Tutorial 4 Solutions

Tutorial 4 Solutions - CHBE 141 . fit/yaw 6’ Swap/{0214...

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Unformatted text preview: CHBE 141 . fit/yaw 6’ Swap/{0214 2003/: 1/0; Q1: 20 CH4 (:02 20 cs2 , $02 10 502 “33"” H20 50 H20 N2 02 N2 02 Also, we know that the NZ/O2 ratio in the air feed stream is 79/21. We could solve this problem either by choosing elements (C, S, H, O, N) or compounds as components. We’ll solve it here using compounds, which means that we need to write the balanced chemical equations. There are only two (SO2 and H20 are already oxidized): CH4 + 202 ~—> €02 +2H20 (R1) C82 + 302 » €02 +2so2 (R2) From steady-state material balance equations for methane and carbon disulfide, we find the extents of reaction: helium = 20 - $1 = 0 51 = 20 fiCSZput = 20 ‘é2 i: 0 5'2 = 20 Now we use these numbers to solve the remaining material balances: ficozput = 31 + 52 = 40 fisozput =10 + 252 = 50 fimom, = so + 251 = 90 fiszut = fiNZjn fiozput = h02,in " 251 ' 352 = {102,1}; " 100 We have 2 equations involving 4 unknowns. We use the stream composition specifications to provide the last 2 equations: fiNZjn = 12 fioz’m 21 fisozpu: = 0 02 z 50 fisozpuz + ficozput + fiszut + fiozput 50 + 40 + fiszut + fiozput (Note: mole fraction SO2 in outlet is on a dry basis, so water is not included in the denominator.) We find the solution by substitution or by using an equation solver: i102 in = 527 fiozpu: = 427 fiszut = fiN2,in =1983 The % excess oxygen is calculated from the amount of oxygen fed that is in excess of stoiChiometric requirements, considering both reactions: r'z -— I+3' _ wxwm=wxiom=42m 251+3§2 100 or, rounding up just to be safe, minimum oxygen excess required is 430%. The composition of the combustion gases is calculated from the solution of the material balances, knoWing that the total outlet flow (at the chosen basis ) is 40+50+90+1983+427 = 2590 gmol/min: 77 mol% N, 16.6 mol% 02, 1.93 mol% $02, 3.5 mol% H20, 0.77 mol% C02. ’ ‘ ' ' ' 715M 7LF0+ flm "(Mw‘ MM = 300 -— g g 3100:300§1§3 yufm/ -g'v : gufjgf/yw 52mg 200—; - ‘ (a 9:412 ...
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Tutorial 4 Solutions - CHBE 141 . fit/yaw 6’ Swap/{0214...

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