Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 565 of 707

What is the total exhaust time per day? What are the heating degree days for your location? What is the building heating (and possibly cooling) cost by month? Are the plating line ventilation systems tied into automatic tank covers? Baseline questions for the acid and alkaline tanks: What are the tank volumes? What is the tank chemistry concentration? Cost of the chemistry per tank refill? Tank dumps per year, and reason for tank dumps? Cost to treat the chemistry after the tank dump (labor, neutralization chemicals, sludge disposal, etc.)? Once armed with the baseline information, it is relatively easy to determine the real cost for each area. Then it is possible to prioritize the costs and target cost reduction changes. The following baseline example is from a medium-sized job shop plating company that was part of a direct assistance program through the New York State Pollution Prevention Institute. The baseline list has been ranked by cost. 1. Water use = 6,310,000 gpy (gallons per year) = $32,900/yr. ($5.22/1000 gallons) 2. Acid purchases (HCl) = $19,700 ($1.25 /gallon, 15,760 gallons) 3. Waste treatment sludge disposal = $15,600/year 4. Exhaust blower = 10,000 cfm = $7,899/yr. for 40 hours per week ($.09/kwh) 5. Caustic purchases (NaOH) = $6,400 ($2.10/lb, 3,048 lbs.) 6. Heating of make-up air = 431 decatherms = $2,154 /yr. ($5/decatherm for natural gas) Total cost per year = $66,923/year In this example, the water cost was by far the highest single cost to the com- pany for their plating lines. A close second and third were the acid purchases (included line acid and waste treatment acid), and waste treatment sludge disposal. RINSE WATER OPTIONS It might not be typical for all metal finishing operations but it is fairly common to have water costs at or near the top of the cost of operations. Rinsing is criti- cal in the metal finishing process, but more water use does not necessarily mean better rinsing. Best practices for producing effective rinsing are: • Multiple counterflowing immersion rinse tanks between process tanks • Reactive rinsing for the appropriate process chemistry combinations • Spray rinsing • Combination rinses such as immersion rinsing, followed by spray rinsing or reactive rinsing combined with counterflow rinsing 564

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