Backflow protection for mercaptan injection into LPG header

[Razif]

Hi,

I wish to check if there was sufficient backflow protection in the mercaptan injection facilities to a LPG header. Diaphragm pumps are used for the service and each line has 2 dissimilar NRVs at present.

The reason I am reviewing this is that there was an incident where an operations staff observed the mercaptan storage vessel sweating.

I am somewhat pressured into putting in additional backflow protection, but I would like to run through an objective study to check if the above arrangement is already sufficient.

The header pressure is 6-8 barg and the storage vessels are under N2 blanket. I would appreciate some advice. Thanks.

RR

 

[EGT01]

Razif,

I wonder if you didn't answer your own question. If the incident that you refer to is unacceptable and you think it is related to backflow from the LPG header, then your existing backflow arrangement is not sufficient.

My suggestion is that you perform a hazard analysis of your operation to determine the level of backflow prevention needed. Unfortunately, I think this is something only you can do since we are not privleged with knowing all the details of your system to perform such analysis.

Something you should thoroughly investigate are the safety and/or operability concerns if LPG does backflow into the mercaptan injection facilities. Obviously, this is best done with the operations staff so that everyone's concerns can be discussed.

Good Luck.

 

[roker]

hello,

the diaphragm dosing pump can be considered also as a backflow protection, according to the pressure the LPG is at gas state so it can not cause cooling of the mercaptan.

do you have a temperature transmitter in the mercaptan vessel?

regards

 

[Razif]

Thanks for the responses.

The observation of a sweating mercaptan vessel came only once, and its hard to verify as it was observed in the wee morning hours of the night shift. Only one operator observed this and made the report.

Based on design guidelines that we have in house, having two dissimilar NRVs is suficient for backflow protection. Furthermore the diaphragm pump itself provides backflow protection as well.

I'm afraid there isn't a temperature tranmitter on the mercaptan vessel, only a TG. I have my doubts that it is regularly checked.


RR