A lithium bromide absorption chiller incorporating zeolite membrane technology and a method of refrigeration

Abstract

The present application relates to the technical field of refrigerators, in particular to a lithium bromide absorption refrigerator combined with zeolite membrane technology and a refrigeration method, the refrigerant comprising an absorber, a membrane separation unit, a compression unit and an evaporator; the membrane separation unit is installed between the absorber and the compression unit, the feed side inlet of the membrane separation unit is connected with the dilute solution discharge port of the absorber, and the retentate side outlet is connected with the concentrated liquid inlet of the absorber; the permeation side outlet of the membrane separation unit is connected with the inlet of the compression unit, the liquefied water outlet of the compression unit is connected with the inlet of the evaporator, and the steam outlet of the evaporator is connected with the water vapor inlet of the absorber. The present application uses the normal temperature concentration technology of zeolite membrane, can omit the generator in the traditional lithium bromide absorption refrigerator, simultaneously reduces the heat exchange network, significantly improves the concentration efficiency of the lithium bromide refrigeration system, effectively reduces the energy consumption and the dependence on high temperature heat source, and reduces the traditional high temperature concentration.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refrigerators, in particular to a lithium bromide absorption refrigerator combined with zeolite membrane technology and a refrigeration method. BACKGROUND

[0002] As a common energy-saving refrigeration equipment, lithium bromide absorption refrigerator is widely used in industrial and commercial fields, and plays an important role in the scene of using waste heat or solar energy and other renewable energy sources. Lithium bromide absorption refrigeration technology uses water as refrigerant and lithium bromide solution as absorbent, and realizes refrigeration cycle and produces refrigeration effect through evaporation and absorption two key processes. Because it uses water as refrigerant, it avoids the damage of traditional refrigerant to the environment, so lithium bromide refrigeration technology is considered as an environmentally friendly refrigeration technology, which has great market application prospect.

[0003] Lithium bromide refrigerator contains four core components for heating lithium bromide dilute solution to release water vapor (refrigerant), condenser to condense water vapor into liquid water and release heat, evaporator to evaporate liquid water at low pressure to achieve refrigeration effect, and absorption to absorb lithium bromide concentrated solution produced by evaporator. First, the concentration of lithium bromide solution in lithium bromide refrigerator depends highly on high-temperature heat source, resulting in high energy consumption, especially in the case where suitable high-temperature heat source cannot be provided, the system efficiency will decrease significantly. If the temperature of the heat source is unstable, the solution may crystallize in the pipeline. Secondly, the high-temperature lithium bromide concentrated solution after evaporation needs to be cooled by heat exchange with low-temperature lithium bromide dilute solution from the absorber before entering the absorber, which makes the heat exchange network of the refrigerator complex. The above results in large size and complex structure of lithium bromide refrigerator, which also increases the risk of lithium bromide solution leakage and the maintenance cost of the device. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a lithium bromide absorption refrigerator combined with zeolite membrane technology and a refrigeration method. By introducing a zeolite membrane concentration unit in the system, low-temperature concentration of lithium bromide solution is realized, the dependence on high-temperature heat source is reduced, and the energy efficiency and stability of the system are improved.

[0005] To achieve the above purpose, the present application adopts the following technical solutions:

[0006] A lithium bromide absorption refrigerator combined with zeolite membrane technology, comprising an absorber, a membrane separation unit, a compression unit, and an evaporator; the membrane separation unit is installed between the absorber and the compression unit, the feed side inlet of the membrane separation unit is connected with the dilute solution discharge port of the absorber, and the retentate side outlet is connected with the concentrated solution inlet of the absorber; the permeate side outlet of the membrane separation unit is connected with the inlet of the compression unit, the liquefied water outlet of the compression unit is connected with the inlet of the evaporator, and the steam outlet of the evaporator is connected with the water vapor inlet of the absorber.

[0007] The lithium bromide aqueous solution is separated and concentrated by the membrane separation unit to produce lithium bromide concentrate and water vapor, and the lithium bromide concentrate enters the absorber.

[0008] The absorber is cooled by cooling water, the evaporator absorbs heat to change liquid water into steam, the water is cooled, the cooling water is circulated to cool the environment, and the refrigeration is completed.

[0009] Preferably, the zeolite membrane concentration of lithium bromide solution is realized by a pervaporation membrane process. The membrane separation unit comprises a membrane assembly and a vacuum pump, and the membrane is a zeolite membrane.

[0010] The membrane assembly comprises a shell and a zeolite membrane in the shell, the zeolite membrane divides the inner cavity of the shell into a retentate side and a permeate side, the permeate side is provided with a water vapor outlet, and the retentate side is provided with a lithium bromide concentrate outlet. The water vapor outlet is connected with the inlet of the compression unit through the vacuum pump.

[0011] The zeolite membrane concentration unit (membrane separation unit) can selectively permeate water molecules, realize efficient concentration of lithium bromide solution, reduce dependence on high-temperature heat sources, and improve system energy efficiency. The zeolite membrane of the zeolite membrane concentration unit can include various zeolite membrane materials, such as NaA type, FAU type, ZSM-5 type, SSZ-13 type, or other porous materials with selective water permeability.

[0012] Preferably, the zeolite membrane material is SSZ-13 and ZSM-5.

[0013] Further preferably, at the working temperature, the zeolite membrane satisfies water flux > 0.1 kg m -2 h -1 , lithium bromide rejection rate ≥ 90%.

[0014] Preferably, the membrane separation unit is composed of a primary zeolite membrane unit and a secondary zeolite membrane unit in series; wherein, at the working temperature, the primary zeolite membrane unit satisfies water flux > 0.5 kg m -2 h -1 , lithium bromide rejection rate ≥ 90%; the secondary zeolite membrane unit satisfies water flux > 5 kg m -2 h -1 , lithium bromide rejection rate ≥ 99.9%.

[0015] The application also provides a refrigeration method of a lithium bromide absorption refrigerator, comprising the following steps:

[0016] The liquefied water absorbs heat in the evaporator to cool the circulating cooling water, and at the same time, the liquefied water is vaporized into water vapor, which enters the absorber to be absorbed by the concentrated lithium bromide solution to generate a dilute lithium bromide solution; the membrane separation unit uses the selective permeation of the zeolite membrane to water molecules to concentrate the dilute lithium bromide solution in the absorber and return it to the absorber for circulation, and the separated water vapor enters the compression unit to liquefy the water vapor separated by the separation unit, and then the liquefied water is transported to the evaporator for re-evaporation to complete the refrigeration cycle.

[0017] Preferably, the working temperature of the absorber is 10-50℃, and the working temperature of the evaporator is 5-30℃.

[0018] The working temperature of the compression unit is 10-40℃.

[0019] The working temperature of the membrane separation unit is 10-50℃, the pressure on the feed side is normal pressure, and the pressure on the permeation side is 0-100kPa.

[0020] Due to the difference in water vapor partial pressure on both sides of the zeolite membrane, the water in the dilute lithium bromide solution selectively permeates through the membrane layer to concentrate the feed liquid, and the permeated water enters the compression unit in the form of water vapor.

[0021] Preferably, the concentration of the lithium bromide solution after concentration by the membrane separation unit is generally 60-65wt%, and the concentration of the dilute lithium bromide solution after dilution by the absorber is 50-55wt%.

[0022] The membrane separation unit can work under low temperature conditions and use the selective permeation of the zeolite membrane to water molecules to concentrate the dilute lithium bromide solution in the absorber and return it to the absorber for circulation. The selective water permeation performance of the zeolite membrane enables the unit to work efficiently under normal temperature or low temperature conditions, reducing the need for high-temperature heating.

[0023] The absorber is used to absorb the water vapor generated in the evaporator and react with the concentrated lithium bromide solution to generate a dilute solution. The dilute solution is transported by a pump to the zeolite membrane concentration unit for concentration. Through the separation effect of the zeolite membrane, the lithium bromide solution is concentrated and returned to the absorber, thereby maintaining the continuous circulation of the system.

[0024] The compression unit is used to liquefy the water vapor separated by the zeolite membrane concentration unit, and then the liquefied water is transported to the evaporator for re-evaporation, thereby completing the refrigeration cycle.

[0025] The use of the zeolite membrane concentration unit effectively reduces heat loss in the heat exchange process of the stream, while improving the energy utilization efficiency of the system. By reducing the dependence on high-temperature heat sources, a more energy-efficient refrigeration effect can be achieved.

[0026] Based on the optimized design of the zeolite membrane technology, the present application can realize the compact structure of the refrigerator, reduce the equipment volume and floor area, and is suitable for wide application in industrial and commercial occasions.

[0027] The zeolite membrane concentration unit of the present application not only can concentrate lithium bromide solution at room temperature, but also can work with low-grade heat sources, using low-temperature waste heat or other low-temperature heat sources to heat the solution, realizing medium and low temperature concentration, and reducing the demand for high-temperature heat sources.

[0028] Compared with the prior art, the present application has the following advantages:

[0029] 1. The present application uses zeolite membrane room temperature concentration technology, which can eliminate the generator in the traditional lithium bromide absorption refrigerator, while reducing the heat exchange network, significantly improving the concentration efficiency of the lithium bromide refrigeration system, effectively reducing the energy consumption and the dependence on high-temperature heat sources, reducing the problems of equipment corrosion and heat loss caused by traditional high-temperature concentration, and significantly improving the operation flexibility, economy, compactness and safety of the equipment.

[0030] 2. The refrigerator of the present application reduces the heat consumption of the generator and the heat exchange steps of the stream, which helps to reduce the overall energy consumption. The concentration unit can also be integrated with the existing system to reduce high-temperature components and pipelines, making the system structure more compact and suitable for small and modular design. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The figure is a schematic diagram of the refrigeration system of the lithium bromide absorption refrigerator of the present application.

[0032] Figure 2 The figure is a schematic diagram of the structure of the membrane separation unit.

[0033] Reference signs:

[0034] 1-absorber; 2-membrane separation unit; 3-compression unit; 4-evaporator; 5-zeolite membrane; 6-retentate side; 7-permeate side; 8-vacuum pump. DETAILED DESCRIPTION

[0035] The present application will be further described below in conjunction with the drawings and examples.

[0036] In this example, how to use zeolite membrane technology to concentrate lithium bromide solution at low temperature is introduced. In order to illustrate the effectiveness of the process, a typical dilute lithium bromide solution (initial mass concentration 56%) is used in the experiment, and zeolite membrane is used for separation and concentration.

[0037] Example 1

[0038] like Figure 1 As shown, a lithium bromide absorption chiller includes an absorber 1, a membrane separation unit 2, a compression unit 3, and an evaporator 4. The membrane separation unit 2 is installed between the absorber 1 and the compression unit 3. The feed inlet of the membrane separation unit 2 is connected to the dilute solution outlet of the absorber 1, and the osmosis outlet 6 is connected to the concentrated solution inlet of the absorber 1. The permeate outlet 7 of the membrane separation unit 2 is connected to the inlet of the compression unit 3, the liquefied water outlet of the compression unit 3 is connected to the inlet of the evaporator 4, and the vapor outlet of the evaporator 4 is connected to the water vapor inlet of the absorber 1. The compression unit 3 is a compressor. The membrane separation unit 2 includes a shell, a zeolite membrane 5 located inside the shell, and a vacuum pump 8 connected to the shell. The zeolite membrane 5 divides the inner cavity of the shell into a permeate side 7 and an osmosis side 6. The permeate side 7 has a water vapor outlet, and the osmosis side 6 has a concentrated lithium bromide solution outlet. The water vapor outlet is connected to the inlet of the compression unit 3 through the vacuum pump 8. The zeolite membrane material used in the zeolite membrane assembly is type ZSM-5.

[0039] The refrigeration process is as follows:

[0040] First, a 55wt% dilute lithium bromide solution is pumped from the absorber to the membrane separation unit. The initial temperature of the membrane separation unit is set to 40°C, with atmospheric pressure on the feed side and 1 kPa on the permeate side. After the dilute solution enters the membrane separation unit, the membrane exhibits excellent selective permeability to water molecules (water flux = 1 kg / m³). -2 (Lithium bromide rejection rate = 99.5%). Through pervaporation, water permeates and exits the membrane separation concentration unit as vapor, which is then pumped into the compression unit (compressor) via a vacuum pump. Lithium bromide is blocked, resulting in a higher concentration lithium bromide solution. After concentration, the solution reaches 60 wt%, with the temperature maintained at 30°C. The concentrated lithium bromide solution is then pumped back to the absorber. In the absorber, the concentrated lithium bromide solution absorbs water vapor, becoming a dilute lithium bromide solution with a concentration of 55 wt%. This solution is then circulated back into the membrane separation unit, where it is cooled by cooling water to a temperature of 30°C. Water vapor separated from the membrane separation unit (approximately 30°C) is pumped into the compressor and compressed into liquefied water, also at approximately 30°C. The liquefied water then enters the evaporator, absorbs heat, and evaporates into water vapor, which is then used to refrigerate the environment via circulating chilled water.

[0041] The results show that after adopting the membrane separation unit, the system's energy consumption is reduced by more than 25% compared with the traditional high-temperature regeneration method, and the concentration effect of the solution is significantly improved, with the final solution concentration reaching 60%.

[0042] The absorber and the membrane separation unit are designed in series. The dilute lithium bromide solution is concentrated directly at a lower temperature by the membrane separation unit, which can save the generator in the traditional device, reduce the weight and size of the device, and avoid the waste of energy caused by directly heating the dilute solution by a high-temperature heat source. In addition, the fluid heat exchange system between the absorber and the membrane separation unit can be omitted, further reducing energy consumption and saving equipment space. The results show that the energy utilization rate of the optimized system is more than 30% higher than that of the traditional lithium bromide refrigeration system. The reduction of high-temperature parts enhances the operation flexibility of the system, making it able to adapt to a wider range of environmental temperatures. At the same time, due to the reduction of the heat exchange step of the material flow, the system structure is more compact, reducing the risk of pipe wear and fluid leakage.

[0043] Example 2

[0044] A lithium bromide absorption refrigeration machine, different from example 1, in order to further improve the concentration efficiency of lithium bromide solution, the membrane separation unit provided in this embodiment adopts a two-stage zeolite membrane concentration process. The membrane separation unit used in the two-stage zeolite membrane concentration process is composed of a series connection of a first-stage zeolite membrane unit and a second-stage zeolite membrane unit. The lithium bromide solution from the absorber is connected to the feed side of the first-stage zeolite membrane unit. The retentate side of the first-stage zeolite membrane unit is connected to the feed side of the second-stage zeolite membrane unit. The retentate side of the second-stage zeolite membrane unit is connected to the absorber. The permeate sides of the first-stage zeolite membrane unit and the second-stage zeolite membrane unit are both connected to the inlet of a vacuum pump. The pump is connected to a compression unit after being pumped out. -2 h -1 The first-stage zeolite membrane sacrifices part of the rejection rate to obtain a higher permeation flux (water flux = 3 kg m -2 h -1 , lithium bromide rejection rate = 90%), which can effectively reduce the area of the membrane to save equipment cost. The feed of the second-stage zeolite membrane is the permeate side product of the first-stage zeolite membrane, in which the concentration of lithium bromide is greatly reduced. At this time, the activity of water is greatly increased, so the zeolite membrane can show high flux and high selectivity (water flux = 10 kg m

[0045] The two-stage zeolite membrane concentration device includes a first-stage zeolite membrane unit and a second-stage zeolite membrane unit, which are connected in series.

[0046] The dilute lithium bromide solution first enters the first-stage zeolite membrane unit, and the initial temperature is set to 35°C. The first-stage zeolite membrane is mainly responsible for increasing the concentration of the solution from 50% to 60%. Due to the large permeation flux of the first-stage membrane (3 kg m -2 h -1, lithium bromide rejection = 90%), the membrane area and energy consumption can be effectively reduced. Subsequently, the solution after the first stage of concentration is pumped to the second stage of zeolite membrane unit, with the operating temperature set at 50 °C and the solution concentration further increased to 65%. The flux and salt rejection of the second stage of membrane are higher (water flux = 10 kg m -2 h -1 , lithium bromide rejection = 99.9%), and the raw material to be treated is greatly reduced, which can achieve efficient separation of water molecules at a higher temperature. The high-concentration lithium bromide solution after two-stage concentration is returned to the absorber, and the concentration of the solution can reach 65% required for regeneration. Compared with single-stage zeolite membrane concentration, the energy efficiency of the multi-stage zeolite membrane concentration system is increased by more than 15%. Although the initial investment of the multi-stage membrane system is large, the energy cost saved in the long-term operation is significant.

Claims

1. A lithium bromide absorption chiller incorporating zeolite membrane technology, characterized in that, It includes an absorber, a membrane separation unit, a compression unit, and an evaporator; the membrane separation unit is installed between the absorber and the compression unit, the feed inlet of the membrane separation unit is connected to the dilute solution outlet of the absorber, and the osmosis outlet is connected to the concentrate inlet of the absorber; the permeate outlet of the membrane separation unit is connected to the inlet of the compression unit, the liquefied water outlet of the compression unit is connected to the inlet of the evaporator, and the steam outlet of the evaporator is connected to the water vapor inlet of the absorber; The membrane separation unit includes a membrane module and a vacuum pump, and the membrane is a zeolite membrane. The membrane assembly includes a housing and a zeolite membrane inside the housing. The zeolite membrane divides the inner cavity of the housing into two parts: a osmotic side and a permeation side. The permeation side is provided with a water vapor outlet, and the osmotic side is provided with a concentrated lithium bromide solution outlet. The water vapor outlet is connected to the inlet of the compression unit via a vacuum pump. The membrane separation unit consists of a primary zeolite membrane unit and a secondary zeolite membrane unit connected in series; wherein, the water flux of the primary zeolite membrane unit is >0.5 kg m³. -2 h -1 Lithium bromide rejection rate ≥90%; water flux of the secondary zeolite membrane unit >5 kg m³ -2 h -1 Lithium bromide rejection rate ≥99.9%.

2. The lithium bromide absorption chiller combining zeolite membrane technology according to claim 1, characterized in that, The zeolite membrane material is selected from NaA type, FAU type, ZSM-5 type or SSZ-13 type.

3. A refrigeration method based on a lithium bromide absorption chiller incorporating zeolite membrane technology as described in any one of claims 1-2, characterized in that, Includes the following steps: Liquefied water absorbs heat in the evaporator to cool the circulating cooling water, achieving refrigeration. At the same time, the liquefied water vaporizes into water vapor, which enters the absorber and is absorbed by the concentrated lithium bromide solution to generate a dilute lithium bromide solution. The membrane separation unit utilizes the selective permeation of water molecules through a zeolite membrane to concentrate the dilute lithium bromide solution in the absorber and return it to the absorber for circulation. The separated water vapor enters the compression unit for liquefaction, and then the liquefied water is sent to the evaporator for further evaporation, completing the refrigeration cycle.

4. The refrigeration method according to claim 3, characterized in that, The absorber operates at a temperature of 10-50℃, the evaporator at a temperature of 5-30℃, and the compression unit at a temperature of 10-40℃.

5. The refrigeration method according to claim 3, characterized in that, The membrane separation unit operates at a temperature of 10~50℃, with atmospheric pressure on the feed side and 0-100kPa pressure on the permeate side.

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