An experimental study on optimization of ammonia co-firing in an 80kWth pulverized coal combustion system

Co-firing ammonia with pulverized coal in power plants has become one of the most feasible options for reducing CO2 emissions. This study aims to investigate the combustion and NOx emission characteristics for various methods of ammonia injection, and to find an optimal solution for system modifications in a single burner in low co-firing ratio up to 20% (basis of lower heating value). An 80 kWth-scale furnace and pulverized coal burner were used for the combustion tests, and four different nozzles with various directions and velocities of ammonia injection were tested for co-firing ratios in the range of 0 to 20%. Side-wall injection at various positions was also tested for a 20% co-firing ratio. Composition of combustion gas (O-2, CO2, CO, NO and unburned ammonia) for each experimental case was measured. From the experimental results, Experimental is found the optimal injection velocity and direction for different co-firing ratios, and side-wall injection was observed to not be advantageous due to higher NOx emissions or the detection of unburned ammonia in the combustion gas. It was also found that the addition of ammonia could provide another viable option for controlling combustion and NOx formation by injecting it into a zone of high temperature and reducing atmosphere formed by the intensive release of volatiles from the coal. Temperature distribution and heat flux up to 60% in the upper of the furnace were also measured, and they decreased considerably at higher co-firing ratios. These lower flame temperatures and reduced particle concentrations are the major causes of the decrease in radiative heat transfer. Combustion efficiency slightly decreased for the case of 20% co-firing, but the change was not significant, as supported by the experimental results showing low concentrations of carbon monoxide and no unburned ammonia. These results can be utilized for retrofitting the design of coal power plants to ammonia co-fired plants, with minimum modifications.