Low-grade waste heat driven two-stage absorption refrigeration system and method

Abstract

This invention relates to a low-grade waste heat-driven two-stage absorption refrigeration system and method, comprising: a low-pressure stage solution circulation loop, a high-pressure stage solution circulation loop, and a refrigerant circulation loop; saturated liquid output from the condenser in the refrigerant circulation loop mixes with condensed saturated liquid output from the high-pressure stage solution circulation loop, and then undergoes primary throttling and pressure reduction to an intermediate pressure via a first throttling valve before entering a gas-liquid separator for separation; the separated saturated vapor is absorbed by the high-pressure stage solution circulation loop; the separated saturated liquid mixes with condensed saturated liquid output from the low-pressure stage solution circulation loop, and then undergoes secondary throttling and pressure reduction to an evaporation pressure via a second throttling valve before entering an evaporator for evaporation and cooling to generate cooling capacity. This invention utilizes two-stage throttling of the refrigerant at the condenser outlet to reduce irreversible losses, and simultaneously utilizes superheated steam from the generator outlet to preheat the dilute solution, fully utilizing waste heat, which can significantly improve the performance of traditional two-stage absorption refrigeration systems.

Description

Technical Field

[0001] This invention relates to the field of absorption refrigeration and waste heat utilization technology, and in particular to a two-stage absorption refrigeration system and refrigeration method driven by low-grade waste heat. Background Technology

[0002] Absorption refrigeration systems can utilize low-grade energy sources, such as solar energy and industrial waste heat, and have high energy-saving potential. Many scholars have conducted extensive research on them and proposed different system structures to improve system performance, such as GAX, dual-effect, 1.5-effect, and two-stage systems. Compared with other absorption refrigeration systems, the two-stage absorption refrigeration system can utilize low-temperature heat sources (around 70°C) and has high energy-saving potential; however, its lower COP (around 0.4) limits its further widespread application.

[0003] In a two-stage absorption refrigeration system, the high-pressure liquid refrigerant (saturated aqueous solution) at the condenser outlet is directly throttled and depressurized to a low pressure, resulting in significant irreversible losses. Furthermore, the high-temperature superheated steam at the generator outlet is directly fed into the condenser for condensation, failing to be fully utilized and causing energy waste.

[0004] As can be seen from the above analysis, reducing the irreversible losses generated during the throttling and pressure reduction process, and making reasonable use of superheated steam, play a very important role in improving the performance of a two-stage absorption refrigeration system. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a low-grade waste heat-driven two-stage absorption refrigeration system and refrigeration method. This system utilizes two-stage throttling of the refrigerant at the condenser outlet to reduce irreversible losses, while simultaneously using superheated steam at the generator outlet to preheat the dilute solution, fully utilizing waste heat and significantly improving the performance of traditional two-stage absorption refrigeration systems.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a low-grade waste heat-driven two-stage absorption refrigeration system, comprising: a low-pressure stage solution circulation loop, a high-pressure stage solution circulation loop, and a refrigerant circulation loop; the refrigerant circulation loop includes a condenser, a first throttling valve, a gas-liquid separator, a second throttling valve, and an evaporator; the saturated liquid output from the condenser mixes with the condensed saturated liquid output from the high-pressure stage solution circulation loop, and then undergoes a first-stage throttling and pressure reduction to an intermediate pressure via the first throttling valve before entering the gas-liquid separator for separation; the separated saturated vapor is absorbed by the high-pressure stage solution circulation loop; the separated saturated liquid mixes with the condensed saturated liquid output from the low-pressure stage solution circulation loop, and then undergoes a second-stage throttling and pressure reduction to an evaporation pressure via the second throttling valve before entering the evaporator for evaporation and cooling to generate cooling capacity.

[0007] Furthermore, the low-pressure stage solution circulation loop includes: a low-pressure stage absorber, a low-pressure stage solution pump, a low-pressure stage gas-liquid heat exchanger, a low-pressure stage solution heat exchanger, a low-pressure stage generator, and a low-pressure stage throttle valve;

[0008] The steam inlet of the low-pressure stage absorber is connected to the steam outlet of the evaporator, and the solution outlet of the low-pressure stage absorber is connected to the first solution inlet of the low-pressure stage gas-liquid heat exchanger via a low-pressure stage solution pump.

[0009] The first solution output terminal of the low-pressure stage gas-liquid heat exchanger is connected to the solution input terminal of the low-pressure stage generator through the low-pressure stage solution heat exchanger, and the second solution output terminal of the low-pressure stage gas-liquid heat exchanger is connected to the solution output terminal of the gas-liquid separator.

[0010] The solution output terminal of the low-pressure stage generator is connected to the solution input terminal of the low-pressure stage absorber in sequence through a low-pressure stage solution heat exchanger and a low-pressure stage throttling valve.

[0011] The steam input end of the low-pressure stage gas-liquid heat exchanger is connected to the steam output end of the low-pressure stage generator, and the steam output end of the low-pressure stage gas-liquid heat exchanger is connected to the high-pressure stage solution circulation loop.

[0012] Furthermore, the high-pressure stage solution circulation loop includes: a high-pressure stage absorber, a high-pressure stage solution pump, a high-pressure stage gas-liquid heat exchanger, a high-pressure stage solution heat exchanger, a high-pressure stage generator, and a high-pressure stage throttle valve;

[0013] The first steam input terminal of the high-pressure stage absorber is connected to the steam output terminal of the low-pressure stage gas-liquid heat exchanger 4, and the second steam input terminal of the high-pressure stage absorber is connected to the steam output terminal of the gas-liquid separator.

[0014] The solution output terminal of the high-pressure stage absorber is connected to the first solution input terminal of the high-pressure stage gas-liquid heat exchanger via a high-pressure stage solution pump.

[0015] The first solution output terminal of the high-pressure stage gas-liquid heat exchanger is connected to the solution input terminal of the high-pressure stage generator through the high-pressure stage solution heat exchanger, and the second solution output terminal of the high-pressure stage gas-liquid heat exchanger is connected to the solution output terminal of the condenser.

[0016] The solution output terminal of the high-pressure stage generator is connected to the solution input terminal of the high-pressure stage absorber in sequence through the high-pressure stage solution heat exchanger and the high-pressure stage throttle valve.

[0017] The steam input end of the high-pressure stage gas-liquid heat exchanger is connected to the steam output end of the high-pressure stage generator, and the steam output end of the high-pressure stage gas-liquid heat exchanger is connected to the steam input end of the condenser.

[0018] Furthermore, both the low-pressure stage generator and the high-pressure stage generator are connected to external heat sources.

[0019] Furthermore, the heat source is solar energy.

[0020] Furthermore, the solutions in the high-pressure stage solution circulation loop and the low-pressure stage solution circulation loop can be the same type of solution or different types of solutions.

[0021] On the other hand, the technical solution adopted by the present invention is as follows: a low-grade waste heat driven two-stage absorption refrigeration method, which includes: saturated liquid output from the condenser is mixed with saturated liquid condensed from the high-pressure stage solution circulation loop, and then the mixture is subjected to a first-stage throttling and pressure reduction to an intermediate pressure through a first throttling valve, and then enters a gas-liquid separator for separation; the separated saturated vapor is absorbed by the high-pressure stage solution circulation loop; the separated saturated liquid is mixed with saturated liquid condensed from the low-pressure stage solution circulation loop, and then subjected to a second-stage throttling and pressure reduction to an evaporation pressure through a second throttling valve, and then enters an evaporator for evaporation and cooling to generate cooling capacity.

[0022] Furthermore, the saturated liquid output from the condenser is mixed with the condensed saturated liquid output from the high-pressure stage solution circulation loop, including:

[0023] The high-pressure stage absorber is used to absorb the saturated vapor at the outlet of the gas-liquid separator and the low-pressure stage gas-liquid heat exchanger, thereby reducing the solution concentration in the high-pressure stage absorber to form a dilute solution.

[0024] After being pressurized to the condensing pressure by a high-pressure solution pump, the dilute solution enters a high-pressure gas-liquid heat exchanger. The pressurized dilute solution exchanges heat with the superheated steam output from the high-pressure generator. The steam temperature drops to the saturation temperature, and at the same time, part of the steam condenses into saturated liquid. The saturated steam is transferred to the condenser, and the condensed saturated liquid mixes with the saturated liquid output from the condenser.

[0025] After initial preheating, the dilute solution enters the high-pressure stage solution heat exchanger for further preheating. The reheated dilute solution then enters the high-pressure stage generator for regeneration. The water in the dilute solution evaporates into superheated steam, and at the same time, the solution temperature and concentration increase.

[0026] The concentrated solution output from the high-pressure stage generator enters the high-pressure stage solution heat exchanger for heat exchange, where its temperature decreases. After being throttled and depressurized by the high-pressure stage throttling valve, it enters the high-pressure stage absorber.

[0027] Furthermore, the separated saturated liquid is mixed with the condensed saturated liquid output from the low-pressure stage solution circulation loop, including:

[0028] The low-pressure stage absorber is used to absorb the saturated vapor generated in the evaporator, reducing the solution concentration in the low-pressure stage absorber to form a dilute solution.

[0029] After being pressurized to an intermediate pressure by a low-pressure stage solution pump, the dilute solution enters a low-pressure stage gas-liquid heat exchanger. The pressurized dilute solution exchanges heat with the superheated steam output from the low-pressure stage generator. The steam temperature drops to the saturation temperature, and some of the steam condenses into saturated liquid. The saturated steam is transferred to the high-pressure stage solution circulation loop, and the condensed saturated liquid mixes with the saturated liquid separated by the gas-liquid separator.

[0030] After initial preheating, the dilute solution enters a low-pressure stage solution heat exchanger for further preheating.

[0031] The preheated dilute solution enters the low-pressure generator for regeneration. The water in the dilute solution evaporates into superheated steam, and at the same time, the solution temperature and concentration increase.

[0032] The concentrated solution output from the low-pressure stage generator enters the low-pressure stage solution heat exchanger for heat exchange, where its temperature decreases. Then, it passes through the low-pressure stage throttling valve to reduce its pressure before entering the low-pressure stage absorber.

[0033] The present invention has the following advantages due to the adoption of the above technical solutions:

[0034] 1. This invention employs a two-stage throttling process for the refrigerant, with the first stage throttling to the intermediate pressure and the second stage throttling to the evaporation pressure. This reduces irreversible losses during the throttling process, while increasing the cooling capacity per unit mass and improving the system COP (cooling capacity to input heat ratio).

[0035] 2. This invention utilizes superheated steam from the generator outlet to preheat a dilute solution, which can effectively utilize the superheated steam, reduce the heat source consumption in the generator, and thus improve the system COP.

[0036] 3. This invention provides a feasible method and solution for improving the COP of traditional two-stage absorption refrigeration cycles. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the overall structure of a low-grade waste heat-driven two-stage absorption refrigeration system in an embodiment of the present invention.

[0038] Figure label:

[0039] 1-Evaporator, 2-Low-pressure stage absorber, 3-Low-pressure stage solution pump, 4-Low-pressure stage gas-liquid heat exchanger, 5-Low-pressure stage solution heat exchanger, 6-Low-pressure stage generator, 7-Low-pressure stage throttle valve, 8-High-pressure stage absorber, 9-High-pressure stage solution pump, 10-High-pressure stage gas-liquid heat exchanger, 11-High-pressure stage solution heat exchanger, 12-High-pressure stage generator, 13-High-pressure stage throttle valve, 14-Condenser, 15-First throttle valve, 16-Gas-liquid separator, 17-Second throttle valve. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0041] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0042] To reduce irreversible losses during the throttling and pressure reduction process and to make rational use of superheated steam, this invention provides a low-grade waste heat-driven two-stage absorption refrigeration system and method to achieve two-stage throttling and rational utilization of superheated steam. The system includes a low-pressure stage solution circulation loop, a high-pressure stage solution circulation loop, and a refrigerant circulation loop. In this circulation system, the saturated liquid at the outlet of condenser 14 mixes with the saturated liquid condensed in the high-pressure stage gas-liquid heat exchanger 10, and after being throttled to an intermediate pressure in the first stage, it enters the gas-liquid separator for separation. The saturated steam is absorbed by the high-pressure stage absorber, while the saturated liquid mixes with the saturated liquid condensed in the low-pressure stage gas-liquid heat exchanger 4, and after being throttled to the evaporation pressure in the second stage, it enters the evaporator 1 for evaporative cooling to generate cooling capacity. This invention can achieve the goals of improving the COP of traditional two-stage absorption refrigeration systems, rationally utilizing superheated steam, and saving energy.

[0043] In one embodiment of the present invention, a low-grade waste heat-driven two-stage absorption refrigeration system is provided. In this embodiment, as... Figure 1 As shown, the dashed lines represent steam pipelines, and the solid lines represent salt solution and aqueous solution pipelines. Therefore, this low-grade waste heat-driven two-stage absorption refrigeration system includes: a low-pressure stage solution circulation loop, a high-pressure stage solution circulation loop, and a refrigerant circulation loop. Wherein:

[0044] The refrigerant circulation loop includes a condenser 14, a first throttle valve 15, a gas-liquid separator 16, a second throttle valve 17, and an evaporator 1. The saturated liquid output from the condenser 14 is mixed with the condensed saturated liquid output from the high-pressure stage solution circulation loop. After passing through the first throttle valve 15, the liquid is depressurized to an intermediate pressure and then enters the gas-liquid separator 16 for separation.

[0045] The separated saturated vapor is absorbed by the high-pressure stage solution circulation loop;

[0046] After separation, the saturated liquid is mixed with the condensed saturated liquid output from the low-pressure stage solution circulation loop. The mixture is then subjected to secondary throttling and pressure reduction through the second throttling valve 17 to the evaporation pressure, and then enters the evaporator 1 for evaporation and cooling to generate cold energy.

[0047] In one alternative embodiment, the low-pressure stage solution circulation loop includes: a low-pressure stage absorber 2, a low-pressure stage solution pump 3, a low-pressure stage gas-liquid heat exchanger 4, a low-pressure stage solution heat exchanger 5, a low-pressure stage generator 6, and a low-pressure stage throttle valve 7.

[0048] The steam input end of the low-pressure stage absorber 2 is connected to the steam output end of the evaporator 1, and the solution output end of the low-pressure stage absorber 2 is connected to the first solution input end of the low-pressure stage gas-liquid heat exchanger 4 through the low-pressure stage solution pump 3.

[0049] The first solution output terminal of the low-pressure stage gas-liquid heat exchanger 4 is connected to the solution input terminal of the low-pressure stage generator 6 through the low-pressure stage solution heat exchanger 5, and the second solution output terminal of the low-pressure stage gas-liquid heat exchanger 4 is connected to the solution output terminal of the gas-liquid separator 16.

[0050] The solution output terminal of the low-pressure stage generator 6 is connected to the solution input terminal of the low-pressure stage absorber 2 in sequence through the low-pressure stage solution heat exchanger 5 and the low-pressure stage throttle valve 7.

[0051] The steam input end of the low-pressure stage gas-liquid heat exchanger 4 is connected to the steam output end of the low-pressure stage generator 6, and the steam output end of the low-pressure stage gas-liquid heat exchanger 4 is connected to the high-pressure stage solution circulation loop.

[0052] Among them, the low-pressure stage generator 6 is connected to an external heat source.

[0053] In one alternative embodiment, the high-pressure stage solution circulation loop includes: a high-pressure stage absorber 8, a high-pressure stage solution pump 9, a high-pressure stage gas-liquid heat exchanger 10, a high-pressure stage solution heat exchanger 11, a high-pressure stage generator 12, and a high-pressure stage throttle valve 13.

[0054] The first steam input end of the high-pressure stage absorber 8 is connected to the steam output end of the low-pressure stage gas-liquid heat exchanger 4, and the second steam input end of the high-pressure stage absorber 8 is connected to the steam output end of the gas-liquid separator 16.

[0055] The solution output end of the high-pressure stage absorber 8 is connected to the first solution input end of the high-pressure stage gas-liquid heat exchanger 10 via the high-pressure stage solution pump 9.

[0056] The first solution output terminal of the high-pressure stage gas-liquid heat exchanger 10 is connected to the solution input terminal of the high-pressure stage generator 12 through the high-pressure stage solution heat exchanger 11, and the second solution output terminal of the high-pressure stage gas-liquid heat exchanger 10 is connected to the solution output terminal of the liquid and condenser 14.

[0057] The solution output terminal of the high-pressure stage generator 12 is connected to the solution input terminal of the high-pressure stage absorber 8 in sequence through the high-pressure stage solution heat exchanger 11 and the high-pressure stage throttle valve 13.

[0058] The steam input end of the high-pressure stage gas-liquid heat exchanger 10 is connected to the steam output end of the high-pressure stage generator 12, and the steam output end of the high-pressure stage gas-liquid heat exchanger 10 is connected to the steam input end of the condenser 14.

[0059] Among them, the high-voltage generator 12 is connected to an external heat source.

[0060] In the above embodiments, the solutions in the high-pressure stage solution circulation loop and the low-pressure stage solution circulation loop can be the same solution or different solutions, such as aqueous solutions of LiBr, LiCl, CaCl2, etc.

[0061] In the above embodiments, the heat source connected to the low-pressure stage generator 6 and the high-pressure stage generator 12 can be a low-grade heat source such as solar energy or industrial waste heat.

[0062] In an optional embodiment, in the refrigerant circulation loop, the solution output terminal of the condenser 14 is connected to the solution input terminal of the gas-liquid separator 16 through the first throttle valve 15, and the solution output terminal of the condenser 14 is also connected to the second solution output terminal of the high-pressure stage gas-liquid heat exchanger 10.

[0063] The solution output end of the gas-liquid separator 16 is connected to the solution input end of the evaporator 1 via the second throttle valve 17, and the solution output end of the gas-liquid separator 16 is also connected to the second solution output end of the low-pressure stage gas-liquid heat exchanger 4; the steam output end of the gas-liquid separator 16 is connected to the second steam input end of the high-pressure stage absorber 8.

[0064] The steam output end of evaporator 1 is connected to the steam input end of low-pressure stage absorber 2.

[0065] In one embodiment of the present invention, a low-grade waste heat-driven two-stage absorption refrigeration method is provided. In this embodiment, the method is implemented based on the low-grade waste heat-driven two-stage absorption refrigeration system described in the above embodiments, and the refrigeration method includes the following steps:

[0066] 1) The saturated liquid output from the condenser 14 is mixed with the condensed saturated liquid output from the high-pressure stage solution circulation loop. After passing through the first throttle valve 15, the pressure is reduced to the intermediate pressure and then enters the gas-liquid separator 16 for separation.

[0067] 2) The separated saturated vapor is absorbed by the high-pressure stage solution circulation loop;

[0068] 3) After the saturated liquid is separated, it is mixed with the condensed saturated liquid output from the low-pressure stage solution circulation loop. After passing through the second throttling valve 17, the pressure is reduced to the evaporation pressure and then enters the evaporator 1 for evaporation and cooling to generate cold energy.

[0069] In step 1) above, the saturated liquid output from condenser 14 is mixed with the condensed saturated liquid output from the high-pressure stage solution circulation loop, including the following steps:

[0070] 1.1) The high-pressure stage absorber 8 is used to absorb the saturated steam at the outlet of the gas-liquid separator 16 and the low-pressure stage gas-liquid heat exchanger 4, thereby reducing the solution concentration in the high-pressure stage absorber 8 to form a dilute solution.

[0071] 1.2) After the dilute solution is pressurized to the condensing pressure by the high-pressure stage solution pump 9, it enters the high-pressure stage gas-liquid heat exchanger 10. The pressurized dilute solution exchanges heat with the superheated steam output from the high-pressure stage generator 12. The steam temperature drops to the saturation temperature and a small part of the steam condenses into saturated liquid. The saturated steam is transferred to the condenser 14, and the condensed saturated liquid mixes with the saturated liquid output from the condenser 14.

[0072] 1.3) After the dilute solution is initially preheated, it enters the high-pressure stage solution heat exchanger 11 for further preheating. The dilute solution after being preheated again enters the high-pressure stage generator 12 for regeneration. The water in the dilute solution evaporates into superheated steam, and at the same time, the solution temperature and concentration increase.

[0073] 1.4) The concentrated solution output from the high-pressure stage generator 12 enters the high-pressure stage solution heat exchanger 11 for heat exchange, and the temperature decreases. After being throttled and depressurized by the high-pressure stage throttling valve 13, it enters the high-pressure stage absorber 8.

[0074] In step 3) above, the separated saturated liquid is mixed with the condensed saturated liquid output from the low-pressure stage solution circulation loop, including the following steps:

[0075] 3.1) The low-pressure stage absorber 2 is used to absorb the saturated steam generated in the evaporator 1, thereby reducing the solution concentration in the low-pressure stage absorber 2 to form a dilute solution;

[0076] 3.2) After being pressurized to an intermediate pressure by the low-pressure stage solution pump 3, the dilute solution enters the low-pressure stage gas-liquid heat exchanger 4. The pressurized dilute solution exchanges heat with the superheated steam output from the low-pressure stage generator 6. The steam temperature drops to the saturation temperature and a small part of the steam condenses into saturated liquid. The saturated steam is transferred to the high-pressure stage solution circulation loop. The condensed saturated liquid is mixed with the saturated liquid separated by the gas-liquid separator 16.

[0077] 3.3) After initial preheating, the dilute solution enters the low-pressure stage solution heat exchanger 5 for further preheating;

[0078] 3.4) The preheated dilute solution enters the low-pressure stage generator 6 for regeneration. The water in the dilute solution evaporates into superheated steam, and at the same time, the solution temperature and concentration increase.

[0079] 3.5) The concentrated solution output from the low-pressure stage generator 6 enters the low-pressure stage solution heat exchanger 5 for heat exchange, and the temperature decreases. Then, it enters the low-pressure stage absorber 2 after being throttled and depressurized by the low-pressure stage throttling valve 7.

[0080] The method provided in this embodiment is based on the above system embodiments. For specific processes and details, please refer to the above embodiments, which will not be repeated here.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low grade waste heat driven two-stage absorption refrigeration system, characterized in that, Comprise: low pressure stage solution circulation loop, high pressure stage solution circulation loop and refrigerant circulation loop; The refrigerant circulation loop comprises a condenser (14), a first throttling valve (15), a gas-liquid separator (16), a second throttling valve (17) and an evaporator (1); the saturated liquid output by the condenser (14) is mixed with the condensed saturated liquid output by the high pressure stage solution circulation loop, then is throttled to an intermediate pressure by the first throttling valve (15), and is separated in the gas-liquid separator (16); The separated saturated vapor is absorbed by the high pressure stage solution circulation loop; The separated saturated liquid is mixed with the condensed saturated liquid output by the low pressure stage solution circulation loop, then is throttled to an evaporation pressure by the second throttling valve (17), and is evaporated and cooled in the evaporator (1) to generate cold energy; The low pressure stage solution circulation loop comprises a low pressure stage absorber (2), a low pressure stage solution pump (3), a low pressure stage gas-liquid heat exchanger (4), a low pressure stage solution heat exchanger (5), a low pressure stage generator (6) and a low pressure stage throttling valve (7); The vapor input end of the low pressure stage absorber (2) is connected with the vapor output end of the evaporator (1), and the solution output end of the low pressure stage absorber (2) is connected with the first solution input end of the low pressure stage gas-liquid heat exchanger (4) through the low pressure stage solution pump (3); The first solution output end of the low pressure stage gas-liquid heat exchanger (4) is connected with the solution input end of the low pressure stage generator (6) through the low pressure stage solution heat exchanger (5), and the second solution output end of the low pressure stage gas-liquid heat exchanger (4) is connected with the solution output end of the gas-liquid separator (16); The solution output end of the low pressure stage generator (6) is connected with the solution input end of the low pressure stage absorber (2) in sequence through the low pressure stage solution heat exchanger (5) and the low pressure stage throttling valve (7); The vapor input end of the low pressure stage gas-liquid heat exchanger (4) is connected with the vapor output end of the low pressure stage generator (6), and the vapor output end of the low pressure stage gas-liquid heat exchanger (4) is connected with the high pressure stage solution circulation loop; The high pressure stage solution circulation loop comprises a high pressure stage absorber (8), a high pressure stage solution pump (9), a high pressure stage gas-liquid heat exchanger (10), a high pressure stage solution heat exchanger (11), a high pressure stage generator (12) and a high pressure stage throttling valve (13); The first vapor input end of the high pressure stage absorber (8) is connected with the vapor output end of the low pressure stage gas-liquid heat exchanger (4), and the second vapor input end of the high pressure stage absorber (8) is connected with the vapor output end of the gas-liquid separator (16); The solution output end of the high pressure stage absorber (8) is connected with the first solution input end of the high pressure stage gas-liquid heat exchanger (10) through the high pressure stage solution pump (9); The first solution output end of the high pressure stage gas-liquid heat exchanger (10) is connected with the solution input end of the high pressure stage generator (12) through the high pressure stage solution heat exchanger (11), and the second solution output end of the high pressure stage gas-liquid heat exchanger (10) is connected with the solution output end of the condenser (14); The solution output end of the high-pressure stage generator (12) is connected with the solution input end of the high-pressure stage absorber (8) through the high-pressure stage solution heat exchanger (11) and the high-pressure stage throttling valve (13) in sequence. The steam output end of the high-pressure stage gas-liquid heat exchanger (10) is connected with the steam input end of the condenser (14), and the steam input end of the high-pressure stage gas-liquid heat exchanger (10) is connected with the steam output end of the high-pressure stage generator (12).

2. The low grade heat driven two stage absorption refrigeration system as claimed in claim 1 wherein, Both the low-pressure stage generator (6) and the high-pressure stage generator (12) are externally connected with a heat source.

3. The low grade heat driven two stage absorption refrigeration system as claimed in claim 2 wherein, The heat source is solar energy.

4. The low grade heat driven two stage absorption refrigeration system as claimed in claim 1 wherein, The solutions in the high-pressure stage solution circulation loop and the low-pressure stage solution circulation loop are the same kind of solution or different kinds of solution.

5. A low-grade waste heat driven two-stage absorption refrigeration method, realized based on the low-grade waste heat driven two-stage absorption refrigeration system according to any one of claims 1-4, characterized in that, The saturated liquid output by the condenser (14) is mixed with the condensed saturated liquid output by the high-pressure stage solution circulation loop, and then is throttled to an intermediate pressure by the first throttling valve (15) and is separated in the gas-liquid separator (16); The separated saturated steam is absorbed by the high-pressure stage solution circulation loop; The separated saturated liquid is mixed with the condensed saturated liquid output by the low-pressure stage solution circulation loop, and then is throttled to an evaporation pressure by the second throttling valve (17) and is evaporated and cooled in the evaporator (1) to generate cold energy. The saturated liquid output by the condenser (14) is mixed with the condensed saturated liquid output by the high-pressure stage solution circulation loop, and the mixture is throttled to an intermediate pressure by the first throttling valve (15) and is separated in the gas-liquid separator (16); 6. The low grade waste heat driven two stage absorption refrigeration process as claimed in claim 5 wherein, The high-pressure stage absorber (8) is used for absorbing the saturated steam at the outlets of the gas-liquid separator (16) and the low-pressure stage gas-liquid heat exchanger (4), so that the concentration of the solution in the high-pressure stage absorber (8) is reduced to form a dilute solution; After being pressurized to a condensation pressure by the high-pressure stage solution pump (9), the dilute solution enters the high-pressure stage gas-liquid heat exchanger (10), and the pressurized dilute solution exchanges heat with the superheated steam output by the high-pressure stage generator (12), so that the temperature of the steam is reduced to a saturation temperature and part of the steam is condensed into saturated liquid, the saturated steam is transmitted to the condenser (14), and the condensed saturated liquid is mixed with the saturated liquid output by the condenser (14); After being preliminarily preheated, the dilute solution enters the high-pressure stage solution heat exchanger (11) to be preheated again, and the dilute solution that is preheated again enters the high-pressure stage generator (12) to be regenerated, so that the water in the dilute solution is evaporated into superheated steam, and the temperature of the solution is increased and the concentration of the solution is increased; The concentrated solution output by the high-pressure stage generator (12) exchanges heat in the high-pressure stage solution heat exchanger (11), so that the temperature of the concentrated solution is reduced, the concentrated solution is throttled to a low pressure by the high-pressure stage throttling valve (13), and then enters the high-pressure stage absorber (8). The separated saturated liquid is mixed with the condensed saturated liquid output by the low-pressure stage solution circulation loop, and the mixture is throttled to an evaporation pressure by the second throttling valve (17) and is evaporated and cooled in the evaporator (1) to generate cold energy.

7. The low grade waste heat driven two stage absorption refrigeration process as claimed in claim 5 wherein, The low-pressure stage absorber (2) is used for absorbing the saturated steam generated in the evaporator (1), so that the concentration of the solution in the low-pressure stage absorber (2) is reduced to form a dilute solution; ​ The dilute solution is pressurized to an intermediate pressure by a low-pressure stage solution pump (3) and enters a low-pressure stage gas-liquid heat exchanger (4). The pressurized dilute solution exchanges heat with superheated steam output from a low-pressure stage generator (6), and the steam temperature drops to saturation temperature while part of the steam condenses into saturated liquid. The saturated steam is transmitted to a high-pressure stage solution circulation loop, and the condensed saturated liquid is mixed with saturated liquid separated from a gas-liquid separator (16); The dilute solution is preliminarily preheated and then enters a low-pressure stage solution heat exchanger (5) for further preheating; The dilute solution is preliminarily preheated and then enters a low-pressure stage solution heat exchanger (5) for further preheating; The concentrated solution output from the low-pressure stage generator (6) exchanges heat in the low-pressure stage solution heat exchanger (5) and is cooled, and then is throttled and depressurized by a low-pressure stage throttling valve (7) and enters a low-pressure stage absorber (2).

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