Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
  • B01J8/005—Separating solid material from the gas/liquid stream
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
  • B01J8/08—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with moving particles
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C7/00—Digesters

Definitions

• the present invention relates to continuous production of cellulose pulp by means of a combined chemical and mechanical method for digesting plant and wood fibers to cellulose pulp to be used as raw material for paper, board, fiber boards and fiber-containing products.
• the present process is also well suited for deinking, delignification and optionally bleaching of secondary fiber and can also include fiber fractionation.
• a sulphate mill is a complicated system composed of a large number of strongly different process and machinery elements, and the mill is divided into separate departments for respectively cooking, screening, washing and bleaching, each department having separate heat, water, chemicals and effluent systems.
• the sulphate mill of today is usually characterized by upright high pressurized digesters into which the fibers are fed at the top and at a high consistency which cannot be pumped, and later the fibers move vertically down through the digester in accordance with the "free fall” principle, and subsequently the fibers are diluted to a pumpable or "blowable" consistency at the bottom of the digester.
• the temperature and pressure used during the digestion of the pulp are usually determined by the fixed relationship between pressure and temperature of saturated steam which traditionally is used as heat source in the digester.
• the pulp mill comprises a very large number of different machines, operations and functions which all represent possible sources of failure and which demand corresponding surveillance, maintenance and a comprehensive and expensive inventory of several spare parts.
• the present process involves, compared with the conventional cellulose pulp manufacturing process of today, a substantial simplification of the process operation and of the process equipment with reduced demand for capital, area, surveillance and maintenance.
• the invention relates to a process for digesting plant and wood fibers or for delignification,optionally with preceding deinking, of fibers from chemical or mechanical pulps, possibly with subsequent bleaching, in order to obtain a pulp which is suitable as raw material for paper, board, fiber boards and other products containing plant and/ or wood fibers, wherein the fiber-containing raw material is introduced into a digestion zone and is digested or delignified therein in alkaline slurry at elevated temperature and pressure using an alkaline cooking chemical in combination with oxygen and, optionally, minor amounts of other additions, like e.g.
• Fig. 1 shows a flowsheet for an embodiment of the process according to the invention, including four dewatering steps and with stepwise building up of the pressure from the first dewatering step to the fourth dewatering step
• Fig. 2 shows schematically the relative pressure increase according to the flowsheet of Fig. 1, from the start of the digestion process to the termination thereof, from left to right in the Figure,
• Fig. 3 shows a Sankey diagram for the process according to the flowsheet shown in Fig. 1, for the supplied and recirculated amounts of liquids or chemical solutions, and Fig. 4-24 will be more detailed discussed below in connection with the description of the process.
• raw material 1 and fresh water 2 are supplied to a pulper 3, and from the pulper the raw material and fresh water is by means of a pump P 1 and a cleaning device 4 transferred to a pump P 2 in which the pressure exerted upon the slurry, which has a consistency of about 4%, is increased to the pressure level p 2 .
• the slurry is pushed through a dewatering device 5 which will be further described below and in which the slurry is dewatered until it reaches a consistency of from about 10 to 30%.
• the dewatered pulp is diluted with cooking liquor which has been recycled from pressure increasing stages and/or pressure dewatering stages further downstreams in the process.
• fresh solutions of chemicals and/or further heat 6 can be supplied to the slurry in the tube section between the dewatering device and the pump P 3 .
• the liquid 7 pressed out in the dewatering device 5 is mainly transferred to a heat exchanger 8 in which the pressed out liquid (waste liquor or waste water) is passed in heat exchange relationship to fresh water supplied or possibly to waste water 9 from a bleach plant .
• Part of the liquor which has been pressed out from the dewatering device 5 can also be supplied to the pulper 3 in order to form the raw material slurry therein which has a consistency of about 4%.
• the pulper 3 Before the slurry enters the pump P 2 and thence into the dewatering device 5 it is provided with a used solution 12 of cooking chemicals which has been recycled from the digesting tube immediately after the pump P 3 which is responsible for the next following pressure increase stage. From the pumping stage p 3 (Fig.2) the pulp is transferred to a new pumping stage p 4 in which the pressure exerted upon the slurry is further increased and with recirculation of cooking chemicals 13 to the slurry between the two pumping stages p 3 and p 3 .
• the used cooking liquor 14 which is recycled to the tube section between the pumping stage p 3 and the pumping stage p 4 is taken from the digesting tube immediately after the next following pressure increasing pumping stage p 5 . From the pump P 4 the slurry is then, while still at a pulp consistency of about 4%, transferred to the next pressure increasing pumping stage p 5 , and from this pumping stage the slurry is transported further and again with supply of recirculated used cooking liquor 15 to the pressure pump P 6 from which the slurry is conducted further through the next dewatering device 16 in which the slurry is again dewatered until a pulp consistency of from about 10 to 30%.
• the pulp is transported again with dilution in order to form a pulp slurry having a pulp consistency of about 4% by the use of recycled liquid 17, to a next pressure increasing pump P 7 and from this pump into a next dewatering device 18 in which the slurry is again dewatered until a mass consistency of from about 10 to 30%.
• the pulp is transported to the last shown pressure increasing pump P 8 , again with dilution of the slurry until pulp consistency of about 4% by the addition of liquid 19 and fresh water or optionally waste water 9 from a bleaching plant to which the pulp can be transferred after having been removed from the digestion section shown in Fig. 1.
• This liquid ( 9 ) which is supplied prior to the pressure increasing pump P 8 is preferably relatively cool in order to be able to cool the pulp to a such low temperature that when the pulp finally leaves the pressurized tube system it will have temperatures below 100oC at atmospheric pressure, i.e. it will not expand, or, more specifically, it will be "cold blown" when it leaves the pressurized tube system.
• the slurry arrives at the last shown dewatering device 20 in which it is again dewatered to a pulp consistency of from 10 to 30%.
• the dewatered slurry having a pulp consistency of 10 to 30% is then removed from the system through a closure cone 21 at the end of the tube.
• This closure cone is of known construction and yields a back pressure which is controlled by a bellow filled with air and the controllable pressure of which is exerted against trie base of the conical closure means.
• the amount of pressurized water injected into the system is controlled by means of the control valve R 2 , and the effluent from the system is controlled by means of the control valve R 1 .
• the valves are interconnected so that the volume of liquid pressed into the system will approximately correspond to the effluent.
• the flowsheet according to Fig. 1 shows upgrading of secondary fibers or the production of unbleached cellulose of annual plants.
• the main consistency during the conveyance through the tube system is, as mentioned, about 4%, and the consistency after dewatering is about 10-30%.
• three reaction modules (M 1 , M 2 and M 3 ) for delignification has been shown which are succeeded by two washing stages (at P 7 and P 8 ).
• a bleach section can be connected to the system shown in Fig. 1, and for the bleaching the same method may be used as has been described above in connection with the upgrading or the digestion, however, obviously using chemicals of a type and in an amount sufficient to obtain the desired bleaching.
• the present process can be used for all kinds of vegetable fibers, e.g. of bagasse, kenaaf, rice straw, rubber trees, waste from the production of palm oil, bamboo and also for hardwood (leave trees) and softwood (needle trees).
• the process is well suited for delignification and optional bleaching of secondary fibers.
• the layout of the system causes deinking of the raw material without the use of extra mechanical additional equipment.
• the present process offers a wide spectrum of reaction possibilities which cover production of pulp having a quality which varies within the range of from mechanical pulp (MP) through thermo-mechanical pulp (TMP) and chemical-thermomechanical pulp (C-TMP) to pure chemical pulps (CP).
• the flowsheet shown in Fig. 1 pertains to the digestion or cooking of one year old plants, like straw, bagasse or kenaaf or for the upgrading or secondary fibers.
• the process For digestion or cooking of sawdust, hardwood or needlewood the process must be supplied with mechanical processing in refiners. After the refiners pressure screens can be used which separate the coarse chips from the accept and return the coarse chip fraction sorted out for renewed chemical and mechanical treatment. This opens for possibilities for a number of alternative programs which can be adapted to all fiber qualities of interest.
• Fig. 5 shows how the flowsheet for annual plants may look, the flowsheet having been built up into three modules 27, 28 and 29 which each comprises a pulp pump and tube system, whereas an example of the flowsheet for the production of pulp from sawdust, hardwood or needlewood has been shown in Fig. 6.
• the flowsheet of Fig. 6 has been supplied with refiners 30, 31 and 32 for mechanical processing, and after the refiners pressure screens 33, 34 and 35 are arranged which separate the coarse chips from the accept and return the separated coarse chip fraction 36, 37 and 38 to renewed chemical and mechanical treatment.
• delignification and defibration 23 washing 24 is carried out, according to Fig.4, still within the closed pressurized system 22.
• This "cooking"- section is terminated with pressurized dewatering which is preferably carried out in a pressure-plug thickener shown in Fig. 1.
• the pressure-thickening device is further described below.
• the pulp from the digestion can be transferred for washing into a module, and the conveyance of the pulp to a washing module IV (50) has been shown in Fig. 7.
• a washing module IV 50
• Fig. 7 In this module three pressurized dewatering presses are connected in series and in the drawing these have been indicated as three pressurized screw presses, however, they could just as well have been replaced by three pressure-plug thickeners with preceding pressure pumps. It appears from Fig. 7 that fresh water or waste water from bleaching 39 is injected prior to the entrance of the last one of the pressurized dewatering presses connected in series and that the liquid 40 which has been pressed out is recycled to before the entrance to the second pressurized dewatering press. This is done in order to dilute the slurry, after pressurized dewatering, to a pulp consistency which is suitable for the further conveyance of the pulp, e.g. about 4%.
• Fig. 4 the washed pulp, still in a pressurized system, is conveyed to a bleaching plant, and in Fig. 8 it has been shown how this conveyance can take place and how the bleach plant according to the embodiment shown has also been built up of three modules 51, 52 and 53 which each includes a tube system with pressure pump. From the last bleach plant module VII, 53, the bleached pulp, as shown in Fig. 4, is transferred for washing, similarly with three pressurized dewatering presses or with three pressure- plug thickeners (module VIII, 54 ). Prior to each pressurized dewatering the pulp slurry is diluted with liquid.
• Fresh water 55 is being supplied prior to the last pressurized dewatering device whereas liquid 56 which has been pressed out in the last pressurized dewatering device is recirculated to the pressurized tube system in front of the inlet to the other pressurized dewatering device.
• the liquid 57 pressed out therein can if desired by recirculated to the pressurized tube system and/or be introduced into the bleached pulp prior to the inlet to the first pressurized dewatering device 58.
• the pulp can upon impregnation, delignification and defibration also be washed and, if desired, bleached in a subsequent non-pressurized system.
• a such unpressurized washing has been schematically shown in Fig. 9.
• the pulp from the digesting section 45 is then first "blown" 46 (if desired through a heat exchanger 47) before it enters into a module IX, 48,which is a washing plant module and wherein three dewatering presses are used in the same manner as for the pressurized washing, however, the three dewatering presses are, of course, not pressurized.
• the pulp may be transferred for bleaching in conventional manner, i.e. non-pressurized bleaching, or it can be transferred for storage or paper production.
• the termination of the digesting section can be made in two different ways, i.e. a) using the traditional blowing tank, preferably in combination with a scrubber plant for the recovery of heat from released steam, followed by a pressure-less dewatering device with recirculation of pressed out cooking liquor for recovery and transfer to pulper. b) With a pressurized dewatering device the system can be substantially simplified and also yield a more closed system and a more optimum heat economy.
• washing of the pulp is usually desirable as part of the cellulose pulp production, subsequent to the first delignification and defibration of the raw material and after the bleaching.
• the washing can be carried out in a particular washing module which comprises 1, 2 or 3 washing steps after the first dewatering, see module IV in Fig. 7 , 50, or Fig. 9 , 48.
• both the bleaching plant and the associated washing plant can work at atmospheric pressure if the temperature of the pulp line does not exceed 100oC.
• the present process can, after the washing plant in the cellulose mill (i.e. after module IV), be carried out by the use of non-pressurized dewatering presses in the washing section of the bleach plant.
• module IV is pressurized ( 50 in Fig. 7) because "cold blowing" from the pressurized module will here take place due to the cooling down caused by the addition of injected colder washing water in the form of fresh water or as waste water from a subsequent bleach plant.
• the present process makes it possible to obtain maximum heat recovery and economy and simultaneously a significant reduction of the total water consumption.
• the bleaching plant and its washing section can be built up of identical modules which are the same as the ones used for the cellulose pulp roduction and for its associated washing section.
• a pressurized bleaching plant with associated washing section can look like depicted in Fig. 8.
• pressure-plug thickeners are preferable, both in module IV ,50, and in module VIII, 54.
• the waste water from the bleach plant can be used as washing water in the washing section of the cellulose mill, and from the washing section the waste water is recirculated to the beginning of the cellulose pulp process.
• the present process can be carried out utilizing a high degree of self-adjustment.
• a cooking plant and bleach plant which work in pressure stages provided by pulp pumps in series will themselves control the pressure difference by means of recirculation of the chemicals countercurrent to the movement of the fiber pulp through the plant.
• a such interconnection of cooking plant and bleach plant also results in only one place for the discharge of used chemicals from the plant.
• This discharge may be located further forward, almost at the beginning of the process, and the "black liquor" which is withdrawn can, as mentioned, be conveyed in heat exchange relationship 8 to fresh water and/or waste water from the bleach plant, as shown in Fig. 1 and Fig. 3.
• the amount of cooking liquid used which is discharged from the system will be approximately equal to the amount of (fresh) water which is added at the end of the plant as washing water for the pulp subsequent to the bleaching.
• Fig. 1 it appears from Fig. 1 that the addition of chemicals and/or the addition of heat 6 is made immediately in front of the pulp pumps, whereby several advantages are obtained, as follows: a) The process pressure is increased in order to be able to use process temperatures above 100oC. b) The pressure increase is carried out stepwise across the pulp pumps which are arranged in series, with increase to the next pressure stage for each passing through a new pulp pump. c) Increased pressure at each stage also enables recirculation and use of the counter-current principle between fiber flow and chemicals throughout the plant. d) Raw material and chemicals are intensely mixed, a procedure which is steadily repeated. Due to the agitation obtained and the recirculation of the process chemicals the fibers are "washed" more or less free of lignin through influence of the chemicals and through agitation.
• reaction tubes 60 arranged in succession.
• reaction tube parts which together constitute a "package”.
• This tube package together with a pulp pump, optionally also with refiner and screen can be assembled within the frame of a standard transport container, and in the same manner for all succeeding modules.
• a such assembly within a standard transport container has been schematically indicated in Fig. 10.
• a suitable tube quality is ST23-33 with a wall thick ness of 13 mm.
• a such tube quality will endure an operating pressure of 20 bar and an operating temperature of 175oC.
• tubes of quality ST23-43 having a wall thickness of 12 mm can be used.
• valves in the tubes for circulation of liquids and return of liquids and shown in Fig. 1, 2 and 3 are pressure operated automatic valves which open at a preset pressure. Because the pressure increase when carrying out the present process takes place in steps or stages, these valves will automatically adjust the back flow through the process and thereby the counter flow between fiber flow and process chemicals and with respect to amounts determined by the amount of liquid (water) which is pressed into the last step of the process through the valve R 2 in Fig. 1, 2 and 3.
• the principle of the self-adjusting pressure distribution when carrying out the process appears clearly from Fig. 1 and 2.
• the amount of fresh water added (through R 2 ) will also in agreement with this embodiment determine the amount of black liquor discharged from the systems (through R 1 ) and thereby also the concentration of solids in the black liquor.
• the pressure controlled automatic valves between the various pressure increasing stages shown in Fig. 2 will besides providing for automatic control of the back-flow through the process and thereby the counter-flow between fiber flow and process chemicals also control the back pressure and thereby the pressure drop across the pressurized dewatering devices, i.e. the pressure controlled valves will provide for control of the degree of dewatering or the amount of liquid pressed out of the pulp slurry.
• the bleaching is carried out in alkaline environment using chlorine, O 2 , peroxide (oxygen bleaching) or O 3 , and a temperature during the bleaching is maintained between 70 and 120oC.
• the washing between the cooking and the bleaching can be carried out at a temperature of from 70 to 140oC, and the washing time can vary from 0.5 to 10 minutes. Subsequent to the bleaching a finishing washing is carried out. It appears from Table III that all the time fiber flow and liquid flow are conveyed in opposite directions to each other. Because the entire process takes place in a pressurized closed system also ammonia will be well suited as cooking chemical.
• the dewatering is performed as a pressure dewatering. It has further been stated that this dewatering can be performed in a so called "pressure-plug thickener" or in a pressurized screw press.
• Fig. 11 the principle of a such pressure-plug thickening device with preceding pressure pump P has been shown.
• the pressure p I minus the resistance of friction between the sliding pulp plug and the tube wall is higher than the pressure p III .
• the pulp plug which is within the central perforated tube will then be pressed out of the system past the conical discharge control means to the right of the drawing, while pressed out liquid at the pressure p II will be circulated back to one or more places upstreams in the process as indicated by the direction of the arrow at the entrance to the circulation tube shown.
• the device shown in Fig. 12 can be used. This corresponds to the dewatering device which has been shown in Fig. 11, however, in Fig. 12 it has been shown that for the further conveyance of the pulp subsequent to the dewatering in the pressure-plug thickener the pulp is in a tube mixer 70 diluted with process liquor which is returned to the pressurized tube system through one or two tube legs 71 and 72 in order to redilute the pulp which now has a pressure of p 3 , to a low pulp consistency, e.g. about 4%.
• pressure-plug thickeners are without movable parts and have been dimensioned to tolerate operating pressures up to about 16 bar, in the same manner as the pumps which can consist of standard centrifugal pumps for pulp and designed for low consistency or intermediate consistency pulp suspensions, i.e. consistencies within the range of from 6 to 15%.
• high pressure back flushing as disclosed below, it can be required to dimension the jacket around the perforated tube and the pertaining tube system for much higher pressures.
• the pumps are to be certified for pressures up to 15-16 bar in order to endure the pressure which is created when several pumps are connected in series within the system.
• the pressure head for one pump ought to be within the range of from 10 to 20 m or higher.
• the number of revolutions of the pump wheels and the diameter of the pump wheels can advantageously be so dimensioned that the peripheral velocity preferably should not be lower than 20-30 m/seconds in order to obtain the desired mixing and dispersing effect between fiber material, process liquid, the chemicals used and the gases which are added to the pressurized tube system at several places along its length.
• the strength requirements to the inner perforated tube in the pressure-plug thickeners are not so substantial as to the outer surrounding tube which is formed like a mantel around the perforated tube and which, thereby, also functions as protection around the inner tube. Accordingly, the outer tube must comply with all safety regulations which pertain to the working pressures used, i.e. also when, if desired, performing high pressure back flushing at pressures of up to 30 and 50 bar and higher.
• the inner tube can consist of acid resistant steel having a wall thickness of 1-5 mm.
• a perssurized screw press For the last dewatering which is performed when carrying out the present process also a perssurized screw press can be used.
• the pressure-plug dewatering devices or thickening devices, abbreviated PPT have been invented for carrying out the present process and consist of a means which with respect to its design represents a substantial simplification compared with the thickening apparatuses currently used within the pulp industry.
• PPT pressure-plug dewatering devices or thickening devices
• the PPT is compact, requires little space and in addition offers the advantage that it can work at temperatures above 100oC and at pressures substantially higher than 1 bar.
• a natural pressure limit for the PPT is 16 bar which is a conventional classification pressure in connection with dimensioning of materials for pumps and tubes of pressurized process systems with respect to strength. This circumstance opens for new possibilities and degrees of freedom with respect to selection of temperature and pressure for carrying out the present process and, moreover, enables a complete and integrated utilization of the countercurrent principle.
• the pressure-plug thickener comprises an internal thin-walled perforated tube, and outside and around this tube another non-perforated tube has been arranged as a jacket, and in the space formed between the inner perforated tube and the outer tube water or liquid is received which due to the pressure differential between the inner perforated tube and said space is pressed through the perforations of the inner tube.
• the plug of thickened pulp which is successively formed in the inner tube when the pulp suspension is dewatered and the pulp consistency increases will under suitable conditions be axially pushed through the perforated inner tube in the direction of movement of the pulp suspension, and this pushing will be caused by the pump pressure exerted against one end of the perforated tube. This pressure will be higher than the pressure in the surrounding tube.
• the wall of the inner perforated tube is selected to be so thin as possible in order to avoid that the perforations in the tube wall will become obstructed and blocked by fibers from the pulp suspension. Accordingly, the wall thickness of the inner tube has been calculated and dimensioned with modest safety margin and only to endure the stresses caused in the material as a consequence of the pressure differential between the inner and outer tube chamber and which usually does not exceed 2 or 3 bar.
• the outer tube must be dimensioned in order to comply with all safety requirements and regulations with respect to pressurized tube or steam systems to operate under expected elevated working pressure.
• the movement of the pulp plugs through the inner per forated tube is determined by the outlet means in the last step of the process.
• the outlet means can consist of a pressure-loaded, resilient cone which presses against the pumping pressure within the system and balances this or it can consist of a sluice chamber, in principle in the form of a piece of tubing between two valves which open and close alternately in order to sluice out portions of the pulp plug formed within the perforated tube in the last pressure dewatering step of the pressurized system.
• the pulp plug When a pressure cone is used at the outlet of the pressurized system, the pulp plug will under suitable conditions leave the pressurized system continuously and with approximately uniform movement whereas use of a sluice chamber will cause the pulp plug to move forward and out of the pressurized system with rythmic movements and advances determined by the pace at which the valves of the sluice chamber are opened and closed.
• seals 87 are present, and between the tubes 83, 85 and 84 a seal 88 is present, and these seals have been so constructed that the tube 83 will form an inner pressure chamber 89 which has been sealed in the lateral direction against an outer pressure chamber 90.
• the arrows show the direction of flow of the pulp suspension and the water respectively.
• the construction is such that the PPT can easily be opened, whereby the inner perforated tube 83 easily can be replaced by another tube having new perforation or another perforation pattern.
• the PPT functions as follows: At point A the pulp suspension usually has a fiber concentration of 3-6% and a pressure p 1. (So called MC pulp concentrations ("Medium consistency”) can also be used, i.e. a fiber concentration of 6-15%, however, this presupposes use of special so called MC-pumps).
• the pump 81 By means of the pump 81 the pressure is increased to p 2 at the point B at which point by the way the suspension has the same fiber concentration as at point A. When it moves through the tube 83 from point B to point C the pulp suspension will flow past the perforations in the tube 83.
• the pressure p 2 within the tube 83 is higher than the pressure p 4 in the outer and surrounding pressure chamber 90, some of the liquid in the suspension will be pressed out through the perforations in the tube wall, as indicated by the arrows.
• the fibers of the pulp suspension will largely remain in the tube 83, whereby the fiber concentration in the tube 83 will increase correspondingly. Accordingly, the fiber concentration of the pulp suspension will gradually increase while the suspension moves from B to C.
• the fiber concentration at the inlet to the tube 84 will normally vary between 10 and 30% and is dependent upon the existing conditions, like pressure differential (p 2 - p 4), type of fibers, degree of digestion, degree of milling of the fiber suspension, the perforation pattern, the percentage open area in the perforated surface compared with the total tube surface, and the diameter of the perforated tube in relation to said parameters and the pressure drop (p 2 - p 3).
• the liquid pressed out is conveyed from the tube 85 out through the tube 86.
• PPT pressure-plug thickeners
• the tube 83 can be made of relatively thin tube material, preferably of a thin acid resistant steel sheet having a thickness of 0.5-2.0 mm in which the desired perforation pattern is made, e.g. by burning with the aid of a numerically controlled laser machine, whereupon the perforated sheet is polished on the inside before it is bent around and welded into a tube.
• the pumps employed can be conventional centrifugal pulp pumps.
• the inner diameter of the perforated tube similarly plays an important part because the axial resultant force of the pumping pressure across the entire tube cross-section increases with the square of the radius of the tube whereas the internal frictional force between the pulp plug and the inner tube surface only increases linearly with the tube diameter for otherwise equal pressure conditions and equal tube length. Accordingly, this type of plug movement can more easily be obtained when the tube diameter is increased provided the pulp plug having a sufficiently high fiber concentration.
• Fig. 14 shows how pressure-plug thickeners can be connected in series in a closed and pressurized system.
• the thickened pulp suspension at D which is a representative of a fiber plug having a fiber concentration of 10- 30%, is pressed into a diluting chamber 91 in which it is provided with diluting liquid through an inlet tube 92.
• a pump 93 the diluted suspension is pumped into a pressure-plug thickener 94 in which the pulp is again dewatered as described above in connection with Fig. 13.
• the thickened pulp is pushed by the pumping pressure past point G and into a new diluting chamber 97 which similarly to the diluting chamber 91 can have approximately the same main dimensions and the same main design as the pressure-plug thickener but obviously without the inner perforated tube.
• Fig. 15 schematically shows the pulp thickener (PPT) arranged as the last stage of a cellulose process or washing process.
• PPT pulp thickener
• a stop element 101 has been shown at the outlet end of the tube from the pulp thickener, and this stop element 101 preferably is in the shape of a conical device which is pressed against the tube end by means of an adjustable pressure member, preferably an air bellow 102, which exerts pressure against the stop element and thereby against the pulp flow within the tube system.
• the pressure p4 will vary in response to the formation of the plug in the perforated tube, as follows: When the pulp plug which is initially formed at L increases in length in the tube in the direction towards K, the fiber layers will cover an increasingly larger part of the inner surface of the perforated tube, whereby the liquid flow is delayed and the pressure p4 increases. Maximum pumping pressure occurs when the fiber plug covers the entire part of the perforated tube from L to K and the liquid flow through the perforations has approximately ceased.
• Fig. 16 shows another embodiment of a last thickening step of a pressurized pulp suspension system.
• the discharge is controlled by means of a discharge sluice which is constituted by two ball or calotte valves 105 and 106 respectively arranged at a distance from one another in the same tube and being alternatingly opened and closed.
• the flow opening 107 of the valve must be at least equal to the cross-sectional area of the tube 108 in order to ensure an unhindered passage of pulp.
• This type of discharge sluice can be used when the thickened fiber suspension, i.e. the pulp plug, to be discharged from the pressurized system to atmospheric pressure has a temperature higher than 100oC and develops internal steam when the valve 106 is open against atmospheric pressure while the valve 105 is closed. The pulp will then be pushed or blown out of the sluice and the valve 106. The entire sluice volume will thereby be blown approximately empty of fibers and will at the same time become filled with steam at atmospheric pressure.
• valve 106 When the valve 106 is closed and the valve 105 is opened in order to let out the next portion of the pulp plug in the tube 108, the steam or air which is present within the sluice will become compressed to pressure corresponding to the pressure of the pressurized system and thereby give room for a new portion of pulp plug to be sluiced out from the system.
• the valves 105 and 106 may advantageously be designed as flap valves with the flaps having a particularly sharp and cutting design which better can divide or cut the pulp plug.
• Fig. 17 shows the same sluice means as is shown in Fig.
• valve 111 which are used when the content within a sluice 112 does not move out of the sluice by itself.
• two valves 113 and 114 respectively have been shown, and when the valve 113 is closed and the valve 114 is open, pressurized air supplied because the valve 111 is opened will blow the content in the sluice out of the system through the valve 114. Then the valves 111 and 114 are closed and the valve 113 is opened, and the next portion of the pulp plug will be let in, as described above in connection with Fig. 16.
• Fig. 18 shows an additonal means which facilitates the movement of the pulp plug within and out of the thickener.
• a pump 115 and various parts 116, 117, 118 and 119 for constructing the thickener are as disclosed above in connection with Fig. 13.
• the additional means consists of a three-way valve 120 arranged in an outlet conduit 119 and 122 and having supply from a tube 121 which conveys liquid or gas at a higher pressure than the pumping pressure in the pulp tubes.
• a flexible tube connection 123 e.g. in the form of a rubber collar, arranged as a connecting link between a divided pulp tube of the pressurized system can accomodate and absorb the short pressure pulsations occurring in the same tube.
• An alternative means for absorbing pressure pulsations is a standard membrane expansion tank 124 shown in Fig. 18C. The tank is dimensioned in agreement with the pressure pulsations which are expected to occur in the system.
• the additional means is operated as follows: According to Fig.
• FIG. 18B shows how the three-way valve 120 upon a brief turning by 90 in the clock direction closes the outlet 122 and lets in water, mixture of chemicals or gas (e.g. oxygen) at higher pressure in the opposite direction through the outlet tube 119 and into the outer pressure chamber 116, whereupon previously pressed out liquid from the pulp suspension in the tube 117 is pressed back through the perforations and into the tube 117.
• a brief turning by 90 in the clock direction closes the outlet 122 and lets in water, mixture of chemicals or gas (e.g. oxygen) at higher pressure in the opposite direction through the outlet tube 119 and into the outer pressure chamber 116, whereupon previously pressed out liquid from the pulp suspension in the tube 117 is pressed back through the perforations and into the tube 117.
• chemicals or gas e.g. oxygen
• the amount of liquid which in the case shown in Fig.18B is pressed back through the perforations and into the tube 117, can be adjusted by means of the size of the pressure or the length of the time during which the external pressure is allowed to be effective, or both.
• the amounts of liquid pressed back which here will function as lubricant between the pulp plug and the internal surface of the tube 117 are so small that they are of little or no importance to the fiber concentration per se of the pulp plug which for several reasons is wanted to be as high as possible.
• Fig. 19 shows a PPT having the same function as disclosed for the PPT shown in Fig. 18A, 18B and 18C, however, instead of a three-way valve and a separate tube system for injecting medium back into the inner perforated tube in the form of a pressure pulse, the liquid which has been pressed out from the pressure-plug thickener is here used for the same purpose.
• Fig. 19A shows that in an outlet tube 125 a cylinder 126 has been arranged which has a piston 127 which is actuated by means of an actuator, e.g. an air bellow 128.
• an actuator e.g. an air bellow 128.
• Fig. 19B shows that a piston movement of short duration to an upper position as shown in the Figure causes both that the outlet flow from the tube 125 is interrupted and, moreover, that the pressure conditions within the pressure-plug thickener are changed due thereto that a volume of liquid ⁇ V is forced back into the pressure-plug thickener with corresponding thinning and "lubricating" effect as disclosed above in connection with Fig. 18.
• the brief pressure pulse is accomodated by an elastic tube connection 123 or a pressuretank 124, as shown in Fig. 18A and B, or by similar means.
• Fig. 19C and D show the way of working for a corresponding installation, however, where a cylinder, a piston 131 and a movable element 130 constitute a branching from an outlet tube 125.
• Fig. 19C shows the position of a valve 129 and of a piston 131 during dewatering and thickening of the pulp in the perforated tube in the pressure-plug thickener with which the tube 125 is connected.
• Fig. 19D shows a closure of short duration of the valve 129, whereupon the piston 131 by the movable element 130 is moved towards the outlet tube 125. Thereby, reversed pressure conditions in the pressure-plug thickener and a movement of liquid in through the perforations of the perforated tube are caused, as disclosed above.
• Fig. 19E and F show the principle of a means for a pressure-plug thickener where the reverse pulsating pressure is provided by means of an outer pressing body 132 which is pressed against an elastic tube connection or adapter 133 inserted between an outlet tube 134 from the pressure-plug thickener and an outlet tube 135 from the adapter 133 after a valve 136 has been regulated so that it closes the outlet tube 135.
• the adapter 133 can consist of rubber or another elastic material which can endure the relevant pressures and temperatures. This type of means in order to provide the reversed pressure pulse is of particular interest when washing cellulose fibers, and in those cases where the pulp suspension has a relatively low temperature of below 100oC.
• Fig. 20A, B, C and D show various types of perforations for the inner tube 117 of pressure-plug thickeners and of a fiber sorting means (the latter is described below).
• Fig. 20D shows a tube with relatively large openings which on its outside has been covered by a fine mesh of non-corroding metal wires.
• Fig. 20D, I shows wire qauze or screen and openings viewed from outside the tube
• Fig. 20D, II shows wire gauze and openings viewed from the inside of the tube.
• Fig. 20E, I shows in section through the perforated tube wall with the applied fine wire gauze how a fiber suspension is thickened against the wire gauze during the dewatering
• Fig. E, II which shows a section in the same way as I, shows how the fiber accumulation formed which constitutes a part of the pulp plug which is being formed within the tube, is pressed back in direction towards the inner of the tube by means of the pulsating back pressing of pressed out liquid.
• the liquid which has been pressed back through the wire gauze and into the tube will follow the way of least resistance and become distributed as a liquid layer between the pulp plug and the internal surface of the tube wall.
• the TPS process can also include fractionating of fibers, i.e. long and short fibers of the pulp suspension are separated and conveyed out of the pressure system through two separate outlets.
• the separation is carried out in an apparatus built up of the same elements which have been disclosed above in connection with the pressure-plug thickeners (PPT).
• PPT pressure-plug thickeners
• This separation or fiber fractionation has been schematically shown in Fig. 21A and B which shows how a pump 141 transports the diluted pulp suspension from a preceding lower pressure stage through an elastic tube connection 142 or through some other previously disclosed pressure-pulse equalizing means and into a perforated tube 143.
• the separate perforation of the tube 143 are substantially larger than the perforations disclosed above for the pressure- plug thickeners (PPT). Outside and about the perforated tube
• the short fibers will become preferentially collected in the space between the inner perforated tube 143 and the outer tube 144 whereafter they are conveyed out of the system through pressure-plug thickener 150.
• This sorting of fibers or fractionation process which takes place between the inner perforated tube 143 and the space surrounding it occurs without the pulp becoming dewatered or thickened, in contrast to what takes place within the pressure-plug thickeners. This means that the pulp consistency in the inner tube 143 and in the space between the tube 143 and the tube 144 remains approximately the same.
• the two fractions of short fibers and long fibers respectively are conveyed through separate suspension or pulp runs out of the pressurized system and into a pressure-plug thickener 150 and a pressure-plug thickener 158 respectively and provided with associated outlet closure means 151 and 159 respectively.
• the functioning of the two pressure-plug thickeners 150 and 158 is as disclosed in connection with the pressure-plug thickeners shown in the other Figures.
• the two pressure-plug thickeners 150 and 158 shown must have differently dimensioned perforations because the perforation for the long fiber fraction, i.e. for the pressure-plug thickener 158, must be so dimensioned that it is larger than the perforation for the pressure-plug thickener 150 intended for the short fiber fraction.
• the outlet means 151 and 159 respectively can consist of a pressure-loaded cone, as shown, or it can consist of a sluice means with two valves as disclosed above. Moreover, the outlet means can under favourable circumstances consist of a single flow- or pressure-controlled valve.
• valves shown, 147 and 152 (R 4 and R 3 ) respectively, automatically control the desired ratio of flow between the two fiber fractions.
• reduction of the amount of suspension through R 4 will cause a stronger concentration of long fibers in this fraction, whereby the short fibers mainly will be contained in the fraction which is conveyed through R 3 and which has the larger volume.
• a relatively large proportion of fibers through R 4 will cause a larger number of short fibers to be conveyed out of the system along with the long fiber fraction.
• a cylinder piston 154 has been shown which moves in step with a closure valve 156, and similarly a piston 162 work with opposite movements, as shown in Fig. 22A and 22B.
• Two pressure equalizers 148 and 155 have been shown which will dampen and partly eliminate the pressure pulsations in the tubes 143, 149 and 157.
• the pressure variations in the tube 144 caused by a piston 146 is of a far smaller magnitude than the pressures which occur in the tubes 158 and 150 because the larger perforation in the tube 143 yields less resistance to flow and thereby more rapid pressure equalizations when the pressure drop alternates in both directions by movement of the piston 146. Due to the relatively modest pressure drop across the more coarsly perforated tube 143 safety means in the form of overflow valves are here not required.
• the liquid pressed out from the pressure-plug thickeners 158 and 150 is conveyed back through a tube 160 counter- currently to the fiber flow through the process, as disclosed above.
• Fig. 21A and B two actuators 153 and 163 are shown which move at a such frequency that they always work in opposite directions, i.e. not with parallel movements. Further, the actuator 145 can move indepently upon the frequency of movement of the actuators 153 and 163. Moreover, the actuator 145 has a continuous and uninterrupted reciprocating movement whereas the actuators 153 and 163 only have two pulsating movements of short duration against closed outlet valve in order to ensure a brief back-flushing of pressed out liquid back in through the perforations in the tubes 157 and 149 respectively, whereby the movement of the pulp plug out of the pressure system is supported, as disclosed above.
• the dimensioning of the perforations in the tube 143 used for the fiber fractionation must be made in accordance with the type or the types of fibers contained in the pulp suspension. The same relates to the dimensioning of the perforations of the pressure-plug thickeners used for the discharge of the long fiber fraction and the short fiber fraction respectively.
• Table IV examples of design and dimensions of the perforations have been stated.
• Fig. 22 shows how several pressure-plug thickeners (PPT) have been connected in series and work in a synchronized manner and in response to the sluice means for discharge of pulp from the system.
• Fig. 22A shows the normal dewatering and thickening situation using three interconnected PPTs 168, 169 and 170 respctively with water for dilution flowing into diluting vessles 171 and 172 and with the pressed out liquid flowing out of outlets 179, 180 and 181 respectively.
• a valve 173 When a valve 173 is closed, there are no axial movements of the fiber plugs which are continuously formed within the inner perforated tubes of the pressure-plug thickeners.
• Fig. 22B shows the same system as has been shown in Fig. 22A, however, with the pressure drop having been reversed in the pressure-plug thickeners after closing a valve 174 and opening the valve 173.
• the pulp plug in the pressure-plug thickener 170 is thereby allowed to get into an outlet sluice between the valves 173 and 174, as described in details above in connection with Fig. 16 and 17. Further, in Fig.
• injection means 176, 177 and 178 respectively have been shown which concurrently push pressed out liquid back into the pressure-plug thickeners 168, 169 and 170 respectively, and the pulp plugs therein will simultaneously become “lubricated", and as a consequence of the pumping pressure which the pulp pumps together exert on the pulp plugs, the pulp plugs will be concurrently pushed forward towards the outlet sluice until the outlet sluice has become filled with the pulp plug due to compressing of the remaining steam or air from the last emptying of the sluice.
• the pressure pulsations which are caused by the injection means 176, 177 and 178 will be caught by dampers 182, 183 and 184 respectively as disclosed above.
• valve 173 is closed and the valve 174 and, optionally, a valve 175 (the latter for blowing the sluice chamber) are opened concurrently with opening of the injection members 176, 177 and 178 for renewed outlet of pressed out liquid through the outlets 179, 180 and 181 respectively. Thereupon the same pressure pulsation cyclus is repeated.
• pressure pulsation inducers other means as disclosed above in connection with Fig. 18 and 19 can be used in the same manner.
• a flow sheet which is a more detailed flow sheet but which otherwise corresponds to the flow sheet shown in Fig. 1 has been shown in Fig. 23.
• the three reaction modules, M 1 , M 2 and M 3 have been shown in more details in Fig. 23, and it appears from the Figure that in front of each pump there is a tube mixer 70 for mixing chemicals liquid and pulp slurry and after each pump a means constructed in the same manner is arranged, however, the means then functions as distributor for chemicals.
• the means then functions as distributor for chemicals.
• the water consumption is controlled by means of the control valves R 2 and R 1 .
• Fig. 24 shows the principles for the process operation. Again the drawing showing these principles is based on the main steps: delignification (and optionally deinking), washing, bleaching and renewed washing, and the number of circulation and return circuits is dependent upon the number of pumps and thickeners which are used. Similarly, the number of places for addition of chemicals will vary with respect to the different raw materials and will be dependent upon the fiber pulps to be produced. It appears from Fig.
• the Tube Pulping System or abbreviated the “TPS process” production of cellulose
• TPS process production of cellulose
• the washing water which is injected into the system at the end of the process will firstly be converted into bleach liquid and then to cooking liquid by the addition of heat and chemicals on its way towards the beginning of the process.
• the same liquid will on its way to the beginning of the process also take up dissolved matter from the raw material and carry this out of the system when the cooking liquid leaves the system at the beginning of the process, which appears from the Sankey diagram shown in Fig. 3.
• the pumps effect recirculation and reuse of cooking liquid and chemicals and, moreover, mixing and dispersing of added fresh amounts of chemicals and gas to the cooking liquid, stirring and thereby "washing machine effect" within the system and, moreover, internal heat recovery.
• washing zone denote washing zone, B bleaching zone, C washing zone and D the zone for impregnation, delignification and optionally deinking.
• Added washing water 190 is changed into bleach liquor by addition of bleach chemicals 191 before the process liquid is changed into cooking and/or deinking liquid by the addition of chemicals and heat 192 as previously disclosed.
• fiber raw material having a solids content of 33% is supplied to the TPS process and that the amount of raw material is 2 kg, calculated as bone dry substance.
• black liquor is pressed out in the first pressurized dewatering device, and the black liquor will contain about 1 kg of dissolved solids.
• water washing water
• the amount of water is assumed to be X liters per kg of cellulose fibers produced.
• the cellulose fibers which are produced are assumed to have the same solids content as the raw material, i.e.
• the theoretically least amount of water which must be used in order to obtain the said conditions for the cellulose produced, the returned liquid and the black liquor discharged can simplified be calculated as follows: If the black liquor is assumed to contain 15% of the dissolved solids and will thereby be ready for evaporation, the least theoretical amount of liquid (X liters) will be: produced or 6.7 tons of water for each ton of cellulose fibers produced.
• This very low amount of liquid supplied for each ton of produced cellulose is significantly lower than the conventional water consumption when producing cellulose by means of the conventional cellulose manufacturing processes.
• the recovery of chemicals from liquids can be made by adding a basic agent which will enhance the driving off of the volatile gases.
• a basic agent which will enhance the driving off of the volatile gases.
• CaO or CaOH in pulverulent form or in the form of a slurry can be used as agent for enhancing the driving off of NH 3 .
• NH 3 gas is liberated which is conveyed away from the remaining process to become absorbed in fresh water in a scrubber plant whereby fresh cooking chemical, i.e. NH 4 OH, is formed and at the same time the heat content of the NH 4 gas is recovered.
• the countercurrent principle utilized for carrying out the present process enables deinking of secondary fiber from various print qualities to be carried out within the present TPS without having to resort to extra mechanical additional equipment.
• the deinking which is supported by particular chemicals added at this stage of the process takes place in the pulp prior to or at the same time as the pulp arrives for delignification and, if desired, to be subsequently bleached.
• a suitable chemical in order to facilitate the deinking is a non-ionic surface active nonylphenol alkylene oxide adduct.
• so called "explosion pulp” can be produced by causing the pulp to leave the pressurized system without the preceding cooling of the liquid-fiber mixture to a temperature below 100oC before discharging it to atmospheric pressure.
• the uniqueness of the present process is that it also enables "explosions" of pulps from for example relativel elevated pressures of from 15 to 20 bar (dependent upon the number of pressure pumps in the system) and at relatively low temperature in the pressurized system, i.e. from 110 to 150oC, because pressures and temperatures within the TPS used can be selected independently of one another, i.e. in contrast to conventional cellulose production where pressure and temperature are determined by the conventionally used saturated steam.
• the first pressure increasing means of the TPS is the pump P 2 .
• the TPS can be supplied with extra pressure pumps connected in series if the desired temperature in the system should make a corresponding pressure increase necessary in order to prevent development of steam within the system.
• the back flushing mentioned above of liquid back into the perforated tube of the pressure-plug thickeners has also a further effect apart from providing "lubrication" between the fiber plug and the inner surface of the perforated tube.
• the back flushing pressure is controlled by adjustment of a conventional overflow valve, as disclosed above but which has not been shown in the drawings.
• the back flushing pressures used will vary according to the pertaining production conditions and will vary within the range of from 10 to 60 bar absolute pressure, preferably within the range of from 3 to 40 bar above the existing pressure in the inner tube of the pressure-plug thickener.
• the pressure increase caused by each pump in series, i.e. the pressure increase of each pumping stage may be within the range from 0,5 to 10 bar, preferably not above about 5 bar.
• a technical scale plant for carrying out the present process may have a capacity of about 100 tons per day, and a suitable length for the pressure-plug thickeners used in carrying out the present process will correspond to a perforated tube length of from 2 to 5 m with the perforated tube having a diameter of from 100 to 400 mm.

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• 1987
  • 1987-07-07 NO NO872836A patent/NO872836L/no unknown
• 1988
  • 1988-02-03 GB GB8802413A patent/GB2200928B/en not_active Expired - Lifetime
  • 1988-02-11 AU AU12912/88A patent/AU1291288A/en not_active Abandoned
  • 1988-02-11 EP EP88907543A patent/EP0302110A1/en not_active Ceased
  • 1988-02-11 JP JP63501682A patent/JPH01502206A/ja active Pending
  • 1988-02-11 WO PCT/NO1988/000011 patent/WO1988006201A1/en not_active Application Discontinuation
  • 1988-02-12 CN CN198888100825A patent/CN88100825A/zh active Pending
  • 1988-10-12 FI FI884696A patent/FI884696A/fi not_active Application Discontinuation

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