ZERO Pollution Discharge

Transcription

1 Company Approaches ZERO Pollution Discharge BY Bruce Mottweiler Peter 1. Veit Project Engineer & Manager, Midwest Region Elkhart Products Division, Gould, Inc. Lancy laboratories REPRINTED FROM PLATING AND SURFACE FINISHING, DECEMBER 1976

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3 Process tanks are arranged in horseshoe configuration under the monorail. Operation is based on a 135-second cycle: 90-s immersion, 30-s drain, 154 transport. Company Approaches ZERO Pollution Discharge By Bruce Mottweiler Project Engineer Elkhart Products Division, Gould, Inc. & Peter 1. Veit Manager, Midwest Region Lancy Laboratories Is reaching zero pollutant discharge pie-in-the-sky? Elkhart Products, Inc. has four years of operational experience to prove that it s not. By modifying basic processes, the company drastically reduced its discharge of chemicals to the environment eliminating the need for hauling away approximately 3500 gallons per week of worthless copper-chromium sludge. At the same time, it engaged in some resource recovery-copper in the form of electrolytic cathodes is salvaged for sale as scrap. Here s how they did it...

4 Simple process control laboratory located near pickle line. The colorimeter ira fast, simple, day-today production control tool. View from catwalk of control station. In 1969, when the City of Elkhart, Indiana, announced it would soon begin construction on a new sewage treatment plant and that manufacturing plants discharging into the system would have to meet stringent requirements prescribed by the State of Indiana and EPA, management at Elkhart Products decided that an in-house waste treatment program was needed. The company, a Division of Gould, Inc., is a multi-plant operation fabricating over 1000 different copper pipe fittings. After forming, trimming, etc. the final operation consists of bright dipping and passivating. The fittings need a clean, attractive appearance to meet the requirements of a competitive market. The bright dipping and passivating is performed in an automatic line at a rate of approximately 100,000 pounds of fittings per week. The problem: the technique being used was to remove the drawing soap residue in a conventional alkaline cleaner, followed by a cyanide dip to remove some of the oxides, a water rinse, a chromic acid bright dip-passivation, three cold water rinses, and a hot rinse to facilitate drying. The content of the chromic acid tank was usually discarded daily after processing some 20,000 pounds of copper fittings. Average consumption was 2400 pounds of chromic acid per week. No waste treatment was provided for cleaner, cyanide, acid dumps or any of the contaminated rinses. The result: high pollution discharge and high chemical costs stemming from wastefulness. The company engaged a consultant, Lancy Laboratories, to study all possible forms of waste treatment for the plant, including electrodialysis, ion exchange, conventional flow-through treatment and other methods. Specific goals had to be met: (1) pollution control-the proposed system had to meet both current limitations and look forward to meeting more stringent requirements in the future; (2) no reduction in finish quality-if anything, product improvement was to be a secondary goal; (3) lowest total waste treatment cost-the total cost of waste treatment and chemical processing, including sludge haul-away, labor chemical consumption, amortization of equipment, had to be as low as possible; (4) metal recovery-the company wanted to recover large amounts of copper (some pounds per week), which were then going down the sewer. Phase I After the possibilities were considered, instead of providing treatment for the existing chemical processes, the company decided to work with a newly developed copper pickling process, utilizing sulfuric acid and a proprietary* stabilized hydrogen peroxide. This called for a process change, and the line was converted to the following cycle: alkaline clean, water rinse, water rinse, bright pickle in sulfuric acid-hydrogen peroxide, integrated copper treatment (Station I), integrated copper treatment (Station II), cold running rinse and hot rinse containing a proprietary organic material to passivate the surface and facilitate drying. This cycle was incorporated into a comprehensive regeneration and waste treatment system (page 17). The system provides for regeneration of the bright pickle DY transferring the nearly satu- *Co-Bra-Sol. Registered Trademark Electro- Chemical Company, Division of Dart Industries.

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6 A copper sludge decant panel in the raised position. This device filters out about 50 gallons per hour. The electrolvtic recovew - cell fa. series cell) with one cathode suspended. The plant recovers about pounds of copper per month. rated content of the pickle tank to a larger reservoir where the copper sulfate is precipitated as the solution cools. Cooling can be artificially accelerated. The crystals settle to the bottom of the tank, where they are picked up by a pump and recirculated through a cyclonic separator. During Phase I it was planned to collect the copper sulfate crystals for subsequent disposal or sale. The pickle efficiency is continually restored by the addition of sulfuric acid and hydrogen peroxide, as well as some of the proprietary stabilizers. Because of the heavy drag-out caused by the sheer bulk of small parts, the rinses following the bright pickle were converted to a two-stage closed loop integrated copper treatment system, operated in a counterflow mode. In the closed loop, copper is precipitated as cuprous oxide and/or cuprous hydroxide to provide a relatively heavy sludge containing some 20 per cent copper. What Phase I accomplished After installation of Phase I, the company had solved these basic waste treatment problems: it no longer needed to consider reducing the hexavalent chromium to trivalent chromium from daily 480-pound dumps using 720 pounds of sodium metabisulfite, nor did it need to consider precipitating that trivalent chro- mium, using some 720 pounds of caustic soda to form an estimated 700 gallons of sludge; any solid residue produced was either in the form of copper sulfate in the pickle reservoir or copper oxide in the copper treatment reservoir-both are considered salvagable; provisions were made for the slow controlled discharge of the alkaline cleaner dumps to the municipal treatment plant at a rate of 1 to 2 GPM, and for the collection and batch treatment of any solution dumps or accidental spills-no untreated spills can now reach the sewer; provisions were also made for the automatic ph adjustment and recording of all rinse and treated water immediately prior to sewer discharge. The initial installation was made entirely with plant personnel at an equipment cost of approximately $30,000 (1972 prices) and a piping and labor installation cost of approximately $30,- 000-for a total of $60,000. During the first few months, the plant was operated on a. learning period basis. Plant personnel learned to help themselves; many minor operating tricks, specifically for the installation, were developed, such as purging lines before long weekends, continuous operation of the crystal separator, exhaust modifications, and the use of polyelectrolytes to help settle the sludges. Phase II follows After about six months, the plant was ready for the preplanned additions to the basic system, primarily the installation of an electrolytic cell to recover the copper from the copper sulfate crystals and the integrated copper sludge and to regenerate the acid. Crystals and sludge can be redissolved and introduced into the electrolytic cell. The company is now recovering approximately IO00 pounds per month of metallic copper, which is sold as Grade I scrap along with other manufacturing scrap. A simple but important change was the addition of a sulfuric acid precleaner, containing a proprietary wetting agent, immediately ahead of the peroxide pickle. An innovation was made with this cyclone type crystal separator. A motorized dump valve and 30-minute cycle circuit were added to this unit.

7 This prepickles the copper surface prior to the bright pickle, allowing the production line to operate at lower temperatures and peroxide levels. Another improvement was the selection of a more effective alkaline cleaner, which extended the life from three days to three weeks. During this time, a simple, neat process control laboratory was built in the vicinity of the pickle line. The company considers this invaluable, both for the psychological impact on the operators and as a convenient process control station. Process control and waste treatment are now one integrated operation. Frequent analysis and simple, accurate record-keeping are important keys to good process and cost control. A system can be operated for a time by making chemical additions by guess. It will, however, decline in efficiency to a point where everything may go sour at the same time. When this occurs, there is no way to salvage the process solutions. At the Elkhart plant, this can require up to three man days. At any plant, the cost is not justifiable when simple control will prevent the bath breakdown. Cost comparison Based on four years of production experience and record keeping, the c ~ m pany knows what this method of operating costs, both in labor and chemicals. Its former chemical costs were reviewed and calculations made to determine basic price tag and also the added chemical costs for waste treatment had it chosen the end of pipe treatment route. (See above comparison.) To the direct chemical and labor costs would have to be added haul-away charges for some 3500 gallons per week of a mixed chromium-copper bearing sludge at an assumed cost of.io per gallon with the end of pipe treatment. Capital costs of eight per cent per year (or $96 per week) on the $60,000 waste treatment installation was added. Likewise, the $60,000 installation was amortized over 15 years for an additional $80 per week. On the plus side, presently, the plant is recovering in the order of 250 pounds of cupper per week at a current scrap price of.50 per pound. For simplicity, the same capital costs were figured for the end of pipe system, although the cost for that type of installation normally runs about per cent greater than what was installed. Study of this reveals that the present cost is in the order of 0.88 cents per pound of process parts. The former costs with waste treatment would be in the order of 3.2 cents per pound. Therefore, current cost for bright dipping, passivating and waste treatment is approximately 28 per cent of the cost of chromic acid bright dipping and waste treatment. In fact, it is only 54 per cent of the cost of the chromic acid bright dipping without waste treatment. Approaching zero Elkhart Products is now operating a piant in which virtually all of the metal dissolved in bright pickling is being recovered. This reduces the load on the environment with respect to both the sludge generation and to the depletion of natural resources. Besides approaching the zero pollutant discharge concept which is the ultimate aim of the Federal Government, the plant is doing so at a considerable savings over conventional treatment. The key to this success: a combination of engineering ingenuity and careful operation of the plant through good maintenance of the facilities and close control of the chemical processes.

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