Exercise 5 Text

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1 Department of Energy Politecnico di Milano Via Lambruschini 4 - 20156 MILANO Exercises of “ Fundamentals of Chemical Processes” Prof. Gianpiero Groppi Exercise 5 Estimation of the heat supply Q required by the First Stage of a Reformer In the first stage of the reforming process, synthesis gas is prepared starting from natural gas. The process can be summarized with the following two reactions: CH 4 + H 2O ↔ CO + 3 H 2 (1) CO + H 2O ↔ CO 2 + H 2 (2) The second reaction (2) is the Water Gas Shift. The first reaction is the Reforming of methane with steam (steam reforming). This reaction is highly endothermic and the necessary heat is supplied via exchange at the reactor walls. In a typical process, the feed gases (composition given in the Table) enter the reactor at 550°C and exit at 800°C. Assuming that the process reaches the thermodynamic equilibrium, estimate the composition of the outlet gas stream, and find the amount of heat Q to be supplied. Data: Stream 1: P = 30 atm T = 550°C Stream 2: P = 30 atm T = 800°C Hypothesis: Both the reactions reach the thermodynamic equilibrium Ideal mixture of ideal gases Specie Flow Rate (Nm 3/h) CH 4 22486 H2O 94015 2 Solution The problem asks for the estimation of the heat supply Q and of the composition of the outlet gas stream. For each specie, the material balance is written by applying the extent of reaction method: in this case, two reactions are required, the steam reforming and the WGS. Therefore, it is possible to define the extent of reactions λ 1 and λ2. 100 mol/h inlet CH 4 are chosen as the basis for the material balances. The flow rates of the outlet gas stream are expressed as a function of λ1 and λ2: ∑ = ⋅+= NR j jji in i out i nn 1 , λυ The amount of H 2O in the inlet feed is calculated as follows: 1…