把碳封存在地下的方法----中壢英文補習班－金學堂英語的部落格

【聯合報╱By HENRY FOUNTAIN╱陳世欽譯】

A Way to Put Carbon Back Under the Ground

ESTEVAN, Saskatchewan — A new coal plant has been built here in the vast prairie to replace one that used to emit so much soot that clothes drying outside in the area would be covered with grit.

But as with even the most modern coal plants, its smokestacks still emit enormous amounts of carbon dioxide, the invisible gas that is the main contributor to global warming. So this fall, a new maze of pipes and tanks will suck up 90 percent of the carbon dioxide from one of the boilers so it can be shipped out for burial, deep underground.

The effort will be the first major one of its kind at a power plant, the equivalent of taking about 250,000 cars off the road. And at least in theory, that carbon dioxide will be kept out of the atmosphere forever.

Worldwide, coal consumption in 2020 will be about twice what it was in 2000, according to the United States Energy Information Administration, and will continue to grow for decades.

“If you want to carry on using those fossil hydrocarbons, that means cleaning up their emissions,” said Stuart Haszeldine of the University of Edinburgh. Capturing carbon, he said, “is the single best way of doing that.”

Yet because it requires so much energy, sucking up carbon reduces a plant’s ability to make electricity . There are basic questions of whether carbon dioxide can be safely stored underground. And the technology is expensive. Updating the Saskatchewan plant alone cost $1.2 billion .

In the pine woods of central Mississippi, another carbon-capture effort is taking shape, in a massive new power plant that will be fed a steady diet of coal from the strip mine next door.

Bruce Harrington, the operations manager, said an army of workers is cutting, welding and testing underground. The plant’s owner, Southern Company, hopes to open the structure next year. But it is more complex than the Saskatchewan effort, and the price tag is now $5.5 billion.

The United States and other nations have helped some projects — Canada gave $220 million to the Saskatchewan plant’s owner, SaskPower, and Southern Company received $270 million from the United States Department of Energy — but the costs are high enough that few other power companies have done much beyond study the concept.

The technology has been around for nearly a century, used at some refineries and other industrial plants, including large ones in Illinois, North Dakota, Canada and Norway.

But removing carbon dioxide from the swirl of gases unleashed at a power plant is challenging. T he equipment is enormous. At the Saskatchewan plant, called Boundary Dam, a liquid chemical latches onto carbon dioxide molecules after being sprayed onto a plume of combustion gases. The “stripper,” where the carbon dioxide is finally pulled away, is nearly 50 meters high .

In addition, efficiency is lost because some of the steam that would normally generate electricity goes to the stripper instead.

And a monstrous motor compresses the carbon dioxide — until it effectively becomes a liquid — for transport. All told, capturing the carbon dioxide at Boundary Dam will sap electricity generation by about 20 percent . Injecting liquids deep underground can present problems, too. Pumping wastewater from oil and gas production into the ground has been linked to small earthquakes in the United States.

The carbon dioxide could taint drinking water, or bubble up into the atmosphere, defeating the entire purpose.

Still, carbon dioxide has been buried around the world with few problems. In Norway, about a million metric tons have been stored every year since 1996, injected into sandstone about 900 meters beneath the North Sea. Most of Boundary Dam’s carbon dioxide will become a tool to extract and consume oil.

After being sold and shipped through a 60-kilometer pipeline to an oil field, the carbon dioxide will be pumped into old wells, where it will mix with the oil inside, making it flow better. The process is known as enhanced oil recovery . The oil and gas industry has done this for decades, mostly with naturally occurring carbon dioxide that accumulates underground. But each year in North America, more than 13 million metric tons of carbon dioxide from industry are used as well.

The practice could be expanded at many oil fields , experts say, potentially storing billions of metric tons of carbon dioxide and serving as a bridge to the day when it becomes necessary, and economical, to store the gas elsewhere.

The prognosis for carbon capture around the world is unclear.

If the United States moves forward with President Obama’s plans to cut carbon emissions, China and other countries may make bigger strides as well.

“How this will play out over time is hard to tell,” said Edward S. Ruben of Carnegie Mellon University in Pennsylvania. “Inevitably, there will be a balance between technological capability, cost and political realities.”

中譯

加拿大薩斯克徹溫省伊斯得芬的大草原上已建妥一座燃煤發電廠，取代曾經排放大量煤灰，讓戶外晾曬的衣物蒙上一層塵粒的舊發電廠。

燃煤電廠再現代化，煙囪還是會排放大量二氧化碳。這種看不見的氣體是促成全球暖化的關鍵。新的輸送管與儲存槽今秋將自其中一個鍋爐吸取九成二氧化碳，運出並深埋地底。

這將是發電廠首次做此類重大嘗試，相當於減少25萬輛汽車的排放量。至少在理論上這些二氧化碳永遠不會逸入大氣層。

美國能源資訊局表示，2020年全球煤消耗量預估會是2000年的兩倍，其後數十年還會繼續增加。

愛丁堡大學的哈塞爾丁說：「若要繼續使用這些化石碳氫化合物，這意味你必須清理它們的排放物。捕集碳是最好的方法。」

然而捕集碳耗費大量能源，會使發電廠的發電量減低。二氧化碳能否安全儲存於地底，也還有些基本問題尚待解答，而且技術所費不貲。僅是在薩斯克徹溫興建另一座發電廠就耗資12億美元。

在密西西比州中部的松林，另一項捕集碳的嘗試正在進行。一座新建的大型發電廠所需的煤將由毗鄰的露天礦場供應。作業經理哈靈頓表示，工人正在地面下切割、焊接及測試。業主南方公司希望這座設施可於明年啟用。然而這項計畫比薩斯克徹溫的複雜，目前估計的成本是55億美元。

美國與另一些國家已經贊助一些類似的方案。加拿大政府補助經營薩斯克徹溫發電廠的薩斯克電力公司2.2億美元，美國能源部則補助南方公司2.7億美元。然而由於成本太高，絕大多數電力公司僅止於研究這個構想而已。

必要的技術問世已將近一個世紀，主要用於一些煉油廠與其他工廠，包括伊利諾州、北達科他州、加拿大與挪威的一些大型工廠。

然而從發電廠所排放的各種氣體中取出二氧化碳卻是個挑戰。必要的設備體積龐大。在名為「邊界水壩」的薩斯克徹溫發電廠，一種液態化學劑噴向一縷燃燒氣體之後，就會與二氧化碳分子結合。最後取走二氧化碳的清除器高度將近50公尺。

此外，效率也會折損，因為通常用於發電的蒸汽有一部分也會逸入清除器。一部巨大的馬達壓縮二氧化碳，直到它成為便於運送的液態。整體而言，邊界水壩捕集二氧化碳大約會使發電量減少20%。