Patent Description:
Horizontal plate pressure filters have a plurality of horizontally extending superimposed filter plates, between which filter chambers are formed. During operation the filter plates are pressed against each other to seal filter chambers between the filter plates. Slurry is then fed into the filter chambers and filtrate is separated therefrom while the solid contents of the slurry form filter cakes within the filter chambers. Subsequently, the filter plates are moved away from each other to open the filter chambers so that the filter cake may be discharged therefrom, and further moved towards each other to close the filter chamber again. This sequence is then repeated.

<CIT> discloses a vertical fully automated plate-and-frame filter press including for instance a levelling board frame group, a main body support structure, a board frame group opening and holding apparatus, a filtering cloth automatic cycle running gear, a filtering cloth washing device, automatic control system, hydraulic system, and a craft circuitry.

<CIT> discloses an anti-retraction pressing device for a vertical filter press, which ensures consistent sealing pressure by using a displacement compensation oil cylinder, while securely locking the filter plate assembly with anti-retraction clamping plates that engage with cylindrical beam slots.

According to a first aspect of the invention, a pressure filter is disclosed according to claim <NUM>.

According to a second aspect of the invention, a method of determining when plate seals in a pressure filter should be replaced is disclosed according to claim <NUM>.

Additional advantageous features of the invention are set out in the dependent claims.

<FIG> depicts a pressure filter <NUM>. The pressure filter includes a plurality of filter plates <NUM> which are arranged in a vertical stack, i.e. arranged in a column extending along the Z axis as shown in <FIG>. Each filter plate <NUM> lies in a horizontal plane, that is the two major dimensions of the filter plate lie in the X-Y plane as shown in <FIG>, perpendicular to the Z axis. Each filter plate <NUM> is parallel to and offset from the other filter plates. The filter plates <NUM> and other components located between the filter plates are shaped such that when the filter plates <NUM> are pressed together, filter chambers are formed between each adjacent pair of filter plates <NUM>.

Above the filter plates <NUM> is an upper pressing plate <NUM>, sometimes referred to as a head plate, and below the filter plates <NUM> is a lower pressing plate <NUM>, sometimes referred to as a tail plate, rear plate or end plate. By moving the upper pressing plate <NUM> and lower pressing plate <NUM>, the filter plates <NUM> can be moved away and towards one another in order to open and close the filter chambers.

Upper actuator <NUM> is configured to move the upper pressing plate and lower actuator <NUM> is configured to move the lower pressing plate. The pressure and force required for sealing the filter chambers is much greater that that required for opening and closing the filter chambers, and thus the actuators <NUM> and <NUM> must be correspondingly dimensioned for each purpose. In the arrangement shown in <FIG>, upper actuator <NUM> is configured to produce the large displacement and low force required to open and close the filter chambers and lower actuator <NUM> is configured to produce the lower displacement and large force required to seal the filter chambers. The upper pressing plate <NUM> may be locked in place by locking pins <NUM> once the upper pressing plate <NUM> and filter plates <NUM> are in the closed position following actuation of the upper actuator <NUM>.

As a result of the different displacement and force requirements of the upper and lower actuators <NUM>, <NUM>, different types of actuators may be used. In a preferred embodiment, the upper actuator <NUM> is an electrical actuator that may be coupled with mechanical means, such as gears and chains or pulleys, in order to product the required displacement. The lower actuator <NUM> is preferably a hydraulic actuator, which is capable of providing the required force for sealing the filter chambers. However, the specific type of actuator that is used for each of the upper and lower actuators <NUM>, <NUM> is not central to the present invention and the present invention may indeed be used with any horizontal pressure filter regardless of the types of actuators used to move the upper and lower pressing plates.

Furthermore, even though <FIG> shows a pressure filter in which the large-displacement, low force actuator drives movement of the upper pressing plate and the low-displacement, larger force actuator drive movement of the lower pressing plate, the arrangement may be reversed, in which case locking pins <NUM> will also be present on the lower pressing plate <NUM> instead of the upper pressing plate <NUM>. Thus, while this disclosure refers to "upper" and "lower" pressing plates, as depicted in <FIG>, it will be appreciated that the arrangement may be reversed and the actual position of the pressing plates as "upper" or "lower" is not essential to the invention.

The lower pressing plate <NUM> - i.e. the pressing plate that is driven by the lower displacement, higher force actuator - is moveable between a retracted position and a sealed position. The retracted position the lower pressing plate <NUM> is a set position at which the lower pressing plate <NUM> is located before the actuator <NUM> drives movement of the pressing plate <NUM> in order to seal the filter chambers between filter plates <NUM> and to which the lower pressing plate <NUM> returns after a filter cycle is complete, i.e. after the actuator <NUM> retracts the pressing plate <NUM>. Thus, in the context of this disclosure, the term "retracted position" does not mean simply any position that is somewhat retracted from the sealed position, but it is in fact a set position of the pressing plate which is consistent across cycles of the pressure filter.

The sealed position is the position of the lower pressing plate <NUM> after the actuator <NUM> drives movement of the lower pressing plate <NUM> towards the filter plates <NUM> in order to seal the filter chambers between pressing plates. The sealed position is therefore the position of the lower pressing plate <NUM> after the sealing force, which is a predetermined force, is applied to the lower pressing plate <NUM> by the actuator <NUM> and before the filter chambers are pressurised. For example, when the actuator <NUM> is a hydraulic actuator, <NUM>-<NUM> bar of hydraulic pressure may be applied to the lower pressing plate <NUM>. The predetermined force that is applied to the lower pressing plate <NUM> by the actuator <NUM> is consistent between filter cycles.

Plate seals (shown in <FIG>) are located between filter plates <NUM> and in the sealed position, i.e. when the predetermined sealing force is applied, form pressure seals between the filter plates <NUM> to form the filter chambers. The plate seals are typically made from natural rubber, EPDM, butyl or other rubber material, or a combination of these materials.

The pressure filter <NUM> also includes a displacement sensor <NUM>, which measures the displacement of the lower pressing plate <NUM> relative to the stationary elements of the pressure filter <NUM>, e.g. to the lower frame <NUM>. It will be appreciated that in a pressure filter where the functions of the upper and lower pressing plates and actuators are reversed, the displacement sensor will instead measure the displacement of the upper pressing plate relative to the upper frame of the pressure filter.

The displacement sensor is preferably a string displacement sensor connected between the lower pressing plate <NUM> and the lower frame <NUM>. A string displacement sensor, also known a string pot displacement sensor, typically includes a variable resistor with a spring-loaded string that can be pulled out to measure displacements. The resistance of the device changes depending on how much displacement is applied to the string. The spring-loading mechanism is attached to one of the lower pressing plate <NUM> and lower frame <NUM> while the opposite end of the string is fixed to the other of the lower pressing plate <NUM> and lower frame <NUM>, such that movement of the lower pressing plate <NUM> relative to the lower frame <NUM> causes the spring to be pulled out from or retracted by the spring loading mechanism. It will be appreciated that while the invention is described as using a string displacement sensor, the specific type of sensor that is used is not essential to the invention and any displacement sensor capable of measuring displacement of the lower pressing plate <NUM> across the required range may be used.

During operating of the pressure filter <NUM>, the displacement sensor is used to measure the position or displacement of the lower pressing plate <NUM> during and after pressurisation of the filter chambers. As part of the filter cycle, once the lower pressing plate <NUM> is in the sealed position, the filter chambers formed between the pressure plates are pressurised. A typical filter cycle - also referred to as "process" in the art - involves filling the filter chambers with material to be filtered, e.g. slurry, washing the material with a suitable liquid, e.g. water, pressing the washed material by expanding diaphragms within the filter chambers, washing the pressed material and pressing the material again, followed by a final step of air drying. Some of these steps may be omitted depending on the specific material being filtered. After these steps are complete, the pressing plates are disengaged and the filter cakes that are left behind in each filter chamber can be removed.

At each of these steps the filter chambers are pressurised to different extents. For example, during the filling step, the pressure within each filter chamber increases to around <NUM>-<NUM> bar. In the washing steps, the pressure increases by <NUM>-<NUM> bar to around <NUM>-<NUM> bar. Similar pressure is reached in the air blowing stage. In the pressing step, the pressure is highest, reaching up to <NUM> bar in each pressing chamber. It is essential that the force applied to the lower pressing plate <NUM> by the actuator <NUM> is maintained and that the position of the lower pressing plate <NUM> does not change significantly during pressurisation at each of the stages mentioned above, or after pressuring while the filter chambers are pressurised, i.e. when the pressure is static, in order to maintain the seals between the filter plates <NUM>. A large enough change in the force applied to the lower pressing plate <NUM> will result in movement of the lower pressing plate <NUM> while the filter chambers are under pressure, and may be caused, for example, by a leak in the hydraulic actuator <NUM>.

The displacement sensor <NUM> is therefore configured to monitor the position or displacement of the lower pressing plate <NUM> during pressurisation and after pressurisation while the filter chambers are still pressurised, i.e. when the filter chambers are under pressure.

The position of the lower pressing plate <NUM> in the sealed position may be measured before the filter chambers are pressurised. Since the displacement sensor <NUM> is connected to the lower frame <NUM>, the position may be measured relative to the lower frame or to the retracted position. Alternatively, the sensor reading may be initialised, i.e. set to zero in the sealed position before pressurisation.

Subsequently, during and after pressurisation of the filter chambers, until the lower pressing plate is intentionally moved, the position or displacement of the lower pressing plate <NUM> is monitored. Monitoring may be performed at regular intervals or may be performed continuously. If the displacement exceeds a first threshold then a warning is produced. Optionally, if the displacement exceeds a second threshold, then the filter cycle may be interrupted in order to prevent damage to the pressure filter.

The first threshold, or warning threshold, may be anywhere in the range or <NUM>-<NUM> of displacement. The second threshold, or alarm threshold, may be anywhere in the range of <NUM>-<NUM>, although the alarm threshold is always higher than the warning threshold. The precise value depends on the number of filter plates and the types of plate seals that are used between the plates to form the filter chambers, at least.

<FIG> shows a method of operating the filter press in accordance with the present invention.

At step <NUM>, the position of the lower pressing plate <NUM> (or upper pressing plate, if the upper pressing plate is used to provide the sealing pressure for the filter chambers) is moved from the retracted position to the sealed position. The position of the lower pressing plate <NUM> or its displacement relative to the retracted position or lower frame <NUM> may be measured to provide a baseline.

At step <NUM>, the filter chambers are pressured, e.g. by pumping material to be filtered into the filter chambers under pressure or in any other the other stages of the filter cycle described above.

At step <NUM>, the displacement of the pressing plate relative the pre-pressurisation position is measured, e.g. relative to the baseline measured at step <NUM>. At step <NUM>, the displacement is compared to a threshold and, if the threshold is not exceeded, the monitoring process resumes at step <NUM> and <NUM>. The process of monitoring, measuring and comparing the displacement to the threshold may be continuous or performed at regular intervals.

If the threshold is exceeded then, at step <NUM>, a warning is provided, e.g. via a control system or control panel for the pressure filter. Following step <NUM>, the process may continue to step <NUM> where the filtering process and monitoring continues.

Alternatively, the displacement may be compared to a second threshold, also referred to the alarm threshold, at step <NUM>. If the alarm threshold is not exceeded, then the monitoring process continues at step <NUM> and returns to step <NUM>. In this embodiment, the warning of step <NUM> may instead only be provided after step <NUM> when the displacement does not exceed the alarm threshold.

Claim 1:
A pressure filter (<NUM>), comprising:
a plurality of filter plates (<NUM>), wherein the filter plates (<NUM>) are arranged in a stack;
a moveable pressing plate configured to be moved from a retracted position to an engaged position to form filter chambers between adjacent filter plates (<NUM>); and
at least one displacement sensor (<NUM>) configured to measure the displacement of the moveable pressing plate relative to a stationary frame of the pressure filter (<NUM>);
characterized in that the pressure filter (<NUM>) is configured to:
monitor the displacement of the moveable pressing plate during cycle pressurization of the filter chambers; and
provide a warning if the displacement of the moveable pressing plate changes by an amount exceeding a threshold during pressurization.