Lithium nitrate-based composite ammonia carrier and its application in absorption refrigeration system

Abstract

This invention discloses a lithium nitrate-based composite ammonia carrier in the field of refrigeration technology and its application in absorption refrigeration systems. Specifically, the components of the lithium nitrate-based composite ammonia carrier include lithium nitrate, liquid ammonia, lithium bromide, crown ether 12-Crown-4, and sodium lactate. When the lithium nitrate-based composite ammonia carrier is used as an absorbent in an absorption refrigeration system, the synergistic effect of multiple materials improves refrigeration performance while significantly reducing the crystallization concentration of the working fluid under operating conditions. This further reduces the refrigeration temperature, expands the refrigeration temperature range, and improves the system's refrigeration efficiency. Simultaneously, the working fluid formulation does not contain ammonia water, avoiding the disadvantage of requiring a distillation device in ammonia water refrigeration systems and the impact of a certain reflux ratio on refrigeration performance in ammonia water systems. It also overcomes the limitation of water / lithium bromide systems in being unable to produce cold sources below 0°C, significantly improving the system's safety and practicality.

Description

Technical Field

[0001] This invention relates to the field of refrigeration technology, specifically to a lithium nitrate-based composite ammonia carrier and its application in absorption refrigeration systems. Background Technology

[0002] Absorption refrigeration technology plays a vital role in industrial production, especially in the irreplaceable role of recycling low-grade preheating methods. Traditional absorption refrigeration systems use water / lithium bromide or ammonia / water as working fluid pairs, but these systems have some inherent drawbacks. For example, systems using water as a refrigerant cannot produce cold sources below 0°C, while ammonia-water refrigeration systems, although capable of achieving low refrigeration temperatures, suffer from low thermal efficiency, high corrosiveness, easy crystallization, and require distillation equipment.

[0003] To address these issues, researchers have been exploring new working fluid pairs and technical solutions. Among these, lithium nitrate, as a novel refrigerant, has attracted widespread attention. Lithium nitrate possesses favorable physicochemical properties, such as a low freezing point and high saturated vapor pressure, making it a potentially highly efficient refrigerant. However, pure lithium nitrate solutions still exhibit some limitations, such as high viscosity and low thermal conductivity, which may affect the overall performance of the refrigeration system.

[0004] Furthermore, to further improve the efficiency of absorption refrigeration systems, researchers are also exploring new absorbent materials. Traditional lithium bromide absorbents have solubility limitations, are prone to crystallization and clogging of systems, and are corrosive to the environment. Therefore, developing a novel absorbent that can improve solubility, lower crystallization temperature, and enhance physicochemical properties has become a current research focus. These improvements are expected to overcome the shortcomings of existing technologies and promote the application of absorption refrigeration technology in a wider range of fields.

[0005] To address the aforementioned issues, there is an urgent need to develop a new type of absorption refrigeration system that can efficiently utilize the low-grade waste heat from thermal power plants and improve refrigeration efficiency, safety, and environmental friendliness through optimized working fluid formulation and system design. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned technical problems by proposing a lithium nitrate-based composite ammonia carrier and its application in absorption refrigeration systems. Through innovative working fluid formulation and cycle design, it solves the technical problems of efficient utilization of low-grade waste heat and deep refrigeration, and provides a feasible technical path for combined cooling, heating, electricity and ice supply in thermal power plants.

[0007] The present invention achieves the above objectives through the following technical solutions:

[0008] As a first aspect of the present invention, a lithium nitrate-based composite ammonia carrier is provided, wherein, by weight, the lithium nitrate-based composite ammonia carrier comprises 40-50 parts of lithium nitrate, 30-40 parts of liquid ammonia, 10-15 parts of lithium bromide, 0.3-0.6 parts of crown ether 12-Crown-4, and 5-10 parts of sodium lactate.

[0009] As a further optimized embodiment of the present invention, the preparation method of the lithium nitrate-based composite ammonia carrier includes the following steps:

[0010] (1) Add lithium nitrate to the mixing tank A according to the formula amount, seal and evacuate the tank, then draw liquid ammonia from the bottom of the tank, and circulate water to cool the tank A in the jacket. Control the pressure inside the tank to not exceed 0.8 MPa. After the liquid level gauge reading of the mixing tank A reaches 30%, start stirring for 2 to 4 hours to form solution A.

[0011] (2) According to the formula, add lithium bromide, crown ether 12-Crown-4 and sodium lactate to the mixing tank B and mix. Stir at 20~30℃ for 30-60 minutes to form solution B. Vacuum the mixing tank B and set it aside for later use.

[0012] (3) Connect the bottom of the mixing tank A to the bottom of the mixing tank B, slowly draw solution A into solution B, and stir at 20~30℃ for 30~60 minutes to form a uniform solution. Filter to remove solvent impurities and obtain lithium nitrate-based composite ammonia carrier.

[0013] As a second aspect of the present invention, the application of lithium nitrate-based composite ammonia carrier as described in any one of the above claims as an absorbent in an absorption refrigeration system is also provided.

[0014] As a third aspect of the present invention, an absorption refrigeration system is also provided, using ammonia as a refrigerant, and comprising at least one absorption refrigeration unit, wherein the structure of the absorption refrigeration unit includes:

[0015] The generator contains a lithium nitrate-based composite ammonia carrier as described above. The lithium nitrate-based composite ammonia carrier absorbs refrigerant ammonia to form an ammonia-rich composite solution. The generator heats the ammonia-rich composite solution with an external heat source to release gaseous refrigerant ammonia and simultaneously convert it into an ammonia-lean composite solution. The released ammonia gas is then transported to the condenser.

[0016] The condenser has its inlet connected to the ammonia outlet of the generator via a pipeline. The condenser receives ammonia from the generator and condenses the ammonia into liquid ammonia inside it.

[0017] The throttling valve has its inlet connected to the liquid ammonia outlet of the condenser via a pipeline to throttle and reduce the pressure of the liquid ammonia;

[0018] The evaporator has its refrigerant inlet connected to the outlet of the expansion valve via a pipeline. The evaporator is also equipped with a refrigerant circulation pipeline that exchanges heat with the refrigerant. The evaporator causes the liquid ammonia after throttling to evaporate and absorb heat, thereby achieving refrigeration. The refrigerant circulation pipeline is isolated from the refrigerant ammonia and exchanges heat with the refrigerant ammonia through an indirect heat exchange method. This allows the refrigerant to reduce its temperature after absorbing the latent heat of vaporization and then be delivered to the refrigeration user to provide cooling capacity.

[0019] The absorber has its ammonia inlet connected to the refrigerant outlet of the evaporator via a pipeline, and its solution outlet connected to the solution inlet of the generator via a pipeline with a solution pump. The absorber is used to receive ammonia from the evaporator and redissolve the ammonia in the ammonia complex lean solution output from the generator to generate ammonia complex rich solution again. The ammonia complex rich solution flows back to the generator to form a working fluid circulation loop.

[0020] The cooling water system includes a cooling water supply pipeline and a cooling water return pipeline. The cooling water supply pipeline is connected to the cooling water inlets of the condenser and the absorber, respectively, to provide cooling medium for both. The cooling water return pipeline is led out from the cooling water outlets of the condenser and the absorber and forms a closed loop to remove the condensation heat released by the liquefaction of ammonia in the condenser and the absorption heat generated by the dissolution of ammonia in the absorber from the system.

[0021] As a further optimization of the present invention, a GAX heat exchanger is connected between the generator and the absorber via a pipeline for heat exchange between the ammonia complex lean solution from the generator and the ammonia complex rich solution from the absorber, thereby heating the ammonia complex rich solution.

[0022] As a further optimization of the present invention, a GVX heat exchanger is also provided between the evaporator and the condenser for heat exchange between liquid ammonia from the condenser and gaseous ammonia from the evaporator, thereby reducing the temperature of the liquid ammonia.

[0023] As a third aspect of the present invention, a refrigeration method utilizing an absorption refrigeration system as described in any one of the above claims is also provided, comprising the following steps:

[0024] S1, Occurrence Process

[0025] Industrial waste heat is used to heat the ammonia complex rich solution delivered from the absorber in the generator, causing the ammonia to evaporate into high-temperature ammonia vapor and obtain an ammonia complex lean solution. The high-temperature ammonia vapor enters the condenser, and the ammonia complex lean solution is returned to the absorber. The temperature range of the high-temperature ammonia vapor is 100~130℃.

[0026] S2, Condensation process

[0027] In the condenser, high-temperature ammonia vapor is cooled by circulating cooling water and condensed into saturated liquid ammonia. The liquid ammonia is then throttled and depressurized to the evaporation pressure by a throttling valve before entering the evaporator.

[0028] S3, Evaporation process

[0029] After depressurization, the liquid ammonia absorbs heat from the cooling medium in the evaporator to achieve a cooling effect. The liquid ammonia vaporizes into low-temperature, low-pressure ammonia vapor and is sent to the absorber. The temperature range of the low-temperature, low-pressure ammonia vapor is -60~5℃, and the pressure value is 0.0227Mpa(a)~0.52Mpa(a).

[0030] S4, Absorption Process

[0031] In the absorber, low-temperature, low-pressure ammonia vapor is absorbed by the ammonia complex lean solution returning from the generator, reforming the ammonia complex rich solution. The absorption process is exothermic, and the heat is carried away by cooling water to maintain the absorption efficiency. The regenerated ammonia complex rich solution is sent back to the generator to complete the cycle.

[0032] As a further optimization of the present invention, in S1, the industrial waste heat is the waste heat steam discharged from the back-pressure generator set of the thermal power plant, with a temperature of 100~150℃. The waste heat steam re-enters the boiler after passing through the generator and is recycled.

[0033] As a further optimization of the present invention, in step S4, the regenerated ammonia complex rich solution is pressurized by a solution pump and then enters the GAX heat exchanger to exchange heat with the ammonia complex lean solution and recover heat.

[0034] As a further optimization of the present invention, when two or more absorption refrigeration units are used in a stacked manner, the evaporator of the previous unit is used to cool the condenser of the next unit, thereby reducing the condensation temperature of the condenser of the next unit, reducing the condensation pressure and thus reducing the evaporation pressure, and causing the evaporation temperature to drop.

[0035] The beneficial effects of this invention are as follows:

[0036] (1) This invention provides a lithium nitrate-based composite ammonia carrier through the research and design of absorbent components. The components include lithium nitrate, liquid ammonia, lithium bromide, crown ether 12-Crown-4, and sodium lactate. By adding lithium bromide, the activation of nucleation sites is promoted, forming smaller and more regular bubble clusters with a higher detachment frequency. This can reduce the desorption temperature of traditional lithium nitrate ammonia solution by 5-10℃ without affecting the absorption performance of the absorption process, significantly improving the overall system efficiency. Through the analysis of crown ether-metal ion complexation kinetics and its influence mechanism on the heat and mass transfer process, the addition of crown ether 12-Crown-4 can form a LiNO3-Crown ether eutectic mixture. The crown ether cavity size has a very high matching degree with the Li+ ion radius. 12-Crown-4 has a high degree of influence on Li+ ion radius. + Selectivity coefficient > 10 4It can form stable inclusion complexes. Adding 0.3-0.6 parts by mass of 12-Crown-4 can increase solubility by 27% and decrease eutectic temperature by 21.9℃. Adding sodium lactate, through electrostatic interactions, hydrogen bonds, or van der Waals forces, adsorbs onto the crystal surface, increasing the surface energy barrier for nucleation, thereby preventing the orderly arrangement and growth of solute molecules on the crystal surface, inhibiting crystal growth by blocking kinking nucleation, and achieving the purpose of preventing solution crystallization. Simultaneously, it can improve the thermodynamic properties of the working fluid, reduce viscosity, increase thermal conductivity, and improve the overall performance of the system. Adding 5-10 parts by mass of sodium lactate to the solution increases the system's COP from 0.45 to 0.57 under standard operating conditions, while simultaneously reducing the boiling temperature required for desorption from 383.65K to 368.15K.

[0037] (2) The lithium nitrate-based composite ammonia carrier is used as an absorbent in the absorption refrigeration system. Through the synergistic effect of multiple materials, the refrigeration performance is improved while the crystallization concentration of the refrigerant under working conditions is significantly reduced, thereby achieving a further reduction in refrigeration temperature (15~20 ℃). It can produce refrigeration as low as -40 ℃, expand the refrigeration temperature range, and improve the refrigeration efficiency of the system.

[0038] (3) The lithium nitrate-based composite ammonia carrier of the present invention does not contain ammonia water, thus avoiding the disadvantage of ammonia water refrigeration system requiring a distillation device, avoiding the influence of a certain reflux ratio of ammonia water system on refrigeration performance, and overcoming the disadvantage of water / lithium bromide system being unable to produce cold source below 0 ℃, thus greatly improving the safety and practicality of the system. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the refrigeration system based on lithium nitrate-based composite ammonia carrier provided by the present invention. Detailed Implementation

[0040] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0041] The purity of lithium nitrate is 99.8%; the purity of liquid ammonia NH3 is 99.95%; the purity of lithium bromide is 99.5%; the purity of crown ether 12-Crown-4 is 99.8%; and the purity of sodium lactate CH3-CH(OH)COONa is 99.0%.

[0042] Unless otherwise specified, all reagents and materials used in the following examples are commercially available products. Unless otherwise specified, all methods used are conventional methods known to those skilled in the art.

[0043] Example 1

[0044] This embodiment provides a formulation for a lithium nitrate-based composite ammonia carrier, comprising the following components in parts by weight: 48.5 parts lithium nitrate, 31 parts liquid ammonia, 12 parts lithium bromide, 0.5 parts crown ether 12-Crown-4, and 8 parts sodium lactate.

[0045] The preparation method of lithium nitrate-based composite ammonia carrier includes the following steps:

[0046] (1) Prepare lithium nitrate and ammonia NH3 with a mass ratio of 48.5:31. Add lithium nitrate to a completely dry mixing tank A, seal and evacuate, then draw liquid ammonia NH3 from the bottom of the tank. Cool the tank by circulating water in the jacket and control the pressure inside the tank to not exceed 0.8 MPa. After the liquid level gauge reading of the mixing tank reaches 30%, turn on the agitator and stir for 3 hours to form solution A.

[0047] (2) Mix lithium bromide, crown ether 12-Crown-4 and sodium lactate in a mass ratio of 12:0.5:8, stir at 28 °C for 50 minutes to form solution B, and evacuate the mixing vessel B for later use;

[0048] (3) Connect the bottom of the mixing tank A to the bottom of the mixing tank B through a connecting pipe, open the connecting valve to slowly draw solution A into solution B, stir at 28 °C for 1 hour to form a uniform solution, filter the obtained solution to remove solvent impurities, and obtain lithium nitrate-based composite ammonia carrier.

[0049] Example 2

[0050] This embodiment provides a formulation for a lithium nitrate-based composite ammonia carrier, comprising the following components in the following mass ratio: 40 parts lithium nitrate, 30 parts liquid ammonia, 10 parts lithium bromide, 0.3 parts crown ether 12-Crown-4, and 5 parts sodium lactate.

[0051] The preparation method of lithium nitrate-based composite ammonia support includes the following steps:

[0052] (1) Prepare lithium nitrate and ammonia NH3 with a mass ratio of 40:30. Add lithium nitrate to a completely dry mixing tank A, seal and evacuate, and then draw liquid ammonia NH3 from the bottom of the tank. Cool the mixing tank with circulating water in the inner sleeve and control the pressure inside the tank to not exceed 0.8 MPa. After the liquid level gauge reading of the mixing tank reaches 30%, turn on the stirrer and stir for 2 hours to form solution A.

[0053] (2) Lithium bromide, crown ether 12-Crown-4 and sodium lactate were mixed in a mass ratio of 10:0.3:5 and added to a completely dry mixing tank B. The mixture was stirred at 20 °C for 60 minutes to form solution B. The mixing tank B was then evacuated for later use.

[0054] (3) Connect the bottom of the mixing tank A to the bottom of the mixing tank B through a connecting pipe, open the connecting valve to slowly draw solution A into solution B, and stir at 20 °C for 60 minutes to form a uniform solution. Filter the obtained solution to remove solvent impurities and obtain lithium nitrate-based composite ammonia carrier.

[0055] Example 3

[0056] This embodiment provides a formulation for a lithium nitrate-based composite ammonia carrier, comprising the following components by mass percentage: 50 parts lithium nitrate, 40 parts liquid ammonia, 15 parts lithium bromide, 0.6 parts crown ether 12-Crown-4, and 10 parts sodium lactate.

[0057] The preparation method of lithium nitrate-based composite ammonia support includes the following steps:

[0058] (1) Prepare lithium nitrate and ammonia NH3 with a mass ratio of 50:40. Add lithium nitrate to a completely dry mixing tank A. After sealing and evacuating, draw liquid ammonia NH3 from the bottom of the tank. Cool the mixing tank with circulating water in the jacket and control the pressure inside the tank to not exceed 0.8 MPa. After the liquid level gauge reading of the mixing tank reaches 30%, turn on the stirrer and stir for 4 hours to form solution A.

[0059] (2) According to the formula, lithium bromide, crown ether 12-Crown-4 and sodium lactate are mixed in a mass ratio of 15:0.6:10 and added to a completely dry mixing tank B. The mixture is stirred at 30 °C for 30 minutes to form solution B. The mixing tank B is then evacuated for later use.

[0060] (3) Connect the bottom of the mixing tank A to the bottom of the mixing tank B through a connecting pipe, open the connecting valve to slowly draw solution A into solution B, and stir at 30 °C for 30 minutes to form a uniform solution. Filter the obtained solution to remove solvent impurities and obtain lithium nitrate-based composite ammonia carrier.

[0061] To investigate the effects of different component compositions on the performance of lithium nitrate-based composite ammonia carriers, the following comparative examples were set up:

[0062] Comparative Example 1

[0063] The difference from Example 1 is that the lithium nitrate-based composite ammonia carrier provided in this comparative example does not contain lithium bromide.

[0064] Comparative Example 2

[0065] The difference from Example 1 is that the formulation of the lithium nitrate-based composite ammonia carrier provided in this comparative example does not contain crown ether 12-Crown-4.

[0066] Comparative Example 3

[0067] The difference from Example 1 is that sodium lactate was not added to the formulation of the lithium nitrate-based composite ammonia carrier provided in this comparative example.

[0068] Comparative Example 4

[0069] The difference from Example 1 is that the lithium nitrate-based composite ammonia carrier formulation provided in this comparative example does not contain lithium bromide, crown ether 12-Crown-4, or sodium lactate.

[0070] The lithium nitrate-based composite ammonia carriers obtained in Examples 1-3 and Comparative Examples 1-4 were tested in the following ways:

[0071] (1) Determination of ammonia solubility (%): The ambient temperature was 30℃. The same amount of each group of lithium nitrate-based composite ammonia carriers were placed in a sealed container, and ammonia gas was introduced to the equilibrium pressure (0.1 MPaG). The ammonia solubility was recorded.

[0072] (2) Crystallization of lithium nitrate-based composite ammonia carriers at different temperatures: The same amount of each group of lithium nitrate-based composite ammonia carriers were placed at 30℃ for 24 hours and the crystallization was observed; then the same amount of each group of lithium nitrate-based composite ammonia carriers were placed at 120℃ for 24 hours and the crystallization was observed. When observing the crystallization, three additional observation temperatures of -10℃, 0℃ and 15℃ were set.

[0073] (3) Corrosion resistance test: 21 carbon steel sheets were divided into 7 groups of 3 sheets each. They were placed in the same amount of lithium nitrate-based composite ammonia carrier for each group and subjected to 30 days at 120°C. The average weight loss of the 3 carbon steel sheets in each group was taken and the corrosion rate was calculated by the weight loss method. Similarly, 21 304 L stainless steel sheets and 21 316 L stainless steel sheets were subjected to the same experiment and the results were recorded. The corrosion rate was then calculated by the weight loss method.

[0074] The results of the above tests are summarized in Table 1.

[0075] Table 1 Performance test results of lithium nitrate-based composite ammonia carrier

[0076] ;

[0077] As shown in Table 1, the lithium nitrate-based composite ammonia carriers prepared in Examples 1-3 achieved a maximum ammonia solubility of 46% at 0.1 MPaG and 30°C, significantly higher than the comparative group. The lithium nitrate-based composite ammonia carriers prepared according to Examples 1-3 remained in a liquid state and did not crystallize when kept in the temperature range of -10°C to 120°C. The addition of lithium bromide promoted the activation of nucleation sites, forming smaller, more regularly shaped bubble clusters with a higher detachment frequency. This reduced the desorption temperature of traditional lithium nitrate ammonia solutions by 5-10°C without affecting the absorption performance, significantly improving the overall system efficiency. Analysis of the crown ether-metal ion complexation kinetics and its impact on heat and mass transfer revealed that the addition of crown ether 12-Crown-4 formed a LiNO3-Crown ether eutectic mixture. The crown ether cavity size and Li+ ion radius showed a very high degree of matching, and the selectivity coefficient of crown ether 12-Crown-4 for Li+ was >10. 4 It can form stable inclusion complexes. By adding 0.3-0.6 parts by mass of crown ether 12-Crown-4, the solubility can be increased by about 27%, and the eutectic temperature can be reduced by about 21.9℃. Adding sodium lactate, through electrostatic interactions, hydrogen bonds, or van der Waals forces, adsorbs onto the crystal surface, increasing the surface energy barrier for nucleation, thereby preventing the orderly arrangement and growth of solute molecules on the crystal surface, inhibiting crystal growth by blocking kinking nucleation, and achieving the purpose of preventing solution crystallization. Simultaneously, it can improve the thermodynamic properties of the working fluid, reduce viscosity, increase thermal conductivity, and improve the overall performance of the system. Adding 5-10 parts by mass of sodium lactate to the solution increases the COP of the refrigeration system under standard operating conditions from 0.45 to 0.57, while simultaneously reducing the boiling temperature required for desorption from 383.65K to 368.15K.

[0078] In addition, when the equipment and pipelines are made of conventional heat exchanger materials (carbon steel, stainless steel), this lithium nitrate-based composite ammonia carrier also has better corrosion resistance.

[0079] Example 4: Refrigeration system based on lithium nitrate composite ammonia carrier

[0080] This embodiment provides an absorption refrigeration system, using the absorption composite ammonia carrier provided in any one of embodiments 1-3 as the absorbent and ammonia as the refrigerant, including at least one absorption refrigeration unit. The structure of the absorption refrigeration unit includes a generator, a condenser, a throttling valve, an evaporator, an absorber, and a solution pump that are connected in sequence.

[0081] An absorption-type composite ammonia carrier is added to the generator, which absorbs refrigerant ammonia to form an ammonia-rich composite solution. The generator heats the ammonia-rich composite solution with an external heat source, causing it to release gaseous refrigerant ammonia and simultaneously convert it into an ammonia-lean composite solution. The ammonia outlet of the generator is connected to the inlet of the condenser to transport the released ammonia to the condenser. Furthermore, the external heat source is the waste heat steam discharged from the back-pressure generator set of the thermal power plant, with a temperature of 100-150℃. The waste heat steam re-enters the boiler after passing through the generator for recycling.

[0082] The liquid ammonia outlet of the condenser is connected to the inlet of the throttle valve via a pipeline to receive ammonia gas from the generator and condense the ammonia gas into liquid ammonia inside it;

[0083] The outlet of the throttling valve is connected to the refrigerant inlet of the evaporator, and is used to throttle and reduce the pressure of liquid ammonia;

[0084] The refrigerant outlet of the evaporator is connected to the ammonia inlet of the absorber to allow the throttled liquid ammonia to evaporate and absorb heat, thereby achieving refrigeration. Furthermore, the evaporator is also equipped with a refrigerant circulation pipeline, which is isolated from the refrigerant ammonia and exchanges heat with the refrigerant ammonia through a wall-type heat exchange method. This allows the refrigerant to reduce its temperature after absorbing the latent heat of vaporization and then be delivered to the refrigeration user to provide cooling capacity.

[0085] The low-temperature cold produced by the evaporator is used in urban centralized cooling, industrial and commercial ice making, indoor ice and snow venues and large low-temperature cold storage, etc., which can realize a comprehensive energy solution of cold, heat, electricity and ice, and greatly improve the comprehensive energy utilization efficiency of thermal power companies.

[0086] The absorber receives ammonia gas from the evaporator and redissolves it in the ammonia complex lean solution output from the generator to regenerate the ammonia complex rich solution. The solution outlet of the absorber is connected to the solution inlet of the generator, allowing the ammonia complex rich solution to flow back to the generator, forming a working fluid circulation loop.

[0087] The solution pump is used to deliver the ammonia complex rich solution from the absorber to the generator;

[0088] Furthermore, a GAX heat exchanger is installed between the generator and the absorber, where the ammonia complex lean solution from the generator and the ammonia complex rich solution from the absorber exchange heat in the GAX, and the ammonia complex rich solution is heated.

[0089] Furthermore, a GVX heat exchanger is installed between the evaporator and the condenser, where liquid ammonia from the condenser and gaseous ammonia from the evaporator exchange heat, thereby lowering the temperature of the liquid ammonia.

[0090] The refrigeration system also includes a cooling water system, which includes a cooling water supply pipeline and a cooling water return pipeline. The cooling water supply pipeline is connected to the cooling water inlets of the condenser and the absorber, respectively, to provide cooling medium for both. The cooling water return pipeline is led out from the cooling water outlets of the condenser and the absorber and forms a closed loop to remove the condensation heat released by the liquefaction of ammonia in the condenser and the absorption heat generated by the dissolution of ammonia in the absorber from the system.

[0091] Example 5

[0092] This embodiment provides a refrigeration method based on an absorption-type composite ammonia carrier refrigeration system, the flowchart of which is shown below. Figure 1 As shown, it includes the following steps:

[0093] Step S1, the process (desorption)

[0094] Industrial waste heat is used to heat the ammonia complex rich solution delivered from the absorber in the generator, so that most of the ammonia in it evaporates into high-temperature ammonia vapor. The ammonia vapor enters the condenser, and the remaining ammonia complex lean solution is returned to the absorber.

[0095] Step S2, Condensation process

[0096] In the condenser, high-temperature ammonia vapor is cooled by circulating cooling water and condensed into saturated liquid ammonia. The liquid ammonia is then depressurized to the evaporation pressure by a throttling valve and then enters the evaporator.

[0097] Step S3, Evaporation Process (Refrigeration)

[0098] After depressurization, the liquid ammonia absorbs heat from the cooling medium in the evaporator to achieve a cooling effect. The liquid ammonia vaporizes into low-temperature, low-pressure ammonia vapor, which is then sent into the absorber through the low-pressure ammonia pipeline.

[0099] Step S4, Absorption Process (Regeneration)

[0100] In the absorber, low-temperature ammonia vapor is absorbed by the ammonia complex lean solution returning from the generator, and a new ammonia complex rich solution is formed. The absorption process is exothermic, and the heat is carried away by cooling water to maintain the absorption efficiency. The regenerated rich solution is pressurized by a solution pump and enters the GAX heat exchanger to exchange heat with the high-temperature ammonia complex lean solution to recover the heat. It is then sent back to the generator to complete the cycle.

[0101] Example 6, Application Case

[0102] To verify the practical application effect of the refrigeration system provided in Example 4, the system has been put into use in some projects, and its application benefits are shown in Table 2. Analysis of the data in the table shows that the refrigeration system is adaptable to various heat source types and can match refrigeration needs of different scales, possessing broad compatibility in engineering application scenarios. Furthermore, in each application case, the refrigeration system has achieved significant natural resource conservation, effectively reducing coal resource consumption. The system also achieves substantial energy savings, significantly reducing electricity consumption and thus significantly reducing operating costs. In summary, the refrigeration system demonstrates good adaptability, resource conservation, and economy in different engineering scenarios, possessing high practical application value.

[0103] Table 2. Benefits of Refrigeration System Application

[0104] ;

[0105] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A lithium nitrate-based composite ammonia carrier, characterized in that, The lithium nitrate-based composite ammonia carrier comprises, by weight, 40-50 parts lithium nitrate, 30-40 parts liquid ammonia, 10-15 parts lithium bromide, 0.3-0.6 parts crown ether 12-Crown-4, and 5-10 parts sodium lactate.

2. The lithium nitrate-based composite ammonia carrier according to claim 1, characterized in that, The preparation method of the lithium nitrate-based composite ammonia carrier includes the following steps: (1) Add lithium nitrate to the mixing tank A according to the formula amount, seal and evacuate the tank, then draw liquid ammonia from the bottom of the tank, and circulate water to cool the tank A in the jacket. Control the pressure inside the tank to not exceed 0.8 MPa. After the liquid level gauge reading of the mixing tank A reaches 30%, start stirring for 2 to 4 hours to form solution A. (2) According to the formula, add lithium bromide, crown ether 12-Crown-4 and sodium lactate to the mixing tank B and mix. Stir at 20-30 °C for 30-60 minutes to form solution B. Vacuum the mixing tank B and set it aside for later use. (3) Connect the bottom of the mixing tank A to the bottom of the mixing tank B, slowly draw solution A into solution B, and stir at 20~30℃ for 30~60 minutes to form a uniform solution. Filter to remove solvent impurities and obtain lithium nitrate-based composite ammonia carrier.

3. The application of the lithium nitrate-based composite ammonia carrier as described in any one of claims 1 to 2 as an absorbent in an absorption refrigeration system.

4. A refrigeration method for an absorption refrigeration system, characterized in that, The absorption refrigeration system uses ammonia as a refrigerant and includes at least one absorption refrigeration unit. The structure of the absorption refrigeration unit includes: The generator contains a lithium nitrate-based composite ammonia carrier as described in any one of claims 1 to 2. The condenser's inlet is connected to the ammonia outlet of the generator via a pipeline; The throttle valve has its inlet connected to the liquid ammonia outlet of the condenser via a pipeline; The evaporator has a refrigerant inlet connected to the outlet of the expansion valve via a pipeline, and the evaporator is also equipped with a refrigerant circulation pipeline for heat exchange with the refrigerant. The absorber has its ammonia inlet connected to the refrigerant outlet of the evaporator via a pipeline, and the solution outlet of the absorber is connected to the solution inlet of the generator via a pipeline equipped with a solution pump. And a cooling water system, including a cooling water supply pipeline and a cooling water return pipeline. The cooling water supply pipeline is connected to the cooling water inlet of the condenser and the absorber respectively, and the cooling water return pipeline is led out from the cooling water outlet of the condenser and the absorber and forms a closed loop. The refrigeration method of the absorption refrigeration system includes the following steps: S1, Occurrence Process Industrial waste heat is used to heat the ammonia complex rich solution delivered from the absorber in the generator, causing the ammonia to evaporate into high-temperature ammonia vapor and obtain an ammonia complex lean solution. The high-temperature ammonia vapor enters the condenser, and the ammonia complex lean solution is returned to the absorber. S2, Condensation process In the condenser, high-temperature ammonia vapor is cooled by circulating cooling water and condensed into saturated liquid ammonia. The liquid ammonia is then throttled and depressurized to the evaporation pressure by a throttling valve before entering the evaporator. S3, Evaporation process After depressurization, the liquid ammonia absorbs heat from the cooling medium in the evaporator to achieve a cooling effect. The liquid ammonia is then vaporized into low-temperature, low-pressure ammonia vapor and sent to the absorber. S4, Absorption Process In the absorber, low-temperature, low-pressure ammonia vapor is absorbed by the ammonia complex lean solution returning from the generator, reforming the ammonia complex rich solution. The absorption process is exothermic, and the heat is carried away by cooling water to maintain the absorption efficiency. The regenerated ammonia complex rich solution is sent back to the generator to complete the cycle.

5. The refrigeration method according to claim 4, characterized in that, A GAX heat exchanger is connected between the generator and the absorber via a pipeline for heat exchange between the ammonia complex lean solution from the generator and the ammonia complex rich solution from the absorber, thereby heating the ammonia complex rich solution.

6. The refrigeration method according to claim 4, characterized in that, A GVX heat exchanger is also provided between the evaporator and the condenser for heat exchange between liquid ammonia from the condenser and gaseous ammonia from the evaporator, thereby lowering the temperature of the liquid ammonia.

7. The refrigeration method according to claim 4, characterized in that, In S1, the industrial waste heat is the waste heat steam discharged from the back-pressure generator set of the thermal power plant, with a temperature of 100~150℃. The waste heat steam re-enters the boiler after passing through the generator and is recycled.

8. The refrigeration method according to claim 4, characterized in that, In step S4, the regenerated ammonia complex rich solution is pressurized by a solution pump and then enters the GAX heat exchanger to exchange heat with the ammonia complex lean solution and recover heat.

9. The refrigeration method according to claim 4, characterized in that, When two or more absorption refrigeration units are used in cascade, the evaporator of the previous unit is used to cool the condenser of the next unit, thereby reducing the condensing temperature of the condenser of the next unit, reducing the condensing pressure, and thus reducing the evaporating pressure, causing the evaporating temperature to drop.

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