Page 448 - Mechanical Engineers' Handbook (Volume 4)

5 Absorption Systems 437

Dirt and Liquid Carryover. Generally, the carryover of dirt and liquids can be controlled
more effectively by suction scrubbers than by costly compressor design features. Where this
is not possible, all anticipated operating conditions should be stated clearly so that suitable
materials and shaft seals can be provided.

Polymerization. Gases that tend to polymerize may require cooling to keep the gas temper-
ature low throughout compression. This can be handled by liquid injection or by providing
external cooling between stages of compression. Provision may be necessary for internal
cleaning with steam.
These factors are typical of those encountered in open-cycle gas compression. Each job
should be thoroughly reviewed to avoid unnecessary cost, and to obtain the simplest possible
compressor design for ease of operation and maintenance. Direct coordination between the
design engineer and manufacturer during final stages of system design is strongly recom-
mended.

5 ABSORPTION SYSTEMS
2
´
Ferdinand Carre patented the first absorption machine in 1859. He employed an ammonia/
water solution. His design was soon produced in France, England, and Germany. By 1876,
over 600 absorption systems had been sold in the United States. One of the primary uses
for these machines was in the production of ice. During the late 1800s and early 1900s,
different combinations of fluids were tested in absorption machines. These included such
diverse combinations as ammonia with copper sulfate, camphor and naphthol with SO , and
2
water with lithium chloride. The modern solution of lithium bromide and water was not used
industrially until 1940. 2
Absorption systems offer three distinct advantages over conventional vapor compression
refrigeration. First, they do not use CFC or HCFC refrigerants, which are harmful to the
environment. Second, absorption systems can utilize a variety of heat sources, including
natural gas, steam, solar-heated hot water, and waste heat from a turbine or industrial process.
If the source of energy is from waste heat, absorption systems may provide the lowest cost
alternative for providing chilled water or refrigeration applications. Third, absorption systems
do not require any mechanical compression of the refrigerant, which eliminates the need for
a lubricant in the refrigerant. Lubricants can decrease heat transfer in evaporators and con-
densers.
Two different absorption systems are currently in use. These include (1) a water–lithium
bromide system where water is the refrigerant and lithium bromide is the absorbent and (2)
a water–ammonia system where the ammonia is the refrigerant and the water is the absorbent.
Evaporator temperatures ranging from 60 to 10 C are achievable with absorption
systems. For water chilling service, absorption systems generally use water as the refrigerant
1
and lithium bromide as the absorbent solution. For process applications requiring chilled
fluid below 7 C, the ammonia–water pair is used with ammonia serving as the refrigerant.

5.1 Water–Lithium Bromide Absorption Chillers
Water–lithium bromide absorption machines can be classified by the method of heat input.
Indirect-fired chillers use steam or hot liquids as a heat source. Direct-fired chillers use the
heat from the firing of fossil fuels. Heat-recovery chillers use waste gases as the heat source.