An arrangement and a method for heating pulp with steam

Abstract

The invention relates to an arrangement (10) for heating pulp with steam wherein the arrangement (10) comprises. -a tube-like body (11), -an inlet (12) having a first connecting means (21) for 5 connecting the tube-like body (11) to an upstream pulp transfer line for receiving the pulp to be heated to the arrangement (10) from the previous process phase, -an outlet (13) having a second connecting means (22) for connecting the tube-like body (11) to a downstream pulp 10 transfer line to feed the pulp heated by the arrangement (10) to a subsequent processing phase, -a steam channel (14) connected to the tube-like body (11) to feed steam from a steam source into the tube-like body (11), 15 and wherein -the steam channel (14) comprises a spring-loaded steam nozzle (40) arranged to control the amount of steam being fed into the pulp flowing in the tube-like body (11). The invention relates also to a method for heating pulp with 20 steam.

Description

[0001] AN ARRANGEMENT AND A METHOD FOR HEATING PULP WITH

[0002] STEAM

[0003] Field of the invention

[0004] The invention relates to an arrangement and a method for heating pulp with steam.

[0005] Background of the invention

[0006] In past the method considered most economical for rising temperature of fiber suspension (i.e., e.g., cellulose pulp) was to use indirect heat exchangers. Nowadays, it is more usual to heat pulp by supplying steam directly into the pulp stream while it flows in a transfer line. When introducing steam in the pulp the aim is to maintain so called “plug flow” in the transfer line, meaning that all particles in each cross-section of the pulp suspension stream have identical velocity and direction of motion. Typically, pulp temperature is, e.g., in connection with bleaching stages, raised 10 to 20 °C, and in some cases even 30°C by such heating to reach successful conditions for achieving appropriate chemical reaction.

[0007] It is preferably low-pressure steam that is used, the pressure which is usually around 3 to 5 bar. However, in some cases the pressure may also differ from these, most typical values. Anyway, the steam pressure should be appropriately higher than pulp pressure in its heating stage.

[0008] A known pulp heating method and arrangement applying direct heating by steam is described in applicants earlier patent application publication US 2002 / 0040771. In this method cellulose pulp e.g., from a drop leg of a washer is transferred by a pulp transfer means (which may be a MC pump or displacement pump) though a pulp transfer line to a treatment tower. Upstream of the pulp transfer means there are a steam feeding means and pulp mixing means respectively before the pulp enters the said treatment tower. The said pulp mixing means is preferably a fluidizing centrifugal pump, i.e., a centrifugal pump capable of fluidizing the pulp while pumping so that the steam is sufficiently condensed within the pumps suction side before the pulp enters the pumping section. To accomplish this such a pump has further some additional elements, comprising for example ribs, pins, nubs or corresponding members arranged on the wall of the suction channel, by means of which members the turbulence level in the pump is increased as well as a mixing chamber which diameter is larger than smallest diameter of the suction channel and which includes a mixing member that is rotor which may be driven by its own or a separate drive.

[0009] Another known solution is described in an international patent application publication W00044486 which concerns an apparatus for introducing a first fluid into a second fluid (advantageously for admixing of steam into a flow of cellulose pulp). In this document the process of admixing steam into the pulp is accomplished in a pipe conveying the pulp into a cellulose factory bleaching department. The aim of the described solution is to preheat the pulp to a specified temperature suitable for a subsequent bleaching stage in a manner that ensures that good heat distribution is obtained in the downstream pipe, i.e., that very small temperature differences are obtained in an arbitrarily chosen cross section of the downstream pipe. According to the document these aims are reached by an apparatus that includes a pipe body having the same internal diameter as the upstream pipe to which the pipe body is joined. The inside of the pipe body forms a through-flow channel for the pulp which is being conveyed in the pipe. A kind of steam feeding chamber that extends round the rear and central parts of the pipe body is formed on the pipe body. In the region of the rear part of the said chamber, the pipe body has plurality of slits which extend through the wall of the pipe body, and which are evenly distributed round the circumference of pipe body. A steam channel from a steam source is connected to the chamber for providing the steam into the said chamber. Thus, the slits allow the steam coming into the chamber to distribute evenly into the pulp flow flowing in the pipe body. To adjust the size of the openings formed by the slits the apparatus includes further a curved, linearly movable screen that can be moved on and away from the slits and thereby to regulate the amount of steam to be introduced into the pulp flow. To adjust the position of the screen there is a pneumatic cylinder outside the apparatus which piston rod is connected to the screen through a sealed through hole at the respective end wall of the chamber. The cylinder is suitably regulated depending on the temperature which is measured in the pulp transfer pipe downstream of the apparatus. The measured temperature value is sent to an IP transducer in order to control quantity of steam admixed, so that the temperature is maintained at a predetermined set value.

[0010] Regardless of the development made in arrangements for heating pulp with steam, it has been observed that there are still some drawbacks present in these known solutions for heating pulp with the steam. Among others, uneven steam distribution, flow velocity variation and rough patterns may occur when applying these presently known arrangements for heating pulp with steam.

[0011] Summary of the invention

[0012] The aim of the present invention is to provide an arrangement and a method for heating pulp with steam which further improves pulp heating by means of steam being fed in the pulp. Especially, the aim of the invention is to provide an arrangement and a method by means of which improved pattern, flow velocity and steam distribution can be achieved when the steam is introduced within pulp to be heated. Furthermore, it is also an aim of the invention to bring forth an arrangement and a method applying multiple steam nozzles by means of which it is possible to distribute the steam flow evenly through multiple nozzles of an arrangement by single control valve controlling the overall flow.

[0013] The aim of the invention is achieved because in the arrangement and the method steam nozzles applied in admixing the steam in to pulp to be heated through at least one steam channel having one or more spring-loaded steam nozzles to provide steam into the pulp. In case of plurality of spring-loaded steam nozzles are preferably such that they will each open equal amount with the same pressure difference, or their opening behavior as function of pressure difference is known so that steam flowing through the spring- loaded steam nozzles can be managed by controlling the pressure difference between the steam channel and the space where the steam is mixed with the pulp. More specifically, the arrangement according to the invention is characterized by what have been described in the independent claim 1 and the method what have been described in the independent claim 10. The dependent claims 2-9 present some advantageous embodiments of the arrangement and the dependent claims 11 -15 some advantageous embodiments of the method.

[0014] The invented arrangement and method have at least followed advantages:

[0015] -By utilizing spring tension and dedicated nozzle shape, an optimal steam pattern can be obtained to heat pulp in a controlled manner.

[0016] -The spring tension sets the opening degree, and the applied nozzle type ensures optimal velocity and steam distribution into the pulp stream.

[0017] -The use of spring-loaded steam nozzles will also prevent backflow of the pulp to the steam channels, preventing possible clogging issues.

[0018] -The spring-loaded steam nozzles, spring tension will be driving the opening degree on the nozzles and by that way constantly keep the best possible flow regardless of steam addition this is applicable over several nozzles.

[0019] -In an arrangement with multiple sprig-loaded steam nozzles, the spring- loaded steam nozzles will be able to be controlled by one single control valve as the integrated spring will automatically distribute the flow evenly to the various steam channels in the arrangement.

[0020] -In case of low steam heating, the same spring-loaded nozzle applied in the arrangement and the method can be used with a probe-style nozzle inserted into the pulp stream and controlled like multiple nozzle arrangements.

[0021] -The invented arrangement allows making a low-cost steam heating solution utilizing a nozzle concept that is self-regulating and optimizes steam feeding with a small investment cost. It also enables steam feeding solution that is driven by ensuring an even and thin "film" of steam inserted into the pulp stream and the steam spray pattern being optimized by a preloaded spring. The sizes and quantity of the spring-loaded steam nozzles can be fitted in many different applications and solutions. The spring-loaded steam nozzles can also be used as a probe style type of heating device.

[0022] Brief description of the drawings

[0023] In the following, some advantageous embodiments of invention will be described in more detail with reference to the appended drawings in which:

[0024] Fig. 1 shows a front view of a first embodiment of an arrangement according to the invention,

[0025] Fig. 2 shows a cross-section A-A of the arrangement shown in the figure 1 ,

[0026] Fig. 3 shows a side view of a second embodiment of an arrangement according to the invention,

[0027] Fig. 4 shows a cross-section B-B of the arrangement shown in the figure 3,

[0028] Fig. 5 shows a side view of a third embodiment of an arrangement according to the invention,

[0029] Fig. 6 shows a cross-section C-C of the arrangement shown in the figure 5,

[0030] Fig. 7 shows a front view of a first embodiment of a spring-loaded steam nozzle applicable in embodiments of the arrangement according to the figure 1 and 2,

[0031] Fig. 8 shows a cross-section D-D of the spring-loaded steam nozzle of figure 7,

[0032] Fig. 9 shows a front view of a second embodiment of a spring-loaded steam nozzle applicable in embodiments of the arrangement according to the figures 3-6, and

[0033] Fig. 10 shows a cross-section E-E of the spring-loaded steam nozzle of figure 9.

[0034] Detailed description of some advantageous embodiments

[0035] Some preferred embodiments of the arrangement according to the invention will be described hereinbelow. These exemplary embodiments, that may be used according to the method of the invention, have been developed, and designed to be used for admixing steam into pulp prior the bleaching stages. Thus, in these cases, the arrangement locates in a pulp transferring line conveying pulp into subsequent bleaching stage. The purpose of the arrangement is to preheat the pulp to a suitable temperature for the chemical reaction occurring in the forthcoming bleaching stage. However, the method and arrangement described in the present patent application may be applied also in heating of the pulp (or corresponding suspensions) in connection with other process stages of the pulp production, or in production of other suspensions having a corresponding characteristic as cellulose pulp and need to be heated to rise their temperature prior to the subsequent process phase. For instance, the present invention may be alternatively applied, in some earlier process phases of the pulp production, such as e.g., in preheating a mixture of cooking chemicals and wood ships before their cooking in a digester.

[0036] In the figures 1 to 6 some embodiments of the arrangement 10 according to the invention are shown. Each of them comprises a tube-like body 11 , an inlet 12 having a connecting means 21 for connecting the tube-like body 11 to an upstream pulp transfer line for receiving the pulp to the arrangement from the previous process phase, an outlet 13 having a connecting means 22 for connecting the tube-like body 11 to a downstream pulp transfer line to feed the pulp heated by the arrangement 10 to a subsequent process phase. The connecting means 21 and 22 comprise in the embodiments shown in the figures 1-6 flanges that can be used to secure the tube-like body 11 to the respective flanges of the upstream and downstream pulp transfer lines so that inlet opening 12 and outlet opening 13 will become tightly against respective openings in the upstream pulp transfer line and the downstream pulp transfer line (not shown in the figures). However, in other embodiments the connecting means can be any other possible connecting means, for instance muffles, or the connecting means may be formed by welds by means of which the inlet of tube-like body is connected to the upstream pulp transfer line and the outlet to the downstream pulp transfer line. In the first embodiment shown in the figure 1 there is a steam channel 14 being connected to the tube-like body 11 of the arrangement 10. The steam channel 14 comprises a connecting conduit 15 and a nozzle chamber 16. The nozzle chamber 16 has a steam inlet 17, and a steam outlet 18. The steam inlet 17 is an inlet to which the connecting conduit 15 of the steam channel 14 has been connected to provide steam into the nozzle chamber 16. The steam outlet 18 is at the other end of the nozzle chamber 16 and extends from the nozzle chamber 16 into interior of the tube-like body 11 as shown in the figure 2. A spring-loaded steam nozzle 40 is attached to the steam outlet 18 such that steam coming from the nozzle chamber 16 must flow into the tube-like body 11 through the spring-loaded steam nozzle 40. Thus, the flow of the steam through the steam channel 14 into the tube-like body 11 is controlled by the spring-loaded steam nozzle 40.

[0037] In this embodiment the nozzle chamber 16 is arranged entirely in the interior of the tube-like body 11 and oriented parallel to the longitudinal direction of the tube-like body 11 . Thus, it feeds the steam in a direction that is parallel to the flow of the pulp.

[0038] In a second embodiment shown in the figures 3 and 4, the arrangement 10 has steam a channel 14 with includes a connecting conduit 15 and two nozzle chambers 16, each connected to the tube-like body 11 to feed steam into the tube-like body 11. Principally, the nozzle chambers 16 of this embodiment correspond to the nozzle chamber 16 of the embodiment shown in the figure 1 . As shown in the figure 4 the nozzle chambers 16 are attached to the wall of the tube-like body 11 opposite sides of the tube-like body 11 and oriented perpendicularly to the longitudinal direction of the tubelike body 11 . But in some other embodiments they can be directed in some other direction, for instance, obliquely to the pulp flowing direction. Thus, in this embodiment the steam is fed into the tube-like body 11 in a direction that is perpendicular to the flow direction of the pulp. Furthermore, because there is an intermediate conduit 25 between the two nozzle chambers 16, there is no need for two separate connecting conduits 15 for each nozzle chamber 16. However, in some other embodiments having two or more nozzle chambers like this there may be separate connecting conduits for each nozzle chamber. In such embodiments there are no need for intermediate channels since each connecting conduit each has own inlet. Thus, the embodiments are those that can be considered to have two or more steam channels being independent from each other. Such steam channels can be each connected to their own steam source but alternatively to a single common steam source, or such steam source being combination of these alternatives (i.e., e.g., such that four or eight steam channels have one steam source for each pair of steam channels). Furthermore, also in case of several separate steam channels, each steam channel may comprise two or more nozzle chambers and intermediate conduits between them.

[0039] A third example embodiment of the arrangement shown in the figures 5 and 6 corresponds the embodiment of figures 3 and 4 except it has four nozzle chambers 16 arranged around the tube-like body as can be seen from figure 6. Thus, in this embodiment the steam channel 14 comprises a connecting conduit 15, three intermediate conduits 25 and four nozzle chambers 16 to feed steam into the tube-like body 11. As in the embodiment shown in the figures 3 and 4 each nozzle chambers 16 have been connected to each other by means of intermediate conduits 25. Furthermore, the nozzle chambers 16 are principally similar than in the embodiment shown in the figures 3 and 4. There may be further embodiments having e.g., three or more than four nozzle chambers being connected to a connecting conduit by an intermediate conduit. Alternatively, such embodiments may have own connecting conduits and nozzle chambers for each spring-loaded steam nozzles (i.e., independent steam channels for each spring-loaded steam nozzles). Furthermore, there may be embodiments without any nozzle chambers. In such embodiments one or more the spring-loaded steamnozzles have been assembled directly to the connecting conduit extending inside the tube-like body. Thus, in in such embodiments one or more pure connecting conduits forms the one or more steam channels of the arrangement. The tube-like body 11 is in each of these different embodiments an elongate part of the arrangement 10 having, preferably circular cross-section so that each of its parts are symmetric in respect of its longitudinal central axis 33. Of course, there may be embodiments having different than circular shape of the cross-section. The arrangement is preferably made of steel or other suitable material being suitable for transferring pulp and steam.

[0040] In the embodiment shown in the figures 1 and 2 the tube-like body 11 has a securing assembly 20 for connecting the steam channel 14 to the tube-like body 11. The securing assembly 20 in the embodiment of figure 1 and 2 comprises a sleeve 24 that is tightly joined (e.g., by welding) to a respective opening 23 provided to the tube-like body 11. The steam channel 14 is secured gas tightly to the sleeve 24 by an openable ring-like hatch 19 which is fixedly joined to the connection conduit 16 of the steam channel 14 and secured detachably to the sleeve 24 by attachment screws as it is shown in the figure 2. Thus, in case of embodiment shown in the figures 1 and 2 the steam channel 14 can be entirely removed from the tube-like body 11 (e.g., for replacement of the spring-loaded steam nozzle 40) by opening the attachment screws of the ring-like hatch 19 and pulling the steam channel 14 out from the interior of the tube-like body 11 and by attaching it back its intended position by securing the ring-like hatch 19 back to the sleeve 24 with its attachment screws. However, in different embodiments like the one shown in the figures 1 and 2, there could be other kind of structures to arrange respective openability of the steam channel e.g., for carrying out replacement or maintenance for the spring-loaded steam nozzles therein.

[0041] In case of embodiments shown in the figures 3-6 the steam channel 14 is fixedly secured to the openings 23 formed to wall of tube-like body by its nozzle chambers 16. For the replacement of the spring-loaded stem nozzles the nozzle chambers have openable hatches 19 through which the spring- loaded steam nozzles 40 can be assembled and disassembled into the nozzle chambers 16.

[0042] The steam channel 14 in each of the above-described embodiments may have its free end e.g., coupling a flange for connecting it to a steam source. The steam source (not shown in the figures) can be e.g., a steam line providing e.g., low, or medium pressure steam from the pulp mill’s other processes. Preferably, the pressure of the steam in the steam channel is between 5 to 15 bars. However, the suitable steam pressure depends on the pressure of the pulp in the tube-like body 11. For that purpose, there is usually in between the steam source and the steam channels a control valve or corresponding control means for adjusting the steam pressure to be suitable for feeding the steam appropriately into the pulp.

[0043] As described above, each nozzle chamber 16 of the steam channel 14, has a spring-loaded steam nozzle 40 assembled inside the nozzle chamber 16. The purpose of the spring-loaded steam nozzles 40 is to control the amount of steam being fed into the pulp flowing in the tube-like body 11. The positions of spring-loaded steam nozzles 40 can be seen in more detail from the figures 1-6, i.e., they are placed at the nozzle chambers 16 such that they extend at least partly inside the tube-like body 11 through outlet openings 18 of the nozzle chambers 16. Thus, the amount of steam flowing into the tube-like body 11 is affected by the spring-loaded steam nozzles 40.

[0044] Two exemplary embodiments of the spring-loaded steam nozzles 40 have been depicted in the figures 7-10. They comprise nozzle body 41 , valve channel 42, valve pin 43, valve piston 44, limiting sleeve 45, spring 46 and locking pin 47 and casing 48.

[0045] The valve body 41 has threated portion 41 a by means of which the spring- loaded steam nozzle 40 can be attached into the nozzle chamber 16 as it is shown in the figures 1-6. For that purpose, there are respective threads formed to the outlet openings 18 of the nozzle chambers 16.

[0046] The difference between the first embodiment of the steam nozzle (shown in the figures 7 and 8) and the second embodiment (shown in the figures 9 and 10) is that in the said first embodiment the threaded portion 41 a is placed at the inner side of the valve body 41 and in the said second embodiment at outer side of the valve body 41 such that in the former a sealing flange 41 c remains inner side of the steam outlet 18 and in the latter it remains at the outer side of the steam outlet 18. Thus, as can be seen form the figures 2, 4 and 6 the first embodiment is intended to be used with the embodiment of the arrangement 10 according to figures 1 and 2, whereas the second embodiment suits for the embodiments of the arrangement 10 shown in figures 3-6.

[0047] The both types of spring-loaded steam nozzles 40 described above operate so that when the valve piston 44 and the valve pin 43 to which the valve piston 44 is connected moves (e.g., due to pressure difference between the nozzle chamber 16 and interior space of the tube-like body 11 ) into opening direction (i.e., right in the figures 8 and 10) the locking pin 47 at the other end of the valve pin 43 that rests against a groove 45a of the limiting sleeve 45 causes that also the limiting sleeve 45 moves in that direction with the valve piston 44 and the valve pin 43. Due to this movement the spring 46 that is fitted inside the limiting sleeve 45 (as shown in the figure 8 and 10) is compressed since its first end rests against a shoulder 45b at the limiting sleeve 45 and the second end against inner end 41 b of the valve body 41 . Compression of the spring 46 forms a spring force that urges the valve pin

[0048] 43 and the valve 44 to move in the closing direction. Thus, the compressing spring 46 causes to the piston 44 a counterbalance force which balances the force acting on the piston 44 in the steam channel 42 due to the said pressure difference. Therefore, when there is in the arrangement 10 a pressure difference lower than certain threshold value between nozzle chamber 16 and interior of the tube-like body 11 the spring-loaded steam nozzles 40 remains closed since the spring 46 exerts the piston 44 into its closed position with a force that corresponds the force of the said threshold pressure difference acting on the valve piston 44. Then, in case when the pressure difference increases over the said threshold value, the valve piston

[0049] 44 moves into the opening direction amount that depends on the value of the said pressure difference. Thus, in the embodiments of the arrangement shown in the figures 1 -6 it is possible to control the opening of the valve piston 44 of the spring-loaded nozzle 40 and thereby the amount of steam flowing through the steam channel 14 into the tube-like body 11 just by controlling the pressure of the steam in the nozzle chamber 16. In case of multiple spring-loaded steam nozzles 40, the steam nozzles 40 have, preferably, as equal properties as possible (as the case is with the arrangement 10 shown in the figures 3-6). Thus e.g., the spring constant of the spring 46 is the same for each spring-loaded steam nozzle 40 of an arrangement. Advantage of this is that in such case each spring-loaded steam nozzle 40 distributes equal amount of steam into the pulp if steam pressure is the same for each nozzle chamber 16. Typically, in case of multiple nozzle chambers 16 they are connected to the same steam source through a control means (i.e., e.g., a control valve). Therefore, the pressure of the steam is the same in each nozzle chamber 16 and hence also the volume flow into the tube-like body is evenly distributed through each spring- loaded steam nozzles 40. However, the spring-loaded steam nozzles 40 may be alternatively different (i.e., e.g., one or more equipped with springs having different spring constant). In such case the spring-loaded steam nozzles 40 may have been arranged to feed the steam in certain predetermined manner (i.e., depending on the spring constants of the springs) so that appropriately distributed steam flows into the tube-like body is achieved.

[0050] As described above, when there is positive pressure difference present in the arrangement 10 the valve piston 44 of the spring-loaded steam nozzles 40 open automatically depending on the pressure difference. Thus, in case of several steam nozzles having the same outlet dimensions and spring constant multiple steam nozzles distribute the steam evenly into the pulp.

[0051] By multiple steam nozzles that feeds the steam with suitable flow speed a thin steam film is achieved in the pulp suspension flowing in the tube-like body and in the pulp transfer line. This prevents implosions i.e., so called “hammering" that typically occurs in the known arrangements because too large steam bubbles are formed into the pulp due to uneven distribution of the steam within the pulp. Thus, application of multiple (preferably at least two) spring-loaded steam nozzles make the arrangement more silent as well as reduce dynamic stress and thereby structural fatigue because of less vibration. In different embodiments the steam chambers and the spring-loaded steam nozzles therein can be provided in different locations within the tube-like body so that as even as possible distribution of the steam can be achieved. Suitable positions and orientation of the steam channels may be predetermined e.g., by testing and / or by applying suitable mathematical modelling and / or computer simulation. In the embodiments shown in the figures 3-6 the multiple steam chambers are placed in opposite sides of the tube-like body 11 such that they are directed perpendicularly in respect of the longitudinal axis 30 of the tube-like body 11 (i.e., upwards, and downwards when seen from a side) as can be seen from the figures 1 -3. However, in some embodiments the all or part of the steam channels may be alternatively positioned into some inclined angle in respect of the longitudinal axis of the tube-like body.

[0052] Further advantage of the application of the spring-loaded steam nozzles in steam channels is that multiple nozzles can be used without controlling each of them separately. This is because opening proportion of the spring-loaded steam nozzles depends on the pressure difference between the steam channels and the tube-like body. Thus, it is possible to have several spring- loaded steam nozzles in a single arrangement to provide even distribution of steam within the pulp flow in a pulp transfer line by using only a single control valve for controlling the amount of steam to be fed into the arrangement.

[0053] In the embodiments shown in the figures 1 to 6 the spring 46 of the spring- loaded steam nozzles 40 have non-linear spring constant. The spring 46 in that embodiment is designed so that the spring-loaded steam nozzles 40 open 20 to 30%, preferably 25% of its fully open position when the pressure of the steam in the steam channel 14 (and the nozzle chamber 16) is 1 bar higher than the pressure of the pulp in the tube-like body 11. The spring- loaded steam nozzles 40 open into completely open position when the pressure the first steam channel 14 is enough much higher than the pressure of the pulp in the tube-like body 11 , for instance at least 2,5 bars more than the pressure of the pulp in the tube-like body 11. The threshold pressure difference values described above have been found the most appropriate when steam is used for heating pulp which is medium-consistency pulp. However, in some other embodiments the spring-loaded steam nozzles may have different behavior i.e., they may have springs with spring constant which causes that these values differ that of values mentioned above. For instance, in such embodiment the spring constant of the spring-loaded steam nozzle may be linear or non-linear in some alternate manner.

[0054] When using the arrangement 10 according to figures 1 to 6, the inlet 12 is connected to an upstream pulp transfer line by connecting means 21 and the outlet 12 is connected to a downstream pulp transfer line by connecting means 22. The first steam channel 14 is connected to a steam source. The steam source may be controllable or there may be a control valve in the steam channel 14 for controlling the pressure of the steam. Thus, during the operation, pulp flows from the upstream pulp transfer line into the tube-like body 11 through the inlet 12 and from there to the downstream pulp transfer line through the downstream pulp transfer line. To heat the pulp the pressure in the steam channel 14 is adjusted e.g., by the controlling the pressure of the steam source such that pressure difference between the steam and the pulp is, in these embodiments, at least 0,5 bar (which is the threshold value for opening of the steam nozzles 40). Usually, it is considered that practically minimum pressure difference is reached when 20 to 30%, preferably 25% of the fully open position is achieved. This corresponds pressure difference of about 1 bar for the spring-loaded steam nozzle 40. The maximum amount of steam is fed into the pulp when the pressure difference is, in this embodiment, 2.5 bar. In such case the spring-loaded steam nozzles 40 in the nozzle chamber 16 of the steam channel 14 is fully open, i.e., the spring 46 is compressed to the position in which the limiting sleeve 45 has been moved against the body 41 of the spring-loaded steam nozzle 40 and hence the valve pin 43 and the valve piston 44 cannot move further into opening direction. Thus, when heating the pulp with the arrangement 10, the pressure of the steam is most typically adjusted to some value that corresponds pressure difference between 1 to 2.5 bar. When the pressure of the steam is reduced to the value that corresponds pressure difference that is less than the said predetermined threshold value the spring-loaded steam nozzles 40 are closed and no more steam is fed into the pulp flowing through the tube-like body 11 of the arrangement 10.

[0055] Those skilled in the art understand from the above-described explanations that the arrangement and method according to the present invention can be realized in multiple different manners distinguishing from the abovedescribed example embodiments. Thus e.g., their construction and how the heating of the pulp is carried out by applying the explained principles may vary. Therefore, for instance, in some other embodiments the steam can be fed to each steam channel independently, the spring-loaded steam nozzles need-not to be identical (i.e., they can have e.g., each different properties, or they can be divided in such groups wherein one group has properties that are same for that specific group and the other group have those of different but the same for each member of that group). Furthermore, the dimensions and shapes of the steam channel and tube-like body as well as size and number of the other parts can vary in the different embodiments of the arrangement.

[0056] Consequently, the arrangement and the method according to the invention are not limited to the embodiments described above but can vary within the scope of the appended claims.

Claims

Claims1 . An arrangement (10) for heating pulp with steam wherein the arrangement (10) comprises-a tube-like body (11 ),-an inlet (12) having a first connecting means (21 ) for connecting the tubelike body (11 ) to an upstream pulp transfer line for receiving the pulp to be heated to the arrangement (10) from the previous process phase,-an outlet (13) having a second connecting means (22) for connecting the tube-like body (11 ) to a downstream pulp transfer line to feed the pulp heated by the arrangement (10) to a subsequent processing phase,-a steam channel (14) connected to the tube-like body (11 ) to feed steam from a steam source into the tube-like body (11 ), and wherein-the steam channel (14) comprises a spring-loaded steam nozzle (40) arranged to control the amount of steam being fed into the pulp flowing in the tube-like body (11 ).

2. The arrangement (10) according to claim 1 , wherein the steam channel (14) comprises a connecting conduit (15) and a nozzle chamber (16), and wherein the connecting conduit (15) is connected to the nozzle chamber (16).

3. The arrangement (10) according to claim 2, wherein the nozzle chamber (16) has a steam inlet (17), and a steam outlet (18) and wherein the connecting is conduit (15) is connected to the steam inlet (17), and a spring- loaded steam nozzle (40) is attached to the steam outlet (18) such that steam coming from connecting conduit into the nozzle chamber must flow into the tube-like body (11 ) through the spring-loaded steam nozzle (40).

4. The arrangement (10) according to claim 2 or 3, wherein the steam channel (14) comprises plurality of nozzle chambers (16).

5. The arrangement (10) according to claim 4, wherein the nozzle chambers (16) are connected to each other by intermediate conduits (25).

6. The arrangement (10) according to any of preceding claims, wherein the spring-loaded steam nozzle (10) is arranged to open 20 to 30%, preferably 25% of its fully open position when the pressure difference between the steam in the steam channel (14) and the pulp in the tube-like body (11 ) is higher than predetermined threshold value.

7. The arrangement (10) according to claim 6 wherein the spring-loaded steam nozzle (40) is arranged to open 20 to 30%, preferably 25% of its fully open position when the said pressure difference is about 1 bar.

8. The arrangement (10) according to 6 or 7, wherein the spring-loaded steam nozzle (40) is arranged to open into completely open position when the said pressure difference is about 2,5 bars.

9. The arrangement (10) according to any of preceding claims, wherein the spring (46) of the spring-loaded steam nozzle (40) has non-linear spring constant.

10. A method for heating pulp with steam wherein the pulp is heated by steam being fed into the steam channel (14) while the pulp flows in the arrangement (10) according to any of claims 1 to 9.

11. The method according to claim 10, wherein the pressure difference between the steam in the steam channel (14) of the arrangement (10) and the pulp flowing in the tube-like body (11 ) is at least 0.5 bar.

12. The method according to claim 10 or 11 wherein the pressure difference between the steam in the steam channel (14, 15) and the pulp flowing in the tube-like body (11 ) is at most 2.5 bar.

13. The method according to any of preceding claims, wherein the method is applied in heating pulp to be fed in to the first bleaching stage.

14. The method according to any of preceding claims, wherein the method is applied in heating the pulp in between two subsequent bleaching stages.

15. The method according to any of preceding claims, wherein the method is applied in preheating a mixture of cooking chemicals and wood chips before their cooking in a digester.

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