Environmental Engineering Reference
In-Depth Information
pretreatment to remove impurities such as water, NMOC, and carbon dioxide. Numerous
pretreatment methods are available to address the impurities of concern for a specific landfill.
After pretreatment, the purified landfill gas is treated by non combustion technology options.
Figure 10 . Schematic diagram of the Calgary Biocell
2.1. Energy recovery technologies
Energy recovery technologies use landfill gas to produce energy directly. Currently, the
phosphoric acid fuel cell (PAFC) is the only commercially available non-combustion energy
recovery technology. Other types of fuel cells (molten carbonate, solid oxide, and solid
polymer) are still under development. The PAFC system consists of landfill gas collection
and pretreatment, a fuel cell processing system, fuel cell stacks, and a power conditioning
system. Several chemical reactions occur within this system to create water, electricity, heat,
and waste gases. The waste gases are destroyed in a flare.
2.2. Gas to product conversion technologies
Gas-to-product conversion technologies focus on converting landfill gas into commercial
products, such as compressed natural gas, methanol, purified carbon dioxide and methane, or
liquefied natural gas. The processes used to produce each of these products vary, but each
includes landfill gas collection, pretreatment and chemical reactions and/ or purification
techniques. Some of the processes use flares to destroy gaseous wastes.
Non-combustion energy recovery systems are not used as widely as combustion based
systems. Fuel cells are a promising new technology for producing energy from landfill gas
that does not involve combustion. This technology has been demonstrated and in the future
may become more economically competitive with other options. One option that does not
involve combustion of landfill gas at or near the landfill is purifying the landfill gas to remove
constituents other than methane, producing a high British thermal unit (Btu) gas that can be
sold as pipeline quality natural gas. Although the high-Btu gas is eventually combusted, it
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