新技術:20%垃圾可變成運輸燃料 | 環境資訊中心

新技術:20%垃圾可變成運輸燃料

2008年10月21日
摘譯自2008年10月16日ENS美國,印第安那州,西拉法葉市報導;江昱均編譯;莫聞審校

美國普度大學研究員提出一項新的「彈性」措施,從都市固體廢棄物、農業廢棄物、林業殘留物和污水污泥生產新替代性燃料、氫以及電力。他們表示這項新措施可能可提供美國每年高達20%的運輸燃料。這項措施可以為因用玉米作原料,以傳統方法製造、增產乙醇而造成的問題提供可能的解決之道。

以傳統方法提高乙醇生產需要額外的作物和大量施肥,因而增加進入水道造成污染及威脅生態系統的逕流。然而,普度大學電機系副教授趙復(Fu Zhao)表示,普渡大學研究員稱之為碳到液態燃料彈性過程的這項新概念將不需要額外作物,主要是使用廢棄物作為原料。

他表示:「這項技術比傳統技術較為彈性,因為我們處理的原料範圍更廣、更多樣化,也因此我們能同時產生更多不同的產物─不僅只是汽油和柴油,還有乙醇和氫氣。」「或者我們能從提取出的天然氣中直接發電。」他說,這項措施將對玉米和其他作物的市場價格波動免疫,同時也較不會受到原料供給衝擊和市場需要變化的影響。

比起燃燒由石油提煉的汽油,這項方法也將降低50%的溫室氣體排放量。

在9月29日於韓國釜山所舉行的第六屆全球永續產品發展與生命循環工程會議中所發表的這篇論文,對這些發現有更詳細的說明。

這座系統首先需要處理含碳廢棄物,例如廢紙、木材、塑膠和橡膠,將它們切製成只有數公釐大小的小碎片。再將這些碎片放入氣化爐(gasifier)中,所有物質將轉化成含有氫、一氧化碳、二氧化碳、甲烷和其他碳氫化合物的氣體。

接著,再對這種氣體進行進一步處理,去除所有雜質,保留氫和一氧化碳,成為合成氣(synthesis gas 或 syngas,指一氧化碳和氫的混合物, 尤指由低級煤生產的可燃性氣體, 主要用於化學和生物加工以及甲醇的生產)。

合成氣可以直接用在運轉渦輪以產生電力,或者可以轉化為汽油或柴油,用於交通運輸上。這項技術也可以用來製造乙醇,飛機燃料和其他由固體廢棄物提取的生質燃料。

根據數據,美國可以產生足量廢棄物來支持利用這座系統進行大量生產的各種設備。

美國農業部和能源部所準備的一項報告發現美國每年預估能夠產生13億噸的生物質(biomass)。

U.S. Could Derive 20 Percent of Transport Fuel From Waste
WEST LAFAYETTE, Indiana, October 15, 2008 (ENS)

Researchers at Purdue University are proposing a new "flexible" approach to producing alternative fuels, hydrogen and electricity from municipal solid wastes, agricultural wastes, forest residues and sewage sludge. They say the new approach could supply up to 20 percent of transportation fuels in the United States annually.

The method offers a potential solution to problems that might be created by increasing production of ethanol with conventional methods, which use corn grain as a feedstock.

Boosting ethanol production with conventional methods would require additional crops and heavy fertilizer use, increasing runoff into waterways and threatening ecosystems.

But the new concept, which Purdue researchers call a flexible carbon-to-liquid fuel process, would require no additional crops and use primarily wastes as the feedstock, said Fu Zhao, a Purdue assistant professor of mechanical engineering.

"This technique is more flexible than conventional methods because we can process a wider range of very different feedstocks and, at the same time, we can generate a wider range of end products - not just gasoline and diesel but ethanol and hydrogen," he said. "Or we could generate electricity directly from the gas produced."

The method also would be immune to the market fluctuations of corn and other crops and less affected by disturbances such as feedstock supply shocks and market demand changes, the Purdue scientist says.

The method also could reduce greenhouse gas emissions by more than 50 percent compared with burning petroleum-derived gasoline, he says. Findings were detailed in a paper presented on September 29 during the 6th Global Conference on Sustainable Product Development and Life Cycle Engineering in Busan, Korea.

The system first requires processing carbon-containing waste, such as paper, wood, plastic and rubber, into small pieces with a diameter of a few millimeters, or thousandths of a meter.

The pieces would then be fed into a "gasifier," where the materials would be turned into a gas containing hydrogen, carbon monoxide, carbon dioxide, methane and other hydrocarbons.

This gas would be further processed to get rid of everything but the hydrogen and carbon monoxide, referred to as synthesis gas or syngas. The gas could then be used to directly run a turbine to generate electricity, or it could be converted into gasoline and diesel fuel for transportation. The technique could be used to produce ethanol, jet fuel and other biofuels from the solid wastes.

Data indicate enough wastes are generated in the United States to support large production facilities using the system.

A report prepared by the U.S. Department of Agriculture and Department of Energy found that an estimated 1.3 billion tons of biomass - including agricultural and municipal wastes - are generated annually across the country.

The analysis suggests that it is possible to replace 15 percent to 20 percent of transportation fuels consumed daily in the United States with liquids derived from this flexible process. These estimates are based on the present consumption level, which is about 390 million gallons per day, said Fu Zhao.