Low-grade heat driven two-stage ejector-single-stage absorption ammonia-water solution refrigeration process

Abstract

A low-temperature heat-driven two-stage injection-single-stage absorption NH3-H2O solution refrigeration method and system, the concentrated solution temperature analysis process is continuously segmented from-15 DEG C to 85 DEG C: the heat absorption refrigeration of-15 DEG C~15 DEG C, the heat recovery temperature rise of 15 DEG C~64 DEG C, the analysis generates >99% high concentration NH3 vapor to be used as evaporant without rectification, the low-temperature heat supply heat rise of 64 DEG C~85 DEG C, the analysis generates NH3-H2O binary vapor for the low-pressure NH3 vapor generated by injection suction evaporation refrigeration and pressurization to absorption pressure, whereby the traditional single heat consumption concentrated solution analysis process is changed into coupling with output cold quantity and circulating power, and the secondary analysis and tertiary analysis process is carried out in the countercurrent temperature rise isobaric analysis channel structure intersected with the heat medium fluid, is optimized from the two aspects of system thermodynamic principle and process driving force, realizes 80~90 DEG C low-temperature heat energy-5 DEG C~15 DEG C cold quantity, and the performance coefficient COP is not less than 0.60.

Description

Technical Field

[0001] This invention relates to jet refrigeration technology, solar energy utilization and heat-dynamic-cold energy conversion, and in particular to the field of high-efficiency refrigeration technology driven by low-grade heat energy of green working fluid NH3-H2O through jet-absorption coupling. Background Technology

[0002] Near-zero temperature refrigeration technology is widely used in air conditioning of buildings and vehicles, warehousing and preservation, and refrigerants for biological and chemical processes. Its wide distribution and high energy consumption are among the main causes of peak electricity demand in summer. Replacing traditional electric-driven refrigeration with refrigeration driven by renewable or recyclable low-grade heat energy is not only necessary to reduce peak summer electricity demand but also a crucial global task in building a low-carbon, energy-saving social consumption model. The bottlenecks restricting the widespread application of low-grade heat energy refrigeration technology are: firstly, its low coefficient of performance (COP); and secondly, its complex process systems, high operational and management difficulty, and significant investment. Taking solar thermal collector-driven air conditioning refrigeration as an example (Chen Erjian, Dai Yanjun, et al. Progress and application of solar air conditioning and heat pump technology, Huadian Technology, 2021, 43(11): 41~48), the thermal energy in the 80~100℃ temperature range drives the single-effect circulation absorption refrigeration of LiBr-H2O solution with a performance coefficient of 0.6~0.8. However, the application of this solution is limited because it is highly corrosive and easily crystallizes. If the NH3-H2O solution, which is not highly corrosive and does not crystallize, is used instead, a distillation unit needs to be added to increase the NH3 concentration in the binary vapor generated by the generator to 99% (mass concentration, the same below) or higher before condensation, so that the solution absorption circulation based on NH3 evaporation refrigeration can operate continuously and stably. This will not only reduce the COP, but also make the circulation system more complex and difficult to promote and apply. In reality, the temperature of recyclable and usable low-temperature heat sources is generally below 100℃. For example, the commonly used flat-plate solar collectors are designed to drive refrigeration cycles at a temperature not exceeding 90℃ (Zou Tonghua et al. Optimal generation temperature and energy-saving analysis of solar absorption refrigeration, Fluid Machinery, 2004, (2): 50~53). This further limits the COP of the traditional NH3-H2O absorption refrigeration cycle, which directly outputs cooling capacity from the NH3 evaporator, to a range below 0.5 (Wang Zhimin et al. Research on the application of solar absorption refrigeration system in Hohhot area, Renewable Energy, 2014, 32(3): 270~274).

[0003] From the perspectives of economy and applicability, the near-0°C temperature refrigeration technology driven by low-grade heat energy NH3-H2O absorption should seek a new cyclical route that utilizes the driving force of the process more efficiently in principle. Therefore, the low-grade heat energy driven two-stage injection-single-stage absorption NH3-H2O solution refrigeration method and system disclosed in this invention have the following technical advancements: the high-concentration absorbent convective heating and desorption process is carried out continuously in segments from -15℃ to 85℃. In the temperature range of -15℃ to 15℃, convective heat absorption and refrigeration are performed. In the temperature range of 15℃ to 64℃, high-concentration NH3 (>99%) vapor is generated by regenerative convection heating and used directly as the evaporative refrigerant. In the temperature range of 64℃ to 85℃, the NH3-H2O binary vapor generated by the heating convection heating process is used for injection to absorb the low-pressure NH3 vapor generated by evaporative refrigeration and pressurize it to reach the absorption pressure. This couples the traditional purely heat-consuming solution desorption process with the output cooling capacity and output cycle power, thereby constructing a shorter process and eliminating the need for distillation of the NH3-H2O solution absorption refrigeration cycle, achieving a low-grade heat energy refrigeration output of -5℃ to 15℃ from 80℃ to 90℃, with a cycle system COP of not less than 0.60. Summary of the Invention

[0004] This invention discloses a low-grade thermal energy-driven two-stage jet-single-stage absorption NH3-H2O solution absorption refrigeration cycle method and system. The method is applicable to refrigeration using thermal energy at a temperature not lower than 80℃ (especially flat-plate solar collectors or industrial waste heat), outputting a cooling capacity of -5℃ to 15℃. As shown in the attached diagram, the NH3-H2O binary solution (concentrated solution) leaving absorber 1 has an NH3 concentration of 50-70%, a temperature of 30-36℃, and a pressure of 0.4-0.85 MPa. After releasing heat and cooling to 12-18℃ in solution return cooler 2, it adiabatically expands through concentrated solution expansion valve 3 to a temperature of -15 to -3℃ and a pressure of 0.12-0.28 MPa, then enters flash evaporator 4 where it is separated into a gas-liquid two-phase system with a gas / liquid mass ratio of less than 0.1. The gas phase directly enters... In the convection cooler 6, the gas convection heat absorption space and the liquid phase, after being pressurized to 1.2~2.0 MPa by the solution pressurization pump 5, enter the liquid convection heat absorption space of the convection cooler 6, causing the refrigerant temperature to drop from 20~25℃ to -5~15℃, and the gas and liquid phase temperatures to rise to 10~22℃. The gas phase is drawn into the first-stage ejector 11, while the liquid phase absorbs heat and rises to 28~33℃ through the solution return cooler 2, and then enters the solution heat exchanger 7 to continue absorbing heat and rising to the corresponding liquid phase pressure and NH4+. At a saturation temperature of 62-72℃, the NH3 at a concentration of 3 begins to vaporize and then enters the secondary generator 8 to continue receiving heat from the low-grade heat transfer medium at 80-90℃. While heating (to <74℃), it evaporates and separates into a gas-liquid two-phase system (gas / liquid mass ratio less than 0.1). The gas phase NH3 with a concentration >99% enters the NH3 vapor condenser 13 for cooling and condensation into a saturated NH3 liquid at the corresponding pressure. This liquid then enters the condensate subcooler 16 to be cooled to <10℃ and passes through the NH3 condensate expansion valve 14 for insulation. The liquid expands to 0.4~0.6MPa and enters the evaporator 15 to absorb heat from the refrigerant, outputting a cooling capacity of 5~8℃ through the refrigerant. The NH3 liquid is completely vaporized into steam with a temperature of <5℃, which enters the condensate subcooler 16 to absorb heat and rise to <33℃ as working steam. It is then drawn by the first-stage ejector 11 to draw flash steam with a pressure of 0.12~0.28MPa. After the two are mixed, the pressure is 0.25~0.35MPa. The mixture is then drawn and pressurized by the second-stage ejector 12 and sent to the absorber 1 for circulation.

[0005] The liquid phase separated by the secondary generator 8 enters the tertiary generator 9 to receive heat from the low-temperature heat transfer medium at 80~90℃. It continues to be heated (to <85℃) and vaporized, and then separated into gas-liquid two phases again. The mass of the gas phase is 1.01~1.1 times the sum of the mass of the gas phase generated by the flash generator 4 and the mass of the gas phase generated by the secondary generator 8. The pressure of the gas phase is the same as the pressure of the secondary generator 8. The NH3 concentration of the gas phase is <99%. This gas phase is directly used as the working steam of the secondary ejector 12 to draw the mixed gas sent by the primary ejector 11. After the two are mixed, the pressure is 0.42~0.86MPa and sent to the absorber 1 to be absorbed by the dilute solution. The liquid phase separated by the tertiary generator 9 becomes a dilute solution with a pressure of 1.2~2.0MPa, an NH3 concentration of 40~60%, and a temperature of 74~85℃. It enters the solution heat exchanger 7 to release heat and cool down to 30~35℃, and then passes through the dilute solution expansion valve 10 to expand adiabatably to a pressure of 0.42~0.86MPa. It then enters the absorber 1 and undergoes an absorption reaction with the mixed gas sent by the secondary ejector 12. The released heat of reaction is carried away by cooling water, generating a binary concentrated NH3-H2O solution with an NH3 concentration of 50~70%, a temperature of 30~36℃, and a pressure of 0.4~0.85MPa. This constitutes a closed low-grade heat energy driven two-stage ejection-single-stage absorption NH3-H2O solution absorption refrigeration cycle. The COP of this cycle (i.e., the ratio of the sum of the -5℃~15℃ refrigeration capacity output by the convection cooler 6 and the evaporation cooler 15 to the sum of the 80~90℃ low-grade heat energy input by the secondary generator 8 and the tertiary generator 9) is greater than 0.6.

[0006] The secondary generator 8 and the tertiary generator 9 are two identical aluminum plate-fin heat exchangers, stacked together as a single unit. The heat transfer medium continuously enters the heat flow channel of the tertiary generator 9 from the bottom, releasing heat through convection. After flowing vertically up and down three times, it flows through the secondary generator 8 in the same manner, thus creating a heating temperature gradient within the tertiary generator 9 and the secondary generator 8, aligned with the direction of the heat flow. The heated concentrated solution continuously enters the heat-removing channel adjacent to the heat transfer medium outlet at the top of the secondary generator 8, flowing back and forth three times horizontally before overflowing into the downcomer and flowing in the same manner. Through the heating channel adjacent to the heat transfer fluid in the tertiary generator 9, a counter-current heat transfer channel structure is formed, which crosses with the heat transfer fluid. This structure can efficiently utilize the heat transfer temperature difference driving force and meets the requirement that the lower the solution concentration, the higher the heating temperature in the isobaric desorption process of NH3-H2O solution. The concentrated solution flows horizontally in the lower half of the vertical heating desorption channel flow section, while the upper half is the isobaric flow space of the desorption gas phase. The height of the overflow inlet of the downcomer is the height of the liquid level in the generator. The desorption gas phase space of the secondary generator 8 and the desorption gas phase space of the tertiary generator 9 are connected by a balance pipe with an inner diameter of no more than 1 mm to maintain the isobaric conditions between the two. Attached Figure Description

[0007] Appendix Figure 1 This is a schematic diagram of the low-temperature thermal energy driven two-stage injection-single-stage absorption refrigeration cycle system provided by the present invention.

[0008] In the attached diagram: 1 – Absorber; 2 – Solution cooler; 3 – Concentrated solution expansion valve; 4 – Flash evaporator; 5 – Solution pressurization pump; 6 – Convection cooler; 7 – Solution heat exchanger; 8 – Secondary generator; 9 – Tertiary generator; 10 – Dilute solution expansion valve; 11 – First-stage ejector; 12 – Second-stage ejector; 13 – NH3 vapor condenser; 14 – NH3 condensate expansion valve; 15 – Evaporative cooler; 16 – Condensate subcooler The accompanying drawings will be further described below with reference to the embodiments. Detailed Implementation

[0009] The following describes specific embodiments of the present invention in conjunction with, but not limited to, specific examples. Example: Using an 85kW flat-plate solar collector as a heat source, 50kW of 5°C cool water is generated for air conditioning. The solar collector supplies hot water at 88℃ and returns it at 78℃; the air conditioner supplies cool water at 6℃ and returns it at 22℃; the cooling water temperature is 25~30℃. The 22℃ air conditioner return water is divided into two parts according to the ratio of the output cooling capacity of the convection cooler 6 and the evaporative cooler 15. The two parts are then combined to supply 6℃ air conditioner cooling water.

[0010] To achieve this refrigeration task, as shown in the attached diagram, the concentrated NH3-H2O solution leaving absorber 1 has a flow rate of 1000 kg / h, an NH3 concentration of 68%, a temperature of 33°C, and a pressure of 0.8 MPa. After releasing heat and cooling to 15°C in the solution return cooler 2, it adiabatically expands through the concentrated solution expansion valve 3 to a temperature of -5°C and a pressure of 0.25 MPa, and then enters flash evaporator 4 where it is separated into a gas-liquid two-phase system. The gas phase (NH3 concentration of 99.9%) with a flow rate of 73 kg / h directly enters the gas convection heat absorption space of the convection cooler 6. The liquid phase (NH3 concentration 65.5%) is pressurized to 1.7 MPa by the solution pressurization pump 5 and then enters the liquid convection heat absorption space of the convection cooler 6. This causes the 22℃ air conditioning return water to cool down to 3-4℃ through convection heat release, raising both the gas and liquid phase temperatures to 15℃. The gas phase is drawn into the primary ejector 11, while the liquid phase absorbs heat through the solution return cooler 2, reaching a temperature of 31.5℃. It then enters the solution heat exchanger 7 to continue absorbing heat and reaching the saturation temperature of 62-63℃ corresponding to the liquid phase pressure and NH3 concentration, where it begins to vaporize. It then enters the secondary generator 8 to continue receiving heat from the 78-81℃ solar hot water, continuously heating (to 67℃) while vaporizing. Secondary separation occurs, resulting in a gas-liquid two-phase system. kg / h of gaseous NH3 (99.3% NH3 concentration) enters NH3 vapor condenser 13 for cooling and condensation into NH3 liquid at 37°C. It then enters condensate subcooler 16 to be cooled to 8°C. After passing through NH3 condensate expansion valve 14, it expands adiabatically to 0.5MPa and enters evaporative cooler 15 to absorb heat from the 22°C air conditioning return water. It evaporates at 4~5°C, thus cooling the air conditioning return water to <8°C. The 4~5°C NH3 vapor enters subcooler 16 to absorb heat and rise to 32°C, serving as working steam. It is then drawn by primary ejector 11 to draw flash steam at 0.25MPa pressure. The two are mixed and the pressure is 0.32MPa. The mixture is then drawn by secondary ejector 12 and pressurized before being sent to absorber 1 for circulation.

[0011] The 852 kg / h liquid phase separated by the secondary generator 8 enters the tertiary generator 9 to receive heat from the 81~88℃ solar water heater. It continues to heat up (to 78℃) while vaporizing and is separated into gas-liquid two phases again. The gas phase has a mass flow rate of 150 kg / h, a gas phase pressure of 1.7 MPa, and a gas phase NH3 concentration of 98.6%. This gas phase is directly used as the working steam of the secondary ejector 12 to draw the mixed gas sent from the primary ejector 11. After the two are mixed, the pressure is 0.81 MPa and sent to the absorber 1 to be absorbed by the dilute solution. The 702 kg / h dilute solution separated by the tertiary generator 9, with a pressure of 1.7 MPa, an NH3 concentration of 55.2%, and a temperature of 78°C, enters the solution heat exchanger 7 to release heat and cool down to 34°C. It then undergoes adiabatic expansion through the dilute solution expansion valve 10 to a pressure of 0.81 MPa before entering the absorber 1 to react with the mixed gas from the secondary ejector 12. The released heat of reaction is carried away by cooling water, generating a 1000 kg / h concentrated solution with an NH3 concentration of 68%, a temperature of 33°C, and a pressure of 0.8 MPa. This concentrated solution is output from the absorber, forming the two-stage ejector-single-stage absorption NH3-H2O solution absorption refrigeration cycle driven by the solar water heater. The convective cooler 6 outputs 24.7 kW of cooling capacity, and the evaporative cooler 15 outputs 26 kW of cooling capacity. 83.5 kW of solar water heating energy (78-88°C) is input to the secondary generator 8 and the tertiary generator 9. The system's cycle refrigeration COP is 0.61.

[0012] The present invention is not limited to the above embodiments, and its technical solutions have been described in the invention content section.

Claims

1. A method for cooling NH3-H2O solution using a two-stage injection-single-stage absorption method driven by low-grade thermal energy, characterized in that... The absorption liquid convective heating and desorption process is carried out continuously in segments from -15℃ to 85℃. In the temperature range of -15℃ to 15℃, convective heat absorption and cooling are performed. In the temperature range of 15℃ to 64℃, the regenerative heating is used to generate NH3 vapor with a concentration of >99% which is directly used as an evaporative refrigerant. In the temperature range of 64℃ to 85℃, the heating is used to complete the desorption process. The NH3-H2O binary vapor generated is used to inject and absorb the low-pressure NH3 vapor generated by evaporative cooling and pressurize it to the absorption pressure. In this way, the heat-consuming solution desorption process is coupled with the output cooling capacity and the output cycle power process. The concentrated NH3-H2O solution leaving the absorber has an NH3 concentration of 50-70%, a temperature of 30-36℃, and a pressure of 0.4-0.85MPa. After releasing heat and cooling to 12-18℃ in the solution cooler, it expands adiabatically through the concentrated solution expansion valve to a temperature of -15 to -3℃ and a pressure of 0.12-0.28MPa. It then enters the flash evaporator and is separated into a gas-liquid two-phase system with a gas / liquid mass ratio of less than 0.

1. The gas phase directly enters the convection cooler to absorb heat, while the liquid phase is pressurized to 1.2-2.0MPa by the solution pressurization pump before entering the convection cooler to absorb heat, causing the refrigerant temperature to drop from 20-25℃ to -5-15℃. Both the gas and liquid phase temperatures rise to 10-22℃. The gas phase is then drawn into the first-stage ejector, while the liquid phase absorbs heat through the solution cooler and is heated to 28-33℃ before entering the solution heat exchanger. The vapor continues to absorb heat and heat up to the saturation temperature of 62~72℃ at the corresponding liquid phase pressure and NH3 concentration, and begins to vaporize. It then enters the secondary generator and continues to be heated by a low-temperature heat medium of 80~90℃. While evaporating, the temperature is raised to <74℃. It is then separated into two phases of gas and liquid with a gas / liquid mass ratio of less than 0.

1. The gas phase with NH3 concentration >99% enters the steam condenser for cooling and condensation. After cooling and subcooling to <10℃, it expands adiabatically to 0.4~0.6MPa and enters the evaporative cooler to absorb heat and output a cooling capacity of 5~8℃. The vapor generated at a temperature <5℃ passes through the subcooler to absorb heat and heat up to <33℃. It is then used as working steam and is drawn by the first-stage ejector to draw flash steam at a pressure of 0.12~0.28MPa. The two are mixed and the pressure is 0.25~0.35MPa. They are then drawn by the second-stage ejector, mixed, and pressurized, and sent into the absorber for circulation. The liquid phase separated by the secondary generator enters the tertiary generator and receives low-temperature heat of 80~90℃. It continues to vaporize and heat up to <85℃. After three separations, it becomes a gas-liquid two-phase system. The mass of the gas phase is 1.01~1.1 times the sum of the mass of the gas phase generated by the flash generator and the gas phase generated by the secondary generator. The gas phase pressure is the same as the pressure of the secondary generator, and the NH3 concentration in the gas phase is <99%. This gas phase is directly used as the working steam of the secondary ejector to draw the mixed gas pressurized by the primary ejector. After remixing, the gas is sent to the absorber at a pressure of 0.42~0.86MPa to be absorbed by the dilute solution. The dilute solution obtained from the three generators has a pressure of 1.2~2.0 MPa, an NH3 concentration of 40~60%, and a temperature of 74~85℃. It enters the solution heat exchanger to release heat and cool down to 30~35℃, then expands adiabatically to a pressure of 0.42~0.86 MPa. It then enters the absorber and reacts with the mixed gas from the secondary ejector. The heat of reaction released is carried away by cooling water, generating a binary concentrated NH3-H2O solution with an NH3 concentration of 50~70%, a temperature of 30~36℃, and a pressure of 0.4~0.85 MPa. This constitutes a closed low-grade heat energy driven two-stage ejection-single-stage absorption NH3-H2O solution absorption refrigeration cycle with a refrigeration performance coefficient greater than 0.

6.

2. The method for cooling NH3-H2O solution using a low-grade thermal energy-driven two-stage injection-single-stage absorption process according to claim 1, characterized in that... A countercurrent heating isobaric desorption channel structure is formed, intersecting with the heat transfer fluid, to meet the requirement that the lower the solution concentration, the higher the heating temperature in the isobaric desorption process of NH3-H2O solution. The continuous concentrated solution countercurrent heating isobaric desorption process is completed through a secondary generator and a tertiary generator stacked together. These two generators are made of the same aluminum plate-fin heat exchanger structure. The heat transfer fluid continuously enters the heat transfer fluid channel of the lower tertiary generator from the bottom of the lower plate-fin heat exchanger, and after being deflected three times vertically, it is deflected again in the same way through the upper secondary generator for convection and heat release. Thus, the process continues in the tertiary generator and the secondary generator... A heating temperature gradient is formed inside, consistent with the flow direction of the hot fluid. The heated concentrated solution continuously enters the vertical heating and desorption channel at the top of the secondary generator, adjacent to the outlet of the hot medium fluid. After flowing back and forth three times in the horizontal direction, it overflows into the downcomer and flows through the tertiary generator in the same manner. The concentrated solution flows horizontally in the lower half of the flow section of the vertical heating and desorption channel, while the upper half is the isobaric flow space of the gas phase generated by desorption. The height of the overflow inlet of the downcomer is the height of the liquid level inside the generator. The desorption gas phase space of the secondary generator and the desorption gas phase space of the tertiary generator are connected by a balance pipe with an inner diameter of no more than 1 mm to maintain the isobaric conditions between them.

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