Low-temperature methanol washing carbon dioxide turbine expander system and control method

Abstract

The application relates to a CO2 turbine expander system in a low-temperature methanol washing process and a control method, and relates to the field of low-temperature methanol washing processes.The system comprises an expander main body, a generator, a protection system and a control module, one end of the expander main body is communicated with a high-pressure CO2 outlet pipeline of a methanol washing process, a temperature sensor and a pressure regulating valve are arranged on an outlet pipeline of the expander main body; the generator is coaxially connected with the expander main body; the control module is electrically connected with the temperature sensor, the pressure regulating valve and the expander main body; the protection system comprises a temperature-pressure interlocking control device and an emergency shut-off valve, the emergency shut-off valve is arranged on the outlet pipeline of the expander main body, and the temperature-pressure interlocking control device controls opening and closing of the emergency shut-off valve according to a temperature signal of the temperature sensor and a pressure signal of the pressure regulating valve. The application has the effect of improving the working efficiency of the expander.

Description

Technical Field

[0001] This application relates to the field of low-temperature methanol washing process, and in particular to a carbon dioxide turbine expander system and control method for low-temperature methanol washing. Background Technology

[0002] Currently, low-temperature methanol washing technology plays a crucial role in the field of chemical gas separation. With the continuous development of the chemical industry, the demand for efficient removal of acidic gases such as carbon dioxide and H2S from syngas is increasing. The widespread application of this technology has significantly improved the purification effect of syngas, providing cleaner raw materials for subsequent chemical production, helping to improve product quality and production efficiency, and promoting the further development of the chemical industry. Simultaneously, under the major trend of energy conservation and emission reduction in chemical production, the focus on energy recovery and effective utilization in this process is also increasing. In traditional low-temperature methanol washing processes, the treatment of high-pressure carbon dioxide tail gas typically employs a throttle valve for pressure reduction and discharge. This method involves a simple pressure reduction operation using a throttle valve to lower the pressure of the high-pressure carbon dioxide tail gas to a suitable discharge level. Traditional throttle valve pressure reduction and discharge methods suffer from significant energy loss, with a large amount of pressure wasted during the pressure reduction process, making effective energy recovery impossible. Furthermore, the outlet temperature is difficult to control; when carbon dioxide forms dry ice at low temperatures, it can adversely affect the safe operation of the equipment.

[0003] Related technology can be found in Chinese Patent No. CN114788983B, which discloses a low-temperature methanol washing purification method and apparatus. The method includes at least the following steps: condensing and separating the feedstock shift gas to obtain a liquid containing carbon dioxide and the separated feedstock gas; vaporizing and expanding the liquid containing carbon dioxide to obtain a gas containing carbon dioxide; and further washing the separated feedstock gas with methanol to obtain purified gas. This method combines carbon dioxide condensation with an expander, reducing the cooling load of the low-temperature methanol washing system by 60%. Simultaneously, the expander can perform external work, reducing system energy consumption. After condensation, the amount of carbon dioxide entering section B of the desulfurized purified gas in section A of the washing tower is reduced, decreasing the amount of lean methanol circulating and lowering power consumption, thus significantly reducing both the consumption and investment in the regeneration system.

[0004] Regarding the aforementioned technologies, turbo expanders convert the pressure energy of high-pressure gas into mechanical energy by expanding the gas within the expander, thereby achieving energy recovery. However, the carbon dioxide phase change can easily lead to frost formation or liquid slugging inside the expander, causing safety issues and resulting in decreased efficiency, which also decreases under varying operating conditions. Summary of the Invention

[0005] To improve the efficiency of the expander, this application provides a carbon dioxide turbine expander system and control method for low-temperature methanol washing.

[0006] In a first aspect, this application provides a low-temperature methanol washing carbon dioxide turbine expander system, which adopts the following technical solution:

[0007] A carbon dioxide turbine expander system for low-temperature methanol washing includes an expander body, a generator, a protection system, and a control module. One end of the expander body is connected to the high-pressure carbon dioxide outlet pipeline of the methanol washing process. The outlet pipeline of the expander body is equipped with a temperature sensor and a pressure regulating valve. The generator is coaxially connected to the expander body. The control module is electrically connected to the temperature sensor, the pressure regulating valve, and the expander body. The protection system includes a temperature-pressure interlock control device and an emergency shut-off valve. The emergency shut-off valve is located in the outlet pipeline of the expander body. The temperature-pressure interlock control device controls the opening and closing of the emergency shut-off valve based on the temperature signal from the temperature sensor and the pressure signal from the pressure regulating valve.

[0008] By adopting the above technical solution, the expander body is connected to the high-pressure carbon dioxide outlet pipeline of the methanol washing process. This allows the high-pressure carbon dioxide gas from the methanol washing process to be introduced and expanded to perform work, driving a generator coaxially connected to the expander body to generate electricity, achieving energy recovery and improving the overall energy efficiency of the system. A temperature sensor installed on the expander body's outlet pipeline can monitor the carbon dioxide outlet temperature in real time, and a pressure regulating valve can adjust the outlet pressure. The control module collects the temperature signal from the temperature sensor and the pressure signal from the pressure regulating valve in real time, and adjusts the speed of the expander body and the opening of the pressure regulating valve accordingly, thereby effectively controlling the carbon dioxide outlet temperature. The protection system provides mechanical protection for the expander, reducing the probability of damage to the impeller, improving system safety, and increasing the expander's working efficiency.

[0009] Optionally, it also includes an intake regulating unit, which includes a pre-filter and a flow distribution valve. The pre-filter is installed on the high-pressure carbon dioxide outlet pipeline of the methanol washing process, and the flow distribution valve is electrically connected to the control module to regulate the flow of carbon dioxide entering the expander body.

[0010] By adopting the above technical solution, the pre-filter in the intake regulating unit is installed on the intake pipeline between the high-pressure carbon dioxide outlet pipeline and the expander body in the methanol washing process. This filter removes impurities and particulate matter from the carbon dioxide gas entering the expander body, preventing impurities from entering and causing wear and damage to its internal components, thus extending the service life of the expander body. The flow distribution valve is electrically connected to the control module. The control module can precisely adjust the opening of the flow distribution valve according to system operating conditions and requirements, thereby flexibly adjusting the carbon dioxide flow rate entering the expander body. This ensures that the expander body can operate stably under suitable gas flow rates, improving system operating efficiency and stability, and ensuring that the entire system can better adapt to different operating conditions and meet the requirements of the low-temperature methanol washing process.

[0011] Optionally, the temperature-pressure interlock control device is mechanically connected to the emergency shut-off valve. When the temperature detected by the temperature sensor is higher than the preset upper limit or lower than the preset lower limit, the emergency shut-off valve is triggered to close.

[0012] By adopting the above technical solution, the temperature-pressure interlock control device in the protection system can control the opening and closing of the emergency shut-off valve based on the carbon dioxide outlet temperature signal detected by the temperature sensor and the pressure signal detected by the pressure regulating valve. When the temperature detected by the temperature sensor is lower than the preset lower limit or higher than the preset upper limit, it means that carbon dioxide may undergo a phase change, forming dry ice or liquid. At this time, the temperature-pressure interlock control device will quickly trigger the emergency shut-off valve to close, promptly cutting off the outlet pipeline of the expander body, avoiding damage to critical components such as the impeller of the expander body, effectively improving the safety and stability of system operation, and extending the service life of the expander body.

[0013] Optionally, the control module integrates a pressure-temperature-flow coordinated control subsystem. The pressure-temperature-flow coordinated control subsystem dynamically adjusts the operating parameters of the expander body through a PID algorithm and couples and corrects the parameters with the vibration data from the vibration monitoring module.

[0014] By adopting the above technical solution, the pressure-temperature-flow coordinated control subsystem integrated into the control module utilizes a PID algorithm to dynamically adjust the operating parameters of the expander body, such as expansion ratio and speed, based on real-time collected pressure, temperature, and flow signals. Simultaneously, these adjusted operating parameters are coupled and corrected with the vibration data of the expander body monitored by the vibration monitoring module. This ensures stable operation of the expander body under different working conditions, more precise control of the outlet temperature, effective prevention of carbon dioxide dry ice formation, avoidance of impeller damage, and improved system safety. It also enables efficient energy recovery, improving the overall energy efficiency of the system and reducing system energy consumption. Furthermore, real-time adjustment and correction of operating parameters reduces the vibration of the expander body during operation, extends the equipment's service life, and reduces maintenance costs.

[0015] Optionally, a vibration monitoring module is also included. The vibration monitoring module is fixed to the surface of the shell of the expander body and is electrically connected to the control module. It is used to monitor the vibration amplitude of the expander body in real time and send it to the control module.

[0016] By adopting the above technical solution, a vibration monitoring module is installed on the shell surface of the expander body and electrically connected to the control module. This allows for real-time monitoring of the vibration amplitude of the expander body and the transmission of the monitored vibration amplitude data to the control module. Based on this vibration amplitude data, the control module can promptly detect any abnormal vibrations occurring in the expander body during operation. If the vibration amplitude exceeds the normal range, the control module can take appropriate measures, such as issuing an alarm signal to remind operators to inspect and maintain the equipment. This prevents equipment damage or disruption to the normal operation of the system due to abnormal vibrations of the expander body, further improving the stability and safety of the carbon dioxide turbine expander system used in the low-temperature methanol washing process.

[0017] Secondly, this application provides a control method for a carbon dioxide turbine expander system in a low-temperature methanol wash process, comprising the following steps: real-time monitoring of the carbon dioxide temperature at the outlet of the expander body using a temperature sensor; dynamic adjustment of the speed of the expander body and the opening of the pressure regulating valve based on the temperature signal by the control module; when the temperature detected by the temperature sensor is lower than the saturation curve temperature corresponding to the carbon dioxide phase change, the control module activates an electric heating device to heat the outlet pipeline of the expander body; when the temperature detected by the temperature sensor exceeds a preset upper or lower limit, the control module triggers the emergency shut-off valve to close and sends a shutdown command or audible and visual alarm signal to the expander body.

[0018] Optionally, the control module also receives the pressure signal from the pressure regulating valve, correlates the temperature signal with the pressure signal, and generates an expansion ratio adjustment command for the expander body to maintain the outlet temperature of the expander body within a preset safe range.

[0019] By adopting the above technical solution, the control module receives the pressure signal from the pressure regulating valve and correlates it with the temperature signal from the temperature sensor to calculate and accurately generate the expansion ratio adjustment command for the expander body. This precise adjustment process can dynamically adjust the expansion ratio of the expander body according to the actual temperature and pressure of carbon dioxide, thereby effectively maintaining the outlet temperature of the expander body within a preset safe range. This avoids the impact of excessively high outlet temperatures on the overall system operating efficiency, and excessively low temperatures causing carbon dioxide to form dry ice, which could damage the equipment. Precise temperature control ensures the stable and efficient operation of the entire system, improves the system's safety and reliability, and also facilitates effective energy recovery, improving the overall energy efficiency of the system.

[0020] Optionally, an electric heating device is embedded in the outer wall of the expander main outlet pipe, and the control module adjusts the power output of the electric heating device according to the temperature change rate of the temperature sensor.

[0021] By adopting the above technical solution, the electric heating device is embedded in the outer wall of the expander's main outlet pipe, which can more directly and effectively heat the outlet pipe and prevent carbon dioxide from forming dry ice in the pipe due to excessively low temperatures. The control module adjusts the power output of the electric heating device according to the temperature change rate of the temperature sensor, achieving precise control of the outlet temperature and ensuring that the outlet temperature is within the set range. At the same time, reasonable adjustment of power output can avoid energy waste and improve system energy efficiency. When the temperature drops rapidly, the control module increases the power of the electric heating device to quickly raise the pipe temperature and prevent carbon dioxide phase change; when the temperature drops slowly or the temperature tends to stabilize, the control module reduces the power of the electric heating device to reduce unnecessary energy consumption, ensuring both safe system operation and improved energy utilization efficiency.

[0022] In summary, this application includes at least one of the following beneficial technical effects:

[0023] 1. The expander body is connected to the high-pressure carbon dioxide outlet pipeline of the methanol washing process, which can introduce the high-pressure carbon dioxide gas from the methanol washing process and expand it to perform work, driving the generator coaxially connected to the expander body to generate electricity, realizing energy recovery and improving the overall energy efficiency of the system; the temperature sensor installed on the outlet pipeline of the expander body can monitor the outlet temperature of carbon dioxide in real time, and the pressure regulating valve can regulate the outlet pressure; the control module collects the temperature signal from the temperature sensor and the pressure signal from the pressure regulating valve in real time, and adjusts the speed of the expander body and the opening of the pressure regulating valve accordingly, thereby effectively controlling the outlet temperature of carbon dioxide; the protection system can provide mechanical protection for the expander, reduce the probability of damage to the impeller, improve the safety of the system, and improve the working efficiency of the expander;

[0024] 2. The pre-filter in the intake regulating unit is installed on the intake pipe between the high-pressure carbon dioxide outlet pipe and the expander body in the methanol washing process. It filters the carbon dioxide gas entering the expander body, removing impurities and particulate matter, preventing impurities from entering the expander body and causing wear and damage to its internal components, thus extending the service life of the expander body. The flow distribution valve is electrically connected to the control module. The control module can precisely adjust the opening of the flow distribution valve according to system operating conditions and requirements, thereby flexibly adjusting the carbon dioxide flow rate entering the expander body. This allows the expander body to operate stably under suitable gas flow, improving system operating efficiency and stability, and ensuring that the entire system can better adapt to different operating conditions and meet the requirements of the low-temperature methanol washing process.

[0025] 3. The temperature-pressure interlock control device in the protection system can control the opening and closing of the emergency shut-off valve based on the carbon dioxide outlet temperature signal detected by the temperature sensor and the pressure signal detected by the pressure regulating valve. When the temperature detected by the temperature sensor is lower than the preset lower limit or higher than the preset upper limit, it means that carbon dioxide may undergo a phase change, forming dry ice or liquid. At this time, the temperature-pressure interlock control device will quickly trigger the emergency shut-off valve to close, promptly cutting off the expander main body outlet pipeline, avoiding damage to critical components such as the impeller of the expander main body, effectively improving the safety and stability of system operation, and extending the service life of the expander main body. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a carbon dioxide turbine expander system and process flow in a low-temperature methanol washing process.

[0027] Explanation of reference numerals in the attached drawings: 100, heat exchanger; 110, sulfur-free methanol cryostat; 120, sulfur-containing methanol cryostat; 200, expander body. Detailed Implementation

[0028] The present application will be further described in detail below with reference to all the accompanying drawings.

[0029] In one aspect, embodiments of this application disclose a carbon dioxide turbine expander system for low-temperature methanol washing.

[0030] A low-temperature methanol washing carbon dioxide turbine expander system includes an inlet regulating unit, an expander body 200, a generator, a protection system, and a control module. The inlet regulating unit is connected to the inlet pipe of the expander body 200 and is used to regulate the flow rate of carbon dioxide entering the expander body 200. The generator is coaxially connected to the expander body 200, and the expander body 200 drives the generator to generate electricity and achieve energy recovery during operation. The protection system is connected to the outlet pipe of the expander body 200 to prevent liquid slugging within the expander body 200. The control module is electrically connected to components such as a temperature sensor, a pressure regulating valve, and the expander body 200. By collecting signals from these components, it adjusts the rotational speed of the expander body 200 and the opening of the pressure regulating valve, thereby controlling the outlet temperature within a set range. This achieves the beneficial effects of improving system energy efficiency and ensuring safe system operation. This is because the expander body 200 replaces the traditional valve to expand high-pressure carbon dioxide gas to generate electricity, realizing energy recovery and improving the overall energy efficiency of the system; at the same time, the control module's precise control of the outlet temperature effectively prevents carbon dioxide from forming dry ice, avoids solid particles from damaging the expander impeller, and improves the stability and safety of the system's continuous operation.

[0031] The intake regulating unit includes a pre-filter and a flow distribution valve. The pre-filter is located on the intake pipe between the high-pressure carbon dioxide outlet pipe of the methanol wash process and the expander body 200. Its construction features a filter screen structure with filtering function, made of stainless steel or other metal materials, effectively filtering out impurities in the high-pressure carbon dioxide gas and preventing them from entering the expander body 200 and causing damage. Replaceable features could include ceramic filters or other components with filtering functions. The flow distribution valve is electrically connected to the control module. Its construction features an adjustable valve structure. The valve opening is adjusted by signals sent from the control module, thereby regulating the flow of carbon dioxide entering the expander body 200. Replaceable features could include electrically adjustable valves or similar valves. The flow distribution valve is connected to the pre-filter via the intake pipe. Gas filtered by the pre-filter enters the flow distribution valve through the intake pipe. The flow distribution valve adjusts the gas flow according to the instructions of the control module before delivering it to the expander body 200.

[0032] The expander body 200 is connected to the high-pressure carbon dioxide outlet pipeline of the methanol washing process, and the generator is coaxially connected to the expander body 200. The high-pressure carbon dioxide gas from the methanol washing process enters the turbine expander for adiabatic expansion, driving the impeller to rotate and output power, which drives the coaxial generator to generate electricity to achieve energy recovery.

[0033] Reference Figure 1 The high-pressure carbon dioxide generation process in the methanol washing process is as follows: The feed gas entering the low-temperature methanol washing system is first washed with boiler feedwater in the shift converter to reduce the NH3 content to below 2 ppm. The feed gas entering the low-temperature methanol washing system is mixed with the circulating flash vapor after the compressor and a small amount of anti-icing methanol is injected. After passing through the reboiler of the thermal regeneration tower, it is cooled by heat exchange with purified gas, carbon dioxide gas, tail gas, and medium-pressure flash vapor. After water is separated in the tank, it enters the desulfurization section of the lower tower of the washing tower. The feed gas exceeding the original system load is heat exchanged by heat exchanger 100 and water is separated in the intermediate tank. In the desulfurization section, the feed gas is washed with a partially carbon dioxide-rich methanol liquid from the decarbonization section to remove H2S, COS, and some carbon dioxide. After being drawn from the tower, it is further cooled by the cooler. Some of the carbon dioxide condenses and is separated, and the gas phase is returned to the washing tower for decarbonization. The carbon dioxide condensate separated from the cooler is first flashed in the tank at medium pressure to recover the effective gas, and then enters the heat exchanger 100 for evaporation and heat exchange to provide cooling for carbon dioxide condensation. Subsequently, high-pressure carbon dioxide gas is discharged from the heat exchanger 100, and some of the carbon dioxide condensate that has not been completely heat-exchanged returns to the heat exchanger 100 for evaporation and heat exchange through the pipeline.

[0034] Reference Figure 1 The process flow of high-pressure carbon dioxide gas in the expander is as follows: High-pressure carbon dioxide gas discharged from heat exchanger 100 is expanded in the first stage of the expander and its temperature decreases. After exchanging heat with sulfur-free methanol in the sulfur-free methanol cryotherm 110 of the medium-pressure flash distillation tower, it enters the second stage of the expander. After the second stage expansion, low-temperature carbon dioxide gas is obtained. It first exchanges heat with sulfur-containing methanol in the sulfur-containing methanol cryotherm 120 of the medium-pressure flash distillation tower, and then enters the cooler to exchange heat with the raw material gas. After heat exchange, it can be sent out of the boundary as carbon dioxide product gas. When it is not used, the carbon dioxide is fed into the newly added water washing tower, washed, and then vented.

[0035] The outlet pipe of the expander body 200 is equipped with a temperature sensor and a pressure regulating valve. The temperature sensor is used to monitor the outlet temperature of carbon dioxide in real time, and can quickly and accurately detect changes in the outlet temperature. The pressure regulating valve is used to regulate the pressure in the outlet pipe. Its construction features an adjustable valve structure, and the outlet pressure is controlled by adjusting its opening degree through the control module. Both the temperature sensor and the pressure regulating valve are installed on the outlet pipe. The temperature sensor collects the outlet temperature signal in real time and transmits it to the control module. The control module adjusts the opening degree of the pressure regulating valve according to the temperature signal to control the outlet pressure and temperature.

[0036] Carbon dioxide is prone to forming dry ice during expansion when the temperature is below -26.5℃ and the pressure is below 5.2 bar, causing blade wear and equipment blockage. To prevent carbon dioxide from sublimating into dry ice due to excessive cooling during expansion in the expander and to achieve efficient energy recovery, it is crucial to ensure that the gas state (temperature and pressure) at the expander outlet remains within the "gas phase region" of the carbon dioxide phase diagram, avoiding entry into the "solid phase region." This is achieved by dynamically adjusting the expander speed and the opening of the pressure regulating valve, ensuring that the operating conditions are far from the sublimation zone. This effectively prevents dry ice formation, avoids damage to the expander impeller from solid particles, improves the stability and safety of continuous system operation, and increases the expander's working efficiency.

[0037] The protection system includes a temperature-pressure interlock control device and an emergency shut-off valve. The temperature-pressure interlock control device controls the opening and closing of the emergency shut-off valve based on the temperature signal from the temperature sensor and the pressure signal from the pressure regulating valve. Its structural feature is an electronic device with signal processing and control functions, capable of analyzing and processing temperature and pressure signals and issuing control signals according to preset thresholds. An alternative feature could be a control device with similar functions, such as a programmable logic controller (PLC). The emergency shut-off valve is located in the outlet pipeline of the expander body 200. Its structural feature is a valve structure with a rapid shut-off function, capable of cutting off the outlet pipeline in a short time. An alternative feature could be a valve with similar functions, such as an electrically operated shut-off valve. The temperature-pressure interlock control device is mechanically connected to the emergency shut-off valve. When the temperature detected by the temperature sensor is lower than the preset threshold and the pressure of the pressure regulating valve exceeds the critical value, the temperature-pressure interlock control device triggers the emergency shut-off valve to close, preventing liquid slugging from damaging the expander body 200.

[0038] The control module is electrically connected to components such as the temperature sensor, pressure regulating valve, and expander body 200. Its structural feature is an electronic module with data acquisition, processing, and control functions. It can collect signals such as temperature, pressure, and flow rate in real time and automatically adjust the speed of the expander body 200 and the valve opening through built-in algorithms. The material can be a circuit board, etc. A replaceable feature is the use of other devices with control functions, such as an industrial computer. The control module connects to each component via cables, receives signals from each component, and sends control commands to achieve precise control of the entire system.

[0039] The system in this embodiment also includes a vibration monitoring module, which is disposed on the surface of the expander body 200. Its structural feature is a sensor structure with vibration sensing elements, capable of real-time monitoring of the vibration amplitude of the expander body 200. The material can be piezoelectric ceramic, etc. Alternatively, other types of vibration sensors, such as strain gauge vibration sensors, can be used. The vibration monitoring module is electrically connected to the control module, used to monitor the vibration amplitude of the expander body 200 in real time and send the data to the control module. The control module integrates a pressure-temperature-flow coordinated control subsystem. This subsystem dynamically adjusts the operating parameters of the expander body 200 using a PID algorithm and couples and corrects these parameters with the vibration data from the vibration monitoring module. When the vibration amplitude detected by the vibration monitoring module exceeds a preset value, the control module will make a comprehensive judgment based on the vibration data and other parameters, and take corresponding measures, such as adjusting the operating parameters of the expander body 200 or issuing an alarm signal.

[0040] The implementation principle of this embodiment is as follows: High-pressure carbon dioxide gas from the methanol washing process enters a turbine expander for adiabatic expansion, driving the impeller to rotate and output power, which in turn drives a coaxial generator to generate electricity and achieve energy recovery. After expansion, the temperature and pressure of the carbon dioxide are significantly reduced, and the low-temperature, low-pressure gas then enters the subsequent process unit. During this process, key data is continuously collected through the expander's inlet and outlet pipelines and high-precision sensors (including temperature, pressure, flow, and speed sensors), and transmitted in real time to the central control module (such as a PLC or DCS). The core processing program of the control module calculates the safety margin between the current carbon dioxide state and the sublimation temperature based on this real-time data, especially the outlet temperature and pressure, and compares it with the preset safe operating threshold. The expander outlet temperature is stabilized above a safe setpoint (e.g., -25°C) higher than the carbon dioxide sublimation temperature.

[0041] The expansion tank outlet temperature is mainly adjusted through the following two methods:

[0042] 1. Adjusting the expander speed essentially controls the degree of energy conversion. This operation is achieved by changing the load on the coaxial generator: when the system detects that the outlet temperature is approaching the lower limit of sublimation risk, the control module instructs an increase in the generator's electromagnetic load, thereby applying greater braking power to the expander rotor, causing its speed to decrease. According to the principle of thermodynamic enthalpy drop, the decrease in speed prolongs the residence time of high-pressure carbon dioxide gas in the turbine, resulting in more complete energy exchange with the rotor, leading to an increase in enthalpy drop. The gas converts more of its internal energy (thermodynamic enthalpy) into mechanical energy, ultimately manifesting as a significant decrease in outlet temperature. Conversely, if the outlet temperature is too high, the generator load is reduced to increase the speed, shortening the energy exchange time, reducing the enthalpy drop, and causing the outlet temperature to rise again.

[0043] 2. Adjusting the opening of the outlet pressure regulating valve is an auxiliary method, its principle being to change the system's back pressure to affect thermodynamic equilibrium. When it is necessary to suppress excessive temperature drop, the control module will instruct the outlet valve to close slightly. This increases airflow resistance, leading to an increase in the expander outlet back pressure. According to the pressure-temperature characteristics of gas, under given inlet conditions, an increase in outlet pressure will directly lead to a corresponding increase in outlet temperature. This is because a higher back pressure restricts the free expansion of gas in the turbine, increasing its final pressure for work, and consequently, its final temperature. Conversely, opening the valve wider will reduce the back pressure, allowing the gas to expand more fully, thereby achieving a lower outlet temperature.

[0044] Specifically, if the outlet temperature is within the ideal safe range (e.g., above -23°C), the system maintains the current expander speed and valve opening for stable operation. Once the outlet temperature is detected to be approaching the sublimation risk range (e.g., between -25°C and -23°C), the expander speed is reduced first, and the braking power is decreased by adjusting the generator load, thereby reducing the expansion temperature drop and allowing the outlet temperature to rise. Simultaneously, the outlet pressure valve can be closed slightly to increase back pressure, further promoting a temperature increase. Conversely, if the outlet temperature is too high, indicating insufficient cooling, the speed is increased or the valve is opened wider to enhance the expansion effect and lower the temperature.

[0045] On the other hand, embodiments of this application disclose a control method for a carbon dioxide turbine expander system in a low-temperature methanol wash, comprising the following steps:

[0046] S1 monitors the carbon dioxide temperature at the outlet of the expander body 200 in real time using a temperature sensor. The temperature sensor collects the outlet temperature signal in real time and transmits it to the control module. The temperature sensor has a probe structure with a temperature-sensing element, which can quickly and accurately detect changes in the outlet temperature. During operation, ensure that the temperature sensor is installed in a suitable position on the outlet pipeline to ensure accurate measurement of the outlet temperature. Tools such as an installation wrench can be used. During installation, ensure that the temperature sensor is tightly connected to the outlet pipeline to avoid loosening that may affect measurement accuracy.

[0047] S2, the control module dynamically adjusts the rotational speed of the expander body 200 and the opening of the pressure regulating valve based on the temperature signal. After receiving the temperature signal from the temperature sensor, the control module analyzes whether the temperature is within the set range using its built-in algorithm. If it is not within the set range, it sends control signals to the expander body 200 and the pressure regulating valve. The expander body 200 adjusts its rotational speed according to the control signal, and the pressure regulating valve adjusts its opening according to the control signal to control the outlet temperature. The control module is an electronic module with data acquisition, processing, and control functions, connected to the expander body 200 and the pressure regulating valve via cables, etc.

[0048] S3, when the temperature detected by the temperature sensor is lower than the saturation curve temperature corresponding to the carbon dioxide phase change, the control module activates the electric heating device to heat the outlet pipe of the expander body 200. The electric heating device is embedded in the outer wall of the outlet pipe of the expander body 200, and its structural feature is a spiral electric heating wire structure, which can heat the outlet pipe. The control module adjusts the power output of the electric heating device according to the temperature change rate of the temperature sensor to achieve precise temperature control. During operation, ensure that the electric heating device is in close contact with the outlet pipe. Tools such as fixing clamps can be used. During installation, ensure that the electrical connection of the electric heating device is safe and reliable.

[0049] S4 sets the upper and lower temperature limits. When the outlet temperature exceeds the set range, the system automatically takes protective measures. The control module pre-sets the upper and lower temperature limits. When the outlet temperature detected by the temperature sensor exceeds the set range, the system will trigger corresponding protective measures. If the temperature is too high, the system may issue an alarm signal and appropriately reduce the speed of the expander body 200; if the temperature is too low, the system may trigger the emergency shut-off valve to close and stop the machine. The control module determines whether the set range has been exceeded by real-time monitoring and analysis of the temperature signal and takes timely protective measures.

[0050] In practical applications, a suitable expander model and control system are selected based on the specific requirements of the low-temperature methanol washing process. During operation, the outlet temperature of carbon dioxide is monitored in real time by a temperature sensor, and the operating parameters of the expander are automatically adjusted based on feedback signals to ensure that the outlet temperature remains within the set range. For example, the design parameters of the carbon dioxide turbine expander for a certain project are as follows: inlet pressure 0.68MPa, outlet pressure 0.34MPa, inlet temperature 254.15K, isentropic efficiency 85%, and a vibration monitoring module is installed. An alarm is triggered when the vibration value is >70µm, and the emergency shut-off valve response time is <0.5s.

[0051] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A CO2 turbine expander system for low-temperature methanol washing, characterized in that: The system includes an expander body (200), a generator, a protection system, and a control module. One end of the expander body (200) is connected to the high-pressure CO2 outlet pipeline of the methanol washing process. The outlet pipeline of the expander body (200) is equipped with a temperature sensor and a pressure regulating valve. The generator is coaxially connected to the expander body (200). The control module is electrically connected to the temperature sensor, the pressure regulating valve, and the expander body (200). The protection system includes a temperature-pressure interlock control device and an emergency shut-off valve. The emergency shut-off valve is located on the outlet pipeline of the expander body (200). The temperature-pressure interlock control device adjusts the pressure based on the temperature signal from the temperature sensor and the pressure... The pressure signal from the regulating valve controls the opening and closing of the emergency shut-off valve. The temperature sensor monitors the CO2 temperature at the outlet of the expander body (200) in real time. The control module dynamically adjusts the rotation speed of the expander body (200) and the opening of the pressure regulating valve according to the temperature signal. When the temperature detected by the temperature sensor is lower than the saturation curve temperature corresponding to the CO2 phase change, the control module starts the electric heating device to heat the outlet pipeline of the expander body (200). When the temperature detected by the temperature sensor exceeds the preset upper or lower limit, the control module triggers the emergency shut-off valve to close and sends a shutdown command or audible and visual alarm signal to the expander body (200).

2. The CO2 turbine expander system for low-temperature methanol washing according to claim 1, characterized in that: It also includes an intake regulating unit, which includes a pre-filter and a flow distribution valve. The pre-filter is installed on the high-pressure CO2 outlet pipeline of the methanol washing process, and the flow distribution valve is electrically connected to the control module to regulate the CO2 flow rate entering the expander body (200).

3. The CO2 turbine expander system for low-temperature methanol washing according to claim 1, characterized in that: The temperature-pressure interlock control device is mechanically connected to the emergency shut-off valve. When the temperature detected by the temperature sensor is higher than the preset upper limit or lower than the preset lower limit, the emergency shut-off valve is triggered to close.

4. The CO2 turbine expander system for low-temperature methanol washing according to claim 1, characterized in that: The control module integrates a pressure-temperature-flow coordinated control subsystem. The pressure-temperature-flow coordinated control subsystem dynamically adjusts the operating parameters of the expander body (200) through a PID algorithm and couples and corrects the parameters with the vibration data of the vibration monitoring module.

5. The CO2 turbine expander system for low-temperature methanol washing according to claim 1, characterized in that: It also includes a vibration monitoring module, which is fixed on the shell surface of the expander body (200). The vibration monitoring module is electrically connected to the control module and is used to monitor the vibration amplitude of the expander body (200) in real time and send it to the control module.

6. The CO2 turbine expander system for low-temperature methanol washing according to claim 1, characterized in that: The control module also receives the pressure signal from the pressure regulating valve, correlates the temperature signal with the pressure signal, and generates an expansion ratio adjustment command for the expander body (200) to maintain the outlet temperature of the expander body (200) within a preset safe range.

7. The CO2 turbine expander system for low-temperature methanol washing according to claim 1, characterized in that: An electric heating device is embedded in the outer wall of the outlet pipe of the expander body (200), and the control module adjusts the power output of the electric heating device according to the temperature change rate of the temperature sensor.

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