Profits through solid waste recycling.
For 87 years The Chicago Faucet Co has operated as a self-contained manufacturer of plumbing products. Today the company markets its products worldwide. In addition to its foundry, which melts and pours some four million pounds of red brass a year, the company operates machining, nickel-chrome plating, assembly and warehouse facilities.
Until 1987, disposal of solid wastes generated by the foundry was treated as a day-to-day operating expense. However, with rapidly increasing disposal costs and the declining number of disposal sites, together with more stringent environmental laws, we embarked upon a program to reduce or eliminate our hazardous disposal requirements.
The first step in this program involved a survey to establish the areas that produce waste streams and how they relate to each other. This resulted in development of an operational flow chart. The chart (Fig. 1) provided the information necessary to develop a plan of action.
The action plan was composed of two parts, "A" and "B". Part "A" consisted of waste materials from the shotblast, fume and dust collectors, and spent molding sands. Part "B" was composed of materials from shakeout, i.e., core butts and tramp metals, material generated from melting and pour-off operations.
Beginning with Part "A," our first procedure was to chemically identify the major metallics in each waste stream. By doing this, we were able to establish average compositions and resale/recycling potentials of each waste stream. Table 1 shows the average analysis and disposition for each item identified under Part "A."
The shotblast baghouse and discharge, and the material from the furnace baghouse were found to be high in copper or zinc metallic. This made these waste streams attractive for sale for other recovery processes.
On the other hand, materials from the molding system dust collector were extremely low in metallic content and therefore had to be chemically treated or recycled into the molding sand. While its high clay and combustible content makes recycling attractive, this process requires careful monitoring to prevent mineral buildup, which can result in rough casting finish.
Minimizing the disposal of spent molding sands, the foundry's largest single waste stream, required an unorthodox approach. Instead of adding new sand at the recommended rate of 240 lb/ton of metal poured, procedures were implemented to reduce additions to only 40 lb/ton of metal poured. In addition, the only sand lost within the system was through shakeout and dust collection.
This continuous reuse of molding sand without reclaiming created many problems, i.e., rough finish, high permeability, mineral buildup and oxide formation. Solutions to these problems were found and new controls were established to keep them in check.
As a result of reuse without reclaiming molding sand (Table 2), waste disposal in 1988 was reduced by 39%, resulting in a savings of $20,000. When the shotblast and spent molding sand waste streams are combined (Table 3), a waste disposal reduction of 87% was achieved with an annual savings of $41,980.
In addition to these savings, the combined waste streams form a material with a copper content of 17-18%. This material is sold for other recovery processes.
Action Plan: Part "B"
Part "B" of the action plan was to reclaim metallics from waste streams generated at shakeout, sand screening, melting and pour-off operations. These metallics are mixed with various impurities and required some refining before reuse. This refining was accomplished through the use of a ball mill operation, as shown in Fig. 2.
The ball mill operation illustrated in Fig. 2 works as follows: the material for processing starts in the vibrating mill feeder hopper (3). This hopper feeds and regulates material flow into the mill drum (4). The mill drum creates a cleaning action and releases material that is about a quarter of an inch and smaller into a vibrating trough (5) located below the mill drum that carries the material to the first bucket elevator (6).
This elevator carries small granulated material to the storage hopper (7) for distribution across the vibrating screen (8). Material that passes through the screener goes out of the system. Material that does not pass through goes off the end of the screener into the second bucket elevator (9), which transports it to the impactor (10) where the nonmetallics continue to be broken down.
From the impactor, the material goes back to the storage hopper (7); nonmetallics that were fractured by the impactor are again fed into the vibrating screener. This cycle continues until all nonmetallics are removed from the metal and the remaining metal is clean and ready for remelt.
Average results of waste streams processed through a ball mill are shown in Table 4. The important reuse here is the 38.9% metallic recovery that returns directly for remelt. Annualized, this is equivalent to 193,000 lb of clean metal.
Shown at the bottom of Table 4 is the average dollar value of combined waste streams before and after ball mill recycling. These figures are based on gross weights of both metallics and nonmetallics. Note the 258% increase in dollar value per pound from before and after recycling. This dollar increase does not include the value of grinding dust after recycling.
The waste stream generated from the vibrating screener is, in fact, not waste. It contains fine metallic with an average copper content of 13.7% and an average total metallic of 27.1%. This waste stream is high enough in metallic to be sold for other recovery processes, as well.
Total Coast Savings
A brief annualized income and expense summary, which combines the results from Parts "A" and "B" of the program, is shown in Table 5. Savings from landfill and metal recovery from the ball mill operations yield a gross profit of $196,380 or a net profit of $106,125 after deductions are made for freight, processing fees and profits from previous scrap sales.
In our opinion, methods used by The Chicago Faucet Co to control solid hazardous waste disposal will work in part or whole for most foundries. Check your parameters and explore your options before making major decisions on recycling, reclaiming or chemically treating hazardous wastes. We think that you too may realize profits through solid waste recycling.
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|Author:||Baker, William A.|
|Date:||Feb 1, 1990|
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