CN108872102B - Apparatus and method for measuring two-dimensional gas-phase Na concentration field and temperature field of boiler - Google Patents

Abstract

The invention discloses a device and a method for measuring a two-dimensional gas phase Na concentration field and temperature field of a boiler. The device comprises: a mirror rod; a cooling air outlet is provided at a first end of the mirror rod; and a second end of the mirror rod is provided with a cooling air outlet. There is a cooling air inlet; a high temperature resistant lens, three optical imaging lenses and a narrow-band three-channel filter are sequentially arranged along the first end to the second end of the lens rod; end-to-end; color CCD camera, the color CCD camera is arranged in the camera protective shell, and the color CCD camera has a power supply interface for supplying power to the color CCD camera and a network interface for data and control signal transmission, wherein, when When the first end of the mirror rod extends into the boiler, the radiant light of the flame in the boiler enters the sensor of the color CCD camera through the high temperature resistant lens, three optical imaging lenses and narrow-band three-channel filter in turn to generate three different Monochromatic flame image in wavelength.

Description

Apparatus and method for measuring two-dimensional gas-phase Na concentration field and temperature field of boiler

technical field

The invention relates to the technical field of boiler detection, in particular to a device for measuring a two-dimensional gas-phase Na concentration field and temperature field of a boiler and a method for measuring the two-dimensional gas-phase Na concentration field and temperature field of a boiler.

Background technique

Xinjiang Zhundong Coal is an important coal resource discovered in recent years, with an estimated reserve of 390 billion tons, making it the largest proven integrated coal field in China. Zhundong coalfield has the advantages of low mining cost, good coal reactivity, low sulfur content and easy burnout. On the other hand, the Zhundong coalfield is of marine sedimentary type, and the content of K and Na in coal primary minerals is relatively high, especially the content of Na. Studies have shown that the overall content of Na in ash is more than 2%, and Na in coal is of water-soluble type. main. Water-soluble Na is easy to enter the gas phase during the combustion process, and the gas phase Na tends to condense when passing through the heating surface of the boiler with the high-temperature flue gas flow, which in turn causes slagging, which affects the safe and economical operation of the boiler and seriously restricts the use of Zhundong coal in power station boilers. large-scale utilization.

SUMMARY OF THE INVENTION

The present invention aims to solve one of the technical problems in the above technologies at least to a certain extent. Therefore, the purpose of the present invention is to propose a device and method for measuring the two-dimensional gas-phase Na concentration field and temperature field of a boiler. Simultaneous measurement of the two-dimensional gas-phase Na concentration field and the two-dimensional temperature field provides an important guarantee for the safe and economical operation of the boiler.

In order to achieve the above purpose, the present invention proposes a device for measuring the two-dimensional gas phase Na concentration field and temperature field of a boiler, comprising: a mirror rod, the first end of the mirror rod is provided with a cooling air outlet, and the mirror rod is provided with a cooling air outlet. The second end of the lens rod is provided with a cooling air inlet; a high temperature resistant lens, three optical imaging lenses and a narrow-band three-channel filter are sequentially arranged along the first end to the second end of the mirror rod; The camera protective shell is connected to the second end of the mirror rod; a color CCD (ChargeCoupled Device, charge-coupled device) camera, the color CCD camera is arranged in the camera protective shell, and the color CCD camera has a A power interface for supplying power to the color CCD camera and a network interface for transmitting data and control signals, wherein when the first end of the mirror rod extends into the boiler, the radiation of the flame in the boiler Light enters the sensor of the color CCD camera through the high temperature resistant lens, the three optical imaging lenses and the narrow-band three-channel filter in sequence to generate monochromatic flame images with three different wavelengths.

In addition, the device for measuring the two-dimensional gas-phase Na concentration field and temperature field of the boiler proposed according to the above embodiments of the present invention may also have the following additional technical features:

According to an embodiment of the present invention, the narrow-band three-channel filter has three independent optical channels, the center wavelengths of the three optical channels are respectively 460 nm, 520 nm and 589 nm, and the half bandwidths of the three optical channels are all 10 nm , the peak transmittances of the three optical channels are all greater than 90%, the wavelength cut-off ranges of the three optical channels are all 400-780 nm, and the wavelength cut-off depths of the three optical channels are all less than 0.5%.

According to an embodiment of the present invention, the color CCD camera is a 3CCD camera with three CCD chips.

Further, the color CCD camera has the following spectral response characteristics: the relative spectral efficiencies of the three channels of R, G, and B respectively exceed 50% of the maximum relative spectral response efficiency at 589 nm, 520 nm and 460 nm; the camera G band The spectral response of the camera does not exceed 15% of the highest response value at 589 nm; the relative spectral response of the camera G band is less than 1% at 460 nm, and the relative spectral response of the B band is less than 1% at 520 nm.

Further, the color CCD camera outputs a RAW format image, and the color CCD camera ensures a high signal-to-noise ratio of the captured flame image by adjusting the camera shutter, and the color CCD camera transmits image data and performs image data transmission based on Gigabit network communication. Adjustment of camera operating parameters.

The present invention provides a method for measuring the two-dimensional gas-phase Na concentration field and temperature field of a boiler based on the above-mentioned device. The functional relationship of The functional relationship is calculated to obtain the two-dimensional gas-phase Na concentration field and temperature field in the boiler.

Wherein, the functional relationship between the two-dimensional gas phase Na concentration, the temperature field and the gas phase Na radiation intensity is established based on the calibration experiment of the device, specifically including:

a. Prepare a variety of NaCl solutions with different concentrations;

b. Insert an ultrasonic atomizer in a container containing a NaCl solution, and open the ultrasonic atomizer to generate a water mist containing a known concentration of NaCl;

c. the continuous working preset time of the ultrasonic atomizer, calculate the gas phase Na concentration entering the blackbody furnace according to the average atomization rate of the ultrasonic atomizer;

d. setting multiple temperature points of the blackbody furnace;

e. at each temperature point, the water mist generated by the various NaCl solutions of different concentrations is respectively introduced into the blackbody furnace, and the target surface image of the blackbody furnace at the corresponding temperature is collected by the device;

f. Respectively extract R channel image intensity data, G channel image intensity data and B channel image intensity data output by the device;

g. Using Planck's law, respectively convert the R channel image intensity data, G channel image intensity data and B channel image intensity data into absolute radiation intensity values:

Wherein, c ₁ and c ₂ are the first and second radiation constants, respectively;

h. Use polynomial fitting to establish the relationship between the absolute radiation intensity value and the image intensity value:

和黑体炉中气相Na浓度值I_j代入下式：i. The calculated gas phase Na radiation intensity value

And the gas phase Na concentration value I _j in the black body furnace is substituted into the following formula:

Among them, L is the geometric length of the heating cavity of the blackbody furnace, and f ₁ (T) and f ₂ (T) are both fourth-order polynomial functions of the temperature T:

f ₁ (T)=a ₀ +a ₁ ·T+a ₂ ·T ² +a ₃ ·T ³ +a ₄ ·T ⁴

f ₂ (T)=b ₀ +b ₁ ·T+b ₂ ·T ² +b ₃ ·T ³ +b ₄ ·T ⁴ ,

进行求解得到，二维气相Na浓度、温度场和气相Na辐射强度之间的函数关系为：Among them, the unknown parameters in the formula are calculated by particle swarm optimization

After solving, the functional relationship between the two-dimensional gas-phase Na concentration, the temperature field and the gas-phase Na radiation intensity is:

where T is solved using the two-color method:

The device of the invention is simple in structure, low in cost, and easy to operate. The device and method of the invention can realize the simultaneous measurement of the two-dimensional gas-phase Na concentration field and the two-dimensional temperature field in the boiler, and provide important guarantee for the safe and economical operation of the boiler. .

Description of drawings

1 is a schematic structural diagram of a device for measuring two-dimensional gas-phase Na concentration field and temperature field of a boiler according to an embodiment of the present invention;

2 is a relative spectral response curve of a color CCD camera and a three-channel color filter according to an embodiment of the present invention;

3 is a flowchart of a method for measuring a two-dimensional gas-phase Na concentration field and a temperature field of a boiler according to an embodiment of the present invention;

4 is a schematic structural diagram of a calibration system according to an embodiment of the present invention;

FIG. 5 is a schematic structural diagram of a measurement system according to an embodiment of the present invention.

Reference number:

0-mirror rod; 1-high temperature resistant lens; 2-cooling air outlet; 3-optical imaging lens; 4-cooling air inlet; 5-narrow-band three-channel filter; 6-color CCD camera; 7-camera protective case ; 8- power interface; 9- network interface; 10- power supply; 11- measuring device; 12- black body furnace; 13- gas mass flow meter; 14- glass tube container; 15- ultrasonic atomizer; 16- industrial computer; 17-Data transmission line; 18-Gigabit network switch; 19-Cooling air pipeline; 20-Boiler furnace.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

The apparatus and method for measuring the two-dimensional gas-phase Na concentration field and temperature field of a boiler according to embodiments of the present invention are described below with reference to the accompanying drawings.

The boiler of the embodiment of the present invention is a coal-fired boiler, which is preferably suitable for a boiler that burns high-alkali coal such as Zhundong coal.

As shown in FIG. 1, the device for measuring the two-dimensional gas phase Na concentration field and temperature field of a boiler according to an embodiment of the present invention includes: a mirror rod 0; Lens 1, three optical imaging lenses 3 and narrow-band three-channel filter 5; camera protective shell 7; color CCD camera 6. The first end of the mirror rod 0 is provided with a cooling air outlet 2, and the second end of the mirror rod 0 is provided with a cooling air inlet 4; the camera protective shell 7 is connected to the second end of the mirror rod 0; the color CCD camera 6 is provided with Inside the camera protective case 7 , the color CCD camera 6 has a power supply interface 8 for supplying power to the color CCD camera 6 and a network interface 9 for data and control signal transmission.

When the first end of the mirror rod 0 extends into the boiler, the radiated light of the flame in the boiler enters the color CCD camera 6 through the high temperature resistant lens 1, the three optical imaging lenses 3 and the narrow-band three-channel filter 5 in turn. sensor to generate monochrome flame images at three different wavelengths.

In one embodiment of the present invention, the high temperature resistant lens 1 may be made of high temperature resistant glass. The narrow-band three-channel filter can have three independent optical channels, the central wavelengths of the three optical channels are 460nm, 520nm and 589nm, the half bandwidth of the three optical channels is 10nm, and the peak transmittance of the three optical channels All are greater than 90%, the wavelength cut-off ranges of the three optical channels are all 400-780 nm, and the wavelength cut-off depths of the three optical channels are all less than 0.5%.

In an embodiment of the present invention, the color CCD camera 6 is a 3CCD camera with three CCD chips. The color CCD camera 6 can generate monochromatic flame images at three different wavelengths of 460nm, 520nm and 589nm.

Further, referring to FIG. 2 , the color CCD camera 6 has the following spectral response characteristics: the relative spectral efficiencies of the three channels of R, G, and B are respectively higher at 589 nm, 520 nm and 460 nm, all exceeding 50% of the maximum relative spectral response efficiency. %; The spectral response of the camera G band is relatively weak at 589 nm, not exceeding 15% of the highest response value, to avoid the superimposed interference of the gas-phase Na radiation at 589 nm on the received signal of the camera G band, thereby improving the temperature measurement accuracy. The relative spectral response of the camera G band at 460nm is less than 1%, for example, it can be 0, and the relative spectral response of the B band at 520nm is less than 1%, for example, it can be 0, so as to improve the monochromaticity of the G and B signals measured by the camera improve the accuracy of temperature measurement.

Among them, the color CCD camera 6 can output a RAW format image to output an 8-bit image intensity value irrelevant to the shutter time of the camera. The non-saturated and high signal-to-noise ratio of the captured flame images can be guaranteed by adjusting the camera shutter. The color CCD camera 6 can transmit image data and adjust camera operating parameters based on Gigabit network communication.

In a specific embodiment of the present invention, the model of the color CCD camera 6 may be JAR-AT-200GE, but the embodiment of the present invention is not limited to this type of camera.

The device of the above embodiment of the present invention can be used to measure the two-dimensional gas-phase Na concentration field and temperature field of the boiler, and the measurement method will be described in detail in the following embodiments.

As shown in Figure 3, the measurement method includes the following steps:

S1, the functional relationship between the two-dimensional gas-phase Na concentration, the temperature field and the gas-phase Na radiation intensity is established based on the calibration experiment of the device.

In one embodiment of the present invention, the calibration system shown in FIG. 4 can be constructed, and the calibration system includes the above-mentioned device 11 for measuring the two-dimensional gas-phase Na concentration field and temperature field of a boiler, a black body furnace 12, and a gas mass flow meter 13 , a glass tube container 14, an ultrasonic atomizer 15, an industrial computer 16, a data transmission line 17, and a power supply 10 for powering the above-mentioned device 11, ultrasonic atomizer 15, etc.

Establishing the functional relationship through calibration experiments specifically includes the following steps a to i:

a. Prepare a variety of NaCl solutions with different concentrations respectively.

For example, eight different concentrations of NaCl solutions numbered 1 to 8 shown in Table 1 can be prepared.

Table 1

b. Put an ultrasonic atomizer in the container containing the NaCl solution, and turn on the ultrasonic atomizer to generate a water mist containing a known concentration of NaCl.

的水雾。氮气N₂在通过气体质量流量计13后进入玻璃管容器14，氮气的流量设定为100ml/min，氮气携带含有已知NaCl浓度的水雾进入高温黑体炉12中。The ultrasonic atomizer 15 can be turned on through the power switch to generate a concentration of

water mist. Nitrogen N ₂ enters the glass tube container 14 after passing through the gas mass flow meter 13 , the flow rate of nitrogen is set to 100ml/min, and the nitrogen carries water mist containing known NaCl concentration into the high temperature black body furnace 12 .

c. The ultrasonic atomizer works continuously for a preset time, and the gas phase Na concentration entering the blackbody furnace is calculated according to the average atomization rate of the ultrasonic atomizer.

For example, when the ultrasonic atomizer 15 works continuously for 30 minutes, the average atomization rate of the ultrasonic atomizer 15 is measured as V _s (g/min), then the gas phase Na concentration I _j (j=1,2 ,3...7,8) is:

d. Set multiple temperature points of the blackbody furnace.

The high temperature blackbody furnace 12 can be provided with an observation window. During the experiment, the temperature T of the high temperature blackbody furnace 12 is set as follows: the initial temperature is 900°C, the end temperature is 1700°C, and the temperature interval is 20°C, with a total of 41 temperature points set.

e. At each temperature point, the water mist generated by a variety of NaCl solutions with different concentrations was introduced into the blackbody furnace respectively, and the device was used to collect the image of the target surface of the blackbody furnace at the corresponding temperature.

At 41 temperature points, the eight concentrations of NaCl water mist shown in Table 1 were respectively introduced to collect images of the target surface of the blackbody furnace, and a total of 8 × 41 sets of image data were obtained.

f. Respectively extract the R channel image intensity data, G channel image intensity data and B channel image intensity data output by the device.

The R channel image intensity data _SR of 589 nm, the G channel image intensity data SG of 520 nm, and the _{B channel image intensity data S B of} 460 nm output by the above-mentioned device 11 can be extracted by using the Matlab program of the industrial computer 16 .

g. Using Planck's law, respectively convert the R channel image intensity data S _R , the G channel image intensity data S _G and the B channel image intensity data S _B into absolute radiation intensity values:

Wherein, c ₁ and c ₂ are the first and second radiation constants, respectively.

h. Use polynomial fitting to establish the relationship between the absolute radiation intensity value and the image intensity value:

和黑体炉中气相Na浓度值I_j代入下式：i. The calculated gas phase Na radiation intensity value

And the gas phase Na concentration value I _j in the black body furnace is substituted into the following formula:

Among them, L is the geometric length of the heating cavity of the blackbody furnace, and f ₁ (T) and f ₂ (T) are both fourth-order polynomial functions of the temperature T:

f ₁ (T)=a ₀ +a ₁ ·T+a ₂ ·T ² +a ₃ ·T ³ +a ₄ ·T ⁴

f ₂ (T)=b ₀ +b ₁ ·T+b ₂ ·T ² +b ₃ ·T ³ +b ₄ ·T ⁴ (5)

共有328个值，式(5)中未知参数a₀～b₄可利用粒子群算法对

即公式(4)进行求解得到。Among them, the measured

There are 328 values in total, and the unknown parameters a ₀ ~ b ₄ in formula (5) can be determined by particle swarm algorithm

That is, formula (4) is solved to obtain.

After the calibration is completed, the functional relationship between the two-dimensional gas-phase Na concentration, the temperature field and the gas-phase Na radiation intensity can be obtained as:

where T is solved using the two-color method:

S2, the calibrated device is installed on the boiler to collect the radiation image of the flame in the boiler.

As shown in FIG. 5 , the measurement system for the two-dimensional gas-phase Na concentration field and temperature field of the entire boiler includes a plurality of the above-mentioned devices 11 , an industrial computer 16 , a data transmission line 17 , a Gigabit Ethernet switch 18 , and a cooling system corresponding to the above-mentioned cooling air inlet 4 . Air duct 19 and boiler furnace 20.

Refer to Figure 5 for the installation method of the device for measuring the two-dimensional gas-phase Na concentration field and temperature field of the boiler. Multiple devices 11 can be installed at different heights of the boiler furnace 20, and the pulverized coal in the boiler can be collected online through the observation hole on the water wall. Radiant image of a burning flame.

S3, transmit the radiation image to the industrial computer through the network interface.

As shown in FIG. 5 , the radiation images collected by the multiple devices 11 can be transmitted to the industrial computer 16 through the Gigabit Ethernet switch 18 .

S4, the industrial computer obtains the two-dimensional gas-phase Na concentration field and temperature field in the boiler according to the functional relationship.

The industrial computer 16 may be used to calculate and store data. The industrial computer 16 can firstly calculate the two-dimensional temperature field in the furnace based on the above formula (7) and use the radiation images of 520 nm and 460 nm; secondly, the calculated two-dimensional temperature field can be substituted into the above formula (6), and combined with the measurement The obtained 589nm radiation image, the two-dimensional gas-phase Na concentration distribution in the furnace was calculated.

In addition, the interface of the industrial computer 16 can display the flame image, the two-dimensional flame temperature field and the gas phase Na concentration field in real time, and the measurement results can be saved in the computer hard disk in real time.

According to the device and method for measuring the two-dimensional gas-phase Na concentration field and temperature field of a boiler according to the embodiment of the present invention, the device has a simple structure, low cost, and is easy to operate, and the two-dimensional gas-phase Na concentration field in the boiler can be realized by the device and method. Simultaneous measurement of the two-dimensional temperature field provides an important guarantee for the safe and economical operation of the boiler.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", " Back, Left, Right, Vertical, Horizontal, Top, Bottom, Inner, Outer, Clockwise, Counterclockwise, Axial , "radial", "circumferential" and other indicated orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying the indicated device or Elements must have a particular orientation, be constructed and operate in a particular orientation and are therefore not to be construed as limitations of the invention.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature. In the description of the present invention, "plurality" means two or more, unless otherwise expressly and specifically defined.

In the present invention, unless otherwise expressly specified and limited, the terms "installed", "connected", "connected", "fixed" and other terms should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection , or integrated; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of the two elements or the interaction relationship between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

In the present invention, unless otherwise expressly specified and limited, a first feature "on" or "under" a second feature may be in direct contact between the first and second features, or the first and second features indirectly through an intermediary touch. Also, the first feature being "above", "over" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is level higher than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature has a lower level than the second feature.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples", etc., mean specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Embodiments are subject to variations, modifications, substitutions and variations.

Claims (1)

1. A method for measuring a two-dimensional gas phase Na concentration field and a temperature field of a boiler based on an apparatus for measuring a two-dimensional gas phase Na concentration field and a temperature field of a boiler, the apparatus comprising: the first end of the mirror rod is provided with a cooling air outlet, and the second end of the mirror rod is provided with a cooling air inlet; the high-temperature-resistant lens, the three optical imaging lenses and the narrow-band three-channel optical filter are sequentially arranged from the first end to the second end of the mirror rod; the camera protective shell is connected with the second end of the mirror rod; the color CCD camera is arranged in the camera protective shell and provided with a power interface for supplying power to the color CCD camera and a network interface for transmitting data and control signals, when the first end of the lens rod extends into the boiler, radiation light of flames in the boiler sequentially passes through the high-temperature-resistant lens, the three optical imaging lenses and the narrow-band three-channel optical filter and enters a sensor of the color CCD camera to generate monochromatic flame images with three different wavelengths, and the method comprises the following steps:

establishing a functional relation among the two-dimensional gas phase Na concentration, the temperature field and the gas phase Na radiation intensity based on a calibration experiment of the device;

mounting the calibrated device on the boiler to acquire a radiation image of flame in the boiler;

transmitting the radiation image to an industrial personal computer through the network interface;

the industrial personal computer calculates and obtains a two-dimensional gas phase Na concentration field and a temperature field in the boiler according to the functional relation,

wherein, based on the calibration experiment of the device establishes the functional relationship among the two-dimensional gas phase Na concentration, the temperature field and the gas phase Na radiation intensity, and specifically comprises the following steps:

a. respectively preparing a plurality of NaCl solutions with different concentrations;

b. putting an ultrasonic atomizer in a container containing a NaCl solution, and starting the ultrasonic atomizer to generate water mist with known NaCl concentration;

c. the ultrasonic atomizer works continuously for a preset time, and the concentration of gas phase Na entering the black body furnace is calculated according to the average atomization rate of the ultrasonic atomizer;

d. setting a plurality of temperature points of the black body furnace;

e. respectively introducing water mist generated by the NaCl solutions with different concentrations into the black body furnace at each temperature point, and acquiring target surface images of the black body furnace at corresponding temperatures by using the device;

f. respectively extracting R channel image intensity data, G channel image intensity data and B channel image intensity data output by the device;

g. respectively converting the R channel image intensity data, the G channel image intensity data and the B channel image intensity data into absolute radiation intensity values by using Planck's law:

wherein, c₁And c₂Respectively a first radiation constant and a second radiation constant;

h. establishing a relation between the absolute radiation intensity value and the image intensity value by using polynomial fitting:

i. the calculated gas-phase Na radiation intensity value

And gas phase Na concentration value I in black body furnace_jSubstituting the following formula:

wherein L is the geometric length of the heating cavity of the blackbody furnace, f₁(T) and f₂(T) are all fourth order polynomial functions of temperature T:

f₁(T)＝a₀+a₁·T+a₂·T²+a₃·T³+a₄·T⁴

f₂(T)＝b₀+b₁·T+b₂·T²+b₃·T³+b₄·T⁴，

wherein, the unknown parameters in the formula are paired by utilizing a particle swarm algorithm

Is solved to obtainTo that end, the functional relationship between the two-dimensional gas phase Na concentration, the temperature field, and the gas phase Na radiation intensity is:

wherein, T is solved by a bicolor method:

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