Two trends in feed processing around the world are pulling in nearly opposite directions. One trend tugs feed processing technology towards increasing scale and specialisation. Highly efficient, highly automated, single species feed plants favoured by large, integrated food companies. The other trend pulls in the direction of increasing flexibility and customisation of feed products. Super flexibility' of processing in a feed plant offers a range of processing technologies individually and in various combinationsto meet a very wide range of feed customer requirements.

With super flexibility, a single feed processing line may apply different processing technologies as needed in order to optimise feed processing for many different species and stages of animal growth. The line may make pelleted, extruded, or mash products, using conventional or hygienic heat treatment. It may add micro ingredients downstream from heat treatment and other processing, thus keeping upstream processes safe from cross-contamination and avoiding degradation and compensatory over-dosing of the micros. It may optimise the manufacturing process per feed product per customer. It may excel at different size runs of unique or specialised products.

For decades already, some commercial dairy feed compounders have followed a similar approach: The compounder would follow a custom formula, tailoring a unique feed product in order to optimise actual raw materials on-hand at the customer's farm. The goal was to make the best type and quality of feed for the lowest cost per kilogram of product yield, animal growth, or other performance parameter.

Recently, the international feed manufacturing systems and equipment suppliers, Van Aarsen, Dinnissen, and Almex, collaborated with the Netherlands co-operative SaWeCo to design, equip, and install an innovative, highly flexible, feed processing line at the co-op's Oirlo plant (see figure Monitor view'). As the Magi-Con collaborators explained at the recent Victam Asia exhibition in Bangkok: "The main goal was to develop a process that could supply a product that would be superior to existing products on the market and thus stay one step ahead of competition... already suitable for the future market demand."

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Three international feed manufacturing systems and equipment suppliers, based in the Netherlands, have collaborated in design and installation of an innovative, highly flexible, feed processing line for pelleted, extruded, and hygienic mash feed production, pioneered at the Oirlo plant of Dutch co-operative SaWeCo.

The new SaWeCo processing line can produce pellets, crumbles, expandates, extrudates, hygienic meal, and more. Presently, the line produces only chicken and pig feed products, although it offers much greater flexibility. Van Aarsen's Guus Heijnen explains that the processing concept demonstrated at SaWeCo depends upon three interdependent pillars': Hardware' (the processing equipment and physical plant), software' (the process control system), and feedware' (the feedstuffs specifications, formula, process sequencing, and effects of processing on the feedstuffs).

"None of these pillars can stand without the others," Mr Heijnen says. "And one of the biggest challengesand successesis to integrate and optimise each component of each pillar supporting the processing line."

LTC initiates FIFO material flow

In practical terms at SaWeCo, for example, integration and optimisation of the pelleting process mean that each product formula has its own optimal settings along virtually the entire processing line. With the Oirlo plant's post-grind design, automated process optimisation starts upstream in macro proportioning, followed by grinding, in which the control system uses power frequency motor control and screen size to determine the D50' or average particle size as well as particle distribution. Process optimisation continues downstream through micro proportioning and mixing, including liquid additions in the mixer.

Then the feed mash enters the first-in-first-out' (FIFO) Magi-Con processing line (see figure Process flow'). Initial processing occurs in the Van Aarsen long-term conditioner' (LTC), which offers residence time control of 1-4 minutes, adjusted by variable frequency drives (VFD) on the main motor and reductor. Also, the LTC has steam injection at atmospheric pressure in an insulated, stainless steel mixing chamber. Conditioned mash discharges into a vessel with built-in, disc-type feeder for discharge to the expander-extruder or standard conditioner above the pellet press.

"For biosecurity, the LTC has minimum retention time and temperature conditions," Mr Heijnen notes. "Retention time control in the LTC enables increased pelleting capacity with the same physical quality standards while requiring less energy per tonne. In the starch-rich formulas, we may use longer retention times to increase gelatinisation for greater pellet durability."

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The Magi-Con processa collaboration of suppliers Van Aarsen ( http://www.aarsen.com/?st_id=1 ), Almex ( http://www.almex.nl/ ), and Dinnissen ( http://www.dinnissen.nl/features a wide range of optional processing combinations using long-term conditioning, expanding, pelleting, and vacuum coating.

From the LTC, conditioned feed mash routes to the Almex expander-extruder or to the Van Aarsen pellet press.

The steam-injected, screw-type expander can alter the chemical-physical characteristics of the conditioned feed mash in order to optimise bio-availability of nutrients, Mr Heijnen says. For example, the expander can inactivate anti-nutritional factors (ANFs) in peas or beans to yield expandate with an improved nutrient profile for young animals.

The use of the expander typically would reduce mash retention time upstream in the LTC. Using the expander also affects the optimal settings of the pellet press. Mr Heijnen adds that the expander may be converted to an extruder by means of an automatically positioned die and cutter assembly. This application would by-pass the pellet press, enabling production of extrudates with greater starch gelatinisation.

Balance of pellet quality, output, cost

In optimising pelleting at SaWeCo, the focus is on the lowest production cost per ton at the target pellet quality, measured as durability or pellet durability index' (PDI). Automatic process control of the motor frequency controllers adjust pellet die speed. "Higher die speed means a higher output," Mr Heijnen notes, "but also less physical quality and, in general, more energy consumption per ton."

The multi-flexible' processing concept includes online physical pellet quality measurement, which provides direct feedback from any change in the setting of the processing options available. With the main focus on energy consumption (kilowatt-hour per tonne), the system optimises on lowest production cost per ton. The pellet quality is measured immediately downstream from the pellet press (see figure Process flow').

Vacuum coating for micros

"To measure is to know," Mr Heijnen says, "which always is more precise than any calculation based on system settings."

The pellet press itself features automatic roller adjustment in which rollers are adjusted individually. This innovation minimises roller slip, which wastes energy. It also enables the technique of thick-layer pelleting': The leading rollerset for a wider gap or die-to-roll distanceserves to pre-compact' the feed mash; then, the following rollerset for a narrower gapcompletes the compression of the mash into the die holes.

"At start up," Mr Heijnen notes, "we generally have a smaller distance between the roller and the die. Then we increase the distance, applying thick layer pelleting techniques. The maximum distance between the roller and the die is determined by the slip control on the roller as we only allow a maximum percentage of slip, which is determined for each roller individually. At the moment slip exceeds the maximum percentage, automatically the gap between the roller and die decreases to reduce slippage, with this process optimisation taking place on a continuous basis."

The optimal roller gaps depend on the particular feed formula and, when the gaps are optimised for the formula, the control system logs the settings for use in the next run of the product. In effect, the roller gap settings become part of the formula for the ration.

The pelleting process alone consumes about 50% of the energy required to produce pelleted feed. Roller slip causes significant negative impact on the energy usage per ton. Roller slippage also leads to blinding', blocking, or plugging the die, which results in costly down-time.

Automated control of the pelleting parametersparticularly roller adjustment and slip controlhelps extend the working life of the pellet dies and rollers. "Everything that happens in the die chamber becomes visible," Mr Heijnen observes. "Metal-to-metal contact is avoided by any means. Better die and roller management again leads to longer die and roller runs and lower production cost per ton, which offers pay-backs very quickly."

Liquids addition options

Pelleted feed products often incorporate a number of liquid ingredients, with fats and oils typically representing the greatest proportion by weight and volume. High levels of added fats and oils, however, can have a negative impact on pellet quality. To meet this challenge, SaWeCo's new production line provides oil-fat application in the batch mixer, upstream from pelleting, and in the Dinnissen vacuum coater, downstream from pelleting.

"This approach provides much more flexibility in the range of raw materials used in feed manufacture," Mr Heijnen notes, "and enables improvement in pellet quality. Of course, less oil-fat in the batch mixer generally has a positive impact on the pellet quality, but here again we need all the techniques steam conditioning, roller gap control, anti-slip control, die speed control to optimise the pelleting.

"There is no need anymore for fat or oil addition at the expander or at the die, as it is better to add all the remaining liquid at the vacuum coater. However, the exact proportion of fat-oil added at the mixer versus vacuum coater depends upon the requirement of physical pellet quality, that is, durability. Operating costs must be considered, too, because fat addition at the batch mixer is easier but negatively affects pellet durability. Durability is measured online, immediately downstream from the pellet press. Then the split' is made between addition of fat-oil at the batchmixer or at the vacuum coater.

"Also," Mr Heijnen adds, "we can play' with what kind of fat-oil we use at the batchmixer and at the vacuum coater, because the different types of fat-oil have different physical characteristics. Ultimately, we want to supply a consistent physical quality of pelleted feed under all circumstancessuch as change in formulation, different macro ingredients, etcand therefore we need to use all the options available, and fat-oil addition at different points is one of them."

Fat-oil as carrier for micros

Many vitamins, enzymes, and direct-fed microbial micro ingredients are sensitive to heat or pressure. Incorporating fragile micros in the main mixer, upstream from conditioning and pelleting, often requires overdosing to be sure of adequate concentrations in finished products. Vacuum coating of sensitive micros downstream from pelleting keeps these ingredients away from destructive processing effects and avoids overdosing (see figure Vacuum coating').

"If we are adding fat-soluble vitaminssuch as A, D, E, and Kwe can blend them in the fat-oil for vacuum coating," Mr Heijnen advises. "The remaining vitamins can be added with water. Obviously, the sequence of addition is also important. Enzymes are, in general, more sensitive to heat treatments than vitamins, so obviously they are always added at the post pelleting application."

For micros in powder form, the recommended technique is to vacuum coat them via a fat-oil or water carrier, or to coat the pellets with a layer of fat-oil which binds the powders.

Many poultry feed plants already add enzymes in atmospheric pressure fat-oil application systems immediately upstream from bulk loadout. However, the vacuum coater also is one of the last processing steps and an effective point to add contamination-sensitive' micro ingredients, such as medicated products. SaWeCo can add enzymes, vitamins, fat, and oil at the vacuum coater.

Creating the flexible pelleting database

"Ultimately," Mr Heijnen says, "we are creating a database which we use to optimise the process in terms of capacity as well as chemical and physical quality.

"This database describes the interactions among the different processes as well as the use of options or variables in each individual process. Through time, more and more data will become available and the learning curve will expand."