Thermocouple and thermocouple mounting method

Abstract

The application discloses a thermocouple and a thermocouple mounting method, and the thermocouple is composed of a sleeve layer and a lotus root silk layer and a filler layer, each lotus root silk has a diameter of less than or equal to 0.4 mm, the thickness of the filler layer is less than or equal to 0.5 mm, the wall thickness of the sleeve is less than or equal to 2 mm, the inner diameter of the filler is less than or equal to 2 mm, and the inner diameter of the sleeve layer is less than or equal to 4 mm. The thermocouple is mounted in a lens pad with a cylindrical channel, and the distance from the part of the thermocouple in the cylindrical channel of the lens pad to the central axis of the cylindrical channel is 0-1 times the inner diameter of the cylindrical channel. The temperature signal measured by the lotus root silk is transmitted to a DCS and / or SIS system through a temperature transmitter system.

Description

Technical Field

[0001] This invention belongs to the field of instrumentation technology in the field of olefin polymerization, specifically a thermocouple and a method for installing and using the thermocouple, which is particularly suitable for use inside polymerization equipment. Background Technology

[0002] High-pressure free radical polymerization equipment is widely used for low-density polyethylene and ethylene-vinyl acetate copolymers. The reactor is the core equipment of the polymerization unit, and its long-term stable operation is not only related to the stability of product quality, but also to the economic benefits of the unit.

[0003] As is well known in the art, uneven temperature distribution is prone to occur in high-pressure free radical polymerization reactors. Excessive initiator dosage, excessively high reaction water temperature, and scaling on the pipe walls can all lead to large temperature gradients within the reactor. Once the temperature becomes too high, it will induce the decomposition of reactants such as ethylene and vinyl acetate, resulting in reactor overheating, overpressure, and ultimately, plant shutdown.

[0004] In industrial applications, thermocouples are commonly used to monitor the temperature of materials in polymerization reactors. For reactor safety, almost all thermocouple signals are connected to the SIS (System-In-System) system. Damage to a thermocouple can lead to plant shutdown and significant economic losses. To address this issue, one technique employed in this field is to use multiple thermocouples at the same location for temperature monitoring. This undoubtedly increases plant costs, increases sealing surfaces, and raises operating and maintenance costs. Another technique uses dual-wire four-core thermocouples. By comparing the temperature signals measured by the two sets of measuring circuits and judging the thermocouple's operating status based on the difference between the two temperature signals, this method significantly improves thermocouple reliability. However, for safety reasons, a fault in one of the measuring circuits, or even a slightly large deviation, can also be interpreted as a thermocouple malfunction, leading to plant shutdown. Furthermore, the use of dual-wire four-core thermocouples is not always effective due to the susceptibility of thermocouple wire measurements and the potential for deviations in temperature change circuits.

[0005] To address the aforementioned problems, this invention proposes a multi-core thermocouple and a method for using the multi-core thermocouple. Summary of the Invention

[0006] The problem this invention aims to solve is the reliability of thermocouples used for measuring temperature in high-pressure free radical polymerization processes and the long-term safe and stable operation of the device. To address the above technical problems, this invention proposes a thermocouple and a thermocouple installation method.

[0007] The present invention first provides a thermocouple, wherein the temperature measuring end of the thermocouple includes, from the outside to the inside, a sheath layer, a packing layer and a wire layer, wherein the packing layer wraps the wire layer and the sheath layer wraps the packing layer; the wire layer is provided with at least 6 wires, and each pair of wires forms a group, with one end of the two wires in the same group connected and the other end led out from the rear end of the thermocouple and connected to the temperature transmitter unit.

[0008] Among them, the diameter of each lotus root wire is ≤0.4mm, the thickness of the filler layer is ≤0.5mm, the thickness of the sleeve layer is ≤2mm, the inner diameter of the filler layer is ≤2mm, and the inner diameter of the sleeve layer is ≤4mm.

[0009] In a preferred embodiment of the present invention, the filler layer is made of magnesium oxide, the axial length of the lotus root fiber layer is ≥20mm, and the length of the sleeve layer is 0.1-0.5m.

[0010] In a preferred embodiment of the present invention, the thermal response time of the thermocouple to achieve 50% sensing response is ≤1000ms.

[0011] In a preferred embodiment of the present invention, the number of lotus root fibers is even, and every two lotus root fibers form a group to form a measurement loop.

[0012] The present invention also provides a method for installing the thermocouple, wherein the thermocouple is installed in a tubular reactor, comprising the following steps:

[0013] (1) A lens pad with a cylindrical fluid channel is provided, wherein an extension member is provided on the lens pad facing outward, and the extension member has an opening in the middle, the opening being connected to the fluid channel;

[0014] (2) Install the thermocouple in the opening of the extension of the lens pad, and position the front end of the thermocouple in the fluid channel of the lens pad to contact the fluid to be measured.

[0015] (3) Install the lens pad with the thermocouple in the pipeline of the tubular reactor to be tested; the temperature signal measured by the thermocouple is transmitted to the DCS and / or SIS system through the temperature transmitter system.

[0016] The distance from the end of the thermocouple that extends into the cylindrical fluid channel of the lens pad to the central axis of the cylindrical fluid channel is 0-1 times the inner diameter of the cylindrical fluid channel.

[0017] Preferably, the thermocouple and the lens pad extension component are connected by threads. The distance from the end of the thermocouple extending into the cylindrical fluid channel of the lens pad to the central axis of the cylindrical channel is 0.1-0.8 times the inner diameter of the cylindrical channel. The material flow velocity in the cylindrical channel of the lens pad is 1-40 m / s, the temperature is 100-350℃, and the pressure is 15-400 MPa.

[0018] The present invention also provides another method for installing the thermocouple, wherein the thermocouple is installed in a batch reactor, comprising the following steps:

[0019] (1) Provide a seal with an opening;

[0020] (2) Install the thermocouple in the opening of the seal;

[0021] (3) Install the sealing component with the thermocouple in the reactor to be tested, and transmit the temperature signal measured by the thermocouple to the DCS and / or SIS system through the temperature transmitter system.

[0022] The minimum distance between the end of the thermocouple that extends into the reactor and the inner wall of the container is at least 1 mm.

[0023] The present invention further provides a method for temperature measurement using the thermocouple, wherein the measured temperature value of the thermocouple is calculated using the following formula:

[0024]

[0025] Where T o T is the temperature value output by the temperature transmitter. i T j and T k The temperature values ​​measured for the filaments in groups i, j, and k are given, where n is the number of filaments, m is the mode of the temperature values ​​measured for each group of filaments, and δ is the set value for the deviation of the measured temperature.

[0026] The present invention further provides another method for temperature measurement using the thermocouple, wherein the measured temperature value of the thermocouple is calculated using the following formula:

[0027]

[0028] Where T o T is the temperature value output by the temperature transmitter. i and T k T represents the temperature values ​​measured for the filaments in groups i and k. ref The temperature of at least one adjacent thermocouple is used as a reference temperature, x is the correction coefficient for the reference temperature, n is the number of thermocouple wires, m is the mode of the temperature values ​​measured by each group of thermocouple wires, and δ is the deviation setting value for the measured temperature.

[0029] The present invention has the following advantages:

[0030] (1) The thermocouple proposed in this invention integrates at least three temperature measurement circuits. By adopting the strategy of taking two out of three or taking an equal number of three circuits, the accuracy of temperature measurement can be greatly improved and the number of device shutdowns can be reduced.

[0031] (2) If one of the temperature measurement circuits of the thermocouple proposed in this invention fails, it will not affect the accuracy of the other two measurement circuits. The safety level is improved, the reliability of the thermocouple is improved, and the life assessment function is added, which extends the service life of the thermocouple and has significant economic benefits. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the thermocouple structure of the present invention.

[0033] Figure 2 This is a schematic diagram of an installation method for the thermocouple of the present invention.

[0034] Figure 3 This is a schematic diagram of an installation method for the thermocouple of the present invention.

[0035] Figure 4 This is a schematic diagram of an installation method for the thermocouple of the present invention.

[0036] Among them, thermocouple 101; sheath layer 102; packing layer 103; lotus fiber layer 104; lotus fiber 105; thermocouple end 106; lens pad 200; lens pad fluid channel 201; lens pad extension component 202; thermocouple 203; lens pad 300; lens pad fluid channel 301; lens pad extension component 302A / B; thermocouple 303A / B; reactor 400; internal channel 401; reactor wall 402; thermocouple 403. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be further described in detail and completely below with reference to the embodiments and accompanying drawings. The components of the embodiments of the present invention described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0038] Figure 1 A schematic diagram of a thermocouple is shown. The temperature measuring end of the thermocouple includes, from the outside to the inside, a sheath layer 102, a packing layer 103, and a wire layer 104. The wire layer contains at least six wires 105, with two wires forming a group. The wires are led out from the rear end of the thermocouple and connected to the temperature transmitter unit. The diameter of each wire is ≤0.4mm, the thickness of the packing layer is ≤0.5mm, the thickness of the sheath layer is ≤2mm, the inner diameter of the packing layer is ≤2mm, and the inner diameter of the sheath layer is ≤4mm.

[0039] This invention does not impose any special limitations on the material of the lotus root wire; thermocouple lotus root wire known in the prior art is sufficient to meet the requirements of this invention. The filler layer is magnesium oxide, the axial length of the lotus root wire layer is ≥20mm, and the length of the sleeve layer is 0.1-0.5m.

[0040] The thermal response time of the thermocouple reaching 50% sensing response is ≤1000ms. The thermal response time is measured according to the method in "G / BT 18404-2022 Armored Thermocouple Cables and Armored Thermocouples".

[0041] Figure 2 This invention illustrates a method for installing the thermocouple, applicable to tubular reactors, as follows:

[0042] (1) A lens pad 200 with a cylindrical fluid channel 201 is provided, wherein an extension member 202 is provided on the lens pad facing outward, and the extension member has an opening in the middle, the opening being connected to the fluid channel.

[0043] (2) Install the thermocouple 203 in the opening of the extension member 202 of the lens pad 200, and position the front end of the thermocouple 203 in the fluid channel 201 of the lens pad so as to contact the fluid to be measured.

[0044] (3) Install the lens pad with the thermocouple in the pipeline of the tubular reactor to be tested, and transmit the temperature signal measured by the thermocouple to the DCS and / or SIS system through the temperature transmitter system.

[0045] The distance from one end of the thermocouple extending into the cylindrical fluid channel of the lens pad to the central axis of the cylindrical fluid channel is 0-1 times the inner diameter of the cylindrical fluid channel; preferably 0.1-0.8 times, more preferably 0.2-0.7 times.

[0046] Figure 3 This is another method for installing the thermocouple of the present invention, which is also applicable to tubular reactors, and it is similar to... Figure 2 The difference in the illustrated method is that, in addition to the lens pad fluid channel 301, the lens pad 300 also has two lens pad extension components 302A / B, meaning that one lens pad 300 can be used to mount two thermocouples 303A / B. Based on this idea, if necessary, more extension components can be further provided on the lens pad to install a greater number of thermocouples.

[0047] Figure 4 This is another method for installing the thermocouple of the present invention, which is applicable to a batch reactor, and the method is as follows:

[0048] (1) Provide a seal with an opening;

[0049] (2) Install thermocouple 403 in the opening of the seal; the front end of thermocouple 403 should extend into the internal flow channel 401 of the reactor 400;

[0050] (3) Install the sealing component with the thermocouple in the reactor to be tested. The temperature signal measured by the thermocouple 403 is transmitted to the DCS and / or SIS system through the temperature transmitter system. The minimum distance between the end of the thermocouple that extends into the reactor and the reactor wall 402 is at least 1 mm.

[0051] Example 1

[0052] Used in a tubular LDPE plant with an annual production capacity of 200,000 tons. Figure 1 The thermocouples shown are of the three-wire, six-core type, meaning each thermocouple has six wires forming three measurement circuits. The thermocouples on the tubular reactor are installed as follows: Figure 2 The reactor inlet pressure is 260 MPa, the inlet temperature is 88℃, and the maximum temperature is 320℃. The material emanating from the tubular reactor is depressurized and sent to a high-pressure separator, where the maximum pressure is 30 MPa and the maximum temperature is 280℃. The temperatures measured by each thermocouple are calculated using a 2 / 3 selection method. This reduces the number of shutdowns caused by thermocouples by two per year and extends the thermocouple lifespan by two years.

[0053] Example 2

[0054] Used in a 60,000-ton-per-year batch-process LDPE plant Figure 1 The thermocouple shown is a three-wire, six-core type, meaning each thermocouple has six wires forming three measurement circuits. The thermocouple is installed on the reactor as follows: Figure 4 The reactor inlet pressure is 180 MPa, the inlet temperature is 70℃, and the maximum temperature is 280℃. The material outlet from the batch reactor is sent to a high-pressure separator after pressure reduction. The maximum pressure of the high-pressure separator is 30 MPa, and the maximum temperature is 270℃. The temperatures measured by each thermocouple are calculated using a 2 / 3 selection method. This reduces the number of shutdowns caused by thermocouples by 3 per year and extends the thermocouple lifespan by 2 years.

[0055] Example 3

[0056] Used in a tubular EVA plant with an annual production capacity of 200,000 tons. Figure 1 The thermocouples shown are of the three-wire, six-core type, meaning each thermocouple has six wires forming three measurement circuits. The thermocouples on the tubular reactor are installed as follows: Figure 2The reactor inlet pressure is 260 MPa, the inlet temperature is 80℃, and the maximum temperature is 270℃. The material emanating from the tubular reactor is sent to a high-pressure separator after pressure reduction. The maximum pressure of the high-pressure separator is 30 MPa, and the maximum temperature is 250℃. The temperatures measured by each thermocouple are calculated using a 2 / 3 selection method. This reduces the number of shutdowns caused by thermocouples by 2 per year and extends the thermocouple lifespan by 2 years.

[0057] Comparative Example 1

[0058] Thermocouples are used in a tubular LDPE plant with an annual production capacity of 200,000 tons. The thermocouples are of a single-wire, two-core type, meaning each thermocouple has two wires forming a measurement circuit. The installation method of the thermocouples on the tubular reactor is as follows: Figure 2 The reactor inlet pressure is 260 MPa, the inlet temperature is 88°C, and the maximum temperature is 320°C. The material exiting the tubular reactor is sent to a high-pressure separator after pressure reduction. The maximum pressure of the high-pressure separator is 30 MPa, and the maximum temperature is 280°C. The temperatures measured by thermocouples at various locations within the reactor are determined based on thermocouple readings. Compared to Example 1, the number of shutdowns due to thermocouples increases by two per year.

[0059] Comparative Example 2

[0060] Thermocouples are used in a tubular LDPE plant with an annual production capacity of 200,000 tons. The thermocouples are of a two-couple, four-core type, meaning each thermocouple has two coupling wires forming a measurement circuit. The installation method of the thermocouples on the tubular reactor is as follows: Figure 2 The reactor inlet pressure is 260 MPa, the inlet temperature is 88°C, and the maximum temperature is 320°C. The material emanating from the tubular reactor is sent to a high-pressure separator after pressure reduction. The maximum pressure in the high-pressure separator is 30 MPa, and the maximum temperature is 280°C. The temperature measured by each thermocouple is calculated using the average temperature of two thermocouples. Compared to Example 1, there is one more shutdown per year due to thermocouples.

Claims

1. A thermocouple, characterized in that, The temperature measuring end of the thermocouple includes, from the outside to the inside, a sheath layer, a packing layer, and a wire layer. The packing layer wraps the wire layer, and the sheath layer wraps the packing layer. The wire layer contains at least 6 wires, with 2 wires forming a group. The two wires in the same group are connected at one end, and the other end is led out from the rear end of the thermocouple and connected to the temperature transmitter unit. Among them, the diameter of each lotus root wire is ≤0.4mm, the thickness of the filler layer is ≤0.5mm, the thickness of the sleeve layer is ≤2mm, the inner diameter of the filler layer is ≤2mm, and the inner diameter of the sleeve layer is ≤4mm.

2. The thermocouple according to claim 1, characterized in that, The filler layer is made of magnesium oxide, the axial length of the lotus root fiber layer is ≥20mm, and the length of the sleeve layer is 0.1-0.5m.

3. The thermocouple according to claim 1 or 2, characterized in that, The thermocouple has a thermal response time of ≤1000ms to reach 50% of its sensing response.

4. The thermocouple according to claim 1, characterized in that, The number of lotus root fibers is even, and every two lotus root fibers form a group to form a measurement loop.

5. A method for installing the thermocouple according to claim 1, wherein the thermocouple is installed in a tubular reactor, characterized in that, Includes the following steps: (1) A lens pad with a cylindrical fluid channel is provided, wherein an extension member is provided on the lens pad facing outward, and the extension member has an opening in the middle, the opening being connected to the fluid channel; (2) Install the thermocouple in the opening of the extension of the lens pad, and position the front end of the thermocouple in the fluid channel of the lens pad to contact the fluid to be measured. (3) Install the lens pad with the thermocouple in the pipeline of the tubular reactor to be tested; The temperature signal measured by the thermocouple is transmitted to the DCS and / or SIS system through the temperature transmitter system. The distance from the end of the thermocouple that extends into the cylindrical fluid channel of the lens pad to the central axis of the cylindrical fluid channel is 0-1 times the inner diameter of the cylindrical fluid channel.

6. The thermocouple installation method according to claim 5, characterized in that, The openings for the thermocouple and lens pad extension components are connected by threads.

7. The thermocouple installation method according to claim 5, characterized in that, The distance from one end of the thermocouple inserted into the cylindrical fluid channel of the lens pad to the central axis of the cylindrical channel is 0.1-0.8 times the inner diameter of the cylindrical channel.

8. The thermocouple installation method according to claim 5, characterized in that, The material flow rate in the cylindrical channel of the lens pad is 1-40 m / s, the temperature is 100-350℃, and the pressure is 15-400 MPa.

9. A method for installing the thermocouple according to claim 1, wherein the thermocouple is installed in a batch reactor, characterized in that, Includes the following steps: (1) Provide a seal with an opening; (2) Install the thermocouple in the opening of the seal; (3) Install the sealing component with the thermocouple in the reactor to be tested, and transmit the temperature signal measured by the thermocouple to the DCS and / or SIS system through the temperature transmitter system. The minimum distance between the end of the thermocouple that extends into the reactor and the inner wall of the container is at least 1 mm.

10. A method for temperature measurement using the thermocouples described in claims 1-4, wherein the measured temperature value of the thermocouple is calculated using the following formula: Where T o T is the temperature value output by the temperature transmitter. i T j and T k The temperature values ​​measured for the lotus root fibers in groups i, j, and k are given, where n is the number of lotus root fibers, m is the mode of the temperature values ​​measured for each group of lotus root fibers, and δ is the set value for the deviation of the measured temperature.

11. A method for temperature measurement using the thermocouples described in claims 1-4, wherein the measured temperature value of the thermocouple is calculated using the following formula: Where T o T is the temperature value output by the temperature transmitter. i and T k T represents the temperature values ​​measured for the lotus root fibers in groups i and k. ref The temperature of at least one adjacent thermocouple is used as a reference temperature, x is the correction coefficient for the reference temperature, n is the number of lotus root fibers, m is the mode of the temperature values ​​measured by each group of lotus root fibers, and δ is the deviation setting value for the measured temperature.

Images