Coal Gasification

Environmentally clean, affordable power is the goal of research at NETL, and coal gasification is one of the technologies that will make a difference. "There are two issues with coal," says Jack Halow, director of NETL's simulation and multi-phase flow analysis division. "As a solid, it's difficult to transport compared to liquids and gas, and fundamentally it's difficult to remove contaminants from a solid. Once it's gasified, you can pipe it wherever you want, and in the gas phase, it's much easier to separate and remove the environmental contaminants."

In recent studies using LeMieux, PSC's terascale system, NETL researchers under the direction of project managers James Longanbach and Daniel Cicero carried out 3D simulations of the transport reactor from the Power System Development Facility in Wilsonville, Alabama. PSDF is a U.S. Department of Energy demonstration plant for advanced electric-power technologies, and the PSDF transport reactor is a "circulating fluidized-bed" that can operate as a coal gasifier.

In this plant-sized technology - the reactor unit is 80 feet tall - coal and recycled material feed into the lower part of the gasifier, called the mixing zone, where the coal combusts at high temperature and pressure. Hot gas and unburnt solids rise from the mixing zone into the riser. At the top of the riser, unburnt solids are collected and fed back into the bottom of the mixing zone. Eventually coal converts with nearly 100 percent efficiency into gas.

Among the research tools NETL has developed is simulation software called MFIX (Multiphase Flow with Interphase Exchanges), which realistically models the gas and particle dynamics, chemical reactions and heat transfer involved in coal gasification and other power-generating combustion processes. "Capturing the correct hydrodynamics in a circulating fluidized bed," says NETL consulting engineer Chris Guenther, who coordinated the MFIX computations, "is critical."

In this study, the NETL researchers simulate the flow as it moves from the mixing zone into the riser. They track the hydrodynamics of both the gas and solid phases along with heat transfer between the two phases and production of gas species, such as methane, carbon monoxide and carbon dioxide. "Design engineers," says Guenther, "want to see how design changes affect the hydrodynamics and the chemistry, which isn't readily available from experiments. With simulations, design changes can be tested at a fraction of the cost of building and doing experiments with a scale model."

PHOTO:
						The Power Sytems Development Facility IMAGE: Rendering of transport reactor

The transport reactor (green) at The Power Sytems Development Facility, a DOE supported experimental plant in Wilsonville, Alabama. NETL simulations complement testing and development at this plant-sized research facility.

Image from MFIX Simulation.

This image from an MFIX simulation on PSC's LeMieux shows concentrations of methane (blue), carbon monoxide (green) and carbon dioxide (yellow) in the transport reactor mixing zone where it necks down into the riser. The simulation also tracks void fraction, the degree of unburnt solid material. The isosurface (white) represents a void fraction of 0.8 (20 percent solid) and shows how the flow becomes more dilute as it rises.

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