A Comprehensive Review of Solar Milk Pasteurization

Hitesh Panchal Mechanical Engineering Department, Government Engineering College, Patan 384002, Gujarat, India e-mail: [email protected]

Jay Patel Mechanical Engineering Department, Hansaba College of Engineering and Technology, Siddhpur 384151, Gujarat, India

Sudhir Chaudhary Mechanical Engineering Department, Hansaba College of Engineering and Technology, Siddhpur 384151, Gujarat, India

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A Comprehensive Review of Solar Milk Pasteurization System Solar pasteurization system is used to kill harmful bacteria present in the raw milk. It is carried out in dairy industries with the help of boiler and using wood or coal for heating of the milk. Due to the increment of global warming and its harmful effects, coal or wood should not be used for milk pasteurization system. Hence, researchers have started work on renewable energy source like solar energy for pasteurization system. Many scientists from all around the world have attempted to use solar energy for milk pasteurization system. The present review paper shows the research works carried out by researchers on milk pasteurization system. After several reviews, it has been found that solar energy is the best solution for milk pasteurization system. [DOI: 10.1115/1.4038505] Keywords: solar energy, milk pasteurization, temperature

Introduction

The dairy business is included in one of the key food industries in India. In milk dairy plant, a better growth prospect is available because in the U.S. milk produces use accounts for 85% and in India it is 48%. Currently, India produces around 123.7 106 tons of milk every year [1]. It signifies 7.8% of world milk making [2]. In future, demand of milk production will be increased. The world trade of dairy products, namely, butter and butter oil, skim milk powder, whole milk powder, condensed milk, and cheese, amounted to 58.2 106 tons in milk equivalents (excluding trade within the European Union) in 2011 [3]. The dairy sector can play a major role in providing jobs for countryside communities [4]. Milk production and processing provide employment, not only to people who work on dairy farms or in dairy plants but also to the whole communities, from upstream, e.g., inputs and services providers to downstream, e.g., marketing of finished products. Dairy cooperatives have played a very significant role in the procurement, processing and marketing of milk and dairy products and in representing farmers politically at both the state and national level [5]. The pasteurization process is the primary process which consumes a significant amount of energy [6]. The dairy operations performance variation causes the negative impact on product marketing [7,8]. The performance changes in dairy processes can be obtained by continuous energy audit of the plant. Figure 1 shows milk processing plant in dairy. Solar energy is the renewable source of energy, and it is available freely. Nowadays, due to the global warming and many other reasons, solar energy is very much accessible. It can be harnessed by either solar thermal and solar photovoltaic technologies. Solar thermal technologies can supply hot water or steam for cooling and heating purposes. To provide hot water or steam, thermal collectors are used [8–11]. Milk is a required liquid for mankind for the nutrition and growth purpose. Generally, milk is obtained from cow, buffalo, and goat. The milk obtained from the animals cannot consume directly by mankind. Hence, first heating of milk is required. Heating of milk at precise temperature kills bacteria and harmful microorganisms. Capturing the sun’s energy may be a logical solution to solve the energy problem caused by scarce fuels. It is free and has no negative impact on the environment. Gujarat is situated in areas where solar energy is abundant [12,13]. Solar Contributed by the Solar Energy Division of ASME for publication in the JOURNAL SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received August 30, 2017; final manuscript received October 12, 2017; published online December 5, 2017. Assoc. Editor: Gerardo Diaz.

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Journal of Solar Energy Engineering

radiation incident in Gujarat ranges from 3 to 4 kWh/m2/day, with about 300 sunshine days [14]. Thus, the abundance of solar energy paired with the concept of milk pasteurization encourages a new result to purify unsafe milk. The solution has the many advantages: environment conservation, ensure a better human health in remote areas, address the problem of energy and reduce cost, a new use of solar energy applications and the cost of such energy is low which is required only for the necessary apparatus to establish it. Long distances between the production areas and the markets, adverse road conditions, and high ambient temperatures make the development of a dairy industry to be a particularly arduous task. Therefore, this research aims to apply solar energy for pasteurizing the milk at remote areas and in village communities which are deprived of the availability of electricity and gas, where the small quantities of milk are delivered by individual producers [15,16]. The solar energy collectors are special kind of heat exchangers that transform solar radiation energy to internal energy of the transport medium. The flat-plate solar collector is one of the most important types of solar collectors because it is the simplest one and has a wide range of important potential applications [17–19]. The average daily milk production of cows is about 4 kg per head in the winter and about 2.8 kg in the summer. For the buffalo, the average daily milk in the winter is about 6.6 kg per head and about 5.2 kg per head in the summer. The average annual productivity is about 3.1 kg per cow and about 5.9 kg per buffalo. Temperature requirement of pasteurization process required less than 80 C; hence, flat-plate collector is a suitable option [20–22]. Nowadays, some of the more significant environmental problems have their origin in an inappropriate policy and management of the energy resources. Particularly, fossil fuels are in the spotlight of the energy future as they are nonrenewable resources that could be combined with and/or substituted by another kind of environmental, economic and socially sustainable resources, and analysis of the current energy world scenario draws on the combination of energy efficiency improvement and the development and implementation of renewable-type energies with their associated technologies. From the literature review, it has been found that the pasteurization process is very important for mankind. If solar energy is used to pasteurize the milk, then it will also help the environment. Hence, a primary objective of this review paper is to study research work done on pasteurization system based on solar energy.

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What Is Pasteurization Process

Pasteurization is the method of heating a liquid to below the boiling point to kill microorganisms. It was established by Louis

C 2018 by ASME Copyright V

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Fig. 1 Layout of milk processing plant

Fig. 2

Dairy plant scheme for simulation purpose

Pasteur in 1864 to increase the storage qualities of wine. Commercial pasteurization of milk began in the late 1800s in Europe and in the early 1900s in the U.S. Pasteurization developed obligatory for all milk sold within the city of Chicago in 1908, and in 1947 Michigan stated, as the first state, that all milk for sale within the state be pasteurized. Pasteurization is the procedure of the heating liquids for the purpose of destroying viruses and harmful creature. It was developed in 1864 to increase the storage qualities of milk [23]. Pasteurization naturally uses heating and cooling cycle at temperatures above the boiling point of milk and above the freezing point. As society industrialized around the turn of the twentieth century, augmented milk making and delivery led to outbreaks of milk-borne diseases. These illnesses were virtually removed with the commercial application of pasteurization, in combination with better management performs on dairy farms. In 1938, milk products were the source of 25% of all food and waterborne

Fig. 3

Diagram of pasteurization process based on solar panel

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illnesses that were traced to sources, but now they account for far less than 1% of all food and waterborne diseases [24]. Pasteurized milk process is a diary process that consumes the significant amount of energy consisting of electricity and fuel.

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Pasteurization Process Based on Solar Energy

Various procedures working for the pasteurization process grounded on solar power are embodied as follows. 3.1 Waste Milk Pasteurization. Stabel [25] carried out trials on waste milk from the dairy farm for pasteurization process. He made heating of milk for pasteurization purpose for three different temperatures such as 60 deg, 65 deg, and 70 deg. He also used flatplate collector for the purpose of heating of milk. He has also conducted testing of pasteurized milk in laboratory. After a series of experiments, he found that 70 deg temperature is best for the pasteurization process.

Fig. 4

Control strategy of pasteurization system

Transactions of the ASME

Fig. 5 Low-cost Fresnel type concentrator for solar pasteurization process

Fig. 6

Boiler to receive solar rays for pasteurization of milk

3.2 Innovative Milk Pasteurizing Plant Using Solar Energy. Lucentitni et al. [26] have studied the technical and economic feasibility of an innovative milk pasteurization plant through solar energy and tested during varying conditions throughout the year. They used typical heat exchanger which contains various advantages like safety, higher thermal and hydraulic efficiency, and lower height to surface ratio. Typical thermal cycle

Fig. 7 Base temperature versus time interval for solar pasteurizer

Fig. 8 Inner space temperature versus time interval for solar pasteurizer

of a pasteurizer is shown in Fig. 2, which shows milk input temperature, thermal recovery temperature, milk output temperature, and pasteurization temperature. To evaluate the performance of heat cycle, dairy plant scheme has proposed and is shown in Fig. 2. They have also carried out the performance of daily plant system based on incoming solar radiation. From the simulation work, they have found energy payback time of around 100,000 l milk

Table 1 Polynomial regression analysis of different temperatures versus time Temperature of different parts of Schweizer Milchproduzenten

Linear

Day 1: temperature Base temperature Inner space temperature Milk temperature

45.70 36.97 22.91

0.370 0.816 0.557

0.001 0.004 0.001

0.000002 0.000006 0.0000009

98.1 94.8 98.7


50.38 39.44 15.10

0.2295 0.744 0.513

— 0.004 0.001

— 0.00–0007 —

98.1 99.6 99.5


25.50 30.42 19.67

0.856 0.753 0.326

0.003 0.004 0.001

0.000003 0.000008 0.000006

97.9 99.6 98.8


Quadratic

Cubic

R2 (%)

Constant

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They measured milk outlet temperature, pasteurization temperature, water outlet temperature, etc., during experiments. After series of trials, they have found 71 deg is the best temperature for pasteurization process. They have also concluded that the energy payback time is around 20 years.

Fig. 9 Milk temperature versus time interval for solar pasteurizer

per day capacity is around 10–11 years with flat-plate collector as a source.

3.3 Solar Panel-Based Milk Pasteurization System. Nielsen and Pedersen [27] carried out design, development, and analysis of control system employed for solar pasteurization system through solar panel and conducted experiments in the small town of Tanzania. Analysis of pasteurization system is based on various demands with varying energy supply, low cost, low complexity, and simple user interface. Pasteurization system based on the solar panel is shown in Fig. 3. They took demand around 1000 l milk per day with approximately 5 h of sunshine days and hence, pasteurization is around 200 l/h. For the pasteurization process, they prepared solar cells to supply 12 V DC. Figure 4 shows control structure of solar milk pasteurization system. A laboratory model of pasteurization system has been made with a monitoring system. They used the solar panel of 10 kW.

3.4 Pasteurization System by Low-Cost Solar Concentrator. Franco et al. [28] fabricated low-cost solar concentrator (without sun tracking) for pasteurizing of goat milk for cheese production. They used Fresnel type solar concentrator with the focal distance of 55 cm and 6.6 kg of weight for solar pasteurization and fabricated in a home. They also used the homemade boiler, which was used to heat the water in the concentrator inside the Pyrex breaker. They have carried out a series of experiments with different quantity of milk for pasteurization. After a series of tests, they have found that Fresnel type low-cost concentrator achieved pasteurization of 101 l milk about 1 h of a time interval and it has energy payback time around 8 years. Figures 5 and 6 exhibit lowcost Fresnel type concentrator and boiler for pasteurization. 3.5 Prediction of Solar Milk Pasteurizer With Polynomial Regression Analysis. Zahira et al. [29] have prepared a solar milk pasteurizer from standard appliance shipping cardboard with multiple layers of the regular aluminum foil glued onto cardboard which was insulated with a large cardboard box which contained the rectangular area, and a removable glass window has been used. The inner box having a volume of 52.5 24 36 cm is covered on both sides with aluminum foil and a metal tray painted black. They have also carried out the polynomial regression analysis of different temperatures versus time. They have used various temperatures like base temperature, inner space temperature, and milk temperature and found R2 values around 98% as shown in Table 1. This experiment was done on temperature ranging from 65 to 75 C. Figures 7–9 show regression analysis plot of base temperature, inner space temperature, and milk temperature versus time interval.

Fig. 10 Experimental setup of solar pasteurization system with the aid of flat-plate collector

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Fig. 11 Average required time to reach pasteurization temperature during September, October, and November 2009

3.6 Solar Milk Pasteurizer With the Help of Flat-Plate Collector. Atia [30] have carried out performance analysis of solar milk pasteurizer system with the aid of flat-plate collector. Their prime concern was to devote innovative design of solar pasteurizer for the individual dairy producers who do not have the availability of electricity and gas. They have specified aims for the research work like (1) design and construction of innovative solar milk pasteurizer, (2) determination of the average quantity of solar pasteurized milk per day, and (3) analysis of the solar thermal milk pasteurizer. They have conducted many experiments in climate conditions of Ain Shams University, Egypt, with fresh

cow milk (3.5% fat and 8.56% solids not fat). Figures 10 and 11 show experimental setup developed by them. They have carried out experiments during September, October, and December 2009 and found that system attained pasteurization temperature in 3–19 min depending on solar radiation and desired temperature. They have also observed maximum and minimum amount of pasteurization milk of 73.9 l at 63 deg and 37.3 l at 72 deg. Figure 9 shows average time required to reach pasteurization temperature during September, October, and December 2009. Wayua et al. [31] have carried out experiments on low-cost solar milk pasteurizer with the help of flat-plate solar water

Fig. 12 Experimental setup of milk pasteurization system with the help of flat-plate collector


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Fig. 13 Schematic diagram to produce pasteurized milk by the thermal utility of the solar energy

Fig. 14 Line diagram of solar milk pasteurizer setup with the help of evacuated tubes collector

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Table 2 Reference

Comparative analysis of solar pasteurization system Title

Research work on solar pasteurization system

Stabel [25]

On-farm batch pasteurization destroys mycobacterium paratuberculosis in waste milk

He carried out experiments on solar pasteurization system by supplying hot water.

Marco [35]

Mastitis en la oveja Latxa: Epidemiologıa, diagn ostico y control

They made up innovative milk pasteurization system operated by solar still and found 10–11 years of payback period for pasteurization of 100,000 l milk.

Nielsen and Pedersen [27]

Solar panel based milk pasteurization

They performed experiments on solar pasteurization system operated by the solar panel in Tanzania. They made a prototype of 200 l/h and found higher energy payback time around 30 years.

Franco et al. [28]

Pasteurization of goat milk using a low-cost solar concentrator

They prepared designed of pasteurizing goat milk by use of low-cost Fresnel lens concentrator and found that 1 h is required for pasteurizing of 101 l milk.

Zahira et al. [29]

Fabrication and performance study of a solar milk pasteurizer

They prepared solar milk pasteurizer by use of flatplate collector for animal milk. They found that 65–70 deg is the best temperature between 65 deg and 75 deg.

Atia [30]

Solar energy utilization for milk pasteurization

They prepared the innovative design of solar pasteurizer made by flat-plate collector and tested for 3 months September, October and November 2009. They found the maximum and minimum pasteurized amount is 73.9 l and 37.3 l at 63 C and 72 C.

Wayua et al. [31]

Design and performance assessment of a flat-plate solar milk pasteurizer for arid pastoral areas of Kenya

Dobrowsky et al. [32]

Efficiency of a closed coupled solar pasteurization system in treating roof-harvested rainwater

They prepared solar milk pasteurizer consisting of flat-plate collector and stainless steel vat for 80 l capacity. They found that low-cost solar milk pasteurizer is used for arid and remote areas where electricity or gas is not available. They prepared solar pasteurization system consisting of the tank and evacuated tubes. They found 72 C is the best temperature for the killing of bacteria and purpose of pasteurization.

Pandagale et al. [34]

Integration of solar thermal energy in milk processing plant

Mody and Prajapati [33]

Pasteurization process energy optimization for a milk dairy plant by energy audit approach

heating collector and 1.5 mm thick stainless steel milk vat and tested in climate conditions of Kenya for 40 l of raw milk. They used milk container of capacity around 80 l and 50 mm wide hot water jacket insulation. They have found that the present low-cost solar milk pasteurizer with 40 l milk required approximately 1.360.5 h with solar intensity around 700–1000 W/m2. Figure 12 shows experimental setup and milk pasteurization that used for research work. 3.7 Solar Pasteurization System With the Aid of Evacuated Tubes Collector. Dobrowsky et al. [32] have fabricated solar pasteurization system used to produce the large quantity of pasteurized milk with the help of evacuated tube collector. They used aluminum, lead, and nickel leached from the stainless-steel holding tank for the research work. After several experiments, they had found that the bacteria killed in the milk when the temperature reached 72 deg and above. They pasteurized around 500 l of milk. Figure 13 shows a procedure of solar pasteurization system based on diagram and Fig. 14 shows line diagram of solar pasteurization system based on evacuated tubes. Mody and Prajapati [33] compared existing plant layout of pasteurization system with new and improved pasteurization system with the aid of solar electric heater operated by solar energy. He has also carried out the energy payback time comparison between the existing plant and modified plant base on the recommendations. They have found that compared with the current pasteurization plant, the modified plant gives Rs. 7,20,000 per month and energy payback time of around 3 months only. Journal of Solar Energy Engineering

They have carried out the study on solar pasteurization system and found energy payback time and saving of electricity. Compared existing layout of pasteurization system with modified plant and obtained improvement in energy payback time.

3.8 Solar Thermal Energy Integration With Milk Processing Plant for Pasteurization. Pandagale et al. [34] have studied milk processing plant of Akola milk scheme of pasteurization around 100 l per day. They have found following outcomes from their study. (1) The fuel cost per liter of pasteurization is around 31.10 INR. (2) The energy required to raise the desired quantity of water for pasteurization purpose is 3.45 kWh and process 1 l of milk requires 0.657 l. (3) Use of 2000 l per day water used for pasteurization saves 28 l/day furnace oil. (4) The energy conserved by integration of solar energy was found around 97,608 kWh per day. And (5) net annual cost saving by integration of solar energy is around 261,300 INR. Table 2 shows the comparative study of research work done on solar pasteurization system.

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Conclusion

Solar pasteurization system is vital for the killing of bacteria present in milk. From the research work by different scientists, following points are drawn as a conclusion: A direct method was used for obtaining pasteurization temperature by use of solar energy for minimum and maximum fluid temperature of 63 and 78 C. The sun milk pasteurizer attained pasteurization temperature in 1–1.5 h, so it can be used commercially for pasteurization. A low-cost Fresnel solar concentrator obtained pasteurization temperature of around 40 min instead of 1 h, but it depends on temperature. FEBRUARY 2018, Vol. 140 / 010801-7

Solar pasteurization with the use of solar panel is a good solution but energy payback time is higher. Solar pasteurization plant needs energy payback period around 10–11 years, and if maintenance cost is incorporated, then it will reach to 20 years. Hence, sustainable solution is required to overcome increment in energy payback time. Solar flat-plate collector of 1.2 m2 area attained pasteurization temperature in 3–19 min depending on available solar intensity. Solar flat-plate collector pasteurization system produces the yearly quantity of 27.5 ton and 13.8 weight when the average temperature is around 63 and 72 C. Evacuated tube collector is the best solution for solar pasteurization system and attains higher temperature quickly, and head is not obtained precisely and hence, it is not good as compared with flat-plate collector.

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