Advanced Power Generation Technologies

Integrated Gasification Combined Cycle (IGCC)

Background

The utilisation of coal in present technologies produces some undesirable emissions. These include oxides of nitrogen and sulfur, particulate emissions and greenhouse gases such as carbon dioxide. There is strong incentive to reduce these emissions and improve fuel efficiency of coal utilisation technologies.

To address these challenges, new coal utilisation technologies are being developed. One of the more promising of these is the Integrated Gasification Combined Cycle (IGCC) system for use in power generation.

IGCC Power Generation System

Source: IHI Japan

How does IGCC work?

IGCC is a combination of two leading technologies. The first technology is called coal gasification, which uses coal to create a clean-burning gas (syngas). The second technology is called combined-cycle, which is the most efficient method of producing electricity commercially available today.

• Coal Gasification:
  The gasification portion of the IGCC plant produces a clean coal gas (syngas) which fuels the combustion turbine. Coal is combined with oxygen in the gasifier to produce the gaseous fuel, mainly hydrogen and carbon monoxide. The gas is then cleaned by a gas cleanup process. After cleaning, the coal gas is used in the combustion turbine to produce electricity.
  
  
• Combined-cycle:
  This design consists of a combustion turbine/generator, a heat recovery steam generator, and a steam turbine/generator. The exhaust heat from the combustion turbine is recovered in the heat recovery steam generator to produce steam. This steam then passes through a steam turbine to power another generator, which produces more electricity. Combined cycle is more efficient than conventional power generating systems because it re-uses waste heat to produce more electricity.

The integration of these technologies provides the high efficiency of the combined-cycle design with the low cost of coal for fuel.

Advantages of IGCC

IGCC is an advanced technology that represents the cleanest of currently available coal technologies. Advantages of IGCC over current conventional coal-based power generation systems include:

• Higher efficiencies and lower emissions:
  Improvements in efficiency dramatically reduce emissions from coal combustion as the graph at right highlights. Increasing efficiency from 35 to 40%, for example, reduces carbon dioxide emissions by over 10%.
  
  With efficiencies currently approaching 50%, IGCC power plants use less coal and produce much lower emissions of carbon dioxide than conventional power plants.
  
  With development of new gas turbine concepts and increased process temperatures efficiencies of more than 60% are being targetted.
  
  
• Higher output:
  Using syngas in a gas turbine increases its output, especially when nitrogen from an oxygen blown unit is fed to the turbine. Thus a turbine rated at 170MW when fired on natural gas can yield 190MW or more on syngas. Furthermore, output is less dependent on ambient temperature than is the case with natural gas.
  
  
• Product flexibility - including carbon capture and hydrogen production:
  The gasification process in IGCC enables the production of not only electricity, but a range of chemicals, by-products for industrial use, and transport fuels (see graphic).
  
  Carbon dioxide can be captured from the coal syngas (carbon monoxide and hydrogen) through a water/gas shift process.
  
  The CO2 can be captured in a concentrated stream, making it easier to convert into other products, or to sequester (for example, store underground) - see CO2 Capture and Storage.
  
  An added advantage in this process is that there are low additional costs for carbon capture, particularly if the plant is oxygen driven.
  
  In addition to electricity generation, hydrogen produced from the process can potentially be used as a transport fuel, in fuel cells - as outlined below.
  
  
• Pathway to the Hydrogen Economy:
  Hydrogen is gaining prominence as a major fuel and energy source of the future. In terms of transportation, for example, vehicle manufacturers have already begun producing prototype vehicles fuelled by hydrogen, with fuel outlets beginning to appear in Europe and the US.
  
  Research and development in recent years has focused on hydrogen fuel cells which hold great promise as low-pollution automobile engines if certain difficulties can be overcome. Water, the only waste product of a hydrogen-oxygen fuel cell, is non-polluting and can be used to cool the engine. The oxygen the cells need is readily available in air.
  
  Hydrogen, however, is not so readily available, and there is no existing delivery system to convey hydrogen to all the places people would need it to power their cars. In addition, pure hydrogen is not abundant enough to provide power for all the cars on the road today. Instead, hydrogen would need to be extracted from other substances, a process that requires energy and produces pollutants.
  
  While fuel cells may become a principal energy conversion device of this century, they require further development for application in large stationary power plants and are not currently competitive with gas and steam based combined cycles for power generation or in transport applications. Further development and deployment of fuel cells may lead to a demand for central hydrogen production facilities. It is important to note that as hydrogen wells do not exist in nature the energy to produce large quantities of hydrogen will most likely come from fossil fuels. Coal is likely to be the primary source of hydrogen because of its relative abundance and low cost.
  

  For an animated graphic of how fuel cells work, see http://www.eere.energy.gov/hydrogenandfuelcells/
  Click on 'fuel cell animation' under the heading 'For Students and Teachers'.

IGCC Worldwide

In February 1997 9 IGCC plants were operating worldwide and 11 were in the final stages of planning. Some 50 more were under consideration. By 2000 nearly 4 Gigawatts (GW) were in use worldwide with a further 3 GW due to go online by 2004.

IGCC in Australia

While Australia has no IGCC plants, the suitability of local coals for gasification has been extensively researched over recent years, with work centred on an advanced gasification facility at CSIRO’s Pinjarra Hills laboratories in Queensland.

The research program has been a collaborative effort involving the Co-operative Research Centre for Coal in Sustainable Development, CSIRO Division of Energy Technology and the Australian Coal Association Research Program.

The gasifier is one of very few in its class of high pressure and temperature equipment. It is unique in the extent of its capabilities for simulating reaction conditions in commercial entrained-flow gasifiers. [Pictured: CSIRO's IGCC reactor]

The conditions present in these advanced technologies mean that traditional indices used to assess coals for their performance in conventional furnaces may not be suitable. The increased pressures, temperatures and reducing conditions mean that the processes that convert the coal and mineral matter are different. Understanding these processes, and how they affect the use of Australian coals, will be important when Australia builds its first IGCC plant.

For further information see: http://www.det.csiro.au/factsheets/advanced_power_generation.htm

Selected References:

World Coal Institute
http://www.wci-coal.com/

See in particular, 'Clean Coal Technologies/ Technology & Research'. The index here includes information on IGCC including links to a large number of sites.