FI69139B - FOERFARANDE FOER BEHANDLING AV CELLULOSAMASSA I KONTINUERLIG FLYTANDE STROEM GENOM ANVAENDNING AV ETT TRYCKTAETT KAERL MEDETT MASSINLOPP OCH ETT MASSAUTLOPP OCH ETT INLOPP FOER B EHNDLINGSVAETSKAN OCH - Google Patents

Abstract

Cellulosic pulp is treated to obtain simultaneous pulp flow and consistency control, utilizing a pressure-tight vessel (10) having a pulp inlet (12), pulp outlet (13), treatment liquid inlet (26), liquid extraction outlet (17), and movable screen (18) adjacent the liquid outlet (17). Pulp is fed into the pulp inlet (12) at a particular flow rate, and treated pulp is withdrawn through the pulp outlet (13) at a particular flow rate. The flow rate of the pulp being withdrawn is set and controlled by controlling the flow rate of the pulp fed into the pulp inlet (12). Liquid is withdrawn through the liquid outlet (17) at a particular flow rate, and the consistency of the pulp being withdrawn through the pulp outlet (13) is set and controlled by controlling the flow rate of liquid from the liquid outlet (17). Treatment liquid is fed into the liquid inlet (26), the nature of the pulp treatment and the qualities of the pulp being controlled by controlling the temperature and chemical makeup of the pulp introduced into the liquid inlet (26). A plurality of vessels (10, 10 min , 10 sec ) may be provided with the pulp withdrawn from each vessel fed to the subsequent vessel, and the liquid withdrawn from each vessel fed to the preceding vessel.

Description

1 69139

Method for treating a continuously flowing cellulosic pulp using a pressure-resistant vessel having a pulp inlet and outlet and a treatment fluid inlet and a separation fluid outlet 5

The invention relates to a method for treating a substantially continuous flow of cellulosic pulp so as to provide simultaneous control of the flow and consistency of the cellulosic pulp by utilizing a pressure resistant vessel having a pulp inlet and a pulp outlet and a treatment fluid inlet and separation fluid outlet, comprising the steps of: ) feeding a flow of cellulosic pulp to the inlet of the vessel at a predetermined flow rate, (b) removing the treated pulp through the pulp outlet at a predetermined flow rate, (c) discharging the liquid through the liquid outlet at a predetermined flow rate.

Conventional dewatering devices based on a rotating drum, such as vacuum washers, air pressure washers, drum presses, washing buffers, and the like, have, as uniform shadow sides, an unspecified outlet consistency and that the filters must lead to filtration basins at atmospheric pressure. The outlet consistency varies due to temperature fluctuations, changes in feed flow rate, variations in pulp drying properties, and mechanical factors associated with the process equipment.

To compensate for these problems, conventional methods use filter basins as absorbers of smoothing variations, because the outgoing filtration flow varies with the outlet consistency. These large filtration basins must be equipped with level gauges. The dimensions of the basins must be substantial in order to absorb said variations and to allow sufficient air to be removed from the liquid. The large size still leads to significant heat losses as a disadvantage.

Conventional filtration basins also require sufficient ....... 'n.

2,691 39 adjustable pump capacity and hydrostatic pressure control devices for both diluting the incoming mass and circulating the excess liquid upstream to the process. Substantial Hydros-5 static pressure is required in the pump or pumps because the pressure process is conventionally maintained well above the static pressure in the filtration tank exposed to atmospheric pressure.

The introduction of a continuous diffuser, which does not require any dilution of the incoming medium density pulp and in which the outlet density is controlled by adjusting the separation flow with respect to the washing liquid flow, would represent an improvement over conventional processes. However, problems related to the pressure drop of the mass flow and the removal of air from the mass flow remained. Because the pulp suspensions often contain liquids with a fairly high surface tension, the entrained air makes the suspension foamy, elastic, and emits foul-smelling gases, and dewatering becomes cumbersome, causing handling problems in the subsequent process equipment. Placing the diffusers in series as a multistage system in a common tower jacket was only a partial solution due to the practical limitations of the number of stages in one tower.

In addition, the filtration or separation flow of conventional diffusers remains intermittent due to the principle of operation of the device. The intermittent flow requires intermittent injection of liquid into the interior of the diffuser screen. Conventional systems thus require suitable liquid tanks, level gauges, pumps and other equipment.

30 Conventional diffusers still need a separation fluid flow control device and a separate control for the previous stage for the washing liquid flow in multistage arrangements.

It is an object of the present invention to keep all inlet and outlet flows of the diffuser 35 constant and continuous in order to eliminate the problems normally associated with diffusers. The pressurized diffusers can thus be connected to a pressurized system, thus eliminating the need for intermediate leveling tanks, minimizing the pump power requirement and completely eliminating the problems of deaeration and gas emission, as the present invention no longer requires deaeration at atmospheric pressure. Surface level monitoring is no longer required and the number of flow control devices is almost halved, as the one-stage difference control device now simultaneously acts as a washing liquid control device for the previous stage. Variations in pulp properties, discharge rate, and temperature 10 do not affect the consistency of the pulp because they are completely controlled by flow control using simple control devices.

These objects have been achieved by a method such as that mentioned at the outset, preferably for treating a continuous flow of medium consistency (8-15% BD) cellulose suspensions by (d) determining the flow rate and / or other properties of the cellulose pulp removed in step (b); (b) the consistency of the removed cellulosic pulp 20 by adjusting the liquid flow rate from the liquid outlet and adjusting the pulp flow rate to the vessel inlet in step (a) in response to the determinations made in step (d).

In addition, treating the cellulose flow includes supplying the treatment liquid through the liquid inlet and may also include treating the chemical addition and / or temperature control (washing-displacement) of the liquid with respect to the properties of the pulp removed through the pulp outlet.

Further, the application of the method to a multistage pressurized diffuser system comprises connecting the desired number of said diffusers in series using the pulp removed from one diffuser as a feed to the next diffuser pulp and through a selective intermediate temperature of the treatment fluid and chemical control pulp outlet 35.

Further, passing the pulp through the 4 69139 feed tube extension or vessel between the diffusers provides the desired retention time between liquid separations. A rotary mixer at the outlet side end of the first diffuser in the series measures the mass concentration.

5 A method for maintaining constant and continuous cellulose flows is schematically illustrated with reference to the following drawings:

Fig. 1 shows a side view, partly in cross-section, of details of an exemplary diffuser-10 device that can be used in accordance with the method of the invention, Fig. 2 schematically shows a single pressurized diffuser stage, Fig. 3 shows a method for flow control, Fig. 3 shows flow control process independent of screen speed control , Fig. 4 shows a control process involving independent screen speed, temperature and chemical addition control functions, Fig. 5 shows a multistage arrangement using a flow control method, and Fig. 6 shows a multistage arrangement with flow control and showing chemical addition, heating and cooling control and retention operation.

The present inventive method maintains constant and continuous all incoming and outgoing mass or cellulose flows of the pressurized diffuser. An exemplary diffuser that can be utilized in the practice of the present invention is shown in Figure 1.

The exemplary diffuser 10 shown in Figure 1 comprises a conical jacket 11, a top portion 11 'and a base portion 11 ", a pulp inlet 12 and an outlet 13, a power-operated rotating scraper 14 mounted on the bottom of the jacket 11 to facilitate pulp flow.

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5 69139 from the diaper after 11 treatments. The drained opening 17 is located at the top of the jacket 11. The screen body 18 is mounted inside and substantially concentric with the shell 11, the body 18 having perforations or openings formed therein to allow the passage of liquid therethrough but to prevent the passage of suspended solids therethrough. The bearings 19 and 19 'are located between the body 18 and the housing 11 to allow linear movement of the screen 18 with respect to the housing 10 11 in the "A" direction.

The screen 18 is rigidly attached at one end to a bidirectional shaft 23 which passes through a seal 24 at the top of the jacket 11. A conventional actuator 25 (as disclosed in U.S. Patent 4,041,560) 15 moves the shaft 23 back and forth in direction A. Usually, the actuator 25 moves the screen 18 downward at approximately the same speed as the mass flows from the inlet 12 to the outlet 13, and then moves it up much faster, and then begin the downward mouth-2Q contagious motion again. The speed and nature of operation of the actuator 25 may be varied as desired to accomplish the purposes of the present invention, in accordance with the details, dimensions, and relative clearances of the jacket 11 and screen 18.

The treatment fluid inlet 26 is for handling the suspension passing through the jacket 11. The treatment fluid introduced through the inlet 26 is applied by means of vanes 27 arranged circumferentially around the fluid dispenser 30 15 of the sheath portion 11 "concentrically mounted by three supports 15 ', one of the supports 15' being hollow and communicating with the inlet 26.

As shown in Figure 2, an exemplary device that may be used in accordance with the method of the invention includes pressurized diffuser 10 and 35 associated inlet and outlet flow control devices and similar other devices. The mass flow (sludge) from the continuous boiler, storage tower or the like enters the pipeline 28, flows through the pump 29 (which may alternatively comprise a valve), and 5 enters the top of the vertically positioned pressurized diffuser 10 and flows past the movable screen 18. The mass flow of varying consistency to the pressurized diffuser 10 is stabilized as it passes through the diffuser 10 by fine tuning the outlet flow through the outlet 17 with respect to the flow 31 of the washing liquid introduced into the inlets 26 of said pressurized diffuser 10. The bottom discharge mixer 14 of the pressurized diffuser 10 provides a very reliable consistency control output signal to the consistency controller 32 and 15 to control controller 33. This signal controls the setpoint of controller 33 between washer fluid flow controller FIC 34 and exhaust fluid flow controller FIC 35. The operating range of the controller 33 may be limited, for example 0.9-1.3, to keep the outlet flow deviations within the desired tolerances.

The discharge flow 36 at the discharge 13 is measured by a pulp discharge flow meter 37 and a signal is sent to preset the mass flow controller FIC 38, which controls the pump 29 feeding the diffuser 10 (or controls 25 valves, depending on the pressure of the previous vessel and the pressure requirement of subsequent processes). A proportional signal is sent from the mass flow controller FIC 38 to the mass flow controller 39, which in turn controls the set point of the wash liquid controller FIC 34, which controls the flow of the wash liquid 30 to the pressure diffuser 10.

The washing (or displacement) liquid flow controller FIC 34 receives signals from the washing liquid measuring device 40 and the mass flow controller 39 to send a combined signal to the control controller 33. The combined signal from the washing liquid controller FIC 35 34 controls the washing liquid

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7 691 39 flow to the pressurized diffuser 10 through the washer fluid control device 41.

The combined signal is sent from the washer fluid controller FIC 34 to the control controller to the control ratio relay 33. The Sig-5 signal is then sent from the control controller 33 to the outlet flow controller FIC 35. The combination of signals from the outlet flow meter 42 and the control controller 33 controls the outlet flow controller.

1Q Simultaneous control of the pulp flow and consistency is thus achieved by controlling the separation liquid flow with respect to the washing liquid flow depending on the pulp discharge flow, which in turn controls the incoming pulp flow and the washing liquid flow. That is, if the consistency of the incoming mass flow of clay decreases, the separation flow increases to keep the consistency of the effluent constant / while the mass flow to the diffuser increases correspondingly to keep the outflow of fiber from the diffuser constant.

In Figure 3, the flow control system operates generally as described in Figure 2, to further optimize the performance of the pressurized diffuser 10, the speed of the screen 18 can be automatically adjusted to the average velocity of the mass flow through the pressurized diffuser 10 by a differential pressure controller PDC 44. i.e., adjusting the oil flow with the drive 25 being a hydraulic cylinder) with respect to the pressure difference between the top and bottom of the diffuser 10, measured at points 45 and 46. The optimization process is independent of the flow and consistency control system described in Figure 2.

Fig. 4 shows a flow and consistency control system as shown in Fig. 2 and the optimization method shown in Fig. 3 using a differential pressure controller PDC 44 and in addition a chemical addition controller FIC 47 and a pulp 35 temperature controller TIC 48 connected to the washing liquid 31 just before the washing liquid regulator 41 The displacement or 8 69139 wash liquid enters pipeline 49 and the chemical additions made at point 50 are controlled by a chemical addition controller FIC 47 which receives the necessary information, e.g., pH or conductivity, from transmitter 51, which 5 may be located directly in the exiting mass stream 36. Chemical the addition controller combines the signal from the transmitter 51 with the signal from the chemical flow measuring device 52 to determine the number of chemical additions passing through the chemical flow controller 53 (which may be a valve or a pump). Conduction of the scrubbing liquid through the heat exchanger 54 allows indirect heating or cooling of the mass flow through the pressurized diffuser 10. The temperature of the heat exchanger medium is controlled by the temperature controller TIC 48 and the proximity flow control device 55, the temperature data transmitter 56 being located in the outgoing mass flow 36. The location of the temperature data transmitter 56 allows automatic temperature control of the incoming mass flow by adjusting the mass flow out of the previous diffuser.

A multi-stage pressure diffuser arrangement using the flow control method can be understood with reference to Fig. 5. While Figure 2 shows in detail the flow control system of a single diffuser, Figure 5 shows> 25 multistage arrangements. The scrubber flow regulator 34 of block A becomes the differential flow controller of the diffuser 10 'of block B, and the scrubber flow controller 34' of block 8 becomes the differential flow controller of the diffuser 10 "of block C. Correspondingly, the controller 39 sends control signals 57 along control line 57 to the following 34 ', 34 "so that they are automatically set to the same flow rate.

Figure 5 shows the absence of all medium or intermediate leveling basins. Thus, the hydrostatic pressures of the smaller auxiliary pumps 35, 58 ', 58 "need only be sufficient to compensate only for, for example, the pressure drop through the control valves 41, 41' and 41" and the piping. The auxiliary pumps 58, 58 ', 58 "can, for example, increase the pressure of the washing (displacement) liquid in the diffuser 10' to what it is in the previous diffuser 5Q. This need for additional hydrostatic pressure basically corresponds to the friction loss of the mass line between the diffusers.

Since all wash (displacement) and separation fluid flows should be constant in the multistage system, the separation flow 30 from the first pressurized diffuser 10, which controls the consistency of the mass flow in the system, should be free of smoothing variations. The separation flow 30 from the diffuser 10 should thus enter the leveling or liquid basin 59. The basin 59, 15 only needed in the flow control system can be pressurized if the diffusers 10, 10 ', 10 "are connected by a pressure-resistant tube from a pressurized vessel (e.g. a continuous boiler or oxygen reactor). A steam or gas jacket acting on the gas downflow 61 through the valve 62 2Q allows the tank 59 to absorb smoothing variations. 2 according to the steps outlined in the specification.

In block C of Figure 5, the mass flow 36 "from the last diffuser 10" can flow directly to any final treatment or processing stage or storage tower. When using pressure diffusers for high temperature (above 100 ° C) washing, the outlet pressure regulator PIC 64 controls the outlet stream 36 " pressure relative to the corresponding pressure of the last pressure diffuser 10 ”by controlling the valve 65. The present invention is understandably not limited to three-stage systems.

Figure 5 shows a multistage arrangement using the flow control method 10 691 39 and the chemical addition to the washing (displacement) liquid for intermediate treatment. In principle, the chemical addition controller 47 'operates in the same way as described in connection with Figure 4.

5 Indirect heating and cooling of the wash (displacement) fluid in the heat exchanger 54 and related components also operate in the same manner as in Figure 4. However, use of the optional hydraulically filled retention vessel 66 requires the chemical addition treatment controller 10 FIC 47 'to connect the transmitter 52 and the controller 67 received signals, the controller 67 in turn receives a signal relative to the mass flow of the tube 36. A change in mass flow thus results in an immediate and relative change in chemical flow.

At the right time, a possible position correction of the controller 67 takes place via the signal from the chemical addition sensor 51, the sensor being located in the pulp discharge pipe coming from the retention vessel 66. The effect of the additional retention time on the chemical properties of the pulp can thus be detected and compensated.

In a multistage arrangement, as shown in Figure 6, it is preferred to maintain the inlet and outlet flow of the diffusers constant so as not to cause any changes in consistency throughout the system once the stability has been reached once in the first stage. Because the system of Figure 6 combines an additional lower chemical solution flow with the displacement fluid, an equal small flow from the next stage of the separation liquid is diverted and introduced, along with the chemical additions, into the displacement liquid to any previous previous stage having a corresponding pH. This outflow of separating liquid to maintain consistency is controlled by the flow controller FIC 69 together with the flow sensor 70 and the control valve 71. The flow through line 72 is kept the same as the flow through line 49 by means of a controller 68 which sends a 1: 1 control signal from the flow controller

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11 691 39 47 'to the flow controller 69.

All intermediates have similar arrangements to those described above for additives. This is also applicable to the system shown in Figure 4.

The systems described above are capable of following the method of the invention so that the flow rate of pulp discharged through outlet 36 is controlled by controlling the flow rate of 1Q pulp fed to first diffuser stage 10 (by controlling pump 29)} and are capable of setting and adjusting outlets 36, 36 ', 36 " the consistency of the effluent by controlling the flow rate of the effluent through the outlet 17 of the first diffuser stage 10 along the tube 30 (through the flow controller 35). The quality of the pulp treatment and the properties of the effluent from each stage are controlled by adding desired chemicals via pipelines 31, 31 ', 31 " into the treatment fluids introduced into the inlets 26, 26 ', 26 "and by controlling the temperature of the treatment fluid with the temperature-20 state controllers 48, 48', 48" and the associated heat exchangers 54, 54 ', 54 ". Properties of the removed mass in the tubes 36, 36' , 36 "is measured (with components 51, 51 ', 51" and 56, 56', 56 "), and in response to that measurement, the control of the chemical additives and the temperature of the treatment fluid is affected.

Although the invention has been shown and described herein in accordance with what is currently contemplated to be the most preferred and practical embodiment of the invention, it will be apparent to those skilled in the art that many modifications may be made within the scope of the inventive idea, consistent with the broadest interpretation of the appended claims. methods and embodiments.

Claims (9)

A method of treating a cellulose pulp flowing in a substantially continuous stream to achieve simultaneous control of the pulp flow and consistency using a pressure-tight vessel having a pulp inlet and pulp outlet and an inlet for the treatment liquid and an outlet for the separating liquid, the method comprises the steps of (a) feeding the pulp stream into the inlet of the vessel at a predetermined flow rate, (b) draining the treated pulp through the pulp outlet at a predetermined flow rate, (c) draining the liquid through the liquid outlet with a predetermined flow rate. , which method is characterized in that (d) determines the flow rate and / or other properties of the cellulose pulp dropped in step (b), and (e) adjusts and controls the consistency of the pulp dropped in step (b) by controlling the liquid flow rate from the liquid outlet and by controlling the mass flow velocity to the vessel inlet in step (a) in response to the determinations carried out in step (d). Method according to claim 1, further characterized by the step (f) for feeding the treatment vest into the vest entry. 30 Method according to claim 2, further characterized by the steps of (g) controlling the nature of the pulp treatment and the properties of the pulp being drained in step (b) by adding the desired chemicals in the liquid introduced in step (f), and controlling the temperature. of the liquid introduced in step (f); (H) measuring properties of the pulp discharged in step (b); and (i) controlling the chemical additives and the temperature of the liquid introduced in step (f) in response to the measurement result obtained in step (h). Method according to claim 3, further characterized by step (j) for introducing the pulp dropped in step (b) into a second treatment apparatus. 10 Process according to claim 4, further characterized by the step (k) for introducing the pulp dropped from the second apparatus into a third apparatus so that the liquid which has been drained from ice step (c) serves as the feed liquid in step (f) for the previous device. Method according to claim 4 or 5, further characterized by step (1) for storing the pulp which has been drained in step (b) before inserting the same into a subsequent apparatus 20. step (j). Method according to claim 2, further characterized by the steps of (m) measuring the properties of the pulp dropped in step (b); (N) adjusting the temperature of the pulp undergoing treatment by indirect heating or cooling of the liquid introduced in step (f); (o) controlling the chemical properties of the pulp by adding chemical additives to liquids introduced in step (f); and (p) controlling the chemical additives and temperature of the liquid introduced in step (f) in response to measurements obtained in step (m).