lecture+21A+recycle+_+purge - Recycle & Purge: Ammonia...

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ammonia catalytic reactor 900°F, 300 atm N 2 1 H 2 3 A small 3 2 2 20 2 0 11 4 2 1 0 22 4 2 3 3 0 667 4 2 NH N H X ~ % X y . X X y . X X y . X = - - = - - = - A small BP ~ -196 (77K) N 2 BP ~ - 253 (20K) H 2 A NH 3 = 0 condenser NH 3 (liq) BP NH 3 @ 1atm = - 33°C We condense the ammonia : What do we do with all the leftover N 2 2 ? It’s hard to make in ammonia syn gas plant, so we don’t want to throw them away!! We recycle!!!! N 2 + 3H 2 2NH 3
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Real Process: Recycle NH 3 (liq) N 2 + 3H 2 2NH 3 reactor 900°F 300 atm condenser 300 atm -5°C F H 2 /N 2 = 3/1 A/N 2 = 0.934/78.05 X:Conversion per pass (once through) = moles limiting reactant - moles limiting reactant to reactor from reactor moles limiting reactant to reactor N 2 H 2 A NH 3 N 2 H 2 A R RF G
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Givens 1) Conversion per pass (once through) Here X = 0.2 (by reactor design) There is now a problem on what to do with A accumluating since it has no exit
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Real Process: Recycle NH 3 (liq) N 2 + 3H 2 2NH 3 reactor 900°F 300 atm condenser 300 atm -5°C F H 2 /N 2 = 3/1 A/N 2 = 0.934/78.05 N 2 H 2 A NH 3 N 2 H 2 A R RF G X =0.2 What to do with A accumluating? We add a purge
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Givens 2) Purge What do we do with A accumulating? Add purge. We will take = 0.05. Never let build up past this amount. RF A y
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Real Process: Recycle N 2 + 3H 2 2NH 3 reactor 900°F 300 atm condenser 300 atm -5°C NH 3 (liquid) X =0.2 H 2 /N 2 = 3/1 A/N 2 = 0.934/78.05 N 2 H 2 A N 2 H 2 A P RF F G NH 3 N 2 H 2 A CG R y A =0.05
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3) Reactor Feed Composition NB because stoichiometric feed and because no NH 3 from condenser H 2 /N 2 = 3 everywhere. y
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lecture+21A+recycle+_+purge - Recycle & Purge: Ammonia...

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