Mar 11, 2009 04:45 PM in Energy
Cleaning up the dirtiest fossil fuel: One company's coal fix
By John Rennie in 60-Second Science Blog
BOSTON (March 11, 2009) -- In most discussions of energy and climate, coal figures prominently as one of the villains. Burning coal is responsible for more than a third of all energy-related U.S. carbon dioxide emissions and 80 percent of those from electricity production. It is also one of the largest contributors of air pollution, acid rain and even toxic environmental mercury. But because coal is so inexpensive and plentiful—at the current rate of domestic demand, the U.S. has enough coal to last for 250 years—nations find it hard to abandon the fuel without risking economic ruin.
The clean-coal technology developed at GreatPoint Energy (with offices in Chicago and Cambridge) might represent a solution to that dilemma, however. CEO Andrew Perlman advanced that argument in his keynote speech here last night at the GoingGreen East conference in Boston. (Here are our previous posts on Going Green East.) GreatPoint Energy was just named overall winner in the GoingGreen East 50 Top Private Companies list, which recognizes exceptional organizations based on clean technology.
(Scientific American is a partner with the AlwaysOn network in presenting the meeting, which is the first East Coast edition of an event held twice before in California.)
Many environmentalists view “clean coal” as a contradiction in terms because of the damage caused by mining and burning it, but GreatPoint Energy’s “hydromethanation” approach might come closest to deserving that description. The key is that it does not burn coal at all: rather, through a three-step catalytic chemical process, it converts coal into natural gas (methane), which burns more cleanly and produces less carbon dioxide than other fossil fuels. Pollutants, including the generated CO2, would be collected for sale or sequestration.
That process is fundamentally different from traditional coal gasification, in which coal reacts with extremely hot, pressurized water and air to yield “syngas,” a flammable mixture of carbon monoxide and hydrogen.
According to Perlman, a single catalyst facilitates all three steps in the hydromethanation process: the steam gasification (which converts the coal feedstock into carbon monoxide and hydrogen gas), the water-gas shift (which turns the carbon monoxide and water into CO2 and hydrogen gas) and the methanation stage (which changes the hydrogen and remaining carbon into methane). All three of these steps can take place in a single reactor vessel, even though the first is highly endothermic (absorbing energy in the form of heat) and the last is highly exothermic (releasing energy in the form of heat); overall, the reaction is thermally neutral, which helps to keep it affordably efficient. The natural gas product contains about 80 percent of the energy in the coal input.
Pollutants in the coal, such as sulfur, ammonia, mercury and other trace metals, can all be scrubbed from the gaseous mixture by conventional technologies, collected and sold as byproducts. Equally important, the CO2 generated can be collected and sequestered efficiently (which is still not the case for CO2 released from burning coal).
Because coalmines are often located near oil fields, building a hydromethanation plant beside a mine could have strategic advantages, Perlman noted. The stream of CO2 byproduct could be sold to oil companies and used to raise the yield from depleted wells. Alternatively, the CO2 might simply be sequestered underground in the oil field.
The GreatPoint Energy team worked for four years to create the hydromethanation process. Amazingly, it might in principle have been discovered two decades ago: Perlman said that Exxon originally identified a catalyst in the 1980s that proved it was possible to crack coal chemically instead of thermally. But that preliminary work had been supported by the Department of Energy, and after the DOE withdrew funding, the work languished until Perlman’s colleagues unearthed it and recommenced development.
GreatPoint Energy has constructed a demonstration plant, the Mayflower Clean Energy Center, in Seekonk, Mass., that has already logged 1,200 hours of online operation. Perlman stated that the company is looking toward commercial production in 2012, with the goal of building, owning and operating its own plants. However, it would be looking to partner with major energy companies in the U.S., Canada, China, India and other key countries.
So, does GreatPoint Energy’s technology prove that clean coal is not necessarily an oxymoron? Mining coal is still environmentally damaging, although according to Perlman, the company is committed to avoiding deals with mining partners engaged in highly destructive practices such as mountaintop removal. And the natural gas produced by the process would eventually be burned and yield CO2—far less CO2 than burning coal for a corresponding amount of energy would release, but still more than solar or wind. But the advantages of finding a better, cleaner way to use coal while even cleaner technologies are still maturing cannot be overstated, this conference makes clear.
Photo of the inside of the Mayflower Hydromethanation Demonstration Plant, in Somerset, Massachusetts, courtesy GreatPoint Energy
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