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Digital Re-print - January | February 2014Design of an efcient intake pit dedusting system

the state-of-the-art in technology

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Grain & Feed Milling Technology is published six times a year by Perendale Publishers Ltd of the United Kingdom. All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies,the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis ofinformation published.Copyright 2014 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any formor by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1466-3872

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T he unloading of bulk materials suchas cereals into intake pits is general-ly associated with considerable dustemissions. The reasons for the need for an

efficient receiving pit dust control systemcan be diverse. They range from reducingdust emmissions in neighboring residen-tial areas to improving health and safetyat work for those working on site andthe imperative requirement of prevent-ing serious damage to plant and danger offatal injury from dust explosions.

Bhler Grain Logistics offers a choicebetween two systems, depending on applica-

tion requirements: namely central or distrib-uted receiving pit dust control. These can befurther subdivided on the basis of whetherextraction is above or below the grid iron.Both systems are of modular design andcan therefore be customized to the specificconditions of each situation.

To ensure that the required aspirationcapacity of the intake pit dedusting is kept

to the minimum, every component needs tobe optimized. It is therefore an advantage if

there are gates at the entrance area whichare kept closed at all times during unload-

ing so that undesired air draughts and dustescaping to the surrounds can be preventedat the outset. For an optimum air flow inside

the reception area, the upper section of theside wall is fitted with louvers. This preventsdust getting whirled up and ensures that thedust which collects is directed towards theextractors (Figure 1).

Another technical step towards minimis-ing dust emissions can be taken by installinga dust barrier. The barrier has dust retentionpanels (Figure 2) and prevents dust whirlingup in the hopper. Practical experience fromday-to-day operations has shown that up to75 percent of the dust which is generatedis produced when the bulk material hits thefloor of the hopper. The dust barrier reducesair requirements, allows smaller filters andfans and cuts the power requirements of thefans by approximately 60 percent.

Filters for intake pits(decentralized)

For operations such as grain collectionfacilities or farms where the amount of dust

generated is insignificant or plays only aminor role at most, decentralized dedustingis the more appropriate solution (Figure 3).In this case two adjustable inlet openingsallow the air which requires cleaning to flowinto the filter panels, from which it is directed

to the fan through a manifold pipe line. Thefilter modules are connected using elements

to form a single unit and the cleaned dustfalls back into the reception pit via a diagonalplate.

Centralized intake pitdedusting

Centralized dedusting is designed morefor food processors such as grain millsand producers of pasta, where removingdust from the raw product is essential.As in decentralized dedusting, the air tobe cleaned is also caught by an aspirationpanel. The individual aspiration modulesare screwed together, which means that avariety of intake hopper sizes can be createdranging from 4 m to a maximum of 24 min length. The aspiration panel is connected

to a dust manifold pipe line which leads toa Bhler round filter. The round filter is a

central filter with a jet-pulse cleaning system.This is where the flow of raw gas which ispicked up and the dust which is retainedare separated. The dust is conveyed throughdust discharge chutes to separate dust con-

tainers or big bags. As a result, the undesireddust no longer comes into contact with theproduct, thereby ensuring improved hygieneand greater safety. This system could bedescribed as a form of initial pre-cleaning.

FilterTA-Luft directive requirements under

the German Federal Immissions Control Actstipulate emission limits of 20 milligrams ofresidual dust per normal cubic meter of air.The use of antistatic filter bags is one wayof ensuring compliance with these referencevalues. They are more effective at cleaning

than filter cells and also permit h igher airtocloth ratios.

Design of an efficient intakepit dedusting systemthe state-of-the-art in technologyby Andreas Rembeck and Rico Hindemith, Bhler GmbH

Figure 1: Schematic diagram of an intake pit

16 | January - February 2014 GRAIN& FEED MILLING TECHNOLOGYF

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Cleaning is on a time-controlled and/ordifferential pressure controlled basis, whichensures optimum filter performance andsaves energy.

ComparisonThe two types of intake pit dedusting

systems can be designed for both sideand rear unloading. With their adjustabledouble gap they can be customized to localconditions and are capable of aspiring evenif the intake pit is overfilled. Depending on

requirements the walls can be supplied withfilter modules only or with partition walls aswell, enabling sizes ranging from 2x3 to 4x24square meters.

The differences between the two fil- ter sys tems are as fol lows: whereas thedecentral dedusting system has a largersurface and therefore a lower filter load

than the central dust removal sys tem, themaximum dischargeable air rate of 55 mper minute and meter of pit length witha filter load of 5 m per minute and mof filter surface (grain) is less than thedischargeable air rate of the central solu-

tion, which is a maximum of 65 m perminute and meter of pit length for the

same filter load.Separate dust separation means that

the cen tral vers ion requ ires more spacefor Bhler round filters (Figure 4) and

dust containers. On the other hand thedecentralized dedusting system involvesadditional costs in terms of compressedair for cleaning the filter bags.

The purchase costs of the centralreceiving pit dedusting system are gen-erally higher than for a decentralizedsystem because the former has morecomponents. In terms of operating costs,however, the central solution normallyworks out better. Both systems have theiradvantages. The decision as to whether

preference should be given to the centralor decentral option depends on the spe-cific application.

www.buhlergroup.com

About BhlerBhler is a global technology leader

which specializes in the supply of equip-ment, systems and services for the con-version of renewable resources derivedfrom food and synthetic substancesinto top quality functional productsand materials. Bhler operates in over140 countries and has some 10,000employees worldwide. In fiscal 2012,

the Group generated sales revenue ofCHF 2,409 million.

Figure 3. Filters for intake pits (decentralized) Figure 4: Type RB round filter

Figure 2: Dust retention panels

17 | January - February 2014 GRAIN& FEED MILLING TECHNOLOGY17 | January - February 2014 GRAIN& FEED MILLING TECHNOLOGY F

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NIR:Production control inrapeseed processingusing NIR technology

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Design of anefficient intakepit dedustingsystemthe state-of-the-art intechnology

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