Method and apparatus for batchwise gravimetric dosing

Abstract

The invention relates to a method and an apparatus for batchwise gravimetric dosing of bulk material of a batch C from a storage hopper (9) into a collection, mixing or reaction vessel (21) by means of a dosing weigher (1), wherein the dosing weigher (1) is subjected to an overpressure of a process gas (18) during filling from the storage hopper (9) and during dosing into the collection, mixing or reaction container (21). In order to ensure high dosing accuracy while at the same time meeting increased containment requirements, the method according to the invention and the apparatus according to the invention are provided.

Description

[0001] Description

[0002] Title of the invention

[0003] Method and apparatus for discontinuous gravimetric dosing of bulk material

[0004] field of technology

[0005] The invention relates to a method for discontinuous gravimetric dosing of bulk material of a batch from a storage container into a collection, mixing or reaction container by means of a dosing scale.

[0006] Furthermore, the invention relates to a device for the discontinuous gravimetric dosing of bulk material of a batch from a storage container into a collection, mixing or reaction container by means of a dosing scale mounted on force transducers with a weighing container and a dosing device as well as an evaluation and control device, wherein the dosing scale is connected to the storage container via a filling line for its feeding and to a collection, mixing or reaction container for dosing the bulk material.

[0007] State of the art

[0008] In industrial manufacturing and processing, bulk materials are often added to the process gravimetrically. Typically, the bulk material, stored in a container, is fed batchwise into a dosing and weighing device and, after weighing, transferred to a collection, mixing, or reaction vessel. Precise adherence to the batch quantity is essential for obtaining high-quality products at the end of the process.

[0009] To minimize unwanted emissions into the environment during the weighing and dosing of bulk materials and to protect the bulk material from environmental influences that could alter its properties, the use of fully or largely closed systems is common practice. The aim is to meet containment requirements, i.e., to prevent both the escape of bulk material particles from the dosing and weighing device and the ingress of unwanted substances into the dosing and weighing device. For example, in the production of lithium-ion batteries, various active materials such as lithium, manganese, nickel, cobalt, etc., are dosed and mixed, and these are classified as hazardous to health depending on their concentration.At the same time, these materials sometimes possess highly hygroscopic properties, posing a risk that their chemical properties may change adversely when they absorb moisture from the environment, consequently impairing the quality of the final product. Closed systems offer a solution here, but have the disadvantage of amplifying the influence of pressure fluctuations during filling of the dosing and weighing device on the measurement result, which in turn affects dosing accuracy.

[0010] From EP 3491 347 B1, a dosing and weighing device for bulk materials is known, which, except for the inlet and outlet openings, has an externally airtight housing. Inside the housing are a weighing platform with a weight sensor for detecting the batch weight and a differential pressure sensor that detects the pressure difference between areas located upstream of the weighing platform and areas located downstream. For weighing and dosing, the weighing platform is alternately moved between a weighing position, in which the product flow between the inlet and outlet openings is interrupted, and a dosing position, which allows the product flow between the inlet and outlet openings. If the differential pressure sensor detects a pressure difference, a control unit computationally corrects the measured value detected by the weight sensor depending on the existing differential pressure.This procedure represents a direct intervention in the weighing result, which may prove problematic with regard to the calibration capability of the device.

[0011] Furthermore, EP 0644406 A1 discloses a device for the gravimetric dosing of bulk materials, comprising a weighing container supported by load cells. The container is filled with bulk material from a storage hopper, and a reaction or mixing vessel is filled from the weighing container via a discharge device. A pressure sensor inside the weighing container monitors the pressure within the container. The device is controlled by weighing electronics based on the measurement signals received from the load cells and the pressure sensor. Measurement results are only transmitted to the weighing electronics when the pressure in the weighing container reaches a specific limit, in particular atmospheric pressure. In this way, measurement results that are unusable due to pressure fluctuations are disregarded, leading to increased dosing accuracy. Since the measurement results remain unaltered, the device is inherently verifiable.

[0012] Description of the invention

[0013] Against this background, the invention is based on the objective of providing a method and a device for gravimetric dosing of bulk materials, which is characterized by high dosing accuracy and at the same time meets increased containment requirements.

[0014] This problem is solved by a method for the discontinuous gravimetric dosing of bulk material of a batch C from a storage container into a collection, mixing, or reaction vessel using a dosing scale, wherein the dosing scale is pressurized with a process gas during filling from the storage container and dosing into the collection, mixing, or reaction vessel, comprising the following process steps: a) filling the dosing scale from the storage container to an initial fill level, b) equalizing the pressure between the inside of the dosing scale and the surrounding environment, c) determining an initial weight value Gj ed) weighing batch C at the initial fill level in the dosing scale, d) creating an overpressure in the dosing scale relative to ambient pressure by introducing a process gas into the dosing scale, e) dosing batch C from the dosing scale into the collection, mixing, or reaction vessel, f) equalizing the pressure between the inside of the dosing scale and the surrounding environment, g) determining a second weight value Gj Z h) Determining the weight G of batch C by weighing, at a second fill level in the dosing scale after dosing has taken place, by calculating the difference between the weight values ​​Gj. e and Gj Z , i) Generating an overpressure in the dosing scale relative to the ambient pressure by introducing a process gas into the dosing scale.

[0015] Furthermore, this task is solved by a device of the type described above, which is designed to perform the above-mentioned process steps a) to i).

[0016] Advantageous further training opportunities arise from the sub-requirements.

[0017] The invention is based on the concept of keeping the bulk material to be dosed under a process gas cover for most of the dosing process. The dosing scale is only briefly and controllably opened to the surrounding environment before and after weighing to determine relevant weight values, i.e., pressure equalization is performed. In this way, it is possible to avoid pressure influences that could negatively affect the measurement result and to meet the inherently conflicting requirements of high accuracy of the weighing result on the one hand and containment requirements to protect the operating personnel and the bulk material on the other. The measurement result remains unaffected, so that any required calibration of the inventive method and device is not compromised.Advantageously, at the beginning of the inventive process, it is checked whether the quantity of bulk material currently present in the weighing container is sufficient for the dosing to be carried out, and if necessary, filling is initiated to support a smooth and efficient process. The minimum quantity of bulk material to be made available in a dosing section for a batch or sub-batch is determined by the difference between a weight-related maximum fill limit F. ma x of the dosing scale and a weight-related minimum filling limit F m in-

[0018] To minimize the time required for pressure equalization with the environment and to ensure high dosing accuracy, an advantageous embodiment of the invention provides for dosing the majority of the batch until a predetermined pre-shutdown value is reached by introducing process gas under pressure, and only the remaining quantity is dosed when the pressure ratio between the interior of the dosing scale and the surrounding environment is balanced. Since the pre-shutdown value is detected under masking with process gas, suitable parameterization of the pre-shutdown value is necessary to ensure that the actual batch quantity has not yet been exceeded when the pre-shutdown value is reached.

[0019] The pre-shutdown value can, for example, be a percentage value based on the weight of the total batch. Pre-shutdown values ​​of 90% or higher, preferably 95%, and particularly 98%, are preferred according to the invention, as the aforementioned advantages become clearly apparent.

[0020] Preferably, reaching the pre-shutdown value serves as a trigger for switching from coarse to fine flow when dosing a batch or the last partial batch. By appropriately controlling the discharge device, the flow rate for dosing in the fine flow can be reduced to a value that is only a fraction of the flow rate in the coarse flow. In this way, the remaining quantity of the batch can be dosed with high precision. Since the remaining quantity to be dosed is usually in the range of a few percent by weight, fine flow dosing does not result in any significant increase in dosing time. On the other hand, dosing the majority of a batch in the coarse flow enables very efficient and therefore economical dosing.

[0021] The invention is suitable for feeding a batch to be dosed into the collection, mixing, or reaction vessel in a single dosing operation, provided the weighing vessel is sufficiently large to accommodate the entire batch. This enables efficient and highly accurate dosing.

[0022] Nevertheless, the invention is capable of dispensing a batch C into a collection, mixing, or reaction vessel in several recursively successive dosing sections, with a partial batch being dispensed in each dosing section until the quantity of the entire batch is reached. This has the advantage that even larger batches can be dispensed with relatively little mechanical effort.

[0023] In an advantageous embodiment of the invention, when dosing in partial batches, the partial weights of each batch are determined individually and added together. For each weighing required to determine the partial weights, the supply of process gas is briefly interrupted for the duration of the weighing process, and pressure equalization is performed. In this way, high weighing accuracy is ensured even when dosing in partial batches.

[0024] In the aforementioned context, it proves particularly advantageous to meter the individual sub-batches in the coarse flow under pressure with process gas until the pre-shutdown value is reached, and only the last sub-batch in the fine flow. This ensures a high metering rate and minimizes the detrimental effects of pressure during the weighing of the last sub-batch.

[0025] Without limiting ourselves to this, the invention is explained in more detail below with reference to an embodiment illustrated in the drawing, whereby further features and advantages of the invention become apparent. Brief description of the drawings

[0026] It shows

[0027] Fig. 1 shows a schematic representation of a device according to the invention, and

[0028] Fig. 2 shows a flowchart illustrating the process of a method according to the invention.

[0029] Description of the embodiments

[0030] Fig. 1 shows a schematic representation of a device according to the invention. The device 1 serves to meter two substances of different properties during the manufacturing process of a product. The following descriptions apply analogously to devices in which only one or more than two substances are to be metered.

[0031] The device according to the invention has a dosing scale 1 with a weighing hopper 2, discharge element 3, and discharge outlet 4 for each substance. The discharge element 3 can, for example, be a metering screw, a vibrating feeder, or the like. The dosing scales 1 are mounted on load cells 5, by means of which a weight value can be determined for each of the dosing scales 1 at any given time. The dosing scales 1 each form a closed system that is largely gas-tight from the environment, or at least dust-tight. Advantageously or optionally, the device has a differential pressure sensor 6 for each dosing scale 1 in order to monitor the pressure equalization and detect the differential pressure between the interior of a dosing scale 1 and its environment. The measured values ​​of the load cells 5 and the differential pressure sensors 6 are transmitted via the data lines 7 to an electronic evaluation and control unit 8 for further processing.The evaluation and control unit 8 outputs signals to the various functional units, such as the discharge element 3, shut-off devices, valves, flaps, and the like, depending on the measured values, for controlling the device and the method according to the invention. Each dosing scale 1 is assigned a storage container 9 for filling the weighing containers 2, and different substances can be stored in different storage containers 9. The storage containers 9 are each connected to the dosing scale 1 via a filling line 10 and a shut-off device 11. A compensator 12 is integrated into the filling line 10 to decouple the dosing scale 1 from the storage container 9 or the filling line 10, thus preventing force bypasses.

[0032] To vent the dosing scale 1 during filling, a venting line 13 with a shut-off device 14 is connected to the dosing scale 1 via an intermediate compensator 12, which vents to the environment via a filter 15.

[0033] Furthermore, a pressure line 16 leads into the interior of the dosing scale 1. This line, via a three-way valve 17, can be alternately pressurized with a process gas 18, such as air, dry gas, inert gas, or the like, relative to the environment of the dosing scale 1, or opened to allow pressure equalization 19 between the interior of the dosing scale 1 and its environment. The pressure line 16 also includes a filter 20 and a compensator 12 for compensating for force shunts. Alternatively, the process gas 18 and the pressure equalization 19 can be supplied or carried out using separate lines and valves.

[0034] The discharge element 3 of the metering device 1 terminates in a material discharge 4 with a quick-closing flap 26, which is connected via pipelines to a collection, mixing, or reaction vessel 21 that receives the metered bulk material. Compensators 12 are inserted into the pipelines to decouple the metering scale 1 with discharge element 3 and material discharge 4 from the collection, mixing, or reaction vessel 21 for weighing purposes. A vent line 22 is provided for venting the collection, mixing, or reaction vessel 21 during metering; this line leads via the filter 14 to the environment surrounding the metering scale 1. The metered batches are drawn off from the collection, mixing, or reaction vessel 21 via a discharge line 23 with a shut-off valve 24.

[0035] The inventive method for the discontinuous gravimetric dosing of bulk material of a batch C is the subject of the flow diagram shown in Fig. 2. As can be seen from the flow diagram, the batch C can be dosed all at once in a single batch Ci with weight Gj (with i=1), provided that sufficient bulk material is present in the weighing container 2. Otherwise, the bulk material can be dosed in several sub-batches Ci with sub-weights Gi (with i=1 to n, where n=number of sub-batches). The determination of the weight Gi or the individual sub-weights Gi is carried out in each case by determining a first weight value Gi. e and a second weight value Gi Z , where the index i refers to the number of batch Ci or sub-batch Ci, the index e to the state before dosing, and the index z to the state after dosing of a batch Ci or sub-batch Ci. The difference between the two weight values ​​Gie and Gi Z, yields the weight Gi of a batch Ci or the individual weight Gi of a sub-batch Ci.

[0036] Before the start of the individual process steps, the device is in a rest state, characterized by a veil of process gas 18. For this purpose, the shut-off devices 11 and 14 as well as the quick-closing flap 26 are closed and a substantially constant overpressure relative to the ambient pressure is generated by feeding process gas 18 into the dosing scale 1.

[0037] From this resting state, the procedure shown in Fig. 2 first checks whether there is sufficient bulk material in the weighing hopper 2 of the dosing scale 1 to dose an entire batch Ci or partial batch Ci. For this purpose, the current weight value Gakt of the batch Ci or partial batch Ci is determined by the load cells 5 and evaluated and controlled by the evaluation and control unit 8 with a maximum fill limit F. maThe corresponding weight value was compared. The test shows that the maximum fill limit F ma If the fill level x in weighing container 2 has not yet been reached, the evaluation and control unit 8 issues a refill request, which causes the shut-off valves 11 and 14 to open and leads to the filling of weighing container 2 from the storage container 9 with simultaneous venting via line 13. These steps are carried out under a veil of process gas 18, thus protecting the bulk material from external influences. Inaccuracies in determining the fill level F caused by the veiling are minimized. ma The x values ​​can be accepted, as they have no influence on the accuracy in determining the batch weight Gi or the individual weights Gi of the sub-batches Ci. If the maximum fill limit F in weighing container 2 is reached... maWhen x is reached, the shut-off devices 11 and 14 are closed again, and the supply of process gas 18 is interrupted by switching the three-way valve 17. Pressure equalization 19 between the interior of the dosing scale 1 and its environment is carried out by opening the line 16. The differential pressure sensor 6 detects when uniform pressure conditions are reached inside and outside the dosing scale 1, and this is registered by the evaluation and control unit 8, triggering the determination of an initial weight value Gj. e at the time before dosing. In embodiments according to the invention without a differential pressure sensor 6, a certain time can also be waited during which pressure equalization is expected to occur. The first weight value Gj detected by the load cells 5 e is stored in the evaluation and control unit 8.

[0038] Immediately afterwards, the pressure equalization 19 is interrupted by switching the three-way valve 17 again and process gas 18 is fed into the dosing scale 1 under overpressure.

[0039] Subsequently, under overpressure, the dosage of batch Ci or partial batch Ci begins in the collection, mixing or reaction vessel 21. By activating the discharge device 3, the bulk material is conveyed in a coarse flow to the material discharge 4, where, after opening the quick-closing valve 26, it enters the collection, mixing or reaction vessel 21.

[0040] During dosing, the current weight value G is continuously measured by the load cells 5. aThe unit determines the total weight (Gt) of the already dosed bulk material and then compares it to the target weight (Gsoii) of the total batch C to be dosed. It checks whether a predefined pre-shutdown value has already been reached. The pre-shutdown value can be a percentage of the total batch C's weight (G), for example, 90%, 95%, or 98%.

[0041] As long as the pre-shutdown value has not yet been reached, the continuous weight determination continues to check whether a weight-related minimum fill limit F exists in weighing container 2. m in is reached. The minimum fill limit F m The operator must parameterize the system so that, taking into account the pressure influence from the veiling, the quantity of bulk material in the weighing container 2 remains below the minimum fill limit F. m in is sufficient to be able to dispense the entire batch C without further refilling of the weighing container 2.

[0042] The test to determine whether the pre-shutdown value or the minimum fill limit F has been reached. m This process is carried out under a masking with process gas 18, thus protecting the bulk material from external influences. Inaccuracies in determining the pre-shutdown value or the fill limit F are caused by the masking. m However, these can be accepted, as they have no influence on the accuracy in determining the batch weight Gj or individual weights Gj of the sub-batches Ci.

[0043] Does the continuous testing lead to the result that the minimum fill limit F m Once the maximum fill level is reached, the evaluation and control unit 8 issues a refill request, which leads to the refilling of the weighing container 2 from the storage container 9. This is part of the previously described continuous determination of the current weight value Gakt during filling and its comparison with the maximum fill limit F. max ensures sufficient filling of the weighing container 2 for the next partial batch Ci.

[0044] The described process is repeated with the next partial batch of Ci until continuous monitoring during dosing shows that the minimum fill limit F is reached before the minimum fill limit is reached. m The pre-shutdown value is reached in weighing container 2. With each repetition, the partial weight Gi of a partial batch Ci is added to the previously determined partial weights Gi to G of the partial batches Ci to CM. For example, a pre-shutdown value of 98% would mean that 98% of the entire batch C has already been dosed into the collection, mixing, or reaction vessel 21, and the remaining quantity in weighing container 2 is sufficient to complete the dose of batch C.

[0045] Once the pre-shutdown value is reached, the system switches to dosing the remaining batch into the fine stream via the discharge device 3. For this purpose, the supply of process gas 18 is again interrupted by switching the three-way valve 17, and pressure equalization 19 between the interior of the dosing scale 1 and its surroundings is carried out by opening the line 16. The differential pressure sensor 6 detects when uniform pressure conditions inside and outside the dosing scale 1 are achieved, and this is registered by the evaluation and control unit 25.

[0046] Subsequently, the fine stream is dosed into the collection, mixing or reaction vessel 21 while maintaining pressure equalization, and a second weight value Gj is continuously recorded by the load cells 5. Z The weight (Gj) is determined in the evaluation and control unit 8. St of the batch C dosed into the collection, mixing or reaction vessel 21 from the difference of the two weight values ​​Gj e and Gj Z and in the case of several partial batches Cj, additionally determined from the sum of the already dosed individual weights Gj and compared with the target weight G so ii compared to the batch C to be dosed.

[0047] Upon reaching the target weight G S0 The dosing in the fine stream is stopped, and by switching the three-way valve 17 again, the pressure equalization 19 is interrupted, and process gas 18 is fed into the dosing scale 1 under overpressure. The device is thus back in its resting state after the dosing process is complete.

Claims

Claims 1. A method for the discontinuous gravimetric dosing of bulk material of a batch C from a storage container (9) into a collection, mixing or reaction vessel (21) by means of a dosing scale (1), wherein the dosing scale (1) is pressurized with a process gas (18) during filling from the storage container (9) and dosing into the collection, mixing or reaction vessel (21), comprising the following process steps: a) filling the dosing scale (1) from the storage container (9) to a first fill level, b) equalizing the pressure between the inside of the dosing scale (1) and the surroundings of the dosing scale (1), c) determining a first weight value Gj ed) weighing batch C at the first fill level in the dosing scale (1), d) generating an overpressure in the dosing scale (1) relative to the ambient pressure by introducing a process gas (18) into the dosing scale (1), e) dosing batch C from the dosing scale (1) into the collection, mixing or reaction vessel (21), f) equalizing the pressure between the inside of the dosing scale (1) and the surroundings, g) determining a second weight value Gj Z of batch C by weighing, at a second fill level in the dosing scale (1) after dosing has taken place, h) Determine the weight G of batch C by calculating the difference between the weight values ​​Gj e and Gj Z i) Generating an overpressure in the dosing scale (1) relative to the ambient pressure by injecting a process gas into the dosing scale (1).

2. Method according to claim 1, characterized in that, before carrying out method step a), it is checked whether the actual fill level in the dosing scale (1) exceeds a maximum fill limit F ma x has been reached and filling from the storage container (9) up to at least the maximum fill limit F ma x if the maximum fill limit F max has not been reached.

3. Method according to claim 1 or 2, characterized in that, during the execution of method step e), the dosing - in a first partial step up to a pre-shutdown value under overpressure by injecting process gas (18) and - in a second step, the remaining quantity is dosed after pressure equalization under continuous weighing until the weight Gi of batch C is reached.

4. Method according to claim 3, characterized in that the pre-shutdown value is at least 90 wt.% of the weight G of the entire batch C, preferably at least 95 wt.%, most preferably at least 98 wt.% 5. Method according to one of claims 1 to 4, characterized in that the dosing of the entire batch C is carried out in several sub-batches Ci to Cj with the individual weights Gi to Gj.

6. Method according to claim 5, characterized in that the individual weight Gj of a partial batch Ci is determined by weighing. - a first weight value (Gj) before dosing e the partial batch Ci is determined in the dosing scale (1) at the first fill level, and - after dosing, a second weight value Gi Z the partial batch Ci is determined in the dosing scale (1) at the second fill level, and - the individual weight Gi of the sub-batch Ci from the difference of the weight values ​​Gi e and Giz is determined, whereby - before determining the first weight value Gj e and second weight value Gj Z In each case, pressure equalization is carried out with the surroundings of the dosing scale (1) and - after determining the first weight value Gj e and second weight value Gj Z In each case, an overpressure is generated by feeding a process gas (18) into the dosing scale (1).

7. Method according to claim 5 or 6, characterized in that, to determine the total weight G of batch C, the individual weight Gj of sub-batch Cj is added to the sum of all previously determined individual weights Gi to GM.

8. Method according to one of claims 5 to 7, characterized in that, prior to dosing a partial batch Ci, it is checked whether the sum of all individual weights Gi to GM of the partial batches Ci to C and the first weight value Gj ethe partial batch Ci is smaller than the total weight G of the total batch C to be dosed or larger.

9. Method according to claim 8, characterized in that the dosage of the entire sub-batch Ci into the collection, mixing or reaction vessel (21) is carried out under overpressure by feeding in process gas (18), if the sum of all individual weights Gi to GM of the sub-batches Ci to CM and the first weight value Gie of the sub-batch Ci is less than the total weight G of the total batch C to be dosed.

10. Method according to claim 8, characterized in that the dosing of the whole or a part of the sub-batch Ci is carried out while simultaneously weighing, with pressure equalization between the interior of the dosing scale (1) and the environment of the dosing scale (1) until the total weight G of the total batch C is reached, if the sum of all individual weights Gi to GM of the sub-batches Ci to CM and the first weight value Gie of the sub-batch Ci is greater than the total weight G of the total batch C to be dosed, 1. Device for discontinuous gravimetric dosing of bulk material with - a dosing scale (1) mounted on load cells (5) comprising a weighing container (2) and a dosing device (3), - a storage container (9) which is connected to the dosing scale (1) via a filling line (10) for the purpose of filling the dosing scale (1), - a collection, mixing or reaction vessel (21) for receiving the metered bulk material, and - an evaluation and control unit (8), wherein - the dosing scale (1) has a connection (16) for supplying process gas (18) under pressure and a connection (16) for carrying out pressure equalization between the interior of the dosing scale (1) and the environment of the dosing scale (1), characterized in that the evaluation and control device (8) is configured to carry out a method according to one of claims 1 to 10.

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