Boiler drum water level measuring device and method

Abstract

The boiler drum water level measuring device comprises a balance container, the balance container is installed on a pipeline on the steam side of a drum, one end of the balance container is connected with a low-pressure side flange, the other end of the balance container is connected with a high-pressure side flange, and a pipeline water column is arranged between the vertically upward position where the high-pressure side flange is located and the liquid level of the balance container. Defining as a reference water column; the device further comprises a double-flange differential pressure transmitter, and the double-flange differential pressure transmitter is used for measuring the pressure of the reference water column. The pressure of the reference water column is directly measured, the height and temperature parameters of the reference water column are not needed, unmeasurable and uncertain parameters in water level calculation are completely eliminated, and the steam drum water level measurement precision is improved; and as long as the height of the reference water column is at any position in the H section, the water level can be accurately measured, that is, the water level can be normally measured in the boiler starting, normal operation and boiler shutdown processes.

Description

Technical Field

[0001] The invention relates to the technical field of power station boiler drum measurement, and in particular to a boiler drum water level measurement device and method. Background Art

[0002] Preventing boiler drum water overflow and water shortage accidents is one of the "Twenty-five Key Requirements for Preventing Major Accidents in Power Production". During normal operation of the boiler, the indication deviation between each drum water level measuring device should be checked frequently. When the deviation exceeds 30mm, the cause should be found and eliminated as soon as possible.

[0003] Boiler drum differential pressure water level gauge has become a commonly used method for drum water level measurement due to its simple structure and measurement principle. However, its reliability is currently questioned by users, and other forms of liquid level measurement instruments such as guided wave radar level gauges are used. The main reason is that the water level density compensation calculation currently used requires the reference water column height and average temperature. These two parameters often have large errors in actual use, and many users do not fully understand the impact of the reference water column on differential pressure water level measurement. They only use the reference water column height design value and the estimated average temperature as water level density compensation calculation parameters. They cannot find the reason for the water level indication out of tolerance, and therefore believe that the differential pressure water level gauge is unreliable.

[0004] When installing the steam-water side sampling tube of the single-chamber balanced container differential pressure water level gauge, the inclination of the pipeline should be no less than 1:100. For the steam side sampling tube, the sampling hole side should be low, and for the water side sampling tube, the sampling hole side should be high. If the sampling tube is installed according to the specification and is 1.5m long, its actual H will be about 30mm larger than the design height after the reference water column condenses, and when the boiler is started, the actual H and the design height may also have a large deviation during the condensation process of the reference water column. These situations cause the water level measurement indication to exceed the tolerance.

[0005] At the same time, during boiler operation, the temperature of the upper part of the reference water column is high, and the temperature in the single-chamber balance container is close to the saturated water temperature under drum pressure; the temperature of the lower part is low and close to the ambient temperature. Therefore, its actual average temperature cannot be directly measured, the density distribution is uneven, and its density cannot be accurately calculated. In practical applications, a fixed estimated average temperature is often used for density calculation, which will also cause water level indication errors.

[0006] The water level indication error caused by the reference water column height error and the average temperature error is calculated by simulating the water level calculation formula. Figure 2 and Figure 3 . Summary of the invention

[0007] The object of the present invention is to provide a boiler drum water level measuring device and method to solve the problems raised in the above background technology.

[0008] To achieve the above object, the present invention provides the following technical solution: a boiler drum water level measuring device, comprising a balancing container, the balancing container is installed on the pipeline on the steam side of the drum, one end of the balancing container is connected to the low-pressure side flange, and the other end is connected to the high-pressure side flange, and the pipeline water column between the vertical upward position of the high-pressure side flange and the liquid level of the balancing container is defined as a reference water column;

[0009] Also included is a double flange differential pressure transmitter, which is used to measure the pressure of a reference water column.

[0010] Preferably, one end of the double flange differential pressure transmitter is connected to the low-pressure side flange through a capillary tube, and the other end of the double flange differential pressure transmitter is connected to the high-pressure side flange through another capillary tube.

[0011] Preferably, the balancing container includes a double-chamber balancing container, an external single-chamber balancing container, and an internal single-chamber balancing container.

[0012] The present invention also provides a method for measuring the water level of a boiler drum, which uses the above-mentioned measuring device and is calculated by the following formula:

[0013] dp×10 3 =ρ a gH-ρ w g(A+h)-ρ s g(Bh) (1)

[0014] h is the water level to be measured

[0015] dp is differential pressure

[0016] ρw is the density of saturated water

[0017] ρs is the density of saturated steam

[0018] ρa is the density of the reference water column

[0019] g is the acceleration due to gravity;

[0020] Reference water column pressure: dp a =ρ a HkDJ

[0021] The water level calculation formula (2) is obtained:

[0022]

[0023] The reference water column pressure dpa is measured by a double flange differential pressure transmitter, and dp is measured by a conventional differential pressure transmitter. A and B are the structural dimensions of the steam drum. The water density ρw and steam density ρs in the steam drum are calculated through the steam drum pressure using the fitting formula of saturated water and saturated steam density.

[0024] Compared with the prior art, the invention has the following beneficial effects: the invention adds a double-flange differential pressure transmitter to the differential pressure single-chamber balance container water level gauge, and the low-pressure side flange and the high-pressure side flange are respectively installed on the reference water column (see Figure 1 The double flange differential pressure transmitter signal is connected to the control system to obtain the reference water column pressure, and the drum water level is calculated using this pressure value. The reference water column pressure can be directly measured without the need for reference water column height and temperature parameters, completely eliminating unmeasurable and uncertain parameters in water level calculation, and improving the measurement accuracy of drum water level; and as long as the reference water column height is at any position within the H section, it can be measured correctly, that is, the water level can be measured normally during boiler startup, normal operation, and shutdown. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0026] Figure 2 The water level indication error Δh is caused by the error ΔH of different reference water column heights (calculated H minus actual H);

[0027] Figure 3 It is the water level indication error Δh caused by different reference water column temperature errors ΔT (calculated T - actual T). DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] 3. Such as Figure 1-3 As shown, the present invention provides a technical solution: a boiler drum water level measurement device and method, including a balancing container, the balancing container is installed on the pipeline on the steam side of the drum, one end of the balancing container is connected to the low-pressure side flange, and the other end is connected to the high-pressure side flange, and the pipeline water column between the vertical upward position of the high-pressure side flange and the liquid level of the balancing container is defined as a reference water column;

[0030] It also includes a double flange differential pressure transmitter, which is used to measure the pressure of a reference water column. One end of the double flange differential pressure transmitter is connected to the low-pressure side flange through a capillary tube, and the other end of the double flange differential pressure transmitter is connected to the high-pressure side flange through another capillary tube. The balancing vessel includes a double-chamber balancing vessel, an external single-chamber balancing vessel, and an internal single-chamber balancing vessel.

[0031] Calculated by the following formula:

[0032] dp×10 3 =ρ a gH-ρ w g(A+h)-ρ s g(Bh) (1)

[0033] h water level to be measured mm

[0034] dp Differential pressure Pa

[0035] ρw Density of saturated water kg / m3

[0036] ρs Density of saturated steam kg / m3

[0037] ρa Density of reference water column kg / m3

[0038] g Gravity acceleration 9.81 m / s 2 ;

[0039] Reference water column pressure: dp a =ρ a HkDJ

[0040] The water level calculation formula (2) is obtained:

[0041]

[0042] The reference water column pressure dpa is measured by a double flange differential pressure transmitter, and dp is measured by a conventional differential pressure transmitter. A and B are the structural dimensions of the steam drum. The water density ρw and steam density ρs in the steam drum are calculated through the steam drum pressure (measured by the pressure transmitter) using the fitting formula of saturated water and saturated steam density.

[0043] From formula (2), we can see that the system error of the high-precision, full-process measurement method of the boiler drum water level single-chamber balance container is independent of the reference water column height and temperature, completely eliminating unmeasurable and uncertain calculation parameters, and can greatly improve the water level measurement accuracy. And because formula (2) is independent of the reference water column height H, as long as the water column height is above the positive pressure side flange and below the negative pressure side flange, the water level can be measured normally.

[0044] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A boiler drum water level measuring device, characterized in that: It includes a balancing container, which is installed on the pipeline on the steam side of the drum, one end of the balancing container is connected to the low-pressure side flange, and the other end is connected to the high-pressure side flange. The pipeline water column between the vertical upward position of the high-pressure side flange and the liquid level of the balancing container is defined as the reference water column; Also included is a double flange differential pressure transmitter, which is used to measure the pressure of a reference water column.

2. A boiler drum water level measuring device according to claim 1, characterized in that: One end of the double flange differential pressure transmitter is connected to the low-pressure side flange through a capillary tube, and the other end of the double flange differential pressure transmitter is connected to the high-pressure side flange through another capillary tube.

3. A boiler drum water level measuring device according to claim 2, characterized in that: The balancing container includes a double-chamber balancing container, an external single-chamber balancing container, and an internal single-chamber balancing container.

4. A method for measuring the water level of a boiler drum, characterized in that: A boiler drum water level measuring device according to any one of claims 1 to 3 is used; Calculated by the following formula: dp×10 3 =ρ a gH-ρ w g(A+h)-ρ s g(Bh) (1) h is the water level to be measured dp is differential pressure ρw is the density of saturated water ρs is the density of saturated steam ρa is the density of the reference water column g is the acceleration due to gravity; Reference water column pressure: dp a =ρ a HkDJ The water level calculation formula (2) is obtained: The reference water column pressure dpa is measured by a double flange differential pressure transmitter, and dp is measured by a conventional differential pressure transmitter. A and B are the structural dimensions of the steam drum. The water density ρw and steam density ρs in the steam drum are calculated through the steam drum pressure using the fitting formula of saturated water and saturated steam density.

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