SOLVENT EMISSION CONTROL

Transcription

1 ACTVATED CARBON FBER ADSORPTON -8 SYSTEMS FOR PANT SPRAYBOOTH SOLVENT EMSSON CONTROL Z7 Robert E. Kenson Met-Pro Corporation Harleysville, PA Abstract The control of solvent emissions from paint spraybooths has been a challenging environmental management problem. Technical and cost problems have inhibited the installation of addon controls. Limitations of new paints and painting technologies, however, have resulted in the need for addon controls to meet more stringent enviromental regulations. More costeffective methods for control of these large air volume/low solvent concentration emissions have been developed. Combination of activated carbon fiber adsorption/ hot air desorption systems with catalytic or thermal incineration systems reduces significantly the operating costs of addon controls for paint spraybooths by concentrating the emissions before incineraation. Since operating costs are more significant over a five to fifteen year time period than installed equipment costs, the use of activated carbon fiber adsorption and hot air desorption makes in-cineration a more costeffective solvent emission control for paint spraybooths than direct incineration. Examples of actual installation performance and economics show the technical and economic effectiveness of activated carbon fiber adsorption systems THE CONTROL OF PANT SPRAYBOOTH SOLVENT EMSSONS is a technically and economically challenging problem. The technical challenge includes the following factors : 1. Removal of Paint Overspray Particles in the Booth Exhaust. 2. Capture and/or Destruction of the Dilute Solvent Emissions. 3. Designing for Mixed Solvents of Different Chemical Structure. 4. Scale Up to Very Large Air Flows 5. Solvent Purification or Disposal To add to these complications, there are some economic challenges as well. These include : 1. High Capital Costs of Control Systems 2. High Disposal Costs for Control Systems 3. High Utility Costs for Control Systems 4. High Replacement Costs for Prefilters 5. High Replacement Cost for Adsorption Media A VOC control technology has been developed which is well suited to control VOC emissions from paint spray booths. t is based on activated carbon fiber adsorbent, which preconcentrates the solvent adsorption. The operating costs of the final solvent emission control svstem are thereby reduced and

2 ~ the annual costs per ton of VOC emission controlled are substantially less than conventional technologies for solvent emission control on paint spray booths in most cases. Rotary carbon fiber concentration followed by incineration has been used for over ten years in the control of paint spraybooth solvent emissions in overseas installations and some installations in the United States have been in operation for over three years. The rotary carbon apparatus serves as a concentrator using hot air, of about one tenth the volume of the paint booth exhaust, to desorb the carbon and sending this concentrated hot air/desorbed solvent stream to the final control device. n most cases, this is a thermal or catalytic incinerator but in cases where the solvent disposal costs are incurred and the solvent has value for recycle, a solvent recovery system can be applied. When incineration is used operating costs are low because no solvent disposal costs are incurred and the heat valve of the solvent combustion can be recovered internal to the system to reduce incinerator fuel usage. PROCESS DETALS The activated carbon fiber based adsorption system is specifically engineered for efficient control of low concentration, high volume hydrocarbon fume emissions. The system achieves a range of 90 to 95 percent efficiency, with concentration. n brief, the control process involves preconditioning to remove particulates and high boiling hydocarbons, followed by three continuous process stages that operate automatically and independently of one another: ADSORPTON OF LOW CONCEN- TRATON HYDROCARBON SOLVENTS FROM LARGE VOLUME CARRER GAS STREAM - The large volume stream is conveyed through the unique honeycomb structure of the activated carbon fiber adsorbent material (paper). There the hydrocarbon solvents are captured from the process exhaust. The large volume stream is safely exhausted to atmosphere with over 95% of the hydrocarbon emissions removed. CONCENTRATON OF HYDROCARBOW SOLVENTS - The hydrocarbon solvents previously adsorbed are then desorbed by hot air of a much lower volume than the original carrier gas. Since the mass of the solvent removed is essentially the same as the initial amount into the system, the concentration of removed solvent in the desorption air is substantially higher. NCNERATON OF HYDROCARBON SOLVENT CONTAMNANTS - The solvent laden hot desorption air is then passed into a catalytic or thermal incinerator where oxidation of hydrocarbon contaminants occurs. The safe products of combustion are then vented into the atmosphere with over 95% of the hydrocarbon contaminants removed. The system is fully automatic and operates continuously without any cycling. ts carbon fiber adsorbent material possesses high adsorption capacity that enables it to capture hydocarbon solvents present in low concentrations. Paint spray booths are one such type of emission source. 232

3 The basic apparatus is designed to concentrate dilute solvent emission sources before final treatment by incineration or carbon adsorption. The system concentrates the dilute solvent emissions by a factor of 5 to 15. This substantially lowers both the capital and operating cost of the final emission control system. The key component of the system is the rotor. t consists of a honeycomb structure element made of activated carbon fiber paper in a corrugated form. The rotor is cylindrical and Figures 1 and 2 show a schematic representation of one for large size systems. The rotor turns continuously at a slow speed and is divided into two sectors; one for adsorption and one for desorption. The process exhaust to be treated and the desorbing hot air flow in opposite directions along the tubular paths through the honeycomb. The hydrocarbons in the process exhaust are adsorbed on the activated carbon fiber in the adsorption sector of the rotor. The carbon fiber is simultaneously regenerated in the desorption sector of the rotor. This is done with hot air of only 1/5 to 1/15 volume of the original exhaust stream. This hot air stream which now contains 5 to 15 times the concentration of solvents is conveyed to the final control devise. Pressure diffarentials are maintained between the inlets and outlets of each section. This insures that any leakage which might occur will not result in reduced efficiency. Figure 3 show how an activated carbon fiber adsorber/concentrator is coupled to a catalytic incinerator. The dilute exhaust stream (A) is introduced into the KPR by the main blower (1) and the stream is prefiltered (2) to remove particulates. The dilute stream is passed through the adsorption sector honeycomb of activated carbon fiber (3) where adsorption of the hydrocarbons occurs. The cleaned exhaust (B) is emitted to atmosphere. The desorption sector is purged by outside air (C) introduced to the system by the desorption blower and heated by an air-to-air heat exchanger (11). A bypass (10) is provided to control desorber air temperature. The desorption honeycomb and exhausts as a hot air stream containing the concentrated hydrocarbons (E). The solvent laden air is introduced into the catalytic incinerator (7) by a second blower (5) and preheated with incinerator exhaust gas by another air-to-air heat exchanger (6). The solvent laden air passes through a preheat burner (8) and passes over the catalyst (9) where combustion of the hydrocarbons occurs. After passing through heat exchangers (6) and (11) to extract heat generated by the hydrocarbon combustion, the cleaned stream exhausts to atmosphere (F). APPLCATONS Activated carbon fiber based adsorber/concentrator control have been in operation 233

4 ~ for over 10 years in some cases. Over thirty concentrating systems have been applied to VOC emission control, and most of these applications are for paint spraybooths. n Table 1, the brealcdown of processes to which this technology has been applied is presented. Almost half are in the automotive industry, but a wide variety of processes are represented. They range, from can coating to ship module painting in size of items to which a paint or coating is applied. Air flows range 51,000 to 500,000 SCFM in total volume to be treated. The technology can also be applied to a number of industries not shown in Table 1. Table 2 identifies some specific industries where activated carbon fiber adsorption/concentration technology could be employed for VOC emission control in future applications. The activated carbon fiber based adsorption/hot air desorption system has been installed in three U.S. auto parts plants to control emissions from paint finishing operations. The second system was purchased by the same customer as the first system. Under a turnkey contract, the first system was started up and acceptance tested by within ten months of order. Space at ground level close to the paint booth was not available, and it was impossible to use a conventional crane. Therefore, the first KPR-C System was lifted into place, component by component, by helicopter. Figure 4 shows the system installed at roof top level. Table 3 summarizes acceptance test results for both the first two auto industry KPR systems. A recent application has been an auto parts plant where the cutomer already had installed an 80,000 CFM capacity regenerative heat exchanged thermal incinerator to control automatic paint line spraybooth and oven emissions. Although this system met state air emission standards, operating costs exceed $l,000,000jyear. when time came to control emissions from the manual paint lines, the customer decided that an activated carbon fiber based adsorber/concentrator system would be a better choice for paint solvent emission control. By concentrating the 100,000 CFM paint booth and oven emissions to 10,000 CFM using the activated carbon fiber rotor, the concentrated solvent/hot air stream could be sent to the present regenerative thermal incinerator. This combined concept, which could be applied in almost any case where there presently is an incinerator large enough onsite, results in no net increase in incinerator fuel consumption yet can double the amount of paintbooth and oven emissions handled by the already existing incinerator. Paint solvent emission control systems have also been applied in the aerospace industry. For example, there were three aircraft parts painting facilities which needed to be in compliance at the end of Each was large in air flow but low in solvent concentration, which is typical of large aerospace painting operations. After evaluation of alternative emission controls, the activated carbon fiber 234

5 concentrator/catalytic incinerator system was chosen for these similar applications. The full project schedules for two applications included less than six months from initial engineering phase start to system installation completion. The projects were initiated by release of a preliminary engineering contract by the Aerospace firms. These contracts allowed the customer time to obtain corporate funding for the projects while simultaneously preparing for system design and installation in advance of release of an equipment purchase order. Once the preliminary engineering phase was completed and the equipment purchase order received detailed system fabrication/installation drawings and order of long lead materials began at once. Once completed, all components were shipped directly to the jobsite for contractor installation on elevated platforms provided by the customer. Ground level space was at a premium, so both systems were installed at essentially roof level on a platform supported by steel columns. The small size and light weight of the activated carbon systems facilitated this. For example, the 105,000 SCFM capacity system occupied a space 50' wide by 100' long and weighed less than 65 tons. Figure 5 is a plan view of this KPR system installation. Onsite installation took approximately one month, and each of the two systems was installed at the same time. Table 4 shows the acceptance test results which were 90-95% emission control efficiency in these cases plus a third aerospace industry application where an activated carbon fiber adsorber/concentrator system was installed soon after these first two systems. CONCLUSONS n summary, activated carbon technology has been successfully used to control VOC emissions from paint spraybooths, in some cases for over 10 years. There are over 30 installed worldwide including the United States. The system can be used to dispose of the paint solvents without generating any wastes, or used to recover valuable solvents for reuse. t is capital cost-competitive with other VOC emission control technologies on an installed basis and is usually the most cost-effective when compared to the other technologies on a 5 to 15 year operating life cycle. 235

6 Table 1 - Applications of KPR Technology for Painting and Coating Process VOC Emission Control Automobile Painting Automobile Parts Painting Can Coating Tractor/Bulldozer Painting Agricultural Equipment Painting Appliance Painting Railway Car Painting Ship Module Painting Aircraft Parts Painting Steel Coil Coating TOTAL (35) Table 2 - ndustries Where KPR Technology Could Be Effectively Applied Metal and Wood Furniture Painting Architectural and Structural Steel Painting Railroad Locomotive Painting Aircraft Painting Boat Painting Manufacturing Plant Air Vents Computer Components Painting Truck and Bus Painting Bicycle and Motorcycle Painting Architectural Aluminum Painting Electric Transformer Painting Plastic and Rubber Products Painting

7 TABLE 3 - Summary Of Results From KPR System Operation n Automotive Paint Spray Booth Applications Applications Auto Parts Painting Auto Parts Painting Air Flow Concentratina Ratio Removal Effcy 15,050 SCFM 5.6:l 95% 11,850 SCFM % TABLE 4 - Summary of Results From KPR System Operation n Aerospace Paint Spray Booth Applications Application Air Flow, Concentratina Ratio Removal Effw. Aircraft Parts Painting 31,940 SCFM 6.8:l Aircraft Parts Painting 56,140 SCFM 9.1:1 Aircraft Parts Painting 86,260 SCFM 10.8:l 95% 90% 95% AASM 91.REK 237

8 Figure 1 KPR CYLNDER TYPE ROTOR ADSORBNG Solvent Laden Air (Typ.) 238

9 Figure 2 KPR CYLNDER TYPE ROTOR DESORBNG Regenerating Air n \ / V Solvent Laden Regenerating Air u Solvent Laden Regenerating Air Honeycomb (Typ.) 239

10 Figure 3 FLOW DAGRAM OF KPR APPARATUS

11 l i j L Figure KPR NSTALLATON AT AN AEROSPACE PLANT N TEXAS -- / \ / \ / \ ~ ~ --- m HEAT EXCHANGER HEATEXCHAN6ER XHAUSlSTAcK J-

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