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10.3.1 Clean fossil-fuel-based power technology

Programmes are underway to develop power plants of the future, using coal and natural gas as the primary fuel, that:

● are essentially pollution free;

● nearly double the current generating efficiency;

● have the capability to produce a varied slate of co-products, such as chemicals, process heat, and clean fuels.

Gasification technologies are an essential part of this effort because they pro-vide the means to vastly expand the clean fuel base to more-abundant and lower cost resources (including biomass and wastes) and enable co-production of power and high value by products.

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1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

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%

−EU −27 −EEA

Figure 10.4 Development of efficiency of conventional thermal electricity and heat production [Source: EEA 2013 [5]]

Gasification breaks feed stocks down into basic constituents so that pollutants can be readily removed and clean fuels or chemicals can be produced. Aiming at:

● Resultant clean fuels can be used to power highly efficient and clean gas tur-bines, fuel cells, and fuel cell/turbine hybrids.

● Gasification concentrates the CO2 constituent, which facilitates capture and recycle or sequestration.

● A clean-coal technology programme has sponsored integrated-gasification combined-cycle (IGCC) projects, representing a diversity of gasifiers and clean-up systems that are helping to pioneer the commercial introduction of this next generation power concept.

● Circulating fluidised bed (CFB) combustion: Because CFBs have unique advantages with regards to fuel adaptability, load following, emission reduc-tions, and operating costs, it is likely that the utilisation of CFBs will continue.

New CFBs are becoming increasingly efficient, larger, more reliable, and have decreasing emissions. The world’s largest and most efficient 600 MW super-critical CFB was placed into operation at the end of 2012. It can be expected that, within this century, coal-fired CFB technology will experience continued development, and become increasingly important for obtaining high-efficiency coal-fired power generation.

● Polygeneration based on coal gasification: Generating synthesis gas after gasification of coal is the foundation for polygeneration (or coproduction).

Using coal as the feedstock, polygeneration technologies can result in a range of products, such as electricity, chemicals, heat, liquid fuels, and natural gas.

Both electricity and higher value products (e.g. chemical products and fuel gas used by urban residents) can be produced at the same facility. Integrated gasification and combined cycle (IGCC) technology is a combination of gasification used for the production of clean coal-based electricity production.

Electricity generation based on IGCC has demonstrated significantly lower emission levels and can also facilitate the separation of CO2. Power plants that implement polygeneration operate in such a way that they achieve the goals of efficient electricity production and full utilisation of coal as a resource. This technology offers benefits across multi-disciplinary fields, and it is one of the best options for the high-efficiency, clean, and low-carbon-utilisation of coal.

Therefore, development and demonstration of polygeneration facilities should be supported in such a way to promote the technology and increase the number of demonstration projects.

Gas separation membranes are important for enhancing the cost and performance of technologies on many fronts, by offering the promise of displacing energy-intensive, costly cryogenic and chemical means of separating out selected con-stituents from a gas stream, such as oxygen, hydrogen, CO2, or pollutants.

● Separation membranes have the potential to significantly enhance the cost and performance of gasification-based technologies.

● Ion transport membranes for oxygen separation are in an advanced stage of development.

Electricity generation in a carbon-constrained world 149

● In addition to gasification applications, ion transport membranes create the possibility of combustion with oxygen rather than air to eliminate nitrogen-based pollutants and to concentrate the CO2 constituent, which enables capture.

● High-temperature ceramic membranes hold the promise of making a hydrogen-based economy feasible and have immediate application to fuel cells, and fuels and chemical production.

● CO2separation membranes have the potential to significantly reduce the cost of CO2 capture, which is the most costly facet of the carbon sequestration process.

Advanced gas-turbine development is essential because gas-turbines will be a mainstay in the power-generation industry for the foreseeable future, operating on natural gas in the near- to mid-term and on gasification-derived synthesis gas in the longer term. Advanced turbine system programmes for the future aim to:

● improve the efficiency and overall performance of the smaller gas turbines in electric-generation service that are subjected to highly cyclic loads, and

● link these gas turbines to fuel cells to push efficiency and environmental per-formance even higher.

Fuel cells have the potential to revolutionise future power generation because they:

● operate on a range of hydrogen-rich fuels (natural gas, methanol, and gasification-derived synthesis gas);

● represent a bridge to a hydrogen economy;

● offer inherently high efficiency and are essentially pollution free (emitting water, CO2and heat);

● lend themselves to distributed generation applications because of low emis-sions and quiet operation (owing to few moving parts).

Phosphoric acid fuel cells are offered commercially and are penetrating niche markets, with efficiencies of 40 per cent – a many 250 kW units have already been sold.

Second-generation, high-temperature molten carbonate fuel cell and solid oxide fuel cells are poised to enter the market, with efficiencies approaching 60 per cent when operated in a combined-cycle mode that uses the process heat to produce steam.

Fuel cell/turbine hybrids that have the potential to raise efficiencies up to 70 per cent by using the process heat from high-temperature fuel cells to drive a gas turbine are under development. Fuel cell energy announced the start-up of a 250 kW molten carbonate fuel cell/capstone micro-turbine system, and a solid oxide fuel-cell-based system is soon to follow.

Fuel cells are unlikely to take the power markets by storm. As long as a developed hydrogen infrastructure is not available (and it may take decades), fuel cells are just another fairly efficient means of converting gas into power and heat;

no more, no less. To succeed, manufacturing costs must first drop to a level that

allows prices barely to exceed the $2 000 kW ¹ threshold. This may take quite some time.

Distributed generation alleviates electricity transmission and distribution constraints (enhancing the reliability of electrical grids), enables combined heat and power applications (boosting thermal efficiencies upwards of 80–90 per cent), and offers an option to central-power generation.

10.4 Carbon capture, usage and storage (CCS)