Case study in metal finishing industry
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1. Type
Case studies
2. Industry Sector
Metal finishing industry
3. Industrial application
In 2000 a three- year- demonstration project was started in South Africa to assist the local metal finishing industry to reduce its negative impacts on the environment. The project was initiated by the Danish Cooperation for Environment and Development (DANCED). The primary target group was the metal plating and hot dip galvanising in South Africa. A survey indicates that there are 500-600 independent metal finishers in the country. The number of firms with significant metal finishing operations is fixed with 1200.
Project objectives:
- To implement CP strategies in companies;
- To develop capacity in metal industry;
- To increase environmental awareness among people in companies;
Project Outputs:
- To perform training of consultants, metal plating managers and plating staffs;
- To perform CP benchmarking assessments of metal finishing companies;
- To perform feasibility studies on CP options;
- To perform 20 demonstration CP programs in MF plants;
- To enhance CP capacity of the metal finishing industry and within the sustainable metal finishing trade organisations.
4. Process description
The main problems of the metal finishing industry in South Africa are poor maintenance and old equipment which causes a high consumption level of energy and water and a high amount of generated waste. Furthermore poor housekeeping and bad education, trainings and skills of working people are responsible for the condition of the industry. As major areas of wastage the high water consumption and the losses of chemicals due of spillage and drag-out are identified. The electroplating, anodising and chemical surface treatment processes are water intensive and cause a high generation of wastewater. 80% of the annual consumed water is used for rinsing, so the primary source of generated waste is found in this part of procedure. The high amounts of water are necessary to remove drag-outs from parts after removal from the process bath shop. Rinsing is responsible for a high amount of chemicals and heavy metal ions in the wastewater. Furthermore the depleted process baths are added to the wastewater.
In the metal finishing industry the installation of end-pipe technologies is common. The generated wastewater treatment sludge is the largest solid waste stream in the metal industry. It needs careful disposal for example in an approved landfill. Often it is not operated lawfully and serious loads of heavy metal ions and chemicals enter the sewerage system. This can cause in return problems downstream at the sewerage treatment plants:
- The metal ion can not easily be removed from the stream. They are still present in the effluent which is discharged to the waterways and cause impacts on the aquatic life.
- They inhibit the biological treatment processes and reduce so the working efficiency of the plant.
- The high concentration of metal ions like chrome and cadmium limits safe disposal and reuse options.
The sludge in often used as a soil amendment on farmlands in South Africa, but with a high content of heavy metal ions this way of application is not possible any more without significant impacts on the environment. The alternative way is to dispose the sludge in landfill, but the government and private owners generally charge a high price from the companies for the disposal.
5. Assessment of Cleaner Production
For the assessment of the possibility of the implementation of CP strategies in the companies a model which bases upon the unit operation/mass balance principle was used. The model is called BCPT (Benchmarking Cleaner Production Tools) and was developed by Dahl. It describes the CP profile of a plating plant by eight parameters:
- Occupational health and safety;
- Operational practice at the wastewater treatment plant;
- Chemical consumption at the wastewater treatment plant;
- Waste minimisation;
- Water savings;
- The state of the rinsing system;
- Maintenance of the process baths;
- Consumption of process chemicals.
Detailed plant data for each parameter is collected and inputted into the tool. Then the tool generates the outputs with a summary graph. The efficiency of the plant is calculated as a result of consumed metals, chemicals, water, generated wastewater and produced sludge per production unit.
The first step in the review process is an inspection of the plant and to identify areas of improvements and potential savings. The second step is to write a pre-review document which is used to obtain the basic plant operations data. Therefore various pieces of data of different plant categories were required such as the production rate of the plant or the plating thickness. Furthermore several tables have to be completed:
- A table about the annual water and chemical consumption for every component of each reactor.
- A table with the maintenance of all process baths on a weekly basis.
- Rinse tables with information about the hardware of the rinse system and the exact amount of water for each individual process.
- A table with amounts and compositions of generated hazardous and toxic waste. It includes steps of the treatment process and the costs associated with treatment and disposal.
As it can be seen many data are necessary for the application of the BCPT. Just few companies with metal plating plants had data available and no metal plating job shops had data about production load or consumption.
As alternative an introductory company assessment called “a walk through” was performed. It is a visit of the plant and the consultant and the manager follow the production flow of raw materials through the plant until the final packaging and distribution. The report briefly describes the history of the company and its production. A flow sheet of the plant is added to the report and is later presented together with rough data of consumption of water, energy and raw materials. Furthermore the need of further assistance is discussed.
In a two- year period the project benchmarked more than 30 companies and conducted a review which reports in detail potential savings in water and chemicals an on waste generation. The largest potential improvements were
- 1. in water savings and
- 2. process bath maintenance.
There were also other significant potential improvements in parameters:
- in occupation health and safety (OHS),
- practices of wastewater treatment plants,
- state of the rinsing system,
- process chemical consumption and
- their savings in wastewater treatment plants
- 1. Improved housekeeping
The object is to minimize the material losses and to prevent so unnecessary generation of waste. For the metal finishing industry good housekeeping includes
- Segregation waste, all waste is not treated together. For example chrome-containing waste has to be reduced in pH, treated and then the pH has to be increased. If this were done collectively, with all the waste collectively, then the treatment chemical requirements would be larger than single streams.
- Monitoring of dosing chemicals ensures optimum dosing.
- Production based on surface area measurement - plant production needs to be determined by surface area as compared to mass of components.
- Lengthen drag-out times reduces the losses of process chemicals by allowing for longer drip-off times above the tanks.
- Position pieces so as to optimize dripping. Optimum liquid run off can be facilitated by ensuring components are hung properly.
- Ensure adequate training of staff ensures awareness on all operations and need for operating efficiently.
- Optimum temperature regulation prevents excessive vaporization of chemicals and ensures optimum chemical efficiency.
- 2. Chemical/water reuse/recycle/recovery
Wastewater is generally treated before being released into waste collections system. Its quality may be sufficient for reuse.
Strategies:
- Usage of low flow, counter current rinses throughout the plant. This implies that the process liquid that has been dragged out can be recovered through the rinse system.
- The acid/degreaser can be stored and used as dosage chemicals for the wastewater treatment facility.
- The rinse water from the acid system can be re-used as a reactive rinse in the degreaser section.
- 3. Process optimisation
Changes in the processes are made to ensure the maximal efficiency of each unit.
- Optimum bath chemistry ensures that anode and cathode efficiency are maintained according to the supplier’s specifications.
- Optimum mixing and dilution of rinse water by agitation, inlet/outlet location and prevention of back mixing e this ensures that the components are effectively cleaned in the rinse tanks.
- Maintaining optimum chemical concentrations for all processes will ensure product quality and production efficiency.
- Optimum measurement and dosing of wastewater ensures optimum chemical usage and reduces the risk of fines due to irregular releases.
- Regulation of water flow into the process ensures minimum water usage; optimum process tank temperatures ensure efficient cleaning/plating while maintaining sufficient evaporation for closed circuit operations.
- 4. Optimum use of resources
It has to be ensured that chemicals and water are just used as required in the process. Some chemicals have to be recovered and it is tried to limit or avoid chemical losses to the wastewater.
- 5. Improved product quality
High product quality is the result of optimum operations.
- Optimum cleaning ensures proper adhesion of coating.
- Measurement of plated thickness on a regular basis ensures quality of finished product and reduces the wastage of raw expensive materials.
- Optimum temperatures and chemical dosages reduce the risk of exposure of operators to chemicals.
- Improved staff training results in motivated, effective and efficient workforce.
- 6. Chemical substitution
Toxic and hazardous chemicals such as cadmium, cyanide and hexavalent chrome are replaced with more environment friendly and “greener” chemicals.
6. Results
Various companies implemented strategies based on the review. Two of them are described briefly:
- 1. Small electroplating shop
Age of shop: 20 years
Number of staff: 50
Annual savings R200.000 (Includes metals, chemicals, electricity, water, effluent discharges)
Savings measured relative to pre-CP conditions
Water: 30%
Effluent: 33%
Chemicals: 15%
Electricity: 20%
- 2. Old nickel chrome plating plant
Period of rehabilitation: 2001-2001
Total investment costs: R1.4 Mio
Costs of CP equipment: R400.000 (25%)
Savings measured relative to pre-CP conditions after three months
Water: 80%
Chemicals: 45%
Production: doubled
Source: Telukdarie A., Buckley C. , Koefoed M.: The importance of assessment tools in promoting cleaner production in the metal finishing industry, published in the Journal of Cleaner Production Vol. 14, 2006
