battery manufacture

INTERNATIONAL CLEANER PRODUCTION INFORMATION CLEARINGHOUSE

CASE STUDY #35 1. Headline: Process improvements in lead battery manufacture 2. Background: La SociÆtÆ Tunisienne de l'Accumulateur NOUR manufactures starting, lighting and ignition (SLI) batteries. The plant has six main operations, and uses the dry charge (tank formation) process for 60 per cent of the production, and the wet charge (container formation) process for the remaining 40 per cent. The company was subject of a pollution prevention diagnostic assessment carried out by the United States Agency for International Developments (USAID) Environmental Pollution Prevention Project (EP3). La SociÆtÆ Tunisienne de l'Accumulateur NOUR's battery manufacturing operation began in the 1950s. NOUR is a privately owned Tunisian enterprise that occupies a prominent position in the SLI battery market. The company faces increased competition, however, as a result of the Tunisian import liberalization program. 3. Cleaner Production Principle: Process modification 4. Description of Cleaner Production Application: Recommendations were made for all six unit operations. For example, smelting has been improved by covering the large piles of slag, dross and baghouse dust that present major environmental problems and risks to workers through exposure to lead. During the pasting operation, the lead-rich waste is shovelled back into the hopper for reuse. The moisture content of the paste recipes (both positive and negative) is increased so that the panels enter the drying oven at between 14-15 per cent moisture. Enabling technology: Temperature measuring instruments, accurate in the range of 1000-1300 C, help to ensure that the kiln temperature stays close to 1150 C, so that organic materials are burned off and maximum effectiveness is achieved. An improved design of casting molds eliminates the oversized lugs and unnecessary rigid connectors (feet) between the two grids that make up a panel, reducing waste, energy, lead and paste usage, and material handling, and eliminate the dusty, high-scrap plate cutting operation. To convert virgin lead into lead oxide, an appropriately sized mill makes the lead oxide in large, spherical particles, using air to atomize and oxidize the molten lead. The particles provide greater interstitial spaces and hold more moisture - critical to improving the curing process. Later, the interstitial space holds more sulfuric acid, giving the battery more 'cold cranking power', an important measure of battery value and quality. Water flow to the wetting roller on the pasting machine is reduced, and de-ionized water is used, reducing water use and generation of lead sulphate-contaminated water. A simple moisture analysis oven is used for each batch of paste, and plates are sampled before entering and after leaving the drying oven. This saves energy and gives more complete conversion of the elemental lead to lead oxide. During curing, vertical racks accommodate the larger batch sizes that are possible to produce because of the higher moisture in the plates. A higher residual moisture content allows a longer wait until more plates are available for curing. More heat is generated during the curing of larger batch sizes because the formation of lead oxide also generates heat. Higher temperature and saturation humidity transforms the elemental lead into a tetrabasic lead oxide, thus improving the mechanical bond, the cold cranking power, and the reserve capacity of the battery. The container formation process has been improved by applying a low current as soon as possible after the batteries are filled with acid. Temperatures of about 50C improve the performance of the negative plate, and help convert residual lead sulphate and oxide into lead peroxide. Finally, tank formation is eliminated, so the cured panels now go directly to battery assembly, eliminating the washing and drying needed after tank formation. This significantly reduces worker exposure to sulfuric acid and lead dust, saves energy, and reduces the volume of contaminated water from the plant. 5. Economics: The 19 pollution prevention options could produce savings of over US $2.1million in the first two years for an investment of $396 116. Capital investment cost for end-of-pipe equipment will be reduced by at least 35%, and treatment chemical costs by at least 66%. The following table shows just some of the savings achieved by the 19 options being implemented. Operation Cost Savings Payback US $ US $ period Smelting: - cover slag and dust piles; clean smelting from smelting room 500 10 000 3 weeks - temperature monitoring 1 000 1 000 1 year Cutting: eliminate the cutting process 100 000 401 712 <3months Container formation: apply charge to batteries immediately after filling 0 70 000 Immediate Tank formation: - eliminate the process 300 000 669 000 <6 months - stop washing plates 0 125 000 Immediate 6. Advantages: The new process reduces: - employee exposure to lead dust - toxic emissions, slag and waste - energy and water use - the amount of lead needed - lead acid contamination waste water Product quality is also improved by the increase in service life. 7. Constraints: N/A 8. Contacts:Ms Halima Bali M'rad Mr Rachid Nafti EP3 Tunisia 75, Ave Mohamed V 1002 Tunis Belvedere Tunisia Tel: +216 1 788 244 or +216 1 786 680 Fax: +216 1 787 245 9. Keywords:Tunisia, battery, lead battery, process modification, lead, EP3, USAID 10. Reviewer comments: This case study was originally published in the UNEP IE document "Cleaner Production Worldwide", Volume II. In the process of preparing the document the case study underwent a technical review.