Types of Gasifiers
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The moving, or fixed, bed gasifiers, exemplified by the Lurgi dry ash gasifiers, are installed at both Sasol coal to liquids (CTL) plants and the Great Plains Synfuels Plant. When these plants were designed, the only commercial gasification process was Lurgi’s. Although fixed bed technology is 42% of the world’s total installed gasification capacity, the moving bed gasifier’s inherent limitations - relatively high maintenance costs, large capital investment to handle byproducts such as tars and ammonia, and relatively small throughput per foot of plot space - have stymied future installations.
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The fluid bed gasifiers, such as the KBR transport reactor under development at the Wilsonville Power Systems Development Facility (PSDF), may be a viable alternative, especially for low rank coals. Although currently only 2% of the installed capacity, fluid bed gasifiers may have the potential to provide a compact IGCC-specific product line. It also appears to be a good solution for lower ranked coals. The scale-up issues with this technology will be explored in the Southern Company DOE-funded Orlando Project, scheduled for a 2011 startup.
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The entrained bed gasifiers, licensed by ConocoPhillips, Future Energy, GE Energy, and Shell, are the current market leaders, with 56% of the installed base and the vast majority of all sales during the last 20 years. The reasons for the entrained bed gasifiers commercial dominance include:
  • reliable and proven design (widely used in chemical industry);
  • no internal moving parts;
  • compact size compared to other gasifiers;
  • minimal byproducts; and
  • ability to supply syngas at higher pressures.

GASIFIER COMPARISON
Gasifier Type
Moving (fixed bed)
Fluid Bed
Entrained Bed
Process Description
Moving bed, also known as fixed bed, gasifiers, feed coal in the top. The coal moves down through the reactor by gravity. Steam and oxygen are fed in through the bottom of the gasifier.
The solid particles are fluidized with the gas and then the gases and remaining solid particles are separated. The gasifier typically operates at a low temperature (non-slagging). Attempts are being made to operate at high temperature (slagging).
Solid and gas flow together in an “entrained” bed. Short residence times and high temperature operation. High carbon conversion is achieved through the use of high-purity oxygen. These gasifiers operate in the slagging mode.
Technology Providers BGL, Lurgi HTW, KRW, KBR transport reactor, Winkler ConocoPhillips, Future Energy, GE Energy, ICCT, Shell
Installed Capactiy 18.7 GWth (42%) 0.9 GWth (2%) 25.4 GWth (56%)
Feed Issues :
Size 6-50 mm 6-10 mm <100 μm
Acceptability of fines Limited Good Unlimited
Caking Coal Yes Yes Dry feed - Yes
Coal Rank Any Any Dry feed – any; slurry feed – high rank
Operating Issues:
Outlet gas temp Low (800-1200°F) Moderate (1650-1900°F) High (2250-3000°F)
Oxidant demand Low Moderate High (ASU required)
Steam demand High Moderate Low
Internal moving parts Yes, reactor stirrer (affects reliability) No No
Other Hydrocarbons in gas (additional BOP investment) Lower carbon conversion (high recycle rate) High purity syngas, high carbon conversion, high throughput


Each of the entrained bed technology providers tackles the technology issues differently, as shown below.