Vapor compressor full-automatic start-stop control method based on DeltaV system
By using the adaptive control strategy of the DeltaV system to monitor the rate of change of operating parameters and the theoretical temperature rise of steam in real time, the problems of current surge and mechanical damage during the start-up process of the steam compressor are solved, achieving flexible soft start and thermodynamic balance, thus improving start-up reliability and lifespan.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INNER MONGOLIA TONGWEI HIGH PURITY CRYSTAL SILICON CO LTD
- Filing Date
- 2026-03-06
- Publication Date
- 2026-05-12
AI Technical Summary
The existing steam compressor control logic suffers from problems such as excessive current surge, pressure overshoot, and mechanical damage caused by improper water injection during startup, failing to effectively maintain the system's thermodynamic balance and mechanical safety.
A fully automatic start-stop control method based on the DeltaV system is adopted. By monitoring the rate of change of operating parameters in real time, adaptive ramp-up and spray control are executed. Combined with frequency segmented anti-surge and steam theoretical temperature rise interlock, flexible soft start and thermodynamic balance are achieved.
It effectively eliminates the risk of tripping during startup, eliminates the hidden danger of liquid slugging, ensures thermodynamic balance under all operating conditions, and extends the service life of the compressor.
Smart Images
Figure CN122014655A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of steam compressor automation control technology, and specifically relates to a fully automatic start-stop control method for a steam compressor based on the DeltaV system. Background Technology
[0002] Steam compressor control typically relies on advanced distributed control systems. During startup, precise coordination of the operating states of various components is required to complete the transition from static standby to high-speed operation. Simultaneously, real-time monitoring of key thermodynamic parameters such as vibration, displacement, temperature, and pressure is necessary to maintain the system's thermodynamic balance and mechanical safety. Existing steam compressor control logic has certain limitations. Firstly, during the startup ramp-up phase, traditional control strategies often employ fixed linear rate-of-flight frequency converter regulation, failing to adequately consider the nonlinear fluctuations during outlet pressure build-up. This leads to the frequency converter tripping easily due to excessive current surges or pressure overshoot when pressure rises too rapidly or load changes abruptly, affecting startup success rates. Secondly, traditional spray cooling control often uses fixed temperature setpoints for PID regulation, neglecting the impact of drastic exhaust pressure changes on saturation temperature during unsteady-state processes. When outlet operating conditions fluctuate, liquid slugging due to excessive spray volume or exhaust overheating due to insufficient spray volume can easily occur, causing irreversible mechanical damage to the compressor impeller and sealing components. Summary of the Invention
[0003] To address the shortcomings of existing technologies, this invention provides a fully automatic start-stop control method for a steam compressor based on a DeltaV system, thereby solving the aforementioned technical problems.
[0004] A fully automatic start-stop control method for a steam compressor based on a DeltaV system includes the following steps: Step S1: Based on the received start command, start the oil pump, spray water pump and main motor in sequence, and set the initial operating frequency of the compressor; Step S2: The compressor starts to automatically climb according to the climbing endpoint frequency. During the automatic climbing process, the change rate of operating parameters is monitored in real time. Based on the monitored change rate of operating parameters, the compressor performs operations such as continuing to increase the frequency, pausing the frequency increase, or slightly decreasing the frequency. The change rate of operating parameters includes at least one of the compressor outlet pressure change rate or the main motor current rise rate. Step S3: During the automatic climb phase, the theoretical steam temperature rise is calculated synchronously; when the theoretical steam temperature rise is lower than the preset lockout threshold, the automatic climb of the compressor is forcibly stopped, and the automatic climb phase continues after the theoretical steam temperature rise exceeds the lockout threshold. Step S4: The compressor operates normally after reaching the peak frequency.
[0005] Preferably, the specific steps for sequentially starting the oil pump, spray water pump, and main motor in step S1 are as follows: Start the oil pump, and after the inlet oil pressure is greater than the starting threshold during the first start-up period and continues to be greater than the starting threshold until the second start-up period, start the main motor fan and the main motor. If the inlet oil pressure does not reach the starting threshold within the first starting time, or if the inlet oil pressure does not remain above the starting threshold for the second starting time, the pump will be stopped and the valve closed.
[0006] Preferably, step S2 further includes a surge prevention control step based on frequency segmentation, as shown below: The compressor's automatic climbing process is divided into low-frequency and high-frequency zones, with the anti-surge threshold as the boundary. In the low-frequency range at or below the anti-surge threshold, the anti-surge valve is forced to remain fully open, allowing for rapid passage through the surge zone in an open-loop manner; In the high-frequency range above the anti-surge threshold, the opening of the anti-surge valve is adjusted by PID control based on the distance between the operating point and the surge line.
[0007] Preferably, step S2, when performing operations such as continuing frequency increase, pausing frequency increase, or slightly decreasing frequency based on the monitored rate of change of operating parameters, specifically includes the following steps: A first pressure change rate threshold and a second pressure change rate threshold are set, wherein the first pressure change rate threshold is less than the second pressure change rate threshold; When the monitored rate of change of compressor outlet pressure is less than or equal to the first rate of change threshold, a frequency upsampling operation is performed. When the monitored rate of change of compressor outlet pressure is between the first and second pressure change rate thresholds, the frequency increase is paused, the current frequency is maintained, and the pressure change rate is allowed to fall back. When the monitored rate of change of compressor outlet pressure is greater than or equal to the second rate of change threshold, a slight frequency reduction operation is performed, which reduces the preset step size of the operating frequency and maintains a preset stable interval before attempting to increase the frequency again.
[0008] Preferably, the specific execution parameters for the micro-frequency reduction are: Frequency reduction is performed in a set step size, and the interval between two adjacent frequency reduction operations is the set time.
[0009] Preferably, step S3 further includes an exhaust spray control process, as shown below: Based on the fixed characteristic parameters of the compressor impeller and casing, the compression ratio of the real-time compressor outlet pressure and compressor inlet pressure, and the compressor inlet temperature, calculate the theoretical discharge temperature of the compressor under the current operating conditions. The theoretical exhaust temperature of the compressor is used as the set value for exhaust spraying, and the opening of the spray valve is automatically adjusted by PID control according to the set value.
[0010] Preferably, the specific triggering condition for forcibly stopping the compressor's automatic climbing in step S3 is as follows: The difference between the compressor exhaust theoretical temperature and the compressor inlet steam temperature is calculated in real time as the steam theoretical temperature rise. When the theoretical steam temperature rise is less than the lockout threshold, it is determined that the theoretical steam temperature rise is too low, and the automatic rise of the compressor is forcibly stopped. When the difference recovers to above the lockout threshold, the compressor resumes automatic ramping.
[0011] Preferably, the exhaust spray control process also includes a low-load forced manual mode, as shown below: Preset the minimum opening value of the spray valve; Real-time monitoring of compressor operating frequency and theoretical steam temperature rise; When the compressor operating frequency is detected to be lower than the initial operating frequency, or the theoretical steam temperature rise is lower than the forced manual threshold, the PID control is switched to manual control and the spray valve opening is set to the minimum opening value. The manual control of the exhaust spray control will be switched back to PID control only when the theoretical steam temperature rises above the forced manual threshold.
[0012] Preferably, a tiered shutdown step is also included, as shown below: Real-time monitoring of the compressor's radial vibration and high-speed shaft displacement values; When the compressor outlet pressure change rate is detected to exceed the third pressure change rate threshold, or the radial vibration value is in the dangerous vibration range, or the high-speed shaft displacement exceeds the displacement threshold, the normal shutdown procedure is triggered. When the radial vibration value is detected to exceed the dangerous vibration range, an emergency shutdown procedure is triggered.
[0013] Preferably, the staged shutdown process also includes a shutdown spray control step, as shown below: When executing the shutdown procedure, the compressor inlet steam pressure is collected in real time, and the saturation temperature corresponding to the pressure is looked up or calculated. Adjust the spray valve opening until the compressor inlet temperature equals the saturation temperature, and maintain this opening during shutdown.
[0014] The beneficial effects of this invention are as follows: By introducing a multi-dimensional adaptive control strategy, it abandons the rigid fixed-ratio acceleration and innovatively establishes an adaptive ramping mechanism based on the pressure change rate and current rise rate. This not only automatically pauses frequency increase during pressure fluctuations but also performs a slight frequency reduction and backoff in critical moments, effectively eliminating the risk of tripping during startup and achieving flexible soft start. Furthermore, it uses the real-time theoretical steam temperature rise as the highest priority constraint for mechanical actions. By dynamically calculating the theoretical exhaust temperature as the spray target and forcibly locking the frequency increase and switching the spray valve to the manual minimum opening under low load or low theoretical steam temperature rise, it not only completely eliminates the risk of liquid slugging caused by PID integral saturation but also ensures thermodynamic balance under all operating conditions, significantly extending the compressor's service life. Attached Figure Description
[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0016] Figure 1 This invention provides a schematic flowchart of a fully automatic start-stop control method for a steam compressor based on a DeltaV system. Detailed Implementation
[0017] The following disclosure provides many different embodiments or examples for implementing various embodiments of the invention. To simplify the disclosure, specific embodiments are described below. Of course, these are merely examples and are not intended to limit the scope of the invention.
[0018] The embodiments of the invention will now be described in detail with reference to the accompanying drawings.
[0019] like Figure 1 As shown, a fully automatic start-stop control method for a steam compressor based on a DeltaV system includes the following steps: Step S1: Based on the received start command, start the oil pump, spray water pump and main motor in sequence, and set the initial operating frequency of the compressor; Step S2: The compressor starts to automatically climb according to the climbing endpoint frequency. During the automatic climbing process, the change rate of operating parameters is monitored in real time. Based on the monitored change rate of operating parameters, the compressor performs operations such as continuing to increase the frequency, pausing the frequency increase, or slightly decreasing the frequency. The change rate of operating parameters includes at least one of the compressor outlet pressure change rate or the main motor current rise rate. Step S3: During the automatic climb phase, the theoretical steam temperature rise is calculated synchronously; when the theoretical steam temperature rise is lower than the preset lockout threshold, the automatic climb of the compressor is forcibly stopped, and the automatic climb phase continues after the theoretical steam temperature rise exceeds the lockout threshold. Step S4: The compressor operates normally after reaching the peak frequency.
[0020] This invention realizes fully automatic start-up and shutdown of a steam compressor based on the DeltaV distributed control system. It can be implemented on an Emerson DeltaV DCS system via configuration software, or on systems such as Siemens PCS7 and Honeywell PKS. After completing the pre-processing logic such as establishing oil pressure in the oil pump and starting the spray pump, the main motor is driven by a frequency converter to enter the adaptive ramp-up phase. In one embodiment, a graded pressure change rate control is adopted: the differential value of the outlet pressure is calculated in real time. When the pressure change rate is detected to be in the range of 0.0018 to 0.020 MPa / s, the logic module triggers a ramp-up pause command, locking the current frequency output until the pressure fluctuation converges. If the change rate suddenly increases beyond 0.020 MPa / s, the system immediately executes a micro-backoff strategy, instructing the frequency converter to reduce the frequency by 1 Hz and lock it for 5 seconds. This temporary decrease in mechanical speed actively reduces pressure overshoot, preventing current surges from triggering a high-voltage trip of the frequency converter. In step S3, parallel thermodynamic interlock protection is implemented: the system collects inlet temperature and exhaust pressure in real time and calculates the theoretical steam temperature rise; when the theoretical steam temperature rise is less than the preset lockout threshold of 1.5℃, the system is determined to be in a low superheat liquid-carrying risk zone, and the frequency increase command is immediately forcibly blocked to maintain the compressor running at a constant speed. At this time, although the frequency increase action stops, the compressor continues to do work on the fluid, causing the exhaust temperature to gradually rise until the theoretical steam temperature rises back to above 1.0℃, at which point the system automatically releases the lockout and continues to ramp up. Compared with the fixed slope start-up and single PID regulation in the prior art, this scheme eliminates the overcurrent trip fault caused by intake fluctuations during the start-up stage through bidirectional coupling control; through the unidirectional lockout logic corresponding to temperature rise and frequency, it ensures that the compressor always accelerates under dry steam conditions, avoiding the risk of liquid slugging in the early stage of start-up.
[0021] The core principle of this design lies in using a non-steady-state response to counteract a non-steady-state process. The startup process in step S2 is essentially a non-linear time-varying process. Traditional linear frequency ramping ignores the reaction force of the load. This design transforms frequency control from open-loop time extrapolation to closed-loop state response, actively unloading before the pressure surges and maintaining the dynamic balance between the electrical and mechanical systems. The theoretical steam temperature rise in step S3 is a direct indicator of the efficiency of gas compression. If the temperature rise is too low, it physically means that most of the compression work is absorbed by latent heat, i.e., there is liquid carryover. This thermodynamic parameter is used as the gating signal for frequency control, constructing the highest priority constraint of physical state on mechanical action. In specific implementation, forcibly stopping the compressor's automatic ramp-up means pausing the frequency ramp-up and maintaining the current frequency, rather than shutting down or reducing the frequency to zero.
[0022] More specifically, the steps for sequentially starting the oil pump, spray water pump, and main motor in step S1 are as follows: Start the oil pump, and after the inlet oil pressure is greater than the starting threshold during the first start-up period and continues to be greater than the starting threshold until the second start-up period, start the main motor fan and the main motor. If the inlet oil pressure does not reach the starting threshold within the first starting time, or if the inlet oil pressure does not remain above the starting threshold for the second starting time, the pump will be stopped and the valve closed.
[0023] In one implementation, the first startup duration is 3.5 minutes, the second startup duration is 3 minutes, and the startup threshold is 0.13 MPa. After the electric oil pump is started, a timer is activated. When the feedback inlet oil pressure value rises above the startup threshold within the first startup duration, the system activates the pressure stabilization timing logic. The cold start is completed only after the inlet oil pressure value remains above the startup threshold without fluctuations or drops for the second startup duration. If, after the oil pump starts, the inlet oil pressure value remains below the startup threshold when the first startup duration expires due to oil filter blockage or pipeline leakage, or if a momentary pressure drop occurs during the pressure stabilization timing, the oil pump is immediately shut down and the inlet valve is locked, preventing the main motor from being powered on. Compared to the existing technology's coarse logic of starting the motor only when the momentary oil pressure meets the standard, this effectively filters out transient interference and false alarms in the oil pressure signal. This forced start-up ensures that a sufficient and stable hydrodynamic lubrication film is established between the main bearing and gearbox before the motor rotates, avoiding the risk of dry friction and burning of the bearing bushes due to excessively high oil pressure or intermittent oil supply. This significantly improves the starting reliability and life-cycle safety of large rotating machinery. The first start-up duration provides ample time for pressure build-up, accommodating the pressure build-up delay caused by the high viscosity of the oil at low temperatures. The second start-up duration requires continuous pressure maintenance to allow the lubricating oil to fill the entire oil circuit and expel air bubbles, ensuring that the oil film stiffness meets design requirements. The prohibition of using lubrication status as an absolute prerequisite for motor operation during start-up aligns with the inherent safety principle that machinery cannot rotate without lubrication.
[0024] More specifically, step S2 also includes a surge prevention control step based on frequency segmentation, as shown below: The compressor's automatic climbing process is divided into low-frequency and high-frequency zones, with the anti-surge threshold as the boundary. In the low-frequency range at or below the anti-surge threshold, the anti-surge valve is forced to remain fully open, allowing for rapid passage through the surge zone in an open-loop manner; In the high-frequency range above the anti-surge threshold, the opening of the anti-surge valve is adjusted by PID control based on the distance between the operating point and the surge line.
[0025] In this embodiment, the anti-surge threshold is set to 40Hz. When the operating frequency is in a high-frequency range higher than the anti-surge threshold, closed-loop anti-surge control is activated. The deviation between the current operating point and the preset surge line in the compressor characteristic curve coordinate system is calculated in real time. This deviation is used as the control deviation, and the opening of the anti-surge valve is adjusted using a PID algorithm to keep the compressor operating within the preset safe operating range. The surge line is obtained by fitting a variable performance curve provided by the compressor manufacturer, or by connecting surge points determined through on-site anti-surge testing; the distance represents the surge margin. An anti-surge control line is set parallel to the surge line and located to the lower right of the surge line. The controller's goal is to keep the operating point to the right of the control line. When the operating point crosses the control line to the left, the PID controller output increases, opening the anti-surge valve.
[0026] Within the 0-40Hz range, the compressor impeller speed is low, the gas flow field is unstable, and the signal-to-noise ratio of the pressure / flow sensor measurements is poor. In this case, a forced full-open strategy is adopted, artificially increasing system damping by maximizing bypass flow. Essentially, this trades energy consumption for stability during startup. When the compressor frequency is ≤40Hz, a 100% opening command is forcibly output to the anti-surge valve actuator, while simultaneously disabling all closed-loop PID calculations. In this mode, the frequency is rapidly increased, using a large-flow bypass to forcibly move the operating point away from the low-frequency surge zone, crossing the 20-40Hz high-risk surge zone within 5 seconds. Above 40Hz, the compressor enters a stable and efficient region, and the surge boundary is clearly measurable. When the frequency exceeds the 40Hz threshold, it automatically switches to closed-loop mode, real-time acquiring the current flow rate and outlet pressure ratio, and calculating the distance between the operating point and the preset surge line in the compressor characteristic coordinate system. This surge line is fitted from the manufacturer's variable efficiency curve using cubic spline interpolation, and the safety control line is set as a curve offset by 15% flow margin. When the operating point approaches the control line, the PID controller immediately increases the valve opening command, pushing the operating point back to the safe zone by increasing the bypass flow. Compared to existing technologies that use a single closed-loop control throughout the entire process, this invention solves the control oscillation problem caused by the low sensor signal-to-noise ratio in the initial startup stage through a low-frequency forced full-open strategy; and avoids over-adjustment of traditional fixed threshold control during load fluctuations through high-frequency dynamic margin control, reducing valve wear caused by frequent operation of the anti-surge valve.
[0027] More specifically, in step S2, when performing operations such as continuing frequency increase, pausing frequency increase, or slightly decreasing frequency based on the monitored rate of change of operating parameters, the specific steps include: A first pressure change rate threshold and a second pressure change rate threshold are set, wherein the first pressure change rate threshold is less than the second pressure change rate threshold; When the monitored rate of change of compressor outlet pressure is less than or equal to the first rate of change threshold, a frequency upsampling operation is performed. When the monitored rate of change of compressor outlet pressure is between the first and second pressure change rate thresholds, the frequency increase is paused, the current frequency is maintained, and the pressure change rate is allowed to fall back. When the monitored rate of change of compressor outlet pressure is greater than or equal to the second rate of change threshold, a slight frequency reduction operation is performed, which reduces the preset step size of the operating frequency and maintains a preset stable interval before attempting to increase the frequency again.
[0028] The first pressure change rate threshold is 0.0018 MPa / s, representing the safe limit for pressure build-up. Exceeding this value indicates excessive energy accumulation, necessitating a halt to energy injection. During compressor frequency ramp-up, the outlet steam pressure signal is collected in real time. When the measured outlet pressure change rate falls between the first and second pressure change rate thresholds due to downstream user load fluctuations, the system determines that the current pipeline resistance build-up is too rapid, forcing the inverter to lock the current output frequency and ceasing to respond to the original linear frequency ramp-up command. This pause continues until the outlet pressure change rate falls below the first pressure change rate, at which point the system automatically resumes frequency ramp-up, smoothing out pressure peaks by trading time for space. The second pressure change rate threshold is 0.020 MPa / s, representing the critical point where overcurrent tripping or surge is imminent. At this point, a simple pause is insufficient to curb the pressure rise inertia, requiring negative adjustments such as frequency reduction to quickly unload the pressure. If the outlet pressure change rate suddenly increases to a level greater than or equal to the second pressure change rate threshold, indicating a serious risk of pressure build-up, the inverter is instructed to instantaneously reduce its frequency and forcibly lock the frequency to a preset interval. This action proactively reduces the compressor's power output, preventing excessive back pressure from causing stator current overshoot in the motor. Compared to the passive protection in existing technologies that rely solely on current threshold tripping, this method uses a pressure differential signal as a feedforward quantity to intervene before overload occurs. This effectively solves the problem of frequent tripping caused by excessive rigidity in the start-up curve, achieving flexible adaptive start-up under complex operating conditions and significantly reducing the impact of the start-up process on the power grid and mechanical components.
[0029] More specifically, the specific execution parameters for the micro-frequency reduction are: Frequency reduction is performed in a set step size, and the interval between two adjacent frequency reduction operations is the set time.
[0030] In practice, each frequency reduction operation has a step size of 1Hz. Too large a step size can cause a sudden pressure drop and trigger surge, while too small a step size will fail to curb the upward pressure trend. A minimum 5-second interval is set between each frequency reduction operation; this time constant is based on the physical response characteristics of the compressor and piping network. When the system detects a sudden increase in the outlet pressure change rate exceeding the second pressure change rate threshold, the current frequency increase command is immediately interrupted, and a -1Hz bias is added to the current operating frequency, forcing the inverter output to decrease. A 5-second interval is simultaneously initiated when the command is issued. During this period, regardless of fluctuations in the pressure change rate, no new frequency reduction or increase requests are responded to, waiting for the fluid condition's response to speed changes to stabilize. If, after 5 seconds, the sampled pressure change rate is still higher than the second pressure change rate threshold, it indicates that a single frequency reduction is insufficient to offset the load increase, triggering a second action to further reduce the frequency by 1Hz, and resetting the 5-second interval again. This logic is executed cyclically until the change rate returns to a safe range. Compared to existing PID control technologies, this solution limits the amplitude of a single adjustment by using a fixed step size, preventing compressor surge caused by significant frequency reduction. Furthermore, it establishes a dead zone at fixed intervals to mitigate the inertial lag of the fluid system. This effectively prevents back EMF surges caused by frequent acceleration and deceleration of the inverter, ensuring a smooth, uninterrupted operation under extreme conditions.
[0031] More specifically, step S3 also includes an exhaust spray control process, as shown below: Based on the fixed characteristic parameters of the compressor impeller and casing, the compression ratio of the real-time compressor outlet pressure and compressor inlet pressure, and the compressor inlet temperature, calculate the theoretical discharge temperature of the compressor under the current operating conditions. The theoretical exhaust temperature of the compressor is used as the set value for exhaust spraying, and the opening of the spray valve is automatically adjusted by PID control according to the set value.
[0032] In a specific implementation, since the increase in exhaust temperature during the operation of the steam compressor mainly comes from the conversion of compression work, the following calculation process needs to be performed to accurately control the exhaust temperature and avoid high-temperature damage to the impeller and casing:
[0033]
[0034] Among them, T theo Based on the theoretical exhaust temperature, X is the intermediate pressure variable, and P is the exhaust temperature. gauge P is the compressor outlet gauge pressure collected in real time. atmK1 is the local atmospheric pressure correction value, K2 is the pressure unit conversion factor, A is the characteristic constant of heat of vaporization, B is the characteristic constant of ultimate pressure, and C is the temperature scale correction constant. In one implementation, considering the complexity of computing resources and on-site working conditions, the following empirical formula based on experimental data fitting is used for rapid calculation: the local atmospheric pressure correction value is taken as 90 kPa to cope with specific altitude working conditions, the pressure unit conversion factor is taken as 100, the standard unit conversion factor is taken as 760 to simulate the saturation relationship corresponding to millimeters of mercury, and after fitting based on the compressor impeller characteristics, the vaporization heat characteristic constant is taken as 1668.21, the ultimate pressure characteristic constant is taken as 7.96681, and the temperature scale correction constant is taken as 228.8.
[0035] More specifically, the specific triggering condition for forcibly stopping the compressor's automatic climb in step S3 is as follows: The difference between the compressor exhaust theoretical temperature and the compressor inlet steam temperature is calculated in real time as the steam theoretical temperature rise. When the theoretical steam temperature rise is less than the lockout threshold, it is determined that the theoretical steam temperature rise is too low, and the automatic rise of the compressor is forcibly stopped. When the difference recovers to above the lockout threshold, the compressor resumes automatic ramping.
[0036] In one implementation, the lockout threshold is set to 1.5°C. This threshold is based on the premise that the energy input to the compressor is only slightly or insufficient to offset the latent heat change under saturated pressure, making gas highly susceptible to condensation in the impeller channel. If the frequency continues to increase at this point, the increased centrifugal force will eject droplets that strike the impeller like bullets. The theoretical exhaust temperature is calculated by real-time acquisition of inlet temperature and outlet pressure during the initial compressor startup, thus determining the theoretical steam temperature rise. If the theoretical steam temperature rise is detected to be below the lockout threshold, the system determines that the current compression ratio is insufficient to establish effective superheat and forces the inverter to maintain constant speed at the current frequency. The compressor rotor continuously heats the fluid by stirring the gas until the theoretical steam temperature rise rises above the threshold. At this point, the lockout signal is reset, allowing the frequency to continue increasing. This solution, by monitoring the theoretical temperature rise, eliminates the risk of condensate erosion caused by rapid compression of saturated steam, effectively protecting the high-speed impeller and dry gas sealing system. More specifically, the exhaust spray control process also includes a low-load forced manual mode, as detailed below: Preset the minimum opening value of the spray valve; Real-time monitoring of compressor operating frequency and theoretical steam temperature rise; When the compressor operating frequency is detected to be lower than the initial operating frequency, or the theoretical steam temperature rise is lower than the forced manual threshold, the PID control is switched to manual control and the spray valve opening is set to the minimum opening value. The manual control of the exhaust spray control will be switched back to PID control only when the theoretical steam temperature rises above the forced manual threshold.
[0037] In one implementation, the forced manual threshold is set to 0.5℃. During the initial cold start of the compressor, when the inverter output frequency climbs below the initial operating frequency, even if the exhaust thermocouple detects a temperature higher than the set value, it is still forcibly locked in manual mode, and the spray valve is set to a preset minimum holding opening to prevent the valve from fully opening due to PID integral accumulation at low airflow speeds, which could cause water accumulation at the bottom of the casing. When the compressor is running and the inlet conditions deteriorate, causing the real-time calculated theoretical steam temperature rise to drop below the forced manual threshold, the forced manual logic is immediately reactivated, cutting off the spray water supply and maintaining only the minimum opening to keep the pipeline full; until the temperature rise recovers, the PID controller resumes automatic adjustment. Compared to the existing technology where the PID loop is closed throughout, which is prone to integral saturation in the low-load area and thus causes the valve to open erroneously, this solution eliminates the risk of flooding at low flow rates and the risk of liquid hammer during the start-up phase through forced intervention at the operating condition threshold, ensuring that the spray water is injected only when the fluid has the effective operating condition of instantaneous evaporation and heat absorption capacity.
[0038] More specifically, it also includes a tiered shutdown procedure, as shown below: Real-time monitoring of the compressor's radial vibration and high-speed shaft displacement values; When the compressor outlet pressure change rate is detected to exceed the third pressure change rate threshold, or the radial vibration value is in the dangerous vibration range, or the high-speed shaft displacement exceeds the displacement threshold, the normal shutdown procedure is triggered. When the radial vibration value is detected to exceed the dangerous vibration range, an emergency shutdown procedure is triggered.
[0039] In one implementation, the third pressure change rate threshold is 0.2 MPa / s, the dangerous vibration range is greater than 40 micrometers and less than 50 micrometers, and the displacement threshold is 500 micrometers. When the online monitoring system detects that the high-speed shaft radial vibration value slowly rises to the dangerous vibration range, or the shaft displacement reaches the displacement threshold due to the accumulation of thrust load, or the outlet pressure change rate is measured to exceed the third pressure change rate threshold, it is determined that although the unit deviates from the optimal operating condition, it has not yet faced the risk of immediate disintegration. Then, the following steps are implemented: the frequency converter performs controlled deceleration, the anti-surge valve opens linearly in sync with the speed, and the oil pump continues to run until the speed returns to zero and then enters the turning gear cooling mode. The controlled deceleration process dissipates the rotor kinetic energy to avoid surge impact caused by sudden power failure.
[0040] More specifically, the tiered shutdown process also includes a shutdown spray control step, as detailed below: When executing the shutdown procedure, the compressor inlet steam pressure is collected in real time, and the saturation temperature corresponding to the pressure is looked up or calculated. Adjust the spray valve opening until the compressor inlet temperature equals the saturation temperature, and maintain this opening during shutdown.
[0041] During the deceleration process of executing the normal shutdown procedure, the compressor inlet pressure is sampled every 50ms, and the corresponding saturation temperature is obtained in real time using the built-in IAPWS-IF97 water vapor property table. If the inlet temperature is detected to be 105℃, indicating a superheated state, the PID controller adjusts the spray valve opening. When the inlet temperature approaches and stabilizes at 99.6℃, the system immediately locks the current valve opening and maintains this fixed opening during the subsequent speed coasting to zero, utilizing latent heat to absorb the residual heat generated by rotor resistance.
[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.
Claims
1. A fully automatic start-stop control method for a steam compressor based on a DeltaV system, characterized in that, Includes the following steps: Step S1: Based on the received start command, start the oil pump, spray water pump and main motor in sequence, and set the initial operating frequency of the compressor; Step S2: The compressor starts to automatically climb according to the climbing endpoint frequency. During the automatic climbing process, the change rate of operating parameters is monitored in real time. Based on the monitored change rate of operating parameters, the compressor performs operations such as continuing to increase the frequency, pausing the frequency increase, or slightly decreasing the frequency. The change rate of operating parameters includes at least one of the compressor outlet pressure change rate or the main motor current rise rate. Step S3: During the automatic climb phase, the theoretical steam temperature rise is calculated synchronously; when the theoretical steam temperature rise is lower than the preset lockout threshold, the automatic climb of the compressor is forcibly stopped, and the automatic climb phase continues after the theoretical steam temperature rise exceeds the lockout threshold. Step S4: The compressor operates normally after reaching the peak frequency.
2. The fully automatic start-stop control method for a steam compressor based on a DeltaV system according to claim 1, characterized in that, The specific steps for starting the oil pump, spray water pump, and main motor in sequence in step S1 are as follows: Start the oil pump, and after the inlet oil pressure is greater than the starting threshold during the first start-up period and continues to be greater than the starting threshold until the second start-up period, start the main motor fan and the main motor. If the inlet oil pressure does not reach the starting threshold within the first starting time, or if the inlet oil pressure does not remain above the starting threshold for the second starting time, the pump will be stopped and the valve closed.
3. The fully automatic start-stop control method for a steam compressor based on a DeltaV system according to claim 1, characterized in that, Step S2 also includes a frequency segmentation-based anti-surge control step, as detailed below: The compressor's automatic climbing process is divided into low-frequency and high-frequency zones, with the anti-surge threshold as the boundary. In the low-frequency range at or below the anti-surge threshold, the anti-surge valve is forced to remain fully open, allowing for rapid passage through the surge zone in an open-loop manner; In the high-frequency range above the anti-surge threshold, the opening of the anti-surge valve is adjusted by PID control based on the distance between the operating point and the surge line.
4. The fully automatic start-stop control method for a steam compressor based on a DeltaV system according to claim 1, characterized in that, In step S2, when performing operations such as continuing frequency increase, pausing frequency increase, or slightly decreasing frequency based on the monitored rate of change of operating parameters, the specific steps include: A first pressure change rate threshold and a second pressure change rate threshold are set, wherein the first pressure change rate threshold is less than the second pressure change rate threshold; When the monitored rate of change of compressor outlet pressure is less than or equal to the first rate of change threshold, a frequency upsampling operation is performed. When the monitored rate of change of compressor outlet pressure is between the first and second pressure change rate thresholds, the frequency increase is paused, the current frequency is maintained, and the pressure change rate is allowed to fall back. When the monitored rate of change of compressor outlet pressure is greater than or equal to the second rate of change threshold, a slight frequency reduction operation is performed, which reduces the preset step size of the operating frequency and maintains a preset stable interval before attempting to increase the frequency again.
5. The fully automatic start-stop control method for a steam compressor based on a DeltaV system according to claim 4, characterized in that, The specific execution parameters for the micro-frequency reduction are: Frequency reduction is performed in a set step size, and the interval between two adjacent frequency reduction operations is the set time.
6. The fully automatic start-stop control method for a steam compressor based on a DeltaV system according to claim 1, characterized in that, Step S3 also includes an exhaust spray control process, as detailed below: Based on the fixed characteristic parameters of the compressor impeller and casing, the compression ratio of the real-time compressor outlet pressure and compressor inlet pressure, and the compressor inlet temperature, calculate the theoretical discharge temperature of the compressor under the current operating conditions. The theoretical exhaust temperature of the compressor is used as the set value for exhaust spraying, and the opening of the spray valve is automatically adjusted by PID control according to the set value.
7. The fully automatic start-stop control method for a steam compressor based on a DeltaV system according to claim 1, characterized in that, The specific triggering condition for forcibly stopping the compressor's automatic climb in step S3 is as follows: The difference between the compressor exhaust theoretical temperature and the compressor inlet steam temperature is calculated in real time as the steam theoretical temperature rise. When the theoretical steam temperature rise is less than the lockout threshold, it is determined that the theoretical steam temperature rise is too low, and the automatic rise of the compressor is forcibly stopped. When the difference recovers to above the lockout threshold, the compressor resumes automatic ramping.
8. The fully automatic start-stop control method for a steam compressor based on a DeltaV system according to claim 7, characterized in that, The exhaust spray control process also includes a low-load forced manual mode, as detailed below: Preset the minimum opening value of the spray valve; Real-time monitoring of compressor operating frequency and theoretical steam temperature rise; When the compressor operating frequency is detected to be lower than the initial operating frequency, or the theoretical steam temperature rise is lower than the forced manual threshold, the PID control is switched to manual control and the spray valve opening is set to the minimum opening value. The manual control of the exhaust spray control will be switched back to PID control only when the theoretical steam temperature rises above the forced manual threshold.
9. The fully automatic start-stop control method for a steam compressor based on a DeltaV system according to claim 1, characterized in that, It also includes a tiered shutdown procedure, as detailed below: Real-time monitoring of the compressor's radial vibration and high-speed shaft displacement values; When the compressor outlet pressure change rate is detected to exceed the third pressure change rate threshold, or the radial vibration value is in the dangerous vibration range, or the high-speed shaft displacement exceeds the displacement threshold, the normal shutdown procedure is triggered. When the radial vibration value is detected to exceed the dangerous vibration range, an emergency shutdown procedure is triggered.
10. The fully automatic start-stop control method for a steam compressor based on a DeltaV system according to claim 9, characterized in that, The tiered shutdown process also includes a shutdown spray control step, as detailed below: When executing the shutdown procedure, the compressor inlet steam pressure is collected in real time, and the saturation temperature corresponding to the pressure is looked up or calculated. Adjust the spray valve opening until the compressor inlet temperature equals the saturation temperature, and maintain this opening during shutdown.