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THE BASIC CYCLE
1. Refrigerant
vapor from the evaporator, instead of going to compressor, goes to an
absorber, where it is dissolved with lean ammonia-water at low pressure.
2. The
rich ammonia-water mixture is pumped to high pressure. As the volume
handled is much lower, the pump consumes only a fraction of the
compressor power.
3. To
separate the binary mixture, now at high pressure, it is heated with
steam (or other heating media). Ammonia gas separates from the mixture.
4. Ammonia
gas is purified in a rectification column. The lean mixture left behind
is cooled through solution exchangers, and returned to the absorber to
dissolve more ammonia.
5. Purified
ammonia vapor goes to the condenser where it is cooled to liquid, and
returned to the evaporator to close the refrigeration cycle.
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Industrial compression
refrigerators consume substantial electric power to
compress
the large volume of refrigerant vapor.
In ammonia absorption
refrigeration, the vapor is
dissolved
in water, and
pumped
to high pressure. The following sequence summarizes the operation
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EFFICIENCY IMPROVEMENTS
Modern day Ammonia
Absorption Refrigeration units squeeze out the maximum refrigeration for
every unit of energy used. The main additions to the basic cycle are:
· Partial stripping of incoming
rich solution using the hot, lean solution leaving the stripper. This
reduces the overall steam consumption by using heat in the outgoing
solution itself to pre-heat and strip vapor from the rich solution.
· Hot gas from stripper
exchanges heat to rich solution, substantially reducing the load on the
reflux condenser and rectifier.
· Absorber GAX allows cold,
rich solution from the pump discharge to pick up the heat from the heat
of absorption generated by the dissolution of ammonia in lean solution.
This allows partial recovery of the heat that would be otherwise lost to
cooling water. |
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Other innovations
include two effect systems for using very low grade heat, and the half
cycle, where the efficiency is improved by absorbing more ammonia into
the same amount of solution. However, this needs two separate
evaporation pressures as shown here.
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