Conveyed Material Breakdown
Conveying air velocity is the main parameter here. Damage increases exponentially with increase in velocity. If velocity can be reduced go for it. If you are using a high air supply pressure I would recommend that you step the pipeline to a larger bore part way along the length to reduce the conveying air velocity at the end of the pipeline, where most of the damage is likely to occur.
The angle of impact against any retaining surfaces must be kept as low as possible. So use long radius bends. If it is possible replace steel bends with rubber hose. Rubber is a resilient material and will absorb the energy of impact of particles and result in much less damage on impact than steel. ■
Re: Particle Breakdown
Dezirak
If you are unfamiliar with the concept of line stepping as suggested by Dr. Mills, have a look at www.powderandbulk.com, go to the "ASK JOE" column and you will find a current article which addresses the concept.
We'd be happy to assist you in addressing your problem.
Regards ■
Re: Particle Breakdown
dear Mr Dezirak,
You do not state the product you are conveying.
If you drop your product from f.i.25 m high to a hard floor and the particles already break apart, then it very likely that pneumatic conveying is not for this material.
good luck ■
Teus
Re: Particle Breakdown
Thank you all for your input.
Someone I worked with said that long radius 90's are not good to use for dense phase flow because they could potentially break the plug seal. He also said that the piping shouldn't be diagonal if it was going up or down. Is this true?
You guys have been a big help so far. ■
Re: Particle Breakdown
Long radius bends are commonly used in dense phase conveying systems. Plug breakage due to long radius bends is not a concern. In fact, for most materials, these bends are better than short radius bends in preventing plug breakage.
Sloped lines can be used in dense phase as long as the angle of the pipeline from the horizontal is less than the sliding wall angle for the material being conveyed. This criteria is used to prevent slugs from sliding and breaking up.
Regards,
Amrit Agarwal
Consulting Engineer
Pneumatic Conveying Consulting
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Re: Particle Breakdown
http://www.hammertek.com/Main/home.asp
These are the type of 90s in place that I was calling "water-hammer" 90's.
The website claims that these 90s reduce wear and particle degredation.
My question is do they reduce particle degredation more than long radius 90's during dense phase plug flow? I have emailed the company already but was wondering if anyone here has had any personal experience with them.
Thank you all for your help.
Daniel McClure
Louisiana Pigment ■
Re: Particle Breakdown
Daniel,
I am surprised that you are worried about particle breakdown, the problem with you guys in the Pigments industry is normally that you want things to be such a small particle size that the powders are a pig to handle !
I would also be surprised if you saw an appreciable improvement in performance going from these bends which are specially designed to reduce breakage to a LR bend. You may see an increase in breakage but my guess would be that you probably won't see any measurable difference.
As with the previous responses, I would always look at velocity first with this type of problem, it does vary depending upon material but breakage can typically be proportional to velocity to the power of 3 or 5. Small changes to velocity can have a marked effect on breakage.
It is also worth checking the pipe itself, what is the internal finish like (rough surfaces cause more dust), are the inner bores of these special elbows the same bore as the pipe or do you have a sharp edge where the bore changes, are all the pipe section the same pipe schedule, are all the connections (flanges or couplings) aligned properly, etc.
In general if you convey something 100 metres and you Y ppm of dust and you then convey 200 m under similar conditions, i would expect you to get a bit less than 2 x Y ppm of dust. If you measure the dust levels before you convey and after conveying to each destination, it may help you analyse the problem. If the dust generation / m is similar or greater on the shorter run then you have a general conveying problem (look at reduyciung velocities). If the dust generation / m is higher on the longer system then you probably have a problem with bend type, pipe route, alignment, or whatever, there is something wrong on that section of line. ■
Dune Phase More Suitable?
The only real solution to friable product breakdown is Dune Phase conveying where particle velocities are in the order of 4 m/sec in a 'shuffling' or dune movement in the pipe. However, this technique is restricted to products that are either granular (breadcrumbs or granulated coffee etc), pelletised (HDPE & LDPE plastic pellets etc), or grain (barley etc).
Most systems can be converted without changing the piping or infeed arrangement so it is worth investigating. Airflows are in the order of 40% of the equivalent lean phase systems too.
Can you let me know the product, it's format (eg - similar to silica sand), its initial dust content, the worst route, and the transfer rate? From that I will be able to predict whether Dune Phase conversion is a possiblity.
Incidentally - with this technology there is NO increase in dust generation within the product during transfer. ■
Particle Breakdown
The plant is using a continuous dense phase pneumatic conveying system, (storage bin to 2 alternating pressurized transporters to the recieving bins), to convey solids to either to the A line recieving bin or to the B line recieving bin. The problem is that solids going to the B line recieving bin are being broke down more than the plant would like. I believe the reason is that the line to the B line recieving bin has 4 more 90's than the A line. The 90's are not long radius 90's, rather they are water-hammer 90's. These have an area in them that accumulates material so that the pulsating impact isn't as great I think... I think that the particles break down in these. Anyway I was wondering about possible solutions to this problem and if the breakdown of particles would be significantly less if long radius 90's were used instead. The position of the recieving bins doesn't allow for much alteration of piping. Any thoughts on the problem or potential solutions would be appreciated. This is my first time to really look at solids conveying so pardon any ignorance on my part. ■