5 replies to this topic

[sheiko]

Hello everyone

I was wondering if there is any standard or recommended practice regarding typical alarms and trips to be implemented around centrifugal pumps?

The reason is: in the refinery I am working in, I see plenty of alarms and trips that I don't see the purpose.

For exemple, on pumps (canned motor pumps coming with their own winding TSHH) discharging LPG from debutanisers (gasoline HDT and catalytic reformer) to deethaniser, we can see:

ALARMS:
- PDAH on suction filters (OK)
- PAL on suction (OK)
- TAH on suction (redundant with PAL on suction?)
- FAL in discharge (OK)
- PAL on discharge (why?)

TRIPS:
- LSLL on suction drums (OK)
- PSLL on suction (OK)
- TSHH on suction (redundant with PSLL?)
- PSLL on discharge (why?)
- FSHH on discharge (redundant with PSLL on discharge? but maybe a better option?)

On other pumps, I have also seen PDAL and PDSLL (between pump suction flange and suction drum) to trip the pump on low NPSHA (similar to PSLL on suction)...

So could you please let me know your thoughts on that (I have indicated my comments next to the above items)?

I do understand that alarms and trips are selected on a case by case basis, but maybe there is a minimum set to implement, but I don't know where to find this information.

Thanks

Edited by sheiko, 12 July 2017 - 12:06 AM.

[ankur2061]

Dear Sheiko,

 

You may not find standards related to centrifugal pump alarms and trips since each application may be unique. IMHO it is related to experience of individual operators based on application. As an example if I am collecting steam condensate from various units of the plant and then route it to a common condensate collection vessel before returning to Boiler unit I would provide any kind of analyzer (say VOC analyzer) in the common condensate facility. However, operators like Shell prefer to provide analyzers for each individual condensate collection facility. This I believe is a philosophy developed by them based on their own operating experience over the years.

 

Similarly many other operators have their own unique operational experiences and the alarm and trip instrumentation is based on such experience. However, I do know that many experienced plant operating personnel do feel that a lot of unnecessary alarms exist in the plant, and have more nuisance value then actual value, and hence sometimes suppress the alarms on the DCS or alarm annunciator, for ease of operations.

 

This is the reason that when you are conducting a HAZOP study of the plant at the final engineering phase, experienced plant operators must actively participate in HAZOP studies, to give a realistic picture of what kinds of alarms and trips are necessary, and what are unnecessary.

 

I hope this helps.

 

Regards,

Ankur.

[sheiko]

Sure this helps Ankur. Thanks.
But, in your opinion, do you see any situation when a TSHH on suction could be useful? (air-cooler failure on debutaniser reflux?)
Also, why put a PSLL on discharge? (in case of tube rupture? to limit the flowrate?)
I have participated in two HAZOPs in my refinery but there was no risk quantification (no safety matrix, frequencies values), so hard to know if such safety trips are really necessary...

Edited by sheiko, 12 July 2017 - 12:02 AM.

[ankur2061]

Dear Sheiko,

 

Haven't encountered a TSHH trip on pump suction. PSLL or source LALL yes, but not TSHH. Again PSLL on pump discharge is a rarity unless specifics related to the process application dictated it.

 

My experience of HAZOP study sessions is that many times there is very little participation of experienced plant operating personnel and very junior operations engineers are sent to participate, where they come up with theoretical possibilities of HAZARDS and apply alarms and interlocks when practically there is no such need. The engineering design team (consultant) normally doesn't argue against additional alarms and interlocks when the plant operator insists for additional safeguards in terms of alarms and interlocks. The feeling is that after all it is the operators money, and if he is willing to spend for some extra safeguards, than why should we get into an argument.

 

Regards,

Ankur

[rdcrags]

My experience matches Ankur"s exactly. Well put.

[spchauhan12]

Dear All,

 

         I have observed during my one of the project in which Diketene Liquid is  being  circulated through Centrifugal Pump. Diketene

 

Liquid  is having low flash  point ( 33°C). To avoid any possible temperature rise leading liquid temperature above 33°C & thereby

 

 leading to fire /hazardous even, TSHH trip & with its sensor installed at Pump casing.

 

 

This is just to share my experience.

 

Regards,

 

SPC