Field of the application

The present application relates to a rotary vacuum disc filter apparatus comprising electronic controlling means arranged to carry out a cleaning run, and to a method for carrying out the cleaning run. The present application also relates to a data storage medium comprising a program code arranged to carry out the method.

Background

Rotary vacuum disc filters are used to filter aqueous suspensions containing particulate material to dewater and dry the material. Usually a plurality of sector shaped filter elements (sectors) are arranged as a rotary assembly of coaxial filter discs in a horizontal central axis above a basin or a vat, which contains the suspension to be filtered. Vacuum is arranged to the interior of the filter discs, which draws water from the aqueous suspension, and the particulate matter will build up a filter cake on the surface of the filter discs.

The formed filter cake is subsequently dewatered and removed and the filter discs are cleaned at intervals by using a variety of methods, such as washing with pressurized aqueous solution directed towards the surface of the filter discs, by providing reversed pressure to the interior of the filter discs, by providing pressurized aqueous solution to the interior of the filter discs, or by using ultrasound, which must be carried out below the surface of the liquid in the basin. The washing is usually carried out by continuing the rotation of the rotary filter assembly. However such washing cycles are not satisfactory in all the cases, especially with challenging materials which tend to block the filter and with challenging filter types, there is need to obtain more efficient washing. This is also desired to prolong the working life of the filter discs, which are large and expensive entities. Especially with ceramic filters, which do not contain separate filter cloths on the surface of the filters, and which have very small pore size, the efficiency of the washing is essential.

Further, in the prior art washing methods the acid is diluted and cooled by the water in the vat, which decreases the efficiency of the cleaning and makes the further processing of used acid complicated and expensive. In practice large volume of hazardous acid waste is formed, which is an environmental risk and requires specific and expensive handling and processing.

Summary

It was found out how to enhance the efficiency of a washing cycle of rotary capillary vacuum disc filters. The present method can be carried out with existing filter devices with small modifications, which requires no or only small investments in new equipment. The present method and devices can overcome drawbacks of prior art.

The present disclosure provides a rotary vacuum disc filter apparatus comprising -a rotary assembly 10 comprising a plurality of coaxial filter discs 12 each comprising a plurality of filter elements 14 in a vat 18 arranged to receive a suspension of particulate material, the rotary assembly 10 being connected to a means 16 for rotating the rotary assembly to a first direction during filtration, -means for providing negative pressure 24 to interior of each filter element 14, -means for providing liquid 26, such as aqueous solution, to interior of each filter element 14,

-means for providing liquid to the vat and means for emptying the vat,

-means for providing ultrasound 20 to the surfaces of the filter elements 14, preferably the means for providing ultrasound being located below the level of the suspension and/or the liquid arranged in the vat 18,

-electronic controlling means 22 arranged to control the operation of the means 16 for rotating the rotary assembly, optionally also the means for providing negative pressure, the means for providing liquid and/or the means for providing ultrasound 20, wherein the electronic controlling means 22 is arranged to carry out a cleaning run comprising

-providing an empty vat, preferably at least to below the level of the filter elements, by operating the means for emptying the vat and/or by detecting an empty vat,

- providing acid solution through the filter elements with the means for providing liquid 26 to interior of each filter element 14, while

-operating the means 16 for rotating the rotary assembly to rotate the rotary assembly in the empty vat.

The present disclosure also provides a method for cleaning filter discs of a rotary vacuum disc filter apparatus comprising -a rotary assembly 10 comprising a plurality of coaxial filter discs 12 each comprising a plurality of filter elements 14 in a vat 18 arranged to receive a suspension of particulate material, the rotary assembly 10 being connected to a means 16 for rotating the rotary assembly to a first direction during filtration, -means for providing negative pressure 24 to interior of each filter element 14, -means for providing liquid 26, such as aqueous solution, to interior of each filter element 14,

-means for providing liquid to the vat and means for emptying the vat,

-means for providing ultrasound 20 to the surfaces of the filter elements 14, preferably the means for providing ultrasound being located below the level of the suspension and/or the liquid arranged in the vat 18,

-electronic controlling means 22 arranged to control the operation of the means 16 for rotating the rotary assembly, optionally also the means for providing negative pressure to interior of each filter element, the means for providing liquid to interior of each filter element and/or the means for providing ultrasound 20, wherein the method comprises carrying out a cleaning run comprising

-providing 42 an empty vat, preferably at least to below the level of the filter elements 14, by operating the means for emptying the vat and/or by detecting an empty vat,

- providing 44 acid solution through the filter elements 14 with the means for providing liquid 26 to interior of each filter element 14, while

-operating 46 the means 16 for rotating the rotary assembly to rotate the rotary assembly in the empty vat.

The present disclosure also provides a computer program product embodied on a non-transitory computer readable medium, comprising computer program code configured to, when executed on at least one processor of the rotary vacuum disc filter apparatus, cause the apparatus or the system to perform the method .

The main embodiments are characterized in the independent claims. Various embodiments are disclosed in the dependent claims. The features of the embodiments and the examples disclosed herein are mutually freely combinable unless otherwise explicitly stated.

The present method and device provide more effective acid wash compared to prior art methods devices. The filter service life is increased, which leads to cost reductions in filter elements and service time. With the present wash there will be less blockages in the filter elements, which provides more capacity for filtering. The washing time is shorter, which also provides more capacity and longer service life for filter elements and for the ultrasonic cleaners. Further, the washing result is uniform all over the filter disk area. As the washing time is decreased, more time is provided for the actual filtering use, which enhances productivity.

The amount of acid required in the process is decreased, which results in cost saves in respect of the acid. Also as the acid can be recovered in concentrated form, the volume of formed acid waste is decreased, thus requiring less capacity for handling of the problematic waste and less environmental load.

The benefits are especially present when ceramic filter elements are used. It is also possible to use ceramic filter elements in new applications, where blocked filters have been an issue, such as for filtering problematic materials.

All filters with same basic structure can be upgraded, which provides a big service potential for existing filter installations. The upgrade can be done only by automation modifications in many cases.

Brief description of the figures

Figure 1 shows a setup of a vacuum disc filter apparatus and connected devices and tanks

Figure 2 shows a core of a vacuum disc filter apparatus from different sides (A-D)

Figure 3 shows an example of a sector-shaped filter element

Figure 4 shows a cross-section (B) of a vacuum disc filter apparatus (A) along a plane X-X

Figure 5 shows the operation of a conventional filtration with the system disclosed in Figure 2

Figure 6 shows the operation of a conventional acid wash with the system disclosed in Figure 5 Figure 7 shows the operation of a first step of the present washing process with the system disclosed in Figure 4

Figure 8 shows the operation of a second step of the present washing process

Figure 9 shows a photograph of a view of a control panel display of a vacuum disc filter apparatus

Figure 10 shows flowcharts of embodiments of the cleaning run. Figure 10A shows an embodiment including a first step comprising steps 42-46, and Figure 10B shows an embodiment including a first step comprising steps 40-46 and a second step comprising steps 48-50

Detailed description

In this specification, percentage values, unless specifically indicated otherwise, are based on weight (w/w, by weight, or wt%). If any numerical ranges are provided, the ranges include also the upper and lower values. The open term “comprise” also includes a closed term “consisting of’ as one option. The diameters or sizes disclosed herein, unless specifically indicated otherwise, refer to the smallest diameter or size, and may be presented as average or number-average diameter or size and may be determined microscopically or by other suitable means.

The present vacuum disc filter apparatus, which is often called as filter, comprises a rotary assembly 10 of plurality of coaxial filter discs 12. The rotary assembly 10 may called as a filter assembly or a rotary filter assembly. Preferably each filter disc 12 comprises a plurality of filter elements 14, which may be sector-shaped filter elements, and which may form a substantially annular disc. The filter elements may comprise or be ceramic filter elements or other suitable filter elements, such as filter elements comprising or made of metal, plastics, fiberglass or wood, which may be covered with a filter fabric or a cloth, such as a bag which may be removable. The rotary assembly is connected to means 16 for rotating the rotary assembly 10 about or along an axis to a first direction during filtration in a vat arranged to receive aqueous suspension of particulate material i.e. solid particles. The means 16 for rotating the rotary assembly 10, or rotating means, comprises or is connected to the axis and arranged to rotate the axis. The present filter apparatus may be called a filter, a system, a filter system, a filtering system, a dewatering and/or drying system, or any suitable combination of terms used herein. The means for rotating the rotary assembly comprises an actuator or a device for providing the rotating movement, for example an actuator configured to rotate the rotary assembly, such as an electric motor 17, and/or or other means for providing rotating energy, preferably which means is controllable by electronic controlling means 22. The means for rotating the rotary assembly comprises the actuator and possible any other parts or accessories required to provide the rotating action, such as the axis, bearings, transmission, chain, belt, rolls, any required (control) electronics and/or wiring, and the like parts. In one example the means for rotating the rotary assembly comprises an electric motor 17, or is an electric motor, preferably comprising the required accessories. The axis may include or be connected to a barrel assembly or a central shaft assembly 15 comprising the tubing required to operate the filter assembly 10 during filtration and washes, which tubing comprises a series of tubes, preferably one for each filter element. The central shaft assembly 15 may be arranged to connect tubing via a series of apertures to a distribution valve 19, so that required negative pressure and liquid may be provided to each of the filter elements in turn when the filter assembly 10 is rotated.

The rotary assembly 10 comprises a central axis to which the plurality of coaxial filter discs is installed. Usually the discs are fixed to the axis and/or in relation to each other, i.e. the rotary assembly is fixed. The axis is horizontal in the filter apparatus, when installed for use, and it is arranged above a vat 18, which may be any suitable basin, container, tank or the like, which is arranged to receive and/or hold fluid. Usually the vat is at least partially open from the upper part and/or sides, and it may for example be in a form of a half cylinder, i.e. a truncated cylinder. The rotary assembly 10 is positioned in such way that during usage only parts of the filter discs 12, preferably the filter elements 14, are submerged in fluid, such as liquid, solution or suspension, contained in the vat 18. The vat is filled or is arranged to be filled with the fluid to an intended level, such as fluid level, which is used in the method steps and which is selected so that the desired submerging of a filter element during rotation is obtained. Each filter element is moved to the fluid contained in the vat in turn and subsequently from the fluid in the vat. The vat may comprise one or more agitators or mixers, such as propeller or paddle agitators, preferably at the bottom of the vat, for mixing the suspension or slurry or other fluid contained in the vat. Location of parts of the apparatus, such as location of adding acid or location of means for providing ultrasound, may be selected according to the (intended) level of fluid in the vat. Usually the axis is above the (intended) level of the fluid in the vat, or above the vat. It is usually desired that filter parts or filter elements of the filter discs are submerged to fluid in the vat, such as liquid, solution, dispersion or suspension, which filter parts or filter elements are usually at a distance from the axis, as can be seen from the figures.

The filter elements 14 may be also called as filter sectors or filter plates, such as ceramic sectors or ceramic plates in case of ceramic filter elements. The filter elements 14 comprise pores or are porous, or contain porous parts, such as at least on the surface. The pore size may be selected according to the particle size of the material to be treated, for example to enable separating liquid and solids from the suspension. When the material and pore size are correct only liquid passes through the filter elements. Air cannot pass the filter elements because of the capillary action of water.

In one embodiment the filters or the filter elements are or comprise ceramic filter or ceramic filter elements. The filter elements may be non-fibrous porous filter elements or fibrous filter elements. A non-fibrous porous ceramic filter is more resistant in alkaline and acidic conditions compared to fibrous ceramic filters, or many other types of filters. However ceramic filters are challenging because of the small pore sizes on the surfaces of the filters, and because there are usually no separate parts in ceramic filters that could be changed if they are permanently or severely blocked or damaged. In one embodiment the filters or the filter elements comprise a porous surface having an average pore size in the range of 0.5-5.0 pm, for example 1-3 pm, such as about 2.8 pm. The thickness of the porous surface may be in the range of 0.1-5.0 mm, such as 0.2-3.0 mm. For example the pore size may be selected to and/or the filter may be arranged to filter material having an average particle size of at least 1 pm, at least 2 pm, at least 3 pm, at least 5 pm, at least 10 pm, at least 50 pm or at least 100 pm, such as in the range of 1-800 pm, 5-800 pm or 10-800 pm.

When ceramic filter elements are used, the surface 30 thereof may contain pores with a first average pore size at a thickness of the surface. The interior of the filter element 14 may be filled with reinforcing granular material and/or other structures and may contain pores with a second average pore size, wherein the first average pore size may be smaller than the second average pore size. In theory optimum first average pore size in ceramic elements is about 2.8 pm for 1 bar bubble point pressure. In such case the surface of the filter elements is therefore more prone to be blocked in the process, and requires especial case when the filter elements are cleaned. The interior of a filter disc, or the interior of a filter element, is connected or connectable to a source of pressure and/or liquid, and it contains one or more connecting part(s) for connecting to a source of pressure and/or solution, which may be different or the same. The connecting part 32 may be a tube (Figure 3), which is connected or connectable to a connecting tube for connecting to means for providing negative pressure, such as to provide a filtrate and/or drainage channel, and/or to means for providing liquid, such as aqueous solution including water and/or acid, and/or to the like means. The connecting tube may be connected or connectable to a distribution valve.

The filter discs 12 may comprise a plurality of sector-shaped filter elements 14, such as 8-16 sector-shaped filter elements, which form a disc shape and which may have a gap between the elements. As can be seen from the figures the sector-shaped filter elements are in the form of truncated sectors, i.e. sectors of a ring rather than sectors of a full disc, so the filter elements 14 are at a distance from the axis. The distance is required to enable connecting the filter elements with required tubing to the sources of vacuum and washing liquid, and to provide suitable distance form the axis so that the filter elements can be fully submerged to the suspension or solution in the vat. The diameter of a filter disc may be in the range of 2-6 m, which may depend on the application. The filter elements may comprise a filter area in the range of 1-12 m ² per filter disc, such as 3-6 m ² . The filter assembly may contain a plurality of such filter discs, such as 5-20, and the filter area of a vacuum disc filter apparatus may be for example in the range of 15- 120 m ² . However the system is scalable to lower and higher capacities as well, for example up to 250 m ² or more. The filtration capacity of such an apparatus may be up to 2000 kg DS/m ² per hour. This equals to 240 tons per hour with a single unit with a 120 m ² filter area.

The filter apparatus may be used for filtering, dewatering and/or drying any suitable particulate solid matter, which may be inorganic and/or organic. Examples of inorganic solids and/or particulates include materials from mineral and mining industry, for example concentrates of iron, chromium, copper, zinc, nickel, gold or phosphates, or tailings of iron, copper, molybdenum, phosphorus or quartz sand. The filter apparatuses may be used for filtering cellulosic materials and the like organic materials as well. The particulate and/or solid matter or material as discussed herein refers to any applicable suspension, dispersion and/or slurry of (solid) particles, which can be filtered to remove liquid and to separate the solids, preferably as a dry filter cake, and to dewater and dry the suspension, dispersion and/or slurry. The system comprises means 24 for providing negative pressure to interior of each filter element 14. Negative pressure refers to a pressure, which is lower than the ambient pressure, such as vacuum. These means may comprise one or more sources of negative pressure, such as a source of vacuum, which may be full or partial vacuum. The pressure may be gaseous pressure. The means for providing negative pressure to interior of each filter element are therefore in gas or pressure communication with the interior of the filter or each filter element. The means for providing negative pressure may also be used to provide positive pressure, if applicable, for example by reversing operation of a pump or by other means. The means for providing negative pressure to interior of each filter element may comprise a source of negative pressure, such as a vacuum pump, a vacuum container and/or any other source of vacuum, including any required accessories such as connecting tube(s), electronics, containers and the like, to the source of negative pressure, fort example external source of vacuum. The means for providing negative pressure to interior of each filter element may be controllable by a controlling means, such as by operating an actuator, a valve, a pump and/or other devices disclosed herein. In one example the means for providing negative pressure to interior of each filter element comprises two separate means for providing negative pressure to interior of each filter element. In such case the separate means may provide different negative pressure, wherein a first means may be used for cake formation and the second means may be used for cake drying. These separate means may be connected with separated tubes to a distribution valve, which contains separate zones and/or apertures for each means.

The system comprises means for providing liquid, such as aqueous solution, to interior of each filter element 14. These means may comprise one or more sources of liquid, which may be pressurized. The means for providing liquid are therefore in liquid communication with the interior of the filter or each filter element, or can be arranged into such liquid communication, for example the means may be (controllably) arrangeable in liquid communication with the interior of each filter element. The means for providing liquid may comprise a (liquid) pump, a liquid container and/or any other source of liquid and optionally any required accessories such as tube(s), electronics, containers and the like. The liquid may be aqueous solution, such as aqueous solution of acid or water, so the system may contain a source of acid solution, such as a container of acid solution, connected to a pump and/or a source of water. The system may also be arranged to mix acid and water to obtain a desired concentration of aqueous acid solution. The means for providing liquid to interior of each filter element may be controllable by a controlling means, such as by operating a valve.

The apparatus may contain one or more inlet(s) and/or outlet(s), and/or one or more valves, for example coupled to inlet and/or outlet and/or to an actuator, or the like parts operatively connected to electronic controlling means, for controlling flow of liquids or gases, or providing pressure. Therefore opening and/or closing of gas and/or liquid communication in the apparatus can be controlled.

The distribution of vacuum and liquid to the filter elements is usually controlled by using a distribution valve. A distribution valve 19 may include two or more inlets for the functions disclosed herein, such as for the means for providing negative pressure 24 to interior of each filter element and for the means for providing liquid 26 to interior of each filter element. The distribution valve may comprise or it may be connected to one or more outlets connectable or connected to interior of each filter element. The distribution valve may include a distributing part arranged to convey the negative pressure and liquid to a desired target, which distributing part may be for example a disc comprising apertures arranged to provide a communication to each filter element. Each filter element may be provided with pressure and/or liquid at a time when the filter assembly rotates. In one example the central barrel of the rotating filter assembly is provided with a dynamic ring (moving piece or part) having a number of apertures, preferably one for each element row, and connected to the interiors of the filter elements, preferably in a row. A distributing part in a form of a static ring (fixed piece or part) comprising zones in the form of apertures is comprised in the distribution valve, such as inside a valve body, which is arranged to handle the timing for each filtration phase. Hoses or tubes are connected to the distribution valve body. When the dynamic ring rotates, the apertures (zones) in the distributing part (static ring, piece or part) will provide negative pressure or liquid to each aperture in turn for a time period, so the filtering or washing sequence disclosed herein can be obtained. Usually there is one or two elongated apertures (vacuum apertures or vacuum zones) for providing negative pressure (vacuum connection) for a prolonged time and one round aperture for providing liquid for a short time (backwash aperture or backwash zone, wash connection). The backwash aperture or zone can be used for the acid wash disclosed herein.

In one embodiment the rotary vacuum disc filter apparatus comprises -a distribution valve 19,

-means for providing negative pressure 24 to interior of each filter element 14 via one or more vacuum aperture(s) of the distribution valve 19,

-means for providing liquid 26, such as aqueous solution, to interior of each filter element 14 via a backwash aperture of the distribution valve 19. In other words a distribution valve 19 may be arranged to provide negative pressure, preferably from and/or with the means for providing negative pressure 24, to interior of each filter element 14 via one or more vacuum aperture(s) of the distribution valve and/or to provide liquid, preferably from and/or with the means for providing liquid 26, to interior of each filter element 14 via a backwash aperture of the distribution valve 19, more particularly to provide or obtain the filtering and/or washing/cleaning sequence(s) disclosed herein.

By operating one or more means and/or actuators controlled by the electronic controlling means 22, a desired source and/or type of pressure or liquid may be controlled and/or provided, for example water, acid or a mixture of water and acid may be obtained and/or provided and the mixing ratio can be controlled, and/or temperature and/or the pressure may be controlled. Therefore the electronic controlling means can control what is provided to the filter elements.

The system may comprise means for providing liquid to the vat and/or means for emptying the vat. The means for providing liquid to the vat may comprise means for providing and/or pumping aqueous suspension and/or aqueous solution to the vat and/or from the vat, or means for conveying aqueous suspension and/or aqueous solution to the vat. These means may comprise one or more pumps and/or a source of pressure and/or liquid, such as pressurized liquid, which may comprise or be connected to a source of aqueous suspension and/or water or other aqueous solution and/or to another container. The means for providing liquid may comprise an inlet for a source of water, which may be connectable to an outlet of water distribution system or other liquid system, which may be connected to the apparatus, such as to an inlet in the vat, preferably equipped with a valve operatively connected to electronic controlling means. The apparatus may be connectable or connected to a water supply network or to other source of water. These means can be used to fill the vat and/or to empty the vat, for example to fill with the suspension to be filtered and/or with washing liquid, such as water or other aqueous solution, or to remove such suspension or solution or other fluid. In similar way, the system may comprise a separate means for providing the suspension to the vat, which means may comprise a source of suspension or which means may be connectable or connected to a source of suspension. The means for providing the suspension to the vat may comprise means for providing and/or pumping aqueous suspension to the vat and/or from the vat, or means for conveying aqueous suspension to the vat. These means may comprise one or more pumps and/or a source of pressure and/or suspension, such as pressurized suspension, which may be connected to a source of aqueous suspension and/or to another container. The means for providing suspension may comprise an inlet for a source of suspension, such as for an outlet of a container of the suspension or other suspension system, which may be connected to the apparatus, such as to an inlet in the vat, preferably equipped with a valve operatively connected to electronic controlling means.

The means for emptying the vat may comprise one or more outlets in the vat, for example in the bottom of the vat, which may comprise one or more valves or the like devices, which may be operatively connected to electronic controlling means, and/or one or more pumps, which may be operatively connected to electronic controlling means. The valve(s) may be also operated by other way, if applicable, such as manually.

The term “aqueous solution” used herein is intended to include water as one option, which may be tap water or similar water suitable for the present purposes. The water may be recycled water or pure water, but usually highly purified water is not required in most cases. The term “liquid” is intended to include any fluids suitable for the present applications, including water and other aqueous solutions, or other solvents such as organic solvents, if applicable, wherein the fluid may or may not include other substances, which may be soluble and/or insoluble.

The system comprises means for providing ultrasound 20 to the surfaces of the filter elements 14, the means for providing ultrasound being located below the (intended) level of the suspension and/or solution arranged in the vat at least during a washing run. The source of ultrasound must be immersed in liquid in order it to be fully operative. The means for providing ultrasound may comprise one or more ultrasound emitters or transducers, which are electronic devices and can be operatively connected to a controlling means, so that the function of the electronic means for providing ultrasound can be automatically controlled by the electronic controlling means. The means for providing ultrasound are positioned to direct the ultrasound towards the surfaces of the filters or filter elements, typically one source of ultrasound, such as ultrasound transducer, between two filter discs. In existing systems utilizing ultrasound the means for providing ultrasound are usually located below the surface of the suspension or solution in the vat in such way that when the filter assembly continues to rotate to a first direction, which is the same rotating direction as during the filtration, the ultrasound is provided to a filter element substantially immediately, i.e. as the next step, after the filter element is submerged to liquid, and/or substantially immediately after acid has been injected to the filter element, as shown in Figure 6B.

The system comprises one or more electronic controlling means 22, such as a control unit, operatively connected to the means 16 for rotating the rotary assembly, optionally also to the means for providing negative pressure 24, to the means for providing aqueous solution 26, to the means for providing liquid to the vat, to the means for emptying the vat, and/or to the means for providing ultrasound. The electronic control means may be also operatively connected to any other controllable parts of the system, such as disclosed herein, for example valves, actuators, pumps, switches, sensors, and/or heating and/or cooling means. One example provides a control system comprising the control unit for implementing the present method in the rotary vacuum disc filter apparatus.

The electronic controlling means comprises one or more processors and memory, and a user interface, a display, a keyboard, a touch screen and/or other inputting means, power connection, a network connection, which may be wired and/or wireless, and/or connections to each of the controllable means of the apparatus as disclosed herein. The electronic controlling means may comprise one or more computers and/or embedded systems, such as Programmable Logic Controller (PLC). The electronic controlling means may be programmable and may comprise software, which is arranged when run with the processor, to carry out one or more controlling actions to carry out the present method and optionally one or more other methods, in general the operation of the apparatus. As the means of the apparatus, including one or more of actuators, valves, ultrasonic emitters, relays, motors, such as electric motors, pumps, heating means, sensors, such as temperature sensors, pressure sensors, light sensors, position sensors and/or flow sensors, cameras and the like parts, which may be required to monitor and carry out operations, are electronically connected to the controlling means, the controlling means can be arranged, including programmed, to operate these means. The software contained in the controlling means can be updated to provide new functionalities and/or properties. By controlling said means it is possible to obtain and/or maintain the desired operation of the apparatus or system comprising the apparatus. A desired operation may comprise for example obtaining and/or maintaining a certain (predetermined) value, such as keeping a variable at a defined range by providing controlling actions having effect to the variable, such as temperature, flow speed, rotation speed, level of liquid or suspension, level of negative and/or positive pressure, pH, concentration of an acid or other substance, and the like. An example of a display and user interface of an electronic controlling means is disclosed in Figure 9, wherein the display shows information from an automated system.

A control unit with the connected sensors, actuators, motors, pumps, relays and other applicable devices, as well as any switches, connectors, controlling devices, adapters, transformers and the like, which are required in the system, or with connections to said devices, may form a control system or the electronic controlling means or be a part of it. The control system includes required wiring between the parts thereof, and/or wireless connections. The electronic controlling means, the control system and/or the control unit may be connected and connectable to a remote system, which may have a display and a user interface, and which enables controlling and/or monitoring the operation of the system or the apparatus from remote.

In one embodiment the rotary vacuum disc filter apparatus comprises electronic controlling means (22), such as a control unit, comprising at least one processor, memory including computer program code, the memory and the computer program code being configured, with the at least one processor, to control the operation of the rotary vacuum disc filter apparatus, such as to control the means for rotating (16) the rotary assembly, optionally also the means for providing negative pressure (24) to interior of each filter element, the means for providing liquid (26) to interior of each filter element, and/or the means for providing ultrasound (20), to carry out the method disclosed herein or part thereof, such as to carry out the cleaning run or part thereof.

One embodiment provides a rotary vacuum disc filter apparatus comprising

-a rotary assembly (10) comprising a plurality of coaxial filter discs (12) each comprising a plurality of filter elements (14) in a vat (18) arranged to receive a suspension of particulate material, the rotary assembly (10) being connected to rotating means (16) configured to rotate the rotary assembly to a first direction during filtration, preferably wherein the rotating means comprises an actuator configured to rotate the rotary assembly,

-means for providing negative pressure (24) to interior of each filter element (14), preferably comprising a (controllable) source of negative pressure connectable to interior of each filter element (14),

-means for providing liquid (26) to interior of each filter element (14), preferably comprising one or more (controllable) sources of liquid arrangeable in liquid communication with the interior of each filter element,

-means for providing liquid to the vat, preferably comprising one or more (controllable) sources of liquid arrangeable in liquid communication with the vat, and means for emptying the vat, preferably comprising one or more (controllable) outlets in the vat,

-means for providing ultrasound (20), preferably one or more ultrasound emitters or transducers arranged to provide ultrasound, to the surfaces of the filter elements (14), preferably the means for providing ultrasound being located below the level of the suspension and/or the liquid arranged in the vat (18),

-electronic controlling means (22), such as a control unit, comprising at least one processor, memory including computer program code, the memory and the computer program code being configured, with the at least one processor, to control the operation of the rotary vacuum disc filter apparatus, such as to control the means for rotating (16) the rotary assembly, optionally also the means for providing negative pressure (24) to interior of each filter element, the means for providing liquid (26) to interior of each filter element, and/or the means for providing ultrasound (20), to carry out a cleaning run comprising

-providing an empty vat, preferably at least to below the level of the filter elements, by operating the means for emptying the vat and/or by detecting an empty vat, -providing acid solution through the filter elements (14) with the means for providing liquid (26) to interior of each filter element, while

-operating the means for rotating (16) the rotary assembly to rotate the rotary assembly in the empty vat.

The operation of a vacuum disc filter in general includes filtration or filtering, wherein filtrate from the internal passages of the filter elements is removed by vacuum, while the pressure differential across the filter element causes cake formation; dewatering and drying, where water is drawn from the slurry by capillary action; cake drying, and cake discharge, where final cakes are discharged by blade or wire scrapers on either side of the filter discs. In the process filtrate is obtained, which goes usually into a filtrate tank. The filtrate is usually recyclable and has low suspended solid content. The filtrate may be used to flush the filter elements during a back flow washing and in the other cleaning or washing operations disclosed herein, for example the filtrate may be water which is substantially pure for the washing purposes.

More particularly, in the filtering use of the system the filter elements are submerged in suspension, which may be a slurry of solids, to remove the liquid from the suspension by pressure difference, i.e. by using negative pressure or vacuum. A filter cake is formed on to the surface of a filter element. Only liquid, which usually is or comprises water, passes through the elements. In many cases a vacuum pump is used to create the driving force to move liquid from elements to a filtrate tank. The filtering may be carried out continuously or as a batch process. In a continuous process the suspension is fed to the vat in such way, that the vat is filled to a predetermined level, for example to 40-60% of the volume of the vat. This may be controlled by the electronic controlling means. The level of the suspension in the vat may be maintained automatically. When the level of the suspension in the vat decreased during the filtering process, more suspension may be conveyed to the vat. This may be carried out until all the suspension is filtered and/or when a cleaning run is to be carried out.

The present disclosure describes the system in context of aqueous suspensions and solutions. However, when applicable the system and the method may be applied to other fluids as well, such as suspensions, solutions and/or emulsions comprising organic solvents, non-polar substances, fats and the like, which may or may not contain water.

As the filter elements rotate to above the slurry level free liquid, such as water, is removed and residual moisture of the formed filter cake continuously decreases until the filter cake is discharged.

The filter cake may be discharged continuously. The system may comprise means 13 for discharging filter cake from the surfaces of the filter element, such as blades or scrapers, such as ceramic scrapers, which are positioned in such way that they do not touch the filter elements to prevent damaging the surface of the elements. There is a small gap between filter elements, such as 0.5-1 .0 mm, and the blades or scrapers. The removed filter cake is conveyed away from the vat and the filters, and can be recovered. The means 13 for discharging filter cake from the surfaces of the filter element may further comprise or may be connected to discharge chutes or the like elements, which are arranged to capture and receive the dried solid filter cake from a filter element before the filter element re-enters the suspension and/or the backwash step. A thin residual filter cake layer remains on the surface of the filter element, and must be removed. As shown in Figure 5B, the filter cake is discharged at step C, and the filter assembly is rotated in such direction that the corresponding filter element proceeds towards the vat and a backwash is step D is carried out. The backwash must be carried out after the discharge of the filter cake and below the discharge point, such as a discharge chute. The backwash must also be carried out before the filter element enters the suspension in the vat. These features determine the direction of rotation during the filtering. The backwash is carried out by using a suitable liquid pressure, such as a pressure in the range of 0.9-2.5 bar.

Residual thin cake is usually washed off with water (backwash), such as by clean water or recycled water. Water is pumped in opposite direction through the filter element. This backwash removes residual cake and cleans pores in the filter element. Backwash may be done in every rotation. In a commonly used distribution valve there is usually an aperture for the backwash, which aperture may be substantially round and therefore defines a relatively short backwash period. However the backwash cannot remove all the residual material, which is especially the case with ceramic filters with small pore size and specific structure. This leads to blocking of the filer and adverse effects such as loss of filtration capacity, which is caused i.a. by increased filter medium resistance, decreased filer rate and difficulties in cake discharge.

Currently in prior art regeneration of ceramic elements is needed to keep the elements functioning properly. Usually this is done 1-2 times a day. For regeneration the slurry vat is emptied and filled with water. There are three main wash modes: ultrasonic wash, chemical wash and combined wash (ultrasonic + chemical). Combined wash is the most effective. Any suitable acid can be used, but nitric acid and oxalic acid are the most used ones.

In prior art washing methods acid is pumped to filter elements through a backwash connection, and filter elements are submerged in water and treated with ultrasonic washers. When the backwash defined by a common distribution valve is used, the acid wash is relatively short and the timing of the acid was is fixed. The filter elements continue rotating in original direction submerged in water. In this method however time for acid to react on filters is really short, such as only 10% of a full revolution before the treated filter element goes to water in the vat and to ultrasound wash. When the filter discs rotate in water or subsequently air there is a long inefficient dead time in the wash. The water in the vat is usually cold, which slows down the chemical reactions with acid. The acid is injected at a location which is subsequently submerged in the water, so the acid will be diluted immediately. Therefore the acid wash is not very effective and takes a long time, typically 45-60 minutes acid injection time is used. This results in high consumption of acid and is time-consuming. Acid is ending into the liquid in vat and therefore high amount of weak acid must be handled after washing cycle.

In the present case the washing was reorganized, which led to several advantages over the prior art washes.

The system disclosed herein may be used in a method for cleaning the filter discs of a rotary vacuum disc filter apparatus. The method comprises carrying out a cleaning run, as disclosed in Figure 10A, comprising

-providing an empty vat 42, optionally by emptying the vat, for example by operating means for emptying the vat and/or by detecting an empty vat,

-providing liquid to interior of each filter element to provide acid solution 44 through the filters or the filter elements, preferably once per revolution, and

-operating the means for rotating the rotary assembly to rotate the rotary assembly 46. The method may comprise rotating 40 the rotary assembly to a second direction, which is reverse or opposite to the first direction, which rotating 40 may be started already before providing the empty vat, or which can be started later, such as during step 46 or after carrying out the first cleaning run after step 46, which options are disclosed in Figures 10A and B.

The method may be arranged to be carried out automatically. The cleaning run may be started automatically and/or it may be started manually. In automated use, which can be controlled by the electronic controlling means, the cleaning run may be started after one or more predetermined conditions are fulfilled, such as after a predetermined time, after predetermined number of filtering runs and/or filter assembly revolutions are detected, after a detected decrease below a predetermined threshold in the filtering speed, capacity and/or flow is detected, or a detected increase of pressure above a predetermined threshold in the system, after all or substantially all the suspension is filtered, and/or after one or more other corresponding conditions are detected from the system. The cleaning run may be carried out for example 1 or 2 times a day, such as once in 10-24 hours, such as with 12 or 24 hours interval. The electronic controlling means may be arranged to carry out a cleaning run comprising

-providing 42 an empty vat, optionally by operating means for emptying the vat and/or by detecting an empty vat,

-providing 44 liquid to interior of each filter element to provide acid solution through the filters or the filter elements, and

-operating 46 the means for rotating the rotary assembly to rotate the rotary assembly. The electronic controlling means may be arranged to operate the means for providing liquid, which may be carried out to control the pressure, composition, concentration, temperature and/or other properties of the liquid. The system may comprise a T-connection, which may comprise a valve and/or an actuator operatively connected to the electronic controlling means, which T- connection is connected to a source of acid and to a source of water, wherein the acid or water can be selected to be provided to the filter elements or to a distribution valve, of a mixture or acid and water may be obtained and the mixing may be controlled, which mixture may be used in the acid wash.

Providing the empty vat 42 may comprise emptying the vat and/or detecting an empty or an emptied vat. The vat may be emptied to the desired level already during the filtering, wherein liquid is removed and the formed filter cake is conveyed away from the system. The vat may be empty at least to below the level of the filter discs and/or filter elements, especially below the lowermost filter element, so that none of the filter elements are in contact with any material possibly contained in the vat. If any suspension is left in the vat, it may be removed, for example pumped away and/or removed by operating a valve or other outlet, until the vat is empty enough and the filters or filter elements do not touch any remaining suspension or other fluid in the vat. Preferably the vat is rinsed and/or washed with aqueous solution after removing the suspension. The level of fluid and/or substances such as liquid, suspension and/or solids in the vat may be detected by one or more sensors, cameras or the like detecting means or detectors operatively connected to the electronic controlling means, and when an empty vat, or sufficiently empty vat, or rinsed and/or washed vat, is detected, the cleaning run may be carried out. This can be controlled by the electronic controlling means. Providing the empty vat may also comprise providing a signal to the electronic controlling means to indicate that the vat is empty or emptied, for example automatically and/or manually, and/or arranged by electronic and/or mechanic means, such as by an electronic and/or mechanic sensor detecting the level of fluid in the vat, conductivity measured in the vat, detecting a pressure in the vat and/or with any other suitable detecting means.

After empty vat is provided, acid may be provided 44 and the rotary assembly may be rotated in air 46, i.e. without submerging into liquid or suspension, in the absence of liquid in the vat and/or in the emptied vat. This may be called dry rotating. The acid may be provided, such as pumped and/or injected, through each filter element at a time, such as when a filter element rotates to a certain location, which may be at a level of the axis or slightly below the level of the axis, but preferably above the liquid level of the vat, which is the level the liquid is intended to be added. This location of adding acid is the location generally used in prior art systems. The acid may be provided for a relatively short time at each revolution, which may be defined by the backwash connection of a distribution valve. In such system the step of providing acid is an integral feature of the system defined by the structure of the system, i.e. the arrangement of the distribution valve and the tubing connected to the filter elements.

The acid solution is provided, injected or pumped into the interior of the filter elements, and through the filter elements, so a pressure from inside to outside of the filter is formed, and the acid removes or releases blocking and contaminating substances. The acid may be relatively dilute, such as 0.5-5.0% by weight of acid, such as 0.5-2.0% by weight, for example about 1 % by weight. During and after providing the acid through the filters via the backwash connection, the filters rotate in air, i.e. the vat is kept empty. The backpressure caused by the filter element, especially ceramic filter element, may be such high that the acid solution usually does not pass the filter element with high speed and cause spraying, but it rather wets the surface of the filter element. However to ensure safety it is advantageous that the rotating direction during this step is such that the filter element moves towards the vat after the acid wash. Therefor any risks of spilling the acid can be decreased and the used acid can be better recovered in the vat. The filters may rotate one or more full revolutions at this step and/or for a certain time. The rotation speed may be adjusted, for example the rotation at this step may be lower or higher than during the filtration. Fresh acid may be pumped to the filters once on every rotation. At this point the vat is empty, or at least the filter elements are not in contact with any residual suspension, liquid or solids in the vat. Sources of ultrasound are not used at this point, and it would not be practical as the ultrasonic devices need to be submerged in liquid for operation. This procedure may be called as a first step. The acid solution may be aqueous acid solution, or it may be based on other solvent and/or substances, such as one or more organic solvents, oxidants, reducing agents and/or bases where applicable. The acid solution may be formed by combining and/or mixing water and acid in the system, which may be controlled by the electronic controlling means. The acid solution may be heated to speed up chemical reactions. The acid solution may be provided as heated, and the system may comprise means for heating the liquid provided to interior of each filter element, such as aqueous solution, more particularly the acid solution. The means for heating may comprise a source of heat, for example an electric heating element or a source of heated liquid or air. In one embodiment the acid solution provided to interior of each filter element is heated to or has a temperature of 30°C or more, such as in the range of 30-50°C. When ceramic filter elements are used, higher temperatures may be used compared to other types of filters. However it is necessary to control the temperature to avoid too rapid chances in the temperature, which may break ceramic elements. This may happen for example if also cold water is used. The temperature may be determined at the source of the acid solution, such as a container, which may include a heating element and means for detecting the temperature of the solution, such as a sensor. However the heated solution may be cooled when conveyed to the filter elements, and the measured temperature does no longer represent the temperature in the filter elements. To overcome this problem, the temperature may be determined from the filter elements by using remote sensing means such as the means for detecting the temperature, for example infra red sensor or heat camera, which may be positioned to measure the temperature of a filter element after the filter element is heated, for example immediately after heated solution has been injected into a filter element or after a filter element has been heated with other means, such as by other means for heating the filter elements and/or the filter discs operatively connected to the electronic controlling means disclosed herein. The remote sensing means are located in the air, i.e. they are not immersed into liquid.

The means for heating and the means for detecting the temperature may be operatively connected to the electronic controlling means, which may be arranged to control the heating means to obtain and maintain the temperature at a desired or predetermined range, such as the ranges disclosed herein, preferably by controlling and/or adjusting the heating means as feedback to the temperature detected with the means for detecting the temperature. In the first step the acid can react on the filter all the time, i.e. 100% of full revolution. As the filter elements are not submerged in water or other liquid, the acid concentration remains constant, and the filter elements will be fully soaked with washing acid. The vat is not filled at this step, and as the vat is empty or substantially empty, there is no cold water present to cool the filter discs. When ceramic filter elements are used, they tolerate heating and can be heated externally to speed up the chemical reactions. The acid strength (pH) can be measured easily from the discs.

In the beginning of the wash the acid concentration can be higher to displace water in the filter elements. This can be controlled by controlling a ratio of mixed water and acid, wherein applicable. Acid injection or pumping to the filter elements may start before the actual wash to displace water in pipelines and filter elements, especially ceramic filter elements.

The steps of providing acid solution through the filter elements, and operating the means for rotating the rotary assembly to rotate the rotary assembly, preferably for a period of time, such as for a time used for rotating the filter disc one or more times, enable the acid to react with impurities to clean the filter elements. It was found out that this dry acid injection step with continuing rotation of the discs efficiently removed most of the contaminating substances even without the presence of washing water in the vat. The filter elements are cleaned to a first level, which may be enough for certain purposes or certain uses, for example when certain materials are filtered, which are relatively easy to remove from the filter elements. However it may be desired to continue with the cleaning to clean the filter elements to a second or further cleaning level, for example in more challenging cases, wherein the filter elements are blocked or contaminated more severely and which are challenging to clean.

After the first step is completed the washing acid can be recovered and recycled by draining the vat. It is also possible to carry out a long duration plate regeneration with low acid and energy consumption. For example, acid wash may be done with empty vat for 24 hours. Fresh acid may be pumped to plates for 5 minutes every 30 minutes. It is also possible to easily use different, even unusual or experimental, washing chemicals with low consumption for long duration plate regeneration. The rotation direction may be reversed at the first step. The rotation direction may be reversed at a possible second step, or the already reversed rotation direction may be maintained at the second step.

In one embodiment the cleaning run comprises operating 40 the means for rotating the rotary assembly to rotate the rotary assembly to a second direction, which is reverse or opposite to the first direction. Correspondingly, the method may comprise operating 40 the means for rotating the rotary assembly to rotate the rotary assembly to a second direction, which is reverse or opposite to the first direction. The first rotating direction may be used during filtration. The carry out this step the means for rotating the rotary assembly must be capable to reversing the rotating direction, i.e. the rotating direction is reversable.

After the first step has been carried out for a suitable period of time, such as for 5- 15 minutes, such as 5-10 minutes, or longer or even shorter, for desired number of revolutions, and/or when a desired cleaning result is obtained, a second step may be carried out.

In one embodiment the electronic controlling means is arranged to carry out a cleaning run further comprising

-after at least one rotation of the rotary assembly in the empty vat, operating the means for providing liquid to the vat to provide liquid 48, such as aqueous solution, to the vat to submerge the filter elements 14 to the liquid,

-operating 50 the means for providing ultrasound 20 to provide ultrasound to the filter elements 14 while continuing rotating the rotary assembly. The rotary assembly is rotated in the liquid in the vat, preferably so that the filter elements 14 are fully submerged to the liquid. The step of providing acid solution through the filter elements is repeated in each revolution of the filter assembly. The ultrasound is preferably provided to a filter element after the filter element has been rotated through the liquid in the vat, i.e. immediately prior to rotating the filter element from the water and providing acid.

Correspondingly the method may comprise

-after at least one rotation of the rotary assembly in the empty vat, providing 48 liquid to the, such as aqueous solution, to the vat to submerge the filter elements 14 to the liquid, preferably during rotating the rotary assembly,

-operating 50 the means for providing ultrasound 20 to provide ultrasound to the filter elements 14 while continuing rotating the rotary assembly. The vat may be filled with water or other suitable liquid, preferably to an intended fluid level, such as liquid level, which allows submerging each filter element to the liquid while the filter assembly is rotated. The filter discs are submerged in the liquid in the vat. The providing of acid at each revolution may be continued. The acid is pumped to a filter or a filter element preferably at a location which is immediately above the liquid level so that when the filter discs rotate, the acid- treated part is rotated away from the liquid, to avoid washing away the freshly pumped acid. Ultrasound can be used prior to this step, when the liquid level is above the ultrasonic cleaners. The filter elements are fully submerged. The means for providing ultrasound may be located immediately before the location of providing acid in respect of the rotation direction, as can be seen from the figures. The location of providing acid is immediately above the level of liquid in the vat, and the location of the means for providing ultrasound are next to the location of providing acid but immediately below the level of liquid in the vat.

More particularly the method may comprise operating 50 the means for providing ultrasound 20 to provide ultrasound to the filter elements 14 below the level of liquid in the vat while continuing rotating the rotary assembly to a direction, wherein acid is subsequently (immediately) provided to the filter element above the level of liquid in the vat. The rotation is continued to a direction wherein the acid-treated filter element is rotated in the air, i.e. away from the liquid in the vat. This rotating direction usually corresponds to the second direction.

One example provides the rotary vacuum disc filter apparatus comprising

-a rotary assembly 10 comprising a plurality of coaxial filter discs 12 each comprising a plurality of filter elements 14 in a vat 18 arranged to receive a suspension of particulate material, the rotary assembly 10 being connected to a means for rotating 16 the rotary assembly to a first direction during filtration, -a distribution valve 19,

-means for providing negative pressure 24 to interior of each filter element 14 via the distribution valve 19, such as via one or more vacuum aperture(s) of the distribution valve 19,

-means for providing liquid 26, such as aqueous solution, to interior of each filter element 14 via the distribution valve 19, such as via a backwash aperture of the distribution valve 19,

-means for providing liquid to the vat and means for emptying the vat, -means for providing ultrasound 20 to the surfaces of the filter elements 14, preferably the means for providing ultrasound being located below the level of the suspension and/or the liquid arranged in the vat 18,

-wherein during a filtration, when rotating to the first direction, the formed filter cake is arranged to be discharged from the surfaces of the filter element by one or more means for discharging filter cake from the surfaces of the filter element, and subsequently, i.e. immediately after which, said filter element 14 is arranged to be rotated to a point of washing by the means for providing liquid 26 to interior of each filter element 14 via a backwash aperture of a distribution valve 19, preferably before rotating the filter element to the suspension in the vat,

-electronic controlling means 22 arranged to control the operation of the means for rotating 16 the rotary assembly, optionally also the means for providing negative pressure, the means for providing liquid and/or the means for providing ultrasound 20, wherein the electronic controlling means 22 is arranged to carry out a cleaning run comprising

-operating the means for rotating 16 to rotate 40 the rotary assembly 10 to a second direction, which is reverse to the first direction,

-providing 42 an empty vat,

-providing 44 acid solution through the filter elements 14 with the means for providing liquid 26 to interior of each filter element 14 via the distribution valve 19, such as via a backwash aperture of the distribution valve 19, while

-operating 46 the means for rotating 16 the rotary assembly to rotate the rotary assembly in the empty vat, and preferably

-after at least one rotation of the rotary assembly 10 in the empty vat, operating 48 the means for providing liquid to the vat to provide liquid, such as aqueous solution, to the vat to submerge the filter elements 14 to the liquid,

-operating 50 the means for providing ultrasound 20 to provide ultrasound to the filter elements 14 while continuing rotating the rotary assembly.

Correspondingly one example provides a method (Fig. comprising providing the rotary vacuum filter apparatus comprising

-a rotary assembly 10 comprising a plurality of coaxial filter discs 12 each comprising a plurality of filter elements 14 in a vat 18 arranged to receive a suspension of particulate material, the rotary assembly 10 being connected to a means for rotating 16 the rotary assembly to a first direction during filtration, -a distribution valve 19, -means for providing negative pressure 24 to interior of each filter element 14 via the distribution valve 19, such as via one or more vacuum aperture(s) of the distribution valve 19,

-means for providing liquid 26, such as aqueous solution, to interior of each filter element 14 via the distribution valve 19, such as via a backwash aperture of the distribution valve 19,

-means for providing liquid to the vat and means for emptying the vat,

-means for providing ultrasound 20 to the surfaces of the filter elements 14, preferably the means for providing ultrasound being located below the level of the suspension and/or the liquid arranged in the vat 18, wherein during a filtration, when rotating to the first direction, the formed filter cake is arranged to be discharged from the surfaces of the filter element by one or more means for discharging filter cake from the surfaces of the filter element, and subsequently, i.e. immediately after which, said filter element 14 is arranged to be rotated to a point of washing by the means for providing liquid 26 to interior of each filter element 14 via a backwash aperture of a distribution valve 19, preferably before rotating the filter element to the suspension in the vat,

-electronic controlling means 22 arranged to control the operation of the means for rotating 16 the rotary assembly, optionally also the means for providing negative pressure, the means for providing liquid and/or the means for providing ultrasound 20, and carrying out a cleaning run, as disclosed in Figure 10B, comprising

-rotating 40 the rotary assembly 10 to a second direction, which is reverse to the first direction,

-providing an empty vat 42,

-providing 44 acid solution through the filter elements 14 with the means for providing liquid 26 to interior of each filter element 14 the distribution valve 19, such as via a backwash aperture of the distribution valve 19, while

-rotating 46 the rotary assembly in the empty vat, and preferably

-after at least one rotation of the rotary assembly 10 in the empty vat providing 48 liquid to the vat to submerge the filter elements 14 to the liquid, such as by operating the means for providing liquid to the vat to provide liquid, such as aqueous solution, to the vat to submerge the filter elements 14 to the liquid, -providing ultrasound 50 to the filter elements 14 while continuing rotating the rotary assembly.

In the second step the acid can react on a filter part or element approximately 70% of a full revolution before the filter part or element is submerged or immersed in the liquid in the vat. Also in this step the filter elements, especially ceramic plates, can be heated externally to speed up the chemical reactions. The acid strength (pH) can be measured easily from the filter elements.

In one embodiment the rotary vacuum disc filter apparatus comprises means for heating the liquid, which is arranged to be provided to the vat or which is provided to the vat, preferably the means for heating being operatively connected to the electronic controlling means. The means for heating may comprise one or more electric heaters or heating elements, such as a resistance wire, or a source of external heat, such as heated liquid, which can be provided via heating pipes or other elements. The liquid provided to the vat may be heated to, or may have a temperature of, 30°C or more, such as in the range of 30-50°C. The temperature of the filter elements may be detected as discussed in previous, and the temperature of the liquid in the vat may be controlled in analogous way by controlling the means for heating.

In one embodiment the rotary vacuum disc filter apparatus comprises means for heating the filter elements and/or the filter discs operatively connected to the electronic controlling means, preferably means for externally heating the surfaces of the filter elements and/or the filter discs, such as infrared heaters and/or source of hot air, preferably the means for heating being located above the level of the suspension and/or the liquid arranged in the vat. The means may be located immediately after the location of providing acid, so the heat may be provided immediately subsequent to providing acid to the filter elements. The method may comprise heating the filter elements and/or the filter discs, such as with infrared heaters and/or with a source of hot air. Heating enhances the chemical reactions with acid, thus less acid, less revolutions in cleaning cycle, shorter cleaning time and/or lower acid pressure can be used.

In one embodiment the rotary vacuum disc filter apparatus comprises means for recovering used acid solution from the vat and/or means for conveying the recovered used acid solution to reuse and/or further processing, preferably the means being operatively connected to the electronic controlling means. Correspondingly, the method may comprise recovering the used acid solution from the vat and conveying the recovered used acid solution to reuse and/or further processing. As acid is not diluted with water or other liquid, the acid concentration remains high, and the volume remains small. The acid may be conveyed, such as pumped with a pump, to a container, such as an acid tank. The used acid can be treated as waste, which may require further processing, for example in waste treatment plant.

The apparatus may comprise means for monitoring and/or detecting the properties of the liquid in the system and/or in the vat, such as washing water, aqueous suspension or solution and/or acid, and/or pressure in the system. The monitored and/or detected properties can be used to control the function of the apparatus, preferably as feedback to one or more detected properties. For example acid wash can be stopped when flow is returned to a set value.

The present method may be implemented in existing rotary vacuum disc filter apparatuses, for example by updating or upgrading the control unit, such as the software of the control unit. Therefore the control unit may be reprogrammed to carry out one or more steps, such as all the steps, of the present method. A data storage medium may be provided to provide a program code for the upgrade. The program code, i.e. a computer program code or program instructions, may be embodied in a network location, in a computer, in a physical data storage medium or in any other suitable source, which may be local or remote, and/or may be installed to the apparatus from such source. The expressions “data storage medium”, “computer-readable medium” and the like medium include said sources. The program code is preferably run in a processor of the apparatus and may be embodied in a memory, such as a non-transitory computer readable memory or medium, of the apparatus or in an external or remote medium.

The present disclosure provides a computer program product embodied on a non- transitory computer readable medium, comprising computer program code configured to, when executed on at least one processor, cause the apparatus or the system to perform the present method. One example provides a data storage medium comprising instructions, or a program code, stored thereon, arranged to carry out the present method when executed with a (compatible) processor of electronic controlling means, such as a control unit, of a suitable rotary vacuum disc filter apparatus, such as a rotary vacuum disc filter apparatus disclosed herein, or for causing the apparatus to perform the method. One example provides a computer program comprising instructions, or a computer readable medium comprising program instructions, for causing a rotary vacuum disc filter apparatus to perform the present method. One example provides a non-transitory computer readable medium comprising program instructions for causing the apparatus to perform the present method. The features disclosed herein are freely combinable. In some cases the updating or upgrading may also require changing one or more mechanical and/or electronic parts of the apparatus as well, such as one or more parts relating to the rotating of the rotary assembly, for example the frequency converter of the means for rotating the rotary assembly, i.e. an electrical motor, and/or adding one or more parts or accessories, such as one or more of relays, actuators, wiring and/or the like parts required for implementing the present system. Certain older apparatuses may have been designed to operate to only one rotation direction as there has not been any motivation to change the direction of rotation during the process. Such apparatuses may not be able to change the direction of rotation without modifications. It is also possible to provide a completely new controlling unit, means for rotating or part thereof and/or related equipment as a solution for upgrading older systems and apparatuses, the new equipment being able to carry out the present method. The apparatus provided herein and used in the present method may comprise means for rotating the rotary assembly arranged and/or capable to reverse the direction of rotation. The direction of rotation can be controlled by the electronic controlling means.

Examples

Figure 1 shows an example of a rotary vacuum disc filter apparatus setup with connected devices and tanks. A filter assembly 10 is installed in a frame comprising the vat 18 so that the central shaft assembly comprising the axle is above the vat 18 and the filter discs 12 are fixed coaxially to the central shaft assembly 15, each filter discs 12 comprising a plurality of sector-shaped filter elements, which are arranged so that each filter element 14 will be submerged to the suspension or liquid contained in the vat when the filter assembly 10 is rotated by using the means for rotating 16 the rotary assembly comprising the electric motor 17 at the second end of the apparatus. The frame is arranged to be installed on a horizontal plane surface, such as on a floor, so that the apparatus would be at the operating position. At the first end of the apparatus there is a distribution valve 19 connected with tubes to a filtrate/vacuum tank 24 and to an acid tank 26 equipped with a pump. The filtrate/vacuum tank 24 acts as means for providing negative pressure to interior of each filter element 14. In the example of Figure 1 two discharge tubes are connected from the filtrate/vacuum tank 24 to the distribution valve, wherein first tube providing a first level of vacuum is connected to a filter cake formation step and second tube providing a second level of vacuum is connected to a filter cake drying step via the distribution valve The acid tank 26 equipped with the pump acts as means for providing liquid to interior of each filter element 14.

The system comprises a control cabinet comprising electronic controlling means 22 and an ultrasonic power source 21 . The related wiring is not shown.

Figure 2 shows an example of a closer view of the core unit of a rotary vacuum disc filter apparatus. The connected devices, tanks and relating connections are not shown. Figure 2A shows the apparatus from a first end, and Figure 2C shows the apparatus from a second end. Figure 2B shows the apparatus from a side, and Figure 2D shows the apparatus from above, when the apparatus is at a position of use, i.e. installed on a surface such as a floor.

At the second end of the apparatus there is means for rotating 16 the rotary assembly comprising an electric motor 17 for rotating the rotary assembly. The electric motor 17 is connected to the rotary assembly of plurality of coaxial filter discs 12, which rotary assembly contains ten fixed filter discs 12 is this example. The filter discs are installed coaxially in an axis, which is bearing-mounted to a frame of the apparatus so that the axis can be rotated by operating the means for rotating 16 the rotary assembly. The filter discs 12 comprise a plurality of sectorshaped filter elements 14 with a gap between the elements.

The rotary assembly 10 is installed above a vat 18 for receiving the suspensions and liquids in such way that the axis is above the level of the suspension or liquid in the vat, but in such way that the separate filter elements 14 of a filter disc 12 can be immersed to the suspension or liquid during the use.

At the end of the axis or the central shaft, i.e. at the first end of the apparatus (Figure 2A) a distribution valve 19 can be seen comprising three inlets for tubes for providing functions discussed herein. The apertures are in liquid or gas communication with the interiors of the filter elements 14.

Figure 3 shows an example of a sector-shaped filter element comprising a filter surface 30, a tube 32 connected to the interior of the filter element and connectable to a distribution valve with a tube, and mounting means 34 for attaching the filter element 14 to a filter disc 12. This example corresponds to a ceramic filter element.

RECTIFIED SHEET (RULE 91) Figure 4A shows a view of a corresponding vacuum disc filter apparatus with a marked plane X-X corresponding to a plane of a filter disc 12 in the middle of the filter assembly, which filter disc 12 is shown in Figure 4B. The separate filter elements 14 substantially forming an annular disc can be seen from Figure 4B.

Means for providing ultrasound 20 comprising an ultrasound emitter is arranged in such position that would be below the level of liquid, when the vat is filled with liquid during the washing cycle, and which ultrasound emitter is arranged to provide ultrasound to a filter element 14 currently rotated to the location of the ultrasound emitter. When the filter disc 12 is rotated, each filter element 14 will be in turn at the effective area of the ultrasound provided by the ultrasound emitter to remove the remains of the filter cake from the surfaces of the filter elements with the effect of the ultrasound. Only part of the filter elements 14 are numbered in the figures. Means 13 for discharging filter cake from the surfaces of the filter element comprise scrapers shown in figure 4B connected to chutes for conveying the discharged filer cake away from the apparatus.

Figure 5 shows the operation of a conventional filtration with the system disclosed in Figure 2. The filter assembly is rotated counterclockwise. During filtration the distribution valve in the axis of the filter assembly provides either vacuum to the filter elements (A, B) or washing liquid to the filter elements to obtain back-wash (D), which are shown with arrows in Figure 5A. Figure 5B shows the filtration cycle during rotation of the filter assembly. The vat is filled with the suspension containing particulate material, which is to be filtered with the apparatus. When the filter disc 12 is rotated, each filter element 14 will be submerged into the suspension in turn. During this step, which is shown as sector A in Figure 5B, vacuum A is provided by the distribution valve, as shown in Figure 5A, to the interior of the immersed filter element 14 so that liquid is sucked into the filter element and conveyed away via a tube, and the cake forms on the surface of the filter element. The step A may be called cake forming step. In the next step, which can be called cake drying step, which is shown as sector B, the filter element is rotated away from the suspension and the cake is dried in the air by providing vacuum B via the distribution valve, as shown in Figure 5A. When the cake is dried on the surface of the filter element, it is removed by scrapers 13 in a cake removal step C. The removed dried filter cake is conveyed away from the apparatus and recovered. The removal of filter cake is carried out before the filter element will be again rotated to submerge to the remaining suspension. Immediately after the cake removal a back-wash step D is carried out by injecting back-washing liquid via the distribution valve to the interior of the filter element and through the filter element 14. The back-washing liquid may be aqueous liquid, such as the filtrate. The back-wash step D is repeated is each filtering cycle, as defined by the structure of the distribution valve. After the filtering it is necessary to purify the filters more efficiently to remove the remains of the filter cake and possible other contaminants. This is conventionally carried out in an acid wash.

Figure 6 shows the operation of a conventional acid wash with the system disclosed in Figure 5. The filter assembly is rotated counterclockwise, which is the same rotating direction that was used during the filtering. The filter elements 14 are subjected to acid wash E by injecting acid solution via the distribution valve in the axis as shown in Figure 6A towards the filter elements 14. The acid is provided to interior of a filter element 14 at a point wherein the filter element is rotated to a location which is just above the level of liquid in the vat (sector E in Figure 6B). Immediately after this the same filter element will be rotated to a location of the source of ultrasound, i.e. to a range of the ultrasound emitter 20, and at the same time the filter element is immersed in the liquid. The acid is provided in step E to release the impurities in the filter, and the immediate subsequent ultrasound wash step F is provided to treat the filter element previously treated with acid. The combination of these actions has been conventionally considered providing enough washing action for most cases. However it can be seen from Figure 6B that the dead time in liquid (sector G) is relatively long and will very quickly wash the acid away from the filter elements. The dead time in liquid, as well as subsequent dead time in air (sector H), are phases wherein very little or substantially no purification of filter element takes place. Therefore such acid wash may have to be repeated and carried out for a relatively long time, such as 60 minutes.

Figure 7 shows the operation of the present washing process with the system disclosed in Figure 4. The rotation direction of the filter assembly is reversed after the filtering process of Figure 5 and the filter assembly is rotated clockwise. This could be achieved by updating the software of the control unit of a Roxia (Flowrox) filter apparatus. The vat is emptied, and acid wash I is initiated by providing aqueous acid solution through the distribution valve into the interior of each filter element in turn via the backwash aperture in the distribution valve. The acid is provided to interior of a filter element 14 at a point wherein the filter element is rotated to a location (sector I in Figure 7B), which is immediately after the location of the ultrasound emitter 20. The filter assembly is rotated in the air, i.e. the filter

RECTIFIED SHEET (RULE 91) elements are not immersed in liquid of any kind but the acid injected in step I can effect each filter element during the rotating for a long acid reaction time in air indicated with sector K. The step can be carried out for a desired period of time or number of revolutions, such as one or more revolutions. If more cleaning effect is desired, a second step can be carried out subsequently as shown in Figure 8.

In the next step the vat is filled with liquid, which may be water or other aqueous liquid. This can be controlled by the control unit by opening a valve controlling water supply to the vat. Acid wash L is continued by providing acid through the distribution valve (Figure 8A), which may be the same acid as in step I or different. As the acid is injected to each filter elements at a point where the filter element is not immersed in the liquid in the vat (sector L), as shown in Figure 8B, and the filter assembly is rotated clockwise, the acid continues to have effect in the air (acid reaction time in air M) and is not washed away by the liquid contained in the vat. After this the acid will be immersed in liquid, which results in dead time in liquid (sector N), before the filter element proceeds to a location of the ultrasound emitter, wherein the ultrasound wash (sector O) is carried out while the filter element is submerged in the liquid. After this the filter element is rotated again to the acid wash step L, wherein mor acid is provided, and the contaminants released by the ultrasound can be further released with the effect of the acid during the long acid reaction time in air M. This process can be carried out for a desired period of time or number of revolutions, and/or until a desired washing result is obtained.

It was found out that especially the two-step washing process shown in Figures 7 and 8 resulted in very good washing efficiency and shortened washing time. Less acid was used, and it was possible to recover the acid used in the first step as undiluted.

Figure 9 shows a view of a control panel of the vacuum disc filter apparatus used in the tests. The display shows the filter assembly arranged in a vat. A slurry feed is arranged via valve V01 to the vat. A source of water is arranged via valve V03 to the vat and via valve V13 to the discharge line from the bottom of the vat. Washing acid is provided with a pump M08 to line leading to distribution valve, which line is also used to feed pure water to the distribution valve via valve V79. Sources of vacuum are connected to the distribution valve of the filter assembly via valves V02 (cake forming) and V12 (cake drying) connected to a source of vacuum M04. A discharge outlet is arranged in the bottom of the vat controllable primarily by valve V07. It can be seen from the view that measurements from the system can be monitored, and the measured values are utilized by the automated system to control the operation of the system.