Construction has begun in Swindon, in southwest England, on a plant to convert household waste to bio-substitute natural gas (BioSNG), which emits 80% less carbon dioxide than the diesel used widely in the UK.

The plant, which is scheduled to begin operations in 2018, will take in 10,000 metric tons of waste from the local area and produce 22 GWh of BioSNG, enough to heat 1,500 homes. Utilizing waste in this way allows extra value to be derived from a product that would otherwise have been sent to landfill.

Schematic illustrating the waste-to-BioSNG conversion process. Image credit: Go Green Gas.The technology has already been demonstrated at a £5m pilot plant in Swindon—a joint project among National Grid, Advanced Plasma Power and Progressive Energy. In the pilot, as in the plant now under construction, the conversion process involves:

· Fuel preparation/thermal conversion—Waste is shredded and dried, and metals and dense plastics are removed. The feedstock is then heated to convert it to syngas.

· Tar treatment—Tars are converted to syngas using thermal, catalytic or plasma treatment, or via water- or oil-based scrubbing.

· Gas cooling and cleaning—The gas is cooled, and ash and heavy metals are removed along with other contaminants, such as acid or alkaline gases.

· Compression/water gas shift/methanation—The syngas is compressed to simplify further processing, then reacted with steam over a catalyst bed to increase the ratio of hydrogen to carbon monoxide and finally passed over a catalyst bed to convert carbon monoxide and hydrogen to methane and water.

· Separation—Carbon dioxide is removed to produce methane-rich gas.

· Upgrading—Propane is added to match the calorific value of the BioSNG with the gas grid.

BioSNG can be used in existing appliances, such as boilers and cookers, and distributed in existing gas networks—as well as in transport—potentially representing a major step forward in decarbonizing the energy system. While Britain's power generation sector has made progress toward decarbonization in recent years, heat and transport—which amounts to 74% of energy usage—have proven to be a more stubborn environmental challenge.

According to Advanced Plasma Power and National Grid Gas Distribution, the technology has the potential to generate 100 terawatt hours of BioSNG each year if deployed nationwide. This could fulfill one-third of the UK’s annual heating requirements or power all of the UK’s heavy-goods vehicles