January | February 2012
Feature title: Bulk storage & handling
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The International magazine for the aquaculture feed industry
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
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
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
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
processing it into feed and selling the resultant explosion relief panels at prescribed intervals, in exhaust fans at convenient locations will LS
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
information to the designer or manufacturer
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 email@example.com E firstname.lastname@example.org
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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