Copyright 2011 International
Innovations Incorporated. All rights reserved. Photos courtesy of AMK.
Reproduction by written permission only.
Gas Production Process –
Gasification is a
thermo chemical process, the result of the correct observance and
interpretation of numerous scientific principles requiring a certain
order of execution and accompanied by predictable and measurable
The fixed bed, downdraft, linear hearth process exemplifies the above
statement and underscores the simplicity of the technology required
for the gasification process.
Beginning with a “start-up” charge of
charcoal and kindling in the combustion zone of the hearth,
gasification proceeds as follows:
A controlled flow of intake air is drawn laterally into the hearth and
a momentary flame enters to ignite the start-up charge and combustion
Drying, distillation and
Feedstock is slowly introduced. Heat
radiating upward from the hearth drives moisture from the feedstock
at 100 C. and as charcoal beneath is consumed, the feedstock sinks
closer to the source of heat. At this point, the temperature is
250-450 C. and volatile substances distilled from the feedstock may
ignite, raising temperature further and rapidly. At 600 C. the
charred feedstock ignites, rapidly increasing the temperature.
Oxidation and combustion
Very high temperatures are achieved in
the system at this level when air entering the combustion zone
contacts and reacts with incandescent char to produce carbon
monoxide, a fuel gas, which diffuses back into the gasified spaces
between the char pieces where it oxidizes and burns to form carbon
dioxide, a flue gas. As the carbon dioxide increases in the gasified
spaces, a counterbalancing decrease in the free oxygen occurs in the
same spaces and concentrations of both these gases approach
equilibrium . . . The carbon monoxide produced in the initial
charcoal/air oxygen reaction quickly falls to a low concentration at
which it is held in dynamic stability . . . . .
steam from the feedstock has joined with the air also to react with
the incandescent char where it decomposes to carbon monoxide and
hydrogen, which together, also diffuse back into the gasified spaces
between the char pieces where they too are oxidized to form carbon
dioxide and steam respectively . . . The process temperature during
the above reaction is 800 C to 1,100 C.
At this time the heat requirements of the process balance the heat
created and the temperature is at its maximum, approximately 1,100 C.
to 1,250 C. and the oxygen is nearly depleted.
Below this level, much of the heat involved in the process of
"Oxidation and Combustion" is consumed in the process of reduction.
At this stage in the process, the carbon
dioxide and the steam in the gas spaces diffuse to, and react with,
the hot char in the Reduction Zone to produce carbon monoxide and
hydrogen, the main fuel constituents of “Producer Gas'. These
reactions consume both heat and char. As the process temperature
continues to decrease, the rates of these reactions also decrease,
until, when the temperature falls to 700-800 C. and/or the hot char
supply is exhausted, the gasification process stops.
The main product gases; carbon monoxide and hydrogen can be piped away
for use as fuel, producing flame temperatures of 2,100 and 1,960 C.
Although some stages of the process occur
sequentially and others simultaneously, they are continuous and in
equilibrium, while a feedstock and managed primary air are fed to the
'hearth' to sustain the process.
Except for the feedstock “drying” stage, the other gasification
processes occur within the reaction vessel called the 'hearth'.
Because of the high temperature plus the oxidizing and reducing
atmospheres which must be developed and sustained within it, the
'hearth;' incorporates special refractory materials, surface treatment
and thermal insulating materials, selectively placed to withstand the
rigor of the main gasification processes and equally distribute the
Please note: several generations of 3i Energy
System have evolved since this document was prepared by Jack P.
Humphries, P.E. Associated with the modifications are interior
architectural changes and/or modifications, method of feedstock
introduction and producer gas handling. Though many of the changes
and modifications are proprietary, limited information is available
upon request. ~3i
3i Energy System: The power of energy independence!