Hybrid solar flameless combustion system: Modeling and thermodynamic analysis

In this paper, the idea of using flameless combustion in a hybrid solar combustion system is investigated by modeling and thermodynamically analyzing a gas turbine system. In this regard, a gas turbine system coupling with hybrid solar flameless combustion including heliostat solar field, central receiver, flameless combustor and power generation system are modeled. In conditions that sun power is not adequate to heat up the combustion air over auto-ignition temperature of the fuel, air is passed through the first stage combustor. To provide a basic cycle for comparison, a common gas turbine with preheater is modeled as well. Energy and exergitic-based analyses of various systems are evaluated and environmental footprints reduction of proposed optimum cycle is assessed and compared to the basic case. The results illustrate that Nitrogen Oxides formation in hybrid solar flameless combustion is significantly lower than common gas turbine system. While the gas turbine with preheater generates 67 μg Nitrogen Oxides per kWh, hybrid solar combustion system produces less than 7 μg Nitrogen Oxides per kWh. In comparison to gas turbine system, fuel consumption decreases in hybrid solar flameless combustion system from 0.1875 kg/s to 0.16 kg/s (about 14.7%) when solar share is considered just 40%. Since the inlet air of flameless combustor is charged from solar heater outlet, increasing air temperature enhances the share of solar energy in the system which results in overall exergy reduction in the system. The proposed system shows significant environmental benefits and based on the available technologies, it is suitable for high temperature solar towers.