A METHOD OF FEEDING A SEALING MEDIUM INTO A LIQUOR FILTER AND A LIQUOR FILTER

Abstract

A method and a liquor filter, in which liquor filter sealing medium is fed via a sealing medium channel (3) into an innermost sealing zone formed by an innermost sealing member (1), an outer seal (2) and the space between them at a causticizing plant of a chemical pulp mill. The sealing medium used is an alkaline sealing liquid and/or gas, which does not substantially dilute the liquor being filtered. Advantageously the sealing medium is filtrate from the liquor filter and/or gas taken from the interior of the liquor filter.

Claims

1. A method of feeding a sealing medium into a sealing arrangement of a liquor filter in a causticizing plant of a chemical pulp mill, which arrangement seals a shaft of the filter and which sealing arrangement comprises a sealing sleeve provided with an innermost sealing zone formed by an innermost sealing member and an outer sealing member, a space between them, whereto a first sealing medium channel is led for feeding a sealing medium, wherein the sealing medium utilized is an alkaline liquid, a gas or a mixture thereof, and the alkaline liquid or gas does not substantially dilute the alkali-content of the liquor being filtered and leakage of the alkali-containing sealing liquid and/or gas out of the liquor filter is prevented by an outermost pair of seals formed of an outermost seal and an outer seal.

2. The method according to claim 1, wherein the liquor-containing sealing liquid that is used is filtrate produced by said liquor filter or group of filters in question.

3. The method according to claim 1, wherein the sealing medium in the innermost sealing zone is gas obtained from the interior of the liquor filter.

4. The method according to claim 1, wherein filtrate produced by the liquor filter or group of filters and/or gas taken from inside the liquor filter is cleaned to remove impurities before feeding the filtrate to the innermost sealing zone.

5. The method according to claim 1, wherein water is admixed into the sealing medium or fed instead of the sealing medium.

6. The method according to claim 1, wherein the innermost sealing zone seals the shaft of the filter is moving in the longitudinal direction.

7. The method according to claim 1, wherein a second sealing medium, which is water or gas, is fed into a sealing zone formed of the outermost sealing member and the outer sealing member and a space between them.

8. A liquor filter of a causticizing plant at a chemical pulp mill, wherein the liquor filter comprises: at least one sealing member arranged on a shaft that is bearing-mounted in a frame of the filter, whereby the shaft is sealed to the frame by a sealing arrangement comprising a sealing sleeve having an innermost sealing zone formed by an innermost sealing member, an outer sealing member and a space between the innermost and outer sealing member, wherein the innermost sealing zone is in fluid communication with a first sealing medium channel, wherein the first sealing medium channel is configured to connect with a pressurized flow connection from a filtrate channel in fluid communication with the liquor filter or group of liquid filters and/or with a source of an alkali liquid and/or with a source of a pressurized gas and wherein the sealing sleeve includes an outermost sealing member which together with the outer sealing member define an outermost sealing zone which is in fluid communication with a second sealing medium channel coupled to a source of a second sealing medium.

9. The filter according to claim 8, wherein leaking of liquor-containing sealing liquid out of the liquor filter has been prevented by an outermost pair of seals formed of the outermost seal and the outer seal.

10. The liquor filter according to claim 8, wherein the flow connection leading into the first sealing medium channel comprises a filter removing impurities.

11. The liquor filter according to claim 8, wherein a pressure-increasing pump, fan or compressor is connected to the flow connection leading into the first sealing medium channel.

12. The liquor filter according to claim 8, wherein the innermost sealing zone seals the shaft of the filter, which shaft is arranged movable in the longitudinal direction.

13. The liquor filter according to claim 8, wherein the surface of shaft, the innermost seal, the sealing sleeve and/or another innermost sealing member is notched and/or threaded and/or the innermost sealing zone is eccentric with respect to the shaft.

14. The liquor filter according to claim 8, wherein the lower surface of the shaft is arranged to extend into the basin underneath the level of the liquor being filtered.

15. A method to operate a sealing arrangement of a liquor filter in a causticizing plant of a chemical pulp mill, the method comprising: rotating a filter member liquor suspension in a basin of the liquor filter; extracting from the liquor filter a liquid filtrate or a gas; sealing a gap between a rotating shaft of the liquor and a sleeve or housing supporting the shaft, wherein the sealing is performed using an innermost sealing member positioned in the gap and nearest the basin in the liquor filter, a second sealing member in the gap outward of the basin along the shaft, and an outermost sealing member outward of the second sealing member along the shaft; and injecting a sealing fluid through a sealing medium channel extending through the sleeve or housing and having an opening to inject the sealing fluid into the gap and between the innermost sealing member and the second sealing member, wherein the sealing fluid includes at least one of the liquid filtrate or gas extracted from the liquor filter.

16. The method of claim 15 wherein the sealing fluid is filtered to remove particles before being injected.

17. The method of claim 15 wherein the sealing fluid is pumped or compressed to a pressure above a pressure in the gap before being injected.

18. The method of claim 15 further comprising injecting the sealing fluid into the gap and between the second sealing member and the outermost sealing member.

19. The method of claim 15 wherein the extraction of the liquid from the liquor filter includes extracting an alkaline liquid.

20. The method of claim 15 wherein the extraction of the liquid from the liquor filter includes extracting an alkaline liquid from the basin.

Description

LIST OF DRAWINGS

[0021] In the following, examples of the embodiments of the invention are disclosed in more detail with reference to the appended drawings, of which

[0022] FIG. 1 illustrates a pair of axial seals, in which sealing medium can be fed at least in between the innermost seal and the outer seal and

[0023] FIG. 2 illustrates a filter according to an embodiment of the invention, which is provided with a filter disc shaft arranged movable in the longitudinal direction and a liquid cycle arrangement using liquor as sealing medium.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Axial seals 1, 2 according to FIG. 1, which form an innermost pair of seals, are commonly used in the apparatuses of the chemical pulping industry for sealing the shaft with respect to the frame of the apparatus, such as with respect to the basin of the filter. Typically, sealing water has been led in between the seals 1, 2 via a sealing medium channel 3. The innermost seal 1 seals the shaft 10 on the side of the space to be sealed, i.e. on the side of the filter. The outer seal 2 is located outer than the innermost seal 1, on the side of the outer surface. A pressurized sealing medium channel 3 leads through a seal housing (sealing sleeve) 4 into the innermost sealing zone formed by these seals 1, 2 and the space 23 between them. Leakage from between the innermost seal 1 and the shaft 10 is not very detrimental in view of operation of the seal, but it keeps the innermost sealing surfaces clean despite the corrosive and abrasive impact of the substance inside the filter. Since impurities are prevented from getting into the innermost sealing zone due to overpressure, the outer seal 2 keeps clean and does not wear because of impurities. The innermost seal 1 can comprise, in addition to the actual seal, also other typical elements, such as a lip limiting the entry of solid substance onto the actual sealing surfaces.

[0025] In the solution according to the invention, the innermost sealing member 1 can advantageously be replaced with another type of sealing member, such as a narrow gap surrounding the shaft, or a longer sleeve or a labyrinth sealing, whereby the sealing medium continuously flows into the filter therethrough and the flow keeps the shaft clean. The smaller the clearance between the innermost seal 1 arranged to leak or the sealing members replacing it and the shaft 10, and the slower the flow, the less sealing medium needs to be pumped to flush the sealing zone. Leaking of liquor-containing sealing medium decreases the capacity of the filter, because the clean or cleaned feed liquor has to be further filtered in the filter. Therefore, its leaking is to be minimized. The surface of the shaft 10, the innermost seal 1, the seal housing (sealing sleeve) 4 and/or other sealing member can advantageously be transversely grooved or threaded for controlling the flush flow and keeping it uniformly adequate. The innermost sealing zone can also be eccentric with respect to the shaft 10 for maintaining a uniformly steady flush flow.

[0026] A third outermost seal 5 or another channeling or other arrangement leading the sealing liquid out can be arranged for ensuring that the outwardly leaking liquor-containing sealing liquid from between the outer seal 2 and the shaft 10 cannot cause problems for other components of the filter, such as the bearings of the shaft 10 and their lubrication. This outermost pair of seals or the outermost sealing zone formed by the outermost seal 5 and the outer seal 2 can be pressurized with a sealing medium, preferably water, by leading the medium into the space 24 between them via a second sealing medium channel 6. The outermost pair of seals can be pressurized also e.g. with compressed air or a mixture of compressed air and water. The pressure of the sealing medium of the outermost pair of seals is preferably only slightly higher than the pressure of the liquor-containing sealing liquid. If the pressure of the sealing water would be substantially higher than the pressure of the liquor-containing sealing liquid, leaking of sealing water into the liquor-containing innermost sealing zone could result in the leaking of the same amount of diluting water into the interior of the liquor filter. Since the outer seal 2 operates in cleaner, less abrasive and less corrosive conditions, leaking of sealing water via the innermost sealing zone can in practice be kept insignificant. Flow amounts of leakages, i.e. liquid feeds can be measured for controlling the condition of the seals. The leakage of liquor-containing sealing liquid outwardly can be controlled also by channeling the leakage flow and leading it to a separate vessel or by returning the leaked liquor into the chemical cycle or as sealing liquid. Also then it is advantageous to use the outermost seal 5 or another sealing member for preventing uncontrolled exit of alkaline sealing liquid.

[0027] If the aim is to accomplish both channeling the outward leakage and leakage control by means of sealing medium, two outer seals 2 are used, whereby two separate pairs of seals or sealing zones are formed which are sealed with a pressurized sealing medium, from between which outward leakage of liquor-containing sealing liquid and sealing medium of the outer pair of seals is led out. Then the pressure of the sealing medium between the outermost pair of seals need not be higher than the pressure of the liquor-containing sealing liquid of the innermost sealing zone.

[0028] The seals 1, 2, 5 of the pairs of seals need not be axial seals, but any connection between two parts that is to be sealed may be used, said connection having an innermost sealing zone formed of an innermost sealing member 1 and on outer seal 2, into which sealing zone a sealing medium is led. Static pairs of seals, however, are not as prone to leakage flows caused by wearing as seals of rotary, and especially longitudinally moving, parts.

[0029] FIG. 2 illustrates as a cross section the main parts of a disc filter. The liquor filter can also be a drum filter. The apparatus shown in the example is provided with a shaft 10 moving in the axial direction and provided with filter discs 21. The discs are partly inside the basin 12, and at least one discharge chute 20 is provided between them. The shaft 10 is bearing-mounted to the frame of the apparatus. Usually the filter is enclosed and sealed as a pressurized vessel for facilitating a pressure difference that intensifies the filtration. The shaft 10 is sealed at its ends by means of seal seats 4 joined to the casing of the filter. In this case the diameters of the sealing zones are of different size at different ends for minimizing leakages by means of a diameter as small as possible. An actuator moving the shaft receives the axial force caused by the diameters of different size. Several filters may be arranged in parallel, whereby they form a group of filters, the filtrate channels 19 of which, led through the shafts 10 can be connected to each other.

[0030] White or green liquor suspension to be filtered is fed into the basin 12. Solids are filtered onto the filtering surfaces of the discs and they are scraped off by means of scrapers 22 into discharge chutes 20. The shaft 10 is sealed at its both ends with respect to the frame or the casing of the apparatus by means of the innermost pairs of seals. Sealing medium is fed into the innermost sealing zone. The sealing medium, i.e. in this case sealing liquid is preferably filtrate flown through the filtering surfaces of the filter or group of filters in question. Impurities that wear and foul the sealing surfaces and components of the sealing liquid circulation are preferably filtered off from the sealing liquid. The filtrate can be obtained into the sealing liquid circulation from a filtrate channel 19 connected to the shaft 10 of the filter or group of filters, to which channel 19 a flow connection 15 is joined. Preferably the filtrate is cleaned by leading it via a filter 17. Most preferably the liquor-containing sealing liquid is taken from between the filtrate pump and the filtrate discharge control valve, where the prevailing pressure often is higher than the pressure of the filter.

[0031] The pressure of the sealing liquid is to be higher than the internal pressure of the apparatus. If needed, the pressure of the sealing liquid is increased by means of a pump 18. From the pump 18 the filtrate is led via a flow connection 16 into a sealing medium channel 3 of the seal seats 4. If the liquor for the sealing liquid is taken from a source that is pressurized or has a height difference, the pump 18 may be unnecessary. The flow connection 15 for the sealing liquid circulation or the flow connection 16 may be connected to a system feeding pressurized water, for allowing dilution of the sealing liquid or periodical flushing of the components of the sealing liquid circulation and the sealing surfaces of the pair of seals. Pressurized water or compressed air can also be led in between the outer seal 2 and the third seal 5 as sealing medium.

[0032] Often it is needed to add sodium chemical into the chemical cycle of a chemical pulp mill for compensating losses. The sodium added to the process can be introduced as a clean liquor solution via the innermost sealing zone of the liquor filter.

[0033] If gas is used as a sealing medium, it is preferably taken from inside the apparatus and after a pressure increase by means of a fan, a pump or a compressor it is fed, possibly filtered, into the sealing medium channel 3. A main principal difference compared to FIG. 2 is omitting the filtrate channel connection 19. Then the flow connection 15 is connected to the interior of the apparatus. The use of an external compressed air source does not necessarily lead to a continuous flow inside the sealing zone, and therefore its use is most appropriate when the innermost seal 1 is not arranged to leak or is not worn. Otherwise it is inevitable to let gas out from the interior of the apparatus, which causes odor disturbances.

[0034] In case an outer pair of seals formed of the outermost seal 5 and the outer seal 2 is used, sealing water and/or compressed air can be led into the space between them with the corresponding arrangements as have been used in the present apparatuses.