Emerging Technologies to Meet $44 Billion U.S. Coal Gasification Market

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Researched by Industrial Info Resources (Sugar Land, Texas). At the turn of the millennium, development of coal-fired generation in the U.S. was limited to a few projects. Coal had been replaced by cleaner burning natural gas as the fuel of choice for new generation development. Today, the tables have turned. The unstable cost of natural gas coupled with supply issues has forced power generators to look at natural gas alternatives for new generation development, including traditional sources of nuclear, hydro, and coal, as well as non-traditional emerging technologies such as renewable fuels and coal gasification.

Solid fuels, such as coal, waste coal and petroleum coke are less expensive than natural gas, but burn dirty, emitting NOx, SOx and particulate pollution. Since the U.S. Clean Air Act was passed in the 1970’s, development of new coal-fired generation declined, eventually becoming negligible. Improvements to coal unit emission control and generation technology are making coal more attractive than ever for future electricity production. Gasification is one technology that could provide inexpensive electricity from readily available fuel and at the same time greatly reduce emissions.

Currently, there are more than 50 proposed Integrated Gasification Combined Cycle (IGCC) units, totaling in excess of $44 billion in total investment value that will supply about 16,000 megawatts in the United States. Most of the units are in the 250 to 600-megawatt (MW) range, and are located in the central United States near existing coal, waste coal, or petroleum coke sources.

Click on the image at right to view a chart showing the breakdown of IGCC projects by market region

IGCC is one of the most efficient ways to utilize solid fuels. The IGCC process gasifies the fuel first, and then the gas is used in a conventional combined cycle configuration. This combines the best of both worlds – readily available fuel (coal) and efficient combined cycle technology. After being gasified, the fuel (syngas) is fed into a boiler/syngas cooler or can be cooled by water quenching. The cooled gas is cleansed of sulfur compounds and used to fire a combustion turbine/generator (GT) allowing waste heat to be recovered by heat recovery steam generators (HRSG) to drive a steam turbine/generator (ST). This configuration also allows for natural gas to be utilized, if for some reason the coal source or gasification process is interrupted.

Two of the largest projects to incorporate the gasification with boiler/syngas cooler process in the United States are Tampa Electric Company’s Polk County Generation project in Mulberry, Florida and Global Energy’s Wabash project in West Terre Haute, Indiana.

There are three basic types of gasification processes that are currently being utilized in creating fuel for the power island of an IGCC plant. They are the moving-bed asifier, fluidized bed gasifier and the entrained-flow gasifier.

The entrained-flow gasifier, such as the Shell/Prenflo that Uhde GmbH utilized to build a coal-fed IGCC, with a capacity of 318 megawatts, in Puertollano, Spain, is one example of the new technology being put to use. GE Energy (formerly Chevron Texaco), ConocoPhillips (slurry fed two stage oxygen blown), Mitsubishi (dry fed two stage air blown) and Future Energy (formerly Noell/GSP), recently bought by Siemens, have developed contending designs. All use high purity oxygen for gasification and all are in commercial plant operation.

John Griffiths, Senior Consultant with Jacobs Consultancy UK, Limited (London, England) states, “We have put water quench technology before boiler since first evaluating the options in the mid-eighties and typically advise clients to use a water quench gasifier on the grounds of high availability, low capital cost, and good thermal efficiency using Jacobs flow scheme technologies.” Jacobs recently received a contract from the Northern Lights Partnership to provide engineering and procurement on an upgrader unit that will reduce emissions and require less natural gas. Mr. Griffiths adds, “Water quench gasifier is the technology of choice for most non-U.S. applications.” Several European and Asian groups have gone with the water quenching technology including the world’s biggest IGCC plant Sarlux (551 MW) at the Saras Refinery in Sardinia, Italy, two other IGCCs in Italy, and one at Negishi in Japan.

Industrial Info was intrigued by the fact that many IGCC projects outside of the U.S. utilized water quench technology, and asked Mr. Griffiths the following questions.

Industrial Info: What are the main differences between water quench gasifier and boiler gasifier?
Mr. Griffiths: Gasification uses about 20% of the chemical energy in the feedstock to react with oxygen to raise the temperature to about 1300 to 1500° C. The hot synthesis gas (syngas) has to be cooled down and the heat recovered to maintain a good thermal efficiency. For those who are seeking high efficiency IGCC plants, a syngas cooler or boiler may be attached to the gasifier, such as at Tampa and Wabash. This is expensive with a potentially lower availability because of the cost of installing spare gasification capacity. The quick and easy answer is to quench the very hot syngas in water. The heat is then used up in raising a large quantity of steam mixed with the syngas. This low cost engineering option has a high reliability – but it is not as efficient as a boiler.

Industrial Info: Are there any other technologies being used?
Mr. Griffiths: The only other technology in commercial use for cooling hot gasification syngas is a moving-bed gasifier as used at the Great Plains project. Here the hot syngas is used to directly heat up the coal moving down the gasifier. This is a very efficient way of using the heat but means that the syngas contains tars, phenols and other hydrocarbons absent in entrained-flow gasifiers, and is suitable for use as high performance gas turbine fuel only after extensive clean-up and treatment.

Industrial Info: What are some examples of successful water quench gasifiers in IGCC?
Mr. Griffiths: Successful IGCC plants operating with water quenches are the three Italian IGCC projects Sarlux, API and ISAB. The Japanese successfully commissioned a water quench IGCC at Negishi three years ago. These plants all use refinery residues as feedstock, however, two examples of successfully operating coal-fed quench gasifiers are those of Eastman Chemical at Kingsport in Tennessee, and the Coffeyville urea fertilizer plant in Kansas.

Industrial Info: In your opinion why isn't the water quench gasifier being considered for IGCC application in the U.S.?
Mr. Griffiths: U.S. power companies wish their plants to run at the highest possible operating efficiency in order to reduce cost, especially the running cost of coal consumption. However, it was shown in an EPRI Study (EPRI report AP 3486) carried out by Fluor and published in April 1984, that a quench gasifier IGCC produces lower cost electricity than an IGCC using a gasifier fitted with any form of boiler.

Gasification can also be used to produce multiple co-products (known as polygeneration), including hydrogen, syngas for Fischer-Tropsch synthesis of liquid fuels, carbon dioxide for capture and storage as well as produces by-products of high purity elemental sulfur plus an inert solid waste or slag that can be used in the manufacture of building and road construction materials. These side products can help to keep the cost of power production down.

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