INTEGRATED GASIFICATION COMBINED CYCLE
The Integrated Gasification Combined Cycle (IGCC) plant is a means of
using coal and steam to produce hydrogen and carbon monoxide (CO) from
the coal and these are then burned in a gas turbine with secondary steam
turbine (ie combined cycle) to produce electricity.
If the IGCC gasifier is fed with oxygen rather than air, the flue gas contains
highly-concentrated CO2 which can readily be captured post-combustion as
Research is being conducted on Integrated Gasification Combined-Cycle
(IGCC) systems, in which the syn gas is burned as fuel in a combustion
turbine, which drives an electric generator. Exhaust heat from the combustion
turbine is recovered and used to boil water, creating steam for a steam
The use of these two types of turbines together (combined cycle) is one
reason why gasification-based power systems can achieve high power
The raw gas thus produced is cleaned of most pollutants. It is then burned in
the combustion chamber of the gas turbine generator for power generation.
The heat from the raw gas and hot exhaust gas from the turbine is used to
generate steam which is fed into the steam turbine for power generation.
The main subsystems of a power plant with integrated gasification are:
1. Gasification plant
2. Raw gas heat recovery systems
3. Gas purification with sulphur recovery
4. Air separation unit (only for oxygen blown gasification)
5. Gas turbine with heat recovery steam generator
6. Steam turbine generator
Adoption of IGCC technology in India has ‘Global’ as well as ‘National’
FLEXIBILITY TO ACCEPT A WIDE RANGE OF FUELS
IGCC technology has been proven for a variety of fuels, particularly heavy
oils, heavy oil residues, petcokes, and bituminous coals in different parts of
the globe. In fact the same gasifiers can handle different types of fuels.
POTENTIAL FOR HIGHER EFFICIENCIES
Increasing the firing temperatures and utilizing materials that withstand
higher temperatures can increase the efficiency of gas turbine. Continuous
developments have been taking place in the newer materials of construction
thus consequent higher gas turbine performance. At present the efficiency of
gas turbines is in the range of 45-50% which is projected to go upto 60%
with the development of H-technology by GE. The advances in gas turbines
would improve the overall efficiency of IGCC plant.
ENVIRONMENT FRIENDLY TECHNOLOGY
IGCC is an environmentally beginning technology. The emission levels in
terms of NOx, SOx and particulate from an IGCC plant have been
demonstrated to be much lower when compared to the emission levels from a
conventional PC fired steam plant. In fact, no additional equipment is
required to meet the environment standards.
LOWER HEAT RATES & INCREASED OUTPUT
The heat rates of the plants based on IGCC technology are projected to be
around 2100 kCal/kWh compared to the heat rates values of around 2500
kCal/kWh for the conventional PC fired plants.
Fig.18 shows Heat Rate characterstics in different technologies
CARBON CAPTURE AND STORAGE
Carbon capture and storage (CCS) means separation and capture of CO2 from
fossil fuel-fired power plants and the recovery of a concentrated stream of
that CO2 that can be transported by pipeline and stored, in either an
underground formation, or the sea bed.
CCS technologies include:
Post-Combustion (captures CO2 from power plant flue gases),
Pre-Combustion (widely used in fertilizer manufacturing and in
hydrogen production without any CCS) and
Oxy-Fuel Combustion (still in the demonstration phase, but showing
great potential because recycling the flue gas through the boiler
concentrates the CO2 level in the flue gas, making it easier to separate
GAS CLEAN-UP SYSTEM
Steps for Gas Clean-up System aim at particulate removal, sulfur removal
and NOx removal.
Hot Gas Clean-Up technology is currently under demonstration phase and
various demonstrations have not been successful so far. Wet scrubbing
technology, though with a lower efficiency, still remains the preferred option
for gas clean-up systems in IGCC.
This is achieved as follows:
Particulate Removal: Combination of Cyclone Filters & Ceramic candle
SOx & NOx removal: Combination of steam/water washing and
removing the sulfur compounds for recovery of sulfur as a salable
ACID GAS REMOVAL (AGR).
The MDEA/Claus/SCOT process is used for acid gas removal and sulfur
In the MDEA process, the cooled gas enters an absorber where it comes into
contact with the MDEA solvent. As it moves through the absorber, almost all
of the H2S and some of the CO2 are removed.
The solute-rich MDEA exits the absorber and is heated in a heat exchanger
before entering the stripping unit.
Acid gases from the top of the stripper are sent to the Claus/SCOT unit for
The lean MDEA solvent exits the bottom of the stripper and is cooled
through several heat exchangers. It is then filtered and sent to a storage tank
for the next cycle.
IGCC is essentially the only coal technology that can effectively remove
mercury from the environment.
Carbon beds have demonstrated 99.9% mercury removal from syngas.
Carbon beds are less expensive and produce vastly smaller volumes of solid
waste than activated carbon injection at PC plant. Carbon bed waste is
managed as hazardous waste which inhibits re-emission.
Initial Synge mercury removal is in gas-clean-up system (before mercury
bed). Much of this mercury is captured in wastes managed as hazardous,
which inhibits re-emission(according to the data analysis of COAL INDIA
Limited & other mining industries. Coal India is a coal producing PSU of
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