Advanced Burners for Coal Fired Boilers

Reburning or fuel staging is a technology that can be applied as a retro-fit to burners as a means of reducing NOx emissions. This paper concentrates on using existing knowledge of reburning techniques, with the aim of developing an Integrated Fuel Staged Burner whereby the reburning fuel can be introduced within the burner itself. The investigations were conducted in a simulated boIler chamber with internal dimensions of 2x2x6.3 m. The single burner experiments were performed with Gottelbom (HVB), EI Cerejon (HVB), Middelburg (MVB) and Klein Kopje (MVB) coal. The experiments were conducted at the scale of 2.5 MWt with a swirl stabilised Internally Fuel Staged Burner (IFSB). The primary fuel was a bituminous coal of either high or medium volatile content and the reburning fuels were natural gas or a bituminous coal, again with a high or medium volatile content. The rebum fuel fraction varied from 0% to 40% on a fuel input basis. The main parameters affecting emissions of NOx and burnout were the primary zone stoichiometry, rebum fuel fraction, tertiary air position, coal type and flame type. With reburning conditions of 20% gas (reburn fuel) /80% coal (primary fuel) NOx could be reduced in the range 55-78%, relative to a baseline 100% coal flame, depending on the location of the tertiary air and coal type. Reburning of pulverised coal with pulverised coal led to reduced concentrations of NOx relative to the baseline flames, but increased concentrations compared to conditions where natural gas was used as the rebum fuel, which is consistent with the higher concentration of fuel-bound nitrogen. In addition to the above investigation, further experiments were conducted whereby a number of coals were fired with a municipal sewage sludge containing a high fuel nitrogen content.