Thermochemical recuperative combined cycle with methane-steam reforming combustion

Thermochemical recuperative combined cycles with methane-steam reforming ar e proposed for improving their thermal efficiency and for peak-load levelin g. For targeting higher thermal efficiency, a cycle with methane-steam refo rming reaction heated by gas turbine exhaust was analyzed. The inlet temper ature of gas turbine was set at 1,350 degrees C. Low-pressure steam extract ed from a steam turbine is mixed with methane, and then this mixture is hea ted by part of the gas turbine exhaust to promote a reforming reaction. The rest of the exhaust heat is used tu produce steam, which drives steam turb ines to generate electricity. The effect of steam-to-methane ratio (S/C) on thermal efficiency of the cycle, as well as on methane conversion, is inve stigated by using the ASPEN Plus process simulator. The methane feed rate w as fixed at constant and S/C ratio was varied from 2.25 to 4.75. Methane co nversion shows an increasing trend toward the ratio and has a maximum value of 17.9% at S/C=4.0. Thermal efficiency for the system is about 51%, which is 1% higher than that calculated for a conventional 1,300 degrees C class combined cycle under similar conditions. A thermochemical recuperative combined cycle is designed for peak-load leve ling. In night lime operation from 20 : 00 to 8 : 00 it stores hydrogen pro duced by methane steam reforming at S/C=3.9 to save power generation. The g as turbine inlet temperature is 1,330 degrees C. In daytime operation from 8 : 00 to 20 : 00 the chemically recuperated combined cycle operated at S/C =2.0 is driven by the mixture of methane and the stored hydrogen. The outpu t at night-time operation decreases down to 0.70 of that for a combined cyc le operated at constant load with the same methane feed rate. whereas dayti me operation generated power 1.26 times larger than that of the combined cy cle.