SE537925C2 - Method and system for washing cellulose pulp - Google Patents

Abstract

537 9 SUMMARY A method and system for washing cellulosic pulp is provided. The pulp is washed twice in the same washing space in a washing device (10) with a movable permeable treatment surface (11), whereby filtrate from the pulp passes through the treatment surface while the pulp is transported together with the treatment surface. There is an intermediate mass storage (20) connected to the washing device (10) and arranged to store the mass between the two washing moments (I, II).

Description

TECHNICAL FIELD The present invention relates to the treatment of cellulose pulp and in particular to a method and system for washing cellulose pulp.

BACKGROUND Pulp watering (alien called fiber washing) is a key operation in the treatment of cellulose pulp. Washing is carried out in several places in the pulp line, such as after the boiler, in the silage and after oxygen reactors and bleaches, in order to remove lye (with chemicals, dirt, discharged substances, etc.) from the pulp.

The market offers many different types of washers, including washers, drainage presses, wire presses, screwdrivers, diffusers, filters and drum washers. A roller and washing device is a twin-roll press of the general type shown, for example, in U.S. Pat. No. 3,980,518. Such a roller press has two rotating rollers with perforated outer surfaces. The incoming mass is distributed on each water in the longitudinal direction. A pulp web is formed on the respective roller and is transported in the direction of rotation in a funnel which therefore encloses the rollers, until the so-called press nip between the rollers. The roller press uses the washing principles displacement, when dirty liquid (lye) in the pulp is replaced by cleaner washing liquid added to the hopper, and pressing, when dirty liquid is pressed / squeezed out of the mass, especially at the press nip.

A washing device, such as the roller press, has limited performance. Sometimes two or more washing presses are arranged in series one after the other in order to achieve the desired washing efficiency.

However, television sets such as roller presses are expensive and space scraping machines. They also consume a lot of energy. In addition, it is generally problematic to introduce additional machines into a pulp mill. SUMMARY An object of the invention is to provide an improved method of washing cellulosic pulp. Another object is to provide an efficient method for washing cellulosic pulp, which is relatively inexpensive and / or requires little space.

These objects are achieved in accordance with the appended claims.

The present invention is based on the insight that it is possible to achieve efficient washing by using one and the same washing device for two (or more) non-simultaneous washing steps. The washing moments are separated in time by an intermediate mass storage, so that mass is washed batchwise in the washing device and stored in the intermediate mass storage between the washing moments.

More specifically, there is provided a method of washing cellulosic pulp, said method comprising washing, in a first wash step, the pulp for a first predetermined period of time by using a washing device with a movable permeable treatment surface. The filtrate from the pulp passes through the treatment surface while the pulp is transported together with the treatment surface. The pulp washed in the first washing step is received by an intermediate pulp storage connected to the washing device and stored in the intermediate pulp storage. The pulp is then washed in a second washing step for a second predetermined period of time by using the washing device, the pulp being received from the intermediate pulp storage and applied to the treatment surface of the washing device, so that the pulp is washed again in the same washing space in the washing device.

The washing and storage are preferably repeated so that the pulp is washed batchwise using the intermediate pulp storage, each batch of pulp being washed in two separate washing steps, which take place in the same washing space in the same washing device but are separated in time.

According to another aspect of the invention, there is provided a system for washing cellulosic pulp. 2 537 9 A general view in the pulp industry is that one should always strive for a continuous pulp flow and stable conditions in the pulp line. The invention proposes, in direct contrast to this, to interrupt the mass flow and carry out washing in a loop in batchwise manner.

Surprisingly, the performance / result is satisfactory despite the non-continuous flow through the washing device.

Two (or more) conventional washing devices can be replaced with a stone washing device and an intermediate pulp storage arranged according to the invention. The washing devices that have been replaced can be arranged next to each other in the pulp line or come from different parts of the pulp line associated with similar process conditions. The invention also meant that requirements for increased washing efficiency can be handled without the need for an additional washing device. The proposed solution is relatively inexpensive and consumes less energy than conventional washing with series-connected presses. It also requires less space in the pulp mill.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, and further objects and advantages thereof, will be best understood by reference to the following description and accompanying drawings, in which: Fig. 1 is a schematic block diagram of a cellulosic pulp washing system according to an exemplary embodiment of the invention; Fig. 2 is a schematic block diagram of a cellulosic pulp washing system according to another exemplary embodiment of the invention; Fig. 3 is a schematic block diagram of a cellulosic pulp washing system according to still another exemplary embodiment of the invention; Fig. 4 is a schematic cross-sectional view illustrating a roller press used in an exemplary embodiment of the invention; and Fig. 5 is a flow diagram of a method for washing cellulosic pulp according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION In the drawings, similar or corresponding parts are denoted by the same reference numerals.

Fig. 1 is a schematic block diagram of a cellulosic pulp washing system according to an exemplary embodiment of the invention. The illustrated system 100 comprises a washing device 10, an intermediate pulp storage 20, a first and a second process vessel 30, 40 connected to the washing device 10, and a first and a second filter tank 51, 52. When the system is in operation, a first washing step takes place. , then pulp from the first process vessel 30 is washed in the washing device 10 during transport together with a movable permeable treatment surface 11 (e.g. a rotatable surface, such as the perforated outer surface of a press roll 15), and then led to the intermediate pulp storage 20. a subsequent second washing step II, mass frail is washed from the intermediate mass storage 20 in the same washing space in the same washing device 10 as in the first washing step I and is then carried out to the second process vessel 40.

During the first wash step I, filtrate passing through the permeable treatment surface 11 is collected in the first filtrate tank 51. During the second wash step II, filtrate passing through the permeable treatment surface 11 is collected in the second filtrate tank 52. In a preferred embodiment, filtrate is returned from the second filtrate from the second filtrate tank. II to the first washing step I and is used as washing water. The filtrate can also be used for spreading the pulp.

When the system 100 is in operation, there is normally a continuous mass flow in to the first process vessel 30 and out of the second process vessel 40 but a non-continuous mass flow within the system (arrows I and II, respectively). The pulp is preferably washed batchwise using the intermediate pulp storage 20, so that each batch of pulp is washed in two separate washing steps I, II, which take place in the same washing space in the same washing device 10 but are separated in time.

"Laundry space" refers to a space inside the washing device 10 where the pulp is transported on the treatment surface 11 and washed or dewatered. The treatment surface 11, i.e. the permeable surface on which the mass is applied is identical in the first and second washing steps I, II. Preferably, the full axial length of the washing device is used. In the case of a roller press 10 (twin-roll press), then essentially the entire length of the press rollers 15 is used in each torque I, II. The feed circumference of the washing device 10, where the pulp is distributed on the treatment surface 11, is essentially the same in washing steps I and II. On similar salt is the discharge area of the washing device 10, i.e. where the pulp is removed from the treatment surface 11, essentially the same in steps I and II.

The intermediate mass storage 20 is typically a tank / cart with a storage volume exceeding the volume of mass produced in the respective two-step steps I, II. In other words, the intermediate mass storage 20 is dimensioned to store mass between torques I and II. The intermediate pulp storage 20 may be a pure pulp storage / buffer or, alternatively, may act as a treatment tank / kdr1 with chemical addition, temperature control, spading, or other treatment of the pulp. Examples include an average concentration tank (MC), a high concentration tank (HC), an acid step (A) and bleach / bleach reactors, e.g. chlorine dioxide (D), oxygen (0), peroxide (P), treatment with complexing agent (Q), alkali oxygen (E0), or alkali oxygen peroxide (EOP). In applications with relatively short wash cycles, it may also be possible to use an enlarged standpipe or the like.

The intermediate pulp storage 20 is external in relation to the washing device 10, i.e. a separate physical unit. The mass thus leaves the washing device 10 between the washing in the washing step I resp. II. The embodiments where the intermediate mass storage 20 comprises two or more parallel tanks are tankable. The process vessels 30, 40 are vessels / tanks in the pulp process (i.e. the pulp line) which discharge or receive pulp which is washed in accordance with the invention. Each process vessel 30, 40 may be a treatment plant / reactor / tank or, alternatively, a pure pulp storage. Examples include a blast tank (BT), an MC / HC tank, an A stage, and a bleach tower / bleach reactor, e.g. D, 0, P, Q, EO, EOP.

The intermediate pulp storage 20 acts as a pulp buffer which alternates between a filling layer, during the first washing step 1, and an emptying layer, during the second washing step II. The first and second process vessels 30, 40 are also arranged to alternate between an emptying layer and a filling layer, but the emptying layer belongs to the first washing step I and the filling layer belongs to the second washing step II.

It should be noted that "emptying" did not necessarily mean that the boiler is completely empty after the washing step. In particular for the process man 30, 40 firms often have a minimum level. mass as required in the vessel for aft the whole process should go smoothly. In addition, after mass flow into the first process vessel 30 is also emptied, but the outgoing flow is stone. Correspondingly, there is a mass flow out of the second process vessel 40 alien in fill layer, but the incoming flow is stone. In Fig. 1, valves indicate that the rivers in the first and second washing moments I, II are not continuous. A pump 21 is also shown, arranged to discharge pulp from the intermediate pulp storage 20 during the second washing step II. The pulp can be shoveled with a suitable shovel means so that it can be pumped from the intermediate pulp storage 20. The system according to the invention can be implemented by using conventional equipment, such as pipelines, valves, pumps, shovel screws, etc. Details such as where valves are needed are routine guards. which do not require flaw inventor competence.

The first washing moment I takes place during a first predetermined time period, while the second washing moment II takes place during a second predetermined time period. These predetermined time periods need not be fixed time intervals, but can also be determined, for example, as the time it takes for a certain volume of mass to pass through the washing device 10. A possible approach is to determine the time period based on at least one process parameter, e.g. so that the level of pulp in a given process tank does not fall outside a maximum or minimum value. Or the time period can be determined based on process parameters that indicate pulp quality, degree of bleaching, system performance, etc. Different control strategies are possible.

The process conditions, such as pH and temperature, should preferably be approximately the same or similar in the first and second washing steps. In cases where the intermediate pulp storage 20 involves treatment of the pulp, and not only storage, the treatment should thus preferably be of a similar nature to the treatment of the pulp in the process vessel 30 before the first washing step I. In particular, it is advantageous to divide a washing device between process steps similar content of corrosive substances, such as chlorides. A high content of chlorides meant that the parts of the washing device which come into contact with the pulp must be made of a durable, expensive material.

Examples of combinations of intermediate pulp storages 20 and first and second process vessels 30, 40 in accordance with the invention are provided in Table 1. (D1 and D2 are chlorine dioxide stages, P1 and P2 peroxide stages, etc.) Depending on the application, tanks / vessels in a conventional pulp line may either used in all three positions, or at least one new tank / new man needs to be introduced. HC tanks can, depending on the application, be used instead of motorcycle tanks.

In Example 2, the first process vessel 30, the intermediate pulp storage 20 and the second process vessel 40 are pure storage tanks. In the other examples, acid or bleaching chemicals are added to at least one of the first process vessel 30, the intermediate pulp storage 20 and the second process vessel 40.

Table 1.

Example # la process vessel Intermediate mass storage 2 process vessel 1 BT MC A 2 BT MC MC 3 D1 D2 MC 4 MC MC 02 P1 P2 MC 7 537 9 6POMC In principle, two conventional washing machines, each with production volume V, can be replaced by a large washing machine with production volume V + V, which crosses according to the invention. The invention requires pipelines, valves, etc. and in some cases an extra tank / an extra card with an associated pump. Nevertheless, the proposed system reduces costs, since a larger washing machine is much cheaper per mass of mass produced than two smaller washing machines. Another important advantage is that less energy is consumed by the system according to the invention than by conventional washing systems.

Typically, each of the first and second washing steps I, II crosses over a period of 0.03 to 2 hours. In general, a short wash cycle is preferable, as the volume of pulp in the buffer (s) can otherwise be responsive. It is also good for filtrate handling with a short wash cycle. For example, a time period of about 3-5 minutes per torque can be used. For applications that use bleach reactors as pulp buffers, a longer period of time would be possible due to the larger tank size. However, the television cycle can not be too long, since the residence time of the pulp dd. will vary too much Mom reactor. For example, a time period of about 10-30 minutes per torque can be used. Thus, a preferred time period for each torque Mom is in the range of about 3 to 30 minutes.

Again, the invention goes against the prevailing view in the pulp industry that stable conditions in the pulp line are always the means. In line with the traditional visual acuity, the wash cycle should be as long as possible due to system stability, but this is proposed instead for a short period of time.

In order to obtain an efficient system for washing, means can be provided for relieving the settings of the washing device 10 between washing steps I and II. In particular, the amount of laundry (not shown in the drawings) added to the pulp on the treatment surface 11 can be adapted to the respective washing steps I, II. Another parameter that can be adjusted is the rotational speed of the movable permeable treatment surface 11. Another parameter that can be adapted to the respective washing steps I, II is the amount of added diluent, which dilutes the mass to pumpable concentration after washing in the washing device 10. Adjustment of these parameters 8 537 9 (change of installations or intervals) can e.g. be exemplary if the pulp concentrations are different in steps I and II.

It is to be understood that although the washing device 10 is illustrated as a twin-roll press, this is only an example. Another washing device, such as a diffuser, a filter, a drum washing (e.g., drum displacement wash), or another type of press (e.g., a wire press), may also be used in accordance with the invention. The movable permeable treatment surface 11 may consequently comprise a perforated press roll or drum surface, a vim, or a sieve plate of a diffuser.

Fig. 2 illustrates another exemplary system according to the invention with three washing steps I, II, III in the same washing device. This system 200 includes a second intermediate pulp storage 60 in addition to the intermediate pulp storage 20 in Fig. 1. The second intermediate pulp storage 60 is connected to the washing device 10. During the second washing step II, the washed pulp is led to the second intermediate pulp storage 60 and in a third washing step III, the pulp is washed a third time on the treatment surface 11 in the same washing space in the washing device 10.

The third torque III has an associated third predetermined time period. What has been said above about the first and second predetermined time periods can also be applied to the third time period. The process conditions, such as pH and temperature, should preferably be approximately the same or similar in all three washing steps I, II, III.

There is preferably a filtrate tank 51, 52, 53 for selecting the torque and the filtrate can be used as a washing liquid in a previous washing torque.

The washing principles of Fig. 2 can be used to replace three conventional washing devices with a single, larger washing device. In principle, three washing machines each with production volume V can be replaced by a single washing machine with production volume V + V + V, which meant that the total benefit will be even greater than in the case of only two washing steps I, II. Fig. 3 illustrates another exemplary system 300 according to the invention with two washing steps I, II in the same washing device 10. The washing device 10 is connected to the intermediate pulp storage 20 via further processing equipment 70, so that further treatment, such as bleaching, is carried out between the the first washing in the washing device 10 and the storage in the intermediate pulp storage 20.

The additional process equipment 70 may include, for example, after the bleacher with an associated wash and other associated equipment such as a pump, paddle screw, etc. In such a case, a mass flow through the water of the additional process equipment 70 (i.e., water arranged after the bleach atom) is present under the ram washing moments I, II. The bleach atom of the further processing equipment 70 functions as an additional pulp buffer, arranged to alternate between a filling layer, during the first washing step I, and an emptying layer, during the second washing step II.

By applying the principles according to Fig. 3, a washing device can be divided between process steps, e.g. pale steps, which do not lie directly one after the other in the mass line. The process conditions should preferably be approximately the same or similar in the first and second washing steps I, II.

Examples of combinations of intermediate pulp storages 20 and first and second process vessels 30, 40 in embodiments with additional process equipment 70 are provided in Table 2.

Table 2.

Example # la process vessel Additional treatment Intermediate pulp storage 2 process vessel 7 DO EOP D1 D2 8 MC DO EO D1 Example 7 relates to a pulp line comprising the bleaching sequence DO EOP D1 D2 (generally with wash after each bleach atom). Steps D0 and D1 share the same washing device, which crosses according to the principles of the invention. In other words, washing is performed in one and the same washing device 10 between the DO and EOP atoms and between the D1 and D2 towers. Sharing washing device between two. D-step, as in Example 7, has the advantage that the process conditions of the two washing steps I, II in the washing device are very similar (same pH, etc.).

Example 8 relates to a pulp line comprising the bleaching sequence MC DO EO D1 (generally with wash after each bleaching tower). Depending on the application, the motorcycle tower can be replaced by an HC tower.

The MC / HC tower and the EO share the same washing device as the cross according to the principles of the invention. In this example, as in Example 7, existing tanks / tanks in the bleaching stages can be used and there is no need to introduce a new tank / tank as a pulp buffer. Furthermore, the principles according to Figs. 2 and 3 can be combined into a system with three washing steps I, II, III, ddr first and second washing steps I, II and / or the second and third washing steps II, III do not need to be performed directly one after the other. In principle, three washing machines from different parts of the pulp line and each with an associated production volume V can thus be replaced by a single washing machine with a production volume V + V + V.

For the sake of simplicity, no valves, pumps, spade means, etc. are shown in Figs. 2 and 3. A person skilled in the art understands that the invention can be implemented by using conventional equipment arranged according to the described principles. 2 0Fig. 4 is a schematic cross-sectional view of an exemplary washing device, a twin-roll press, 10, in a preferred system according to the invention. The roll press 10 comprises two cooperating cylindrical press roll rollers 15. The two press rolls 15 are arranged to rotate in opposite directions D1 during operation and each has a transparent outer surface 11, more specifically a perforated metal plate. The press rollers are therefore enclosed by a funnel 16 formed by guide surfaces arranged at a distance from the perforated outer surface 11 of the respective press roll 15 so that the press roll is partially enclosed in the circumferential direction.

To each press roll 15 belongs a mass distribution device 12. The mass distribution device 12 is arranged at the upper part of the press roll 15 for distributing mass on the perforated roll surface 11. It comprises an elongate housing 18 which extends along a substantial part of the press roll 15 in the longitudinal direction and is connected to the hopper 16. During operation, the pulp enters the pulp distribution device 12 via its inlet, which may, for example, be arranged in the middle of the roller press 10 seen in the longitudinal direction.

In the pulp distribution device 12, the pulp is distributed in the longitudinal direction and carried out through the outlet 13 so that a pulp web is formed on the perforated roll surface 11. The pulp web is transported, guided by the trough 16, in the direction of rotation D1 and pressed in a nip 17. . The press rolls 15 may comprise axial filtrate channels (not shown) which receive the filtrate which passes through the perforated roll surface 11 and transports it towards the spirits of the press rolls 15, where it is taken out. Tvattvatska can e.g. is fed to the pulp web in the hopper 16. 10The pulp is lifted out with the aid of a discharge screw 19.

In Fig. 4, two press rollers 15 are arranged next to each other with centers of rotation in the same horizontal plane. The invention also applies to washing and / or dewatering devices where the rollers are arranged differently, for example, or only a perforated roller is used, as well as to other devices where the mass is dewatered on a movable permeable surface.

Another exemplary system according to the invention comprises a roller press 10 with a non-converging trough 16, i.e. a trough which is parallel or diverges from the free position where the mass is applied on the press roll 15 to the press nip 17. The non-converging trough 16 system according to the invention is less susceptible to variations in the process conditions, such as varying mass concentration and flow.

Another advantageous system according to the invention comprises a roller press 10 with means for adjusting the distance between the press rollers 15 in response to varying operating conditions of the respective washing steps I, II, III. For example, it may be that the nip is different (i.e. different between a first and second interval) if the pulp concentration is different in washing steps I and II. The press nip 17 is preferably varied automatically during operation, between the washing steps I, II, III and preferably also during each washing step. With the aid of nip control, the washing in the roller press 10 becomes more efficient and the press 10 becomes less susceptible to varying loads.

Yet another advantageous system according to the invention comprises a roller press 10, whose press rollers 15 have a diameter in the range 0.8-3m, preferably 1.5-3m and a length in the range 12 537 9 1.2-11m, preferably 4-11m . By using a large roller press, the production volume can be maintained even though the press is arranged to handle two different washing steps. Two conventional presses 10, each with production volume V, can be replaced by a large press with production volume V + V which crosses according to the invention.

Yet another advantageous system according to the invention comprises a washing device with an open pulp distribution device, such as the pulp distribution device 12 illustrated in Fig. 4. The pulp distribution device 12 comprises a rotatable distribution means 14 arranged to distribute pulp on the movable transparent treatment surface 11 and an outlet 13 , which during operation is formed on the permeable treatment surface 11.

The outlet has a length corresponding to the width of the pulp web and the rotatable distributing means 14 is arranged to distribute pulp along substantially the entire length of the outlet 13. There are no flow preventing parts between the rotatable distributor 14 and the permeable treatment surface 11 in Fig. 4.

The outlet 13 of an open mass distribution device 12 is open in the sense that no cradle or other significant obstacle is provided in the outlet opening. The open outlet 13 creates a free mass flow from the mass distribution device 12 towards the permeable treatment surface 11.

The open mass distribution device 12 can advantageously be of the type described in the Swedish patent SE 532 366, in particular with respect to the position of the rotatable distribution means 14. Such a device provides both distribution and formation of the mass on the press roll 15.

The open design of the pulp distribution device 12 means that the system according to the invention can handle varying process conditions, such as variations in pulp concentration and flow.

An open pulp distribution device 12 can be used in a double roll press 10, but it can also be used to apply pulp to the movable permeable treatment surface 11 of another washing device 10 which crosses according to the invention. Fig. 5 is a flow chart of a method of washing cellulosic pulp according to an exemplary embodiment of the invention. In step Si, pulp is washed in a first washing step I by using a washing device 10 with a movable permeable treatment surface 11.

The initial concentration of the pulp is preferably in the range 2-13%. The pulp is then transported to an intermediate pulp storage 20 (step S2). Chemicals can be added to the pulp in the intermediate pulp storage 20. Step S3 asks if the torque I is finished, i.e. if a predetermined condition determining the time for tvdttmoment I is met. If not, the process returns to step Si. If so, the installations of the washing device 10 or its associated equipment, such as valves, spouts, etc., can be adjusted in step S4 (optional) to suit the next washing steps. The amount of tvdttvdtska can, for example, Andras. In step S5, stored pulp is washed in a second washing step II by using the same washing device 10 with the movable permeable treatment surface 11. The solids concentration of the pulp is preferably in the range 2-13%. Step S6 asks if torque II is complete. If not, the process returns to step S5. If so, the installations of the washing device 10 can be adjusted in step S7 (optional) to suit the next washing steps. The process then returns to step Si.

According to Fig. 5, the washing and storage steps S1, S2, S5 are preferably repeated so that the pulp is washed batchwise using the intermediate pulp storage 20, each batch of mass being washed in two separate washing steps I, II, which take place in the same washing space. in the same washing device 10 but are separated in time.

The adjustment in step S4 may, for example, comprise adjusting at least one parameter of: a flood added TV, a rotational speed, a flood of sod and a distance between the press rollers 15.

The invention is not limited to the illustrated embodiments, but also owes equivalents to the features shown and can be varied within the scope of the patent claims. For example, there may be embodiments with more than three washing torques in the same washing device. It is also possible to have a system in which a washing device is arranged so that it can be operated both conventionally, with a mass flow through the washing device, and according to the invention, with two mass flows, temporally separated, through the washing device. This can be useful, for example, when a mass line crosses with two different mass types with different requirements for water results and / or very different mass flows.

Claims (29)

1. A method for Washing of cellulose pulp, comprising the steps of Washing, in a first Washing operation (I), the pulp for a first predetermined period oftime using a Washing apparatus (10) With a movable penneable processing surface (11),filtrate from the pulp passing through the processing surface as the pulp is transported togetherwith the processing surface, storing the pulp in an interrnediate pulp storage (20) connected to the Washing apparatus(10) and arranged to receive the pulp washed in the first Washing operation, and Washing, in a second Washing operation (II), the pulp for a second predeterrnined periodof time using the Washing apparatus (10), the pulp being received from the intermediate pulpstorage (20) and applied onto the processing surface (11) of the Washing apparatus, such thatthe pulp is washed again in the same Washing space of the Washing apparatus, the Washing and storing steps being repeated such that the pulp is washed batch-wiseusing the intermediate pulp storage (20), each batch of pulp being washed in two separateWashing operations (I, II), which occur in the same Washing space of the same Washing apparatus (10) but are separate in time.

2. The method of claim 1, wherein the input area of the Washing apparatus ( 10), where thepulp is distributed onto the processing surface (11), is the same in the first and second Washing operation (I, II), and the output area of the Washing apparatus ( 10), Where the pulp is withdrawn from the processing surface ( 11), is the same in the first and second Washing operation (I, II).

3. The method of claim 1 or 2, comprising the further step of adding chemicals to the pulp inthe interrnediate pulp storage (20).

4. The method of any of previous claims, comprising the further steps of receiving the pulp to be washed in the first Washing operation (I) from a first processvessel (30) connected to the Washing apparatus (10), and outputting the pulp washed in the second Washing operation (II) to a second processvessel (40) connected to the Washing apparatus (10), the first process vessel (30) and thesecond process vessel (40) being arranged to altemate between an emptying mode, during the first Washing operation (I), and a filling mode, during the second Washing operation (II).

5. The method of any of previous claims, wherein the first process vessel (30), the interrnediate pulp storage (20), and the second process vessel (40) are pure storage tanks.

6. The method of any of claims 1-4, wherein at least one of the first process vessel (30), the interrnediate pulp storage (20), and the second process vessel (40) is a bleaching reactor.

7. The method of any of previous claims, comprising additional processing of the pulpbetween the Washing of the first Washing operation (I) and the storing in the interrnediate pulp storage (20).

8. The method of any of previous claims, comprising the further steps of collecting, during the first Washing operation (I), filtrate passing through the movablepermeable processing surface (11) into a first filtrate tank (51), and collecting, during the second Washing operation (II), filtrate passing through the movable permeable processing surface (11) into a second filtrate tank (52).

9. The method of claim 8, wherein the filtrate collected during the second Washing operation (II) is used as Washing liquid in the first Washing operation (I).

10. The method of any of previous claims, comprising the further steps of storing the pulp in a second interrnediate pulp storage (60) connected to the Washingapparatus (10) and arranged to receive the pulp washed in the second Washing operation (II),and Washing, in a third Washing operation (III), the pulp for a third predetermined period of time using the Washing apparatus (10), the pulp being received from the second interrnediate pulp storage (60) and applied onto the processing surface (11) of the Washing apparatus, such that the pulp is washed again in the same Washing space of the Washing apparatus.

11. The method of any of previous claims, wherein the Washing operations (I, II, III) are associated with similar process conditions.

12. The method of any of previous claims, wherein each Washing operation (I, II, III) is run during a period of time in the range of about 3 to 30 min.

13. The method of any of previous claims, comprising the further step of adjusting a pararneter of the Washing apparatus (10) or its associated equipment to therespective Washing operation (I, II, III), the parameter being selected from the group of: a flowof added Washing liquid; a rotation speed; a flow of added dilution liquid; and a distance between press rolls (15).

14. A system (100) for Washing of cellulose pulp, comprising a Washing apparatus (10) with a movable perrneable processing surface (11), arrangedfor Washing, in a first Washing operation (I), the pulp for a first predetermined period of time,filtrate from the pulp passing through the processing surface as the pulp is transpoited togetherwith the processing surface, and an interrnediate pulp storage (20), connected to the Washing apparatus (10) and arrangedto receive and store the pulp washed in the first Washing operation, and wherein the Washing apparatus (10) is further arranged for receiving the pulp from theinterrnediate pulp storage (20) and Washing, in a second Washing operation (II), for a secondpredetennined period of time, the pulp again on the processing surface (ll) in the sameWashing space of the Washing apparatus, the system further comprising means for repetition of the Washing operations ( I, II) and the storing in the interrnediatepulp storage (20), such that the system is arranged for batch-Wise operation, each batch ofpulp being washed in two separate Washing operations (I, II), which occur in the same Washing space of the Washing apparatus (10) but are separate in time.

15. The system of claim 14, wherein the input area of the washing apparatus ( 10), where thepulp is distributed onto the processing surface (11), is the same in the first and secondwashing operation (I, II), and the output area of the washing apparatus ( 10), where the pulp is Withdrawn from the processing surface ( 11), is the same in the first and second washing operation (I, II). .

16. The system of claim 14 or 15, further comprising means for adding chemicals to the pulp in the interrnediate pulp storage (20).

17. The system of any of claims 14-16, further comprising a first process vessel (30) connected to the washing apparatus (10), means for receiving, at the washing apparatus (10), the pulp to be washed in the firstwashing operation (I) from the first process vessel (3 0), a second process vessel (40) connected to the washing apparatus (10), and means for outputting, from the washing apparatus (10), the pulp washed in the secondwashing operation (II) to the second process vessel (40), the first process vessel (30) and thesecond process vessel (40) being arranged to alternate between an emptying mode, during the first washing operation (I), and a filling mode, during the second washing operation (II).

18. The system of any of claims 14-17, wherein the first process vessel (30), the intermediate pulp storage (20), and the second process vessel (40) are pure storage tanks.

19. The system of any of claims 14-17, wherein at least one of the first process vessel (30), the intermediate pulp storage (20), and the second process vessel (40) is a bleaching reactor.

20. The system of any of claims 14-19, further comprising means (70) for additionalprocessing of the pulp arranged between the first washing in the washing apparatus (10) and the interrnediate pulp storage (20).

21. The system of any of claims 14-20, further comprising a first filtrate tank (51) arranged to collect filtrate passing through the movableperrneable processing surface (11) during the first Washing operation (I), and a second filtrate tank (52), arranged to collect filtrate passing through the movable permeable processing surface (11) during the second Washing operation (II).

22. The system of claim 21, further comprising means for using the filtrate collected during the second Washing operation (II) as Washing liquid in the first Washing operation (I).

23. The system of any of claims 14-22, further comprising a second intermediate pulp storage (60) connected to the Washing apparatus (10) andarranged to receive and store the pulp washed in the second Washing operation (II), andwherein the Washing apparatus (10) is further arranged for receiving the pulp from theintermediate pulp storage (60) and Washing, in a third Washing operation (III), for a thirdpredetermined period of time, the pulp again on the processing surface (11) in the same Washing space of the Washing apparatus.

24. The system of any of claims 14-23, adapted for operating each Washing operation (I, II, III) during a period of time in the range of about 3 to 30 min.

25. The system of any of claims 14-24, further comprising adjustment means for adjusting a parameter of the Washing apparatus (10) or itsassociated equipment to the respective Washing operation (I, II, III), the parameter beingselected from the group of: a flow of added Washing liquid; a rotation speed; a flow of added dilution liquid; and a distance between press rolls (15).

26. The system of any of claims 14-25, wherein the Washing apparatus (10) comprises an openpulp distribution device (12) with a rotatable distribution means (14) and an outlet (13) which opens towards the movable permeable processing surface (11).

27. The system of any of claims 14-26, wherein the Washing apparatus (10) is a roll press withtwo co-operating press rolls (15) and the movable permeable processing surface (11) is arotatable perforated outer surface of the press roll, a pulp web in operation being formed onthe respective rolls and transported in the direction of rotation in a non-converging vat (16) partially surrounding the press rolls, until the press nip (17) between the rolls.

28. The system of claim 27, wherein the press rolls (15) have a diameter in the range of 1.5- 3m and a length in the range of 4-1 lm.

29. The system of any of claims 27 or 28, further comprisingmeans for automatically varying the distance between the press rolls (15) in response tovarying operating conditions between the first and second Washing operation (I, II), respectively.