Optical fiber sensing on-line monitoring system for temperature of furnace tube of tubular heating furnace

Abstract

The utility model discloses an optical fiber sensing on-line monitoring system for the temperature of a furnace tube of a tubular heating furnace. The optical fiber sensing on-line monitoring system comprises a high-temperature sensor, a heat insulation protection device and a signal processing module, the fiber bragg grating array adopted by the high-temperature sensor is prepared by femtosecond laser direct writing, the fiber bragg grating penetrates into the high-temperature alloy capillary tube with the diameter of 1mm, the high-temperature sensor is used in the temperature range of 450-850 DEG C, and the fiber coating is ceramized when the high-temperature sensor is used, so that the temperature can be measured at the temperature. In actual use, the sensor is bound on the outer wall of a heating coking furnace tube, the surface of the sensor is wrapped by high-temperature asbestos and high-temperature pipe pieces to isolate radiation heat of a heating furnace, and optical signals collected by the array fiber bragg grating at high temperature are demodulated by a demodulator and then transmitted to an upper computer display and a PLC / DCS control system in real time. Accurate on-line measurement of the temperatures of different positions of the coking heating furnace tube is realized.

Description

Technical Field

[0001] This utility model relates to an online monitoring system for the temperature of a tubular heating furnace tube using fiber optic sensing, belonging to the field of temperature monitoring technology. Background Technology

[0002] The coking oven is the core equipment of a delayed coking unit, and its safe operation directly affects the long-term production and economic benefits of the coking unit. To avoid severe coking inside the tubes, it is essential to reduce the local maximum temperature of the tube walls; however, accurately controlling the temperature field of the furnace and tubes has always been a challenging problem. Temperature is one of the fundamental parameters describing thermodynamic processes and is a crucial factor affecting petrochemical safety, control, and efficiency. Monitoring and controlling the temperature field inside the furnace can prevent excessively high furnace outlet temperatures that could lead to coking in the tubes, tube wall overheating, and correct uneven combustion, allowing for timely detection and adjustment. Precise control of the furnace temperature field ensures that the thermodynamic process operates within a set safe and efficient range, thereby extending equipment life and improving production efficiency.

[0003] Currently, the main methods for monitoring the temperature inside petrochemical high-temperature furnaces are as follows:

[0004] The Chinese patent (patent number CN201610122254.X) "Online Monitoring System for Furnace Temperature Based on Acoustic Technology" describes a self-designed electric sound source detection system that transmits sound through a sound wave transmitter and receiver to a sound wave detector, thereby measuring the flue gas temperature at the furnace outlet and monitoring furnace ignition. This method can measure the furnace temperature, but the sound waves are affected by thermal radiation and radiation from other components inside the furnace.

[0005] Traditional methods for measuring furnace temperature include thermocouple measurement and infrared thermal imaging. Thermocouples are installed at different locations within the furnace and on the furnace tubes; however, thermocouples are easily damaged or drift in high-temperature environments, posing significant challenges to process control. Infrared thermal imaging for measuring the surface temperature of coking furnace tubes has limitations, as the instrument cannot be placed too close to the tubes, is affected by flame radiation within the furnace, and is also subject to absorption of infrared radiation by various gases within the furnace. Therefore, the temperature measured using infrared thermal imaging is not the true temperature of the furnace tubes, resulting in significant measurement errors. Thus, a new technology for monitoring the temperature of coking furnace tubes urgently needs to be developed. Utility Model Content

[0006] To address the aforementioned issues, this invention proposes an online fiber optic sensing system for monitoring the temperature of tubular heating furnace tubes. This system enables precise online measurement of the temperature at different locations within the coking furnace tubes, solving the problem of a limited number of measurement points and thus providing a more comprehensive understanding of the actual temperature of the furnace tubes.

[0007] To achieve the above-mentioned utility model, the present utility model adopts the following technical solution:

[0008] An online monitoring system for the temperature of a tubular heating furnace tube using fiber optic sensing, comprising a high-temperature sensor, a thermal insulation protection device, and a signal processing module; characterized in that,

[0009] The high-temperature sensor 3 is a fiber optic grating array cable with a polyimide coating, and is installed inside a high-temperature alloy capillary tube.

[0010] The heat insulation protection device includes a high-temperature coating 1, a high-temperature cover 2, and a high-temperature heat-insulating asbestos 4, which are tied to the outer wall 5 of the tubular heating furnace tube by metal cable ties. The high-temperature cover 2 is a U-shaped metal cover. The high-temperature sensor 3 is installed on the outer wall 5 of the coking heating furnace tube and is covered by the high-temperature cover 2. The high-temperature heat-insulating asbestos 4 is placed between the high-temperature sensor and the high-temperature cover. A layer of high-temperature coating 1 is coated on the outer surface of the high-temperature cover 2 for heat insulation.

[0011] The aforementioned fiber optic sensing online monitoring system for the temperature of a tubular heating furnace tube includes a high-temperature sensor 3 constructed by inserting a fiber optic grating into a high-temperature alloy capillary tube with a diameter of approximately 1 mm.

[0012] The fiber optic sensing online monitoring system for the temperature of a tubular heating furnace tubes, wherein the optical signal collected by the high-temperature sensor 3 at high temperature is transmitted in real time to the instrument room via optical cable, and then processed by the signal processing module before being transmitted to the host computer for display and the health status database.

[0013] The fiber optic sensing online monitoring system for the temperature of a tubular heating furnace tube, wherein the fiber optic grating array is fabricated by femtosecond laser direct writing to obtain the grating array, and the grating array is directly written on the fiber optic cable with a polyimide coating by femtosecond laser.

[0014] The aforementioned fiber optic sensing online monitoring system for the temperature of a tubular heating furnace tube comprises inserting a fiber optic grating into a high-temperature alloy capillary tube with an inner diameter of approximately 0.3 mm and an outer diameter of approximately 1 mm.

[0015] The aforementioned fiber optic sensing online monitoring system for the temperature of a tubular heating furnace tube involves pre-tensioning a fiber optic grating with a certain force through a spiral micro-motion, opening micro-holes in the tube wall approximately every 0.5m, injecting inorganic high-temperature adhesive, and sealing it using laser welding to initially fix the fiber optic grating array.

[0016] When used in a temperature range of 450°C to 850°C, the polyimide coating on the optical fiber undergoes ceramization, ensuring temperature measurement within this range. In practical applications, the sensor is strapped to the outer wall of the heating coking furnace tube, and its exterior is encased in high-temperature asbestos and a high-temperature shroud to isolate it from radiant heat from other heating furnaces. The optical signal collected by the array fiber grating at high temperature is demodulated by a demodulator and transmitted in real time to the host computer display and PLC control system, enabling precise online measurement of the temperature at different locations on the coking furnace tube.

[0017] The polyimide coating is ceramicized at high temperatures ranging from 450 to 850 degrees Celsius, and the outer high-temperature alloy capillary protects it, allowing the sensor to operate normally for a long time at high temperatures.

[0018] The beneficial effects of this utility model are:

[0019] This invention proposes an online monitoring system for the temperature of tubular heating furnace tubes using fiber optic sensing. This system encases the tubes in high-temperature asbestos and a high-temperature enclosure to isolate them from radiant heat from other heating furnaces, enabling precise online measurement of the temperature at different locations within the coking furnace tubes. Fiber optic sensing is characterized by its small size, high sensitivity, resistance to electromagnetic interference, and explosion-proof properties. After being encapsulated in a high-temperature alloy capillary tube, it is suitable as a sensor for the complex environments of petrochemical pipelines, solving the problem of a limited number of measurement points. This allows for a more comprehensive understanding of the actual temperature of the furnace tubes, overcoming the drawbacks of traditional monitoring methods, such as the need for time-consuming and labor-intensive periodic manual inspections and poor resistance to sudden risks, thus improving production safety.

[0020] The applicant used a polyimide-coated fiber grating array to monitor the temperature field of the furnace tube, which achieved excellent results. It can accurately understand the operating status of the coking furnace, provide reliable assurance, and generate significant economic benefits. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the fiber optic grating linear sensing system for online distributed measurement of temperature in petrochemical coking furnace tubes, as described in this utility model.

[0022] Figure 2 This is a schematic diagram of the installation of the high-temperature sensor of this utility model. Detailed Implementation

[0023] The following detailed description, in conjunction with specific embodiments and accompanying drawings, provides a further description of the fiber optic sensing online monitoring system for the temperature of a tubular heating furnace tube according to this utility model.

[0024] like Figure 1As shown, this utility model discloses an online fiber optic sensing system for monitoring the temperature of a tubular heating furnace tube. The system mainly consists of a high-temperature linear sensing fiber optic cable, a signal processing system, and a data acquisition and communication system. The high-temperature linear sensing fiber optic cable senses changes in the furnace tube temperature in real time and transmits the collected signal to the control room via a cable approximately 150m long. In the control room (instrument room), the optical signal is received, the signal processing system decouples and converts the signal into a digital signal, thereby obtaining information such as the furnace tube temperature and accurate position, and displaying the data in real time on a host computer. Specifically, this utility model uses a high-temperature fiber optic grating array cable as the high-temperature sensor.

[0025] The high-temperature sensor is installed on the outer wall of the coking furnace tube through a heat insulation protection device, such as... Figure 2 As shown, the heat insulation protection device includes: a high-temperature coating 1, a high-temperature cover 2, and high-temperature insulating asbestos 4. A high-temperature sensor 3 is installed close to the outer wall 5 of the coking furnace tube, with the high-temperature cover 2 covering it. High-temperature insulating asbestos is placed between the high-temperature sensor and the high-temperature cover. A layer of high-temperature coating is applied to the outer surface of the high-temperature cover 2 for heat insulation. The high-temperature coating consists of two parts: SL8306 high-temperature resistant adhesive and powdered zirconium oxide. First, SL8306 high-temperature resistant adhesive is applied to the metal surface, and then a dense layer of powdered zirconium oxide is sprinkled on top of the SL8306 high-temperature resistant adhesive to form the high-temperature coating, thus isolating the radiant heat of the furnace and reducing the influence of the external environment on the high-temperature sensor. The high-temperature sensor 3 has a diameter of 1 mm, and the high-temperature cover has a diameter of 5-10 mm.

[0026] The specific embodiments of this utility model are explained in further detail below:

[0027] See Figure 2 As shown, the present invention provides an online monitoring system for the temperature of a tubular heating furnace tube using fiber optic sensing, comprising a high-temperature sensor, a thermal insulation protection device, a fiber optic grating wavelength signal demodulation module, an industrial control computer, etc.

[0028] The high-temperature sensor 3 is a high-temperature fiber optic grating array cable with a polyimide coating, and is installed inside a high-temperature alloy capillary tube; the heat insulation protection device includes a high-temperature coating 1, a high-temperature cover 2, and a high-temperature heat-insulating asbestos 4, which are tied to the outer wall 5 of the coking furnace tube by metal cable ties. The high-temperature cover 2 is a U-shaped metal cover. The high-temperature sensor 3 is installed on the outer wall 5 of the coking furnace tube and is covered by the high-temperature cover 2. The high-temperature heat-insulating asbestos 4 is placed between the high-temperature sensor and the high-temperature cover. A layer of high-temperature coating 1 is coated on the outer surface of the high-temperature cover 2 for heat insulation.

[0029] The fiber Bragg grating array used in this system is fabricated using femtosecond laser direct writing. The high-temperature sensor inserts the fiber Bragg grating into a 1mm diameter high-temperature alloy capillary tube and operates within a temperature range of 450°C to 850°C. During operation, the polyimide coating of the fiber undergoes ceramization. This serves two purposes: first, it further enhances the protection of the fiber; the ceramized coating exhibits better high-temperature resistance and corrosion resistance, effectively preventing damage to the fiber itself from high-temperature environments and extending the service life of the fiber Bragg grating; second, the ceramized coating maintains stable physical and chemical properties at high temperatures, without significant expansion, contraction, or other deformation due to temperature changes. This ensures the fiber Bragg grating can operate normally in high-temperature environments, enabling accurate temperature measurement and guaranteeing the accuracy and stability of the measurement results within this temperature range. In actual use, this high-temperature sensor is tied to the outer wall of the heating coking furnace tube. Its outer surface is wrapped with high-temperature asbestos and a high-temperature cover 2 to isolate it from the radiant heat of other heating furnaces. The optical signal collected by the array fiber optic grating at high temperature is demodulated by the demodulator and transmitted in real time to the host computer display and PLC control system, so as to realize the accurate online measurement of the temperature at different positions of the coking furnace tube.

[0030] The grating array is directly written onto the polyimide-coated optical fiber using a femtosecond laser, eliminating the need for a stripping and recoating process. This femtosecond laser direct-write grating avoids performance degradation at high temperatures.

[0031] The fiber grating array is inserted into a high-temperature alloy tube with an inner diameter of about 0.3 mm and an outer diameter of about 1 mm. A certain force is pre-stressed by spiral micro-motion (existing technology). Inorganic high-temperature adhesive is injected into the micro-holes on the outer wall of the tube every 0.5 m and sealed by laser welding, so that the fiber grating array is initially fixed. The polyimide coating is ceramicized at a high temperature of 450 to 850 degrees Celsius, and the outer high-temperature alloy capillary protects it. The sensor can work normally for a long time at high temperature.

[0032] The demodulation instrument requires power. Since the light source module and signal demodulation components in the instrument require power and heat dissipation, the demodulation instrument has a low explosion-proof rating. The separation of the unpowered probe from the signal demodulation system is a characteristic of fiber optic sensing and monitoring. Based on this characteristic, the signal demodulation system will be placed in the central control room for demodulation.

[0033] A coupled thermodynamic model under high-temperature load was established, and the temperature and stress characteristics of the sensor were studied and simulated using finite element software to determine the optimal structure and size parameters of the FBG sensor probe.

[0034] An analysis model of FBG coupling effect was established, and the optical characteristics of FBG were simulated and analyzed using optical software. A method for suppressing interference noise of fiber optic FBG high-temperature sensor was proposed to overcome the problems of cross-sensitivity of multiple physical parameters and accurate orientation measurement.

Claims

1. A fiber optic sensing online monitoring system for the temperature of a tubular heating furnace tube, comprising a high-temperature sensor, a thermal insulation protection device, and a signal processing module; characterized in that, The high-temperature sensor (3) is a fiber optic grating array cable with a polyimide coating, and is installed inside a high-temperature alloy capillary. The heat insulation protection device includes a high-temperature coating (1), a high-temperature cover (2), and a high-temperature heat-insulating asbestos (4), which are tied to the outer wall (5) of the tubular heating furnace tube by metal cable ties. The high-temperature cover (2) is a U-shaped metal cover. The high-temperature sensor (3) is installed on the outer wall (5) of the coking heating furnace tube and is covered by the high-temperature cover (2). The high-temperature heat-insulating asbestos (4) is placed between the high-temperature sensor and the high-temperature cover. A layer of high-temperature coating (1) is coated on the outer surface of the high-temperature cover (2) for heat insulation.

2. The on-line monitoring system for the temperature of the furnace tube of the tubular heating furnace according to claim 1, characterized in that, The high-temperature sensor (3) is constructed by inserting a fiber optic grating into a high-temperature alloy capillary tube with a diameter of about 1 mm.

3. The on-line monitoring system for the temperature of the furnace tube of a tubular heating furnace according to claim 1, characterized in that, The fiber grating array optical cable is fabricated by femtosecond laser direct writing to obtain the grating array, which is directly written on the optical fiber with a polyimide coating by femtosecond laser.

4. The on-line monitoring system for the temperature of the furnace tube of a tubular heating furnace according to claim 2, characterized in that, The fiber grating is inserted into the high-temperature alloy capillary tube with an inner diameter of about 0.3 mm and an outer diameter of about 1 mm.

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