Numerical Concept Study for Part-Load Operation of the Ansaldo Constant Pressure Sequential Combustion System Operated in Rich-Dilute-Lean Mode Using Ammonia-Based Gaseous Fuels

Two earlier concept studies [1,2], exploiting high-resolution numerical simulations, have shown that Ansaldo’s Constant Pressure Sequential Combustion (CPSC) at full load is theoretically capable of switching from conventional Lean Pre-Mixed (LPM) combustion to a Rich-Dilute-Lean (RDL) type staging strategy. However, an intrinsic challenge related to operation of RDL combustion systems is the implementation of a fuel-rich primary combustion stage during part-load operation, when significantly less fuel is required because of the lower target flame temperature. The present work complements and extends the scope of the two earlier numerical studies. Large-Eddy Simulation (LES) with detailed chemical kinetics are carried out to assess the impact of part-load operating conditions on the emissions performance of the Multi-Burner First Stage (MBFS) fired in RDL mode with ammonia-based fuels. The numerical investigation compares alternative implementations at 40% and 50% part-load operating conditions. These two part-load operating conditions of the MBFS combustion system are numerically investigated considering different combinations of switch-off burners. Part-load performance of the MBFS for several switch-off burners scenarios is assessed in terms of predicted flame stability, NOx and N2O emissions. It is shown that low-emissions operation of the CPSC with ammonia-based fuels is achievable even at the globally fuel-lean conditions required by part-load operating conditions as long as a RDL staging strategy is implemented at the level of the single burner.