ACCELERATION OF VEGETABLE OIL DISTILLATION PROCESSES TO INCREASE CONDENSER EFFICIENCY

ABSTRACT

In order to increase the efficiency of the technological line where vegetable oil distillation processes are carried out, it is necessary to increase the efficiency of the condensers in the system and to develop the optimal modes of the process. The maximum use of the working volume of the condenser is of great importance in distillation. the temperature of the heat transfer agents, the consumption, the secondary vapors separated from the distillation with the solvent also affect the efficiency of the device. raw materials and intermediate products are subjected to various mechanical, physical and chemical effects during the process. reducing these effects is achieved by reducing the excess costs that cannot be fully utilized in the working volume of two devices.

АННОТАЦИЯ

Для повышения эффективности технологической линии, осуществляющей процессы дистилляции растительного масла, необходимо повысить эффективность конденсаторов в системе и разработать оптимальные режимы процесса. В процессе дистилляции большое значение имеет максимальное использование рабочего объёма конденсатора. На эффективность аппарата также влияют температура теплоносителей, расход, вторичные пары, отделяемые от дистилляции с растворителем. В процессе дистилляции сырье и промежуточные продукты подвергаются различным механическим, физическим и химическим воздействиям. Снижение этих воздействий достигается за счёт снижения избыточных расходов, которые невозможно полностью использовать в рабочем объёме двух аппаратов.

Keywords: solvent vapor, cooling water, condensation, vapor phase, liquid phase, layer, heat exchange surface, condensation surface, cooling surface.

Ключевые слова: пары растворителя, охлаждающая вода, конденсация, паровая фаза, жидкая фаза, слой, поверхность теплообмена, поверхность конденсации, поверхность охлаждения.

INTRODUCTION

In the world has seen a steady increase in vegetable oil production over the past decade. The volume of vegetable oil production was 605 million tons in 2021, and this indicator reached 625 million tons in 2022. For this reason, great attention is paid to research on the improvement of vegetable oil production technologies based on scientific and technical achievements, creation of new, energy-efficient constructions of technological equipment. in this aspect, finding solutions to technical and technological problems related to the expansion of the production of high-quality vegetable oils that meet the requirements of international standards in edible oil enterprises is also of particular importance.

In the world, extensive scientific research is being conducted to improve the existing technologies of vegetable oil production, to fully use the unit working volume of technological equipment, to create modern new constructions of devices. in this regard, special attention is paid to the maximum extraction of the solvent in the distillation stages of vegetable oil mistella, to the improvement of the methods of organizing jars and to the creation of new, intensive and energy-efficient constructions of technological equipment with improved hydrodynamic parameters.

METHODS

In the process of solvent distillation, when the solvent vapor pressure is equal to the ambient pressure, the solvent changes from a liquid state to a vapor state [1]. Solvent vapor is sent to the condensers to transfer to the liquid phase [2]. The process of transferring steam and gases from the gas phase to the liquid phase by cooling the air and water is called condensation [1;3;4;5;6;7].

Condensation is used in the chemical and food industry to transfer various gaseous substances to the liquid phase, and condensers are used to carry out the process. The main reason for the formation of vacuum in condensers is that the volume of condensed steam is 1000 times smaller than the volume of steam, which leads to rarefaction in the condenser [7]. Rarefaction in the condenser depends on the temperature, the lower the temperature, the greater the rarefaction. The condensation process is an auxiliary process, and the product vapor entering the condenser is first carried out after evaporation, distillation, vacuum drying and other related processes[3;4;6].

Condensation occurs in two different forms in condensers: droplet and film. In film condensation, the film resistance during heat transfer from steam to the cooling agent is high, and in droplet condensation, the heat transfer coefficient is higher [6;8].

 Air condensers are used to condense all the distillation processes and solvent vapors from the toaster.[9].

Two types of condensers are used for condensing solvent and water vapors: vertical and horizontal [1;7;9]. In surface condensers, condensation occurs on the inside and outside of the wall, while cold water and hot water are supplied from the other side. Given solvent vapors and water vapors contact and mix with water and wet water in mixing condensers [7;9]. After the solvent is condensed, the water contained in the solvent is separated in a separator due to the difference in density. Horizontal condensers have higher heat transfer efficiency than vertical condensers[7;10]. But vertical condensers have the advantage of being self-cleaning. When using ditches, drains and other cooling water, sand, clay and similar substances in the water sink to the apparatus in horizontal condensers[7].

RESULTS AND DISCUSSION

Figure 1. Heat transfer during condensation

Steam cooling in chemical and food equipment is heated by two steams, the steam condenses in a thin layer and the main thermal resistance occurs in the thin layer. The thermal resistance of the vapor phase is lower than the thermal resistance of the thin layer. Thin layer mode of condensed steam depends on reynolds number, physical properties of condensate (heat conductivity, density, viscosity), wall dimensions, spatial location and turbulence depend on heat transfer rate of condensed steam. The increase of the vertical wall, the increase of roughness on the wall surface causes the condensable layer to increase downward[4].

Usually in vertical condensers a large part of the vapor accumulates at the top, because the solvent vapor moves to the upper part, the heat exchange process does not go well, it requires a large surface for condensing, and the overall size of the apparatus increases. As a result, it requires high consumption

The total heat transfer coefficient of the water condensing on the surface of the building:

Nu=ϝ (Ga, Pr, K);                                                                    (1)

here Ga=(gt³ρ)/μ² – Galilean criterion; Pr=cμ/λ – Prandtl criterion; K=r/cΔt – Condensation criterion.

The Galilean criterion determines the ratio of the gravitational force to the kinetic energy in the flow, and the condensation criterion is determined by the change in the state of the aggregate.

As a result of processing the above equation, the following theoretical equation was developed for the laminar movement of a thin layer of condensate on a cylindrical or vertical flat surface: 

                                                                                                                         (2)

The following equation is used for steam condensation on the outer surface of the horizontal pipe:

                                                                                                                         (3)

In the surface condensation process, water and air are used as cooling agents, and heat exchange is carried out in the devices through the separating wall of the cooling agent and the condensing steam and as a result, the condensed steam keeps its condition without mixing with the cooling agent [3;4;5;9].

Condensation in condensers can take place in both the inner and outer parts of the device pipes, and the condensed steam is reused in the industry depending on its economic importance. Depending on the movement of the capacitors, they move oppositely and in parallel [3, 4].

In condensers, the heat transfer surface consists of 3 parts, which are divided into: superheated steam cooling part surface (F1), condensing part surface (F2), condensate cooling part (F3) [2, 5].

In the condenser, the total heat exchange rate is as follows:

                                                                (4)

In the process of condensation, the condensed liquid moves downward and the new vapor approaches the wall. If the wall temperature is low, the movement of vapor molecules and condensation are high[6].

Condensate cooling increases due to a decrease in the condensation temperature, an increase in pressure loss, a decrease in the amount of condensable steam, an increase in the condensation surface, an increase in the composition of air and gases due to an increase in the partial pressure of steam in the steam-gas mixture under the total pressure [5]

The number of condensers is also three due to the fact that the distillation process is carried out in three stages in oil factory.

Table 1.

Mass consumption of the micelle distillation process [11]

The table above shows the material balance of the distillation workshop of the cottonseed oil production plant with a daily capacity of 400 tons. Using this information, we determine the geometric dimensions, material and heat calculation of a simple shell-and-tube condenser.

We determine the amount of water consumed in the condensation process:

Heat balance equation for condensers:

                                                    (5)

Here, G_e, G_s – mass consumption of solvent steam and water, c_ec_s – heat capacity of solvent vapor and water, t_e1, t_e2, t_s1, t_s2 – initial and final temperatures of solvent vapor and water.

We can find water consumption from formula 10:

                                               (6)

Based on the above information, we find the mass consumption of the capacitors of the three stages:

The amount of water consumed in the 1st stage condenser:

G_s =9805*2.53*(71.23-40)/(1*(35-20)) = 51647.445 kg/hour,

The amount of water consumed in the 2 nd stage condenser:

G_s2=1165.83*2.53*(80-40)/(1*(35-20)) = 7865.466 kg/hour,

The amount of water consumed in the 3 rd stage condenser:

G_s3=100*2.70*(105-40)/(1*(35-20)) = 1170 kg/hour,

Heat load of condensers:

                                                              (7)

In Table 1, the mass consumption of the solvent is given in tons per day, and when finding the heat load of the condensers, we change it to kg/hours.

 = 9805*2.47*(71.23-40) = 756339.071kJ/kg

 = 1165.83*2.53*(80-40) = 117981.996kJ/kg

 = 100*2.7*(105-40) = 17550kJ/kg

Heat calculation of the condensation process is found based on the information given above.

Average temperature of the solvent vapor:

                                                                        (8)

 55.6 ℃

 = 60 ℃

 = 72.5 ℃                                                        (12)

Average temperature difference:

 = 71.23-35 = 36.23 ℃

 = 40-20 = 20 ℃

 = 80-35 = 45 ℃

 = 40-20 = 20 ℃

 = 105-35 = 70 ℃

 = 40-20 = 20 ℃

[13], using Table 2-2 given in the literature, we accept the approximate value of the heat transfer coefficient as 300 W/(m²*k). Coefficient of heat transfer from solvent vapor to the wall  = 350 W/(m²*k), heat transfer coefficient of the wall to water  = 500 W/(m²*k)

Heat flux density:

 = 300*28.115 = 8434.5 W/m²

 = 300*32.5 = 9750 W/m²

 = 300*45 = 13500 W/m²

The temperature of the tube wall in which the solvent moves:

 = 79.698 ℃

 = 87.857 ℃

 = 111.071 ℃

Wall temperature of the pipe in which the cooling water is moving:

                                                             (9)

We take the thermal conductivity coefficient λ = 86 [3]

 = 79.894 ℃

 = 88.083 ℃

 = 111.384 ℃

We find the necessary surface for the heat load calculated above:

                                                              (10)

 = 89.672 m²

 = 12.100 m²

 = 1.3 m²

We select capacitors suitable for these surfaces [12]:

Table 2.

Capacitors suitable for these surfaces

 Figure 2. Internal structure of the proposed condenser

The internal structure of the recommended capacitor is shown in Figure 2. In the solvent vapor movement, spiral barriers are installed on the outer surface of the water moving tube and the inner surface of the solvent vapor moving wall. Spiral baffles prevent solvent vapor from accumulating at the top of the device, ensure uniform distribution of vapor along the wall, and extend the contact period of the solvent vapor through the wall with the cooling water.

CONCLUSION

In conclusion, based on the above calculations, in the ordinary tube condensers, the absence of helical baffles results in disordered contact with the solvent vapor selling agent. Due to the accumulation of solvent vapors in the upper part, the geometric dimensions of the apparatus increase, the solvent vapor requires an additional surface for condensation. Therefore, additional material, high energy and additional cost are used for the hardware. The spiral baffles in the recommended condenser ensure that the steam moves through the device and the condensation process is carried out evenly. During condensation, the solvent vapor spreads evenly and the heat exchange process accelerates. Reduces the geometric dimensions and reduces the cost.

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