柳杉生質燃料及生質炭利用之生命週期評估

Abstract

在現今全球面臨化石燃料短缺、環境污染與溫室效應等問題下，替代能源的發展為未來不可或缺之事，其中以生質能的應用最為廣泛。而國內所栽植之柳杉為外來物種且經濟價值低，未來柳杉將為具潛力之生質燃料來源。故本研究以生命週期方法研究國內利用柳杉做為生質能在人體健康、生態品質、氣候變遷與資源等方面之環境效益探討。 本研究將柳杉以生質燃料和生質炭兩種不同方式進行利用，與燃煤混燒發熱，並使用生命週期評估軟體SimaPro 7.3.3進行評估。研究先進行盤查分析，以得知各階段之投入產出，再以IMPACT 2002+進行衝擊評估量化其潛在衝擊，並分別與燃煤供應及燃煤燃燒進行比較，以評估柳杉做為生質能取代部分燃煤進行發熱之環境衝擊與效益。 結果顯示，燃煤燃燒發熱在人體健康之吸入性有機物、生態品質之水體生態毒性、陸地生態毒性及水體優養化、氣候變遷之全球暖化與資源之非再生資源等類別中較柳杉生質燃料混燒發熱和柳杉生質炭混燒發熱造成較高的衝擊，所以利用柳杉生質能發熱在上述類別中具有衝擊減量之環境效益，且衝擊量隨著混燒比之上升而下降；而在人體健康之致癌性、非致癌性、吸入性無機物、游離輻射及臭氧層破壞、生態品質之土地佔用、陸地酸化及水體酸化與資源之礦物開採，則以利用柳杉生質能造成更多的衝擊，而無環境效益。整體來說，柳杉生質燃料或柳杉生質炭混燒發熱造成的環境衝擊皆低於燃煤燃燒，其中在相同混燒比下柳杉生質燃料混燒之損害量又低於柳杉生質炭混燒所產生之。可見以柳杉做為生質能具有取代部分燃煤的潛力。

The development of alternative energy became one of the important issues under the circumstances of growing fossil fuel shortages, environmental pollution and greenhouse effect. The most widely applied one is bioenergy. Japanese cedar (Cryptomeria japonica) in Taiwan are potential biofuel sources because they are not native species and have low economic value. By using life cycle assessment, this study investigates the environmental impact and benefit on human health, ecosystem quality, climate change and resources of applying Japanese cedar for bioenergy in Taiwan. In this study, Japanese cedar are used in two forms, biowood and biochar, and co-fired with coal. Life cycle assessment software of SimaPro 7.3.3 was need to assess the environmental impact and benefit of partly replacement of coal by employing Japanese cedar as bioenergy. Firstly, we examined the input and output through every step of life by life cycle inventory, then quantified the potential impact by using IMPACT 2002+ for impact assessment, and compared with coal supply and total coal-fired system, respectively. The results show that the total coal-fired system causes more impacts on categories of respiratory organics of human health, aquatic ecotoxicity, terrestrial ecotoxicity and aquatic eutrophication of ecosystem quality, global warming of climate change and non-renewable energy of resources than Japanese cedar biowood and biocoal co-firing systems. Therefore applying Japanese cedar to bioenergy decreases the environmental impacts in above said categories which increase with co-firing ratio of biowood or biochar. However, applying Japanese cedar to bioenergy causes more impacts on categories of carcinogens, non-carcinogens, respiratory inorganics, ionizing radiation and ozone layer depletion of human health, land occupation, terrestrial acid and aquatic acidification of ecosystem quality and mineral extraction of resources. To sum up, the environmental impacts caused by both Japanese cedar biowood and biocoal co-firing systems are less than those by total coal-fired system. Further, the environmental impacts caused by Japanese cedar biowood co-firing are less than those by Japanese cedar biocoal co-firing at the same co-firing ratio. The results indicate that the bioenergy from Japanese cedar has the potential to replace a part of coal for either direct firing or co-firing.