Biogas Refrigeration

India is now the second largest producer of fruits and vegetables in the world and is the leader of several other major horticulture crops [1].During 2015-16, the production of horticulture crops was about 283.36 million tons [2]. This large quantity of horticulture production is not utilized in the country therefore it needs advance cold storage structures for its later utilization. Biogas offers a renewable and economical feasible energy source for large scale cold storage of these produced fruits and vegetables in the country. Biogas can be produced from agriculture waste, animal waste, fruits and vegetables waste, slaughterhouse waste, municipal solid waste etc. Large quantity of these biodegradable wastes is available in the country for biogas production. Biogas produced from these waste materials offers sustainable solution for refrigeration of horticulture products.There is high demand for cold storage of fruits and vegetables in many parts of the world including India. In many parts of rural India, conventional electricity is not available and it is not economical viable option for small holding farmers in India. Biogas based refrigeration system helps to reduce losses of fruits and vegetables during post-harvest operation. Vaccines, medicines and stored blood need to be kept at low temperature during transportation and storage. Biogas can be used as a source of energy to drive refrigeration cycle. Till now biogas is little utilized commercially for refrigeration but in future it could be used in large scale as renewable source for cold storage of horticulture crops. Biogas refrigerators replace conventional refrigerators or other kerosene fueled cooling devices which ultimately helps to reduce greenhouse gas emissions in the environment. Biogas based refrigeration system could play a vital role in achieving millennium development goals. Therefore, there is huge demand of non-conventional energy based economical feasible refrigeration system for preservation of horticultural products and storage of lifesaving vaccines.

Biogas based vapour absorption refrigeration system

Biogas based vapour absorption refrigeration system consists of absorber, generator, condenser, throttle valve, evaporator and heat source from biogas as shown in following figure. In absorber there is solution of water and ammonia refrigerant at low temperature. This low temperature mixture of ammonia and water is send to the generator through pump where it is heated externally using biogas. Due to heat from biogas, ammonia gets separated from ammonia-water mixture and converts in to high pressure ammonia vapour. This high pressure ammonia from the generator is send to the condenser where it rejects heat to the atmosphere and becomes high pressure liquid ammonia. High pressure liquid ammonia is throttled and passed to the evaporator. At evaporator low pressure ammonia refrigerant absorb heat from the place where cooling is to be done. After heat absorption from the cooling room low pressure ammonia liquid gets evaporated and passed again to absorber in the form vapour ammonia. This vapour ammonia gets mixed with ammonia and water mixture and cycle continues again. Refrigeration effect is due to absorption of heat at evaporator from the room.

Biogas based vapour absorption refrigeration system
1. Absorber 2. Pump 3. Heat from biogas 4.Ammonia with high pressure 5.Generator 6. High pressure ammonia vapour 7. Condenser 8. Throttle valve 9. Evaporator 10.Low Pressure ammonia vapour

Development Status

The application of biogas based refrigeration system is restricted to places where biogas is available or can be produced from waste resources. Generally in rural areas there is availability of animal dung and agricultural residues for biogas production, so it can be utilized for refrigeration of agriculture produce such as perishable fruits and vegetables. Technology of biogas refrigeration is little used commercially in the field. The technology has significant potential for its development and simultaneous application for power generation and heat along with refrigeration utility. Research is needed to know the refrigeration potential, technology development, efficiency improvement and for marketing of developed technology for its widespread utilization.

Scope for Improvement of Technology

There is scope to improve efficiency of biogas refrigeration system and possibility of multiple application of biogas energy to fulfill need of electricity, heat and refrigeration. Commercialization of small as well as large scale models of biogas refrigerators is the key research area for technology development and its widespread application. Biogas refrigeration system provides non-conventional based feasible alternate option to unelectrified rural areas. Therefore, it is necessary to work on cost reduction options to make economic feasibility of complete technology package.

Environment issues

Biogas refrigeration system can save emission of harmful greenhouse gases in the environment and contribute to climate change mitigation. Refrigerant such as ammonia and water used in the biogas refrigeration cycle is not providing any harm to environment. The introduction of biogas refrigeration system provides alternate non-conventional economical feasible option which replace existing conventional cooling devices.

Conclusions

Biogas refrigeration system provides economical feasible renewable option for cold storage of horticulture crops to rural India. Technology reduces emission of hazardous greenhouse gases in the atmosphere and helps in climate change mitigation. The refrigeration system helps to reduce post-harvest losses of perishable fruits and vegetables and contribute to food security and nutritional availability. Large scale cold storage structures can store bulk quantity of agricultural produce for longer time and can give additional surplus income to grower. Biogas refrigeration system is little implemented commercially in the field therefore key research is needed for its efficiency improvement, advance technology development and marketing of developed system in the field for its widespread utilization.

References

• Horticulture statistics at a glance.2015. Government of India
• 3rd advance estimate of area and production of horticulture crops, 2015-2016, National Horticulture Board, Government of India.

AUTHORS CREDIT & PHOTOGRAPH

N L Panwar
Assistant Professor
Maharana Pratap University of Agriculture & Technology
Udaipur, Rajasthan

Pradip Narale
Research Fellow
Maharana Pratap University of Agriculture & Technology
Udaipur, Rajasthan