Learn together* "Lithium Bromide Refrigeration Technology"

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Lithium bromide absorption refrigerator uses lithium bromide solution as the absorbent and water as the refrigerant. It uses water to evaporate and absorb heat under high vacuum to achieve the purpose of refrigeration. In order to make the refrigeration process continue continuously, the evaporated refrigerant water vapor is absorbed by the lithium bromide solution, and the solution becomes dilute. This process occurs in the absorber. Then, the solution is heated using heat energy to separate the water content, and the solution becomes thicker. This process is performed in the generator. The steam obtained in the generator is condensed into water in the condenser, and then sent to the evaporator for evaporation after throttling. This cycle achieves the purpose of continuous refrigeration. It can be seen that the lithium bromide absorption refrigerator is mainly composed of four parts: absorber, generator, condenser and evaporator. The dilute lithium bromide solution coming out of the absorber is boosted by the solution pump (i.e. the generator pump) and passes through the solution heat exchanger. After being heated by the high-temperature concentrated solution coming out of the generator and increasing its temperature, it enters the generator. In the generator, it is heated by the heat source steam in the heat transfer tube, and the temperature of the solution increases until it boils. The water in the solution gradually evaporates, and the solution concentration continues to increase. The heat source steam pressure of single-effect lithium bromide absorption refrigerator is generally 0.098MPa (gauge pressure). The refrigerant water vapor evaporated from the generator enters the condenser through the liquid baffle plate. The liquid baffle plate plays the role of vapor-liquid separation and prevents liquid droplets from entering the condenser with the steam. Cooling water is introduced into the heat transfer tube of the condenser, so the refrigerant water vapor outside the tube is cooled by the cooling water and condenses into water, which is refrigerant water. The refrigerant water accumulated in the lower part of the condenser flows into the evaporator after being throttled, because the pressure in the condenser is higher than the pressure in the evaporator. like: When the condenser temperature is 45°C, the condensation pressure is 9580Pa (71.9mmHg) ； When the evaporation temperature is 5°C, the evaporation pressure is 872Pa (6.45mmHg). The U-shaped tube acts as a liquid seal to prevent steam in the condenser from entering the evaporator directly. After the refrigerant water enters the evaporator, part of the refrigerant water vapor first flashes out due to the pressure drop. Because the evaporator is a spray heat exchanger, the amount of spray is many times greater than the amount of evaporation, so most of the refrigerant water is collected in the water pan of the evaporator. It is then boosted by the refrigerant water pump and sent to the spray pipe of the evaporator. It is sprayed to the outer surface of the tube cluster through the nozzle. After absorbing the heat of the refrigerant water flowing through the pipe, it evaporates into low-pressure refrigerant water vapor. Since the pressure inside the evaporator is low, low-temperature refrigerant water required for the production process or air conditioning system can be obtained to achieve the purpose of refrigeration. For example, when the evaporator pressure is 872Pa, the evaporation temperature of the refrigerant water is 5°C. At this time, the refrigerant water can be obtained at 7°C. The evaporated refrigerant vapor separates the mixed droplets through the liquid baffle and then enters the absorber. It is absorbed by the intermediate solution pumped from the absorber and evenly sprayed on the surface of the absorption tube cluster, and the solution becomes dilute again. The intermediate solution is obtained by mixing the concentrated solution after exothermic cooling from the solution heat exchanger and the dilute solution in the absorber capsule. In order to ensure the continuous progress of the absorption process, the heat released during the absorption process needs to be taken away in time by the cooling water in the heat transfer tube. The intermediate solution absorbs a certain amount of water vapor and becomes a dilute solution, which collects in the liquid sac at the bottom of the absorber and is then pumped to the generator by the generator, and the cycle continues. It can be seen from the above cycle working process that the absorption refrigerator and the compression refrigerator have the same principle of obtaining cold energy. They both use high-pressure liquid refrigerant to be throttled and decompressed by a throttle valve (or U-shaped pipe), and then evaporate under low pressure to obtain cold energy. They all have condensation, evaporation and throttling devices that play the same role. The main difference lies in the different methods used to convert low-pressure refrigerant vapor into high-pressure steam. Compression refrigerators are realized by driving the compressor through a prime mover, while absorption refrigerators are realized by equipment such as absorbers, solution pumps and generators. The dilute solution coming out of the absorber is cooler, and the cooler the dilute solution, the more heat is required in the generator. The temperature of the concentrated solution coming out of the generator is higher, and the higher the temperature of the concentrated solution, the more cooling water is required in the absorber. Therefore, a solution exchanger is set up to heat the dilute solution with a lower temperature from a concentrated solution with a higher temperature. This not only reduces the heating load of the generator, but also reduces the cooling load of the absorber. It can be said to kill two birds with one stone. In addition to the above two internal cycles of refrigerant water and lithium bromide solution, the lithium bromide absorption refrigerator also has three systems connected to the outside, which are: ①heat source system ； ②cooling water system ； ③Refrigerant water system. The heat source steam (or hot water) is passed into the generator and flows through the tube. The solution outside the heating tube is heated to boil and evaporate the refrigerant steam. The heat source steam releases the latent heat of vaporization and condenses into water and is discharged. Under normal circumstances, the condensate should be recovered and returned to the boiler for utilization. In the absorber, the solution absorbs the low-pressure refrigerant vapor from the evaporator, which is an exothermic process. In order to continue the absorption process, it needs to be continuously cooled. Cooling water is also required in the condenser to convert the high-pressure refrigerant vapor from the generator into refrigerant water. The cooling water first flows through the absorber, and then flows through the condenser. The cooling water leaving the condenser has a higher temperature. It is usually passed into the cooling water tower, and after cooling, it is pumped into the absorber for recycling. The refrigerant water from the user flows into the tube cluster of the evaporator. As the refrigerant water outside the tube evaporates and absorbs heat, the refrigerant water cools down. The purpose of the refrigerator is to obtain low-temperature (such as 7°C) refrigerant water, which is the "media" of cooling capacity. It is realized by using lithium bromide solution, that is, the two-media medium of water and lithium bromide. Due to the different boiling points and hygroscopicity, when the lithium bromide solution is heated, the water is evaporated, and the evaporated water flows into the evaporator and evaporates and absorbs heat. Then the steam is condensed and mixed with lithium bromide again to form a solution. During these processes, it is heated by the heat source, and then the end that needs to be cooled is cooled through evaporation. At the same time, the condensed heat is cooled through the outdoor cooling tower or sent to the indoor heating, etc. This is achieved. Cooling with heat is like an airport. If 1% of the energy of solar radiation is collected on a ground as large as an airport, then water is used as a medium for transportation, and the lithium bromide solution is heated to evaporate, thereby achieving refrigeration. This is refrigeration with heat. . At the same time, the only thing that the lithium bromide unit needs to operate is a pump. This pump pumps the lithium bromide solution to flow. It does not require high-pressure pumping like a compressor like an air conditioner. In fact, it is just an ordinary water pump, and it does not require high flow and pressure. In this way, the unit actually only needs to consume less than a few kilowatts of electricity (most of which is consumed by the cooling tower fan) to achieve cooling. The energy required for cooling is heat. As long as there is heat, it can be done by burning fire, geothermal heat or solar energy.