• Cooling India
  • Oct 15, 2016

Bio-Solar Chilling System

Approximately 15% of all the electricity produced in the whole world is employed for refrigeration and air-conditioning processes. The time has come to look at the alternative ways...

- Prof. (Dr.) Deepak Sharma,
Er. Vijayendra Singh Sankhla, 
Er. Kapil Samar


 In a tropical country, like India, refrigeration is most widely used and generally the most energy consuming process. In general, refrigeration is defined as any process of heat removal from a place for preserving foods and medicines by enhancing their shelf life. In today’s situation the energy demand is rising with growth in population. Energy is the crucial input to the development of any country. The International Institute of Refrigeration in Paris (IIF/IIR) has estimated that almost 15% of all the electricity produced in the whole world is employed for refrigeration and air-conditioning processes.

Fig. 1: Schematic diagrams of non concentrating solar collectors
(a) flat plate type... and (b) evacuated type...

Fig. 2: Solar absorption ref. system...

  At the time of independence milk production in India was only 17 million tons per annum. Today India has become number one in milk production, producing 127 million tons per annum with approx. 20% of the total milk production is handled by the organised sectors.

  Farmers mostly dairy farmers who sell their products to export markets, refrigeration could play an important role to increase their annual income. Without cooling capabilities the dairy products have to be sold immediately after taking form animals.

  This reduces the chance of negotiating good prices, because the buyer is in a better bargaining position. Particularly in these sectors, farmers have the potential to produce a lot of biogas through available cattle dung. Solar- Biogas Hybrid based cold Storage technology would be a good opportunity for such farmers to take maximum benefits.

System Features

  Hybrid Solar-Biogas thermal systems use solar energy in day time and biogas for night time as a heat source to produce refrigeration effect. Solar heating system consisting flat-plate solar collectors including a metallic absorber and an insulated casing topped with glass plate(s). Evacuated collectors may also perform better at high temperatures.

  Evacuated collectors are typically made in a glass tube design, i.e., a metallic absorber inserted in an evacuated glass tube, to withstand the pressure difference between the vacuum and the atmosphere. Figure 1 shows schematic diagrams of these two collectors.

Fig.3 Schematic view of biogas based absorption refrigeration system... 

  Hybrid Solar-Biogas thermal sorption refrigeration system uses physical or chemical attraction between a pair of substances to produce refrigeration effect. A sorption system has a unique capability of transforming thermal energy directly into cooling power. Among the pair of substances, the substance with lower boiling temperature is called sorbate and the other is called sorbent. The sorbate plays the role of refrigerant. Fig. 2. And Fig.3 shows schematic diagram of solar powered and biogas power closed sorption system respectively. Working of a sorption refrigeration system is described as under:

• In the evaporator, the fluid refrigerant evaporates by extracting heat from the product or room being refrigerated.
• The evaporated refrigerant flows into the absorber where it mixes with the secondary fluid.
• The resulting solution is then driven into the generator, where it is heated. This heat causes the refrigerant to vaporise.
• The resulting vapour passes into the condenser, where it returns to liquid state and is ready to start a new cycle.

Fig.4: Biogas plant...

Biogas

  Biogas is produced by decomposition of any organic matter in the absence of oxygen/air. Biogas comprises of 60-65 percent methane (CH4), 35- 40 percent carbon dioxide (CO2), 0.5-1.0 per cent hydrogen sulphide (H2S) and traces of water vapours. It is almost 20 percent lighter than air. Biogas cannot be converted into liquid like Liquefied Petroleum Gas (LPG) under normal temperature and pressure. The slurry coming from digester is rich in nitrogen which is an essential nutrient for plant growth.

  Biogas is an easy and healthy cooking fuel since methane emissions from untreated cattle dung and biomass wastes can also be avoided. Since there is no pollution from biogas plants, these are one of the most potent tools for mitigating climatic change and being earth.

Properties

• Biogas is a non-toxic, colourless and flammable gas.
• It has an ignition temperature of 650 – 750 °C.
• Its density is 1.214 kg/ m3
• About 60 percent methane and 40 percent CO2 content
• Calorific value is 20 MJ/m3 (4700 kcal).
• Almost 20 percent lighter than air
• It liquefies at a pressure of about 47.4 kg/cm2 at a critical temperature of - 82.1°C.

  Purified biogas (bio-methane) has a higher calorific value in comparison to raw biogas.

Conclusion

  Dairy and food industries are fast growing industries and day-by-day newer technologies are being introduced to get better quality of foods. Use of conventional energy is common practice for major processing of milk. At present almost all dairy operations are performed using grid supply with diesel gen-set as backup. Milk procurement system has changed in India and now milk is being procured by maintaining cold chain to improve its microbial quality. In this article, an idea has been proposed – by which it is possible to use solar energy and biogas energy to operate vapour sorption refrigeration systems.


Prof. (Dr.) Deepak Sharma
Professor & Head Department of Renewable Energy
Engineering College of Technology & Engineering

Er. Vijayendra Singh Sankhla
Assistant Professor
Department of Mechanical Engineering
Geetanjali Institute of Technical Studies

Er. Kapil Samar
Project Manager
Biogas Development and Training Centre (BDTC),
College of Technology & Engineering, MPUAT Udaipur

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