Compressor protection

[vjr0512]

Hi

This is with regard to the shutdown signals of a four stage Reciprocating COmpressor for process Air service (disc pressure of 32 barg). The compressor is of API618 compliance...As per table 5 of API 618, there are four signals that calls for shutdown of the equipment.

All the four signals ( Vibration, Lube oil pressure, Inter stage Separator moisture /water level and inter-stage air temp). The first two are already connected to ESD system where as the Inter stage separator level and air temp are presently connected to DCS system to initiate trip when these two parameters go for HiHi. We also have pre-alarm Hi for the above two signals.

The clarification here is whether these two signals are also to be connected to the ESD as a part of Equipment protection? It is argued that DCS system is not reliable as ESD. How shall we approach this ? IPF study has been conducted and it allowed these two signals to get connected to the DCS system but Client does not agree to this ....

Thanks to guide .

 

[rotw]

I am not instrument specialist, so just my two cents on it:
You did not specify what is the voting philosophy for shutdown (2oo3 ?) - and is it same for all of the four signals ?
If clients want these trips to be initiated by ESD then why not just do it and kill the subject?
Don´t know which type / stage of engineering you are in (concept design, execution, upgrade or modification of existing system...)... If IPF study says DCS is okay (BTW : Did the client approve the IPF study?), going for ESD would be then a bit of an "over-kill", but if clients wants so - where is the problem?
Point here is we talk just two signals, so cost and effort seem minor (unless you would have a dozen of machines across plant that are to follow same philosophy...).

 

[zdas04]

It is a four stage unit, so there are 3 interstages, each with a temperature sensor and an interstage scrubber. All of the kills required by API 618 are quite independent from each other (e.g. a stuck third stage suction valve will give you a 3rd stage discharge high temp and an interstage trip without any vibration, with good lube oil pressure, and good temps in the other stages, should still shut the machine down. Whether you shut it down with the DCS or the ESD systems just depends on your process philosophy. All of the kills must be part of the safety systems and be subject to calibration and testing protocols.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist