Gasification is a process that converts carbonaceous materials, such as coal, petroleum, biofuel, or biomass, into carbon monoxide and hydrogen by reacting the raw material at high temperatures with a controlled amount of oxygen and/or steam.
The resulting gas mixture is called synthesis gas or syngas and is itself a fuel.Gasification is a method for extracting energy from many different types of organic materials.
The advantage of gasification is that using the syngas is potentially more efficient than direct combustion of the original fuel because it can be combusted at higher temperatures or even in fuel cells, so that the thermodynamic upper limit to the efficiency defined by Carnot’s rule is higher or not applicable.
Syngas may be burned directly in internal combustion engines, used to produce methanol and hydrogen, or converted via the Fischer-Tropsch process into synthetic fuel. Gasification can also begin with materials that are not otherwise useful fuels, such as biomass or organic waste.
In addition, the high-temperature combustion refines out corrosive ash elements such as chloride and potassium, allowing clean gas production from otherwise problematic fuels.
Gasification of fossil fuels is currently widely used on industrial scales to generate electricity. However, almost any type of organic material can be used as the raw material for gasification, such as wood, biomass, or even plastic waste.
Gasification relies on chemical processes at elevated temperatures >700°C, which distinguishes it from biological processes such as anaerobic digestion that produce biogas.
Potential for renewable energy
In principle, gasification can proceed from just about any organic material, including biomass and plastic waste. The resulting syngas can be combusted. Alternatively, if the syngas is clean enough, it may be used for power production in gas engines, gas turbines or even fuel cells, or converted efficiently to dimethyl ether (DME) by methanol dehydration,methane via the Sabatier reaction, or diesel-like synthetic fuel via the Fischer-Tropsch process.
In many gasification processes most of the inorganic components of the input material, such as metals and minerals, are retained in the ash.
In some gasification processes (slagging gasification) this ash has the form of a glassy solid with low leaching properties,but the net power production in slagging gasification is low (sometimes negative) and costs are higher.
Regardless of the final fuel form, gasification itself and subsequent processing neither directly emits nor traps greenhouse gasses such as carbon dioxide. Power consumption in the gasification and syngas conversion processes may be significant though, and may indirectly cause CO2 emissions; in slagging and plasma gasification, the electricity consumption may even exceed any power production from the syngas.
Combustion of syngas or derived fuels emits exactly the same amount of carbon dioxide as would have been emitted from direct combustion of the initial fuel. Biomass gasification and combustion could play a significant role in a renewable energy economy, because biomass production removes the same amount of CO2 from the atmosphere as is emitted from gasification and combustion.
While other biofuel technologies such as biogas and biodiesel are carbon neutral, gasification in principle may run on a wider variety of input materials and can be used to produce a wider variety of output fuels.