Report Biogas Study Tour to New Delhi and Gujarat, India 20 ... - SNV
Report Biogas Study Tour to New Delhi and Gujarat, India 20 ... - SNV
Report Biogas Study Tour to New Delhi and Gujarat, India 20 ... - SNV
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<strong>Report</strong><br />
on<br />
<strong>Biogas</strong> <strong>Study</strong> <strong>Tour</strong> <strong>to</strong> <strong>New</strong> <strong>Delhi</strong> <strong>and</strong> <strong>Gujarat</strong>, <strong>India</strong><br />
<strong>20</strong> - 28 September, 1995<br />
<strong>Biogas</strong> Support Programme:<br />
Jan Lam<br />
Ravi B. Chettri<br />
Saroj Kumar Shrestha<br />
Ang Rinji Sherpa<br />
Roop Singh Thapa<br />
December, 1995
<strong>Tour</strong> schedule:<br />
Wednesday <strong>20</strong>/09/1995:<br />
Afternoon flight from Kathm<strong>and</strong>u <strong>to</strong> <strong>New</strong> <strong>Delhi</strong>.<br />
Thursday 21/09/1995:<br />
Visit <strong>to</strong> the Ministry of Non-Conventional Energy Sources in <strong>New</strong> <strong>Delhi</strong>. Meetings with<br />
Dr. Kh<strong>and</strong>elwal (Advisor <strong>to</strong> the Ministry) <strong>and</strong> Mr. Anil Dhussa, Direc<strong>to</strong>r of the <strong>Biogas</strong><br />
Department.<br />
Friday 22/09/1995:<br />
Meeting with Mr. Mark Paul, Energy Specialist of Action For Food Programme (AFPRO).<br />
Meeting with Mr. P. Raman at the Tata Energy Research Institute (TERI).<br />
Saturday 23/09/1995:<br />
Cultural excursion <strong>to</strong> Agra, visiting the Taj Mahal <strong>and</strong> Red Fort.<br />
Sunday 24/09/1995:<br />
Morning flight <strong>to</strong> Ahmedabad (<strong>Gujarat</strong>). Meeting with Major P.P. Kushare, General Manager<br />
of the Energy Division of <strong>Gujarat</strong> Agro Industries Corporation Limited (GAIC). Visit <strong>to</strong><br />
Mech-ci-co, an engineering <strong>and</strong> manufacturing company of biogas appliances like various<br />
sized burners, pressure regula<strong>to</strong>rs, au<strong>to</strong>matic water removers <strong>and</strong> valves.<br />
Monday 25/09/1995:<br />
Morning visit <strong>to</strong> the GAIC Energy Division Head-Office for a briefing on the<br />
Organizational set-up of the Corporation.<br />
Afternoon field visit <strong>to</strong> a near by village, observing biogas plants in various stages of<br />
construction <strong>and</strong> newly completed plants.<br />
Tuesday 26/09/1995:<br />
Excursion <strong>to</strong> GIAC Service Centre in Mehsana. Discussions with the centre's staff <strong>and</strong><br />
field visit <strong>to</strong> a cluster of older plants.<br />
Wednesday 27/09/1995:<br />
Morning site-seeing of Ahmedabad <strong>to</strong>wn. Afternoon final discussion with GAIC GM.<br />
Thursday 28/09/1995:<br />
Morning flight from Ahmedabad <strong>to</strong> <strong>New</strong> <strong>Delhi</strong>. Afternoon flight from <strong>New</strong> <strong>Delhi</strong> <strong>to</strong><br />
Kathm<strong>and</strong>u.
Introduction:<br />
An biogas observation <strong>to</strong>ur <strong>to</strong> <strong>India</strong> for BSP technicians was scheduled the first quarter of the<br />
FY <strong>20</strong>52/53. The aims of the <strong>to</strong>ur were:<br />
- <strong>to</strong> give the BSP staff a possibility <strong>to</strong> be able <strong>to</strong> look at their own work from some distance<br />
by observing other biogas programmes <strong>and</strong><br />
- <strong>to</strong> learn about new idea's on technical items, extension <strong>and</strong> promotion, slurry use, NGO<br />
involvement, subsidy etc.<br />
<strong>India</strong> was chosen <strong>to</strong> be visited because it is near <strong>to</strong> Nepal, its vast biogas programme <strong>and</strong> the<br />
useful relations that were already established between the Ministry of Non-Conventional<br />
Energy Sources (MNES) in <strong>New</strong> <strong>Delhi</strong> <strong>and</strong> BSP.<br />
<strong>Gujarat</strong> was recommended by the above mentioned ministry as an interesting state <strong>to</strong> visit<br />
because of the impressive quantity <strong>and</strong> quality of then- biogas programme. A visit <strong>to</strong> <strong>New</strong><br />
<strong>Delhi</strong> was included in the trip <strong>to</strong> allow for discussions with representatives from MNES,<br />
Action For Food Production (AFPRO) <strong>and</strong> the Tata Energy Research Institute (TERI).<br />
Both aims of the <strong>to</strong>ur have been achieved. For this we owe our gratitude <strong>to</strong> Mr. Anil Dussa<br />
who arranged the <strong>to</strong>ur in <strong>India</strong> <strong>and</strong> specially <strong>to</strong> Major P.P. Kushare <strong>and</strong> his staff of <strong>Gujarat</strong><br />
Agro Industries Corporation (GAIC) who through their hospitality <strong>and</strong> openness made the<br />
journey <strong>to</strong> <strong>Gujarat</strong> a very rewarding experience.<br />
MNES:<br />
The direct charge for this Ministry lies with the Priminister of <strong>India</strong>. This fiscal year a<br />
<strong>to</strong>tal of IRs. 245 crore is allocated <strong>to</strong> the Ministry from the national budget of which 60<br />
crore is earmarked for the biogas programme. <strong>Biogas</strong> has <strong>to</strong> compete for a slice of the<br />
Ministerial cake with programmes like wind energy, biomass (gasification) <strong>and</strong> solar<br />
energy.<br />
A disadvantage of this system is that biogas is only judged on its energy values. Other<br />
benefits of biogas <strong>to</strong> the society, specially in regard <strong>to</strong> other energy carriers, like<br />
production of organic fertilizer <strong>and</strong> improved health are not taken in <strong>to</strong> account <strong>and</strong> thus<br />
no funds for the promotion of these aspects are available.<br />
Out of the biogas budget the national subsidy scheme is funded which amounts <strong>to</strong><br />
approximately 60% of the <strong>to</strong>tal budget. The remaining 40% is used <strong>to</strong> fund a training<br />
centre in every state (5 lakh/centre), for the development of training <strong>and</strong> extension<br />
material, for trainings <strong>and</strong> for special programmes in regions where the biogas technology<br />
fails <strong>to</strong> become popular. Such programmes can be cash prizes for model fanners with well<br />
maintained plants, well published visits <strong>to</strong> biogas programmes by dignitaries etc.<br />
Every third year the Ministry conducts an extensive nation wide survey in which 10,000<br />
plants are sampled. Depending on the outcome of this survey, modifications are made in<br />
the plan of action.<br />
Annex 1 gives the structural set up of the biogas division of MNES.
AFPRO:<br />
Action For Food Production (AFPRO) is a NGO since long active in the diffusion of biogas<br />
technology in <strong>India</strong>. They act as an support body for grassroot NGO's active in this field.<br />
Presently some 62 organizations are actively involved. Some of the support activities<br />
undertaken by AFPRO are:<br />
- Organization of an annual meeting where the grassroot organizations can share their<br />
experiences.<br />
- Training of masons, coordina<strong>to</strong>rs <strong>and</strong> women motiva<strong>to</strong>rs.<br />
- Provision of mo<strong>to</strong>rcycles for supervisors.<br />
- Construction of demonstration plants in new localities.<br />
Our team had discussions with Mr. Mark Paul, the energy expert of AFPRO, <strong>and</strong> the<br />
points raised were mostly related with their long term experiences with the popularization<br />
of the programme. For BSP interesting experiences were:<br />
Funded by Hunger Foundation Canada, IRs.500 additional subsidy was set aside for<br />
additional subsidy for the poorer sections of the society. This programme completely<br />
failed because of the following reasons:<br />
- It created big divisions in the villages.<br />
- It was very difficult <strong>to</strong> identify the "real poor".<br />
- There were large financial organizational problems as such a scheme is very sensitive <strong>to</strong><br />
fraud.<br />
Because of these problems the programme has been ab<strong>and</strong>oned.<br />
Another project which ran in <strong>to</strong> problems was the establishment of revolving funds on<br />
village level from which farmers can borrow money <strong>to</strong> finance their biogas plant. The<br />
repayment proved <strong>to</strong> be very difficult. The experience is that repayment is only satisfac<strong>to</strong>ry<br />
when the beneficiary finds that his investment is income generating.<br />
A technical set-back that was accountered by AFPRO is the strong nation wide promotion of<br />
the Deenb<strong>and</strong>hu plants. Although this model has proven it's value at many places, in some<br />
regions the quality of available building materials is not good enough <strong>to</strong> come <strong>to</strong> a reliable<br />
result <strong>and</strong> other, now ab<strong>and</strong>oned designs, would be more appropriate.<br />
AFPRO now is favoring NGO's with an integrated approach, where biogas is one of many<br />
activities aimed at improving the quality of life for rural people. Further more it was stressed<br />
by AFPRO that NGO involvement can only be successful if there is a long term <strong>and</strong> stable<br />
support programme which allows the involved organizations <strong>to</strong> build up their infra-structure.
TERI:<br />
The Tata Energy Research Institute (TERI) is a non profit institution engaged in finding<br />
solutions for <strong>India</strong>'s energy problems. An important part of the activities is the analysis of<br />
energy problems in the rural areas <strong>and</strong> the development of technologies <strong>to</strong> harness renewable<br />
energy sources on a decentralized basis. In this respect research is done on solar energy,<br />
biomass (gasification) <strong>and</strong> <strong>to</strong> a lesser extent biogas. Further more TERI takes care of<br />
publications regarding the national biogas programme on behalf of MNES who funds these<br />
activities.<br />
There are no recent research activities as far as biogas is concerned. The studies shown 10 us<br />
were related <strong>to</strong> the hydraulic retention time, the performance of spherical type plant, the<br />
operation of a scum breaking mesh in dome plants <strong>and</strong> the performance of gas regula<strong>to</strong>rs on<br />
dome plants. The youngest of these studies dates back from 1990. Non of the<br />
recommendations from these studies has been adopted yet in the national programme,<br />
according <strong>to</strong> TERI because of the lengthy procedures at the ministry. Annex 2 gives a<br />
summery of the outcome of the above mentioned studies.<br />
GUJARAT:<br />
The schedule of the visit, transport <strong>and</strong> accommodation were (very well) organized by<br />
<strong>Gujarat</strong> Agro Industries Corporation (GAIC).<br />
After meeting with Major P.P. Kushare. the General Manager of the Energy Division of<br />
GAIC. an excursion <strong>to</strong> MECH-CI-CO (P) Ltd. located in the industrial estate of <strong>Gujarat</strong> was<br />
made. This company is the manufacturer of MARUTI biogas appliances <strong>and</strong> has earned a<br />
reputation for it's innovating work on biogas appliances. Among others their products are:<br />
- pressure regula<strong>to</strong>rs for dome type biogas plants<br />
- au<strong>to</strong>matic water removers<br />
- main valves-emu reduction elbows<br />
- single <strong>and</strong> double s<strong>to</strong>ves<br />
Specially the au<strong>to</strong>matic water remover <strong>and</strong> the pressure regula<strong>to</strong>rs were of great interest <strong>and</strong> a<br />
source of discussion between the visiting team including the GAIC GM <strong>and</strong> the producers.<br />
Under labora<strong>to</strong>ry conditions these items have proven their value, e.g. the pressure regula<strong>to</strong>r<br />
can lead <strong>to</strong> a considerable reduction in gas consumption (see annex 3). However the sustain<br />
ability of such fairly complicated equipment when in use by untrained people in rural areas is<br />
questionable.<br />
GAIC has in the last year installed several thous<strong>and</strong>s of these appliances <strong>and</strong> will keep a close<br />
eye on their performance. Based on the information gathered by them, BSP can decide <strong>to</strong><br />
introduce this technology in Nepal on an experimental basis.
A <strong>to</strong>ur through the MECH-CI-CO workshop <strong>and</strong> office showed that it is possible by means of<br />
good management <strong>and</strong> skillful staff <strong>to</strong> cater with a small mechanical company for the<br />
appliances needs of a large market.<br />
GAIC:<br />
The <strong>Gujarat</strong> Agro Industries Corporation Limited is an <strong>Gujarat</strong> State owned enterprise which<br />
serves the <strong>Gujarat</strong>i farmer through a wide range of activities. It sells <strong>and</strong> services agricultural<br />
hardware such as trac<strong>to</strong>rs <strong>and</strong> other machinery. It gives advise on <strong>and</strong> provides fertilizers,<br />
seeds, pest <strong>and</strong> decease control chemicals etc. Further more it buys, processes <strong>and</strong> markets<br />
agricultural produce such as jams, fruit juices <strong>and</strong> vegetable oils. To accomplish its tasks<br />
GAIC has 11 agro service centres, covering about 100 villages each, from where all activities<br />
are executed.<br />
The <strong>Gujarat</strong> Government has appointed GAIC as a nodal agency for the implementation of<br />
the National Programme on <strong>Biogas</strong> Development (NPDB). For this it set up a separate energy<br />
division with field level arrangements for the implementation of the programme. Specifically,<br />
GAIC performs the following functions under its biogas programme:<br />
1. Procurement, s<strong>to</strong>rage <strong>and</strong> distribution of construction materials <strong>and</strong> other inputs required<br />
for biogas plant construction <strong>and</strong> maintenance.<br />
2. Receipt <strong>and</strong> disbursement of subsidy <strong>to</strong> beneficiaries.<br />
3. Training of masons, supervisors, motiva<strong>to</strong>rs <strong>and</strong> users as well as arranging grants <strong>and</strong><br />
assistance for the same.<br />
4. Publicity <strong>and</strong> promotion of the biogas programme<br />
5. Post installation repair <strong>and</strong> maintenance<br />
6. Coordination with MNES <strong>and</strong> the Govt. of <strong>Gujarat</strong> on one h<strong>and</strong> <strong>and</strong> a number of<br />
implementing organizations like KVIC on the other.<br />
Procedure:<br />
The energy division of GAIC is using the corporation's infrastructure which was already well<br />
developed before the biogas activities were launched. At every agro service centre a biogas<br />
incharge is posted who, depending on the scale of their activities, has a number of assistants.<br />
At village level young unemployed but educated people are selected <strong>and</strong> trained <strong>to</strong> become<br />
Self Employed <strong>Biogas</strong> Supervisors (SEBS) or Turn Key Workers who are engaged in<br />
dem<strong>and</strong> collection <strong>and</strong> construction supervision. These people are not employees of GAIC<br />
but work under the guidance <strong>and</strong> supervision of GAIC staff at the agro service centres. The<br />
SEBS is paid a fee of IRs 300 for every plant constructed <strong>and</strong> for which he has <strong>to</strong> ensure<br />
trouble free functioning of the plant for three years after the installation. During this<br />
guarantee period it is obliga<strong>to</strong>ry for the SEBS <strong>to</strong> visit each plant at least once every six<br />
months. As the plants are constructed in clusters in the area where the SEBS lives, this is a<br />
rather simple task.
The construction work is carried out by trained masons. The masons are attached <strong>to</strong> a<br />
particular NGO or SEBS. They are engaged on a daily wages basis (approx. Rs 400/plant)<br />
<strong>and</strong> on average one mason can construct 25-30 plants/year.<br />
After completion of a plant, the site is visited by a staff member of the agro service centre<br />
who, when everything is found in order, issues a completion certificate. Up on this the SEBS<br />
is paid his commission. For the control on the plants the GAIC staff is using a format<br />
which enables them <strong>to</strong> spot common mistakes in a certain cluster of plants immediately (see<br />
annex 4)<br />
Furthermore, each constructed plant gets a specific code which is engraved on the inlet,<br />
giving the year of construction, code number of the SEBS <strong>and</strong> serial number of the subsidy<br />
register maintained at the agro service centre.<br />
The farmer receives from GAIC a detailed instruction booklet on operation <strong>and</strong> maintenance<br />
as well as two postcards <strong>to</strong> be addressed <strong>to</strong> the SEBS in case of any problem. If the problems<br />
are beyond the capacity of the SEBS, he can call up on a mobile repair service who are well<br />
trained <strong>and</strong> equipped with mo<strong>to</strong>rcycles. These mobile units are stationed at the service<br />
centres. This set up has resulted in a rate of 95% of the plants build in operation.<br />
Subsidy:<br />
Besides the national subsidy provided through MNES, the <strong>Gujarat</strong> Government provides a<br />
additional subsidy of IRs 1000/plant. The subsidy is partly provided before construction<br />
commences in the form of building material such as cement, s<strong>and</strong>, bricks, gravel pipe <strong>and</strong><br />
pipe fittings <strong>and</strong> appliances, partly afterwards through payment of the SEBS <strong>and</strong> cash <strong>to</strong> the<br />
farmer. The farmers contribution is on average approximately IRs 1000. GAIC favors this<br />
system as it enables them <strong>to</strong> by-pass the banks. No pre-financing is necessary <strong>to</strong> start the<br />
construction. This is speeding up the administrative procedures. GAIC also has the<br />
experience that plants financed through bank loans are sometimes left unused even <strong>to</strong>ugh<br />
they are in a good condition. This gives an excuse <strong>to</strong> the fanner not <strong>to</strong> repay his loan in the<br />
hope that his debt will be written of this has happened hi the past as promotional stunt by the<br />
ruling party during election campaigns.<br />
Potential <strong>and</strong> Conditions:<br />
The state of <strong>Gujarat</strong> has a very favorable environment for the implementation of a large scale<br />
biogas programme. The climate is ideal, in fact while plants with a 40 days retention times<br />
are build, the GAIC staff believes that a 30 day retention time would be sufficient for almost<br />
complete digestion the whole year round. There are no difficult accessible areas <strong>and</strong> the state<br />
has a very well developed roads infrastructure. The literacy rate is very high which makes<br />
promotion, extension <strong>and</strong> training easy. An innovative <strong>and</strong> quality conscious manufacturer of<br />
appliances with enough production capacity is located in Ahmedabad. Main' farmers are<br />
organized in the more than 9000 Milk Producers Co-operative Societies. These societies run<br />
their own veterinary services, provide the members with supplementary feed s<strong>to</strong>ck for their<br />
cattle, etc. These co-operatives are a very good vehicle <strong>to</strong> reach the cattle owners. Further<br />
more, through the dairy industry the farmers have a permanent source of income which
makes it easy for them <strong>to</strong> buy a biogas plant even without bank involvement. Last but not<br />
least, the <strong>Gujarat</strong> Government has a long term commitment <strong>to</strong> the biogas programme which<br />
materializes through the additional subsidy it provides.<br />
GAIC considers a long term stable financial support programme essential for large scale<br />
construction. Special programmes for scheduled casts <strong>and</strong> tribes, the poorer sections of<br />
society, were seen as problematic <strong>and</strong> not very productive.<br />
Out of the about 41 lakhs families owning cattle it is estimated that <strong>20</strong> lakhs qualify for the<br />
construction of a biogas plant. More than 1.5 lakh plants have been constructed so far while<br />
the annual building rate hovers around 30,000 units. A list showing district wise the<br />
cattle population is given in annex 5.<br />
Design:<br />
To be able <strong>to</strong> implement their large scale programme, GAIC has opted for a single model<br />
approach <strong>and</strong> virtually a single size as well. The Deenb<strong>and</strong>hu 2 m 3 plant has been found most<br />
suitable for 80% of the households. Only for large families with many cattle, 3 m 3 plants can<br />
be build. The advantages of this policy are:<br />
- Easy <strong>to</strong> train technicians in construction, maintenance <strong>and</strong> repair<br />
- Simplification of promotion materials<br />
- Small number of different items that have <strong>to</strong> be kept in s<strong>to</strong>ck for construction<br />
- Simplification of administration<br />
- No over-sizing by "status conscious" farmers, by this approach GAIC has managed <strong>to</strong><br />
eliminate the problem of oversized plants.<br />
On the st<strong>and</strong>ard Deenb<strong>and</strong>hu design the following modifications have been made:<br />
- The brick work is 110 mm wide instead of 55 mm.<br />
- The <strong>to</strong>p section of the dome is casted concrete for properly securing the gas pipe.<br />
- Every plant is fitted with a vertical mixing device.<br />
- A small brick chamber is constructed directly after the outlet overflow from where the<br />
farmer can remove slurry with a bucket <strong>to</strong> poor it on the traditional compost heap.<br />
- No paint is used <strong>to</strong> make the dome gas tight, instead very good quality fine s<strong>and</strong> is used <strong>to</strong><br />
apply 3 coats of cement plaster.<br />
Concluding Remarks:<br />
The biogas programme in <strong>Gujarat</strong> is. because of its scale <strong>and</strong> success rate, very interesting for<br />
Nepal Although the conditions are more favorable in <strong>Gujarat</strong>, there are still many experiences<br />
which can be of use here. Technical aspects like use of more sophisticated appliances <strong>and</strong>/or<br />
nylon appliances, slurry h<strong>and</strong>ling, etc. need <strong>to</strong> be studied further. Programme wise the<br />
channeling of subsidy, single model limited size approach, training methods, collaboration<br />
with agricultural NGO's <strong>and</strong> co-op's etc. are of interest. Therefore it will be very much<br />
worthwhile <strong>to</strong> keep in <strong>to</strong>uch with our <strong>Gujarat</strong>i counter parts.
Annex 1
Residence Time Distribution Studies<br />
of <strong>Biogas</strong> Digester Models<br />
P. Raman, K. Sujatha, S. Dasgupta <strong>and</strong> V. V. N. Kishore<br />
Tata Energy Research Institute, <strong>New</strong> <strong>Delhi</strong><br />
Annex 2<br />
ABSTRACT<br />
A tracer method has been employed for determining residence time distribution in<br />
labora<strong>to</strong>ry models of biogas plants. Plastic beads with density equal <strong>to</strong> that of dung slurry<br />
have been used as" tracer material. The tracer concentration (No. of beads per unit volume of<br />
slurry) in the output has been moni<strong>to</strong>red following a pulse input. The residence time<br />
distribution <strong>and</strong> the average residence time for a given model is thus experimentally obtained<br />
for comparison sake.<br />
INTRODUCTION<br />
The hydraulic retention time (HRT) is a basic design parameter in constructing biogas<br />
plants. HRT values of 35 - LOO days had been used for different climatic conditions. It is<br />
widely known that HRT, which is related <strong>to</strong> the effective time spent by the slurry in the<br />
digester, is a function of temperature. As a biogas plant is essentially a chemical reac<strong>to</strong>r, it is<br />
apparent that the effective residence time of the slurry in the reac<strong>to</strong>r would also depend upon<br />
the design of the reac<strong>to</strong>r. The dependency of effective residence time on the geometry of the<br />
digester has so far been not well investigated <strong>and</strong> except for the work of Hamad et al. [1],<br />
there is no literature on the subject. Some labora<strong>to</strong>ry models of fixed dome plants have been<br />
studied for their residence time distribution (RTD) characteristics using a tracer method, <strong>and</strong><br />
in this paper preliminary results are presented.<br />
EXPERIMENTAL<br />
Selection of Tracer Material<br />
Slurry sampled from different depths of two biogas plants installed in the village<br />
Dhanawas, Haryana, was analysed for density. Spherical, plastic beads of density 0.941<br />
gm/cc were ' manipulated by adding small quantities of M- seal so as.<strong>to</strong> make the density of<br />
each bead equal <strong>to</strong> that of slurry. After sufficient number of beads were prepared, they were<br />
mixed with the slurry <strong>and</strong> allowed <strong>to</strong> settle. Only those beads which are neither sinking <strong>to</strong> the<br />
bot<strong>to</strong>m nor floating <strong>to</strong> the <strong>to</strong>p were selected for experimentation. .<br />
Selection of Models<br />
Two models of digesters, viz., (i) cylindrical <strong>and</strong> (Ii) spherical were selected. The<br />
cylindrical digester has a diameter of 27 cm <strong>and</strong> a height of 13.5 cm so that the D/H ratio is<br />
kept at 2.0.<br />
© 1989, Solar Energy Society of <strong>India</strong><br />
Renewable Energy for Rural Development, Tata McGraw-Hill, <strong>New</strong> <strong>Delhi</strong>
The diameter of the spherical digester is 3 0 cm. The position of inlet is varied in .both the<br />
models. In some experiments, the <strong>to</strong>p of the digester was connected <strong>to</strong> an air compressor <strong>to</strong><br />
simulate conditions existing in the larger biogas plants. For the cylindrical digester the<br />
variations tried were - (i) inlet at the bot<strong>to</strong>m, outlet at the <strong>to</strong>p, (ii) inlet, outlet at the same<br />
level, <strong>and</strong> (iii) inlet, outlet at the same level <strong>and</strong> pressurising the digester, for the spherical<br />
digester model, the variations tried were - (i) inlet <strong>and</strong> outlet at the same level, (ii) a baffle<br />
incorporated in the centre <strong>and</strong> (iii) a diffuser incorporated at the bot<strong>to</strong>m of the digester with<br />
an inlet pipe connected <strong>to</strong> it; this was thought <strong>to</strong> produce near plug flow conditions (Fig. 1).<br />
CYLINDRICAL DIGESTERS<br />
ANALYSIS<br />
Procedure for Determining RTD<br />
The volume of slurry needed <strong>to</strong> fill the digester <strong>to</strong> the point of overflow from the<br />
outlet was first obtained. This was divided by 50 so that the volume per feed is calculated.<br />
Each feed will displace an equal volume through the outlet. The quantum of feed <strong>and</strong> the <strong>to</strong>tal<br />
active volume of the digester correspond <strong>to</strong> the HRT of 50 days.
The digester was filled with slurry- A first charge of slurry mixed with about 150 -<br />
250 beads was then fed in<strong>to</strong> the reac<strong>to</strong>r. This represents a pulse input of the tracer. The slurry<br />
overflowing from the outlet was collected <strong>and</strong> sieved <strong>to</strong> note the number of beads present.<br />
The next charge is fed <strong>and</strong> the out-flow was again collected <strong>and</strong> screened. This procedure is<br />
repeated a number of times till almost all the beads come out of the digester. A plot of the<br />
number of beads collected in a given out-flow against the serial number of the charge gives<br />
the residence time distribution. The effective retention time (ERT) is calculated using the<br />
equation<br />
Effective Retention Time<br />
where t i is the i th day <strong>and</strong> c i is the tracer concentration of that corresponding day <strong>and</strong> ∆t. is<br />
the time interval between two measurements.<br />
RESULTS AND DISCUSSION<br />
The different geometries with their variations are schematically shown in Fig. 1. The<br />
residence time distribution curves along with cumulative curves are given in Figs 2 <strong>and</strong> 3. A<br />
summary of the results is given in Table 1. The main conclusions, which are bound <strong>to</strong> be<br />
tentative considering the preliminary nature of the present experiments are as follows:<br />
1. The effective retention time is considerably less than the hydraulic retention time for<br />
most of the cases considered. A similar conclusion for the Chinese type fixed dome<br />
plant was obtained by Hamad et al. (1).<br />
2. Introduction of a baffle with a view <strong>to</strong> increasing the residence time was found <strong>to</strong> be<br />
not effective.<br />
3. The method of removing the slurry from outlet - either by simple overflow or by<br />
pressurisation (as occurring in actual larger plants) does not affect the residence time<br />
distribution significantly.<br />
4. It appears that a bot<strong>to</strong>m inlet with horizontal injection by means of a diffuser gives the<br />
highest effective residence time.<br />
The last conclusion mentioned above is significant because it provides a way of<br />
achieving near plug flow conditions in the digester in a simple way. Further experimentation<br />
is under way <strong>to</strong> firm up this conclusion as well as <strong>to</strong> refine the experimental methods <strong>and</strong> <strong>to</strong><br />
extend the study <strong>to</strong> other reac<strong>to</strong>r designs.
Table 1: Details of the Experiments <strong>and</strong> Results<br />
Expt.<br />
Type of<br />
Position of<br />
Beads<br />
Beads<br />
Design-<br />
Effective<br />
No.<br />
Digesters<br />
Inlet <strong>and</strong> Outlet<br />
In<br />
Out<br />
ed HRT<br />
HRT<br />
1. Cylindrical I.L at the bot<strong>to</strong>m O.L at the <strong>to</strong>p 129 127 50 32<br />
2. Cylindrical I.L <strong>and</strong> O.L. at the same level 165 160 50 29<br />
3. Cylindrical I.L <strong>and</strong> O.L. at the same level 150 149 50 30<br />
(Ex. with pressurizing)<br />
4. Spherical Without baffle <strong>20</strong>0 187 50 25<br />
5. Spherical With baffle <strong>20</strong>0 186 50 <strong>20</strong><br />
6. Spherical Inlet with Diffuser 250 242 50 42<br />
I.L-Inlet, O.L-Outlet<br />
REFERENCES<br />
1. Hamad, M.A., Abdel, A.M. <strong>and</strong> Ei Halwagi, K.M., Pilot Plant Labora<strong>to</strong>ry, N.R.C.,<br />
Dokkai, Cairo (Egypt), 19S2.<br />
2. Kishore, V.V.N., Raman, P. <strong>and</strong> Kanga Rao, V.V., Fixed Dome <strong>Biogas</strong> Plants - A<br />
Design, Construction <strong>and</strong> Operation Manual, TERI Publication, 1987.<br />
3. Ludwig Sasse, <strong>Biogas</strong> Plants, GATE, 1984.
A Gas Regula<strong>to</strong>r for Fixed Dome <strong>Biogas</strong> Plants<br />
Dome <strong>Biogas</strong> Plants<br />
V.V.N. Kishore, Sunil Dhingra ∗<br />
Abstract<br />
An LPG regula<strong>to</strong>r was tested for its suitability for controlling the pressure <strong>and</strong> flow<br />
rate of biogas from fixed dome biogas plant. Though the operating characteristics of the LPG<br />
regula<strong>to</strong>r are not ideally suited for biogas applications, it was found that some degree of<br />
control could be achieved. Thermal efficiency measurements on the biogas burners showed<br />
that there was improvement in thermal efficiency by about 56% when a regula<strong>to</strong>r was<br />
incorporated. However, the thermal efficiency improvement was associated with a reduction<br />
in thermal power of the burner.<br />
Introduction<br />
Fixed dome biogas plants are characterized by a varying gas pressure, up<strong>to</strong> 100 cm<br />
water gauge, in contrast with K.VIC type biogas plants which deliver gas for utilization at a<br />
constant pressure of about 7.5 cm water gauge. As most of the biogas appliances such as<br />
burners, lamps etc. are usually designed <strong>and</strong> st<strong>and</strong>ardized <strong>to</strong> perform optimally at a given<br />
pressure, it should be expected that these devices would not be performing optimally on a<br />
continuous basis when used in conjunction with fixed dome plants. In fact, it has been<br />
reported [I] that the thermal efficiency of domestic burners connected with fixed dome biogas<br />
plants is much below the 55% mark recommended by KVIC <strong>and</strong> BIS (Bureau of <strong>India</strong>n<br />
St<strong>and</strong>ards). The <strong>India</strong>n St<strong>and</strong>ard specification for <strong>Biogas</strong> S<strong>to</strong>ve (IS : 8749 I9iii) stipulates that<br />
the inlet gas pressure should be constant at 747 N/ m 3 (7.6 cm WG) while testing the s<strong>to</strong>ves.<br />
There is no need <strong>to</strong> stress the importance of appliance efficiency in the context of the overall<br />
economics of biogas utilization. It has been shown [2] that the levelized annual cost of<br />
thermal energy can be reduced from a value of 0 69 Rs/ kWh(th) <strong>to</strong> 0,53 Rs/kWh(th) by<br />
improving the burner efficiency, resulting in an effective cost reduction of 23%. However, it<br />
is a difficult proposition <strong>to</strong> design a s<strong>to</strong>ve which can operate at a constant, high thermal<br />
efficiency over a range of inlet pressures <strong>and</strong> hence over a range of gas flow rates. A simpler<br />
thing would be <strong>to</strong> incorporate a pressure regula<strong>to</strong>r in the gas stream so that Die inlet pressure<br />
<strong>and</strong> flow rate would be kept nearly constant, throughout the period of use.<br />
In the present work, at attempt bas been made <strong>to</strong> improve the performance of biogas<br />
s<strong>to</strong>ves by incorporating an ordinary LPG regula<strong>to</strong>r in fixed dome biogas plants, with lie<br />
ultimate aim of designing a suitable regula<strong>to</strong>r for use with fixed dome plants.<br />
Operating Characteristics of an LPG Regula<strong>to</strong>r<br />
∗ Tata Energy Research Institute, 232 Jor Bag <strong>New</strong> <strong>Delhi</strong> 110003.
The specifications for low pressure regula<strong>to</strong>rs for use with Liquified" Petroleum Gas (LPG)<br />
mixtures are laid down in the <strong>India</strong>n St<strong>and</strong>ard IS: 9798-1981. According <strong>to</strong> these<br />
specifications, the regula<strong>to</strong>r outlet pressure should be 30±0.5 g/cm 3 (29.5—30.5 cm water<br />
gauge) when the inlet pressure is kept at 7.0 kg/cm 8 . Also, the outlet pressure should not be<br />
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<br />
pressure varies from 0.5 kg/cm 3 <strong>to</strong> 17 kg/cm 3 . The st<strong>and</strong>ard rated capacity for LPG regula<strong>to</strong>rs<br />
for domestic use is up<strong>to</strong> 500 litres/hr.<br />
From the above specifications, it is apparent that the inlet pressure range for LPG<br />
regula<strong>to</strong>rs is much higher than that encountered in biogas plants, viz 0.100 cm WG. However,<br />
it was decided <strong>to</strong> study the characteristics of the LPG regula<strong>to</strong>r at inlet pressure below the<br />
specified lower limit <strong>to</strong> see if it would be suitable for biogas application. The inlet pleasure,<br />
outlet pressure <strong>and</strong> ihe flow rate have been measured over a wide range using both<br />
compressed air <strong>and</strong> biogas. A plot of flow rates vs. inlet pressure is shown in Fig. 1 (a) <strong>and</strong> a<br />
plot of outlet pressure vs. inlet pressure is shown in Fig. 1(b). Figure l (a) shows that the flow<br />
rate is constant at about 500 lit/hr even at inlet pressure as low as 100 cm WG, which is much<br />
lower than the stipulated lower limit of 500 cm WG. Figure 1 (b) shows that the outlet<br />
pressure is constant at about 31 cm WG when the inlet pressure is reduced right down <strong>to</strong><br />
about 60 cm WG. When the inlet pressure is reduced below 100 cm WG, there is a sudden<br />
drop in flow rate, followed by an almost linear variation with inlet pressure. The flow rate<br />
varied between 240—250 litres/hr for inlet pressure variation of 30—100 cm WG- The gas<br />
flow rate recommended for domestic biogas burners is between <strong>20</strong>0—450 litres/hr [3], A<br />
similar trend can be seen in the outlet pressures, which varied from 7,5—15.0 cm WG. Thus,<br />
it is apparent that the LPG regula<strong>to</strong>r, though not designed for use with biogas, might be<br />
suitable, in a limited sense, <strong>to</strong> biogas applications. Hence it has been decided <strong>to</strong> install a LPG<br />
regula<strong>to</strong>r on an actual biogas plant <strong>and</strong> conduct some tests on thermal efficiency in the field<br />
Thermal Efficiency Measurements<br />
The thermal efficiency tests have been carried out in the village Dhanawas in<br />
Haryana, where TERI had constructed seven fixed dome biogas plants of various designs [4].<br />
The plants are in regular use <strong>and</strong> all except one have a rated capacity of 2m 8 . The procedure<br />
outlined in <strong>India</strong>n St<strong>and</strong>ard IS : 8749—1988 has been followed for evaluating the thermal<br />
efficiency. Briefly, water is heated from ambient temperature <strong>to</strong> about 95°C in aluminium<br />
pots <strong>and</strong> the gas consumption is measured by means of a wet flow meter. The thermal<br />
efficiency is given as<br />
where<br />
µ=thermal efficiency of the burner in percent<br />
G=quantity of water in the vessel in kg<br />
W=water equivalent of the vessel with lid<br />
T a —final temperature of water in °C
T 1 = initial temperature of water in °C<br />
V=gas consumption in m f <strong>and</strong> H=calorific value of gas in kcal/.m 3<br />
The calorific value of the gas is taken as 4700 kcal/m 3 . The initial <strong>and</strong> final inlet<br />
pressures <strong>and</strong> the time taken for the test have also been noted down. Tests have been<br />
conducted with <strong>and</strong> without the regula<strong>to</strong>r <strong>and</strong> on two different plants. The results of thermal<br />
efficiency tests are summarized in Table 1. The average thermal efficiency without the<br />
regula<strong>to</strong>r was about 30.8% <strong>and</strong> the average thermal efficiency with regula<strong>to</strong>r was about<br />
48.0%, showing an improvement in efficiency by about 55.8%. It can thus be seen that using<br />
a regula<strong>to</strong>r for fixed dome biogas plants is indeed beneficial from thermal efficiency point of<br />
view.<br />
Discussion<br />
An examination of Table 1 reveals that the thermal efficiencies are ' generally lower<br />
when the gas flow rates are higher. The gas flow rate is a ' direct measure of the burner<br />
thermal power, given by the equation<br />
where<br />
P=Power, kW<br />
V=Gas flow rate, m 3 /hr<br />
H=Calorific value of gas, kcal/m 3<br />
In order <strong>to</strong> sec if there is a correlation between thermal efficiency <strong>and</strong> power, YJ is<br />
plotted against P for all the experiments conducted, as shown in Fig. 2. It can be seen from<br />
this figure that the thermal efficiency drops significantly with increase in power. A similar<br />
correlation seems <strong>to</strong> .exist for wood burning s<strong>to</strong>ves also [5]. This means that the efficiency of<br />
the burner can be increased only by decreasing the power of the burner. It fact, for domestic<br />
biogas burners, the gas flow rates are typically 450 litres/hr (large) <strong>and</strong> 225 lit/hr (small),<br />
corresponding <strong>to</strong> power levels of 2 46 kW <strong>and</strong> 1.23 kW respectively. A report of KV1C states<br />
that a thermal efficiency of 59.5% could be obtained, but the corresponding power was 1.61<br />
kW. These figures indicate that biogas burners are designed <strong>to</strong> operate efficiently only at low<br />
power levels- However, the desirable power levels for cooking applications seem <strong>to</strong> be<br />
higher. The power levels for
LPG s<strong>to</strong>ves are typically between 4.4-7.6 k\V. The time taken for cooking is inversely<br />
proportional <strong>to</strong> the burner power, <strong>and</strong> hence laying emphasis only on thermal efficiency may<br />
not be entirely desirable. In fact, a few modifications had <strong>to</strong> be effected in the LPG regula<strong>to</strong>r<br />
resulting in a higher gas flow rate, following complaints from the user that (he time taken for<br />
cooking has increased after installing the regula<strong>to</strong>r. The problem of optimal utilization of<br />
biogas from fixed dome plants thus essentially boils down <strong>to</strong> the optimal design of the <strong>to</strong>tal<br />
system consisting of regula<strong>to</strong>r <strong>and</strong> burner such that thermal efficiencies of the order of 55%<br />
are achieved with power levels of 4 - 6 kW. Work is in progress <strong>to</strong> design a regula<strong>to</strong>r<br />
specifically for biogas used <strong>and</strong> <strong>to</strong> design an efficient biogas burner for high power levels<br />
Conclusion<br />
An LPG regula<strong>to</strong>r was tested for its use with fixed dome biogas plants in order <strong>to</strong> control the<br />
gas pressure <strong>and</strong> flow rate. The regula<strong>to</strong>r was found <strong>to</strong> be suitable, in a limited sense, for<br />
biogas applications. Measurements showed that the thermal efficiency of the biogas burners<br />
improved significantly when a regula<strong>to</strong>r was incorporated. The improvement of thermal<br />
efficiency, however, was associated with a reduction of burner power.<br />
Acknowledgements<br />
The authors are grateful <strong>to</strong> Mr. Shishupal Sharma, Mr. Manjit Siogh, Mr, Guruvinder Singh<br />
<strong>and</strong> Mr. Vellaikkannu for their help in experimental work.<br />
REFERENCES<br />
V.V.N. Kishore, P. Raman <strong>and</strong> V.V. Ranga Rao, "The <strong>Biogas</strong> System for Cooking Energy<br />
Production—Is it more efficient ?'\ <strong>Biogas</strong> Forum, No 32/.9S8, BORDA, Bremen,<br />
FRG.<br />
V.V.N. Kishore, "Cooking Energy Systems—A Comparative <strong>Study</strong>", Energy Policy Issues.<br />
Vol. 4 (1988). (tds) K.K Pachauri <strong>and</strong> Leena Srivasuva, Tata Energy Research<br />
Institute, pp. 37-46, 1989.<br />
V.V.N. Kishore, p. Raman <strong>and</strong> V.V. Ranga Rao, "Fixed Dome <strong>Biogas</strong> Plants—A Design,<br />
Construction <strong>and</strong> Operation Manual", Tata Energy Research Institute, 1987.<br />
V.V.N. Kishore, P. Raman <strong>and</strong> V.V. Ranga Rao, "Fixed Dome <strong>Biogas</strong> Plants Developed by<br />
TERV, Rural Technology Journal, pp. 26-40, . September 1987.<br />
Veena Joshi, Ch<strong>and</strong>ra Venkataraman <strong>and</strong> Dilip R. Ahuja, "Emissions ' from Burning Biofuels<br />
in Metal Cooks<strong>to</strong>ves", Environmental Management, Vol. 13, No. 6, 1989.
TABLE 1<br />
Summary of Thermal Efficiency Tests<br />
S. No. Initial Final Power Time Gas Av.<br />
Pressure Pressure Taker. Consumed Rate<br />
(cm WG) (cm WG) (kW) (min.) (lit) (lit/hr) (%)<br />
Experiments Without<br />
Regula<strong>to</strong>r<br />
1. 60.0 41.0 5.7 14 243.0 1041.0 28.7<br />
2. 28.0 12.5 3.4 19 197.1 622.0 34.5<br />
3. 21.5 9.0 2.5 26 19S.0 457.0 29.4<br />
4. 38.5 22.0 3.4 21 216.6 619.0 30.4<br />
Experiments with Regula<strong>to</strong>r<br />
70.0 60.0 1.8 28 153.2 328.0 46.8<br />
37.5 28.0 1,3 33 127.5 232.0 56.3<br />
28.0 21.5 1.4 31 132.0 255.5 42.7<br />
48.0 38.5 1.8 26- 145.5 336.0 46.0<br />
List of Figures<br />
Figure 1 : Performance characteristics of LPG regula<strong>to</strong>r.<br />
Figure 2 : Efficiency—power relation for biogas burners.
Design <strong>and</strong> Performance of Spherical Type <strong>Biogas</strong> Plants<br />
P Raman, R C Pal <strong>and</strong> V V N Kishore<br />
Tata Energy Research Institute<br />
232 Jor Bagh<br />
<strong>New</strong> <strong>Delhi</strong> 110 003<br />
Abstract<br />
A spherical" -'type biogas plant had been developed taking in<strong>to</strong> consideration the<br />
drawbacks <strong>and</strong> problems associated with existing fixed dome biogas models.<br />
The new design of spherical type biogas plant has several advantages such as lesser<br />
chance of dome failure, increased gas s<strong>to</strong>rage space, etc. The slurry inlet is located in such a<br />
way as <strong>to</strong> ensure that the effective HRT will be closer <strong>to</strong> the design HRT, which is not the<br />
case with the existing biogas plant models.<br />
A detailed procedure for calculating the dimensions of all the components of spherical<br />
type biogas plant is presented along with the field level gas production data of a 2 m biogas<br />
plant. The performance of the new model is compared with that of existing models.<br />
Introduction<br />
Fixed dome (Chinese) models of biogas plants are built in various shapes. While the<br />
Janata model uses a combination of cylindrical <strong>and</strong> spherical shapes, the Deenb<strong>and</strong>hu model<br />
is a combination of two spheres of different diameters. However, from materials<br />
consideration; it is desirable <strong>to</strong> have a completely spherical shape as this geometry offers the<br />
lowest surface area per unit volume.<br />
It has been shown [l] that the location <strong>and</strong> mode of slurry inlet has an important<br />
bearing or. the effective HRT of a biogas plant. The effective HRT of both KVIC <strong>and</strong> Janata<br />
models is much less than the design value, as shown by studies on residence time distribution<br />
[2]. From consideration of material optimization <strong>and</strong> residence time distribution <strong>and</strong> from<br />
practical considerations of field level problems such as choking of gas lines with slurry in<br />
winter, under-utilization of biogas, etc. TERI evolved a spherical model biogas plant. Though<br />
the first plant with spherical design was built in 1987 in the village Dhanawas in Haryana,<br />
efforts were made <strong>to</strong> gradually improve the plant design in each subsequent plant built, <strong>and</strong><br />
the model described in this paper has been now st<strong>and</strong>ardized <strong>to</strong> a large extent.<br />
Method of Designing the Plant<br />
The biogas plant consists of i) the digester, ii) inlet, iii) outlet <strong>and</strong> iv) other accessories.<br />
The digester in turn consists of active slurry volume, gas s<strong>to</strong>rage space (slurry<br />
displacement volume) <strong>and</strong> a 1 buffer space' <strong>to</strong> prevent entry of slurry in<strong>to</strong> the gas line. A<br />
schematic diagram of the plant with relevant parameters is shown in Figure 1. Referring <strong>to</strong>
Figure 1, the radius of the plant is R. <strong>and</strong> h 1 is the distance between the gas outlet (at the <strong>to</strong>p<br />
of the sphere) <strong>and</strong> the slurry exit level of the outlet tank. h 2 is the distance between the gas<br />
outlet <strong>and</strong> initial slurry level in the biogas plant (slurry level at nil pressure). h 3 is the distance<br />
between the gas outlet <strong>and</strong> the final slurry level in the digester {slurry level at full pressure).<br />
V 1 is the volume of buffer space provided' in the dome <strong>to</strong> accommodate any<br />
volumetric increase in slurry space. V 2 <strong>and</strong> V 3 are volumes of the spherical segments<br />
corresponding <strong>to</strong> heights h 2 <strong>and</strong> h 3 .<br />
The equations relating the different volumes <strong>to</strong> heights are:<br />
V 1 = (π/3) h 2 (3R-h 1 ) ... (1)<br />
V 2 = (π/3) h 21 (3R-h 2 ) ... (2)<br />
V 3 = (π/3) h 2 3 (3R-h 3 ) ... (3)<br />
The volume of slurry displaced within the digester is equal <strong>to</strong> the volume of slurry<br />
displaced in the outlet tank. If Ao is the cross sectional area of the outlet tank, we have<br />
(V 3 -V 2 ) = Ao x (h 2 -h 1 ) ... (4)<br />
Field experience indicated that the gas s<strong>to</strong>rage space be as high as possible from user<br />
preference point of view. A large gas s<strong>to</strong>rage space also ensures maximum utilization of gas.<br />
Earlier TERI models [3] used about 40% of the design daily gas production as s<strong>to</strong>rage space,<br />
but in the present model, a value of 60% is taken. If G is the design daily gas production, we<br />
have<br />
(V 3 -V 2 ) = 0 . 6 G ... (5)
The minimum pressure of the gas was selected <strong>to</strong> be 0.5m of water column <strong>and</strong> as the<br />
density of -the slurry is only marginally higher than that of water, one can write<br />
h 3 - h 1 > 0.5 ... (6)<br />
Field experience showed that a maximum of about 1 ft. (0.3 m) clearance- has <strong>to</strong> be provided<br />
between the points of slurry exit <strong>and</strong> gas exit in order <strong>to</strong> solve the problem of gas line<br />
choking effectively. Hence we get the condition<br />
h 1 = 0.3 ...(7)<br />
The plant is designed <strong>to</strong> have a 40 day HRT <strong>and</strong> it can be shown that assuming a<br />
specific gas production of 40 lit/kg dung <strong>and</strong> a dilution of 1:1 for slurry, the active slurry<br />
volume is equal <strong>to</strong> 2G. Hence one can write<br />
(4/3) πR 3 - V 3 = 2G ... (8)<br />
The above set of equations have been solved using the software EUREKA. Dimensions for<br />
1,2,3,4 m 3 plants are given in Table 1.<br />
Table 1: Relevant Dimensions for Various<br />
Components of <strong>Biogas</strong> Plants<br />
S.<br />
No.<br />
G R h 1 h 2<br />
1 1 0. 98 0.30 0.78 0. 98 1. 24<br />
2 3 1.16 0.30 0.78 1.07 2.52<br />
3 3 1.34 0.30 0.83 1.17 3.38<br />
4 4 1 .43 0 .30 0 .70 1.14 5.93<br />
h 3<br />
Ao<br />
The lateral dimensions of the outlet tank are chosen in such a way that length <strong>to</strong><br />
breadth ratio is 2. Thus, if b is the breadth, length is 2b <strong>and</strong> b can be obtained as:<br />
b = √(AO/2) . . . (9)<br />
A cylindrical mixing tank. with volume slightly larger than the daily slurry input is<br />
also provided. A vertical axis stirrer made with MS reds <strong>and</strong> bars is also provided in the<br />
mixing tank, <strong>and</strong> it was noticed that there was a significant difference in gas outputs for<br />
mechanically stirred vs. manually mixed slurry. The users also preferred <strong>to</strong> have a mechanical<br />
stirrer.<br />
The inlet pipe is installed in such a way that the fluid path is reversed when exiting
in<strong>to</strong> the digester. The pipe is tangential <strong>to</strong> the cross section of the digester <strong>and</strong> the discharge<br />
end of the pipe is surrounded by a small Ferro cement box open on one side.<br />
While charging, the slurry will impinge on one side of the box, flow is reversed <strong>and</strong><br />
the slurry exits in the opposite direction through the opening in the box. This method of<br />
charging was thought <strong>to</strong> provide lesser dead volumes, lesser short circuits <strong>and</strong> a better<br />
residence time distribution resulting in a higher effective residence time. The actual plant<br />
dimensions with the above mentioned slurry inlet arrangement are shown in Figure 2.<br />
Constructional Features<br />
The entire plant is constructed with a single dimension <strong>and</strong> hence the time for construction<br />
is lesser. The hook method [4] is used for construction. Cicco is used <strong>to</strong> facilitate faster<br />
setting of mortar during construction. An extra layer of tiles is provided in the gas s<strong>to</strong>rage<br />
space <strong>to</strong> almost eliminate the chances of dome cracking. A combination of cement primer <strong>and</strong><br />
paint is used for making the gas space leak proof. A ball valve is used instead of gate valve <strong>to</strong><br />
minimize recurring expenses. S<strong>to</strong>ne slabs are used for covering the outlet tank.<br />
Performance of the Plant<br />
The daily gas production values as measured by a wet type gas flow meter are shown in<br />
Figure 3 for the period of 1st Oc<strong>to</strong>ber - 30th November 1991. The monthly average values in<br />
the units of m 3 /(m 3 )(day) for the spherical plant are shown in Figure 4 for the months of<br />
Oc<strong>to</strong>ber 1991 <strong>and</strong> November 1991 along with those reported [5] for Janata <strong>and</strong> Deenb<strong>and</strong>hu<br />
models. It is apparent that the gas production values are highest for the model described in<br />
this paper.<br />
Financial Consideration<br />
The cost break-up for a 2 m 3 plant of spherical model is shown in Table 2 along with that for<br />
Deenb<strong>and</strong>hu model. It can be seen that the cost of the spherical model is roughly the same as<br />
that of Deenb<strong>and</strong>hu model.<br />
Conclusions<br />
Design <strong>and</strong> performance details of a spherical model biogas plant are described in this paper.<br />
The advantages of the spherical model are i) very low chances of dome cracking, ii) absence<br />
cf problems such as choking of gas lines, iii) higher gas s<strong>to</strong>rage space <strong>and</strong> hence better<br />
utilization of gas <strong>and</strong> iv) higher gas production rates. Considering that the spherical model<br />
costs about the same as Deenb<strong>and</strong>hu model but yields higher quantities of gas, the overall<br />
economics of the spherical model are much better.<br />
Acknowledgment<br />
There are several people who have contributed <strong>to</strong> the evolution of field activity in biogas<br />
within TERI . Notably, Mr. V.V. Ranga Rao <strong>and</strong> Ms. Sangeeta Kohli were involved <strong>to</strong> a large<br />
extent in the initial developmental <strong>and</strong> extension activities. Mr. Shishupal Sharma helped in<br />
collecting field level gas production data. Planning <strong>and</strong> coordination of activities in the
villages Dhanawas <strong>and</strong> Berka Alimuddin were done by Dr. Veena Joshi. The help provided<br />
by Suresh <strong>and</strong> Mr. B N Mishra is sincerely appreciated. Finally, the authors are grateful <strong>to</strong><br />
Dr. R K Pachauri for his encouragement throughout the work.<br />
Table 2: Material Requirement <strong>and</strong> Cost Break-up<br />
for 2 m 3 <strong>Biogas</strong> Plant<br />
Material Unit Unit Quantity<br />
Cost<br />
Cost<br />
Deen*- Spheri- Deen- Spherib<strong>and</strong>hu<br />
cal b<strong>and</strong>hu cal<br />
1 Bricks Rs/1000 1050 1000 1<strong>20</strong>0 1050 1260 -<br />
2 Tiles Rs/1000 1050 300 315<br />
3 Cement Rs/Bag 105 14 11 1470 1155<br />
4 St. Chips Rs/Cft. 4 40 3 160 12<br />
5 S<strong>and</strong> Rs/Cft. 3 40 75 1<strong>20</strong> 225<br />
6 CO. S<strong>and</strong> Rs/Cft. 3 40 1<strong>20</strong> 0<br />
7 GI Pipe Rs/Foot 25 0.7 1 18 25<br />
8 AC Pipe Rs/Foot 15 6 12 90 180<br />
9 OL Slab Rs/Sq. m. 100 2 0 <strong>20</strong>0<br />
10 MS Bar Rs/KG <strong>20</strong> 7 2 140 40<br />
11 C Primer Rs/Lit. 60 1 0 60<br />
12 Cicco Rs/Lit. 30 3 0 90<br />
13 Paint Rs/Lit. 60 1 1 60 60<br />
14 Lab (Dig) Rs/M Day 35 1.0 10 350 3 50<br />
15 Mason Rs/M Day 90 11 8 990 7<strong>20</strong><br />
16 Lab (Con) Rs/M Day 40 22 16 880 640<br />
17 Misls ----- 300 1 1 300 3 00<br />
18 Stirrer ----- 150 - 1 0 150<br />
19 Ball Valve 67 - 1 - 67<br />
<strong>20</strong> Gate Valve 85 1 - 85 -<br />
21 Burner + pipe 700 1 1 700 700<br />
line system<br />
TOTAL 6533 6 54 9<br />
Source: Manual on Deenb<strong>and</strong>hu <strong>Biogas</strong> Plant, by J 3 Singh et al,<br />
Tata McGraw Hill Publishing Company Ltd., <strong>New</strong> <strong>Delhi</strong><br />
References<br />
[1] P Raman, K Sujatha, S Dasgupta <strong>and</strong> V V N Kishore, "Residence Time Distribution<br />
Studies in Non-continuous Flow UN-stirred Tank Reac<strong>to</strong>rs with Reference <strong>to</strong> <strong>Biogas</strong><br />
Digesters", SESI Journal, Vol. 3, No.2, pp. 1-12, 1989.
[2] M A Hamad, A M Abdel <strong>and</strong> M M Ei Halwagi, "Evaluation of the Performance of Two<br />
Rural <strong>Biogas</strong> Units of <strong>India</strong>n <strong>and</strong> Chinese Design", Energy in Agriculture, Vol.1, Issue<br />
No. 3, pp. 235-250, l983.<br />
[3] V V N Kishore, P Raman <strong>and</strong> V V Ranga Rao, "Fixed Dome <strong>Biogas</strong> Plants Developed by<br />
TERI", Rural Technology Journal, pp. 26-40, September 1987.<br />
[4] V V N Kishore, P Raman <strong>and</strong> V V Ranga Rao, "Fixed Dome <strong>Biogas</strong> Plants - A Design<br />
Construction <strong>and</strong> Operation Manual", TERI, <strong>New</strong> <strong>Delhi</strong>, 1987.<br />
[5] R Myles <strong>and</strong> A Dhussa, "Comparison of Performance of Janata <strong>and</strong> Deenb<strong>and</strong>hu <strong>Biogas</strong><br />
Plants, Paper presented at the National Solar Energy Convention, <strong>New</strong> <strong>Delhi</strong>, <strong>India</strong>.
* MARUTI BIOGAS PRESSURE REGULATOR *<br />
<strong>Biogas</strong> Pressure Regula<strong>to</strong>r reduces the plant pressure up <strong>to</strong> 3" of W/C <strong>and</strong> delivers the gas <strong>to</strong><br />
the appliance at this constant value when s<strong>to</strong>ve is in ON position. Plant supp1y pressure will<br />
go on reducing continuously when the gas is consumed. When the plant pressure drops <strong>to</strong> the<br />
value of 3" of W/C, the regula<strong>to</strong>r au<strong>to</strong>matically s<strong>to</strong>ps its working <strong>and</strong> thereafter the delivery<br />
pressure will be the same as the plant supply pressure. To some extent regulation of the gas<br />
consumption can be done by taking care continuously <strong>and</strong> operating the gas tap of the s<strong>to</strong>ve.<br />
But the people would never bother about this <strong>and</strong> they never take car& <strong>to</strong> operate the tapwhatever<br />
the instruct ions passed <strong>to</strong> them, <strong>and</strong> hence this <strong>Biogas</strong> Pressure Regula<strong>to</strong>r is very<br />
essential <strong>to</strong> be installed on the supp1y 1ine in the kitchen near the s<strong>to</strong>ve, <strong>and</strong> the consumer<br />
will never <strong>to</strong> bother <strong>to</strong> operate anything by very nominal cost.<br />
In fixed dome type of plants very high pressure is deve1oped <strong>and</strong> we can't get the supp1y at<br />
constant pressure. When 6 Cmt. capacity Dinb<strong>and</strong>hu type of plant is full of gas, the maximum<br />
plant pressure developed is 30" of W/C <strong>and</strong> it goes on reducing up <strong>to</strong> zero when the gas is<br />
consumed continuously <strong>and</strong> the plant is emptied. For different capacities of Dinb<strong>and</strong>hu type<br />
of plant the design of permits the maximum pressure <strong>to</strong> be developed as follows. . .<br />
Capacity in Cmt.<br />
Maximum Pressure Developed<br />
Cms. of W/C<br />
inches of W/S<br />
1 45.00 17.71<br />
5 57.50 22.63<br />
3 63.00 24.80<br />
4 70.00 97.55<br />
6 75.00 29.50<br />
All the <strong>Biogas</strong> appliances are designed <strong>to</strong> operate at 3" of W/C. pressure. That means at that<br />
particular pressure only the maximum Thermal Efficiency of the appliance can be achieved,<br />
<strong>and</strong> at that pressure only the consumption of the gas will be as per its rated capacity as printed<br />
over the name plate of the appliance. We have mentioned earlier that by experiments we have<br />
concluded that consumption rate is about 40 % higher if the delivery-pressure <strong>to</strong> the<br />
appliance is daub led up. Hence at a very high consump11on rate we suffer a great loss of<br />
fuel as the size of the burner is insufficient <strong>to</strong> burn complete gas entering in<strong>to</strong> it due <strong>to</strong><br />
improper air-fuel ratio <strong>and</strong> insufficient opening area of holes. Thus when we operate the<br />
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<br />
monoxide <strong>and</strong> methane which are hazardous <strong>to</strong> human 1ife are spread in kitchen atmosphere.<br />
Means we not only lose the utility of valuable fuel, but adds the pollution in kitchen which<br />
proves nonhygenic.<br />
The installation of a <strong>Biogas</strong> Pressure Regula<strong>to</strong>r solves all these problems as it delivers the gas<br />
at required pressure only <strong>to</strong> the appliance.<br />
In order <strong>to</strong> find out that how much fue1 can be saved by using a Pressure regula<strong>to</strong>r, we<br />
carried out -six thermal efficiency tests on 2 cmt. Dinb<strong>and</strong>hu plant at different delivery<br />
pressure without using pressure regula<strong>to</strong>r. The thermal efficiency tests were carried out as per<br />
the procedure laid down by B.I.S. in IS:8749. The connections of the equipments are shown<br />
on a Separate Sheet No. 1, Diagram No, 1 - Observations, readings <strong>and</strong> calculated results are<br />
shown in Separate Sheet No. 2 in a tabular form.<br />
We also carried out three Thermal Efficiency tests at different supply pressure, but at a<br />
constant delivery pressure of 3" of W/C with a use O-F a pressure regula<strong>to</strong>r <strong>to</strong> get the<br />
maximum Thermal Efficiency, The connections of equipments are shown in a Separate Sheet<br />
No. 1 Diagram No. 2. The results are recorded in a tabular form in Sheet No. 3. Dry type gas<br />
flow meter was used in both the cases. The flow meter was caliberated precisely using a very<br />
accurate wet type gas flow meter in labora<strong>to</strong>ry. 151 marked Single Burner Cock s<strong>to</strong>ve having<br />
rated capacity of 450 1/h et S.T.P. was used for all the tests,. the methane content of the gas<br />
was 55 % <strong>and</strong> the colorific value of pure methane is taken 8 Kcal/litre at S.T.P.<br />
From the reading available for above nine tests, we plotted following graphs.<br />
(1) Average delivery pressure v/s Thermal Efficiency. (Graph No. 1)<br />
(2) Average delivery pressure v/s Rate of Consumption. (Graph No. 2)<br />
In full utilisation of gas in a fixed dome type of a plant percentage saving due <strong>to</strong> the<br />
presence of regula<strong>to</strong>r can be found out from Graph No. 1 by finding the Thermal Efficiency<br />
at Average pressure<br />
<strong>and</strong><br />
% saving for that particular plant can be arrived by using formula given below.<br />
Percentage Saving in different capacity Dinb<strong>and</strong>ha plant is shown in tabular form on Graph<br />
No. 1 itself.<br />
From the above table it is quite clear that higher the plant pressure, the percentage saving of<br />
the gas is more. Means higher the plant capacity, the percentage saving of the gas is more,<br />
because maximum pressure that can be developed in higher capacity of plants is higher as per<br />
design of the plants.
A comparison table of different capacity of Dinb<strong>and</strong>hu plants is given below.<br />
Size of plant in Cmt. 1 2 3 4 6<br />
1. Gas Holding capacity in ltrs.- 330.00 666.00 1000.00 1235.00 <strong>20</strong>00.00<br />
2. Average working pressure in - 10.35 12.80 13.90 15.27 16.<strong>20</strong><br />
inches of W/C.<br />
3. Corresponding Consumption - 865.00 980.00 1025.00 1085.00 11<strong>20</strong>.00<br />
rate in 1/h at ambient cond.<br />
4. Total running time of the - 22.89 39.27 58.53 68.29 107.14<br />
regula<strong>to</strong>r in minutes.<br />
5. Total running time of the - 44.00 88.80 133.33 164.66 266.66<br />
plant with the use of a regula<strong>to</strong>r<br />
in minutes.<br />
This shows that running time of the plant is more than two times if regula<strong>to</strong>r is used <strong>and</strong><br />
delivery pressure is maintained constant 3" of W/C.<br />
As conclusion we can say that the advantages of using a <strong>Biogas</strong> Pressure Regula<strong>to</strong>r are as<br />
follows.<br />
(1) There is a very considerable saving of gas depending upon size of the plant <strong>and</strong><br />
that saving is from 22 % <strong>to</strong> 42%.<br />
(2) Running time of the plant is more than two time5, <strong>and</strong> hence enough time is available<br />
for cooking before the gas is exhausted.<br />
(3) Life of appliance is increased, because gas taps of the appliance are not getting<br />
jammed. This is because of sudden pressure drop because of the presence of<br />
Regula<strong>to</strong>r, water vapour on verge of condensation gets completely vepourised, <strong>and</strong><br />
passes through tap in complete gaseous form at low velocity. Otherwise gas<br />
containing vapour in semi 1iquid state at very high pressure washes away the<br />
lubricants applied on the tapered plug of the tap, <strong>and</strong> in very short period taps get<br />
jammed.<br />
(4) We do not have <strong>to</strong> set air shutter every now <strong>and</strong> then.<br />
(5) Pollution is reduced <strong>to</strong> minimum.<br />
(6) KVIC type of plant can deliver the gas at constant pressure, but the installation <strong>and</strong><br />
maintenance cost of KVIC type of plants is very very high as compared <strong>to</strong> that of<br />
fixed dome type of plant of the same capacity. Hence by installing a pressure<br />
regula<strong>to</strong>r on fixed dome type of plant at a very nomincal extra cost, the benefits of<br />
both the types can be availed.<br />
(7) Because of high saving of the gas, a fixed dome type of plant of a smaller capacity<br />
can be installed for the same requirement of the gas during a day. That will again<br />
reduce the installation cost of the plant being of a smaller capacity. Hence with the<br />
same funds available for biogas activity, more number of plant can be installed.
Annex 4
Sr.<br />
No.<br />
District<br />
POTENTIAL IN GUJARAT<br />
Cattle<br />
population<br />
(in lacs)<br />
Milk<br />
producer<br />
Co-op.<br />
Soc.<br />
Member<br />
of Milk<br />
Producers<br />
Co-op.<br />
Societies<br />
('000 Nos<br />
Potential<br />
1. Jamnagar 4.92 30 1 49,<strong>20</strong>0<br />
2. Rajkot 6-73 423 27 67,300<br />
3. Surendranagar 3.95 323 21. 39,500<br />
4. Bhavnagar 6.55 219 15 68,500<br />