CFD Simulations of an Additional H₂ Combustor for Improving Efficiency in Chemical Looping Combustion Power Plants

Chemical looping combustion (CLC) is a promising technology for hydrocarbon fuel combustion with integrated CO₂ capture. The CLC process imposes almost no direct energy penalty for separating CO₂, but a large indirect energy penalty is encountered when CLC reactors are integrated into a combined cycle power plant due to the maximum reactor operating temperature that is far below the inlet temperature of modern gas turbines. Previous works have shown that additional fuel combustion after the CLC reactors can almost eliminate this energy penalty, although more expensive hydrogen fuel must be used to avoid CO₂ emissions. This study conducts CFD simulations of an added combustor fired with hydrogen, focusing mainly on mechanisms to reduce NO_x formation. Three mechanisms are explored: 1) a greater number of fuel injectors, 2) increased turbulence, 3) and lower O₂ content of the air stream due to flue gas recirculation. Option 2 proved the most effective at reducing NO_x, followed by Option 3. When combined, these mechanisms could result in NO_x emissions below 50 ppm using a very compact combustor. In conclusion, low-NO_x operation of the added combustor appears to be feasible and it is recommended for inclusion in future studies of CLC combined cycle power plants.