COAL GASIFICATIONAJITH KUMAR M

What is gasification

• Gasification is a proven manufacturing process that converts hydrocarbons such as coal, petroleum coke (petcoke), and biomass to a synthesis gas (syngas).

• which can be further processed to produce chemicals, fertilizers, liquid fuels, hydrogen or electricity

Gasification• A partial oxidation process that can convert any hydrocarbon into

hydrogen and carbon monoxide (synthesis gas or syngas).

• (CH)n + O2 H2 + CO

• For example:

• 2 CH4 + O2 4H2 + 2 CO

• [ Methane] [Oxygen] [Hydrogen] [Carbon Monoxide]

• Liquid and gaseous fuels are easy to handle• Synthetic fuels burn more cleanly than coal• Carbon capture and sequestration is easier in

gasification system

INFLUENCE OF COAL PROPERTY ON GASSIFICATION• Moisture• Ash• Volatile matter• Caking tendencies• Ash fusion• Coal size

How does gasificationwork?

• A hydrocarbon feedstock is injected with oxygen and steam into a high temperature pressurized

reactor until the chemical bonds of the feedstock are broken.• The resulting reaction produces the syngas.• The syngas is then cleansed to remove impurities such as

sulfur, mercury, particulates, and trace minerals.• The clean syngas is then used to make either a single product

such as fertilizer or multiple products such as hydrogen, steam, and electric power.

Which industries usegasification?

• fertilizer industries• by the chemical industries• Electric power • Gasification is also available to help in the

production of oil from the vast Canadian oil sand deposits and substitute natural gas from America’s abundant coal resources

• There are more than 420 gasifiers currently in use worldwide

environmental benefitsof gasification?

• Gasification enables the use of domestic coal,petcoke, and biomass to produce electricity with significantly reduced environmental impacts compared to combustion technologies

• The syngas is cleaned before combustion, gasification plants produce significantly fewer quantities of criteria air pollutants

• Gasification enables the recovery of available energy from low-value materials (such as petcoke and municipal solid waste), thereby reducing both environmental impacts and disposal costs.

• The byproducts from gasification (sulfur and slag) are non-hazardous

• Gasification plants use significantly less water than coal combustion plants, and can be designed as zero liquid water discharge facilities.

• Carbon dioxide (CO2) can be captured from a gasification-based plant using latest technologies prior to combustion of the synthesis gas in the gas turbines

• It converts low-value feedstocks to highvalue products, thereby increasing the use of available energy in the feedstocks while reducing disposal

Types of feed

• Solids: All types of coal and petroleum coke (a low-value byproduct of refining) and biomass, such as wood waste, agricultural waste, and household waste

• Liquids: Liquid refinery residuals (including asphalts, bitumen, and other oil sands residues) and liquid wastes from chemical plants and refineries.

• Gas: Natural gas or refinery/chemical off-gas

Gasifier

• The core of the gasification system is the gasifier, a pressurized vessel where the feed material reacts with oxygen (or air) and steam at high temperatures

• There are several basic gasifier designs, distinguished by the use of wet or dry feed

• The use of air or oxygen, the reactor’s flow direction (up-flow, downflow, or circulating)

• and the gas cooling process

• Gasifiers are capable of handling up to 3,000 tons/day of feedstock

• The feedstock is injected into the gasifier, along with a controlled amount of air or oxygen and steam

• Temperatures in a gasifier range from 1,400-2,800 degrees Fahrenheit.

• The heat and pressure inside the gasifier break apart the chemical bonds of the feedstock, forming syngas.

• The syngas consists primarily of hydrogen and carbon monoxide

• Smaller quantities of methane, carbon dioxide, hydrogen sulfide, and water vapor

• Syngas generally has a heating value of 250-300 Btu/scf, compared to natural gas at approximately 1,000 Btu/scf.

• Typically, 70–85% of the carbon in the feedstock is converted into the syngas.

• The ratio of carbon monoxide to hydrogen depends in part upon the hydrogen and carbon content of the feedstock and the type of gasifier used.

oxygen plant

• Most gasification systems use almost pure oxygen (as opposed to air) to help facilitate the reaction in the gasifier

• This oxygen (95–99% purity) is generated in a plant using cryogenic technology

• The oxygen is then fed into the gasifier through separate co-feed ports in the feed injector.

Gas Clean-Up

• The raw syngas produced in the gasifier contains trace levels of impurities that must be removed prior to its use.

• The trace minerals, particulates, sulfur, mercury, and unconverted carbon are removed to very low levels

• feeds (such as coal) containing mercury, more than 95% of the mercury can be removed from the syngas using relatively small and commercially available activated carbon beds.

• Carbon dioxide (CO2) should be removed from syngas

• removed with ammonia and hydrogen manufacturing plants

• Ammonia plants capture approximately 90% of the CO2

• methanol plants capture approximately 70% of the CO2.

Chemicals and Fertilizers

• the chemical industry uses gasification to produce methanol as well as chemicals — such as ammonia and urea — which form the foundation of nitrogen based fertilizers.

Hydrogen for Oil Refining

• Hydrogen, one of the two major components of syngas, is used to strip impurities from gasoline, diesel fuel, and jet fuel

• Hydrogen is also used to upgrade heavy crude oil.• hydrogen. • Refineries can gasify low value residuals, such as

petroleum coke, asphalts, tars, and some oily wastes from the refining process to generate hydrogen

Transportation Fuels• Gasification is the foundation for converting coal and other

solid feedstocks and natural gas into transportation fuels.• Fuels such as gasoline, ultra-clean diesel fuel, jet fuel,

naphtha, and synthetic oils.• Fischer-Tropsch (FT) reaction, to convert it to a liquid

petroleum product.• Methanol to Gasoline (MTG), the syngas is first converted

to methanol (a commercially used process) and the methanol is converted to gasoline by reacting it over a bed of catalysts

Power Generation withGasification

• coal can be used as a feedstock to produce electricity from gasification.

• This particular coal-to-power technology allows the continued use of coal without the high level of air emissions

An Integrated Gasification Combined Cycle (IGCC) power plant

Fixed-Bed gasifier

– 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

FIXED BED

• Fuel size 0.25-2 in• Preffered feedstock lignite bituminous coal• Ash content no limit • Ash melting temperature >2200• Exit flue gas temp (800-1200)• Gasification pressure 435 psig• Oxidant requirement low• Steam requirement high

Kellogg Rust Gasifier• Coal with 0.125 in is fed into

gasifier using a screw feeder.• The upward flow of air keeps

the coal and ash in a fluidized state

• Fine particles of ash ond dust mix with synthesis gas and is removed by cyclone seoerator.

• Operating pressure upto 154 psig.

• Temperature upto 2000 F

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FLUIDIZED TYPE

• Fuel size <0.25 in• Preffered feedstock lignite bituminous coal• Ash content no limit • Ash melting temperature >2000• Exit flue gas temp (1700-1900)• Gasification pressure 15 psig• Oxidant requirement MODERATE• Steam requirement MODERATE

Entrained-Flow gasifier• Entrained flow reactors (Shell, Texaco,

E-gas, Noell, KT - Slagging)• pulverized coal(<0.005 in.) is used

– 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

Figure 1: Texaco Gasifier

• pulverized coal is pressurized in lock hoppers and fed into gasifier.

• During high temperature ash is coverted into molten slag

• Sepetate water bath arrangement• Operating pressure upto 350-3 6 0 psig.• Temperature upto 2700 F• The raw gas leaves at 2500 to 3000 F

• Ability to gasify all coal• Lowest ash contents • Very short fuel residence times in gasifier

DISADVANTAGES• Very finely sized and homogenous solid fuel required• Relatively large oxidant requirements• Large amount of sensible heat in raw gas• Entrainment of some molten slag in raw gas

ADVANTAGE OF ENTRAINED-FLOW GASIFIER

• Fuel size <0.25 in• Preffered feedstock lignite bituminous coal• Ash content no limit • Ash melting temperature >2000• Exit flue gas temp (1700-1900)• Gasification pressure 15 -435psig• Oxidant requirement MODERATE• Steam requirement MODERATE

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

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