DEVELOPMENT OF POWER GENERATION SYSTEM USING LIVESTOCK WASTES AS FUEL

本文介绍了一种以畜禽粪便为燃料的发电系统的研究。主要研究结果如下：1)研究了发热量与含水率的关系。尽管准备好的畜禽粪便的水分有足够的波动(10-80wt%)，但它对干基较低的热值影响不大。水分含量高达80%的猪粪可以通过与肉鸡粪便混合燃烧的方式进行焚烧。确定了猪粪自燃混合比(重量比)的上限约为40%。2)燃烧效率定义为床层产热量与所供燃料热值的比值，采用床层热平衡法进行评价。在此基础上，给出了估算燃烧效率的经验公式。用经验…估算沸腾床温度3)采用有限体积法对炉膛内的燃烧特性进行了数值模拟。炉内温度的计算值与实验值基本吻合。燃料的水分含量较高会导致燃烧气体的温度降低，因为燃烧热被浪费在从燃料所含的水产生蒸汽的过程中。然而，即使对于含水率在50%以上的混合燃料，燃烧气体的出口温度也在1000K以上。4)在宫崎县引进畜禽粪便发电系统后，采用压力为5.88 Mpa、温度为400℃的锅炉蒸汽条件，结合回热循环，可获得约15 MW的发电量和23%的总热效率。从焚烧炉床温保持在600-620ppm，废气中CO浓度保持在5ppm以下的数据，证实了肉鸡粪便燃烧既稳定又完全是可能的。对于肉鸡和猪粪混合燃烧的情况，证实了猪粪的混合比例在重量基础上可以提高到45%。考虑到尾气可能对周围环境造成的问题，虽然NOx浓度相对较高，但单燃料燃烧与肉鸡排泄物混合燃烧的NOx浓度仍为314ppm。因此，它完全符合环境质量标准。针对床料中低熔点物质(Na、K、P)的浓度会导致沸腾炉内流态化不足的问题，实验结果表明，该浓度在燃烧开始后的7~8小时内达到饱和，K、P的饱和浓度约为0.5%，说明畜禽垃圾长期焚烧是可行的。较少

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