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Научни трудове на Съюза на учените в България-Пловдив. Серия В. Техника и технологии, т. XV, ISSN 1311 -9419 (Print), ISSN 2534-9384 (On- line), 2017. Scientific Works of the Union of Scientists in Bulgaria-Plovdiv, series C. Technics and Technologies, Vol. XV., ISSN 1311 -9419 (Print), ISSN 2534-9384 (On- line), 2017.
MOST OFTEN USED HEAT EXCHANGERS IN THE FOOD INDUSTRY AND FORMING A PRECIPITATE AS NEGATIVE SIDE IN THEIR
FUNCTIONING Keti Hristovska, Vangelica Jovanovska FacultyofbiotecHnicaG sdence-Bitola, University et.Climent OhridsM-BitoC RopBblic of MacedBtia
Abstract
Pasteurizers of tehnical aspect is heat exchangers which are widely used in milk-processing capacities.With their help is happening proces of pasteurization in order to prolong the shelf life of the products. In milk-processing capacities are meet plate and tubular pasteurizers which are characterized with certain performances, but their negative side is forming a precipitate which affect in big part in quality in product and consumption of energy.
Key words: pasteurization, pasteurizers, plate pasteurizers, tubular pasteurizers, sediment
1. Introduction
In our daily life we meet various food products and goods, produced by different companies and made in various ways. All consumers prefer that food is prepared by certain standards of quality, while nutritional values be maintained. Food is exposed on microbiological contamination and therefore in most cases food is treated on high temperature with purpose for inhibition of growth, development and destruction of microbial flora. Existence of microbial flora in food is causer on process of boiling and spoilage of food. Long ago in 1862 process of pasteurization was implemented for the first time by French chemist and chemist and biologist Louis Pasteur. Primary goal of pasteurization is exposure of goods on high temperature, but under the point of boiling on that product with purpose to destroy only some of existing pathogenic bacteria and microorganisms and reduce the enzyme activity in that product. Such process is mostly present in milk industry, because milk is biological secretion of mammary gland in mammals and It contains more than 90 different substances necessary for normal processes in human body. In process of pasteurization most sophisticated and modern heat interchanged devices are used, so called pasteurization devices. Process of pasteurization is most dependent by level of resistance on heat of certain microorganisms in food, as well as of sensibility of that same food product. In this manner there are two kinds of pasteurization: -pasteurization on high temperature in short time (HTST),
-pasteurization on low temperature in longer time, or treatment of extended shelf life (ESL)
Pasteurization of milk was suggested by Franz van Soxhlet in 1886, with purpose to prevent from diseases like: tuberculosis, diphtheria, brucellosis and for destroy harmful bacteria like
2. Plate heat exchanger
Number of companies exist on market that produce pasteurization devices with different capacity of production, performance and price. Not always most expensive pasteurization device is better to include in production. Pasteurization devices are heat exchangers from technical aspect, but dependent of their construction most used are plate and tubular heat exchangers.
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Fig. 1: Elements of plate heat exchanger
Plate heat exchanger contains certain number of sheets made of stainless steel joined in one frame. In that frame only one section can go on (heating) or more sections during different levels of processing (preheating, heating, temperature maintenance and cooling). During that exchange of heat is done by transport of it between two media on stainless steel. This is great advantage towards conventional heat exchangers, since the exchange of heat is done over greater surface, so that transfer of heat is facilitated and speed of temperature exchange is increased.
Sheets are made of stainless steel because of its durability on high temperature and its resistance of corrosion. Construction of sheets is such that allows optimally efficient heat transfer. The sheets are fastened to the frame and touching points of wavy parts form through channels that allows fluid movement. The distance between sheets, or size of channels is about 1,3-1,5 mm. Placement affect in that way forming of composition of parallel channels with double sided flow of fluids. Attention to be paid on maintaining turbulent flow of fluids, because high degree of turbulences helps to low rates of flow and coefficient of transfer of high heat.
3. Tubular heat exchanger
The construction concept of tubular heat exchangers (Image 2) is by use of eccentrically mounted pipes through which flows one fluid, while other fluid is in chamber around pipes with its purpose for heating or cooling by process of transfer of heat between two fluids (Image 3). Attention should be paid that the pipes should be made of stainless metal or different substance characterized by high coefficient for transport of heat. Also tubular pasteurization devices can work on principle of purification and re-heating of flowing media used for heating or pasteurization of food product. In comparison with plate pasteurization device advantage is that the process is done in much shorter time period because of circulation of both media which can be in same or opposite direction.
4.Forming of sediment
During thermal processing of milk comes to degradation of proteins and their accumulation on surfaces of pasteurization devices. According Burton (1988), occurrence of sediment and its control contribute for increase of costs, energy, time to maintain, loss of production and quality change of products. Sediment increase the wall thickness, and it contains materials with low thermal conductivity of metal sheets. Further this sediment considerably reduces the rate of heat transfer. Occurrence of sediment instantly leads towards reduction of free space between sheets and lower flow of fluids, which results by great spent of electric energy. pH value of products have certain role on forming sediment. But, we can conclude that by reducing of pH value sedimentation is increasing, or that is inversely proportional.
For cleaning of pasteurization devices from this problem great investments are needed. This is additional problem for milk processing capacities.
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Fig. 4: Variation of the amount of sediment formed depending on pH-value of milk 5. Conclusion
From being mentioned above conclusion can be made that pasteurization is a necessary process in manufacturing industry, and particular in milk industry primarily because of great benefits by its use. As benefits we find are obtaining quality milk and quality milky - sour products without impact of its chemical composition and characteristics, reduce of number of present microorganisms and their fully destroy, as well as extending of shelf life of this products. Dependent of the amount of production, exterior characteristics, amount of energy spent and available funds for profitability, each milk manufacturing company make its own decision of what kind of heat exchanger will implement in their producing process. Despite number of benefits that this pasteurization devices possess yet their greater shortage is forming of sediment, that affect on producing process, spent of electric energy, large investments for its elimination and in the end biggest problem change of composition of food products.
Literature
http //www.ovobel.com/images/filelib/plate pasteurizers.pdf
http //www.ovobel.com/images/filelib/uht triple tube pasteurizers.pdf
http //www.redaspa.com/en/sectors/juice-and-drinks/pasteurisation-2/plate-pasteurizers/
http //www.iec-il.com/dairv1.aspx?gclid=Ci0KEQiw2fLGBRDopP-
vg7PLgvsBEiQAUOnIXEfDp01GZe1uMQmvacW34ZMILXcqI9vku56IAiMOvG0aAiY58P8HAQ http://www.interupgrade.com/en/products/modules/pasteurizers http://scindeks-clanci.ceon.rs/data/pdf/1450-5029/2004/1450-50290404087B.pdf http://www.gold-bar.co.i1/new/products/heat-exchangers/plate-heat-exchangers/#Tvpe info http://www.imp1etum.zavod-irc.si/docs/Skriti dokumenti/Tehnologija m1eka-Bajt.pdf
