Built-in compensation-free steam drum liquid level measuring device and method

Abstract

The invention discloses a built-in compensation-free steam drum liquid level measuring device and method, belongs to the field of ship boiler operation, and aims at solving the problem that errors exist in the measuring result when a differential pressure transmitter is adopted for measuring the water level. The device comprises a primary coil, a secondary coil, an iron core floater and a coil framework, the coil framework is in a cylinder shape with an upper opening and a lower opening, the primary coil is arranged in the middle of the coil framework, the secondary coils S1 and S2 are arranged on the upper side and the lower side of the coil framework respectively, the secondary coils S1 and S2 are symmetrically arranged on the two sides of the primary coil, and the secondary coils S1 and S2 are connected in series in an anti-phase mode; an iron core floater is arranged in the cavity of the coil framework and moves up and down along the center rod along with changes of the bubble liquid level, and an output voltage value and the displacement amount of the iron core floater are in a linear relation and used for representing the bubble liquid level.

Description

Technical Field

[0001] The present invention relates to an in-built non-compensated steam drum liquid level measuring device and method, belonging to the field of marine boiler operation. Background Art

[0002] The accurate measured value of the steam drum water level is one of the important measured parameters in a power plant. There are many measuring methods, and the commonly used ones at present are the communicating liquid level gauge and differential pressure liquid level gauge in the static pressure measuring method. However, when there is a temperature difference between the liquid level gauge and the liquid in the measured steam drum, the displayed liquid level is different from the liquid level in the steam drum, and its error will also change with the change of the steam drum pressure. Moreover, due to the reasons of rolling and pitching of the marine boiler, the liquid level deviation of the high-pressure boiler drum is relatively large.

[0003] Importance of accurately measuring the steam drum water level: All large units are designed with a full-range feed water control system. During the start-up to full load, shutdown and load reduction, or load fluctuation of the unit, the steam drum pressure is constantly changing, and the densities of the steam and water in the steam drum also change accordingly, thus affecting the accuracy of the steam drum water level measurement and the operation of the full-range feed water control system, and endangering the safety of the unit. Because too high a steam drum water level may cause steam to carry water, deteriorating the steam quality. In the light case, it will increase the fouling of pipelines and steam turbines, reducing the output and efficiency. In the severe case, it will cause accidents to the steam turbine. If the steam drum water level is too low, it is not conducive to the water circulation, and may lead to local overheating and even tube explosion of the water-cooled wall. Therefore, the accurate measured value of the steam drum water level is one of the most important measured parameters in a power plant.

[0004] Measuring methods of the steam drum water level and existing problems: There are many measuring methods for the steam drum water level, which can generally be divided into: (1) static pressure type; (2) buoyancy type; (3) electrical type; (4) ultrasonic type; (5) nuclear radiation type. The most commonly used ones in power plants at present are the communicating liquid level gauge and differential pressure liquid level gauge in the static pressure measuring method. The communicating liquid level gauge includes mica water level gauge and electric contact water level gauge. These liquid level gauges are intuitive and convenient for reading, but their common disadvantage is that when there is a difference in the liquid temperature between the liquid level gauge and the measured steam drum, the displayed liquid level is different from the liquid level in the steam drum, and this error will also change with the change of the steam drum pressure. In order to reduce the error caused by the temperature difference, the liquid level gauge is often insulated. However, since the density changes with the temperature and pressure of the steam drum, especially during the start-up and shutdown processes, the difference in the liquid level between the liquid level gauge and the liquid level in the steam drum is always changing.

[0005] For the electric contact water level gauge, since it does not provide continuous indication and cannot reflect the water level changes between the contacts, and also because the arrangement of the contacts in the electric contact water level gauge is non-uniform, with a small spacing near the normal water level (i.e., the zero water level) and a large spacing on both sides far from the zero water level. When the actual water level in the steam drum is around the zero water level under rated conditions, due to the lower water level in the electric contact water level gauge and the spacing of the contacts here, the error will be even greater. Therefore, the electric contact water level gauge can only be effective during the startup process and low-load operation. At high loads, it can only be used as a reference for the steam drum water level and cannot be used as a regulating and protection signal.

[0006] Problems and measures when using a differential pressure transmitter for measurement: The analog signal of the steam drum water level is measured using a differential pressure transmitter. See Figure 1 , with a single-chamber equalizing vessel installed on the steam side, and a sampling pipe connected between the steam drum 5 and the liquid level gauge 6 to form.

[0007] The density of the water in the equalizing vessel will also change due to temperature and pressure variations, resulting in errors. Therefore, the equalizing vessel is not insulated to keep the temperature of the water in the equalizing vessel constant at around room temperature of 38 °C, reducing the influence of temperature changes on the density of the water in the equalizing vessel. In engineering, the influence of temperature on the density of the water in the equalizing vessel can be ignored. Therefore, when using a differential pressure transmitter to measure the steam drum water level, compensation for the steam drum pressure must be carried out. The compensated and corrected steam drum water level H is:

[0008] H = B + A = L(ρ a -ρ s )g - ΔP + A

[0009] (ρ ω - ρ s )g

[0010] In the formula,

[0011] B is the height from the lower sampling pipe to the steam drum liquid level;

[0012] A is the height from the lower sampling pipe to the zero point of the steam drum water level;

[0013] L is the height between the upper sampling pipe and the lower sampling pipe;

[0014] ρ a is the density of the condensate water in the liquid level gauge;

[0015] ρ ω is the density of the saturated water in the steam drum;

[0016] ρ s is the density of the saturated steam;

[0017] ΔP is the differential pressure value of the transmitter.

[0018] It can be seen that when measuring the water level with a differential pressure transmitter, temperature and pressure compensation measurements and calculations are required for the water level. The measurement result is affected by the temperature and pressure inside the steam drum, and there are errors in the measurement result. Summary of the Invention

[0019] Aiming at the problem that there are errors in the measurement result when measuring the water level with a differential pressure transmitter, the present invention provides an in - built non - compensation steam drum liquid level measurement device and method.

[0020] On one hand, the present invention provides an in - built non - compensation steam drum liquid level measurement device, including a primary coil 1, a secondary coil 2, an iron - core float 3 and a coil skeleton; the coil skeleton is a cylindrical shape with openings at both the upper and lower ends. The primary coil 1 is arranged in the middle of the coil skeleton, and one secondary coil 2 is arranged on each of the upper and lower sides of the coil skeleton, namely secondary coil S1 and secondary coil S2. The secondary coil S1 and secondary coil S2 are symmetrically arranged on both sides of the primary coil 1, and the secondary coil S1 and secondary coil S2 are connected in anti - phase series.

[0021] An iron - core float 3 is arranged in the cavity of the coil skeleton. The iron - core float 3 moves up and down along the center rod 4 with the change of the steam - bubble liquid level. The output voltage value is linearly related to the displacement of the iron - core float 3 and is used to represent the steam - bubble liquid level.

[0022] Preferably, it further includes a rigid outer shell, and the rigid outer shell is used to wrap the primary coil 1, the secondary coil 2 and the coil skeleton, and the rigid outer shell is fixed on the top shell of the center line of the sphere of the steam drum 5.

[0023] Preferably, it further includes an end cover and a liquid level gauge terminal 7. An end cover is arranged at the upper - end opening of the coil skeleton. The center of the lower surface of the end cover is fixedly connected to the center rod 4, and a liquid level gauge terminal 7 is arranged on the upper surface of the end cover. The primary coil 1 is electrically connected to an external constant - amplitude AC power supply through the liquid level gauge terminal 7, and after the secondary coil S1 and secondary coil S2 are connected in anti - phase series, they output a voltage value for calculating the liquid level through the liquid level gauge terminal 7.

[0024] Preferably, it further includes a liquid level gauge vent hole 6. A plurality of liquid level gauge vent holes 6 are arranged on the rigid outer shell to enable the upper space of the float to communicate with the steam side of the steam drum, and the lower part of the float to communicate with the liquid side of the steam drum.

[0025] On the other hand, the present invention provides an in - built non - compensation steam drum liquid level measurement method, and the method is as follows:

[0026] The primary coil 1 is powered by a constant - amplitude AC power supply. The magnetic flux formed thereby is coupled to the adjacent secondary coils S1 and S2 by the iron - core float 3; the differential voltage output is E2 - E1, where E2 is the output voltage of the secondary coil S2 and E1 is the output voltage of the secondary coil S1.

[0027] When the longitudinal position of the iron core float 3 is in the middle position, the magnetic fluxes coupled to the adjacent secondary coils S1 and S2 are equal, and the differential voltage is zero;

[0028] When the longitudinal position of the iron core float 3 is shifted upward or downward, the differential voltage is greater than zero;

[0029] The drum liquid level is obtained according to the differential voltage as:

[0030] H = β + k(E2 - E1)

[0031] In the formula, β is the liquid level correction value, and k is the proportionality coefficient.

[0032] Preferably, the output range of the differential voltage E2 - E1 is -Q to +Q. It is set that -Q corresponds to the lower limit of the measurable liquid level range, and +Q corresponds to the upper limit of the measurable liquid level range.

[0033] Preferably, when the iron core float 3 is in the upper or lower limit position and the differential voltage no longer changes following the continuous rise or fall of the bubble liquid level, it indicates that the liquid level gauge is out of range, and corresponding alarms are given.

[0034] The beneficial effects of the present invention:

[0035] (1) Frictionless measurement: There is no physical contact between the float and the coil, that is, there are no friction components.

[0036] (2) Infinite mechanical life: There is no friction and contact between the coil and the float, so no wear will occur. In this way, the mechanical life of the liquid level gauge is theoretically infinite.

[0037] (3) Infinite resolution: Its frictionless operation and induction principle endow it with two remarkable characteristics. The first characteristic is true infinite resolution. This means that the liquid level gauge can respond to the slightest movement of the float and generate an output. The readability of external electronic devices is the only limit to the resolution.

[0038] (4) Zero position repeatability: The liquid level gauge is symmetrically constructed, and the zero position can be restored. The electrical zero position repeatability is high and extremely stable.

[0039] (5) Axial suppression: It is very sensitive to the axial movement of the float and relatively insensitive to the radial movement. In this way, the liquid level gauge can be used to measure a float that does not move in a precise straight line, which is quite beneficial for measuring the swing and tilt of a ship.

[0040] (6) Robust and durable: The float and the coil are separated from each other. A non-magnetic isolator is inserted between the float and the inner wall of the coil, which can isolate the pressurized, corrosive or alkaline liquid from the coil group. In this way, the coil group is hermetically sealed, and there is no need for dynamic sealing of moving components. For the coil group in a pressurized system, only static sealing is required.

[0041] (7) Environmental adaptability: The sealed liquid level gauge can adopt a stainless steel shell, can be placed in corrosive liquids or gases, and can work stably in high-temperature and high-pressure environments.

[0042] (8) Input / output isolation: This liquid level gauge can be considered a kind of transformer because its exciting input (primary) and output (secondary) are completely isolated. Without a buffer amplifier, it can be considered an effective analog signal computing element. In an efficient measurement and control loop, its signal line is separated from the power ground wire. The output signal is a standard 0 - 5V or 4 - 20mA that can be used by a computer or PLC.

[0043] (9) No compensation required: Since the liquid level gauge is built into the steam drum, there is no need for temperature and pressure compensation measurement and calculation. Moreover, the liquid level gauge coil is built inside the stainless steel shell of the liquid level gauge, not affected by the temperature and pressure inside the steam drum, and the measurement result is more accurate than the compensated method.

[0044] (10) Liquid level gauge ball center arrangement: For a ship's steam drum, a spherical structure is mostly adopted, and the liquid level gauge is arranged on the center line of the steam drum sphere. This structure and arrangement can effectively eliminate the influence of ship sway on the steam drum liquid level.

[0045] (11) Liquid level gauge built-in vent hole: Since the liquid level gauge is built into the steam drum, a vent hole is provided at its top, so that the upper space of the float communicates with the steam side of the steam drum, and the lower part of the float communicates with the liquid side of the steam drum, ensuring the normal operation of the float. Description of the Drawings

[0046] Figure 1 is the schematic diagram of measurement using a differential pressure transmitter involved in the background technology;

[0047] Figure 2 is the structural schematic diagram of an in-built type steam drum liquid level measurement device without compensation according to the present invention;

[0048] Figure 3 is the schematic diagram of the mechanical part of the steam drum liquid level measurement according to the present invention;

[0049] Figure 4 is the schematic diagram of the electrical part of the steam drum liquid level measurement according to the present invention. Detailed Implementation Modes

[0050] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0051] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0052] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but it is not limited to the present invention.

[0053] Specific Embodiment 1: The following will be described in conjunction with Figures 2 to 4 This embodiment will be described. The built-in non-compensated steam drum liquid level measuring device described in this embodiment includes a primary coil 1, a secondary coil 2, an iron core float 3, and a coil skeleton; the coil skeleton is a cylindrical shape with openings at both the top and bottom. The primary coil 1 is arranged in the middle of the coil skeleton, and a secondary coil 2 is arranged on each of the upper and lower sides of the coil skeleton, namely the secondary coil S1 and S2. The secondary coil S1 and S2 are symmetrically arranged on both sides of the primary coil 1, and the secondary coil S1 and S2 are connected in anti-phase series;

[0054] An iron core float 3 is arranged in the cavity of the coil skeleton. The iron core float 3 moves up and down along the central rod 4 with the change of the steam bubble liquid level, and the output voltage value is linearly related to the displacement of the iron core float 3, which is used to characterize the steam bubble liquid level.

[0055] Furthermore, it also includes a rigid outer shell, and the rigid outer shell is used to wrap the primary coil 1, the secondary coil 2, and the coil skeleton, and the rigid outer shell is fixed on the top shell of the center line of the sphere of the steam drum 5.

[0056] Furthermore, it also includes an end cover and a liquid level gauge terminal 7. An end cover is arranged at the upper opening of the coil skeleton. The center of the lower surface of the end cover is fixedly connected to the central rod 4, and a liquid level gauge terminal 7 is arranged on the upper surface of the end cover. The primary coil 1 is electrically connected to an external constant amplitude AC power supply through the liquid level gauge terminal 7, and the secondary coil S1 and S2 are connected in anti-phase series and then output the voltage value for calculating the liquid level through the liquid level gauge terminal 7.

[0057] Furthermore, it also includes a liquid level gauge vent hole 6. A plurality of liquid level gauge vent holes 6 are arranged on the rigid outer shell to make the upper space of the float communicate with the steam side of the steam drum, and the lower part of the float communicate with the liquid side of the steam drum.

[0058] Combining the iron core buoyancy measurement with the magnetosensitive measurement, the iron core float 3 can provide an accurate liquid level position, and the magnetosensitive sensor (primary coil P + secondary coils S1, S2) can convert the object displacement into a highly sensitive and stable electrical signal. Through the linear motion of the iron core float 3, the change in the high-pressure steam drum water level is converted into a linear mechanical displacement electrical signal. To achieve this effect, the iron core float 3 can be sleeved on a smooth rod (central rod 4) to limit the movement trajectory of the iron core float 3, and a transformer bushing is fixed outside the iron core float 3. Briefly speaking, the working principle is an iron core float variable transformer. It consists of a primary coil, two secondary coils, an iron core float, a coil skeleton, a housing and other components.

[0059] The primary coil P and secondary coils S1, S2 are distributed on the coil skeleton, and inside the coil is a freely movable rod-shaped float. When the float is in the middle position, the induced electromotive forces generated by the two secondary coils are equal, so the output voltage is zero; when the float moves inside the coil and deviates from the center position, the induced electromotive forces generated by the two coils are not equal, and there is a voltage output, and the magnitude of the voltage depends on the magnitude of the displacement. In order to improve the sensitivity of the sensor, improve the linearity of the sensor, and increase the linear range of the sensor, when designing, the two coils are connected in series in reverse, and the voltage polarities of the two secondary coils are opposite. The voltage output by the liquid level gauge is the difference between the voltages of the two secondary coils, and this output voltage value is linearly related to the displacement of the float.

[0060] Specific implementation method two: The following is combined with Figures 2 to 4 to illustrate this implementation method. The built-in non-compensated steam drum liquid level measurement method described in this implementation method is realized based on the built-in non-compensated steam drum liquid level measurement device described in implementation method one. This method is as follows:

[0061] The primary coil 1 is energized by a constant amplitude AC power supply. The magnetic flux formed thereby is coupled by the iron core float 3 to the adjacent secondary coils S1 and S2; the differential voltage output is E2 - E1, where E2 is the output voltage of the secondary coil S2 and E1 is the output voltage of the secondary coil S1;

[0062] When the longitudinal position of the iron core float 3 is in the middle position, the magnetic fluxes coupled to the adjacent secondary coils S1 and S2 are equal, and the differential voltage is zero;

[0063] When the longitudinal position of the iron core float 3 is offset upward or downward, the differential voltage is greater than zero;

[0064] The steam drum liquid level is obtained according to the differential voltage as:

[0065] H = β + k(E2 - E1)

[0066] In the formula, β is the liquid level correction value, and k is the proportionality coefficient.

[0067] The output range of the differential voltage E2 - E1 is -Q to +Q, for example, -5V to +5V. It is set that -Q corresponds to the lower limit of the measurable liquid level range, and +Q corresponds to the upper limit of the measurable liquid level range.

[0068] When the iron core float 3 is in the upper or lower position, when the differential voltage no longer changes following the rise or fall of the bubble liquid level, it indicates that the liquid level gauge is out of range and corresponding alarms are given.

[0069] For the measurement principle, see Figure 4 , when the float is in the middle position, the induced electromotive forces generated by the two secondary coils are equal, so the output voltage is zero; when the float moves inside the coil and deviates from the center position, the induced electromotive forces generated by the two coils are not equal, and there is a voltage output. The magnitude of the voltage depends on the magnitude of the displacement. In order to improve the sensitivity of the sensor, improve the linearity of the sensor, and increase the linear range of the sensor, during design, the two coils are connected in series reverse, and the voltage polarities of the two secondary coils are opposite. The output voltage is the difference between the voltages of the two secondary coils. This output voltage value has a linear relationship with the displacement of the float.

[0070] The primary coil P of the liquid level gauge is energized by a constant amplitude AC power supply. The magnetic flux formed thereby is coupled by the float to the adjacent secondary coils S1 and S2. If the float is located in the middle of S1 and S2, an equal amount of magnetic flux will be coupled to each secondary coil. Therefore, E1 and E2 contained in the coils S1 and S2 respectively are equal. At this reference intermediate float position (referred to as the electrical zero position), the differential voltage output (E1 - E2) is essentially zero. As Figure 4 shown, if the float moves so that its distance from S1 is less than its distance from S2, the magnetic flux coupled into S1 will increase, while the magnetic flux coupled into S2 will decrease. Therefore, the induced voltage E1 increases and E2 decreases, thus generating a differential voltage (E1 - E2). On the contrary, if the float moves closer to S2, the magnetic flux coupled into S2 will increase, while the magnetic flux coupled into S1 will decrease. Therefore, E2 increases and E1 decreases, thus generating a differential voltage (E2 - E1).

[0071] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed, as long as they do not depart from the spirit and scope of the present invention as defined by the appended claims. It should be understood that different dependent claims and the features described herein can be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a single embodiment can be used in other described embodiments.

Claims

1. A built-in compensation-free drum liquid level measuring device, characterized in that: The invention comprises a primary coil (1), a secondary coil (2), an iron core float (3) and a coil frame; the coil frame is in the shape of a cylinder with openings at the top and bottom, the primary coil (1) is arranged in the middle of the coil frame, and a secondary coil (2) is arranged on each of the upper and lower sides of the coil frame, which are the secondary coils S1 and S2 respectively, the secondary coils S1 and S2 are symmetrically arranged on both sides of the primary coil (1), and the secondary coils S1 and S2 are connected in anti-phase series; An iron core float (3) is arranged in the cavity of the coil frame. The iron core float (3) moves up and down along the central rod (4) as the bubble liquid level changes. The output voltage value is linearly related to the displacement of the iron core float (3) and is used to characterize the bubble liquid level.

2. According to claim 1, a built-in compensation-free drum liquid level measuring device is characterized in that: It also includes a rigid shell, which is used to wrap the primary coil (1), the secondary coil (2) and the coil frame, and the rigid shell is fixed on the top shell of the center line of the steam drum (5) sphere.

3. According to claim 2, a built-in compensation-free drum liquid level measuring device is characterized in that: It also includes an end cover and a liquid level meter terminal (7), wherein the end cover is arranged at the upper end opening of the coil skeleton, the center of the lower surface of the end cover is fixedly connected to the center rod (4), and the upper surface of the end cover is arranged with a liquid level meter terminal (7), the primary coil (1) is electrically connected to an external constant amplitude AC power source through the liquid level meter terminal (7), and the secondary coils S1 and S2 are connected in anti-phase series and output a voltage value for calculating the liquid level through the liquid level meter terminal (7).

4. The built-in compensation-free drum level measuring device according to claim 2, characterized in that: It also comprises a liquid level gauge vent hole (6). A plurality of liquid level gauge vent holes (6) are arranged on the rigid shell to enable the upper space of the float to communicate with the steam side of the drum, and the lower space of the float to communicate with the liquid side of the drum.

5. A built-in compensation-free drum liquid level measurement method, which is implemented based on the built-in compensation-free drum liquid level measurement device according to any one of claims 1 to 4, characterized in that: The method is: The primary coil (1) is energized by a constant amplitude AC power supply. The magnetic flux thus formed is coupled to the adjacent secondary coils S1 and S2 by the core float (3); the differential voltage output is E2-E1, where E2 is the output voltage of the secondary coil S2 and E1 is the output voltage of the secondary coil S1; When the longitudinal position of the core float (3) is in the middle position, the magnetic fluxes coupled to the adjacent secondary coils S1 and S2 are equal, and the differential voltage is zero; When the longitudinal position of the core float (3) is offset upward or downward, the differential voltage is greater than zero; The drum liquid level is obtained according to the differential voltage: H=β+k(E2-E1) In the formula, β is the liquid level correction value and k is the proportional coefficient.

6. A built-in compensation-free drum level measurement method according to claim 5, characterized in that: The output range of the differential voltage E2-E1 is -Q to +Q. Setting -Q corresponds to the lower limit of the measurable liquid level range, and +Q corresponds to the upper limit of the measurable liquid level range.

7. A built-in compensation-free drum level measurement method according to claim 6, characterized in that: When the core float (3) is at the upper limit or lower limit position, and the differential voltage no longer changes with the bubble liquid level continuing to rise or fall, it indicates that the liquid level meter exceeds the range and a corresponding alarm is issued.

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