Biomass Gasification for Thermal and Electrical Applications
Introduction
Biomass gasification is thermo-chemical conversion of solid biomass into a combustible gas mixture (producer gas) through a partial combustion route with air supply restricted to less than that theoretically required for full combustion. Typical composition of producer gas is as follows.
| Carbon monoxide | 18%-20% |
| Hydrogen | 15%-20% |
| Methane | 1%-5% |
| Carbon dioxide | 9%-12% |
| Nitrogen | 45%-55% |
| Calorific value | 1000-1200 Kcal/m3 |
- Producer gas can be used as a fuel in place of diesel in suitable designed/adopted internal combustion (IC) engines coupled with generators for electricity generation.
- Producer gas can replace conventional forms of energy such as oil in many heating applications in the industry.
- The gasification process renders use of biomass relatively clean and acceptable in environmental terms.
- Large monetary savings can accrue through even partial substitution of diesel in existing diesel generator (DG) sets.
Most commonly available gasifiers use would/woody biomass; some can use rice husk as well. Many other non-woody biomass materials can also be gasified, although gasifiers have to be specially designed to suit these materials and the biomass may have to be compacted in many cases.
Gasifiers can be of 'updraft' or 'downdraft' types. The working of biomass gasification systems can be explained by considering a typical downdraft gasifier. In this type of gasifier, fuel and air move in a co-current manner. In updraft gasifiers, on the other hand, fuel and air move in counter-current manner. However, the basic reaction zones remain the same.
Fuel is loaded into the reactor from the top. As the fuel moves down, it is subjected to drying and pyrolysis. Air is injected into the reactor in the oxidation zone, and through the partial combustion of pyrolysis products and solid biomass, the temperature rises to 1100oC. This helps in breaking down heavier hydrocarbons and tars. As these products move downwards, they enter the reduction zone where producer gas is formed by the action of carbon dioxide and water vapour on red-hot charcoal. The hot and dirty gas is passed through a system of coolers, cleaners, and filters before it is sent to engines.
Typical capacities
Biomass gasifier-based systems are being made in capacities ranging from a few kilowatts to a megawatt of electricity equivalent. For heating applications, the current upper limit on the unit size is equivalent to 200-300 kg/h of oil consumption.
Technology and equipment
There are about a dozen known manufacturers in the country for gasification systems. A list of these can be obtained from the respective state nodal agencies for renewable energy development.
Achievements
The biomass gasifier-based thermal and electricity generation applications are at a 'take off' stage in the country. The MNES has so far provided partial financial support for installation of about 1900 biomass gasification systems in the country. Many systems have also been installed without support by the MNES, reflecting the improving commercial viability of the technology, especially in niche applications. A few megawatt-scale projects have also been planned by independent power producers, and are likely to come on line in the coming years.
Costs
The typical costs of biomass gasifier-based electricity generation systems range from Rs 4 crores/MW to Rs 4.5 crores/MW. The cost of power generation depends on cost of biomass, plant load factor, etc., and is estimated to be between Rs 2.50/ k Wh and Rs 3.50/kWh. For thermal applications, the capital costs are estimated to be about Rs 0.5-0.7 crores for each 1 million kcal capacity.
Financial incentives
The MNES offers financial support for biomass gasifier projects as listed in Table below. These are subject to change without prior notice. Information on the latest scheme of incentives can be obtained from the MNES webstie: www.mnes.nic.in
Financial support by the MNES for biomass gasifier projects
Type of application |
Capital subsidy |
| Thermal applications, including cooking (up to 3 MW megawatt thermal) | Rs 1.25 lakhs/300 kW (kilowatt thermal) on pro-rata basis or in multiples thereof |
| Electrical application, including pumping and captive power, with provision for surplus power to grid (up to 1 MW) | Rs. 1.50 lakhs/100 kW for electrical applications, including pumping and captive power on pro-rata basis, or in multiples thereof, preferably with provisions of surplus power to grid |
| Electricity generation with 100% producer gas-based engines, up to 100 projects | Rs 15 lakhs/100 kW on pro-rata basis or in multiples thereof, or Rs 10 lakhs/ 100 kW for engines alone |
Main Application
Energy
For further information please contact
Ministry of Non-Conventonal Energy Sources,
Govt. of India
Block-14, CGO Complex, Lodi Road
New Delhi – 110 003
Tel: 91 11 2436 0707/ 2436 0404
Fax: 91 11 2436 1298
