Pollution Prevention and Control Technologies for Plating Operations

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Section 3 - Chemical Recovery

3.2 ATMOSPHERIC EVAPORATORS

3.2.7 Operational and Maintenance Experience

The following summarizes the respondents O&M experiences and provides operating labor information relative to atmospheric evaporators.

• The quantity of labor required for the operation of this technology is relatively low compared to other recovery technologies. For shops providing data, the average number of annual operating hours per evaporator were: 157 hours per year. The skill requirement commonly needed for operating this technology is a trained technician, a wastewater treatment system operator, a plumber/pipe fitter or common labor. The following is a breakdown of the responses for skill requirements:

      Environmental Engineer:................0 
      Process/Chemical Engineer:.............3 
      Chemist:...............................5 
      Consultant:............................0 
      Plumber/Pipe Fitter:..................15 
      Electrician:...........................9 
      Vendor:................................1 
      Senior-Level Plater:...................8 
      Junior Level Plater:..................11 
      Trained Technician:...................24 
      Wastewater Treatment Plant Operator:..16 
      Common Labor:.........................16
      

• Approximately 90 percent of the atmospheric evaporator installations identified in the Users Survey were in operation at the time of the survey. The following is a breakdown of the responses for current operating status:

      Currently in use:..........................................89.6% 
      Not currently in use and have no intention of future use:...7.5% 
      Not currently in use, but intend to use in the future:......3.0%
      

• The average percent of downtime experienced with this technology was 7%. Only 15 percent of the respondents indicated that their downtime was greater than 5% (those with greater than 5% downtime included: PS 045, PS 101, PS 105, PS 139, PS 213, PS 239, PS 282, PS 298, PS 300 and PS 317).
• Generally, this technology is free of complex mechanical operational and maintenance problems because of the simple design and limited number of moving parts. There are however, some common maintenance requirements, most of which relate to cleaning. A list of the most frequently reported maintenance requirements follows (the percentage of all respondents identifying the problem is given in parenthesis):

      Cleaning of evaporation chamber packing
         or evaporative panels:............................11% 
      Cleaning of nozzles that spray solution 
        over packing or evaporative panels:.................4.7% 
      Maintaining pumps:....................................4.7% 
      Unplugging of pipes:..................................1.6% 
      Maintaining timers:...................................1.6%
      

• Fifty-seven percent of the plating shops that reported cleaning as a maintenance item have purchased the units equipped with evaporative panels rather than the plastic packing. The company that manufactures the panel-type unit has recently introduced a model that is designed better handle high solids conditions (see 3.2.4). In some cases, the cleaning requirement was blamed on carbonates that precipitated from aerating cyanide containing solutions in the evaporator (PS 089, PS 101, PS 239, PS 258). In two other cases, crystals that formed from the drying of plating chemicals were blamed (PS 045, PS 172).
• According to the literature, plating chemical crystals can be removed from the packing and nozzles by a weekly recirculation of hot water through the evaporator with the fan shutoff. Salts that have formed on the nozzles and packing will dissolve (ref. 355). Carbonate deposits present a more significant problem and most likely will require mechanical (e.g., scraping) removal.
• One shop indicated that operation of their atmospheric evaporator for chromium plating solution recovery resulted in degrading of the unit and piping and that the manufacturer has replaced their evaporator twice in the past five years (PS 252). This shop also operates units for cyanide copper and nickel plating and has not experienced any problems with these other units. A leaking problem around welds was reported by another shop (PS 300). Eventually, PS 300 discontinued use of three of their atmospheric evaporation units because of leaking.
• Many shops indicated that use of an atmospheric evaporator has caused a build-up of contaminants in the plating bath. The most frequently identified problem was carbonate build-up in cyanide containing baths such as zinc, cadmium and copper (ref. PS 081, PS 089, PS 183). Respondents also indicated problems with contaminant build-up in chromium baths (PS 089, PS 172, PS 252 and PS 255), and nickel baths (PS 038, PS 105 and PS 139). PS 139 reported a build-up of brightner and iron in their nickel bath. Twice PS 139 has tried evaporative recovery for nickel and abandoned their efforts.
• Other bath problems attributed to use of an atmospheric evaporator include a breakdown of nickel bath chemicals (PS 039) and increased bath chemistry maintenance for trivalent chromium plating (PS 191).
• Several shops reported that climatic conditions effect the evaporative capacity of their atmospheric evaporator (PS 160, PS 183 and PS 224). These three shops are located in different regions (survey regions SE, FW and MW).

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