CA1049923A - Dust filter apparatus - Google Patents
Dust filter apparatusInfo
- Publication number
- CA1049923A CA1049923A CA242,275A CA242275A CA1049923A CA 1049923 A CA1049923 A CA 1049923A CA 242275 A CA242275 A CA 242275A CA 1049923 A CA1049923 A CA 1049923A
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- CA
- Canada
- Prior art keywords
- filter
- mat
- liquid
- duct
- thickness
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT
Dust filter equipment includes a fibrous mat filter having a low fibre density and a low loft so that when water is fed onto the filter it saturates the filter throughout its thickness and flows freely down the filter to form an effectively continuous body of water having a thickness virtually equal to the thickness of the mat filter.
Dust filter equipment includes a fibrous mat filter having a low fibre density and a low loft so that when water is fed onto the filter it saturates the filter throughout its thickness and flows freely down the filter to form an effectively continuous body of water having a thickness virtually equal to the thickness of the mat filter.
Description
1049923 c~s~; 3335 ~his invention relates to dust filter apparatus.
In particular, although not exclusively, the i~vention relates to dust filter apparatus for use in underground mines where it is known to induce an air flow away from a dust generating source, for example, a rock cutting head or a conveyor discharge station and to pas~ the induced air flow through the dust filter apparatus to remove particles of dust from the air.
Such dust filter apparatus which has been proposed for use with an underground coal or rock mining machine, comprised a fibrous mat filter and a nozzle which discharged a continuous spr~y of water onto the upstream facing surface of the mat filter, the intention of the spray being to continuously wash dust particles off the mat filter and so keep the filter clean and thereby ; eliminate the need for frequent replacement of uhe mat filter as is necessar~ when the mat filter is not sprayed with water. ~ibrous mat filters when wet tend to form a relatively thick bod~ of water which is contained in the passages of the fibrous mat filter by the fine fibres. With such filters their dust collection properties tend to be due to contact between the water in the body of water and the dust particles drawn through the mat filter by the air flow. As will be seen later the actual conditions of the water in the e~
body~contained by the fibres varies depending .. .
. ;~ .
upon the form of the fibrou~ mat filter.
The prior known fibrous mat filters which were sprayed with water were high fibre density filters initially i~tended for use in the dry dust filter apparatus without the water spray.
Such high fibre density fibrou~ mat filters have the fibres packed tightly or densely together to form narrow tortuous passages within the mat filter. When the fibrous mat filter becomes wet, these narrow tortuous passages produce a capillary action which tends to absorb or draw water into the passages away from the outer surface of t'ne mat filter. The water drawn into ; these passages tends to form a zone of stationary or slow moving water which tends to form a restriction in the passages. ~hus a high fibre density mat filter has a h gh resistance to air flow a~d consequently a large pressure difference is required to i~duce a desired quantity of air ,~ flow through the clean dust free, wet mat filter.
As more water is sprayed onto the high density mat filter~ the virtually stationary water remains absorbed within the mat filter while the water freshly sprayed onto the mat filter tends to run down the upstream surface of the mat filter. Upon dust particles initially being delivered onto the upstream surface of the mat filter the majorlty of particles become wetted and are discharged with the water running down the mat filter into a collection or ., , .. ..
.
1049g23 settling tank. However, some vf the particles are drawn to~ards the zon3 of virtually stationary water where they collect in the naIrow tortuous passages, the velocity of the water in the zone being insufficient to wash the dust particles out of the passages a~d off the mat filter. As the dust filtering proces~ continue~
and more particles move towards the zone of virtually stationary water~ the passages rapidly tend to become blocked with the particles.
Consequently~ the resistance to air flow through the mat filter increases with a corresponding increase in pressure d~op across the filter.
Thus, the operational life of the high fibre density fibrous mat filter is short and it is necessary to change the mat filter at frequent , intervals of time. Since the replacement of the mat filter usually interferes with an associated min~ng operation the mat filter tended to be changed less frequently than was necessary for efficient operation.
A further disadvantage of high fibre density fibrous mat filters is that the mat filter when dry and clean still efficiently collects dust particles. Thus if, in use, the water spray is cut off, say for example due to a broken supply hose~ the filter efficiently collects the dust particle~ from the air flow without being ~s continuously sprayed. Consequently, the passages of the mat filter tend to become , 104~923 blocked more rapidly and ~o the resi~tance to air flow through the mat filter would increase more rapidly than expected. ~herefore, even with regular replacement of the mat filter there is still a danger that the dust ff lter apparatus can operate in a potentlally dangerous condition.
In order to try and overcome the disadvantages encountered with ~igh fibre density fibrous mat filters it was proposed to u~e low fibre density or relatively open mat filters of high loft, for example a mat thickness of over three quarters o~
an inch. A~ain with high loft fibrous mat filters;
it was intended to continuously spray the up~tream surface with water. Unfortunately, in trials it was found that when using acceptable quantities of water, the water tended only to penetrate into the upstream margin of the mat filter. When a larger quantity of water was sprayed into the mat filter, instead of saturating all the mat filter the additional water tended to form streams ;
i running down the upstream surface of the mat filter. A further disadvantage of high loft filters is that the zone existing between the wet upstream marg-n and the dry downstream margin tends to be damp. ~he water in this damp zone tends to be stationary rather than flow down the ~ mat filter. Thus any dust particles drawn into `l the damp zone tend to stick to the mat filter and not be washed away by the low velocity water flow in t~e damp zone. Thus, the passages of the ., ,, , . - . - , .. . :: - : ,, . . :, . ........................ .
. . . . .
10~9923 mat filter tend to rapldl~ become blocked~
Conse~uently hlKh loft filters have the disadvantage that, in use, dust particles tsnd to be retained by the mat filter and block up the passages through the mat filter.
From the above descr~ption it will be appreciated that prior known fibrous mat filtera when subjected to water sprays have many disadvantages which have restricted the adoption of the fibrous mat filters in favour of dust filter apparatus comprising relatively coarse metal screens with relatively short, large cross-sectional area apertures. These metal screens are sprayed with water and dust particles tend to be removed from the air flow by impaction with the relatively th~n broken curtain of water on the flooded screen. Such dust filter apparatus has the advantage that the metal ecreen does not have to be frequently replaced but, unfortunately, it tends not to be as efficient as the previously mentioned fibrous mat filter apparatus which as previou61y stated tend to form a continuous relatively thick body of water contained in the fine fibres cGmpared with the relatively thin broken curtain of water associated with metal screens.
An object of the present invention is to provide improved dust filter apparatus which overcomes or reduces the above me~tioned disadvantages.
According to the present invention there is provided dust filter apparatus comprising a hollow chamber defining a gaseous flow duct, a filter unit including a fibrous mat filter means arranged across the duct, and nozzle means in the duct for spraying liquid into gas flowing in the gaseous flow duct on an upstream side of the mat filter means, fibers of the mat filter means being nondensely packed, the mat filter means having a low fiber density such that the mat filter tends not to retain the liquid by capillary action and permits flow of liquid throughout the thickness of the filter means in the directions parellel to, and transverse to, the direction of the gaseous flow and having a thickness such that the liquid from the nozzle means saturates the whole of the mat filter means, the arrangement being such that, in use, an effectively continuous body of flowing liquid is formed across the gaseous flow passage, the body of flowing liquid having a thickness virtually equal to the thickness of the mat filter means.
Preferably, the mat filter unit comprises a pre-filter located on the upstream side of the fibrous mat filter.
Preferably, a driven fan is provided for inducing the gaseous flow through the filter unit.
Advantageously, the mat filter and the pre-filter are mounted in a frame.
Conveniently, the frame engages in a slide arranged transversely to the gaseous flow duct.
Preferably, the frame has a formation which engages a formation on the slide to ensure correct assembly of the dust filter apparatus.
''' .
., .
' .
1049gZ3 Conveniently, a sealed settling tank is provided belo~ the mat filver unit.
Advantageously, the dust filter appara-tus comprises a pump for recirculating liquid from the settling tank to the nozzle mean~.
Preferably, a suction pipe section is provided in the settling tank for feeding liquid to the pump, the cross-sectional area of the suction pipe section being such that, in use, collected coarse particles tend not to be ca.rried by the flow of liquid along the suction pipe.
Advantageously, tbe pump is drivably coupled to the fan drive.
Conveniently, the settling ta~k is providea with means for maintaining the level of liquid in the settling tan~.
Preferably, the means ~omprises a valve which i8 connected to a liquid ~upply an1 which opens when the liquid level in the settling tank falls below a preselected level.
Preferably~ the control valve feeds liquid into the settling tank through a pipe, at least the discharge portion of which extends in the .. direction of the settling tank floor so that~ in : 25 use~ liquid fed into the settlin~ tank from the liquid supply scours the floor and urges dust ~ partic].es which have settled on the floor towards discharge means for the removal of the collected dust particles.
~0 Preferably, means are provided on the ,~ . " ' ' downstream side of the mat filter unit for removing liquid from the 1`iltered air flow.
By w~y of example only, one embodiment of the present invention will be described with reference to the accompanying drawings, in which:-Figure 1 is a set of graphs illustrating characte~istics for three different forms of fibrous mat filter;
Flgure 2 is a si.de view of dust filter apparatus;
Figure 3 is a front view of Figure 2;
; Figure 4 is a side detail of Figure 2;
Figure 5 is an end vie~ of the detail of ~igure 4;
~igure 6 is a sectional plan of the detall of Figure 4;
Figure 7 is a detail ~f Figure 6 sho~ on an enlarged scale;
Figure 8 is a side view of another detail of Figure 2;
Figure 9 is an incomplete front view of the . detail of Figure 8;
Figure 10 is an incomplete sectional pla~ of ; the details of Figure 8; and Figure 11 is an incomplete sectional side ; view of the detail of Figure 8.
Ref~rring to Figure 1 which shows three graphs A, B and C illustrating the "pressure drop across the fibrous mat filter" against the "dust incident cn the mat filter" characteristics for _ 9 _ three different forms of fibrou~ mat filter, all three mat filter~ being co~tlnuously ~prayèd with water. ~he forms of dust filter apparatus associated with graphs A and B are prior kno~m whilst the mat filter associated with graph C i8 according to the present invention.
~hroughout the testing period for each o~
the three forms of mat filters a co~stant air velocity of five meters per second wa~ maintained through the mat filter and three quarters of a gallon per minute of water was fed onto the mat filter for each square foot of mat filter surface area. Dust particles were introduced into the air flow on the upstream side of the mat filter at a constant rate.
~he form of the mat filter associated with Graph A was a high fibre density fibrous mat filter, the fibres being densely racked together so that tortuous narrow passages are provided through the mat filter. ~he mat filter had a low loft having a thickness of approximately one eight of an lnch.
As can be seen from Graph h, the clean filter has a relatively high resistance to air flow indicated by the relatively high pressure drop across the filter (almost three and a half inches of water gauge) with zero dust incident on the '~ filter mat. This is due to the resistance to air flow through the tortuous narrow passages and to water which because of the capillary action of _ 10 -: . . .
10~9923 the passages becomes absorbed into the mat filter and lodges ir the passages and thereby further increaæes the resistance to air flow through the passages. Also, because the water lodged ln the passages is held there by capillary action, the high fibre density fibrous mat filter tends to prevent the water flowing through the filter both in the directions parallel to and transverse to, the direction of air flow. Thus once the tortuous narrow passages of the high ~ibre density fibrous mat filter contain water there i5 a tendency for a zone to be formed where the water tends to remain stationary and not to flow through the filter. As more water is sprayed onto the high ~5 fibre density mat filter it tends not to ~enetrate into the passages which are already full of water but flows down th~ upstream surface of the mat filter.
When duæt particles are fed into the air stream the maaority of the particles become wetted and are removed or washed from the mat filter by the water flowing down the upstream facing surface of the mat filter. However, a proportion of the dust particles find their way into the passages i~ the zone of the mat filter containing the stationary or slow moving water where the velocity of the water is insufficient to carry the particles. Thus these dust particles tend to ætay in the paæsages and are not washed off the filters. As more dust particles are fed into 10499Z~
the air flow, an increasing number find their way into the passages which thereby rapidly become bl~cked with the particles.
Consequentl~, the pressure drop across the high fibre density fibrous mat filter increases rapidly and by the time two hundred grammes o~
dust have been fed onto each square foot of filter the pressure drop across the filter is approximately five inches of water gauge. As can ~0 be seen from the graph A upon more dust being fed onto the filter the pressure drop across the filter rapidly increases. The rapid increase in the pre~sure drop acros~ the high density mat filter and therefore~ the rapid increase to air flow through the filter is due to the dust particles blocking in the tortuous narrow passages in the mat filter~ It will be appreciated from Graph A that in order to use ; high fibre density fibrous mat filters it would be necessary to change the mat filter at very - frequent interval 8 of time. Such frequent changing of the mat filter has not proved practical in use and as a result such mat filters are not popular despite their initial high dust collection efficiency when clean and free from dust particles.
Referring now to Graph B this shows a ; similar characteristic to Graph A except the form of fibrous mat filter is of a low fibre density a~d high loft, the mat filter thickness - ~2 --being approximately three quarters of an inch.
~he fibres of the mat filter are more widely spaced from one another than the first discussed mat filter so that the tortuous passages formed through the mat filter have a larger cross sectional area than those in the prevlously discussed mat filter. The passages of the mat filter associated with Graph B are of such a large cross-sectional area that little or no capillary action affects the flow of water through the mat fi;ter and the water tends not to be absorbed by the mat filter.
The effect of the low fibre density o~ this second mat filter can be seen by looking at Graph B where the pres~ure drop across the clean or dust ~ree filter is low~ i.e. less than one half o~ an inch of water gauge, the large cross-sect,ion passages providing little resistance to air flow.
~' Since the mat filter is of a high lOft the water sprayed onto the mat filter tends to penetrate into only the upstream margin of the mat filter.
~he downstream margin of the mat filter tends to remain substantially dry and a damp zone is formed intermediate the wet and substantially dry margins. ~hus~ as soon as dust is fed into the air flow~ dust particles tend to collect in the ' damp zone and rapidly block the passages in this zone, The effect of this can be seen by the rapid increase in pressure drop across the filter , 30 as the dust fed onto the filter increases. (see , .-Graph B). The effect is similar to that for the first di8cussed mat filter and therefore, the hi~h loft fibrous mat filter has not been widely adopted for the reason previousl~ given with reference to the high den~ity fibrous mat filter.
Graph C shows the "pressure drop across the filter" against "dust incident on the mat filter"
characteristic fo~ a fibrou~ mat fi ter which is in accorda~ce with the present invention~ which has a low fibre density~ the fibres being relativel~ wi~ely spaced and which has a low loft, for example, the thickness of the mat filter being approximately one-eigh~hof an inch.
~he low fibre density ensures that the mat filter tends not to absorb water, there being little or no capillary effect a~d water tends to flow freely through the mat filter in directions parallel to~ and tra~sverse to~ the direction of air flcw.
When water is fed onto the clean mat filter it flows, as previously explained, both through the mat filter and down the mat filter. Since the fibre density is low and relatively large cross-section passages are provided by the mat ; 25 filter~ ~ater is free to flow down the mat filter throughout the whole thickness of the mat filter. ~hus, no zone of effectively stationary water i3 formed in the mat filter.
Instead a relatively thick body of water flows down the mat filter, the thickness of the body ..
1~49~Z3 of water bein~ substantially equal to the loft or thick~ess of the mat filt~r.
~he effect of the relatively thick body of water flowing down the whole thickne~s of filter can be seen in Graph C where a relatively high pressure drop across the mat filter (compared to Graph B) is encountered with zero or low amounts of dust on the we~ filter, the Graph C very rapidly approaches a maximum value. ~hus even though the mat filter has a low fibre density the effect of ~he relatively thick body of water is to provide a resistance to air flow through the filter.
However, once a maximum value for the pressure drop across the filter is reached the -pressure drop remains substantially constant irrespective of the amount of dust fed onto the filter. It can be seen from Graph C that the pressure drop across the mat filter remained constant at approximately two inches of water gauge throughout the testing period.
The reason for this constant readin~ is that because no zone of virtually stationary or slow flowing water exists in the mat filter there is no , or littl~ tendency for dust particles to remain in the mat filter. ~hroughout the whole thickness of the filtar the velocity of the water is sufficient to wash the dust pdrticles out of the passages ~; and down the filter, a large proportion of the dust particles being discharged with the water .
~ .~
. , .
- 15 _ '` ` -.
. . : . ~-lO~99Z3 falling from the bottom of the mat filter. ~he dust particles are constantly washed from the fibres of the mat filter and there i8 little or no tendency for them to be retained in and block the passages.
~hus dust filter apparatus constructed in accordance with the present invention comprising ~ low fibre density, Low loft fibrou~ mat filter can be used continuousl~ with a minimum of attention.
It should also be noted that because a low fibre density fibrous mat filter does not tend to collect dust particles when used dry, there is no danger of the pressure difference across the mat filter increasing to a dangerous condition if the water supply is cut off. If the water ~pray was inoperative the air would flow through the ~ilter and be discharged from the apparatus uncleaned.
~he dust filter apparatus will now be described in more detail with reference to Figures
In particular, although not exclusively, the i~vention relates to dust filter apparatus for use in underground mines where it is known to induce an air flow away from a dust generating source, for example, a rock cutting head or a conveyor discharge station and to pas~ the induced air flow through the dust filter apparatus to remove particles of dust from the air.
Such dust filter apparatus which has been proposed for use with an underground coal or rock mining machine, comprised a fibrous mat filter and a nozzle which discharged a continuous spr~y of water onto the upstream facing surface of the mat filter, the intention of the spray being to continuously wash dust particles off the mat filter and so keep the filter clean and thereby ; eliminate the need for frequent replacement of uhe mat filter as is necessar~ when the mat filter is not sprayed with water. ~ibrous mat filters when wet tend to form a relatively thick bod~ of water which is contained in the passages of the fibrous mat filter by the fine fibres. With such filters their dust collection properties tend to be due to contact between the water in the body of water and the dust particles drawn through the mat filter by the air flow. As will be seen later the actual conditions of the water in the e~
body~contained by the fibres varies depending .. .
. ;~ .
upon the form of the fibrou~ mat filter.
The prior known fibrous mat filters which were sprayed with water were high fibre density filters initially i~tended for use in the dry dust filter apparatus without the water spray.
Such high fibre density fibrou~ mat filters have the fibres packed tightly or densely together to form narrow tortuous passages within the mat filter. When the fibrous mat filter becomes wet, these narrow tortuous passages produce a capillary action which tends to absorb or draw water into the passages away from the outer surface of t'ne mat filter. The water drawn into ; these passages tends to form a zone of stationary or slow moving water which tends to form a restriction in the passages. ~hus a high fibre density mat filter has a h gh resistance to air flow a~d consequently a large pressure difference is required to i~duce a desired quantity of air ,~ flow through the clean dust free, wet mat filter.
As more water is sprayed onto the high density mat filter~ the virtually stationary water remains absorbed within the mat filter while the water freshly sprayed onto the mat filter tends to run down the upstream surface of the mat filter. Upon dust particles initially being delivered onto the upstream surface of the mat filter the majorlty of particles become wetted and are discharged with the water running down the mat filter into a collection or ., , .. ..
.
1049g23 settling tank. However, some vf the particles are drawn to~ards the zon3 of virtually stationary water where they collect in the naIrow tortuous passages, the velocity of the water in the zone being insufficient to wash the dust particles out of the passages a~d off the mat filter. As the dust filtering proces~ continue~
and more particles move towards the zone of virtually stationary water~ the passages rapidly tend to become blocked with the particles.
Consequently~ the resistance to air flow through the mat filter increases with a corresponding increase in pressure d~op across the filter.
Thus, the operational life of the high fibre density fibrous mat filter is short and it is necessary to change the mat filter at frequent , intervals of time. Since the replacement of the mat filter usually interferes with an associated min~ng operation the mat filter tended to be changed less frequently than was necessary for efficient operation.
A further disadvantage of high fibre density fibrous mat filters is that the mat filter when dry and clean still efficiently collects dust particles. Thus if, in use, the water spray is cut off, say for example due to a broken supply hose~ the filter efficiently collects the dust particle~ from the air flow without being ~s continuously sprayed. Consequently, the passages of the mat filter tend to become , 104~923 blocked more rapidly and ~o the resi~tance to air flow through the mat filter would increase more rapidly than expected. ~herefore, even with regular replacement of the mat filter there is still a danger that the dust ff lter apparatus can operate in a potentlally dangerous condition.
In order to try and overcome the disadvantages encountered with ~igh fibre density fibrous mat filters it was proposed to u~e low fibre density or relatively open mat filters of high loft, for example a mat thickness of over three quarters o~
an inch. A~ain with high loft fibrous mat filters;
it was intended to continuously spray the up~tream surface with water. Unfortunately, in trials it was found that when using acceptable quantities of water, the water tended only to penetrate into the upstream margin of the mat filter. When a larger quantity of water was sprayed into the mat filter, instead of saturating all the mat filter the additional water tended to form streams ;
i running down the upstream surface of the mat filter. A further disadvantage of high loft filters is that the zone existing between the wet upstream marg-n and the dry downstream margin tends to be damp. ~he water in this damp zone tends to be stationary rather than flow down the ~ mat filter. Thus any dust particles drawn into `l the damp zone tend to stick to the mat filter and not be washed away by the low velocity water flow in t~e damp zone. Thus, the passages of the ., ,, , . - . - , .. . :: - : ,, . . :, . ........................ .
. . . . .
10~9923 mat filter tend to rapldl~ become blocked~
Conse~uently hlKh loft filters have the disadvantage that, in use, dust particles tsnd to be retained by the mat filter and block up the passages through the mat filter.
From the above descr~ption it will be appreciated that prior known fibrous mat filtera when subjected to water sprays have many disadvantages which have restricted the adoption of the fibrous mat filters in favour of dust filter apparatus comprising relatively coarse metal screens with relatively short, large cross-sectional area apertures. These metal screens are sprayed with water and dust particles tend to be removed from the air flow by impaction with the relatively th~n broken curtain of water on the flooded screen. Such dust filter apparatus has the advantage that the metal ecreen does not have to be frequently replaced but, unfortunately, it tends not to be as efficient as the previously mentioned fibrous mat filter apparatus which as previou61y stated tend to form a continuous relatively thick body of water contained in the fine fibres cGmpared with the relatively thin broken curtain of water associated with metal screens.
An object of the present invention is to provide improved dust filter apparatus which overcomes or reduces the above me~tioned disadvantages.
According to the present invention there is provided dust filter apparatus comprising a hollow chamber defining a gaseous flow duct, a filter unit including a fibrous mat filter means arranged across the duct, and nozzle means in the duct for spraying liquid into gas flowing in the gaseous flow duct on an upstream side of the mat filter means, fibers of the mat filter means being nondensely packed, the mat filter means having a low fiber density such that the mat filter tends not to retain the liquid by capillary action and permits flow of liquid throughout the thickness of the filter means in the directions parellel to, and transverse to, the direction of the gaseous flow and having a thickness such that the liquid from the nozzle means saturates the whole of the mat filter means, the arrangement being such that, in use, an effectively continuous body of flowing liquid is formed across the gaseous flow passage, the body of flowing liquid having a thickness virtually equal to the thickness of the mat filter means.
Preferably, the mat filter unit comprises a pre-filter located on the upstream side of the fibrous mat filter.
Preferably, a driven fan is provided for inducing the gaseous flow through the filter unit.
Advantageously, the mat filter and the pre-filter are mounted in a frame.
Conveniently, the frame engages in a slide arranged transversely to the gaseous flow duct.
Preferably, the frame has a formation which engages a formation on the slide to ensure correct assembly of the dust filter apparatus.
''' .
., .
' .
1049gZ3 Conveniently, a sealed settling tank is provided belo~ the mat filver unit.
Advantageously, the dust filter appara-tus comprises a pump for recirculating liquid from the settling tank to the nozzle mean~.
Preferably, a suction pipe section is provided in the settling tank for feeding liquid to the pump, the cross-sectional area of the suction pipe section being such that, in use, collected coarse particles tend not to be ca.rried by the flow of liquid along the suction pipe.
Advantageously, tbe pump is drivably coupled to the fan drive.
Conveniently, the settling ta~k is providea with means for maintaining the level of liquid in the settling tan~.
Preferably, the means ~omprises a valve which i8 connected to a liquid ~upply an1 which opens when the liquid level in the settling tank falls below a preselected level.
Preferably~ the control valve feeds liquid into the settling tank through a pipe, at least the discharge portion of which extends in the .. direction of the settling tank floor so that~ in : 25 use~ liquid fed into the settlin~ tank from the liquid supply scours the floor and urges dust ~ partic].es which have settled on the floor towards discharge means for the removal of the collected dust particles.
~0 Preferably, means are provided on the ,~ . " ' ' downstream side of the mat filter unit for removing liquid from the 1`iltered air flow.
By w~y of example only, one embodiment of the present invention will be described with reference to the accompanying drawings, in which:-Figure 1 is a set of graphs illustrating characte~istics for three different forms of fibrous mat filter;
Flgure 2 is a si.de view of dust filter apparatus;
Figure 3 is a front view of Figure 2;
; Figure 4 is a side detail of Figure 2;
Figure 5 is an end vie~ of the detail of ~igure 4;
~igure 6 is a sectional plan of the detall of Figure 4;
Figure 7 is a detail ~f Figure 6 sho~ on an enlarged scale;
Figure 8 is a side view of another detail of Figure 2;
Figure 9 is an incomplete front view of the . detail of Figure 8;
Figure 10 is an incomplete sectional pla~ of ; the details of Figure 8; and Figure 11 is an incomplete sectional side ; view of the detail of Figure 8.
Ref~rring to Figure 1 which shows three graphs A, B and C illustrating the "pressure drop across the fibrous mat filter" against the "dust incident cn the mat filter" characteristics for _ 9 _ three different forms of fibrou~ mat filter, all three mat filter~ being co~tlnuously ~prayèd with water. ~he forms of dust filter apparatus associated with graphs A and B are prior kno~m whilst the mat filter associated with graph C i8 according to the present invention.
~hroughout the testing period for each o~
the three forms of mat filters a co~stant air velocity of five meters per second wa~ maintained through the mat filter and three quarters of a gallon per minute of water was fed onto the mat filter for each square foot of mat filter surface area. Dust particles were introduced into the air flow on the upstream side of the mat filter at a constant rate.
~he form of the mat filter associated with Graph A was a high fibre density fibrous mat filter, the fibres being densely racked together so that tortuous narrow passages are provided through the mat filter. ~he mat filter had a low loft having a thickness of approximately one eight of an lnch.
As can be seen from Graph h, the clean filter has a relatively high resistance to air flow indicated by the relatively high pressure drop across the filter (almost three and a half inches of water gauge) with zero dust incident on the '~ filter mat. This is due to the resistance to air flow through the tortuous narrow passages and to water which because of the capillary action of _ 10 -: . . .
10~9923 the passages becomes absorbed into the mat filter and lodges ir the passages and thereby further increaæes the resistance to air flow through the passages. Also, because the water lodged ln the passages is held there by capillary action, the high fibre density fibrous mat filter tends to prevent the water flowing through the filter both in the directions parallel to and transverse to, the direction of air flow. Thus once the tortuous narrow passages of the high ~ibre density fibrous mat filter contain water there i5 a tendency for a zone to be formed where the water tends to remain stationary and not to flow through the filter. As more water is sprayed onto the high ~5 fibre density mat filter it tends not to ~enetrate into the passages which are already full of water but flows down th~ upstream surface of the mat filter.
When duæt particles are fed into the air stream the maaority of the particles become wetted and are removed or washed from the mat filter by the water flowing down the upstream facing surface of the mat filter. However, a proportion of the dust particles find their way into the passages i~ the zone of the mat filter containing the stationary or slow moving water where the velocity of the water is insufficient to carry the particles. Thus these dust particles tend to ætay in the paæsages and are not washed off the filters. As more dust particles are fed into 10499Z~
the air flow, an increasing number find their way into the passages which thereby rapidly become bl~cked with the particles.
Consequentl~, the pressure drop across the high fibre density fibrous mat filter increases rapidly and by the time two hundred grammes o~
dust have been fed onto each square foot of filter the pressure drop across the filter is approximately five inches of water gauge. As can ~0 be seen from the graph A upon more dust being fed onto the filter the pressure drop across the filter rapidly increases. The rapid increase in the pre~sure drop acros~ the high density mat filter and therefore~ the rapid increase to air flow through the filter is due to the dust particles blocking in the tortuous narrow passages in the mat filter~ It will be appreciated from Graph A that in order to use ; high fibre density fibrous mat filters it would be necessary to change the mat filter at very - frequent interval 8 of time. Such frequent changing of the mat filter has not proved practical in use and as a result such mat filters are not popular despite their initial high dust collection efficiency when clean and free from dust particles.
Referring now to Graph B this shows a ; similar characteristic to Graph A except the form of fibrous mat filter is of a low fibre density a~d high loft, the mat filter thickness - ~2 --being approximately three quarters of an inch.
~he fibres of the mat filter are more widely spaced from one another than the first discussed mat filter so that the tortuous passages formed through the mat filter have a larger cross sectional area than those in the prevlously discussed mat filter. The passages of the mat filter associated with Graph B are of such a large cross-sectional area that little or no capillary action affects the flow of water through the mat fi;ter and the water tends not to be absorbed by the mat filter.
The effect of the low fibre density o~ this second mat filter can be seen by looking at Graph B where the pres~ure drop across the clean or dust ~ree filter is low~ i.e. less than one half o~ an inch of water gauge, the large cross-sect,ion passages providing little resistance to air flow.
~' Since the mat filter is of a high lOft the water sprayed onto the mat filter tends to penetrate into only the upstream margin of the mat filter.
~he downstream margin of the mat filter tends to remain substantially dry and a damp zone is formed intermediate the wet and substantially dry margins. ~hus~ as soon as dust is fed into the air flow~ dust particles tend to collect in the ' damp zone and rapidly block the passages in this zone, The effect of this can be seen by the rapid increase in pressure drop across the filter , 30 as the dust fed onto the filter increases. (see , .-Graph B). The effect is similar to that for the first di8cussed mat filter and therefore, the hi~h loft fibrous mat filter has not been widely adopted for the reason previousl~ given with reference to the high den~ity fibrous mat filter.
Graph C shows the "pressure drop across the filter" against "dust incident on the mat filter"
characteristic fo~ a fibrou~ mat fi ter which is in accorda~ce with the present invention~ which has a low fibre density~ the fibres being relativel~ wi~ely spaced and which has a low loft, for example, the thickness of the mat filter being approximately one-eigh~hof an inch.
~he low fibre density ensures that the mat filter tends not to absorb water, there being little or no capillary effect a~d water tends to flow freely through the mat filter in directions parallel to~ and tra~sverse to~ the direction of air flcw.
When water is fed onto the clean mat filter it flows, as previously explained, both through the mat filter and down the mat filter. Since the fibre density is low and relatively large cross-section passages are provided by the mat ; 25 filter~ ~ater is free to flow down the mat filter throughout the whole thickness of the mat filter. ~hus, no zone of effectively stationary water i3 formed in the mat filter.
Instead a relatively thick body of water flows down the mat filter, the thickness of the body ..
1~49~Z3 of water bein~ substantially equal to the loft or thick~ess of the mat filt~r.
~he effect of the relatively thick body of water flowing down the whole thickne~s of filter can be seen in Graph C where a relatively high pressure drop across the mat filter (compared to Graph B) is encountered with zero or low amounts of dust on the we~ filter, the Graph C very rapidly approaches a maximum value. ~hus even though the mat filter has a low fibre density the effect of ~he relatively thick body of water is to provide a resistance to air flow through the filter.
However, once a maximum value for the pressure drop across the filter is reached the -pressure drop remains substantially constant irrespective of the amount of dust fed onto the filter. It can be seen from Graph C that the pressure drop across the mat filter remained constant at approximately two inches of water gauge throughout the testing period.
The reason for this constant readin~ is that because no zone of virtually stationary or slow flowing water exists in the mat filter there is no , or littl~ tendency for dust particles to remain in the mat filter. ~hroughout the whole thickness of the filtar the velocity of the water is sufficient to wash the dust pdrticles out of the passages ~; and down the filter, a large proportion of the dust particles being discharged with the water .
~ .~
. , .
- 15 _ '` ` -.
. . : . ~-lO~99Z3 falling from the bottom of the mat filter. ~he dust particles are constantly washed from the fibres of the mat filter and there i8 little or no tendency for them to be retained in and block the passages.
~hus dust filter apparatus constructed in accordance with the present invention comprising ~ low fibre density, Low loft fibrou~ mat filter can be used continuousl~ with a minimum of attention.
It should also be noted that because a low fibre density fibrous mat filter does not tend to collect dust particles when used dry, there is no danger of the pressure difference across the mat filter increasing to a dangerous condition if the water supply is cut off. If the water ~pray was inoperative the air would flow through the ~ilter and be discharged from the apparatus uncleaned.
~he dust filter apparatus will now be described in more detail with reference to Figures
2 to 11 of the drawings.
~he dust filter apparatus comprises a hollow chamber 2 which provides an air flow duct extending the length of the dust filter apparatus.
lhe ends of the chamber 2 have flarges 3 for the attachme~t of extension ducting fnot shown). Air i8 induced to flow through the apparatus by a fan 4 having an im~ellor 5 located within the 'portion of the air flow duct adjacent to the inlet of the chamber 2, the inlet duct being I
',~ :
provided with a guard screen 9 (see Figure,~).
~he fan i~ driven by an electric motor 6 which ia ho~sed within the fan bifurcation between the upper and lower branches 7 and 8, the air flow duct being divided into upper or lower branches to accommodate the fan drive motor 6. The motor 6 is drivably connected through a mechanical drive mechanism 10 provided on the rear of the motor to a pu~p 11 which i8 conveniently housed alongside the motor 6. W~th such an arrangement the pump is housed within a protected zone a~d ; the one drive motor 6 drives both the fan and the pump.
~he pump 11 reciroulates water from a sealed collectio~ or settling tank 12 through pipe~ 14 ~nd 1~ to a bank of three nozzles 16 located upstream of the fan ad~aceLt to the duct inlet.
~he inlet section of the suction ~ipe 14 is located within the settling tank 12 and at least the portion 15 of the suction pipe 14 submerged ; in the water in the tank is of a sufficie~t cross-sectional area to ensure that the upward velocity of 'he water in the pipe is insufficient for collected coarse particles in the t~nk to be carried by the water flow and thereby block the noæzles 16.
The water level in the settli~g tank 12 is kept substantially at a preselected level by a control valve 18 which is actuated by a ~loating ~0 ball 19 and which feeds water from the mai~s via .. . . . . . .
~049g23 branch pipe 20 into a pa~ r of discharge pipe~ 21.
The discharg~ portion of ~ach of the pipes 21 extends in the direction of the inclined tank floox 23 so that water discharging from the pipes 21 tends to scour the floor of the tPnk to urge settled du6t particles towards a di~char~e valve 25. ~he inclination of the floor 23 also tends to assist flow of the settled dust particles towards the discharge valve 25.
~he settling tank 12 is sealed from the atmosphere to ensure air i8 not exhausted from the air flow duct through the tank. 3y adoptin~
a sealed settling tank it is possible to mount the tank immediately below the air ~low ducting.
A filter unit 30 (see particularly Figures 8 to 11) is provided across the air flow duct above the settling tank 12. Access to the filter unit is by means of doors 31 provided in each side of the chamber 2. The filter unit comprises a rigid frame 33 which slides along a slideway provided bg the chamber 2 and extending transverse to the direction of air flow. The base of the frame has a reces~ed formation 34 which is 'off' set from the centre of the frame and whicn engages in a projecting formation 35 provided on the chamber sl1deway~ The formations 34 and 35 ensure that the filter unit i c~nnot be incorrec~ly assembled in the chamber 2, A handle ~6 is provided on each qide of the frame to facilitate removal of the filter unit.
, . , . . - :
104~9~3 A fibrous mat filter 37 i8 positioned acros~
the rigid frame 33, the mat filter havin~ a low fibre density and a low loft ag previously discussed with reference to Graph C of Figure 1.
The mat filter 37 i8 supported b~ a mesh of rigid members 38 secured between the sides of the frame 33 and re].easably secured to the mat filter by spring clips (not shown).
A rigid pre-filter or screen 40 is also provided acroæs the rigid frame 33 on the upstream side of the mat filter 37. ~he pre-filter 40 removes coarse particles which otherwise may have damaged the fibrouæ mat filter and which fall into the settling tank 12 via recesses 42 formed in the base of the frame 33.
~wo series of holes 41 are provided i.n the lower æide of the frame 33 to permit free flow of water discharging from the filters 37 a~d 40 into the settling tank 12. A plurality of baffle plates 4~ (see Figure 2) are provided to prevent the air flow short circuiting below the filter uni-t 30 and below a plurality of catchment plate . assemblies 44 provided within the air flow ducting ;I on the downstream side of the filter unit.
The catchment plate assemblies 44 are shown in more detail in Figures 4, 5 and 6. Each catchment plate assembly comprises a series of inclined plate sections 45, 46, 47 and a final inline guide plate sectio~ 48. Each of the inclined plateæ 45, 46 and 47 is provided with ' i()499Z3 a water trap 51. In use, the moist air flow leaving the Lat filter has to travel along the tOItUOUS paths formed by the catchment plate assemblies. Upon the direction of air flow being changed, due to the inclined plate sections~ the water droplets which are denser ~han air are more likely to keep in a straight path and therefore tend to be trapped. The procedure is repeated by each inclined plate section until b~ the time the air flow reaches the in~ine plate æections 48 it is substaLtially free from water droplets. ~he inline plate ~ections 48 tend to direct the air ~low along the duct.
~he fibrous mat filter 37 acts to agglomerate the fine water droplets incident on the filter so that relati~ely large drops of water are carried by the a r flow leaving the filterO ~hese relatively large drops can be efficiently collected by the relatively low resistance catchment plate assemblies 44.
Drain pipes 50 are provided in the bottom of the chamber 2 ad~acent to the filter unit 30 a~d catchment plate assemblies 44 to feed the dus~
containing water towards the floor of the settling tank 12.
In operation, the dust filter apparatus is inætalled in an underground working and extension ducting extends from the apparatus towards a working face or conveyor transfer station. The filter unit is assembled on its . . . ~ - - . : .
, '~ : . .
.
slideway and located across the air flow duct.
The doors 31 are securely closed and the drive motor 6 switched on to simultaneously drive the fan and the pump to induce an ~ir flow along the duct and to spray water into the air flowing tkrough the fan. The water tends to pass through the pre-filter 40 and collects on the fibrous mat ff lter 37. A~ explained previou~ly a large proportion of the water flows freely down the mat filter thr~ughout the whole of ~ts thickne~s. A
portion of the water is carried by the air flow from the mat filter towards the oatchment plate assemblies where it is caught in the water tr~ps 51 as previou61y explai~ed. An~ wetted dust particles carried by the air flow towards the catchment plate assemblies are discharged with the water into the settling tank.
The water is collected in the settling tank 12 and recirculated through the nozzles 16 via the pump 11.
~he air ~lo~ induoed along the ducting will extract dust particles from the dust source and carry them along through the fan to the filter unit 30. ~he pre-filter 40 will collect any relatively large dust particles which thereby fall into the settling tank 12 via the recesses 42 formed i.~ the base of the frame 33 and drain pipe 50.
~he remainder of the dust particles are carried to the fibrous mat filter 37 where they ... .
~0499Z3 are wetted by contact with the relatiYely thick, continuous body of water flowing through the mat filter. Since the water throughout the thickness of the filter is flowing at a relatively high velocity the collectet wetted dust particles tend to be continuously washed off the mat filter and into the settling tank 12 via drain pipes 50.
Since the dust particles are continuously and efficiently washed off the mat filter it is not necessary for the filter to be changed frequently. The only servicing which has to be carried out is the infrequent cleaning of the settling tank 12. This is simply and quickly achieved by stopping the drive motor 6 opening the discharge valve 25 to allow dirty water to drain from the settling tank. As soon as the water level falls below a preselected level the control valve 18 is actuated by the ball 19 to feed mains water into the tank through the discharge pipes 21. The ends of the discharge pipes 21 are adapted to provide fan shaped sprays which scour the floor 23 of the tank to urge the settled dust towards the discharge valve 25.
Thus the settling tank 12 is quickly and easily cleaned and the dust filter apparatus ready for operation.
In a typical installation the cross-sectional area of the fibrous mat filter is approximately six square feet, the volume of the air flow is eight thousand cubic feet per minute ~' .-- - ~
104g923 and the pressure drop across the dust filter apparatus is five inches of water gauge. A
typical volume of water used is five gallons per minute.
Owing to increasing amounts of air breaking through the body on ~he fibrous filter as ai~
flow is increased, the resistance of the dust filter apparatus to air flow tends to be reduced at higher air volumes.
The reason for this is that water breaks away from the downstream facing surface of the mat filter and thus, at any instant of time there i5 less water present in the body of water on the filter at high air flow rates. This feature is due to the low fibre density of ~he filter which permits free flow of water through the whole thickness of the mat filter.
Consequently, the filter unit can be uset over a wide range of air flow rates maintaining high dust collection efficiencies without excessive pressure drop.
In the typical example referred to above, the same filter unit can be used with an air volume of two thousand cubic feet per minute with a pressure drop of apprcximately two inches of water gauge.
With such conditions the dust filter apparatus provides a very efficient, simple and continuous dust filter which can operate efficiently throughout a range of air flows.
. . ~ - : .
10499'~3 In Figures 2 and 3 of the drawings the dust filter appar~tus is shown floor mounted on skids 60. The apparatus may be provided with monorail mounting equipment 61 for engagement with an overhead mono~
rail track system which permits easy movement of the apparatus as the posltion of the dust source varies.
In a modification of the invention the fan may be located downstream of the filter unit so as to draw air through the filter.
In further modifications of the invention the filter unit may comprise a plurality of over lapping mat filters.
In still further modifications the mat filter may be inclined across the air flow ducting.
- 24 _
~he dust filter apparatus comprises a hollow chamber 2 which provides an air flow duct extending the length of the dust filter apparatus.
lhe ends of the chamber 2 have flarges 3 for the attachme~t of extension ducting fnot shown). Air i8 induced to flow through the apparatus by a fan 4 having an im~ellor 5 located within the 'portion of the air flow duct adjacent to the inlet of the chamber 2, the inlet duct being I
',~ :
provided with a guard screen 9 (see Figure,~).
~he fan i~ driven by an electric motor 6 which ia ho~sed within the fan bifurcation between the upper and lower branches 7 and 8, the air flow duct being divided into upper or lower branches to accommodate the fan drive motor 6. The motor 6 is drivably connected through a mechanical drive mechanism 10 provided on the rear of the motor to a pu~p 11 which i8 conveniently housed alongside the motor 6. W~th such an arrangement the pump is housed within a protected zone a~d ; the one drive motor 6 drives both the fan and the pump.
~he pump 11 reciroulates water from a sealed collectio~ or settling tank 12 through pipe~ 14 ~nd 1~ to a bank of three nozzles 16 located upstream of the fan ad~aceLt to the duct inlet.
~he inlet section of the suction ~ipe 14 is located within the settling tank 12 and at least the portion 15 of the suction pipe 14 submerged ; in the water in the tank is of a sufficie~t cross-sectional area to ensure that the upward velocity of 'he water in the pipe is insufficient for collected coarse particles in the t~nk to be carried by the water flow and thereby block the noæzles 16.
The water level in the settli~g tank 12 is kept substantially at a preselected level by a control valve 18 which is actuated by a ~loating ~0 ball 19 and which feeds water from the mai~s via .. . . . . . .
~049g23 branch pipe 20 into a pa~ r of discharge pipe~ 21.
The discharg~ portion of ~ach of the pipes 21 extends in the direction of the inclined tank floox 23 so that water discharging from the pipes 21 tends to scour the floor of the tPnk to urge settled du6t particles towards a di~char~e valve 25. ~he inclination of the floor 23 also tends to assist flow of the settled dust particles towards the discharge valve 25.
~he settling tank 12 is sealed from the atmosphere to ensure air i8 not exhausted from the air flow duct through the tank. 3y adoptin~
a sealed settling tank it is possible to mount the tank immediately below the air ~low ducting.
A filter unit 30 (see particularly Figures 8 to 11) is provided across the air flow duct above the settling tank 12. Access to the filter unit is by means of doors 31 provided in each side of the chamber 2. The filter unit comprises a rigid frame 33 which slides along a slideway provided bg the chamber 2 and extending transverse to the direction of air flow. The base of the frame has a reces~ed formation 34 which is 'off' set from the centre of the frame and whicn engages in a projecting formation 35 provided on the chamber sl1deway~ The formations 34 and 35 ensure that the filter unit i c~nnot be incorrec~ly assembled in the chamber 2, A handle ~6 is provided on each qide of the frame to facilitate removal of the filter unit.
, . , . . - :
104~9~3 A fibrous mat filter 37 i8 positioned acros~
the rigid frame 33, the mat filter havin~ a low fibre density and a low loft ag previously discussed with reference to Graph C of Figure 1.
The mat filter 37 i8 supported b~ a mesh of rigid members 38 secured between the sides of the frame 33 and re].easably secured to the mat filter by spring clips (not shown).
A rigid pre-filter or screen 40 is also provided acroæs the rigid frame 33 on the upstream side of the mat filter 37. ~he pre-filter 40 removes coarse particles which otherwise may have damaged the fibrouæ mat filter and which fall into the settling tank 12 via recesses 42 formed in the base of the frame 33.
~wo series of holes 41 are provided i.n the lower æide of the frame 33 to permit free flow of water discharging from the filters 37 a~d 40 into the settling tank 12. A plurality of baffle plates 4~ (see Figure 2) are provided to prevent the air flow short circuiting below the filter uni-t 30 and below a plurality of catchment plate . assemblies 44 provided within the air flow ducting ;I on the downstream side of the filter unit.
The catchment plate assemblies 44 are shown in more detail in Figures 4, 5 and 6. Each catchment plate assembly comprises a series of inclined plate sections 45, 46, 47 and a final inline guide plate sectio~ 48. Each of the inclined plateæ 45, 46 and 47 is provided with ' i()499Z3 a water trap 51. In use, the moist air flow leaving the Lat filter has to travel along the tOItUOUS paths formed by the catchment plate assemblies. Upon the direction of air flow being changed, due to the inclined plate sections~ the water droplets which are denser ~han air are more likely to keep in a straight path and therefore tend to be trapped. The procedure is repeated by each inclined plate section until b~ the time the air flow reaches the in~ine plate æections 48 it is substaLtially free from water droplets. ~he inline plate ~ections 48 tend to direct the air ~low along the duct.
~he fibrous mat filter 37 acts to agglomerate the fine water droplets incident on the filter so that relati~ely large drops of water are carried by the a r flow leaving the filterO ~hese relatively large drops can be efficiently collected by the relatively low resistance catchment plate assemblies 44.
Drain pipes 50 are provided in the bottom of the chamber 2 ad~acent to the filter unit 30 a~d catchment plate assemblies 44 to feed the dus~
containing water towards the floor of the settling tank 12.
In operation, the dust filter apparatus is inætalled in an underground working and extension ducting extends from the apparatus towards a working face or conveyor transfer station. The filter unit is assembled on its . . . ~ - - . : .
, '~ : . .
.
slideway and located across the air flow duct.
The doors 31 are securely closed and the drive motor 6 switched on to simultaneously drive the fan and the pump to induce an ~ir flow along the duct and to spray water into the air flowing tkrough the fan. The water tends to pass through the pre-filter 40 and collects on the fibrous mat ff lter 37. A~ explained previou~ly a large proportion of the water flows freely down the mat filter thr~ughout the whole of ~ts thickne~s. A
portion of the water is carried by the air flow from the mat filter towards the oatchment plate assemblies where it is caught in the water tr~ps 51 as previou61y explai~ed. An~ wetted dust particles carried by the air flow towards the catchment plate assemblies are discharged with the water into the settling tank.
The water is collected in the settling tank 12 and recirculated through the nozzles 16 via the pump 11.
~he air ~lo~ induoed along the ducting will extract dust particles from the dust source and carry them along through the fan to the filter unit 30. ~he pre-filter 40 will collect any relatively large dust particles which thereby fall into the settling tank 12 via the recesses 42 formed i.~ the base of the frame 33 and drain pipe 50.
~he remainder of the dust particles are carried to the fibrous mat filter 37 where they ... .
~0499Z3 are wetted by contact with the relatiYely thick, continuous body of water flowing through the mat filter. Since the water throughout the thickness of the filter is flowing at a relatively high velocity the collectet wetted dust particles tend to be continuously washed off the mat filter and into the settling tank 12 via drain pipes 50.
Since the dust particles are continuously and efficiently washed off the mat filter it is not necessary for the filter to be changed frequently. The only servicing which has to be carried out is the infrequent cleaning of the settling tank 12. This is simply and quickly achieved by stopping the drive motor 6 opening the discharge valve 25 to allow dirty water to drain from the settling tank. As soon as the water level falls below a preselected level the control valve 18 is actuated by the ball 19 to feed mains water into the tank through the discharge pipes 21. The ends of the discharge pipes 21 are adapted to provide fan shaped sprays which scour the floor 23 of the tank to urge the settled dust towards the discharge valve 25.
Thus the settling tank 12 is quickly and easily cleaned and the dust filter apparatus ready for operation.
In a typical installation the cross-sectional area of the fibrous mat filter is approximately six square feet, the volume of the air flow is eight thousand cubic feet per minute ~' .-- - ~
104g923 and the pressure drop across the dust filter apparatus is five inches of water gauge. A
typical volume of water used is five gallons per minute.
Owing to increasing amounts of air breaking through the body on ~he fibrous filter as ai~
flow is increased, the resistance of the dust filter apparatus to air flow tends to be reduced at higher air volumes.
The reason for this is that water breaks away from the downstream facing surface of the mat filter and thus, at any instant of time there i5 less water present in the body of water on the filter at high air flow rates. This feature is due to the low fibre density of ~he filter which permits free flow of water through the whole thickness of the mat filter.
Consequently, the filter unit can be uset over a wide range of air flow rates maintaining high dust collection efficiencies without excessive pressure drop.
In the typical example referred to above, the same filter unit can be used with an air volume of two thousand cubic feet per minute with a pressure drop of apprcximately two inches of water gauge.
With such conditions the dust filter apparatus provides a very efficient, simple and continuous dust filter which can operate efficiently throughout a range of air flows.
. . ~ - : .
10499'~3 In Figures 2 and 3 of the drawings the dust filter appar~tus is shown floor mounted on skids 60. The apparatus may be provided with monorail mounting equipment 61 for engagement with an overhead mono~
rail track system which permits easy movement of the apparatus as the posltion of the dust source varies.
In a modification of the invention the fan may be located downstream of the filter unit so as to draw air through the filter.
In further modifications of the invention the filter unit may comprise a plurality of over lapping mat filters.
In still further modifications the mat filter may be inclined across the air flow ducting.
- 24 _
Claims (17)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Dust filter apparatus comprising a hollow chamber defining a gaseous flow duct, a filter unit including a fibrous mat filter means arranged across the duct, and nozzle means in the duct for spraying liquid into gas flowing in the gaseous flow duct on an upstream side of the mat filter means, fibers of the mat filter means being nondensely packed, the mat filter means having a low fiber density such that the mat filter tends not to retain the liquid by capillary action and permits flow of liquid throughout the thickness of the filter means in the directions parallel to, and transverse to, the direction of the gaseous flow and having a thickness such that the liquid from the nozzle means saturates the whole of the mat filter means, the arrangement being such that, in use, an effectively continuous body of flowing liquid is formed across the gaseous flow passage, the body of flowing liquid having a thickness virtually equal to the thickness of the mat filter means.
2. Apparatus as claimed in claim 1, in which the filter unit comprises a pre-filter located upstream of the fibrous mat filter means.
3. Apparatus as claimed in claim 2, in which the fibrous mat filter means and the pre-filter are mounted in a frame.
4. Apparatus as claimed in claim 3, in which the frame engages in a slide arranged transversely to the gaseous flow duct.
5. Apparatus as claimed in claim 4, in which the frame has a formation which engages a formation on the slide to ensure correct assembly of the dust filter apparatus.
6. Dust filter apparatus comprising a hollow chamber defining a gaseous flow duct, a filter unit including a fibrous mat filter arranged across the duct, and nozzle means in the duct for spraying liquid into gas flowing in the gaseous flow duct on an upstream side of the mat filter, the mat filter having a low fibre density such that the mat filter tends not to retain the liquid by capillary action and permits flow of liquid throughout the thickness of the filter in the directions parallel to, and transverse to, the direction of gaseous flow and having a thickness such that the liquid from the nozzle means saturates the whole of the mat filter, the arrangement being such that, in use, an effectively continuous body of flowing liquid is formed across the gaseous flow passage, the body of flowing liquid having a thickness virtually equal to the thickness of the mat filter, fan means for inducing the gaseous flow through the filter unit, and a sealed settling tank connect-ed to a bottom of the duct below the filter mat.
7. Apparatus as claimed in claim 6, comprising a pump having a suction pipe connected to the settling tank having an outlet pipe connected to the nozzle means for recirculating liquid from the sealed settling tank to the nozzle means.
8. Apparatus as claimed in claim 7, in which the suction pipe section is provided in the settling tank for feeding liquid to the pump, a diameter of the suction pipe being sufficiently large such that, in use, collected coarse particles tend not to be carried by the flow of liquid along the suction pipe.
9. Apparatus as claimed in claim 8, in which the pump is driveably coupled to the fan drive.
10. Dust filter apparatus comprising a hollow chamber defining a gaseous flow duct, a filter unit including a fibrous mat filter arranged across the duct, and nozzle means in the duct for spraying liquid into gas flowing in the gaseous flow duct on an upstream side of the mat filter, the mat filter having a low fibre density such that the mat filter tends not to retain the liquid by capillary action and permits flow of liquid throughout a thickness of the filter in the directions parallel to, and transverse to, the direction of gaseous flow and having a thickness such that the liquid from the nozzle means saturates the whole of the mat filter, the arrangement being such that, in use, an effectively continuous body of flowing liquid is formed across the gaseous flow passage, the body of flowing liquid having a thickness virtually equal to the thickness of the mat filter, fan means for inducing flow through the filter unit, a sealed settling tank provided below the filter unit, and means for maintaining the level of liquid in the settling tank to a preselected level.
11. Apparatus as claimed in claim 10, in which the said means for maintaining the level comprises a valve which is connected to a liquid supply and which opens when the liquid level in the settling tank falls below a preselected level.
12. Apparatus as claimed in claim 11, in which a control valve feeds liquid into the settling tank through a pipe, at least the discharge portion of which extends in the direction of a settling tank flow so that, in use, liquid fed into the settling tank from the liquid supply scours the floor and urges dust particles which have settled on the floor towards discharge means for the removal of the collected dust particles.
13. Dust filter apparatus comprising a hollow chamber defining a gaseous flow duct, a filter unit including a fibrous mat filter arranged across the duct, and nozzle means in the duct for spraying liquid into gas flowing in the gaseous flow duct on an upstream side of the mat filter, the mat filter having a low fibre density such that the mat filter tends not to retain the liquid by capillary action and permits flow of liquid throughout the thickness of the filter in the directions parallel to, and transverse to, the direction of gaseous flow and having a thickness such that the liquid from the nozzle means saturates the whole of the mat filter, the arrangement being such that, in use, an effectively continuous body of flowing liquid is formed across the gaseous flow passage, the body of flowing liquid having a thickness virtually equal to the thickness of the mat filter, and means on the downstream side of the mat filter for removing liquid from the filtered gas flow.
14. The dust filter apparatus of claim 13 further comprising gaseous flow inducing means intermediate the nozzle means and the filter unit for inducing gaseous flow in the duct.
15. The dust filter apparatus of claim 1 further comprising gaseous flow inducing means intermediate the nozzle means and the filter unit for inducing gaseous flow in the duct.
16. The dust filter apparatus of claim 6 wherein the fan means is positioned in the duct intermediate the nozzle means and the filter unit for inducing gaseous flow in the duct.
17. The dust filter apparatus of claim 1 wherein the mat filter means has a thickness of approximately one-eighth of an inch.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA242,275A CA1049923A (en) | 1975-12-22 | 1975-12-22 | Dust filter apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA242,275A CA1049923A (en) | 1975-12-22 | 1975-12-22 | Dust filter apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1049923A true CA1049923A (en) | 1979-03-06 |
Family
ID=4104807
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA242,275A Expired CA1049923A (en) | 1975-12-22 | 1975-12-22 | Dust filter apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1049923A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4380353A (en) * | 1979-03-14 | 1983-04-19 | Peabody Coal Company | Dust control system and method of operation |
| US6478859B1 (en) | 2000-11-03 | 2002-11-12 | Keith A. Ferlin | Airborne particulate removal apparatus |
-
1975
- 1975-12-22 CA CA242,275A patent/CA1049923A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4380353A (en) * | 1979-03-14 | 1983-04-19 | Peabody Coal Company | Dust control system and method of operation |
| US6478859B1 (en) | 2000-11-03 | 2002-11-12 | Keith A. Ferlin | Airborne particulate removal apparatus |
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