Smelter Onahama

Even minor residual emissions from the Onahama smelter are treated. The tail gases from the acid plants are scrubbed with caustic soda to reduce the final sulfur dioxide concentration to about 20 ppm. The converter building is enclosed to prevent escape to the atmosphere of untreated gases that leak from the furnaces. Leaking gases are collected as close to the sources as possible and are scrubbed in a limerock tower before release. Virtually all of the sulfur dioxide from the smelter is reportedly contained (32). 

After the system described above was devised, the Onahama smelter was expanded, and a commercial magnesia-base absorption system developed by the company was applied to the reverberatory furnace gases (27). As described (27), the process is essentially the same as the Chemico-Basic process (33) although equipment details are not reported. The magnesium sulfite is decomposed in a rotary kiln in the presence of added carbon. The magnesia is returned to the absorption process, and the rich kiln gas stream (13-15% sulfur dioxide) is sent to a sulfuric acid plant. 

As illustrated by the Onahama smelter, it is essential to minimize the volume of the off-gases from a source. The capital and operating costs of a control system are determined primarily by the volume of gas that must be treated (9, 10). The growing application of emission controls has led recently to much more active development of methods and equipment for capture and cooling of waste gases as well as heat recovery from them (34,35). 

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