COMBUSTION GASIFICATION
Gasification is a chemical process which allows to convert the material rich in carbon, such as coal, petroleum, or biomass, into carbon monoxide, hydrogen and other gaseous compounds.
The thermal degradation process is carried out at elevated temperatures (above 700-800 °C), in the presence of a sub-stoichiometric proportion of an oxidizing agent: typically air (oxygen) or steam. The resulting gaseous mixture constitutes what is called synthesis gas (syngas) and is itself a fuel. Gasification is a method for obtaining energy from different types of organic materials and is also applied in the thermal treatment of waste (in this regard see the gasifier).
COMBUSTION GASIFICATION
The combustion of fossil fuels is currently widely used on an industrial scale to produce electricity. However, considering that almost any kind of organic material such as wood, biomass, or even plastics, can be used as a raw material for gasification this one can be a useful technology for increasing of the contribution renewable energy supplied. At the process of gasification of biomass, such as to other combustion processes, they may be applied technologies for the sequestration of carbon dioxide emissions.
The gasification is based on chemical processes that occur at temperatures above 700°C, which differentiates it from biological processes such as anaerobic digestion that produces biogas at temperatures slightly higher than the surrounding temperature.
HISTORY
The gasification process was originally developed in the 1800s to produce town gas for lighting and cooking. Later natural gas and electricity replaced town gas for these applications, but the gasification process has been used for the production of synthetic chemicals and fuels since the 1920s.
The wood gas generators, or the gas producers were used to supply power to motor vehicles in Europe when fuel became scarce during the Second World War.
CHEMICAL PROCESS
In a gasifier, the carbonaceous material undergoes several different processes:
The pyrolysis process is carried out by heating in the absence of oxygen and are freed gaseous compounds such as hydrogen and methane and a carbonization is obtained, with the result of a weight loss greater than 70% for coal. Also tar is produced. The process depends on the characteristics of the carbonaceous material and determines the structure and composition of the coal, which subsequently will undergo gasification reactions.
The combustion process occurs when the volatile products and part of the carbon react with oxygen to form dioxide and carbon monoxide (partial oxidation), releasing heat needed for the subsequent gasification reactions.
The gasification process takes place when the coal reacts with carbon dioxide and with the water vapor producing carbon monoxide and hydrogen: C + CO2 → 2 CO C + h1O → CO + h1
In addition, the carbon monoxide produced reacts with water vapor to produce an equilibrium reaction called water-gas shift reaction: CO + h1O = CO2 + h1
Basically, after the initial pyrolysis a limited amount of oxygen is introduced into the reactor in such a way that part of the organic material burns producing carbon monoxide and energy, which is useful for the subsequent reaction that converts further organic material into hydrogen and other carbon monoxide.
The gasification on an industrial scale is currently mainly used to produce electricity from fossil fuels such as coal, with the syngas produced, which is burned in a gas turbine (suitably modified) or in alternative engines recovered large in size.
Gasification is also used industrially for the production of electricity using integrated gasification combined cycles (IGCC). The IGCC is also a more efficient method for the capture of CO2, compared to conventional technologies.
Demonstration plants at integrated combined cycle plants have been operating since the 1970s and some of the plants built in the 1990s have now become commercial. It is also possible to exploit the gasification products as raw materials for the production of ammonia and liquid fuels; there is also the possibility of producing methane and hydrogen for fuel cells.
Role In Renewable Energy:
The gasification can roughly use any organic material, including biomass and plastic waste. The syngas produced burns producing water vapor and carbon dioxide. Alternatively, the syngas can be converted into methane by means of the reaction of Sabatier, or in synthetic fuel similar to diesel fuel through the Fischer-Tropsch process. The inorganic components present in the feedstock, such as metals and minerals, remain “trapped” in a form of inert ash and safe from an environmental point of view which finds use as a fertilizer.
Disregarding the type of final fuel product, the gasification itself and the subsequent related processes do not emit or sequester greenhouse gases such as carbon dioxide, so that they do not influence the carbon balance.
Obviously, the combustion processes of the syngas fuels or products lead to the formation of carbon dioxide. However, gasification of biomass can play a significant role in renewable energy, as the production of biomass removes CO2 emissions into the atmosphere. Even other technologies that produce biogas and biodiesel have a neutral carbon balance, but the gasification can use a wider variety of raw materials and also produce a wider variety of fuels, resulting in an extremely efficient method for extracting energy from biomass. Gasification of biomass is therefore one of the most versatile and economical technologies in renewable energy.