About biogas heating introduction , types and designs of heating technologies through solar thermal.

1. HEATING OF BIOGAS DIGESTER THROUGH SOLAR THERMAL
By: R. Lavanya , Dr. Deepak Sharma
Department of Renewable Energy Engineering, College of Technology And Engineering,
Udaipur.
1. Introduction:
Biogas can be produced from agriculture manure by anaerobic digestion. This technology
has many benefits in view of environment, agriculture and sustainability. Biogas plants for
family have been extensively used in most of the farms in India. Temperature is an important
factor that affects the performance of anaerobic digestion. Because of temperature methane
production is less and quality of gas will be less. By mounting Solar heating system to the biogas
plant is used for the enhancement of biogas production in hilly areas.
2. Why to Study Temperature and Anaerobic Digestions?
Anaerobic digestion is a process that results in the production of biogas that can be used a
renewable source of electricity on-farm or sold to the distribution grid. Temperature is a critical
parameter for anaerobic digestion since it influences both system heat requirements and methane
production. Although anaerobic digestion can take place under psychrophilic (15-25°C),
mesophilic (35-40°C), and thermophilic (50-60°C) conditions, temperatures of 35-37°C are
typically recommended for methane production from animal manure. However, digesters require
significant amount of heat energy to maintain temperatures at these levels. There is limited
information about methane production from dairy digesters at temperatures less than 35°C and
results in the literature are presented from laboratory-scale rather than field-scale systems.
From one ton of biological mixture
Temperature Production Rate Digestion Period
Degrees C Cubic metres/day (months)
15 0.15 12
20 0.3 6
25 0.6 3
30 1 2
35 2 1

2. 3. Description of solar heating system for biogas production:
Figure shows the schematic diagram of the proposed system. Solar collectors
scombined with a heat exchanger was used to heating the manure in the bioreactor, and increased
the bioreactor temperature to an optimum value in a steady condition. In order to keep the system
run in steady condition, the control unit was adopted. If there was not enough solar thermal
energy input into the bioreactor (e.g. cloudy), or the water temperature in solar tank is below 45
,the solar heating system stops working, then the auxiliary electrical heating system starts to
supply the heat to the bioreactor. The bioreactor was positioned under the ground. The biogas
produced from the bioreactor was transported to the kitchen by the designed pipe for cooking.
Schematic of the system configuration
4. Types of solar heating system
Supply of solar heat to the biogas digester in three distinct ways.
1. Active solar system
2. Passive solar system
3. Solar canopy.
4.1.Active system:
The active system involves heating of the digester feed or direct of the digester content.
The incoming feed is pre-heated using solar energy during day and is fed to the digester when it
attains the decreased temperature. By constructing a shallow solar pond water heater over the gas
holder with an idea to have a solar water heater, so that hot water could be used for hot charging.
Another method is the circulation of hot water from the solar pond through the coils in the
digester by a biogas powered pump.

3. 4.2.Passive system:
This method involves the construction of a greenhouse around the digester to
capture the radiant heat energy.
4.3.Solar canopy:
Polythene/plastic sheet is used as a canopy for tapping solar energy. This method
is used to enhance the biogas production for the low temperature in winter. This method is not
effective at higher hills because of snow & low temperature , where the plastic /polythene sheet
used for canopy could not last long.
5. Designs using in solar heated biogas plant
5.1.Solar Hut:
A black plastic hut is made over the dome of a biogas digester so that solar
radiation is absorbed by the hut and consequently rising the temperature of the digester
PROS CONS
Simple in design and less costly as it requires
an erection of a simple hut with black cover on
the top.
Heat transfer from the hut to the digester will
not be efficient enough to maintain high yield
of biogas during a cold climate.
Susceptible to vandalism or theft.
Life span of the hut which needs to be replaced
periodically.
5.2.Use of solar water heater:
In this design the slurry inside the digester is kept underground and heated via heat
exchanger using the hot water from the solar water heaters so as to maintain the desired
temperature for better production of biogas
PROS. CONS
Efficient system if enough sunlight is available
as it serves to increase the digester’s reaction
temperature and/or reduce reactor’s volume.
If water gets overheated, unnecessary reactions
take place within the digester. Extra stirrer
may be required.

4. Occasional maintenance and monitoring.
Simple design and easier to make
Low temperature in the night may freeze the
heat transfer fluid in the solar collector.
Water used to cool the generator or in solar
water heater needs to be filtered so as to
prevent scaling.
Initial capital investment can be an obstacle to
its successful implementation.
5.3.Heating the biogas by using reverse absorber type solar heater:
PROS CONS
The convective and radiative heat losses in this
type of solar air collector are reduced due to
the down facing of the absorber.
Difficult to mount the biogas digester on the
top of the solar system.
Suitable only for small biogas system
References :
1. Application Of Solar Heating System In Biogas Production. By Rong Dai1,2 , Chang
Chun2, Zhibin Xu1, Xiaobing Liu1,2, Ζhifeng Wang2, 1Himin Solar Energy Group Co.,
Ltd, Dezhou, Shangdong 253090, P.R. China, 2Institute of Electrical Engineering,
Chinese Academy of Sciences, Beijing 100080, P.R.China.
2. Effect of Temperature on Methane Production from Field-Scale Anaerobic Digesters
Treating Dairy Manure. By Osman Arikan, Assoc. Prof., Istanbul Technical Univ., Dept.
of Environmental Eng., Istanbul, Turkey. Visiting Scientist, USDA-ARS, BARC,
Beltsville, MD, Visiting Assoc. Prof., University of Maryland, Dept. of Environmental
Science&Tech., College Park, MD. arikan@itu.edu.tr.
3. “Optimization of Biogas Plants using Digester Heating Technologies”. By MinErgy Pvt.
Ltd. Lalitpur, Nepal info@minergynepal.com www.minergynepal.com.submitted on
30thJune, 2014