When considering the design of a bin for storing a hygroscopic or time dependant material, it is important to ensure that the bin will operate on a first-in, first-out basis. Establishment of mass flow discharge within the bin will allow this to occur (although at inventory levels approaching and below that of the hip the velocity profile across the bin will be non-uniform). Design of the bin convergent angles and critical outlet dimension for reliable discharge can be derived from flow property testing using shear cells (of which several types are commonly used by the various organisations offering this type of design service). The capacity required, headroom availability and general plant layout into which the bin is to integrated will have an influence over the choice of mass flow bin shape - but the need to feed from the bin and subsequently transfer the material within a closed system could be met by using a plane flow bin interfaced to a correctly designed screw feeder (i.e. increasing capacity type) housed in a "U" shaped trough. This last point is most important, since the presence of non-flowing regions generated by the use of a "V" trough or standard (constant capacity) screw will disrupt the discharge pattern for which the bin has been designed and lead to the establishment of extended storage periods for material in the non-flowing regions. If the bin is small capacity and regularly drained down, the length of time that material is resident within the bin will be minimised and the opportunity for aging or agglomerating will significantly reduced. If the bin is medium/large capacity and is used in a continuous process (i.e. topped up) then there is great opportunity for product quality and flow issues to develop unless the points outlined above are considered and incorporated into the design.

I hope this helps answer your question!

Regards

Richard Farnish

The Wolfson Centre for Bulk Solids Handling Technology, Univ.Greenwich, London, UK

http://www.bulksolids.com

mailto:r.j.farnish@gre.ac.uk ■

Mr. Farnish,

I am extremely curious about your comment on making the bin a "first-in & last-out". Please excuse my ignorance and inabililty to comprehend, can you refer me to a publication or explanation on how this is done.

My thinking process would lead me to believe that the bin is a paradox and WILL never empty (ie. what goes in must wait till later, in order not to proceed before the next in line, to be "last-out").

Always in need of help,

Lawrence Nordell

Conveyor Dynamics, Inc. ■

Thanks for picking up on the unintentional typing error.

I actually meant to write "first-in first out" in reference to mass flow discharge (fingers typing before brain fully engaged!). Obtaining first in last out is quite easy - as this is what you get with core flow bins.

Apologies for the confusion caused - fingers suitably chastised!

Richard ■

Ah!

Thank you Richard. I see clearly now.

First in, never out is the same as: "core flow bins".

Sympathetically, I often encounter these days of no brain and all fingers.

Keeping the faith till chastised do we part.

LKN ■

I must be missing something, as I cannot see a reference in Richard’s original contribution to ‘first-in and last out’. However, the crux of the matter is that a mass flow design is recommended and this essentially requires that the bulk material will slip on all the container contact surfaces. As this behavior is mainly determined by the wall friction value of the product, this physical property should be measured in relation to the material of constructed selected. It is also essential that the material will reliably flow through the outlet and this ability depends on the size and shape of the outlet in relation to the shear strength acquired by the product in the outlet region. The size of outlet required for a small storage hopper is probably verified most easily by practical trials, allowing some margin for variable operating conditions. The flow benefits of a Vee hopper, compared with a cone, combined with the space saving and discharge control advantages of a screw feeder, usually favor the use of an integral screw feeder and hopper as a reliable and controllable dispenser. It is essential that the screw will generate progressive extraction along the full length of axis exposed to the stored material in order to provide a live flow pattern over the total interface area with the hopper, otherwise mass flow just will not occur.

Regarding the operation of dispensing a specific amount to a vessel in which the batch is weighed, the machine can be set to work at a specific rotational speed and stopped when the required amount is discharged. A two-speed drive can be employed to give greater accuracy by finer control of the feed rate. Be set to provide a high bulk discharge rate until about 95% of the required amount is fed out, switching to a slower speed for the make-up quantity. The screw will provide a shut-off facility, but with the discharge channel being exposing a hygroscopic product to a liquor mixing tank it is good practice to include a pneumatically operated end-seal valve to isolate the material resting in the feeder outlet tube from the ambient atmosphere above the mixing vessel. This seal plate is opened as the screw commences to rotate, and closed as soon as the drive is stopped. An advantage of this feature is that it is a non-clog valve and, together with an expanded outlet neck, provides an economical and effective seal for a screw feeder. ■

We have expoerience with this matter and there is was not so very difficult.

Some advises:

- used fully closed conveyors and valves

- fifo is always good

- if necessary put in overpressure of dry air into the bin.

- make sure the CaCl is really dry and has no free water in it!

If you have a drawing or more technical description we can mak ean offer for this system.

Jur Lommerts

Jansen & Heuning Bulk Handling Systems

www.jh.nl

jfl@jh.nl

tel. +31 50 3 126 448 ■

DEAR MR. RIDELGAD,

IPT IS SPECIALIST FOR SILOS AND DISCHARGE EQUIPMENT. PLEASE CONSULT OUR WEBSITE WWW.IPT-ONLINE.COM.

IF YOU SEND US DETAILED DATA – USE THE QUESTIONNAIRE FOR SILOS, WE WILL SEND YOU A PROPOSAL

BEST REGARDS

R. WOHLWEND ■