Energy
Techonologies - 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
