Fermentation heat-expansion work self-circulation refrigerating system and control method

Abstract

The invention relates to the technical field of industrial refrigeration, and discloses a fermentation heat-expansion work self-circulation refrigeration system which comprises a refrigerant circulation loop used for bearing carbon dioxide serving as a refrigerant to circularly flow in the refrigerant circulation loop, the refrigerant circulation loop is sequentially provided with an evaporator, a compressor, a condenser and an expansion machine with a power output shaft in series; and the chilled water circulation loop comprises a heat exchange component arranged in the fermentation tank, a circulating water pump and a connecting pipeline, and the chilled water circulation loop exchanges heat with the refrigerant circulation loop through the evaporator and is used for transferring fermentation heat generated in the fermentation tank to the carbon dioxide refrigerant. The radial centripetal turbine expansion machine is arranged to replace a traditional throttling valve, and is matched with work recovery and coupling mechanisms such as the planetary gear reduction box and the electromagnetic clutch, high-pressure potential energy released by supercritical carbon dioxide in the expansion process is converted into mechanical work, and the mechanical work is directly used for driving the compressor to run.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of industrial refrigeration technology, in particular to a fermentation heat-expansion work self-circulation refrigeration system and a control method. BACKGROUND

[0002] In the modern industrial system, accurate temperature control is the core prerequisite for ensuring the stable operation of many chemical reactions and biological processes. Especially in the fields of biopharmaceuticals, fine chemicals, and food engineering, large-scale biological fermentation processes, such as using Pichia pastoris and other engineering strains for recombinant protein expression or using microorganisms for antibiotic production, are essentially a highly complex biochemical reaction system. In this process, the metabolic activity of microorganisms releases a large amount of biological reaction heat. If this heat cannot be removed in time and stably, the temperature in the fermenter will rise rapidly, thereby severely inhibiting, even destroying, the synthesis pathway of the target product, leading to a decrease in yield, an increase in impurities, and ultimately affecting product quality and economic benefits. Therefore, providing a high-efficiency and reliable refrigeration system to provide constant temperature chilled water for the fermenter is the cornerstone of ensuring the smooth implementation of industrial production.

[0003] In the prior art, substances such as freon or ammonia are usually used as refrigerants to achieve heat transfer through a closed thermodynamic cycle. The working process mainly includes four core links: first, the liquid refrigerant exchanges heat with the circulating cooling water from the fermenter in the evaporator, absorbs the fermentation heat, and evaporates into low-temperature and low-pressure gas; then, the gas is sucked into the compressor and compressed into high-temperature and high-pressure superheated steam, which requires a large amount of external electrical energy; next, the high-temperature and high-pressure steam enters the condenser to release heat to the environment (such as cooling tower circulating water or air), and condenses into high-pressure liquid; finally, the high-pressure liquid flows through the throttle valve, and the pressure and temperature drop sharply, becoming low-temperature and low-pressure liquid or gas-liquid mixture, entering the evaporator to start the next cycle.

[0004] However, after searching, it was found that in the traditional technology, the compressor consumes electrical energy to raise the refrigerant to a high-pressure state, giving the working fluid a very high pressure potential. But in the subsequent throttle valve link, the working fluid undergoes an isenthalpic throttling process, and the high-pressure potential is not recovered in the form of work, but is directly dissipated due to resistance loss, which is not only one of the main sources of system entropy increase, but also the fundamental reason for low energy efficiency.

[0005] Furthermore, traditional systems often rely on crude adjustments to the fermenter's temperature by starting and stopping the compressor or adjusting the opening of the circulating water valve. Due to the system's inherent thermal inertia and the lack of an endogenous energy regulation mechanism that precisely matches the dynamic changes in fermentation heat, this control approach can easily lead to fluctuations in the tank temperature of ±1.5°C or more around the set point. For environmentally sensitive biological processes like Pichia pastoris protein expression, such temperature fluctuations can trigger cellular stress responses, significantly impacting proper protein folding and expression efficiency. Summary of the Invention

[0006] (1) Technical problems solved

[0007] In view of the deficiencies of the prior art, the present invention provides a fermentation heat-expansion work self-circulating refrigeration system and a control method, which solves the problem of "low working efficiency" in the above-mentioned background technology.

[0008] (2) Technical solution

[0009] To achieve the above objectives, the present invention is implemented through the following technical solutions: a fermentation heat-expansion work self-circulating refrigeration system, comprising:

[0010] a refrigerant circulation circuit for carrying carbon dioxide as a refrigerant to circulate therein, wherein the refrigerant circulation circuit is sequentially provided with an evaporator, a compressor, a condenser, and an expander having a power output shaft;

[0011] a chilled water circulation circuit, comprising a heat exchange component, a circulating water pump, and connecting pipes disposed in the fermentation tank, wherein the chilled water circulation circuit exchanges heat with the refrigerant circulation circuit via the evaporator, and is used to transfer fermentation heat generated in the fermentation tank to the carbon dioxide refrigerant;

[0012] a work recovery and coupling mechanism for mechanically connecting the power output shaft of the expander to the power input shaft of the compressor, so as to transmit the mechanical energy output by the expander due to the expansion work of the carbon dioxide refrigerant and use it to assist in driving the compressor;

[0013] A centralized control unit is electrically connected to and controls the operation of the compressor, the expander, and the circulating water pump, so as to coordinately adjust the refrigeration capacity and operating state of the system according to the fermentation heat load.

[0014] Preferably, the power recovery and coupling mechanism includes a planetary gear reduction box, an electromagnetic clutch and a rigid coupling;

[0015] The system further comprises a variable frequency motor for driving the compressor;

[0016] The power output shaft of the expander is connected to the high-speed input end of the planetary gear reducer, and the power input shaft of the compressor is connected to the low-speed output end of the planetary gear reducer;

[0017] The output shaft of the variable frequency motor is coaxially connected with the power input shaft of the compressor through the electromagnetic clutch and the rigid coupling to form a power convergence, so that the power recovered by the expander and the power provided by the variable frequency motor can jointly drive the compressor;

[0018] The electromagnetic clutch is controlled by the centralized control unit to selectively disconnect or engage the power transmission between the variable frequency motor and the compressor under preset working conditions.

[0019] Preferably, the compressor is a variable frequency motor driven screw compressor for compressing low-temperature and low-pressure gaseous carbon dioxide flowing out of the evaporator into high-temperature and high-pressure supercritical state, and the expander is a radial centripetal turbine expander for making high-temperature and high-pressure supercritical carbon dioxide flowing out of the condenser to do adiabatic expansion work to convert its pressure potential energy into mechanical energy.

[0020] Preferably, the radial centripetal turbine expander adopts magnetic suspension bearing to support the rotor, and a variable opening inlet guide vane mechanism is arranged at the inlet thereof, the inlet guide vane mechanism is controlled by the centralized control unit to accurately adjust the mass flow and flow attack angle of the carbon dioxide refrigerant entering the expander, thereby realizing dynamic adjustment of the output power of the expander.

[0021] Preferably, a high-precision temperature sensor is arranged on the chilled water circulation circuit, specifically including:

[0022] First and second temperature sensors are arranged at the water inlet and outlet of the heat exchange component of the fermenter respectively for real-time monitoring of the chilled water temperature entering and leaving the fermenter, and third and fourth temperature sensors are arranged at the water inlet and outlet of the fluid passage for passing through the chilled water in the evaporator respectively for real-time monitoring of the chilled water temperature entering and leaving the evaporator, the first, second, third and fourth temperature sensors are all four-wire high-precision platinum resistance thermometers, and the measurement data is transmitted to the centralized control unit as the basis for heat load calculation and feedback control.

[0023] Preferably, the centralized control unit is embedded with control logic and adopts a composite control strategy combining predictive feedforward with dynamic feedback correction. The predictive feedforward control means that a metabolic heat generation prediction model corresponding to the fermentation process is pre-stored in the centralized control unit, and the predicted heat load in the next control cycle is calculated based on the fermentation process parameters collected in real time, and a benchmark carbon dioxide refrigerant mass flow rate is calculated accordingly. The dynamic feedback correction control means that the centralized control unit calculates a correction adjustment amount through a controller based on the deviation between the actual temperature of the chilled water measured by the second temperature sensor and the preset target temperature. The correction adjustment amount is used to fine-tune the benchmark carbon dioxide refrigerant mass flow rate to obtain the final target mass flow rate.

[0024] Preferably, after determining the final target mass flow, the centralized control unit executes a multivariable collaborative optimization subroutine to determine the specific operating parameters of the compressor and the expander. The objective function of the multivariable collaborative optimization subroutine is: to maximize the instantaneous comprehensive performance coefficient of the system under the constraint condition of satisfying the final target mass flow, wherein the instantaneous comprehensive performance coefficient is defined as the ratio of the actual heat exchange of the evaporator to the net input work of the system, and the net input work is the difference between the measured input power of the compressor and the measured output power of the expander. The optimization variables of the multivariable collaborative optimization subroutine are the inverter output frequency of the compressor and the inlet guide vane opening of the expander. The centralized control unit solves the optimal frequency and optimal opening combination that maximizes the objective function, and sends it as a control instruction to the corresponding actuator.

[0025] Preferably, the metabolic heat generation prediction model adopts the Kalman filter algorithm for online real-time correction. The centralized control unit calculates the actual heat exchange capacity of the evaporator side in real time based on the measurement values ​​of the third temperature sensor and the fourth temperature sensor and the flow rate of the chilled water, and uses it as the actual fermentation heat load. The Kalman filter algorithm uses the actual fermentation heat load as the observation value to update and correct the state variables or model parameters inside the metabolic heat generation prediction model, so that the prediction output of the model can dynamically track the changes in the metabolic characteristics of the actual fermentation process, so as to improve the accuracy of the predictive feedforward control.

[0026] Preferably, a method for controlling a fermentation heat-expansion work self-circulating refrigeration system is performed by the centralized control unit and comprises the following steps:

[0027] Step 1: Prediction feedforward step: A metabolic heat generation prediction model matching the fermentation process is used, and based on the fermentation process parameters acquired in real time, the predicted heat load generated by the fermenter during the next control cycle is calculated. The baseline CO2 refrigerant mass flow rate required to remove this heat is calculated based on this predicted heat load.

[0028] Step 2: Dynamic feedback correction step: Real-time monitoring of the chilled water outlet temperature of the fermentation tank, comparison with a preset target temperature to obtain a temperature deviation, and calculation of a correction adjustment amount using the temperature deviation through a PID controller. The correction adjustment amount is combined with the reference carbon dioxide refrigerant mass flow rate to obtain a final target mass flow rate;

[0029] Step 3: Multivariable collaborative optimization execution step: with the ultimate target mass flow rate as the constraint condition and the maximization of the instantaneous comprehensive performance coefficient of the system as the optimization goal, the optimal operating frequency of the compressor and the optimal inlet guide vane opening of the expander are collaboratively solved, and the compressor and expander are controlled to operate according to the set of optimal parameters.

[0030] (3) Beneficial effects

[0031] The present invention provides a fermentation heat-expansion work self-circulating refrigeration system and control method. It has the following beneficial effects:

[0032] (1) When in use, the fermentation heat-expansion work self-circulating refrigeration system and control method replaces the traditional throttle valve by setting a radial centripetal turbo expander, and cooperates with a planetary gear reducer, electromagnetic clutch and other power recovery and coupling mechanisms to convert the high-pressure potential energy released by supercritical carbon dioxide during the expansion process into mechanical work, which is directly used to drive the operation of the compressor. This changes the disadvantage of the throttle valve in the traditional refrigeration system that dissipates the high-pressure potential energy in the form of resistance loss, allowing the expansion work to directly compensate for the energy consumption required by the compressor, greatly reducing the system's dependence on external electricity, effectively reducing the system's entropy increase, significantly improving energy utilization efficiency, and realizing the self-circulating utilization of fermentation heat and expansion work.

[0033] (2) When in use, the fermentation heat-expansion work self-circulating refrigeration system and control method adopts a collaborative control strategy of "predictive feedforward control + dynamic feedback correction", combined with a metabolic heat generation prediction model with online correction of the Kalman filter and a cascade PID control structure, to respond to the dynamic changes of fermentation heat in real time. The chilled water temperature is monitored in real time by a high-precision platinum resistance thermometer (measurement error ±0.1°C), and the control deviation of the chilled water temperature is stabilized within ±0.2°C by precise adjustment of the compressor speed and the expansion machine guide vane opening. Large fluctuations of the tank temperature above ±1.5°C are avoided, providing a stable environment for temperature-sensitive biological fermentation processes and ensuring the synthesis efficiency and quality of the target product.

[0034] (2) The fermentation heat-expansion work self-circulation refrigeration system and control method, when in use, by adopting supercritical carbon dioxide as the working medium, the evaporator selects a 316L stainless steel micro-channel plate finned heat exchanger and is formed by a vacuum brazing process, can withstand the acid corrosion of carbon dioxide in the wet area and a working pressure of up to 13.0 MPa or more, solves the adaptation problem of traditional freon or ammonia refrigerant in a high-pressure, corrosive environment. At the same time, supercritical carbon dioxide has the characteristics of environmental friendliness, non-flammability and non-toxicity, avoiding the environmental risk of traditional refrigerants; and the optimized design of the semi-closed double-screw compressor and the magnetic suspension bearing expander further improves the long-term stable operation capability of the system under the working condition of high pressure and drastic change of physical properties. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a schematic diagram of the system architecture of the present application.

[0036] In the figure: 1, evaporator; 2, compressor; 3, condenser; 4, expander; 5, work recovery and coupling mechanism; 6, planetary gear reduction box; 7, electromagnetic clutch; 8, rigid coupling; 9, variable frequency motor; 10, fermentation tank; 11, circulating water pump; 12, centralized control unit; 13, first temperature sensor; 14, second temperature sensor; 15, third temperature sensor; 16, fourth temperature sensor; 17, pressure sensor; 18, mass flow meter. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0038] Please refer to Figure 1 The present application provides a fermentation heat-expansion work self-circulation refrigeration system, which comprises a refrigerant circulation loop for carrying and circulating carbon dioxide refrigerant, a chilled water circulation loop for transferring the biological heat generated by the fermentation tank to the refrigerant, a work recovery and coupling mechanism 5 for realizing energy recovery and reuse, and a centralized control unit 12 as the nerve center of the whole system.

[0039] Specifically, the refrigerant circuit is a closed, high-pressure piping system, with supercritical carbon dioxide circulating as the working fluid. The core function of this circuit is to achieve the targeted transfer of heat from the chilled water to the external environment through the controlled phase transition and work conversion of carbon dioxide between different thermodynamic states. During steady-state operation, the carbon dioxide refrigerant flows sequentially through evaporator 1, compressor 2, condenser 3, and expander 4, forming a complete transcritical thermodynamic cycle.

[0040] Evaporator 1 utilizes a microchannel plate-fin heat exchanger, integrally formed from 316L stainless steel using a vacuum brazing process, to withstand the potential acidic corrosion caused by the CO2 working fluid in wet areas and the overall high operating pressure of the system. It contains two completely isolated but closely thermally connected fluid channels: the first, connected to the chilled water circuit, transports low-temperature chilled water carrying fermentation heat; the second, part of the refrigerant circuit, transports low-temperature, low-pressure liquid or gas-liquid two-phase CO2 refrigerant. The two fluids flow in countercurrent within evaporator 1 to maximize the heat exchange temperature difference and efficiency. During the heat exchange process, the CO2 refrigerant absorbs heat from the low-temperature chilled water, undergoing a constant-pressure evaporation process, transforming from its entry state, a low-temperature, low-pressure liquid or gas-liquid two-phase (e.g., pressure 4.0 MPa, temperature -10°C), to its exit state, a low-temperature, low-pressure gas (e.g., pressure 4.0 MPa, temperature -5°C). The refrigerant outlet of the evaporator 1 is fluidically connected to the air intake of the compressor 2 via a first pipeline. A pressure sensor 17 and a temperature sensor for monitoring the state of the refrigerant are installed on the first pipeline.

[0041] The function of compressor 2 is to pressurize the low-temperature, low-pressure gaseous carbon dioxide flowing out of evaporator 1, raising it to a high-temperature, high-pressure supercritical state, and providing the necessary pressure potential energy for subsequent heat release and expansion work. Compressor 2 is a semi-enclosed twin-screw compressor. Its internal rotor profile has been specially optimized to adapt to the characteristics of carbon dioxide's drastic changes in physical properties near the critical point, and to withstand exhaust pressures of up to 13.0 MPa. Compressor 2 is directly driven by a variable frequency motor 9, which is preferably a permanent magnet synchronous motor. In conjunction with a vector control inverter, it can achieve wide-range, high-precision adjustment of the speed. The exhaust port of compressor 2 is connected to the first inlet of condenser 3 through a second high-pressure pipeline with a pressure rating of not less than 15.0 MPa. A pressure sensor 17 and a temperature sensor are also provided on the second high-pressure pipeline for real-time monitoring of the exhaust status of the compressor.

[0042] Condenser 3 is a shell-and-tube heat exchanger, wherein the tube side is connected to the second high-pressure pipeline for passing high-temperature, high-pressure supercritical carbon dioxide fluid, while the shell side is connected to an external cooling system (e.g., a cooling tower circulating water system) for passing cooler cooling water. As the supercritical carbon dioxide flows through the tube side, it releases a large amount of heat to the cooling water in the shell side, significantly dropping its temperature. However, since its state remains above the critical pressure (7.38 MPa), it does not undergo a phase change and remains a high-pressure, but cooled, supercritical fluid upon leaving condenser 3. The first outlet of condenser 3 is connected to the air inlet fluid of expander 4 via a third high-pressure pipeline.

[0043] Expander 4 is a radial-centrifugal turboexpander. To achieve stable operation at ultra-high speeds (e.g., 80,000 to 120,000 rpm) and eliminate the risk of refrigerant contamination from traditional lubricating oil systems, it utilizes magnetic bearing technology. A variable-opening inlet guide vane mechanism, driven by an external servo actuator, precisely adjusts the flow rate and angle of attack of the fluid entering the turbine impeller, thereby dynamically controlling the expander's power and refrigerant flow. High-temperature, high-pressure supercritical carbon dioxide flows through the third high-pressure pipeline into expander 4. It undergoes a nearly adiabatic expansion process within the turbine, driving the turbine impeller to rotate at high speed and output mechanical work. During this process, the pressure and temperature of the carbon dioxide drop dramatically, for example, from 12.0 MPa and 80°C upon entry to 4.0 MPa and 45°C upon exit, transforming into a gas-liquid two-phase state or a near-saturated vapor state. The exhaust port of expander 4 is connected to the inlet of the second fluid channel of evaporator 1 via a fourth pipeline, thus completing the refrigerant circulation loop. The inlet and outlet ports of the expander 4 are also respectively provided with a pressure sensor 17 , a temperature sensor and a mass flow meter 18 for precise measurement.

[0044] The power recovery and coupling mechanism 5 converts the high-speed, low-torque mechanical work output by the expander 4 into low-speed, high-torque mechanical work suitable for driving the compressor 2, and superimposes this work with the output power of the main drive motor 9. Specifically, it comprises a planetary gearbox 6, an electromagnetic clutch 7, and a rigid coupling 8. The power output shaft of the expander 4, namely the high-speed rotor shaft supported by magnetic bearings, is connected to the high-speed input end (typically the sun gear) of the planetary gearbox 6. The power input shaft of the compressor 2 is a double-extension structure, one end of which is connected to the low-speed output end (typically the planetary carrier) of the planetary gearbox 6. The planetary gearbox 6 offers the advantages of a high transmission ratio (e.g., 4.5:1 to 10:1), a compact structure, and a coaxial output, perfectly matching the speed difference between the expander and compressor. The output shaft of the variable frequency motor 9 is coaxially connected to the other end of the power input shaft of the compressor 2 via the electromagnetic clutch 7 and the rigid coupling 8. The power recovered by the expander 4 is transferred to the compressor shaft via the planetary gearbox 6, while the supplementary power provided by the variable frequency motor 9 is input from the other end. Together, they drive compressor 2, allowing expansion work to directly offset some of the compressor's energy consumption. Electromagnetic clutch 7, controlled by centralized control unit 12, disconnects variable-frequency motor 9 from compressor 2 during initial system startup or during specific commissioning modes, allowing for step-by-step commissioning or standalone operation.

[0045] The chilled water circulation loop includes a jacket located outside the fermenter 10 or a cooling coil located inside the fermenter 10, a circulating water pump 11, and connecting pipes. When the system is in operation, the circulating water pump 11 pumps low-temperature chilled water (e.g., 13°C) cooled through the first fluid channel of the evaporator 1 into the jacket or cooling coil of the fermenter 10. As the chilled water flows through the jacket or coil, it exchanges heat with the fermentation liquid, absorbing a large amount of bioreaction heat generated by microbial metabolism, causing its own temperature to rise (e.g., to 16°C). The heated chilled water is then pumped back to the inlet of the first fluid channel of the evaporator 1, transferring the absorbed heat to the carbon dioxide refrigerant, completing the heat transfer cycle. To achieve precise temperature control of the fermentation process, four high-precision temperature sensors are installed in the chilled water circulation loop. Specifically, a first temperature sensor 13 and a second temperature sensor 14 are installed at the water inlet and outlet of the cooling jacket of the fermenter 10, respectively. Similarly, a third temperature sensor 15 and a fourth temperature sensor 16 are respectively installed at the water inlet and outlet of the first fluid channel of the evaporator 1. These four temperature sensors are preferably four-wire, Class AA precision platinum resistance thermometers with a measurement error of less than ±0.1°C, providing a reliable data basis for subsequent accurate heat load calculation and feedback control.

[0046] The centralized control unit 12 is usually built on the hardware of a high-performance industrial programmable logic controller (PLC) or an embedded real-time controller to ensure the determinism and high response speed of the control algorithm. Its internal logical functions can be divided into a data acquisition module, a state monitoring module, a core control processor and a control execution module. The data acquisition module is electrically connected to sensors arranged throughout the system through a high-resolution analog input channel, including a first temperature sensor (13), a second temperature sensor (14), a second temperature sensor (14), a third temperature sensor (15), a pressure sensor 17 at a key node of the refrigerant circuit (compressor suction and exhaust ports, expander suction and exhaust ports), and a mass flow meter 18 for accurately measuring the refrigerant circulation volume. The data acquisition module samples and digitizes all analog signals at a frequency of not less than 100 Hz, and receives status information from each frequency converter and actuator through a digital communication interface. The state monitoring module is specifically responsible for monitoring the operating parameters of the rotating components in the system, for example, by connecting a power analyzer to monitor the instantaneous input power P of the variable frequency motor 9. comp , the instantaneous output power P is monitored by the torque or power sensor built into the expander 4 exp , and monitor the actual speed of the compressor and expander through an encoder or speed sensor. The core control processor is the calculation center, which is equipped with a metabolic heat generation prediction model for a specific fermentation process and runs a set of advanced multivariable collaborative control algorithms in real time. The control execution module generates specific control instructions based on the calculation results of the core control processor, and sends frequency setting signals to the inverter of the compressor 2 and the inverter of the circulating water pump 11 through the analog output channel (such as 4-20mA current signal), and sends opening instructions to the inlet guide vane actuator of the expander 4 through the servo control signal or PWM signal, and controls the on and off of the electromagnetic clutch 7 through the digital output channel.

[0047] In addition, the present invention also provides a method for controlling a fermentation heat-expansion work self-circulating refrigeration system, which specifically comprises the following steps:

[0048] Step 1: System initialization and target parameter setting. During the system startup phase, the operator selects the type of bio-fermentation process to be carried out through the human-computer interaction interface. Based on the selection, the core control processor retrieves the metabolic heat generation prediction model that matches it from its memory. This model is essentially a description of the heat generation rate Q per unit volume of fermentation liquid per unit time. ferm The mathematical equations of the functional relationship between the key state variables of the fermentation process can be in the form of: Where X is the bacterial concentration, q s is the specific substrate consumption rate, Y x / s is the yield coefficient of the bacteria to the substrate, m sAt the same time, the operator sets the core control target of this process, that is, the target supply temperature of chilled water T setpoint (For example, accurate to 15.0°C), and the allowable temperature control deviation window ΔT allow (For example, set to ±0.2°C).

[0049] Step 2: Predictive feedforward control based on metabolic model. After the system enters steady-state operation, the feedforward control logic is triggered once in a relatively long time period (for example, every 60 seconds). The data acquisition module obtains real-time process parameters related to the model from the fermenter's monitoring system (through industrial Ethernet protocols such as OPC or Modbus), such as the substrate consumption rate calculated by accurately measuring the flow rate of the feed pump, or the oxygen consumption rate (OUR) and carbon dioxide release rate (CER) measured by the exhaust gas analyzer to indirectly infer the intensity of metabolic activity. These real-time parameters are substituted into the loaded metabolic heat generation prediction model, and the core control processor calculates the total heat load Q that the fermenter is expected to generate in the next control cycle based on this. pred Based on this predicted heat load, combined with the specific heat capacity Cp of the chilled water and the target temperature designed in the evaporator 1, the processor calculates a reference CO2 refrigerant mass flow rate that is theoretically just enough to remove this heat. Then, the processor consults the performance curves (MAPs) of the compressor 2 and expander 4 pre-stored in the memory. These MAPs are digital matrices that describe the performance (efficiency, power) of the equipment under different working conditions (speed, pressure ratio, flow). By reverse lookup or interpolation calculation, the processor can find the value to achieve The reference compressor 2 speed corresponding to this target flow rate and the reference expander guide vane opening α exp base This set of reference parameters constitutes the main output of the feedforward control.

[0050] Step 3: Dynamic feedback correction based on high-precision temperature measurement. Between two cycles of feedforward control, in order to cope with model prediction deviations, instantaneous fluctuations in the fermentation process, and external environmental disturbances, the system performs rapid feedback correction at a frequency much higher than the feedforward cycle (for example, every 1 second). The data acquisition module reads the measurement value of the second temperature sensor 14 at the water outlet of the cooling jacket of the fermenter 10 in real time at intervals of 1 second to obtain the actual supply temperature T of the chilled water. actual The core control processor compares this actual value with the target set value T setpoint Compare and calculate the real-time temperature deviation e(t) = T setpoint -T actualThe proportional-integral-derivative (PID) controller calculates a correction adjustment based on the current deviation e(t), the accumulation of the deviation, and the rate of change of the deviation. This adjustment is interpreted by the core control processor as a fine-tuning requirement for the refrigerant mass flow rate. Finally, the target refrigerant mass flow rate of the current cycle is determined as the sum of the feedforward reference value and the feedback correction value, that is,

[0051] Step 4: Multivariable collaborative optimization and execution. After determining the final target mass flow After that, the core control processor does not directly convert it into a single actuator instruction, but starts a multi-variable collaborative optimization subroutine. The core objective function of this subroutine is to strictly meet Under the premise of constraints, maximize the instantaneous comprehensive performance coefficient COP of the entire system inst , the coefficient of performance is defined as: where Q evap is the actual heat exchange of evaporator 1 (which can be accurately calculated by the temperature difference and flow rate on the chilled water side), P comp is the measured input power of the variable frequency motor 9 of the compressor 2, P exp is the measured output power of expander 4. The decision variable of this optimization problem is the inverter output frequency f of compressor 2. comp and the inlet guide vane opening α of expander 4 exp The core control processor uses the stored performance MAP diagram, combined with the real-time pressure and temperature conditions, to quickly solve the optimal operating point that can make the COP inst A set of optimal operating parameter combinations that achieves the maximum value After the solution is completed, the control execution module immediately and These signals are sent as control instructions to the inverter of compressor 2 and the guide vane servo actuator of expander 4. Simultaneously, the processor dynamically adjusts the inverter frequency of circulating water pump 11 based on the real-time temperature difference of the chilled water circuit and the total system heat load, ensuring that the chilled water flow rate matches the refrigerant flow rate, maintaining efficient heat exchange in evaporator 1.

[0052] Step 5: Power recovery rate monitoring and system status self-diagnosis. During the operation of the entire system, the status monitoring module continuously collects the input power P of compressor 2. comp and the expander output power P exp , and calculate the expansion work recovery rate in real time The recovery rate is used as a key system health indicator and is continuously recorded and trended. It is not a direct control variable, but when η is monitoredrec If an irreversible, sustained downward trend (e.g., a drop exceeding 5%) occurs under similar operating conditions (i.e., similar pressure ratios and mass flow rates), the system automatically triggers an alert and, through the HMI, alerts the operator to potential issues such as expander turbine blade fouling or wear, bearing degradation, or minor leaks in the refrigerant lines. Furthermore, the control system has built-in sensor self-diagnostic logic. For example, by comparing the readings of the fermenter 10 outlet temperature with the evaporator 1 inlet temperature, it can determine whether a sensor is drifting or failing.

[0053] The metabolic heat generation prediction model can be modified online in real time by introducing the Kalman filter algorithm. Specifically, the temperature difference T in -T out The actual fermentation heat load Q calculated from the flow rate (obtained by the water pump inverter frequency or dedicated flow meter) actual =m water ·C p,water ·(T in -T out ) serves as the "observation" of the Kalman filter. Key parameters within the metabolic heat model serve as the "state variables" to be estimated. During each control cycle, the filter uses the residual between the observed values ​​and the model's predicted values ​​to update and correct the state variables. This adaptive mechanism enables the predictive model to dynamically track changes in metabolic characteristics during the actual fermentation process due to batch differences or subtle changes in culture conditions, significantly improving the long-term accuracy of feedforward control.

[0054] In addition, the PID controller can be designed as a cascade control structure to improve the dynamic response performance and anti-interference ability of the system. In this structure, the main controller of the outer loop is responsible for processing the temperature deviation e(t) with a slower response. Its input is T sctpoint -T actual , its output is no longer a direct actuator command, but a set value of the inner loop slave controller, which is the target refrigerant mass flow rate The slave controller of the inner loop is a high-speed flow controller, whose input is The actual refrigerant flow rate m measured by the mass flow meter 18 co2_actual The output directly affects the two fast actuators, compressor 2 speed and expander guide vane opening. This cascade structure decouples the control of the slow process (heat transfer) from the fast process (fluid dynamics), allowing the inner loop to quickly and accurately track the flow command issued by the outer loop, greatly improving the system's response speed to sudden load changes and control stability.

[0055] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A fermentation heat-expansion work self-circulating refrigeration system, characterized in that: include: A refrigerant circulation circuit for carrying carbon dioxide as a refrigerant to circulate therein, wherein the refrigerant circulation circuit is sequentially provided with an evaporator (1), a compressor (2), a condenser (3), and an expander (4) having a power output shaft; A chilled water circulation circuit, comprising a heat exchange component, a circulating water pump (11), and connecting pipes arranged in the fermentation tank (10), wherein the chilled water circulation circuit performs heat exchange with the refrigerant circulation circuit via the evaporator (1) and is used to transfer fermentation heat generated in the fermentation tank (10) to the carbon dioxide refrigerant; a work recovery and coupling mechanism (5) for mechanically connecting the power output shaft of the expander (4) with the power input shaft of the compressor (2) so as to transmit the mechanical energy output by the expander (4) due to the expansion work of the carbon dioxide refrigerant and use it to assist in driving the compressor (2); A centralized control unit (12) is electrically connected to and controls the operation of the compressor (2), the expander (4) and the circulating water pump (11) to coordinately adjust the cooling capacity and operating state of the system according to the fermentation heat load.

2. The fermentation heat-expansion work self-circulating refrigeration system according to claim 1, characterized in that: The power recovery and coupling mechanism (5) includes a planetary gear reduction box (6), an electromagnetic clutch (7) and a rigid coupling (8); The system further comprises a variable frequency motor (9) for driving the compressor (2); The power output shaft of the expander (4) is connected to the high-speed input end of the planetary gear reduction box (6), and the power input shaft of the compressor (2) is connected to the low-speed output end of the planetary gear reduction box (6); The output shaft of the variable frequency motor (9) is coaxially connected to the power input shaft of the compressor (2) through the electromagnetic clutch (7) and the rigid coupling (8) to form a power confluence, so that the power recovered by the expander (4) and the power provided by the variable frequency motor (9) can jointly drive the compressor (2); The electromagnetic clutch (7) is controlled by the centralized control unit (12) and is used to selectively disconnect or connect the power transmission between the variable frequency motor (9) and the compressor (2) under preset working conditions.

3. The fermentation heat-expansion work self-circulating refrigeration system according to claim 2, characterized in that: The compressor (2) is a screw compressor driven by a variable frequency motor (9), and is used to compress the low-temperature, low-pressure gaseous carbon dioxide flowing out of the evaporator (1) into a high-temperature, high-pressure supercritical state. The expander (4) is a radial-centripetal turbine expander, and is used to adiabatically expand the high-temperature, high-pressure supercritical carbon dioxide flowing out of the condenser (3) to perform work, so as to convert its pressure potential energy into mechanical energy.

4. The fermentation heat-expansion work self-circulating refrigeration system according to claim 1, characterized in that: The radial centripetal turbine expander (4) uses a magnetic bearing to support the rotor, and is provided with an inlet guide vane mechanism with a variable opening at its air inlet. The inlet guide vane mechanism is controlled by the centralized control unit (12) and is used to accurately adjust the mass flow rate and flow attack angle of the carbon dioxide refrigerant entering the expander (4), thereby achieving dynamic adjustment of the output power of the expander (4).

5. The fermentation heat-expansion work self-circulating refrigeration system according to claim 1, characterized in that: The chilled water circulation loop is provided with a high-precision temperature sensor, specifically including: A first temperature sensor (13) and a second temperature sensor (14) are respectively provided at the water inlet and the water outlet of the heat exchange component of the fermentation tank (10), for real-time monitoring of the temperature of the chilled water entering and leaving the fermentation tank (10). In addition, a third temperature sensor (15) and a fourth temperature sensor (16) are respectively provided at the water inlet and the water outlet of the fluid channel for passing the chilled water in the evaporator (1), for real-time monitoring of the temperature of the chilled water entering and leaving the evaporator (1). The first temperature sensor (13), the second temperature sensor (14), the third temperature sensor (15) and the fourth temperature sensor (16) are all four-wire high-precision platinum resistance thermometers. The measurement data are transmitted to the centralized control unit (12) as a basis for heat load calculation and feedback control.

6. The fermentation heat-expansion work self-circulating refrigeration system according to claim 1, characterized in that: The centralized control unit (12) is embedded with control logic and adopts a composite control strategy combining predictive feedforward with dynamic feedback correction. The predictive feedforward control refers to the centralized control unit (12) pre-stored with a metabolic heat generation prediction model corresponding to the fermentation process, and the predicted heat load in the next control cycle is calculated based on the fermentation process parameters collected in real time, and a benchmark carbon dioxide refrigerant mass flow is calculated accordingly. The dynamic feedback correction control refers to the centralized control unit (12) calculating a correction adjustment amount through a controller based on the deviation between the actual temperature of the chilled water measured by the second temperature sensor (14) and the preset target temperature. The correction adjustment amount is used to fine-tune the benchmark carbon dioxide refrigerant mass flow, thereby obtaining a final target mass flow.

7. The fermentation heat-expansion work self-circulating refrigeration system according to claim 1, characterized in that: After determining the final target mass flow, the centralized control unit (12) executes a multivariable collaborative optimization subroutine to determine specific operating parameters of the compressor (2) and the expander (4). The objective function of the multivariable collaborative optimization subroutine is to maximize the instantaneous comprehensive performance coefficient of the system under the constraint condition of satisfying the final target mass flow, wherein the instantaneous comprehensive performance coefficient is defined as the ratio of the actual heat exchange of the evaporator (1) to the net input work of the system, and the net input work is the difference between the measured input power of the compressor (2) and the measured output power of the expander (4). The optimization variables of the multivariable collaborative optimization subroutine are the inverter output frequency of the compressor (2) and the inlet guide vane opening of the expander (4). The centralized control unit (12) solves the optimal frequency and optimal opening combination that maximizes the objective function and sends it as a control instruction to the corresponding actuator.

8. The fermentation heat-expansion work self-circulating refrigeration system according to claim 1, characterized in that: The metabolic heat generation prediction model adopts a Kalman filter algorithm for online real-time correction. The centralized control unit (12) calculates the actual heat exchange rate on the evaporator (1) side in real time based on the measurement values ​​of the third temperature sensor (15) and the fourth temperature sensor (16) and the flow rate of the chilled water, and uses it as the actual fermentation heat load. The Kalman filter algorithm uses the actual fermentation heat load as an observation value to update and correct the state variables or model parameters inside the metabolic heat generation prediction model, so that the prediction output of the model can dynamically track the changes in the metabolic characteristics of the actual fermentation process, so as to improve the accuracy of the prediction feedforward control.

9. A control method for a fermentation heat-expansion work self-circulating refrigeration system according to any one of claims 1 to 8, characterized in that: The method is executed by the centralized control unit (12) and comprises the following steps: Step 1: Prediction feedforward step: by generating a prediction model of metabolic heat that matches the fermentation process and based on the fermentation process parameters obtained in real time, the predicted heat load that will be generated by the fermentation tank (10) in the next control cycle is calculated, and the reference carbon dioxide refrigerant mass flow rate required to remove this heat is calculated based on the predicted heat load; Step 2: Dynamic feedback correction step: monitoring the chilled water outlet temperature of the fermentation tank (10) in real time, comparing it with a preset target temperature to obtain a temperature deviation, and calculating a correction adjustment amount through a PID controller based on the temperature deviation, combining the correction adjustment amount with the reference carbon dioxide refrigerant mass flow rate to obtain a final target mass flow rate; Step 3: Multivariable collaborative optimization execution step: with the ultimate target mass flow rate being the constraint condition and the instantaneous comprehensive performance coefficient of the system being maximized as the optimization goal, the optimal operating frequency of the compressor (2) and the optimal inlet guide vane opening of the expander (4) are collaboratively solved, and the compressor (2) and the expander (4) are controlled to operate according to the set of optimal parameters.

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