Method for continuous twice countercurrent leaching and degreasing of fish meal

Abstract

The invention discloses a method for continuous twice countercurrent leaching and degreasing of fish meal, which comprises the following steps: primary countercurrent leaching and degreasing: putting raw material fish meal into a primary countercurrent leaching device, carrying out countercurrent leaching and degreasing on the raw material fish meal through an ethanol solvent, drying the obtained primary wet fish meal to prepare primary low-fat high-protein fish meal, and recovering a solution to obtain primary low-fat high-protein fish meal; preparing crude fish oil; and secondary countercurrent leaching and degreasing: putting the primary low-fat high-protein fish meal into a secondary countercurrent leaching device, carrying out countercurrent leaching and degreasing on the primary low-fat high-protein fish meal through a normal hexane solvent, and carrying out deamination, dehydration and drying on the obtained wet fish meal to obtain the low-fat high-protein fish meal. Through continuous twice countercurrent leaching and degreasing, not only is the quality of the low-fat high-protein fish meal improved, but also the crude fish oil can be recycled, the crude fish oil is subjected to next-step deep processing in the later period to prepare DHA and EPA, and waste of the fish oil is avoided.

Description

Technical Field

[0001] The present invention relates to a method for degreasing fish meal, and more particularly to a method for continuously degreasing fish meal by two - stage counter - current leaching. Background Art

[0002] The oil extraction technology is the core process for extracting oil from animal and plant raw materials. The design and optimization of its process and equipment directly affect the oil quality, production efficiency and environmental protection. It is commonly used in the production of fish oil, krill oil, peanut oil, soybean oil, etc. For the fish oil remaining in fish protein after pressing, the n - hexane extraction process is generally selected due to its high oil solubility, low boiling point and easy recovery characteristics. By using the high solubility of n - hexane in oil, the oil in the raw material is dissolved through osmosis and diffusion, and then the solvent is recovered by evaporation to separate the oil.

[0003] The n - hexane extraction technology for fish protein has become the main process in the fish protein extraction fish oil industry due to its high extraction rate, simple process, easy continuous and automated implementation. In 2013, Shen Jinhua et al. published "A Method for Continuously Counter - Current Leaching and Degreasing of Fish Oil" (Patent No. ZL201310021853.9). This method uses the high solubility of n - hexane in oil to dissolve the oil in the raw material through osmosis and diffusion, and then recovers the solvent by evaporation to separate the oil. It can extract 90% - 95% of the oil in fish meal at one time. The residual oil content of the obtained low - fat and high - protein fish meal is less than 3.3%, and the protein content is increased to 68% - 75%. The contents of toxic and harmful factors such as histamine and volatile basic nitrogen in the product are significantly reduced. However, due to the high extraction rate of n - hexane, the quality of the extracted fish oil is not high. The fish oil cannot be further processed, and can only be used as waste, resulting in waste of fish oil. Summary of the Invention

[0004] To overcome the above - mentioned drawbacks, the object of the present invention is to provide a method for continuously degreasing fish meal by two - stage counter - current leaching. By continuously degreasing fish meal by two - stage counter - current leaching, not only the quality of low - fat and high - protein fish meal is improved, but also crude fish oil can be recovered, and DHA and EPA can be prepared by further processing the crude fish oil in the later stage, thus avoiding waste of fish oil.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for continuously degreasing fish meal by two - stage counter - current leaching, comprising the following steps: First - stage counter - current leaching and degreasing: Put the raw material fish meal into a first - stage counter - current leaching device, carry out counter - current leaching and degreasing on the raw material fish meal with an ethanol solvent, dry the obtained primary wet fish meal to obtain primary low - fat and high - protein fish meal, recover the solution to obtain crude fish oil; Secondary countercurrent leaching for degreasing: Put the primary low-fat high-protein fish meal into the secondary countercurrent leaching device, and carry out countercurrent leaching and degreasing of the primary low-fat high-protein fish meal with n-hexane solvent. Then carry out deamination, dehydration and drying on the obtained wet fish meal to produce low-fat high-protein fish meal.

[0006] Furthermore, the liquid-to-material ratio of ethanol solvent to raw fish meal is 1-2:1 (v / w), and the temperature of the first-stage countercurrent leaching for degreasing is 40-50 °C. Exemplarily, the liquid-to-material ratio of ethanol solvent to raw fish meal is 1:1, 1:1.2, 1:1.4, 1:1.5, 1:1.6, 1:1.8, 1:2.

[0007] Furthermore, the liquid-to-material ratio of n-hexane solvent to the primary low-fat high-protein fish meal is 1-2:1 (v / w), and the temperature of the secondary countercurrent leaching for degreasing is 50-60 °C. Exemplarily, the liquid-to-material ratio of n-hexane solvent to raw fish meal is 1:1, 1:1.2, 1:1.4, 1:1.5, 1:1.6, 1:1.8, 1:2.

[0008] Furthermore, the raw fish meal is continuously fed into the first-stage countercurrent leaching device at a feeding speed of 4-8 tons per hour. By continuously feeding the raw fish meal into the first-stage countercurrent leaching device, the continuous leaching of the raw fish meal is realized, and the extraction efficiency of the raw fish meal is improved.

[0009] Furthermore, the first-stage countercurrent leaching device includes a first-stage vertical countercurrent mixing extractor and a first-stage chain bucket countercurrent extractor connected by a first-stage transfer device at the bottom. The raw fish meal is continuously fed into the top of the first-stage vertical countercurrent mixing extractor, and ethanol is continuously fed into the top of the first-stage chain bucket countercurrent extractor. Ethanol and the raw fish meal are mixed in the first-stage vertical countercurrent mixing extractor.

[0010] Furthermore, the raw fish meal sinks to the bottom of the first-stage vertical countercurrent mixing extractor under the action of gravity, is transferred to the bottom of the first-stage chain bucket countercurrent extractor by the first-stage transfer device, and is lifted upward by the chain bucket. During the lifting process, it comes into full contact with ethanol again. Ethanol flows from the top to the bottom of the first-stage chain bucket countercurrent extractor, then enters the bottom of the first-stage vertical countercurrent mixing extractor through the first-stage transfer device, and finally overflows from the top of the first-stage vertical countercurrent mixing extractor. During the flow of ethanol, it is in countercurrent contact with the raw fish meal all the time, making the contact between the fish meal and ethanol sufficient and improving the leaching efficiency.

[0011] Furthermore, the first-stage countercurrent leaching for degreasing further includes the following steps: The fish meal is lifted to the top outlet of the first-stage chain bucket countercurrent extractor by the chain bucket, and then transferred to a horizontal desolventizer to evaporate and dry the primary wet fish meal to produce the primary low-fat high-protein fish meal.

[0012] Furthermore, the primary countercurrent leaching device and the secondary countercurrent leaching device are connected by a screw conveyor. The primary low-fat and high-protein fish meal prepared by the primary countercurrent leaching device is continuously conveyed to the secondary countercurrent leaching device through the screw conveyor. By pushing the solid phase to move through the screw and the solvent flowing reversely, the leaching of oil is realized.

[0013] Furthermore, the secondary countercurrent leaching device includes a secondary vertical countercurrent mixing extractor and a secondary chain bucket countercurrent extractor connected at the bottom through a secondary transfer device. The primary low-fat and high-protein fish meal is continuously fed into the top of the secondary vertical countercurrent mixing extractor, and n-hexane is continuously fed into the top of the secondary chain bucket countercurrent extractor. The n-hexane and the primary low-fat and high-protein fish meal are mixed in the secondary vertical countercurrent mixing extractor; The primary low-fat and high-protein fish meal sinks to the bottom of the secondary vertical countercurrent mixing extractor under the action of gravity, is transferred to the bottom of the secondary chain bucket countercurrent extractor by the secondary transfer device, and is lifted upward by the chain bucket. During the lifting process, it comes into full contact with n-hexane again.

[0014] Furthermore, the secondary countercurrent leaching and degreasing also includes the following steps: The fish meal is lifted to the top outlet of the secondary chain bucket countercurrent extractor by the chain bucket, transferred to a horizontal desolventizer, and the wet fish meal is evaporated and dried to obtain low-fat and high-protein fish meal; The n-hexane solution overflows from the top of the secondary vertical countercurrent mixing extractor and is collected in the secondary fish oil solution tank after passing through a filter.

[0015] The beneficial effects of adopting the technical solution of the present invention are as follows: 1) The low-fat and high-protein fish meal prepared by two-stage countercurrent leaching and degreasing has the crude protein content increased to 74.91%, the residual oil content less than 0.5%. The low-fat and high-protein fish meal has a higher crude protein content, less residual oil, and better quality.

[0016] 2) By first extracting the raw fish meal with ethanol, ethanol is a polar solvent and preferentially dissolves the polar components in fish oil (such as EPA, DHA, free fatty acids, phospholipids, etc.) to obtain crude fish oil. The total content of EPA and DHA in the crude fish oil is as high as 24.8%. In the later stage, the crude fish oil can be further processed to obtain DHA and EPA, improving the total yield of DHA and EPA and avoiding the waste of fish oil.

[0017] 3) By first using ethanol for extraction and leaching, the later consumption of n-hexane is reduced. Ethanol has passed the GRAS certification and is safer. The residual n-hexane needs to be strictly monitored (the FDA limit is 5 ppm), which can reduce the risk of solvent residue. And ethanol is biodegradable, and the comprehensive toxicity load is reduced by 60%. N-hexane has neurotoxicity and high energy consumption for recovery. Ethanol is more environmentally friendly.

[0018] 4) The ethanol extraction temperature is 40 - 50 °C, and the n - hexane extraction temperature is 50 - 60 °C (the temperature is relatively mild). In contrast, the existing single - stage extraction requires long - time n - hexane extraction at 60 - 70 °C (the temperature is relatively high), which increases the risk of protein denaturation. The low - fat and high - protein fish meal prepared by this application has significantly improved flavor and color, and significantly enhanced storage stability and nutritional value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is a schematic diagram of the device for single - stage counter - current leaching and degreasing of the present invention; Figure 2 It is a schematic diagram of the device for two - stage counter - current leaching and degreasing of the present invention.

[0022] Wherein: 1. Feed conveyor; 2. Feed chain - bucket elevator; 3. First - stage counter - current leaching device; 31. First - stage vertical counter - current mixing extractor; 32. First - stage transfer device; 33. First - stage chain - bucket counter - current extractor; 4. Horizontal desolventizer; 5. Screw conveyor; 6. First - stage fish oil solution tank; 7. Second - stage counter - current leaching device; 71. Second - stage vertical counter - current mixing extractor; 72. Second - stage transfer device; 73. Second - stage chain - bucket counter - current extractor; 8. Vertical desolventizing, denitrifying and cooling device; 9. Second - stage fish oil solution tank. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to make the above - mentioned objects, features and advantages of the present invention more obvious and understandable, the following will give a detailed description of the specific embodiments of the present invention with reference to the drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0024] The object of the present invention is to provide a method for continuous two - stage counter - current leaching and degreasing of fish meal, which can improve the quality of low - fat and high - protein fish meal, and can also recover crude fish oil. The crude fish oil is further processed in the later stage to produce DHA and EPA, avoiding the waste of fish oil.

[0025] The implementation steps of the technical solution of the present invention are as follows: S1. Primary countercurrent leaching and degreasing: Continuously feed raw fish meal into the primary countercurrent leaching device at a feeding speed of 4 - 8 tons per hour. Perform countercurrent leaching and degreasing on the raw fish meal with an ethanol solvent. The liquid - to - material ratio of the ethanol solvent to the raw fish meal is 1 - 2:1 (v / w), and the temperature of the primary countercurrent leaching and degreasing is 40 - 50 °C. Dry the obtained primary wet fish meal to obtain primary low - fat and high - protein fish meal.

[0026] Specifically, as shown in the attached Figure 1 As shown, the feeding conveyor 1 transports the raw fish meal from the previous processing step to the bottom of the feeding chain - bucket elevator 2. The feeding chain - bucket elevator 2 is vertically placed, and the fish meal is transported into the primary countercurrent leaching device 3 through the feeding chain - bucket elevator 2.

[0027] The primary countercurrent leaching device 3 includes a primary vertical countercurrent mixing extractor 31 and a primary chain - bucket countercurrent extractor 33 connected at the bottom through a primary transfer device 32. The raw fish meal is continuously fed into the top of the primary vertical countercurrent mixing extractor 31, and ethanol is continuously fed into the top of the primary chain - bucket countercurrent extractor 33. The ethanol and the raw fish meal are mixed in the primary vertical countercurrent mixing extractor 31. The raw fish meal sinks to the bottom of the primary vertical countercurrent mixing extractor 31 under the action of gravity, is transferred to the bottom of the primary chain - bucket countercurrent extractor 33 by the primary transfer device 32, and is lifted upward by the chain - bucket. During the lifting process, it comes into full contact with ethanol again. The fish meal is lifted to the top outlet of the primary chain - bucket countercurrent extractor 33, and then transferred to the horizontal desolventizer 4 to evaporate and dry the primary wet fish meal to obtain primary low - fat and high - protein fish meal.

[0028] The ethanol solution overflows from the top of the primary vertical countercurrent mixing extractor 31, and after passing through the filter, it is collected into the primary fish oil solution tank 6. Ethanol is a polar solvent (dielectric constant ~24.3), which preferentially dissolves polar components in fish oil (such as EPA, DHA, free fatty acids, phospholipids, etc.) to obtain crude fish oil. After detecting the crude fish oil, the content of EPA is 14.4%, the content of DHA is 10.4%, and the total content of EPA and DHA is as high as 24.8%. In the later stage, the crude fish oil can be further processed to obtain DHA and EPA, improving the total yield of DHA and EPA and avoiding the waste of fish oil.

[0029] Moreover, the hydroxyl group of ethanol forms hydrogen bonds with water molecules, reducing the water activity of the system, inhibiting the activity of lipase and lipid oxidation, and protecting the quality of fish oil. Ethanol dehydrates part of the protein to form a rigid structure, reducing the dissolution and damage of the subsequent solvent to the protein and improving the quality of the protein.

[0030] S2. Secondary countercurrent leaching and degreasing: Put the primary low-fat and high-protein fish meal into the secondary countercurrent leaching device 7, and conduct countercurrent leaching and degreasing on the primary low-fat and high-protein fish meal with n-hexane solvent. The liquid-to-solid ratio of the n-hexane solvent to the primary low-fat and high-protein fish meal is 1-2:1 (v / w), and the temperature of the secondary countercurrent leaching and degreasing is 50-60 °C. Dry the obtained wet fish meal to obtain low-fat and high-protein fish meal.

[0031] Specifically, refer to the appendix Figure 2 As shown, the primary countercurrent leaching device 3 and the secondary countercurrent leaching device 7 are connected by a screw conveyor 5. The primary low-fat and high-protein fish meal prepared by the primary countercurrent leaching device 3 is continuously transported to the secondary countercurrent leaching device 7 through the screw conveyor 5.

[0032] In some embodiments, the secondary countercurrent leaching device 7 includes a secondary vertical countercurrent mixing extractor 71 and a secondary chain bucket countercurrent extractor 73 connected at the bottom by a secondary transfer device 72. The primary low-fat and high-protein fish meal is continuously fed into the top of the secondary vertical countercurrent mixing extractor 71, and n-hexane is continuously fed into the top of the secondary chain bucket countercurrent extractor 73. The n-hexane and the primary low-fat and high-protein fish meal are mixed in the secondary vertical countercurrent mixing extractor 71. The n-hexane solution overflows from the top of the secondary vertical countercurrent mixing extractor 71 and is collected in the secondary fish oil solution tank 9 after passing through a filter.

[0033] The primary low-fat and high-protein fish meal sinks to the bottom of the secondary vertical countercurrent mixing extractor 71 under the action of gravity, is transferred to the bottom of the secondary chain bucket countercurrent extractor 73 by the secondary transfer device 72, and is lifted upward by the chain bucket. During the lifting process, it comes into full contact with n-hexane again.

[0034] In some embodiments, the secondary countercurrent leaching and degreasing further includes the following steps: The fish meal is lifted to the top outlet of the secondary chain bucket countercurrent extractor 73 by the chain bucket, transferred to the horizontal desolventizer 4, the wet fish meal is evaporated and dried, and then passed through the vertical desolventizing and denitrifying cooler 8 to obtain low-fat and high-protein fish meal.

[0035] N-hexane is a non-polar solvent (dielectric constant ~1.9), which is easy to extract the remaining neutral triglycerides and long-chain non-polar lipids. Ethanol extracts the remaining polar impurities for the first time, and n-hexane is easier to extract. Through the double-solvent extraction of ethanol and n-hexane, not only can crude fish oil be recovered, but the quality of the prepared low-fat and high-protein fish meal is also better.

[0036] Examples The following examples describe more specifically the disclosure of the present invention. These examples are for illustrative purposes only, as various modifications and variations within the scope of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized by conventional methods and can be used directly without further treatment, and all instruments used in the examples are commercially available.

[0037] Example 1 Raw materials: Pressed sardine powder, containing 9% moisture, 10.5% residual oil, 65% crude protein, and 70 mg / 100 g of volatile basic nitrogen in the sardine powder.

[0038] S1. Primary countercurrent extraction for degreasing: Continuously feed the raw material fish meal into a primary countercurrent extraction device at a feeding speed of 6 tons per hour, and perform countercurrent extraction and degreasing on the raw material fish meal with an ethanol solvent. The liquid-to-material ratio of the ethanol solvent to the raw material fish meal is 1.8:1 (v / w), and the temperature of the primary countercurrent extraction for degreasing is 45°C. Dry the obtained primary wet fish meal to obtain a primary low-fat and high-protein fish meal. Recover the ethanol solution from the countercurrent extraction and degreasing to obtain crude fish oil.

[0039] S2. Secondary countercurrent extraction for degreasing: Feed the primary low-fat and high-protein fish meal into a secondary countercurrent extraction device, and perform countercurrent extraction and degreasing on the primary low-fat and high-protein fish meal with a n-hexane solvent. The liquid-to-material ratio of the n-hexane solvent to the primary low-fat and high-protein fish meal is 1.2:1 (v / w), and the temperature of the secondary countercurrent extraction for degreasing is 55°C. Dry the obtained wet fish meal to obtain a low-fat and high-protein fish meal.

[0040] Comparative Example 1 All raw materials in Comparative Example 1 and Example 1 are the same, which is pressed sardine powder.

[0041] Continuously feed the raw material fish meal into a primary countercurrent extraction device at a feeding speed of 6 tons per hour, and perform countercurrent extraction and degreasing on the raw material fish meal with a n-hexane solvent. The liquid-to-material ratio of the n-hexane solvent to the raw material fish meal is 3:1 (v / w), and the temperature of the primary countercurrent extraction for degreasing is 65°C. Dry the obtained primary wet fish meal to obtain a low-fat and high-protein fish meal. Recover the n-hexane solution from the countercurrent extraction and degreasing.

[0042] Test Example Test the low-fat and high-protein fish meals prepared in Example 1 and Comparative Example 1 and the crude fish oil after the first extraction. The test results are shown in Table 1.

[0043]

[0044] As can be seen from the data in Table 1, for the low-fat and high-protein fish meal prepared by two-stage countercurrent leaching for degreasing, the crude protein content increased from 69.26% to 74.91%, an increase of 8.1%, and the residual oil content decreased from 4.4% to 0.42%, a reduction of 10.5 times. The low-fat and high-protein fish meal has a higher crude protein content, less residual oil, and better quality.

[0045] First, the raw fish meal is extracted with ethanol. Ethanol is a polar solvent that preferentially dissolves polar components in fish oil (such as EPA, DHA, free fatty acids, phospholipids, etc.) to obtain crude fish oil. After testing the crude fish oil, the acid value, iodine value, impurities, and moisture in the crude fish oil are greatly reduced, and the contents of EPA and DHA increase. The total content of EPA and DHA is as high as 24.8%. In the later stage, the crude fish oil can be further processed to obtain DHA and EPA, improving the total yield of DHA and EPA and avoiding waste of fish oil.

[0046] Moreover, in this solution, using ethanol for extraction first reduces the amount of n-hexane used in the later stage. Ethanol has passed the GRAS certification and is safer, while n-hexane residues need to be strictly monitored (FDA limit: 5 ppm), which can reduce the risk of solvent residues.

[0047] Environmental impact: Ethanol is biodegradable, and the comprehensive toxicity load is reduced by 60%. n-Hexane has neurotoxicity and high energy consumption for recovery (small boiling point difference). Ethanol is more environmentally friendly.

[0048] Process conditions: In this solution, the extraction temperature of ethanol is 40 - 50°C, and the extraction temperature of n-hexane is 50 - 60°C (relatively mild). In the existing single extraction process, n-hexane extraction at 60 - 70°C for a long time increases the risk of protein denaturation.

[0049] The above embodiments are only used to illustrate the technical concept and features of the present invention, and the purpose is to enable those familiar with this technology to understand the content of the present invention and implement it. It should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for degreasing fish meal by two consecutive countercurrent leaching, characterized in that: The following steps are involved: Primary countercurrent leaching and defatting: the raw fish meal is put into a primary countercurrent leaching device (3), the raw fish meal is subjected to countercurrent leaching and defatting by using an ethanol solvent, the obtained primary wet fish meal is dried to obtain a primary low-fat high-protein fish meal, and the ethanol solution is recovered to obtain crude fish oil; Secondary countercurrent leaching and defatting: The primary low-fat high-protein fish meal is placed in a secondary countercurrent leaching device (7), and the primary low-fat high-protein fish meal is subjected to countercurrent leaching and defatting by using n-hexane solvent. The obtained wet fish meal is deamined, dehydrated and dried to obtain low-fat high-protein fish meal.

2. The method for degreasing fish meal by countercurrent leaching twice continuously according to claim 1, characterized in that: The liquid-to-solid ratio of the ethanol solvent to the raw fish meal is 1-2:1, and the temperature of the primary countercurrent leaching and degreasing is 40-50°C.

3. The method for degreasing fish meal by countercurrent leaching twice continuously according to claim 1, characterized in that: The liquid-to-solid ratio of n-hexane solvent to primary low-fat high-protein fish meal is 1-2:1, and the temperature of secondary countercurrent leaching and degreasing is 50-60°C.

4. The method for degreasing fish meal by countercurrent leaching twice continuously according to claim 1, characterized in that: The raw fish meal is continuously fed into the primary countercurrent leaching device at a feeding rate of 4 to 8 tons per hour.

5. The method for degreasing fish meal by two consecutive countercurrent leaching according to claim 1, characterized in that: The primary countercurrent leaching device (3) comprises a primary vertical countercurrent mixing extractor (31) and a primary chain bucket countercurrent extractor (33) connected at the bottom via a primary material transfer device (32); raw fish meal is continuously fed into the top of the primary vertical countercurrent mixing extractor (31); ethanol is continuously fed into the top of the primary chain bucket countercurrent extractor (33); ethanol and raw fish meal are mixed in the primary vertical countercurrent mixing extractor (31); ethanol solution overflows from the top of the primary vertical countercurrent mixing extractor (31) and is collected in a primary fish oil solution tank (6) after passing through a filter.

6. The method for degreasing fish meal by two consecutive countercurrent leaching according to claim 5, characterized in that: The raw fish meal settles to the bottom of the first-stage vertical countercurrent mixing extractor (31) under the action of gravity, is transferred to the bottom of the first-stage chain bucket countercurrent extractor (33) by the first-stage material transfer device (32), and is lifted upward by the chain bucket. During the lifting process, it is fully contacted with ethanol again.

7. The method for degreasing fish meal by two consecutive countercurrent leaching according to claim 1, characterized in that: The primary countercurrent leaching and degreasing process further comprises the following steps: the fish meal is lifted by the chain bucket to the top outlet of the primary chain bucket countercurrent extractor (33), and then transferred to the horizontal desolventizer (4), where the primary wet fish meal is evaporated and dried to obtain primary low-fat high-protein fish meal.

8. The method for degreasing fish meal by two consecutive countercurrent leaching according to any one of claims 1 to 7, characterized in that: The primary countercurrent leaching device (3) and the secondary countercurrent leaching device (7) are connected via a screw conveyor (5), and the primary low-fat, high-protein fish meal prepared by the primary countercurrent leaching device (3) is continuously conveyed to the secondary countercurrent leaching device (7) via the screw conveyor (5).

9. The method for degreasing fish meal by two consecutive countercurrent leaching according to claim 8, characterized in that: The secondary countercurrent leaching device (7) comprises a secondary vertical countercurrent mixing extractor (71) and a secondary chain bucket countercurrent extractor (73) connected at the bottom via a secondary material transfer device (72); primary low-fat high-protein fish meal is continuously fed into the top of the secondary vertical countercurrent mixing extractor (71); n-hexane is continuously fed into the top of the secondary chain bucket countercurrent extractor (73); and n-hexane and the primary low-fat high-protein fish meal are mixed in the secondary vertical countercurrent mixing extractor (71); The primary low-fat high-protein fish meal settles to the bottom of the secondary vertical countercurrent mixing extractor (71) under the action of gravity, is transferred to the bottom of the secondary chain bucket countercurrent extractor (73) by the secondary material transfer device (72), and is lifted upward by the chain bucket. During the lifting process, it is fully contacted with n-hexane again.

10. The method for degreasing fish meal by two consecutive countercurrent leaching according to claim 9, characterized in that: The secondary countercurrent leaching and degreasing process further comprises the following steps: the fish meal is lifted by the chain bucket to the top outlet of the secondary chain bucket countercurrent extractor (73), and then transferred to the horizontal desolventizer (4), where the wet fish meal is evaporated and dried to obtain low-fat and high-protein fish meal.

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