Exercise 1 Solution

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Prof. Gianpiero Groppi – Exercises – Fundamentals of Chemical Processes – A.A. 2023-2024 1 EXERCISE 1 Adiabatic flame temperature for propane combustion The combustion of propane with air is carried out in an adiabatic reactor: C3H8 + 5O2 ↔ 3CO2 + 4H2O Calculate the temperature of the exhaust gas stream at the outlet of the reactor (T OUT) in the following cases: 1. Stoichiometric feed of the reactants; 2. Air in excess of 30% (molar basis); 3. Considering the case with excess air, assume that due to ill -combustion CO is present in the exhaust, with a selectivity of 10% with respect to the moles of carbon converted. DATA: C3H8 stream: T = 25°C P = 1 atm AIR stream: T = 25°C P = 1 atm R.H. = 60%, with PSATH2O (25°C) = 3.167 kPa ΔH0C,C3H8 (25°C) = -2043 kJ/mol ΔH0C,CO (25°C) = -283 kJ/mol Cp equation and parameters from J.M. Smith, H.C. Van Ness, M. M. Abbott, Introduction to Chemical Engineering Thermodynamics, 7th edition, McGraw Hill (2005). Standard formation enthalpies from NIST website. Specie ΔH0F [kJ/mol] 𝐂𝐏,𝐢̅̅̅̅̅ = 𝐑𝐠𝐚𝐬. (𝐚𝐢 + 𝐛𝐢. 𝐓 + 𝐂𝐢 𝐓𝟐) [kJ/mol/K], T in [K] a b c C3H8 -104.7 1.213 2.897E-04 - N2 0 3.280 5.930E-04 -4.000E+03 CO2 -393.5 5.457 1.045E-03 -1.157E+05 H2O -241.8 3.470 1.450E-03 1.210E+04 O2 0 3.639 5.060E-04 -2.270E+04 CO -110.5 3.376 5.570E-04 -3.100E+03 Prof. Gianpiero Groppi – Exercises – Fundamentals of Chemical Processes – A.A. 2023-2024 2 SOLUTION The problem requires the calculation of the temperature of the exhaust gas stream at the outlet of the reactor (TOUT) in three different cases. CASE 1: Stoichiometric feed of the reactants In this case the propane combustion reaction is the only one occurring in the system, and we can assign to this and extent of reaction ε. The variation in the number of moles of the i -th species with respect…