Shell-and-tube heat exchanger abnormity diagnosis method based on multi-parameter monitoring

Abstract

The invention discloses a shell-and-tube heat exchanger abnormity diagnosis method based on multi-parameter monitoring. The method specifically comprises the following steps that 1, temperature values and pressure values of a shell-and-tube heat exchanger tube pass inlet, all-pass connecting positions and a tube pass outlet are collected; step 2, carrying out segmented pressure difference calculation based on the collected pressure values, verifying the total pressure difference, if a verification result exceeds an error range, carrying out pressure value collection and calculation again, and if the verification result is within the error range, carrying out step 3; 3, calculating the proportion of the differential pressure of each process in the total differential pressure, then carrying out dynamic threshold judgment, and carrying out flow fluctuation alarm or carrying out the step 4 according to a judgment result; and 4, performing temperature gradient calculation based on the acquired temperature value, and diagnosing the abnormal pressure difference position as blockage or leakage based on the temperature gradient. The problem that in the prior art, due to the fact that the detection parameter is single, the accuracy of the detection result is poor is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat exchanger operation fault diagnosis, and specifically relates to an abnormal diagnosis method for shell-and-tube heat exchangers based on multi-parameter monitoring. Background Art

[0002] Heat exchangers are widely used in industrial production and national life, and their efficient and reliable operation has a crucial impact on the economic benefits of these industries. However, faults such as fouling, blockage, and leakage in heat exchangers are common problems in actual operation and need to be solved. According to investigations, more than 90% of heat exchangers have problems of fouling, blockage, and leakage. Due to the existence of these problems, the heat transfer coefficient of the heat exchanger is reduced, the flow resistance is increased, and the equipment life is shortened, resulting in a series of economic problems. Developing heat exchanger fault diagnosis technology can better ensure the efficient and reliable operation of heat exchangers, save energy, and reduce costs.

[0003] The current fault diagnosis technologies for shell-and-tube heat exchangers generally have the following problems: (1) Only detecting the total pressure difference at the inlet of the shell-and-tube heat exchanger cannot locate the specific number of passes where the fault occurs; (2) Only using a single parameter for detection, such as temperature or pressure, results in a large error in the results and it is difficult to distinguish whether it is a simple flow rate change or an abnormality. Summary of the Invention

[0004] The purpose of the present invention is to provide an abnormal diagnosis method for shell-and-tube heat exchangers based on multi-parameter monitoring, which solves the problem of poor accuracy of detection results due to single detection parameters in the prior art.

[0005] The technical solution adopted by the present invention is an abnormal diagnosis method for shell-and-tube heat exchangers based on multi-parameter monitoring, which specifically includes the following steps: Step 1, collect the temperature values and pressure values at the inlet of the tube side of the shell-and-tube heat exchanger, at the connection between each pass, and at the outlet of the tube side; Step 2, calculate the sectional pressure difference based on the collected pressure values and check the total pressure difference. If the check result exceeds the error range, collect the pressure values again and calculate. If the check result is within the error range, proceed to Step 3; Step 3, calculate the proportion of the pressure difference of each pass in the total pressure difference and then perform dynamic threshold determination. According to the determination result, issue a flow rate fluctuation alarm or proceed to Step 4; Step 4, calculate the temperature gradient based on the collected temperature values, and diagnose the position of the abnormal pressure difference as blockage or leakage based on the temperature gradient.

[0006] The present invention is further characterized in that In Step 1, pressure sensors for collecting pressure values and temperature sensors for collecting temperature values are respectively installed at the inlet of the tube side of the shell-and-tube heat exchanger, at the connection between each pass, and at the outlet of the tube side.

[0007] In Step 2, the segmented pressure difference calculation is specifically as shown in the following formula: ; ; When verifying the total pressure difference, the error range is ±5%, specifically as shown in the following formula: .

[0008] In Step 2, when the pressure value collection is repeated 3 times, check whether the pressure sensor is abnormal.

[0009] In Step 3, calculate the proportion of the pressure difference of each pass in the total pressure difference, specifically as shown in the following formula: ; Perform dynamic threshold determination as shown in the following formula: ; When <1%, it is determined as a flow fluctuation alarm; when >5%, trigger temperature verification to proceed to Step 4.

[0010] In Step 4, perform temperature gradient calculation specifically as shown in the following formula: ; In the formula, are respectively the inlet temperatures of each pass, is the outlet temperature, is the equivalent heat transfer length of a tube side after the temperature sensor.

[0011] In Step 4, diagnose the position of the abnormal pressure difference based on the temperature gradient, specifically analyze and the gradient change rate of, and conduct verification in two stages. In the first stage, calculate for the abnormal pass, specifically as shown in the following formula: ; In the formula, is the temperature gradient of the pass, is the temperature gradient under the designed operation of the pass, is the defined change rate of the temperature gradient; If , then proceed to the second stage. In the second stage, correlation judgment is carried out. If the pressure difference before the process increases and > , then it is confirmed that the process is blocked; if the pressure difference before the process decreases and < , then it is confirmed that the process leaks.

[0012] The fusion confidence of the diagnosis result is calculated as follows: ; In the formula, is the difference between the actual value of the single-pass pressure drop and the designed operation, is the total pressure drop in the tube side of the shell-and-tube heat exchanger, is the change rate of the temperature gradient defined by a single pass, is the sum of the total change rates of the temperature gradient in the tube side.

[0013] The beneficial effects of the present invention are as follows: The abnormal diagnosis method of the shell-and-tube heat exchanger based on multi-parameter monitoring of the present invention sets temperature and pressure sensors at the inlet, the connection positions between each pass, and the outlet position of the shell-and-tube heat exchanger respectively, collects pressure data and temperature data, and determines the pass with a significant deviation from the average value as abnormal by calculating the ratio of the pressure difference of each pass to the total pressure difference between the passes. Then, in combination with the abnormal change rate of the temperature between adjacent passes, the blocked or leaked position is confirmed, and the flow fluctuation interference is excluded, thereby improving the diagnosis reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic flow chart of the abnormal diagnosis method of the shell-and-tube heat exchanger based on multi-parameter monitoring of the present invention; Figure 2 is a schematic diagram of the distribution pressure gauge and temperature sensor at the inlet and outlet of the heat exchanger of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0016] Example 1 The abnormal diagnosis method of the shell-and-tube heat exchanger based on multi-parameter monitoring of the present invention, as Figure 1 shown, specifically includes the following steps: Step 1, collect the temperature values and pressure values at the inlet of the tube side of the shell-and-tube heat exchanger, at the connections between each pass, and at the outlet of the tube side; Specifically, pressure sensors for collecting pressure values and temperature sensors for collecting temperature values are respectively installed at the inlet of the tube side of the shell-and-tube heat exchanger, at the connections between each pass, and at the outlet of the tube side.

[0017] Step 2, perform segmented differential pressure calculation based on the collected pressure values and conduct verification of the total differential pressure. If the verification result exceeds the error range, collect the pressure values again and perform the calculation. If the verification result is within the error range, proceed to Step 3; Step 3, calculate the proportion of the differential pressure of each pass in the total differential pressure and then conduct dynamic threshold determination. Based on the determination result, issue a flow fluctuation alarm or proceed to Step 4; Step 4, calculate the temperature gradient based on the collected temperature values and diagnose the abnormal differential pressure position as blocked or leaking based on the temperature gradient.

[0018] In the present invention, by respectively arranging temperature and pressure sensors at the inlet of the shell-and-tube heat exchanger, at the connections between each pass, and at the outlet, pressure data and temperature data are collected. By calculating the ratio of the differential pressure of each pass to the total differential pressure between the passes, the pass with a significant deviation from the average value is determined as abnormal. Combining the abnormal temperature change rate between adjacent passes at the abnormal position to confirm the blocked or leaking position, eliminating the interference of flow fluctuations, thereby improving the diagnostic reliability.

[0019] Embodiment 2 Based on the above Embodiment 1, the specific segmented differential pressure calculation in Step 2 is shown as the following formula: ; ; When verifying the total differential pressure, the error range is ±5%, which is specifically shown as the following formula: .

[0020] The specific calculation of the proportion of the differential pressure of each pass in the total differential pressure in Step 3 is shown as the following formula: ; The dynamic threshold determination is shown as the following formula: ; When <1%, it is determined as a flow fluctuation alarm; when >5%, trigger temperature verification and proceed to Step 4.

[0021] The specific temperature gradient calculation in Step 4 is shown as the following formula: ; In the formula, are respectively the inlet temperatures of each pass, is the outlet temperature, is the equivalent heat transfer length of one tube pass after the temperature sensor, and this value can be simplified to the product of the number of heat exchange tubes passing through this pass and the length of a single tube.

[0022] Specific analysis of diagnosing the abnormal pressure difference position based on the temperature gradient in Step 4 and the gradient change rate of, which is verified in two stages. In the first stage, calculations are performed for the abnormal pass, as shown in the following formula: ; In the formula, is the temperature gradient of the pass, is the temperature gradient under the designed operation of the pass, is the defined gradient change rate of the temperature gradient.

[0023] If , then the second stage is carried out; otherwise, the pressure monitoring signal is eliminated, and after a certain relaxation time, the pressure monitoring is restarted.

[0024] In the second stage, correlation judgment is carried out. If the pressure difference before the pass increases and > , then it is confirmed that the pass is blocked; if the pressure difference before the pass decreases and < , then it is confirmed that the pass leaks.

[0025] Embodiment 3 Based on the above Embodiment 2, this embodiment calculates the fusion confidence of the diagnosis result, as shown in the following formula: ; In the formula, is the difference between the actual value of the single-pass pressure drop and the designed operation, is the total pressure drop of the tube passes in the shell-and-tube heat exchanger, is the defined gradient change rate of the temperature gradient of a single pass, is the sum of the total temperature gradient change rates of the tube passes.

[0026] Furthermore, the requirement is greater than 5%, the larger, the higher the resulting confidence D, and the contribution to the confidence is the same.

[0027] Example 4 The abnormal diagnosis method of the shell-and-tube heat exchanger based on multi-parameter monitoring of the present invention is as Figure 1 shown, and specifically includes the following steps: Step 1, as Figure 2 shown, install pressure and temperature sensors at the inlet of the tube side of the shell-and-tube heat exchanger ( , ), at the connection between each pass ( - , - ), and at the outlet ( , ). When the fluctuations of the inlet and outlet pressures and temperatures are less than a threshold value (2%) for a certain period of time, it indicates that the heat exchanger has entered a stable operation state. The setting of this threshold value and time is related to the use of the heat exchanger and the characteristics of the process side. For example, oil coolers, kettle reboilers, vaporization flashers, waste steam condensers, etc. are all different and are set according to experience.

[0028] After stable operation, synchronously collect the instantaneous values of all pressures and temperatures, denoted as , , , , , , , , , .

[0029] Step 2, perform segmented differential pressure calculation based on the collected pressure values, as shown in the following formula: ; ; ; ; ; Then perform the verification of the total differential pressure to check whether the sum of the differential pressures of each pass is consistent with the total differential pressure, allowing an error of ±5%, as shown in the following formula: ; If the verification result exceeds the error range, collect the pressure values again and perform the calculation. When the pressure value collection is repeated 3 times, check whether the pressure sensor is abnormal. If the verification result is within the error range, proceed to Step 3; Step 3, calculate the proportion of the differential pressure of each pass in the total differential pressure and then perform dynamic threshold determination, and issue a flow fluctuation alarm according to the determination result or proceed to Step 4; Specifically, the proportion calculation formula is as shown in the following formula: ; The benchmark condition for dynamic threshold determination is that when the heat exchanger is first put into use, there is no fouling on the heat exchanger, and the pressure difference ratio can be approximated as 25% of the total allowable pressure difference in design. Therefore, when performing deviation calculation, when < 1%, it is determined as a flow fluctuation alarm; when > 5%, trigger temperature verification to proceed to step 4.

[0030] Step 4: Calculate the temperature gradient based on the collected temperature values, and diagnose the abnormal pressure difference position as blocked or leaking based on the temperature gradient.

[0031] This step enters temperature verification. Based on the pressure difference judgment, the accuracy of the pressure difference judgment conclusion is verified through the change rate of the temperature gradient, further determining whether it is a blockage or leakage problem, and eliminating other external interference factors.

[0032] Because when verifying with temperature, the operating temperature of the heat exchanger may deviate too much from the design temperature, and when verifying with temperature difference, the number of heat exchange tubes in each pass may be different, and it is easy to make mistakes in temperature difference verification. Therefore, temperature gradient is used for verification, which deepens the correlation with the heat exchanger structure.

[0033] Example 5 Based on the above Example 4, in this example, step 4 is specifically shown as the following formula when calculating the temperature gradient: ; After calculating the temperature gradient, deviation calculation with the design state also needs to be performed. Similar to the benchmark condition of the pressure difference, when the heat exchanger is first put into use, there is , this value already exists in the design stage of the heat exchanger and can be obtained according to the drawings. The calculation formula is the same as the formula during pressure difference verification.

[0034] After passing the verification, determine the temperature gradient. If the pressure difference anomaly is in the th pass, then focus on analyzing the (current pass) and (downstream) gradient change rates, and conduct verification in two stages: The first stage: Only for the abnormal th pass, if the following formula data calculation exceeds the set value, trigger a red alarm.

[0035] ; The second stage: Conduct an associated judgment. If the pressure difference before the th pass increases and > , then confirm that the th pass is blocked; if the pressure difference before the th pass decreases and < , it is confirmed that the process leaks, a warning message is issued, and the values of A and B can be taken according to the degree to which the actual operating conditions deviate from the designed operating conditions. Finally, the fusion confidence level of the diagnostic results is calculated, and the judgment of blockage and leakage and the data results of the confidence level report are given, as shown in the following formula: .

[0036] Embodiment 6 In order to verify the present invention, an experimental verification was carried out in a chemical plant in China. A heat exchanger with 4 tube passes and 1 shell pass that had been in operation for 8 years had pressure and temperature sensors installed at the inlet and outlet of the heat exchanger. It was found through the DCS (Distributed Control System) that the temperature at the hot side outlet was 2°C lower than the normal temperature, but the reason was unknown. Pressure and temperature sensors were installed between the tube passes on site, and corresponding points were added on the DCS. After data processing as described in this article, it was presented on the DCS as an abnormal detection interface for the heat exchanger.

[0037] The design parameters are as follows: Table 1 Shell-and-tube heat exchanger of a certain factory

[0038] The display on the DCS interface is as follows: Table 2 Shell-and-tube heat exchanger of a certain factory

[0039] After disassembly and inspection, a heat exchange tube in the first pass was internally fouled and blocked, thus verifying the accuracy of the diagnosis of the present invention.

[0040] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other.

[0041] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for diagnosing abnormalities of a shell and tube heat exchanger based on multi-parameter monitoring, characterized in that: The specific steps include: Step 1, collecting the temperature and pressure values ​​at the tube inlet, the connection between each tube and the tube outlet of the shell and tube heat exchanger; Step 2, based on the collected pressure values, perform segmented pressure difference calculation and verify the total pressure difference. If the verification result exceeds the error range, collect the pressure values ​​again and perform calculation. If the verification result is within the error range, proceed to step 3. Step 3, calculate the ratio of each pressure difference to the total pressure difference and then make a dynamic threshold determination, and issue a flow fluctuation alarm or proceed to step 4 according to the determination result; Step 4: Calculate the temperature gradient based on the collected temperature value, and diagnose the abnormal pressure difference position as a blockage or leakage based on the temperature gradient.

2. The method for diagnosing abnormality of a shell and tube heat exchanger based on multi-parameter monitoring according to claim 1, characterized in that: In the step 1, a pressure sensor for collecting pressure values ​​and a temperature sensor for collecting temperature values ​​are respectively installed at the tube inlet, the connection between each tube and the tube outlet of the shell and tube heat exchanger.

3. The method for diagnosing abnormality of a shell and tube heat exchanger based on multi-parameter monitoring according to claim 1, characterized in that: The step 2 is to calculate the segmented pressure difference as shown in the following formula: ； ； The error range when calibrating the total pressure difference is ±5%, as shown in the following formula: 。 4. The method for diagnosing abnormality of a shell and tube heat exchanger based on multi-parameter monitoring according to claim 2, characterized in that: When the pressure value collection is repeated for three times in step 2, whether the pressure sensor is abnormal is detected.

5. The method for diagnosing abnormality of a shell and tube heat exchanger based on multi-parameter monitoring according to claim 1, characterized in that: The proportion of each pressure difference to the total pressure difference calculated in step 3 is specifically shown in the following formula: ； The dynamic threshold determination is shown as follows: ； when <1%, it is judged as a flow fluctuation alarm; when When >5%, the temperature verification is triggered to proceed to step 4.

6. The method for diagnosing abnormality of a shell and tube heat exchanger based on multi-parameter monitoring according to claim 1, characterized in that: The temperature gradient calculation in step 4 is specifically shown in the following formula: ； In the formula, are the inlet temperatures of each pass, is the outlet temperature, yes The equivalent heat transfer length of one tube pass after the temperature sensor.

7. The method for diagnosing abnormality of a shell and tube heat exchanger based on multi-parameter monitoring according to claim 6, characterized in that: In step 4, specific analysis is performed on the abnormal pressure difference position based on the temperature gradient. and The gradient change rate is divided into two stages of verification. In the first stage, the abnormal The specific calculation is as follows: ； In the formula, For the The temperature gradient of the process, For the The temperature gradient under the design operation of the process, is the rate of change of the defined temperature gradient; like , then proceed to the second stage, In the second stage, the association judgment is carried out. The pressure difference before the process increases and > , then confirm If the process is blocked; The pressure difference before the process is reduced and < , then confirm Process leak.

8. The method for diagnosing abnormality of a shell and tube heat exchanger based on multi-parameter monitoring according to claim 7, characterized in that: The fusion confidence of the diagnosis results is calculated as shown in the following formula: ; In the formula, is the difference between the actual value of the one-way pressure drop and the design value. is the total pressure drop in the tube side of the shell and tube heat exchanger, is the rate of change of the temperature gradient defined for a single pass, It is the sum of the total temperature gradient change rates in the tube.

Images