FI110580B - Process for the recovery of fiber and fiber-based solids and for the separation of lipophilic extractant - Google Patents

Abstract

The present invention relates to a separation method of fibre and fibre-based material and lipophilic extractive material; the method permits a reduction in the water consumption of a pulp mill and the use of wood species having higher extractives content in the mechanical and chemi-mechanical pulp production. In a preferred embodiment of the invention, a decanter centrifuge is used to recover solids and to separate solids and lipophilic extractives. With a decanter centrifuge a situation is reached in which the colloids containing lipophilic extractive material do not settle but fibre and fibre-based solids settle due to a higher density.

Description

110580

A method for recovering a fiber and a fiber-based solid and for separating fat-soluble extracts

The present invention relates to a process for recovering a fiber and a fiber-based solid and separating a fat-soluble extractant.

Grease-soluble extracts, or wood ash, cause various problems in pulp and paper making. The most common problems are dirt and clogging problems in wires and showers and paper machine deposits. In addition, the fat-soluble extract-10 substances and their precipitates decrease the strength and brightness properties of the paper and cause holes in the paper.

Several studies show that tighter emission limits and reduced water use in the future will add to the problems caused by pollutants in papermaking. According to relevant studies, enrichment of water-soluble extract of fat-soluble extractants is one of the major problems in reducing water use. On the other hand, there is a growing interest in the use of higher extractive wood species such as prickly pine and wound, which also contributes to the need for more efficient extraction methods.

: '· In current processes, the amount of extractants in a papermaking machine is limited by the use of pulp and various chemicals. However, on the basis of both the studies carried out and practical experience, current methods are not sufficient to inhibit extraction agents. 25 den enrichment cycles when closing water circuits. This is due to the fact that as water consumption decreases, the dispersibility of extractives in water decreases and extract retention in scrubbers increases. On the basis of both factory scale measurements and the results of various simulations, the enrichment of the extractives would continue. ·. ; however, they can be prevented in the following ways.

. ··· '30' * '. 1. By changing the pulp mill's water circulation so that filtrates with higher extractant content can be removed from the process.

: '': 2. By replacing existing washing equipment with more efficient ones (eg screw presses).

; '; '3. Using various internal cleaning methods.

·: ··: 35 110580

In practice, changing the water cycle and using more efficient washing machines means multiplying the solids losses many times over. Changing the water cycle alone would increase solids losses by up to 4-5 times. More efficient presses for washing fat-soluble extracts would increase solids killing even 3 to 6 times. In addition, more efficient presses extract a finely divided solid from the pulp, which would clearly improve the optical properties of the paper being manufactured. Thus, if the filtrate of that press was removed from the process, the optical properties of the pulp would also be impaired. Changing water cycles and using more efficient presses therefore require the development and deployment of more efficient fiber recovery equipment.

Table I shows the solids and solids contents of the various filtrates in the prior art process and Table II the solids and extract concentrations of the filtrates of the various prior art presses.

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Table I.

Pulp mill filtrate Extract- Solids concentration, mg / l mg / l; ·, PGW hot circulation 40-80 100-200 * 'Disc precipitant cloudy filtrate 75-150 100-200 200 clear filtrate 50-120 50-150. · · · Super clear filtrate 40-100 <50

Press filtrate 200 - 600 cf. Table II. 1 '»·

Table II.

Extract Filtrate Press. . retention, solids content,% mg / l

Roll Press 20-50 200-1000: ':' Wire Press 10-40 350 -1000. * · · Multi-press * 1500 - 3000

Screw press ~ 0 2000-4000 110580 * No extract retention for this press is known. Based on the operation of the device, the retention is lower than that of a wire press.

The solids in the filtrate also degrade evaporation and filtration for internal purification. During evaporation, the filtrate solid is known to decrease the consistency of the concentrate. In membrane filtration, fibers are known to break the membrane.

At present, mechanical and chemical pulping processes generally do not involve fiber recovery or, if used, fiber recovery is based on screening, filtration or flotation techniques. The problem with these methods is the low consistency of the recovered solid and the retention of the fat soluble extracts in the recovered solid or poor solid recovery. The separation problems are mainly due to the high fines content of the filtrate, the fat-soluble extract colloids having a size of about 0.1 to 2 µm and the fiber to size> 5 µm, which necessitates a small hole size in screening and filtration processes. The result obtained with current fiber recovery methods is, therefore, a trade-off between the amount of fiber recovered and the load of extractant returned to the process. Table III shows the results obtained with different fiber recovery devices.

20: "· My spreadsheet.

• p • »v 'Method Solid Extract-Output-Separation Method Function ··· Recovery Degree Substances Consistency Principle% Returns% ___% ___. · · Wafers 90 - 95 20 - 50 10 - 20 Filtration Through Pulp Cake

Flotation 85 - 98 30 - 55 1 - 15 20 - 80 pm air bubble

Micro screen 30-60 10-15 <1 20 -150 pm on a mesh screen

Certus microfil -100 93-99 * 1 pm mesh frame filter. Decanter Spin> 85 -0 25-30 Centrifugal Deposition _ * · · l - l 1 - 1 -. i t ·.;. * * Output consistency is not given.

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The most common fiber recovery devices are disk or drum shoppers with fiber as well. , · Try to filter the fines as closely as possible through the solid cake. With this, ·. · The method achieves a reasonably high solids recovery rate, but the 110580 solids cake also effectively filters the colloidal substances out of the water. If the thickness of the solid cake is reduced, the retention of the colloids decreases, but also the degree of solid recovery.

5 In screening methods, such as Microscreen and arc screen, in which flow or a scraper wipes the screen surface to prevent the formation of a solid cake, the retention of colloidal material in the recovered fiber is reduced or non-existent, but the solid recovery rate is poor. The screening methods mainly remove long fibers. Also, the final consistency of the recovered solid remains low, which means that the recovered solid cannot be returned to the thick mass without loss of its consistency. If the recovered solid has to be returned to the press feed mass or filtrate container, a finely divided portion of the solid begins to concentrate in the circulation, thereby degrading the press itself. When slowing down the flow or scraper movement, solid cake formation begins, which increases the retention of 15 colloidal substances.

The flotation method achieves a high solids recovery rate. In the flotator, air bubbles also remove colloidal material along with the solid. The weakness of the flotator is the low consistency of the recovered solids and the high rate of colloidal interference-20 return to the process.

• ►:, 'The disadvantages of the prior art methods described above can be! Can be removed using the centrifugation methods of the invention for solids recovery, in which the solids are mechanically removed. By selecting the appropriate medium ... 25 march, a situation is achieved in which fat soluble extract colloids do not settle,. '' But the fiber and the fiber-based solid settle under the effect of the higher density. This allows the solids to be separated in pure form without binding to fat soluble extracts.

The process of the invention provides both a high consistency of recovered solid and a high degree of fiber recovery without the retention of fat soluble extracts. ta. There is therefore no need to make the aforementioned compromise. According to the invention: .the method allows the use of water better than the prior art methods. Reduction in paper mills and wood with higher extractivity>. . · 35 uses in mechanical and chemimechanical pulping.

I | 110580

Other features of the fiber and fiber-based solid recovery and fat soluble extraction separation process of the invention are disclosed in the appended claims.

In the following, the recovery and separation method according to the invention will be explained in more detail with reference to the accompanying figures, in which Figures 1a and 1b schematically show the operation of two different centrifuges, Fig. 2 shows a so-called. Screen Bowl centrifuge, Fig. 3 Fig. 4 shows the results of a factory run run of the method according to the invention; Process solids losses from the simulation in accordance with the function of the amount of filtrate leaving the process with different process filtrates,::. Figure 8 shows the separation efficiency of the fat soluble extractants obtained from the simulation of Figure 5: '· as a function of the amount of filtrate leaving the process with various pro-:' * ': process filtrates, - ···;' Figure 9 shows the resolution efficiencies of the fat soluble extractants '', 25 obtained from the simulation of Figure 5 as a function of the amount of solids recovered by the different solids recovery methods; ·. 30 * · · First, a closer look will be taken of the method of separation used in the process of the invention and the devices used therewith. Centrifugation refers to a centrifugal sorting or separation process. The centrifugal force generated by centrifugation has the same effect on the substance as gravity-35 clubs in sedimentation. However, the centrifugal force generated by centrifugation is 6,110,580 hundreds or thousands of times greater gravity, resulting in centrifugation: - a higher particle settling rate, - a more solid solids layer, and 5 - smaller particles than sedimented.

Centrifuges are divided into sedimentation and filtration centrifuges and combinations thereof. Sedimentation centrifuges are devices in which separation is achieved solely by centrifugal force (Fig. 1a). These include e.g. plate and decanter centrifuges and laboratory tube and bottle centrifuges. Filtration centrifuges, in turn, are some kind of combinations of filtration devices and centrifuges (Fig. 1b). In filtration centrifuges, the actual particle separation is effected by filtration. In other words, by utilizing a porous, routed, slit or similar surface. However, the driving force behind the filtration is the hydrostatic pressure exerted by the centrifugal subject-15, and therefore the methods are considered to be centrifugal separation methods. In a combination of sedimentation and filtration centrifuges, the particles are separated by centrifugal force as in sedimentation centrifugation. The combination devices also include a washing / thickening zone which operates on the same principle as a filtration centrifuge.

20 • 'Centrifugation for fiber recovery or separation of fiber and extractant':. · The method requires, among other things, following things. The method must be continuous:. · · Because industrial processes in the industry are continuous and there are large volumes of liquid to be processed. One cannot think of a stake-type action. Capacity must be high, ''; 25 at least ten liters per second. The method must also be suitable for fibrous:. t for handling sludges and suspensions. Long-fiber suspensions are also possible, which will further increase the hardware requirements. The fiber recovery rate should be good because fiber is a valuable raw material for papermaking and cannot be wasted. Of course, no significant extractant retention should occur as well, since a solution is being sought to overcome as much as possible the problems caused by the extractants in both pulp and paper production. In addition, the device should achieve a high degree of final consistency there is no need to return the fiber to be recovered through the precipitator back to the process.

:: 35 Experience with filtering centrifuges with centrifuges: Similar problems to current screening and filtration methods. In other words 7 110580, compromises have to be made between extractant retention and fiber recovery rate. Also, continuous sedimentation centrifuges in which solid matter is removed through nozzles or slits (these are known commercially as nozzle bowl, solid-ejecting bowl and nozzle-valve Bowl centrifuges).

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These centrifuges are not working fiber or fiber recovery and separation of extractives kiintoainepuolen because of the risk of clogging. Of course, it is possible to reduce the risk of clogging by diluting the fiber fraction, but this results in a too low removal consistency.

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According to both the literature and practical experience, the only possibilities for such applications today would be the decanter centrifuge (Fig. 2) and the so-called centrifuge. Screen Bowl decanter (Fig. 3) (composite device). The separation methods applied in these devices have the advantage that they are capable of separating solids of very different lengths (5 to 5000 to 15 µm) and can remove the solid at high consistency.

The following describes a factory run run where the decanter centrifuge was tested for extractant extraction. The method for solids recovery and separation of solids and fat soluble extract was subjected to a test run at a production scale PGW pulp mill at a paper mill 20. Wood species: '' was six and the filtrate was a washing press filtrate. The bleaching was dithionite bleaching pulp was fed to the washing press directly from the disk filter. The bleaching press was not working. The decanter centrifuge with a capacity of 20 m3 / h was specified by the manufacturer as a solid recovery device. The centrifuge was 3975 mm long, 25 1140 mm wide and 1570 mm high. Figure 4 shows the solid recovery rates at different feed rates and at different rotational speeds.

From the test results, it is worth mentioning that, as is clear from the theory, the centrifuge's resolution improved as the RPM increased. With a capacity of 20 m3 / h, increasing the RPM: from 30,260 rpm to 2640 rpm increased the recovery rate from 82% to 88%. Also note: '' note that the maximum capacity at 2640 rpm was still in the 82% range.

':'. The test apparatus was adjusted so that the solids outlet consistency was as high as possible.

'· 35 This type of control is better suited to concentrating the sewage plant bio-slurry 810580 than treating the pulping water. Device optimization can further improve the solid recovery rate and capacity.

The following simulation (Fig. 5) discusses the application of the process of the invention to a conventional mechanical pulping process. In Figure 5, reference numeral 100 represents the wood entering the process, which is diluted to a suitable consistency for screening at step 102. The dilution uses the filtrate of the process circulation tank 104. The pulp obtained from the dilution is subjected to sorting 106, from which the authorized fraction obtained is precipitated, for example, by a disk filter 108. The purpose of the precipitation 10 is both to increase the consistency of the pulp and to remove extracts from the pulp. The precipitated pulp is reintroduced into dilution 110 where the consistency is adjusted to suit the downstream process. Next, the pulp is fed to a scrubber 112, preferably operated by a press, either a screw or wire press. After washing, the pulp 114 is led either directly to the paper mill or to bleaching.

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Figure 5 also shows how the filtrate of the precipitator 108, in this example, the disk filter and also the washing filter of the scrubber 112, though through its own filtrate tank 116, is introduced into a circulating water tank 104, where

Up to now, only the prior art mechanical pulping process has been described. Now, in order to test the method of the invention, a decanter centrifuge 60 is connected to the process for receiving through the valve 118 the filtrate from the filtrate tank 116 of the washer 112. The centrifuge 60 is intended to recover the · · · filtrate from the filtrate. mass 114, and separates the fat-soluble extractants from the filtrate into its own flow 122.

Further, Fig. 5 shows, by reference numeral 124, the pure fresh product entering the process. ·. : water that replaces the amount of water leaving the process. The water is removed eg. 30 from the process 114, and from both the circulation tank 104 as a flow 126 and the filtrate tank 116 with the extractants as a flow 122.

'' A simulation model was used to examine the above process, which yielded well: V realistic results. The simulation is done in Balas- • · ·. 35 Simulation Software Version 2.4.08. The flowchart shown in Figure 5 has been drawn with FloSheet version 4.45 included with the Balas simulation program.

9 110580

In the simulation model, the arrows represent the direction of the current in question. The following calculation methods and parameters are used in the simulation model: - The simulation takes place at a steady state where the process is stable.

- In the simulation, the 'softwood' component, the fat-soluble extracts in both the aqueous and solid phases as the 'org' component and the water as the 'water' component are treated as solids.

- The consistency is defined as the 'softwood' flow divided by the total flow, ie fat soluble extracts are not calculated as solids.

- Only the fat-soluble extracts in the aqueous phase can be separated by debris with a press / thickener, the fat-soluble extracts in the solid phase moving with the solids. Thus, the retention of fat-soluble extracts relates only to the behavior of the fat-soluble extracts in the aqueous phase.

Retentated fat-soluble extracts remain in the aqueous phase.

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Streams and devices in the simulation model: 40. Incoming wood in the process. A solid flow rate of 1 kg / s is taken. The total amount of fat soluble extractants is known to be 8 mg / g and their proportion in the aqueous phase is 60%. The water flow is 0.992 kg / s. Thus, the consistency is: '50% and the total flow is 2 kg / s.

·: 42. Dilution to 0.65% consistency for sorting (not used in simulation).

: .., 'Dilution takes place with the filtrate of the circulation tank 7. Module used 25 CONSIS.

'48. Thickening, simulation uses typical disk filter values. Final fraction 13%, fat soluble extract retention 30%, solids recovery 99%, calculation module FLOTA2 used. For simplicity, this wafer-like precipitate produces only one filtrate. Solids in the filtrate; ' · ,. The concentration is 68.4 mg / l.

»· · * *,;. * 50. Dilution with water filtrate 44 in filtration tank to 6% consistency. Module CONSIS used.

: t: 35 52. Clamp acting as a washer. For the sake of comparison, both typical wireframe and screw press values are used for comparison.

10 110580 - Wireframe Values: final consistency 40%, fat soluble extract retention 30%, solids recovery 99%, module FLOTA2 used. The solids content of this press filtrate is 704.6 mg / l.

- Screw press values: final consistency 40%, fat soluble extract retention 0%, solids recovery 97%, module FLOTA2 used. The solids content of this press filtrate is 2106.5 mg / l.

54. Outgoing pulp either directly to a paper mill or bleaching. Also included in this mass is a solid 62 obtained by solids recovery.

44. A circulating water tank in which the incoming waters are perfectly mixed. Used MIXDIV module.

15 56. Press filtrate tank. Used MIXDIV module.

58. Solids recovery. Previously measured or otherwise known beaker centrifuge parameters, as well as typical screening method and Kiek filter parameters are used. In some of the simulations, solid-20 recovery was not used, in which case the filtrate was passed to the filtrate 64 of the press 52 leaving unchanged the solid.

'. - Beaker centrifuge values: final consistency 27%, fat soluble extract retention * 0%, solids recovery 90%, module FLOTA2 used.

•.,.: - Screening method values: 1% final consistency, 0% fat soluble extract retention, 60% solids recovery, FLOTA2 module used.

- Disc filter values: 15% final consistency, 30% fat soluble extract retention, 95% solids recovery, FLOTA2 module used.

66. Fresh water fed to the process to replace the amount of water leaving. Water Off-: * ·. '30 is supplied with the pulp 54 leaving the process, as well as any recirculation * due to dewatering 68 and filter 52 of the press 52. This replacement.!. * Fresh water is pure water.

'; *, 64. Water fraction from solid recovery, which exits the process.

:: 35 • I ·:, '* ·' 68. Water fraction from a circulating water tank that leaves the process.

"110580 60. Valve to control filtrate flow rate for solids recovery. Used FSET module.

5 70. Valve for controlling the fraction of water leaving the process water tank 68. Used module FSET.

From the results shown in Figures 6-10, it is clear that the removal of the filtrate 10 from the circulating water tank results in a significantly lower separation efficiency than the removal of the filtrate which acts as a press. The separation efficiency can be further improved by replacing the wire press with a screw press that does not retard fat soluble extractants. Improving separation efficiency also significantly increases the solids loss. Such large solids losses are no longer acceptable.

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The use of a decanter centrifuge does not degrade separation efficiency, while other solid recovery methods degrade (Fig. 9). In addition, the problem with the screening method is a high loss of solids (Fig. 6) and a decrease in the consistency of the outgoing pulp (Fig. 10). The decrease in the consistency of the outgoing pulp prevents the recovered solid 20 from being returned to the viscous pulp of the press at high points in the process; · Consistency is important (eg high consistency bleaching).

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"! The results show that the use of a decanter centrifuge for solids recovery and an efficient press (eg a screw press) can significantly reduce the use of process water from the present state. In spite of the reduction in water use,. desosane, the solubility of the fat soluble extractives is almost doubled.

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Claims (6)

110580 A method for recovering a fiber and a fiber-based solid from filtrates containing both solids and fat solids in the mechanical or chemo-mechanical pulp industry, characterized in that: a. grease-soluble extracts into the aqueous phase, b. mechanically removing the separated fiber and fibrous solids from the device; and c. removing the aqueous phase containing the fat soluble extractants as a separate flow from the device. 15 Method according to Claim 1, characterized in that the recovery of the fibers and the fiber-based solid and / or the separation of said fiber and the fiber-based solid and the fat-soluble extract is carried out by means of a beaker. 20 A process according to claim 1, characterized in that the recovery of the fibers as well as the fiber-based solids and / or the separation of said fiber and the fiber-based solids and the fat-soluble extract are carried out in a so-called. screen Bowl • ,,. a centrifuge. 25 <t The process according to claim 1, characterized in that the removal of the fiber and fiber-based solid from step b. Is carried out by means of a mechanical conveyor or scraper. ; '', 30 A process according to claim 1, characterized in that said filtrate is a filtrate of a pulp mill. • I * «* f» i t The process according to claim 1, characterized in that said fiber *: * and the fiber-based solids are removed from the device at high consistency, whereby it can be returned either directly to the paper mill or to the bleaching stream: ·. 110580