Adding gas from biomass to the gas grid - SGC

• Removal of sand from mixing tanks and reactors• Abatement of smell from the plants• Cleaning of gas for hydrogen sulphide, ammonia and particulate.Farm biogas plantsThe biogas production on farms uses basically the same processes as centralised plants andnormally the farm also establishes a CHP facility. Heat is usually distributed to the farm itself and tonearby users. Electricity is sold to the power grid.The size and the set-up vary. The reactors include horizontal and vertical steel tanks as well asconcrete basins. The mixing devices range from stirrer and propeller to pump.Some plants have a gas storage facility to be able to take advantage of power peak hours. Thestorage may be established as a gasbag covering the reactor or as a gasbag in a separate building.Like the centralised plants, the smaller farm plants have found it attractive to mix manure andorganic waste to stabilise and increase productivity. However, the requirement of heat treatment ofwaste at 70 °C for one hour in some countries seems to be a blockage.Sewage plantsThe biogas technology has its origin in sewage plants where digestion of biomass is used to reducethe amount of dry content as opposed to oxygenation. The energy production through biogas wassecondary to these plants. Today the biogas energy production attracts attention as opposed to theenergy consumption required for oxygenation.It is noted that half of the potential biogas energy available in sewage plants is used forde-nitrification. Environmentally and economically it is therefore preferable to treat the sewage slurryin centralised biogas plants where the de-nitrification is avoided and the nitrogen recycled. Thissolution is not applicable however, when the content of environmental foreign elements is high.LandfillLandfill gas is produced biologically from organic material in waste deposits. The gas productionpeaks at about 20 years after closure and continues for more than 50 years.The gas is extracted by vertical or horizontal perforated tubes and filtered. The blower orcompressor used also establishes the supply pressure.The extraction of the gas is seen not only as a source of energy, but also as a precaution againstgreen house gas emission to the atmosphere. An additional advantage is also the reduction, ofteneven elimination, of odour emissions. The occurrence of fires and explosions caused by involuntarymethane emissions is reduced to zero.page: 17