DEVELOPMENT OF POWER GENERATION SYSTEM USING LIVESTOCK WASTES AS FUEL

本文介绍了一种利用畜禽粪便作为燃料的发电系统的研究。结果总结如下：1)考察了热值与含水率的关系。虽然制备的畜禽粪便的水分含量有足够的波动（10-80wt%），但它不会强烈影响干基的较低热值。含水率高达80%的猪粪可与肉鸡粪混合焚烧。猪粪自燃混合比（重量比）的上限为40%左右。2)燃烧效率，定义为流化床中产生的热量与供给燃料的热值之比，是用流化床中的热平衡来评估的。在此基础上，提出了估算燃烧效率的经验公式。利用经验方程和热平衡计算得到的流化床温度与实验结果基本吻合。3)采用有限体积法对炉内燃烧特性进行了数值模拟分析。炉内计算温度与实验温度基本吻合。燃料中较高的水分含量导致燃烧气体的温度降低，因为燃烧的热量被浪费掉了，燃料中含有的水产生了蒸汽。然而，即使混合燃料的水分含量在50%以上，燃烧气体的出口温度也高于1000k。计算表明，燃料气体在炉内完全燃烧，使炉保持高温。4)引进宫崎县Koyu及其周边地区畜禽废弃物发电系统，采用压力5.88 MPa、温度400℃的锅炉蒸汽工况，利用蓄热循环，可实现发电量约15MW，总热效率约23%。从焚烧炉床温保持在600 ~ 620℃，废气CO浓度保持在5ppm以下的数据证实，燃烧肉鸡粪便可以实现稳定、完全的燃烧。以肉鸡与猪粪混合燃烧为例，确定了以体重为基础，猪粪混合比例可提高到45%。考虑到废气对周围环境可能造成的问题，虽然NOx浓度较高，但单燃料燃烧肉鸡粪便的NOx浓度达到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）的浓度可能导致流化床焚烧炉流化不足的问题，实验结果表明，该浓度在燃烧开始后7- 8小时内达到饱和，检测到K和P的饱和浓度约为0.5%，由此得出畜粪长期燃烧是可行的。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