Automatic detection device for foam in an aquaculture wastewater anaerobic tank

Abstract

This invention discloses an automatic foam detection device for anaerobic ponds used in aquaculture wastewater, belonging to the field of biogas engineering detection technology. The device includes a sampling component, a level gauge, a sampling pump, a detection chamber, a return pipe, a return pump, and a controller. The sampling component includes first, second, and third sampling ports located on the side wall of the anaerobic pond, and corresponding first, second, and third sampling valves. The level gauge detects the liquid level in the pond. The sampling pump sequentially draws the medium from each sampling port into the detection chamber outside the pond. Capacitive and conductive sensors inside the chamber determine whether the medium is liquid, foam, or gas. The controller calculates the foam layer thickness based on the liquid level and outputs an alarm. The return pump outlet is split into two paths via a three-way connector: the first path returns to the anaerobic pond via a return valve, and the second path connects to a foam collection tank via a defoaming valve. When foam exceeds a threshold, the two valves are switched to send the foam into the collection tank. The sensor is external to the pond, does not scale, is explosion-proof and simplified, and adapts to liquid level fluctuations, achieving integrated detection and defoaming.

Description

Technical Field

[0001] This invention relates to the field of anaerobic treatment of aquaculture wastewater and biogas engineering detection technology, specifically to an automatic foam detection device for anaerobic ponds of aquaculture wastewater. Background Technology

[0002] Livestock farm wastewater is characterized by high chemical oxygen demand (COD), high ammonia nitrogen, and high suspended solids. It is typically treated by anaerobic digestion in anaerobic ponds (such as enamel-lined tanks or black membrane biogas digesters) after solid-liquid separation. Because livestock wastewater is rich in proteins, fats, and long-chain fatty acids, a stable foam layer easily forms on the surface during anaerobic digestion.

[0003] In existing technologies, the detection of foam in anaerobic ponds mainly relies on manual inspection. However, anaerobic ponds in livestock farms are mostly closed structures, making it impossible for operators to directly observe the foam condition on the liquid surface. Foam bursts often occur within hours, making timely warnings difficult to obtain manually. Among published patent documents, Chinese patent application CN116676182A discloses a fully automatic defoaming control device for bioreactors or fermenters. It uses multiple vertically and horizontally arranged detection electrodes to detect foam overflow and trigger the defoaming device. However, its detection method is based on foam arrival, not continuous detection of foam layer thickness. Furthermore, the detection electrodes are located inside the pond, raising concerns about electrode scaling and potential explosion-proof issues in the closed biogas environment. Chinese patent application CN107151629A discloses an intelligent two-stage desulfurization device for biogas, which uses a foam sensor above the bioreactor liquid surface and triggers a spray defoaming mechanism. However, this device is designed for desulfurization bioreactors and uses a single-point detection method, making it impossible to obtain real-time foam layer thickness. Chinese patent application CN112390326A discloses a device for absorbing floating foam on the surface of sewage. It absorbs foam through a lifting mechanism and a collection chamber. However, the device only has the function of absorbing foam and defoaming, but does not have the function of foam detection and early warning, and it is not designed for anaerobic ponds.

[0004] In summary, existing technologies lack an automatic detection device that can adapt to the closed biogas environment of anaerobic ponds for aquaculture wastewater, whose sensors do not come into contact with poor water quality, can adapt to liquid level fluctuations and detect foam layer thickness in real time, and integrate detection and defoaming. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an automatic foam detection device for aquaculture wastewater anaerobic ponds that can be adapted to the closed biogas environment of anaerobic ponds, where the sensor does not have long-term contact with the poor water quality in the pond, and integrates detection and defoaming functions.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: An automatic foam detection device for anaerobic ponds of aquaculture wastewater includes a sampling component, a level gauge, a sampling pump, a detection chamber, a return pipe, and a controller. The sampling assembly includes a first sampling port, a second sampling port, and a third sampling port arranged sequentially along the height direction on the side wall of the anaerobic tank, and correspondingly connected to a first sampling valve, a second sampling valve, and a third sampling valve; a level gauge is installed inside the anaerobic tank to detect the liquid level; the inlet of the sampling pump is connected to the first sampling valve, the second sampling valve, and the third sampling valve via pipelines; a detection chamber is located outside the anaerobic tank, with its inlet connected to the outlet of the sampling pump, and a capacitance sensor and a conductivity sensor are installed inside the chamber to determine whether the medium entering the chamber is in the liquid phase, foam layer, or gas phase; a return pipe is connected to the outlet of the detection chamber, and a return pump is installed on the return pipe to return the detected medium to the anaerobic tank; a controller is electrically connected to the level gauge, each sampling valve, the sampling pump, the return pump, the capacitance sensor, and the conductivity sensor, and is used to determine the foam layer thickness based on the liquid level and the medium determination results of each sampling port, and output the detection results and alarm signals.

[0007] Furthermore, the first sampling port is located above the liquid surface in the anaerobic tank, the second sampling port is located at the liquid surface, and the third sampling port is located in the liquid phase below the liquid surface in the anaerobic tank. The height distance between the first and third sampling ports covers the liquid level fluctuation range of the anaerobic tank.

[0008] Furthermore, the level gauge is a hydrostatic level gauge. The pressure probe of the hydrostatic level gauge is set in the anaerobic tank near the bottom of the tank. The hydrostatic level gauge calculates the position of the liquid level based on the detected hydrostatic pressure of the liquid column.

[0009] Furthermore, the detection chamber is equipped with an inlet, an outlet, and an exhaust port. The inlet is connected to the outlet of the sampling pump, the outlet is connected to the return pipe, and the exhaust port is located at the top of the detection chamber to discharge the gas inside the detection chamber.

[0010] Furthermore, the controller uses the liquid level detected by the level gauge as a reference, compares the medium determination result of the corresponding sampling port when each sampling valve is opened in sequence with the liquid level position, determines the highest sampling port position of the foam layer as the upper surface of the foam layer, and takes the difference between the upper surface of the foam layer and the liquid level position as the thickness of the foam layer.

[0011] Furthermore, the controller sequentially opens the first sampling valve, the second sampling valve, and the third sampling valve according to a preset cycle, and only one sampling valve is opened at any given time. During the opening of the sampling valve, the controller controls the sampling pump to draw the medium at the corresponding sampling port into the detection chamber.

[0012] Furthermore, the controller compares the foam layer thickness with a first preset threshold and a second preset threshold: when the foam layer thickness exceeds the first preset threshold, a warning signal is output; when the foam layer thickness exceeds the second preset threshold, an alarm signal is output. The first and second preset thresholds are predetermined through on-site calibration.

[0013] Furthermore, the outlet of the return pump is divided into two paths via a three-way connector: the first path is connected to the anaerobic tank via a return valve, and the second path is connected to the defoaming branch pipe via a defoaming valve. The end of the defoaming branch pipe is connected to the foam collection tank. When the foam layer thickness exceeds the preset threshold, the controller closes the return valve and opens the defoaming valve. The return pump sends the medium discharged from the detection chamber into the foam collection tank via the defoaming branch pipe.

[0014] Furthermore, the bottom of the foam collection tank is equipped with a drain outlet, which is connected to the anaerobic tank or an external treatment unit via a drain pipe. The foam collection tank is also equipped with a liquid level detector, which outputs a prompt signal when the liquid level in the foam collection tank reaches the preset level.

[0015] Furthermore, filters are installed at the first, second, and third sampling ports, and the first, second, and third sampling valves are all solenoid valves. The sampling pump and return pump are diaphragm pumps.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention places the sampling port directly on the side wall of the anaerobic tank. The sampling pump draws the medium near the liquid surface to the detection chamber outside the tank for judgment. The sensors (capacitive sensors and conductivity sensors) are set in the detection chamber outside the tank, so they are not in long-term contact with the poor water quality of high suspended solids and high oil content inside the tank, which reduces the problem of sensor scaling and failure. After detection, the medium is pressurized by the return pump and returned to the anaerobic tank. During maintenance, only the detection chamber and the return pump need to be disassembled and cleaned outside the tank.

[0017] This invention measures the liquid level in real time using a level gauge. Based on the liquid level position and the medium determination results from three sampling ports, the upper surface of the foam layer is determined, and the thickness of the foam layer is calculated. Even if the liquid level fluctuates due to intermittent feeding in the anaerobic tank, the level gauge can track the liquid level reference in real time, and the determination logic adapts to the liquid level change, overcoming the problem of fixed sampling ports failing when the liquid level fluctuates.

[0018] This invention achieves integrated detection and defoaming through a two-way flow structure where the return pump outlet is split into two paths via a three-way connector (the first path returns to the anaerobic tank via a return valve, and the second path enters the collection tank via a defoaming valve, with the two valves switching independently). During normal detection, the return pump returns the detected medium to the anaerobic tank via the return valve. When the foam layer exceeds the threshold, the return valve is closed and the defoaming valve is opened. The return pump sends the foam discharged from the detection chamber to the foam collection tank outside the tank for centralized disposal via the defoaming branch pipe. The same set of sampling pipelines and return pump simultaneously achieve the dual functions of detection and defoaming, eliminating the need for an additional independent defoaming device.

[0019] During defoaming and suction, the controller pauses foam layer thickness detection and shields the judgment signals of the capacitance and conductivity sensors to prevent the sensors from being covered by foam when a large amount of foam flows through the detection chamber, which could lead to false judgments. The controller adopts an intermittent cyclic defoaming strategy. After each preset period of defoaming and suction, it temporarily exits the defoaming mode and resumes detection. Based on the detection results, it determines whether the foam layer thickness has fallen back to a safe range. If it has fallen back, the defoaming ends; if it has not fallen back, the next defoaming cycle continues. This cycle continues until the defoaming target is met or a failure alarm is triggered. This ensures accurate determination of the defoaming endpoint while avoiding sensor misjudgments and guarantees that the defoaming treatment and detection functions do not interfere with each other. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of an automatic foam detection device for anaerobic ponds of aquaculture wastewater, installed on an enamel-lined assembled tank according to the present invention. Figure 2 This is a schematic diagram of the detection cavity in this invention; The markings in the diagram are as follows: 1. Anaerobic tank; 3. Sampling pump; 4. Detection chamber; 6. Return pump; 7. Level gauge; 11. Side wall; 21. First sampling port; 22. Second sampling port; 23. Third sampling port; 24. First sampling valve; 25. Second sampling valve; 26. Third sampling valve; 41. Inlet; 42. Outlet; 43. Exhaust port; 44. Capacitive sensor; 45. Conductivity sensor; 51. Return pipe; 52. Reflux valve; 53. Defoaming branch pipe; 54. Defoaming valve; 55. Foam collection tank. Detailed Implementation

[0021] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0022] like Figure 1 and Figure 2 As shown in this embodiment, the overall structure of the automatic foam detection device for anaerobic ponds of aquaculture wastewater according to the present invention will be described.

[0023] The device includes a sampling assembly, a level gauge 7, a sampling pump 3, a detection chamber 4, a return pipe 51, a return pump 6, and a controller. The sampling assembly includes a first sampling port 21, a second sampling port 22, and a third sampling port 23, arranged sequentially along the height direction on the side wall 11 of the anaerobic tank 1, and a first sampling valve 24, a second sampling valve 25, and a third sampling valve 26 respectively connected to the three sampling ports. The level gauge 7 is installed inside the anaerobic tank 1 to detect the liquid level within the anaerobic tank 1.

[0024] The inlet of sampling pump 3 is connected to three sampling valves via pipelines. The detection chamber 4 is located outside the anaerobic tank 1, and its inlet 41 is connected to the outlet of sampling pump 3. The chamber is equipped with a capacitive sensor 44 and a conductivity sensor 45 to determine whether the medium entering the chamber is in the liquid phase, foam layer or gas phase.

[0025] The return pipe 51 is connected to the outlet 42 of the detection chamber 4. A return pump 6 is installed on the return pipe 51 to return the detected medium to the anaerobic tank 1. The controller is electrically connected to the level gauge 7, three sampling valves, sampling pump 3, return pump 6, capacitance sensor 44, and conductivity sensor 45. Based on the liquid level detected by the level gauge 7 and the judgment result of the medium extracted from the corresponding sampling port when each sampling valve is opened in sequence, the thickness of the foam layer is determined and the detection result and alarm signal are output.

[0026] Specifically, anaerobic tank 1 is an enamel-lined assembled tank for anaerobic digestion treatment of aquaculture wastewater, with a biogas collection pipe 12 installed on the top of the tank to collect anaerobic gas. During operation, the controller sequentially opens the first sampling valve 24, the second sampling valve 25, and the third sampling valve 26 according to a preset cycle. Only one sampling valve is open at any given time. During the opening of that valve, the sampling pump 3 draws the medium from the corresponding sampling port into the detection chamber 4. The capacitance sensor 44 and conductivity sensor 45 in the detection chamber 4 perform a dual-mode judgment on the drawn-in medium to determine whether it is a liquid phase, a foam layer, or a gas phase. The level gauge 7 measures the liquid level in real time. The controller calculates the foam layer thickness based on the liquid level and the judgment results from each sampling port, and outputs an alarm signal when the foam layer thickness exceeds a preset threshold. The detected medium is pressurized by the return pump 6 on the return pipe 51 and then returned to anaerobic tank 1. Based on the above scheme, the device realizes automatic detection of the foam layer in the anaerobic pond of aquaculture wastewater. The sensor is set outside the pond and does not come into long-term contact with the poor water quality. There are no electrical components such as live detection electrodes or probes inside the pond that are prone to scaling. It is explosion-proof and simple, and the detection results are reliable, providing timely early warning for accidents such as foam overflow and material spillage.

[0027] In this embodiment, the arrangement of the three sampling ports is further explained. The first sampling port 21 is located above the liquid surface (normal) in the anaerobic tank 1, the second sampling port 22 is located near the liquid surface (normal), and the third sampling port 23 is located in the liquid phase below the liquid surface (normal). The height distance between the first sampling port 21 and the third sampling port 23 covers the liquid level fluctuation range of the anaerobic tank 1. Specifically, the anaerobic tank for livestock farm wastewater usually adopts an intermittent feeding method, feeding several times a day. During feeding, the liquid level rises, and during digestion, the liquid level slowly falls back. During normal operation, the liquid level has a certain fluctuation range.

[0028] During installation, the arrangement of the three sampling ports is determined according to the normal liquid level fluctuation range of the anaerobic tank 1: the first sampling port 21 is arranged at a predetermined distance above the normal liquid level, the second sampling port 22 is arranged at the normal liquid level, and the third sampling port 23 is arranged at a predetermined distance below the normal liquid level. The height distance between the first sampling port 21 and the third sampling port 23 covers the liquid level fluctuation range and leaves sufficient margin.

[0029] The third sampling port 23 is positioned at a depth exceeding the normal liquid level fluctuation range. This is to ensure that pure liquid phase medium is drawn in under any liquid level fluctuation condition, providing a stable liquid phase reference signal for the capacitive sensor 44 and the conductivity sensor 45. This prevents the judgment logic from failing due to all sampling ports being removed from the liquid phase caused by a drop in liquid level. All three sampling ports are located on the side wall 11, with filters installed at each port to prevent suspended matter from entering the pipeline. The port diameter is selected based on the pipeline specifications and medium characteristics, facilitating pipeline connection and maintenance. Based on this arrangement, regardless of the liquid level's position within the fluctuation range, at least one sampling port is located in the liquid phase below the liquid surface as a reference, while at least one sampling port is located in the foam layer or gas phase region above the liquid surface, thus ensuring the reliability of the foam layer thickness determination. To prevent the liquid level from exceeding the coverage of the sampling port under extreme operating conditions, the level gauge 7 detects the liquid level position in real time and compares it with the positions of the second sampling port 22 and the first sampling port 21. When the liquid level is lower than the second sampling port 22 or higher than the first sampling port 21, the controller outputs a liquid level abnormality warning signal to prompt the operator to adjust the feed rate or check the liquid level control equipment, so as to avoid the liquid level deviating from the coverage of the sampling port for a long time, which would cause the foam layer detection to fail.

[0030] In this embodiment, the structure and installation of the level gauge 7 are further described. The level gauge 7 is a hydrostatic level gauge, and its pressure probe is set in the anaerobic tank 1 near the bottom of the tank. The position of the liquid level is calculated based on the detected hydrostatic pressure of the liquid column. Specifically, the hydrostatic level gauge calculates the liquid level height by measuring the hydrostatic pressure of the liquid at the depth of the probe and combining it with the liquid density. The pressure probe is installed in the anaerobic tank 1 near the bottom of the tank, avoiding the disturbed area near the foam layer and the liquid surface. The advantage of using a hydrostatic level gauge is that the density of the foam layer is much lower than that of the liquid, and its hydrostatic pressure contribution is negligible. Therefore, the presence of the foam layer will not significantly affect the measurement of the hydrostatic pressure of the liquid column. The measured liquid level position is the true liquid level position, which is not affected by the foam lifting, and overcomes the problem of falsely high liquid levels in the foam condition of float-type level gauges. The level gauge 7 is an intrinsically safe instrument and meets the explosion-proof requirements of closed environments containing biogas. Based on the above scheme, the controller can obtain accurate real-time liquid level position, providing a reliable benchmark for the joint determination of foam layer thickness. Even if intermittent feeding in the anaerobic tank causes liquid level fluctuations, the liquid level gauge 7 can track the liquid level changes in real time, ensuring the adaptability of the determination logic.

[0031] In this embodiment, the structure of the detection chamber 4 is further described. The detection chamber 4 is provided with an inlet 41, an outlet 42, and an exhaust port 43. The inlet 41 is connected to the outlet of the sampling pump 3, the outlet 42 is connected to the return pipe 51, and the exhaust port 43 (with a one-way valve at the connection point with the external pipeline) is located at the top of the detection chamber 4 to discharge the gas inside the detection chamber 4. Specifically, the detection chamber 4 is a closed cavity located outside the anaerobic tank 1, and its volume is matched with the suction flow rate of the sampling pump 3. The medium pumped in by the sampling pump 3 enters the detection chamber 4 through the inlet 41. A capacitance sensor 44 and a conductivity sensor 45 are installed inside the detection chamber 4. The capacitance sensor 44 measures the dielectric constant of the medium inside the chamber, and the conductivity sensor 45 measures the conductivity of the medium inside the chamber. The two sensors are used together to determine whether the medium inside the chamber is a liquid phase, a foam layer, or a gas phase. The joint determination by the capacitance sensor 44 and the conductivity sensor 45 is based on pre-calibrated first capacitance threshold, second capacitance threshold, first conductivity threshold, and second conductivity threshold: when the detection value of the capacitance sensor 44 is higher than the first capacitance threshold and the detection value of the conductivity sensor 45 is higher than the first conductivity threshold, the medium in the chamber is determined to be liquid; when the detection value of the capacitance sensor 44 is between the first capacitance threshold and the second capacitance threshold, and the detection value of the conductivity sensor 45 is between the first conductivity threshold and the second conductivity threshold, the medium in the chamber is determined to be a foam layer; when the detection value of the capacitance sensor 44 is lower than the second capacitance threshold and the detection value of the conductivity sensor 45 is lower than the second conductivity threshold, the medium in the chamber is determined to be gas. Each determination threshold is determined through on-site calibration before the device is put into operation: the first capacitance threshold and the first conductivity threshold are calibrated using the clarified liquid medium in the anaerobic tank 1, and the second capacitance threshold and the second conductivity threshold are calibrated using the foam layer medium near the liquid surface under normal foaming conditions, and are periodically checked according to seasonal changes in water quality. The first capacitance threshold is greater than the second capacitance threshold, and the first conductivity threshold is greater than the second conductivity threshold. Since the foam layer is a gas-liquid mixture, its dielectric constant and conductivity are between the liquid and gas phases, and vary with the foam's moisture content. The aforementioned dual-threshold range determination method can distinguish between wet foam with high moisture content and the liquid phase, avoiding difficulties in determining the gas-liquid transition range using a single sensor parameter. After detection, the medium flows into the return pipe 51 through the outlet 42, and the gas accumulated in the cavity is discharged through the top exhaust port 43 to prevent gas accumulation from affecting detection accuracy. The diameter of the exhaust port 43 matches the suction flow rate of the sampling pump 3 in normal detection mode. In defoaming suction mode, the exhaust port 43 remains open and is connected to the biogas collection pipe 12 at the top of the anaerobic tank 1 via a pipeline (equipped with a one-way valve and a flame arrester). This allows for the timely extraction of gas released during the defoaming process as a large amount of foam enters the detection chamber 4, maintaining pressure balance within the detection chamber 4 and ensuring that foam continues to enter the detection chamber 4 without being hindered by the internal gas pressure.Based on the above scheme, the sensor works in the detection chamber outside the pool, without being in direct contact with the poor water quality of high suspended solids and high oil content inside the pool for a long time. This reduces the problem of sensor scaling and failure. During maintenance, only the detection chamber 4 needs to be disassembled and cleaned outside the pool. There is no need to enter the pool or stop production, which significantly reduces the operating and maintenance costs.

[0032] In this embodiment, the joint determination method of the controller is further explained. The controller uses the liquid level position detected by the level gauge 7 as a reference, compares the medium determination result of the corresponding sampling port when each sampling valve is opened sequentially with the liquid level position, and determines the highest sampling port position of the foam layer as the upper surface of the foam layer. The difference between the upper surface of the foam layer and the liquid level position is taken as the foam layer thickness. Specifically, the height positions of the three sampling ports are known; let the height of the first sampling port 21 be H31, the height of the second sampling port 22 be H32, and the height of the third sampling port 23 be H33. The liquid level position measured by the level gauge 7 is H_liquid_level.

[0033] The controller sequentially opens three sampling valves and collects the medium determination results from the corresponding sampling ports: if the medium sampled from a certain sampling port is determined to be a foam layer, then the sampling port is located within the foam layer; if it is determined to be a liquid phase, then the sampling port is located below the liquid surface; if it is determined to be a gas phase, then the sampling port is located above the foam layer. The controller determines the highest position among all sampling ports that sample the foam layer as the upper surface Hupper of the foam layer, and the thickness of the foam layer Hbubble is equal to Hupper minus Hliquid surface.

[0034] For example, when the first sampling port 21 and the second sampling port 22 collect foam while the third sampling port 23 collects liquid, the upper surface of the foam layer is located near the first sampling port 21, and the foam layer thickness is H31 minus H (liquid surface). Since the sampling ports are discretely arranged along the height direction, when the highest sampling port position that collects the foam layer is taken as the upper surface of the foam layer, the calculated value of the foam layer thickness has a negative deviation (i.e., a conservative value) relative to the true value that is no greater than the distance between adjacent sampling ports. This deviation direction prevents the device from prematurely alarming when the foam layer approaches the warning threshold, and this deviation can be further reduced by appropriately reducing the distance between adjacent sampling ports, without affecting the reliability of the foam overflow warning function. Based on the above joint judgment method, even if the anaerobic tank liquid level fluctuates, the liquid level position provided by the level gauge 7 in real time always serves as an accurate reference. The calculation of the foam layer thickness is independent of the absolute position of the liquid surface, and the judgment result adapts to changes in liquid level, overcoming the problem that fixed sampling ports cannot locate the foam layer when the liquid level fluctuates.

[0035] In this embodiment, the sampling control process is further described. The controller sequentially opens the first sampling valve 24, the second sampling valve 25, and the third sampling valve 26 according to a preset cycle, and only one sampling valve is open at any given time. During the opening of the sampling valve, the controller controls the sampling pump 3 to draw the medium at the corresponding sampling port into the detection chamber 4. Specifically, the preset cycle can be adjusted and set by the controller according to the foaming susceptibility. In each sampling cycle, the controller first opens the first sampling valve 24 and starts the sampling pump 3 to run for a few seconds, drawing the medium at the first sampling port 21 into the detection chamber 4 to complete the determination. After that, the sampling pump 3 is stopped and the first sampling valve 24 is closed. Then, the same operation is performed on the second sampling valve 25 and the third sampling valve 26 in sequence. After sampling pump 3 starts, it first undergoes a preset pipeline flushing time to drain any residual medium from the previous sampling port. During this flushing phase, the judgment results of capacitive sensor 44 and conductivity sensor 45 are not included in the valid data. After flushing, the detection chamber 4 is filled with fresh medium from the current sampling port. At this time, the judgment values ​​of capacitive sensor 44 and conductivity sensor 45 are collected as valid judgment results. Only one sampling valve is opened at any given time to ensure that the medium in the detection chamber 4 is judged from a single sampling port, avoiding misjudgment caused by the mixing of media from multiple sampling ports. Sampling pump 3 is a diaphragm pump, which can withstand short-term idling and reduces the risk of damage even if the sampling port is in the gas phase region and gas is drawn in. Based on the above control method, the media from the three sampling ports are independently drawn in and judged in sequence. The controller obtains the medium state distribution at each sampling port, providing complete data for the calculation of foam layer thickness.

[0036] In this embodiment, the graded alarm method is further explained. The controller compares the foam layer thickness with a first preset threshold and a second preset threshold: when the foam layer thickness exceeds the first preset threshold, a warning signal is output; when the foam layer thickness exceeds the second preset threshold, an alarm signal is output. The first and second preset thresholds are predetermined through on-site calibration. Specifically, the first and second preset thresholds can be adjusted through the controller's human-machine interface or calibrated on-site based on the historical foaming patterns of anaerobic tank 1. When the foam layer thickness exceeds the first preset threshold, a warning signal is output to alert operators to the foam development trend; when the foam layer thickness exceeds the second preset threshold, an alarm signal is output to alert operators that the foam is in a high-risk state and should be dealt with immediately. Based on the above graded alarm strategy, operators can take different response measures according to the alarm level, and intervene when the foam layer thickness is low, avoiding the passive situation of triggering a single alarm only when the foam layer thickens to the overflow critical state, thus improving the practicality of the device.

[0037] In this embodiment, the integrated detection and defoaming structure is further described. The outlet of the return pump 6 is divided into two paths via a three-way connector: the first path is connected to the anaerobic tank 1 via the return valve 52, and the second path is connected to the defoaming branch pipe 53 via the defoaming valve 54. The end of the defoaming branch pipe 53 is connected to the foam collection tank 55. When the foam layer thickness exceeds a preset threshold, the controller closes the return valve 52 and opens the defoaming valve 54. The return pump 6 sends the medium discharged from the detection chamber 4 into the foam collection tank 55 via the defoaming branch pipe 53. Specifically, in normal detection mode, the sampling pump 3 operates at the normal detection flow rate, and the return pump 6 pressurizes and pumps the detected medium through the return pipe 51. The return valve 52 of the first path remains open, and the defoaming valve 54 of the second path remains closed. The detected medium flows back into the anaerobic tank 1 via the return valve 52. The defoaming suction employs an intermittent cyclic control strategy: when the controller determines that the foam layer thickness exceeds the second preset threshold and triggers defoaming, the controller first closes the first-path return valve 52 and opens the second-path defoaming valve 54. The return pump 6 continues to run, sending the medium discharged from the detection chamber 4 into the foam collection tank 55 via the defoaming branch pipe 53, and continues to run for a preset first defoaming time, which can be pre-calibrated according to the foam characteristics on site. After the first defoaming time ends, the controller immediately closes the defoaming valve 54 and opens the return valve 52, temporarily exiting the defoaming mode and resuming foam layer thickness detection to evaluate the current defoaming effect. During defoaming suction, a large amount of foam continuously flows through the detection chamber 4. To avoid foam covering the capacitance sensor 44 and conductivity sensor 45, causing distortion of the judgment signal, the controller... During defoaming and suction, the device pauses the calculation of foam layer thickness and shields the judgment signals of capacitive sensor 44 and conductivity sensor 45. Judgments from capacitive sensor 44 and conductivity sensor 45 are only restored during the detection window when the defoaming mode is temporarily exited. If the detection result shows that the foam layer thickness is still higher than the preset defoaming termination threshold (which is set to be equal to or lower than the first preset threshold), the controller switches back to defoaming mode and continues suction, repeating the above cycle until the detection result shows that the foam layer thickness has fallen below the defoaming termination threshold. At this point, the controller determines that the defoaming process has completely ended and maintains the reflux detection mode. If the foam layer thickness does not decrease significantly after several consecutive cycles, and the decrease is less than the preset value, the controller outputs a defoaming failure alarm signal, prompting manual intervention. Based on the above scheme, the return pump 6 provides reflux power in detection mode and feeding power in defoaming mode. The dual functions of detection and defoaming can be achieved by independently switching the two valves on their respective branches. After detecting foam, the foam is automatically extracted from the tank for centralized disposal. Intermittent cyclic control solves the problem of the detection signal being shielded during defoaming, making it impossible to determine the defoaming endpoint.

[0038] In this embodiment, the structure of the foam collection tank 55 is further described. The bottom of the foam collection tank 55 is equipped with a drain port, which is connected to the anaerobic tank 1 or an external treatment unit via a drain pipe. A level detector is also installed on the foam collection tank 55, which outputs a prompt signal when the liquid level inside the foam collection tank 55 reaches a preset level. In defoaming mode, the return pump 6 sends the medium discharged from the detection chamber 4 through the second path of the three-way connector, the defoaming valve 54, and the defoaming branch pipe 53 into the foam collection tank 55 for centralized treatment. Specifically, the foam collection tank 55 is a sealed container located outside the anaerobic tank 1. Its volume is determined according to the defoaming cycle and the amount of foam generated. An exhaust port is installed at the top, which is connected to the biogas collection pipe 12 at the top of the anaerobic tank 1 via a pipeline, allowing the biogas with a high methane content released by foam defoaming to enter the subsequent utilization or flare combustion system. A flame arrester is installed on the exhaust pipe to prevent flames from returning to the foam collection tank 55. A drain port is located at the bottom. After entering the foam collection tank 55, the foam naturally breaks down. The resulting liquid, rich in organic matter, can be returned to the anaerobic digester 1 for further fermentation and reuse, or transported to external treatment units such as solid-liquid separation and biogas utilization for resource-based disposal. The foam collection tank 55 is equipped with a level detector (such as a capacitive or hydrostatic level switch). When the liquid level in the tank reaches the preset level, an alert signal is output to remind operators to drain the liquid in time, preventing the foam collection tank 55 from overflowing. Based on the above scheme, the collected foam is properly disposed of and utilized as a resource, the biogas released from the broken foam safely enters the biogas utilization system, and the foam collection tank 55 has overflow protection, achieving a complete closed loop from foam detection and collection to disposal.

[0039] In this embodiment, the key materials and explosion-proof design of the device are further explained. A filter screen is installed at the sampling port, the sampling valve is a solenoid valve, the sampling pump 3 and the return pump 6 are diaphragm pumps, and the level gauge 7 is an intrinsically safe instrument. Specifically, stainless steel filters are installed at all three sampling ports to prevent suspended solids and hair from entering the pipeline and causing blockage; the sampling valve is a solenoid valve, directly controlled by the controller for rapid response; the sampling pump 3 is a diaphragm pump, capable of self-priming and tolerating short-term idling, suitable for drawing gas when the sampling port is in the gas phase region; the return pump 6 is a diaphragm pump, capable of withstanding gas-liquid mixtures such as foam, and the pumping flow rate can be adjusted by changing the drive frequency or stroke length; the level gauge 7 is an intrinsically safe instrument, with the energy of the measurement circuit limited within the intrinsically safe parameter range. Anaerobic tank 1 contains a methane-containing biogas environment, which is a flammable and explosive location. This device only has a passive sampling port and a pressure probe for the level gauge 7 inside the tank. There are no electrical components that are prone to scaling, such as live detection electrodes or probes. The sampling valve, sampling pump 3, detection chamber 4, and controller are all located in a safe area outside the tank, which fundamentally simplifies the explosion-proof design. There is no need to install explosion-proof electrical equipment inside the tank, which reduces equipment costs and installation difficulty.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An automatic foam detection device for anaerobic ponds used for aquaculture wastewater, characterized in that, include: The sampling assembly includes a first sampling port (21), a second sampling port (22) and a third sampling port (23) arranged sequentially along the height direction on the side wall (11) of the anaerobic tank (1), and a first sampling valve (24), a second sampling valve (25) and a third sampling valve (26) respectively connected to each other. A level gauge (7) is installed in the anaerobic tank (1) to detect the position of the liquid level; The sampling pump (3) has its inlet connected to the first sampling valve (24), the second sampling valve (25) and the third sampling valve (26) respectively via pipelines; The detection chamber (4) is located outside the anaerobic tank (1), and its inlet (41) is connected to the outlet of the sampling pump (3). The chamber is equipped with a capacitance sensor (44) and a conductivity sensor (45) for determining whether the medium entering the chamber is liquid, foam layer or gas phase. The return pipe (51) is connected to the outlet (42) of the detection chamber (4). The return pipe (51) is equipped with a return pump (6) for returning the detected medium to the anaerobic tank (1). The controller is electrically connected to the level gauge (7), each sampling valve, the sampling pump (3), the return pump (6), the capacitance sensor (44), and the conductivity sensor (45), and is used to determine the thickness of the foam layer based on the liquid level position and the medium determination result of each sampling port, and output the detection result and alarm signal.

2. The automatic foam detection device for anaerobic ponds of aquaculture wastewater according to claim 1, characterized in that, The first sampling port (21) is located above the liquid surface in the anaerobic tank (1), the second sampling port (22) is located at the liquid surface, and the third sampling port (23) is located in the liquid phase below the liquid surface in the anaerobic tank (1). The height distance between the first sampling port (21) and the third sampling port (23) covers the liquid level fluctuation range of the anaerobic tank (1).

3. The automatic foam detection device for anaerobic ponds of aquaculture wastewater according to claim 1, characterized in that, The level gauge (7) is a hydrostatic level gauge. The pressure probe of the hydrostatic level gauge is set in the anaerobic tank (1) near the bottom of the tank. The hydrostatic level gauge calculates the position of the liquid surface based on the detected hydrostatic pressure of the liquid column.

4. The automatic foam detection device for anaerobic ponds of aquaculture wastewater according to claim 1, characterized in that, The detection chamber (4) is provided with an inlet (41), an outlet (42) and an exhaust port (43). The inlet (41) is connected to the outlet of the sampling pump (3), the outlet (42) is connected to the return pipe (51), and the exhaust port (43) is located at the top of the detection chamber (4) to discharge the gas in the detection chamber (4).

5. The automatic foam detection device for anaerobic ponds of aquaculture wastewater according to claim 1, characterized in that, The controller uses the liquid level detected by the liquid level gauge (7) as a reference, compares the medium determination result of the corresponding sampling port when each sampling valve is opened in sequence with the liquid level position, determines the highest sampling port position of the foam layer as the upper surface of the foam layer, and takes the difference between the upper surface of the foam layer and the liquid level position as the thickness of the foam layer.

6. The automatic foam detection device for anaerobic ponds of aquaculture wastewater according to claim 1, characterized in that, The controller sequentially opens the first sampling valve (24), the second sampling valve (25) and the third sampling valve (26) according to a preset cycle, and only one sampling valve is opened at any time. During the opening of the sampling valve, the controller controls the sampling pump (3) to draw the medium at the corresponding sampling port into the detection chamber (4).

7. The automatic foam detection device for anaerobic ponds of aquaculture wastewater according to claim 1, characterized in that, The controller compares the thickness of the foam layer with a first preset threshold and a second preset threshold: when the thickness of the foam layer exceeds the first preset threshold, it outputs a warning signal; when the thickness of the foam layer exceeds the second preset threshold, it outputs an alarm signal. The first preset threshold and the second preset threshold are predetermined through on-site calibration.

8. The automatic foam detection device for anaerobic ponds of aquaculture wastewater according to claim 1, characterized in that, The outlet of the return pump (6) is divided into two paths via a three-way connector: the first path is connected to the anaerobic tank (1) via the return valve (52), and the second path is connected to the defoaming branch pipe (53) via the defoaming valve (54). The end of the defoaming branch pipe (53) is connected to the foam collection tank (55). When the thickness of the foam layer exceeds the preset threshold, the controller closes the return valve (52) and opens the defoaming valve (54). The return pump (6) sends the medium discharged from the detection chamber (4) into the foam collection tank (55) via the defoaming branch pipe (53).

9. The automatic foam detection device for anaerobic ponds of aquaculture wastewater according to claim 8, characterized in that, The bottom of the foam collection tank (55) is provided with a drain port, which is connected to the anaerobic tank (1) or an external treatment unit via a drain pipe. The foam collection tank (55) is also provided with a liquid level detector, which outputs a prompt signal when the liquid level in the foam collection tank (55) reaches the preset liquid level.

10. The automatic foam detection device for anaerobic ponds of aquaculture wastewater according to claim 1, characterized in that, A filter screen is provided at the first sampling port (21), the second sampling port (22) and the third sampling port (23). The first sampling valve (24), the second sampling valve (25) and the third sampling valve (26) are all solenoid valves. The sampling pump (3) and the return pump (6) are diaphragm pumps.

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