Detonation In Pneumatic Connveying Pipes
Dear Dr. Groenewold,
I do not wish to be pedantic, but I think we are dealing with potential dust explosions, not with detonations. or? You indicate that the dust is sugar.
We are protecting ducts and connecting pipes with the HOERBIGER explosion relief valve. Please establish contact and I will send you a few photos of Australian applications in a starch / dextrin mill.
There is no need for burst panels, especially if the hoppers are indoors or in enclosed areas. Our relief valves will do the job.
Our website is www.hoerbiger-kt.com and follow the link PRODUCTS down to Explosion Relief Valve.
Many thousands of valves are in service in Europe, fully ATEX compliant.
Kind regards
Dieter M Blaufelder ■
Dust Explosions
Dear Mr. Groenewold,
I made several pneumatic conveying system for sugar (dilute fase) and I had never problems with sugar dust in the pipe. Normally, the dust concentration in the conveying pipe is above of the explosion limit. You must be careful with dust collector (antistatic felt and burst panel ). As far the pipe line, you can use wire between flanges for static energy elimination. All installation must be grounded.
Regards,
Gumercindo Campos Brito Neto
Technical Engineer
B&M Controle Ambiental ■
Detonation In Pipe
let me see if I understand your concern.
You are conveying sugar neumatically in diluted phase .
you believe that your product can explote in your pipeline (no it cant, not in the pipeline).
You have a potentially explosive mixture at the start and end of conveying (yes, not a problem though).
Does sugar form crusts in the pipeline?
Is the pipeline insulated? I believe it is not, right?
Can hot or ignited matter enter your pipeline? Not really.
Then you are more concerned with dust explosion in the dust collector plennum or fire in the cyclone, or in the filter.
It is very difficult if not impossible, to burst a pneumatic conveying pipeline because of an explosion in the dust collector.
I have done it , but you really have to work hard at it.
Not what you encounter in the open world ( not experimental) at all.
You can burst your collector open with little problem though, and you can burn your cyclones and filters.
I believe sugar standards force you to have explosion (rupture disks) vents on your collectors, many industries do it, not only sugar.
Now what are you going to do with the sugar inside the collector if a rupture disc bursts or a vent gate opens, you cannot dump it with the rest of the sugar.... See that your supplier considers a diverter gate for material compromised in a fire or explosion. and ways to inspect and clean up.
Good luck.
You will do fine. Dust explosions in sugar pneumatic conveying, I understand, are not frequent. Ask Jack Hilbert or Paul Solt (pccsolt@enter.net), they might know, they have been installing systems world wide for ages.
Marco ■
Detonations Within Dust Conveying Lines
Mr Groenewold,
I understand your question and would like to address this with some clarity.
As you quite rightly noted, dust explosions (Deflagration) which are driven into pipelines can accelerate and lead to the transition from deflagration to detonation, this is a well known and proven fact.
As one of your previous replies suggests deflagrations within pipelines would not normally cause an inormous amount of damage, however if the transition from deflagration to detonation should occurr then the pressure regium would immediately increase to many tens of bars and the flame / pressure velocity could be in the region of 1000's m / s
Although an incipient dust explosion originating within a pipe is possible, providing the correct dust mixed with air is presented with the optimum ignition. In real terms this would be very un-ilkey, however all steps should be made to prevent an ignition source enterring or originating within the pipe.
The real threat from detonation is when a dust explosion (deflagration) originates within one of the vessels connected to the pipe, ie. The dust filter or the cyclones.
Here in addition to protecting the vessel from the effects of an explosion it is fundamental to de-couple the vessel (explosion Isolation) to prevent the explosion propogating to other process equipment or indeed leading to detonation within the pipeline as required under ATEX EN1127
Explosion isolation on pneumatic conveying lines can be achieved by the installation of explosion barriers, either chemical suppression or mechanical fast acting slam valves.
Please find attached a shortened version of a paper some of my colleagues published early this year in association with the ICHEME.
Please don't hesitate to contact me for any further assistance.
Regards,
Dave Price ■
Re: Detonation In Conveying Pipes - Atex
I concur with Mr. Price. The real danger is in the vessels that connect to the pipeline.
At least from my experience, having an explosion in the pipeline is not that easy. I believe my previous comment could have been misunderstood.
I would like to know if Mr. Price has experienced a pipeline explosion (not a receiving hopper explosion).
To my knowledge, I am the only one that has been capable of doing it, and I am not going to tell you how to do it.
Regards,
Marco ■
Dust Explosion Protection For Pneumatic Conveying Pipelines
To prevent dust explosion hazards in pneumatic conveying pipelines the method that I have used is NFPA approved method "pressure containment". To implement this method first find out the Kst of the dust being conveyed, and then select the pipeline material and pipeline wall thickness that will contain this pressure. Pipelines must be protected against dust explosions if the conditions for a dust explosion "triangle" can occur.
Regards,
Amrit T. Agarwal
Consuting Engineer
Pneumatic Conveying Consulting
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Re: Detonation In Conveying Pipes - Atex
Interesting.
Long time ago when we were designing the HYL 1 reactors for SIDOR Venezuela , the issue of explosion containment cane again into discussion.
We were handling Hidrogen and Carbon Monoxide atmospheres, in a reactor (fixed bed that had to be oppened to the athmosphere every 8 hrs or so,
There were 4 reactors for each unit and the particular plant had if i remember well 12 reactors , Large things though 1000 metric tons each. , it was descided then to contain any potential explosion . Not to vent, but contain .
Therefore the vessels were design for the maximun pressure that could be generated by the worst explosive mixture possible . the vessels became thicker . explosions did occur and still ocurr ,( this plant is 25 years old and is still in operation, not for long I hope),
The equipment took the punishment fine.
A note here.
We did not needed to modify the specification of the pipework that fed and collected from the reactors , the stesses on the pipework even during an explosion were not enough to need beefing up the piping. The work was done at the time with Pulmann (Kellog) Swindell , our partner at he time.
Regards
Marco ■
Re: Detonation In Conveying Pipes - Atex
Dear Mr Groenewold,
It comes as a surprise to note that sugar dust is considered as a potentially explsosive substance. However that being the case and thinking laterally is it feasible to go in for a close looped nitrogen conveying system thereby starving the process of any oxygen to initiate & sustain an expslosion.
This way we do not have to worry about a whole lot of expensive safeguards.
Regards
Harish ■
Re: Detonation In Conveying Pipes - Atex
Dear colleagues,
thank you for all the elaborated answers.
The experts that we work together with, share the opinion of Mr Price. Their technical solution is to but a burst panel on the receiving hopper and a fast acting valve on the nozzle to conveying line - for decoupling. This prevents the explosion to propagate into the line. The second measure is to pass the product through a metal detector before charging it.
This a logical and clear concept. I know that there are other technical solution, but the result is the same.
The thing is: I do not BELIEVE that the explosion can enter the conveying line. If I am right, the fast acting valve can be omitted. The background is that a valve in a conveying line never is a good solution (though possible). And it is very expensive, because you of complicated mechanics and you need electronics for it (which are not necessary for the burst panel alone).
So here as a more resticted question:
Can an explosion enter a pneumatic conveying line (assuming that there is an explosive atmosphere)????
p.s.: At my first posting, I did not want to restrict my question that much because I did not want to restrict the discussion too much. Thank you again for all the answers.
pp.s.: Sugar IS regarded as explosive in Europe. But I took sugar only as an example. ■
Safe Pneumatic Conveying System
Just to sum-up the discussion I would like to recommend to visit
www.Volkmann.info
where you can see safe Vacuum Conveying Systems for all
kind of dust-EX-zones as well as gas-EX-zones. These conveyors
are fully ATEX approved by the German TUV.
Best Regards
Thomas Ramme ■
Re: Detonation In Conveying Pipes - Atex
Try this link:
http://www.safetynet.de/Publications/articles/Lunn2.PDF
It is 4 years old but I found it useful summary of knowledge on flame behavior in pipelines at the time.
I also have a vague recollection of some work that was done in the UK which said that if was impossible for a flame front to pass through a pipe of less than a certain diameter, and it wasn't that small, 3 or 4"? I think the theory was something around the cooling effect of the pipe wall extinguishing the flame. The proposition was that if you had a large diameter pipe you could split it into a number of parallel lines and you then didn't need to worry about propogation between vessels.
I didn't feel comfortable with the concept so filed it in the bottom draw but I can't find it now, it must have fallen out of the bottom draw into the bin. Can anyone remember what it was about, it may have some bearing on the original question? ■
Re: Detonation In Conveying Pipes - Atex
I concurr, the flame cannot enter the conveying line if there are solids flowing trough it. I believe it is a question of the speed pf sound being smaller in a pneumatic conveying line .
I am sure David Mills has written somethingabouth that.
Marco ■
Re: Detonation In Conveying Pipes - Atex
I feel uncomfortable with the statement "the flame can not enter the pipe if there are solids flowing in it".
That is probably true if the solids concentration is above the Max Explosible Concentration.
If it is in the explosible range however, and aren't systems often during start up and shutdown for example, then does the powder not act as a fuel rather than an extinguishant? ■
Re: Detonation In Conveying Pipes - Atex
Yes, I would myself, but I have tried it out.
I have been handling explosive metallic dust with air, with Nitrogen, with Hydrogen, with Carbon Oxide and with Oxygen enriched air, for more than 10 years.
I am not sure how it works, but the flame will not enter the pipeline when there are solids flowing.
I believe I remember a paper from the Thames Institute, a long time ago, mentioning that the Mach number is a function of the square root of K/M, which means that the higher the mass of the conveying solids, or phase density, the lower the Mach number.
So a flame, and for that matter, an explosion, can only propagate at the speed of sound, which means that the speed of sound, in a conveying line, with solids flowing, will be very low, so a flame will not be able to penetrate. Essentially, it will be pushed out.
Regards,
Marco
P.S. I will attach a picture when I find it. ■
Re: Detonation In Conveying Pipes - Atex
Hello Mr. Groenewold,
please look at out our Homepage: www.piab.de, here you will find some applications for conveying systems. We are also able, to find an layout with Atex proven conveyors for your need. We have still some installations with our pneumatic driven conveyors for sugar transport. In case of interest, please contact us.
Kind Regards
Johannes Krumme ■
Explosion Entyering A Pipeline
Lets see if i have this right
a pressure wave explosion
can only travel at the speed of sound,
the speed of sound is related to the mass and the termal conductivity of the media.
the pneumatic conveyor has much lower speed of sound due to the mas being conveyed
if the speed of sound of the media is smaller than the conveying velocity , the explosion cannot enter the conveying line .
some people handle gunpowder in pneumatic conveying lines.
and sugar of course .
when an explosion occurs it is generally in the reception hopper .
very rarely in the line .
You should use appropiate explosion venting on the hoppers .
Calculate the air voluimen , calculalte the amount of material to thet can react using that air . calculate the products of combustion, calculate the adiabatic temperature , from there you can calculate the gas volumen , confine that gas volumen in your bin and you can acalcualte the after explosion pressure on the bin , if the bin can not hold it then, use explosion venting.
you should consider the way the pressure wave will travel in your bin , simulating different ignition points , use the worst case to locate your vents .
Talk with Paul Solt
regards
Marco ■
Re: Detonation In Conveying Pipes - Atex
It will be very interesting to know if any body is aware of any incidence of explosion within pneumatic conveying lines for a ST 1 (up to Kst 200) products, while the system is running under normal steady state lean phase conditions. Isn’t the solid concentration above the “maximum combustible concentration” so one corner of explosion triangle is missing. I have asked this question to a number of experts on explosive testing but have never got a clear answer.
As far as propagation in the conveying lines again it is considered that upto 4” line the quenching effect of pipe wall is so high that the flame does not travel again it is debatable and I have also read somewhere work showing propagation of flame in ” pipes up to 100m. It would be nice to know if anyone has any experience of it or have any literature about it and would like to share it everyone.
Explosions in silos and hoppers are documented and yes venting, containment, suppression or inerting should be used. ■
Re: Detonation In Conveying Pipes - Atex
We had handled higly combustible metal concentrates in lean fase for 22 years now , we started with a 20 ton per hr plant , scaling up to a 200 ton per hr plant , this has logged more than 10 million tons of metal this year .
we have never had an explosion ride into the pipeline although we have conveyed for years using air to transport hot metal , fires in reception hoppers were frequent , even meltdown , we have had explosion at the discharge but they have never traveled into the pipeline .
Foto of the discharge 10 t/h facility attached thsi was previowly published at the IFPS meeting in pittsburgh many years ago ,republished in ask Joe . Hot pneumatic conveying . and in the ADIAT price publication , the project was awarded thge national ADIAT price for industrial Innovation 2000
there is now another large facility in Kwinana Australia also logging abouth 100 tons per hr and in the future we might be transporting hot radioactive materials .
Marco
Attachments
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Untitled
In a pipe lower of 100mm, the wave detonation not spreads. ■
Detonation
i actually believe it depends on the speed of sound .
a pressure wave can only propagate at the speed of sound , a pneumatic conveying system has the speed of sound lowered by the solids loading , this a n explosion cannot propagate trough the pipe , the expansion of the explosion increase the volumen and thius the speed if it reaches the speed of sound of the media that is it .
You can find multiple references in Tn books , Klinzing- Marcus et all for one.
Marco
Marco ■
Pipe Diameter And Speed Of Sound
Dear LBa77,
I have heard and read this statement often, that a detonation does not develop in a pipe of less than 100 mm (4").
Do you know: Has it been verified by experiments?. If so, please tell us the publication!
Dear Marco,
Of course, the speed of sound is the maximum velocity that a detonation can reach (that's physics). I assume that the detonation may be slower because there is also a chemical reaction involved (the combustion of dust).
But: Do you know how to calculate the speed of sound of a gas with solids dispersed into it. I guess it is not only a matter of the average density (but I don't know).
Thank you for your contributions. ■
Re: Detonation In Conveying Pipes - Atex
many books deal with the speed of sound
the general formula c= sqr (Cp/Cv x p/ro) from Eshbach
where ro is the density of the gas solid mixture, the higher the phase density the slower the speed of sound Cp and Cv also applies to the solid gas mixture
more specific experimental data can be found in J. Klinzings , R Marcus , and F. Risk work , almost avery publication in Pneumatic conveying deals with the number , as it is believed that you cannot go beyond this value , I understand Hismelt in australia works at or beyond the limit value, but you might need to contact them. ■
Brass Fittings In A High Explosive Athmosphere
Of course you are kidding , brass fittings in diameters bigger than 2 inches get expensive compared with Iron and aluminum and even stainless steel.
and they are heavy, low melting point, fragile fracture treads tend to wear fast .
Not my pet material for pneumatic conveyumg.
Marco ■
Spark Detecting Devices
Hello,
to detect ignition sources like sparks you can consider spark and fire detection with automatic extinguishing (water, gas, ...)
This is NOT for incipient explosions, it is designed to recognize and extinguish some ignition sources in ducts and vessels
For a view you can go to:
http://www.explosioncontrolada.com/excon-tbdemo.html
Remember:
this is complementary to the other protetion devices you where adviced to and do NOT replace inertization or explosion vents, u.so.
Regards
Carlos Schultz
ex.control@gmail.com
buenos aires
. ■
Re: Detonation In Conveying Pipes - Atex
Is this working in an industrial scale or large pilot plant. if so where.
marco ■
Water In A Conveying Line Is Not A Good Idea
as we mentioned before , if there is to be a conflagration in an uninsulated pneumatic conveying line it will take place in the reception hopper .
you might want to consider inerting the hopper , but if the feed line uses air as conveying media, its effect will be at bets marginal , using water can plugg the exit or generate crusts in the pipeline and the disengagement area , if tou generate a crust in the pipeline the fire will propagate to the line and might damage it , or even melt it .
Have it from one that knows , I melted one .
if you want to turn off a fire in the disengagement hopper , i would try switching the conveying gas to CO2 or nitrogen, or turning it off , before trying anything else or steam or water. Even more, if it is DRI. remember DRI reacts with water and the conveying line will undergo a radical thermal excursion that can brake it . and remember to redirect the discharge to a safe container , not to the furnace or the reception bins unless it is a hot pneumatic conveying system , but then a fire will not be , an exception , the material inside will already be at 800c and the gas will either be inert or reducing gas, if conveying with air , your disengagement bin will be hopefully designed for the oxygen fraction- / material combustion temperature.
just my grain of sand friends ..
marco
Originally Posted by explocontrol
to detect ignition sources like sparks you can consider spark and fire detection with automatic extinguishing (water, gas, ...)
This is NOT for incipient explosions, it is designed to recognize and extinguish some ignition sources in ducts and vessels
For a view you can go to:
http://www.explosioncontrolada.com/excon-tbdemo.html
Remember:
this is complementary to the other protetion devices you where adviced to and do NOT replace inertization or explosion vents, u.so.
Regards
Carlos Schultz
ex.control@gmail.com
buenos aires
.
■
Detonation in Conveying Pipes - ATEX
Dear colleagues,
with the ATEX regulations we have to face the question of the probability of (dust) detonations in pipes for (dilute phase) pneumatic conveying.
Assume the following plant:
Blower - product charging with rotary valve - conveying line 3 inch - receiving hopper with filter hoses inside. Discharge with rotary valve. Material to convey: sugar.
The dust explosion protect may be like follows:
- antistatic needle felt for filters
- burst panel to protect receiving hopper
- pipe: ????
At least during startup and shut down, we have an explosive atmosphere in the pipe. Experts say:
(1) An explosion may be ignited by either by a foreign body or coming from the receiving hopper.
(2) In a pipe, a (dust) explosion turns into a detonation resulting in pressures far beyond the max. explosion pressure of the product.
Protection measures against this are both, complex and expensive.
Is there any expertise "proving" that in the fundamental plant descibed above, detonation cannot take place?
Has a detonation ever taken place in such a system? ■