Negative pressure type oil continuous drying and refining method

Abstract

The application discloses a kind of negative pressure type oil continuous drying refining method, belong to oil refining processing technical field, including raw material pretreatment, drying and dehydration and discharging process, its characterized in that, the method is continuously carried out in closed negative pressure system, no outside air intervention, specifically includes the following steps: S1, raw material pretreatment and continuous feeding;S2, micro negative pressure pretreatment dehydration;S3, negative pressure drying refining;S4, negative pressure pressure stabilization fine impurity removal;S5, water vapor waste heat recovery processing;S6, closed cooling discharging.The application adopts the above-mentioned negative pressure type oil continuous drying refining method, realizes oil low-temperature continuous feeding, gradient negative pressure drying, closed loop continuous discharging, greatly reduces oil oxidation loss, improves drying precision and product consistency, adapts to large-scale industrial continuous production.

Description

Technical Field

[0001] This invention relates to the field of oil refining and processing technology, and in particular to a negative pressure continuous drying and refining method for oils. Background Technology

[0002] Oil refining is a core process in the production of edible and industrial oils, with drying and refining directly determining the moisture content, peroxide value, color, and storage stability of the oils. Currently, existing oil drying and refining processes mostly employ methods such as atmospheric pressure high-temperature drying, intermittent vacuum drying, and plate heat exchanger dehydration, which have numerous technical shortcomings.

[0003] Traditional ambient temperature high-pressure drying processes require heating oils to over 150°C for dehydration. Under these high temperatures, oils are highly susceptible to oxidation, rancidity, and polymerization, leading to increased peroxide value, darker color, and loss of nutrients. This process also results in high energy consumption and significant heat loss. Conventional intermittent vacuum drying processes are designed for batch production, but suffer from uneven heating, low drying precision, and low production efficiency, making them unsuitable for large-scale continuous production. Furthermore, air can easily be introduced during batch changes, causing secondary oxidation of the oils.

[0004] Existing negative pressure drying technologies are mostly single vacuum flash dehydration, which has a limited function and can only remove free water from oils. It cannot simultaneously remove bound water, trace amounts of colloids, and small molecule impurities with odors from oils. As a result, it is difficult to stably control the moisture content of refined oils below 0.05%, leading to poor product quality consistency.

[0005] In summary, existing oil drying and refining technologies suffer from technical pain points such as severe oxidation, low drying precision, inability to produce continuously, high energy consumption, large material loss, and unstable product quality. There is an urgent need for a negative pressure oil drying and refining method that can operate continuously, at low temperature and low oxidation, and with multiple functions for simultaneous refining. Summary of the Invention

[0006] The purpose of this invention is to provide a negative pressure continuous drying and refining method for oils, which realizes low-temperature continuous feeding of oils, gradient negative pressure drying, and closed-loop continuous discharge, significantly reducing oil oxidation loss, improving drying accuracy and product consistency, and is suitable for large-scale industrial continuous production.

[0007] To achieve the above objectives, the present invention provides a negative pressure continuous drying and refining method for oils, including raw material pretreatment, drying and dehydration, and discharge processes. The method is carried out continuously throughout the entire process within a closed negative pressure system without the intervention of external air, and specifically includes the following steps: S1. Raw material pretreatment and continuous feeding: After removing solid impurities by primary filtration, the crude oil to be refined is quantitatively and continuously fed to the waste heat recovery heat exchange unit, where the waste heat from the water vapor generated in the drying process is used to preheat the oil to 80~95℃. S2. Micro-negative pressure pretreatment dehydration: The preheated oil is sent into the primary drying chamber, and the absolute pressure inside the chamber is controlled at 15~25kPa and the temperature at 95~110℃ to remove free water and light volatile impurities from the oil. After pretreatment, the moisture content of the oil is reduced to below 0.3%. S3. Negative Pressure Drying and Refining: The pretreated oil is continuously fed into the secondary drying chamber, where the absolute pressure is controlled at 3~8 kPa and the temperature at 110~130℃. This process removes bound water, residual trace moisture, and light colloids from the oil, resulting in an oil moisture content of ≤0.08% after primary drying. S4. Negative pressure stabilization and fine finishing: The grease after primary drying is continuously fed into a three-stage drying chamber, with the absolute pressure inside the chamber controlled at 8~12kPa and the temperature at 100~115℃, to remove residual pigments, oxides and odor impurities. The moisture content of the grease after fine finishing is ≤0.05%. S5. Waste heat recovery treatment of water vapor: Collect the mixed water vapor generated by the first to third stage drying chambers, and pass it into the waste heat recovery heat exchange unit of step S1 to preheat the raw material oil. The water vapor after heat exchange is condensed and discharged in a centralized manner. S6. Closed-loop cooling discharge: The refined grease is cooled to below 40°C in a closed-loop micro-negative pressure environment, and then continuously discharged as finished refined grease after filtration.

[0008] Preferably, in step S2, the grease is atomized into micron-sized droplets by a high-speed atomizing nozzle in the primary drying chamber for flash evaporation and dehydration. The low-speed spiral stirring mechanism in the primary drying chamber continuously scrapes off the grease adhering to the inner wall of the chamber to avoid grease residue. The high-speed atomizing nozzle atomizes the oil into droplets with a particle size of 50~200μm, and the residence time of the oil in the primary drying chamber during the flash evaporation process is 3~6 minutes.

[0009] Preferably, in step S3, the walls of the secondary drying chamber are provided with layered heat-conducting jackets, and a turbulent stirring structure with guide plates is provided inside the secondary drying chamber, so that the effective residence time of the oil in the chamber is 8~15 minutes.

[0010] Preferably, the layered heat-conducting jacket is provided with at least two independent heat-conducting oil chambers along the axial direction of the secondary drying chamber, and the temperature of each heat-conducting oil chamber increases gradually along the material flow direction, with the temperature difference controlled at 5~10℃.

[0011] Preferably, in step S4, a removable activated carbon adsorption packing layer is provided in the three-stage drying chamber. The oil flows through the activated carbon adsorption packing layer from top to bottom. The residence time of the oil in the three-stage drying chamber is 5~8 minutes, and the peroxide value of the refined oil is ≤5 meq / kg.

[0012] Preferably, in step S1, the primary filtration adopts screen filtration to remove oil residue and solid impurities with a particle size ≥0.5mm. The feed flow rate is controlled at 0.8~2.5t / h by a variable frequency quantitative conveying pump, and the feed flow rate is matched with the processing capacity of each drying chamber.

[0013] Preferably, the drying chambers in steps S2 to S4 are seamlessly connected from top to bottom through a sealed connecting pipeline. The grease is continuously transported by gravity flow due to pressure difference. Pressure isolation valves are installed between the chambers to ensure the stability of each pressure gradient.

[0014] Preferably, in step S5, a water ring vacuum pump unit is used to provide a negative pressure environment for the entire closed system. The vacuum pump unit and the condenser unit operate in conjunction, and the mixed water vapor is condensed to achieve oil-water separation, with no volatile oils being discharged.

[0015] Preferably, in step S6, the cooling process uses a closed-loop tube cooler, and the cooling medium is circulating cooling water; the cooled grease is continuously discharged through a precision filter with an accuracy of 50~100μm and directly connected to the finished product storage unit or the deep processing process.

[0016] Preferably, the crude oil to be refined is any one of crude vegetable oil, crude animal oil, or waste recycled oil.

[0017] Furthermore, the maximum temperature of the oil during the entire refining process does not exceed 130℃, and the oil loss rate during the entire refining process is ≤0.8%.

[0018] Therefore, the present invention employs the above-mentioned negative pressure continuous drying and refining method for oils, and the technical effects are as follows: 1) Gradient negative pressure segmented drying: Abandoning the traditional single negative pressure drying mode, a three-stage gradient pressure and temperature control process is adopted to specifically remove free water, bound water and trace volatile impurities. The drying precision is far superior to the traditional process, solving the problems of incomplete dehydration and uneven quality of oils.

[0019] 2) Closed-loop continuous operation: The entire process is closed and negative pressure with no air intrusion, realizing continuous operation of the entire process of feeding, heat exchange, drying, impurity removal and discharge, eliminating the problem of secondary oxidation in batch production, increasing production efficiency by more than 40%, and is suitable for large-scale industrial production.

[0020] 3) Stirring + Atomization Dual-Effect Drying: The drying mode combines atomization flash evaporation and spiral stirring heat conduction, ensuring uniform heating of materials without local overheating. It simultaneously removes moisture, light colloids, and odor impurities, achieving integrated drying, refining, and quality improvement.

[0021] 4) Closed-loop energy recovery of waste heat: The waste heat from the water vapor generated during drying is recovered and used for preheating of raw materials, which greatly reduces heating energy consumption. At the same time, the water vapor is discharged in a closed loop, with no material volatilization loss, and the oil loss rate is reduced to below 0.8%.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a flowchart of an embodiment of a negative pressure continuous oil drying and refining method according to the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0026] like Figure 1 As shown, the negative pressure continuous drying and refining method for oils and fats described in this invention is carried out continuously within a closed negative pressure system without the intervention of external air. It sequentially completes raw material pretreatment and preheating, three-stage gradient negative pressure drying, waste heat recovery, and closed cooling and discharge. The feasibility and technical effects of this invention are verified through specific embodiments below: Example 1 In this embodiment, crude rapeseed oil is used as the raw material to be refined. The initial moisture content of the raw material is 1.21%, the peroxide value is 12.3 meq / kg, and the Lovibond colorimetric index (25.4 mm cell) is 35 for yellow and 4.2 for red. The specific refining steps are as follows: S1. Raw material pretreatment and continuous feeding: Crude rapeseed oil is passed through a screen filtration device to remove oil residue and solid impurities with a particle size ≥0.5 mm; it is then continuously transported to the waste heat recovery heat exchange unit at a flow rate of 1.5 t / h by a variable frequency quantitative conveying pump, and the oil is preheated to 90℃ by the waste heat of water vapor generated in the drying process.

[0027] S2. Micro-negative pressure pretreatment dehydration: The preheated grease is continuously fed into the primary drying chamber, and the absolute pressure inside the chamber is controlled at 20 kPa. The temperature inside the chamber is stabilized at 105℃ by heat transfer oil in the chamber wall jacket. The grease is atomized into micron-sized droplets with an average particle size of 120 μm by a high-speed atomizing nozzle inside the chamber for flash dehydration. At the same time, the low-speed spiral stirring mechanism inside the chamber continuously scrapes off the grease adhering to the inner wall of the chamber to avoid residue. The grease stays in the primary drying chamber for 4 minutes, removing most of the free water and light volatile impurities. The moisture content of the discharged grease is 0.27%.

[0028] S3. Negative Pressure Drying and Refining: The pretreated oil flows into the secondary drying chamber through a closed connecting pipeline by gravity and pressure difference. A pressure isolation valve is set between the two chambers to maintain the pressure gradient. The absolute pressure in the secondary drying chamber is controlled at 5 kPa. The chamber wall has a layered heat-conducting jacket with two independent heat-conducting oil chambers. The temperature of the lower layer (feed end) is 116℃ and the temperature of the upper layer (discharge end) is 122℃, with an axial temperature difference of 6℃. The turbulent stirring structure with baffles in the chamber ensures that the oil is heated evenly. The effective residence time of the oil in the chamber is 12 minutes, removing bound water, residual trace moisture and light colloids. The moisture content of the discharged oil is 0.072%.

[0029] S4. Negative Pressure Stabilization and Refining: The grease after primary drying is continuously fed into a three-stage drying chamber, with the absolute pressure inside the chamber controlled at 10 kPa and the temperature inside the chamber stabilized at 110℃. A removable granular activated carbon adsorption packing layer is installed inside the chamber. The grease flows through the packing layer from top to bottom, with a residence time of 6 minutes, adsorbing and removing residual pigments, peroxides, and odor impurities. The output grease has a moisture content of 0.038% and a peroxide value of 4.1 meq / kg.

[0030] S5. Waste heat recovery treatment of water vapor: Collect the mixed water vapor discharged from the top of the first to third stage drying chambers, and pass it into the waste heat recovery heat exchange unit of step S1 to exchange heat with the raw material oil. After the water vapor is cooled by heat exchange, it enters the condenser unit for condensation. After oil-water separation, the wastewater is discharged in a centralized manner, and there is no volatile oil discharge. The whole system uses a water ring vacuum pump group to provide negative pressure power.

[0031] S6. Closed-loop cooling discharge: The refined grease is sent to a closed-loop tube cooler, where circulating cooling water is used as the cooling medium to cool the grease to 36°C under a slight negative pressure environment; then it is continuously discharged through a precision filter with an accuracy of 80μm and connected to the finished product storage unit.

[0032] This embodiment can operate continuously and stably for 24 hours, with the highest oil temperature throughout the process reaching 122℃. The calculated oil loss rate during the entire refining process is 0.62%. All indicators of the finished rapeseed oil are superior to the first-grade standard of GB1536-2021 "Rapeseed Oil". The moisture content fluctuation between batches during continuous production is ≤0.005%, demonstrating excellent quality consistency.

[0033] Example 2 In this embodiment, crude animal lard is used as the raw material to be refined. The initial moisture content of the raw material is 1.53%, the peroxide value is 9.8 meq / kg, and it has a slight fishy and muttony odor. The specific refining steps are as follows: S1. Raw material pretreatment and continuous feeding: After the crude lard is heated and melted, it is filtered through a screen to remove solid impurities. It is then continuously transported to the waste heat recovery heat exchange unit at a flow rate of 1.0t / h by a variable frequency quantitative conveying pump and preheated to 85℃.

[0034] S2. Micro-negative pressure pretreatment dehydration: The preheated oil is sent into the primary drying chamber, and the absolute pressure inside the chamber is controlled at 18 kPa and the temperature at 100℃. It is then atomized into droplets with an average particle size of 80 μm by a high-speed atomizing nozzle for flash dehydration. Combined with low-speed spiral stirring to prevent wall adhesion, the residence time is 5 min, and the output moisture content is 0.25%.

[0035] S3. Negative pressure drying and refining: The oil flows into the secondary drying chamber by gravity, and the absolute pressure inside the chamber is controlled at 4 kPa. The layered heat-conducting jacket is equipped with two layers of heat-conducting oil chambers. The temperature at the feed end is 112℃ and the temperature at the discharge end is 118℃, with a temperature difference of 6℃. With the help of the turbulent stirring structure, the effective residence time is 10 min, and the moisture content of the discharge is 0.065%.

[0036] S4. Negative pressure stabilization and fine cleaning: The grease enters the three-stage drying chamber, where the absolute pressure is controlled at 9 kPa and the temperature at 105℃. The activated carbon adsorption packing layer flows from top to bottom, with a residence time of 7 minutes. The output moisture content is 0.032%, the peroxide value is 3.7 meq / kg, and the fishy and muttony odors are completely removed.

[0037] S5. Waste heat recovery treatment of water vapor: Same as in Example 1, the mixed water vapor is condensed and separated after waste heat recovery, and no volatile oils are discharged.

[0038] S6. Closed-loop cooling discharge: The grease is cooled to 38°C through a closed tube array and then continuously discharged after passing through a 100μm precision filter.

[0039] This embodiment can operate continuously and stably for 12 hours, with a maximum temperature of 118℃ throughout the process and a grease loss rate of 0.71%. The finished lard is white in color and odorless. It does not show rancidity or separation after being stored at room temperature in a sealed container for 6 months, and its storage stability is significantly improved.

[0040] Comparative Example Using the same batch of crude rapeseed oil as in Example 1 as raw material, the process was carried out intermittently in a conventional single vacuum drying tank. The process parameters were: vacuum absolute pressure 10 kPa, drying temperature 140°C, drying time 30 min, and the single batch processing capacity was equivalent to the unit time processing capacity of Example 1.

[0041] Post-processing test results: The finished oil has a water content of 0.132%, a peroxide value of 8.6 meq / kg, a Lovibond colorimetric red value of 5.8, and an oil loss rate of 3.3%. Furthermore, the batch production switching process requires vacuum feeding, which can easily cause secondary oxidation of the oil. The single batch production cycle is long, the production efficiency is only 55% of that in Example 1 of this invention, and the quality fluctuation range between batches is >15%.

[0042] Table 1. Comparison of the technical effects of different oil refining processes

[0043] The comparison between the above embodiments and comparative examples shows that the integrated process of the present invention, which employs a three-stage gradient negative pressure, a fully enclosed and continuous process, atomization + stirring dual-effect drying, and waste heat recovery, is superior to the traditional single vacuum drying process. Significantly improved drying precision: The moisture content of the finished product is reduced by more than 71% and can be stably controlled below 0.05%; Outstanding oxidation inhibition effect: peroxide value is reduced by more than 50%, oil color does not darken, and nutrient content is well preserved; Material loss has been significantly reduced: the oil loss rate has decreased by more than 75%, down to less than 0.8%; Significantly improved production efficiency: Continuous operation is more than 40% more efficient than intermittent process, and the product quality is more consistent.

[0044] Therefore, the present invention adopts the above-mentioned negative pressure continuous drying and refining method for oils and fats, which realizes low-temperature continuous feeding of oils and fats, gradient negative pressure drying, and closed-loop continuous discharge, significantly reducing the oxidation loss of oils and fats, improving drying accuracy and product consistency, and is suitable for large-scale industrial continuous production.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for continuous drying and refining of oils under negative pressure, comprising raw material pretreatment, drying and dehydration, and discharge processes, characterized in that, The method is carried out continuously within a closed negative pressure system without the intrusion of external air, and specifically includes the following steps: S1. Raw material pretreatment and continuous feeding: After removing solid impurities by primary filtration, the crude oil to be refined is quantitatively and continuously fed to the waste heat recovery heat exchange unit, where the waste heat from the water vapor generated in the drying process is used to preheat the oil to 80~95℃. S2. Micro-negative pressure pretreatment dehydration: The preheated oil is sent into the primary drying chamber, and the absolute pressure inside the chamber is controlled at 15~25kPa and the temperature at 95~110℃ to remove free water and light volatile impurities from the oil. After pretreatment, the moisture content of the oil is reduced to below 0.3%. S3. Negative Pressure Drying and Refining: The pretreated oil is continuously fed into the secondary drying chamber, where the absolute pressure is controlled at 3~8 kPa and the temperature at 110~130℃. This process removes bound water, residual trace moisture, and light colloids from the oil, resulting in an oil moisture content of ≤0.08% after primary drying. S4. Negative pressure stabilization and fine finishing: The grease after primary drying is continuously fed into a three-stage drying chamber, with the absolute pressure inside the chamber controlled at 8~12kPa and the temperature at 100~115℃, to remove residual pigments, oxides and odor impurities. The moisture content of the grease after fine finishing is ≤0.05%. S5. Waste heat recovery treatment of water vapor: Collect the mixed water vapor generated by the first to third stage drying chambers, and pass it into the waste heat recovery heat exchange unit of step S1 to preheat the raw material oil. The water vapor after heat exchange is condensed and discharged in a centralized manner. S6. Closed-loop cooling discharge: The refined oil is cooled to below 40°C in a closed-loop micro-negative pressure environment, and then continuously discharged as finished refined oil after filtration.

2. The method for continuous drying and refining of oils under negative pressure according to claim 1, characterized in that: In step S2, the grease is atomized into micron-sized droplets by a high-speed atomizing nozzle in the primary drying chamber for flash evaporation and dehydration. The low-speed spiral stirring mechanism in the primary drying chamber continuously scrapes off the grease adhering to the inner wall of the chamber. The high-speed atomizing nozzle atomizes the oil into droplets with a particle size of 50~200μm, and the residence time of the oil in the primary drying chamber during the flash evaporation process is 3~6 minutes.

3. The method for continuous drying and refining of oils under negative pressure according to claim 1, characterized in that: In step S3, the walls of the secondary drying chamber are equipped with layered heat-conducting jackets, and a turbulent stirring structure with guide plates is installed inside the secondary drying chamber. The effective residence time of the oil in the chamber is 8~15 minutes.

4. The negative pressure continuous drying and refining method for oils according to claim 3, characterized in that: The layered heat-conducting jacket is provided with at least two independent heat-conducting oil chambers along the axial direction of the secondary drying chamber. The temperature of each heat-conducting oil chamber increases gradually along the material flow direction, and the temperature difference is controlled at 5~10℃.

5. The method for continuous drying and refining of oils under negative pressure according to claim 1, characterized in that: In step S4, a removable activated carbon adsorption packing layer is set in the three-stage drying chamber. The oil flows through the activated carbon adsorption packing layer from top to bottom. The residence time of the oil in the three-stage drying chamber is 5~8 minutes. After refining, the peroxide value of the oil is ≤5 meq / kg.

6. The method for continuous drying and refining of oils under negative pressure according to claim 1, characterized in that: In step S1, the primary filtration uses screen filtration to remove oil residue and solid impurities with a particle size ≥0.5mm. The feed flow rate is controlled at 0.8~2.5t / h by a variable frequency quantitative conveying pump, and the feed flow rate is matched with the processing capacity of each drying chamber.

7. The method for continuous drying and refining of oils under negative pressure according to claim 1, characterized in that: The drying chambers in steps S2 to S4 are seamlessly connected from top to bottom through a sealed connecting pipeline. The grease is continuously transported by gravity and pressure difference. Pressure isolation valves are installed between the chambers.

8. The method for continuous drying and refining of oils under negative pressure according to claim 1, characterized in that: In step S5, a water ring vacuum pump unit is used to provide a negative pressure environment for the entire closed system. The vacuum pump unit and the condenser unit operate in conjunction. The mixed water vapor is condensed to achieve oil-water separation, and no volatile oils are discharged.

9. The negative pressure continuous drying and refining method for oils according to claim 1, characterized in that: In step S6, the cooling process uses a closed-loop tube cooler with circulating cooling water as the cooling medium. The cooled grease is continuously discharged through a precision filter with an accuracy of 50~100μm and directly connected to the finished product storage unit or the deep processing process.

10. The method for continuous drying and refining of oils under negative pressure according to claim 1, characterized in that: The crude oil to be refined is any one of vegetable crude oil, animal crude oil, or waste recycled oil.

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