Coal gasification is said to have greater efficiency than conventional coal-burning because it can effectively use the gases twice: the coal gases are first cleansed of impurities and fired in a turbine to generate electricity. Then, the exhaust heat from the gas turbine can be captured and used to generate steam for a steam turbine-generator. This is called a combined cycle,and a coal gasification plant using this dual process can potentially achieve an efficiency of 50 percent or more, compared with a conventional coal power plant, which is often just above 30 percent.

Syngas Applications :

The raw gas produced by gasification needs to be treated before it can be used for the production of various products such as hydrogen, SNG, ammonia, methanol, liquid fuels, electricity, or direct regulation gas.

There are vatious routes available for obtaining the desired composition, which may be a mixture of corbon monoxide and hydrogen or either pure hydrogen or carbon monoxide alone.

Hydrogen, for example can be used in the refinery industry to achieve lighter and cleaner liquid fuels or for new applications such as fuel cells for power generation or cars.

Hydrogen-rich syngas can be prodruced via the sour CO shift process. In this case, the CO in the raw gas produced by gasfication is shifted with steam to form hydrogen and carbon dioxide before the sour gas components are removed.

A number of processes are available for desuphurisation and carbon dioxide removal, such as MDEA, aMDEA, Genosorb, Slexol, Sulfinol, Rectisol.

For the production of ammonia synthesis gas,a a liquid nitrogen process can be used for the final cleaning and to obtain the correct mixture of hydrogen and nitrogen.

ADVANTAGES AND EFFICIENCY OF GASIFICATION :

Clean power generation, through integrated gasification combined cycle (IGCC) and repowering older coal-based plants, is the primary market for gasification technology into the future. Initial market entry will primarily use coal, or refinery bottoms and petcoke, which offer economic advantages and are a competitive technology even at today's natural gas prices. Coal-based IGCC power generation will follow and is predicted to achieve a large electric market share due to its domestic abundance and relatively low, stable price. IGCC is predicted to be the ultimate, dominant market for gasification given a strong power market.

Clean Energy Conversion :
Clean energy conversion refers to the conversion of one energy source (typically coal or biomass, although there are many potential feedstocks) into another, usually for convenience or further use. For example, coal is not practical to power an automobile, but gasoline is.

Synthesis gas (syngas) from gasification can be used as a basis for producing clean transportation fuels, chemicals, and gaseous fuel for fuel cells. Chemical production through syngas is already a proven technology, with almost 29 GWth capacity installed by 2010, but it is the generation of ultra-clean transportation fuels production that is expected to have the greatest market growth in the near term. Gasification and subsequent synthesis of fuels has the potential to meet a growing need for low-sulfur, high-quality diesel. Gasification-derived syngas is the feedstock for a variety of additional products including methanol and other chemical and precursors. The market for methanol and other hydrocarbons for use as blending stock should grow, especially as cleaner fuel regulations increase. The market for gaseous fuels from coal, like SNG has been proved, while H2 for use in highly efficient fuel cells is expected to develop as supporting technology and fuel cells themselves improve.

An advantage of gasification is its applicability to a variety of feedstocks, either singly or in combinations. Almost any carbonaceous substance can be gasified: fossil fuels such as coal (varying in rank) and oil, refinery waste, byproducts such as asphalt or black liquor, biomass (which is any kind of agricultural waste such as corn stover, or various crops), or even sewage, plastics, and municipal solid waste.

MARKETS FOR GASIFICATION :

A variety of commodities can be produced from syngas, the primary product of gasification, providing for many potential markets. This product flexibility as well as the versatility and efficiency of gasification, make it an attractive technology now and for the future.

Currently, the main markets for gasification, as judged by analysis of current and planned projects, are:
Electricity production
Chemicals and fertilizers
Transportation fuels such as diesel and gasoline
Gaseous fuels (synthetic natural gas [SNG] or hydrogen H2)