rated power of 10 to 100 kWe.
• The system combines the process of gasification of biomass to
produce combustible gases and the subsequent conditioning of
gas (cleaning and cooling) to make it suitable as fuel for internal
combustion engines.
• The gas, which is derived from burning rice husks in an oxygenstarved environment inside a reactor, is a mixture of carbon
monoxide (CO), hydrogen (H2), and little amount of methane (CH4).
• The plant is designed to produce mechanical power and
electrical power. In the latter, however, the gasifier needs to be
coupled to a generator.
• The size of the plant varies from 10 kWe up to less than 100
kWe, depending on the required power and on the available
supply of rice husks.
• The gasifier reactor operates on a moving-bed downdraft
mode with no grate. Air is supplied by a blower on a positive
pressure mode.
• Air is preheated at the reactor before it is used for burning
rice husks.
• A temperature of around 800 to 1000 C is maintained at the
reactor during operation.
• Fire zone is maintained at the middle of the reactor where
fuel and air react producing combustible gas.
• Rice husk is fed at the top of the reactor manually or with
the use of an elevator. Char is discharged from the bottom
by means of a sweeper, scraper, and/or conveyor.
• The gas is then cleaned by spraying it with water and by
mechanically-screening it with the use of wet scrubber and
filters to remove dusts, tars, and particulates.
• The gas produced from the reactor is fueled to a
reconditioned surplus spark-ignition engine or by means of
compression-ignition engine operating on a dual fuel mode.
• The engine is directly coupled to a single- or three-phase
generator to produce electricity.
• Without any modification on the engine, it runs at 1,500 to
2000 rpm which is enough to drive a generator or other
stationary agricultural machines.
• Parasitic load is up to 15% of the overall power generated.
Advantages and Limitations
• Makes use of local resources as construction materials for theplant.
• Makes use of reconditioned surplus spark-ignition engines as
the power-driven device for the gasifier .
• Size can be scaled-up to 100 kWe generator using
reconditioned surplus engines.
• Produces electricity either in single- or in three-phase line,
whichever is applicable.
• Provides mechanical or electrical power, whichever is needed.
• Only applicable for rice husks and needs to be redesigned if
intended to use other biomass as fuel.
• Training on operation and maintenance is a must to ensure
proper operation and longer life span of the machine.
OPERATION AND MAINTENANCE
• The engine of the gasifier plant is initially operated withgasoline as fuel to energize the blower, pumps and motors.
The engine runs on gasoline for approximately 10 to 20
minutes from the ignition of rice husks.
• The gas coming out of the gasifier is ignited to check gas
quality whether it can now be fed to the engine. Normally,
flame color is blue-to-pink.
• Once the desired quality of the gas is obtained, the engine
fuel is shifted to producer gas by simply switching the fuelinjection valve. The producer gas is then used until the
entire operation is finished.
• Before stopping the engine, gasoline fuel is used again for
the engine for 5 minutes to clean the engine combustion
chamber from tars or particulates, if ever there is.
• Cleaning of the wet scrubber and of the tar condenser is
needed once a month to eliminate tar and particle
accumulation on the gas train.
• Filter media for the packed-bed filter needs to be backwashed during cleaning period to prevent gas suppression
during operation.
• Liquid tars collected can also be used as fuel to co-fire with
rice husks gasifier when used for thermal application.
SOCIO-ECONOMIC IMPACT
• Provides market for the local suppliers of materials for thefabrication and construction of the gasifier plant.
• Provides employment opportunities for the rural people in the
production and operation of the gasifier .
• Provides low-cost supply of electricity.
• Makes electric power available for various social and business
activities which can improve the life of the people, especially
those in off-grid areas in the country.
• Farmers can make use of their rice husks as fuel or it can be a
source of additional income, instead of just throwing them that
contributes to environmental problem of the community.
• Provides additional revenue for the local government unit in
terms of taxes.
ENVIRONMENTAL BENEFIT
• Waste disposal problem, particularly rice husks as well as charand tar, is eliminated.
• Greenhouse gas emission is reduced since the system
operates on the principle of gasification, approximate 0.6 kg
of CO
2
per ton of rice husks only.
• Black carbon emission is very low, only around 50 ug per m
3
of
gas.
• By-product of the plant, especially char holds water 5 to 7
times of its weight. It is a good soil conditioner material to
improve the water holding capacity of the soil.
• The silica in char can also increase the resistance of
vegetables against weevil infestation. It also provides the
silica requirement of rice plants to withstand lodging.
• Char can be used as an ingredient in the production of
torrefied pellets, which in turn can be used as fuel for
gasifier stoves for domestic cooking.
• Char, when burned further, can be used as ingredient for
the production of locally-mixed construction materials
such as cement fiber board, refractory cement, and
geopolymer .
POWER GENERATING COST AND PAYBACK PERIOD
• Investment requirement for the gasifier power-generatingunit is around P30 per watt, depending on the size and on the
complexity of parts.
• Only one person is required to operate the entire plant.
• Power generating cost is higher for smaller unit (10 kWe)
than bigger unit (100 kWe).
• Cost to generate power ranges from P4.00 for the 100-kWe
unit to P10 per kW-hr for the 10-kWe unit.
• Comparing with the cost from the grid of P10.00 per kw-hr, a
savings from P75.86 for the 10-kWe at 8 hours per day
operation to P9,634.76 for the 100-kWe operating at 16
hours per day can be realized.
• Payback period is around 0.9 year to 6 years if the gasifier will
be operated for 16 hours per day.
• Comparing with the cost of generating using diesel fuel for a
diesel-generator system as shown below , a savings from
P275.86 for the 10-kWe at 8 hours per day operation to
P13,642.76 for the 100-kWe operating at 16 hours per day
can be realized. Payback period is 3 years for 10 kWe unit to
less than a year for 100 kWe plant.
• However, considering land and building for the plant
including the investment for accessories such as bucket
elevator for loading rice husks and screw conveyors for ease
of disposal of char will provide a lesser saving and slightly
longer time to recover the cost for the investment.
CONCLUDING REMARKS
• The small-scale rice husk gasifier is a simple technology thatcan generate electricity from rice husks.
• The technology is a good alternative energy source for
producing electricity for decentralized electrification and for
energizing off-grid areas in the country.
• Surplus spark-ignition engines commonly used in transport
vehicles can be reconditioned to be fueled with producer
gas from the gasifier to generate electricity.
• The gasifier can be locally produced which offers economic
benefits to the local people in terms of its production and
utilization.
• Operation and maintenance of the gasifier can be done by
the local people as well as repair, in case of trouble.
• The investment and operating costs for a unit of the gasifier
is at the reach of the farmers’ organizations, millers, cottage
industries as well as by the local government units.
• A substantial savings can be realized as compared to the
cost of grid and diesel generation system. The investment
can be recovered within a shorter period when the gasifier
is to be operated for a longer period of 16 hours.
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