Cascade steam heat pump unit and control method thereof

Abstract

The invention discloses a cascade type steam heat pump unit and a control method thereof. The cascade type steam heat pump unit comprises a first compressor, a second compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a first expansion valve, a second expansion valve, a first water pump, a second water pump, a third water pump, a flash tank and a first water tank. According to the cascade type high-temperature steam heat pump unit, different modes can be switched through the specific connection relation of all the components, the functions of heat storage at night and steam preparation in the daytime can be achieved, the advantage of valley electricity is fully played, the cascade type high-temperature steam heat pump unit is more energy-saving, and the operation cost is further reduced; in addition, the unit can obtain heat from chilled water to prepare steam, the purpose of combined supply of cold and heat is achieved, and the comprehensive energy efficiency of the system is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of heat pumps, and in particular to a cascade steam heat pump unit and a control method thereof. Background Art

[0002] The steam heat pump unit is a new type of compression high-temperature heat pump device for the purpose of generating high-temperature steam. As a clean energy industrial heat system, its main components are heat pump steam units, flash tanks and steam compressors. The high-temperature heat pump unit generates high-temperature hot water of 80-90°C, which enters the flash tank for flash evaporation to generate low-temperature and low-pressure steam. Usually, the steam at this temperature and pressure cannot meet the industrial heat demand. Therefore, the steam generated by the flash tank needs to be compressed by the steam compressor to increase the pressure and temperature before it can be used at the end. At the same time, as the water in the flash tank is continuously converted into steam, the liquid level in the tank continues to drop. The conventional system uses the method of directly adding tap water to the inside of the flash tank. The tap water temperature is relatively low. Directly adding low-temperature water can easily cause the temperature inside the flash tank to drop, resulting in the inability of the water to boil, resulting in the inability to continue the steam production process, unstable steam flow, and too low steam temperature; at the same time, the heat pump system needs to reach a higher condensing temperature to meet the heat source temperature to make the water boil. The heat pump unit is in a relatively harsh operating condition, and it is easy to damage the compressor and system accessories. In addition, with the continuous advancement of industrialization, electricity resources are becoming increasingly scarce. Relatively speaking, electricity consumption during the day is greater than at night, and the price is relatively higher. Therefore, how to achieve the supply of high-temperature steam at a relatively low cost is an urgent problem to be solved in this field. Summary of the invention

[0003] The object of the present invention is to overcome the deficiencies of the prior art and to provide an improved cascade steam heat pump unit which can at least solve one problem existing in the prior art.

[0004] In order to achieve the above object, a technical solution adopted by the present invention is:

[0005] A cascade steam heat pump unit, comprising a first compressor, a second compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a first expansion valve, a second expansion valve, a first water pump, a second water pump, a third water pump, a flash tank, and a first water tank;

[0006] The outlet of the first compressor, a refrigerant passage of the first heat exchanger, the first expansion valve, the second heat exchanger, and the inlet of the first compressor are connected in sequence to form a first refrigerant circulation loop;

[0007] The outlet of the second compressor, a refrigerant passage of the third heat exchanger, the second expansion valve, a refrigerant passage of the fourth heat exchanger, and the inlet of the second compressor are connected in sequence to form a second refrigerant circulation loop;

[0008] The inlet of the first water pump is connected to the flash tank, and the outlet of the first water pump is connected to another refrigerant passage of the third heat exchanger and another refrigerant passage of the first heat exchanger respectively; wherein the another refrigerant passage of the third heat exchanger is also connected to the flash tank, and the another refrigerant passage of the first heat exchanger is also connected to the flash tank and the first water tank respectively;

[0009] Another refrigerant passage of the fourth heat exchanger is arranged in parallel with the one refrigerant passage of the first heat exchanger;

[0010] Two ends of the second water pump are respectively connected to the first water tank and the other refrigerant passage of the first heat exchanger;

[0011] Two ends of the third water pump are respectively connected to the first water tank and the flash tank.

[0012] According to the present invention, the cascade steam heat pump unit includes a hot water mode, a steam mode, a water-supplementing steam mode, a first water tank constant temperature mode, and a first water tank constant temperature steam mode;

[0013] When the cascade steam heat pump unit is in the hot water mode, the first compressor is in a working state, the second compressor is in a non-working state, the first water pump and the second water pump are respectively in an open state, and the third water pump is in a closed state;

[0014] When the cascade steam heat pump unit is in the steam mode, the first compressor and the second compressor are both in working state, the first water pump is in the on state, and the second water pump and the third water pump are respectively in the off state;

[0015] When the cascade steam heat pump unit is in the water-steam replenishment mode, the first compressor and the second compressor are both in working state, the first water pump and the third water pump are respectively in the open state, and the second water pump is in the closed state;

[0016] When the cascade steam heat pump unit is in the first water tank constant temperature mode, the first compressor is in a working state, the second compressor is in a non-working state, the first water pump and the third water pump are respectively in a closed state, and the second water pump is in an open state;

[0017] When the cascade steam heat pump unit is in the first water tank constant temperature steam mode, the first compressor and the second compressor are both in working state, and the first water pump and the second water pump are respectively in the open state.

[0018] According to some preferred aspects of the present invention, the cascade steam heat pump unit further comprises a first valve, a second valve, a third valve, a fourth valve, a fifth valve and a sixth valve;

[0019] The two ends of the first valve are respectively connected to the outlet of the first compressor and the one refrigerant passage of the first heat exchanger;

[0020] The two ends of the second valve are respectively connected to the outlet of the first compressor and the other refrigerant passage of the fourth heat exchanger;

[0021] Two ends of the third valve are respectively connected to the outlet of the first water pump and the other refrigerant passage of the first heat exchanger;

[0022] Two ends of the fourth valve are respectively connected to the outlet of the first water pump and the other refrigerant passage of the third heat exchanger;

[0023] Both ends of the fifth valve are respectively connected to the other refrigerant passage of the first heat exchanger and the flash tank;

[0024] Both ends of the sixth valve are communicated with the other refrigerant passage of the first heat exchanger and the first water tank, respectively.

[0025] In some embodiments of the present invention, when the cascade steam heat pump unit is in the hot water mode, the first valve, the third valve, the fifth valve, and the sixth valve are all in an open state, and the second valve and the fourth valve are all in a closed state;

[0026] When the cascade steam heat pump unit is in the steam mode or the water-steam mode, the first valve, the third valve, the fifth valve, and the sixth valve are all in a closed state, and the second valve and the fourth valve are all in an open state;

[0027] When the cascade steam heat pump unit is in the first water tank constant temperature mode, the first valve and the sixth valve are both in an open state, and the second valve, the third valve, the fourth valve, and the fifth valve are all in a closed state;

[0028] When the cascade steam heat pump unit is in the first water tank constant temperature steam mode, the first valve, the second valve, the fourth valve, and the sixth valve are all in an open state, and the third valve and the fifth valve are both in a closed state.

[0029] In some embodiments of the present invention, the first valve and the second valve are electric regulating valves, respectively, and the third valve, the fourth valve, the fifth valve, and the sixth valve are solenoid valves, respectively.

[0030] In some embodiments of the present invention, the cascade steam heat pump unit also includes a steam output pipe connected to the flash tank and a pressure reducing valve arranged on the steam output pipe; when the cascade steam heat pump unit is in the hot water mode and the first water tank constant temperature mode, the pressure reducing valve is in a closed state; when the cascade steam heat pump unit is in the steam mode, the water replenishment steam mode and the first water tank constant temperature steam mode, the pressure reducing valve is in an open state.

[0031] In some embodiments of the present invention, the second compressor also includes an air supply port; the cascade steam heat pump unit also includes an economizer and a third expansion valve, one refrigerant passage of the economizer is connected in series between the one refrigerant passage of the third heat exchanger and the second expansion valve, another refrigerant passage of the economizer is respectively connected to the air supply port of the second compressor and the outlet of the third expansion valve, and the inlet of the third expansion valve is connected to the one refrigerant passage of the economizer.

[0032] In some embodiments of the present invention, the cascade steam heat pump unit also includes a second water tank, a fourth water pump, a seventh valve and an eighth valve, the second water tank, the fourth water pump, the seventh valve and the flash tank are connected in sequence, and the second water tank, the fourth water pump, the eighth valve and the first water tank are connected in sequence.

[0033] In some embodiments of the present invention, the cascade steam heat pump unit further includes a gas-liquid separator, and the gas-liquid separator is respectively connected to the inlet of the second heat exchanger and the inlet of the first compressor.

[0034] In some embodiments of the present invention, the first compressor is a variable frequency compressor, the second compressor is a fixed frequency compressor, the first water pump and the second water pump are respectively fixed frequency water pumps, and the third water pump is a variable frequency water pump.

[0035] In some embodiments of the present invention, the cascade steam heat pump unit further includes a temperature sensor, a pressure sensor and a liquid level sensor respectively arranged on the flash tank.

[0036] In some embodiments of the present invention, the first water pump is connected to the bottom of the flash tank, the other refrigerant passage of the third heat exchanger is connected to the middle of the flash tank, and a steam outlet is provided at the top of the flash tank.

[0037] In some embodiments of the present invention, the refrigerant in the first refrigerant circulation loop includes R515B refrigerant or R1234ze(E) refrigerant, and the refrigerant in the second refrigerant circulation loop includes R245fa refrigerant.

[0038] Another technical solution provided by the present invention is: a control method for the above-mentioned cascade steam heat pump unit,

[0039] The control method includes at least one of the following (a)-(e):

[0040] (a) when it is detected that the liquid level in the flash tank is greater than a first preset warning liquid level and the temperature in the flash tank is greater than or equal to 90° C., controlling the cascade steam heat pump unit to be in steam mode;

[0041] (b) when it is detected that the liquid level in the flash tank is lower than the first preset warning liquid level, the liquid level in the first water tank is higher than the second preset warning liquid level, and the water temperature is greater than 90° C., turning on the third water pump and controlling the cascade steam heat pump unit to the water replenishment steam mode;

[0042] (c) when it is detected that the liquid level in the flash tank is lower than the first preset warning liquid level and the water temperature in the first water tank is lower than 90° C., turning on the second water pump and controlling the cascade steam heat pump unit to the first water tank constant temperature steam mode;

[0043] (d) when steam production is stopped and it is detected that the liquid level in the first water tank is lower than a third preset warning liquid level and the temperature is lower than 90° C., controlling the cascade steam heat pump unit to a first water tank constant temperature mode;

[0044] (e) When it is night time, the cascade steam heat pump unit is controlled to be in hot water mode.

[0045] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0046] The present invention solves the problems of unstable steam flow and too low steam temperature caused by too low water supply temperature when the high-temperature heat pump steam unit produces steam. At the same time, by switching between different modes, the function of storing heat at night and producing steam during the day can be realized, giving full play to the advantages of valley electricity, making the cascade high-temperature steam heat pump unit more energy-efficient and further reducing operating costs. In addition, the unit can produce steam by taking heat from chilled water, achieving the purpose of combined cooling and heating, and further improving the overall energy efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0048] Figure 1 This is a schematic structural diagram of a cascade steam heat pump unit according to an embodiment of the present invention;

[0049] In the accompanying drawings, 1, first compressor; 2, second compressor; 3, first heat exchanger; 4, second heat exchanger; 5, third heat exchanger; 6, fourth heat exchanger; 7, first expansion valve; 8, second expansion valve; 9, first water pump; 10, second water pump; 11, third water pump; 12, flash tank; 13, first water tank; 14, first valve; 15, second valve; 16, third valve; 17, fourth valve; 18, fifth valve; 19, sixth valve; 20, steam output pipe; 21, pressure reducing valve; 22, economizer; 23, third expansion valve; 24, second water tank; 25, fourth water pump; 26, seventh valve; 27, eighth valve; 28, gas-liquid separator. DETAILED DESCRIPTION

[0050] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0051] In the description of the present invention, “plurality” means at least two, for example, two, three, etc., unless otherwise clearly and specifically defined.

[0052] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it 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 an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] In the invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0054] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element at the same time.

[0055] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0056] like Figure 1 As shown, this example provides a cascade steam heat pump unit, which includes a first compressor 1, a second compressor 2, a first heat exchanger 3, a second heat exchanger 4, a third heat exchanger 5, a fourth heat exchanger 6, a first expansion valve 7, a second expansion valve 8, a first water pump 9, a second water pump 10, a third water pump 11, a flash tank 12, and a first water tank 13.

[0057] In this example, the outlet of the first compressor 1, a refrigerant passage of the first heat exchanger 3, the first expansion valve 7, the second heat exchanger 4, and the inlet of the first compressor 1 are connected in sequence to form a first refrigerant circulation loop; the outlet of the second compressor 2, a refrigerant passage of the third heat exchanger 5, the second expansion valve 8, a refrigerant passage of the fourth heat exchanger 6, and the inlet of the second compressor 2 are connected in sequence to form a second refrigerant circulation loop; the inlet of the first water pump 9 is connected to the flash tank 12, and the outlet of the first water pump 9 is connected to another refrigerant passage of the third heat exchanger 5, respectively. The refrigerant passage of the fourth heat exchanger 6 is connected with a refrigerant passage of the first heat exchanger 3; the two ends of the second water pump 10 are respectively connected with the first water tank 13 and the other refrigerant passage of the first heat exchanger 3; the two ends of the third water pump 11 are respectively connected with the first water tank 13 and the flash tank 12.

[0058] The first compressor 1 can be a low-temperature compressor, specifically a variable frequency compressor. The refrigerant in the first refrigerant circulation loop includes R515B refrigerant or R1234ze(E) refrigerant, etc.; further, the steam heat pump unit also includes a gas-liquid separator 28, and the gas-liquid separator 28 is respectively connected to the second heat exchanger 4 and the inlet of the first compressor 1. The first heat exchanger 3 is a condenser, and the second heat exchanger 4 is an evaporator.

[0059] The second compressor 2 is a high-temperature compressor, which has an air supply port and can be a fixed-frequency compressor. The refrigerant in the second refrigerant circulation loop includes R245fa refrigerant; further, the cascade steam heat pump unit also includes an economizer 22 and a third expansion valve 23, a refrigerant passage of the economizer 22 is connected in series between a refrigerant passage of the third heat exchanger 5 and the second expansion valve 8, another refrigerant passage of the economizer 22 is connected to the air supply port of the second compressor 2 and the outlet of the third expansion valve 23, and the inlet of the third expansion valve 23 is connected to a refrigerant passage of the economizer 22. The third expansion valve 23 and the economizer 22 are connected, and the inlet temperature of the second expansion valve 8 can be lowered by setting the economizer 22 and the third expansion valve 23, which is beneficial to protect the second expansion valve 8 and avoid damage to it due to too high inlet temperature; specifically, a part of the refrigerant flowing through a refrigerant passage of the economizer 22 is throttled by the third expansion valve 23, and the temperature rises, and then the heat exchange in the economizer 22 is further heated up, which in disguise cools the refrigerant in a refrigerant passage of the economizer 22, making it supercooled, and then enters the second expansion valve 8 and the third expansion valve 23 at a relatively low temperature. The third heat exchanger 5 is a condenser, and the fourth heat exchanger 6 is an evaporative condenser.

[0060] In this example, see Figure 1 As shown, the first water pump 9 is connected to the bottom of the flash tank 12, another refrigerant passage of the third heat exchanger 5 is connected to the middle of the flash tank 12, and a steam outlet is provided at the top of the flash tank 12, and the steam outlet is connected to the steam output pipe 20.

[0061] In this example, the cascade steam heat pump unit includes a hot water mode, a steam mode, a water-steam makeup mode, a first water tank constant temperature mode, and a first water tank constant temperature steam mode;

[0062] When the cascade steam heat pump unit is in hot water mode, the first compressor 1 is in working state, the second compressor 2 is in non-working state, the first water pump 9 and the second water pump 10 are respectively in the open state, and the third water pump 11 is in the closed state;

[0063] When the cascade steam heat pump unit is in steam mode, the first compressor 1 and the second compressor 2 are both in working state, the first water pump 9 is in the open state, and the second water pump 10 and the third water pump 11 are in the closed state respectively;

[0064] When the cascade steam heat pump unit is in the water-steam replenishment mode, the first compressor 1 and the second compressor 2 are both in working state, the first water pump 9 and the third water pump 11 are respectively in the open state, and the second water pump 10 is in the closed state;

[0065] When the cascade steam heat pump unit is in the first water tank constant temperature mode, the first compressor 1 is in working state, the second compressor 2 is in non-working state, the first water pump 9 and the third water pump 11 are respectively in the closed state, and the second water pump 10 is in the open state;

[0066] When the cascade steam heat pump unit is in the first water tank constant temperature steam mode, the first compressor 1 and the second compressor 2 are both in working state, and the first water pump 9 and the second water pump 10 are respectively in the open state.

[0067] In this example, the cascade steam heat pump unit also includes a first valve 14, a second valve 15, a third valve 16, a fourth valve 17, a fifth valve 18 and a sixth valve 19; the two ends of the first valve 14 are respectively connected to the outlet of the first compressor 1 and a refrigerant passage of the first heat exchanger 3; the two ends of the second valve 15 are respectively connected to the outlet of the first compressor 1 and another refrigerant passage of the fourth heat exchanger 6; the two ends of the third valve 16 are respectively connected to the outlet of the first water pump 9 and another refrigerant passage of the first heat exchanger 3; the two ends of the fourth valve 17 are respectively connected to the outlet of the first water pump 9 and another refrigerant passage of the third heat exchanger 5; the two ends of the fifth valve 18 are respectively connected to another refrigerant passage of the first heat exchanger 3 and the flash tank 12; the two ends of the sixth valve 19 are respectively connected to another refrigerant passage of the first heat exchanger 3 and the first water tank 13.

[0068] Further, when the cascade steam heat pump unit is in hot water mode, the first valve 14, the third valve 16, the fifth valve 18, and the sixth valve 19 are all in an open state, and the second valve 15 and the fourth valve 17 are all in a closed state;

[0069] When the cascade steam heat pump unit is in the steam mode or the water-steam mode, the first valve 14, the third valve 16, the fifth valve 18, and the sixth valve 19 are all in the closed state, and the second valve 15 and the fourth valve 17 are all in the open state;

[0070] When the cascade steam heat pump unit is in the first water tank constant temperature mode, the first valve 14 and the sixth valve 19 are both in the open state, and the second valve 15, the third valve 16, the fourth valve 17, and the fifth valve 18 are all in the closed state;

[0071] When the cascade steam heat pump unit is in the first water tank constant temperature steam mode, the first valve 14, the second valve 15, the fourth valve 17, and the sixth valve 19 are all in an open state, and the third valve 16 and the fifth valve 18 are all in a closed state.

[0072] In this example, the cascade steam heat pump unit also includes a steam output pipe 20 connected to the flash tank 12, a pressure reducing valve 21 arranged on the steam output pipe 20, a second water tank 24, a fourth water pump 25, a seventh valve 26 and an eighth valve 27. The second water tank 24, the fourth water pump 25, the seventh valve 26 and the flash tank 12 are connected in sequence, and the second water tank 24, the fourth water pump 25, the eighth valve 27 and the first water tank 13 are connected in sequence; further, when the cascade steam heat pump unit is in hot water mode and the first water tank constant temperature mode, the pressure reducing valve 21 is in a closed state; when the cascade steam heat pump unit is in steam mode, water replenishment steam mode and the first water tank constant temperature steam mode, the pressure reducing valve 21 is in an open state.

[0073] In this example, the first valve 14 and the second valve 15 can be electric regulating valves respectively, the third valve 16, the fourth valve 17, the fifth valve 18, the sixth valve 19, the seventh valve 26 and the eighth valve 27 can be solenoid valves respectively, the first water pump 9 and the second water pump 10 can be fixed frequency water pumps respectively, and the third water pump 11 and the fourth water pump 25 can be variable frequency water pumps.

[0074] In this example, the cascade steam heat pump unit further includes a temperature sensor, a pressure sensor and a liquid level sensor which are respectively arranged on the flash tank.

[0075] This example also provides a control method for the above-mentioned cascade steam heat pump unit, and the control method includes at least one of the following (a)-(e):

[0076] (a) when it is detected that the liquid level in the flash tank is greater than a first preset warning liquid level and the temperature in the flash tank is greater than or equal to 90° C., controlling the cascade steam heat pump unit to be in steam mode;

[0077] (b) when it is detected that the liquid level in the flash tank is lower than the first preset warning liquid level, the liquid level in the first water tank is higher than the second preset warning liquid level, and the water temperature is greater than 90° C., the third water pump is turned on to control the cascade steam heat pump unit to the water replenishment steam mode;

[0078] (c) when it is detected that the liquid level in the flash tank is lower than the first preset warning liquid level and the water temperature in the first water tank is lower than 90° C., the second water pump is turned on to control the cascade steam heat pump unit to the first water tank constant temperature steam mode;

[0079] (d) when steam production is stopped and it is detected that the liquid level in the first water tank is lower than the third preset warning liquid level and the temperature is lower than 90° C., the cascade steam heat pump unit is controlled to be in a constant temperature mode for the first water tank;

[0080] (e) When it is night time, the cascade steam heat pump unit is controlled to be in hot water mode.

[0081] The working process is roughly as follows:

[0082] (1) At night, when valley electricity is used for heat storage, the first compressor 1 works, and the high-temperature and high-pressure first refrigerant releases heat at the first heat exchanger 3 (the released heat is absorbed by the water to be heated), and then absorbs heat and transforms into gas at the second heat exchanger 4 (evaporator) after throttling through the first expansion valve 7. The liquid is separated out at the gas-liquid separator 28, and the gas refrigerant enters the first compressor 1 for compression to realize circulation; the second compressor 2 stops, the first valve 14 opens, the second valve 15 closes, the third valve 16 opens, the fourth valve 17 closes, the fifth valve 18 and the sixth valve 19 are both opened, the pressure reducing valve 21 is closed, the first water pump 9 and the second water pump 10 are started respectively, and the water in the flash tank 12 is pumped out by the first water pump 9, and flows to the first heat exchanger 3 (which is the condenser) through the third valve 13 for heat exchange (absorption). Heat), and at the same time, the water in the first water tank 13 is pumped out by the second water pump 10, and directly flows through the first heat exchanger 3 (which is a condenser) for heat exchange (absorbing heat). After heating, a part of it returns to the flash tank 12 from the middle of the flash tank 12 through the fifth valve 18, and the other part returns to the first water tank 13 through the sixth valve 19. In this way, the water in the flash tank 12 and the first water tank 13 is heated to about 90°C by valley electricity at night; of course, if the water level in the flash tank 12 and the first water tank 13 is less than the set value, the water in the second water tank 24 can be replenished to the flash tank 12 through the seventh valve 26 and to the first water tank 13 through the eighth valve 27 by starting the fourth water pump 25 in advance. After the replenishment is completed, the fourth water pump 25, the seventh valve 26 and the eighth valve 27 are closed. The above process can be the working state of the hot water mode.

[0083] (2) When the cascade steam heat pump unit is in the first water tank constant temperature mode, this mode is preferably completed at night, the first compressor 1 is in working state, the second compressor 2 is in non-working state, the first water pump 9 and the third water pump 11 are respectively in the closed state, the second water pump 10 is in the open state, the first valve 14 and the sixth valve 19 are both opened, and the second valve 15, the third valve 16, the fourth valve 17, the fifth valve 18, and the seventh valve 26 are closed. If the liquid level in the first water tank 13 is insufficient, the water in the second water tank 24 can be replenished into the first water tank 13 through the eighth valve 27 by starting the fourth water pump 25 in advance. After the replenishment is completed, the fourth water pump 25 and the eighth valve 27 are closed.

[0084] (3) When producing steam, it can be roughly divided into three states, the first state is the steam mode, the second state is the water replenishment steam mode, and the third state is the first water tank constant temperature steam mode; when in the steam mode, water is not replenished from the first water tank 13 to the flash tank 12; when in the water replenishment steam mode, water needs to be replenished from the first water tank 13 to the flash tank 12; when in the first water tank constant temperature steam mode, according to the liquid level in the flash tank 12, if the liquid level is appropriate, water is not replenished from the first water tank 13 to the flash tank 12, and if the liquid level is relatively low, water is replenished from the first water tank 13 to the flash tank 12; in the above three states, the first compressor 1 and the second compressor 2 are both working;

[0085] Further, (3-1) when in steam mode, the first compressor 1 and the second compressor 2 are both working, the first valve 14, the third valve 16, the fifth valve 18, the sixth valve 19 and the seventh valve 26 are all closed, the second valve 15 and the fourth valve 17 are all opened, the pressure reducing valve 21 is opened, the first water pump 9 is turned on, the second water pump 10 and the third water pump 11 are all closed, the high-temperature refrigerant in the first refrigerant circulation loop supplies heat to the second refrigerant circulation loop at the fourth heat exchanger 6, the high-temperature refrigerant in the second refrigerant circulation loop exchanges heat with the high-temperature water in the flash tank 12 (extracted by the first water pump 9) at the third heat exchanger 5 and heats the high-temperature water, and then returns to the flash tank 12 through the middle of the flash tank 12 to produce steam, and the steam produced in the flash tank 12 is supplied to the outside through the pressure reducing valve 21, and the supplied steam temperature can reach above 120 degrees Celsius;

[0086] (3-2) When in the water-steam replenishment mode, the first compressor 1 and the second compressor 2 are both working, the first valve 14, the third valve 16, the fifth valve 18, the sixth valve 19 and the seventh valve 26 are all closed, the second valve 15 and the fourth valve 17 are all open, the pressure reducing valve 21 is open, the first water pump 9 and the third water pump 11 are both turned on, and the second water pump 10 is turned off. The high-temperature refrigerant in the first refrigerant circulation loop supplies heat to the second refrigerant circulation loop at the fourth heat exchanger 6, and the high-temperature refrigerant in the second refrigerant circulation loop supplies heat to the second refrigerant circulation loop at the third heat exchanger. The hot water in the first water tank 13 is pumped out by the third water pump 11 and supplied to the flash tank 12 to ensure that the hot water in the flash tank 12 has a sufficient liquid level for stable steam production.

[0087] (3-3) When in the first water tank constant temperature steam mode, the first compressor 1 and the second compressor 2 are both working, the first valve 14, the third valve 16, the fifth valve 18, the sixth valve 19 and the seventh valve 26 are all closed, the second valve 15 and the fourth valve 17 are all open, the pressure reducing valve 21 is opened, the first water pump 9 and the second water pump 10 are turned on, and the high-temperature refrigerant in the first refrigerant circulation loop supplies heat to the second refrigerant circulation loop at the fourth heat exchanger 6, and the high-temperature refrigerant in the second refrigerant circulation loop exchanges heat with the high-temperature water in the flash tank 12 (extracted by the first water pump 9) at the third heat exchanger 5 and heats the high-temperature water, and then returns to the flash tank 12 through the middle of the flash tank 12 for steam production, and the steam produced in the flash tank 12 is supplied to the outside through the pressure reducing valve 21, and the supplied steam temperature can reach above 120 degrees Celsius;

[0088] Among them, the third water pump 11 has two working states. The first is that when the liquid level in the flash tank 12 is insufficient, the third water pump 11 is turned on and the hot water in the first water tank 13 is added to the flash tank 12. The second is that when the liquid level in the flash tank 12 is still sufficient, the third water pump 11 can be turned off. At this time, it is possible to further determine whether the liquid level in the first water tank 13 is sufficient. If not, the water in the second water tank 24 is added to the first water tank 13 by starting the fourth water pump 25. Since the first water tank 13 is in a constant temperature mode, the added water can be heated to an ideal temperature, thereby realizing heat extraction from chilled water to produce steam and realizing combined cold and heat supply. If the liquid level in the first water tank 13 is sufficient, it is only necessary to maintain the operation of the second water pump 10 and keep the sixth valve 19 open, so that the water in the first water tank 13 can be kept warm by the first heat exchanger 3 to maintain its constant temperature state.

[0089] In summary, the present invention solves the problems of unstable steam flow and low steam temperature caused by too low water supply temperature when the high-temperature heat pump steam unit produces steam. At the same time, by switching between different modes, the function of storing heat at night and producing steam during the day can be realized, giving full play to the advantages of valley electricity, making the cascade high-temperature steam heat pump unit more energy-efficient and further reducing operating costs. In addition, the unit can extract heat from chilled water to produce steam, achieving the purpose of combined cooling and heating, and further improving the overall energy efficiency of the system.

[0090] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A cascade steam heat pump unit, characterized in that: The cascade steam heat pump unit comprises a first compressor, a second compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a first expansion valve, a second expansion valve, a first water pump, a second water pump, a third water pump, a flash tank, and a first water tank; The outlet of the first compressor, a refrigerant passage of the first heat exchanger, the first expansion valve, the second heat exchanger, and the inlet of the first compressor are connected in sequence to form a first refrigerant circulation loop; The outlet of the second compressor, a refrigerant passage of the third heat exchanger, the second expansion valve, a refrigerant passage of the fourth heat exchanger, and the inlet of the second compressor are connected in sequence to form a second refrigerant circulation loop; The inlet of the first water pump is connected to the flash tank, and the outlet of the first water pump is connected to another refrigerant passage of the third heat exchanger and another refrigerant passage of the first heat exchanger respectively; wherein the another refrigerant passage of the third heat exchanger is also connected to the flash tank, and the another refrigerant passage of the first heat exchanger is also connected to the flash tank and the first water tank respectively; Another refrigerant passage of the fourth heat exchanger is arranged in parallel with the one refrigerant passage of the first heat exchanger; Two ends of the second water pump are respectively connected to the first water tank and the other refrigerant passage of the first heat exchanger; Two ends of the third water pump are respectively connected to the first water tank and the flash tank.

2. The cascade steam heat pump unit according to claim 1, characterized in that: The cascade steam heat pump unit includes a hot water mode, a steam mode, a water-supplementing steam mode, a first water tank constant temperature mode and a first water tank constant temperature steam mode; When the cascade steam heat pump unit is in the hot water mode, the first compressor is in a working state, the second compressor is in a non-working state, the first water pump and the second water pump are respectively in an open state, and the third water pump is in a closed state; When the cascade steam heat pump unit is in the steam mode, the first compressor and the second compressor are both in working state, the first water pump is in the on state, and the second water pump and the third water pump are respectively in the off state; When the cascade steam heat pump unit is in the water-steam replenishment mode, the first compressor and the second compressor are both in working state, the first water pump and the third water pump are respectively in the open state, and the second water pump is in the closed state; When the cascade steam heat pump unit is in the first water tank constant temperature mode, the first compressor is in a working state, the second compressor is in a non-working state, the first water pump and the third water pump are respectively in a closed state, and the second water pump is in an open state; When the cascade steam heat pump unit is in the first water tank constant temperature steam mode, the first compressor and the second compressor are both in working state, and the first water pump and the second water pump are respectively in the open state.

3. The cascade steam heat pump unit according to claim 2, characterized in that: The cascade steam heat pump unit further includes a first valve, a second valve, a third valve, a fourth valve, a fifth valve and a sixth valve; The two ends of the first valve are respectively connected to the outlet of the first compressor and the one refrigerant passage of the first heat exchanger; The two ends of the second valve are respectively connected to the outlet of the first compressor and the other refrigerant passage of the fourth heat exchanger; Two ends of the third valve are respectively connected to the outlet of the first water pump and the other refrigerant passage of the first heat exchanger; Two ends of the fourth valve are respectively connected to the outlet of the first water pump and the other refrigerant passage of the third heat exchanger; The two ends of the fifth valve are respectively connected to the other refrigerant passage of the first heat exchanger and the flash tank; Both ends of the sixth valve are communicated with the other refrigerant passage of the first heat exchanger and the first water tank, respectively.

4. The cascade steam heat pump unit according to claim 3, characterized in that: When the cascade steam heat pump unit is in the hot water mode, the first valve, the third valve, the fifth valve, and the sixth valve are all in an open state, and the second valve and the fourth valve are all in a closed state; When the cascade steam heat pump unit is in the steam mode or the water-steam mode, the first valve, the third valve, the fifth valve, and the sixth valve are all in a closed state, and the second valve and the fourth valve are all in an open state; When the cascade steam heat pump unit is in the first water tank constant temperature mode, the first valve and the sixth valve are both in an open state, and the second valve, the third valve, the fourth valve, and the fifth valve are all in a closed state; When the cascade steam heat pump unit is in the first water tank constant temperature steam mode, the first valve, the second valve, the fourth valve, and the sixth valve are all in an open state, and the third valve and the fifth valve are both in a closed state.

5. The cascade steam heat pump unit according to claim 3, characterized in that: The first valve and the second valve are electric regulating valves respectively, and the third valve, the fourth valve, the fifth valve and the sixth valve are solenoid valves respectively.

6. The cascade steam heat pump unit according to claim 2, characterized in that: The cascade steam heat pump unit also includes a steam output pipe connected to the flash tank and a pressure reducing valve arranged on the steam output pipe; when the cascade steam heat pump unit is in the hot water mode and the first water tank constant temperature mode, the pressure reducing valve is in a closed state; when the cascade steam heat pump unit is in the steam mode, the water replenishment steam mode and the first water tank constant temperature steam mode, the pressure reducing valve is in an open state.

7. The cascade steam heat pump unit according to claim 1, characterized in that: The second compressor further includes an air supply port; the cascade steam heat pump unit further includes an economizer and a third expansion valve, one refrigerant passage of the economizer is connected in series between the one refrigerant passage of the third heat exchanger and the second expansion valve, another refrigerant passage of the economizer is respectively connected to the air supply port of the second compressor and the outlet of the third expansion valve, and the inlet of the third expansion valve is connected to the one refrigerant passage of the economizer; and / or, The cascade steam heat pump unit also includes a second water tank, a fourth water pump, a seventh valve and an eighth valve. The second water tank, the fourth water pump, the seventh valve and the flash tank are connected in sequence. The second water tank, the fourth water pump, the eighth valve and the first water tank are connected in sequence.

8. The cascade steam heat pump unit according to claim 1, characterized in that: The cascade steam heat pump unit also includes a gas-liquid separator, which is connected to the inlet of the second heat exchanger and the first compressor respectively; and / or the first compressor is a variable frequency compressor, the second compressor is a fixed frequency compressor, the first water pump and the second water pump are respectively fixed frequency water pumps, and the third water pump is a variable frequency water pump.

9. The cascade steam heat pump unit according to claim 1, characterized in that: The cascade steam heat pump unit also includes a temperature sensor, a pressure sensor and a liquid level sensor respectively arranged on the flash tank; and / or the first water pump is connected to the bottom of the flash tank, the other refrigerant passage of the third heat exchanger is connected to the middle of the flash tank, and a steam outlet is provided at the top of the flash tank.

10. A control method for a cascade steam heat pump unit according to any one of claims 1 to 9, characterized in that: The control method includes at least one of the following (a)-(e): (a) when it is detected that the liquid level in the flash tank is greater than a first preset warning liquid level and the temperature in the flash tank is greater than or equal to 90° C., controlling the cascade steam heat pump unit to be in steam mode; (b) when it is detected that the liquid level in the flash tank is lower than the first preset warning liquid level, the liquid level in the first water tank is higher than the second preset warning liquid level, and the water temperature is greater than 90° C., turning on the third water pump and controlling the cascade steam heat pump unit to the water replenishment steam mode; (c) when it is detected that the liquid level in the flash tank is lower than the first preset warning liquid level and the water temperature in the first water tank is lower than 90° C., turning on the second water pump and controlling the cascade steam heat pump unit to the first water tank constant temperature steam mode; (d) when steam production is stopped and it is detected that the liquid level in the first water tank is lower than a third preset warning liquid level and the temperature is lower than 90° C., controlling the cascade steam heat pump unit to a first water tank constant temperature mode; (e) When it is night time, the cascade steam heat pump unit is controlled to be in hot water mode.

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