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    Analysis and elimination of crystallization failure of lithium bromide absorption chiller

    TIME:2019/01/02 09:56:00 NUM:

            The lithium bromide absorption refrigeration unit is a refrigeration device in which water is used as a refrigerant and lithium bromide solution is used as an absorbent. During the operation of the bromine cooler, crystallization of the lithium bromide solution often occurs, resulting in a decrease in refrigeration capacity. Therefore, it is very important that the maintenance operator of the lithium bromide refrigerator can skillfully analyze the cause of the crystallization and its elimination.

            1 Lithium bromide solution concentration and crystallization temperature

            At a certain concentration, when the temperature is lower than a certain value, or the temperature is constant, when the concentration is higher than a certain value, the lithium bromide solution will cause crystallization. As can be seen from Table 1, the crystallization depends on the concentration and temperature of the solution, and the solution concentration is slightly increased, and the crystallization temperature is increased a lot. In order to prevent crystallization, the solution concentration is controlled to be below 65%.
            2 performance characteristics of solution crystallization

            There are three performance characteristics when the lithium bromide solution is crystallized during unit operation: first, the cooling effect of the unit is significantly reduced; second, the flow of the concentrated solution is blocked in the low temperature heat exchanger, the liquid level of the low pressure generator rises, and the automatic melting tube is hot; Third, the concentrated solution pipe entering the absorber becomes cool.

            3 analysis of several causes of crystallization

            3.1 cooling water temperature is too low

            When the temperature of the cooling water is too low, the heat exchange degree between the dilute solution and the concentrated solution at the inlet and outlet of the heat exchanger is too severe, so that the temperature of the concentrated solution is too low to crystallize.

            3.2 The circulation of the solution sent to the high pressure generator is too small, causing the concentration of the concentrated solution to increase continuously, resulting in crystallization of the solution.

            3.3 heat source medium parameters are too high

            The steam pressure of the steam unit is too high, so that the evaporation of the lithium bromide solution in the high pressure generator is too large, resulting in an increase in the concentration of the concentrated solution flowing to the heat exchanger. After the solution is cooled by the heat exchanger, the temperature of the lithium bromide solution falls below the crystallization temperature. , the solution crystallizes.

            3.4 The unit vacuum is not good

            The vacuum of the unit is not good, so that the capacity of the absorber to absorb the water vapor of the refrigerant is lowered, thereby causing the concentration of the outlet solution of the generator to be too high to crystallize.

            3.5 solution crystallization after parking

            The dilution cycle time during parking is too short, the solution of each part is not evenly mixed, or the ambient temperature around the unit is too low.

            4 crystallization exclusion

            4.1 Elimination of crystallization during operation

            The concentrated solution with a higher temperature after crystallization directly enters the absorber through the J-shaped tube to raise the temperature of the dilute solution. The dilute solution passes through the heat exchanger to dissolve the crystals [2]. The initial stage of crystallization is generally eliminated after about 15 minutes. However, when the crystallization is severe, it is excluded by the following method.

            (1) Stop the cooling tower fan, increase the cooling water temperature, and reduce the cooling water amount appropriately, so that the temperature of the dilute solution rises to about 60 °C.

            (2) Properly increase the circulation amount of the solution of the high pressure generator.

            (3) Reduce the steam pressure and reduce the evaporation of the coolant water in the high pressure generator.

            (4) Pump the vacuum pump until the vacuum pressure of the gas storage chamber shows ≤50Pa.

            (5) Open the refrigerant water bypass valve and pass the refrigerant water to the absorber to reduce the concentration of the solution. When the refrigerant pump begins to cavitation, it is considered that most of the refrigerant water has bypassed into the absorber, that is, the refrigerant water bypass valve is closed.

            (6) Stop the solution pump operation, wait for the high temperature solution to flow through the dilute solution tube, and then start the solution pump. When the solution is heated to the generator, the pump is stopped. By repeating this operation, the concentrated solution crystallized in the heat exchanger tube is heated and dissolved by the high temperature solution returned from the generator.

            In order to accelerate the crystallization rate, it can be used in combination with the following crystallization method, but it is necessary to pay attention to safety.

            (1) Fully heat the heat exchanger with a steam hose or a blowtorch.

            (2) When the internal crystallization of the solution pump cannot be operated, heat the pump casing and the connecting pipe together.

            4.2 Elimination of solution crystallization after shutdown

            (1) If the solution is crystallized in the solution pipe or in the dilute solution capsule, steam or other heat source may be used to heat the portion which may be crystallized while tapping with a wooden hammer until the crystallization is eliminated.

            (2) The solution is diluted with cold water to make it not crystallize under the environment.