Exercise 6 Text

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Department of Energy Politecnico di Milano Via Lambruschini 4 - 20156 MILANO Exercises of “ Fundamentals of Chemical Processes” Prof. Gianpiero Groppi Exercise 6 Estimation of the temperature and the composition at the exit of an adiabatic reactor for the partial oxidation of CH 4 The partial oxidation of CH4 is carried out in an adiabatic reactor: CH 4 + ½ O 2 → CO + 2 H 2 Calculate the composition and the temperature of the gas at the exit of the reactor, assuming that equilibrium conditions are reached. CO, H 2, H 2O and CO 2 are present among the products while O 2 is absent. DATA: Stream 1: P = 30 atm T = 500°C Stream 2: P = 30 atm Tout = ? Hypotheses: Thermodynamic equilibrium Ideal Gas Adiabatic Reactor Specie Flow Rate (Nm 3/h) CH 4 1 O2 0.6 H2O 1 ∆G 0 R is cal/mol, T is K ( ) ( ) TTG TTG SRR WGSR ⋅−+=∆ ⋅+−=∆ 25.6053717 71. 78514 0 , 0 , 2 Solution The problem asks for the estimation of the composition and the temperature T out of the gas stream at the exit of the partial oxidation reactor. To solve the problem, the material balances and the enthalpy balance must be coupled, assuming that the reactor is adiabatic and that the gas reaches the thermodynamic equilibrium. 1 mol/h of incoming CH 4 is chosen as the basis for the material balances. Considering the number of the species involved in the process (NS = 6) and the number of the atomic species (NA = 3), the number of independent reactions that are required to define the solving system are: 36 −=−= NANSNR 3 reactions are required to write the material balances. For each of these reactions, it is possible to define an extent of reaction λ i. The following reactions are chosen: OHCOOCH 2224 22 +→+ λ1 complete combustion 224 3HCOOHCH +↔+ λ2 steam reforming 222 HCOOHCO +↔+ λ3 WGS The choice of the reactions is…