Biomass gasification means incomplete combustion of biomass resulting in production of combustible gases consisting of Carbon monoxide (CO), Hydrogen (H2) and traces of Methane (CH4).
Advantages of gasification are,
- Can be used for thermal application and electricity generation.
- Low cost of power production and low initial investment.
- It is highly efficient process.
- Gasification has thermo chemical conversion efficiency in the range of 70 % to 90% which is highest among different alternatives.
- The area requirement for gasification equipment is the lowest per unit output of energy in the form of heat and/or electricity.
- Gasification output capacity, especially in the high output ranges, is controlled only by availability of adequate feed materials rather than other
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The gasifiers main function is to pyrolyze the biomass and produce VM, producer gas and carbon and convert volatile matter into permanent gases in form of CO, H2 and CH4.
• Down draft gasifier
In down draft gasifier there are four zones are placed named, drying zone pyrolysis zone, oxidation zone and reduction zone. From upside feed stock is provided and biomass is fed from upside.
The cross sectional area of throated gasifier is reduced at throat and then expanded. Oxidation zone is at the narrowest part of throat and forces all of the pyrolysis gas to pass through this narrow passage. Throated down draft gasifier is shown in below figure. Air is injected through nozzles just above the constriction. The height of the injection is about one-third of the way up from the bottom. The movement of the entire mass of pyrolysis product through this hot and narrow zone results in a uniform temperature distribution over the cross-section and allows most of the tar to crack there. Throated downdraft gasifier is not suitable for scale-up to larger sizes because they do not allow for uniform distribution of flow and temperature in the constricted