Nowadays, the requirements of edible vegetable oil plants on energy consumption indicators are increasing. Low energy consumption and high efficiency are the goals of oil plants. The solvent extraction processes in the world are roughly the same, and it is more appropriate to meet the process requirements by upgrading and optimizing the supporting equipment. The edible oil solvent extractor is a very key equipment in the solvent extraction process. Its performance in the oil extraction process is not only related to the solvent consumption index but also affects the residual oil index of the meal.
The solvent extractor is a device that uses solvent (such as n-hexane) to contact and soak the oil and extract the oils&fats from the raw material. The extractor includes spraying, soaking, and draining processes. The solvent extraction results are balanced by adjusting the spraying amount and the material walking speed. In order to improve the design and manufacturing quality of the extractor, ensure good extraction effect, and provide an extractor with stable performance and convenient use for oil plants, several key points that should be paid attention to in the structural design of the extractor are described according to Chemsta years of experience in design, manufacturing, and use.
1 The Design Trend And Equipment Appearance Of The Extractor
At present, the extraction tonnage of oils&fats plants has developed to medium and large scale, and many of them have a daily processing capacity of more than 3000 tons per day. The specification of the extractor has also increased. In order to consider the factors such as site, extraction efficiency, production, and installation, the extractor is designed with a shallow material layer and a double-layer structure. The design of shallow material layer reduces the travel distance of solvent in materials. The design of a double-material layer extractor not only reduces the requirements of plant size but also ensures the extraction time. It ensures the length of the extraction section and the length of the drainage section, thus improving the drainage effect. Originally, there were deep material layers (material layer height is about 2 m) and shallow material layers (material layer height is 0.8~1.2 m). Now, shallow material layers are mainly used, and the structure is rectangular and double-layer.
2 Some Problems In The Design Of Extractor
2.1 Extractor Specification
The solvent extraction process is divided into a pre-extraction section, extraction section, and drainage section. The specification of the extractor is comprehensively determined according to the processing capacity, extraction time, extraction area, etc. The large tonnage extraction area is large, while the small tonnage extraction area is small. During the design, the length of the extraction section is determined by calculating the required extraction stages, spraying amount of each stage, the volume of the collecting bucket, etc., and combining the specific requirements of the extraction workshop space, extraction indicators, etc., and then the lengths of the pre-extraction section and the extraction section are determined, after the above length is determined, the space size of the internal conveying structure is determined. Under the condition of ensuring the normal and stable operation of the conveying structure, the structural design should be as compact and simple as possible, and finally, it should be reasonably designed into two layers.
2.2 Extraction Level Adjustment Device
The material level of the extractor can be adjusted. In order to adapt to the processing of a variety of oil-bearing crops, the material level baffle is usually designed to be adjustable from top to bottom. The material level of the extractor can be adjusted freely within the range of 800~1200 mm. The material level can be adjusted outside the extractor even during start-up. The material level control device consists of a baffle plate and a regulating device. The baffle plate is inside the extractor and the regulating device is outside the extractor. The baffle plate should be connected with the regulating device. The structure should be able to adjust the movement of the baffle plate up and down through the regulating device. The baffle plate can be bent or welded with stainless steel plate, and the overall rigidity of the baffle plate shall be ensured. As the height of the material layer is adjusted less frequently, it is unnecessary to take the structure into consideration when designing the adjustment device, as long as it can ensure flexible rotation, no jamming and no deformation. When designing the regulating device, it is necessary to consider that the structure should be able to prevent the solvent gas from flowing out of the extractor, so the structure should ensure sealing. The sealing material can be made of PTFE, which is resistant to solvent corrosion.
2.3 Tail Discharge Form
There is a certain distance between the upper screen surface and the tail-driven wheel at the tail of the extractor, which is the space distance for the upper material to fall to the lower layer. As the material is soaked and squeezed between materials, the material is easy to form an arching “bridging” phenomenon. When the material reaches the tail, it should fall to the lower layer, but because of the “bridging” delay, it falls to the lower layer. During the design, attention should be paid to the spacing between two chains, or the “bridging” should be broken by external forces. Let the materials fall at the same time as much as possible, and the falling time difference will not be too long, so as to ensure the flatness of the material surface of the lower layer.
2.4 Spraying System
The spraying system is one of the important parts of the solvent extractor. The solvent is sprayed onto the materials through the spraying device. How to make the solvent sprayed onto the materials reasonably is the key. The amount of spraying has an impact on whether the materials can be soaked, and uneven spraying has a considerable impact on the residual oil index. Therefore, the design of the spraying structure should be considered carefully. At present, it can be realized through direct spraying pipe spraying and spraying pipe plus overflow launder, among which, direct spraying pipe spraying is the direct spraying of solvent from the spraying pipe; The spray pipe plus overflow launder is used to spray the solvent to the overflow tank through the spray pipe and then onto the materials. Spray pipe can choose standard seamless steel pipe, according to the flow of the selection of steel pipe specifications, spray pipe hole area according to the size of the spray volume to determine the number and size of the hole. The spray device is recommended to choose stainless steel material, relative to carbon steel material, long service life.
2.5 Material Rake
During the extraction process, the material moves forward slowly with the pusher plate, and the upper spray sprays the material. The solvent penetrates down through the gap between the materials due to gravity, so as to extract the oils&fats in the material. However, a certain amount of powder in the material will be sprayed circularly with the solvent, so that part of the powder in the mixed oil from the spray pipe will cover the surface of the material bed, As a result, the mixed oil is not easy to penetrate. Therefore, the designed material rake should have the function of loosening and breaking materials and turning materials. First, the dense layer on the surface of the material bed should be destroyed, and the material rake teeth arranged in the sequence should plow “furrow” on the surface of the material layer. The spacing of the rake teeth is about 150 mm. Since a large amount of spraying by the spraying device will flush and level the“furrow”, the number of rakes can be determined according to the actual materials, Normally, a group of rakes can be placed at an interval of about 3m. In addition, when designing the material rake, pay attention to that the material rake can be adjusted up and down.
2.6 Automatic Control System
The rotation speed of the motor is decelerated and transmitted to the conveying chain wheel inside the extractor. The chain wheel drives the chain scraper to push the material forward. The traveling speed of the material is controlled by the level of the material in the storage tank. The high and low-level sensors in the storage tank transmit the signal to the PLC. Adjust the rotation speed of the frequency-changing motor to adjust the speed of the extractor to adjust the speed of the chain scraper . That is to say, the automatic control system requires that when the low-level alarm occurs, the signal is sent to the PLC to reduce the motor frequency and material speed; In case of a high material-level alarm, the signal will be sent to the PLC to increase the motor frequency and material speed. In this way, a chain control is formed to ensure that the storage tank has a certain level of height and prevent the solvent gas in the extractor from entering the pretreatment section along the conveying equipment.
2.7 Oil Hopper Access Port
The oil hopper is used to store the mixed oil chamber. The normal lower oil hopper has a large upper and small lower closure structure. Because the equipment needs to be repaired after the extraction workshop is used for a period of time, therefore, the access port is designed on the oil hopper, the size is generally DN500, the standard maintenance manhole has a straight section, if the maintenance port is welded to the inclined plane of the receiving port, then the manhole straight section and the oil hopper inclined plane welding, because the oil hopper is a large and small structure, the maintenance port inclined down, the straight section of the maintenance port will have a part of the mixed oil. Therefore, in order to prevent the accumulation of mixed oil, the access manhole should be designed with an inner core, such as a 130mm straight section, and a manhole cover with a 130mm inner core.
2.8 Shaft End Sealing Device
There is a large amount of solvent gas in the extractor, which is toxic, flammable, and explosive. When designing the extractor, ensure the overall tightness of the equipment to prevent gas from escaping, the drive part of the extractor is the shaft end seal. If the sealing effect of the shaft is not good when it rotates, it is easy to leak. When designing the seal, the shape and specification of the seal should be calculated according to the shaft diameter and pressure. The seal can be made of anti-corrosion materials such as polytetrafluoroethylene, as the sealing performance of the sealing element decreases after being used for a period of time, the replacement of the sealing element should be considered. Therefore, when designing this structure, on the premise of ensuring good sealing performance, simple structure, and convenient disassembly should be considered.
2.9 Instrument Port
The extractor is equipped with an on-site thermometer, temperature sensor, pressure gauge, pressure sensor, liquid level gauge, and other instruments, in which the gas phase and material are measured, and different instruments shall be set at different parts. The gas phase thermometer, pressure sensor, etc. shall be set at the top cover of the equipment. High and low-level gauges shall be set at the side of the oil hopper to detect the level of the oil hopper. Thermometers for measuring the temperature of materials can be set at the lower part of the storage tank.
2.10 Other Technical Requirements And Main Process Parameters
In addition to structural design, there are also some relevant technical requirements that need to be noted. The following points are listed: The box body is formed by welding steel plates. The thickness of the side plates of the box body is 16 mm, 10 mm, 8 mm, 4 mm, and other different thicknesses. After the thick steel plates are formed by welding, the flatness of the plate surface is good. However, for the thin steel plates, after welding, the plate surface is easy to deform and uneven, which will affect the operation of internal components and the appearance. When designing the box body, it should be noted that the flatness of the side plates of the box body is ≤ 1.5 mm/m2; Technical requirements shall be made for coaxial and parallelism between two mounting plate holes of the transmission shaft inside the equipment; The welding seam of the overall equipment must have technical requirements, dye penetrant inspection, water test, and pressure test, and check the welding seam.
For more than 40 years, Chemsta has designed and manufactured hundreds of edible oils&fats solvent extractors for customers all over the world and has accumulated a wealth of experience in design and manufacture. If you have questions about the solvent extractor, please contact us and our engineers will be happy to have a technical discussion with you.