The document analyzes the performance of a micro turbine-based biogas power plant in Purulia, West Bengal over 6 years. It finds that the plant's electricity generation degraded significantly over time due to a gradual decrease in biogas production from the horizontal plug-flow digester. As the unstirred digester aged, stagnant regions developed and solids accumulated, reducing the residence time and leading to incomplete digestion of waste. This caused biogas output and the plant's operating hours to decline steadily. The document recommends cleaning and recharging the digester periodically, installing agitators, utilizing the second available turbine, and adding another digester to improve sustainability.

1. Paper code: 079
Performance analysis of micro turbine
based grid connected biogas power
plant in Purulia in West Bengal
Krishna Singh1*, Tushar Jash1
1 School
of Energy Studies, Jadavpur University, Kolkata-700032, India
* Corresponding Author. Ph: +919609744215,
E-mail: krishnasingh.jgec@gmail.com

2. Introduction:
o With the rapid increase in population, industrialization
and development the demand for electricity is
increasing in both cities and in rural areas.
o This has forced the Government to think about the
renewable sources of electricity generation. Biogas is
one such option.
o If electricity can be generated from cow dung based
biogas plants, it can significantly reduce
consumption of coal as well as the pollution load.
the

3. Cont...

This in turn can reduce the import of coal thereby
providing financial benefits.

The first micro turbine based biogas power plant was
commissioned in Mohan Dairy Farm in Purulia in
West Bengal in August 2007 for electrification of
two villages through grid.

4. Objectives of the present study:
(1) To analyze the performance of the Purulia plant, for
a longer period (about 6 years).
(2) To study the variation in the production of biogas
and consequent electricity generation as the plant
becomes older.

5. Purulia Power Plant:




The Purulia power plant consists of :
a 125m3 horizontal plug flow type biogas digester fed with
cow dung and water slurry. The digester is neither heated
nor stirred.
two units of Capstone micro turbine each having capacity
of 30 kW but the plant runs at a fixed capacity of 25kW
since commissioning.
The produced biogas is collected in a movable gas holder
inverted on water.
The effluent of the digester is left in the sun to dry.

6. Cont...

The biogas first passes through a heat exchanger where
it is cooled to 210C.

Then the gas enters the suction scrubber for moisture
removal.

Finally, the dry biogas is passed through a sour gas filter
kit, which removes H2S.

The gas pressure is then regulated to 75 psi and fed into
the micro turbine.

7. Schematic diagram of Purulia biogas based power plant

8. Cont...




The dairy farm has 300 cows and the quantity of cow
dung collected is about 6000 kg per day. Out of this, only
2500 kg of cow dung is fed to the biogas digester daily.
The micro turbine generates a 3 phase output, with 46 A
and 400-480 VAC per phase.
The generated power is then transmitted to the demand
centres (nearby villages) through grid.
In standalone mode the electricity is used for charging
the batteries. These batteries provide power to the dairy
and also the starting power to the gas conditioning unit.

9. Methodology and data sources:

The electricity generation data and hours of
operation of the micro turbine were collected from
daily log book of the power plant.

Power details and other techno-economic
components were obtained from the operators of the
plant, Synergy Renewable Energy (P) Limited and
West Bengal Renewable Energy Development
Agency (WBREDA).

10. Performance of the power plant:
Date (mm-dd-yyyy)
Daily average biogas
production (m3d-1)
(1)
09/20/2007
124.59
390
162.77
(2)
10/15/2007
121.40
380
158.01
(3)
12/10/2007
115.01
360
152.92
(4)
01/15/2008
111.81
350
147.49
(5)
03/20/2008
108.62
340
141.73
(6)
09/12/2008
103.83
325
135.64
(7)
11/20/2008
99.03
310
129.21
(8)
02/12/2009
92.65
290
122.45
(9)
06/20/2009
86.26
270
115.35
(10)
09/15/2009
83.06
260
107.92
Sl. No.
Daily operation of
the power plant
(min.)
Electricity generation
(kWh d-1)

11. Cont…
(11)
11/20/2009
76.67
240
100.16
(12)
01/25/2010
70.28
220
92.06
(13)
04/10/2010
63.89
200
83.62
(14)
09/20/2010
57.50
180
74.85
(15)
12/15/2010
51.11
160
65.75
(16)
03/15/2011
43.13
135
56.31
(17)
09/15/2011
35.14
110
46.54
(18)
02/15/2012
28.75
90
36.43
(19)
03/12/2013
19.17
60
25.00

12. Cont…

Biogas feed rate to the micro turbine was obtained
from the turbine specification .

It is observed that there was a gradual decrease in
biogas production rate and the consequent electricity
generation from the power plant over the years.

13. Possible Reasons behind the
decrease in gas production rate:

In an unstirred horizontal plug-flow biogas digester fed
with cow dung and water mixture, the gas production
rate decreases with time because of two reasons.

(1) In the absence of agitation in a horizontal digester,
it is expected that there will be stagnant regions and,
consequently, slurry flow will occur through a channel.
(2) If the digester is unheated and unstirred there will
be accumulation of solid inside the digester and the rate
of biogas production will decrease with time.


14. Cont…

With progressive accumulation of solid in a biogas
digester, the mean residence time decreases
gradually, that may lead to washout of bacteria,
resulting in incomplete digestion of cow dung which
in turn reduces the biogas production.

15. Horizontal plug-flow biogas digester with expected
stagnant zones and solid accumulation:

16. Conclusions and Recommendations:
(1)The performance analysis of the Purulia micro turbine based
biogas power plant revealed poor success of the project.
(2)The power plant has failed to sustain the power generation
at a reasonably higher output level for a longer period.
(3)The performance of the plant has degraded largely because
of decrease in biogas production rate which reduced the
hours of operation of the micro turbine with time.
(4)In the absence of agitation in a plug flow biogas digester
there exists stagnant regions inside the digester and
consequently, slurry flow occurs through a channel.

17. Cont...
(5) As it grows older, solid accumulates inside the digester.
(6) Due to presence of stagnant regions and accumulation of
solids, the actual residence time gradually decreases with time
resulting in incomplete digestion of the organic residues and
consequent reduction in gas generation.

18. Cont...
Recommendations:
(1)To overcome these problems, it is recommended to clean
the digester periodically (once in a year) and recharge it
with fresh waste or the digester be fitted with stirrers.
(2)To clean the digester it is advised to pump water into the
digester to break the accumulated solids first, then employ
a slurry pump to remove the slurry from the digester.
(3)The Purulia power plant uses only one turbine since its
inception although two are available, because of dearth of
sufficient biogas production.

19. Cont…
(4) It is recommended to install another similar
capacity biogas plant and sufficient feed material is
available at the dairy farm to run the second
digester.
(5) Sustainability of the power plant with respect to
electricity generation can be ensured if the above
recommendations are followed.

20. References:
[1] West Bengal Renewable Energy Development Agency, Govt. of West
Bengal, Bio energy programme. http://www.wbreda.org/bio-energyprogramme/ (Viewed Sept 2013).
[2] Unison Solutions, Digester Gas Compression Skid Owners Manual.
http://www.unisonsolutions.com (Viewed Sept 2013).
[3] Capstone Turbine Corporation, Capstone C65 Biogas. http://www.global
microturbine.com/Site/Microturbine/Entries/2013/9/10 _ Capstone_C65__New_-_9_Available.html (Viewed Sept 2013).
[4] Jash, T. and Ghosh, D. N. (1990) Studies on residence time distribution in
cylindrical and rectangular biogas digesters, Energy, 15(11), pp. 987-991.

21. THANK YOU
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