solar energy assisted ice plant...solar energy assisted ice plant prof. r.s. bhatt mechanical...

SOLAR ENERGY ASSISTED ICE PLANT

Prof. R.S. BhattMechanical Engineering Department,

Birla Vishvakarma Mahavidyalaya (Engineering College)Vallabh Vidyanagar

Gujarat.Email: [email protected]

Siddharth RaghavanDirector,

Mamata Energy Ltd., Ahmedabad

Email: [email protected]

Deval Dixit Suraj Andharia Mechanical Engineering Department, Mechanical Engineering Department, Birla Vishvakarma Mahavidyalaya (Engineering College) Birla Vishvakarma Mahavidyalaya (Engineering College) Vallabh Vidyanagar Vallabh Vidyanagar Gujarat. Gujarat.

Email: [email protected] Email: [email protected]

Abstract— Energy conservation and use of the renewable sources of the energy in most efficient manner is the main challenge faced by the engineers in today’s world. Energy conservation can be implied strongly only if the energy is utilized in the optimum manner. To fulfill the increasing amount of the energy ,conservation of the energy is very important. So only where ever possible we should use the non conventional sources of the energy. With this idea we entered in thinking about ice plant. Here we have made an attempt to design the ice plant operating with solar energy. Presently in industrial field the ice plants are operated using compressors which consume large amount of the electrical energy. As per one survey it is estimated that out of total electricity utilized, 15% goes for the purpose of refrigeration. So if we are able to make our refrigeration system work on solar energy, lot of saving of energy can be done. Here we have tried to use solar energy for producing ice in an ice plant.

I. INTRODUCTION

The first recorded solar-driven machine was in 1872 by Albel Pifre, in Paris, for producing a small amount of ice. In the beginning of the 20th century, many countries were interested in using solar energy, but the technology was focused only on the heating of water or air. Research in ‘solar air-conditioning’ increased only after 1965. During the first oil crisis in 1973, the air conditioning system was considered as a luxury and an unnecessary system. The attention was focused on improvement of design and efficiency of the refrigeration system rather than investigation of it as a novel system. The solar energy is the everlasting source of energy and our country’s geographical location allows tremendous scope of utilizing the solar energy. Many countries have fundedresearch and development project, in order to develop commercial units as an alternative of continuing the dependence on the use of conventional fuels. The world started searching for new energy sources. But the same can be viable only if 1) Its availability is in abundance 2) It can be harnessed as per need 3) It is economically viable

The use of solar energy can be made in many fields like water heating, space cooling, space heating, electric conversion, power generation, distillation etc. Now, here we have tried to work on producing refrigeration using solar energy. We have done analysis of ice plant and represented here its functioning using solar energy with all the required data. Here we selected the ice plant of fixed capacity. The enthalpy drop taking place at the various components is found using enthalpy concentration chart. On completion, we were able to find out the amount of energy needed to be supplied in the generator by the solar energy source. To collect this energy various components like the solar collector, storage tank, and manifoldare used. The type of collector used is evacuated tube collectoras it will give us the temperature of water around 85˚C. Due to the collector efficiency and storage efficiency the net amount of heat produced is more than that required in the generator.

This system being practically possible to be operated by the solar energy, its only drawback is that its initial cost is very high. But with the increasing demand of such products and government support provided on such innovative products, will help to decrease the initial cost of the product. Besidesthis, its easy and free availability and pollution free naturemakes its use for the refrigeration very effective.

II. USE OF SOLAR ENERGY FOR REFRIGERATION

To use the solar energy for the purpose of refrigeration, there are two ways in which the solar energy can be used:1) Converting solar energy into electrical energy and use the same for refrigeration2) Directly using the heat energy for refrigeration. So many refrigeration cycles are available for producing refrigeration, but for our application of ice plant, we require either VCR or VAR system to be operated. Hence for selecting one of the two cycles, comparison is made between the two to find best suitable refrigeration cycle for our “Solar Energy Assisted Refrigeration”.

13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India

National Conference on Recent Trends in Engineering & Technology

III. COMPARISION BETWEEN VCR AND VAR

In VCR system, compressor is used. It consumes more electrical energy as it has to work against large decrease in volume of refrigerant. For e.g. vapour refrigerant at 0.0061 bar has a volume of 206.31 m3/kg and when compressed to 0.07375 bar its volume has to be decreased to 19.546 m3/kg. So, large electrical energy will be required.

Maintenance of VAR is less, as there is only one moving part & others are steady parts. Pump does not consume more power like compressor.

VAR system is not dependent on the increase or decrease in evaporator pressure because it can be adjusted easily by increase or decrease in the generator temperature.

Quality of refrigerant leaving the evaporator in VCR system is important as compressor cannot compress liquid while it is not so important in VAR system as absorber is there.

As shown below if VCR has to be operated, solar energy has to pass through many conversions and loss increases. Solar → Heat → Electrical → Mechanical

Energy Energy Energy Energy While in VAR only one conversion from solar to Thermal energy takes place. Solar → Heat Energy Energy

VCR cycle requires photovoltaic cells, which are

costlier as compared with the solar collectors.

IV. VAR SYSTEM OF AQUA – AMMONIA

In our application we have selected the VAR cycle working on the aqua ammonia pair.Some substances have more affinity for another substance at desired temperature and pressure. This principle is used in working of VAR system.It is one of the refrigeration systems which mainly use heat energy instead of mechanical work. Its main components are generator, condenser, absorber, evaporator, pump etc.Here one fluid is used as the refrigerant, while the other fluid is used as absorbent. Ammonia is used as refrigerant and water as absorbent. With ammonia as refrigerant we can attain much lower temperature. The compressor of VCR is replaced by generator, pump, absorber, and liquid throttle valve.

In this project as discussed earlier we are going to replace this VCR system by VAR.The water is made to flow surrounding ice cans. This water has salt dissolved in it to decreases the freezing point of the water and takes it up to -8˚C. This water gets cooled as it passes through the space surrounding the evaporator tubes. This cooled water will in turn produce ice in cans.

Up till here this was the basic information of the systems which will be used in solar energy assisted refrigeration. Now assuming that a vendor in GIDC needs to supply 10 tonnes of ice per day, and he is interested in doing it using solar energy,how can he do it?He has to first find the enthalpy drop at evaporator, absorber, generator, and condenser. From this, he will be able to know the heat needed to be supplied to the generator. This heat to the generator will be given by solar energy.

V. CALCULATION FOR SOLAR ENERGY ASSISTEDICE PLANT

Suppose we want to produce ice from water at (30˚C) to ice at (-5˚C). This is our aim on which complete design of VAR system is based.Calculations:-Total Energy required to be extracted from water is = 30˚C – 0˚C + 0˚C – 0˚C + 0˚C – (–5˚C) Water Water – Ice Ice = (m Cp ∆t) + ENTHALPY + (m Cp ∆t) Water Fusion Ice

= (1000kg * 4.187 kJ/kg K *30K) + 335*1000 kJ + (1000 * 1.94 * 5) = 470280 kJFor 10 tonnes of ice = 10*470280 =4702800 kJ

So refrigeration capacity = 4702800/ (24 * 3600) =54.43 kJ/S capacity in TR = 54.43/3.5 = 15.55 TR

So to produce 10 tonnes per day we require system of 15.55 TR capacities. Now to produce this much TR using NH3-H2O system, we need to design the appropriate VAR system.



Here we are going with certain assumptions in designing VAR system, while the evaporator and condenser condition are knownPlant capacity = 15.55 TRCondenser temperature = 30˚C and corresponding pressure is 12 barEvaporator temperature = –5˚C and corresponding pressure is 3.5 barConcentration of strong solution leaving the absorber = 0.4Temperature of aqua ammonia leaving the generator = 85˚C

Now based on this, we used the enthalpy concentration chart.We were able to find the enthalpy drop across various components and the mass flow rate too.After finding the enthalpy drop across each component we multiplied it by mass flow rate to get the energy required in that section...by this way we got the energy required to be given in the generatorMass flow of refrigerant (m)= Capacity / RE = 0.05 kg / s (obtained by doing calculation)So, we get heat required to be given in generator Qg = 116.5 kW

So, our interest lies in that 116.5 kW. Nowadays this energy is supplied with the help of fuel like petrol, diesel and even coal and kerosene. Theses are all going to vanish one day, so instead of this thing if we use something that is permanent and not harmful to human being, than there cannot be another option better than solar energy. So if we are able to supply this 116.5kW energy with help of solar energy, than “solar energy assisted refrigeration” will truly come into existence. But now the question comes how to collect the solar energy? In which form to collect the energy and in which form supply it to thegenerator?

VI. EVACUATED TUBE COLLECTORS

There are many ways to collect the solar energy. We need to find out how many pipes are needed to produce 116.5kW. But we need to supply 116.5kW in generator. But the hot water comes in the generator through hot water tank, which has the efficiency of 85%. The water enters the hot tank through manifold, in which the heat is given to water by collector. The efficiency of the collector is taken as 76%. For this we can use flat plate collector, concentrated collector and recently developed and most efficient the evacuated tube collectorswhich can work in both direct and diffused sun light. Temperature around 90˚c to 100˚c can be obtained. Vacuum is maintained between outer pipe surface and inner plate:-- Radiation loss α t4

Where t= temperature As no air in between absorbing surface and surrounding,radiation losses are minimized to a great extent. Our aim is to achieve 80˚C-85˚C temperature hence for our refrigeration purpose we select this collector. Before linking this collector

with our VAR ice plant we need to know about the working of the evacuated tube collectors.

The blue colour rectangular strip present in the middle is a metal strip having coating of aluminum nitrate. It has a very high absorbing capacity of almost 92% i.e. out of the entiresolar energy incident on it; it will absorb 92% of solar radiation.Between the rectangular strips there is a small cylindrical copper tube. The heat absorbed by the aluminum nitrate will be passed on to this copper tube. In this hollow copper tube, a solution of propylene glycol is present, which on receiving the heat from copper tube will evaporate.The tubes are kept slanted, so the evaporated propylene glycol will move upwards as this is the tendency of most of the gases.This vapour propylene glycol reaches the heat pipe as shown in the figure. At this end the water is passed through the heat pipe which is at low temperature than that of vapour propylene glycol. During the heat exchange propylene glycol losses latent heat of vaporization and gets converted into liquid and moves down the tube. This latent heat it received by the water flowing and so temperature of water increases. This liquid propylene glycol again gets heated and comes at top of the heat pipe and same process gets repeated.High efficiency is obtained by using powerful insulation like glass wool and Rockwool.So 180.34 ≈ 181 kw energy to produced.Energy incident on earth surface is 500W/m2 to 1000W/m2.Designing for worst condition i.e. for winter when sun intensity is not large enough 500W/m2.Selecting pipe of 2m length and 0.1m width So energy produced by one pipe = 0.5 kW/m2 * (2 * 0.1) m2

= 0.1kW / pipe So total number of pipe needed to produce 53kW is: n = 181 /0.1 = 1810 pipes

Assuming each collector is made up of 20 pipes, total 91 collectors will be needed. By keeping these many collectors,we will be able to operate our ice plant from 9 A.M to 6 P.M. During the remaining time we must use some other source of energy like kerosene, coal etc.

VII. ANGLE OF COLLECTOR

Collectors should be kept such that maximum absorption of the sun rays is done by collectors. This is possible only when sun rays are at 90˚ to the collector surface. Latitude indicates the angle at which the sun rays are incident at a place. So if collectors are kept at an angle equal to latitude of that place than we will get maximum absorption of sun rays. VV Nagar lies at tropic of cancer which is at 23.5˚. So to make this plant in VV Nagar we have to keep collector at 23.5˚.



VIII. LIMITATION WHICH CAN BE OVERCOME

As discussed earlier, this plant will be in operation during day time. But to operate this plant in the night time it will be possible, if another circuit of solar system is kept similar to the one discussed earlier. So to operate the plant in the night we need to keep another solar collector of evacuated type only, and use other two water tank. Advantage of this system is that we will be able to make our system work for 14 – 15 hours. Due to this, the operating cost will decrease as theconsumption of the conventional energy source like coal, kerosene will decrease. The major disadvantage of this system is that the initial cost due to 2 solar panels will increase. Breakeven of this system will be around 7.79 years, means after this many years we will be able to overcome our cost and start earning profit.

IX. CONCLUSION

This system is highly dependent on the cost of the solar collectors. These collectors are produced in china, and it is being imported to India. Due to this the cost of the each collector is around 300 rupees. But in future if production of these collector pipes is started in India than, the cost of the pipe would come around to 170 – 200 rupees, and thereby decreasing the initial cost of the installation The government policy influences the cost very

much. If the government provides proper tax relaxation and subsidies for the products which areusing non conventional energy, than cost of the solar energy assisted refrigeration will decrease.

The system has still not been introduced in the practice, so because of less consumption its initial cost is high, but as the consumption increases its cost will decrease.

The cost is also high because during the night time we were using the conventional source of the energy. So to decrease this cost it is also possible to use the hybrid system, in which bio mass can be used to heat the water. This alternative would be very much useful to us, in making this system feasible.

REFRENCES Dr MOHANA SIR ( Sardar Patel Renewable

Energy Resources Institute )

SIDDHARATH RAGHAVAN SIR (Mamata EnergyLtd.)

Ice Plant ( GIDC, Vitthal Udyognagar.)

Material by Prof. P.S. Desai and C.P. Arora



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