WO2021225498A1

WO2021225498A1 - Defibrator assembly, and method for monitoring a defibrator assembly

Info

Publication number: WO2021225498A1
Application number: PCT/SE2021/050402
Authority: WO
Inventors: Thommy LINDBLOM; Örjan AHLGREN; Jan Laredius
Original assignee: Valmet Ab
Priority date: 2020-05-07
Filing date: 2021-04-30
Publication date: 2021-11-11
Also published as: EP4146859A4; EP4146859A1

Abstract

The present invention relates to a defibrator assembly (10) comprising - a preheater (11) for treating lignocellulosic material before defibration, - a defibrator (12) for receiving lignocellulosic material from the preheater (11) and defibrating the lignocellulosic material, the defibrator (12) comprising a feed screw arrangement (31) for receiving lignocellulosic material from the preheater (11) and feeding it towards a refiner housing (13), a refiner housing (13) comprising at least one blade pair (41) for refining the lignocellulosic material, an outlet (14) for discharging refined lignocellulosic material from the refiner housing (13), wherein the defibrator assembly (10) further comprises a first sensor (51) for detecting at least one parameter of the defibrator (12), said first sensor (51) being configured to detect the at least one parameter in a feed screw environment (6) formed inside the defibrator (12). The invention also relates to a method for monitoring a defibrator assembly.

Description

DEFIBRATOR ASSEMBLY, AND METHOD FOR MONITORING A DEFIBRATOR ASSEMBLY

TECHNICAL FIELD

The present invention relates to a defibrator assembly for refining lignocellulosic material, comprising a preheater and a defibrator that in turn comprises a feed screw arrangement for receiving lignocellulosic material from the preheater and feeding it towards a refiner housing, a refiner housing comprising at least one blade pair for refining the lignocellulosic material, and an outlet for discharging refined lignocellulosic material from the refiner housing of the feed screw environment.

BACKGROUND

When producing pulp from a lignocellulosic material such as wood chips, a defibrator is used to refine the material. Generally, the lignocellulosic material is heated in a preheater and then transported into a defibrator where it is fed to a refiner housing with at least one pair of refiner blades, so that the lignocellulosic material passes a between the refiner blades and is refined before exiting through an outlet.

Inside the defibrator, the lignocellulosic material is transported in a direction towards the refiner blades, and simultaneously steam is transported in a direction away from the refiner blades, back to the preheater. The steam may have been added to the lignocellulosic material but may also have been generated when the lignocellulosic material is heated under pressure.

In order to efficiently refine the lignocellulosic material, it is important that the flow of material towards the refiner blades and the flow of steam back from the refiner is smooth and efficient. However, during certain conditions the steam is not able to flow backwards and evacuate into the preheater and this may result in a build-up of steam in the defibrator and a significant loss of performance of the refiner blades. Ways to remedy this includes regular cleaning of a steam pipe or balance pipe that leads steam back from the defibrator to the preheater, and also attempting to control input of lignocellulosic material into the preheater or into the defibrator. However, none of these measures actually solve these problems and the efficient operation of the defibrator assembly therefore cannot be achieved.

There is therefore a need for an assembly and method that are able to improve operation of a defibrator assembly.

SUMMARY

The object of the present invention is to eliminate or at least to minimize the problems discussed above. This is achieved by defibrator assembly and a method for monitoring a defibrator assembly according to the appended independent claims.

The defibrator assembly of the present invention comprises a preheater for treating lignocellulosic material before defibration and a defibrator for receiving lignocellulosic material from the preheater and defibrating the lignocellulosic material. The defibrator comprises a feed screw arrangement for receiving lignocellulosic material from the preheater and feeding it towards a refiner housing, a refiner housing comprising at least one blade pair for refining the lignocellulosic material, and an outlet for discharging refined lignocellulosic material from the refiner housing of the feed screw environment. Further, the defibrator assembly comprises a first sensor for detecting at least one parameter of the defibrator, said first sensor being configured to detect the at least one parameter in a feed screw environment formed inside the defibrator. By detecting the parameter inside the defibrator in the feed screw environment, the operation of the defibrator assembly can be monitored in a more accurate way than has previously been possible. This allows for accurately assessing conditions inside the feed screw environment of the defibrator and optionally also for controlling those conditions by adjusting other parameters or operational conditions so that an increased efficiency of the defibrator assembly can be achieved.

Suitably, the feed screw environment comprises an interior of a housing in which at least part of the feed screw arrangement is arranged. Thereby, the first parameter can be detected in an internal space of the defibrator where the lignocellulosic material and the steam pass on their way to the refiner blades or upstream towards the preheater.

The feed screw arrangement may comprise a feed screw for feeding lignocellulosic material to the at least one blade pair, said feed screw preferably being a ribbon feeder. Thereby, lignocellulosic material may be efficiently fed to the refiner while also allowing steam to pass in an opposite direction.

Suitably, the feed screw arrangement further comprises a second screw for feeding lignocellulosic material from the preheater to the feed screw, said second screw preferably being a plug screw feeder. Also, the feed screw environment may comprise at least a part of an interior of the second screw. Thereby, lignocellulosic material is fed from the preheater into the defibrator in an efficient way, and a part of the second screw that is in fluid communication with the inside of the defibrator may be included in the feed screw environment so that the first parameter may be detected there. By using a plug screw as the second screw, a plug of material is formed as it is transported from the preheater and this serves to divide the preheater from the defibrator so that parameters of the feed screw environment may differ from parameters of the preheater. For instance, pressure in the feed screw environment may differ from a pressure in the preheater, or temperatures may vary as well as a flow of material and steam.

The feed screw arrangement could further comprise a chute or conduit for transporting lignocellulosic material from the preheater to the feed screw. Thereby, rather than a second screw a conduit or chute can be used to efficiently transport the lignocellulosic material. This also allows for the accumulation of a volume of lignocellulosic material that can be kept in the chute or conduit waiting to be introduced into the defibrator. It is thus possible to use the chute or conduit for storage or stockpiling of material and to form a plug with such material so that parameters of the feed screw environment may differ from parameters inside the chute or conduit and inside the preheater. Such parameters may include pressure, temperature and flow of material and/or steam. Suitably, the feed screw environment comprises at least part of the refiner housing. Thereby, the at least one parameter may be detected also downstream from the feed screw arrangement inside the refiner. It is advantageous to detect the parameter upstream from the refiner blades, i.e. before the lignocellulosic material enters a refiner gap where the refining takes place so that the location of the first sensor is in a space that is in fluid communication with the feed screw arrangement.

The defibrator assembly may also comprise a steam return conduit for transporting steam from the defibrator to the preheater. The feed screw environment may further comprise at least a part of an interior of said steam return conduit, said part preferably being a part at a defibrator end of the steam return conduit or a part at a distance from said defibrator end, wherein said distance is not longer than i of a length of the steam return conduit. Thereby, steam can be lead from the defibrator to the preheater, and the at least one parameter can be detected by a first sensor inside the steam return conduit. In order to accurately detect the at least one parameter, it is advantageous to place the first sensor close to the defibrator since the parameter may change as the steam passes through the conduit so that a value in the conduit close to the preheater may differ from a value close to the defibrator.

Suitably, the first sensor is arranged inside the feed screw environment. Thereby it is possible to detect the parameter with high accuracy. The at least one parameter may advantageously be a pressure, a temperature or a flow.

The defibrator assembly may further comprise a second sensor for detecting at least one parameter, wherein the second sensor is configured to detect the at least one parameter in an interior of the preheater or an interior of a component that is in fluid communication with the interior of the preheater. Thereby, a parameter can be detected also in the preheater or in a space that is connected to the preheater in such a way that the parameter has the same value as in the preheater or only differs slightly. This makes it possible to compare the same parameter as detected in the feed screw environment with the parameter of the preheater.

Suitably, the defibrator assembly also comprises a third sensor for detecting at least one parameter, said third sensor being configured to detect the at least one parameter in the outlet, or in an interior of a component that is in fluid communication with the outlet. This allows for detecting the same parameter in the defibrator assembly downstream of the refiner blades, i.e. where the lignocellulosic material has already been refined. The value detected by the third sensor can then be compared to what is detected by the first sensor or optionally also by the second sensor, in order to give an even more accurate information of operating conditions inside the defibrator assembly.

The defibrator assembly may also comprise a control unit configured to receive the detected at least one parameter as input from the first sensor and optionally from the second and/or third sensor. Thereby, information from each of the sensors can be received, processed, stored and/or displayed. This allows for monitoring operation of the defibrator assembly so that detailed information regarding the defibrator assembly and the condition of lignocellulosic material and steam during operation is achieved.

Suitably, the control unit is further configured to control operation of the defibrator assembly based on the detected at least one parameter, wherein controlling operation of the defibrator assembly includes controlling at least one of an input of lignocellulosic material to the feed screw arrangement and/or to the preheater, input of steam to the preheater, feed screw or refiner housing, or output of steam from the feed screw. Thereby operation of the defibrator assembly can be adjusted so that optimal conditions are reached and an increased efficiency can be achieved.

According to the present invention a method for monitoring a defibrator assembly for refining lignocellulosic material is also provided. The method comprises detecting a first parameter in a feed screw environment inside a defibrator of the defibrator assembly, and a first sensor is used for detecting the first parameter. Thereby, information regarding operating conditions inside the feed screw environment is gathered so that operation can be monitored. Suitably, the method also comprises using a second sensor for detecting the first parameter inside a preheater of the defibrator assembly or in a component that is in fluid communication with an inside of the preheater, and determining a first difference between the first parameter detected by the first sensor and the first parameter detected by the second sensor Thereby, the first difference can be used to further understand operation of the defibrator assembly and to more accurately see the flow of lignocellulosic material and steam between the preheater and the defibrator.

The method may also comprise controlling at least one operational parameter of the preheater in response to the first difference, said at least one operational parameter preferably being a supply of steam or a supply of lignocellulosic material. Thereby, the first difference can be adjusted by changing the flow of lignocellulosic material and / or steam to the preheater in order to increase or decrease the first parameter in the preheater so that the difference between conditions in the preheater and conditions in the feed screw environment also increased or decreased.

Suitably, the method comprises using a third sensor to detect the first parameter in an outlet of the defibrator assembly or in a component that is in fluid communication with the outlet, and to determine a second difference between the first parameter detected by the first sensor and the first parameter detected by the third sensor. This allows for detailed information regarding the refiner itself so that the flow of lignocellulosic material through the refiner is more accurately described.

The method may also comprise controlling at least one operational parameter of the defibrator assembly in response to the second difference, said at least one operational parameter preferably being a supply of steam to a refiner housing or an output of material through the outlet. Thereby, operation of the refiner may be optimized so that the lignocellulosic material is refined in a more efficient way.

The first parameter may suitably be a pressure, a temperature, or a flow of lignocellulosic material and/or steam. The present invention also includes a data processing device, a computer program product and a computer-readable storage medium that serve to carry out the inventive method in order to monitor and optionally to control operation of a defibrator assembly.

Many additional benefits and advantages of the present invention will be readily understood by the skilled person in view of the detailed description below.

DRAWINGS

The invention will now be described in more detail with reference to the appended drawings, wherein Fig. 1 discloses a defibrator assembly according to a preferred embodiment of the present invention; and

Fig. 2 discloses the defibrator assembly of Fig. 1 showing a first and second difference in a detected first parameter for monitoring the defibrator assembly. All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Any reference number appearing in multiple drawings refers to the same object or feature throughout the drawings, unless otherwise indicated. DETAILED DESCRIPTION

The term lignocellulosic material is used herein to mean materials containing lignin, cellulose and hemicellulose. One example of such materials is wood, others include other agricultural or forestry wastes. When it is stated herein that a first component is in fluid communication with a second component, this is to be interpreted as the component being connected in such a way that a space is formed inside the first component and extends up to and at least partly inside the second component. A parameter detected in that space would then have a constant or near constant value in the space so that the parameter as detected in the space is constant across the space.

When the term constant is used herein this is to be interpreted as being the same value within manufacturing tolerances or a detected parameter not varying more than 10 %.

The terms upstream and downstream as used herein refer to how lignocellulosic material passes through the defibrator assembly. Thus, a downstream direction will be a direction along which a flow of lignocellulosic material passes, whereas an upstream direction will be a direction against the flow of lignocellulosic material.

Fig. 1 discloses a defibrator assembly 10 according to a preferred embodiment of the present invention. The defibrator assembly 10 comprises a preheater 11 where lignocellulosic material M is treated to prepare it for defibrating in a defibrator 12, where it passes between refiner blades 41 in order to be refined into smaller fibers before being discharged through an outlet 14.

In the drawings, a flow of lignocellulosic material M during operation is indicated by dashed arrows, and a flow of steam S during operation is indicated by continuous arrows. The defibrator assembly 10 will now be described in detail, along with a description of how lignocellulosic material M is refined in the defibrator assembly 10. With reference to Fig. 2, the method for monitoring the defibrator assembly 10 will also be described.

Thus, lignocellulosic material M that is to be refined enters the preheater 11 through a material inlet 24 at a top 21 of the preheater 11. Also present at the top are a steam inlet 25 and a steam outlet 26 for supplying or discharging steam S to and from the preheater 11.

In the preheater 11 , lignocellulosic material M is treated to prepare it for refining in a manner that is already well known within the art. During treatment, the lignocellulosic material M progresses in a downward direction in the preheater so that new lignocellulosic material M can be continuously supplied through the material inlet 24. Near a bottom 22 of the preheater

11, another steam inlet 27 is also provided to make it possible to add steam S to the lignocellulosic material M also as it is about to pass into the refiner

12.

From the preheater 11 lignocellulosic material M is transported in a transporter 33 that may be in the form of a second screw 33 as shown in Fig. 1 or that may alternatively be a chute or conduit that connects the preheater 11 to the refiner 12. The refiner 12 is connected to the transporter 33 so that the lignocellulosic material M can be received and fed into a feed screw 32 that in turn transports the lignocellulosic material M towards a refiner housing 13 where at least one blade pair 41 is arranged to receive the lignocellulosic material M and refine it in a process that is also well known in the art. After refining, the lignocellulosic material M is transported to the outlet 14 and suitably passes a discharge valve 42 on its way out of the refiner assembly 10.

A steam return conduit 23 is connected to an inner space of the refiner 12 and to the top 21 of the preheater 11 for allowing a flow of steam S to be evacuated from the refiner 12 and supplied to the preheater 11.

The feed screw 32 is suitably in the form of a ribbon feeder that is arranged on a central shaft 34 that in turn is preferably concentrically arranged with the blade pair 41.

Collectively those components that serve to transport lignocellulosic material M from the preheater 11 to the refiner housing 13 are herein referred to as a feed screw arrangement 31. Thus, the feed screw arrangement 31 in this embodiment comprises the feed screw 32 and the transporter 33, i.e. either the second screw 33 or the conduit or chute.

In the refiner housing 13, there is also a steam inlet 43 for supplying steam into the refiner housing 13 downstream of the refiner blades 41. Dashed lines in Fig. 1 indicate a feed screw environment 6 that is formed inside the refiner 12 and that forms an internal space connected to a refiner zone between blades of the blade pair 41. In this feed screw environment a first sensor 51 is arranged to detect at a first parameter that is indicative of operation of the refiner assembly 10. In some embodiments, it is also advantageous to detect a plurality of parameters but in every embodiments herein at least one parameter is detected.

The feed screw environment 6 comprises at least a part of the feed screw arrangement 31 , namely a space in which the feed screw 32 is arranged and optionally also a portion of the transporter 33 that is in fluid communication with the space in which the feed screw 32 is arranged. Furthermore, the feed screw environment 6 comprises a space downstream of the feed screw 32 up to and including a part of the refiner zone of the blade pair 41 that is located upstream of an area where a pressure peak is achieved during operation of the defibrator assembly 10. The feed screw environment may also include other spaces that are in fluid communication with the space inside the refiner 12 where the feed screw 32 is mounted, such as the steam return conduit 23 or at least a part of the steam return conduit 23 that is adjacent to the refiner 12. Suitably, such a part would a part at a defibrator end of the steam return conduit or a part at a distance from said defibrator end, wherein said distance is not longer than i of a length of the steam return conduit 23.

As lignocellulosic material M enters the preheater 11 it is inserted into a preheater environment 7 that is formed by an inner space in the preheater 11 and any components that are in fluid connection with that inner space. Such components can be the steam inlets 25, 27 and the steam outlet 26 as well as the material inlet 24 itself and a part of the transporter 33 that is adjacent to the preheater 11. A part of the steam return conduit 23 that is adjacent to the preheater 11 may also form part of the preheater environment 7, and suitably up to i of a total length of the steam return conduit 23 can be seen as being in fluid communication with the preheater environment 7. Inside the preheater environment 7 operating parameters of the refiner assembly 10 can be said to be constant or nearly constant. A second sensor 52 may suitably be placed inside or in connection with the preheater environment 7 so that it can detect at least one parameter of the preheater environment 7. The first parameter may suitably be a pressure, a temperature or a flow of lignocellulosic material M.

As the lignocellulosic material M is fed from the preheater 11 into the refiner 12, it passes from the preheater environment to the feed screw environment 6. If the transporter 33 is in the form of a second screw 33 it is advantageous to provide a plug screw feeder that operates so that a material plug is formed, since this further assists in dividing the preheater environment 7 from the feed screw environment 6.

In the feed screw environment 6, the lignocellulosic material M is fed towards the refiner housing 13 and into a refiner zone between the pair of refiner blades 41. Due to the operation and function of the refining, temperature and pressure is generally significantly increased in the feed screw environment 6 as compared to the preheater environment 7. Due to the increased temperature, moisture in the lignocellulosic material M is evaporated to form additional steam S which also serves to further increase pressure and thereby also temperature in the feed screw environment 6. Due to the pressure peak between the blade pair 41, steam S is not able to pass downstream from the blade pair 41 and instead flows upstream, i.e. towards the left-hand side of Fig. 1 as indicated by the arrows. The steam return conduit 23 serves to allow this additional steam S to evacuate from the refiner 12 back into the preheater 11. The lignocellulosic material M is refined in the refiner zone of the blade pair 41 and passes downstream into a space of the refiner housing 13 that forms an outlet environment 8. The outlet environment 8 thus comprises a space between the blade pair 41 that is downstream of the pressure peak, and also comprises a part of the refiner housing 13 that is not in fluid communication with the feed screw environment 6, and further comprises the steam inlet 43 and the outlet 14, as well as a part of a conduit connected to the outlet 14 wherein said part is adjacent to the outlet 14. In the outlet environment 8, pressure and temperature and also the flow of lignocellulosic material M is generally lower than in the feed screw environment 6. A third sensor 53 is suitably arranged in the outlet environment 8 or in connection with the outlet environment 8 so that at least the first parameter of the outlet environment 8 can be measured.

Also included in the refiner assembly 10 is a control unit 100 that may be arranged in or on the refiner assembly 10 but that may alternatively be arranged remotely. The control unit 100 is operatively connected to the first sensor 51, the second sensor 52 and the third sensor 53 so that it can receive signals from the sensors 51, 52, 53, and it may also be operatively connected to the refiner assembly 10 so that it can control at least one operational parameter of the refiner assembly 10. Such operational parameters include the supply of steam through steam inlets 25, 27, 43; the supply of lignocellulosic material through the material inlet 24, transport of steam S through the steam return conduit 23 and operation of the transporter 33 and the feed screw 32. It may also include operation of the blade pair 41, discharge of lignocellulosic material M through the outlet 14 and any other factors that affect operation of the refiner assembly 10.

The inventive method for monitoring the refiner assembly 10 will now be described with reference to Fig. 2.

In prior art arrangements and methods for refiner assemblies, a parameter such as a pressure is generally measured in a part of the preheater environment 7, e.g. in a steam supply or a steam outlet conduit. The same parameter is also generally measured in a part of the outlet environment, e.g. in a steam supply near the outlet or in the outlet itself. A comparison of these measurements, DR, is then used to determine properties of the refining of lignocellulosic material in the defibrator assembly and optionally also to adjust the operation of the defibrator assembly to increase efficiency.

The present inventors have realized that it is highly advantageous to instead measure a parameter such as pressure, temperature, or flow of lignocellulosic material M or alternatively a flow of steam S, inside the feed screw environment 6. This makes it possible to determine more accurately how the refining of lignocellulosic material M is progressing and also to determine which operational parameters if any that can be adjusted in order to increase efficiency or quality of the refining that takes place in the refining assembly 10.

Thus, to detect at least one parameter by means of the first sensor 51 allows for a monitoring of the defibrator assembly 10. Based on the detected parameter, the refining can be evaluated and conclusions can be drawn regarding possible adjustments for future operation of the refining assembly 10.

It is also highly advantageous to determine a first difference DRB between at least one parameter as detected by the first sensor 51 in the feed screw environment 6 with at least one parameter as detected by the second sensor 52 in the preheater environment 7. When the first difference DRB is large, steam S can be efficiently evacuated via the steam return conduit 23 so that feeding of lignocellulosic material M by the feed screw arrangement 31 to the refiner housing 13 is efficient. However, when the first difference DRB is smaller and especially when it is smaller than a threshold value steam S cannot be evacuated from the refiner 12 into the preheater 11, and the steam return conduit 23 is filled with steam S that is kept stationary and possibly also condenses inside the steam return conduit 23 resulting in a buildup of moisture on inner walls of the conduit 23. The threshold is suitably 0.5 bar when the detected parameter is a pressure, more preferably 0.3 bar and even more preferably 0.2 bar. For efficient evacuation of steam a suitable DRB could be about 5 bar, but this is merely to be seen as an example since it is affected to a great deal by properties of the defibrator assembly and of the lignocellulosic material that is to be refined. The detected at least one parameter in the feed screw environment 6 and in the preheater environment 7 and the first difference DR_B calculated based thereon may also advantageously be used to control operation of the defibrator assembly so that refining of lignocellulosic material is rendered more efficient. Thus, when the first difference DR_B is at the threshold, or alternatively when it deviates from an optimal value or an optimal range in which refining is deemed sufficiently efficient, the operation of the refining assembly 10 may be adjusted in order to increase the first difference DR_B or to return it to the desired optimal value or optimal range. Such adjustments may include supplying additional steam S into the preheater environment 7 through the steam inlets 25, 27 in order to increase pressure and/or temperature inside the preheater. Also, the supply of lignocellulosic material M to the preheater may be adjusted, along with the discharge of steam S through the steam outlet 26. A supply of steam S to the preheater through the steam return conduit 23 may also increase pressure and/or temperature inside the preheater 11 , and a discharge of lignocellulosic material M from the preheater to the transporter 33 may be increased or decreased.

Furthermore, it is highly advantageous to detect the at least one parameter in the outlet environment 8 by means of the third sensor 53 and to determine a second difference DRϋ between the parameter as detected by the third sensor 53 and the parameter as detected by the first sensor 51 in the feed screw environment 6. The second difference DRϋ may provide important information regarding the refining since it discloses a difference in the at least one parameter immediately before refining takes place and the same parameter after refining. It therefore allows for a more detailed understanding of the refining than is possible using prior art technology. In some applications, a DRϋ with a magnitude of about 5 bar when the at least one parameter is a pressure can be suitable to ensure efficient refining of the lignocellulosic material, but it is to be noted that this will differ depending on properties of the defibrator assembly and also on properties of the lignocellulosic material itself. The main advantage of the present invention is the realization that the refining can be monitored and optionally also controlled in a more efficient way by determining conditions in the feed screw environment 6.

To summarize, the method according to a preferred embodiment of the present invention comprises using the first sensor 51 to detect the first parameter in the feed screw environment 6. This makes it possible to monitor the operation of the defibrator assembly 10 to determine how refining of lignocellulosic material M is performed.

Suitably, the method also comprises using the second sensor 52 to detect the same parameter in the preheater environment 7 and comparing it with the parameter as detected by the first sensor 51 to form the first difference DRB. If the first difference DRB is too small to ensure efficient operation of the refiner assembly 10, operational parameters such as the supply and discharge of material to and from the preheater 11 may be adjusted accordingly. Also, the method of the present invention may include using the third sensor 53 to detect the same parameter in the outlet environment 8, to determine a second difference AP_D by relating the parameter as detected by the third sensor 53 with the parameter as detected by the first sensor 51. Operational parameters that can be adjusted in the refiner housing 13 include the supply of steam through the steam inlet as well as discharge of lignocellulosic material M through the outlet 14.

Inside the refiner 12, operation of the feed screw 32 may also be adjusted in order to affect the first parameter as detected by the first sensor 51.

The control unit 100 may be configured to perform at least some steps of the method as described herein. This may include receiving input signals from the first sensor 51 and optionally also from the second sensor 52 or third sensor 53, and it may also include processing said signals in order to e.g. determine the first difference or the second difference. Furthermore, it may include sending at least one control signal to any part of the system for controlling operation of said part of the system. This may for instance involve controlling operation of the feed screw 32 to increase or decrease a rotational speed of the feed screw 32.

Although embodiments of the invention described above with reference to Fig. 1-2 comprise a control unit 100, and processes performed in at least one processor, the invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The programs may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, comprise software or firmware, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system, or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital Video/ Versatile Disk), a CD (Compact Disc) or a semiconductor ROM, an

EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal which may be conveyed directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

In one or more embodiments, there may be provided a computer program loadable into a memory communicatively connected or coupled to at least one data processor, e.g. the control unit 100, comprising software or hardware for executing the method according any of the embodiments herein when the program is run on the at least one data processor. In one or more further embodiment, there may be provided a processor- readable medium, having a program recorded thereon, where the program is to make at least one data processor, e.g. the control unit 100, execute the method according to of any of the embodiments herein when the program is loaded into the at least one data processor.

It is to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

Claims

1. Defibrator assembly for refining lignocellulosic material, the defibrator assembly (10) comprising

- a preheater (11) for treating lignocellulosic material before defibration,

- a defibrator (12) for receiving lignocellulosic material from the preheater (11) and defibrating the lignocellulosic material, the defibrator (12) comprising a feed screw arrangement (31) for receiving lignocellulosic material from the preheater (11) and feeding it towards a refiner housing

(13) , a refiner housing (13) comprising at least one blade pair (41) for refining the lignocellulosic material, an outlet (14) for discharging refined lignocellulosic material from the refiner housing (13), wherein the defibrator assembly (10) further comprises a first sensor (51) for detecting at least one parameter of the defibrator (12), said first sensor (51) being configured to detect the at least one parameter in a feed screw environment (6) formed inside the defibrator (12).

2. Defibrator assembly according to claim 1, wherein the feed screw environment (6) comprises an interior of a housing of the defibrator (12) in which at least part of the feed screw arrangement (31) is arranged, and wherein the first sensor (51) is configured to detect the at least one parameter in said interior of the housing.

3. Defibrator according to claim 1 or 2, wherein the feed screw arrangement (31) comprises a feed screw (32) for feeding lignocellulosic material to the at least one blade pair (41), said feed screw (32) preferably being a ribbon feeder.

4. Defibrator according to claim 3, wherein the feed screw arrangement (31) further comprises a second screw (33) for feeding lignocellulosic material from the preheater (11) to the feed screw (32), said second screw (33) preferably being a plug screw feeder, and wherein the feed screw environment (6) comprises at least a part of an interior of the second screw (33), and wherein further the first sensor (51) is configured to detect the at least one parameter in said interior of the second screw (33).

5. Defibrator according to claim 3, wherein the feed screw arrangement (31) further comprises a chute or conduit for transporting lignocellulosic material from the preheater (11) to the feed screw (32), and wherein the first sensor (51) is configured to detect the at least one parameter in the chute or conduit.

6. Defibrator assembly according to any previous claim, wherein the feed screw environment (6) comprises at least part of the refiner housing (13), said part being a part that is upstream of the at least one blade pair (41), and wherein the first sensor (51) is configured to detect the at least one parameter in said part of the refiner housing (13).

7. Defibrator assembly according to any previous claim, further comprising a steam return conduit (23) for transporting steam from the defibrator (12) to the preheater (11), and wherein the feed screw environment (6) further comprises at least a part of an interior of said steam return conduit (23), said part preferably being a part at a defibrator end of the steam return conduit (23) or a part at a distance from said defibrator end, wherein said distance is not longer than i of a length of the steam return conduit (23).

8. Defibrator assembly according to any previous claim, wherein the first sensor (51) is arranged inside the feed screw environment.

9. Defibrator assembly according to any previous claim, wherein the first sensor (51) is configured to detect a pressure, a temperature or a flow as the at least one parameter.

10. Defibrator assembly according to any previous claim, further comprising a second sensor (52) for detecting at least one parameter, said second sensor (52) being configured to detect the at least one parameter in an interior of the preheater (11) or an interior of a component that is in fluid communication with the interior of the preheater (11).

11. Defibrator assembly according to any previous claim, further comprising a third sensor (53) for detecting at least one parameter, said third sensor (53) being configured to detect the at least one parameter in the outlet (14), or in an interior of a component that is in fluid communication with the outlet (14).

12. Defibrator assembly according to any previous claim, further comprising a control unit (100) configured to receive the detected at least one parameter as input from the first sensor (51) and optionally from the second and/or third sensor (52, 53).

13. Defibrator assembly according to claim 12, wherein the control unit (100) is further configured to control operation of the defibrator assembly (10) based on the detected at least one parameter, wherein controlling operation of the defibrator assembly (10) includes controlling at least one of an input of lignocellulosic material to the feed screw arrangement (31) and/or to the preheater (11), input of steam to the preheater (11), feed screw (32) or refiner housing (13), or output of steam from the feed screw (32).

14. Method for monitoring a defibrator assembly for refining lignocellulosic material, the method comprising

- with a first sensor (51), detecting a first parameter in a feed screw environment (6) inside a defibrator (12) of the defibrator assembly (10).

15. Method according to claim 14, further comprising

- with a second sensor (52), detecting the first parameter inside a preheater (11) of the defibrator assembly (10) or in a component that is in fluid communication with an inside of the preheater (11),

- determining a first difference between the first parameter detected by the first sensor (51) and the first parameter detected by the second sensor (52).

16. Method according to claim 15, further comprising

- controlling at least one operational parameter of the preheater (11) in response to the first difference, said at least one operational parameter preferably being a supply of steam or a supply of lignocellulosic material.

17. Method according to any of claims 14-16, further comprising

- with a third sensor (53), detecting the first parameter in an outlet (14) of the defibrator assembly (10) or in a component that is in fluid communication with the outlet (14),

- determining a second difference between the first parameter detected by the first sensor (51) and the first parameter detected by the third sensor (53).

18. Method according to claim 17, further comprising

- controlling at least one operational parameter of the defibrator assembly (10) in response to the second difference, said at least one operational parameter preferably being a supply of steam to a refiner housing (13) or an output of material through the outlet (14).

19. Method according to any of claims 14-18, wherein the first parameter is a pressure, a temperature or a flow.

20. A data processing device comprising means for carrying out the method of claim any of claims 14-19.

21. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any of claims 14-19.

22. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of any of claims 14-19.