Q. Are there any ongoing or planned pilot to test your discussed strategy – namely grid
synchronized decentralized biomass gasifierof lets say 500KW? We would be inclined
to participate in that. We could identify otherwise a common project to work together?
What role IISC Bangalore could play?
A. We did a number of experiments in 1985 – 2000 at an un-electrified village called
Hosahalli on which much has been written. You can download them from our website.
These experiments at 3.7 and 25 kWe were performed to understand the
techno-economic feasibility of such systems. The change from 3.7 to 25 kWe is due
to rise in user demand from lighting, drinking water and flour milling to irrigation
water.The principal conclusion we came to was that it is technically feasible as
they supplied electricity for about six hours a day for over ten years; but
economic viability required a number of systems in a cluster or a larger package
that operates on a meaningful plant load factor of 75% or better. The water for
irrigation would be a good opportunity. This was also tested in another location
and assessment after two years indicated that the revenues from water pump
supported irrigation led tothree to three and a half times the revenue (from
5000 Rs/acre per year to 15000 to 18000 Rs per acre per year).The projects
got closed because there was no support for O & M and the fragmented return
on services was barely able to meet the demand on O & M. This is the reason
that I have put together the aspects in the PPT.
Q. Can you kindly enlist successful rural electrification models that you have come
across including any(full/partial) realization of your suggested model as well?
A. Currently, a project called BERI (Biomass energy for rural India) is being executed in
Karnataka.Though this project came out of IISc’s thinking and experience, there are
several problems associated with it, a large number of which can be directly
related to its management. It is still struggling hard to come to grips. We were
kept out for over four years and we are currently being brought in – you know
somewhat like a person with a difficult disease being brought to a high quality
medical centre after visiting several quacks who would have created many issues
with the system.
Q. How load building with time can be accounted in design of the plant and investments?
A. Our experience is captured in the work on Hosahalli (1988 to 2001). Whatever
additional aspect I write on this subject is simply theory. It is important to account for
load build up sooner than later. Minimum most investment is obtained when all of it is
planned in one go. More things can be stated only when you give the scenarios of the
power utilization possibilities or the environment.
Q. Does biofuel has a role to play in biomass gasifier ecosystem?
A. Biofuel is a word that encompasses solid and liquid forms even though most people
use it for liquid bio-fuel somewhat incorrectly. If the aim of an oil-importing country
like India is to find an alternate for high speed diesel used in heavy vehicle transport,
something that affects national economy very significantly, it can be done only with
plant oils (or bio-diesel). Hence it is vital to preserve liquid bio-fuels for a better
purpose,namely transportation. If rural needs are considered primary, then they
can be conveniently used in tractors and similar vehicles. If there is excess or if the
locally produced oil is expensive to transport to the market at a distance if there is
no alternative, then the use for stationary power generation should be contemplated.
You can download one of my articles called “foreign exchange outgo..” on our website
to get more details.
The beauty of the solution for stationary power generation is that solid fuels can be
converted to clean gaseous fuels (through gasifier) so that power generation can be
Q. It takes 1 kg dry biomass to get 1 KWh costing say, Rs. 2 and it takes 300 ml of
diesel or biodiesel to get 1 kWh costing Rs. 9 to 10 depending on the state.
Do you see the fantastic merit of using gasifiers for gas based power generation?
A. However, for standby power generation used as a backup, one can easily
contemplate using biodiesel. If this is produced locally the actual production
cost should be lower than diesel cost and it therefore becomes economically
meaningful to use it that way. If there is base load operation then depending
on gasifier – gas engine –alternator is the simplest and cost effective solution.
Q. What performance metrics to monitor daily for effective plant management?
A. If the capacity is reasonable and some instrumentation and data acquisition are
planned, then one can monitor the performance continuously. It is advisable to
do this in an era when electronics and instrumentation have been relatively cheap.
The primary parameters on the gasifier side are:
a. Pressure at the end of the reactor, the cyclone, the scrubbers and the outlet of
the blower before the gas goes into the engine. These are routinely expected to
be logged every ten to fifteen minutes in a start-up or transient and every 30
minutes to an hour in a well stabilized situation. A cursory check on the water
flow rates just by looking at the flow behaviour – into the sump or some other
location is useful. The moisture content of the biomass must be measured
(in rainy seasons, for instance) or assessed (during summer, for instance). The
biomass loaded and the time of loading must be logged. When loading is
completed, the ash extraction of about 10 percent on wet basis or 5 % of
the biomass on dry basis should be done. This ensures that the reactor
behaviour after initial transients is steady, implying that the reactor
pressure drop will fluctuate around a mean (this is typically between 150 to
250 mm water gauge at nominal load).
b. On the engine, the aspects of load, frequency, the energy meter reading and
power factor should be recorded. Occasional examination of the lubrication oil
is desirable (one in 100 hours, tests after cursory examination shows the need for
quantitative assessment.These data when sent to any person who understands
the gasifiers can draw conclusions on the health of the system.
Q. What calibration curves and numbers will help you rate the operational efficiency of the
entire power plant to suggest better technology/plant management?
A. If you analyse the data and get 1 kg biomass (at 10 % moisture)/kWh (the biomass that
should be fed in should have a moisture of preferably less than 10 %) you are doing OK.
The number of hours before the filter is to be altered or cleaned should be about 250 in
small systems. There is additional information provided in a user manual for the particular
size system that can be looked at.
Q. What are the established curves for specific fuel consumption (both biomass and diesel) vs.
% loading with different types & sizes of engines (pure gas and Dual fuel mode)?
A. On gas engine it is as I indicated above.In dual fuel mode, one should get a 75%
diesel replacement and biomass consumption of 0.85 to 0.9 kg biomass (at 10%
Q. DESI Power keeps a back up of dual fuel mode together with Pure gas engine set. How to
really economize this redundancy? Can a dual fuel engine works with zero diesel i.e
becomes a pure gas engine?
A. Technically, a dual fuel engine cannot become a gas engine unless the compression ignition
is converted to spark ignition. Therefore, a dual fuel engine cannot be run without diesel
supplement of at least 10 % , perhaps 15 %)
Q. They are currently buying small 10KW Ankur gasifiers that can self start through batteries
to replace their dual fuel engine and make their plant 'zero-diesel'. Their thought line is
that this small 10KW in addition to existing 50 or 75 KW gasifiers would economize
their plant operations?
A. I cannot see the logic of this thinking. The backup of dual fuel mode is to ensure that one
can deliver full power when gas engine in under maintenance – scheduled or
break-down. When the gas engine based power generation fails would
10 kWe meet the demand?
Q. Any technology to reconfigure (or control) the gasifier and/or engine to accommodate
to varying loads with good efficiencies (for cases where there is no grid to absorb
demand fluctuation problems)?
A. Our current understanding based on a large number of experiments on gasifier - gas
engine combination is that up to 30 % load fluctuation can be accommodated.If there
is a larger load change, one can design a resistive load that cuts in and slowly drops off
to reduce the sharpness of the transient. If it is too much of a fluctuation like a
heavy cutting machine coming in and going off, then one has to go to grid or diesel
engine (and even in a diesel engine, the fuel consumption will be more than under
With regard to efficiencies, you must know that kg/kWh increases as the load decreases.
This is inescapable. To derive better efficiencies, you have to match the load to
the power delivered. As long as peak power is about 10 – 15% higher than the demand
except for short durations, you will derive economic benefit significantly.
Q. What relationship between gasifier size and engine size?
A. As indicated earlier, if the engine output is 100 kWe, you design the gasifier for a
throughput of 130 kg/hr, generally since the user does not always keep the biomass
Q. Can biomass supply be controlled to affect change in electric output with high
A. No. The inertia of the gaifier allows you to instantly reduce or draw more gas with no
apparent effect on the biomass. In actuality the consumption will go down or up.
This is because there is a stock of biomass in the reactor.