Full exam for Energy Systems LM in the Mechanical Engineering degree programme at Politecnico di Milano. The document covers: PROBLEM 1: Data boiler water inlet temperature, °C 20 air inlet temperature, °C 15 boiler water inlet pressure, bar 20 steam pressure, bar 10 outlet steam temp, °C 350 Stack temperature, °C 120 Flue gas temp at inlet of air preheater, °C 250 excess of air 20% fuel = pure CH4
Full exam for Energy Systems LM in the Mechanical Engineering degree programme at Politecnico di Milano. The document covers: PROBLEM 1: Data boiler water inlet temperature, °C 20 air inlet temperature, °C 15 boiler water inlet pressure, bar 20 steam pressure, bar 10 outlet steam temp, °C 350 Stack temperature, °C 120 Flue gas temp at inlet of air preheater, °C 250 excess of air 20% fuel = pure CH4
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PROBLEM 1: Data boiler water inlet temperature, °C 20 air inlet temperature, °C 15 boiler water inlet pressure, bar 20 steam pressure, bar 10 outlet steam temp, °C 350 Stack temperature, °C 120 Flue gas temp at inlet of air preheater, °C 250 excess of air 20% fuel = pure CH4 molar mass CH4, kg/kmol 16 LHV CH4, MJ/kg 50,1 Cp air, kJ/kg/K 1,02 Cp flue gases, kJ/kgK 1,1 thermal losses from boiler walls 1,20% of LHV power unburned fuel losses 0,50% of LHV power mass flow rate of steam 10 O2 conc. In air, O2_air 0,21 molar mass of air, kg/kmol 28,9 pressure at turbine outlet 0,06 turbine isentropic efficiency 0,9 turbine mechanical efficency 0,98 molar mass of CO2, kg/kmol 44 PROBLEM 1: Results stoichiometric O2/fuel molar ratio, O2/fuel_stoich 2,00 From the stoichiometric complete combustion reaction of CH4: CH4+2O2--> CO2+2H2O stoichiometric air/fuel molar ratio, air/fuel_stoich 9,52 Calculated as: (O2/fuel_stoich)/(x_O2air) stoichiometric air/fuel mass ratio, alpha_stoich 17,20 Calculated as: (air/fuel_stoich)*(Mm_air/Mm_fuel) air/fuel mass ratio, alpha 20,64 Calculated as: alpha_stoich*(1+excess_air) enthalpy of generated steam, kJ/kg (h_SH) 3158,16 from Mollier diagram enthalpy of inlet feedwater, kJ/kg (h_SC) 85,80 from equations for calculating the enthalpy of subcooled water thermal power transferred to steam, kW Q_steam 30723,65 derived from energy balance of the heat exchanger: Q_steam = m_steam*(h_SH-h_SC) derived from the energy balance of whole boiler: mair*Cpair*(Tair-25)+mfuel*LHV°(1-unb_losses-th_losses) Q_steam+mflue_gas*Cp_gas*(Tstack-25) boiler efficiency 0,93 from the defintion of boiler efficiency: Q_steam/(mfuel*LHV) preheated air temperature, °C 161,99 derived from the energy balance of air-preheater: mair*Cpair*(Tair_out-Tair_in) =…
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