System and method for large-scale production of biodiesel from low-acid-value catering waste oil

Abstract

The application discloses a kind of low acid value catering waste oil scale production biodiesel system and production method, solve the technical problems such as high glycerol containing soap, difficult separation, poor quality, large separation system investment, low total yield of biodiesel in the process of biodiesel production of existing low acid value catering waste oil.The biodiesel system of the application includes pretreatment system and solid acid catalysis system.The production method is that low acid value catering waste oil is hydrolyzed to obtain hydrolyzed fatty acid by pretreatment system, and then enters solid acid catalysis system to react with methanol, and high-purity biodiesel is efficiently generated after solid acid catalysis.The application integrates oil hydrolysis and solid acid catalysis into continuous biodiesel production system, with low production cost, short process route, reduced methanol loss and complete glycerol separation.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste animal and vegetable oil processing, and particularly relates to a system and method for large-scale production of biodiesel from low-acid value waste restaurant oil. Background Art

[0002] Biodiesel refers to fatty acid methyl or ethyl esters formed by converting waste animal and plant oils, such as vegetable and animal oils, or microbial oils, with methanol or ethanol through esterification. Biodiesel is a "green energy" that, compared to petroleum diesel, offers improved environmental performance, better engine starting performance, better fuel properties, and a wide range of renewable raw materials. my country currently consumes 17 million tons of oil and fat, generating over 2.5 million tons of waste cooking oil annually. Through technology, waste cooking oil can be converted into biodiesel. Compared to mineral diesel, biodiesel is environmentally friendly, with only one-tenth the toxic organic compounds found in diesel vehicle exhaust, 20% of particulate matter, and only 10% of CO2 and CO emissions. However, low-acid-value waste cooking oil, with its high triglyceride content, results in high soap content, difficult separation, poor quality, and high separation system investment compared to traditional biodiesel production methods. This results in a low overall biodiesel yield.

[0003] Therefore, designing a system and method for large-scale production of biodiesel from low-acid value restaurant waste oil to at least solve some of the above technical problems has become a technical problem that needs to be solved urgently by technicians in the relevant technical field. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a system and a production method for large-scale production of biodiesel from low-acid-value waste cooking oil, so as to solve the technical problems of high glycerol soap content, difficult separation, poor quality, large investment in the separation system and low total biodiesel yield in the existing production of biodiesel from low-acid-value waste cooking oil.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A system for large-scale production of biodiesel from low-acid-value waste cooking oil comprises a pretreatment system for enzymatically hydrolyzing the low-acid-value waste cooking oil into hydrolyzed fatty acids, and a solid acid catalytic system connected to the pretreatment system for catalyzing the hydrolyzed fatty acids into fatty acid methyl esters.

[0007] The pretreatment system includes a grease buffer tank, a hydrolase buffer tank, a pure water buffer tank, enzyme hydrolysis tanks for grease hydrolysis reaction connected to the grease buffer tank, the hydrolase buffer tank and the pure water buffer tank respectively, spray dryers for drying product fatty acids and three-phase separators for separating reaction mixtures connected to the enzyme hydrolysis tank respectively, a residue pool for collecting reaction residues, a grease tank for collecting unreacted grease and a membrane separator for oil-water separation connected to the three-phase separator respectively, and a clear phase collection tank for collecting water enzyme liquid and a dense phase collection tank for collecting glycerol connected to the membrane separator respectively; the spray dryer includes a first-level spray dryer connected to the enzyme hydrolysis tank and a second-level spray dryer connected to the first-level spray dryer.

[0008] Furthermore, the solid acid catalytic system includes a first static mixer for mixing fatty acids and methanol, which is connected to the secondary spray dryer and the liquid methanol buffer tank respectively, a first reaction tower connected to the first static mixer, a liquid supercharger for regulating the pressure of the primary reaction product, which is connected to the first reaction tower, a second raw material steam heater for heating the primary reaction product, which is connected to the liquid methanol buffer tank and the second raw material steam heater respectively, and a second reaction tower connected to the second static mixer; the first reaction tower is connected to the methanol recovery section, and the second reaction tower is connected to the liquid methanol buffer tank;

[0009] A high-purity fatty acid delivery pipe is provided between the first static mixer and the secondary spray dryer, and a first raw material steam heater for heating the high-purity fatty acid is provided on the high-purity fatty acid delivery pipe; a first liquid methanol delivery pipe is provided between the first static mixer and the liquid methanol buffer tank, and a first methanol steam heater for preheating methanol is provided on the first liquid methanol delivery pipe; a second liquid methanol delivery pipe is provided between the second static mixer and the liquid methanol buffer tank, and a second methanol steam heater for preheating methanol is provided on the second liquid methanol delivery pipe.

[0010] Furthermore, the enzymatic hydrolysis tank includes an enzymatic hydrolysis tank body, and a circulation mechanism provided on the enzymatic hydrolysis tank body for circulating hydrolysis; the circulation mechanism includes a main circulating liquid outlet channel connected from the bottom of the enzymatic hydrolysis tank body, and a first sub-circulation pipe and a second sub-circulation pipe respectively connected from the main circulating liquid outlet channel, the first sub-circulation pipe is connected to the top of the enzymatic hydrolysis tank body, and the second sub-circulation pipe is connected to the middle of the enzymatic hydrolysis tank body, a first liquid outlet valve is provided on the main circulating liquid outlet, a first circulation pump is provided on the first sub-circulation pipe, and a second circulation pump is provided on the second sub-circulation pipe.

[0011] Furthermore, the top of the enzymatic hydrolysis tank is provided with a first circulation liquid inlet pipe, a second circulation liquid inlet pipe and a third circulation liquid inlet pipe distributed in the shape of a finished product, and the first sub-circulation pipeline is connected to the first circulation liquid inlet pipe, the second circulation liquid inlet pipe and the third circulation liquid inlet pipe respectively; the first circulation liquid inlet pipe, the second circulation liquid inlet pipe and the third circulation liquid inlet pipe are respectively provided with a first liquid inlet valve, a second liquid inlet valve and a third liquid inlet valve;

[0012] A fourth circulation liquid inlet pipe, a fifth circulation liquid inlet pipe, and a sixth circulation liquid inlet pipe are provided in the middle of the enzymatic hydrolysis tank body, and a second sub-circulation pipeline is connected to the fourth circulation liquid inlet pipe, the fifth circulation liquid inlet pipe, and the sixth circulation liquid inlet pipe respectively. The fourth circulation liquid inlet pipe, the fifth circulation liquid inlet pipe, and the sixth circulation liquid inlet pipe are all tangentially distributed with the cylindrical shell of the enzymatic hydrolysis tank body. A fourth liquid inlet valve, a fifth liquid inlet valve, and a sixth liquid inlet valve are respectively provided on the fourth circulation liquid inlet pipe, the fifth circulation liquid inlet pipe, and the sixth circulation liquid inlet pipe;

[0013] A circulating liquid outlet channel is connected between the enzyme hydrolysis tank body and the second sub-circulation pipeline. A first circulating liquid outlet pipe, a second circulating liquid outlet pipe and a third circulating liquid outlet pipe are provided at the lower part of the enzyme hydrolysis tank body. One end of the circulating liquid outlet channel is connected to the first circulating liquid outlet pipe, the second circulating liquid outlet pipe and the third circulating liquid outlet pipe respectively, and the other end is connected to the second sub-circulation pipeline. The access point of the circulating liquid outlet channel and the second sub-circulation pipeline is located between the second circulation pump and the circulating main liquid outlet channel. The first circulating liquid outlet pipe, the second circulating liquid outlet pipe and the third circulating liquid outlet pipe are all tangent to the cylindrical shell of the enzyme hydrolysis tank body. The first circulating liquid outlet pipe, the second circulating liquid outlet pipe and the third circulating liquid outlet pipe are respectively provided with a second liquid outlet valve, a third liquid outlet valve and a fourth liquid outlet valve.

[0014] Furthermore, a grease inlet is provided on the top of the enzymatic hydrolysis tank, and a first input valve is provided on the grease inlet; a grease delivery pipe is provided between the grease inlet and the grease buffer tank, and a first delivery pump and a first output valve are provided on the grease delivery pipe respectively;

[0015] A hydrolase liquid inlet is provided on the top of the enzyme hydrolysis tank body, and a second input valve is provided on the hydrolase liquid inlet; a hydrolase delivery pipe is provided between the hydrolase liquid inlet and the hydrolase buffer tank, and a second delivery pump and a second output valve are provided on the hydrolase delivery pipe; a pure water delivery pipe is provided between the hydrolase liquid inlet and the pure water buffer tank, and a third delivery pump and a third output valve are provided on the pure water delivery pipe;

[0016] The enzymatic hydrolysis tank is provided with a propeller stirrer for mixing oil and hydrolytic enzyme liquid, and the enzymatic hydrolysis tank is provided with a sight glass for observing the internal material condition. The enzymatic hydrolysis tank has a double-layer structure, and heating coils for heating the internal material are evenly distributed in the interlayer; the bottom of the enzymatic hydrolysis tank is connected to the primary spray dryer through a fatty acid delivery pipe and to the three-phase separator through a reactant delivery pipe; the fatty acid delivery pipe is provided with a fourth delivery pump and a steam heater, and the reactant delivery pipe is provided with a fifth delivery pump.

[0017] Furthermore, the pretreatment system also includes a vacuum pump. The top of the first-stage spray dryer is connected to the vacuum pump through a first exhaust pipe, and the top of the second-stage spray dryer is connected to the vacuum pump through a second exhaust pipe. The first exhaust pipe is provided with a first exhaust valve, and the second exhaust pipe is provided with a second exhaust valve.

[0018] The first-stage spray dryer and the second-stage spray dryer have the same structure, with an arc-shaped baffle on the top and a liquid level gauge on the outer wall. A first-stage drying delivery pipe is connected between the bottom of the first-stage spray dryer and the top of the second-stage spray dryer. The first-stage drying delivery pipe is provided with a sixth delivery pump, and the high-purity fatty acid delivery pipe is provided with a seventh delivery pump.

[0019] Furthermore, the first reaction tower and the second reaction tower have the same structure, both comprising a reaction tower body for mixing materials for reaction, a separation body connected to the reaction tower body and integrally structured for separating slag water, and a drainage pipe connected to the separation body. The reaction tower body is provided with a drainage area and a reaction area interconnected from bottom to top;

[0020] The separation body has an inverted cone-shaped structure. The top surface of the inverted cone is connected to the reaction zone, and the bottom surface of the inverted cone is connected to the drain pipe. The drain pipe is provided with an inverted U-shaped pipe section. The top of the inverted U-shaped pipe section is flush with the top surface of the separation body. The outlet of the drain pipe is connected to the methanol purification section.

[0021] Furthermore, the reaction zone is provided with a solid acid catalyst and a stirrer for stirring the materials therein, and the stirrer is a submersible push-flow stirrer;

[0022] The bottom of the reaction zone is provided with a catalyst loading hole for loading and unloading the solid acid catalyst and a feed port for inputting the mixed material. The feed port is connected to the first static mixer or the second static mixer through a feed pipe.

[0023] A feed distribution plate is provided at the bottom of the reaction zone, which is connected to the feed inlet and is used for uniform feeding. The feed distribution plate is evenly distributed with feed distribution holes.

[0024] A first filter screen and a second filter screen are respectively provided at both ends of the reaction zone to prevent the solid acid catalyst from flowing out. The first filter screen and the second filter screen have the same structure, their diameters are consistent with the inner diameter of the reaction zone, and their filter pore diameters are smaller than the diameter of the solid acid catalyst.

[0025] Furthermore, a discharge port for discharging the product is opened on the side wall of the liquid discharge area. The discharge port of the first reaction tower is connected to the liquid supercharger, and the discharge port of the second reaction tower is connected to the product collection section.

[0026] The top of the drainage area is equipped with a pressure regulating valve for adjusting the internal medium pressure, a safety valve for protecting the system safety, and a methanol outlet for methanol recovery. The methanol outlet of the first reaction tower is connected to the methanol recovery section, and the methanol outlet of the second reaction tower is connected to the liquid methanol buffer tank.

[0027] A method for producing a biodiesel system on a large scale using low-acid-value waste cooking oil comprises the following steps:

[0028] Step A: The low-acid-value catering waste oil in the oil buffer tank, the hydrolase in the hydrolase buffer tank, and the pure water in the pure water buffer tank are uniformly mixed in the enzyme hydrolysis tank, and then the oil hydrolysis reaction is carried out to generate product fatty acids, by-product glycerol and other mixtures. The reaction conditions are that the volume ratio of oil to water is 6:4, the mass of the hydrolase is 5% of the weight of the oil, the hydrolysis pressure is normal pressure, the hydrolysis temperature is 55°C, and the hydrolysis time is 48 hours; the by-product glycerol and other mixtures are transported and separated into a three-phase separator through a reactant transport pipe to separate the residue, remaining oil, and water-enzyme-glycerol mixture, wherein the residue is collected into a residue pool and the oil is collected into an oil tank; the water-enzyme-glycerol mixture enters a membrane separator, and is separated and filtered again to obtain by-product glycerol and a water-enzyme mixture, wherein the by-product glycerol is collected into a dense phase collection tank, and the water-enzyme mixture is collected into a clear phase collection tank;

[0029] Step B: The fatty acid product in step A is transported to a primary spray dryer through a fatty acid delivery pipe for primary spray drying. During the transportation process, the fatty acid is pressurized to 0.4 MPa by a fourth delivery pump and preheated to 120° C. by a steam heater. After primary spray drying, a primary dried fatty acid product is obtained. The drying pressure in the primary spray dryer is -0.088 MPa and the drying temperature is 120° C.;

[0030] Step C: The fatty acid primary drying product in step B enters a secondary spray dryer for secondary spray drying to obtain high-purity fatty acids at a drying pressure of -0.088 MPa and a drying temperature of 120°C;

[0031] Step D: The high-purity fatty acid in step C is heated to 110-120° C. by a first raw material steam heater and then fully mixed with liquid methanol heated to 55° C. by a first methanol steam heater in a first static mixer to obtain a raw material mixture;

[0032] Step E: The raw material mixture in step D enters the first reaction tower for the first catalytic reaction to obtain the primary reaction product. The catalytic conditions are normal pressure, 110°C, and the solid acid catalyst is sulfuric acid / titanium dioxide SO4. 2- / TiO2 catalyst;

[0033] Step F: The primary reaction product in step E is adjusted to a slightly positive pressure by a liquid booster, heated to 110-120° C. by a second raw material steam heater, and then fully mixed with liquid methanol heated to 55° C. by a second methanol steam heater in a second static mixer to obtain a second mixture;

[0034] Step G: The second mixture in step F enters the second reaction tower for a second catalytic reaction to obtain high-purity biodiesel. The catalytic conditions are normal pressure, 110°C, and the solid acid catalyst is sulfuric acid / titanium dioxide SO4. 2- / TiO2 catalyst.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention has a simple structure, scientific and rational design, and is easy to use. It solves the technical problems of existing biodiesel production from low-acid-value restaurant waste oil, such as high glycerin soap content, difficult separation, poor quality, large investment in the separation system, and low overall biodiesel yield. The present invention integrates the hydrolysis of low-acid-value restaurant waste oil with solid acid catalysis into a continuous biodiesel production system, eliminating the independent transesterification system and glycerin separation system. This reduces production costs, shortens the process route, and reduces overall investment by more than 40%. In addition, the use of a pretreatment system capable of cyclic hydrolysis and simultaneous glycerin separation, as well as a continuous solid acid catalysis system capable of online separation of methanol and water, reduces methanol loss, thoroughly separates glycerin, and increases oil utilization, thereby increasing the overall biodiesel yield by 3-5%.

[0037] The present invention includes a pretreatment system and a solid acid catalytic system connected to the pretreatment system, wherein the waste gas grease completes the generation and drying of fatty acids and the separation and recovery of by-product glycerol in the pretreatment system, and the high-purity fatty acids generated and treated by the pretreatment system enter the solid acid catalytic system for catalysis to generate biodiesel. The pretreatment system for oil hydrolysis and the solid acid catalytic system are integrated into a continuous large-scale industrial production system, which greatly enhances production continuity and industrial process, and reduces investment area and investment cost.

[0038] The pretreatment system of the present invention comprises a grease buffer tank, a hydrolase buffer tank, a pure water buffer tank, an enzyme hydrolysis tank, a spray dryer, a three-phase separator, a residue pool, a membrane separator, a clear phase collection tank and a dense phase collection tank. The grease in the grease buffer tank, the hydrolase in the hydrolase buffer tank and the pure water in the pure water buffer tank are simultaneously fed into the enzyme hydrolysis tank in a certain proportion to carry out a hydrolysis reaction. After the reaction is completed, the main product fatty acid is fed into the spray dryer for two spray dryings to obtain high-purity fatty acid, and then directly fed into a subsequent solid acid catalysis system. While the fatty acid is being dried, a by-product mixture is fed into the three-phase separator for separation to obtain a mixture of residue, grease, hydrolase and glycerol. The mixture is then separated into a clear phase water enzyme liquid and a dense phase glycerol by the membrane separator. The glycerol can be used to produce propylene glycol, thereby increasing enterprise income.

[0039] The solid acid catalytic system of the present invention includes a first static mixer, a first reaction tower, a liquid supercharger, a second raw material steam heater, a second static mixer, and a second reaction tower. High-purity fatty acids hydrolyzed and dried by a pretreatment system are heated by the first raw material steam heater and fully mixed with methanol heated by the first methanol steam heater in the first static mixer, and react in the first reaction tower. The primary reaction product after the first reaction is adjusted to a slightly positive pressure by the liquid supercharger, heated by the second raw material steam heater, and fully mixed with methanol heated by the second methanol steam heater in the second static mixer, and react in the second reaction tower to obtain a secondary reaction product, namely biodiesel with high purity and high yield. The solid acid catalytic system uses two reaction towers in series to achieve full reaction of the fatty acids, effectively improving reaction efficiency and greatly increasing the yield of biodiesel. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a structural schematic diagram of the present invention.

[0041] Figure 2 This is an enlarged view of the pre-treatment system.

[0042] Figure 3 Schematic diagram of the enzyme hydrolysis tank.

[0043] Figure 4 This is a top view of the enzymatic hydrolysis tank.

[0044] Figure 5 This is a cross-sectional view of the enzymatic hydrolysis tank.

[0045] Figure 6 This is an enlarged view of the solid acid catalytic system.

[0046] Figure 7 It is a schematic diagram of the structure of the first reaction tower or the second reaction tower.

[0047] Figure 8 Schematic diagram of the feed distribution plate structure.

[0048] The names corresponding to the reference numerals are:

[0049] 1- Grease buffer tank, 2- Hydrolase buffer tank, 3- Pure water buffer tank, 4- Enzyme hydrolysis tank, 5- Three-phase separator, 6- Residue tank, 7- Grease tank, 8- Membrane separator, 9- Clear phase collection tank, 10- Dense phase collection tank, 11- Primary spray dryer, 12- Secondary spray dryer, 13- Liquid methanol buffer tank, 14- First static mixer, 15- First reaction tower, 16- Liquid booster, 17- Second raw material steam heater, 18- Second static mixer, 19- Second reaction tower, 20- High-purity fatty acid delivery pipe, 21- First raw material steam heater, 22- First liquid methanol delivery pipe, 23- First methanol steam heater, 24- Second liquid methanol delivery pipe, 25 -Second methanol steam heater, 26-oil delivery pipe, 27-first delivery pump, 28-first output valve, 29-hydrolase delivery pipe, 30-second delivery pump, 31-second output valve, 32-pure water delivery pipe, 33-third delivery pump, 34-third output valve, 35-fatty acid delivery pipe, 36-reactant delivery pipe, 37-fourth delivery pump, 38-steam heater, 39-fifth delivery pump, 40-vacuum pump, 41-enzyme hydrolysis tank, 42-circulation main liquid outlet, 43-first sub-circulation pipeline, 44-second sub-circulation pipeline, 45-first liquid outlet valve, 46-first circulation liquid inlet pipe, 47-second circulation liquid inlet pipe, 48-third circulation liquid inlet pipe, 49-first circulation pump, 50-first exhaust pipe, 51-second exhaust pipe, 52-first exhaust valve, 53-second exhaust valve, 54-arc baffle, 55-liquid level gauge, 56-first drying delivery pipe, 57-sixth delivery pump, 58-seventh delivery pump, 59-reaction tower body, 60-separation body, 61-drain pipe, 62-drainage area, 63-reaction area, 64-solid acid catalyst, 65-agitator, 66-catalyst loading hole, 67-feed port, 68-feed pipe, 69-feed distribution plate, 70-feed distribution hole, 71-first filter screen, 72-second filter screen, 73-discharge port, 74-pressure regulating valve, 75-safety valve, 76-methanol outlet, 410-second circulation pump, 411- First liquid inlet valve, 412-second liquid inlet valve, 413-third liquid inlet valve, 414-fourth circulation liquid inlet pipe, 415-fifth circulation liquid inlet pipe, 416-sixth circulation liquid inlet pipe, 417-fourth liquid inlet valve, 418-fifth liquid inlet valve, 419-sixth liquid inlet valve, 420-circulation liquid outlet channel, 421-first circulation liquid outlet pipe, 422-second circulation liquid outlet pipe, 423-third circulation liquid outlet pipe, 424-second liquid outlet valve, 425-third liquid outlet valve, 426-fourth liquid outlet valve, 427-grease inlet, 428-first input valve, 429-hydrolase liquid inlet, 430-second input valve, 431-propeller agitator, 432-sight glass, 433-heating coil. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0051] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0052] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; of course, they may also refer to mechanical connections or electrical connections; in addition, they may refer to direct connections, indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0053] like Figure 1-8 As shown, the present invention provides a system and method for large-scale production of biodiesel using low-acid value restaurant waste oil. The system and method have a simple structure, a scientific and reasonable design, and are easy to use. They solve the technical problems of existing low-acid value restaurant waste oil production of biodiesel, such as high glycerol soap content, difficulty in separation, poor quality, large investment in the separation system, and low total biodiesel yield. The present invention integrates the hydrolysis of low-acid value restaurant waste oil with solid acid catalysis into a continuous biodiesel production system, eliminating the independent ester exchange system and glycerol separation system, resulting in low production costs, a short process route, and a reduction of more than 40% in overall investment. In addition, the use of a pre-treatment system capable of cyclic hydrolysis and synchronous glycerol separation and a continuous solid acid catalysis system capable of online separation of methanol and water reduces methanol loss, thoroughly separates glycerol, and increases oil utilization, thereby increasing the total biodiesel yield by 3-5%.

[0054] The present invention includes a pretreatment system for enzymatic hydrolysis of low-acid-value catering waste oil, and a solid acid catalytic system for fatty acid catalysis connected to the pretreatment system. The waste oil and fat complete the generation and drying of fatty acids and the separation and recovery of by-product glycerol in the pretreatment system. The high-purity fatty acids generated and treated by the pretreatment system enter the solid acid catalytic system for catalytic generation of biodiesel. The pretreatment system for oil and fat hydrolysis and the solid acid catalytic system are integrated into a continuous large-scale industrial production system, which greatly enhances production continuity and industrial process performance and reduces investment area and investment cost.

[0055] The pretreatment system of the present invention includes a grease buffer tank 1, a hydrolase buffer tank 2, a pure water buffer tank 3, an enzyme hydrolysis tank 4 for grease hydrolysis reaction connected to the grease buffer tank 1, the hydrolase buffer tank 2 and the pure water buffer tank 3 respectively, a spray dryer for drying product fatty acids and a three-phase separator 5 for separating the reaction mixture connected to the enzyme hydrolysis tank 4 respectively, a residue pool 6 for collecting reaction residues, a grease tank 7 for collecting unreacted grease and a membrane separator 8 for oil-water separation connected to the three-phase separator 5 respectively, and a clear phase collection tank 9 for collecting water enzyme liquid and a dense phase collection tank 10 for collecting glycerol connected to the membrane separator 8 respectively; the spray dryer includes a primary spray dryer 11 connected to the enzyme hydrolysis tank 4, and a secondary spray dryer 12 connected to the primary spray dryer 11. The grease in the grease buffer tank 1, the hydrolase in the hydrolase buffer tank 2 and the pure water in the pure water buffer tank 3 enter the enzyme hydrolysis tank 4 at the same time in a certain proportion for hydrolysis reaction. After the reaction is completed, the main product fatty acid enters the spray dryer for two spray drying to obtain high-purity fatty acid, and then directly enters the subsequent production conditions; while the fatty acid is drying, the by-product mixture enters the three-phase separator 5 for separation to obtain a mixture of residue, grease, hydrolase and glycerol. The mixture is then separated by the membrane separator 8 to obtain a clear phase of water enzyme liquid and a concentrated phase of glycerol. The glycerol can be used to produce propylene glycol, which increases the company's income.

[0056] The enzymatic hydrolysis tank 4 of the present invention includes an enzymatic hydrolysis tank body 41 and a circulation mechanism provided on the enzymatic hydrolysis tank body 41 for circulating hydrolysis; the circulation mechanism includes a main circulating liquid outlet 42, a first sub-circulation pipe 43, and a second sub-circulation pipe 44. The main circulating liquid outlet 42 is connected to the bottom of the enzymatic hydrolysis tank body 41, the first sub-circulation pipe 43 is connected to the main circulating liquid outlet 42 and connected to the top of the enzymatic hydrolysis tank body 41, and the second sub-circulation pipe 44 is connected to the main circulating liquid outlet 42 and connected to the middle of the enzymatic hydrolysis tank body 41. The first sub-circulation pipe 43 and the second sub-circulation pipe 44 can circulate and mix the materials in the enzymatic hydrolysis tank body in a vertical direction, thereby increasing the contact and mixing reaction between the oil and the hydrolytic enzyme liquid, and greatly improving the efficiency of industrial large-scale hydrolysis reactions. The main circulation liquid outlet 42 is provided with a first liquid outlet valve 45 , which can control the outflow of materials at the bottom of the enzyme hydrolysis tank 41 and lead them to the first sub-circulation pipeline 43 and the second sub-circulation pipeline 44 respectively, thereby realizing different cycles in sequence.

[0057] The first sub-circulation pipeline 43 of the present invention is connected to the main circulation outlet 42. The first sub-circulation pipeline 43 is provided with a first circulation pump 49, which can pump the bottom material into the top of the enzymatic hydrolysis tank 41. The top of the enzymatic hydrolysis tank 41 is provided with a first circulation inlet pipe 46, a second circulation inlet pipe 47, and a third circulation inlet pipe 48 arranged in a "product" shape. The first sub-circulation pipeline 43 is connected to the first circulation inlet pipe 46, the second circulation inlet pipe 47, and the third circulation inlet pipe 48 respectively. The first circulation inlet pipe 46, the second circulation inlet pipe 47, and the third circulation inlet pipe 48 reduce the pressure of the circulating liquid inlet. At the same time, their "product" shape distribution can effectively increase the uniformity of the circulating liquid inlet. The first circulation inlet pipe 46, the second circulation inlet pipe 47, and the third circulation inlet pipe 48 are respectively provided with a first inlet valve 411, a second inlet valve 412, and a third inlet valve 413. The opening and closing of different inlet valves can be reasonably adjusted according to the size of the circulation flow to achieve the most reasonable circulation hydrolysis.

[0058] The second sub-circulation pipeline 44 of the present invention is connected to the main circulation outlet 42. The second sub-circulation pipeline 44 is provided with a second circulation pump 410, which can pump the bottom material into the middle of the enzymatic hydrolysis tank 41. The middle of the enzymatic hydrolysis tank 41 is provided with a fourth circulation liquid inlet pipe 414, a fifth circulation liquid inlet pipe 415, and a sixth circulation liquid inlet pipe 416. The second sub-circulation pipeline 44 is connected to the fourth circulation liquid inlet pipe 414, the fifth circulation liquid inlet pipe 415, and the sixth circulation liquid inlet pipe 416 respectively. The fourth circulation liquid inlet pipe 414, the fifth circulation liquid inlet pipe 415, and the sixth circulation liquid inlet pipe 416 are all tangentially distributed with the cylindrical shell of the enzymatic hydrolysis tank 41. The tangential distribution ensures uniform and stable entry of materials. The fourth circulation liquid inlet pipe 414, the fifth circulation liquid inlet pipe 415 and the sixth circulation liquid inlet pipe 416 are respectively provided with a fourth liquid inlet valve 417, a fifth liquid inlet valve 418 and a sixth liquid inlet valve 419. The circulation opening and closing can be controlled by different liquid inlet valves, which on the one hand adapts to the circulation of different liquid flow rates and on the other hand ensures the uniformity of the liquid inlet.

[0059] A circulating liquid outlet channel 420 is connected between the enzymatic hydrolysis tank body 41 and the second sub-circulation pipeline 44 of the present invention. A first circulating liquid outlet pipe 421, a second circulating liquid outlet pipe 422 and a third circulating liquid outlet pipe 423 are provided at the lower part of the enzymatic hydrolysis tank body 41. One end of the circulating liquid outlet channel 420 is respectively connected to the first circulating liquid outlet pipe 421, the second circulating liquid outlet pipe 422 and the third circulating liquid outlet pipe 423, and the other end is connected to the second sub-circulation pipeline 44. The material at the lower part of the enzymatic hydrolysis tank body 41 enters the circulating liquid outlet channel 420 through the first circulating liquid outlet pipe 421, the second circulating liquid outlet pipe 422 and the third circulating liquid outlet pipe 423 respectively, and then passes through the second sub-circulation pipeline 44 and is pumped into the middle part of the enzymatic hydrolysis tank body 41 by the second circulation pump 410, thereby realizing horizontal circulating hydrolysis. The first, second, and third circulating liquid outlet pipes 421, 422, and 423 are all tangentially arranged with the cylindrical outer shell of the enzymatic hydrolysis tank 41. This tangential distribution ensures uniform and stable liquid discharge. A second outlet valve 424, a third outlet valve 425, and a fourth outlet valve 426 are respectively provided on the first, second, and third circulating liquid outlet pipes 421, 422, and 423. Each valve can be opened and closed according to the actual hydrolysis volume, achieving optimal horizontal circulating hydrolysis.

[0060] The top of the hydrolysis tank 41 of the present invention is provided with a grease inlet 427, which is equipped with a first input valve 428. A grease delivery pipe 26 is provided between the grease inlet 427 and the grease buffer tank 1, and the grease delivery pipe 26 is respectively equipped with a first delivery pump 14 and a first output valve 15. The top of the enzymatic hydrolysis tank 41 is provided with a hydrolase liquid inlet 429, which is equipped with a second input valve 430. A hydrolase delivery pipe 29 is provided between the hydrolase liquid inlet 429 and the hydrolase buffer tank 2, and the hydrolase delivery pipe 29 is respectively equipped with a second delivery pump 22 and a second output valve 23. A pure water delivery pipe 31 is provided between the hydrolase liquid inlet 429 and the pure water buffer tank 3, and the pure water delivery pipe 31 is respectively equipped with a third delivery pump 32 and a third output valve 33. Since grease, water and hydrolase are insoluble, they need to be transported from different buffer tanks to the enzyme hydrolysis tank 41 before the reaction. The volume ratio of grease to water is 6:4, and the mass of hydrolase is 5% of the weight of grease.

[0061] The enzymatic hydrolysis tank 41 of the present invention is provided with a propeller stirrer 431 on top and a sight glass 432 on the enzymatic hydrolysis tank 41. The mixture of oil, water, and hydrolytic enzyme is continuously stirred and reacted under the action of the propeller stirrer 431. The size and number of the propeller stirrer 431 blades are set according to the size of the enzymatic hydrolysis tank 41 and the volume of the hydrolysis mixture. The sight glass 432 can be mounted on the enzymatic hydrolysis tank 41 by welding, bolting, or clamping, and is used to detect the reaction state of the internal materials and the liquid level in the enzymatic hydrolysis tank 41, facilitating monitoring of the hydrolysis reaction. The enzymatic hydrolysis tank 41 has a double-layer structure, and its interlayer is evenly distributed with heating coils 433 for heating the internal materials. 70°C hot water is dynamically circulated from bottom to top within the heating coils 433 to provide a suitable hydrolysis temperature for the internal hydrolysis mixture. The heating coils 433 are circulated with a boiler system. The hydrolysis reaction conditions in the enzymatic hydrolysis tank 41 are as follows: hydrolysis pressure at normal pressure, hydrolysis temperature at 55° C., and hydrolysis time at 48 hours.

[0062] The oil of the present invention is continuously hydrolyzed back and forth in each circulation pipeline of the enzyme hydrolysis tank body 41, obtaining a main product fatty acid and a by-product mixture, wherein the main product fatty acid is transported to the spray dryer of the drying section of the pre-treatment system through the fatty acid delivery pipe 35, and the by-product mixture is transported to the three-phase separator 5 of the by-product separation section via the reactant delivery pipe 36, thereby simultaneously performing main product drying and by-product recovery. The by-product mixture is separated in the three-phase separator 5 to obtain residue, a small amount of oil remaining without participating in the reaction, and a water-enzyme-glycerol mixture. The residue is concentrated in the residue pool 6, the oil is collected in the oil tank 7, and the water-enzyme-glycerol mixture is separated and filtered by the membrane separator 8 to obtain a water-enzyme mixture and glycerol. The water-enzyme mixture is concentrated in the clear phase collection tank 9, and the glycerol is concentrated in the dense phase collection tank 10 for further concentration and purification. Glycerol, as a by-product of oil hydrolysis, can be used to produce propylene glycol, which has a high added value and can bring great profits to the enterprise.

[0063] The main product fatty acid in the pre-treatment system of the present invention enters the spray dryer and is dried and solidified. Before spray drying, the steam heater 38 on the fatty acid delivery pipe 35 is preheated by the fatty acid delivery pipe, and the 4th delivery pump 37 on the fatty acid delivery pipe 35 is pressurized to 0.4MPa. The pressurized and preheated fatty acid is spray dried immediately. Spray drying is twice, which is followed by one-level spray drying and two-level spray drying. To fully remove the moisture in the fatty acid, the pressure in the one-level spray dryer 11 and the two-level spray dryer 12 is-0.088MPa, and the temperature is 120 ℃. The fatty acid enters the one-level spray dryer 11 by the fatty acid delivery pipe 35 successively and is carried out one-level drying. Then, the one-level drying delivery pipe 56 is transported to the two-level spray dryer 12 and is carried out two-level drying. This obtains powdery or granular high-purity fatty acid, and finally is transported to the solid acid catalyst system by the high-purity fatty acid delivery pipe 20 and is carried out catalytic reaction.

[0064] The pretreatment system of the present invention also includes a vacuum pump 40. The top of the first-stage spray dryer 11 is connected to the vacuum pump 40 via a first exhaust pipe 50, and the top of the second-stage spray dryer 12 is connected to the vacuum pump 40 via a second exhaust pipe 51. The first exhaust pipe 50 is provided with a first exhaust valve 52, and the second exhaust pipe 51 is provided with a second exhaust valve 53. The first-stage spray dryer 11 and the second-stage spray dryer 12 have the same structure. After the fatty acids are atomized in the drying chamber of the spray dryer and then come into contact with the hot air in the drying chamber, the moisture inside them is rapidly vaporized and discharged through the exhaust pipe by the vacuum pump 40. At the same time, the arc-shaped baffle 54 on the top of each of the first-stage spray dryer 11 and the second-stage spray dryer 12 prevents the fatty acids from being discharged from the top; and the liquid level gauge 55 on the outer wall of each of the first-stage spray dryer 11 and the second-stage spray dryer 12 facilitates observation of the drying status of the fatty acids inside.

[0065] The solid acid catalytic system of the present invention includes a first static mixer 14 for mixing fatty acids and methanol, which is connected to the secondary spray dryer 12 and the liquid methanol buffer tank 13 respectively, a first reaction tower 15 connected to the first static mixer 14, a liquid supercharger 16 for regulating the pressure of the primary reaction product, which is connected to the first reaction tower 15, a second raw material steam heater 17 for heating the primary reaction product, which is connected to the liquid supercharger 16, a second static mixer 18 for mixing the primary reaction product and methanol, which is connected to the liquid methanol buffer tank 13 and the second raw material steam heater 17 respectively, and a second reaction tower 19 connected to the second static mixer 18.

[0066] A high-purity fatty acid delivery pipe 20 is provided between the first static mixer 14 and the secondary spray dryer 12, and a first raw material steam heater 21 for heating high-purity fatty acids is provided on the high-purity fatty acid delivery pipe 20; a first liquid methanol delivery pipe 22 is provided between the first static mixer 14 and the liquid methanol buffer tank 13, and a first methanol steam heater 23 for preheating methanol is provided on the first liquid methanol delivery pipe 22; a second liquid methanol delivery pipe 24 is provided between the second static mixer 18 and the liquid methanol buffer tank 13, and a second methanol steam heater 25 for preheating methanol is provided on the second liquid methanol delivery pipe 24.

[0067] High-purity fatty acids are produced and transported by the pretreatment system to this working system. The high-purity fatty acids are mixed with methanol twice and complete two catalytic reactions. The high-purity fatty acids are heated by the first raw material steam heater 21 and fully mixed with the methanol heated by the first methanol steam heater 23 in the first static mixer 14, and react in the first reaction tower 15; the primary reaction product after the first reaction is adjusted to a slightly positive pressure by the liquid booster 16, and is heated by the second raw material steam heater 17 and fully mixed with the methanol heated by the second methanol steam heater 24 in the second static mixer 18, and react in the second reaction tower 19 to obtain a secondary reaction product, which is biodiesel with high purity and high yield.

[0068] The solid acid catalytic system of the present invention adopts a structure of two reaction towers connected in series, thereby performing two catalytic reactions of fatty acids to achieve full reaction of oils and fats, effectively improving reaction efficiency and greatly increasing the yield of biodiesel.

[0069] The first and second reaction towers 15 and 19 of the present invention have the same structure, each comprising a reaction tower body 59 for reacting the mixed materials, a separator 60 connected to the reaction tower body 59 for separating the slag and water, and a drain pipe 61 extending from the separator 60. After the mixed materials are thoroughly mixed, they are fed into the reaction tower body 59, where they are catalyzed by a solid acid catalyst 64 therein to produce biodiesel. This structure enables simultaneous biodiesel production and separation of the slag and water. Biodiesel production occurs within the reaction tower body 59, while the slag and water settle into the separator 60, and the methanol-slag-water mixture is separated through the drain pipe 61. This allows for simultaneous and continuous biodiesel production and separation of the methanol-slag-water mixture, significantly reducing impurities in the biodiesel and simplifying subsequent biodiesel refining and purification steps. Furthermore, the methanol-slag-water mixture obtained from the separation enters the methanol purification stage, where it can be rapidly refined into high-purity methanol.

[0070] In addition, the methanol in the first and second reaction towers 15, 19 can be discharged through the methanol outlet 76. The methanol in the first reaction tower 15 flows from the methanol outlet 76 to the methanol recovery section for purification and subsequent operation. The methanol in the second reaction tower 19, which has a higher purity, is directly recovered from the methanol outlet 76 into the liquid methanol buffer tank 13 for recycling in the pretreatment system and catalytic system. This structure enables continuous online separation and recycling of methanol, significantly improving production efficiency and reducing production costs.

[0071] The reaction tower body 59 of the present invention is divided from bottom to top into a drainage area 62 and a reaction area 63 that are interconnected. The reaction area 63 is provided with a solid acid catalyst 64 and an agitator 65 for stirring the material therein. The agitator 63 is provided on the side wall of the reaction area 63. The agitator 65 is a submerged push-flow agitator, which can provide stirring and mixing force for the material inside, so that the contact of the reaction materials is more sufficient and the reaction is more complete. In addition, the submerged push-flow agitator can also be used for regeneration catalysis of the solid acid catalyst. The solid acid catalyst 64 is in solid form and is uniformly distributed in the reaction area 63, which can greatly increase the contact area with the reaction mixture and improve the reaction efficiency. The solid acid catalyst 64 can be loaded and unloaded through a catalyst loading hole 66 opened at the bottom of the reaction area 63. The catalyst loading hole 66 is provided with a loading valve for opening and closing, which is convenient for staff to operate on the one hand and ensures the sealed reaction of the reaction tower body 59 on the other hand.

[0072] The separator 60 of the present invention has an inverted conical structure, with its top surface connected to the reaction zone 63 and its bottom surface connected to the drain pipe 61. The inlet volume flow rate is greater than the outlet overflow volume flow rate, which improves separation efficiency. The drain pipe 61, connected to the outlet of the separator 60, features an inverted U-shaped section, the top of which is flush with the top of the separator 60. This design prevents backflow of materials from the reaction tower body 59 into the drain pipe 61. The outlet of the drain pipe 61 is connected to the methanol purification section, allowing for further purification and rapid recycling of the resulting pure methanol.

[0073] The present invention provides a first filter screen 71 and a second filter screen 72 at both ends of the reaction zone 63, respectively, to prevent the outflow of the solid acid catalyst 64. The first filter screen 71 and the second filter screen 72 have identical structures, with diameters corresponding to the inner diameter of the reaction zone 63 and pore diameters smaller than the diameter of the solid acid catalyst 64. The first filter screen 71 and the second filter screen 72 respectively intercept the solid acid catalyst 64 from flowing into the drainage zone 62 and the separator 60, thereby reducing the loss of the solid acid catalyst 64 and achieving more efficient production compared to conventional biodiesel reactors.

[0074] The bottom of the reaction zone 63 of the present invention is provided with feed ports 67 for inputting a high-purity fatty acid and methanol mixture. Feed ports 67 are connected to external feed pipes 68, which are connected to the first static mixer 14 or the second static mixer 18 in the previous operating mode. A feed distribution plate 69 is provided at the bottom of the reaction zone 63, communicating with feed ports 67 and providing uniform feeding. Feed distribution plates 69 are uniformly distributed with feed distribution holes 70. The high-purity fatty acid and methanol mixture enters the feed distribution plate 69 through feed pipes 68 and is uniformly distributed throughout the reaction zone 63 through the plurality of feed distribution holes 70. A discharge port 73 is provided on the sidewall of the drainage zone 62 for discharging the product. Discharge port 73 is connected to the product collection section, where the product is collected and then fed into the subsequent biodiesel refining and purification process.

[0075] The top of the drain area 62 of the present invention is equipped with a pressure regulating valve 74 for regulating the internal medium pressure and a safety valve 75 for protecting the system. The reaction pressure of the medium in the reaction tower body 59 is normal pressure. The pressure regulating valve 74 can stably control the internal reaction pressure to ensure normal reaction. If the internal medium pressure exceeds the specified safety value, the safety valve 75 opens, discharging some of the gas or fluid in the system to the atmosphere, reducing the system pressure to the specified safety value and thus protecting the system from accidents caused by excessive pressure. The safety valve 75 is an automatic valve and must undergo a pressure test before use.

[0076] The three-phase separator 5, membrane separator 8, spray dryer, various delivery pumps, vacuum pump 16, liquid level gauge 55, various valves, propeller agitator 431, sight glass 432, heating coil 433, various steam heaters, static mixer, liquid booster 16, submersible push flow agitator, pressure regulating valve 74 and safety valve 75 used in the present invention are all existing known electrical equipment and can be directly purchased and used on the market. Their structures, circuits, and control principles are all existing known technologies. Therefore, the structures, circuits, and control principles of the three-phase separator 5, membrane separator 8, spray dryer, various delivery pumps, vacuum pump 16, liquid level gauge 55, various valves, propeller agitator 431, sight glass 432, heating coil 433, various steam heaters, static mixer, liquid booster 16, submersible push flow agitator, pressure regulating valve 74 and safety valve 75 are not described in detail here.

[0077] The method for producing biodiesel on a large scale using low-acid-value waste cooking oil according to the present invention comprises the following steps:

[0078] Step A: The low-acid-value catering waste oil in the oil buffer tank, the hydrolase in the hydrolase buffer tank, and the pure water in the pure water buffer tank are uniformly mixed in the enzyme hydrolysis tank, and then the oil is hydrolyzed to generate fatty acids, glycerol as a by-product, and other mixtures. The reaction conditions are a volume ratio of oil to water of 6:4, the mass of the hydrolase is 5% of the weight of the oil, the hydrolysis pressure is normal pressure, the hydrolysis temperature is 55°C, and the hydrolysis time is 48 hours;

[0079] Step B: The fatty acid product in step A is transported and separated through a fatty acid delivery pipe, pressurized to 0.4 MPa by a fourth delivery pump, preheated by a steam heater, and then fed into a primary spray dryer for primary spray drying to obtain a primary dried fatty acid product. The drying pressure is -0.088 MPa and the drying temperature is 120°C.

[0080] Step C: The fatty acid primary drying product in step B enters a secondary spray dryer for secondary spray drying to obtain high-purity fatty acids at a drying pressure of -0.088 MPa and a drying temperature of 120°C;

[0081] Step D: The by-product glycerol and other mixtures in step A are transported through the reactant transport pipe to a three-phase separator for separation of the residue, the remaining grease, and the water-enzyme-glycerol mixture, wherein the residue is collected in a residue pool and the grease is collected in a grease tank;

[0082] Step E: The water-enzyme-glycerol mixture in step D enters a membrane separator and is separated and filtered again to obtain by-product glycerol and a water-enzyme mixture, wherein the by-product glycerol is collected in a dense phase collection tank, and the water-enzyme mixture is collected in a clear phase collection tank;

[0083] Step F: The high-purity fatty acid in step C is heated to 110-120° C. by a first raw material steam heater and then fully mixed with liquid methanol heated to 55° C. by a first methanol steam heater in a first static mixer to obtain a raw material mixture;

[0084] Step G: The raw material mixture in step F enters the first reaction tower for the first catalytic reaction to obtain the primary reaction product, i.e., biodiesel of low purity. The catalytic conditions are normal pressure, 110°C, and the solid acid catalyst is sulfuric acid / titanium dioxide SO4. 2- / TiO2 catalyst;

[0085] Step H: The primary reaction product in step G is adjusted to a slightly positive pressure by a liquid booster, heated to 110-120° C. by a second raw material steam heater, and then fully mixed with liquid methanol heated to 55° C. by a second methanol steam heater in a second static mixer to obtain a second mixture;

[0086] Step I: The second mixture in step H enters the second reaction tower for a second catalytic reaction to obtain a secondary reaction product, i.e., biodiesel of extremely high purity. The catalytic conditions are normal pressure, 110°C, and the solid acid catalyst is sulfuric acid / titanium dioxide SO4. 2- / TiO2 catalyst.

[0087] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention and are intended to illustrate the technical solutions of the present invention, rather than limiting them, and certainly not limiting the patent scope of the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they may still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention. In other words, any changes or embellishments made to the main design concept and spirit of the present invention that have no substantive significance, provided that the technical problems they solve are still consistent with those of the present invention, should be included in the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields should also be included in the patent protection scope of the present invention.

Claims

1. A system for large-scale production of biodiesel from low-acid value restaurant waste oil, characterized in that: It includes a pre-treatment system for enzymatically hydrolyzing low-acid-value waste cooking oil into hydrolyzed fatty acids, and a solid acid catalytic system connected from the pre-treatment system for catalyzing the hydrolyzed fatty acids into fatty acid methyl esters through solid acid. The pretreatment system comprises a grease buffer tank (1), a hydrolase buffer tank (2), a pure water buffer tank (3), an enzyme hydrolysis tank (4) for grease hydrolysis reaction respectively connected from the grease buffer tank (1), the hydrolase buffer tank (2) and the pure water buffer tank (3), a spray dryer for drying product fatty acids and a three-phase separator (5) for separating the reaction mixture respectively connected from the enzyme hydrolysis tank (4), a residue pool (6) for collecting reaction residues, a grease tank (7) for collecting unreacted grease and a membrane separator (8) for oil-water separation respectively connected from the three-phase separator (5), and a clear phase collection tank (9) for collecting water enzyme liquid and a dense phase collection tank (10) for collecting glycerol respectively connected from the membrane separator (8); the spray dryer comprises a primary spray dryer (11) connected from the enzyme hydrolysis tank (4), and a secondary spray dryer (12) connected from the primary spray dryer (11); The solid acid catalytic system comprises a first static mixer (14) for mixing fatty acid and methanol, connected respectively from a secondary spray dryer (12) and a liquid methanol buffer tank (13), a first reaction tower (15) connected from the first static mixer (14), a liquid supercharger (16) for regulating the pressure of a primary reaction product, connected from the first reaction tower (15), a second raw material steam heater (17) for heating the primary reaction product, connected from the liquid supercharger (16), a second static mixer (18) for mixing the primary reaction product and methanol, connected respectively from the liquid methanol buffer tank (13) and the second raw material steam heater (17), and a second reaction tower (19) connected from the second static mixer (18); the first reaction tower (15) is connected to a methanol recovery section, and the second reaction tower (19) is connected to the liquid methanol buffer tank (13); A high-purity fatty acid delivery pipe (20) is provided between the first static mixer (14) and the secondary spray dryer (12), and a first raw material steam heater (21) for heating the high-purity fatty acid is provided on the high-purity fatty acid delivery pipe (20); a first liquid methanol delivery pipe (22) is provided between the first static mixer (14) and the liquid methanol buffer tank (13), and a first methanol steam heater (23) for preheating methanol is provided on the first liquid methanol delivery pipe (22); a second liquid methanol delivery pipe (24) is provided between the second static mixer (18) and the liquid methanol buffer tank (13), and a second methanol steam heater (25) for preheating methanol is provided on the second liquid methanol delivery pipe (24); The enzyme hydrolysis tank (4) comprises an enzyme hydrolysis tank body (41) and a circulation mechanism provided on the enzyme hydrolysis tank body (41) for circulating hydrolysis; the circulation mechanism comprises a circulating main liquid outlet (42) connected from the bottom of the enzyme hydrolysis tank body (41), and a first sub-circulation pipe (43) and a second sub-circulation pipe (44) respectively connected from the circulating main liquid outlet (42); the first sub-circulation pipe (43) is connected to the top of the enzyme hydrolysis tank body (41), and the second sub-circulation pipe (44) is connected to the middle of the enzyme hydrolysis tank body (41); a first liquid outlet valve (45) is provided on the circulating main liquid outlet (42), a first circulation pump (49) is provided on the first sub-circulation pipe (43), and a second circulation pump (410) is provided on the second sub-circulation pipe (44).

2. The system for large-scale production of biodiesel from low-acid-value waste cooking oil according to claim 1, characterized in that: A first circulation liquid inlet pipe (46), a second circulation liquid inlet pipe (47) and a third circulation liquid inlet pipe (48) are provided on the top of the enzyme hydrolysis tank (41) in the shape of a finished product. The first branch circulation pipeline (43) is connected to the first circulation liquid inlet pipe (46), the second circulation liquid inlet pipe (47) and the third circulation liquid inlet pipe (48) respectively. A first liquid inlet valve (411), a second liquid inlet valve (412) and a third liquid inlet valve (413) are provided on the first circulation liquid inlet pipe (46), the second circulation liquid inlet pipe (47) and the third circulation liquid inlet pipe (48) respectively. A fourth circulation liquid inlet pipe (414), a fifth circulation liquid inlet pipe (415) and a sixth circulation liquid inlet pipe (416) are provided in the middle of the enzymatic hydrolysis tank body (41); a second sub-circulation pipeline (44) is connected to the fourth circulation liquid inlet pipe (414), the fifth circulation liquid inlet pipe (415) and the sixth circulation liquid inlet pipe (416) respectively; the fourth circulation liquid inlet pipe (414), the fifth circulation liquid inlet pipe (415) and the sixth circulation liquid inlet pipe (416) are all tangentially distributed with the cylindrical shell of the enzymatic hydrolysis tank body (41); a fourth liquid inlet valve (417), a fifth liquid inlet valve (418) and a sixth liquid inlet valve (419) are provided on the fourth circulation liquid inlet pipe (414), the fifth circulation liquid inlet pipe (415) and the sixth circulation liquid inlet pipe (416) respectively; A circulating liquid outlet channel (420) is connected between the enzyme hydrolysis tank body (41) and the second sub-circulation pipeline (44). A first circulating liquid outlet pipe (421), a second circulating liquid outlet pipe (422) and a third circulating liquid outlet pipe (423) are provided at the lower part of the enzyme hydrolysis tank body (41). One end of the circulating liquid outlet channel (420) is connected to the first circulating liquid outlet pipe (421), the second circulating liquid outlet pipe (422) and the third circulating liquid outlet pipe (423), respectively, and the other end is connected to the second sub-circulation pipeline (44). The circulating liquid outlet channel (420) is connected to the first circulating liquid outlet pipe (421), the second circulating liquid outlet pipe (422) and the third circulating liquid outlet pipe (423). The access point of the two-way circulation pipeline (44) is located between the second circulation pump (410) and the main circulation liquid outlet (42). The first circulation liquid outlet pipe (421), the second circulation liquid outlet pipe (422) and the third circulation liquid outlet pipe (423) are all tangentially distributed with the cylindrical outer shell of the enzymatic hydrolysis tank (41). The first circulation liquid outlet pipe (421), the second circulation liquid outlet pipe (422) and the third circulation liquid outlet pipe (423) are respectively provided with a second liquid outlet valve (424), a third liquid outlet valve (425) and a fourth liquid outlet valve (426).

3. The system for large-scale production of biodiesel from low-acid value waste cooking oil according to claim 1, characterized in that: A grease inlet (427) is provided on the top of the enzymatic hydrolysis tank (41), and a first input valve (428) is provided on the grease inlet (427); a grease delivery pipe (26) is provided between the grease inlet (427) and the grease buffer tank (1), and a first delivery pump (27) and a first output valve (28) are provided on the grease delivery pipe (26); A hydrolase liquid inlet (429) is provided on the top of the enzyme hydrolysis tank body (41), and the hydrolase liquid inlet (429) is provided with a second input valve (430); a hydrolase delivery pipe (29) is provided between the hydrolase liquid inlet (429) and the hydrolase buffer tank (2), and the hydrolase delivery pipe (29) is provided with a second delivery pump (30) and a second output valve (31); a pure water delivery pipe (32) is provided between the hydrolase liquid inlet (429) and the pure water buffer tank (3), and the pure water delivery pipe (32) is provided with a third delivery pump (33) and a third output valve (34); The enzymatic hydrolysis tank (41) is provided with a propeller stirrer (431) for mixing oil and hydrolytic enzyme liquid, and the enzymatic hydrolysis tank (41) is provided with a sight glass (432). The enzymatic hydrolysis tank (41) is a double-layer structure, and a heating coil (433) for heating the internal material is uniformly distributed in the interlayer; the bottom of the enzymatic hydrolysis tank (41) is connected to the primary spray dryer (11) through a fatty acid delivery pipe (35) and is connected to the three-phase separator (5) through a reactant delivery pipe (36); the fatty acid delivery pipe (35) is provided with a fourth delivery pump (37) and a steam heater (38), and the reactant delivery pipe (36) is provided with a fifth delivery pump (39).

4. The system for large-scale production of biodiesel from low-acid value waste cooking oil according to claim 1, characterized in that: The pretreatment system further includes a vacuum pump (40), the top of the first-stage spray dryer (11) is connected to the vacuum pump (40) through a first exhaust pipe (50), the top of the second-stage spray dryer (12) is connected to the vacuum pump (40) through a second exhaust pipe (51), the first exhaust pipe (50) is provided with a first exhaust valve (52), and the second exhaust pipe (51) is provided with a second exhaust valve (53); The primary spray dryer (11) and the secondary spray dryer (12) have the same structure, and are both provided with an arc-shaped baffle (54) on the top of the inner part and a liquid level gauge (55) on the outer wall. A primary drying delivery pipe (56) is connected between the bottom of the primary spray dryer (11) and the top of the secondary spray dryer (12), and a sixth delivery pump (57) is provided on the primary drying delivery pipe (56), and a seventh delivery pump (58) is provided on the high-purity fatty acid delivery pipe (20).

5. The system for large-scale production of biodiesel from low-acid value waste cooking oil according to claim 1, characterized in that: The first reaction tower (15) and the second reaction tower (19) have the same structure, both comprising a reaction tower body (59) for mixing materials for reaction, a separation body (60) connected to the reaction tower body (59) and forming an integrated structure for separating slag water, and a drainage pipe (61) connected to the separation body (60). The reaction tower body (59) is provided with a drainage area (62) and a reaction area (63) that are interconnected from bottom to top. The separation body (60) is an inverted cone-shaped structure, the top surface of the inverted cone is connected to the reaction zone (63), and the bottom surface of the inverted cone is connected to the drainage pipe (61). The drainage pipe (61) is provided with an inverted U-shaped pipe section, the top of the inverted U-shaped pipe section is flush with the top surface of the separation body (60), and the outlet of the drainage pipe (61) is connected to the methanol purification section.

6. The system for large-scale production of biodiesel from low-acid value waste cooking oil according to claim 5, characterized in that: A solid acid catalyst (64) and a stirrer (65) for stirring the materials therein are provided in the reaction zone (63), wherein the stirrer (65) is a submersible push-flow type stirrer; The bottom of the reaction zone (63) is provided with a catalyst loading hole (66) for loading and unloading the solid acid catalyst (64), and a feed port (67) for inputting the mixed material. The feed port (67) is connected to the first static mixer (14) or the second static mixer (18) through a feed pipe (68); A feed distribution plate (69) is provided at the bottom of the reaction zone (63) and is connected to the feed port (67) and used for uniform feeding. The feed distribution plate (69) is evenly distributed with feed distribution holes (70); A first filter screen (71) and a second filter screen (72) are respectively provided at both ends of the reaction zone (63) for preventing the solid acid catalyst (64) from flowing out. The first filter screen (71) and the second filter screen (72) have the same structure, and their diameters are consistent with the inner diameter of the reaction zone (63). The filter pore diameters are smaller than the diameter of the solid acid catalyst (64).

7. The system for large-scale production of biodiesel from low-acid value waste cooking oil according to claim 5, characterized in that: A discharge port (73) for discharging the product is provided on the side wall of the liquid discharge area (62). The discharge port (73) of the first reaction tower (15) is connected to the liquid supercharger (16), and the discharge port (73) of the second reaction tower (19) is connected to the product collection section. A pressure regulating valve (74) for regulating the internal medium pressure, a safety valve (75) for protecting the system safety, and a methanol outlet (76) for methanol recovery are provided on the top of the drainage area (62). The methanol outlet (76) of the first reaction tower (15) is connected to the methanol recovery section, and the methanol outlet (76) of the second reaction tower (19) is connected to the liquid methanol buffer tank (13).

8. The method for producing biodiesel on a large scale using low-acid-value waste cooking oil according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step A: The low-acid-value catering waste oil in the oil buffer tank, the hydrolase in the hydrolase buffer tank, and the pure water in the pure water buffer tank are uniformly mixed in the enzyme hydrolysis tank, and then the oil hydrolysis reaction is carried out to generate product fatty acids, by-product glycerol and other mixtures. The reaction conditions are that the volume ratio of oil to water is 6:4, the mass of the hydrolase is 5% of the weight of the oil, the hydrolysis pressure is normal pressure, the hydrolysis temperature is 55°C, and the hydrolysis time is 48 hours; the by-product glycerol and other mixtures are transported and separated into a three-phase separator through a reactant transport pipe to separate the residue, remaining oil, and water-enzyme-glycerol mixture, wherein the residue is collected into a residue pool and the oil is collected into an oil tank; the water-enzyme-glycerol mixture enters a membrane separator, and is separated and filtered again to obtain by-product glycerol and a water-enzyme mixture, wherein the by-product glycerol is collected into a dense phase collection tank, and the water-enzyme mixture is collected into a clear phase collection tank; Step B: The fatty acid product in step A is transported to a primary spray dryer through a fatty acid delivery pipe for primary spray drying. During the transportation process, the fatty acid is pressurized to 0.4 MPa by a fourth delivery pump and preheated to 120° C. by a steam heater. After primary spray drying, a primary dried fatty acid product is obtained. The drying pressure in the primary spray dryer is -0.088 MPa and the drying temperature is 120° C.; Step C: The fatty acid primary drying product in step B enters a secondary spray dryer for secondary spray drying to obtain high-purity fatty acids at a drying pressure of -0.088 MPa and a drying temperature of 120°C; Step D: The high-purity fatty acid in step C is heated to 110-120° C. by a first raw material steam heater and then fully mixed with liquid methanol heated to 55° C. by a first methanol steam heater in a first static mixer to obtain a raw material mixture; Step E: The raw material mixture in step D enters the first reaction tower for the first catalytic reaction to obtain the primary reaction product. The catalytic conditions are normal pressure, 110°C, and the solid acid catalyst is sulfuric acid / titanium dioxide SO4. 2- / TiO2 catalyst; Step F: The primary reaction product in step E is adjusted to a slightly positive pressure by a liquid booster, heated to 110-120° C. by a second raw material steam heater, and then fully mixed with liquid methanol heated to 55° C. by a second methanol steam heater in a second static mixer to obtain a second mixture; Step G: The second mixture in step F enters the second reaction tower for a second catalytic reaction to obtain high-purity biodiesel. The catalytic conditions are normal pressure, 110°C, and the solid acid catalyst is sulfuric acid / titanium dioxide SO4. 2- / TiO2 catalyst.

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