BACKGROUND OF THE INVENTION :

Field of the Invention :

The present application generally relates to sludge processing . In particular, the present application relates to automatic control of a belt filter press that is used in sludge processing .

Description of the Related Art :

In pulp and paper industry, sludge processing or more specifically sludge dewatering, is utili zed to handle pulp and paper mill sludge , such as primary, biological and chemical sludges .

Obj ectives for the dewatering of sludge include reducing the volume of sludge to reduce transport and storage costs , reducing fuel requirements before further drying or incineration, and optimi zing other drying processes in order to increase dry solids content in the sludge .

A form of compression filter called belt filter press ( or belt press filter) is typically used as a part of a sludge dewatering line in the pulp and paper industry . The process of filtration is primarily obtained by passing a pair of filtering or filter cloths through a system of rollers or rolls . The belt filter press takes the sludge as a feed, and separates it into a filtrate and a solid cake .

The efficiency of a belt filter press is often assessed based on dry solids content of the cake and solids recovery, as well as a quality of the dry solids . Solids recovery refers to a percentage of dry solids recovered from the feed sludge . Dry solids content refers to a measure of the degree of dewatering . Traditionally, a belt filter press is operated manually by one or more human operators . Thus , the ef ficiency of the belt filter press is highly dependent on the skill level of these human operators .

SUMMARY OF THE INVENTION :

This summary is provided to introduce a selection of concepts in a s implif ied form that are further described below in the detailed description . This summary is not intended to identify key features or essential features of the claimed subj ect matter, nor is it intended to be used to limit the scope of the claimed subj ect matter .

It is an obj ect of the present disclosure to allow automatic control of a belt f ilter pres s that is used in sludge processing . The foregoing and other obj ects are achieved by the features of the independent claims . Further implementation forms are apparent from the dependent claims , the description and the figures .

According to a first aspect of the disclosure , a control apparatus for automatically controlling a belt filter press is provided . The belt f ilter pres s is for use in sludge processing, and the belt filter press has a lower filter cloth, an upper filter cloth, and a first pair of nip rolls . The control apparatus comprises at least one processor, and at least one memory including computer program code . The at least one memory and the computer program code are configured to , with the at least one processor, cause the control apparatus to at least receive a first monitoring signal from a first optoelectronic measurement device . The first monitoring signal indicates a level of packing of the upper filter cloth in front of the first pair of nip rolls in a rotation direction of the upper filter cloth . The at least one memory and the computer program code are further configured to , with the at least one processor, cause the control apparatus to at least determine whether the indicated level of packing is below a first packing threshold or exceeds a second packing threshold . In response to the indicated level of packing being below the first packing threshold or exceeding the second packing threshold, the at least one memory and the computer program code are further configured to , with the at least one processor, cause the control apparatus to cause a f irst control signal to be sent to the belt filter press , the first control signal instructing the belt filter press to increase or decrease a nip pressure of the first pair of nip rolls , respectively .

In an implementation form of the first aspect , the belt fi lter pres s further has a second pair of nip roll s located after the f irst pair of nip rol ls in the rotation direction of the lower filter cloth, and the at least one memory and the computer program code are further configured to, with the at least one processor, cause the control apparatus to receive a second monitoring signal from a second optoelectronic measurement device . The second monitoring signal indicates a level of adhesion of sludge to the upper filter cloth after the second pair of nip rol ls in the rotation direction of the upper f ilter cloth . The at least one memory and the computer program code are further configured to , with the at least one processor, cause the control apparatus to determine whether the indicated level of adhesion exceeds an adhesion threshold . In response to the indicated level of adhesion exceeding the adhesion threshold, the at least one memory and the computer program code are further configured to , with the at least one processor, cause the control apparatus to cause a second control signal to be sent to the belt filter press , the second control signal instructing the belt filter press to perform a first nip pressure adj ustment by decreasing at least one of the nip pressure of the first pair of nip rolls or a nip pressure of the second pair of nip rolls . In an implementation form of the first aspect , the belt fi lter pres s further has a second pair of nip rolls located after the first pair of nip rol ls in the rotation direction of the lower filter cloth, and the at least one memory and the computer program code are further configured to , with the at least one processor, cause the control apparatus to receive a third monitoring signal from a filtrate quality measurement device , the third monitoring signal indicating a level of quality of filtrate output by the belt filter press . The at least one memory and the computer program code are further configured to , with the at least one processor, cause the control apparatus to determine whether the indicated level of quality of filtrate is below a fi ltrate quality threshold . In response to the indicated level of quality of filtrate being below the filtrate quality threshold, the at least one memory and the computer program code are further configured to , with the at least one processor, cause the control apparatus to cause a third control signal to be sent to the belt filter press , the third control signal instructing the belt filter press to perform a second nip pressure adj ustment by decreasing at least one of the nip pressure of the first pair of nip rol ls or the nip pressure of the second pair of nip rolls .

In an implementation form of the first aspect , the at least one memory and the computer program code are further configured to , with the at least one processor, cause the control apparatus to instruct the belt filter press to keep the nip pressure of the second pair of nip roll s higher than the nip pressure of the first pair of nip rolls .

In an implementation form of the first aspect , the control apparatus is comprised in a distributed control system . In an implementation form of the first aspect , the control apparatus is implemented with one or more programmable logic controllers .

According to a second aspect of the disclosure , a method of automatically control ling a belt filter press is provided . The belt f ilter pres s is for use in sludge processing, and the belt filter press has a lower filter cloth, an upper filter cloth, and a first pair of nip rolls . The method comprises receiving, at a processor, a first monitoring signal from a first optoelectronic measurement device . The first monitoring signal indicates a level of packing of the upper filter cloth in front of the first pair of nip rolls in a rotation direction of the upper filter cloth . The method further comprises determining, by the processor, whether the indicated level of packing is below a first packing threshold or exceeds a second packing threshold . In response to the indicated level of packing being below the first packing threshold or exceeding the second packing threshold, the method further comprises causing, by the processor, a first control signal to be sent to the belt filter press , the first control signal instructing the belt filter press to increase or decrease a nip pressure of the first pair of nip rolls , respectively .

In an implementation form of the second aspect , the belt fi lter pres s further has a second pair of nip rolls located after the first pair of nip rol ls in the rotation direction of the lower filter cloth, and the method further comprises receiving, at the processor, a second monitoring signal from a second optoelectronic measurement device . The second monitoring signal indicates a level of adhesion of sludge to the upper filter cloth after the second pair of nip rolls in the rotation direction of the upper filter cloth . The method further comprises determining, by the processor, whether the indicated level of adhesion exceeds an adhesion threshold . In response to the indicated level of adhesion exceeding the adhesion threshold, the method further comprises causing, by the processor, a second control signal to be sent to the belt fi lter press , the second control signal instructing the belt filter press to perform a first nip pressure adj ustment by decreasing at least one of the nip pressure of the first pair of nip rolls or a nip pressure of the second pair of nip rolls .

In an implementation form of the second aspect , the belt fi lter pres s further has a second pair of nip rolls located after the first pair of nip rol ls in the rotation direction of the lower filter cloth, and the method further comprises receiving, at the processor, a third monitoring signal from a filtrate quality measurement device . The third monitoring signal indicates a level of quality of filtrate output by the belt filter press . The method further comprises determining, by the processor, whether the indicated level of quality of filtrate is below a filtrate quality threshold . In response to the indicated level of quality of filtrate being below the filtrate quality threshold, the method further comprises causing, by the processor, a third control signal to be sent to the belt filter press , the third control signal instructing the belt filter press to perform a second nip pressure adj ustment by decreasing at least one of the nip pres sure of the f irst pair of nip roll s or the nip pressure of the second pair of nip rolls .

In an implementation form of the second aspect , the method further comprises instructing, by the proces sor , the belt f ilter press to keep the nip pressure of the second pair of nip rolls higher than the nip pressure of the first pair of nip rolls .

According to a third aspect of the disclosure , a computer program product is provided . The computer program product comprises program code that is configured to perform the method according to the second aspect , when the program code is executed on a computer . According to a fourth aspect of the disclosure , a system for automatically controlling a belt filter press is provided . The system comprises the belt filter press for use in sludge processing . The belt filter press has a lower filter cloth, an upper filter cloth, a first pair of nip rolls , and a second pair of nip rolls located after the first pair of nip rolls in a rotation direction of the lower filter cloth . The system further comprises a first optoelectronic measurement device arranged in front of the first pair of nip rolls in the rotation direction of the lower filter cloth . The system further comprises a second optoelectronic measurement device arranged after the second pair of nip rolls in a rotation direction of the upper filter cloth . The system further comprises a filtrate quality measurement device arranged at or after a filtrate output of the belt fi lter pres s . The system further comprises the control apparatus according to the first aspect .

In an implementation form of the fourth aspect , the first optoelectronic measurement device comprises one of : a light curtain sensor, an imaging sensor, or a vision sensor .

In an implementation form of the fourth aspect , the second optoelectronic measurement device comprises one of : at least one infrared light transmitter-receiver pair, an infrared light -based imaging sensor, or a visible light -based imaging sensor .

At least some of the embodiments allow automatic control of a belt filter press that is used in sludge processing . More specifically, at least some of the embodiments allow automatic control of nip pressure ( s ) of such a belt filter press . Such automatic control in turn allows easier operation of the belt filter press since less experience is required from the operator ( s ) . Furthermore , such automatic control allows more stable operation of the belt filter press . Furthermore , such automatic control allows better sludge dry content and thus better fuel value , even when the ratio of incoming sludge varies during the dewatering process . Furthermore , such automatic control allows better filtrate quality . Furthermore , such automatic control allows lower chemical costs .

BRIEF DESCRIPTION OF THE DRAWINGS :

The accompanying drawings , which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention . In the drawings :

Fig . 1A illustrates an overview of an example sludge processing line , where various embodiments of the present disclosure may be implemented;

Fig . IB illustrates an overview of an example belt filter press , where various embodiments of the present disclosure may be implemented;

Fig . 1C illustrates examples of filter cloth packing in a belt filter press ;

Fig . 2 is a block diagram i llustrating a control apparatus for automatically controlling a belt filter press for use in sludge processing, according to an embodiment of the present disclosure ;

Fig . 3 is a diagram illustrating a system for automatically controlling a belt filter press for use in sludge processing, according to an embodiment of the present disclosure ; and

Fig . 4 is a flow diagram illustrating a method of automatically controlling a belt filter press for use in sludge processing, according to an embodiment of the present disclosure .

Like reference numerals are used to designate like parts in the accompanying drawings . DETAILED DESCRIPTION OF THE INVENTION :

In the following description, reference is made to the accompanying drawings , which form part of the disclosure and show, by way of illustration, specific aspects of the present disclosure . It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure . The following detailed description, therefore , is not to be taken in a limiting sense , as the scope of the present disclosure is defined in the appended claims .

For instance , it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa . For example , if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or il lustrated in the f igures . On the other hand, for example , if a specific apparatus or device is described based on functional units , a corresponding method may include a step performing the described functionality, even if such step is not explicitly described or illustrated in the figures . Further, it is understood that the features of the various example aspects described herein may be combined with each other, unles s specifically noted otherwise .

Fig . 1A illustrates an overview of an example sludge dewatering line 100 , where various embodiments of the present disclosure may be implemented .

The sludge dewatering line 100 comprises a predewatering unit or drum 110 and a belt filter press 120 . The pre-dewatering unit 110 may comprise a flocculator Herein, the terms "sludge processing" and "sludge dewatering" refer specifically sludge processing and sludge dewatering utilized in pulp and paper industry .

A pulp/paper mill produces various sludges , such as primary sludge , biological sludge and chemical sludge . Mixed sludge is a blend of the primary, chemical and biological sludges . The term ratio of sludge refers to the ratio of primary sludge to biological sludge in the mixed sludge . The sludge dewatering line 100 is used to separate solids and liquids from the mixed sludge . The mixed sludge discharged from the pulp/paper mill typically first enters the pre-dewatering unit 110 which may comprise e . g . a flat or inclined belt where gravity -based drainage of free water occurs . Typically, the sludge is conditioned with a suitable polymer before the actual dewatering . The flocculator 115 is used to agglomerate particles in the conditioned sludge into aggregates called flocs , via mixing the sludge with a suitable flocculant . The formation of flocs induces release of water from the sludge . Thus , this water can be easily eliminated during the dewatering .

The pre-dewatering unit 110 produces thickened sludge which then enters the belt filter press 120 . The belt filter press 120 takes the thickened sludge as a feed, and separates it into a filtrate ( liquid, primarily water) and a sol id cake , by way of fi ltration . The process of filtration is primarily obtained by passing thickened sludge between a pair of filter cloths through a system of rolls . The produced solid cake is typically incinerated later .

Fig . IB illustrates a simplified overview of an example belt fi lter press 120 , where various embodiments of the present disclosure may be implemented . The belt filter press 120 comprises a headbox 121 , a wedge zone 122 , pre-press rolls 123 , S-rolls 124A and 124B, and optionally one or two pairs of nip rolls . In the example of Fig . IB, nip rolls 125A1 and 125A2 form a first pair of nip rolls , and nip rolls 125B1 and 125B2 form a second pair of nip rolls .

The thickened sludge produced by the pre-de- watering unit 110 enters the headbox 121 . From the headbox 121 , the sludge is passed between a lower filter cloth and an upper filter cloth which are first arranged in a wedge like formation forming the wedge zone 122 . As the sludge moves on, the wedge zone 122 tapers or narrows down in the vertical direction, thus applying increasing pressure on the sludge .

After the wedge zone 122 , the lower filter cloth and the upper filter cloth ( and the sludge between them) is passed through a system of rolls such that each subsequent rol l element of the system of roll s appl ies higher pressure than a previous roll element . One reason for this is that the further along the belt filter press 120 the sludge proceeds , the drier the sludge gets , thus necess itating the use of higher and higher pres sure to extract the still remaining water . Accordingly, in the example of Fig . IB, the pre-press rolls 123 apply the lowest pressure and the second pair of nip rolls (nip rolls 125B1 and 125B2 ) applies the highest pressure .

The filtered water is pressed through the lower and upper filter cloths , collected in a suitable container or tank, and then e . g . passed on outside the sludge dewatering line 100 for further processing .

As can be seen from Fig . IB, a pair of nip rolls is characteri zed in that the two powered nip rol ls forming the pair are arranged opposite each other such that they squeeze the material passing between them . The contact point or near-contact point between the nip rolls is called a nip point and is the point at which the pressure ( i . e . nip pressure ) created by the nip rolls is at its ' highest . To increase the nip pressure the nip rolls of the pair are moved closer together, and to decrease the nip pressure the nip rolls of the pair are moved farther apart .

The end product after the last roll element ( the nip rolls 125B1 and 125B2 forming the second pair of nip rolls in the example of Fig . IB) of the system of rolls is solid cake . The produced solid cake is usually incinerated later . Thus , an obj ective of the belt filter press 120 is to produce as dry solid cake as possible , since the drier the solid cake is , the better its ' heat of combustion value is .

However, producing as dry solid cake as possible i s not as simple as j ust applying a maximum amount of pressure to the sludge at the belt filter press 120 . For example , if too much pressure is applied to the sludge at any point at the belt filter press 120 , the sludge will start to protrude from the sides of the fi lter cloths or forced through the filter cloths , and thus ends up in the same container or tank in which the filtered water is collected, thereby reducing filtrate quality of the filtered water . Reduced filtrate quality in turn causes an unneces sary burden on a later water treatment plant .

Typically, an obj ective for operating a belt filter press is to rotate the filter cloths as slowly as possible in order to al low as long a detention time for the sludge in the belt filter press as possible . Traditionally, the various operating parameters ( the amount of polymer acting as a flocculant , rotation speeds of the filter cloths , applied pressure level ( s ) , and the like ) of a sludge dewatering line are controlled and adj usted by human operators who must continually monitor the operation of the belt filter press in order to maintain an optimal performance level .

Fig . 1C illustrates examples of filter cloth packing in a belt filter press . The filter cloth packing is a phenomenon typical for belt filter presses that utili ze one or more nip roll pairs . The filter cloth packing occurs in front of the first nip roll pair of the one or more nip roll pairs in the rotation direction of the lower filter cloth . As can be seen from Fig . 1C, the filter cloth packing involves the upper filter cloth packing or bulging upwards ( i . e . away from the upper level of the s ludge between the lower and upper filter cloths . The filter cloth packing is caused by the sludge packing or bulging between the lower and upper filter cloths j ust before the filter cloths and the sludge between them proceed between the first nip roll pair of the one or more nip roll pairs , due to an increasing amount of applied pressure .

In the example of diagram 150A, the level of packing of the upper filter cloth in front of the first nip roll pair is too low, indicating that the nip pressure of the first nip roll pair is too low . The nip pressure of the first nip roll pair being too low results in the dry solids content of the solid cake being too low . Thus , the nip pres sure of the f irst nip rol l pair being too low is undesirable .

In the example of diagram 150C, the level of packing of the upper filter cloth in front of the first nip roll pair is too high, indicating that the nip pressure of the first nip roll pair is too high . The nip pressure of the f irst nip rol l pair being too high can result in the sludge starting to protrude from the sides of the filter cloths , thus ending up in the same container or tank in which the filtered water is collected, and thereby reducing filtrate quality of the filtered water . Furthermore , the nip pressure of the first nip roll pair being too high can result in clogging of the filter cloth ( s ) , and/or mechanical damage to the filter cloth ( s ) . Thus , the nip pressure of the first nip roll pair being too high is also undesirable .

It is to be noted that the sludge may start to protrude from the sides of the filter cloths even in some situations in which the nip pressure of the first nip roll pair is not too high ( or in extreme cases even without any nip pressure of the f irst nip roll pair at all ) . For example , this may happen if the ratio of sludge is too low which means that there is not enough fiber in the mixed s ludge which in turn results in the mixed sludge being too runny so that it may start to run over the sides of the filter cloths even without nip pressure applied, particularly if the rotation speed of the filter cloths is high or a feed flow of the sludge is too high . This and other issues are addressed in the disclosed embodiments e . g . via use of several different measurement devices at different points .

In the example of diagram 150B, the level of packing of the upper filter cloth in front of the first nip roll pair is correct , i . e . not too low and not too high, facilitating optimal operation belt filter press . Traditionally, filter cloth packing has been monitored by experienced human operators (via e . g . visual inspection) .

Fig . 3 is a diagram illustrating a system 300 for automatically controlling a belt filter press 310 for use in sludge processing, according to an embodiment of the present disclosure .

The system 300 comprises the belt filter press 310 . The belt filter press 310 is for use in sludge processing in pulp and paper industry . The belt filter press 310 comprises a lower filter cloth 301 , an upper filter cloth 302 , and at least a first pair 303 of nip rolls . The lower filter cloth 301 forms a first loop rotating in a rotation direction 361 , and the upper fi lter cloth 302 forms a second loop rotating in a rotation direction 362 .

As shown in the example embodiment of Fig . 3 , the belt filter press 310 may further comprise a second pair 304 of nip rolls . The second pair 304 of nip rolls is located after the first pair 303 of nip rolls in a rotation direction 361 of the lower filter cloth 301 . In an embodiment , the nip pres sures of the first pair 303 of nip rolls and the second pair 304 of nip rolls may each vary from zero to four bar .

The rotation directions 361 , 362 of the lower and upper filter cloths 301 , 302 are from a sludge input 305 towards an output 306 for discharging the dried sludge . In other words , in the example embodiment of Fig . 3 , the rotation direction 361 of the lower fi lter cloth 301 is anticlockwise or counterclockwise , and the rotation direction 362 of the upper filter cloth 302 is clockwise .

The system 300 further comprises a first optoelectronic measurement device 351 . The first optoelectronic measurement device 351 is configured to measure or detect the level of packing of the upper filter cloth 302 . In other words , the first optoelectronic measurement device 351 is used to facilitate determining whether the nip pressure of the first pair 303 of nip rolls is correct . The first optoelectronic measurement device 351 is arranged in front of the first pair 303 of nip rolls in the rotation direction 361 of the lower filter cloth 301 in such a location and position and/or orientation that the level of potential packing of the upper filter cloth 302 in front of the first pair 303 of nip rolls in the rotation direction 361 of the upper fi lter cloth 302 is measurably in the f ield of view of the first optoelectronic measurement device 351 .

The first optoelectronic measurement device 351 may comprise e . g . a light curtain sensor, an imaging sensor, or a vision sensor . The light curtain sensor may comprise e . g . a transmitter and a receiver arranged at opposite sides of the fi lter cloths 301 , 302 in a hori zontal direction . The transmitter may proj ect an array of parallel infrared light beams to the receiver which may comprise a number of photoelectric cells . When packing of the upper filter cloth 302 (and thus the packing of the s ludge ) breaks one or more of the beams , a corresponding first monitoring signal may be sent to a control apparatus 200 . The imaging sensor may be located e . g . to one side of the packing region and used to produce a digital image ( or a sequence of digital images ) that may be analyzed by suitable software in order to measure or detect the level of packing of the upper fi lter cloth 302 ( and thus the packing of the s ludge ) . The vision sensor is a device that comprises a digital camera, a light source and a controller in a single unit . The digital image thus produced may be at least partly analyzed by the included control ler in order to measure or detect the level of packing of the upper filter cloth 302 ( and thus the packing of the sludge ) .

The system 300 may further comprise an optional second optoelectronic measurement device 352 . The second optoelectronic measurement device 352 may be configured to measure or detect a level of adhesion of sludge to the upper filter cloth 302 after the second pair 304 of nip rolls in the rotation direction of the upper filter cloth 302 . In other words , the second optoelectronic measurement device 352 may be used to facilitate determining whether the nip pressure of the second pair 304 of nip rolls is correct in relation to the nip pressure of the first pair 303 of nip rolls . I f the level of adhesion of sludge to the upper filter cloth 302 is too high, it indicates that the nip pres sure of the second pair 304 of nip rolls is too high in relation to the nip pressure of the first pair 303 of nip rolls . The second optoelectronic measurement device 352 may be arranged after the second pair of nip roll s in the rotation di rection of the upper filter cloth 302 in such a location and position and/or orientation that the level of potential adhesion of sludge to the upper filter cloth 302 after the second pair 304 of nip rolls in the rotation direction of the upper filter cloth 302 is measurably in the field of view of the second optoelectronic measurement device 352 . Since the second optoelectronic measurement device 352 measures or detects the level of adhesion of sludge to the upper fi lter cloth 302 after the second pair 304 of nip rolls , it is effectively measuring how a scraper (not shown in Fig . 3 ) or the like is removing sludge from the upper filter cloth 302 . In other words , the second optoelectronic measurement device 352 is measuring the purity of the upper fi lter cloth 302 .

The second optoelectronic measurement device 352 may comprise e . g . at least one infrared light transmitter-receiver pair, an infrared light -based imaging sensor, or a visible light -based imaging sensor . The one or more infrared light transmitter-receiver pairs may be arranged e . g . at opposite sides of the upper filter cloth 302 in a vertical direction . In other words , an infrared light transmitter located e . g . above the upper filter cloth 302 may emit an infrared light beam towards the upper filter cloth 302 , the emitted infrared light beam traversing through the upper filter cloth 302 and received by the infrared light receiver located below the upper filter cloth 302 , or vice versa . Based on a measured/detected transmittance of the infrared light through the upper filter cloth 302 and the sludge potentially stuck to the upper filter cloth 302 , the level of adhesion of sludge to the upper filter cloth 302 can be determined .

The infrared light -based imaging sensor or the visible light -based imaging sensor may be located e . g . above the upper filter cloth 302 ( i . e . on the side of the upper filter cloth 302 to which the sludge may potentially be stuck) and used to produce a digital image ( or a sequence of digital images ) that may be analyzed by suitable software in order to measure or detect the level of adhesion of sludge to the upper filter cloth 302 after the second pair 304 of nip rolls . For example , the produced digital image may be analyzed to determine which pixels represent sludge adhered to the upper filter cloth 302 , and then the number or percentage of such pixels may be calculated to determine the level of adhesion of sludge to the upper filter cloth 302 . In an example, no more than 20 % of the pixels of the produced digital image representing sludge adhered to the upper filter cloth 302 is interpreted as the upper filter cloth 302 being clean, 20 %-40 % of the pixels of the produced digital image representing sludge adhered to the upper filter cloth 302 is interpreted as the upper filter cloth 302 being in good condition, 40 %- 60 % of the pixels of the produced digital image representing sludge adhered to the upper filter cloth 302 is interpreted as the upper filter cloth 302 being slightly dirty, 60 %- 80 % of the pixels of the produced digital image representing sludge adhered to the upper filter cloth 302 is interpreted as the upper filter cloth 302 dirty, and 80 %- 100 % of the pixels of the produced digital image representing sludge adhered to the upper filter cloth 302 is interpreted as the upper fi lter cloth 302 being very dirty .

The system 300 may further comprise an optional filtrate quality measurement device 353 . The filtrate quality measurement device 353 may be arranged at or after a filtrate output 307 of the belt filter press 310 . The filtrate quality measurement device 353 may be configured to measure or detect a level of quality of fi ltrate output by the belt f ilter pres s 310 . In other words , the filtrate quality measurement device 353 may be used to facilitate determining whether the nip pressure of the second pair 304 of nip roll s i s correct in relation to the nip pressure of the first pair 303 of nip rolls . I f the level of quality of filtrate is too low, it indicates that the nip pressure of the second pair 304 of nip rolls is too high in relation to the nip pressure of the first pair 303 of nip rolls , causing the sludge to protrude from the sides of the filter cloths , thus ending up in the same container or tank in which the filtered water is collected, and thereby reducing filtrate quality of the filtered water .

The filtrate quality may comprise e . g . turbidity of the filtrate . The turbidity may be expres sed as a percentage .

The filtrate quality measurement device 353 may comprise e . g . an optical measurement device , such as a turbidity sensor suitable for stationary measurement of the turbidity or of the suspended solids concentration ( total suspended solids ) in water/wastewater applications . For example , such a turbidity sensor may comprise a nephelometer .

As discussed in connection with Fig . 1C, there may be situations in which the sludge may start to protrude from the sides of the filter cloths even when the nip pressure of the first nip roll pair is not too high ( or in extreme cases even without any nip pressure of the first nip roll pair at all ) . For example , thi s may happen if the ratio of sludge is too low which means that there is not enough fiber (which acts as an adhesive medium or binding agent in the sludge ) in the mixed sludge which in turn results in the mixed sludge being too runny so that it may start to run over the sides of the filter cloths even without nip pressure applied, particularly if the rotation speed of the filter cloths is too high or the feed flow of the sludge is too high . Other reasons for the sludge being too runny include : the polymer that the sludge i s conditioned with in the pre-dewatering unit 110 is not suitable for the current mixed sludge or the dosage of the polymer is incorrect . Use of the filtrate quality measurement device 353 allows detecting these situations and reacting accordingly . The system 300 further comprises a control apparatus 200 for automatically controlling the belt filter press 310 for use in sludge processing . The control apparatus 200 is communicatively connected (via wired and/or wireless connection ( s ) ) to the belt filter press 310 .

Next , an example embodiment of the control apparatus 200 for automatically controlling the belt filter press 310 is described based on Fig . 2 . Some of the features of the described units are optional features which provide further advantages .

Fig . 2 is a block diagram illustrating the control apparatus 200 for automatically controlling the belt filter press 310 for use in sludge processing, according to an embodiment of the present disclosure .

The control apparatus 200 may be comprised in a distributed control system . Alternatively and/or additionally, the control apparatus 200 may be implemented with one or more programmable logic controllers .

The control apparatus control 200 comprises at least one processor or a processing unit 201 , and at least one memory 202 including computer program code 203 and coupled to the at least one processor 202 , which may be used to implement the functionalities described later in more detail .

The at least one processor 201 may include , e . g . , one or more of various processing devices , such as a co-processor, a microprocessor, a controller, a digital signal processor ( DSP) , a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as , for example , an application specific integrated circuit (AS IC) , a field programmable gate array (FPGA) , a microcontroller unit (MCU) , a hardware accelerator, a special-purpose computer chip, or the like .

The at least one memory 202 may be conf igured to store e . g . computer programs and the like . The at least one memory 202 may include one or more volatile memory devices , one or more non-volatile memory devices , and/or a combination of one or more volatile memory devices and non-volatile memory devices . For example , the at least one memory 202 may be embodied as magnetic storage devices ( such as hard disk drives , etc . ) , optical magnetic storage devices , and semiconductor memories ( such as mask ROM, PROM (programmable ROM) , EPROM (erasable PROM) , flash ROM, RAM ( random access memory) , etc . ) .

The at least one memory 202 and the computer program code 203 are configured to , with the at least one processor 201 , cause the control apparatus 200 to at least receive a first monitoring signal from the first optoelectronic measurement device 351 . The first monitoring signal indicates a level of packing of the upper filter cloth 302 in front of the first pair 303 of nip rolls in the rotation direction 361 of the upper filter cloth 302 .

The at least one memory 202 and the computer program code 203 are further configured to , with the at least one processor 201 , cause the control apparatus 200 to at least determine whether the indicated level of packing is below a first packing threshold or whether the indicated level of packing exceeds a second packing threshold . For example , the first packing threshold may be substantially one centimetre . For example , the second packing threshold may be in the range between four and seven centimetres , e . g . substantially five centimetres .

In response to the indicated level of packing being below the first packing threshold, the at least one memory 202 and the computer program code 203 are further configured to , with the at least one proces sor 201 , cause the control apparatus 200 to cause a first control signal to be sent to the belt filter press 310 , such that the first control signal instructs the belt filter press 310 to increase a nip pressure of the first pair 303 of nip rolls .

In response to the indicated level of packing exceeding the second packing threshold, the at least one memory 202 and the computer program code 203 are further configured to , with the at least one processor 201 , cause the control apparatus 200 to cause the first control signal to be sent to the belt filter press 310 , such that the first control signal instructs the belt filter press 310 to decrease the nip pressure of the first pair 303 of nip rolls .

The at least one memory 202 and the computer program code 203 may be further configured to , with the at least one processor 201 , cause the control apparatus 200 to receive a second monitoring signal from the second optoelectronic measurement device 352 . The second monitoring signal indicates a level of adhesion of sludge to the upper filter cloth 302 after the second pair 304 of nip rolls in the rotation direction 362 of the upper filter cloth 302 .

The at least one memory 202 and the computer program code 203 may be further configured to , with the at least one processor 201 , cause the control apparatus 200 to determine whether the indicated level of adhesion exceeds an adhesion threshold . In an embodiment , the adhesion threshold may comprise a percentage ( selectable e . g . between 20 . . . 70 % ) of the monitored/measured area of the upper filter cloth 302 that has been determined to be covered by adhered sludge .

In response to the indicated level of adhesion exceeding the adhesion threshold, the at least one memory 202 and the computer program code 203 may be further configured to , with the at least one proces sor 201 , cause the control apparatus 200 to cause a second control signal to be sent to the belt filter press 310 . The second control signal instructs the belt filter press 310 to perform a first nip pressure adj ustment by decreasing the nip pressure of the first pair 303 of nip rolls and/or a nip pressure of the second pair 304 of nip rolls.

The at least one memory 202 and the computer program code 203 may be further configured to, with the at least one processor 201, cause the control apparatus 200 to receive a third monitoring signal from the filtrate quality measurement device 353. The third monitoring signal indicates a level of quality of filtrate output by the belt filter press 310.

The at least one memory 202 and the computer program code 203 may be further configured to, with the at least one processor 201, cause the control apparatus 200 to determine whether the indicated level of quality of filtrate is below a filtrate quality threshold.

In response to the indicated level of quality of filtrate being below the filtrate quality threshold, the at least one memory 202 and the computer program code 203 may be further configured to, with the at least one processor 201, cause the control apparatus 200 to cause a third control signal to be sent to the belt filter press 310. The third control signal instructs the belt filter press 310 to perform a second nip pressure adjustment by decreasing the nip pressure of the first pair 303 of nip rolls and/or the nip pressure of the second pair 304 of nip rolls.

As discussed above, the filtrate quality may comprise e.g. turbidity (0...100%) of the filtrate. Accordingly, the filtrate quality threshold may comprise a selectable value (e.g. between 20...70%) of the turbidity percentage.

The at least one memory 202 and the computer program code 203 may be further configured to, with the at least one processor 201, cause the control apparatus 200 to instruct the belt filter press 310 to keep the nip pressure of the second pair 304 of nip rolls higher than the nip pressure of the first pair 303 of nip rolls. Fig . 4 is a flow diagram illustrating a method 400 of automatically controlling the belt filter press 310 for use in sludge process ing, according to an embodiment of the present disclosure .

At operation 401 , the belt filter press is instructed by a processor to keep a nip pressure of the second pair of nip rol ls higher than the nip pressure of the first pair of nip rolls .

At operation 402 , the first monitoring signal is received at the processor from the first optoelectronic measurement device . The first monitoring signal indicates the level of packing of the upper filter cloth in front of the first pair of nip rolls in the rotation direction of the upper filter cloth .

At operation 403 , the processor determines whether the indicated level of packing is below the first packing threshold . I f the indicated level of packing is below the first packing threshold, the method 400 proceeds to operation 405 . I f the indicated level of packing is not below the first packing threshold, the method 400 proceeds to operation 404 .

At operation 404 , the processor determines whether the indicated level of packing exceeds the second packing threshold . I f the indicated level of packing exceeds the second packing threshold, the method 400 proceeds to operation 406 . I f the indicated level of packing does not exceed the second packing threshold, the method 400 proceeds to operation 407 or operation 410 , depending on which of the second and third monitoring signals are in use and received next .

At operation 405 , the processor causes the first control signal to be sent to the belt filter press , such that the first control signal instructs the belt filter press to increase the nip pres sure of the first pair of nip rolls . Alternatively, at operation 406 , the processor causes the first control signal to be sent to the belt filter press , such that the first control signal instructs the belt filter press to decrease the nip pressure of the first pair of nip rolls .

At operation 407 , the second monitoring signal is received at the processor from the second optoelectronic measurement device . The second monitoring signal indicates a level of adhesion of sludge to the upper fi lter cloth after the second pair of nip rol ls in the rotation direction of the upper filter cloth .

At operation 408 , the processor determines whether the indicated level of adhesion exceeds an adhesion threshold . I f the indicated level of adhesion exceeds the adhesion threshold, the method proceeds to operation 409 . I f the indicated level of adhesion does not exceed the adhesion threshold, the method proceeds to operation 410 .

At operation 409 , the processor causes the second control signal to be sent to the belt filter press . The second control signal instructs the belt filter press to perform a first nip pressure adj ustment by decreasing the nip pressure of the first pair of nip rolls and/or the nip pressure of the second pair of nip rolls .

At operation 410 , the third monitoring signal is received at the processor from the f iltrate qual ity measurement device . The third monitoring signal indicates a level of quality of filtrate output by the belt filter press .

At operation 411 , the processor determines whether the indicated level of quality of filtrate is below a filtrate quality threshold . I f the indicated level of quality of filtrate is below the filtrate quality threshold, the method proceeds to operation 412 . I f the indicated level of quality of filtrate is not below the filtrate quality threshold, the method 400 may e . g . return back to operation 401 . Alternatively, the method 400 may e . g . return back to operation 402 (not shown in Fig. 4) if the indicated level of quality of filtrate is not below the filtrate quality threshold. Alternatively, the method 400 may exit (not shown in Fig. 4) if the indicated level of quality of filtrate is not below the filtrate quality threshold.

At operation 412, the processor causes the third control signal to be sent to the belt filter press. The third control signal instructs the belt filter press to perform a second nip pressure adjustment by decreasing the nip pressure of the first pair of nip rolls and/or the nip pressure of the second pair of nip rolls. After operation 412, the method 400 may e.g. return back to operation 401, or return back to operation 402 (not shown in Fig. 4) , or exit (not shown in Fig. 4) .

The method 400 may be performed by the control apparatus 200 for automatically controlling the belt filter press 310 for use in sludge processing. The operations 401-418 can, for example, be performed by the at least one processor 201, the memory 202 and the computer program code 203. Further features of the method 400 directly result from the functionalities and parameters of the control apparatus 200 and the system 300, and thus are not repeated here. The method 400 can be performed by a computer program.

The exemplary embodiments can include, for example, any suitable computer devices, such as distributed control systems, programmable logic controllers, servers, workstations, personal computers, laptop computers, other devices, and the like, capable of performing the processes of the exemplary embodiments. The devices and subsystems of the exemplary embodiments can communicate with each other using any suitable protocol and can be implemented using one or more programmed computer systems or devices.

One or more interface mechanisms can be used with the exemplary embodiments, including, for example, Internet access, telecommunications in any suitable form (e.g., voice, modem, and the like) , wireless communications media, and the like. For example, employed communications networks or links can include one or more satellite communications networks, wireless communications networks, cellular communications networks, 3G communications networks, 4G communications networks, 5G communications networks, Public Switched Telephone Network (PSTNs) , Packet Data Networks (PDNs) , the Internet, intranets, a combination thereof, and the like.

It is to be understood that the exemplary embodiments are for exemplary purposes, as many variations of the specific hardware used to implement the exemplary embodiments are possible, as will be appreciated by those skilled in the hardware and/or software art(s) . For example, the functionality of one or more of the components of the exemplary embodiments can be implemented via one or more hardware and/or software devices.

The exemplary embodiments can store information relating to various processes described herein. This information can be stored in one or more memories, such as a hard disk, optical disk, magneto-optical disk, RAM, and the like. One or more databases can store the information used to implement the exemplary embodiments of the present inventions. The databases can be organized using data structures (e.g., records, tables, arrays, fields, graphs, trees, lists, and the like) included in one or more memories or storage devices listed herein. The processes described with respect to the exemplary embodiments can include appropriate data structures for storing data collected and/or generated by the processes of the devices and subsystems of the exemplary embodiments in one or more databases.

All or a portion of the exemplary embodiments can be conveniently implemented using one or more general purpose processors, microprocessors, digital signal processors, micro-controllers, and the like, pro- grammed according to the teachings of the exemplary embodiments of the present inventions , as will be appreciated by those skilled in the computer and/or software art ( s ) . Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the exemplary embodiments , as wil l be appreciated by those skilled in the software art . In addition, the exemplary embodiments can be implemented by the preparation of application-specific integrated circuits or by interconnecting an appropriate network of conventional component circuits , as wil l be appreciated by those skilled in the electrical art ( s ) . Thus , the exemplary embodiments are not l imited to any speci fic combination of hardware and/or software .

Stored on any one or on a combination of computer readable media, the exemplary embodiments of the present inventions can include software for controlling the components of the exemplary embodiments , for driving the components of the exemplary embodiments , for enabling the components of the exemplary embodiments to interact with a human user, and the like . Such software can include , but is not limited to , device drivers , firmware , operating systems , development tools , applications software , and the like . Such computer readable media further can include the computer program product of an embodiment of the present inventions for performing all or a portion ( i f process ing is distributed) of the processing performed in implementing the inventions . Computer code devices of the exemplary embodiments of the present inventions can include any suitable interpretable or executable code mechanism, including but not limited to scripts , interpretable programs , dynamic link libraries ( DLLs ) , Java classes and applets , complete executable programs , Common Passenger Request Broker Architecture (CORBA) passengers , and the like . Moreover, parts of the processing of the exemplary embodiments of the present inventions can be distributed for better performance , reliability, cost , and the like .

As stated above , the components of the exemplary embodiments can include computer readable medium or memories for holding instructions programmed according to the teachings of the present inventions and for holding data structures , tables , records , and/or other data described herein . Computer readable medium can include any suitable medium that participates in providing instructions to a processor for execution . Such a medium can take many forms , including but not limited to , nonvolatile media, volatile media, and the like . Non-volatile media can include , for example , optical or magnetic disks , magneto-optical disks , and the like . Volatile media can include dynamic memories , and the like . Common forms of computer-readable media can include , for example , a floppy di sk, a flexible disk, hard di sk, or any other suitable medium from which a computer can read .

It is to be understood that aspects and embodiments of the present disclosure described above may be used in any combination with each other . Several of the aspects and embodiments may be combined together to form a further embodiment of the present disclosure .

While the present inventions have been described in connection with a number of exemplary embodiments , and implementations , the present inventions are not so limited, but rather cover various modifications , and equivalent arrangements , which fall within the purview of prospective claims .