Methylene Chloride from Paint Stripping Applications

Transcription

1 Vapor Recovery and Recycling Methylene Chloride from Paint Stripping Applications of Paul E. Scheihing Office of lndustriol Technologies U.S. Department of hergy i'/ashington. D. C. Introduction The predominant factors affecting the costs of control technologies are the volume flow of the methylene chlorlde-laden alrstream. and more lmportantly. the concentration of methylene chloride. Annual vapor emlsslon control costs have been projected for solvent-laden airflows ranging from 1,000 cublc feet per minute (cfml to cfm. wlth alrborne concentratlons of methylene chloride from 100 parts per mllllon by volume (ppmv) to ppmv. The results of thls study showed that applications above 500 ppmv would allow control costs to be kept under per ton of methylene chlorlde controlled. The competitlve technologles all used adsorption as a method to remove methylene chloride vapor from the solvent-laden airstream and concentrate It: however, thelr methods to regenerate the adsorptlon bed differed. The three technologies evaluated were: Adsorption with steam regeneration. Adsorption with Inert gas regeneratlon that uses a reverse Brayton cycle condensarlon system. and Adsorption with "decoupled" Inert gas reqeneratlon that uses a reverse Brayton cycle condensatlon svstem. A "decoupled" inert gas regeneratlon system can be physically separated from the adsorptlon side of the vapor recovery equlpment. Slnce the regeneratlon (desorptlon) equipment Is moblle. It can be transported from one adsorptlon concentrator to another. Therefore. the cost of the regeneration equlpment Is shared among many adsorption control devices and locatlons. Other technologles that are technically feaslble. such as the destruction of methylene chlorlde by Inclneratlon. direct condensatlon of the vapors from the solvent-laden airstream (using a reverse Ranklne or Brayton cycle). and off-slte reactivation of adsorbents were screened ln the prelimlnary stages of the study and not found cost.competltive. under the previously discussed condltions. Competitive Technologies Adsorption with Steam Regeneration Flgure 1 shows a typical steam-regenerated adsorption system that could be applled to control methylene chloride emisstons. Solvent vapors are collected on the adsorbent (assumed to be actlvated carbon In thls studv) and periodlcallv the adsorbent is regenerated with steam. The equlpmen1 consists of a steam boiler. at least two

2 .C SCHEIkING Figure 1.4leam regenarallon system with decantlng solvent and water SeDaralion. separate adsorbers (one adsorber 1s adsorbing while the other is being regenerated). a blower to circulate the solvent-laden airflow through the adsorbers. condenser. separator. decanting system to separate the steam condensate from the recovered solvents. and an air stripper to clean the steam condensate. Slnce methylene chlorlde Is slightly miscible with water. the decantlng process does not remove it completely: however. air stripping takes the remalnlng methylene chloride from the condensate. Then the cleaned condensate can be returned to the boiler or dlscharged to the environment. The air dlscharged from the stripper 1s returned to the adsorbers to prevent dlscharge of methylene chloride-laden emissions. Adsorption with "Coupled" Brayton Cycle Inert Gus Regeneration Flgure 2 shows an inert Initrogen) gas regenerated adsorption system that uses a reverse Bravton cycle to condense vapors. Solvent vapors are collected on the adsorptlon bed In the same manner as the steam-regenerated system: the difference lies In the length of the adsorptlon and reqeneralion cycle of the adsorbers and in the use of an inert <as In place ofsteam. Step-by-step. ihe iner: 2x5 re&?enerauon process: Strips the solvents from the adsorber wlth hot [above 300'F) Inert gas. Condenses the solvent vapors from the solvent-laden Inert gas stream by chllllng to extremely low temperatures (- 100'Fl wlth a reverse Brayton cycle. and Returns the essentlally solvent-free hot inert gas to the adsorber lor further regeneration. Adsorption with "Decoupled" Bra yfon Cycle Gas Regeneration Thls method physically separates Inert gas regeneratlon system from the adsorbers. Therefore. the equipment components are essentlallv the same as those shown In Figure 2. but the adsorbers and the solvent-laden air blower are sratloned at the emission source and the inert gas regeneration system is mobile and can be "decoupled" from the adsorbers (see Flg. 3). In this way. the reverse Brayton cycle inert gas regenera- Lion system can serve many adsorbers at qeographlcallv different industrial sites. The reverse Bravton cycle produces low <as >Iream temperatures bv removlne heat with a low 146

3 " c musi I, -, ', :eavcmo iilsx in Pain! Sirinping B 3 Y t PL MU Flgurs?.--'Coupled' Brayton cycle Inert gas regeneratlon system (courtesy 01 Nucon Internatlonal, InC.). Moblle Regeneratlon Truck Uquld Solvent L I From Process'A Statlonary Concentrator Bed iegsneratlng bed Flgure J.--'Decoupled' Brayton cycle her( gas regeneratlon system. temperature chiller heat exchanger (heat regeneration): extracting work enera from the gas Streamwith a turbo-expander to cool it: reqenerat- Ins heat from the cold qas scream bv passlnq ic on theother sideofthe low temperature chlller again: ihen compressing. and thus heating. the gas stream with a turbo-compressor that Is driven bv ilie turbo-c.xpander and a motor-driven vacuum 147

4 - E. SCHElHlNG compressor. The gas stream contatnlng solvent ;'apors 1s cooled signtflcantlv enough to condense a majority of the vapors. Also. it Is heated bv compression to a temperature level (above 300'F) satisfactory for Inert gas adsorption bed stripping irlthout supplemental heaung. In the case of methylene chlorlde. the inert gas stream must be cooled to -150'F to remove a majorlty (99 percent) of the very low bolllng polnt solvent. Since the reverse Brayton cycle can reach a low condensation temperature In a single stage of turbo compression and expansion. it is a good method to recover methylene chlorlde. Critical components of this system are two separate adsorbers with a solvent-laden alrblower. and the reverse Brayton cycle regeneration system. which consists of a dehumldffler. a motordriven vacuum compressor, a turbo compressor-expander. a low temperature chiller lregeneratlve heat exchanger). two separators. and a pump for circulating the recovered llquld solvent. Vapor Recovery Control Cost Estimations The primary Influences on the cost of the three vapor recovery technologles are the volume flow of the solvent-laden airstream and the concentration of the methylene chloride within It. For purposes of evaluation. it was assumed that pant strlpplng appllcatlons produce airstreams laden with methylene chlorlde solvent concentrations under ppmv and the volume flow ranged between and cfm. Many of the paint stripping applications have concentratlons under 100 ppmv. However. for appllcatlons wtth very low concentratlons (under 100 ppmvl. the cost to control these emissions by recovery is exceedingly high-greater than S per ton of solvent controlled. Therefore, vapor recovery control costs were analyzed at concentratlons of 100 ppmv. 1,000 ppmv. and ppmv. Table 1 llsts kev economic factors In the overall cost of vapor recovery control. Table 1.-Economic factors assumed to project control cost for vapor recovery of methylene chloride. Methylene chloride recovery value Solvent-laden airstream time Steam cost Electricity cost Type of adsorbent Cost 01 adsorbent Cost 01 adsoroer structure Capital depreciation period Interest rate Equipment installation laclor per ib. (excludes!axes1 (8 hours per day. 5 days per week. 50 weeks per year, hoursiyear) Der 1,000 Ibs. steam $0.040 per kw-hr. Activated carbon $2.00 oer Ib. S1 1.OO Der lb. (steam regen. maae of Hastellovl S3.00 Der Ib. (both Bravton in. en regen. systems maae stainless steel) 10 years 10 oercent S20 per CFM 01 solvent-laden volume airtlow Table 2 summarizes the control cost results of the study. As you can see, concentratlons above 500 ppmv are generally necessary to achieve control costs below $5.000 per ton. Figure 4 summarlzes the regions of applicability for the three vapor recoverytechnologles evaluated. The reglons of applicability were made by assuming that control costs need to be under S5.000 per ton of methylene chloride controlled and by comparlne the relatlve costs of the three technologies. Table Z.-Control cost tor paint stripping with methylene chloride (dollars per year per ton of solvent). COSTS OF VAPOR RECOVERY CONTROL TECHNOLOGIES STEAM BRAYTON INERT BRAYTON INERT FLOW (CFW CONC. IPPMVY REGENERATION COUPLED REGEN. DECOUPLEO REGEN t ',000 : 00 S $38,800 $17,000 ' : !, ' ',000 :, '0.000 ' : 000 l ', ' ' , ubic lee! oer minute "%I5 oer mlllmn Dy volume 148

5 ' \ \ Reaeneration 1 I'ouoiea Bravlon '>en Reqeneralion "Decoupled" Brayton Inert Regeneration L I I I I I I Solvent Concentration 1PPMVl 'Regions of adpiicability are aefined by control costs at under S5 000 Der Ion of solvent and the competitiveness 01 lne technologies 10 each other Figure 4.--Reglons of applicability for methylene chloride vapor recovety. Future Development Needs The reduction of vapor recovery control costs will be impacted by the followng critical factors and developments: 9 Production of paint strippins equipment ihat includes solvent recovery control equipment. That Is. every step must be iaken to get the solvent-laden airflow down and solvent-laden air concentration up. Of course. the equipment must be deslgned to protect the worker from unsafe levels of solvent vapors. Development of a solvent recovery market infrastructure that will sewice many industrial users of solvents. such as the decoupled regeneration approach. Development of low-cost continuous solvent-laden air concentrators (that is rotating wheel adsorber beds1 to Increase the concentratlon of the solvent-laden alr downstream of the process but upstream of the fked bed concentrators. This will allow storage of more solvent on!he fixed bed, which therefore. reduces the fied bed cost. The ability to fabricate adsorbers out of low-cost materials. Conclusions The recovery of methylene chloride from paint stripping applications looks promising U the concentratlon level of the vapor stream from the process exceeds 500 ppmv. Paint stripping equlpment development should be directed at maxlmizing concentration levels. keeping the safety of the worker in mind.

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9 Solvent Related Tech Transfer Solvent Recycling 3 So/vent RecMing Con&"es (proceedings availab/e) Numerous technical papers (see Paul Scheihing) Soluentless processes

10 Solvent MMed R & D Brayion Solvent Recovery Heat Pump Large system - SM/Nucon Small system - Nucon/SCE/Dow/EPRI/S~~D Solventless Fmsesses Multiple (within OIT Industrial Waste Reduction Program) (see Bruce Cranford s handout)

11 So/vent Related Twhno/ogy/AppIhtion Assessment VOC Controt Cost Assessment Mode/ waste stream evaluation studies (21 R&D Opportunity Assessments (2)

12 CHOICES IN SOLVING A VOLATILE ORGANIC COMPOUND (VOC) EMISSION PROBLEM Switch to Environmentally Benign Solvent Change Process Develop Solvent Free Process Develop Reduced VOC * Emitting Process * Control VOC

13 VOC Control Cost Elements capital Cost Energy and Other Operating Cost Maintenance Cost Recowred Solvent Disposal Cost Other Waste Tmatment (combustion products, waste water streams1 Regulation compllame cost/ Fees

14 RECYCLING OF SOLVENTS IS ENERGY EFFICIENT No Control BTU/Lb Solvent Solvent Solvent Destruction e Control BTUlLb Recovery and Recycle Control 4000 BTU/Lb Control VOC by Recover and Recycle Solvent

15 GLOBAL ENERGY REQUIREMENTS IN CONTROLLING ~- EMISSIONS IS M!NIMIZED WiTH RECYCLING Global Solvent Energy Requirement No Control Control by Control by Control by Control by Destruction Destruction, Recover Heat Recovery, Recycle Solvent Recovery, Burn Solvent

16 CHOOSING SOLVENT RECOVERY AND RECYCLING IS ECONOMICALLY OR REGULATORY DRIVEN Solvent Use (TonsNear) I Driven by Economics (Recovers Valuable Solvents) Y m Driven by Regulation (Least Cost Approach) t Solvent Price (Wb)

17 JUSTIFYING SOLVENT RECYCLING IS STRONGLY EFFECTED BY SOLVENT PRICE Total Annual Cost Using Solvents ($ILb) 2.50 Destructive Control Cost 2.00 No Control Cost 1.50 Recycling Control Cost 1.oo Total Solvent Price (Market Plus Excise Tax) ($/Lb)

18 SOLVENT RECYCLING CONTROL LESSENS THE IMPACT OF HIGHER ENERGY PRICE Cost of Using Solvent w 0 Destructive Control No Control Recycle Control Energy Price

19 SOLVENT RECYCLING GIVES INDUSTRY AN OPTION N Y Can Be the Least Cost Approach to Complying with Environmental Regulation Can Avoid Creating Another Environmental Problem in Attempting to Solve a VOC Problem Can Cushion the Long Term Cost of Using Solvents

20 DOE Solwent Recycling Applicaths Status SM Gmenville, SC Plant Brayton Solvent Recouwy Pmjk?ct Nucon Decoupled Solvent Recovery Project Pfirer Pharmacuetical Brayton Solvent Recowry System VOC Control Cost Assessment Model DOE Weapons Plant Application

21 ~ ~~ ~ ~ ~ Advanced L atge Brayton Solwent Recovery System * For 3M t3reenvillew SC Plant * Operational Spring, 92 * Brayton inett gas regeneration system/ carbon adsorption * Handles 8000 SCFM VOC steam * $1.6 Million Capital Cost

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23 Mobile Brayton regeneration 5? truck k I I 10 r. Not in use while truck is regenerating bed

24 ?fbr Pharmacuetical Brayton SOIvent Recovllery mtem * Installed at Pfiw PharmwetW plant in Puerto R b * Operating since June, 1991 * Tim 1500 SCFM Brayton direct conchsation systems * Nucon is vendor * No DOE assistance

25 DOE Mkapons Plant Application * possib/e appmcation of decwpled Brayton system * For soil remediation application * Some solvents are habgenated