FR2617877A1 - PROCESS FOR BLEACHING OR DELIGNIFYING A CELLULOSIC PASTE WITH OXYGEN, AND INSTALLATION FOR IMPLEMENTING SAME - Google Patents

Abstract

In this continuous process of bleaching or delignification of a cellulose pulp with oxygen, the pulp, in the form of an aqueous suspension, is passed through a diffuser and mixer duct 123, at a rate at which this pulp dissolves. behaves as a turbulent liquid and, then, in a holding tank 137, at a rate at which the suspension assumes a piston-like flow. A mixture of oxygen and water vapor is diffused through a microporous wall which forms an interface with the suspension circulating in the duct, to form a mass of small oxygen bubbles where the vapor separates by condensation, bringing heat to the suspension and leaving the oxygen in the form of smaller bubbles which disperse throughout the volume of the suspension, exhibiting a considerably larger total surface area than the bubbles which would result from the injection of oxygen alone through the same microporous wall under the same conditions. The oxygen bubbles remain dispersed throughout the volume of the suspension when the latter assumes a piston-like flow, to give the oxygen time to exert its bleaching effect. The invention also relates to an installation for implementing the method.

Description

DESCRIPTION

  The present invention relates to laundering or

  delignification of a cellulose paper pulp.

  It is known to use oxygen for bleaching a suspension of a cellulose pulp presented in the form of an aqueous suspension having a consistency of 8% to 16%, by introducing oxygen into the suspension in the form of small bubbles, while the suspension under the melting of small bubbles, while the suspension passes, under discharge pressure, through a diffuser and mixer duct which confines the suspension in a section such that, at the discharge pressure, it circulates at a high speed which has the effect of generating a turbulent liquid flow. The phenomenon of the liquid carryover of the pulp suspension confined under a high speed is explained in an article entitled "Medium Consistency

  Technology ", published in the TAPPI Journal, Vol. 64, no 6, June 1981.

  I [immediately at the outlet of the mixing duct, the suspension containing the bubbles is passed into and through a reaction vessel which expands the suspension by bringing it to a section in which it takes a relatively slow piston-type flow to allow to the oxygen bubbles dispersed throughout its volume the time to react with

cellulose.

  The treated suspension is recovered at the outlet of the reaction tank. The bubbles are dispersed in the turbulent liquid suspension by passing the oxygen through a microporous wall under a pressure higher than that of the suspension to bring it into contact.

contact with the suspension.

  The suspension can be preheated by passing it through a steam mixer, on a path going to the pump, and the heated suspension can be deposited in an upstream storage tank.

of the pcmpe.

  The smallness of bubbles, which are initially produced by diffusing oxygen into the suspension through the porous wall, promotes good dispersion throughout the mass of the dough and, therefore, it therefore promotes the establishment of good contact. , effective

  for bleaching or delignification, with the fibers of the dough.

  An object of the present invention is to further improve the contact with oxygen and the paste so as to obtain a

  better whitening action with the same amount of oxygen.

  According to the invention, this result is achieved by injecting oxygen into the mixer-diffusing duct as described above, but in the form of a mixture of oxygen and water vapor. Small bubbles of oxygen-vapor mixture form momentarily when the mixture leaves the small pores of the wall of the injector but, at the moment when each bubble meets the paste, the vapor condenses and releases its oxygen content in the form of 'a smaller bubble. Steam

  condensing brings additional heat to the dough.

  Preferably, as large a fraction of the vapor which is necessary to bring the suspension to the reaction temperature, in a single phase, is injected through the diffuser-shuffler. The achievement of this result depends on the capacity of the diffuser-mixer. It is therefore possible to inject an additional quantity of heat if necessary into a steam mixer, in order to bring the suspension to a supply temperature in a preliminary stage, through a caompris injector between the pump and the oxygen-vapor diffuser-mixer. , to bring the temperature to a value closer to the reaction. You can also inject steam to preheat

  the suspension upstream of the pump.

  The invention therefore provides for the following phases: a) preferably injecting all of the steam, into the diffuser-mixer, in the form of an oxygen-vapor mixture, or b) injecting a certain portion of the steam between the pump and the diffuser-mixer, to bring the dough to an intermediate temperature; and c) in combination with a) or b), inject steam to preheat the dough upstream of the pumpkin, to bring it to the temperature

preheated feed.

  By injecting oxygen into the suspension with liquid carrier, in an oxygen-vapor mixture, contrary to what is obtained by injecting oxygen exclusively through the microporous surface, under the same conditions, we can multiply by a factor from two to ten, the effective surface area of the oxygen in contact with the dough, the preferred growth factor being three to five. This results in a corresponding increase in the oxygen bleaching effect and a consequent saving on the chemical bleach. It is also advantageous to heat the

  suspension, with the vapor injected, in this step.

  For bleaching, the proportion between oxygen and steam can vary from 20 to 200: 1 by weight, the range from 100 to 150: 1 being preferred. Or, by volume, the proportion between oxygen and vapor

  can range from 50 to 500: 1, with the range 300 to 400: 1 being preferred.

  For delignification, the oxygen ratio can vary from 80 to 800: 1 by weight, the range from 400 to 600: 1 being preferred. Or, by volume, the oxygen can vary from 200 to 2000: 1, the range from 1200 to

1600 being preferred.

  The ratio of oxygen to dough can vary from 5 kg to 1 kg per tonne of dry dough. It is then desirable to add as much vapor as possible with the oxygen-vapor mixture. Since the amount of steam that can be added is limited by the capacity of the diffuser, it may be necessary to also add steam in an earlier phase, in order to inject enough heat to bring

  the suspension at reaction temperature.

  The invention makes it possible to obtain the maximum of the potential use of oxygen and of steam in the delignification or bleaching treatment by acting as follows. The total amount of vapor injected into the dough is a controlled amount which will bring the suspension to reaction temperature in the reaction vessel. According to the invention, the proportion of the total quantity of vapor injected with the oxygen-vapor mixture into the diffuser would preferably be substantially the maximum allowed by the injection capacity of the diffuser, or a selected portion quantity, close to this maximum, or 80%

or more.

  The rest of the vapor which is necessary to bring the suspension to the reaction temperature can then be injected into the suspension upstream of the diffuser. The optimal proportion of oxygen to be injected into the dough to obtain good delignification or good bleaching is determined by tests, as is known in the art, and it is chosen according to the particular installation and the conditions particular that are involved. The oxygen injection is then adjusted so as to continuously supply the suspension with the selected oxygen flow rate. The injection of steam together with oxygen has the effect that oxygen is injected under the form of smaller bubbles than if oxygen was injected alone, which in turn has the effect of creating a larger area of oxygen surface in contact with the paste and ensure better absorption for a given oxygen flow. The invention therefore provides several advantages, namely, the fact that a large quantity of steam used for heating is injected at the place where it is necessary, just before the reaction zone and that, at the same time, the injecting oxygen simultaneously with the vapor results in a larger surface area of the injected oxygen and in a better reaction with the paste for a given quantity of oxygen. In this way, the use of oxygen as well as that of steam is substantially increased.

  maximum for the particular installation considered.

  If all of the vapor which is necessary to bring the suspension to reaction temperature can be added to the diffuser, control can be continuously exercised by adjusting the amount of vapor introduced into the vapor-oxygen mixture by the temperature of the suspension downstream of the oxygen-vapor diffuser, while keeping the oxygen supply constant, or by having it adjusted by maintaining a certain important variable. If it is necessary to add an additional quantity of oxygen upstream of the diffuser, the temperature regulation will also ensure the regulation of this injection.

upstream.

  The invention is particularly suitable for incremental dosing of the pulp suspension with oxygen. This is done by passing a stream of suspension of cellulose pulp under pressure, arriving from a feed, through a reaction path composed of a plurality of successive stages in each of which the stream is firstly confined to a section in which it has a speed capable of fluidizing it to give it a flow of liquid flow and is then expanded so as to occupy a section in which it has a speed capable of giving rise to a piston-type flow. In each step, oxygen is injected into the liquid flow under pressure, under the form of a mass of small bubbles, to disperse them throughout the flow, so that most of the oxygen reacts with the paste which is in flow of piston type in this stage. The

  treated suspension is then recovered at the end of the final stage.

  The invention also provides for an additional mixing of the suspension leaving the oxygen diffuser obtained by passing it through a pulp fluidizer mixer. This mixer can be placed adjacent to the diffuser or placed some distance downstream. This mixer effectively ensures additional mixing and the dispersion of any oxygen agglomerations, so that the oxygen remains in a finely divided form and that it is mixed more intimately with the suspension. A preferred static mixer is composed of a tube whose section decreases towards a constriction followed by a tube which widens to the diameter of the tube in which the suspension of dough circulates. The speed of passage through the constriction will be approximately equal to that

that we observe in the diffuser.

  The invention also provides means for coordinating the flow of oxygen with the flow of the pulp suspension so as to maintain the appropriate dosage of oxygen. This can be achieved by an apparatus which includes a flow measurement device, for example, an orifice plate placed in the path of the suspension, in front of the diffuser, the orifice plate being connected to a differential pressure cell which is in turn connected to a cOm! ande device. The dunnage device sends a signal to a carmande valve

  of the oxygen flow which controls the supply of oxygen to the diffuser.

  An orifice plate or other device that measures the flow of oxygen is provided in the oxygen supply line. The control mechanism may include a computer that maintains a constant, predetermined and regulated oxygen-to-dough ratio, which is achieved by increasing or reducing the dosage to account for variations

  the flow rate of the pulp suspension.

  An installation according to the invention comprises a supply tank for the suspension, an injection and mixing pipe substantially free of obstruction, intended to confine the suspension to a current to determine a substantially free flow in this pipe, a tank having a larger cross-section than said duct and which is connected thereto, means for continuously forcing the suspension under pressure from the tank

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  supply to the conduit, and means for adjusting the supply pressure so that the suspension circulating in the conduit has an appropriate speed to create a turbulent liquid flow in this conduit and to cause a piston type flow to take effect to the dough in the reactor. Diffusing means are provided, which comprise an extended microporous surface which is in contact with the suspension in the duct to diffuse an oxygen-vapor mixture in the suspension under a pressure higher than the pressure for conveying the paste, to form in this way a mass of small oxygen bubbles and mix them throughout the volume of the suspension which circulates in the conduit, so that these bubbles remain in contact with the thick paste over the entire path of the piston-type flow to ensure a delignification or bleaching effect. The control mechanism comprises a supply duct serving to supply a mixture of oxygen and vapor to the diffusing means and means serving to regulate the flow rate of oxygen passing through this duct, a steam duct which leads from a source of steam to said supply duct, and means serving to regulate the flow of steam in this duct, the means which serve to regulate the supply of steam corresponding to the temperature of the suspension

  as it passes from the mixing line to the reaction tank.

  Means can also be provided for injecting steam into the suspension upstream of the diffusing means. In this case, the means for controlling the supply of steam in response to the temperature of the suspension can also control the additional supply of steam. In a preferred installation, the pulp suspension passes through a primary oxygen diffuser and a plurality of reactors, each of which is preceded by an oxygen diffuser. Any or all of the pulp suspension can be sent to a tower

  reaction for the execution of a new extraction with caustic soda.

  The invention will be explained more fully with reference to the accompanying drawings, in which: FIG. 1 is a side elevation view, partly in section, of an installation of the type currently used for adding steam and oxygen to a paste in a bleaching treatment; FIG. 2 is a similar view, in side elevation and partly in section, of a preferred installation capable of carrying out a preferred method according to the invention; and Figure 3 is a side elevational view, partly in section, of a preferred diffuser device. FIG. 1 illustrates a prior method in which steam and oxygen are used jointly for bleaching

of a paste.

  In FIG. 1, a mixture of dough which is normally a thick and heavy mass passes continuously from a supply source through a steam mixer 15 which preheats it to a temperature ranging from 37.8 C to 65.6 C , then at 76.7 C, then at 93.3 C and, then, this mixture is sent, via a line 16, to the submount of a storage hopper 17. From the storage hopper 17, the dough, mixed with steam is discharged, in the form of a suspension, by a pacpe, and passing through another pipe 21, in a dispersing duct

  oxygen 23 which is shown in more detail in FIG. 3.

  The pressure at which the suspension is discharged is sufficient to circulate this suspension in the conduit 23 at a speed such that it behaves cA..e a turbulent liquid. Steam is sent to the steam mixer 15 by an alignment source, passing through a tube 25. The steam supply is regulated by a temperature controller 27 which is itself connected to an interposed valve 29 in the

tube 25.

  Oxygen is supplied to a diffusing device contained in the conduit 23, by a conduit 31 which arrives from an oxygen supply source, through a pressure regulating apparatus 33. The diffusing device comprises a microporous wall which forms

the interface with the suspension.

  Oxygen is thus continuously introduced into the suspension of heated dough through the diffusing device, in the form of a mass of small bubbles, at a time when this suspension is carried out canoe a turbulent liquid, so that the bubbles oxygen diffuse in the suspension and mix throughout the volume of the latter. The oxygen-containing suspension passes through a pipe 35 into the bottom of a retention tube 37 fitted with a valve 39 for adjusting the back pressure. The suspension slows down in

2 6 1 7 8 7 7

  the tube 37 to take a piston-type flow speed, at which it returns to its thick normal state and it is kept under pressure, so that it gradually absorbs the reacting oxygen

with her.

  The pulp is retained in the retention tube long enough to allow oxygen to react with the cellulose. For the preferred apparatus of Figure 2, we used

  numbers similar to those in Figure 1 but increased by 100.

  The installation according to the invention is implemented as follows. In the installation of FIG. 2, which illustrates a preferred method according to the invention, steam is added to the line 131 which sends the oxygen to the diffusing device A (see FIG. 3), which is housed

  in the disperser conduit 123, to form an oxygen-vapor mixture.

  The oxygen supply is supplied by a temperature control member 127 which is connected to the tube 135 at a point between the disperser 123 and the retention tube 137. In this way, the vapor is firstly mixed with the oxygen and the oxygen-vapor mixture is then added to the suspension, by the diffusing device A, in the form of a mass of small bubbles. When the oxygen-vapor mixture comes into contact with the dough, the vapor condenses into water, thereby bringing heat to the dough, and it leaves the gaseous oxygen inside the dough in the form of bubbles more small (smaller than oxygen-vapor bubbles) which disperse throughout the suspension due to its turbulence. A better subdivision and a better dispersion of the oxygen are obtained, which gives a much greater effective surface area to the oxygen which is in contact with the suspension than that which would be observed in the absence of vapor. This therefore increases the oxygen transfer rate and requires less oxygen than it does.

  would otherwise be the case to obtain the same bleaching effect.

  The pressure of the oxygen-vapor mixture, when injected, is about equal to or slightly higher than the oxygen pressure

  used in the process of figure 1.

  Unlike the prior art, the vapor is mixed with oxygen just before the mixture is injected into the diffuser A and the regulation of the vapor flow is ensured by a control member

2 6 1 7 8 7 7

  o prature 127 which captures the temperature of the dough downstream of the disperser. The dough then enters the pressure retention tube 137, in which it takes a piston type flow and circulates at a relatively slow speed, under pressure, the oxygen being dispersed throughout the mass in the form of small bubbles to react. with cellulose. If several diffusers are used in series, the

  steam is added to the first floor.

  The diffuser in which the oxygen-vapor mixture is injected into the suspension, in the diffuser A, can take different forms, and all of which comprise a microporous wall which forms the interface with the suspension and through which the oxygen-vapor mixture is diffused. This wall is preferably a sintered stainless steel element, cate described in Bulletin M 201 of Pall Trinity Micro Corporation, subsidiary of the Pall Corporation, and in US Patent 2,554,343. Elements of this type are generally used for the filtration. The size of the pores should be in the range of from about 2 microns to 100 microns, and is preferably less than about 10 microns. The porosity must be substantially uniform, the voids having to represent approximately 40% to 50% of the volume of the wall, which has a thickness of between approximately 0.8 mm and approximately

13 mins.

  A preferred form of diffuser A is shown in FIG. 3. This diffuser is concealed by a cylinder 123 which gives passage to the paste suspension. The cylinder has flanges 63, 64 at its ends, for connection to a pipe. A tube 65 extends transversely to the axis and in a central position across the passage 123 and is held in this passage by a suitable housing 69 formed on the wall of the cylinder 123. The pipe 131 serving to supply the

  oxygen-vapor mixture on the 65 m tube. ne on the diffuser tube 65.

  When the mixture passes through the pores of the wall of the tube 65, the small streams of oxygen-vapor mixture, at the moment when they leave the porous surface, are carried away from this surface, in the form of small bubbles, by the suspension. . The vapor of each bubble condenses as soon as this bubble comes into contact with the suspension, and it leaves an oxygen bubble whose size is a fraction of the

26 1 7877

  dinension that the bubble would have taken if one had injected oxygen alone. Although there may be some coalescence, in general the mass of oxygen bubbles disperses in the suspension under the effect of the turbulence of the latter, when the latter passes at high speed in the duct 123 and the bubbles are entrained in the suspension to enter the reaction chamber 137, or the

  suspension takes a relatively slow piston type flow mode.

  Oxygen therefore has time to react with the paste and it is absorbed when the mass of suspension passes relatively slowly through the

tank 137.

  The diffusing element may be in the form of a conduit or cylinder through which the suspension passes, the wall of the cylinder defining the flow path. The diffuser element can be part of the cylinder wall, it can take the form of a porous tube which extends transversely to the axis of the cylinder, or it can take the form of a porous tube which s' extends along the axis of the cylinder. In all cases, the path of the suspension is relatively free from obstruction. In the case of a tube housed in the cylinder, this tube occupies only a small space, so that the major part of the interior space of the cylinder is occupied by the suspension which circulates there, by coming into contact with the

porous diffusing surface.

  The starting material used in the present process will depend on the fact that the process is used in the phase of

  delignification or in the bleaching phase of the pulp treatment.

  For delignification, the aqueous suspension of pulp comes from three or four washing phases which follow the washing phase of the unbleached pulp, the pulp containing a considerable amount of lignin, this is indicated by the value of the index Kappa between 30 and 60, typically between 40 and 50. It contains 10 to 12%, preferably 10 to 12%, by weight, of solids. According to the invention, caustic soda will be added in a proportion of 2 to 4% by weight, typically 3% before

delignification.

  According to the invention, bleaching is usually carried out after the suspension has been washed following the first chlorination phase. Then, it will have a Kappa index of 3 to 8, typically from 4 to 5. It will contain from 8 to 16%, preferably from 8 to 16%, by weight, of solids. We will again add caustic soda in a proportion

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  from 2 to 4% by weight, typically 3%, to obtain the starting material

  for bleaching according to the invention.

  A typical diffuser and mixer duct 123 may vary in cross-sectional area between about 26 and about 110 year3. To produce a turbulent flow, the suspension is passed through the conduit at a pressure of about 1.4 to about 14 bar. This gives the suspension a speed of about 0.5 to about 50 meters per second, from

  preferably about 3 to about 10 meters per second.

  The residence time in the conduit 123 varies between approximately 0.01 and approximately 0.120 seconds. The residence time in the reactor tube 137

  varies between about 1 and about 5 minutes.

  The vapor performs both the heating function of the suspension and the vehicle function for the injection of oxygen, so as to reduce the size of the bubbles of the latter gas which is injected and mixed in the suspension. The typical preferred temperatures are as follows: a) the suspension of starting paste upstream of the mixer 15 will have

  usually a temperature below about 54.4 C.

  b) in the mixer 15, the temperature will rise from approximately 54.4 C to approximately 60 C; c) after the preliminary injection downstream of the pump and upstream of the oxygen-vapor diffuser, at a prohibited temperature of between approximately 601C and approximately 71.1 C; d) downstream of the diffuser-mixer, at a reaction temperature in the range of about 71.1 C to about 82.21 C; e) before entering the holding tank, the dough should have a temperature in the range of about 71.1 C to about

82.20C.

  The surface of the porous wall which forms the interface with the suspension may preferably have an area ranging from approximately 46 cm2 to approximately 186 can3, covered with pores having a diameter campris in

  the range from about 10 to about 100 mincrú tres.

  The oxygen used can be molecular oxygen, such as that found in cauerce and which contains 90% or more and preferably 98% or more oxygen. Alternatively, oxygen can be presented as a gas containing more than 50% oxygen. The starting paste suspension can contain about 10 to about 20% air by volume of the dispersed paste, which dilutes the added oxygen. For a dough that

26 17877

  contains little air or which does not contain air, the concentration of the gas containing added oxygen can be found at the lower end of the range of oxygen contents and, for a dough containing a lot of air, the added gas may contain oxygen towards the upper end of the oxygen content range. To adjust the oxygen dosage so that it meets the required conditions, the oxygen content of the exhaust gas which exits through the vent of the final treatment tank is measured. Based on this dosage, we can check if we have obtained a good mixture. Adjustments can be made accordingly and incremental dosing can be

  manipulated to obtain the best results.

  In a multi-phase process such as that described, it is therefore possible to add large total amounts of oxygen in increments to a suspension of pulp by adding small amounts to each phase, in accordance with the following formula: Volume of oxygen + gas <0.1 <0.1 volume (oxygen + gas + paste + vapor) This formula is calculated at the working pressure of this

particular phase.

  The dosage can be proportioned in the same way for each phase or it can be modified in order to adapt to variable conditions such as variations in the nature of the dough or

other conditions.

  The oxygen used must have a volume concentration of at least 90% oxygen, preferably more than 98%, measured in the

standard conditions.

  The steam must be saturated steam.

  The injection pressure of the oxygen-vapor mixture must be

  approximately 1 to 10 bars higher than the pressure of the pulp suspension.

  The temperature of the oxygen-vapor mixture, at the time of injection, must

  be about 129 C to about 198.9 C.

  The injection rate of the oxygen-vapor mixture should be in the range from about 5 kg of oxygen to about 25 kg

  oxygen per ton of dry pulp.

  As will be easy to understand for a person skilled in the art, the tubes and pipes should be insulated so as to

retain heat.

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Claims (18)

REVENDICATI (ONS   1. continuous process of bleaching or delignification of a cellulosic paste in which the pulp is passed under pressure, in the form of an aqueous stream of suspension, from a supply source in a diffuser and mixer duct, to by means of pumping means, at a speed such that this current is carried away like a turbulent liquid, then through a pressure reaction tank, at a speed at which the dough takes a flow of the piston type, and injected with oxygen, at a pressure higher than that of the suspension, in the suspension circulating in the conduit, through a microporous wall and in the form of small bubbles which disperse throughout the suspension, process characterized in that oxygen is injected into the current, through the microporous wall, in the form of an oxygen-water vapor mixture, so that the vapor condenses in the suspension and heats the latter, leaving the oxygen in the form of smaller bubbles, so that the effective surface area of the oxygen in contact with the suspension is significantly larger than the surface area that would be obtained by injecting oxygen alone into the suspension in the very conditions.   2. Method according to claim 1, characterized in that the injection of steam has the effect of bringing the temperature of the suspension at least 71.1 C.   3. Method according to claim 1 or 2, characterized in that the steam is further mixed in the dough, in a preliminary phase, between the pumping means and the oxygen-water vapor diffuser, to bring the temperature dough from preheated feed temperature to an intermediate temperature   lower than the reaction temperature.   4. Method according to one of claims 1 to 3, characterized in   that the steam is injected and mixed with the dough, bringing in pumping toys, to bring this dough to a temperature preheated feed.   5. Process according to one of claims 1 to 4, characterized in   that the oxygen-water vapor mixture is prepared by sending at least a major proportion of the vapor used to heat the suspension to oxygen just before injection into the suspension, and continuously adjusting the amount of vapor mixed with oxygen in   response to the suspension temperature.   6. Method according to claim 1, characterized in that a total quantity of vapor is injected into the suspension which has the effect of bringing the paste to the reaction temperature and in that the vapor supplied in the oxygen-vapor mixture is set to at least 80% of the nmaximurm vapor treatment capacity of the diffuser while the   rest of the steam is supplied upstream of the diffuser.   7. Method according to claim 6, characterized in that the oxygen is injected in the interval ranging from approximately 5 to approximately 25 kg per tonne of dry dough.   8. Continuous process according to one of claims 1 to 7,   characterized in that the proportion between the vapor and the oxygen in the mixture is in the range from about 50 volumes of vapor for one volume of oxygen to about 400 volumes of vapor for one volume of oxygen.   9. Method according to one of claims 1 to 8, characterized in   what the pore size of the mincroporous wall is not greater than 100 micrometers.   10. Method according to one of claims 1 to 9, characterized in   that the suspension stream is discharged, at a pressure in the range from about 3.5 to about 10.5 bars, through a conduit having a cross-sectional area in the range from about 26 to about 100 cm2   11. Method according to one of claims 1 to 10, characterized   in that the oxygen-vapor mixture is injected at a higher pressure   than that of the suspension, in particular between about 1.4 and 14 bars.   12. Method according to one of claims 1 to 11, characterized   in that the reaction temperature of the suspension is controlled by adjusting the amount of vapor supplied to the oxygen-vapor mixture in response to the temperature of the suspension measured downstream of   the introduction of the oxygen-vapor mixture.   13. Method according to one of claims 2 to 12, characterized   in that the steam is injected and mixed in the dough, upstream of the delivery means, to bring the dough to a temperature preheated feed. 26 1 7 8 7 7   14. Method according to one of claims 1 to 13, characterized   in that the reaction temperature is in the range of 71.1 C to 82.2 C.   15. Installation intended to react an oxygen-containing gas with a suspension of cellulose pulp having a consistency of 8% to 13% and which, at rest, consists of a thick aqueous dispersion of pulp fibers, to carry out the delignification or bleaching, characterized in that it comprises: a dough supply tank (117); an injection and mixing conduit (123), practically free of obstruction, intended to contain the suspension in the form of a current which can circulate substantially freely in this conduit; a reaction vessel (137) having a cross section greater than that of said conduit (123) and connected to this conduit; means making it possible to continuously and forcely pressurize the suspension under pressure from the supply tank (117) to the conduit (123);   means for adjusting the supply pressure in such a way that the suspension circulating in the conduit (123) has a speed capable of circulating the suspension in this conduit in the form of a turbulent liquid flow and in such a way that this suspension takes a piston type flow in the reaction tank; diffusing means, which comprise an extended microporous surface forming an interface with the suspension contained in the duct, for diffusing an oxygen-containing gas in the suspension under a pressure higher than the pressure for supplying the paste, to form this so a mass of small bubbles and mix these bubbles in all the volume of the suspension contained in the conduit, so that they remain in contact with the thick paste during all el time of the flow of the piston type, in order to achieve delignification to laundering action; a gas connection leading to the diffusing means; means for supplying oxygen to the gas connection means; toys for supplying steam to the gas connection; toys used to regulate the steam supply; and means used to recover the suspension treated at its exit from the reactor.   16. Installation according to claim 15, characterized in that the means serving to regulate the steam supply respond to the temperature of the suspension which leaves said mixing duct. 17. Installation according to claim 15 or 16, characterized in that it comprises means serving to inject steam into the   suspension, between the pope and said mixing duct.   18. Installation according to one of claims 15 to 17,   characterized in that it comprises a steam mixer serving to   mix the suspension with steam upstream of the pamper.