Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
  • D21D5/26—De-aeration of paper stock
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D19/00—Degasification of liquids
  • B01D19/0042—Degasification of liquids modifying the liquid flow
  • B01D19/0052—Degasification of liquids modifying the liquid flow in rotating vessels, vessels containing movable parts or in which centrifugal movement is caused
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/18—Rotors
  • F04D29/22—Rotors specially for centrifugal pumps
  • F04D29/2261—Rotors specially for centrifugal pumps with special measures
  • F04D29/2288—Rotors specially for centrifugal pumps with special measures for comminuting, mixing or separating
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D7/00—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts
  • F04D7/02—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts of centrifugal type
  • F04D7/04—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts of centrifugal type the fluids being viscous or non-homogenous
  • F04D7/045—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts of centrifugal type the fluids being viscous or non-homogenous with means for comminuting, mixing stirring or otherwise treating

Definitions

• the present invention relates to an apparatus and a process for separating a gas such as air from a low viscosity liquid such as water in connection with pumping a mixture of said gas and liquid.
• the invention also relates to the use of the apparatus for pumping backwater draining through a forming fabric of a paper machine and for pumping fluid material separated by flotation.
• gas enclosed or generated in a fluid to be pumped causes prob ⁇ lems.
• the gas disturbs the pumping.
• the gas separating from the fluid under the influence of the centrifugal forces in the pumping chamber forms a gradually growing gas bubble, which decreases the power of the pump until the bubble finally is discharged.
• such irregular function causes great disturbances.
• the backwater draining through the forming fabric in a paperma- king process normally, contains a large amount of enclosed air. Since the short circulation of a paper machine requires a particularly constant flow, the disturbing air is normally removed by conducting the drained backwater, by means of special pipe or channel systems, from the dewatering box or boxes to an open backwater tank, from where it is pumped back to the fibre process of the short circulation preceding sheet forming.
• Air contained in the thin stock of the papermaking process also disturbs the stability of flow in the short circulation and disturbs the forming of the paper sheet by causing voids or holes in the sheet and by retarding the drainage of water.
• the backwater tanks and other parts of the system are traditionally desig ⁇ ned for very low flow speeds in order to provide sufficient time for the enclo ⁇ sed air to emerge and be removed before the backwater is pumped into the closed part of the short circulation.
• Pumps which are able to separate gas from a fluid to be pumped are well known as such, but the objective of such pumps is normally just to remove a sufficient portion of the gas to enable regular pumping.
• the known pumps are normally not capable of removing enough gas for achieving the degree of free ⁇ dom of air, which is required for using the fluid directly for example in a paper- making process without further deaeration.
• Deaerating pumps have also been designed for the treatment of fibre suspensions with a rather high solids con ⁇ tent and having a high viscosity. In such pumps the separation of gas is gene ⁇ rally caused by high shear forces in the highly viscous fluid which is to be pumped.
• Patents such as US 2,575,568, US 3,203,354, US 3,323,465, US 3,856,483, US 4,201 ,555, US 3,942,961 , US 4,600,413, US 4,908,048 and EP 430636.
• the object of the present invention is to improve the function of known proces ⁇ ses and apparatuses in order to provide an essentially complete separation of gas from a liquid of relatively low viscosity such as water.
• the object of the invention is also to provide the liquid to be pumped essential ⁇ ly free of gas and the gas essentially free of liquid.
• the process and the apparatus according to the invention are particularly well suited for fast and controlled recycling of backwater drained at the forming of a paper or board web back into the short circulation fibre process, whereby the degassed backwater can be recycled without separate deaeration.
• the object of the invention is to provide a technically simple pump which can remove gas such as air essentially totally from a low viscosity liquid such as water and separate the liquid essentially completely from the removed gas.
• the object of the invention is further to provide a pump which does not influen ⁇ ce the incoming flow of liquid to the pump and which is substantially self adjus ⁇ ting according to the incoming flow within a function range.
• the object is further to provide a self adjusting gas separating pump, the func ⁇ tion range of which can easily be adjusted by adjusting its speed of rotation.
• the object of the invention is further to provide a gas separating pump, which can be connected to a vacuum source, and particularly so that the pump can be connected between the vacuum source and the suction object.
• the object of the invention is also to provide a means for extinguishing foam and to pump foaming liquid while separating gas from said the liquid.
• the object of the invention is further to provide a process for separating gas in combination with pumping.
• the object of the invention is to enable fast and controlled recycling of backwater from a paper or board forming process to the fibre process. Further the object of the invention is to enable air separation and controlled processing of fluid material separated by flotation.
• the present invention thus relates to an apparatus for pumping a mixture of a gas such as air and a low viscosity liquid such as water and for separating said gas and said liquid from each other.
• Said apparatus comprises a hollow shell of a circular cross-section having at one end thereof an inlet for said mixture and at the opposite end an outlet for separated liquid.
• Said apparatus further com ⁇ prises a rotor having vanes for causing said mixture to rotate and a gas outlet extending into a gas column formed in the center of said pump chamber.
• said shell consists essential ⁇ ly of a gas separation part at said inlet end and a larger diameter pump cham ⁇ ber at said outlet end, the inner wall of said gas separation part comprising a large gas separation surface for the essentially complete separation of said gas from said mixture, and said vanes of said rotor have essentially the same confi ⁇ guration as said gas separation surface and extend close to said surface.
• Sard shell of said apparatus has an elongated centrifugal separation part provi ⁇ ding said large gas separation surface.
• Said separation part is smoothly connec ⁇ ted to said larger diameter centrifugal pump chamber.
• Said vanes of said rotor are preferably cut away at the center of said pump chamber so as to leave an open space defining a vortex chamber for the gas.
• a vacuum source connected to said gas outlet provides means for the suction of gas from the apparatus.
• the vacuum source can simultaneously act as a vacuum source for the forming zone of a paper machine, said vacuum being applied through the apparatus.
• nozzles are provided in the rotor shaft and/or at the outlet end of the shell, for spraying fluid into said open vortex so that foam generated or supplied to the gas separation surface will be extinguished through the action of the sprays.
• the present invention also relates to a process for separating a liquid of low viscosity such as water or the like aqueous liquid from a relatively lighter gas such as air, and pumping the liquid separately from said gas.
• the steps of said process comprise bringing said mixture into rotation in a gas separation part of a gas separation pump having a circular cross-section for causing said mixture to flow towards a large gas separation surface formed by a wall of ;d gas separation part; causing said rotating mixture to flow along said gas separation surface in an essentially laminar flow in a thin fluid layer on said gas separation surface and causing said gas to separate from said liquid due to said rotation of said mixture to form a gas column at the center of said gas separation part; causing said separated liquid to flow along said gas separa ⁇ tion surface into a larger diameter pump chamber connected to said gas separa ⁇ tion part while continuing said rotation, thus causing said liquid to form a liquid ring at the periphery of said pump chamber; and discharging said liquid from said periphery of said pump chamber and discharging said gas from said gas column at the center of said pump chamber or said gas separation part.
• the gas is discharged by means of vacuum applied to said central gas column through said gas outlet. Due to the central gas column vacuum applied to said outlet also causes vacuum in the inlet pipe of the pump. Applied vacuum also causes the gas bubbles enclosed in the liquid to expand which further facilitates the separation of gas and liquid.
• foam floating on the separa ⁇ tion surface is extinguished by spraying fluid into the central gas column.
• Fig. 1 shows a section of a gas separation pump according to a preferred embodiment of the invention seen from the side. This Figure also shows the liquid and gas flowing in the pump;
• Fig. 2 shows a section of the gas separation pump of Fig. 1 along line A-A;
• Fig. 3 shows a section of the gas separation pump of Fig. 1 along line B-B;
• Figs. 4 and 5 show sections of gas separation pumps according to other embodiments of the invention seen from the side;
• Fig. 6 shows a section of the gas separation pump of Fig. 4 along line C-C
• Fig. 7 shows a section of a gas separation pump according to a 'favorable embodiment with foam extinction nozzles of the invention seen from the side;
• Figs. 8 and 9 show the use of gas separation pumps according to the inven ⁇ tion in papermaking processes
• Fig. 10 shows the use of a gas separation pump according to the invention in connection with a compact flotation device.
• the gas separa ⁇ tion pump indicated by a general reference 10 comprises a hollow shell 12 having a circular cross-section and in said shell a rotor 16 having vanes 14 which essentially follow the shape of the inner surface of said shell 12.
• a rotor 16 having vanes 14 which essentially follow the shape of the inner surface of said shell 12.
• Said shell 12 at said inlet end 18 forms an elongated gas separation part 26, the wall of which provides a large separation surface.
• the gas separation part shall, according to the invention be sufficiently long, for allowing sufficient time and space for the liquid fed through inlet 20 and possible sprays resulting from the action of rotor 16 in the inlet end of the apparatus, to settle at said separation surface and for any gas enclosed during this settling to separate.
• the diameter of separation part 26 should be relatively small compa ⁇ red to the length of said separation part 26.
• the separation part 26 should have a diameter which is smaller than its length, preferably smaller than half of its length.
• the gas separation surface shall, according to the invention, be sufficiently large for letting the gas separate from the liquid when the mixture flows through said separation part.
• a thin fluid layer 27 of the mixture forms on the surfaces of the separation part 26. In the thin layer the distance for the gas to reach the surface 31 of the mixture is short.
• the separated gas forms a gas column 28 surrounded by the mixture layer 27. Said layer 27 gradually releases ail contained gas and trans ⁇ forms into a gas free liquid layer.
• the present invention is mainly designed to be used only for liquids of a relati ⁇ vely low viscosity which flow easily along a surface. No excessive shearing forces are applied to the liquid-gas mixture by the pump. On the contrary a laminar flow of liquid is desired so as to avoid mixing gas into the liquid.
• the fluid layer 27 Due to the rotation of said rotor 16 the fluid layer 27 is caused to rotate rapid ⁇ ly in said shell 12 and is subject to a centrifugal force, which causes the enclo ⁇ sed gas bubbles in the mixture to raise rapidly to the surface of the mixture and from there towards the center of the gas separation pump forming gas column 28.
• the vanes 14 of rotor 16 In the separation part 26 the vanes 14 of rotor 16 must extend so closely to the inner surface of said shell 12 that the fluid layer 27 is not disrup ⁇ ted through the force of the vanes 14 but retains an essentially laminar flow.
• said vanes 14 are at this point preferably shaped in a spiral form which follows the natural flow path of the mixture when accelerating.
• the gas sepa ⁇ ration pump according to the invention is thus self adjusting within certain limits.
• the pressure of the pumped liquid can also be adjusted by adjusting the rotation speed of the rotor 16, and thus the range of self adjustment can be set to meet prevailing operating conditions.
• the separation part 26 smoothly trans ⁇ forms into the pumping chamber 30 without any distinct transition point.
• the shell 12 enlarges like a funnel and smoothly from a separation part to a pump chamber. Thanks to the smooth construction the liquid layer 27 can flow without disruption from separation part 26 to pump chamber 30. A violent transition might cause a disruption of the laminar flow and cause gas to mix into the liquid already freed from gas. In order to avoid violent acceleration at the transition area between separation part and pump chamber, where the gas column might enlarge, it is favorable to let the vanes 1 follow a spiral path at this point.
• the geometrical shape of the separation part 26 is not limited to this form.
• the invention functions also if the separation part is shaped like a cone or has an intermediary shape.
• the gas column should occupy a significant portion, preferably not less than half of the available volume of the gas separation part 26 of shell 12.
• the fluid layer 27 will remain relatively thin, preferably less than one sixth of the diameter of the gas separation part, whereby the centrifugal forces cause only a modest pressure build up in said fluid layer, and excessive compression of the gas bubbles enclosed in said fluid layer is avoided.
• the diameter of the pump chamber 30 is favorably significantly larger than that of gas separation part 26.
• the space between vanes 14 and shell 12 In order to maintain a smooth laminar flow throughout the apparatus and for avoiding disruptions in the laminar flow of fluid layer 27, the space between vanes 14 and shell 12 must be small compared to the thickness of fluid layer 27.
• the space between said vanes 14 and said separation surface should thus be less than 1/10 of said diameter of said gas separation part 26 and prefe ⁇ rably about 1 20 to about 1 /60 of said diameter.
• vanes 14 of rotor 16 therefore preferably increase in diameter in the same way as the shell 12, following closely the inner surface of the shell all the way from the separation part 26 to the pump chamber 30.
• the rotor 16 is driven by a shaft, which extends through both ends of the shell 12, but in other embodiments, the shaft may be arranged to go through only one of the two ends.
• the vanes are preferably shaped so that in the center of the pumping chamber 30 at the outlet end 22 remains a central space without vanes constituting a vortex chamber 34.
• a gas outlet 32 through which the gas accumulating in the gas column 28 is removed.
• the gas is always remo ⁇ ved from the gas column 28 and preferably from vortex chamber 34, where the liquid has essentially totally been separated from the gas.
• the gas outlet may alternatively be arranged centrally or decentrally through the outlet end 22 of the shell 12 or through a tubular shaft of rotor 16 through either end of the shell 12.
• gas outlet 32 is connected to a va ⁇ cuum source (not shown), so that the gas cumulating in gas column 28 may be removed by suction.
• the vacuum causes the gas bubbles enclosed in the fluid layer 27 to expand, thus increasing their flow speed towards the liquid surface 31 and into gas column 28. If the applied vacuum is deep enough, it causes the liquid in fluid layer 27 to boil, whereby also dissolved gas is libe ⁇ rated and removed from the liquid.
• gas separation pump 10 according to the present inven ⁇ tion will be especially evident when said pump is used in a paper making pro ⁇ cess and the vacuum needed for drainage at the papermaking machine forming fabric is caused by suction through the gas outlet 32 of the pump.
• the vacuum at the forming fabric can be applied either through the inlet pipe 20 or through a separate suction pipe (not shown) connected to the inlet end 18 of pump 10.
• a stable flow of backwater to the pump 10 may be provided either by feeding the drained backwater to said pump 10 through an inlet pipe so spacious that the backwater surface always remains open, or by keeping the inlet pipe cons ⁇ tantly full of water when applying the vacuum at the forming fabric through said separate suction pipe.
• FIG. 2 shows a section A-A of the pump 10 of Fig. 1 , which shows the pre ⁇ ferred tangential junction of inlet 20 to the inlet end 18 of shell 12. Due to the tangential feeding the mixture of gas and liquid has an initial spiral motion. The mixture can also be fed into the pump 10 through multiple, preferably circu ⁇ larly arranged inlet pipes (not shown). As seen in Fig 2 the vanes 14 of rotor 16 extend close to the inner surface of shell 12. The vanes 14 are formed in a spiral shape in order to allow a smooth acceleration of the liquid, avoiding excessive turbulence.
• the gas column 28 continues as a void space 21 in the spa ⁇ cious inlet pipe 20 so that the gas pressure in the gas column 28 and the inlet pipe 20 are the same, and the liquid can freely flow into the shell 12 forming a relatively thin fluid layer 27 on the inner surface of shell 12 by influence of the centrifugal force caused by vanes 14.
• Fig 3 represents the section B-B, at the outlet end of the pump 10 of Fig 1.
• Fig 3 shows the pump chamber 30 with its larger diameter, the outlet 24 which extends in a spiral form around the pump chamber 30 and the liquid ring 29 formed during use in the pump chamber.
• the inner diameter of the liquid ring 29 varies according to the operating conditions, changing the shape and diameter of the inner surface 31 of fluid layer 27.
• Fig 4 shows another embodiment of the present invention.
• the reference num ⁇ bers used in Fig 4 correspond to those presented in Fig 1.
• the shaft of rotor 16 passes only through the inlet end 18 of shell 12.
• the inlet 20 is shaped as a spiral, permitting a smooth and symmetrical distribution of the inlet flow to the fluid layer 27 of separation part 26.
• Fig 5 shows an other embodiment of the present invention.
• the reference num ⁇ bers used in Fig 5 correspond to the parts presented in Fig 1.
• the gas outlet 32' is in this embodiment incorporated into the shaft of the rotor 16, and said shaft goes through only the inlet end 18 of shell 12.
• there may be other arrangements of the rotor shaft and gas outlet which are obvious to those skilled in the art and which do not alter the overall function of the apparatus.
• Fig 6 representing a section of the pump of Fig 5 along line C-C, although drawn in smaller scale, the number of vanes 14 in the pump chamber 30 can be larger than that in the separation part 26, additional winglets 36 are provided in order to improve the circulation of the liquid in the liquid ring (not shown) and decrease pressure pulsations at the liquid discharge 25.
• the wing ⁇ lets 36 are fixed to the rotor 16 in any known manner (not shown).
• Fig 7 represents a preferred embodiment of the apparatus for separating gas and pumping the essentially gas free liquid when the fluid mixture is a foam or strongly tends to form foam.
• the apparatus is in other respects essentially similar to the embodiment of Fig 1 but it further comprises feeding pipes 40 for spraying fluid into gas column 28 through nozzles 41 arranged in the outlet end of shell 12.
• the pipes 40 and nozzles 41 are preferably adapted for spraying fluid into vortex chamber 34.
• the vortex chamber has been expanded in order to permit free access of sprayed fluid to a larger part of liquid surface 31 .
• the vanes 14 have deflectors 43 turned towards nozzles 41 . Further towards inlet end 18 of the apparatus other deflectors 44 are fixed on the rotor 16.
• the deflectors 43, 44 are designed so that they will be hit by a distinct fluid jet 42 from a nozzle 41 , causing the jet to disintegrate into droplets 45 and directing these droplets towards the fluid surface 31 of fluid layer 27 on the inner wall of the shell 12.
• nozzle 41 A Another type of nozzle is shown at 41 A.
• This nozzle 41 A is of a known type for direct spray of fluid droplets onto surface 31.
• spray nozzles (not shown) may be incorporated into the rotor and fed through a duct in the rotor shaft in a way easily understood by those skilled . in the art.
• a combina ⁇ tion of different types of spray nozzles is contemplated within the scope of the present invention.
• Droplets 45 sprayed from the nozzles and hitting the surface 31 cause foam on this surface to collapse.
• a large gas separation surface is formed in the separation part 26 and that the rotor vanes 14 closely follow this surface so that a thin rotating liquid layer 27 can be formed on said surface.
• Gas separated by means of the centrifugal force is collected into a distinct gas column 28, from where it is removed.
• the large separation surface is provided by the elongated separation part 26 having a length substantially exceeding its diameter.
• suction needed for other purposes can be applied through the present apparatus.
• foam will be extinguished by spraying fluid into the gas column.
• a mixture of gas and liquid is separated into an essentially gas-free liquid an essentially liquid-free gas.
• the liquid is a low viscosity liquid like water and the gas is air or another gas subs- tantially lighter than the liquid component of the mixture.
• the liquid- may con ⁇ tain minor amounts of fibers or other impurities such as ink particles which do not, however, make the fluid mixture viscous.
• the gas/liquid mixture is fed for instance into the gas separation pump 10 of Fig. 1 through inlet pipe 20.
• the mixture is brought into rotation by rotor 1 6 so that it is slung onto the gas separation surface formed on the inner surface of shell 1 2 in gas separation part 26.
• a rotating liquid layer 27 is formed on said surface.
• the lighter gas enclosed in the liquid strives out from the liquid towards the center of the apparatus for ⁇ ming a gas column 28.
• the heavier liquid droplets collect at the shell wall and form a liquid layer 27 on the gas separation surface. The enclosed gas will easily pass through the thin liquid layer, separate from the liquid and transfer into the gas column in the center of the apparatus.
• the liquid flows continuously from the inlet end 18 towards the outlet end 22 along the separation surface of the separation part 26 reaching the pump chamber 30 which is smoothly connected to the separation part 26.
• the diame ⁇ ter of the shell 12 increases at the transition between separation part 26 and pump chamber 30, whereby the rotating, now essentially gas free liquid is pressed toward the periphery of the pumping chamber 30, forming a liquid ring 29.
• the liquid ring due to centrifugal forces, is pressed into the liquid outlet 24, which extends as a spiral around the periphery of the pump chamber 30, and is discharged through the discharge pipe 25.
• the lighter gas correspondingly, collects into the center of the apparatus, and forms a gas column 28, limited towards the rotating fluid 27 by a surface 31 . From this gas column 28 the gas can be removed and thus separated from the liquid.
• the gas is preferably removed from a vortex chamber 34 at the center of the pump chamber 30.
• the gas may be discharged either through a gas outlet 32 in the outlet end 22 of the shell 12 or through the rotor shaft in either outlet or inlet direction.
• the depth of liquid ring 29 in pump chamber 30 automatically adjusts, within certain limits, to the flow of entering fluid so that a pumping pressure suffi ⁇ cient for pumping the liquid forward is obtained.
• the more fluid that enters the pump the deeper the liquid ring and the higher the pumping pressure.
• the depth of the water ring as a function of the pressure difference can be adjus ⁇ ted by adjusting the rotation speed of the rotor. By adjusting the rotation speed the depth of the water ring can be adjusted according to the flow of incoming gas and liquid mixture and the required pumping pressure.
• the pump is self-adjusting. Without disturbing the process, the depth of the liquid ring in the pumping chamber can vary within a relatively large range, as long as the fluid layer 27 is not disrupted, no gas enters the liquid outlet 24 and no significant amount of liquid enters the gas outlet 32.
• a suction source may be connected to the gas outlet 32 for improving the gas separation.
• a suction source is particularly preferred when suction is needed at the source of the mixture of gas and liquid. Due to the open gas column 28 formed in the center of the pump being in direct connection with a void space 21 in the inlet pipe 20, the suction applied at the gas outlet 32 will affect also equipment upstream of the pump 10. Particularly in the case when the mixture contains considerable amounts of gas, so that it rather consists of liquid droplets in an aerosol, the flow speed of the mixture can be increased by connecting suction to a pump according to the invention.
• Foam flowing into the pump or forming in the same concentrates on the sur ⁇ face 31 of the fluid layer 27 and collapses rapidly due to the centrifugal forces, whereby the gas is liberated and strives towards the center.
• Particularly stable foam may be extinguished by directing sprays of a fluid, such as a liquid, towards the surface 31 of fluid layer 27.
• Spray nozzles are designed to spray the fluid within the void space of gas column 28, preferably through vortex chamber 34.
• the gas separation pump according to the present invention is especially well suited for recycling paper machine backwater into the short circulation fibre process.
• Figs 8 and 9 represent a particularly favourable use of gas separation pumps in a process according to the co-pending patent application FI 922285, by the same inventor. It is obvious for the person skilled in the art that the present invention offers significant improvement also to conventional paper ⁇ making processes, by increasing recycling speed of backwater and eliminating the need for huge backwater tanks.
• the solution according to Fig. 8 represents a papermaking process, where thin stock is fed through a head box 100 onto a forming wire, for the forming of a web.
• Backwater draining through the forming wire is collected in drainage boxes 101 , suction boxes 102 and the suction roll 103 and flows directly into gas separations pumps 1 0, 10' and 10", according to the present invention.
• the gas separation pumps 10 r and 10" relating respectively to suction boxes and to a suction roll may be connected to a vacuum source (not shown) for providing the suction needed in said suction boxes and said suction roll.
• the gas separating pumps 10, 10' and 10" separate the air contained in the backwater and feed the backwater as separate air free flows to various dilution points in the primary fibre process.
• Sard fibre process goes from stock prepara ⁇ tion 1 24 through a mixer 123, centrifugal cleaner 1 22, screen 1 21 and stock distributor 1 25 to the headbox 100 and further to paper web forming.
• the solution according to Fig. 9 represents a papermaking process, wherein essentially the same reference numbering is used as in Fig. 8. in the process according to Fig. 9 the first part of web forming is made in a closed space and closed draining boxes are used for an air free recycling of backwater from the forming fabric to the fibre process. In the first, closed part of forming the back ⁇ water is thus recycled free of air by means of conventional centrifugal pumps 1 1 , whereas backwater resulting from that part of the fabric where air will or can be pass through the fibre web is recycled by gas separation pumps 10 according to the present invention.
• the gas separation pumps according to the present invention thus provide means for fast and direct recycling of essentially air free backwater into the fibre process of a papermaking machine wet end.
• a part of the collected backwater is fed to a fibre recovery unit 50 which is preferably designed according to co-pending patent application FI 930247 by the same inventor.
• this fibre recovery unit represented in detail in Fig. 10
• fibres are separated from the backwater flow 61 by means of an air sparged hydrocyclone 51 , forming a foam column 65 in the center of said hydrocyclone.
• Clear water, essentially free from solids is dis ⁇ charged through clear water discharge 63 and fed out from the short circula ⁇ tion.
• the foam from column 65 is extinguished in a foam extinguisher 52 by influence of white water fed into spray lines 62 and flows further into gas separation pump 53, which feeds the recovered stock 64, essentially free of air, directly into the fibre process.
• the present invention thus provides a means for separating air from the pro- duct of such a compact flotation process, providing a means for the fast recyc ⁇ ling of recovered fibres in the paper machine wet end.
• the gas separa ⁇ tion pump according to the present invention provides a means for handling foam resulting from other flotation processes, like deinking of waste paper.
• Gas separation pumps for handling foam from flotation processes can favorab ⁇ ly be of the type with integrated foam extinguishing, as represented by Fig. 7.
• the present invention is further illustrated by the following Table, in which a small pump designed in accordance with the present invention runs with a flow of 10 and 20 liters per second, respectively (two first columns), and a bigger pump with a capacity of 200 liters per second.
• the Table shows the principal dimensions of a pump in millimeters, the rotation speed in revolutions per minute, the thickness of the liquid layer in the separation part in millime ⁇ ters.
• the increase of the vortex between separation part and pump chamber in millimeters represents the step, i.e. the increase in radius of the gas column in the vortex chamber.
• the equivalent separation surface represents an open surface, which would have the same gas separa ⁇ tion capacity as the gas separation pump in the example.
• the equivalent flota ⁇ tion speed indicates the minimum separation speed in an open flotation basin for gas which is essentially totally separatable by a separation pump.
• the pump of the first column would separate all gas having a flota ⁇ tion speed of 4.53 centimeters per minute or more in an open basin.
• the foam containing ink may preferably be handled by a gas separation pump according to the present invention in the same manner as the fibre material recovered according to the process described above.
• the suspension of deinked fibres resulting from a deinking flotation process is typically saturated by air and the relatively stable fibre network traps the enclo ⁇ sed air bubbles and makes the handling thereof in gas separating pumps parti ⁇ cularly difficult.
• the separation of gas will be only partial, but due to the huge gas separation capa ⁇ bility and smooth flow in the pump, the pumping will be very stable and the pump will function in a self regulating manner as explained above.
• the fibre suspension can also be brought to boil, whereby the enclosed bubbles expand and a total separation of gas is obtai ⁇ ned.
• the present invention has been described principally as a pump solution rela ⁇ ting to the paper industry, ft is, however, obvious for the persons skilled in the art that the pump can be used for many other purposes when gas is to be removed from a liquid, and a liquid containing gas is to be pumped substantial ⁇ ly free of gas.

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Cited By (6)

Citations (4)

• 1993
  • 1993-05-19 WO PCT/FI1993/000212 patent/WO1993023135A1/en active Application Filing
  • 1993-05-19 AU AU40712/93A patent/AU4071293A/en not_active Abandoned

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