TECHNOLOGY DESCRIPTION

A complete Biomass gasification includes a fuel metering bin, the reactor/gasifier, the combustion 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 control over the process. The entire gasification/combustion process, from in-feed to ash discharge, can be controlled manually or by computer.

The gasifeir basically a vertical cylindrical steel shell reduced in diameter in the upper portion and lined with a refractory capable of withstanding temperature as high as 1560 Deg. C in a reducing atmosphere. The cross section al area of the upper portion of the gasifier is reduced to provide the turbulence required to ensure proper mixing of the product gas and the combustion air introduced in to the combustion tubes in this area of the gasifier. The lower portion of the gasifier contains an appropriately sized grate and develops a design heat rate of 350000Btu/ft Sq. of grate area.


Fuel is metered to the gasifier from the fuel-meter in bin. This bin is equipped with an in-feed conveyor that delivers fuel to the gasifier. The speed of the out-feed conveyor is automatically adjusted by the automatic control system to maintain a preset temperature in the first stage gasifcation zone. Discharge from the out feed conveyor is directed through an impact weigh metering devices that provides precise indication and control of the fuel feed rate.

The gasification process is controlled by the proportional application of gasification and combustion air in a manner that supports efficient gasifiacation. Residence time in the gasifeir is varied by a residence control system that is adjusted to achieve a target quality of the ash residue.

In the gasification zone of the gasifier, approximately 10 to 12 percent of the stoichiometric air requirement is admitted into the gasification air distribution area. The application of gasification air is multi-zoned and is controlled to maintain the proper temperature required to volatize the Biomass and allow partial combustion of the fixed carbon. Temperatures in this zone are controlled between 600 Deg C and 800 Deg C, depending on the perticular biomass fuel and the required ash quality. A low gasification air – flow rate (0.1 m/s) through the gasification zone, coupled with a low feed stock entry point and continuous ash discharge minimizes the amount of the particulate matter entrained in the gasifier exhaust.

Heat/ Steam/Electricity Cycle

Combustion of the gases starts in the combustion tube assembly where the temperature of the gas is increased to promote thermal cracking of tars and hydrocarbons that were liberated during gasification. Partial combustion of gas in the combustion tube assembly, automatic continuous ash discharge and precise control of the zoning of the gasification air produces a clean, low Btu content gas that can be burned in the combustion tube and chamber for drying applications or in the radiant section of the boiler. The boiler exhaust is clean and may be used for direct drying applications including good grains.

Gas/turbine Cycle

The evolved hot biogas is directed to a gas conditioning system, which includes a biogas cooler, and cleaner which utilizes re-circulated cooling water to cool and clean the biogas to a temperature and quality suitable for injection into internal combustion engines. The engines are turbochargers, inter-cooled, lean combustion design coupled with appropriately sized synchronous or induction generators.