Reburning Technologies for the Control of Nitrogen Oxides Emissions from Coal-Fired Boilers

The Clean Coal Technology (CCT) Demonstration Program is a government and industry co-funded effort to demonstrate a new generation of innovative coal utilization processes in a series of " showcase " facilities built across the country. These projects are carried out on a scale sufficiently large to demonstrate commercial worthiness and to generate data for design, construction, operation, and technical/economic evaluation of full-scale commercial applications. The goal of the CCT Program is to furnish the U.S. energy marketplace with a number of advanced, more efficient coal-based technologies meeting strict environmental standards. These technologies will mitigate the economic and environmental impediments that limit the full utilization of coal as a continuing viable energy resource. To achieve this goal, beginning in 1985, a multiphased effort consisting of five separate solicitations was administered by the U.S. Department of Energy's (DOE) Federal Energy Technology Center (FETC). Projects selected through these solicitations have demonstrated technology options with the potential to meet the needs of energy markets while satisfying relevant environmental requirements. Part of this program is the demonstration of reburning technologies on existing coal-fired utility boilers to reduce emissions of nitrogen oxides (NOx). NOx is an acid rain precursor and a contributor to the formation of ground-level ozone, which is a health hazard and a major component of smog. NOx emissions are regulated under the provisions of the 1990 Clean Air Act Amendments (CAAA). In applying reburning to a coal-fired boiler, the furnace is subdivided into three zones: (1) the primary combustion zone, where the bulk of the coal is burned with relatively low levels of excess air (NOx is formed in this zone); (2) the reburn zone, where 10% to 30% of the total heat is provided as reburn fuel and where, under reducing conditions , NOx is converted to molecular nitrogen ; and (3) the burnout zone, where overfire air is injected to complete burnout of the remaining combustibles. This report discusses three CCT reburning projects: • Coal Reburning for Cyclone Boiler NOx Control was tested by The Babcock & Wilcox Company on a 110-MWe (gross) cyclone boiler at Wisconsin Power & Light Company's Nelson Dewey plant in Cassville, Wisconsin. The objective was to demonstrate 50% or greater NOx reduction. This goal was achieved, using both bituminous and subbitu-minous coals. The technology was effective at turndown ratios of 66% and 63%, respectively. Process flexibility was excellent. • Gas Reburning-Low-NOx Burners (GR-LNB) was tested …