Landfill gas valorization plant

2001/05/01 Astobiza, Amaia Iturria: Elhuyar aldizkaria

• Energia

The methane content of the gases produced in the combustion of waste is very high, so it can be used for obtaining electricity or heat. Subsequently, this electricity or heat obtained can be used in the landfill installation itself or in other uses.

About 1 kWh of electric power can be produced from 620 litres of biogas. For this purpose waste is accumulated and anaerobic reaction is allowed. The landfill is covered with a waterproof material above and below to prevent anaerobic fermentation and leakage of formed gases. Gas collection is carried out through pipes that penetrate about 30 m of depth. The stored gas is hot and saturated. When circulating through the pipes, the gas cools and the water condenses. The separation between water and gas is done by point drains. Finally, the collected gas is driven to the measuring station, where the composition, temperature, pressure and flow are measured.

The values measured are, in general, the methane content (which is usually slightly higher than 50%) and the concentrations of volatile organic compounds, sulfuric acid and water vapor. The last three are very corrosive and can cause engine damage. Ammonia concentration is also measured, but it is usually low and does not cause motor problems. Finally, low oxygen concentration must be guaranteed to meet safety conditions. If the composition is acceptable but the humidity is excessive, biogas is transferred to the dehumidifier, otherwise condensation problems would occur.

Normally, part of the electricity produced is used in the landfill itself and the rest is transferred to the electricity grid. When an excess of biogas is collected, the surplus passes directly from the dehumidifier to the torch where it is burned. Otherwise, the direct emission of biogas would cause an increase in the greenhouse effect. However, burning methane releases carbon dioxide and other pollutants. However, their concentrations are lower than those of conventional thermal power plants.