Low-pressure high-power concentration device and concentration method for plant extract

Abstract

The invention belongs to the field of plant extracting solution concentration, and discloses a low-pressure high-power concentration device for a plant extracting solution and a concentration method using the low-pressure high-power concentration device. The device is based on a series reverse osmosis membrane stack and a feeding pump, a fresh water collecting tank, a booster pump, three types of pressure sensors, two types of osmometers, a water inlet pressure control system and a one-way valve are additionally arranged, the three types of pressure sensors are used for detecting the pressure of a feeding header pipe, the pressure of concentrated water and the pressure of a fresh water header pipe respectively, and the two types of osmometers are used for detecting the osmotic pressure of the feeding header pipe and the osmotic pressure of the concentrated water respectively. The water inlet pressure control system adjusts the design pressure of the device and the osmotic pressure of the plant extracting solution by adjusting the frequencies of the booster pump and the feeding pump, so that accurate monitoring of parameters is realized, efficient concentration of the plant extracting solution under low pressure is guaranteed, scaling on the surface of a reverse osmosis membrane is delayed, the service life of a membrane stack is prolonged, and continuous production of membrane concentration and filtration is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of plant extract concentration, in particular to a device for concentrating plant extract using reverse osmosis membrane and a method for concentrating using the device. BACKGROUND

[0002] Reverse osmosis is a membrane separation operation that separates solvent from solution driven by pressure difference. The principle of reverse osmosis is that when a semi-permeable membrane is used to separate two solutions with different concentrations, solvent molecules will spontaneously diffuse from the low concentration side to the high concentration side until the chemical potential on both sides reaches equilibrium. However, in reverse osmosis, a pressure greater than the osmotic pressure is applied to the high concentration side to make the solvent molecules flow in the opposite direction, from the high concentration side to the low concentration side. In the reverse osmosis process, raw water (solution containing solutes) is pumped by a pressure pump to the reverse osmosis membrane module. Under the action of pressure, water molecules permeate through the reverse osmosis membrane to become purified water; while the solutes such as salts, organic matter and microorganisms in the water are retained on the other side of the membrane and discharged with the concentrated water.

[0003] The application of reverse osmosis technology in plant extract concentration is mainly through the reverse osmosis membrane, which can remove water from the extract at room temperature, concentrate the effective components such as flavonoids, polysaccharides and alkaloids, and improve their content and purity.

[0004] The reverse osmosis membrane has the characteristics of high rejection rate, which can effectively remove inorganic salts, small molecular organic matter, microorganisms and other impurities in plant extract, improve the quality and stability of the extract, which is of great significance for subsequent preparation and application, and avoids the loss and denaturation of effective components caused by traditional concentration methods (such as heating evaporation), better preserving the biological activity of plant extract.

[0005] The concentration of natural plant extract usually adopts evaporation concentration and reverse osmosis membrane concentration. In recent ten years, some enterprises in China have applied reverse osmosis membrane concentration technology to concentrate natural plant extract. However, due to the complex composition of natural plants, containing polysaccharides, pectin, starch protein, lipid and other high molecular substances, it is easy to cause pollution and blockage of reverse osmosis membrane elements during the concentration process, resulting in membrane pollution, membrane flux decline, operation pressure rise and concentration efficiency reduction. In addition, in order to realize the reverse osmosis process, high pressure is required, which requires the provision of high pressure pump and other equipment, increasing the equipment investment and operation cost, and the high pressure operation also has certain safety risk, the concentration process is not easy to control, and the maintenance and management of the equipment need to be strengthened. Therefore, the application of reverse osmosis membrane concentration technology has the disadvantages of low concentration multiple, low final product concentration and short continuous production cycle. The low pressure high multiple membrane concentration technology currently used for plant extract concentration greatly improves the concentration multiple of plant extract and reduces the operating cost of enterprises.

[0006] Generally, the plant extract liquid is concentrated by using reverse osmosis membrane, and the reverse osmosis membrane stacks are connected in series to improve the concentration effect. During the concentration process, impurities such as polysaccharides, fructose, microorganisms and minerals will adhere to the surface of the reverse osmosis membrane, resulting in membrane pollution. The membrane pollution will cause the local osmotic pressure of the membrane surface to abnormally increase and the water production to decrease, thereby affecting the concentration effect. The conventional method for solving the membrane pollution is to monitor the total dissolved solids of the plant extract liquid, the pressure difference before and after the membrane, the recovery rate or the water production, etc. When the monitoring values are found to be abnormal, the membrane surface is cleaned manually or automatically by using flushing water. The membrane surface can also be cleaned regularly.

[0007] However, no matter which cleaning method is used, the filtration operation needs to be paused, so that the concentration filtration process cannot be continuously performed. The introduction of flushing water for cleaning may cause secondary pollution of the membrane. If the filtration operation is not paused, the water inlet pressure needs to be increased to be higher than the osmotic pressure at that time, so that the filtration process can be effectively performed. In this way, the energy consumption is increased, and the high pressure is more likely to cause the pollutants to gather on the membrane surface to form a filter cake layer, thereby blocking the membrane holes. Another negative effect of cleaning the membrane surface in the intermittent mode is that the "high concentration concentration mode" is switched back immediately after the cleaning, especially for the plant extract liquid with high viscosity. The instantaneous high concentration difference on the membrane surface causes the osmotic pressure to fluctuate for a short time, thereby interfering with the stable operation of the system. SUMMARY

[0008] To solve the above problems, the present application provides a low-pressure high-concentration plant extract liquid concentration device and a concentration method. The device can detect the osmotic pressure of the plant extract liquid in real time, and use the osmotic pressure as a reference variable. The osmotic pressure of the plant extract liquid is adjusted by diluting the water inlet with the dilute water after concentration, and the water inlet pressure is slightly higher than the design pressure of the device according to the change of the osmotic pressure. Finally, the device concentrates and filters the plant extract liquid under a relatively low pressure.

[0009] To achieve the above object, the technical scheme of the present application is as follows: The low-pressure high-concentration plant extract concentration device comprises a reverse osmosis membrane stack, a feed pump, a booster pump, a fresh water collection tank, and a water inlet pressure control system. The reverse osmosis membrane stack is connected in series. The reverse osmosis membrane stack uses a low-pressure high-concentration reverse osmosis membrane. The fresh water outlet of the reverse osmosis membrane stack is connected to a fresh water branch pipe. Each fresh water branch pipe is connected to a fresh water main pipe. The fresh water main pipe is connected to the inlet of the fresh water collection tank. The outlet of the fresh water collection tank is connected to the inlet of the booster pump. The outlet of the booster pump is connected to the inlet of the feed pump. The low-pressure high-concentration plant extract concentration device further comprises an inlet pressure sensor located on the first group of reverse osmosis membrane stack water inlet pipes after the feed pump, a water inlet osmotic pressure instrument located on the first group of reverse osmosis membrane stack water inlet pipes, a concentrated water osmotic pressure instrument located on the last group of reverse osmosis membrane stack concentrated water pipes, a concentrated water pressure sensor located on the last group of reverse osmosis membrane stack concentrated water pipes, and a fresh water pressure sensor located on the fresh water main pipe. The booster pump and the feed pump are variable frequency pumps with adjustable power frequency. The first group of reverse osmosis membrane stack uses a high desalination rate reverse osmosis membrane.

[0010] The inlet pressure sensor is used to detect the water inlet pressure of the device. The osmotic pressure instrument is used to detect the water inlet osmotic pressure of the first group of reverse osmosis membrane stack and the concentrated water osmotic pressure of the last group of reverse osmosis membrane stack. The concentrated water pressure sensor is used to detect the water outlet pressure of the device. The fresh water pressure sensor is used to detect the fresh water side pressure of the reverse osmosis membrane.

[0011] Further, the outlet of the booster pump is provided with a one-way valve.

[0012] Further, the number of reverse osmosis membrane stacks connected in series is 2 to 5 groups.

[0013] The method for concentrating using the low-pressure high-concentration plant extract concentration device comprises the following steps: The water inlet pressure control system starts the feed pump to begin concentration filtration. The water inlet pressure control system controls the value range of the water inlet pressure P by adjusting the frequency of the booster pump, so that the water inlet pressure P is greater than or equal to the design pressure P f and less than or equal to P f +0.2.

[0014] The design pressure P f is calculated by the following formula: wherein, P f represents the design pressure; APF is the average water flux of the low-pressure high-concentration plant extract concentration device; SPF represents the characteristic water flux of the reverse osmosis membrane, which is a fixed parameter related to the reverse osmosis itself; P0 represents the average osmotic pressure of the water inlet and the concentrated water. In the present application, the water inlet control system collects the data of the water inlet osmotic pressure and the concentrated water osmotic pressure, and the result obtained by the arithmetic average operation of the water inlet osmotic pressure and the concentrated water osmotic pressure is the average osmotic pressure of the water inlet and the concentrated water, that is, the arithmetic average of the water inlet osmotic pressure and the concentrated water osmotic pressure is the average osmotic pressure of the water inlet and the concentrated water; P dThe import and export pressure difference of the low-pressure high-concentration device, which is obtained by subtracting the value detected by the concentrated water pressure sensor from the value detected by the water inlet pressure sensor; P p The fresh water pressure on the fresh water main.

[0015] When the water inlet pressure P value of the low-pressure high-concentration device is less than the design pressure P f , the water inlet pressure control system starts the booster pump and increases the power frequency until the water inlet pressure P reaches the above control range.

[0016] After starting the booster pump, when the water inlet pressure P value of the low-pressure high-concentration device is greater than the design pressure P f +0.2, the water inlet pressure control system reduces the booster pump power frequency until the water inlet pressure P reaches the above control range.

[0017] Further, the water inlet pressure control system can also adjust the water inlet pressure P by cooperating the feed pump and the booster pump, specifically as follows: The water inlet pressure control system collects the data of the water inlet pressure, the water inlet osmotic pressure, the concentrated water osmotic pressure, and the device import and export pressure, compares the water inlet pressure at this time with the control range of the design pressure calculated, and when the water inlet pressure P exceeds the control range, if the booster pump has been started, the water inlet pressure control system reduces the frequency of the booster pump; when the frequency of the booster pump is reduced to 0 and still exceeds the control range, the frequency of the feed pump is reduced until the water inlet pressure P returns to the control range; if the booster pump has not been started, the water inlet pressure control system reduces the frequency of the feed pump until the water inlet pressure P reaches the control range.

[0018] The water inlet pressure control system collects the data of the water inlet pressure, the water inlet osmotic pressure, the concentrated water osmotic pressure, and the device import and export pressure, compares the water inlet pressure at this time with the control range of the design pressure calculated, and when the water inlet pressure P is lower than the control range, the water inlet pressure control system increases the frequency of the booster pump; when the frequency of the booster pump reaches the highest and still is lower than the control range, the frequency of the feed pump is increased until the water inlet pressure P returns to the control range. Specifically, the frequency adjustment range of the booster pump and the feed pump is 1 Hz each time, that is, the frequency of the booster pump is increased by 1 Hz each time, or the frequency of the feed pump is increased by 1 Hz each time, or the frequency of the booster pump is reduced by 1 Hz each time, or the frequency of the feed pump is reduced by 1 Hz each time, to prevent flow fluctuation from causing osmotic pressure to change greatly.

[0019] Specifically, the water inlet pressure control system collects data and adjusts the water inlet every 15 minutes, and the system can be set to collect data every 15 minutes, every 40 minutes, or every 60 minutes.

[0020] As another technical solution of the application, the power frequency of the booster pump is not adjustable, and a pressure regulating valve is arranged at the outlet of the booster pump.

[0021] The method for concentrating using another technical solution comprises the following steps: Different from the first technical solution, when the water inlet pressure P of the low-pressure high-multiple concentration device is less than the design pressure P f , the water inlet pressure control system starts the booster pump and opens the pressure regulating valve until the water inlet pressure P reaches the control range; After starting the booster pump, when the water inlet pressure P of the low-pressure high-multiple concentration device is greater than the design pressure P f +0.2, the water inlet pressure control system closes the pressure regulating valve until the water inlet pressure P reaches the control range.

[0022] In summary, the beneficial technical effects of the present application are: Because the osmotic pressure on both sides of the reverse osmosis membrane for concentrating and filtering plant extract liquid is large, a relatively high operating driving pressure is required. The water inlet pressure control system collects the osmotic pressure of the first group of reverse osmosis membrane stacks, the osmotic pressure of the concentrated water of the last group of reverse osmosis membrane stacks, the pressure difference between the inlet and outlet of the device, and the fresh water pressure on the fresh water main as parameters to calculate the design pressure. The fresh water separated by the reverse osmosis membrane is sent to the inlet of the feed pump by the booster pump in a small amount, which slightly dilutes the concentration of the plant extract liquid, reduces the osmotic pressure of the plant extract liquid and the design pressure of the device, thereby ensuring that the water inlet pressure is slightly higher than the design pressure, the water inlet pressure is within a reasonable range, the water inlet pressure is not too high, and the energy consumption is saved. It also avoids the problem that high pressure causes impurities to accumulate on the surface of the membrane, affecting the service life of the membrane stack. At the same time, it avoids the problem that insufficient water inlet pressure leads to poor concentration effect of the plant extract liquid.

[0023] By slowly adjusting the frequency of the booster pump and the feed pump in a small range, the flow rate of the fresh water into the inlet of the feed pump and the water inlet pressure of the reverse osmosis membrane stack can be fine-tuned, avoiding the disadvantages of stopping the concentration and filtration operation when using intermittent cleaning of the membrane surface, so that the device can be continuously produced. It also avoids the problem that using intermittent cleaning of the membrane surface causes local concentration to be extremely poor on the surface of the membrane. The water inlet pressure control system adjusts the design pressure and the water inlet pressure of the device according to the collected real-time data, which is more reliable and accurate than the method of regularly cleaning the membrane surface.

[0024] The fresh water separated by the reverse osmosis membrane is boosted and returned to the reverse osmosis membrane stack, which plays a role in flushing and cleaning the reverse osmosis membrane, prolonging the service period and service life of the reverse osmosis membrane.

[0025] The water inlet pressure control system uses an osmometer to measure the osmotic pressure of the water inlet and the concentrated water, and the measurement result is more accurate than using salt concentration to calculate the osmotic pressure. The water inlet pressure is determined based on this measurement result, and the water inlet pressure can be accurately adjusted. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1The process flow chart of the low-pressure high-concentration plant extract device with a variable-frequency booster pump; Figure 2 The process flow chart of the low-pressure high-concentration plant extract device with a pressure regulating valve.

[0027] Wherein, the numbers are respectively: 1. Reverse osmosis membrane stack; 2. Fresh water collection tank; 3. Feed pump; 4. Booster pump; 5. Inlet pressure sensor; 6. Water inlet osmotic pressure instrument; 7. Concentrated water osmotic pressure instrument; 8. Fresh water pressure sensor; 9. Concentrated water pressure sensor; 10. Pressure regulating valve; 11. Check valve. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments.

[0029] Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0030] Embodiment 1

[0031] Referring to Figure 1 , the embodiment provides a low-pressure high-concentration plant extract device.

[0032] In the embodiment, tea leaves are immersed in hot water at 80℃ for 2 hours, and the obtained mixture is filtered through a ceramic membrane to remove tea residue and gum. The tea extract is cooled to room temperature and used as a raw material for concentration. The booster pump (4) and the feed pump (3) are variable-frequency booster pumps.

[0033] The feed pump (3) is started to deliver the pretreated tea extract to the low-pressure high-concentration device composed of 5 groups of reverse osmosis membrane stacks (1) in series.

[0034] The extract flows through the 5 groups of reverse osmosis membrane stacks (1) in series, and the fresh water produced under the action of membrane separation is collected to the fresh water main through the fresh water branch pipe of each membrane stack, and then enters the fresh water collection tank (2) for temporary storage.

[0035] After the fresh water is collected in the fresh water collecting tank (2), the water inlet pressure control system controls the start and stop of the booster pump (4) according to whether the measured water inlet pressure is within the system set water inlet pressure control range, the fresh water in the fresh water collecting tank (2) is pressurized, and then is delivered to the inlet of the feed pump (3) through the one-way valve (11) to mix with the newly entered tea extract liquid, and the mixed liquid enters the first group of reverse osmosis membrane stacks (1) again for cyclic concentration. The inlet pressure sensor (5), the osmotic pressure instrument (6) on the water inlet pipe of the first group of membrane stacks, the osmotic pressure instrument (7) on the concentrated water pipe of the fifth group of membrane stacks, the concentrated water pressure sensor (9) on the concentrated water pipe of the fifth group of membrane stacks and the fresh water pressure sensor (8) on the fresh water main pipe of the fifth group of membrane stacks collect real-time data, and the water inlet pressure control system calculates the design pressure P according to the data according to the formula P = P0 - P0 - P0 + SPF - APF f .

[0036] Specifically, the sensor detects that the average osmotic pressure P0 of the water inlet and the concentrated water is 0.6 MPa, the system inlet and outlet pressure drop P d is 0.2 MPa, the fresh water pressure P p on the fresh water main pipe is 0.1 MPa, the single group of membrane stacks characteristic water flux SPF is equal to 0.018 m³ / (m²·h·Mpa), the design average water flux APF is equal to 0.0252 m³ / (m²·h), the net driving pressure is equal to 1.4 Mpa, and the design pressure P f is 2.3 MPa. At the beginning of operation, the water inlet pressure control system controls the water inlet pressure to be within the range of 2.3-2.5 MPa, and the water inlet pressure control system maintains the water inlet pressure at 2.4 MPa.

[0037] When the water inlet pressure exceeds the range, the water inlet pressure control system reduces the frequency of the booster pump (4); when the frequency of the booster pump (4) is reduced to 0 and still exceeds the control range, the frequency of the feed pump (3) is reduced until the water inlet pressure returns to the control range.

[0038] When the water inlet pressure is lower than the range, the water inlet pressure control system increases the frequency of the booster pump (4); when the frequency of the booster pump (4) reaches the highest and is still lower than the control range, the frequency of the feed pump (3) is increased until the water inlet pressure returns to the control range.

[0039] After 3 hours of continuous operation, the feed pump (3) and the booster pump (4) are stopped, the concentration multiple reaches 5 times, the fresh water recovery rate is 78%, and the concentration process is completed.

[0040] Example 2

[0041] As another technical solution of the application, different from example 1, the frequency of the power supply of the booster pump (4) is not adjustable, and a pressure regulating valve (10) is arranged at the outlet of the booster pump (4).

[0042] Comparative Example 1 In this comparative example, the same tea extract solution as in the example was used, cooled to room temperature, and 5 sets of the same type of membrane stack as in Example 1 were used in series, without a booster pump and fresh water return line, and the fresh water was directly discharged into a collection tank. The device inlet water pressure was maintained at 2.4 MPa, and the operation was continued for 3 hours, with a concentration factor of 4.4 times and a fresh water recovery rate of 72%.

[0043] Comparative Example 2 In this comparative example, the same tea extract solution as in the example was used, cooled to room temperature, and 5 sets of the same type of membrane stack as in Example 1 were used in series, without a booster pump and fresh water return line, and the fresh water was directly discharged into a collection tank.

[0044] The device inlet water pressure was raised to 4.0 MPa, and the operation was continued for 3 hours, with the inlet water pressure being directly controlled by the feed pump. After 3 hours of operation, the fifth set of membrane stack had an inlet water osmotic pressure P0 equal to 0.8 MPa, the system inlet and outlet pressure difference P d was equal to 0.6 MPa, the concentrated water pressure was 3.4 MPa, and the fresh water main pressure P p was equal to 0.12 MPa.

[0045] After 3 hours of operation, the concentration factor was 4.8 times, close to the effect of the example.

Claims

1. A low pressure high concentration plant extract device comprising a stack of reverse osmosis membranes and a feed pump, said stack of reverse osmosis membranes being connected in series, characterized in that, Also comprising: a fresh water collection tank, a fresh water outlet of the reverse osmosis membrane stack is connected to a fresh water branch pipe, each of the fresh water branch pipes is connected to a fresh water main pipe, the fresh water main pipe is connected to an inlet of the fresh water collection tank, the fresh water collection tank is used to collect fresh water filtered by the reverse osmosis membrane stack; a booster pump, an outlet of the fresh water collection tank is connected to an inlet of the booster pump, an outlet of the booster pump is connected to an inlet of the feed pump, the booster pump is a variable frequency pump, the booster pump is used to deliver fresh water in the fresh water collection tank to the inlet of the feed pump; an inlet pressure sensor, located on a water inlet pipe of the first group of reverse osmosis membrane stacks after the feed pump, the inlet pressure sensor is used to detect the pressure of the plant extract water inlet; a concentrated water pressure sensor, located on a concentrated water pipe of the last group of reverse osmosis membrane stacks, the concentrated water pressure sensor is used to detect the pressure of the concentrated water obtained by concentrating and filtering the plant extract water inlet through the last group of reverse osmosis membrane stacks; a fresh water pressure sensor, located on the fresh water main pipe, the fresh water pressure sensor is used to detect the pressure of the fresh water obtained by filtering the plant extract water inlet through each reverse osmosis membrane stack; an inlet osmotic pressure instrument, located on the water inlet pipe of the first group of reverse osmosis membrane stacks, the inlet osmotic pressure instrument is used to detect the osmotic pressure of the plant extract water inlet; a concentrated water osmotic pressure instrument, located on the concentrated water pipe of the last group of reverse osmosis membrane stacks, the concentrated water osmotic pressure instrument is used to detect the osmotic pressure of the concentrated water obtained by concentrating and filtering the plant extract water inlet through each reverse osmosis membrane stack; a water inlet pressure control system, the water inlet pressure control system is used to control the booster pump to deliver fresh water to the inlet of the feed pump; a one-way valve, provided at the outlet of the booster pump.

2. A method of concentrating using the low pressure high concentration device of claim 1, characterized in that, The water inlet pressure control system adjusts the control range of the water inlet pressure P to be greater than or equal to the design pressure P f , and less than or equal to P f +0.2; Design pressure P f Calculated by the following equation: ； where P f represents the design pressure, APF is the design average water flux of the low pressure high multiple concentration device, SPF represents the characteristic water flux of the permeation membrane, P0 represents the arithmetic mean of the permeation pressure of the inlet water and the permeation pressure of the concentrated water, P d represents the pressure difference between the inlet and outlet of the low pressure high multiple concentration device, P p represents the fresh water pressure on the fresh water main.

3. The method of concentrating using a low-pressure high-concentration device according to claim 2, wherein When the water inlet pressure P is less than the design pressure P f If the booster pump is not started, the water inlet pressure control system starts the booster pump and increases the power frequency until the water inlet pressure P reaches the control range. If the booster pump frequency reaches the maximum value and the water pressure P is still less than the design pressure P f , then increase the feed pump frequency until the water pressure P reaches the control range.

4. The method of concentrating using a low-pressure high-concentration device according to claim 2, wherein When the water inlet pressure P is greater than the design pressure P f +0.2, if the booster pump has started, the water inlet pressure control system reduces the booster pump frequency until the water inlet pressure P reaches the control range. If the booster pump frequency is reduced to 0 and the water inlet pressure P is still greater than the design pressure P + 0.2, the water inlet pressure control system reduces the feed pump frequency until the water inlet pressure P reaches the control range. f + 0.2, the water inlet pressure control system reduces the feed pump frequency until the water inlet pressure P reaches the control range. If the booster pump is not started, the water inlet pressure control system reduces the frequency of the feed pump until the inlet water pressure P reaches the control range.

5. The method of concentrating using a low-pressure high-concentration device according to claim 3 or 4, wherein the water inlet pressure control system collects data and adjusts at least every 15 minutes.

6. The method of concentrating using a low-pressure high-concentration device according to claim 5, wherein the frequency adjustment range of the booster pump is 1 Hz each time.

7. The method of concentrating using a low-pressure high-concentration device according to claim 6, wherein the frequency adjustment range of the feed pump is 1 Hz each time.

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