JP2002221303A - Method of measuring furnace interior side temperature of membrane panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiler structure which is high in reliability or requires little maintenance by accurately and inexpensively grasping the temperature distribution in the whole furnace wall of a boiler by measuring the surface temperature of a membrane panel on the furnace interior side with accuracy by using the surface temperature of the panel on the outside of the furnace. SOLUTION: The temperature distribution in the membrane panel is calculated through numerical analysis, such as the finite element method, etc., by variously changing the shape of the panel, such as the dimensions, etc., of heat exchanger tubes 1 and thermal boundary conditions, such as heat transfer, radiation, etc., on the furnace interior side and stored as a data base. Then a multiple recurrence formula is found by using the temperatures at a plurality of temperature measuring points (where thermometers 5 are installed) on the furnace exterior side as independent variables and a surface temperature to be found on the furnace interior side as a dependent variable by using the data base. Finally, an arbitrary surface temperature to be found on the furnace interior side is estimated by substituting an actually measured surface temperature on the furnace exterior side into the multiple recurrence formula.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the temperature of a membrane panel of a boiler furnace wall comprising a plurality of tubes and a membrane bar, and more particularly to a method for easily measuring the inside surface temperature of a heat transfer tube or a membrane bar from outside the furnace. It relates to a method of measuring.

[0002]

2. Description of the Related Art FIG. 2 shows a schematic external structure of a combustion chamber of a boiler furnace and the entire furnace. In this type of boiler, a high airtightness is provided by a front wall 7, a side wall 8, a cage side wall 9, a cage bottom wall 10, and a ceiling wall 11 formed of a membrane panel in which a membrane bar is welded between pipes. A box-shaped combustion chamber and a furnace are configured.

FIG. 3 shows a detailed view of the connecting portion 12 of the side wall tube 17, the cage wall tube 18 and the cage bottom tube 19. The plurality of side wall pipes 17, the cage wall pipes 18 and the cage bottom pipes 19 are each provided with a plate called a membrane bar 2 on both sides of the pipes in order to enhance the heat transfer effect, and are connected by continuous welding in the axial direction of the pipes to secure the airtight. To form an integral combustion chamber having a characteristic. The lower end of the cage wall tube 18 is connected to a cage side wall header 20.

[0004] The connecting portion 12 is composed of three types of tube groups (sidewall tube 17,
Since the cage wall tube 18 and the cage bottom tube 19) are three-dimensionally united and have a complicated structure, the structure is formed with a shape discontinuity which requires the most attention in terms of strength. I have.

[0005]

In the boiler furnace having the above-described structure, the temperature difference between the front wall 7, the side wall 8, the cage side wall 9, the cage bottom wall 10, and the ceiling wall 11, respectively, is used. As shown in FIG. 4, the heat transfer tube 1 is formed at the joint 12 between the side wall 8 and the cage side wall 9.
The problem is that a crack 13 is generated from the weld 3 of the membrane bar 2 as a starting point. Crack 13 found
Is repaired and reinforced as needed each time. However, each time the periodic inspection is performed after the repair and reinforcement, a new crack is found in the joint 12 between the same side wall 8 and the cage side wall 9. It takes a great deal of time and money to remove and repair.

[0006] The above-mentioned temperature difference between the wall surfaces is generated because the fluid temperature in the membrane panel is not constant but rises along the fluid path. In particular, when the boiler is started, the internal fluid having a low temperature is supplied into the boiler by the water filling operation, and flows slowly along the fluid path. This generates thermal stress. In addition, the joining structure may be discontinuous in the connecting portion 12, and an excessive thermal stress may be generated, thereby restricting the operation of the boiler in some cases.

On the other hand, the furnace wall may be locally overheated due to contamination of the heat transfer tube 1 inside the furnace, lack of fluid inside the heat transfer tube 1, abnormal combustion of the boiler, and the like. The strength of the overheated region is extremely reduced, and the thickness of the heat transfer tube 1 may be reduced in a short time due to abrasion, or the heat transfer tube 1 may be ruptured due to internal pressure. If a steam leak occurs due to these factors, the boiler must be stopped, which is a problem in operation particularly in a plant where the number of times of starting and stopping is repeated.

In order to prevent these problems and to monitor the temperature of the furnace wall of the boiler, a thermometer called the “CRIEPI system” is usually installed on the membrane panel.
A circumferential groove 14 is machined on the surface of the heat transfer tube 1 as shown in the cross-sectional view of the membrane panel in FIG.
Wire 16 from the thermometer 5 provided on the heat transfer tube 1
Through which the temperature of the heat transfer tube 1 is measured. However, it is only possible to measure the metal temperature inside the heat transfer tube 1 and it is difficult to measure the surface temperature inside the furnace of the heat transfer tube 1 which is the highest. Further, as shown in a detailed sectional view of the heat transfer tube surface side shown in FIG.
After machining the lead wire 4 and passing the lead wire 16, the groove 1
Since 4 is filled with the protection plate 28 by welding, the installation cost of the thermometer 5 also increases.

[0009] An object of the present invention is to accurately and inexpensively grasp the temperature distribution of the entire boiler furnace wall by accurately measuring the surface temperature of the membrane panel inside the furnace using the surface temperature of the membrane panel outside the furnace. It is an object of the present invention to provide a boiler structure having high performance or requiring less maintenance.

[0010]

SUMMARY OF THE INVENTION The above object of the present invention is shown in FIG.
As shown in (1), it is achieved by measuring several points of the outer membrane panel surface temperature and regressively calculating the membrane panel surface temperature prediction point 6 inside the furnace using these values.

Specifically, first, as shown in FIG. 11, the membrane panel shape such as the size of the heat transfer tube and the temperature boundary conditions such as heat transfer and radiation inside the furnace are variously changed, and numerical analysis such as the finite element method is performed. Calculate the temperature distribution of the membrane panel and create a database.

Next, using this database, a multiple regression equation is determined using the temperatures at a plurality of temperature measurement points outside the furnace as independent variables and the surface temperature inside the furnace to be determined as a dependent variable.

Finally, the surface temperature inside the furnace to be determined is estimated by substituting the actually measured temperature outside the furnace into the multiple regression equation obtained as described above.

Further, since the temperature distribution of the membrane panel is made into a database as described above, not only the surface temperature inside the furnace but also the temperature at an arbitrary position of the membrane panel can be estimated from the temperature at the temperature measurement point outside the furnace. Become.
The computing unit 4 in FIG. 1 corresponds to the measuring device in FIG.

[0015]

As shown in FIG. 1, a heat transfer tube 1 and a membrane bar 2 which normally constitute a membrane panel receive a thermal load from a furnace inside by a burner and are cooled by an internal fluid flowing inside the heat transfer tube 1. In this case, the temperature distribution of the membrane panel is as shown in FIG.

In this temperature distribution, the temperature gradient from the temperature measurement point 21 of the heat transfer tube 1 to the temperature measurement point 22 of the welded portion is greatly related to the temperature of the internal fluid in the heat transfer tube 1 and the heat transfer coefficient. The lower the temperature or the higher the heat transfer coefficient, the tighter the temperature gradient. On the other hand, the temperature gradient from the temperature measurement point 22 of the welded portion to the temperature measurement point 23 of the membrane panel is greatly related to the heat load inside the furnace, and the higher the heat load, the tighter the temperature gradient. Therefore, if the temperature gradient between these temperature measurement points 21 to 23 is known, the temperature distribution of the entire membrane panel as shown in FIG. 6 can be predicted to some extent from the temperature gradient. The temperature at the inner temperature prediction point 6 can be estimated.

A specific method for estimating the temperature when the number of temperature measurement points is three will be described below. First, the temperature at the temperature measurement points 21 to 23 and the temperature at the temperature prediction point 6 are measured by variously changing the heat load of the membrane panel, the internal fluid temperature of the heat transfer tube 1, and the heat transfer coefficient.

Next, multiple regression is performed using the temperature of the temperature prediction point 6 as a dependent variable and the temperatures of the temperature measurement points 21 to 23 as independent variables to determine a multiple regression coefficient for each of the temperature measurement points 21 to 23. .

The multiple regression equation obtained in this manner is used to calculate the temperature measurement points 21 to 23 actually measured on the actual membrane panel.
By substituting the above temperature, the surface temperature of the heat transfer tube inside the furnace (the temperature at the temperature prediction point 6) can be estimated.

Next, the relationship between the temperature estimation error between the outside temperature measurement point and the inside temperature prediction point will be described.
It is considered that the temperature estimation error decreases as the number of temperature measurement points increases, but increasing it more than necessary is not preferable in terms of cost. FIG. 8 shows the relationship between the number of temperature measurement points and the temperature estimation error.

Here, the number of temperature measurement points = 1 is the temperature measurement point 21 of the heat transfer tube 1 shown in FIG.
Temperature measurement point 21 of membrane panel and temperature measurement point 2 of membrane panel
3, the number of temperature measurement points = 3 indicates the temperature measurement point 21 of the heat transfer tube 1, the temperature measurement point 22 of the welded portion, and the temperature measurement point 23 of the membrane panel. Further, the number of temperature measurement points = 4 is obtained by adding the temperature measurement points 24, and the number of temperature measurement points = 5 is obtained by adding the temperature measurement points 25 thereto.

As can be seen from FIG. 8, as the number of temperature measurement points increases, the temperature estimation error decreases, but the number of temperature measurement points decreases by three.
Above the point, the temperature estimation error converges to about 3 ° C. or less. Therefore, it is considered that three temperature measurement points are sufficient.

Further, when the temperature measurement points are set to the temperature measurement point 21 of the heat transfer tube 1, the temperature measurement point 22 of the welded portion, and the temperature measurement point 23 of the membrane panel shown in FIG. When local overheating occurs, only the temperature gradient from the temperature measurement point 22 of the welded portion to the temperature measurement point 23 of the membrane panel becomes denser than in the normal operation, so that local overheating of the furnace wall can be detected. On the other hand, even when the heat transfer coefficient in the heat transfer tube 1 becomes extremely low due to film boiling or the like, only the temperature gradient from the temperature measurement point 21 of the heat transfer tube 1 to the temperature measurement point 22 of the welded portion becomes sparse. Can also be detected.

[0024]

Embodiments of the present invention will be described with reference to the drawings. FIG. 7 is a sectional view of a membrane panel including a heat transfer tube 1 and a membrane bar 2 of a boiler furnace wall according to the first embodiment of the present invention. The heat transfer tube 1 and the membrane bar 2 are connected by a welded portion 3, and 3
Two temperature measurement points 21 to 23 are attached, and the temperature of the temperature prediction point 6 on the surface of the heat transfer tube 1 inside the furnace is predicted.

The material of the heat transfer tube 1 is 1Cr-0.5Mo steel,
The dimensions were φ38.1 mm × t6.7 mm. On the other hand, the material of the membrane 2 is 1Cr-0.5Mo steel, and the dimensions are 12.7 mm in width × 9 mm in thickness. The membrane bar 2 is joined to the heat transfer tube 1 by welding.
The welding leg length is about 3 for both the heat transfer tube 1 side and the membrane bar 2 side.
mm.

The heat load inside the furnace is 2.78 to 13.89 ×
10 ⁻⁵ kcal / mm ² sec, the internal fluid temperature of the heat transfer tube 1 is 300 to 500 ° C., and the heat transfer coefficient is 2.78 to 8.
In the case where the temperature is variously changed to 33 × 10 ⁻⁶ kcal / mm ² sec ° C., the measured temperature of the temperature measurement points 21 to 23 outside the furnace and the temperature measured from the measured temperature of the temperature prediction point 6 inside the furnace and multiple regression. FIG. 9 shows the estimation result.

The number of temperature measurement points is the above-mentioned temperature measurement points 21 to 23.
The multiple regression coefficients were determined from multiple regression using the three measured temperature points outside the furnace as independent variables and the actual measurement results of the heat transfer tube temperature inside the furnace as dependent variables. In this embodiment, the determination coefficient R ² is 0.998, and the maximum estimated temperature error is 3
° C, and a temperature prediction point 6 on the surface of the heat transfer tube 1 inside the furnace.
It can be seen that the temperature of the heat transfer tube surface inside the furnace, that is, the surface temperature of the heat transfer tube was accurately estimated.

FIG. 10 shows a second embodiment of the present invention. In the first embodiment described above, assuming that there is no temperature distribution in the tube axis direction of the membrane panel, the heat transfer tubes 1 and the membrane bar on the same plane in the direction perpendicular to the tube axis are used as temperature measurement points outside the furnace. 2, 3 points of the welded portion. However, when local overheating occurs in the membrane panel, a temperature deviation also occurs in the tube axis direction. In this embodiment, since the temperature gradient in the tube axis direction is also considered,
In addition to the three temperature measurement points 21 to 23 of the embodiment,
Two more temperature measurement points 26 and 27 are added above and below the heat transfer tube axis direction of the welded portion 3 to make a total of five temperature measurement points 21 to 2
3, 26, 27. Accordingly, the temperature deviation in the axial direction of the heat transfer tube of the membrane panel is also reflected in the above-described multiple regression equation, so that the furnace inside temperature can be more accurately estimated. Accordingly, even for local overheating of the membrane panel due to unbalanced heat load inside the furnace, the temperature and the overheating range can be estimated.

[0029]

According to the present invention, it is possible to accurately and inexpensively grasp the temperature distribution of the entire boiler furnace wall by accurately measuring the surface temperature of the membrane panel inside the furnace, and to obtain high reliability or maintenance. And a boiler structure with a small number is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a membrane panel for explaining a method of measuring a surface temperature of a heat transfer tube inside a furnace according to the present invention.

FIG. 2 is a schematic view of a combustion chamber and a furnace of a boiler for a power plant.

FIG. 3 is a detailed view of a tube wall connection part of the membrane panel of FIG. 2;

FIG. 4 is a diagram showing an example of occurrence of cracks in the membrane panel of FIG.

FIG. 5 is a cross-sectional view of a membrane panel for explaining a method of measuring a surface temperature of a heat transfer tube inside a furnace according to a conventional method (FIG. 5A).
FIG. 6 is a detailed cross-sectional view taken along the line AA of FIG. 5A (FIG. 5B).

FIG. 6 is a diagram illustrating an example of a temperature distribution of a membrane panel.

FIG. 7 is a cross-sectional view of the membrane panel according to the embodiment of the present invention.

8 is a diagram illustrating a relationship between the number of temperature measurement points and a temperature estimation error in the embodiment of FIG. 7;

9 is a comparison diagram of the estimation result and the measurement result of the surface temperature of the heat transfer tube inside the furnace in the embodiment of FIG. 7;

FIG. 10 is a perspective view of a membrane panel according to another embodiment of the present invention.

FIG. 11 is a diagram illustrating a procedure of a method for estimating a surface temperature of a heat transfer tube inside a furnace according to the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Heat transfer tube 2 Membrane 3 Welded part 4 Computing unit 5 Thermometer 6 Temperature prediction point 7 Front wall 8 Side wall 9 Cage side wall 10 Cage bottom wall 11 Ceiling wall 12 Connection part 13 Crack 14 Groove 15 Membrane bar 16 Lead wire 17 Side wall pipe Reference Signs List 18 Cage side wall tube 19 Cage bottom tube 20 Cage side wall header 21 Temperature measurement point of heat transfer tube 22 Temperature measurement point of welded part 23 Temperature measurement point of membrane panel 24 to 27 Temperature measurement point 28 Protective plate

Claims (2)

[Claims] In a tube panel having a plurality of heat transfer tubes, two or more membrane panel surface temperatures outside the furnace are measured, and an arbitrary membrane panel surface temperature inside the furnace is estimated from these values. A method for measuring a temperature inside a furnace of a membrane panel. 2. The method according to claim 1, wherein two or more points on the outside of the furnace are three points on the surface of the heat transfer tube, the membrane bar, and a boundary between them.