Flash roasters

New flash roasters dry on the bottom hearth the ore is introduced in two opposed burners for increased turbulence (24). Such roasters with combustion chambers of 8—9 m high are capable of dead roasting (sulfide removal to <0.5%) over 300 t of zinc concentrates per day with 10% sulfur dioxide in the off-gas. 

The flash roaster is flexible ia handling various flotation concentrates and reaching the degree of desulfurization desired, ie, 0.5—3.0% sulfate sulfur. Waste heat is easily recovered. However, grinding and rabbling must be done mechanically. 

A major portion of the reaction is found to occur in the vapor space between trays. A unit in which most of the trays are replaced oy empty space is called a. flash roaster its mode of operation is like that of a spray dryer. 

Roasting furnaces are in a class of reactors used by the metallurgical industry in a preparatory step for the conversion of ores to metals. There are three widely used roasted furnaces multiple hearth, fluidized bed, and flash roasters. In the multiple hearth configuration hot gases pass over beds of ore concentrate. The flash roaster injects pulverized ore with air into a hot combustion chamber. The fluidized bed roaster operates as described in a separate heading. 

All of these roasting furnace reactors operate continuously. They are noncatalytic gas-solid heterogeneous reactors. The multiple hearth has characteristics similar to plug flow operation. The flash roaster approaches CSTR, and the third option is a fluidized bed configuration. 

For environmental and economic reasons, the eady practice of roasting zinc sulfide and discharging the sulfur dioxide to the atmosphere gave way to plants where the sulfur dioxide is converted to sulfuric acid. Desulfurization takes place while the ore particles are suspended in hot gases. Called flash-and fluid-bed roasters, these processes are described below. Some plants use combinations of roasters and sintering for desulfurization. 

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