Pollution Prevention and Control Technologies for Plating Operations

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Section 3 - Chemical Recovery

3.3 VACUUM EVAPORATORS

3.3.7 Operational and Maintenance Experience

The following summarizes the respondent's O&M experiences and provides operating labor information relative to vacuum evaporators.

• The average number of annual man-hours spent for operating and maintaining a vacuum evaporation unit were: 657 hrs/yr. The skill requirement commonly needed for operating this technology is trained technician or a wastewater treatment plant operator. The following is a breakdown of the responses for skill requirements:

     Environmental Engineer:...............1
     Process/Chemical Engineer:............1
     Chemist:..............................1
     Consultant:...........................1
     Plumber/Pipe Fitter:..................4
     Electrician:..........................4
     Vendor:...............................1
     Senior-Level Plater:..................4
     Junior Level Plater:..................1
     Wastewater Treatment Plant Operator:..8
     Trained Technician:...................9
     Common Labor:.........................1
     Other:................................0
      

• The most frequent and significant operational and maintenance problems identified with vacuum evaporation include: (1) mechanical problems with pumps; (2) damage to components by aggressive plating chemicals; and (3) contamination build-up in the plating bath.
• Approximately 26% of the total number of vacuum evaporation units reported in the survey forms are no longer in use. On the average, these units were purchased 16 years ago. Of those units still in use, the average age is 6 years. The oldest working unit was 14 years old.
• PS 034 indicated that they have weekly problems with their pump and vacuum system. They attribute the pump problems to improper design. PS 039 also indicated that they problems with the vacuum pump. On a second unit, PS 039 had problems with the eductors. They have abandoned use of both of these units.
• Although they have installed both ion exchange and electrolytic purification, PS 082 indicated that they have trouble keeping their chromium bath free of contaminants because of the closed-loop recovery process. PS 102 used their unit for 4 years and then abandoned its use because of plating bath (copper, cyanide) contamination. PS 125 is experiencing a build-up of sodium and chloride in their nickel bath.
• PS 088 reported that their cooling water was too warm in the summer to effectively condense the vapors and operate their system.
• PS 088, which employs a four stage counter-flow rinse prior to evaporation, indicated that users of this technology should concentrate on reducing rinse water flow and the resultant feed to the evaporator.
• PS 124 indicated that they need to clean the condenser of their unit approximately twice per year.
• PS 124 indicated that the maximum feed concentration to their unit is 1 oz/gal CrO3 (presumably because higher concentrations will etch the glass of their Corning evaporation unit.) PS 196 reported some etching of their glass unit. PS 280, which operates a Corning unit with a fluoride bath, indicated that this application results in a shorter than average equipment life-span and higher maintenance costs. Their unit is three years old.
• PS 125 indicated that they must operate one of their units at <150oF because of nickel brightener considerations (nickel plating) and the other unit at ²140oF due to fluoride considerations (decorative chromium plating).
• PS 196 indicated that they must operate their unit at >150oF to boil the chromium solution.
• PS 298 indicated that their distillate is sometimes contaminated beyond the limit for good rinsing. When this occurs, they recycle the distillate to the first rinse rather than the final rinse of their 3 stage counterflow rinse system. This results in a need to blow down rinse water to the treatment system.

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