Device and method for monitoring wall temperature of heat exchange tube in furnace using compressed air cooling protection

Abstract

The invention relates to a device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection, comprising a heat conduction block, a compressed gas pipe, a thermocouple and a boiler heat exchange tube; a heat conduction block is arranged on the outer wall surface of the boiler heat exchange tube, a compressed gas pipe is fixed above the heat conduction block, and the thermocouple passes through the compressed gas pipe and is inserted into the heat conduction block; the outer surfaces of the compressed gas pipe and the heat conduction block are coated with a layer of zirconium oxide thermal barrier layer; the heat conduction block is made of the same metal material as the boiler heat exchange tube, and its width is 50%-85% of the diameter of the boiler heat exchange tube, the ratio of height to width is 1-1.5, and the thickness is 5mm-12mm. The beneficial effects of the invention are: the heat conduction block and the thermocouple of the invention are installed on the outer wall of the boiler heat exchange tube, and the thermal resistance between the thermocouple and the boiler heat exchange tube is very small, and because the outer surface of the heat conduction block is coated with the zirconium oxide thermal barrier layer, the thermal resistance between the thermocouple and the high-temperature flue gas is large, so the thermocouple can accurately reflect the wall temperature of the boiler heat exchange tube, and the measurement accuracy is high.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature measurement, and in particular to a device and method capable of monitoring a boiler heat exchange tube in a furnace. Background Art

[0002] Power plant boilers are widely used in the production field of power plants in my country. In order to obtain high-temperature and high-pressure steam to drive the steam turbine to do work, a large number of heating surfaces need to be arranged in the furnace, including platen superheaters, high-temperature superheaters and reheaters. Taking ultra-supercritical coal-fired boilers as an example, the temperature of high-temperature and high-pressure steam in the superheater tube group is as high as 500℃-600℃, while the temperature of high-temperature flue gas outside the tube group is as high as 800℃-1000℃. The working conditions of boiler heat exchange tubes are harsh, and the local tube wall temperature is close to the upper limit of the temperature tolerance of metal materials. In the case of improper operation or internal foreign matter blockage, overheating and even tube burst accidents are prone to occur. Therefore, it is very necessary to monitor and measure the wall temperature of the boiler heat exchange tubes of power plant boilers to improve boiler safety.

[0003] Since the temperature of boiler heat exchange tubes and external flue gas is very high, it is not easy to directly measure the temperature of boiler heat exchange tubes in the furnace. The wires of conventional thermocouples are prone to oxidation, deformation or even breakage at high temperatures, which damages the temperature measuring components. At present, the wall temperature monitoring method commonly used in power plants is to arrange thermocouples at the inlet and outlet sections of the heat exchange tubes on the top of the furnace. Since this position is outside the furnace and there is no high-temperature flue gas scouring, the life of the thermocouples is greatly improved. However, this measurement method cannot reflect the actual wall temperature of the heat exchange tube in the furnace.

[0004] In summary, in order to ensure the safe operation of the boiler and prevent the tubes from bursting on the heating surface, it is urgent to develop a device and method for long-term and effective monitoring of the wall temperature of the boiler heat exchange tubes in the furnace. Summary of the invention

[0005] The object of the present invention is to overcome the deficiencies in the prior art and to provide a device and method for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection.

[0006] This device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection includes a heat conductive block, a compressed gas pipe, a thermocouple and a boiler heat exchange tube; a heat conductive block is arranged on the outer wall surface of the boiler heat exchange tube, a compressed gas pipe is fixed above the heat conductive block, and the thermocouple passes through the compressed gas pipe and is inserted into the heat conductive block; the outer surfaces of the compressed gas pipe and the heat conductive block are coated with a zirconium oxide thermal barrier layer.

[0007] Preferably, the heat conducting block is made of the same metal material as the boiler heat exchange tube, with a width of 50%-85% of the diameter of the boiler heat exchange tube, a height-to-width ratio of 1-1.5, and a thickness of 5mm-12mm.

[0008] As a preferred embodiment, the heat conducting block is connected to the boiler heat exchange tube by full welding on all sides.

[0009] As a preferred embodiment, a small hole is provided at the upper end of the heat conducting block, a thermocouple is inserted into the small hole, and the thermocouple is fixed in the heat conducting block by fastening bolts.

[0010] Preferably, the compressed gas pipe is made of heat-resistant stainless steel with a pipe diameter of 20mm-35mm, and a compressed gas exhaust port is provided at the lower part of the compressed gas pipe.

[0011] Preferably, the thickness of the zirconium oxide thermal barrier layer is 0.1 mm-0.3 mm.

[0012] Preferably, the thermocouple is a K-type nickel-chromium-nickel-silicon thermocouple or an S-type thermocouple.

[0013] Preferably, the compressed gas pipe is connected to compressed air or compressed nitrogen.

[0014] As a preferred embodiment, the upper tube body of the compressed gas pipe is arranged parallel to the boiler heat exchange tube, and the bottom tube body of the compressed gas pipe is inclined toward the boiler heat exchange tube and connected to the heat conduction block.

[0015] The installation and use method of the device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection is characterized in that it includes the following steps:

[0016] S1. Connect the heat transfer block and the boiler heat exchange tube by welding, fix the compressed gas pipe with the compressed gas exhaust port on the top of the heat transfer block, and fix the thermocouple inside the heat transfer block by fastening bolts;

[0017] S2. A zirconium oxide thermal barrier layer with a thickness of 0.1 mm to 0.3 mm is coated on the outer surface of the compressed gas pipe and the heat conducting block;

[0018] S3, compressed gas is connected from the upper end of the compressed gas pipe, with an initial pressure of 0.3MPa-0.6MPa. The gas flows from top to bottom, cools the wire of the thermocouple, and then is discharged from the compressed gas exhaust port;

[0019] S4. The thermocouple is within the safe temperature range below 700℃, and the wall temperature of the boiler heat exchange tube in the furnace is continuously monitored.

[0020] The beneficial effects of the present invention are:

[0021] 1. The heat conductive block and the thermocouple of the present invention are installed on the outer wall of the boiler heat exchange tube. The thermal resistance between the thermocouple and the boiler heat exchange tube is very small. Since the outer surface of the heat conductive block is coated with a zirconium oxide thermal barrier layer, the thermal resistance between the thermocouple and the high-temperature flue gas is large. Therefore, the thermocouple can accurately reflect the wall temperature of the boiler heat exchange tube with high measurement accuracy.

[0022] 2. The thermocouple of the present invention is cooled by compressed gas, and the compressed gas pipe is coated with a zirconium oxide thermal barrier layer with heat insulation effect. The temperature of the thermocouple wire is controlled within a safe range, the life of the measuring device is extended, and long-term online measurement can be achieved to ensure safe and reliable operation of the boiler.

[0023] 3. The device of the present invention has a simple and reasonable structure, can use cheap K-type thermocouples, and the compressed gas is not expensive and can be obtained locally, so it has lower operating costs and better operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of a device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection;

[0025] Figure 2 A front view of a device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection;

[0026] Figure 3 A side view of a device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection;

[0027] Figure 4 A top view of a device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection;

[0028] Figure 5 for Figure 2 AA section view;

[0029] Figure 6 for Figure 4 BB cross-section diagram;

[0030] Figure 7 The numerical simulation of the device is Figure 4 Temperature field distribution diagram of BB section;

[0031] Figure 8 The numerical simulation of the device is Figure 2 AA section temperature field distribution diagram.

[0032] Explanation of the reference numerals: 1 - heat conducting block; 2 - compressed gas pipe; 3 - compressed gas exhaust port; 4 - thermocouple; 5 - boiler heat exchange tube; 6 - fastening bolt. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with embodiments. The description of the following embodiments is only used to help understand the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principles of the present invention, several improvements and modifications may be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0034] Embodiment 1

[0035] The device for monitoring the wall temperature of the heat exchange tube in the furnace using compressed air cooling protection comprises a heat conduction block 1, a compressed gas pipe 2, a compressed gas exhaust port 3, a thermocouple 4 and a boiler heat exchange tube 5. The heat conduction block 1 is arranged on the outer wall surface of the boiler heat exchange tube 5, the compressed gas pipe 2 is fixed above the heat conduction block 1, and the thermocouple 4 passes through the compressed gas pipe 2 and then is inserted into the heat conduction block 1.

[0036] The heat-conducting block 1 is made of the same metal material as the boiler heat exchange tube, with a width of 50%-85% of the diameter of the boiler heat exchange tube, a height-to-width ratio of 1-1.5, and a thickness of 5mm-12mm; the heat-conducting block 1 is connected to the boiler heat exchange tube 5 by full welding all around; a small hole is provided at the upper end of the heat-conducting block 1 for inserting a thermocouple 4, and the thermocouple 4 is fixed by a fastening bolt 6.

[0037] The compressed gas pipe 2 is made of heat-resistant stainless steel with a diameter of 20mm-35mm. Its bottom is connected to the heat conductive block 1, and a compressed gas exhaust port 3 is arranged at the lower part of the compressed gas pipe 2. The compressed air discharged from the compressed gas exhaust port 3 will not blow to the heat conductive block.

[0038] The outer surfaces of the compressed gas pipe 2 and the heat conducting block 1 are coated with a zirconium oxide thermal barrier layer with a thickness of about 0.1 mm to 0.3 mm.

[0039] The thermocouple 4 used to measure the wall temperature can be a common K-type nickel-chromium-nickel-silicon thermocouple, or other types of thermocouples such as S-type.

[0040] The upper end of the compressed gas pipe 2 is connected to compressed air or compressed nitrogen, and the pressure is 0.3MPa-0.6MPa.

[0041] When working, compressed gas flows in from the upper end of the compressed gas pipe to cool the wire of the thermocouple. In addition, the zirconium oxide thermal barrier layer is used to insulate the wires of the thermocouple, ensuring that all the wires of the thermocouple are thermally shielded and work within a safe temperature range without being burned. The device can operate reliably for a long time and realize continuous monitoring of the wall temperature of the boiler heat exchange tube in the furnace.

[0042] Embodiment 2

[0043] The device for monitoring the wall temperature of the heat exchange tube in the furnace with compressed air cooling protection is installed and used as follows: the heat conduction block 1 is connected to the boiler heat exchange tube 5 by welding, and the thermocouple 4 is fixed inside the heat conduction block 1 by the fastening bolts 6, ensuring that the contact thermal resistance between the thermocouple 4 and the boiler heat exchange tube 5 is reduced to a minimum. At the same time, since the outer surfaces of the compressed gas pipe 2 and the heat conduction block 1 are coated with a zirconium oxide thermal barrier layer, the convection, heat conduction and radiation effects of the high-temperature flue gas on the boiler heat exchange tube 5 are reduced, so the thermocouple 4 is very close to the wall temperature of the boiler heat exchange tube 5. The compressed gas is connected from the upper end of the compressed gas pipe 2, with an initial pressure of 0.3MPa-0.6MPa. The gas flows from top to bottom, cools the wire of the thermocouple 4, and then is discharged from the compressed gas exhaust port 3. Since the outer surface of the compressed gas pipe 2 is coated with a zirconium oxide thermal barrier layer, the heating of the gas inside the compressed gas pipe 2 by the high-temperature flue gas outside the pipe is reduced, ensuring that the thermocouple 4 is within a safe temperature range below 700°C. Therefore, the device can operate reliably for a long time and realize continuous monitoring of the wall temperature of the boiler heat exchange tube in the furnace.

[0044] ANSYS Fluent was used to conduct numerical simulation experiments on the flow and heat transfer of a device for monitoring the wall temperature of heat exchange tubes in a furnace with compressed air cooling protection, and the measured temperature in the heat transfer block and the temperature at 1 / 2 of the wall thickness of the boiler heat exchange tube were compared and analyzed:

[0045] 1) Calculation boundary conditions

[0046] To simulate the flow and heat transfer process in an actual boiler, the incoming flue gas velocity is 10m / s and the temperature is 900℃, the steam velocity in the heat receiver tube (boiler heat exchange tube) is 13m / s and the temperature is 600℃, and the air velocity in the cooling tube (compressed gas tube) is 20m / s and the temperature is 25℃;

[0047] 2) Computational Model

[0048] The turbulence model is Realizable k-ε, and the radiation model uses the P1 model;

[0049] After calculation, the temperature at 1 / 2 wall thickness of the boiler heat exchange tube in this embodiment is 641°C, and the temperature inside the heat transfer block is 662°C, with a difference of only 21°C, which can meet the measurement requirements of the boiler heating surface.

Claims

1. A device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection, characterized in that: The invention comprises a heat conducting block (1), a compressed gas pipe (2), a thermocouple (4) and a boiler heat exchange pipe (5); the heat conducting block (1) is arranged on the outer wall surface of the boiler heat exchange pipe (5), the compressed gas pipe (2) is fixed above the heat conducting block (1), and the thermocouple (4) passes through the compressed gas pipe (2) and is inserted into the heat conducting block (1); the outer surfaces of the compressed gas pipe (2) and the heat conducting block (1) are coated with a zirconium oxide thermal barrier layer; a compressed gas exhaust port (3) is arranged at the lower part of the compressed gas pipe (2); the upper end of the compressed gas pipe (2) is connected to compressed air or compressed nitrogen; the upper pipe body of the compressed gas pipe (2) is arranged parallel to the boiler heat exchange pipe (5), and the bottom pipe body of the compressed gas pipe (2) is inclined toward the boiler heat exchange pipe (5) and is connected to the heat conducting block (1).

2. The device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection according to claim 1 is characterized in that: The heat conducting block (1) is made of the same metal material as the boiler heat exchange tube, has a width of 50%-85% of the diameter of the boiler heat exchange tube, a height-to-width ratio of 1-1.5, and a thickness of 5mm-12mm.

3. The device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection according to claim 1, characterized in that: The heat conducting block (1) is connected to the boiler heat exchange tube (5) by full welding all around.

4. The device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection according to claim 1, characterized in that: A small hole is provided at the upper end of the heat conducting block (1), a thermocouple (4) is inserted into the small hole, and the thermocouple (4) is fixed in the heat conducting block (1) by means of a fastening bolt (6).

5. The device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection according to claim 1, characterized in that: The compressed gas pipe (2) is made of heat-resistant stainless steel and has a pipe diameter of 20 mm to 35 mm.

6. The device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection according to claim 1, characterized in that: The thickness of the zirconium oxide thermal barrier layer is 0.1mm-0.3mm.

7. The device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection according to claim 1, characterized in that: The thermocouple (4) adopts a K-type nickel-chromium-nickel-silicon thermocouple or an S-type thermocouple.

8. A method for installing and using the device for monitoring the wall temperature of heat exchange tubes in a furnace using compressed air cooling protection as claimed in claim 1, characterized in that: The following steps are involved: S1, connecting the heat conducting block (1) and the boiler heat exchange tube (5) by welding, fixing the compressed gas pipe (2) with the compressed gas exhaust port (3) above the heat conducting block (1), and fixing the thermocouple (4) inside the heat conducting block (1) by fastening bolts (6); S2, coating the outer surfaces of the compressed gas pipe (2) and the heat conducting block (1) with a zirconium oxide thermal barrier layer having a thickness of 0.1 mm to 0.3 mm; S3, compressed gas is introduced from the upper end of the compressed gas pipe (2), with an initial pressure of 0.3MPa-0.6MPa, and the gas flows from top to bottom to cool the wire of the thermocouple (4), and then is discharged from the compressed gas exhaust port (3); S4, the thermocouple (4) is within the safe temperature range below 700°C, and the wall temperature of the boiler heat exchange tube in the furnace is continuously monitored.

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