Fluidized beds roasters

Use suspension or fluidized bed roasters, where appropriate, to achieve high SO2 concentrations when roasting zinc sulfides. 

Sulfur dioxide is generated in large quantities during the primary zinc refining process and sulfur fixation is carried out concurrently with the primary production process in order to meet CAA emission standards. Concentrations of sulfur dioxide in the off-gas vary with the type of roaster operation. Typical concentrations for multiple-hearth, suspension, and fluidized-bed roasters are 4.5 to 6.5%, 10 to 13%, and 7 to 12%, respectively. This sulfur dioxide is then converted into sulfuric acid. 

Figure 11.7 is a schematic diagram of a fluidized-bed roaster for oxidizing zinc concentrate (ZnS) to ZnO as part of the process for making Zn metal ... 

Murthy, K.V., Jayaprakashan, S.T.G. and Murugan, R.E, Continuous vibro fluidized bed roaster using flue gas. United States Patent, US 6810794 B2, 2004. 

Adoption of high-capacitv, low-labor fluidized-bed roasters... 

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. 

Roasting involves heating the concentrate in the presence of air to temperatures of 750-800°C in a multiple hearth, or fluidized bed roaster (Fig. 13.6). The charge remains more or less solid throughout. This completes the drying of the concentrate and removes a part of the sulfur from both the copper and iron present, producing oxides from some of the iron (Eqs. 13.4-13.7). 

FIGURE 13.6 Diagrams of multiple hearth type and fluidized bed roasters, such as used to decrease the sulfur content of copper sulfide ores. (Courtesy of Inco Ltd., Toronto.)... 

Many modern roasting operations now collect and use the sulfur dioxide present in roaster exit gases to produce sulfuric acid. Fluidized bed roasters are favored since they can give 15% sulfur dioxide concentrations, compared to the 3-6% range expected from earlier designs. 

The gas composition from the fluidized bed roasters at Falconbridge was a somewhat special circumstance in that the oxygen content was quite low, approximately 1%, and the sulfur dioxide concentration approached the theoretical maximum for pyrrhotite ore roasting. The Allied reactor-regenerator system was ideally suited to this gas composition. 

Three roasters operate in parallel to produce calcine. There are two 84-m fluidized bed roasters and a suspension roaster. Off-gas from the roasters is mixed with off-gas from the KIVCET furnace and is then processed in the sulphur gas handling area. By-products include calomel, sulphuric acid, liquid sulphur dioxide, and ammonium sulphate fertilizers. 

Fluidized bed roasters are sized according to the concentrate throughput requirements considering the mineralogical, chemical and physical properties of the available feed concentrates. The physical construction and dimensions of the roaster must at least allow for the following. 

A high level of MgCOs can create a thermal demand on the roaster, resulting in the need for auxiliary fuel (e.g. coal). Furthermore, the dolomite content in the roaster product will be a net acid user in the downstream atmospheric leach step. On the other hand, the MgO inside the fluidized bed roaster can capture some of the released SO2 values, and lower the amount of neutralizing agent (e.g. hydrated lime) required for the off-gas scrubbing. 

Ore concentrate Roasting at 700°C The process occurs in a fluidized bed roaster. A part of the sulfur is oxidized to sulfur dioxide, SO, which is used to manufacture sulfuric add. Roasted stuff... 

FIG. 1.3. Schematic diagram of a fluidized bed roaster for sulfide ores. 

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