Biomass Resources
The term "biomass" means any plant derived organic matter available on a renewable basis, including dedicated energy crops and trees, agricultural food and feed crops, agricultural crop wastes and residues, wood wastes and residues, aquatic plants, animal wastes, municipal wastes, and other waste materials.
Biomass is comprised of cellulose, hemi-cellulose and lignin, having an average composition of C6H10O5, with slight variations. For the complete combustion of biomass the amount of air required is 6 to 6.5 kg, per kg of biomass and the end products are CO2 and H2O. In gasification, biomass is subjected to partial pyrolysis under sub-stoichiometric conditions with the air quantity being limited to 1.5 - 1.8kg/per kg of biomass. The resultant mixture of gases generated during the gasification process is called synthetic gas, which contains CO and H2 and is combustible. The raw producer gas also contains tar and particulate matter which have to be removed prior to use.
Biomass Heating Value
The raw heating value of biomass is ~20GJ/dry tonne HHV, or about 18.5GJ/t LHV at 10% moisture (ash free). By example, a litre of petrol has ~26.4MJ of energy (LHV), so a metric ton of dry biomass will contain nearly 704 litres of gasoline equivalent energy in its raw, unconverted state.
Agni’s Gasification technology
Agni’s gasification process has the following features: fast fluidisation which enhances the heat and mass transfer so as to speed up the gasification process; and the circulation of the char which increases the residence time of char so as to satisfy the need of reduction reaction and decrease the char loss.
Biomass gasification is basically conversion of solid Biomass (Wood, agriculture residues etc.) in to a combustible gas mixture normally called “Producer Gas” (or low Btu gas). The process involves partial combustion of Biomass. Partial combustion is carried out in absence of air or less air than the stoichiometric requirement of air for complete combustion.
Partial combustion produces Carbon Monoxide (CO) as well as hydrogen (H2) which are both combustible gases. Solid Biomass fuels, which are usually inconvenient and have low efficiency of utilisation can thus be converted into a high quality gaseous fuel with associated convenience etc.
The synthetic gas delivered from the gasifier has the following average chemical composition:
CO: 20±2%; CH4: 3±1%; H2: 20±2% ; CO2: 12±1% ; Rest: N2
The lower calorific value is about 4.5- 5.0MJ / kg (1000 - 1200kcal / m3).
Air is blown through a bed of solid particles at a sufficient velocity to keep these in a state of suspension. The bed is originally externally heated and the feedstock is introduced as soon as a sufficiently high temperature is reached. The fuel particles are introduced at the bottom of the reactor, very quickly mixed with the bed material and almost instantaneously heated up to the bed temperature. As a result of this treatment the fuel is pyrolysed very fast, resulting in a component mix with a relatively large amount of gaseous materials. Further gasification and tar-conversion reactions occur in the gas phase. Agni’s gasification systems are equipped with an internal cyclone in order to minimise char blow-out as much as possible.
The gas produced is usually contaminated with tar and dust that are removed before feeding into Agni’s Integrated Fuel Cell Engine (IFCE). This is done using a rotating particle separator which is integrated in the gasification process and efficiently removes particles from the gas flow.
