GB1584016A - Water supply system for a coal washbox - Google Patents

Description

(54) A WATER SUPPLY SYSTEM FOR A COAL WASHBOX (71) We, SIMONACCO LIMITED, a British Company, of Durranhill, Carlisle, CA1 3ND, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention provides a water supply system for a coal washbox, the washbox being composed of a plurality of individual compartments connected together to allow a continuous flow of coal and washing water from one compartment to the next along the washbox.

Each compartment of a washbox is generally U-shaped having in the upper region of one limb thereof a mesh screen over which a bed of coal to be washed travels, the screens of the individual compartments being joined together to define a continuous flow path along the washbox, the other limb of each compartment being closed at its upper end and having means for introducing air under pressure in a cyclic manner so as to produce a swinging action to the water throughout the compartment thereby jigging the material above the screen.

As the water flows out of the box along with the washed coal and separated shale it is necessary continuously to supply fresh water to the box. This is usually carried out by providing a water main extending along the washbox and connected separately to each compartment via an individual control valve so that the flow fate of water to each compartment can be determined.

In operation the density of the bed of material passing over the screen tends to vary so that a sudden increase in density of the material, usually ocurring in the compartments nearer to the input end of the washbox, will cause the mean pressure of the water below the screen to increase thus producing a back pressure and preventing the adequate supply of water to those compartments. As the pressure of water in the main is substantially constant, this will result in an excessive supply of water to the downstream compartments, and the overall effect is to upset the flow characteristics of water and solids through the washbox.

An object of the present invention is to provide a water supply system for a coal washbox, wherein each compartment is supplied with water in substantially the required quantity.

According to the present invention there is provided a water supply system for a coal washbox where the washbox is composed of a plurality of individual compartments to be supplied separately with washing water at different flow rates, the system comprising a plurality of standpipes for connection, in a generally upstanding manner, one to each such compartment, and each having a tundish at its upper end, the system further including a water supply main having branch pipes positioned therealong to dispense water from the main separately into the tundishes, and a control valve in each branch pipe to control the flow of water from the main into the associated standpipe.

The invention will be more readily understood from the following description, given by way of example only with reference to the accompanying drawings, in which: Fig. 1 illustrates, in schematic cross section, a coal washbox with a conventional water supply system connected thereto; Fig. 2 is a similar view of a washbox having a water supply system made in accordance with one embodiment of the invention; and Fig. 3 shows a part of a modified form of the invention.

Referring initially to Fig. 1, a typical washbox comprises a plurality of individual, substantially U-shaped, water-filled compartments 10 which are separated one from the next by a plate 50, but joined together in one limb of each compartment above a mesh: screen 11. The plate 50 is terminated at or slightly above the level of the screens 11 which are joined together along the washbox. A bed of solid materials to be washed is fed into the water in the washbox at one end and flows with the water above the screens 11 towards the other end wherein the materials separated by stratification are removed by flowing over suitably positioned weir edges.

Stratification is assisted by ajigging action which is created by a swinging motion of the water in each compartment as indicated by the double arrows 12. This swinging motion is generated by supplying pulses of compressed air from a main 13 via a rotary or sliding valve 14 to the interior of each compartment above the water level in the closed limb. During the period between pulses, the air in the compartment is allowed to escape via the valve 14 to atmosphere.

In a conventional arrangement water is supplied to each compartment from a main 15 via a branch pipe 16 and control valve 17.

The valve 17 is intended to control the flow rate of water to the associated compartment.

However, when, for example, the density of the bed of material increases, as frequently happens particularly in those compartments near to the input end of the washbox, there is a sudden increase in the mean pressure of the water immediately below the mesh screen 11 which results in an increase in pressure at the point of connection of the branch pipe 16 to the compartment. Thus the supply of water to the particular compartment is temporarily reduced at a time when a greater quantity of water is required within the compartment to handle the increased density of materials above the screen.

Furthermore, as the pressure in the main 15 is substantially constant, a reduced quantity of water into one or more compartments will result in an increased quantity in the other compartments where the extra water is not required. The normal balanced flow of the water to the washbox is therefore upset. resulting in reduced performance.

Referring now to Fig. 2 in accordance with the invention, a standpipe 20 is connected to each compartment in place of the branch pipe 16 of Fig. 1. Each standpipe 20 etxends above the washbox and has a tundish 21 at its upper end. The standpipe and tundish arrangements are fed from a common water main 22 via associated pipes 23 each having a control valve 24. The height of the standpipes will be determined according to the peak pressure applied to the water in the compartment by the compressed air feed, in addition to the height of water necessary to deliver the maximum required flow rate to the compartment.

With this arrangement, therefore, if the mean pressure in the washbox compartment increases, the continuing flow of water from main 22 into the standpipe 20 will cause the mean level of water therein to rise accordingly and ensure that the desired quantity of water will continue to flow into the compartment with the minimum of fluctuation.

A non-return valve as indicated at 25 can optionally be provided in the lower region of each standpipe 20 to reduce the rise and fall of the water level therein as a result of the cyclic or swinging action within the compartment.

Referring now to Fig. 3, for the achievement of even greater control of the quantity of water supplied to a washbox compartment the supply of water from the main 22 to a tundish 21 can be via a reservoir 26 having a V-notch weir 27 at its point of delivery into the tundish 21. A baffle 28 will be provided to reduce turbulence in the reservoir 26.

A pressure responsive transducer, or similar arrangement, indicated at 29 can be provided to measure the depth of water in the reservoir 26 and thus the quantity of water fed over the weir into the standpipe.

It will be appreciated that a water supply system made in accordance with the present invention ensures that the required quantity of water for each washbox compartment is achieved, and this can be monitored by a visual inspection at each tundish as opposed to the conventional arrangement wherein the valves 17 are opened to produce different flow rates but wherein no means is available for checking that the desired quantities of water are in fact being dispensed into the respective compartments.

It is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible without departing from the scope of the invention.

WHAT WE CLAIM IS: 1. A water supply system for a coal washbox where the washbox is composed of a plurality of individual compartments to be supplied separately with washing water at different flow rates, the system comprising a plurality of standpipes for connection, in a generally upstanding manner, one to each such compartment, and each having a tundish at its upper end, the system further including a water supply main having branch pipes positioned therealong to dispense water from the main separately into the tundishes, and a control valve in each branch pipe to control the flow of water from the main into the associated standpipe.

2. A water supply system according to claim 1, wherein the height of each standpipe is such that it will extend above the washbox.

3. A water supply system according to claim 1 or claim 2, wherein each standpipe includes a non-return valve to reduce the rise and fall of the water level therein as a result of the cyclic action within the associated washbox compartment.

4. A water supply system according to any one of the preceding claims including, for each standpipe, an individual reservoir adapted to be fed from said supply main, and having a weir edge over which water in the reservoir may pass into the associated standpipe.

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. flowing over suitably positioned weir edges. Stratification is assisted by ajigging action which is created by a swinging motion of the water in each compartment as indicated by the double arrows 12. This swinging motion is generated by supplying pulses of compressed air from a main 13 via a rotary or sliding valve 14 to the interior of each compartment above the water level in the closed limb. During the period between pulses, the air in the compartment is allowed to escape via the valve 14 to atmosphere. In a conventional arrangement water is supplied to each compartment from a main 15 via a branch pipe 16 and control valve 17. The valve 17 is intended to control the flow rate of water to the associated compartment. However, when, for example, the density of the bed of material increases, as frequently happens particularly in those compartments near to the input end of the washbox, there is a sudden increase in the mean pressure of the water immediately below the mesh screen 11 which results in an increase in pressure at the point of connection of the branch pipe 16 to the compartment. Thus the supply of water to the particular compartment is temporarily reduced at a time when a greater quantity of water is required within the compartment to handle the increased density of materials above the screen. Furthermore, as the pressure in the main 15 is substantially constant, a reduced quantity of water into one or more compartments will result in an increased quantity in the other compartments where the extra water is not required. The normal balanced flow of the water to the washbox is therefore upset. resulting in reduced performance. Referring now to Fig. 2 in accordance with the invention, a standpipe 20 is connected to each compartment in place of the branch pipe 16 of Fig. 1. Each standpipe 20 etxends above the washbox and has a tundish 21 at its upper end. The standpipe and tundish arrangements are fed from a common water main 22 via associated pipes 23 each having a control valve 24. The height of the standpipes will be determined according to the peak pressure applied to the water in the compartment by the compressed air feed, in addition to the height of water necessary to deliver the maximum required flow rate to the compartment. With this arrangement, therefore, if the mean pressure in the washbox compartment increases, the continuing flow of water from main 22 into the standpipe 20 will cause the mean level of water therein to rise accordingly and ensure that the desired quantity of water will continue to flow into the compartment with the minimum of fluctuation. A non-return valve as indicated at 25 can optionally be provided in the lower region of each standpipe 20 to reduce the rise and fall of the water level therein as a result of the cyclic or swinging action within the compartment. Referring now to Fig. 3, for the achievement of even greater control of the quantity of water supplied to a washbox compartment the supply of water from the main 22 to a tundish 21 can be via a reservoir 26 having a V-notch weir 27 at its point of delivery into the tundish 21. A baffle 28 will be provided to reduce turbulence in the reservoir 26. A pressure responsive transducer, or similar arrangement, indicated at 29 can be provided to measure the depth of water in the reservoir 26 and thus the quantity of water fed over the weir into the standpipe. It will be appreciated that a water supply system made in accordance with the present invention ensures that the required quantity of water for each washbox compartment is achieved, and this can be monitored by a visual inspection at each tundish as opposed to the conventional arrangement wherein the valves 17 are opened to produce different flow rates but wherein no means is available for checking that the desired quantities of water are in fact being dispensed into the respective compartments. It is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible without departing from the scope of the invention. WHAT WE CLAIM IS:

1. A water supply system for a coal washbox where the washbox is composed of a plurality of individual compartments to be supplied separately with washing water at different flow rates, the system comprising a plurality of standpipes for connection, in a generally upstanding manner, one to each such compartment, and each having a tundish at its upper end, the system further including a water supply main having branch pipes positioned therealong to dispense water from the main separately into the tundishes, and a control valve in each branch pipe to control the flow of water from the main into the associated standpipe.

2. A water supply system according to claim 1, wherein the height of each standpipe is such that it will extend above the washbox.

3. A water supply system according to claim 1 or claim 2, wherein each standpipe includes a non-return valve to reduce the rise and fall of the water level therein as a result of the cyclic action within the associated washbox compartment.

4. A water supply system according to any one of the preceding claims including, for each standpipe, an individual reservoir adapted to be fed from said supply main, and having a weir edge over which water in the reservoir may pass into the associated standpipe.

5. A water supply system according to

claim 4, wherein a baffle is provided in said reservoir to reduce turbulence therein.

6. A water supply system according to claim 4 or claim 5, wherein a transducer is provided in said reservoir to sense the depth of water therein.

7. A water supply system for a coal washbox, substantially as hereinbefore described, with reference to and as illustrated in Figs. 2 and 3 of the accompanying drawings.