PuraSiv S process for removing acid plant tail gas

The PuraSiv S process, a commercially demonstrated system for the removal and recovery of sulfur dioxide from sulfuric acid plant tail gas, is discussed and described. The SO/sub 2/ is adsorbed on a tailor-made molecular sieve adsorbent. Upon the regeneration of the molecular sieve, the SO/sub 2/ is recycled to the front end of the acid plant for recovery and conversion to H/sub 2/SO/sub 4/. Typically, the recovered SO/sub 2/ contributes a 2 to 3% increase in the H/sub 2/SO/sub 4/ production rate. The molecular sieve is equally effective in removing SO/sub 2/ in the presence of 7 to 10% carbon dioxide and trace amounts of nitrogen oxides found in sludge acid plant vent gas. The commercial experience with this system at Coulton Chemical Corporation's 200-ton/day spent acid plant is described. In the commercial unit, SO/sub 2/ in the tail gas is reduced to less than 50 ppM. Operation of the unit is fully automatic, requiring only an occasional check by the acid plant operator. Total treating costs for an add-on PuraSiv S unit range from $1 to $2.25/ton of acid, depending upon acid plant size and the concentration of SO/sub 2/ in the tail gas leaving the absorber tower.more » Treating costs for a new plant would be approximately 20% less if the PuraSiv S unit is included in the initial design of the plant. Based on the first six months of operation, the PuraSiv S unit at Coulton has a net treating cost of $1.93/ton of acid produced. Because the cyclic life of the adsorbent is guaranteed, this is the maximum treating cost. The standard PuraSiv S unit can process a feed containing 3500 ppM by volume SO/sub 2/ and can be extended to higher concentrations by including additional molecular sieve in the vessels. This permits a richer SO/sub 2/ gas strength to the converter in the base acid plant. For a new plant, the size of the acid plant can be reduced by handling a stronger gas. In an existing plant, it is possible to increase production by increasing the SO/sub 2/ strength to the converter.« less