12.07.2015 Views

Simulation of Water-Gas Shift Membrane Reactor for Integrated ...

Simulation of Water-Gas Shift Membrane Reactor for Integrated ...

Simulation of Water-Gas Shift Membrane Reactor for Integrated ...

SHOW MORE
SHOW LESS
  • No tags were found...

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Strojniški vestnik - Journal <strong>of</strong> Mechanical Engineering 57(2011)12, 911-926Table 2. Activation energies and pre-exponential factors <strong>for</strong> <strong>for</strong>ward and backward WGSR obtained fromliterature; the rate constants <strong>for</strong> WGSR were calculated at operating temperature 1073 KSourceE af[J/mol]k 0f[(l/mol) 0.5 s -1 ]E ab[J/mol]k 0b[(l/mol) 0.5 s -1 ]k f[(cm 3 /mol) 0.5 s -1 ]k b[(cm 3 /mol) 0.5 s -1 ]Culbertson [8] 334.72 7.7·10 45·T-10 (i) / / 6.10 /Graven & Long [9] 281.58 5.0·10 12 238.49 9.5·10 10 3.10 7.37Bustamante [10] 253.55 1.52·10 10 218.40 6.65·10 8 0.22 0.49(i)The pre-exponential factor is also temperature dependant there<strong>for</strong>e the correct unit is K 10 (l/mol) 0.5 s -1 .xji , + 1n=nji , + 1Ri , + 1,(29)where j represents individual specie (H 2 , CO 2 , COor H 2 O).Similarly, the concentration <strong>of</strong> each specieswas calculated:nji , + 1 pRpRc ji , + 1 = ⋅ = x ji , + 1 ⋅ , (30)nRi , + 1 RT ⋅ RT ⋅where the pressure on the retentate side was heldat constant value p R = 50 bar. The partial H 2pressure on the retentate side was calculated as:p = x ⋅ p(31)RH2, i+ 1 RH2, i+1 R .In order to calculate heat duty the heat <strong>of</strong>reaction DH R needs to be calculated. This wasdone by using the van’t H<strong>of</strong>f Relation based onsource [6]:2 ∂∆HR=−R⋅T⋅ ln Keq( T, p ), (32)∂Twhere the logarithm <strong>of</strong> equilibrium constantK eq was obtained with the equation reported inBustamante [10] which was based on the studyfrom Singh and Saraf [7]:⎛ 9998.22 ⎞⎜ − 10 . 213 +T⎟⎜⎟ln K. Teq = 1.⋅ −3⎜ + 2 7456⋅10⋅ − ⎟.(33)1 987 ⎜−6 ⎜ −0.453⋅10⋅T2 ⎟− ⎟⎜⎝ −0. 201⋅lnT⎟⎠And the CO conversion X CO was deducedas follows:nCO, in − nCO,i+1XCO,i+1 =. (34)nCO,inb) Permeate side:Similarly as on the retentate side the Law<strong>of</strong> Conservation <strong>of</strong> Mass must also apply <strong>for</strong> eachsection on the permeate side. The molar flow <strong>of</strong>H 2 and N 2 mixture was calculated as:nPi , + 1 = nPi , −nH 2, i+1.(35)Because the molar flow <strong>of</strong> the N 2 sweepinggas is constant throughout the reactor, the molarflow <strong>of</strong> H 2 on the permeated side can be writtenas:n = n − n(36)PH2, i+ 1 Pi , + 1 N2.Samilarly as on the retentate side, themolar fraction <strong>of</strong> each species was calculatedusing the Eq.:nji , + 1x ji , + 1 = ,(37)nRi , + 1where j represents individual specie (H 2 or N 2 ).The partial H 2 pressure on the permeateside was calculated as:pPH2, i+ 1 = xPH2, i+1⋅ pP. (38)where the pressure on the permeate side was heldat the constant value p P = 1 bar.2.3 Model Design in Aspen PlusThe simulation was per<strong>for</strong>med using theAspen Plus reactor model unit where chemicalreactions <strong>of</strong> WGS and side reactions (H 2 S andCOS <strong>for</strong>mation) were modelled. The inputdata were temperature, pressure, molar flow,composition <strong>of</strong> syngas and <strong>for</strong>mulas <strong>of</strong> chemicalreactions that take place inside the reactor. Theshortcoming <strong>of</strong> the model was that the programhad no in<strong>for</strong>mation about the kinetics <strong>of</strong> the WGSRand hence no knowledge <strong>of</strong> the extent <strong>of</strong> the COconversion and the H 2 permeation through themembrane. These two parameters were calculatedbased on the kinetics <strong>of</strong> the WGSR and importedfrom Mathematica (see Fig. 4). That gave us moreaccurate predictions <strong>of</strong> the molar flow <strong>of</strong> H 2 in thepermeate stream and the achieved CO conversion918 Lotrič, A. ‒ Sekavčnik, M. ‒ Kunze, C. ‒ Splieth<strong>of</strong>f, H.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!