Flame simulations lift
combustion energy’s future
Posted September 15, 2009
Gasifying coal to produce hydrogen and other synthetic fuels is an ambitious project in its own right. But DOE’s Office of Fossil Energy (FE) is taking the process a step further with the FutureGen power plant project, which seeks near-zero-emissions combustion technology that not only produces fuel but also sequesters carbon dioxide the process generates.
FutureGen would equip coal-gasifying power plants with advanced carbon capture and storage (CCS) systems and would make fuels for what are known as “ultra-lean, premixed combustion systems.”
Premixed systems mix fuel and air before they enter the combustion chamber. Lean-premixed systems have the potential for clean, efficient, fuel-flexible systems; they operate at high efficiency and burn gas at lower temperatures to generate low emissions of nitrous oxides (NOx).
Nonetheless, “most industrial flames are not premixed,” says Paul Ronney, a University of Southern California mechanical and aerospace engineering professor and a combustion-engineering expert. “At ignition, you have pure air meeting pure fuel at high temperatures that produces excess nitrous oxides emissions.”
It’s difficult to design safe and reliable systems based on premixed combustion, John Bell, Lawrence Berkeley National Laboratory (LBNL) senior scientist, noted in an FE research review. In non-premixed systems the flame location and stability are controlled by the mixing of fuel and oxidizer; premixed flames require device-scale stabilization. Developing such systems is particularly challenging for the hydrogen-rich fuels the gasification process produces.
The dilemma shows “there are significant gaps in our understanding of combustion,” Bell says. “Theory provides a foundation for basic flame physics but can’t address the complexity of realistic flames. Laboratory measurements are difficult to make and limited in the detail they provide. Computation, with its ability to deal with complexity and unlimited access to data, has the potential for closing the gap between theory and experiment and enabling dramatic progress in combustion science.”