AU2010265841A1

AU2010265841A1 - Uni-directional air supply throttle

Info

Publication number: AU2010265841A1
Application number: AU2010265841A
Authority: AU
Inventors: Karl August Christiansson
Original assignee: Outotec Oyj
Current assignee: Metso Outotec Oyj
Priority date: 2009-06-23
Filing date: 2010-06-22
Publication date: 2012-01-19
Anticipated expiration: 2030-06-22
Also published as: EP2445608A4; EP2445608A1; AU2010265841B2; NZ597265A; WO2010148437A1

Abstract

A fabric filter is disclosed including a clean air plenum and a dirty gas side separated by a cell plate which includes concentric rings of holes providing gas communication between the two sections. The holes have connected thereto respective filter media bags for collecting contamination held in suspension in the gas being filtered. In order to clean the filter bags there is provided a back flushing gas pulse generator which includes a main diaphragm valve in direct communication with a hollow rotatable shaft which leads to a gas pulse distributor having arms which sweep across the clean air plenum side of the cell plate. A supply throttle is located in a supply line to the gas pulse generator such that reverse flow is restricted when a gas pulse generator associated with an adjacent fabric filter if operated. The supply throttle is a static device that has a preferred direction of flow.

Description

WO 2010/148437 PCT/AU2010/000779 Uni-directional air supply throttle Introduction The present invention relates to a baghouse or fabric filter apparatus of the gas 5 pulse type and more particularly to such apparatus which includes an improved means for isolating individual reservoirs of parallel operated pulse generators from an air supply mains during periods of low pressure when one such reservoir is at a low pressure during or after injecting an air pulse into filter bags to be back-flushed. 10 Background Baghouse or fabric filter apparatus for dust collection is known in which a gas stream to be cleaned is directed through an elongate filter bag from its outside to its inside and the bag is periodically cleaned by injecting into it, against the gas stream, a gas pulse which serves to very briefly pressurise the interior of the bag and to reverse 15 the direction of gas flow through the filter bag and to thereby remove from the bag particulate matter that had been retained on the filter medium from which the filter bag is constructed. In one known type of such filter low pressure cleaning air is used for cleaning the filter bags. The unique feature of this type of filter is that each pulse valve is able 20 to clean a large number of filter bags. The number of bags flushed by each cleaning pulse valve can be up to 2000 and the length of the filter bags can be up to 9 metres. The cleaning pulse valve is a diaphragm pulse valve and is integrated with a reservoir or tank making a pulse valve/tank assembly. The cleaning air pulse is generated by a rapid opening of the diaphragm valve, which allows the pressurized air in the tank to 25 discharge rapidly into a centre extension pipe. This cleaning air pulse is then delivered to a number of rotating manifold arms that are fitted with nozzles. These nozzles rotate over coaxial rows of filter bags that hang below the rotating manifold arms such that each pulse flushes a plurality of bags in each sector over which a manifold arm is present. 30 US Patent No. 4,854,951 discloses a fabric filter apparatus of the gas pulse type having: a) a housing body including a dirty gas side with an inlet thereto and a clean air plenum with an outlet therefrom; b) a cell plate cell plate mounted in the housing body separating the dirty 35 gas side from the clean air plenum and having a plurality of concentric rings of holes in the cell plate which are circularly spaced thereon, each hole in a ring having a filter bag depending therefrom; WO 2010/148437 PCT/AU2010/000779 2 c) a gas pulse generator, for generating pulses of back-flushing gas from a single source and having an outlet therefrom; and d) a high volume low pressure pulse jet manifold arm extending radially across and spaced above the concentric rings of holes in the cell plate within 5 the clean air plenum and, having an inlet in fluid communication with the outlet of the back-flushing gas pulse generator and a plurality of radially spaced orifices therefrom, each of the orifices being fitted with a nozzle and being spaced to rotationally traverse over and successively fluid communicate with some or all of the holes in a one of the radially spaced concentric rings. 10 In this apparatus the back-flushing gas pulse generator includes a gas reservoir which is located over and connected to the inlet of the high volume low pressure pulse jet manifold arm by a pulsing valve provided between the pulsing tank and the rotating manifold arm to periodically allow a pulse of gas to flow from the pulsing tank, into the manifold arm from which it is directed into filter bags over which the 15 nozzles of the manifold arm are currently located. Typically pulse jet systems are built with a number of housing bodies located adjacent to one another with a corresponding number of gas pulse generators operated in parallel such that one gas pulse generator services each housing body. A pulse tank (i.e. reservoir) of each gas pulse generator is connected to a common supply main 20 from which it is refilled after discharging to clean a set of bags. Therefore gas will flow in reverse toward the supply main from other pulse tanks while one tank is discharged or at a lower pressure when compared to the pressure in the supply main or the other pulse tanks. Check valves or non return valves might be employed to isolate the pulse tanks preventing reverse flow to the supply main but such valves can reduce 25 operational reliability and have parts which wear over time, presenting increased maintenance issues. Summary In a broad form the present invention may be said to provide a gas filter 30 apparatus having a housing body including a dusty gas section with a main inlet thereto and a clean gas section with a main outlet therefrom; a cell plate mounted in the housing body separating the dusty gas section from the clean gas section and having a plurality holes, each having a filter media sleeve depending therefrom; a gas pulse generator mounted on the body for generating pulses of back-flushing gas from 35 a single source and having a generator outlet for discharging gas therefrom; and a rotary back-flushing gas pulse distributor within the clean gas section, extending across the cell plate and spaced from the holes in the cell plate, having a distributor inlet in fluid communication with the generator outlet and a plurality of spaced WO 2010/148437 PCT/AU2010/000779 3 orifices, each respective orifice being aligned with one of the holes so as to provide gas communication therewith; the apparatus being characterised in that in that the gas pulse generator includes an air pulse tank connected to a supply main through a flow restrictor having a control element with an internal cross sectional area which reduces 5 in the direction from the supply side to the pulse tank side, whereby resistance to flow in a first direction towards the pulse tank from a supply side is lower than resistance to flow in the opposite direction. The flow restrictor is preferably a static device. The restrictor element may comprise a hollow frustconical element inserted 10 within a supply pipe connected to the pulse tank and through which air is supplied to the pulse tank. The restrictor element may include a flange at a wide end thereof, the flange having a diameter matched to a diameter of facing flanges on adjacent ends of supply pipe segments such that the restrictor is mounted in the supply pipe by clamping the 15 flange of the restrictor between the facing flanges of the supply pipe segments. Alternately the restrictor element may extend from the inner wall of a tube arranged to be connected in line in a supply line pipe. The frustconical element may be bounded at its open (narrow) end by a short constant diameter tubular section. A similar (but larger diameter) constant diameter 20 tubular section may be located at the wide end of the frustconical element. Each of the constant diameter sections of the flow restrictor are in the range of 25-35% of the length of the frustconical element and the internal diameter of the frustconical element at its narrow end is in the range of 40-60% of the diameter at the wider end giving an area ratio of approximately 16-36%. The length of the frustconical element is 25 preferably in the range of 0.95 to 2.10 times the internal diameter of the frustconical element at its narrow end. The holes in the cell plate will generally be formed in radially spaced, concentric rings with each hole in a ring having a filter media depending therefrom although other configurations are also possible. 30 The manifolds generally extend radially across and spaced from the concentric rings of holes in the cell plate and include a plurality of radially spaced orifices, one respective orifice for each respective ring of holes, each respective orifice subscribing a circular path over the ports of the respective ring of holes. The orifices are preferably aligned with the holes of a respective ring so as to provide successive 35 flushing of the holes in the ring.

WO 2010/148437 PCT/AU2010/000779 4 Brief description of the drawings Hereinafter given by way of example only is a preferred embodiment of the present invention described with reference to the accompanying drawings in which: Fig. 1 is a perspective top view of a filter installation having four individual 5 sets of pulse jet filters; Fig. 2 is a vertical sectional view through an upper part of apparatus according to the present invention; Fig. 3 is a side view of the gas pulse generator of the apparatus of Fig. 2 on an enlarged scale showing the location of the flow restrictor relative to the gas 10 pulse generator; Fig. 4 is an end elevation and sectional side elevation of an embodiment of a flow restrictor for controlling gas flow between a supply mains and a pulse tank; Fig 5 is a schematic side view of the supply throttle fitted to a supply line; Fig. 6 is a schematic diagram of a slotted nozzle for a rotating manifold arm; 15 Fig.7 is a sectional side view of a check valve in the closed position; Fig. 8 is a sectional side view of the check valve of Fig. 7 modified to limit its opening aperture, shown in the closed position; and Fig. 9 is a sectional side view of the modified check valve of Fig. 7 in the open position. 20 Detailed description Fig. I provides an overview of the bag house or fabric filter apparatus 100 for dust collection to which the present invention applies. The installation illustrated in Fig. 1 has 4 pulse jet filters 101, 102, 103, 104 constructed in a single structure. Each 25 Pulse jet filter includes an air pulse generator 18 supplied from a common blower 105 via a common supply line 106 and individual branch supply lines 51. Inlet ducting 107 under the baghouse 100 provides dirty air to inlets 108 in the bottom of the apparatus. The individual filter apparatus 10, as is best seen in Fig. 2 comprises: 30 (a) a housing 11 which includes a dirty gas side 12 having an inlet 108 (see Fig. 1) and a clean air plenum 13 with an outlet 109 (see Fig. 2); (b) a cell plate 14 mounted in the housing 11 and separating the dirty gas side 12 from the clean air plenum 13 and having a plurality of concentric rings of holes 15 circularly spaced on the cell plate 14; each hole 15 has a filter bag 16 depending 35 therefrom. Each of the bags 16 is supported against collapse by a wire cage 17; (c) air pulse generator 18 mounted on the housing 11 for generating pulses of back-flushing gas; and WO 2010/148437 PCT/AU2010/000779 5 (d) high volume low pressure pulse jet manifold arms 23, 24 extending radially across and spaced above the concentric rings of holes 15 in the cell plate 14 within the clean air plenum 13 of the housing 11. The housing 11, cell plate 14, and filter bags 15 may be of entirely 5 conventional construction and will not be further described herein. The high volume low pressure pulse jet manifold 19 includes a vertical extension tube 21 which is in fluid communication with an outlet tube or blow pipe 22 (see Fig. 3) of the gas pulse generator 18. At its lower end tube 21 is connected to a pair of radially extending gas manifolds 23 and 24. Each manifold arm 23 and 24 extends across and 10 above the cell plate 14 and carries a plurality of downwardly directed nozzles 25. The nozzles 25 of the manifold arms 23, 24 are so positioned that they distribute cleaning air pulses to clean all filter bags evenly. Clearly the manifold arms 23 and 24 can be produced in alternative manners as a matter of design preference. For example, the nozzle 25 of each manifold arm 23 and 24 can be arranged as a 15 plurality of equally radially spaced pairs, each nozzle 25 of a respective pair aligning upon rotation with its respective ring of holes 15. Referring to Fig. 6 each nozzle 25 incorporates a simple primary nozzle 125 and a slotted inductor 140 to improve the effectiveness of the cleaning air pulse in the filter bag. The slotted inductor 140 comprises two pairs of converging plates 141, 20 142. A lower pair of the converging plates 141 is located either side of the outlet port 143 of the primary nozzle 125 and extends below the outlet port 143 by a distance 145 to form a secondary outlet port 144. The second pair of converging plates 142 is located either side of the primary nozzle 125 above the first pair of plates and angled towards the space between the first pair of plates 141 and the primary nozzle 125 to 25 form a first pair of slots between the second pair of plates 142 and the first pair of plates 141 through which air 151 is drawn, and a second pair of slots between the second pair of plates and the sides of the primary nozzle 125 through which air 152 is also drawn as a result of a low pressure area created by the flow of the air 150 through the port 143 of the primary nozzle 125 and the secondary port 145 formed by the first 30 pair of plates. The resultant flow 153 through the secondary port 145 comprises the combination of air flows 150, 151 & 152. This increased flow through each nozzle 25 and into a respective bag to be back flushed results in a higher flow of flushing air into the respective bag for a given flow through the primary nozzle 125, thereby 35 allowing more nozzles to operate from a single pulse tank. The tube 21 and manifolds 23 and 24 are supported by an upper bearing 26 connected to the housing 11 and by a support 27 and a lower bearing 28. A seal 36 is provided around the tube 21 where it penetrates the housing 11.

WO 2010/148437 PCT/AU2010/000779 6 Referring to Fig. 3 the air pulse generator 18 is illustrated in greater detail. Associated with the upper bearing 26 is a drive assembly comprising a motor 43 and a gearbox 42 which cause the high volume low pressure pulse jet manifold 19 to rotate The air pulse generator 18 includes a body 40 which is mounted directly above 5 housing 11. The body 40 constitutes an air pulse tank or reservoir which receives air from the blower 105 through the common supply line 106 (see Fig. 1) and the branch supply line 51, isolation valve 52, a compression connector 53 and inlet stub 44. The housing 40 includes a substantially cylindrical side wall 54 and a curved top wall 55 and bottom wall 49. A main diaphragm valve assembly 56 is bolted onto brackets 45 10 extending from the top wall 55 and sits in concentric alignment with the blow pipe 22. The diaphragm valve 56 includes a normally closed two way unloading valve 57 which cooperates with a valve seat 60 formed on the upper end of the blow pipe 22. The valve 57 comprises a main valve diaphragm 58 made of a neoprene impregnated woven nylon fabric sheet which has two small diametrically spaced 15 orifices in it (not shown). A circular seal plate 59 and a backing plate 61 are connected to the diaphragm 58 concentrically therewith. The seal plate 59 serves to make sealing engagement with the valve seat 60 at the upper end of the blow pipe 22. A coned cover 62 having a flat centre (top) section 63 incorporates an O.D. flange 64 which is bolted to the bracket 45. A bumper 65 is bonded to the underside 20 of the flat section 63 of cover 62 in concentric relation therewith. A main diaphragm spring upper retainer cup 66 mounts a main valve exhaust port 67 in concentric and inverted relationship atop the cover section 63. A main valve compression spring 70 seats in the upper retainer cup 66 and bears against the backing plate 61 to urge the seal plate 59 against the valve seat 60. 25 A reverse logic, normally closed, two-way pilot diaphragm valve 68 is mounted on the top side of cover 62. The pilot diaphragm valve 68 comprises a cylindrical body 69 which encompasses the spring retainer cup 66 and main valve exhaust port (not shown) and has a plurality of exhaust ports (not shown) in the wall thereof. 30 A solenoid operated or pneumatically-operated trigger valve 74 sits on top of the pilot diaphragm valve 68 and when operated, dumps the pilot diaphragm valve to generate a pulse of gas by unloading the main valve thereby allowing the gas pulse to flow through the blow pipe 22 into the high volume low pressure pulse jet manifold 19. The valves 56, 68 and 74 are housed within a silencer 81 to reduce operating 35 noise. When the pulse air tank is opened to the blowpipe 22 and the high volume low pressure pulse jet manifold 19 in prior art systems, wastage occurs when there is a sudden drop in pressure in the pulse tank 54 causing back flow from other pulse tanks WO 2010/148437 PCT/AU2010/000779 7 of other fabric filter apparatus connected to the same blower 105 and common supply line 166 (see Fig. 1). This happens immediately after a back-flush pulse and until the pulse valve is closed again and pressure builds in the pulse tank 54. By inserting an air supply throttle 111 in the branch supply line 51 reduces this wastage by limiting 5 back flow from other pulse tanks (i.e. those that have not just created a back-flush pulse). The air supply throttle 111 is less resistant to air flow in the forward direction, while the tank is being filled from common supply main 106 and therefore allows filling of the tank in sufficient time, but offers greater resistance to flow in the reverse direction when another tank is being dumped to generate a back-flush pulse. 10 The air supply throttle 111 is located in the branch supply line 51 between the common supply line 106 and the isolation valve 52 of the respective pulse tank 54. Referring to Figs. 4 and 5, the air supply throttle 111 is an in-line device having a flange 112 and a tapered throat 113, extending from the flange and having an inlet external diameter similar to the internal diameter of the branch supply line 51 into 15 which it is connected. The throttle may be connected into the branch supply line 51 by clamping the flange 112 between two abutting flanged line ends 114, 115 with the tapered throat 113 extending into the line end 115 on the pulse tank side. The flanged end 114 of the branch supply line 51 is provided with clamping bolt holes 118 which align with similar holes 119 in the flanged end 115 of the adjacent branch supply line 20 section. The tapered throat 113 is bounded at its open (narrow) end by a short constant diameter tubular section 116. A similar (but larger diameter) constant diameter tubular section 117 is located at the flanged end of the throat 113. Each of the constant diameter sections 116, 117 of the throttle 111 are in the range of 25-35% of the length of the tapered throat 113 and the internal diameter of the throat at its 25 smaller end is in the range of 40-60% of the diameter at the wider end giving an area ratio of approximately 16-36%. The length of the tapered throat 113 is preferably in the range of 0.95 to 2.10 times the internal diameter of the throat at its narrow end. The air supply throttle 111 has different pressure drop coefficient depending on the direction of the flow. This is caused by the tapered-throat 113 located within the 30 branch supply line 51, the throat tapering to a reduced internal diameter in the direction of flow "A" towards the pulse tank with which it is associated. In the forward flow direction "A", air entering the throat 113 is compressed smoothly resulting in relatively non-turbulent flow through the throat. Flow eddying will be expected after air exits the down stream side of the throat. On the other hand if flow 35 is in the reverse direction to direction "A", more turbulent flow will be generated as air encounters the narrow end of the throat and a lower pressure on the larger diameter, down stream side (i.e. the opposite end to the previously mentioned downstream end) resulting in a higher pressure differential across the throttle and a WO 2010/148437 PCT/AU2010/000779 8 corresponding reduction in flow in the reverse direction compared to the forward direction "A". While the supply throttle 111 is described a tapered throat 113 extending from a flange 112 that permits mounting in a supply line, it is possible for other 5 configurations to be implemented. For example the throat could be incorporated into a tube segment which is then attached into the supply line by suitable pipe connection methods such as screw threads, universal joints (e.g. d-ring sealed) or flanged ends connected by clamping screws. In an alternative arrangement the throttle function may be incorporated into 10 another device such as a valve. Referring to Fig. 7 a standard check valve 131 is illustrated in its closed position. The check valve 131 comprises a valve body 132, having a valve seat 133 and a pair of semicircular plates 134 terminating in inter engaging barrel portions 137 which are connected by a pin 136 about which they pivot to allow opening and closing of the valve. A stop 135 limits travel of the plates 15 134 when in the open position, and buffers 138 absorb impact as the valve plates 134 open fully against the stop 138. Figs. 8 & 9 show a modified form of the valve of Fig. 7 in the open and closed states. The valve of Figs. 8 & 9 is modified over the design of Fig. 6 by the inclusion of an enlarged stop 145 (which may be attached over the existing stop 135 or the existing stop may be replaced). The enlarged stop 145 20 restricts the opening movement of the plates 134 such that in the fully open position against the stop 145, the plates 134 angle outwardly creating a tapered opening with the area of the opening reducing on a taper in the flow direction 'A' before the orifice increasing suddenly in a step like manner at the end of the plates 134 to resume the full area of the body of the valve (or the pipe in which the valve is located). When 25 flow is in the opposite direction to direction 'A', the fluid passing through the open valve first meets a large obstruction with the area of the opening in the valve decreasing suddenly in stepwise manner and then opening out in an increasing taper in the reverse flow direction. This arrangement has the advantage of reducing the number of components that must be inserted into the air supply line 51 and also 30 allows for simple adjustment of the aperture by altering size of the stop 145 to change the restriction on the opening of the plates 134. As with the throttle illustrated in Fig. 5, air entering the valve 131, in the forward flow direction "A", is compressed smoothly resulting in relatively non turbulent flow through the valve. Flow eddying will be expected after air exits the 35 down stream side of the valve. On the other hand if flow is in the reverse direction to direction "A", more turbulent flow will be generated as air encounters the narrow end of the valve opening and a lower pressure on the larger diameter, down stream side (i.e. the opposite end to the previously mentioned downstream end) resulting in a WO 2010/148437 PCT/AU2010/000779 9 higher pressure differential across the valve and a corresponding reduction in flow in the reverse direction compared to the forward direction "A". It will be recognised by persons skilled in the art that numerous variations and modifications may be made to the invention as described above without departing 5 from the spirit or scope of the invention as broadly described.

Claims

1. A gas filter apparatus having a housing body including: a dusty gas section with a main inlet thereto and a clean gas section with a 5 main outlet therefrom; a cell plate mounted in the housing body separating the dusty gas section from the clean gas section and having a plurality holes, each having a filter media sleeve depending therefrom; a gas pulse generator mounted on the body for generating pulses of back 10 flushing gas from a single source and having a generator outlet for discharging gas therefrom; and a rotary back-flushing gas pulse distributor within the clean gas section, extending across the cell plate and spaced from the holes in the cell plate, having a distributor inlet in fluid communication with the generator outlet and a plurality of 15 spaced orifices, each respective orifice being aligned with one of the holes so as to provide gas communication therewith; the apparatus being characterised in that in that the gas pulse generator includes an air pulse tank connected to a supply main through a flow restrictor having a control element with an internal cross sectional area which reduces in the direction 20 from the supply side to the pulse tank side, whereby resistance to flow in a first direction towards the pulse tank from a supply side is lower than resistance to flow in the opposite direction.

2. The gas filter apparatus as claimed in claim I wherein the flow restrictor is a static device. 25

3. The gas filter apparatus as claimed in claim 1 or 2 wherein the restrictor element comprises a hollow frustconical element inserted within a supply pipe connected to the pulse tank and through which air is supplied to the pulse tank.

4. The gas filter apparatus as claimed in claim 1, 2 or 3 wherein the restrictor element includes a flange at a wide end thereof, the flange having a diameter matched 30 to a diameter of facing flanges on adjacent ends of supply pipe segments such that the restrictor is mounted in the supply pipe by clamping the flange of the restrictor between the facing flanges of the supply pipe segments.

5. The gas filter apparatus as claimed in any one of claims 1 to 4 wherein the restrictor element extends from an inner wall of a tube arranged to be connected in 35 line in a supply line pipe.

6. The gas filter apparatus as claimed in any one of claims 1 to 5 wherein the frustconical element is bounded at its open (narrow) end by a short constant diameter tubular section. WO 2010/148437 PCT/AU2010/000779 11

7. The gas filter apparatus as claimed in any one of claims 1 to 5 wherein a constant diameter tubular section is located at a wide end of the frustconical element.

8. The gas filter apparatus as claimed in claim 6 or 7 wherein the constant diameter sections of the flow restrictor are in the range of 25-35% of the length of the 5 frustconical element.

9. The gas filter apparatus as claimed in any one of claims 1 to 8 wherein the internal diameter of the frustconical element at its narrow end is in the range of 40 60% of the diameter at the wider end giving an area ratio of approximately 16-36%.

10. The gas filter apparatus as claimed in any one of claims 1 to 9 wherein the 10 length of the frustconical element is in the range of 0.95 to 2.10 times the internal diameter of the frustconical element at its narrow end.

11. The gas filter apparatus as claimed in any one of claims 1 to 10 wherein the holes in the cell plate are formed generally in radially spaced, concentric rings with each hole in a ring having a filter media depending therefrom. 15

12. The gas filter apparatus as claimed in any one of claims 1 to 11 wherein the manifolds extend generally radially across and spaced from the concentric rings of holes in the cell plate and include a plurality of radially spaced orifices, one orifice being provided for each ring of holes, each orifice subscribing a circular path over ports of the respective ring of holes and aligned with the holes of a respective ring so 20 as to provide successive flushing of the holes in the ring.