Ammonia as a Fuel for Gas-Turbine Units with Thermochemical Recuperation of Exhaust Gas Heat

Abstract

The prospects are examined for application of ammonia-fired gas turbine units (GTUs) with thermochemical recuperation of the exhaust gas heat. Examples of operating ammonia-fired gas turbine units are given, and the main operating restrictions for the use of existing gas turbine units are specified. A thermodynamic analysis of a simple gas turbine unit with thermochemical heat recuperation (TCR) was performed in a wide range of operating conditions: the gas temperature at the turbine inlet varied from 700 to 1300°C and the compressor pressure ratio from 5 to 20. It has been established that the thermochemical heat recuperation can increase the GTU efficiency by as much as 9%. The effectiveness of TCR application has been demonstrated to depend on such operating parameters as pressure and temperature. At a temperature above 500°C, the enthalpy of the ammonia decomposition reaction reaches a value close to the maximum of approximately 3.0 MJ/kg NH₃. Thermochemical recuperation leads to the decomposition of ammonia with production of a hydrogen-rich gas (up to 75% (by volume)), which is burned in the combustion chamber, thereby changing the combustion process characteristics. The flame propagation velocity in a gas mixture consisting of hydrogen, nitrogen, and ammonia in different proportions was calculated on the basis of the GRI-Mech 3.0 list of elementary reactions in the Chemkin-Pro module. It has been found that the products of complete thermochemical decomposition of ammonia have a flame propagation velocity that is approximately two times higher than that for methane and more than ten times higher than that for ammonia. Thus, the implementation of the thermochemical heat recuperation in ammonia-fired gas turbine units is expected to increase the energy efficiency and improve the combustion process stability.