The process of isothermal compression of gasses at sub-atmospheric pressures through regulated water injection in Braysson cycles

Although the Braysson cycle constitutes the ideal limit for the Combined Cycle Power Plants, its actual implementation has not been achieved due to the difficulty in building the required isothermal compressor. The present study proposes the incorporation of regulated water injection during the final compression, which could maintain the temperature constant due to the evaporation. The analysis for the thermodynamic implications of the injection on the ideal version of the Braysson cycle indicates that the (ideal cycle) efficiency reduction will be minimal. The study provides an analysis for the water injection rate that will permit such a process and shows that the additional work needed to drive the process will not be affected significantly by the injection. In addition, it shows that the minimum temperature of the Braysson cycle will be lower than the corresponding level of the conventional (Gas–Steam turbine Combined cycle plants), something that could improve the efficiency as well. Finally it shows that the process may be expressed by a polytropic relationship of the type pvβ = constant, where β ≈ 1.06.