Originally Posted by sganesh

Dear Experts,

....... The problem is Fe dust is extremely light & flows like water. I find difficult in handling them.

If the product really flows like water then surely the thing to do is to pump it.■

Dear sganesh,

How about pneumatic conveying?

have a nice day

Teus ■

It can be handled quite easily on conventional conveyors after all it is much easier to handle than alumina given it is heavier and does not build up a static charge to the same extent and conveyors handling alumina are very common. The key is transfer chute design and keeping the conveyors covered and the transfers sealed. I cannot be more specific than this without more details

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

colin.benjamin@gcsm.com.au

www.conveyorsystemstechnology.com ■

Dear sganesh,

Considered hiring a mobile suction/pressure pneumatic unloader?

have a nice day

Teus ■

Dear Sirs and/or Madams,

I am working for an iron & steel company which have a linear sinter plant. We prove cooling process by a linear cooler. After furnace, sinter is coming through this linear cooler by a chute. While sinter is flowing over the chute smaller parts is falling down before bigger parts. And these small parts is blocking the cooling air holes. This blocking causes some problems about cooling fans. How can we solve this flowing problem? There is a segregation region just before ignition furnace. But we can not use the same system after chute before linear cooler. Because the sinter is 600 Celsius Degree. How could we prevent falling of the smaller parts before bigger parts through the linear cooler?

Thank you for your interest. ■

This is a process issue which needs a lot more clarification. As a reply: it is totally unrelated to the original thread which in itself is meaningless and vague. Please start a new thread and explain your problem with more detail and try to be more specific about the feed and process objectives. You seem to be plagued by an inversion of normal segregation behaviour and this itself is quite interesting if properly described. Your issue deserves to stand on its own in a new thread. At present it risks oblivion; hidden by the superficial starting thread which some of the better qualified experts will dismiss on first reading.

Good luck with a new thread. ■

If it flows like water, a trough conveyor will be a disaster. Spillage and fugitive dust will mean most of it does not arrive at its intended destination. Use pneumatic conveying or airslides.

Michael Reid. ■

With all due respects Michael, rubbish. If this was the case we would never use troughed belts with alumina

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com ■

Seen it happen Colin, first hand. First option should be pneumatic conveyor (or airslide if downhill).

Cheers,

Michael. ■

Originally Posted by Michael Reid

Seen it happen Colin, first hand. First option should be pneumatic conveyor (or airslide if downhill).

Cheers,

Michael.

Gentlemen,

This thread starter has eliminated pneumatic conveying from the equation and vaguely asked for improvements to his exisitng system. However without elaboration of the actual issues faced it is rather pointless to continue. ■

Michael so have I but that is because the designer of the system had no idea how to set up a troughed conveyor system for dry dusty materials. Had a recent example where a troughed system was extremely dusty and by simple fine tuning we eliminated the dust at no great expense. Everyone looks for some "new idea" or falls for some great sales speil when the reality is doing the basics right.

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com ■

Originally Posted by louispanjang

Gentlemen,

This thread starter has eliminated pneumatic conveying from the equation and vaguely asked for improvements to his exisitng system. However without elaboration of the actual issues faced it is rather pointless to continue.

Thank you Louis on bringing the reality that the obvious is that there is no better solution required as the question is how to better control using the original equipment in a better way.

As others have mentioned, there needs to be some diagrams or photos of the issue and then a viable solution can be advised from the vast array of content subscribers to the portal.

It may be that a different technology solution may be required at a latter stage in the life of the process, but that is something that can be addressed when ALL the parameters of product, transport route, equipment, people etc. are known.

Saying:- 'Thinking out side the Square or (Box)', it is first advised to Know what lies within that 'Square/Box' and fully identify them, then also Know how that 'Square / Box' is truly interfaced with All surrounding equipment allied to the project, ie:- (Conveyors, Vehicle movements, Plant & Equipment, people etc.).

I have been involved where the interface has caused more hazards and a great deal of angst of further problems/issues to be solved. ■

The basic problem of dealing with finepowders is that their fine nature allows then to entrain air when dilated by such actions as free fall, vibrating conveyors, pneumatic conveying and the collapse of dynamic arches and ‘ratholes’ in non-mass flow hoppers. The preresence of excess air in the voids of the bulk material holds the constituent particles apart to allow their relative movement with little interal friction and the bulk can deform to flow with very little resistance. This condition is aggravated in conditions of elevated temperature, as the air content is then more viscous and hence slower to escape from the fine interstices between the voids in the bulk so that it takes much longer for the material to settle to a stable condition. Bulk material in a fluid condition will flush readily through belt and vibratory feeders. Screw feeders offer a little more restraint but will not check a highly fluid condition, as a well-aerated fine powder can flow under hydrostatic pressure with a viscosity much less than that of water and can only be restrained by total containment. The ‘last-in, first-out’ flow pattern of a non-mass flow hopper provides only a short retention time for freshly loaded material to travel through the narrow flow path developed through the contents to the outlet and gives little time or opportunity for excess air to escape, as the flow velocity is counter-current to the upward escape path of air.

Even with a mass flow hopper, the velocity gradient that moves material faster in the centre regions can be amplified by the hydrostatic pressure of fluidised material restraining the radial in-flow of surrounding material and result in the loose material progressively penetrating the bed. Once the loose material reaches the outlet, such a fluid flow route will flush out all the fluidised content of the hopper, and often more besides that is loosened by the rapid change of flow rate. Loading a hopper via an ‘anti-aeration’ chute avoids the dilatation caused by free fall and also inhibits segregation by ‘impact penetration’, which favours the capture of coarser fractions and aggravates the flushing potential by concentrating the location of fines. Rotary valves are commonly used to restrict the uncontrolled discharge from hoppers, but even fine working clearances can be penetrated by the searching effect of fluidised powders and these gaps tend to grow by virtue of wear. Also, material that enters the returning pockets between the vanes of a rotary valve displaces the air that they contain and effectively pumps further air into the bulk awaiting discharge. Another process that amplifies fluidisation problems is discharge from a container that has a positive pressure differential, such as the collecting hopper of a bag filter that employs the pressure to drive air through the filters. As the bulk material passes to a location of reduced ambient pressure, the gas in the voids expand to dilate the powder, which is usually already in a loose condition.

Conversely, when such fine powders settle they tends to be both cohesive and stubbornly resistant to flow because molecular forces attract small particles in close proximity and the low bulk permeability prevents ambient air reaching the voids that need to expand to allow freer particle movement, so a partial void vacuum acts as an internal normal force holding the particles together. A common method of securing flow of fine, settled bulk materials is to inject air; often by ‘Magic mushrooms’, air cannons or with air lances, which can solve one problem to cause another because these methods do not control the amount of air that is supplied. Vibrators used to destroy stables arches disturbs the bulk material causes the boundary layer to fall away from the underside of the arch surface in an unconfined manner and entrain air, often creating a fluid condition that is difficult to control and gives rise to associated problems, such as the instability of big bags and sacks failing to align on sack sticking machines. Apart from adverse behavioural aspects, excess dilation is responsible for may packing difficulties, ranging from the inability of sack and packs to contain the required weight to variable density conditions that necessitates excess ‘giveaway’ on volumetric packing lines to ensure that statutory weight limits are satisfied.

To address this phenomenon, the system has to be examined as a whole, as the bulk state at the point of interest is dependent on both the current state of stress acting on the material and the historical stress situation. A mass flow hopper, with or without means to accelerate de-aeration, inhibits first-in, first-out pattern of funnel flow, which offers little residence time to attain a stable condition, but the subsequent flow route could undue any benefits secured unless it is carefully constructed. Getting rid of excess air quickly is not an easy task, particularly at high flow rates and from deep bed, where the rising air from the lower regions replaces that escaping from higher location. As a result, the surface layers remain in a fluid condition, which is bad news for non-mass flow hoppers. De-aerationf rames can overcome this handicap by providing paths of low resistance through the bed. This exploits the driving pressure of the differential between the hydrostatic void pressure and ambient and serves all levels

Screw feeders provide continuous extraction without introducing air and the use of extended length, short-pitch, close clearances and a ‘plug seal’ can severely restrict uncontrolled flow, provided the fluidity and hydrostatic head are not excessive as a result of good hopper design. It should be noted that a compacting screw or ‘plug seal’ screw cannot work if the powder is excessively dilated as the powder will run through or be expressed from the compacting region as it does not offer gas tight confinement and, even if successful in compressing the gas, the bulk will re-expand when the compacting pressure is released.

There are many tools available to an experience designer. Unfortunately, many bulk storage systems do not receive a systematic flow audit as it is often assumed that flow reliability is all that matters, and even that is sometimes taken for granted if there is an open path available for a flow route. A system designed for ‘powder state control’ will take steps to ensure that flow is at least partially confined, with a flow route that inhibits undue expansion and maintains the bulk material in a stable flow condition in storage by avoiding excess dilatation, providing de-aeration facilities where appropriate and using limited volume air injection, to replace air expressed from the voids at the rate that takes place when the powder is in a suitable flow condition. A publication on dealing with aerated powders is available from lyn@ajax.co.uk. ■