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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 condensibles
as minor products
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In the Energy
Quest fluidized bed gasifier, a
granular sand-like material is fluidized by the upward passage of air from a
porous plate structure below the sand bed and preheated to 1200oF. 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. |
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