Metallurgical Offgas Cooling and Cleaning

About 20% of the world s sulfuric acid is made from SO2 in smelter and roaster offgases. The gases contain 10 to 75 volume% SO2, Table 4.1. They are hot and dusty. They may also contain impurity vapors, e.g. chlorine and gaseous arsenic compounds. 

The SO2 is suitable for sulfuric acid manufacture, but the gases must be  

This chapter describes gas cooling, cleaning, dilution and H20(g) condensation. Final dehydration by contact with strong sulfuric acid is described in Chapter 6. 

As applied to metallurgical plants, acidmaking serves two purposes. It  

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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. 4.5. Dynawave scrubber for removing particulate and soluble impurities from cooled (600 K), partially cleaned furnace offgas (Puricelli et al., 1998 Enviro-chem, 2005). Note the (i) upward sprays in and (ii) the weir atop the downcomer. The sprays clean the gas. The weir continuously overflows water, which wets and cools the downcomer walls. These scrubbers are used for both metallurgical and spent acid regeneration furnace gases. Large scrubber details are downcomer diameter 1 m (Hastelloy G30)...

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