Transcript Slide 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. 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. 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. 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 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. 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. 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%. Oxyfuel Coal Combustion Flue gas (with CO2) Coal Boiler Oxygen Air Air Separation Unit N2 off gas 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. 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 Coal + Combustion Unit CO2-rich flue gas scrubber Air CO2-rich solvent CO2-deficient flue gas Underground Coal Gasification CO2 CO2 Syn gas Oxygen, steam separator COMBINED CYCLE Ground level Coal seam 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. Chemical Looping Combustion N2 MeO CO2 reduction oxidation MeO O2 AIR Syn gas gasifier + Coal