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Comparative analysis of loop type extractor and drag chain extractor (I)

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(Last Updated On: March 23, 2021)

Comparative analysis of loop type extractor and drag chain extractor (I)

In recent years, with the continuous expansion of the oil processing scale, the application of new types of extractors has gradually become popular and mature. Among them, loop type extractor and drag chain extractor are two representative types of extractors. This article analyzes and compares them in depth from the perspective of design, production and use, and discusses some typical issues so that relevant personnel can refer to them when selecting, designing or purchasing.

1 Comparison of structure and process characteristics of two kinds of extractors

The main structure of loop type extractor is shown in Figure 1. 

loop type extractor
drag chain extractor

The material first enters the storage box at the upper part of the extractor, and slowly advances to the spray leaching section (straight section) under the push of the scraper chain frame. After multiple spraying, the material enters the lower layer through the bending section to continue leaching. In the final stage of leaching, fresh solvent is used to spray, and then the wet meal continues to move forward through the leaching section and naturally leach, and finally discharged from the outlet (lower layer). The biggest feature of the loop type extractor is that the material can be turned over when it enters the lower layer from the bending section, which makes the material leaching more uniform and thorough, the material layer is shallow, the wet meal contains less soluble, and the residual oil is easy to be reduced to less than 1%.

drag chain extractor, also known as chain scraper type extractor, is quite similar to crawler extractor in structural form. It can also be regarded as a derivative of loop type extractor, which is equivalent to canceling the bending section and combining the rotocel structure separated from the upper and lower layers into a unified box structure. See Figure 2 for the specific structure. The leaching principle of the drag chain extractor is similar to that of the loop type extractor. Although the bending section is eliminated, when the material falls from the upper layer to the lower layer, the material can be completely turned over under the action of the turning mechanism, so the good permeability can also be ensured. In practice, the residual oil can reach 0.6% – 0.8%. Because there is no bending section, the overall height of the drag chain extractor is much lower than that of the loop type extractor.

The power of the loop type extractor is output to the driving shaft through the cycloidal reducer-hard tooth surface reducer-chain transmission. The driving shaft rotates and drives the heavy-duty conveyor chain and the chain frame through the active sprocket to make a cyclic motion. Some loop type extractor are equipped with a tensioning device above the driving shaft (see Figure 3(a)), and some loop type extractors are directly equipped with a tensioning device on the driving shaft, eliminating the need for a tensioning shaft and a tensioning sprocket (see Figure 3(a)). 3(b)).


The transmission form of the drag chain extractor is basically the same as the loop type extractor. It can be a cycloid reducer-hard tooth surface reducer-chain drive three-stage transmission, or it can be a cycloid reducer-chain drive two-stage transmission

In addition to the driving shaft, the drag chain extractor has 3 guide shafts, one of which is used as a tensioning shaft.

The spray device of loop type extractor and drag chain extractor can adopt the same form, and the grid plate adopts V-shaped grid bar with a gap of about 0.7 ~ 0.9 mm, which can be appropriately reduced for rapeseed cake and other oil.

2 Comparison of main technical indicators

In order to compare the advantages and disadvantages of the loop type extractor and the drag chain extractor more intuitively, Table 1 lists some technical indicators of the loop type extractor and the  drag chain extractor with the same daily processing capacity of 3 000 t [3]. Both types of equipment have been successfully applied to many large-scale oil processing plants. The processing capacity of processed soybean puffed materials has reached or exceeded 3 000 t/d, and the residual oil rate is below 1%, so they have typical representative significance.

3 Equipment production cost analysis

It can be seen from Table 1 that under the same processing capacity, the width and length of the two types of extractors are basically the same, but the equipment height of the drag chain extractor is only 59% of the loop type extractor, so for the loop type extractor, It has high requirements for plant infrastructure and large investment, and it is difficult to transport or hoist on site.

Large capacity drag chain extractors are also less likely to be manufactured and transported as a whole, especially the box body, which usually needs to be manufactured on site or assembled in a single body, but because the overall height is relatively low, manufacturing, transportation and installation are relatively low. The difficulty is less.

The total weight of the drag chain extractor is only equivalent to about 75% of the loop type extractor, and the proportion of its transmission parts to the total weight of the equipment is also low, and the power of the configured motor is also small. There are several factors here:

(1) Chain transmission inevitably has polygonal effect. The less the number of teeth and the larger the pitch, the more obvious the polygonal effect and the more unstable the transmission. Although the curved section of the loop type extractor is not a sprocket, the running track of the chain on the guide rail is also affected by the polygon effect and becomes less stable, which increases the impact and wear on the guide rail. To reduce this negative impact, it is necessary to reduce the pitch of the chain or increase the radius of gyration of the curved section. Both of these measures have an adverse effect on the production of the extractor. To ensure the same tensile load strength, reducing the pitch must increase the thickness of the chain plate, and at the same time the number of rollers also increase, the chain appears more cumbersome; increasing the radius of gyration of the bending section will further increase the height of the extractor, Not only does the material consumption increase, but the requirements for the strength and rigidity of the shell structure also increase, and the manufacturing difficulty also increases.

(2) The structure of the loop type extractor determines that the height of the chain scraper should not be too low, otherwise the material in the curved section will be difficult to maintain and slide directly to the lower layer, and the advantages of the curved section will not be played; at the same time, the chain frame plate The overall rigidity should be good, otherwise it will be compressed and deformed by the material in the bending section; while the drag chain extractor does not need to consider the material holding requirements of the bending section, it can reduce the height of the chain frame plate as much as possible and use the “material pushing” method to move the animal material forward, so The weight of the chain scraper of the drag chain extractor is much smaller, and the motor power required is correspondingly smaller.

(3) The upper and lower layers of the loop type extractor are relatively independent, and the upper weight is mainly supported by the tension transition section and bending section at both ends. In order to ensure the overall strength and stiffness requirements of the equipment, the thickness of the side plate of the box should not be too small. It can be seen from table 1 that the box plate thickness of the loop type extractor needs to be 16 mm, which is much larger than the 10 mm of the drag chain extractor, and the manufacturing accuracy and difficulty of the bending section are higher.

(4) The chain frame plate of loop type extractor will produce large friction resistance in the bending section, and the chain frame plate will inevitably swing, which increases the power consumption of the motor.

From the above analysis, it can be seen that the special structural characteristics of the loop type extractor, such as the bending section, determine that the production and installation costs of the loop type extractor are higher than those of the drag chain extractor. According to the domestic production conditions, the total cost of the loop type extractor is more than 30% higher than that of the drag chain extractor, and its operation power consumption is also higher. Obviously, for investors, the drag chain extractor is undoubtedly more attractive.

(unfinished to be continued)

Chemsta has 45 years of experience in the design and production of vegetable oil processing equipment. Over the past 45 years, we have produced hundreds of drag chain extractors, which are used for extracting soybean oil, extracting peanut oil, extracting rapeseed oil, etc. We have also developed special drag chain extractors for soybean white flake, soybean protein concentrate(SPC), etc.

In the next article we will continue to analyze the process operation of loop type extractor and drag drag chain extractor.

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