Pumping Aromatic Hydrocarbons

[EmmanuelTop]

I am looking to find a reliable solution for pumping mixture of water and gas condensate that contains about 80% aromatic components (Benzene, Toluene, Ethylbenzene, Xylene). Suction temperature is 50 degC (~120 degF) and pressure is close to atmospheric. Discharge pressure variable - often close to atmospheric but sometimes up to 4 bar abs hence gravity flow is not an option. Capacity is about 1 m3/hr (4.4 GPM). The service in question is TEG regenerator overhead drum.

Due to possibility of running dry, the designer opted initially for peristaltic pump. However the pump rubber tubes were failing quite frequently due to incompatibility of tube material with Aromatics/BTEX, and after being replaced with Viton tubes they failed even faster (could anybody throw a hint why? - chemical resistance charts are saying something else). Viton tubes failed within just 48 hours.

Due to variable discharge pressure and possibility of running dry, centrifugal pump is not considered as an option. Someone came up with an idea to employ Eccentric Disc Pump (see e.g.

http://handpump.com/files/atk1101-029.pdf

but the concern here are O-rings. I guess we could use perfluoroelastomers but nobody can say for sure (especially after seeing Viton tubes fail so fast and they were supposed to have solid resistance to BTEX).

Fugitive emissions are not a concern here.

Anyone with hands-on experience with Benzene pumping?


Dejan IVANOVIC
Process Engineer, MSChE

 

[georgeverghese]

Does this pump vendor have an option for PTFE rather than Viton ?

Is there H2S in this TEG regen offgas stream ?

 

[micalbrch]

Go with a diaphragm pump with PTFE diaphragms, balls and seats. An air driven pump for that flow is really cheap and works well. If compressed air is not available or if you cannot accept the pressure depending flow, search for "electric diaphragm pump". They are of course more expensive because you buy the drive with the pump. In any case PTFE is what you should look for. The wetted parts (housing) can be made of stainless steel.

 

[EdStainless]

Often the reason for elastomer failure in aromatic is related to filler and curing agents more than the base resin. We used to by Aflas o-rings for high temp (500F) water service with oil present, the only ones that would work were from Seals Eastern.

For your app a PTFE diaphragm pump is the way to go.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

Traces of H2S laden water (??) in the BTEX stream being pumped may also partly be the reason for the failure of the previous Buna N and Viton stators in the progressive cavity pump.

 

[moltenmetal]

Agree that the diaphragm pump is likely the best solution. If designed correctly, the diaphragms can be faced with PTFE with a backing of a more flexible material and should give adequate service life. At only 4.4 gpm, it will be a very small pump so you won't be too concerned about the cost of air versus electricity despite the fact that the air diaphragm pump will waste a lot more electricity at your compressor than a direct-driven diaphragm pump would. But if you want a direct driven diaphragm pump, a Hydracell might be a good choice. They have PTFE diaphragms which apparently give adequate service life, which itself is a bit of a surprise.