Coal conversion technology
gets computational tweaks
Posted September 8, 2009
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New ways to use coal more efficiently and cleanly must be found, since the world is likely to rely on it for decades to come, says Madhava Syamlal of the National Energy Technology Laboratory. Computation is fueling refinements to gasification, one of the most promising options. |
There’s no way around it: For now, we can’t live without coal.
Today it provides more than 40 percent of all the world’s electric power — about as much as oil, gas and nuclear fuels combined. About half of U.S. electricity and nearly 80 percent of electricity used in China comes from coal, and existing coal-fired power plants are expected to be in service for decades.
Although we can’t cut the coal connection for now, researchers at the Department of Energy’s National Energy Technology Laboratory (NETL) and Oak Ridge National Laboratory (ORNL) are using high-performance computers to help perfect one of the most promising ways to use it cleanly. Their simulations already have shed light on ways to improve coal gasifier designs, and an allocation of millions of computer processor hours will accelerate their work.
The models they develop also could have a wide-ranging impact on carbon-based alternative power generation, says Madhava Syamlal, the project’s leader and area leader for computational and basic sciences at NETL. “Municipal waste combustion, biomass, combined coal and biomass — they’re all flows using a gas and solids,” Syamlal explains. “We can use our models to describe all these systems.”
Gasification, the cleanest coal-based power system available today, uses heat, pressure and steam to turn carbon-containing material into synthetic gas (syngas), a mixture of carbon monoxide and hydrogen. Besides power-plant fuel, syngas can be used to produce liquid fuels, chemicals or pure hydrogen gas — itself an ultra-clean fuel.
Power production from syngas generates about as much carbon dioxide (CO2) as traditional coal-burning plants. But the CO2 produced by integrated gasification combined cycle (IGCC) plants is more easily captured than that produced by older designs. IGCC plants also have other advantages over older designs, including far better control of nitrous oxides, sulfur and mercury emissions. That makes it easier to cut or control the plant’s climate-changing and hazardous discharges.
Syamlal and his team at NETL model conditions inside the transport gasifier, the high-pressure chamber where a source of carbon — coal — reacts with steam and air at high temperature in a reducing atmosphere to produce syngas. Besides factors like the size and shape of the reaction chamber, the computer model includes variables as diverse as temperature and pressure, coal analytes (ash and volatile gas content, percent fixed carbon and similar factors), gas and fluid flows, and the packing of moving solid materials.
“The basic idea here is to use physics-based models for describing gas-solids systems,” Syamlal says. “We use a continuum approach, treating coal particles — solids — as a fluid superimposed on a gas — essentially air, steam and other gases.”
