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The fresh feed to an ammonia synthesis reactor contains nitrogen, hydrogen and 2.0 mole per cent inerts. The molar ratio of H2:N2 is 3:1. The product stream consists of pure ammonia. Since conversion in the reactor is only 15%, a recycle stream is used and in order to avoid build-up of inerts, a purge stream is withdrawn. The rate of purge stream is adjusted to keep inert concentration in the recycle stream at 8 mole per cent. For a fresh feed rate of 100 moles/hr. Note that recycle stream contains only nitrogen, hydrogen and inerts. The N2:H2 ratio of 1:3 is maintained in every process stream, and calculate the number of moles, moles of inerts and moles of hydrogen in the recycle stream?(a) 437 moles/hr, 35 moles/hr, 301.5 moles/hr(b) 237 moles/hr, 30 moles/hr, 200 moles/hr(c) 567 moles/hr, 35 moles/hr, 205 moles/hr(d) 347 moles/hr, 30 moles/hr, 500 moles/hrThe question was posed to me in an interview.My doubt is from Material Balances with Recycle, By topic in chapter Material Balance of Bioprocess Engineering

Answer»

Right option is (a) 437 moles/hr, 35 moles/hr, 301.5 moles/hr

To explain I would say: TOTAL NUMBER of moles in the RECYCLE STREAM = 100.50×4/0.92 = 437 moles/hr

Moles of inerts in the recycle stream = 437 – 100.50×4=35 moles/hr

Moles of hydrogen in the recycle stream = 100.50×3 = 301.50 moles/hr.



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