Intelligent measurement and control method for condensate water of steam system

Abstract

The invention relates to the technical field of heat energy engineering, in particular to an intelligent measurement and control method for condensate water of a steam system, which is reasonable in structure, accurate in monitoring, low in cost and capable of ensuring that the liquid level of the condensate water is kept in a specified interval and ensuring that steam is not leaked. A low liquid level sensor and a high liquid level sensor which are used for monitoring the liquid level of a water storage tank in the steam system are arranged, and a drain valve is installed on a drain outlet of the water storage tank. And corresponding measures are given by utilizing intelligent program judgment, so that the liquid level control failure caused by the abnormal electrode is avoided, the low-cost electrode type liquid level detection can be more widely applied, and the control level is improved.

Description

Technical Field:

[0001] The present invention relates to the technical field of thermal energy engineering, and specifically to an intelligent measurement and control method for condensate in a steam system with reasonable structure, accurate monitoring, low cost, which can ensure that the condensate level is maintained within a specified range and ensure no steam leakage. Background Art:

[0002] The steam system includes a steam heating device and a water storage tank connected to the steam heating device for storing condensate. The measurement and control of the liquid level in the water storage tank are extremely important for the normal operation of the system: if the liquid level in the tank is too high, the condensate will cool down due to too long storage time, and then it may cause the temperature of the heating device to be lower than the process requirements because the low-temperature condensate level rises to the heating device; while if the liquid level in the tank is too low, it cannot be ensured that steam will not be discharged every time condensate is drained. In order to measure and control the liquid level in the tank in real time, an electrode type liquid level measurement and control device can be used to achieve this.

[0003] The electrode type liquid level measurement and control device utilizes the conductivity of the liquid to detect the liquid level height, with simple structure and convenient use; currently, the corresponding control switch can control the pump or valve to discharge liquid to lower the liquid level or control the pump or valve to supplement liquid to raise the liquid level when detecting high and low liquid levels, so as to achieve the purpose of controlling the liquid level stability. In actual application, this currently commonly used measurement and control mode has no feedback on the on-off state of the electrode, cannot observe the liquid level change from the control device, and is even less able to achieve intelligent control. It often encounters problems such as scale formation on the electrode surface, resulting in liquid level detection failure and thus liquid level out of control.

[0004] Therefore, there is an urgent need for a liquid level conversion control device that can convert the liquid level signal detected by the electrode into a signal that can be input into an intelligent control device such as a PLC, so as to utilize an intelligent program to judge and give corresponding measures. Summary of the Invention:

[0005] The present invention aims at the disadvantages and deficiencies existing in the prior art, and proposes an intelligent measurement and control method for condensate in a steam system with reasonable structure, accurate monitoring, low cost, which can ensure that the condensate level is maintained within a specified range and ensure no steam leakage.

[0006] The present invention is achieved by the following measures:

[0007] An intelligent measurement and control method for condensate in a steam system, provided with a low liquid level detection electrode and a high liquid level detection electrode for monitoring the liquid level height in the water storage tank of the steam system, and a drain valve is installed at the drain port of the water storage tank, characterized in that the following steps are executed:

[0008] Step 1: During the preheating and temperature-rising stage when the steam system is initially put into use, it operates in a mode where the drain valve is opened when the high-level sensor detects a signal and closed when the low-level sensor detects a signal; after the steam system completes the preheating time and the temperature of the heating device stabilizes within the process-set range, it enters the stable operation stage. The frequency of opening and closing the drain valve and the duration of each opening will tend to be stable. The PLC program automatically statistically records the frequency and duration. After statistically recording multiple production cycles and confirming reliable control, the PLC calculates the average drainage duration t1. Step 2: When the PLC statistically determines that the drainage frequency and duration have become stable, a prompt is given through the human-machine interface computer. After confirmation by the operator, the mode of controlling drainage according to high and low liquid level signals is switched to a mode where the target is the high liquid level and the condensate is drained for a fixed duration t: Whenever the liquid level reaches the high liquid level, the drain valve is opened and the drainage time is maintained for the fixed duration t. The fixed duration t is equal to the average drainage duration t1 during the stable period mentioned above, plus the adjustable time t2. The determination of the adjustable time t2 is to ensure through manual observation in this mode that each drainage will make the actual liquid level lower than the low-level detection electrode. In this mode, the PLC automatically calculates the drainage cycle T, that is, the average interval time between two emissions.

[0009] In step 2 of the present invention, if the on (high level) and off (low level) signals of the high and low liquid level sensors can always be detected during the opening and closing process of the drain valve, it indicates that both the high and low liquid level detection electrodes are normal; if the low-level sensor does not receive a signal indicating a change from on to off during a certain drainage, a prompt for an abnormal low-level detection electrode is given, and t2 is manually adjusted. Specifically: the adjustable time t2 is lengthened. If it is lengthened by 3 seconds each time and still cannot return to normal after being lengthened multiple times so that t2 is greater than or equal to t1, the low-level detection electrode needs to be repaired and the repair process is started; if the low-level signal is disconnected during a certain drainage but the high-level signal remains disconnected all the time, a prompt for an abnormal high-level detection electrode is given and the repair process is started; if the low-level signal remains on all the time and the high-level signal has not become on after exceeding the drainage cycle T, a prompt for an abnormal high-level detection electrode is given to remind for manual judgment or repair. During the waiting period for repair, control is set with the low-level detection electrode as the target, that is: whenever the low-level signal is detected, the drain valve is immediately opened and the previous fixed duration t is maintained. Since the low-level sensor is set in the middle of the condensate storage tank, this drainage method always retains a certain water level at the bottom of the condensate storage tank to ensure that steam is not discharged.

[0010] In the present invention, a low liquid level detection electrode and a high liquid level detection electrode are respectively used to detect the liquid level in the water storage tank. The high liquid level detection electrode is installed above the low liquid level detection electrode, and the low liquid level detection electrode is installed in the middle of the water storage tank body; and further provided with an electrode type liquid level detection signal conversion circuit connected to the detection electrode, the electrode type liquid level detection signal conversion circuit is provided with a chip having at least two 2-input NOR gates, each NOR gate of the chip having two signal input terminals and one signal output terminal, the two NOR gate chips are respectively denoted as IC1A and IC1E, wherein the NOR gate chip I The two signal input terminals of C1A are connected to the high liquid level terminal E1, the high liquid level terminal E1 is connected to the adjustable resistor R1, the other end of the adjustable resistor R1 is connected to the positive power supply terminal A1, and the output terminal of the NOT gate chip IC1A is connected to the high liquid level signal output terminal X1; the two signal input terminals of the NOT gate chip IC1E are both connected to the low liquid level terminal E2, the low liquid level terminal E2 is connected to one end of the adjustable resistor R2, the other end of the adjustable resistor R2 is connected to the positive power supply terminal A1, and the signal output terminal of the NOT gate chip IC1E is connected to the low liquid level signal output terminal X2.

[0011] The high-level terminal E1 of the present invention is used to connect to the high-level detection electrode in an electrode-type liquid level detection device, while the low-level terminal E2 is connected to the low-level detection electrode in the electrode-type liquid level detection device. Terminal E0 is used to connect to the water storage tank and the negative power supply terminal A2. The high-level signal output terminal X1 and the low-level signal output terminal X2 can be directly connected to the signal input terminal of a programmable logic controller (PLC) to transmit signals from the electrode-type liquid level detection device. The PLC programmable logic controller communicates with the human-machine interface computer in real time.

[0012] The adjustable resistor R1 and the adjustable resistor R2 of the present invention both have a resistance range of 10-100 kΩ. The sensitivity of liquid level detection can be increased or decreased by reducing or increasing the resistance and increasing or decreasing the current flowing through the electrode.

[0013] The NOR gate chip in the present invention adopts a four-way two-input NOR gate chip 74HC02D,653, or a five-way two-input NOR gate chip 74LS02, and its GND end is connected to the negative power supply terminal A2.

[0014] The present invention further provides a liquid level detection control circuit to facilitate linkage with the water supply pump or drainage pump of the water storage tank to realize automatic control of water supply or drainage according to the liquid level information. The liquid level detection control circuit is provided with three-way NOR gates, respectively denoted as IC1B, IC1C, and IC1D, and also includes a light-emitting diode D1 used as an indicator light and an NPN transistor Q1;

[0015] In the described liquid level detection and control circuit, one input terminal of the NOR gate chip IC1B is connected to the output terminal of the NOR gate chip IC1A in the signal conversion circuit for electrode type liquid level detection. The other input terminal of the NOR gate chip IC1B is connected to the output terminal of the NOR gate chip IC1C, and the two input terminals of the NOR gate chip IC1D are both connected to the single-pole double-throw switch SW1. The single-pole double-throw switch SW1 is connected to the B pole of the triode Q1 via the resistor R3. The output terminal of the NOR gate chip IC1B is connected to one input terminal of the NOR gate chip IC1C. The other input terminal of the NOR gate chip IC1C is connected to the low liquid level terminal E2. The GND terminal of the NOR gate chip IC1C is grounded. The output terminal of the NOR gate chip IC1D is connected to the single-pole double-throw switch SW1. The C pole of the triode Q1 is connected to the negative electrode of the light-emitting diode D1 via the resistor R4. The positive electrode of the light-emitting diode D1 is connected to the positive power supply. The E pole of the triode Q1 is grounded. The C pole of the triode Q1 is connected to the terminal C2. The terminal C2 is used to connect to the negative electrode of the control coil of the drainage pump or drainage valve. The positive electrode of the light-emitting diode D1 is also connected to the terminal C1. The terminal C1 is used to connect to the positive electrode of the control coil of the drainage valve or drainage pump.

[0016] During operation, by using the liquid level detection and control circuit connected to the signal conversion circuit for electrode type liquid level detection, and connecting the terminal C1 and the terminal C2 to the control coil of the drainage pump or drainage valve respectively, it is possible to achieve drainage control of the water storage tank according to the liquid level, or to achieve water replenishment control of the water storage tank after toggling the single-pole double-throw switch SW1. In addition, by setting the light-emitting diode D1, it is possible to display the control signal of the pump or valve, which is convenient for the operator to intuitively understand.

[0017] In the present invention, the NOR gate chip of the signal conversion and liquid level detection control circuit uses a five-way 2-input NOR gate chip 74LS02, and its GND terminal is connected to the power input terminal A2.

[0018] The present invention uses a liquid level conversion control switch to convert the corresponding on-off state of the electrodes into signals that can be recognized by intelligent control devices such as PLCs, and then uses an intelligent program to judge and give corresponding measures to avoid liquid level control failure caused by electrode abnormalities, thus enabling the more widespread application of low-cost electrode type liquid level detection and improving the control level. Description of the Drawings:

[0019] Attached Figure 1 is the circuit schematic diagram of the present invention.

[0020] Reference Numerals: Water storage tank liquid level measurement and control device 1, water storage tank 2. Detailed Embodiment:

[0021] The following will further illustrate the present invention in conjunction with the drawings and embodiments.

[0022] Example:

[0023] This example provides an intelligent measurement and control method for condensate in a steam system, which is implemented based on the liquid level measurement and control device of the water storage tank in the steam system as shown in the attached Figure 1 figure:

[0024] This example is equipped with a liquid level measurement and control device 1 for the water storage tank, which internally has five two-input NOR gate CMOS IC chips IC1A, IC1B, IC1C, IC1D, IC1E, adjustable resistors R1, R2, resistors R3, R4, light-emitting diode D1, NPN bipolar junction transistor Q1, and a selection switch SW1. Connect them according to the illustrated circuit diagram and set nine connection terminals as shown. Among them, the high liquid level connection terminal E1 is connected to the two input terminals of the two-input NOR gate CMOS IC chip IC1A; the low liquid level connection terminal E2 is connected to the two input terminals of the two-input NOR gate CMOS IC chip IC1E; the liquid level signal terminals X1 and X2 are respectively connected to the output terminals of the two-input NOR gate CMOS IC chips IC1A and IC1BE; the connection terminals A1 and A2 are power input terminals; the connection terminal E0 is set on the line connected to the connection terminal A2; the connection terminals C1 and C2 are control output terminals;

[0025] When the high and low liquid level detection electrodes and the conductive housing of the water storage tank 2 whose liquid level needs to be measured and controlled are respectively connected to the above connection terminals E1, E2, and E0 through wires, and the power supply is connected to the connection terminals A1 and A2 according to the polarity, then according to the liquid level change in the water storage tank 2, the following results are obtained at the connection terminals X1, X2, C1, C2, and the light-emitting diode D1 respectively:

[0026] When the liquid level is lower than the low liquid level detection electrode, both the connection terminals X1 and X2 output low levels, both the connection terminals C1 and C2 output high levels, and the light-emitting diode D1 goes out; when the liquid level reaches the low liquid level detection electrode, the connection terminal X1 remains at a low level, the connection terminal X2 outputs a high level, both the connection terminals C1 and C2 output high levels, and the light-emitting diode D1 still remains off; when the liquid level reaches the high liquid level detection electrode, both the connection terminals X1 and X2 output high levels, the connection terminal C1 outputs a high level, the connection terminal C2 outputs a low level, and the light-emitting diode D1 lights up; when the liquid level gradually decreases and is lower than the high liquid level detection electrode, the connection terminal X1 outputs a low level, the connection terminal X2 outputs a high level, the connection terminal C1 outputs a high level, the connection terminal C2 remains at a low level, and the light-emitting diode D1 remains lit; when the liquid level continues to gradually decrease and is lower than the low liquid level detection electrode, both the connection terminals X1 and X2 output low levels, both the connection terminals C1 and C2 output high levels, and the light-emitting diode D1 goes out.

[0027] According to the above logical relationship, if the control coils of the drain valve or the drain pump are connected to the terminals C1 and C2, the drain control according to the liquid level can be realized. By toggling the selection switch SW1, the make-up water control according to the liquid level can be realized;

[0028] If the output signals of the terminals X1 and X2 are connected to the PLC, and the PLC communicates with the human-machine interface computer in real time, through the PLC control program and the human-machine interface computer screen, not only the above functions can be realized, but also the diagnosis of the abnormal conditions of the high and low liquid level detection electrodes of the water storage tank 2 can be realized through the intelligent judgment program and the corresponding measures can be given.

[0029] When implementing the intelligent measurement and control method for the condensate of the steam system in this example, it specifically includes the following contents:

[0030] High and low liquid level detection electrodes are respectively arranged at the upper and middle parts of the steam condensate storage tank, and the high and low liquid level detection electrodes and the shell are respectively connected to the terminals E1, E2, and E0 of the liquid level measurement and control device 1 of the water storage tank. During the preheating and warming-up stage when the steam system is initially put into use, it is controlled in the mode of automatically opening the discharge valve according to the high liquid level signal from the terminal E1 and automatically closing the discharge valve according to the low liquid level signal of the low liquid level detection electrode from the terminal E2, ensuring that the heating system will not have a low temperature due to too high a condensate level, nor will there be steam leakage due to too low a condensate level;

[0031] After the steam system has completed the preheating time and the temperature of the heating device is stable within the process setting range, it enters the stable operation stage. The frequency of opening and closing of the discharge valve and the duration of each opening will tend to be stable. The PLC program automatically statistically records the frequency and duration. After statistically recording multiple production cycles and confirming the reliability of the control, the PLC calculates the average discharge duration t1.

[0032] When the PLC statistically determines that the discharge frequency and duration become stable, a prompt is given through the human-machine interface computer. After being confirmed by the operator, the above mode of controlling the discharge according to the high and low liquid level signals is switched to the mode of discharging condensate with a fixed duration t with the high liquid level as the target: whenever the liquid level reaches the high liquid level, the discharge valve is opened and the discharge time is maintained for a fixed duration t. The fixed duration t is equal to the average discharge duration t1 of the stable period plus the adjustable time t2. The determination of the adjustable time t2 is to ensure that each discharge will make the actual liquid level lower than the low liquid level detection electrode through manual observation in this mode. In this mode, the PLC automatically statistically records the discharge cycle T, that is, the average interval time between two discharges.

[0033] In this mode, if the on (high level) and off (low level) signals of the high and low liquid level sensors can always be detected during the opening and closing process of the drain valve, it indicates that both the high and low liquid level detection electrodes are normal; if the signal of the low liquid level sensor changing from on to off is not obtained during a certain discharge, an abnormal prompt for the low liquid level detection electrode will be given, and the adjustable time t2 will be manually adjusted to increase it by 3 seconds each time. If it still cannot return to normal after increasing it multiple times so that t2 is greater than or equal to t1, the low liquid level detection electrode needs to be repaired and the repair process is started; if the low liquid level signal is disconnected during a certain discharge, but the high liquid level signal has not been disconnected, an abnormal prompt for the high liquid level detection electrode will be given and the repair process is started; if the low liquid level signal remains on all the time and the high liquid level signal has not been on after exceeding the discharge cycle T, an abnormal prompt for the high liquid level detection electrode will be given to remind for manual judgment or repair. During the waiting period for repair, it is set to control with the low liquid level detection electrode as the target, that is: whenever the low liquid level signal is detected, the discharge valve is immediately opened and maintained for the previous fixed duration t. Since the low liquid level sensor is set in the middle of the condensate storage tank, this discharge method always retains a certain water level at the bottom of the condensate storage tank to ensure that steam is not discharged.

[0034] The present invention uses a liquid level conversion control switch to convert the on-off states of the corresponding electrodes into signals that can be recognized by intelligent control devices such as PLCs, and then uses an intelligent program to judge and give corresponding measures to avoid the failure of liquid level control caused by electrode abnormalities, thus enabling the more extensive application of the low-cost electrode type liquid level detection and improving the control level.

Claims

1. An intelligent measurement and control method for condensate in a steam system, which is provided with a low liquid level detection electrode and a high liquid level detection electrode for monitoring the liquid level in the water storage tank of the steam system. A drain valve is installed at the drain outlet of the water storage tank. It is characterized in that, Perform the following steps: Step 1: During the preheating and temperature-rising stage when the steam system is initially put into use, operate in the mode of opening the drain valve when the high-level sensor detects a signal and closing the drain valve when the low-level sensor detects a signal; after the steam system has completed the preheating time and the temperature of the heating device has stabilized within the process-set range, it enters the stable operation stage. The frequency of opening and closing the drain valve and the duration of each opening will tend to be stable. The PLC program automatically statistically records the frequency and duration. After statistically recording multiple production cycles and confirming reliable control, the PLC calculates the average drain duration t1; Step 2: When the PLC statistically determines that the drain frequency and duration have become stable, a prompt is given through the human-machine interface computer. After being confirmed by the operator, the mode of controlling the drain according to the high and low liquid level signals is switched to the mode of discharging condensate with a fixed duration t with the high liquid level as the target: whenever the liquid level reaches the high liquid level, the drain valve is opened and the drain time is maintained for a fixed duration t. The fixed duration t is equal to the average drain duration t1 in the above stable period plus the adjustable time t2. The determination of the adjustable time t2 is to ensure through manual observation in this mode that each drain will make the actual liquid level lower than the low-level detection electrode. In this mode, the PLC automatically calculates the drain cycle T, that is, the average interval time between two drains.

2. The intelligent measurement and control method for condensate of a steam system according to claim 1, characterized in that, In Step 2, if the on-off signals of the high and low liquid level sensors can be detected during the opening and closing process of the drain valve all the time, it indicates that both the high and low liquid level detection electrodes are normal; if the low-level sensor does not receive the signal of changing from on to off during a certain drain, an abnormal prompt for the low-level detection electrode is given, and t2 is manually adjusted. Specifically: lengthen the adjustable time t2. If each time it is lengthened by 3 seconds and still cannot return to normal after multiple lengthenings when t2 is greater than or equal to t1, the low-level detection electrode needs to be repaired and the repair process is started; If during a certain drain, the low-level signal is disconnected while the high-level signal remains continuously connected, an abnormal prompt for the high-level detection electrode is given and the repair process is started; If the low-level signal remains continuously on and the high-level signal has not been turned on after exceeding the drain cycle T, an abnormal prompt for the high-level detection electrode is given to remind for manual judgment or repair. During the waiting period for repair, set the control with the low-level detection electrode as the target, that is: whenever the low-level signal is detected, the drain valve is immediately opened and the previous fixed duration t is maintained. Since the low-level sensor is set in the middle of the condensate storage tank, this drainage method always retains a certain water level at the bottom of the condensate storage tank to ensure that steam is not discharged.

3. The intelligent measurement and control method for condensate of a steam system according to claim 2, wherein The low liquid level detection electrode and the high liquid level detection electrode are used to detect the liquid level in the water tank. The high liquid level detection electrode is installed above the low liquid level detection electrode, and the low liquid level detection electrode is installed in the middle of the water tank body; and an electrode type liquid level detection signal conversion circuit connected to the detection electrode is provided. The electrode type liquid level detection signal conversion circuit is provided with a chip having at least two 2-input NOR gates. Each NOR gate of the chip has two signal input terminals and one signal output terminal. The two NOR gate chips are respectively recorded as IC1A and IC1E. Among them, the NOR gate chip IC1A The two signal input terminals are connected to the high liquid level terminal E1, the high liquid level terminal E1 is connected to the adjustable resistor R1, the other end of the adjustable resistor R1 is connected to the positive power supply terminal A1, and the output terminal of the NOT gate chip IC1A is connected to the high liquid level signal output terminal X1; the two signal input terminals of the NOT gate chip IC1E are both connected to the low liquid level terminal E2, the low liquid level terminal E2 is connected to one end of the adjustable resistor R2, the other end of the adjustable resistor R2 is connected to the positive power supply terminal A1, and the signal output terminal of the NOT gate chip IC1E is connected to the low liquid level signal output terminal X2.

4. The intelligent measurement and control method for condensate of a steam system according to claim 3, characterized in that The high liquid level terminal E1 is used to connect to the high liquid level detection electrode in the electrode type liquid level detection device, and the low liquid level terminal E2 is connected to the low liquid level detection electrode in the electrode type liquid level detection device. The terminal E0 is used to connect to the water tank body and the negative power supply terminal A2, and the high liquid level signal output terminal X1 and the low liquid level signal output terminal X2 can be directly connected to the signal input terminal of the PLC programmable logic controller to complete the transmission of the signal of the electrode type liquid level detection device. The PLC programmable logic controller communicates with the human-machine interface computer in real time.

5. A method for intelligent measurement and control of condensate in a steam system according to claim 2, characterized in that, The resistance range of the adjustable resistor R1 and the adjustable resistor R2 is the same as 10-100 kΩ. The sensitivity of liquid level detection can be increased or decreased by reducing or increasing the resistance and increasing or decreasing the current flowing through the electrode.

6. The intelligent measurement and control method for condensate water of a steam system according to claim 4, wherein A liquid level detection and control circuit is also provided to facilitate linkage with the makeup water pump or drain pump of the water storage tank, realizing automatic control of water replenishment or drainage according to the liquid level information. The liquid level detection and control circuit is provided with three NOR gates, denoted as IC1B, IC1C, and IC1D respectively, and also includes a light-emitting diode D1 used as an indicator and an NPN transistor Q1. In the liquid level detection and control circuit, one input terminal of the NOR gate chip IC1B is connected to the output terminal of the NOR gate chip IC1A in the signal conversion circuit for electrode type liquid level detection. The other input terminal of the NOR gate chip IC1B, the output terminal of the NOR gate chip IC1C, and the two input terminals of the NOR gate chip IC1D are all connected to the single-pole double-throw switch SW1. The single-pole double-throw switch SW1 is connected to the B pole of the transistor Q1 through the resistor R3. The output terminal of the NOR gate chip IC1B is connected to one input terminal of the NOR gate chip IC1C. The other input terminal of the NOR gate chip IC1C is connected to the low liquid level terminal E2. The GND terminal of the NOR gate chip IC1C is grounded. The output terminal of the NOR gate chip IC1D is connected to the single-pole double-throw switch SW1. The C pole of the transistor Q1 is connected to the negative electrode of the light-emitting diode D1 through the resistor R4. The positive electrode of the light-emitting diode D1 is connected to the positive power supply. The E pole of the transistor Q1 is grounded. The C pole of the transistor Q1 is connected to the terminal C2. The terminal C2 is used to connect to the negative electrode of the control coil of the drain pump or drain valve. The positive electrode of the light-emitting diode D1 is also connected to the terminal C1. The terminal C1 is used to connect to the positive electrode of the control coil of the drain valve or drain pump.

Images