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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 of information published. ©Copyright 2010 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1466-3872

Digital Re-print - May | June 2011 Conditioning as part of the pelleting process

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While conditioning is a process that has kept the attention of the modern feed milling industry

for some time now, the pelleting process of press meal is a subject that is no longer considered to be very important.

It needs to be understood that feed milling is about the balance between the different processes being used.

As one process is linked to another, it is difficult to discuss only one process without having to take another into consideration. The following is a discussion of two proc-esses, which interact frequently with one another and also with all the other processes used in feed milling.

ConditioningConditioning is a process in the feed mill-

ing industry, which takes place from intake to out-loading.

However, in many cases when referring to conditioning, it is the treatment of press meal prior to the pelleting process that is meant.

Conditioning of press meal is a process with the variables time, humidity, tempera-ture and pressure. Pressure is only used in unconventional processes where expander

or extruder techniques are being used. In the conventional conditioning process, only time, humidity and temperature are applicable.

Whereas in the past the aim of condition-ing was to optimise the pelleting process, nowadays it is much more the intention to optimise the nutritional and physical quality of the feed.

When using the variables in the conven-tional conditioning process, it should first need to be understood that temperature and humidity are related as steam is gener-ally used to increase the temperature of the press meal.

Furthermore, there is also a maximum level of humidity of the press meal in order to avoid blockages of the pellet press.

In general it can be said that the maxi-mum percentage of steam that can be added to the press meal is approximately maximum five percent and for each percentage of dry steam added, the temperature of the press meal will increase by approximately 15 degrees Celsius.

Of course, the steam quality is influential and the above mentioned values are only applicable when a good quality steam is being used. Besides steam quality, the influ-ence of the humidity of raw materials as

well as the feed composition are of great importance.

Steam quality and steam quantity control are subjects enough alone to warrant further discussion, however, in many practical cases, steam quality and steam control are subjects that are not usually given the attention they need in order to optimise the conditioning process.

As temperature and humidity are strongly related, the actual variable available in a con-ventional conditioning process is time.

It should, however, be kept in mind that the conditioning process is an optimisation and not a maximzation. Where single con-ditioners were a common choice for quite a number of years, now double and even triple conditioners are being used prior to the pelleting process. Conditioning times lasted, in most cases, less than a minute and more importantly these types of conditioners did not guarantee the ‘first-in, first-out’ principle.

For many years, the only conventional conditioning process that could guarantee a given time and that extended a maximum retention time of one minute, while also guaranteeing ‘first-in, first-out’,were ripeners; a kind of cooking vessel which has been in the feed milling industry for over 20 years and in many varieties.

Conditioning as part of the pelleting process

by Harold Schroijen, Van Aarsen International, The Netherlands

The global go-getters at Van Aarsen are ready and willing to assist in optimising processes, resulting in higher returns and more ease in operation

Grain&feed millinG technoloGy18 | may - June 2011

FEATURE

The main concern when using the ripen-ers in the feed milling industry is contamina-tion but when much longer conditioning times (that is >4 minutes) are required, the ripeners are still a valid option.

As already stated the conditioning proc-ess is about optimisation and therefore the time factor is mainly determined by the conditioning temperature and the formula-tion. The temperature level can be varied according to the retention time in order to avoid destructive effects on the nutrients in the feed (that is protein de-naturation).

Whereas the formulation has an influence on the retention time meaning that the opti-mum availability of nutrients in the feed can be reached as well as optimising the physical quality of the pellets.

Recently other aspects have had to be taken into account due to consumer con-cerns, for instance salmonella. Also this needs to be considered and treated in the conditioning process.

Therefore, the new generation of con-ventional conditioners (without using pres-sure) are focussing on the variables time, temperature and humidity where time is maximized to four minutes at temperatures of approximately 85 degrees Celsius and capacities of up to 20tph.

These types of conditioners should guar-antee a ‘first-in, first-out’ while also guaran-teeing retention time. The principle is rather simple as generally the feed is brought up to the required temperature by means of steam and subsequently transferred into a large screw conveyor in which the speed of the mash is determined by a frequency controller. The screw conveyor is steam or electrically heated and insulated.

So, by means of the filling degree and the frequency (at a certain pitch of the screw), retention time can be guaranteed. For those involved with feed milling practises, it is well known that there are a few concerns.

Firstly, the height of installation for this new generation of conditioners is not often available. For this reason, Van Aarsen

International BV in the Netherlands is able to position the conditioner beside the Long Time Conditioner (LTC).

The second concern is the control of the pelleting process because the long retention time leads to a delayed reaction of the pellet press on changed variables. This complicates the matter even further due to the fact that the pel-let mill cannot be fed directly from the retention time screw.

Some suppli-ers therefore use small intermedi-ate bins between the retention time screw and the pellet press with a feed-ing screw for the pelletpress below the bin, leading possibly to contamina-tion as well as loss of tempera-ture. Once again more height is required and control becomes even more to maintain due to the use of buffer bins.

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holes or the open area surface (OAS) and the wall thickness of the die including possible counter-drill.

When discussing capacity, using the same formulation and the required pellet quality, the die surface of the pellet mill (with the same OAS) and the die

thickness are the major factors influencing capacity. These together with the drive installed, determine the KW per cm2, which is a factor to be consid-ered when researching the operational costs.

Practical trials carried out under 100 percent identical circumstances, have indicated that differ-ences in operational costs among different types of pellet mills can vary up to EUR50.000 per year which are, of course, significant figures but realistic never-theless.

Van Aarsen pellet mills are well know for their design criteria, a huge die surface and low die speed so that an acceptable

capacity is reached while still maintaining focus on pellet quality (which is also influ-enced by the retention time of the press meal in the die).

This, of course, combined with an inter-mediate drive allowing the possibility to change die speed relatively easily (changing a small pulley) without installing frequency controllers for the generally larger drives used on pellet mills.

Furthermore, large roller diameters cre-ate a small angle between the die and the roller, which compacts the feed smoothly before forced it into the die.

Of course, variables differ when using the pellet mill for traditional-, untraditional- or aqua- feed but the principles remain the same. As circumstances differ constantly, only general guidelines can be provided except for when detailed information is avail-able and a custom-made solution given by those in the feed milling industry with both feed on the ground.

difference can be explained by formulation, die specifications and the required pellet quality. Also a proper conditioning process influences the output of the pellet mill.

However, the figures above are based on the same conditioning process.

Of course, the pellet mill has a number of variables that can be used to optimise the process. These variables vary from speed of the die to hydraulic roller adjustment and should only be used when the influence of these options are thoroughly understood by the operating personnel.

This practical know- how could also be delivered by an intelligent pelleting line auto-mation system such as PressM@nager. This system is capable of combining the different variables in order to optimise the process.

However, before continuing the pelleting process, a small note needs to be made about the dies being used.

As dies of reputable suppliers are gen-erally all of the same material, which is completely hardened, difference is generally found in the open area surface - OAS (that is, the number of holes), which, of course, is related to the capacity of the pellet mill.

Therefore when comparing dies, the aspects that need to be considered are the types of material to be used, the hardness and whether surface hardening or complete hardening will be used, the number of

In order to avoid this, Van Aarsen has integrated a feeding device in the Long Time Conditioner, facilitating the control and the required height is easily a few less meters. All these features have been integrated into one conventional conditioner, which is called the ‘Conditioner LTC’.

For a standard control a PLC is integrated into the pelleting line control system and for a more sophisticated control a PressM@nager, the Van Aarsen pelleting line automa-tion based on remote I/O with intelligence (meaning the system is capable of achieving even higher goals than a well-trained pellet mill operator).

PelletingAfter conditioning of the press meal

either the mash is cooled when heat-treated mash is required (for instance breeders) or, in most cases, the pelleting process starts.

The pelleting process also has an effect on the nutritional as well as the physical qual-ity of the feed. Experience has shown that it is not only the capacity of the pellet mill but the formulation, die specifications as well as the required pellet quality are also aspects that should be taken into account.

Where a Van Aarsen C900 is produc-ing 45tph in South America, the same machine is capable of reaching a capacity of 18tph in a Dutch environment. The big

More inforMation:Van Aarsen International BVPO Box 5010, Heel, NL-6097 ZG The Netherlands

Tel: + 31 475 579444Website: www.aarsen.com

Grain&feed millinG technoloGy20 | may - June 2011

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In this issue:

• Synthesis of animal feed formulation techniques:

Linear and Non-Linear model

• Pellet production

to save energy,

improve feed efficiency

and safety

May 2011

• Choosing the right Hazard Monitoring System

• Pelleting: The link between practice and engineering

• Conditioning as part of the pelleting process

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