CC BY
2
УДК 66.023.01
Ализафаров Б.М.
ассистент кафедры «Технологические машины и оборудования»
Ферганский политехнический институт Республика Узбекистан, г. Фергана
ЭКОЛОГИЧЕСКАЯ СУШКА ТОНКОДИСПЕРСНЫХ МАТЕРИАЛОВ В КОНТАКТНОЙ СУШИЛКЕ
Аннотация: В работе изучена возможность экологически чистой сушки тонкодисперсных материалов в контактной сушилке с быстровращающимся ротором в химической и смежных отраслей промышленности. Дано описание конструкции, принципа работы барабанной сушилки с электрическим нагревом. Дан анализ исследований по тепло и массообменным процессам при сушке тонкодисперсных материалов. Показана возможность организации безуносной сушки при непрерывном режиме работы аппарата.
Ключевые слова: контактная сушка, конструкция сушилки, тонкодисперсный материал, роторная сушка, экологически чистая сушка, непрерывный режим.
Alizafarov B.M. assistant
Department of Technological machines and equipment
Ferghana Polytechnic Institute Republic of Uzbekistan, Ferghana
ECOLOGICAL DRYING OF FINE DISPERSED MATERIALS IN A
CONTACT DRYER
Annotation: The possibility of environmentally friendly drying of finely dispersed materials in a contact dryer with a rapidly rotating rotor in the chemical and related industries was studied. A description of the design, the principle of operation of a drum dryer with electric heating. The analysis of studies on heat and mass transfer processes in the drying of finely dispersed materials is given. The possibility of organizing a snowless drying during continuous operation of the apparatus is shown.
Keywords: Contact drying, dryer design, fine material, rotary drying, environmentally friendly drying, continuous operation.
Introduction
Drying of wet dispersed materials is usually carried out in convective dryers of a suspended layer. If it is necessary to dry wet, finely dispersed materials having
a particle size of 5-50 ^m. This method of drying is not always effective. The reason for this is that part of the product is carried away by waste gases and pollutes the environment [1]. As a consequence, there is a need to clean secondary air. This method requires rather bulky equipment for dust collection since several stages of cleaning are required. Undesirable convective drying is for low-tonnage production, with a wide range of products, in some cases having environmentally harmful components, the losses of which affect the ecological situation, especially when drying toxic materials [2]. Several enterprises of small chemistry, dyes, for which a frequent change of assortment and consequently, more thorough cleaning of the equipment from the previous product is necessary to several such manufactures [3].
Related works
Rotary-drum type of dryers was developed in several countries, but as far as we know, in the industry, they are not widely used. Based on the above conclusions, it is expedient to investigate the drying process of aggressive, environmentally harmful fine-dispersed materials in apparatus of this type, since it became necessary to use them in production. The studies were carried out with several finely dispersed materials (less than 20 ^m) for deep drying (to 0.01%) of phenylene C2, for drying highly moist sodium nitrate and other finely dispersed materials. The apparatus (Fig. 1) is a stationary horizontal heated drum (D = 180 mm, L = 300 mm), inside there is a rotating rotor with blades; with the blades, the material is thrown to the periphery, where a moving intermixing layer is formed, which contacts the heated wall. The material is dried in a layer whose maximum thickness, and, consequently, the residence time of the particles in the apparatus is determined by the gap between the body and the blades (the thickness of the layer can be smaller).
Fig. 1. The scheme of the experimental apparatus:
1 - body; 2 - rotor; 3 - blades; 4 - auger feeder; 5 - fitting for the indicator; 6 secondary steam connection; 7 - unloading threshold;
When the rotor rotates with the blades, the material is thrown to the periphery, where a moving intermixing layer is formed, which contacts the heated wall. The material is dried in a layer whose maximum thickness, and
consequently, the residence time of the particles in the apparatus is determined by the gap between the body and the blades (the thickness of the layer can be smaller). The necessary heat flow was maintained constant or regulated, if necessary to maintain a constant temperature of the wall by a voltage regulator. Secondary steam with a small amount of non-condensable gases was removed from the apparatus along its axis and condensed in a heat exchanger, so product losses and environmental pollution were eliminated [4].
The used methods
The kinetics of drying was studied in a periodic and continuous process (samples of the material were periodically sampled). The temperature of the material in the layer was measured, as well as the temperature of the inner surface of the drum wall. On the basis of the experiments, kinetic curves were obtained for the change in humidity and temperature of the material to be dried in a batch process at different rotor speeds. Analysis of the data showed that with increasing rotor speed, the drying intensity increases, and the temperature of the material approaches the temperature of the heating surface at the end of the process. The effect of the number of revolutions on the coefficient of heat transfer under different initial moisture of the material was also studied. With an increase in the initial humidity, the heat transfer coefficient increases substantially and reaches a high value - of the order of 500 W/m2K, but decreases significantly with a decrease in humidity (less than 200 W/m2K). It was interesting to reveal the change in the heat transfer coefficient along the perimeter of the drum. The experiments were conducted with dry material and the local values of the heat transfer coefficient were measured by a thermic sensor. The heat transfer coefficient was measured at 8 points along the inner perimeter of the drum. The experimental data showed that at low rotor speeds, the heat transfer coefficient is low, which is due to poor mixing of the layer, and in the upper part of the drum, there is a separation of the particles since at given rotor speeds the centrifugal forces are small compared to gravitational forces. Due to this, the profile of the heat transfer coefficient is uneven along the perimeter of the drum. With a further increase in the angular velocity of the rotor, the heat transfer coefficient increases, since the mixing of the particles improves and the number of their contacts with the hot surface increases, while the centrifugal forces also increase. With the increasing angular velocity of the rotor, the ratio of centrifugal force to gravity increases rapidly. This results in a uniform distribution of the material in the gap along its perimeter and, as a result, an increase in the contact heat exchange surface due to the use of the upper part of the drum as the angular velocity of the rotor increases and to equalize the local heat transfer coefficients.
Analysis of studies on heat and mass transfer processes occurring during drying in rotary dryers shows that, based on existing studies of the drying process, it is impossible to take into account all the characteristics and changes in the kinetics of such process. A more complete model would be that which would take into account the temperature change of the material in each of the drying stages,
the equilibrium between the wet material, the additional supply of heat from the energy dissipation due to the rapid movement of the dispersed material and the heated structural elements of the drum, as well as the effect of longitudinal mixing of the dispersed material. On the basis of general concepts of drying and its laws, the physical picture of the process is examined according to the stages that take place in the drying plant, the developed mathematical models are described and their solution is given. The development of the mathematical model is based on the known laws of conservation of energy and mass of matter, the positions from the theory of drying and the laws of equilibrium between the material and the drying agent. The period of removal of free moisture is characterized by the fact that evaporation proceeds according to the laws of the transformation of a free liquid into vapour. During this period, the drying process is mainly determined by the rate of heat input from the heated wall to the material to be dried [5].
Conclusion
One of the most important parameters that determine the drying regime is the wall temperature. In a continuous drying process, the temperature of the wall along the length of the dryer varies due to the heat release to evaporation of the liquid, to heating the material and the rotor blades. The calculation of the removal of bound moisture differs from the calculation of the free moisture removal period in that the surface temperature of the material is increased, it is necessary to calculate using the changed relationship between the wall and the dried material. As a result of thermal contact of the material with hot walls and rotor blades, a layer of dried material appears, the thickness of which gradually increases. And in the dried state, the dispersed material in terms of heat-conducting properties is not so far from the properties of heat-insulating materials. This is connected with the fact that the main resistance to heat transfer is concentrated in the area of the material in contact with the heat-releasing surface. The processes taking place in this zone essentially depend on the Lykov criterion. At its small values, the liquid will not have time to be supplied from the inner layers of the material to the contact surface, a layer of dry material separating the contact surface and the evaporation surface will appear. The temperature of this layer on the contact surface is the same as the temperature of the heated wall, and on the opposite side is equal to the evaporation temperature of the liquid, determined by the value of the pressure in the drying drum.
The results of the research were used when designing and testing a pilot plant in JSC "QUARTZ", in particular for a finely dispersed material with a capacity of 100 kg of moisture per hour. The dimensions of the pilot plant were 450 mm in diameter and 1500 mm in length. For phenylon C2, the overall dimensions of the pilot plant are identical to the laboratory installation at the Department of Technological machines and equipment Fergana polytechnic institute.
References:
1. Ivanov V.E. "Drying of dispersed materials in the continuous fluidized-bed drier". The thesis of a Cand.Tech.Sci .: 05.17.08. - Ivanovo, -p 121.
2. Lukyanenko V.I. Teplomassoobmen process of drying of disperse materials in the centrifugal fluidized bed: the thesis of a Cand.Tech.Sci .: 05.14.04. Voronezh, - 2007. -p. 177.
3. Izmailov M.T. Increase of efficiency of drying of disperses materials at the expense of application of vibroacoustic influences: the Dissertation of the candidate tehn. Sciences: 05.17.08: - Moscow, - 2004. - p. 172.
4. Axunbayev A.A. Mirsharipov R.X. "Issledovanie gidrodinamiki rotornoy sushilki s bistrovrashayushiy rotorom"// TAYI Bulletin Scientific and Technical Journal.: Issue 2. - 2018. - p. 79-82.
5. Tojiyev R.J. Axunbayev A.A. Mirsharipov R.X. "Termicheskaya sushka dispersnix materialov v barabannix sushilkax" // Scientific and technical journal of Fergana Polytechnic Institute.: - 2019. - Special Issue - №3. - p. 129-132.
