A frost-free air source cascade heat pump steam generator and its operating method

Abstract

The present invention discloses a frost-free air-source heat pump steam generator, comprising a low-temperature stage circulation system, a high-temperature stage circulation system, and a water system. The evaporator of the low-temperature stage circulation system is an air-source evaporator equipped with a water heat exchange pipeline on the air inlet side. The low-temperature stage circulation system is connected to the high-temperature stage circulation system via an evaporative condenser. The refrigerant gas of the high-temperature stage circulation system is evaporated by spraying water outside the heating tube of a vertical shell-and-tube heat exchanger to produce water vapor. The refrigerant liquid of both the low-temperature stage circulation system and the high-temperature stage circulation system first undergoes throttling and gas-liquid separation. The refrigerant gas generated after throttling is used to heat the feed water. The liquefied refrigerant liquid and the separated liquid are then throttled and enter the corresponding evaporator to absorb heat and evaporate. The present invention combines an air-source heat pump with an efficient steam generation heat exchanger, ensuring sufficient steam supply while effectively solving the problem of frosting and defrosting of the air-source evaporator in winter.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste heat recovery, and in particular relates to a frost-free air source cascade heat pump steam generator and an operating method thereof. Background Art

[0002] Steam, as a common production medium and heat carrier in industrial production, is widely used in printing and dyeing, chemical industry and other fields. Currently, boilers or electric heaters are generally used to directly heat water to generate steam, but the use of boilers will emit a large amount of carbon dioxide.

[0003] Compared to boilers and electric heating, the most prominent advantage of heat pump technology is that it consumes very little electricity. This means it can convert low-quality heat into high-quality heat, thereby generating a large amount of required heat energy. Its significant energy-saving effects have also made it increasingly popular. Air-source heat pumps are highly energy-efficient systems, but during winter operation, frost forms on the surface of the outdoor heat exchanger. This frost not only increases the thermal resistance between the heat exchanger and the air, but also increases air flow resistance, reducing flow, and reducing the unit's heating capacity, even causing it to malfunction. Currently, the most commonly used defrosting methods are reverse cycle hot gas defrosting or hot gas bypass defrosting. However, these methods can lead to intermittent operation of the heat pump and high defrosting energy consumption, making them difficult to apply in winter environments where ambient temperatures are low and the heat pump system requires continuous operation. Furthermore, when using a heat pump for steam generation, an efficient steam generation heat exchanger is crucial. Traditional methods involving hot water circulation, flash evaporators, and gas-liquid separators require large equipment investments and are not competitive in the market. Therefore, there is an urgent need for a new type of heat pump steam generator that can effectively prevent frost on the heat exchanger in winter and can replace traditional coal-fired or gas-fired boilers. Summary of the Invention

[0004] The purpose of the present invention is to provide a frost-free air source cascade heat pump steam generator and an operating method thereof in view of the problems and shortcomings of the above prior art.

[0005] To achieve the purpose of the present invention, the technical solution adopted by the present invention is:

[0006] A frost-free air source cascade heat pump steam generator includes a low-temperature stage circulation system, a high-temperature stage circulation system and a water system. The low-temperature stage circulation system includes: a first compressor 1, an evaporative condenser 2, a first throttle valve 3, a first gas-liquid separator 4, a second throttle valve 5, a first preheater 6, a third throttle valve 7 and an air source evaporator 8. The outlet of the first compressor 1 is connected to the lower inlet d4 of the evaporative condenser 2, the lower outlet d3 of the evaporative condenser 2 is connected to the middle inlet e2 of the first gas-liquid separator 4 through the first throttle valve 3, the upper outlet e1 of the first gas-liquid separator 4 is connected to the lower inlet f3 of the first preheater 6, and the lower outlet f4 of the first preheater 6 is connected to the upper inlet g1 of the air source evaporator 8 through the third throttle valve 7; the lower outlet e3 of the first gas-liquid separator 4 is connected to the upper inlet g1 of the air source evaporator 8 through the second throttle valve 5, and the outlet g2 of the air source evaporator 8 is connected to the inlet of the first compressor 1 through a pipeline.

[0007] The high-temperature stage circulation system includes: a second compressor 9, a water evaporator 10, a fourth throttle valve 11, a second gas-liquid separator 12, a fifth throttle valve 13, a second preheater 14, a sixth throttle valve 15 and an evaporative condenser 2. The outlet of the second compressor 9 is connected to the middle inlet a1 of the water evaporator 10, the left outlet a3 of the water evaporator 10 is connected to the middle inlet b2 of the second gas-liquid separator 12 through the fourth throttle valve 11, the upper outlet b1 of the second gas-liquid separator 12 is connected to the left inlet c1 of the second preheater 14, the left outlet c2 of the second preheater 14 is connected to the upper inlet d1 of the evaporative condenser 2 through the sixth throttle valve 15, the lower outlet b3 of the second gas-liquid separator 12 is connected to the upper inlet d1 of the evaporative condenser 2 through the fifth throttle valve 13, and the outlet d2 of the evaporative condenser 2 is connected to the inlet of the second compressor 9 through a pipeline.

[0008] The water system includes: an inlet valve 16, a water pretreatment device 17, a first water pump 18, a first preheater 6, a second preheater 14, a second water pump 19, a one-way valve 20, a stop valve 21, a steam regulating valve 22 and a hot water regulating valve 23. The feed water is connected to the upper inlet h1 of the water pretreatment device 17 through the inlet valve 16, the lower outlet h2 of the water pretreatment device 17 is connected to the inlet of the first water pump 18, the outlet of the first water pump 18 is connected to the upper inlet f2 of the first preheater 6, the upper outlet f1 of the first preheater 6 together with the one-way valve The outlets of the valve 20 are connected to the right inlet c4 of the second preheater 14 through a pipeline. The right outlet c3 of the second preheater 14 is connected to the inlet of the second water pump 19. The outlet of the second water pump 19 is connected to the water inlet of the water evaporator 10. The upper outlet a4 of the water evaporator 10 outputs steam through the steam regulating valve 22. The lower outlet a2 of the water evaporator 10 is connected to the lower inlet g3 of the air source evaporator 8 through the stop valve 21 and the hot water regulating valve 23. The lower outlet g4 of the air source evaporator 8 is connected to the inlet of the one-way valve 20 through a pipeline.

[0009] Further preferably, the water evaporator 10 is a vertical shell and tube heat exchanger, and a number of vertical heat exchange copper tubes 10c, a water spray pipe 10b, and a demisting filter 10a are arranged in sequence from bottom to top inside. A pressure controller 24 is provided on the top, and the pressure controller 24 is connected to the steam regulating valve 22 through a signal line; the water spray pipe 10b is connected to the water inlet of the water evaporator 10.

[0010] Further preferably, the air source evaporator 8 is a multi-row fin-tube heat exchanger containing water heat exchange tubes and refrigerant heat exchange tubes, and the water heat exchange tubes are arranged on the air inlet side; a first temperature controller 27 is provided at the air outlet of the air source evaporator 8, and the signal of the first temperature controller 27 is connected to the hot water regulating valve 23 through a wire.

[0011] Further preferably, the first throttle valve 3 and the fourth throttle valve 11 are electronic expansion valves;

[0012] Further preferably, the second water pump (19) is a high-lift, high-temperature water pump;

[0013] Further preferably, a second temperature controller 26 is provided on the water inlet pipeline of the first preheater 6, and the signal of the second temperature controller 26 is connected to the first throttle valve 3 through a wire. A third temperature controller 25 is provided on the water inlet pipeline of the second preheater 14, and the signal of the third temperature controller 25 is connected to the fourth throttle valve 11 through a wire.

[0014] A method for operating a frost-free air source cascade heat pump steam generator specifically includes the following two operating modes:

[0015] 1. Normal operation mode:

[0016] Open the water inlet valve 16, the first water pump 18, the second water pump 19, the first compressor 1 and the second compressor 9, and close the stop valve 21. The feed water enters the water pretreatment equipment 17 through the water inlet valve 16 for pretreatment such as softening, and then enters the first preheater 6 and the second preheater 14 by the first water pump 18 for preheating. The preheated water is increased in head by the second water pump 19 and then sprayed into the water evaporator 10 through the water spray pipe 10b in the water evaporator 10;

[0017] The refrigerant gas compressed by the first compressor 1 enters the evaporative condenser 2 to release heat and condense. The refrigerant liquid obtained by condensation is first throttled once by the first throttle valve 3, and then enters the first gas-liquid separator 4. The separated refrigerant gas enters the first preheater 6 and is condensed by the feed water. It is then throttled by the third throttle valve 7 and enters the air source evaporator 8 together with the refrigerant liquid in the first gas-liquid separator 4 after throttling and reducing the pressure by the second throttle valve 5 to absorb the heat of the ambient air and evaporate to produce refrigerant gas, and then enters the first compressor 1 to participate in the next cycle; the opening of the first throttle valve 3 is adjusted according to the feed water temperature at the inlet of the first preheater 6 to ensure that the phase change temperature of the refrigerant gas in the first preheater 6 and the feed water temperature have a suitable heat transfer temperature difference.

[0018] The refrigerant gas compressed by the second compressor 9 enters the vertical heat exchange tube in the water evaporator 10 from the inlet a1, forms a falling film evaporation with the spray water outside the evaporator tube to obtain steam, and then the steam pressure in the water evaporator 10 is controlled by adjusting the opening of the steam regulating valve 22. The refrigerant gas condensed after releasing heat to obtain refrigerant liquid flows out from the left outlet a3 and enters the second gas-liquid separator 12 through the fourth throttle valve 11. The separated refrigerant gas enters the second preheater 14 and is condensed by the feed water. Then, it is throttled by the sixth throttle valve 15 and enters the evaporative condenser (2) together with the refrigerant liquid in the second gas-liquid separator 12 after throttling and reducing the pressure by the fifth throttle valve 13 to absorb the condensation heat of the refrigerant after compression in the low-temperature stage cycle and evaporate into refrigerant gas. Then, it enters the second compressor 9 to participate in the next cycle. The valve opening of the fourth throttle valve 11 is adjusted according to the feed water temperature at the inlet of the second preheater 14 to ensure that the phase change temperature of the refrigerant gas in the second preheater 14 and the feed water temperature have a suitable heat transfer temperature difference.

[0019] 2. Frost-free operation mode:

[0020] When the ambient air temperature is low, in order to avoid frost on the air source evaporator 8, the frost-free operation mode is turned on. On the basis of the normal operation mode, the stop valve 21 is opened to allow part of the high-temperature hot water at the bottom of the water evaporator 10 to enter the heat exchange pipe on the air inlet side of the air source evaporator 8 after the flow is adjusted by the hot water regulating valve 23, so that the air temperature is increased and then heat exchanged with the refrigerant to avoid frost on the surface of the refrigerant heat exchange pipe. The hot water after heat release continues to enter the second preheater 14 through the one-way valve 20 together with the feed water at the outlet of the first preheater 6 to participate in the circulation; the opening of the hot water regulating valve 23 is controlled by the air temperature at the outlet of the air source evaporator 8.

[0021] It is further preferred that the steam regulating valve 22 is controlled by the steam pressure in the water evaporator 10, and the valve opening of the steam regulating valve 22 is adjusted in direct proportion to the steam pressure in the water evaporator 10; the hot water regulating valve 23 is controlled by the air temperature at the outlet of the air source evaporator 8, and the valve opening of the hot water regulating valve 23 is adjusted in inverse proportion to the air temperature at the outlet of the air source evaporator 8; the first throttle valve 3 is controlled by the temperature of the water inlet pipeline of the first preheater 6, and the valve opening of the first throttle valve 3 is adjusted in direct proportion to the temperature of the water inlet pipeline of the first preheater 6; the fourth throttle valve 11 is controlled by the temperature of the water inlet pipeline of the second preheater 14, and the valve opening of the fourth throttle valve 11 is adjusted in direct proportion to the temperature of the water inlet pipeline of the second preheater 14.

[0022] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0023] The present invention combines an air source heat pump with an efficient steam generating heat exchanger, utilizes a cascade heat pump to absorb ambient air heat, unloads the heat in a water evaporator, and generates steam through heat exchange with hot water, thereby replacing traditional coal-fired or gas-fired boilers, reducing the investment cost of equipment, and reducing the operating cost and carbon dioxide emissions of the steam generator, which is in line with my country's green development policy. At the same time, a hot water heat exchange pipeline is arranged through the inlet of the air source evaporator, which can effectively overcome the problems of low energy efficiency and intermittent heating operation caused by frosting and defrosting in winter of traditional air source heat pumps. The refrigerant liquid at the outlet of the condenser is throttled in stages, and the throttled gas refrigerant is liquefied with feed water before entering the evaporator, which can improve the area utilization rate and heat transfer efficiency of the evaporator. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the system structure of an embodiment of the present invention;

[0025] In the figure: 1. is the first compressor, 2. is the evaporative condenser, 3. is the first throttle valve, 4. is the first gas-liquid separator, 5. is the second throttle valve, 6. is the first preheater, 7. is the third throttle valve, 8. is the air source evaporator, 9. is the second compressor, 10. is the water evaporator, 11. is the fourth throttle valve, 12. is the second gas-liquid separator, 13. is the fifth throttle valve, 14. is the second preheater, 15. is the sixth throttle valve, 16. is the water inlet valve, 17. is the water pretreatment equipment, 18. is the first water pump, 19. is the second water pump, 20. is the one-way valve, 21. is the stop valve, 22. is the steam regulating valve, 23. is the hot water regulating valve, 24. is the pressure controller, 25. is the third temperature controller, 26. is the second temperature controller, and 27. is the first temperature controller. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the technical solutions of the present invention are further described in detail below with reference to the accompanying drawings and embodiments.

[0027] like Figure 1 Shown is a frost-free air source cascade heat pump steam generator of the present invention, comprising a low-temperature stage circulation system, a high-temperature stage circulation system and a water system.

[0028] The low-temperature stage circulation system includes: a first compressor 1, an evaporative condenser 2, a first throttle valve 3, a first gas-liquid separator 4, a second throttle valve 5, a first preheater 6, a third throttle valve 7 and an air source evaporator 8, the outlet of the first compressor 1 is connected to the lower inlet d4 of the evaporative condenser 2, the lower outlet d3 of the evaporative condenser 2 is connected to the middle inlet e2 of the first gas-liquid separator 4 through the first throttle valve 3, the upper outlet e1 of the first gas-liquid separator 4 is connected to the lower inlet f3 of the first preheater 6, the lower outlet f4 of the first preheater 6 is connected to the upper inlet g1 of the air source evaporator 12 through the third throttle valve 7, and the lower outlet e3 of the first gas-liquid separator 4 is connected to the upper inlet g1 of the air source evaporator 8 through the second throttle valve 5;

[0029] The high-temperature stage circulation system includes: a second compressor 9, a water evaporator 10, a fourth throttle valve 11, a second gas-liquid separator 12, a fifth throttle valve 13, a second preheater 14, a sixth throttle valve 15 and an evaporative condenser 2, wherein the outlet of the second compressor 9 is connected to the middle inlet a1 of the water evaporator 10, the left outlet a3 of the water evaporator 10 is connected to the middle inlet b2 of the second gas-liquid separator 12 through the fourth throttle valve 11, the upper outlet b1 of the second gas-liquid separator 12 is connected to the left inlet c1 of the second preheater 14, the left outlet c2 of the second preheater 14 is connected to the upper inlet d1 of the evaporative condenser 2 through the sixth throttle valve 15, and the lower outlet b3 of the second gas-liquid separator 12 is connected to the upper inlet d1 of the evaporative condenser 2 through the fifth throttle valve 13;

[0030] The water system includes: an inlet valve 16, a water pretreatment device 17, a first water pump 18, a first preheater 6, a second preheater 14, a second water pump 19, a one-way valve 20, a stop valve 21, a steam regulating valve 22 and a hot water regulating valve 23. The feed water is connected to the upper inlet h1 of the water pretreatment device 17 through the inlet valve 16, the lower outlet h2 of the water pretreatment device 17 is connected to the inlet of the first water pump 18, the outlet of the first water pump 18 is connected to the upper inlet f2 of the first preheater 6, and the upper outlet f1 of the first preheater 6 is connected to The right inlet c4 of the second preheater 14 and the right outlet c3 of the second preheater 14 are connected to the inlet of the second water pump 19, the outlet of the second water pump 19 is connected to the water spray pipe 1b in the water evaporator 10, the upper outlet a4 of the water evaporator 10 outputs steam through the steam regulating valve 22, the lower outlet a2 of the water evaporator 10 is connected to the lower inlet g3 of the air source evaporator 8 through the stop valve 21 and the hot water regulating valve 23, and the lower outlet g4 of the air source evaporator 8 is connected to the right inlet c4 of the second preheater 14 through the one-way valve 20.

[0031] The above-mentioned water evaporator 10 is a vertical shell and tube heat exchanger, and is equipped with a vertical heat exchange copper tube 10c, a water spray pipe 10b, a demisting filter 10a and a pressure controller 24 from bottom to top. The pressure controller 24 is connected to the steam regulating valve 22 through a signal line, mainly to control the steam pressure in the water evaporator 10; the water spray pipe 10b is connected to the water inlet of the water evaporator 10.

[0032] The above-mentioned air source evaporator 8 is a multi-row fin-tube heat exchanger containing water heat exchange tubes and refrigerant heat exchange tubes, and the water heat exchange tubes are arranged on the air inlet side; in this way, the air entering the air source evaporator 8 exchanges heat with hot water, and the temperature rises to above the frost point temperature, thereby preventing the air source evaporator 8 from frosting under extreme working conditions in winter; a first temperature controller 27 is provided at the air outlet of the air source evaporator 8, and the signal of the first temperature controller 27 is connected to the hot water regulating valve 23 through a wire. When the ambient air parameters are found to change, the hot water flow rate is controlled according to the temperature on its air outlet side, so that the air at the inlet of the air source evaporator 8 maintains a relatively stable temperature to prevent frosting.

[0033] The first throttle valve 3 and the fourth throttle valve 11 are electronic expansion valves; the high-pressure stage circulating refrigerant is a refrigerant that can achieve a condensation temperature higher than 100° C., such as R245fa.

[0034] The water inlet pipeline of the above-mentioned first preheater 6 is provided with a second temperature controller 26, and the signal of the second temperature controller 26 is connected to the first throttle valve 3 through a wire, which is used to control the flow rate of the refrigerant entering the first gas-liquid separator 4. The water inlet pipeline of the second preheater 14 is provided with a third temperature controller 25. The signal of the third temperature controller 25 is connected to the fourth throttle valve 11 through a wire, which is used to control the flow rate of the refrigerant entering the second gas-liquid separator 12.

[0035] The operating method of a frost-free air source cascade heat pump steam generator of the present invention specifically includes the following two operating modes:

[0036] 1. Normal operation mode:

[0037] Open the water inlet valve 16, the first water pump 18, the second water pump 19, the first compressor 1 and the second compressor 9, and close the stop valve 21. The feed water enters the water pretreatment device 17 through the water inlet valve 16 for softening and other pretreatments, then enters the first preheater 6 and the gaseous refrigerant flowing out of the first gas-liquid separator 4 by the first water pump 18 for preheating, and then enters the second preheater 14 for further preheating with the gaseous refrigerant flowing out of the second gas-liquid separator 12. The preheated water is increased in head by the second water pump 19 and then sprayed into the water evaporator 10 through the water spray pipe 10b in the water evaporator 10;

[0038] The refrigerant gas compressed by the first compressor 1 enters the evaporative condenser 2 to release heat and condense. The refrigerant liquid obtained by condensation is first throttled once by the first throttle valve 3, and then enters the first gas-liquid separator 4. The separated refrigerant gas flows out from the upper outlet e1 of the first gas-liquid separator 4, enters the first preheater 6, exchanges heat with the feed water, and is condensed, and then is throttled by the third throttle valve 7. At the same time, the refrigerant liquid flows out from the bottom outlet e3 of the first gas-liquid separator 4, is throttled and reduced in pressure by the second throttle valve 5, and enters the air source evaporator 8 together with the refrigerant flowing out through the third throttle valve 7 to absorb the heat of the ambient air and evaporate to produce refrigerant gas, and then enters the first compressor 1 to participate in the next cycle; the valve opening of the first throttle valve 3 is adjusted according to the feed water temperature at the inlet of the first preheater 6. When the feed water temperature changes, the valve opening of the first throttle valve 3 needs to be adjusted to ensure that the phase change temperature of the refrigerant gas in the first preheater 6 and the feed water temperature have a suitable heat transfer temperature difference.

[0039] The refrigerant gas compressed by the second compressor 9 enters the vertical heat exchange tube in the water evaporator 10 from the inlet a1, and the refrigerant gas forms a falling film evaporation with the spray water outside the evaporation tube to obtain steam. The steam flows out from the outlet a4 at the top of the water evaporator 10 and flows to the user through the steam regulating valve 22. At this time, the valve opening of the steam regulating valve 22 is adjusted to control the steam pressure in the water evaporator 10. The refrigerant liquid obtained by condensing the refrigerant gas after heat release flows out from the left outlet a3 of the water evaporator 10, and then enters the second gas-liquid separator 12 through the fourth throttle valve 11 for gas-liquid separation. The separated refrigerant gas flows out from the outlet b1 at the top of the second gas-liquid separator 12, and then enters the second preheater 14 to mix with the feed water. After heat exchange, it is condensed and then throttled by the sixth throttle valve 15. At the same time, the refrigerant liquid flows out from the bottom outlet b3 of the second gas-liquid separator 12, and after throttling and reducing the pressure by the fifth throttle valve 13, it enters the evaporative condenser (2) together with the refrigerant flowing out of the sixth throttle valve 15 to absorb the condensation heat of the refrigerant after the low-temperature stage cycle compression and evaporates into refrigerant gas, and then enters the second compressor 9 to participate in the next cycle; the valve opening of the fourth throttle valve 11 is adjusted according to the feed water temperature at the inlet of the second preheater 14. When the temperature of the right inlet c4 of the second preheater 14 changes, the valve opening of the fourth throttle valve 11 needs to be adjusted to ensure that the phase change temperature of the refrigerant gas in the second preheater 14 and the feed water temperature have a suitable heat transfer temperature difference.

[0040] 2. Frost-free operation mode:

[0041] When the ambient air temperature is low, in order to avoid frost on the air source evaporator 8, a frost-free operation mode can be turned on. Based on the normal operation mode, the stop valve 21 is opened, and part of the high-temperature hot water at the bottom of the water evaporator 10 flows out from the bottom outlet a2 of the water evaporator 10, passes through the stop valve 21 and enters the hot water regulating valve 23. After the flow rate is adjusted by the hot water regulating valve 23, it enters the heat exchange pipe on the air inlet side of the air source evaporator 8 to exchange heat with the air, so that the air temperature is increased and then heat exchanged with the refrigerant to avoid frost on the surface of the refrigerant heat exchange pipe. The hot water after heat release is mixed with the feed water at the outlet of the first preheater 6 through the one-way valve 20, and then enters the second preheater 14 to exchange heat with the refrigerant gas. After that, the head is increased by the second water pump 19 and sprayed into the water evaporator 10 through the water spray pipe 10b in the water evaporator 10 for the next cycle; the valve opening of the hot water regulating valve 23 is controlled by the air temperature at the outlet of the air source evaporator 8. When the temperature of the air side outlet of the air source evaporator 8 changes, the valve opening of the hot water regulating valve 23 needs to be adjusted.

[0042] Among them, the steam regulating valve 22 is controlled by the steam pressure in the water evaporator 10, and the valve opening of the steam regulating valve 22 is adjusted in direct proportion to the steam pressure in the water evaporator 10; when the steam pressure in the water evaporator 10 is too high, it is necessary to increase the valve opening of the steam regulating valve 22 to discharge more steam and maintain system stability; the hot water regulating valve 23 is controlled by the air temperature at the outlet of the air source evaporator 8, and the valve opening of the hot water regulating valve 23 is adjusted in inverse proportion to the air temperature at the outlet of the air source evaporator 8. When the low-temperature cycle runs stably and the temperature of the air side outlet of the air source evaporator 8 becomes low, it means that the hot water supply is insufficient at this time, and the valve opening of the hot water regulating valve 23 needs to be increased to avoid frosting of the air source evaporator 8; the first throttle valve 3 is controlled by the water inlet pipeline temperature of the first preheater 6 Control, the valve opening of the first throttle valve 3 is adjusted in direct proportion to the water inlet pipe temperature of the first preheater 6. When the water inlet pipe temperature of the first preheater 6 increases, the valve opening of the first throttle valve 3 should be increased to increase the pressure of the refrigerant after throttling, so as to ensure that the phase change temperature of the refrigerant gas in the first preheater 6 and the feed water temperature have a suitable heat transfer temperature difference; the fourth throttle valve 11 is controlled by the water inlet pipe temperature of the second preheater 14, and the valve opening of the fourth throttle valve 11 is adjusted in direct proportion to the water inlet pipe temperature of the second preheater 14; when the water inlet pipe temperature of the second preheater 14 increases, the valve opening of the fourth throttle valve 11 should be increased to increase the pressure of the refrigerant after throttling, so as to ensure that the phase change temperature of the refrigerant gas in the second preheater 14 and the feed water temperature have a suitable heat transfer temperature difference.

[0043] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A frost-free air source cascade heat pump steam generator, characterized in that: The invention comprises a low-temperature stage circulation system, a high-temperature stage circulation system and a water system, wherein the low-temperature stage circulation system comprises: a first compressor (1), an evaporative condenser (2), a first throttle valve (3), a first gas-liquid separator (4), a second throttle valve (5), a first preheater (6), a third throttle valve (7) and an air source evaporator (8). The outlet of the first compressor (1) is connected to the lower inlet (d4) of the evaporative condenser (2), the lower outlet (d3) of the evaporative condenser (2) is connected to the middle inlet (e2) of the first gas-liquid separator (4) through the first throttle valve (3), the upper outlet (e1) of the first gas-liquid separator (4) is connected to the lower inlet (f3) of the first preheater (6), the lower outlet (f4) of the first preheater (6) is connected to the upper inlet (g1) of the air source evaporator (8) through the third throttle valve (7); the lower outlet (e3) of the first gas-liquid separator (4) is connected to the upper inlet (g1) of the air source evaporator (8) through the second throttle valve (5); the outlet (g2) of the air source evaporator (8) is connected to the inlet of the first compressor (1) through a pipeline; The high-temperature stage circulation system comprises: a second compressor (9), a water evaporator (10), a fourth throttle valve (11), a second gas-liquid separator (12), a fifth throttle valve (13), a second preheater (14), a sixth throttle valve (15) and an evaporative condenser (2); the outlet of the second compressor (9) is connected to the middle inlet (a1) of the water evaporator (10), the left outlet (a3) ​​of the water evaporator (10) is connected to the middle inlet (b2) of the second gas-liquid separator (12) through the fourth throttle valve (11), The upper outlet (b1) of the second gas-liquid separator (12) is connected to the left inlet (c1) of the second preheater (14); the left outlet (c2) of the second preheater (14) is connected to the upper inlet (d1) of the evaporative condenser (2) through the sixth throttle valve (15); the lower outlet (b3) of the second gas-liquid separator (12) is connected to the upper inlet (d1) of the evaporative condenser (2) through the fifth throttle valve (13); the outlet (d2) of the evaporative condenser (2) is connected to the inlet of the second compressor (9) through a pipeline; The water system comprises: an inlet valve (16), a water pretreatment device (17), a first water pump (18), a first preheater (6), a second preheater (14), a second water pump (19), a one-way valve (20), a stop valve (21), a steam regulating valve (22) and a hot water regulating valve (23); the feed water is connected to the upper inlet (h1) of the water pretreatment device (17) through the inlet valve (16), the lower outlet (h2) of the water pretreatment device (17) is connected to the inlet of the first water pump (18), the outlet of the first water pump (18) is connected to the upper inlet (f2) of the first preheater (6), the upper outlet (f1) of the first preheater (6) together with the one-way valve (20), the water pretreatment device (17) is connected to the upper inlet (h2) of the first preheater (6), the water pretreatment device (17) is connected to the lower outlet (h2) of the first water pump (18), the outlet of the first water pump (18) is connected to the upper inlet (f2) of the first preheater (6), the upper outlet (f1) of the first preheater (6) and the one-way valve (20). The outlets of the two-way valve (20) are connected to the right inlet (c4) of the second preheater (14) through a pipeline. The right outlet (c3) of the second preheater (14) is connected to the inlet of the second water pump (19). The outlet of the second water pump (19) is connected to the water inlet of the water evaporator (10). The upper outlet (a4) of the water evaporator (10) outputs steam through the steam regulating valve (22). The lower outlet (a2) of the water evaporator (10) is connected to the lower inlet (g3) of the air source evaporator (8) through the stop valve (21) and the hot water regulating valve (23). The lower outlet (g4) of the air source evaporator (8) is connected to the inlet of the one-way valve (20) through a pipeline.

2. The frost-free air source cascade heat pump steam generator according to claim 1, characterized in that: The water evaporator (10) is a vertical shell-and-tube heat exchanger, and is provided with a plurality of vertical heat exchange copper tubes (10c), a water spray pipe (10b), and a demisting filter (10a) in sequence from bottom to top. A pressure controller (24) is provided on the top, and the pressure controller (24) is connected to the steam regulating valve (22) via a signal line; the water spray pipe (10b) is connected to the water inlet of the water evaporator (10).

3. The frost-free air source cascade heat pump steam generator according to claim 1, characterized in that: The air source evaporator (8) is a multi-row fin-tube heat exchanger containing water heat exchange tubes and refrigerant heat exchange tubes, and the water heat exchange tubes are arranged on the air inlet side; a first temperature controller (27) is provided at the air outlet of the air source evaporator (8), and a signal of the first temperature controller (27) is connected to the hot water regulating valve (23) through a wire.

4. The frost-free air source cascade heat pump steam generator according to claim 1, characterized in that: The first throttle valve (3) and the fourth throttle valve (11) are both electronic expansion valves.

5. The frost-free air source cascade heat pump steam generator according to claim 1, characterized in that: The second water pump (19) is a high-lift, high-temperature water pump.

6. The frost-free air source cascade heat pump steam generator according to claim 1, characterized in that: A second temperature controller (26) is provided on the water inlet pipeline of the first preheater (6), and a signal of the second temperature controller (26) is connected to the first throttle valve (3) through a wire. A third temperature controller (25) is provided on the water inlet pipeline of the second preheater (14), and a signal of the third temperature controller (25) is connected to the fourth throttle valve (11) through a wire.

7. An operating method of a frost-free air source cascade heat pump steam generator according to any one of claims 1 to 6, characterized in that: There are two operating modes:

1. Normal operation mode: The water inlet valve (16), the first water pump (18), the second water pump (19), the first compressor (1) and the second compressor (9) are opened, and the stop valve (21) is closed. The feed water enters the water pretreatment device (17) through the water inlet valve (16) for softening pretreatment, and then enters the first preheater (6) and the second preheater (14) for preheating by the first water pump (18). The preheated water is raised by the second water pump (19) and then sprayed into the water evaporator (10) through the water spray pipe (10b) in the water evaporator (10); The refrigerant gas compressed by the first compressor (1) enters the evaporative condenser (2) to release heat and condense. The refrigerant liquid obtained by condensation is first throttled by the first throttle valve (3) and then enters the first gas-liquid separator (4). The separated refrigerant gas enters the first preheater (6) and is condensed by the feed water. Then, it is throttled by the third throttle valve (7) and enters the air source evaporator (8) together with the refrigerant liquid in the first gas-liquid separator (4) after throttling and reducing the pressure by the second throttle valve (5) to absorb the heat of the ambient air and evaporate to produce refrigerant gas. Then, it enters the first compressor (1) to participate in the next cycle. The opening degree of the first throttle valve (3) is adjusted according to the feed water temperature at the inlet of the first preheater (6) to ensure that the phase change temperature of the refrigerant gas in the first preheater (6) and the feed water temperature have a suitable heat transfer temperature difference. The refrigerant gas compressed by the second compressor (9) enters the vertical heat exchange tube in the water evaporator (10) from the inlet (a1), forms a falling film evaporation with the spray water outside the evaporator tube to obtain steam, and then the steam pressure in the water evaporator (10) is controlled by adjusting the opening of the steam regulating valve (22). The refrigerant liquid obtained by condensing the refrigerant gas after heat release flows out from the left outlet (a3) ​​and enters the second gas-liquid separator (12) through the fourth throttle valve (11). The separated refrigerant gas enters the second preheater (14) and is supplied with water cooling. Condensed, then throttled by the sixth throttle valve (15) and the refrigerant liquid in the second gas-liquid separator (12) throttled and depressurized by the fifth throttle valve (13) enter the evaporative condenser (2) together with the refrigerant to absorb the condensation heat of the refrigerant after the low-temperature stage cycle compression and evaporate into refrigerant gas, and then enter the second compressor (9) to participate in the next cycle; the opening degree of the fourth throttle valve (11) is adjusted according to the feed water temperature at the inlet of the second preheater (14) to ensure that the phase change temperature of the refrigerant gas in the second preheater (14) and the feed water temperature have a suitable heat transfer temperature difference; 2. Frost-free operation mode: When the ambient air temperature is low, in order to avoid frost on the air source evaporator (8), the frost-free operation mode is turned on. On the basis of the normal operation mode, the stop valve (21) is opened to allow part of the high-temperature hot water at the bottom of the water evaporator (10) to enter the heat exchange pipe on the air inlet side of the air source evaporator (8) after the flow rate is regulated by the hot water regulating valve (23). After the air temperature is increased, heat is exchanged with the refrigerant to avoid frost on the surface of the refrigerant heat exchange pipe. The hot water after heat release continues to enter the second preheater (14) through the one-way valve (20) together with the feed water at the outlet of the first preheater (6) to participate in the circulation; the valve opening of the hot water regulating valve (23) is controlled by the air temperature at the outlet of the air source evaporator (8).

8. The method for operating a frost-free air source cascade heat pump steam generator according to claim 7, characterized in that: The steam regulating valve (22) is controlled by the steam pressure in the water evaporator (10), and the valve opening of the steam regulating valve (22) is adjusted in direct proportion to the steam pressure in the water evaporator (10).

9. The method for operating a frost-free air source cascade heat pump steam generator according to claim 7, characterized in that: The hot water regulating valve (23) is controlled by the air temperature at the outlet of the air source evaporator (8), and the valve opening of the hot water regulating valve (23) is adjusted in inverse proportion to the air temperature at the outlet of the air source evaporator (8).

10. The operating method of a frost-free air source cascade heat pump steam generator according to claim 7, characterized in that: The first throttle valve (3) is controlled by the temperature of the water inlet pipeline of the first preheater (6), and the valve opening of the first throttle valve (3) is adjusted in direct proportion to the temperature of the water inlet pipeline of the first preheater (6); the fourth throttle valve (11) is controlled by the temperature of the water inlet pipeline of the second preheater (14), and the valve opening of the fourth throttle valve (11) is adjusted in direct proportion to the temperature of the water inlet pipeline of the second preheater (14).

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