This article is a continuation of the last article: Comparative analysis of loop type extractor and drag chain extractor (I)
4. Process operation analysis
The material in the loop type extractor is completely turned over in the bending section, and the solvent immersion of the material can be formed in the bending section. Limited by the structure of bending section, the height of material layer is generally 700-900 mm, which belongs to shallow layer leaching. The advantages of the method are that it is advantageous to the penetration and draining of solvent and mixed oil to the material layer, the shorter the leaching time, less soluble in wet meal and lower residual oil; the disadvantage is that the unit treatment quantity is small, and the filtering effect of the material layer on the mixed oil is poor, the content of the meal in the concentrated oil is higher, which is not conducive to the extraction of oil such as the pre pressed rapeseed cake with high powder degree. But there are many disadvantages to improve the height of the material layer. In order to ensure the holding effect of the chain frame plate in the bending section, the radial dimension of the bending section should be increased, and the height of the chain frame plate should be increased accordingly, so as to increase the self-weight, power consumption and cost of the chain frame plate.
In practice, it is usually necessary to adjust the position of the material level baffle at the bottom of the storage box before driving, and set the material level at a specific height. In the middle part of the leach, a flat device is provided, which can rake loose surface materials which are compressed by soaking, besides leveling the surface of the material. Special attention should be paid to the material level of the expanded material, otherwise, the expansion material will form material resistance at the entrance of the bending section due to the volume expansion after immersion, and the material cannot enter the bending section.
The tension of the chain of the loop type extractor can be adjusted by moving the tension shaft. During operation, it is necessary to keep the proper tightness, and there are several big problems when the chain is too tight: ① increase the pressure of the chain on the guide rail of the bending section, thus aggravating the wear of the guide plate, and in case of serious conditions, the deep groove will be worn out on the guide rail. ② The chain is pulled up at the exit of the bending section, and the flipped chain frame plate is difficult to take away the material sliding into the lower layer from the outside of the bending section, thus forming a dead angle. ③ The increase of chain resistance not only increases the power consumption of the motor, but also reduces the service life of the chain itself.
On the contrary, too loose chain will cause chain to run and swing back and forth, and in serious cases, the chain frame plate and shell will scratch, causing deformation of chain frame plate; in addition, the phenomenon of “chain climbing” will occur when the loose chain is up from the tension section to the leach layer. Although the transition section is usually considered to eliminate the chain climbing phenomenon in design, it is impossible to do a long transition section due to the factors such as workshop space and production cost. Therefore, it is very important to adjust the tightness of the chain to the proper state before driving, which puts forward higher requirements for the operators. They should be familiar with the structure and operation characteristics of the equipment, and know when to adjust and how much they adjust.
The height of the material layer of the drag chain extractor is also controlled by the level baffle at the bottom of the bin. In order to adapt to the processing of various oil, the material level baffle is usually designed to be adjustable from the upper to the lower. The level height of the leach layer can be freely adjusted within 800-1200 mm. Even during the start-up, the level height can be adjusted outside the extractor. Because the chain scraper of the drag chain extractor r is low, it can further reduce the level height to handle special oil, especially when stainless steel is used for the contact part of the material. Obviously, the flexibility of the material level control of the drag chain extractor s better than that of the loop type extractor.
In the upper and lower leach section, a set of rake device is set at a certain distance to “plow” the material layer to loose the material layer to prevent short circuit of mixed oil and ensure good permeability effect.
The scraper chain of the chain of the drag chain extractor can be reversed by means of “driving wheel guide wheel”. The running track of scraper chain is always controllable, so it is more stable and not easy to produce deviation and chain climbing, and the degree of chain tightness is easy to adjust and control.
In addition, the material flow of the loop type extractor determines that the space of the tension section is basically wasted. The larger the radius of the bending section, the more space is wasted in this part; however, the drag chain extractor r has a high utilization rate of space due to the close distance between the upper and lower layers, and the space utilization rate of the box is high, and there is little waste.
It is important to note that when the moisture content of the material is high, a small amount of material may move with the chain scraper, and the accumulated material may be formed in the groove of the sprocket and cause the chain “tooth jumping”. This problem will occur no matter which kind of leach, the solution is simple, only the cleaning mechanism is set in the radial position of the sprocket, and the accumulated material in the groove can be removed in time.
In the case of the same raw material and processing capacity, the overall complexity, manufacturing difficulty and manufacturing cost of the loop type extractor are higher than those of the drag chain extractor, and due to its heavy weight, the construction requirements of the plant are also high. In contrast, the drag chain extractor overcomes several important defects of the loop type extractor, so it has better application prospects and promotion value. In the specific use, we can optimize the equipment structure, select high-quality alloy steel and other measures to reduce the production cost of the loop type extractor, develop the advantages and avoid the disadvantages, and continue to play the advantages of the loop type extractor.