Environmental Engineering Reference
In-Depth Information
when functional, the compressor load will be proportional to the pressure added
to the fluid and the volume flow rate that it processes. Consequently, compressors
require a large amount of power in order to increase the pressure levels throughout
the network. This power is usually supplied by a gas turbine, conveniently taking
advantage of the fact that natural gas is the resource being transported, although
steam or electricity could also be utilised.
In the UK, natural gas DNOs state that power losses in local distribution zones
(LDZ) are approximately 2-3%, while their leakage rate is about 1% [185].
Within the gas industry,
compressors are generally categorised into three
groups [175]:
Jet compressors : Are commonly used in natural gas and oil wells where suction
and discharge pressures do not vary greatly over time.
Centrifugal compressors : Are used for 'radial flow' and thus are seen fre-
quently in distribution systems where the pressure differential is usually not very
high.
Reciprocating compressors : Are not so popular since their efficiencies are
generally lower than the centrifugal type due to the many moving parts that com-
pose them.
Aside from proper housing, some additional equipment at compressor stations
include: filters, water-cooling systems for engines, lubricating oil purifiers, safety
devices, standby generators, instrumentation and remote control devices.
Figure 4.5 depicts the basic construction and inner workings of a centrifugal
compressor, these units commonly have a mechanical efficiency in the range of 99%
although adiabatic efficiencies vary depending on the manufacturing type.
Diffuser
Volute
Seal
Impeller
Thrust
bearing
Barrel
Shaft
Journal
bearings
Figure 4.5
Compressor schematic diagram [175]
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