The milk production of India has reached 140 mn tons/ annum in the year 2013-14. About 60% of milk is consumed in liquid form, while the remaining 40% is used for the production of butter, cheese, curd, paneer, ice cream, dairy whiteners and traditional sweets (Vijayaraghavan etal., 2011). Bennan et al. (1989) found that dairy industries have 60% of total energy consumption in refrigeration plants and the rest is consumed in other plants. So, energy conservation in refrigeration plant has more value with respect to the economics of the plant and for reducing the production cost.
Most commonly used refrigeration and AC systems for industrial and commercial requirements are Vapour Compression Refrigeration Systems (VCRS) and Vapour Absorption Refrigeration Systems. The first known machine to produce continuous cooling was invented by the Frenchman Ferdinand Carre in 1859. It was the earliest version of ‘aqua ammonia’ absorption system. But, commercially viable compression refrigeration system working with NH3 was introduced in 1875.
Although, the diary industry is not identified as an energy intensive industry, to be competitive in today’s global business environment, effective and efficient use of energy as well as its conservation is pivotal to the productivity and profitability. Energy conservation is closely related to the environmental issues in terms of polluting effect caused by emission of CO2 and other GHGs. Moreover, with the increasing fuel prices and global warming, there is an urgent need to conserve energy and manage energy consumption across all facets of dairy industry (Singh et al. 2010).With enhanced economical activity, the energy demand as well commercial energy consumption has been increasing at ~6% during last two decades; India ranking 5th in the world. The sector wise energy consumption details are indicated below: agriculture (5%), residential (10%); transport (22%); industry (49%); others (14%). Import dependency is 9% for coal, 77% for crude oil and petroleum product and 31% for natural gas (Desai and Zala, 2010). The recent trend is to change over from VCRS to waste heat assisted Vapour Absorption Refrigeration System (VARS). It utilises the waste energy efficiently and helps in reducing the consumption of electric grid supply. VARS is widely used in dairy industry to utilise the waste energy generated by various operations to save electricity and help in minimizing green house effect problem over the world.
Vapour Absorption Ref. System
VARS is widely used in industry when low grade thermal energy is available and fuel is cheaper than electricity. This system replaces the compressor with a generator and an absorber. The absorber acts like the suction side of the compressor, it draws in the refrigerant vapour to mix with the absorbent. A pump pushes the mixture of refrigerant and absorbent up to the high-pressure side of the system. The generator delivers the refrigerant vapour to the rest of the system. The refrigerant vapour leaving the generator enters the condenser, where heat is transferred to water at a lower temperature, causing the refrigerant vapour to condense into a liquid. Therefore, it produces refrigeration effect in evaporator (Butz et al., 1989; Fan et al., 2007).
Ammonia-Water VARs
In industry to maintain the below sub zero temperature and freeze milk products the ammonia-water system is used. The boiling point temperature difference between ammonia and water is not very high, both ammonia and water are generated from the solution in the generator. Properties of ammonia are not compatible with materials such as copper or brass, normally the entire system is fabricated out of steel. Another important difference between this system and water-lithium bromide systems is in the operating pressures. While water-lithium bromide systems operate under very low (high vacuum) pressures, the ammonia-water system is operated at pressures much higher than atmospheric (Modahl et al., 2002). It is also important unlike water, ammonia is both toxic and flammable. Hence, these systems need safety precautions. In an ammonia-water absorption refrigeration system compared to water-lithium bromide systems, three additional components are used: a rectification column, a dephlegmator and a sub-cooling heat exchanger.
Water-Libr VARs
VARS using water-lithium bromide pair is extensively used in dairy industry. Water is used as refrigerant; using these systems, it is not possible to provide refrigeration at sub-zero temperatures. A twin drum system consists of two vessels operating at high and low pressures. The cooling water flows first to absorber, extracts heat from absorber, and then flows to the condenser for condenser heat extraction. This is known as series arrangement. This arrangement is advantageous _ as the required cooling water flow rate will be small and also by sending the cooling water first to the absorber, the condenser can be operated at a higher pressure to prevent crystallisation (Young et al., 1997). A refrigerant pump circulates liquid water in evaporator and the water is sprayed onto evaporator tubes for good heat and mass transfer. Heater tubes (steam or hot water or hot oil) are immersed in the strong solution pool of generator for vapour generation. Pressure drops between evaporator and absorber and between generator and condenser are minimized, large sized vapour lines are eliminated, and air leakages can also be reduced due to less number of joints. In multi-effect systems a series of generators operating at progressively reducing pressures are used (Kang et al., 2008).
The effects of the inlet concentration of lithium bromide solution on the heat transfer. In the range of the inlet solution concentration between 60% and 64%, the heat transfer coefficients increase with the increase of the solution concentration.
A car AC system based on an absorption refrigeration cycle using energy from exhaust gas of an internal combustion engine…
The choice of Ammonia-water combination is not made without considering certain disadvantages: ammonia attacks copper and its alloys when it has been hydrated. Therefore, all components are made from mild steel or stainless steel. The American National Standards Institute (ANSI) (King, 1977) classified refrigerants into three groups considering their safety in use. Ammonia, due to its toxicity, falls into group 2, which means it cannot be used in AC systems in direct expansion in the evaporator coil. Equipment must be installed outside of the inhabitant space. To circumvent the toxicity problem, water or glycol is used as a secondary fluid to transfer the heat from the passenger space to the evaporator. Thus, the chance of ammonia contact with the passengers is minimized.
Design of the Prototype System
Preliminary analysis (Wang, 1997) showed that an absorption refrigeration plant with a 2 kW cooling load at 0OC and with water as a secondary fluid, is more than sufficient to aircondition the passenger space of the NISSAN 1400 truck.
This prototype unit shown in Fig. 1 consists of the generator and analyser
- Reflux condenser
- Condenser
- Accumulator
- Evaporator
- Absorber
- Solution pump
- Expansion valve
- Solution expansion valve
- Heat exchanger
- The fan coil
- Serves for both heating and cooling of the passenger’s space
The theoretical analysis, is verified by both laboratory and road tests through the results obtained. This work results from a prototype which will have to be improved for further development. The claim that is made from this work is that it has shown the feasibility of such a system in a positive frame.
- In the exhaust gases of motor vehicles, there is enough heat energy that can be utilized to power an air-conditioning system. Therefore, if air-conditioning is achieved without using the engine’s mechanical output, there will be a net reduction in fuel consumption & emissions.
- Once a secondary fluid such as water or glycol is used, the aqua-ammonia combination appears to be a good candidate as a working fluid for an absorption car air-conditioning system. This minimizes any potential hazard to the passengers ( Vicatos et al,.2008)
Solar Assisted Cooling
The 1st cooling system assisted by ARUN solar boiler has been installed at the office building of Turbo Energy Limited (TEL), Paiyanoor, near Chennai.
TEL has successfully installed one ARUN solar boiler system for fulfilling its hot water requirements for operating a Vapor Absorption Machine (VAM) for air-conditioning/comfort cooling for its administrative block. It is in the process of installing another dish for increasing its air-conditioning capacity. The process of hot water generation for operating the Vapour Absorption Machine for airconditioning with the help of ARUN solar boiler is as explained in the figure below:
Description of Schematic
The vapour absorption machine (VAM) installed at TEL, is hot water driven. Pressurized water at 180°C is required for the machine to operate at an optimal level. The return temperature of the hot water is 160 °C. The machine with 40 TR capacity requires 5 m³/hr of the pressurized hot water which can be catered to by 2 ARUN dishes. The solar circuit is kept pressurized at 15 bar using the nitrogen pressurization system. The nitrogen cylinders are connected to the expansion tank in the circuit for this purpose. The cooling system is used for air conditioning of the administration office at the plant.
Operation Philosophy
The system is kept pressurised at 15 bar pressure to avoid steam formation within the circuit. The water at 160OC, from the VAM, is taken as inlet to the ARUN®160 dishes and it is heated to 180OC. The average heat output from the two dishes is about 1,00,000 kcal/hr, which is sufficient for the heat requirement of the vapor absorption machine.
Cooling At NTPC
Thermal enabled air-conditioning / comfort cooling system with storage, developed by Clique Solar. This Solar Thermal air-conditioning or solar thermal air cooling system consists of two dual-axis tracking solar concentrator of Fresnel design, named ARUN. The ARUN solar boiler provides dry saturated steam at 180OC at about 200kg per hour. The steam is fed to a 50 TR (i.e. about 175 kW of cooling) Vapour Absorption Machine (VAM). In turn, the VAM utilises the thermal energy of the steam to produce the cooling effect. The distinguishing feature of the system is the storage tank that can store up to 2 days of chilling capabilities. Offices are generally closed on weekends. To avoid wasting the solar energy, this 2-day storage facility has been included. This stored energy can be utilised to provide AC during lean/non-solar periods or to cool a larger area. The system is also capable of running as a heat pump in winter without any alteration of pipe work. This Solar Thermal AC system is a low carbon, green house gas free air conditioning solution. It has an efficiency of 80%, consumes negligible auxiliary power and occupies less area compared to conventional AC system.
Conclusion
- India is among the world leaders in agricultural production however much of our produce goes waste due to absence of proper storage facilities. Refrigeration is thus vitally important for our country.
- Milk produce is also adversely affected due to lack of refrigeration.
- Cool drinking water is unavailable to the people in non electrified villages.
- Medical facilities are also adversely affected due to break in the cold chain as the medicines move from the production zone to the rural areas.
- Usage of CFCs affect the environment adversely.
