How does an Integrated Coal Gasification Combined Cycle (IGCC) Power Plant Work

IGCC is one more step in man's quest for high efficiency power generation with reduced emissions. The highly efficient and proven combined cycle, the main stay of power generation with Natural gas, is limited to firing gas or distillate oils. Aim of IGCC power plant is to close this gap by making it possible to fire coal in the combined cycle mode. The nett result is an increased efficiency coal based power plant with reduced emissions.

There are three steps for the power generation in an IGCC.

1. Produce clean gas from the coal also called syngas.
2. Burn the gas in a gas turbine to produce power.
3. Use the exhaust heat of the gas turbine to produce steam in an HRSG and use it in a steam turbine to produce power.

Step 1 is the new technology, which is in an advanced state of development with many plants already running in various parts of the world.

Step 2 is already proven for distillate oil and natural gas firing. However, for the coal gas firing the gas turbine technology require improvements and modifications to fire the synthetic gas.

Step 3 is the same as in the natural gas combined cycle except for some additional heat exchangers to recover heat from the hot syngas.

The gasification of coal produces heat. This heat recovery takes place by integrating the gasifier and the combined cycle. Hence the name 'Integrated Gasification Combined Cycle.'

Gas from coal itself is not a new process. This has been in use for firing in large furnaces as producer gas and as town gas for domestic purposes and public lighting from the beginning of the twentieth century.

The basic gasifier consists of steam passing through a hot bed of coal. The air or oxygen provided is less than required for full combustion. In this reducing environment the following chemical reactions takes place.

Carbon + Oxygen giving Carbon monoxide and Carbon Dioxide

Carbon+ Water giving Hydrogen and Carbon monoxide.

Carbon monoxide + Water giving Carbon dioxide and Hydrogen also called the water shift reaction.

Carbon Monoxide + Hydrogen giving Methane.

The result is gas with a composition of Carbon monoxide and Hydrogen and Methane.

The problems of this earlier gasifier were the formation of tar and other impurities, which made it unsuitable for firing in gas turbines.

The modern gasifier tries to eliminate these drawbacks to give clean pure gas.