A METHOD AND APPARATUS FOR TRANSPORTING A VISCOUS OR NON-FLOWING, LIQUID-CONTAINING PULP

Abstract: A method in the transportation of viscous or non-flowing, liquid-containing pulp, such as papermaking pulp, peat sludge and the like, through a conduit while using a pump arrangement connected to the inlet end of the conduit. In accordance with the method, liquid forced from the pulp as a result of the compression forces to which the pulp is subjected when generating the requisite pump pressure is led away, and at least part of this liquid is supplied to the outlet of the pump, between the surface of the pulp exiting in plug form and the inner surface of the conduit. The pump arrangement suitably has the form of a screw pump having a part which converges conically in the pulpfeed direction, this part of the screw pump being surrounded by a casing having the form of a screen through which water pressed from the pulp is led away. The application also relates to apparatus for carrying out the method.

Description: A METHOD AND APPARATUS FOR TRANSPORT!?.. A VISCOUS OR NON-FLOWING, LIQUID-CONTAIi.ING PULP 5 Technical Field A method for transporting viscous or non-flowing liquid-containing pulp, particularly a fibrous aqueous slurry, such as papermaking pulp, peat pulp and the like, 10 having a concentration corresponding to a dry-solids content of 6-40%, through a conduit with the aid of a pump means located at the inlet end of said conduit.The invention also relates to apparatus for carrying out the method. 15 Background Art In recent years, intensive efforts have be-.r. made to provide possibilitiesof carrying out certain 20 part-processes in the manufacture of pulp at average pulp concentrations, by which is meant at pulp concen¬ trations of 6-20%. Examples of such part-processes include pulp washing, pulp bleaching, chlorine mixing, beating, etc.. 25 The advantages gained when working with average con¬ centrations as opposed to working with low concentra¬ tions, e.g. concentrations in the range of 2-61, i accordance with conventional methods, are that less water is required, which reduces the deleterious e fect 30 of the effluent on the environment among other thin g s; that the volumes to be transported <_re smaller; that smaller apparatus of smaller volumetric capacity c".r. be used; that the chemic.il reaction; are quicker; that less heat is required to heat the suspension to the j. r . requisite reaction temperatures, etc.. RAO ORIGINAL As will readily be seen, there are many advan¬ tages to be had when working with suspensions of average concentration. Conventional apparatus, however, are encumbered with deficiencies and drawbacks whic make working with average concentrations difficult. For example, it is difficult to transport the viscous or non-flowing pulp stock between different treatment stages in a manner which is both rational and economic with respect to energy consumption. Those apparatus normally used to this end are complicated, expensive in manufacture and maintenance, and consume large quantities of energy per quantity of material transported. These high energy costs are primarily caused by the fact that the fricti ' onal forces generated between the pulp and the conduit walls greatly increase with increasing pulp concentrations. These high frictional forces increase the amount of work required of the pump to a much greater extent than the work which is saved by the fact that the total amount of pulp transported decreases at elevated concentrations . Known apparatus for transporting viscous pulp through the various treatment stages include, inter alia, rotary vane pumps, centrifugal pumps which in- corporate means for fluidizing the fibre pulp, and screw pumps. These known apparatus also have other defi¬ ciencies and drawbacks. For example, vane pumps have low efficiency, particularly at concentrations in excess of 15-18%, and feed the stock intermittently, in a pulsating fashion. As a result hereof, it is frequently necessary to overcome the stativ or thresh- hold friction generated thereby. This friction is many times greater than the sliding friction under corresponding conditions. Centrifugal pumps require considerable amounts of energy for fibre-pulp fluidizing alone, and the maximum concentrations at which such pumps can be used is limited to 10-12%. Present day screw pumps have a poor efficiency and create problems with dewatering of the pump on the pressure side of the pump, since there is a tendency for the water released from the pulp to move back into the screw. Objects of the invention The main object of the present invention is to provide a method of the aforedescribed kind which will enable both sluggishly flowing and non-flowing pulp stocks to be transported between treatment stages with far less friction between pulp and the inner wall of the conduit than is possible when applying previously known techniques . Another object is to provide an apparatus for carrying out the method. Disclosure of the Invention Accordingly, the method according to the present invention is characterized by leading away liquid forced from the pulp as a result of the com¬ pression forces to which the pulp is subjected when the requisite pump pressure is generated; and by feeding at least part of this liquid to the outlet end of the pump, between the outer surface of the exiting pulp plug and the inner surface of the conduit. In a preferred embodiment of the method according to the invention, suitable for application when transporting aqueous fibre-slurries, such as papermaking pulp, peat stock and the like through a conduit between different treatment stages, there is suitably used a screw pump having a part or section which converges conically in the feed direction and _.:.I tR>\AT\0 which is surrounded by a casing having a screening plate, through which water presssed from the pulp is led away. Preferably, at leasτ parr of the water pressed from the pulp slurry or stock is passed 5 to the surface of the pulp plug via an annular gap formed between a tubular part of the outlet, end of the pump and the inner surface of the conduit, said tubu¬ lar part projecting into said conduit. This method of procedure results in highly efficient de-watering 10 of the pulp stock and therewith increased concentra¬ tion, while the water which is conducted away is used as a lubricant during transportation of the pulp plug through the conduit connected to the system. An apparatus for carrying out the method 15 according to the invention has the characterizing features set forth in the following claims . Brief Description of the Drawings 20 The invention will now be described in more detail with reference to the accompanying drawings . Figure I is a side view of an apparatus according to the invention, the apparatus casing being partly cut away for the εa e of clarity. 25 Figure 2 is a cro_s-se:ti r.al view taken on the line II-II in Figure 1. Figure 3 is a diagram illustrating the oressure Y of the :ul_. along a diε . a.ι : _- pump conduit. 30 Figux'β - illustrates the pump outlet in the conduit, and also shows how the friction- reducing water is supplied to the pulp plug. Figure 5 is a diagram illustrating the friction generated between pulp and conduit wall, 35 and the total amount of pulp per unit of weight flAD ORIGW-AL dry-solids transported at different pulp concentra¬ tions in a conventional arrangement. Description of a Preferred Embodiment of the invention The screw pump arrangement illustrated in Figures 1 and 2 includes an inlet 1 for pulp which is to be dewatered and transported through a conduit 2. The reference 3 identifies a pump casing which encloses a screw 4, said screw being mounted on a rotatable shaft or core 5. The shaft 5 is unilaterally mounted in a conventional bearing housing 6. Both the casing 3 and the screw . have, downstream of the inlet 1, a cylindrical part which extends over a length LI. The casing and the screw then converge conically over a distance L2. The screw shaft 5 has a free end-part 7 which extends into a cylindri¬ cal casing section S having a length L3. The conical part of the casing comprises a perforated plate, which can be changed when worn. The perforations have the form of conical holes , with a radially, outwardly extending relief taper. The perforated casing 9 is enclosed by an imper ious, sealir.gly fitting outer jacket 1C , εo -is tc form between said jacket and the perforated eating . an annular chamber, which is divided into two separate chambers 11 and 12, by means of a partition wall 13. The conduit 2 is sealingly connected to the outer surface of the pump casing via a flange coupling 1*+, part of the cylindrical end portion 3 of the casing extending into the conduit 2. I this way there iε formed an annular gap 15 between the inner surface of the conduit 2 and the outer surface of the casing 2. The chamber 12 communicates with a circular pipe or tube 17 encircling the casing, via a plurality β*D ORIGINAL of radially extending pipes 15 , see Figure 2 , said pipe or tube 17 in turn communicating with the gap 15 through a plurality of pipes 13 extending from the ring-like tube 17. The references 13 and 20 identify 5 respectively a pipe and a valve for draining away surplus water. A drainage pipe 21 also extends from chamber 11. In the case of a conventional pump arrange¬ ment for raised pulp-concentrations , the total amount 10 of pulp which must be transported decreases for each unit of weight of dry-solid substance, due to the in¬ creased concentration. The wcrk required of the pump, however, is, at the same time, considerably increased as a result of the greater frictional forces occuining between the 15 fibre plug and the inner surface of the conduit wall. This is illustrated in Figure 5, where curve 22 shows the relationship between the pulp concentration in percent plotted on. he abscissa and the amount of pule transported in kg per kg of dry-solid substance, plotted 20 on the ordinate to the right of the diagram, while curve 23 illustrates the friction ' L - i" ' -'._.. ' ir. *" per 3.3m water column plotted on the ordinate to the left of the diagram, in relation to the pulp concentration. With ._ pulp concentration of 8%, for example, friction is 25 relatively low, about 3.*. .-:... m ~ . ?.lthc_.rh the total amount of pulp transported is relatively large, about 12.5kg per kilo of dry-soliJ c__tεtar.ce transported. On the other hand, with a pulp concentration of ~ 20%, the friction is relatively high, about ? k... ' m ' , 30 although the total amount of pulp transported is relatively small, about 5kg per transported . ilo of dry-solid substance. When using a pump arrangement according to the invention, pulp can be pumped at a concentration of, 35 for example, 20%, whereupon, in accordance with the __ «ι_! t ^SXti*- BAD aforegoing, only about 5 kg total quantity pulp need be transported per kilo of dry solid substance, at a friction which is much lower, not exceeding about 2 2.0 kN/m , than the friction generated in known arrange- ments at the same concentrations . This is achieved in accordance with the present invention, by leading away at least part of the water pressed from the pulp when said pulp is compressed as a result of the compression forces to which it is subject- ed when generating the requisite pump pressure; and passing this water in the form of a lubricating water film to the surface of the pulp plug at the outlet end of the pump, thereby to greatly lower the friction between the fibre plug and the inner surface of the con- duit wall. This is achieved with the apparatus illustrated in Figure 1 , by passing part of the water pressed from the pulp plug as it is compressed in the conical casing part 9 to the gap 15, via the pipes 16, 17 and 18, the pulp plug being subjected to a compression in the order of 1,2:1 to 3:1, preferably 1,5:1 to 2,0:1. The water is then passed from the gap 15 and applied in the form of a film between the exiting pulp plug and the inner wall of the conduit 2. This is illustrated more closely in Figure 4, in which the reference 24 identifies the liquid film surrounding the pulp plug 25. The thickness of the film 24 is greatest at its beginning, and then de¬ creases along the length of the conduit. This conforms well with the magnitude of the frictional forces, since these forces are also greatest at the beginning of the conduit, and decrease towards the outlet end. This is illustrated in Figure 3 by means of a diagram showing the pulp pressure Y against the inner wall of the conduit along its length X. It will be seen from the diagram that the pressure is greatest immediately downstream of the pump 26 and decreases towards the container 27 which receives the pulp. As the pulp is compressed in the conical casing part 9 r in the aforedescribed manner, the water pressed from the pulp passing the perforations in the casing, there is normally obtained in the chamber 12 sufficient pressure to transport the water to the gap 15. Alternatively, the water may also be supplied to the gap 15 with the aid of a liquid pump. In order to prevent the water squeezed from the pulp plug from passing back to the cylindrical part LI of the pump, the chamber 11 is provided with a drainage pipe 21, as mentioned in the aforegoing, from which water can run freely. The chamber 11 is therefor pressureless. If desired, however, the partition wall 13 can be omitted, in which case the space surrounding the conical casing part 9 is suitably connected to a pump arranged to transport all of the water pressed through the conical casing part, or part of said water, to the gap 15. When the compressed pulp has left the conical casing part, the pulp as a result of the increasing concentration forming a plug comprising a network of fibres, is fed through the cylindrical part 8 of the casing, and finally leaves through the free end part 7 of the screw 5. In this way there is formed in the plug a cavity 28, as best seen from Figure ■*.. When the pulp plug leaves the cylindrical casing part, the plug 25 attempts to expand.This .expansion, however, is counteracted by the vacuum formed in the- cavity 28. This enables the water to be supplied more readily around the cylindrical surface of the plug, through the gap 15. Generation of the pump force by means of a screw arrangement according to the invention is advan*- tageous in many respects. For example, the screw arrangement according to the invention will advance the pulp plug continuously. Over a certain speed this will eliminate the troublesome tendency towards intermittent or pulsating pulp feed, which as before- mentioned requires considerably more pump energy. The arrangement can also be used for evacu¬ ating air enclosed in the pulp. When the pulp plug is compressed in the conical casing part 9, substan- tial quantities of air are forced from the plug, together with the water. Effective evacuation of this air can be achieved, by allowing the water to pass to a separate container. The shaft 5 can also be pro¬ vided with an axially extending bore, which is connected to a vaccuum pump, for evacuating air from the cavity 28 in the pulp plug 25. The invention is not restricted to the afore¬ described embodiment, which can be modified in several respects within the scope of the Claims. For example, a pump arrangement according to the invention can also be used for pumping other viscous or non-flowing sub¬ stances of different natures, up to concentrations of about 40%. Although the aforedescribed screw pump affords considerable advantages, it is also possible in certain cases to use other kinds of pumps. Naturally, in screw pumps the number of screw threads and the thread pitch can be varied as desired. The tubular part of the pump casing projecting into the conduit may alternatively comprise a tubular section mounted to the pump casing. The screw pump may also be modi¬ fied in other respects and adapted to the particular use to which it is to be put. The gap 15 may also be replaced by a ring of holes, slots or other orifices through which liquid can be supplied to the surface of the pulp plug.

Claims: C A I M S 1. A method in the transportation of viscous or non-flowing, liquid-containing pulp through a conduit with the use of a pump arrangement connected to the inlet end of said conduit, characterized by leading away liquid forced from the pulp as a result of the compression forces to which the pulp is subjected when the requisite pump pressure is generated; and bysupplying at least part of this liquid to the outlet end of the " pump between the outer ' surface of the exiting pulp plug and the inner surface . of the conduit. 2. A method according to Claim 1 for transporting aqueous fibre-slurries, such as papermaking pulp, peat sludge and the like, characterized by using as said pump arrangement a screw pump having a part which con¬ verges conically in the pulp-feed direction, said part being surrounded by a casing having the form of a screen through which the water pressed from the pulp, is led away. 3. A method according to Claim 2, characterized by passing at least part of the water pressed from the pulp to the surface of the pulp plug, via an annular gap formed between a tubular part of the outlet end of said pump projecting into the conduit and the inner surface of said conduit. 4. A method according to any one of Claims 1 - 3, characterized in that the pulp.concentration corresponds to a dry-solids content of 6-40%. 5. Apparatus for transporting a viscous or non- ■< _.E Cf OMPI_ flowing liquid-containing pulp through a conduit (2), said apparatus comprising a pump arrangement connected to the inlet end of said conduit, characterized by • means (9) for leading away liquid forced from the pulp as a result of the compression forces to which the pulp is subjected when the requisite pump pressure is genera¬ ted, and means (15-18) for supplying at least part of said liquid to the outlet end of the pump, between the surface of the exiting pulp plug (25) and the inner surface of the conduit (2). 6. Apparatus according to Claim 5 intended for the transportation of aqueous fibre-slurries ' , such as paper- making pulp, peat sludge and the like, characterized in that the pump arrangement comprises a screw pump having a part (L2) which converges conically in the pulp-feed direction, said part being surrounded by a casing having the form of a screen (9) through which the water pressed from the pulp is led away. 7. Apparatus according to Claim 6, characterized by an annular gap (15) formed between an tubular part (8) of the outlet end of said pump and the inner surface of said conduit, said tubular part projecting into said conduit (2), and by passages (16-18) for supplying at least a part of the water pressed from said pulp to the surface of the pulp plug (25) via said gap (15). 8. Apparatus according to Claim 6 or Claim 7, characterized in that a liquid pump is provided for feeding the water through said passages (16-18). 9. Apparatus according to- Claim 7 or Claim 8 , characterized in that a free end part (7) of the screw core (5) projects into the tubular part (8) of the outlet end of said pump projecting into said conduit (2) 10. Apparatus according to Claim 9 , characterized in that an air pump is connected to a central aperture in the screw core (5) , for evacuating airpressed * but into the cavity (8) formed in the pulp plug (25) by the screw free end part (7) of the screw core (5). OMPI

Inventors: BERGGREN TORSTEN LENNART, BERGGREN, TORSTEN, LENNART
Applicants: BERGGREN TORSTEN L, BERGGREN, TORSTEN, LENNART
Application year: 1983
Main classification: B65G33
IPC codes: B30B9, B65G53, D21G9