GB2449700A - Determining the Durability of Animal Feed Pellets - Google Patents

Abstract

A method of assessing feed pellet durability which comprises subjecting feed pellets to impact and determining the resulting proportion of pellet fragments.

Description

Method This invention relates to a method for determining the

durability of animal feed and to apparatus for the performance of said method.

Animal feed, e.g. for farmed animals such as cattle and chickens, is frequently provided as feed pellets. These may be produced by extrusion or by compaction, ie by pelletization. In general, feed pellets for poultry and land mammals tend to be produced by compaction, whereas feed pellets for aquaculture tend to be produced by extrusion, optionally followed by lipid coating or impregnation. As used herein, the term "feed pellets" covers the product of any appropriate process and not simply compaction processes.

Feed pellets may be packed in sacks or may be delivered in bulk containers and pneumatically pumped into the farmer's storage silo.

The post-production and pre-consumption handling of feed pellets (eg drying, cooling, packing, storage, transport and silo delivery) causes pellet damage, e.g. fragmentation or dust generation. In general, dust will not be consumed and thus ends as waste at the feeding site. Moreover, some animals (e.g. cattle) will consume a lesser proportion of fragmented (or "broken") feed pellets and thus pellet fragments may contribute significantly to the proportion of feed that is wasted.

In the development and performance of feed pellet production processes, it is thus common for the feed producer to test the durability of the feed pellets produced. Typically this involves subjecting a sample of feed pellets to impacts mimicking the nature of those impacts encountered during post-production, pre-consumption handling, and determining the quantity of pellets that remain intact, e.g. as a percentage by weight of the intact pellets initially present in the sample.

We have now found that a better measure of feed pellet durability is provided by the proportion of feed that is in the form of pellet fragments than by the proportion that is unfragmented or the proportion that is in the form of dust or fines, i.e. that where the feed following handling comprises x% UBP (unfragmented pellets), y% BP (particle fragments) and z% TD (dust and fines), y is a more sensitive measure of durability than is x or z. Thus viewed from one aspect the invention provides a method of assessing feed pellet durability which comprises subjecting feed pellets to impact and determining the resulting proportion of pellet fragments.

The pellet fragments detected using the method of the invention will generally be fragments distinguishably smaller in size or weight than the starting unfragmented pellets and distinguishably larger in size or weight than any resulting dust or fines -distinguishing from unfragmented pellets and from dust or fines may readily be effected using conventional particle separation techniques, e.g. screening or sieving, cyclone separation, air blowing (e.g. using a fluidized bed), automatic optical recognition, etc. Typically, however, separation will be effected by screening using mesh sizes capable of allowing passage of particles (a) having a minimum dimension of no more than 95% of the minimum dimension of the initial unfragmented particles, eg no more than 85%, especially no more than 80%, more especially no more than 75%, particularly rio more than 70%, and (b) having a minimum dimension of no more than 25% of the minimum dimension of the initial unfragmented particles, especially mo more than 20%, particularly no more than 15%. Thus, for example, for cylindrical pellets having a diameter of 4 mm, the unfragmentedJfragment screen may have a mesh size of 3.15 mm and the fragment/dust-fines screen may have a mesh size of 0.5 mm.

The proportion of pellet fragments will typically be calculated as a weight percentage of the total starting sample; however it can of course be expressed as a volume percent or as a number ratio (e.g. fragments to unfragmented particles or fragments to total pellet number in the starting sample).

In the method of the invention, the starting sample may be pre-screened (e.g. using any of the methods above) to remove dust or fines; however this is not required.

In the method of the invention it is desirable also to determine the proportion of intact ("unfragmented") pellets and/or of dust or fines after the impact. Here it will be understood that the "unfragmented" pellets so determined will include pellets that have suffered some, but only minor, material loss as a result of impact.

Before impact in the method of the invention, the pellets may if desired be dried and/or cooled as desirably the pellets tested will have a moisture content and temperature comparable to that of the pellets during transport and delivery. Such drying and/or cooling may be effected on individual pellets, on batches of pellets, or continuously, and is especially preferably done where the method of the invention forms part of the online monitoring of a pellet production process.

The impact the pellets are subjected to during the method of the invention will typically be impact with a container or conduit wall or with a target surface. For pellets produced by compaction (eg pelletizarion), it is preferably impact with a conduit wall, while for lipid-containing or coated extruded pellets it is preferably impact with a target surface.

Since feed pellets are frequently delivered by a gas pressure differential (e.g by use of pressurized air), impact is preferably of pellets in a gas pressure differential-induced or -enhanced flow. Thus, for example, for compacted pellets this may be caused by placing the pellets in a spiral or helical conduit with a gas pressure differential between the conduit ends. In travelling through such a conduit, the pellets will impact the conduit walls, especially if the conduit path is curved or angled, eg as in the case of a helix of rectangular cross-section. Likewise, extruded pellets may be accelerated along a linear conduit under a gas pressure differential to impact a target surface at the downstream conduit end. Impact may likewise be gravity-induced or gravity-enhanced (e.g. by having the conduit entry above the conduit outlet).

Feed pellets to be subjected to the method of the invention may be selected batchwise from pre-produced feed pellets or more preferably may be taken online from the feed pellet production process either continuously or batchwise. Unfragmented pellets may of course be returned for use as feed, and fragments and dust or fines may be recycled into the feed pellet production process.

The feed pellets to be subjected to the method of the invention may be feed pellets of any shape or size; typically however they will be of conventional elongate cylindrical form, e.g. 2.0 to 5.0 mm diameter and 3 to 20 mm length.

The method of the invention may be performed on apparatus capable of causing pellet impact and separating Out the fragmented pellets, from the intact pellets and the dust and fines. Such apparatus forms a further aspect of the present invention.

Viewed from this aspect the invention provides a feed pellet durability tester comprising a pellet impact surface, and a particle separator for separating feed pellet fragments from larger particles and from smaller particles.

The tester of the invention preferably has a pellet flow conduit, especially preferably one attached to a gas pressure supply to facilitate pellet flow through the conduit. This may be a positive pressure supply at the upstream end of the conduit, i.e. to blow the pellets through the conduit, or a negative pressure supply at the downstream end of the conduit, i.e. to suck the pellets through the conduit.

The conduit itself may be linear or non-linear and open (eg trough-like) or, more preferably, closed (eg tube-like). Linear conduits are preferred for use with extruded lipid-coated pellets to avoid conduit blockage, whereas non-linear conduits are preferred for use with compacted pellets as the inner walls of the conduit serve as a pellet impact surface. Non-linear conduits are preferably in spiral or more preferably helical form and preferably have corners to ensure large numbers of impacts occur. Thus a helical or spiral conduit is preferably of polygonal, e.g. rectangular, shape with curved corners, eg corners where the conduit turns through 60 to 1200, especially 90 . In the case of a linear conduit, it is preferred to provide an impact surface at the downstream end of the conduit, e.g. a target surface onto which pellets leaving the conduit impact. Typically this surface will be at 40 to 90 degrees to the pellet flow direction. In order that gravity should assist the pellets, fragments and dust to leave the conduit, it is preferred that the upstream conduit entrance is above the downstream conduit exit. In particular it is preferred that the conduit should be substantially vertical if linear and that the helix axis be substantially vertical if the conduit is helical.

The conduit length may typically be in the range 0.5 to 50 m depending on whether a linear or non-linear conduit is used. For a non-linear conduit, the length is preferably at least lOm. For a linear conduit, the minimum length is preferably 50cm, more preferably 1.Om and the maximum length is preferably 3m. Conduit internal diameter will typically be at least three times the pellet diameter -a dimension of 15 to 50 mm, e.g. about 20 mm, will generally be suitable for non-linear conduits. For linear conduits, the internal diameter may be smaller and the value will typically be 3 to 30mm, eg 10 to 25mm. The gas velocity within the conduit will preferably be in the range 10 to 60 mIs, especially 20 to 40 m/s, particularly about 35 rn/s.

The conduit may be constructed of any suitable material, e.g. metal, glass or plastic; however it is preferably transparent so that blockages can be detected. If non-linear it is preferably constructed of components, e.g. linear tubes and curved elbows, so as to facilitate blockage removal. PVC is a preferred material.

The particle separator in the tester of the invention may achieve isolation of the fragmented pellets in a single step or in multiple steps -thus for example the pellets following impact may be placed in an upwards gas flow set at a velocity such that only the fragmented pellets are suspended with the unfragmented pellets dropping out and the dust and fines being blown off.

More preferably however, for simplicity of construction and operation, the separator comprises at least two screens (e.g. sieves or meshes or the like), an earlier one of which serves to separate out the unfragmented pellets and a later of which serves to separate out the dust and fines. Conventional screen constructions may be used with the separation size limit being selected to be appropriate for the feed pellets being tested. Thus, for example, for 2.5 mm diameter cylindrical pellets screens of 2.0 mm and 500.tm may be used, for 3 mm diameter cylindrical pellets screens of 2.5 mm and 500 jm may be used, and for 4 mm diameter cylindrical pellets screens of 3.15 mm and 500 im may be used.

The tester preferably contains at least one particle weigher or counter, for simplicity of construction and use preferably the former. This serves to determine the weight or number of fragmented pellets and preferably also at least one of: the unfragmented pellets; the dust and fines; and the pellets before impact (typically before entry into the conduit). If the tester is being used to monitor feed pellet production, it may not be necessary to convert the measured number or weight into a percentage or ratio, however generally the tester will be preferred to include a calculator so as to determine a numerical value for the proportion of fragmented pellets, and a display or a data exporter to display or export this value, e.g. to a central control unit for the feed pellet production process. Typical values determined might be selected from: fragmented pellets as a weight % of starting pellets; fragmented pellets as a number % of starting pellets; unfragmented pellets as a weight % of starting pellets; unfragmented pellets as a number % of starting pellets; fines and dust as a weight % of starting pellets; fragmented pellets in weight divided by number of starting pellets, etc. In a particularly preferred embodiment, the tester comprises two inclined screens, preferably one above the other, each provided with a chute to a separate particle weigher, and each attached to a vibration generator, e.g. a motor, which serves to vibrate the screens and chutes so that unfragmented pellets are retained by the upper screen and pass down its chute to a particle weigher while fragmented pellets but not dust or fines are retained by the lower screen and pass down its chute to another particle weigher. This assembly is preferably provided with a suction device below the lower screen to remove the dust and fines. The weighers are preferably provided with a movable surface, e.g. a conveyor belt, so that weighed pellets and fragments may be removed, e.g. into a collection trap from which they can be removed by suction. Where the impact surface is outside any conduit, e.g. where a linear conduit is used, this may desirably be disposed above the upper screen.

The tester of the invention preferably includes a hopper for the initial pellets and also preferably means for transferring pellets from the hopper to the conduit. Such a hopper may serve to allow pellets to dry and cool, to allow pellets to be weighed or counted, to allow pellets to be sieved free of dust and fines, to allow pellets to be collected into batches of appropriate size before testing, etc. The transferring means may be as simple as a valve allowing the hopper contents to enter the conduit or may comprise a conveyor, e.g. a belt conveyor or a pneumatic conveyor, such that pellet entry into the conduit is staggered. In a particularly preferred embodiment, the hopper takes the form of a load cell allowing the sample to be weighed and provided with a conveyor belt for transporting the sample to the conduit.

While pellets may be tested individually, eg with the results for successive individual pellets being averaged to produce an indication of pellet durability, the sample tested preferably comprises a plurality of pellets (eg at least 10).

Indeed, the sample size may typically be in the range 10 to 1000 g, especially to 400 g, particularly about 100g.

The tester is preferably provided with a casing with ports for pellet inlet, gas pressure supply and pellet, fragment, dust and fines removal, an inlet for electricity supply, and optionally a data display and/or a data export port. In this way the generator is not exposed to pellet debris.

Embodiments of the invention will now be described with reference to the following non-limiting Example and the accompanying drawings, in which: Figure 1 is a schematic perspective view of a first tester according to the invention; Figure 2 is a partial schematic view of the first tester according to the invention, Figure 3 is a partial schematic view of the first tester according to the invention; Figure 4 is a schematic perspective view of a second tester according to the invention; Figure 5 is a partial schematic view of the second tester according to the invention; and Figures 6 to 8 are graphs of percentage (wt.) unfragmented pellets, pellet fragments, and dust/fines.

Referring to Figure 1 there is shown a tester I having a casing 2 containing a rectangular helical conduit 3 of PVC piping of about 21 mm internal diameter and about 37.5 m length. At its upstream end, conduit 3 has an inlet 4 for compressed air from a compressed air supply (not shown).

Above conduit 3 is a load cell 5 for weighing samples of feed pellets. The load cell 5 is provided with a conveyor belt 6 for transporting the pellets to the inlet of conduit 3. At its downstream end, conduit 3 opens into an inclined screening unit 7 having a first, upper, inclined screen 8 and a second, lower, inclined screen 9. At their lower ends, screens 8 and 9 are attached to chutes and 11 respectively. The screening unit 7 is attached to a vibration motor 12 which vibrates the unit enhancing screening and causing unfragmented pellets and pellet fragments to pass along the surface of screens 8 and 9 and down chutes 10 and 11 respectively.

Below screen 9 is a chamber attached to suction duct 13 which is connected to port 14 to which a vacuum supply (not shown) is attached to remove dust and fines from the tester.

Chutes 10 and 11 are disposed to place particles onto load cells 15 and 16 respectively for weighing. Load cells 15 and 16 are each provided on their upper surfaces with conveyor belts 17 and 18 respectively, which when moved deposit the particles from the load cells into a hopper 19 to which is attached a suction duct 20. Suction duct 20 is attached to port 14 so that the particles in hopper 19 may be removed from the tester. The casing 2 of the tester is provided with a pressure valve 20 to enable the pressure within the casing to be controlled.

Weight data from load cells 5, 15 and 16 is passed to a calculator (not shown) to enable the values for the proportions of pellet fragments and unfragmented pellets to be calculated and displayed on a display unit (not shown).

Referring to Figures 4 and 5 there is shown a second tester differing from the tester of Figures 1 to 3 in that conduit 3 is replaced by a linear PVC tube 21 of length 1.2m and internal diameter 21 mm and in that an impact plate 22 is disposed below the downstream end of tube 21 and above screen 8. This tester is suited for durability testing of extruded, lipid-coated pellets.

Example I

Durability Testing Compacted animal feed pellets in cylindrical form with diameters of 2.5, 3 and 4 mm were tested in 100 g aliquots three times using the tester of Figures 1 to 3. For all tests, the fines screen was of size 500j.im. For tests on the 2.5, 3 and 4 mm pellets, the coarser screen size was respectively 2.0, 2.5 and 3.15 mm. The weight percentages of unfragmented pellets (UBP) and pellet fragments (BP) were calculated from the values recorded by load cells 5, 15 and 16. The weight percentages of dust and fines (total dust) were determined as total dust percentage = 100-UBP-BP. The results are set out in Figures 6 to 8 (the solid circles, hollow squares and grey-shade diamonds are respectively the data points for the 2.5, 3 and 4mm diameter pellets). The results show how total dust is relatively independent of pellet size, whereas UBP shows a minimum as pellet size increases. The tester can thus be used to optimize pellet size and shape.

Claims (11)

1. Claims 1. A method of assessing feed pellet durability which comprises

   subjecting feed pellets to impact and determining the resulting proportion of pellet fragments.
2. 2. A method as claimed in claim I wherein the resulting proportion of pellet dust and fines is also determined.
3. 3. A method as claimed in either of claims 1 and 2 wherein feed pellets are subjected to impact by passage through a helical conduit.
4. 4. A method as claimed in either of claims I and 2 wherein feed pellets are subjected to impact by passage through a linear conduit and onto an impact surface.
5. 5. A method as claimed in any one of claims I to 4 wherein after impact the feed pellets and any resulting debris are screened to separate pellet fragments from unfragmented pellets and from dust and fines.
6. 6. A feed pellet durability tester comprising a pellet impact surface, and a particle separator for separating feed pellet fragments from larger particles and from smaller particles.
7. 7. A tester as claimed in claim 6 having a helical conduit for pellet flow, the interior walls of said conduit providing said pellet impact surface.
8. 8. A tester as claimed in claim 6 having a linear conduit for pellet flow, said impact surface being disposed at the outlet of said conduit.
9. 9. A tester as claimed in any one of claims 6 to 8 having a double screen to separate pellet fragments from unfragmented pellets and from dust and fines.
10. 10. A tester as claimed in claim 9 having a first particle weigher disposed to weigh particles retained by a first screen of said double screen and a second particle weigher disposed to weigh particles retained by a second screen of said double screen.
11. 11. A tester as claimed in any one of claims 7 to 9 wherein said conduits, impact surface, double screen and weighers where present are disposed within a dust-tight container.