Patent Publication Number: US-10328399-B2

Title: High speed injector with two stage turbulence flap

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus and a method for mixing a first fluid with a second fluid, particularly for mixing steam into pulp. 
     BACKGROUND ART 
     As used herein, fluid means a gas, a liquid, a steam or a mixture of these. As used herein, the notion fluid is also mean to include a system consisting of a mixture of solid particles and a liquid or gas, where the mixture has fluid-like properties. One example of such a system is a suspension, e.g. a cellulose pulp suspension. 
     As used herein, introducing one fluid into the flow path of another fluid means injection, mixing, dispersion or other admixing of one fluid, which is also called the admixture fluid, into the flow path of the other fluid. 
     It is not unusual in industrial processes that fluids are mixed with each other. In e.g. the paper industry, it is not unusual that process chemicals, e.g. oxygen gas, chlorine dioxide or ozone, are introduced into a flow of pulp suspension. It is also common in this industry that steam is introduced into the flow of pulp suspension with the purpose of heating the pulp suspension. 
     There are a number of previously known methods and apparatuses for introducing one fluid into another fluid. One problem with these devices is that they are relatively energy intensive and that they require relatively much maintenance. 
     When introducing one fluid into the flow path of another fluid, it is generally always desirable to obtain a mixing or dispersion of the fluids which is as effective and uniform as possible. 
     One objective when injecting one fluid into another fluid, particularly when injecting steam into pulp suspension, is to admix i.e. to mix and disperse the added steam. 
     If the mixing or dispersion is not sufficient, there is a risk of steam bubbles forming in the liquid or suspension, wherein said steam bubbles may subsequently implode. These steam implosions cause pressure shocks in the liquid or suspension, which in their turn may propagate to machine supports, apparatuses and other process equipment and cause knocks and vibrations, which can be so powerful that mechanical damage results. This is especially a problem when a large amount of steam is added to a cellulose pulp suspension and especially to a cellulose pulp suspension of medium consistency. As used herein, a pulp suspension of medium consistency means a pulp suspension having a dry solids content in the range of approx. 8-14%. 
     Accordingly, there is a need to maximize and improve the mixing and dispersion of the fluids, in order to increase efficiency and minimize the risks of e.g. damaging equipment. 
     SUMMARY OF THE INVENTION 
     It is an object of the solution to address at least some of the problems outlined above. It is possible to achieve this object, and others, by using methods and apparatuses as defined in the attached claims. 
     According to a first aspect, an apparatus for mixing a second fluid into a first fluid is provided. The apparatus comprises a chamber enclosing a flow path of the first fluid, the chamber having a first inlet for receiving the first fluid and a second inlet arranged downstream of the first inlet for receiving the second fluid. It further comprises an outlet, arranged downstream of the second inlet, for discharging a mixture of said first fluid and said second fluid, wherein the flow path of the first fluid extends from the first inlet to the outlet and the second inlet opens into the flow path of the first fluid. The apparatus also comprises a vertically adjustable throttle body having a first end disposed at a bottom portion of the chamber and a second end comprising an end portion. The throttle body is arranged inside the chamber, downstream of the first inlet and upstream of the second inlet, for controlling the flow area of the flow path. The throttle body is adapted to be vertically adjustable in such a way that the flow area decreases with a decreasing flow rate of the first fluid and increases with an increasing flow rate of the first fluid. The end portion of the throttle body comprises three parts, the first part being upstream of the second part, the third part being downstream of the second part. In an operating position, the second inlet is upstream of the third part of the throttle body and downstream of the first inlet, with the first part and the third part of the end portion being adapted to achieve a higher flow velocity than the second part. By having a throttle body arranged as described herein, the mixture of the fluids is improved because of the end portion of the throttle body causing a higher turbulence. The end part of the throttle body is typically positioned downstream of the second inlet, i.e. downstream of where the second fluid is injected since it is aimed at improving the mixing of both fluids rather than increasing the turbulence in just one fluid. 
     There may be spring means disposed between a bottom side of the throttle body and the bottom portion of the chamber, the spring means being adapted to counteract the force exerted on the throttle body by the first fluid. 
     The end portion of the throttle body may be adapted such that the flow area at the first part and the third part is smaller than the flow area at the second part. This results in a velocity increase right before the injection point, as well as a velocity increase after the mixing of the first and the second fluids, which results in more turbulence and therefore better mixing of the fluids. 
     The first part and the third part of the end portion may be protrusions and the second part may be an indentation, resulting in the end portion of the throttle body being shaped as a substantially angular U or V. The form of the end portion of the throttle body is intended to accomplish the abovementioned increase in velocity before and after the mixing of fluids. 
     The second inlet may comprise a valve adapted for controlling the velocity of the second fluid at a point where the first fluid and the second fluid are mixed. By having such a valve, it becomes possible to have a greater control of the velocity of the second fluid, which in turn facilitates the mixing of the fluids. 
     The apparatus may further comprise a baffle disposed downstream of the second inlet, the baffle being adapted to redirect the flow. By having such a baffle which redirects the flow, the turbulence increases and the mixing is improved. 
     The baffle may further be adapted to redirect the flow towards the outlet. 
     The second inlet may be arranged substantially perpendicular to the flow path of the first fluid. By having an angle between the flow path of the first fluid and the inlet of the second fluid that is substantially perpendicular, the turbulence increases and mixing is improved. 
     According to a second aspect, there is also provided a method for mixing a second fluid into a first fluid. The method comprises causing the first fluid to flow in a chamber from a first inlet to an outlet, the chamber enclosing the flow path. The method further comprises supplying the second fluid into the flow path of the first fluid via a second inlet of the chamber, the second inlet being arranged downstream of the first inlet and upstream of the outlet, and causing a vertically adjustable throttle body, having a first end connected to a bottom portion of the chamber and a second end comprising an end portion and being arranged in the flow path, to adjust its position to control the flow area of the flow path, in such a way that the flow area decreases with a decreasing flow rate of the first fluid and increases with an increasing flow rate of the first fluid. The end portion of the throttle body comprises three parts, the first part being upstream of the second part, the third part being downstream of the second part. In an operating position, the end portion is upstream of or aligned with the second inlet, and downstream of the first inlet, with the first and third parts of the end portion being adapted to achieve a higher flow velocity than the second part. 
     By implementing a solution as described herein, it is possible to improve existing technologies for mixing a second fluid into a first fluid, particularly wherein the first fluid is a pulp suspension and the second fluid is steam. By implementing the herein suggested solution, the turbulence of the fluids may be increased which in turn results in a better mixing of the fluids. This entails both a better end product due to improved mixing as well as less damage caused by steam bubbles. 
     The above apparatuses and methods may be configured and implemented according to different various optional embodiments. Further possible features and benefits of this solution will become apparent from the detailed description below. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The solution will now be described in more detail, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a first embodiment of an apparatus according to the invention in a cross-sectional side view. 
         FIG. 2  shows the apparatus in in a top view. 
         FIG. 3  shows the apparatus in a side view. 
         FIG. 4  shows the apparatus in a front view. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The embodiment of the invention that will be described in the following is intended to be used in a process plant for mixing a second fluid, in the form of steam, into the flow path of a first fluid, in the form of a cellulose pulp suspension, wherein the hot steam is intended for heating the pulp suspension to a desired temperature, e.g. to a temperature that is suitable for a subsequent bleaching step. It will be appreciated, however, that the principle of the invention may be used for mixing other fluids, such as gases, e.g. oxygen gas, chlorine gas or ozone, or liquids, e.g. pH-adjusting liquids, chlorine dioxide or other treatment liquid, into a pulp suspension. It will also be appreciated that the first fluid may be of another type than a pulp suspension, e.g. process liquor. 
     The apparatus comprises a substantially parallelepipedic housing  1 , for receiving a pulp suspension from a first conduit, as well as for discharging the pulp suspension into a second conduit located downstream of the first conduit. The apparatus further comprises a supply means  2  for supplying steam to the flow of pulp suspension. The apparatus further comprises a control unit  3  with a main throttle body  22 , which ensures that there is a suitable flow velocity in the pulp suspension when supplying the steam, in order to avoid the occurrence of steam implosions. Accordingly, the control unit  3 , particularly the throttle body  22  ensures that the flow velocity of the pulp suspension exceeds a certain predetermined minimum value when supplying the steam. 
     The housing  1  is delimited externally by an upper delimiting surface, constituted by a roof portion  4 , lateral delimiting surfaces, constituted by side walls  5  and  6  and by a short side wall  7  on a front side of the housing  1  and a short side wall  8  located on a back side of the housing  1 , and a lower delimiting surface, constituted by a base portion  9 . 
     Internally, the housing  1  comprises a substantially parallelepipedic chamber  10 , which in some embodiments is approx. 500-700 mm long, approx. 200-250 mm wide, and approx. 150-300 mm high. The chamber  10  exhibits a circular first inlet  11  located in the side wall  7  for receiving the pulp suspension from the first conduit disposed upstream, and an outlet  12  located in the side wall  8  for discharging the pulp suspension into the second conduit disposed downstream. The first inlet  11  is formed by an opening in the short side wall  7  and in some embodiments has a diameter of approx. 80-200 mm. The inlet  11  has an area that is smaller than the cross-sectional area of the chamber  10 . The outlet  12  is typically substantially the same size as the cross-sectional area of the chamber  10 . Accordingly, the chamber  10  encloses a flow passage  13  for the pulp suspension, the flow passage  13  extending from the first inlet  11  to the outlet  12 . 
     Furthermore, the chamber  10  exhibits an elongated second inlet  14  for receiving the pressurized, hot steam from the supply means  2 , said inlet  14  opening into the flow passage  13 . The inlet  14  is arranged in the roof portion  4  of the housing  1  and is located downstream of the first inlet  11  and upstream of the outlet  12 . The supply means  2  connects to the second inlet  14  from the top side of the roof portion  4 . The second inlet  14  is arranged with its longitudinal direction transversely to the chamber  10  and the flow passage, i.e. transversely to the flow direction of the pulp suspension, and extends across substantially the entire width of the flew passage  13 . In other words, the second inlet  14  has a length that is substantially equal to the width of the chamber  10 . The width of the inlet  14 , i.e. its extension in the longitudinal direction of the chamber  10 , is approx. 2-50 mm. 
     Removable stoppers may be arranged in the base portion  9  of the housing  1 . The stoppers enable rinsing of the housing  1  in case of so-called plugging, i.e. that the pulp suspension clogs the housing  1 . 
     The supply means  2 , for supplying the pressurized, hot steam to the chamber  10  and the flow passage  13  via the second inlet  14 , comprises a pipe flange  15  that may connect to a steam conduit for feeding pressurized steam to the supply means  2 . Furthermore, the supply means  2  comprises a pipe part  16 , which exhibits a first end  17  and a second end  18 . The first end  17  connects to the pipe flange  15  and the second end  18  connects to a valve  19  of the supply means  2 . The second end  18  is compressed, as is evident from  FIG. 1 , making the pipe opening of the second end  18  elongated. The valve  19  connects to the second inlet  14  of the chamber  10 . In a typical embodiment the valve  19  is a rotatable valve, but in other embodiments it may also be for instance a knife gate valve. 
     The valve  19  may comprise a pivotal valve spindle and a valve spindle housing  20 , enclosing the valve spindle. By turning the valve spindle, the valve  19  may be adjusted to a fully open position, to a fully closed position, or to a desired position therebetween. However, in some embodiments the means for adjusting the opening of the valve may for instance be a button or a lever. The position of the valve spindle is controlled by a control means  21 , which is disposed on the valve spindle housing  20  at one end of the valve spindle. 
     The valve  19  is directly connected to the second inlet  14 , in order to achieve as much control as possible over fluid that will be injected, specifically control over the amount of fluid. The valve  19  may also be used to control the pressure. By having the valve  19  in as dose proximity as possible to the inlet  14 , a higher control of both the amount of fluid and the velocity of the fluid is achieved as compared to having a gap between the valve  19  and the inlet  14 . Typically, it is desirable to achieve a high velocity of the second fluid as it is injected into the first fluid, for achieving higher turbulence and better mixing. 
     The control unit  3  typically comprises a throttle body  22  in the form of a flap or lip  22 , and is vertically adjustable to adjust the area of the flow path. In some embodiments, the throttle body  22  is vertically adjustable by is by having a pivotal axle  23 , and is movable by use of the pivotal axel  23 . However, in some embodiments there is not needed a pivotal axle  23 . The control unit  3 , more specifically the throttle body  22 , may instead be movable vertically by use of height adjusting means, with the purpose of altering the area of the flow path. 
     The flap  22  is arranged inside the chamber  10  and has the shape of a substantially rectangular plate, having a thickness of approx. 10-40 mm. The flap  22  exhibits a top side  24 , facing away from the base portion  9  of the housing  1 , a bottom side  25 , facing toward the base portion  9  of the housing, two parallel long sides facing toward the side walls of the housing, a first end  26  or short side  26  and second end  27  or short side  27  located downstream of the first end  26 . 
     The flap  22  has its first end  26  fixedly connected to the pivotal axle  23  and extends downstream in the flow direction of the pulp suspension. The second end  27  of the flap  22  is free. The flap  22  typically has a length that is approx. 240-450 mm, i.e. slightly longer than the height of the chamber  10  and slightly shorter than the length of the chamber  10 , so that its free end  27 , located downstream, is substantially aligned with the second inlet  14  in an operating position. 
     The free end  27  generally has the form of a substantially angularly shaped U or V, more specifically it comprises at least three parts where the first part  28  and the third part  30  extend further in a vertical direction than the second part  29 . This may be thought of as the first  28  and third  30  parts being protrusions and the second part  29  being an indentation. The free end  27  is shaped in this way in order to achieve a high velocity, which in turns creates more turbulence, of the first fluid and the second fluid, in order to improve the mixing of the fluids. The free end  27  comprises three parts, the first part  28  being located upstream of the second part  29 , the second part  29  being upstream of the third part  30 . The distance from the roof portion  4  of the chamber to the first part  28 , and the distance from the roof portion  4  of the chamber to the third part  30 , are substantially the same, while the distance from the roof portion  4  to the second part  29  is greater than the distances from the roof portion to the first part  28  and third part  30 . 
     The first part  28  of the free end  27  is positioned and shaped such that the flow area is smaller than the flow area directly upstream of the first part  28  of the free end  27 . This provides for a first velocity increase of the fluid at the first part  28 . The end portion of the throttle body  27  is positioned substantially aligned with or downstream of the second inlet  14 , since the end portion of the throttle body is intended to improve the mixture of the fluids it has to be disposed downstream of the injection point of the second fluid. 
     In some embodiments, the second part  29  of the free end  27  is positioned substantially directly below the second inlet  14 , while the first part  28  is located just upstream of the inlet  14 , and the third part  30  is located just downstream of the second inlet  14 . As mentioned, the distance from the second part  29  to the roof portion  4  is greater than the distances from the first part  28  and the third part  30  to the roof portion  4 , which entails that the flow area is larger at the second part  29  of the free end  27  than at the first part  28  and the third part  30 . The third part  30  is positioned substantially the same as the first part in a vertical direction, which means that the flow area at the third part  30  is smaller than at the second part. This achieves a second velocity increase of the fluids when they pass from the second part  29  to the third part  30 . One of the most prevalent problems of current systems is that the mixing is not sufficient, and increasing the turbulence in the fluids improves the mixing. 
     The first part  28  and the third part  30  are adapted to achieve a higher flow velocity of the fluid as compared to the second part  29 , as well as relative to the flow velocity directly upstream of the first part  28 . Typically, the higher and lower flow velocities are achieved by decreasing and increasing the flow area, respectively. This may be done as described above, with the first and third parts having a shorter distance to the roof portion  4  than the second part  29 , thus decreasing the flow area relative to the flow area at the second part  29 , as well as upstream of the first part  28 . 
     In a typical embodiment, the surfaces of first part  27 , the second part  28  and the third part  30  are flat and, in an operating position, substantially aligned with the roof portion and bottom portion of the chamber. In other embodiments the surfaces may be angled in order to achieve a gradual increase and/or decrease in flowrate. The top side  34  of the throttle body  22  is typically angled relative to the roof portion  4  and bottom portion  9  of the chamber, with the throttle body  22  virtually forming an upwards slope for the flow of the first fluid. 
     The flap  23  is possible to vertically adjust, in some embodiments by pivoting it, between a lower end position, where the bottom side  25  of the flap abuts against the base portion  9  of the chamber  10 , and an upper end position, where the free end  27  of the flap  22  abuts against the roof portion  4  of the chamber  10 . The flap  22  has a width that is substantially equal to the width of the chamber  10 . Accordingly, when using the apparatus, the pulp suspension is forced to pass over the top side  24  of the flap  22 . 
     When the flap  22  is located between its end positions, the flap  22  forms a constriction in the flow passage  13 , where the flow area of the flow passage  13  decreases continuously from the first end  26  of the flap  22  to the free end  27 . 
     Immediately downstream of the flap  22 , i.e., directly downstream of its free end  27 , there may be arranged a baffle  31  for redirecting the flow in order to create more turbulence and thus further improve the mixing of the fluids. Typically, the baffle  31  redirects the flow of the two mixed fluids towards the center of the chamber  10 , and the flow area increases downstream of the baffle  31 . The flow area of the flow passage  13 , downstream of the flap  22 , increases to substantially its initial value, i.e. to the same value as directly upstream of the flap  22 . The inlet  14  opens near the free end  27  of the flap  22 , and the steam is typically supplied at or upstream of the free end  27 , in order to maximize the mixing of the fluids. The flap  22  is preferably disposed downstream of where the second fluid is injected into the first fluid, in order to achieve a better mixing of the two fluids. 
     While the pulp suspension passes over the flap  22 , in an embodiment with the throttle body  22  being pivotally arranged, the pulp suspension exerts a torque about the axle  23  on the flap  22 , which tends to push the flap  22  down, i.e. to pivot the flap  22  clockwise about the axle  23 . Accordingly, the top side  24  of the flap  22  constitutes a guiding or diverting surface, which diverts the direction of flow of the flow path  13 , with which surface the pulp suspension interacts to produce said downward torque. 
     There may be arranged spring means which are positioned on a bottom side of the control unit  3  and/or at the bottom portion  9  directly below the control unit  3 . The spring means are intended to act as a counteracting force to the force exerted by the flow of fluid. The spring means may for example be bellows cylinders, pressurized to a predetermined pressure. When the spring means are compressed, they exert a torque on the flap  22  and the axle  23 , which strives to push the flap up, i.e. to pivot the flap  22  anti-clockwise about the axle  23 . 
     At a constant flow rate of the pulp suspension, the flap  22  adjusts itself to an equilibrium position, where the torque that the flow of pulp suspension exerts on the flap  22  is balanced by the torque that the spring means exert on the flap  22  in the other direction. In other words, the spring means are adapted to continuously exert a torque on the flap  22 , which balances the torque that the pulp suspension exerts on the flap  22  at every flow rate of the pulp suspension. 
     If the flow rate of the pulp suspension increases, the flap  22  is pushed down, so that the smallest flow area of the flow passage  13 , i.e. its flow area at the end  27 , increases. If the flow rate of the pulp suspension stabilizes at this new, higher level, the flap  22  adjusts itself to a new equilibrium position, where the flow area of the flow passage  13  at the end  27  is larger than in the previous equilibrium position. If the flow rate of the pulp suspension decreases, the flap  22  is pushed up by the spring means, so that the flow area of the flow passage  13  at the end  27  decreases. If the flow rate of the pulp suspension stabilizes at this new, lower level, the flap  22  thus adjusts itself to a new equilibrium position, where the flow area of the flow passage  13  at the end  27  is smaller than in the previous equilibrium position. Accordingly, an increasing flow rate of the pulp suspension causes the flow area of the flow passage at the end  27  to increase, and a decreasing flow rate causes the flow area to decrease. 
     It will be appreciated that this controlling of the flow area compensates for the decrease and increase, respectively, in the flow velocity of the pulp suspension that results from a decrease and an increase, respectively, of its flow rate. If e.g. the flow rate of the pulp suspension decreases, also the flow velocity of the pulp suspension in the region upstream of the flap  22  decreases, since the flow area in this region is unchanged. However, due to the decreasing pressure of the pulp suspension on the flap  22  in this situation, the flap is pivoted  22  upward and the flow area at the flap  22  decreases. This, in its turn, implies that the flow velocity of the pulp suspension at the end  27  increases and is maintained at substantially the same level as before the flow rate decrease. If the flow rate of the pulp suspension increases, an adjustment is effected in the other direction, i.e. due to the increasing pressure of the pulp suspension on the flap  22 , the flap  22  is pushed down, the flow area above the flap  22  increases, and the flow velocity of the pulp suspension at the end  27  decreases and is thereby maintained at substantially the same level as before the flow rate increase. Accordingly, the flap  22  acts as a throttle body, which controls the flow area of the flow passage  13  while being actuated by the spring means, so that the flow velocity of the pulp suspension is maintained within a desired range. Accordingly, the control unit  3  ensures that a decrease of the flow rate of the pulp suspension does not lead to a situation, where the flow velocity of the pulp suspension at the steam supply position falls below a level where the mixing of the steam risks becoming so inadequate that there is a risk of damaging steam implosions occurring. This is due to the fact that decreasing flow velocity equals decreased turbulence in the fluids, which in turns results in a less effective mixing. 
     In addition to the fact that the spring means abut against the flap  22  with a pushing force, the spring means also dampen any pressure waves which may occur in the pulp suspension, e.g. when the pulp suspension passes over the flap  22 , or if damaging steam implosions still occur. Accordingly, the spring means may also constitute damping means. 
     Accordingly, the flap  22  adjusts itself to an equilibrium position, where the flow of pulp suspension imposes a pushing force on the flap  22 , which is balanced by the force from the spring means. Thus, the flap  22  is self-adjusting and its actual angle relative to the base portion  9  is dependent on the magnitude of the pulp flow. A predetermined flow velocity range may be set by adjusting the abutting force of the spring means against the flap  22 , whereby the desired equilibrium position may be set. By increasing the abutting force of the spring means the axle  23  is rotated so that the flap  22  is pushed up to a new equilibrium position. This implies that the cross-sectional area above the flap decreases, which causes the flow velocity of the pulp suspension at the second inlet  14  to increase as long as the flow rate is kept substantially the same. 
     Accordingly, the apparatus is self-adjusting in that the control unit  3  ensures that the flow velocity of the pulp flow at the second inlet  14  is always within a certain predetermined range, which typically is sufficiently high to avoid, or at least reduce the occurrence of steam implosions. The control unit  3  also ensures that an increase of the flow rate of the pulp suspension does not lead to an undesirably high flow resistance across the apparatus. 
     It will be appreciated that the minimum allowable flow velocity of the pulp suspension at the steam supply position is dependent on a number of factors, e.g. the concentration of the pulp suspension, the steam flow rate, i.e. the amount of steam supplied, etc. As an example of a suitable flow velocity range when supplying steam to a pulp suspension, it may be mentioned that, when mixing steam at a flow rate of approx. 2-20 kg/s into a pulp suspension of medium consistency, the flow velocity of the pulp suspension at the free end  27  should be within the range of approx. 24-35 m/s, if the embodiment shown in the figures is used. 
     In the foregoing, the invention has been described based on a specific embodiment. It will be appreciated, however, that further embodiments and variants are possible within the scope of the following claims. With reference to the above-described embodiment, for example another type of spring means may be used when applicable, e.g. cylinders of piston rod-type. It will also be appreciated that another pushing means may be used, e.g. a piston rod cylinder, a spring-loaded cylinder, or a mechanical spring, e.g. a torsion spring. 
     It will also be appreciated that the throttle body may have a different design than the above-described flap  22 , as long as the intended purpose is still fulfilled. The throttle body may e.g. be wedge-shaped.