EP0034095A1 - Process and installation for feeding vegetal material to processing enclosures before it is being cooked or reacted under pressure - Google Patents

Abstract

a) The reaction under pressure, such as cooking or hydrolysis, involves delivering under pressure, by means of a pump, a liquid mixture obtained by diluting substances of vegetable origin with the liquid in the presence of which the intended treatment is to take place. b) Provision is made to subject these substances, in addition to, or with, this dilution operation, to a thorough impregnation with this liquid, for example inside an apparatus (3) for dilution and impregnation. The delivery of the mixture obtained is then carried out by means of a Vortex pump (6) capable of conveying a liquid-solid mixture and driven at a variable speed by means of a control device comprising a flow detector (6a) and arranged so as to keep constant the flow rate in the delivery pipe (10). <IMAGE>

Description

The subject of the present invention is a method and an installation intended to supply the processing chambers with plant materials which are to undergo cooking or a reaction under pressure. This method and this installation are in particular intended to be used for supplying treatment chambers inside which the cooking of annual plants is carried out (wheat straw, rice, bagasse, reeds, etc.), in a detergent for the production of cellulose. However, this method and this installation are also designed to be able to be used for feeding treatment chambers in which a hydrolysis of such plants is carried out to extract the pentosannes.

Such treatments are generally carried out under pressures of up to 10 to 12 bars. They can be carried out either continuously or, conversely, discontinuously.

The latter solution is obviously less advantageous than a continuous treatment and this, particularly from an economic point of view. This is the reason why this solution is only used for relatively low productions and for products which are difficult to process, such as linters, hemp, etc.

Despite their economic advantages, installations operating continuously have various drawbacks, due in particular to the fact that the materials to be treated must be introduced inside a treatment enclosure which is itself at a relatively high pressure.

In general, the materials to be treated are introduced in the dry state, without prior impregnation, and the introduction device may consist of a rotary valve with cells, or an airlock with a drawer, or even a conical screw whose action has the effect of forming a pad of material supporting the pressure difference between the interior and the exterior. However, these are complex and expensive devices, because they must be made so as to be able to withstand relatively high pressure and temperature differences. In addition, these systems undergo very rapid wear, because despite prior cleaning, the plant materials to introduce contain silica dust incorporated into the fibers. This therefore requires an anti-abrasion treatment to be provided for the wearing parts. However, such treatment is very expensive and despite this and the other precautions taken, the parts must be changed frequently.

On the other hand, it should be noted that the screw introduction devices present the danger of accidental expansion of steam upstream in the event of a supply fault, as a result of the disappearance of the plug from the material forming the plug, and supporting the pressure difference. In addition, screw devices only work properly with dry materials; it is therefore impossible to pre-impregnate the products, an operation which significantly improves the quality of cooking.

To avoid the drawbacks of the devices carrying out the introduction in the dry state of the materials to be treated, it has already been proposed to ensure this introduction in liquid form: see for example French patent N ° 1 226 093. For this purpose , there is provision for a prior dilution of the materials which must feed the treatment enclosure, in order to produce a pumpable liquid mixture. Then, this mixture is discharged, by means of a centrifugal pump into the corresponding treatment enclosure.

However, the device thus provided may not be suitable for the introduction of annual plants or the like. Indeed, by the very nature of these plants, they tend to float when we try to dilute them in order to achieve a ponpable mixture. This is, moreover, the reason why such dilution is very difficult to achieve. Furthermore, as far as a liquid mixture could be obtained from such plants, this mixture can hardly be aspirated by a centrifugal pump. Indeed, as they affect the shape of fibers or stems of a certain length, annual plants tend to stuff in a centrifugal pump and can thus block its operation.

Furthermore and above all, for the plant introduction devices, in the form of a liquid mixture, to be able to function, the discharge pressure should always be higher than that prevailing in the treatment enclosure so that there constantly flow of the liquid-solid mixture in the line of repression. In fact, if this is not the case, the introduction cannot take place and there can even be a backward flow of the materials contained in the discharge pipe, or even already introduced inside the treatment enclosure, with all the resulting disadvantages.

However, current devices, such as that described in French patent 1 226 093, do not include any control or safety system capable of constituting a sort of "anti-retazr" valve and capable of ensuring that in any state of cause, there is always a flow of the liquid-solid mixture in the direction of the treatment chamber, despite the possible difficulties and irregularities of flow and introduction, due to the particular nature of the products conveyed. Consequently, in the device described in this patent, the flow of materials, and consequently their introduction into the treatment enclosure, can be disturbed and no longer be carried out, in certain cases. In addition, there can be a backtracking of the discharged materials and this, under the effect of the pressure prevailing in the treatment enclosure.

This is why the object of the present invention is to provide a method and an installation making it possible to avoid the drawbacks of the various prior systems mentioned above. To this end, the invention proposes to carry out the introduction of plant materials in liquid form, but by providing for a certain number of means and of particular provisions making it possible to obtain complete satisfaction.

The method according to the invention is characterized in that in addition to, or with, the dilution operation of the plant materials to be introduced, they are subjected to a thorough impregnation with the liquid in the presence of which must be carried out the treatment, then the discharge of the mixture obtained is carried out by means of a Vortex type pump, capable of conveying a liquid-solid mixture and which is driven at variable speed by means of a control device subject to a detector flow connected to the line from the discharge pump, so as to maintain constant the flow rate in this line.

Thanks to the arrangement thus provided, there is always a constant flow of flow towards the treatment enclosure, even if certain irregularities occur downstream. Indeed, in the event of a drop in the planned flow, and for which the flow detector, the control device accelerates the pump speed to restore the flow rate to its normal value. This system therefore also plays the role of a kind of non-return valve avoiding any risk of backward flow of the discharged materials.

• - un appareil d'imprégnation poussée des matières correspondantes avec le liquide en présence duquel doit s'effectuer le traitement prévu et éventuellement un appareil de dilution au cas où l'appareil d'imprégnation n'assure pas également cette fonction ;
• - une pompe de type Vortex ou autre pompe capable de véhiculer le mélange liquide-solide obtenu par dilution des matières correspondantes ;
• - un moteur à vitesse variable pour l'entraînement de cette ponpe ;
• - un dispositif de commande de la variation de vitesse de ce moteur, assujetti à un détecteur de débit branché sur la conduite partant de la pompe de refoulement et assurant le maintien constant du débit d'écoulement dans cette conduite.

As for the installation according to the invention, it is characterized in that it comprises in combination:

• - a device for impregnating the corresponding materials with the liquid in the presence of which the intended treatment must be carried out and possibly a dilution device in the event that the impregnation device does not also perform this function;
• - a Vortex type pump or other pump capable of conveying the liquid-solid mixture obtained by diluting the corresponding materials;
• - a variable speed motor for driving this ponp;
• - a device for controlling the speed variation of this motor, subject to a flow detector connected to the pipe leaving the delivery pump and ensuring constant maintenance of the flow rate in this pipe.

• La figure 1 est une vue schématique de l'ensemble d'une installation d'alimentation selon l'invention ;
• La figure 2 est une vue partielle d'une variante.
• La présente installation est destinée à assurer l'alimentation d'une enceinte de traitement 1, ou d'une succession d'enceintes de traitement, à l'intérieur desquelles doit être réalisé un traitement sous pression de matières végétales, par exemple la cuisson de plantes annuelles dans une lessive pour la production de cellulose, ou bien encore l'hydrolyse de ces mêmes plantes pour l'extraction, des pentosannes.

However, the various features and advantages of this installation and of the corresponding process will become apparent during the following description, given with reference to the accompanying drawing for information, and in which:

• Figure 1 is a schematic view of the assembly of a supply installation according to the invention;
• Figure 2 is a partial view of a variant.
• The present installation is intended to supply a treatment chamber 1, or a succession of treatment chambers, inside which a pressure treatment of plant materials must be carried out, for example the cooking of annual plants in a detergent for the production of cellulose, or even the hydrolysis of these same plants for the extraction, of pentosannes.

The installation shown in FIG. 1 comprises, first of all, an apparatus capable of ensuring both, and at the same time, the prepreg and the dilution of the corresponding plant materials with the liquid in the presence of which the planned treatment, in this case a detergent in the case of cooking for the production of cellulose. This device is designated by the general reference 3 on the attached drawing.

It is a device of the type generally designated by the name "pulper". This device comprises a tank containing a bath of the treatment liquid and in the bottom of which there is provided a rotor 4 provided with crushing fins capable of ensuring the separation of the fibers from the plant materials discharged into the tank as well as their shredding and their fragmentation into short pieces. An efficient impregnation of the fibers of these materials is thus obtained with the treatment liquid. However, this impregnation is also accompanied by a dilution of these fibers in the bath of the corresponding liquid, so as to produce a liquid-solid mixture capable of being pumped.

In this regard, it should be noted that in the present case, this dilution is carried out under perfect conditions, even if the materials to be treated are annual plants of the type indicated above. Indeed, as these materials are subjected to extensive impregnation with the treatment liquid, their dilution poses no problem, although normally they would have tended to float.

The liquid mixture obtained leaves the tank of the device 3 by an outlet nozzle 5. However, this is connected to a Vortex type pump, designated by the general reference 6 and which will be described in more detail below. .

A pipe 7 for the arrival of treatment liquid opens into the pulper 3. To this liquid may optionally be added water as will be explained later. The purpose of this arrival of liquid is to ensure the dilution of the plant materials in the treatment liquid to a concentration of approximately 5-6% in dry matter in order to obtain a liquid mixture capable of being pumped by the pump 6 of Vortex type.

The body of this pump has a large flow passage with regular flow and without any hindrance. It comprises an open wheel 8 provided with a body 9 of aerodynamic shape and the arrangement is such that there is no vacuum at the rear of this wheel.

Due to its design, and in particular the fact that in a Vortex stern, the sucked liquid is not brought to pass through the rotor (contrary to what is the case in a centrifugal pump), the ponp 6 is able to pump the liquid-solid mixture contained in the pulper 3. This pump then pressurizes this mixture at a pressure of the order of 5 to 8 bars and discharges it into a pipe 10. In fact, the role of pump 6 is both to convey the corresponding product and to overcome the pressure inside the treatment chamber.

As already indicated, the pressure of the pumped liquid mixture must be greater than the pressure prevailing in the treatment enclosure and, consequently, there must always be a flow rate in the discharge line. To obtain this result, the pump 6 is driven by a variable speed motor 6b and the speed thereof is adjusted so as to keep the delivery rate constant for a given production value in the treatment enclosure.

For this purpose, the flow rate inside the discharge line 10 is controlled by a flow meter 6a. The latter is connected to an electrical circuit 6c connected to the motor 6b, so as to constitute a control device varying the speed of this motor as a function of the flow rate.

Thus, if for any reason, for example downstream flow irregularities, there is a drop in the flow rate in the pipe 10, this device controls an acceleration of the pump speed to restore the flow rate. flow at the expected value. This system therefore makes it possible to obtain, with absolute safety, that there is always flow in the direction of the treatment enclosure to be supplied despite the pressure prevailing therein and the flow irregularities which may occur downstream. . Of course, this system also plays, therefore, the role of a kind of non-return valve avoiding any risk of backtracking of the rejected materials, or those already introduced into the unit and this, under the effect of the pressure prevailing inside it.

When putting this installation into service, it suffices to set the flow meter 6a to a set value for the desired flow rate inside the discharge line 10, the value of this flow rate being determined by function of the value of the desired hourly output in the processing enclosure. As for the pressure inside the treatment enclosure, it is adjusted and kept constant by the opening or closing of the injection of the heating steam sent into this enclosure.

The discharge pipe 10 leads to the inlet orifice 11 of a draining device 12 capable of wringing out the fibrous material while bringing it to the inlet tubing 13 of the treatment enclosure 1 to feed.

This drip device 12 is capable of safely resisting the working pressure. Its external cylindrical envelope 14 contains a perforated cylinder 15 inside which is disposed a screw 16 capable of ensuring the movement of the fibrous material up to the outlet tube 17 connected to the inlet of the treatment enclosure 1 The shaft of the screw 15 is rotated by a gearmotor group, not shown. The assembly thus formed is placed in an inclined position relative to the horizontal and a nozzle 18 for discharging the recovery liquid is provided at the lower part of the lowest end of the external envelope 12.

Of course, the inlet nozzle 11 opens into the space delimited by the perforated cylinder 15. Under these conditions, the mixture of liquid and fibrous material is sent under pressure into this space and taken up by the screw 16. That -ci causes this mixture to the outlet nozzle. However, the fibrous material is wrung out and the liquid eliminated flows through the perforations of the cylinder 15 to gain the gap existing around it and finally the outlet nozzle 18.

It should be noted that the transport screw 16 rotates with a reduced clearance inside the cylinder 15, which ensures the advance of the fibrous material while operating a constant cleaning of this grid. It should also be observed that this screw is provided, at its upper end, with a back-turn 19 which aims to avoid any risk of jamming at the location of the outlet 17 of the draining device. At its entrance, the latter receives the mixture loaded with vegetable fibers at a maximum concentration of 6% and minimum of 2%. After draining in this apparatus, the concentration is brought to the outlet to about 18 or 20%.

To avoid the risk of steam entering the liquid circuit, a minimum level of liquid is maintained in the drainage device 12 as well as in a balance pot 20 communicating with the latter. To this end, a level adjustment device 27 is provided, subject to two level detectors 27a and 27b. This device is capable of controlling, via circuits 28a and 28b, two valves respectively 28 and 29. The first is a valve for adjusting the flow rate inside a pipe 21 connected to the outlet of the pot 20 for recycling the treatment liquid used to transport and entrain the plant materials. As for the second valve 29, it consists of a quick-closing safety valve, which is connected to the discharge line 10.

Thus, this device makes it possible to maintain constant the level of liquid contained in the lower part of the draining apparatus, which makes it possible to avoid the entry of vapor into the liquid circuit.

Finally, the present installation comprises, in combination with the devices already described, a circuit for recycling the treatment liquid, which circuit comprises a device for settling and removing heavy particles suspended in this liquid. This device consists of a centrifugal separator 23 inside which the recovered liquid is brought by line 21 connected to the balance pot 20. After elimination of the particles in suspension, the liquid leaves this separator through a pipe 22. Quant particles and impurities that have been removed - in this case particles of sand, silica - they are collected in the lower hopper of the separator 22. This hopper communicates with a pot 24 intended to serve as an airlock for the evacuation of impurities . The inlet and outlet ports of this airlock are closed by valves, 25 and 26 respectively.

The liquid recovered in line 22 is returned to line 7 intended to dilute the impregnated materials, and this, by lover of the pump 6. However, there is provided a regulating device 34 ensuring the expansion of this liquid, from the discharge pressure up to the injection pressure in the pulper 3. This device operates automatically by measuring the pressure and valve of the liquid stream by means of a valve 35.

However, the pipe 7 for supplying the dilution liquid is connected not only to the pipe 22 for recycling but also to a pipe 36 intended to ensure the arrival of make-up liquid. An automatic level control device 37 regulates the supply of make-up liquid or the discharge of the excess to keep the level constant in the pulper 3.

During the operation of this installation, the pump 6 ensures the continuous supply of the treatment enclosure 1 with plant materials which are in suspension in a liquid mixture having a concentration of approximately 18 to 20% of fibers. This supply is ensured at a relatively reduced pressure of the order of 4 to 8 bars which will constitute the pressure at which the treatment will be carried out inside the enclosure.

As this treatment pressure is lower than that of the usual continuous running installations, supplied by devices for introducing the products in dry form, the duration of the treatment is longer. But the overall cost of the installation is lower.

The installation according to the invention makes it possible to ensure, in an optimum manner, the introduction of plant materials into a treatment enclosure, even when annual plants are involved. However, the process of introducing these materials takes place under perfect conditions, because the adjustment of the speed of this pump makes it possible to maintain a constant flow rate inside the discharge pipe.

But of course, the present installation is not limited to the single example described above. Thus, in the variant represented in FIG. 2, the pulper apparatus 3, carrying out both the impregnation and the dilution of the materials to be treated, is replaced by two separate apparatuses 3a and 3b ensuring respectively the one and the other of these two functions. In such a case, the impregnation device 3a is arranged upstream of the dilution device 3b. The first of these devices may consist of a drum fitted with blades and rotating inside a housing containing a bath of the treatment liquid. On leaving this device, the plant materials are therefore perfectly impregnated with this liquid. As for the dilution device 3b, it consists of a tank inside which is disposed a simple rotary agitator 4b, this tank being supplied with treatment liquid by the pipe 7, as in the previous embodiment. A discharge pipe 5b leads the mixture obtained to the pump 6 (not shown) and the rest of the installation is identical to what is provided in the previous embodiment.

Claims (5)

1. Method for supplying treatment chambers with plant materials which must undergo a reaction under pressure therein, such as cooking or hydrolysis, this supply being ensured by diluting the corresponding materials with the liquid in the presence of which the intended treatment is to be carried out , and delivery under pressure of the mixture obtained and this, by means of a pump, characterized in that before this dilution operation, or at the same time as this, these materials are subjected to extensive impregnation with this liquid , then the delivery of the mixture obtained is carried out by means of a pump (6) of the Vortex or other type capable of conveying a liquid-solid mixture, and which is driven at variable speed by means of a subject control device to a flow detector (6a) connected to the line (10) starting from the delivery pump (6), so as to keep the flow rate constant in this line. 2. Installation for supplying treatment chambers with plant materials which must undergo a pressure reaction therein such as cooking or hydrolysis, by implementing the method according to claim 1, characterized in that it comprises in combination: - an apparatus (3) for the advanced impregnation of the corresponding materials with the liquid in the presence of which the intended treatment is to be carried out and possibly a dilution apparatus in case the impregnation apparatus does not also perform this function; - a pump (6) of Vortex type or other pump capable of conveying the liquid-solid mixture obtained by dilution of the corresponding materials; - a variable speed motor (6b) for driving this pump; - a device for controlling the speed variation of this motor subject to a flow detector (6a) connected to the line (10) starting from the delivery pump (6) and ensuring constant maintenance of the flow rate in this conduct. 3. Installation according to claim 2, characterized in that it comprises a draining device connected to the outlet of the pump and which is constituted by a rotary screw (16) drive placed inside a perforated cylinder (15) disposed in an inclined position, the end of this screw, located on the side of the outlet carrying a counter-screw, (19) intended to avoid any risk of jamming of the entrained material. 4. Installation according to one of claims 2 and 3, characterized in that the liquid level in the lower part of the drip device (12) is controlled by a control device (27) capable of acting at both on a valve (28) for adjusting the flow rate, connected to the pipe (21) for adjusting the drive liquid, and on a valve (29) for quick closing connected to the line (10) starting from the pump ( 6) backflow. 5. Installation according to one of claims 2 to 4, characterized in that it comprises a device for separating particles in suspension in the recycled liquid, this device being constituted by a centrifugal separator (23) whose lower orifice d 'evacuation communicates with an airlock (24) allowing the evacuation of impurities.

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