Coal Gasification Technology and Syngas Production

Ruben Reyes

ChE379

Purpose/Outline

• Gasification technology– Different types of gasifiers– Products from gasification

• Syngas production, Gasifiers used for IGCC power plants

• Conclusion

Coal Gasification Technologies

– Basic Overview of gasification• Coal or other fuels• Oxidation carefully controlled• H2, CO2, CH4, other products • H2 can be purified • Ash/slag leftovers

– 3 types of gasifiers• Moving bed• Fluid Bed• Entrained Flow

– Underground Coal Gasification• Vertical wells and pathway creation• Controlled retraction injection point

Above ground gasification

• Moving bed reactor (Lurgi – dry ash and BGL - slagging)– Counter-current flow of

coal and oxidizing blast– Blast composed of air and

hot syngas, so low oxygen consumption

– Operates on reactive carbon sources

– Good heat transfer heats the carbon source creating methane and tar

– Post production cleaning and scrubbing requires greater energy use

BGL gasifier (fixed bed, slagging)

Figure 1: BGL Gasifier

Above Ground Gasification• Fluid-bed reactor (Winkler,

HTW, CFB – dry ash; KRW, U-Gas – Agglomerating)– Air fluidizes a bed and carbon

containing particles added– Proper mixing of fuel and

oxidant provide good mass transfer and heat transfer

– Fine particle will escape with syngas and needs to be cleaned

– Very good heat/mass transfer so partially reacted carbon may settle with ash

– Slagging will reduce fluidization, so temp remains below softening point for ash

Winkler Gasifier (Fluid bed, dry ash)

Figure 2: Winkler Gasifier

Above Ground Gasification• Entrained flow reactors (Shell,

Texaco, E-gas, Noell, KT - Slagging)

– Carbon source is made of very fine particles in a liquid or slurry for very good mass transfer

– Very little residence time– Co-current flow with oxygen where

high temperatures can be reached– Low heat transfer means hot

exiting gas with no methane or tar, but more oxygen required.

– High temperature and very small carbon sources make it an ideal process for coal gasification.

• High temperatures without charring

• No agglomeration because of fine particle size preparation

Texaco Gasifier (entrained flow, slagging)

Figure 1: Texaco Gasifier

Underground Coal Gasification

• Vertical wells, soviet technology– H2 and O2 are injected and

ignited to create syngas, CO2 and methane

– Coal deposits do not allow for transport of the gases from the injection well to recovery well very easily

– Closely spaced wells and reverse combustion methods are employed to create a cavity between wells

– This process works, but requires many wells to be constructed

Figure 5: Current UGC

Underground Coal Gasification

• Controlled retraction injection point from oil technology (CRIP)– The oil industry’s horizontal

drilling for production and injection wells to deliver and absorb syngas continuously

– Only one injection well, the ignition continues through the inseam as the injection wells are retreated.

– The product is collected in a product well

– Concerns about ground water inhibit the use of UCG.

Figure 6: CRIP UGC

Syngas production and energy industry

• CO2 removal– Used for oil reclamation– Can be injected back in ground

• Combined cycle– Combustion turbine– Heat used for generating steam

• Fuel cell uses

Conclusions• There are many ways that carbon containing compounds may be gasified• Coal gasification occurs best in entrained flow reactors such as the Texaco

gasifier– The coal will not heat up as much and will not create methane and tar.– The requirement for fine particles into the gasifier prevents agglomeration

• Underground coal gasification technology is present and used today but with certain challenges

– Water contamination – Impact on environment and land

• Potential benefits are many – Syngas used in combined cycle energy production– Hydrogen fuel cell use for energy production and transportation purposes– Methane and hydrogen have applications in the chemical industry where they

can be used.– Not mentioned, gasification is first step in coal liquefaction process.– Coal gasification could reduce dependence on foreign oil– CO2 sequestration

References• Gasification reference shelf - images and photos. (n.d.). National Energy

Technology Laboratory.     Retrieved November 20, 2007, from http://www.netl.doe.gov/technologies/coalpower/gasification/pubs/photo.html

• Gasification Technology and R&D. (n.d.). U.S. Department of energy. Retrieved November 20, 2007, from http://www.fossil.energy.gov/programs/powersystems/gasification/index.htm

• l Higman, C., & Van Der Burgt, M. (n.d.). Gasification. Elsevier. Retrieved November 20, 2007, from     Google Book Search database: http://books.google.com.ezproxy.lib.utexas.edu/     books?id=ZUlRaUrX8IUC&printsec=frontcover&dq=gasification&sig=Sxb9s5qmKK03xe9INbsiuoJwwX8#PPP1,M1

• Underground Coal Gasification. (n.d.). World Coal Institute. Retrieved November 20, 2007, from World     Coal Institute Web site: http://www.worldcoal.org/pages/content/index