<?xml version="1.0" encoding="UTF-8"?><rss version="2.0"><channel><title><![CDATA[Feed Milling Articles and Resources]]></title><description><![CDATA[Articles]]></description><link>http://www.feedmachinery.com/articles/</link><copyright><![CDATA[Copyright Feed Milling Articles and Resources]]></copyright><generator>sNews CMS</generator><item><title><![CDATA[The Art (Science) Of Pelleting]]></title><description><![CDATA[  
       
           Keith C. Behnke     
         Kansas State University    

        
    
 
       Pelleting has been, and continues to be, a popular processing technique in feed manufacturing. In basic
       terms, pelleting converts a finely ground blend of ingredients into dense, free flowing agglomerates
       (pellets). There are many reasons used to justify the process, but it may be appropriate to list just a few:  
       • improved animal performance,  
       • decreased feed wastage,  
       • reduced selective feeding,  
       • improved bulk density,  
       • better material handling characteristics,  
       • destruction of deleterious organisms, and  
       • customer expectations.  
       Pelleting operations are not without cost. It is a fairly expensive process in terms of both capital and
       variable costs, but the expense is usually justified in improved plant profit as well as animal performance.   
     
         The purpose of this paper is to discuss the pelleting process in terms of operations and to describe
     how the success or failure of the operation can impact on profits as well as animal performance.   
  The Process        
  The formation of the pellet actually occurs at the "nip"
  between the rolls and the die. All other activities associated
  with the operation such as conditioning, cooling, etc. really
  support and augment the action at that point in the system.
  In order to understand the process and be in a position to
  make intelligent decision to improve throughput, quality or
  appearance, one must have a thorough understanding of
  what happens at the nip point. Figure 1 is a representation
  of the die-roll assembly and will help the reader understand
  the process.  
  
  Depending upon the physical characteristics of the feed, a
  lesser or greater proportion of the work done by the pellet
  mill is used for compression. For example, if the formula
  contains a high level of fibrous ingredients such as bagasse,
  bran, or ground alfalfa, the mill will expend a large amount
  of energy simply compressing the mash to the density of
  the subsequent pellet. Conversely, for a relatively dense feed
  such as high grain and soy meal, the mill will expend a lesser
  amount of energy for compression and a greater amount
  for throughput.   
  The "extrusion area" shown in the figure is the point at which
  the mash has reached pellet density and begins to flow
  through the die holes. There are many physical forces that
  must be dealt with in the pelleting process. Figure 2 is included
  to familiarize the reader with some of the major forces involved.  
  The primary purpose of the roll is to provide a force on the mash to densify the feed and cause it to
  flow toward the die. The gap between the roll and the die, the roll surface characteristics and the
physical properties of the mash determine how great this potential force might be.   
  The die provides, not only the final diameter of the pellet, but the resistance force on the feed and
  has a direct influence on throughput rate and pellet quality. These two forces (roll and die) are apposite
  each other as shown in the diagram, but must work together to provide quality pellets at an acceptable
  production rate. The force generated by the roll must be greater than the resistive force provided by
  the die; if not, throughput is zero.   
  With a general understanding of the process inside the pellet chamber, it is appropriate to move to
  a discussion of various factors that affect both throughput and pellet quality.  




  

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       Other Parts to this Article    
   Art of Pelleting: Part 2 - Pellet Quality, Formulation, Minerals    

  Art of Pelleting: Part 3 - Particle Size, Mash Conditioning, Die Specifications, Conclusion  
   

]]></description><pubDate>Thu, 11 Jun 2009 05:21:00 +0000</pubDate><link>http://www.feedmachinery.com/articles/feed_technology/the-art-science-of-pelleting/</link><guid>http://www.feedmachinery.com/articles/feed_technology/the-art-science-of-pelleting/</guid></item><item><title><![CDATA[The Art (Science) Of Pelleting: Part 2]]></title><description><![CDATA[  

  Pellet Quality  
For purposes of this paper, pellet quality will be equated to the ability of pellets to withstand repeated
handling without excessive breakage or fines generation. There are many factors that affect pellet
quality, but the following will be discussed in some detail:  
• formulation  
• ingredient particle size  
• mash conditioning  
• feed rate  
• die speed  
• die specifications (design)  
• other factors  
  
  Formulation  
There are feedstuff materials that pellet well and produce a durable pellet and others that will not.
MacBain (1966) developed a pelletability chart in which he ranked feed ingredients in their pelletability
and degree or abrasiveness. Bartikoski (1962) experimented with applying numerical value to each
major (feed) ingredient to indicate its "stickiness" or its ability to help form a tough, durable pellet.
He called that value a "stick factor" and fed that factor into the computer along with the various
nutritive values of each ingredient to provide formulas that meet all nutritional specifications as well
as supplying a formula that will produce a quality pellet at least cost.  
Those early workers led others to experiment with the effects of various ingredients - grains, milled
grain by-products, fats, pellet binders, minerals, etc. - on pellet quality or durability. They also led to
the development of a standard method for testing pellet durability perfected in the 1960's by Dr. Harry
B. Pfost at Kansas State University and accepted as a standard by the American Association of
Agricultural Engineer - ASAE S-269.3 (ASAE, 2003). That method is generally known as the K-State,
or tumbling can, durability test; and it provided a means of quantifying the toughness of pellets or
their ability to withstand the downstream handling that is typical in feed plants and feed delivery
systems. That was a major breakthrough in the technology of pelleting and has served the industry
for all these years.  
  
  Minerals  
Pellet mill performance can be significantly affected by the physical and chemical forms of the calcium
and phosphorus sources used in the formula. Sutton (1979) investigated the effect of deflourinated
phosphate (two particle sizes) and dicalcium phosphate (18.5%) on pellet mill performance with a
broiler grower formula. He found the production rate for the diet containing regular grind deflourinated
phosphate to be 68.9% greater than for the diet containing an equal amount of dicalcium phosphate.
The finely ground deflourinated phosphate had a 52.5% advantage over dicalcium phosphate.
In a similar study (Behnke, 1981) we also studied the effect of mineral sources on pellet mill performance
and pellet quality. Two deflourinated phosphate sources, a fine grind (DPF) and a regular grind (DPR), and an 18.5% dicalcium phosphate (DCP) were used. A practical layer diet was used in which each
test mineral source was evaluated at both high (2.5%) and low (1.5%) levels in the diet.
At both levels tested, the production rate for the deflourinated phosphate sources significantly
outperformed dicalcium phosphate; while the DCP had a slightly, but not significantly, higher pellet
durability index. That would indicate that a physical change - thicker die or reduced feed rate - could
be made to improve pellet quality without a substantial loss of system throughput. Behnke (ibid),
Verner (1988), and McEllhiney and Zarr (1983) reported similar results comparing phosphorus sources
in a variety of pelleted feeds produced under many conditions.  
Those studies are cited, not to encourage or discourage the use of any mineral source or any other
ingredient - that's the nutritionist's decision - but to indicate that those sources and ingredients can
affect pellet quality and production rate and should be considered in the quest for improved pellet quality.    

  

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  &nbsp;  
  


       Other Parts to this Article    
   Art of Pelleting: Part 1 - The Process    

  Art of Pelleting: Part 3 - Particle Size, Mash Conditioning, Die Specifications, Conclusion  
   
]]></description><pubDate>Wed, 10 Jun 2009 06:46:00 +0000</pubDate><link>http://www.feedmachinery.com/articles/feed_technology/the-art-science-of-pelleting2/</link><guid>http://www.feedmachinery.com/articles/feed_technology/the-art-science-of-pelleting2/</guid></item><item><title><![CDATA[The Art (Science) Of Pelleting: Part 3]]></title><description><![CDATA[
  
  Particle Size  
Optimum particle size for best pelleting results has been a matter of controversy for almost as long
as feeds have been pelleted. Young (1960) found no significant differences in pellet durability when
he experimented with feed rations containing 40, 60, and 70 percent ground corn or grain sorghum
when the grain portions were ground coarse, medium, and fine.  
Martin (1984) compared pelleting efficiencies and durabilities using a hammermill and a roller mill to grind
the corn portion (59.5%) of a pelleted feed. He did not find any differences (P ]]></description><pubDate>Tue, 09 Jun 2009 06:50:00 +0000</pubDate><link>http://www.feedmachinery.com/articles/feed_technology/the-art-science-of-pelleting3/</link><guid>http://www.feedmachinery.com/articles/feed_technology/the-art-science-of-pelleting3/</guid></item><item><title><![CDATA[Post-Pelleting Liquid Application: A Practical Guide: Part 1]]></title><description><![CDATA[   
 
  
       
           Doug Decksheimer     
         Comco Systems Inc.    

        
    
 
 
 
  Introduction And Background  
  In most cases, post-heat liquid application treatment has been limited to fat additions of 1-10 percent.
  Equipment to apply fat is present in many mills and in some cases can be adapted to apply other liquid
  ingredients. In the past five years, several hundred pellet lines globally have been retrofitted to dispense
  enzymes. This increasing trend in Asia has been mostly in high capacity integrated operations. However,
  today, benefits can be realized in most mills as technology has changed to offer more cost effective solutions.    
  When determining equipment needs for heat-sensitive liquid ingredients such as enzymes, every
  effort should be made to ensure that these products are applied with precision and accuracy. Systems
  to apply liquids post-heat treatment work in a continuous flow setting in most instances. The aim is
  to apply the liquid after the fines are returned and before the feed goes to the feed truck.
  Parameters must be defined to monitor the equipment's efficiency. The installation of a liquid addition
  system can add a number of requirements to the feed process and existing equipment. These will
  be discussed in this paper.   
  The accuracy of a liquid application system should be determined by its ability to consistently deliver
  precise amounts at the feedmill. It should not be measured by animal or bird performance after
  consumption of the finished feed.   

  The Problem  
  High temperatures are used to satisfy requirements of quality feed and hygiene. Most pelleting mills
  operate at temperatures between 70 - 80°C. Health issues, such as salmonella have created the
  need for pelleting temperatures in excess of 90°C. Thermal treatment provides the following advantages:  
  • Gelatization of starch  
  • Enhancing the pellet quality  
  • Enhancing digestibility  
  • Hygiene treatment  
    
  Typically, the pelleting process involves conditioning, pressing and then cooling. Those mills utilizing
  expanders, process at higher temperatures and pressure. Heat, moisture, pressure and friction,
  reduction and oxidation reactions and light are stress factors which can negatively influence additives
  (Schwartz, 1998; Putnam and Taylor, 1997; Perry, 1997; Blair, 1996) Therefore, heat sensitive feed
  stuffs such as enzymes, vitamins, amino acids, probiotics and antibiotics, may require optional
  processing equipment.   
  Getting Started  
  The application of well-defined feed additives is becoming an indispensable tool for feed producers.
  There is a constant drive to produce low cost feed with maximum nutritional availability. In fact, postpelleting
  application can increase profitability.   
  As mentioned previously, post-pelleting application is not entirely new to the industry. However,
  enzymes and other heat-sensitive concentrates have changed the paradigm for post-pelleting addition.
  Inclusion rates of 40 to 250 grams per ton of finished feed have created the need for precision
  equipment and have raised some notable concern within the feed industry.   
  Following are some factors that influence the success of any post-pelleting application system:  
  1. Coefficient of Variation - the additive must be presented with uniformity to pellets  
  2. Accuracy - over-dosing or under-dosing is undesirable  
  3. Precision - the system must provide consistent and repeatable dosing  
  The answers to the following questions will provide some basic information to consider when making
  equipment changes and adapting new processes to the mill. The answers will also assist in successfully
  achieving the above points.   
Determining Questions:  
  1. Where is it possible to add liquid ingredients in the feed process?
  Heat-sensitive ingredients must be added after cooling/sieving and prior to load-out.  
  2. Where is it possible to measure or calculate the flow of feed pellets or crumbles?
  In order to accurately dose precise amounts of liquids, the rate of dry flow must be accurately
  determined.  
  3. How much automation is needed to meet quality control requirements?
  To ensure repeatability and guarantee the application, a means of implementing both robust
  hardware and controls/software is necessary.   
  Some Useful Resources in Helping to Evaluate Equipment Needs:  
  1. The liquid supplier may have feed engineers or technicians available  
  2. The liquid equipment supplier will have varied experience  
  3. Consulting or engineering firms may help assess mill needs  
  Equipment suppliers in conjunction with nutritionists, mill managers and maintenance personnel can
  all provide input to creating a well-defined system. In short, if you do your homework, your application
  will be successful.   
  

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       Other Parts to this Article    
   Post-Pelleting Liquid Application: Part 2 - The Application
    

  Post-Pelleting Liquid Application: Part 3 - Quality Assurance & Automation, Summary  
   
]]></description><pubDate>Sun, 07 Jun 2009 07:14:00 +0000</pubDate><link>http://www.feedmachinery.com/articles/feed_technology/postpelleting-liquid-application/</link><guid>http://www.feedmachinery.com/articles/feed_technology/postpelleting-liquid-application/</guid></item><item><title><![CDATA[Post-Pelleting Liquid Application: A Practical Guide: Part 2]]></title><description><![CDATA[  

  The Application  
    Dry Flow Measuring    
  
  Achieving the desired accuracy is greatly dependent upon the level of accuracy obtained from the
  dry-flow measuring device. In general, the steadier the dry flow, the more accurate the liquid can be
  applied. (Aicher, 1998).
  
  Several options are available for measuring and controlling the dry flow of pellets or crumbles. It is
  relatively safe to say that the more money spent on dry flow monitoring, the more accurate the system
  should be, however, one must consider serviceability and ease of calibration within that equation.
  For many mills where bulk density of the finished feed is consistent, volumetric measuring (Figure 1)
  is a proven solution. This cost-effective method uses a surge or buffer hopper with a low and high
  level switch; the system is calibrated by determining the decreasing amount of pellets over a specified
  amount of time. Once product reaches the low level switch, a screw auger stops, allowing the bin
  to fill until product reaches the high level switch and the process then repeats itself.
  
  Several systems employ weigh belts. This method uses a surge bin directly above a belt or mixing
  screw, which is suspended by a load cell. Weigh belts are not affected by changes in bulk density
  and can easily be retrofitted into existing mills. They do however, require a high level control system
  for calibration. Most weight systems are marketed as a package and require a large footprint.
  Impact Scales - involve calculating weight by the force of pellets hitting a plate. This method has
  been widely used in many feedmilling applications. These devices are compact. Impact scales should
  
  only be installed in constant flow applications or inconsistency will occur. Bulk density changes may
  impact the calibration.
        
  Newer yet, is a technology that uses a curved chute resting on a sensing element or load cell. The
  system determines flow by measuring the sum of forces necessary to re-direct the incoming flow of
  material from near vertical to near horizontal. Hence, a momentum measurement. Realized accuracy
  of 99.5% or better is achievable.
  In essence, dry flow measuring is the heart of the application, and inaccuracies are compounded
  through the remainder of the process. Each of the above methods of monitoring pellet flow will work
  successfully provided the application of the equipment is correct. It is important to ask questions and
  provide equipment manufacturers with all the relevant data necessary to design an appropriate
system.   
    Liquid Monitoring And Delivery    
  
  Currently, there are three methods employed for monitoring the liquid ingredient: measurement can
  be volumetrically, loss-in-weigh or by flow meter. There are advantages and disadvantages to all;
Volumetric (Figure 2) is by far the most cost effective.   
  This system uses a positive displacement pump
  to dispense precise amount by two methods;  

  a. time base by calculating the amount of liquid delivered over a specific time and relating that amount
  in a given minute or hour.  
  b. Pulse emulation where each stroke of the pump is proportioned to deliver a given amount. The
  control system then reads the pulses and records the flow rate.  
        
  Because volumetric systems do not have true flow knowledge, it is important that these systems
  have low level detection and in-line no flow monitors or switches to alarm the operator. Volumetric
  systems installed correctly can provide superior accuracy with a low cost.

  Loss-in-weigh is a weight-based system using a positive displacement pump to dispense the precise
amount from a day tank.   
  Some advantages of this method are:  

  
  • Liquid densities do not effect the system  
  • Real-time weight processing  
• Inventory is easier to reconcile by weight  
  The scale offers further benefits by allowing low level monitoring and re-filling set points.
  Flow Meters are the traditional means of monitoring liquid flow. Reliability and accuracy can be
  proportional to the money spent on the flow meter.
  In flow-meter type systems, a positive displacement pump forces liquid into the flow meter producing
  an electrical out-put to flow. Flow meter based systems require limited space. It is advisable to use
  a mass flow meter with critical ingredients and those liquids that are subject to density changes with
  temperature.
  
  Because of the low inclusion (40 - 250 grams per ton) of critical ingredients, it seems logical to dilute
  additives with water or oil. This will also increase the number of droplets, which will have a positive
  effect on distribution (Van der Poel and Engelen 1998).
  In practice, dilution is simply used to increase the accuracy of the installation. Although the objective
  is a minimum level of water inclusion, an amount of 500 - 1,000 grams per ton add rate has been
proven effective.   
  When it is necessary to mix heat-liable liquids with water, the application system
  must meet the following criteria:
    
  1. Mixing should take place as close to the spray application as possible.  
  2. The system should be purged if extended mix times exist  
3. A mechanical static mixer should be used  
  It is possible to spray one or more liquids together in a post-pelleting installation. Compatibility must
  be determined. Due to contamination and stability concerns, it is recommended that liquids be dosed
  independently if from varying suppliers.
  
  
  At times, addition of enzyme or other heat-liable ingredients will take place just before or just after
  coating the feed pellets with fat. Even if the pellets are coated with fat first, the low levels of enzyme
  added may be absorbed (Figure 3). The small amount of water added with the enzyme does not alter
  the humidity of the pellets significantly, primarily because addition rates are well below one litre/ton
  (Perry, 1997).
  
  Further, information on the effects and interaction with fat can also be seen in Figure 3. The recovery
  of Xylan LC® was shown to be sufficient irrespective of the fat temperature or the fat level. (Annonier
et al., 1998).  
        
    It is practical to apply the critical ingredients prior or in conjunction with the fat or oil. This application
  will provide a sealed pellet of the ingredient and reduce the need for penetration if applied after fat
or oil coating.   
    Spraying And Mixing    
  
In practice, it is not feasible to disperse the liquid additive over all the pellets.   
  Homogenous distribution
  is achievable but only considering the following:  
  
  1. Fines must be minimized. Sieving of the fines prior to application increases accuracy  
  2. Post mixing after application increases distribution lowering the co-efficient of variation  
  3. The droplets of liquids must be maximized  
  Liquid droplets are created by using force and properly selected nozzles. Nozzle sizing is very specialized
  and many factors must be considered. Nozzles that are not sized correctly can produce over or under
  spraying and negatively impact the installation. A "one size" fits all approach will not work.
  Some systems typically used for fat application use a high speed disc which produces a fine atomized
  mist. This is also an effective method of application and dispersion.
  
  Fines present challenges in post-pelleting systems, particularly in crumb feeds. The wide particle size
  range and the presence of substantial amounts of fines make the occurrence of segregation practically
  unavoidable (Barendse,1995). Fine particles that have comparatively large surface/weight ratios will
  absorb a relatively high percentage of the additive.
  
  Further, fines created or contained in the feed, reduce mixability. In consideration of this, post-pelleting
  systems should be engineered to minimize pellet degradation during and after spraying.
  
  
  When spraying or applying liquids, four methods are often used:  

  1. Mixing Screws - can be retrofitted to allow feed to drop in a flat curtain. A ribbon flight with mixing
  bars welded at every pitch at 90 degrees apart can produce the needed curtain. A benchmark
  of 20 seconds retention time will produce excellent mixability.  
  2. A Spray Chamber - is created by use of cones or baffles in a closed compartment. Feed is thinned
  to a curtain. For areas with limited space, this may be the only option. Care should be taken to
  avoid overspraying. The chamber should be accessible for regular cleaning.  
  3. Roto Coater type systems have been developed primarily for the application of fat. The design
  of these features two discs. Pellets land on the top of a low speed rotating disc which provides
  a 360 degree curtain around a second disc. Liquid droplets landing on a second high speed
  rotating disc cause a fine atomized mist, which is forced on to the pellets. Several manufacturers
  provide similar type systems.  
  4. Batch mixing - has been used successfully in Europe for adding liquid post-pelleting. The need
  for a pre-hopper is required and this creates space problems. These mixers are typically paddle
  type and the weighing of liquid and mixing is completed over a short period. The advantage of
  this type of system is that it allows for the flexibility of adding both liquid and powder ingredients.  
  Post mixing after spraying improves uniformity in all application systems. Although some mixing occurs
  during transportation of the feed, it is expected that the homogeneity will be better when a complete
  mixing is performed. The object is to have the liquid contact a maximum number of pellets (Aicher,
  1998). Sufficient retention time and agitation are necessary to accomplish the desired result (Figure 4).         
  
  
  
  

    3    

    2    
    1    
  &nbsp;  
  


       Other Parts to this Article    
   Post-Pelleting Liquid Application: Part 1 - Introduction, The Problem, Getting Started
    

  Post-Pelleting Liquid Application: Part 3 - Quality Assurance & Automation, Summary  
   
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