Oxy-combustion typically consists of burning coal with a combination of oxygen and a large amount of recycled flue gas (60-70%). The recycled flue gas is used to manage wall heat flux and match the radiative/convective heat transfer ratios of air-fired combustion systems. Although this approach may be justified for retrofitting air-fired power plants, for green-field applications, other methods for heat flux control and heat transfer are possible. Several new oxy- combustion process concepts have been proposed in recent years, where the level of flue gas recycle ranges from near zero to 80%. By comparing different processes with different amounts of flue gas recycle, studies have shown significant improvements in efficiency for low-recycle processes. In this work, we employ a fundamental thermodynamic analysis to evaluate the impact of flue- gas recycle on the efficiency of oxy-combustion systems. It is shown that for 1 generation oxy- combustion systems, the inefficiency caused by flue gas recycle could lead to as much as 8-10% reduction in efficiency compared to a process with negligible recycle. Furthermore, at high flue- gas-recycle ratios, the fan power for recycle is significant, and adds an additional loss to that caused by thermodynamic inefficiencies. Analysis of the impact of recycle ratio on pressurized oxy-combustion (POC) is also presented, including a discussions on the valorization strategies of the latent heat recovery (made possible due to the higher pressure).
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