WO2019119164A1

WO2019119164A1 - System and method for sampling fibres continuously

Info

Publication number: WO2019119164A1
Application number: PCT/CL2017/050078
Authority: WO
Inventors: Klaus Erwin BORNHARDT BRACHMANN
Original assignee: Investigaciones Forestales Bioforest S.A.
Priority date: 2017-12-20
Filing date: 2017-12-20
Publication date: 2019-06-27
Also published as: BR112020012649A2

Abstract

The invention relates to a system and method for sampling fibres continuously in the production of MDF panels, with less reaction time to make changes to the type of wood feed or in the defibration stage, keeping fibre quality constant at minimum cost. The system comprises: a fibre-extracting belt (22) located in the path of fibre falling from a fibre dryer (21); a fibre receiver (23) that receives the fibre from the extractor belt; a forming and pressing belt (24); a measuring device (25) for measuring fibre size optically; and a duct (26) that returns the fibre to the drying conveyor. According to the invention, a small mat of fibre is formed, which is made uniform using the forming and pressing belt (24), to measure the size of the fibre sample, and the fibre is returned to the MDF production process.

Description

SYSTEM AND METHOD FOR FIBER SAMPLING IN

CONTINUOUS FORM.

Field of the invention:

The present invention relates to a method and a system for producing MDF boards (for its acronym in English: Medium Density Fiberboard), with a constant fiber quality. By means of a control method and a system that allows the continuous and rapid sampling of the fibers that are produced in the defibrator of the MDF production line. State of the art:

The MDF board is a type of excellent substitute for natural wood with a wide range of applications.

The MDF must present a uniform and homogeneous structure and a fine texture that allows its faces and edges to have a perfect finish. The panels are characterized by a firm and smooth surface, a uniform core layer and a very good performance. It works practically the same as solid wood, being able to mill and carve in its entirety. It is perfect for varnishing or painting. It can also be varnished, glue easily and without problems. It is usually light brown. Due to these characteristics, the MDF board is widely used in fields such as furniture, construction, decoration.

To obtain the MDF, roughly, a urea formaldehyde resin or forms of other adhesives are added to materials such as wood and plant fibers to be then pressed at 450-880 kg / m ³ by means of a press hot The production line of MDF consists of the preparation of the chips, the preparation of the fiber, the application of the glue, the formation of the

i blanket, hot pressing, cooling, rectification of measures and sanding.

The MDF production line usually includes the following stages (see reference to figure 1):

1. Preparation of the chips

The wood (100) is processed in a debarker (101), cutting it into pieces of a defined size, providing wood chips to the production plant of boards and / or panels. The wood chips are sent to cleaning and sorting processes (102) to remove bark and sand residues. The chips pass to the washing station (103) of chips where the materials whose density prevents them from floating, mainly sand and metals, are eliminated. By means of a drain screw (104) the cleaned chips are brought to a vaporizer silo (105).

2. Fiber preparation section

In the vaporizer silo (105), the air occluded in the chips is eliminated, which makes the subsequent process of heat transfer in the digester more efficient (106). The chips in the silo (105) are heated with saturated steam to a pressure of 3 bar in order to standardize the temperature, homogenize the moisture and soften them making the elimination of water and natural resins of the wood more effective. From the vaporizer silo (105) they pass to the digester (106).

The digester (106), consists of a vertical tube of variable diameter in which the chips are heated by saturated steam at a pressure of 7 to 9 bar, during a retention period of 2 to 7 minutes. The flow of steam, pressure and temperature are controlled automatically. A variable speed feed outlet screw (107) in the lower part of the digester (106) determines the volume of material flow to the defibrator / refiner (108). The chips are transported to a feed screw (107) towards the defibrator / refiner (108), where, as the name implies, the material is shredded, where the chips are converted into fibers. Two cutting discs are located in the shredder housing. One disc is fixed, and the other is rotary. The separation between the stationary and rotating discs in the body of the defibrator defines the size of the fiber and has the greatest impact on the energy consumption of the MDF manufacturing process. The chips are introduced through the center of the fixed disc and are forced to enter through the narrow opening between the discs by centrifugal force. The vapor pressure in the disc housing blows the fiber through an adjustable blow valve, mounted on the shredder casing and then through a blow line to the drying duct.

3. Glue application A paraffinic emulsion or wax and water-proof additive is fed to refine, in the feed screw (107) and mixed with the fiber uniformly during the refining process under the strength of the refiner plates; or also, this paraffinic emulsion can be injected into the blow line. The adhesive is prepared by mixing the various components, such as resins, urea solution, catalyst (if present), and water in a certain proportion with respect to weight, preferably 65% by weight of resin, the rest being water. The resin is stored in ponds from where it is pumped to the injection unit near the defibrator / refiner (108). It can be injected to the inlet or outlet of the defibrator / refiner (108) or to the outlet of the dryer (21), in case the gluing process is dry (dry blending).

4. Drying section of the fiber Drying is carried out in a dryer (21) of one or two stages and the heat source used consists of hot gases or hot air coming from the thermal plant through ducts in which it is mixed with fresh air to control the temperature. The fiber-vapor mixture from the defibrator / refiner (108), is driven to the dryer duct (blow duct). The hot air stream evaporates the moisture and conducts the fiber to the dryer cyclones, where the dry fiber is separated from the drying gas. The humid gas is expelled towards the top of the cyclone. The fiber falls to fiber transport (109).

To the transport of fiber (109) arrive the dry fibers of the dryer (21), the fibers of recycle of the former (1 10) and the fibers of the line of formation and systems of suction of saws.

The fiber transport (109) acts as a small storage lung between the fiber preparation area and the mantle formation line that is fed to the press (112). It maintains a constant flow of fiber to the training station (110), as well as ensuring that the different types of fiber that are fed to the transport are mixed before entering the training process.

A variable speed conveyor, located at the bottom of the equipment, controls the height of the fiber volume in the transport. A pneumatic separator specially designed to separate and remove high density particles such as adhesive lumps, fiber knots, metal, etc., is located at the end of the discharge of the fiber transport. Here the amount of inferior quality material that goes to the fiber flow towards the training stage is minimized. The fiber that comes from the fiber transport (109) is transported by air current to the formation station (1 10). 5. Mantle formation section and hot pressing

The fiber that comes from the transport of fibers (109) is introduced into a forming head (1 10) either by wind formation, or mechanical formation generating a continuous mantle, of different height according to the thickness and density of the board. you want to manufacture. Subsequently, this mantle goes through a pre-pressing process

(1 1 1) The objective of the pre-press is basically to reduce the height of the mattress to provide greater stability to the mantle and reduce the pressing time.

Then comes the pressing process (112), either in multiplat press or in continuous presses. In this stage, the board consolidation process takes place, through the application of pressure and temperature, for a determined time, depending on the density of the board, thickness, and other process conditions.

6. Cooling section, formatting and sanding The pressed board crosses several work stations, where it is subjected to measurement (1 13), classification (1 14), cooling (1 15), storage (1 16) after the cooling, sanding (1 17), formatting (1 18) and packing (1 19).

The crucial part of the MDF manufacturing process is the defibering area, since fiber is generated there and represents the highest energy consumption of the process. To obtain a homogeneous board that can be routed for use in moldings or pieces of furniture, fiber is required very fine, however, energy consumption and cost increase significantly when generating finer fiber. Therefore, it is economically inappropriate to generate fiber that is finer than required. Therefore it is very important to find the optimal point of operation, producing the appropriate fiber at the minimum cost. Variations in the wood used, or the mixture of woods, as well as the variables of time of stay in the vaporizer silo, temperature in the digester, etc. directly influence the quality of the fiber generated. For this reason it is vitally important to be able to measure the quality of the fiber and to be able to react quickly, in order to keep the quality of the fiber constant. The alternative of always working with fiber finer than required, generates a high operating cost. In general, the measurement of fiber quality is carried out discreetly and manually, with fiber samples that are measured in screens in the laboratory, where these samples are usually obtained in the line of formation.

FR 2846977 discloses a method for use in a nonwoven fiber layer forming machine, which consists in the measurement of mass of fibers at multiple points and using a small number of regulators linked to a control unit to influence the distribution along the width of the layer. The number of measuring points along the width of the layer is at least 5 times greater than the number of fiber regulators and the measuring elements are in the form of photosensitive detectors arranged approximately transverse relative to the direction of travel of the material non-woven Other measurement systems may comprise an ultrasound sensor, photo detectors or a radioactive receiver alternating across the travel line of the layer and the fibers may be distributed with the help of an air flow in a duct forming the fiber mantle.

It can be seen that said document refers to fibers of non-woven fabrics and does not refer to wood fibers in a panel manufacturing process, so the stages of the MDF manufacturing process can not be observed in this document, where you can only see the formation of a fiber (cloth) mantle and the need for this mantle to be uniform, since the type of fabric to be produced corresponds to veils (very thin), so that its uniformity is essential to obtain the desired product. It can only be seen that to achieve the objective of maintaining the uniformity of the mantle, a series of photosensitive detectors, connected to a computer, are used at the outlet of the mantle formation in order to react and modify the feeding of the fibers in case of be necessary.

In recent years, the instrumentation company Grecon, developed a device that allows detecting the coarse fiber (shives), in the already formed mantle, before the pressing stage (point A in figure 1). With this equipment you can detect when there is an increase in coarse fiber, with which you can take some action to return the process to the desired conditions. The quality of the fiber and therefore the appearance of coarse fiber (shives) is a function of the wood mix, opening of disks with respect to the volume of wood being fed, time and temperature in the digester, etc., varies widely by varying the feed to the defibrator (see figure 2).

The GreCon team allows an objective and continuous evaluation of the quality of the fiber in the production process. The values measured and supplied by the GreCon team allow the refiner operator to produce a consistent fiber quality, when there is no change in the wood mix and the process is stable with slow variations. The cooking and refining processes can be adjusted and thus the energy consumption and the quality of the fiber can be optimized. The fiber blanket is inspected by a camera system after pre-pressing on the top surface. Different sizes of coarse fiber are analyzed. This process is carried out continuously during production, so that representative information on fiber distribution is available. With this information, uniform surface properties can be guaranteed if the process conditions are stable. The energy-intensive fiber processing process can be optimized.

The GreCon team is based on an image method. The surface of the fiber blanket that passes to the pressing stage is continuously inspected by an in-line scanning chamber with vertical illumination over a width of approximately 400 mm.

The basic construction of the measurement system is a solid frame construction. The visual field of the camera is protected from dirt, dust, splinters and light intrusion by means of a closed tube. The system is equipped with an automatic height adjustment so that the camera and the lighting unit adjust automatically to changes in the height of the mantle, depending on the carpet's humidity and, of course, on product changes. Therefore, it is guaranteed that the surface to be inspected is always in the focus of the camera and that sharp images are taken. In addition, the lighting of the system is automatically adjusted to compensate for the influences by color of different cooking conditions or types of wood. However, the time elapsed between the defibering process and the measuring point with this equipment is approximately 20 minutes, which means that the detection of a change in the quality of the fiber is delayed. Additionally, the adjustment is slow, because before any action, you must wait 20 minutes to observe the effect of the change made. At present, if in a specific measure of the fibers, there are thick fibers or there is an alarm from the laboratory where the analysis of fiber samples and boards has been carried out, Energy Consumption tends to increase Specific (SEC for its acronym in English: "Specific Energy Consumption", in MWh / ton of wood) above what is required, to ensure the final quality of the MDF boards. In addition, since there is no continuous measure of the quality of the fibers, one must work with a sufficiently large margin of error. Therefore, a method and a system that allows reacting with the minimum dead time is required, much less than the 20 minutes that the GreCon machine can deliver, which can only be installed between the pre-pressing and pressing stage. , due to the need to have a uniform layer of fiber formed for sampling and measuring the size of the fibers through the chamber.

Description of the figures:

Figure 1: description of the production line of MDF with location in A (state of the art) and location in B (invention) for fiber sampling. Figure 2: Graph showing the variation of the appearance of coarse fiber (shives) when varying the feeding and opening of the defibrator discs.

Figure 3: system of the detailed invention.

Figure 4: Measurement of granulometry with a Gilson screen in the course of 2 months of production

Detailed description of the invention: A system has been designed that achieves the taking of fiber sample for its measurement at the fiber dryer exit (where there is no formation of a stable layer of fiber, point B in figure 1), just seconds later of the process of defibrado, managing to reduce the time of reaction before an eventual need of change in the conditions of the process of desfibrado or before the change in the feeding of the wood. With this measurement, it acts automatically (or manually) on the opening of the defibration discs in order to keep the quality of the fiber constant. The new system of the invention manages to work in conjunction with the team of GreCon or any other similar system, which can measure the fibers from a uniform mantle of the same.

The new system is located at the exit of the dryer, where thanks to the system of the invention, it is possible to form a uniform mattress of fibers (dry) and continuous so that a team like GreCon (which is a simplified equipment with respect to the original, as it does not require height regulation) can measure the size of the fibers in optical form. After the measurement of the size of the fibers, they are returned to the process and continue their path towards the formation of the fiber mantle, without loss of material.

The system of the invention consists of the following elements: i. Fiber extractor tape (22), located in the fiber drop from the fiber dryer (21).

ii. Fiber receiver (23) from the extractor belt, which includes a level sensor (27) and a comb roller (28).

i¡¡¡ Formation and pressing tapes (24).

iv. Location of measurement equipment (25) of fiber size in optical form (for example, simplified GreCon equipment).

v. Pipe that returns the fiber (26) to the drying transport. Both tapes (22, 24) have a variable speed and controlled by the level sensor (27) of the fiber receiver (23) from the extractor belt.

The fiber extractor belt (22) is connected to the outlet of the fiber dryer (21) to receive part of the dry fiber and make it fall into the fiber receiver (23), which has a level sensor (27) that it will indicate the maximum level of filling for the formation of a small fiber mattress with the help of a combing roller (28), of a width of 10 cms. The fiber mattress passes to the forming and pressing belt (24), to uniform it and pass it through the optical measuring equipment (25), such as Grego's Fiberview ® equipment. Once the measurement of the size of the fiber is made by the measuring equipment (25), the fiber is returned to the manufacturing process of MDF, through the return duct (26) to the drying transport. The speed of the extractor belt (22) is automatically adjusted so as to maintain the appropriate filling level of the fiber receiver (23), measured through the level sensor (27). The speed of the forming belt (24) is automatically adjusted, so that the speed of the extractor belt (22) moves around a predetermined value, for example 80%. This control is necessary, since the volume of fiber in the drying depends on the product and other process conditions.

After the measurement equipment (25) has made the measurement of the amount of coarse fiber per area, it is plotted on the operation screen (29) and actions can be taken by decision of the operator (manual mode), or control can be performed of the opening of the discs of the defibrador (in automatic way) keeping constant the quality of the fiber, within a defined band.

Example: To show what is happening now, with discrete measures of the fiber, without performing actions, a change of product is shown in figure 2, which implies a change in the amount of fiber required (Screw (RPM), line ( a), bottom of the graph). The measurement of the fiber is not shown to the operator, to consider a real situation. Normally we work keeping the specific energy constant (SEC KWh / t, line (e), upper part of the graph) (automatic control). In this case this generates an opening of the defibrator disks (Rot Pos (mm), line (b), second line from bottom to top in the graph). The control of the opening of the discs is slow, starting in position 1, with a greater step in position 2. It is observed how the required power goes down (MM Power KW, line (d), second line from top to bottom in the graphic). It is observed how simultaneously the measure of the coarse fiber increases (shives, line (c), in the middle of the graph), practically without delay. This measurement of the quality of the fiber (line (c) in figure 2) is made with the system of the invention in position B indicated in figure 1. However, to show the real situation, in this case the measurement does not is informed to the operator, to achieve graphing the current problems, which would be solved by knowing the information obtained. In position 3, two and a half hours after the beginning of the change, the operator takes a sample of fiber and is measured with the Gilson screen, to see how the fiber is, if it is in the required values for the manufacture of fiber. MDF panels, generating the reaction to strongly increase the specific energy, because the size of the fibers is very thick compared to what is required. It can be seen that after the action of increasing the specific energy to decrease the size of the fiber due to the result of the sampling in position 3 by the operator, the final result is a finer fiber (line (c) after position 3), that required (starting condition) and therefore continues to spend more energy than required. This is how during the product change it was generated a very thick fiber that will generate problems in the quality of the MDF board, and after the action taken by the operator (in late form), it is still working with a much finer fiber than the required one which generates an excessive energy expenditure. Both situations are avoided by the present invention.

This example demonstrates the need for a rapid reaction to changes in fiber size. By having the system in point B of Figure 1, it is shown that with the rapid measurement action measures can be taken before point 2 and keeping the fiber size within the same size as before the change.

With the help of the system and the method of the invention it can be said that:

• The measurement of fiber quality works.

• The measurement is fast.

• Having the measurement in a shorter time than currently available, it is possible to react manually or automatically quickly.

• With the measurement, the fiber can be maintained in a desired range avoiding fiber of poor quality and / or avoiding excessive energy expenditure, by generating fiber that is finer than required. Advantages of the invention:

The main advantage of the system and the method of the invention correspond to the decrease in the reaction time that allows to implement an automatic control or to react manually, avoiding the appearance of very thick fiber, which influences the quality of the MDF board, or very fiber. fine that involves an unnecessary expenditure of energy.

In Figure 4, you can see the measurements taken with the Gilson screen for 2 months, with samples taken 3 times by shift, indicating the percentages of coarse fiber measured. These measurements correspond to those obtained in a Gilson screen that allows obtaining the geometric distribution of the fiber (quantifies the size of the fiber), corresponds to a manual and slow method, for punctual checks.

Line A (upper line) indicates the maximum accepted fiber value for a uniform MDF board production. Values superior to this line, imply very thick fiber, which generate problems of quality in the boards and that can be avoided with a control based on the continuous and rapid measurement of the fiber, in order to work around the value indicated in line A. The values under the line A, imply that the fiber is smaller than what is required and that therefore a greater energy (SEC) is being spent and increasing the wear of the defibrator disks, which are responsible for the defibration of timber. The more these discs come together, the finer the fiber comes out (better routing quality of the boards), but with it these discs wear out faster (their useful life goes down from 40 to 20 days), which increases the cost of operation . At the same time, the cost of electricity for each cubic meter of defibrated wood is increased. It is for this reason that fiber should be worked as thick as possible (which implies a minimum electrical energy and longer life of the disks), but under the limit of accepted coarse fiber (shives). Therefore to work in a stable manner with constant quality and at minimum cost is that you must control the appearance of shives in the shortest possible time. With the invention, it is possible to implement a control loop that keeps the fiber around line A at +/- 0.1%, which is acceptable to obtain uniform MDF boards of constant quality at minimum cost.

In figure 4, line A corresponds to 2.7% of the coarse fiber requested as the maximum value for the production of the boards. From the figure it can be seen that 52% of the trials gave as resulted in a percentage of thickness of 2.6% (middle line, B), while 22% (in the first month and 25% in the second month) was less than or equal to 2.0% (bottom line, C). Therefore, it is considered that 30% of the monthly production of fiber has a particle size smaller than what is required, which implies a higher production cost (according to what was explained in the previous paragraph).

On average, the value of coarse fiber according to the measurements with the Gilson screen, is 0.52% below what is required (for the example of figure 4, what is required corresponds to 2.7% of coarse fiber). This percentage (0.52%) is equivalent to a delta around 150 KW depending on the wood and wear of the discs. Therefore, an annual saving of US $ 63,000 would be obtained, considering a cost of US $ 50 / MWh (the annual average has been US $ 60 / MWh). Lowering the consumption of electricity by 150 KW, implies a saving of 4.2% in the plant analyzed. In addition considering a wear of the discs that depends linearly on the power and a disc cost of US $ 22,000 / set of discs, this amounts to an annual saving of US $ 1,000 / year. Given the calculations mentioned above, savings of approximately US $ 74,000 / year can be obtained, without taking into account the savings due to the reduction of claims for coarse fiber and savings in resin and wood, by constantly working at a desired operating point.

Claims

1. System for the taking of a sample of fibers in continuous form in the production of MDF panels, with a shorter reaction time to make modifications with the type of wood feed or in the defibration stage, keeping the quality of fiber constant at minimum cost, CHARACTERIZED because it includes: i. a fiber extractor belt (22), located in the fiber drop from the fiber dryer (21); ii. a fiber receiver (23) from the extractor belt; i¡¡¡ a forming and pressing belt (24); iv. a measurement device (25) of fiber size in optical form; v. a duct that returns the fiber (26) to the drying transport.

2. System for taking a fiber sample according to claim 1, CHARACTERIZED in that the fiber receiver (23) includes a level sensor (27) and a comb roll (28).

3. System for taking a sample of fibers according to claim 1, characterized in that the extractor (22) and forming tape (24) have a variable speed, controlled based on the level sensor (27).

4. System for taking a sample of fibers according to claim 1, CHARACTERIZED because it also comprises a software (29) with which the results obtained by the optical measurement equipment (25) are analyzed and allows to generate automatic response, to keep the quality of the fiber under control.

5. Method for taking a sample of fibers continuously in the production of MDF panels, with a shorter reaction time to make changes with the type of wood feed or in the defibration stage, maintaining constant fiber quality at the minimum cost, CHARACTERIZED because it includes the stages of: a. connecting a fiber extractor belt (22) with the output of a fiber dryer (21); b. receive part of the dry fiber in the fiber extractor belt

(22); c. connecting a fiber receiver (23) with the fiber extractor belt (22) to receive the dry fiber to be subjected to the sampling; d. form a small fiber mattress; and. uniform the fiber mattress by means of a forming and pressing tape (24); F. performing the measurement of the sample size of the fibers by an optical measuring device (25); g. return the fiber to the manufacturing process of MDF by means of a pipe that returns the fiber (26).

6. Method for taking a fiber sample according to claim 5, CHARACTERIZED in that it comprises providing a level sensor (27) and a comb roll (28) in the fiber receiver (23).

7. Method for taking a sample of fibers according to claim 6, CHARACTERIZED because the formation of the small fiber mattress is made with the help of the comb roller (28).

8. Method for taking a sample of fibers according to claim 5, CHARACTERIZED because the speeds of the extractor belts (22) and former (24) are controlled based on the measurement of the level sensor (27), so there is no clogging or lack of material during the measurement process.

9. Method for taking a sample of fibers according to claim 5, CHARACTERIZED because after the measurement of the size of the fibers by the optical measuring equipment (25), these are analyzed by a software (29), the which will indicate the need to make a decision regarding the feed to the defibrator, the operating conditions of the defibrator or the feeding of the wood to the process in manual or automatic mode.