Designing grain terminals with Tebodin Consultants & Engineers
The reasons for large bulk terminals are very diverse: stock for
trading, stock for production facilities, stock for emergency
reasons. Usually supply comes together with the harvesting
season while the demand is spread throughout the year for
animal feed production, human consumption or other uses.
While the requirements for a grain terminal may not be
complicated, providing the necessary equipment can be; it needs
to comply with strict requirements relating to product quality,
cost effectiveness and optimal logistics.
To start off with, a grain terminal (or bulk goods terminal in
general) should be designed in such a way that it can handle
goods from all means of transport that are desired. The
waterside often plays an important role in determining the
layout. However, it is also necessary to consider what the best
infrastructure will be in terms of railway and traffic roads for
access and movement on site.
The fact is that often most of the goods are brought in by
ships, which means that the terminal needs to be designed in
such a way that large volumes can be handled in a short period
of time. Waiting times for ships need to be minimized and
should meet the schedules agreed by the chartering contractors
and ship owners. When schedules are exceeded, demurrage
costs are incurred which results in higher quay dues and harbour
charges. This means that the processing capacity needs to meet
these high volumes. Next to terminal intake with a weighing
system, this is the capacity of the cleaning process such as
grinding and waste separation processes (sieving and magnet).
The transport means of outgoing goods depend on specific
circumstances and the way that the product is to be stored,
processed or packed.
For storing the goods, a construction needs to be chosen
that is most cost effective. The complexity of choosing the right
construction of silo storage depends on many variables. Silo
storage is usually defined in volume (m3) rather than in metric
tonnes. In order to achieve the most economical way of storage,
one would consider a silo that is as large as possible. However,
it might be necessary to store various products so that several
silo cells or compartments are required. Or, the available plot of
land could have its restrictions. And what about the flowability
of the product: can the product be stored in storage bins or is a
flatstore a better option?
The flowability of the product to be stored is the first
consideration when thinking about the storage solution. Freeflowing
products can be stored best in storage bins, while it is
preferable to use a flatstore for non-free-flowing products or
products with a high humidity level.
Storage bins have several advantages: they can be automated
easily for loading and unloading; the compact way of storage
offers an economical construction method; and the stored
product can be completely protected from external influences
such as weather, insects, etcetera.
Depending on the purpose of the storage bin, one can
choose a flat bottom bin or a bin with cone.
Flat bottom bins can be provided with reclaimers for
products with more difficult flowing characteristics. During
unloading, the reclaimer transports the products continuously to
the outlet in the centre of the bottom. In the case of
free-flowing material, the product flows automatically to the
outlet; only the last part needs to be conveyed to the centre by
means of a rotating screw conveyor.
After leaving the storage bin, the product will be elevated to
the next process step, often a process bin. Bins with a cone are
regularly installed if the product is used for a dosing process
such as a truck loading facility or comparable application. The
slope of a cone should be 40–50° with the horizontal for freeflowing
products and to 65°–70° for products with more difficult
flow characteristics. The material for storage bins depends on
various ideologies. The building height of bins made of steel will
be limited by the strength of the construction; usually 30 metres
can be reached. Concrete storage bins technically do not have a
limit in building height (in grain terminals often 70 metres are
reached). Limitations are caused by soil characteristics or the
development plan.
Flat stores are selected regularly for non-free-flowing products,
for wet products to be aerated or dried, when the maximum
height is limited and in cases where the available ground is not
suitable for storage bins. Also the flexibility of changing the size
of compartments and the availability of the store for storing
other products or materials play a role in choosing a flat store.
The volume of flat stores can be unlimited due to the nature
of the construction; however there is a maximum height to be
considered of about 15 metres. In general, it is fair to say that
flat stores are more difficult to protect against external
influences such as weather or animals. Furthermore, the
operational costs are higher. The variety in flat stores is
principally based on the loading and unloading facilities. The
most simple versions of flat stores have no filling or reclaiming
machinery. They are loaded and unloaded by shovels or other
mechanical means. Choosing this option is interesting for a
storage that has a low turnaround time (number of times per
year that storage load is handled). In this case, the costs for
manual handling are relatively low as they occur only a few times
per year, sometimes only once. Special attention needs to be
paid to the requirements for product quality: flat stores without
any filling or reclaiming machinery incur a higher risk of
contamination, and there is a high impact on product quality due
to shovel movement and the risk of construction pieces in the
product due to shovel activity. For a storage facility with a high
turnaround time, more automated flat stores should be
considered. The level of automation depends on specific
circumstances and wishes. Moreover, a flat store can be fully
automated in such a way that it needs no further manual activity.
Finally, all storage means will need to comply with quality,
hygiene and safety standards. For every single storage facility, the
question remains as to what level hygiene needs to be optimized.
For flat stores, the question is whether shovel transport is
accepted or if other cleaner solutions (for example belt
conveyors) need to be used. For storage bins, special treatment
of the inner wall can be applied to create a smooth and tight top
layer. This is one of many options to avoid cross-contamination
of various products to be stored. Condensation needs to be
prevented at all times by using wall insulation, and self-heating of
the grain can be minimized by integrating an efficient aeration
system. ATEX guidelines apply for minimizing the risk of a dust
So, when designing a grain (or bulk goods) terminal, the first
question would be what product needs to be stored and what
type of silo can be applicable. Furthermore, the shape of silos
needs to be determined. Several options are possible, depending
on the utilization of the silo complex. For flat stores, various
alternatives are possible; the shape mainly depends on the
product to be stored and the soil on which it will be built. The
right combination of silo qualities and features achieves
operational efficiency and compliance with hygiene, safety and
environmental regulations.
Tebodin Consultants & Engineers is well known for its
in-depth knowledge of, and experience in, dry bulk handling
projects. Grain terminals and silos are being built for clients in
sectors such as the agro industry, food, bulk handling and
logistics and bio-energy sector. With a worldwide network of
more than 50 offices, Tebodin combines this knowledge during
the engineering phase with the ability to use local support during
construction phase.