Fixed (Moving) Bed Gasifiers

Lurgi Dry-Ash Gasifier

Lurgi GmbH first developed Lurgi dry-ash gasification technology in the early 1930s to produce what was still known as town gas, in one of the first practical applications of gasification. The first commercial plant based on this technology was built in 1936. In the 1950s, Lurgi and Ruhrgas further developed the technology to handle bituminous coals in addition to the traditional lignite feedstock. Lurgi dry-ash gasification technology has since been used worldwide to produce synthesis gas (syngas), and is the basis of such major projects as the Sasol synfuel plants in South Africa, and the Great Plains Synfuels Plant in North Dakota. An estimated 150 Lurgi gasifiers are in operation today, mainly in South Africa, China and the United States (North Dakota).

Diagram of the Lurgi Dry-Ash Gasifier

Diagram of the Lurgi Dry-Ash Gasifier (source: Sasol)

Operation
The Lurgi gasifier is a pressurized, dry-ash, moving bed gasifier that produces syngas from lump coal, steam, and oxygen as an oxidant. A high ratio of steam to oxygen helps moderate the temperature such that the ash does not melt, but rather is removed as dry ash. More reactive feedstocks are preferred due to the relatively low-temperature operation.

Coal enters the top of the gasifier through a lock hopper and is handled by a rotary distributor as it begins its descent through the gasifier. Steam and oxygen enter from the bottom, while ash is removed at the bottom by a rotating grate and lock hopper. A top temperature of about 1,000°F and bottom temperature of about 1,800°F creates a temperature gradient in the gasifier. Exiting raw syngas at up to 1,000°F is cooled and quenched using recycle water to condense tars and oils. A water jacket cools the gasifier vessel and generates part of the steam needed by the gasifier.

Demonstration and Commercialization 
For several decades, Lurgi has been the leader of coal gasification process, producing town gas and syngas for various applications, including conversion of solid waste to fuel gas. The most significant commercial applications of Lurgi dry-ash gasifiers include:

  • Sasol's synfuel coal-to-liquids facilities in South Africa producing Fischer-Tropsch liquids and chemicals.
  • Great Plains Synfuels Plant in North Dakota producing SNG, as well as ammonia, phenol, and carbon dioxide as byproducts.
  • A large number of Lurgi gasifiers (about 50) are located in China with about another 50 planned or under construction; see the China Gasification Database for further information. (Lurgi dry ash and British Gas Lurgi slagging gasifiers are not differentiated in this database).
References/Further Reading

Lurgi Multi Purpose Gasification (MPG)

Gasifier

 

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