Background
The temperature of the metal wall surface of the heating surface of the boiler is required to be lower than the highest required temperature of the metal material, otherwise the strength of the material is reduced, and plastic deformation and even tube explosion occur. Therefore, the heating surface wall temperature is a parameter which needs to be strictly detected and controlled in the operation of the boiler. With the improvement of boiler parameters, the service temperature of metal materials is higher and higher, the service limit of the materials is closer and closer, and the accuracy of wall temperature measurement is higher and higher.
In a pulverized coal combustion boiler, when measuring the wall temperature, a support is generally welded on the surface of a heated surface heated in the boiler, threads are arranged on the support, a thermocouple to be measured is positioned by using bolts, and the thermocouple is fixed on a measuring position. This conventional measurement method is widely used. The method has the biggest problems that the bracket and the bolt bear high temperature and high temperature relaxation, and the measurement result is unreliable. The traditional method for measuring the wall temperature is not applicable to the heating surface in the hearth of the circulating fluidized bed boiler or the external heat exchanger, because the heat transfer of the heating surface in the hearth of the circulating fluidized bed boiler or the external heat exchanger is the heat transfer from gas-solid two-phase flow to the heating surface, the wall surface is severely washed by high-concentration solid particles, and any protrusion on the surface of a pipe of the heating surface can cause fatal abrasion, so the abrasion of a thermocouple support for traditional wall temperature measurement and the abrasion of the heating surface caused by the abrasion are inevitable, the reliability of wall temperature measurement and the safety of the heating surface are influenced, and the traditional method cannot be adopted.
A number of innovations have been made with respect to the wall temperature measurement problem. CN201720281590.9 proposes that a stainless steel round table is welded on the outer wall of the high-voltage equipment barrel, an internal thread joint is welded on the stainless steel round table, and a thermocouple is screwed into the thread joint after being assembled with the bolt sleeve, so that the thermocouple is tightly contacted with the stainless steel round table. This method is essentially an improvement over conventional measurement methods. CN201611125215.1 discloses a wall temperature measuring method, which includes a thermode temperature measuring ring, a thermocouple, a compensation wire, a tail accessory and a plug, and further improves the conventional wall temperature measuring method. CN201410369981.7 and CN201420430683.X disclose a real wall temperature test system of high temperature heating surface pipe, it includes thermocouple, heat collecting block, protective sleeve, staple bolt and heat insulation material, the said thermocouple is at least one, it is inserted and set up in the protective sleeve, and its one end is welded on the pipe wall, another end is fixed outside the boiler and connected with junction box outside the boiler after drawing out, the said heat collecting block peripheral weld on the pipe wall where the said thermocouple weld part locates, is used for fixing the said thermocouple and transmitting heat fast; the heat insulation material is wrapped on the periphery of the heat collection block and fixed through the hoop. However, in these improvements, the problems associated with the wall temperature measuring device itself and the wear caused thereby still remain. CN201310652008.1 discloses an on-line monitoring method for metal wall temperature of heating surface of boiler superheater/reheater, which utilizes neural network to predict and monitor flue gas temperature and speed of each section in front of the pipe according to boiler operation parameters, and on the basis, obtains the distribution of wall temperature of heating surface of superheater and reheater according to heating surface heat transfer mathematical model, and has the advantages of simplicity, rapidness, continuous operation and regular automatic learning. CN201610890688.4 provides a method for arranging boiler temperature monitoring measuring points, for a platen superheater, a high-temperature section superheater, a platen reheater and a high-temperature reheater, pipe wall temperature measuring points are arranged at an outlet of the outermost circle at the bottom of the platen superheater and on the outer walls of outlet pipes of pipe rings of sections of the high-temperature section superheater, the platen reheater and the high-temperature reheater; a desuperheater outlet steam temperature measuring point is arranged at a position where steam and water are fully mixed; for a W-shaped flame boiler, a water-cooled wall is provided with an intermediate mixing header, and a lower water-cooled wall outlet section and an upper water-cooled wall tube outlet section are both provided with wall temperature measuring points; each heating surface is provided with an inlet smoke temperature measuring point, an outlet smoke temperature measuring point, a steam inlet temperature measuring point, a steam outlet temperature measuring point and a water outlet temperature measuring point. The method provided by the invention gives guidance to the arrangement of pipe wall temperature measuring points, smoke temperature measuring points and steam-water temperature measuring points of the boiler unit, but the reliability of wall temperature measurement cannot be improved. In order to avoid the problems caused by the thermocouple, CN201210003667.8 discloses an on-line monitoring system and a monitoring method for the temperature of the side wall of the water cooling wall of the boiler facing the fire, sound waves are used for measurement, a sound wave receiving and transmitting system consisting of a sound wave guide pipe, an electric loudspeaker and a special electret microphone is arranged on the section of a hearth, and receiving and transmitting measuring points are arranged on the heating surface at the same side of the water cooling wall; the electric loudspeaker sends out sound signals, the sound signals are received by the enhanced microphone and converted into voltage signals, the voltage signals are input into the signal conditioner through a cable and then enter the data acquisition card to be converted into digital signals, the flying time is estimated through generalized cross-correlation time delay, and finally the temperature of the side wall of the water cooling wall facing the fire is calculated through a computer and software. The method can only be used for the water-cooled wall with a single-sided heating surface, and cannot be used for the superheater and the reheater with double-sided heating surfaces. CN200710010198.1 discloses a method for measuring the temperature of a membrane water-cooled wall of a supercritical once-through boiler, which measures the temperature of the wall of a fin on the fire side by embedding a thermocouple in the fin on the fire side of the membrane wall heated on one side. The method can only be used for measuring the wall temperature of the fins, which is not the most concerned problem in practice, the tube wall temperature is more concerned in operation, and the measurement objects are more superheater and reheater and not water wall. CN201510349688.9 discloses a wall-mounted temperature measurement method, which includes attaching a thermocouple sensor to an object to be measured by an adhesive, acquiring physical parameter data of the object to be measured and physical parameter data of the adhesive, checking environmental real-time data of a measurement location, reading a real-time temperature value measured on the thermocouple sensor, acquiring a thermal contact resistance between the thermocouple patch and the object to be measured, and calculating the real-time temperature value by a correction formula to obtain a corrected temperature value. According to the wall-mounted temperature measurement method, the real-time temperature value of the object to be measured is obtained, the temperature value is calculated through the correction formula, the corrected temperature value is obtained, and compared with the real-time temperature value obtained through measurement in the prior art, the real-time temperature value is closer to the temperature value of the object to be measured actually. The biggest problem of this invention is the high temperature binder. In addition, the wall surface of the pipe is not smooth any more due to the adherent thermocouple, and the abrasion is inevitable.
Disclosure of Invention
The invention aims to provide a method for realizing temperature measurement by fixing a thermocouple on the outer surface of the wall surface of a heating surface of a boiler to be measured through deposited metal, the thermocouple and a pipe are integrated, the bulge on the surface of the pipe is avoided, and meanwhile, the wall temperature can be directly and reliably measured.
The invention is realized by the following technical scheme:
a method of measuring the metal wall temperature of a heating surface of a boiler, the method comprising:
placing a thermocouple on a metal wall surface of a heating surface of a boiler to be measured in an adherence manner, and attaching the tail end of the thermocouple to a point to be measured on the metal wall surface of the heating surface of the boiler;
melting deposited metal, and then laying the molten metal on the surface of the thermocouple to form a deposited layer, so that the thermocouple and the wall surface of the heating surface of the boiler are fixed together and transfer heat;
and extending the lead end of the thermocouple out of the heating surface of the boiler, and connecting the lead end of the thermocouple with a recording device to read and/or record the readings of the thermocouple to obtain the temperature of the point to be measured on the heating surface of the boiler.
In the technical scheme, the boiler heating surface comprises one or more of a water wall, a superheater, an evaporator, an economizer and a reheater.
In the technical scheme, the thermocouple is arranged on the fire facing side or the windward side of the heating surface of the boiler; the thermocouple is arranged on the windward side of the heating surface of the boiler, and is preferably arranged on the metal wall surface in the center of the windward side.
In the technical scheme, when the boiler heating surface structure is a membrane water-cooled wall or a heating tube bundle comprising a plurality of heating tubes, the thermocouple is arranged on the metal wall surface of any heating tube to be detected of the boiler heating surface, and the axis of the thermocouple is parallel to the central axis of the heating tube to be detected.
In the technical scheme, the thickness of the cladding layer of the cladding metal is uniformly distributed along the axial direction of the heated tube to be measured by taking the thermocouple as a central axis, and the cladding metal forms a cladding layer with the thickness of at least 1mm on the surface of the thermocouple.
In the technical scheme, the cross section of the cladding layer of the cladding metal is in a circular ring shape, a semicircular ring shape or a crescent shape surrounding the heated pipe to be measured, or the metal wall surface of the heated surface of the boiler is in a hemispherical shape wrapping a thermocouple.
In the technical scheme, when the boiler heating surface structure is a screen type heating surface, the thermocouple is arranged on the metal wall surface of the point to be measured of the boiler heating surface.
In the technical scheme, the cladding layer of the cladding metal is uniformly laid on the metal wall surface of the heating surface of the boiler along the axis of the thermocouple by taking the thermocouple as the center, and the thickness of the cladding layer is uniformly distributed along the axis of the thermocouple.
In the technical scheme, the cross section of the cladding layer of the cladding metal is in a hemispherical shape wrapping the thermocouple on the metal wall surface of the heating surface of the boiler, and the cladding layer with the thickness of at least 1mm is formed on the surface of the thermocouple by the cladding metal.
In the technical scheme, the heat conductivity coefficient of the material selected for the deposited metal is not lower than 21W/m.K.
In the above technical scheme, when the heating surface of the boiler is a single-surface heating membrane wall, the thermocouple is arranged on the fire facing side of the heating surface of the boiler. When the double surfaces of the heating surface of the boiler are heated, the thermocouple is arranged on the heated outer wall surface of any one side of the heating surface.
The invention has the following advantages and beneficial effects: the thermocouple directly sticks to a metal wall temperature point to be measured of the heating surface of the boiler, and the temperature of the measuring point is directly read, so that additional errors of indirect measurement are avoided, and the measuring errors are small; the laying mode of the deposited metal plays a role in protecting the thermocouple, and has an anti-abrasion effect on the outer wall of the heating surface, so that the service life of the thermocouple is prolonged.
Detailed Description
The following describes the embodiments and operation of the present invention with reference to the accompanying drawings.
The terms of orientation such as up, down, left, right, front, and rear in the present specification are established based on the positional relationship shown in the drawings. The corresponding positional relationship may also vary depending on the drawings, and therefore, should not be construed as limiting the scope of protection.
The invention provides a method for directly measuring the metal wall temperature of a heating surface of a boiler by fixing a thermocouple on the outer wall surface of the heating surface of the boiler through deposited metal. The heat conductivity coefficient of the selected deposited metal material is not lower than 21W/m.K.
The boiler heating surface 1 comprises one or more of a water wall, an economizer, an evaporator, a superheater and a reheater. These boiler heating surfaces 1 may be membrane walls or bundles of heating tubes comprising several heating tubes, or may be screen heating surfaces.
The specific method comprises the following steps:
placing the thermocouple on the metal wall surface of the heating surface of the boiler to be measured in an adherence manner, and attaching the tail end of the thermocouple to the point to be measured on the metal wall surface of the heating surface of the boiler;
melting the deposited metal, and then laying the molten metal on the surface of the thermocouple to form a deposited layer, so that the thermocouple and the wall surface of the heating surface of the boiler are fixed together and transfer heat;
and extending the lead ends of the thermocouples out of the heated surface of the boiler (such as outside a hearth or outside a heated surface unit such as an economizer, a superheater and the like), and connecting the lead ends with a recording device arranged outside the heated surface of the boiler to read and/or record readings of the thermocouples so as to obtain the temperature of points to be measured on the heated surface of the boiler.
When the structure of the boiler heating surface 1 is a membrane water-cooled wall or a heating tube bundle comprising a plurality of heating tubes, the thermocouple 1 is arranged on the metal wall surface of any heating tube to be measured on the boiler heating surface, and the axis of the thermocouple is parallel to the central axis of the heating tube to be measured. The tube of the boiler heating surface 3 is internally provided with a heat absorption working medium, and the outer side metal wall surface is provided with a thermocouple 1. The measuring end point of the thermocouple 1 is attached to a point to be measured on the heating surface of the boiler, so that the temperature of the point to be measured can be detected. And then laying the deposited metal on the surface of the heated tube to be measured. The thickness of the cladding layer of the cladding metal is uniformly distributed along the axial direction of the heated pipe to be measured by taking the thermocouple as a central shaft, and the cladding metal forms a cladding layer with the thickness of at least 1mm on the surface of the thermocouple.
When the boiler heating surface 1 is arranged in the furnace, the thermocouple 3 is arranged on the fire-facing side of the boiler heating surface 1, namely the side facing the flame. When the boiler heating surface 1 is arranged on a flue above a hearth or outside the hearth, the thermocouple 3 is arranged on the windward side of the boiler heating surface 1, and in this case, the thermocouple is preferably arranged on the metal wall surface at the center of the windward side of the boiler heating surface.
For the heated tube to be measured as the heated light tube, the deposited metal forms a layer of fused coating with uniform circumferential thickness outside the thermocouple and the heated light tube, that is, as shown in fig. 1a, the cross section of the fused coating 2 of the deposited metal is in a ring shape surrounding the heated tube to be measured; or, a crescent-shaped fused layer 2 with uneven circumferential thickness but smooth transition is formed on the fused layer by fusing the fused layer by taking the thermocouple 3 as the center on the heating side of the heating surface 1 of the boiler (as shown in figure 1 b), the thermocouple 3 is fixed in the fused layer 2, the metal fused layer 2 on the surface of the pipe is a local protective layer of the pipe on the heating surface, and the heat conduction between the end point of the thermocouple 3 and the metal outer wall of the pipe is enhanced, so that the thermocouple accurately reflects the metal wall temperature of a measuring point. Furthermore, a spherical or hemispherical cladding layer 2 with uneven circumferential thickness but smooth transition can be formed on the heated side of the boiler heating surface 1 by welding around the thermocouple 3 and connected to the metal wall surface of the boiler heating surface, as shown in fig. 1 c. The cross section of the cladding layer 2 can also be in a semicircular ring shape surrounding the heated tube to be measured, and the thermocouple 3 and the cladding layer 3 of the cladding metal thereof are both arranged on the fire facing side or the windward side of the heated light tube.
For the heated tube to be measured is a heated film type wall, a layer of semicircular annular cladding layer with uniform circumferential thickness is formed on the heated side no matter the heated tube is heated on one side or on both sides (as shown in figure 2 a); or, a crescent-shaped fused layer 2 with uneven circumferential thickness but smooth transition is formed on the fused layer by fusing on the heating side of the boiler heating surface 1 by taking the thermocouple 3 as the center (as shown in fig. 2 b); or a spherical or hemispherical cladding layer 2 with uneven circumferential thickness but smooth transition is formed on the heated side of the heated surface 1 of the boiler by cladding with the thermocouple 3 as the center and is connected on the metal wall surface of the heated surface of the boiler (as shown in figure 2 c), the thermocouple 3 is fixed in the cladding layer 2, the metal cladding layer 2 on the surface of the pipe is a protective layer of the pipe of the heated surface, and the heat conduction between the end point of the thermocouple 3 and the metal outer wall of the pipe is enhanced, so that the thermocouple 3 accurately reflects the metal wall temperature of a measuring point.
When the structure of the boiler heating surface 1 is a screen type heating surface, the thermocouple 3 is arranged on the metal wall surface of the point to be measured of the boiler heating surface 1. The cladding layer 2 of the cladding metal is uniformly laid on the metal wall surface of the heating surface of the boiler along the axis of the thermocouple by taking the thermocouple as the center, and the thickness of the cladding layer is uniformly distributed along the axis of the thermocouple. In general, the cross section of the cladding layer of the deposited metal is in a sphere-like shape or a hemisphere shape wrapping the thermocouple on the metal wall surface of the heating surface of the boiler, and the deposited metal forms a cladding layer with a thickness of at least 1mm on the surface of the thermocouple 3.
Whether the deposited cross-sectional shape is circular, semi-circular, crescent, spherical or hemispherical, the generatrix of the deposited layer is parallel to the axis of the tube or thermocouple. Thus, the thermocouple 3 is entirely laid in the cladding layer 2.
The outer surface of the metal cladding layer 2 is uniform in the axial direction on the outer wall surface of the heated tube, i.e., any cross section is the same. The wall thickness of the cladding layer equivalent to the heating surface is increased, so that the cladding layer plays a role in wear prevention and protection on the heating surface. The axis of the thermocouple is positioned in the right middle of the windward side, so that the protection effect of the cladding layer is ensured.
FIG. 3 is a distribution diagram of measured point temperature measured directly by a thermocouple arranged by the deposited metal laying method of the invention, and the measurement error is less than 2.2 ℃ when the deposited layer 2 is in a ring shape (FIG. 1 a)/a semi-ring shape (FIG. 2a) or a crescent shape (FIG. 1b, FIG. 2 b); the measurement error is less than 4.7 ℃ when the fusion layer 2 is in the form of a hemisphere (fig. 1 c).
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.