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Pollution Prevention and Control Technologies for Plating Operations


Section 3 - Chemical Recovery

3.3 VACUUM EVAPORATORS

3.3.6 Performance Experience

A partial summary of the user data relative to vacuum evaporation is presented in Exhibit 3-21. There are a number of observations that can be made from these data and other data contained in the database and literature:

  • The average satisfaction level for chemical recovery applications is 3.5 (on a scale of 1 to 5, with 5 being most satisfactory), which higher than the average rating for all recovery technologies. Seventy-five percent of the shops using vacuum evaporation for chemical recovery indicated that this technology satisfied the need for which it was purchased. The following is a breakdown of the reasons why shops purchased this technology:
     To meet of help meet effluent regulations:.........14
     To reduce plating chemical purchases:..............12
     To reduce the quantity of waste shipped off-site:..12
     To reduce wastewater treatment costs:..............11
     To improve product quantity:........................0
     To close-loop a particular process:.................1
      
  • Vacuum evaporators were successful for most applications identified in the Users Survey except for zinc-cyanide plating solution recovery. The average annual savings from using vacuum evaporators exceeded the sum of the average capital cost plus the average annual operating cost. The most significant savings were derived from reductions of bath chemical and treatment chemical usage.
  • The use of vacuum evaporation as a recovery technology generally did not impact production quality or the rate of production for the survey respondents. The following responses were provided:
                Product Quality    Production Rate     
     Improved         1                   1
     No Change       13                  13
     Decreased        2                   0
      
  • PS 298 indicated that use of their evaporator decreases product quality because their distillate is contaminated and not adequate for good rinsing. PS 102 also indicated that their unit decreases product quality.
  • The respondents indicated, that based on their experience with this technology and, if given the opportunity, they would:
     Purchase the same technology from the same vendor:....12
     Purchase the same technology from a different vendor:..4
     Purchase a different technology:.......................3
     Do nothing:............................................0
      
  • Two of the respondents indicated that their vacuum evaporation system was the cause of an effluent compliance excursion (PS 039 and PS 088). PS 280 did not respond to the question. All other respondents indicated that their vacuum evaporation system was not the cause of an effluent compliance excursion.
  • Several respondents provided the following quantitative performance data:
    • PS 082 indicated that the supplier stated capacity of their unit is 300 gph and that the actual capacity is 175 gph.
    • PS 123 has an evaporation rate of only 6 gph. It is used to make head-room in their tin-lead plating tank so that recovery rinsing can be used. The feed to their unit (tin-lead plating solution), has a concentration of 16 to 18 oz/gal and the concentrated return has a concentration of 32 to 36 oz/gal.
    • PS 088 indicated that the capacity of their unit is 60 gph and that they are able to operate their cadmium plating process on a closed-loop basis. Their drag-out rate is 1.5 gph and they have a three stage counterflow rinse system feeding the evaporator. The cadmium bath is operated at 75_F and there is essentially no surface evaporation.
    • PS 124 indicated that their unit has a capacity of 90 gph.
    • PS 125 indicated that their unit has a capacity of 100 gph.
    • PS 196 indicated that both the supplier stated capacities and actual capacities of their units (3) were 90, 75 and 50 gph.
    • PS 213 indicated that both the supplier stated capacity and actual capacity of their unit was 75 gph.
    • PS 298 indicated that their "unit does not meet levels stated in promotional" and that the "quality of distilled water is poor." The supplier stated capacity of their unit is 100 gph and the actual capacity is 70 to 80 gph.
    • PS 132 indicated that their evaporator "never performed as sold." No details of their problems were provided.
    • PS 034 expressed their feelings about their unit as follows: "Poor design, good technology."

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