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ABSTRACT
A combined gas power cycle with humidification has been investigated using the advanced exergy analysis. The combustion chamber and humidifier were found to be the components with the largest exergy destruction. For a prescribed overall power generation, the exergy destruction at the combustion chamber increased, while that at the humidifier decreased when the humidification ratio at the bottoming cycle was increased. However, most of the irreversibility generation at these components was shown to be unavoidable. The topping cycle turbine and compressor were revealed to be the components with the largest endogenous and avoidable irreversibility generation. This means that there is a real potential of improving the overall performance of the cycle by improving the operation of these two components. The endogenous avoidable exergy destruction at the topping cycle turbine and compressor decreased monotonically when the humidification ratio, the combustion chamber exit temperature or the mass flowrate ratio between the bottoming and topping cycles were increased, and increased when the topping cycle pressure ratio was increased. On the other hand, varying the humidification ratio at the bottoming cycle from zero to one resulted in as much as 26% reduction of the irreversibility generation at the topping cycle turbine and compressor.
Acknowledgments
The financial support of the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Defense Academic Research Program (CDARP) is acknowledged.
Highlights
A humidified gas cycle has been studied using the advanced exergy analysis.
The combustion chamber, humidifier and recovery heat exchanger were the most inefficient components.
The combustion chamber, humidifier and recovery heat exchanger irreversibility was found to be mainly endogenous and unavoidable.
Most of the avoidable irreversibility occurred at the topping cycle turbine and compressor.
The sensitivity of the endogenous avoidable irreversibility at the topping cycle turbine and compressor to a selection of operating parameters was discussed.
Nomenclature
| = | Exergy [kW] | |
| = | Specific enthalpy [kJ/kg] | |
| = | Mass flowrate [kg/s] | |
| = | Pressure [kPa] | |
| = | Heat transfer rate [kW] | |
| = | Temperature [K] | |
| = | Specific power [kJ/kg] | |
| = | Mechanical power [kW] | |
| Greek letters | = | |
| = | Humidification ratio [-] | |
| = | Air mass flowrate ratio between bottoming and topping cycles [-] | |
| = | Isentropic efficiency, Effectiveness [-] | |
| = | Density [kg/m3] | |
| = | Exergy to energy ratio [-] | |
| Abbreviations | = | |
| BCC | = | Bottoming cycle compressor |
| = | Bottoming cycle pressure ratio | |
| BCT | = | Bottoming cycle turbine |
| = | Combustion chamber | |
| HEX | = | Recovery heat exchanger |
| HUM | = | Humidifier |
| = | Fuel lower heating value | |
| PP | = | Pump |
| TCC | = | Topping cycle compressor |
| = | Topping cycle pressure ratio | |
| TCT | = | Topping cycle turbine |
| = | Turbine inlet temperature | |
| Subscripts | = | |
| = | Atmospheric air | |
| = | Destruction | |
| = | Heat exchanger | |
| = | Input | |
| = | Product | |
| = | Pump | |
| = | Water vapor | |
| Superscripts | = | |
| = | Avoidable | |
| = | Bottoming cycle | |
| = | Endogenous | |
| = | Exogenous | |
| sat | = | Saturation conditions |
| = | Topping cycle | |
| = | Unavoidable |