2 Heat recovery steam cycle Report B

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Energy Conversion, 2014-­‐2015, Prof. Valenti Project 2: Heat Recovery Steam Cycle Artoni Alessandro Bortolotti Alberto Cordisco Giuliano It is required to perform the analysis of a heat recovery steam cycle combined with a simple gas cycle. Its technical characteristics are provided and supposed to be unchanged after the installation of the bottoming cycle. In fact, the presence of the HRSG determines a slight change in the outlet pressure of the gas turbine. Instead of the ambient pressure (101325 Pa) we need to have a higher value due to pressure drop (3000 Pa) throughout the steam generator. Therefore, the outlet temperature of the gas turbine will change as well as the work extracted. We can calculate the thermodynamic points of the gas cycle using the Cp (T) in its polynomial formulation (fourth order expression). In order to obtain the new outlet temperature Tocc of the turbine we need to solve a system of two equations in two unknowns: -­‐ efficiency constraint: 𝜂!",!"=!!"##!!!"#$!!"##!!!"##.!"=0.925 -­‐ isentropic expansion: 𝑠𝑇𝑜𝑐𝑐,𝑃𝑐𝑐=𝑠!"𝑇𝑜𝑐𝑐.𝑖𝑠,𝑃𝑠𝑐 where: Tosc = outlet gas turbine temperature in case of simple gas cycle (unknown) Tocc = outlet gas turbine temperature in case of combined cycle (544.6°C) Tocc.is = outlet gas turbine temperature in case of isentropic expansion (unknown) Using the goal seek function on Excel we can find an optimized Tocc = 550.16°C. Energy Conversion, 2014-­‐2015, Prof. Valenti We can compute the subsequent loss in electrical power from the gas turbine: ∆𝑊!",!"= 𝑚!"# (ℎ!""−ℎ!"#) 𝜂!" 𝜂!"#,!"=4195.5 𝑘𝑊𝑒 Now that we have found the correction on the gas turbine outlet temperature, we can determine the thermodynamic quantities for each point in the HRSG. In the following tables we have reported the values corresponding to the…