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Suggestions for a 15% clay solids / 85% water slurry pump
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(Mechanical)
(OP)
22 Apr 10 16:09I am looking to see if anyone has any experience and guidance regarding what type of pump to consider for moving about 10 USGPM of a luke-warm water / clay solids "milkshake" slurry (15% solids, 2-50 microns) at a differential head of about 150 ft.I am thinking maybe a small progressive cavity pump or wobbler pump with a viton stator and 1 bhp motor (I am told to also consider a hydraulic drive but...for 1 bhp...why?) from Moyno, Seepex, Allweiler or Roper.I searched previous threads and I think the direction was similar for a slightly different (submerged) application, which oddly enough was also described as a "milkshake". In fact, in a sample jar containing what I am trying to pump, when you shake it it ends up looking just like Nestle's Quick, although it doesn't taste nearly as good.Since this is for a little pilot skid with a short life expectancy, I could even consider a little Grundfos CR1 and just live with it wearing out...Anyone have any thoughts?Thanks in advance...
Regards,
SNORGY.
(Mechanical)
22 Apr 10 16:4415 % solids is not that much but don't use a rotating positive displacement pump. Wear will be too high with this kind of slurry unless you oversize the pump (low rpm). Perhaps a small rubber lined centrifugal can do it although the viscosity seems to be rather high. For sure a diaphragm (membrane) pump can easily do it and wear won't be that high. If you have compressed air availabe and as this is not a 24/7 operation, look for an AOD. Otherwise (no compressed air available) look for an electromechanically driven diaphragm pump. Forget the hydraulic drive. That does not make sense for 10 GPM and 150 ft.
(Mechanical)
22 Apr 10 17:56Although a AOD sounds a good selection - but can it generate the head?
As this is only a pilot scheme you could consider a small ANSI or similar process pump with a duplex SS impeller, this will give reasonable life.
(Mechanical)
(OP)
22 Apr 10 18:02Thanks micalbrch.There would be air - and pressurized nitrogen - available, but the client prefers to stay away from that. I don't know much about the electromechanical driven diaphragm pump, but from what I could find out, it's a good option. One of my initial thoughts had in fact been a Sandpiper pump, but I ruled it out due to client's reluctance to use pneumatically driven pumps.I also looked at DiscFlo, but I thought that it would be inefficient at low viscosity - 50 cP and lower - and the fine nature of the slurry didn't warrant it. Another option I thought about was Wanner HydraCell. I am thinking that, for what I am trying to accomplish, that's a bit too much pump and too much pump technology for this application.I just don't want to send out a generic request for quote and get a whole bunch of declined bids, thereby wasting everyone's time.With respect to the hydraulic drive, there would be several similar (mostly smaller) slurry pumps on this package, moving the same stuff at different rates. I envisaged an electric-driven hydraulic supply pump (could even be a hydrostatic drive / swashplate type) and a maze of tubing (or hoses) and valves to route to the various hydraulic motors, and decided that I didn't prefer such a scheme when compared with half a dozen small motors.
Regards,
SNORGY.
(Mechanical)
(OP)
22 Apr 10 18:03Artisi - thanks also.That's in keeping with my "buy a little Grundfos and accept that I am going to wreck it" philosophy...
Regards,
SNORGY.
(Mechanical)
22 Apr 10 18:26I think a "grundfos" wouldn't go the distance, the impellers on most of these small units are usually pressed SS sheet - and wouldn't be suitable.
Years back I had a client who unbeknown to myself until much later put one of our ANSI process pumps(CI case, Cd4mcu impeller - 2900rpm) on a china clay filter-press application, this application meant it was running at near to CV for hrs on end maintaining pressure to the filter. The wear life was unbelievable considering the application.
(Mechanical)
22 Apr 10 20:31You may want to consider a plunger pump. I've known of them to be used for pumping ash & water slurries with good durability. I'm not sure of the availability of such pumps in this small size range.
Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.
(Industrial)
22 Apr 10 22:52I tend to agree with staying away from any type of positive displacement pump. I do agree with micalbrch in that any centrifugal pump, it would be best to buy a slightly overized one and then lower the rpm.However, if you need specific amounts of liquid, it is cheaper to buy a PD pump, rather than a centrifugal with an associated flow control valve(in MOST cases.
Will Chevron Corp.
(Mechanical)
(OP)
23 Apr 10 09:37Some of these pumps will be driven via VFD...I agree with the assessments re: Grundfos...It's not easy to source "readily available" minute little pumps for a service like this.Sounds like a mechanically driven diaphragm pump might be the best fit.The service life will be measured in terms of months, not years, and the pilot that they are going into is intended to test (hopefully prove) a process technology. I don't mind chewing up a few wetted ends during the exercise. I am inclined to try Hydracell and / or PC pumps with spare wetted ends, depending on whatever sparing philosophy the client chooses to adopt.Thanks for your advice, everyone...it has helped (and continues to help) a lot. It's good to bounce things off you folks.
Regards,
SNORGY.
(Civil/Environmental)
23 Apr 10 09:57Look at a Watson-Marlow SPX-32, 10 GPM @ 100 PSISteve
(Mechanical)
(OP)
23 Apr 10 14:27Thanks all, and stars all around (am I allowed to do that? I just did...)SteveWag:I like this concept at first glance, and I will be looking into it in further depth.
Regards,
SNORGY.
(Mechanical)
23 Apr 10 21:07Here is a company that made their name pumping slurries.rmw
(Mechanical)
(OP)
24 Apr 10 11:04Thanks rmw...It's been too long that I have "dabbled in everything". I should have thought of these guys.
Regards,
SNORGY.
(Mechanical)
25 Apr 10 18:16I'd look at a progressing cavity pump; that's what pretty much every paper mill uses for their clay pumps, and they seem happy with them. Keep the speed to 200 rpm or less, and you'll see good life out of it.
(Chemical)
26 Apr 10 07:34150 ft is a bit too much head, but you might consider an industrial hose pump. Barring that, an air operated diaphragm. A low flow, high head application like that is probably going to be the death of your typical slurry pump in short order.
(Mechanical)
(OP)
26 Apr 10 09:47Thanks folks.These will be sacrificial pumps with a short life expectancy in a non-dangerous service. If I can find a small enough slurry pump I'll go that route, otherwise probably a PC and a whole bunch of stators.
Regards,
SNORGY.
(Mechanical)
29 Apr 10 02:53I would be using a progressive cavity pump from Mono Pumps Australia. They make them with ceramic coated wetted components for slurry duties. Your slurry is just dirty water.As for sizing it is more appropriate to have them run slow to make them last. it is not oversizing, just good engineering. Too many "Johnny come latelies" have been flogging their UNDER sized PG pumps into the market. They sell you a fast running small size frame and make a killing on the spare parts.When I specify PG pumps I always include a five year no fault warranty clause. This keeps the dodgy salesman out of the arena and I end up with a decent engineering solution.I have seen Mono Australia pumps in action for nigh on 30 years in a large scale sewage facility for Sydney Water. they pump everything including the kitchen sink.I have also used them for mine dewatering pumping tailings and coal debris.
(Mechanical)
(OP)
29 Apr 10 20:42I will advise the outcome as things progress...We will try to get proper centrifugal slurry pumps if we can get them that small.
Regards,
SNORGY.
(Mechanical)
30 Apr 10 06:07If pump life is not all that important and you are only looking for a short-life and a small "slurry" is not available I would seriously consider an ANSI or similar pump with hard SS impeller ie CD4Mcu or similar.
(Mechanical)
(OP)
30 Apr 10 09:26Artisi:Oddly enough, I raised that very thing in a design review yesterday. The pilot is intended to prove a process technology, not to prove the durability of its equipment. The various maintenance and design life issues can be addressed with larger equipment in a commercial scale development once the processing technology is proven. Meanwhile, I don't mind beating up this equipment for a few months - but it does have to work for those few months.
Regards,
SNORGY.
(Mechanical)
30 Apr 10 11:07You can get a nice PC Pump for this service, running about 160 rpm, with probably a 3 hp or so gearmotor. That's what I'd look at.
(Mechanical)
1 May 10 08:04A properly selected progressive cavity will do that duty just fine. Properly selected means <200 rpm and two stage. You can pump far worse than that with a PC pump and still get decent life. I'd choose the second company you list but I am biased!
Regards
Nick
(Mechanical)
3 May 10 18:00An AODD or AO Pistin Pump can handle this. You can get an AODD Pump with an Output pressure of more then the air inlet pressure. So lets say it is water and 150 ft of head is approx 65 psi. An AODD pump can have a max air inlet pressure of 120 psi with a 1:1 ratio and pump your fluid at a maxiumum of 120 psi. Their are piston pumps with a 26:1 ratio but this is often used when pumping extremely viscous fluids, ink, resins, etc. If you look at say ARO pumps they will show the fluid output and how many CFM's are required and all the other gory details.
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Nnamdi Nwaokocha offers practical advice on pump selection
PUMPS are the backbone of the process industry. In a process plant, it is necessary to move material from one point to another. In keeping with the laws of thermodynamics, fluids move from an area of high pressure to low, and depending on the plant layout often require the assistance of a pump to achieve this. With many different pump types available, selecting the right pump can be tricky, especially when slurries are involved.
This article will discuss some of the variables to consider when characterising a slurry and selecting a suitable pump for transporting those slurries in a plant. This is not definitive and is by no means a complete review of handling slurries by pumping but is meant to provide some useful information and a good starting point of what to consider.
In a spin: Slurry centrifugal pump with rubber lined casing and rubber impeller
Pumping of slurries can often lead to blockages or equipment failure. The job of the designer is to assess all the factors of each situation, including client and existing site preferences to design a system and select a pump which is robust enough to minimise blockages and makes maintenance for operators as easy as capital would permit whilst providing a safe system of work.
What is a slurry? Typically, the term slurry is used to refer to a mixture of a liquid and a solid or combination of solids. The liquid is often referred to as the carrier fluid and in most cases is water, although it can be anything from an acid solution (eg nitric acid) to a hydrocarbon (eg diesel).
Producing a slurry or maintaining solid suspension in static conditions is outside the scope of this article.
Slurries can broadly be broken down into two types: settling, and non-settling slurries. This characterisation is based on the nature of the solid(s). Non-settling slurries contain solids made up of fine particles, which largely remain in suspension when the applied mixing energy ceases. Settling slurries, as the name suggests, contain solids whose particles settle out when the applied mixing energy ceases. From a designer’s perspective, it is important to know the type of slurry. For example, non-settling slurries can be transported around under laminar flow conditions, whereas turbulent flow conditions are required for settling slurries, particularly in horizontal sections.
A useful rule of thumb provided in Sinnot and Towler’s Chemical Engineering Design states that solids with particles of less than 200 microns (0.2 mm) will usually be expected to produce non-settling slurries. Larger particle sizes will produce settling slurries.1
Before selecting the right pump, the first step is to determine the pressure drop requirements using the system characteristics. The parameters required are:
The following equations2 are useful in determining the slurry’s density:
For settling slurries, the velocity in the pipework is the key design criteria.
Perry’s Chemical Engineers’ Handbook
Figure 1: The relationship between the pressure drop and the slurry’s velocity compared to a pure liquid in horizontal pipework
Figure 1, an extract from Perry’s Chemical Engineers’ Handbook, depicts the relationship between the pressure drop and the slurry’s velocity compared to a pure liquid in horizontal pipework. The important point to note is that the horizontal pipe velocity should be above the point labelled Vm2 (minimum transport velocity). This is the point at which the solids are fully suspended. This is determined using the Durand equation3.
where:
Once the minimum transport velocity is calculated, it is common to add a safety factor, but care is needed. If the velocity is too high, the required pressure drop and the subsequent work required by the pump can increase significantly. For vertical flow, a good starting velocity can be taken as twice the solid’s settling velocity. The main aim is to stop the solids from dropping out. Velocities in the range of 1-3 m/s is a useful rule of thumb.3
The pressure drop for settling slurries can now be determined at the calculated velocity assuming pseudo-homogeneous behaviour, using the slurry’s density and the carrier fluid’s viscosity in established pressure drop calculation and applying a correction factor. A correction factor of 25% is suggested in Perry’s Chemical Engineers’ Handbook3.
Note that the above is for solids heavier than the carrier fluid. Depending on the solid particle size, at particular concentrations the particles begin to interact with each other and can start to affect the slurry’s viscosity. This is discussed further with calculations provided in the Processing of Solid-Liquid Suspensions, Chapter 112. Appendix 3, Warman Slurry Pumping Handbook4, also has useful calculations and correlations for water-based slurries.
Perry’s Chemical Engineers’ Handbook
Figure 2: Durand factor for minimum suspension velocity (from Govier and Aziz, the flow of complex mixtures in pipes, Van Nostrand Reinhold, New York, 1972)
For non-settling slurries, the resultant slurry typically displays non-Newtonian behaviour, and its rheology and behaviour must be determined empirically to ascertain the work required by the pump. The pressure drop for these can then be calculated using established pressure drop calculations depending on the slurry viscosity and density calculated.
Other things to consider before moving onto pump selection are:
The solid particle will play a crucial part in selecting the material of the wetted parts. The following, amongst other things, should be considered:
As with many pump duties, both rotary and positive-displacement pumps can be utilised. The following are some of the aspects to consider when selecting the type of pump for your slurry. However, always check with specialist pump suppliers before making a final decision.
The most common pumps generally in use are centrifugal pumps. When specifying this type of pump, as a minimum, the following must be considered:
These are just some of the things to consider when selecting a centrifugal pump for a slurry duty. In direct liaison with a pump vendor, the designer must choose the best options for their system. They should also consider any impact on the shaft and seals, and ensure there will be no issues with cavitation.
Centrifugal pumps are differential head devices and therefore, the head generated is based on properties of the fluid.
Warman Slurry Pumping Handbook
Figure 3: Example operating curve and efficiency curve for a mixture of solids and water only
Often, the operating curve and efficiency curve provided by pump vendors are that of water, so a way of translating those figures is often needed. An example is shown in Figure 34. It also includes a ratio for the driver efficiency which would also assist in confirming the pump motor.
Note that the curve is only for slurries whose carrier fluid is water. Moreover, it is for Warman pumps. For similar correlations and fluids other than water, speak to your pump vendor.
There are various types of positive displacement pumps which may be utilised in pumping slurries: air-operated diaphragm pumps, peristaltic, rotary lobe, progressive cavity pumps, and piston diaphragm pumps to name a few. Assessing all of these to the same degree as the centrifugal pump above will be a significant undertaking and is outside the scope of this article. Instead, I’ve summarised different pump types used in my experience and highlighted specific things to consider in relation to handling slurries.
Positive displacement (PD) pumps are generally useful for fluids, which demonstrate pseudo-plastic behaviour. The pumps are better equipped to overcome that initial resistance to flow. They generally run at lower speeds compared to centrifugal pumps and are therefore consequently gentler on the solid particles. However, some PD pumps are known to generate acceleration losses, which must be accounted for.
Generally, I have found air-driven diaphragm pumps to be suitable for handling slurries. However, as with centrifugal pumps, abrasion and erosion can be an issue, particularly with the balls and seats that form part of the check valve assembly. If the right material is not selected, the balls can be eroded to a point where they no longer seal properly, causing the pump to not operate efficiently. The same thoughts can be applied to piston diaphragm pumps.
Things to consider (specifically related to slurry handling) include material of check valve assembly; material of diaphragm; and clearances (the maximum particle size the pump can handle).
Peristaltic pumps are alternatives to air-driven diaphragm pumps. Unlike the diaphragm pumps, there are no balls or check valves to maintain. To put it simply, the only things which require maintenance are the motor and the tube. The main advantage of this pump type is the capability to handle slurries up to 80% w/w solids (this is the highest value I’ve seen claimed, and should be confirmed with your pump vendor). A limiting factor in its selection is the maximum discharge pressure, and this is limited ultimately by the tube properties. Things to consider include tube material (hence tube life), and maximum discharge pressure.
In these pump types, fluid is moved in the spaces between the teeth of the gear pump, lobes or pistons. They typically are specified for slurries with soft particles. ECP pumps are known for dealing well with slurries that contain solids which settle readily, as they can be scooped up once flow is resumed. The clearances are usually quite tight in these pump types and any slurries which contain abrasive solids would cause excessive wear on these pumps5.
Things to consider include slurry type, and solid characteristics.
Cross section of an ECP pump: Learn how it works at https://bit.ly/2FXMGbU
Used extensively in the wastewater and process industries, this pump is well known for handling slurries. To improve wear resistance whilst pumping slurries, the rotor may be coated. The more abrasive the solids in the slurry the better it may be to operate the pump more slowly, ie select a larger pump and operate at a slower speed. Additionally however, if the pump is operated slower then solids may fall out of suspension and cause blockages within the pump. Be careful when looking to handle larger diameter solids. A limit of 45 mm is stated in Jones’ Pump Station Design.7
Things to consider include solid characteristics (size and abrasiveness), slurry type (do they settle easily?) and seal arrangement.
Selecting a suitable pump for a slurry application can be a tricky business. There are many variables to consider, some of which have been mentioned in this article. The overriding message though is to ensure that the solids remain in suspension and to minimise wear and blockages. The above is provided for discussion and general guidance purposes only. For specific cases, you should gather as much information as possible on the carrier fluid and solids, and discuss options with a relevant pump vendor.
1. Sinnot, R and Towler, G, Chemical Engineering Design, Fifth Edition, Elsevier, 2009.
2. Processing of Solid-Liquid Suspension, ed Ayazi Shamlou, P, Chapter 11 by Shook, CA, Chapter 12 Etchells, AW, Butterworth-Heinemann, 1993.
3. Green, DW and Perry, RH, Perry’s Chemical Engineers’ Handbook, Chapter 6, 8th Edition, McGraw-Hill, 2007.
4. Warman Slurry Pumping Handbook, Warman International, Feb 2000.
5. https://bit.ly/2Ud76ls
6. Coulson, JM, Richardson, JF, Backhurst, JR, Harker, JH, Coulson and Richardson’s Chemical Engineering Volume 1 - Fluid Flow, Heat Transfer and Mass Transfer, 6th Edition, Elsevier, 1999.
7. Jones, GM, Pumping Station Design, revised 3rd edition), Elsevier, 2008.