Factors Favouring the Dual-Pressure Process

In the single-pressure and dual-pressure processes, the catalyst volatilizes at a rate determined by the converter exit-gas temperature. Experimental work indicates that the rate loss of catalyst (without a catalyst recovery system) is approximately three times more rapid at 973°C than at 866°C (Ref. PT18). From plant operation data, the loss from a dual-pressure converter (operating at 866°C) is estimated at about 0.10 g/tonne of 100% acid, and from a single-pressure converter (operating at 937°C) it is estimated at about 0.38 g/tonne of 100% acid. 

In the single-pressure process, the ammonia content of the mixture should not exceed 10.5% because of the lower explosive limit. In the dual-pressure process with lower converter pressures, the explosive limit is higher providing additional operating flexibility. 

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