SILO DESIGN AND
by Bentall Rowlands Storage Systems Limited, UK
torage systems must be individually designed for each client. Each
project must have a bespoke design
that ensures it matches, if not exceeds
client expectations,” says Kevin Groom,
technical director of Bentall Rowlands
Storage Systems Limited in the UK.
“We are extremely proud of the projects
that we have undertaken in geographically
challenged areas, proving that whatever the
specification, we are sure to provide the
most suitable design necessary.
“We have designed and installed silos
worldwide in countries that include the UK,
Kenya, Thailand, Holland, France, Ukraine,
Malawi, New Zealand and many more.
With over a century of experience in
the design, quality and installation of grain
storage systems, Bentall Rowlands have
developed new technologies that have been
applied to the manufacture as well as the
installation of grain storage and processing
Bentall Rowlands is a leading UK manufacturer in complete storage and processing
equipment solutions for the agricultural and
It offers a wide range of galvanised steel
silos, flat bottom and hopper bottom, water
tanks, catwalks and platforms, material handling equipment, cleaning and grading and
weighing and drying systems that can be
“Our engineering and technical expertise
combined with continued focus on customer
satisfaction places us in a strong position to
capitalise on the expanding market in storage
With capabilities to design, manufacture,
supply and install storage systems from
an extensive range of products, Bentall
Rowlands provides a comprehensive end-toend solution which can be designed to any
As the demand for bulk storage and
handling equipment increases worldwide,
volumes and competitive pricing in grain
handling charges require efficient solutions.
We manufacture the right quality of product
to produce the efficiency savings required to
justify the investment.
Each project undertaken is designed differently and will need to take into account
a number of factors. This includes geographical issues, including large temperature
fluctuations, seismic activity, high winds and
Why do silos fail?
On a number of occasions, the failure
may only involve distortion or deformation,
which doesn’t necessarily pose an immediate
On the other hand, failure can mean
complete collapse of the structure resulting
in the loss of use and in some cases, the
loss of life.
The major causes of these failures are
predominately down to design errors, construction errors and utilisation errors.
“It is important that silos are built to meet
the specifications set out in the design, eliminating any chance of silo failure. We work hard to
build the best relationships with our customers
and spend time making sure that they receive
the best possible service from the initial design
concepts through to installation and completion of the project,” adds Mr Groom.
“When we are tasked with the job of
designing a new storage facility, there has to
be a thorough inspection and survey of the
site done prior to any work taking place.
“The geology of the area is key to the
design. For example we were chosen to
design a site in New Zealand.
“This country is known for its volcanic
activity, earthquakes and geothermal areas
because of its position on the boundary of
the Australian Plate and Pacific Plates. We
needed to know the area in great detail
to make sure we designed the size and
structure of the silos accordingly to dismiss
any chances of collapse or damage if seismic
activity does occur.
“When designing a storage system for
erection in a known earthquake region, they
must be designed to the countries relevant
seismic standards. All silos will need to be
built a great deal stronger to cater for the
horizontal loading at ground level. It is far
better to keep the silos height down.
“Silos that are shorter and wider are far
better than those that are tall and thin. When
seismic activity strikes, a structure that has a
larger base area is more likely to withstand
the pressures and remain intact. If you have
a taller and thinner structure, this presents a
huge amount of stress to the lower sections
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20 | January - February 2014
of the silo which will ultimately result in the
collapse of this structure.
“Due to the fact that the magnitude
of earthquakes varies greatly, all our silos
are individually designed to suit each areas
“The contract was originally built for the
New Zealand Government to store oil seed
rape. The stored grain would then be sent
for crushing to be turned into biofuel. The
silos were designed to hold the wet oil seed
rape prior to going through a continuous
flow drier,” he says.
Dealing with high winds
High winds can cause great problems for
a number of structures, including our storage
“We make sure that our silos are designed
to withstand gusts of 50m per second, which
equates to 180km per hour.
“During the recent storms that occurred
in the North of England and Scotland, we
had reports that all of the silos withstood the
gale force winds, with no reported problems
In areas where silos could be prone to these
high winds, the structure needs to be quite
similar to that where seismic activity takes place.
Silos will withstand these huge wind speeds
when they are designed to cover a greater base
area. This gives them the stability needed to
remain intact once a storm has passed.
For countries that are prone to temperature fluctuations, the design of the storage
system needs to be carefully thought out.
More so for
countries prone to
high levels of moisture. In severe cold
snow can be quite
extreme, it is the
roof of the structure
that needs to be one
of the main focuses.
Snow load is the
reason for engineering changes.
When designing the roof, it is
important to know
what depth of snow
can be expected in a
a bespoke storage
system for an area
within the Ukraine
where the snow can
get extremely deep.
designed the roof
on each silo to be
able to withstand a
pressure of 1kn/m2
which equates to
one meter of snow,”
changes within the
actual stored prod-
uct will affect the design of the silo, as does
the moisture content of the stored product.
“We look at the bulk solid that is being
stored, and take into account the levels
of moisture. Increased moisture within a
storage system will affect the grain, causing
expansion within the silo.”
If this occurs when the materials are
not being taken out, upward expansion is
restrained. This means that the majority of
the expansion will occur in the horizontal
direction, resulting in increased lateral pressure, and hoop stresses in the silo walls.
“In situations like this, we have to assess
the area and the likelihood of significant
moisture migration as this will affect the
design of the system.
Our silo roofs are designed with an area
of overhang, meaning that in areas where
rainfall will be a potential problem, we have
that ‘run-off’ effect from the roof that protects the grain within the silos.
“If our storage systems were designed
differently, it would result in added moisture
content within the silo, causing expansion
and increased hoop stresses, but also the
danger of losing the grain to mould.”
The need for galvanising
Galvanisation is the process of applying
a protective coating of zinc to the silos in
order to prevent rusting occurring.
In areas where high levels of corrosion
could be present, this is a necessity.
“Compared to other companies, we use
G600 as a standard whereas some companies may only use G90. This greatly increases
the life expectancy of our silos.”
For example, in tropical marine areas
where storage systems are required, you
can expect them to last somewhere around
35 years which is a huge advantage over
other companies. Countries that have high
levels of precipitation and humidity will rely
on the galvanising of the silos in order to
protect them from this corrosion. This is
standard on all types of storage equipment,
to add that extra bit of security on life
Getting the shipments right
“Not only do we have to take into
account the design of the silos in these geographically challenged areas, but the vast job
of sorting the logistical side out.
“All our shipments have to be correct at
all times, especially the ones going to these
Getting it right first time is imperative.
“To start shipping missing goods is not
only a logistical nightmare, but can be
a very expensive mishap, extremely time
consuming and can hold up the project by a
significant amount of time.
“At Bentall Rowlands, when building large
grain stores, it is common to agree a spares
package that can be shipped with the main
contract. More likely than not, some of the
parts may become damaged or misplaced
and parts that may only cost a few pounds
could cost thousands if it has to be air
freighted,” he notes.
SOYBEANS AND SOYBEAN MEAL
by Pablo Fernández , Southeast Asia Area Manager Silos Cordoba
toring soybean and soybean meal
leads to specific storage problems.
That is why we need to know more
For example, the structure of the bean
impacts its handling and:
• Handling involves conveying and
transporting from the farm to enduser. During this phase there are many
different movements from harvest to
the production into oil and meal
• The structure of a soybean seed makes
it susceptible to splitting and breakage
during mechanical handling. The
extent of breakage in soybeans during
conveying varies with the impact force
imposed on each individual seed. The
least breakage occurs when soybeans
are conveyed in a bucket elevator as
compared to other conveying methods
Figure 1 shows the extent of soya bean
breakage with four methods of conveying:
the first one represents the percentage of
breakage of the grain in a free fall of 30, 21
and 12 meters.
The storability of soybeans is affected
by the degree of damage to the seed coat
and by other factors such as mold or insect
attack. It is therefore important to inspect
soybeans for mechanical and other forms of
damage prior to storage.
If the amount of broken or split soybeans
is very high, it may be prudent to separate
the broken or split grains by sieving. This
material can then be used first as opposed to
long-term storage within the original stock.
Soybean meal is difficult to handle
because of its poor flowability and bridging
characteristics. Soybean meal tends to settle
or consolidate over time. This phenomenon occurs in most granular materials and
becomes more severe with increased moisture, time and when particle sizes are small.
The flow characteristics of bulk materials
are dependent on individual particle shape,
density, frictional property and moisture content. Granular materials have three typical flow
patterns during discharge from hopper bottom
bins: normal discharge pattern (there is no
problem here), bridging and funneling. These
two latter problems occur in grains containing
high content of foreign material or moisture.
Typical flow problems of meal products
discharged from storage silos are hang-ups,
dead pocket and piping (see figure 2).
These are usually due to a combination
of factors such as poor hopper design, high
moisture content and storage time.
Beside all of the above soybean and soybean meal consideration, we have to keep
in mind the most important external factors:
moisture content, temperature and duration
The general condition of the product and
amount of foreign materials also affect its
Table 1: Moisture content and safe storage
Safe storage period
storability. By focusing on these three elements, we can assure the perfect storage of
soya bean and soya bean meal:
Depending on the percentage of moisture, the periods of storage change. Soybeans
contain moisture ranging from 12 percent to
15 percent at harvest time. Above 13 percent should be dried to reduce the risk of
deterioration due to seed respiration, mold
attack, spontaneous heating and reduced
Temperature is another very important factor influencing in soybean storage.
Growth of fungi and chemical changes, such
as oxidation, increased with temperature in
both meal and whole beans.
Moreover, it is really important to con-
The right storage solution starts with the right advice.
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Storage decisions can affect your operation for decades. That’s why so many companies around the world trust Westeel with
their storage needs. Not only do we supply some of the most advanced storage products available, we support our products
with the expert project leadership and sound engineering advice necessary to ensure that the decisions you make today
continue to serve your company well for years to come.
&Feed millinG technoloGy
24 | January - February 2014
BREAKAGE IN SOYBEANS
TYPICAL PROBLEMS WITH MEAL PRODUCTS
sider the climate in the different regions
of the world. Experience indicates that
under hot and humid tropical conditions,
grains stored in metal bins exhibit sweating. This problem arises with extreme high
temperatures reached on the inner surface
of the metal silo on a hot day, then, at
night, the rapid cooling of the metal results
in moisture condensation as the dew point
Caking and charring in metal silos can be
attributed to this phenomenon. Installing the
proper devices of ventilation and cooling
machines keep the correct temperature and
avoid these problems.
Time of storage:
Shorter better! Fine foreign materials
tend to segregate during bin loading and
occupy void spaces in the central region of
the grain mass.
Meanwhile the large and lighter materials
will accumulate close to the walls of the
silo. Then, during aeration, the air will flow
around spots with a higher concentration of
fine foreign materials and through pockets of
high concentration of large foreign materials.
This condition creates a non-uniform
flow of air during aeration, thus, making it
an ineffective operation. Hence, cleaning
soybeans prior to storage will minimise the
risk of spoilage and economic loss.
Detecting possible problems
Here you have some indicators that will
help you to detect any possible problems
with the products storage inside the silos.
Heating is the most common indicator
of a problem in stored grains and oilseeds.
High grain temperatures normally indicate either microbial or insect activity. If left
unchecked, this may lead to heat-damaged
or charred grains due to the phenomenon
of stack burning. Because of this danger, hot
spots in stored soybeans must be cooled or
dissipated before they reach the critical level.
If no action is taken when heating in soybeans occurs, either the product will be lost
by stack burning (charring) or at worst, the
entire facility will be lost through fire.
Aerating soybeans when fire has already
started makes the situation worse. A temperature monitoring system in soybean storage
silos is essential. Immediate corrective measures for heating cannot be over-emphasised.
Change in color and general
In general, sound soybeans are plump
with bright uniform tan with no trace of
green colour and free from unusual spots
and shriveled appearance.
Discoloured soybeans usually indicate
inferior quality and lower market value.
The change in colour is usually associated
with mold invasion accompanied by microbial respiration and subsequent heating. This
deterioration process can be detected by
periodic drawing of samples from the silos
as part of an integrated approach of quality
Once detected, appropriate measures
can then be taken such as cooling the grain
either by aeration or use of a portable
cooling unit. Another corrective measure
is to transfer the grain to another silo thus
breaking any hot spots present and cooling
the soybeans during the conveying process.
However, this should be done only as a
last resort since it is costly and will increase
the amount of broken or split soybean seed.
Mustiness and off-odor condition:
Musty odor usually indicates an advanced
stage of insect or mold infestation and
should be dealt with immediately. If this is
detected, the soybean should be aerated to
remove the bad odor and cool the material.
Seeds should then be used at the earliest
opportunity. The grain should be fumigated
immediately if insects are present. A sharp
odor may indicate rancidity due to chemical
changes in the oil component.
Lumping and caking:
Lumping and caking indicate a very
advanced stage of fungi invasion in soybeans
and soybean meal. In metal bins, caking usually
occurs on the bin walls as a result of sweating
or moisture condensing on the inner surface
of the cold bin wall. The condensing moisture
is absorbed by the adjacent grains resulting in
either sprouting or mold growth.
Useful tips for soybean and
soybean meal storage
For all of this, low product moisture, low
temperature and short storage periods are
desirable. After this brief analysis we can
give some tips for those who need to store
either soybean meal or soya bean:
The proper devices for storing soybean
and soybean meal are:
1. Hydraulic sweep auger (for soybean
meal). This sweep auger effectively
reclaims meal products from silos
because it is able to work with full silos.
One full rotation of the screw once
a day is mandatory to prevent the
mentioned discharge problems.
&Feed millinG technoloGy
26 | January - February 2014
2. Smoother wall ring+washer outside
the silos and head-round bolts inside
the silos. Different silos manufacturers
using different wall ring waves. We have
to be careful and choose a long wave.
3. Pre-cleaner. “Fine foreign materials
tend to segregate during bin loading and
occupy void spaces in the central region
of the grain mass. Meanwhile the large
and lighter materials will accumulate
close to the walls silos”.
That fact effects the ventilation,
“the air will flow around spots with
higher concentration of fine foreign
materials and through pockets of high
concentration of large foreign materials.
This condition will create a non-uniform
flow of air during aeration, thus, making
it an ineffective operation.” Cleaning the
product prior to storage will minimise
the risk of spoilage and economic loss.
Moreover, if the product has to be
dried it is totally necessary to avoid the
burn of the waste (fine foreign materials
like straw, dust, etc) inside the dryer.
4. Dryer. Soybean moisture above 13
percent should be dried to reduce
the risk of deterioration due to seed
respiration, mold attack, spontaneous
heating and reduced germination.
5. Ventilation. Centrifugal fans. The primary
purpose of aeration is to make the
temperature of the grain bulk uniform. This
prevents moisture migration in the grain
mass due to natural convection. Aeration
may also be used to hold partially dried
soybean for a few days to prevent spoilage
before proper drying. It should be noted
that aeration is not intended to dry grains.
6. Cooling machines. Strongly recommended
in tropical climates with high heat and high
humidity. Soybean, even after harvested,
still keeps on breathing.
The grain once chilled, keeps its low
temperature for a long time, without the
need for a continuous cooling. Direct
consequences of non-controlled storing
of wet grain are the appearance of fungi
and toxins, which are very dangerous
for the health of humans and animals.
The proper storing of grain by means
of chilled and dry air fix completely or
widely minimise the problem.
7. Temperature monitoring system. This
device is essential to control and correct
any deviation of the optimum.
8. Belt conveyors. To prevent the
breakage of the grain. This kind of
conveyor can move grains for great
distances without damage.
9. Periodic drawing of product samples
and accurately testing them.
By following all these steps you can be
assured of avoiding change in color, risk of
deterioration due to seed respiration, mold
attack, spontaneous heating, reduced germination, mustiness and off-odor conditions,
presence of insects, lumping and caking and
finally economic loss.
Answering your questions
What flat bottom silos are suitable for
storing soybean meal? In order to avoid
long storage in soymeal silos, we of course
recommend our model:
Silo model: 12.22/12
Silo diameter: 12.22m
Eave height: 13.73m
Total capacity: 1.749m3 (1120T)
Discharge capacity: 50T/h approx
Please note that few silos in the same site
can share the same hydraulic unit, and therefore the unitary price decreases. With several
silos they can rotate the product between
them; that is especially useful for long storage.
What extraction screws do you
deliver together with above flat
We have worked with hydraulic sweep
augers from Morillon. According to the
capacity required they can be single arm or
What hopper silos are suitable for
storing soybean meal?
Due to the poor flow characteristics of
the soy, hopper silos with a reinforced cone
of 60º are suitable. These silos should be
equipped with screw discharge conveyors
The biggest hopper silo model we have
installed so far for this product is our model
60º hopper silo 6.88/9, with the 467m3.
STORAGE SYSTEMS WORLDWIDE
We take looking after
grain very seriously
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Bentall Rowlands Storage Systems Limited
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