Bulk storage & handling

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					                                   January | February 2012
                Feature title: Bulk storage & handling

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The International magazine for the aquaculture feed industry
         FEATURE                                                                                                                                                                                                                                                                                          FEATURE

                                                                                                                                                             of individual clients, bearing in mind the large
                                                                                                                                                             number of different materials to be handled
                                                                                                                                                             and stored in the feed industry. Ranging from
                                                                                                                                                             free flowing grains to a variety of meals and
                                                                                                                                                             moisture content, the bins and discharge
                                                                                                                                                             equipment should be designed to cater for
                                                                                                                                                             those with the worst flow characteristics to
                                                                                                                                                             ensure maximum flexibility so that individual

                                        & handling
                                                                                                                                                             bins can be used for the storage of any ingre-
                                                                                                                                                             dients should the need arise.
Bulk storage                                                                                                                                                       Level probes are required to prevent over-
                                                                                                                                                             filling, as are policed explosion panels.
                                                                                                                                                                   Provision will be required for minerals and
by Alf Croston, Managing Director, Croston Engineering, UK                                                                                                   other ingredients that are delivered by bulk
                                                                                                                                                             tanker and pneumatically conveyed to dedi-
                                                                                                                                                             cated bins utilising either a blower mounted
                                                                                                                                                             on the tanker chassis or, in some cases, by

                                                                                                                                                             coupling up from a land-based blower. To
           s with most things in life, the          rial handling must still apply, as do health and   Elevators should also incorporate tensioning          prevent static electricity causing a spark, the
           basics remain the same although          safety requirements, adherence to DSEAR/           gear at the boot, anti-runback device to cater        tanker will be connected to an earthing point
           they may become more sophisti-           ATEX Explosion Regulations, plus health and        for a choke or power failure, rotation sensor         prior to starting the discharge process. Care is    important in ensuring the free flow of materi-   a three tier mix-
           cated, or complicated, dependent         hygiene control.                                   to indicate if the belt is slipping and side align-   needed to ensure that the tanker only couples       als from the bins to the blending operation.     ing assembly consisting of pre-mix bin, mixer
on one’s viewpoint.                                     Hence this résumé.                             ment indication.                                      up to the correct intake line feeding the des-      For accuracy this will include one or more       and dump bin. Molasses and fats are added
                                                                                                           Intake points are frequently out of sight of      ignated bin and that intake lines are of correct    main weigh hoppers, a small weigh hopper         at the mixer.
    And so it is with this overview covering the    Interruptions in production                        the control room so, to avoid being allowed           diameter, earthed and routed with minimum           for minerals, and a smaller one for micro            Although heat treatment is outside this
bulk storage and handling of materials in the           The interconnection of process plant is        to run empty for long periods, and a proce-           horizontal length and number of bends in            ingredients.                                     remit covering bulk handling it is a matter
animal feed and human food industries, from         designed to be fail-safe and so prevent chokes     dure should be in place to shut down when             order to reduce the pressure needed to carry            The blended batch is fed to the grinding     that requires attention whether it is for
the intake of raw materials through to the          and interruption to production.                    not in use.                                           out the conveying operation.                        plant preceded by a screen to allow meals        conditioning of mashes for direct sales or for
discharge of finished products.                         Intake capacity from bulk tankers has              A rotary drum pre-cleaner located at the                As referred to earlier, the configuration     and minerals to bypass the grinder before        pelleting. The three essentials being moisture,
    It is barely 60 years since a very high         greatly increased over the years and is nor-       top of the Mill to remove foreign matter prior        of hopper design and type of discharge is all-      re-joining the ground materials and passing to   temperature and time, whilst bearing in mind
proportion of the milling industry was located      mally well in excess of 100 tonnes/hour via an     to the material being conveyed to raw mate-
at the major ports with raw materials in            intake hopper with safety grid located under       rial bins will protect subsequent equipment
sacks being transported from the docks by           cover plus an efficient dust extraction system,    from being damaged.
horse and cart and then hoisted up to the           and discharging into a screw or chain type             The conveyors feeding silos and bins will
various floor levels for storage there to be        conveyor which may, if wished, be fitted with      have multiple outlets and the electrical control                                                                                                                                                            DP

cut and tipped into process bins as and when        a variable speed drive so that the intake rate     system must be designed so that only one
                                                                                                                                                                                                                                                                                                     LS   LS


required.                                           may be varied to suit the characteristics of the   slide is open at a time in order to prevent the
    Gradually, as more home grown grain             particular material being dealt with in order to   propagation of an explosion from one bin to                                                                                                                                                                                                   LS

became available, together with the advent of       prevent overloading subsequent equipment.          another. As with the intake conveyor, all con-
purpose-built bulk vehicles and an improved             The conveyor should be fitted with rota-       veyors should incorporate overfeed detection


road network, there was a move to country           tion control and overfeed detection.               and rotation sensing.
mills more conveniently located to service the          The intake bucket elevator, as with all            To cater for dust laden air displacement
                                                                                                                                                                                                                                                                               M        M
                                                                                                                                                                                                                                                                                                                        6   6               6


farming community by buying grain locally,          similar units in the mill, must incorporate        at transfer points, small dust units with built-                                                                                                                            DP

                                                                                                                                                                                                                                                                       MCC 2

processing it into feed and selling the resultant   explosion relief panels at prescribed intervals,   in exhaust fans at convenient locations will                                                                                                                                         LS
                                                                                                                                                                                                                                                                                                 L                                              10

                                                                                                                                                                                                                                                                                                                                MCC 1

product back to the farmer.                         electrically linked to shut down the plant in      ensure a clean atmosphere.                                                                                                                                                                                                                         LS

    The use of computers and automation             the event of an explosion occurring.
throughout the milling process has reduced              Because of their inherent design, bucket       Storing different materials
what was a labour intensive industry to one         elevators have a built-in explosion risk factor       The number, location and holding capacity
controlled by a few technically proficient          and, if located within a building, the explo-      of new material bins is determined by site
operators, but to whom the basics of mate-          sion panels should be ducted to atmosphere.        conditions and the particular requirements

                                               18 | InternatIonal AquAFeed | January-February 2012                                                                                                           January-February 2012 | InternatIonal AquAFeed | 19
         FEATURE                                                                                                                                                                                                                                                                FEATURE

                                                                                                     information to the designer or manufacturer
                                                                                                     of equipment.
                                                                                                         These are defined under four Kst classifica-
                                                                                                     tions (K staube = Class of dust), and relate to                                                                                                               Changing the way
                                                                                                     rate of pressure rise.                                                  more than 100 years a reliable partner
                                                                                                                                                                                                                                                                   fish, and the industry,
                                                                                                        Kst.   0   =   Non-explosive                                            Feed mills                Silos                                                    view protein.
                                                                                                        Kst.   1   =   Weak to moderate                                         Flourmills                Bulk handling systems
                                                                                                        Kst.   2   =   Strong                                                   Pet Food plants           Electric control &
                                                                                                        Kst.   3   =   Very strong                                                                        Automation systems
                                                                                                                                                                                Aqua feed mills

                                                                                                        Most materials used in feed mills are cov-                              Premix & concentrate
                                                                                                     ered under Kst. 1 but there are a few to which
                                                                                                     Kst. 2 could apply.                                                        Cereal Processing
                                                                                                     Zoning                                                                     Oil seed processing
                                                                                                          In addition to dust classification, the user
                                                                                                     is required to carry out a survey and to               WWW.OTTEVANGER.COM
                                                                                                     designate plant and buildings into zones which
                                                                                                     will be appropriately signed at points of entry.                        Aalten - Holland            Moerkapelle - Holland
                                                                                                     Zones 20, 21 and 22 are the most likely to                              T +31 (0)543 47 26 88       T +31 (0)79 593 52 97
                                                                                                     apply to feed milling and associated industries.                        F +31 (0)543 47 54 75       F +31 (0)79 593 11 47
                                                                                                          Zone 20 covers an area in which an                                 E aalten@ottevanger.com     E mkp@ottevanger.com
                                                                                                     explosive atmosphere consisting of combus-
                                                                                                     tible dust in air is present frequently for long
                                                                                                     periods or continuously.
                                                                                                          Zone 21 is where an explosive atmos-
                                                                                                     phere is likely to occur occasionally in normal
                                                                                                          Zone 22 is where an explosive atmos-
                                                                                                                                                            CRAFTMANSHIP IN THE ANIMAL FEED AND FOOD PROCESSING INDUSTRY
                                                                                                     phere would not normally occur but, if it does,
                                                                                                     it would only be for a short period.
                                                                                                          Obviously it is the duty of management to
                                                                                                     ensure that standards of operation and cleanli-
                                                                                                     ness are maintained to meet the requirements
                                                                                                     of Zone 22 as far as is practical.
                                                                                                                                                            Silo Construction & Engineering
                                                                                                          In carrying out risk assessments it is natural                                        Modular square bins
                                                                                                     to concentrate on major processing equip-
                                                                                                     ment such as silos, grinders, elevators, dust
                                                                                                     collectors, etc., and to overlook the myriad
                                                                                                     range of smaller ancillary items that also need
                                                                                                     to be checked. Typical items include lighting,
                                                                                                     electrical fittings, motors, level indicators, sole-
the heat sensitivity of some ingredients. For       The Directives                                   noid valves, control panels. In fact, anything
pelleting, correct conditioning is necessary to          The Directives apply from July 1, 2003,     that can generate a spark.
ensure starch gelatinisation and pellet quality.    to all new equipment and any existing that            It is well known that three elements are
    An efficient cooling system is essential        is modified or relocated after this date. This   required to cause an explosion – dust in
prior to finished products being conveyed to        has particular relevance in ensuring that, if    suspension at a critical level, oxygen, and a
packing or bulk out loading bins, the latter        purchasing any second-hand equipment, it         spark or hot surface. The first two are always
discharging either directly to bulk vehicle or      complies or can be economically altered to       there, so it is against the third item that every
via a travelling weigher.                           comply.                                          precaution must be taken, including satisfac-

    Most of the materials processed in the               Good housekeeping, regular inspection       tory earthing throughout the plant.
animal feed, pet and fish food, grain, flour,       and maintenance, plus an awareness of poten-          Bear in mind that dust in suspension                                                                                                          Empyreal 75 is a corn protein

bakery, sugar, starch and fertiliser industries     tially hazardous processes or areas, are a       appearing as a light fog provides the condi-                                                                                                 concentrate that provides a unique, safe
are subject to the DSEAR/ATEX Explosion             requisite for trouble free operation. The        tion in which a spark can cause an explosion.
Regulations that came into operation on July        Directives combine these aspirations into        The finer the dust particles the greater the                                                                                                      and consistent source of protein.
1, 2003. There are many misconceptions              requirements and apply not only to the sup-      danger because of the increased surface area                                                        SCE is a partner with                        To learn more, visit e75aqua.com.
and confusion as to the requirements of the         pliers of equipment but, in particular, to the   exposed to atmosphere.                                                                                 the international
Directives. It is timely to reiterate the general   users themselves.                                     The duties of the user having been
                                                                                                                                                                                                      feed & food industries •
principles relating to the regulations, particu-                                                     described in general terms, what about the                                              consultancy & engineering firms •                       And introducing Lysto,

larly for those who have only recently become       Dust classification                              supplier of the equipment? Firstly, he has to                                                machine & plant designers •                  the newest innovation in the
involved in one or other of the industries              It is the obligation of the user to sat-     satisfy himself that the user has provided him                                                                                              Empyreal line of products.
in which potentially explosive materials are        isfy himself as to the class or classes of the   with all the necessary details concerning clas-                                                       www.sce.be
handled.                                            materials to be handled and to provide this      sifications of materials to be processed and

                                               20 | InternatIonal AquAFeed | January-February 2012                                                                                                        January-February 2012 | InternatIonal AquAFeed | 21

   the areas in which equipment is to be located,     think of, it is sod’s law that incidents still take   helpful as an “aide memoire” towards good
   together with any other relevant information.      place – thankfully not too often in view of           housekeeping;
       The supplier then has to ensure that the       increased awareness of the dangers that are             • Enforce a strict no-smoking rule, on pain
   equipment he supplies is designed, manufac-        always present.                                           of dismissal.
   tured and installed to satisfy requirements by                                                             • Ensure that all electrical equipment,
   taking all precautions to prevent an explosion     Examples                                                  cabling and control panels conform to
   but also, and most importantly, to mitigate            Three examples illustrate the variety of              relevant standards and regulations, and
   against an explosion should such an event          incidents that can happen.                                are kept free of dust.
   occur.                                                 The first resulted from smouldering mate-           • Use only totally enclosed, fan-cooled
       Equipment can be manufactured in such          rial entering a bin, setting off a primary                motors, ensuring they are adequately
   heavy construction that an explosion would         explosion which ruptured the explosion panel              earthed.
   be contained but this is so expensive as to be     as it was designed to do. Unfortunately the             • Ensure light fittings are dust-proof.
   impractical. The alternative is to fit a certi-    escaping gases caused a secondary explosion             • Test cables and wiring regularly.
   fied explosion panel vented to atmosphere          which devastated the top floor of the build-            • Locate switchgear and process control
   through a nearby wall or roof.                     ing. As it was impractical to vent every bin              panels in dust-free rooms under light
                                                      to atmosphere it was subsequently agreed                  negative pressure.
                                                                                 with HSE that the top        • Inspect liquid lines regularly for leaks.
                                                                                  floor over the bins           Ensure that insulation, if used, has not
                                                                                 would in future be a           become impregnated, as this could be
                                                                                 “no go” area whilst            ignited by electrical trace heating.
"Many fires have occurred during periods                                         the plant was in pro-        • Bund walls around main storage tanks
                                                                                 duction and for ten            should be sized to suit.
of repair, renovation or plant modification                                      minutes afterwards. A        • Check that bearings, particularly those
                                                                                lockable gate was fit-          fitted to elevators and grinders, are not
(as in the case of Windsor Castle a few
                                                                                ted to the access stairs        over-heating.
years ago). During these special periods,                                       and a warning notice          • Detect belt slip and misalignment on
                                                                                affixed.                        elevators – a major source of fires – by
in addition to taking fire precautions, it is                                       The second result-          rotation and side alignment sensing, and
                                                                               ed from a hot spot due           anti-run-back protection.
advisable to inspect the area closely for at
                                                                               to a malfunction in the        • Check for possible temperature rise in
least an hour at the end of each working day"                                  motor of a dust unit fit-        stored bulk materials, which could result
                                                                               ted on top of a grinder          in spontaneous combustion.
                                                                              expansion hopper. The           • Inspect bin interiors using only battery-
                                                                              explosion panel rup-              operated, non-glass, flameproof inspec-
                                                                              tured but had not been            tion lamps, which are suitably secured
                                                                             vented to atmosphere               and never allowed to be in contact
                                                                             through a nearby wall.             with the product. (In the past it was not
        Due to the location of plant within a build-      Unfortunately, two employees were stand-              unusual for naked electric bulbs to be
   ing venting may not be practical and so the ing nearby at the time and were badly burned.                    lowered into bins – at best protected
   fitting of expensive flame quenching or explo- It was interesting to note that a choke had                   with a wire guard).
   sion suppression equipment may be required. been fitted to the bin discharger beneath the                  • Ensure hot work is carried out only on
        To prevent the propagation of an explo- expansion hopper and prevented the explo-                       isolated, cleaned-out plant, against Work
   sion, items of equipment should be isolated sive gases passing into a subsequent elevator                    Permit issued by management, and pro-
   from each other. An example being to incor- and storage bins, otherwise the result would                     vision of fire blankets, extinguishers, etc.
   porate valves or slides so that only one bin have been even more serious.                                    Many fires have occurred during periods of
   can be filled and exhausted at a time. Bin             The third was caused by welding being             repair, renovation or plant modification (as in
   dischargers and screw conveyors can be carried out on the side of a silo, one of several                 the case of Windsor Castle a few years ago).
   designed with chokes incorporated.                 such accidents over the years, in which the           During these special periods, in addition to
        The installation of a rubble separator on operator was injured. In this case it was not             taking fire precautions, it is advisable to inspect
   the intake system and magnets at appropri- the result of negligence. The silo had been                   the area closely for at least an hour at the end
   ate points throughout the plant are obvious isolated from its feeding conveyor, cleaned                  of each working day.
   precautions.                                       down internally and the subject of a work per-            Adherence to these principles will ensure
        Very often a primary explosion in itself is mit. Unfortunately, a small amount of material          not only a pleasant environment in which to
   not dangerous but the vibration it sets up dis- had remained in an inaccessible spot and on              work but also one that is as intrinsically safe
   turbs any dust lying on floors, beams, rafters, being disturbed created the conditions for an            as possible.                                     ■
   into the atmosphere. If a source of ignition is explosion to take place.
   present it can result in a secondary and dev-          The foregoing describes
   astating explosion. So, cleanliness throughout in broad outline the rationale             About the author:
   the plant is of first priority with particular behind the ATEX Directives.                    Mr Alf Croston is managing director of Croston
   attention being paid to “out of sight” areas Many of the requirements                     Engineering, at Tarvin, near Chester, which was founded
   and cleaning up spillages immediately – using are common sense, but com-                  in 1976. His company specialises in the design and
   one of a variety of vacuum cleaning systems mon sense has to be backed                    building of bulk storage, handling and process plants
   available. Brushing up is definitely out – it only up with documentation in               throughout the UK and Ireland for many household
   disperses the dust elsewhere.                      this day and age. However,             names in industry.
        Despite taking all precautions that one can the following may be found

                                                 22 | InternatIonal AquAFeed | January-February 2012
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Description: As with most things in life, the basics remain the same although they may become more sophisticated, or complicated, dependent on one’s viewpoint.