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Pollution Prevention and Control Technologies for Plating Operations


Section 4 - Chemical Solution Maintenance

4.4 ION EXCHANGE

4.4.7 Operational and Maintenance Experience

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

  • Six shops provided operating labor data. For these shops, the average number of annual operating hours per ion exchange system were 220 hrs/yr. The labor category most frequently used for O&M was a trained technician or a wastewater treatment plant operator. The following is a breakdown of the responses for skill requirements:
            Environmental Engineer:       0
            Process/Chemical Engineer:    0
            Chemist:                      2
            Consultant:                   0
            Plumber/Pipe Fitter:          0
            Electrician:                  0
            Vendor:                       0
            Senior-Level Plater:          2
            Junior Level Plater:          0
            Wastewater Treatment Operator:4 
            Trained Technician:           6
            Common Labor:                 0
            Other:                        0
      
  • In general, the commercial equipment used for chromium bath maintenance requires little maintenance and has a relatively long equipment life. Most shops indicated that the downtime for this technology was low and none identified any major O&M problems except for PS 273.
  • Long equipment life was evidenced by the fact that only one shop (PS 273) in the survey indicated that they used this process and subsequently discarded it due to deterioration (note that one shop purchased their equipment in 1983 and later sold it and that PS 244 eliminated the need for this equipment). The oldest system identified in the survey that is still operating was purchased in 1975 (PS 131). Shops estimated the life of this equipment to be between 5 and 20 years and the average estimate was 11.5 years.
  • The percentage of down time for this technology was low. Nearly one-half of the respondents indicated that downtime was 1% or less.
  • Several shops pointed out that there are two key technical restrictions for this technology: chromic acid concentration and temperature (PS 049, PS 150, PS 165, PS 273). Two shops indicated that the solution temperature must be 90oF or less before ion exchange treatment is performed (PS 165). Two shops pointed out that the chromic acid concentration must be below 142.5 g/l (19.0 oz/gal) CrO3 for treatment (PS 165). One respondent indicated that their operating conditions (160°F and 16 oz/gal CrO3) may have contributed to resin damage (PS 273).
  • One shop indicated that elements and filters must be changed two times per year (PS 165).
  • The shop operating an ion exchange unit for trivalent chromium bath maintenance reported that they experience mechanical breakdowns about four times per year. They also indicated that the downtime of their unit was less than one percent.
  • PS 131, the respondent that has used this process the longest (since 1975), indicated that the process dilutes the hard chrome bath and raises the sulfate level, causing them to adjust the solution chemistry following treatment.

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