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MEMORANDUM

DATE:		January 31, 2005

SUBJECT:	Evaluation of the Feasibility, Costs, and Impacts of Switching from a Halogenated Solvent with a High Cancer Unit Risk Value to a Halogenated Solvent with a Lower Cancer Unit Risk Value

FROM:	Chris Sarsony
            Alpha-Gamma Technologies, Inc.

TO:		Lynn Dail
            U.S. Environmental Protection Agency




1.0  	Overview
      There are primarily three halogenated solvents being used for degreasing applications today:
 Perchloroethylene (PCE)
 Trichloroethylene (TCE)
 Methylene Chloride (MC)

      Table 1 shows that switching from one halogenated solvent to another halogentated solvent can result in significant reductions in cancer risk.  For example, switching from PCE or TCE to MC reduces the cancer risk by 93% and 70%, respectively.  This reduction in risk is primarily the result of differences in the cancer unit risk values, which are discussed in Section 2.0.  Also, affecting the cancer risk are differences in solvent consumption rates, which are discussed in Section 3.0.  
                                       
Table 1 - Change in Cancer Risk Resulting from Switching Halogenated Solvents[a]


                                       

                               Perchloroethylene

                               Trichloroethylene

                              Methylene Chloride

                                  PCE to TCE 

--------------------------------------------------------------------------------


                      77 Percent Decrease in Cancer Risk



                                   TCE to MC



--------------------------------------------------------------------------------


                      70 Percent Decrease in Cancer Risk

                                   PCE to MC

--------------------------------------------------------------------------------


                      93 Percent Decrease in Cancer Risk
a - Considers differences in cancer unit risk values (Table 2) and differences in solvent consumption (Table 3).

      In the preliminary risk analysis conducted by ICF, 32 facilities using PCE or TCE were found to have a cancer risk above 1 x 10[-6].  All 5 of the facilities using only PCE and half of the 25 facilities using only TCE could reduce their risk to below 1 x 10[-6] by switching to MC.  Another 25% of the facilities using TCE could lower their risk to below 1 x 10[-6] by switching to MC and reducing their solvent emissions by 10% or less.  Therefore, 80 percent of the facilities with risk above 1 x 10[-6] could lower their risk to below 1 x 10[-6] simply by switching to MC and decreasing their emissions by 10% or less.

      Each of the three halogenated solvents has advantages and disadvantages, which are discussed in Section 4.0.  As a result, some halogenated solvents may not be appropriate for some specific cleaning applications.  Since solvent cleaning is application specific, each facility would need to determine whether switching to another halogenated solvent is a viable option for their particular cleaning application.  However, Dow Chemical Corporation, one of the largest manufacturers of halogenated solvents, states that in general:

      "Most vapor degreasing operations can be performed with any of the three solvents (PCE, TCE, and MC), so the choice is often based on other performance characteristics, safety, environmental considerations, or cost."[1]


      Costs of the solvent switching options are discussed in Section 5.0.  Costs related to switching from one halogenated solvent to another halogenated solvent include:
 Changes in the cost of the solvent
 Changes in solvent consumption
 Changes in energy requirements
 Costs for equipment modifications
 Changes in productivity

      Costs were evaluated for each solvent switching option using a large (1.5 m[2]) model open top cleaning machine.  The costs were calculated to be as follows:
 PCE to TCE = Savings of $5,125 per year
 PCE to MC = Savings of $1,719 per year
 TCE to MC = Cost of $2,825 per year


2.0	Cancer Unit Risk
      Since the cancer unit risk values for the three solvents are different, a facility could achieve a substantial decrease in cancer risk simply by switching from one halogenated solvent to another.  Table 2 shows that, when looking at cancer unit risk alone, switching from PCE to TCE or MC reduces the cancer risk by 66% or 92%, respectively.  Switching from TCE to MC reduces the cancer risk by 76.5%.
                                       
      Table 2 - Relative Cancer Unit Risk Values for Halogenated Solvents
                                       

                                       

                               Perchloroethylene

                               Trichloroethylene

                              Methylene Chloride

                            Cancer Unit Risk Value

                                 5.9 x 10[-6]

                                 2.0 x 10[-6]

                                 4.7 x 10[-7]

                                  PCE to TCE 

--------------------------------------------------------------------------------


                    66 Percent Decrease in Cancer Unit Risk



                                   TCE to MC



--------------------------------------------------------------------------------


                   76.5 Percent Decrease in Cancer Unit Risk

                                   PCE to MC

--------------------------------------------------------------------------------


                    92 Percent Decrease in Cancer Unit Risk

3.0	Solvent Consumption
      Solvent is consumed when it is emitted to the atmosphere from the solvent cleaning machine.  Dow Corporation conducted solvent consumption tests on an idling (i.e., the machine is turned on and ready to operate) open-top degreaser with a 24" x 58" opening using PCE, TCE, and MC.  The comparison of the resulting solvent consumption rates is shown in Table 3.  

    Table 3 - Relative Solvent Consumption Rates for Halogenated Solvents 
              (based on the vapor loss from an idling degreaser)
                                       

                                       

                               Perchloroethylene

                               Trichloroethylene

                              Methylene Chloride

                            Solvent Consumption[a] 

                                0.293 lb/ft2/hr

                                0.201 lb/ft2/hr

                                0.260 lb/ft2/hr

                                  PCE to TCE 

--------------------------------------------------------------------------------


                  31 Percent Decrease in Solvent Consumption



                                   TCE to MC



--------------------------------------------------------------------------------


                  29 Percent Increase in Solvent Consumption

                                   PCE to MC

--------------------------------------------------------------------------------


                  11 Percent Decrease in Solvent Consumption
a - Reference 1.

      Air/solvent vapor interface loses during idling (i.e., when the machine is turned on and ready to operate) consist of solvent vapor diffusion (or evaporation from liquid solvent in a cold cleaner) and solvent vapor convection induced by warm freeboards.  Diffusion occurs because molecules of solvent move from higher concentrations in the vapor zone to lower concentrations in the air.  Because molecular activity increases at higher temperatures, diffusion rates are temperature-dependent.[2]  The rate of diffusion is also dependent on the vapor density of the solvent and the boiling point of the solvent.  The lower the vapor density, the more susceptible the solvent is to losses due to air disturbances and work transfer.[1]  The higher the boiling point of the solvent, and thus, the higher the solvent temperature, the greater the diffusion losses.[2]  Table 4 shows the vapor density and boiling point for each of the three halogenated solvents.  

       Table 4 - Vapor Density and Boiling Point of PCE, TCE, and MC[a]
                                       

                                    Solvent

                                 Vapor Density

                           Boiling Point (degrees F)

                               Perchloroethylene

                                     5.76

                                      250

                               Trichloroethylene

                                     4.53

                                      189

                              Methylene Chloride

                                     2.93

                                      104
a - Reference 1

      Table 3 shows that PCE had the highest solvent consumption rate at 0.293 lb/ft2/hr.  Although PCE has a high vapor density, the high consumption rate of PCE relative to the other solvents is due to its very high boiling point.  Methylene Chloride had the second highest solvent consumption rate at 0.260 lb/ft2/hr.  The high consumption rate of MC relative to TCE is due to the very low vapor density of MC.  

      Differences in the rates of solvent consumption between the halogenated solvents directly affect the level of cancer risk.   Table 3 shows that, when looking at solvent consumption alone, switching from PCE or TCE to MC reduces the cancer risk by 31% and 11%, respectively.  Switching from TCE to MC increases the cancer risk by 29%.


4.0	Advantages and Disadvantages of PCE, TCE, and MC
      Each of the three halogenated solvents has advantages and disadvantages, some of which are illustrated in Table 5.  As a result, some halogenated solvents may not be appropriate for some specific cleaning applications.  Since solvent cleaning is application specific, each facility would need to determine whether switching to another halogenated solvent is a viable option for their particular cleaning application.  However, Dow Chemical Corporation, one of the largest manufacturers of halogenated solvents, states that in general:
      "Most vapor degreasing operations can be performed with any of the three solvents (PCE, TCE, and MC), so the choice is often based on other performance characteristics, safety, environmental considerations, or cost."[1]


      The Kauri Butanol (KB) number is an indication of solvency power that is measured by the formation of turbidity with solvent mixed with Kauri resin and n-butanol.  The higher the KB number the greater the solvency.  Table 6 shows the KB number for each of the three halogenated solvents.

      In general, PCE's high boiling point makes it an excellent choice for drying wet parts, for removing high-melting pitches and waxes, and cleaning light-gauge metals without staining.  However, because of PCE's high boiling point: a greater heat input is required; it can damage aircraft aluminum alloys, printed circuit boards, and plastic materials; and a longer cooling time is required.[1]

      Trichloroethylene has a high solvency power (KB number of 129), which makes it excellent for removing oils, greases, waxes, tars, lubricants, coolants, semicured varnish, paint films, heavy rosins, and buffing compounds.  However, TCE does attack some plastics, is reactive with caustic soda forming dichloroacetylene (toxic and spontaneously combustible), and degrades in UV light creating phosgene (a highly toxic and reactive gas).[1]    

      Methylene chloride has the highest solvency power of the three solvents (KB number of 136), and therefore, can perform well in a diverse range of cleaning applications.  Due to its low boiling point, methylene chloride is the best choice for cleaning temperature sensitive parts.  In addition, MC is low in cost compared to alternative (non-halogenated) low-temperature solvents.  Due to its low vapor density and high evaporation rate, cleaning machines using MC must have a higher freeboard height, additional freeboard chilling capacity, and covers in order to prevent excessive solvent emissions.[1]	

      All three of the halogenated solvents are considered to be nonflammable.  Therefore, flammability is not an issue when choosing among the three halogenated solvents. 	
      
         Table 5 - Advantages and Disadvantages of PCE, TCE, and MC[a]

                                    Solvent

                                  Advantages 

                                 Disadvantages

                                      PCE

Effective with Wet Metals - High boiling point allows complete drying of moisture on parts.

High Heat Required - High boiling point requires additional heat, and thus, higher utility costs to bring work up to the solvent vapor temperature.


Reduced Staining - High boiling point allows a longer and more thorough rinsing action and may reduce staining in cleaning operations employing vapor exposure only (esp. for light-gauge metals).

Steam Stripping - Steam stripping is commonly practiced to recover  solvent without causing thermal degradation.  Results in undesirable water contamination and requires operator attention. 


Removes Stubborn Soils - High boiling point makes PCE effective for removing high-melting pitches and waxes and for cleaning grossly contaminated parts.

Heat Effects - Certain aircraft aluminum alloys, printed circuit boards, and plastic materials cannot handle the 250 degree temperature.


Stability - Shows little tendency to hydrolyze (degrade with water), but can decompose in the presence of UV light, releasing phosgene.

Additional Insulation May Be Needed to Reduce Heat Loss


Decreased Corrosion - DOW's double stabilized PCE contains an inhibitor system that provides extra corrosion protection for cleaned parts and the degreaser.

Not Recommended for Cold Cleaning


Vapor Recoverable by Carbon Adsorption

Longer Cooling Time

                                      TCE

High Solvent Power - High solvency for oils, greases, waxes, tars, lubricants, and coolants generally found in the metal processing industries.  Often chosen for removing difficult soils, such as semicured varnish or paint films, heavy rosins, buffing compounds, etc.

Steam Stripping - Steam stripping is commonly practiced to recover solvent without causing thermal degradation.  Results in undesirable water contamination and requires operator attention. 


No Conversion Costs - Most equipment was originally designed for TCE.

Reactive with Caustic Soda (NaOH) - Forms toxic and spontaneously combustible, dichloroacetylene


Recoverable by Carbon Adsorption

Attacks Some Plastics


Energy Efficient

Degrades in UV Light creating phosgene

                                      MC

High Solvent Power - MC is the strongest of the common vapor degreasing solvents. Can perform effectively in such diverse tasks as paint mask cleaning and removing excess impregnating resin from castings.

Rapid Evaporation Rate - MC evaporates more rapidly than other vapor degreasing solvents.  Covering the degreaser during non-operating periods is imperative to prevent excessive solvent losses.


Good for Temperature-Sensitive Parts - Low boiling point makes it possible to degrease thermal switches, thermometers, etc., which would be damaged by higher temperatures.  MC is also chosen when parts must be near room temperature after cleaning, such as for immediate handling.

Low Vapor Density - MC's low vapor density makes it more susceptible to losses from air movement around the equipment.  Specialized equipment design, with a higher freeboard and adequate chilling is recommended for efficient use. 


Low Cost - Low in cost compared to alternative low-temperature solvents used for similar applications. 


                                       

High Throughput - Due to the low boiling point MC has the highest work throughput potential.


a - Adapted from Reference 1.

           Table 6 - Kauri Butanol Numbers for Halogenated Solvents


                                    Solvent

                             Kauri Butanol Number

                                      PCE

                                      90

                                      TCE

                                      129

                                      MC

                                      136


5.0	Costs
      Costs related to switching from one halogenated solvent to another halogenated solvent include:
 Changes in the cost of the solvent
 Changes in solvent consumption
 Changes in energy requirements
 Costs for equipment modifications
 Changes in productivity

      Table 7 shows the solvent costs, solvent consumption rates, and energy usage rates for PCE, TCE, and MC.  Trichloroethylene has the highest cost per gallon, PCE has the second highest cost per gallon, and MC has the lowest cost per gallon.  The solvent consumption rates are explained in more detail in section 3.0.  The energy usage values are derived from tests conducted by Dow Chemical Corporation.[1]  "During the tests the degreasers cleaned five loads of steel (100 lbs each) and provided 20 gallons of solvent spray per hour."[1]  The energy requirements for MC include the energy required to provide extra cooling capacity for adequate vapor condensation. 


      The solvent costs per gallon, solvent consumption rates, and energy usage rates for PCE, TCE and MC are shown in Table 7.  Using the values in Table 7 and Appendix A, the solvent costs, energy costs, and equipment costs were calculated for a large (1.5 m2) model open top vapor degreaser (Table 8).  For the PCE and TCE base units it was assumed that the unit operated 8,760 hrs per year (24 hrs/day for 365 days/year) and that 1,350 gallons of solvent were used per year.  The solvent usage value of 1,350 gallons per year represents the average solvent usage for units using PCE and TCE with risk above 10[-6] in the preliminary risk analysis.  The annual solvent cost of the base units was calculated by multiplying 1,350 gallons by the cost of the solvent per gallon.  The annual energy cost for the base units was calculated by multiplying the energy usage by the electricity cost per kWh.  The solvent cost for switching from one solvent to another was calculated as follows:
	
      Annual Solvent Cost = (base solvent volume) * (new solvent consumption/base solvent consumption) * (new solvent price) 

In all cases, a savings in solvent costs results from switching from one solvent to another.

      The energy cost for switching from one solvent to another was calculated by taking the difference between the base unit energy requirements and the energy requirements of the unit with the new solvent.  When switching from PCE to TCE there is a savings in energy costs, whereas, when switching from PCE or TCE to MC there is a higher energy cost.  This is a result of the additional freeboard chilling capacity that is required when using MC.  

      There are no equipment costs when switching from PCE to TCE.  However, when switching from PCE or TCE to MC the unit must have additional freeboard height (1.0 freeboard ratio) and additional freeboard chilling capacity (freeboard refrigeration device).  Capital and operational costs were estimated for these devices and are shown in the tables in Appendix A.

      The final column of Table 8 shows the total annual costs for each solvent switching option.  Switching from PCE to TCE or MC both result in an annual cost savings.  Switching from TCE to MC results in an increase in annual costs.  Since MC has a low boiling point, the cleaning cycle is shorter for MC than the other solvents.  A shorter cleaning cycle means increased productivity.  Therefore, some of the additional cost of using MC may be offset by productivity gains.  
      
Table 7 - Solvent costs, solvent consumption, and energy usage for PCE, TCE and MC


                                   Cost Item

                                      PCE

                                      TCE

                                      MC

                     2004 Cost of Solvent per Gallon[3][a]

                                    $11.10

                                    $12.83

                                     $8.86

                     Solvent Consumption During Idling[1]

                                0.293 lb/ft2/hr

                                0.201 lb/ft2/hr

                                0.260 lb/ft2/hr

                              Energy Usage[1][b] 

                                   20.8 kWh

                                   16.3 kWh

                                   21.47 kWh
a - Based on purchase in 55 gallon drums.
b - For MC the energy usage includes the additional energy used by a freeboard refrigeration device.


         Table 8 - Estimates of Solvent, Energy, and Equipment Costs 
                         for Solvent Switching Options
                                       

                                       
                                    Option

                                 Solvent Costs

                                 Energy Costs

                                       
                           Annualized Equipment Cost

                                       
                        Total Annual  Costs for Option
                                       

                            Annual Solvent Cost[a]

                            Annual Change in Costs

                              Annual Energy Cost

                            Annual Change in Costs
                                       
                                       

Base PCE Unit

                                    $14,985

                                      NA

                                    $9,347

                                      NA

                                      NA

                                      NA

PCE to TCE

                                    $11,882

                                   ($3,103)

                                    $7,325

                                   ($2,022)

                                     None

                                   ($5,125)

PCE to MC

                                    $10,614

                                   ($4,371)

                                    $9,648

                                     $301

                                    $2,351

                                   ($1,719)

Base TCE Unit

                                    $17,321

                                      NA

                                    $7,325

                                      NA

                                      NA

                                      NA

TCE to MC

                                    $15,472

                                   ($1,849)

                                    $9,648

                                    $2,323

                                    $2,351

                                    $2,825
a - Calculated using the following equation:
(Base solvent volume) * (New solvent consumption/Base solvent consumption) * (New solvent price)


References

1 - "Degreasing: Economical and Efficient Degreasing with Chlorinated Solvents from Dow", Dow Chemical Company, November 1999.

2 - "National Emission Standards for Hazardous Air Pollutants: Halogenated Solvent Cleaning - Background Information Document", U.S. EPA, EPA-453/R-93-054, November 1993.

3 - Price quote from Univar USA Inc., Charlotte, NC.  Univar is a direct distributor for Dow Chemicals Company.   January 25, 2005.













                         Appendix A - Equipment Costs
                                       
                                       
                                       

                     Freeboard Refrigeration Device Costs

                                                                               

                                                                               

                                       

1.  Capital Costs

                                                                               

                                                                               

1990 Installed Capital Costs [1, 2]

                                    $9,000

                                                                               

Scaling Factor from 1990 to 2004 Based on the PPI

                                     1.30

                                                                               

2004 Installed Capital Costs

                                    $11,717

                                                                               

Cost of Additional Floor Space[3]

                                     $315

                                                                               



                                       

                                                                               

Total Capital Costs

                                    $12,032

                                                                               



                                       

                                                                               

Annualized Total Capital Costs (15yr @ 7%)

                                    $1,324

                                                                               



                                       

2. Annual Operation Costs

                                       

                                                                               

Labor [4]

                                     $146

                                                                               

Misc. Operating Costs [5]

                                     $481

                                                                               



                                       

                                                                               

Total Annual Operation Costs

                                     $627

                                                                               



                                       

3.  Total Annualized Cost (Annualized Total Capital Cost plus Total Annual Operating Costs)

                                    $1,950

[1] - C. Sarsony, Radian Corp. to Paul Almodovar, U.S. EPA. "Revised Cost and Cost Effectiveness Values Associated with Emission Reductions for Selected Control Techniques for Halogenated Solvent Cleaners."  August 19, 1994.  Docket A-92-39, Item Number IV-B-3.

[2] - Based on the Large Open Top Vapor Cleaner Size (1.5 m[2]).  This is the closest to the average size of the units using PCE and TCE with risk above 10-6 (2.92 m[2]).

[3] - Scaled from 1990 (Source 1) using the PPI.

[4] - Assumed operating 8,760 hrs per year.  1,095 shifts/year * $13.29/hr * 0.01 hrs/shift = labor cost.  Labor rate was obtained from BLS - Private Industry Blue Collar Machine Operators, July 2003.

[5] - Calculated as 4% of capital costs (Source 1).
                                       
                                       
                                       

                           1.0 Freeboard Ratio Costs

                                                                               

                                                                               

                                       

1.  Capital Costs

                                                                               

                                                                               

1990 Installed Capital Costs [1, 2]

                                    $2,800

                                                                               

Scaling Factor from 1990 to 2004 Based on the PPI

                                     1.30

                                                                               

2004 Installed Capital Costs

                                    $3,645

                                                                               

Cost of Additional Floor Space[3]

                                      $0

                                                                               



                                       

                                                                               

Total Capital Costs

                                    $3,645

                                                                               



                                       

                                                                               

Annualized Total Capital Costs (15yr @ 7%)

                                     $401

                                                                               



                                       

2. Annual Operation Costs

                                       

                                                                               

Labor [4]

                                      $0

                                                                               

Misc. Operating Costs [5]

                                      $0

                                                                               



                                       

                                                                               

Total Annual Operation Costs

                                      $0

                                                                               



                                       

3.  Total Annualized Cost (Annualized Total Capital Cost plus Total Annual Operating Costs)

                                     $401

[1] - C. Sarsony, Radian Corp. to Paul Almodovar, U.S. EPA. "Revised Cost and Cost Effectiveness Values Associated with Emission Reductions for Selected Control Techniques for Halogenated Solvent Cleaners."  August 19, 1994.  Docket A-92-39, Item Number IV-B-3.

[2] - Based on the Large Open Top Vapor Cleaner Size (1.5 m[2]).  This is the closest to the size of the units using PCE and TCE with risk above 10-6 (average of 2.93 m2, median of 1.67m[2]).

[3] - Scaled from 1990 (Source 1) using the PPI.

[4] - Assumed operating 8,760 hrs per year.  1,095 shifts/year * $13.29/hr * 0.01 hrs/shift = labor cost.  Labor rate was obtained from BLS - Private Industry Blue Collar Machine Operators, July 2003.

[5] - Calculated as 4% of capital costs (Source 1).



