生質能源之經濟與環保效益研究-以稻殼氣化發電為例

Abstract

生質能源之經濟與環保效益研究—以稻殼氣化發電為例 研究生:何錦城 指導教授:蔡春進 教授 國立交通大學工學院產業安全與防災學程碩士班 摘 要 本研究的目的在於評估下吸式稻殼氣化發電系統，應用在中大型碾米廠之經濟與環保效益。研究結果顯示，在經濟上是可行的，主要由於目前國內稻穀收割後，直接運往農會或中大型碾米廠，經烘乾、暫存、碾製、包裝、販售一貫作業。因此在農會或中大型碾米廠設置稻殼氣化發電系統，就地將稻殼廢棄物加以利用，無需支付運輸費用及稻殼廢棄物處理費，除了發電之效益外，其副產品稻殼灰之價格遠高於發電之效益。 以每天24小時，碾製稻穀54公噸之農會或中大型碾米廠產生10.8公噸之稻殼為例，設置100KW規模之稻殼氣化發電系統，每年淨發電量達375,360度，每度電力以2元計，可節省電費750,720元/年。可產生540公噸的稻殼灰，每公噸稻殼灰以6,000元計，產值達3,240,000元/年。稻殼若以廢棄物方式處理，每噸需支付300元之委託清運處理費，每年2,700公噸稻殼可節省810,000元/年。另外燃氣之冷凝液（俗稱木醋液，可做為農業之有機栽培及病蟲害防治）每年也有345.6公噸，產值達172,800元/年。因此每年每座氣化爐之生產毛額達4,973,520元/年，扣除十年折舊攤提、貸款利息、保險、操作、維修等直接與間接費用後，每座仍有1,394,520元/年之淨收益，約二至三年可回收成本。依問卷調查統計分析結果，有72.5 ﹪約290,191公噸之稻殼集中在中大型碾米廠，以每度電需稻殼0.0045公噸計算，290,191公噸之稻殼可發64,486,888度電。以每度電淨收益3.71元計，其年總淨收益達239,246,355元/年。 由於生質能源碳之來源係由生質物吸收空氣中之二氧化碳進行光合作用而生成，生質能源之利用所產生之二氧化碳，又完全回歸於生質物之成長所需，對整體環境之溫室效應氣體淨排放為零。經研究評估結果，若以直接燃燒稻殼回收能源時，每公斤稻殼之利用，可獲得1.00公斤二氧化碳之排放減量效益，即每年可獲得290,191公噸之二氧化碳排放減量效益，佔1999年全國二氧化碳總排放總量（204百萬公噸）的0.142 ﹪。 相對於火力發電，稻殼氣化每發一度電，可獲得0.85 公斤二氧化碳之排放減量效益，即64,486,888度電每年可獲得54,814公噸之二氧化碳排放減量效益，佔1999年全國二氧化碳總排放總量（204百萬噸）的0.0268 ﹪。另外稻殼含硫量極低，亦可減少NOx及SO2之排放，其環保效益相當明顯。

Abstract The objective of this study is to evaluate the economical and environmental benefits of the down-draft rice husk gasifier for power generation system which applied in middle and large rice-hulling mills. The result shows that it is economically feasible . After havesting, the rice is transported to the Agricultural Association or rice-hulling mills for the processes of drying, milling, packing and selling. Hence, installing a rice husk gasifier for power generation system can recover the energy of rice husk and save waste treating and transportation fees. Besides the benefit of power generation, the by-product of husk ash is even more valuable. Taking a 54 tons rice production plant in the Agricultural Association or rice-hulling mills for example, there are 10.8 tons rice husk produced for 24 hours operation per day, net power generation is 375,360 kw/year, the benefit of power is 750,720 NT＄/year. The quantity of husk ash is 540 tons/year, the benefit of husk ash is 3,240,000 NT＄/year, for 6,000 NT＄/ton. If rice husk is treated as a waste, the total treating fees will be 810,000 NT＄/year, for 300 NT＄/ton. Besides, the condensed liquid of the gasifier syn-gas, can be used as a fertilizer and pesticide, the quantity is 345.6 tons/year, and the benefit is 172,800 NT＄/year. Hence, the benefit of a rice husk gasifier for power generation system is 4,973,520 NT＄/year, after deducting the direct and indirect cost of compensation, interests, insurances, operation, maintenance, the net profit is 1,394,520 NT＄/year. The investment cost can be recovered in 2~3 years. According to estimation, 72.5 ﹪rice husk（about 290,191 tons/year）is collected by the Agricultural Association or middle and large rice-hulling mills, the total profits will be 239,246,355 NT＄/year. The carbon source of biomass-energy is from the photosynthesis of the plant absorbing carbon dioxide. The utilization of carbon producing carbon dioxide which recycles to organisms for growing. There is no effect for the discharge of globe warming gases. Without considering the problems of waste treatment and by-product recovery, Applying rice husk combustion to generate energy can reduce emission of 1.0 kg carbon dioxide per 1kg utilization of rice husk, which reduces emission of 290,191 tons/year carbon dioxide. Comparing with the power generation by fuel oil or coal combustion, rice husk gasifier power generation can reduce 0.85kg CO2 emission per 1kw power, total amount of 64,486,888 kw generated reduces emission of 54,814 tons/year carbon dioxide. In addition, rice husk contains trace sulfur, it may reduce the emission of NOX and SO2 , and therefore there is an obvious benefit in environmental protection.