Page 240 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 3 .26 Compressor Best Practices

Fig 3.26.5 A single parameter surge
protection system

The second system encountered has been surge alarm type This system consists of flow measurement and differential
systems. Again, the process designer assesses a particular system pressure measurement across the compressor, and results in
and determines that the possibility of surge is minimal. In ad- a surge control line that roughly parallels the actual surge line of
dition, the application, hopefully, is such that a shutdown can be the compressor. It allows operation across a wider range than the
achieved without significant revenue loss. Therefore, the surge single parameter system and, if properly sized, can adequately
system is simply an alarm or shutdown system that will stop protect the compressor.
compressor operation in the event of surge, thus protecting the The final system in the evolution of surge controls is the
machine. It should be mentioned, however, that a full assess- modern microprocessor system, which affords many options to
ment should be made to determine the cost impact of such fully protect the turbo-compressor against surge occurrences.
a shutdown, and the potential problems incurred on the start- These systems usually employ compressor inlet and discharge
up. A properly installed surge system can eliminate these un- temperature inputs in addition to flow and DP for each
necessary shutdowns.
Before leaving this subject, the need for a reliable of the surge
detection system should be mentioned. Frequently, these de-
tection systems are simply differential pressure switches.
Depending on the application, surge can be either very violent or
very light. However, in the case of low pressure applications or
low molecular weight applications the effect of surge (flow and
pressure pulsations) will be minimal and the sensitivity of the
surge sensor device must be investigated to ensure that such an
event is detected.
Figure 3.26.5 shows a single parameter surge protection
system. These systems have been employed extensively, and in
simple terms, consist of a flow measuring device and an anti-
surge valve. These systems can work if properly sized and in-
stalled. However, it must be understood that a one parameter
system will not be economical in that a rather large area of op-
eration as in the cases of suction throttle constant speed devices
and variable speed drives will not be allowed. The result will be
unnecessary re-circulation and a loss of product revenue. The
next system shown in Figure 3.26.6 is the standard, two
parameter, or biased system that has been employed almost
exclusively in the industry over the years. Fig 3.26.6 The standard two parameter or biased system

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