NZ758627B2 - Method and mixing device for controlling the introduction of a pulverulent material into a liquid for a batch mixing method - Google Patents

Abstract

The invention relates to a method for controlling the introduction of a pulverulent material (P) into a liquid (F) consisting of at least one component for a batch mixing method according to the preamble of claim 1 and to a mixing device for carrying out the method, said method and mixing device ensuring that the disadvantages of the prior art which have become known are prevented. This is achieved by a method in that, among others, • the pulverulent material (P) is supplied in a discontinuous manner in pulses by means of a chronological sequence of metering pulses (i), each of which is characterized by a mass flow of the pulverulent material (ṁP), a duration of the metering pulse (Δt1), and a time interval between adjacent metering pulses (Δt2), • a time-dependent power consumption (l(t)) is ascertained which is proportional to a stirring and/or shearing and homogenizing power required for a temporarily available mixing product (M*), and • at the end of the time interval between adjacent metering pulses (Δt2) and in the event of a deviation of the time-dependent power consumption (l(t)) from the respective assigned value in the time-dependent curve of a reference power consumption (lo) by more than a specified tolerance, either upwards or downwards, the duration of the metering pulse (Δt1) for the following metering pulse (i) is shortened in the first case and lengthened in the second case. uring that the disadvantages of the prior art which have become known are prevented. This is achieved by a method in that, among others, • the pulverulent material (P) is supplied in a discontinuous manner in pulses by means of a chronological sequence of metering pulses (i), each of which is characterized by a mass flow of the pulverulent material (ṁP), a duration of the metering pulse (Δt1), and a time interval between adjacent metering pulses (Δt2), • a time-dependent power consumption (l(t)) is ascertained which is proportional to a stirring and/or shearing and homogenizing power required for a temporarily available mixing product (M*), and • at the end of the time interval between adjacent metering pulses (Δt2) and in the event of a deviation of the time-dependent power consumption (l(t)) from the respective assigned value in the time-dependent curve of a reference power consumption (lo) by more than a specified tolerance, either upwards or downwards, the duration of the metering pulse (Δt1) for the following metering pulse (i) is shortened in the first case and lengthened in the second case.

Description

Method and mixing device for controlling the uction of a pulverulent material into a liquid for a batch mixing method TECHNICAL FIELD The invention relates to a method for controlling the introduction of a pulverulent material into a liquid consisting of at least one component for a batch mixing method in ance with the preamble of Claim 1, in which the introduction and treatment of the pulverulent material are effected virtually under the reaction kinetics-related conditions of a residence time behavior of a homogeneous reaction vessel working in a discontinuous manner, as well as a mixing device for ng out the .

PRIOR ART With a view to the introduction of a pulverulent material into a liquid and the m distribution and, if applicable, dissolution thereof in the liquid, mixing methods which are operated batchwise (so-called batch methods) or continuously (so-called inline methods) are ar methods within mixer technology.

In the case of the batch method, the mixing of the liquid and pulverulent material is performed by means of reaction kinetics in a so-called reaction vessel (mixing tank) which is operated in a discontinuous manner. A specific quantity of liquid is made available in the mixing tank and ulent material is supplied until such time as a d or respectively systematically specified dry matter concentration of the pulverulent material is available in the liquid. ulent material and liquid are ably constantly stirred and/or mixed to form a mixing product and the mixing product is homogenized with the aim of mly distributing the pulverulent material.

The pulverulent material can be supplied in a continuous or discontinuous manner.

In the case of the inline method, the liquid and pulverulent material are mixed by means of reaction kinetics in a so-called continuously operated reaction vessel (mixing tank). Liquid and pulverulent material are ly supplied to the mixing tank, with said pulverulent material either being supplied in a continuous or discontinuous manner, and a mixing product is discharged in a continuous manner from the mixing tank in accordance with the supplied quantities of liquid and pulverulent material.

[Link] http://www.qea.com/de/products/ Stirring and/or mixing or respectively shearing and homogenizing guarantee this.

Thus, the theoretical postulate is that the mixing product has the same composition (e.g. dry matter concentration) at any point and no temperature ences occur.

The dry matter concentration in the rged mixing product remains unchanged, viewed over the duration of the mixing process, i.e. it is constant.

The present invention deals exclusively with mixing methods which are operated using the batch method and in all possible manifestations. A mixing method in this t and the assigned mixing device have been disclosed to the public, for example under the ing internet link: “http://www.qea.com/de/products/High- Batch-Mixer.jsp”.

The mixing devices ted above also preferably comprise so-called vacuum mixers which have a mixing tank with a stirring and/or shearing and homogenizing apparatus. The free surface of the liquid, which can have, for example, a free filling level with a height between 0.4 and 4 m in the mixing tank, is subjected to a negative pressure with respect to atmospheric pressure of, for example, 0.2 to 0.8 bar which is accordingly assigned to this height range, so that the liquid can be freed more easily of gas constituents, on the one hand, during the mixing process and, on the other hand, has a negative pressure with respect to atmospheric pressure in the bottom region of the mixing tank under all of the operating conditions. The pulverulent material is uced into the mixing tank via an g in the tank wall below the free filling level. This opening continues in a tubular inlet connection in the direction of the outer side of the mixing tank, to which a pipe leading, for example, to a powder storage tank is attached. The inlet connection and, therefore, the pipe are configured to be capable of being shut off via an inlet valve which controls the supply of the pulverulent material so that, on the one hand, the mixing device is closed off via this channel with respect to its ndings and, on the other hand, a quantity of the pulverulent material made ble in the powder storage tank can be supplied independently, if necessary, to the liquid based on the prevailing pressure conditions.

A mixing device in this respect having a preferably discontinuous supply of the pulverulent material is described in the printed publication DE 10 2015 016 766 A1, wherein the latter is generic.

A discontinuous supply of the pulverulent material, as disclosed for example in DE 10 2015 016 766 A, has the advantage that the supply is always effected via the fully open position of the inlet valve which is configured as a lift valve and, as a result, the risk of the inlet valve clogging is minimized. Depending on the duration of the respective open position, more or less large quantities of the pulverulent material are introduced intermittently into the liquid so that there is, in principle, the risk of corresponding agglomerations of the pulverulent material occurring, which have to be completely dissolved by the stirring and/or shearing and homogenizing apparatus by the time that the subsequent quantity of pulverulent material enters, wherein a distribution of the ulent material which is as far as possible uniform is to simultaneously be striven for. In connection with this, it has been shown that the intermittent supply of the pulverulent material is rated in an increase in the stirring and/or shearing and homogenizing power (driving power for the assigned tuses), which is necessary in order to treat the temporarily available mixing product in this phase of the mixing s. The curve of the driving power in this respect, which is proportional to the power consumption of the assigned drive motors, corresponds approximately to a Gaussian normal distribution curve.

An additional complicating factor in the mixing process is that the residence time behavior of a reaction vessel or tively mixing tank, which is operated in a discontinuous manner, does indeed tically postulate an identical composition of the mixing t at any point, but it can, in practice, increasingly result in ogeneously buted agglomerations of the pulverulent material due to the operational discontinuous supply of the pulverulent material, which agglomerations have not completely dissolved at all points of the mixing tank by the next supply of the pulverulent material. As a result, there is the risk of a blockage of the mixing tank due to too high a dry matter concentration.

On the one hand, the possibility cannot therefore be ed that more or less large agglomerations do not completely dissolve and are present for a long time in the mixing product. Due to the inhomogeneities of the pulverulent material in the mixing product, which are described above, there is, on the other hand, the risk of microbiological growth (growth of bacteria) in said mixing product, which, in particular if the mixing tank is heated, is promoted under these thermal conditions. Moreover, there is increasingly a chance of a coat forming (so-called product fouling) on the heated walls of the mixing tank under the last-mentioned conditions, which on the one hand hinders the transfer of heat and, on the other hand, ns the service life of the mixing tank until the next cleaning cycle is due.

Since there have not to date been any expedient control mechanisms in order to prevent inhomogeneities in terms of the distribution and the degree of dissolution of agglomerations of the ulent material and disproportionately large fluctuations in the supply of pulverulent material, and to t a blockage of the mixing device due to too high a dry matter concentration in the mixing tank, the stirring and/or shearing and homogenizing of the temporarily available mixing product have, up to now, been operated more intensively, in mixing devices of the type discussed here, over the entire duration of the mixing process than is required over large periods of time – ably to be on the safe side. This too intensive treatment can, on the one hand, have a t-damaging effect and is, on the other hand, not energy efficient.

The object of the present invention is to further develop a c method for controlling the introduction of a pulverulent material into a liquid consisting of at least one component for a batch mixing method, and an assigned mixing device for carrying out the method such that the disadvantages of the prior art indicated above are eliminated.

SUMMARY OF THE INVENTION This object is achieved by a method having the features of Claim 1. The object is additionally achieved by a mixing device for ng out the method having the es of the alternative ndent Claim 9. An advantageous configuration of the mixing device is the subject matter of the dependent Claim 10.

Method The invention starts, in view of a method according to the invention, from a known method for controlling the introduction of a pulverulent material into a liquid consisting of at least one component for a batch mixing , wherein the term “component” is to be understood to mean that said components can, as a general rule, be discrete liquids which are separated from one another, which can also be supplied separately from one another to the mixing process. The batch mixing method is typically applied to medium-viscosity to high-viscosity mixing products having a medium-high to high dry matter concentration in the end result and also to mixing methods having le liquid ents which do not need any further processing or only need a little further processing in the downstream process. The introduction and treatment of the pulverulent material, viewed in terms of reaction kinetics, are effected virtually under the conditions of a residence time behavior of a homogeneous reaction vessel working in a discontinuous manner.

The method is distinguished in the known manner such that a quantity of liquid is made available and the ulent material is supplied to said liquid in a discontinuous manner, and the liquid and the pulverulent material are ntly d and/or mixed to form a mixing product and the mixing product is homogenized.

The pulverulent material is supplied until such time as a time-dependent curve of a dry matter concentration of the pulverulent material in the mixing product has grown to a specified final value.

The ive concept of the solution in the case of the method is that a formulation of the mixing t at least in terms of the time-dependent curve of a dry matter concentration assigned to the specified final value and, respectively, the reaction conditions are specified in the form of default data. Furthermore, it is ed that the pulverulent material is supplied in a discontinuous manner in the known manner in pulses by means of a chronological ce of metering pulses. In this respect, the reaction conditions provide, in a preferred configuration, that the pulverulent material is sucked in by a negative pressure (vacuum) in the head space of the mixing tank with respect to atmospheric re. The metering pulses are each characterized by a mass flow of the pulverulent material m? P, a duration of the metering pulse ?t1 and a time interval between adjacent metering pulses ?t2.

The method produces a time-dependent curve of a dry matter concentration c(t), which systematically ends in the ied final value, wherein a distinction is to be made between the curve of a dry matter concentration without saturation character (an approximate linear curve) or with saturation character (degressive curve).

• In the case of the curve without saturation character, the same quantities of ulent material can be metered within the ork of the absorption ty or the solubility limit of the liquid in identical time intervals, so that during complete homogenization of the mixing t, a time-dependent approximately linearly rising curve of a dry matter concentration is adjusted.

• In the case of the curve with saturation character, only steadily decreasing quantities of pulverulent material can be metered within the framework of the absorption ty or the solubility limit of the liquid in identical time intervals, so that during te homogenization of the mixing t, a timedependent degressively climbing curve of a dry matter concentration is adjusted.

The time-dependent curve of a dry matter concentration ending in the specified final value is defined, according to the invention, by the sequence of clearly determined metering pulses.

One significant control-engineering feature is that a time-dependent power consumption l(t) is ascertained, which is proportional to a stirring and/or shearing and nizing power required for a temporarily available mixing product. Said timedependent power consumption always occurs in the form approximately of a Gaussian normal distribution if a defined quantity of ulent material is introduced in pulses into the mixing process or respectively the mixing tank and treated.

As soon as the pulverulent material is uniformly distributed in the absorbing liquid or in the absorbing mixing t, i.e. has been distributed as homogeneously as possible and, if applicable, has dissolved, the ependent power consumption l(t) subsides and does so on a time-dependent curve of a reference power consumption l0(t), which is characteristic of the stirring and/or shearing and homogenizing power to be provided to the homogenized mixing product under the conditions of the assigned time-dependent curve of a dry matter concentration (c(t)). The time- dependent curve of the reference power consumption l0(t) in this respect is stored in the default data and can be utilized from there, and it is dependent on the formulation of the mixing product and the reaction conditions for the mixing process.

At the end of the time interval between adjacent metering pulses ?t2 and in the event of a ion of the time-dependent power consumption l(t) from the respective assigned value in the time-dependent curve of a reference power ption l0(t) by more than a specified tolerance, n a deviation either upwards or downwards can exist, the duration of the metering pulse ?t1 for the following metering pulse is shortened in the first case and lengthened in the second case.

For time-dependent curves of a dry matter concentration c(t) without saturation character, a first uration of the method provides that these curves are each defined by a fixed duration-time interval ratio V between the duration of the metering pulse ?t1 and the assigned time interval between adjacent metering pulses ?t2 (V = ?t1/?t2 = constant).

The respective curve of a dry matter tration c(t) climbs over time t, because the mass flow of the pulverulent material m? P which is constantly metered in pulses, said mass flow being, in the most l case, a time-dependent mass flow of pulverulent material m? P(t), viewed over the entire duration t of the mixing process, is constant (m? P = constant). The mass flow of pulverulent material m? P is introduced multiple times, namely (t/?t2)-times, in the duration t, with an approximately invariable filling level in the mixing tank, into an invariable ty of liquid mF of the available mixing product, n the time-dependent curve of a dry matter concentration c(t) constitutes the ing according to equation (1): ?P ?t1 c(t) = ?t2 t (1) mF+ ?P ?t1 In most practice-oriented cases, because the first term of the following relationship is, as a general rule, small compared to the second term, ?P ?t1 « mF can be set approximately so that, in accordance with equation (1a), the ing results approximately for the time-dependent curve of a dry matter tration c(t) with a first proportionality constant k1 = mP ?P ?t1 c(t) ˜ ?t2 = ?P ?t1 t = ?P V t = k1 V t (1a) mF mF ?t2 mF This control engineering measure which has a fixed duration-time interval ratio V (V = ?t1/?t2 = constant) essentially leads, proportionally, to a corresponding shortening or lengthening of the time interval between adjacent metering pulses ?t2, based on the following metering pulse.

For time-dependent curves of the dry matter concentration c(t) with saturation character, a second configuration of the method provides that these curves are d by a variable duration-time interval ratio V between the duration of the metering pulse ?t1 and the assigned time interval between adjacent ng pulses ?t2 (V = ?t1/?t2 ? constant), wherein • in the event of a deviation of the time-dependent power consumption l(t) from the respective assigned value in the time-dependent curve of a reference power consumption l0(t) by more than the specified tolerance upwards, the on-time al ratio V is reduced, and • in the event of a deviation of the time-dependent power consumption l(t) from the respective assigned value in the ependent curve of a reference power consumption l0(t) by more than the specified tolerance downwards, the ontime interval ratio V is enlarged.

The respective curve of a dry matter concentration c(t) climbs degressively over time t, because the mass flow of the pulverulent material m? P which is constantly d in pulses, viewed over the entire duration t of the mixing s, is indeed constant (m? P = nt), however the duration of the metering pulse ?t1 steadily decreases and, consequently, a steadily decreasing quantity of pulverulent material is metered.

The mass flow of pulverulent material m? P is introduced, in the duration t with an approximately invariable filling level in the mixing tank, into an available virtually invariable volume of the mixing product VM (VM ˜ constant), wherein a density ?M of the mixing t increases in ance with the time-dependent curve of a dry matter concentration c(t) and the latter is represented in accordance with equation (2) with a second proportionality nt k2 = ?P : ????? (?P(t)?t1) ?P ?t ?t1 ?t ?t1 c(t) = ???? =0 = t=0 ˜ k2 t=0 ?M(t) VM VM ?M(t) ?M(t) This control engineering measure having a variable duration-time interval ratio V requires the control to be able to shorten or lengthen the duration of the metering pulse ?t1 with an invariable time interval between adjacent metering pulses ?t2 or, in the case of an unaltered duration of the metering pulse ?t1, to en or shorten the time interval between adjacent metering pulses ?t2 in an appropriate manner.

Consequently, the control-engineering measure according to the invention essentially consists, in both configurations of the method, of the fact that the duration of the ng pulse ?t1 and the time interval between adjacent metering pulses ?t2 are selected such that at the respective end of the time interval between adjacent metering pulses ?t2, the power consumption l(t) for ng and/or shearing and homogenizing the temporarily available mixing product, which power consumption is ascertained ing on the time, approaches the time-dependent curve of a reference power consumption l0(t), which is required in order to treat the nized mixing product in this respect, within the framework of a practiceoriented permissible tolerance.

In order to design the metering of the pulverulent material so that it is as trouble-free as possible, it is proposed for the method that the mass flow of the pulverulent material be constant over the duration of the metering pulse. This is in particular ensured in that a controllable opening for the supply of the pulverulent material only takes up either a fully open position or a closed position.

In order to make the control of the mixing process as easy to handle as le, another configuration of the method es that the shortening or the lengthening of the duration of the metering pulse is then effected if a current corridor specified in each case by a permissible overcurrent or a permissible undercurrent is left by an upwardly deviating power consumption or a downwardly deviating power ption. The permissible overcurrent and the permissible undercurrent are each determined by a tage proportion of the assigned time-dependent curve of a reference power consumption. To ensure that the l works as precisely as possible in this respect, it is furthermore proposed that the degree of the shortening or the ening of the duration of the metering pulse be determined as a function of the degree of the deviation of the time-dependent power consumption from the assigned curve of a reference power consumption.

In order to make the operating data obtained in practical operation for a specific formulation usable for following mixing processes having the same formulation, another configuration of the method provides that the r formulation-dependent default data underlying the control of the introduction of the pulverulent al into the at least one liquid are ed from empirical values of earlier mixing processes and are saved, wherein said default data are a mixing or on temperature, a pressure above the liquid column, from which a reaction pressure results, rates of rotation of apparatuses for stirring and/or shearing and homogenizing and a permissible rrent dependent on the assigned time-dependent curve of a reference power consumption and a permissible undercurrent.

In order to make the operating data ed in practical operation for a specific formulation usable for following mixing processes having the same formulation, r configuration of the method provides that the expedient formulationdependent control parameters obtained in the course of lling the introduction of the pulverulent material into the at least one liquid, namely the duration of the metering pulse and the time interval between adjacent metering pulses, are saved and utilized for following controls of the same formulations.

Mixing device A mixing device for carrying out the method consists in the known way of a mixing tank which has a feed tion for supplying for a liquid, an outlet connection for discharging for a mixing product and a stirring apparatus and/or a shearing and homogenizing apparatus. An inlet valve with a valve closure member is arranged on the mixing tank. The inlet valve can be adjusted with the valve closure member either between completely closed (closed position) or completely open (open position). A ulent material is introduced with the inlet valve into the liquid, wherein the valve closure member can be moved into the closed or into the open position with a control apparatus assigned to the inlet valve.

According to the invention, the control apparatus provides the mixing device with formulation-dependent default data and formulation-dependent control parameters in the form of the duration of the metering pulse and the time interval n adjacent metering pulses. Furthermore, the control apparatus has, according to the invention, at least one signal p configured as a measuring tus, which signal pickup detects a time-dependent power consumption of the stirring apparatus and/or of the ng and homogenizing apparatus. ed with these properties, the control apparatus actuates the closed or the open position of the valve closure member as a function of the time-dependent power consumption and in relation to the t data and the control parameters.

In order to optimize the inlet valve which is configured as a lift valve, which exclusively supplies pulverulent material in its fully open position and consequently minimizes the tibility to clogging from the outset, even further in this t and, by way of e, to t dead and hollow spaces in the region of the valve housing of the inlet valve which is acted upon by powder, an advantageous embodiment provides that the valve closure member is configured at least in its region which is acted upon by powder as a cylindrical rod having the same er, on which a valve disk having the same diameter is molded. If the inlet valve is located in its fully open position, the valve closure member with its valve disk is extended to its greatest extent, due to this embodiment, from the fully configured flow of the pulverulent material, so that it does not on the one hand constitute a flow obstruction and, on the other hand, a seat seal, which is received in the valve disk, is located in the proximity of the wall of a valve housing and therefore outside the fully configured flow region of the pipe flow and is, as a result, anyway only tangent to the stagnating flow close to the wall in said edge BRIEF DESCRIPTION OF THE DRAWINGS The invention is represented in more detail by the following description and the appended figures of the drawing and the claims. Whilst the invention is realized in the very different configurations of a method for controlling the uction of a pulverulent material into a liquid consisting of at least one component for a batch mixing , a preferred method and a mixing device for carrying out the method are described in the drawing, wherein Fig. 1 shows, in a schematic representation, a mixing device for a batch mixing method; Fig. 2 shows, in a perspective representation and in a half-section, an inlet valve for supplying the pulverulent material into a mixing device according to Fig. 1 without a control head housing; Fig. 3 shows, in a qualitative representation of the method and in order to basically represent the control features according to the invention, a timedependent power consumption l(t) for a sequence of metering pulses having a constant duration of the metering pulse ?t1 and having a time interval between nt metering pulses ?t2, wherein a time-dependent curve of a dry matter concentration c(t) t saturation character is taken as the basis; Fig. 4 shows, in a qualitative representation of the method, a time-dependent power consumption l(t) for a ce of ng pulses having a constant duration of the metering pulse ?t1/2 and having a time interval between adjacent metering pulses ?t2/2, wherein the ependent curve of a dry matter concentration c(t) according to Fig. 3 is taken as the basis; Fig. 5 shows, in a qualitative representation of the , a time-dependent power consumption l(t) for a larger sequence of metering pulses having a constant duration of the metering pulse ?t1 and having a constant time interval between adjacent metering pulses ?t2 in order to realize a time- dependent approximately ly climbing curve of a dry matter concentration (without saturation character) in accordance with Figs. 3 and 4, and Fig. 6 shows, in a qualitative representation of the method, a ependent power consumption l(t) for a sequence of metering pulses having a steadily decreasing duration of the metering pulse ?t1 and having a constant time al n adjacent metering impulses ?t2 in order to realize a timedependent degressive curve of a dry matter concentration (with saturation character).

Mixing device (Figs. 1 and 2) A mixing device 1000 has, among other things, a mixing tank 100 which consists of a ably rical tank casing 100.1, an upper tank bottom 100.2 and a lower tank bottom 100.3. The lower tank bottom 100.3 preferably tapers downward, mostly conically or in the form of a circular cone, and has at the lower end an outlet connection 100.4 for a mixing product M. In the mixing tank 100, a liquid F is made available in a quantity of liquid mF via a feed connection 100.5, which configures a free filling level N, via which as a rule a pressure above the liquid column p, a negative pressure with respect to atmospheric pressure, prevails in the mixing device 1000 (e.g. vacuum mixer) discussed here.

An inlet valve 20 is arranged on the tank casing 100.1 or the lower tank bottom 100.3.

The inlet valve 20 helps to supply a pulverulent material P in a discontinuous manner with a mass flow of pulverulent material m? P, which is ed via a supply line 18, into the liquid F or into the mixing product M. A control tus 30 which communicates with a control head housing 14 of the inlet valve 20 via a signal line 22 and moves the inlet valve 20, if required, into its open or closed position, is assigned to the inlet valve 20. In the mixing tank 100 there is located a stirring apparatus 24 which is driven via a first drive motor 40 with a rather low first rate of rotation n1, preferably centrally arranged and mechanically , which preferably extends into the region of the lower tank bottom 100.3. The required stirring action can also be achieved or supported by flow mechanical means, for example by repumping the liquid F or the mixing product M via a circulation line (not represented) with a preferably tangential entry of the liquid F or the mixing product M into the mixing tank 100.

Alternatively or additionally to the stirring apparatus 24, a shearing and homogenizing apparatus 26 which is driven by means of a second drive motor 50 with a rather high second rate of rotation n2 is preferably provided in the lower region of the lower tank bottom 100.3 and preferably eccentrically therein. Said shearing and homogenizing tus preferably sucks the liquid F or the mixing product M in, on the one hand, from above and ejects these, on the other hand, rly in the region close to the wall of the lower tank bottom 100.3 such that a circulation flow directed from the outside inward is preferably configured in the mixing tank 100. During the passage through the shearing and homogenizing apparatus 26, liquid F and pulverulent al P or the resulting mixing product M are very intensively mechanically mixed and preferably homogenized y.

The inlet valve 20 is ured as a lift valve (Fig. 2). It has in a valve housing 2 a valve seat 2a and a valve disk 8a interacting with this, which valve disk is configured on a valve closure member 8. As a rule, the valve closure member 8 receives a seat seal 10 which brings about the g in the closed position of the inlet valve 20 in the interaction with the valve seat 2a. The valve seat 2a has a seat g 2b, through which the pulverulent material P supplied via a pipe connection 2c from the supply line 18 is introduced into the liquid F (Fig. 1).

The queuing liquid F above the connection point of the inlet valve 20, which is preferably arranged directly in the wall of the mixing tank 100, configures with its liquid column a height h (Fig. 1), so that the static pressure in the region of the aforementioned connection point and therefore also in the region of the seat opening 2b is ed of the pressure above the liquid column p (preferably negative pressure) and the static pressure, which results from the height of the liquid column h. In the case of a vacuum mixer having a negative pressure of, for example, p = 0.2 to 0.8 bar and a height of the liquid column h = 0.2 to 4 m, which is ed in accordance with this pressure range, a negative pressure with respect to atmospheric pressure still constantly prevails in the region of the seat opening 2b, so that the seat opening 2b is sucked out of the mixing tank 100 and therefore the pulverulent material P is sucked in. The seat opening 2b can be adjusted with the valve disk 8a between completely closed, the closed position, or completely opened, the open position. The valve housing 2 is connected via a lantern-type housing 4 to a drive g 6 for driving the valve closure member 8. It is preferably a spring/piston drive acted upon by a pressure medium, wherein a return spring 12 moves the valve closure member 8, as a general rule, into its closed position if the drive housing 6 is not acted upon with re means, preferably compressed air. A valve rod 8b, which acts upon the valve disk 8a of the valve closure member 8 and is guided through the drive housing 6 and up into the control head housing 14, serves on the drive side to y guide the valve closure member 8. The valve closure member 8 is configured at least in its region acted upon by powder as a rical rod having the same diameter, on which the valve disk 8a having the same diameter is molded. Thanks to this design configuration, hollow and dead spaces in the valve housing 2 in the movement region acted upon by powder of the valve closure member 8 are ted, wherein the valve closure member 8 with its end valve disk 8a and the assigned seat seal 10 can be withdrawn to the greatest le extent from the region of the valve housing 2 which is fully flowed through.

The control tus 30 (Fig. 1) has at least one signal pick-up 16. The at least one signal pick-up 16 is a measuring apparatus, for example, for mixing parameters such as, for example, the pressure above the liquid column p in the mixing tank 100, a mixing or solution temperature T of the liquid F, a dry matter concentration c or a timedependent curve of a dry matter concentration c(t), rates of rotation n1, n2 and a timedependent power consumption l(t) of the stirring and/or shearing and homogenizing apparatus 24, 26. The signal pick-up 16 is represented, by way of example, in Fig. 1 for the ependent power consumption l(t) of the second drive motor 50 of the shearing and homogenizing apparatus 26. Similarly, further measuring tuses can additionally or alternatively be provided, which establish the other mixing parameters.

Method (Figs. 3 to 6 in conjunction with Figs. 1 and 2) The introduction and treatment of the pulverulent material P are ed virtually under the reaction kinetics-related conditions of a nce time behavior of a homogeneous reaction vessel working in a discontinuous manner. The method is distinguished in the known manner such that a quantity of liquid mF is made available in the mixing tank 100 (supply via the feed connection 100.5) and the pulverulent material P is supplied to said liquid F in a discontinuous manner via the inlet valve 20 with the mass flow of pulverulent material m? P, which can, in the most l case, be a time-dependent mass flow of pulverulent material m? P(t). The liquid F and the pulverulent material P are constantly stirred and/or mixed to form a mixing product M and the mixing product M is homogenized. The pulverulent material P is supplied until such time as the time-dependent curve of a dry matter concentration c(t) of the pulverulent material P in the mixing product M has grown to a specified final value CE.

In the case of the mixing method discussed here, a ation of the mixing product M at least in terms of the time-dependent curve of a dry matter concentration c(t) assigned to the specified final value CE and, respectively, the reaction conditions are specified in the form of default data D.

The pulverulent material P is supplied in a discontinuous manner over a duration t in pulses by means of a chronological sequence of metering pulses i (Figs. 3 and 4), which are each terized by the mass flow of the ulent material m? P, a duration of the metering pulse ?t1 and a time interval between adjacent metering pulses ?t2. The mass flow of the pulverulent material m? P is essentially a timedependent mass flow of pulverulent al m? P(t), as already indicated above, wherein in the case of the present subject matter of the application due to the construction and the switching characteristics of the inlet valve 20, approximately a time-independent and therefore constant mass flow of ulent material m? P is assumed (m? P = constant).

The time-dependent power consumption l(t), which is y d in Fig. 3 over the corresponding duration t, is established or respectively ed, for example at the second drive motor 50 of the shearing and homogenizing apparatus 26 for the duration of the metering pulse ?t1 according to Fig. 3. Said time-dependent power consumption is proportional to a stirring and/or shearing and homogenizing power required for a temporarily available mixing product M* in the mixing tank 100 immediately after the metering pulse i (Fig. 1), which stirring and/or shearing and homogenizing power is to be applied by the stirring and/or shearing and homogenizing apparatus 24, 26. The curve of the time-dependent power consumption l(t) is similar to a Gaussian normal distribution curve, it climbs with the mass flow of pulverulent material m? P entering intermittently and reaches a maximum, in order to then gradually fall, following dissolution of the pulverulent material P, i.e. in the case of a homogenized mixing product M which is then achieved, to a timedependent power consumption l(t) required for this nized mixing t M.

This typical behavior is used in control engineering terms, according to the invention, in that a time-dependent curve of a reference power consumption l0(t) is ed from the default data D, which curve is characteristic of the stirring and/or shearing and homogenizing power to be provided to the nized mixing product M.

If the time al between adjacent metering pulses ?t2 is not sufficient in order to dissolve, mix in and homogenize a metered quantity of pulverulent al mP = m? P ?t1, a time-dependent upwardly deviating power consumption l*(t) is measured, so that in this ion of the temporarily available mixing product M*, a renewed metering pulse i is not yet displayed at the end of the time interval between adjacent metering pulses ?t2. If under comparable conditions, a time-dependent downwardly deviating power consumption l**(t) is ascertained, this can be an indication that the ng and/or shearing and homogenizing phase which is also d by the time interval between adjacent metering pulses ?t2 is excessively long or that no quantity of pulverulent material mP adequate for this phase has been metered.

As soon as the pulverulent material P is uniformly distributed in the absorbing liquid F or in the absorbing mixing product M, i.e. distributed as neously as possible and, if applicable, has dissolved, the time-dependent power consumption l(t) subsides, and does so on the time-dependent curve of a reference power consumption l0(t), which is characteristic of the stirring and/or shearing and homogenizing power to be provided to the homogenized mixing product M under the conditions of the assigned time-dependent curve of the dry matter concentration c(t) (see Figs. 3 to 5: approximately linear time-dependent curve of a reference power consumption l0(t); Fig. 6: degressive time-dependent curve of a nce power consumption l0(t)). The time-dependent curve of a reference power consumption l0(t) begins at time t = 0, at which only the pure liquid F is available, with an initial value of a nce power consumption l0(t = 0) = l0 (see Figs. 3 to 6). The curve of a reference power consumption l0(t) in this respect is stored in the default data D, and it is dependent on the formulation of the mixing product M and the reaction conditions for the mixing s.

At the end of the time interval between adjacent metering pulses ?t2 and in the event of a deviation of the time-dependent power consumption l(t) from the respective assigned value in the time-dependent curve of a reference power consumption l0(t) by more than a specified tolerance, wherein a deviation either upward or downward can exist (see Figs. 3, 4), the duration of the metering pulse ?t1 for the following metering pulse is shortened in the first case and lengthened in the second case. The tolerance consists of a specification of a permissible overcurrent ?I1 and of a permissible undercurrent ?I2 (Fig. 3).

The case of the shortening is represented in Fig. 4, wherein in the represented case example the duration of the ng pulse ?t1 and, therefore, also the assigned period of time between adjacent metering pulses ?t2 have been halved by way of example (?t1/2; ?t2/2). In the case of this metering mode as well, an tion is in turn d out at the end of the period of time between adjacent metering pulses ?t2/2, whether, within the framework of the specified tolerance, a time-dependent upwardly or downwardly deviating power ption l*(t), l**(t) is present, which makes a necessary correction in the sense represented above essential.

The duration of the metering pulse ?t1 is shortened or lengthened if a current corridor ined in each case by the permissible overcurrent ?I1 or the permissible urrent ?I2 is left by the ependent ly or downwardly deviating power consumption l*(t), l**(t). The permissible overcurrent and the sible undercurrent ?I1, ?I2 are preferably each determined by a percentage proportion of the assigned time-dependent curve of a reference power consumption l0(t).

Furthermore, the degree of the shortening or the lengthening of the duration of the metering pulse ?t1 is preferably determined as a function of the degree of the deviation of the ependent power consumption l(t) from the assigned timedependent curve of a reference power consumption l0(t). The permissible overcurrent ?I1 and permissible undercurrent ?I2 ultimately determined by the respective formulation of the mixing product M can be part of the default data D for the mixing process.

Expedient formulation-dependent control parameters S obtained in the course of controlling the uction of the pulverulent material P into the at least one liquid F, namely the duration of the metering pulse ?t1 and the time interval between adjacent metering pulses ?t2, are saved and utilized for following controls of the same formulations.

The control apparatus 30 of the mixing device 100 is set up, according to the invention, such that this can provide the formulation-dependent default data D as well as the formulation-dependent control parameters S in the form of the duration of the metering pulse ?t1 and the time interval between adjacent metering pulses ?t2. The control apparatus 30 furthermore has at least the signal pick-up 16 which is configured as a ing tus (Fig. 1), which s the time-dependent power consumption l(t) of the stirring apparatus 24 and/or of the shearing and homogenizing apparatus 26 (Figs. 3, 4). The control apparatus 30 actuates, according to the invention, the closed or the open position of the valve closure member 8 (Fig. 2) as a function of the time-dependent power consumption l(t) and in relation to the t data D and the control parameters S.

The method s in the time-dependent curve of a dry matter concentration c(t), which systematically ends in the specified final value CE, wherein a distinction is to be made between the time-dependent curve of a dry matter concentration c(t) without saturation character (approximately linear time-dependent curve; see Figs. 3 to 5) or the time-dependent curve of a dry matter concentration with saturation ter (degressive time-dependent curve; see Fig. 6). The time-dependent curve of a dry matter concentration c(t) ending in the ied final value CE is d by the sequence of specific metering pulses i, i.e. clearly ated by the duration of the metering pulse ?t1 and the time interval between adjacent metering pulses ?t2.

For the time-dependent curve of a dry matter tration c(t) without saturation character, beginning at c(t = 0) = 0 for the pure liquid F (Fig. 5), as this can be described by the aforementioned equations (1, 1a) (c(t) = k1 V t), a configuration of the method provides that this curve is defined by a fixed duration-time al ratio V between the on of the metering pulse ?t1 and the assigned time al between adjacent metering pulses ?t2 (V = ?t1/?t2 = constant). In the event of deviations from the time-dependent curve of a reference power consumption l0(t), according to the invention, with a constant duration-time interval ratio V, the duration of the ng pulse ?t1 is shortened (as this is shown by way of example qualitatively in Fig. 4 in contrast to Fig. 3) or lengthened. This control engineering measure which has a fixed duration-time interval ratio V inevitably leads, proportionally, to a corresponding ning or lengthening of the time interval between adjacent metering pulses ?t2, based on the following metering pulse i.

For the time-dependent curve of a dry matter concentration c(t) with tion ter (Fig. 6), as it can be described by the equation (2) indicated above, ???? (???? (???? ) ˜ ???? 2 ????? =0 ????? 1), a r configuration of the method provides that this curve is ???? ???? (???? ) defined by a variable duration-time interval-ratio V between the duration of the metering pulse ?t1 and the assigned time interval between adjacent metering pulses ?t2 (V = ?t1/?t2 ? constant), wherein • in the event of a deviation of the time-dependent power ption l(t) from the respective assigned value in the time-dependent curve of a reference power consumption l0(t) by more than the specified tolerance upward, the duration-time interval ratio V is reduced, and • in the event of a deviation of the time-dependent power consumption l(t) from the respective assigned value in the time-dependent curve of a reference power consumption l0(t) by more than the specified tolerance downward, the durationtime interval ratio V is enlarged.

The tive curve of a dry matter concentration c(t) climbs degressively over the duration t, beginning at c(t = 0) = 0 for the pure liquid F (Fig. 6), because the mass flow of the pulverulent material m? P which is constantly metered in pulses, viewed over the entire duration t of the mixing process, is indeed preferably nt (m? P = constant), the on of the metering pulse ?t1, however, steadily decreases and, consequently, a steadily decreasing quantity of pulverulent material mP is d.

The mass flow of pulverulent al m? P is introduced, in the duration t of the entire mixing process with an approximately invariable filling level N in the mixing tank 100, into an available, virtually invariable volume of the mixing product VM (VM ˜ constant), wherein a density ?M of the mixing product M increases, namely in accordance with the time-dependent curve of a dry matter concentration c(t), which grows to the specified final value CE.

Fig. 6 illustrates, as a function of the time-dependent curve of a dry matter concentration c(t), how the respectively metered quantity of pulverulent material mP = m? p?t1 steadily decreases, wherein the respective assigned time-dependent power consumption l(t) has, in each case, approached the assigned time-dependent curve of a reference power consumption l0(t) at the end of the time interval between nt metering pulses ?t2 or respectively is to the greatest possible extent congruent therewith. A curve in this respect describes a successful mixing s which, on the one hand, protects the mixing product M and, on the other hand, is configured in an energy-efficient manner. It does not e any control-engineering measures in the sense ned above. Only if deviations from the permissible overcurrent or undercurrent ?I1, ?I2 occur, do the control isms engage in a similar way to how they have been described for the first method in connection with Figs. 3 and 4.

These control-engineering measures which have a variable duration-time interval ratio V require the control apparatus 30 to be able to shorten or lengthen the duration of the metering pulse ?t1 with an invariable time interval n adjacent ng pulses ?t2 or, if the duration of the ng pulse ?t1 does not vary, to lengthen or to shorten the time interval between adjacent metering pulses ?t2 in an appropriate manner.

Consequently, the control-engineering measures according to the invention, essentially consist, in both configurations of the method, of the fact that the duration of the metering pulse ?t1 and the time interval between adjacent metering pulses ?t2 are selected such that at the respective end of the time interval between adjacent ng pulses ?t2, the power consumption l(t) for stirring and/or shearing and homogenizing the arily available mixing product M*, which power consumption is ascertained depending on the time, ches the time-dependent curve of a reference power consumption l0(t), which is ed in order to treat the homogenized mixing product M in this respect, within the framework of a practiceoriented permissible tolerance.

LIST OF REFERENCE NUMERALS FOR THE ABBREVIATIONS USED 1000 Mixing device 100 Mixing tank 100.1 Tank casing 100.2 Upper tank bottom 100.3 Lower tank bottom (conical; tapered) 100.4 Outlet connection 100.5 Feed connection Inlet valve Control tus 40 First drive motor 50 Second drive motor 2 Valve housing 2a Valve seat 2b Seat opening 2c Pipe connection 4 Lantern-type housing 6 Drive housing 8 Valve closure member 8a Valve disk 8b Valve rod Seat seal 12 Return spring 14 Control head housing 16 Signal pick-up 18 Supply line 22 Signal line 24 Stirring apparatus 26 Shearing and homogenizing apparatus D Default data F Liquid l0 Initial value of a reference power consumption (for the homogenized mixing product M; l0(t =0) = I0) l0(t) Time-dependent curve of a reference power consumption l(t) ependent power consumption (for the temporarily available mixing product M*) l*(t) Time-dependent upwardly deviating power ption l**(t) Time-dependent downwardly deviating power consumption ?l1 sible overcurrent ?I2 Permissible undercurrent M Mixing product M* Temporarily available mixing product N Filling level P Pulverulent material S Control parameter T Mixing or solution temperature V Duration-time al ratio (V = ?t1/?t2) VM Volume of the mixing product ?M Density of the mixing product c Dry matter concentration c(t) Time-dependent curve of a dry matter concentration CE Specified final value (of the time-dependent curve) h Height of the liquid column i Metering pulse ???? ???? k1 First proportionality constant ????? 1 = ? ???? ???? k2 Second proportionality constant ????? 2 = ???? ???? ? ???? ???? mF Quantity of liquid mP Quantity of pulverulent al m? P Mass flow of pulverulent material m? P(t) ependent mass flow of pulverulent material n1 First rate of rotation n2 Second rate of rotation p Pressure above the liquid column t Time (generally) or time interval of the mixing process ?t1 Duration of the metering pulse ?t2 Time interval between adjacent metering pulses

Claims (10)

Claims 1.

1. A method for controlling the introduction of a pulverulent material (P) into a liquid (F) consisting of at least one component for a batch mixing method, • in which the introduction and treatment of the pulverulent material (P) are effected under the conditions of a residence time behavior of a homogeneous reaction vessel working in a tinuous manner in such a way that o a quantity of liquid (mF) is made available and the pulverulent material (P) is supplied into said liquid (F) in a discontinuous manner, o the liquid (F) and the pulverulent material (P) are ntly stirred and/or mixed to form a mixing product (M) and the mixing product (M) is homogenized, and o the pulverulent material (P) is ed until such time as a timedependent curve of a dry matter concentration (c(t)) of the pulverulent material (P) in the mixing t (M) has grown to a specified final value (CE), terized in that • a formulation of the mixing product (M) at least in terms of the time-dependent curve of a dry matter concentration (c(t)) assigned to the specified final value (CE) and, respectively, the reaction conditions are specified in the form of default data (D), • the pulverulent material (P) is supplied in a discontinuous manner in pulses by means of a chronological sequence of metering pulses (i), each of which is characterized by a mass flow of the pulverulent al (m? P), a duration of the metering pulse (?t1) and a time interval n adjacent metering pulses (?t2), • the time-dependent curve of a dry matter concentration (c(t)) ending in the specified final value (CE) is defined by the sequence of clearly determined metering pulses (i), • a time-dependent power consumption (l(t)) is ascertained which is proportional to a stirring and/or shearing and homogenizing power required for a temporarily ble mixing product (M*), • a time-dependent curve of a reference power consumption (l0(t)) is utilized from the default data (D), which is characteristic of the stirring and/or shearing and homogenizing power to be provided to the homogenized mixing product (M) under the conditions of the assigned time-dependent curve of a dry matter tration (c(t)), and • at the end of the time interval between adjacent metering pulses (?t2) and in the event of a deviation of the time-dependent power consumption (l(t)) from the respective assigned value in the time-dependent curve of a reference power consumption (l0(t)) by more than a specified tolerance, either upwards or downwards, the duration of the metering pulse (?t1) for the following metering pulse (i) is shortened in the first case and lengthened in the second case.

2. The method according to Claim 1, characterized in that time-dependent curves of a dry matter tration (c(t)) without saturation character are defined by a fixed duration-time interval ratio (V) n the duration of the metering pulse (?t1) and the ed time interval between adjacent metering pulses (?t2) (V = ?t1/?t2 = nt).

3. The method according to Claim 1, characterized in that time-dependent curves of a dry matter concentration (c(t)) with saturation character are d by a variable duration-time interval ratio (V) between the duration of the metering pulse (?t1) and the assigned time interval between adjacent metering pulses (?t2) (V = ?t1/?t2), wherein • in the event of a deviation of the time-dependent power consumption (l(t)) from the respective assigned value in the time-dependent curve of a reference power consumption (l0(t)) by more than the specified tolerance upwards, the ontime interval ratio (V) is d, and • in the event of a deviation of the time-dependent power consumption (l(t)) from the respective assigned value in the time-dependent curve of a reference power ption ) by more than the specified tolerance downwards, the duration-time al ratio (V) is enlarged.

4. The method ing to any one of the preceding claims, characterized in that the mass flow of the pulverulent material (m? P) is constant over the duration of the metering pulse (?t1).

5. The method according to any one of the preceding claims, characterized in that the shortening or the lengthening of the duration of the metering pulse (?t1) is effected if a current or determined in each case by a permissible overcurrent (?l1) or a permissible undercurrent (?l2) is left by an upwardly deviating power ption (l*(t)) or a downwardly deviating power consumption (l**(t)), wherein the permissible overcurrent and the permissible undercurrent (?l1, ?I2) are each determined by a percentage proportion of the assigned time-dependent curve of a reference power consumption (l0(t)).

6. The method according to any one of the ing claims, characterized in that the degree of the shortening or the lengthening of the duration of the metering pulse (?t1) is determined as a on of the degree of the deviation of the time-dependent power ption (l(t), l*(t), l**(t)) from the ed time-dependent curve of a reference power consumption (l0(t)).

7. The method according to any one of the preceding claims, characterized in that the further formulation-dependent default data (D) underlying the control of the introduction of the pulverulent material (P) into the at least one liquid (F) are obtained from empirical values of earlier mixing processes and are saved, wherein said default data (D) are • a mixing or solution temperature (T), • a pressure above the liquid column (p), • rates of on (n1, n2) of tuses for stirring and/or shearing and homogenizing, and • a permissible overcurrent (?I1) dependent on the assigned curve of a reference power consumption (l0(t)) and a sible undercurrent (?I2).

8. The method according to any one of the preceding claims, characterized in that the ent ation-dependent control parameters (S) obtained in the course of controlling the uction of the pulverulent material (P) into the at least one liquid (F), namely • the duration of the metering pulse (?t1) and • the time interval between adjacent metering pulses (?t2), are saved and are utilized for following controls of identical formulations.

9. A mixing device for carrying out the method according to Claim 1, having a mixing tank (100) which has a feed connection (100.5) for supplying for a liquid (F), an outlet connection (100.4) for discharging for a mixing product (M) and a stirring apparatus (24) and/or a shearing and homogenizing apparatus (26), having an inlet valve (20) with a valve closure member (8) arranged on the mixing tank (100), having the valve closure member (8) with which the inlet valve (20) can be adjusted either between tely closed (closed position) or tely open (open position), having the inlet valve (20), by means of which a pulverulent material (P) is introduced into the liquid (F), having a control apparatus (30) assigned to the inlet valve (20), with which the valve e member (8) can be moved into the closed or into the open position, characterized in that • the l apparatus (30) provides formulation-dependent t data (D) and formulation-dependent control parameters (S) in the form of the duration of the metering pulse (?t1) and the time interval between adjacent metering pulses (?t2), • the control apparatus (30) has at least one signal pick-up (16) configured as a measuring apparatus, which signal pick-up detects a time-dependent power consumption (l(t)) of the stirring apparatus (24) and/or of the shearing and homogenizing apparatus (26), and • the control apparatus (30) actuates the closed or the open position of the valve closure member (8) as a function of the time-dependent power consumption (l(t)) and in on to the t data (D) and the control parameters (S).

10. The mixing device according to Claim 9, characterized in that the valve closure member (8) is configured at least in its region acted upon by powder as a cylindrical rod having the same diameter, on which a valve disk (8a) having the same diameter is molded. 1