32nd Expert Forum For Explosion Protection, ATEX And Powder Transport
In early February 2014, this established theoretical and practical seminar was held for the first time in our new buildings. Almost 50 participants accepted the invitation to update their knowledge about explosion protection and to better understand powder and bulk material transport.
We were particularly pleased that we could again offer Dr. Martin Glor from SWISSI Process Safety as a speaker with special explosion protection and ATEX expertise for the 32nd VOLKMANN Expert forum.
On the first day of the seminar, based on the ATEX guidelines 95 and 137, the legal framework for equipment and plant manufacturers as well as for the operators was discussed. As part of the new internationalisation, the introduction of the equipment protection level EPL (Equipment Protection Level) according to IEC 60079-14:2007 into the groups Ga, Gb & Gc for gases (corresponding to zone 0, 1 & 2) and Da, Db & Dc for dusts (corresponding to zone 20, 21 & 22) were new.
Basic information on explosions and their emergence as well as the special features of hybrid mixtures rounded out the first day of the seminar. As a foretaste of the second day of the seminar, practical experiments on electrostatics were performed.
In the first part of the presentation, the initial subject was the principle of vacuum conveying and its differentiation and advantages over mechanical conveyors. The individual assemblies
of a vacuum conveyor were examined more closely and it turned out that our Multijector gas jet vacuum pumps and the pneumatic controls allow a vacuum conveyor to be constructed without an ignition source. The characterisation of bulk materials combined with the different conveying phases (lean phase, dilute phase & plug conveying) lead to the various practical application examples of
our vacuum conveyors. During the breaks, there were plenty of opportunities to delve into the topics and for further intensive discussion.
After being given sufficient information for the first day, a recreational and an informative guided tour through the historical town centre of Soest was followed by a visit to the brewery pub Zwiebel where the pleasant atmosphere was enjoyed.
On the second day, using the example of silo feeding, it was demonstrated how low the energy consumption with a targeted and pulsed use of compressed air and the application of the multi-stage ejector principle of our pneumatic vacuum conveying systems can be. And this even with a conveying distance of 51 metres and 1.500 kg/h of transport performance!
Concerning explosion protection, the “mysterious” field of electrostatics was in the spot light. Charging mechanisms, charge accumulations, their possible dissipation or discharge and their incendivity led to the basic scheme of electrostatics. Besides the quite famous spark discharge which was also shown in a practical experiment, a propagating brush discharge could be impressively demonstrated with a loud bang and highly visible sparks. Electronic equipment was preventively removed from the surrounding area beforehand. This kind of discharge, incendive also for dusts, absolutely must be avoided in pneumatic conveying systems and leads directly to the often discussed requirements towards feed hoses. Dr Glor, Senior Expert, SWISSI Process Safety, commented:
“Extensive vacuum conveying tests and measurements at Volkmann have shown that the specific resistance of the material in which the metallic spiral-wound filament of a feed hose is embedded, has to be less than 109 ohms to exclude incendive propagating brush discharges. Further details of these research results will be planned in the new edition of TRBS 2153 (technical rules for operational safety).
In addition, the recognition that brush discharges arenon-incendive for pure dusts (in the absence of flammable gases) has also been taken into consideration in relevant rulebooks, such as TRBS 2153.
As a protective measure, earthing is certainly central, however, it should be kept in mind that “good housekeeping“, i.e. a plant without excessive dust deposits, significantly contributes to avoiding secondary explosions due to raised dust. Our vacuum conveyors make a valuable contribution here since they not only safely transport dusts but also ensure a clean environment through the vacuum applied.
As long as there are no flammable gases and the substances are not spontaneously ignitable, our standard vacuum conveyors can be applied for all kinds of dusts. Even for those with low minimum ignition energies. Dr Glor comments:
“For large and complex systems, in case of dusts with low minimum ignition energies, the “avoidance of effective ignition sources“ should not be used as the only protective measure. However, Volkmann vacuum conveyors are compact, simple, small (d < 450 mm) and due to their design, they can be overviewed so that the “avoidance of effective ignition sources” can be applied as an effective protective measure.
Since by means of vacuum conveyors, among other things, also big bags can be filled and emptied, the special requirements towards those and other packaging were considered more closely, depending on the zone present and the minimum ignition energy.
At the end of the lecture, the collected findings were summarised and applied to our vacuum conveyors. For the pneumatic standard vacuum conveyors from the 13 possible ignition sources, only the one of the“electrostatic charge” remains. And finally, this one occurs only when our customer transports substances with the equipment. However, we do not leave our customers alone with the evaluation of this ignition source, and in 2002 decided to submit the equipment and risk analyses to a notified body for inspection. In this way, every standard vacuum conveyor can be delivered with an EC type- examination certificate (“ATEX certificate”) and allows the application in all practicable EX zones for dust, without the necessity of an inert gas as a further preventive measure.
Only when flammable gases are present, a standard vacuum conveyor upgrades to an INEX system and the emptying or conveying takes place under inert conditions. A typical application is the feeding of stirring vessels or reactors in which flammable solvents are filled or flammable gases are present. All this is documented in a further EC type-examination certificate (ATEX certificate for INEX). Since the permission for charging a zone 0 (cat. 1) is explicitly given there, this inevitably results in the highest requirements on the intrinsic safety of the special INEX control.
It has to be kept in mind that a pressure-resistant construction alone does not represent a protective measure because during the operation of every vacuum conveyor there are always several fittings open, and an explosion could spread out and accelerate unhindered (detonation). Here, all connections would have to be elaborately isolated in terms of explosion protection. For that reason, we at Volkmann take the previously described path of “avoidance of effective ignition sources” so that the pressure-resistant construction is only then applied when feeding has to be performed against an existing overpressure in a container.
Before the seminar proceeded to the practical session, there was the opportunity to present some examples of the numerous other powder handling solutions from our company. Loading stations, sack, drum & big bag emptying systems, suction scales & dosing devices, lump breakers, mobile conveyors and, of course, individually constructed feeding and conveying systems lead to perfectly matched solutions from a single source.
At the beginning of the practical session, it was vividly demonstrated in our pilot plant in small groups, which charges occur in a container when it is filled with bulk material and at the same time not earthed.
It was demonstrated with a loud bang that when this energy is released in the form of spark discharge, a gas-air mixture can easily be ignited. Practical tips on the behaviour in case of earth faults and the demonstration of a dust explosion caused a lot of excitement and further discussion.
Apart from the explosion protection tests, our vacuum conveyors could be extensively shown in action in the exhibition and every group had a competent advisor at its side.
Then subsequently, a tour through the production facility was given. It was very interesting for the participants to see how a piece of stainless steel sheet becomes a vacuum conveyor or a loading station and how varied the range of manufacture and how extensive the flexibility at our company is.
Many participants were not aware of the fact that even the multi-stage vacuum generators are produced at our facility. It is always exciting to see the ideas our customers come up with when they see the various“powder handling” products in use and in the production facility. For the seminar participants, it was also interesting to look over the shoulder of the development engineers at their CAD workstations when generating 3D models.
All in all a successful event that we would like to repeat. It should be highlighted that, apart from the actual programme parts, there was sufficient time for individual questions and talks – also among the participants. One participant has attended his fourth seminar to be
really up to date in terms of explosion protection and conveyor technology. The thesis “when you don’t know why it came to an explosion, it was always the electrostatics“ shown at the beginning of the seminar can now certainly be regarded in many more ways by the seminar participants. After having clarified the last questions in individual discussions, the participants were wished an“uneventful”
future goodbye (from the perspective of explosion protection).
Meinung der Teilnehmer:
“I enjoyed the seminar very much – (contents, presentation and organisation). I could pick up something new and important for my professional everyday life. I would also like to thank you for the excellent support from the Volkmann people. I will recommend the seminar to my colleagues.”
Ulrich J. Müller, Leitung Technika, Clariant
„I really liked the seminar.“
Ralf Degener, Dipl.-Ing. M.Sc., Momentive Specialty Chemicals
“I gained a lot from the participation in the expert forum. I can only recommend this seminar. The seminar was organised very well and the technical aspects and specialist presentations fully met my expectations.”
Michael Deuerling, Process Design & Support, Basell Polyolefine
“The seminar was interesting and rich in content. Mr. Ramme and Mr. Dr. Glor gave the presentations in a competent and entertaining manner.”
Ferdinand Schnitker, Dipl.-Kfm., Deutsche Saatveredelung
“I liked the seminar very much!” Everything was perfect. The guided tour and the dinner together were also a successful end on the first seminar day.“
Knut Warnecke, Zentralbereich Forschung und Entwicklung, H.C. Starck
“The seminar was very informative. I found the mix of theory and practice very pleasant.”
Christian Diller, Entwicklungsingenieur, Concept Laser
“The presentations were very interesting and the info was very useful for the everyday life in the company.”
Robert Gaffke, Asset- & Processmanager, BASF