Integrated Gasification Combined Cycle (IGCC)

1. Integrated Gasification Combined Cycle (IGCC) • IGCC is basically the combination of the gasification unit and the combined cycle. • It has high efficiency (over 50%). • In February 1997, 9 IGCC plants in operation worldwide and 11 in final stages of completion. Some 50 more were under consideration. • There are currently 4 coal-fired IGCC plants worldwide operating for more than 7 years • Efforts have been made to include CO2 capture in the pre-combustion step of IGCC. FutureGen is the one such project, which is estimated to cost $950million with 74% funded by DoE.

4. IGCC is basically the combination of the gasification unit and the combined cycle. • It has high efficiency (over 50%). • In February 1997, 9 IGCC plants in operation worldwide and 11 in final stages of completion. Some 50 more were under consideration. • There are currently 4 coal-fired IGCC plants worldwide operating for more than 7 years • Efforts have been made to include CO2 capture in the pre-combustion step of IGCC. FutureGen is the one such project, which is estimated to cost $950million with 74% funded by DoE. Integrated Gasification Combined Cycle (IGCC)

6. Integrated Gasification Combined Cycle (IGCC) • How does it work? • Air and coal are mixed and partially oxidized in the gasifier to produce syn gas (CO and H2). • The syn gas is then burnt with air to produce a stream of CO2 and H2O to drive the gas turbine to generate electricity. • The hot gases emitting from the gas turbine transfer its heat to a stream of water circulating in the steam cycle. The water gains heat and vaporizes to form steam that drives the steam turbine to produce more electricity. • How is the CO2 removed? • Steam is introduced in the water-gas-shift reaction to convert the CO in syn gas to CO2. • The CO2 is then removed through a removal unit for sequestration. The removal could be done via a number of processes such as membrane separation and etc.

7. Integrated Gasification Combined Cycle (IGCC) • Advantages • CO2 is available at high partial pressure • CO2 removal step can be carried out with proven technologies such as physical solvent scrubbing and membrane extraction • Disadvantage • Greater plant complexity • Partial oxidation of coal required

8. Supercritical Coal Combustion • This involves the use of specially developed high-strength alloys, to design pulverised coal boilers and turbines which can withstand supercritical or even ultra-supercritical steam pressures of 3000 to 4500 psig, compared to the conventional 2400 psig subcritical boilers. • This leads to higher thermal efficiency and hence less CO2 emission because less coal is used per kilowatt-hour to generate power. Current thermal efficiency is around 38%. • More than 400 supercritical plants are in operation worldwide now. • Two of the most recent plants are the Tarong North Power station and Millmerran Coal Thermal Power Plant in Australia which cost $1.5billion and $650million respectively.

9. Supercritical Coal Combustion • Advantages • can burn low-grade coal and completely stop emission of NOx and keep SOx production to a minimum, thereby reducing costs for denitrification and desulphurisation equipments • Disadvantages • Large amount of energy is required to create supercritical water/steam.

10. Oxyfuel Coal Combustion • This technology is still in development and has not been used on a commercial scale yet. It involves burning the coal with pure oxygen instead of air in a pulverised coal boiler. • The use of oxygen instead of air results in a lower volume of flue gas which has a much higher concentration of CO2, which can be captured for sequestration. • Oxygen combustion combined with flue gas recycle increases the CO2 concentration in the off-gases from around 15% to about 95%.

11. Oxyfuel Coal Combustion Flue gas (with CO2) Coal Boiler Oxygen Air Air Separation Unit N2 off gas

12. Oxyfuel Coal Combustion • Advanatges • Combustors would be fairly conventional. • Potential to avoid Flue Gas Desulphurisation (FGD) as the SOx and NOx can be captured and stored together with the CO2. • Disadvantages • High cost of separating oxygen from the air. • Need to recycle large quantity of flue gas.

13. Amine Scrubbing • It involves capturing CO2 through a post-combustion mass transfer unit. Special solvent is used to dissolve the CO2 the flue gases. The CO2-rich solvent is then boiled to release the CO2 for storage. • Actual costs vary and depend on process conditions. • Amine srubbing has the advantage that it is a proven technology and has been in use for quite some time. However, it is expensive and involves large equipment size. CO2-deficient solvent CO2-rich flue gas Coal + Air Combustion Unit CO2-deficient flue gas scrubber CO2-rich solvent

14. Underground Coal Gasification CO2 CO2 separator COMBINED CYCLE Syn gas Oxygen, steam Ground level Coal seam

15. Underground Coal Gasification Advantages of UCG (in deep seams) •Pre-combustion processing of gas (Hg, SOx). •High CO2 partial pressure – smaller capture plant. •Pressure energy for power (up to 20%) available. •Self-sustaining for water injection.

16. Chemical Looping Combustion N2 CO2 MeO reduction oxidation MeO O2 + Coal AIR gasifier Syn gas