IGCC Technology

Process Optimization

IGCC is a process in which a low-value fuel such as coal, petroleum coke, orimulsion, biomass or municipal waste is converted to low heating value, high-hydrogen gas in a process called gasification. The gas is then used as the primary fuel for a gas turbine.

IGCC can also be viewed as the two-stage combustion of an opportunity feedstock. First, the feedstock is partially combusted in a reactor or gasifier. Then the combustion is completed in the gas turbine.

IGCC Consists of Four Process

Gasification

A feedstock can be gasified in several ways. The most common technique partially oxidizes the feedstock with pure oxygen inside a reactor. The carbon and hydrogen from the feedstock are converted into a mixture composed primarily of hydrogen and carbon monoxide. This mixture is commonly called synthetic gas, or syngas. Syngas has a heating value of 125 to 350 BTU/scf, which is three to eight times lower than that of natural gas.

Syngas Cleanup

The syngas from the reactor must be cleaned before it can be used as a gas turbine fuel. The cleanup process typically involves removing sulphur compounds, ammonia, metals, alkalytes, ash and particulates to meet the gas turbine's fuel gas specifications. To make IGCC more economically attractive, you can make marketable products such as methanol, ammonia, fertilizers and other chemicals from the compounds you remove from the syngas. This process often further reduces the hydrogen content and therefore the heating value of the syngas.

Gas Turbine Combined Cycle

The cleaned syngas is combusted in the gas turbine.

Cryogenic Air Separation

A cryogenic air separation unit provides pure oxygen to the gasification reactor, often using or supplemented with post-compression air bleed from the gas turbine.

IGCC Plant Considerations

Integration

The four process islands must be integrated to optimize the plant. Syngas, air, nitrogen and multi-pressure steam must be piped across the plant. Thus, the gas turbine, gasifier and ASU suppliers must be involved early in the design cycle.

Size

The physical IGCC plant is comparable in size to a conventional coal-fired power boiler plant, but unlike a conventional coal plant, an IGCC plant does not require additional area for scrubber sludge treatment or ash dewatering.

Utilities

Water consumption of an IGCC plant is approximately 30 percent lower than a conventional coal plant. Also, lime or limestone is not required for desulphurization.

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