Gas turbines for polygeneration? A thermodynamic investigation of a fuel rich gas turbine cycle

Abstract

Gas turbines as used nowadays are working far in the fuel lean regime, which is most reasonable for mobile applications, since the formation of pollutants and soot are avoided while the temperatures remain low enough to avoid damage of the turbine. However, from a thermodynamic point of view the exergy utilization is far from optimum at such conditions. For stationary conditions a different approach may be worth a second thought: the use of gas turbines as chemical reactors for hydrogen and carbon monoxide production in combination with power generation and the utilization of the exhaust enthalpy stream. A gas turbine model cycle is analyzed using complex equilibria including radicals and chemical exergies. Chemical exergies were calculated from equilibrating the gas mixtures at different points in each process with a large excess of moist air. Methane was studied as an example fuel. Comparing the exergy losses of the idealized gas turbine process, the losses for fuel rich mixtures are lower than for lean mixtures used in gas turbines nowadays. The exact values of the exergetic efficiency depend on the pressure ratio, which was studied in the range of 10 to 30. The hydrogen to carbon monoxide ratio would be typically near 2.2, while the adiabatic flame temperature would be in a range which either would cause no damage to typical gas turbines or could be handled with carbon fiber reinforced carbon. The composition of the gases is likely to change within the turbine, where temperature and enthalpy drops. This was considered in additional calculations where chemical equilibration of the gas mixture in the turbine is considered. The possibility to combine a partial oxidation with an energy conversion process and thus produce syngas mixtures would add an additional flexibility to the gas turbine process, which is worth consideration.

Numerical optimization and reaction flow analysis of syngas production via partial oxidation of natural gas in internal combustion engines

“…The produced syngas could be fed to a gas-to-liquid process, the mechanical energy converted to electricity and the excess heat used for preheating the fuel or in other nearby industrial processes. Although gas turbines were the focus of the work in the publication by Atakan [1], similar considerations hold for ICEs, which are addressed in this study. The use of ICEs to produce more useful products instead of CO 2 and H 2 O is thus motivated by two different aspects: Firstly, the potential to increase overall process efficiency and secondly, the possibility to achieve conditions that are not feasible in conventional reactors arising from the piston motion.…”

“…An interesting idea is outlined by Atakan [1], where he proposes to operate gas turbines as polygenerators in order to produce gaseous base chemicals together with mechanical power. When operated under fuel-rich conditions with methane as fuel, the process has been shown to be thermodynamically more favorable.…”

Flexible energy conversion and storage via high-temperature gas-phase reactions: The piston engine as a polygeneration reactor

“…Lean combustion generally leads to much exergy destruction, limiting the efficiency of such processes. The exergetic analysis of fuel-rich combustion in gas-turbine cycles [24] shows that the exergy is conserved to more than 85% at equivalence ratios above 2, while it was below 70% in the fuel-lean regime. Thus, fuel-rich combustion with work transfer from the system seems to be promising.…”

Enthalpy of Formation Modeling Using Third Order Group Contribution Technics and Calculation by DFT Method.

“…A gas turbine is a combustion engine that can convert gas or other liquid fuels to mechanical energy [3][4][5][6][7][8]. So developing a theoretical method to estimate formation enthalpy especially for gas stat became a necessary for ameliorating the gas turbine performance [9][10][11][12].…”