Many utilities have implemented fuel switching schemes as a means of complying with the 1990 Clean Air Act Amendment SO_2 emissions requirements. One approach considered has consisted of blending traditional mid- to high-sulfur Eastern bituminous (EB) coals with low-sulfur sub-bituminous Powder River Basin (PRB) coals. With the advent of more stringent environmental constraints in terms of NO_x emissions limits, utilities equipped with low-NO_x burners are finding that optimizing the operation of the boiler and low-NO_x firing system is a challenging task. Operation at reduced NO_x levels is impacted by the characteristics of the fuel blend and associated constraints. This paper discusses issues related to the impact of EB/PRB coal blends on NO_x emissions and unit performance, and reports case studies where these issues were factored into combustion optimization programs for NO_x control. Two case studies are presented which involve testing at two tangentially-fired units rated at 535 and 320 MW and retrofitted with advanced low-NO_x firing systems with SOFA ports. Coal blends in these units can fluctuate by as much as 20 percent and they are constrained by slagging and plugging, which occur in the upper furnace and in the superheater and reheater sections.
展开▼
