3 Analysis of diverse heat recovery steam cycles Report B

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* Peva = 33 bar – optimized value of project 2 Project 3: Analysis of diverse heat recovery Steam Cycles Artoni Alessandro Bortolotti Alberto Cordisco Giuliano We consider a combined cycle with the same simple cycle gas turbine described in the 2nd project. With the aid of the software Turbogas we find the following operating conditions: -­‐ Air mass flow rate supplied to the compressor: 650 kg/s -­‐ TIT – turbine inlet temperature: 1277°C -­‐ Compressor pressure ratio : 18.6 The aim of the project is the analysis of the different obtainable performances of the following heat recovery steam cycles: a. ONE EVAPORATION LEVEL* b. TWO EVAPORATION LEVELS c. THREE EVAPORATION LEVELS WITH SUPERHEATING OF THE HIGH PRESSURE STEAM We post-­‐process the data given out by Turbogas, set with the appropriate working conditions. In the following table we report the most interesting results for a comparison between the three layouts: η cv [%] η rec,th [%] η rec [%] η2 overall [%] η2 sc [%] Pel,sc [MW] Tstack [°C] Case a 32.31 76.98 24.87 50.12 55.85 95.62 142.8 Case b 32.20 85.93 27.67 51.77 62.08 106.38 93.4 Case c 34.26 87.01 29.81 52.03 66.87 114.59 87.4 We clearly see that if the plant has more than one evaporation level, all efficiency terms increase. This is due to the fact that the steam cycle better exploits the heat available from the exhaust gases, because the working fluid better follows the cooling curve of the flue gases, reducing the irreversibilities related to heat exchange between finite ΔT. Hence, thermal recovery in the HRSG increases. As a result, the adoption of more evaporation levels leads to higher steam cycle net power and better performance of the system. In addition, the exhaust gas temperature at the chimney is lower since there is a better thermal recovery…