Effect of cofiring coal with low ash dairy biomass on NO_x in a 100,000 BTU/hr low NO_x burner

摘要

Due to restrictions regarding maximum total daily loads of phosphorus, animal waste can no longer be disposed of by land application and an alternate, cost effective disposal method must be developed. Simultaneously, NO_x emission restrictions for fossil fueled power plants are becoming increasingly stricter and with the adoption of the Cross State Air Pollution Rule, they will only become tighter. Cofiring coal with animal waste, termed as dairy biomass, is proposed as one of the methods to address both concerns for power plants located near dairy farms. In the current work, dairy biomass is evaluated as a cofiring fuel with Wyoming Powder River Basin subbituminous coal in a small scale 29 kWt burner boiler facility equipped with air staged combustion for low NO_x control. Proximate and ultimate analyses performed on coal and dairy biomass (DB) reveal the following: higher heating value of about 30,000 kJ/kg for dry ash free (DAF) coal and 21,000 kJ/kg for DAF dairy biomass; nitrogen and sulfur loading of 0.15 and 0.48 kg/GJ for the coal and 0.33 and 2.67 kg/GJ for the DB ; ash loading of 3.10 kg/GJ for the coal and 11.57 kg/GJ for the DB. The cofiring experiments were performed with 90:10 (by mass percent) coal: dairy biomass blended fuels as well as pure coal. Standard emissions from solid fuel combustion (O_2, CO_2, CO, NO_x, and SO_2) were measured in addition to the temperature profile along the axial length of the furnace. In addition to these emissions measurements, NO_x on a heat basis (g/GJ) was calculated. At equivalence ratio of 0.85 burning pure coal produced 475 ppm of NO_x. Burning pure coal at a 0.85 equivalence ratio with 30% of the total combustion air staged into over fire air reduced NO_x to 419 ppm.