prob+set+_10B+.09 - Chemical Engineering 140 Problem Set...

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Chemical Engineering 140 November 28, 2009 Problem Set #10B 48. Design of an Ammonia Plant for Differing Single-Pass Conversions Due November 13, 2009 The reaction rate for the production of ammonia over a promoted iron catalyst is written at 300 atm as 2 2 3 2 3 2 2 3 2 2 2 1 1 2 2 3 2 N H NH N / / NH H H k [ y y y /( K P )] r [ y y y ] β - - = + (1) where at 900 ° F (and 300 atm) β = 0.00140, k 1 = 1.20 lbmol/ft 3 hr and K = 4.67(10 -3 ). The recycle ratio is fixed at 4 and the production capacity of the plant is 40,000 ton/yr of ammonia. For the specific ammonia plant considered in homework problems 41 and 42, the reaction rate in Eqn (1) can be implemented in the reactor design equation as function of conversion (see solution to homework problem 42) As the single-pass conversion increases, the reactor size grows. Conversely, for a fixed plant size the feed flow diminishes as the single-pass conversion increases. Assume that the plant costs (amortized capital and operating) increase with both reactor size and feed. When reactor
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