Pump Selection: low flow, high head, and highly abrasive 6

[brs766]

I currently work with a 30% (wt) Alumina (Al2O3) slurry that has a relative hardness of 9 (mohs). This application is shear sensitive (and non-newtonian, shear thinning to be precise) and because of that we are using a DiscFlo pump. Unfortunately our system design leads to an unsustainable operating point for our DiscFlo pump.

The process conditions are as follows: 200-250 ft of head and 20-25 GPM. This produces an operating point on the far left hand side of the curve which causes a lot of internal re-circulation (greatly accelerating the wear mechanism). In fact, our pump discpack (DiscFlo equivalent to an impeller) lasts 2-3 months.

I am trying to determine what type of pump would be best for this application. I have some general ideas in mind (piston/ plunger pump, triplex piston pump - to eliminate dampening, and flexible membrane pumps - piston diaphragm). I am staying away from anything that isn't a positive displacement pump (because imparting velocity on shear sensitive fluid does not seem like the best route and the flow conditions provide a very challenging hurdle for a centrifugal pumps). I had considered using two Centrifugal or DiscFlo pumps in series but I figured that would cost a lot of money and give me two failure points.

The vendors I have reached out to are CAT Pumps, Hydra-Cell, and Abel. My question is, do you think these are the proper pumps for this application?

Please let me know if I left out any pertinent information, I will be looking forward to your responses.

Thank you so much!

Ben

 

[SteveWag]

Try;

http://www.moyno.com

and

http://www.netzschusa.com/

Both positive and low shear, metering flow and very high head.
Steve

 

[brs766]

SteveWag,

We have a lot of those on site and they tend to work well enough (3 month failure rates due to high back pressures and not enough stages) but for this particular application we have a very limited foot-print (15 to 25 sq. ft. or 3' x 4' / 4' x 5'). I am sorry I left that out.

Thank you,
Ben

 

[SteveWag]

Vertical mount? Use belt drives, alignment is a bitch.
Steve

 

[EdStainless]

What about the correct size of disc pump?

I like the idea of a Moyno. You can get rotors in Co based wear resistant alloys.

Regardless of the style of pump I would suggest Stellite internals, You will need them.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[brs766]

EdStainless,

The applications where we have correctly sized our DiscFlo pumps get 6-12 months of lifetime and are fairly pricey to replace (difference in lifetime result of acidic vs basic and solids content, currently reviewing MOC to eliminate metals that require passivation (sp) layers). We have kicked this idea around with DiscFlo but the proposal involves rebuilding the system to constantly re-circulate and by doing so purchasing a much larger pump. There are no DiscFlo pumps from their curve catalog that comfortably fit (middle of the curve) the initial system requirements (200-250 ft of head and 20-25 GPM). Now it becomes cost constraints coupled with size constraints and the dependence on a re-circulation line never plugging.

We have cycled through the wear resistant alloys with Moyno and Netzsch and have found that the urethane stator coupled with a high chrome rotor tend to work the best (stator lifetime cycle of 3 months). The next step to preventing wear with these pieces of equipment would be to add more stages (which goes against the size constraint I discussed with SteveWag).

Stellite actually goes pretty quickly in our erosive applications (centrifugal pumps surface fatigue 3-4 months lifetime) but tends to last better in our abrasive applications (prog. cavity stator life of a year) but all of these things depend heavily on the rotational speed and proper pump sizing (minimizing internal re-circulation for centrifugal and minimizing the pressure per stage for prog. cavity).

Thank you,
Ben

 

[Artisi]

Look at peristaltic pumps (hose pump) size might be a problem but nothing is impossible if you try hard enough.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[moltenmetal]

Your pressure isn't high enough and your flow is too high to recommend a hydraulic double diaphragm pump in my opinion. A Hydracell would be a fair compromise, assuming your temperature and chemistry permit the use of wear-resistant elastomers and very hard check valve parts.

If the fluid isn't too hot, an air double diaphragm pump is also worth considering, given your limited footprint. They're inefficient, and the check valves will wear out (as they will with an abrasive slurry in any true PD pump), and the flow will be heavily pulsile (good for keeping the stuff moving, but hard on the process and piping). You can put the real driver (the air compressor) somewhere else, which is a big benefit for your limited space. Be sure to pipe the air outlet to a noise-insensitive location, preferably on the roof- that works better than any discharge muffler. Be sure to get a couple pumps and choose a design with renewable/replaceable check valve seats and balls.

Pressure is likely too high for a peristaltic pump to give adequate service life.

A number of smaller DiscFlo pumps in series would give you more service life out of the impellers, assuming you could find more room to fit them in an arrangement with piping designed for decent wear life and plug resistance with slurries. Good slurry piping design requires some real estate.

In this kind of service, it's all experimentation. 2-3 months is already a pretty good service life!

 

[Artisi]

Moltenmetal, I not an expert in hose pumps but believe they are handle reasonable high pressure / abrasive solid. Worth the OP checking Bredel peristaltic pumps.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[brs766]

Artsi,

We have peristaltic hose pumps in a similar service (same fluid, same temperature, less pressure) and the hoses last 1 month at best (in fact they are on a monthly PM for change out - vendor recommended). I would expect them to last less time for this application because of the higher back pressure. To my understanding, a higher back pressure doesn't only cause issues related to the pressure but how that pressure is achieved - the interface between the motor and the hose (I guess it's the rotor) goes from a roller to a shoe. The shoe design is more detrimental to hose pump life than the roller.

moltenmetal,

Temperature will never exceed 200 F and typically runs at 100 F so I believe elastomers have not been ruled out. The chemistry is something I'll have to test for, I'd imagine I wouldn't want my elastomer to swell. Thanks for bringing up that point.

Do you have experience with a Hydracell? I am debating between that and another flexible membrane pump manufacturer (Abel). I think these are the right pumps for the application, I just have absolutely no experience with them.

Thank you both for the responses, in fact all of you have truly been quite the help.

Regards,
Ben

 

[micalbrch]

Forget CAT. They have piston and plunger pumps only. Good quality but the wrong pump type for alumina slurry with 30 % solids. The same applies (for me) to any progressive cavity pump due to the hardness of the particles, the pressure and the solids content. For peristaltics the pressure is probably too high. A piston diaphragm pump like Abel will work for sure (PTFE diaphragms if temperature is high and a pulsation dampener is standard) but is not cheap compared to a Hydracell pump. The Hydracells are pretty good but (over)sizing is important to avoid frequent wear.

 

[brs766]

micalbrch,

Thank you for the insight! Would you recommend any other type of pump for this application? Or do you think I've got it narrowed down to the most appropriate ones? I was looking into purchasing the largest Hydra-cell (I believe it is a 35 model) and running it at half capacity. The ABEL pump looks like it would solve my issues but does seem a lot larger (and pricey - but that isn't too much of a concern as long as it works well).

Regards,
Ben

 

[micalbrch]

Yes, the Abel is much bigger than a Hydracell. So, the Hydracell is a good choice but do not buy it without talking to some sales guy with technical experience. Describe your application, ask all you want to know and follow his/her recommendation.

 

[moltenmetal]

Low temperature is good- you may get away with a hose pump. 200 F + that much pressure is probably too hot for the hose pump to give you adequate durability, but 100 F is going to be much less of a problem.

Thick slurries, (fortunately shear thinning in your case) tend to be moved nicely by AODD pumps in our experience as I mentioned. They're frequently used for services like thickener bottoms- the motion of the diaphragm seems to be particularly good at keeping things moving and suspended, particularly into the suction. The elastomers can be quite good at resisting wear if they are selected properly. But it's hell on check valves, so the tendency there is to go for hard seat and ball materials- tungsten carbide, silicon carbide and the like. The cheap pumps have non-renewable seats so you need to steer clear of them. Hose pumps are also used and have the obvious benefit of no check valves- but the hotter you go, the shorter your hose life will be and the fewer elastomer choices you will have.

We've used the small Hydracells before for a number of applications but not yet for abrasive mineral slurries, so I don't know how they handle the check valves. What I do recommend though is to stay away from Teflon diaphragms in these- use the true elastomers, because they will give you better life even if slurry wear weren't an issue, which it definitely will be for you.

If your slurry is not rapid settling, try to keep the velocities low in the pump. A larger pump spinning slower will do that for you as has already been mentioned. If your slurry is rapid settling, you need the velocities to keep it from settling so you're pretty much screwed- and wear is going to be a problem whatever you do.

 

[JJJ2000]

You might try a multistage disc pump. I could have sworn Discflo was working on this. I know the guys making the knock-off discflo pumps at Adeptek pumps have these on their website. You might also look at the eccentric disc pumps by Mouvex. I haven't used any eccentric disc pumps myself.

 

[MartinLe]

You might want to look at concrete pumps (piston), putzmeister and Klein are to vendors.
I've seen them in environmental applications with slurries around 20%Ts, part of that solids chicken manure and part sand-like bedding material (pretty abrasive).
I think (but I'm not sure) that you can ,ount them vertically, that would be the only way to get one into your footprint.

 

[micalbrch]

@MartinLe: You cannot get a concrete pump in vertical design, they are way oversized for the head and way too expensive compared to any other pump type which was recommended here. Concrete pump or better solids pumps (= concrete pumps for industrial applications) are a good choice for paste-like or sticky sludgge or for slurries with very big particles like the chicken manure you mentioned. But for a rather thin slurry with small particles - no. There are many other pumps types available for 10 % of the price. You mentioned 20 % solids which is reasonable but keep in mind that the solids' SG in this (environmental application) is around 1. That means that a slurry with 20 % solids by weight is sticky. OP's slurry has 30 % solids by weight but it is alumina slurry with a higher SG. So, it is still flowable. A bit viscous - o.k. But not a cake like municipal sludge with 20 % solids.

 

[btrueblood]

The diaphragm-type pd pumps take one abrasive-sensitive seal (plunger seal) out of the problem, but you still have check valves to worry about as molten and others have mentioned. Pretty sure the hydracell pumps have a "cartridge" style check valve, with limited metallurgy combinations. If you can find replacement check valves with elastomeric (urethane or similar) seats, you may be able to get there. Oversize the pump volume per stroke and reduce the pump rotational speed to reduce erosion problems elsewhere and minimize the shear thinning effects. From experience, Hydracell pumps have trouble with higher temperatures (e.g. water at ambient suction pressure and 180-200F temperature inlet), due to hysteresis (in the diaphragm and backing fluid), leading to heating and subsequent cavitation within the diaphragm backing fluid - this was ~15 or 20 years ago, though, and they may have made progress on the problem since then.

 

[cannondale]

I'd go either diaphragm or recip. Plenty of choice on pumps and materials, and pressure is no issue. I'm seeing the Putzmeister rep tomorrow so ill ask if I remember. I pump much larger particles and volumes/pressures with recips all the time, and yes valves and packings can be an issue, but if you get the lubrication and materials right it's just a factor you have to live with, but that could be more expensive than the pumps you've already got (don't know what they cost). Double diaphragm pumps are really simple and relatively cheap if you can make them work, but beware of the power/air the need. Footprint is an issue though.

I'd be interested in how you get on.

 

[brs766]

I am sorry I have not responded recently. I have been away for quite some time due to training and vacation. Thank you all for your input! I'll let you know what we decide on.

Regards,
Ben