The most basic definition of gasification is that it is any chemical or heat process used to convert a substance to a gas.
Coal has been gasified ever since the industrial revolution to produce “town gas”. This was once done in the local gas works, and every town had one. Heating the coal under controlled conditions with insufficient air to provide complete combustion produces a gaseous fuel known as syngas, which is also what is known as town gas when cooled cleaned and compressed. As we all know using gas as a fuel for so many jobs is vastly more controllable and vastly preferable to using coal.
Gasification technology is at the forefront in the efforts to develop alternatives for conventional furnaces. It is of particular interest because it offers an opportunity to use the product fuel gas in integrated gasification combined-cycle electric power generation (IGCC). Great hopes are pinned on IGCC as a highly efficient and low polluting emissions technology.
Gasification can also be fueled by materials that are not otherwise useful fuels, such as biomass or organic waste. In addition, it also solves many worries about reducing air quality. This is because the high temperature conversion reaction essential to the process also refines out corrosive ash elements such as chloride and potassium, allowing clean gas production.
Furthermore, many have reported that using their technology product gas heating (calorific) value can be made stable regardless of changes in feedstock type, ash content, or moisture content.
In some types of gasification plant, gasification takes place on the three by-products of pyrolosis and uses them to fuel a second reaction by concentrating the heat onto a bed of charcoal. These coals normally reach 1800+ degrees F, in the gasifier, which is hot enough to break the water vapor into hydrogen, and the CO2 into carbon monoxide.
Gasification is extremely environmentally friendly in that if properly designed, gasification systems produce very minimal pollution even when processing dirty feedstocks, such as high sulfur coals. In addition, gasification can effect large volume reductions in solid wastes while producing an environmentally friendly inert slag-type byproduct.
Jan Becker, Technical Director, of a US energy company growing fast on its gasification skills, added that; “the gasifier is becoming an important factor in the race toward the ‘greening of America’ as there is more and more awareness that many of the substances that America throws away can be gasified and then made into useful products like electricity, ethanol, methanol, and bio-diesel.”
The gas produced by gasifiers (mainly comprising of 15-25% carbon monoxide, 10-20% hydrogen and 1-5% methane), is combusted in special burners for maximum efficiency. The best high quality gasifier systems can be fed on what are otherwise just low-grade waste oils or tar oils and slurries. Some slurry fed, O2 blown, entrained gasifiers operate at between 2400 degrees F and 2700 degrees F.
In these latest high technology systems high pressure steam is produced for internal and local CHP (Combined Heat and Power) use, by cooling the syngas in a radiant syngas cooler and then using (in this case) two parallel fire tube convective syngas coolers.
That is the top of the range in technological development. At the bottom. Most basic, level of he gasifier it is really simple. Simply wood burning gasifier stoves can be made to designs freely available as templates which can be made almost completely from junk parts found in various trash bins.
Gasifiers are now also available which are intended for the processing of biomass and organic waste, and this has been found viable at current oil prices, when it is considered that the numerical calculations are based on low-grade coal. It has also been shown shown that the process can be both stable and controllable. New designs can be assessed in advance by taking an appraisal of the numerically derived analysis produced by RESORT software, in order to predict the physical and chemical processes in the gasifier. The Euler-Lagrange approach for gas and particle phase is employed and Navier-Stokes equations are analyzed by the finite volume method.