[May 2006]  The time is right for the return of coal as a major source of energy to produce electricity:

• Indigenous gas and oil supplies are nearing the end of their life and the UK plans to depend on imported gas to meet demand
• Replacing some of the CCGT output from the present stock of PF stations is an option, but will not help our commitment under Kyoto and other initiatives to reduce our national CO2 emissions
• Renewables have a role to play, but their contribution to date has been too little, too late
• Nuclear power also has a role to play, but capacity is reducing as the Magnox stations are retired, and new build is still some way off.

If only we could use coal without its traditional emissions (NOx, particulates, Co2) then the situation could be different.

The good news is that we can! Progressive Energy is presently developing a number of IGCC projects in the UK.

Integrated Gasification Combined Cycle (IGCC) is a technology established at Wabash River (USA) 15 years ago. There are many variant processes, but typically, coal is reacted under pressure in the presence of steam with a controlled amount of high purity oxygen. This process is called gasification. The result is that a gas mixture of CO, CO2 and H2 is produced (instead of CO2, which is formed during combustion). This is called Syngas, a mixture used in chemical processing in plants all over the world. Sulphur from the coal forms H2S, there being insufficient oxygen for SO2 to form.

Ash from the coal melts at the reaction temperatures achieved (~1600°C), and falls under gravity into a water bath. Here it solidifies into a hard glassy compound (frit) in which heavy metals are frozen in an almost unleachable form. Frit can safely be used as construction filler, and to produce high density concrete blocks.

When the syngas leaves the gasification plant, it is cooled (raising steam), filtered (to remove particulate and mercury) and then cleaned using processes common to refineries and chemical synthesis. The cleaning washes out the H2S, from which the sulphur can be extracted as pure yellow crystals for subsequent sale. The CO2 gas can be removed at this stage, too: if this stage is intended, it can be concentrated upstream by converting the CO into CO2 by reacting it with water, releasing more H2 at the same time. Again, removing the CO2 uses technology already proven at scale in the chemical industry.

The remaining hydrogen-rich mixture can be burned in an industrial gas turbine, the only significant emission from which is water vapour. Emissions of NOx can be controlled to levels achievable using natural gas, or lower. Overall plant efficiency is high, typically over 42%.

IGCC is a route to use coal without its traditional emissions (NOx, particulates, CO2).

But it gets better! The CO2 removed can be cost-effectively compressed and piped offshore to enhance the extraction of oil, for instance, from the North Sea, enabling access to reserves that would otherwise be left in the ground when present operations cease. The potential is vast, equal to discovering another Brent field! In this process, some of the CO2 remains trapped underground, stored forever.

The time is certainly right for IGCC to start to make a contribution to the UK energy mix; it offers:

• Clean energy from coal
• Access to additional north sea oil reserves
• An opportunity to pioneer IGCC technology with carbon capture and storage

Andy Brown
Progressive Energy Limited

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