Hi Yogesh,

More information please. I tried a search on Pfister pumps, but there was nothing relevant.

Are you talking a fuel injection pump which is clogging up with coal fines? Trouble shooting is like detective work - you must look for clues, then put forward a theory, or idea of what you think might be happening. Then you go back looking for more clues to either support or reject the theory.

Give us more clues.

Regards - John.rz ■

It would seem that the difficulty rests with the silo design. The flow condition of fine coal is very sensitive to moisture content, so this may account for the variable performance. Moreover, injecting compressed air to stimulate flow is a crude device that can have very mixed results and offers no control of the discharge density. The basic problem is that the silo design is inadequate for the duty of reliable gravity flow.

The silo design, and particualrly the outlet region of the silo, should be reviewed on the basis of powder tests to determine the critical arching span of the coal and, preferably, examine the prospects of using a short mass flow section to secure consistent conditioning of the flow for reliable discharge at the required rate and a stable density. If space does not permit a simple extension, the options are an internal fitting to form a multi-stage flow regime or the use of an insert to redress the shape of the flow channel. See www.ajax.co.uk

The technology is well established and specialists experience is available to retrofit improved geometry. ■

Hello,

Interesting to note the terminology as Pfister Pump

Pfister Rotor Scales have this difficulty of coal inflow. It originates from the concept of the feeder - it blows coal direct into the calciner - so the entire inside of the Rotor feeder operates at the pneumatic transport system pressure . Depending on the pipe size selected and the feed rate - the pressure can be anywhere 300 to 500 mBar - please check it out !

The incoming coal has to overcome this pressure to come into the rotor pockets . Depending on the arrangement - you may have a standpipe - or a vessel - to offer a counterpressure of the coal head - so it can enter against the transport line pressure.

The system being in place - choices will be limited . One tip is to keep as much coal in the bin as you can - means you have to run your coal mill more frequently .

The other tip is to play with the bin bottom aeration level - so you get the maximum standing pressure at the Rotor inlet . More air will make the coal bulk density fall - so the bottom pressure falls - but it also reduces the wall friction - which helps . Less air does the opposite. So there will be an optimum point.

Good luck ■

Hello,

One more input : devices working under transport system pressure will always have a leakage air fraction moving up into the bin - and dispersing. In Pfister rotor - the inlet and outlet are on the same axis - rather near - so the leak air probability is strong .

The bin bottom aeration needs to take this into consideration. During running, one may not need additional aeration - except start up after some hours of stoppage .

There should be an agitator somewhere in the bin bottom . This must be run - it disperses leak air and improves coal entry pressure . ■

Yogesh - I have come across this particular problem before and found that it can be cured by the installation of a small model of acoustic cleaner at the discharge/chute area (see attached photograph). These acoustic cleaners use sound waves to 'excite' fine particles making them debond from other particles and also from the surface to which they tend to adhere. A few seconds 'sounding' at periodic intervals is sufficient to prevent bridging/bonding and to facilitate continious material flow.

If you are unfarmilar with Acoustic Cleaners please take a look through our web sites which can be found at:-

href="http://www.primasonics.com" target="blank">www.primasonics.com and

href="http://www.sonic-horns.com" target="blank">www.sonic-horns.com

A particular link regarding hoppers can be found at:-

href="http://www.primasonics.com/hopperapplications.htm" target="blank">http://www.primasonics.com/hopperapplications.htm

On our web site we provide a series of Application Questionnaires both as online and PDF formats and should you wish us to help you further, please complete and forward the appropriate form.

We look forward to hearing from you.

Best regards

Donald F Cameron

Primasonics International Limited

href="http://www.don@primasonics.com" target="blank">www.don@primasonics.com

Attachments

pas 210 cullet hopper 1 (JPG)

■

Dear Sir,

We can propose a solution of Air Cannons, which is widely used in industries dealing with very fine material like coal dust, cement,carbon black, etc. Our solution brought them complete removal of material and continuous flow inside the chutes and bunkers.

I would like to send you some application photos(to your personal e-mail) regarding to coal process.

Please check our web site for details.

Thanks in advance,

Ufuk YUNEL

(M.Sc. Mining Eng-M.E.T.U Ankara / Turkey; M.B.A.-S.I.U.E IL, USA)

Sales Coordinator

YUNEL LTD., STI.

Address: Ankara Cankiri Yolu 26. Km. 06750 Akyurt - Ankara / TURKEY

Tel: +90 312 847 52 00

Fax: +90 312 847 52 05

e-mail: sales@yunel.com

Web: www.yunel.com ■

Solutions that introduce air into the coal storage or processing chamber can cause combustion issues.

We have an alternative and safe solution that is simple to install. The mounting plate simply welds to the bunker wall. The BH vibrator is then bolted to the mounting plate. Cutting or drilling of the bunker wall is not required. Air blasters require complex and expensive installation. The bunker wall must be drilled or cut to accommodate the blaster nozzle. Additional access holes must be cut to attach the nozzle inside the bunker. The bunker must be emptied and cleaned prior to installation of air blasters and cannons – **adding to the cost and down-time.**

NAVCO BH vibrators produce energy that is transmitted efficiently through the bunker wall and into the coal. Through the principles of conservation of momentum and energy, energy produced by NAVCO BH vibrators propagate through the hopper structure affecting material over a large area of influence. NAVCO BH vibrators effectively reduce sliding wall friction and material strength.On the other hand, Air Blasters direct a high pressure burst of air into the bunker. The burst dissipates quickly and is not transmitted efficiently throughout the bunker. Air Blasters have a limited area of influence, **especially with difficult wet or frozen coal.**

NAVCO BH vibrators have excellent clean-out characteristics, effectively removing stagnant pockets of coal and reducing potential for spontaneous combustion. Additionally, the external installation and activation of the BH vibrator does not introduce additional air into the bunker. Air Blasters principle of operation is to introduce a blast of high pressure air into the bunker. In a bunker full of combustible material (fine coal), blasting air into the bunker by air cannon type devices can increase the potential for spontaneous combustion.

NAVCO

The Vibration Experts

href="http://www.navco.us" target="blank">www.navco.us

Attachments

coal bunker bh (JPG)

■

I would take issue that installing a vibrator is anything like as effective as installing an acoustic cleaner. I personally have come accross many instances where the vibrator has caused stress cracks in the hopper as, unlike acoustic cleaners, all the vibrational 'energy' first has to pass through the vessel before it can have any effect on the fine coal. I have also seen applications where indeed the vibrator has simply compacted the material further. Acoustic energy is 100% absorbed by the fine coal, causing maximum debonding and Acoustic Cleaners do not cause any damage to the vessel or structure. ■

If the vibrator is causing stress cracks it is not being run properly as is usually the case when suppliers sell off the shelf vibrators, not flow solutions, and they do not provide any experience or support for installation and operation techniques. Several things can cause this: - air pressure too high, poor installation (probably the biggest), operating the vibrator too long, vibrator too large for the application.

It is true that vibrators can cause compaction with certain materials - and also if not installed and operated correctly.

Running too long instead of intermittently, running when the discharge opening is closed/blocked off.

I recommend the proprietary Bin Map Solution to virtually guarantee material flow for any material in any vessel.

The unique NAVCO® Bin Mapping methodology involves a detailed evaluation of the storage vessel and its intended bulk material. Recommendations are made based on a variety of factors including bulk density, particle size, moisture content, temperature, vessel size and shape as well as material of construction. NAVCO® pneumatic piston vibrators are sized for the application and their area of influence is determined. As shown in the Diagram on this page

http://www.navco.us/industrial-bin-v...s/bhbinmap.htm

the vibrators are located on the hopper so that the areas of influence overlap; vibrations are controlled through a sequence that provides optimal flow pattern and minimal utility consumption which is also provided in detail on a complete Bin Map Solution Drawing by NAVCO®.

This solution is provided for free upon request when applicable. ■

Hello,

I just give you a tip: instead use air purging to deblock the sticky coal, you should study to apply Agigator:

- You put system to fire risk because of increasing Oxygen inside fine coal bin by compressed air.

- If the compressed air is not a dry one, you get more sticky on the bin wall.

Regards ■

dbthai said: You increase "...fire risk because of increasing Oxygen inside fine coal bin by compressed air ."

AND

"If the compressed air is not a dry one, you get more sticky on the bin wall."

THAT IS CORRECT!

Here is our Bulletin detailing these drawbacks of air surge type vibratory devices which require penetration of the bin wall and also introduce air into the coal bunker, which NAVCO vibrators do not do. NAVCO Piston vibrators are very safe for use on coal bunkers.

lWhite Paper: Air Cannons VS Piston Vibrators on Coal Bunkers ■

Air Cannons have just taken a good blasting haven't they? I was never tempted to use them on anything, something about Newtons words on action and reaction. Hoppers are tricky things. You can't put a dither on the wall and expect vibration to all go away from the wall and into the material. Otherwise you wouldn't need to bolt the ditherer to the wall so well! Assume that a modern hopper has been designed to a Standard and then examine what safety factors are available before you start shaking it to bits. Ultrasonics might have come of age if the hopper is a bit on the delicate side..like a powder tub would be. ■

louispanjang said: "You can't put a dither on the wall and expect vibration to all go away from the wall and into the material. Otherwise you wouldn't need to bolt the ditherer to the wall so well! Assume that a modern hopper has been designed to a Standard and then examine what safety factors are available before you start shaking it to bits. "

I am assuming by 'dither' you meant piston vibrator?

If so let me point out how a vibrator works, so you understand how it can vibrate material to cause flow, with out 'shaking the bunker to bits'.

It sometimes helps to view this animation attached:

You can also read this White Paper to learn how vibration works:

Vibration Comparison

And read this for a White Paper on Energy Assisted Gravity Flow Theory as it relates to storage vessels.

To learn about NAVCO Vibrators for Power Plants read this:Industrial Vibrators for Power ■

Here is a video showing why blasters are not a very good solution for coal bunkers. They way they shoot compressed air quickly into the bunker is very dangerous and can cause spontaneous combustion in coal fines:

Air Blaster Video ■

Originally Posted by Yogesh

Dear John,

Thank you very much for your reply, Actualy we are not facing any problem with the pfister pump. We are using the Pfister pump to transport the fine coal from silo to the calciner

Fine coal flows from the silo to the Pfister pump (gravitational flow) which is placed below the silo. We are giving compressed air to the silo bottom area for a smoother flow

If this flow is normal, then the load on the Pfister pump will be normal and required amount of coal will be transported

Our problem is the coal is not flowing in sufficient amount from silo to the Pfister pump. This problem is not a continues problem

Intermediately the coal will fail to flow from silo..

Hi dear,

please don't give compressed air directly.

a sonic horn by compressed air could work better. obviously you have problem with smooth flow of fine coal out of silo.

if the particles are fine enough, bridging or ratholing occurs quite common.

regards.

charlie ■

This problem was reported in 2008 so I would think it has been resolved. Discussion on the relative merits of vibrators, air cannons, air injection and sonic horns omitted to include sledge hammers, but do not address the basic reason for flow problems, that of hopper design. A design based on measured bulk property values will provide reliable performance, whereas brute force has unpredictable consequences. This first step in a failure analysis is to examine the shortfall of the basic design and establish if that can be rectified. ■