Mitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)
27

Development of Coal Gasification System forProducing Chemical Synthesis Source Gas
TAKAO HASHIMOTO*1

KOICHI SAKAMOTO*1

KATSUHIRO OTA*2

TAKASHI IWAHASHI*3

YUUICHIROU KITAGAWA*4 KATSUHIKO YOKOHAMA*5

Mitsubishi Heavy Industries, Ltd. (MHI) has developed its own air-blown gasification
technology and has been smoothly operating an IGCC demonstration plant. On the basis of this2-stage, 2-chamber gasification method, MHI continues to develop an oxygen-blown gasifiersystem for chemical synthesis by applying the basic gasifier structure of the IGCC demonstration
plant to that of the oxygen-blown gasifier. The current status of oxygen-blown gasifier
development for chemical synthesis is presented in this paper.

|1. Introduction
In view of energy issues, since coal reserves are abundant all over the world and the price ofcoal is stable, the effective and clean use of coal should be promoted as an alternative to the heavy
dependence on natural gas and oil. With this in mind, coal-gasification technologies which produceliquefied fuels from solid coal as feed materials or synthesize chemical products are spotlighted.
For liquefied fuels and chemical products, a reduction in the amount of nitrogen (N2) gas, which isan inert component in syngas generated in a downstream process, is desired. Therefore, an
oxygen-blown method is the mainly applied for chemical synthesis. MHI has already developed its
own air-blown gasification technology for power generation and has been smoothly operating an
IGCC demonstration plant. We are now committed to developing a commercial IGCC plant withthe world’s highest efficiency using an air-blown gasification method. On the basis of this 2-stage,
2-chamber entrained bed gasification method, MHI has been continuing to develop an
oxygen-blown gasifier system for chemical synthesis by applying the basic gasifier structure of theIGCC demonstration plant to that of the oxygen-blown gasifier.

|2. Features of Mitsubishi oxygen-blown coal gasifier
2.1

Principle of Mitsubishi 2-stage, 2-chamber entrained bed gasifier

Figure 1 shows the principle of the Mitsubishi 2-stage, 2-chamber entrained bed gasifier.
This gasifier includes a combustor (combustion section), where high temperature combustion withstable discharge of melting ash is conducted, as well as a reductor, where the gasification reaction
is conducted with the high temperature gas from the combustor. By separating functions, the gas
temperature required for coal ash melting and the stable discharge of slag (even in the case of an
air-blown system), as well as the syngas heating value resulting in stable combustion in a gas
turbine in the case of power generation, are all compatible. Moreover, melting ash particles
contained in the syngas can be effectively quenched by the endothermic reaction of coalgasification, so that a quenching system using a large radiant exchanger or low temperature syngas
is not required. It provides the advantage of being able to manufacture the gasifier compactly. The
sensible heat of the syngas from the gasifier and char containing unreacted carbon can be cooled tothe predetermined temperature and recovered as high pressure steam by exchangers in thedownstream of the gasifier.
*1

Manager, Power Systems Plant Engineering & Construction Division, Power Systems Headquarters*２

Manager, Power Systems Business Strategy & Planning Department, Power Systems Headquarters*3Power Systems Plant Engineering & Construction Division, Power Systems Headquarters*4Manager, Boiler Engineering Department, Power Systems Headquarters*5Manager, Nagasaki Research and Development Center, Technical Headquarters

Mitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)
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Figure 1 Principle of Mitsubishi 2-stage, 2-chamber entrained bed gasifier

2.2

Feature of Mitsubishi oxygen-blown coal gasifier

On the basis of our differentiated air-blown coal gasification technology as stated above, webegan to develop an oxygen-blown coal gasifier, aiming to apply it to chemical synthesis such as
CTL (Coal to Liquid), DME, SNG and ammonia, etc.
The development concepts are: (1) to minimize the development items associated withoxygen-blown technologies, with maximum sharing of the construction, equipment and component
technologies of the air-blown gasifier, which has already been developed and verified, and (2) todevelop a commercial plant by making the best use of the findings from the IGCC demonstration
plant.
Figure 2 shows the features of the Mitsubishi oxygen-blown gasifier. By applying the basic
design criteria of the Mitsubishi 2-stage, 2-chamber entrained bed gasifier to the oxygen-blown
gasifier, the structure of the oxygen-blown gasifier may be similar to that of the IGCC
demonstration plant. Although the change of the oxidizing agent from air to oxygen affects theflow characteristics, heat transfer and reaction conditions inside gasifier, an appropriate risk study
was conducted through component research, combustion simulation and verification of the test
equipment.

Figure 2

Features of Mitsubishi oxygen-blown gasifierMitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)
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Since the dry-feed method shows low latent heat loss of water compared with slurry feed
method, dry feed is adopted in the air-blown gasifier. By combining the dry-feed method with the2-stage, 2-chamber entrained bed method, the Mitsubishi oxygen-blown coal gasifier can reduce
oxygen consumption by 15-25% compared with the oxygen-blown gasifiers of other companies asshown in Figure 3 and can contribute to the power reduction of oxygen-production units, realizing
high cold-gas efficiency.
The sensible heat of the syngas and char from the SGC (Syn Gas Cooler) may be recovered
as steam for other uses, so that it may be used in a wide range of steam conditions in response touser needs.

Figure 3

Comparison of oxygen consumption rate

|3. Coal gasification test results
3.1

Coal gasification test results

In order to verify the application feasibility of the oxygen-blown gasifier, a coal-gasification
test was planned using our existing coal-gasification testing facilities. Prior to the oxygen-blown
gasification test, only minor changes were made in the utility system of the testing facilities –which had been used as air-blown gasification testing facilities – and were used without modifying
the gasifier itself.
After the coal feeding rate for the testing gasifier was increased to the maximum level of thegasifier under oxygen-blown conditions, while stable slag discharge from the bottom of the gasifier
was checked, the amount of syngas for stable gasification, the syngas property and other necessary
data was examined. As a result, it was confirmed from the above test data that continuous operation
will be feasible. In addition, internal inspection after completion of the tests proved that the interiorof the combustor was in a sound condition. This means that our air-blown gasifier design may be
applicable to the oxygen-blown gasifier design without major equipment modifications. The test
results are shown in Figure 4 and the slag discharge conditions are shown in Figure 5.
■Operation pressure■CoalAshMoisture■Oxidizing agent■Syngas property
COH2
HHV (dry)

1 MPa
28wt%
18wt%
Oxygen48vol%
22vol%
9.6 MJ/m3N(2,300 kcal/ m3N)

Figure 4 Test results of oxygen-blown gasification test
in MHI testing facilities

Mitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)
30Figure 5

3.2

Slag discharge conditions during oxygen-blown gasification test

Commercial plant plan

In developing a commercial plant, it is common to proceed with due consideration ofscale-up risk, from pilot scale to demonstration plant. As the structure of air-blown gasification wasproven to be applied to that of oxygen-blown gasification, as stated above, it was confirmed thatthe commercial gasification plant could be implemented by reflecting the newly developedcomponents. This was confirmed in these tests.
Figure 6 shows the road map for the commercial development of the oxygen-blown gasifier
plant. Table 1 shows an example of the plans of the commercial plant.

Figure 6 Road map for commercial development of oxygen-blown gasifier plant
Table 1 Commercial oxygen-blown gasifier plant
Coal throughput (as received)
Operation pressure
Oxidizing agent
Amount of syngas
Gross calorific value of syngas
H2/CO ratio
Gasifier SGC outlet high pressure steam
conditions (example)

3,500-4,000 t/d
2.8-4.0 MPa (changeable by process request)
Oxygen270-330 t/h
2,500 kcal/Nm3-dry
0.35 (- 0.6 at steam injection)
160-190 t/h
13 Mpa 430°C

Mitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)31|4. Application of low-grade coal
As shown in Figure 7, low-grade coal such as brown coal and sub-bituminous coal, which isvery common in Australia, Indonesia, the U.S., Europe and China, etc., accounts for about 50% ofrecoverable coal reserves. If this low-grade coal is put to effective use, the energy supply isexpected to stabilize on a global basis.

Figure 7

Global distribution of coal resources

Brown coal, a low-grade coal, can have moisture content in excess of 50%. Due to the latent
heat loss caused by the moisture content in the coal, the efficiency of the power generation plantcan be as low as about 30% and the CO2 emissions rate as high as 1.2-1.6 kg-CO2/kWh (about
1.5-2 times that of bituminous coal). This is a major challenge to be overcome in making efficientuse of low-grade coal.
As a national subsidy project from fiscal 2010, MHI began to newly develop a pre-drying
system that can dry high moisture-content coal with high efficiency by effectively recovering latent
heat; that is, the heat associated with the vaporization of the water contained in coal.
After completion of the newly developed pre-drying system in this project, if brown coal isplaced in the upstream of a boiler in a conventional brown-coal fired plant, the efficiency of thepower generation may be greatly improved. To promote the effective use of brown coal, it isfavorably applied to IGCC.
In a conventional thermal power plant, when low-grade coal such as brown coal, etc., is used,slagging is likely to occur compared with high-grade coal because the ash-melting temperature of
the coal is generally lower. Therefore, the body structure of the boiler must be large to avoidproblems, resulting in an economic disadvantage. In a coal gasifier, on the other hand, because theash is drained in a melting condition, the structure of the gasifier even in the case of low-grade coalis almost equal compared with high-grade coal as shown in Figure 8. This means that theeconomies of scale in the case of low-grade coal compared with high-grade coal are also equal.

Figure 8Comparison between brown-coal-fired boiler and gasifierMitsubishi Heavy Industries Technical Review Vol. 47 No. 4 (December 2010)32

In addition, the technology of this pre-drying system can be applied to chemical synthesis.
For example, given that synthesis fuels are produced by the combination of a brown-coal
pre-drying system and oxygen-blown gasifier in brown-coal production regions, the production ofhighly value-added fuels, i.e., from low-grade coal to clean energy fuels, may contribute to theenergy security of our country as new fuel sources.

|5. Conclusion
From the viewpoint of the effective utilization of energy and CO2 emissions reduction
associated with global warming, coal-utilization technologies including low-grade coal will be ofgreater importance in the future.
MHI has developed an oxygen-blown gasifier for chemical synthesis and is now committed
to developing a commercial gasifier plant. With the highest level of oxygen-blown gasifier
technologies, along with air-blown technologies established for power generation, we will do ourbest for an effective response to customer needs and to make a contribution toward energy andglobal environmental issues.

Reference
1.

Hashimoto, T. et al., Latest Technology of Clean Coal Power Production and CO2 Recovery, Gas
Turbine Society of Japan Vol. 38 No. 5 (2010)