GB2105848A

GB2105848A - A device for detecting conditions in a jig washbox

Info

Publication number: GB2105848A
Application number: GB08223839A
Authority: GB
Inventors: James Donald Menzies; Geoffrey Berry
Original assignee: Simonacco Ltd
Current assignee: Simonacco Ltd
Priority date: 1981-09-05
Filing date: 1982-08-18
Publication date: 1983-03-30
Also published as: AU8798082A; ZA822063B; AU565111B2; GB2105848B

Abstract

A device for detecting conditions in a jig washbox (10) e.g. in a coal preparation plant comprises a stand pipe (13) closed at its upper end and connected at its base to the interior of the washbox below the liquid level (S) therein, a first flexible diaphragm (16) occluding the base of the pipe, a second flexible diaphragm (18) occluding the pipe substantially at the same level as the liquid in the washbox, there being liquid in the zone 17 between the flexible diaphragms, a rigid diaphragm (20) above the diaphragm (18) with valve means permitting free passage of air upwardly in the pipe, a bleed valve (22) permitting a controlled bleed of air in the reverse direction, and a transducer (23) adapted to detect the air pressure in the pipe above the diaphragm (20). The diaphragm (16) prevents air entering the pipe (17) and producing inconsistent results. <IMAGE>

Description

SPECIFICATION A device for detecting conditions in a jig washbox This invention relates to a jig washbox of the kind used, for example, in coal preparation plant, wherein a bed of solids such a coal and shale is deposited into a water-filled vessel having a submerged perforated deck, so that the bed of material can classify, and the denser fraction descends onto the deck. A device is usually included to generate upwardly directed surges or pulses of current in the water which serve repeatedly to liftthe bed of material thus to assist the classification process.

To monitor and control the operation of the washbox it is known to provide a stand pipe which communicates with the latter below the perforated deck, and which includes a pressure transducer adapted to sense the instantaneous pressure in the stand pipe as determined according to the density of the bed of material in the washbox.

British patent specification no. 2062500A describes a system of this general kind wherein a flexible diaphragm is disposed within the stand pipe near its base to isolate an upper portion of the pipe from the water in the washbox. Ideally in this kind of arrangement, the flexible diaphragm should be arranged near to the mean water level in the washbox, but this causes air to be trapped at the top of the column of water in the stand pipe, which varyingly affects the pressure detected by the transducer at the top of the pipe. To place the diaphragm near the bottom of the pipe would subject it to extreme pressures and the inherently hostile environment created by the abrasive nature of the solid particles present in the base of the washbox.The aforementioned specification describes a small-bore bleed pipe immediately below the diaphragm to enable trapped air to bleed into the body of the washbox above the perforated deck, but such a pipe may readily become blocked by fine solid particles.

An object of the present invention is to provide a device of this general kind wherein the aforementioned difficulties are at least substantially overcome.

According to the present invention there is provided a device for detecting conditions in a jig washbox comprising a pipe closed at one end and connected at the other to the interior of the washbox below the liquid level therein, a first flexible diaphragm occluding the pipe near said other end of same, and a second flexible diaphragm occluding the pipe at a position therein spaced from said first flexible diaphragm, a rigid diaphragm beyond the second flexible diaphragm with valve means permitting free passage of air along the pipe in one direction away from the second diaphragm, means permitting a controlled bleed of air past the said rigid diaphragm in the reverse direction, and a transducer adapted to detect the air pressure in the pipe beyond the rigid diaphragm.

Preferably, the pipe is a stand pipe and a base part thereof housing the first flexible diaphragm is of greater cross-sectional area than that part housing the second flexible diaphragm, the pipe between said diaphragms being isolated thereby and filled with a liquid.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying schematic drawing which illustrates a fragmentary vertical section of a jig washbox having attached thereto a stand pipe embodying the invention.

The washbox comprises a vessel 10 containing water and having a fixed perforated deck 11 therein upon which rests the denser fraction of the solids being treated.

The water in the vessel 10 is caused to pulsate to and fro as indicated by the arrows 12, to assist in the treatment process.

Communicating with the interior of the vessel 10 below the water level S therein is a chamber 13 in the form of a vertically disposed stand pipe located outside the vessel and closed at its upper end.

The stand pipe 13 comprises a base portion 14 of increased cross-sectional area when compared with the remainder of the pipe.

Afirstflexible diaphragm 16 in the base portion 14 isolates the water in the vessel from a first zone 17 which is liquid filled and is defined at its upper end by a second flexible diaphragm 18. Both diaphragms are capable of flexural movement thus to displace equal volumes of the liquid contained in the zone 17.

The diaphragm 18 isolates an upper zone 19 containing air and in which is located a rigid diaphragm 20 which permits passage of air only in a direction away from the second flexible diaphragm 18. A controlled bleed of air past the rigid diaphragm in the reverse direction is permitted by means of by-pass line 21 and valve 22.

A transducer 23 is provided at the top of the stand pipe 13 to sense the instantaneous pressure therein.

In use, therefore, as the mean density of the solids in the vessel increases due to an increased proportion of dense constituents, so the resistance to the pulsating flow of water through the materials above the perforated deck 11 increases, causing a build up of pressure below the deck. This is reflected in an increased tendency of the water to flow into the pipe 13 thus raising the flexible diaphragms 16 and 18, and in turn increasing the air pressure in the upper zone 19. The varying pressure in zone 19 may be measured by the transducer 23, and a signal representative of that pressure may be transmitted to a control device (not shown).

It will be appreciated that the location of the first flexible diaphragm at the level of communication between the vessel and the stand pipe prevents the accumulation of air in the pipe, and the increased cross-sectional area of the pipe in the base portion 14 demands less deflection of the diaphragm for a relatively large volumetric displacement past the rigid diaphragm 20.

1. A device for detecting conditions in a jig washbox comprising a pipe closed at one end and connected at the other to the interior of the washbox below the liquid level therein, a first flexible di

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A device for detecting conditions in a jig washbox This invention relates to a jig washbox of the kind used, for example, in coal preparation plant, wherein a bed of solids such a coal and shale is deposited into a water-filled vessel having a submerged perforated deck, so that the bed of material can classify, and the denser fraction descends onto the deck. A device is usually included to generate upwardly directed surges or pulses of current in the water which serve repeatedly to liftthe bed of material thus to assist the classification process. To monitor and control the operation of the washbox it is known to provide a stand pipe which communicates with the latter below the perforated deck, and which includes a pressure transducer adapted to sense the instantaneous pressure in the stand pipe as determined according to the density of the bed of material in the washbox. British patent specification no. 2062500A describes a system of this general kind wherein a flexible diaphragm is disposed within the stand pipe near its base to isolate an upper portion of the pipe from the water in the washbox. Ideally in this kind of arrangement, the flexible diaphragm should be arranged near to the mean water level in the washbox, but this causes air to be trapped at the top of the column of water in the stand pipe, which varyingly affects the pressure detected by the transducer at the top of the pipe. To place the diaphragm near the bottom of the pipe would subject it to extreme pressures and the inherently hostile environment created by the abrasive nature of the solid particles present in the base of the washbox.The aforementioned specification describes a small-bore bleed pipe immediately below the diaphragm to enable trapped air to bleed into the body of the washbox above the perforated deck, but such a pipe may readily become blocked by fine solid particles. An object of the present invention is to provide a device of this general kind wherein the aforementioned difficulties are at least substantially overcome. According to the present invention there is provided a device for detecting conditions in a jig washbox comprising a pipe closed at one end and connected at the other to the interior of the washbox below the liquid level therein, a first flexible diaphragm occluding the pipe near said other end of same, and a second flexible diaphragm occluding the pipe at a position therein spaced from said first flexible diaphragm, a rigid diaphragm beyond the second flexible diaphragm with valve means permitting free passage of air along the pipe in one direction away from the second diaphragm, means permitting a controlled bleed of air past the said rigid diaphragm in the reverse direction, and a transducer adapted to detect the air pressure in the pipe beyond the rigid diaphragm. Preferably, the pipe is a stand pipe and a base part thereof housing the first flexible diaphragm is of greater cross-sectional area than that part housing the second flexible diaphragm, the pipe between said diaphragms being isolated thereby and filled with a liquid. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying schematic drawing which illustrates a fragmentary vertical section of a jig washbox having attached thereto a stand pipe embodying the invention. The washbox comprises a vessel 10 containing water and having a fixed perforated deck 11 therein upon which rests the denser fraction of the solids being treated. The water in the vessel 10 is caused to pulsate to and fro as indicated by the arrows 12, to assist in the treatment process. Communicating with the interior of the vessel 10 below the water level S therein is a chamber 13 in the form of a vertically disposed stand pipe located outside the vessel and closed at its upper end. The stand pipe 13 comprises a base portion 14 of increased cross-sectional area when compared with the remainder of the pipe. Afirstflexible diaphragm 16 in the base portion 14 isolates the water in the vessel from a first zone 17 which is liquid filled and is defined at its upper end by a second flexible diaphragm 18. Both diaphragms are capable of flexural movement thus to displace equal volumes of the liquid contained in the zone 17. The diaphragm 18 isolates an upper zone 19 containing air and in which is located a rigid diaphragm 20 which permits passage of air only in a direction away from the second flexible diaphragm 18. A controlled bleed of air past the rigid diaphragm in the reverse direction is permitted by means of by-pass line 21 and valve 22. A transducer 23 is provided at the top of the stand pipe 13 to sense the instantaneous pressure therein. In use, therefore, as the mean density of the solids in the vessel increases due to an increased proportion of dense constituents, so the resistance to the pulsating flow of water through the materials above the perforated deck 11 increases, causing a build up of pressure below the deck. This is reflected in an increased tendency of the water to flow into the pipe 13 thus raising the flexible diaphragms 16 and 18, and in turn increasing the air pressure in the upper zone 19. The varying pressure in zone 19 may be measured by the transducer 23, and a signal representative of that pressure may be transmitted to a control device (not shown). It will be appreciated that the location of the first flexible diaphragm at the level of communication between the vessel and the stand pipe prevents the accumulation of air in the pipe, and the increased cross-sectional area of the pipe in the base portion 14 demands less deflection of the diaphragm for a relatively large volumetric displacement past the rigid diaphragm 20. CLAIMS

1. A device for detecting conditions in a jig washbox comprising a pipe closed at one end and connected at the other to the interior of the washbox below the liquid level therein, a first flexible di aphragm occluding the pipe near said other end of same, and a second flexible diaphragm occluding the pipe at a position therein spaced from said first flexible diaphragm, a rigid diaphragm beyond the second flexible diaphragm with valve means permitting free passage of air along the pipe in one direction away from the second diaphragm, means permitting a controlled bleed of air past the said rigid diaphragm in the reverse direction, and a transducer adapted to detect the air pressure in the pipe beyond the rigid diaphragm.

2. A device according to claim 1 in which the pipe is a standpipe and a base part thereof housing the first flexible diaphragm is of greater cross-sectional area than the part housing the second flexible diaphragm.

3. A device according to claim 1, or claim 2, wherein the part of the pipe between said diaphragms is isolated thereby and filled with a liquid.

4. A device according to any preceding claim, wherein said flexible diaphragms are capable of flexural movement to produce equal volumetric displacements.

5. A device according to any preceding claim, wheren said controlled bleed of air past the rigid diaphragm in the reverse direction is permitted by means of a bypass line containing a valve.

6. Awashbox incorporating a device according to any preceding claim and comprising a vessel containing a liquid and having a fixed perforated deck therein below the liquid level therein, said other end of said pipe communicating with the interior of said vessel at a level below said fixed perforated deck.

7. A washbox according to claim 6, including means controlling operation thereof, said means being responsive to said transducer.

8. A device for detecting conditions in a jig washbox, substantially as herenbefore described, with reference to and as iilustrated in the accompanying drawings.