OCR Text |
Show Paper No. 12 IFRFDocNoK70/y/113 -1- AFRC Spring IJmuiden, April 1997 meeting 1997 FIRING OF COAL AND MUNICIPAL WASTE SLUDGES FOR UTILITY BOILERS D J Morgan, P Dacombe and W L van de Kamp International Flame Research Foundation ABSTRACT The reduction of emissions of pollutants such as NOx, S02 and particulates from coal fired utility boilers, whilst maintaining good combustion efficiency, is one of the key issues in present utility boiler burner development. This paper presents the results of semi-industrial scale (2.5 M W t J furnace studies using swirl stabilised burners in a boiler chamber simulator with internal dimensions of 2x2x6.3 m. The experimental burners were designed to be flexible in terms of geometry and fuel-air staging. They incorporated a number of channels which were used for the primary fuel (in this case coal), and the reburn fuel, which included municipal sewage sludge, high or low volatile matter coal or natural gas. 1. BACKGROUND It has long been recognised that fuel staging in combination with air staging has potential for reducing emissions of pollutants such as NOx, S 0 2 and particulates. However, modifying existing equipment to employ techniques such as furnace fuel staging [1] so that the entire furnace is physically segregated into a primary, reburn and tertiary air zone, has proved to be a complex and costly task. In order to retain the fuel staging concept as a NOx reduction technique, while removing the complexities of injecting fuel and air above the burner, a number of investigations were made to explore the possibilities of integrating the staged (also refened to as reburn) fuel and air into a single burner arrangement [2,3,4]. In this paper the results of semi-industrial scale (2.5 MWJ experiments on swirl stabilised internally fuel staged burners are presented. The burners were designed to be flexible in terms of geometry and fuel-air staging. They incorporated a number of channels which were used for the primary fuel (in this case coal), and the staged fuel; which included municipal sewage sludge, high or low volatile matter coal or natural gas. The burner relied on the creation of three zones; a swirl stabilised primary zone, formed from the primary fuel and the swirled combustion air, a reburn zone formed by injecting the staged fuel at various locations in the burner and a tertiary or burnout zone. Fuel staging with biomass fuels such as sewage sludge, also helps to address several of concern relating to waste disposal and the control of 'greenhouse' gases. This is because fuels derived from biomass are renewable and contain low concentrations of sulphur and nitrogen [5, 6]. 2. FACILITIES 2.1 General All investigations presented in this paper were performed on the IFRF semi-industrial scale furnace which has internal dimensions of 2*2*6.3 m. The furnace consists of |