A system and method for extending the service life of a concentrator membrane.

Abstract

This invention relates to a system and method for extending the service life of a concentration membrane. The system includes a feed tank, a concentrate tank, and at least two circulating membrane units. Concentration membranes are installed in each circulating membrane unit to concentrate the low-concentration feed solution flowing through the unit to obtain a high-concentration concentrate. A proportional control valve is installed on the return pipeline. A first pneumatic control valve is installed on the return pipeline between the feed tank's return port and the proportional control valve. A second pneumatic control valve is installed on the concentrate pipeline. An online refractometer is installed on the discharge pipeline. The online refractometer is interlocked with the control signals of the first and second pneumatic control valves, controlling their respective valve openings. This invention stabilizes the feed concentration by interlocking the feed concentration with the discharge destination, reducing the osmotic pressure of the concentration membrane, extending its service life, and reducing production costs.

Description

Technical Field

[0001] This invention belongs to the field of sugar alcohol preparation technology, and specifically relates to a system and method for extending the service life of a concentration membrane. Background Technology

[0002] Maltitol is a novel sweetener widely used in the processing of sweetened foods. The industrial production of crystalline maltitol primarily involves chromatographic purification, evaporation crystallization, and centrifugal drying. During chromatographic separation, in addition to the extract needed to produce crystalline maltitol, a large amount of low-refractive-index residue is generated. This low-refractive-index residue, when sold commercially, needs to be concentrated to a 70% concentration. Conventional concentration methods include falling film evaporation, MVR evaporation, or membrane concentration systems. Membrane concentration utilizes the sieving principle of a membrane; pressure forces water through the membrane, achieving enrichment and concentration.

[0003] For example, Chinese patent CN215782753U discloses a continuous-feed, online-cleaning membrane separation device. It switches the feed to the membrane stack using valves, controls the number of material separations, and controls the membrane stack for material separation or cleaning output. Pressure difference is used to determine if cleaning is needed, and valves automatically perform online top-feeding and cleaning of the membrane stack, ensuring that the top-feeding, cleaning, and separation operations between membrane stacks do not interfere with each other, achieving a continuous-feed, online-cleaning membrane separation process. Another example is Chinese patent CN217698704U, which discloses a continuous membrane concentration device for maltitol dilute solution. It uses a high-temperature resistant filter membrane and directly feeds the 70°C dilute maltitol solution generated in the previous process, eliminating the need for cooling. This allows for a one-time increase in maltitol concentration to 15-18%, simplifying the process and improving production efficiency. This illustrates that membrane concentration systems are a technology that reforms traditional processes to achieve efficient purification and concentration. Membrane concentration equipment utilizes the difference in molecular weight between the effective components and the liquid to achieve targeted separation, thus achieving concentration. Compared to traditional heating concentration, this method has advantages such as low energy consumption, operation at room temperature, and minimal impact on the product. However, the above equipment often encounters the following problems in actual production: 1) When abnormal feed concentration fluctuations occur in the previous process, it is often impossible to adjust in time, causing frequent pressure fluctuations in the membrane elements due to different refractive indices, affecting the service life of the equipment and membrane elements; 2) When the refractive index of the chromatographic residue in the previous process is low, only 0.5-1.0%, and the required refractive index of the output is 15-18%, the concentration factor is more than 15-20 times. This causes most of the permeate to permeate from the previous membrane module, while the subsequent membrane module operates at a low flow rate and high velocity. Especially when the operating temperature exceeds 65℃, the excessively high concentration factor will cause excessive membrane osmotic pressure drop, making the membrane prone to deformation and permeation problems, greatly reducing the service life of the membrane elements. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a system and method for extending the service life of a concentration membrane. By interlocking the feed concentration and the discharge destination of the concentration membrane, the feed concentration is stabilized, reducing the problem of high osmotic pressure drop that occurs during the concentration of materials with excessively low concentrations, and greatly extending the service life of the concentration membrane.

[0005] This invention provides a system for extending the lifespan of a concentrator membrane, comprising a feed tank, a concentrate tank, and at least two circulating membrane units. The feed tank stores low-concentration feed solutions. Concentrator membranes are installed in each circulating membrane unit to concentrate the low-concentration feed solutions flowing through the circulating membrane units to obtain high-concentration concentrates. The concentrate tank collects the high-concentration concentrates. The feed tank has an inlet for the low-concentration feed solution connected to a feed pipe, an outlet connected to an outlet pipe, and a return inlet connected to a return pipe. The concentrate tank has a concentrate inlet connected to a concentrate pipeline. Each circulating membrane unit has a membrane unit inlet connected to a membrane unit inlet pipeline and a concentrate outlet connected to a concentrate outlet pipeline. Connecting pipelines connect the membrane unit inlet pipeline and the concentrate outlet pipeline of each circulating membrane unit. The outlet pipeline is also connected to the membrane unit inlet pipeline of the foremost circulating membrane unit. The front end of the pipeline and connecting pipeline is connected, and the return pipeline is simultaneously connected to the rear end of the concentrate outlet pipeline and connecting pipeline of the last circulating membrane unit. A first pneumatic ball valve and a circulating pump are respectively installed on the membrane unit inlet pipeline, a second pneumatic ball valve is installed on the concentrate outlet pipeline, and a third pneumatic ball valve is installed on the connecting pipeline connecting the membrane unit inlet pipeline and the concentrate outlet pipeline of each circulating membrane unit. A proportional regulating valve is installed on the return pipeline. A first pneumatic regulating valve is installed on the return pipeline between the return port of the raw material tank and the proportional regulating valve. The front end of the concentrate pipeline is connected to the return pipeline located between the first pneumatic regulating valve and the proportional regulating valve. A second pneumatic regulating valve is installed on the concentrate pipeline. A high-pressure pump and an online refractometer are respectively installed on the outlet pipeline. The online refractometer is interlocked with the control signals of the first and second pneumatic regulating valves to control the valve opening of the first and second pneumatic regulating valves respectively.

[0006] Furthermore, the system also includes a dilute liquid tank. After the low-concentration feed liquid is concentrated by the concentrator membrane of the circulating membrane unit, permeate water is obtained. The dilute liquid tank is used to collect the permeate water. A dilute liquid inlet is provided on the dilute liquid tank and connected to the dilute liquid pipeline. A permeate water outlet is also provided on each circulating membrane unit and connected to the permeate water pipeline. The permeate water pipeline of each circulating membrane unit is connected to the dilute liquid pipeline respectively.

[0007] Furthermore, a pneumatic butterfly valve is installed on the dilute liquid pipeline.

[0008] Furthermore, a discharge pump is also installed on the discharge pipe.

[0009] Furthermore, a stirring device is installed inside the raw material tank.

[0010] This invention is implemented as follows, and also provides a method for extending the service life of a concentration membrane. This method uses the system for extending the service life of a concentration membrane as described above, and includes the following steps:

[0011] The parameters of the proportional control valve are set to correspond to the concentration range of the high-concentration feed solution, and the parameters of the online refractometer are set to correspond to the refractive range of the high-concentration feed solution. The high-pressure pump, as well as the first, second, and third pneumatic ball valves and the circulation pump corresponding to each circulating membrane unit, are turned on, and the system starts to operate. The low-concentration feed solution circulates continuously between the raw material tank, the circulating membrane unit, and the raw material tank through the connecting pipes. The low-concentration feed solution is continuously concentrated by the concentrator membrane of the circulating membrane unit, so that its concentration gradually increases to reach the set high concentration.

[0012] Initially, due to the low initial concentration of the low-concentration liquid, the online refractometer controls the first pneumatic regulating valve to be fully open, while the second pneumatic regulating valve is closed. When the online refractometer detects that the refraction of the liquid reaches the set value, it gradually reduces the opening of the first pneumatic regulating valve to maintain the refraction of the liquid, while gradually increasing the opening of the second pneumatic regulating valve to the normal discharge position. The parameters of the proportional regulating valve are adjusted to stabilize the concentration of the liquid within the set high concentration range.

[0013] Compared with existing technologies, the present invention provides a system and method for extending the service life of a concentrator membrane. The system includes a feed tank, a concentrate tank, and at least two circulating membrane units. The feed tank stores low-concentration feed solutions. Concentrator membranes are installed in each circulating membrane unit to concentrate the low-concentration feed solutions flowing through the circulating membrane units to obtain high-concentration concentrates. A proportional control valve is installed on the return pipeline. A first pneumatic control valve is installed on the return pipeline between the feed inlet of the feed tank and the proportional control valve. The front end of the concentrate pipeline is connected to the return pipeline located between the first pneumatic control valve and the proportional control valve. A second pneumatic control valve is installed on the concentrate pipeline. A high-pressure pump and an online refractive index detector are installed on the discharge pipeline. The online refractive index detector is interlocked with the control signals of the first and second pneumatic control valves, respectively controlling the valve openings of the first and second pneumatic control valves. This invention stabilizes the feed concentration by linking the feed concentration with the discharge destination, reduces the osmotic pressure of the concentration membrane, and extends the service life of the concentration membrane, thereby greatly reducing the subsequent membrane element investment cost and solving problems such as frequent membrane element replacement, unstable production operation, and high labor intensity for personnel during the production process. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a preferred embodiment of the system for extending the service life of the concentrator membrane according to the present invention;

[0015] Figure 2 This is a schematic diagram of the concentration system in Comparative Example 3. Detailed Implementation

[0016] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0017] Please refer to Figure 1 As shown in the figure, the arrows indicate the flow direction of materials in the system. A preferred embodiment of the system for extending the service life of the concentration membrane according to the present invention includes a raw material tank 1, a concentrate tank 2, a dilute liquid tank 3, and at least two circulating membrane modules 4. This embodiment provides three circulating membrane modules 4.

[0018] Raw material tank 1 is used to store low-concentration feed solution. Concentrating membranes (not shown in the figure) are installed in each circulating membrane group 4 to concentrate the low-concentration feed solution flowing through the circulating membrane group 4 to obtain a high-concentration concentrate. Concentrate tank 2 is used to collect the high-concentration concentrate. After the low-concentration feed solution is concentrated by the concentrating membranes in the circulating membrane group 4, permeate water is also obtained; dilute tank 3 is used to collect the permeate water.

[0019] The raw material tank 1 is equipped with an inlet for low-concentration feed solution, connected to the feed pipe 11; an outlet for low-concentration feed solution, connected to the outlet pipe 12; and a return outlet for low-concentration feed solution, connected to the return pipe 13. The concentrate tank 2 has a concentrate inlet connected to the concentrate pipe 21, and the dilute tank 3 has a dilute inlet connected to the dilute pipe 31. Each circulating membrane module 4 has a membrane module inlet connected to the membrane module feed pipe 41, a concentrate outlet connected to the concentrate outlet pipe 42, and a permeate outlet connected to the permeate pipe 43. The permeate pipe 43 of each circulating membrane module 4 is connected to the dilute pipe 31. Connecting pipes 5 connect the membrane module inlet pipe 41 and the concentrate outlet pipe 42 of each circulating membrane module 4 to each other.

[0020] The discharge pipe 12 is simultaneously connected to the front end of the membrane inlet pipe 41 and the connecting pipe 5 of the foremost circulating membrane module 4, and the return pipe 13 is simultaneously connected to the rear end of the concentrate outlet pipe 42 and the connecting pipe 5 of the last circulating membrane module 4. The three circulating membrane modules 4 are connected in series via the connecting pipe 5. A first pneumatic ball valve 44 and a circulating pump 45 are respectively installed on the membrane inlet pipe 41 of each circulating membrane module 4, a second pneumatic ball valve 46 is installed on the concentrate outlet pipe 42 of each circulating membrane module 4, and a third pneumatic ball valve 47 is installed on the connecting pipe 5 connecting the membrane inlet pipe 41 and the concentrate outlet pipe 42 of each circulating membrane module 4.

[0021] A proportional regulating valve 6 is installed on the return pipe 13, and a first pneumatic regulating valve 7 is installed on the return pipe 13 between the return port of the raw material tank 1 and the proportional regulating valve 6. The front end of the concentrate pipe 21 is connected to the return pipe 13 located between the first pneumatic regulating valve 7 and the proportional regulating valve 6, and a second pneumatic regulating valve 8 is installed on the concentrate pipe 21. A high-pressure pump 14 and an online refractive index detector 9 are respectively installed on the discharge pipe 12. The online refractive index detector 9 is interlocked with the control signals of the first pneumatic regulating valve 7 and the second pneumatic regulating valve 8, respectively controlling the valve opening of the first pneumatic regulating valve 7 and the second pneumatic regulating valve 8.

[0022] The concentration of the liquid in the return pipe 13 is adjusted by the pressure of the three circulating membrane modules 4, the frequency of the circulating pump 45, and the valve opening of the proportional control valve 6.

[0023] This invention utilizes multiple circulating membrane units 4 connected in series. By increasing the feed concentration of the next circulating membrane unit 4 through the previous circulating membrane unit 4, the concentration factor of a single circulating membrane unit 4 is reduced, the osmotic pressure drop of a single circulating membrane unit 4 is reduced, and the service life of the concentration membrane is extended.

[0024] Specifically, a pneumatic butterfly valve 32 is installed on the dilute liquid pipeline 31 to control the flow rate of the recycled permeate water.

[0025] A discharge pump 15 is also installed on the discharge pipe 12 to increase the discharge pressure of low-concentration liquid.

[0026] A stirring device 16 is installed inside the raw material tank 1.

[0027] The present invention also discloses a method for extending the service life of a concentrator membrane, the method using the system for extending the service life of a concentrator membrane as described above, the method comprising the following steps:

[0028] The parameters of the proportional control valve 6 are set to correspond to the concentration range of the high-concentration feed solution, and the parameters of the online refractometer 9 are set to correspond to the refractive range of the high-concentration feed solution. The high-pressure pump 14, and the first pneumatic ball valve 44, second pneumatic ball valve 46, third pneumatic ball valve 47, and circulation pump 45 corresponding to each circulating membrane module 4 are then activated, and the system begins operation. The low-concentration feed solution continuously circulates within the system between the raw material tank 1, the circulating membrane module 4, and the raw material tank 1 through connecting pipes. The low-concentration feed solution is continuously concentrated by the concentrator membrane of the circulating membrane module 4, gradually increasing its concentration to reach the set high concentration.

[0029] Initially, due to the low initial concentration of the low-concentration feed solution, the online refractive index detector 9 controls the first pneumatic regulating valve 7 to be fully open, while the second pneumatic regulating valve 8 remains closed. When the online refractive index detector 9 detects that the refractive index of the feed solution reaches the set value, it gradually reduces the opening of the first pneumatic regulating valve 7 to maintain the refractive index, while gradually increasing the opening of the second pneumatic regulating valve 8 to the normal discharge position. Adjusting the parameters of the proportional regulating valve 6 stabilizes the concentration of the feed solution within the set high concentration range.

[0030] The method for extending the service life of the concentration film according to the present invention is further illustrated below through specific embodiments.

[0031] Example 1

[0032] The first embodiment of the method for extending the service life of a concentrated membrane according to the present invention takes the production process of preparing multi-nutrient alcohols using maltitol chromatographic residue as an example. A low-concentration chromatographic residue is concentrated by the system to obtain a high-concentration chromatographic residue. The method includes the following steps:

[0033] Step 11: The chromatographic extract is filtered to remove impurities and then transferred to raw material tank 1. The initial concentration of the chromatographic extract is 1.0% (actual concentration may vary).

[0034] Step 12: Set the refractive index of the online refractive index detector 9 to 2.5%, and adjust the value of the proportional control valve to 7.2 according to the requirement of 18.0% discharge concentration.

[0035] Step 13: Turn on the discharge pump 15, the high-pressure pump 14, and the first pneumatic ball valve 44, the second pneumatic ball valve 46, the third pneumatic ball valve 47, and the circulation pump 45 corresponding to the three circulating membrane modules 4 respectively. The system starts to operate. Because the initial concentration of the chromatographic residue displayed by the online refractometer 9 is too low, the valve opening of the first pneumatic regulating valve 7 is fully open, while the valve opening of the second pneumatic regulating valve 8 is closed.

[0036] Step 14: When the refraction of the liquid reaches the set value of 2.5%, the opening of the first pneumatic regulating valve 7 is gradually reduced according to the refraction of the liquid to maintain the refraction of the liquid, while the opening of the second pneumatic regulating valve 8 is gradually increased to the normal discharge position. By adjusting the value of the proportional regulating valve 6, the discharge concentration is stabilized at 18.0-18.5%.

[0037] Example 2

[0038] A second embodiment of the method for extending the service life of a concentrated membrane according to the present invention takes the production process of preparing multi-nutrient alcohols using maltitol chromatographic residue as an example. The low-concentration chromatographic residue is concentrated by the system, and the method includes the following steps:

[0039] Step 21: The chromatographic extract is filtered to remove impurities and then transferred to raw material tank 1. The initial concentration of the chromatographic extract is 0.8% (the actual range may vary).

[0040] Step 22: Set the refractive index of the online refractive index detector 9 to 3.0%, and adjust the value of the proportional control valve to 6.0 according to the requirement of 18.0% discharge concentration.

[0041] Step 23: Turn on the discharge pump 15, the high-pressure pump 14, and the first pneumatic ball valve 44, the second pneumatic ball valve 46, the third pneumatic ball valve 47, and the circulation pump 45 corresponding to the three circulating membrane modules 4 respectively. The system starts to operate. Because the initial concentration of the chromatographic residue displayed by the online refractometer 9 is too low, the valve opening of the first pneumatic regulating valve 7 is fully open, while the valve opening of the second pneumatic regulating valve 8 is closed.

[0042] Step 24: When the refraction of the liquid reaches the set value of 3.0%, the opening of the first pneumatic regulating valve 7 is gradually reduced according to the refraction of the liquid to maintain the refraction of the liquid, while the opening of the second pneumatic regulating valve 8 is gradually increased to the normal discharge position. By adjusting the value of the proportional regulating valve 6, the discharge concentration is stabilized at 18.0-19.0%.

[0043] Comparative Example 3

[0044] The difference between the concentration system in this comparative example and that in Example 1 is that the concentration system in Comparative Example 3 does not include the concentrate pipeline 21, the first pneumatic regulating valve 7, and the second pneumatic regulating valve 8; all other settings are the same as in Example 1. Please refer to... Figure 2 As shown. This comparative example also uses the production process of preparing multi-nutrient alcohols using maltitol chromatographic residue as an example. The low-concentration chromatographic residue is concentrated by the system to obtain a high-concentration chromatographic residue. The method includes the following steps:

[0045] Step 31: The chromatographic extract is filtered to remove impurities and then transferred to raw material tank 1. The initial concentration of the chromatographic extract is 0.8-1.5%.

[0046] Step 32: Calculate and set the value of the proportional control valve 6 to 12-18 based on the requirement of 18.0% discharge concentration.

[0047] Step 33: Turn on the discharge pump 15, the high-pressure pump 14, and the first pneumatic ball valve 44, the second pneumatic ball valve 46, the third pneumatic ball valve 47, and the circulation pump 45 corresponding to the three circulating membrane modules 4 respectively. The system then begins operation. Because the refractive index of the chromatographic residue fluctuates, the value of the proportional control valve 6 needs to be continuously adjusted according to the discharge concentration to stabilize the discharge concentration within the range of 14.4% to 20.0%.

[0048] Table 1 is a compilation of the experimental data from Examples 1 and 2 and Comparative Example 3.

[0049] Table 1. Comparison of experimental data from Examples 1-2 and Comparative Example 3

[0050]

[0051] Therefore, it can be seen that Examples 1-2 and Comparative Example 3 using the method of the present invention all achieve the same concentration effect, but the differences are as follows: 1. The feed concentration of Examples 1-2 is more stable through internal adjustment, resulting in a more stable overall operation and pressure. In contrast, the operating pressure of Comparative Example 3 fluctuates significantly due to feed concentration fluctuations, which greatly impacts the stability of the overall equipment and the concentration membrane; 2. Examples 1-2 have a lower concentration ratio than Comparative Example 3. The fluctuation of feed concentration in Comparative Example 3 requires constant adjustments by personnel, greatly increasing the labor intensity; 3. The higher concentration ratio in Comparative Example 3 leads to excessive osmotic pressure of the concentration membrane, which can easily cause deformation and permeation problems, especially at high temperatures, greatly reducing the service life of the concentration membrane.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for extending the service life of a concentrator membrane, comprising a feed tank, a concentrate tank, and at least two circulating membrane units, wherein the feed tank is used to store low-concentration feed solutions, and the concentrator membranes are respectively installed in each circulating membrane unit to concentrate the low-concentration feed solutions flowing through the circulating membrane unit to obtain high-concentration concentrates, and the concentrate tanks are used to collect the high-concentration concentrates, characterized in that, The raw material tank is equipped with an inlet for low-concentration feed solution, connected to the feed pipe; an outlet for low-concentration feed solution, connected to the outlet pipe; and a return inlet for low-concentration feed solution, connected to the return pipe. The concentrate tank is equipped with a concentrate inlet connected to the concentrate pipeline. Each circulating membrane unit is equipped with a membrane unit inlet connected to the membrane unit feed pipeline and a concentrate outlet connected to the concentrate outlet pipeline. Connecting pipelines connect the membrane unit inlet pipeline and the concentrate outlet pipeline of each circulating membrane unit to each other. The discharge pipeline is simultaneously connected to the front end of the membrane unit inlet pipeline and the connecting pipeline of the foremost circulating membrane unit, and the return pipeline is simultaneously connected to the rear end of the concentrate outlet pipeline and the connecting pipeline of the last circulating membrane unit. A first... A pneumatic ball valve and a circulating pump are provided. A second pneumatic ball valve is installed on the concentrate outlet pipeline. A third pneumatic ball valve is installed on the connecting pipeline between the membrane inlet pipeline and the concentrate outlet pipeline of each circulating membrane unit. A proportional regulating valve is installed on the return pipeline. A first pneumatic regulating valve is installed on the return pipeline between the return port of the raw material tank and the proportional regulating valve. The front end of the concentrate pipeline is connected to the return pipeline located between the first pneumatic regulating valve and the proportional regulating valve. A second pneumatic regulating valve is installed on the concentrate pipeline. A high-pressure pump and an online refractometer are installed on the outlet pipeline. The online refractometer is interlocked with the control signals of the first and second pneumatic regulating valves to control the valve opening of the first and second pneumatic regulating valves respectively. The system also includes a dilute liquid tank. After the low-concentration feed liquid is concentrated by the concentrator membrane of the circulating membrane unit, permeate water is obtained. The dilute liquid tank is used to collect the permeate water. A dilute liquid inlet is provided on the dilute liquid tank and connected to the dilute liquid pipeline. A permeate water outlet is also provided on each circulating membrane unit and connected to the permeate water pipeline. The permeate water pipeline of each circulating membrane unit is connected to the dilute liquid pipeline.

2. The system for extending the service life of a concentrator membrane as described in claim 1, characterized in that, A pneumatic butterfly valve is installed on the dilute liquid pipeline.

3. The system for extending the service life of a concentrator membrane as described in claim 1, characterized in that, A discharge pump is also installed on the discharge pipe.

4. The system for extending the service life of a concentrator membrane as described in claim 1, characterized in that, A stirring device is installed inside the raw material tank.

5. A method for extending the service life of a concentrator membrane, characterized in that, This method uses the system for extending the lifespan of a concentrator membrane as described in any one of claims 1 to 4, the method comprising the following steps: The parameters of the proportional control valve are set to correspond to the concentration range of the high-concentration feed solution, and the parameters of the online refractometer are set to correspond to the refractive range of the high-concentration feed solution. The high-pressure pump, as well as the first, second, and third pneumatic ball valves and the circulation pump corresponding to each circulating membrane unit, are turned on, and the system starts to operate. The low-concentration feed solution circulates continuously between the raw material tank, the circulating membrane unit, and the raw material tank through the connecting pipes. The low-concentration feed solution is continuously concentrated by the concentrator membrane of the circulating membrane unit, so that its concentration gradually increases to reach the set high concentration. Initially, due to the low initial concentration of the low-concentration liquid, the online refractometer controls the first pneumatic regulating valve to be fully open, while the second pneumatic regulating valve is closed. When the online refractometer detects that the refraction of the liquid reaches the set value, it gradually reduces the opening of the first pneumatic regulating valve to maintain the refraction of the liquid, while gradually increasing the opening of the second pneumatic regulating valve to the normal discharge position. The parameters of the proportional regulating valve are adjusted to stabilize the concentration of the liquid within the set high concentration range.

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