MULTI-STAGE PLATE-TYPE EVAPORATION ABSORPTION COOLING DEVICE AND METHOD

Abstract

Provided is a multi-stage plate-type evaporation absorption refrigerating device, including components such as a refrigerant water evaporator, a condensed water level gauge, a four-path solution heat exchanger, a vapor mixing tank, a first plate-type inner-coupling phase-changing heat exchanger, a second plate-type inner-coupling phase-changing heat exchanger, a third plate-type inner-coupling phase-changing heat exchanger, a first flash separation tank, a second flash separation tank, a third flash separation tank, a mechanical vapor compression pump and a condensed water level gauge.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to PCT Application No. PCT/CN2016/091993, filed on Jul. 28, 2016 which is based upon and claims priority to Chinese Patent Application No. 201510465086.X, filed on Jul. 31, 2015, the entire contents both of which are incorporated herein by reference.

FIELD OF TECHNOLOGY

The following relates to a waste heat recovering apparatus and method, and particularly relates to a multi-stage plate-type evaporation absorption cooling device and method.

BACKGROUND

A traditional absorption refrigerating method has a production history of nearly a century, and adopts basically standardized thermodynamic processes and devices. In practical use, lithium bromide absorption refrigerating cycle for air conditioning and ammonia absorption refrigeration cycle for refrigerating and air conditioning are adopted most frequently. In recent decades, because of effects of specifications of Montreal Protocol, reduction of use of fluorocarbons and significance of use of waste heat as a driving heat source to reduction of carbon emission, the absorption refrigerating method is greatly popularized and developed. For example, in a Chinese Patent CN200510060377.7 “Multi-energy-driven lithium bromide refrigeration air conditioning device”, a variety of energies, such as solar energy, microwave and fuel (gas), are utilized. In Japanese Patents 2009-236440 “Gas heat pup type air conditioning device or refrigerating device” and 2009-236441 “Heat pup type refrigerating device”, an absorption refrigerating method for using the waste heat of a gas engine as a heat source of the air conditioning device and the refrigerating device is developed. Such a refrigerating method is mostly applied to utilization of low-temperature waste heat. However, these improvements cannot increase a coefficient of performance (COP) of the absorption refrigerating cycle. In standards of the latest GB 29540-2013 Minimum Allowable Values of Energy Efficiency and Energy Efficiency Grades for Lithium Bromide Absorption Chillers, the COP of a double-effect lithium bromide absorption refrigerating unit is determined as 1.12-1.4, while a temperature of an input heat source vapor of a double-effect lithium bromide refrigerator is 150° C. or even higher, but the COP of an ammonia-water absorption refrigerating unit is only 0.3-0.4. A mechanical vapor compression heat pump gets attention in a heat energy system because of rising sensible heat of low-temperature waste heat vapor with small mechanical work, changing into high-temperature vapor, and then recycling the latent heat to serve as a high-temperature heat source. In a Chinese patent CN201010198705.0 “System for heating condensed water with waste heat extracted from power plant by heat pump”, a Chinese patent CN20101063699.5 “System and method for regional combined cooling and heating by thermoelectric cogeneration coupling heat pump”, a Chinese patent CN200910223748.7 “Self-coupling cold source heat pump circulating apparatus for exhaust vapor condensing process of low-temperature waste heat power generation system” and a Chinese patent CN201010163688.7 “Concentrated heating system and method for thermoelectric cogeneration of heat pump coupling by circulating water in power plant”, a problem of utilizing a low-temperature heat source, including water and vapor, to increase the COP of an entire thermoelectric cogeneration power-generating and heating system by a heat pump unit is involved; but a problem of applying the mechanical vapor compression heat pump to refrigerating and air conditioning cycles to increase the COP of the refrigerating unit is not involved.

One of basic reasons for low COP in the absorption refrigerating method is that refrigerant vapor generated by absorbing heat when refrigerant water of a high-pressure generator is concentrated needs to absorb a large amount of heat energy, and heat contained in the refrigerant vapor releases heat of phase change during condensation, but the heat of phase change is discharged out of the system and cannot be recycled. However, a refrigerant absorbs low-temperature heat energy of coolant circulating water in a low-pressure evaporator to generate the low-temperature and low-pressure refrigerant vapor which enters an absorber and is converted from a vapor phase into a liquid phase; and the heat released by the phase change is usually also discharged out of the refrigerating system and is not recycled. In CN201020188184.6 “Double-effect type II lithium bromide absorption heat pump unit”, only one heat pump unit for heating is developed, and recycling of the discharged heat in the above cycles is not solved. In CN200820115165.3 “Single-effect type III absorption heat pump simultaneously utilized in both cooling and heating directions”, since a portion of discharged heat is used for heating, cooling and heating can be performed simultaneously, and COP can reach 2.2-2.6. But the discharged heat is not reused in the system to reduce input of energy for driving the refrigerating system, so the problem of recycling the discharged heat cannot be solved fundamentally. The problem of low COP is not solved, so the COP for refrigerating and heating is still very low.

Absorption refrigerating and air conditioning cycles are high in cost mainly because traditionally a shell-and-tube type heat exchanging device and a spraying mass-transfer method are adopted and have low heat and mass transfer coefficients and large heat exchange areas with the need of a circulating pump for spraying an adsorption solution and the refrigerant repeatedly. In a Chinese Patent CN200480010361.9 “Absorber and heat exchanger with external loop as well as heat pump system and air conditioning system including the absorber or the heat exchanger”, a plate-type heat exchanger is used as the absorber or the condenser to increase heat exchanging efficiency. In a U.S. Pat. No. 6,176,101 B1 “FLAT-PLATE ABSORBERS AND EVAPORATORS FOR ABSORPTION COOLERS”, the condensers and the absorbers are assembled in one plate-type heat exchanger which provides a possibility for recovery of condensation heat, but the patent does not provide a solution for increasing the COP and reducing system cost in the absorption refrigerating method.

SUMMARY

An aspect relates to increasing a COP of a multi-stage plate-type evaporation absorption cooling device.

In order to achieve the above purpose, a multi-stage plate-type evaporation absorption cooling device is invented, including:

a refrigerant water evaporator including an inlet; and
an absorber including an outlet and an inlet.

The multi-stage plate-type evaporation absorption cooling device further includes the following devices:

a four-path solution heat exchanger including two cold-side paths: a first and a second cold-side paths, and a hot-side path, wherein an inlet of the first cold-side path is connected with the outlet of the absorber by a pipeline; an outlet of the hot-side path is connected with the inlet of the absorber by a pipeline; the second cold-side path is connected with a domestic water pipeline; and the first cold-side path has two outlets: a first outlet of the first cold-side path and a second outlet of the first cold-side path;
a vapor mixer having a fresh vapor inlet, a regenerated vapor inlet and an outlet, wherein the fresh vapor inlet is connected with a fresh vapor pipeline;
a first phase-changing heat exchanger having a hot-side inlet connected with the outlet of the vapor mixer by a pipeline, and having a cold-side inlet connected with the first outlet of the first cold-side path of the four-path solution heat exchanger by a pipeline;
a fourth plate-type heat exchanger having a hot-side inlet connected with the hot-side outlet of the first phase-changing heat exchanger by a pipeline, and having a cold-side inlet connected with the domestic water pipeline;
a first flash vapor-liquid separator having an inlet, a top gas-phase outlet and a bottom liquid-phase outlet, wherein the inlet is connected with the cold-side outlet of the first phase-changing heat exchanger by a pipeline;
a second phase-changing heat exchanger having a hot-side inlet connected with the gas-phase outlet of the first flash vapor-liquid separator by a pipeline, and having a cold-side inlet connected with the second outlet of the first cold-side path of the four-path solution heat exchanger by a pipeline;
a second flash vapor-liquid separator having an inlet, a top gas-phase outlet and a bottom liquid-phase outlet, wherein the inlet is connected with the cold-side outlet of the second phase-changing heat exchanger by a pipeline, and a liquid-phase outlet of the second flash vapor-liquid separator is combined with the outlet of the first flash vapor-liquid separator by a pipeline and then is connected with the hot-side inlet of the four-path solution heat exchanger;
a third phase-changing heat exchanger having a hot-side inlet connected with the gas-phase outlet of the second flash vapor-liquid separator by a pipeline, having a cold-side inlet connected with the hot-side outlet of the fourth plate-type heat exchanger by a pipeline, and having a hot-side outlet combined with the hot-side outlet of the second phase-changing heat exchanger by a pipeline and then connected with the inlet of the refrigerant water evaporator by a pipeline;
a condensed water level controller having an outlet, an inlet and a water outlet, wherein the outlet is connected with a pipeline connected between the fourth plate-type heat exchanger and the third phase-changing heat exchanger by a pipeline;
a third flash vapor-liquid separator having an inlet, a top gas-phase outlet and a bottom liquid-phase outlet, wherein the inlet is connected with the cold-side outlet of the third phase-changing heat exchanger by a pipeline, and the liquid-phase outlet is connected with the inlet of the condensed water level controller by a pipeline; and
a mechanical vapor compression pump having an inlet connected with the gas-phase outlet of the third flash vapor-liquid separator by a pipeline, and having an outlet connected with the regenerated vapor inlet of the vapor mixer by a pipeline.

The apparatus also has optimized structures as follows:

The mechanical vapor compression pump has a water replenishing tank capable of measuring a saturation degree automatically.

The first, the second and the third phase-changing heat exchangers are plate-type heat exchangers, plate-type evaporators, plate-type condensers or shell-and-tube type heat exchangers.

The mechanical vapor compression pump is a combination of single-stage or multi-stage fans and compression pumps, and is in a structural form of Roots, centrifuging, reciprocating or screw rod.

The present disclosure also provides a refrigerating method of the multi-stage plate-type evaporation absorption cooling device, including:

feeding a dilute solution from the absorber into the four-path solution heat exchanger to exchange heat with a concentrated solution, and then respectively feeding into the first and the second phase-changing heat exchangers;
feeding a portion of the dilute solution from the absorber into the first phase-changing heat exchanger to exchange heat, and feeding refrigerant water after exchanging heat into a first flash vapor-liquid separation tank to separate into gas-phase refrigerant water vapor and liquid-phase concentrated solution;
feeding another portion of the dilute solution from the absorber into the second phase-changing heat exchanger to exchange heat with the refrigerant water vapor from the first flash vapor-liquid separation tank, and feeding the dilute solution after exchanging heat into a second flash vapor-liquid separation tank to separate into the gas-phase refrigerant water vapor and the liquid-phase concentrated solution; and
absorbing waste heat of the concentrated solution of the refrigerant water from the first and the second flash vapor-liquid separation tanks by cold water in another path and refrigerant water from an absorption tank through the four-path solution heat exchanger so as to generate hot water.

The above process also has optimized solutions as follows.

A vapor mixture after exchanging heat in the first phase-changing heat exchanger enters the third phase-changing heat exchanger to absorb heat of phase change of the refrigerant water vapor from the second flash vapor-liquid separation tank, and then enters a third flash vapor-liquid separation tank. The vapor mixture of the gas phase enters the mechanical vapor compression pump to generate regenerated vapor, and is mixed with fresh vapor in a vapor mixing tank to generate vapor mixture which enters the first phase-changing heat exchanger to exchange heat with the dilute solution.

Refrigerant water vapor condensate after exchanging heat by the second and the third phase-changing heat exchangers enters the absorber and is cooled by chilled water.

The present disclosure proposes an optimized design of lithium bromide absorption refrigeration, so that the unit can have an ultra-high COP which can reach 5.5-6.

In the present disclosure, waste heat of heat source vapor condensed water and concentrated solution is recovered through the plate-type heat exchangers to generate domestic hot water for output and use.

The present disclosure also proposes a concept of circulating absorption refrigeration, air conditioning and heat-pump heating of a rectification type vapor phase-changing heat recovery unit component, such as an ammonia-water absorption refrigerating unit, in view of small differences in boiling points of various refrigerants and absorbents.

BRIEF DESCRIPTION

Some of the embodiments will be described in detail, with reference to the following FIGURES, wherein like designations denote like members, wherein:

FIG. 1 is a schematic structural diagram illustrating a device of an embodiment.

In the FIGURE:

1: vapor mixing tank; 2: first plate-type inner-coupling phase-changing heat exchanger; 3: first flash separation tank; 4: second plate-type inner-coupling phase-changing heat exchanger; 5: second flash separation tank; 6: third plate-type inner-coupling phase-changing heat exchanger; 7: third flash separation tank; 8: automatic water replenishing tank; 9: vacuum pump; 10: four-path solution heat exchanger; 11: mechanical vapor compression pump; 12: plate-type heat exchanger; 13: fresh vapor inlet; 14: domestic water inlet-outlet; 15: domestic water inlet-outlet; 16: chilled water inlet-outlet; 17: cooling water inlet-outlet; 20: condensed water level gauge; 21: refrigerant water evaporator; 22: low-pressure absorber; C: water-replenishing inlet.

DETAILED DESCRIPTION

The present disclosure is further described below in combination with embodiments and drawings which are only used for explaining, rather than limiting a protection scope of the present disclosure.

As shown in FIG. 1, the apparatus in the present embodiment is as follows:

as shown in FIG. 1, the apparatus includes:
a refrigerant water evaporator, including an inlet;
an absorber, including an outlet and an inlet;
a four-path solution heat exchanger including two cold-side paths: a first and a second cold-side paths, and a hot-side path, wherein an inlet of the first cold-side path is connected with the outlet of the absorber by a pipeline; an outlet of the hot-side path is connected with the inlet of the absorber by a pipeline; the second cold-side path is connected with a domestic water pipeline; and the first cold-side path has two outlets: a first outlet of the first cold-side path and a second outlet of the first cold-side path;
a vapor mixer, having a fresh vapor inlet, a regenerated vapor inlet and an outlet, wherein the fresh vapor inlet is connected with a fresh vapor pipeline;
a first phase-changing heat exchanger having a hot-side inlet connected with the outlet of the vapor mixer by a pipeline and a cold-side inlet connected with the first outlet of the first cold-side path of the four-path solution heat exchanger by a pipeline;
a fourth plate-type heat exchanger having a hot-side inlet connected with the hot-side outlet of the first phase-changing heat exchanger by a pipeline and a cold-side inlet connected with the domestic water pipeline;
a first flash vapor-liquid separator, having an inlet, a top gas-phase outlet and a bottom liquid-phase outlet, wherein the inlet is connected with the cold-side outlet of the first phase-changing heat exchanger by a pipeline;
a second phase-changing heat exchanger having a hot-side inlet connected with the gas-phase outlet of the first flash vapor-liquid separator by a pipeline and a cold-side inlet connected with the second outlet of the first cold-side path of the four-path solution heat exchanger by a pipeline;
a second flash vapor-liquid separator, having an inlet, a top gas-phase outlet and a bottom liquid-phase outlet, wherein the inlet is connected with the cold-side outlet of the second phase-changing heat exchanger by a pipeline, and the liquid-phase outlet is combined with the outlet of the first flash vapor-liquid separator by a pipeline and then connected with the hot-side inlet of the four-path solution heat exchanger;
a third phase-changing heat exchanger having a hot-side inlet connected with the gas-phase outlet of the second flash vapor-liquid separator by a pipeline, a cold-side inlet connected with the hot-side outlet of the fourth plate-type heat exchanger by a pipeline, and a hot-side outlet combined with the hot-side outlet of the second phase-changing heat exchanger by a pipeline and then connected with the inlet of the refrigerant water evaporator by a pipeline, wherein
the first, the second and the third phase-changing heat exchangers may be plate-type inner-coupling phase-changing heat exchangers, and may also be other conventional heat exchangers such as plate-type heat exchangers, plate-type evaporators, plate-type condensers or shell-and-tube type heat exchangers and the like;
a condensed water level controller, having an outlet, an inlet and a water outlet, wherein the outlet is connected with the pipeline connected between the fourth plate-type heat exchanger and the third phase-changing heat exchanger by a pipeline;
a third flash vapor-liquid separator, having an inlet, a top gas-phase outlet and a bottom liquid-phase outlet, wherein the inlet is connected with the cold-side outlet of the third phase-changing heat exchanger by a pipeline, and the liquid-phase outlet is connected with the inlet of the condensed water level controller by a pipeline; and
a mechanical vapor compression pump having an inlet connected with the gas-phase outlet of the third flash vapor-liquid separator by a pipeline and an outlet connected with the regenerated vapor inlet of the vapor mixer by a pipeline, wherein the mechanical vapor compression pump has a water replenishing tank capable of measuring a saturation degree automatically, may be a conventional vapor compression pump, is a combination of single-stage or multi-stage fans and compression pumps, and is in a structural form of Roots, centrifuging, reciprocating or screw rod.

An original heat source in the present embodiment is a mixture of fresh vapor and regenerated vapor, and certainly, can also be vapor or hot water. An upper portion of the absorber has a refrigerant pipeline. In the FIGURE, 16 is a refrigerant working medium inlet-outlet. A lower portion of the absorber has a cooling water pipeline. In the FIGURE, 17 is a cooling water inlet, and C is a water-replenishing inlet. In such a unit, a heat pump 11 in a mechanical vapor compressor, three groups of plate-type inner-coupling phase-changing heat exchangers 2, 4 and 6, and three groups of flash vapor-liquid separation tanks 3, 5 and 7 matched with the heat exchangers are adopted. First two combined groups are mainly used for heating and evaporating a dilute solution of refrigerant water to complete concentration of the dilute solution of refrigerant water and generation of refrigerant water vapor. A third group is used for recovering heat of phase change of refrigerant vapor and generating regenerated vapor. The three groups of systems composed of the plate-type inner-coupling phase-changing heat exchangers and the flash vapor-liquid separation tanks are operated in a vacuum state, and need to be communicated with a vacuum pump unit 9 so as to keep a vacuum degree and maintain relatively high heat exchanging efficiency. The vacuum pump pumps incondensable gas, and the systems are preset in the vacuum state. Each group has a corresponding absolute pressure value. The regenerated vapor (with relatively low potential energy) generated by the plate-type inner-coupling phase-changing heat exchanger 6 and the flash vapor-liquid separation tank 7 in the third group enters the mechanical vapor compression pump 11, and is supercharged by the mechanical vapor compression pump 11 in a manner of closing heat to output and generate saturated vapor with a higher level of potential energy. The saturated vapor enters a vapor mixing tank 1 through a pipeline and is mixed with the fresh vapor 13. The heat source vapor entering the first plate-type inner-coupling phase-changing heat exchanger 2 exchanges heat with the dilute solution of the refrigerant water on the other side in the plate-type inner-coupling phase-changing heat exchanger, and then is condensed into condensed water which enters a hot side of the plate-type heat exchanger 12 from the pipeline and exchanges heat with domestic water on the other side in the heat exchanger. The heated domestic hot water is output and used by users, while the cooled condensed water is input to the third plate-type inner-coupling phase-changing heat exchanger 6 through a condensed water circulating pump. The condensed water is vaporized into the regenerated vapor in the plate-type inner-coupling phase-changing heat exchanger and the flash vapor-liquid separation tanks 6 and 8. The dilute solution of the refrigerant water flowing out of a low-pressure generator is pressed into a four-path plate-type heat exchanger 10 by the circulating pump. The dilute solution of the refrigerant water enters the four-path plate-type heat exchanger and then is divided into two paths. One path is heated after indirectly exchanging heat with a concentrated solution, then flows out of the heat exchanger, and then enters the first plate-type inner-coupling phase-changing heat exchanger 2; and the other path is adjusted in temperature in the heat exchanger, then flows out of the heat exchanger, and then enters the second plate-type inner-coupling phase-changing heat exchanger 4. The dilute solution of the refrigerant water enters the first plate-type inner-coupling phase-changing heat exchanger 2 to generate a vapor-liquid mixed state substance which enters the flash vapor-liquid separation tank 3 and is separated into a vapor phase and a liquid phase. The liquid phase is the concentrated solution, while the vapor phase is secondary saturated vapor which is used as a heat source of a next stage and enters the second plate-type inner-coupling phase-changing heat exchanger 4 and the second flash vapor-liquid separation tank 5. At the hot-side inlet of the second plate-type inner-coupling phase-changing heat exchanger 4, the secondary vapor (the refrigerant water vapor) generated in the last stage exchanges heat with the refrigerant water on the cold side and then is condensed into refrigerant water which is discharged out of the second plate-type inner-coupling phase-changing heat exchanger 4 and enters an evaporator through a U pipe. On the other (cold) side of the second plate-type inner-coupling phase-changing heat exchanger 4, the refrigerant water from the four-path solution heat exchanger 10 exchanges heat with the refrigerant water vapor on the hot side in the heat exchanger to generate a vapor-liquid mixed state substance which enters the second flash vapor-liquid separation tank 5. The liquid phase separated by the second flash vapor-liquid separation tank 5 is the concentrated solution which is returned from the lower portion to the four-path solution heat exchanger 10. The vapor phase is the refrigerant water vapor which is discharged out of the upper portion, enters the hot side of the third plate-type inner-coupling phase-changing heat exchanger 6 at the next stage and is used as the heat source. The refrigerant water vapor on the hot side of the third plate-type inner-coupling phase-changing heat exchanger 6 exchanges heat with the condensed water on the cold side and is subjected to phase change to generate the refrigerant water which flows out of the lower portion of the third plate-type inner-coupling phase-changing heat exchanger 6 and enters the evaporator 21 through the U pipe. The circulated condensed water on the cold side of the third plate-type inner-coupling phase-changing heat exchanger 6 absorbs energy of the hot side and then enters the vapor-liquid separator 7 for vaporization to remove liquid drops so as to generate the saturated vapor (called regenerated vapor) with relatively low potential energy. The regenerated vapor from the vapor-liquid separator 7 enters the mechanical vapor compression pump 11, and is supercharged and heated by the mechanical vapor compression pump 11 in a manner of closing heat to generate the regenerated vapor with a higher level of potential energy. The regenerated vapor is a main heat source entering the vapor mixing tank 1 and the first plate-type inner-coupling phase-changing heat exchanger 2. The four-path solution heat exchanger 10 receives the concentrated solution of a relatively high temperature from the flash vapor-liquid separation tank 3 and the second flash vapor-liquid separation tank 5, wherein one portion of heat energy exchanges heat with the dilute solution of the refrigerant water of a relatively low temperature on the other side to increase the temperature of the dilute solution of the refrigerant water, while the other portion of heat energy heats the cold domestic water on the other side. The four-path solution heat exchanger 10 respectively has one inlet and one outlet for the domestic water, one inlet and two outlets for the dilute solution of the refrigerant water, and one inlet and one outlet for the concentrated solution, so that the concentrated solution is also cooled to a set temperature by the four-path solution heat exchanger 10 and then enters an absorber 22.

The refrigerant water enters the low-pressure evaporator 21. An absolute pressure of the low-pressure evaporator 21 is only 0.00087 Pa. The refrigerant water is vaporized at about 5° C. under the low-pressure condition. When vaporization conditions are satisfied, equivalent energy in the refrigerant circulating water needs to be absorbed simultaneously, so the chilled water is also cooled to approach a vaporization temperature. The refrigerant vapor in the absorber 22 enters the absorber 22 with the same vacuum degree. A lithium bromide solution with a relatively high concentration in the absorber 22 has strong capacity to absorb vapor. The concentrated solution fully absorbs cold vapor and then is diluted into the refrigerant water; and the refrigerant water is pumped out by the refrigerant water circulating pump and enters 14. In order to meet and increase the absorption efficiency, the absorber 22 is also equipped with a refrigerant water spraying and circulating pump, and the absorber 22 is also provided with a refrigerant water circulating pump to ensure an evaporation effect of the refrigerant water. The absorber 22 may absorb the heat of phase change of the refrigerant water vapor while operation, so the absorber is equipped with a shell-and-tube cooler. External cooling water takes away refrigerant water vapor condensing heat by the cooler so as to cool the solution.

The process of the present disclosure retains low-pressure barrel type evaporators and absorber apparatuses of traditional evaporation absorption refrigerating units, and retains relevant configurations of the original process, such as a refrigerant water pump, a refrigerant water spraying pump, a refrigerant water circulating pump, a vacuum incondensable gas discharge system and relevant original configurations. Such a design route is conducive to upgrading of an existing absorption refrigerating unit, conducive to understanding by those skilled in the art or relevant arts, and convenient for popularization and promotion of the present disclosure. Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

For the sake of clarity, it is to be understood that the use of ‘a’ or ‘an’ throughout this application does not exclude a plurality, and ‘comprising’ does not exclude other steps or elements.

Claims

1. A multi-stage plate-type evaporation absorption cooling device, comprising:

a refrigerant water evaporator comprising an inlet; and

an absorber comprising an outlet and an inlet,

wherein the multi-stage plate-type evaporation absorption cooling device further comprises following devices: a four-path solution heat exchanger comprising two cold-side paths: a first and a second cold-side paths, and a hot-side path, wherein an inlet of the first cold-side path is connected with the outlet of the absorber by a pipeline; an outlet of the hot-side path is connected with the inlet of the absorber by a pipeline; the second cold-side path is connected with a domestic water pipeline; and the first cold-side path has two outlets: a first outlet of the first cold-side path and a second outlet of the first cold-side path; a vapor mixer having a fresh vapor inlet, a regenerated vapor inlet and an outlet, wherein the fresh vapor inlet is connected with a fresh vapor pipeline; a first phase-changing heat exchanger having a hot-side inlet connected with the outlet of the vapor mixer by a pipeline, and having a cold-side inlet connected with the first outlet of the first cold-side path of the four-path solution heat exchanger by a pipeline; a fourth plate-type heat exchanger having a hot-side inlet connected with the hot-side outlet of the first phase-changing heat exchanger by a pipeline, and having a cold-side inlet connected with the domestic water pipeline; a first flash vapor-liquid separator having an inlet, a top gas-phase outlet and a bottom liquid-phase outlet, wherein the inlet is connected with the cold-side outlet of the first phase-changing heat exchanger by a pipeline; a second phase-changing heat exchanger having a hot-side inlet connected with the gas-phase outlet of the first flash vapor-liquid separator by a pipeline, and having a cold-side inlet connected with the second outlet of the first cold-side path of the four-path solution heat exchanger by a pipeline; a second flash vapor-liquid separator having an inlet, a top gas-phase outlet and a bottom liquid-phase outlet, wherein the inlet is connected with the cold-side outlet of the second phase-changing heat exchanger by a pipeline, and a liquid-phase outlet of the second flash vapor-liquid separator is combined with the outlet of the first flash vapor-liquid separator by a pipeline and then is connected with the hot-side inlet of the four-path solution heat exchanger; a third phase-changing heat exchanger having a hot-side inlet connected with the gas-phase outlet of the second flash vapor-liquid separator by a pipeline, having a cold-side inlet connected with the hot-side outlet of the fourth plate-type heat exchanger by a pipeline, and having a hot-side outlet combined with the hot-side outlet of the second phase-changing heat exchanger by a pipeline and then connected with the inlet of the refrigerant water evaporator by a pipeline; a condensed water level controller having an outlet, an inlet and a water outlet, wherein the outlet is connected with a pipeline connected between the fourth plate-type heat exchanger and the third phase-changing heat exchanger by a pipeline; a third flash vapor-liquid separator having an inlet, a top gas-phase outlet and a bottom liquid-phase outlet, wherein the inlet is connected with the cold-side outlet of the third phase-changing heat exchanger by a pipeline, and the liquid-phase outlet is connected with the inlet of the condensed water level controller by a pipeline; and a mechanical vapor compression pump having an inlet connected with the gas-phase outlet of the third flash vapor-liquid separator by a pipeline, and having an outlet connected with the regenerated vapor inlet of the vapor mixer by a pipeline.

2. The multi-stage plate-type evaporation absorption cooling device according to claim 1, wherein the mechanical vapor compression pump has a water replenishing tank capable of measuring a saturation degree automatically.

3. The multi-stage plate-type evaporation absorption cooling device according to claim 1, wherein the first, the second and the third phase-changing heat exchangers are plate-type heat exchangers, plate-type evaporators, plate-type condensers or shell-and-tube type heat exchangers.

4. The multi-stage plate-type evaporation absorption cooling device according to claim 1, wherein the mechanical vapor compression pump is a combination of single-stage or multi-stage fans and compression pumps, and is in a structural form of Roots, centrifuging, reciprocating or screw rod.

5. A refrigerating method of a multi-stage plate-type evaporation absorption cooling device according to claim 1, comprising:

feeding a dilute solution from a absorber into a four-path solution heat exchanger to exchange heat with a concentrated solution, and then respectively feeding into a first and a second phase-changing heat exchangers;

feeding a portion of the dilute solution from the absorber into the first phase-changing heat exchanger to exchange heat, and feeding refrigerant water after exchanging heat into a first flash vapor-liquid separation tank to separate into gas-phase refrigerant water vapor and liquid-phase concentrated solution;

feeding another portion of the dilute solution from the absorber into the second phase-changing heat exchanger to exchange heat with the refrigerant water vapor from the first flash vapor-liquid separation tank, and feeding the dilute solution after exchanging heat into a second flash vapor-liquid separation tank to separate into gas-phase refrigerant water vapor and liquid-phase concentrated solution; and

absorbing waste heat of the concentrated solution of the refrigerant water from the first and the second flash vapor-liquid separation tanks by cold water in another path and refrigerant water from an absorption tank through the four-path solution heat exchanger so as to generate hot water.

6. The refrigerating method according to claim 5, wherein a vapor mixture after exchanging heat in the first phase-changing heat exchanger enters a third phase-changing heat exchanger to absorb heat of phase change of the refrigerant water vapor from the second flash vapor-liquid separation tank, and then enters a third flash vapor-liquid separation tank; and the vapor mixture of the gas phase enters a mechanical vapor compression pump to generate regenerated vapor, and is mixed with fresh vapor in a vapor mixing tank to generate vapor mixture which enters the first phase-changing heat exchanger to exchange heat with the dilute solution.

7. The refrigerating method according to claim 5, wherein refrigerant water vapor condensate after exchanging heat by the second and the third phase-changing heat exchangers enters the absorber and is cooled by chilled water.