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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
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
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