TREATING A PULP SLURRY

TECHNICAL FIELD

The invention relates to the field of apparatuses for treating biomass containing material, and more specifically controlling the operation of such apparatuses.

BACKGROUND

Apparatuses for treating biomass containing material are known in the art. For example, in a pulping process, apparatuses such as dewatering and/or washing devices, pressurized cooking vessels, bleaching towers, storage towers, mixing devices and/or screening devices are used. Such apparatuses all share the common property that the pulp flows within a housing portion, for example in the vat of a twin roll press. Today, these flows are normally monitored using pressure and/or temperature sensors, and control of various operating parameters such as a rotational speed and/or a flow rate of a fluid or suspension associated with the apparatus may take place based on these measurements or parameters estimated from these measurements.

There is a need for further improved control of such apparatuses, for example to improve utilization and to avoid channelizing or plugging.

SUMMARY

An object of the invention is to solve or improve on at least some of the problems mentioned above in the background section.

These and other objects are achieved by the present invention by means of a method and a control system according to the independent claims.

According to a first aspect of the invention, a method for controlling an apparatus for treating biomass containing material is provided. The apparatus comprises a housing portion in which said material flows during treatment. At least one ultrasonic measurement device is provided on an outer surface of said housing portion, which ultrasonic measurement device is configured to transmit ultrasonic pulses into said housing portion and receive reflected ultrasonic pulses therefrom. The method comprises conducting at least one measurement using the at least one ultrasonic measurement device to obtain measurement data indicative of the reflected ultrasonic pulses, adjusting at least one operating parameter for said apparatus based on said measurement data from said at least one ultrasonic measurement device, and controlling operation of said apparatus based on said at least one operating parameter.

In other words, a method for controlling an apparatus for treating (washing, dewatering, distributing, mixing for example) biomass containing material is provided, where the biomass containing material may be a suspension or slurry comprising biomass particles, which biomass may be lignocellulose containing biomass. In particular, the biomass containing material may be a pulp suspension or slurry. The pulp may be of woody origin and/or may be from other sources such as recycled textiles. In other words, the biomass containing material/suspension/slurry may comprise recycled textile fibres. The housing portion of the apparatus may alternatively be referred to as a shell portion, compartment, vessel portion or passageway through which the material flows or is conveyed during treatment. The housing portion may be provided with an inlet to which the biomass containing material/suspension/slurry to be treated is fed, and an outlet through which the biomass containing material/suspension/slurry leaves the housing portion after treatment. The at least one ultrasonic measurement device is provided on an at least one outer surface of the housing portion, which outer surface may also be referred to as an outer surface of a wall portion delimiting the housing portion. It is understood that the material flows inside the wall portion on the opposite side of the outer surface. The at least one ultrasonic measurement device is configured to transmit ultrasonic pulses into the housing portion and receive reflected or back-scattered ultrasonic pulses therefrom and may comprise at least one ultrasonic transmitter and at least one ultrasonic receiver for this purpose. Since the at least one ultrasonic measurement device is provided on at least one outer surface (of a wall portion) of the housing portion, it is understood that the ultrasonic pulses are transmitted and received through the at least one outer surface (of the wall portion) of the housing portion. The measurement data obtained by means of the at least one measurement performed using the at least one ultrasonic measurement device is used to adjust at least one operating parameter for the apparatus, i.e. is used to determine new value(s) of the at least one operating parameter. The adjusted operating parameter is used to control the apparatus. The at least one operating parameter may comprise a rotational speed of the apparatus and/or of an associated device. The at least one operating parameter may comprise a flow rate of a fluid or suspension associated with the apparatus. More specifically, the at least one operating parameter may be a flow of dilution liquid, which allows the consistency of the biomass containing material to be adjusted.

The invention is based on the insight that further improved control of an apparatus for treating biomass material is achievable by having better knowledge of the material flow inside the apparatus. The inventors have surprisingly realized that such flow measurements may be conducted by means of non-invasive ultrasonic measurement devices placed on an outer (metallic) surface of a housing portion of the apparatus. Such measurements may provide improved control compared to conducting corresponding ultrasonic measurements upstream and/or downstream of the apparatus in the pipes connected thereto.

Non-invasive ultrasonic measurements techniques per se are known in the art. If the material contains a relatively small number of particles, the so-called time transit method may be used, which is based on the principle to conduct two measurements, one measurement with the ultrasonic beam directed in a downstream direction and one in an upstream direction, and compare the time from when the ultrasonic pulses or signal is transmitted until it is received in the upstream measurement with the corresponding time from the downstream measurement. The difference in time may be used to determine the flow rate for instance. If the material contains a large number of particles, the so-called doppler shift method may be preferrable, which is based on the principle that the ultrasonic pulses are transmitted into the housing portion and reflected or back-scattered on the particles in the material, where the frequency shift caused by the motion of the particles can be used to determine the flow rate for instance.

In embodiments, the method further comprises estimating a velocity profile of a flow of the material in the housing portion based on the obtained measurement data indicative of the reflected ultrasonic pulses. A comparison between the velocity profile and a desired reference velocity profile may also be performed. The estimated velocity profile and/or the results of the comparison may be used in the adjusting step to adjust the operating parameter.

In embodiments, the method further comprises determining a consistency of the material, wherein said adjusting at least one operating parameter comprises adjusting additionally based on said consistency.

In embodiments, the method further comprises measuring at least one differential pressure using at least two pressure sensors arranged along a length of the housing and/or measuring at least one temperature of the material using at least one temperature sensor, wherein said at least one operating parameter for said apparatus is adjusted additionally based on said at least one differential pressure and/or said at least one temperature.

According to a second aspect of the invention, a control system for controlling an apparatus for treating biomass containing material is provided. The apparatus comprises a housing portion in which said material flows during treatment. The control system comprising an ultrasonic measurement device and an electronic control unit to which said ultrasonic measurement device is electrically connected. The ultrasonic measurement device is provided on an outer surface of said housing portion, which ultrasonic measurement device configured to transmit ultrasonic pulses into said housing portion and receive back-scattered ultrasonic pulses therefrom. The electronic control unit is configured to adjust at least one operating parameter for said apparatus based on said measurement data received from said ultrasonic measurement device and generate a control signal for said apparatus based on said at least one operating parameter.

According to a third aspect of the invention, an apparatus for treating biomass containing material is provided. The apparatus comprises a control system according to the second aspect of the invention or embodiments thereof, wherein the apparatus is electrically connected to said electronic control unit of said control system to receive said control signal therefrom. In embodiments of the first, second or third aspect of the invention, the at least one ultrasonic measurement device is arranged such that the ultrasonic beam is directed at an angle relative the flow direction of the biomass material, for instance at an angle in a range between 10-80 degrees, such as between 25-65 degrees, such as about 45 degrees. The angle may alternatively be defined relative a normal direction of the outer surface of the housing portion, which angle may be in a range between 10-80 degrees, such as between 25-65 degrees, such as about 45 degrees.

In embodiments of the first, second or third aspect of the invention, the apparatus is a dewatering and/or washing apparatus (such as a twin roll press) comprising at least one rotatable drum having a permeable outer surface, said drum being arranged in a vat, wherein said housing portion is said vat or a portion thereof, wherein the at least one ultrasonic measurement device is configured to transmit said ultrasonic pulses into the vat towards the drum, preferably at an angle relative the radial direction of the drum. The at least one operating parameter may comprise a rotational speed of said at least one drum and/or one or more flows of dilution liquid upstream of said dewatering and/or washing apparatus and/or one or more flows of wash liquid added in the vat. By adjusting one or more of these operating parameters, the flow profile in the vat may be optimized, aiming towards a plug flow profile. Further, by conducting ultrasonic measurements and estimating a velocity profile, a measure of the dewatering characteristics may be obtained, which measure may be used to compare different dewatering apparatuses.

The dewatering and/or washing apparatus may be provided with a plurality of ultrasonic measurement devices distributed along the axial length of the rotatable drum, wherein said determining at least one operating parameter comprises comparing measurement data from the plurality of measurement devices. The dewatering and/or washing apparatus normally comprises liquor distribution nozzles which are also distributed along the axial length, which means that the plurality of ultrasonic measurement devices may be used to detect plugging of the nozzles by comparing velocity profiles over the axial length of the drum/vat.

The dewatering and/or washing apparatus may comprise a device for distribution of cellulose pulp onto said at least one rotatable drum, wherein said device comprises a rotatably arranged distribution screw, and wherein said operating parameters comprises a rotational speed of said distribution screw. This embodiment is advantageously combined with the above-described embodiment comprising a plurality of ultrasonic measurement devices. The rotational speed of the distribution screw is advantageously adjusted to achieve as uniform distribution as possible in the axial direction. In other words, an estimated axial uniformity may be used in the adjustment of the operating parameter(s).

In another embodiment of the first, second or third aspect of the invention, the apparatus is a device for distribution of material onto a movable processing surface, for example the permeable outer surface of the drum of the dewatering and/or washing apparatus described above. The distribution device comprises an inlet box which comprises an inlet for incoming material and an outlet for transfer of the material to the processing surface, wherein a distribution screw is rotatably arranged in said inlet box, wherein said housing portion is a portion of said inlet box, and wherein said operating parameters comprises a rotational speed of said distribution screw. The device for distribution may furthermore comprise throttling and/or guiding vanes, wherein the operating parameters comprises position parameters for said vanes. The device for distribution may be provided with a plurality of ultrasonic measurement devices distributed along the axial length of the distribution screw, wherein said adjusting at least one operating parameter comprises comparing measurement data from the plurality of measurement devices. The rotational speed of the distribution screw and/or the positions of the vanes is/are advantageously adjusted to achieve as uniform distribution as possible in the axial direction. In other words, an estimated axial uniformity may be used in the adjustment of the operating parameter(s).

In yet another embodiment of the first, second or third aspect of the invention, the apparatus is a vessel, for instance a vertical or horizontally disposed vessel, such as a pressurized cooking vessel, a bleaching tower, a storage tower or the like, wherein said housing portion is a portion of said vessel, and wherein said operating parameters comprises a flow rate of biomass containing material into said vessel and/or a flow rate of a dilution liquid into said vessel. By arranging the ultrasonic measurement device to allow estimation of the velocity profile along the diameter of the tower, detection of channelling may be detected and acted upon by adjusting one or more of the above-mentioned operating parameters. A vertical vessel may be provided with agitation means in a bottom portion thereof defining an agitation zone, wherein at least one ultrasonic measurement device is arranged to transmit ultrasonic pulses into said agitation zone, wherein said at least one operating parameter comprises a rotational speed of said agitation means. By conducting ultrasonic measurements through the agitation zone, the cavern size can be estimated and adjusted by adjusting the rotational speed of the agitation means. In other words, the estimated cavern size may be used in the adjustment of the operating parameter(s). Thereby, the cavern size may be adjusted to suit the incoming flow of biomass containing material such that sufficient agitation is achieved.

In yet another embodiment of the first, second or third aspect of the invention, the apparatus is mixing device, wherein said housing portion is a portion of an outlet of said mixing device, and wherein said at least one operating parameter comprises a rotational speed of said mixing device. This is advantageous since the homogeneity of the biomass containing material after mixing can be estimated, which estimation may be used in the adjustment of the operating parameter(s).

In yet another embodiment of the first, second or third aspect of the invention, the apparatus is screening device having a screen basked rotatably arranged in a screen housing, wherein said housing portion is a portion of said screen housing, and wherein said at least one operating parameter comprises a rotational speed of said screen basket. The screening device may be provided with at least two ultrasonic measurement devices distributed along the extension of the screen basket. This is advantageous since plugging of the basket may be detected, and if detected, the rotational speed may be increased to attempt to relieve the plugging.

The features of the embodiments described above are combinable in any practically realizable way to form embodiments having combinations of these features. Further, all features and advantages of embodiments described above with reference to the first aspect of the invention may be applied in corresponding embodiments of the second and third aspects of the invention and vice versa. In particular, in embodiments of the control system according to the second aspect of the invention, the electronic control system may be configured to perform operations which correspond to the method steps of corresponding embodiments of the method according to the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Above discussed and other aspects of the present invention will now be described in more detail using the appended drawings, which show presently preferred embodiments of the invention, wherein: fig. 1 shows a flowchart of an embodiment of the method according to the first aspect of the invention; fig. 2 shows an embodiment of an apparatus according to the third aspect of the invention comprising a control system according to the second aspect of the invention; fig. 3 shows a detail view of the apparatus in fig. 2; fig. 4 shows an example of an estimated flow profile obtained in an apparatus as shown in fig. 2-3; fig. 5 shows another embodiment of an apparatus according to the third aspect of the invention comprising a control system according to the second aspect of the invention; fig. 6 shows yet another embodiment of an apparatus according to the third aspect of the invention comprising a control system according to the second aspect of the invention; fig. 7 shows yet another embodiment of an apparatus according to the third aspect of the invention comprising a control system according to the second aspect of the invention, and fig. 8 shows yet another embodiment of an apparatus according to the third aspect of the invention comprising a control system according to the second aspect of the invention.

DETAILED DESCRIPTION

Fig. 1 shows a flowchart of an embodiment of the method according to the first aspect of the invention. The method comprises conducting at least one measurement 1 using at least one ultrasonic measurement device to obtain measurement data indicative of the reflected ultrasonic pulses, adjusting 5 at least one operating parameter for said apparatus based on said measurement data from said at least one ultrasonic measurement device, and controlling 6 operation of said apparatus based on said at least one operating parameter. The method optionally comprises estimating 2 a velocity profile of a flow of the material in the housing portion based on the obtained measurement data indicative of the reflected ultrasonic pulses. A comparison between the velocity profile and a desired reference velocity profile may also be performed. The estimated velocity profile and/or the results of the comparison may be used in the adjusting step 5 to adjust the operating parameter.

The method optionally comprises determining a consistency 3 of the material, wherein said adjusting 5 at least one operating parameter comprises adjusting additionally based on said consistency. The method optionally comprises measuring at least one differential pressure 4 using at least two pressure sensors arranged along a length of the housing and/or measuring at least one temperature of the material using at least one temperature sensor. The at least one operating parameter for said apparatus is adjusted 5 additionally based on said at least one differential pressure and/or said at least one temperature.

Fig. 2 shows a cross-section view of an embodiment of an apparatus 101 according to the third aspect of the invention comprising a control system 121 according to the second aspect of the invention. The apparatus is a dewatering and washing apparatus or more specifically a twin roll press. The twin roll press will only be briefly described herein since it is well known to the person skilled in the art. The press comprises a rotatable drum 102b having a permeable outer surface 103b, the drum being arranged in a vat 103b. An ultrasonic measurement device 105b is arranged on the outside of the vat, i.e. the housing portion is a portion of the vat. The ultrasonic measurement device is configured to transmit said ultrasonic pulses into the vat towards the drum at an angle relative the radial direction of the drum (see fig. 3). It is understood that the ultrasonic pulses are transmitted and received through the vat wall. A wash liquor injection nozzles 11 lb is arranged adjacent and upstream of the ultrasonic measurement device 105b. Although not shown in the cross-section view in fig. 2, it is understood that a plurality of wash liquor injection nozzles are distributed on the drum along the axial length thereof. In the same manner, a plurality of ultrasonic measurement devices are distributed along the axial length. The electronic control unit (ECU) 121 is electrically connected to the ultrasonic measurement device 105b and also to drum driving means (for instance an electrical motor, shown schematically as a dotted circle within the drum 102b), to the wash liquor injection nozzle 11 lb, and may furthermore be connected to dilution liquid nozzles upstream of the vat (not shown in fig. 2). The operating parameters thus comprise a rotational speed of the drum, flows of wash liquid added in the vat and optionally one or more flows of dilution liquid.

The twin roll press is furthermore provided with a device 106b for distribution of material onto the permeable outer surface 103b of the drum 102b. The distribution device comprises an inlet box 108b which comprises an inlet 109b for incoming material and an outlet 110b for transfer of the material onto the drum. A distribution screw 107b is rotatably arranged in said inlet box. The ECU 121 may optionally be electrically connected with driving means such as an electric motor for the distribution screw. The operating parameters may thus comprise also the rotational speed of the distribution screw.

The description above regarding drum 102b also applies to the other drum 102a with permeable surface 103a arranged in vat 104a, provided with wash liquor injection nozzle 111a, ultrasonic measurement device 105a and device for distribution 106a with inlet box 108a, inlet 109a, outlet 110a and distribution screw 107a.

Fig. 3 shows a detail view of the apparatus in fig. 2. Here, it can be seen that the ultrasonic beam, illustrated as a dotted arrow, is at an angle relative the direction of biomass containing material flow, indicated as an arrow between permeable outer surface 103b of the drum and vat 104b. It is understood that the direction of the ultrasonic beam and the transducer part of the ultrasonic measurement device are only schematically shown - the beam will be deflected when passing through the housing portion wall. The ultrasonic measurement devices in this embodiment (and all other embodiments described herein) may be of the type disclosed in fig. 7 of WO 2013/017969, which is a doppler shift type of device comprising one or more ultrasonic transducers. Other types of ultrasonic measurement devices and configurations thereof are of course also viable within the scope of the invention, for example having transducers and receivers arranged in a V-, W- or Z- configuration. Fig. 4 shows an example of an estimated flow profile obtained in an apparatus as shown in fig. 2-3. As can be seen, the flow velocity is close to zero at the vat wall (distance 0 mm). By using the inventive method, the operating parameters have been adjusted such that the flow velocity is substantially constant over a substantial part of the distance between the permeable outer surface and the vat.

Fig. 5 shows a cross-section view of another embodiment of an apparatus according to the third aspect of the invention comprising a control system according to the second aspect of the invention. The apparatus is a device 206 for distribution of material onto a movable processing surface 203, for example the permeable outer surface of the drum of the dewatering and/or washing apparatus shown in fig. 2-3. The distribution device comprises an inlet box 208 which comprises an inlet (not shown) for incoming material and an outlet 210 for transfer of the material to the processing surface 203, wherein a distribution screw 207 is rotatably arranged in the inlet box. A plurality of ultrasonic measurement devices 205 (only one can be seen in the fig. 5) are fixed to an outer surface of a wall portion of the inlet box and are distributed along the axial length of the distribution screw. The ultrasonic measurement devices 205 are arranged to transmit ultrasonic pulses through the wall portion into the inlet box 208 and receive reflected pulses therefrom (through the wall portion). Throttling vanes 222 are arranged at the outlet 210. An electric actuator 223 is provided to adjust the positions of the throttling vanes. The ECU 221 is electrically connected to the ultrasonic measurement devices 205 and also to screw driving means (for instance an electrical motor, shown schematically as a dotted circle within the screw 207), to the vane actuator(s) 223, and may furthermore be connected to dilution liquid nozzles upstream of the device (not shown in fig. 5). The operating parameters thus comprise a rotational speed of the screw, vane position(s) and optionally one or more flows of dilution liquid.

Fig. 6 shows a cross-section view of yet another embodiment of an apparatus according to the third aspect of the invention comprising a control system according to the second aspect of the invention. The apparatus is vertical vessel 313, more specifically a pressurized cooking vessel (digester). The vessel is provided with agitation means 314 (a rotor) at a bottom portion thereof defining an agitation zone 315, wherein an ultrasonic measurement device 305 is provided on an outer surface of vertical vessel 313 and is arranged to transmit ultrasonic pulses into the agitation zone. It is understood that the ultrasonic pulses are transmitted and received through the wall of the vertical vessel 313. The ECU 321 is electrically connected to the ultrasonic measurement device 305 and also to driving means for the rotor 314 (for instance an electrical motor, shown schematically below the rotor) and optionally to one or more flow adjusting means (such as valves) for adjusting a flow rate of biomass containing material into said vessel (inlet shown at top of the vessel 313) and/or a flow rate of a dilution liquid into said vessel (shown as arrows in fig. 6). The ECU may furthermore be connected to dilution liquid nozzles upstream of the device (not shown in fig. 5). The operating parameters thus comprise a rotational speed of the agitation means and optionally one or more flows of biomass containing material and/or dilution liquid.

Fig. 7 shows a cross-section view of yet another embodiment of an apparatus according to the third aspect of the invention comprising a control system according to the second aspect of the invention. The apparatus is mixing device 416 of the type disclosed in WO 2020/091640, but may be any type of mixer known in the art. The inlet to the mixer is shown to the left, and the outlet 417 is at the top. An ultrasonic measurement device 405 is arranged on the outer surface of the wall of the outlet 417, which thus forms the housing portion. The ultrasonic measurement device 405 is arranged to transmit ultrasonic pulses through the wall into the outlet 417 and receive reflected pulses therefrom (through the wall). The ECU 421 is electrically connected to the ultrasonic measurement device 405 and also to driving means (for instance an electrical motor, shown schematically to the right of the mixing device) for the rotor drum (shown as dotted lines inside the mixing device). The operating parameters thus comprise a rotational speed of the rotor drum.

Fig. 8 shows a cross section view of yet another embodiment of an apparatus according to the third aspect of the invention comprising a control system according to the second aspect of the invention. The apparatus is screening device 518 having a screen basket 519 rotatably arranged in a screen housing. Screening devices of this type are well known in the art and will not be described in further detail herein. At least two ultrasonic measurement devices 505a-b are distributed along the vertical extension of the screen basket 519. The measurement devices 505a-b are arranged on an outer surface of the wall of the screening housing to transmit ultrasonic pulses through the wall into the screening device and receive reflected pulses therefrom (through the wall). The ECU 521 is electrically connected to the ultrasonic measurement devices 505a-b and also to driving means (for instance an electrical motor, shown schematically at the bottom of the figure) for the screen basket. The operating parameters thus comprise a rotational speed of the screen basket. The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, the number of ultrasonic measurement devices may be different, and may be of a different type, and may be arranged with its ultrasonic beam having a different direction.