Compressed air graded freeze-drying system and control method thereof

Abstract

The invention discloses a compressed air graded freeze-drying system which comprises a refrigeration compressor, a condenser, a refrigeration heat regenerator, a high-temperature evaporator, a low-temperature evaporator and an air heat regenerator, compressed air is pre-cooled through the air heat regenerator and then sequentially enters the high-temperature evaporator and the low-temperature evaporator to be freeze-dried, and then the compressed air enters the high-temperature evaporator and the low-temperature evaporator to be freeze-dried. And finally, rewarming is conducted through the air regenerator. The pressure dew-point temperature of the dried air is set through a dew-point temperature controller, when the outlet air temperature pressure dew-point temperature is higher than a set value, the driving frequency of a refrigeration compressor is increased, the system refrigerating capacity is increased, and the driving frequency of the refrigeration compressor is reduced, and the system refrigerating capacity is reduced; by introducing the high-temperature evaporator and the refrigeration compressor with the air supply function, the design difficulty of a single evaporator is reduced, the heat exchange efficiency is enhanced, stable control over a low-pressure dew point is facilitated, the compression work of a refrigerant is saved, and the operation energy efficiency of the compressed air freeze drying system is improved.

Description

Technical Field

[0001] The invention relates to the technical field of compressed air drying systems, and in particular to a compressed air graded freeze drying system and a control method thereof. Background Art

[0002] Compressed air is the most important modern industrial power source besides electricity. Due to its cleanliness and easy transportation, it is widely used in pneumatic tools and instruments in the production process of textile, shipbuilding and other industries. Using an air compressor to compress ambient air is the main way to obtain high-pressure compressed air. Because there is water vapor in the air, according to the physical properties of air, the dew point temperature of the air will increase with the increase of moisture content and gas pressure. Under high humidity conditions in summer, the dew point temperature of 0.8MPa compressed air can be as high as 50℃. If it is used without use, the water vapor in the air will condense due to factors such as heat dissipation to the environment during the use of air, which will affect the performance and stability of the air-using equipment and cause production failures. Therefore, compressed air needs to be filtered and dried before it can be used.

[0003] The dryer is the main equipment for removing water vapor from the air and lowering its dew point temperature in the post-processing of compressed air. According to different working principles, the dryers used for compressed air drying can be divided into refrigeration dryers, adsorption dryers and combined dryers that combine refrigeration and adsorption. Refrigeration dryers are the most widely used due to their low cost, high energy efficiency and stability.

[0004] How to deal with the difference in compressed air consumption during the day and night, as well as the changes in the temperature and humidity of the air at the inlet of the dryer, and to achieve stable control of the dew point temperature of the compressed air has always been an important direction of technical development in the dryer industry. With the maturity of frequency conversion technology and the reduction of costs, variable frequency freeze dryers have solved the problem of energy waste caused by load changes to a certain extent, but it is still difficult for dryers to simultaneously meet the technical requirements of low cost and high energy efficiency under low dew point temperature conditions. This is because the compressed air entering the dryer needs to be reduced from a temperature of about 40°C through the regenerator and evaporator to the required dew point temperature (4-10°C) for dehumidification. The larger temperature drop places higher requirements on the heat exchanger. Since the heat exchanger must also withstand pressure, the lower the required pressure dew point temperature, the higher the cost of the heat exchanger. In addition, when the dryer is doing load adjustment, it is easy to have a phenomenon of too low evaporation temperature. Once the evaporation temperature is lower than 0°C, ice blockage will occur, causing the dryer to fail.

[0005] Therefore, how to achieve the requirement of stable control of compressed air low pressure dew point temperature, low cost and high energy efficiency of cold dryer is an urgent need for the development of cold dryer technology. For this reason, we propose a compressed air graded freeze drying system and its control method. Summary of the invention

[0006] The purpose of the present invention is to solve the problem of how to efficiently achieve a low dew point temperature of compressed air during the freeze-drying process, and to propose a compressed air graded freeze-drying system and a control method thereof.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A compressed air graded freeze-drying system comprises a refrigeration compressor, a condenser, a refrigeration regenerator, a first expansion valve, a high-temperature evaporator, a second expansion valve, a low-temperature evaporator, a constant pressure valve and an air regenerator, wherein the refrigeration compressor is provided with an intermediate air supply port i, the outlet of the refrigeration compressor is connected to the refrigerant inlet of the condenser, the refrigerant outlet of the condenser is connected to the h1 inlet of the refrigeration regenerator, the h2 outlet of the refrigeration regenerator is connected to the d1 inlet of the high-temperature evaporator via a first solenoid valve and a first expansion valve, the h2 outlet of the refrigeration regenerator is connected to the f1 port of the low-temperature evaporator via a second solenoid valve and a second expansion valve, the f2 outlet of the low-temperature evaporator is connected to the inlet of the refrigeration compressor via the constant pressure valve, the g1 inlet and the g2 outlet of the refrigeration regenerator, and the d2 outlet of the high-temperature evaporator is connected to the air supply port i of the refrigeration compressor;

[0009] The compressed air is connected to the a1 inlet of the air regenerator through the first stop valve through the pipeline, and is connected to the c1 inlet of the high-temperature evaporator through the a2 outlet. The air outlet c2 of the high-temperature evaporator is connected to the b1 inlet of the air regenerator through the e1 inlet and e2 outlet of the low-temperature evaporator, and is connected to the second stop valve through the b2 outlet of the air regenerator, and the dry compressed air is output from the second stop valve;

[0010] Furthermore, the refrigeration compressor is a variable frequency volumetric refrigeration compressor, and a high temperature and high pressure alarm is provided on the refrigeration compressor; the air regenerator, the high temperature evaporator and the low temperature evaporator can be made into an integrated type and equipped with a unified condensate drainage device;

[0011] Further, a first temperature controller is provided on the d2 outlet pipeline of the high temperature evaporator, and the first temperature controller is connected to the first expansion valve through a signal line; a second temperature controller is provided on the g2 outlet pipeline of the refrigeration regenerator, and the second temperature controller is connected to the second expansion valve through a signal line;

[0012] Furthermore, a third temperature controller is provided on the condenser outlet pipeline. When the second condenser is an air-cooled condenser, the third temperature controller is connected to the fan drive motor through a signal line. When the second condenser is a water-cooled condenser, the third temperature controller is connected to the cooling water flow regulating valve through a signal line.

[0013] Furthermore, a dew point temperature controller is provided on the b2 outlet pipeline of the air regenerator, and the dew point temperature controller is connected to the refrigeration compressor via a signal line;

[0014] A control method for a compressed air graded freeze drying system, a compressed air dew point temperature control method: the dew point temperature of the air pressure after drying is set by a dew point temperature controller, when the outlet air temperature pressure dew point temperature is higher than the set value, the driving frequency of the refrigeration compressor is increased to increase the system refrigeration capacity, otherwise the driving frequency of the refrigeration compressor is reduced to reduce the system refrigeration capacity;

[0015] Furthermore, the outlet refrigerant superheat of the high-temperature evaporator is controlled by the first temperature controller, and the outlet refrigerant superheat of the low-temperature evaporator is controlled by the second temperature controller. When the superheat is higher than the set value, the openings of the first expansion valve and the second expansion valve are increased respectively to increase the refrigerant flow rate entering the evaporator, and vice versa, the opening of the expansion valve is reduced;

[0016] Furthermore, the refrigerant subcooling degree at the condenser outlet is controlled by a third temperature controller. When the refrigerant outlet temperature is higher than a set value, the air volume of the condenser's driving fan or the flow rate of cooling water is increased to increase the heat exchange capacity of the condenser. Otherwise, the air volume of the condenser's driving fan or the flow rate of cooling water is reduced to reduce the heat exchange capacity of the condenser.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] By adding a high-temperature evaporator with a high evaporation temperature, the inlet air temperature and humidity of the low-temperature evaporator used to achieve a low dew point temperature are reduced, and its design requirements are reduced. Through the three-stage dehumidification of the air regenerator, high-temperature evaporator and low-temperature evaporator, the efficiency of each heat exchanger is improved, which is also conducive to improving the overall energy efficiency of the system. In addition, due to the reduction of heat exchanger design requirements, costs can also be reduced;

[0019] In addition, the use of a refrigeration compressor with air replenishment can divert the refrigerant liquid into a high-temperature evaporator with a high evaporation temperature and a low-temperature evaporator with a low evaporation temperature, which can greatly save the compression energy consumption of the refrigerant. A constant pressure valve is set at the outlet of the low-temperature evaporator to effectively avoid ice blockage caused by the evaporation temperature being lower than 0°C, and the dew point temperature of the compressed air can be adjusted by setting the pressure of the constant pressure valve.

[0020] The setting of the refrigeration compressor inlet heat regenerator can ensure that when an air-cooled condenser is used, even under high ambient temperature conditions, a larger condenser heat exchange area is not required to ensure sufficient condensation of the refrigerant gas, further improving the system stability of the cold dryer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of a compressed air graded freeze-drying system proposed by the present invention.

[0022] In the figure: 1-refrigeration compressor; 2-condenser; 3-refrigeration regenerator; 4-first expansion valve; 5-high-temperature evaporator; 6-second expansion valve; 7-low-temperature evaporator; 8-constant pressure valve; 9-air regenerator; 10-first temperature controller; 11-second temperature controller; 12-third temperature controller; 13-dew point temperature controller; 14-first stop valve; 15-second stop valve; 16-first solenoid valve; 17-second solenoid valve. DETAILED DESCRIPTION

[0023] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0024] In the description of the present invention, “plurality” means two or more than two, unless otherwise clearly and specifically defined.

[0025] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "mounted / connected", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0027] Reference Figure 1A compressed air graded freeze drying system comprises a refrigeration compressor 1, a condenser 2, a refrigeration regenerator 3, a first expansion valve 4, a high-temperature evaporator 5, a second expansion valve 6, a low-temperature evaporator 7, a constant pressure valve 8 and an air regenerator 9. The refrigeration compressor 1 has an intermediate air supply port i. The refrigerant gas compressed by the refrigeration compressor first enters the condenser 2 for heat release and condensation, and then enters the h1 interface of the refrigeration regenerator 3, and is further cooled by the low-temperature refrigerant gas that is about to enter the refrigeration compressor. After the supercooling degree increases, it flows out from h2 and is divided into two paths. One path enters the high-temperature evaporator through the d1 interface through the first solenoid valve 16 and the first expansion valve 4, and the other path flows into the low-temperature evaporator 7 through the f1 interface through the second solenoid valve 17 and the second expansion valve 6; when the expansion valve is an electronic expansion valve, the first solenoid valve 16 and the second solenoid valve 17 can be omitted;

[0028] The refrigerant in the low-temperature evaporator 7 absorbs heat and evaporates, then flows out from the f2 outlet, and is connected to the g1 interface of the refrigeration regenerator 3 through the constant pressure valve 8. After being heated in the refrigeration regenerator 3 to obtain a certain degree of superheat, it flows out from the g2 outlet and enters the air intake port of the refrigeration compressor 1, and is sucked in and compressed by the refrigeration compressor; the refrigerant in the high-temperature evaporator 5 absorbs heat and evaporates, then flows out from the d2 interface, and enters the refrigeration compressor through the air inlet i of the refrigeration compressor 1, and is compressed together with the refrigerant gas coming out of the low-temperature evaporator 7. After being heated and pressurized, it continues to enter the condenser 2 for the next refrigeration cycle.

[0029] When the system is running, the first stop valve 14 and the second stop valve 15 are opened, and the compressed air flows into the a1 inlet of the air regenerator 9 through the first stop valve 14 to reheat the dried air, and its own temperature is reduced to perform primary freezing and dehumidification, and then flows out through the a2 outlet and enters the high-temperature evaporator 5 through the c1 interface. Under the action of the evaporation and heat absorption of the refrigerant in the high-temperature evaporator, secondary freezing and dehumidification is achieved; then it flows out from c2 and enters the low-temperature evaporator 7 through the e1 inlet, and continues to be evaporated by the refrigerant with a lower evaporation temperature. Heat absorption, third-stage freezing and dehumidification is achieved, and finally flows out from the e2 outlet to enter the air regenerator 9 for reheating, and then outputs the dry compressed air to the outside through the second stop valve 15.

[0030] The traditional cold dryer has only one evaporator. The refrigerant liquid coming out of the condenser directly enters the evaporator through the expansion valve to absorb heat and evaporate, and then is sucked into and compressed by the compressor. The arrangement of two evaporators in the present invention, on the one hand, reduces the temperature drop of a single heat exchanger and improves the heat exchange efficiency. On the other hand, the refrigerant gas pressure in the high-temperature evaporator is relatively high, and it directly enters the compressor air supply port and is then compressed, which can save the compression energy consumption of the refrigerant and ultimately improve the operating energy efficiency of the cold dryer.

[0031] The refrigeration compressor 1 is a variable frequency positive displacement refrigeration compressor, which is used to adjust the refrigeration capacity of the system, and to adapt to the changes in ambient temperature and humidity and compressed air flow, and to achieve stable control of dew point temperature and energy saving. To avoid failures, high temperature and high pressure alarms are provided on the refrigeration compressor 1. Once the compressor exhaust temperature and pressure are higher than the alarm setting values, a failure alarm is issued and an emergency shutdown is triggered. As needed, the air reheater 9, the high temperature evaporator 5 and the low temperature evaporator 7 can be made into an integrated type and equipped with a unified condensate drainage device to improve the compactness of the entire device.

[0032] A first temperature controller 10 is provided on the d2 outlet pipeline of the high-temperature evaporator 5, and the first temperature controller 10 is connected to the first expansion valve 4 through a signal line; a second temperature controller 11 is provided on the g2 outlet pipeline of the refrigeration regenerator 3, and the second temperature controller 11 is connected to the second expansion valve 6 through a signal line; when the expansion valve is a thermal expansion valve, the first temperature controller 10 and the second temperature controller 11 can be replaced by the temperature sensing package of the thermal expansion valve;

[0033] A third temperature controller 12 is provided on the outlet pipe of the condenser 2. When the second condenser 2 is an air-cooled condenser, the third temperature controller 12 is connected to the fan drive motor through a signal line. When the second condenser 2 is a water-cooled condenser, the third temperature controller 12 is connected to the cooling water flow regulating valve through a signal line. The heat exchange capacity of the condenser is regulated by the changes in the cooling water flow and the fan air volume.

[0034] A dew point temperature controller 13 is provided on the b2 outlet pipeline of the air regenerator 9, and the dew point temperature controller 13 is connected to the refrigeration compressor 1 through a signal line;

[0035] A control method for a compressed air graded freeze-drying system includes a compressed air dew point temperature control method: the pressure dew point temperature of the air after drying is set by a dew point temperature controller 13, and a negative feedback regulation mechanism is adopted. When the outlet air temperature pressure dew point temperature is higher than the set value, the driving frequency of the refrigeration compressor 1 is increased to increase the circulation amount of the refrigerant, thereby increasing the refrigeration capacity of the system. Otherwise, the driving frequency of the refrigeration compressor 1 is reduced to reduce the refrigeration capacity of the system to maintain the stability of the air outlet working condition. When the required compressed air dew point temperature changes, the control pressure of the constant pressure valve 8 can be adjusted in the same manner to adjust the evaporation pressure of the refrigerant in the low-temperature evaporator 7, thereby reducing unnecessary compression energy consumption.

[0036] The outlet refrigerant superheat of the high-temperature evaporator 5 of the compressed air graded freeze-drying system is controlled by the first temperature controller 10, and the outlet refrigerant superheat of the low-temperature evaporator 7 is controlled by the second temperature controller 11. A positive feedback regulation mechanism is adopted. When the superheat is higher than the set value, the opening of the first expansion valve 4 and the second expansion valve 6 are increased respectively to increase the refrigerant flow entering the evaporator, and vice versa, the opening of the expansion valve is reduced;

[0037] The refrigerant subcooling degree at the outlet of the condenser 2 of the compressed air graded freeze-drying system is controlled by the third temperature controller 12, and a positive feedback regulation mechanism is adopted. When the refrigerant outlet temperature is higher than the set value, in order to ensure the normal operation of the regenerator, the condenser driving fan air volume or the cooling water flow rate should be increased to increase the heat exchange of the condenser. Otherwise, the condenser driving fan air volume or the cooling water flow rate should be reduced to reduce the heat exchange of the condenser.

[0038] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention. Any technical personnel in this field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be based on the scope defined by the claims.

Claims

1. A compressed air graded freeze drying system, characterized in that: It comprises a refrigeration compressor (1), a condenser (2), a refrigeration regenerator (3), a first expansion valve (4), a high-temperature evaporator (5), a second expansion valve (6), a low-temperature evaporator (7), a constant pressure valve (8) and an air regenerator (9); The refrigeration compressor (1) has an intermediate air supply port i, the outlet of the refrigeration compressor (1) is connected to the refrigerant inlet of the condenser (2), the refrigerant outlet of the condenser (2) is connected to the h1 inlet of the refrigeration heat exchanger (3), the h2 outlet of the refrigeration heat exchanger (3) is connected to the d1 inlet of the high-temperature evaporator (5) through the first solenoid valve (16) and the first expansion valve (4), the h2 outlet of the refrigeration heat exchanger (3) is connected to the f1 inlet of the low-temperature evaporator (7) through the second solenoid valve (17) and the second expansion valve (6), and the low-temperature evaporator ( The f2 outlet of the high-temperature evaporator (5) is connected to the inlet of the refrigeration compressor (1) via the constant pressure valve (8) and the g1 inlet and g2 outlet of the refrigeration regenerator (3); the d2 outlet of the high-temperature evaporator (5) is connected to the air supply port i of the refrigeration compressor (1); the a1 inlet of the air regenerator (9) is connected to the first stop valve (14); the air outlet c2 of the high-temperature evaporator (5) is connected to the b1 inlet of the air regenerator (9) via the e1 inlet and e2 outlet of the low-temperature evaporator (7), and is connected to the second stop valve (15) via the b2 outlet of the air regenerator (9).

2. A compressed air graded freeze drying system according to claim 1, characterized in that: The refrigeration compressor (1) is a variable frequency volumetric refrigeration compressor, and a high temperature and high pressure alarm is provided on the refrigeration compressor (1).

3. A compressed air graded freeze drying system according to claim 1, characterized in that: A first temperature controller (10) is provided on the d2 outlet pipeline of the high-temperature evaporator (5), and the first temperature controller (10) is connected to the first expansion valve (4) via a signal line; A second temperature controller (11) is provided on the g2 outlet pipeline of the refrigeration regenerator (3), and the second temperature controller (11) is connected to the second expansion valve (6) via a signal line.

4. A compressed air graded freeze drying system according to claim 1, characterized in that: A third temperature controller (12) is provided on the outlet pipeline of the condenser (2), and the third temperature controller (12) is connected to the fan drive motor via a signal line, and the third temperature controller (12) is connected to the cooling water flow regulating valve via a signal line.

5. A compressed air graded freeze drying system according to claim 1, characterized in that: A dew point temperature controller (13) is provided on the b2 outlet pipeline of the air regenerator (9), and the dew point temperature controller (13) is connected to the refrigeration compressor (1) via a signal line.

6. A control method for a compressed air graded freeze drying system according to any one of claims 1 to 5, characterized in that: The invention comprises a compressed air dew point temperature control method: the pressure dew point temperature of the air after drying is set by a dew point temperature controller (13); when the outlet air pressure dew point temperature is higher than the set value, the driving frequency of the refrigeration compressor (1) is increased to increase the system refrigeration capacity; otherwise, the driving frequency of the refrigeration compressor (1) is reduced to reduce the system refrigeration capacity.

7. A method for controlling a compressed air graded freeze drying system according to any one of claims 1 to 6, characterized in that: The outlet refrigerant superheat of the high-temperature evaporator (5) is controlled by a first temperature controller (10), and the outlet refrigerant superheat of the low-temperature evaporator (7) is controlled by a second temperature controller (11). When the superheat is higher than a set value, the openings of the first expansion valve (4) and the second expansion valve (6) are increased respectively to increase the refrigerant flow rate entering the evaporator. Otherwise, the openings of the expansion valves are reduced.

8. A method for controlling compressed air graded freeze drying according to any one of claims 1 to 7, characterized in that: The refrigerant subcooling degree at the outlet of the condenser (2) is controlled by a third temperature controller (12). When the refrigerant outlet temperature is higher than a set value, the air volume of the condenser's driving fan or the flow rate of cooling water is increased to increase the heat exchange of the condenser. Conversely, the air volume of the condenser's driving fan or the flow rate of cooling water is reduced to reduce the heat exchange of the condenser.

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