58 MAKALE / ARTICLE load flexibility. The wide range of fuels envisaged, makes the challenge even tougher. The range of planned fuels is from high moisture content peat, bark or wood residue - moisture content 50-58 per cent, heating value 7.5 MJ/kg -to bituminous coal (25 MJ/kg). The huge difference in flue gas amounts is compensated with recirculation gas in coal combustion mode. ECOGENERATION WORLD The boiler is equipped with four independent fuel feeding lines. Each line serves three fuel feeding openings. The feeding points are staggered so that the stoppage of one feeding line only causes a small disturbance in the combustion process. Three feeding lines can achieve full boiler capacity, one of several design features incorporated in the plant to increase the reliability of the whole process. Emission control Good combustion and emission control requires even fuel and air distribution and combustion air staging. in the boiler the SO 2 emission limit is so tight (100 mg/MJ) that limestone feeding is needed not only with coal combustion but also with peat combustion. When the share of wood based fuels is increased, the mass flow of limestone is reduced since the alkalis in the ash react with fuel sulfur resulting in lower sulfur dioxide emissions. The limestone is injected pneumatically, close to the fuel feeding points. Nitrogen oxide emission is controlled by using low-NO 2 technologies. An SNCR (selective non-catalytic reduction) system is used to fulfil the NO 2 emission requirement with all loads. lf NO 2 emissions reach the limit of 50 mg/MJ, ammonia spraying is started in the cyclones. Ammonia can be injected either to the cyclone inlets or into the furnace with lower loads. Dust control is handled with a four-field ESP (electrostatic precipitator). it is intended to recycle fly ash and the gypsum from the sulfur retention reaction. Fuel handling The large size of the Alholmens Kraft plant and the diversity of fuels to be dealt meant that the biofuel handling system, supplied by Roxon Oy, posed a number of challenges. Some totally new components had to be developed, for example, the automated sampling system. The totally unprecedented dimensions and the new approaches being adopted required a good deal of broad-mindedness when developing the equipment and carrying out tests during the design phase. Fuel is handled in two treatment zones, western and eastern. The fuels handled in the western area are peat, wood based materials and waste pellets. The eastern zone receives
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