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Integrated Gasification Combined Cycle without Carbon Capture and Storage
While gasification has many possible process applications, integrated gasification combined cycle (IGCC) power generation has been the most common large-scale gasification application in the United States in the past 30 years. Similar to a natural gas combined cycle (NGCC), IGCC uses gas and steam turbines to generate electricity, but in this case the gas is synthesis gas (syngas; a mixture of primarily hydrogen [H2] and carbon monoxide [CO]) produced by the gasifier (see Gasifiers for more information). Potentially any carbon-based feedstock might be gasified, including such varied materials as waste plastics, oil refinery bottoms, municipal waste, and biomass, but in practice coal and petcoke have been the most common. IGCC-based electrical power generation is proven to be economical. In addition, cofiring with opportunity materials such as municipal waste and biomass feedstocks in this context may enable IGCC-based power generation (especially when combined with carbon capture and storage) to find an increased role in future economies under anticipated decarbonization scenarios.
Integration of the gasifier, gas turbine, and steam turbine (for reclaiming heat in the gas turbine exhaust) allows for high efficiencies. In fact, current designs can rival the most advanced pulverized coal plants in efficiency, while research and development leading to technological advances in integration, turbine design, and supporting processes might increase efficiency even further. The following discussion provides an overview of additional information about IGCC including technical advantages, challenges, and market trends.
Advantages
IGCC plants benefit from the advantages of gasification technology, particularly environmental benefits, ease of carbon dioxide (CO2) capture, the ability to use a variety of feedstocks, and high efficiency relative to other power generation technologies. Note that Mitsubishi Power has recently claimed that their Nakoso IGCC plant’s advanced system is 10% to 15% more efficient than a 600C–class ultrasupercritical coal-fired unit.1
For environmental protection from harmful compounds produced during power generation, pulverized coal (PC) and natural gas plants typically clean exhaust after combustion—after the exhaust has mixed with air and the controlled compounds are diluted. In general, the less concentrated the unwanted compounds, the more difficult they are to remove. In IGCC operation, however, syngas from the gasifier is cleaned before the gas turbines, when it is at high pressure and more concentrated. Particulate control is particularly stringent because of operational requirements for the gas turbine. This allows for cleaner operation than power generation by current PC combustion technology (and much cleaner operation than legacy coal plants).
Average emissions comparison for sulfur dioxide (SO2), nitrogen oxides (NOx), and particulate matter (PM) between IGCC and pulverized coal (PC; super- and subcritical) power plants, without carbon capture. Data is from Cost and Performance Baseline for Fossil Energy Plants, Vol. 1, DOE/NETL-2023/4320, October 2022).
Concentrated CO2 in the syngas at high pressure makes CO2 capture easier in a gasification plant compared to removal from a dilute exhaust stream. As greenhouse gas regulations (involving CO2 capture and storage) are expected to figure strongly in future energy policy, gasification and IGCC can play a key role in decarbonization/net-zero carbon emissions scenarios of the future.
As mentioned above, feedstocks for gasification include most carbonaceous fuels such as coal of different ranks, as well as petroleum coke, refinery bottoms, biomass, waste, etc., but most IGCC applications have focused on high calorific-value coals for efficiency reasons. Circumstances, however, can change the economic balance; e.g. consider the case of solid waste. Waste gasification in IGCC frees up landfill space, can reclaim valuable materials, and generates electricity and useful byproducts. Gasifying a fraction of biomass with coal can generate electricity with a lower carbon dioxide emission impact as biomass is considered nearly carbon neutral.
IGCC, given its distinct differences from conventional coal-fired power plants, can be as or more efficient than PC power plants. IGCC plants are particularly well-suited to co-generation. An IGCC plant could produce power when electricity prices or demands are high, but divert syngas for another product like hydrogen, transportation fuels or chemicals, as profitability considerations dictate.
Challenges
Challenges to the wide-spread adoption of IGCC technology mainly include cost and policy factors, and complexity of operations. Cost is widely cited as the greatest barrier to IGCC acceptance. Capital costs for IGCC are high compared with alternative power plant designs, particularly NGCC, and financial viability is often dependent upon subsidies or tax credits. As a relatively new technology relative to PC and NGCC, development and design costs are higher for IGCC. The complexity of IGCC relative to older, more established plant designs can increase operating costs and even impact availability and the generation of capital for plant development.
Market Trends for IGCC
The current market situation has involved both closure and ceased operations of several iconic IGCC units—cost pressures and uncertainty about carbon emissions policy seem to have driven the closures of the well-known Puertollano and Buggenum units in Europe, while Tampa Polk Power Unit 1 is currently not operating, and the Wabash IGCC unit has similarly been out of operation with possible revision to a hydrogen production with CCUS configuration still uncertain. Only a few IGCC units remain in current operation, including the new 540-MW Nakoso IGCC and Hirono IGCC units in Japan and Duke Energy’s 2013-built 618-MW Edwardsport IGCC Station in Indiana, and possibly the 400-MW Vresová project in the Czech Republic, and Korea Western Power Co.’s 300-MW Taean pilot plant.1
IEA surveyed the situation with IGCC in its 2021 report on high efficiency, low emissions coal power plants, noting that from the late 2000s, IGCC technology experienced renewed interest due to its potential application in pre-combustion capture of CO2, but that FutureGen (USA) and Zerogen (Australia) did not proceed, while the Kemper County IGCC plant in Mississippi was completed but ultimately aborted coal gasification-based operation, and is now operating on natural gas due to huge cost overruns, operational issues, and the declining cost of natural gas in the USA. In China, the 250 MW GreenGen IGCC was completed in 2015, but planned phases to introduce CCUS and construct a larger scale unit have apparently stalled2.
Nevertheless, IGCC for power generation is currently being promoted for export by Mitsubishi as a superior coal-fired option for power generation. USA-based vendor Air Products acquired the Shell and GE gasification technologies and can offer both dry feed and slurry feed gasifier designs suitable for IGCC application, with either licensing arrangements or over the fence supply of syngas. Lummus Technology acquired the E-Gas gasification technology, and currently offers it for possible IGCC application. A combination of market factors including high natural gas prices and local availability of inexpensive coal may combine to make IGCC a preferred option for power generation in certain markets and geographies (e.g. India) that have not ruled out coal utilization in the future.
References/Further Reading
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