The semi-dry sulphuric acid process lets the converted gas to leap over the identical concentration point and using a moisture absorption tower to reduce water in the gas.It does not add water or crossflow acid,and the circulating acid concentration remains unchanged in the tower.The circulating acid concentration is maintained by controlling the water-sulphur ratio and the inlet acid temperature.The surface condensation and absorption in the packing are parallel.The water in the gas is the whole area water for the process,and it can produce about 5 tons of steam for per ton of water.The steam yield per ton of production acid is 0.93 tons,including 0.35 tons of medium pressure superheated steam and 0.58 tons of low pressure saturated steam.If all low pressure steam is produced,it will reach 1.02 tons.It can achieve zero cooling water and zero discharge of weak acid from tail suction tower.The semi-dry acid process has low corrosiveness and is the limit of dry acid production.It appears to be an acid heat recovery process without adding water,and is safer than the acid heat recovery process.The acid formation rate from SO3 in the gas at inlet the moisture absorption tower exceeds 70%,and the heat of acid formation is equivalent to a gas temperature rise of 190℃.The operating load can be reduced to 30%,or the SO2 gas strength into the plant is as low as 3%.
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