. Vapor Recovery and Recycling Methylene Chloride from Paint Stripping Applications

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 lm- por tan t ly . the concent ra t ion 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 30.000 cfm. wlth alrborne concentratlons of methylene chloride from 100 parts per mllllon by volume (ppmv) to 3.000 ppmv. The results of thls study showed that applications above 500 ppmv would allow control costs to be kept under 55.000 per ton of methylene chlorlde controlled.

The competitlve technologles all used adsorp- tion as a method to remove methylene chloride vapor from the solvent-laden airstream and con- centrate 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.

of

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 con- centrator to another. Therefore. the cost of the regeneration equlpment Is shared among many adsorption control devices and locatlons.

Other technologles tha t a r e 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 ad- sorption system that could be applled to control methylene chloride emisstons. Solvent vapors are collected on the adsorbent (assumed to be ac- tlvated carbon In thls studv) and periodlcallv the adsorbent is regenerated with steam. The equlp- men1 consists of a steam boiler. a t least two

.C SCHEIkING

Figure 1 . 4 l e a m 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 sys- tem to separate the steam condensate from the recovered solvents. and a n 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 conden- sate. 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 col- lected on the adsorptlon bed In the same manner a s the steam-regenerated system: the difference lies In the length of the adsorptlon and reqenera- lion 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. There- fore. 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 a n d can be "decoupled" from the adsorbers (see Flg. 3 ) . In this way. the reverse Brayton cycle inert gas regenera- Lion system c a n serve many adsorbers a t qeographlcallv different industrial sites.

The reverse Bravton cycle produces low <as >Iream temperatures bv removlne heat with a low

146

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Flgurs ?.--'Coupled' Brayton cycle Inert gas regeneratlon system (courtesy 01 Nucon Internatlonal, InC.).

Moblle Regeneratlon Truck

Uquld Solvent L I From Process'A

Statlonary iegsneratlng bed Concentrator

Bed

Flgure J.--'Decoupled' Brayton cycle h e r ( gas regeneratlon system.

t e m p e r a t u r e chi l ler h e a t exchanger ( h e a t theother sideofthe low temperature chlller again: regeneration): extracting work e n e r a from the gas ihen compressing. and thus heating. the gas Streamwith a turbo-expander to cool i t : reqenerat- stream with a turbo-compressor that Is driven bv Ins heat from the cold qas scream bv passlnq i c on ilie turbo-c.xpander and a motor-driven vacuum

147

- E. SCHElHlNG

compressor. The gas stream contatnlng solvent ;'apors 1s cooled signtflcantlv enough to condense a maJority of the vapors. Also. i t 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 sys- tem. which consists of a dehumldffler. a motor- dr iven v a c u u m 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 p a n t strlpplng appllcatlons produce airs t reams laden with methylene chlorlde solvent concentrations under 3.000 ppmv and the volume flow ranged between 1.000 and 50.000 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 con- trol these emissions by recovery is exceedingly high-greater than S10.000 per ton of solvent controlled. Therefore, vapor recovery control costs were analyzed a t concentratlons of 100 ppmv. 1,000 ppmv. and 3.000 ppmv. Table 1 llsts kev economic factors In the overall cost of vapor recovery control.

Table 1.-Economic factors assumed to project con- trol cost for vapor recovery of methylene chloride. Methylene chloride recovery 50.25 per ib. (excludes !axes1

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

(8 hours per day. 5 days per week. 50 weeks per year, 2.000 hoursiyear)

55.00 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.

e n regen. systems maae 01 3161 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 con- trol costs below $5.000 per ton. Figure 4 sum- marlzes the regions of applicability for the three vapor recoverytechnologles evaluated. The reglons of applicability were made by assuming that con- trol 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 S62.400 $38,800 $17,000 '0.000 100 38.700 20.000 12.100 50.000 : 00 21.300 11.900 11.700 ! ,000 500 12.100 10.800 5.600

'0.000 500 - 400 1.800 4.400 50.000 500 1500 2.600 4.300 ' ,000 : ,000 5.800 6.000 3.100

'0 .000 '. 000 3.400 2.500 2.400 50.000 : 000 l.000 1200 2.300 ' ,000 3 000 ' 600 2.400 1400

50.000 3.000 350 720 230 '0.000 3 000 330 750 1,100

-ubic lee! oer minute "%I5 oer mlllmn Dy volume

148

100.000

10.000

1.000

1 ' Reaeneration \ \

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I'ouoiea Brav lon ' >en Reqeneralion

"Decoupled" Brayton Inert Regeneration

L I I I I I I 10 100 500 1000 3 000 10 000

Solvent Concentration 1PPMVl

'Regions of aDpiiCability are aefined by control costs at under S5 000 Der Ion o f 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 f i e d 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 con- centratlon level of the vapor stream from the process exceeds 500 ppmv. Paint stripping equlp- ment development should be directed at maxlmiz- ing concentration levels. keeping the safety of the worker in mind.

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Solvent Related Tech Transfer

Solvent Recycling

3 So/vent RecMing Con&"es

(proceedings availab/e)

Numerous technical papers

(see Paul Scheihing)

Soluentless processes

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)

So/vent Related Twhno/ogy/AppIhtion Assessment

VOC Controt Cost Assessment Mode/

waste stream evaluation studies (21

R&D Opportunity Assessments (2)

CHOICES IN SOLVING A VOLATILE ORGANIC

*

Develop Reduced VOC * Emitting Process

COMPOUND (VOC) EMISSION PROBLEM

Control VOC

Switch to Environmentally Benign Solvent

Develop Solvent Free Process Change Process

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

RECYCLING OF SOLVENTS IS ENERGY EFFICIENT

Solvent Solvent Solvent No Control 24000 BTU/Lb

23000 1000

+ Destruction e

Control 34000 BTUlLb

Recovery and Recycle

Control 4000 BTU/Lb

Control VOC by

Recover and Recycle

Solvent

GLOBAL ENERGY REQUIREMENTS IN CONTROLLING ~-

EMISSIONS IS M!NIMIZED WiTH RECYCLING Global Solvent Energy Requirement

24000

34000

9000

5000 - 4000

No Control Control by Control by Control by Control by Destruction Destruction, Recovery, Recovery,

Recover Heat Recycle Solvent Burn Solvent

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 ( W b )

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

Recycling Control Cost

1.50

1 .oo

0.50

0 0 0.50 1.00 1.50 2.00 2.50

Total Solvent Price

(Market Plus Excise Tax) ($/Lb)

SOLVENT RECYCLING CONTROL LESSENS THE IMPACT OF HIGHER ENERGY PRICE

Cost of Using Solvent

w 0

Energy Price

Destructive Control No Control Recycle Control

SOLVENT RECYCLING GIVES INDUSTRY AN OPTION

Can Be the Least Cost Approach to Complying with Environmental Regulation

Can Avoid Creating Another Environmental Problem in Attempting to Solve a VOC Problem

N Y

Can Cushion the Long Term Cost of Using Solvents

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

~ ~~ ~ ~ ~

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

Mobile Brayton regeneration 5? k

I I 10 r.

truck

Not in use while truck is regenerating bed

? f b r Pharmacuetical Brayton SOIvent Recovllery mtem

* Installed at P f i w P h a r m w e t W plant in Puerto R b

* Operating since June, 1991

* Tim 1500 SCFM Brayton direct conchsation systems

* Nucon is vendor

* No DOE assistance

DOE Mkapons Plant Application

* possib/e appMcation of decwpled Brayton system

* For soil remediation application

* Some solvents are habgenated