Low energy penalty near-zero carbon emission coal-fired power generation system with chemical looping CO2-for-N2 substitution

Chemical looping air separation (CLAS) has been considered an alternative to cryogenic air separation for reducing the high efficiency penalty of oxy-fuel combustion. In conventional CLAS-integrated oxy-fuel combustion systems, the reduction and oxidation reactors are externally coupled as a subsystem for oxygen production, and the heat required for the endothermic reduction process is supplied by auxiliary energy sources or by the sensible heat of the circulating oxygen carrier and sweep gas in fluidized-bed reactors. To improve system integration, this study proposes a coal-fired power generation system integrated with chemical looping CO2-for-N2 substitution. In the proposed system, the reduction and oxidation reactors are decoupled, and system-level heat integration is designed according to the principle of energy cascade utilization. Recycled flue gas is used as the sweep gas to release oxygen from the oxygen carrier, forming an O2/CO2 oxidant that directly replaces air for coal combustion and avoids N2 dilution. Meanwhile, the oxygen carrier reaction unit is integrated with the boiler heat transfer surface by replacing part of the waterwall with fixed-bed reactors. High-energy-level combustion heat drives oxygen carrier reduction, while the heat released during oxidation is recovered for low-energy-level steam generation. Thermodynamic assessment results show that the proposed system reduces the efficiency penalty by 3.42 percentage points and increases the exergy efficiency by 3.25 percentage points compared with conventional oxy-fuel combustion. This study reveals the intrinsic mechanism by which the proposed system reduces the carbon capture efficiency penalty and system irreversibility.