Investigation of constructive and technological parameters of an energy-efficient screw oil press

The article presents the investigation of constructive and technological parameters of an energy-efficient screw oil press. It is outlined the principle of operation of an energy-efficient screw oil press. The construction of the oil press is improved by the steam atomizer that is installed in the receiving hopper under the rifled rollers for moisture-thermal treatment with steam, which is completed with the heat exchanger, heating element, expansion tank and hydro group. Also, a steam generator connected to a steam atomizer which is embodied into the receiving hopper. It was analyzed the influence of the optimization criteria (oil yield, energy consumption and press productivity) on the efficiency of the technological process. These optimization criteria depend on the main independent factors: the length of the reception and preparation chamber, the material (sunflower pulp) moisture; the heating temperature, the screw rotation speed, the linear speed of movement of screw shaft turns. The optimal constructive and technological parameters of energy-efficient screw oil press are considered. The energy-efficient screw oil press refers to the equipment of the oil enterprises of small productivity and due to its design, it allows to use a simple technological scheme of oil pressing and to reduce the amount of energy and resources spent on the technological process in the context of use in sustainable food systems.


Introduction
At the current stage of economic evolution, in the conditions of the need to transfer the state's economy to an intensive path of development, the most rational use of production potentials is an urgent problem.One of the main tasks of sustainable food systems is the implementation of new technologies for the processing of agricultural products in the conditions of enterprises and farms as well as the production of small-sized, low-energy-consuming equipment for completing technological lines.In Ukraine sunflower is one of the most widespread agricultural crops.This is due primarily to the high profitability of crop cultivation, the possibility of effective sale of both seeds and vegetable oil.There are two methods to get oil from sunflower seeds: pressing and extraction method.However, the costs of producing oil by pressing are 8-10 times lower compared to extraction.All known types of screw presses can be divided into three groups: presses for preliminary and final removal of oil and double-acting presses (both types of removal of vegetable oil is carried out in one machine).The industry of such countries as the USA, Japan, India, China produces many options of oil presses.The geometric parameters of the oil presses, their kinematic and energy indicators are determined by the physical and mechanical properties of oil-containing seeds.Oil-separating presses can be part of oil raw material processing lines, 1254 (2023) 012135 IOP Publishing doi:10.1088/1755-1315/1254/1/012135 2 or be independent units.However, according to the principle of action and work process, they are all of the same type.Oil presses that are used in the conditions of farms that process small volumes of sunflower have a number of disadvantages: low yield of oil in one pass, increased time spent on cleaning the press from clogging, which contributes to a significant decrease in the productivity and demands to manually push the oilcake from the hopper into the receiving and preparation chamber during repeated pressing, due to its poor flowability.
Food production is used as an entry point to improving food system sustainability [1].Furthermore, it is important to provide the conceptual foundations of the mechanism of management of enterprise interaction with environment [2].Ukrainian sunflower oil is export oriented product and positive trend on the world market will bring benefits for processing enterprises despite on uncertainty of country environment [3].Various production sources including sunflower oil have the potential for producing improved food and fuel products such as biodiesel production and a renewable solvent phase [4].Ukraine is one of the world-leading countries in production and export of sunflower oil and integration of the Ukrainian and the EU market is prospective way for economics and further biogas production [5].The screw presses for different oil crops have almost identical principles of operation, but the technological regimes and constructive peculiarities can be varied [6].There is some development of modern constructions of oil presses on the basis of analysis of the basic operational concepts for the screw channel and the influence of its parameters on the productivity [7].It is considered the chemical, chromatography research carried out in the area of assessment of edible oils [8], also it was made a systematic review on effects of plant oil consumption [9].The rapeseed and sunflower oil are most widespread not only in food technology but also in production of biogas, but there is a need to investigate different operating regimes [10] with use analysis methods to optimize the dimensional parameters and constructional characteristics [11].The extraction method of processing vegetable oil is usually used in the conditions of big enterprises and there are a lot of issues [12], it is challenging during using high-moisture material [13].The aspect of optimizing the processing technologies is important for the green manufacturing of oils [14].It is important to take into account features of oil sunflower seeds and its input parameters [15].There are a lot of by-products during processing sunflower oil such as press cakes and oil meal, which are high-protein feeds for farm animals [16].The standardization of biomasses is going to be a key aspect to get good quality biofuels from those residues [17] and the thermal behaviour of these materials need to be studied [18].With regards to the condition of pre-and post-processing techniques it is suggested to implement the new construction of expellers for oil millers in order to the fatty acid compositions of sunflower oil did not significantly change [19].
The screw presses have some common technical and technological drawbacks.The service condition of an oil screw press was analyzed.It was researched the fracture failure of the bearing rings [20].Also, there were investigated the major components of the palm oil screw press [21].The cases of shaft failure indicate common areas of failure that occur around the lower edges of the keyway and shaft shoulders [22].The effectiveness of screw presses is evaluated for throughput capacity, feed rate, press cake oil content, oil expelling efficiency, percentage un-pressed grits output, percentage sludge output, and specific energy consumption [23].The driveshaft of screw press is often found to be susceptible to failure, it is important to discover the root cause of this failure and the ways of its prevention [24].The mechanical oil extraction using a commercial screw press was evaluated in the study [25].The stress concentration occurred on the keyway of the tooth wheel holder, which finally caused the fracture at this area [26].It is proposed to assess quality management systems through the values of the set of interconnected processes, to combine the assessments of different processes into one set of data and to estimate this set, which will allow assessing the system with higher objectivity and reliability, particularly in the conditions of enterprises of pressing sunflower oil [27].The optimal constructive and technological parameters of technological equipment in the processes of agricultural production are considered [28], designing modern processing machines requires a study of the regularities of technological processes, dynamics and conditions of operation [29], but the investigation of constructive and technological parameters of an energy-efficient screw oil press was not the specific subject of research.
The aim of the article is to conduct the investigation of constructive and technological parameters of an energy-efficient screw oil press.

Methods
On the basis of the investigation of theoretical provisions of the process of oil separation by pressing sunflower seeds and engineering calculating methods it is proposed the constructive and technological parameters of an energy-efficient screw oil press.
In order to intensify the processing of sunflower seeds, the design of the screw press was improved, the laboratory and experimental studies of the pressing were carried out, the mathematical model on the basis of the main technological parameters has been developed.There was theoretically justified method of calculating the constructive and technological parameters of the screw press, conducted the factor ranking, the insignificant factors were excluded from further consideration.
The research outlined the optimization criteria and selected the coefficients of variation, according to which the optimal design and technological parameters of the energy-efficient screw oil press are presented.In the investigation were used the methods of generalization of theoretical and laboratory experimental studies, mathematical modelling of the process, substantiation of the method of processing experimental data, solution of the optimization problem in determining the constructive and technological parameters of an energy-efficient screw oil press [30].

Principle of operation of an energy-efficient screw oil press
The main process of the press method of obtaining oil is squeezing it from the sunflower pulp, which is a loose, porous material.At the beginning of the squeezing, as a result of the convergence of the particles, the oil, which was held on their surfaces, begins to flow through the channels between the particles.Then, with the onset of deformation of the particles, the oil begins to flow through the capillaries that make up the inner part of the particles themselves.From this moment the oil phase is considered continuous.Thus, the squeezing of oil from the sunflower pulp can be considered as the movement of an incompressible fluid in a porous, deformable medium.As the particles of the pressing sunflower pulp come together, the movement of the oil obeys the laws of hydrodynamics.When the oil is pressed deeply under high pressure, the surfaces of the sunflower pulp particles fuse with the encapsulation of the oil in separate areas of the cake.This phenomenon determines the uneven oiliness of the total mass of cake briquettes (shells).The part of the material, from which oil is squeezed out, undergoes elastic and plastic deformations during this process.As a result of the study of the influence of the character of the deformation on the degree of oil squeezing, it was found that the shear stress of the material created during squeezing should be less than the shear stress, which contributes to the emergence of plastic flow.This condition must be observed because in the case of plastic flow, together with the oil, the sunflower pulp will come out through the holes for its draining.At the same time, due to the drop in pressure, oil extraction will deteriorate.
When oil is squeezed out in screw presses, the pressure on the pressed material increases and the oil flows out not only due to the action of external conditions, but also as a result of the resistance of the sunflower pulp itself as it is compacted and the oil is squeezed out.In turn, the resistance of the sunflower pulp in the press depends on its plastic properties.When the sunflower pulp is over-dried, the formation of the cake into a shell stops and the pressed material begins to leave the press in the form of dry, stiff flour or groats with a high oil content.This transition is initially accompanied by an increase in the load on the drive electric motor of the press, and with the cessation of shell formation, its sharp drop.Often at this moment, structurally weak presses fail due to breakage of the most heavily loaded elements or stop under load, forming a pressing due to the failure of safety pins or tripping of protection.When the sunflower pulp is over moistened, the formation of the cake into a shell also stops and the pressed material comes out in the form of a shapeless soft mass.This transition is accompanied by a decrease in the load on the electric drive of the press.Thus, the pressure in the perforated cylinder is mainly depend on the plasticity of the sunflower pulp, the humidity and the temperature of the pressed material.In the process of pressing, the volume of the sunflower pulp is reduced due to the squeezing out of oil, convergence of the inner and outer surfaces of the particles, as well as due to some evaporation of moisture.The time the sunflower pulp stays in the screw press during squeezing depends on the speed of rotation of the screw shaft, the degree of capture of the material by the first turn of screw shaft, the physical and mechanical properties of the material and the degree of wear of the surfaces of the screw turns.
The energy-efficient screw oil press refers to the equipment of the oil and fat industry, namely to small-sized screw presses, which can be used in the enterprises of small productivity.During the development of an improved model, the task of creating a screw press for oil crops was set, in which, after crushing the seed core with rollers, the wet-thermal treatment of the sunflower seed pulp will be carried out using a steam-generating device.It will contribute to the improvement of the intensification of the separation of oil during pressing, and the process of steam heat treatment will not affect the quality of the oil.The energy-efficient screw oil press consists of a bed, a receiving hopper with rifled rollers, a perforated cylinder with slats collected in it, a screw shaft, a steam-generating device, a cone-type adjusting nut and a drive unit.The main attention during the development of the improved design was paid to the implementation of a steam-generating device, which makes it possible to intensify the separation of sunflower oil and thus increase its yield.The use of additional steaming will also contribute to the reduction of frictional forces and resistance of the processing material, which will allow to reduce the operation of the screw shaft and parts of the perforated cylinder and increase the service life of the press.The use of a steam-generating device for moisture-thermal processing makes it possible to increase the productivity of the press when processing oilseeds, reduce the oiliness of the cake, and increase the yield of sunflower oil.
The screw shaft is structurally made of individual screw turns, which differ in pitch and diameter, and intermediate rings, which are mounted on a smooth shaft and fixed against turning with a key.In the receiving hopper, there is a damper, a pair of threaded rollers, which receive a rotational movement from the screw shaft through a V-belt transmission.The main element of the press is the perforated cylinder, which has a welded cylindrical shape.Inside the cylindrical surface there are slats, which are held in place by a tension wedge.The installation of rifled rollers in the receiving hopper turns the sunflower seeds into a pulp, which contributes to the intensification of the oil separation process and the effective use of the perforated cylinder.Figure 1 shows a screw press for separating oil with a steam-generating device for wet-thermal processing; figure 2 shows a section of the receiving hopper with rifled rollers and a steam atomizer, a side view.
The screw press is fixed on the carcass 1.The material is fed into the receiving hopper 5, which is crushed by the rifled rollers 4, and turns into a sunflower pulp.The gap between the rollers is regulated depending on the physical and mechanical properties of the material being pressed.In the hopper, the sunflower pulp is subjected to moisture and thermal treatment with steam, the yield of the oil increases.In addition, the softening of the sunflower pulp will contribute to reducing the wear of the oil press parts.After moisture and thermal treatment, through the loading hole regulated by the valve 11, the material is sent to the middle of the reception and preparation chamber of the perforated cylinder 15, where it is captured by the turns of the screw shaft 13 and moves to the exit from the press.When the screw shaft rotates, the material is  transported into the working space, where oil is gradually squeezed out, which passes through the gaps between the perforated panels 16.Depending on the state of pressing material, the pressure in the working chamber is regulated using the adjustable nut 14.The area between the outer surface of the screw shaft and the inner surface of the perforated cylinder is the working space.Inside the cylindrical surface there are slats, which are held in place by the tension wedge 12. Steam generator 17 consists of: steam atomizer -6; heat exchanger -7; tubular electric heater -8; expansion tank -9; hydro groups -10.The press and rollers are driven by the electric motor 2 through the V-belt transmission 3. Thus, the use of a steam-generating device in the design of the screw press will contribute to the intensification of oil separation to increase its yield, and will extend the service life of the structural elements of the machine.

Results
Analytical expressions obtained as a result of theoretical studies reflect an idealized technological process.Therefore, the purpose of research was to check the technological reliability, as well as quality indicators of the technological process according to three optimization criteria: maximum oil yield, minimum energy consumption, maximum press productivity.Achieving the set goal was carried out by solving a number of problems, for which: the factors that have the greatest influence on the quality of the technological process and are subject to regulation have been determined; the length of the reception and preparation chamber was increased and a steaming apparatus was installed in the experimental sample of the press; the dependence of oil yield (OY), energy consumption (EC) and press productivity (PP) on the identified variation factors was experimentally investigated.According to the results of optimization and determination of the optimal combination of factors on a sample of the screw press that operated as part of the sunflower seed processing line, the regularities of the technological process of pressing sunflower seeds were revealed.
At the initial stage of the study of any object using the theory of experiment planning, it is necessary, in addition to a thorough study of the literature, to conduct an a priori ranking of factors, which is performed by the method of expert evaluation.The essence of this method is in that the researchers are asked to arrange the factors that affect the progress of the process in the sequence of decreasing influence on the optimization criteria, that is, it is necessary to rank the correspondingly determined ordinal numbers (ranks) 1, 2, 3, . . ., k. Factor ranking must be conducted in order to reduce the volume of experimental work, since insignificant factors can be quickly excluded from further consideration.This facilitates further stages of solving the experimental problem.The process of ranking the experiment is carried out as follows.During the interview, each specialist is asked to fill out a questionnaire, in which the factors, their dimensions and the expected intervals of variation of the factors are indicated.The specialist must assign the place of each factor, as well as supplement the questionnaire with other factors not included in the consideration.
The diagram of factor ranks shown in figure 3.There are chosen the factors: X1 -degree of crushing, mm; X2 -the length of the reception and preparation chamber, m; X3 -the width of the perforated channels, m; X4 -the working area of the perforated chamber, m 2 ; X5 -material (sunflower pulp) moisture, %; X6 -density of sunflower seeds, kg/m 3 ; X7 -heating temperature, C 0 ; X8 -screw rotation speed, s −1 ; X9 -linear speed of movement of screw shaft turns, m/s; X10 -level of mass input for pressing, kg/s; X11 -total area of perforated channels, m 2 ; X12the length of the perforated cylinder, m.
Conducted experimental studies showed that with an increase in press productivity, the oil yield ratio decreases, when extracting oil from the cake, oil drains along the entire length of the perforated chamber, it leads to clogging and stopping the press.The established facts allow to conclude that the sunflower seeds in the reception and preparation chamber do not have time to go into the state of pulp, that is, the material is not crushed enough and does not have enough time to heat up.Getting into the main chamber, this mass continues its transition into the sunflower pulp.Therefore, the initial part of the main chamber, almost to the middle, does not work as intended, but performs the functions of a reception and preparation chamber.
In order to increase the efficiency of the process of extracting oil from sunflower seeds with a screw press it was enlarged the length of the reception and preparation chamber, that is, the conditions for obtaining high-quality crushed seeds were ensured.The particle size should be within 0.2-0.8mm, and the heating temperature should be 80-125 • C.
Obtained experimental data allowed to make an assumption that doubling the length of the reception and preparation chamber allows a significant increase in the percentage of oil yield.
In accordance with the experimental plan, an assessment of the dependence of technological process indicators, which have the greatest influence, was carried out.The most important indicators are: the length of the reception and preparation chamber, m (X2), the moisture content of the material (sunflower pulp), % (X5), the heating temperature, C 0 (X7), the speed of rotation of the screw shaft, s −1 (X8) and the linear speed of movement of the screw shaft turns, m/s (X9), which have the greatest effect on the quality of the screw press.The levels of setting of independent variables (factors) and the range of their variation adopted during the experiments are given in the table 1.The repeatability of experiments for each of the optimization criteria is three times.In each line of the plan, the average value of OY (oil yield), EC (energy consumption) and PP (press productivity) was calculated.Two-dimensional intersections of the response surfaces for the considered cases are shown in figure 4, figure 5 and figure 6.
With an increase in the length of the reception and preparation chamber and the humidity of the material (sunflower pulp), an increase in the percentage of oil yield and the productivity of the press is observed (figure 4).The zone of optimal combination of factors is limited by the arcs of the OY, EI and PP curves.The yield of oil will be in the range of 45-50 %; the energy consumption will not exceed 59 kW, and the press productivity will increase to 260 kg/h.For this technological regime, the speed of rotation of the screw shaft is equal to 0.025 s −1 , and the linear speed of movement of the turns of the screw shaft is 0.004 m/s.
The analysis of the results of the experiment demonstrates the higher quality of indicators of the technological process when the length of the reception and preparation chamber is 560  mm (figure 5).It is possible to achieve an oil yield of up to 50 % with an equipment power of 55-60 kW and a productivity of 260 kg/h.Humidity in the range of 9-15 % promotes better oil separation.
In order to achieve better values of the quality indicators of the technological process, compared to the two previously considered options, it is necessary that the length of the reception and preparation chamber be increased by 280 mm.As a result, it will be obtained more qualitatively crushed mass, and the pressing temperature is in the range of 105 -130C 0 (figure 6).The selected combination of factors corresponds to the figure limited by the shaded area, the curves OY=50%, EC= 55kW and PP=260kg/h.

Discussion
In the context of the discussion of the obtained results it is necessary to point that the study of oil extraction process showed that the remaining oil in the sunflower pulp depends on the  total and hydrodynamic pressure [31].On the oil extraction process affect the thickness of the sunflower pulp layer, the permeability of the deforming sunflower pulp layer and its porosity, the viscosity of the oil, the duration of extraction, the degree compaction of the volumetric mass at the beginning and end of pressing and the density of the pressed oil [32].Presses for extracting oil from vegetable raw materials have a similar principle of operation, but different constructive and technological parameters depending on the crop [33].As well as the small enterprises or farms need the improvement of technological process indicators through the development of the energy efficient equipment in particular for producing sunflower oil [34].The squeezing of oil in the screw press occurs as a result of the gradual compaction of the sunflower pulp mass due to: reduction of the volume of mass located between turns, as a result of a gradual decrease in the pitch of individual turns and their height [35].The mechanical effect of these turns on the sunflower IOP Publishing doi:10.1088/1755-1315/1254/1/01213511 pulp occurs during the rotation of the screw shaft [36].The friction of the pressed material arises on the surface of the turns, the walls of the perforated cylinder and the friction of the particles among themselves [37].Also, it is important to take into account the resistance of the mechanism that regulates the size of the outlet opening for the cake (cone, diaphragm, ring) [38].The friction of the pressed material arises on the surface of the turns, the walls of the perforated cylinder and the friction of the particles among themselves [39].The modernization of the energyefficient screw oil press, namely the increase of length of the reception and preparation chamber and installation of steaming device can improve the indicators of the factors that determine the quality of oil extraction such as oil yield, energy consumption, press productivity, that was checked experimentally.

Conclusion
The technical solutions for pressing oil raw materials in the conditions of farms or small enterprises usually need the improvement of its efficiency.Also, they are not always technological when when it comes to increasing oil yield and equipment productivity.Thus, the urgent task is the production of small-sized, low-energy-consuming equipment for the completion of technological lines for the processing of agricultural products in the conditions of small enterprises in the context of food production sustainability.In order to eliminate these shortcomings, it is proposed to use energy-efficient screw oil press which consist of a carcass, a receiving hopper with rifled rollers, a perforated cylinder, a screw shaft, a steam-generating device, a cone-type adjusting nut and a drive unit.
The special feature of the design of screw oil press is that a steam atomizer is installed in the receiving hopper under the rifled rollers for carrying out moisture-thermal treatment.It is completed with a heat exchanger, a heating element, an expansion tank and a hydraulic group.Additionally, a steam generator connected to a steam atomizer that is implemented into the receiving hopper.The energy consumption of the pressing process is mainly influenced by the independent factors: the length of the reception and preparation chamber, the material (sunflower pulp) moisture; the heating temperature, the screw rotation speed, the linear speed of movement of screw shaft turns.The purpose of research is to check the quality indicators of the technological process according to the following optimization criteria: oil yield, energy consumption, press productivity.On the basis of theoretical and experimental studies, the most profitable constructional and technological parameters of the screw press have been established, namely: the length of the reception and preparation chamber is 560 mm, the moisture content of the pulp is within 9-15 %, and the pressing temperature is 130 • C. At the same time, the yield of oil is 45-50 %.

Figure 2 .
Figure 2. A section of the receiving hopper with rifled rollers and a steam atomizer: 4 -rifled rollers; 6 -steam atomizer.

Figure 3 .
Figure 3. Ranking diagram of factors that affect the quality of work: a) to statistical assessment of the importance of factors; b) after ranking and determining non-significant factors.

Table 1 .
Levels and range of variation factors.