PROCESS MONITORING AND CONTROL OF FILTRATION THROUGH FILTRATE MEASUREMENTS

Description

[0001] The application relates to solutions for monitoring, process control, and surveillance of solid filtration, in particular the washing process of this solid in a filtration system. This solid is a free-flowing material, typically the result of crystallization or precipitation in the form of granules or powder, and is also commonly referred to as bulk solid.

[0002] The usual production process for the manufacture of solid active ingredients is divided into the following steps, starting with crystallization or precipitation: 1. Crystallization / precipitation, also called solid formation: In this step of the production process, the solid is suspended in mother liquor, 2. Filtration: the solid is separated from the mother liquor in a filter apparatus for pressure, vacuum or centrifugal filtration (also referred to collectively as filter apparatuses below).

[0003] Common filter devices include Nutsche filters, centrifuges, drum or disc filters, etc., but also porcelain or glass funnels with flat sieve bottoms or frits, or other porous filter elements. When using a Nutsche filter, for example, the suspension to be filtered is transferred to the device, the filtrate is separated from the solids under pressure or vacuum, and then discharged. A Nutsche filter is used, for example, in Fig. 1 shown schematically.

[0004] Typically, step 3 of a solids filtration process involves washing the filter cake in a displacement and / or resuspension wash process to "wash clean" the solids, i.e., to achieve the required quality characteristics for the solids. In this step, specified amounts of solvent (fresh or recycled) are evenly distributed over the filter cake in a specified number of wash steps. The number of washes depends on the required purity of the solids. Typically, the filter apparatus is not opened between wash steps, so sampling the filter cake is not possible for this and other reasons.

[0005] In step 4, the solid is dried. This is usually done either on the pressure filter (nutsche dryer) or in a separate drying apparatus.

[0006] Between steps 3 and 4 there may be formulation steps, e.g. addition of plasticizers, stabilizers, etc.

[0007] Typically, the filtration and washing process is viewed as a "black box" that is optimized through trial and error (Ruslim et al., Chemical Engineering Science 62 (2007) 3951-3961). Ruslim et al. addresses the problem of heterogeneous distribution of the washing agent in a filtration and washing process. He investigates online measurement of the filter cake, but prefers offline measurement, stating that filter cake measurements are better than filtrate flow measurements. He uses filtrate flow measurements only for a complete check for impurities.

[0008] Louhi-Kultanen et al. describe a method and measuring apparatus for monitoring a filtration and washing process using a Raman spectrometer, which also performs a measurement in the filter cake. This can be a local measurement (on the cake surface) or an invasive measurement method (immersion optics) that damages the filter cake. Furthermore, this method does not allow for trace measurements, as the measurement limit of a Raman spectrometer is 1%. Louhi-Kultanen et al. There is no indication of a measurement of the filtrate flow (LOUHI-KULTANEN et al.: "Filter cake washing: Partial dissolution of organic particles and real-time monitoring based on Raman spectroscopy", SEPARATION AND PURIFICATION TECHNOLOGY, ELSEVIER SCIENCE, AMSTERDAM, NL, Vol. 59, No. 3, 4 February 2008 (2008-02-04), pages 270-276, XP022453823, ISSN: 1383-5866, DOI: 10.1016 / J.SEPPUR.2007.06.017).

[0009] According to the current state of the art, quality control of the solids while they are still in the filter apparatus (i.e. points 2 and 3) does not take place in industrial filtration and washing processes. As a rule, analysis is only carried out after completion of step 4. Typically, solids samples are taken from the dried filter cake and analyzed in the laboratory, usually using chromatography. It is generally assumed in the professional world that the quality of the filter cake can only be determined by direct filter cake analysis. As a result, the monitoring of the quality of filter cakes in the filtration process has not been affected by advances in online measurement technology to date. If the checked filter cake does not meet the specification, the dried product must be reprocessed, discarded, or blended. The amount of washing medium and the washing strategy (displacement, countercurrent, orMash wash) is typically determined experimentally once and validated by analysis of the filter cake.

[0010] If early quality control of the solid were possible, immediate action could be taken in the event of poor quality, for example, by performing an additional wash (assuming the impurities can be washed out and are not trapped in the crystal). In the case of very good quality, washing or the washing medium, and thus solvents or even water, could be omitted. Both options would immediately enable massive time and cost savings.

[0011] Kopra et al. discloses a method and measuring apparatus for monitoring the filtration and washing process in a pulp washing plant for the paper industry using a refractometer. In this method, the refractive index of the washing medium fed into and out of the filter apparatus is determined with the aim of determining whether the washing medium can be reused. The washing agent supply is adjusted based on the measured values ​​to avoid undesirable washing losses. Kopra et al. does not provide any information about using these measured values ​​to draw conclusions about the progress of the washing process or the quality of the filter cake. Given the filter apparatus, this would not be possible, as no separate measurement is available from the respective washing zones. (Kopra et al. "Application of the refractometer in the measurement and monitoring of brown stock washing, doctoral dissertation", January 1, 2015 (2015-01-01), XP055374630, URL: https: / / aaltodoc.aalto.fi / bitstream / handle / 123456789 / 15451 / is bn9789526061344.pdf?sequence=l&isAllowed=y).].

[0012] EP0009527A1 describes an automated solution for intermittent washing, in which the change in conductivity is monitored over a predefined "on" time. A timer is used to measure the time during which the conductivity cell probe is washed with highly conductive wash fluid for a period sufficient to establish an initial equilibrium. Another timer controls the wash period(s) or "on" and "off" periods. The method requires wash interruptions of a minimum duration. To monitor the wash process, the measured value is compared with a predefined value.

[0013] US Patent No. 3,3815,745 A describes an apparatus with cake washing degree sensors. To monitor the washing process, the difference between the conductivity of the washing liquid in the distributor and the used washing liquid in the pipe is measured. The difference between the conductivity of the fresh washing liquid and that of the drained used washing liquid decreases during the cake washing step. Once the desired cake washing degree is reached, the washing process is interrupted.

[0014] The task was therefore to provide a solution for the monitoring of filtration and washing processes that can be used for online monitoring, allows conclusions to be drawn about the course of the process, in particular about the quality of the filter cake, does not require an interruption of the washing process for the quality control of a filter cake, and does not cause damage to the filter cake.

[0015] The problem was solved by using measurement technology for measuring the filtrate stream from a filter apparatus. Parameter values ​​of the filtrate stream are measured over the washing process, and their changes over time are analyzed. The parameters of the filtrate stream are selected from the group comprising refractive index, density, ultrasonic propagation time, redox potential, as well as spectroscopic cumulative properties and / or substance-specific properties of one or more main or secondary components. Surprisingly, it was found that this computer-implemented analysis, during filtration, allows conclusions to be drawn about the progress and quality of the filtration and washing process. The invention is described in the appended set of claims.

[0016] The first subject matter of the application is a method for monitoring and controlling a filtration and washing process of a bulk solid in a filter apparatus for cake filtration according to claim 1 and the claims dependent thereon.

[0017] Suitable measurable parameters of the filtrate stream within the meaning of the application include refractive index, density, ultrasonic propagation time, redox potential, and spectroscopic aggregate and / or substance-specific properties of at least one representative component in the filtrate stream (major and / or minor component), such as absorption, impedance, color, or the fluorescence signal of the filtrate. For aqueous media, pH and / or conductivity can also be used.

[0018] However, the choice of measurement method depends on the substances used in the process (especially product(s) and / or by-product(s)). Measurement of the refractive index and / or density of the filtrate during filtration and washing is particularly preferred. One or more of the above-mentioned methods can also be combined. Likewise, for quality control purposes, concentrations of (by-)components can be determined in addition to the pure measured values ​​(raw data) using previously determined calibration functions.

[0019] In a preferred embodiment of the method, a parallel recording of the refractive index and the measurement of the filtrate mass as usual in the state of the art (according to VDI guideline 2762) are carried out.

[0020] The method is suitable for monitoring both continuous and batch processes. In a continuous washing process as defined in the application, the washing medium is continuously dosed onto the filter cake so that the filter cake is evenly covered over its entire surface. In a batch process, a predefined amount of washing medium is applied to the filter cake for washing.

[0021] Preferably, the method includes computer-implemented steps for analyzing the measurement data. These steps are typically performed by an appropriately configured computer system.

[0022] For analysis, the measurement data is transferred from the measuring device(s), e.g., via a data interface (OPC, SQL, fieldbus, e.g., Profibus, Modbus, Ethernet, analog signal, etc.). The imported measurement data is stored in an archiving module, e.g., a database module, in which the measurement data and a timestamp (t), as well as, preferably, all information for uniquely identifying the production batch, are stored.

[0023] The database module is connected to an evaluation system. An evaluation system, as defined in the application, is a measurement control system or a computer configured to perform the process steps.

[0024] A further subject of the application is therefore a computer system for controlling a filtration and washing process of a bulk solid in a filter apparatus for cake filtration, the computer system comprising: an archiving module configured to store parameter values ​​of a filtrate stream with a time stamp t transmitted from at least one measuring device in or at a filtrate outlet of the filter apparatus over the time of the filtration and washing process and for forwarding these to an evaluation system, the evaluation system which is connected to the archiving module and is configured to carry out the method defined in the attached set of claims in order to analyze changes in the parameter values ​​over time and to determine the end of the filtration and washing process and / or the effectiveness of the washing process from this change analysis, an element for displaying the end of the filtration and washing process and / or the effectiveness of the washing process, and / or an element for issuing a command to end the filtration and washing process.

[0025] Typically, the evaluation system is connected to a system for controlling a washing medium supply and configured to issue commands to continue or stop the washing medium supply.

[0026] Particularly preferably, the supply of the washing medium is started and stopped with the aid of the evaluation system, or a new washing process is initiated by the evaluation system issuing the corresponding command to a controllable washing medium supply (e.g., valves). Typically, the washing medium supply is controllable via one or more control elements for controlling the washing medium supply (e.g., a process control system).

[0027] In a special embodiment of the method, a limit value analysis is carried out.

[0028] When considering limit values ​​for the raw data or the concentration values ​​calculated from them, the measurement data analysis typically includes the following steps: 1. Transfer of the measured values ​​of the monitored parameters of the filtrate flow to the evaluation system over a predefined period of time of the filtration and washing process at least until To reach a predefined parameter value, previously determined experimentally or from experience, that corresponds to the desired quality of the filter cake. If this value is reached, it can be assumed that the filter cake has been washed in accordance with the specification; the washing process can be terminated. 1.1. In a continuous When the parameter value from 1 is reached, the supply of the washing medium is stopped; the filter cake is further processed. 1.2. In a BatchThe end of the washing process is communicated to the process. For the next batch wash of another filter cake, the detergent quantity can be adjusted (typically reduced) according to the predefined parameter from 1. The method for adjusting the detergent quantity is described in more detail below. 2. If the predefined parameter value (see 1.) not reached, it can be assumed that the filter cake was not washed optimally; the washing process is continued by. 2.1. In a continuous process the detergent supply is extended. 2.2. In a Batch Process, an additional wash can be added for the already washed cake. In the next batch with a new filter cake, the amount of detergent can be increased.

[0029] If the predefined parameter value is not achieved despite the measures described (see 2.1 or 2.2), purification by displacement of the mother liquor alone is insufficient. Typically, the washing strategy is changed; for example, a slurry wash (suspension wash) or a combination of displacement and slurry washes can be performed.

[0030] The measurement data analysis includes the following steps for a change analysis of the raw data or the concentration values ​​calculated from it: 3. Transfer of the measured values ​​of the monitored parameters of the filtrate stream to the evaluation system over a predefined period of the filtration and washing process. Calculating the first derivative of a curve generated from the measured values. If the first derivative (=slope) of the measurement curve no longer changes or is below a predefined value, the following measures can be taken: 3.1. In a continuous process, the supply of the washing medium is stopped. Depending on the limit value assessment from 1. (reached / not reached), further measures are taken if necessary, e.g., changing the washing strategy. 3.2. In a batch process, the end of the washing process is communicated. For the next washing step, the amount of detergent is adjusted (reduced or increased) if necessary, according to the limit value assessment from 1.

[0031] In a particular embodiment of the method, the quality of the laundry is determined from the measured data using one or more additional data analyses. For this purpose, the slope of the measured value curve (between two measured values, e.g., between measured values ​​at timestamps t-1 and t) is preferably calculated in section C. The calculated slope is compared with a predefined, permissible value range (working range) for the slope; this was typically determined from previous washes with satisfactory quality. Possible deviations and thus disruptions in the washing process or in the effectiveness of the laundry occur if the slope leaves the working range during the wash cycle.

[0032] Possible malfunctions occur when: a) The gradient is too shallow, caused, for example, by cracks in the filter cake. b) The gradient is uneven, caused, for example, by holes or channels in the filter cake.

[0033] By observing the gradient, process understanding and monitoring becomes possible, allowing appropriate countermeasures to be initiated. These can include, for example, monitoring the (under)saturation of the filter cake, checking the filter media used for defects, smoothing the filter cake, etc.

[0034] In general, the gradient is equivalent to the washing speed ΔConc / ΔTime or ΔMeasurement signal / ΔTime, where Δ=change. This allows for process optimizations, e.g. a) An increased gradient means an increased washing speed, which can be achieved, for example, by increasing the pressure. This results in a shorter washing time, thereby reducing the cycle time. b) A decreased gradient means an increased washing time. This increases the diffusion time of the washing medium into the solid pore system, which can increase the washing effectiveness.

[0035] If faults are detected, the system issues a warning and, if necessary, terminates the washing process. - Effectiveness of the laundry

[0036] In a particular embodiment of the method, the effectiveness of the washing process is determined using the following steps: a) A section C is determined from the measurement curve (see Figure 2), in which the measurement curve changes with a gradient of at least or equal to a predefined value X. b) A gradient value is calculated as the average gradient over section C from a), c) A variability of the gradient in section C from a) is calculated, d) If the gradient value is within the predefined working range and the variability of the gradient is less than X, the washing process is running effectively, the washing process is continued until the gradient value reaches a predefined value for sufficient washing quality, e) If the gradient value is ≤ a predefined minimum value (flat gradient) and / or the variability of the gradient value is high, a gradient formation or discontinuity in the cake is to be suspected. A warning is issued and / or the filtration pressure is increased.

[0037] The determination of the optimal washing ratio is carried out by analyzing the washing curve (measured value via washing ratio Fig. 3 or5 ) for the following batches. If the measured value no longer changes, the optimal washing ratio, i.e. the optimal amount of detergent, has been exceeded.

[0038] In a particular embodiment of the method according to the invention, the amount of washing medium consumed for the washing process is determined up to the calculated end of the washing process and defined as the optimal amount of washing medium for the next washing process. In the case of a batch washing process, the new amount of washing medium is added to wash the filter cake. In a continuous process, the amount of washing medium is calculated online, and, for example, a warning is issued if the optimal amount of washing medium is exceeded.

[0039] The measured values ​​can be evaluated online as well as subsequently viewed / interpreted in their entirety (process optimization).

[0040] In particular, by measuring the filtrate stream from a filter apparatus for cake filtration and the subsequent analysis of the measured values ​​obtained, a product-specific validation of the quality of the filter cake in relation to the concentration of the secondary components in the filtrate stream or with the measurable sum parameter of the filtrate stream can be achieved.

[0041] The procedure described provides the following information about the progress of the process: Assessment of process progress, detection of termination / end point criteria Detection of process disturbances e.g. irregular filter cake structure Stability of the process Advice on optimising the amount of detergent

[0042] From this information, an indirect filter cake analysis is carried out.

[0043] In a first embodiment of the method according to the invention, the determination of the refractive index is used as a sum signal over the secondary components.

[0044] Using a measuring device placed appropriately in the filter device, the measured value, e.g., the refractive index in the filtrate stream, is determined online. The measuring device is preferably installed in filtrate outlet 5 – either pressure-free or, if necessary, in a pressure line (Fig. 1).

[0045] The measured value and its variation over time can be used as a quality control feature. Typically, the online measured value is compared with a previously determined calibration function between the measured value and the secondary components / product quality ( Fig. 2 ).

[0046] The application further relates to a filter apparatus comprising a washing medium supply, a filter element, a filtrate outlet, and a measuring device for measuring in the filtrate stream, as well as the system defined in the appended set of claims for controlling a filtration and washing process, wherein the measuring device is selected to measure one or more parameters such as refractive index, density, ultrasonic transit time, pH value, conductivity, redox potential, and / or spectroscopic properties of the filtrate stream. According to the invention, the measuring device is incorporated in or on the filtrate outlet. Typically, the measuring device is incorporated into the filtrate line of the filter apparatus.

[0047] Preferably, the filter apparatus additionally comprises a measuring device for measuring the filtrate mass. Typically, the filtrate mass in the filtrate collection vessel is determined / recorded using a scale. Alternatively, the filtrate mass is determined / recorded from the volume flow / mass flow using a flow meter.

[0048] Preferably, the measurement(s) of the filtrate flow parameter described in the claims is combined with a measurement of the filtrate mass.

[0049] Suitable filter devices include, but are not limited to, Nutsche filters, centrifuges, Buchner funnels, frits, filter crucibles, drum filters, disc filters, belt filters and filter presses. Example A for the qualitative assessment of a solids wash:

[0050] In a first set of experiments, the analysis of wash filtrates in a displacement wash was investigated using the refractive index and is exemplified using the product Sivanto.

[0051] For this purpose, fractional samples were taken from the filtrate stream at defined times during filtration / washing. The refractive index was measured offline using a refractometer (Abbemat300 from Anton Paar) and compared with the refractive index of the wash solution ( Fig. 3 ). As the process progressed normally, the measured value approached the refractive index of the wash solution. Initially, the filtrate consisted of mother liquor, which is why a plateau in the refractive index curve is visible at the beginning. As the mother liquor is gradually displaced by the wash medium in the displacement wash, the refractive index decreases until it reaches a constant value. Ideally, this value is close to that of the wash medium used.

[0052] This showed that the refractive index is suitable as a sum signal to detect concentration decreases in the filtrate; deviations from the expected value in the concentration and the filtration rate per unit time can be displayed and detected.

[0053] A correlation with the quality of the filter cake must be verified on a case-by-case basis and was possible for Sivanto. Samples from the filtrate stream during washing and the filter cake after each wash (each experiment was conducted with different amounts of washing medium) were analyzed by HPLC.

[0054] In further experiments, a process refractometer was integrated into the filtrate outlet of the laboratory filtration test rig as an online measurement device. A KPatents PR-43 process refractometer with a measuring range of nD 1.32–1.53 was used. A flow-through adapter was used for the laboratory experiments. Example B for the qualitative and quantitative assessment of a solids wash for model particles: i. Experimental procedure:

[0055] The filtration and washing tests were conducted according to VDI Guideline 2762 on a 100 cm² laboratory pressure filter at 0.2 bar overpressure and room temperature. A process refractometer (Abbemat300 from Anton) was integrated into the filtrate line. The refractive index and filtrate mass were recorded with time resolution. After the test, the height and mass of the filter cake were determined.

[0056] Filtration was terminated at a filter cake saturation S of S=1. Ultrapure water was carefully layered onto the filter cake for washing, followed by washing and mechanical dehumidification. After the experiment, the refractive index of the mother liquor filtrate and the wash filtrate was determined using an Anton Paar Abbemat 300 at 23°C.

[0057] To convert the (online) determined refractive indices into NaCl concentrations and masses, a calibration curve was recorded with the offline refractometer.

[0058] Washed SiLibeads glass beads, type S0-50 µm (purchased from Sigmund Lindner GmbH), were used as model particles. The solids concentration was 400 g / kg. NaCl was used as an impurity at a concentration of 200 g / kg. The suspension quantity added was approximately 1000 g, meaning 120 g of NaCl was added to the system as dissolved impurity. 1192 g of ultrapure water was used for washing (corresponding to a wash ratio of 4.3 l water / l dry filter cake) to obtain a very clean filter cake.

[0059] The dried filter cake was resuspended in ultrapure water and stirred. After centrifugation, the refractive index of the supernatant was determined. This value corresponded to that of water. In addition, free Cl-< in the supernatant was determined to be 0 using a cuvette test. This means that the washed filter cake in this example did not contain any NaCl. iii. Experimental evaluation: • Online analytics: qualitative evaluation

[0060] When measuring filtrate mass and refractive index in parallel, the curve is shown in the experiment according to Figure 4 observed: The filtrate mass increases during filtration and washing before remaining constant during dehumidification of the filter cake at the end of the experiment. The refractive index remains constant during filtration, as only mother liquor leaves the filter cake. During the subsequent washing, the refractive index decreases from the mother liquor value to the value of the pure washing medium.

[0061] If the plateau value of the nearly pure washing medium is reached, it can be assumed that the filter cake cannot be further washed out by the displacement wash. This means that for further purification, a different washing strategy, such as slurry washing, must be considered. If the refractive index value no longer changes, the wash can be terminated.

[0062] If the above data are related to the washing ratio, the required amount of washing medium can be determined directly (see description below).

[0063] In Figure 5 The curve of the refractive index (RI) versus the wash ratio is shown. It is clearly visible that the constant measured value of the mother liquor filtrate is reduced by the increasing amount of water. A plateau value is reached at the end of the wash.

[0064] The decrease in the RI and its stabilization at a constant value indicates that no further washing effect can be achieved. This means that even with larger washing ratios, the filter cake washout effect is not further improved. This purely qualitative evaluation can be used to end the wash in this example at a washing ratio of 1.5. This directly saves time and costs for washing medium. By recording such data during operation, a sufficient data basis can be established for optimizations regarding washing time and washing medium consumption.

[0065] A quantitative evaluation can be more complex for real products. This is described below for the model product. • Online analytics: quantitative evaluation

[0066] For the quantitative evaluation of the online measurement data, the RI and the filtrate mass are plotted over time for filtration and washing (see Figure 5). For each time period, the filtrate mass and NaCl mass can be calculated from the recorded data using a calibration curve NaCl concentration-refractive index. m NaCl , 1 = m Filtrat , 1 − m Filtrat , 0 ∗ C NaCl , 1

[0067] Alternatively, the curve can be integrated as follows: The area under the curve can be determined using the trapezoidal rule, so that for each time period the related area in s*g / kg can be determined: Area in the time period: A 1 = 0.5 * ( t 1 - t 0 ) * ( c NaCl, 1 - C NaCl, 0 )

[0068] By referring to the time interval and the filtrate mass absorbed in this time interval, the mass of NaCl in the time interval can be determined (see Tables 1 and 2). m NaCl , 1 = A 1 t 1 − t 0 ∗ m Filtrat , 1 − m Filtrat , 0 Table 1: Integration of measurement data for filtration Time Delta t RI mass Delta m NaCl Single area Single area Mass of NaCl s s g g g / kg s*g / kg g / kg g 0,00 1,00 1,36823 12,4 12,4 200,2 197,7 197,7 2,46 1,00 1,00 1,36821 25,8 13,4 200,1 200,2 200,2 2,68 2,00 1,00 1,36824 41,2 15,4 200,3 200,2 200,2 3,08 3,00 1,00 1,36816 53,0 11,8 199,8 200,1 200,1 2,36 4,00 1,00 1,36813 66,1 13,1 199,7 199,7 199,7 2,62 5,00 1,00 1,36816 80,1 14,0 199,8 199,7 199,7 2,79 6,00 1,00 1,36812 90,8 10,7 199,6 199,7 199,7 2,14 7,00 1,00 1,36811 103,1 12,3 199,5 199,6 199,6 2,45 8,00 1,00 1,3681 115,8 12,7 199,5 199,5 199,5 2,54 9,00 1,00 1,36811 126,1 10,4 199,5 199,5 199,5 2,07 10,00 1,00 1,36812 134,6 8,5 199,6 199,6 199,6 1,69 11,00 1,00 1,36808 144,1 9,4 199,4 199,5 199,5 1,88 12,00 1,00 1,36806 152,9 8,8 199,3 199,3 199,3 1,76 13,00 1,00 1,36808 166,6 13,7 199,4 199,3 199,3 2,73 14,00 1,00 1,36805 176,0 9,5 199,2 199,3 199,3 1,89 15,00 1,00 1,36811 186,0 10,0 199,5 199,4 199,4 1,99 16,00 1,00 1,3681 194,8 8,7 199,5 199,5 199,5 1,74 17,00 1,00 1,36808 202,7 7,9 199,4 199,4 199,4 1,57 18,00 1,00 1,36803 211,1 8,4 199,1 199,2 199,2 1,68 19,00 1,00 1,36803 220,1 9,0 199,1 199,1 199,1 1,79 20,00 1,00 1,36802 228,3 8,2 199,0 199,1 199,1 1,63 21,00 1,00 1,36803 236,6 8,3 199,1 199,1 199,1 1,65 22,00 1,00 1,36804 243,7 7,2 199,2 199,1 199,1 1,43 23,00 1,00 1,36803 252,4 8,7 199,1 199,1 199,1 1,73 24,00 1,00 1,36803 258,0 5,6 199,1 199,1 199,1 1,12 25,00 1,00 1,36803 266,9 8,9 199,1 199,1 199,1 1,78 26,00 1,00 1,36803 273,8 6,9 199,1 199,1 199,1 1,37 27,00 1,00 1,36802 280,8 7,0 199,0 199,1 199,1 1,40 28,00 1,00 1,36803 289,3 8,5 199,1 199,1 199,1 1,70 29,00 1,00 1,36803 297,8 8,5 199,1 199,1 199,1 1,69 30,00 1,00 1,36803 305,2 7,4 199,1 199,1 199,1 1,47 31,00 1,00 1,36802 313,2 8,0 199,0 199,1 199,1 1,58 32,00 1,00 1,368 320,6 7,4 198,9 199,0 199,0 1,47 33,00 1,00 1,36797 328,4 7,9 198,8 198,8 198,8 1,56 34,00 1,00 1,368 335,3 6,8 198,9 198,8 198,8 1,36 35,00 1,00 1,36797 342,6 7,3 198,8 198,8 198,8 1,45 36,00 1,00 1,36803 350,1 7,5 199,1 198,9 198,9 1,49 37,00 1,00 1,36803 357,3 7,3 199,1 199,1 199,1 1,44 38,00 1,00 1,368 365,2 7,8 198,9 199,0 199,0 1,56 39,00 1,00 1,36795 373,2 8,0 198,6 198,8 198,8 1,59 40,00 1,00 1,36798 380,3 7,2 198,8 198,7 198,7 1,43 41,00 1,00 1,368 387,4 7,1 198,9 198,9 198,9 1,41 42,00 1,00 1,36797 393,4 5,9 198,8 198,8 198,8 1,18 43,00 1,00 1,36803 400,8 7,4 199,1 198,9 198,9 1,47 44,00 1,00 1,368 409,0 8,2 198,9 199,0 199,0 1,63 45,00 1,00 1,36794 411,4 2,4 198,6 198,8 198,8 0,48 46,00 1,00 1,36794 412,8 1,4 198,6 198,6 198,6 0,27 47,00 1,00 1,36794 413,4 0,6 198,6 198,6 198,6 0,13 48,00 1,00 1,36794 413,7 0,3 198,6 198,6 198,6 0,06 49,00 1,00 1,36794 414,0 0,3 198,6 198,6 198,6 0,06 50,00 1,00 1,36792 414,2 0,2 198,5 198,5 198,5 0,04 51,00 1,00 1,3679 414,2 0,0 198,4 198,4 198,4 0,00 52,00 1,00 1,36794 414,2 0,0 198,6 198,5 198,5 0,00 Total NaCl filtration: 83 g Table 2: Integration of measurement data for laundry Time Delta t RI mass Delta m NaCl Single area Single area Mass of NaCl s s g g g / kg s*g / kg g / kg g 172,00 1,00 1,36804 0,0 0,0 199,2 199,3 199,3 0,00 173,00 1,00 1,36805 0,0 0,0 199,2 199,2 199,2 0,00 174,00 1,00 1,36811 1,1 1,1 199,5 199,4 199,4 0,22 175,00 1,00 1,36811 5,7 4,6 199,5 199,5 199,5 0,91 176,00 1,00 1,36811 13,5 7,8 199,5 199,5 199,5 1,56 177,00 1,00 1,36813 19,9 6,4 199,7 199,6 199,6 1,27 178,00 1,00 1,36817 26,0 6,1 199,9 199,8 199,8 1,21 179,00 1,00 1,36812 33,1 7,2 199,6 199,7 199,7 1,43 180,00 1,00 1,36811 38,2 5,0 199,5 199,6 199,6 1,00 181,00 1,00 1,36811 46,7 8,5 199,5 199,5 199,5 1,70 182,00 1,00 1,36811 52,9 6,2 199,5 199,5 199,5 1,24 183,00 1,00 1,3681 59,4 6,6 199,5 199,5 199,5 1,31 184,00 1,00 1,36809 63,6 4,2 199,4 199,5 199,5 0,83 185,00 1,00 1,36804 72,2 8,6 199,2 199,3 199,3 1,71 186,00 1,00 1,36811 79,9 7,7 199,5 199,3 199,3 1,54 187,00 1,00 1,36812 90,9 11,0 199,6 199,6 199,6 2,19 188,00 1,00 1,36809 100,2 9,3 199,4 199,5 199,5 1,86 189,00 1,00 1,36803 108,6 8,3 199,1 199,3 199,3 1,66 190,00 1,00 1,36803 117,0 8,4 199,1 199,1 199,1 1,68 191,00 1,00 1,36799 125,5 8,5 198,9 199,0 199,0 1,69 192,00 1,00 1,36763 133,8 8,3 196,8 197,8 197,8 1,65 193,00 1,00 1,36597 142,3 8,5 187,4 192,1 192,1 1,63 194,00 1,00 1,36174 153,2 10,9 163,3 175,3 175,3 1,91 195,00 1,00 1,35479 161,6 8,5 123,8 143,6 143,6 1,22 196,00 1,00 1,34658 170,0 8,3 77,1 100,4 100,4 0,84 197,00 1,00 1,3408 179,9 9,9 44,2 60,7 60,7 0,60 198,00 1,00 1,33723 186,3 6,5 23,9 34,1 34,1 0,22 199,00 1,00 1,33544 195,9 9,6 13,7 18,8 18,8 0,18 200,00 1,00 1,33457 204,0 8,1 8,8 11,3 11,3 0,09 201,00 1,00 1,33406 211,9 7,9 5,9 7,3 7,3 0,06 202,00 1,00 1,33376 221,4 9,6 4,2 5,0 5,0 0,05 203,00 1,00 1,33355 230,6 9,2 3,0 3,6 3,6 0,03 204,00 1,00 1,33348 236,5 5,9 2,6 2,8 2,8 0,02 205,00 1,00 1,33339 244,9 8,4 2,1 2,3 2,3 0,02 206,00 1,00 1,33331 252,8 7,9 1,6 1,8 1,8 0,01 207,00 1,00 1,33323 263,6 10,8 1,2 1,4 1,4 0,01 208,00 1,00 1,33316 271,5 7,9 0,8 1,0 1,0 0,01 209,00 1,00 1,33309 281,7 10,2 0,4 0,6 0,6 0,01 210,00 1,00 1,33307 289,7 8,0 0,3 0,3 0,3 0,00 211,00 1,00 1,333 297,7 8,0 -0,1 0,1 0,1 0,00 212,00 1,00 1,33299 305,8 8,1 -0,2 -0,2 -0,2 0,00 Total NaCl laundry: 33g

[0069] If all the NaCl masses from the individual sections are added together—i.e., the measurement curves are integrated—the resulting leached NaCl mass for the entire experiment is obtained. In this example, this amounts to 116 g NaCl, which corresponds to a deviation of approximately 3% from the amount of NaCl used. • Mass balance from offline determinations:

[0070] To verify the mass balance from the online measurements, the filtrate masses and the refractive indices in the collected filtrates were determined. From this, a mass balance can be calculated. In the experiment presented, 120 g of NaCl were used. 414 g of mother liquor filtrate with a concentration of 200 g / kg NaCl and 1347 g of wash filtrate with a concentration of 24 g / kg NaCl were collected. This resulted in 83 g of NaCl dissolved in the mother liquor filtrate and 32 g of NaCl dissolved in the wash filtrate. Since no NaCl was detectable in the filter cake, 115 g of NaCl was recovered in the filtrates by measurement. • Statements on the quality of the laundry carried out

[0071] The refractive index decreases during the wash cycle from the initial value of the mother liquor to a lower (plateau) value at the end of the wash cycle. The curve thus falls at a certain gradient. A change in this gradient can be used to determine the quality of the wash.

[0072] The following is an example using the model system described above: Rods were inserted into the applied suspension to create artificial channels in the filter cake. The filter cake was dehydrated after mother liquor filtration ( Figure 6A). Figure 7 shows the progression and, in particular, the renewed increase in the refractive index. This suggests that the wash front does not run homogeneously through the filter cake, but rather that discontinuities – in this case, channels – have formed. This would not be apparent from a visual inspection of the filter cake after washing, as in Figure 6B can be seen. When inspecting the filter cake from above, as is technically possible, no cracks, channels, etc. hidden inside the filter cake can be detected. Description of the characters:

[0073] Fig. 1 : Schematic representation of a pressure filter 1 Pressure filter, 2 Filter cake, 3 Measuring device (e.g. example RI) Fig. 2 : Trend representation of the measured value (RI) over time (t) divided into process phases: A- displacement of the mother liquor, B- intermediate range, C- permitted range, D- diffusion range, E- end of the washing effect. Fig. 3 : Comparison of refractive index (□) and sum of minor components (∘) for the product Sivanto. The refractive index of pure butanol is 1.39932 at 20°C. (Example A). Fig. 4 : Filtrate mass M (∘) and refractive index RI (■) as a function of time t. Area 1: Filtration; Area 2: Washing. Fig. 5 : NaCl concentration ( ■ ) and refractive index RI (∘) as a function of the washing ratio. Fig. 6A : Filter cake with channels, dehumidified after mother liquor filtration. Fig. 6B : Filter cake after mechanical dehumidification after washing. Fig. 7 : □ Mass (M) and • Refractive index (RI) as a function of time (t). Fig. 8 : Block diagram of the washing process control procedure 1 - Input of measurement data 2 - Calculation of the first derivative 3 - First derivative > 0 or greater than a predefined value? 4 - End of the wash cycle 5 - Error message 6 - First derivative within a predefined range C? 7 - Calculation of the average slope and variability (steps e.g.) 8 - Average slope and variability within the predefined ranges?

Claims

1. Method of monitoring a filtration and washing operation on a solid-state bulk material in a filter apparatus for cake filtration, wherein - the filter apparatus has a wash medium feed, a filter element for cake filtration, a filtrate outlet for removal of a filtrate stream and, in or on the filtrate outlet, at least one measuring apparatus for measuring one or more parameter values of the filtrate stream, - during the filtering and washing operation, the solid-state bulk material in a suspension medium is separated from the suspension medium in the form of a cake with the aid of a filter element for cake filtration, the suspension medium is led off in the form of a filtrate stream into a filtrate outlet, and the measuring apparatus measures at least one or more than one parameter value of the filtrate stream over the period of the washing operation, characterized in that a computer-implemented change analysis of the parameter values measured is conducted over the period of time, this change analysis is used to ascertain the end of the washing operation and / or the effectiveness of the washing operation, and the change analysis is used for ending of the washing operation, - wherein the parameters of the filtrate stream are selected from the group comprising refractive index, density, ultrasound transit time, redox potential and cumulative spectroscopic properties and / or substancespecific properties of one or more main or secondary components, and - wherein the end of the washing operation is ascertained by the following steps: a) providing the parameter values measured to an evaluation system; b) calculating the first derivative of a measurement curve between the measurement data at the times t-1 and t; c) if the first derivative from b) is more than zero or more than a predefined value for the derivative of the measurement curve at which the method is considered to have ended, the washing operation is continued; step b) is repeated for a further measurement curve; d) if the first derivative from b) is zero, if it is less than or equal to the predefined value, the washing operation is ended and the end of the washing operation is optionally communicated via a user interface; and / or - wherein the effectiveness of the washing operation is ascertained by the following steps: a. transferring the measurement values of the measurement data to the evaluation system over a predefined period of time in the washing operation; b. calculating the first derivative of a measurement curve between the measurement data at the times t-1 and t; c. comparing the first derivative with an approved predefined range of values for the first derivative in which the washing operation is considered to be effective; d. ending the washing operation and / or giving notice of the variance via a user interface if the first derivative is outside the predefined range of values from c); alternatively or additionally to step d), e. calculating a period C in which the first derivative is within the predefined range of values from c); f. calculating a slope value as the average slope over the period C from e); g. calculating a variability of the slope value over the period C from e); h. if the slope value from f) is within a predefined working range for the slope value and the variability of the slope from g) is less than or equal to a predefined tolerance limit for the variability at which the washing operation is considered to be effective, the washing operation is continued; i. if the slope value from f) is outside the predefined working range for the slope value and / or the variability of the slope value from g) is above the predefined tolerance limit for the variability, a warning is issued and / or the washing operation is ended.

2. Method according to Claim 1, wherein the refractive index and / or the density of the filtrate stream is measured.

3. Method according to either of Claims 1 and 2, wherein the parameter values over the period of time are transmitted as measurement data to an archiving module for storage of the measurement data and stored with a timestamp t.

4. Method according to Claim 1, in which the amount of wash medium consumed for the washing operation until the end of the washing operation is ascertained and fixed as the optimal amount of wash medium for the next washing operation.

5. Method according to any of Claims 1 to 4, wherein the method is used for online monitoring of the washing operation.

6. Method according to any of Claims 1 to 4, wherein at least one concentration of at least one component in the filtrate stream and / or at least one measurable cumulative parameter of the filtrate stream is ascertained.

7. System for monitoring a filtration and washing operation on a solid-state bulk material in a filter apparatus for cake filtration, wherein the system comprises: - an archiving module configured for the storage of parameter values of a filtrate stream with a timestamp t transmitted from at least one measurement apparatus in or on a filtrate outlet of the filter apparatus over the period of the filtration and washing operation and for the transfer of the measurement values to an evaluation system, - the evaluation system connected to the archiving module and configured to perform the method according to any of Claims 1 to 7, in order to analyse changes in the parameter values over the period of time, and to use this change analysis to ascertain the end of the filtration and washing operation and / or the effectiveness of the washing operation, - an element for issuing a control command for ending of the filtration and washing operation and / or - a display element for the end of the filtration and washing operation and / or the effectiveness of the washing operation.

8. Filter apparatus comprising a wash medium feed, a filter element for cake filtration and a filtrate outlet, at least one measurement apparatus for measurement of parameter values in the filtrate stream, installed in or on the filtrate outlet, and the system according to Claim 7.

9. Filter apparatus according to Claim 8, wherein the measurement apparatus can measure one or more parameters selected from the group consisting of refractive index, density, ultrasound transit time, pH, conductivity, redox potential and / or spectroscopic properties of the filtrate stream as cumulative parameters, or alternatively of at least one representative constituent, in the filtrate stream.

10. Filter apparatus according to Claim 8 or 9, selected from the group consisting of suction filters, centrifuges, Büchner funnels, frits, filter crucible, drum filter, disk filter, belt filter and filter press.

11. Filter apparatus according to Claim 8, wherein the filter apparatus has a controllable wash medium feed that can receive commands for opening or closing of the wash medium feed.