Adding gas from biomass to the gas grid - SGC

negative pressure. Depending upon the feed stock, the air blown system produces a syngas containing alow calorific value of 3.7 to 7.5 MJ/m 3 . A higher calorific value can be reached with the use of oxygeninstead of air.A complete PRME biomass gasification system includes a fuel metering bin, the reactor/gasifier, thecombustion tube and chamber, the gasifier cooling water system, water cooled ash discharge conveyors,multi-zoned combustion air supply, rotary feeders and instrumentation required to provide automatic controlover the process. The entire gasification/combustion process, from feed to ash discharge, is controlledmanually or by computer.The PRME gasifier is basically a vertical cylindrical steel shell, reduced in diameter in the upper portion andlined with a refractory capable of withstanding temperatures as high as 1560 ºC in a reducing atmosphere.The cross sectional area of the upper portion of the gasifier is reduced to provide the turbulence required toinsure proper mixing of the product gas and the combustion air introduced into the combustion tubes in thisarea of the gasifier.Fuel is metered to the gasifier from the fuel metering bin. This bin is equipped with an input conveyor and anoutput conveyor that delivers fuel to the gasifier. The speed of the output conveyor is automatically adjustedby the automatic control system to maintain a pre-set temperature in the first stage gasification zone.Discharge from the output conveyor is directed through an impact weigh metering device that providesprecise indication and control of the fuel feed rate.Fuel is introduced to the gasifier by a water-cooled screw conveyor that discharges into the drying andheating zone of the gasifier. The gasification process is controlled by the proportioned application ofgasification and combustion air in a manner that supports efficient gasification.Residence time in the gasifier is varied by a residence control system that is adjusted to achieve a targetcarbon content of the ash residue. In the gasification zone of the gasifier, approximately 10 to 12% of thestoichiometric air requirement is admitted into the gasification air distribution area. The application ofgasification air is multi-zoned and is controlled to maintain the proper temperature required to volatilise thebiomass and allow partial combustion of the fixed carbon. Temperatures in this zone is controlled between600 o C and 1300 o C, depending on the particular biomass fuel and the required ash quality. A lowgasification airflow rate (< 0.1m/s) through the gasification zone, coupled with a low feed stock entrypointand continuous ash discharge minimises the amount of particulate matter entrained in the gasifier exhaust.Combustion of the gases starts in the combustion tube assembly where the temperature of the gases isincreased to promote thermal cracking of tars and hydrocarbons that were liberated during gasification.Partial combustion of gases in the combustion tube assembly, the use of mechanical bed agitation andprecise control of the zoning of gasification air produces a clean, low energy content gas that can be burnedin the combustion tube and chamber for drying applications or in the radiant section of the boiler. Thegasification rate is controlled by demand from the dryer or boiler. The boiler exhaust is clean and may bepage: 127