Conveying Abrasive Material
James,
In dilute-phase you will want to convey at the lowest possible velocity to minimize abrasion to the pipeline, this velocity will correspond to the point of minimum pressure on a Zenz diagram.
The existing bends in the pipeline should be replaced with special bends (a compromise design between sweeps and blind tees). These designs effectively minimize component erosion and at the same time minimize pressure loss. The Pelbow by Pelletron and the Gamma Bend by Waeschle are recommended.
A rotary feeder is the preferred feeding method but it is imperative that the feeder be a low leakage design. Even though a 1.5 bar design is normally adequate for dilute-phase it would be my recommendation to use a high-pressure 3.5 bar design. The valve venting design is critical to avoid wear, in this case I would recommend a vent accumulator to further reduce wear in the inlet area of the valve.
The above are recommended for dilute-phase but the better answer could well be low-velocity dense-phase conveyance. If the feed must be continuous you might consider combining dense-phase with accumulation and a continuous gravity feed at the end of the system.
These are my thoughts.
Dennis Hauch, PE ■
Re: Lean Phase Conveying Of Abrasive Cell Liner
Have you considered the use of stacked pressure tanks where the bottom tank is always under pressure and delivering a continuous stream into the pipeline and the upper tank cycles between being pressurized when it is recharging the lower tank, and atmospheric when it is being refilled from above?
This arrangement would eliminate any pressure differential across the rotary airlock and therefore increase it's life significantly. The upper tank could also be on load cells to replace the existing scale hopper.
With respect to the pipe line elbows, I would recommend the use of short radius elbows with abrasion resistant wearbacks which can either be integral or replaceable.
We'd be happy to help you work up a suitable pressufre tank arrangement if you so desire. Just send me an e-mail to discuss in more detail.
Regards ■
Lean Phase Wear
Gents
Thanks for your comments to date.
The stacked system sounds interesting.
Just some further info,
The original valve is a closed cell/rotor with a floating Nihard wear shoe riding on the rotor.
The alternative valve is an open rotor with fixed side end plates for sealing. There was pronounced wear at the end of the rotor in the body. I assume that the fixed end plates with some end clearance is not ideal. I doubt that we can proceed further on this type of valve.
The floating shoe valve had wear in the show and rotor blades...cutting and gouge out grooves.
The nett effect is aeration of the feed material and reduction in line capacity.
The system is designed for 1 to 2.5tph and the line pressure are a little bit higher then predicted. At the end of the line, we connect to the burner pipe whiohc has a smaller pipe size than the line (80NB) becase we could not fit anything larger in it.
The feed must be continious and stable.
The option of a dosing system at the end will work but more cost.
The SCL is a haz. material (cynanide is released upon contact with water)and we need to keep things simple and easier to control the risks.
We are thinking of attacking the issue with a better wear material in the floating shoe valve and also better venting of valve thru the surge hopper.
Any other comments welcome
Cheers
James ■
Lean Phase Conveying Of Abrasive Cell Liner
James,
There is a company in Australia which specialises in hard linings and rotary valves for difficult applications. www.avweld.com. Talk to Nathan Henry.
Regards,
Michael Reid. ■
Scl
Thanks Michael,
We have had the AV Weld experience before.
Attached are some photos of the new valve wear fyi.
The original valve is a Lisbon type.
Thanks
James
Attachments
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Lean Phase Conveying Of Abrasive Cell Liner
James,
as a leading supplier of rotary valves we have various experiences with wear applications. Alumina is an application with a high wear on the components.
Because of this reason we have made investigations about the wear resistance of rotary valves in the alumina transport to find out which material leads to the longest lifetime. There are some materials that can extend the lifetime compared to a NiHard valve.
For this application it is important to use a drop-through valve with a closed end rotor without any product touched sealings.
One important parameter is the conveying pressure, but I haven´t found the figure in your E-mail.
For wear resistant bends there are also different possibilities in design and material.
If your are interested in our solution you can reach me by e-mail:
bruno.zinser@coperion.com
or by phone:
0049 751 408 539
Best Regards
Bruno Zinser ■
Scl
Hi Bruno
It is spent cell liner and not alumina that is being conveyed.
Pressure at blower is about 40-60kPa.
We have a drop thru with closed cell rotor and aslo tried the open cell (as per photos).
Closed cell lasted for 4 weeks and open cell for 2 weeks.
Closed cell had floating NiHard shoe. Open cell had ceramic wear lining.
Cheers
James ■
Lean Phase Conveying Of Abrasive Cell Liner
All,
We are lean phase conveying spent cell liner from the Aluminium smelter industry for disposal.
Rates are up to 2.5tph.
Distance is about 60-80m with 5 bends and 2 45deg. bends and 80NB pipe.
The system was selected for lean phase on the following basis:
Need a continous stream of material being transported and not discrete intermittent streams.
The lenght of the piping run meant higher line pressures and that a eductor type system was not suitable (acc. to the supplier)
The material abrasivity was known and the wear on lean phase was accepted to be higher
The system has a weighing hopper/screw and thoughput hopper flood feeding a rotary star type valve feeding the conveying line.
The material is very abrasive.
The long radius bends (lined) have worn out.
The main wear issue is the feeder. The feeder was a conventioanl dust collector type and lasted 4 weeks before the bypass became too excessive leading to loss of capacity.
A much more expensive UK based valve was bought that was supposed to give an expected life of 12 months but lasted only 2 weeks.
So, we are back to square one on trying to address the wear.
What do some of the experts suggest in terms of trying to get a system that has a bit longer service life?
Continue with rotary valve development
Look at handling the valve bypass and accept the wear ie try to get the rate even with the wear
Re visit the eductor - maybe increase line size - stepped
Dense phase transport over to injection point and then lean phase inject (more complicated).
Cheers
James ■