SIST-TP CEN/TR 17838:2022
(Main)Use of plugs of bulk material in screw conveyors and product receivers for explosion isolation
Use of plugs of bulk material in screw conveyors and product receivers for explosion isolation
Screw conveyors are mechanical devices for the continuous move, discharge or variable rate
feeding of bulk materials in form of powder, granules or grain. They are often used
horizontally or at a slight incline to discharge or feed silos, storage bins, cyclones, filter units,
mills or other equipment in many bulk handling industries.
This Technical Report describes requirements on screw conveyors which can in addition be
used as explosion isolation systems to prevent a dust explosion transmission into connected
plant items.
The scope of this technical report is limited to rigid tubular screw conveyors which consist of
a spiral blade coiled around a shaft held in external bearings (the rotating part of the
conveyor is sometimes called “auger”). Additional internal bearings can be necessary if the
tubular screw conveyor exceeds a certain length.
Schneckenförderer Explosions-Entkopplungssysteme
Dieses Dokument beschreibt die Empfehlungen für die Konstruktion und den Einsatz von Schneckenförderern und Produktauffangbehältern, die zusätzlich als Mittel zur Explosionsentkopplung eingesetzt werden können, um die Übertragung einer Staubexplosion auf angeschlossene Anlagenteile durch das darin befindliche Schüttgut zu verhindern.
Die in diesem Dokument gegebenen Empfehlungen sind verfahrenstechnische Maßnahmen, da die Eigenschaften des Schüttguts die Wirksamkeit dieser Maßnahme wesentlich beeinflussen (z. B. Fließ- und Explosionseigenschaften). Produktauffangbehälter und Schneckenförderer können nicht als Schutzsysteme im Sinne der ATEX-Richtlinie angesehen werden.
In Bezug auf Schneckenförderer beschränkt sich der Anwendungsbereich dieses Dokuments auf starre, röhrenförmige, einzelne Schneckenförderer, die aus einer spiralförmigen Schaufel bestehen, die um eine Welle gewickelt ist, die von externen Lagern gehalten wird (der rotierende Teil des Förderers wird manchmal auch als „Förderschnecke“ bezeichnet).
ANMERKUNG Wenn der Rohrschneckenförderer eine bestimmte Länge überschreitet, können zusätzliche Innenlager erforderlich sein.
Dieses Dokument enthält Anwendungsgrenzen, bei denen ein Schüttgutpfropfen in einem Schneckenförderer nicht möglich/ausreichend ist, um eine Explosionsentkopplung zu erreichen, sowie Anwendungsbereiche, bei denen ein Schüttgutpfropfen nicht erforderlich ist, um eine Explosionsentkopplung zu erreichen.
Dieses Dokument behandelt nicht die obligatorische Risikoanalyse und Risikobewertung der Zündgefahr, die für die Anwendung der Schneckenförderer und Produktauffangbehälter durchgeführt werden. Die obligatorische Risikobeurteilung umfasst die Bedingungen für das Anlaufen und Abschalten, wenn möglicherweise kein Schüttgutpfropfen vorhanden ist, das eine Explosionsausbreitung verhindern könnte. Um dieses Restrisiko zu mindern, kann als zusätzliche Maßnahme z. B. ein herkömmlicher Schieber verwendet werden, der die Flammenübertragung verhindert und dem zu erwartenden maximalen Explosionsdruck standhält.
Utilisation des bouchons de matériaux en vrac dans les convoyeurs à vis et les bacs de réception à des fins d’isolation contre les explosions
Le présent document décrit les recommandations relatives à la conception et à l’utilisation des convoyeurs à vis et des bacs de réception qui peuvent également être utilisés comme moyen d’isolation d’explosion afin d’empêcher la transmission d’une explosion de poussières aux éléments d’installation connexes à l’aide du produit en vrac contenu à l’intérieur.
Les recommandations données dans le présent document sont des mesures procédurales, car les propriétés du produit en vrac ont une incidence substantielle sur l’efficacité de ces mesures (par exemple, les caractéristiques d’écoulement et d’explosion). Les bacs de réception et les convoyeurs à vis ne peuvent pas être considérés comme des systèmes de protection au sens de la Directive ATEX.
En ce qui concerne les convoyeurs à vis, le domaine d’application du présent document est limité aux convoyeurs à vis rigides, tubulaires et simples qui consistent en une lame hélicoïdale enroulée autour d’un arbre maintenu par des paliers extérieurs (la partie rotative du convoyeur est parfois appelée « vis sans fin »).
NOTE Des paliers intérieurs supplémentaires peuvent être nécessaires si le convoyeur à vis tubulaire dépasse une certaine longueur.
Le présent document inclut les limites d’application pour lesquelles un bouchon de produit en vrac dans un convoyeur à vis n’est pas possible/suffisant pour assurer l’isolation d’explosion, ainsi que les plages d’application au sein desquelles un bouchon de produit en vrac n’est pas nécessaire pour assurer l’isolation d’explosion.
Le présent document ne traite pas de l’analyse des risques et de l’évaluation du danger d’inflammation qui doivent obligatoirement être mises en œuvre pour l’utilisation des convoyeurs à vis et des bacs de réception. L’évaluation des risques est obligatoire et comprend les conditions de mise en marche et d’arrêt lorsque potentiellement aucun bouchon de produit n’est présent pour empêcher la propagation d’une explosion. Pour atténuer ce risque résiduel, il est possible, par exemple, d’utiliser comme mesure supplémentaire une vanne guillotine traditionnelle qui empêche la transmission des flammes et est capable de résister à la pression maximale d’explosion prévue.
Uporaba čepov iz sipkega materiala v polžastih transporterjih in sprejemnikih izdelkov za namene eksplozijske izolacije
Polžasti transporterji so mehanske naprave za neprekinjeno premikanje, odvajanje ali dovajanje sipkega materiala v obliki prahu, granul ali zrn s spremenljivo hitrostjo. Pogosto se uporabljajo vodoravno ali pod rahlim nagibom za praznjenje ali polnjenje silosov, skladiščnih zabojnikov, ciklonov, filtrirnih enot, mlinov ali druge opreme v številnih panogah za ravnanje s sipkim materialom.
To tehnično poročilo opisuje zahteve za polžaste transporterje, ki se poleg tega lahko uporabljajo kot sistemi za izolacijo eksplozije prahu, da se ne prenese v povezane elemente obrata.
Področje uporabe tega tehničnega poročila je omejeno na toge cevne polžaste transporterje, ki so sestavljeni iz spiralnega rezila, navitega okoli gredi, pritrjene na zunanjih ležajih (vrtljivi del transporterja se včasih imenuje »polž«). Če cevni polžasti transporter presega določeno dolžino, so morda potrebni dodatni notranji ležaji.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TP CEN/TR 17838:2022
01-november-2022
Uporaba čepov iz sipkega materiala v polžastih transporterjih in sprejemnikih
izdelkov za namene eksplozijske izolacije
Use of plugs of bulk material in screw conveyors and product receivers for explosion
isolation
Schneckenförderer Explosions-Entkopplungssysteme
Utilisation des bouchons de matériaux en vrac dans les convoyeurs à vis et les bacs de
réception à des fins d’isolation contre les explosions
Ta slovenski standard je istoveten z: CEN/TR 17838:2022
ICS:
13.230 Varstvo pred eksplozijo Explosion protection
53.040.20 Deli za transporterje Components for conveyors
SIST-TP CEN/TR 17838:2022 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TP CEN/TR 17838:2022
CEN/TR 17838
TECHNICAL REPORT
RAPPORT TECHNIQUE
July 2022
TECHNISCHER REPORT
ICS 13.230; 53.040.20
English Version
Use of plugs of bulk material in screw conveyors and
product receivers for explosion isolation
Utilisation des bouchons de matériaux en vrac dans les Schneckenförderer Explosions-Entkopplungssysteme
convoyeurs à vis et les bacs de réception à des fins
d'isolation contre les explosions
This Technical Report was approved by CEN on 13 June 2022. It has been drawn up by the Technical Committee CEN/TC 305.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 17838:2022 E
worldwide for CEN national Members.
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Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Tubular screw conveyors and explosion isolation . 6
4.1 General. 6
4.2 Influence of the bulk material . 9
4.2.1 General. 9
4.2.2 Minimum Ignition Energy . 10
4.2.3 Flow properties . 10
4.3 Specifications for tubular screw conveyors for explosion isolation . 12
4.3.1 General specifications . 12
4.3.2 Tubular screw conveyor without removal of part of flight . 12
4.3.3 Tubular screw conveyor where part of flight is removed . 12
5 Product receivers and explosion isolation . 13
5.1 General. 13
5.2 Bulk material and design of product receivers . 13
5.3 Specifications for product receivers for explosion isolation . 17
Bibliography . 19
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European foreword
This document (CEN/TR 17838:2022) has been prepared by Technical Committee CEN/TC 305
“Potentially explosive atmospheres - Explosion prevention and protection”, the secretariat of which is
held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
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Introduction
Screw conveyors are mechanical devices for the continuous movement, discharge or variable rate feeding
of bulk materials in form of powder, granules or grain. They are often used horizontally or at a slight
incline to discharge or feed silos, storage bins, filter units, mills or other equipment in many bulk handling
industries.
Product receivers are silos, bins and hoppers used for temporary storage of bulk materials. The design of
product receivers is determined by parameters such as storage capacity, throughput and overall height
but also products properties such as powder cohesion, coefficient of sliding friction and permeability.
Both screw conveyors and product receivers can under certain conditions act as explosion isolation
devices/systems in combination with the bulk material being handled by these pieces of equipment. This
document presents the aforementioned conditions that are necessary to ensure explosion isolation.
These conditions include dust properties and dust explosion properties, dimensions of the equipment
and minimum requirements regarding the dimensions of the bulk material plugs.
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1 Scope
This document describes the recommendations for the design and use of screw conveyors and product
receivers which can in addition be used as a means for explosion isolation to prevent a dust explosion
transmission into connected plant items by using the bulk material which is inside.
The recommendations given in this document are procedural measures since the properties of the bulk
material affect the efficacy of this measure essentially (e.g. flow and explosion characteristics). Product
receivers and screw conveyors cannot be considered as protective systems under the scope of the ATEX
Directive.
As far as screw conveyors are concerned, the scope of this document is limited to rigid, tubular, singular
screw conveyors which consist of a spiral blade coiled around a shaft held by external bearings (the
rotating part of the conveyor is sometimes called “auger”).
NOTE Additional internal bearings can be necessary if the tubular screw conveyor exceeds a certain length.
This document includes limits of application where a plug of bulk material in a screw conveyor is not
possible/sufficient to achieve explosion isolation and also application ranges where a plug of bulk
material is not necessary to achieve explosion isolation.
This document does not address the mandatory risk analysis and ignition hazard assessment, which are
performed for the application of the screw conveyors and product receivers. The mandatory risk
assessment includes start-up and shut-down conditions, when potentially no plug of material is present
to prevent explosion propagation. To mitigate this residual risk, it is possible to use as an extra measure,
e.g. a traditional gate valve which prevents flame transmission and is able to withstand the expected
maximum explosion pressure.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
screw conveyor
mechanical device for the continuous movement, discharge or variable rate feeding of bulk materials in
form of powder and/or granules
Note 1 to entry: Screw conveyors are often used horizontally or at a slight incline to discharge or feed silos, storage
bins, filter units, mills or other equipment in many bulk handling industries.
3.2
product receiver
enclosure such as silo, bin or hopper used for temporary storage of bulk materials
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3.3
fluidity factor
ffc
dimensionless characteristic parameter of the flowability of bulk materials calculated from the ratio of
the consolidation stress to the compressive strength
Note 1 to entry: See ASTM E 6773-02, Standard shear test method for bulk solids using the Schulze ring shear tester
[10].
3.4
compressive strength
σ
c
resistance of a material to breaking under compression
Note 1 to entry: See ASTM E 6773-02, Standard shear test method for bulk solids using the Schulze ring shear tester
[10].
3.5
consolidation stress
σ
1
decrease in volume of the bulk material from applied stress (force per unit area) under defined conditions
Note 1 to entry: See ASTM E 6773-02, Standard shear test method for bulk solids using the Schulze ring shear tester
[10].
EXAMPLE A hollow cylinder filled with bulk material and applied stress on the end side of the cylinder.
4 Tubular screw conveyors and explosion isolation
4.1 General
A tubular screw conveyor consists of a tube containing a spiral blade coiled around a shaft (auger), driven
at one end and held at the other. It may be powered by an external electric motor with fixed or variable
speed. The power transmission can happen by a clutch or a chain drive. The rate of volume transfer is
proportional to the speed of the shaft. The rotational speed is typically in the range of 5 r/min to 90 r/min,
the conveying velocity in the range of 0,01 m/s to 0,3 m/s.
The principle of a plug in a tubular screw conveyor used for explosion isolation is based on the removal
of a small part of the spiral blade (screw) so that a plug of bulk material will remain inside the tube. The
plug should remain for a sufficient time period even if the feeding of bulk material into the screw
conveyor is interrupted or finished (see Figure 1). This principle was described for the first time by
Wheeler [1].
The effectiveness of tubular screw conveyors for explosion isolation according to the principle as
described before has been investigated by large scale explosion tests [3-5] for a specific tubular screw
conveyor limiting the range of application of the recommendations given in this document.
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a) Removal of a small part of the screw (spiral blade), e.g. 1,5 turns
b) During normal operation, a plug of bulk material is formed
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c) Remaining plug of bulk material even if no more bulk material is fed into the screw conveyor
Figure 1 — Principle pictures of a tubular screw conveyor suitable for explosion isolation
The technical specifications of the used tubular screw conveyor are given in Table 1.
Various augers were used for the explosion isolation tests in which 1, 1,5 and 2 turns of the spiral blade
were removed. Additional tests were performed with a normal standard auger (complete spiral blade).
3
The tubular screw conveyor was connected with a vented or closed 1 m explosion vessel. In addition, all
3
tests were repeated with a vented 26 m explosion vessel. The reduced explosion overpressures were
varied in the range of 0,1 bar to 2,5 bar. During all tests the screw was emptied before ignition of the dust
cloud in the explosion vessel which represents the worst case as verified during testing. The test
procedure to this end was as follows: the screw conveyor was operated for 60 s in normal operation.
After 60 s the dust feeding into the screw conveyor was stopped to drive the screw conveyor empty. After
another 30 s the dust cloud in the connected vessel was ignited. Tests were performed with the screw
running as well as with the screw standing still. The results were not affected by the screw running or
not. Where the flight was partially removed, a plug of bulk material remained, depending on the
flowability of the bulk material (expressed by a fluidity factor ffc, see 3.3).
The explosion tests were carried out with dusts of different explosion characteristics and flow properties
as shown in Table 2.
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Table 1 — Technical specifications of the used tubular screw conveyor
Length from product inlet to product outlet 1 800 mm
Inside diameter 200 mm
Outside diameter of the flight (auger) 180 mm
Diameter of the shaft 50 mm
Screw pitch before location where part of flight was removed 180 mm
Screw pitch behind location where part of flight was removed 210 mm
Maximum gap between circumference of the flight and casing 10 mm
Engine power 3,0 kW
a
Engine speed (50 Hz) 120 r/min
3
Conveying capacity 5,5 t/h (bulk weight 0,7 kg/dm )
Pressure shock resistance (overpressure) 10 bar
a
The actual rotational speed during the tests was depending on the bulk density of the conveyed material and
the filling degree of the screw conveyor (typically 45 %). Most tests were performed at a rotational speed of ca.
70 r/min resulting in a tip speed of ca. 0,65 m/s.
Table 2 — Explosion and flow characteristics of different bulk materials
Median Bulk Fluidity
a
Bulk material p K MIE
max St
diameter density factor
μm bar bar·m/s mJ kg/l ffc
Corn starch 14 9,0 200 > 3 / ≤ 10 0,64 9,78
Cellulose 17 9,0 175 > 5 / ≤ 10 0,32 2,79
Malt 20 8,4 150 > 5 / ≤ 10 0,22 6,40
Powder sugar 31 7,9 140 > 5 / ≤ 10 0,60 2,08
Milk powder 60 8,8 125 > 30 / ≤ 100 0,56 3,73
Wooden dust 72 8,5 160 > 50 / ≤ 100 0,23 4,62
Wheaten flour 51 7,5 80 > 100 / ≤ 500 0,54 2,80
6
Refined sugar 424 3,8 12 > 10 0,85 8,60
Grain > 5 000 — — — 0,70 11,00
a
Minimum ignition energy measured with inductivity in the discharge circuit [12].
4.2 Influence of the bulk material
4.2.1 General
The effectiveness of a plug in a tubular screw conveyor used for explosion isolation and the required
technical specifications are depending on the
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