The unloading of bulk materials such as cereals into intake pits is generally associated with considerable dust emissions. The reasons for the need for an efficient receiving pit dust control system can be diverse. They range from reducing dust emmissions in neighboring residential areas to improving health and safety at work for those working on site and the imperative requirement of preventing serious damage to plant and danger of fatal injury from dust explosions.

1. Digital Re-print January | February 2014
Design of an efficient intake pit dedusting system
the state-of-the-art in technology
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3. F
&Feed millinG technoloGy
16 | January - February 2014
Grain
Design of an efficient intake
pit dedusting system
the state-of-the-art in technology
by Andreas Rembeck and Rico Hindemith, Bühler GmbH
T
he unloading of bulk materials such
as cereals into intake pits is generally associated with considerable dust
emissions. The reasons for the need for an
efficient receiving pit dust control system
can be diverse. They range from reducing
dust emmissions in neighboring residential areas to improving health and safety
at work for those working on site and
the imperative requirement of preventing serious damage to plant and danger of
fatal injury from dust explosions.
Bühler Grain Logistics offers a choice
between two systems, depending on application requirements: namely central or distributed receiving pit dust control. These can be
further subdivided on the basis of whether
extraction is above or below the grid iron.
Both systems are of modular design and
can therefore be customized to the specific
conditions of each situation.
To ensure that the required aspiration
capacity of the intake pit dedusting is kept
to the minimum, every component needs to
be optimized. It is therefore an advantage if
there are gates at the entrance area which
are kept closed at all times during unloading so that undesired air draughts and dust
escaping to the surrounds can be prevented
at the outset. For an optimum air flow inside
the reception area, the upper section of the
side wall is fitted with louvers. This prevents
dust getting whirled up and ensures that the
dust which collects is directed towards the
extractors (Figure 1).
Another technical step towards minimising dust emissions can be taken by installing
a dust barrier. The barrier has dust retention
panels (Figure 2) and prevents dust whirling
up in the hopper. Practical experience from
day-to-day operations has shown that up to
75 percent of the dust which is generated
is produced when the bulk material hits the
floor of the hopper. The dust barrier reduces
air requirements, allows smaller filters and
fans and cuts the power requirements of the
fans by approximately 60 percent.
Filters for intake pits
(decentralized)
For operations such as grain collection
facilities or farms where the amount of dust
generated is insignificant or plays only a
minor role at most, decentralized dedusting
is the more appropriate solution (Figure 3).
In this case two adjustable inlet openings
allow the air which requires cleaning to flow
into the filter panels, from which it is directed
to the fan through a manifold pipe line. The
filter modules are connected using elements
to form a single unit and the cleaned dust
falls back into the reception pit via a diagonal
plate.
Centralized intake pit
dedusting
Centralized dedusting is designed more
for food processors such as grain mills
and producers of pasta, where removing
dust from the raw product is essential.
As in decentralized dedusting, the air to
be cleaned is also caught by an aspiration
panel. The individual aspiration modules
are screwed together, which means that a
variety of intake hopper sizes can be created
ranging from 4 m to a maximum of 24 m
in length. The aspiration panel is connected
to a dust manifold pipe line which leads to
a Bühler round filter. The round filter is a
central filter with a jet-pulse cleaning system.
This is where the flow of raw gas which is
picked up and the dust which is retained
are separated. The dust is conveyed through
dust discharge chutes to separate dust containers or big bags. As a result, the undesired
dust no longer comes into contact with the
product, thereby ensuring improved hygiene
and greater safety. This system could be
described as a form of initial pre-cleaning.
Filter
Figure 1: Schematic diagram of an intake pit
TA-Luft directive requirements under
the German Federal Immissions Control Act
stipulate emission limits of 20 milligrams of
residual dust per normal cubic meter of air.
The use of antistatic filter bags is one way
of ensuring compliance with these reference
values. They are more effective at cleaning
than filter cells and also permit higher airto
cloth ratios.

4. 17 | January - February 2014
Grain
Figure 3. Filters for intake pits (decentralized)
Cleaning is on a time-controlled and/or
differential pressure controlled basis, which
ensures optimum filter performance and
saves energy.
Comparison
The two types of intake pit dedusting
systems can be designed for both side
and rear unloading. With their adjustable
double gap they can be customized to local
conditions and are capable of aspiring even
if the intake pit is overfilled. Depending on
requirements the walls can be supplied with
filter modules only or with partition walls as
well, enabling sizes ranging from 2x3 to 4x24
square meters.
&Feed millinG technoloGy
Figure 4: Type RB round filter
The differences between the two filter systems are as follows: whereas the
decentral dedusting system has a larger
surface and therefore a lower filter load
than the central dust removal system, the
maximum dischargeable air rate of 55 m³
per minute and meter of pit length with
a filter load of 5 m³ per minute and m²
of filter surface (grain) is less than the
dischargeable air rate of the central solution, which is a maximum of 65 m³ per
minute and meter of pit length for the
same filter load.
Separate dust separation means that
the central version requires more space
for Bühler round filters (Figure 4) and
dust containers. On the other hand the
decentralized dedusting system involves
additional costs in terms of compressed
air for cleaning the filter bags.
The purchase costs of the central
receiving pit dedusting system are generally higher than for a decentralized
system because the former has more
components. In terms of operating costs,
however, the central solution normally
works out better. Both systems have their
advantages. The decision as to whether
preference should be given to the central
or decentral option depends on the specific application.
www.buhlergroup.com
About Bühler
Figure 2: Dust retention panels
Bühler is a global technology leader
which specializes in the supply of equipment, systems and services for the conversion of renewable resources derived
from food and synthetic substances
into top quality functional products
and materials. Bühler operates in over
140 countries and has some 10,000
employees worldwide. In fiscal 2012,
the Group generated sales revenue of
CHF 2,409 million.
F

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