Gasification is a building block technology for the manufacturing of chemicals, electricity, fuels, and other valuable energy products that have conventionally been produced from natural gas or crude oil.
Gasification is a combination of molecular chemical reactions that convert complex hydrocarbons and lower value energy sources such as coals, municipal solid wastes (MSW) and biomass materials into synthesis gas, or “syngas,” which is generally defined as hydrogen (H2) and carbon monoxide (CO) molecules. These syngas molecules are the building blocks for numerous and varied products, such as electricity, fuels and other high value energy products, and chemicals and precursors that have conventionally been produced from natural gas or crude oil. Gasification is an economic and efficient way to manufacture these products from locally abundant and affordable natural resources or MSW.
A gasifier is the vessel in which the reactions occur to chemically convert hydrocarbon resources into syngas. Generally gasification takes place under pressure, ranging from atmospheric conditions to as high as 55 bar(g). Gasification requires a limited amount of oxygen, less than combustion, as the resulting chain reactions are more thermally efficient with a balance of exothermic and endothermic constituent reactions. Generally the reaction temperatures required for gasification range from 900-3000°F (480-1650°C). Steam or water and an oxidant plus the hydrocarbon source are required for the gasification reactions to occur and be sustained.
Products and by-products of gasification include syngas – gaseous form of hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), water (H2O), methane (CH4), hydrogen sulfide (H2S) and COS (if sulfur is present in the original feedstock), nitrogen (N2) and other compounds in reduced quantity – ash, heat, and water.
The gasification process is fundamentally clean and environmentally friendly, as it deals with reactants and product species in their lowest molecular form. Complex organic feeds are reduced to simple molecules, with metals and other non-organic trace impurities vitrified in the ash by-product which may be safely disposed of or resold. Downstream processing of the syngas is often simple and cost-effective as waste products have already been removed.
The syngas produced from gasification is the replacement for natural gas and crude oil for the formation of a plethora of energy and chemical products. When low-cost feedstocks are available and used for conversion, these products are economically competitive with products derived from natural gas and oil and often have a lower environmental footprint.
AIR SEPARATION UNIT (ASU)
The Air Separation Unit, or ASU, brings in air from the outside and uses a specialized process to separate the oxygen from the air. This purified oxygen stream is fed to the gasifier to drive the reactions.
GASIFICATION
In the Gasification Section, coal is combined with oxygen in the gasifier to generate syngas. The non-reactive parts of the coal feed are removed from the bottom of the gasifier as an ash by-product. This can be sold for use in road paving or making cement.
HIGH TEMPERATURE HEAT RECOVERY
In the High Temperature Heat Recovery section, the hot syngas is cooled while generating high pressure steam to improve the overall efficiency of the plant. This steam can be used to generate electricity or to provide thermal energy.
FINES RECYCLE
In the Fines Recycle section, any remaining solid particles that are still in the syngas are removed. The fines are collected and returned to the gasifier to minimize solid waste and to improve overall efficiency.
SULFUR AND CO2 REMOVAL
In the Sulfur and CO2 removal section, the syngas is processed to remove any sulfur and CO2. Since the sulfur and CO2 are removed prior to combustion and while the syngas is still at elevated pressure, very deep removal is easily achieved. The technologies that are used to capture the CO2 and sulfur are fully mature, commercially proven technologies that have been used for decades in the gasification and refining industries.
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