We are designing a desulfurization process for a client overseas. The client produces a wet coke gas that must be treated for COS, H2S, and HCN before it can be used to make chemicals. A knock-out pot serves double duty collecting the circulating spent slurry and vapor from the clients gasification plant (Figure 1). The vapor flow in is 50,000 lb/hr and the liquid flow is 519 gal/min. The pot operates at 200°F and 560 psig with a barometric pressure of only 12 psia. A k of 0.27 was used with a velocity allowance of 0.15 to size the tank for vapor separation. The residence time is set at 30 minutes. The calculated diameter is 13 ft. with a length/diameter ratio of 3.4. The vapor passes through a mesh pad mist eliminator that is only partially used because of low vapor flow. Several problems are anticipated with the design: the liquid drains to atmospheric; foaming sometimes occurs, disrupting level measurement; the mesh pad fouls every four months; and the process water used on a timer to keep the pad clean may contain particulates. How would you improve the design?
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