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

Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 911-926rate and the permeation through the membrane.The calculated data were then imported in AspenPlus as input (or initial) values for simulations.Aspen Plus was used to predict thebehaviour of a WGSMR by using basic engineeringrelationships, such as mass and energy balances,and phase and chemical equilibrium. According tothe calculated data from Mathematica, predictedoperating conditions, and different design models,the behaviour of MR was simulated.around 1.1 can be reached with quench waterat 260 °C.2.1 Initial and Boundary ConditionsIn IGCC system the MR will be situatedafter the gasifier and before the gas turbinecombustor, replacing the WGS reactor and PSAsystem (see Fig. 1).The boundaries for the modelled systemare marked with the dashed line in Fig. 4. Inthis figure n represents the molar flow, x thecomposition, T the temperature and p the pressureof gas stream. Heat duty is represented with Qand CO conversion with X CO . Index GAS stands forsyngas, R for retentate side and P for permeate sideof the membrane.Based on the position in the chain ofprocesses that take part in the IGCC, the initialand boundary conditions for “base case” studieswere defined:a) Based on gasifier:• The modelling is based on a dry-feedentrained-flow gasifier with water quench.Therefore, the maximum outlet pressure fromthe gasifier is presumed to be around 50 bar.• The outlet temperature from the gasifier is setto 1500 °C.• Composition of syngas has a major role indefining the steam-to-CO ratio and especiallyin defining the H 2 partial pressure.b) Based on quench:• The quench temperature is set to 800 °C. Inorder to reach this temperature the syngas hasto be quenched with water and not steam.• With pressure of 50 bar, equal to syngas,quench water can only reach temperaturesup to 264 °C, otherwise it would begin tovaporise.• Steam-to-CO ratio is also dependent on thetemperature of quench water. Maximum ratioFig. 5. Schematic presentation of the reactormodelc) Based on MR:• For modelling the tubular MR with gaugemeasurements L = 40 m and a = 10 m wasselected (see Fig. 5). The outer tubularmembrane diameter was set to the value 2r =7.5 cm.• The operational temperature range of the MRis presumed to be between 700 and 900 °C.• The pressure on the retentate side is definedby the outlet from the gasifier. In this study itis presumed to be 50 bar.• Low pressure on the permeate side increasesthe driving force through the membrane.However, from the point of energy lossneeded for compression the minimumpressure should not be less than 1 bar.• In order to improve the driving force the N 2sweep gas is introduced. In view of syngasthe flow of N 2 is in counter-current directionwhere H 2 -to-N 2 molar ratio at the exit is 1:1.• Since the WGSR is an exothermal reaction,the reactor is water cooled. In the presentstudy the MR will operate at isothermalconditions.• The desired CO conversion is set to be around95%.• Based on the temperature range, pressureconditions, hydrogen purity and permeability,the selected membrane material isPalladium based with permeance:k′ = 3·10 -4 mol m -2 s -1 Pa -0.5 .916 Lotrič, A. ‒ Sekavčnik, M. ‒ Kunze, C. ‒ Spliethoff, H.