Sintering recycle ratios

Reduced levels of return sinter will cause a decrease in bed permeabihty, reducing possible gas flow and hence, sinter machine capacity. On the other hand gas permeability is enhanced by increased levels of return sinter, but fuel value of the charge is reduced and peak bed temperature is lowered. This leads to poorer quality sinter with increased fines, which report to returns and reduce sinter bed permeability, thus reducing gas flow and machine capacity. The product sinter in this case is also weak and readily breaks up in the shaft of the blast furnace, reducing permeability and blast furnace throughput. Hence, there is an optimum level of recycle sinter and of fuel to maximise sinter machine capacity. This normally corresponds to a sulfide sulfur content of sinter feed of six to seven per cent and a minimum recycle ratio of 1 1 (recycle net sinter production), or 50 per cent of total sinter production. 

Coarse product sinter from the primary screen is sent directly to surge bins from where it is proportioned and mixed with lump coke to provide feed to the blast furnace. Provision is made to crush and return product sinter to make up the required recycle ratio if necessary. Under steady state operation of the sinter machine, control of the amount of product sinter returned is normally through the level of material in the returns sinter surge bin, which is drawn off at a steady rate to satisfy feed blend requirements. 

When the distribution ratio is low, continuous methods of extraction are used. This procedure makes use of a continuous flow of immiscible solvent through the solution if the solvent is volatile, it is recycled by distillation and condensation and is dispersed in the aqueous phase by means of a sintered glass disc or equivalent device. Apparatus is available for effecting such continuous extractions with automatic return of the volatilised solvent (see the Bibliography, Section 9.10). 

Pelletizing (Fig. 8.31) is applied to convert waste and by-products from a steel mill that also operates a sinter plant into agglomerates vhth improved handling characteristics. The pellet composition is site specific. It depends on the number of components to be incorporated and their physical and chemical characteristics, including moisture content. By preparing the materials in this way, not only is recycling achieved but the productivity of the sinter plant is also enhanced. The inputs and ratios depend on the mill s specifications for so-called control elements, such as zinc, alkali, and oil. To date, Heckett MultiServ operates two pelletizing plants, both in Europe, with annual capacities of 100 000 and 200 000 t/year. 

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