I fear that there is probably no other solution than mechanical cleaning because the deposit will be quite tough. The process is not cheap therefore, once cleaned, attention should be directed to avoid a repeat of the situation. This is a classic mistake that has befallen many users of soda ash silos. The only sure way to prevent caking is to ensure the material moves regularly. Modification to an existing storage hopper calls for some degree of specialisation. We know of a specific example where the potential performance of two well designed silos is negated by a spectactuarly poor interface with a discharging device but, in most cases, the design is not adequate to salvage by lining with low friction materials although wall friction tests will quickly determine this prospect. Generally an insert system is required or radical surgery to the converging portion of the unit. If you care to send outline details to lyn@ajax.co.uk I will be pleased to examine and advise on the options. ■

Re: caked silo

It is unlikely that the caking can be eliminated other than by a thorough mechanical cleaning. The key to efficient silo storage is to keep the product in storage ‘live’ at all times. Have you considered a Circle Feeder for installation on the silo bottom? This device will give you mass product flow over the entire diameter and will eliminate not only the need for steep side conical outlets, but will solve problems of ratholing and/or bridging in the silo.

Please email details and we will be pleased to offer specific advice.

Kind regards,

Brian Milnes

Robin Engineering Services

Email: robinengineering@aol.com ■

When considering "post cleaning" modifications to the silo, be aware that simply changing the feeder may not be sufficient if the basic geometry is flawed. Changing the feeder (for whatever type) will not necessarily give you mass flow (i.e. flow at the walls) if the wall friction for the soda ash against the bounding surfaces is too high relative to the convergent angle. Lyn Bates comments should be noted.

Regards

Richard Farnish

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

mailto:r.j.farnish@gre.ac.uk

http://www.bulksolids.com ■

You will probably know the basic patterns of flow that can take place in a silo, the main categories being distinguished by whether all the contents become engaged in moving during discharge or not. I prepared a detailed review of flow regimes for the University of Florida web site on particulate solids behaviour as attached article. A more comprehensive examination of flow problems prepared for this site, but not yet put on, is also ncluded.

The current storage capacities of your silos reflects the volume of the 'live' flow channels that exists in the silos plus what remains sufficiently loose of the recently entered product to drain by repose flow into this narrow flow channel. Assuming that the outlet is fully open and not impeded by surrounding build up, the initial deflection of the surface indicates the degree of 'spread' of the flow path from the orifice to the top surface of the stored material. The size of the un-caked draining region should also

be visible from the top when no more will discharge. The first step is therefore to establish these dimensions in relation to the geometry of the empty silos. The options then depend on what access is available to enter and support internal fittings to modify the flow regime that is generated when discharge take place.

It is clear that the present situation is that the flow pattern is not mass flow, so an internal column of material moves through a surrounding static bed and draws fresh product from the surface of the stored contents. the divergence of this path is probably quite small but when the surface immediately above the outlet is lowered material at the top side of the depression will drain into the centre according to the repose angle that develops. When the silos were first used the whole contents were relatively

fresh and, provided the storage period was short, the bulk of the material would have probably emptied. However, as new material was entered it was drawn down through the bed and the older regions progressively grew firmer the longer they stayed without moving. Crystal bridges soon form in soda ash to bind the particles together and to the wall so unless the bulk is

disturbed it will adsorb moisture from the atmosphere and develop bulk strength that is difficult to shift.

With a non-mass flow silo the only chance to prevent caking is to run out the whole contents before re-filling. This is not usually practical with big silos and even then, the material that is loaded into the silo first is last out because the silo content empties form the top be draining down into the flow channel. If the silos were clean the position would be easier to consider. The general objective is to spread the flow channel so that all, or as much as possible, of the silo contents are in motion during discharge

and there is roughly a 'first-in, first-out' pattern. This prevents some material having an indefinite residence time during which it can cake and then never come out as and when its time comes as the silo level falls.

There are two problems if the silo is not clean: -

One, it will be difficult to fit a flow insert to spread the flow channel unless the local walls are clear.

Two, the present cross section of flow channel cannot be enlarged if it is surrounded by caked product.

My assessment is that the flow channel diverges only slightly, if at all, so the only way to avoid further reduction in the very limited storage capacity remaining is to make sure that the silo empties as much as possible before being refilled. Otherwise, product left from a previous fill may cake and not come out later. This may not be practical, in which case there is a problem.

Much depends on the action that can be taken. If the silo can be partially cleared it is possible to look at fitting an insert to mobilise a broad flow channel that will keep more material in motion. I suggest that you send details of the basic silo dimensions and whatever information can be gleaned from the current position, i.e. level of product in bins, assessment of

rathole dimensions and any other information you have and I will examine the information and see what can be advised. If you look on the Ajax web site, www.ajax.co.uk, there is further information on hopper design and associated topics. ■

Omitted ref, to Florida Univ. site.

it is - Educ. Reso. Part. Techn. 1(1):#3(1999) or @> ■

It may be worth asking the various silo cleaning contractors to try cleaning your caked silo.

Usually done with air motor on the end of long air hose fed in through a manhole - nobody enters the silo.

Attached to the air motor are various designs of "whips"

- type of "whip" depends on how difficult material is to dislodge. ■

Acoustic cleaners would probably not be suitable for removing this build up but could be installed after cleaning using something like a Gyro Whip which are described above. Fitting an acoustic cleaner after cleaning the bins out would prevent build up and is certaintly cheaper than major surgery to your silo geometries

For more information on acoustic cleaner or gyro whips please visit our website at www.primasonics.com ■

I recommend that you read the recent article published in the October issue of Chemical Enginering. This article was published in two issues of Chemical Engineering. It not only covers all of the presently commercially available discharge aids but it also gives selection guidelines for each device. I can send a free copy if you are interested.

Regards,

Amrit T. Agarwal

Consulting Engineer

Pneumatic Conveying Consulting Services

Email: polypcc@aol.com

Phn and Fax: 304 346 5125 ■

Dear Sir,

We have encountered with such kinds of situations in soda ash silos before. We have brought up solutions for the same phenomena in glass factories, soda ash and chromic acid factories.

We are manufacturers of air cannon systems with very high shock power to exceed such kind of caking, sticking, rat holing and bridging problems.

Not only the equipment but also the correct allignment of the cannons are matters of concern.

We guarantee exact solution for your problems. Therefore, please do not hesitate to contact us via our contact information.

Thanks for your valuable attention from now and,

Best Regards,

Ufuk YUNEL

(M.Sc Mining Eng; M.B.A)

YUNEL LTD., STI

Tel: 0090 312 419 3285

Fax: 0090 312 4193289

e-mail: sales@yunel.com

Web:www.yunel.com ■

Sorry to learn that your attempt to clear the silo was not successful. If it is not practical to clean out thoroughly, at least the arrangement should be reviewed to establish if the current volume can be fully employed, and perhaps further enlarged by use erosion, if slip is generated on the existing material. A common mistake is to clean out an unsuitable silo and then refil without making any changes.

If you care to send details of the silo construction and current state of the contents to lyn@ajax.co.uk, we will be pleased to consider what options may be available. ■

Dear Sir,

Next to a not correct design cone as the discharge device Soda Ash temperature can influence caking tendencies. It is often seen that a low Soda Ash temperature will result in easier handling and often less caking tendencies.

Our company is specialized in indirect cooling of Bulk solids. No air is required and no moving parts, therefore the energy consumption is very low.

Please do not hesitate in contacting me if you require further information ■

Sorry to hear the gyro whip didn't complete the job, if you are considering a second attempt at removing the "caked" soda ash, try pneumat systems (europe)ltd.

http://www.pneumat-europe.com/

Or e-mail Mr S Gallagher at team@pneumat-europe.com ■

I seem to recall a soda ash silo in the UK that eventually needed explosives to remove the dead material. ■

I'm guessing the "explosives" would of been cardox.

As we all know , each silo is different, the way the material is built up, the shape of the silo etc.etc.

Pneumat Systems (europe) ltd can use Cardox as a part of their cleaning process, but it realy depends on the situation at hand.

I may of been one of the engineers who cleared the soda ash silo in the uk ;-) ■

The implication was that it 'proper' explosives, but I don't know for sure. I know it was a big silo, I think with a flat bottom? ■

Explosives or an Air Cannon are your most promising solutions.

An air cannon will at least give you a permanent solution.

Another manufacturer of air cannons is:

MARTIN ENGINEERING

One Martin Place

Neponset, IL 61345-9766

Email: info@martin-eng.com

Phone: 309-594-2384

Toll Free Phone: 800-544-2947

Air cannon website:

http://www.martin-eng.com/products.php?category=9

Good luck, ■

I'm not too surprised that you consider the Gyro whip a little slow. As has already been mentioned a certain amount of operator skill and experiance is needed. I consider the air whips to be inefficient compared to the modern hydraulic whips.

Air whips do not have the power or control of the newer hydraulic version. In a nutshell the hydraulic whips get the job done faster, and are easier to use.

I have personally worked on several soda ash silos using both hydraulic Binwhip and Cardox, ALL with success.

The only thing that does supprise me is that the old compressed air whips are still on the market.

http://www.pneumat-europe.com/index.html

Here is an interesting artical on this subject

http://www.engineeringtalk.com/news/pny/pny100.html ■

I suggest you use Atlantic Blowers centrifugal blowers or even maybe their regenerative blowers for the transport of the ash. You can visit their website at

href="http://www.atlanticblowers.com" target="blank">www.atlanticblowers.com or you can e-mail them at

href="mailto:sales@atlanticblowers.com">sales@atlanticblowers.com.

Attachments

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Enough has been said on the way to avoid this problem. Air connons, air injection, vibrators, blasters, agitators are all inadequate to correct a hopper that will not provide slip on the walls during discharge. There is no substitute for scientific design and if users do not go this way they must pay the price of uncertainty and risk of failure. ■

Dear bNOCH!

To clear stubborn caked products from silo conditions, I suggest that you look at the website for CARDOX(Carbon Dioide) high pressure breaking and cleaning and fire fighting systems. It uses rapid discharge of heated compressed liquid CO2 which breaks and aerates without vibration. Works effectively on cement kilns without dislodging bricks in the internals of the kiln.

Check the website http://www.cardox.co.uk

I think you may find a simple solution to years of neglect in housekeeping operations. ■

For all your problems of clog, we have the solution!!

- A reliable solution

--> Construction of the cast iron body

- A simple solution

--> Accessibility during maintenance

- An economic solution

--> No more stop of silos, hoppers

I also invite you to please visit our website www.staminair.com and if you have any inquiry, you can write us at service@staminair.com

Do not hesitate to contact us.

Sincerely,

Ferlicoq Damien

Export Sales Manager ■

VORTEX BLASTAIR - Air Cannon

Reliable, efficient and cost-effective material build up removal products, solutions and services.

Staminair Corporation's material build up removal products, solutions and services are all intended to offer better material flow, improved safety and economic process optimisation. ■

hi there

there will be a device fit for this purpose i suggest a company called primasonics

although before installing such a device on your hopper it is recommended that you clean any hang ups or resisdual product the best means of doing this would be a system called giro-whip as a company we specialise in this and can supply you a quote i also have a relationship with primasonics and can supply you with the relevant contact deatails ■

as a company specialising in cardox and giro-whip we are higly confident that these two disciplines in the hands off experianced operators are the best methods to empty silos

we have in the past put rope access men in silos to accomplish the same goals the only difference is from a health and safety point of view and men suffer from fatique the process of rope acces is higly costly and there will always be an element of danger no matter how much emphasis is placed on managing safety

we can supply all methods of emptying silos in conjunction with our purpose built suckand blow vaccum machines which have developed to blow material in a pressurised state not reverse air!!

Scott Beeching ■