DEVELOPMENT OF POWER GENERATION SYSTEM USING LIVESTOCK WASTES AS FUEL

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This paper describes a study on a power generation system using livestock wastes as fuel. The results are summarized below :1) The relationship between calorific value and moisture content is cxamined. Although moisture content of the prepared livestock wastes shows sufficient fluctuations (10-80wt%), it dose not strongly affect the lower calorific values at dry base. Swine excrement having moisture content as high as 80% can be incinerated by means of mixed combustion with broiler excrement. The upper limit of mixing ratio (weight ratio) of swine excrement for autogenous combustion was confirmed to be approximately 40%.2) The combustion efficiency, which is defined as the ratio of the heat generation in the fluidized bed to thc calorific value of the supplied fuel, is evaluated using a heat balance in the fluidized bed. On the basis of the result, the empirical equation for estimating the combustion efficiency is presentcd. The fluidized-bed temperatures estimated using the empirical … More equation and the heat balance almost agree with the experimental ones.3) Numerical simulations are carried out to analyze the combustion characteristics in the furnace by using finite volume method. The calculated temperatures in the furnace almost agree with the experimental ones. Higher moisture content of the fuels results in decreases in the temperatures of the combustion gases because the heat of combustion is wasted to generate steam from water contained by the fuels. However, the outlet temperature of the combustion gas was found to be above 1000 K even for the mixed fuels whose moisture contents are above 50%. The calculations show that the fuel gases are completely burned in the furnace, maintaining the furnace at high temperatures.4) With the introduction of power generation system using livestock-waste from the Koyu and its surrounding area in Miyazaki Prefecture, about 15MW of electric power output and 23% of gross thermal efficiency can be achieved by adopting the boiler steam conditions of 5.88 MPa in pressure and 400℃ in temperature, together with utilizing a regenerative cycle. From the data that incinerator bed temperature maintains at 600 - 620℃ and CO concentration in the exhaust gas maintains below 5ppm, it is confirmed that both stable and complete combustion is possible with combustion of broiler excrement. For the case of mixed-fuel combustion with broiler and swine excrement, it is confirmed that the mixture ratio of swine excrement can be increased up to 45% on weight base. Considering the possible problem to surrounding environment by exhaust gas, although NOx concentration is relatively high, to a value of 314ppm for single-fuel combustion with broiler excrement. As a result, it meets the environmental quality standards sufficiently. For the question that the concentration of low-melting-point substances (Na, K, P) in bed material may cause insufficient fluidization in fluidized-bed incinerators, experiment results show that this concentration saturates is within 7- 8 hours after start of combustion, and the saturation concentration is detected to be approximately 0.5% for K and P.Thus it leads to the conclusion that long-term livestock-waste combustion is feasible. Less