WO2002053259A2

WO2002053259A2 - Rotary filter with a blowback valve

Info

Publication number: WO2002053259A2
Application number: PCT/US2002/000251
Authority: WO
Inventors: John O. Beard
Original assignee: Baker Hughes Incorporated
Priority date: 2001-01-03
Filing date: 2002-01-03
Publication date: 2002-07-11
Also published as: WO2002053259A3; CN1257001C; AU2002235304A1; CN1484544A

Abstract

A filter assembly includes a tank and a filter drum rotatably disposed inside the tank. The drum has an inner surface and an outer surface and is provided long the outer surface with a plurality of recessed compartments or cells, each of the compartments being provided with a filter element. A pressure let-down valve is disposed in the tank, the pressure let-down valve communicating sequentially with the compartments or cells during rotation of the drum, to draw off an overpressure in the compartments or cells. In addition, a blowback valve is disposed in the tank downstream of the pressure let-down valve as defined by a direction of rotation of the drum. The blowback valve communicates sequentially with the compartments or cells during rotation of the drum after the compartments or cells have passed the pressure let-down valve. This apparatus enables discharge of solids from the compartments or cells at atmospheric or ambient pressure.

Description

ROTARY FILTER ASSEMBLY WITH INTERNAL PRESSURE LET-DOWN BACKGROUND OF THE INVENTION

This invention relates to a rotary filter. More particularly, this invention relates to a rotary pressure filter.

Rotary pressure filters are in widespread use in the chemical, food, pharmaceutical and mining industries. During the production process, a cylindrical filter drum rotates in a tank or housing. The tank or housing is subjected to a pressure of up to 150 PSIG (lbs./in.² gauge). Inside the filter drum, a differential pressure is generated. The resulting pressure differential forces liquid through the filter drum from a slurry in the tank. The slurry is fed to the housing to a point radially outward of the filter. Solids in the slurry are deposited on the outer surface of the drum and form a cake layer thereon.

As the filter drum rotates, the deposited layer is often times transported past a washing station where a washing fluid or liquor is dispensed onto the layer and drawn through the filter into the rotating drum. Subsequently, the cake rotates to a discharge station where a jet of pressurized gas from inside the rotating cylinder pushes the deposited cake from the outer surface of the filter and into a discharge outlet.

At the point of discharge, the cake is pressurized to a level depending on the overpressure in the tank. The overpressure is reduced to atmospheric pressure in a batch-type pressure-relief valving operation downstream of the rotary pressure filter. This technique leads to difficulties common in pairing batch processes and continuous processes. In addition, the pressure let-down apparatus is expensive and costs approximately as much as the rotary pressure filter. SUMMARY OF THE INVENTION

The present invention seeks to improve rotary pressure filter installations. More particularly, the present invention seeks to simplify the apparatus and reduce capitalization and operation costs.

A filter assembly comprises, in accordance with the present invention, a tank and a filter drum rotatably disposed inside the tank. The drum has an inner surface and an outer surface and is provided along the outer surface with a plurality of recessed compartments or cells each provided with a filter element. A pressure let-down valve is disposed in the tank, the pressure let-down valve communicating sequentially with the compartments or cells during rotation of the drum, to draw off an overpressure in the compartments or cells. In addition, a blowback valve is disposed in the tank downstream of the pressure let-down valve as defined by a direction of rotation of the drum. The blowback valve communicates sequentially with the compartments or cells during rotation of the drum after the compartments or cells have passed the pressure let-down valve. This apparatus enables discharge of solids from the compartments or cells at atmospheric or ambient pressure.

In accordance with another feature of the present invention, the pressure let-down valve and the blowback valve include an outer shoe disposed in the tank along the outer surface of the drum and at least one inner shoe disposed along the inner surface of the drum. The outer shoe and the inner shoe overlap one another to establish a pressure seal around at least two of the compartments or cells. The pressure let-down valve is defined in part by a first flow pathway in the inner shoe and the outer shoe, while the blowback valve is defined in part by a second flow pathway in the inner shoe and the outer shoe.

It is possible to have separate outer shoes and separate inner shoes for the pressure let-down valve and the blowback valve. Preferably, there are multiple inner shoes disposed side-by-side along the length of the drum, each shoe including a respective pressure let-down valve and a respective blowback valve. These inner shoes may be each approximately one-foot wide so that a drum which is six feet long will have six inner shoes. The separate inner shoes are individually adjustable to better conform to the inner surface or diameter of the drum. Also, there is preferably a single outer shoe disposed along the outer surface of the drum. The outer shoe is aligned across all of the inner shoes and is thus shared by them.

The pressure let-down and blowback valves of the inner shoes are basically defined by respective ducts extending from the inner surface of the drum through the respective inner shoes.

Generally, the drum defines an enclosed inner space, while each of the compartments or cells communicates with that space via one or more respective apertures in the drum. The filter assembly further comprises a source of gaseous overpressure operatively connected to the tank for generating an overpressure in the tank outside of the drum, a suction source communicating with the space to generate a differential pressure in the space for pumping filtrate through the filter elements during rotation of the drum, and a blowback pipe extending into the space toward the inner surface. The blowback pipe is connected to the inner shoe so as to communicate with the second flow pathway.

In accordance with a further feature of the present invention, an isolation valve is provided for isolating an outer side of the drum from pressure in the tank. The isolation valve is disposed along an outer side of the drum in a region about the pressure let-down valve.

A method for operating a rotary pressure filter comprises, in accordance with the present invention, rotating a drum inside a tank, drawing liquid from a slurry in the tank through the filter element during the rotation, depositing solids from the slurry along the outer surface of the rotating drum, maintaining the tank at an overpressure during drum rotation, releasing the overpressure in the deposited solids at a pressure let-down position along the drum, and blowing the pressure-released solids off of the drum, whereby the solids may be discharged at atmospheric pressure.

The release of the overpressure preferably includes drawing off pressure via a pressure let-down valve, while the blowing off of the pressure released solids includes directing a gaseous medium through apertures in the drum. As discussed above, the pressure reduction and the blow-off are preferably implemented via an integrated valve assembly including multiple inner shoes disposed along the inner surface of the drum and a single shoe along the outer surface of the drum. The drawing off of the overpressure may be implemented by directing pressurized gases from the deposited solids into the drum through the apertures in the drum.

The present invention will replace current technology which require two stages of equipment, namely, a pressure centrifuge where the discharged cake is reslurried and further de-watered and washed by filters, or a pressure filter followed by a pressure let-down apparatus. The present invention will reduce original equipment costs inasmuch as the two-stage equipment is more expensive than a single stage.

A single-stage filtering and pressure let-down apparatus in accordance with the present invention can be manufactured in standard sizes to better match customer requirements for plant capacity. This provides flexibility as well as a far less expensive alternative than current multiple units with their sizing requirements.

A single-stage filtering and pressure let-down apparatus in accordance with the present invention provides a continuous device rather than the batch operation of a separate let-down device. The continuous mode of operation is particularly well suited to standard designs for plants processing such substances as terephthalic acid. Atmospheric discharge directly onto a conveyor or into a dryer is advantageous for existing manufacturing methods.

A single-stage filtering and pressure let-down apparatus in accordance with the present invention has smaller space requirements than existing rotary pressure filters with the associated pressure let-down apparatus.

It is expected that capacity and purity of cake production will be enhanced by the present invention. The single-unit system will be less expensive to maintain and will have less down time than existing systems. BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 is a schematic transverse cross-sectional view of a rotary pressure filter in accordance with the present invention, showing a rotatable drum and a valve assembly including a valve plate or shoe disposed along an outer surface of the drum.

Fig. 2 is a schematic partial front elevational of the rotatable drum shown in Fig. 1.

Fig. 3 is a plan view of the valve plate or shoe shown in Fig. 1.

Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in Fig. 1 , a pressure filter assembly comprises a tank or housing 12 and a filter drum 14 rotatably disposed inside tank 12. Drum 14 has an inner surface 16 and an outer surface 18 and is provided along the outer surface with a plurality of rectangular recesses, compartments or cells 20.

As illustrated in Fig. 2, each compartment 20 is provided with a filter element 22 overlying a support grid or screen 24. Grid 24 in turn lies in contact with a floor or base surface 26 of the respective compartment 20. The base 26 is perforated with a plurality of apertures 28.

During operation of the filter assembly of Fig. 1 , drum 14 is rotated by a drive 30 and passes through a slurry pool 32 carried in a reservoir 34 disposed in tank 12. Slurry is fed to pool 32 via a port element 36.

Drum 14 defines a substantially cylindrical inner space 38 which is operatively connected to a suction source 40, whereby the inner space is subjected to a differential pressure during apparatus operation. In addition, tank 12 communicates with a pressure source 42, such as a compressor, whereby a space 44 around drum 14 is subjected to an overpressure of 65-70 lbs. /in.². During rotation of drum 14 by drive 30, the pressure differential between space 44 and space 38 forces liquid from slurry pool 32 through filter elements 22, grids 24 and apertures 28 and deposits solids from the slurry onto filter elements 22 in compartments 20. Liquid is also drawn from the deposited cake in compartments 20, after the rotation of the compartments from slurry pool 32. Spray nozzles 46 disposed in tank 12 direct a washing spray 47 onto the deposited cake in compartments 20. The wash liquid is also forced into space 38 by the overpressure in space 44 and the lower pressure in space 38.

The rotating drum 14 passes a pressure let-down valve 48 disposed in tank 12 upstream of a cake discharge or blowback valve 50 as defined by a direction of rotation of drum 14. Pressure let-down valve 48 communicates sequentially with compartments 20 during rotation of drum 14, to draw off an overpressure extant in compartments 20 owing to the overpressure in space 44. Blowback valve 50 communicates sequentially with compartments 20 during rotation of drum 14 after the compartments 20 have passed pressure let-down valve 48. This apparatus enables or facilitates discharge of solids from compartments 20 at atmospheric or ambient pressure.

Pressure let-down valve 48 and blowback valve 50 are formed by an outer shoe 52 and at least one but preferably a plurality of inner shoes 54. Outer shoe 52 is disposed in tank 12 along outer surface 18 of drum 14, while inner shoes 54 are disposed side-by-side in a linear array along inner surface 26 of drum 14. Inner shoes 54 may be each approximately one-foot wide and together extend along the length of drum 14 so that a drum which is six feet long will have six inner shoes. Separate inner shoes 54 are individually adjustable to better conform to the inner surface or diameter 16 of drum 14. Each inner shoe 54 includes a respective pressure let-down duct 56 and a respective blowback duct 58. Each inner shoe 54 substantially overlaps outer shoe 52 to establish a pressure seal around at least two compartments 20 which are adjacent to one another in a circumferential direction.

At every moment during rotation of drum 14, at least one compartment 20 is in communication with the pressure let-down duct 56 in each inner shoe 54, while at least one compartment is simultaneously in communication with the pressure blowback duct 58 in the same inner shoe 54. Ducts 56 and 58 define respective gas flow pathways in pressure let-down valve 48 and blowback valve 50, respectively, and communicate with respective pipes 60 and 62 inside drum 14. Air flow is indicated by arrows 64 and 66. Pipe 62 is operatively connected to a pressure source 68 providing air at slightly above atmospheric pressure for discharging deposited solids from compartments 20 through an opening 82 in outer shoe 52 into a discharge chute 70 which is at atmospheric pressure.

Outer shoe 52 includes an inner layer 72 of low-friction polymeric material (Figs. 1 and 4) in contact with outer surface 18 of drum 14 and further includes an outer metallic layer 74 (Figs. 1 , 3, and 4) to which the polymeric layer is mounted. Similarly, inner shoes 54 each comprise an outer part 76 of low-friction polymeric material in contact with inner surface 16 of drum 14 and additionally comprise an inner part 78 to which outer part 76 is attached.

An isolation valve 80 is provided for isolating an outer side of drum 14 from pressure in tank 12. Isolation valve 80 is disposed along an outer side of drum 14 in a region about the pressure let-down valve 48.

In operating the rotary pressure filter, drum 14 is rotated inside tank 12, while differential pressure source 40 evacuates inner space 38 and compressor 42 pressurizes space 44, thereby generating a pressure gradient which forces or draws liquid from slurry pool 32 and deposits a layer of cake solids along outer surface 18 of drum 14. The overpressure produced in space 44 by compressor 42 is released in the deposited cake layer at a pressure let-down position along drum 14, specifically the circumferential position occupied by pressure let-down valve 48 and specifically valve ducts 56. Downstream of the pressure let-down valve 48 (ducts 56), the pressure-released solids are blown off of drum 14 by gas supplied via ducts 58, thereby enabling a discharge of the solids at atmospheric pressure, for example, onto a conveyor (not shown) or into a drying oven (not shown). As indicated above, the release of the overpressure is accomplished by pressure let-down valve 48 (ducts 56), while the blowing off of the pressure- released solids entails a directing of a gaseous medium through apertures 28 in drum 14. Pressure let-down valve 48 and blowback valve 50 are implemented via an integrated valve assembly including outer shoe 52 disposed along the outer surface 18 of drum 14 and multiple inner shoes 54 disposed side-by-side along the inner surface 16 of drum 14.

Fig. 4 shows an assembly 84 for pressing outer shoe 52 against the outer surface 18 of drum 14. Adjustable bolts 86 are mounted to a bracket support 88 which is provided with O-ring packing 90 or other seals.

Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. For example, it is possible to construct each inner shoe 54 of two separate sections, one section containing a pressure let-down duct 56 and the other section being provided with the pressure blowback duct 58. Outer shoe 52 may also be constructed of multiple segments. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.

Claims

WHAT IS CLAIMED IS:

1. A filter assembly comprising: a tank; a filter drum rotatably disposed inside said tank, said drum having an inner surface and an outer surface, said drum being provided along said outer surface with a plurality of recessed compartments or cells, each of said compartments being provided with a filter element; a pressure let-down valve disposed in said tank, said pressure let-down valve communicating sequentially with said compartments or cells during rotation of said drum, to draw off an overpressure in said compartments or cells; and a blowback valve disposed in said tank downstream of said pressure letdown valve as defined by a direction of rotation of said drum, said blowback valve communicating sequentially with said compartments or cells during rotation of said drum after said compartments or cells have passed said pressure let-down valve, whereby solids discharged from said compartments or cells by said blowback valve are dischargeable at atmospheric or ambient pressure.

2. The filter assembly defined in claim 1 wherein said pressure let-down valve and said blowback valve include an outer shoe disposed in said tank and along said outer surface of said drum and an inner shoe disposed along said inner surface of said drum, said outer shoe and said inner shoe overlapping one another to establish a pressure seal around at least two of said compartments or cells, said pressure let-down valve being defined by a first flow pathway in said inner shoe and said blowback valve being defined by a second flow pathway in said inner shoe and said outer shoe.

3. The filter assembly defined in claim 2 wherein said first flow pathway and said second flow pathway each includes a duct in said inner shoe.

4. The filter assembly defined in claim 2 wherein said drum defines an enclosed inner space, each of said compartments or cells communicating with said space via a respective aperture in said drum, further comprising: a source of gaseous overpressure operatively connected to said tank for generating an overpressure in said tank outside of said drum; a suction source communicating with said space to generate a lower pressure in said space for pulling filtrate through the filter elements during rotation of said drum; and a blowback pipe extending into said space toward said inner surface, said blowback pipe being connected to said inner shoe so as to communicate with said second flow pathway.

5. The filter assembly defined in claim 1 , further comprising an isolation valve for isolating an outer side of said drum from pressure in said tank, said isolation valve being disposed along an outer side of said drum in a region about said pressure let-down valve.

6. The filter assembly defined in claim 5 wherein said isolation valve is a single piece unit.

7. The filter assembly defined in claim 1 wherein said pressure let-down valve includes an outer shoe disposed in said tank and along said outer surface of said drum and an inner shoe disposed in said space along said inner surface of said drum, said outer shoe and said inner shoe overlapping one another to establish a pressure seal around at least one of said compartments or cells.

8. The filter assembly defined in claim 1 wherein said blowback valve includes an outer shoe disposed in said tank and along said outer surface of said drum and an inner shoe disposed in said space along said inner surface of said drum, said outer shoe and said inner shoe overlapping one another to establish a pressure seal around at least one of said compartments or cells.

9. A filter assembly comprising: a tank; a filter drum rotatably disposed inside said tank, said drum having an inner surface and an outer surface, said drum defining an enclosed inner space, said drum being provided along said outer surface with a plurality of recessed compartments or cells, each of said compartments being provided with a filter element, each of said compartments or cells communicating with said space via a respective aperture in said drum; an outer shoe disposed in said tank and along said outer surface of said drum; and an inner shoe disposed in said space along said inner surface of said drum, said outer shoe and said inner shoe overlapping one another to establish a pressure seal around at least one of said compartments or cells, a first duct being provided in one of said outer shoe and said inner shoe for releasing overpressure from said one of said compartments or cells, a second duct being provided in said inner shoe for blowing, from said compartments or cells, solids collected during rotation of said drum in said tank.

10. The filter assembly defined in claim 9, further comprising: a source of gaseous overpressure operatively connected to said tank for generating an overpressure in said tank outside of said drum; a suction source communicating with said space to generate an underpressure in said space for pulling filtrate through the filter elements during rotation of said drum; and a blowback pipe extending into said space toward said inner surface, said blowback pipe communicating with said second duct, said second duct being located downstream of said first duct as defined by a direction of rotation of said drum.

11. The filter assembly defined in claim 10 wherein said first duct is provided in said inner shoe, further comprising a pressure let-down pipe extending into said space toward said inner surface, said pressure let-down pipe communicating with said first duct.

12. A method for operating a rotary pressure filter, comprising: rotating a drum inside a tank, said drum carrying at least one filter element on an outer surface; during rotating of said drum, maintaining said tank at an overpressure; during rotating of said drum, forcing liquid from a slurry in said tank through said filter element; during rotating of said drum, depositing particulate solids from said slurry along said outer surface of said drum; releasing said overpressure in the deposited solids at a pressure let-down position along said drum; and blowing the pressure-released solids off of said drum, whereby the solids may be discharged at atmospheric pressure.

13. The method defined in claim 12 wherein the release of said overpressure includes drawing off pressure via a pressure let-down valve, the blowing off of the pressure released solids including directing a gaseous medium through apertures in said drum.

14. The method defined in claim 13 wherein the drawing off of pressure from said deposited solids includes directing pressurized gases from said deposited solids into said drum through said apertures in said drum.