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Status of IGCC
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Adapted from a paper presented at the 1st Annual Conference of CRC Participants by Allen Lowe and Peter Benyon, Pacific Power International and Paul O'Neill, Rio Tinto Research Technology and Development.
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Integrated Gasification Combined Cycle (IGCC) is a potential alternative technology to conventional pulverised coal (PF) combustion for the generation of electricity from coal. Although PF technology remains dominant in both new and existing coal fired power plants in most areas of the world, a number of commercial scale IGCC plants have recently entered service. The CRC has taken this opportunity to review the progress toward commercial competitiveness of IGCC technology.
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Figure 1: Process Diagram for IGCC Plant |
IGCC Basics
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An IGCC plant combines a coal gasification unit with a gas fired combined cycle power generation plant. In this way, IGCC has the potential to produce electricity from coal with higher efficiency and with very low emissions. A typical process diagram is shown in Figure 1.
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Gasification is achieved by reacting the coal at high temperature and pressure with a limited amount of oxygen. This produces a fuel gas mostly consisting of carbon monoxide and hydrogen. The raw fuel gas passes to a clean-up stage where particulates, sulphur and nitrogen compounds are removed.
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Table 1: Commercial Gasifier Experience |
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The cleaned gas is burnt in a conventional gas turbine to produce electric power, and the hot turbine exhaust gas is used to produce steam for a conventional steam turbine. Typically, the gas turbine will produce 65% of the power while the steam turbine produces about 35%.
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While coal is the principal interest of the CRC, it must be recognised that IGCC is suitable for a wide range of fuels. Significant niche market opportunities exist for low value, poor quality fuels such as oil residuals, Orimulsion, biomass and waste materials such as municipal rubbish. There may be a minor potential for these fuels to take market share from coal in certain areas of the world.
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Commercial IGCC Experience.
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The gasification of coal and other solid fuels is widely applied for the production of liquid fuels, chemical feedstock and fuel gases. Present developments are aimed at achieving higher efficiency of gasification, greater throughput, lower capital cost and improved environmental performance.
Most current IGCC development work is being performed on either fluidised bed or entrained flow gasifiers. Fluidised bed gasifiers are well suited to low rank coals while entrained flow gasifiers are generally preferred for high rank coals.
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Table 2: Commercial Coal Fired IGCC Plants |
Numerous coal gasifiers are in commercial operation around the world. Lurgi fixed bed reactors are dominant, however most of the newer plants are based on Shell or Texaco entrained flow designs. The largest plants produce chemical feedstock, and a 1,500 t/day Texaco plant at Ube, in Japan, has logged more than 140,000 operating hours to date on coal and petroleum coke. In addition, a number of large-scale gasifiers have started operation in China in recent years. These plants are mostly based on the Texaco entrained flow design. Table 1 indicates some of the characteristics of the major gasifier technologies used for coal.
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Relatively limited experience exists with the integration of the gasifier and the combined cycle power plant. However, a number of commercial scale IGCC plants have entered service in recent years. Selected plants and design concepts are listed in Table 2, and Figure 2 shows unit capacity and year of start-up of recent IGCC plants. The progressive increase in capacity and in number of operating plants is clear.
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Figure 2: Capacity and Timing of Recent IGCC Plants
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Operating Experience
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A significant amount of experience is now accumulating on the operation of IGCC plants. The Cool Water Plant demonstrated very high levels of pollution control. The low efficiency of this plant was due to low levels of integration and to the low technology (compared to present designs) of the gas turbine employed at the plant. The Plaquemine plant was built by Dow Chemical Company as a commercial venture and operated for six years before closing down in 1994. It is understood that the plant closure followed restructuring within the Dow Company.
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Of the present generation of IGCC plants, the Buggenum plant has operated since 1994 with Wabash River and Polk Power entering service in 1995/96. All of these plants have suffered significant plant and process difficulties, mainly in the ancillary plant and related to the integration of the various processes, as much as to the processes themselves.
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A diverse range of coals has been tested in the demonstration units. The design coals for some of the plants are listed in Table 3.
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Table 3: Coals Used in Operating IGCC Plants |
The ultimate success of the IGCC technology will depend on the economics of the process relative to alternative technologies for electric power generation, particularly pulverised coal and natural gas combined cycle. The principal factors affecting IGCC economics include the capital cost, availability and O&M costs for the plant, fuel costs and the efficiency of conversion.
Capital cost is a prime consideration, and some published capital costs for IGCC plant are listed in Table 5. These first generation costs are substantially above that of mature technologies. Indicative costs for PF technology and for natural gas combined cycle plants are included for comparison in Figure 3.
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Figure 3: Cost Competitiveness of IGCC
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Substantial changes in technology have become available even in the short time since these latest plants were committed, and the costs have changed accordingly. Applying a number of cost factors to account for these changes, it is estimated that a 4x2000MWe power station will have in capital costs about 60% of those in Table 5. Further substantial cost reductions will also be achieved as experience with the technology increases.
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Based on this information, it would appear that coal fired IGCC plant may now be competitive with PF plant of similar size. Further implementation appears to depend on the utility industry developing confidence that current plant availability and reliability projections can be sustained in the longer term.
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For further information contact:
Allen Lowe, Pacific Power International
Phone: (02) 9268 7561
Fax: (02) 9268 6141
Email: allen.lowe@pp.nsw.gov.au
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