Condenser
The refrigerant vapors leaving the generator condense in the condenser section into liquid
refrigerant, using cooling (condenser) water. The liquid refrigerant water is then distributed first in
the lower evaporator section.
Crystallization
All absorption chillers that use LiBr and water as the solution/refrigerant pair are subject to
crystallization. This is due to the fact that some areas of the unit operate with solution liquid
concentration levels that are only possible at higher than the normal ambient temperature
surrounding the unit. For example, the solution concentration in the generator of a single stage
absorption unit is usually 64.3% LiBr by weight. LiBr solutions begin to crystallize at 110°F.
Crystallization happens when the LiBr solution temperature drops too low or the concentration is
too high. The LiBr solution becomes like slush. At this point the LiBr solution can not absorb any
more water and starts to solidify (crystallize).
Crystallization occurs in the solution heat exchanger. In addition, it happens in the generator. It
also happens in pipes that are not well insulated and are located in rooms where the temperature
can affect the solution moving through the pipes.
To prevent crystallization, make sure that the solution temperature is high and the concentration at
the optimum percentage is less than 64%.
Because the solution temperature in the generator is normally high enough, no crystallization
occurs as long as the higher temperature is maintained. Before the unit is shut down, make sure
the solution is sufficiently diluted in all areas of the unit to prevent crystallization during the off
cycle. Remember, the solution temperature eventually becomes equal to the ambient temperature
of the room.
To prevent crystallization, all units employ a dilution cycle. As long as the unit is able to dilute itself
during an orderly shutdown sequence, the unit is able to sit idle at fairly low plant room ambient
temperatures without any potential of crystallization. Usually, after a dilution cycle, the average
solution concentration in the chiller is lower than 45% LiBr by weight. Although the crystallization
line on Figure 74 does not extend that far, you can see that the solution at 45% concentration does
not have a tendency to crystallize at normal ambient temperatures.
YHAU-C Single Effect Steam-Fired Absorption Chiller18
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