Smelter off-gases

Scmbbers for removing sulfur dioxide from smelter off-gases have been under development for many years. They are widely used in Japan. The calcium sulfate (gypsum) obtained from this process is suitable feed for waUboard production (see Calcium compound, calcium sulfate Sulfur removal and recovery). 

Boliden/Norzink A method for removing mercury vapor from zinc smelter off-gases by scrubbing with a solution of mercuric chloride ... 

Owing to the cycHc nature of the TBRC operation, waste heat recovery from the off-gases is not practical and the SO2 content of the gas varies with the converter cycle. In order to supply a relatively uniform flow and strength SO2 gas to a sulfuric acid plant, a system has been installed at RonnskAr whereby the SO2 from fluctuating smelter gases is partially absorbed in water. During smelter gas intermption, SO2 is stripped with air and the concentrated gas deflvered to the acid plant. 

A few smelters have waste heat boilers to recover heat from converter off-gases (48). Most smelters do not have these waste heat boilers because the cycHc operation of converters results in unsteady production of steam. 

Primary copper processing results in air emissions, process wastes, and other solid-phase wastes. Particulate matter and sulfur dioxide are the principal air contaminants emitted by primary copper smelters. Copper and iron oxides are the primary constituents of the particulate matter, but other oxides, such as arsenic, antimony, cadmium, lead, mercury, and zinc, may also be present, with metallic sulfates and sulfuric acid mist. Single-stage electrostatic precipitators are widely used in the primary copper industry to control these particulate emissions. Sulfur oxides contained in the off-gases are collected, filtered, and made into sulfuric acid. 

Carbonyl sulfide is an intermediate in this reaction. A mixture of sulfur dioxide and oxygen was blown into the bottom of coke-fired reduction furnace and sulfur vapor condensed from the off-gases. Trail is the location of a large mine and smelter in British Columbia. The process was originally used in the 1930s for abating air pollution from the smelter, but when the demand for sulfuric acid for fertilizer production increased in 1943 it became obsolete. See also Boliden (1), RESOX. 

Lead is also produced in a blast furnace using coke as the primary reductant. Much like the iron blast furnaces, the off-gases from the smelting of lead oxides will primarily contain CO and CO2. This gas is recycled back to the blast furnace to use the reducing power of the CO and the heating value otherwise lost. This helps to reduce the total amoimt of carbon that would be needed to produce lead. In many smelters, galena (the natural mineral PbS) is the feedstock. The... 

Tn the last several years, much of the work in sulfur oxide emission - control has been aimed at emissions from power plant stacks. However, there are many other stationary sources of sulfur emissions including non-ferrous smelters, sulfuric acid plants, and petroleum refineries. The papers in this collection are concerned with these other sources of sulfur-bearing off-gases. This volume is intended to be a consolidated reference source for those interested in the latest sulfur recovery methods. 

The use of cyclic absorption processes for concentrating sulfur dioxide from smelter gases is still very limited. If and when sulfur dioxide reduction is practiced, concentration processes must be used more extensively unless metallurgical processes are used that deliver richer off-gases, probably with sulfur dioxide concentrations not lower than 20-25%. The Asarco DMA absorption process (9, 10) is coming into renewed use, partly to produce liquid sulfur dioxide and partly to provide enriched feed to sulfuric acid plants. 

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). 

Four process streams closely link the zinc and lead operations. Iron and lead residues produced in Ae zinc operation are treated in the lead operation, and comprise nearly half of the total feed to the lead operation. Zinc-rich smelter fume makes up about 15% of the total feed to the zinc operation. Lead smelter sulphur dioxide off-gases are fed to the sulphur gas handling plants in the zinc operation, and waste water streams from both lead and zinc operations are treated in the effluent treatment plant. 

The biggest problem area in sulfur-dioxide emission control at smelters arises from converting which utilizes rotary (PS-) converters and the transfer of molten material in ladles, both open processes which release off-gases, including sulfur-dioxide into the working atmosphere. One... 

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