SE535262C2

SE535262C2 - Method of pelletizing

Info

Publication number: SE535262C2
Application number: SE1050517A
Authority: SE
Inventors: Sylvia Larsson; Torbjoern Lestander; Haakan Oerberg; Kal N Gunnar; Mikael Thyrel; Magnus Rudolfsson; Mikael Wallin
Original assignee: Sweden Power Chippers Ab
Priority date: 2010-05-25
Filing date: 2010-05-25
Publication date: 2012-06-05
Also published as: SE1050517A1; WO2011149418A1

Abstract

lO ABSTRACT The invention relates to a method for providing continuous feed-layers ofmaterials of mainly organic origin for the production of biofuel pellets, in apelletizer. The status of the feed-layer in the pelletizer is monitored bymeasuring at least one process and/ or equipment Variable. In response to saidmeasurement, a comparison With preset target values and threshold values forsaid Variable is performed and depending on the result of said comparison,signals are sent to at least one regulator adapted to adjust process variables soas to enhance the binding properties of the feed layer to the die surface. Asystem is also provide comprising monitoring means (1), comparing means (2)and regulating means (3), that in response to measurements on the processand/ or equipment adjusts process variables so as to maintain a continuous feed-layer. (Pig. 2)

Description

METHOD OF MAKING PELLETS The present invention relates in general to production of biofuel pellets and thelike, and more particularly to an improved method wherein intermittentproduction and complete interruptions in the production process are eliminated or at least minimized, due to an improved control of feed layer formation.

Background of the Invention A pelletizer for production of fuel pellets or animal feed pellets has at least onedie with at least one press channel and a device to apply force to press materialof mainly organic (e. g. biomass) origin through the press Channels. There are three main techniques for such pellet production systems. l) a die where at least one roller applies pressure When it passes a presschannel; 2) at least two matched cylinders where each cylinder may act both as a dieand a pressure applying roller; 3) a die and at least one piston where either the die or piston applies PTCSSUIC.

Pelletizers using a system with at least one die and at least one roller, as in 1)above, are mostly based on free rolling rollers. For matched cylinder systems,as in 2) above, at least one cylinder may be free rotating. Such free rolling devices are dependent on friction against a raw material feed layer to rotate.

Free rolling press rollers, as in 1) above, are mounted with a gap (e. g. fractionsof millimetres) with respect to the die. This is also the case for free rollingcylinders as in 2) above. The distance to the free rolling device (e. g. roller) isrequired to enhance the formation of a compressed raw material film, feedlayer, e.g. between rollers and die. The free rolling device needs friction againstthe feed layer to rotate. When this occurs the feed layer is successively pressedinto die channels for each turnover by the roller and the material is successively fed into the pelletizer to obtain continuous pellet production.

Therefore, a stable feed layer formation is essential to sustain continuous pelletproduction and to obtain consistently high pellet quality. Feed layer formationdepends on material specific Characteristics, such as compressibility, relaxationand binding properties between particles as well as between particles and die surface, preventing the feed layer from being swept off from the die surface.

Due to occasionally occurring poor feed layer formation, pelletizing by roller~die-channel techniques, such as described above, suffers from serious problemswith discontinuous production e. g. intermittent production and, in severecases, complete interruptions in the production of pellets. Intermittent pelletproduction causes trernendous stress on the pelletizer and produced pellets areof Variable quality. Especially prone to this kind of behaviour are straw-typebiomass materials, e. g. rice husks, straw of wheat, oat, barley and the like,grasses like switchgrass, Miscanthus sp., reed canary grass etc., but has alsobeen experienced with other feedstock, e. g. woody materials. Problems arecaused by in-homogeneities in the development of a continuous feed-layerand/ or by feed layer breakages. Larsson et al. (vide infra) defined continuouspellet production as a production pattern When the coefficient of variation (CV)of the pelletizer motor current Was lower or equal to 0.2 over a 2 to 3 minuteperiod. They found when pelletizing reed canary grass, that continuous pelletproduction (CV S 0.2) could only be obtained using pre~densified material ofreed canary grass with densities above c. 260 up to c. 350 kg/ m3 if also one ofthe following settings within the investigated Variable range was fulfilled:moisture content of the raw material >l3.8%; die temperature <83 °C; raw pre- compacted material density >324 kg/ m3.

Manufacture of pellets from biological material is the subject of a large numberof patents. As mentioned above, one problem that is commonly occurring is thatthe so called feed layer, which is the layer of material present on the extrusiondie, is not maintained in the desired continuous condition, which frequently leads to interruptions in the production.

In US-4,529,40'7 (Johnston) an extruder is used to produce pellets with 1 - 3 % thermoplastic material where the injection temperature of at least 95 °C.

US- 4,834,777 (Endebrock) is based on a piston technique and comprises areciprocating punch press having a movable punch plate and a stationaiy dieholder and formation of pellets done under controlled temperature conditions at preferable 12 1- l77°C.

US-5,643,342 and 5,980,595 (Andrews) focus on cooling of already formattedpellets containing of least 1% thermoplastic material in a mix With coal and cellulosíc material.

US-ó, l65,238 (Parkinson et. al.) have invented an improved palletized Waterresistant compacted solid fuel produced preferable at 121-177 °C from amixture of 70-98% coal and 2-30% thermoplastic polymeríc materials preheated to 204 and 100 °C, respectively.

In US patent application 2009 / 0064569 (Khater) temperature is controlled toabout 100-l 10 °C at pelletizing. A desired temperature of the fixed ﬂat die ismaintained by circulating hot or cold Water. Temperature control may beachieved by directly heating or cooling the die, or by controlling temperature ofnot only the die but additional adjacent equipment as Well, or by relying entirelyupon thermal conduction and thermally coupling of a heating and cooling source such as a temperature-controlled Water line to the die.

In an article by Larsson et al, “ High quality biofuel pellet production from pre-compacted low density raw materials”, Bioresource Technology 99 (2008) 717 6-7182, the authors found that pre-compaction is a Way to reach conditions for continuous pellet production provided a number of conditions are met.

Temperature control is required in the above cited patents, but none of themfocuses explicitly on the feed layer formation nor do they give any suggestions how to tackle the problem of feed layer disturbances.

The article presents Ways to alleviate the problem of díscontinuous production, but die temperature is specifically mentioned as an uncontrolled Variable.

Summary of the Invention Thus, in order to overcome the drawbacks of prior art systems and methods thatsuffer from frequently occurring intermittent production and often completeinterruptions in the production due to the inability to maintain a continuous feedlayer, the inventors have devised a method and a system for controlling the feedlayer formation in a method of producing pellets from biomaterial of numerous various kinds.

The method according to the invention is defined in claim l, and a system according to the invention is defined in claim 15.

The method provides continuous feed-layers of materials of mainly organicorigin for the production of biofuel pellets, feed pellets and the like in apelletizer, said pelletizer comprising a die, means for pressing feed materialthrough said die, and a motor, preferably electric, coupled in drivingengagement With the pressing means, and is characterised by continuouslymonitoring the status of the feed-layer in the pelletizer by measuring at leastone process and/ or equipment Variable; in response to said measurement,performing a comparison With preset target values and threshold values for saidvariable; depending on the result of said comparison, sending signals to at leastone regulator adapted to adjust process variables so as to enhance the binding properties of the feed layer to the die surface.

In a preferred embodiment the method makes use of a regulator, Which is adevice regulating the infusion of cooling media for cooling the feed layer, the die surface and/ or the die. ln a still more preferred embodiment the method is implemented in a pelletizerin Which the motor is an electric motor, and the measurement performed is ameasurement of the variation in motor current of the pelletizer to provided motor current data. lO The present invention makes it possible to use raw materials for the productionof biofuel pellets, feed pellets and of the like. Possible raw materials includestraw-type raw materials without any costly pre-densification or other pre-treatments to improve stable feed-layer formation. Thus, materials havingnatural bulk densities lower than 260 kg/ m3, (e. g. reed canary grass has at amoisture content of l5-20% (wet basis) a density of about 140-160 kg/ m3 whenmilled over a sieve size of 4 mm), when milled to particle sizes sufficient forpellet production can be utilised. This simplifies machínery equipment andlower the costs of material handling prior pelletizíng. The invention also makespelletizers using free rolling devices more general concerning different rawmaterials, especially concerning straw~type materials for biofuel production.Furthermore, the invention lowers stresses on the pelletizer and lower quality Variations caused by intermittent pellet production.

The system according to the invention provides continuous feed-layers ofmaterials of mainly organic origin for the production of biofuel pellets, feedpellets and the like in a pelletizer. The pelletizer comprises an extrusion die, dieheating and/ or cooling means, means for pressing feed material through saiddie, and a motor coupled in driving engagement with the pressing means. Thesystem is characterised by means for continuously monitoring the status of thefeed~layer in the pelletizer by measuring at least one process and/ or equipmentVariable; means for performing a comparison with preset target values andthreshold values for said Variable, in response to said measurement; means forsending signals to at least one regulator adapted to adjust process variables soas to enhance the bindíng properties of the feed layer to the die surface, depending on the result of said comparison.

In a preferred embodiment the monitoring means comprises means for on-line collection of electrical data of the pelletizer motor.

The invention is especially useful for materials that have showed poorpelletizing Characteristics like this in terms of uneven pellet production when die temperature is rising. lO Further scope of applicability of the present invention Will become apparent fromthe detailed description given hereinafter and the accompanying drawings whichare given by Way of illustration only, and thus not to be considered limiting on the present invention, and Wherein Fig. la is a block diagram for schematically representing a system to enhancebinding properties of the feed layer to the die surface and to control feed layer formation according to the embodiment of the present invention.Fig. lb schematically illustrates the core components of a pelletizer; Fig. 2 is a flowchart for schematically representing the general principles forenhancing binding properties of the feed layer to the die surface and control of feed layer formation according to the embodiment of the present invention.

Fig. 3 shows pelletizer motor current (A) (grey thin line) at three different die temperatures (°C) (black thick line) ; Fig. 4 shows pelletizer motor current (A) (grey thin line) when die temperature(°C) (black thick line) is first increased from about 30 °C to 50°C and further to60°C and then lowered from 60 to about 30°C.

Detailed Description of Preferred EmbodimentsFor the purpose of the present application the term “process Variable” shall betaken to mean any measurable quantity that is relevant for carrying out the process, and in particular that is related to the feed-layer formation.

Non-limiting examples are raw material feed rate, material properties (density, particle size etc.), thickness of the feed-layer.

The term “equipment Variable” shall be taken to mean any measurable property of the components of the equipment, i.e. the pelletizer, that affects or is inﬂuenced by the process that is being carried out, and in particular that can be correlated With the formation of the feed-layer.

Non-limiting examples are motor current, die temperature, die surface temperature, cooling media temperature, cooling media flow rate.

The inventors have identified that die surface temperature is the most criticalfactor for binding of the feed layer to the die surface and thus to maintaincontinuous pelletizing conditions. However, the reason for this is not fully clear.Without wishing to be bound by theory, it is believed that lower evaporationrates of moisture in the raw material at lower die surface temperatures already at feed layer formation can be of importance.

One observation is that the mechanical work during pelletizing generates heat.The heat is mainly absorbed by the produced pellets, by vaporizing moisture inthe pelletizing material or by the machinery. At continuous and even processconditions, a particular steady state process temperature is reached whenradiation and convection of heat from the goods of the pelletizer reach a stablelevel. When die temperature is increased from a primary level in the range of20~50°C to 50-80°C and further to 80-120°C during pelletizing of somematerials the production is going from even to uneven and further to extremely uneven production and sometime no production at all.

An embodiment of the method according to the present invention will now be described in detail with reference to Figs. 1 and 2.

Fig. la schematically illustrates a system according to the present invention. Nodetails of the pelletizer as such are shown since the apparatus can be generic.Instead the actual apparatus is represented by the motor l driving theapparatus. A computer 2 is coupled to the apparatus via suitable sensors forregistering relevant process and/ or equipment related variables. The signalsfrom said sensors are processed in the computer 2 and instructions based onthe calculations are fed to device 3 regulating the infusion of cooling media that cool the feed layer, the die surface and/ or the die, or into channels in the die or onto flanges connected to the die. There are also provided back-up systems 4, 5that are activated if the normal operation according to the invention nevertheless should fail.

Fig. lb is a schematic illustration showing the main functional components of a pelletizer in which the invention suitably is implemented.

It comprises a die 10 in the form of a circular drum, inside of Which there arefree rolling devices 12 exerting a pressure on a raw material feed-layer 14 that forms inside the drum on its Walls.

Fig. 2 is a block diagram for schematically representing a process according toone embodiment of the present invention, for enhancing binding properties ofthe feed layer to the die surface and to control feed layer formation in a pelletizer for making pellets from biomaterials.

A pelletizer With which the present invention can be implemented in verygeneral terms comprises feeding means for feeding raw material to the actualpelletizíng device. The pelletizíng device comprises a die having a plurality ofapertures through which the feed material is pressed. The feed material forms alayer on the die, referred to as a “feed layer”. The pressing is suitably achievedby utilizing free rolling devices, thus forming elongated material strings. Thereis also provide a cutting means for chopping up the material strings to shorter segments, referred to as pellets.

There are also provided means for heating and cooling the die, since temperature is a critical Variable in the pelletizíng process.

The method according to a first embodiment of the present invention comprisescontinuously collecting actual electric current data from the pelletizer motor bymeans of a measurement device 1 in Fig.l. In particular the variation in electricmotor current is measured. Data is sent to a computer system 2 that in realtime stores data and registration time, and further continuously processes (i.e. compares) the data according to target values and threshold values. Target values are Within a desired interval and threshold values are outside thesmallest of such an interval but both values are used for regulation. Dependingon the results of these continuous calculations, signals are sent to a device 3regulating the infusion of cooling media that cool the feed layer, the die surface and/ or the die, or into channels in the die or onto ﬂanges connected to the die.

During operation of the pelletizer calculations are also performed in thecomputer system 2 to optimise the target values and the threshold values inorder to minimise cooling While at the same time lower feed layer disturbances.In one embodiment there is a backup system 4 (Which is an optional feature)based on at least one temperature sensor, Which is a much slower reactingsignal of feed layer disturbances then the electric motor current. This sensor isadapted to send actual temperature data to the computer system 2. In case of afailure of the device 1, i.e. the device that reads or measures the actual current,these temperature data signals are stored, processed (in the same manner asfor the motor current data) according to target values and threshold values fortemperature and optimisations of those values are done in the computerised system 2. Resulting signals are sent to the regulator device 3.

Another back-up system 5 is provided for the purpose of adding stabilisers tothe feed layer if the cooling provided by the regulator device 3 is not enough tostabilise feed-layer formation. Such stabilisers can be e.g. natural binders likestarch, lignin, proteins, sugars, Water etc. or synthetic binders like plastics etc.Such binders are only used until the feed layer is recovered into a continuous feed layer formation in pelletizing.

In a situation Where cooling of the feed layer, the die surface and/ or the diealone is not sufficient to cancel disturbances in the feed-layer formation, themethod preferably comprises adding feed-layer stabilizers, such as powder orgranules of lignin, starch, plastics, sugar, oils, fats, rape seed cake, Water and mixtures of one or more components thereof.

The system for providing continuous feed-layers of materials of mainly organic origin for the production of biofuel pellets, feed pellets and the like according to the present invention comprises a pelletizer. The pelletizer comprises anextrusion die, die heating and/ or Cooling means, means for pressing feedmaterial through said die, and a motor, preferably an electric motor althoughany other type of motor is usable, coupled in driving engagement With the pressing means. lt further comprises means for continuously monitoring the status of the feed-layer in the pelletizer by measuring at least one process and/ or equipmentVariable. There are also provided means for performing a comparison Withpreset target values and threshold values for said Variable, in response to saidmeasurement. Also the system comprises means for sending signals to at leastone regulator adapted to adjust process variables so as to enhance the bindingproperties of the feed layer to the die surface, depending on the result of said comparison.

The monitoring means suitably comprises means for on-line collection ofelectrical data of the pelletizer motor, Which preferably is a computer assisteddevice for continuously testing if said motor current is Within set targetedvalues regarding the actual read-out of electrical data and regarding variabilitymeasures Within a successive moving Window of actual and preceding observed read-outs of electrical data.

The at least one regulator is adapted to control infusion of cooling media eitherto the feed layer or the die surface or to both, or into channels or onto ﬂanges connected to the die.

The computer assisted device is suitably adapted to generate regulation signalsto regulators controlling infusion of cooling media, either to the feed layer or tothe die surface or to both, or in channels or on ﬂanges connected to the dieWhen the actual current and/ or the actual variability measurement pass set targeted values.

Suitably there is provided at least one sensor for recording feed layer temperature, die surface temperature and/ or die temperature. lO ll The cooling media that is used for the die can be any of water aerosols, liquids and/ or gases (e.g. air).

The system for enhancing binding properties of the feed layer to the die surfaceand control of feed layer formation according to the embodiment of the presentinvention, as indicated in Fig 1, may also contain algorithms to analyse andpresent trends e.g. of average number of disturbances over a time period, butalso to minimise cooling while at the same time minimise number of feed layer disturbances per time period.

In Fig. 2 a ﬂowchart which schematically represents a method according to anembodiment of the present innovation, is shown. The different steps Sl-Sl 1 inFig. 2 are presented in the direction (indicated by arrows) of the signal andactions according to one embodiment. This setup is suitable for enhancingbinding properties of the feed layer to the die surface and control of feed layerformation according to the embodiment of the present invention. First, themethod comprises a step S1 of more or less continuously measuring the electriccurrent of the pelletizer motor. These data are checked in S3 and S5 accordingto set target values and threshold values in S2. An example of such targetvalues is values inside an interval covering mean current (u) at the ongoingproduction rate at continuous production plus / minus one standard deviation(io) of the current at said continuous production, i.e. u i o, preferably anasymmetrical interval from j> value between 1 and 1,5 and k is a value between l and 3.

Examples of disturbances in feed layer formation are shown in Figures 3 and 4and it should be noticed that a breakage of the feed layer is manifested in asudden drop of electric current of the pelletizer motor close to idle current.Outside each end of the interval there is at least one threshold value. When theactual electric current data passes such a threshold at least one signal ischanged and sent S4 to a regulator device that dependent on the type of signalmay start/ stop or increase / decrease the cooling of the feed layer, the die surface and /or the die. The regulator device is inﬂuenced by signals from the 12 check S5 of electrical data done regarding variability of the electrical current ofthe pelletizer motor. Here at S2, there are set target values inside a lowerinterval based on some variability measure of the motor current. This variabilityof the current is calculated e. g. within a moving window that may havemathematical weights on the observations in relation to passed time since theactual observation. Example of a variability measurement is coefficient ofvariation (CV) and a CV interval starting from zero and the upper end e. g. at0.1. Example of window size is shortest time of one cycle of said disturbance,i.e. from stating of disturbance to recovering of continuous feed layer formation.Outside the interval there is at least one set threshold value and a signal ischanged when such a threshold value is passed by the actual electricalvariability and sent S4 to the regulator device to e. g. increase cooling if the CV is higher than e.g. 0.2 or decrease cooling if the CV is lower than e.g. 0.2.

In particular targets for the electrical variability measurement are set at severalcoefficients of variation in the range of 0-3, preferably between 0 and 0,75, or still more preferred between 0 and 0,2.

The preset target value for basic cooling preferably should equal the heatremaining after heating of the raw material, evaporating moisture etc, e. g. about25-80% of the mechanical work done by the motor at continuous pelletproduction minus that of idle running at no production at all plus possible heat originating from steam addition.

Furthermore, said preset value for basic cooling should be evaluated at everymajor disturbance of the feed layer formation, e. g. after an intermittent pellet production cycle, to calculate if said preset value should be changed.

The feed layer temperature, die surface temperature and/ or die temperatureis/ are suitably in preferred embodiments controlled to between 0 to 80°C and preferably 0-70°C, more preferably 0-60°C, and most preferably 0-50°C.

Feed layer disturbances manifested as electric current variation and resulting in initiated cooling actions in S4 are recorded and the number of such 13 disturbances is calculated per time unit Within at least one moving window, e.g.covering at least one cycle of said disturbance, í.e. from stating of disturbanceto recovering of continuous feed layer formation. Another moving window over alonger time period register only events of feed layer breakage, í.e. when aboutidle current is reached followed by a clear peak value (see Figs. 3 and 4). Alsothese moving windows over a time period contains the actual electrical data andpreceding electrical data. Also these windows may have mathematical weightson the observations in relation to passed time since the actual observation. Alsoat S6 and S7 there are target values within a suitable interval and thresholdvalues outside this interval. Example of an interval for S6 is O to 2 events ofsaid breakages over the last hour, but of caorse a lower number of events is preferable.

If the checks Within S6 and S7 show higher numbers of said disturbances pertime unit and/ or of said events over a time interval than set target values, newtarget values of basic cooling is set to decrease the number of feed layer disturbances. Thus, this is an iterative process.

If cooling is not enough (checked in S8) to recover a continuous feed layerformation a back-up system S10, indicated by the dashed lines, may be used for adding a stabilizer to the feed layer.

Another back-up, if the system to collect electric current data fails, is to registertemperature data of the feed-layer, the die surface or the die, box S9. Thenintervals, target values, threshold values and variability measures at S2-S7 are done, set and calculated for temperature data.

A still further alternative embodiment of carrying out the method is to use non-contact monitoring of the thickness of the feed-layer itself. Suitably, radar typemonitoring could be used. In this way immediate changes in the status of thefeed-layer can be registered and fed to the control system and the regulators can be activated accordingly. l0 14 The invention will now be further illustrated by the following non-limiting examples.

Example experiments - manufacturing of pellets Examples of die temperature inﬂuence on motor current variability are takenfrom pelletizing runs using reed canary grass as a model species for materialswith poor feed layer sustainability and with natural powder bulk densities ofabout 140-160 kg/ m3 (Figures 1 and 2). Motor current curves (grey thin lines)at three different die temperatures (black thick lines) are shown in Figure 1. Ata die temperature of about 30°C, motor current is continuous (CV S 0.2) at alow, steady level. At higher die temperatures, motor current becomesinterrnittent (CV > 0.2), with periods of idle running (c. 17 A) in between short,high peak loads.

The effect of die surface cooling during on-going operation is shown in Figure 2.The intermittent (CV > 0.2) production pattern developed at high dietemperatures is interrupted and replaced by a continuous (CV S 0.2) production pattern when cooling the die from 60 to 35°C.

Claims

:

1. l. A method for providing continuous feed-layers of materials of mainly organicorigin for the production of biofuel pellets, feed pellets and the like in apelletizer, said pelletizer comprising a die, means for pressing feed materialthrough said die, and a motor coupled in driving engagement With the pressing means;characterised by continuously monitoring the status of the feed-layer in the pelletizerby measuring at least one process and/ or equipment variable; in response to said measurement, performing a comparison Withpreset target values and threshold values for said variable; depending on the result of said comparison, sending signals to atleast one regulator adapted to adjust process variables so as to enhance the binding properties of the feed layer to the die surface.

2. The method as claimed in claim 1 or 2, Wherein the regulator is a deviceregulating the infusion of cooling media for cooling the feed layer, the die surface and/ or the die.

3. The method as claimed in claim 1, 2 or 3, Wherein the motor is an electricmotor and the measurement performed is a measurement of the motor current of the pelletizer to provide motor current data.

4. The method as claimed in claim 3, Wherein the measurements of the electricmotor current are continuous in pelletizer operation and Wherein the method further comprises continuous calculations of the variability measure of the current.

5. The method as claimed in claim 3 or 4, comprising selecting target values forsaid variable from values inside an interval covering mean motor current (u) at the ongoing production rate at continuous production plus / minus one standard 16 deviatíon (io) of the current at continuous production, i.e. u i o, preferable u ikXo where k is a value between 1 and 3, preferably an asymmetrical intervalfrom jxlidh, to u+k> and k is a value between l and 3.

6. The method as claimed in any preceding claim, wherein the at least oneregulator control infusion of cooling media either to the feed layer or to the die surface or to both, or into channels in the die or onto ﬂanges connected to the die.

7. The method as claimed in any preceding claim, wherein the method is aniterative process to set suitable target values for the electrical current and thevariability measurement of that current and to set a basic cooling of the die surface using cooling media.

8. The method as claimed in any preceding claim, wherein targets for theelectrical variability measurement are set at several coefficients of variation inthe range of 0-3, preferably between 0 and 0,75, or still more preferred between 0 and 0,2.

9. The method as claimed in any preceding claim, wherein the preset targetvalue for basic cooling equals the heat remaining after heating of the rawmaterial, evaporating moisture etc, e. g. about 25-80% of the mechanical workdone by the motor at continuous pellet production minus that of idle running at no production at all plus possible heat originating from steam addition.

10. The method as claimed in any preceding claim, further comprisingevaluating said preset value for basic cooling at every major disturbance of thefeed layer formation, e. g. after an intermittent pellet production cycle, to calculate if said preset value should be changed.

11. l 1. The method as claimed in any of claims 6-10, wherein the feed layertemperature, die surface temperature and/ or die temperature is / are controlled to between 0 to 80°C and preferable 20-'70°C. 17

12. The method as claimed in any of claims 6-10, Wherein the measurement performed is a measurement of the die temperature and/ or the die surface temperature.

13. The method as claimed in any of claims 6-10, Wherein the measurement performed is a measurement of the feed-layer thickness.

14. The method as claimed in any preceding claims, further comprising, in asituation Where Cooling of the feed layer, the die surface and/ or the die alone isnot sufficient to cancel disturbances in the feed-layer formation, adding presshelpers, such as powder or granules of lignin, starch, plastics, sugar, oils, fats, rape seed cake, Water and mixtures of one or more components thereof.

15. A system for providing continuous feed-layers of materials of mainly organicorigin for the production of biofuel pellets, feed pellets and the like in apelletizer, said pelletizer comprising an extrusion die, die heating and/ orcooling means, means for pressing feed material through said die, and a motor coupled in driving engagement with the pressing means; characterised by means (1) for continuously monitoring the status of the feed-layer inthe pelletizer by measuring at least one process and/ or equipment Variable; means (2) for performing a comparison With preset target values andthreshold values for said Variable, in response to said measurement; means for sending signals to at least one regulator (3) adapted toadjust process variables so as to enhance the binding properties of the feed layer to the die surface, depending on the result of said comparison.

16. The system as claimed in claim 15, Wherein the monitoring means comprises means for on-line collection of electrical data of the pelletizer motor. 18

17. The system as claimed in claim 15 or 16, Wherein the comparison means isa computer assisted device for continuously testing if said motor current isWithin set targeted values regarding the actual read-out of electrical data andregarding variability measurement Within a successive moving Window of actual and preceding observed read-outs of electrical data.

18. The system as claimed in claim 15, 16 or 17, Wherein the at least oneregulator is adapted to control infusion of cooling media either to the feed layeror the die surface or to both, or into channels or onto ﬂanges connected to the die.

19. The system as claimed in claim 17 or 18, Wherein said computer assisteddevice is adapted to generate regulation signals to regulators controllinginfusion of cooling media, either to the feed layer or to the die surface or toboth, or in channels or on ﬂanges connected to the die When the actual current and/ or the actual variability measurement pass set targeted values

20. The system as claimed in any of claim 15-19, further comprising a sensorfor recording feed layer temperature, die surface temperature and/ or die temperature.

21. The system according to any of claims 15-20, Wherein the cooling media is any of Water aerosols, liquids and/ or gases (e.g. air).

22. The system as claimed in any of claims 15-21, Wherein targets for theelectrical variability measurement are set at several coefficients of variation inthe range of 0-3, preferably between 0 and 0,75, or still more preferred between O and 0,2.

23. The system as claimed in any of claims 15-22, Wherein the preset targetvalue for basic cooling equals the heat remaining after heating of the rawmaterial, evaporating moisture etc, e.g. about 25-80% of the mechanical Workdone by the motor at continuous pellet production minus that of idle running at no production at all. 19

24. The system as claimed in any of claims 15-23 further comprísing a controlunit for evaluating said preset value for basic Cooling at every majordisturbance of the feed layer formation, e. g. after an intermittent pellet production cycle, to calculate if said preset value should be changed.

25. The system as claimed in any of claims 15-24, comprísing means forcontrolling the feed layer temperature, die surface temperature and/ or dietemperature is/ are to between O to 80°C and preferably 20-7 O°C, more preferably O~60°C, and most preferably O~50°C.

26. The system as claimed in any of claims 15-25, further comprísing means foradding press helpers (e.g. powder or granules of lignin, starch, plastics, Sugar,oils, fats, rape seed cake, Water and mixtures of one or more components thereof.