Pollution Prevention and Control Technologies for Plating
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
- 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
- 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
- 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
- PS 125 indicated that their unit has a capacity of
- 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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