Improved detection of metallic contaminants in the flow of shredded tobacco

Abstract

A method for detecting and removing metallic contaminants from a stream of shredded tobacco is disclosed, comprising: i) passing a stream of shredded tobacco through a first metal detector at a first flow rate; ii) if the first metal detector detects the presence of metallic contaminants in the stream of shredded tobacco, diverting the stream of shredded tobacco to a secondary flow until the first metal detector no longer detects the presence of metallic contaminants; iii) passing the secondary stream of shredded tobacco containing metallic contaminants through a second metal detector at a second flow rate less than the first flow rate; iv) if the second metal detector detects the presence of metallic contaminants in the secondary stream of shredded tobacco, diverting the secondary stream of shredded tobacco to a tertiary flow until the second metal detector no longer detects the presence of metallic contaminants; and v) returning the secondary stream of shredded tobacco substantially free of metallic contaminants to the first metal detector in step i).

Description

Technical Field

[0001] The present disclosure relates to a method for detecting contaminants, such as metal contaminants, in a stream of shredded tobacco, particularly but not limited to, on a line for coarsely grinding the shredded tobacco.

Background Art

[0002] During the manufacture of products such as tobacco cast leaves, which are sheets of reconstituted coarse tobacco powder mixed with a pulp of cellulose fibers and a binder, it is first necessary to prepare the coarse tobacco powder. This is done on a line for coarsely grinding, where the vein of the leaf tobacco is cut by a shredder to form a stream of shredded tobacco. The stream of shredded tobacco passes through a coarse grinding mill so as to be ground into coarse tobacco powder. The coarse tobacco powder can be further subjected to a blending step and a fine grinding step before being mixed with a pulp of cellulose fibers and a binder to create a slurry from which a tobacco cast leaf can be formed.

[0003] Metal contaminants may be present in the tobacco vein, and these metal contaminants may cause small pieces of metal to occur in the stream of shredded tobacco. If these small metal pieces are not removed before the coarsely grinding step and subsequent steps, the pieces may contaminate the tobacco cast leaf and degrade the quality of the final product. Further, the metal pieces may damage the grinding machine.

[0004] Therefore, it is well known to provide a metal detector between the shredder and the coarse grinder to detect metallic contaminants and redirect a portion of the flow of shredded tobacco containing metallic contaminants. This is currently done by allowing the flow of shredded tobacco to pass through a gravity-drop metal detector. The gravity-drop metal detector comprises a throat section through which the shredded tobacco falls under gravity, and a metal sensing device (such as an electromagnetic coil) arranged around the throat section. The metal sensing device can detect the presence of metallic contaminants in the shredded tobacco falling through the throat section, and can redirect the flow of falling shredded tobacco to waste by, for example, moving a flap or gate within the throat section until the metal sensing device no longer indicates the presence of metallic contaminants, at which point the flap or gate is returned to its original position to direct the flow of shredded tobacco towards the coarse grinder.

[0005] While the use of gravity-drop metal detectors themselves may be effective in removing metal contaminants, each time metal contaminants are detected, a large amount of shredded tobacco is diverted to waste. In fact, this process is one of the main sources of waste in the tobacco castle leaf manufacturing process. It is estimated that, on average, about 0.1 percent of the shredded tobacco supply is lost as waste due to the diversion of the shredded tobacco flow upon detection of metal contaminants. This calculation suggests that for a batch of 4980 kg of shredded tobacco, approximately 5 kg of waste tobacco on a dry weight basis may be generated. [Overview of the project]

[0006] According to a first aspect of the present invention, a method for detecting and removing metal contaminants from a stream of shredded tobacco, i) A step of passing a stream of shredded tobacco through a first metal detector at a first flow rate, ii) If the first metal detector detects the presence of a metal contaminant in the flow of shredded tobacco, the process of diverting the flow of shredded tobacco to a secondary flow until the first metal detector no longer detects the presence of a metal contaminant, iii) A step of passing a secondary flow of shredded tobacco containing metal contaminants through a second metal detector at a second flow rate less than the first flow rate, iv) If the second metal detector detects the presence of a metal contaminant in the secondary flow of shredded tobacco, the process involves redirecting the secondary flow of shredded tobacco to a tertiary flow until the second metal detector no longer detects the presence of a metal contaminant. A method is provided which includes the step of (v) returning a secondary stream of shredded tobacco substantially free of metal contaminants to the first metal detector in step (i).

[0007] The tertiary flow of shredded tobacco containing metallic contaminants can be treated as waste.

[0008] Because the second flow rate is smaller than the first flow rate, the second metal detector can detect the presence of metal contaminants more accurately than the first metal detector. Also, because the second flow rate is smaller than the first flow rate, diverting the secondary flow of shredded tobacco containing metal contaminants to the tertiary flow results in less waste, as only a portion of the secondary flow is diverted to waste, and the remainder is returned to process i).

[0009] Since the secondary flow is returned to the tobacco flow in step i), the presence of metallic contaminants is effectively checked at least three times: first by the first metal detector, second by the second metal detector, and third by the first metal detector again.

[0010] Since the secondary flow passes through the second metal detector at a lower flow rate than the flow rate through the first metal detector, it may be even possible to accurately detect even smaller metal contaminant fragments. For example, the second metal detector may be configured to detect metal contaminant fragments with a maximum dimension of 5 mm or less. For example, the first metal detector may be configured to detect metal contaminant fragments with a maximum dimension of more than 5 mm.

[0011] Alternatively, a tertiary flow of shredded tobacco containing metallic contaminants may pass through a third metal detector at a third flow rate lower than the second flow rate. When the third metal detector detects the presence of metallic contaminants in the tertiary flow of shredded tobacco, the tertiary flow of shredded tobacco is redirected to a quaternary flow until the third metal detector no longer detects the presence of metallic contaminants. A tertiary flow substantially free of metallic contaminants may be returned to the first or second metal detector. A quaternary flow substantially free of metallic contaminants may be treated as waste.

[0012] The second flow rate may be 50 percent or less of the first flow rate. The second flow rate may also be 10 percent or less of the first flow rate. Generally, the lower the second flow rate, the more accurately the second metal detector can detect the presence of metal contaminants. Furthermore, the lower the second flow rate, the less tobacco is discarded. This is because, by diverting a portion of the secondary flow of tobacco containing metal contaminants over a given period of time, a smaller volume of tobacco is sent to the waste than at a higher flow rate.

[0013] Similarly, in embodiments having a third metal detector, the third flow rate may be smaller than the second flow rate. For example, the third flow rate may be 50 percent or less of the second flow rate. For example, the third flow rate may be 10 percent or less of the second flow rate.

[0014] The flow of shredded tobacco in step i) may be temporarily interrupted, while the secondary flow of shredded tobacco in step v) is returned to the first metal detector in step v). It will be understood that most of the shredded tobacco flow originating from the shredder does not contain metallic contaminants. Therefore, under normal operation, most or almost all of the shredded tobacco flow passes through the first metal detector and is not redirected to the secondary flow. The unredirected shredded tobacco flow can be passed through subsequent processing steps such as coarse grinding and fine grinding. The redirected secondary flow of shredded tobacco containing metallic contaminants tends to pass through the second metal detector in batches. Therefore, portions of the secondary flow that pass straight through the second metal detector tend to be returned to the first metal detector in batches. Thus, to reduce the risk of overfilling or shutting down the first metal detector, it may be advantageous to temporarily interrupt the addition of shredded tobacco flow from the shredder into the first metal detector when batch portions of the secondary flow are recycled to the first metal detector.

[0015] The flow rate of the shredded tobacco in step i) may be temporarily reduced, while the secondary flow of shredded tobacco in step v) is returned to the first metal detector in step v). This may be done to reduce the risk of overfilling or blocking the first metal detector, as described in the preceding paragraph.

[0016] The first metal detector may be a gravity-drop metal detector. In a gravity-drop metal detector, the flow of shredded tobacco falls through the throat portion under gravity at a first flow rate. The throat portion may have an upper input end and a lower output end. At least one metal sensor may be positioned adjacent to the throat portion. At least one metal sensor may be positioned around the throat portion. At least one metal sensor may be positioned on the inner surface of the throat portion. The throat portion may be substantially vertical. The throat portion may have a section that is substantially vertical. The throat portion or a section of the throat portion may be angled up to 45 degrees from the vertical. Preferably, the throat portion or a section of the throat portion is angled 10 degrees or less from the vertical. Preferably, the throat portion or a section of the throat portion is angled 5 degrees or less from the vertical.

[0017] The first metal detector may include a throat portion through which a stream of shredded tobacco falls, and the throat portion is movable to redirect the stream of shredded tobacco into a secondary flow in step ii). The throat portion may be articulated with respect to the frame of the first metal detector to allow relative movement. The throat portion may move automatically in response to the first metal detector sensing the presence of a metallic contaminant in the stream of shredded tobacco. Preferably, the lower output end of the throat portion is movable, while the upper input end of the throat portion remains substantially stationary. The throat portion, or at least the lower output end of the throat portion, may be moved by an electric motor. The throat portion, or at least the lower output end of the throat portion, may be moved by a hydraulic or pneumatic actuator. The throat portion, or at least the lower output end of the throat portion, may be moved by energizing an electromagnet. At least one metal sensor may be positioned toward the upper input end of the throat portion. This means that at least one metal sensor detects the presence of a metallic contaminant in the tobacco flow and sends a signal to an electric motor, hydraulic or pneumatic actuator, or electromagnet, and that the electric motor, hydraulic or pneumatic actuator, or electromagnet has sufficient time to move the lower output end of the throat portion to redirect the tobacco flow to a secondary flow before the metallic contaminant reaches the lower output end of the throat portion. If at least one metal sensor senses that there is no longer a metallic contaminant in the tobacco flow at the upper input end of the throat portion, the at least one metal sensor may send a signal to the electric motor, hydraulic or pneumatic actuator, or electromagnet, returning the lower output end of the throat portion to its initial position and ending the redirection to a secondary flow.

[0018] The first metal detector may include a throat portion through which a stream of shredded tobacco falls, and the throat portion includes a diverter member that is movable to redirect the stream of shredded tobacco into a secondary flow in step ii). The diverter member may include a flap or deflector that can be selectively engaged at two different positions. One position allows the stream of shredded tobacco to pass directly through the gravity-fall metal detector, while the other position redirects the stream of shredded tobacco (containing metallic contaminants) into a secondary flow. At least one metal sensor may be positioned toward the upper input end of the throat portion. The diverter member may be positioned toward the lower output end of the throat portion. This means that at least one metal sensor detects the presence of a metallic contaminant in the tobacco flow and transmits a signal to an electric motor, hydraulic or pneumatic actuator, or electromagnet, and that the electric motor, hydraulic or pneumatic actuator, or electromagnet has sufficient time to move the diverter member of the throat portion from a first position to a second position in order to redirect the tobacco flow to a secondary flow before the metallic contaminant reaches the lower output end of the throat portion. If at least one metal sensor senses that there is no longer any metallic contaminant in the tobacco flow at the upper input end of the throat portion, the at least one metal sensor may transmit a signal to the electric motor, hydraulic or pneumatic actuator, or electromagnet, and return the diverter member of the throat portion to its first position, thereby ending the redirection to a secondary flow.

[0019] The second metal detector may be a gravity-dropped metal detector.

[0020] The second metal detector may include a throat portion through which a secondary flow of shredded tobacco falls, and the throat portion is movable to redirect the secondary flow of shredded tobacco into a tertiary flow in step iv).

[0021] The second metal detector may include a throat portion through which a secondary flow of shredded tobacco falls, and the throat portion includes a diverter member that is movable to redirect the secondary flow of shredded tobacco into a tertiary flow in step iv).

[0022] The second metal detector may operate in the same manner as the first metal detector.

[0023] The stream of cut tobacco may include tobacco pieces having a maximum dimension of 500 mm or less. The stream of cut tobacco may include tobacco pieces having a maximum dimension of 100 mm or less.

[0024] The tertiary stream of cut tobacco having metal contaminants may be sent to waste. It should be noted that the volume of cut tobacco containing metal contaminants sent to waste as the tertiary stream is significantly less than the volume of cut tobacco containing metal contaminants forming the secondary stream. Thus, the method of the present disclosure can result in significantly less waste of cut tobacco when separating a portion of the stream of cut tobacco containing metal contaminants than existing methods.

[0025] Alternatively, the tertiary stream of cut tobacco having metal contaminants may pass through a third metal detector and be passed at a third flow rate that is less than the second flow rate.

[0026] The third metal detector may be a gravity-drop metal detector similar to the first and second metal detectors.

[0027] If the third metal detector detects the presence of metal contaminants within the tertiary stream of cut tobacco, the tertiary stream of cut tobacco may be diverted to a quaternary stream until the third metal detector no longer detects the presence of metal contaminants, and the tertiary stream of cut tobacco substantially free of metal contaminants may be returned to either the first metal detector or the second metal detector. The quaternary stream of cut tobacco having metal contaminants may be sent to waste.

[0028] The provision of the third metal detector may be useful for providing even higher accuracy in the detection of metal contaminants and for reducing waste of cut tobacco.

[0029] The first metal detector may be a pneumatically supplied metal detector. The second metal detector may be a pneumatically supplied metal detector. The third metal detector may be a pneumatically supplied metal detector. At least one of the first, second, and third metal detectors may be a pneumatically supplied metal detector, and the remaining metal detectors may be gravity-dropped metal detectors.

[0030] In a pneumatically supplied metal detector, in contrast to a gravity-fed metal detector, the flow of shredded tobacco containing metallic contaminants is carried along the path by a flow of air or other suitable gas. The pneumatically supplied metal detector may be configured as a horizontal pneumatically supplied metal detector, where the main path through the metal detector is substantially horizontal, or at least closer to horizontal than vertical. Similar to a gravity-fed metal detector, at least one metal sensor is provided upstream of the diverter member. If at least one sensor detects the presence of metallic contaminants in the flow of shredded tobacco carried along the main path by the airflow, a signal is generated to move the diverter from a first position where the flow of shredded tobacco passes directly through the pneumatically supplied metal detector to a second position where the flow of shredded tobacco containing metallic contaminants is redirected to a secondary flow by a secondary outlet. If at least one metal sensor no longer detects the presence of metallic contaminants, a signal is generated to move the diverter back from the second position to the first position. The diverter member may be moved between the first and second positions by an electric motor, a hydraulic or pneumatic actuator, or an electromagnet.

[0031] The first metal detector may include at least one sensor selected from a magnetic sensor, an X-ray sensor, a capacitive sensor, an inductive sensor, and an ultrasonic sensor.

[0032] The second metal detector may include at least one sensor selected from a magnetic sensor, an X-ray sensor, a capacitive sensor, an inductive sensor, and an ultrasonic sensor.

[0033] The second metal detector may be equipped with the same type of sensor as the first metal detector. The second metal detector may be equipped with a different type of sensor than the first metal detector.

[0034] The third metal detector may, if provided, comprise at least one sensor selected from a magnetic sensor, an X-ray sensor, a capacitive sensor, an inductive sensor, and an ultrasonic sensor.

[0035] The third metal detector may be equipped with the same type of sensor as the first metal detector. The third metal detector may be equipped with a different type of sensor than the first metal detector. The third metal detector may be equipped with the same type of sensor as the second metal detector. The third metal detector may be equipped with a different type of sensor than the second metal detector.

[0036] The first flow rate passing through the first metal detector can be between 1000 kg / hour and 5000 kg / hour.

[0037] The second flow rate passing through the second metal detector can be between 100 kg / hour and 500 kg / hour.

[0038] The first flow rate passing through the first metal detector can be 2500 kg / hour to 3500 kg / hour, or optionally, approximately 3000 kg / hour.

[0039] The second flow rate passing through the second metal detector can be 250 kg / hour to 350 kg / hour, or optionally, approximately 300 kg / hour.

[0040] In the context of this disclosure, the term “metallic contaminants” is intended to mean any undesirable metal fragments, whether ferrous or nonferrous, that may be present in the stream of shredded tobacco produced by shredding bales of tobacco leaves. Metallic contaminants may result from accidental shredding of the straps holding the bales of tobacco leaves together, or may be present in the bales of tobacco leaves as a result of contamination occurring before or during baling or handling of the bales. Some metal fragments may be greater than 5 mm in maximum size. Some metal fragments may be less than 5 mm in maximum size.

[0041] In the context of this disclosure, the term “divertor member” is intended to mean a component that is movable between a first position and a second position so as to be controllable in directing the flow of shredded tobacco along a first or second path.

[0042] In the context of this disclosure, the term “gravity-dropping metal detector” is intended to mean a metal detector through which a stream of shredded tobacco falls primarily under gravity.

[0043] In the context of this disclosure, the term “metal detector” is intended to mean a device or component configured to sense the presence of metallic contaminants in a stream of tobacco. The metal detector may comprise one or more of the following: magnetic sensors, X-ray sensors, capacitive sensors, and inductive sensors and ultrasonic sensors.

[0044] In the context of this disclosure, the term “pneumatically supplied metal detector” is intended to mean a metal detector through which a stream of shredded tobacco passes using a pneumatically supplied stream of air or other gas.

[0045] In the context of this disclosure, the term “shredded tobacco” is intended to mean tobacco leaves and related tobacco plant material that have passed through a shredder to form a stream of tobacco pieces. The tobacco pieces may have an average maximum dimension of 500 mm or less.

[0046] In the context of this disclosure, the term “flow” is intended to mean the flow of a product, such as shredded tobacco, being transported through a system by, for example, a pneumatic conveyor pipe.

[0047] In the context of this disclosure, the term “throat portion” is intended to mean a substantially tubular member configured to allow the passage of a stream of shredded tobacco and to restrict the passage of the stream of shredded tobacco to a defined cross-sectional area or a defined volume. [Examples]

[0048] The present invention is defined in the claims. However, the following provides a non-exclusive list of non-limiting embodiments. One or more features of these embodiments may be combined with one or more features of any of the features described above, for example, one or more features of other embodiments, forms, or aspects described herein.

[0049] Example 1: A method for detecting and removing metal contaminants from a stream of shredded tobacco, i) A step of passing a stream of shredded tobacco through a first metal detector at a first flow rate, ii) If the first metal detector detects the presence of a metal contaminant in the flow of shredded tobacco, the process of diverting the flow of shredded tobacco to a secondary flow until the first metal detector no longer detects the presence of a metal contaminant, iii) A step of passing a secondary flow of shredded tobacco containing metal contaminants through a second metal detector at a second flow rate less than the first flow rate, iv) If the second metal detector detects the presence of a metal contaminant in the secondary flow of shredded tobacco, the process involves redirecting the secondary flow of shredded tobacco to a tertiary flow until the second metal detector no longer detects the presence of a metal contaminant. v) A method comprising the step of returning a secondary stream of shredded tobacco substantially free of metallic contaminants to the first metal detector in step i). Example 2: The method according to Example 1, wherein the second flow rate is 50 percent or less of the first flow rate. Example 3: The method according to Example 1, wherein the second flow rate is 10 percent or less of the first flow rate. Example 4: The method according to any one of Examples 1 to 3, wherein the flow of shredded tobacco in step i) is temporarily interrupted while the secondary flow of shredded tobacco in step v) is returned to the first metal detector in step v). Example 5: The method according to any one of Examples 1 to 3, wherein the flow rate of the shredded tobacco in step i) is temporarily reduced while the secondary flow of shredded tobacco in step v) is returned to the first metal detector in step v). Example 6: The first metal detector is a gravity-fall metal detector, as described in any of Examples 1 to 5. Example 7: The method according to Embodiment 6, wherein the first metal detector comprises a throat portion through which a stream of shredded tobacco falls, and the throat portion is movable to redirect the stream of shredded tobacco into a secondary flow in step ii). Example 8: The method according to Embodiment 6, wherein the first metal detector comprises a throat portion through which a flow of shredded tobacco falls, and the throat portion comprises a movable diverter member to redirect the flow of shredded tobacco to a secondary flow in step ii). Example 9: The first metal detector is a pneumatically supplied metal detector, according to any one of Examples 1 to 5. Example 10: The method according to Embodiment 9, wherein the first metal detector comprises a throat portion through which a flow of shredded tobacco is carried by an airflow, and a movable diverter member is provided to redirect the flow of shredded tobacco to a secondary flow in step ii). Example 11: The second metal detector is a gravity-fall metal detector, as described in any of Examples 1 to 10. Example 12: The method according to Example 11, wherein the second metal detector comprises a throat portion through which a secondary flow of shredded tobacco falls, and the throat portion is movable to redirect the secondary flow of shredded tobacco into a tertiary flow in step iv). Example 13: The method according to Embodiment 11, wherein the second metal detector comprises a throat portion through which a secondary flow of shredded tobacco falls, and the throat portion comprises a movable diverter member that redirects the secondary flow of shredded tobacco to a tertiary flow in step iv). Example 14: The second metal detector is a pneumatically supplied metal detector, according to any one of Examples 1 to 10. Example 15: The method according to Embodiment 14, wherein the second metal detector comprises a throat portion through which a secondary flow of shredded tobacco is carried by an airflow, and a movable diverter member is provided to redirect the secondary flow of shredded tobacco into a tertiary flow in step iv). Example 16: The shredded tobacco flow is the method according to any one of Examples 1 to 15, including tobacco pieces having a maximum dimension of 500 mm or less. Example 17: The method according to any one of Examples 1 to 16, wherein the tertiary flow of shredded tobacco containing metallic contaminants is sent to waste. Example 18: The method according to any one of Examples 1 to 16, wherein a tertiary flow of shredded tobacco containing metal contaminants passes through a third metal detector at a third flow rate smaller than the second flow rate. Example 19: If the third metal detector detects the presence of a metallic contaminant in the tertiary flow of shredded tobacco, the tertiary flow of shredded tobacco is redirected to a quaternary flow until the third metal detector no longer detects the presence of a metallic contaminant. The method according to Example 18, wherein a tertiary flow of shredded tobacco substantially free of metallic contaminants is returned to either the first or second metal detector. Example 20: The method according to Example 19, wherein a fourth stream of shredded tobacco containing metallic contaminants is sent to waste. Example 21: The method according to any one of Examples 1 to 20, wherein the first metal detector comprises at least one sensor selected from a magnetic sensor, an X-ray sensor, a capacitive sensor, an inductive sensor, and an ultrasonic sensor. Example 22: The method according to any one of Examples 1 to 21, wherein the second metal detector comprises at least one sensor selected from a magnetic sensor, an X-ray sensor, a capacitive sensor, an inductive sensor, and an ultrasonic sensor. Example 23: The method according to any one of Examples 18 to 20, wherein the third metal detector comprises at least one sensor selected from a magnetic sensor, an X-ray sensor, a capacitive sensor, an inductive sensor, and an ultrasonic sensor. Example 24: The first flow rate is 1000 kg / hour to 5000 kg / hour, according to any of Examples 1 to 23. Example 25: The second flow rate is 100 kg / hour to 500 kg / hour, as described in Example 24. Example 26: The first flow rate is 2500 kg / hour to 3500 kg / hour, optionally approximately 3000 kg / hour, according to one of Examples 1 to 23. Example 27: The second flow rate is 250 kg / hour to 350 kg / hour, optionally selected, and is approximately 300 kg / hour, as described in Example 26. [Brief explanation of the drawing]

[0050] Here, we will further describe the examples with reference to the figures.

[0051] [Figure 1] Figure 1 shows a schematic process overview of the tobacco grinding line. [Figure 2] Figure 2 shows a schematic flowchart illustrating the method of this disclosure. [Figure 3]Figure 3 shows schematic diagrams of the first and second metal detectors of this disclosure. [Figure 4] Figure 4 shows a schematic diagram of a gravity-dropped metal detector. [Figure 5] Figure 5 shows a schematic diagram of a pneumatically supplied metal detector. [Modes for carrying out the invention]

[0052] Figure 1 shows a schematic diagram of a tobacco grinding line 200 suitable for forming a homogenized tobacco slurry from tobacco leaves. The homogenized tobacco slurry is used to produce sheets of tobacco cast leaf.

[0053] The tobacco grinding line 200 includes a tobacco receiving station 201 for stacking, transshipping, weighing, and inspecting different types of tobacco. Optionally, if the tobacco is shipped in cartons, the removal of the cartons is carried out at the receiving station 201. The tobacco receiving station 201 also optionally includes a tobacco bale packaging splitting unit.

[0054] The bale of tobacco leaves is introduced into a shredder 202 and shredded. The shredder 202 may be, for example, a pin shredder. Preferably, the shredder 202 is adapted to handle bales of all sizes in order to break down the tobacco fragments and shred the fragments into smaller leaf pieces. The shredded tobacco is then transported to a mill 204, for example, by a pneumatic conveyor 203, and coarsely ground. Control is performed during transport between the shredder 202 and the mill 204 so that foreign matter in the shredded tobacco is removed. A metal detector, commonly shown in 220, is provided. In the illustrated embodiment, the metal detector 220 is a gravity-drop metal detector. However, other types of metal detectors, such as a pneumatic wire metal detector, may be used. If the metal detector 205 detects the presence of a metallic contaminant in the shredded tobacco, the portion of the shredded tobacco containing the metallic contaminant is discarded in 205. The remaining shredded tobacco is held along the pneumatic conveyor 203 to the mill 204. The Mill 204 is adapted to coarsely grind tobacco flakes to a size of approximately 0.25 mm to 2 mm. The rotor speed of the Mill 204 can be controlled and varied based on the flow rate of tobacco.

[0055] A buffer silo 206 for uniform mass flow control may be located after the coarse grinder mill 204. For safety reasons, the mill 204 may be equipped with a spark detector and a safety stop system 207.

[0056] Tobacco particles are transported from the mill 204 to the blender 210, for example, by a pneumatic conveyor 208. The blender 210 may include a silo containing a suitable valve control system. Within the blender 210, various tobacco particles of different types of tobacco selected for a predetermined blend are introduced. Within the blender 210, the tobacco particles are mixed into a uniform blend. The blend of tobacco particles is transported from the blender 210 to the grinding station 211.

[0057] The fine grinding station 211 may be, for example, an impact sorting mill with appropriately designed auxiliary equipment to produce fine tobacco powder according to desired specifications, for example, tobacco powder having an average particle size of about 0.03 mm to about 0.12 mm. After the fine grinding station 211, the pneumatic conveying line 212 is adapted to move the fine tobacco powder to a buffer powder silo 213 for continuous supply to a downstream slurry batch mixing tank 214 where the slurry preparation process takes place.

[0058] Figure 2 shows a schematic flowchart illustrating the method of the present disclosure. A first metal detector 320 receives a stream of shredded tobacco 301 from a shredder, for example, the shredder 202 in Figure 1. In Figure 2, shredded tobacco is indicated by white circles and metallic contaminants are indicated by black circles. The first metal detector 320 detects metallic contaminants in the stream of shredded tobacco 301 and is operable to temporarily redirect the metallic contaminants and some shredded tobacco to a secondary stream 302. Shredded tobacco that does not contain metallic contaminants can pass through the first metal detector 320 in a substantially contaminant-free stream 330, which can be fed to a coarse grinding mill 204 in Figure 1. The secondary stream 302, which contains metallic contaminants mixed with shredded tobacco, is then passed through a second metal detector 340. The flow rate of the secondary stream 302 is smaller than the flow rate of the stream 301. The flow rate of the secondary flow 302 is preferably 50 percent or less of the flow rate of the flow 301. More preferably, the flow rate of the secondary flow 302 is 10 percent or less of the flow rate of the flow 301.

[0059] The second metal detector 340 is operable to detect metallic contaminants in the secondary flow 302 of shredded tobacco and to temporarily redirect the metallic contaminants and a small amount of shredded tobacco to the tertiary flow 303. The tertiary flow 303 is passed through the waste 304. The secondary flow 302 of shredded tobacco, which passes through the second metal detector 340 without being redirected to the waste 304, is returned to the first metal detector 320 along with the shredded tobacco flow 301 from the shredder 202. Any residual metallic contaminants that may be present in the secondary flow 302 after passing through the second metal detector 340 should be finally separated from the shredded tobacco by repeatedly passing the secondary flow 302 and the tertiary flow 304 through the first metal detector 320 and the second metal detector 340. A control circuit 350 is provided to control the first metal detector 320 and the second metal detector 340.

[0060] It should be noted that the secondary flow 302 of tobacco and metal contaminants leaving the first metal detector 320 contains a considerable amount of tobacco in addition to the metal contaminants. This is mainly due to the relatively high flow rate of tobacco passing through the first metal detector 320. In response to the detection of metal contaminants in the tobacco flow, a considerable amount of tobacco containing metal contaminants is redirected to the secondary flow 302 by the operation of a diverter member or by the redirection of the throat portion of the first metal detector 320, as will be described in more detail below. By passing the secondary flow 302 of tobacco and metal contaminants through the second metal detector 340 at a lower flow rate, for example, 50 percent or less, preferably 10 percent or less, of the flow rate passing through the first metal detector 320, it is possible to more accurately separate the metal contaminants with less tobacco waste. Furthermore, the secondary flow 302 of tobacco output from the second metal detector 340 is recycled back to the first metal detector 320 rather than being sent to waste.

[0061] Figure 3 shows a schematic diagram of a first metal detector 320 and a second metal detector 340 arranged in a double-loop configuration of the coarse grinding line downstream of the shredder 202. As previously mentioned, the bale of tobacco leaves is introduced into the shredder 202, shredded, and forms a stream of shredded tobacco 301. The stream of shredded tobacco 301 may contain metallic contaminants. The stream of shredded tobacco 301 is fed to the first metal detector 320. The first metal detector 320 includes or is operably connected to a diverter 321. Unless the first metal detector 320 detects the presence of any metallic contaminants in the stream of shredded tobacco 301, the stream of shredded tobacco 301 passes straight through the diverter 321 as a stream of shredded tobacco 330 that does not contain metallic contaminants, and then, as shown in Figure 1, the stream 330 is passed through to subsequent steps in the grinding process. However, if the first metal detector 320 detects the presence of a metallic contaminant in the tobacco flow 301, the first metal detector 320 transmits a signal to the diverter 321 to temporarily redirect a portion of the tobacco flow 301 containing the metallic contaminant to the secondary flow 302. This continues until the first metal detector 320 senses that there is no metallic contaminant in the tobacco flow 301, and then transmits a signal to the diverter 321 to return the tobacco flow 301 to the tobacco flow 330 which does not contain the metallic contaminant.

[0062] Subsequently, the secondary flow 302 of the shredded tobacco containing the metal contaminants is passed through the second metal detector 340. The flow rate of the secondary flow 302 of shredded tobacco passing through the second metal detector 340 is lower than the flow rate of the shredded tobacco flow 301 passing through the first metal detector 320. Preferably, the flow rate of the secondary flow 302 is 50 percent or less of the flow rate of flow 301, and more preferably, it is 10 percent or less of the flow rate of flow 301. The reduction in flow rate can be achieved by appropriate control of the pneumatic conveyor 315 between the first metal detector 320 and the second metal detector 340.

[0063] Subsequently, the secondary flow 302 of the shredded tobacco containing the metallic contaminant passes through a second metal detector 340, which includes or is operably connected to a diverter 341. The second metal detector 340 and diverter 341 operate similarly to the first metal detector 320 and diverter 321, except that the flow rate of the secondary flow 302 of shredded tobacco and metallic contaminant passing through the second metal detector 340 is lower than the flow rate of the shredded tobacco flow 301 passing through the first metal detector 320. Unless the second metal detector 340 detects the presence of metallic contaminant, the secondary flow 302 passes straight through the diverter 341 and is recycled to the first metal detector 320 by a pneumatic conveyor 316. However, if the second metal detector 340 detects the presence of a metallic contaminant in the secondary flow 302, a signal is sent to the diverter 341, and the metallic contaminant, along with a small amount of shredded tobacco, is redirected to the tertiary flow 303 and subsequently discarded in 304.

[0064] The main flow 301 of shredded tobacco from the shredder 202 is preferably temporarily interrupted or slowed down when the pneumatic conveyor 316 recycles the secondary flow 302 of shredded tobacco to the first metal detector 320, in order to reduce the risk of the pneumatic conveyor 316 overfilling or blocking the first metal detector 320. This can be controlled by the control device 350 shown in Figure 2.

[0065] Figure 4 shows a schematic diagram of a gravity-drop metal detector, for example, a first metal detector 320. The description may also apply to a second metal detector 340. Generally, the metal detector shown in 320 comprises a throat portion 400 in the form of a hollow tube. A metal sensor 401 is mounted around the upper end of the throat portion 400. Towards the lower end of the throat portion 400, below the metal sensor 401, is provided a side tube 402 angled downward from the side of the lower end of the throat portion 400. Here, a diverter member 403, shown in the form of a flap, is pivotably mounted below the junction between the side tube 402 and the lower end of the throat portion 400. In the illustrated embodiment, the diverter member 403 may be substantially elliptical. The diverter member 403 is movable between a first position and a second position. In the first position, the diverter member covers the junction between the lower end of the throat portion 400 and the inlet to the side tube 402. When the diverter member 403 is in the first position, the flow of shredded tobacco 301 passes straight through the throat portion 400 and exits the lower end of the throat portion as flow 330. The diverter member 403 is operably connected to a metal sensor 401 and is movable between the first and second positions by, for example, an electric motor, a hydraulic or pneumatic actuator, or an electromagnet. Unless the metal sensor 401 detects the presence of any metallic contaminants in the flow of shredded tobacco 301, the diverter member 403 remains in the first position, and the flow of shredded tobacco 301, which does not contain metallic contaminants, passes straight through the throat portion 400. However, if the metal sensor 401 detects the presence of a metallic contaminant in the tobacco flow 301, the metal sensor 401 transmits a signal to move the diverter member 403 to a second position, which blocks the lower end of the throat portion 400 and redirects the tobacco flow 301 containing the metallic contaminant 410 through the side tube 402 as a secondary flow 302 of tobacco containing the metallic contaminant 410. If the metal sensor 401 no longer detects the presence of the metallic contaminant 410 in the tobacco flow 301, a signal is transmitted and the diverter member 403 returns to the first position.A short delay between the metal sensor 401 no longer detecting the presence of the metal contaminant 410 and the diverter member 403 being activated to return to its first position may be advantageous as it allows time for the metal contaminant to reach the diverter member 403 and be redirected into the side tube 402.

[0066] If the metal sensor 401 is a magnetic sensor, it comprises a coil configured to generate an alternating magnetic field within the throat portion 400. Metallic contaminants 410 passing through the metal sensor 401 disrupt the magnetic field, and this disruption then causes fluctuations in the alternating current within the coil.

[0067] In one embodiment, the coil of the metal sensor may be supplied with an alternating current having a frequency of 5 kHz to 30 kHz. The current may be selected to provide a sensitivity of 600 mA to 1000 mA, for example, about 950 mA.

[0068] Since the metallic contaminant 410 can be ferrous and nonferrous, the metal sensor 401 should be configured to detect the presence of both types of contaminants. This may be done by cycling the frequency of the alternating magnetic field between lower and higher frequencies. The cycle length may be on the order of seconds. The cycle length may be about 1 second. Lower frequencies are suitable for detecting ferrous metals, while higher frequencies are suitable for detecting nonferrous metals. The metal sensor 401 should also be tuned to reduce the occurrence of false alarms.

[0069] Alternatively or additionally, the metal sensor 401 may be one or more of the following: an X-ray sensor, a capacitive sensor, an inductive sensor, and an ultrasonic sensor.

[0070] In a working example of the method of this disclosure, 4980 kg of shredded tobacco containing a metallic contaminant was passed through a first metal detector at a flow rate of approximately 3200 kg / hour. Due to the presence of the metallic contaminant detected by the metal detector, a total of 5.14 kg of shredded tobacco was redirected to a secondary flow by the first metal detector. The secondary flow of shredded tobacco and metallic contaminant passed through a second metal detector at a flow rate of approximately 320 kg / hour. 0.42 kg of shredded tobacco, along with the metallic contaminant, was redirected to a tertiary flow by the second metal detector. 4.72 kg of shredded tobacco powder passed through the second metal detector without being redirected to a tertiary flow and was returned to the first metal detector.

[0071] By using the method of this disclosure, only 0.008 percent (0.42 kg) of shredded tobacco is sent to the waste, instead of 0.1 percent (5.14 kg), which contributes to the recovery of 0.09 percent (4.72 kg) of shredded tobacco.

[0072] Figure 5 shows a schematic diagram of a pneumatically supplied metal detector, for example, a first metal detector 320. The description may also apply to a second metal detector 340. The pneumatically supplied metal detector is an alternative to the gravity-fall metal detector in Figure 4. The metal detector, generally shown as 320, comprises a throat portion 500 in the form of a hollow tube. The throat portion 500 is shown here in a substantially horizontal orientation. However, it will be understood that the throat portion 500 does not need to be substantially horizontal, since the flow 301 of shredded tobacco containing the metallic contaminant 410 is carried along the tube of the throat portion 500 by the airflow. This is in contrast to the gravity-fall metal detector in Figure 4, where the flow 301 falls through the throat portion 400, mainly due to gravity. The metal sensor 501 is mounted around the upstream end of the throat portion 500. Downstream of the metal sensor 501, at the right end of the throat section 500, the flow 301 exits the outlet 502 of the throat section 500 and crosses across the opening of the hopper 510. A corresponding pipe 511 is provided on the opposite side of the opening of the hopper 510. The corresponding pipe 511 may have a funnel-shaped inlet to facilitate the capture of the flow 301 as it is pneumatically transported across the opening of the hopper 510. The diverter member 520 is movable between a first position, where the flow 301 can pass substantially unobstructed from the outlet 502 across the opening of the open hopper 510 to the inlet of the corresponding pipe 511, and a second position (shown in Figure 5), where the flow 301 is diverted into the hopper 510. The diverter member 520 is operably connected to the metal sensor 501 and is movable between the first and second positions by, for example, an electric motor, a hydraulic or pneumatic actuator, or an electromagnet. Unless the metal sensor 501 detects the presence of metal contaminants 410 in the tobacco stream 301, the diverter member 520 remains in the first position, and the tobacco stream 301, which does not contain metal contaminants 410, passes straight across the opening of the hopper 510 into the corresponding pipe 511, defining a tobacco stream 330 that is substantially free of metal contaminants.However, if the metal sensor 501 detects the presence of the metal contaminant 410 in the tobacco flow 301, the metal sensor 501 transmits a signal to move the diverter member 520 to a second position, and the diverter member 520 redirects the tobacco flow 301 containing the metal contaminant 410 downward towards the mouth of the hopper 510. The secondary flow 302 of tobacco containing the metal contaminant 410 can be drawn out from the bottom of the hopper 510. If the metal sensor 501 no longer detects the presence of the metal contaminant 410 in the tobacco flow 301, a signal is transmitted to return the diverter member 520 to its first position. A short delay between the metal sensor 501 no longer detecting the presence of the metal contaminant 410 and the diverter member 520 being activated to return to its first position may be advantageous as it allows time for the metal contaminant 410 to reach the diverter member 520 and be redirected into the hopper 510.

[0073] If the metal sensor 501 is a magnetic sensor, it comprises a coil configured to generate an alternating magnetic field within the throat portion 500. Metallic contaminants 410 passing through the metal sensor 501 disrupt the magnetic field, and this disruption then causes fluctuations in the alternating current within the coil.

[0074] Since the metallic contaminant 410 can be ferrous and nonferrous, the metal sensor 501 should be configured to detect the presence of both types of contaminants. This may be done by cycling the frequency of the alternating magnetic field between lower and higher frequencies. The cycle length may be on the order of seconds. The cycle length may be about 1 second. Lower frequencies are suitable for detecting ferrous metals, while higher frequencies are suitable for detecting nonferrous metals. The metal sensor 501 should also be tuned to reduce the occurrence of false alarms.

[0075] Alternatively or additionally, the metal sensor 501 may be one or more of the following: an X-ray sensor, a capacitive sensor, an inductive sensor, and an ultrasonic sensor.

[0076] For the purposes of this specification and the appended claims, unless otherwise indicated, all numerical values ​​representing quantities, amounts, percentages, etc., should be understood in all instances as being modified by the term “approximately.” Furthermore, all ranges include the disclosed maximum and minimum points and any intermediate ranges therewith, which may or may not be specifically listed herein. Thus, in this context, number A is understood as 5 percent of A ± A. In this context, number A may be considered to include numerical values ​​that fall within the general standard error to the measured value of the characteristic modified by number A. In some instances used in the appended claims, number A may deviate by the percentages listed above, provided that the amount of deviation of A does not substantially affect the basic and novel characteristics of the claimed invention. Furthermore, all ranges include the disclosed maximum and minimum points and any intermediate ranges therewith, which may or may not be specifically listed herein.

Claims

1. A method for detecting and removing metal contaminants from a stream of shredded tobacco, i) A step of passing the flow of the shredded tobacco through a first metal detector at a first flow rate, ii) If the first metal detector detects the presence of a metal contaminant in the flow of shredded tobacco, the process of redirecting the flow of shredded tobacco to a secondary flow until the first metal detector no longer detects the presence of the metal contaminant; iii) A step of passing the secondary flow of the shredded tobacco having the metal contaminant through a second metal detector at a second flow rate less than the first flow rate, iv) If the second metal detector detects the presence of the metal contaminant in the secondary flow of the shredded tobacco, the second metal detector is redirected to a tertiary flow until it no longer detects the presence of the metal contaminant; v) A method comprising the step of returning the secondary flow of the shredded tobacco, which is substantially free of the metal contaminants, to the first metal detector in step i).

2. The method according to claim 1, wherein the second flow rate is 50 percent or less of the first flow rate.

3. The method according to claim 1, wherein the second flow rate is 10 percent or less of the first flow rate.

4. The method according to any one of claims 1 to 3, wherein the flow of the shredded tobacco in step i) is temporarily interrupted while the secondary flow of the shredded tobacco in step v) is returned to the first metal detector in step v).

5. The method according to any one of claims 1 to 3, wherein the flow rate of the tobacco in step i) is temporarily reduced while the secondary flow of the tobacco in step v) is returned to the first metal detector in step v).

6. The method according to any one of claims 1 to 5, wherein the first metal detector is a gravity-fall metal detector.

7. The method according to claim 6, wherein the first metal detector comprises a throat portion through which the flow of shredded tobacco falls, and the throat portion comprises a diverter member that is movable to redirect the flow of shredded tobacco to the secondary flow in step ii).

8. The method according to any one of claims 1 to 5, wherein the first metal detector is a pneumatically supplied metal detector.

9. The method according to claim 8, wherein the first metal detector comprises a throat portion through which the flow of shredded tobacco is carried by an airflow, and a movable diverter member is provided to redirect the flow of shredded tobacco to the secondary flow in step ii).

10. The method according to any one of claims 1 to 9, wherein the second metal detector is a gravity-fall metal detector.

11. The method according to claim 10, wherein the second metal detector comprises a throat portion through which the secondary flow of the shredded tobacco falls, and the throat portion comprises a movable diverter member that redirects the secondary flow of the shredded tobacco to the tertiary flow in step iv).

12. The method according to any one of claims 1 to 9, wherein the second metal detector is a pneumatically supplied metal detector.

13. The method according to claim 12, wherein the second metal detector comprises a throat portion through which the secondary flow of the shredded tobacco is carried by an airflow, and a diverter member is provided which is movable to redirect the secondary flow of the shredded tobacco to the tertiary flow in step iv).

14. The method according to any one of claims 1 to 13, wherein the tertiary flow of the shredded tobacco having the metal contaminant is sent to waste.

15. The method according to any one of claims 1 to 13, wherein the tertiary flow of the shredded tobacco having the metal contaminant passes through a third metal detector and is passed through at a third flow rate smaller than the second flow rate.

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