Gasifiers are devices used for converting solid fuel into gaseous fuel. In biomass systems, the process is also referred to as pyrolitic distillation.
Gasification is a chemical and heat process used to convert a solid material such as coal, biomass and any carbonaceous material into a gas for use as a fuel.
Gasification is the Thermal conversion of organic materials at elevated temperature and reducing conditions to produce primarily permanent gases (CO,H2, CH4, etc.), with char, water, and condensable as minor products
In the Energy Quest fluidized bed gasifier, a granular sand-like material is fluidized by the upward passage of air from a manifold of bubble caps below the sand bed and preheated to 1000oF. Solid or liquid wastes are injected into the bed, and when they are mixed with the hot sand, the wastes are quickly decomposed into a combustible gas. The flow of air is controlled so that only about 25% of the incoming wastes are “burned” in the bed to raise and maintain the temperature at 1500oF. The remaining material is decomposed into gas. Once the bed is preheated, no more fossil fuels are needed. The wastes supply all required heat.
The size of the “sand” particles is chosen such that the passage of air through the bed moves and agitates the “sand bed” giving it a fluid like character. The bed resembles a rapidly boiling pot of water. The boiling action assures good mixing of the fuel and air. The bed also acts a very efficient “thermal flywheel” smoothing out variations in the fuel supply heat values.
Mixing of the waste with a relatively large quantity of hot sand, heats the waste very quickly, causing pyrolysis at the volatile portion of the waste with minimal tar formation. Unlike the fixed bed gasifiers, the fluidized bed does not impose the same types of restrictions on the fuel. In normal operations the bed is typically about 98 – 99% by weight ‘sand’ and only 1 – 2% fuel, thus the behavior of the bed (including the passage of air and gas through the bed) is determined by the character of the sand bed, and not by the character of the fuel particles. This allows fluidized bed gasifiers to operate with fuels that are not pelletized but in their raw state, including wastes that are powdery, flaky, fibrous, or chunky. Finally the fluid bed gasifier is not restricted to low moisture fuels like the downdraft gasifier. The moisture in the fuel is evaporated in the bed and exits the gasifier in the vapor phase as a component of the gas stream, acting as a diluent, thereby reducing the energy content of the gas. This has the effect of reducing the gas heating value and resulting gas temperature, causing the gas to become progressively harder to burn as the moisture content is increased. For these reasons it is desirable to keep moisture content generally below 25 – 30% although successful gasification and gas combustion have been achieved with fuels having moisture contents of up to 50%.
In summary then, the fluid bed gasifier has a much greater tolerance for a wide range of biomass fuels, accepting fuel with broad ranges of physical characteristics and moisture contents. This innovative process provides a quantum leap in expanding the commercial potential of the Energy from Waste market. The Gasification system can utilize the by-products (having heat value) of processing industries as a fuel to produce heat and/or electrical energy. In addition gases such as hydrogen and methane can be synthesized.
The syngas can also be further processed using commercially available technologies to produce fuels, chemicals, fertilizer, methanol, synthetic natural gas or other industrial gases.