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Ammonia Absorption : Comparisons
Ammonia
Absorption vs. Lithium Bromide vs. Compressor refrigeration
Electrical energy, and hence the operating cost of
compressors, is becoming expensive everyday. LiBr (Lithium Bromide) based
absorption units have an inherent temperature limitation of +7oC.
Wherever there is cheap heat energy available, Ammonia absorption refrigeration
will be the ideal choice. From the prevailing costs of steam and electricity,
economy and selection can be analyzed. The following table gives a quick, comparative check-list.
| |
Compression |
Ammonia Absorption |
Lithium Bromide |
| Electrical energy |
Runs fully on electrical power. Varies from
1KW/TR at 0oC
to 2KW/RT at -25oC |
Typically uses about 7%-10% of compressor electric energy for
pump. |
Typically uses about 5% of compressor electric energy for
pump. |
| Refrigerant used |
Varies with application. |
Ammonia, with water as absorbent. Environment
friendly, and low cost refrigerant. |
Water, with Lithium Bromide as absorbent. Absorbent
charging / disposal is expensive. |
| Temperature limitation |
Depends on refrigerant. |
Up to -33oC and lower. |
Only up to +7oC |
| Thermal energy required. |
None |
Low pressure steam, hot water or equivalent waste heat
sources. |
Low pressure steam (single stage units) and high pressure
steam (two stage units) |
| Thermal energy quantity (as steam) |
None |
Varies from about 9kg/TR (at 0oC operation) to
11kg/TR (-25oC operation) |
About 8kg/TR (single stage. About
5kg/TR (two stage)
for +7oC operation. |
| Installation. |
Indoor installations. |
Skid-mounted outdoor installations. No building
cost. |
Skid-mounted indoor / outdoor installation. |
| Remarks. |
Requires standby for critical service. Vulnerable to
fluctuations in cooling water temperature. Moving parts wear and
tear means low operating life. |
Low maintenance, industrial standard heat-exchangers as per
TEMA. Stand-by pump for reliability. Flexible operation.
Higher steam temperatures can offset cooling water temperature
fluctuation.
Operation is easily understood and picked up by ammonia compressor
operators.
Pungent, characteristic ammonia smell acts as a natural alarm in
event of leakage. |
Vulnerable to fluctuations in cooling water
temperature. Vacuum service leakages are difficult to
identify. Refrigerant may need to be changed if exposed to air
during maintenance.
Exotic material construction. Site repair and maintenance is
difficult. |
