Re: Silo Honking
Silo Honking is due to the slip-stick behaviour of the granular material between the material itself and the silo wall. For smooth wall, thin tall silos pulsations occur mostly in mass and mixed flow patterns but some core flow silos have also been known to honk. The pulsations occur up to a certain height known as critical height and below that they stop. Since you are designing aluminium silos there are severe structural implications and also variable discharge rate issues. There are a number of ways to address this issue easiest remedy is to roughen the cone wall surface up to critical region. Silo cone inserts work also. ■
Re: Silo Honking
Thanks for the information Mantoo.
Is there a way to determine the critical height of the product up to where honking can occur?
We are also considering to add small internal cones at certain heights of the cylinder, thus reducing the pressure in the cylindrical shell in order to avoid the slip-stick behaviour.
This in case roughening up the cone (and part of the cylinder) is rejected by the client. (These silos need to have mass flow at any time as the product stored comes from a mixing blender, and need to be withdrawn from the silo in a "first in first out" sequence.) ■
Re: Silo Honking
If mass flow is required then wall roughening is not an option. Only method I am aware of measuring this critical height is experimental maybe there is a way of calculating it also.
Since silo cone insert is an art rather then a science be very careful in its designing. There are few manufactures who sell these cones under various trade names. Normally single cone of suitable diameter is fitted at appropriate vertical distance from the silo outlet. I would prefer the cone angle to be similar to the silo cone angle so that there is no preferential flow either on the insert or silo cone. ■
Re: Silo Honking
Thanks Mantoo for your reply. This is very helpfull.
By the way, I am aware of the "art" of inserts in silos. We have learned from years of experience that the design loads on these inserts should be taken very conservative.
Simple assumptions combined with increased safety factors do the job, rather than trying to figure out what really happens in the silo with inserts.
The disadvantage of this "state of the art" engineering is that when whe have to compete with other firms, that do not have this experience, we often loose the project. But this is an other discussion.
Kind regards
Stef. R. ■
Re: Silo Honking
Edinburgh University led a research project into this a couple of years ago and produced quite a good report on the causes and looked at some alternative solutions.
The contact at Edinburgh is Dr Jin Ooi (J.Ooi@ed.ac.uk), it may be worth making contact with him. ■
Re: Silo Honking
Thanks RPD
I will contact him immediately.
Stef.R. ■
Re: Silo Honking
We have been very successful in designing anti-dynamic tubes in our aluminum welded silos to prevent honking and quaking. They are simple and inexpensive, and they work. Please e-mail our company for more information. info@tanks.com
Keith McGuire, PE
Columbian TecTank ■
Re: Silo Honking
Dear Sir
the University of Karlsruhe in Germany has done quite good research in that field under a special research program SFB219. There is a doctorial thesis of Dr. Tejchman. He is now Professor in Polen (Katedra Podstaw Budownictwa i In¿ynierii Materiaowej
Wydzia Inynierii Ldowej i Œrodowiska
Politechnika Gdaska
tel: (058) 347-14-81
e-mail: tejchmk@pg.gda.pl).
You may ask him or the University of Karlsruhe about this matter. Tell him you got his contact data through me.
Best of luck
Dr. Tarek Nasr
Scherr+Klimke AG
Ulm, Germany ■
Silo Honking
Although the term 'silo honking' is new to me the problem is not! There is a safe, remove and effective method to prevent this occuring with any dry material, powders, ash, granuals etc., within silos and hoppers. Primasonics Acoustic Cleaners have been installed on hoppers and silos in a wide range of industries in over 40 countries worldwide with excellent results By installing the correct model of sonic horn and sounding it for a few seconds at pre-determined intervals, both ratholing and bridging of material within silos and hoppers is eliminated and mass flow at maximum output is the result.
Can I suggest that you visit one of the following web sites to gain a better insight into how these acoustic cleaners are designed and operate. There is a US web site - www.sonic-horns.com - which contains 'An Irishman's Guide to Acoustic Cleaning' along with specific information on their application within silos & hoppers. There is also a silo questionnaire which can either be filled in on line or downloaded. The other web site worth visiting is - www.primasonics.com - which is a little bit more technical.
If you prefer you can e-mail me directly on - sound@primasonics.com
The end of your problem is in sight!
Donald F Cameron
Managing Director
Primasonics International Limited ■
Re: Silo Honking
Thank you Mr. McGuire. I will contact your company for the information about the anti-dynamic tubes within a few days.
Also thank you Dr. Tarek Nasr. I have just sent an e-mail to Professor Tejchman for information about his doctoral thesis.
I did not forget to mention I got his name from you.
Thank you Mr. Cameron for your suggestion to use sonic horns. Although the problem here is not directly ratholing or bridging, I will consider this solution.
Anyhow, we are very interested in this product as we often have to deal with these problems as well. For further project we will not hesitate to contact you. ■
Sonic Horn
Originally Posted by Stef R.
I have to design 650 m3 Aluminium Silos for the storage of PET-granules.
These products are known to induce the famous "Silo honking".
I know this phenomena can be counteracted by building in internals in the silos to create a "first in - last out" flow. However these internals are quit expensive and often cause problems for the stability of the silos.
Please let me know if there are any other solutions to prevent the silos from honking.
All help will be much appreciated.
Many thanks
Stef.R.
Obviously we are not talking about bridging or ratholing in a hopper or silo. But still grateful for Mr. Cameron's kind advice. this is "silo honking".
Silo honking is an acoustical emission with a fundamental frequency of several hundred Hertz and an intensity often greater than 100dB. It occurs when a silo is discharging and is similar to the “honk” of a lorry horn. The high amplitude of the honk makes it a significant noise pollution issue for workers at the site and for neighboring businesses and residents.
Sonic horn is acoustic cleaning technology by generating vibration under low frequency & high energy sonic wave. It is installed on hopper & silo with powder, ash, granules inside. It helps to get good mass flow.
Two different topics we are talking about.
Charlie
Konli Environmental Sci-Tech
Engineer ■
Silo Honking
Dear forum
I have to design 650 m3 Aluminium Silos for the storage of PET-granules.
These products are known to induce the famous "Silo honking".
I know this phenomena can be counteracted by building in internals in the silos to create a "first in - last out" flow. However these internals are quit expensive and often cause problems for the stability of the silos.
Please let me know if there are any other solutions to prevent the silos from honking.
All help will be much appreciated.
Many thanks
Stef.R. ■