Unfortunately most such companies will not do so as they would perhaps leave themselves open for critism or even possible claim if they did. Climatic conditions as well as variations in material mositure are a major cause of 'dry' materials building up in silos, baghouse filters, ductwork etc.

However do not be so concerned with such moisture/climatic variations - our range of Acoustic Cleaners (also know as Sonic Horns) can alleviate these negative variations. Sound waves will make the material debond and indeed prevent the build up from ocuring in the first place. They will also prevent bridging of the material over the silo outlet, thus ensuring maximum mass flow. The following link is indeed such a case study in a cement plant in Haiti (http://www.primasonics.com/downloads...enationale.pdf) and this next link will show a short video clip to demonstrate how sound waves enhance material flow

(http://www.primasonics.com/videodownloads.htm).

Contact me if I can help you further

Regards

Donald F Cameron

Primasonics International Limited

don@primasonics.com

www.primasonics.com ■

Yes, any materials handling specification issued to suppliers of equipment should include a full material specification including flow properties.

But mostly they won't! Sometimes due to ignorance, sometimes (mostly) to pass the responsibility buck to someone else.

And even if they do, it usually turns out to be the suppliers fault if the material is nothing like the specification and the kit doesn't work. (common practice when specifications are issued by consultants) ■

Any contract involving the supply of equipment to handle bulk solids that has not previously been proven for the specific duty, should include details of all the relevant physical properties of the material to be handled. Sadly, this is rarely the case for various reasons. The equipment supplier cannot specify these, as he does not have control of the supply, at best, he can only specify the bounds of these values for which his equipment is suitable.

The user often does not know what measurements are relevant, is unlikely to have means of measuring these and usually depends on the equipment supplier to evaluate the position from the provision of a ‘representative’ sample. The problem is that samples should represent the ‘worst’ condition, rather than a ‘typical’ condition of the material to be handled and some judgement may be required to determine these. Main contractors are often the worst offenders in these matters, publishing reams on painting, welding, and other general engineering features, but frequently confining the bulk material description to a few woolly lines of text and offer an impenetrable barrier to direct access of product conditions. These circumstances account for many of the operating difficulties that arise in practice. This may suit the supplies of flow aid equipment that prosper on installations that fail to deal with the condition of material that is required to be handled, but is not a satisfactory state of affairs and is the root cause of many disputes between users and suppliers.

The responsibility for perfomance invariably rests with the equipment supplier, but this can only be prudently accepted if knowledge is available of all the bulk material conditions that may apply and it must be the responsibility of the user to supply this.

An experienced supplier will seek to co-operate with the user to ascertain the full range of working conditions to be accommodated and offer the facilities to test the bulk material if necessary. A publication - “Guide to the Specification of Bulk Materials Properties for Storage and Handling Equipment’, was prepared by a working party of the Bulk Materials Handling Committee of the Institution of Mechanical Engineers to address this position. The British Material Handling Board has long recognised the need for widespread industrial education in this field to improve the efficiency of Industry in this major field of activity and has promoted the publication of various ‘User Guides’. Those concerned with the purchase or specification of equipment for handing loose solids would be wise to secure a grounding in the basics of bulk technology and the multiple-attributes of particulate solids. A document available from Ajax Equipment Ltd: – ‘Industrial characterisation of Bulk Solids’, that outlines these basic powder properties and indicates methods of evaluating and testing flow values. ■

Is this publication still available? I looked for it recently but couldn't find it listed anywhere. ■

I believe that the document was published by the Institution, rather than their normal route of Professional Engineering Publications, which was later disbanded. If you cannot secure a copy from the Manager of the Process Division of the I.Mech.E. at 1 Birdcage Walk, London. SW1H 9JJ because it may now be out of print, I would be pleased to make a photocopy for you. ■

Correction - The actual name is 'Guide to the specification of Bulk Solids for Storage and Handling Application'. It was published in 1994 under a working party that I chaired. ■

Yes. A comprehensive specification is necessary and if the equipment subsequently receives out of spec. material then the customer doesn't have leg to stand on. This issue goes far beyond flowability and rears its ugly head in assaying and plant performance disputes as well. At the end of the day it is incumbent on the supplier to cover himself against petulant clients by anticipating conflict and pitching his tender prices to suit. ■

Some types of systems may be required to handle multiple products, including future "unknown" powders. The ability to adjust to varying flow-ability characteristics and varying particle sizes may also be required.

For example, a metal porous-plate fluidizing medium can be engineered to be strong enough to allow "cranking up the air flow" if a difficult flow-resistant powder is encountered. The pore-size of the fluidizing medium can be selected with a safety factor (to prevent ingress of the powder) in case a future product with small particles is introduced.

Such systems may require a means to prevent or minimize cross contamination. Cleanable materials or even disposable/replaceable materials may be required.

Porous Materials for Powder Handling, Fluidizing and Powder Containment

Porvair Filtration Group manufactures porous materials used for fluidizing and powder containment.

* SINTERFLO (R) M sintered porous metallic plate for fluidizing hot materials or for long-life systems.

* VYON (R) Porous Plastic for fluidizing ambient temperature powders where a material more rugged than canvass or polyester is required.

* Automated pulsed-jet filter systems made with metallic filters for containment of high-temperature, corrosive, toxic or radio-active contaminants, product or catalyst (where an ordinary bag filter system or HEPA filter is not sufficient or suitable.)

SINTERFLO(R) M porous plate: This robust, cleanable and corrosion-resistant material is used to fluidize powder in hot or challenging environements where other materials would fail. It is also used where a long-lasting or permanent (rather than disposable) solution is needed. Fluidization is used to:

-move powders on an air slide

-prevent arching, bridging or ratholing during emptying of a hopper

- speed the unloading of a tank car or other vessel

- enable contact between catalyst and/or reactants in a fluidized reactor vessel

This porous material is made from multiple layers of woven metal mesh sintered (diffusion bonded) together. The mesh can be manufactured from 316L stainless steel or a special alloy. We customize the mesh-composite layers so that our customers can specify the flow rate at a given pressure (typically cubic meters per min air flow per square meter of surface area at a specified pressure in mbar - or for Americans, cubic feet per min air flow per square foot at a specified pressure in inches water column.) Our customers often don't want ingress of powder into or through the porous material, so we can also customized the pore size. The sintered porous plate fluidizing material can be provided as a flat sheet for our customers to cut, weld, fabricate into cones, air slides, etc. We also fabricate the SINTERFLO M porous plate into cones, cut it into discs, or fabricate other customized shapes. We also make complete hopper-bottoms containing the fluidizing cones.

VYON (R) Porous Polymer - This sintered porous plastic material is available in USA "FDA-grade" - in other words, suitable for food and pharmaceutical contact applications. It is economical enough to be disposable but rugged enough to be cleaned and re-used. We or our customers can cut and weld it into customized shapes such as fluidization cones. It is easier to mount than many other materials, and being strong and semi-rigid tends to require less support and is very resistant to sagging. We have a range of flow rates and porosities to control both the degree of fluidization and to prevent powder ingress.

Pulsed Jet Systems with Metal Filters: When a high-temperature range of bag filters just isn't temperature tolerant enough, Porvair Filtration Group can often solve the problem with metallic filters in a specially-designed pulsed-jet system. A sonic back-pulse of air lasting a fraction of a second knocks dust, powder, fly-ash or catalyst off of the filter down into a collection hopper. Materials are available to withstand hundreds of degrees C (well over a thousand degrees F) in corrosive environments. We even work in the HEPA and ULPA filtration ranges. The metallic-filter pulsed-jet systems from Porvair Filtration Group are used in both ambient and extreme-temperature applications where the dust or powder is toxic or radioactive. The metal filters are very pulsed-jet cleanable and long-lasting, often lessening or altogether preventing the need for periodic filter change-out, and thus protecting humans from exposure to dangerous materials.

www.porvairfiltration.com

infous@porvairfiltration.com ■