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.
Air-blown IGCC
System Configuration
Air-blown IGCC systems use air for coal gasification.
Schematic of the Air-blown IGCC System
First, coal is processed into coal gas in the gasifier, where air 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 gas turbine combined cycle (GTCC) facility.
The gas turbine combined cycle (GTCC) facility burns the cleaned gas as fuel to turn the gas turbine for power generation. The heat of the exhaust gas is recovered at the heat recovery steam generator (HRSG) by heat exchange with water and the generated steam drives steam turbine for additional power generation.
Placed downstream from the gasifier, the heat exchanger 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.
Air-blown Gasifier
Mechanism of the Air-blown Gasifier
The air-blown gasifier causes a reaction between the supplied coal with a gasification agent to generate high temperature combustible gas mainly composed of carbon monoxide (CO) and hydrogen (H2).
The gasifier has a two-chamber two-stage structure, consisting of a combustor at the lower (first) stage and a reductor at the upper (second) stage. Securing the calorie amount of gasified coal gas necessary for operation of the gas turbine, it melts ash and discharges it smoothly. Therefore, it plays two different roles at the same time.
Features of the Air-blown IGCC
a. High Power Generation Efficiency
Comparison Between the Simple Cycle and the Combined Cycle
IGCC exhibits higher power generation efficiency in combined power generation with the Rankine cycle and the Brayton cycle than in the conventional coal-fired thermal power generation with only the Rankine cycle. Gasification using air leads to lower power consumption for oxygen production and results in higher net plant efficiency.
In addition, as in natural gas-fired GTCC, higher temperature operation in the gas turbine means higher power generation efficiency. Application of a 1,600°C-class gas turbine, which has a track record in natural gas-fired GTCC, and a 1,700°C-class gas turbine under development is expected to increase the efficiency of the IGCC.
b. A Wide Variety of Coal Types are Applicable
Coal Types Applicable to IGCC
In conventional coal-fired thermal power generation, it is difficult to use coal with low ash melting temperature for the prevention of slagging and fouling. In the IGCC, the gasifier melts and discharges ash. It is suited to types of coal with low ash melting temperature.
It opens the way for using types of low rank coal and petcoke that are conventionally difficult to use in power generation.
c. Effective Use of Slag
Fly Ash and Slag
Use in Road Paving Asphalt
Conventional coal-fired thermal power generation discharges ash in the form of fly ash, whereas the IGCC releases ash in the form of glassy slag. With the same weight, slag has a volume that is half or less than that of fly ash. Given that it is glassy, slag can be effectively utilized as a material for cement and road surfaces.
d. Integration
Air-blown IGCC applies following integrations for performance improvement.
- The air for gasification is bled from the air compressor of the gas turbine and pressurized with the bleed air compressor to the necessary level prior to use.
- From the water bled from HRSG, steam is generated at the heat exchanger in the gasifier and merged back into the HRSG steam line so that it may be used for power generation with the steam turbine. Heat is thus effectively utilized.
- High temperature exhaust gas from the HRSG is used for drying coal. In comparison with air drying, it results in lower oxygen concentration, a higher level of safety and suppression of a decline in efficiency to a low level.
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