Waste-to-energy refers to a few viable techniques for producing energy. Icineration of municipal solid waste has been practiced for almost 150 years as a technique to produce energy, and reduce landfill waste. Incineration is particularly effective when combined with combined heat and power (cogeneration) - making the most of energy and district heating. Unfortunately this technique also produces a vast amount of noxious fumes. Incineration produces vast amounts of dioxin and furan emissions, air pollutants of a significant proportion, to put it mildly. Less destructive, not quite 100% 'green and clean' methods of waste-to-energy, are gasification (discussed here), and anaerobic digestion.
The creation of syngas (or synthetic natural gas - SNG) is a technology based on coal gasification for the majority of plants, although it can also be based on petrolium, natural gas, or biomass. Gasification uses fossil fuels or organic based carbon materials to create the gases which make up syngas (by combining the feedstock and oxygen at extremely high temperature, after which the gas unergoes a clean-up process). Gasification tends to be a lot more environmentally friendly than incineration.
Since it is usually based on a nonrenewable fossil fuel, and involves a high level of emissions of greenhouse gasses like CO2, it can’t be described as a truly “green” technology. However, when coal gasification is used in conjunction with carbon capture and storage (CCS), or a green technology like (IGCC), or when syngas is created using biomass, the technology is certainly “greener” than just burning a fossil fuel. IGCC is a fairly new technology that uses a gasifier in converting coal and biomass into syngas, and has come to be known as "clean coal".
Lignite, a brownish type of coal, is most often used as a source in the process of creating syngas. Gasification uses the coal (or other feedstock), along with steam and oxygen to create syngas - mostly hydrogen, CO2 and carbon monoxide. The syngas goes through a clean-up process, and can then be burned directly to create energy used to generate electricity or heat for homes and businesses, or the syngas can be converted to create products including methanol, nitrogen-based fertilizers or hydrogen for oil refining and transportation fuels, among other products. Coal gasification is sometimes called "clean coal" because it can create energy with less harm to the environment than traditional fossil fuel use.
A significantly more environmentally friendly version of gasification, other than coal use, is available in biomass. Biomass gasification uses feedstocks like: agricultural residues (such as wheat and straw), energy crops (like switchgrass), forestry residues and urban wood waste (for example, from construction sites). Agricultural waste, along with other waste, can also be used in the gasification process. The resulting product is known as bio-SNG.
The leading region in the world for syngas production is Asia/ Australia, in particular China. China mostly uses coal for its syngas production, relying on their vast coal deposits, thus still producing significant quantities of greenhouse gas emissions. China is trying to rely more on domestic sources for gas and less on importing liquefied natural gas. A significant number of gasification plants are also found in India, South Korea, Taiwan and Singapore.
The Africa/ Middle East region also produces a significant quantity of syngas, more than Europe. However, production of syngas in Europe uses a wider selection of feedstocks, technologies and products than other regions. The coal-based units primarily utilize IGCC technologies. There are petroleum, natural gas and biomass plants that produce either power or chemicals.
A fairly new plant in Swindon, England illustrates the advancements that European nations are making with gasification. Methanization is used to transform gasified biomass into grid-quality syngas in the Swindon plant, the biosynthetic natural gas (bio-SNG) then providing power to the grid.
Most syngas production in North America lies within the United States. These plants include: natural gas facilities that primarily produce chemicals, coal and petroleum based plants that produce either power, chemicals and fertilizers or syngas, including a couple of IGCC plants. In Canada, gasification is also used to produce hydrogen and power to upgrade synthetic crude oil from the tar sands.
Please also see: creating clean coal - carbon capture and storage