Creating Value from Landfill Gas

by Terry Mazanec (Lee Enterprises Consulting/Biofuels Digest) ... The US EPA estimates that 250 million tons of municipal solid wastes are sent to landfills each year. These materials have a wide range of chemicals in them, including aromatics, paraffins, oxygenates, and nitrogen- and sulfur-containing compounds. Moreover, they are mixed with a variety of other non-organic debris such as cement and metals. Finding value in this mess seems counterintuitive.

Mixed biomass digested under the anaerobic conditions in a landfill slowly forms bio-gas. Biogas has an objectionable odor and can move through soil and collect in nearby buildings or escape to the atmosphere. Biogas may contain more than 500 different impurities, including sulfur compounds that are corrosive in the presence of water, halogenated compounds (e.g., carbon tetrachloride, chlorobenzene, chloroform) that produce corrosive combustion products, and organic silicon compounds (e.g., siloxanes) that form siliceous deposits in downstream applications — like internal combustion engines. Thus, an initial cleanup or pre-purification step is needed before biogas can be used in any application involving combustion.

For every million tons of municipal solid waste (MSW) about 450,000 cubic feet per day of biogas is produced.

Gas purification methods are well established. Many gas upgrading processes are commercially available.

In many cases most of the CO2 must be removed from the methane before upgrading. Steam or oxidative reforming can be used to convert the biogas to syngas, from which hydrogen may be separated, if desired. Syngas conversion to methanol, diesel, gasoline, or DME can follow.

A typical biogas conversion plant at a landfill will be scaled to produce a few hundred to a few thousand barrels per day of liquids.

Velocys has steel on the ground. The company has put aside its own Marcellus shale gas play in Ashtabula, OH, to concentrate its resources on ENVIA, a commercial reference plant to convert landfill gas to hydrocarbons.

Landfill gases are available throughout the world, but the individual sites are relatively small and dispersed compared to natural gas deposits. So the solutions need to be tailored to the scale of the resources. At least a dozen companies are developing solutions that can produce chemicals or fuels. Very soon we expect one of these companies to break out from the pack and spark a landfill gas to products revolution. READ MORE