4 replies to this topic

[curious_cat]

Is it practical to use a barometric overflow leg for draining a slurry from a system under a vacuum? Anyone using / seen such a system? Any pitfalls / tips / guidance?

 

The slurry is pretty low conc. : approx. 5% to 10% hard, crystalline solids in water.  200 mm Hg abs pressure. More than 34 feet of elevation is available. 

 

In particular, how does one design the liquid seal so that it drains but doesn't clog up.

[Zauberberg]

See attached article - it provides excellent guidelines on vacuum piping: http://www.graham-mf...bVacuum/213.PDF

 

In addition to what you'll read in Graham's article, I'd recommend a higher-than-usual liquid level in the barometric receiver, to accommodate for solids coming with the slurry. You need to come up with a design that will ensure continuous removal of solids and prevent from solids buildup just below the dip leg. Perhaps a "/\"-shaped diffuser or a boot underneath the dip leg can prevent from these issues.

[curious_cat]

See attached article - it provides excellent guidelines on vacuum piping: http://www.graham-mf...bVacuum/213.PDF

 

In addition to what you'll read in Graham's article, I'd recommend a higher-than-usual liquid level in the barometric receiver, to accommodate for solids coming with the slurry. You need to come up with a design that will ensure continuous removal of solids and prevent from solids buildup just below the dip leg. Perhaps a "/\"-shaped diffuser or a boot underneath the dip leg can prevent from these issues.

 

@Zaurberg

 

Thanks! The article has some excellent guidelines. I will use them. 

 

The part that stumps me is the seal design. How do I prevent the solid buildup? Can you elaborate on that design? I'd want to keep things as simple as I can. The  total solids are approx. 250 kgs/ hr.so it isn't a large system. 

 

If it helps, the slurry is supposed to go to a Downstream Nutsche Filter. 

[breizh]

Hi ,

My experience with this kind of technology/material : seal leg large enough going to a Sump with a sufficient enough volume in case of solid deposit , regularly request operator to remove the solid which could block the foot of the seal . Periodically , during shut down , take out the solid from the sump , filtrate and wash it for reprocess if possible.

Not an easy task .

Good luck

Breizh

[Zauberberg]

As the slurry enters the receiver vessel through dip leg(s), agitation - and hence the forces which keep the solid particles suspended in liquid - are reduced to minimum. This will likely cause buildup of solids underneath the dip leg and inside the entire vessel. As Pierre suggested, you would need an effective way to remove solids.

 

I was proposing a deflector plate (essentially an L-shape) which would be oriented towards the dip leg and cause deflection of the slurry on both sides of the plate, thus keeping the particles from building up in the area which is directly underneath the dip leg. A shape of "/\" should have the angle of 90 degrees at least, to aid in distributing particles left and right from the dip leg as much as possible.

 

Another thing which helps is to design an internal piping ring around the vessel (on the inner side and close to the bottom of the receiver vessel) with small holes drilled at each 200-300mm along the ring. This provides an effective way for "online washing" by introducing jets of liquid which will agitate the slurry and help in moving particles downstream to the process/disposal. Make sure you have a compatible, relatively clean liquid which you can pump into the ring and eventually get it mixed with the slurry without intolerable consequences/contamination. If there is no such liquid, you can still have the system installed for offline washing with water during shutdowns.