CARBON ADSORPTION I EMISSION CONTROL

Transcription

1 CARBON ADSORPTION I EMISSION CONTROL BENEFITS AND LIMITATIONS VIC MANUFACTURING COMPANY 1620 Central Ave N E, Minneapolis, Mlnnesota 55413

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3 SUMMARY The EPA has produced a guideline series for the CONTROL OF VOLATILE ORGANIC EMISSIONS FROM EXISTING STATIONARY SOURCES. It consists of eight volumes, and is published by OFFICE OF AIR QUALITY PLANNING AND STANDARDS, Research Triangle Park, North Carolina. The series discusses four different abatement methods used to reduce the emissions of volatile organic compounds (VOC) from various surface coating operations. They are: 1. "Add-On" technology to destroy or recover VOC from exhaust gases. 2. Reformulation of coatings to minimize organic solvent content. 3. Modification of the process to reduce the quantity of VOC which escapes from a coating line. 4. Substitution of less photo-chemically reactive solvents in surface coating formulations. Carbon adsorption is a means of reducing VOC falling under category #l. It is obvious that any industry facing compliance with emission regulations would first evaluate the possibilities for control under categories #2 and #3. Where low solvent coatings cannot be utilized as a compliance technique, stack gas treatment utilizing "ADD-ON" technology may be the only answer. This presentation will discuss the benefits and limitations of fixed bed CARBON ADSORPTION (CA) as a suitable means of compliance under that category. This presentation includes practical guidelines for those considering CA for emission control. Examples will be utilized wherever possible. Benefits and limitations will be described as they apply to some of the more important design criteria. It is left to the individual to decide what effect each will have on his particular application.

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5 . CARBON ADSORPTION/EMISSION CONTROL BENEFITS AND LIMITATIONS Carbon adsorption benefits most often considered are: 1. Solvent recovery for reuse, 2. Energy recovery, 3. Odor removal, 4. Emission control for compliance, or a combination of any or all of the above. In evaluating these benefits, it is essential to know which VOC's are most suitable for adsorption. Compounds best suited for adsorption can be described by molecular weight and boiling point range. These limitations, and there are exceptions, are generally described as follows: A. Molecular weight range of 50 to 200. B. Boiling point range from 200 C. to 175O C. Table 1 lists a few of the industrial organic compounds falling into this category, along with some of their physical properties. Unfortunately, the list represents a small percentage of the total organic compounds available to.industry. Fortunately, it does represent many of the most often used. The list is a practical guide for some of the solvents falling within the boiling point and molecular weight ranges indicated. An organic compound should not be discounted just because it is not included in the list. Table 2 represents families of VOC's or types of compounds which should be avoided. These are categorized into two groups, i.e. Reactive Compounds and High Boilers. Obviously, pages could be written on this subject. It will be helpful for the prospective user of CA equipment to understand the basic criteria affecting the general design. The primary parameters are throughput expressed as standard cubic feet per minute (SCFM), rate of recovery in pounds per hour (lbs./hr.), and solvent composition in percent by weight

6 Page 2 (% wt.). CA systems will normally be designed for air velocities between 80 and 100 ft./min. through the adsorption bed. It would be difficult to achieve a 90% system efficiency (coater, dryer, and CAI at velocities in excess of 100 ft./min. Efficiencies across the CA unit alone are usually well in excess of 95%. CA unit throughput is the product of velocity times bed area, and is usually the single most important parameter affecting price of the CA system. The maximum rate of recovery (lbs./hr.) is a function of the total weight of carbon provided, and the depth of the bed needed to provide an adequate transfer zone (TZ). In the vast majority of cases, where medium to high concentrations of solvent are to be handled, the volume of carbon capable of being handled by the adsorber exceeds the requirement for the recovery rate. The solvent composition will have an effect upon the total amount of carbon to be utilized, and the lowest steam requirements will be met by systems utilizing the least amount of carbon necessary to meet the stated efficiency requirements. A practical example will illustrate these points. The results of this example are summarized in Table 3. A solvent coater is exhausting 20,000 SCFM of toluene laden air. The source is operating at 10% lower explosive limit (LEL). The LEL for toluene is 1.2% by volume. Therefore, the exhaust contains 20,000 SCFM x 1.2% (LEL) x 10% (LEL level of the source). Therefore, the source contains 24 SCFM of toluene vapor. Remembering that one gram mole of any vapor will occupy 22.4 liters under standard temperature and pressure conditions (STP), it is calculated that the total amount of toluene present is 369 lbs./hr. In this calculation, 22.4 liters is converted to the equivalent 359 cu. ft. The equation is 24 (CFM)/359 (CFM) x 92.1 (molecular weight of toluene) x 60 (min./hr.) = Value of Toluene in lbs./hr. The bed cross-sectional area required is 20,000 (SCFM)/100 (ft./min.) or 200 sq. ft. This could be met by a horizontally oriented 10 ft. diameter by 20 ft. long cylindrical adsorber. Carbon bed depths in systems of this design may be up to 4 ft. Carbon density is typically 30 lbs./cu. ft. The maximum amount of carbon which could be provided then is 200 ft. sq. x 4 ft. x 30 lbs./ft.3 or 24,000 lbs. The amount of carbon actually required is determined by an adsorption isotherm; i.e.,a plot of saturation capacity in weight percent versus concentration of the organic in the air stream at a fixed temperature. Concentration is usually expressed as partial pressure in mm Hg of VOC. Figure 1 is a reproduction of such an adsorption

7 Page 3 isotherm, plotted at constant temperature, for toluene. The partial pressure of toluene in this application is the volume fraction 24 SCFM/20,000 SCFM x 760 mm mercury vapor pressure at STP or mm of mercury. The saturation capacity (SC) from this adsorption isotherm is 30%: The system working capacity (WC) is derived from this figure. SC is defined in weight percent as the ratio of a VOC in pounds to the total weight of carbon required to adsorb and retain it. In other words, it is a weight percent of solvent to carbon. Retentivity is a measure of the ability of the carbon to retain an adsorbed vapor, and is often based upon the experience of the designer with respect to the particular type of solvent or solvent mixture. For toluene concentrations in the range being discussed, a transfer zone of 18 inches would normally be used in order to achieve efficiencies across the process of 90% or better. WC is a somewhat arbitrary number, based upon a fraction of the SC. The fraction varies all the way from 25% to 50% of SC. Most designers use a 25% to 30% factor. Assuming a 25% factor in this example, the WC will be 7.5%. In other words, 100 lbs. of carbon will be required for each 7.5 lbs. of toluene to be adsorbed. Working capacities are normally calculated for a 1-hour cycle, since efficient desorption with steam at low pressure will require approximately 60 minutes. The difference between SC (-1 WC is the HEEL of VOC which once adsorbed will remain on the carbon. From the above, it can be seen that the designer has a great deal of latitude and that his approach may have a considerable effect upon the system s ability to perform at a high efficiency. The actual amount of carbon required for this application is 369 lbs. of toluene/7.5% WC = 4,920 lbs. If one were to utilize the 10 ft. x 20 ft. adsorption vessel previously referenced, the carbon bed depth would be only approximately 10 inches, not satisfactory for the transfer zone requirement. Most designers would go to a three vessel adsorption system with each vessel having approximately 100 sq. ft. of crosssectional area. Utilizing this design, two vessels would adsorb in parallel, while the third was either desorbing, drying or idle. The adsorber would be constructed in order to give at least an 18-inch bed depth; i.e.,probably 6 ft. diameter by 16 ft. long. Such a system meets all of the design parameters previously discussed, i.e. velocities of 100 ft./min. or less; an amount of carbon sufficient to meet the WC required; and a TZ satisfactory to meet the efficiency requirement. Photo I depicts such a CA system.

8 Page 4 Steam usage is usually referred to in terms of the wt. ratio of steam to VOC adsorbed. However, most designers are concerned with the steam required to heat the carbon charge in a specified time interval, and to achieve total desorption in not more than sixty minutes. Practically speaking, this is a function more of the total carbon charge than it is of the amount of VOC adsorbed. A typical system will require 0.25 to 0.35 pounds of low pressure steam per lb. of carbon, and a 15 minute heat-up will be achieved. The heat-up time is the amount of time required for the initiation of VOC vapor flow to the system condenser once the steam valve has been opened. This application would require 0.30 lbs. of steam per lb. of carbon, or 1,476 lbs./hr. instantaneous steam demand. This may not be continuous, since the regeneration mode may not always be active. Horsepower requirements for a fixed deep bed horizontal system will run about six horsepower per 1,000 CFM, or 120 HP. Static pressure runs about 0.5 inches water column per inch of bed depth for typical carbons. Table 3 summarizes some of these important designco;lsidt.?;ltions. Utilizing this information, the plant engineer will be able to calculate the approximate size and utility requirements for any deep bed application under consideration. Most coaters can be run at 25% of the LEL or greater. At 25% LEL, this same system would require only 8,000 SCEM of total throughput. The bed area, at 100 ft./min.,would be only 80 sq. ft. Transfer zone requirements could be met utilizing a 2-adsorber system (1 bed adsorbing; the other bed desorbing, cooling or idle). The toluene, present at the same 369 lbs./hr.,will have a higher partial pressure of approximately 2.20 mm of mercury; and from the adsorption isothern, in Figure 1 it can be seen that the saturation capacity will now be 358, allowing us to use an 8.75% working capacity. This reduces the carbon charge required to 4,211 lbs. of carbon with a resultant reduction in steam requirements to 1,260 lbs./hr. for the same amount of toluene. Photo I1 depicts such a system. Comparison of the two systems is summarized in Table 4 and will affect a price reduction in the system of approximately 62.5%, and a reduced steam requirement of nearly 15%. Horsepower requirements for the 25% of LEL application will be only 50 HP, and this represents a 58% reduction. CA system costs for applications of this type run about $15-20 per (2% of ab to be handled.

9 Page 5 The previous example is general. It is presented to give the prospective user of CA equipment a better feel for the importance of general process conditions, and how they affect the overall CA system design. This example of a fixed, deep bed system is typical of many applications where VQC concentrations vary between 500 and 5,000 PPM. Tray coating, dip coating, gravure coating and printing, and the majority of other CA applications fall into this range. We have seen that the higher the concentration, the more attractive the rate of return on an investment will be. It is recognized that some potential users cannot reach these preferred exhaust concentrations. For them, deep bed designs are often unattractive and represent a lengthy amortization. Spray coaters are among those which fall into this category. Spray coating applications may involve spray booths of the electrostatic, water wash, or solid media type. Typical VOC concentrations are in the 300 PPM range. Carrying on the previous example for toluene, in 20,000 SCFM of exhaust, 300 PPM represents approximately 2.5% of LEL. Another benefit of CA systems is their versatility. Applications falling in concentration range of up to 500 PPM are usually well-suited to thin bed design. Designers will take various approaches to this condition, but the end result is to separate the deep carbon bed into several horizontal sections contained within the same adsorption vessel. The cross-sectional area is now a multiple of the number of sections, and therefore the air handling capacity is increased by the same multiple. This approach will work for concentrations up to 500 PPM in most applications. At these concentrations, TZ requirements are reduced and vary between 4 and 18 inches, depending upon the application. A typical cost factor for this type system is $10.00 per SCFM (10,000 SCFM systems and larger), a 50% reduction over the deep bed design. CA versatility and its benefits do not stop here. Although not usually found in the coating industry, there are a number of very high, odor-producing VOC's which will be present in exhaust emissions at extremely low concentrations; i.e.? between 1 and 2 PPM. These organics may be found in emissions from municipal sewerage treatment plants, from the production of flavors and fragrances, from various institutional type facilities, from storage and warehouse facilities, and from bake oven exhausts utilized in a large cross section of industrial applications. Although such emissions are not normally in violation of EPA standards, they may become the Source of enforcement under nuisance regulations. Some of the obvious VOC's which may fall into this category are the

10 Page 6 acrylates, high molecular weight dopes and resins, monomers such as styrene and vinylchloride, low order emissions of various VOC's emitted from stored products which are still curing, and the limitless list of decomposition products formed in high temperature bake ovens, just to name a few. Obviously, typical deep and/or thin bed systems designed for regeneration in place and solvent recovery will not be suitable for this type application. Limitations are the excessive cost with virtually no return on the investment, the size of the equipment required to handle these applications, and of course the technical problems caused by the fact that many of these odor producing compounds fall outside of the upper boiling point and molecular weight ranges previously discussed. These characteristics which are limitations to the classically designed system often become benefits in the design of non-regenerable systems for odor removal. Photo I11 depicts a typical non-regenerable adsorption system for odor removal. Normally, it will consist simply of a blower and some type of a carbon chamber designed for easy replacement and withdrawal of the carbon, and usually equipped with duct transitions for inline mounting. The basis for design is that higher molecular weight, low vapor pressure, high boiling point type emissions will be selectively adsorbed on activated carbon. Many of them will undergo chemical reaction such as polymerization, which may enhance the utility of these non-regenerable units. CA systems specified for regeneration in place are designed around the lower carbon utility which has previously been described as working capacity. The non-regenerable systems utilize the saturation capacity, and for high molecular weight materials, this may fall in the 50 to 60% category. The result is carbon life of 4 to 6 months, and sometimes longer in those applications where the total exhaust concentration is in the 1 to 2 PPM range. At the end of the useful life of the carbon; i.e.,when it reaches saturation or begins to bleed, it is withdrawn and replaced. The spent carbon may be returned to the producer for reactivation, and 90% yields may be possible. This will help to de-emphasize the obvious major disadvantage of this system, the fact that the carbon is expended. Similar units may be utilized as sacrificial beds, or front end filters for the classically designed regenerable adsorbers, where low concentrations of VOC contaminants might otherwise make the use of CA systems impractical or technically infeasible. Some of these will be discussed later in this presentation.

11 Page 7 Another practical application of non-regenerable adsorbers involves the emergency supply of fresh air to building interiors. Included are production facilities where hazardous chemicals are being produced, and where the possibility of a hazardous chemical spill is a threat to the safety and well-being of personnel. Non-regenerable adsorbers have been used to filter fresh air supplies to administrative and laboratory facilities for the purpose of providing additional time for evacuation. Table 5 is a comparison of some of the more important factors involved in the operation of deep bed, thin bed and nonregenerable odor removal systems. The operating cost of CA systems is generally low in comparison with other types of emission "Add-On" control. One of the most important benefits to be derived is the total recovery of operating expenses based upon the value of the recovered organics. In a large number of applications, the value of the recovered solvent will also totally amortize the system, and its installation. Every application is different and must be evaluated upon its own merits. Most systems will amortize in from 1 to 10 years, a rate which although unsatisfactory or the consideration of most production oriented equipment, does offer a great advantage when considering the solution of an emission violation which could shut down the production line and/or necessitate costly modifications far exceeding the cost of an "Add-On" control device. Table 6 lists the major operating cost factors for steam, electrical power and condensing water. Utilizing this information along with design parameters already discussed, it is possible to estimate fairly closely the operating costs for a CA unit. So far, the examples represent nearly ideal conditions for solvent recovery by CA. Indeed, there are a host of factors which will affect both the capital equipment cost and the reusability or amortization rate of recovered VOC's. Some of these factors will be considered in the following paragraphs. Amortization of CA equipment will vary in relationship to a number of design factors. Many are related to application conditions. Refer to Table 7 or a summary of these. It is worthwhile to consider the effects of these factors individually. Multiple VOC's Solvent laden air streams (SLA) containing two or more VOC's

12 Page 0 will have the following effects: A. Adsorption of organic compounds having higher molecular weights will tend to displace those having lower molecular weights. Lighter compounds will tend to be separated or partitioned from the heavier and will pass through the bed at a faster rate. This will increase the mass transfer zone, and may require additional carbon bed depth, or shorter operating cycles. B. Carbon retentivity may be reduced in accord with the above, and bleed conditions may result for the lower boiling materials. C. Efficiency of any given system will tend to be lower on a multiple organic feed versus a single organic, because of the above factors. D. LEL of the mixture will vary directly as the LEL of the individual components. Safety considerations might require more or possibly less dilution air with multiple organic feeds. In the previously used examples, toluene, which is waterimmiscible and of less density, will separate in a gravity decanter, and is usually suitable for direct reuse. The organic layer where multiple solvents are involved will be a mixture of the compounds roughly paralleling their feed stream concentrations. In some mixtures, immiscible organics may have densities greater than water, and this could result in three layer decanter separations requiring multiple decantation for recovery. In all cases, the recovered organics will be a mixture and their amortization value will depend upon the following questions: A. Can the mixture be reused, as decanted? B. If not, is it possible to reconstitute the mixture for reuse by solvent additions? C. If mixture cannot be reused, is it possible to sell it to a central refiner who would fractionate it and resell it as used solvent? Many such recycle and recovery firms are now in operation, and can be located through the usual references; i.e., Yellow Pages, Thomas Register, etc.

13 Page 9 D. E. If the mixture cannot be made suitable for reuse, can it be used as a fuel for generation of thermal energy? Is the recovered mixture of high enough value to consider on site distillation equipment? Consideration of solvent availability may form even a more important factor than dollar value of the material which will continue to escalate. Water Soluble Organics This category presents possibly the greatest adverse condition for the CA system. The SLA feed stream may contain both soluble and insoluble VOC's. The factors relating to mixtures of the insoluble organics covered in the previous section will continue to apply. The heavy or liquid layer in the decanter will contain all of the watersoluble components even though some of them may be only partially water-soluble. In some cases, the aqueous layer contains sufficient organic concentration to make it worth distillation, either in a simple system designed only to strip out the water, or in a more complex system designed to also fractionate the compounds into their original components. One option or the other must usually be exercised since most local authorities will not allow the discharge of percentage quantities of organics into the municipal sewerage treatment system. Cost factors for distillation systems vary greatly. Separate inquiries should be made, on an individual basis, to obtain budgetary figures. Where the distillation costs prohibit further consideration of a CA system, it might still be worth considering CA with a vapor phase incineration system, as depicted in Figure 11. This option may be impractical if halogenated solvents are involved. However, in most cases, It offers the advantage of providing an incineration feed stream which is concentrated with respect to volatile organic compounds, as opposed to a high-volume air stream containing perhaps only 1,000 PPM plus or minus of the volatile material. In these cases, the amortization rate will be affected only by the heating value of the incinerated organic, but the overall cost of the system will be less because of the reduced cost of the ancillary equipment. Finally, even PPM contaminants of some water soluble organics will not be tolerated by municipal waste facilities. Depending

14 Page 10 upon the requirements, and the mixture to be treated, the waste can be purified using simple distillation techniques. Even less expensive extraction procedures involving liquid to air or liquid/liquid phase extraction processes may be considered. In other cases, liquid phase carbon adsorption is suitable. Each designer will have his own preferred method. Let it suffice to say, that even though ancillary equipment does represent additional cost, it will make practical the use of CA systems,meeting EPA requirements and at the same time offering the benefit of an ROI. Corrosive Organics Materials of construction will, of course, have a considerable effect upon the cost of a CA system. Corrosion is the principle factor to be considered, and must be prevented or retarded if long-term operation is expected. Many VOC's are not particularly corrosive and may be handled in carbon steel. Some are subject to hydrolysis and/or other chemical reactions, with the formation of corrosive by-products. These must be dealt with by the use of either coatings or base metals such as stainless steel, alloys or even base metal such as titanium, having a high resistance to acid attack. Corrosion in CA systems is usually evident in the areas where condensate collects. This includes all areas where steam and solvent vapors are present and at drainage points. Most CA systems, if they are built of carbon steel, will utilize some type of protective coating to isolate the activated carbon from direct contact with the interior of the adsorption vessel. This is necessary to prevent galvanic action. Considering the dissimilar metals used in vessel construction, the electrolytic solution formed by the steam condensate mixed with hydrolysis and decomposition products of the organic material and the presence of activated carbon, the origin of the galvanic action can be understood. The carbon vessel becomes the anode, and will be sacrificed, if not protected. The result is pitting and corrosion. Various types of interior coatings are used to prevent this in most systems. A base metal of sufficient resistance to withstand corrosive attack is still the best solution for the industrial applications. The cycle time and/or manner in which the system is to be utilized will also be a factor. Systems which are to be regenerated only once or twice a day will tend to be dryer than those which are cycled on an hourly basis, and may be satisfactorily designed using coatings. More

15 expensive materials of construction would be provided only in those inaccessible areas such as vapor lines and small valves, drain connections, and damper housings where the satisfactory applications of coatings would be difficult. Where corrosive compounds are utilized, and where systems are to be cycled on a frequent basis, it is well to consider the more resistant types of construction material. Reference is again made to Table 1. All hydrocarbon materials are characterized as either aliphatic or aromatic. Aromatic compounds exhibit a special type of unsaturation having to do with resonance, and the stable nucleus provided by the six carbon benzene ring configuration. Aromatics of the simpler type will resist the formation of by-products and may be used with mild steel. Those listed in the table under Aromatic are typical examples. Many of the aliphatic compounds that we deal with are the saturated alkanes or paraffins, and these do not usually react with aqueous solutions of acids, bases or oxidizing agents. Therefore, they are usually also handled in mild steel. Those listed under Aliphatic fall into this category. The major families of corrosive hydrocarbons are the halogenated ketones or aldehydes, and the esters. Esters are the product or reaction between an acid and an alcohol. Such reactions are reversible, and the hydrolysis of an ester will yield the acid and alcohol from which they were produced. Most esters require the use of stainless steel and involve the formation of acetic acid. The halogenated compounds represent a saturated hydrocarbon in which a hydrogen atom is replaced by a halide. The halogen atom is easily displaced from its associated carbon atom, and the formation of other compounds - often acidic - can be expected. Many halogenated materials are stabilized, and carbon steel with coatings will be sufficient. Others will require less ferritic metals of the various stainless categories. Even Monel, Hastelloy, or Titanium are sometimes used in connection with halogenated compounds. Ketones and aldehydes are both characterized by the presence of a carbonyl group. This carbon/oxygen group is subject to chemical reaction. Let it suffice to say that a number of corrosive by-products may be formed, and stainless steel construction materials are required. Cost differentials

16 Page 12 are caused more by labor factors in construction than in material costs. No good rule of thumb applies for evaluating the amount of cost increase. Reactive Organics The ketones also form the major category of "reactive organics." Again, it is the presence of the carbonyl group, and its ability to undergo chemical reaction, which causes the problem. Often, these reactions are exothermic, and the adsorption of "reactive organics" will require additional peripheral hardware, and modified control sequences. These changes usually involve relatively minor cost increase. Temperature Temperature and relative humidity will also have to be considered. The adsorption efficiency is directly related to temperature of the solvent laden air being processed. At temperatures in excess of 1000 F., both adsorption efficiency and carbon life will be affected. Front end, solvent laden air coolers will be required where air temperatures are in excess of 1000 F. for prolonged periods. Usually provided are heat exchangers of the water cooled, extended finned tube type. See also the section on Contaminants. Humidity Relative humidities in excess of 50% may have an effect on the overall working capacity of a CA system. Each application must be dealt with individually, but it is fair to say that applications with relative humidity approaching 100% will require additional peripheral equipn,ent in order to create a satisfactory degree of unsaturation with respect to water or moisture content. The cost factor will be about $1/CEM. Contaminants Contaminants may be broken down into three categories. They are : A. Particulates

17 Page 13 B. Entrained liquids C. High boilers Almost all industrial applications will require solid media type filtration systems for the removal of airborne dust, lint, and general dirt falling in the particle size down to 3 to 5 microns. Solid media filters of the type generally available made of cloth or fiberglass are usually satisfactory for this application. Automatically operated filters of the moving media type, controlled by pressure drop across the filter material, usually offer a satisfactory solution for ordinary particulate contamination. Filters and coolers are usually provided as packaged units and will be assessed at approximately $l/cfm. In other applications, where fine particles of resin or other solids used in the coating process have diameters of one micron or less, special filtration systems will be required. Electrostatic precipitators, for instance, may find application in this area. Entrained liquid is also a form of contaminant. Obviously, if the liquid is water, then it should be removed for reasons discussed under Humidity; and, if it is volatile organic carried over in the liquid form from the process, it. should be removed in order to prevent the high heats of adsorption associated with liquid droplets. There are a number of mist eliminators available. Fi,me 111 depicts such an inline mist eliminator. High boilers have been previously discussed and listed in Table 2. These are VOC's having boiling points in excess of 500 F., such as resins, plasticizers, and/or compounds which react chemically on the carbon to form solid or polymerization products which will not be removed during steam desorption. In conclusion, this paper is a simplistic overview of the factors affecting the design of typical CA units. Its purpose is to familiarize the plant engineer with these factors and to help him evaluate the process parameters having the greatest effect on system design and operation. These will determine the benefits and limitations of the CA unit.

18 TABLE I PHYSICAL PROPERTIES OF SOME V.0.C'S SUITABLE FOR CARBON ADSORPTION ALIPHATIC HEPTANE HEXANE PENTANE NAPTHA MINERAL SPIRITS STODDARD SOLVENT 8. P. 'C -- (OF) 98.4 (209) 68.7 (156) 36.1 (97) (288) (381) (379) MW SOLUBILITY (H20) FLAMMABLE * *L.E.L.(% VOL) I < AROMATIC BENZENE 80.1 (176) 78.1 I.40 TOLUENE XYLENE (231) (292) 92. I I.OO ESTER BUTYL ACETATE ETHYL ACETATE (259) ) I HALOGENATED CARBON TETRACHLORIDE ) N. F. ETHYLENE DICHLORIDE 99.0 (210) *T SOLUBLE = <I% WT. * * N.F. = N FLAMMABLE

19 TABLE I (CONTINUED) B. P. SOLUBILITY (H20) FLAMMABLE L.E.L.(X VOL) HALOGENATED (CONTINUED) '5 rf) METHYLENE CHLORIDE 40.2 (104) 84.9 N. F. PERCHLORETHYLENE (250) N F. TRICHLORETHYLENE ) N. F. TRICHLORETHANE 74.0 (165) N.F. FLUORINATED (75-199) N.F. K ET0 N ES ACETONE DIACETONE ALCOHOL 56.2 ( (293) METHYL ETHYL KETONE 79.0 (174) METHYL ISOBUTYL KETONE ( I.20 ALCOHOLS BUTYL ALCOHOL (241) 74. I 1.40 ETHAL 74.0 (165) PROPYL ALCOHOL 96.0 (205)

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21 TABLE 3 SOME APPROXIMATE DESIGN PARAMETERS (FIXED, DEEP, HORIZONTAL BEDS) V.O.C. B.P. LIMITS - 24'-14SoC WORKING CAPACITY-5-20% V.O.C. MW EFFICIENCY REQUIRED- 95% DESIGN VELOCITY- 100 FTIMIN MAX. *STEAM AT 15 PSlG-0.3 LB/LB CARBON **CONDENSER WATER-12 GPM / 100 LE STEAM DESIGN L.E.L.'S % HORSEPOWER-6 HP/1000 CFM CONCENTRATION RANGE PPM PRESSURE DROP-0.5 IN / IN OF CARBON DEPTH BED DEPTH LIMITATION- 4 FT BED DEPTH -18 INCHES MIN. CARBON DENSITY LB/FT3 COST 2 $20/CFM *TOTAL STEAM USEAGE MAY BE SIGNIFICANTLY REDUCED IN SOME APPLICATIONS BY THE USE OF "ANALYZER CONTROL" OPTIONS. f **WATER USEAGE WILL BE SIGNIFICANTLY REDUCED IN A RECYCLING, CIRCULATING SYSTEM.

22 TABLE 4 DESIGN CONSIDERATIONS VS TOTAL THRUPUT. (FIXED RECOVERY RATE) SOLVENT RECOVERY RATE (LB/HR) TOTAL THRUPUT (SCFM) TOLUENE (PARTIAL PRESS. MM HG) CARBON WORKING CAPACITY LB. CARBON /VESSEL CARBON DEPTH. ADSORB VESSELS TOTAL CARBON (LBS) HORSEPOWER *STEAM (LBIHRI *WATER (GPM) % REDUCTION 10% L.E.L. 25% L.E.L. FOR 25% L.E.L. TOLUENE , % IN 3 14,700 I TOLUENE % IN I5 I % 14.3% - 33 % 42.8% 58 x 14.5% 14.6% *USED ONLY DURING DESORPTION. DESORPTION MAY T BE CONTINUOUS.

23 . TABLE 5 A COMPARISON DEEP BED VS THIN BED VS ODOR REMOVAL DESIGN VELOCITY (FT/ MINI PI00 >IO0 >IO0 CARBON BED DEPTH (INCHES) UP TO 18 CONCENTRATION RANGE UP TO 500 UP TO I PPM IPPM) TYPICAL AIR HANDLING CAPACITY (UNITS/ FIXED VESSEL) I UP TO SCFM MODULES TYPICAL TYPICAL STEAM USEAGE AT 0.30 UP TO 0.5 NE 15 PSlG ( LB / LB CARBON 1 TYPICAL HORSEPOWER (HP/1000 SCFM) TYPICAL CARBON LIFE (YRS) IO MONTHS TYPICAL COST ( $ / SCFM 1 $ 20 $10 $5

24 TABLE 6 APPROXIMATE COST OF REQUIRED UTILITIES STEAM - GENERATED AT IS PSI0 ELECTRICAL POWER $ LB $0.06/ KW-HR WATER $0.04/ 1000 GAL

25 . TABLE 7 FACTORS AFFECTING CAPITAL COST AND AMORTIZATION RATE EFFECTS CAPITAL COST AMORTIZATION RATE [VALUE OF RECOVERED ORGANIC) ADDITIONAL ANCILLARY EQUIPMENT MULTIPLE V.O.C.'S X X MAYBE WATER SOLUBLE ORGANICS X MAYBE CORROSIVE ORGANICS X REACTIVE ORGANICS X TEMPERATURE OF S.L.A. X HUMIDITY OF S.L.A. X CONTAMINANTS PARTICULATES X HIGH BOILERS X ENTRAINED LIQUIDS X

26 QUESTIONS AFFECTING AMORTIZATION (MULTIPLE V.O.C.'S) 1. CAN THE RECOVERED MIXTURE BE REUSED AS DECANTED? 2. IF T, CAN IT BE RECONSTITUTED? 3. CAN IT BE SOLD TO SOMEONE ELSE? 4. IS IT SUITABLE FOR USE AS A FUEL? 5. DOES IT HAVE SUFFICIENT VALUE TO CONSIDER DISTILLATION?

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