Effect of limestone addition on no emission during petroleum coke combustion in CFBB.

Combustion in a circulating fluidzed bed boiler (CFBB) for power generation is the most effective pathway for petroleum coke utilization, and during which, limestone is usually employed to capture SO2 to meet the emission demand. However, it also was found accidentally that limestone can play a very active role to reduce NO emission. To investigate the effect mechanism of limestone addition on NO reduction, laboratory and industrial experiments were performed in a lab-scale circulating fluidzed bed (CFB) reactor and industrial CFBB, respectively. The results showed that the reduction of NO with limestone addition was caused by the catalysis of CaSO4 on the reduction reaction of NO by CO into N2 in the dilute phase of the CFBB. Then, the catalysis of CaSO4 on the reduction reaction of NO and CO was further experimentally studied in a horizontal tube furnace. CaSO4 was found to be a strong catalyst on the reaction with a reduction rate of NO up to 99%.