Advantages
- World-class Power Generation Efficiency - 48% LHV
- Low Grade Coal is Applicable - Coal Flexibility
- Low NOx, Low SOx and Low Dust Concentration - Superior Environmental Performance
- CO2 Emissions Compared with Those of Conventional Coal-fired Thermal Power Generation - About 15% Lower
Next-generation power generation system characterized with coal gasification for high efficiency and environmental performance
A Power Generation System with High Efficiency
Integrated coal gasification combined cycle (IGCC) power plants are a next-generation thermal power system with significantly enhanced power generation efficiency and environmental performance due to its combination with coal gasification and the Gas Turbine Combined Cycle (GTCC) system. Large-type IGCC systems can improve power generation efficiency by approximately 15% and reduce CO2 compared with conventional coal-fired thermal power systems.
IGCC = Integrated coal Gasification Combined Cycle
High Environmental Performance
With enhanced system efficiency, IGCC lowers SOx, NOx and dust emissions per kilowatt-hour of electric power generated. It discharges hot wastewater that is about 30% smaller than the conventional coal-fired thermal power generation.
While the flue gas desulfurization equipment in conventional coal-fired thermal power generation required a large amount of water for treating flue gas after fuel operation, IGCC consumes a much smaller amount of water because it treats fuel gas that is higher in pressure and smaller in volume.
Our IGCC Business
Mitsubishi Hitachi Power Systems (MHPS) retains two types of coal gasification technology, namely, air-blown and oxygen-blown technologies, and leads the world in terms of its technological capabilities. In line with expectations that the need for the IGCC system will increase further due to its ability to both effectively utilize coal resources and protect the environment, this system has been gaining attention around the world.
Oxygen-blown IGCC
System Configuration
System Configuration of the Oxygen-blown IGCC System
First, coal is processed into coal gas in the gasifier, where oxygen is used as the gasification agent. Coal gas undergoes desulfurization and dedusting treatment in the gas clean-up unit to comply with the standards for gas turbine fuel and exhaust gas. The cleaned gas is supplied to the GTCC facility.
The GTCC facility burns the cleaned gas as fuel to turn the gas turbine for power generation. The heat of the exhaust gas is used to drive the heat recovery steam generator (HRSG) for heat exchange with water, which also generates steam for power generation from the steam turbine.
Placed downstream from the gasifier, the heat exchanger (or the syngas cooler (SGC)) cools the hot coal gas. At that time, steam is generated. It is merged into the HRSG and used for power generation with the steam turbine. It further increases power generation efficiency.
Features of the Oxygen-blown Gasifier
a. Oxygen-blown Gasifier
Our oxygen-blown gasifier is based on a single-chamber, two-stage, swirl-flow entrained-bed equipped with burners in the upper and lower stages of a cylindrical furnace. Appropriate oxygen/coal ratios can be allocated to the upper and lower stages in order to match the lower stage to the temperature required for melting ash and the upper stage to the conditions for an efficient gasification reaction according to the type of coal used. Moreover, a swirl flow can be generated in the gasifier to allow residence time for coal particles and to suppress the dispersion of char.
The measures described below were applied to the oxygen-blown gasifier: 1. The oxygen/coal ratios in the upper and lower stages were optimized, and the way of supplying seal gas was improved at the gasifier outlet (throat) to protect the throat from ash deposits (slagging). 2 The water-cooled piping on the gasifier wall was narrowed to step up cooling, and heat-resistant material was fusion-injected into the local high-temperature parts, in order to protect the gasifier walls. 3. The high-temperature gas flow (self-circulating flow) in the furnace and the slag flow-down promoting nozzle were used to insulate and heat the molten ash (slag) tapping hole, in order to cause slag to flow down stably. These measures solved the problems associated with the oxygen-blown gasifier.
Features of the Oxygen-blown Gasifier
Coal Types Applicable to the Oxygen-blown Gasifier
c. Net Thermal Efficiency
IGCC can increase net efficiency by applying high-efficiency technology based on a heated natural gas-fired gas turbine. Commercial oxygen-blown IGCC equipment based on a gas turbine has a net efficiency of about 46% (HHV), thereby saving CO2 emissions by about 10% from leading-edge pulverized coal-fired power plants. Oxygen-blown coal gasification captures CO2 from gas having a high CO2 content of about 40% under pressure ranging from 2.5 megapascals to 3.0 megapascals (pre-operation CO2 capture), so that the gas flow to be treated is lower than the CO2 content to be captured (post-operation CO2 capture) from the boiler exhaust gas. This makes it possible to use a smaller CO2 recovery unit and suppress the decline in net efficiency.
d. Effective Use of Ash
Ash discharged from IGCC has a lower unburned content than conventional pulverized coal-fired thermal power plants, and thus is recycled in road surface materials and others. The ash is also high in bulk density and has a volume ratio as small as 50%, thereby reducing the area needed to dispose of unused ash.
Comparison of oxygen-blown IGCC with conventional coal-fired power plant in ash volume, characteristics, etc.
Source: Mitsubishi Hitachi Power Systems, Ltd.
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