1 reply to this topic

[fseipel]

I'm working for a crankcase oil rerefinery & we have two rotary lobe roots blowers in series, followed by a liquid ring vacuum pump with oil as its seal fluid.  The boosters have proved rather unreliable.  Every time they shut down, it's hard to get them re-started, and NOT just in the wintertime.  We often have to dump solvent down the throat to restart them & they need rebuilt often.  In the winter, they're impossible to start without steaming them. Rebuilds are frequent.  The vacuum system pulls on wiped film evaporators that serve to separate LVGO, HVGO, and HVGO residual. We're using Tuthill KMBD's and KLRC LRVP. 

 

That said, I'm wondering if this design has merit:

 

1.) Inject overhead distillate from first WFE continuously into the throat of the first booster to keep the rotors clean.  It's a 12"x12" booster.  I'd inject at, say, 1/4 or 1/2 GPM.

2.) Allow overhead distillate oil to flow through second booster & go through liquid ring pump as well.  It would end up in seal fluid tank.

3.) Continuously withdrawl from seal fluid tank bottom to maintain level (at 1/4 or 1/2 GPM) using level controller.  This would purge the heavy entrained asphalt from the system.  It would go back to the wiped film evaporator feed but wouldn't accumulate, since the vast majority of it, exits with the WFE bottoms.  Seems to me this would keep the blower lobes cleaner & lubricated & help cool the process gases?

 

I'm also wondering if anyone has had success in such applications using a rotary piston style vacuum pump; I am wondering if I set up the vac pump for continuous feed/bleed of oil, it would stay clean.  The problem that arises is some of the heavy/tarry/asphaltene components come up from the last WFE in the train & contaminate the vacuum system.  There is currently NO entrainment separator.  I am thinking if I DO put in an entrainment separator, a spray chamber would be a good choice.  Currently oil is changed batch wise and there is a small knockout between first blower and second blower that must be manually drained.  The gas coming off LRVP looks like smoke.

Edited by fseipel, 30 March 2014 - 04:02 PM.

[PingPong]

I don't have experience with this kind of system, so I base my comments on my general process design experience.

 

You intend in future to use continuous injection of liquid into the roots blowers. Did you check with the vendor whether that will not harm the blowers in the long run?

 

What kind of liquid is presently used as seal fluid in the liquid ring vacuum pump?

 

There is currently NO entrainment separator.

I would assume that each WFE has a condensor with a downstream collecting vessel (separator) for the distillate.

 

Do you have a P&ID of the whole system of WFE's and vacuum pumps?

Edited by PingPong, 31 March 2014 - 06:36 AM.