|
Thursday, January 04, 2007 Part I: China's Coal FutureContinued from page 2 By Peter Fairley
China's government in Beijing created Shenhua a decade ago to bring economies of scale and modern technology to bear on the Dongsheng coalfields. The company's $1.5 billion coal-to-fuels plant is an expression of that strategy--a facility so technically ambitious that many experts, Chinese and Western alike, doubted it would ever be built. The production of transportation fuels from coal dates to early-20th-century Germany, where chemists developed two approaches to converting coal's solid long-chain hydrocarbons into the shorter liquid hydrocarbons found in motor fuels. (Nazi Germany, with little access to oil, relied heavily on these processes to fuel its highly mechanized army and air force, producing gasoline, diesel, and aviation fuel from coal.) Franz Fischer and Hans Tropsch invented the better known of the two approaches in the 1920s. Fischer-Tropsch synthesis reduces coal to syngas, a mixture of hydrogen and carbon monoxide. A catalyst, often cobalt, then causes the carbon and hydrogen atoms to reconnect into new compounds, such as alcohols and fuels. Fischer-Tropsch synthesis is conventional chemistry today: in South Africa, for example, Johannesburg-based Sasol built Fischer-Tropsch coal-to-oil plants to ensure the country's fuel supply during the trade boycotts of the apartheid years; and by swapping in different catalysts, China's coal-to-chemicals gasification plants have employed Fischer-Tropsch for decades to yield products such as synthetic fertilizers and methanol. Shenhua's plant, in contrast, chose Fischer-Tropsch's lesser-known rival, invented by Friedrich Bergius a decade earlier. Though used extensively by the Nazis, Bergius's process was subsequently abandoned. The process has come to be known as direct liquefaction, because it bypasses the syngas step. In direct liquefaction, the bulk of the coal is pulverized and blended with some of the plant's synthetic oil, then treated with hydrogen and heated to 450 °C in the presence of an iron catalyst, which breaks the hydrocarbon chains into the shorter chains suitable for refining into liquid fuels. Direct liquefaction produces more fuel per ton of coal than Fischer-Tropsch synthesis. Experts at the Chinese Coal Research Institute in Beijing estimate that the process captures 55 to 56 percent of the energy in coal, compared to just 45 percent for Fischer-Tropsch. However, direct liquefaction is also far more complicated, requiring separate power and gasification plants to deliver heat and hydrogen and considerable recycling of oil, hydrogen, and coal sludge between separate sections of the plant. And breaking down hydrocarbons to just the right length requires exquisite control of the operating conditions and a consistent coal supply. Shenhua redesigned the process over the last five years to boost efficiency and reduce waste but, at the same time, increased its complexity. And the company is taking a huge engineering and economic risk by pursuing so novel a technology on such a vast scale. By the end of this year, Shenhua hopes to be pumping out 20,000 barrels of synthetic oil per day, nearly 500 times as much as its pilot plant in Shanghai produces. According to Jerald Fletcher, a natural-resource economist at West Virginia University in Morgantown, the Erdos plant constitutes a $1.5 billion experiment that could only take place in China. "It would be hard to get that kind of commitment of funds in the West without a more proven technology," says Fletcher. Eric Larson, an expert in energy technology and modeling at Princeton University, puts it more bluntly: "It doesn't make a lot of sense to build a huge plant like that, because it may not work." |
Audio »
Share »
Digg this
Add to del.icio.us
Add to Reddit
Add to Facebook
Slashdot It!
Stumble It!
Add to Newsvine
Add to Connotea
Add to CiteUlike
Add to Furl
Googlize this
Add to Rojo
Add to MyWeb
Favorite
Print
E-mail
China Closes the Clean-Coal Gap
12/17/2008
Massachusetts Institute of Technology
Tags
China efficiency emissions energy global warming pollution