United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
EPA453/R-92-019
December 1992
Air
wEPA
Alternative Control
Technology Document -
Carbon Reactivation
Processes
-------
co EPA453/R-92-019
---i
o
Alternative Control
Technology Document -
Carbon Reactivation
Processes
Emission Standards Division
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th Floor
Chicago, IL 60604-3590
U.S. Environmental Protection Agency
Office of Air and Radiation
Office of Air Quality Planning and Standard*
fteaaarch Triangto Park. North Carolina 27711
DaeamiMr 1992
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ALTERNATIVE CONTROL TECHNOLOGY DOCUMENTS
This report is issued by the Emission Standards Division,
Office of Air Quality Planning and Standards,
U.S. Environmental Protection Agency, to provide information
to State and local air pollution control agencies. Mention of
trade names or commercial products is not intended to
constitute endorsement or recommendation for use. Copies of
this report are available - as supplies permit - from the
Library Services Office (MD-35), U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina 27711, or for
a nominal fee, from National Technical Information Services,
5285 Port Royal Road, Springfield, Virginia 22161.
ii
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CONTENTS
4
Chapter Page
List of Figures v
List of Tables vi
1.0 INTRODUCTION 1-1
2.0 INDUSTRY DESCRIPTION, PROCESSES, AND
EMISSIONS 2-1
2.1 Description of Carbon Reactivation
Industry 2-1
2.1.1 Commercial Carbon Reactivation
Industry 2-2
2.1.2 Industrial Carbon Reactivation
Industry 2-5
2.2 Carbon Reactivation Processes 2-6
2.2.1 Multiple Hearth Furnace 2-9
2.2.2 Rotary Kiln 2-9
2.2.3 Fluidized-Bed Furnace 2-12
2.2.4 Infrared Furnace 2-12
2.3 Carbon Reactivation Air Emissions .... 2-15
2.3.1 Organic Air Emissions 2-15
2.3.2 Acid Gas Emissions 2-16
2.3.3 Particulate Emissions 2-18
2.3.4 Metal Emissions 2-19
2.4 References 2-21
3.0 EMISSION CONTROL TECHNIQUES 3-1
3.1 Organic Emission Control 3-2
3.2 Acid Gas Emission Control 3-7
3.2.1 Absorption Principles for Acid Gas
Emission Control 3-7
3.2.2 Absorption Equipment for Acid Gas
Emission Control 3-8
3.2.2.1 Packed Towers 3-9
3.2.2.2 Spray Towers 3-11
3.2.2.3 Dry Scrubbers 3-13
3.3 Particulate Emission Control 3-15
3.3.1 Venturi Scrubbers 3-16
3.3.2 Impingement Scrubbers 3-18
3.3.3 Spray Towers 3-20
3.3.4 Cyclones 3-21
3.3.5 Baghouse Filters 3-25
3.4 Metal Emission Control 3-28
3.5 References 3-29
4.0 ENVIRONMENTAL IMPACTS AND COSTS ANALYSIS . . . 4-1
4.1 Control Technology Alternatives - Model
Systems 4-1
4.2 Control Costs 4-2
111
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CONTENTS (continued)
Chapter
4.2.1 Model Unit 1: An Afterburner . . . 4-4
4.2.2 Model Unit 2: An Afterburner and
Wet Scrubber 4-8
4.3 Cross-Media and Secondary Environmental
Impacts 4-9
4.4 References 4-14
Append ijg
Appendix A
Calculation Methodology for Cost
Analysis A-l
IV
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LIST OF FIGURES
Number Page
2-1 Multiple hearth furnace 2-10
2-2 Rotary kiln 2-11
2-3 Fluidized-bed furnace 2-13
2-4 Infrared furnace 2-14
3-1 Thermal afterburner 3-3
3-2 Thermal afterburner with a distributed burner . 3-5
3-3 Countercurrent packed tower 3-10
3-4 Spray tower 3-12
3-5 Dry scrubbing system 3-14
3-6 Venturi wet collector 3-17
3-7 Impingement scrubber (top);
impingement baffle plate (bottom) 3-19
3-8 Cyclone collector 3-23
3-9 Baghouse filter 3-26
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LIST OF TABLES
Number
2-1 Summary of Commercial Carbon Reactivation
Facilities and Process Equipment ,
2-2 Summary of Industrial Carbon Reactivation
Facilities and Process Equipment ,
3-1 Efficiency Range of Cyclones ,
4-1 Design Parameters for Thermal Incinerator . . .
4-2 Control Costs and Cost Effectiveness for Model
Unit 1: Afterburner
4-3 Design Parameters for Model Unit 2: Thermal
Incinerator and Wet Scrubber
4-4 Control Costs and Cost Effectiveness for Model
Unit 2: Afterburner and Wet Scrubber
4-5 Annual Energy Requirements for Control
Systems ,
2-3
2-7
3-22
4-6
4-7
4-10
4-11
4-13
VI
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1.0 INTRODUCTION
Carbon adsorption is one of the most commonly used
organic air emission control technologies at hazardous waste
treatment, storage, and disposal facilities (TSDF) and
industrial manufacturing concerns. Activated carbon is
effective in capturing nearly all types of organic vapors by
the physical adsorption mechanism. As physical adsorption is
a surface phenomenon, activated carbon has a finite or
"equilibrium" adsorption capacity (i.e., a finite surface area
available for adsorption). When the equilibrium adsorption
capacity is reached, the carbon is "saturated" and no further
adsorption can occur. At this point, referred to as
"breakthrough," the removal efficiency of the carbon
adsorption control device approaches zero and the saturated
carbon either must be replaced with new carbon or the organic
compounds must be removed from the carbon before adsorption
can resume. The process of removing organics from saturated
carbon can be accomplished by regeneration or reactivation.
In this document, the term "carbon regeneration" refers
to the onsite, in situ desorption of organics from the carbon
that typically takes place routinely as part of the operation
of the carbon adsorption system. Desorption can be achieved
by application of either steam or vacuum. In carbon
regeneration, the carbon is not removed from the adsorption
bed or column. Over time, the carbon loses a significant
portion of its reactivity and conventional regeneration is no
longer adequate to restore the adsorptive capacity of the
carbon. At this point, the carbon must be replaced. The
spent carbon can either be disposed of or reactivated.
1-1
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In carbon reactivation, the carbon is removed from the
adsorption bed or column and reactivated in a separate
processing unit or furnace. The carbon reactivation process
involves exposure of the spent carbon to high temperatures
(i.e., thermal reactivation) in an activating atmosphere with
sufficient oxygen and steam to remove the organic contaminants
from the carbon. Combustion conditions within the furnace are
controlled to effect oxidation of the adsorbed material rather
than the carbon.
The U.S. Environmental Protection Agency (EPA) issued a
statement in the preamble to the boilers and industrial
furnaces (BIF) rules (56 FR 7200, Feb. 21, 1991) clarifying
the regulatory status of carbon regeneration/reactivation
units under the Resource Conservation and Recovery Act (RCRA).
Under the definition of a carbon regeneration/reactivation
promulgated in the BIF rules (40 CFR 260.10), these units are
now regulated as thermal treatment units under the interim
status standards of Part 265, Subpart P, and the permit
standards of Part 264, Subpart X. Previously, there was some
confusion as to whether regeneration/reactivation units had
been classified as incinerators, thermal treatment units, or
exempt recycling units.
As EPA interprets its rules, the regeneration or
reactivation of spent carbon from a carbon adsorption system
used in the treatment of a listed hazardous waste or used to
capture emissions from a listed hazardous waste is subject to
regulation as a RCRA thermal treatment unit because the
carbon, with the adsorbed organics, is classified as a
hazardous waste under the "derived-from" rule. The derived-
from rule (40 CFR 261.3(c)(2)(i)), in short, states that any
solid waste generated from the treatment of a listed hazardous
waste is a hazardous waste. For other applications of carbon
adsorption systems such as the control of air emissions from a
production operation or for the treatment of a nonhazardous
industrial waste, the regeneration or reactivation of
spent carbon is subject to regulation as a RCRA thermal
1-2
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treatment unit only when the spent carbon is listed as a
hazardous waste or exhibits one or more of the hazardous waste
characteristics.
To help EPA, State, and local regulators identify the
types of air pollutants emitted during carbon reactivation and
the kinds of air emission control technologies available for
carbon reactivation systems, the EPA has prepared this
Alternative Control Technologies (ACT) document. Carbon
reactivation systems are a potential source of organic air
emissions. For example, as the spent carbon reactivation
furnace is operated to minimize the oxidation of the carbon,
some of the desorbed organics may be released into the
atmosphere prior to complete oxidation. Organic emissions
from carbon reactivation systems potentially include
photochemically reactive and nonphotochemically reactive
organics, some of which are toxic or carcinogenic.
The purpose of this ACT document is to provide
information about air emissions (i.e., organics, particulates,
toxic metals, sulfur dioxide, and nitrogen oxides) from carbon
reactivation processes, some of which are subject to RCRA
regulations. It is important to note that the emission
control technologies for nonhazardous waste carbon
reactivation units are the same as those for hazardous waste
carbon reactivation units that are regulated as RCRA thermal
treatment units. Information regarding in situ carbon
regeneration systems, their emissions, or applicable emission
control techniques is not within the scope of this ACT
document.
This ACT document presents technical information that
Federal, State, and local agencies can use to develop
strategies for reducing volatile organic compound (VOC)
emissions from carbon reactivation processes. The information
in this document will enable writers of permits and State
implementation plans to identify carbon reactivation emission
sources, identify available control alternatives, and evaluate
the VOC reduction and cost of implementing controls.
1-3
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Chapter 2.0 describes the carbon reactivation industry,
the process equipment commonly used for reactivation, and
types of emissions associated with carbon reactivation.
Chapter 3.0 describes alternative control technologies for the
reduction of VOC emissions from carbon reactivation.
Chapter 4.0 presents air and cross-media environmental impacts
and capital and annual cost analyses of the alternative
control technologies.
1-4
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2.0 INDUSTRY DESCRIPTION, PROCESSES, AND EMISSIONS
This chapter provides an overview of the carbon
reactivation industry and the processes used to reactivate
spent carbon. The sources of organic air emissions and the
types of air pollutants emitted from carbon reactivation
processes are identified. Air emission estimates are provided
when adequate data are available.
2.1 DESCRIPTION OF CARBON REACTIVATION INDUSTRY
For the purposes of this industry overview, it is
beneficial to define a few terms. The carbon reactivation
industry can be divided into two segments: commercial
reactivation and industrial reactivation. The commercial
reactivation industry is comprised of facilities that accept
spent carbon from off site, reactivate it, and then return it
to the originator or sell the reactivated carbon. The
commercial reactivation industry typically includes virgin
carbon manufacturers.
The industrial reactivation industry consists of
manufacturers that employ carbon adsorption on site and
generate enough spent carbon to justify operating their own
onsite carbon reactivation furnaces. Due to the amount and
rate of carbon usage in typical air pollution control
applications, spent carbon from carbon adsorption systems used
for air pollution control is usually reactivated at commercial
facilities.
2-1
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2.1.1 Commercial Carbon Reactivation Industry
Nationwide, 10 companies, representing a total of
14 facilities, were identified that operate commercial carbon
reactivation processes.1'12 A total of 22 furnaces are
operated at these 14 facilities. In addition, four of these
companies also produce virgin carbon as a commercial product.
Based on information gathered during telephone contacts with
selected facilities, the commercial reactivation industry
appears to be dominated by two or three large companies.
These are Calgon Carbon Corporation and Envirotrol, Inc., on
the east coast, with Calgon being the larger of the two, and
Cameron-Yakima on the west coast. No figures were available
on production or market share for any of the companies.
Interestingly, half (or five) of the commercial
reactivation companies identified had new units coming on line
or had plans for construction of new units. A total of nine
new reactivation furnaces are planned. Five of these furnaces
are being built at a single new facility location and a sixth
furnace is being built at a second new facility location. The
remaining three furnaces are being built to expand existing
capabilities at each of three separate facility locations.
Table 2-1 lists the commercial carbon reactivation processes
identified by EPA in the initial information-gathering phase
of this task. This list is not intended to be an exhaustive
list of all commercial reactivation facilities, but it
includes all the major commercial carbon reactivation
facilities in the United States contacted by EPA as a part of
information-gathering activities.
Within the commercial carbon reactivation industry, there
are two processing routes. One is generally referred to as
pooled carbon processing. In this case, the carbon user
merely sends the spent carbon to the reactivation facility,
and the facility sends the user an amount of replacement
carbon from the pool of reactivated carbon at the facility.
The spent carbon received is added to the pool of other users'
carbon.
2-2
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TABLE 2-1. SUMMARY OF COMMERCIAL CARBON REACTIVATION FACILITIES AND PROCESS
EQUIPMENT1'12
Company/facility location
Calgon Carbon Corporation
Pittsburgh, PA
Ashland, KY
Envirotrol Incorporated
Beaver Falls, PA
Darlington, PA
Cameron-Yakima
Yakima, WA
No. Of Furnace Air pollution
furnaces type equipment
^a MHF A, DS, BH
1" MHF A, DS, BH
3* (+1)*'b RK A, V, WS
4 RK A, V, WS
1" MHF A
1 RK A
Barnebey-Sutcliffe
Columbus, OH
Atochem North America, Incorporated
Pryor, OK
Adsorption Systems
Morgantown, WV
West States Carbon
Los Angeles, CA
(Wilmington, CA)
Parker, AZ
California Carbon Company
Wilmington, CA
Trans-Pacific Carbon
Blue Lake, CA
3 ( + 1)
1
1*b
RK
MHF
RK
FB
RK
MHF
RK
RK
WS
A
A, BH, WS
C, A, V, WS
A
A, WS
(continued)
2-3
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TABLE 2-1. (continued)
No. of Furnace
Company/facility location furnaces type
Air pollution
equipment
Northwest Carbon
A
BH
C
DS
FB
IRF
MHF
RK
V
WS
Anderson, CA 1 RK
Red Bluff, CA 1 b RK
2b MHF
2«.b ,RF-
= Afterburner.
- Baghouse.
= Cyclone.
= Dry scrubber.
= Fluidized-bed furnace.
= Infrared furnace.
= Multiple hearth furnace.
= Rotary kiln.
= Venturi scrubber.
= Wet scrubber (e.g., packed column).
A, WS/DS
Unknown15
Unknown5
Unknownb
aAccept, or submitting a permit to accept, hazardous waste.
bUnder construction.
The second processing route is segregated processing, or
custom carbon reactivation. In segregated processing, each
customer's spent carbon is processed separately without
contacting any other user's carbon. Reactivation companies
guarantee the return of the same carbon to the same
application. According to the carbon companies, the
segregated approach allows them to optimize furnace conditions
to suit each customer's spent carbon. This method yields the
highest quality reactivated product, typically meeting 90 to
100 percent of virgin carbon activity. The other reported
advantage of custom reactivation is that segregated processing
keeps the customer's and the reactivation facility's
contaminant liability controllable and separate from all other
carbon users. Keeping carbon wastes separate provides a
2-4
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"closed loop" between the customer's plant and the
reactivation facility and permits cradle to grave tracking of
contaminants. Custom reactivation costs range from one-half
to one-third the cost of virgin carbon depending on the
quality and intensity of reactivation required.
Another division within the commercial reactivation
industry is based on the classification of the spent carbon as
hazardous or nonhazardous. Currently, 6 of the 10 commercial
reactivation companies report that they do not handle any
carbon that is classified as hazardous waste either under RCRA
or State regulations. A total of five facilities,
representing four different companies, process spent carbon
that is considered hazardous waste under RCRA. However, the
majority of the processes currently under construction plan to
treat spent carbon that is considered to be hazardous waste.
If all of the new units are permitted as planned, a total of
8 facility locations, including 6 of the 10 commercial
reactivation companies, will have the capability of processing
spent carbon considered to be hazardous waste under RCRA or
State regulations.
2.1.2 Industrial Carbon Reactivation Industry
Few industrial applications of carbon adsorption systems
generate enough spent carbon at a rate sufficient to justify
the capital expense of an onsite carbon reactivation process.
One notable exception is the corn wet milling industry, which
often uses carbon adsorption to remove protein impurities from
corn syrup and then reactivates the spent carbon in-house.
The other exception is carbon adsorption systems used for the
treatment of high-strength wastewaters. Carbon adsorption is
commonly used as a polishing step in some wastewater treatment
systems, but this application does not usually generate spent
carbon at a sufficient rate to justify the capital expense of
an onsite carbon reactivation process. Also note that most
carbon adsorption systems used for air pollution control do
not generate spent carbon at a rate sufficient to justify the
capital expense of an onsite carbon reactivation process;
2-5
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therefore, the spent carbon from air pollution control
equipment is usually reactivated at a commercial facility.
In its information-gathering efforts, the EPA was able to
identify four companies that operate industrial carbon
reactivation facilities nationally.14""19 Of these four
companies, three represent the corn wet milling industry. The
EPA did not attempt to identify every industrial carbon
reactivation facility in the United States. Even so, the four
industrial companies identified represent 14 separate
facilities that operate a total of 21 reactivation furnaces.
Thus, from EPA's preliminary review of the industrial segment
of the carbon reactivation industry, it would appear that,
based on the number of facilities, the number of furnaces in
use, and the apparent overall spent carbon treatment capacity,
the industrial reactivation industry is comparable to the
commercial reactivation industry. However, in contrast to the
commercial reactivation industry, no new industrial carbon
reactivation processes were identified as being planned or
currently under construction. Table 2-2 summarizes the
industrial carbon reactivation facilities contacted by EPA and
the process equipment used at these facilities.
2.2 CARBON REACTIVATION PROCESSES
This subsection describes the types and operation of
reactivation furnaces currently employed by carbon
reactivators and discusses the major types and sources of air
emissions resulting from carbon reactivation. The air
pollution control equipment used to handle the furnace off-gas
is discussed in Section 3.
Thermal reactivation, whether conducted at a commercial
or an industrial facility, is quite similar to the process
used to manufacture new activated carbon. High temperature
and steam are combined to produce an activating atmosphere
that removes contaminants from the carbon's existing pore
structure.
2-6
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TABLE 2-2. SUMMARY OF INDUSTRIAL CARBON REACTIVATION FACILITIES AND PROCESS
EQUIPMENT1409
No. of Furnace
Company/facility location furnaces
type
Air pollution
equipment
Mobay Chemical Company
Kansas City, MO
New Martinsville, WV
Baytown, TX
1
1
1
FB
MHF
MHF
A, V, WS
A, V, WS
A, V
Cargill, Incorporated
A. E.
Eddyville, IA
Dayton, OH
Cedar Rapids, IA
Memphis, TN
Staley
Decatur, IL
Lowden, TN
Lafayette, IN
2
1
1
1
1
1
1
1
1
MHF
MHF
MHF
MHF
MHF
MHF
IRF
IRF
MHF
A, V, IS
A, V, IS
A
A, V, IS
A
A, V, IS
A
A
WHB
Archer Daniels Midland Company (ADM)
A
FB
IRF
IS
MHF
V
WHB
WS
Montezuma, NY
Cedar Rapids, IA
Decatur, IL
Clinton, IA
= Afterburner.
- Fluidized-bed furnace.
= Infrared furnace.
= Impingement scrubber.
= Multiple hearth furnace.
= Venturi scrubber.
= Waste heat boiler.
= Wet scrubber (e.g., packed
2
2
2
2
column)
MHF
MHF
MHF
MHF
.
WS
WS
WS
WS
2-7
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A carbon reactivation system consists of the following
equipment groups:21
1. Receiving, conveying, and feeding;
2. Reactivation furnace;
3. Quenching, cooling, and conveying of the carbon;
4. Off-gas equipment (i.e., air pollution controls); and
5. Process controls and instrumentation.
Four types of reactivation furnaces were identified as
being used in current reactivation"processes: multiple hearth
furnaces, rotary kilns, fluidized-bed furnaces, and infrared
furnaces. The most prevalent furnace type is the multiple
hearth furnace, followed closely by rotary kilns. Only two
furnaces were identified that employed fluidized-bed
technology and two other furnaces were identified that used
infrared technology. All four of these furnace types are
simply devices to accomplish heat and mass transfer between
gases and solids. Heat transfer is, for the most part, by
direct convection and radiation from the gas to the solid.
Mass transfer is accomplished solely by convection as the
gases pass over the solids.
Thermal reactivation of carbon generally occurs at
temperatures of 870 to 1,010 °C (1,600 to 1,850 °F) by the
reaction of water vapor and/or carbon dioxide with the
adsorbate. As a rule of thumb, 1 pound of steam is fed to the
furnace per pound of carbon. Air is used to supply a small
amount of excess oxygen, typically 4 to 10 percent of the
amount required for burning at stoichiometric conditions. The
retention time of carbon in the furnace varies with the
furnace type and with the operating conditions for a given
furnace. Typically, about 15 minutes are required at the
reactivation temperature for optimal reactivation of spent
carbon. The different types of reactivation furnaces are
described in the next subsection.
2-8
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2.2.1 Multiple Hearth Furnace22' 23
A multiple hearth furnace consists of a number of
annular-shaped refractory compartments called hearths, mounted
vertically, one on top of the other. Rabble arms connected to
a rotating shaft at the center axis of the furnace are used to
move the carbon through the furnace. The spent carbon is fed
near the center of the upper hearth and is pushed toward the
periphery by the rabble arms. At the periphery, the carbon
falls to the next hearth where it is then directed back toward
the center. It falls to the next hearth, where it is moved
back toward the periphery, and so on, until the carbon reaches
the final hearth. Burners may be mounted at any hearth to
optimize the drying, heating, and reactivation of the spent
carbon. A diagram of a multiple hearth furnace is provided in
Figure 2-1.
Most multiple hearth furnaces operate countercurrently,
with the air stream moving upward through the hearths, but
concurrent multiple hearth furnaces are also employed. The
sizing of the furnace is based on the sum total of the hearth
floor surface areas. The reactivation furnace with the
highest spent carbon throughput in the United States is a
multiple hearth furnace that processes 40 to 50 ton/day of
spent carbon. The typical residence time for spent carbon in
a multiple hearth furnace ranges from 30 to 90 minutes.
2.2.2 Rotary Kiln24
A rotary kiln is usually a cylindrical, refractory-lined
shell that is positioned at a slight incline from horizontal
and that rotates around that horizontal axis. A diagram of a
rotary kiln is provided in Figure 2-2. The spent carbon is
fed at the higher end of the kiln and moves, driven by
gravity, down the length of the kiln as the kiln rotates.
Most reactivation kilns are fired at the discharge end with
air flow countercurrent to the flow of carbon. The rotational
speed of the kiln can be varied, and some kilns have two
2-9
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Figure 2-1. Multiple hearth furnace.
2-10
-------
Afterburner
Spent
Carbon
Feed
^^^*'*\y.v.J
Reactivated
Carbon
Conveyor System
Flue
Gas
(to scrubber or quench)
Figure 2-2. Rotary kiln.
2-11
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different diameters to vary the peripheral speed of the kiln
rotation as the carbon moves down the kiln. Peripheral speeds
of 0.5 to 2 m/min are typical. The residence time in a rotary
kiln is typically less than in a multiple hearth furnace, with
average retention times of 20 to 30 minutes.
2.2.3 Fluidized-Bed Furnace25
A fluidized-bed furnace is a cylindrical vertical vessel
with an air feed at the bottom of the vessel. The air blowing
up through the bed lifts or "fluidizes" the carbon, creating a
turbulent cloud of carbon particles. Because of the air flow
rate required to fluidize the carbon particles, fluidized-bed
furnaces have a larger exhaust volume than other types of
reactivation furnaces with the same carbon throughput rate.
The larger air flow rate tends to increase the amount of
carbon fines that are carried over with the exhaust. On the
other hand, the high air flow rate creates turbulence in the
fluidized bed, and the intimate contact of the air with
individual carbon particles provides a very efficient means
for heat and mass transfer. A diagram of a fluidized-bed
furnace is provided in Figure 2-3.
2.2.4 Infrared Furnace26
Infrared furnaces have only recently been used for carbon
reactivation. The energy required for the desorption and
volatilization of the adsorbed organics is provided by heating
a series of heating elements to incandescence using electrical
energy. The spent carbon is typically transported through the
furnace via a metal grate. The infrared radiation heats the
carbon, and an induced draft fan is used to draw air through
the furnace and remove the desorbed gases as they are released
from the carbon. Residence time in the furnace is controlled
by varying the speed of the grate used to transport the carbon
through the furnace. Typical residence times for this furnace
type when employed for spent carbon reactivation were not
available. A diagram of an infrared furnace is provided in
Figure 2-4.
2-12
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Fluidized
Bed
Spent
Carbon
Feed
Fluidizing
Air
Flue
Gas
(to afterburner or scrubber)
Reactivated
Carbon
Figure 2-3. Fluidized-bed furnace.
2-13
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o
u
(0
c
•o
2
2
H—
si
I
O)
2-14
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2.3 CARBON REACTIVATION AIR EMISSIONS
There are up to four different types of air emissions
from carbon reactivation process units: organic emissions,
acid gas emissions, particulate emissions, and metal
emissions. This section will discuss the sources of these
emissions and provide estimates of their emission rates based
on carbon throughput rates. Most of the available emission
data are from emission measurements made at the final stack
exhaust, after emissions passed through all the air pollution
control equipment. Therefore, most of the uncontrolled
emission rates reported in this section are only order-of-
magnitude estimates. An actual emission source test is
recommended if more precise emission data are needed for a
specific reactivation system.
2.3.1 Organic Air Emissions
The primary source of organic air emissions is the
reactivation furnace exhaust gas. The organic emissions from
the reactivation furnace consist of organic compounds driven
off the spent carbon or formed as products of incomplete
combustion. Organic loading on spent carbon can range from a
few percent up to 20 percent by weight on a dry basis.
Because of the high temperatures at which carbon
reactivation occurs (i.e., 870 to 1,010 °C), a significant
portion of desorbed organics pyrolizes or chars on the carbon
and is oxidized in the reactivation furnace. No test data for
field operating reactivation furnaces were available to
determine the actual percentage range of adsorbate oxidized in
the reactivation furnace. Estimates provided by the industry
varied significantly. The estimated values, based on
engineering judgment and operating experience, ranged from a
low of about 10 percent to a high of about 90 percent.4'23'27"29
The variation in the percentage of desorbed organics combusted
in the reactivation furnace has a tremendous impact on the
estimate of uncontrolled organic emissions. If, for example,
the organic loading of the spent carbon averages about
2-15
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10 percent by weight and the reactivation furnace ranges from
10 to 90 percent efficient in destroying the released or
desorbed organics, then the organic air emissions from a
carbon reactivation furnace with no afterburner can be
estimated as 0.01 to 0.09 times the carbon feed rate on a dry
basis. A reactivation unit that processes 11 Mg/day
(1,000 Ib/hr) of spent carbon may have total organic emissions
from the reactivation furnace on the order of 40 to 360 Mg/yr
(10 to 90 Ib/hr).
Data on total hydrocarbon (as methane) emission rates
measured after an afterburner were available for two carbon
reactivation systems.30'31 For these systems, which had
average carbon throughput rates of 26 and 48 Mg/day (2,400 and
4,400 Ib/hr), the total hydrocarbon emission rates measured
for a given run ranged from 0.3 to 7 Mg/yr (0.08 to
1.8 Ib/hr). The concentration of total hydrocarbons in the
exhaust ranged from 3 to 32 ppm as methane. Based on these
data and assuming a 98 percent control efficiency for the
afterburner, the uncontrolled hydrocarbon emission rate for a
system with a carbon throughput of 11 Mg/day (1,000 Ib/hr) is
estimated to be 4 to 100 Mg/yr.
2.3.2 Acid Gas Emissions
Acid gases (e.g., hydrogen chloride and hydrogen
fluoride) are produced as by-products of the combustion of
either the fuel, the adsorbed organics, or the activated
carbon itself. As such, the types and amounts of acid gases
created in the carbon reactivation furnace (and, if present,
the afterburner) are highly variable.
Hydrogen chloride (HC1), hydrogen fluoride (HF), hydrogen
bromide (HBr), and hydrogen iodide (HI) are formed by the
combustion of halogenated organics contained in the adsorbate.
If there are no halogenated organics, there will be no
significant halide acid gas emissions. If there are
halogenated organics present, a stoichiometric quantity of
acid gas in the form of HC1, HF, and/or HBr will be produced.
2-16
-------
One facility, while testing the destruction efficiency of
its reactivation furnace and afterburner system, measured HC1
emissions'prior to the acid gas control device.32 The
measurements were made on a system that was processing
9.7 Mg/day (890 Ib/hr) of carbon with an organic loading of
1,1,1-trichloroethane at 7 percent (0.68 Mg/day or 62.3 Ib/hr
of 1,1,1-trichloroethane), which is expected to be an upper
limit for halogenated organics adsorbed on carbon. An
uncontrolled HC1 emission rate of 55 Mg/yr (13.8 Ib/hr) was
measured. The destruction efficiency of the reactivation
furnace and afterburner system based on 1,1,1-trichloroethane
mass emissions indicated a destruction efficiency of greater
than 99.99 percent. However, if the 1,1,1-trichloroethane had
been completely oxidized to carbon dioxide, water, and HC1,
the HC1 emission rate should have been approximately 200 Mg/yr
(51 Ib/hr). Thus, estimates based on stoichiometric
conversion of halogenated organics to halide acid gases may
overestimate the acid gas emissions, but they will provide a
reasonable and environmentally conservative estimate of the
emission potential. Additionally, these results suggest that
there exists a potential problem with products of incomplete
combustion (PICs).
Sulfur dioxide (SO2) is formed from sulfur contained in
the reactivation furnace and afterburner fuel and from sulfur
contained in the spent carbon. The quantity of sulfur dioxide
produced is dependent on the type of fuel used to fire the
furnace and afterburner, the sulfur content of the spent
carbon, and the amount of carbon combusted during the
reactivation process. The sulfur content of carbon typically
ranges from 2 to 5 percent. If there is a 5 percent carbon
attrition rate (i.e., 5 percent of the carbon is combusted in
processing), then for a reactivation unit that processes
11 Mg/day (1,000 Ib/hr) of spent carbon, 4 to 10 Mg/yr (1 to
2.5 Ib/hr) of sulfur is expected to be released. As the
molecular weight of sulfur dioxide is twice that of sulfur,
2-17
-------
approximately 8 to 20 Mg/yr (2 to 5 Ib/hr) of sulfur dioxide
could be emitted from an uncontrolled reactivation furnace
processing 11 Mg/day (1,000 Ib/hr) of spent carbon.
Emission source test data from a facility processing
26 Mg/day (2,400 Ib/hr) of spent carbon revealed an
uncontrolled sulfur dioxide emission rate of 86.8 Mg/yr
(21.8 Ib/hr).33 This is slightly higher than expected based
on the combustion of the activated carbon, but there are other
potential sources of sulfur, such as in the adsorbed organics
or in the fuel if oil or coal were used to fire the furnace or
afterburner, that can contribute to the total SO2 emissions.
Another facility that does not have an acid gas emission
control device has a permit limit of 30 Mg/yr (7.6 Ib/hr) of
SO2 for a unit that typically processes 10 Mg/day (900 Ib/hr)
of spent carbon.34
Nitrogen oxides (NOX) are formed in the reactivation
furnace and afterburner combustion processes. The
temperatures, residence times, and oxygen contents of typical
reactivation operations are just in the range where NOX
formation tends to increase; therefore, it is difficult to
make any predictions on NOX emissions from these carbon
reactivation units. The only available NOX emission data are
from measurements taken at one facility subsequent to a dry
scrubber used for acid gas removal. The controlled NOX
emission rate for this facility was 9.5 Mg/yr (2.4 Ib/hr)
while processing approximately 49 Mg/day (4,500 Ib/hr) of
spent carbon.35
2.3.3 Particulate Emissions
There are two sources of particulate emissions from
thermal reactivation of spent carbon. From the reactivation
furnace itself, the primary particulate emissions consist of
carbon fines entrained in the furnace exhaust gas. There are
already economic incentives to minimize this source of
particulate emissions to minimize the amount of carbon loss.
Additionally, the carbon fines are effectively destroyed in
2-18
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most afterburners. Therefore, particulate emissions from most
carbon reactivation furnaces that are equipped with
afterburners are typically not significant.
In some reactivation systems, however, a second potential
source of particulate emissions exists. Some air pollution
control technologies, particularly dry or spray scrubbers used
for acid gas removal, may form particulates as a by-product,
which subsequently need to be removed from the air stream
prior to release to the atmosphere. All available particulate
emission measurements for carbon reactivation systems were
made downstream of particulate removal devices. From these
data, the "controlled11 particulate emissions ranged from
0.0013 to 0.057 gr/dscf. Using the exhaust air flow rates for
each furnace, the "controlled" particulate emissions ranged
from 0.3 to 6 Mg/yr (or 0.08 to 1.5 lb/hr).36"38
2.3.4 Metal Emissions
There are two sources of metals in spent carbon: the
trace metals that occur naturally in the carbon itself and the
metals that are adsorbed on the spent carbon. As reported by
the industry, all carbon has some inherent or intrinsic metal
content. Most carbons are produced from- coal and, in general,
have the same basic range/distribution of naturally occurring
metals, including mercury (Hg), lead (Pb), barium (Ba),
chromium (Cr), and nickel (Ni). The most common process that
results in adsorption of metals onto activated carbon is
carbon adsorption used in wastewater treatment. Metals other
than iron would not likely be encountered when using carbon
for treatment of potable water; in addition, it is highly
unlikely that metals would be encountered when carbon is used
for vapor control.
Metal emissions can occur either as particulate matter or
as metal vapors. Metal emissions occurring as particulate
matter are primarily metals that remain adsorbed on, or are
naturally occurring in, the entrained carbon fines (see
Section 2.3.3). Metal particulates can also be formed when
2-19
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metal vapors condense prior to the final exhaust. The oxides
of certa.in metals such as mercury, lead, selenium, and
cadmium have relatively high vapor pressures (volatilities).
When they are formed in the combustion zone, a
disproportionate fraction is present in the postflame as a
vapor. A portion of this metallic vapor is present in the
combustion products; later it condenses as the postflame gases
cool when passing through various ducts and appears as ash,
particulate, or aerosol in the exhaust gas. Before discharge
to the atmosphere, these particulates are typically controlled
by methods described in Section 3.3. The remaining portion of
the metallic vapor typically exits the stack uncontrolled to
the atmosphere.
Carbon reactivators report that they routinely do a
metals analysis of the carbon that enters the facility for
reactivation. Reactivation facilities are most sensitive
about Hg content. If highly volatile metals are present in
"significant" amounts, then the carbon is not accepted for
reactivation. There are exceptions on a case-by-case basis
for treatment of carbons that contain metals; for example, if
the client wants a custom reactivation job where the carbon is
isolated and returned to the client following reactivation.
The fate of metals contained in spent activated carbon
that is thermally reactivated can be traced in three routes.
A portion of the metals will remain in the carbon, including
the collected particulate matter and residual ash; a portion
of the metals present will be controlled or captured in the
wet or dry scrubbing system that is typically present on
nearly all reactivation processes; and a portion of the metals
will be emitted out the stack to the atmosphere.
No data were available to quantify what percentage of
metals are emitted to the atmosphere for carbon reactivation
operations, but there are comparable operations that give some
idea of the variability that occurs from metal to metal. A
study of incineration of waste sludges revealed that: for Hg,
2-20
-------
0.4 percent of the Hg remained in the ash, 2 percent was in
the scrubber water, and 97.6 percent exited the stack; for Pb,
87 percent remained in the ash, 12 percent was in the scrubber
water, and 1 percent was emitted out the stack; for Cd,
80 percent remained in the ash, 20 percent was in the
scrubber, and 0 percent was emitted.39
2.4 REFERENCES
1. Telecon. Heflin, B., and Sengupta, P., Calgon Carbon
Corporation, with Zerbonia, R., Research Triangle
Institute. March 1991. Carbon reactivation.
2. Trip Report. Plant Visit to Calgon Carbon Corporation,
Neville Island, Pennsylvania and Carbon Reactivation
Facility. May 14, 1991. Report dated July 1991.
3. Telecon. Sokol, T., and Stallard, M., Envirotrol (Beaver
Falls, Pennsylvania), with Zerbonia, R., Research
Triangle Institute. March 1991. Carbon reactivation.
4. Trip Report. Plant Visit to Envirotrol, Incorporated,
Swickley, Pennsylvania. May 13, 1991 (Darlington plant
and Beaver Falls plant). Report dated August 1991.
5. Telecon. Robinson, D., Cameron-Yakima, with Zerbonia,
R., Research Triangle Institute. January 1991. Carbon
reactivation.
6. Telecon. Eubanks, B., Barnebey-Sutcliffe, with Zerbonia,
R., Research Triangle Institute. March 1991. Carbon
reactivation.
7. Telecon. Yacoe, P., Atochem North America, Incorporated,
with Zerbonia, R., Research Triangle Institute. March
1991. Carbon reactivation.
8. Telecon. Clovis, C., Adsorption Systems, with Zerbonia,
R., Research Triangle Institute. March 1991. Carbon
reactivation.
9. Telecon. Babbitt, B., West States Carbon, with Zerbonia,
R., Research Triangle Institute. March 1991. Carbon
reactivation.
10. Telecon. Lio, R., California Carbon Company, with
Zerbonia, R., Research Triangle Institute. March 1991.
Carbon reactivation.
2-21
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11. Telecon. Quigley, K., Trans-Pacific Carbon, with
Zerbonia, R., Research Triangle Institute. March 1991.
Carbon reactivation.
12. Telecon. Culbertson, J., Northwest Carbon, with
Zerbonia, R., Research Triangle Institute. April 1991.
Carbon reactivation.
13. Federal Register, Vol. 56, No. 35. Thursday,
February 21, 1991. p. 7200.
14. Telecon. Wey, M., Mobay Chemical Company, with Zerbonia,
R., Research Triangle Institute. April 1991. Carbon
reactivation.
15. Telecon. Myers, J., Mobay Chemical Company, with
Zerbonia, R., Research Triangle Institute. April 1991.
Carbon reactivation.
16. Telecon. Parigi, J., Mobay Chemical Company, with
Zerbonia, R., Research Triangle Institute. April 1991.
Carbon reactivation.
17. Letter and enclosures from Ishihara, M., Archer Daniels
Midland (ADM) Company, to Jordan, B., EPA/OAQPS/ESD.
October 16, 1991.
18. Letter and enclosures from Hobby, G., Cargill, Inc., to
Jordan, B., EPA/OAQPS/ESD. September 27, 1991.
19. Telecon. Labs, W. and B. Marshall, A.E. Staley
Manufacturing Company, with Coburn, J., Research Triangle
Institute. June 1991. Carbon reactivation.
20. Ref. 13.
21. Lombana, L.A., and D. Halaby. Carbon Regeneration
Systems, Chapter 25. In: Carbon Adsorption Handbook.
P.N. Cheremistinoff and F. Ellerbush,. editors. Ann Arbor
Science Publishers, Ann Arbor, MI. 1978. p. 905-992.
22. von Dreusche, Jr., C. Process Aspects of Regeneration in
a Multiple-Hearth Furnace, Chapter 26. In: Carbon
Adsorption Handbook. P.N. Cheremistinoff and F.
Ellerbush, editors. Ann Arbor Science Publishers, Ann
Arbor, MI. 1978. p. 923-929.
23. Schuliger, W., and L.G. Knapil. Reactivation Systems.
In: AWWA Seminar on Engineering Considerations for GAC
Treatment Facilities, Cincinnati, OH. June 17, 1990.
ISBN: 0-89867-545-6. pp. 91 through 122.
2-22
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24. Johnson, N.P., and M.G. Cosmos. Thermal Treatment
Technologies for Hazardous Waste Remediation. Pollution
Engineering. October 1989. pp. 70-72.
25. Ref. 24, pp. 72-75.
26. Ref. 24, pp. 68-70.
27. Telecon. Dickinson, R., A.E. Stanley Manufacturing
Company, with Coburn, J., Research Triangle Institute.
January 1993. Carbon reactivation furnace operations.
28. Telecon. Junker, T., Consultant, with Zerbonia, R.,
Research Triangle Institute. January 1993. Carbon
reactivation furnace operations.
29. Telecon. Loeffelholz, M., Calgon Carbon Corporation,
with Zerbonia, R., Research Triangle Institute.
February 1993. Carbon reactivation furnace operations.
30. Ref. 2, Attachment 2.
31. Ref. 2, Attachment 6.
32. Pennsylvania Department of Environmental Resources.
Source Test Report for Envirotrol Inc., Beaver Falls,
Pennsylvania. Source test conducted on May 24, 1988.
33. Ref. 2, Attachment 5.
34. Ref. 19.
35. Ref. 2, Attachment 6.
36. Ref. 2, p. 5.
37. Ref. 4, p. 4.
38. Ref. 18.
39. Brunner, Calvin R. Incineration Systems Selection and
Design. Van Nostrand Reinhold Company, Inc., New York,
NY. 1988. p. 125.
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3.0 EMISSION CONTROL TECHNIQUES
This chapter discusses emission control techniques
applicable to spent carbon reactivation off-gas streams.
These control techniques are grouped into four broad emission
categories: organics, acid gases, particulates, and metals.
Equipment utilized for the control of these emissions includes
afterburners, packed towers, spray towers, venturi scrubbers,
impingement scrubbers, cyclones, and baghouses. This
equipment is described with respect to its applicability to
control carbon reactivation emissions, and equipment design
and performance are discussed.
The four emission categories characteristic of carbon
reactivation processes present numerous options in terms of
the selection and sequencing of air pollution control
equipment and techniques. Due to the high temperature of the
off-gases from the carbon reactivation furnace, the first
control step typically used is an afterburner immediately
following the reactivation furnace to destroy the organic
materials that were driven from the spent carbon. The next
step is typically wet scrubbing by use of either a packed bed
or spray tower to: (1) cool the gas, (2) remove the inorganic
acid gases and metal vapors from the afterburner exhaust, and
(3) remove the particulates. In some cases, especially if a
dry scrubber that generates particulates is used, a
particulate control device such as a baghouse may also be used
as a final control step.
3-1
-------
3.1 ORGANIC EMISSION CONTROL
Organic air emissions from carbon reactivation process
units consist of organic/hydrocarbon compounds driven from the
spent carbon or formed as products of incomplete combustion.
Because of the high temperatures of the off-gas exiting
reactivation furnaces, this organic matter is usually
destroyed by use of a combustion control device. If
combustion were complete in these devices, all organics would
be converted to carbon dioxide, water, and trace acids.
However, since actual combustion is never 100 percent
complete, the remaining organics exit from the stack either in
vapor form or adsorbed onto particulate matter.
There are two types of combustion control devices:
thermal afterburners and catalytic afterburners. Thermal
afterburners require less capital investment and therefore are
less expensive to install than catalytic afterburners;
however, catalytic afterburners operate at lower temperatures
and therefore typically require less fuel and are less
expensive to operate depending on the life of the catalyst.
However, the temperature of the exhaust from the reactivation
furnace is already very high (approximately 800 °C [1500 °F]
or higher) and carbon fines, which may be entrained with the
exhaust, tend to foul most catalysts and thereby shorten the
catalyst's useful life. That is, the usual advantages of
catalytic afterburners do not apply when considering the
control of a reactivation furnace exhaust. Consequently,
thermal afterburners are used almost exclusively for the
control of organic emissions in the carbon reactivation
industry.
A thermal afterburner is shown in Figure 3-1. It usually
consists of a refractory-lined chamber that is equipped with
one or more sets of burners. The organic-laden stream passes
through the burners and is heated above its ignition
temperature. The gas is then sent through one or more
residence chambers where it is held for a certain length of
time to achieve the desired combustion efficiency.
3-2
-------
Dirty
gas «
Fuel
and
air
Dirty,
gas
Clean
gas
out
Figure 3-1. Thermal afterburner.
3-3
-------
Residence times of 0.3 to 2 seconds are common when thermal
afterburners are used at carbon reactivation facilities.1
Thermal afterburners designed specifically for organic
incineration with natural gas as the auxiliary fuel may also
use a grid-type (distributed) gas burner as shown in
Figure 3-2. The tiny gas flame jets on the grid surface
ignite the vapors as they pass through the grid. The grid
acts as a baffle for mixing the gases entering the chamber.
This arrangement ensures burning of all vapors at lower
chamber temperature and uses less fuel. This system makes
possible a shorter reaction chamber yet maintains high
efficiency.
Thermal afterburners operate on the basic principle that
any hydrocarbon heated to a high enough temperature in the
presence of enough oxygen will be oxidized to CO2 and water.
The theoretical temperature required for thermal oxidation to
occur depends on the structure of the chemical involved. Some
chemicals are oxidized at temperatures much lower than others.
Information collected through site visits to, and telephone
contacts with, facilities that have carbon reactivation
furnaces with thermal afterburners indicates that typical
afterburner temperatures range from 850 to 1,050 °C (1,560 to
1,900 °F) .2~5 The organic destruction efficiency of a thermal
afterburner can be affected by variations in chamber
temperature, residence time, inlet organic concentration,
compound type, and flow regime (mixing). Other parameters
affecting afterburner performance are the amount of excess
combustion air and the water content and heating value of the
off-gas.
The heating value of the off-gas is a measure of the heat
available from the combustion of the organics in that stream.
Off-gas with heating value below 1.86 MJ/Nm3 (50 Btu/scf)
usually requires auxiliary fuel to maintain combustion
temperatures. Off-gas with a heating value above 1.86 MJ/Nm3
(50 Btu/scf) may support combustion but may need
3-4
-------
FUEL GAS
FUME
STREAM
I- CLEANED STREAM
TO HEAT
RECOVERY
OR STACK
Figure 3-2. Thermal afterburner with a distributed burner,
3-5
-------
auxiliary fuel for flame stability. Auxiliary fuel
requirements can be lessened by the use of recuperative heat
exchangers to preheat combustion air. An afterburner handling
carbon reactivation off-gases with varying heating values and
moisture content requires careful adjustment to maintain the
proper chamber temperatures and operating efficiency. Water
requires a great deal of heat to vaporize. Entrained water
droplets in the off-gas can substantially increase auxiliary
fuel requirements due to the additional energy needed to
vaporize the water and raise it to the combustion chamber
temperature.
Sufficient oxygen to provide for complete theoretical
oxidation of both the pollutant and the fuel required must
always be ensured when designing the afterburner. The oxygen
source for afterburners is air that can enter with the
pollutant stream and/or through the afterburner combustion
system. The amount of excess air used varies with the fuel
and burner type, but it is generally kept to a minimum. Using
too much excess air wastes fuel because the additional air
must be heated to the combustion chamber temperature. A large
amount of excess air also increases flue gas volume and will
increase the size and cost of the system. For these reasons,
a heat exchanger is sometimes used to preheat the auxiliary
air using the afterburner exhaust. In carbon reactivation
processes, afterburners used to control organic emissions
typically use 6 to 8 percent excess air.6
Concerning afterburner capacity, there is no theoretical
limit. Units with capacities over 30,000 scfm of process
fumes are relatively common. Inlet stream temperatures are
typically -7 to 425 °C (20 to 800 °F); however, equipment can
be designed to accommodate temperatures outside this range.
The destruction efficiency of thermal afterburners can be
affected by various parameters; test results show that they
can achieve 98 percent for most organic compounds.7 The
98 percent efficiency estimate is predicated upon thermal
afterburners operated at 870 eC (1,600 °F) with a 0.75-sec
3-6
-------
residence time for nonhalogenated organic compounds. If the
vapor stream contains halogenated compounds, a temperature of
1,100 °C (2,000 °F) and a residence time of 1 second is needed
to achieve a 98 percent destruction efficiency. Test results
provided by two commercial carbon reactivators show organic
destruction efficiencies for a reactivation furnace/thermal
afterburner combination greater than 99 percent and as high as
99.9999 percent were achieved.8' 9
3.2 ACID GAS EMISSION CONTROL
Acid gas pollutants present in the off-gas from carbon
reactivation process units include hydrogen halides (HCl, HF,
HBr, and HI), NOX, and SO2. These pollutants can be
efficiently removed by absorption. An alternate term for
absorption is scrubbing. This section describes the basic
theoretical operating principles of absorption, then describes
the process control equipment used for controlling acid gas
emissions from reactivation furnace off-gas. Control devices
primarily used include packed-bed scrubbers and spray towers.
Venturi scrubbers and impingement scrubbers have limited acid
gas scrubbing capabilities and are also discussed briefly in
this chapter. Removal efficiency and applicability of these
devices to reactivation off-gas streams are also discussed.
3.2.1 Absorption Principles for Acid Gas Emission Control
Absorption is the selective transfer of one or more
components of a gas mixture into a solvent liquid. The
transfer consists of solute diffusion and dissolution into a
solvent. For any given solvent, solute, and set of operating
conditions, there is an equilibrium ratio of solute
concentration in the gas mixture to solute concentration in
the solvent. The driving force for mass transfer at a given
point in an absorption tower is a function of the difference
between the actual concentration ratio and the equilibrium
ratio. The absorbed material may dissolve physically in the
liquid (physical scrubbing) or react chemically with it
(chemical scrubbing).
3-7
-------
In physical scrubbing, the off-gas and scrubbing liquor
temperatures, the concentrations of the pollutant in both
gaseous and liquid phases, and the solubility of the pollutant
in the scrubbing liquor are the major factors that determine
effectiveness. The ionic nature of acids, bases, and salts
makes these compounds good candidates for removal from off-
gases by wet scrubbing. Water by itself is efficient at
removing acidic soluble gases such as HC1, HF, and silicon
fluoride (SiF4), especially if the last contact is made with
water having a slightly alkaline pH.10 For pollutant gases
with limited water solubility such as SO2, very large
quantities of water are required. For these pollutants,
simple wet scrubbing is usually impractical, but may
occasionally be employed in unusual circumstances.
Chemical scrubbing, such as use of a caustic solution,
often further enhances removal of acid gases and can be used
effectively to remove pollutants from reactivation off-gases.
Factors that affect chemical reactions, such as reaction
rates, temperature, pH of liquor, and concentrations, are also
important in determining the effectiveness of this method.
Some examples of chemical scrubbing techniques are the
absorption of sulfur dioxide using calcium carbonate, calcium
oxide, magnesium oxide, sodium hydroxide, and other alkali and
the absorption of nitrogen oxides using a urea solution.11
The rate of absorption of the acid gas, for either
physical or chemical scrubbing, depends on the physical
properties of the gas liquid system such as density,
diffusivity, equilibrium, solubility, and viscosity. These
properties are temperature dependent, and lower temperatures
generally favor absorption of gases by the scrubbing liquid.
3.2.2 Absorption Equipment for Acid Gas Emission Control
The most prevalent method of control for inorganic
emissions is wet scrubbing. Control devices most commonly
used for wet scrubbing are packed-bed and spray tower
scrubbers. Tray towers, although potentially applicable, were
not used by any of the reactivation facilities identified in
3-8
-------
Section 2. Other wet scrubbing technologies that are
available and have been used for emission control at carbon
reactivation facilities are venturi scrubbers and impingement
scrubbers. These devices, however, are used primarily for
particulate removal and are discussed in Section 3.3 on
particulate emission controls. An alternative method of
control for inorganic emissions is dry scrubbing. This
section describes both wet and dry absorption equipment used
primarily for acid gas emissions control.
3.2.2.1 Packed Towers.12 A packed-tower or packed-bed
scrubber is shown in Figure 3-3. In these systems, liquid
solvent is sprayed through the top of the column on specially
designed packing and is allowed to flow through the system.
As a result, the large surface area provided by the packing
enhances the opportunity for absorption of the pollutant
solute. Finely packed beds can remove finer mists, while
coarser packing is used to prevent fouling in the presence of
coarse particulates. Although gas flow may be countercurrent,
crosscurrent or concurrent, most packed towers use a
countercurrent gas flow design. The pollutant solute in the
gas phase is absorbed by the solvent, usually water, which
carries the dissolved solute out the bottom of the tower.
Cleaned gas exits at the top for release to the atmosphere or
for further treatment as necessary. In some cases, the
saturated liquid solvent is directed to a regeneration unit
where the solution is treated so that the solvent may be
recycled and the pollutant disposed of appropriately or
recovered. When water is used as the solvent or absorbent,
the solution may be pumped directly to an onsite wastewater
treatment system where secondary emissions may occur.
The major packed tower design parameters to be determined
for absorbing any substance are column diameter and height,
system pressure drop, and liquid flow rate required. These
parameters are derived from consideration of the total surface
area provided by the .tower packing material, the solubility
and concentrations of the components, and the quality of the
3-9
-------
Clean gas out
Mist eliminator
Liquid sprays
Packing
Dl>ty gas in
Liquid outlet
Figure 3-3. Countercurrent packed tower.
3-10
-------
gas to be treated. Liquid-to-gas ratios in packed towers
generally range from 0.3 to 3 L/m3 (2 to 20 gal/1,000 ft3).
Typical pressure drops are 0.12 to 0.25 kPa per foot of
packing (0.5 to 1 inches of H2o/ft).
Packed-tower scrubbers can achieve higher removal
efficiencies than spray towers and have relatively lower water
consumption requirements. Some disadvantages are high-
pressure drops, more fouling potential, potentially higher
maintenance cost, and wastewater disposal requirements.
Flooding is an important consideration in the design of
packed towers. Flooding occurs when the gas stream approaches
the flooding velocity and results in liquid being carried back
up the column by the gas stream. Tower diameter should be
established based on a superficial gas velocity from 50 to
•75 percent of the flooding velocity.
3.2.2.2 Sprav Towers.13 Spray towers or chambers are
the simplest and least expensive device employed for acid gas
scrubbing. They consist of an empty tower and a set of
nozzles to spray liquid. Typically, the contaminated gas
stream enters the bottom of the tower and passes up through
the device while the solvent liquid is being sprayed at one or
more levels by nozzles. Liquid and gas streams typically flow
countercurrent to each other (see Figure 3-4).
To provide a large surface for contacting the gas, nozzles
are arranged to wet the entire cross section of the tower with
fine liquid droplets. After falling short distances, the
liquid droplets tend to agglomerate or hit the sides of the
tower. This effect reduces the total liquid surface in
contact with the gas stream and the residence time. Therefore,
spray towers used for acid gas emission control are limited to
applications where either the gases are extremely soluble or a
high removal efficiency is not required.
Mass transfer is significant when droplets of 500 to
1,000 /zm diameter are used.14 In general, the smaller the
droplet size and the .greater the turbulence, the more chance
for absorption of the gas. Production of fine droplets
3-11
-------
Clean gas out
Spray nozzles
. .
••'."-•'•'; •"•• .•.'v::—x''-';: ;'••.V\' '.•'•'•
•'• \'-\ j&:::••'-''•; •" ^n ''•
Dirty gas in
Figure 3-4. Spray tower.
3-12
-------
requires the use of high-pressure spray nozzles that consume
more energy than do low-pressure nozzles.
Spray tower height has an effect on efficiency but is much
less significant than droplet size and liquid-to-gas ratios.
Increasing the height of a given tower only slightly increases
efficiency due to wall losses and agglomeration. Variations
in pressure have little effect on efficiency of these systems
while changes in liquid rate have a large effect on
efficiency. In general, spray towers are not as efficient as
packed towers but may be adequate for specific applications.
Spray towers have a low pressure drop, about 0.5 to 1 kPa
(2 to 4 inches of H2O). Design liquid-to-gas ratios typically
average between 3 and 13 L/m3 (20 to 100 gal/1,000 ft3). As
with packed towers, liquid may be recirculated to reduce
requirements for makeup water.
For acid gas removal in both spray tower and packed-bed
applications, aqueous scrubbing liquids are the most common.
However, equilibrium conditions may favor the use of other
low-volatility solvents, such as nonvolatile hydrocarbon oils.
Flooding is also an important design consideration for
spray towers. As recommended for packed towers, spray tower
diameter should be established based on a superficial gas
velocity from 50 to 75 percent of the flooding velocity.
3.2.2.3 Drv Scrubbers.1S Dry scrubbing devices are also
frequently used for controlling acid gas emissions, especially
sulfur dioxide. Spray dryers (see Figure 3-5) contact an acid
gas-contaminated stream with a finely sprayed slurry of either
lime or soda ash. The water in this slurry is evaporated by
the heat in the off-gas, yielding a dry waste stream. Dry
sorbent containing the inorganic pollutant, together with
other particulate matter in the waste gases, is captured in a
particulate matter collection system (e.g., a fabric filter
baghouse) connected to the spray dryer.
The SO2 in the off-gas reacts with the alkali solution or
slurry by adsorption .or absorption mechanisms, or both, to
form liquid-phase salts, which are dried to about 1 percent
3-13
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Spray diyen
Baghouse
b baghouse
Figure 3-5. Dry scrubbing system.
(Top: spray dryer with baghouse. Bottom: spray dryer.)
3-14
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free moisture by the heat in the off-gas. These solids are
carried out of the dryer to a particulate collection device,
such as a fabric filter baghouse.
In some designs, a portion of the solids is collected from
the bottom of the spray dryer. Usually, the dry waste product
is disposed of in landfills. To take advantage of any
unreacted reagent left in the solids and reduce fresh reagent
requirements, some of the solids can be recycled back to the
dryer.
The technology of spray drying is less complex
mechanically, and no more complex chemically, than wet calcium
or wet sodium-based scrubbing systems. High SO2 removal
efficiencies, typically above 90 percent, can be obtained
using either lime or sodium-based sorbents and high molar feed
rates of reagent. Sodium-based reagents such as sodium
hydroxide and sodium carbonate are more reactive than calcium-
based reagents such as lime or limestone but are also more
expensive.
3.3 PARTICULATE EMISSION CONTROL16
Particulates from carbon reactivation processes are mostly
carbon fines and solid material formed from dry scrubbing
processes used to remove acid gases. Particulate collection
devices applicable for carbon reactivation off-gas include wet
scrubbers (e.g., venturi, impingement, and spray towers),
baghouses, cyclones, and electrostatic precipitators (ESPs).
Although potentially applicable, none of the facilities
identified in Secion 2 used ESPs. Therefore, no further
discussion is provided regarding ESPs. When heavy particulate
loads are present or submicron particulates must be recovered
along with gaseous pollutants, it is common to use wet
collection devices having high particulate collection
efficiencies. In the case of carbon reactivation emissions
where particulates are in the presence of acid gases, it is
advantageous to apply control devices that also have some
capability for gas absorption. Wet scrubbers, such as packed
3-15
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beds, are commonly used for acid gas removal, but may trap
particles effectively as well. The particulates, however,
tend to clog such units too quickly to make them useful for
particulate removal of gas streams with heavy particulate
loads. Venturi scrubbers, as well as impingement scrubbers,
are some of the more versatile wet scrubbing devices effective
for both particulate and acid gas removal. This section
describes each of these particulate control devices, their
applicability, design, and efficiency.
3.3.1 Venturi Scrubbers
A typical venturi configuration is shown in Figure 3-6.
The particulate laden off-gas enters the scrubber and is
accelerated to a high velocity while passing through the
converging section and approaching the throat section. The
velocity of the gas is at its greatest in the throat section
of the scrubber. Atomized droplets are formed by the impact
of the high-velocity gas upon the liquid stream in the throat.
The particulates and the liquor droplets then collide and
agglomerate. After the particles have been trapped within the
liquor droplets, the resulting agglomerates are easily removed
from the ^as stream. Although venturi scrubbers can have
collection efficiencies greater than 90 percent for submicron
particulates, power costs are relatively high for this device
because of the high inlet gas drop. Removal efficiencies are
a function of particle sizes and head loss.
Absorption of pollutant gases is limited with venturi
collection because of the short time that the gas is in
contact with the liquid. The venturi scrubber has, however,
been used successfully to remove S02 and particulates from the
off-gas stream.
Numerous venturi scrubbers are available with the
principal differences being in:
1. Methods for varying throat area for changes in gas
flow rate;
2. Methods for injecting the liquor ahead of the throat;
3-16
-------
Clean gas out
Gas inlet
Dirty gas in
Water and condensate out
I
Water and condensate out
Figure 3-6. Venturi wet collector.
3-17
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3. Presence or absence of a diverging section; and
4. Design of entrained liquor droplet separator following
the throat.
Water is injected into the venturi in quantities ranging
from 0.6 to 13 L/m3 (4 to 100 gal/1,000 ft3 of gas).
Operating pressure drops ranging from 1.5 to 18 kPa (6 to 70
inches of water).17 Velocities in the throat can range from
30 to 250 m/sec (100 to 800 ft/sec).
3.3.2 Impingement Scrubbers
Impingement scrubbers are also commonly employed by carbon
reactivation facilities. Although they serve primarily as
particulate control devices, the versatility of impingement
scrubbers makes them suitable for both particulate and acid
gas removal. They are similar in design to spray towers but
have one important difference: a series of baffles have been
added. The major function of these baffles is not to promote
mixing but to provide additional impingement surfaces.
The particulate-laden gas stream is forced to make many
90 degree turns around the baffles, forcing the large
particulates to impinge on the baffles rather than flow with
the air stream around the barriers. Scrubbing liquid, usually
water, is continually added above the baffles. The high
velocity of the gas stream causes the liquid to atomize into
drops that are entrained by the gas and collecting particles.
A typical unit is shown in Figure 3-7. The baffle plate has
numerous orifices and a baffle directly over each orifice. The
orifices provide additional velocity for the gas. The
entrained particles that are not collected on one baffle are
accelerated as they pass through orifices to the next stage.18
Particle collection is generally by inertial impaction
caused by impingement on the liquid surface and the atomized
drops. The performance of an impingement scrubber seems to be
comparable to a venturi scrubber operating at the same gas
phase pressure drop. The baffle acts as a multiple venturi.
One difference between this type of scrubber and a venturi is
3-18
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CLEAN GAS OUTLET
SCRUBBING LIQUOR INLET
NOZZLE
IMPINGEMENT BAFFLE STAGE
SPRAY LIQUOR
Figure 3-7. Impingement scrubber (top);
baffle plate (bottom).
3-19
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that in the venturi, all the gas is accelerated through one
opening with a resulting large pressure drop and tremendous
particulate acceleration. The impingement scrubber, however,
uses a relatively modest gas phase acceleration in which the
sum of the pressure drop across all of the orifices is less
than that in a venturi. Impingement scrubbers are, therefore,
not as effective for fine particulate removal as venturi
scrubbers.
Several baffle impingement stages may be needed to achieve
the desired degree of performance. Rarely are more than two
or three stages used due to the trade-off between energy
requirements and mass removal efficiency. Each impingement
baffle plate stage has a plate with 600 to 3,000 orifices per
square foot.
The impingement scrubber removes over 97 percent by weight
of particles above 1 ^m and a considerable percentage of
smaller particles. The pressure drop through these units is
usually about 1.5 inches of water per stage. Water side
pressure is not too high, about 5 psig with superficial
velocities on the order of a few feet per second to 20 feet
per second. The gas handling capacity of these units is
easily 50,000 ft3/min.
3.3.3 Spray Towers
Spray towers (described in Section 3.2.2.2) are effective
for dual removal of particulate and gaseous contaminants.
They can handle gases with fairly high concentrations of
particulates without plugging. The units cause very little
pressure loss and can handle large volumes of gases. As the
gas flows upward, entrained particles collide with liquid
droplets sprayed across the flow passage, and liquid droplets
containing the particles settle by gravity to the bottom of
the chamber. They are effective in removing particles in
excess of 10 ^m and can be modified to improve efficiencies
for smaller particles.19
3-20
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For all wet collectors, disposal of the wastewater in
which the particulates have been collected poses problems.
Often the wastewater will require some form of treatment
before being charged into a receiving stream. This will
typically be a settling tank or pond or a centrifugal device.
In areas where water supplies are limited or water costs are
unusually high, further treatment before recycling of the
water may be necessary.
3.3.4 Cyclones
In industrial applications, cyclones are often used as a
precleaner for the more complex air pollution control
equipment such as baghouses or wet scrubbers. In carbon
reactivation processes, cyclones have been used to collect
fine particulates generated in the fluidized-bed reactivation
process. Because fluidized-bed furnaces have a higher
exhaust volume than other furnace types, more of the fines are
carried over in the exhaust. Once the cyclone has removed the
fines, the gas can then be further purified by the use of
other emission control techniques such as afterburning.
Cyclones are centrifugal collectors that employ a
centrifugal force instead of gravity to separate particles
from the gas stream. Because centrifugal forces can be
generated that are several times greater than gravitational
forces, particles can be removed in centrifugal collectors
that are much smaller than those that can be removed in
gravity settling chambers.
A cyclone collector such as the one shown in Figure 3-8
consists of a cylindrical shell, conical base, dust hopper,
and inlet where the dust-laden gas enters tangentially. Under
the influence of the centrifugal force generated by the
spinning gas, the solid particles are thrown to the walls of
the cyclone as the gas spirals upward at the inside of the
cone. The particles slide down the walls of the cone and into
the hopper.
The cyclone has no moving parts and is simple and
inexpensive. It is less efficient than a wet scrubber or a
3-21
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baghouse for removing particulate matter. As a class of
equipment, cyclones provide the lowest collection efficiency
of devices in general commercial use for control of particles.
However, their ability to handle a hot gas without appreciable
cooling makes cyclones best suited for the removal of large
particulates between the reactivation furnace and an
afterburner.
The efficiency of a cyclone depends on the magnitude of
the centrifugal force exerted on the particles. The greater
the centrifugal force, the greater the separating efficiency.
The magnitude of the centrifugal force generated depends on
particle mass, gas velocity within the cyclone, and cyclone
diameter. Efficiency will increase with an increase in dust
particle size or dust particle density, gas inlet velocity,
cyclone body length, and ratio of body diameter to gas outlet
diameter. Conversely, efficiency will decrease with an
increase in gas viscosity or gas density/ cyclone diameter,
gas outlet diameter, and inlet width or inlet area.
Disappointing results from cyclone installations are usually
due to overly optimistic estimates of efficiency. Ranges of
efficiency to be expected from cyclone collector installations
are shown in Table 3-I.20
Usually the pressure drop in cyclones varies from l to
6 inches of H2O. Volumetric flows range from 50,000 to
100,000 ft3/min, depending on the type of cyclone. Concerning
temperature limitations, a cyclone is limited only by the
TABLE 3-1. EFFICIENCY RANGE OF CYCLONES
Efficiency range,
Particle size range (/xm) weight % collected
Less than 5 Less than 50
5-20 50-80
15 - 40 80 - 95
Greater than 40 95-99
3-22
-------
r Clean
Gas and
particulates
in
JS^J Collected dust
$H out
Figure 3-8. Cyclone collector.
3-23
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material of which it is constructed, and it can be constructed
of almost any type of material - a distinct advantage if
condensed acids are present. Typical temperature limits are
375 to 550 °C (700 to 1,000 °F) ;21 however, cyclones have been
operated at temperatures higher than 1,000 °C using refractory
linings.22
Potential problems encountered in operating cyclones
include erosion, fouling, and corrosion. Erosion in cyclones
is caused by the rubbing of dust particles on the cyclone
wall. This condition becomes more severe with high dust
loadings, high inlet velocities, and large or hard dust
particles. Erosion can be minimized by a wise choice of
cyclone diameter size as well as special construction
features. Such construction features include the use of
heavier-gauge metal for cones, the use of abrasion-resistant
removable wear plates at the impingement zone, avoidance of
welds and joints that cannot be ground smooth, and the use of
larger cyclones for prevention of excess gas velocities. Any
defect in cyclone design or operation that tends to
concentrate dust moving at high velocity will accelerate
erosion.
Fouling can also be a problem with cyclones. Fouling
generally occurs either through plugging of the dust outlet or
through the buildup of materials on the cyclone wall. It
results in decreased efficiency, increased erosion, and
increased pressure drop. Corrosion can become a problem if
the cyclone is operating below the condensation point when
reactive gases are present in the off-gas stream. It is
usually caused by chlorides and sulfides in contact with the
metal walls and can be minimized by using the proper
materials—alloys or, in some applications, plastics.
An advantage of cyclones, as well as bag filters, over the
wet scrubbing devices previously described is that the removed
particulates are collected as a dry stream; thus, further
wastewater treatment is not needed. Additionally, since the
primary particulate matter for carbon reactivation off-gases
3-24
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is carbon fines, especially for fluidized-bed furnaces,
cyclones can be used to recover the larger carbon fines and
thereby reduce carbon loss during the reactivation process.
3.3.5 Baghouse Filters
Fabric filter dust collectors, commonly referred to as
baghouses, are among the oldest and most widely applied
particulate emission control devices. They find utility in
carbon reactivation processes in several ways. One way is by
collecting particulate matter formed when dry scrubbing is
used to remove acid gases from the off-gas as discussed in
Section 3.2.2.3. Another use for baghouse filters in carbon
regeneration facilities is the removal of particulate matter
from emissions leaving the reactivation furnace. The
temperature of the off-gas is first lowered by a quenching
process to eliminate potential fire hazards. A baghouse then
removes particulate matter from the cooled gas after which the
gas may go to an afterburner or scrubber.
A typical baghouse filter is shown in Figure 3-9. In
fabric filter systems, particulate-laden gas streams pass
through a fabric that allows gaseous matter to pass though and
filters out particulate matter. A dust mat is initially
formed from the retention of small particles on the fabric by
direct interception, inertial impaction, diffusion,
electrostatic attraction, and gravitational settling.
Submicron particles are then collected more efficiently by
sieving.
As particulates build up on the inside of the bag, the
pressure drop across the bag increases and must eventually be
relieved. This is typically done by mechanical shaking,
reverse-air cleaning, or pulse-jet cleaning of the particulate
layer. The particulates then fall into a collection hopper
and are removed for disposal.
Several problems are associated with fabric filter use.
One potential problem is the possibility of explosion or fire
if sparks are discharged in a baghouse area where organic
dusts are being filtered. Other problems include the
3-25
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Mechanism for shaking,
rapping, or vibrating bags
Clean
air out
Dirty
air in
Collected
dust out
Figure 3-9. Baghouse filter.
3-26
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possibility of rupture or other adverse effects because of
temperatures too high for the fabric medium or because of the
moisture, acidity, or alkalinity content of the particulate-
laden gas stream.23 Judicious fabric choice can minimize these
problems.
Filter bags are usually tubular in shape. Other filter
bag shapes include envelopes and pleated cartridges. As to
size, a baghouse arrangement may be small enough to fit into
an ordinary room or large enough to dwarf many industrial
buildings.
Design of baghouses is based on filtering rates, the air-
to-cloth ratios, and pressure drops. The air-to-cloth ratio
is the volumetric flow rate of the gas stream divided by the
surface area of the fabric. The higher the ratio, the smaller
the baghouse and the higher the pressure drop. Filtering
rates range from 0.5 to 5 m3 of air per minute per square
meter of cloth depending on factors such as the dust loading,
fabric material, and method of cleaning.24
Pressure drop across the filter is a function of both the
velocity of the gas through the filter and the combined
resistance of the fabric and accumulated dust layer. In order
to avoid operational problems and excessive power
requirements, the maximum pressure across the filter should be
5 to 10 inches of water.
Advantages of using baghouses to control particles include
performance that is independent of flow rate, uniform
collection efficiency over a wide range of particle sizes, and
collection efficiency that is independent of particle
resistivity. Efficiencies in excess of 99 percent and often
as high as 99.99 percent on a weight basis can be expected for
well-designed systems. Most inefficiency in these units is
the result of either bypass due to damaged fabric, faulty
seals, or leaks. Seldom is penetration of particles through
the filter cake or fabric the cause of poor performance.
Usually, any penetration that does occur is greatest during or
immediately after cleaning.
3-27
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Drawbacks of baghouse systems include: clogging of the
filter medium due to condensation in the gas stream;
cementation of filter cake in humid, low-temperature gases,
especially in the presence of lime from a scrubber; and
excursions of high-particulate concentrations when a bag
breaks. Also, sticky or high-moisture particles can adhere to
the fabric and be difficult to release.
3.4 METAL EMISSION CONTROL
Metal emissions can occur in two forms: either as
particulate matter or as metal vapors. Metal emissions
occurring as particulate matter are primarily metals that
remain adsorbed on, or are naturally occurring in, the
entrained carbon fines. Metal particulates can also be formed
when metal vapors condense prior to the final exhaust. The
oxides of certain metals such as mercury, lead, selenium, and
cadmium have relatively high vapor pressures or volatilities
and, when they are formed in the combustion zone, a
disproportionate fraction is present in the postflame as a
vapor. A portion of this metallic vapor present in the
combustion products later condenses as the postflame gases
cool when passing through various ducts. Prior to discharge
to the atmosphere, these particles are typically controlled
using one of the particulate emission control devices
described in Section 3.3.
Only a limited number of control methods are applicable to
the remaining portion of the metallic vapor. Absorption is
the most widely used and accepted method for inorganic vapor
control. The absorption equipment used to control metal
emissions are described in Section 3.2.2. The removal
efficiency of metal vapors achievable with absorbers can be
greater than 99 percent and is typically determined by the
actual concentrations of the inorganic in the gas and liquid
streams and the corresponding equilibrium concentrations.
Water is often the ideal solvent for vapor control by
absorption. It offers distinct advantages over other
3-28
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solvents, particularly its low cost. It is typically used on
a once-through basis and then discharged to a wastewater
treatment system. The effluent may require pH adjustment to
precipitate the metals.
3.5 REFERENCES
1. Memo and attachments from J. Coburn, RTI, to M. Smith,
EPA/CPB. November 7, 1991.
2. Trip Report. Plant Visit to Calgon Carbon Corporation,
Neville Island, Pennsylvania and Carbon Reactivation
Facility. May 14, 1991. Report dated July 1991.
3. Trip Report. Plant Visit to Environtrol, Incorporated,
Sewickley, Pennsylvania. May 13, 1991 (Darlington plant
and Beaver Falls plant). Report dated August 1991.
4. Telecon. Myers, J., Mobay Chemical Company, with
Zerbonia, R., Research Triangle Institute. April 1991.
Carbon reactivation.
5. Telecon. Robinson, D., Cameron-Yakima, with Zerbonia, R.,
Research Triangle Institute. January 1991. Carbon
reactivation.
6. Ref. 1.
7. Memo and attachments from Farmer, J.R., EPA, to
Distribution. August 22, 1980. pp. 1-29. Thermal
incinerator performance for NSPS.
8. Ref. 2, p. 5 and Attachments 2 and 6.
9. Ref. 3, p. 4.
10. Calvert, S., and H. M. Englund. Handbook of Air Pollution
Technology. New York, NY, John Wiley and Sons. 1984.
pp. 135-142.
11. Liptak, B. G. Environmental Engineer's Handbook. Randor,
PA, Chiton Book Company. 1974. pp. 759.
12. U.S. Environmental Protection Agency. Gas Absorbers,
Chapter 9. In: OAQPS Control Cost Manual. Research
Triangle Park, NC. Publication No. EPA-450/3-90-006.
April 1992. pp. 9-1 through 9-75.
13. Mclnnes, R., K. Jameson, and D. Austin. Scrubbing Toxic
Inorganics. Chemical Engineering. September 1990.
pp. 116-121.
3-29
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14. U.S. Environmental Protection Agency. Air Pollution
Engineering Manual. 2nd Edition. Research Triangle Park,
NC. Publication No. AP-40. May 1973. p. 228.
15. Mclnnes, R., and R. V. Royen. Desulfurizing Fluegases.
Chemical Engineering. September 1990. p. 127.
16. U.S. Environmental Protection Agency. Wet Scrubber
Inspection and Evaluation Manual. Washington, DC.
Publication No. EPA-340/1-83-022. September 1983.
17. Theodore , L., and A. Buonicore. Air Pollution Control
Equipment Selection, Design, and Maintenance. Englewood
Cliffs, NJ, Prentice-Hall, Inc. 1982. pp. 247-249.
18. Bethea, R. M. Air Pollution Control Technology, An
Engineering Analysis Point of View. New York, NY, Van
Nostrand Reinhold Company. 1978. pp. 277-280.
19. Wark, Kenneth, and Cecil F. Warner. Air Pollution: Its
Origin and Control. New York, NY, Dun-Dunnelley. 1976.
pp. 4-19 through 4-37.
20. Stern, A. C., Editor. Air Pollution, Volume IV,
Engineering Control of Air Pollution 3rd ed. New York,
NY, Academic Press. 1977. pp. 104-131.
21. Liptak, B. G. Environmental Engineer's Handbook. Randor,
PA, Chiton Book Company. 1974. pp. 563-573.
22. U.S. Environmental Protection Agency. Air Pollution
Control Systems for Selected Industries. Research
Triangle Park, NC. Publication No. EPA-450/2-82-006.
June 1983. pp. 2-8.
23. Danielson, J. A. Air Pollution Engineering Manual, 2nd
ed. EPA Office of Air and Water Programs, Research
Triangle Park, NC. 1973.
24. Peavy, H., D. Rowe, and G. Tchobanoglous. Environmental
Engineering. New York, NY, McGraw-Hill, Inc. 1985.
pp. 533-535.
3-30
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4.0 ENVIRONMENTAL IMPACTS AND COST ANALYSIS
This chapter presents the emission reductions, costs, and
cost-effectiveness values of various options for the control
of air emissions from carbon reactivation process units. The
different types of carbon reactivation furnaces are described
in Section 2, and the technologies available to control the
air emissions are described in Section 3. The precise
sequence of air pollution control devices used depends, in
part, on the type and throughput of the reactivation furnace
and the types of pollutants adsorbed on the spent carbon. In
this section, example control options typical to the
reactivation industry are developed and cost analyses for each
control option at low, medium, and high exhaust gas flow rates
are presented.
4.1 CONTROL TECHNOLOGY ALTERNATIVES - MODEL SYSTEMS
As discussed in Section 3, there are three types of
pollutants emitted from carbon reactivation units: organics,
acid gases, and particulates. From the information collected
from the reactivation industry (Tables 2-1 and 2-2), the most
prevalent organic air emission control device employed is a
thermal afterburner; over 70 percent of the reactivation
furnaces currently operating already have thermal afterburners
in place. Therefore, an afterburner is included for all model
systems for control of organic air emissions.
Wet scrubbers are the next most common air pollution
control device^used for carbon reactivation furnaces.
Approximately 50 percent of the currently operating
reactivation furnaces have a wet scrubber for either acid gas
4-1
-------
or particulate matter emission control. Venturi scrubbers are
the most commonly used particulate emission control device;
37 percent of the currently operating reactivation furnaces
have a venturi scrubber for particulate emission control. All
other emission control devices combined (dry scrubbers,
cyclones, impingement scrubbers, and baghouses) represent
approximately 25 percent of the population of emission control
devices used at operating carbon reactivation systems.
These industry profile data indicate that the majority of
the carbon reactivation pollution control systems can be
represented by two model systems. The first model system
consists simply of an afterburner to control nonhalogenated
organic emissions (Model Unit 1). The second model system
(Model Unit 2) consists of an afterburner and a packed-bed wet
scrubber to control acid gas emissions resulting from the
combustion of a halogenated organic exhaust waste stream.
Particulate emissions would also be controlled by the
scrubber; however, these are considered negligible. For each
model system, control units will be designed and their costs
estimated based on three different exhaust gas flow rates
representative of small, medium, and large carbon reactivation
furnaces. The reactivation furnace exhaust rates investigated
are: 500 scfm for small furnaces, 1,500 scfm for medium-sized
furnaces, and 4,500 scfm for large furnaces.
4.2 CONTROL COSTS
With the exception of fluidized-bed furnaces, which
represent only about 5 percent of the operating reactivation
furnaces, different types of reactivation furnaces employ
similar gas flow rates for similar carbon throughput rates.
Thus, some useful generalizations can be made concerning the
carbon throughput and the composition of the reactivation
furnace exhaust.
Information gathered during the preliminary data-gathering
activities and site visits reveals that gas flow rates range
from 93 to 287 dscf in the final stack exhaust per pound of
4-2
-------
carbon produced, with an average of 183 dscf/lb carbon.1'8
These measurements were taken after the afterburner. Because
of the need to add auxiliary air to supply an adequate amount
of oxygen, the final gas flow rate from the afterburner will
always be greater than the reactivation furnace exhaust gas
flow rate. Therefore, it was assumed that a gas flow rate in
the reactivation furnace was 100 dscf/lb carbon produced.
After performing the mass and energy balances, this ratio
between the reactivation furnace exhaust rate and the
afterburner exhaust rate proved to be a reasonable
approximation.
As a rule of thumb, 1 Ib of steam is added per pound of
dry carbon in the furnace to create the reactivating
atmosphere.9'10 Therefore, the moisture content in the
reactivation furnace is approximately 22 scf of steam/100 dscf
of air, based on the 100 dscf/lb carbon assumption, or
18 percent by volume. This also implies that an average gas
flow rate of 100 dscf/lb carbon is equivalent to 122 scf/lb
carbon.
The organic loading on the spent carbon can range from as
little as 1 to 2 percent for potable water treatment carbons
to as high as 25 percent depending on the application of the
carbon. Typically, however, the organic loading rate ranges
from 8 to 13 weight percent.11'12 Assuming a 10 weight percent
organic loading on the spent carbon, a 90 percent destruction
efficiency in the reactivation furnace, and using the assumed
gas flow rate of 122 scf/lb carbon produced, the organic
concentration in the exhaust air can range from 250 ppmv for
an organic waste gas stream with an average molecular weight
of 140 g/mol to 1,500 ppmv for an organic waste gas stream
with an average molecular weight of 24 g/mol. To investigate
the influence of the organic loading of the carbon, control
costs were determined at three different organic loading rates
(5, 10, and 15 weight percent). Since the organic destruction
efficiency in the reactivation furnace also directly
influences the organic concentration in the exhaust gas
4-3
-------
stream, two values, a low of 10 percent and a high of
90 percent, were used in the model plant design and cost
analyses. Sample calculations of the design and cost of each
of the model units is provided in Appendix A.
4.2.1 Model Unit 1: An Afterburner
The OAQPS Control Cost Manual13 was used to investigate
different operating conditions and estimate the control costs
for Model Unit 1. In this case, a thermal incinerator is used
as an afterburner for the control of nonhalogenated organic
air emissions. The control cost for an afterburner (thermal
incinerator) is largely driven by the total volumetric gas
flow rate through the afterburner. This flow rate is the sum
of the waste gas flow rate (exhaust from the reactivation
furnace), the fuel feed flow rate, and the auxiliary air flow
rate needed to maintain the desired oxygen concentration.
From the information gathered from facilities operating
carbon reactivation furnaces, the reactivation furnace is
typically operated with a minimum of excess oxygen; furnace
exhaust oxygen concentrations on the range of 1 to 8 percent
are typical of the industry. The afterburner is typically
operated with slightly more excess oxygen than the
reactivation furnace; afterburner exhaust oxygen
concentrations range from 6 to 10 percent.14*17 Therefore, it
is necessary to add auxiliary air to maintain the oxygen
concentration in the afterburner.
To minimize the amount of auxiliary air required to be
added in the afterburner, the amount of fuel burned needs to
be minimized. The waste gas is already very hot (550 to
800 °C), so a preheater for the waste gas is not required.
However, the auxiliary air required to maintain sufficient
oxygen in the afterburner is presumably at ambient air
temperature (25 °C or 77 °F), and a significant amount of the
total energy requirement for the afterburner is needed to heat
the auxiliary air. For these anticipated gas stream
temperatures, a 35 percent efficient heat recovery preheater
for the auxiliary air reduces the afterburner fuel requirement
4-4
-------
by approximately a factor of four and reduces the auxiliary
air requirement by approximately a factor of two. The
preheater increases the total capital investment (TCI) for the
afterburner compared to a system with no heat recovery, but
this increase in TCI is small because the total afterburner
gas flow rate is less in the system with a preheater.
Additionally, the large decrease in the fuel requirements for
the system with a preheater leads to a lower total annual cost
(TAG) for a system with a preheater compared to a system
without one.
The energy balance and the oxygen mass balance dictate the
design of the afterburner. Because the reactivation furnace
off-gas is a dilute organic waste stream, its composition and
concentration have limited effect on the design of the
afterburner. That is, a compositional change in the furnace
off-gas, although it may provide some impact on the fuel
requirements, will not significantly alter the total gas
throughput in the afterburner and will not, therefore,
significantly affect the TCI. Changes in the fuel requirement
will, however, directly affect the fuel costs, and the fuel
costs become a significant contributor to the TAG for larger
systems, as the total gas flow increases.
The operating parameters used to develop the control costs
are summarized in Table 4-1. These parameters were determined
based on the information gathered from facilities operating
carbon reactivation furnaces, the generalizations discussed in
Section 4.2, and preliminary cost estimates to determine the
optimal heat recovery factor.
The results of the control cost analyses for Model Unit l
are summarized in Table 4-2 (refer to Appendix A for sample
calculations). At a given concentration, increasing the
exhaust gas flow rate for larger reactivation furnace
throughput causes an increase in the TCI and TAG, but not
proportionally to the increase in the flow rate. Therefore,
the cost effectiveness of the afterburner control device
4-5
-------
TABLE 4-1. DESIGN PARAMETERS FOR THERMAL INCINERATOR
Design parameter
Input value
For reactivation furnace exhaust
Furnace exhaust flow rate (varied)
Small furnace throughput
Medium furnace throughput
Large furnace throughput
Benzene concentration (varied)
5% org./lb carbon and 90% destruction
10% org./lb carbon and 90% destruction
15% org./lb carbon and 90% destruction
5% org./lb carbon and 10% destruction
10% org./lb carbon and 10% destruction
15% org./lb carbon and 10% destruction
Furnace exhaust temperature
Furnace exhaust oxygen concentration
Furnace exhaust moisture content
For afterburner
Fuel inlet temperature
Auxiliary air inlet temperature
(after 35% heat recovery)
Afterburner design temperature
Afterburner exhaust oxygen concentration
Energy recovery (used to preheat aux. air)
Afterburner destruction efficiency
500 scfm
1,500 scfm
4,500 scfm
216 ppmv
456 ppmv
725 ppmv
1,950 ppmv
4,110 ppmv
6,520 ppmv
1,100 °F
4% by volume
18% by volume
77 °F
1,500 °F
1,700 °F
8% by volume
35%
99%
4-6
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improves with the increased gas flow rate. At a given exhaust
gas flow rate, increasing the exhaust gas organic
concentration, either through higher organic loading on the
spent carbon or through less combustion of desorbed organics
in the reactivation furnace, has a very limited effect on the
TCI and TAG. Therefore, the cost effectiveness of the
afterburner control device improves in proportion to an
increase in gas organic concentration.
4.2.2 Model Unit 2: An Afterburner and Wet Scrubber
For reactivation furnace exhaust air streams that contain
halogenated organics, a wet scrubber is needed to remove the
acid gases generated as the halogenated organics are
incinerated. A chapter of the OAOPS Control Cost Manual is
currently being drafted to estimate the costs of a packed-
tower wet scrubber. Although the final draft of that chapter
was not available when this document was written, the cost
curves to determine the equipment costs for the tower were
available.18
The design inputs for the afterburner in Model Unit 2 use
the same exhaust gas flow rates, the same organic carbon
loading levels, and the same reactivation furnace organic
destruction efficiencies as Model Unit 1 (see Table 4-1). In
this case, however, the organic pollutant is
1,1,1-trichloroethane and the exhaust from the afterburner
contains HC1, which must be removed. The design for the
packed-tower wet scrubber was, therefore, based on the
afterburner exhaust gas flow conditions. The total
afterburner exhaust gas flow rates were 880 scfm, 2,640 scfm,
and 7,910 scfm, corresponding to the reactivation furnace
exhaust flow rates of 500 scfm, 1,500 scfm and 4,500 scfm,
respectively. The afterburner exhaust was used to preheat the
auxiliary air, so the afterburner exhaust temperature exiting
the heat exchanger was 593 °C (1,100 °F). Due to the
relatively high solubility of HC1 in water, the tower design
was driven by the energy balance (i.e., the amount of water
required to cool the gas stream). The sizing and costing of
4-8
-------
the packed-tower wet scrubber was then determined using the
design and cost information provided in References 19 through
22. Table 4-3 summarizes the design parameters for Model
Unit 2.
The calculated control costs for Model Unit 2, the combined
afterburner and packed-tower wet scrubber emission control
train, are summarized in Table 4-4 (see Appendix A for sample
calculations). The same relative effects caused by changing
the exhaust gas flow rate and the exhaust gas organic
concentration that were seen in Model Unit I are found in
Model Unit 2. That is, increasing the exhaust gas flow rate,
at a set organic concentration, increases the TCI and the TAG
but lowers the cost-effectiveness factor. Increasing the
organic pollutant concentration at a set gas flow rate does
not affect the TCI or the TAG and, therefore, proportionally
lowers the cost-effectiveness factor.
4.3 CROSS-MEDIA AND SECONDARY ENVIRONMENTAL IMPACTS
Although thermal incinerators are used to prevent air
pollution, thermal incinerators themselves exhibit an air
pollution potential and can produce cross-media impacts and
secondary emissions depending on their operation. It is
possible to create a major pollution problem when burning any
waste gas if the waste gas is not burned with sufficient air
for combustion. Improper operating conditions can result in
carbon monoxide (CO) generation. If proper combustion
conditions are observed, such as correct air-to-fuel ratio,
sufficient mixing, adequate residence time, peak flame
temperature, and proper cooling rate of combustion products,
essentially all the carbon present in the waste gas should end
up as carbon dioxide (C02). All the hydrogen should result in
water as a product of combustion, and unburned hydrocarbons
should be minimal.
4-9
-------
TABLE 4-3.
DESIGN PARAMETERS FOR MODEL UNIT 2:
INCINERATOR AND WET SCRUBBER
THERMAL
Design parameter
Input value
For reactivation furnace exhaust
Furnace exhaust flow rate (varied)
Small furnace throughput
Medium furnace throughput
Large furnace throughput
1,1,1-Trichloroethane concentr'n (varied)
5% organic/Ib carbon and 90% destruction
10% organic/Ib carbon and 90% destruction
15% organic/Ib carbon and 90% destruction
5% organic/Ib carbon and 10% destruction
10% organic/Ib carbon and 10% destruction
15% organic/Ib carbon and 10% destruction
Furnace exhaust temperature
Furnace exhaust oxygen concentration
Furnace exhaust moisture content
For afterburner
Fuel inlet temperature
Auxiliary after air inlet temperature
(after 35% heat recovery)
Afterburner design temperature
Excess oxygen (exhaust 02 concentration)
Energy recovery (used to preheat aux. air)
Afterburner destruction efficiency
For afterburner exhaust/wet scrubber feed
Afterburner exhaust flow rate for:
Small furnace throughput
Medium furnace throughput
Large furnace throughput
Afterburner exhaust temperature
(i.e., after 35% heat recovery)
For wet scrubber
Liquid inlet temperature
Liquid outlet temperature
Gas outlet temperature
Liquid-to-gas ratio
(calculated based on energy balance)
Packing material
Scrubber removal efficiency
500 scfm
1,500 scfm
4,500 scfm
127 ppmv
267 ppmv
425 ppmv
1,140 ppmv
2,410 ppmv
3,820 ppmv
1,100 °F
4% by volume
20% by volume
77 op
1,500 °F
1,700 °F
8% by volume
35%
99%
880 scfm
2,640 smfm
7,910 scfm
1,100 °F
70 °F
200 °F
100 °F
2:1 by weight
(6.1 gal/1,000 ft3)
l^-in. berl saddles
98%
4-10
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NOX emissions from thermal incinerators are another
secondary pollutant impact produced by thermal incinerators.
Nitrogen oxides have two sources: nitrogen in the fuel and
the reaction between atmospheric nitrogen and oxygen at high
temperatures. One problem encountered in reducing emissions
from combustion sources is the fact that modifications that
reduce carbon monoxide and hydrocarbon emissions generally
increase NOX emissions and vice versa.
As noted above, some adverse effects on air quality can be
associated with the use of combustion devices to control
organic emissions from spent carbon reactivation units.
Pollutants generated by the combustion process—SO2, CO, and
particularly NOX—may have an unfavorable impact on ambient
air quality. One facility was identified that has tested for
NOX emissions. Three 1-hr emission tests were conducted on
the final stack, subsequent to an afterburner, venturi
scrubber, and impingement scrubber, at a carbon reactivation
system processing 41 Mg/day (3,750 Ib/hr) of carbon. The NOX
concentrations ranged from 20 to 27 ppmv on a dry basis, and
the NOX emission rates ranged from 1.7 to 2.3 Mg/yr (0.44 to
0.61 Ib/hr),23
There is increasing concern about HC1 emissions from
incinerators owing to the growing amount of halogenated
polymers, such as polyvinyl chloride (PVC), and halogenated
solvent, such as methylene chloride, used in chemical
processes and therefore potentially present in waste streams.
In addition, HF emissions arise from the combustion of
fluorinated hydrocarbons. Water scrubbing, as used in Model
Unit 2, appears to be an effective means of controlling these
acid gases. An increase in wastewater, however, will result
from the wet scrubbing of these gases. The scrubber
wastewater may require neutralization by addition of a caustic
before being released into the wastewater treatment and
disposal system. The salts produced from the neutralization,
though small, may need to be disposed of as hazardous waste.
4-12
-------
TABLE 4-5. ANNUAL ENERGY REQUIREMENTS FOR CONTROL SYSTEMS
Control system/ Natural gas Electricity
design air consumption consumption
flow rate (thousand ft3/yr) (MWh/yr)
Model Unit la
500 SCfm 715-5,850 18.8-23.1
1,500 scfB 2,145-17,550 56.4-69.3
4,500 SCfm 6,440-56,600 169-208
Model Unit 2b
500 scfm 5,690-6,090 28.7-29.1
4,500 SCfm 17,100-18,300 86.0-87.2
4,500 SCfm 51,200-54,800 258-262
aModel Unit 1 is an afterburner, with operating conditions as
provided in Table 4-1. Increasing the concentration of
benzene in the reactivation furnace exhaust causes a
decrease in both the natural gas consumption rate and
the electricity consumption rates up to 25% of the LEL
for benzene (4,375 ppm).
''Model Unit 2 is an afterburner and packed-tower wet scrubber
system, with operating conditions as provided in Table 4-3.
Increasing the concentration of 1,1,l-trichloroethane in the
reactivation furnace exhaust causes only a slight decrease
in the natural gas consumption rate and has less than a 1%
effect on the electricity comsumption rate.
4-13
-------
Therefore, carbon reactivation may produce a small solid waste
impact, but this impact is much smaller than the solid waste
impact caused by directly disposing of the spent carbon rather
than reactivating the spent carbon.
The use of an afterburner to control organic emissions from
carbon reactivation furnaces results in a net energy usage for
both model units because supplemental fuel is needed to
support combustion. These supplemental fuel requirements in
the form of natural gas are presented in Table 4-5.
Electrical energy is required to operate the pumps, fans,
blowers, and instrumentation that may be necessary to control
organics using an afterburner. Electrical energy requirements
as estimated by the costing model are presented in Table 4-5
as well. The natural gas consumption varies only slightly
with an afterburner of a given size due to the low organic
concentrations in the gas stream. Model Unit 2 requires
approximately twice the electrical energy, primarily due to
the increased pressure drop caused by the packed-tower wet
scrubber.
4.4 REFERENCES
1. Trip Report. Plant Visit to Calgon Carbon Corporation,
Neville Island, Pennsylvania, and Carbon Reactivation
Facility. May 14, 1991. Report dated July 1991.
2. Trip Report. Plant Visit to Environtrol, Incorporated,
Sewickley, Pennsylvania. May 13, 1991 (Darlington plant
and Beaver Falls plant). Report dated August 1991.
3. Letter and enclosures from Ishihara, M., Archer Daniels
Midland (ADM) Company, to Jordan, B., EPA/OAQPS/ESD.
October 16, 1991.
4. Letter and enclosures from Hobby, G., Cargill, Inc., to
Jordan, B., EPA/OAQPS/ESD. September 27, 1991.
5. Pennsylvania Department of Environmental Resources.
Source Test Report for Environtrol Inc., Beaver Falls, PA.
Source test conducted on May 24, 1988.
4-14
-------
6. Pennsylvania Department of Environmental Resources.
Source Test Report for Environtrol Inc., Beaver Falls, PA.
Source test conducted on April 12, 1988.
7. PEDCo Environmental, Inc. Emission Test Report. Carbon
Reactivation Furnace, calgon Carbon Corporation,
Pittsburgh, PA. August 1980.
8. PEDCo Environmental, Inc. Compliance Test Report. Carbon
Reactivation Furnace. Calgon Carbon Corporation,
Catlettsburg, KY. September 1982.
9. Schuliger, W.G., and L.G. Knapil. Reactivation Systems.
In: AWWA Seminar on Engineering Considerations for GAC
Treatment Facilities, Cincinnati, OH. June 17, 1990.
ISBN: 0-89867-545-6. pp. 91 through 122.
10. Lombana, L.A., and D. Halaby. Carbon Regeneration
Systems, Chapter 25. In: Carbon Adsorption Handbook,
Cheremistinoff, P.N., and Ellerbush, F., (ed.) Ann Arbor,
MI, Ann Arbor science Publishers. 1978. p. 920.
11. Ref. 1, p. 3.
12. U.S. Environmental Protection Agency. Design and Cost of
HAP Control Techniques, Chapter 4. In: Control
Technologies for Hazardous Air Pollutants Handbook.
Washington, DC. Publication No. EPA/625/6-91/014.
June 1991.
13. Van der Vaart, D.R., J.J. Spivey, W.M.. Vatavuk, and A.
Wehe. Thermal and Catalytic Incinerators, Chapter 3. In:
OAQPS Control Cost Manual. U.S. Environmental Protection
Agency. Research Triangle Park, NC. Publication No.
EPA 450/3-90-006. November 1989. pp. 3-1 through 3-63.
14. Ref. 4.
15. Ref. 1, p. 3.
16. Ref. 2, p. 4.
17. Ref. 9, pp. 97 and 98.
18. Memorandum from Vatavuk, W., Environmental Protection
Agency, to Smith, M., Environmental Protection Agency.
March 27, 1992. Discussion of gas absorber cost
equations.
19. U.S. Environmental Protection Agency. Design and Cost of
HAP Control Techniques, Chapter 4. In: Control
Technologies for Hazardous Air Pollutants Handbook.
4-15
-------
Washington, DC. EPA/625/6-91/014. June 1991. pp. 4-34,
4-35, and 4-44 through 4-54.
20. Vatavuk, W. Pricing Equipment for Pollution Control.
Chemical Engineering. May 1990. pp. 126-130.
21. A.P.T., Incorporated. Wet Scrubber System Study. Volume
1: Scrubber Handbook. Prepared for U.S. Environmental
Protection Agency. Research Triangle Park, NC. NTIS-PB-
213-016. July 1972. NTIS-PB-213-016. p. 29.
22. U.S. Environmental Protection Agency. Organic Chemical
Manufacturing. Volume 5: Adsorption, Condensation, and
Absorption Devices. Research Triangle Park, NC.
Publication No. EPA-450/3-80-027. December 1980. pp. B-3
through B-20.
23. Telecon. Faler, M., Cargill, Inc., with Coburn, J.,
Research Triangle Institute. November 1992. Carbon
reactivation NOX emission stack test results.
4-16
-------
CARBON REACTIVATION ACT
APPENDIX A
CALCULATION METHODOLOGY FOR COST ANALYSIS
This appendix provides detail regarding the methodologies
used to calculate the cost effectiveness of emission controls
applied to carbon reactivation furnace off-gas. For the
afterburner (thermal incinerator), the cost calculations follow
the example provided in Chapter 3 of the OAQPS Control Cost
Manual (4th Edition, EPA 450/3-90-006). The major difference
between the calculations presented here and those presented in
the OAQPS Control Cost Manual (or simply the Cost Manual) for
thermal incinerators is that the reactivation furnace exhaust
(inlet waste gas for the afterburner) does not contain an
adequate amount of oxygen to sustain combustion of the auxiliary
fuel (assumed inlet [O2] = 4 vol%). Therefore, auxiliary air was
required to provide the oxygen necessary for combustion of the
fuel and the organics in the waste gas.
The cost calculations for the wet scrubber follow the
example provided in Chapter 4.7 of the Handbook: Control
Technologies for Hazardous Air Pollutants (EPA/625/6-91/014)
(referred to hereon as the HAP Handbook). The main difference
between the calculations presented here and those presented in
the HAP Handbook for wet scrubbers is that the scrubbing water
flow rate was driven more by the energy balance than the
solubility of the acid gas (HC1 in this case).
It may be useful to read (or have available) copies of the
Cost Manual and HAP Handbook prior to (or while) studying the
sample calculations provided in this appendix.
A-l
-------
Step 1. Establish design specifications
From Table 4-1 of this document.
Waste Gas Volumetric Flow Rate
Waste Gas Temperature
Oxygen Content
Chemical Composition*
Heating Value (from Table 3-14)
Paniculate Content
Design Control Efficiency
Combustion Chamber Outlet
Percent Energy Recovery
Moisture Content
Qw = 500, 1500, 4500 scfm
Tw = 1,100°F
[O2] = 4 vol. %
[Bz] = 216, 456, 725 ppm
-Ahc, Bz = 17,446 Btu/lb
-Ahc,CH4 = 21,502 Btu/lb
Not critical for thermal units
99%
1700°F
35%
18 vol. %
The chemical composition of the waste gas is calculated from the organic
loading of the spent carbon based on the assumptions outlines in Section 6.
Specifically, the gas flow rate is assumed to be 122 scf/lb carbon produced.
and 90% of the organics are assumed to be destroyed in the reactivation
furnace. Thus, given a 10 wt% organic loading there will be 10 Ibs of
benzene per 100 Ibs of spent carbon or 10 Ibs of benzene per 90 Ibs of actual
carbon (that can be produced). Then the concentration of benzene is:
10% organic loading
ai **
* 1 lb Carbon ^ _
0.9 lb Carbon 122 scf
m 9J £_5 Jfi
At standard conditons and noting MWt^ = 78 g/mol
. 24,41 , 0.0353^ .
scf lb 78 g mol L
A-2
-------
Step 2. Verify oxygen requirements
Since the waste gas oxygen concentration is only 4%, auxiliary air is needed to provide
adequate oxygen to burn the fuel. The design thermal incinerator exhaust oxygen
concentration if 6%. Oxygen requirements are:
for Methane CH4 + 2O2 = CO2 + 2 H2O 2 moles O2/mol CH4
for Benzene C6H6 + 7.5O2 = 6CO2 + 3 H2O 7.5 moles O2/mol C6H6
(Note: assuming ideal gas, a mole balance is equivalent to volumetric balance.)
Oxygen Balance
O2 In
O2 Out
O2 Consumption
Auxiliary Air = 0.21 Qair
Waste Gas = 0.04 Qw
Waste Gas = 0.08 (Qair + Qw + Qf)
for Methane = 2 Qf
for Waste Gas = 7.5 [Bz] Qw = 0.0034 Qw (for [Bz] = 456 ppm)
In = Out + Consumption
0.21 Qair + 0.04 Qw = 0.08 (Qair
0.0034 Qw
Qair = 0.334 Qw + 16 Qf
Step 3. Determine % of LEL
LEL for Benzene = 14,000 ppmv (from Table 3.12 of Cost Manual)
% LEL = 456/14000 * 100% = 2.3%
Which is well below the desired 25% LEL for fire safety.
Eqn. 1
A-3
-------
Step 4. Calculate the volumetric heat of combustion for waste gas (Ahw)%.
454 g mol 0.861 scf)
-Jiw = -tJic& * [Bz] = 3,480 * 456 * 10"6 = 1.59 Btu/scf
As the waste gas has a moisture content of 18 vol%, the average molecular weight and
density of waste gas is :
pair -29** * *- - 0.0742
pJZ,O = 18 gjmol * -i-^- * 1 m°l = 0,04605
454 g 0.861
pw = 0.18 pH2O + 0.82 par = 0,0691 Ibfscf
.-. -AAw = (1.59 Btu/scfl/(Q.Q691 Ib/scfl = 23.0 Btu/lb
Step^S. Establish temperature for the incinerator.
From the survey of the industry, and afterburner temperature of 1700 °F was selected.
Step 6. Calculate the waste gas temperature at the exit of the preheater.
As the reactivation furnace exhaust is typically over 1000 °F to start, preliminary cost
estimates discovered that most of the energy requirement for the afterburner was due to the
heating of the auxiliary air when the auxiliary air was assumed to be at 77 °F. If was
subsequently determined that it was more cost efficient to pre-heat the auxiliary air than to
pre-heat (or further heat) the waste gas. It was assumed that the air could be pre-heated to
1500 °F. This assumption will be checked in Step 9.
Step 7. Calculate the auxiliary fuel requirement (Qf).
For this example, the determination of the auxiliary fuel requirement requires that the energy
and oxygen balances be simultaneously balanced.
pw = 0.0691 Ibjscf
pair = 0.0742 Ib/scf
A-4
-------
pH2O = 0.0460 Ib/sj
_ 0.50 (0.18) 0.046 + 0.26 (0.82) 0.0742
~ (1 scf) (0.0691)
Cpw = 0.289 Btu/lb °F
Tref = 77 °F
Tdesign = 1700 °F
Tove = 900 °F
C/w> = 026 Btu/lb °F
CpH2O = 0.50 Btu/lb °F
pair Cpair = 0.0193 Btu/scf - °F
pw Cpw = 0.0200 flftf/scf - °F
Note: The product of the density * heat capacity for the afterburner exhaust (waste stream)
and the auxiliary air are nearly identical. As these terms always appear as products in the
heat balance, it is reasonable to assume that the density * heat capacity for the afterburner
exhaust is the same as the waste gas'.
The energy balance is: In - Out + Generation = 0
Value
(Btu/min)
Heat In pQCp(T-Tref)
Auxiliary Air « 0.0193 Qair (1500-77) = 27.46 Qair
Waste Gas = 0.020 Qw (1100-77) = 20.46 Qw
Auxiliary Fuel = 0 (since inlet temperature = reference temperature
Heat Out pQCp(T-Tref)
Waste Stream = 0.020 (Qw + Qair + Qf) (1700-77) = 32.46 (Qw + Qair+ Qf)
Heat Out -» heat loss = 10% of the total energy input (heat out waste stream) =3.25 (Qw + Qair + Qf)
A-5
-------
Heat Generation (-Ah)pQ
Waste Gas = (23.0)(0.0691)Qw = 1.59 Qw
Auxiliary Fuel = (21,502)(0.0408)Qf = 877.3 Qf
Heat Balance Equation:
27.46 Qair + 20.46 Qw - 35.71 (Qw + Qair + Q) + 1.59 Qw + 877.3 Qf = 0
Solving for Qair yields:
Qair = 102 Qf - 1.656 Qw Eqn. 2
Solving Equation 1 and 2 simultaneously and using Qw = 1500 scfm yields
0.334 Qw + 16 Qf = 102 Qf - 1.656 Qw
Qf - 34.7 $c/5n
On. » 1,055 jc/m
Qm - 2,590
Step 8. Verify sufficiency auxiliary fuel.
Want heat generated by the fuel to equal or exceed 5 % of the total energy input.
Energy input = 32.46 (2,590) = 84,070 Btu/min
Auxiliary fuel = 877.3 (34.7) = 30,440 Btu/min
.'. auxiliary fuel provides 36% of energy input, and is therefore sufficient to stabilize the
flame.
Step 9. Check total volumetric flow and pre-heater energy balance.
Qtot = 2,590 scfm; Max available heat = 84,070 Btu/min
Heat required to pre-heat air to 1500 °F = 27.46 (1,055) = 28,970 Btu/min
That is a heat recovery of 34.5%. Therefore, the assumed inlet temperature of the air is
approximately correct.
A-6
-------
Note: Pre-heating the waste stream (instead of the air) does not reduce the total afterburner
volumetric flow rate as much as the air stream preheater due to the oxygen balance
requirements. As the cost equations provided in the OAQPS Control Costs Manual were not
developed for a dual preheater system, the 35% heat recovery (used for preheating air) cost
equations used. It may be possible to pre-heat the waste gas, and then pre-heat the air to
recover more of the exhaust streams sensible heat energy. To solve the equations for this
option requires estimates of inlet temperatures, calculating total gas flow rates, calculate heat
recoveries based on the calculated flow rates, estimating new inlet gas temperatures and
re-iterating the process until the assumed inlet temperatures equal the actual inlet
temperatures for a given level of heat recovery. Then, to determine the most cost effective
design, calculate the cost of the systems for each level of heat recovery. This process was
done for a single pre-heater system, and the optimal design is presented here. A 50% heat
recovery system was more than was needed to pre-heat the air (i.e., could not use the full
50% heat recovery), and subsequently, it did not yield lower costs.
Step 10. Calculate Equipment Cost (EC).
From Equation 3.25 of the Cost Manual:
Equipment Costs = EC = l3,l49Qmro:iai9
From Step 7, Q^f = 2,590 scfm .-. EC = $102,200
Step 11. Calculate Total Capital Investment (TCI) using Table 3.8 of the Cost Manual and
assuuming no auxiliary equipment is required:
Purchased Equipment Cost = PEC = 1.18 EC
PEC = $120,600
Direct Installation Cost = 0.3 PEC = $36,200
Site preparation -» not required
Buildings -» not required
Therefore, Total Direct Cost = DC = 1.30 PEC = 156,800
Total Indirect Costs = 1C = 0.31 PEC = 37,400
Total Capital Investment = TCI = DC + 1C = $194,200
A-7
-------
Step 12. Calculate power requirement for fan.
From Table 3.11 of the Cost Manual, the total pressure drop of the system is:
^ = ^«c* + ^B&E, = 4 + 4 = 8 m #20
From Equation 3.37 of the Cost Manual,
Power^ = (1.17 x 10"4 Qgt a APy<=
At 1,100 °F Qg. a ' CTOT 46°11QO - 2590(2.905) = 7,524 scjm
where € = fan efficiency = 0.6 (assumed)
.'. Power,^ = 11.74kW
Step 13. Calculate annual utility costs.
Actual operating hours are assumed to be 24 hours/day, 7 days/wk, 48 wks/yr.
For utility consumption, operating hours are: 8,064 hrs/yr
Electricity cost = $0.059/kWhr * 11.74 kW * 8064 hrs/yr = $5,600/yr
Natural Gas Cost = $3.30/1000 ft3 * 34.7 scfm * 60 min/hr * 8064 hrs/yr = $55,400/yr
Step 14. Calculate labor and material costs.
Annual operating days = 7 days/wk * 48 wk/yr = 336 days
Operating Labor = $12.96/hr(0.5 hr/shift)(3 shifts/day)(336 days/yr)
= $6,530
Supervisory Labor =15% of operating labor = $980
Maintenance Labor = $14.26/hr(0.5 hr/shift)(3 shifts/day)(336 days/yr)
= $7,190
Material = 100% of Maintenance Labor = $7,190
A-8
-------
Step 15. Calculate direct annual cost (DAC)
Direct annual cost (DAC) equals the sum of utility, labor, and material costs
DAC = $5,600 + 55,400 + 6,530 + 980 + 7,190 + 7,190
= $82,900/yr
Step 16. Calculate Indirect Annual Costs (I AC).
Overhead = 60% of (labor + materials)
= 0.6 (6,530 + 980 + 7,190 + 7,190)
= $13,100
Administration, Property Tax, + Insurance = 4% TCI
= $7,800
Capital Recovery (7% interest; 10 yrs life) = 0.1424 TCI = $27,600
LAC = Overhead + Administration + Taxes + Insurance + Capital Recovery
13,100 + 7,800 + 27,600
$48,500/yr
Step 17. Calculate Total Annual Cost (TAG)
TAG = DAC + LAC = 82,900 + 48,500
TAG = $131,000/yr
Step 18. Calculate Total Annual Emissions.
Design efficiency of Afterburner is 99%.
Uncontrolled Emissions = Qw [Bz] (pBz) 60 min/Ar * 8064 hr/yr
= 1500 scfin (456 x 10"*) f 78 E~6 Mg] 60 * 8064
\ 0.861 scf )
= 30 Mg/yr
Controlled Emissions = Uncontrolled Emissions * (1 - Destruction Efficiency)
= 30 (0.01) = 0.30 Mg/yr
A-9
-------
Step 19. Calculate Cost Effectiveness.
The cost effectiveness is calculated as:
Cost effectiveness = TACjEnussion Reduction
= 131,000/(30 - 0.30)
= $4,400/A/g
Design and Cost of Incinerator/Wet Scrubber System
To control the air emissions from the reactivation of spent carbon containing halogenated
organics, and incinerator/wet scrubber system was designed. The design and cost of the
incinerator follow the example for benzene containing waste gas previously provided.
The oxidation reaction of 1,1,1-trichloroethane (TCE)
CH3 CCZj + 2O2 - 2CO2 + 3HCI
Therefore, for every mole of 1,1,1-TCE oxidized, 3 moles of HC1 are produced.
At 10% organic loading, the maximum amount of 1,1,1-TCE is:
0.1 g TCE
0.9 g carbon
(^carbon] f454g] (ImolTCE} __ 3
( 122 scf ) ( Ib )( 133.1 g )
:. Max Amount HC1 = 9.3 x 10'3 mol HCl/scf
The reactivation furnace off-gas, 90% destruction efficiency is:
[HCl\ - 0.9 (9.3 x lO'3 mot) f°'861 S
-------
Note: additional fuel was required for the 1,1,1-TCE waste gas than for the Benzene waste
gas due to 1 , 1 , 1-TCE's lower heat of combustion.
Assuming 99% destruction in the after burner, the afterburner exhaust HC1 concentration is:
HCl = [7,200 -i- 10* (0.99) (0.1) (9.3 x 10'3) 0.861] * (1
V 2,637;
= 4,550 ppmv
Thus, the auxiliary air diluted the concentration of HCl. Nonetheless, the total mass flow
rate of HCl is higher in the afterburner exhaust than the reactivation furnace exhaust.
Two factors were considered when designing the packed tower: 1) needed to ensure
sufficient water flow rate to absorb the HCl; and 2) needed to use sufficient water to cool the
hot gas stream. As the solubility of HCl is temperature dependent, the scrubber water
exiting the packed tower needed to be low enough to achieve adequate absorption.
Step la. Calculate the inlet gas temperature.
Energy needed to heat air stream to 1500 °C is
E, '
-------
Step 2a. Calculate Liquid flow rate using energy balance.
Due to the relatively high solubility of HC1 in water, the design approach used was to:
1) assume desired outlet water and gas temperatures; 2) determine the liquid flow rate needed
to achieve that temperature, then check to determine if sufficient water is being used to
achieve the desired control efficiency.
Using Tg = Tgti = 1,130 °F
and Assuming T^ = 77 °F
Tj^ = 200 °F
T = 100 °F
(Wanted this cool to minimize
safety hazard of gas exhaust)
For water @ 140 °F (average temperature):
pL = 0.9832 g/cm3 = 61.43 Ibtft3
CfL = 1.05 Btu/lb °F
PL CpL = 64.5
Energy needed to cool to gas stream:
= 2,637(0.0200)(1,130-100)
= 54,322 BtujwxL
The liquid flow rate required to match that energy requirement is:
QL = _ s _
1 Pi CfL Pi, - TJ
- 54*322
[64.5(200-77)]
6.85 J*
A-12
-------
To check the sufficiency of this flow rate, the calculation provided in HAP Control
Technology Handbook, Section 4.7, are used. First, need to calculate the molar flow rates:
MWtg = 3% CO2 + 13% H2O + 4% O2 + 80% N2 = 27.3 Ib/lb mol
= 6.67 Ib mol/mia.
L = QL9jMWtL = 6.85(61.43)/(18)
= 23.4 Ib-mol/min
Step 3a. Check liquid flow rate using equilibrium absorption data
To calculate the slope of the equilibrium curve, the following data was calculated from the
data given in Perry's Chemical Engineer Handbook, 5th Edition, p. 33-98. (Note: Partial
pressure of HC1 is 760*MOO"6 =1.06 mm Hg.)
Solubility For Given Temperature and Partial Pressure
Temperature
50 °C (122 °F)
80 °C (176 °F)
Pv = 1.06 mm Hg
21 g/100 g H2O
12 g/100 g H20
Pv = 0.053 mm Hg (95% removal)
96 g/100 g H2O
3 g/100 g H2O
•t
., , mol fraction in gas } y
M — \ ——^————^—^—^—^—— \ — —
^ mol fraction in liquid at equilibrium J x
MWt HCl = 36.46 g/mol
1.06 mm Hr. X =
Y = 1.4 x 10'3
M = - = 1.4 xlQ-3 = 0.025
A
Of the conditions presented, this is the largest value of m. To ensure sufficient liquid flow
for absorption want:
L > 1.6 m G
L = 23.4 to-mol/min > 1.6(0.025)6.67 = 0.27 Ib mol/tom
Therefore, the liquid flow rate is more than sufficient to achieve high HCl removal
efficiencies (>98%).
A-13
-------
Step 4a. Calculate the Column Diameter using Figure 4.7-2 of HAP Handbook.
First calculate the abscissa (ABS):
ABS =
(G MWtJ ( pL)
The average gas temperature is 600 °F, therefore
ao691 *
ao35
ABS
421 flfr™ 0-035
"
= 2.313(0.0239)
= 0.055
From Figure 4.7-2, the ordinate (ORD) is:
ORD = 0.14
ORD p.
gc\
For 1- Berl Saddles: a = 44
e = 0.75
e3 = 0.422
The gravitational constant, g,,, is: 32.2 ft/sec2 *
ty of water is: \IL = 0.495 c/^ @ 140 °F (Perr/J />. 3-213)
^a2 = 0.869
_ [Q.14(Q.Q35)(61.43)(32.2)
" [ (44/0.422)(0.869)
= 0.327 0fl*2-sec
A-14
-------
Assuming a fraction of flooding velocity, f, of 0.60
/ (7^ = 0.60(0.327)
Ga = 0.196 Ib(ft2-sec
The column area is: A
MWt*
(60 sec/min)(Gd)
(182 te/min)
(60 sec/min)(0.196)
15.46 ft2
The column diameter is then:
-4.5 ft
Step 5a. Calculate column height.
Hfadc = NoG HoG
Design for 98% removal: (HAPg/HAPJ = 50
For the flow rates used, the worst (largest) m occurs at the water outlet
8 HCl
(Temp = 200 °C; XM = — 5 - = 0.038 moles/mole', m = 0.037)
100 # #20
.'. (1/AF) = 0.037.
Then NOQ = 3.91 (from Eqn 4.7-13 HAP Handbook)
= Ha * ()
For 1-" fler/ Saddles: b = 5.05
2
c = 0.32
rf » 0.45
A-15
-------
L" = 6QL(MWtj)/Ac = 60(421)/(15.46) = 1,634 lb/hr-ft2
Schmidt number = Scg = ngl(pg D^)
@600 °F \ig = 0.0287 cp (from Perry's p.3-21) = 2.87 x 10"4 g/cm-scc
Iblft3 - 5.61 x 10-4 g/cm3
(I/A/. + I/A/.)"
—— —^— (Perry's p. 3-231)
(315 °C or 588 °£) pg = 0.035
[10.85-2.5(1/A/, + 1/Afj)] j: 10-4 A/ = Molecular Wts
[10.85 - 2.5 (1/27.3 + 1/36.46)"] jr 10"4
[10.85 - 2.5 (0.253)] x 10"4
1.02 j: 1Q-3
= (588)u = 14,258
P = I aim
3.6117 t 3.305
(from Perry's Table 3-308 />. 3-234)
r,2 = 3.461
r122 = 11.98
To calculate ID: 6/Kt= 97.0; e/K2= 360
(from Perry's Table 3-308 p. 3-234)
(97.360)" = 187
588
3.14
From Table 3-309 Perry's p. 3-234
ID = 0.4688
DU, = 1.02 x 10'3 (14^58) (0.253y[l(11.98) (0.4688)]
DAB = 0.655 cw2/sec
A-16
-------
, 2.87 X IP
[(5.61 x IQ
= 0.781
.-. HG = [5.05[(3600)0.196f 32/(1634)(U5] (0.781)
HG = 1.30
HL =
0-5
For 1-" Berl Saddles: Y = 0.00625
2
s = 0.28
(From Perrjs Fig 3.45, p. 3-213) nr = 0.495 cp = 4.95 A; 10'3 g/cm-sec @ 140 °
\IL = 1.197 W-/w
5ci = (VI/PL x DAB)
T= 60°F (T = 333 °K)
lP jO \f jm T \
DM = 8,931 ^ 10'10 ^-^1 * + ' (Eqn 3-34 Ferris p. 3-235)
A* \ ZJZV )
For H* It - 349.8 + 4.816^7 = 1.031 x lO'^I)2 - 7.67 x lQ~5^Tf
Ar = 60 - 25 = 35
.-. It - 502.4
For Cr f. = 76.35 * 1.54 AJ = 4.65 x lO'^T)2 = 1.28 x lO'5^!)3
= 135.4
A' - It + It - 637.8
Z+ = Z. = 1
DM = 8.931 10"3(333) (502-4K135-4)(2)
637.8
DM = 6J44 x 10'5 cm2/sec
5
-------
/ 1 fAA. '\0t28
/. HL = 0.00625 77^- (79.4)
v 1-197 /
fft = 0.42
H
OG
3.91(1.32)
5.2 ft
Step 6a. Calculate volume of packing.
Step 7a. Calculate Pressure Drop through column.
10
'8
For l" fler/ Saddles: g = 8.10
r = 0.0025
Pa = 8.1 x 10-8
Pa = 1.343 U>fft2-ft
(3600 Garea?/pg
.43)] ,705.6)2/0.035
TOT
1.343(5.2)
6.98
1.34 i
Step 8a. Calculate the surface area of the column.
5 » -KDJiH^f + DJ2)
Hmr = 2-81 * !-4 apa* * I-02 Dc
- 2.81 + 1.4(5^) + 102(4.5)
= 14.68^
S = 7t(4.5) (15 + 4.5/2)
5
Eqn 2 of Vatavuk memo
°f
A-18
-------
Step 9a. Calculate Column Cost.
Ccoi = 1155 =$28,060 Eqn 1 of memo
Step IQa. Calculate equipment costs. EC.
(Using Porcelain Flexisaddles for Berl Saddle = 1'A" in Table 4.7-2 of HAP Handbook)
- 82.7(17.75)
- $1.470
Caux = Cost Auxiliary Equipment.
Assuming 40 feet of ductwork is needed, then using Equation 4.12-6 (p. 4-100) of HAP
Handbook.
\Ta = 7,660 ft3/w
inches
40 ft$53lfi) = $2,120
28,060 + 1,470 * 2,120
EC = $31,650
A-19
-------
Step 11?. Calculate total capital investment (TCI)
Purchased equipment cost (PEC) is:
PEC = 1.18EC = $37,350
Direct Cost (DC) assuming no site preparation and no building is:
DC = LS5PEC = $69,100
Indirect cost (1C) is:
1C = Q.35PEC = $13,070
Then, TCI = DC + 1C
TCI = $82,200
Step 12a. Calculate power requirement for fan from Step 7a:
Power = 1.17 x 10"4 Qg a AP/e
From Step 7a: AP = 1.5 in H2O and using e = 0.6 then,
Power = 1.95 x 10"4 (7660)1.5
= 2.24 kW
Step 13a. Calculate annual utility costs.
Electricity cost = $O.Q59/kW-hr * 224 * 8,064
= $1,070
Water cost = $0.20/1000 gal (6.85^3/min) -SE * 8,064
I ** )\ ft3 )
= $4,960
Step 14a. Calculate labor and material costs.
These are the same as Step 14 for the afterburner.
Operating Labor = $6,530
Supervisory Labor = 980
Maintinance Labor = 7,190
Material = 7,190
A-20
-------
Step 15a. Calculate direct annual cost (DAC).
DAC = sum of utility, labor, and material costs
= 1,070 + 4,960 * 6,530 + 980 + 7,190 + 7,190
= $27,920
Step 16a. Calculate indirect annual cost (IAC).
Overhead = Q.6(labor + materials) = $13,100
Admin, Taxes, and Insurance = 4%TCI = 3,300
Capital Recovery (7%; 10 yrs) = Q.1424TCI = 11,700
IAC = sum of the above = $28,100
Step 17a. Calculate total annual cost.
TAG = DAC + IAC
= 27,920 + 28,100
- $56,000/yr
Step 18a. Calculate TCI and TAG for afterburner/wet scrubber system.
= TCI
a
194,000 + 82,000
$276,000
= TACa
- 135,000 + 56,000
= $191,000/yr
Step 19a. Calculate cost effectiveness.
Emission reduction of VO = 30.0 - 0.30 = 29.7 Mg/yr
Cost Effectivenss = TAC^/Emission Reduction
= 191,000/29.7
- $6,4QQ/Mg
A-21
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TECHNICAL REPORT DATA
fPfease read instructions on the reverse before completing)
1. REPORT NO.
EPA463/R-92-019
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Alternative Control Technology Document
Carbon Reactivation Processes
5. REPORT DATE
December 1992
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Office of Air Quality Planning and Standards
Environmental Protection Agency
Research Triangle Park, North Carolina 27711
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-4326
12. SPONSORING AGENCY NAME AND ADDRESS
DAA for Air Quality Planning and Standards
Office of Air and Radiation
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final 1992
14. SPONSORING AGENCY CODE
EPA/200/04
15. SUPPLEMENTARY NOTES
EPA Work Assignment Manager:
Martha Smith (919) 641-2421
16. ABSTRACT
The purpose of this Alternative Control Technology (ACT) document is to provide technical information
to address air emissions of volatile organic compounds (VOC) from carbon reactivation processes, some
of which are subject to RCRA regulations. This document contains technical information on carbon
reactivation process operations, air emission rates, control technologies, and environmental and cost
impacts of alternative control technologies.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a.
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air pollution
Carbon reactivation
Hazardous waste
Volatile organics
Thermal treatment units
Emission controls
Air pollution control
13 B
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (THIS REPORT)
Unclassified
21. NO. OF PAGES
110
21. SECURITY CLASS (THIS PAGE)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION IS OBSOLETE
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