Different Types of Gasifiers and Their Integration withGas Turbines

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Jeffrey Phillips
The GE Energy process has also been used in several coal and petroleum coke-to-chemicals applications. Besides the Kansas
coke-to-ammonia plant, GE Energy gasifiers featuring the water quench design have been installed at the Ube Industries coke-to-am-
monia plant in Japan and the Eastman Chemical coal-to-chemicals facility in Tennessee. These plants have operated with the very high
availability factors expected in the chemicals industry for more than 20 years.
The GE Energy gasifier can also be used to gasify petroleum refinery liquid by-products such as asphalt residues. Several IGCC
projects based on these feedstocks have been built at refineries around the world.
Shell Coal Gasification Process (SCGP)
The Royal Dutch Shell group of companies (Shell) has developed two different gasification processes. The first, called the
Shell Gasification Process or SGP, was developed to gasify liquid and gaseous feedstocks. It features a refractory-lined gasifier with a
single feed injection point at the top of the gasifier. The gasification products pass through a syngas cooler before entering a wet scrub-
ber.
The second process, called the Shell Coal Gasification Process (SCGP), was developed specifically to gasify solid feeds. The
SCGP gasifier features a water-cooled “membrane wall” similar to the membrane walls used in conventional coal boilers. There are four
feed injectors oriented horizontally in the mid-section of gasifier vessel. Slag flows out of a slag tap at the bottom of the vessel where
it falls into a water bath and syngas flows out the top of the vessel. As the syngas exits the gasifier it is quenched with cool, recycled
syngas to a temperature well below the ash melting point of the coal. The quenched syngas is still quite warm (typically 900°C) and
passes through a syngas cooler and a dry solids filter before a portion of the gas is split off for recycle to the quench zone.
The coal is fed to the SCGP gasifier pneumatically using high pressure nitrogen as the transport medium. The coal must first
be dried and finely ground in a roller mill where warm, inert gas flows through the mill to remove the coal’s moisture. The dried coal is
then pressurized via a system of lockhoppers. SCGP gasifiers operate at pressures up to approximately 40 bar.
Shell began development of the SGP process in the 1950s, and work on the SCGP process started as a joint project with Krupp
Koppers in the mid-1970s. Both companies agreed to go their separate ways in the development of coal gasification in 1981, and Krupp
Koppers developed a competing dry-feed, membrane wall gasifier with the trade name PRENFLO. The only commercial application of
the PRENFLO process has been the 280 MW Elcogas IGCC in Puertollano Spain. In 1999, Shell and Krupp Uhde agreed to join forces
again in coal gasification. However, now only SCGP is being offered commercially by the two organizations.
The first commercial application of SCGP was the 250 MW Demkolec IGCC built in 1994 in Buggenum, The Netherlands. The
plant was originally owned by a consortium of Dutch electric utilities, but was sold to Nuon in the late 1990s. It is now operating as an
independent power producer in the deregulated Dutch electricity market.
Shell has also sold licenses for 12 SCGP gasifiers which will be used in coal-to-chemicals projects in China. The first of those
projects is expected to begin operations in 2006.
Perhaps the greatest advantage of Shell’s coal gasification process is its feed flexibility. The 240 tpd SCGP demonstration built
at Shell’s refinery in Deer Park, Texas in the 1980s was able to process a full range of feedstocks including lignite, sub-bituminous coal,
bituminous coal and pet coke. The reason for SCGP’s flexibility is the coal milling and drying process which eliminates the impact of
moisture on the gasifier performance (however, the fuel for the drying process has a negative impact on thermal efficiency).
The biggest disadvantage of the SCGP has been its higher capital cost which is inherent in the more expensive nature of the
gasifier design (boiler tubes are more expensive than refractory brick) and its dry feed system.
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ConocoPhillips E-Gas
ConocoPhillips owns the E-Gas gasification technology which was originally developed by Dow Chemical. The E-Gas process
features a unique two-stage gasifier design. The gasifier is refractory-lined and uses coal-water slurry feed. The first stage of the gasifier
has two opposed, horizontally-oriented feed injectors. The syngas exits the top of the first stage and slag flows out of the bottom into
a water bath. The syngas produced by the first stage enters the second stage at temperatures comparable to the exit temperatures of the
other two entrained flow gasifiers, GE Energy and SCGP. Additional coal-water slurry is injected into this hot syngas in the second gas-
ifier stage, but no additional oxygen is injected. Endothermic gasification reactions occur between the hot syngas and the second stage
coal feed. This lowers the temperature of the syngas and increases the cold gas efficiency of the process. Upon exiting the top of the
second stage of the gasifer, the syngas passes through a syngas cooler which features a firetube design. The cooled syngas then enters a
rigid barrier filter where any unconverted char from the second stage is collected and recycled back to the first stage of the gasifier where
the hotter temperatures ensure near complete carbon conversion.
Dow began development of the E-Gas process in 1976 with a bench scale reactor. The work progressed to a 36 tpd pilot plant
and then a 550 tpd “proto plant” located at Dow’s chemical manufacturing complex in Plaquemine, Louisiana. The main feedstock
tested in these early gasifiers was lignite.
In 1984 Dow entered an agreement with the federal US government’s Synthetic Fuels Corporation in which Dow received a
price guarantee for syngas to be produced from a commercial scale E-Gas gasification plant built in Plaquemine. The plant began opera-
tion in 1987 and was operated by the Dow subsidiary Louisiana Gasification Technology Inc. (LTGI). The LGTI facility was designed to
process 1600 tpd (dry basis) of sub-bituminous coal from the Powder River Basin. The clean syngas was sent to two Westinghouse 501D
gas turbines which were already operating on natural gas at the Plaquemine complex. The total power output from the two turbines was
184 MW.