doi:10.14720/aas.2020.115.2.1359 Original research article / izvirni znanstveni članek Intensification of the drying process of small seed oilseeds using microwave electromagnetic radiation Ildar GANEEV 1 2, Khasan KARIMOV \ Shamil FAYZRAKHMANOV \ Ilgam MASALIMOV \ Valeri PERMYAKOV 1 Received November 28, 2019; accepted March 3, 2020. Delo je prispelo 28. novembra 2019, sprejeto 03. marca 2020 Intensification of the drying process of small seed oilseeds using microwave electromagnetic radiation Abstract: One of the important and crucial stages of post-harvest treatment of rapeseed is drying. The purpose of the article is to improve the drying process of seeds of small seed oil crops using electromagnetic radiation of the microwave range in order to increase its productivity and determine the optimal operating parameters. The article describes the construction of a new microwave (UHF) dryer with a capacity of 200 kg h-1 for drying small-seeded crops. Curves were obtained that show the dependence of the heating temperature of seeds on microwave power, the effect of initial seed moisture and heating temperature on drying kinetics. The ratio of the stages of microwave heating and cooling was determined, which allows to increase the drying efficiency. Key words: grain drying; rapeseed; electromagnetic radiation; drying kinetics; drying device Pospeševanje sušenja majhnih semen oljnih poljščin z mikrovalovnim elektromagnetnim sevanjem Izvleček: Eden od pomembnejših in ključnih postopkov pri požetveni obravnavi semen oljne ogrščice je sušenje. Namen prispevka je izboljšanje procesa sušenja majhnih semen oljnih rastlin z mikrovalovnim elektromagnetnim sevanjem z namenom povečanja produktivnosti in določiti optimalne operacijske parametre. Članek opisuje zgradbo novega mikrovalovnega (UHF) sušilnika z zmogljivostjo 200 kg h-1 za sušenje majhnih semen oljnih poljščin. Krivulje kažejo odvisnost temperature segretih semen od moči mikrovalovnega sušilnika, učinka začetne vlažnosti semen in odvisnost sušilne temperature od kinetike sušenja. Določeno je bilo razmerje med gretjem in hlajenjem mikrovalovnega sušilnika, ki omogoča povečanje učinkovitosti sušenja. Ključne besede: sušenje zrnja; oljna ogrščica; elektromagnetno sevanje; kinetika sušenja; sušilnik 1 Federal State Budgetary Educational Establishment of Higher Education "Bashkir State Agrarian University", Department of Mechanics and machine construction, Ufa, Russia 2 Corresponding author, e-mail: ganeev.il11@rambler.ru Acta agriculturae Slovenica, 115/2, 261-271, Ljubljana 2020 115-2 vsebina.indd 261 23. 06. 2020 07:25:17 I. GANEEV et al. 1 INTRODUCTION In agricultural practice, small seed oil crops such as rapeseed, mustard, and saffron milk, which are in great demand for agriculture and industry, are becoming increasingly important (Hakansson et al., 2013; Kovaly-shyn, 2015; Kovalyshyn et al., 2015). One of the most important operations of oilseed cultivation technology is post-harvest seed treatment (Hakansson et al., 2013; Soares et al., 2016; Moreno et al., 2017). After ripening, rapeseed has a moisture content that amount from 14 to 27 %, and the recommended humidity for storage should be no more than 7 to 8 %. Due to the high humidity in the seeds of oilseeds, oxidative processes can begin, leading to a decrease in their quality. Therefore, timely drying will allow to maintain high sowing and technological qualities of seeds (Ganeev et al., 2009; Ganeev & Masali-mov, 2009; Masalimov et al., 2018). Due to the lack of special technological equipment, drying of oilseed grain is performed on grain drying equipment, which are distinguished by type and method of action (Gabitov et al., 2018). Existing drying methods are mainly based on thermal effects on the material, which in turn leads to a deterioration in the quality of the finished product (Jokiniemi & Ahokas, 2014; Skakov, Rakhadilov & Sheffler, 2013). The choice of drying equipment must be made taking into account the physical and mechanical parameters of a particular culture. It is necessary to classify them to determine the most optimal construction of dryers. Drying devices can be classified according to a number of features, the main ones being the method of supplying heat, the construction of the drying chamber, the operating mode, the state of the grain layer and the construction (GOST, 2008; Sutjagin et al., 2017). The most widespread is the direction of drying grain using the convective method of heat supply. The convective grain dryers are simple and most productive (Soares et al., 2016; Maier, 2017; Manikantan et al., 2018). However, these grain dryers are characterized by high metal consumption, high cost and high energy costs (Sutjagin et al., 2017). In shaft type grain dryers operating on gaseous and liquid fuels, when drying food and industrial grain crops, the regulated specific energy consumption should not exceed 4.56 MJ kg-1 of evaporated moisture, and 5.74 MJ kg-1 when drying seed grain (GOST, 2008). In practice, convective drying devices that operate without heat recovery consume up to 6 MJ kg-1 of evaporated moisture due to the fact that most of the thermal energy is carried away irrevocably by the drying agent. On the territory of the Russian Federation, the drum and shaft grain dryers with convective heat supply are most common, which, when drying the seed, often lead to grain injury. In addition, in shaft dryers, grain is often subjected to local overheating, which in turn leads to protein denaturation in the germ (Shizhuang et al., 2017). The main significant drawback of convective grain dryers is the high energy costs due to the occurrence of a temperature gradient in the material being dried, which leads to a decrease in the drying rate (Jokiniemi et al., 2015). One of the solutions to this drawback is the differentiation of the supply of thermal energy consisting in the alternation of heating the material with its cooling (Jokiniemi et al., 2015). With the development of technology and technics, recently drying methods such as microwave and thermos-radiation methods have begun to spread, the feature of which is the penetration of electromagnetic waves into the depth of the material being dried. This leads to heating of the inner part of the grain bypassing the outer layer (Rogov, 1988). During infrared drying (thermal radiation), the rays are absorbed by the product, which ensures a more uniform heating of the material in depth compared to convective drying (Rogov, 1988). This, in turn, leads to a decrease in the temperature gradient and direct transfer of steam from inside to outside under the influence of the gradient of total pressure (Darvishi et al., 2013; Bet-tega et al., 2014; Zhao et al., 2017). It should be borne in mind that increasing the temperature of infrared heating can lead to damage to the grain germ. In turn, a forced decrease in the heating temperature leads to a decrease in the drying rate and, as a consequence, to an increase in the duration of the drying process, a decrease in the productivity of the dryer, and an increase in energy consumption (Rogov, 2015; Karimov et al., 2016; Martynov et al., 2018). The microwave drying is characterized by internal heating of the material (Li et al., 2014; Zhao et al., 2017). Therefore, thermal diffusion of moisture, directed from the center to the surface of the body, increases the speed of microwave drying. However, in the case of microwave drying of grain, in the absence of temperature and moisture control inside the grain, the probability of germ death due to possible local overheating is high (Ganeev, 2011; Fajzrahmanov et al., 2014; Fajzrahmanov, 2015). At the moment, the problem of the dependence of grain temperature in the inner layers on the power of electromagnetic radiation from microwave is poorly studied. Therefore, the most promising direction is the development of a drying device based on microwave heating of the material and conducting experimental research to identify the operating parameters of the installation, which allows to obtain a high-quality finished product. The purpose of the study is to increase the 262 Acta agriculturae Slovenica, 115/2 - 2020 115-2 vsebina.indd 262 23. 06. 2020 07:25:18 Intensification of the drying process of small seed oilseeds using microwave electromagnetic radiation drying efficiency of small seed oilseeds by applying microwave electromagnetic radiation. 2 METHODS The choice of the type of dryer and drying method for a particular material is impossible without taking into account its physical and thermophysical properties. In addition, the correct use of the laws of heat and moisture transfer is necessary to determine the most suitable drying mode. The drying process is characterized by internal and external moisture transfer. The optimal combination of technological methods used to increase internal and external moisture transfer will significantly intensify the drying process. The kinetics of moisture transfer in capillary-porous colloidal bodies, which include seeds of agricultural crops, is generally determined by the difference in its potentials (temperature, moisture content). The intensity of internal moisture transfer is described by the well-known equation of non-isothermal moisture conductivity: (1) where is the density of the moisture conduction flux, kg (m-2 ■ h-1); is the flux density of thermal moisture conductivity, kg (m-2 ■ h-1); is the moisture diffusion coefficient in the grain, m2 s-1; is the density of absolutely dry grain, kg m-3; is the thermogradient coefficient, 1 K-1; and are the gradients of concentration (moisture content) and temperature, kg . (kg-' m-1) and K m-1. 1 °moist v ° dry matter ' In this equation, the first term characterizes the movement of moisture in the material under the influ- ence of a moisture gradient, and the second - under the influence of a temperature gradient. When convectively dried, the heat from the upper layers of the material is transferred to the inside, therefore, the gradientsandhave opposite signs, i.e. thermal moisture conduction impedes the advancement of moisture from the surface of the material to its surface (Fajzrahmanov, 2015). As can be seen from equation (1), by reducing the inhibitory effect of thermal moisture conduction or by increasing the flow of moisture conduction, the intensity of internal moisture transfer can be increased. The moisture flow can be increased by increasing the moisture gradient. This can be achieved by exposing the material to electromagnetic radiation in the microwave range (Ganeev, 2011). During microwave heating, the humidity and temperature gradients have the same orientation, and in this case, moisture is removed not only under the influence of thermodynamic forces, but also under the influence of excess pressure arising inside the material (Budnikov, 2008): 1m = -am P