Pollution Prevention and Control Technologies for Plating
Section 3 - Chemical Recovery
3.2 ATMOSPHERIC EVAPORATORS
3.2.6 Performance Experience
A partial summary of the NCMS Users Survey data relative to atmospheric
evaporators is presented in Exhibit 3-9. There are a number of
observations that can be made from these data and other data contained
in the database and literature:
- The majority of shops that have used atmospheric evaporators
have found them to perform adequately. The average satisfaction
level for this technology is 3.8 (on a scale of 1 to 5, with 5
being most satisfactory), which is the highest level rating for
any of the chemical recovery technologies, except for meshpad
mist eliminators. Also, 81 percent of the shops indicated that
this technology satisfied the need for which it was purchased.
The following is a breakdown of the reasons why shops purchased
To meet or help meet effluent regulations:.........46
To reduce plating chemical purchases:..............45
To reduce the quantity of waste shipped off-site:..35
To reduce wastewater treatment costs:..............39
To improve product quantity:........................9
- The use of atmospheric evaporators generally did not impact
production quality or the rate of production. The following responses
Product Quality Production Rate
Improved 7 3
No Change 52 53
Decreased 6 9
- Where the product quality was impacted (PS 098, PS 118, PS
139 and PS 306), PS 098 and PS 139 indicated that contaminant
build-up occurred in their chromium plating and nickel plating
baths and PS 118 indicated that product quality is only impacted
occasionally due to low rinse water flows.
- Where the production rate was impacted (PS 098, PS 139, PS
252, PS 262 and PS 306), PS 098 and PS 252 attributed work slowdowns
to bath contamination.
- Most plating shops indicated, that based on their experience
with this technology, they would purchase the same type of equipment
from the same vendor. The following is a breakdown of their responses:
Purchase the same technology from the same vendor:.....73%
Purchase the same technology from a different vendor:..12%
Purchase a different technology:.......................12%
- The reported savings from use of atmospheric evaporators was
mostly due to reduced purchases of plating chemicals. The average
annual savings per shop were slightly less than the sum of the
average capital costs plus annual operating costs. This indicates,
that on the average, shops experienced a payback period of approximately
- Very few survey respondents reported the evaporation rate
they were achieving with their atmospheric evaporator. Presumably,
this is because such data are not routinely collected. The highest
evaporation rate reported by a respondent was 60 to 75 gph (PS
183). Oddly, with this particular application, the shop connected
the evaporator to a heated, 150°F cadmium cyanide transfer
tank. (This is not a recommended application because heating of
the cadmium solution will destroy cyanide and create carbonates.)
PS 183 indicated in their survey form that they would have achieved
a closed-loop "if it were not for the carbonate problem."
For more traditional applications (nickel and chrome operated
at 130 to 140oF), the highest reported evaporation rates were
in the range of 20 to 50 gph (e.g., PS 228, PS 213).
- Some of the plating shops that gave atmospheric evaporation
a lower rating may have misapplied the technology. The most frequent
misapplication is the use of this technology for the concentration
of ambient temperature process solutions or drag-out. The commercial
units do not have a direct heat source, but rather use heat from
the process or transfer tank to evaporate water (see complete
explanation in Section 3.2.1). When applied
to an ambient solution, very little evaporation will take place.
For example, PS 081 attains an evaporation rate of only 3 gph
from a unit connected to a zinc cyanide bath that is operated
at 85 oF. PS 279 attains a rate of 2 to 5 gph for an ambient acid
zinc application. Other plating shops that may have misapplied
the technology include (based on a review of supplied schematics):
PS 040, PS 045, PS 101, and PS 143.
- The high incidence of misapplication for this technology may
be due in part to the fact that 54% of the commercial atmospheric
evaporators purchased by survey respondents were sold to them
by manufacturer's representatives rather than direct purchases.
The manufacturer's representatives may not have had sufficient
knowledge of the technology to recommend proper installation.
- In some cases, performance was hampered by operational and
maintenance problems. These are discussed in Section 3.2.7.
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