Pollution Prevention and Control Technologies for Plating Operations

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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 this technology:

          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 
          Other:..............................................6
      

• The use of atmospheric evaporators generally did not impact production quality or the rate of production. The following responses were provided:

                     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% 
        Do nothing:.............................................3%
      

• 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 one year.
• 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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