WO2011054109A1 - Improved pelletizing system, method and apparatus - Google Patents

Abstract

A pellet mill is provided in which steam generated by the heat produced by the friction during extrusion of the pellets is captured and returned to the conditioning stage rather than employing steam produced externally. The steam produced by the pellet mill as a by-product of the process is captured and used to condition the fibre instead of generating steam from another energy source. As a result the power consumption per tonne of pellets produced is lowered, the volume of production from the pellet mill is increased, and die and roll life is improved.

Description

IMPROVED PELLETIZING SYSTEM. METHOD AND

APPARATUS

Cross Reference To Related Application

[0001] The present application claims the benefits, under 35

U.S.C.§ 1 19(e), of U.S. Provisional Application Serial No. 61/258,982 filed November 6, 2009 entitled "Improved

Pelletizing System, Method and Apparatus" which is incorporated herein by this reference.

Technical Field

[0002] The invention relates to the field of pellet mills and pelletizing devices and methods. Background

[0003] Pellet mills are used to produce pellets of various types of materials from particulate material, such as biofuel wood pellets from sawdust, wood shavings, bark and/or wood chips by an extrusion process. In existing pellet mills, the

particulate material is fed into a conditioner which heats the material with steam from an external source and adds binders, and mixes the particles in an auger feed. The material is then fed to the pellet mill where rollers press the material through a die, forming cylinders which are cut off as pellets which are discharged and cooled. An example of a wood pelleting pellet mill is that manufactured by Andritz AG as an ANDRITZ Feed & Biofuel LM26 Pellet Mill.

[0004] The existing pellet mills require a large input of energy in the form of heat to provide steam for the conditioning stage. Such heat is lost to the atmosphere when the pellets are cooled for further processing. [0005] While some attempts have been made to recycle the external steam heat, these have not been effective. For example US 7404262 Jurkovich discloses a pelletizing system in which warm, moist exhaust air from the pellet cooler/dryer is recycled to transfer heat to the incoming material. However steam must still be used from an external source in the steam conditioner. Swedish patent SE446066 discloses a pelletizing system in which steam is recycled from a "thermopress" to be retained within the material prior to the pellet press. The thermopress pulverizes and drains the material. Again steam is not recycled from the pellet press but is added from an external source to the thermopress.

[0006] The foregoing examples of the related art and limitations

related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings. Summary

[0007] The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.

[0008] The present invention provides a pellet mill in which steam generated by the heat produced by the friction during extrusion of the pellets is captured and returned to the conditioning stage rather than employing steam produced externally. The steam produced by a pellet mill as a by-product of the process is captured and used to condition the fiber instead of generating steam from another energy source. As a result the power consumption per tonne of pellets produced is lowered, tonnes per hour from a pellet mill is increased, and die and roll life is improved.

The invention therefore provides a method and apparatus for producing extruded pellets from particulate material wherein a conditioning section heats the particulate material prior to delivery to an extruder for extruding said particulate material into pellets, wherein steam generated by the heat produced by the friction during extrusion of the pellets is captured and returned to the conditioning section. The steam may be captured from the housing of the extruder or from a conveyor for the extruded pellets.

According to one aspect of the invention, a fan is provided to draw steam directly from the pellet mill door or pellet conveyor and blow it back into the back of the conditioner. A return pipe is provided from the outfeed end of the conditioner to the other side of the door on the pellet mill or to a cooler cyclone to get better flow through the conditioner. Baffles are added to the inside of the pellet mill door and the outlet from the conditioner to prevent excess fiber getting into the steam pipes. Rubber seals at joints in the steam outlet and inlet pipes are provided to facilitate opening the pellet mill door.

In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions. Brief Description of Drawings

[00012] Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

[00013] Fig. 1 is a front elevation view of the invention.

[00014] Fig. 2 is a side elevation view of the invention.

[00015] Fig. 3 is a top plan view of the invention with the pellet mill door open in phantom outline.

[00016] Fig. 4 is a view of the inside of the pallet mill door showing the steam inlet and outlet.

[00017] Fig. 5 is a front view of the invention with the pellet mill door open showing the seal connections in open position.

[00018] Fig. 6 is a detail view of the fan connection.

[00019] Fig. 7 is a detail view of the steam inlet to the pellet mill door.

[00020] Fig. 8 is a detail view of the steam outlet from the pellet mill door.

[00021] Fig. 9 is a cross-section taken along lines 9-9 of Fig. 2.

[00022] Fig. 10 is a cross-section taken along lines 10-10 of Fig. 3.

[00023] Fig. 11 is a detail view of the steam outlet from the pellet mill door.

[00024] Fig. 9 is a cross-section taken along lines 9-9 of Fig. 2.

[00025] Fig. 10 is a cross-section taken along lines 10-10 of Fig. 3.

[00026] Fig. 11 is a front elevation view of a second embodiment of the invention.

[00027] Fig. 12 is a side elevation view of the embodiment of the

invention shown in Fig. 1 1.

[00028] Fig. 13 is a top plan view of the embodiment of the invention shown in Fig. 1 1 with the pellet mill door open in phantom outline. Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid

unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

The present improvement shown in the attached drawings uses the fact that steam is also produced by a pellet mill as a byproduct of the extruding process due to the heat generated by friction. That steam is captured and used to condition the fiber instead of generating steam from an external energy source. The need for an external source of steam is thereby reduced or eliminated. The result is that power consumption per tonne of pellets produced is lowered, the production of the pellet mill is increased, and die and roll life is improved.

With reference to Fig. 1-3, a pellet mill 110 has an infeed auger 12 which feeds particulate material such as wood fibre to a conditioner 14 where the particles are heated by reclaimed steam as described further below, while being fed along conditioner 14 by auger 15 which has blades 17. Binders can be added at this stage if desired. Preferably no external steam is supplied. The conditioned wood fibre is fed through conduit 16 to the pellet mill roll 18 where the material is pressed through a die by a roller (not shown) to form pellets, which fall out through discharge 20. Motor 24 drives the roller by a drive belt and gears. Motor 26 drives an auger 37 (Fig. 4) which feeds the conditioned fibres into the roller. [00032] The process of pressing the particles through the die generates considerable heat through friction. Due to the moisture in the wood fibres, steam is generated in the roller housing which is ducted through steam outlet pipe 28 from the door 22 of the pellet mill discharge auger to the conditioner 14. A duct fan 30 adjacent the conditioner 14 draws the steam from the roller housing at 39 and pushes the steam into the conditioner 14. The fan 30 is positioned close to the conditioner 14 to minimize the length of the pipes 28, 32, and a baffle 40 is provided into the conditioner 14. A return pipe 32 from the outfeed end of the conditioner 14 to the other side of the door 22 on the pellet mill at 35 balances the pressure to provide better steam flow through the conditioner 14. Baffle 36 to the inside of the pellet mill door 22, baffle 40 and baffle 41 on the outlet from the conditioner 14 prevent excess fiber from getting into the steam pipes. Joints 42, 44 are provided in the pipes to facilitate opening the pellet mill door 22 and are sealed by rubber seals when closed. [00033] Plugging of the pipes with wood fibre from the conditioner 14 is made manageable by the use of baffles at the points of entry and exit of the recirculated steam from conditioner 14 and pellet mill door 22. All the baffles may be fixed in place by welding. Fig. 4 shows the pellet mill door 22 swung open to show where the steam is ducted from the left side (front view) of the pellet mill discharge auger at 39 to the conditioner 14 and returned to the right side of the pellet mill at 35. The baffle 36 inside the door 22 that helps keep fibre out of the pipe 28 which draws steam out of the pellet mill is preferably a flat piece of steel welded onto the door 22 to block a direct route from the die. The baffle 40 from the fan duct 31 into the conditioner 14 is two plates at about a 45 degree angle from vertical as shown in Fig. 9. Other baffle designs may be used to block a straight path from the conditioner 14 up into the duct 31 to prevent wood fibre from being flung up into the fan 30. Wings (not shown) may be welded to the ends of the conditioner blades 17 to help keep the fiber from flinging out and up into the duct 31. There is another baffle 41 (Fig. 10) inside the conditioner 14 at the outlet end into the steam pipe 32 that diverts the fiber away from the inlet 47 of the pipe 32 that returns the steam to the door 22. Auger 15 stops just short of the baffle 41 to provide clearance for blades 17.

Alternatively to ducting the steam return pipe 32 into the pellet mill door, the steam that has passed through the conditioner 14 can be ducted to the cooler cyclone, as shown in Fig. 1 1-13. The cooler cyclone 54 is the receiving vessel for the air drawn through the pellet cooler which has a lower pressure to suck air though the cooler. This thereby provides an alternate way to expel and draw out the steam and air blown into the

conditioner 14 into a lower pressure vessel.

Fig. 11-13 illustrate a second embodiment of the invention in which the recycled steam is drawn from the pellet conveyor 50 rather than from the pellet mill door. In this embodiment the steaming pellets are dropped through discharge 20 onto conveyor or auger 50. Steam from conveyor 50 is drawn by fan 30 through steam return pipe 52 into conditioner 14. After being drawn through the conditioner 14, the steam-laden air is drawn through pipe 33 to the cooler cyclone 54.

By way of example it was found that the current drawn by the 450 horsepower pellet mill motor 24 dropped by 50 amperes after implementing the invention. Further by way of example, fan 30 was selected with a 1 horsepower fan motor. Fan 30 may be provided with a variable frequency drive to run the fan at different speeds in order to vary the velocity and pressure of the recirculated steam. At a frequency of 80 hz, a current reduction of 50 amperes on the main 450 hp motor was obtained. If the pressure is too high, however, too much wood fibre may be drawn from the conditioner 14 into the recirculating pipes and fan. At a frequency of 60 hz a current reduction of 40 amperes on the main 450 hp motor was obtained. The preferred diameter for pipes 28, 32 is 6".

Smaller diameter pipes will also work. The pipes needs to be large enough to capture enough steam, since the internally generated steam is not as dense as steam from a boiler.

[00037] Thus by implementing the invention, a reduction of power required for the pellet mill motor is obtained. An increase in production per pellet mill was found to result and die and roll wear was reduced. Further, a cheap supply of steam is produced which provides energy savings.

[00038] While preferably all of the heat required for the conditioning step is recycled heat from the extrusion process, the method and apparatus as described will also be useful if only a portion of the heat required for conditioning is recycled, with the remainder of the heat being provided from an external source. [00039] While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the invention be interpreted to include all such modifications, permutations, additions and sub-combinations as are within its true spirit and scope.

Claims

WHAT IS CLAIMED IS:

1. Apparatus for producing extruded pellets from particulate material wherein a conditioning section heats said particulate material prior to delivery to an extruder for extruding said particulate material into pellets, wherein steam generated by the heat produced by the friction during extrusion of the pellets is captured and returned to the conditioning section.

The apparatus of claim 1 wherein said extruder has a housing and said steam is captured from within said extruder housing.

The apparatus of claim 1 wherein said pellets are conveyed from said extruder by a conveyor and said steam is captured from said conveyor.

The apparatus of claim 1 wherein said particulate material contains water, and heat generated by friction during said extrusion produces said steam.

The apparatus of claim 1 wherein a fan is provided to draw steam from said extruder and conduit means carry said steam to said the conditioner.

The apparatus of claim 5 wherein said fan is provided with a variable frequency drive whereby the speed of the fan is variable to vary the pressure and velocity of the recirculated steam.

7. The apparatus of claim 5 wherein a return conduit is provided from the outfeed end of the conditioner to the extruder to generate improved steam flow through the conditioner.

8. The apparatus of claim 5 wherein a return conduit is provided from the outfeed end of the conditioner to a cooler cyclone to generate improved steam flow through the conditioner.

9. The apparatus of claim 7 wherein baffles are provided to prevent particulate material from entering said conduits.

10. The apparatus of claim 8 wherein baffles are provided to prevent particulate material from entering said conduits.

1 1. The apparatus of claim 2 wherein the extruder is a pellet mill

comprising a hinged door and rubber seals at joints in steam outlet and inlet pipes are provided to facilitate opening said pellet mill door.

12. A method of producing pellets comprising providing a pellet mill in which steam generated by the heat produced by the friction during extrusion of the pellets is captured and returned to the conditioning stage.

13. The method of claim 12 wherein said pellet mill has a housing and said steam is captured from within said housing.

14. The method of claim 12 wherein said pellets are conveyed from said pellet mill by a conveyor and said steam is captured from said conveyor.

15. The method of claim 13 wherein steam produced by said pellet mill as a by-product of the process is captured by a fan which is provided to draw steam from the extruded pellets and blow it into the conditioning stage.