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OAR Box 1870 

Prepped by Ollie Stewart 

Document Number: 

Docket Number: 

A-90-17 

Printed 11/28/2008 7:05:05 AM 

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Sheet 46 of 67 
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A-90-19 

ll-A-29 

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— J 

CORPORATIO N 
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EPA Contract No. 68-02-4378 

ESD No. 83/18 

Work Assignment 20 

CARBON ADSORPTION FOR CONTROL OF VOC EMISSIONS: 

THEORY AND FULL SCALE SYSTEM PERFORMANCE 

FINAL REPORT 

Prepared for: 

Karen Catlett - Work Assignment Manager 

Chemicals and Petroleum Branch 

Emission Standards Division 

Office of Air Quality Planning and Standards 

U. S. Environmental Protection Agency 

Research Triangle Park, North Carolina 27711 

Prepared by: 

K. W. Barnett 

P. A. May 

J. A. Elliott 

Radian Corporation 

3200 E. Chapel Hill Road/Nelson Hwy. 

P.O. Box 13000 

Research Triangle Park, North Carolina 27709 

June 6, 1988 
P.4 

TABLE OF CONTENTS 

Section Page 

1 INTRODUCTION 1-1 

2 SUMMARY AND CONCLUSIONS 2-1 

3 THEORY AND PERFORMANCE OF CONVENTIONAL FIXED BED 

CARBON ADSORBERS 3-1 

3.1 Mechanism of Adsorption and Desorption 3-1 

3.2 Full Scale Adsorption Systems 3-13 

3.2.1 System Overview 3-13 

3.2.2 Full Scale System Design Considerations 3-15 

3.3 Carbon Adsorber Long- and Short-Term Efficiency 3-22 

3.3.1 Calculation of Carbon Adsorber Efficiency 3-23 

3.3.2 Variability of Short-Term Removal Efficiency 3-25 

3.3.3 Relationship of Outlet Concentration and 

Efficiency 3-25 

3.4 Effect of Operating Variables on Adsorber Performance 3-29 

3.4.1 Temperature 3-29 

3.4.2 Concentration 3-33 

3.4.3 Humidity 3-34 

3.4.4 Vol umetri c Fl owrate 3-38 

3.4.5 Bed Fouling 3-41 

3.4.6 Channeling 3-43 

3.5 Deliberate Changes from Initial Design 

Operating Conditions 3-43 

3.5.1 Adsorbate 3-45 

3.5.2 Steaming Conditions 3-45 

3.6 Performance Information on Industrial Adsorbers 3-46 

3.6.1 Data Sources 3-47 

3.6.2 Removal Efficiency Data for Performance Test 3-52 

3.6.3 Continuous Removal Efficiency Data 3-57 

3.7 Conclusions Regarding Carbon Adsorber Performance 3-60 

n 
P.5 

TABLE OF CONTENTS, Continued 

Section Page 

4 CARBON ADSORPTION SYSTEM AT COMMENTER'S FACILITY 4-1 

5 REFERENCES 5-1 

m 
P.6 

LIST OF TABLES 

Tables Page 

3-1 Reported Bed Lives for Various Solvent Blends 3-44 

3-2 Performance Test Data for Carbon Adsorption Systems 3-48 

3-3 Performance Test Data for Carbon Adsorption Systems on a 

Per Bed Basi s 3-50 

iv 
P.7 

LIST OF FIGURES 

Figure Page 

3-1 Representation of Carbon Pellets/Particles in Carbon Bed 3-3 

3-2 Representation of Pores in Activated Carbon Particle 3-4 

3-3 Mechanism of Adsorption 3-6 

3-4 Simplified Representation of Carbon Capacity 3-8 

3-5 Available Working Capacity as a Function of Distance 

Through Bed for an Operating Bed 3-9 

3-6 Simplified Pore Representation of Capacity as a Function 

of Distance Through Bed 3-11 

3-7 Vapor stream Concentration as a Function of Distance 

Through Bed 3-12 

3-8 Carbon Adsorber System Process Flow Diagram 3-14 

3-9 Steam Consumption Versus Working Capacities 3-18 

3-10 Adsorbate Concentration in Bed After Steaming Countercurrently 

as a Function of Distance Through Bed... 3-19 

3-11 Adsorption/Desorption Cycles in a 2 Bed System 3-21 

3-12 Determination of Carbon Adsorber Removal Efficiency 3-24 

3-13 Typical Carbon Adsorption Breakthrough Curve 3-26 

3-14 Carbon Capacity vs. Temperature at Constant Pressure 3-31 

3-15 Carbon Adsorber Removal Efficiency with Varying Bed 

Temperature for a Complete Adsorption Cycle 3-32 

3-16 GTR Test Number 6 Continuous Inlet/Outlet VOC Concentration 

Data and Removal Efficiency 3-35 

3-17 GTR Test Number 5 Continuous Inlet/Outlet VOC Concentration 

Data and Removal Efficiency 3-36 

3-18 Effect of Relative Humidity on Working Capacity 3-37 

3-19 Effect of Variation in Volumetric Flowrate on the Shape 

of the Breakthrough Curve 3-39 
P.8 

LIST OF FIGURES, Continued 

Figure Page 

3-20 Carbon Adsorber Removal Efficiency with Varying Flowrate 

for a Complete Adsorption Cycle 3-40 

3-21 Carbon Adsorber Removal Efficiency as a Function of Bed 

Age for a Ketone Containing System 3-42 

3-22 Inlet/Outlet Concentration Curve for Test 3 3-54 

3-23 GTR Test Number 5 Continuous Inlet/Outlet VOC Concentration 

Data and Removal Efficiency 3-58 

3-24 GTR Test Number 6 Continuous Inlet/Outlet VOC Concentration 

Data and Removal Efficiency 3-59 

3-25a Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber #1 3-61 

3-25b Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #1 3-61 

3-25c Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber #2 3-62 

3-25d Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #2 3-62 

3-25e Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber #3 3-63 

3-25f Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #3 3-63 

3-25g Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber # 4 3-64 

3-25h Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #4 3-64 

3-25i Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber #5 3-65 

3-25j Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #5 3-65 

vi 
P.9 

LIST OF FIGURES, Continued 

Figure Page 

3-25k Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber #6 3-66 

3-251 Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #6 3-66 

vn 
P.10 

1. INTRODUCTION 

This report presents the results of an investigation into the performance 

and operation of vapor phase carbon adsorption systems. This investigation 

was initiated as a result of comments received by the U. S. Environmental 

Protection Agency (EPA). These comments were in reference to the draft new 

source performance standards (NSPS) for control of VOC emissions from the 

manufacture of magnetic tape. The commenter challenged EPA's supporting data 

for the proposed performance requirements for carbon adsorption systems and 

the costs for operating and maintaining carbon adsorption systems at the 

required performance level. Specifically, the commenter contended that the 

95 percent efficiency requirement is not achievable on a continuous basis due 

to the inherent variability of carbon adsorption systems. They also stated 

that ketones, which are commonly used solvents in magnetic tape manufacture, 

reduce the performance of carbon adsorbers and increase system variability and 

shorten bed life which increases the cost of using carbon adsorption. 

In order to respond to these comments, the EPA requested additional 

information from manufacturers and users of carbon adsorber systems to further 

investigate system performance and costs. The EPA also again reviewed 

information obtained from previous studies by the Agency. This report 

summarizes the results of this study. 

This report is organized as follows. Section 2 presents the conclusions 

of this study. Section 3 presents a description of the vapor phase adsorption 

process, discusses impacts of changes in inlet vent stream characteristics on 

adsorber performance, and presents supporting test data. Section 4 presents a 

description of the carbon adsorber system which the commenter used as a basis 

for developing their comments, and a discussion of the design and operation of 

that system. 

1-1 
P.11 

2. SUMMARY AND CONCLUSIONS 

This report was specifically designed to address comments submitted 

concerning the proposed new source performance standards for magnetic tape 

manufacture. These comments may be summarized as follows: 

§ One commenter questioned whether any supporting data exist for the 

Agency's position that 95 percent VOC removal efficiency can be 

achieved continuously by carbon adsorption systems over all 

averaging periods, including short-term periods. The commenter 

submitted information indicating that 24-hour averages of efficiency 

of his adsorption system vary dramatically from day to day. Days 

when the average efficiency was above 95 percent were followed 

quickly by days with an average efficiency of less than 90 percent. 

It was this information that caused the commenter to question the 

Agency's decision to determine compliance and assess adsorber 

operation and maintenance based on short-term measurements of 

adsorber performance. 

• The same commenter also stated that the evaluation of carbon 

adsorption to control VOC emissions has not adequately addressed the 

problems associated with the use of ketones by the magnetic tape 

industry. The commenter submitted data that, in the commenter's 

opinion, demonstrated reduced adsorber efficiency caused by the use 

of ketones. The commenter also implied that the variability in 

carbon adsorber performance is greater when ketones are present in 

the solvent laden air stream and that ketones shorten the useful 

life of the carbon in adsorption systems, resulting in greater cost 

impacts attributable to the NSPS than indicated by the cost analysis 

carried out by EPA prior to proposal. 

In order to address these comments, information was requested from a 

number of sources. These included both magnetic tape manufacturers and other 

types of coating operations using carbon adsorbers to control VOC emissions. 

A meeting was also held with representatives of a major supplier of activated 

carbon to obtain their perspective on proper adsorber system design and 

operation based on their long term experience in this field. In addition, two 

sites were visited to obtain first hand information on the operation of carbon 

adsorber systems. Emission test data from 15 tests performed for the Emission 

Standards Division of EPA and the Office of Research and Development were also 

reviewed to provide additional substantiation of adsorber performance and to 

attempt to compare long- and short-term removal efficiency. 

2-1 
P.12 

Based on the data collected for this study, the following conclusions 

have been made. 

• When the carbon adsorber system is properly designed and operated, 

the adsorption/desorption process is predictable and reproducible 

from cycle to cycle. 

t For well designed and operated carbon adsorber systems, continuous 

VOC removal efficiencies of over 95 percent are achievable over 

long- and short-term periods for a variety of solvents, including 

mixtures that contain ketones such as methyl ethyl ketone (MEK) and 

cyclohexanone. Several plants have been shown to continuously 

achieve removal efficiencies of 97-99 percent. 

• All facilities identified by this study which had removal 

efficiencies below 95 percent had identifiable operational problems 

which contributed to their poor performance. All of the operational 

problems identified were correctable. 

• A carbon adsorption system must be designed based on the following 

process parameters: 1) particular solvent or solvent blend being 

recovered, 2) solvent load, 3) vent stream flowrate, and 4) vent 

stream temperature. Assuming the initial design provides sufficient 

capacity to account for normal daily process variations and the 

adsorber is properly operated, the performance of a carbon adsorber 

system will be essentially constant from cycle to cycle, and 

long-term and short-term efficiency will be the same. 

• If a carbon adsorber bed is left on-line after breakthrough, 

adsorber efficiency will be significantly reduced and may also 

become much more variable. A key to maintaining high continuous 

removal efficiencies is to detect breakthrough and bring a fresh bed 

on-line. There should always be a fresh bed available if the system 

is properly designed and operated. 

• Because continuous high removal efficiency can be achieved by a 

properly designed and operated carbon adsorber system, short-term 

performance testing and monitoring requirements are appropriate as 

long as the complete system cycle is included in the test or 

monitoring period. 

t A consensus of carbon suppliers, carbon adsorption system vendors, 

and carbon adsorption system operators indicates that when 

cyclohexanone is adsorbed, it exothermally reacts on the carbon 

surface to form higher molecular weight products which cannot be 

removed by normal steam desorption. The subsequent build up of 

these compounds results in a steady decrease in the adsorptive 

capacity of the carbon. This loss in adsorptive capacity decreases 

the time which a carbon bed can remain on-line before breakthrough 

occurs. When the adsorption cycle time approaches the time required 

2-2 
P.13 

for off-line bed regeneration and proper cool down, the carbon must 

be replaced. If the carbon is not replaced the point will be 

reached where the operator will be forced to either: 1) leave the 

bed on-line past breakthrough in order to properly regenerate the 

off-line bed or 2) switch to the regenerating bed before it has been 

adequately steamed and cooled. The result in either case will be a 

dramatic drop in removal efficiency. 

The carbon adsorber system of which the commenter reported as having 

highly variable and frequently low removal efficiencies is 

significantly under-designed for the actual solvent loading it is 

required to control. This results in the system being operated a 

significant portion of the time after breakthrough has occurred. As 

a result, the efficiency of this system is extremely sensitive to 

variations in the process conditions and therefore exhibits 

significant variations in efficiency from day-to-day and 

cycle to cycle. The variations also result in significantly reduced 

long-term efficiency. If the system was operated within the design 

limits, then the reduced efficiency and efficiency variation should 

not occur. 

As a carbon bed ages and its total adsorptive capacity gradually 

decreases due to fouling, the working capacity can in some cases be 

maintained at the desired level by increasing the steam flow during 

desorption. This will increase steam costs. The decision of 

whether to use higher steam flow or replace the carbon is based on 

the cost of additional steam versus the cost of new carbon. 

A key parameter to maintaining continuously high removal efficiency 

is replacing the carbon well before fouling reduces the adsorptive 

capcity. More frequent carbon replacement results in higher 

annualized carbon costs, but also prevents reaching the point where 

the adsorber performance falls below the design value. 

2-3 
P.14 

3. THEORY AND PERFORMANCE OF CONVENTIONAL FIXED BED CARBON ADSORBERS 

This section presents a general description of carbon adsorbers used to 

remove volatile organic compounds (VOC) from a gaseous process stream. The 

purpose of this presentation is to provide information necessary to draw 

conclusions concerning the following: 

• The ability of carbon adsorbers to remove 95 percent or more of the 

VOC in a process stream on both a short-term and long-term basis; 

t the effect of various operating parameters such as solvent type, bed 

age, inlet stream temperature, concentration, flowrate, and 

regeneration steam flow on adsorber performance. 

The information presented here was obtained from industry and vendor responses 

to information requests from EPA, evaluation of carbon adsorber emission test 

data gathered for this and previous EPA studies, and a meeting with a major 

vendor of activated carbon and carbon adsorption/incineration systems. 

The first part of this section is a discussion of the basic theory of 

carbon adsorption (Section 3.1). Section 3.2 describes the design 

considerations for full scale systems, Section 3.3 presents a discussion of 

how adsorber efficiency is calculated, and Section 3.4 presents the impact of 

operating variables on system performance. Section 3.5 presents emission test 

data to substantiate the performance of carbon adsorbers. Finally Section 3.6 

presents conclusions concerning carbon adsorber performance. 

3.1 MECHANISM OF ADSORPTION AND DESORPTION 

This section presents a detailed description of the mechanisms of carbon 

adsorption and desorption. To describe the mechanisms involved, a simplified 

approach using a single bed of activated carbon is developed. The principles 

involved in the single bed system are then applied to describe the operation 

of a typical carbon adsorber system. 

For gas phase carbon adsorption applications, the adsorber system does 

not actually recover the VOC. It is used to transfer the VOC from a medium 

where it is difficult to recover (the vent stream gas), to a more 

concentrated form in a different medium (usually steam) where the VOC can be 

more easily recovered. This transfer occurs in two steps. The first is the 

3-1 
P.15 

adsorption step where the VOC (adsorbate) is adsorbed onto the surface of 

activated carbon (adsorbent). The second step is where the adsorbate is 

removed from the carbon (desorption) and recovered for reuse. Both of these 

steps are equally important in the overall process. 

The adsorption process can be either physical or chemical. In physical 

adsorption the organic molecule is held to the surface by weak van der Waal 

type forces or intermolecular cohesion. The chemical, nature of the adsorbed 

gas remains unchanged, thus the process is readily reversible. Regenerative 

pollution control equipment requires the adsorption process be physical. In 

chemical adsorption, electrons are exchanged thus chemically bonding the 

2 

molecule to the surface of the carbon particle. Chemical adsorption is not 

readily reversible and, therefore, is not suitable for the regenerative 

3 adsorber systems used in air pollution control applications. 

Figure 3-1 presents a series of exploded views which describe the 

subsystems which make up a carbon adsorber bed. A carbon bed is comprised of 

carbon pellets. The pellets are made up of carbon particles which have been 

sintered together. The carbon used in adsorption is made by a two step 

process. In the first, material from various sources such as coconut shells, 

petroleum products, wood and coal is carbonized by heating it in the absence 

of air until all organic compounds except the carbon are volatilized. Then 

using high temperature steam, air, or carbon dioxide, the carbon is made 

4 

porous or activated. Depending upon the extent of this process and the 

original source, the carbon can be made to fit the use for which it is 

desired. 

The pore structure within a carbon particle is illustrated in Figure 3-2. 

The external surface area of a carbon particle is a few square meters per 

gram; however, within the pores the available surface area is hundreds of 

square meters per gram. 

The pores within the carbon are classified according to their size. 

Large pores (greater than 2,000 nanometers in diameter) are called macropores 

and smaller pores (less than 200 nanometers) are called micropores. Pores 

with diameters between these ranges are called transitional pores. 

Micropores are where the majority of the adsorption occurs so it is desirable 

to have a large amount of the pore space in this form. 

3-2 
P.16 

Carbon Pellets in 

Cross Section of Carbon Bed 

Carbon Particle 

cc 

o 

o 

i 

Figure 3-1. Representation of Carbon Pellets/Particles in Carbon Bed 

3-3 
Adsorbate Adsorbent 

> / -

CO 

. . . ' 

• . • . • 

. . • • 

• • • 

Figure 3-2. Representation of Pores in Activated Carbon Particle 
P.18 

The adsorption process begins with the mechanical movement of the vent 

stream through the carbon bed, which brings the organic molecules into contact 

with the carbon pellets. The remainder of the adsorption process consists of 

three steps as illustrated in Figure 3-3. The adsorbate must first diffuse 

into the carbon pellet to the surface of the carbon particle. Next, the 

adsorbate molecule must diffuse from the surface into the pores within the 

carbon particle. The extent of the diffusion within the pores is dependent on 

the size of the molecules and the pore structure of the carbon. Diffusion 

into the larger pores occurs fairly rapidly, but as the pore diameters become 

smaller the diffusing molecule strikes the walls and sticks for short periods 

g 

of time. This diffusion process continues until the molecule reaches a 

location where it no longer has sufficient energy to escape the forces which 

hold it to the pore wall. This usually occurs where the pore diameter is not 

more than approximately twice the diameter of the adsorbate molecule. 

The adsorption process continues until the amount of adsorbate on the 

carbon reaches a thermodynamic equilibrium with the adsorbate in the gas 

phase. The thermodynamic equilibrium is a function of the carbon type, 

temperature of the carbon and adsorbate, and the adsorbate partial pressure 

(concentration) in the vent stream. The amount of adsorbate a particular 

carbon can hold is called the equilibrium capacity. 

As previously mentioned, the purpose of the carbon adsorber is to 

actually transfer the adsorbate from the gas stream to a medium where it can 

more easily be recovered or disposed of. Therefore, at some point the 

adsorbate must be removed from the carbon. This process is called desorption 

or regeneration. Desorption is accomplished by shifting the thermodynamic 

equilibrium established during the adsorption step. There are three ways to 

shift the equilibrium: 1) increase the temperature, which is usually brought 

about by the addition of steam, 2) reduce the pressure of the atmosphere 

surrounding the carbon, and 3) reduce the concentration in the gas stream 

outside the carbon to a value less than the concentration inside the carbon. 

In most air pollution control applications, increasing the temperature is used 

for desorption. 

During desorption some adsorbed molecules are not removed. The reason is 

that to remove all the adsorbate requires sufficient time for the adsorbate 

3-5 
Step 1: diffusion to 

adsorbent surface 

Step 2: migration into 

pores of adsorbent 

Step 3: monolayer 

buildup of adsorbate 

Adsorbate molecules 

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P.20 

molecules to diffuse out of the carbon particle, and that the temperature be 

high enough to cause all the adsorbate to desorb. However, the energy cost to 

accomplish this is higher than the cost to leave some adsorbate in the carbon 

and use a larger amount of carbon to achieve the desired system performance. 

Adsorbate remaining in the carbon after desorption is called the heel. 

The amount of heel is a function of the desorption time and temperature. 

Increasing adsorption time and/or temperature will reduce the heel. In virgin 

carbon, a stable heel is established after two to three adsorption/ desorption 

cycles. 

The process discussed above is summarized by the simplified 

representation of a carbon pore shown in Figure 3-4. As shown, the pore has 

three different volumes: the equilibrium capacity, working capacity, and the 

12 heel. As previously discussed, the equilibrium capacity is a function of 

the carbon type, bed temperature, and the partial pressure of the adsorbate in 

the vent stream. It represents the maximum amount of adsorbate which can be 

adsorbed by the carbon when it is at equilibrium with the surrounding 

conditions. The heel represents the adsorbate which remains in the pore after 

desorption. It is a function of the particular carbon, the adsorbates in the 

vent stream, and the steaming conditions. 

The practical application of the adsorption process to a full size carbon 

bed is illustrated in Figure 3-5. In this figure, the solvent laden air (SLA) 

flows from left to right. As shown, there are three zones in the bed labeled 

saturated, mass transfer, and fresh. The saturated zone is located at the 

entrance to the bed and represents the carbon which has already adsorbed its 

working capacity of adsorbate. The saturated carbon is at thermodynamic 

equilibrium with the incoming vent stream. Therefore, no net mass transfer 

occurs in this zone. The mass transfer zone (MTZ) is the section of the 

carbon bed where the adsorbate is removed from the carrier stream. The carbon 

in this zone is at various degrees of saturation, but is still able to adsorb 

some adsorbate. For a typical system, the mass transfer occurs within a 

13 section approximately three inches in depth. The fresh zone is downstream 

of the mass transfer zone and represents the region of the bed where no new 

adsorbate has passed since the last regeneration. This zone still has all its 

working capacity (i.e., equilibrium capacity minus the heel) available. 

3-7 
P.21 

A = Residual or Heel (located deep in the pore and difficult to dislodge) 

B = Working Capacity (bounded by the heel remaining from previous cycles and portion of pore 

too large in diameter to retain organic) 

C = Equilibrium Capacity 

1 

Figure 3-4. Simplified Representation of Carbon Capacity12 3 

3-8 
SLA Flow 

100% 

% Of Total Equilbrium 

Capacity Available 

ut 

I 

vo 

Saturated 

Zone 

-•I Mass I*-

Transfer Zone 

Fresh 

Zone 

Heel 

Remaining 

Working 

Capacity 

Distance Through Bed 

Figure 3-5. Available Working Capacity as a Function of Distance 

Through Bed for an Operating Bed 

8 

8 
P.23 

During operation the mass transfer zone moves down the bed in the direction of 

flow. Breakthrough occurs when the mass transfer zone first reaches the bed 

outlet. The breakthrough point is characterized by the beginning of a sharp 

increase in the outlet concentration. The available adsorption time for a 

specific bed before breakthrough occurs is a function of the amount of carbon 

present, its working capacity, and the concentration and mass flowrate of 

adsorbate. 

Figure 3-6 shows a simplified representation of the carbon pores in each 

of the three zones. Pores A through E represent typical pores at different 

locations in the bed. Pore A, which is at the front of the bed, is already 

completely saturated while Pore E, which has not been exposed to adsorbate 

during this cycle, still retains its entire working capacity. Pores B, C, and 

D which are located in the MTZ, depict various degrees of saturation. A cross 

section of the bed perpendicular to the air flow will reveal pores at similar 

levels of saturation. In the MTZ, pore B has been exposed to the adsorbate 

for the longest period of time and is nearly saturated while the MTZ has just 

reached pore D which still retains most of its adsorptive capacity. As the 

adsorption cycle continues and more adsorbate enters the bed, the mass 

transfer zone will continue to move through the bed. 

Figure 3-7 depicts the VOC concentration within the carrier gas as a 

function of axial distance down the bed. Since equilibrium has been reached 

with the incoming adsorbate in the region prior to the mass transfer zone, the 

vapor stream concentration is equal to the inlet concentration. Within the 

mass transfer zone, the concentration of the vapor stream drops off because 

the organic is being adsorbed into the pores. 

14 Theoretically, the concentration in the third zone should be zero. 

However, a small amount of adsorbate is typically present. This is a result 

of two factors: 

1. A small amount of SLA may pass through the adsorber without actually 

contacting the carbon. 

2. Due to the low concentration of adsorbate in the vent stream in the 

last few inches of the bed, the heel remaining from the previous 

cycle will slowly desorb. 

3-10 
SLA Flow 

Saturated Zone • MTZ < Fresh Zone 

A ! B C D ! E 

» I X X X ' X 

4 

Jl 

Saturated Zone 

V 

MTZ 

B 

\ 

^ almost all 

working capacity 

consumed 

\ 

Fresh Zone 

working 

capacity 

consumed 

half of working 

capacity consumed 

all working 

capacity available 

almost all working 

capacity available 

Figure 3-6. Simplified Pore Representation of Capacity as a Function of 

Distance Through Bed 

3-11 
SLA Flow i 

Inlet Concentration 

Ui 

ro 

Vapor Stream 

Concentration 

(ppm) 

% 

\ 

Outlet 

Concentration 

-I Mass 

Transfer Zone IExit 

Concentration 

Distance Through Bed 

Figure 3-7. Vapor Stream Concentration as a Function of 

Distance Through Bed 

CE 

c-J 

§ 
P.26 

Test results on full scale systems have shown outlet concentrations as low 

15 

as 0.5 ppm. This outlet concentration can be minimized by proper system 

design, as discussed in the next section. 

The breakthrough curve, which is the outlet concentration as a function 

of time, is a mirror image of the concentration profile in the mass transfer 

zone. As the mass transfer zone reaches the end of the bed, the outlet 

concentration rises. This will continue until the outlet equals the inlet 

concentration. 

3.2 FULL SCALE ADSORPTION SYSTEMS 

This section describes full scale adsorption system design and 

operation. The basic mechanisms were previously described in Section 3.1. 

Section 3.2.1 presents an overview of the adsorber system. Section 3.2.2 

discusses specific design considerations for a full scale system. 

3.2.1 System Overview 

The process flow diagram for a typical two bed carbon adsorber system 

is shown in Figure 3-8. The adsorber system can be broken down into three 

separate sections; pretreatment, carbon adsorber, and recovery/waste 

treatment. The vent stream containing the adsorbate enters the adsorption 

system via the pretreatment section. If the vent stream is above the 

maximum design temperature it is reduced within the pretreatment section, 

usually with a heat exchanger. In addition, a filter is included in the 

pretreatment section to remove any particulate present in the vent stream. 

From the pretreatment section, the vent stream enters the adsorber. 

Figure 3-8 depicts a two bed adsorber system. In order to provide 

continuous emission control, at least two adsorber beds are needed so that 

one is on-line while the other is regenerated. Adsorber systems with three or 

more beds are operated similarly. During operation, the organic-laden vent 

stream passes through the on-line bed for a predetermined time period or 

until breakthrough occurs. The on-line bed is then taken off-line for 

regeneration (desorption) and the other bed is brought on-line. 

Regeneration of the off-line bed is usually accomplished by passing 

steam through the bed countercurrent to the direction of vent stream flow. 

The steam which is injected into the bed serves several purposes; 1) it 

3-13 
Vent Stream 

ca 

r Filte Filterr Blower 

Heat Exchanger 

(optional) 

Ambient 

Air Intake 

for Cooling/Drying CH 

Filter Blower 

Steam —-.-—•.•.•— 

I 

=&Lt 

-t*3-

Carbon 

Absorber 

*-K*3-i 

* 

X 

mf\ 

i 

Carbon 

Absorber 

=X*yy 

Exhaust 

Vent 

Aqueou s Phase to 

Disposal or 

Treatment 

Condenser 

Organic Phase to Recovery 

Figure 3-8. Carbon Adsorber System Process Flow Diagram s 
provides the energy to raise and hold the bed at an elevated temperature, 

2) it provides the energy required to desorb the adsorbate from the carbon, 

and 3) it carries the desorbed adsorbate from the bed. The steam is condensed 

and then decanted. There are two liquid phases present in the decanter, the 

aqueous and organic. The organic phase is generally recovered for reuse. The 

aqueous phase is either disposed of or, if the level of organics is high, 

treated prior to disposal. After the desorption step, the bed is sometimes 

dried using heated air. However, this is not required in most cases because 

removing water from the carbon usually has little effect on the adsorption 

process. In fact, the moisture left on the bed can be beneficial because it 

acts as a heat sink during the adsorption process. 

Finally, the regenerated bed is then cooled by passing ambient air 

through it. In a well designed system both cooling and drying are performed 

with the air flow countercurrent to the direction of flow when the adsorber is 

on-line. The air exiting the regenerating bed is directed through the on-line 

bed to remove any trace adsorbate. 

3.2.2 Full Scale System Design Considerations 

Section 3.2.1 discussed the overall adsorption system. This section 

focuses on the design of the adsorber section itself. Both the physical 

system design and the system control and operation during adsorption and 

desorption are important in order to achieve high removal efficiencies on a 

continuous basis. 

The design of full scale carbon adsorption systems begins with a 

determination of the inlet stream characteristics. The characteristics 

which may be important are: 

• Specific compound(s) present; 

• flowrate and temperature (range and average); 

• adsorbate concentration (range and average; and 

§ relative humidity. 

Any commercial activated carbon should be capable of providing acceptable 

performance if the system is designed based on that particular carbon. 

However, selecting a carbon which has a majority of micropores which are 

3-15 
smaller than approximately twice the diameter of the adsorbate molecules, will 

result in the greatest adsorptive forces. 

Once the carbon has been selected, the required bed area is calculated 

based on the desired superficial velocity. For a specified flowrate, the bed 

area determines the superficial velocity of the vent stream through the bed. 

The lower limit of superficial velocity is 20 ft/min to insure proper air 

18 distribution. The upper limit is usually 100 ft/min. This upper limit is 

to keep bed pressure drops within the discharge head capacities of the types 

of fans used in these applications, and to avoid excessively high system power 

costs. Typical superficial velocities are based on vendor experience and the 

results of pilot scale testing and will usually be between 50 and 100 ft/min. 

19 Generally, carbon adsorber bed depths range from 1.5 to 3.0 feet. A 

bed depth of at least 1.5 feet is used to insure that the bed is substantially 

20 deeper than the MTZ, which is normally three inches deep. If the MTZ is 

longer than the bed, breakthrough will occur almost immediately. The maximum 

bed depth of three feet is based on keeping system pressure drop within 

reasonable limits. 

Within the constraints discussed above determination of the bed depth 

becomes a function of the volume of carbon required for one adsorption cycle. 

The minimum volume of carbon is determined by the solvent mass loading, the 

carbon's working capacity, carbon density, and the desired available 

adsorption time. The solvent mass loading and carbon density are fixed by the 

stream being treated and the choices of carbon, respectively. The working 

capacity and available adsorption time are interrelated and are determined by 

the particular carbon, design temperature, adsorbate concentration, specific 

compounds present, superficial velocity, and regeneration parameters. The 

available adsorption time as a minimum must be greater than the time required 

to regenerate (steam and cool) the off-line bed(s). 

If the adsorbate contains multiple organic compounds, interactions 

between those compounds must also be considered in the estimation of working 

capacity. More strongly adsorbed compounds displace the less strongly 

21 adsorbed and push them through the bed. This creates a wave front of the 

lower molecular weight compounds (which tend to be the compounds less strongly 

3-16 
P.30 

adsorbed) at the front of the MTZ. The phenomenon must be accounted for in 

estimating the system design working capacity to insure that breakthrough of 

any of the compounds does not occur. 

At this point it is necessary to determine the working capacity and 

specify an adsorption time to determine the carbon volume. Empirical data 

from pilot scale testing are usually required to accurately determine working 

capacity for a specified set of inlet conditions, superficial velocity, and 

desorption steam flow. However, the desorption steam flow selected, in turn, 

affects the working capacity and the minimum required adsorption time. The 

economic trade-offs of system capital costs versus steam costs will determine 

what set of regeneration conditions will result in the lowest annual costs. 

Steaming requirements are set as part of the initial system design. The 

longer the bed steaming time the greater the amount of adsorbate removed, and 

therefore the smaller the amount of removable heel remaining. As previously 

discussed, the working capacity of a carbon bed, which is the amount of 

adsorbate the bed can remove during an adsorption'cycle, is the difference 

between the heel and the equilibrium capacity. Therefore, the longer the bed 

is steamed, the greater the available working capacity. An example of the 

relationship of working capacity versus steam consumption for three compounds 

22 is shown in Figure 3-9. The shape of this curve is similar for most 

compounds. However, specific values of working capacity versus steam flow 

vary from compound to compound. The curve usually begins to flatten out at 

some steam consumption. Increasing steam use beyond the point where the curve 

begins to flatten out will result in only a small increase in working 

capacity. 

In well designed systems the bed is steamed countercurrent to the 

23 direction of flow during adsorption. This will help minimize the adsorbate 

emitted at the adsorber outlet prior to breakthrough. Figure 3-10, which is a 

plot of the adsorbate concentration left on the bed after steaming as a 

function of axial distance through the bed, illustrates why this is true. 

After steaming, the concentration of adsorbate (i.e., the amount of heel which 

remains) is lower at the end of the bed where the steam enters. When the 

adsorber is brought on-line, the lower amount of heel where the SLA exits the 

bed means less adsorbate is available to desorb. Also, having more working 

3-17 
ut 

I (—• 

00 

•o 

o 

*3 

nj o 

O a> 

£ o 

£ $ O Q 

> (0 

• D 

C 

3 

s. 

2 4 6 8 10 

Pounds of Steam per Pound of Desorbed Hydrocarbons 

Figure 3-9. Steam Consumption versus Working Capacities 

tc 

3 

S 

TJ 

CO 
<1 

Direction of Adsorption Air Flow 

Direction of Steam Flow 

e> 

CO 

I 

I—* 

Adsorbate 

Left on 

Bed After 

Steaming 

* 

Distance Through Bed 

Figure 3-10. Adsorbate Concentration in Bed After Steaming Countercurrently 

as a Function of Distance Through Bed 

<r 

CO 

o 

y 

O 

s 
capacity available at the bed exit helps prevent momentary increases in outlet 

concentration as a result of changes in inlet conditions caused by process 

upsets. If the bed is steamed cocurrent to the direction of flow during 

adsorption, the reverse heel profile exists and a higher outlet concentrations 

will result. 

Another consideration in adsorber design is fouling. Fouling occurs when 

compounds are present in the vent stream which will not desorb from the bed. 

These compounds can be solid particles, high molecular weight compounds, or 

compounds which chemically react on the surface of the carbon (such as some 

ketones). Regardless of the source, bed fouling gradually reduces the carbon 

adsorption capacity. 

There are two methods to compensate for fouling. One is to increase 

volume of carbon beyond the minimum required to achieve the desired adsorption 

time. The second is to gradually increase the amount of steam used to 

regenerate the bed. Increasing the steam used in regeneration reduces the 

heel, which helps maintain sufficient working capacity. A combination of 

these methods can also be used. 

A typical adsorption/desorption cycling arrangement for a two bed 

adsorber system is shown in Figure 3-11. For the purpose of discussion, 

illustrative times are shown on the figure corresponding to operational 

aspects of the system. The sequence begins with bed 1 coming on-line as bed 2 

goes off-line at t . For the example shown, adsorption lasts 90 minutes, the 

steaming time is fixed at 30 minutes, and the cooling/drying time is also 

30 minutes. The off-line bed has 30 minutes during which it is on standby. 

In this example, the 30 minutes of standby time allows the operator to 

compensate any daily variations in vent stream conditions and bed fouling 

without having to leave a bed on-line after breakthrough. It is important 

that a bed not be left on-line after breakthrough because that will 

significantly reduce the overall removal efficiency for that cycle. 

Two types of trigger mechanisms are used for controlling the adsorption/ 

desorption cycles: continuous monitors and timers. Continuous monitors take 

a bed off-line when a specified outlet concentration is reached. Timers cycle 

the bed at a specified time. A combination may also be used. One advantage 

to using continuous monitors is that they allow the beds to remain on-line 

3-20 
Bed#1 

Time 

(min) 

Adsorption 

T " 

30 60 

Regeneration 

Steaming | Drying I Stand-By 

90 120 150 180 

Adsorption 

i 

210 

-T— 

240 270 

ut 

i 

ro 

Bed #2 

Time 

(min) 

Regeneration 

I Steaming i Drying i Stand-By Adsorption 

30 60 90 120 

i 

150 

Regeneration 

Steaming | Drying - Stand-By 

180 210 240 270 

Figure 3-11. Adsorption/Desorption Cycles in a 2 Bed System s 
P.35 

until breakthrough, thus fully utilizing their capacity during each cycle. 

This is not the case for a timer based system, because to properly guard 

against breakthrough allowances must be made for variations in the 

breakthrough time due to changes in the inlet stream characteristics. 

Although continuous monitors allow for the use of more of the available 

adsorption capacity than timers, do, timers can be used in many situations as 

the trigger mechanism. They are especially appropriate for adsorbates which 

do not foul the bed or where inlet stream characteristics are very stable. If 

a timer is used, continuous monitors or a periodic sampling program should be 

used to adjust the adsorption times as necessary. Deviations in operating 

conditions do not affect properly designed systems which use timers unless the 

conditions exceed the range of the design specifications. If this is allowed 

to occur, a bed may be kept on-line after breakthrough has occurred, This 

would result in a significantly reduced removal efficiency. 

A final, and important, consideration in system design is prevention of 

channeling. Channeling occurs when a portion of the SLA bypasses the bed, or 

a certain section of the bed receives a greater portion of the flow than other 

sections. The inlet of the vessel must be designed to achieve proper 

distribution of the SLA so that it does not impinge on a portion of the bed at 

high velocity. The potential for channeling can be minimized by the use of 

distribution baffles. It is also important to achieve proper distribution of 

the regeneration steam. If steam is not well distributed the steam flow can 

also cause channels to form in the bed. Also, poor steam distribution will 

result in some portion of the bed not being properly regenerated. 

Proper design can minimize the potential for channeling. However, 

maintenance of the distribution baffles and steam distribution system should 

be performed during scheduled system shutdowns or whenever an increase is 

detected in the adsorber outlet VOC concentration which is significant enough 

to result in a removal efficiency below the minimum design level. 

3.3 CARBON ADSORBER LONG- AND SHORT-TERM EFFICIENCY 

This section discusses the relationship of long and short-term carbon 

adsorber efficiency. Section 3.3.1 discusses the calculation of instantaneous 

3-22 
P.36 

versus cycle efficiency. Section 3.3.2 discusses the variability of 

short-term efficiency. Section 3.3.3 discusses the relationship of outlet 

concentration and efficiency. 

3.3.1 Calculation of Carbon Adsorber Efficiency 

In order to discuss carbon adsorber long- and short-term efficiency, a 

short discussion of the relationship of efficiency to the inlet and outlet 

concentrations over time is necessary. 

The inlet and outlet concentration as a function of time for a single 

adsorption cycle of a typical carbon adsorber is shown in Figure 3-12. The 

outlet concentration curve is also called the breakthrough curve. For the 

example shown, the inlet concentration is C. and the outlet concentration is 

•C . The adsorber was brought on-line at tQ and taken off-line at t- when the 

outlet concentration reached some predetermined set point concentration level. 

At any point in time the instantaneous removal efficiency (IRE) for this 

adsorber is determined as the difference between the inlet and outlet 

concentration divided by the inlet concentration. At time t, the 

instantaneous removal efficiency is: 

C-i " C n 

-*E* - " ^ 

The overall removal efficiency (ORE) at any given time during the cycle is 

determined by the difference between the areas under the inlet and outlet 

curves divided by the area under the outlet curve. For the adsorber shown 

in Figures 3-12 at time t, the overall removal efficiency is: 

ORE, =• Area (ADEF) - Area (BCEF) 

1 Area (ADEF) 

As an example, in the magnetic tape manufacturing industry a typical inlet 

concentration might be 3000 ppmv and a typical outlet concentration might be 

24 

30 ppmv or less prior to breakthrough. To achieve a 95 percent removal 

efficiency over the period of an adsorption cycle a system with an inlet 

concentration of 3,000 ppm must have a time weighted average outlet 

concentration of 150 ppm or less. At an outlet concentration of 30 ppmv the 

removal efficiency is 99 percent for most of the cycle. Therefore, when 

breakthrough occurs the outlet concentration can rise above the 150 ppm point 

3-23 
c4 -

c 

o 

c 

(D 

U 

c 

Removal Efficiency at t, 

Instantaneous = I --=-* C,-C„ 100 

ut 

I 

ro 

c„" j p -

Overall = f Are^ADEF) - AreatBCEFA 

\ Area(ADEF) / 

C, = Inlet Concentration 

C0 = Outlet Concentration 

Cap - Set Point Concentration 

c„ - B 

E 

T 

t. 

C 

F 

t, 

Time 

T

-

t, 

CL 

in 

Figure 3-12. Determination of Carbon Adsorber Removal Efficiency 
without the overall removal efficiency going below of the required 95 percent. 

Therefore, for a system designed and operated to maintain a certain minimum 

instantaneous removal efficiency, the cycle efficiency will be higher than the 

instantaneous efficiency. At one site the cycling set point for their system 

is 2 hours or whenever the instantaneous removal efficiency reaches 

95 percent. The result is an overall removal efficiency greater than 

25 99 percent. 

3.3.2 Variability of Short-Term Removal Efficiency 

A significant issue raised is the variability of short-term carbon 

adsorber removal efficiency. Assuming that inlet stream characteristics never 

vary, and the adsorber is always operated the same way, cycle efficiencies 

26 should be almost identical. The only change expected would be a gradual 

decrease in carbon working capacity due to bed aging. However, the change in 

performance from one cycle to the next due to bed aging will be insignificant. 

However, in actual applications, inlet stream characteristics such as 

concentration, temperature, and flowrate may vary. Also, the operator may 

make deliberate changes in the solvent being adsorbed, or in system operation. 

If for a well designed and operated system it can be shown that changes in 

inlet stream characteristics or operation do not significantly affect 

cycle-to-cycle efficiency, then the short-term removal efficiency can be 

expected to be essentially constant for industrial applications. These 

evaluations are shown in Section 3-4. 

3.3.3 Relationship of Outlet Concentration and Efficiency 

A typical plot of inlet and outlet concentrations versus time for a 

carbon adsorber was previously presented in Figure 3-12. Figure 3-13 presents 

a similar curve for the outlet concentration only. In this example Y 

represents the outlet concentration at the beginning of the cycle. At the 

breakthrough time the outlet concentration begins a sharp increase. At this 

time a fresh bed should be put on-line, and the other bed which has just 

broken through regenerated. 

The dashed line represents what happens if the operator does not remove 

the bed which has broken through from service. The outlet concentration will 

increase until it equals the adsorber inlet concentration, which in this 

example is X. 

3-25 
P.39 

Xc 

o 

mma 

CO 

c 

o 

u 

c 

5 

"3 

O £ 

Point where bed should 

be taken off-line. 

\ 

<5X 

Outlet concentration curve 

which results if bed is not 

taken off-line at breakthrough. 

I brmakthrtmgh 

Time 

• saturation 

Figure 3-13. Typical Carbon Adsorption Breakthrough Curve § 

3-26 
P.40 

Also shown in this figure are arrows labeled "A" and "B". These arrows 

represent the two possible shifts in the breakthrough curve which could occur. 

The shift labeled "A" indicates a decrease in the adsorption cycle time prior 

to breakthrough. A shift of this type normally should have little effect on 

the efficiency of the adsorber, because the bed can be taken off-line for 

regeneration prior to the release of any significant emissions. A slight 

efficiency reduction over multiple cycles will occur because breakthrough will 

occur more frequently. The magnitude of the efficiency change, however, will 

be very smal1. 

A shift of the A type will significantly affect efficiency if a bed is 

left on-line after breakthrough. There are three possible reasons for a bed 

to be left on-line after breakthrough. 

1. The operator may not be aware of how quickly the concentration rises 

after breakthrough and the resulting deleterious effect on the 

efficiency of his adsorption system. 

2. The operator may have no way of knowing when breakthrough occurs 

(suitable analytical instruments have not been installed). 

3. The operator may not have a replacement bed properly desorbed and 

cooled, ready for service. 

The first two reasons are operational problems and easily overcome. The 

third should not occur if the system was designed properly and is being 

operated within the design specifications, and the carbon is replaced when 

necessary. 

If beds are left on-line after breakthrough removal efficiencies will 

also become much more variable. As an example, assume that the adsorber 

system discussed in Section 3.3.1 has a three hour adsorption time at which 

point breakthrough occurs, a 3,000 ppmv inlet concentration, and a 30 ppmv 

outlet concentration. Due to a process change the inlet concentration of VOC 

now increases to 3,500 ppmv. occasionally and this variability was not 

accounted for in the system design. In this case, breakthrough would now 

occur approximately 26 minutes earlier. If the operator does not take the bed 

off-line at this time, the outlet concentration increases very quickly to 

3,500 ppm, and for that cycle the adsorber efficiency will be reduced to 

approximately 85 percent. If the inlet concentration varies from 3,000 to 

3-27 
P.41 

3,500 ppm on a daily basis, then the adsorber removal efficiency will also 

vary from 99 to 85 percent on a daily basis. This example demonstrates that 

if the system is not designed to account for normal process variations, 

efficiency will both be reduced, and become much more variable than is 

normally the case with well designed and operated systems. 

The shift "B" indicates an increase in the baseline outlet concentration 

prior to breakthrough. A shift of this type could result in a significant 

decrease in the removal efficiency achievable by the adsorber depending on the 

inlet concentration and the magnitude of the outlet concentration change. 

For the purpose of this analysis, it is important to understand the two 

potential shifts in the breakthrough curve relative to the adsorption 

mechanism itself. Assuming a constant adsorbate loading rate, a shift of type 

"A" indicates a change in the working capacity of the carbon for a given 

adsorbate. The working capacity is a function of fouling and the equilibrium 

conditions (i.e., temperature, pressure, and partial pressure of the 

adsorbate) for a particular set of operating conditions (i.e., steaming time, 

temperature, and duration). Therefore, changes in the equilibrium conditions 

which effect the working capacity lead to type "A" shifts in the breakthrough 

curve. 

A shift of type "B" indicates one of two possibilities: 1) A portion of 

the inlet stream has bypassed the bed by either short circuiting or channeling 

(as previously discussed, channeling can be avoided with proper design and 

maintenance). 2) A greater amount of heel is present in the last few inches 

of the carbon bed. As stated previously, the amount of heel is a function of 

the conditions which are established at the end of the steaming cycle. The 

amount of heel related to the steaming time, temperature, and flow. 

Each of the potential operational variables for a carbon adsorber is 

evaluated in the next section relative to its ability to shift the 

breakthrough curve of Figure 3-13 in either the "A" or "B" direction. Proper 

operation practices necessary to prevent degradation of the adsorber system 

are also discussed where appropriate. The results from this evaluation are 

then used to determine the effect on the removal efficiency which is 

3-28 
achievable by the system. In presenting this discussion, data and information 

available from industry, vendors and emission test reports are used where 

available. 

3.4 EFFECT OF OPERATING VARIABLES ON ADSORBER PERFORMANCE 

The objective of this section is to determine if the normal expected 

day-to-day process variations would be expected to necessarily cause daily 

variations in carbon adsorber performance. Also assessed are impacts of 

deliberate process changes, such as a change in solvent, on adsorber 

performance. Potential daily operating variables include the operating 

temperature, inlet adsorbate concentration, humidity, volumetric flowrate, and 

bed fouling. Changes from the initial design operating conditions include the 

adsorbate types(s), and steaming conditions. Channeling will also be 

discussed. 

Each of the daily normal operational variables is evaluated relative to 

its effect on the breakthrough curve from a typical carbon adsorber bed. For 

the purpose of this discussion, the assumption is made that any affect on the 

performance of a single bed may be taken as representative of the effect on 

the overall adsorber system's performance. 

3.4.1 Temperature 

The operating temperature of an adsorber can be affected in three ways: 

changes in the inlet stream temperature, exothermic chemical reactions taking 

place inside the adsorber, or failure of the cooling step after regeneration. 

Changes in the inlet stream's temperature lead to changes in the adsorber 

operating temperature. Changes in the inlet solvent loading can change the 

rate of heat generation due to the heat of adsorption. Heat can also be 

generated within the system from chemical reactions taking place on the bed. 

Ketones in particular, have been identified by several studies as particularly 

27 reactive compounds. The problem is usually not serious, however, unless the 

concentration of adsorbate is extremely high, the gas flowrate through the 

carbon is relatively low, and the carbon is dry and contains no heel. 

Each of the possible scenarios given above results in a variation in the 

temperature at which the adsorption process takes place. Therefore, the 

effect of temperature on the breakthrough curve must be evaluated. As 

3-29 
previously discussed, the two possible shift directions "A" and "B" can be 

assessed by studying the effect of temperature on the working capacity and the 

heel, respectively. As shown in Figure 3-14, the relationship between carbon 

capacity and temperature indicates that as the temperature within the bed 

increases, the adsorptive capacity of the carbon decreases. Thus, as the 

temperature increases, the working capacity of the carbon also decreases. 

Therefore, a shift in the breakthrough curve is to the left or to shorter 

adsorption times. A shift in this direction has no effect on the achievable 

removal efficiency but does require a change in the cycle time to compensate 

for the shift. 

Changes in operating temperature should not cause a B shift in the 

breakthrough curve. This is because the outlet concentration at the beginning 

of the cycle is primarily a function of the heel remaining in the last few 

inches of the bed. The amount of heel is established by the bed steaming 

conditions during desorption. Only if the temperature of the carbon in the 

adsorber rises to values close to those during steaming is there a chance the 

removable heel will desorb and subsequently decrease the achievable removal 

efficiency. 

Temperature fluctuations in the inlet stream can be essentially 

eliminated with installation of a heat exchanger upstream of the carbon 

adsorber. A properly designed system will not permit the inlet temperature to 

exceed the maximum design temperature. 

To illustrate the insensitivity of carbon adsorber efficiency to minor 

changes in the bed temperature, the bed temperature and the corresponding 

instantaneous removal efficiencies for an operating adsorber system are 

28 presented in Figure 3-15. As shown, the carbon bed temperature varies from 

60 to 90°F during the adsorption cycle while the corresponding removal 

efficiencies remain well above 99 percent. The outlet VOC concentration 

29 remained constant at approximately 20 ppm. 

As discussed in the section describing the effect of changes in the 

adsorbates, ketones are known to exothermically polymerize on the carbon bed. 

A system designed for ketones must assure the air flow through the bed is 

sufficient to remove the heat of reaction to insure the bed temperature is not 

30 be significantly affected. 

3-30 
ut 

Temperature 

IT 

a> 

Figure 3-14. Carbon Capacity vs. Temperature at Constant Pressure 
100 

co 

to 

ro 

CD 

+-a 

<0 

k_ 

CD 

Q. 

E 

<D 

Legend 

• Bed Temperature 

• Efficiency 

" 1 — 

130 

T — 

150 

100 

33 

CD 3 

o 

< 

80 § 

g 

CD" 

O 

-70 

Time, minutes 

Figure 3-15. Carbon Adsorber Removal Efficiency with Varying Bed Temperature 

for a Complete Adsorption Cycle 

CO 
P.46 

A properly designed and operated system will limit unacceptable heat 

buildup due to reactions in the in any of the following ways: 

• Thorough steam desorption and cool down, 

e use of the maximum superficial velocity to aid in heat removal, 

t avoiding prolonged adsorption periods, and 

• humidity control or even use of liquid water to act as a heat sink. 

When a system is designed to handle a ketone-bearing stream, bed temperature 

is normally monitored to detect hot spots and initiate protective action for 

the carbon bed. 

3.4.2 Concentration 

The concentration of organics in the inlet stream may vary because of 

process changes. Short-term variations are those which occur within a given 

cycle while long term variations may last over several cycles. Changes can 

occur as equipment or product lines are either brought on or taken off-line. 

For the purpose of this discussion, the flowrate through the bed is 

assumed to remain constant. Therefore, when the concentration increases, the 

loading rate to the adsorber increases. 

Increasing the concentration will increase the working capacity of the 

carbon. However, the working capacity increase will not be large enough to 

completely offset the increase in mass loading. Therefore, the net effect 

will be a breakthrough curve shift in the A direction. The effect of 

variations in inlet concentration on the outlet concentration prior to 

breakthrough should be negligible. As stated previously, the outlet 

concentration is a function of the heel in the last few inches of the bed that 

remains after regeneration. Because the inlet stream reaches equilibrium with 

the carbon within the mass transfer zone, the amount of heel at the adsorber 

outlet is independent of inlet concentration. Therefore, short-term 

variations in the inlet concentration will not cause a B shift in the 

breakthrough curve. 

To illustrate the independence of the outlet concentration on short-term 

variations in the inlet concentration, the inlet and outlet concentration and 

corresponding removal efficiency for an operating adsorber system are 

3-33 
presented in Figure 3-16. (GTR Test #6) 3 1 As shown in Figure 3-16 the inlet 

concentration varies continuously over the six hour period shown while the 

corresponding outlet concentrations and removal efficiencies show little 

variation. For inlet variations between 200 and 550 ppm the outlet 

concentration varies only from 5 to 15 ppm and the corresponding removal 

efficiency varies from 95 to 99 percent. 

Figure 3-17 also presents inlet concentration, outlet concentration, and 

the corresponding removal efficiency for a similar performance test conducted 

32 

on the same adsorber system discussed above. As shown in Figure 3-17, the 

outlet concentration (0 to 5 ppm) remains relatively constant for the entire 

test period, although the inlet concentration varies from 40 ppm to 880 ppm. 

Figure 3-17 also shows the removal efficiency over the test period. During 

the majority of the test period the removal efficiency was well above 

95 percent. However, when the inlet concentration dropped below 50 ppm, the 

removal efficiency was also significantly reduced. This is as expected 

because carbon adsorbers are essentially constant outlet devices, so a large 

decrease in inlet concentration will reduce short-term removal efficiency. 

Because the outlet concentration remains constant throughout an 

adsorption cycle, large variations in the inlet concentration will result in 

corresponding variations in removal efficiency. However, if the bed is 

properly regenerated, the outlet concentration can be set at a level where 

greater than 95 percent removal is achieved for the entire range of inlet 

concentrations. In addition, in many applications of carbon adsorption, a 

reduction in inlet concentration is the result of equipment (such as coating 

lines) being shut down. By diverting or shutting off the air flow from idle 

equipment, inlet concentrations can be maintained at higher levels required to 

ensure the desired removal efficiency. 

3.4.3 Humidity 

Working capacity as a function of steam consumption is shown for relative 

33 humidities of 50 and 100 percent, in Figure 3-18. As shown, relative 

humidity does not significantly affect working capacity. This is generally 

34 the case for adsorbate concentrations greater than 1,000 ppm. Therefore, 

there should be only a slight change in the breakthrough time associated with 

variations in relative humidity in this case. 

3-34 
a-y 500 

E 

a 

a 

C 400 

o 

c • 

u 

c 

o 

u 

c 

1 a 1 — , 

r 

r 

— i 1 

" In 

10:00 11:00 12:00 13:00 14:00 15:00 16:00 

Tim. 

Inlet Concentration vs. Time 

E 

a 

a 

\m* 

C 

o 

aa O %. 

ma 

C • 

U 

c 

o 

o 

3 

o 

10:00 11:00 12:00 13:00 1400 15:00 16:00 

Tim* 

Outlet Concentration va. Time 

>» u 

c 

Ul 

o 

> 

o 

E 

9:00 1000 11:00 12:00 13 00 14 00 15:00 18:00 

Tim. 

Removal Efficiency va. Time 

Figure 3-16. GTR Test Number 6 Continuous inlet/outlet VOC concentration data 

and removal efficiency. 

3-35 
P.49 

E 

a 

a. 

•^ 

c 

o 

c • 

u 

c 

o 

U 

ma 

• 

C 

900 -i 

800 -

700 -

600 -

500 -

400 -

300 -

200 -1 

100 -

, r* 

V 

T 

1 V 

1 

1 

-a— 

9 0 0 1200 

Tim« 

Inlet Concentration vs. Time 

E 

a 

a 

C 

o 

o 

L. 

c • 

u 

c 

o u 

3 

o 

9:00 12:00 

>. 

U 

c 

mm 

o 

> 

o 

E 

100 

99 -

ae 

97 -

96 

95 

94 -

93 

92 

91 

90 -

89 

88 

87 

86 

85 -

84 

83 

82 -

81 

80 

Tim« 

Outlet Concentration va. Time 

9:00 10:00 11:00 

Removal Efficiency va. Time 

Figure 3-17. GTR Test Number 5 Continuous Inlet/outlet VOC concentration data 

and removal efficiency. 

3-36 
15 

c 

o 

JQ 

k_ 

cs 

O 

CO 

JQ 

O 

o 

•C 10 

o 

c 

c« 

a> 

EPA Stream B 

Toluene - 600 ppm 

MEK -1,000 ppm 

Cyclohexanone - 400 ppm 

Adsorption - 75 fpm 

50% Relative Humidity 

CO 

I 

CO 

*»sl 

CO 

J3 

U 

CO 

Q . 

ca 

o 

c 

100% Relative Humidity 

1.0 1.5 

lbs. Steam/lbs. Carbon 

2.0 

or 

3 

Figure 3-18. Effect of Relative Humidity on Working Capacity 

TJ 

bi 
P.51 

Below adsorbate concentrations of 1,000 ppm water begins to compete with 

adsorbate for the available adsorption sites and the bed working capacity for 

that adsorbate is then affected. In this case, some type of dehumidification 

system upstream of the bed or dilution with ambient air may be required. 

Relative humidity has no effect on the amount of heel which is retained 

within the carbon pore. Therefore, there is no B shift in the breakthrough 

curve and no subsequent change in the achievable removal efficiency on a 

long- or short-term basis. 

High relative humidities are present in most operating systems regardless 

of the vent stream conditions because of the water remaining on the bed after 

steaming. As shown in Figure 3-18, the working capacity gained by reducing 

the humidity is small. In this case, reducing steam humidity would probably 

not be cost-effective. In addition, the water content in the bed provides a 

heat sink valuable in controlling bed temperature. 

3.4.4 Volumetric Flowrate 

The superficial bed velocity for a system changes as the volumetric flow 

to the system changes. The primary effect is to change the width of the mass 

transfer zone within the bed. As the superficial velocity increases, the 

width of the mass transfer zone also increases because the individual carbon 

pellets are exposed to the adsorbate for a shorter period of time, thus the 

quantity removed at a given point decreases. The effect of a wider mass 

transfer zone on the shape of the breakthrough curve is shown in the top of 

Figure 3-19. As shown in the bottom figure, the time prior to breakthrough is 

shortened by increases in volumetric flowrate because of the wider MTZ. 

To illustrate the independence of carbon adsorber removal efficiency to 

short-term variations in the volumetric flowrate, the flowrate and 

corresponding instantaneous removal efficiencies for an operating adsorber 

35 

system are presented in Figure 3-20. As shown, the flowrate varies randomly 

during the entire adsorption cycle while the corresponding removal 

efficiencies show little variation. For flowrate variations from 45,000 to 

25,000 scfm the removal efficiency varies less than 0.5 percent with all 

efficiencies being well above 99 percent. 

Since variations in the volumetric flowrate do not affect the amount of 

heel on the bed at a given time, there is no B shift in the outlet 

3-38 
P.52 

E 

a 

c 

o 

CB 

k. *^ C 

<u 

o 

c 

o 

O 

E 

CO 

<u 

55 

o 

Q . 

CO 

> 

Constant Loading 

Increasing Flowrate 

Distance Through Bed 

c g 

« 

•*•• » 

C 

CD 

O 

c 

o o 

.2 

"3 

O 

Constant Loading 

Increasing Flowrate 

Time 

Figure 3-19. Effect of Variation in Volumetric Flowrate on the Shape 

of the Breakthrough Curve 

3-39 
60,000 

CO 

u 

tn 

CD 

3 

t_ 

o 

u. 

Time, minutes 

Figure 3-20. Carbon Adsorber Removal Efficiency with Varying Flowrate for a 

Complete Adsorption Cycle 

s 
P.54 

concentration prior to breakthrough, due to either long- or short-term 

variations in the flowrate. Consequently, there is no effect on the long- or 

short-term removal efficiency achievable by the system. 

3.4.5 Bed Fouling 

This section discusses the effect of bed fouling an adsorber removal 

efficiency. The causes of bed fouling were previously discussed in 

Section 3.2.2. Bed fouling gradually decreases working capacity by tying up 

the active adsorption sites in the micropores or blocking the pores which 

prevent adsorbate molecules from entering. Because the capacity of the system 

is decreased, the time prior to breakthrough is shortened. As discussed 

previously, this has no effect on an adsorber's removal efficiency until the 

shortened length of the adsorption cycle begins to conflict with the 

regeneration time. At this point the carbon should be replaced. 

36 

Fouling will not affect the outlet concentration prior to breakthrough. 

Therefore there will be no B shift in the breakthrough curve. The reason is 

that fouling will not affect the amount of heel left in the bed. 

As previously discussed, fouling does gradually reduce bed working 

capacity. In some cases the steam flow and/or temperature can be increased to 

reduce the heel and therefore increase working capacity the bed ages. 

However, as previously shown in Figure 3-9, the point will be reached where 

increasing the steam flow will have little beneficial effect on working 

capacity. Therefore, even if the system is well designed and operated, a 

point will be approached where there is insufficient time to regenerate the 

off-line bed before the on-line bed reaches breakthrough. At this time, 

carbon will need to be replaced. 

Figure 3-21 presents overall removal efficiency plotted as function of 

carbon bed age for a system on a vent stream containing cyclohexanone, 

37 tetrahydrofuran, methyl ethyl ketone (MEK), and toluene. Both cyclohexanone 

and MEK are known to cause bed fouling. As shown, there is only a slight 

decline in the removal efficiency from 99.6 percent for the newest bed to 99.4 

percent for the oldest bed. 

Though fouling of the carbon bed has no affect on the efficiency of an 

adsorber system, it does reduce bed life, which in turn increases the annual 

operating cost of the system. The fouling rate is affected by numerous 

3-41 
100 

99-

98-

co 

ro 

u 

c 

a> 

<o 

m— 

xvUJ 

96-

95 T " 

4 

—r12 16 

Legend 

Average Composition of 

Recovered Solvent (Wt %) 

Cyclohexanone 44 

THF 23 

MEK 19 

Toluene 14 

i 

20 24 28 

Bed Age, weeks 

Figure 3-21. Carbon Adsorber Removal Efficiency as a Function of Bed Age for a 

Ketone Containing System 

IT 

CM 

CO 

CO 

o 
P.56 

factors, but the adsorbate characteristics can be considered the most 

dramatic. The effect of several solvent blends on bed life is shown in 

Table 3-1. For the toluene and isopropylacetate (IPA) application shown, the 

beds have not yet been changed after six years of operation and no shortening 

of the adsorption time prior to breakthrough has been detected. For the 

toluene and hexane application shown, the bed life is reported to be 10 years. 

Lifetime removal efficiencies are also shown in Table 3-1. High removal 

efficiencies are shown even for streams containing high concentrations of 

cyclohexanone, a known fouling agent. Facility A has a 99.4 percent removal 

efficiency on a six bed adsorption system. The bed life for this facility is 

significantly less than the other facilities shown. The overall removal 

efficiency at Facility A reflects the aggregate for a system with beds at 

various stages of life. The solvent recovered at this facility includes 

approximately 44 percent by weight cyclohexanone and 19 percent methyl ethyl 

ketone. Based on the overall system removal efficiency for this system of 

99.4 percent, it can be concluded that all the beds in the system are 

achieving well above 95 percent removal. 

3.4.6 Channeling 

As discussed in Section 3.3, a carbon adsorber system should be designed 

with adequate flow baffles and proper steam distribution to prevent 

channeling. If channeling does occur, it will cause elevation of the 

background outlet concentration over a cycle, or a gradual increase during the 

cycle. For systems with VOC monitors, these increases will be readily 

apparent. If the amount of channeling is small, the system may still be able 

to retain the required removal efficiency. If significant channeling occurs, 

then adsorber removal efficiency would be significantly degraded. 

In a well designed system, channeling need not occur. From the 

perspective of the ability of a carbon adsorber to meet a specific regulatory 

removal requirement channeling is actually a malfunction of the system, rather 

than a factor causing inherent variability in short-term efficiency. 

3.5 DELIBERATE CHANGES FROM INITIAL DESIGN OPERATING CONDITIONS 

This section discusses the effect of changing the adsorbate type(s) and 

steaming conditions. To assess the impact of each change on the future 

3-43 
P.57 

TABLE 3-1. REPORTED BED LIVES FOR VARIOUS SOLVENT BLENDS3 8"

41 

Facil 

A 

B 

C 

D 

ity Solvent blend 

44% Cyclohexanone0 

14% Methyl Ethyl Ketone 

23% Tetrahydrofuran 

19% Toluene 

50% Toluene 

50% Isopropyl Acetate 

95% Toluene 

5% Hexane 

Methyl Ethyl Ketone 

Reported 

bed life 

_d 

>6 Years 

10 Years 

5 Years 

Reported removal 

efficiency (%) 

99.4 

98a 

99.5b 

99.6 

Value reported by company. No data was provided to verify. 

Estimation: Assumed average inlet loading was mid range in design 

specification range, and outlet loading was the reported value. 

cActual solvent blends at this facility vary. The values are typical of the 

total solvent recovered daily. 

The specific bed life at this facility is confidential business information. 

However, it is significantly lower than the other values shown. This reduced 

bed life is believed to be at least partially due to the presence of 

cyclohexanone and methyl ethyl ketone. 

3-44 
P.58 

operation and performance of the adsorber system, the logic associated with 

the initial specification of each design parameter is discussed. 

3.5.1 Adsorbate 

The concentration and type of organic are key factors in the design of a 

carbon adsorption system. The adsorption characteristics of each compound are 

assessed by using their physical properties data, such as: polarity; 

refractive index; boiling point; molecular weight; and solubility in water. 

Nonpolar compounds and compounds with high refractive indices tend to be 

42 adsorbed more readily. High vapor pressure/low boiling point adsorbates and 

43 low molecular weight compounds adsorb less readily. Compounds with 

molecular weights greater than 142 adsorb readily but are difficult to 

44 desorb. 

If the adsorbate is water soluble, water left as condensate in the bed 

45 after steaming and cooling can contain adsorbate. When the adsorber is 

brought on-line, the water and adsorbate will evaporate from the bed during 

the first part of the adsorption cycle, slightly increasing the initial outlet 

concentration for a brief time until the concentration falls rapidly to a 

normal baseline value. 

The properties and adsorption characteristics affect both the design and 

operating conditions. If the feed stream is changed, the adsorber system must 

be re-evaluated. If it can accommodate the new feed, there will be no effect 

on the achievable removal efficiency; although on-line adsorption time and 

steaming requirements may need to be changed. If timers are used as the 

trigger mechanisms, the new working capacity of the beds must be determined. 

Using this working capacity and a maximum inlet loading, the appropriate new 

adsorption time can be determined so that the timers can be reset for the new 

operating conditions. 

Changing the adsorbate can also affect the desorption cycle. The 

relationship between steam usage and working capacity was previously shown for 

three different compounds in Figure 3-9. As can be seen, if the adsorbate 

blend is changed, the optimum steam requirements may also change. 

3.5.2 Steaming Conditions 

As previously discussed, steaming requirements are determined as part of 

the initial system design. Variables which must be considered are the 

3-45 
P.59 

steaming temperature, duration, and rate. Generally, steam temperature is 

fixed with a given plant. For this reason, the effect of temperature is not 

discussed. The amount of steam required is determined by the required working 

capacity. Once the initial design is set, as long as the amount of steam used 

per desorption cycle remains constant, the available working capacity will 

remain constant assuming no fouling or other degradation of the carbon bed. 

In actual application, however, the carbon's total absorption capacity 

gradually decreases over time due to fouling. If the operator desires to 

maintain the same breakthrough time, steam use per desorption cycle must be 

gradually increased. (Alternately, if sufficient standby time is available, 

the length of the adsorption cycle can be gradually decreased as previously 

discussed.) At some point the amount of steam required per desorption cycle 

becomes so great that either there is insufficient time to complete desorption 

before breakthrough of the on-line bed, or the cost of steam becomes too 

great. At this point the carbon must be replaced. 

Although steaming amount is important in the desorption process, duration 

is also a consideration. In order to remove the adsorbate, sufficient time at 

the steaming temperature is required. This is to allow for diffusion of the 

adsorbate out of the pores and out of the carbon particle. Without sufficient 

time, increasing the flow of steam will not remove the adsorbate from deep 

within the pores of the carbon. 

3.6 PERFORMANCE INFORMATION ON INDUSTRIAL ADSORBERS 

Available data concerning the ability of carbon adsorber systems to 

achieve 95 percent removal efficiencies are summarized in this section. Data 

from performance tests sponsored by EPA's Office of Research and Development 

(ORD), three test programs sponsored by EPA's Emissions Standards Division 

(ESD), and industry are used to support the conclusions reached. For each of 

the tests, the design parameters, operating conditions during testing, and 

test information and results are given. A comparison between design and 

operating information is then used to evaluate if a given system was operated 

within design limits during testing. 

Data sources along with the site codes and test numbering scheme used in 

the presentation are discussed in Section 3.6.1. In Section 3.6.2 the 

3-46 
P.60 

adsorber system operation is discussed with respect to the removal 

efficiencies achieved at a given site. Specifically, poor system operating 

procedures which were identified are explained. Finally, in Section 3.6 the 

conclusions reached regarding adsorber performance are presented. 

3.6.1 Data Sources 

A summary of the available carbon adsorber emissions test results is 

given in Table 3-2. Average overall removal efficiencies, design and actual 

operating conditions, and testing information are given for each of 12 sites. 

Emissions test data were available for 11 of the 12 sites. The twelfth 

reported efficiencies, but provided no supporting data. For each of the tests 

1-15, a unique test number is reported. Repeat tests were done at 4 of the 

twelve sites. Table 3-3 presents individual average bed removal efficiencies 

for several of these sites. 

Tests 1-10 were performance tests performed as part of an EPA/ORD study 

46 

of carbon adsorber performance in various industries. The manufacturing 

processes included are rubberized fabric, magnetic tape, flexible packaging, 

and rotogravure printing. Test 6 of this study was not presented for reasons 

discussed in Section 3.6.2. Six of the 10 tests were conducted in early 1982. 

The four follow-up tests were performed one to two years after the initial 

test. Tests 11-13 were performed as part of EPA/ESD performance evaluations 

47-49 

at three specific sites. Results from Tests 14 and 15 were provided by 

. . a. 50,51 

industry. ' 

Tests 1-13 were conducted in accordance with approved EPA methods. Inlet 

and outlet concentrations were measured semicontinuously with flame ionization 

detector total hydrocarbon instrumentation as described in EPA Method 25A. 

Volumetric flow rates were measured according to EPA Methods 1 and 2. All 

tests were verified by EPA-specified quality assurance/quality control 

procedures. 

Tests 14 and 15 were performed in accordance with EPA Methods 1,2, 

and 25. Method 25 differs from Method 25A in that integrated bag samples are 

taken and the concentration of the gas within the bag is used to determine the 

removal efficiency over the sampling period. Although this method does not 

give the semicontinuous data provided by Method 25A, it provides a means for 

accurately assessing the average removal efficiency over the sampling period. 

3-47 
TABLE 3-2. PERFORMANCE TEST DATA FOR CARBON ADSORPTION SYSTEMS 

Design Parameters Conditions During Test 

Test Flowrate 

No. Site (SCFM) 

Components 

in inlet stream 

Adsorbate Steam 

Loading Temperature Flow Flowrate Components in 

(lb/hr) (F) (lb/hr) (SCFM) Inlet Stream3 

Average 

Adsorbate Steam Bed Removal 

Loading Temperature Flow Age Efficiency 

(lb/hr) (F) (lb/hr) (years) (X) 

CJ 

I 

-p. 

CO 

1 A 11,200 

2 B 12,700 

3 B 12,700 

4 C 23,000 

5 D 22,000 

7 E 11,100 

8 E 11,100 

9 F 80,000 

10 F 80,000 

MEK - 60Z 

Toluene - 40 

THF - 50Z 

Toluene - 50Z 

THF - 50Z 

Toluene - 50% 

THF, Toluene, MEK, 

MIBK, Cyclohexanone 

11 C NR NR 

12 H NR NR 

13 I 75,000 NR 

575 

140 

140 

600 

NR 

NR 

NR 

14 

15 

J 

K 

L 

10,000 -

83,700 

24,000 

28,000 

MEK - 20-50Z 

Cyclohexanone -

THF - 5-25Z 

Toluene - 5-25Z 

MEK - 100Z 

Toluene - 95Z 

Hexane - 5Z 

20 -50Z 

180 -

2,800 

1,200 

860 -

1,070 

95 

90 

90 

85 

2,375 11,400 MEK - 100Z 

Hexane - 100Z 

Toluene - 100Z 

Toluene - 100Z 

Toluene - 60Z 

IPAC - 40X 

Toluene - 60X 

IPAC - 40X 

1,300 

204 

204 

810 

810 

95 

100 

100 

120 

120 

NR 

NR 

NR 

<200 

NR 

120 

900 9,800 

900 9,500 

2,400 19,800 

4,130 17,700 

1,170 9,100 

1,170 7,800 

1,180 33,400 

1,180 33,900 

NR 8,400 

THF - 50Z 

Toluene =50 % 

THF - 75Z 

Toluene - 25X 

THF, Toluene, MEK, 

MIBK, Cyclohexanone 

Hexane - 100Z 

Toluene - 100Z 

Toluene - 100Z 

Toluene - 60Z 

IPAC - 40Z 

Toluene - 60Z 

IPAC - 40Z 

MEK - 95Z 

MIBK, Toluene - 5Z 

284 94 

195 74 

140 90 

1,260 81 

892 67 

3,550 NR 

2,410 

600 

860 

3,300 

0.4 84.9 

99.7 

3.8 95.3 

2,900 0.4 94.8 

355 

c 

249 

101 

929° 

89 

104 

132 

91 

3,200 

3,000 

2,800 

3,400 

3 

5 

6.5 

0.2 

99.1 

97.6 

94.6 

97.5 

8,h 

1.6 97.8 

NR NR 98.9 

98J NR 

NR 

2,000 

1,750 

3,000 

48,800 

61,200 

60,000-

70,000 

24,000 

28,000 

Toluene - 10OZ 

Toluene - 30Z 

Xylene - 4Z 

Lactol Spirits - 66Z 

THF - 5,410 (lb 

per day) 

Toluene - 3,210 

MEK - 4,480 

Cyclohexanone - 10,500 

MEK - 100Z 

HR 

980 

1,279 

NR 

402k 

NR 

94 

100 

120 

83 

120 

11,000 

NR 

12,000 

1,750 

3,000 

NR 

NR 

Vartal 

2 

N/A] 

95.8 

99.6 

99.5 
TABLE 3-2. PERFORMANCE TEST DATA FOR CARBON ADSORPTION SYSTEMS (Continued) 

CO 

I 

VO 

*MEK «*- Methyl ethyl ketone: THF •» Tetrahydrofuran; MIBK = Methyl isobutyl ketone; IPAC = Isopropyl acetate. 

The low removal efficiency was a result of adsorbate blend being different from system design specifications, cocurrent steaming, 

cooling with adsorbate laden air, and malfunction in condenser system. 

Solvent loading was above design specification during test. 

ttemoval efficiency was reduced due to reduction ln desorption steam temperature, change in solvents, and elevated adsorber inlet 

temperature. 

Removal efficiency was likely reduced due to high adsorbate loading causing premature system breakthrough. 

Inlet stream temperature was above design specifications during test. 

Data from bed 2 were not included in average because a steam valve leak caused a severe reduction in bed capacity. 

Overall system removal efficiency was reduced due to the inlet stream temperature being above design. 

NR •= Data not reported. 

Removal efficiency is time weighted according to length of time Individual lines were operating. 

lr 

Inlet adsorbate loading expressed as 67 lb C /hr. To convert to loading in terms of lb MEK/hr need to multiply by 6 (MW MEK = 72/MW 

C -12). 

l 

Not applicable. These data are not from a specific performance test. Removal efficiency was calculated from inlet and outlet 

concentrations reported by the facility. 

Continuous average, including distillation steam. 

"The average of the removal efficiency of the individual beds. 
P.63 

TABLE 3-3. PERFORMANCE TEST DATA FOR CARBON ADSORPTION SYSTEMS53"

55 

ON A PER BED BASIS 

Data collection Removal 

Test number Bed designation time period efficiency, % 

1 A NAb 87.2a 

B NA 78.9a 

2 1 NA 99.6 

2 NA 99.8 

3 NA 99.8 

3 1 NA 97.3 

2 NA 92.7 

3 NA 95.9 

4 IA 705 min. 94.0 

IB 826 min. 94.0 

IB 382 min. 94.3r . 

IB 280 min. 89.2c , a 

2A 247 min. 92.9 

2A 279 min. 91.3 

2B 105 min. 88.9d'

e 

2B 247 min. 95.5 

3A 128 min. 96.2 

3A 271 min. 97.7 

3A 647 min. 96.6 

3B 898 min. 98.0 

3B 781 min. 96.2 

5 1 451 min. 99.4 

2 388 min. 99.3 

2 507 min. 99.0 

2 228 min. 99.4e 

3 295 min. 98.9f 

A NA 97.0 

B NA 97.6 

C NA 98.3 

(continued) 

3-50 
P.64 

TABLE 3-3. (Continued) 

Test number 

8 

9 

10 

11 

Bed designation 

A 

B 

C 

1-1 

1-1 

1-1 

1-1 

1-1 

1-1 

1-2 

1-2 

1-2 

1-2 

1-3 

1-3 

1-3 

1-1 

1-2 

1-3 

1 

1 

1 

1 

1 

3 

3 

3 

3 

3 

Data collection 

time period 

NA 

NA 

NA 

7.6 hrs. 

9.1 hrs. 

8.6 hrs. 

8.1 hrs. 

5.5 hrs. 

6.8 hrs. 

8.5 

9.4 

8.2 

6.0 

8.1 

6.4 

7.4 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

Removal 

efficiency, % 

91.4 

91.4 

97.8 

98.0 

97.4 

97.8 

96.6 

97.3 

97.6 

97.9 

96.8 

97.0 

97.6 

97.8 

97.5 

98.1 

97.9 

98.1 

97.5 

99.8 

95.5 

97.7 

97.8 

98.9 

99.4 

96.4 

98.5 

98.8 

98.7 

Data are from one cycle; overall system efficiency was 84.9 percent. 

bNA = Not available. 

c0nly one coating line in operation. 

Collected during startup of one of the lines. 

eCoating process unsteady during this period. 

Not representative of normal operation; system returning to steady-state 

after all beds on adsorption. 

3-51 
P.65 

Site L supplied no detailed information so only the reported removal 

52 efficiency is presented. 

3.6.2 Removal Efficiency Data for Performance Tests 

The overall removal efficiencies presented in Table 3-2 range from 

84.9 to 99.7 percent for a variety of adsorbates including MEK, toluene, THF, 

MIBK, cyclohexanone, hexane, and IPAC. On a per bed basis, the range of 

removal efficiencies is 52.3 to 99.8 percent. As shown, the bed ages 

associated with the adsorbers tested range from 3 to 78 months. 

The overall removal efficiency of 84.9 percent reported for Test 1 is the 

result of both operating outside of the original design range and poor 

operation during the test. The system was designed to recover an adsorbate 

blend consisting of 60 percent methyl ethyl ketone and 40 percent toluene. At 

the time of the test, the organic feed was 100 percent methyl ethyl ketone. 

As discussed in Section 3.5.1, switching adsorbate blends can have a 

detrimental effect on removal efficiency. In addition, several operating 

practices at this site may have contributed to the reduced control efficiency. 

These include cocurrent steaming of the bed, cocurrent cooling of the bed with 

the adsorbate laden stream, and operating with a malfunctioning steam 

condenser. 

Cocurrent steaming leaves more residual solvent at the bed outlet than 

countercurrent steaming, thus increasing the outlet concentration when the bed 

is brought on-line. Cooling the bed with the adsorbate laden vent stream 

further aggravates this problem because it allows adsorbate laden air to enter 

the bed when the system working capacity is at its lowest. This allows 

adsorbate to spread down the bed much further than if the system is operated 

correctly. For reasons which have been discussed in Section 3.4.1 this caused 

the system to be more sensitive to variations in the operating temperature. 

The final problem associated with this system was a malfunction in the 

condenser system. The system was not cooling the desorbate stream 

sufficiently. Since the steam from the condenser was recycled to the on-line 

bed, unusually high amounts of solvent were allowed to enter the bed from the 

recycle stream. This additional solvent loading led to premature 

breakthrough. 

3-52 
P.66 

In summary, these problems would indicate that this system was not well 

designed and was poorly operated. Its removal efficiency is not 

representative of a well designed and operated system. It should be noted 

that several of the problems would have been discovered as part of normal 

operation if the system had used continuous outlet monitors. 

The average overall removal efficiency presented for Test 2 is 

99.7 percent. 

The individual bed efficiencies range from 99.6 to 99.8 

percent. The solvent blend for this system was 50 percent toluene and 

50 percent tetrahydrofuran, and all of the operating conditions were within 

design specifications with the exception of the loading rate. The design 

specification was 140 lb/hr, but the actual loading rate was 195 lb/hr. 

Test 3 is a follow-up test at site B. For this test, the average 

system overall removal efficiency was 95.3 percent with the individual bed 

efficiencies ranging from 92.7 to 97.3 percent. All of the beds had lower 

removal efficiencies than in the initial test, Test 2. The reduced removal 

efficiency during the second test was attributed to the following in the 

57 

test report: 

• Increased carbon age; 

• lower regeneration steam temperature; 

• higher SLA inlet temperature; and 

• change in solvent formulation to 75 tetrahydrofuran and 25 percent 

toluene. 

58 Figure 3-22 presents a typical outlet concentration curve for this test. 

During the initial test (Test 2), the typical outlet concentration had an 

initial spike and then decreased to approximately 1 ppm for the remainder 

adsorption cycle. However, during Test 3, the outlet concentration was much 

higher and an upward trend indicating the beginning of breakthrough can be 

CQ 

seen at the end of the cycle. This result would be expected due to the 

factors shown above. If the desorption and adsorption cycles had been 

adjusted to account for the changes in SLA inlet temperature, solvent 

3-53 
P.67 

LL. 

I 

c 

© 

O 

r-

> E 

a. 

o. 

c 

o 

* f 

CO 

m-a 

c 

0) 

o 

c 

o o 

o 

O 

> 

1,500-

1,400-

1,300 

1,200 

1,100-

1,000-

900-

800 

700-

10-

0 

Adsorption 

Average Cin =1180 ppmv 1 

Average Cou, = 25 ppmv 

10 20 30 40 "io" 60 

Time (min.) 

Figure 3-22. Inlet/Outlet Concentration Curve for Test 3 

3-54 
P.68 

composition, and regeneration steam temperature, and carbon age then the 

performance during Test 3 should have been similar to the Test 2 performance. 

However, even though this system did show reduced efficiency in Test 3, 

the average system efficiency was over 95 percent, which would be sufficient 

to meet the 95 percent removal efficiency requirement in the proposed magnetic 

tapes regulation. 

The adsorbate blend concentrations for Test 4 are not specified, but the 

blend included tetrahydrofuran, toluene, methyl ethyl ketone, methyl isobutyl 

ketone, and cyclohexanone. The average overall removal efficiency for Test 4 

is 94.8 percent. Individual bed removal efficiencies ranged between 89.2 and 

98.0 percent. The average loading for the test period was 1,260 lb/hr which 

is over twice the design level of 600 lb/hr. If the adsorption time had been 

shortened to account for the increased loading (as discussed in Section 3.4), 

removal efficiencies for all beds would have been higher and as discussed in 

Section 3.3.3, the variability would be less. 

Hexane is the only adsorbate at Test 5. The overall removal efficiency 

shown for this test period is 99.1 percent with individual bed efficiencies 

ranging between 98.9 and 99.4 percent. All of the operating conditions were 

within design specifications. 

The follow up test at this site was Test 6. In this test, an extremely 

low removal efficiency was achieved due to a leaking steam valve. Excursions 

in the outlet concentration were shown to coincide with the steaming cycle for 

the off-line bed. In this system, the steam flow is cocurrent, in the same 

direction as the air flow during adsorption. Consequently, the steam leak 

allowed the solvent laden steam from the off-line bed to enter the outlet 

stream of the on line beds. This resulted in false readings at the adsorber 

outlet. For this reason no data from this test were included in this report. 

The results shown for Test 7 are for a single component system in which 

toluene is recovered. The overall removal efficiency for this test is 

97.6 percent even through both the inlet temperature and loading rate were 

slightly above design specifications. The individual bed removal efficiencies 

were between 97.0 and 98.3 percent. 

The follow up to Test 7 is Test 8. Toluene was also the only adsorbate 

for this test. The removal efficiency for bed 2 is not included in the 

3-55 
P.69 

average removal efficiency of 94.6 percent which is shown for this test. 

(Table 3-2) A steam valve leak allowed steam to leak into bed 2 raising the 

temperature significantly, and severely reducing the working capacity. As in 

Test 6, the outlet concentration peaks were shown to coincide with the 

desorption period of the off-line bed. Since the data for this bed are not 

representative, they were not included. The lower removal efficiency for the 

other two beds is the result of two related problems. A malfunctioning inlet 

air cooler allowed the inlet temperature to rise 32°F above the design maximum 

and also a timer occasionally malfunctioned. Once again, the use of 

continuous outlet monitors in the operation of this system would have helped 

to uncover the malfunction in operation. 

Tests 9 and 10 were both conducted at site F with an adsorbate blend of 

60 percent toluene and 40 percent isopropyl acetate. The overall removal 

efficiencies for these two tests were 97.5 percent and 97.8 percent, 

respectively. The individual bed removal efficiencies were 96.8 to 

98.1 percent. These removal efficiencies agree well with what would be 

expected for the two sets of operating conditions. In both tests, the inlet 

adsorbate loading was above the design specifications of 810 lb/hr. All of 

the other operating conditions were within design specifications during both 

tests. 

No design parameters or individual bed removal efficiencies were 

available for Tests 11, 12, and 13. Therefore, it was not possible to assess 

the system operation in terms of design. The adsorbates for Test 11 were 

methyl ethyl ketone, methyl isobutyl ketone, and toluene. The overall removal 

efficiency shown for Test 11 is 98.9 percent. For Test 12 the overall removal 

efficiency was 98 percent for a adsorbate of 100 percent toluene. The 

adsorbate mixture for Test 13 was 30 percent toluene, 4 percent xylene, and 66 

percent lactol spirits, and the overall removal efficiency is 95.8 percent. 

The overall removal efficiency shown for Test 14 is 99.4 percent. The 

average composition of the recovered VOC at this site is as follows: 

44 percent cyclohexanone, 23 percent tetrahydrofuran, 19 percent methyl ethyl 

ketone, and 14 percent toluene. All of the operating conditions shown for 

this test are within the design limits. In Test 15, the adsorbate is 

3-56 
P.70 

100 percent methyl ethyl ketone and the overall removal efficiency is 

99.6 percent. None of the operating conditions at this site were outside of 

the design conditions reported. 

No actual test data are available for site L, but the overall removal 

efficiency was reported by the company 99.5 percent. The adsorbate blend at 

this site was 95 percent toluene and 5 percent hexane. 

The performance test data shown in this section generally show removal 

efficiencies above 95 percent. For cases where the removal efficiency was 

below 95 percent, correctable problems were identified which were the cause of 

the lower removal efficiencies. It should be noted that these performance 

test data are fairly short duration ranging from less than 2 hours up to 

15 hours. If the time periods of startup and system malfunctions are not 

considered, the removal efficiencies are fairly consistent with little 

variability from bed to bed. 

3.6.3 Continuous Removal Efficiency Data 

Continuous efficiency data are available from two sites. These data are 

presented to show a short-term efficiency variability. The data encompass a 

relatively broad range of solvent blends, adsorbate loadings, flowrates, and 

inlet temperatures. 

Figures 3-23 and 3-24 present continuous inlet and outlet concentration 

and removal efficiency data versus time for two test runs from site G in 

Table 3-2. As shown in the figures, the inlet concentrations vary 

significantly throughout the respective testing periods. However, the outlet 

concentrations remain fairly consistent regardless of the inlet 

concentrations, and are almost always less than 10 ppm. The removal 

efficiencies are also fairly consistent and are generally above 95 percent. 

The only time the removal efficiency is below 95 percent is when the inlet 

concentration falls below about 50 ppm. This is expected since as previously 

discussed, the outlet concentration is independent of the inlet concentration. 

Therefore, if the inlet concentration is allowed to fall below the design 

value, the instantaneous removal efficiency can also decrease below design 

levels. 

3-57 
P.71 

MO 

SOO -

| 700 -

a 

yyf 

600 -

O 

aa 

O 900 

k. 

aa 

c 

• 400 -

U 

c 

I -

rV~ 

y 

9:00 10:00 11:00 

E 

a 

a 

c 

o 

S 

u 

e 

o 

o 

3 

o 

40 -

30 -

20 -

10 -

9:00 

—.—*-"~ 

Tim* 

InM Concentration va. TIma 

, , » 

IO-OO ii-oo 12*00 

»«•% 

K 

>, 

u 

c 

• 

u ffi 

u 

o 

o 

E o 

c 

sa -

90 -

8 / -

sa -

SS -

94 -

S3 -

S3 -

SI -

90 -

aa -

aa -

a» -

aa -

as -

•4 -

U -

S3 -

SI -

ao -

Tlnw 

Outtal Concentration va. TIma 

^n 

- - . 1 ——+—» — 

u 

_^ 

too 10410 11:00 

Nanoval Efficiency va. Tana 

Figure 3-23. GTR Test Number 5 Continuous Inlet/Outlet VOC Concentration 

Data and Removal Efficiency 

3-58 
- » SOO 

a 

a 

c 

o 

a 

v. 

aa 

C 

e 

u 

c 

o u 

J00 - "U 

h 

/ l 

i 

i — * -

9:00 10:00 11:00 12:00 13 00 14 00 15:00 18:00 

Time 

Inlet Concentration vs. Time 

E 

a 

a 

mf C 

o 

at O 

i . 

ma C 

e 

u 

c 0 

o 

e 

aa 3 

o 

too 

90 

80 

70 

80 

SO 

40 

30 

20 

10 

0 

8:00 11-00 12-00 13:00 14:00 18:00 18:00 

Mmoval Effldenc-tf va. TIma 

Figure 3-24. GTR Test Number 6 Continuous Inlet/Outlet VOC Concentration 

Data and Removal Efficiency 

3-59 
P.73 

Inlet and outlet concentrations and instantaneous and cumulative removal 

efficiencies for six adsorber beds at site J are presented in Figures 3-25a 

through 3-25j. The continuous data shown were obtained at the request of EPA 

and are typical of normal facility operation. As previously discussed, the 

solvent blend at this facility ranges from 20-25 weight percent cyclohexanone 

and 20-50 weight percent methyl ethyl ketone (MEK). Both cyclohexanone and 

MEK have been identified as chemicals which react on carbon to cause fouling. 

The data are continuous monitor readouts for each of the six carbon beds which 

comprise the complete system. The inlet concentrations vary between about 

2,000 ppm and 3,000 ppm, with adsorbers #1 and #2 having the highest inlet 

concentrations. The continuous outlet concentrations from all 6 adsorbers are 

below 50 ppm. Of particular note is the fact that both the instantaneous 

removal efficiency and the cumulative efficiency over the entire monitoring 

period for all adsorbers are above 98.5 percent. 

The instantaneous removal efficiencies of the newest bed ranged from 

99.3 to 99.8 percent. The efficiency of the oldest bed ranged from 99.9 to 

98.5 percent. One reason the removal efficiencies of the beds stay well above 

95 percent is that the beds are changed frequently. This facility could 

operate the beds until their removal efficiency has reached 95 percent, 

but has chosen not be do so to avoid operation problems which could cause 

overall removal efficiency to fall below the desired value. 

The data from these two sites indicate that the 95 percent removal 

efficiency can be maintained continuously if the carbon absorber is properly 

designed, operated within its design specifications, and well maintained. 

3.7 CONCLUSIONS REGARDING CARBON ADSORBER PERFORMANCE 

The data presented in Section 3.6 demonstrate that properly designed and 

operated carbon adsorption systems can achieve 95 percent removal on a 

continuous basis. This removal efficiency is shown for numerous solvent 

blends and bed ages. Greater than 95 percent removal efficiency is shown for 

streams that contain mixtures of ketones that include cyclohexanone, and for 

which claims have been made that 95 percent is not achievable using carbon 

3-60 
P.74 

E a a 

._• 

z 

o 

z 

Ui 

u 

z 

o 

u 

is 

0 

t 

Ul 

400 

350 -

300 -

250 

II O O 

200 -

150 -

100 -

50 

-a-& 

V-o- s » » • » s » »--»•-*->»•»•, • »»•»•»••«»•»- • 

- i i • i i I I i • • • •• — 

»»»•> » o -»-•»-< 

20 40 

O Inlet (xl/10) 

TIME (min) 

Outlet 

Figure 3-25a. Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber #1 

Inatantonaous 

TIME (min) 

Cummutative 

Figure 3-25b. Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #1 

3-61 
E 

a 

a 

•** 

z 

o 1. 

z 

Ul 

o 

z 

o 

u 

400 

350 -

300 

250 -

200 -

150 -

100 

Outlet 

Figure 3-25c. Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber #2 

o 

a 

z 

u 

G 

E 

ui 

Instantoneous 

TIME (min) 

Cummutative 

Figure 3-25d. Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #2 

3-62 
P.76 

E 

a 

a 

z 

o 

1. z 

Ul 

o 

z 

o 

u 

a 

s 

o 

It 

Ul 

300 -

280 -

260 -

240 -

220 -j 

200 -

180 -

160 -

140 -

120 -

100 -

80 -

60 -

40 -

20 -

0 

O O O 

-a-a60 

~T i 1 r 

80 100 

Inlet (xl/10 ) 

TIME (min) 

—I 

120 

Outlet 

Figure 3-25e. Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber #3 

99.8 

Instontoneoua 

TIME (min) 

Cummulotive 

Figure 3-25f. Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #3 

3-63 
P.77 

E 

a 

a 

y.* 

z 

o 

Ul 

u 

z 

o 

u 

>• 

o 

z 

u. 

u 

fc 

Ul 

260 

240 -

220 -

200 

180 

160 -

140 -

120 -

100 -

80 -

60 -

40 -

20 -

^B-B-ar^ BOtf^SoO B \a4Hi****** TM 

200 

Figure 3-25g. Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber # 4 

99.9 

99.8 -

99.7 -

99.6 

99.5 -

99.4 -

99.3 -

99.2 -

99.1 -

99 1 1 I I ' I " 

140 160 ISO 200 

Instantaneous Cummutative 

Figure 3-25h. Instantaneous and Cumulative Efficiency Versus Cycle Time 

or Adsorber #4 

3-64 
P.78 

300 

280 H 

260 

240 -

220 -

200 -

180 -

160 

140 -

120 -

100 -

80 -

60 -

40 

20 H 

0 

V. e-e-

- B ^ 

•• • » » o a 

a Inlet (xl/10 ) 

TIME (min) 

- 1 1 1 1 1 1— 

120 140 160 ISO 

Outlet 

Figure 3-25i. Inlet and Outlet Concentration Versus Cycle Time for 

Adsorber #5 

c 

a 

u 

k 

o 

a 

o 

S 

o 

E 

Ul 

180 

Inatantonaous 

TIME (min) 

Cummutative 

Figure 3-25J. Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #5 

3-65 
P.79 

300 

E & 

a 

^a 

Z 

o 

s. 

z 

Ul 

o 

z 

o 

o 

280 

260 H 

240 

220 

200 -

180 -

160 -

140 -

120 -

100 -

80 -

60 -

40 

20 H 

0 

jr^^-^B-B - oooo o OOOOO O ^Sr'N, 

•—•»-

20 40 60 

Inlet (xl/10 ) 

TIME (min) 

Oudet 

Figure 3-25k. Inlet and Outlet Concentration Versus Cycle Time 

for Adsorber #6. 

c 

a 

o 

a 

>-

u 

z 

Ul 

u 

Ul 

100 -

99.9 -

99.8 -

99.7 -

99.6 -

99.5 -

99.4 -

99.3 -

99.2 -

99.1 -

99 -

98.9 -

98.8 -

98.7 -

98.6 -

98.5 - • I -

20 

•— I'" I 

4 0 

Instantaneous 

I • 

60 80 

... r _ 

100 

TIME (min) 

— •. 1 

120 

Cummutative 

. I 

140 

T " 

160 

Figure 3-251. Instantaneous and Cumulative Efficiency Versus Cycle Time 

for Adsorber #6. 

3-66 
P.80 

adsorption. In every case where the removal efficiency was less than 

95 percent, correctable and easily identifiable operational problems were 

responsible for lower removal efficiencies. 

The key to achieving 95 percent removal is proper design and operation 

of the adsorption system. If this is done, maintaining a removal efficiency 

of 95 percent becomes only a matter of cost where the economic trade-offs 

come in the form of steam cost versus carbon replacement costs. The carbon 

must be steamed sufficiently to desorb the adsorbate, but excessive steam 

use raises the operating costs. The adsorption time must be sufficiently 

long to allow regeneration of the other bed(s). This will require 

replacement of the carbon when its working capacity gets too low. 

In Section 3.4 it was shown that if a system is designed for a full range 

of operating conditions, operated correctly, and the carbon is replaced 

before its working capacity has been reduced to the point where beds are 

operated after breakthrough, the short-term removal efficiency should not 

vary significantly. Based on the information and data presented here, it 

can be concluded that a removal efficiency of 95 percent or greater is 

continuously achievable. 

3-67 
P.81 

4. CARBON ADSORPTION SYSTEM AT COMMENTER'S FACILITY 

This section presents an analysis of the carbon adsorption system located 

at the commenter's facility. The information presented contains data for 

which the commenter has made a claim of confidentiality. This information is 

located in the confidential files of the Director, Emission Standards 

Division, Office of Air Quality Planning and Standards, U. S. Environmental 

Protection Agency, Research Triangle Park, North Carolina. This information 

is confidential, pending final determination by the Administrator, and is not 

available for public inspection. 

4-1 
P.82 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

15. 

16. 

17. 

18. 

19. 

20. 

21. 

22. 

5. REFERENCES 

U. S. Environmental Protection Agency, APTI Course 415: Control of 

Gaseous Emissions. EPA-450/2-81-005. Research Triangle Park, 

North Carolina. December 1981. p. 5-4. 

Reference 1. 

Reference 1, p. 5-6. 

Reference 1, p. 5-13. 

Reference 1, p. 5-2. 

Reference 1, p. 5-14. 

Reference 1, p. 5-14. 

Reference 1, p. 5-14. 

Reference 1, p. 5-3. 

Reference 1, p. 5-14. 

Memorandum from Barnett, K. W., Radian Corporation to Carbon Adsorber/ 

Condensation Project File. February 29, 1988. Meeting Minutes 

EPA/Calgon Carbon Corporation, p. 8. 

Reference 11, p. 7. 

Reference 11, p. 14. 

Reference 11, p. 18. 

Crane, G., Carbon Adsorption for VOC Control. U. S. Environmental 

Protection Agency. January 1982. p. 18. 

Reference 11, pp. 17-18. 

Reference 1, p. 5-14. 

Reference 1, p. 5-20. 

Reference 11, p. 14. 

Reference 11, p. 14. 

Reference 11, p. 12. 

Reference 11, p. A-8. 

5-1 
23. Reference 11, p. 18. 

24. Magnetic tape Manufacturing Industry - Background Information for 

Proposed Standards. U. S. Enviormental Protection Agency. Research 

Triangle Park, North Caronlina. Publication No. EPA-450/3-85-029a. 

December 1985. Appendix C. 

25. Memorandum from Crumpler, D., U. S. Environmental Protection Agency to 

Berry, J., U. S. Environmental Protection Agency. April 21, 1988. 

Plant Visit to Ampex Corporation, p. 2. 

26. Reference 11, p. 14. 

27. Miller, K. J., C. R. Noddings, and R. C. Nattkemper. 3M Company. St. 

Paul, Minnesota. (Presented at Air Pollution Control Association 

Meeting. New York, New York. June 21-26, 1987.) p. 4. 

28. Memorandum from May, P., Radian Corporation, to file. May 23, 1988. 

Ampex Data Analysis, p. 14. 

29. Reference 28, p. 14. 

30. Reference 11, pp. 14, 17. 

31. U. S. Environmental Protection Agency, Industrial Surface Coating 

Emission Test Report: General Tire and Rubber Company; Reading, 

Massachusetts; Test Series 2. EPA/EMB-80-VNC-1B. Research Triangle 

Park, North Carolina. July 1982. Appendix B.l. 

32. Reference 31. 

33. Reference 11, p. 10. 

34. Letter from Shuliger, W., Calgon Carbon Corporation to Wyatt, S. R., 

EPA. November 11, 1987. Response to information request. 

35. Reference 28, p. 5. 

36. Reference 11, p. 19. 

37. Reference 28, p. 14. 

38. Reference 28, p. 13. 

39. Letter and attachments from Sapovich, M., Diversitech General, to 

Farmer, J., U. S. Environmental Protection Agency. January 12, 1988. 

Response to Section 114 information request. 

5-2 
P.84 

40. 

41. 

42. 

43. 

44. 

45. 

46. 

47. 

48. 

49. 

50. 

51. 

52. 

53. 

54. 

55. 

Letter and attachments from Jackson, P., Dayco Products, Inc., to Farmer, 

J. U. S. Environmental Protection Agency. December 12, 1987. Response 

to Section 114 information request. 

Letter and attachments from Johnson, W., R. J. Reynolds Tobacco (Archer), 

to Farmer, J., U. S. Environmental Protection Agency. December 21, 1987. 

Response to Section 114 information request. 

Reference 11, p. 4. 

Reference 11, p. 4. 

Reference 11, p. 8. 

Reference 11, p. 10. 

Blacksmith, J. R., T. P. Nelson, and J. L. Randall (Radian 

Corporation). Full Scale Carbon Adsorption Applications Study. 

Prepared for U. S. Environmental Protection Agency. Cincinnati, Ohio. 

Contract No. 68-03-3038. May 1984. 211 p. 

Feairheller, W. R. (Monsanto Research Corporation). Graphic Arts 

Emissions Test Report: Meredith Burda, Lynchburg, Virginia. Prepared 

for U. S. Environmental Protection Agency. Research Triangle Park, 

North Carolina. Publication No. 79-GRA-l. March 1979. 30 p. 

Feairheller, W..R. (Monsanto Research Corporation). Graphic Arts 

Emission Test Report: Texas Color Printers, Dallas, Texas. Prepared 

for U. S. Environmental Protection Agency. Research Triangle Park, 

North Carolina. Publication No. 79-GRA-3. August, 1979. 

Reference 31. 

Letter and attachments from Gilbert, R., Ampex to Farmer, J. R., U. S. 

Environmental Protection Agency. December 16, 1987. Response to 

Section 114 questionnaire. 

Reference 39. 

Reference 40. 

Reference 46. 

Full Scale Carbon Adsorption Applications Study. Plant 3. Radian 

Corporation (Prepared for the U. S. Environmental Protection Agency). 

Cincinnati, Ohio. August 19, 1982. Draft Report. 

Full Scale Carbon Adsorption Application Study. Plant 4. Radian 

Corporation (Prepared for the U. S. Environmental Protection Agency). 

Cincinnati, Ohio. February 25, 1983. 

5-3 
P.85 

56. Full Scale Carbon Adsortpion Application Study. Plant 6. Radian 

Corporation (Prepared for the U. S. Environmental Protection Agency). 

Cincinnati, Ohio. October 29, 1982. 

57. Reference 46, p. 108. 

58. Reference 46, p. 109. 

59. Reference 46, p. 110. 

60. Reference 24, pp. 3-4. 

5-4