Intelligent cascade refrigeration system for food-grade partial freezing liquid and control method

Abstract

The invention discloses an intelligent cascade refrigeration system for food-grade partial freezing liquid and a control method. The intelligent cascade refrigeration system comprises a cascade refrigeration loop, a partial freezing liquid circulation loop, a sensor group and an intelligent controller, the cascade refrigeration loop comprises a high-temperature-stage cycle and a low-temperature-stage cycle which are thermally coupled through a condensation evaporator; the partial freezing liquid circulation loop comprises a partial freezing liquid heat exchanger made of 316 stainless steel and a titanium alloy material; the intelligent controller monitors the density of the partial freezing liquid in real time and automatically controls the metering pump to supplement the concentrated partial freezing liquid and the deionized water, so that the density is stable. Intelligent and accurate compensation of components of the food-grade partial freezing liquid is realized, and the operation stability of the system and the freezing quality of food are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refrigeration technology and food processing equipment, and particularly relates to an intelligent cascade refrigeration system for food-grade micro-frozen liquid and a control method. BACKGROUND

[0002] With the rapid development of the food industry, higher requirements are put forward for food freezing and preservation. Food-grade micro-frozen liquid, as a safe and hygienic freezing carrier, is gradually applied to the field of high-end food processing. The refrigeration process of micro-frozen liquid requires an ultra-low temperature environment. Due to the limitation of the evaporation temperature of the refrigerant, the single-stage compression refrigeration system is difficult to achieve an ultra-low temperature of minus sixty degrees Celsius or below. Therefore, a cascade refrigeration system is usually used in conventional applications.

[0003] The existing cascade refrigeration system is generally composed of a high-temperature refrigeration cycle and a low-temperature refrigeration cycle. The high-temperature refrigeration cycle compresses the refrigerant, which is vaporized and absorbs heat at the evaporation side of the heat exchange device after condensation and throttling. The low-temperature refrigeration cycle compresses the refrigerant, which is condensed and releases heat at the condensation side of the heat exchange device, thereby achieving an ultra-low temperature refrigeration effect. At present, this type of cascade refrigeration system has been widely used in the fields of medicine, electronics and other industries, and can realize a relatively stable ultra-low temperature environment. However, since its original design is not intended for the food processing industry, there are obvious technical defects in the application of food freezing.

[0004] During the food processing process, the micro-frozen liquid will directly contact with the food, and all the materials in contact with the liquid in the equipment are required to have food-grade hygiene and safety performance and high corrosion resistance. However, the metal materials commonly used in the existing cascade refrigeration system are prone to chemical reaction or corrosion with special components in the micro-frozen liquid, which increases the risk of micro-frozen liquid contamination. At the same time, the density and composition of the micro-frozen liquid may deviate due to long-term evaporation, dilution or mixing with food juice during actual use, which significantly reduces the freezing effect. The existing cascade refrigeration system does not consider real-time monitoring and compensation of the cold carrier, lacks online density detection and automatic liquid supplement mechanism, and therefore the system is difficult to maintain the best freezing effect for a long time, which significantly affects the food preservation quality and production efficiency.

[0005] In addition, different types of food have different optimal freezing temperatures and process requirements. The temperature control mode of the existing cascade refrigeration system is single, lacks intelligent and flexible temperature precise control strategy, and is difficult to adapt to the differentiated processing requirements of multi-variety food, which restricts the further improvement of production efficiency and product quality.

[0006] Therefore, how to provide an intelligent cascade refrigeration system for food-grade micro-frozen liquid and a control method is a problem that needs to be solved by those skilled in the art. SUMMARY

[0007] One purpose of the present application is to provide an intelligent cascade refrigeration system and control method for food-grade micro-frozen liquid, aiming at the problem that the existing cascade refrigeration system lacks real-time monitoring and automatic compensation mechanism for micro-frozen liquid density, a system scheme including a cascade refrigeration circuit, a micro-frozen liquid circulation circuit, an online density sensor and an intelligent controller is proposed, through real-time density monitoring, concentrated micro-frozen liquid and deionized water are automatically and accurately supplemented, and the system has the advantages of long-term stable composition, reliable operation and high food freezing quality.

[0008] The intelligent cascade refrigeration system for food-grade micro-frozen liquid according to the embodiments of the present application comprises a cascade refrigeration circuit, a micro-frozen liquid circulation circuit, a sensor group and an intelligent controller. The cascade refrigeration circuit comprises a high-temperature cycle and a low-temperature cycle which are thermally coupled through a condensation evaporator, wherein the high-temperature cycle comprises a high-temperature compressor, a high-temperature condenser and a high-temperature throttling device connected in sequence, and the low-temperature cycle comprises a low-temperature compressor, a condensation evaporator, a low-temperature throttling device and a micro-frozen liquid heat exchanger connected in sequence. The micro-frozen liquid circulation circuit comprises a micro-frozen liquid storage tank, a circulating pump and a freezing tank in contact with food, and the part of the micro-frozen liquid heat exchanger in the micro-frozen liquid circulation circuit which is in direct contact with the micro-frozen liquid is made of 316 stainless steel and titanium alloy material. The sensor group comprises an online density sensor for real-time monitoring of the density of the micro-frozen liquid. The intelligent controller is electrically connected with the sensor group, real-time micro-frozen liquid density monitoring data are obtained, and the intelligent controller automatically controls the metering pumps of the concentrated micro-frozen liquid supply tank and the deionized water supply tank in the micro-frozen liquid circulation circuit according to the density monitoring data, so as to supplement the concentrated micro-frozen liquid and the deionized water to the micro-frozen liquid circulation circuit, and the density of the micro-frozen liquid is stabilized within a preset range.

[0009] Optionally, the high-temperature cycle adopts R404A refrigerant, and the low-temperature cycle adopts R23 refrigerant. The high-temperature compressor is a medium-temperature type semi-closed piston compressor, and the low-temperature compressor is a low-temperature type semi-closed piston compressor equipped with a crankcase heater. The condensation evaporator is a brazed stainless steel plate heat exchanger, and the evaporation side of the high-temperature cycle and the condensation side of the low-temperature cycle are thermally coupled in the condensation evaporator.

[0010] Optionally, the micro-frozen liquid storage tank, the circulating pump, the freezing tank, the concentrated micro-frozen liquid supply tank and the deionized water supply tank in the micro-frozen liquid circulation circuit which are in direct contact with the micro-frozen liquid are made of 316 stainless steel and titanium alloy material.

[0011] Optionally, the micro-frozen liquid circulation loop further comprises a concentrated micro-frozen liquid supply tank and a deionized water supply tank in communication with the micro-frozen liquid storage tank, and the concentrated micro-frozen liquid supply tank and the deionized water supply tank are respectively provided with metering pumps controlled by the intelligent controller; The intelligent controller automatically controls the metering pumps to accurately supplement concentrated micro-frozen liquid and deionized water into the micro-frozen liquid circulation loop according to the comparison result of the micro-frozen liquid density data monitored by the online density sensor in real time and the preset standard density value, so as to realize automatic compensation of the micro-frozen liquid composition.

[0012] Optionally, the intelligent controller is provided with a human-computer interaction interface, and the human-computer interaction interface pre-stores freezing modes for different food types and target temperatures corresponding thereto; after a user selects a required freezing mode through the human-computer interaction interface, the intelligent controller automatically controls the operating state of the cascade refrigeration loop according to the corresponding target temperature, so as to intelligently control the freezing process of different food types.

[0013] The intelligent cascade refrigeration control method for food-grade micro-frozen liquid comprises: Receiving a target temperature set by a user through a human-computer interaction interface of an intelligent controller, starting a cascade refrigeration loop and adopting a PID algorithm to real-time adjust the operating frequency of high-temperature and low-temperature compressors and the opening degree of high-temperature and low-temperature throttling devices, so that the micro-frozen liquid temperature rapidly reaches and stabilizes at the target temperature; Real-time monitoring the density of the micro-frozen liquid through an online density sensor, and comparing the real-time monitored density value with a preset standard density value; According to the comparison result of the density value, when the real-time monitored density value is higher than the allowable range of the standard density value, the intelligent controller controls the metering pump of the deionized water supply tank to supplement deionized water into the micro-frozen liquid circulation loop; when the real-time monitored density value is lower than the allowable range of the standard density value, the intelligent controller controls the metering pump of the concentrated micro-frozen liquid supply tank to supplement concentrated micro-frozen liquid into the micro-frozen liquid circulation loop, so as to automatically restore and maintain the micro-frozen liquid density in the allowable range of the standard density value.

[0014] Optionally, the allowable range of the density value is ±0.01 g / cm³ of the standard density value: When the real-time monitored density value exceeds the standard density value by 0.01 g / cm³, it is determined that the water or ethanol component in the micro-frozen liquid is volatilized, the metering pump of the deionized water supply tank is started to quantitatively supplement deionized water until the real-time monitored density value returns to the allowable range; When the real-time monitored density value is lower than the standard density value by 0.01 g / cm³, it is determined that the micro-frozen liquid is diluted by food juice or the ethanol component is excessively volatilized, the metering pump of the concentrated micro-frozen liquid supply tank is started to quantitatively supplement concentrated micro-frozen liquid until the real-time monitored density value returns to the allowable range.

[0015] Optionally, the energy-saving operation comprises: The intelligent controller monitors the load state of the freezing tank in real time, and when it is detected that there is no load in the freezing tank for 1 hour continuously, the running state of the cascade refrigeration circuit is automatically controlled to make the temperature of the micro-frozen liquid rise and stably maintain at an energy-saving temperature 10 DEG C higher than the target temperature. When it is detected again that there is a load in the freezing tank, the intelligent controller automatically controls the running state of the cascade refrigeration circuit to make the temperature of the micro-frozen liquid quickly recover to the target temperature set by the user.

[0016] The beneficial effects of the present application are: (1) The present application realizes real-time accurate monitoring and dynamic component supplementing of the micro-frozen liquid through the automatic linkage compensation mechanism of the real-time online density sensor and the intelligent controller, effectively improves the component stability of the micro-frozen liquid, and enhances the reliability of long-term operation and the consistency of the frozen quality of the system.

[0017] (2) The present application significantly improves the sanitary safety performance and corrosion resistance of the system by using food-grade 316 stainless steel and titanium alloy materials in the cascade refrigeration circuit and combining intelligent density compensation control, and shows better adaptability and effect in food freezing processing applications.

[0018] (3) In the field of micro-frozen liquid ultra-low temperature refrigeration for food processing, the present application adjusts the running frequency of the high-temperature compressor and the low-temperature compressor and the opening degree of the high-temperature throttling device and the low-temperature throttling device in real time through the intelligent controller, effectively solves the defects of single temperature control and insufficient flexibility in the prior art, breaks through the bottleneck of limited food type adaptability, realizes specific and significant improvement of the food type differentiation freezing process, and effectively improves the food freezing processing quality and efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0019] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, illustrate the present application and explain the principles of the present application, and do not constitute a limitation of the present application. In the drawings: Figure 1 The principle structure diagram of the intelligent cascade refrigeration system and control method for food-grade micro-frozen liquid proposed by the present application. DETAILED DESCRIPTION

[0020] The present application will now be described in further detail with reference to the accompanying drawings. These drawings are all simplified schematic diagrams, and only schematically show the basic structure of the present application, and therefore only show the components related to the present application.

[0021] Reference Figure 1The application discloses an intelligent cascade refrigeration system for food-grade slush liquid, which comprises a cascade refrigeration circuit, a slush liquid circulation circuit, a sensor group and an intelligent controller. A user selects a freezing mode corresponding to a food type and sets a target temperature through a man-machine interactive interface of the intelligent controller; The intelligent controller starts the cascade refrigeration circuit, and a high-temperature compressor and a low-temperature compressor start to operate. The low-temperature compressor compresses R23 refrigerant into medium-temperature high-pressure gaseous refrigerant, the medium-temperature high-pressure gaseous refrigerant enters a low-temperature level circulating condensing side of the condensing evaporator to perform condensing heat release, and the medium-temperature high-pressure gaseous refrigerant is condensed into medium-temperature high-pressure liquid refrigerant after being coupled with the high-temperature level circulating evaporating side. The slush liquid in the slush liquid storage tank is driven into a slush liquid side channel of the slush liquid heat exchanger by a circulating pump, and is cooled to the set target temperature through indirect heat exchange with the refrigerant. An online density sensor monitors density data of the food-grade slush liquid in circulation in real time and sends the density data to the intelligent controller. When the real-time monitored density value is lower than the standard density value, the intelligent controller automatically controls a metering pump of a concentrated slush liquid supply tank to start and quantitatively supplement the slush liquid circulation circuit with the concentrated slush liquid until the real-time monitored density value recovers to an allowable range.

[0022] In the embodiment, the high-temperature level circulation adopts R404A refrigerant, and the low-temperature level circulation adopts R23 refrigerant. The high-temperature compressor is a medium-temperature type semi-closed piston compressor with a rated power of 5 HP, and the refrigerant used is R404A. The low-temperature compressor is a low-temperature type semi-closed piston compressor with a rated power of 3 HP, and the refrigerant used is R23. The condensing evaporator adopts a brazed stainless steel plate heat exchanger, and the evaporation side of the high-temperature cycle and the condensing side of the low-temperature cycle are coupled in the condensing evaporator; The high-temperature high-pressure gaseous R404A refrigerant discharged by the high-temperature compressor enters the high-temperature condenser, is converted into high-pressure liquid R404A refrigerant after heat dissipation, and is throttled by the high-temperature throttling device to form low-temperature low-pressure liquid R404A refrigerant; The low-temperature low-pressure liquid R404A refrigerant enters the high-temperature cycle evaporation side of the condensing evaporator, is evaporated and vaporized into low-pressure gaseous R404A refrigerant after heat absorption, and then flows back to the suction side of the high-temperature compressor to complete the high-temperature cycle; The medium-temperature high-pressure gaseous R23 refrigerant discharged by the low-temperature compressor enters the low-temperature cycle condensing side of the condensing evaporator, is converted into medium-temperature high-pressure liquid R23 refrigerant after heat release, and is throttled by the low-temperature throttling device to form ultra-low-temperature low-pressure liquid R23 refrigerant; The ultra-low-temperature low-pressure liquid R23 refrigerant enters the refrigerant side channel of the micro-frozen liquid heat exchanger and evaporates and vaporizes, and the gaseous R23 refrigerant after heat absorption flows back to the suction side of the low-temperature compressor to complete the low-temperature cycle.

[0023] In the embodiment, the micro-frozen liquid storage tank, the circulating pump, the freezing tank, the concentrated micro-frozen liquid supply tank and the deionized water supply tank in the micro-frozen liquid circulating loop which directly contact with the micro-frozen liquid are made of 316 stainless steel and titanium alloy materials: The micro-frozen liquid storage tank is made of 316 stainless steel and titanium alloy materials, the inner wall of the storage tank is polished, the top of the storage tank is provided with a liquid level observation port, and the bottom is provided with a micro-frozen liquid circulating outlet and an inlet pipeline interface; The circulating pump is a low-temperature resistant magnetic circulating pump, the pump body, impeller and all parts in the pump which directly contact with the micro-frozen liquid are made of 316 stainless steel and titanium alloy materials, the rated flow of the pump is 5m³ / h, and the head is 20m, and the circulating pump is installed on the outlet pipeline of the micro-frozen liquid storage tank; The freezing tank is made of 316 stainless steel and titanium alloy materials, the freezing tank is designed as an open structure and is provided with an inlet and an outlet connected with the micro-frozen liquid circulating loop, the inlet is located at one side of the bottom of the freezing tank, and the outlet is located at the opposite side of the upper part of the freezing tank, so that the food is immersed in the circulating micro-frozen liquid; The concentrated micro-frozen liquid supply tank is made of 316 stainless steel and titanium alloy materials, the tank body is sealed, is provided with a top liquid supplement port and a bottom liquid outlet, the liquid outlet is communicated with the micro-frozen liquid storage tank through a pipeline, and a metering pump is installed; The deionized water supply tank is made of 316 stainless steel and titanium alloy materials, the tank body is sealed, is provided with a top liquid supplement port and a bottom liquid outlet, the liquid outlet is communicated with the micro-frozen liquid storage tank through a pipeline, and a metering pump is installed.

[0024] In the embodiment, the micro-frozen liquid circulation loop further comprises a concentrated micro-frozen liquid supply tank and a deionized water supply tank in communication with the micro-frozen liquid storage tank, and the concentrated micro-frozen liquid supply tank and the deionized water supply tank are respectively provided with a metering pump controlled by the intelligent controller: The concentrated micro-frozen liquid supply tank and the micro-frozen liquid storage tank are connected by a 316 stainless steel and titanium alloy pipeline, and a high-precision metering pump automatically controlled by the intelligent controller is installed on the pipeline. The rated flow range of the metering pump is 0.1-2 L / min, and the concentrated micro-frozen liquid can be accurately quantitatively delivered into the micro-frozen liquid storage tank according to the instructions of the intelligent controller; The deionized water supply tank and the micro-frozen liquid storage tank are connected by a 316 stainless steel and titanium alloy pipeline, and a high-precision metering pump automatically controlled by the intelligent controller is installed on the pipeline. The rated flow range of the metering pump is 0.1-2 L / min, and the deionized water can be accurately quantitatively delivered into the micro-frozen liquid storage tank according to the instructions of the intelligent controller; The online density sensor monitors the density data of the micro-frozen liquid in the micro-frozen liquid circulation loop in real time, and transmits the real-time monitored density data to the intelligent controller; The intelligent controller is pre-set with a standard density value and an allowable range of ±0.01 g / cm³. When the real-time monitored density value deviates from the pre-set standard density value beyond the allowable range, the intelligent controller automatically outputs a control signal to the corresponding metering pump; When the real-time monitored density value is higher than the allowable range of the standard density value, the intelligent controller automatically starts the metering pump of the deionized water supply tank, and quantitatively adds deionized water into the micro-frozen liquid storage tank through the metering pump; When the real-time monitored density value is lower than the allowable range of the standard density value, the intelligent controller automatically starts the metering pump of the concentrated micro-frozen liquid supply tank, and quantitatively adds concentrated micro-frozen liquid into the micro-frozen liquid storage tank through the metering pump; The above supplementing actions continue until the real-time monitored density value returns to and stably maintains within the allowable range of the standard density value.

[0025] In the embodiment, the intelligent controller is provided with a man-machine interaction interface, which comprises: The intelligent controller adopts a Siemens S7-1200 series PLC as a core control unit, and the man-machine interaction interface adopts a Siemens KTP700 series touch screen connected with the PLC; The man-machine interaction interface pre-stores different food types corresponding to freezing modes and target temperatures, at least including a tuna mode (the target temperature is set to -60°C) and a fresh shrimp mode (the target temperature is set to -30°C); The user selects the freezing mode corresponding to the food type through the man-machine interaction interface according to actual needs; After the user completes the selection, the intelligent controller immediately reads the target temperature corresponding to the selected freezing mode from the internal memory and automatically calculates the initial control parameters of the refrigeration circuit according to the read target temperature; The intelligent controller automatically starts the cascade refrigeration circuit and continuously collects real-time monitoring temperature values of the temperature sensor, automatically calculates and adjusts the running frequency of the high-temperature compressor and the low-temperature compressor and the opening degree parameters of the high-temperature throttling device and the low-temperature throttling device in real time through the built-in PID algorithm, so that the micro-frozen liquid temperature accurately reaches and stably maintains at the target temperature of the selected mode; The man-machine interaction interface displays the currently selected freezing mode, target temperature, real-time micro-frozen liquid temperature, real-time density value, system running state and alarm information in real time, and the user can intuitively monitor the running state of the entire refrigeration system.

[0026] In this embodiment, the intelligent cascade refrigeration control method for food-grade micro-frozen liquid includes: The user selects the freezing mode corresponding to the food type through the man-machine interaction interface of the intelligent controller and sets the target temperature; The intelligent controller starts the cascade refrigeration circuit according to the target temperature set by the user, and the high-temperature compressor and the low-temperature compressor run at the same time. The high-temperature compressor compresses the R404A refrigerant to form high-temperature and high-pressure gaseous refrigerant, which is condensed into high-temperature and high-pressure liquid refrigerant after passing through the high-temperature condenser, and then is throttled and decompressed by the high-temperature throttling device to form low-temperature and low-pressure liquid refrigerant. The low-temperature and low-pressure liquid refrigerant enters the condenser evaporator to evaporate and absorb heat, and is vaporized into low-pressure gaseous refrigerant and then backflows to the suction end of the high-temperature compressor; The low-temperature compressor compresses the R23 refrigerant to form medium-temperature and high-pressure gaseous refrigerant, which is condensed into medium-temperature and high-pressure liquid refrigerant after passing through the condenser evaporator, and then is throttled and decompressed by the low-temperature throttling device to form ultra-low-temperature and low-pressure liquid refrigerant. The ultra-low-temperature and low-pressure liquid refrigerant enters the refrigerant side channel of the micro-frozen liquid heat exchanger to evaporate and absorb heat, and is vaporized into low-pressure gaseous refrigerant and then backflows to the suction end of the low-temperature compressor; The intelligent controller monitors the micro-frozen liquid temperature in the micro-frozen liquid circulation loop in real time through the temperature sensor, and automatically calculates the running frequency of the high-temperature compressor and the low-temperature compressor and the real-time opening degree of the high-temperature throttling device and the low-temperature throttling device through the PID algorithm, so as to ensure that the micro-frozen liquid temperature quickly reaches and stably maintains at the target temperature set by the user; The online density sensor monitors the density data of the micro-frozen liquid in the micro-frozen liquid circulation loop in real time and transmits them to the intelligent controller, and the intelligent controller automatically compares the real-time monitoring density value with the pre-stored standard density value; When the real-time monitored density value is higher than the allowed range (±0.01 g / cm³) of the standard density value, the intelligent controller automatically starts the metering pump of the deionized water supply tank, and quantitatively supplements the deionized water into the micro-frozen liquid circulation loop through the metering pump until the real-time monitored density value returns to the allowed range of the standard density value. When the real-time monitored density value is lower than the allowed range (±0.01 g / cm³) of the standard density value, the intelligent controller automatically starts the metering pump of the concentrated micro-frozen liquid supply tank, and quantitatively supplements the concentrated micro-frozen liquid into the micro-frozen liquid circulation loop through the metering pump until the real-time monitored density value returns to the allowed range of the standard density value.

[0027] In the embodiment, the allowed range of the density value is ±0.01 g / cm³ of the standard density value, including: The intelligent controller pre-stores the standard density value and sets the allowed range as ±0.01 g / cm³ of the standard density value; The online density sensor monitors the density data of the micro-frozen liquid in the micro-frozen liquid circulation loop in real time, and the intelligent controller continuously receives and automatically compares the real-time monitored density value with the pre-stored standard density value one by one; When the real-time monitored density value exceeds the standard density value by 0.01 g / cm³, the intelligent controller automatically judges that the moisture or ethanol component in the micro-frozen liquid has been volatilized, and the intelligent controller automatically outputs a start instruction to the metering pump of the deionized water supply tank; After receiving the start instruction, the metering pump of the deionized water supply tank automatically operates, quantitatively supplements the deionized water into the micro-frozen liquid circulation loop through the 316 stainless steel and titanium alloy pipeline, and until the real-time monitored density value of the online density sensor returns to the allowed range; When the real-time monitored density value is lower than the standard density value by 0.01 g / cm³, the intelligent controller automatically judges that the micro-frozen liquid is diluted by food juice or the ethanol component has been excessively volatilized, and the intelligent controller automatically outputs a start instruction to the metering pump of the concentrated micro-frozen liquid supply tank; After receiving the start instruction, the metering pump of the concentrated micro-frozen liquid supply tank automatically operates, quantitatively supplements the concentrated micro-frozen liquid into the micro-frozen liquid circulation loop through the 316 stainless steel and titanium alloy pipeline, and until the real-time monitored density value of the online density sensor returns to the allowed range.

[0028] In the embodiment, the energy-saving operation includes: The intelligent controller collects the temperature sensor data installed in the freezing tank in real time, automatically calculates the change rate of the micro-frozen liquid temperature in the freezing tank per unit time, and continuously judges the real-time load state; The intelligent controller pre-sets the no-load judgment condition as: when the micro-frozen liquid temperature in the freezing tank does not appear a temperature decreasing trend for 1 hour continuously, it is determined that the freezing tank is in a no-load state; The intelligent controller automatically adjusts the operating parameters of the cascade refrigeration circuit after determining that the freezing tank is in a no-load state, so that the temperature of the micro-frozen liquid slowly rises and is stably maintained at an energy-saving temperature 10 DEG C higher than the target temperature set by the user; The intelligent controller continuously monitors the load state in the freezing tank in real time, and automatically determines that there is a load in the freezing tank when the temperature sensor detects a downward trend of the temperature of the micro-frozen liquid. After determining that there is a load in the freezing tank again, the intelligent controller automatically adjusts the operating parameters of the cascade refrigeration circuit, increases the operating frequency of the high-temperature compressor and the low-temperature compressor, and automatically adjusts the opening degree of the high-temperature throttling device and the low-temperature throttling device, so that the temperature of the micro-frozen liquid rapidly decreases and is stably maintained at the target temperature set by the user again. Embodiment

[0029] In order to verify the feasibility of the application in implementation, the intelligent cascade refrigeration system for food-grade micro-frozen liquid is applied to the ultra-low temperature food freezing production line of a certain large food processing enterprise for long-term stable freezing treatment and quality maintenance test of various foods. In specific implementation, the enterprise needs to implement rapid and accurate ultra-low temperature freezing of different varieties of food raw materials to maintain food quality. The micro-frozen liquid used in freezing treatment directly contacts food, so the stability of the composition of the micro-frozen liquid, the sanitary safety of the refrigeration system and the temperature control accuracy are particularly important.

[0030] At present, the industrial cascade refrigeration system used by the enterprise can reach ultra-low temperature in a short time, but in the long-term operation process, due to the gradual evaporation of water or ethanol components in the micro-frozen liquid, the dilution of food juice and the corrosion of system materials, the density of the micro-frozen liquid cannot be stably maintained for a long time, the composition ratio gradually deviates from the expected range, and the food freezing effect is significantly reduced. At the same time, the existing equipment materials mostly use copper pipelines or ordinary stainless steel, which has corrosion risk in a long-term low-temperature environment and may contaminate food, seriously restricting the stability of food preservation quality. In addition, due to different freezing temperature requirements of different food raw materials, the existing system lacks flexible temperature control strategies and is difficult to accurately control the temperature.

[0031] In view of the above problems, the application builds an intelligent cascade refrigeration system for actual application verification. In specific implementation, the cascade refrigeration circuit adopts two-stage circulation of high-temperature and low-temperature levels, the high-temperature level circulation adopts a medium-temperature type semi-closed piston compressor with a rated power of 5HP, the refrigerant is R404A, the high-temperature condenser selects a brazed stainless steel plate heat exchanger, and the refrigerant is throttled and decompressed by a high-temperature throttling device and then enters the evaporation side of the condensation evaporator to absorb heat; the low-temperature level circulation adopts a low-temperature type semi-closed piston compressor with a rated power of 3HP and is equipped with a crankcase heater, the refrigerant is R23, the refrigerant is condensed by the condensation side of the condensation evaporator, then is decompressed by a low-temperature throttling device and enters the micro-frozen liquid heat exchanger to evaporate and absorb heat, so as to realize stable ultra-low temperature output.

[0032] The micro-frozen liquid storage tank, circulating pump, freezing tank, concentrated micro-frozen liquid supply tank and deionized water supply tank in the micro-frozen liquid circulating loop of the system which are in direct contact with the food are made of 316 stainless steel and titanium alloy materials to ensure the food-grade safety requirements. The system is configured with online density sensors, temperature sensors and pressure sensors to monitor the changes of the micro-frozen liquid density, temperature and pressure in real time through the intelligent controller. The intelligent controller has preset standard density values and an allowable range of ±0.01 g / cm³. The running frequency of the high-temperature compressor and the low-temperature compressor and the opening degree of the high-temperature throttling device and the low-temperature throttling device are adjusted in real time through the PID algorithm to ensure accurate temperature control of the micro-frozen liquid.

[0033] During actual operation, the system is tested for a long time with tuna (target temperature -60℃) and fresh shrimp (target temperature -30℃) as representative foods. The intelligent controller realizes one-key mode switching and target temperature setting through the human-machine interface. The online density sensor monitors the density value of the micro-frozen liquid in real time. When the real-time monitored density value exceeds the standard density value by 0.01 g / cm³, the metering pump of the deionized water supply tank is automatically started to quantitatively supplement deionized water. When the real-time monitored density value is lower than the standard density value by 0.01 g / cm³, the metering pump of the concentrated micro-frozen liquid supply tank is automatically started to quantitatively supplement concentrated micro-frozen liquid. The density deviation is quickly corrected and maintained within the allowable range.

[0034] Table 1 below shows the specific test data of the micro-frozen liquid key performance parameters and system operation effect recorded at different time points during the actual operation of the system for 2000 hours.

[0035] Table 1 Comparison table of micro-frozen liquid key performance parameters and system operation effect data Run time (hours) Density measured value (g / cm3) Density standard value (g / cm3) Microfrozen liquid temperature measured (°C) Temperature set value (°C) Compressor operating frequency (Hz) 0 1.250 1.250 -60.0 -60 50 500 1.248 1.250 -59.8 -60 52 1000 1.249 1.250 -60.1 -60 51 1500 1.251 1.250 -59.9 -60 50 2000 1.250 1.250 -60.0 -60 50 As can be seen from Table 1, during the operation of the intelligent cascade refrigeration system for 2000 hours, the micro-frozen liquid density always remains within the allowable range of the standard density value ±0.01 g / cm³. The maximum deviation between the actual monitored density value and the standard value is only 0.002 g / cm³, which fully proves the high efficiency of the automatic compensation mechanism. The micro-frozen liquid temperature is long-term maintained within the target temperature ±0.2℃ range, and the running frequency of the refrigeration system compressor also shows high stability with a very small fluctuation range, which reflects the high efficiency and accuracy of the PID accurate temperature control algorithm.

[0036] At the same time, through actual testing, the quality of tuna and fresh shrimp processed by the intelligent cascade refrigeration system of the present application is significantly better than that of the original system of the enterprise. Specifically, the organization structure of the thawed food is more complete, the juice loss is significantly reduced, and the color and taste of the food are obviously improved, which reflects significant technical advantages and good economic benefits.

[0037] The system scheme and the control method of the application have high stability, accurate component control ability, food safety and health, and good adaptability to different food freezing temperature requirements in practical application environment, and have wide industrial application prospect and high popularization value.

[0038] The above merely describes preferred specific embodiments of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art can make equivalent replacements or changes to the technical scheme and the inventive concept of the application within the technical scope disclosed by the application, which should be covered within the protection scope of the application.

Claims

1. An intelligent cascade refrigeration system for food grade slush, characterized in that, The refrigeration system comprises a cascade refrigeration circuit, a micro-frozen liquid circulation circuit, a sensor group and an intelligent controller. The cascade refrigeration circuit comprises a high-temperature cycle and a low-temperature cycle which are thermally coupled through a condensation evaporator, wherein the high-temperature cycle comprises a high-temperature compressor, a high-temperature condenser and a high-temperature throttling device which are connected in sequence, and the low-temperature cycle comprises a low-temperature compressor, a condensation evaporator, a low-temperature throttling device and a micro-frozen liquid heat exchanger which are connected in sequence. The micro-frozen liquid circulation circuit comprises a micro-frozen liquid storage tank, a circulation pump and a frozen tank which is in contact with food, and the micro-frozen liquid heat exchanger is made of 316 stainless steel and titanium alloy material and is directly in contact with the micro-frozen liquid in the micro-frozen liquid circulation circuit. The sensor group comprises an online density sensor which monitors the density of the micro-frozen liquid in real time. The intelligent controller is electrically connected with the sensor group, acquires the density monitoring data of the micro-frozen liquid in real time, and automatically controls the metering pumps of the concentrated micro-frozen liquid supply tank and the deionized water supply tank in the micro-frozen liquid circulation circuit according to the density monitoring data, so as to supplement the concentrated micro-frozen liquid and the deionized water to the micro-frozen liquid circulation circuit and stabilize the density of the micro-frozen liquid in a preset range.

2. The intelligent cascade refrigeration system for food grade slush liquids as claimed in claim 1 wherein, The high-temperature cycle adopts R404A refrigerant, and the low-temperature cycle adopts R23 refrigerant. The high-temperature compressor is a medium-temperature semi-enclosed piston compressor, and the low-temperature compressor is a low-temperature semi-enclosed piston compressor which is equipped with a crankcase heater. The condensation evaporator is a brazed stainless steel plate heat exchanger, and the evaporation side of the high-temperature cycle and the condensation side of the low-temperature cycle are thermally coupled in the condensation evaporator.

3. The intelligent cascade refrigeration system for food grade slush liquids as claimed in claim 1 wherein, The micro-frozen liquid storage tank, the circulation pump, the frozen tank, the concentrated micro-frozen liquid supply tank and the deionized water supply tank which are directly in contact with the micro-frozen liquid in the micro-frozen liquid circulation circuit are made of 316 stainless steel and titanium alloy material.

4. The intelligent cascade refrigeration system for food grade slush liquids as claimed in claim 1 wherein, The micro-frozen liquid circulation circuit further comprises the concentrated micro-frozen liquid supply tank and the deionized water supply tank which are in communication with the micro-frozen liquid storage tank, and the concentrated micro-frozen liquid supply tank and the deionized water supply tank are respectively provided with metering pumps which are controlled by the intelligent controller. The intelligent controller automatically controls the metering pumps to accurately supplement the concentrated micro-frozen liquid and the deionized water to the micro-frozen liquid circulation circuit according to the comparison result of the micro-frozen liquid density data monitored by the online density sensor in real time and the preset standard density value, so as to automatically compensate the composition of the micro-frozen liquid.

5. The intelligent cascade refrigeration system for food grade slush liquids as claimed in claim 1 wherein, The intelligent controller is provided with a human-computer interaction interface, the human-computer interaction interface pre-stores frozen modes for different food types and target temperatures corresponding to the frozen modes, and after a user selects a required frozen mode through the human-computer interaction interface, the intelligent controller automatically controls the running state of the cascade refrigeration circuit according to the corresponding target temperature, so as to intelligently control the frozen process of different food types.

6. A control method for the intelligent cascade refrigeration control system for food-grade slush liquid according to claim 1, characterized in that, The refrigeration system comprises: receiving a target temperature set by a user through a human-computer interaction interface of an intelligent controller, starting the cascade refrigeration circuit and using a PID algorithm to adjust the running frequency of the high-temperature compressor and the low-temperature compressor and the opening degree of the high-temperature throttling device and the low-temperature throttling device in real time, so that the temperature of the micro-frozen liquid quickly reaches and stabilizes at the target temperature; The density of the micro-frozen liquid is monitored in real time by an online density sensor, and the real-time monitored density value is compared with a preset standard density value; According to the comparison result of the density value, when the real-time monitored density value is higher than the allowable range of the standard density value, the intelligent controller controls the metering pump of the deionized water supply tank to supplement deionized water to the micro-frozen liquid circulation loop, and when the real-time monitored density value is lower than the allowable range of the standard density value, the intelligent controller controls the metering pump of the concentrated micro-frozen liquid supply tank to supplement concentrated micro-frozen liquid to the micro-frozen liquid circulation loop, so as to automatically restore and maintain the density of the micro-frozen liquid in the allowable range of the standard density value.

7. The control method according to claim 6, characterized by The allowable range of the density value is ±0.01 g / cm³ of the standard density value: When the real-time monitored density value exceeds the standard density value by 0.01 g / cm³, it is determined that the water or ethanol component in the micro-frozen liquid is volatilized, and the metering pump of the deionized water supply tank is started to quantitatively supplement deionized water until the real-time monitored density value returns to the allowable range; When the real-time monitored density value is lower than the standard density value by 0.01 g / cm³, it is determined that the micro-frozen liquid is diluted by food juice or the ethanol component is excessively volatilized, and the metering pump of the concentrated micro-frozen liquid supply tank is started to quantitatively supplement concentrated micro-frozen liquid until the real-time monitored density value returns to the allowable range.

8. The control method according to claim 6, characterized by The energy-saving operation includes: The intelligent controller monitors the load state of the freezing tank in real time, and when no load is detected in the freezing tank for 1 hour continuously, the intelligent controller automatically controls the operation state of the cascade refrigeration circuit to make the micro-frozen liquid temperature rise and stably maintain at an energy-saving temperature which is 10℃ higher than the target temperature; When the presence of load in the freezing tank is monitored again, the intelligent controller automatically controls the operation state of the cascade refrigeration circuit to make the micro-frozen liquid temperature quickly return to the target temperature set by the user.

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