CN101655381A - Circulating cooling water flow measuring method of condenser for steam turbine and on-line measuring device thereof - Google Patents

Abstract

A method for measuring the circulating cooling water flow of a steam turbine condenser, which is characterized in that it includes the steps of installation of measuring points and data acquisition, calculation of circulating cooling water flow, device calibration, device commissioning, actual measurement and data display; the online measuring device includes The circulating cooling water pipe of the steam turbine is connected to the condenser through a vertical bend, and the inner and outer pressure pipes are respectively installed on the inside and outside of the 45° section of the vertical bend. The pressure transmitter is connected, the differential pressure transmitter is electrically connected to the piezoresistor, the piezoresistor is electrically connected to the data collector, and the data collector is electrically connected to the computer. The measuring method is scientific, easy to grasp and has strong applicability; the online measuring device has a simple structure and low cost, and can automatically and accurately measure the flow rate of the circulating cooling water of the steam turbine.

Description

Method for Measuring the Flow Rate of Circulating Cooling Water in Steam Turbine Condenser and Its Online Measurement Device

technical field

The invention relates to the field of thermal equipment state monitoring, and relates to a method for measuring the flow rate of circulating cooling water in a condenser of a steam turbine and an online measuring device thereof.

Background technique

The circulating cooling water flow rate is one of the important factors determining the vacuum of the steam turbine condenser. The circulating cooling water flow rate not only affects the economy of the steam turbine operation, but also has a great impact on the power consumption of the circulating cooling water pump. At the same time, it is necessary to measure the flow rate of circulating cooling water to analyze the cause of the vacuum reduction of the condenser and to study the performance of the circulating cooling water pump and the cooling tower.

One of the existing methods of measuring the flow rate of circulating cooling water is to use the heat balance method of the condenser. The basic principle is to use the heat released by the steam in the condenser to be equal to the heat absorbed by the circulating cooling water, so that the flow rate of the circulating cooling water can be obtained by solving the problem. , but in the actual operation process, the measurement accuracy of the steam volume entering the condenser and the drainage volume is not high, which affects the accurate measurement of the circulating cooling water flow. Another method is to use the enthalpy rise of the inlet and outlet water of the circulating cooling water pump to measure the circulating cooling water flow rate. It is very small, which also affects the measurement accuracy of the circulating cooling water flow.

At present, the flow of circulating cooling water in thermal power plants is generally measured by ultrasonic flowmeters. However, ultrasonic flowmeters are not only expensive, but also greatly affected by electromagnetic waves. At the same time, because corrosion often occurs inside the pipeline, it also affects the measurement accuracy of the ultrasonic flowmeter.

With the gradual increase of the unit capacity of the thermal power unit, the water consumption of the thermal power plant is also gradually increasing, which makes the capacity of the circulating cooling water pump and the diameter of the delivery pipeline increase accordingly. For example, for a 300MW steam turbine, the circulating cooling water flow rate is 37512t/h under rated conditions, and the diameter of the circulating cooling water pipe is usually in the range of 1.2-2.2m. Such a large circulating cooling water flow rate and the diameter of the circulating cooling water pipe have brought great difficulties to the installation of flow measuring devices such as orifice plates. People have been working hard to create a practical method for measuring the circulating cooling water flow rate of the steam turbine condenser. Eager to actually solve the problem of online measurement of circulating cooling water flow, but it has not been solved so far.

Contents of the invention

The object of the present invention is to provide a scientific method, easy to grasp, and strong applicability for measuring the circulating cooling water flow rate of the steam turbine condenser, and to provide a simple structure, low cost, which can automatically and accurately measure the flow rate of the steam turbine condenser circulation. Cooling water flow online measuring device.

Realize the technical scheme that the object of the present invention takes is:

A method for measuring the circulating cooling water flow of a steam turbine condenser is characterized in that it comprises the following steps:

1) Measuring point installation and data collection, the circulating cooling water pipe of the steam turbine is connected to the condenser through a vertical bend, and the inner pressure pipe and the outer pressure pipe are respectively installed on the inner and outer sides of the 45° section of the vertical bend. The pressure-taking tubes are all connected to the differential pressure transmitter through rubber tubes; the differential pressure transmitter is electrically connected to the piezoresistor, the piezoresistor is electrically connected to the data collector, and the data collector is electrically connected to the computer. The differential pressure data is stored in the computer data file;

2) Calculation of circulating cooling water flow,

(1) According to the free vortex theory, the velocity distribution of the fluid in the vertical elbow is obtained from the Bernoulli equation as

$\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, C ₁ is the integral constant, m ² /s; R is the distance from the center of curvature to a certain point in the tube, m,

For a vertical elbow, the relationship between the ideal flow rate and the pressure difference inside and outside the vertical elbow is

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; vt</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">C</figure-callout></span><figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">C</figure-callout></span><figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; -</span>\sqrt{{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{\sqrt{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}$

Among them, Q _vt is the ideal flow rate through the vertical bend, m ³ /s; C _e1 is a coefficient related only to the geometric size of the vertical bend; Δp is the pressure difference between the inside and outside of the vertical bend at a 45° angle, Pa; ρ is the density of the fluid, kg/m ³ ; r ₀ is the inner radius of the vertical bend, m; R ₀ is the radius of curvature of the center of the vertical bend, m; for the vertical bend at the inlet of the condenser, after derivation,

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; vt</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">C</figure-callout></span><figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; gz</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Among them, Δp is the pressure difference between the inside and outside of the 45° angle direction of the vertical elbow, ρ is the density of the fluid, kg/m ³ ; g is the acceleration of gravity; z is the height difference between the inside and outside of the 45° angle direction of the vertical elbow; z=Φ ×cos45°, Φ is the pipe diameter;

(2) The actual flow rate through the vertical elbow, due to the existence of flow loss, makes the actual flow rate of the fluid not equal to the ideal flow rate of the fluid under the same internal and external pressure difference conditions, and the relationship between them is expressed as

_Qv = _αQvt (5)

Among them, Q _v is the actual measured flow rate, m ³ /s; Q _vt is the ideal flow rate through the elbow, m ³ /s; α is called the flow coefficient, and its value is determined through experimental calibration;

3) Calibration of the device, measuring the pressure difference between the inside and outside of the vertical elbow with a mercury differential pressure gauge. The measurement of the fluid flow is to select a position with a long enough straight pipe section on the cooling water pipeline to install an Annubar flowmeter to measure the fluid flowing through the pipeline. Flow rate, change the flow rate, so as to determine the coefficient, remove the mercury differential pressure meter and Annubar flowmeter after calibration;

4) When the device is put into operation, actual measurement and data display, the circulating cooling water flow rate is calculated according to the software program and displayed on the computer monitor.

An on-line measuring device for circulating cooling water flow in a steam turbine condenser, which includes a circulating cooling water pipe of a steam turbine connected to the condenser through a vertical bend. The inner pressure tube, the outer pressure tube, the inner and outer pressure tubes are connected to the differential pressure transmitter through rubber tubes, the differential pressure transmitter is electrically connected to the piezoresistor, and the piezoresistor is electrically connected to the data collector. The data collector is electrically connected with the computer.

The method for measuring the circulating cooling water flow rate of the steam turbine condenser is scientific, easy to grasp and strong in applicability.

The online measuring device for circulating cooling water flow of steam turbine condenser has simple structure and low cost, and can automatically and accurately measure the circulating cooling water flow of steam turbine.

Description of drawings

Figure 1 is a block diagram of a method for measuring the flow rate of circulating cooling water in a steam turbine condenser.

Figure 2 is a schematic diagram of the connection structure between the circulating cooling water pipe of the steam turbine and the condenser through a vertical bend.

Figure 3 is a schematic diagram of the velocity distribution in a vertical bend.

Fig. 4 is a schematic diagram of the structure of the vertical elbow of the embodiment.

Fig. 5 is a structural schematic diagram of an online measurement device for circulating cooling water flow in a steam turbine condenser.

In the figure: 1 steam turbine, 2 condenser, 3 circulating cooling water pipe, 4A inner pressure pipe, 4B outer pressure pipe, 5 differential pressure transmitter, 6 piezoresistor, 7 data collector, 8USB interface, 9computer , 10 data processing software, 11 monitors.

Detailed ways

Referring to Figures 1, 2 and 5: the method for measuring the circulating cooling water flow rate of the steam turbine condenser includes the following steps:

1) Measuring point installation and data collection: The exhaust steam of steam turbine 1 in the thermal power plant enters condenser 2, and the exhaust steam of steam turbine 1 is condensed into water by the circulating cooling water of steam turbine 1. The circulating cooling water is pumped into the condenser 2 through the circulating cooling water pump. Usually the circulating cooling water pipe 3 is arranged underground, and the circulating cooling water pipe 3 arranged underground is connected to the condenser 1 through a vertical elbow, and the inner pressure taking pipe 4A and the outer pressure taking pipe 4A are respectively installed on the inner and outer sides of the 45° section of the vertical elbow Tube 4B, inner and outer pressure tubes 4A, 4B are all connected to differential pressure transmitter 5 through rubber tubes, differential pressure transmitter 5 is electrically connected to piezoresistor 6, and piezoresistor 6 is electrically connected to data collector 7 , the data collector 7 is electrically connected to the computer 9, and stores the differential pressure data collected once per second into the data file of the computer 9.

2) Calculation of circulating cooling water flow:

(1) The relationship between the ideal flow rate and the internal and external pressure difference in the vertical elbow. According to the free vortex theory, the theoretical method assumes that: ① the fluid is in a stable and steady flow, the fluid is filled with the pipe, and does not contain air bubbles; ② the fluid is incompressible and the flow is continuous ③ The vertical elbow maintains the same radius of curvature, the ellipticity of the elbow itself is negligible, and the inner wall of the pipe is smooth. This theory believes that the fluid in the elbow is free to rotate around the center of curvature of the elbow. According to the Bernoulli equation and ignoring the friction between the fluids in the process of fluid flow, the velocity distribution of the fluid in the elbow is obtained as

$\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, C ₁ is the integral constant, m ² /s; R is the distance from the center of curvature to a certain point in the tube, m.

It can be seen from formula (1) that when the fluid flows along the vertical elbow, as the radius of curvature increases, the fluid velocity gradually decreases, while the fluid pressure gradually increases. The velocity distribution of the fluid flow is shown in Figure 3.

For a vertical elbow, the relationship between the ideal flow rate and the pressure difference inside and outside the vertical elbow is

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; vt</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">C</figure-callout></span><figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">C</figure-callout></span><figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; -</span>\sqrt{{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{\sqrt{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}$

Among them, Q _vt is the ideal flow rate through the vertical bend, m ³ /s; C _e1 is a coefficient related only to the geometric size of the vertical bend; Δp is the pressure difference between the inside and outside of the vertical bend at a 45° angle, Pa; ρ is the density of the fluid, kg/m ³ ; r ₀ is the inner radius of the vertical bend, m; R ₀ is the radius of curvature of the center of the vertical bend, m.

For the vertical bend at the inlet of the condenser, after derivation, we get

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; vt</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">C</figure-callout></span><figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; gz</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Among them, Q _vt is the ideal flow through the vertical bend, m ³ /s; Δp is the pressure difference between the inside and outside of the vertical bend at a 45° angle, ρ is the density of the fluid, kg/m ³ ; g is the acceleration of gravity; z is The height difference between the inner and outer sides of the cross-section in the 45° angle direction of the vertical elbow; z=Φ×cos45°, Φ is the pipe diameter.

(2) The actual flow rate through the vertical elbow. The relationship between the ideal flow rate of the fluid in the vertical elbow and the internal and external pressure difference established above treats the fluid as an ideal fluid without considering the loss in the process of fluid flow. In fact, when the fluid flows in the vertical elbow, there is inevitably a certain loss. These losses include the friction between the fluid and the pipe wall, the internal friction of the fluid, the vortex and the loss caused by the secondary flow of the fluid. Due to the existence of these losses, under the same internal and external pressure difference conditions, the actual flow rate of the fluid may not be equal to the ideal flow rate of the fluid, and the relationship between them can be expressed as

_Qv = _αQvt (5)

Among them, Q _v is the actual measured flow rate, m ³ /s; Q _vt is the ideal flow rate through the vertical elbow, m ³ /s; α is called the flow coefficient, and its value is determined through experimental calibration.

3) Device calibration: the purpose of calibration is to determine the flow coefficient α. The specific method is to measure the differential pressure with a mercury differential pressure meter, and measure the circulating cooling water flow rate with an Annubar flowmeter, so as to calibrate the above-mentioned devices. The specific calibration method is to measure the pressure difference between the inside and outside of the vertical elbow with a mercury differential pressure meter. The fluid flow is measured on the circulating cooling water pipeline 3 outside the plant. Choose a location with a long enough straight pipe to install an Annubar flowmeter to measure the fluid flow through the pipe. Change the flow rate to determine the coefficient. After calibration, remove the mercury differential pressure gauge and the Annubar flowmeter.

4) Device commissioning, actual measurement and data display: the circulating cooling water flow is calculated according to the data processing software 10 and displayed on the display 11 of the computer 9 .

An on-line measurement device for the circulating cooling water flow of a steam turbine condenser, which includes a circulating cooling water pipe 3 of a steam turbine 1 connected to the condenser 2 through a vertical bend, and the inside and outside of the 45° section of the vertical bend are respectively installed with inner pressure Pipe 4A, outer pressure-taking pipe 4B, inner and outer pressure-taking pipes 4A, 4B are all connected to differential pressure transmitter 5 through rubber tubes; differential pressure transmitter 5 is electrically connected to piezoresistor 6, and piezoresistor 6 is connected to The data collector 7 is electrically connected, and the data collector 7 is electrically connected with the USB interface 8 of the computer 9, and the interface USB of the computer 9 submits the data collected to the data processing software 10 installed in the computer 9; the data processing software installed in the computer 10 make the computer display on the computer monitor 11 after obtaining the circulating cooling water flow.

Referring to Figs. 4 and 5, the specific application example of the method for measuring the circulating cooling water flow of the steam turbine condenser of the present invention is a measurement test of the cooling water flow of a single condenser of a 300MW steam turbine.

1) Measuring point installation and data collection:

The circulating cooling water pipe 3 arranged underground is connected to the condenser 1 through a vertical bend, the inner diameter of the vertical bend is 1.220m, and the radius of curvature is 1.250m. The pressure difference measuring point is selected at the 45° section of the vertical elbow, and the inner pressure taking pipe 4A and the outer pressure taking pipe 4B are respectively installed on the inside and outside of the 45° section of the vertical elbow pipe. The tube is connected to the differential pressure transmitter 5, the differential pressure transmitter 5 is electrically connected to the piezoresistor 6, the piezoresistor 6 is electrically connected to the data collector 7, the data collector 7 is electrically connected to the computer 9, and the data collected per second One time differential pressure data is stored in computer 9 data files.

2) Calculation of circulating cooling water flow:

The inner diameter of the vertical bend is 1220mm, that is, 1.212m, so r ₀ =0.606m, the radius of curvature is R=1.250m, $x=\frac{R_0}{r_0},$ So x=2.06, bring into (3) formula $C_e$$1_{}=\sqrt{2}\mathrm{\&pi;}{r}_0^2\frac{(x^2-1)(x-\sqrt{x^2-1})}{\sqrt{x}}$ A value of C _e1 =0.945801 is obtained;

Using formula (4) $Q_{\mathrm{vt}}={\mathrm{<figure-callout\; id="1"\; label="C\; e"\; filenames="A2009100675270013H1.png,A2009100675270014H1.png"\; state="\{\{state\}\}">C</figure-callout>}}_e\sqrt{\frac{\mathrm{\&Delta;p}}{\mathrm{\&rho;}}-\mathrm{gz}}$ Find the ideal fluid flow rate Q _vt ; where Δp is the pressure difference between the inside and outside of the 45° angle direction of the vertical elbow, which is the data collected by the acquisition system; ρ is the density of the fluid, kg/m ³ , that is, the water density; g is the acceleration of gravity, the value is 9.8; z is the height difference between the inner and outer sides of the section at a 45° angle of the vertical bend; z=Φ×cos45°, Φ is the diameter of the pipeline 1.212m, and z=Φ×cos45°=0.86m is obtained, and the above is brought into (4) formula, and taking the first row of Table 1 Δp=25649.37Pa, the formula is: Q _vt =3.937299m ³ /s.

3) Device calibration:

The above-mentioned device is calibrated, and the purpose of the calibration is to determine the flow coefficient α. The specific method is to measure the differential pressure with a mercury differential pressure meter, and measure the flow rate of circulating cold water with an Annubar flowmeter, so as to calibrate the above-mentioned devices. The specific calibration method is as follows: measure the pressure difference between the inside and outside of the vertical elbow with a mercury differential pressure meter. The fluid flow is measured on the circulating cooling water pipe 3 outside the factory building. Choose a location with a long enough straight pipe to install an Annubar flowmeter to measure the fluid flow through the pipe. Change the flow rate to determine the coefficient.

Adjust the regulating valve at the outlet of the circulating cooling water pump, and the flow rate is from large to small. The test data and calculation results are shown in Table 1. Flow coefficient α = measured flow / (4) calculation result Q _vt (that is, the ideal flow through the vertical elbow) = 3.835717/3.937299 = 0.9742

Table 1 Test data and calculation results

It can be seen from Table 1 that in the range of large flow changes, the flow coefficient changes very little with the flow, which proves that the circulating cooling water flow is only a function of the pressure difference between the inside and outside of the vertical elbow. Then calculate the average of the flow coefficient α. Flow coefficient α = 0.9716, remove the mercury differential pressure gauge and Annubar flowmeter after calibration.

It can be seen from the above calibration that the flow rate of the fluid is the formula (5) Q _v =αQ _vt =3.937298883×0.9716=3.835716572m ³ /s.

4) Device operation, actual measurement and data display:

The circulating cooling water flow is calculated according to the data processing software 10 and displayed on the display 11 of the computer 9 . The programming of the data processing software 10 is based on automatic control and computer processing technology which is well known in the art.

Claims (2)

1. circulating cooling water flow measuring method of condenser for steam turbine is characterized in that it may further comprise the steps:

1) measuring point is installed and data acquisition: the circulating cooling water pipe of steam turbine is connected with condenser by normal bend, inboard pressure pipe, outside pressure pipe are installed respectively in the medial and lateral in 45 ° of cross sections of normal bend, and pressure Guan Jun in medial and lateral is connected with differential pressure transmitter by rubber tube; Differential pressure transmitter is electrically connected with pressure measurement resistance, and pressure measurement resistance is electrically connected with data acquisition unit, and data acquisition unit is electrically connected with computing machine, and per second collection differential pressure data is once deposited in the computer data file;

2) circulating cooling water flow calculates:

(1) according to the free vortex flow theory, the velocity distribution that is obtained the normal bend inner fluid by Bernoulli equation is

$v=\frac{C_1}{R}---\left(1\right)$

In the formula, C ₁Be integration constant, m ²/ s; R is the distance that the center of curvature arrives certain point in the pipe, m,

For normal bend, the relational expression between desirable flow and the normal bend external and internal pressure difference is

$Q_{\mathrm{vt}}=C_{e1}\sqrt{\frac{\mathrm{\&Delta;p}}{\mathrm{\&rho;}}}---\left(2\right)$

$C_{e1}=\sqrt{2}\mathrm{\&pi;}{r}_0^2\frac{(x^2-1)(x-\sqrt{x^2-1})}{\sqrt{x}}---\left(3\right)$

$x=\frac{R_0}{r_0}$

Wherein, Q _VtBe the desirable flow by normal bend, m ³/ s; C _E1Be a coefficient relevant with the normal bend physical dimension; Δ p is that outside pressure is poor in the normal bend 45 direction cross section, Pa; ρ is the density of fluid, kg/m ³r ₀Be the inside radius of normal bend, m; R ₀Be the radius-of-curvature at normal bend center, m;

For the normal bend of condenser inlet,, get through deriving

$Q_{\mathrm{vt}}=C_{e1}\sqrt{\frac{\mathrm{\&Delta;p}}{\mathrm{\&rho;}}-\mathrm{gz}}---\left(4\right)$

Wherein Δ p is that outside pressure is poor in the normal bend 45 direction cross section, and ρ is the density of fluid, kg/m ³G is an acceleration of gravity; Z is an outside difference in height in the normal bend 45 direction cross section; Z=Φ * cos45 °, Φ is a pipeline diameter;

(2) actual flow by normal bend, because the existence of flow loss makes under same inside and outside differential pressure condition, the fluid actual flow also is not equal to the desirable flow of fluid, the relation table between it is shown

Q _v＝αQ _vt (5)

Wherein, Q _vBe actual measurement flow, m ³/ s; Q _VtBe the desirable flow by bend pipe, m ³/ s; α is called coefficient of flow, and it is demarcated by experiment and determines its value;

3) device normalization: poor with the inside and outside side pressure of mercury difference-pressure meter measuring vertical bend pipe, the measurement of fluid flow is to select a certain position with long enough straight length that the flow through fluid flow of pipeline of Annular Round Model PFB measurement is installed on cooling water pipeline, change the flow size, thereby coefficient is determined, after the demarcation mercury differential manometer and Annular Round Model PFB are taken off;

4) device put into operation, actual measurement and data presentation: calculate circulating cooling water flow according to software program, and show by graphoscope.

2. turbine condenser circulating cooling water flow on-line measurement device, it comprises that the circulating cooling water pipe of steam turbine is connected with condenser by normal bend, it is characterized in that: inboard pressure pipe, outside pressure pipe are installed respectively in the medial and lateral in 45 ° of cross sections of normal bend, pressure Guan Jun in medial and lateral is connected with differential pressure transmitter by rubber tube, differential pressure transmitter is electrically connected with pressure measurement resistance, pressure measurement resistance is electrically connected with data acquisition unit, and data acquisition unit is electrically connected with computing machine.

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