H5CH2C02H
(butanofc acid)
Carbonochlorldk acid
Carbon tetrachlorlde CC14
(tetrachloromethane)
Chloroacetaldehyde
CKHjCH.O
(chloroethanol)
Chlorodlbromomethane
CICHBrj
Chloroethane CiHsCI
(ethyl chloride)
Solubility Vapor Pressure
CEBCLA In HjO Temperature In Hg Pure
Class (ppm) (°C) Source Solute
III 10.200 25
Decomposes In
hot vater
11.000 20
VI 1700 25
III
Deconp to
formaldehyde
and NCI
VI v.sl.s
Photolyzes
VI 17.500 20
Forms hydrate
13.200 25
V 90.000 15
9.1 ml/10 mg
69.000 25
180.000 30
V
III
III
VI 800 25
800 20
970 0
III Forms hydrate
VI 1
IX 5700 25
4500 0
19
23
5
19
5
24
25
5
25
24
31
5
24.32
5.19
5
24
23
19.32
5
760
57
1.2
45
760
30
760
725
50
760
1420
1633
3
6
760
U
72
760
113
760
1500
760
317
50
42B
760
760
1190.0
8900
Temperature
179
100
25
100
1B7
25
106
137
64
4
20
25
15
25
118
42
100
164
25
77
100
86
25
100
120
12
25
100
Source
5
19
26
19
6,19,23
19
24
24
23
24
23
6.25
5
5
24
33
5
5
26.32
5
6.19
23.24
34
19
19.23
17.23.24
6.24
6.19,24
Henry's La«
Constant
Theoretical
(at 1 Atm)
15.0
2.58 x 10-5
1.2
I.I x IO-«
14.7
58.3
2.50 x 19-«
1.17 10-7
9.3 x 10-2
0 106
12,400
14,800
0.02
7.0 x 10-6
0.09
3200
1600
1600
4.7 x 10-6
44
235
0 7B3 x 10-3
811
625
1282
980
Temperature
Units (°C)
N.U.'
b
N.U.
b
N.U.
N.U.
b
b
b
b
N U.
N U.
N.U.
b
N.U.
N.U
N.U
N.U
b
N .
N. .
b
N.
N .
N .
N. .
100
25
25
20
25
100
25
25
20
25
25
too
15
25
100
100
25
25
25
25
100
25
25
25
100
25
Henry's Lav
Constant
Experimental Temperature
Source (at 1 Atm) Units (°C) Source
6.19
26
Calc.
26.35
Calc.
6.19
26
26
35
26
6.34
6,34
Calc. 27.5 N.U. 100 36
26
Calc. 1.0 N.U. 100 37
6.19
32
Calc
26
6
6.19
26
6
32
6.19
Calc.
-------
CEKCLA Chemical
Compound Form la
(Synonym)
Chloroform CHCU
(trlchloroBethane)
Chloraoethane CH3CI
(methyl chloride)
Chlorooethoxyaethane
(C1CHZOCH3
(chlorodlKthy) ether)
Cyanogen NC-CN
(onallc nltrlle)
Dlbroanecthane CHjBrj
(nthylene bromide)
Dlchlarobronethane
BCHC1Z (bronodl-
chloromethane)
1.4-Dlchloro-2-butene
(CCH;CH CHCH2C1
Dlchlorodlfluoronethane
CIZCFZ IFreon 121
Dlchloromethane CHjClj
(nethylene chloride)
Dlch loromethylbeniene
(2.8-dfchlorotoluene)
N,N-dtethylhydrarlne
(CjHjIjNNH;
Solubility Vapor Pressure
CERCLA In H*0 Temperature In Ha Pure Temperature
Class (ppm) (°C) Source Solute (°C)
VI
IX
VI
IX
VI
VI
VI
IX
VI
VI
V
7840 25
S200 20
5380 2S
280 A/100 16
72SO 25
Decoop. 25
450 cc (gas) 20
100 g N;0
Kydrolyied
slovly
11.400 20
1 1 .900 30
1
1
28 25
7.6 ml/1009 "20 26
19.400 25
20,000 20
1
» s.
32
19.23
32
19
23
5
24
5
38
23
23
19
5
32
19.24
23
23
182
760
2300
760
4700
30.300
760
760
12
340
760
760
1010
758 (els)
3 (els)
758 (trans)
20 (trans)
1700
?i6000
438
760
4500
760
756
25
62
100
-24
25
100
59
-21
0
25
97
90
100
153
23
156
56
25
138
25
40
100
198
99
Source
26.32
19.18
19
23
19
19
23
2.23
2
26
5.23
19.23
19
23
23
39
23
19.23
H
6j26.32
6.19
23
23
Henry's Lw
Constant
Theoretical
(at 1 Atn)
217
636
3200
3 39 « 10-3
182
1480
0.38
2800
9.91
360
820
3 16 > 10-6
118
262
2.12 x 10-5
6.78 > 10-5
641.000
537.000
2 75
136
178
941
1800
3.19 » IQ-3
Units
N.U
N.U.
N.U
b
N.U.
N U.
b
N.U.
b
N.U.
N.U.
b
N.U.
N U
b
b
N.U
N.U.
b
N U.
N.U
N.U.
N.U.
b
Tenperatui
(°C)
25
100
100
25
25
100
25
25
25
2S
97
25
25
100
25
25
100
25
25
25
25
100
100
25
Henry's lav
Constant
re Experlnental Tenperature
Source (at 1 Aim) Units (°CI Source
32 177 N.U. 25 32
19
6
26
Calc.
6.19
26
Calc.
26
Calc.
Calc.
26
6
6.19
26
26
19
Calc.
26
32 149 N.U. 25 32
6
19
6
26
112 N U 25 40
-------
CERCLA Che»lcal Solubility Vapor Pressure
Compound Formula CERCLA In H20 Temperature In Kg Pure
(Synonya) Class (ppml («C) Source Solute
Dlpropylwlne III S
(C2H5CH2)2NH Foros hydrate
Ethlon C4K2j04.P2S4 VI S
(Niagara 1240. Slalatel
Ethylene bromide BrCiH^Br VI 4300 25
(1.2-dlbromoethane) 4300 30
Formic add HCOOH III
(ethanolc acid)
Hexachlorobutadlene VI 2 20
CC1; CCICCl-CClz 1 25
(he«achloro,1,3-butadlene)
Heiachlorocyclopentadlene VI 13 25
' 6
lodowthane CH3I III 18.000 15
(ethyl Iodide)
isobutyl alcohol V 100.000 10
(2-neuiyl-l-propanol)
Isophorone CgH)40 V 9 600
(3.5.5-trlmethyl-2- ' K
cyclohexen-l-onel
Hethacrylonltrlle v 25.700 20
(CHz.C(CHj)C:N
(Isopropenylnltrlle)
Methanol CHiOH ||I
(ethyl alcohol)
5
24
24
41
5
5.23
19.34
23
19
5.24
5
19
24
5,23
760
760
10
11
280
33
120
743
760
0.15
20
760
5.4
0.3
753
760
281
400
4 6
760
0.2
19
760
760
S6.5
760
400
100
73
Temperature
110
131
29
25
100
25
50
100
101
20
101
215
100
49
239
42
15
25
10
108
20
100
215
90
20
65
50
21
15
Source
5.23
23
23
26,41
6
26
23
5
23
24
19,23
19,23
19
23
19.23
5.22,24
2
26
2
24
42
19
19.42
24
2
23
24
24
24
Henry's L«»
Constant
Theoretical
(at 1 MB)
3.32 « 10-4
49
32
204
6 25 x 10-«
0.04
i.o
4.4 > 10-'
150
25.7 i 10-3
1431
580
4200
36.2 x 10-3
34
900
2500
512
3 3
6 0 x 10-3
0.23
1.03 » 10-5
5.2
4.2
0.32
10.6
0.13
1 1 i IO-&
Units
b
N.U. «
N.U.
N.U
b
N U.
N.U.
b
N.U.
b
N.U.
N.U.
N.U.
b
N.U.
N.U.
N.U.
N.U.
b
N U.
b
N U
N.U.
N.U.
N.U.
N.U.
b
Henry's Lav
Constant
Temperature Experimental Temperature
(°C) Source (at 1 Atm) Units (°C) Source
25
25
25
25
25
25
100
25
100
20
20
25
100
25
25
100
100
15
25
10
25
100
100
25
20
21
25
26 279 N.U. 89 38
6
Calc
6
26
Calc. 0.45 N.U. 100 43
Calc
26
19
34
Calc.
6
6
34 16.4 x 10-3 b 25
6
6
19
Calc.
26
Calc.
26
19
6
6
Calc.
Calc.
26
-------
(J1
CERCLA Chemical
Compound Formula
(Synonym)
Nethapyrllene C|4H|9H3S
(lullamln)
1 -methyl ethyl beniene
C2M5C&H4CH3
(o.m.p-ethyl toluene)
Hethyl Isobutyl ketone
CH3COC4H9
(MTBX. Isopropylacetonel
2-Hethyl -5-nltrobenieneamlne
C7H8«2<>2 (2-amlno-4-nltro
toluene)
Hethylthlouracll
(l-me!hyl-2-thlouracll)
2-Nltropropane CH3CH(NOj)CH3
Paraldehyde CeH|203
(paraceialdehyde)
Phthallc anhydride
2-P1collne C5HiN(CH3)
(2-methylpyrldlne)
Propargyl alcohol HCiCCHjflH
(2-propyn-l-ol)
Proplonlc acid CH3CH2COOH
(Propanolc acid)
(methylacetlc acid)
Proplonlc anhydride
IC2HjCO)20
PropylenelBlne CjH7N
Ipropylenlmlne)
CERCLA
Class
III
V
III
VI
III
V
III
VI
III
III
III
III
III
Solubility
In H20
(ppm)
670.000
1
20.000
S
6600
17.000
60.000
125,000
v.sl.s
v.s.
s
-
Decomp.
-
Temperature
(°C) Source
25 24
23
20 5
23
100 24
20 5
100 24
25 24
25 5
5
5
23
5
23
Vapor Pressure
In Hg Pure
Solute
3
0.45
760 (0)
760 (M)
760 (P)
20 (0)
10 IN)
10 (P)
5
16
760
13.4
760
25
760
0.0002
760
10
760
490
21
12
760
10
760
1
760
748
Temperature
173
130
165
161
162
62
46
46
20
38
118
20
120
25
128
25
129
25
114
100
50
20
141
42
167
9n
ell
67
63
Henry's Ian
Constant
Theoretical
Source (at 1 Atm) Units
23, 42 7-6 i 10-5 b
24
23
23
23
23
23
23
23 1.8 N.U.*
23
23. 24
1.80 x 10-' '
2 5.1 N.U.
23
1.7 N.U.
23.24 3.66,10-5
26 1.0 i lO-'O b
23.42 2.4,,0-S
42
23. 24.
42
24
23
24
23. 42 1 N.U.
23 0.45 N U
42
42
23
Henry's Leu
Constant
Temperature Experimental Temperature
(DC) Source (at 1 Atm) Units (°C1 Source
25 26
173 N.U. 25 40
20 Calc 95 N.U. 100 39
43 35
20 Calc.
25 Calc.
25 26
25 26
25 26
100 6 1.19 N.U. 100 44
80 6
-------
CERCLA Cheailcal
Compound Foraula
(Synonym)
Pyrethrlnj
II: *22H2805
I.I. 1 ,2-Tetrach loroethane
(Cl3CCH2Cl)
1 . 1 .2. 2-Ietrach loroethane
CI2CKCHCl2
(acetylene tetrachlorlde)
Tetraethyl lead
(CvHcliPb
Tetraethylpyrophosphate
(CjHjUP^O;
Tetrahydrofuren CiHsO
(dlethylene oilde)
TrlbroBomcthane Qttrj
(bronoform)
l.l.l-Trtchloroethane
CH3CCl3
(ethyl chloroform)
1 . 1 ,2-Trlchloroethane
CI2CHCH2CI
Trlchloroethylene
CICH CC12
(trlchloroethene)
(elhylene trichloride)
Tr Ichlorof luoroaethane
CCI3F
(Frion II)
Solubility
CERCLA In H20
Class (ppm)
VI
VI
VI
VI
VI
III
VI
VI
VI
VI
VI
I
1100
200
3000
2850
0.2
-, Hydro Hies
tilth H?0
Decomp'
s
3130
1000
2890
730
4400
4420
4500
1100
1100
Teiperature
25
20
25
25
25
170
25
(cold)
25
20
25
25
25
20
25
Vapor Pressure
In Hg Pure
Source Solute
24
32
5
32
24
45
24
24
23
34
5
19
32
19
32
19
5.19.32
19. 34
0.0005 (1)
0.0070 (II)
760
13.9
10
6.5
187
6 5
760
10
188
1
760
14
0.00047
760
162
5.6
760
165
15
126
99
760
760
1600
23
760
760
495
59
760
1125
6300
633
760
400
200
Teoperature
(°C) Source
148
193
131
25
22
25
100
25
146
34
100
28
200
80
30
66
25
25
ISO
100
46
24
20
74
134
100
25
114
134
100
20
87
100
100
25
25
7
-9
24
24
23
32
24
6
6
23
19. 23.
24
23
19
26. 45
42
42
24
24
24
24
5. 19. 24
19
23
6
32
5. 23
19
6 19
32
23
19
6. 19
32
19. 23
19
6. 19
34
5.6.19.24
24
24
Henry's Lav
Constant
Theoret lea 1
(at 1 MB)
ISO
155
24
156
2.76 > 10-3
25
27
4.7 « IO-«
120.000
0 08 « 10-4
0.595 > 10-3
30
34
190
1335
800
273
52
51
241
1.18 » 10-3
535
1675
8.92 > 10-3
104 > 10-3
34
9700
5.8 « 10-2
3250
5000
Units
N.U.'
N.U.
N.U.
N.U
b
N.U.
N U.
b
N.U.
b
b
N.U
N.U.
N.U.
N.U.
N U.
N.U.
N.U
N.U.
N.U.
b
N.U.
N.U.
b
b
N.U.
b
N U.
N U.
Henry's Lav
Constant
Temperature E»perlaenta1 Temperaturi
<°C> Source (at 1 At*) Units (°C)
25
25
25
100
25
25
25
25
25
25
25
25
25
100
20
25
25
25
25
100
25
20
100
25
25
100
25
25
100
32
Calc.
6
6.19
26
23
Calc.
26
Calc.
26 1.0 N.U. 64
34 0 532 « 10-3 a 25
6
Calc.
6. 19
23 1870 N.U. 20
6. 19
6
32
Calc.
6.19
26
32 490 N.U. 20
19
26
34 58.3 « 10-3 a
19
26
6
6
!
Source
46
34
32
32
25
Tr Ich loromethancln lol
CCHSH
ItrlchlDronethyl aereaptan)
-------
APPENDIX C
LOWER FLAMMABILITY LIMITS
Summary of limits offlammability,
lower temperature limits (Ti), and minimum
autmgnition temperatures (AIT) oj indindual
gases and vapors in air at atmospheric pressure
Combustible
Acctal
Acetic anhtdnde
Acetone Cyanohx dnn.
A Idol
Allv 1 alcohol
AIM chloride
n-Amvl acetate
ri-Am) 1 propionate
2-Diphen>ldmmc . ..
Butadiene (1,3)
«r-Butvl alcohol ....
(rrl-Butjl alcohol
ice-Butyl benzene
frrf-Bulyl benzene
n-But>l bromide
Carbon monoxide
Cjclohcx}! acetate...
C\mene
Limits of flam-
mabilily (volume-
percent)
£..
1 6
4 0
5 4
2 7
1 0
2 6
1 1
1 7
5 0
2 5
2 8
3 0
2 2
1 6
2 0
2 5
2 2
2 7
2 9
66
15
1 1 0
' 1 4
1 1 4
» 1 6
1 5
7
1 0
1 0
1 4
' 1 2
65
1 1
1 1 3
7
1 2
> 65
70
8
1 6
2 0
1 &
1 9
1 6
1 7
> 1 4
' 1 7
' 1 7
> 1 9
' 1 7
i 82
' 0 77
' 77
i 2 5
1 1
1 8
1 7
« 3
2 1
i 2 0
1 3
12 5
1 4
< 1 1
2 1
' 88
6 6
1 1
1 3
1 2
' 1 2
1 0
2 4
i 85
[/,.
10
60
' 10
13
100
31
12
18
22
4 1
2S
' 7 1
1 10
' 8 6
8 7
1 8 3
1 7 9
5 1
12
S 4
10
9 7
i 8 0
' 12
9 8
9 0
8 9
5.8
5 8
5 8
10 ]]
' 10
8 2
50
74
ii 16
> 6 5
6 7
7 8
10 4
> 6 5
(°C)
37
40
47
-6
22
-32
25
3S
-12
74
110
-72
.. 21
11
21
AIT
(°C)
230
175
465
390
545
465
570
340
390
305
235
420
250
375
295
4S5
450
360
300
435
260
345
170
210
3SO
275
615
540
195
sno
4SO
5S5
245
510
450
565
420
405
395
3S5
325
425
405
4SO
380
410
420
450
265
245
355
450
90
640
425
245
300
335
500
435
Combustible
Dccalm
n- Dc*cane
Diesel fueMGOceiane).
l,4-Dicih\l r>pn7cne.-
Dicth\l c\clohexane..
J,3-Di"cth>l pentaoe..
Dusobutyl carbinol..
Dusobutvl ketone...
Dusopropjl ether
Dimeth}! ainine
2.2-Dimcth\l butane
2.3-Dinicth\l butane
Dimrlh}! d'ccalin
Dirncth}! dichlorosi-
n.n-Dimcthjl forma-
2,3- Dimethyl pcntane.
2,2- Dimeth} 1 propane.
Diphen>l methane
Ethane
Ethyl cyclobutane...
Ethyl cyclohcxane...
Elliyl cyclopi-nlane..
Ethyl mercaplnn
Ethyl propiunate
Ethj 1 propy 1 ether . . .
Gasoline
100/130
115*145
Hydrogen cyanide...
Hydrogen sulfidc
Isoaniyl acetate
Isoamyl alcohol
Limns of flarn-
mabilil} (volume-
percent)
L,,
2
' 74
" 75
4 9
8
1 8
8
> 8
75
1 9
' 7
1 6
> 82
> 79
1 4
2 8
1 2
1 2
' 69
3 4
3 4
> 1 8
1 1
1 4
2 2
2 0
75
7
0 S
7
1 7
60
3 0
2 2
3 3
3 5
> 1 0
3 8
1 2
"20
1 1
2 8
1 5
2 8
4 0
3 0
1 S
1 7
2 7
3 6
3 5
3 6
" 1 S
1 3
1 2
1 05
< 43
1 2
' 1 2
6
4 7
4 0
5 6
4 0
> 1 1
> 1 4
1 8
{/
' 4 9
"56
75
88
10
36
"6 1
' 6 2
7 9
7 0
7 0
5 3
27
i 14
6 S
7 5
20
22
6 1
27
12 4
11
" 19
'6 7
7 7
"66
6 7
16
IS
50
11
9
36
46
100
» 16
7 1
7 1
6 7
7 4
100
75
40
44
1 7 0
i 9 0
8 4
(°C)
57
16
SO
120
57
84
45
74
-130
72
-4
126
-26
25
-81
AIT
(°C)
250
J10
225
630
430
240
160
290
450
400
235
350
435
335
450
205
"265
237
635
620
435
205
515
365
385
430
210
260
260
455
400
300
440
490
320
400
390
440
470
370
215
205
225
185
400
360
350
460
117
-------
Combustible
Isobutyl formate
Jet fuel
JP-4
JP-6
Methane -
Methyl acetylene
3- Methyl butcnc-1
Methjl bul)l kctont.
Methyl cellosohc
Methyl ccllosolvc ace-
tate
Methj 1 chloride
Methyl cyclohexanc..
Methyl cyclopcnta-
Melhyleth>l kptonp. .
Methyl eth>l kctonc
Methyl formate
Melh}l cjclohcxanol.
Methjl isobuijl car-
Methyl isopropi-iij 1
ketone -
Melhvl lactate
o-Meth\l naphthalene
2, Meth>l pentane
Methvl prupionate
Methyl prop) 1 ketone.
Methyl vinvl ether...
Mcthylene chlundu -
Monoisoprop}! bicy-
2-Monoisopropyl
biphenyl ...
Monometh> Ihydra-
Naphthalene. . - .
Nitroethane. ... .
1-Nilropropane. . -
2-Nitropropane. .
n-Nonane -.- .
Paraldch>de
n- Pentane..
Pentamcihjlene gl}-
eol
Phthalic anhydride...
Limits of flam-
inability (volume-
percent)
£..
' 1 7
' 82
2 0
1 8
1. 4
84
1 7
2 2
6
1 3
5 0
3 2
1 7
6 7
' 4 2
10
1 5
1 1 2
"25
' 1 7
22.
7
1 1
> 1 3
1 9
5 0
1 0
1 2
>1 8
i 2 2
8
1 2
2 4
1 6
1 0
2 6
52
10 53
4
' 8S
1 75
3 4
7 3
2 2
2 5
" 85
0 95
1 3
42
1 4
1 I 2
C/,i
i 11
»6 0
8 9
9 6
8
15 0
16
' 3G
15
9 1
18 0
'20
6 7
'7 6
10
23
»9 0
13
8 2
39
114 i
'32
"59
7 8
"92
TL
(°C)
-187
46
49
40
40
49
124
141
30
33
34
27
31
13
-48
140
AIT
(°C)
430
465
460
440
240
230
210
540
385
430
380
250
445
390
465
295
530
495
615
230
435
526
'205
220
260
335
570
Combustible
3-Picolitie
Propadienc . .
Propane... .. .
1,2-rropandiol
0-Propiolactone . .
Propionalilpliyclc.
Propj 1 aniinc .....
n-Prupjl nitrate .
Sulfur
p-Terphriijl .....
Tctralui -
2,2,3,3-Tctmmi-Hiyl
pentane. .
Tclmm»thvlrne gly-
eol.
Toluene
Trichlcmiethx leiie. . .
TriPthyl aminp. . . .
Tricthvlpiip ch ">l
2.2,3- Tnmpilivl l.ii-
tane
Tnmpth)! mnine.- .
2,2.4-Triinplh>l pen-
lane . . . . .
Tnrnelhxlpiip gUml
Triotiinp
Tnrpenliiip
L'nsymniPinriil di-
_ mrtliyllijilr«7ine ..
Vinyl arrtittp . ...
Vinyl chlnndp. . ....
m-Xylrnc. . . ....
o-Xylcnp
p-X}|pne . .
Limits of flam-
inability (volume-
percent)
Lu
I 4
» 74
2 16
2 1
2 5
>2 9
2 9
1 8
"22
2 0
2 4
» 1 S
2 4
3 1
"26
2 S
» 1 S
1 2 4
1 0
" 1 1
"20
96
5
2 0
1 84
0 8
1 1 2
12
1 2
q
1 0
2 0
05
1 7
.1 2
i 7
2 0
2 6
1 ft
1 1 1
1 1 1
1 1 1
I/,.
"72
9 5
17
8
1 14
"100
11
37
» 12
5 0
7 1
.'40
8 0
ii g 2
12
95
33
' 6 4
6 4
i 6 6
TV.
("C)
-102
21
247
71
-
30
- - -
....
AIT
CC)
500
450
410
440
175
4 GO
"sis
200
3S5
430
3PO
4«0
500
420
420
415
400
530
465
530
11-100° C.
«I-47°C.
«-7i»C.
Calculated.
if-SO-C.
«-8S*C.
' I-140* C.
1-150° C.
1-110° C.
ii 1-60° C.
iif-U'C.
»(-86°C.
><<-130°C.
ii 1-72° C.
»«-117°C.
»1-125° C.
"f-200°C.
i«»-78°C.
» 1-122° C.
»(-43°C
»(-195°C
»C-160°C
"I- WC.
»«-70°C.
«»-247°C.
»<-30°C
»«-203°C.
L2s = Lower flammability limit at 25 °C
U25 = Upper flammability limit at 25 °C
Reprinted from:
Zabetakis, Michael G., Flammability Characteristics of Combustible
Gases and Vapors, Bulletin 627, Bureau of Mines, U.S. Department
of the Interior (1965)
118
------- |