Flowsheets offgas

Fig. 4.1. Flowsheet for cooling, diluting and cleaning metallurgical offgas. Gas temperature is lowered from 1500 to 310 K. S02 concentration is lowered from 10-75 volume% S02 to 8-13 volume% S02. Dust plus vapor concentration is lowered from 10-200 g per Nm3 of gas to 0.001 g per Nm3 of gas. Efficient gas cleaning minimizes plugging of downstream catalyst and equipment. It also minimizes poisoning of the catalyst. It is the key to efficient, continuous long term metallurgical acid plant operation. Mercury-from-gas removal is described in Section 4.5.3.

Fig. 5.1. Spent sulfuric acid regeneration flowsheet. H2S04(f) in the contaminated spent acid is decomposed to S02(g), 02(g) and H20(g) in a mildly oxidizing, 1300 K fuel fired furnace. The furnace offgas (6-14 volume% S02, 2 volume% 02, remainder N2, H20, C02) is cooled, cleaned and dried. It is then sent to catalytic S02 + Vi02 —> S03 oxidation and H2S04 making, Eqn. (1.2). Air is added just before dehydration (top right) to provide 02 for catalytic S02 oxidation. Molten sulfur is often burnt as fuel in the decomposition furnace. It provides heat for H2S04 decomposition and S02 for additional H2S04 production. Tables 5.2 and 5.3 give details of industrial operations.

The optimizing calculations were carried out on the simplified flowsheet model illustrated in fig. 4, where RE represents a series of gas-liquid reactors, and WW denotes tRe heat exchanger. The equipment following the reactors is indicated by one block, OPW. Stream 5 is the offgas from the reactor and stream 7 the product from the top of the cyclohexane distillation column. 

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