Sulfur spent acid regeneration

Both of these processes direct the SO2 absorbed from the FCCU flue gas to the refinery SRU, where it is converted to elemental sulfur and added to the marketable sulfur that is generated by the SRU from H2S. Alternately, the SO2 can be converted to sulfuric acid in a dedicated sulfuric acid plant, or in combination with an existing refinery spent acid regeneration unit. When the SO2 is directed to the SRU, 1 ton of SO2 captured in the scrubber is converted to 0.5 tons of marketable elemental sulfur and less than 0.1 ton of sodium sulfate waste is generated per ton of SO2 absorbed. In an acid plant, 1 ton of SO2 generates 1.5 tons of 98% sulfuric acid. Steam is also generated from the conversion of SO2 in both the SRU and the acid plant, which moderates somewhat the steam consumption rate of the solvent regenerator for both the LABSORB and CANSOLV systems. 

Worldwide, about 180 million tonnes of sulfuric acid are produced per year. 70% comes from burning elemental sulfur. The remainder comes from S02 in smelter, roaster and spent acid regeneration furnace offgases. 

Source of SO2 Sulfur burning Spent acid regeneration... 

The investment costs in this chapter focus on sulfur burning and metallurgical type acid plants. Costs for spent acid regeneration acid plants are expected to be slightly higher than sulfur burning acid plants due to their increased furnace complexity and additional gas cleaning equipment. 

This chapter has provided study estimate level investment and production cost estimates for sulfur burning and metallurgical type sulfuric acid plants. Spent acid regeneration type acid plants are expected to have slightly higher investment costs than sulfur burning type acid plants. 

Because sulfur suppHes, either as elemental sulfur or by-product sulfuric acid, have grown owiag to iacreased environmental awareness, demand for sulfur has decreased ia some consuming iadustries for the same reason. Industries such as titanium dioxide productions, which traditionally utilized sulfuric acid, have concerted to more environmentally friendly processes. In addition, many consumers who contiaue to use sulfuric acid are puttiag an emphasis on regenerating or recycling spent acid. 

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.

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