244 Journal on Processing and Energy in Agriculture 15 (2011) 4

Biblid: 1821-4487 (2011) 15; 4; p.244-247 Paper UDK: 66.047.55:641.13:641.12 Stručni rad

EFFECT OF COMBINED TECHNOLOGY OF FRUIT AND VEGETABLES DRYING ON EQUIPMENT DESIGNING

UTICAJ KOMBINOVANE TEHNOLOGIJE SUŠENJA VOĆA I POVRĆA NA PROJEKTOVANJE OPREME

Mirko BABIĆ*, Ljiljana BABIĆ*, Milivoj RADOJČIN*, Ivan PAVKOV*, Milomir BOGIĆEVIĆ** *University of Novi Sad, Faculty of Agriculture, Trg Dositeja Obradovića 8, Serbia,

**„Agros KB proizvodnja“, Veternik - Novi Sad, Serbia e-mail: mbab@polj.uns.ac.rs

ABSTRACT The designing of appropriate equipment is of great importance for the success of technology. Therefore, it is necessary that re-

searchers who introduce a certain technology into practice constantly bear in mind the possible engineering solutions which would be compatible. This technology comprises osmotic dehydration, as a pretreatment, and hot air convective drying. The limit criteria for selection of the technology parameters were formed based on the requirement that the product quality is preserved to a high de-gree. Another important quality of this technology is energy sustainability, which is based on renewable energy sources. Special at-tention was given to the protection of fruits and vegetables from mechanical damage. For this purpose, the system of material han-dling in shallow crates was designed during the process of osmotic drying and sulphurisation. Adhering to the previously mentioned principles, the following original equipment was designed and constructed: osmotic dryer, sulphuring chamber, convective dryer with racks, evaporator of osmotic solution and solar air heater.

Key words: fruit, combine drying technology, osmotic drying, osmotic dryer, solar air heater.

REZIME Projektovanje adekvatne opreme za neku tehnologiju je od važnog značaja za njen uspeh. Zbog toga je potrebno da istraživači,

koji uvode neku tehnologiju u praksu, permanentno imaju na umu moguća inženjerska rešenja koja će biti kompatibilna. Na Poljoprivrednom fakultetu u Novom Sadu u Laboratoriji za biosistemsko inženjerstvo razvijena je tehnologija kombinovanog sušenja voća i povrća. Ona je sastavljena od osmotskog sušenja (saharoza, so i dr), kao predtretmana, i konvektivnog sušenja toplim vazduhom. Granični kriterijumi izbora parametara tehnologije formirani su na osnovu zahteva očuvanja kvaliteta proizvoda na visokom nivou. Ograničenje temperature materijala koji se suši do 45oC, uslovilo je ograničenje temperature rastvora na istu ovu temperaturu. Drugi bitan kvalitet tehnologije je energetska održivost, koja je bazirana na obnovljivim izvorima energije. Oprema je projektovana tako da se koristi solarna energija kao osnovna, a ona se dopunjava toplotnom energijom iz biomase. Projektovano je korišćenje toplovodne instalacije da bi se obezbedilo lako kontrolisanje temperature vazduha tokom konvektivnog sušenja.Posebna pažnja posvećena je očuvanju voća i povrća od mehaničkih oštećenja. U tu svrhu projektovan je sistem manipulacije materijalom u plitkim gajbicama, tokom procesa sumporisanja i osmotskog sušenja. Ove gajbice („holandez“) rasprostranjene su u upotrebi prilikom branja osetljivih voćnih vrsta. One su veoma malo korigovane u odnosu na primarni proizvod sa ciljem da se ostvari kavezna forma tretmana voća tokom osmotskog sušenja. Na taj način intenzivirana je razmena mase i toplote tokom osmotskog sušenja, a da je pri tome ostvaren veoma pažljiv kontakt između materijala i opreme, kao i između samih komada materijala. Korišćenje gajbica uslovno povećava poroznost mase i sprečava kritično naponsko stanje sloja. Poštujući prethodne principe projektovana je i napravljena sledeća originalna oprema: osmostka sušara, komora za sumporisanje, konvektivna sušara sa lesama, uparivač osmotskog rastvora i solarni zagrejač vazduha. Ova oprema predstavlja jedinstvenu celinu koja obezbeđuje obavljanje i kontrolu svih tehnoloških operacija kombinvane tehnologije sušenja voća i povrća.

Ključne reči: voće, kombinovana tehnologija sušenja, osmotsko sušenje, osmotska sušara, solarni zagrejač vazduha.

INTRODUCTION A large number of factors influence food technology equip-

ment designing. The designing of appropriate equipment for a certain technology is of great importance for the success of that technology (Fresco, 2009; Kudra and Mujumdar, 2002). There-fore, it is necessary that researchers who introduce a certain technology into practice constantly bear in mind the possible en-gineering solutions which would be compatible (Zhang et al., 2006).

The standard procedure of creating a production system in food technology starts with the supply of equipment onto the market. The desired volume of production is another important factor. Comparisons of possible solutions come only at the end of the decision. Comparisons of different possible technologies are based on the evaluations of the quality of those products, the evaluation of energy efficiency, the applicability of technology in the planned environment, the cost of equipment, and others. This procedure is rational and successful in the case of technolo-

gies which have already been in application for a considerable period of time. However, the successful development of new technology is based on designing equipment that will meet the following technological principles: the technological diagram, volume of production, energy efficiency, energy sustainability, available human resources and others.

This paper considers the abovementioned approach in the combined technology of fruit drying (Babić M, et al., 2005), which was developed at the Faculty of Agriculture, the Univer-sity of Novi Sad. In this case, the projected quality of the product was derived from the desired technological diagrams. The equipment used in the experiment was specially designed for this purpose. This paper presents and analyzes an example of equip-ment development for the combined technology of fruit drying.

MATERIAL At the Faculty of Agriculture, Novi Sad, at the Laboratory of

Biosystem Engineering, the technology for combined fruit and vegetables drying has been developed. This technology com-

Babić et al. / Effect of Combined Technology of Fruit and Vegetables Drying on Equipment Designing

Journal on Processing and Energy in Agriculture 15 (2011) 4 245

prises osmotic dehydration (sucrose, salt, etc.), as a pretreatment, and hot air convective drying. The limit criteria for selection of the technology parameters were formed based on the require-ment that the product quality is preserved to a high degree. Lim-iting the temperature of the dried material to 45oC resulted in limiting the solution temperature to the same temperature. The air temperature limit during convective drying is dynamic, which arises from the kinetics of the temperature changes of the mate-rial tissue being dried over time. Depending on the type, size and shape of fruit or vegetable pieces, air temperature decreases dur-ing convective drying from 70 to 50oC. The diagram of technol-ogy (Fig. 1), mass and energy balance (Fig. 2) shows the concept of this drying technology.

Fig. 1. Diagram of the combined drying technology

Energy sustainability is based on the use of renewable en-ergy sources. Fruit drying is done mostly in summer, and there-fore solar energy was selected as the main energy source. During insufficient solar radiation (rain, cloud and in the fall), additional energy sources are required. Due to the existence of various forms of biomass in rural Serbia, biomass was chosen as the ad-ditional energy source in this case.

Fig. 2. Mass and energy balance of fruit and vegetable

combined drying technology (Babić M, 2005)

DISCUSSION Crates Special attention was given to the protection of fruits and

vegetables from mechanical damage. For this purpose, the sys-tem of material handling in shallow crates was designed during the process. These crates (“hollandaise”) are widely used in har-vesting sensitive fruits. They were slightly modified compared to the primary product with the aim of obtaining a cage form of fruit treatment during osmotic dehydration. In this way, the ex-change of the mass and heat during the osmotic dehydration was intensified, while achieving very careful contact between the material and equipment, as well as between the material pieces (Fig 3).

Fig. 3. The filled and stacked crates

Sulphuring The antioxidant and antibacterial treatment by SO2 was per-

formed in a special device, in the same crates (Fig. 4). This process was preceded by washing and cutting, and followed by osmotic drying. Using the crates potentially increases the mass porosity and prevents the stress condition of the layer. The height of the layer in the crates is very low, around 80 mm.

Fig. 4. Sulpuring chamber

Osmotic Dryer The osmotic device is the batch dryer (Fig. 5). The osmotic

solution was heated indirectly by hot water. The maximum tem-perature of the solution in fruit drying was 45 oC. The solution temperature was controlled automatically. Fruits were placed in crates and thus mechanical damages caused by their own weight were prevented (Fig. 6). The maximum height of the layer was 80 mm. The porosity of the layer was higher than 50%. The data are suitable for the intensive osmotic process. The batch dryer has been designed to provide the intensive flow of solution be-tween the pieces of fruit (Fig. 7). The position of the entrance and exit of solution conditions favorably the solution flow field.

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246 Journal on Processing and Energy in Agriculture 15 (2011) 4

The solution streamline has the shape of the screw spiral line. Due to this streamline, the effect of turbulence increases, which contributes to more intensive transport of moisture from the fruit into the solution.

Fig. 5. Osmotic dryer

Fig 6. The influence of crates on the auspicious position of fruit pieces during the osmotic drying (a - piece of fruit position when not immersed, b - the most common position of fruit pieces when

immersed in osmotic solution)

Fig. 7. Solution flow in the osmotic dryer

The application of osmotic dehydration depends of the econ-

omy of osmotic solution management (Dalla Rosa and Giroux, 2001; Courel Mathilde et al., 2000). The osmotic solution eva-porator is an important condition for the economical use of os-motic dehydration. It is designed to use solar-heated air (Babić et al., 2009). The osmotic solution evaporator was shown in Figure 8.

Fig. 8. Osmotic solution evaporator

Convective dryer The convective dryer is a traditional design. It is a batch

dryer with racks made of stainless steel. There is a possibility of air recirculation. At the top of the dryer, there is a two-channel fan and ribbed heat water - air exchanger. This dryer is suitable for drying up to 1000 kg of fresh fruit per day. The suitability of manual fruit handling was an important factor for a dryer design. Hot air comes from a solar collector additionally heated in heat exchanger hot water – air (Fig. 9). There is the possibility of re-circulation of air drying. This contributes to a more rational en-ergy drying.

Fig. 9. Convective dryer

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Journal on Processing and Energy in Agriculture 15 (2011) 4 247

Energy support Synergy system of solar end biomass provides energy sup-

port to the combined technology. The principle of collecting en-ergy and external appearance of the device are shown in figure 10.

a)

b)

Fig. 10. Solar energy collecting (a) - Solar radiation receiver profile, 1-Solar ray, 2 – ribbed tube and 3 – reflection area; b) -

External view in practice)

Another energy source is biomass obtained from horticul-tural or filed crop farming (Simon, Sonja and Wiegmann, 2009). A large number of acceptable devices for this use exist on the market.

CONCLUSION Adhering to the previously mentioned principles, the follow-

ing original equipment was designed and constructed: osmotic dryer, sulphuring chamber, convective dryer with racks, evapo-rator of osmotic solution, and solar air heater. This equipment is a single unit which ensures performance and control of all tech-nological operations of combined fruit and vegetable drying technology. A sustainable energy production model has been achieved.

ACKNOWLEDGMENT: The results are a part of the project of the Ministry of Education and Science, the Republic of Serbia, No. TR – 03158, entitled “Combined Technology of Integrated and Organic Fruit and Vegetable Drying”.

REFERENCES Babić, Ljiljana, Babić, M. (2003). Kombinovano osmotsko i

konvektivno sušenje kajsije, PTEP -Časopis za procesnu tehniku i energetiku u poljoprivredi, 7(1-2), 1-3.

Babić, M., Babić, Ljiljana, Pavkov, I., Radojčin, M. (2008). Changes in physical properties through osmotic drying of quince (Cydonia oblonga mill.). Journal on Processing and En-ergy in Agriculture (former PTEP), 12 (3), 101-107.

Babić, M., Babić, Ljiljana, Matić-Kekić, Snežana, Karadžić, B., Pavkov, I. (2005). Energy sustainable model of dried fruit production by combined technology. Journal on Processing and Energy in Agriculture (former PTEP), 9(5), 109-111.

Babić, M, Babić, Ljiljana, Radojčin, M, I Pavkov, I (2009): Sus-tainable energy model of the sucrose solution concentrating održivi energetski model ugušćivanja rastvora saharoze, Journal on Processing and Energy in Agriculture (former PTEP), 13(2), 97-101.

Courel Mathilde, Dornier, M, Herry Jean-Marie, Rios, G.M, Reynes, M (2000),: Effect of operating conditions on water transport during the concentration of sucrose solutions by os-motic distillation, Journal of Membrane Science, 170, 281–289.

Dalla Rosa, M, Giroux, F. (2001): Osmotic treatments (OT) and problems related to the solution management, Journal of Food Engineering, 49(2), 223-236.

Fresco, L.O. (2009): Challenges for food system adaptation today and tomorrow, Environmental science & policy 12, 378 – 385.

Kudra, T., Mujumdar, A.S. (2002): Advanced Drying Technolo-gies; Marcel Dekker, Inc.: New York.

Simon, Sonja, Wiegmann, K. (2009). Modelling sustainable bioenergy potentials from agriculture for Germany and Eastern European countries, Biomass and bioenergy 33; 603 – 609.

Zhang, M, Tang, J, Mujumdar A.S, Wang, S. (2006). Trends in microwaverelated drying of fruits and vegetables, Trends in Food Science & Technology, (17), 524-534.

Received: 08.12.2011. Accepted: 26.12.2011.