• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention allows automatic control of a belt filter press (310) that is used in sludge processing. A first monitoring signal is received at a control apparatus (200) from a first optoelectronic measurement device (351). The first monitoring signal indicates a level of packing of an upper filter cloth (302) in front of a first pair (303) of nip rolls of the belt filter press (310). The control apparatus (200) determines 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 control apparatus (200) causes a first control signal to be sent to the belt filter press (310), the first control signal instructing the belt filter press (310) to increase or decrease a nip pressure of the first pair (303) of nip rolls, respectively.
    公开号:FI20205888A1
    申请号:FI20205888
    申请日:2020-09-15
    公开日:2021-10-29
    发明作者:Sami Pakarinen；Matti Kumpulainen
    申请人:Aquaflow Oy；
    IPC主号:
    专利说明:

    AUTOMATIC CONTROL OF A BELT FILTER PRESS FOR USE IN
    SLUDGE PROCESSING BACKGROUND OF THE INVENTION: Field of the Invention: The present application generally relates to sludge processing. In particular, the present applica- tion 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 utilized to handle pulp and paper mill sludge, such as primary, biological and chemical sludges.
    Objectives 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 optimizing other drying pro- cesses 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 in- dustry. The process of filtration is primarily obtained by passing a pair of filtering or filter cloths through o a system of rollers or rolls. The belt filter press O takes the sludge as a feed, and separates it into a O filtrate and a solid cake.
    7 The efficiency of a belt filter press is often A 30 assessed based on dry solids content of the cake and E solids recovery, as well as a quality of the dry solids. © Solids recovery refers to a percentage of dry solids x recovered from the feed sludge. Dry solids content re- N fers to a measure of the degree of dewatering.N
    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 selec- tion of concepts in a simplified form that are further described below in the detailed description. This sum- mary is not intended to identify key features or essen- tial features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. It is an object of the present disclosure to allow automatic control of a belt filter press that is used in sludge processing. The foregoing and other ob- jects 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 filter press 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 o computer program code. The at least one memory and the N computer program code are configured to, with the at N least one processor, cause the control apparatus to at 7 30 least receive a first monitoring signal from a first TY optoelectronic measurement device. The first monitoring E signal indicates a level of packing of the upper filter © cloth in front of the first pair of nip rolls in a 8 rotation direction of the upper filter cloth. The at N 35 least one memory and the computer program code are fur- N ther 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 sec- ond 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 first control signal to be sent to the belt filter press, the first control signal instructing the belt filter press Lo increase or decrease a nip pressure of the first pair of nip rolls, respectively.
    In an implementation form of the first aspect, the belt filter press further has a second pair of nip rolls located after the first pair of nip rolls 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 moni- toring 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 at least one memory and the computer program code are further configured to, with the at least one processor, cause the control ap- paratus to determine whether the indicated level of ad- hesion exceeds an adhesion threshold. In response to the x indicated level of adhesion exceeding the adhesion N threshold, the at least one memory and the computer 3 30 program code are further configured to, with the at O least one processor, cause the control apparatus to Ek cause a second control signal to be sent to the belt * filter press, the second control signal instructing the 8 belt filter press to perform a first nip pressure ad- S 35 justment by decreasing at least one of the nip pressure S 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 filter press further has a second pair of nip rolls located after the first pair of nip rolls 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 monitor- ing signal from a filtrate quality measurement device, the third monitoring signal indicating a level of qual- ity of filtrate output by the belt filter press. The at least one memory and the computer program code are fur- ther 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 fil- trate 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 com- puter 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 ad- justment by decreasing at least one of the nip pressure of the first pair of nip rolls 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 x are further configured to, with the at least one pro- N cessor, cause the control apparatus to instruct the belt 3 30 filter press to keep the nip pressure of the second pair O of nip rolls higher than the nip pressure of the first =E pair of nip rolls. * In an implementation form of the first aspect, 8 the control apparatus is comprised in a distributed con- S 35 trol system.N
    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, 5 a method of automatically controlling a belt filter press 1s provided.
    The belt filter press 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 pro- cessor, a first monitoring signal from a first optoe- lectronic measurement device.
    The first monitoring sig- nal 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 re- sponse 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 filter press further has a second pair of nip rolls located after the first pair of nip rolls in the Q rotation direction of the lower filter cloth, and the N method further comprises receiving, at the processor, a 3 30 second monitoring signal from a second optoelectronic O measurement device.
    The second monitoring signal indi- I cates a level of adhesion of sludge to the upper filter * cloth after the second pair of nip rolls in the rotation 8 direction of the upper filter cloth.
    The method further S 35 comprises determining, by the processor, whether the S indicated level of adhesion exceeds an adhesion thresh-
    old.
    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 filter press, the second control signal instructing the belt filter press to per- form a first nip pressure adjustment 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 filter press further has a second pair of nip rolls located after the first pair of nip rolls 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 meas- urement 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 re- sponse 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 adjustment by decreas- ing at least one of the nip pressure of the first pair of nip rolls or the nip pressure of the second pair of nip rolls.
    N In an implementation form of the second aspect, N the method further comprises instructing, by the pro- 3 30 cessor, the belt filter press to keep the nip pressure O of the second pair of nip rolls higher than the nip Ek pressure of the first pair of nip rolls. * According to a third aspect of the disclosure, 8 a computer program product is provided. The computer S 35 program product comprises program code that is config- S ured to perform the method according to the second as- pect, 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 meas- urement 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 meas- urement device arranged at or after a filtrate output of the belt filter press.
    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.
    N At least some of the embodiments allow auto- N matic control of a belt filter press that is used in 3 30 sludge processing.
    More specifically, at least some of O the embodiments allow automatic control of nip pres- Ek sure(s) of such a belt filter press.
    Such automatic * control in turn allows easier operation of the belt 8 filter press since less experience is required from the S 35 operator (s). Furthermore, such automatic control allows S more stable operation of the belt filter press.
    Fur- thermore, 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 bet- ter filtrate quality. Furthermore, such automatic con- trol 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 em- bodiments of the invention and together with the de- scription help to explain the principles of the inven- tion. 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. 1B illustrates an overview of an example belt filter press, where various embodiments of the pre- sent disclosure may be implemented; Fig. 1C illustrates examples of filter cloth packing in a belt filter press; Fig. 2 is a block diagram illustrating a con- trol apparatus for automatically controlling a belt fil- ter press for use in sludge processing, according to an embodiment of the present disclosure; Fig. 3 is a diagram illustrating a system for o automatically controlling a belt filter press for use S in sludge processing, according to an embodiment of the N present disclosure; and 7 30 Fig. 4 is a flow diagram illustrating a method A of automatically controlling a belt filter press for use E in sludge processing, according to an embodiment of the © present disclosure. 8 Like reference numerals are used to designate N 35 like parts in the accompanying drawings.N
    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 descrip- tion, 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 disclo- sure 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 de- vice may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. On the other hand, for ex- ample, 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 illus- trated in the figures. Further, it is understood that the features of the various example aspects described herein may be combined with each other, unless specif- o ically noted otherwise.
    O In the following, a general description of an & elevator system 100 in which various embodiments of the 7 30 present disclosure may be implemented is provided with — reference to Fig. 1.
    E Fig. 1A illustrates an overview of an example 0 sludge dewatering line 100, where various embodiments 8 of the present disclosure may be implemented.
    N 35 The sludge dewatering line 100 comprises a pre- N dewatering unit or drum 110 and a belt filter press 120.
    The pre-dewatering unit 110 may comprise a flocculator
    115.
    Herein, the terms “sludge processing” and “sludge dewatering” refer specifically sludge pro- cessing 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 ag- glomerate particles in the conditioned sludge into ag- gregates called flocs, via mixing the sludge with a suitable flocculant. The formation of flocs induces re- lease 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 N feed, and separates it into a filtrate (liguid, primar- N ily water) and a solid cake, by way of filtration. The 3 30 process of filtration is primarily obtained by passing O thickened sludge between a pair of filter cloths through =E a system of rolls. The produced solid cake is typically * incinerated later. 8 Fig. 1B illustrates a simplified overview of S 35 an example belt filter press 120, where various embod- S iments 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. 1B, 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 head- box 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 roll element of the system of rolls applies 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 necessitating the use of higher and higher pressure to extract the still remaining water. Accordingly, in the example of Fig. 1B, 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 con- x tainer or tank, and then e.g. passed on outside the N sludge dewatering line 100 for further processing. 3 30 As can be seen from Fig. 1B, a pair of nip O rolls is characterized in that the two powered nip rolls Ek forming the pair are arranged opposite each other such * that they squeeze the material passing between them. The 8 contact point or near-contact point between the nip S 35 rolls is called a nip point and is the point at which S 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. 1B) of the system of rolls is solid cake.
    The produced solid cake is usu- ally incinerated later.
    Thus, an objective 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 possi- ble is not as simple as just 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 filter 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 unnecessary burden on a later water treatment plant.
    Typically, an objective for operating a belt filter press is to rotate the filter cloths as slowly as possible in order to allow as long a detention time for the sludge in the belt filter press as possible.
    Q Traditionally, the various operating parameters (the N amount of polymer acting as a flocculant, rotation 3 30 speeds of the filter cloths, applied pressure level(s), O and the like) of a sludge dewatering line are controlled I and adjusted by human operators who must continually * monitor the operation of the belt filter press in order 8 to maintain an optimal performance level.
    S 35 Fig. 1C illustrates examples of filter cloth S packing in a belt filter press.
    The filter cloth packing is a phenomenon typical for belt filter presses that utilize 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 sludge 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 just 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 pres- sure 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 pressure of the first nip roll 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 pres- sure of the first nip roll pair is too high. The nip pressure of the first nip roll pair being too high can result in the sludge starting to protrude from the sides x of the filter cloths, thus ending up in the same con- N tainer or tank in which the filtered water is collected, 3 30 and thereby reducing filtrate quality of the filtered O water. Furthermore, the nip pressure of the first nip Ek roll pair being too high can result in clogging of the * filter cloth(s), and/or mechanical damage to the filter 8 cloth (s). Thus, the nip pressure of the first nip roll S 35 pair being too high is also undesirable. S 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 first 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 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 fil- ter cloths is high or a feed flow of the sludge is too high. This and other issues are addressed in the dis- closed 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 inspec- tion). 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 N press 310 comprises a lower filter cloth 301, an upper N filter cloth 302, and at least a first pair 303 of nip 3 30 rolls. The lower filter cloth 301 forms a first loop O rotating in a rotation direction 361, and the upper =E filter cloth 302 forms a second loop rotating in a ro- * tation direction 362. 8 As shown in the example embodiment of Fig. 3, S 35 the belt filter press 310 may further comprise a second S 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 pressures 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 filter 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 opto- electronic measurement device 351. The first optoelec- tronic 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 measure- ment 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 filter cloth 302 is measurably in the field of view of x the first optoelectronic measurement device 351. N The first optoelectronic measurement device 3 30 351 may comprise e.g. a light curtain sensor, an imaging O sensor, or a vision sensor. The light curtain sensor may =E comprise e.g. a transmitter and a receiver arranged at * opposite sides of the filter cloths 301, 302 in a hor- 8 izontal direction. The transmitter may project an array S 35 of parallel infrared light beams to the receiver which S may comprise a number of photoelectric cells. When pack- ing of the upper filter cloth 302 (and thus the packing of the sludge) breaks one or more of the beams, a cor- responding 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 im- ages) that may be analyzed by suitable software in order to measure or detect the level of packing of the upper filter cloth 302 (and thus the packing of the sludge). 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 controller 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 deter- mining 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.
    If the level of adhesion of sludge to the upper filter cloth 302 is too high, it indicates that the nip pressure of the second N pair 304 of nip rolls is too high in relation to the nip N pressure of the first pair 303 of nip rolls.
    The second 3 30 optoelectronic measurement device 352 may be arranged O after the second pair of nip rolls in the rotation di- =E rection of the upper filter cloth 302 in such a location * and position and/or orientation that the level of po- 8 tential adhesion of sludge to the upper filter cloth 302 S 35 after the second pair 304 of nip rolls in the rotation S direction of the upper filter cloth 302 is measurably in the field of view of the second optoelectronic meas- urement device 352. Since the second optoelectronic measurement device 352 measures or detects the level of adhesion of sludge to the upper filter 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 filter cloth 302.
    The second optoelectronic measurement device 352 may comprise e.g. at least one infrared light trans- mitter-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 in- frared 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 N cloth 302 can be determined. N The infrared light -based imaging sensor or the 3 30 visible light -based imaging sensor may be located e.g. O above the upper filter cloth 302 (i.e. on the side of Ek the upper filter cloth 302 to which the sludge may po- * tentially be stuck) and used to produce a digital image 8 (or a sequence of digital images) that may be analyzed S 35 by suitable software in order to measure or detect the S 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 fil- ter cloth 302, and then the number or percentage of such pixels may be calculated to determine the level of ad- hesion 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%- 803 of the pixels of the produced digital image repre- senting sludge adhered to the upper filter cloth 30 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 filter 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 N configured to measure or detect a level of quality of N filtrate output by the belt filter press 310. In other 3 30 words, the filtrate quality measurement device 353 may O be used to facilitate determining whether the nip pres- Ek sure of the second pair 304 of nip rolls is correct in * relation to the nip pressure of the first pair 303 of 8 nip rolls. If the level of quality of filtrate is too S 35 low, it indicates that the nip pressure of the second S 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. turbid- ity of the filtrate. The turbidity may be expressed 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 applica- tions. 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 pro- trude 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, this 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 x is too high or the feed flow of the sludge is too high. N Other reasons for the sludge being too runny include: 3 30 the polymer that the sludge is conditioned with in the O pre-dewatering unit 110 is not suitable for the current =E mixed sludge or the dosage of the polymer is incorrect. * Use of the filtrate quality measurement device 353 al- 8 lows detecting these situations and reacting accord- S 35 ingly.N
    The system 300 further comprises a control ap- paratus 200 for automatically controlling the belt fil- ter 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 ap- paratus 200 for automatically controlling the belt fil- ter 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 con- trol 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 ad- ditionally, 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 N as a co-processor, a microprocessor, a controller, a N digital signal processor (DSP), a processing circuitry 3 30 with or without an accompanying DSP, or various other O processing devices including integrated circuits such =E as, for example, an application specific integrated * circuit (ASIC), a field programmable gate array (FPGA), 8 a microcontroller unit (MCU), a hardware accelerator, a S 35 special-purpose computer chip, or the like. S The at least one memory 202 may be configured 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 N packing threshold may be in the range between four and N seven centimetres, e.g. substantially five centimetres. 3 30 In response to the indicated level of packing O being below the first packing threshold, the at least Ek one memory 202 and the computer program code 203 are * further configured to, with the at least one processor 8 201, cause the control apparatus 200 to cause a first S 35 control signal to be sent to the belt filter press 310, S 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 con- trol 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 sec- ond 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 36 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 x of the upper filter cloth 302 that has been determined N to be covered by adhered sludge. 3 30 In response to the indicated level of adhesion O exceeding the adhesion threshold, the at least one Ek memory 202 and the computer program code 203 may be * further configured to, with the at least one processor 8 201, cause the control apparatus 200 to cause a second S 35 control signal to be sent to the belt filter press 310. S The second control signal instructs the belt filter press 310 to perform a first nip pressure adjustment 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 fil- trate quality measurement device 353. The third moni- toring 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 x comprise e.g. turbidity (0...100%) of the filtrate. Ac- N cordingly, the filtrate quality threshold may comprise 3 30 a selectable value (e.g. between 20...70%) of the tur- O bidity percentage. Ek The at least one memory 202 and the computer * program code 203 may be further configured to, with the 8 at least one processor 201, cause the control apparatus S 35 200 to instruct the belt filter press 310 to keep the S 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 processing, according to an em- bodiment of the present disclosure.
    At operation 401, the belt filter press is in- structed by a processor to keep a nip pressure of the second pair of nip rolls 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 optoelec- tronic 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. If the indicated level of pack- ing is below the first packing threshold, the method 400 proceeds to operation 405. If 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 sec- ond packing threshold. If the indicated level of packing exceeds the second packing threshold, the method 400 proceeds to operation 406. If the indicated level of packing does not exceed the second packing threshold, N the method 400 proceeds to operation 407 or operation N 410, depending on which of the second and third moni- 3 30 toring signals are in use and received next.
    O At operation 405, the processor causes the =E first control signal to be sent to the belt filter press, * such that the first control signal instructs the belt 8 filter press to increase the nip pressure of the first S 35 pair of nip rolls. Alternatively, at operation 406, the S processor causes the first control signal to be sent to the belt filter press, such that the first control sig- nal 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 optoelec- tronic 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.
    At operation 408, the processor determines whether the indicated level of adhesion exceeds an ad- hesion threshold. If the indicated level of adhesion exceeds the adhesion threshold, the method proceeds to operation 409. If the indicated level of adhesion does not exceed the adhesion threshold, the method proceeds to operation 410.
    At operation 409, the processor causes the sec- ond 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 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.
    At operation 410, the third monitoring signal is received at the processor from the filtrate quality measurement device. The third monitoring signal indi- cates a level of quality of filtrate output by the belt N filter press. N At operation 411, the processor determines 3 30 whether the indicated level of quality of filtrate is O below a filtrate auality threshold. If the indicated =E level of quality of filtrate is below the filtrate qual- * ity threshold, the method proceeds to operation 412. If 8 the indicated level of quality of filtrate is not below S 35 the filtrate quality threshold, the method 400 may e.g. S 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. Alterna- tively, the method 400 may exit (not shown in Fig. 4) if the indicated level of quality of filtrate is not below the filtrate auality 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 decreas- ing 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 op- erations 401-418 can, for example, be performed by the at least one processor 201, the memory 202 and the com- puter 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 ex- ample, any suitable computer devices, such as distrik- uted control systems, programmable logic controllers, N servers, workstations, personal computers, laptop com- N puters, other devices, and the like, capable of per- 3 30 forming the processes of the exemplary embodiments. The O devices and subsystems of the exemplary embodiments can =E communicate with each other using any suitable protocol * and can be implemented using one or more programmed 8 computer systems or devices. S 35 One or more interface mechanisms can be used S with the exemplary embodiments, including, for example, Internet access, telecommunications in any suitable form
    (e.g., voice, modem, and the like), wireless communica- tions media, and the like. For example, employed commu- nications networks or links can include one or more satellite communications networks, wireless communica- tions networks, cellular communications networks, 3G communications networks, 4G communications networks, 5G communications networks, Public Switched Telephone Net- work (PSTNs), Packet Data Networks (PDNs), the Internet, intranets, a combination thereof, and the like.
    It is to be understood that the exemplary em- bodiments 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 imple- mented via one or more hardware and/or software devices.
    The exemplary embodiments can store infor- mation 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 orga- nized using data structures (e.g., records, tables, ar- rays, fields, graphs, trees, lists, and the like) in- cluded in one or more memories or storage devices listed N herein. The processes described with respect to the ex- N emplary embodiments can include appropriate data struc- 3 30 tures for storing data collected and/or generated by the O processes of the devices and subsystems of the exemplary =E embodiments in one or more databases.
    > All or a portion of the exemplary embodiments 8 can be conveniently implemented using one or more gen- S 35 eral purpose processors, microprocessors, digital sig- S nal processors, micro-controllers, and the like, pro-
    grammed according to the teachings of the exemplary em- bodiments of the present inventions, as will be appre- ciated 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 will be appreciated by those skilled in the software art. In addition, the exemplary embodiments can be implemented by the prepa- ration of application-specific integrated circuits or by interconnecting an appropriate network of conven- tional component circuits, as will be appreciated by those skilled in the electrical art (s). Thus, the exem- plary embodiments are not limited to any specific com- bination of hardware and/or software.
    Stored on any one or on a combination of com- puter 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 ena- bling 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, appli- cations software, and the like. Such computer readable media further can include the computer program product of an embodiment of the present inventions for perform- ing all or a portion (if processing is distributed) of N the processing performed in implementing the inventions. N Computer code devices of the exemplary embodiments of 3 30 the present inventions can include any suitable inter- O pretable or executable code mechanism, including but not =E limited to scripts, interpretable programs, dynamic link * libraries (DLLs), Java classes and applets, complete 8 executable programs, Common Passenger Request Broker S 35 Architecture (CORBA) passengers, and the like. Moreover, S 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 exem- plary embodiments can include computer readable medium or memories for holding instructions programmed accord- ing to the teachings of the present inventions and for holding data structures, tables, records, and/or other data described herein. Computer readable medium can in- clude 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, non- volatile media, volatile media, and the like. Non-vol- atile media can include, for example, optical or mag- netic disks, magneto-optical disks, and the like. Vol- atile media can include dynamic memories, and the like. Common forms of computer-readable media can include, for example, a floppy disk, a flexible disk, hard disk, or any other suitable medium from which a computer can read.
    It is to be understood that aspects and embod- iments 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 de- scribed in connection with a number of exemplary embod- iments, and implementations, the present inventions are x not so limited, but rather cover various modifications, N and equivalent arrangements, which fall within the pur- 3 30 view of prospective claims.
    O = a > >SN
    权利要求:
    Claims (14)
    [1] 1. A control apparatus (200) for automatically controlling a belt filter press (310) for use in sludge processing, the belt filter press (310) having a lower filter cloth (301), an upper filter cloth (302), and a first pair (303) of nip rolls, and the control apparatus (200) comprising: at least one processor (201); and at least one memory (202) comprising computer program code (203), the at least one memory (202) and the computer program code (203) configured to, with the at least one processor (201), cause the control appa- ratus (200) to at least: receive a first monitoring signal from a first optoelectronic measurement device (351), the first mon- itoring signal indicating a level of packing of the upper filter cloth (302) in front of the first pair (303) of nip rolls in a rotation direction of the upper filter cloth (302); determine whether the indicated level of pack- ing is below a first packing threshold or exceeds a second packing threshold; and in response to the indicated level of packing being below the first packing threshold or exceeding the second packing threshold, cause a first control signal to be sent to the belt filter press (310), the first o control signal instructing the belt filter press (310) O to increase or decrease a nip pressure of the first pair & (303) of nip rolls, respectively. 7 30 2. The control apparatus (200) according to TY claim 1, wherein the belt filter press (310) further has E a second pair (304) of nip rolls located after the first 0 pair (303) of nip rolls in the rotation direction of the 8 lower filter cloth (301), and the at least one memory N 35 (202) and the computer program code (203) are further N configured to, with the at least one processor (201), cause the control apparatus (200) to:
    [2] receive a second monitoring signal from a sec- ond optoelectronic measurement device (352), the second monitoring signal indicating 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); determine whether the indicated level of adhe- sion exceeds an adhesion threshold; and in response to the indicated level of adhesion exceeding the adhesion threshold, cause a second control signal to be sent to the belt filter press (310), the second control signal instructing the belt filter press (310) to perform a first nip pressure adjustment by decreasing at least one of the nip pressure of the first pair (303) of nip rolls or a nip pressure of the second pair (304) of nip rolls.
    [3] 3. The control apparatus (200) according to claim 1 or 2, wherein the belt filter press (310) further has a second pair (304) of nip rolls located after the first pair (303) of nip rolls in the rotation direction of the lower filter cloth (301), and 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: receive a third monitoring signal from a fil- trate quality measurement device (353), the third mon- itoring signal indicating a level of quality of filtrate N output by the belt filter press (310); N determine whether the indicated level of gual- 3 30 ity of filtrate is below a filtrate quality threshold; O and =E in response to the indicated level of quality * of filtrate being below the filtrate quality threshold, 8 cause a third control signal to be sent to the belt S 35 filter press (310), the third control signal instructing S the belt filter press (310) to perform a second nip pressure adjustment by decreasing at least one of the nip pressure of the first pair (303) of nip rolls or the nip pressure of the second pair (304) of nip rolls.
    [4] 4. The control apparatus (200) according to claim 2 or 3, wherein 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 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.
    [5] 5. The control apparatus (200) according to any of claims 1 to 4, wherein the control apparatus (200) is comprised in a distributed control system.
    [6] 6. The control apparatus (200) according to any of claims 1 to 5, wherein the control apparatus (200) is implemented with one or more programmable logic con- trollers.
    [7] 7. A method (400) of automatically controlling a belt filter press for use in sludge processing, the belt filter press having a lower filter cloth, an upper filter cloth, and a first pair of nip rolls, the method (400) comprising: receiving (402), at a processor, a first mon- itoring signal from a first optoelectronic measurement device, the first monitoring signal indicating a level of packing of the upper filter cloth in front of the first pair of nip rolls in a rotation direction of the N upper filter cloth; N determining (403-404), by the processor, 3 30 whether the indicated level of packing is below a first O packing threshold or exceeds a second packing threshold; Ek and * in response to the indicated level of packing 8 being below the first packing threshold or exceeding the S 35 second packing threshold, causing (405-406), by the pro- S cessor, 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.
    [8] 8. The method (400) according to claim 7, wherein the belt filter press further has a second pair (304) of nip rolls located after the first pair (303) of nip rolls in the rotation direction of the lower filter cloth, and the method (400) further comprises: receiving (407), at the processor, a second monitoring signal from a second optoelectronic measure- ment device, the second monitoring signal indicating a level of adhesion of sludge to the upper filter cloth after the second pair of nip rolls in the rotation di- rection of the upper filter cloth; determining (408), by the processor, whether the indicated level of adhesion exceeds an adhesion threshold; and in response to the indicated level of adhesion exceeding the adhesion threshold, causing (409), by the processor, 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 adjustment by decreasing at least one of the nip pres- sure of the first pair of nip rolls or a nip pressure of the second pair of nip rolls.
    [9] 9. The method (400) according to claim 7 or 8, wherein the belt filter press further has a second pair (304) of nip rolls located after the first pair (303) x of nip rolls in the rotation direction of the lower N filter cloth, and the method (400) further comprises: 3 30 receiving (410), at the processor, a third mon- O itoring signal from a filtrate auality measurement de- Ek vice, the third monitoring signal indicating a level of * quality of filtrate output by the belt filter press; 8 determining (411), by the processor, whether S 35 the indicated level of quality of filtrate is below a S filtrate quality threshold; and in response to the indicated level of quality of filtrate being below the filtrate quality threshold, causing (412), 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 adjustment by decreasing at least one of the nip pressure of the first pair of nip rolls or the nip pressure of the second pair of nip rolls.
    [10] 10. The method (400) according to claim 8 or 9, further comprising: instructing (401), by the processor, the belt filter 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.
    [11] 11. A computer program product comprising pro- gram code configured to perform the method according to any of claims 7 to 10, when the program code is executed on a computer.
    [12] 12. A system (300) for automatically control- ling a belt filter press (310), the system (300) com- prising: the belt filter press (310) for use in sludge processing, the belt filter press (310) having a lower filter cloth (301), an upper filter cloth (302), a first pair (303) of nip rolls, and a second pair (304) of nip rolls located after the first pair (303) of nip rolls in a rotation direction of the lower filter cloth (301); N a first optoelectronic measurement device N (351) arranged in front of the first pair (303) of nip 3 30 rolls in the rotation direction of the lower filter O cloth (301); Ek a second optoelectronic measurement device * (352) arranged after the second pair (304) of nip rolls 8 in a rotation direction of the upper filter cloth (302); S 35 a filtrate quality measurement device (353) S arranged at or after a filtrate output (307) of the belt filter press (310); and the control apparatus (200) according to any of claims 1 to 6.
    [13] 13. The system (300) according to claim 12, wherein the first optoelectronic measurement device (351) comprises one of: a light curtain sensor, an im- aging sensor, or a vision sensor.
    [14] 14. The system (300) according to claim 12 or 13, wherein the second optoelectronic measurement device (352) comprises one of: at least one infrared light transmitter-receiver pair, an infrared light -based im- aging sensor, or a visible light -based imaging sensor. oO
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