Report Biogas Study Tour to New Delhi and Gujarat, India 20 ... - SNV

Report
on
Biogas Study Tour to New Delhi and Gujarat, India
20 - 28 September, 1995
Biogas Support Programme:
Jan Lam
Ravi B. Chettri
Saroj Kumar Shrestha
Ang Rinji Sherpa
Roop Singh Thapa
December, 1995

Tour schedule:
Wednesday 20/09/1995:
Afternoon flight from Kathmandu to New Delhi.
Thursday 21/09/1995:
Visit to the Ministry of Non-Conventional Energy Sources in New Delhi. Meetings with
Dr. Khandelwal (Advisor to the Ministry) and Mr. Anil Dhussa, Director of the Biogas
Department.
Friday 22/09/1995:
Meeting with Mr. Mark Paul, Energy Specialist of Action For Food Programme (AFPRO).
Meeting with Mr. P. Raman at the Tata Energy Research Institute (TERI).
Saturday 23/09/1995:
Cultural excursion to Agra, visiting the Taj Mahal and Red Fort.
Sunday 24/09/1995:
Morning flight to Ahmedabad (Gujarat). Meeting with Major P.P. Kushare, General Manager
of the Energy Division of Gujarat Agro Industries Corporation Limited (GAIC). Visit to
Mech-ci-co, an engineering and manufacturing company of biogas appliances like various
sized burners, pressure regulators, automatic water removers and valves.
Monday 25/09/1995:
Morning visit to the GAIC Energy Division Head-Office for a briefing on the
Organizational set-up of the Corporation.
Afternoon field visit to a near by village, observing biogas plants in various stages of
construction and newly completed plants.
Tuesday 26/09/1995:
Excursion to GIAC Service Centre in Mehsana. Discussions with the centre's staff and
field visit to a cluster of older plants.
Wednesday 27/09/1995:
Morning site-seeing of Ahmedabad town. Afternoon final discussion with GAIC GM.
Thursday 28/09/1995:
Morning flight from Ahmedabad to New Delhi. Afternoon flight from New Delhi to
Kathmandu.

Introduction:
An biogas observation tour to India for BSP technicians was scheduled the first quarter of the
FY 2052/53. The aims of the tour were:
- to give the BSP staff a possibility to be able to look at their own work from some distance
by observing other biogas programmes and
- to learn about new idea's on technical items, extension and promotion, slurry use, NGO
involvement, subsidy etc.
India was chosen to be visited because it is near to Nepal, its vast biogas programme and the
useful relations that were already established between the Ministry of Non-Conventional
Energy Sources (MNES) in New Delhi and BSP.
Gujarat was recommended by the above mentioned ministry as an interesting state to visit
because of the impressive quantity and quality of then- biogas programme. A visit to New
Delhi was included in the trip to allow for discussions with representatives from MNES,
Action For Food Production (AFPRO) and the Tata Energy Research Institute (TERI).
Both aims of the tour have been achieved. For this we owe our gratitude to Mr. Anil Dussa
who arranged the tour in India and specially to Major P.P. Kushare and his staff of Gujarat
Agro Industries Corporation (GAIC) who through their hospitality and openness made the
journey to Gujarat a very rewarding experience.
MNES:
The direct charge for this Ministry lies with the Priminister of India. This fiscal year a
total of IRs. 245 crore is allocated to the Ministry from the national budget of which 60
crore is earmarked for the biogas programme. Biogas has to compete for a slice of the
Ministerial cake with programmes like wind energy, biomass (gasification) and solar
energy.
A disadvantage of this system is that biogas is only judged on its energy values. Other
benefits of biogas to the society, specially in regard to other energy carriers, like
production of organic fertilizer and improved health are not taken in to account and thus
no funds for the promotion of these aspects are available.
Out of the biogas budget the national subsidy scheme is funded which amounts to
approximately 60% of the total budget. The remaining 40% is used to fund a training
centre in every state (5 lakh/centre), for the development of training and extension
material, for trainings and for special programmes in regions where the biogas technology
fails to become popular. Such programmes can be cash prizes for model fanners with well
maintained plants, well published visits to biogas programmes by dignitaries etc.
Every third year the Ministry conducts an extensive nation wide survey in which 10,000
plants are sampled. Depending on the outcome of this survey, modifications are made in
the plan of action.
Annex 1 gives the structural set up of the biogas division of MNES.

AFPRO:
Action For Food Production (AFPRO) is a NGO since long active in the diffusion of biogas
technology in India. They act as an support body for grassroot NGO's active in this field.
Presently some 62 organizations are actively involved. Some of the support activities
undertaken by AFPRO are:
- Organization of an annual meeting where the grassroot organizations can share their
experiences.
- Training of masons, coordinators and women motivators.
- Provision of motorcycles for supervisors.
- Construction of demonstration plants in new localities.
Our team had discussions with Mr. Mark Paul, the energy expert of AFPRO, and the
points raised were mostly related with their long term experiences with the popularization
of the programme. For BSP interesting experiences were:
Funded by Hunger Foundation Canada, IRs.500 additional subsidy was set aside for
additional subsidy for the poorer sections of the society. This programme completely
failed because of the following reasons:
- It created big divisions in the villages.
- It was very difficult to identify the "real poor".
- There were large financial organizational problems as such a scheme is very sensitive to
fraud.
Because of these problems the programme has been abandoned.
Another project which ran in to problems was the establishment of revolving funds on
village level from which farmers can borrow money to finance their biogas plant. The
repayment proved to be very difficult. The experience is that repayment is only satisfactory
when the beneficiary finds that his investment is income generating.
A technical set-back that was accountered by AFPRO is the strong nation wide promotion of
the Deenbandhu plants. Although this model has proven it's value at many places, in some
regions the quality of available building materials is not good enough to come to a reliable
result and other, now abandoned designs, would be more appropriate.
AFPRO now is favoring NGO's with an integrated approach, where biogas is one of many
activities aimed at improving the quality of life for rural people. Further more it was stressed
by AFPRO that NGO involvement can only be successful if there is a long term and stable
support programme which allows the involved organizations to build up their infra-structure.

TERI:
The Tata Energy Research Institute (TERI) is a non profit institution engaged in finding
solutions for India's energy problems. An important part of the activities is the analysis of
energy problems in the rural areas and the development of technologies to harness renewable
energy sources on a decentralized basis. In this respect research is done on solar energy,
biomass (gasification) and to a lesser extent biogas. Further more TERI takes care of
publications regarding the national biogas programme on behalf of MNES who funds these
activities.
There are no recent research activities as far as biogas is concerned. The studies shown 10 us
were related to the hydraulic retention time, the performance of spherical type plant, the
operation of a scum breaking mesh in dome plants and the performance of gas regulators on
dome plants. The youngest of these studies dates back from 1990. Non of the
recommendations from these studies has been adopted yet in the national programme,
according to TERI because of the lengthy procedures at the ministry. Annex 2 gives a
summery of the outcome of the above mentioned studies.
GUJARAT:
The schedule of the visit, transport and accommodation were (very well) organized by
Gujarat Agro Industries Corporation (GAIC).
After meeting with Major P.P. Kushare. the General Manager of the Energy Division of
GAIC. an excursion to MECH-CI-CO (P) Ltd. located in the industrial estate of Gujarat was
made. This company is the manufacturer of MARUTI biogas appliances and has earned a
reputation for it's innovating work on biogas appliances. Among others their products are:
- pressure regulators for dome type biogas plants
- automatic water removers
- main valves-emu reduction elbows
- single and double stoves
Specially the automatic water remover and the pressure regulators were of great interest and a
source of discussion between the visiting team including the GAIC GM and the producers.
Under laboratory conditions these items have proven their value, e.g. the pressure regulator
can lead to a considerable reduction in gas consumption (see annex 3). However the sustain
ability of such fairly complicated equipment when in use by untrained people in rural areas is
questionable.
GAIC has in the last year installed several thousands of these appliances and will keep a close
eye on their performance. Based on the information gathered by them, BSP can decide to
introduce this technology in Nepal on an experimental basis.

A tour through the MECH-CI-CO workshop and office showed that it is possible by means of
good management and skillful staff to cater with a small mechanical company for the
appliances needs of a large market.
GAIC:
The Gujarat Agro Industries Corporation Limited is an Gujarat State owned enterprise which
serves the Gujarati farmer through a wide range of activities. It sells and services agricultural
hardware such as tractors and other machinery. It gives advise on and provides fertilizers,
seeds, pest and decease control chemicals etc. Further more it buys, processes and markets
agricultural produce such as jams, fruit juices and vegetable oils. To accomplish its tasks
GAIC has 11 agro service centres, covering about 100 villages each, from where all activities
are executed.
The Gujarat Government has appointed GAIC as a nodal agency for the implementation of
the National Programme on Biogas Development (NPDB). For this it set up a separate energy
division with field level arrangements for the implementation of the programme. Specifically,
GAIC performs the following functions under its biogas programme:
1. Procurement, storage and distribution of construction materials and other inputs required
for biogas plant construction and maintenance.
2. Receipt and disbursement of subsidy to beneficiaries.
3. Training of masons, supervisors, motivators and users as well as arranging grants and
assistance for the same.
4. Publicity and promotion of the biogas programme
5. Post installation repair and maintenance
6. Coordination with MNES and the Govt. of Gujarat on one hand and a number of
implementing organizations like KVIC on the other.
Procedure:
The energy division of GAIC is using the corporation's infrastructure which was already well
developed before the biogas activities were launched. At every agro service centre a biogas
incharge is posted who, depending on the scale of their activities, has a number of assistants.
At village level young unemployed but educated people are selected and trained to become
Self Employed Biogas Supervisors (SEBS) or Turn Key Workers who are engaged in
demand collection and construction supervision. These people are not employees of GAIC
but work under the guidance and supervision of GAIC staff at the agro service centres. The
SEBS is paid a fee of IRs 300 for every plant constructed and for which he has to ensure
trouble free functioning of the plant for three years after the installation. During this
guarantee period it is obligatory for the SEBS to visit each plant at least once every six
months. As the plants are constructed in clusters in the area where the SEBS lives, this is a
rather simple task.

The construction work is carried out by trained masons. The masons are attached to a
particular NGO or SEBS. They are engaged on a daily wages basis (approx. Rs 400/plant)
and on average one mason can construct 25-30 plants/year.
After completion of a plant, the site is visited by a staff member of the agro service centre
who, when everything is found in order, issues a completion certificate. Up on this the SEBS
is paid his commission. For the control on the plants the GAIC staff is using a format
which enables them to spot common mistakes in a certain cluster of plants immediately (see
annex 4)
Furthermore, each constructed plant gets a specific code which is engraved on the inlet,
giving the year of construction, code number of the SEBS and serial number of the subsidy
register maintained at the agro service centre.
The farmer receives from GAIC a detailed instruction booklet on operation and maintenance
as well as two postcards to be addressed to the SEBS in case of any problem. If the problems
are beyond the capacity of the SEBS, he can call up on a mobile repair service who are well
trained and equipped with motorcycles. These mobile units are stationed at the service
centres. This set up has resulted in a rate of 95% of the plants build in operation.
Subsidy:
Besides the national subsidy provided through MNES, the Gujarat Government provides a
additional subsidy of IRs 1000/plant. The subsidy is partly provided before construction
commences in the form of building material such as cement, sand, bricks, gravel pipe and
pipe fittings and appliances, partly afterwards through payment of the SEBS and cash to the
farmer. The farmers contribution is on average approximately IRs 1000. GAIC favors this
system as it enables them to by-pass the banks. No pre-financing is necessary to start the
construction. This is speeding up the administrative procedures. GAIC also has the
experience that plants financed through bank loans are sometimes left unused even tough
they are in a good condition. This gives an excuse to the fanner not to repay his loan in the
hope that his debt will be written of this has happened hi the past as promotional stunt by the
ruling party during election campaigns.
Potential and Conditions:
The state of Gujarat has a very favorable environment for the implementation of a large scale
biogas programme. The climate is ideal, in fact while plants with a 40 days retention times
are build, the GAIC staff believes that a 30 day retention time would be sufficient for almost
complete digestion the whole year round. There are no difficult accessible areas and the state
has a very well developed roads infrastructure. The literacy rate is very high which makes
promotion, extension and training easy. An innovative and quality conscious manufacturer of
appliances with enough production capacity is located in Ahmedabad. Main' farmers are
organized in the more than 9000 Milk Producers Co-operative Societies. These societies run
their own veterinary services, provide the members with supplementary feed stock for their
cattle, etc. These co-operatives are a very good vehicle to reach the cattle owners. Further
more, through the dairy industry the farmers have a permanent source of income which

makes it easy for them to buy a biogas plant even without bank involvement. Last but not
least, the Gujarat Government has a long term commitment to the biogas programme which
materializes through the additional subsidy it provides.
GAIC considers a long term stable financial support programme essential for large scale
construction. Special programmes for scheduled casts and tribes, the poorer sections of
society, were seen as problematic and not very productive.
Out of the about 41 lakhs families owning cattle it is estimated that 20 lakhs qualify for the
construction of a biogas plant. More than 1.5 lakh plants have been constructed so far while
the annual building rate hovers around 30,000 units. A list showing district wise the
cattle population is given in annex 5.
Design:
To be able to implement their large scale programme, GAIC has opted for a single model
approach and virtually a single size as well. The Deenbandhu 2 m 3 plant has been found most
suitable for 80% of the households. Only for large families with many cattle, 3 m 3 plants can
be build. The advantages of this policy are:
- Easy to train technicians in construction, maintenance and repair
- Simplification of promotion materials
- Small number of different items that have to be kept in stock for construction
- Simplification of administration
- No over-sizing by "status conscious" farmers, by this approach GAIC has managed to
eliminate the problem of oversized plants.
On the standard Deenbandhu design the following modifications have been made:
- The brick work is 110 mm wide instead of 55 mm.
- The top section of the dome is casted concrete for properly securing the gas pipe.
- Every plant is fitted with a vertical mixing device.
- A small brick chamber is constructed directly after the outlet overflow from where the
farmer can remove slurry with a bucket to poor it on the traditional compost heap.
- No paint is used to make the dome gas tight, instead very good quality fine sand is used to
apply 3 coats of cement plaster.
Concluding Remarks:
The biogas programme in Gujarat is. because of its scale and success rate, very interesting for
Nepal Although the conditions are more favorable in Gujarat, there are still many experiences
which can be of use here. Technical aspects like use of more sophisticated appliances and/or
nylon appliances, slurry handling, etc. need to be studied further. Programme wise the
channeling of subsidy, single model limited size approach, training methods, collaboration
with agricultural NGO's and co-op's etc. are of interest. Therefore it will be very much
worthwhile to keep in touch with our Gujarati counter parts.

Annex 1

Residence Time Distribution Studies
of Biogas Digester Models
P. Raman, K. Sujatha, S. Dasgupta and V. V. N. Kishore
Tata Energy Research Institute, New Delhi
Annex 2
ABSTRACT
A tracer method has been employed for determining residence time distribution in
laboratory models of biogas plants. Plastic beads with density equal to that of dung slurry
have been used as" tracer material. The tracer concentration (No. of beads per unit volume of
slurry) in the output has been monitored following a pulse input. The residence time
distribution and the average residence time for a given model is thus experimentally obtained
for comparison sake.
INTRODUCTION
The hydraulic retention time (HRT) is a basic design parameter in constructing biogas
plants. HRT values of 35 - LOO days had been used for different climatic conditions. It is
widely known that HRT, which is related to the effective time spent by the slurry in the
digester, is a function of temperature. As a biogas plant is essentially a chemical reactor, it is
apparent that the effective residence time of the slurry in the reactor would also depend upon
the design of the reactor. The dependency of effective residence time on the geometry of the
digester has so far been not well investigated and except for the work of Hamad et al. [1],
there is no literature on the subject. Some laboratory models of fixed dome plants have been
studied for their residence time distribution (RTD) characteristics using a tracer method, and
in this paper preliminary results are presented.
EXPERIMENTAL
Selection of Tracer Material
Slurry sampled from different depths of two biogas plants installed in the village
Dhanawas, Haryana, was analysed for density. Spherical, plastic beads of density 0.941
gm/cc were ' manipulated by adding small quantities of M- seal so as.to make the density of
each bead equal to that of slurry. After sufficient number of beads were prepared, they were
mixed with the slurry and allowed to settle. Only those beads which are neither sinking to the
bottom nor floating to the top were selected for experimentation. .
Selection of Models
Two models of digesters, viz., (i) cylindrical and (Ii) spherical were selected. The
cylindrical digester has a diameter of 27 cm and a height of 13.5 cm so that the D/H ratio is
kept at 2.0.
© 1989, Solar Energy Society of India
Renewable Energy for Rural Development, Tata McGraw-Hill, New Delhi

The diameter of the spherical digester is 3 0 cm. The position of inlet is varied in .both the
models. In some experiments, the top of the digester was connected to an air compressor to
simulate conditions existing in the larger biogas plants. For the cylindrical digester the
variations tried were - (i) inlet at the bottom, outlet at the top, (ii) inlet, outlet at the same
level, and (iii) inlet, outlet at the same level and pressurising the digester, for the spherical
digester model, the variations tried were - (i) inlet and outlet at the same level, (ii) a baffle
incorporated in the centre and (iii) a diffuser incorporated at the bottom of the digester with
an inlet pipe connected to it; this was thought to produce near plug flow conditions (Fig. 1).
CYLINDRICAL DIGESTERS
ANALYSIS
Procedure for Determining RTD
The volume of slurry needed to fill the digester to the point of overflow from the
outlet was first obtained. This was divided by 50 so that the volume per feed is calculated.
Each feed will displace an equal volume through the outlet. The quantum of feed and the total
active volume of the digester correspond to the HRT of 50 days.

The digester was filled with slurry- A first charge of slurry mixed with about 150 -
250 beads was then fed into the reactor. This represents a pulse input of the tracer. The slurry
overflowing from the outlet was collected and sieved to note the number of beads present.
The next charge is fed and the out-flow was again collected and screened. This procedure is
repeated a number of times till almost all the beads come out of the digester. A plot of the
number of beads collected in a given out-flow against the serial number of the charge gives
the residence time distribution. The effective retention time (ERT) is calculated using the
equation
Effective Retention Time
where t i is the i th day and c i is the tracer concentration of that corresponding day and ∆t. is
the time interval between two measurements.
RESULTS AND DISCUSSION
The different geometries with their variations are schematically shown in Fig. 1. The
residence time distribution curves along with cumulative curves are given in Figs 2 and 3. A
summary of the results is given in Table 1. The main conclusions, which are bound to be
tentative considering the preliminary nature of the present experiments are as follows:
1. The effective retention time is considerably less than the hydraulic retention time for
most of the cases considered. A similar conclusion for the Chinese type fixed dome
plant was obtained by Hamad et al. (1).
2. Introduction of a baffle with a view to increasing the residence time was found to be
not effective.
3. The method of removing the slurry from outlet - either by simple overflow or by
pressurisation (as occurring in actual larger plants) does not affect the residence time
distribution significantly.
4. It appears that a bottom inlet with horizontal injection by means of a diffuser gives the
highest effective residence time.
The last conclusion mentioned above is significant because it provides a way of
achieving near plug flow conditions in the digester in a simple way. Further experimentation
is under way to firm up this conclusion as well as to refine the experimental methods and to
extend the study to other reactor designs.

Table 1: Details of the Experiments and Results
Expt.
Type of
Position of
Beads
Beads
Design-
Effective
No.
Digesters
Inlet and Outlet
In
Out
ed HRT
HRT
1. Cylindrical I.L at the bottom O.L at the top 129 127 50 32
2. Cylindrical I.L and O.L. at the same level 165 160 50 29
3. Cylindrical I.L and O.L. at the same level 150 149 50 30
(Ex. with pressurizing)
4. Spherical Without baffle 200 187 50 25
5. Spherical With baffle 200 186 50 20
6. Spherical Inlet with Diffuser 250 242 50 42
I.L-Inlet, O.L-Outlet
REFERENCES
1. Hamad, M.A., Abdel, A.M. and Ei Halwagi, K.M., Pilot Plant Laboratory, N.R.C.,
Dokkai, Cairo (Egypt), 19S2.
2. Kishore, V.V.N., Raman, P. and Kanga Rao, V.V., Fixed Dome Biogas Plants - A
Design, Construction and Operation Manual, TERI Publication, 1987.
3. Ludwig Sasse, Biogas Plants, GATE, 1984.

A Gas Regulator for Fixed Dome Biogas Plants
Dome Biogas Plants
V.V.N. Kishore, Sunil Dhingra ∗
Abstract
An LPG regulator was tested for its suitability for controlling the pressure and flow
rate of biogas from fixed dome biogas plant. Though the operating characteristics of the LPG
regulator are not ideally suited for biogas applications, it was found that some degree of
control could be achieved. Thermal efficiency measurements on the biogas burners showed
that there was improvement in thermal efficiency by about 56% when a regulator was
incorporated. However, the thermal efficiency improvement was associated with a reduction
in thermal power of the burner.
Introduction
Fixed dome biogas plants are characterized by a varying gas pressure, upto 100 cm
water gauge, in contrast with K.VIC type biogas plants which deliver gas for utilization at a
constant pressure of about 7.5 cm water gauge. As most of the biogas appliances such as
burners, lamps etc. are usually designed and standardized to perform optimally at a given
pressure, it should be expected that these devices would not be performing optimally on a
continuous basis when used in conjunction with fixed dome plants. In fact, it has been
reported [I] that the thermal efficiency of domestic burners connected with fixed dome biogas
plants is much below the 55% mark recommended by KVIC and BIS (Bureau of Indian
Standards). The Indian Standard specification for Biogas Stove (IS : 8749 I9iii) stipulates that
the inlet gas pressure should be constant at 747 N/ m 3 (7.6 cm WG) while testing the stoves.
There is no need to stress the importance of appliance efficiency in the context of the overall
economics of biogas utilization. It has been shown [2] that the levelized annual cost of
thermal energy can be reduced from a value of 0 69 Rs/ kWh(th) to 0,53 Rs/kWh(th) by
improving the burner efficiency, resulting in an effective cost reduction of 23%. However, it
is a difficult proposition to design a stove which can operate at a constant, high thermal
efficiency over a range of inlet pressures and hence over a range of gas flow rates. A simpler
thing would be to incorporate a pressure regulator in the gas stream so that Die inlet pressure
and flow rate would be kept nearly constant, throughout the period of use.
In the present work, at attempt bas been made to improve the performance of biogas
stoves by incorporating an ordinary LPG regulator in fixed dome biogas plants, with lie
ultimate aim of designing a suitable regulator for use with fixed dome plants.
Operating Characteristics of an LPG Regulator
∗ Tata Energy Research Institute, 232 Jor Bag New Delhi 110003.

The specifications for low pressure regulators for use with Liquified" Petroleum Gas (LPG)
mixtures are laid down in the Indian Standard IS: 9798-1981. According to these
specifications, the regulator outlet pressure should be 30±0.5 g/cm 3 (29.5—30.5 cm water
gauge) when the inlet pressure is kept at 7.0 kg/cm 8 . Also, the outlet pressure should not be
less than 22 5 g/cm 3 (22.5 cm WG) nor more than 40 g/cm 3 (40.0 cm WG) when the inlet
pressure varies from 0.5 kg/cm 3 to 17 kg/cm 3 . The standard rated capacity for LPG regulators
for domestic use is upto 500 litres/hr.
From the above specifications, it is apparent that the inlet pressure range for LPG
regulators is much higher than that encountered in biogas plants, viz 0.100 cm WG. However,
it was decided to study the characteristics of the LPG regulator at inlet pressure below the
specified lower limit to see if it would be suitable for biogas application. The inlet pleasure,
outlet pressure and ihe flow rate have been measured over a wide range using both
compressed air and biogas. A plot of flow rates vs. inlet pressure is shown in Fig. 1 (a) and a
plot of outlet pressure vs. inlet pressure is shown in Fig. 1(b). Figure l (a) shows that the flow
rate is constant at about 500 lit/hr even at inlet pressure as low as 100 cm WG, which is much
lower than the stipulated lower limit of 500 cm WG. Figure 1 (b) shows that the outlet
pressure is constant at about 31 cm WG when the inlet pressure is reduced right down to
about 60 cm WG. When the inlet pressure is reduced below 100 cm WG, there is a sudden
drop in flow rate, followed by an almost linear variation with inlet pressure. The flow rate
varied between 240—250 litres/hr for inlet pressure variation of 30—100 cm WG- The gas
flow rate recommended for domestic biogas burners is between 200—450 litres/hr [3], A
similar trend can be seen in the outlet pressures, which varied from 7,5—15.0 cm WG. Thus,
it is apparent that the LPG regulator, though not designed for use with biogas, might be
suitable, in a limited sense, to biogas applications. Hence it has been decided to install a LPG
regulator on an actual biogas plant and conduct some tests on thermal efficiency in the field
Thermal Efficiency Measurements
The thermal efficiency tests have been carried out in the village Dhanawas in
Haryana, where TERI had constructed seven fixed dome biogas plants of various designs [4].
The plants are in regular use and all except one have a rated capacity of 2m 8 . The procedure
outlined in Indian Standard IS : 8749—1988 has been followed for evaluating the thermal
efficiency. Briefly, water is heated from ambient temperature to about 95°C in aluminium
pots and the gas consumption is measured by means of a wet flow meter. The thermal
efficiency is given as
where
µ=thermal efficiency of the burner in percent
G=quantity of water in the vessel in kg
W=water equivalent of the vessel with lid
T a —final temperature of water in °C

T 1 = initial temperature of water in °C
V=gas consumption in m f and H=calorific value of gas in kcal/.m 3
The calorific value of the gas is taken as 4700 kcal/m 3 . The initial and final inlet
pressures and the time taken for the test have also been noted down. Tests have been
conducted with and without the regulator and on two different plants. The results of thermal
efficiency tests are summarized in Table 1. The average thermal efficiency without the
regulator was about 30.8% and the average thermal efficiency with regulator was about
48.0%, showing an improvement in efficiency by about 55.8%. It can thus be seen that using
a regulator for fixed dome biogas plants is indeed beneficial from thermal efficiency point of
view.
Discussion
An examination of Table 1 reveals that the thermal efficiencies are ' generally lower
when the gas flow rates are higher. The gas flow rate is a ' direct measure of the burner
thermal power, given by the equation
where
P=Power, kW
V=Gas flow rate, m 3 /hr
H=Calorific value of gas, kcal/m 3
In order to sec if there is a correlation between thermal efficiency and power, YJ is
plotted against P for all the experiments conducted, as shown in Fig. 2. It can be seen from
this figure that the thermal efficiency drops significantly with increase in power. A similar
correlation seems to .exist for wood burning stoves also [5]. This means that the efficiency of
the burner can be increased only by decreasing the power of the burner. It fact, for domestic
biogas burners, the gas flow rates are typically 450 litres/hr (large) and 225 lit/hr (small),
corresponding to power levels of 2 46 kW and 1.23 kW respectively. A report of KV1C states
that a thermal efficiency of 59.5% could be obtained, but the corresponding power was 1.61
kW. These figures indicate that biogas burners are designed to operate efficiently only at low
power levels- However, the desirable power levels for cooking applications seem to be
higher. The power levels for

LPG stoves are typically between 4.4-7.6 k\V. The time taken for cooking is inversely
proportional to the burner power, and hence laying emphasis only on thermal efficiency may
not be entirely desirable. In fact, a few modifications had to be effected in the LPG regulator
resulting in a higher gas flow rate, following complaints from the user that (he time taken for
cooking has increased after installing the regulator. The problem of optimal utilization of
biogas from fixed dome plants thus essentially boils down to the optimal design of the total
system consisting of regulator and burner such that thermal efficiencies of the order of 55%
are achieved with power levels of 4 - 6 kW. Work is in progress to design a regulator
specifically for biogas used and to design an efficient biogas burner for high power levels
Conclusion
An LPG regulator was tested for its use with fixed dome biogas plants in order to control the
gas pressure and flow rate. The regulator was found to be suitable, in a limited sense, for
biogas applications. Measurements showed that the thermal efficiency of the biogas burners
improved significantly when a regulator was incorporated. The improvement of thermal
efficiency, however, was associated with a reduction of burner power.
Acknowledgements
The authors are grateful to Mr. Shishupal Sharma, Mr. Manjit Siogh, Mr, Guruvinder Singh
and Mr. Vellaikkannu for their help in experimental work.
REFERENCES
V.V.N. Kishore, P. Raman and V.V. Ranga Rao, "The Biogas System for Cooking Energy
Production—Is it more efficient ?'\ Biogas Forum, No 32/.9S8, BORDA, Bremen,
FRG.
V.V.N. Kishore, "Cooking Energy Systems—A Comparative Study", Energy Policy Issues.
Vol. 4 (1988). (tds) K.K Pachauri and Leena Srivasuva, Tata Energy Research
Institute, pp. 37-46, 1989.
V.V.N. Kishore, p. Raman and V.V. Ranga Rao, "Fixed Dome Biogas Plants—A Design,
Construction and Operation Manual", Tata Energy Research Institute, 1987.
V.V.N. Kishore, P. Raman and V.V. Ranga Rao, "Fixed Dome Biogas Plants Developed by
TERV, Rural Technology Journal, pp. 26-40, . September 1987.
Veena Joshi, Chandra Venkataraman and Dilip R. Ahuja, "Emissions ' from Burning Biofuels
in Metal Cookstoves", Environmental Management, Vol. 13, No. 6, 1989.

TABLE 1
Summary of Thermal Efficiency Tests
S. No. Initial Final Power Time Gas Av.
Pressure Pressure Taker. Consumed Rate
(cm WG) (cm WG) (kW) (min.) (lit) (lit/hr) (%)
Experiments Without
Regulator
1. 60.0 41.0 5.7 14 243.0 1041.0 28.7
2. 28.0 12.5 3.4 19 197.1 622.0 34.5
3. 21.5 9.0 2.5 26 19S.0 457.0 29.4
4. 38.5 22.0 3.4 21 216.6 619.0 30.4
Experiments with Regulator
70.0 60.0 1.8 28 153.2 328.0 46.8
37.5 28.0 1,3 33 127.5 232.0 56.3
28.0 21.5 1.4 31 132.0 255.5 42.7
48.0 38.5 1.8 26- 145.5 336.0 46.0
List of Figures
Figure 1 : Performance characteristics of LPG regulator.
Figure 2 : Efficiency—power relation for biogas burners.

Design and Performance of Spherical Type Biogas Plants
P Raman, R C Pal and V V N Kishore
Tata Energy Research Institute
232 Jor Bagh
New Delhi 110 003
Abstract
A spherical" -'type biogas plant had been developed taking into consideration the
drawbacks and problems associated with existing fixed dome biogas models.
The new design of spherical type biogas plant has several advantages such as lesser
chance of dome failure, increased gas storage space, etc. The slurry inlet is located in such a
way as to ensure that the effective HRT will be closer to the design HRT, which is not the
case with the existing biogas plant models.
A detailed procedure for calculating the dimensions of all the components of spherical
type biogas plant is presented along with the field level gas production data of a 2 m biogas
plant. The performance of the new model is compared with that of existing models.
Introduction
Fixed dome (Chinese) models of biogas plants are built in various shapes. While the
Janata model uses a combination of cylindrical and spherical shapes, the Deenbandhu model
is a combination of two spheres of different diameters. However, from materials
consideration; it is desirable to have a completely spherical shape as this geometry offers the
lowest surface area per unit volume.
It has been shown [l] that the location and mode of slurry inlet has an important
bearing or. the effective HRT of a biogas plant. The effective HRT of both KVIC and Janata
models is much less than the design value, as shown by studies on residence time distribution
[2]. From consideration of material optimization and residence time distribution and from
practical considerations of field level problems such as choking of gas lines with slurry in
winter, under-utilization of biogas, etc. TERI evolved a spherical model biogas plant. Though
the first plant with spherical design was built in 1987 in the village Dhanawas in Haryana,
efforts were made to gradually improve the plant design in each subsequent plant built, and
the model described in this paper has been now standardized to a large extent.
Method of Designing the Plant
The biogas plant consists of i) the digester, ii) inlet, iii) outlet and iv) other accessories.
The digester in turn consists of active slurry volume, gas storage space (slurry
displacement volume) and a 1 buffer space' to prevent entry of slurry into the gas line. A
schematic diagram of the plant with relevant parameters is shown in Figure 1. Referring to

Figure 1, the radius of the plant is R. and h 1 is the distance between the gas outlet (at the top
of the sphere) and the slurry exit level of the outlet tank. h 2 is the distance between the gas
outlet and initial slurry level in the biogas plant (slurry level at nil pressure). h 3 is the distance
between the gas outlet and the final slurry level in the digester {slurry level at full pressure).
V 1 is the volume of buffer space provided' in the dome to accommodate any
volumetric increase in slurry space. V 2 and V 3 are volumes of the spherical segments
corresponding to heights h 2 and h 3 .
The equations relating the different volumes to heights are:
V 1 = (π/3) h 2 (3R-h 1 ) ... (1)
V 2 = (π/3) h 21 (3R-h 2 ) ... (2)
V 3 = (π/3) h 2 3 (3R-h 3 ) ... (3)
The volume of slurry displaced within the digester is equal to the volume of slurry
displaced in the outlet tank. If Ao is the cross sectional area of the outlet tank, we have
(V 3 -V 2 ) = Ao x (h 2 -h 1 ) ... (4)
Field experience indicated that the gas storage space be as high as possible from user
preference point of view. A large gas storage space also ensures maximum utilization of gas.
Earlier TERI models [3] used about 40% of the design daily gas production as storage space,
but in the present model, a value of 60% is taken. If G is the design daily gas production, we
have
(V 3 -V 2 ) = 0 . 6 G ... (5)

The minimum pressure of the gas was selected to be 0.5m of water column and as the
density of -the slurry is only marginally higher than that of water, one can write
h 3 - h 1 > 0.5 ... (6)
Field experience showed that a maximum of about 1 ft. (0.3 m) clearance- has to be provided
between the points of slurry exit and gas exit in order to solve the problem of gas line
choking effectively. Hence we get the condition
h 1 = 0.3 ...(7)
The plant is designed to have a 40 day HRT and it can be shown that assuming a
specific gas production of 40 lit/kg dung and a dilution of 1:1 for slurry, the active slurry
volume is equal to 2G. Hence one can write
(4/3) πR 3 - V 3 = 2G ... (8)
The above set of equations have been solved using the software EUREKA. Dimensions for
1,2,3,4 m 3 plants are given in Table 1.
Table 1: Relevant Dimensions for Various
Components of Biogas Plants
S.
No.
G R h 1 h 2
1 1 0. 98 0.30 0.78 0. 98 1. 24
2 3 1.16 0.30 0.78 1.07 2.52
3 3 1.34 0.30 0.83 1.17 3.38
4 4 1 .43 0 .30 0 .70 1.14 5.93
h 3
Ao
The lateral dimensions of the outlet tank are chosen in such a way that length to
breadth ratio is 2. Thus, if b is the breadth, length is 2b and b can be obtained as:
b = √(AO/2) . . . (9)
A cylindrical mixing tank. with volume slightly larger than the daily slurry input is
also provided. A vertical axis stirrer made with MS reds and bars is also provided in the
mixing tank, and it was noticed that there was a significant difference in gas outputs for
mechanically stirred vs. manually mixed slurry. The users also preferred to have a mechanical
stirrer.
The inlet pipe is installed in such a way that the fluid path is reversed when exiting

into the digester. The pipe is tangential to the cross section of the digester and the discharge
end of the pipe is surrounded by a small Ferro cement box open on one side.
While charging, the slurry will impinge on one side of the box, flow is reversed and
the slurry exits in the opposite direction through the opening in the box. This method of
charging was thought to provide lesser dead volumes, lesser short circuits and a better
residence time distribution resulting in a higher effective residence time. The actual plant
dimensions with the above mentioned slurry inlet arrangement are shown in Figure 2.
Constructional Features
The entire plant is constructed with a single dimension and hence the time for construction
is lesser. The hook method [4] is used for construction. Cicco is used to facilitate faster
setting of mortar during construction. An extra layer of tiles is provided in the gas storage
space to almost eliminate the chances of dome cracking. A combination of cement primer and
paint is used for making the gas space leak proof. A ball valve is used instead of gate valve to
minimize recurring expenses. Stone slabs are used for covering the outlet tank.
Performance of the Plant
The daily gas production values as measured by a wet type gas flow meter are shown in
Figure 3 for the period of 1st October - 30th November 1991. The monthly average values in
the units of m 3 /(m 3 )(day) for the spherical plant are shown in Figure 4 for the months of
October 1991 and November 1991 along with those reported [5] for Janata and Deenbandhu
models. It is apparent that the gas production values are highest for the model described in
this paper.
Financial Consideration
The cost break-up for a 2 m 3 plant of spherical model is shown in Table 2 along with that for
Deenbandhu model. It can be seen that the cost of the spherical model is roughly the same as
that of Deenbandhu model.
Conclusions
Design and performance details of a spherical model biogas plant are described in this paper.
The advantages of the spherical model are i) very low chances of dome cracking, ii) absence
cf problems such as choking of gas lines, iii) higher gas storage space and hence better
utilization of gas and iv) higher gas production rates. Considering that the spherical model
costs about the same as Deenbandhu model but yields higher quantities of gas, the overall
economics of the spherical model are much better.
Acknowledgment
There are several people who have contributed to the evolution of field activity in biogas
within TERI . Notably, Mr. V.V. Ranga Rao and Ms. Sangeeta Kohli were involved to a large
extent in the initial developmental and extension activities. Mr. Shishupal Sharma helped in
collecting field level gas production data. Planning and coordination of activities in the

villages Dhanawas and Berka Alimuddin were done by Dr. Veena Joshi. The help provided
by Suresh and Mr. B N Mishra is sincerely appreciated. Finally, the authors are grateful to
Dr. R K Pachauri for his encouragement throughout the work.
Table 2: Material Requirement and Cost Break-up
for 2 m 3 Biogas Plant
Material Unit Unit Quantity
Cost
Cost
Deen*- Spheri- Deen- Spheribandhu
cal bandhu cal
1 Bricks Rs/1000 1050 1000 1200 1050 1260 -
2 Tiles Rs/1000 1050 300 315
3 Cement Rs/Bag 105 14 11 1470 1155
4 St. Chips Rs/Cft. 4 40 3 160 12
5 Sand Rs/Cft. 3 40 75 120 225
6 CO. Sand Rs/Cft. 3 40 120 0
7 GI Pipe Rs/Foot 25 0.7 1 18 25
8 AC Pipe Rs/Foot 15 6 12 90 180
9 OL Slab Rs/Sq. m. 100 2 0 200
10 MS Bar Rs/KG 20 7 2 140 40
11 C Primer Rs/Lit. 60 1 0 60
12 Cicco Rs/Lit. 30 3 0 90
13 Paint Rs/Lit. 60 1 1 60 60
14 Lab (Dig) Rs/M Day 35 1.0 10 350 3 50
15 Mason Rs/M Day 90 11 8 990 720
16 Lab (Con) Rs/M Day 40 22 16 880 640
17 Misls ----- 300 1 1 300 3 00
18 Stirrer ----- 150 - 1 0 150
19 Ball Valve 67 - 1 - 67
20 Gate Valve 85 1 - 85 -
21 Burner + pipe 700 1 1 700 700
line system
TOTAL 6533 6 54 9
Source: Manual on Deenbandhu Biogas Plant, by J 3 Singh et al,
Tata McGraw Hill Publishing Company Ltd., New Delhi
References
[1] P Raman, K Sujatha, S Dasgupta and V V N Kishore, "Residence Time Distribution
Studies in Non-continuous Flow UN-stirred Tank Reactors with Reference to Biogas
Digesters", SESI Journal, Vol. 3, No.2, pp. 1-12, 1989.

[2] M A Hamad, A M Abdel and M M Ei Halwagi, "Evaluation of the Performance of Two
Rural Biogas Units of Indian and Chinese Design", Energy in Agriculture, Vol.1, Issue
No. 3, pp. 235-250, l983.
[3] V V N Kishore, P Raman and V V Ranga Rao, "Fixed Dome Biogas Plants Developed by
TERI", Rural Technology Journal, pp. 26-40, September 1987.
[4] V V N Kishore, P Raman and V V Ranga Rao, "Fixed Dome Biogas Plants - A Design
Construction and Operation Manual", TERI, New Delhi, 1987.
[5] R Myles and A Dhussa, "Comparison of Performance of Janata and Deenbandhu Biogas
Plants, Paper presented at the National Solar Energy Convention, New Delhi, India.

* MARUTI BIOGAS PRESSURE REGULATOR *
Biogas Pressure Regulator reduces the plant pressure up to 3" of W/C and delivers the gas to
the appliance at this constant value when stove is in ON position. Plant supp1y pressure will
go on reducing continuously when the gas is consumed. When the plant pressure drops to the
value of 3" of W/C, the regulator automatically stops its working and thereafter the delivery
pressure will be the same as the plant supply pressure. To some extent regulation of the gas
consumption can be done by taking care continuously and operating the gas tap of the stove.
But the people would never bother about this and they never take car& to operate the tapwhatever
the instruct ions passed to them, and hence this Biogas Pressure Regulator is very
essential to be installed on the supp1y 1ine in the kitchen near the stove, and the consumer
will never to bother to operate anything by very nominal cost.
In fixed dome type of plants very high pressure is deve1oped and we can't get the supp1y at
constant pressure. When 6 Cmt. capacity Dinbandhu type of plant is full of gas, the maximum
plant pressure developed is 30" of W/C and it goes on reducing up to zero when the gas is
consumed continuously and the plant is emptied. For different capacities of Dinbandhu type
of plant the design of permits the maximum pressure to be developed as follows. . .
Capacity in Cmt.
Maximum Pressure Developed
Cms. of W/C
inches of W/S
1 45.00 17.71
5 57.50 22.63
3 63.00 24.80
4 70.00 97.55
6 75.00 29.50
All the Biogas appliances are designed to operate at 3" of W/C. pressure. That means at that
particular pressure only the maximum Thermal Efficiency of the appliance can be achieved,
and at that pressure only the consumption of the gas will be as per its rated capacity as printed
over the name plate of the appliance. We have mentioned earlier that by experiments we have
concluded that consumption rate is about 40 % higher if the delivery-pressure to the
appliance is daub led up. Hence at a very high consump11on rate we suffer a great loss of
fuel as the size of the burner is insufficient to burn complete gas entering into it due to
improper air-fuel ratio and insufficient opening area of holes. Thus when we operate the
appliance at higher rate of consumption than its rated value, part of the gas volume escapes in

the kitchen atmosphere quite unburnt. As a result of that, gases like carbon dioxide, carbon
monoxide and methane which are hazardous to human 1ife are spread in kitchen atmosphere.
Means we not only lose the utility of valuable fuel, but adds the pollution in kitchen which
proves nonhygenic.
The installation of a Biogas Pressure Regulator solves all these problems as it delivers the gas
at required pressure only to the appliance.
In order to find out that how much fue1 can be saved by using a Pressure regulator, we
carried out -six thermal efficiency tests on 2 cmt. Dinbandhu plant at different delivery
pressure without using pressure regulator. The thermal efficiency tests were carried out as per
the procedure laid down by B.I.S. in IS:8749. The connections of the equipments are shown
on a Separate Sheet No. 1, Diagram No, 1 - Observations, readings and calculated results are
shown in Separate Sheet No. 2 in a tabular form.
We also carried out three Thermal Efficiency tests at different supply pressure, but at a
constant delivery pressure of 3" of W/C with a use O-F a pressure regulator to get the
maximum Thermal Efficiency, The connections of equipments are shown in a Separate Sheet
No. 1 Diagram No. 2. The results are recorded in a tabular form in Sheet No. 3. Dry type gas
flow meter was used in both the cases. The flow meter was caliberated precisely using a very
accurate wet type gas flow meter in laboratory. 151 marked Single Burner Cock stove having
rated capacity of 450 1/h et S.T.P. was used for all the tests,. the methane content of the gas
was 55 % and the colorific value of pure methane is taken 8 Kcal/litre at S.T.P.
From the reading available for above nine tests, we plotted following graphs.
(1) Average delivery pressure v/s Thermal Efficiency. (Graph No. 1)
(2) Average delivery pressure v/s Rate of Consumption. (Graph No. 2)
In full utilisation of gas in a fixed dome type of a plant percentage saving due to the
presence of regulator can be found out from Graph No. 1 by finding the Thermal Efficiency
at Average pressure
and
% saving for that particular plant can be arrived by using formula given below.
Percentage Saving in different capacity Dinbandha plant is shown in tabular form on Graph
No. 1 itself.
From the above table it is quite clear that higher the plant pressure, the percentage saving of
the gas is more. Means higher the plant capacity, the percentage saving of the gas is more,
because maximum pressure that can be developed in higher capacity of plants is higher as per
design of the plants.

A comparison table of different capacity of Dinbandhu plants is given below.
Size of plant in Cmt. 1 2 3 4 6
1. Gas Holding capacity in ltrs.- 330.00 666.00 1000.00 1235.00 2000.00
2. Average working pressure in - 10.35 12.80 13.90 15.27 16.20
inches of W/C.
3. Corresponding Consumption - 865.00 980.00 1025.00 1085.00 1120.00
rate in 1/h at ambient cond.
4. Total running time of the - 22.89 39.27 58.53 68.29 107.14
regulator in minutes.
5. Total running time of the - 44.00 88.80 133.33 164.66 266.66
plant with the use of a regulator
in minutes.
This shows that running time of the plant is more than two times if regulator is used and
delivery pressure is maintained constant 3" of W/C.
As conclusion we can say that the advantages of using a Biogas Pressure Regulator are as
follows.
(1) There is a very considerable saving of gas depending upon size of the plant and
that saving is from 22 % to 42%.
(2) Running time of the plant is more than two time5, and hence enough time is available
for cooking before the gas is exhausted.
(3) Life of appliance is increased, because gas taps of the appliance are not getting
jammed. This is because of sudden pressure drop because of the presence of
Regulator, water vapour on verge of condensation gets completely vepourised, and
passes through tap in complete gaseous form at low velocity. Otherwise gas
containing vapour in semi 1iquid state at very high pressure washes away the
lubricants applied on the tapered plug of the tap, and in very short period taps get
jammed.
(4) We do not have to set air shutter every now and then.
(5) Pollution is reduced to minimum.
(6) KVIC type of plant can deliver the gas at constant pressure, but the installation and
maintenance cost of KVIC type of plants is very very high as compared to that of
fixed dome type of plant of the same capacity. Hence by installing a pressure
regulator on fixed dome type of plant at a very nomincal extra cost, the benefits of
both the types can be availed.
(7) Because of high saving of the gas, a fixed dome type of plant of a smaller capacity
can be installed for the same requirement of the gas during a day. That will again
reduce the installation cost of the plant being of a smaller capacity. Hence with the
same funds available for biogas activity, more number of plant can be installed.

Annex 4

Sr.
No.
District
POTENTIAL IN GUJARAT
Cattle
population
(in lacs)
Milk
producer
Co-op.
Soc.
Member
of Milk
Producers
Co-op.
Societies
('000 Nos
Potential
1. Jamnagar 4.92 30 1 49,200
2. Rajkot 6-73 423 27 67,300
3. Surendranagar 3.95 323 21. 39,500
4. Bhavnagar 6.55 219 15 68,500