Reduction of N2O emissions from circulating fluidized bed combustors by injection of fuel gases and changing of coal feed point

This paper describes the reduction techniques of N2O emitted from circulating fluidized bed combustion (CFBC) of coal. Two methods, injecting the fuel gases into the riser and changing the position where coal was supplied, were tried to decrease N2O emission. A small lab-scale CFBC whose whole parts were made of quartz was used. In the first method, methane, propane and hydrogen were used as a fuel gas. By injecting these gases into the riser, N2O emission was decreased remarkably. Reduction rate was almost in proportional to the volumetric flow rate of injected gas. At this time, NO emission did not increase. Required flow rate of injected gas to achieve the same N2O reduction was different among the above gases. N2O emission was able to be decreased remarkably by changing the position where coal was supplied. When coal was fed to the top of the downcommer, devolatilization took place and volatile matters were burnt in the cyclone. As the results, the temperature in the cyclone became high enough to reduce N2O.