An on-line cleaning system and method for small diameter heat exchangers

Abstract

The present application relates to heat exchanger cleaning technical field, disclose a kind of for small pipe diameter heat exchanger's on-line cleaning system and method, including storage tank, circulating pump, pulse air inlet device, gas-liquid-solid separation device, differential pressure and temperature detection unit and controller.Circulating pump is delivered to heat exchanger, pulse air inlet device is periodically injected compressed gas by pulse control valve, forms gas-liquid-solid three-phase mixed fluid to mechanically scour heat exchange tube inner wall.Separation device carries out physical separation to effluent, and solid particles return storage tank and are recycled.Use.Collect data by detection unit, and controller is combined with real-time differential pressure and temperature difference determination scale phenomenon, and the opening and closing frequency of pulse control valve is adjusted in section.The present application utilizes three-phase mixed fluid to effectively improve the descaling effect of small pipe diameter heat exchanger, realizes particle on-line closed loop recycling to reduce consumable cost, and dynamically adjusts pulse intensity to reduce overall energy consumption of system.

Description

Technical Field

[0001] This invention relates to the field of heat exchanger cleaning technology, specifically to an online cleaning system and method for small-diameter heat exchangers. Background Technology

[0002] Heat exchangers are devices used in industrial production to transfer heat. Small-diameter heat exchangers are used in many processes because they have a high heat transfer area-to-volume ratio. Online cleaning systems are auxiliary equipment that work in conjunction with the operation of heat exchangers. They can remove dirt from the inside of heat exchange tubes without shutting down the system, thus ensuring the heat transfer performance of the heat exchanger.

[0003] The existing online cleaning process for heat exchangers mainly relies on the flow of the cleaning medium inside the heat exchange tubes. The fluid pumping equipment sends the liquid containing solid particles into the heat exchanger. When the cleaning medium flows through the heat exchange tubes, it uses the shear force of the fluid itself and the physical impact and friction of the solid particles on the tube wall to peel off the scale layer attached to the tube wall. The fluid mixed with the peeled dirt then flows out of the heat exchanger and enters the separation and recovery equipment to complete the solid-liquid component screening and circulation.

[0004] In actual operation, the existing technology has limited ability to generate disturbances in narrow pipes due to the single liquid-solid two-phase fluid. Solid particles cannot obtain sufficient mechanical energy to break up the dense scale layer, resulting in insufficient descaling capacity. At the same time, the existing separation and recovery devices lack a sound anti-clogging design, and the separated solid materials are prone to accumulate at the bottom of the equipment, causing pipeline blockage, increasing the cost of consumable replenishment and disrupting the online closed-loop operation of the system. In addition, the existing control devices lack a feedback adjustment mechanism for the actual resistance of the heat exchange tubes and the scaling status. The drive components are always in a set high-frequency operating state during cleaning. The fixed operating mode not only causes a large consumption of overall energy, but also accelerates the wear of the moving parts of the equipment.

[0005] Therefore, the purpose of this invention is to provide an online cleaning system and method for small-diameter heat exchangers to overcome the shortcomings of the prior art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an online cleaning system and method for small-diameter heat exchangers, solving the problems of insufficient descaling capacity, easy accumulation and blockage during separation and recovery, and high energy consumption due to lack of feedback regulation in existing online cleaning systems for small-diameter heat exchangers.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides an online cleaning system for small-diameter heat exchangers, comprising: Storage tanks; The circulation pump has its inlet connected to the outlet of the storage tank and its outlet connected to the inlet of the heat exchanger. It is used to transport the cleaning medium inside the storage tank to the inlet of the heat exchanger. The pulse air intake device includes a pulse control valve for injecting compressed gas into the heat exchanger through the periodic opening and closing frequency of the pulse control valve, so that the compressed gas and the cleaning medium form a gas-liquid-solid three-phase mixed fluid. A gas-liquid-solid separation device is used to receive and separate a three-phase mixture of gas, liquid, and solid fluid flowing out of the outlet of a heat exchanger. The differential pressure detection unit and the temperature detection unit are used to collect fluid pressure data and temperature data at the inlet and outlet of the heat exchanger, respectively, and send them to the controller. The controller adjusts the opening and closing frequency of the pulse control valve in segments based on fluid pressure and temperature data.

[0008] This invention combines mechanical scouring for physical descaling with dynamic adaptive control. It uses a pulse air intake device to inject compressed gas into a cleaning medium containing solid particles, forming a gas-liquid-solid three-phase mixed fluid inside the heat exchange tube. The gas rises and expands, generating fluid disturbance, which drives the solid particles to physically impact and scour the inner wall of the heat exchange tube.

[0009] Simultaneously, the pressure drop and temperature difference data of the fluid are acquired in real time through the differential pressure detection unit and the temperature detection unit, so as to reflect the reduction of the flow cross-sectional area in the pipe and the state of fouling thermal resistance. The controller determines the degree of fouling based on the dual verification of pressure difference and temperature, and adjusts the injection frequency of pulse gas in stages. Under the premise of not affecting the normal operation of the heat exchanger, the online closed-loop regulation of fluid anti-deposition and pipe wall peeling and descaling is realized.

[0010] Preferably, the pulse air intake device further includes an air storage tank, the air intake end of the pulse control valve is connected to the air storage tank, and the air outlet end of the pulse control valve is connected to the bottom of the heat exchanger through an air distribution pipe. The air distribution pipe is located in the area below the tube sheet at the bottom of the heat exchanger, and multiple gas injection holes are opened on the pipe wall of the air distribution pipe. The cleaning medium includes liquid and solid particles dispersed in the liquid.

[0011] The gas distribution pipe is designed as a ring structure, ensuring that the injected gas is evenly distributed across the cross-section at the bottom of the heat exchanger. The gas injection holes are angled upwards, giving the ejected compressed gas both vertical upward kinetic energy and horizontal tangential velocity. When the gas merges with the liquid and solid particles, the horizontal tangential velocity generates rotational shear force, enhancing the turbulence of the gas-liquid-solid three-phase mixture, interrupting the free settling trajectory of solid particles, and preventing solid particles from depositing and accumulating at the dead corners of the heat exchanger tube inlet plate.

[0012] Preferably, the inlet of the gas-liquid-solid separator is configured as a tangential liquid inlet, which is located on the upper side wall of the gas-liquid-solid separator housing. The bottom of the gas-liquid-solid separator is formed into an inverted conical structure. A solid outlet is provided at the lowest end of the inverted conical structure. An overflow pipe is vertically arranged in the center of the gas-liquid-solid separator housing. The bottom end of the overflow pipe is closed, and the top end of the overflow pipe passes through the housing of the gas-liquid-solid separator housing to form a liquid outlet. A filter screen is fitted on the outer side wall of the overflow pipe. The filter screen is a wedge-shaped wire filter screen.

[0013] The tangential inlet creates a rotating flow field within the casing, causing solid particles to reach the inner wall under centrifugal force. Under gravity, these particles slide down the inverted conical structure to the solid outlet, achieving centrifugal separation. The rotating flow field generates tangential shear force on the outer surface of the wedge-shaped filter screen, washing away solid particles close to the screen surface. This overcomes the radial drag force generated when the liquid penetrates the screen, preventing particle accumulation and the formation of a filter cake. The combination of centrifugal pre-separation and the tangential scouring action of fluid dynamics constitutes the dynamic anti-clogging structure of the gas-liquid-solid separation device.

[0014] Preferably, a fine powder overflow port is provided in the upper part of the side wall of the storage tank, and a microporous intercepting mesh with a pore size between 0.1 mm and 0.4 mm is fixedly provided at the fine powder overflow port. A particle replenishment port is provided at the top of the storage tank, and the solid outlet is connected to the interior of the storage tank through a return pipe. The bottom of the storage tank is formed into an inverted conical structure, and the outlet of the storage tank is located at the lowest point of the inverted conical structure of the storage tank.

[0015] The inverted conical structure prevents solid particles from physically depositing at the bottom edge. The fine powder overflow port and the particle replenishment port form an online closed-loop renewal structure for the granular consumables. Particles within the normal particle size range are physically blocked and retained inside by the microporous interceptor. Particle debris generated by physical wear passes through the microporous interceptor with the waste liquid and is discharged through the fine powder overflow port. Combined with the quantitative replenishment of fresh solid particles at the top, the cleaning medium pumped into the heat exchanger is maintained within the set particle size and volume concentration range, preventing expired powder from entering the downstream system and causing contamination.

[0016] Preferably, the liquid is end-of-pipe wastewater, the particle size of the solid particles is limited to 0.5 mm to 2.0 mm, the volume concentration of solid particles inside the storage tank is set to 5% to 15%, and the density of the solid particles is limited to 1.2 g / cm³. 3 Up to 2.5g / cm 3 Within the range.

[0017] The particle density parameter is configured based on the calculation logic of terminal settling velocity in a still water environment in fluid mechanics. By limiting the density range, the terminal settling velocity of solid particles is kept within the range of the reference upward flow velocity provided by the circulating pump, allowing the system to maintain a suspended state with low pumping power. The upper limit of particle size is set to eliminate the physical conditions for bridging and clogging of particle groups in narrow flow sections, while the lower limit is set in conjunction with the turbulence intensity of the flow field to ensure that small particles penetrate the fluid boundary layer and contact the pipe wall. The set volume concentration provides a continuous scouring surface and prevents the apparent viscosity of the fluid inside the pipeline from exceeding the pump's rated load.

[0018] Preferably, the controller calculates the difference between the fluid pressure data at the inlet and outlet to obtain the real-time differential pressure. The controller stores a reference differential pressure and multiplies the reference differential pressure by a differential pressure threshold coefficient to obtain a preset differential pressure threshold. The controller calculates the difference between the temperature data at the inlet and outlet to obtain the temperature difference. The controller also stores a lower limit threshold for normal heat transfer temperature difference. The lower limit threshold for normal heat transfer temperature difference is calculated by multiplying the fluid temperature difference between the inlet and outlet of the heat exchanger obtained by calibration when the heat exchange tubes inside the heat exchanger are in a scale-free and clean state by an allowable fluctuation coefficient. The controller combines the real-time differential pressure, the preset differential pressure threshold, the temperature difference, and the lower limit threshold for normal heat transfer temperature difference to adjust the opening and closing frequency.

[0019] An increase in fluid pressure drop directly reflects the reduction in the cross-sectional area of ​​the heat exchanger tube and the increase in flow resistance. Extracting fluid pressure data as the primary control parameter for judging the degree of fouling improves the adaptive control response speed. By combining the differential pressure threshold coefficient with numerical comparison and using temperature data as an auxiliary verification parameter to prevent malfunctions, a feedback data path is constructed between the fouling state inside the tube and the online cleaning intensity, avoiding false triggering of the control system due to normal differential pressure changes caused by fluid flow fluctuations.

[0020] Preferably, the controller adjusts the opening and closing frequency of the pulse control valve in segments according to the following rules, and the duration of a single opening of the pulse control valve is set to a constant value: when the real-time differential pressure is less than or equal to a preset differential pressure threshold, the controller outputs a first frequency control signal to the pulse control valve; when the real-time differential pressure is greater than the preset differential pressure threshold and the temperature difference is lower than the lower limit threshold of the normal heat transfer temperature difference, the controller outputs a second frequency control signal to the pulse control valve, and the frequency value corresponding to the second frequency control signal is greater than the frequency value corresponding to the first frequency control signal; when the real-time differential pressure value falls back to less than or equal to the preset differential pressure threshold, the controller resumes outputting the first frequency control signal to the pulse control valve.

[0021] A constant duration of each activation ensures a consistent volume of turbulent gas injected per cycle. A low-frequency first frequency state maintains the suspension of solid particles in the bottom region to prevent deposition, while a high-frequency second frequency state forms a continuous bubble cluster inside the heat exchange tube, providing the kinetic energy for mechanical descaling. The coordinated operation of segmented control functions achieves the removal of scale flakes while avoiding the additional energy consumption and reduced mechanical lifespan caused by pneumatic components operating at high frequencies for extended periods.

[0022] Preferably, a high-pressure one-way check valve is connected in series on the connecting pipeline between the pulse control valve and the gas distribution pipe, and the minimum threshold of the gas supply pressure inside the gas storage tank is greater than the sum of the liquid static pressure at the liquid inlet and the system flow resistance loss.

[0023] The supply pressure and system resistance follow a hydrostatic equilibrium constraint relationship. The lower limit of the supply pressure is set based on the hydrostatic pressure determined by the liquid density and liquid level at the inlet, and the resistance loss caused by the pipeline friction and local resistance coefficient. The parameter configuration of the lower limit of the supply pressure ensures that high-pressure gas forms a bubble flow with physical penetrating power. During the intermittent closing of the pulse control valve, the high-pressure one-way check valve overcomes the fluid back pressure and cuts off the wastewater backflow channel, preventing wastewater containing solid particles from entering the supply pipeline in reverse.

[0024] Preferably, in the pipeline between the outlet of the storage tank and the inlet of the circulating pump, and in the connecting pipeline between the outlet of the circulating pump and the inlet of the heat exchanger, the radius of curvature of the elbow component in the fluid direction change area is 3 to 5 times the inner diameter of the pipeline.

[0025] The area where the flow direction of a solid-liquid mixture changes is a region of concentrated wear. Large-radius bends are used to mitigate the centrifugal impact force when the fluid direction changes. Combined with synchronized control of the upper and lower limits of the fluid velocity within the pipeline, this ensures that the fluid velocity exceeds the particle settling velocity to prevent sedimentation at the bottom of the pipe while reducing the rate of localized physical wear.

[0026] A second aspect of the present invention provides an online cleaning method for small-diameter heat exchangers, applied to the online cleaning system for small-diameter heat exchangers described in the first aspect, comprising the following steps: The cleaning medium is delivered to the inlet of the heat exchanger via a circulating pump; During the process of the cleaning medium entering the heat exchanger, the pulse air intake device injects compressed gas into the heat exchanger through the opening and closing frequency of the pulse control valve. The compressed gas and the cleaning medium merge inside the heat exchanger to form a gas-liquid-solid three-phase mixed fluid. The gas-liquid-solid three-phase mixed fluid flows inside the heat exchanger and mechanically scours the inner wall of the heat exchange tube. After being scourted, the gas-liquid-solid three-phase mixed fluid flows out of the heat exchanger and enters the gas-liquid-solid separation device. The gas-liquid-solid separation device performs physical separation on the gas-liquid-solid three-phase mixed fluid that enters the device, separating the gas-liquid-solid three-phase mixed fluid into gas, liquid and solid particles. The gas is discharged from the cleaning system, the solid particles are returned to the storage tank for recycling, and the liquid is discharged into the downstream pipeline. When the system is in operation, the differential pressure detection unit and the temperature detection unit collect fluid pressure data and temperature data at the inlet and outlet of the heat exchanger, respectively, and send them to the controller. The controller receives fluid pressure data and temperature data, calculates the real-time differential pressure based on the fluid pressure data, retrieves the internally stored reference differential pressure and multiplies it by the differential pressure threshold coefficient to calculate the preset differential pressure threshold. The temperature difference is calculated based on the temperature data. The real-time pressure difference is compared with the preset pressure difference threshold. The scaling phenomenon is determined by comparing the temperature difference with the lower limit threshold of the normal heat transfer temperature difference retrieved from the internal storage. Then, the opening and closing frequency of the pulse control valve is adjusted in segments.

[0027] This invention provides an online cleaning system and method for small-diameter heat exchangers. It offers the following advantages: 1. This invention combines a pulse air intake device with a cleaning medium containing liquid and solid particles. By using the periodic opening and closing frequency of a pulse control valve to inject compressed gas into the heat exchanger, the compressed gas and the cleaning medium merge to form a gas-liquid-solid three-phase mixed fluid. The expansion and flow of the gas inside the heat exchanger generates fluid disturbance, which drives the solid particles to directly mechanically scour the inner wall of the heat exchange tube. This effectively removes the scale layer attached to the inside of the heat exchange tube and improves the descaling effect of small-diameter heat exchangers.

[0028] 2. This invention, by setting up a gas-liquid-solid separation device with a tangential liquid inlet and a wedge-shaped wire filter, combined with a storage tank with an inverted conical bottom structure, allows the three-phase gas-liquid-solid mixture to be separated into gas, liquid, and solid particles through physical separation after entering the gas-liquid-solid separation device. The separated solid particles are directly returned to the storage tank for recycling through the solid outlet and return pipe, realizing online closed-loop renewal and recycling of solid particles within the system, reducing the consumable operating cost of the cleaning system, and avoiding pipeline blockage caused by particle accumulation.

[0029] 3. This invention, by setting up a differential pressure detection unit, a temperature detection unit, and a controller, allows the detection unit to collect real-time fluid pressure and temperature data at the inlet and outlet of the heat exchanger. The controller, combined with the calculated real-time differential pressure and temperature difference, determines the actual scaling phenomenon of the heat exchanger and then performs segmented adjustment of the opening and closing frequency of the pulse control valve. This allows for dynamic adjustment of the pulse intensity of the injected gas according to the actual fouling resistance in the pipe, ensuring cleaning and flushing capabilities while avoiding the pulse control valve being in an ineffective high-frequency operating state for a long time, thus reducing the overall energy consumption of the system. Attached Figure Description

[0030] Figure 1 This is a system architecture diagram of the present invention; Figure 2 This is a flowchart of the method of the present invention; Figure 3 This is a schematic diagram of the overall structure of the device of the present invention; Figure 4 This is a line graph showing the change of the inlet and outlet pressure difference of the heat exchanger and the pulse frequency over time according to the present invention. Figure 5 This is a bar chart comparing the operating cycle and pneumatic system energy consumption of the present invention under different cleaning strategies.

[0031] The components include: 1. Heat exchanger; 2. Gas distribution pipe; 3. Pulse control valve; 4. Gas storage tank; 5. Gas-liquid-solid separation device; 6. Filter screen; 7. Flash tank; 8. Circulating pump; 9. Storage tank; 10. Differential pressure detection unit; and 11. Temperature detection unit. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] See attached document Figure 1 With appendix Figure 3 The present invention provides an online cleaning system for small-diameter heat exchangers. The system includes: a heat exchanger 1, a storage tank 9, a circulating pump 8, a pulse air intake device, a gas-liquid-solid separation device 5, and a control system.

[0034] The heat exchanger 1 has multiple heat exchange tubes inside, and has an inlet at the bottom and an outlet at the top.

[0035] The storage tank 9 is used to contain the cleaning medium, which includes the terminal wastewater and solid particles distributed in the terminal wastewater. The outlet of the storage tank 9 is connected to the inlet of the circulation pump 8 through a pipeline, and the outlet of the circulation pump 8 is connected to the liquid inlet at the bottom of the heat exchanger 1 through a pipeline.

[0036] The pulse air intake device includes an air storage tank 4 and a pulse control valve 3. The air intake end of the pulse control valve 3 is connected to the air storage tank 4, and the air outlet end of the pulse control valve 3 is connected to the bottom of the heat exchanger 1 through the air distribution pipe 2. The air distribution pipe 2 is located in the area below the tube sheet at the bottom of the heat exchanger 1, and multiple gas injection holes are opened on the air distribution pipe 2.

[0037] The inlet of the gas-liquid-solid separator 5 is connected to the liquid outlet at the top of the heat exchanger 1. The gas-liquid-solid separator 5 is equipped with a filter screen 6. The gas-liquid-solid separator 5 has a gas outlet, a liquid outlet and a solid outlet respectively on its shell. The gas outlet is located in the top area of ​​the gas-liquid-solid separator 5. The liquid outlet is connected to the downstream flash tank 7 through a pipeline. The solid outlet is located in the bottom area of ​​the gas-liquid-solid separator 5 and is connected to the storage tank 9 through a return pipe.

[0038] The control system includes a controller, and a differential pressure detection unit 10 and a temperature detection unit 11 installed on the inlet and outlet pipes of the heat exchanger 1. The two ends of the differential pressure detection unit 10 are connected to the liquid inlet pipe and the liquid outlet pipe of the heat exchanger 1, respectively. The temperature detection unit 11 is arranged at the liquid inlet and the liquid outlet of the heat exchanger 1. The differential pressure detection unit 10 and the temperature detection unit 11 are electrically connected to the controller, and the controller is electrically connected to the pulse control valve 3.

[0039] See attached document Figure 2 This invention includes an online cleaning method for small-diameter heat exchangers, specifically comprising the following steps: The cleaning medium containing solid particles inside the storage tank 9 is drawn out by the circulation pump 8 and transported from bottom to top to the heat exchanger 1 through the bottom pipeline. During the process of the cleaning medium entering the heat exchange tube, the controller sends an opening command and a closing command to the pulse control valve 3 according to the preset program. The gas in the gas storage tank 4 flows through the pulse control valve 3 and the gas distribution pipe 2 in sequence, and is injected into the bottom water chamber of the heat exchanger 1 through the gas injection hole on the gas distribution pipe 2. The injected gas and the cleaning medium meet at the inlet of the heat exchange tube to form a gas-liquid-solid three-phase mixed fluid that flows upward along the inside of the heat exchange tube. The gas rises and expands, generating fluid disturbance, which causes solid particles to mechanically scour the inner wall of the heat exchange tube during the flow. The three-phase mixed fluid after the flushing operation flows out from the liquid outlet at the top of the heat exchanger 1 and enters the gas-liquid-solid separation device 5. In the gas-liquid-solid separation device 5, the gas in the mixed fluid floats upward and is discharged from the system through the gas outlet. After sedimentation and separation, the solid particles in the mixed fluid are collected at the bottom solid outlet and returned to the storage tank 9 through the return pipe for recycling. The liquid in the mixed fluid passes through the filter screen 6 and is discharged into the downstream flash tank 7 through the liquid outlet to enter the subsequent concentration process. When the system is in operation, the differential pressure detection unit 10 acquires the differential pressure data between the liquid inlet and liquid outlet of the heat exchanger 1 in real time, and the temperature detection unit 11 acquires the fluid temperature data flowing through the pipeline simultaneously. The differential pressure detection unit 10 and the temperature detection unit 11 send the detection data to the controller. The controller receives the differential pressure data and temperature data, and adjusts the opening and closing frequency of the pulse control valve 3 according to the data changes (the duration of a single opening is set to a constant value), thereby changing the per-unit-time disturbance gas volume and pulse cycle entering the heat exchanger 1.

[0040] The cleaning medium is stored inside the storage tank 9. The cleaning medium includes liquid and solid particles dispersed in the liquid. The liquid is desulfurization wastewater generated by the flash concentration system of the end wastewater of the coal-fired power plant. The specific preparation and parameter selection process of the cleaning medium is as follows, taking into account the scaling characteristics of the heat exchange tubes inside the heat exchanger 1.

[0041] The material of the solid particles is selected based on the physical hardness of the scale layer adhering to the inner wall of the heat exchange tube. When the main deposited scale layer inside the heat exchange tube is formed by calcium sulfate or calcium carbonate, polytetrafluoroethylene (PTFE) particles are used as solid particles. PTFE is relatively soft and can avoid wear on the inner wall of the heat exchange tube during long-term scouring. When the main deposited scale layer inside the heat exchange tube is formed by silicates, glass microspheres, an inorganic non-metallic material, are used as solid particles. Glass microspheres have high hardness and can impact and peel off dense hard scale. For the hardness testing and preparation processing methods of the specific solid particle material, those skilled in the art can use conventional material processing methods.

[0042] The process for setting the particle size distribution range of solid particles is as follows: the inner diameter of the small-diameter heat exchange tube inside heat exchanger 1 is limited to 15mm to 25mm. To prevent particles from getting stuck inside the heat exchange tube and to ensure that a single particle has sufficient impact kinetic energy, the particle size of solid particles is limited to 0.5mm to 2.0mm. The upper limit of the particle size is set to less than 1 / 10 of the inner diameter of the heat exchange tube, thereby eliminating the physical conditions for bridging and blockage of particle groups at narrow flow cross sections. The lower limit of the particle size is set in combination with the turbulence intensity of the flow field provided by the pulse air intake device to ensure that the tiny particles are not completely engulfed by the fluid drag force in the fluid boundary layer and can penetrate the fluid boundary layer and contact the heat exchange tube wall.

[0043] The density parameter configuration process for solid particles is as follows: the terminal wastewater contains a high concentration of evaporated and concentrated salts, and the liquid density of the terminal wastewater is usually higher than that of pure water. To meet the gravity sedimentation separation requirements inside the gas-liquid-solid separation device 5, while also considering the energy consumption of the circulating pump 8, the density range of solid particles is set to 1.2 g / cm³. 3 Up to 2.5g / cm 3 The critical suspension state of solid particles in a fluid satisfies hydrodynamic equilibrium with particle density. Under the basic flow rate condition with pulse control valve 3 not open, the force balance relationship of particles inside the heat exchange tube is characterized by the terminal settling velocity formula: ; In the formula, This represents the terminal settling velocity of solid particles in a still water environment. Represents gravitational acceleration. Indicates the particle size of solid particles. This represents the density of solid particles. This indicates the liquid density of the wastewater. This represents the fluid drag coefficient experienced by the particles. This is a dimensionless parameter, obtained by looking up a table using the particle Reynolds number combined with the drag coefficient curve of a standard sphere.

[0044] Based on the formula for terminal settling velocity, it can be calculated that the density of solid particles should be limited to 1.2 g / cm³. 3 Up to 2.5g / cm 3 Within the range, the final settling velocity of solid particles in a still water environment is within the range of the reference upward flow velocity provided by the circulating pump 8. That is, the reference upward flow velocity is greater than the final settling velocity of solid particles in a still water environment. The system only needs to consume a low pumping power to maintain the suspension of particles. After the mixed fluid enters the gas-liquid-solid separation device 5, the particle group that loses the support of the upward flow velocity can overcome the liquid resistance and settle downward.

[0045] The process of setting the volume concentration of solid particles in the cleaning medium is as follows: the volume concentration determines the frequency of collision between solid particles and the heat exchange tube wall per unit time and the flow resistance loss of the pipeline. The volume concentration of solid particles in the storage tank 9 and the entire pipeline is set to 5% to 15%. When the volume concentration is less than 5%, the spatial distribution density of the particle group is insufficient and it is impossible to form a continuous flushing surface that covers the entire pipe wall.

[0046] When the volume concentration is higher than 15%, the apparent viscosity of the fluid inside the pipeline increases, which can easily exceed the rated head load of the ordinary circulating pump 8. At the same time, it will cause collision and consumption between particles, resulting in an increase in the breakage rate of the particles themselves. During system operation, the storage tank 9 continuously provides a solid-liquid mixture that meets the set volume concentration to ensure that the cleaning medium entering the heat exchanger 1 is maintained within the effective flushing concentration range.

[0047] The storage tank 9 is equipped with an anti-settling structure for the cleaning medium and an online closed-loop updating structure for granular consumables.

[0048] The bottom of the storage tank 9 is formed into an inverted conical structure. The outlet of the storage tank 9 is located at the lowest point of the inverted conical structure. The inlet of the circulation pump 8 is connected to the outlet of the storage tank 9 through a pipeline. The inclination angle of the inner wall of the inverted conical structure is greater than the angle of repose of the solid particles in the desulfurization wastewater. The value of the inclination angle of the inner wall is set to 45° to 60°.

[0049] The solid outlet of the gas-liquid-solid separation device 5 is connected to the inside of the storage tank 9 through a return pipe. After the solid particles enter the storage tank 9 with the desulfurization wastewater through the return pipe, they slide down and collect at the bottom of the storage tank 9 outlet under the action of gravity along the inner wall of the inverted conical structure. The inverted conical structure avoids physical deposition of solid particles in the bottom edge area of ​​the storage tank 9, ensuring that the circulating pump 8 can continuously and uniformly extract the cleaning medium and send it into the heat exchanger 1.

[0050] When the system is in a long-term continuous operation state, solid particles will undergo physical wear and generate small-diameter particle debris under the mechanical impact of the impeller of the circulating pump 8, the turbulent disturbance of the jet airflow of the air distribution pipe 2, and the impact of the tube wall of the heat exchanger 1. The terminal settling velocity of the small-diameter particle debris is much smaller than that of normal particles, resulting in most of the particle debris being suspended and concentrated in the upper layer of the liquid surface inside the storage tank 9.

[0051] To maintain the normal particle size range of the cleaning medium, a fine powder overflow port is provided in the upper part of the side wall of the storage tank 9. The position of the fine powder overflow port is level with the normal operating liquid level inside the storage tank 9. A microporous intercepting mesh is fixedly installed at the fine powder overflow port. The specific structure of the microporous intercepting mesh is a stainless steel sintered filter screen or a wedge wire screen. The pore size of the microporous intercepting mesh is set between 0.1 mm and 0.4 mm. The pore size of the microporous intercepting mesh is strictly smaller than the minimum normal particle size of solid particles set at 0.5 mm, and larger than the particle size of debris generated by physical wear.

[0052] During the cyclic operation of the cleaning system, the waste liquid containing suspended particles and debris in the upper layer inside the storage tank 9 continuously flows towards the fine powder overflow port. Solid particles within the normal particle size range are physically blocked by the microporous interception mesh and retained inside the storage tank 9. Particles and debris with a particle size smaller than the aperture of the microporous interception mesh pass through the microporous interception mesh with the waste liquid, are discharged from the storage tank 9 through the fine powder overflow port, and enter the external waste liquid collection pool. For the specific structural form of the external waste liquid collection pool and the subsequent sewage pipe network layout, those skilled in the art can make conventional configurations based on the on-site plant conditions.

[0053] The top of the storage tank 9 is equipped with a particle replenishment port, which is fitted with a sealing flange cover or a pneumatic slide valve. Equipment maintenance personnel or external automated dosing mechanisms can quantitatively replenish fresh solid particles into the storage tank 9 through the particle replenishment port. The purpose of replenishing fresh solid particles into the storage tank 9 through the particle replenishment port is to restore and maintain the volume concentration of solid particles inside the storage tank 9 within the set range of 5% to 15%. The particle replenishment port and the fine powder overflow port together constitute an online closed-loop renewal structure for granular consumables. The online closed-loop renewal structure ensures that the cleaning medium pumped into the heat exchanger 1 always maintains a particle size range of 0.5mm to 2.0mm and a volume concentration of 5% to 15%, preventing the failure of fine powder from entering the downstream flash tank 7 with the liquid and causing system contamination.

[0054] The circulating pump 8 is responsible for transporting the cleaning medium inside the storage tank 9 to the heat exchanger 1. The cleaning medium contains solid particles with a volume concentration of 5% to 15%. When the solid particles are high-hardness glass microspheres, ordinary water pumps will experience physical wear during high-speed rotation and extraction. The circulating pump 8 uses a wear-resistant, non-clogging slurry pump or a cyclone centrifugal pump. When using a cyclone centrifugal pump, the impeller of the cyclone centrifugal pump is arranged in the rear area of ​​the pump chamber. The solid particles form a vortex inside the pump casing with the water flow and are discharged. Most of the solid particles do not have direct mechanical contact with the impeller, which reduces the mechanical wear of the impeller.

[0055] The internal flow-through components of the circulating pump 8 include an impeller and the inner wall of the pump casing. The surface of the flow-through components is covered with a wear-resistant coating or made of a wear-resistant alloy material. The wear-resistant alloy material is a high-chromium cast iron alloy, and the wear-resistant coating is a silicon carbide ceramic coating. For the specific preparation and adhesion process of the high-chromium cast iron alloy and the silicon carbide ceramic coating, those skilled in the art can use conventional metal smelting or material surface treatment methods.

[0056] The pipelines between the outlet of storage tank 9 and the inlet of circulating pump 8, and between the outlet of circulating pump 8 and the inlet of heat exchanger 1, are subjected to long-term mechanical erosion from the solid-liquid mixture. The connecting pipeline between storage tank 9 and heat exchanger 1 uses wear-resistant composite pipes, which are either polyurethane-lined steel pipes or bimetallic composite wear-resistant pipes. When using polyurethane-lined steel pipes, the internal polyurethane material is elastic, absorbing and buffering some of the kinetic energy generated by solid particles impacting the pipe wall, reducing physical wear on the inner wall of the pipeline. When using bimetallic composite wear-resistant pipes, the outer wall of the bimetallic composite wear-resistant pipe is made of carbon steel to provide pressure resistance, while the inner wall is made of high-chromium wear-resistant alloy to resist mechanical wear from solid particles.

[0057] In the layout of connecting pipelines, areas where fluid direction changes are areas of concentrated wear. Elbows in the connecting pipelines utilize large-radius bends, with the radius of curvature set to 3 to 5 times the pipe's inner diameter. These large-radius bends mitigate the centrifugal impact force when the solid-liquid mixture changes flow direction. The fluid velocity inside the pipeline is limited to between 1.5 m / s and 2.5 m / s. The lower limit of the fluid velocity is greater than the terminal settling velocity of solid particles, ensuring that solid particles do not deposit at the bottom of the pipeline. The upper limit of the fluid velocity is limited to below 2.5 m / s to avoid excessively high flow velocities that increase the wear rate of the pipe walls and valves.

[0058] The gas distribution pipe 2 is located in the area below the tube sheet at the bottom of the heat exchanger 1. The overall shape of the gas distribution pipe 2 is set as a ring structure. The ring structure can make the injected gas evenly distributed on the cross-section of the bottom of the heat exchanger 1. Multiple gas injection holes are opened on the pipe wall of the gas distribution pipe 2. The diameter of the gas injection hole is set between 1.5mm and 2.5mm. The center distance between two adjacent gas injection holes is set between 50mm and 100mm. The diameter limitation avoids the generation of single bubbles with excessive volume, and causes the high-pressure gas to be divided into a group of small bubbles. The group of small bubbles can increase the physical contact area between the gas and the desulfurization wastewater.

[0059] The axis of the gas injection hole forms an angle of 30° to 60° with the horizontal plane. The injection direction of the gas injection hole is inclined upward towards the inlet of the heat exchange tube inside the heat exchanger 1. The inclined design gives the injected compressed gas vertical upward kinetic energy and horizontal tangential velocity. When the gas, desulfurization wastewater and solid particles meet at the inlet of the heat exchange tube, the horizontal tangential velocity generates rotational shear force, which enhances the turbulence of the gas-liquid-solid three-phase mixture. The fluid turbulence interrupts the free settling trajectory of solid particles and prevents solid particles from accumulating and depositing at the dead corner of the edge of the heat exchange tube inlet plate.

[0060] The pulse air intake device injects gas into the heat exchanger 1 through the air distribution pipe 2. The desulfurization wastewater at the bottom of the heat exchanger 1 is under the static water pressure and the dynamic pressure environment provided by the circulating pump 8. During the intermittent period when the pulse control valve 3 is closed, the internal air pressure of the air distribution pipe 2 drops. In order to prevent the high-pressure wastewater containing solid particles from flowing back into the air supply pipeline, a high-pressure one-way check valve is connected in series on the connecting pipe between the pulse control valve 3 and the air distribution pipe 2. The high-pressure one-way check valve adopts a spring-loaded one-way valve or a swing-type hard-seal one-way valve.

[0061] When the pulse control valve 3 is opened, the gas pressure overcomes the spring resistance and pushes the valve core open to inject gas. When the pulse control valve 3 is closed, the valve core adheres to the valve seat under the combined action of the spring force and the wastewater back pressure, cutting off the wastewater backflow channel. For the internal sealing structure and assembly method of the high-pressure one-way check valve, those skilled in the art can perform conventional model matching according to the operating pressure level. The one-way valve assembly technology is a well-known technology in this field.

[0062] The high-pressure compressed gas stored in the gas storage tank 4 is supplied by an external gas source. To ensure that the compressed gas can overcome the system resistance inside the heat exchanger 1 and smoothly enter the bottom of the heat exchanger 1 at the moment the pulse control valve 3 is opened, the gas supply pressure provided by the gas source and the system resistance follow the hydrostatic equilibrium constraint condition. The minimum threshold constraint relationship of the gas supply pressure is expressed as follows: ; In the formula, This indicates the gas supply pressure to the gas storage tank 4. This indicates the static pressure of the desulfurization wastewater generated at the bottom inlet of heat exchanger 1. This represents the system flow resistance loss generated when compressed gas flows through the high-pressure one-way check valve, the gas distribution pipe 2, and the gas injection hole.

[0063] The static pressure of the desulfurization wastewater at the bottom inlet of heat exchanger 1 The value is calculated based on the product of the liquid level inside heat exchanger 1, the gravitational acceleration, and the liquid density of the wastewater. The calculation formula is as follows: ; In the formula, This indicates the static pressure of the desulfurization wastewater generated at the bottom inlet of heat exchanger 1; This indicates the liquid density of the wastewater. Represents gravitational acceleration. This indicates the vertical height of the operating liquid level inside the downstream gas-liquid-solid separation device 5, which is connected to the liquid outlet of heat exchanger 1, from the liquid inlet at the bottom of heat exchanger 1.

[0064] System flow resistance loss generated when compressed gas flows through the high-pressure one-way check valve, gas distribution pipe 2, and gas injection orifice. The values ​​are calculated by superimposing the friction loss along the pipeline and the local resistance loss of the gas. Those skilled in the art can obtain the resistance coefficient of the corresponding pipe fittings and calculate it by consulting fluid mechanics handbooks. The lower limit parameter of the gas supply pressure to the gas storage tank 4 is set according to the minimum threshold constraint formula of the gas supply pressure. This ensures that the high-pressure gas forms a bubble flow with physical penetrating power when it enters the heat exchanger 1, giving the solid particles the mechanical kinetic energy required to prevent deposition and impact the scale layer on the pipe wall.

[0065] The inlet of the gas-liquid-solid separator 5 is configured as a tangential liquid inlet, which is located on the upper side wall of the shell of the gas-liquid-solid separator 5. The tangential liquid inlet is connected to the liquid outlet at the top of the heat exchanger 1. The bottom of the shell of the gas-liquid-solid separator 5 is formed into an inverted conical structure. The solid outlet is located at the lowest end of the inverted conical structure. An overflow pipe is vertically installed in the center of the shell of the gas-liquid-solid separator 5. The bottom end of the overflow pipe is closed, and the top end extends out of the shell of the gas-liquid-solid separator 5 to form a liquid outlet. A filter screen 6 is sleeved on the outer side wall of the overflow pipe. The filter screen 6 is a wedge-shaped wire filter screen.

[0066] After the gas-liquid-solid three-phase mixed fluid flows out of the heat exchanger 1, it enters the gas-liquid-solid separation device 5 through the tangential liquid inlet. The mixed fluid forms a rotating flow field under the constraint of the inner wall of the gas-liquid-solid separation device 5. In the rotating flow field, the centrifugal force on the solid particles is greater than that on the desulfurization wastewater. A large number of solid particles are thrown towards the inner wall of the gas-liquid-solid separation device 5 under the action of centrifugal force, leaving the central liquid mainstream zone. The solid particles that reach the inner wall slide down along the inverted conical structure under the action of gravity and collect at the bottom solid outlet, realizing the initial centrifugal separation of solid and liquid components.

[0067] After centrifugal separation, the desulfurization wastewater converges in the central area of ​​the gas-liquid-solid separation device 5. The desulfurization wastewater passes through the gaps of the filter screen 6 and enters the overflow pipe. It then flows downstream to the flash tank 7 through the liquid outlet. The gap width of the wedge wire filter screen 6 is smaller than the minimum set particle size of the solid particles. Based on the normal particle size and debris particle size parameters in the cleaning medium, the gap width of the wedge wire filter screen 6 is set between 0.1 mm and 0.4 mm. The wedge wire filter screen 6 is made of metal wires with a V-shaped cross-section wound and welded. The tip of the V-shaped metal wire faces the center of the gas-liquid-solid separation device 5, while the flat cross-section faces the rotating flow field. A gradually expanding channel with a narrow outer edge and a wide inner edge is formed between adjacent metal wires. After small particles and debris come into contact with and enter the gradually expanding channel, they can smoothly pass through the gradually expanding channel and fall into the overflow pipe, avoiding small debris from getting stuck in the gaps of the filter screen 6 and causing physical blockage.

[0068] The mixed fluid remains in a rotating state inside the gas-liquid-solid separator 5. The rotating flow field generates tangential shear force on the outer surface of the filter screen 6. The direction of the tangential shear force is perpendicular to the radial flow direction of the desulfurization wastewater through the filter screen 6. When a small number of solid particles that are not thrown off by centrifugal force approach the surface of the filter screen 6 with the desulfurization wastewater, the tangential shear force washes and peels the solid particles off the surface of the filter screen 6. The tangential shear force overcomes the radial drag force generated on the particles when the desulfurization wastewater penetrates the filter screen 6, preventing solid particles from gradually accumulating on the surface of the filter screen 6 and forming a filter cake layer. The combination of cyclone centrifugal pre-separation and the hydrodynamic tangential scouring effect on the surface of the wedge wire filter screen 6 constitutes the dynamic anti-clogging structure of the gas-liquid-solid separator 5.

[0069] The compressed gas carried inside the mixed fluid gathers in the central region of the rotating flow field. The gas density is extremely low, and it rises upward under the buoyancy of the fluid. Finally, it is discharged from the gas outlet system located at the top of the gas-liquid-solid separator 5. The continuous gas discharge process balances the operating pressure inside the gas-liquid-solid separator 5, ensuring the stable separation of the gas-liquid-solid three phases under continuous flow conditions.

[0070] After the gas-liquid-solid three-phase mixed fluid completes physical separation inside the gas-liquid-solid separation device 5, the separated gas, liquid and solid particles enter different fluid destination channels respectively.

[0071] After separation, the compressed gas is discharged from the cleaning system through the gas outlet at the top of the gas-liquid-solid separator 5. To prevent the high-speed discharged gas from carrying desulfurization wastewater droplets, a demister is installed on the exhaust pipe connected to the gas outlet. The demister is either a wire mesh demister or a baffle plate demister. When the desulfurization wastewater droplets pass through the demister, they are physically intercepted and collected, flowing back into the gas-liquid-solid separator 5. The demisted gas is then discharged into the atmosphere or the factory's waste gas collection network. For the specific pipeline layout of the waste gas collection network, those skilled in the art can configure it according to the environmental protection requirements of the site.

[0072] After passing through filter screen 6, the separated desulfurization wastewater is transported to the downstream flash tank 7 via the liquid outlet. The wastewater carries high concentrations of dissolved salts and tiny scale fragments detached from the heat exchanger 1 tube wall. These fragments are smaller than the slit width of filter screen 6 and can flow with the wastewater. Inside the flash tank 7, the wastewater undergoes a flash boiling process under low pressure. Water evaporates to form secondary steam, and the tiny scale fragments mix with the concentrated salts in the concentrated liquid at the bottom of the flash tank 7. This concentrated liquid is then discharged into the subsequent crystallization and drying equipment.

[0073] Solid particles that have undergone physical sedimentation are discharged from the solid outlet at the bottom of the gas-liquid-solid separator 5 and enter the return pipe connecting the solid outlet and the storage tank 9. To reduce the power consumption of the cleaning system, the installation elevation of the gas-liquid-solid separator 5 is higher than that of the storage tank 9. The return pipe is arranged to be inclined downward along the direction of fluid flow, and the inclination angle between the return pipe and the horizontal plane is set between 30° and 80°. The solid particles rely on the elevation difference between the gas-liquid-solid separator 5 and the storage tank 9 and the gravity of the solid particles themselves to slide down the return pipe into the storage tank 9. The elevation difference and the inclined arrangement of the pipeline prevent the solid particles from stagnating and blocking inside the return pipe, thus realizing the non-powered recycling of solid consumables.

[0074] The control system acquires real-time operating status data of the cleaning system through hardware sensors. The two ends of the differential pressure detection unit 10 are connected to the inlet and outlet of the heat exchanger 1, respectively, and are used to collect the fluid pressure at the inlet and outlet of the heat exchanger 1. The temperature detection unit 11 is installed at the inlet and outlet of the heat exchanger 1, respectively, and is used to collect the fluid temperature flowing into and out of the heat exchanger 1. The controller receives the electrical signals sent by the differential pressure detection unit 10 and the temperature detection unit 11, and converts the electrical signals into numerical data for storage and calculation.

[0075] When the terminal wastewater is heated inside heat exchanger 1, the supersaturated salts precipitated adhere to the heat exchange tube wall and form a dense scale layer. The increase in scale layer thickness leads to a reduction in the actual flow cross-sectional area of ​​the heat exchange tube and increases the physical roughness of the tube wall surface. According to the fluid mechanics friction loss theory, the reduction in flow cross-sectional area will lead to an increase in fluid friction loss, which is manifested as an increase in pressure drop between the inlet and outlet of heat exchanger 1. At the same time, the deposited scale layer has a low thermal conductivity, forming additional fouling thermal resistance at the tube wall. The fouling thermal resistance hinders heat transfer, resulting in a decrease in the heat transfer efficiency of heat exchanger 1. This is manifested as the temperature difference between the inlet and outlet of the desulfurization wastewater after being heated by heat exchanger 1 deviating from the design value.

[0076] Compared to the hysteresis effect of heat transfer caused by changes in fluid temperature, an increase in fluid pressure drop directly reflects the reduction in the cross-sectional area of ​​the heat exchanger tube and the increase in flow resistance. To improve the response speed of adaptive control, the controller extracts the fluid pressure data obtained by the differential pressure detection unit 10 as the main control parameter for judging the degree of fouling. The controller calculates the real-time differential pressure between the inlet and outlet of heat exchanger 1 using the following formula: ; In the formula, Indicates real-time differential pressure. This indicates the fluid pressure at the inlet of heat exchanger 1. This indicates the fluid pressure at the outlet of heat exchanger 1.

[0077] The controller has pre-stored the reference pressure difference obtained during the calibration of the cleaning system when the heat exchange tubes are in a scale-free and clean state. The controller retrieves the reference pressure difference data and calculates a preset pressure difference threshold for dynamically determining the severity of scaling. The formula for calculating the preset pressure difference threshold is as follows: ; In the formula, This indicates the preset differential pressure threshold. This represents the differential pressure threshold coefficient. This represents the reference pressure difference obtained during the calibration of the cleaning system when the heat exchange tubes are clean and free of scale.

[0078] To avoid false triggering of the control system due to normal differential pressure changes caused by fluid flow fluctuations, the differential pressure threshold coefficient is set to a range of 1.2 to 1.5. When the real-time differential pressure increases to 1.2 to 1.5 times the reference differential pressure, it indicates that the thickness of the scale layer inside the heat exchange tube not only increases the energy consumption of fluid transport, but also has the thickness to be eroded and peeled off by solid particles. Based on the comparison between the real-time differential pressure and the preset differential pressure threshold, the controller generates control commands for the corresponding pulse control valve 3. Relying on the synergistic effect of real-time differential pressure extraction and preset differential pressure threshold formula setting, the control system constructs a feedback data path between the scale state inside the tube and the online cleaning intensity.

[0079] Based on the extracted real-time differential pressure data, the controller only adjusts the opening frequency of the pulse control valve 3 inside the pulse intake device. To ensure a constant volume of turbulent gas injected into the bottom of the heat exchanger 1 each time, the single opening duration of the pulse control valve 3 is set to a constant value, and the controller only dynamically adjusts the opening frequency.

[0080] The controller compares the real-time differential pressure collected and calculated by the differential pressure detection unit 10 with the preset differential pressure threshold in real time. Based on the comparison result, the controller calls the built-in frequency control function to calculate the action command. The frequency control function adopts a piecewise function form, and the calculation formula is as follows: ; In the formula, This indicates the real-time opening frequency of pulse control valve 3. Indicates the first frequency. Indicates the second frequency. Indicates real-time differential pressure. This indicates the preset differential pressure threshold. The first frequency and the second frequency are set between 0.1Hz and 2.0Hz, and the value of the second frequency is greater than the value of the first frequency.

[0081] When the numerical comparison result shows that the real-time differential pressure is less than or equal to the preset differential pressure threshold, it indicates that no scale layer has formed on the tube wall of the heat exchange tube inside the heat exchanger 1, which hinders the flow. The fluid resistance inside the heat exchanger 1 is in the normal operating range. The controller generates a first frequency control signal and outputs it to the pulse control valve 3. The pulse control valve 3 opens and closes periodically at the first frequency. Under the low-frequency pulse state, the compressed gas injected into the gas distribution pipe 2 maintains the suspension state of solid particles in the bottom area of ​​the heat exchanger 1, preventing solid particles from physically depositing at the bottom of the heat exchanger 1.

[0082] When the numerical comparison result shows that the real-time differential pressure is greater than the preset differential pressure threshold and meets the system temperature auxiliary verification conditions, it indicates that a scale layer that increases fluid resistance has formed inside the heat exchange tube. The controller generates a second frequency control signal and outputs it to the pulse control valve 3. The pulse control valve 3 opens and closes periodically at the second frequency. Under the high-frequency pulse state, the compressed gas injected into the gas distribution pipe 2 forms a continuous bubble group inside the heat exchange tube. The process of bubble expansion and rupture drives solid particles to impact the heat exchange tube wall and peel off the attached scale layer.

[0083] During the second frequency operation phase of the pulse control valve 3, the detached scale flows out of the heat exchanger 1 with the desulfurization wastewater, the flow cross-sectional area inside the heat exchange tube expands, and the flow resistance between the inlet and outlet of the heat exchanger 1 decreases. The controller synchronously monitors the real-time differential pressure through the differential pressure detection unit 10 and finds that the real-time differential pressure value has dropped. When the real-time differential pressure value drops to less than or equal to the preset differential pressure threshold, the controller regenerates the first frequency control signal and outputs it to the pulse control valve 3. The pulse control valve 3 then returns to the periodic opening and closing state of the first frequency.

[0084] During frequency regulation, the controller synchronously receives temperature data collected by the temperature detection unit 11. This temperature data serves as an auxiliary verification parameter to prevent malfunctions. When the controller determines that the real-time differential pressure exceeds the preset differential pressure threshold, and the temperature difference between the inlet and outlet of heat exchanger 1 is lower than the normal heat transfer temperature difference lower limit threshold, the controller comprehensively determines that scaling has occurred inside the heat exchange tube, thereby confirming and maintaining the output of the second frequency control signal. If the real-time differential pressure exceeds the preset differential pressure threshold but the temperature difference remains at or above the normal heat transfer temperature difference lower limit threshold, it is determined that the system flow fluctuation is abnormal, and the second frequency control signal is not triggered. The normal heat transfer temperature difference lower limit threshold is calculated by multiplying the fluid temperature difference between the inlet and outlet of heat exchanger 1, obtained through calibration of the cleaning system under scale-free and clean conditions, by an allowable fluctuation coefficient of 0.8 to 0.95.

[0085] By relying on the coordinated operation of the segmented control function and the detection unit, the control system avoids the pulse control valve 3 from being in a high-frequency operating state for a long time while ensuring the descaling effect of the heat exchange tube. This reduces the energy consumption of the pneumatic system and extends the mechanical service life of the pulse control valve 3.

[0086] Specific application examples: To verify the actual descaling effect of the online cleaning system and method for small-diameter heat exchangers proposed in this invention in the wastewater concentration treatment process at the end of a coal-fired power plant, and to solve the problems of heat exchange efficiency reduction and excessive energy consumption due to scaling in high-salt wastewater, this embodiment is based on the application scenario of heat exchanger 1 in the flash concentration section of desulfurization wastewater in a coal-fired power plant, and in conjunction with the attached... Figure 3 and attached Figure 4 The running test data shown is explained in detail.

[0087] Appendix Figure 4 and attached Figure 5 The data are all engineering operation log data collected from the control system background and comparative test data under different cleaning strategies.

[0088] In this application scenario, the inner diameter of the heat exchange tubes inside heat exchanger 1 is limited to 20mm. Sampling analysis revealed that the main deposits in the wastewater of this section are a hard, dense scale layer formed from silicates; therefore, glass microspheres are selected as the solid particles in the cleaning medium. The liquid density test value of the final wastewater is... (i.e., 1150 kg / m) 3 ).

[0089] Before the system is put into operation, the solid particle parameters and aerodynamic parameters are first calibrated and calculated, and the particle size is selected. (0.0012m), density (i.e., 2400 kg / m) 3 The glass microspheres were set to a volume concentration of 10%, and the fluid velocity in the pipeline from the outlet of the circulating pump 8 to the inlet of the heat exchanger 1 was set to 1.8 m / s.

[0090] Based on the formula for the terminal settling velocity of particles in a fluid Find the fluid drag coefficient at that Reynolds number from the table. The value is 0.44, calculated by substituting the system data. .

[0091] The calculation results show that the terminal settling velocity of 0.20 m / s is much smaller than the fluid running velocity of 1.8 m / s, which verifies that glass microspheres with set density and particle size can maintain a good suspension state inside the pipeline and heat exchange tube, meeting the physical conditions for downward settling separation and pumping to prevent deposition inside the gas-liquid-solid separation device 5.

[0092] In the pressure setting stage of the pulse air intake device, the vertical height of the operating liquid level inside the gas-liquid-solid separator 5 from the bottom liquid inlet of the heat exchanger 1 is known. It is 4.5m, according to the formula Calculate hydrostatic pressure The estimated resistance loss of the system flowing through the high-pressure one-way check valve and gas injection orifice. The pressure is 0.12 MPa, based on the minimum threshold constraint formula for gas supply pressure. , and thus Accordingly, the gas supply pressure from the external gas source to the gas storage tank 4 is stably set at 0.35 MPa, ensuring that the high-pressure gas jet has sufficient penetrating power.

[0093] During the actual circulation descaling phase, the control system performs frequency conversion regulation based on real-time fluid resistance to verify the system's anti-scaling and energy-saving effects.

[0094] The system was calibrated under scale-free and clean conditions on the heat exchange tubes to obtain the reference pressure difference between the inlet and outlet of heat exchanger 1. The system sets the differential pressure threshold coefficient. According to the preset differential pressure threshold formula The preset differential pressure threshold is calculated. .

[0095] The duration of a single opening of pulse control valve 3 is fixed at 0.5 seconds, and the first frequency is set to... =0.2Hz (low frequency to prevent deposition), the second frequency is set to (High-frequency scouring and stripping).

[0096] Appendix Figure 4 This is a line graph showing the operation of the control strategy of the system of the present invention. The horizontal axis represents the operating time (h), the left vertical axis represents the pressure difference between the inlet and outlet of heat exchanger 1 (kPa), and the right vertical axis represents the operating frequency of the pulse control valve 3 (Hz). (See attached diagram.) Figure 4 The data trajectory shows that the real-time pressure difference varies between 0 and 120 hours. Fluctuating between 45kPa and 58kPa, the controller operates according to the formula. Calculate real-time differential pressure, because The system follows the first frequency of segmented function calls. The pulse control valve 3 operates at a low frequency of 0.2Hz to maintain particle suspension.

[0097] When the system reached its 123rd hour of operation, micro-scaling on the pipe wall caused a reduction in the flow cross-section, and the data collected by the differential pressure detection unit showed the real-time differential pressure. It climbed to 62 kPa.

[0098] The numerical comparison result at this time is: The control system synchronously checked the data from the temperature detection unit 11 and found that the temperature difference between the inlet and outlet of the heat exchanger 1 was 15.2℃, which was lower than the calibrated lower limit threshold of normal heat transfer temperature difference of 16.47℃ (calculated by multiplying the temperature difference of 18.3℃ in the clean state by the allowable fluctuation coefficient of 0.9). This eliminated the interference of abnormal flow fluctuation and confirmed that scaling had occurred.

[0099] The controller is based on the frequency control function Switch the output signal to the second frequency. The pulse control valve 3 opens and closes at a high frequency of 1.5Hz, such as... Figure 4 As shown in the curve, within the range of 123 to 128 hours, high-frequency pulsed bubbles enhanced the mechanical scouring and removal of the pipe wall by the glass microspheres. After the scale layer was removed, the real-time pressure difference... The curve shows a clear downward trend, and by the 128th hour, the real-time pressure difference... When the pressure drops to 48 kPa (≤60.75 kPa), the system determines that the pipe wall has returned to cleanliness, and the controller actively adjusts the operating frequency of pulse control valve 3 back to normal. (0.2Hz), the control system realizes a feedback closed loop of dirt monitoring and online cleaning intensity.

[0100] To further verify the comprehensive benefits of the present invention, a comparative test was conducted on three parallel heat exchangers (No. 1, No. 2, and No. 3) of the same specifications, with desulfurization wastewater of the same quality input under the same concentration conditions, and different cleaning strategies were implemented.

[0101] Heat exchanger No. 1 adopts a traditional strategy: pumping only solid-liquid mixed fluid (without pulsed gas injection disturbance).

[0102] Heat exchanger No. 2 adopts a fixed-frequency gas-solid flushing strategy: the system continuously injects gas with a fixed high-frequency pulse of 1.5Hz.

[0103] Heat exchanger No. 3 adopts the strategy of this invention: adaptive variable frequency gas-solid cleaning strategy (0.2Hz / 1.5Hz automatically switching according to pressure difference).

[0104] Appendix Figure 5 The image shows a grayscale bar chart comparing the continuous operating cycle and pneumatic energy consumption of the equipment under three cleaning strategies. The horizontal axis represents different control strategies. The left main vertical axis represents the continuous operating cycle (days) of heat exchanger 1 before forced shutdown for cleaning due to scaling and blockage. The right secondary vertical axis represents the corresponding compressed air energy consumption of the pneumatic system per unit time (kWh / day).

[0105] Depend on Figure 5 Data comparison shows that heat exchanger No. 1 (light gray column) has a continuous operating cycle of only 22 days due to the lack of turbulent disturbance from bubbles, and frequent shutdowns. Heat exchanger No. 2 (medium gray column) has no scaling due to continuous high-frequency gas-solid flushing, and its continuous operating cycle reaches more than 90 days. However, its pneumatic system has an energy consumption of up to 45 kWh / day, and the compressed air is wasted seriously.

[0106] The No. 3 heat exchanger (dark gray column) using this invention also achieved a continuous operating cycle of 92 days, indicating that the adaptive adjustment strategy fully achieved the descaling effect of high-frequency continuous flushing. At the same time, since the equipment is in a low-frequency stable state of 0.2Hz for most of the time, its pneumatic system energy consumption is only 14kWh / day, which is about 68.8% lower than that of the No. 2 heat exchanger.

[0107] Summary of application examples: This embodiment demonstrates the online cleaning system and method for small-diameter heat exchangers provided by the present invention. On the one hand, it accurately limits the physical parameters and pneumatic pressure of the cleaning consumables using fluid dynamics formulas, achieving suspended descaling and non-powered recovery of solid particles. On the other hand, based on the comparison between real-time pressure difference and a set threshold, the frequency of the pulse valve is dynamically switched between anti-deposition and powerful descaling states. While eliminating the thermal resistance of fouling on the pipe wall and extending the operating cycle of heat exchanger 1, it avoids ineffective losses of air source and mechanical valves, effectively ensuring long-term, low-energy-consumption operation of the system.

Claims

1. An online cleaning system for small-diameter heat exchangers, characterized in that, include: Storage tank (9); A circulating pump (8) is provided, the inlet of which is connected to the outlet of the storage tank (9) and the outlet of which is connected to the inlet of the heat exchanger (1), for conveying the cleaning medium inside the storage tank (9) to the inlet of the heat exchanger (1). The pulse air intake device includes a pulse control valve (3) for injecting compressed gas into the heat exchanger (1) by the periodic opening and closing frequency of the pulse control valve (3), so that the compressed gas and the cleaning medium form a gas-liquid-solid three-phase mixed fluid; A gas-liquid-solid separation device (5) is used to receive and separate the gas-liquid-solid three-phase mixed fluid flowing out from the outlet of the heat exchanger (1); The differential pressure detection unit (10) and the temperature detection unit (11) are respectively used to collect the fluid pressure data and temperature data of the inlet and outlet of the heat exchanger (1) and send them to the controller; The controller adjusts the opening and closing frequency of the pulse control valve (3) in segments according to the fluid pressure data and the temperature data.

2. The online cleaning system for small-diameter heat exchangers according to claim 1, characterized in that, The pulse air intake device also includes an air storage tank (4), the air intake end of the pulse control valve (3) is connected to the air storage tank (4), the air outlet end of the pulse control valve (3) is connected to the bottom of the heat exchanger (1) through the air distribution pipe (2), the air distribution pipe (2) is located in the area below the tube sheet at the bottom of the heat exchanger (1), and multiple gas injection holes are opened on the pipe wall of the air distribution pipe (2); The cleaning medium comprises a liquid and solid particles dispersed in the liquid.

3. The online cleaning system for small-diameter heat exchangers according to claim 1, characterized in that, The inlet of the gas-liquid-solid separation device (5) is configured as a tangential liquid inlet, which is located on the upper side wall of the housing of the gas-liquid-solid separation device (5). The bottom of the gas-liquid-solid separation device (5) is formed into an inverted conical structure. The lowest end of the inverted conical structure is provided with a solid outlet. An overflow pipe is vertically arranged in the center of the gas-liquid-solid separation device (5). The bottom end of the overflow pipe is closed. The top end of the overflow pipe passes through the shell of the gas-liquid-solid separation device (5) and forms a liquid outlet. A filter screen (6) is sleeved on the outer side wall of the overflow pipe. The filter screen (6) is a wedge-shaped wire filter screen.

4. The online cleaning system for small-diameter heat exchangers according to claim 3, characterized in that, The upper part of the side wall of the storage tank (9) is provided with a fine powder overflow port. A microporous intercepting mesh with a pore size between 0.1 mm and 0.4 mm is fixedly provided at the fine powder overflow port. A particle replenishment port is provided at the top of the storage tank (9). The solid outlet is connected to the interior of the storage tank (9) through a return pipe. The bottom of the storage tank (9) is formed into an inverted conical structure, and the outlet of the storage tank (9) is located at the lowest point of the inverted conical structure of the storage tank (9).

5. The online cleaning system for small-diameter heat exchangers according to claim 2, characterized in that, The liquid is end-of-pipe wastewater, the particle size of the solid particles is limited to 0.5 mm to 2.0 mm, the volume concentration of the solid particles inside the storage tank (9) is set to 5% to 15%, and the density of the solid particles is limited to 1.2 g / cm³. 3 Up to 2.5g / cm 3 Within the range.

6. The online cleaning system for small-diameter heat exchangers according to claim 1, characterized in that, The controller calculates the difference between the fluid pressure data at the inlet and the outlet to obtain the real-time differential pressure. The controller stores a reference differential pressure and multiplies the reference differential pressure by a differential pressure threshold coefficient to obtain a preset differential pressure threshold. The controller calculates the temperature difference between the inlet and outlet of the liquid exchanger to obtain the temperature difference. The controller also stores a normal heat transfer temperature difference lower limit threshold. The normal heat transfer temperature difference lower limit threshold is calculated by multiplying the fluid temperature difference between the inlet and outlet of the heat exchanger (1) obtained by the cleaning system under the condition of the heat exchange tube inside the heat exchanger (1) being scale-free and clean by the allowable fluctuation coefficient. The controller adjusts the opening and closing frequency by combining the real-time pressure difference, the preset pressure difference threshold, the temperature difference, and the lower limit threshold of the normal heat transfer temperature difference.

7. The online cleaning system for small-diameter heat exchangers according to claim 6, characterized in that, The controller adjusts the opening and closing frequency of the pulse control valve (3) in segments according to the following rules, and the duration of a single opening of the pulse control valve (3) is set to a constant value: When the real-time differential pressure is less than or equal to the preset differential pressure threshold, the controller outputs a first frequency control signal to the pulse control valve (3); When the real-time differential pressure is greater than the preset differential pressure threshold and the temperature difference is lower than the normal heat transfer temperature difference lower limit threshold, the controller outputs a second frequency control signal to the pulse control valve (3), and the frequency value corresponding to the second frequency control signal is greater than the frequency value corresponding to the first frequency control signal. When the real-time differential pressure value falls back to less than or equal to the preset differential pressure threshold, the controller resumes outputting the first frequency control signal to the pulse control valve (3).

8. The online cleaning system for small-diameter heat exchangers according to claim 2, characterized in that, A high-pressure one-way check valve is connected in series on the connecting pipeline between the pulse control valve (3) and the gas distribution pipe (2). The minimum threshold of the gas supply pressure inside the gas storage tank (4) is greater than the sum of the liquid static pressure at the liquid inlet and the system flow resistance loss.

9. The online cleaning system for small-diameter heat exchangers according to claim 1, characterized in that, In the pipeline between the outlet of the storage tank (9) and the inlet of the circulating pump (8), and in the connecting pipeline between the outlet of the circulating pump (8) and the inlet of the heat exchanger (1), the radius of curvature of the elbow component in the fluid direction changing area is 3 to 5 times the inner diameter of the pipeline.

10. An online cleaning method for small-diameter heat exchangers, characterized in that, An online cleaning system for small-diameter heat exchangers according to any one of claims 1-9 includes the following steps: The cleaning medium is delivered to the inlet of the heat exchanger (1) by the circulating pump (8); During the process of the cleaning medium entering the heat exchanger (1), the pulse air intake device injects compressed gas into the heat exchanger (1) through the opening and closing frequency of the pulse control valve (3). The compressed gas and the cleaning medium merge inside the heat exchanger (1) to form a gas-liquid-solid three-phase mixed fluid. The gas-liquid-solid three-phase mixed fluid flows inside the heat exchanger (1) and mechanically scours the inner wall of the heat exchange tube. After being scourted, the gas-liquid-solid three-phase mixed fluid flows out of the heat exchanger (1) and enters the gas-liquid-solid separation device (5). The gas-liquid-solid separation device (5) performs physical separation on the gas-liquid-solid three-phase mixed fluid that enters the device, separating the gas-liquid-solid three-phase mixed fluid into gas, liquid and solid particles. The gas is discharged from the cleaning system, the solid particles are returned to the storage tank (9) for recycling, and the liquid is discharged into the downstream pipeline. When the system is in operation, the differential pressure detection unit (10) and the temperature detection unit (11) respectively collect the fluid pressure data and temperature data of the inlet and outlet of the heat exchanger (1) and send them to the controller; The controller receives the fluid pressure data and the temperature data, calculates the real-time differential pressure based on the fluid pressure data, retrieves the internally stored reference differential pressure and multiplies it by the differential pressure threshold coefficient to calculate the preset differential pressure threshold. The temperature difference is calculated based on the temperature data. The real-time pressure difference is compared with the preset pressure difference threshold. The scaling phenomenon is determined by comparing the temperature difference with the lower limit threshold of the normal heat transfer temperature difference stored in the internal memory. Then, the opening and closing frequency of the pulse control valve (3) is adjusted in segments.

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