Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
  • B01D46/02—Particle separators, e.g. dust precipitators, having hollow filters made of flexible material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
  • B01D46/56—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours with multiple filtering elements, characterised by their mutual disposition
  • B01D46/58—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours with multiple filtering elements, characterised by their mutual disposition connected in parallel
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
  • B01D46/66—Regeneration of the filtering material or filter elements inside the filter
  • B01D46/70—Regeneration of the filtering material or filter elements inside the filter by acting counter-currently on the filtering surface, e.g. by flushing on the non-cake side of the filter
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
  • B01D46/66—Regeneration of the filtering material or filter elements inside the filter
  • B01D46/70—Regeneration of the filtering material or filter elements inside the filter by acting counter-currently on the filtering surface, e.g. by flushing on the non-cake side of the filter
  • B01D46/71—Regeneration of the filtering material or filter elements inside the filter by acting counter-currently on the filtering surface, e.g. by flushing on the non-cake side of the filter with pressurised gas, e.g. pulsed air
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
  • B01D46/90—Devices for taking out of action one or more units of multi-unit filters, e.g. for regeneration or maintenance

Definitions

• This invention relates to improvements in or relating to filtration of entrained particulate matter from a fluid.
• EP-A-244938 there is described a multi-stage fluid filtration apparatus in which a fluid passes through a primary filtration stage, and then through secondary filtration stage, before passing to the outlet.
• a filtration apparatus having a pair of parallel filtration chambers for the primary filtration stage, a pair of parallel filtration chambers for the secondary filtration stage, and one further filtration chamber, a standby chamber brought into operation when one of the other chambers is being cleaned.
• the filtration chambers are all identical.
• the filter screen area of one chamber is called A
• the total filter screen area of the apparatus is 5A whilst the filter screen area for the primary filtration stage is 2A, and the filter screen area for the secondary filtration stage, is also 2A.
• the filter screen ratio (which we define as the total filter screen area divided by the filter screen area used in the primary filtration stage, in normal operation) is 2.5.
• EP-A-602100 there is described a multi-stage filtration apparatus in which there is a pair of identical filtration chambers.
• valves are arranged such that fluid passes through one filtration chamber, in which primary filtration occurs, then through the other filtration chamber, in which secondary filtration occurs, then to the outlet.
• the filter screen ratio is 2.0.
• one of the filtration chambers is taken out of commission and all of the fluid passes through the other filtration chamber.
• the normal operation is one in which the fluid undergoes primary and secondary filtration.
• a method of filtering particulate material from a fluid using filtration apparatus having at least three filtration chambers, wherein fluid is divided into fluid streams passing through respective filtration chambers (hereinafter the "active chambers") arranged in parallel, the apparatus having a filtration chamber through which a fluid stream does not then pass (hereinafter the "standby chamber”) , wherein in each chamber the filtration medium comprises a filter screen and a cake of said particulate material accumulated thereon, and wherein to clean one of the active chambers it is taken out of operation, and at substantially the same time the standby chamber is brought into operation.
• parallel as used herein, applied either to the filtration chambers or to the fluid streams, is not used in its mathematical sense, but in the sense that the fluid is divided into fluid streams.
• the filtration chambers need not be arranged side by side so that these fluid streams are geometrically parallel; although this will often be the most convenient installation arrangement.
• Preferred methods of the present invention includes the following procedures:
• the fluid passing along the inflow conduit is split, to pass as parallel fluid streams through the active chambers, and thence into the outflow conduit.
• the fluid streams thereby undergo primary filtration. There is no secondary filtration.
• a fluid stream is passed through it as a primary filtration stage, but before this fluid stream is allowed to pass out of the apparatus it must undergo a secondary filtration stage.
• the entire fluid stream issuing from the active chamber being brought back into operation is passed through one or more of the other chambers.
• the entire fluid stream issuing from the active chamber being brought back into operation is passed through one other chamber, preferably the said standby chamber.
• the entire fluid stream from the active chamber being brought back into operation is passed back to the upstream region of the inflow conduit, where it mixes with the newly admitted fluid to be filtered.
• the latter embodiment preferably employs a said impeller means.
• the method employs apparatus which comprises a common inflow conduit feeding the respective upstream sides of the filtration chambers with parallel fluid streams, a common outflow conduit leading from the downstream sides of the chambers, a common recirculation conduit leading from the downstream sides of the chambers, the recirculation conduit leading towards the upstream sides of the chambers, impeller means to impel fluid through the recirculation conduit to the upstream sides of the chambers, and valve means downstream of each chamber, able to direct the fluid stream from the respective chamber into the outflow conduit, or into the recirculation conduit.
• the fluid passing through the recirculation conduit is fed into the inflow conduit rather than directly into one or more of the chambers.
• N there are N chambers, with N being at least 3, one chamber will typically be a standby chamber, and N-l chambers will typically be active chambers, at any given time.
• N may, for example, be 3-7.
• Preferably N is at least 4.
• said active chambers are identical to each other.
• Said one or more standby chambers may differ from the active chambers, for example in terms of their cross- sectional area, and/or area of the filter screens.
• a standby chamber may be a dedicated standby chamber, in which case it may differ from the active chambers (but does not have to) , or it may be a designated standby chamber only for a particular time, at other times being designated as an active chamber, with another chamber taking over as a standby chamber. In such embodiments all of the filtration chambers are suitably identical.
• the filter screen is rigid, and is of a material inert to the fluid undergoing filtration, and to the particulate material.
• the filter screen could be of plastics or ceramic material in certain environments but is preferably metallic.
• the filter screen could be a woven mesh or a perforated plate.
• a preferred material for the filter screen is stainless steel.
• the fluid, containing particulates to be removed may be a liquid but is preferably a gas.
• it is a waste stream in which nitrogen gas is the primary carrier.
• nitrogen gas is the primary carrier.
• it may be a waste stream in which particulates are suspended in air, or it may be a combustion gas stream. In each case nitrogen gas is the primary carrier.
• the filtration chambers and the filter screens therein are suitably stationary, in use.
• cleaning can be carried out by taking a filtration chamber out of operation, by interrupting the fluid flow therethrough.
• the cleaning of the cake on the filter screen can in certain cases be carried out by mechanical means, for example by means of a mechanical shaker or a mechanical rub-down arrangement.
• the cake may be removed from the filter screen by high- pressure water jets (this is not to be confused with the aspects expressed above relating to the increase in water content of the cake prior to cleaning) .
• the preferred way of cleaning filter screens is by use of compressed fluid, preferably compressed air. This may be delivered to the filter screen from the side which is downstream in normal use.
• the method may include providing a reverse flow of fluid (i.e. from what is normally the downstream side, to the upstream side) , and there may be superimposed onto that reverse flow one or more fluid pressure pulses.
• Reverse flow may easily be provided for by means, for example a bypass conduit arrangement and valve means controlling the flow therein, whereby fluid already filtered by the apparatus can be received from the outflow conduit and delivered to the downstream side of the chamber to be cleaned, suitably via the recirculation conduit.
• the apparatus may include means for increasing the water content of the cake, intermittently, continually or occasionally, in the method.
• Increasing the water content of the cake may have a number of benefits. Firstly, it may assist the build-up of the cake during the initial stages. Secondly, it may enhance the filtration efficiency of the cake. Thirdly, it may ease cake removal .
• Figures 1 to 3 all relate to a first embodiment of filtration apparatus having three filtration chambers, the figures showing different flow arrangements through the apparatus;
• Figures 4 to 6 relate to a second embodiment having provision for reverse flow of fluid to aid cleaning
• Figures 7 to 10 relate to a third embodiment.
• the apparatus shown in Figures 1 to 3 comprises four filtration chambers A, B, C and D positioned side by side in a row.
• each chamber there is a stainless steel woven mesh as the filter screen (not shown) made up of tubular filter screen sections.
• Each filter screen is intended to have a cake of accumulated particulate material on it.
• An inflow conduit 100 has four inlet branches 102 leading respectively to the upstream side of each chamber, that is, upstream of the filter screen.
• each outlet branch 104 Downstream of each outlet branch 104 there is a bifurcation, whereby fluid, typically combustion gases in the context of the particular apparatus described herein, flows either to an outflow conduit 106, or to a recirculation conduit 108.
• a flap valve 110 is provided at each bifurcation to determine whether fluid flows from a respective chamber into the outflow conduit 106 or the recirculation conduit 108.
• the recirculation conduit 108 is linked to the upstream end of the inflow conduit 100 by a return conduit 112. Located between the recirculation conduit 108 and the return conduit 112 is a fan 114.
• FIG. 1 the chambers A, B and C are shown in operation to filter the fluid passing through the apparatus.
• the respective valves 110 are set so that fluid flows through the outlet branches 104 of chambers A, B and C, and into the outflow conduit 106.
• the valve 110 for the chamber D is located in the alternative position and the fan is not running. This means that there is no flow of fluid through the chamber D.
• D is therefore designated as a standby chamber, but in this embodiment chambers A, B, C and D are identical and each chamber serves as a standby chamber at different times. Chambers A, B and C provide primary filtration. There is no secondary filtration.
• chamber A is shown taken out of filtering operation, for cleaning. This is simply achieved by moving the valve 110 for chamber A to its alternative position to that shown in Figure 1.
• chamber D is brought into filtering operation, this being achieved by the movement of the respective valve 110 for chamber D to its alternative position to that of Figure 1.
• the fan 114 is still not running.
• a fluid stream then passes through chamber D and into the outflow conduit 106.
• Chamber D already had on it a cake of proven efficiency from previous phases of the operation.
• Chambers B, C and D provide primary filtration. There is no secondary filtration.
• chamber A Once chamber A has been cleaned it is necessary to prepare its filter screen for the time when chamber B requires cleaning. It would be unacceptable simply to switch it back into operation then, and take chamber B out of operation.
• the filter screen within chamber A would not have a good cake of accumulated material.
• the filtration efficiency of chamber A would be inadequate and the overall filtration efficiency of the filtration apparatus would be reduced. Therefore, to prepare chamber A the apparatus is operated in a partial recirculation mode. Without altering the positions of the valves 110 from those shown in Figure 2 the fan 114 is operated. Chambers B, C and D remain in filtering operation. However a fluid stream passes through the filtration chamber A, and this fluid stream is then recirculated rather than expelled then from the apparatus.
• fluid to be filtered passes through the inflow conduit 100, and is split, to pass through each of the chambers A, B, C and D.
• the parallel fluid streams which pass through chambers B, C and D are diverted by the respective valves 110 into the outflow conduit 106.
• the fluid stream which passes through chamber A is diverted into the recirculation conduit 108 and then, via the fan 114 and return conduit 112, back into the inflow conduit 100. It then mixes at the upstream end of the inflow conduit 100 with more fluid to be filtered.
• the fluid stream which underwent primary filtration in chamber A, and only this fluid stream must undergo secondary filtration. In this way an efficient cake may be built up on the filter screen in chamber A quickly and efficiently by a primary filtration stage, but with the fluid thereby filtered having to undergo a further filtration stage in chambers B, C or D before it can leave the apparatus.
• the fan is switched off.
• the fan could be controlled by a time period, by a differential pressure switch judging the cake condition or preferably by use of an emission monitoring system (triboelectric or optical) .
• Chamber A can then be left until chamber B is to be cleaned. If wished a short further recirculation stage may be effected using chamber A, to check that its cake is still in good condition, immediately prior to taking chamber B out of operation.
• the valves 110 at the outlet sides of chambers A and B are switched to their respective alternative positions, from those shown in Figure 3, with the fan still off.
• Chamber A then provides primary filtration between the inflow conduit and the outflow conduit, as do chambers C and D.
• chamber B is operated in a recirculation mode, until it is ready, with a good cake on its filter screen.
• the fan is then switched off and chamber B is left out of operation until chamber C requires cleaning; then, chamber C is taken out of operation and chamber B is brought into operation; and so forth.
• FIG. 4 to 6 is similar to that shown in Figures 1 to 3 but additionally has provision by means of a small amount of extra ductwork in the region of the fan, and two extra flap valves, for delivering fluid already filtered by the apparatus to the upstream side of any of the chambers, in order to assist cleaning.
• an additional bypass conduit 120 instead of there being a single flow pathway between the recirculation conduit and the inflow conduit, in which pathway the fan is located (as in Figures 1 to 3), there is an additional bypass conduit 120, in which the fan 114 is located.
• This bypass conduit has a lower end connected to the return conduit 112, between the recirculation conduit 108 and the inflow conduit 100, and an upper end connected to a further conduit 122 colinear with the return conduit 112 and located between the return conduit 112 and the outflow conduit 106. Flap valves 124 are located at the upper and lower ends of the by-pass conduit .
• valves 124 are set such that fluid is drawn by the fan from the outflow conduit, through the bypass conduit 120, and into the recirculation conduit 108 in the reverse direction to that described above in relation to Figures 1 to 3.
• Valve 110 at the top end of chamber A is set such that a fluid stream is impelled through the chamber, in the reverse direction to normal .
• valves 124 are both in their alternative positions from those shown in Figure 5, and the fan is left running.
• chamber A is simply being operated in its recirculation mode to build up its filter cake, in the same manner as was described with reference to Figure 3 of the first embodiment, but with fluid passing through the bypass conduit 120 and thence through the return conduit 112.
• valves 110 and 124 By appropriate selections of the positions of valves 110 and 124, chambers B, C and D can be likewise subjected to reverse fluid streams.
• the third embodiment shown in Figures 7 to 10 does not have a fan and, unlike the embodiments described with reference to Figures 1 to 6 , has a dedicated standby chamber D, which may be different to the other chambers.
• Another difference from the embodiments of Figures 1 to 6 is that there are valves at the inlet sides of the respective chambers, butterfly valves 140 in the case of the active chambers A, B, C, and a flap valve 142 in the case of standby chamber D.
• a third difference is that there is a return conduit 144 leading from the end of the recirculation conduit 108 near the outlet branch from standby chamber D, to active chamber C, connectincj to a low position thereof. At the end of the conduit 144 adjacent to active chamber C there is a butterfly valve 146.
• FIG. 7 the normal operation of the apparatus is shown.
• the butterfly valves 140 are all open, to permit parallel fluid streams to pass through the active chambers A, B and C, from the inflow conduit 100 to the outflow conduit 106, the flap valves 110 on the downstream sides of the chambers A, B and C being configured for this.
• the position of valve 142 prevents fluid from entering standby chamber D.
• standby chamber D has been brought into operation and active chamber A has been taken out of operation for cleaning, this being achieved by switching all four valves at the downstream and upstream sides of chambers A and D to their alternative positions, from those shown in Figure 7.
• the filter in standby chamber D already has on it a good cake from previous phases of the operation.
• the fluid stream passing through standby chamber D passes directly into the outlet pathway 106, because of the position of its downstream valve 110.
• active chamber A After pulse cleaning and permitting the dust to settle for a delay period, active chamber A needs to be prepared to be brought back into operation, and this is achieved by setting the valves as shown in Figure 9, so that a fluid stream passes through chamber A in a primary filtration stage, the valves being set so that the fluid stream filtered in active chamber A is then delivered to standby chamber D, in which it undergoes a secondary filtration stage.
• chamber D fulfils two functions, being a standby filtration chamber and a filtration chamber for use as a secondary filtration stage when any of the active chambers A, B and C need to be prepared for bringing back into operation, after cleaning.
• chamber A has a good cake on it, the valves are switched again so that chamber D is taken out of operation, and the filtration is achieved by means of primary filtration only in chambers A, B and C. That is to say, the operation is once again as shown in Figure 7. This operation is later repeated with chamber B, then with chamber C.
• active chambers A and B filter as before; active chamber C does not receive a fluid stream for a primary filtration stage; standby chamber D does, but the fluid stream issuing from it passes, via the recirculation conduit 108 and return conduit 144, through the active chamber C, in which it undergoes a secondary filtration stage, before passing to the outflow conduit 106.
• the primary filtration is being carried out (sometimes with secondary filtration during cake build up; otherwise not) through three chambers, whilst altogether there are four chambers.
• the filter screen ratios as defined above are 1.33. This is much more space-efficient than the earlier proposals described above, in which the respective filter screen ratios were 2.5 and 2.0. Yet, despite this, it is found that the embodiments of the present invention offer highly effective cleaning, even though secondary filtration is not being carried out as part of the normal filtering operation.
• a number of fluid, preferably air, pulses of lower pressure may be useful in achieving a partial removal, optionally superimposed onto a reverse fluid flow, and that this may be done, in many installations, in a remarkably controlled fashion.
• a cleaning regime, of controlled pressure pulses, superimposed onto a reverse fluid flow remove approximately three-quarters of the cake, leaving one quarter as a residual base layer.
• a similar effect may be achieved by intermittently resisting the outlet from the chamber.
• the use of water in the cleaning operation, as described herein, may assist in controlled, partial cake removal. This is significant because the filtration chamber can be brought back on line at, at the least, a reasonable level of filtration efficiency. The building up of the cake can then take place at a rapid rate, this being assisted because a base layer is already present, and by the delivery of water, and/or by the gradual increase of the flow rate through the filtration chamber, as described above.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Filtering Of Dispersed Particles In Gases (AREA)
• Filtration Of Liquid (AREA)

Applications Claiming Priority (5)

Publications (1)

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Family Applications (1)

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• 1997
  • 1997-03-24 GB GBGB9706100.6A patent/GB9706100D0/en active Pending
  • 1997-08-05 CZ CZ99200A patent/CZ9900200A3/cs unknown
  • 1997-08-05 JP JP10507731A patent/JP2000516132A/ja active Pending
  • 1997-08-05 AU AU37795/97A patent/AU3779597A/en not_active Abandoned
  • 1997-08-05 WO PCT/GB1997/002109 patent/WO1998005407A1/en not_active Application Discontinuation
  • 1997-08-05 EP EP97934653A patent/EP0917489A1/de not_active Withdrawn
  • 1997-08-05 CA CA002262480A patent/CA2262480A1/en not_active Abandoned

Non-Patent Citations (1)

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