15 replies to this topic

[shady othman]

Drying by hot nitrogen should be done after hydro-test for chillers of the refregerent system, but in my company using hot nitrogen is not available so, is it ok for using hot fuel gas instead of hot nitrogen for drying the chillers?

 

thanks

[fallah]

shady,

 

You can use hot air rather than hot nitrogen; but it can't allow the dew point to achieve up to very low temperature, say around -60 C,...

[Zauberberg]

The problem of using (dry) fuel gas is not in effectiveness of drying, but rather in disposing of wet gas.

 

A common drying procedure involves continuous sweeping of dry gas (N2) through predefined loops/sections of the plant, normally between two isolation points. During this process, convenient vent and drain connections are kept open, to enable elimination of liquid water and wet Nitrogen from the system. Now if you imagine hydrocarbon gas employed in this operation, you may end up with vapor clouds inside and outside of the facility. Depending on composition of the fuel gas, ignitable (and possibly toxic) vapor clouds may be formed and, if there are other operating areas around, this can create significant and perhaps intolerable hazard.

 

We don't know any details of your drying procedure, layout of the plant(s), fuel gas parameters, and details of the equipment/piping. It is virtually impossible to provide you with straight "yes" or "no" answer, except to point at the hazards mentioned above. As suggested by Fallah, I'd prefer using other medium (air) if it is available. A typical dew point of Instrument Air is more than low enough to provide complete drying.

[shady othman]

dear fallah & Zauberberg

 

first thanks for your reply,

for the point of draining or venting the drying gas, it will be directed to the flare so it will not make a hazard problem.

Also i thought about using fuel gas as a drying gas as it will be used for drying and oxygen freeing at the same time so it will reduce time.

According to the unit manual, drying is done by instrument air (as fallah says) and then displacement is done by normal fuel gas.

[Zauberberg]

If you have all the drain and vent connections piped to closed systems (closed drain and flare), you are ready to go.

[shady othman]

so you suggest that this is a good way for effeciency and saving time?

[Zauberberg]

I cannot make that final decision for you without seeing the procedure, equipment details, layout and connections, quality of fuel gas etc. What we discussed here are the requirements at a very basic level. If you analyze the system and see that everything will work as intended and no hazards will be created, then you are likely ready to proceed.

[fallah]

shady,

 

Why not to do as per unit manual, i.e. drying with hot instrument air and then replacing the air with fuel gas?

[shady othman]

thanks Zauberberg, fallah

 

dear fallah

 In the unit manual drying is done by normal temperature instrument air not hot instrument air, also fuel gas in my plant enters a drier first before using and it is easy to use it in hot situation.

I suggested that technique for saving time and to be sure that drying is done perfectly by the hot gas.

[fallah]

shady,

 

The dew point of the instrument air in your plant is certainly so low such that has adequate capability for drying out in normal temperature, then probably no need to be hot when drying operation getting started... 

[shady othman]

so it is better to do as manual

[fallah]

shady,

 

I think so, because unit manual has likely been written based on the relevant site conditions, available facilities and economical/safety standpoints...

[Bobby Strain]

Something doesn't seem right about purging air with fuel gas in a closed system. Sounds a bit hazardous to me. Is it your plant practice to purge air from equipment using fuel gas?

 

Bobby

[fallah]

Agreed with Bobby...in fact, if the drying gas (air) venting and subsequent fuel gas for purging is directed to flare sounds the condirions to be a bit hazardous...

[Zauberberg]

Purging of air is - according to Dave Simpson (MuleShoe Engineering, and one of the top contributors at Eng-Tips forums) - one of the most hazardous operations in oil and gas production. He had posted an excellent working manual on removing air from process equipment and piping which I am uploading in this thread.

 

For those who like extended reading on the subject, AGA has developed a document titled "Purging Principles and Practice" which is a legally binding document in the US and can be accessed here: https://law.resource...urging.2001.pdf

 

Attached Files

•  Purging Air from Piping and Vessels in Hydrocarbon Service.pdf   31.07KB   20 downloads

[shady othman]

thanks Zauberberg, thanks fallah for your valuable information.