Difference Between Incineration and Gasification
Incinerators typically operate at atmospheric pressure and temperatures at with the mineral matter or ash in the waste is not
completely fused (as slag) during the incineration processes. Ash solids will either exit the bottom/discharge and of the combustion
chambers as bottom ash or as particular matter entrained in the combustion flue gas stream.
Four major types of combustion chamber designs are used in modern incineration systems: liquid injection, rotary kiln, fixed hearth, and fluidized bed. Boilers and industrial furnaces (BIF units) are also examples of incineration systems; however, according to EPA MACT information, less that 15% of the hazardous waste is disposed of in these units. The application of each type of combustion chamber is a function of the physical form and ash content of the wastes being combusted. In each of these designs, waste material is combusted in the presence of a relatively large excess of oxygen (air) to maximize the conversion of the hydrocarbon-based wastes to carbon dioxide and water (50% to 200%) in some configurations, excess fuel and oxygen must be added to increase incineration temperature to improve destruction and removal efficiency. This also increases the production and emission of carbon dioxide.
Limitations:
Factors that may limit the applicability and effectiveness of the process include:
Gasification technologies differ in many aspects but share certain general production characteristics. Typical raw materials used in gasification are coal, petroleum based materials (crude oil, high sulfur fuel oil, petroleum coke, and other refinery residuals), gases, or materials that would otherwise be disposed of as waste. The feedstock is prepared and fed to the gasifier in either dry or slurried form. The feedstock reacts in the gasifier with steam and oxygen at high temperature and pressure in a reducing (oxygen starved) atmosphere. This produces the synthesis gas, or syngas, made up primarily of carbon monoxide and hydrogen (more than 85% by volume) and smaller quantities of carbon dioxide and methane.
The high temperature in the gasifier converts the inorganic materials in the feedstock (such as ash and metals) into a vitrified material resembling coarse sand. With some feed stocks, valuable metals are concentrated and recovered for reuse. The vitrified material, generally referred to as slag, is inert and has a variety of uses in the construction and building industries.
Gas treatment facilities refine the raw gas using proven commercial technologies that are an integral part of the gasification plant. Trace elements or other impurities are removed from the syngas and are either recirculated to the gasifier or recovered. Sulfur is recovered either in its elemental form or as sulfuric acid, both marketable commodities.
If the syngas is to be used to produce electricity, it is typically used as a fuel in an integrated gasification combined cycle (IGCC) power generation configuration.
IGCC is the cleanest, most efficient means of producing electricity from coal, petroleum residues and other low- or negative-value feed stocks. The combined cycle system has two basic components. A high efficiency gas turbine, widely used in power generation today, burns the clean syngas to produce electricity. Exhaust heat from the gas turbine is recovered to produce steam to power traditional high efficiency steam turbines.
The syngas can also be processed using commercially available technologies to produce a wide range of products, fuels, chemicals, fertilizer or industrial gases. Some facilities have the capability to produce both power and products from the syngas, depending on the plant’s configuration as well as site specific technical and market conditions.
Four major types of combustion chamber designs are used in modern incineration systems: liquid injection, rotary kiln, fixed hearth, and fluidized bed. Boilers and industrial furnaces (BIF units) are also examples of incineration systems; however, according to EPA MACT information, less that 15% of the hazardous waste is disposed of in these units. The application of each type of combustion chamber is a function of the physical form and ash content of the wastes being combusted. In each of these designs, waste material is combusted in the presence of a relatively large excess of oxygen (air) to maximize the conversion of the hydrocarbon-based wastes to carbon dioxide and water (50% to 200%) in some configurations, excess fuel and oxygen must be added to increase incineration temperature to improve destruction and removal efficiency. This also increases the production and emission of carbon dioxide.
Limitations:
Factors that may limit the applicability and effectiveness of the process include:
-
There are specific feed size and materials handling requirements that can impact applicability or cost at specific sites.
Heavy metals can produce a bottom ash that requires stabilization.
Volatile heavy metals, including lead, cadmium, mercury, and arsenic, leave the combustion unit with the flue gases and require the installation of gas cleaning systems for removal.
Metal can react with other elements in the feed stream, such as chlorine or sulfur, forming more volatile and toxic compounds than the original species. Such compounds are likely to be short-lived reaction intermediates that can be destroyed in a caustic quench.
Sodium and potassium form low melting point ashes that can attack the brick lining and form a sticky particulate that fouls gas ducts.
Gasification technologies differ in many aspects but share certain general production characteristics. Typical raw materials used in gasification are coal, petroleum based materials (crude oil, high sulfur fuel oil, petroleum coke, and other refinery residuals), gases, or materials that would otherwise be disposed of as waste. The feedstock is prepared and fed to the gasifier in either dry or slurried form. The feedstock reacts in the gasifier with steam and oxygen at high temperature and pressure in a reducing (oxygen starved) atmosphere. This produces the synthesis gas, or syngas, made up primarily of carbon monoxide and hydrogen (more than 85% by volume) and smaller quantities of carbon dioxide and methane.
The high temperature in the gasifier converts the inorganic materials in the feedstock (such as ash and metals) into a vitrified material resembling coarse sand. With some feed stocks, valuable metals are concentrated and recovered for reuse. The vitrified material, generally referred to as slag, is inert and has a variety of uses in the construction and building industries.
Gas treatment facilities refine the raw gas using proven commercial technologies that are an integral part of the gasification plant. Trace elements or other impurities are removed from the syngas and are either recirculated to the gasifier or recovered. Sulfur is recovered either in its elemental form or as sulfuric acid, both marketable commodities.
If the syngas is to be used to produce electricity, it is typically used as a fuel in an integrated gasification combined cycle (IGCC) power generation configuration.
IGCC is the cleanest, most efficient means of producing electricity from coal, petroleum residues and other low- or negative-value feed stocks. The combined cycle system has two basic components. A high efficiency gas turbine, widely used in power generation today, burns the clean syngas to produce electricity. Exhaust heat from the gas turbine is recovered to produce steam to power traditional high efficiency steam turbines.
The syngas can also be processed using commercially available technologies to produce a wide range of products, fuels, chemicals, fertilizer or industrial gases. Some facilities have the capability to produce both power and products from the syngas, depending on the plant’s configuration as well as site specific technical and market conditions.