Reboiler flue gas heat recovery system and control method thereof

Abstract

The present application discloses a kind of reboiler flue gas heat recovery system and control method thereof, it is related to natural gas dehydration production equipment technical field.The exhaust section of reboiler of the present application is sequentially arranged reboiler flue, flue gas bypass regulating valve and reboiler chimney, heat exchange flue gas pipeline is connected with flue gas inlet valve from reboiler flue, oxygen content sensor, temperature sensor I and pressure sensor are set on the pipeline before valve of flue gas inlet valve, the pipeline after valve of flue gas inlet valve is connected flue gas heat exchanger, the flue gas outlet end of flue gas heat exchanger is connected with the inlet end of induced draft fan by pipeline, and temperature sensor II is arranged on the pipeline between flue gas heat exchanger and induced draft fan, the gas inlet of flue gas outlet valve is connected with the outlet end of induced draft fan, and the outlet of flue gas outlet valve is communicated with reboiler chimney;Control subsystem controls the opening and closing and opening degree of flue gas bypass regulating valve according to the data of oxygen content sensor and pressure sensor, and controls the rotating speed of induced draft fan.The present application promotes that flue gas heat recovery system follows triethylene glycol regeneration load and carries out time-varying regulation, to cope with the complex change in actual production.

Description

Technical Field

[0001] This invention relates to the petroleum gas industry, specifically to the field of natural gas dehydration production equipment technology, and more specifically to a reboiler flue gas heat recovery system and its control method. Background Technology

[0002] In the oil and gas industry, natural gas needs to be extracted from underground formations. The high water content in this natural gas can easily lead to ice blockage, and the presence of condensate accelerates corrosion of subsequent pipelines and equipment. Therefore, dehydration treatment is necessary. In low-temperature separation and solvent absorption dehydration processes, reboilers are required to regenerate the low-temperature ethylene glycol / triethylene glycol-rich solution. Reboilers using natural gas as a heating energy source simultaneously emit large amounts of high-temperature flue gas, resulting in heat emissions and energy waste. In actual production, due to variations in production load and lag in the reboiler's air distribution system, the flue gas emissions and their contained heat energy fluctuate significantly, exacerbating heat waste and leading to low reboiler thermal efficiency.

[0003] Reboilers are essential equipment in the dehydration process of natural gas production. Existing reboilers use fuel gas from the plant as input energy to heat the rich solution, evaporating the moisture and producing lean solution for natural gas dehydration and recycling. The Shunan Gas Field has 9 dehydration stations with 7 single-well dehydration facilities, with a dehydration capacity of 42.73 million cubic meters per day.

[0004] Flue gas heat emissions are a key factor affecting reboiler efficiency. When using reboilers to heat rich liquor, especially triethylene glycol-rich liquor, the exhaust gas temperature is high, resulting in significant heat emissions. Even with a conventional reboiler design efficiency of 85%, the heat loss from flue gas emissions can reach 10%. For reboilers operating year-round, the increase in fouling inside and outside the fire tubes leads to a decrease in reboiler efficiency, and consequently, a gradual increase in flue gas heat loss. Furthermore, traditional reboilers use fuel gas ejector-type air supply with manually adjustable inlet valves, making it difficult to adjust the air volume in a timely manner according to production capacity. Insufficient air volume at high production loads leads to incomplete combustion, while excessive air volume at low production loads further increases flue gas losses. Consequently, the reboiler's thermal efficiency declines significantly, dropping to as low as 50-60%.

[0005] Flue gas heat recovery is a comprehensive and final-line guarantee for improving system thermal efficiency. When reboilers operate at low efficiency, almost all unused heat energy is emitted as flue gas heat. Therefore, recovering heat energy from the final emission flue gas is an effective measure to improve system thermal efficiency. Simultaneously, it can address increased heat emissions caused by any influencing factors at the system's upstream end, and since the heat recovery stage is at the final emission point, it provides the final-line heat recovery guarantee for the system. However, reboiler flue gas heat emissions are time-varying; flow rate and temperature fluctuate with changes in production volume, ambient temperature, and local air pressure. Therefore, effective flue gas heat recovery is a key challenge.

[0006] The variability of reboiler systems during operation is the biggest obstacle to achieving flue gas heat recovery. Due to the combined and complex influence of various parameters at different nodes, the reboiler's production load, air volume, and flue gas heat emissions are all time-varying, characterized by rapid changes, large fluctuations, and the need for timely responses. Excessive changes can cause significant fluctuations in the flow field of the reboiler combustion chamber. Therefore, for flue gas heat recovery systems, the most concrete challenge and the biggest obstacle to achieving flue gas heat recovery is how to establish a control algorithm that can follow the system's amplitude requirements and respond quickly to system changes, and apply it to actual production. Summary of the Invention

[0007] To overcome the defects and shortcomings of the existing technology, this invention provides a reboiler flue gas heat recovery system and its control method. The purpose of this invention is to establish a recovery system and control method that can quickly respond to system changes by following the amplitude requirements of the system. The reboiler flue gas heat recovery system provided by this invention includes a reboiler, a flue gas heat exchanger, and a control subsystem. The exhaust section of the reboiler is sequentially equipped with a reboiler exhaust duct, a flue gas bypass regulating valve, and a reboiler chimney. A heat exchange flue gas pipeline is led out from the reboiler exhaust duct and connected to the flue gas inlet valve. An oxygen content sensor, a temperature sensor I, and a pressure sensor are installed on the pipeline before the flue gas inlet valve. The pipeline after the flue gas inlet valve is connected to the flue gas heat exchanger. The flue gas outlet end of the flue gas heat exchanger is connected to the inlet end of the induced draft fan through a pipeline. Furthermore, a control subsystem is installed on the pipeline between the flue gas heat exchanger and the induced draft fan. A temperature sensor II is installed, and the outlet of the induced draft fan is connected to the inlet of the flue gas outlet valve. The outlet of the flue gas outlet valve is connected to the reboiler chimney. The control subsystem is electrically connected to the flue gas bypass regulating valve, the flue gas inlet valve, the oxygen content sensor, the temperature sensor I, the pressure sensor, the induced draft fan, the temperature sensor II, and the flue gas outlet valve. Based on the data collected by the oxygen content sensor, the temperature sensor I, the pressure sensor, and the temperature sensor II, the control subsystem controls the opening and closing of the flue gas bypass regulating valve, the flue gas inlet valve, and the flue gas outlet valve, as well as the opening speed of the induced draft fan. This invention, through the setting of sensor components and valves at various pipeline locations, enables the flue gas heat recovery system to adjust in a time-varying manner according to the triethylene glycol regeneration load, in order to cope with the complex changes in natural gas production, flue gas flow rate, flue gas temperature, local air temperature, local gas pressure, and natural gas water content in actual production.

[0008] To address the problems existing in the prior art, the present invention is achieved through the following technical solution.

[0009] The first aspect of this invention provides a reboiler flue gas heat recovery system. The system includes a reboiler, a flue gas heat exchanger, and a control subsystem. The reboiler's exhaust section is sequentially equipped with a reboiler exhaust duct, a flue gas bypass regulating valve, and a reboiler chimney. A heat exchange flue gas pipe is led out from the reboiler exhaust duct and connected to a flue gas inlet valve. An oxygen content sensor, a temperature sensor I, and a pressure sensor are installed on the pipe upstream of the flue gas inlet valve. The pipe downstream of the flue gas inlet valve is connected to the flue gas heat exchanger. The flue gas outlet of the flue gas heat exchanger is connected to the inlet of an induced draft fan via a pipe. The flue gas heat exchanger and the induced draft fan are connected... Temperature sensor II is installed on the pipeline. The outlet of the induced draft fan is connected to the inlet of the flue gas outlet valve, and the outlet of the flue gas outlet valve is connected to the reboiler chimney. The control subsystem is electrically connected to the flue gas bypass regulating valve, the flue gas inlet valve, the oxygen content sensor, the temperature sensor I, the pressure sensor, the induced draft fan, the temperature sensor II, and the flue gas outlet valve. The control subsystem controls the opening and closing and the degree of opening of the flue gas bypass regulating valve, the flue gas inlet valve, and the flue gas outlet valve, as well as the speed of the induced draft fan, based on the data collected by the oxygen content sensor, the temperature sensor I, the pressure sensor, and the temperature sensor II.

[0010] More preferably, the induced draft fan is a variable frequency high-temperature induced draft fan.

[0011] More preferably, the rated operating frequency of the induced draft fan is 5Hz-50Hz.

[0012] More preferably, the control subsystem controls the speed of the induced draft fan by controlling the change in the operating frequency of the induced draft fan.

[0013] More preferably, after the control subsystem controls the induced draft fan to start at 5Hz, it increases the speed to the range corresponding to the reboiler load conditions at a fixed rate of 2Hz per second.

[0014] More preferably, the flue gas bypass regulating valve corresponds to the process of closing and fully opening respectively from 0% to 100%. When the control subsystem controls the flue gas bypass regulating valve to close, the change rate is 2% per second for the 0%-40% stage; 1% per second for the 40%-80% stage; and 2% per second for the 80%-100% stage.

[0015] More preferably, the flue gas heat exchanger is provided with a rich liquid inlet and a rich liquid outlet. The rich liquid that enters the flue gas heat exchanger through the rich liquid inlet is heated in the flue gas heat exchanger and then discharged from the rich liquid outlet.

[0016] More preferably, the reboiler is provided with a fuel gas inlet and an air inlet. When the fuel gas enters the reboiler through the fuel gas inlet, the air from the air inlet is drawn into the reboiler.

[0017] More preferably, an air regulating valve is provided at the air inlet.

[0018] More preferably, during the operation of the reboiler, the air regulating valve is configured to be opened at its maximum degree.

[0019] More preferably, the control subsystem is an industrial control computer.

[0020] A second aspect of the present invention provides a control method for a reboiler flue gas heat recovery system based on the first aspect described above, the control method comprising: S1. Power-on control steps, specifically including S101, The control subsystem controls the opening of the flue gas inlet valve and the flue gas outlet valve; S102, The control subsystem controls the flue gas bypass valve to close and simultaneously starts the induced draft fan; The flue gas bypass valve corresponds to fully closed and fully open at 0%-100% respectively. When the control subsystem controls the flue gas bypass regulating valve to close, the change rate is 2% per second for the 0%-40% stage; 1% per second for the 40%-80% stage; and 2% per second for the 80%-100% stage. When the control subsystem starts the induced draft fan, it starts the induced draft fan at the rated frequency of 5Hz and increases the speed of the induced draft fan to the speed range corresponding to half load condition of reboiler at a fixed rate of 2Hz per second. S2. Stable operation control steps, specifically including S201. The control subsystem collects the detection value of the oxygen content sensor and makes a coarse adjustment to the speed of the induced draft fan based on the detection value of the oxygen content sensor. S202. The control subsystem collects the detection value of the pressure sensor and finely adjusts the speed of the induced draft fan based on the detection value of the pressure sensor. S3. Shutdown control procedure: Open the flue gas bypass regulating valve from completely closed to fully open at a rate of 2% per second. When the opening of the flue gas bypass regulating valve is 80%, the control subsystem directly shuts down the induced draft fan. After shutting down the induced draft fan, the flue gas inlet valve and the flue gas outlet valve are closed.

[0021] In a further preferred embodiment, in step S201, the target value for coarse adjustment of the induced draft fan is based on the average parameter corresponding to the oxygen content sensor in the previous 3 seconds. The coarse adjustment target value is calculated by making a difference based on the calibrated reference point. The calibrated reference point refers to the point formed by calibrating the commonly used points and the corresponding induced draft fan speed during the initial operation and debugging.

[0022] A further preferred method involves calculating the coarse adjustment target value of the induced draft fan based on the oxygen content sensor parameters. After long-term operation under multiple operating conditions, the control subsystem performs fourth-order polynomial fitting based on the statistical data from the long-term operation under multiple operating conditions to obtain the calculation method for the coarse adjustment target value of the induced draft fan.

[0023] In a further preferred embodiment, in step S202, the target value for fine-tuning the induced draft fan is, after the induced draft fan has been coarsely adjusted and the target value for coarse adjustment has been reached, the median value of the data collected by the pressure sensor is used as the control value to adjust the induced draft fan's transmission.

[0024] Compared with the prior art, the beneficial technical effects of the present invention are as follows: 1. This invention provides a reboiler flue gas heat recovery system, which achieves the following objectives by incorporating a flue gas heat exchanger, key valves, a variable frequency high-temperature induced draft fan, temperature sensors, pressure sensors, flue gas ducts, and bypass pipelines: (1) Realize the heat recovery and utilization of reboiler flue gas. Through a flue gas heat exchanger device, fully utilize the waste heat of flue gas to heat triethylene glycol-rich liquid; (2) Increase the temperature of the triethylene glycol-rich liquid and reduce the energy consumption of the reboiler to achieve dual energy saving. By preheating the triethylene glycol, the temperature of the triethylene glycol entering the reboiler is increased, reducing the temperature rise that needs to be heated in the reboiler, which can reduce the consumption of reboiler fuel gas; (3) By using the strategy of controlling valves + variable frequency high temperature induced draft fan + control method, the flue gas heat recovery system is made to adjust in time according to the triethylene glycol regeneration load to cope with the complex changes in natural gas production, flue gas flow rate, flue gas temperature, local air temperature, local gas pressure, natural gas water content, etc. in actual production. (4) Data is collected by various sensors distributed throughout the system to support the calculation, operation and judgment of the control algorithm, thereby effectively regulating the flue gas heat recovery system; at the same time, more intelligent algorithms can be incorporated into the control algorithm to control the excess air coefficient of the reboiler combustion within the specified range and improve the intelligence and self-decision performance of the control.

[0025] 2. This invention recovers heat from reboiler flue gas to heat triethylene glycol-rich liquor, reducing flue gas heat emissions and achieving energy saving through heat recovery. It reduces the temperature rise of the triethylene glycol-rich liquor in the reboiler, thereby reducing fuel gas consumption and achieving energy saving. The system + intelligent control method addresses various time-varying characteristics of the production system, ensuring efficient overall system operation. The intelligent adjustment system relies on sensor data collection and operates intelligently according to set targets, requiring minimal human intervention and offering high reliability. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the reboiler flue gas heat recovery system of the present invention; Reference numerals in the attached diagram: 1. Reboiler, 2. Air inlet, 3. Fuel gas inlet, 4. Rich liquor outlet, 5. Rich liquor inlet, 6. Reboiler flue gas duct, 7. Flue gas bypass regulating valve, 8. Reboiler chimney, 9. Flue gas inlet valve, 10. Oxygen content sensor, 11. Temperature sensor I, 12. Pressure sensor, 13. Flue gas heat exchanger, 14. Temperature sensor II, 15. Exhaust fan, 16. Flue gas outlet valve. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 In a preferred embodiment of the present invention, refer to the appendix to the specification. Figure 1 The following is a detailed description: This embodiment carefully constructs a reboiler flue gas heat recovery system. The system mainly consists of three key parts: a reboiler 1, a flue gas heat exchanger 13, and a control subsystem.

[0029] The exhaust section of reboiler 1 features an ingenious structural design, with a reboiler exhaust duct 6, a flue gas bypass regulating valve 7, and a reboiler chimney 8 arranged sequentially and rationally. The heat exchange flue gas pipe cleverly led from the reboiler exhaust duct 6 is tightly connected to the flue gas inlet valve 9. At the critical point of the pipe before the flue gas inlet valve 9, an oxygen content sensor 10, a temperature sensor I 11, and a pressure sensor 12 are precisely installed. These sensors act like sensitive sensory organs, capable of collecting relevant data information in real time and accurately. The pipe after the flue gas inlet valve 9 smoothly connects to the flue gas heat exchanger 13, where the flue gas enters the crucial process of heat exchange after passing through the valve. The flue gas outlet of the flue gas heat exchanger 13 is seamlessly connected to the inlet of the induced draft fan 15 via a dedicated pipe, and a temperature sensor II 14 is cleverly arranged on the pipe between the flue gas heat exchanger 13 and the induced draft fan 15 to accurately monitor the flue gas temperature at this stage. The outlet of the induced draft fan 15 is connected to the inlet of the flue gas outlet valve 16, and the outlet of the flue gas outlet valve 16 is ultimately connected to the reboiler chimney 8, thereby ensuring that the entire flue gas flow path is complete and smooth.

[0030] The reboiler 1 is also equipped with an air inlet 2, a fuel gas inlet 3, a rich liquid outlet 4, and a rich liquid inlet 5. These components work together to ensure the normal operation and function of the reboiler 1.

[0031] The control subsystem plays a crucial "brain" role in the entire system. It establishes a close information exchange network with the flue gas bypass regulating valve 7, flue gas inlet valve 9, oxygen content sensor 10, temperature sensor I 11, pressure sensor 12, induced draft fan 15, temperature sensor II 14, and flue gas outlet valve 16 through electrical connections. Leveraging its powerful data processing and analysis capabilities, the control subsystem skillfully and precisely controls the opening and closing actions and precise adjustments of the opening degree of the flue gas bypass regulating valve 7, flue gas inlet valve 9, and flue gas outlet valve 16 based on the rich and real-time data collected by the oxygen content sensor 10, temperature sensor I 11, pressure sensor 12, and temperature sensor II 14. Simultaneously, it can also flexibly and appropriately control the rotational speed of the induced draft fan 15. Through this intelligent and automated control method, the entire reboiler flue gas heat recovery system can operate efficiently and stably, maximizing the recovery and utilization of flue gas heat energy, effectively improving energy utilization efficiency, reducing energy waste, and making outstanding contributions to energy conservation and emission reduction in related industrial production processes. Furthermore, it demonstrates significant advantages in terms of system stability, reliability, and operability, effectively ensuring the continuous and stable progress of the production process.

[0032] Example 2 In another preferred embodiment of the present invention, this embodiment is based on the above embodiment 1, and provides a more in-depth and detailed supplement and explanation of the technical solution of the present invention.

[0033] In the reboiler flue gas heat recovery system constructed in this embodiment, the induced draft fan is a variable frequency high-temperature resistant induced draft fan 15, which has unique performance parameters and a rated operating frequency in the range of 5Hz-50Hz. The control subsystem utilizes precise regulation of the operating frequency of the induced draft fan 15 to effectively control its speed. For example, at the initial stage of system startup, the control subsystem first controls the induced draft fan 15 to start smoothly at a frequency of 5Hz, and then steadily increases its speed at a fixed rate of 2Hz per second until it reaches a speed range that is compatible with the load conditions of the reboiler 1. This ensures that the entire system can operate stably and efficiently under different operating conditions, fully utilize the efficiency of flue gas heat recovery, and also ensure the operational safety and reliability of the induced draft fan 15, avoiding damage to the equipment due to abnormal situations such as sudden changes in speed, extending the service life of the equipment, reducing equipment maintenance costs and downtime, and providing strong support for the continuity of industrial production.

[0034] Furthermore, the opening adjustment of the flue gas bypass regulating valve 7 follows a specific pattern and rate setting. The 0%-100% range corresponds to the closing-to-fully-opening process. When the control subsystem controls the flue gas bypass regulating valve 7 to close, the rate of change is set to 2% per second in the 0%-40% stage; 1% per second in the 40%-80% stage; and 2% per second in the 80%-100% stage. This phased rate control method allows the flue gas bypass regulating valve 7 to more precisely regulate the flue gas flow during opening and closing, achieving reasonable distribution of flue gas and optimization of heat recovery according to the actual needs of the system. This effectively avoids problems such as system instability, heat waste, or equipment damage caused by the regulating valve operating too quickly or too slowly, further improving the control accuracy and operational stability of the entire reboiler flue gas heat recovery system.

[0035] The flue gas heat exchanger 13 is structurally designed with a rich liquid inlet and a rich liquid outlet. The rich liquid enters the flue gas heat exchanger 13 through the rich liquid inlet. During its flow through the heat exchanger 13, it fully utilizes the thermal energy of the flue gas to heat itself, and after completing the heat exchange process, it is smoothly discharged from the rich liquid outlet. This rich liquid circulation heating process not only achieves effective recovery and utilization of flue gas thermal energy, transferring potentially wasted thermal energy to the rich liquid and raising its temperature to provide thermal support for subsequent related processes, but also improves the overall energy utilization efficiency of the system. This aligns with the industrial development concept of energy conservation and emission reduction, reduces the company's energy costs, and enhances the company's competitiveness in the market.

[0036] The reboiler 1 itself comprises a fuel gas inlet and an air inlet. When the fuel gas enters the reboiler 1 through the fuel gas inlet, it draws air from the air inlet into the reboiler 1 to participate in the combustion reaction and related processes. Specifically, an air regulating valve is carefully installed at the air inlet, and this valve is set to its maximum opening state during the operation of the reboiler 1. This configuration ensures a sufficient air supply, allowing the fuel to burn completely within the reboiler 1, improving combustion efficiency, reducing the generation of incomplete combustion products, and lowering pollutant emissions. It also helps maintain the stability and uniformity of the combustion process within the reboiler 1, ensuring a continuous and stable output of heat energy. This provides a reliable heat energy source for the normal operation of the reboiler flue gas heat recovery system, enhancing the reliability and safety of the entire system.

[0037] Finally, the control subsystem in this embodiment uses an industrial PC or a host computer. Leveraging their powerful data processing capabilities, abundant interface resources, and high reliability, these systems can accurately receive and process large amounts of data collected from various sensors, such as oxygen sensor 10, temperature sensor I 11, pressure sensor 12, and temperature sensor II 14. Then, based on pre-set control algorithms and logic, they quickly and accurately issue control commands to devices such as the flue gas bypass regulating valve 7, flue gas inlet valve 9, flue gas outlet valve 16, and induced draft fan 15, achieving automated and intelligent operation management of the entire reboiler flue gas heat recovery system. Whether in real-time equipment monitoring, fault diagnosis and early warning, or optimization and adjustment of system operating parameters, the industrial PC or host computer demonstrates superior performance advantages, providing solid technical guarantees and support for efficient, stable, and safe operation in industrial production processes.

[0038] Example 3 In this preferred embodiment of the present invention, the technical solution of the present invention is supplemented and explained in more detail based on the above embodiment 1 or embodiment 2.

[0039] like Figure 1 As clearly shown, in the original structure of reboiler 1, only a reboiler chimney 8 was equipped to perform the flue gas emission task. However, in this embodiment, the flue gas exhaust section of reboiler 1 is carefully planned and laid out, with the reboiler exhaust duct 6, the flue gas bypass regulating valve 7, and the reboiler chimney 8 arranged sequentially. Furthermore, a pipe is cleverly led out from the reboiler exhaust duct 6 and tightly connected to the flue gas inlet valve 9. Simultaneously, an oxygen content sensor 10, a temperature sensor I 11, and a pressure sensor 12 are precisely installed on the pipe section before the flue gas inlet valve 9. The rear end of the flue gas inlet valve 9 is firmly connected to the flue gas heat exchanger 13, thereby continuously and smoothly connecting to the inlet end of the variable frequency high-temperature flue gas induced draft fan 15. It is worth mentioning that a temperature sensor II 14 is specifically arranged on the pipe between the flue gas heat exchanger 13 and the variable frequency high-temperature flue gas induced draft fan 15. The outlet of the variable frequency high-temperature flue gas induced draft fan 15 is connected to the inlet of the flue gas outlet valve 16, and finally the outlet of the flue gas outlet valve 16 is effectively connected to the reboiler chimney 8. On the other side of the flue gas heat exchanger 13, there are also rich liquid inlet and rich liquid outlet connected, and the rich liquid can be fully heated inside the flue gas heat exchanger 13.

[0040] In the original reboiler 1 operating mode, when fuel gas is introduced through the fuel gas inlet, its high-speed combustion gases draw air from the air inlet into the reboiler 1 for combustion. However, because the air inlet regulating valve is manually opened to its maximum state to meet full-load requirements, a large excess air coefficient occurs, resulting in a significant waste of heat. In the entire heat recovery system constructed in this invention, the control subsystem plays a crucial role, enabling real-time and precise collection of various parameters during system operation. By implementing precise control operations on the flue gas bypass regulating valve 7, flue gas inlet valve 9, flue gas outlet valve 16, and variable frequency high-temperature flue gas induced draft fan 15, the control system can automatically adjust and control the combustion air distribution inside the reboiler 1, thereby ensuring that the combustion process inside the furnace remains stable and reliable.

[0041] Specifically, the control subsystem uses oxygen sensor 10 and pressure sensor 12 to monitor the flue gas status in real time, thereby effectively controlling the variable frequency high-temperature flue gas induced draft fan 15 to precisely adjust the flue gas flow field. The excess air coefficient in the reboiler 1 under this condition can be calculated from the parameters returned by oxygen sensor 10. Subsequently, the speed of the variable frequency high-temperature flue gas induced draft fan 15 is adjusted to achieve precise airflow regulation. It should be noted that the parameter changes returned by oxygen sensor 10 are relatively slow compared to the changes in the combustion state in reboiler 1, while pressure sensor 12 can collect changes in the flue gas flow field in real time. Therefore, using the flue gas pressure corresponding to a specified excess air coefficient range as the target value, within a small range, the pressure at the location of pressure sensor 12 is kept within the target value range by cleverly adjusting the speed of the variable frequency high-temperature flue gas induced draft fan 15. During the heat exchange process, the rich liquid flows into the flue gas heat exchanger 13 from the rich liquid inlet, fully absorbing the waste heat carried by the flue gas. After being heated, it is smoothly returned to the original system from the rich liquid outlet, thus realizing the effective recovery and utilization of the waste heat of the flue gas, improving the energy utilization efficiency of the entire system, reducing energy waste and loss, and providing strong technical support and guarantee for energy conservation, emission reduction and sustainable development in industrial production.

[0042] Example 4 In this superior embodiment of the present invention, this embodiment focuses on the control method of the reboiler flue gas heat recovery system constructed based on the above embodiment 1, embodiment 2 or embodiment 3, and conducts an in-depth discussion and explanation.

[0043] The first step is the power-on control step S1, which includes the following key sub-steps: S101, the control subsystem precisely controls the opening of the flue gas inlet valve 9 and the flue gas outlet valve 16, thereby ensuring that the flow path of the flue gas in the system is initially established, laying the foundation for the subsequent introduction and treatment of flue gas.

[0044] S102. The control subsystem orderly controls the closure of the flue gas bypass valve 7, and simultaneously starts the induced draft fan 15. During the closure control of the flue gas bypass valve 7, it follows a specific opening change pattern, i.e., 0%-100% corresponds to complete closure and complete opening, respectively. Furthermore, when the control subsystem controls the closure of the flue gas bypass regulating valve 7, the rate of change is set to 2% per second in the 0%-40% stage; 1% per second in the 40%-80% stage; and 2% per second in the 80%-100% stage. This phased rate of change control allows the flue gas bypass valve 7 to smoothly transition during closure, avoiding any impact on the system. When the control subsystem starts the induced draft fan 15, it first starts the fan at a rated frequency of 5Hz, and then gradually increases the speed of the fan 15 at a fixed rate of 2Hz per second to the speed range corresponding to half-load conditions of the reboiler 1. This startup method ensures that the induced draft fan 15 starts smoothly and can quickly adapt to the operating requirements of the reboiler 1, providing a good start for the stable operation of the system.

[0045] Next is the stable operation control step S2, which includes the following important contents: S201. The control subsystem continuously collects the detection values ​​from the oxygen content sensor 10 and coarsely adjusts the speed of the induced draft fan 15 based on these values. During this process, the target value for coarse adjustment of the induced draft fan 15 is calculated by subtracting the average parameter from the oxygen content sensor 10 over the previous 3 seconds, using a calibrated reference point. This calibrated reference point is the one established during initial operation and debugging, after calibrating commonly used points with the corresponding induced draft fan 15 speeds. Furthermore, after a long period of operation under multiple operating conditions, the control subsystem performs a fourth-order polynomial fitting based on the statistical data from this long-term operation, resulting in a more accurate calculation method for the target value of coarse adjustment of the induced draft fan 15. In this way, during stable system operation, the speed of the induced draft fan 15 can be initially and relatively accurately adjusted based on the feedback from the oxygen content sensor 10 to maintain a relatively stable combustion process and a reasonable excess air coefficient within the system.

[0046] S202. The control subsystem collects the detection value from pressure sensor 12 and fine-tunes the rotational speed of induced draft fan 15 based on the detection value. The target value for fine-tuning induced draft fan 15 is determined after coarse adjustment, using the median value of the data collected by pressure sensor 12 as the control value, to further refine the rotational speed of induced draft fan 15. Since pressure sensor 12 can reflect changes in the flue gas flow field in real time, using its median value as the control value for fine-tuning allows for more precise control of the flue gas flow field. This ensures the system maintains stable and efficient operation under various working conditions, maximizing the recovery and utilization of flue gas heat energy, while also guaranteeing the safe and stable operation of the system equipment, reducing adverse effects on the equipment caused by flue gas fluctuations, extending equipment lifespan, and reducing maintenance costs.

[0047] Finally, in shutdown control step S3, the flue gas bypass regulating valve 7 is opened from a fully closed state to a fully open state at a rate of 2% per second. When the flue gas bypass regulating valve 7 is 80% open, the control subsystem directly shuts down the induced draft fan 15. After shutting down the induced draft fan 15, the flue gas inlet valve 9 and the flue gas outlet valve 16 are closed sequentially. This shutdown control process allows the system to gradually adjust the flue gas flow path and equipment operating status during shutdown, avoiding problems such as sudden system pressure changes and equipment damage caused by sudden shutdown. This ensures the stability and safety of the entire reboiler flue gas heat recovery system during shutdown, laying the groundwork for the next system startup and improving the reliability and maintainability of system operation.

[0048] Example 5 In this preferred embodiment of the present invention, based on Embodiment 4, the control method for the reboiler flue gas heat recovery system provided in Embodiments 1, 2, or 3 above is further elaborated. This control method can be mainly divided into three key stages: the start-up stage, the stable operation stage, and the shutdown stage.

[0049] During the power-on phase, this phase is further divided into two important steps: First, opening the flue gas inlet valve 9 and the flue gas outlet valve 16 creates a preliminary channel for the subsequent introduction and discharge of flue gas, providing the basic conditions for the flow of flue gas in the system.

[0050] Secondly, the flue gas bypass regulating valve 7 is closed, and simultaneously the variable frequency high-temperature flue gas induced draft fan 15 is turned on. The closing process of the flue gas bypass regulating valve 7 requires precise rate control. Following the pattern of 0%-100% corresponding to complete closure and complete opening, the rate of change is set to 2% per second in the 0-40% stage; 1% per second in the 40%-80% stage; and 2% per second again in the 80%-100% stage. This staged, variable-rate control method ensures that the flue gas bypass regulating valve 7 closes slowly and smoothly, allowing the entire system to smoothly transition to the flue gas heat recovery system operation mode. The operating frequency of the variable frequency high-temperature flue gas induced draft fan 15 varies between 5Hz and 50Hz. It starts at 5Hz initially, then gradually increases its speed at a fixed rate of 2Hz per second until it reaches the speed range corresponding to half-load conditions of the reboiler 1. During this process, since the flue gas bypass regulating valve 7 has been partially closed, the undesirable situation of local circulation in the loop formed by the flue gas inlet valve 9, the variable frequency high-temperature flue gas induced draft fan 15, the flue gas outlet valve 16, and the flue gas bypass regulating valve 7 is effectively avoided. This lays a solid foundation for the variable frequency high-temperature flue gas induced draft fan 15 to smoothly enter the stable operation stage, ensures the stability and reliability of the start-up process, reduces various potential faults that may be caused by unstable equipment operation during the start-up process, and improves the overall start-up success rate and operational safety of the system.

[0051] When the system enters the stable operation phase, the variable frequency high-temperature flue gas induced draft fan 15 fully utilizes the parameters of the oxygen content sensor 10 and the pressure sensor 12 to achieve precise control. Specifically, the variable frequency high-temperature flue gas induced draft fan 15 first performs a coarse adjustment of the oxygen content of the flue gas discharged from the reboiler 1 based on the parameters of the oxygen content sensor 10. By monitoring and adjusting the oxygen content, the amount of air entering the reboiler 1 can be effectively limited to a reasonable range, thereby ensuring the economy and stability of the combustion process inside the reboiler 1 and avoiding problems such as low combustion efficiency, energy waste, and increased pollutant emissions caused by excessive or insufficient air. On this basis, the variable frequency high-temperature flue gas induced draft fan 15 is then finely adjusted using the parameters of the pressure sensor 12 to ensure that the combustion flow field in the reboiler 1 remains stable after the flue gas heat recovery system is intervened. In actual operation, the target operating value of the variable frequency high-temperature flue gas induced draft fan 15 is based on the average parameter corresponding to the oxygen content sensor 10 over the previous 3 seconds. The target value is calculated by subtracting the value from a previously calibrated reference point (established during initial commissioning by calibrating commonly used points to correspond to the speed of the variable frequency high-temperature flue gas induced draft fan 15). Then, the median value of the pressure sensor 12 under this target value is used as the control value, ultimately achieving precise adjustment of the speed of the variable frequency high-temperature flue gas induced draft fan 15. Furthermore, as the system's operating time increases and multi-condition data accumulates, the target value calculated by the oxygen content sensor 10 parameters, after long-term operation under multiple conditions, allows the control system to automatically perform a fourth-order polynomial fitting operation based on a large amount of statistical data, thereby further optimizing and forming a more accurate and efficient target value calculation method. This dynamic adjustment and optimization mechanism based on sensor feedback data enables the variable frequency high-temperature flue gas induced draft fan 15 to adapt to various changes in the system during the stable operation phase, continuously maintain the efficient and stable operation of the system, maximize the recovery and utilization of flue gas heat energy, effectively extend the service life of system equipment, reduce equipment maintenance costs and operating energy consumption, and provide strong technical support for energy conservation, emission reduction and sustainable development in industrial production processes.

[0052] During the shutdown phase, the flue gas bypass regulating valve 7 is first opened from a fully closed state to a fully open state, and this process can be carried out at a rate of 2% per second throughout. When the opening of the flue gas bypass regulating valve 7 is 80%, the variable frequency high-temperature flue gas induced draft fan 15 is directly shut down. Subsequently, the flue gas inlet valve 9 and the flue gas outlet valve 16 are closed in sequence. At this point, the flue gas heat recovery system is completely out of operation, and the exhaust gas from the reboiler 1 returns to its original state. This shutdown process design ensures that the system can smoothly and orderly perform equipment shutdown and state switching operations during the shutdown process, avoiding problems such as sudden changes in system pressure, equipment damage, and flue gas backflow caused by sudden shutdown. It effectively protects the safety and integrity of the system equipment during the shutdown process, provides a good equipment foundation and operating conditions for the next system startup and operation, improves the overall reliability and operability of the system, reduces the equipment maintenance and replacement costs that may be caused by improper shutdown, and is conducive to the continuity and stability of industrial production processes.

[0053] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A reboiler flue gas heat recovery system, characterized in that: The system includes a reboiler (1), a flue gas heat exchanger (13), and a control subsystem. The reboiler (1) has a reboiler exhaust duct (6), a flue gas bypass regulating valve (7), and a reboiler chimney (8) arranged sequentially in its exhaust section. A heat exchange flue gas pipe is led out from the reboiler exhaust duct (6) and connected to the flue gas inlet valve (9). An oxygen content sensor (10), a temperature sensor I (11), and a pressure sensor (12) are installed on the pipe before the flue gas inlet valve (9). The pipe after the flue gas inlet valve (9) is connected to the flue gas heat exchanger (13). The flue gas outlet of the flue gas heat exchanger (13) is connected to the inlet of the induced draft fan (15) via a pipe. A temperature sensor II (14) is installed on the pipe between the flue gas heat exchanger (13) and the induced draft fan (15). 15) The outlet end is connected to the inlet of the flue gas outlet valve (16), and the outlet of the flue gas outlet valve (16) is connected to the reboiler chimney (8); the control subsystem is electrically connected to the flue gas bypass regulating valve (7), the flue gas inlet valve (9), the oxygen content sensor (10), the temperature sensor I (11), the pressure sensor (12), the induced draft fan (15), the temperature sensor II (14), and the flue gas outlet valve (16), respectively. The control subsystem controls the opening and closing and the degree of opening of the flue gas bypass regulating valve (7), the flue gas inlet valve (9), and the flue gas outlet valve (16), as well as the speed of the induced draft fan (15), based on the data collected by the oxygen content sensor (10), the temperature sensor I (11), the pressure sensor (12), and the temperature sensor II (14).

2. The reboiler flue gas heat recovery system as described in claim 1, characterized in that: The induced draft fan (15) is a variable frequency high temperature induced draft fan.

3. The reboiler flue gas heat recovery system as described in claim 2, characterized in that: The rated operating frequency of the induced draft fan (15) is 5Hz-50Hz.

4. The reboiler flue gas heat recovery system as described in claim 3, characterized in that: The control subsystem controls the speed of the induced draft fan (15) by controlling the change of the working frequency of the induced draft fan (15).

5. The reboiler flue gas heat recovery system as described in claim 3, characterized in that: After the control subsystem controls the induced draft fan (15) to start at 5Hz, it increases the speed to the range corresponding to the load conditions of the reboiler (1) at a fixed rate of 2Hz per second.

6. The reboiler flue gas heat recovery system as described in any one of claims 1-5, characterized in that: The flue gas bypass regulating valve (7) is closed and fully opened respectively according to the process of 0%-100%. When the control subsystem controls the flue gas bypass regulating valve (7) to be closed, the change rate is 2% per second for the 0%-40% stage; 1% per second for the 40%-80% stage; and 2% per second for the 80%-100% stage.

7. The reboiler flue gas heat recovery system as described in any one of claims 1-5, characterized in that: The flue gas heat exchanger (13) is provided with a rich liquid inlet and a rich liquid outlet. The rich liquid that enters the flue gas heat exchanger (13) through the rich liquid inlet is heated in the flue gas heat exchanger (13) and then discharged from the rich liquid outlet.

8. The reboiler flue gas heat recovery system as described in any one of claims 1-5, characterized in that: The reboiler (1) is provided with a fuel gas inlet and an air inlet. When the fuel gas enters the reboiler (1) through the fuel gas inlet, the air from the air inlet enters the reboiler (1).

9. The reboiler flue gas heat recovery system as described in claim 8, characterized in that: An air regulating valve is provided at the air inlet. During the operation of the reboiler (1), the air regulating valve is configured to open at its maximum degree.

10. The reboiler flue gas heat recovery system as described in claim 9, characterized in that: During the operation of the reboiler (1), the air regulating valve is configured to open at its maximum degree.

11. The reboiler flue gas heat recovery system as described in any one of claims 1-5, characterized in that: The control subsystem is an industrial control computer.

12. The control method for the reboiler flue gas heat recovery system according to any one of claims 1-11, characterized in that: The control method includes, S1. Power-on control procedures, specifically including: S101, The control subsystem controls the opening of the flue gas inlet valve (9) and the flue gas outlet valve (16); S102, The control subsystem controls the flue gas bypass valve (7) to close and simultaneously turns on the induced draft fan (15); The flue gas bypass valve (7) corresponds to fully closed and fully open at 0%-100% respectively. When the control subsystem controls the flue gas bypass regulating valve (7) to be closed, the change rate is 2% per second for the 0%-40% stage; 1% per second for the 40%-80% stage; and 2% per second for the 80%-100% stage. When the control subsystem starts the induced draft fan (15), it starts the induced draft fan (15) at a rated frequency of 5Hz and increases the speed of the induced draft fan (15) to the speed range corresponding to half load condition of the reboiler (1) at a fixed rate of 2Hz per second. S2. Stable operation control steps, specifically including: S201. The control subsystem collects the detection value of the oxygen content sensor (10) and makes a coarse adjustment to the speed of the induced draft fan (15) based on the detection value of the oxygen content sensor (10). S202, The control subsystem collects the detection value of the pressure sensor (12) and finely adjusts the speed of the induced draft fan (15) based on the detection value of the pressure sensor (12); S3. Shutdown control steps: Open the flue gas bypass regulating valve (7) from completely closed to fully open at a rate of 2% per second. When the opening degree of the flue gas bypass regulating valve (7) is 80%, the control subsystem directly shuts down the induced draft fan (15). After shutting down the induced draft fan (15), the flue gas inlet valve (9) and the flue gas outlet valve (16) are closed.

13. The control method for the reboiler flue gas heat recovery system as described in claim 12, characterized in that: In step S201, the target value for coarse adjustment of the induced draft fan (15) is based on the average parameter corresponding to the oxygen content sensor (10) in the previous 3 seconds. The coarse adjustment target value is calculated by the difference based on the calibrated reference point. The calibrated reference point refers to the point formed by calibrating the commonly used point and the corresponding induced draft fan (15) speed during the initial operation and debugging.

14. The control method for the reboiler flue gas heat recovery system as described in claim 13, characterized in that: The coarse adjustment target value of the induced draft fan (15) is calculated based on the parameters of the oxygen content sensor (10). After long-term operation under multiple working conditions, the control subsystem performs fourth-order polynomial fitting based on the statistical data of long-term operation under multiple working conditions to obtain the calculation method of the coarse adjustment target value of the induced draft fan (15).

15. The control method for the reboiler flue gas heat recovery system as described in any one of claims 12-14, characterized in that: In step S202, the target value for fine-tuning the induced draft fan (15) is the control value based on the median value of the data collected by the pressure sensor (12) after the induced draft fan (15) has been coarsely tuned and the target value has been reached. The transmission of the induced draft fan (15) is adjusted.

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