Part 2 CCT Overview
Environmental Protection Technologies (Flue Gas Treatment and Gas Cleaning Technologies)

5B5. Gas Cleaning Technology
Technology overview

1. Background
For the development of coal gasification gas-based power

efforts are now underway to develop dry gas purification

generation and fuel synthesis technologies, it is necessary totechnology that purifies hot coal gasification gas as it is.

remove sulfur compounds (H2S, COS), halides (HCl, HF), andother gas contents. As shown in Figure 1, a key application of thisCeramicfilter

technology is found in the wet gas purification process that, after
removing water-soluble halides and other contents with a waterCOS
Scrubber (dehalogenation,deammonification)
conversion catalyst

Coalgasifier

scrubber, desulfurizes the gas with a methyldiethylamine (MDEA)
or other amine-based liquid absorbent for gas purification. Thismethod, however, requires the gas to be cooled to around room
temperature, thus losing much heat. Furthermore, the process

Sulfur recovery
equipment

becomes complex since it requires not only a heat exchanger but
also a catalyst that converts hard-to-remove COS into H2S. It isH 2Sabsorption
tower

also difficult to precisely reduce sulfur compounds to a 1-ppm level.
To solve problems relating to the wet gas purification process,Recycling tower
Reboiler

Fig. 1 Wet gas purification process

2. Technology(1) Dry desulfurization method

Research and development: Japan Coal Energy Center; IGCC Research Association; Central Research Institute of ElectricPower Industry; Kawasaki Heavy Industries, Ltd.; Ishikawajima-Harima Heavy Industries Co., Ltd.; Mitsubishi Heavy Industries, Ltd.
Project type: Entrained bed coal gasification power generation plant, etc.
Overview
As shown in Figure 2, in the dry desulfurization process, metal

Heavy Industries, Ltd. has developed an iron oxide-based highlyoxides are reduced by coal gasification gas, and the reduced

wear-resistant granular desulfurization agent for use in a moving-

metal oxides remove sulfur compounds from the gas, and are

bed combined-desulfurization/dust collection system (Fig. 5) andthen converted to sulfides. This method can be used more thanevaluated its performance in a pilot plant capable of treating one-once by letting the sulfides react with oxygen to release the sulfur

fortieth of the coal gas produced by the the 200-ton/day Nakoso

contents as SO2 to return them to metal oxides.

pilot plant. This indicates that technologies for IGCC have alreadyThe development of this process as a technology for integrated

reached a validation stage.

gasification combined-cycle power generation (IGCC) waspromoted, with a target of reducing sulfur oxides to 100ppm orless in a temperature range of 400-500oC, where economicalReduction

carbon steel can be used for piping. Iron oxide was selected as
the metal oxide to be used and Ishikawajima-Harima Heavy

Mt: Metal elementIndustries Co., Ltd. built a fluidized-bed desulfurization pilot plant(Fig. 3) that can treat all of the coal gas, using 100-200- m ironore particles. It was verified in the 200-ton/day Nakoso IGCC pilotplant (1991-1995). The Central Research Institute of Electric
Reproduction

Power Industry and Mitsubishi Heavy Industries, Ltd., with an eye

Desulfurization

to applications in the fixed-bed desulfurization systems (Fig. 4),
have jointly developed an iron oxide-based honeycomb
desulfurization agent. They also built, under the 200-ton/dayNakoso IGCC pilot plant project (for coal gas production ofFig. 2 Desulfurization reaction cycle

43,600m3N/h), a pilot plant that can treat one-tenth of the amountof coal gas produced. The performance of the honeycomb
desulfurization agent is being verified. Meanwhile, Kawasaki

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Clean Coal Technologies in JapanTo dust collector

Coal gas (from dust collector)

Gas for sulfur reduction

Dust filter
CycloneDesulfurization
agent

Heat
exchanger

Anthracite
AirSOxreduction tower

Reproduction tower

Sulfurcondenser

Desulfurization
tower

Desulfurization process Reduction process

Sulfurrecoveryequipment

Reduction process

Sulfur

AirCarrierTo gas turbine

AshFig. 4 Fixed-bed desulfurization process

SulfurCoal gas

Excess gas

Separator

Soot/dust filter

Fig. 3 Fluidized-bed desulfurization process
Distributor

At present, a desulfurization agent that can reduce sulfur

Soot/dust

compounds to a level of 1ppm is under development for use inTo sulfur recovery
systemsuch applications as molten carbonate fuel cells, solid oxide fuelAircells, and fuel synthesis. At the Central Research Institute ofElectric Power Industry (CRIEPI), a desulfurization agent using

Reduction gas(coal gas)

zinc ferrite (ZnFe2O4), a double oxide of iron and zinc, has been

To sulfur recoverysystemdeveloped and found capable of reducing sulfur compounds to1ppm or less. It is now at the stage of real-gas validation. In

Coal gas

To gas turbine

1. Regeneration tower
2. Reduction tower
3. Desulfurization tower

Desulfurization
agent carrier

addition, efforts to introduce the desulfurization agent into airblown entrained-bed gasification systems have been made.
Another important subject is the application of the agent tooxygen-blown gasification gas with a high carbon-monoxide
concentration, which degrades the desulfurization agent by
allowing carbon to be separated out of it.
Fig. 5 Moving-bed combined dust collection-desulfurization process(2) Dry dehalogenation method

Research and development: Central Research Institute of Electric Power Industry
Project type: Voluntary
Overview
using a sodic compound is under development. CRIEPI

To use coal gasification gas in molten carbonate/solid oxide fuelcells and for fuel synthesis, it is necessary to remove not only

developed and tested a sodium aluminate (NaAlO2)-basedsoot, dust and sulfur compounds but also halogen compounds.

absorbent, confirming a possible reduction to 1ppm or less, but

For these applications, efforts are underway to develop a halidesuch efforts still remain on a laboratory scale as well as at aabsorption agent capable of reducing halogen to 1ppm or less.

development stage. This method faces an important problem ofAt present, a method to remove HCl/HF from gas as NaCl/NaF

how the absorbent should be reproduced or recycled.

References

1) Nakayama et al., "Development State of 3 Dry Gas Cleanup Methods in Dry Gas Cleanup Technology Development for Integrated
Gasification Combined-Cycle Power Generation," the Japan Institute of Energy Journal, Vol. 75, No. 5, 1996.
2) Shirai et al., "Coal Gasification Gas-Based Fixed-Bed Dry Desulfurization Technology Development,"the Society of Powder Technology,
Japan’s Journal, Vol. 40, No. 8, 2003.
3) M. Nunokawa et al., "Developments of Hot Coal Gas Desulfurization and Dehalide Technologies for IG-MCFC Power Generation
System," CEPSI proceedings, Fukuoka, 2002.

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