AU2018285478A1

AU2018285478A1 - Method and mixing device for controlling the introduction of a pulverulent material into a liquid for a batch mixing method

Info

Publication number: AU2018285478A1
Application number: AU2018285478A
Authority: AU
Inventors: Mikkel Mork Nielsen; Claus Patscheider; Ulrich ROLLE; Uwe Schwenzow; Ludger Tacke
Original assignee: GEA TDS GmbH
Current assignee: GEA TDS GmbH
Priority date: 2017-06-13
Filing date: 2018-04-03
Publication date: 2019-11-21
Anticipated expiration: 2038-04-03
Also published as: WO2018228714A1; AU2018285004B2; AU2018285004A1; PL3638409T3; JP2020523188A; NZ758627A; PL3638411T3; EP3638411B1; NZ759145A; AU2018285478B2; EP3638411A1; EP3638409A1; WO2018228713A1; DK3638411T3; DK3638409T3; JP6952802B2; EP3638409B1

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 (ṁ

Description

Method and mixing device for controlling the introduction 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 accordance 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 carrying out the method.

PRIOR ART

With a view to the introduction of a pulverulent material into a liquid and the uniform 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 familiar 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 pulverulent material is supplied until such time as a desired or respectively systematically specified dry matter concentration of the pulverulent material is available in the liquid. Pulverulent material and liquid are preferably constantly stirred and/or mixed to form a mixing product and the mixing product is homogenized with the aim of uniformly 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 steadily 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. 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. drymatter concentration) at any point and no temperature differences occur. The dry 5 matter concentration in the discharged 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 respect 10 and the assigned mixing device have been disclosed to the public, for example under the following internet link: ^,,hltp;//www.qea.cQm/de/products/Hiqh-Shear-BatchMixer.jsp”.

The mixing devices indicated above also preferably comprise so-called vacuum mixers 15 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 20 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 introduced into the mixing tank via an opening 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 25 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 surroundings and, on the other hand, a quantity of the pulverulent material made 30 available 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 pulverulent 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 illustrated in an increase in the stirring and/or shearing and homogenizing power (driving power for the assigned apparatuses), which is necessary in order to treat the temporarily available mixing product in this phase of the mixing process. 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 respectively mixing tank, which is operated in a discontinuous manner, does indeed theoretically postulate an identical composition of the mixing product at any point, but it can, in practice, increasingly result in nonhomogeneously distributed 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 excluded 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, shortens 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 pulverulent material and disproportionately large fluctuations in the supply of pulverulent material, and to prevent 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 - presumably to be on the safe side. This too intensive treatment can, on the one hand, have a product-damaging effect and is, on the other hand, not energy efficient.

The object of the present invention is to further develop a generic 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 carrying out the method having the features of the alternative independent 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 method, 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 multiple liquid components 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 pulverulent material is supplied to said liquid in a discontinuous manner, and the liquid and the pulverulent material are constantly stirred 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 inventive concept of the solution in the case of the method is that a formulation of the mixing product 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 provided that the pulverulent material is supplied in a discontinuous manner in the known manner in pulses by means of a chronological sequence 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 pressure. The metering pulses are each characterized by a mass flow of the pulverulent material rhp, a duration of the metering pulse At1 and a time interval between adjacent metering pulses At2.

The method produces a time-dependent curve of a dry matter concentration c(t), which systematically ends in the specified 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 pulverulent material can be metered within the framework of the absorption capacity or the solubility limit of the liquid in identical time intervals, so that during complete homogenization of the mixing product, 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 capacity or the solubility limit of the liquid in identical time intervals, so that during complete homogenization of the mixing product, a time-dependent 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 homogenizing 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 pulverulent 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 product, i.e. has been distributed as homogeneously as possible and, if applicable, has dissolved, the time-dependent power consumption l(t) subsides and does so on a time-dependent curve of a reference power consumption lo(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 timedependent curve of a dry matter concentration (c(t)). The time-dependent curve of the reference power consumption lo(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 At2 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(t) by more than a specified tolerance, wherein a deviation either upwards or downwards can exist, the duration of the metering pulse At1 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 configuration 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 At1 and the assigned time interval between adjacent metering pulses At2 (V = At 1/At 2 = constant).

The respective curve of a dry matter concentration c(t) climbs over time t, because the mass flow of the pulverulent material rhp which is constantly metered in pulses, said mass flow being, in the most general case, a time-dependent mass flow of pulverulent material rhp(t), viewed over the entire duration t of the mixing process, is constant (rhp = constant). The mass flow of pulverulent material rhp is introduced multiple times, namely (t/At2)-times, in the duration t, with an approximately invariable filling level in the mixing tank, into an invariable quantity of liquid mF of the available mixing product, wherein the time-dependent curve of a dry matter concentration c(t) constitutes the following according to equation (1):

c(t) = m_F + (1)

In most practice-oriented cases, because the first term of the following relationship is, as a general rule, small compared to the second term, t

m_P — Δίΐ « m_F can be set approximately so that, in accordance with equation (1a), the following results approximately for the time-dependent curve of a dry matter concentration c(t) with a first proportionality constant kl = — mp , n rhp Atl rhp _XT . „ _XT c(t) « — = — — t = — V t = kl V t ^m- mp Δΐ2 mp (1a) mp

This control engineering measure which has a fixed duration-time interval ratio V (V = At1/At2 = constant) essentially leads, proportionally, to a corresponding shortening or lengthening of the time interval between adjacent metering pulses Δί2, 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 defined by a variable duration-time interval ratio V between the duration of the metering pulse Δί1 and the assigned time interval between adjacent metering pulses Δί2 (V = Δί1/Δί2 • 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 lo(t) by more than the specified tolerance upwards, 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 lo(t) by more than the specified tolerance downwards, the durationtime 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 rhp which is constantly metered in pulses, viewed over the entire duration t of the mixing process, is indeed constant (rhp = constant), however the duration of the metering pulse At1 steadily decreases and, consequently, a steadily decreasing quantity of pulverulent material is metered. The mass flow of pulverulent material rhp 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 pm of the mixing product increases in accordance 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 constant k2 = :

₌ Zt=o (mp(t)Atl) ₌ m_P Zt=oAtl ~ Zt=pAtl

Ρμ(ϊ) Vm V_m p_M(t) Ρμ(ϊ)

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 At1 with an invariable time interval between adjacent metering pulses At2 or, in the case of an unaltered duration of the metering pulse At1, to lengthen or shorten the time interval between adjacent metering pulses At2 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 metering pulse At1 and the time interval between adjacent metering pulses At2 are selected such that at the respective end of the time interval between adjacent metering pulses At2, the power consumption l(t) for stirring and/or shearing and homogenizing the temporarily available mixing product, which power consumption is ascertained depending on the time, approaches the time-dependent curve of a reference power consumption lo(t), which is required in order to treat the homogenized mixing product in this respect, within the framework of a practice-oriented 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 possible, another configuration of the method provides 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 consumption. The permissible overcurrent and the permissible undercurrent are each determined by a percentage proportion of the assigned time-dependent curve of a reference power consumption. To ensure that the control works as precisely as possible in this respect, it is furthermore proposed that the degree of the shortening or the lengthening 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 further formulation-dependent default data underlying the control of the introduction of the pulverulent material into the at least one liquid are obtained from empirical values of earlier mixing processes and are saved, wherein said default data are a mixing or solution 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 overcurrent dependent on the assigned time-dependent curve of a reference power consumption and a permissible undercurrent.

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 expedient formulation-dependent control parameters obtained in the course of controlling 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 connection 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 pulverulent 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 between adjacent metering pulses. Furthermore, the control apparatus has, according to the invention, at least one signal pick-up configured as a measuring apparatus, which signal pick-up detects a time-dependent power consumption of the stirring apparatus and/or of the shearing and homogenizing apparatus. Equipped 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 default 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 susceptibility to clogging from the outset, even further in this respect and, by way of example, to prevent 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 diameter, 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 region.

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 introduction of a pulverulent material into a liquid consisting of at least one component for a batch mixing method, 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 time-dependent power consumption l(t) for a sequence of metering pulses having a constant duration of the metering pulse At1 and having a time interval between adjacent metering pulses At2, wherein a time-dependent curve of a dry matter concentration c(t) without 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 sequence of metering pulses having a constant duration of the metering pulse Δΐ1 /2 and having a time interval between adjacent metering pulses At2/2, wherein the time-dependent 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 method, a time-dependent power consumption l(t) for a larger sequence of metering pulses having a constant duration of the metering pulse At1 and having a constant time interval between adjacent metering pulses At2 in order to realize a timedependent approximately linearly 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 time-dependent power consumption l(t) for a sequence of metering pulses having a steadily decreasing duration of the metering pulse At1 and having a constant time interval between adjacent metering impulses At2 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 preferably cylindrical 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 rhp, which is supplied via a supply line 18, into the liquid F or into the mixing product M. A control apparatus 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 acting, 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 apparatus preferably sucks the liquid F or the mixing product M in, on the one hand, from above and ejects these, on the other hand, annularly 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 material P or the resulting mixing product M are very intensively mechanically mixed and preferably homogenized thereby.

The inlet valve 20 is configured 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 sealing in the closed position of the inlet valve 20 in the interaction with the valve seat 2a. The valve seat 2a has a seat opening 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 composed 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 assigned 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 housing 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 pressure 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 axially guide the valve closure member 8. 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 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 prevented, wherein the valve closure member 8 with its end valve disk 8a and the assigned seat seal 10 can be withdrawn to the greatest possible extent from the region of the valve housing 2 which is fully flowed through.

The control apparatus 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 time dependent 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 time-dependent power consumption l(t) of the second drive motor 50 of the shearing and homogenizing apparatus 26. Similarly, further measuring apparatuses 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 effected virtually under the reaction kinetics-related conditionsofa 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 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 rtip, which can, in the most general case, be a time-dependent mass flow of pulverulent material rtip(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 timedependent 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 c_E.

In the case of the mixing method discussed here, 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 c_E 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 characterized by the mass flow of the pulverulent material rtip, a duration of the metering pulse At1 and a time interval between adjacent metering pulses At2. The mass flow of the pulverulent material rtip is essentially a timedependent mass flow of pulverulent material rhp(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 pulverulent material rhp is assumed (rhp = constant).

The time-dependent power consumption l(t), which is equally plotted in Fig. 3 over the corresponding duration t, is established or respectively measured, for example at the second drive motor 50 of the shearing and homogenizing apparatus 26 for the duration of the metering pulse At1 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 rhp 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 time-dependent power consumption l(t) required for this homogenized mixing product 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 lo(t) is utilized from the default data D, which curve is characteristic of the stirring and/or shearing and homogenizing power to be provided to the homogenized mixing product M.

If the time interval between adjacent metering pulses At2 is not sufficient in order to dissolve, mix in and homogenize a metered quantity of pulverulent material mp = rhp Δΐ1, a time-dependent upwardly deviating power consumption l*(t) is measured, so that in this condition 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 At2. If under comparable conditions, a time-dependent downwardly deviating power consumption l**(t) is ascertained, this can be an indication that the stirring and/or shearing and homogenizing phase which is also defined by the time interval between adjacent metering pulses At2 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 homogeneously 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 lo(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 lo(t); Fig. 6: degressive time-dependent curve of a reference power consumption lo(t)). The timedependent curve of a reference power consumption lo(t) begins at time t = 0, at which only the pure liquid F is available, with an initial value of a reference power consumption lo(t = 0) = Io (see Figs. 3 to 6). The curve of a reference power consumption lo(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 process.

At the end of the time interval between adjacent metering pulses At2 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(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 At1 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 ΔΙ1 and of a permissible undercurrent ΔΙ2 (Fig. 3).

The case of the shortening is represented in Fig. 4, wherein in the represented case example the duration of the metering pulse Δί1 and, therefore, also the assigned period of time between adjacent metering pulses Δί2 have been halved by way of example (Δΐ1 /2; Δΐ2/2). In the case of this metering mode as well, an inspection is in turn carried out at the end of the period of time between adjacent metering pulses At2/2, whether, within the framework of the specified tolerance, a time-dependent upwardly or downwardly deviating power consumption l*(t), l**(t) is present, which makes a necessary correction in the sense represented above essential.

The duration of the metering pulse At1 is shortened or lengthened if a current corridor determined in each case by the permissible overcurrent ΔΙ1 or the permissible undercurrent ΔΙ2 is left by the time-dependent upwardly or downwardly deviating power consumption l*(t), l**(t). The permissible overcurrent and the permissible undercurrent ΔΙ1, ΔΙ2 are preferably each determined by a percentage proportion of the assigned time-dependent curve of a reference power consumption lo(t). Furthermore, the degree of the shortening or the lengthening of the duration of the metering pulse Δί1 is preferably determined as a function of the degree of the deviation of the time-dependent power consumption l(t) from the assigned time-dependent curve of a reference power consumption lo(t). The permissible overcurrent ΔΙ1 and permissible undercurrent ΔΙ2 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 introduction of the pulverulent material P into the at least one liquid F, namely the duration of the metering pulse Δί1 and the time interval between adjacent metering pulses Δί2, 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 Δί1 and the time interval between adjacent metering pulses Δί2. The control apparatus 30 furthermore has at least the signal pick-up 16 which is configured as a measuring apparatus (Fig. 1), which detects 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 timedependent power consumption l(t) and in relation to the default data D and the control parameters S.

The method results in the time-dependent curve of a dry matter concentration c(t), which systematically ends in the specified final value c_E, 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 character (degressive time-dependent curve; see Fig. 6). The time-dependent curve of a dry matter concentration c(t) ending in the specified final value c_E is defined by the sequence of specific metering pulses i, i.e. clearly stipulated by the duration of the metering pulse At1 and the time interval between adjacent metering pulses At2.

For the time-dependent curve of a dry matter concentration 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 interval ratio V between the duration of the metering pulse At1 and the assigned time interval between adjacent metering pulses Δί2 (V = At1/At2 = constant). In the event of deviations from the timedependent curve of a reference power consumption lo(t), according to the invention, with a constant duration-time interval ratio V, the duration of the metering pulse Δΐ1 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 shortening or lengthening of the time interval between adjacent metering pulses Δί2, based on the following metering pulse i.

For the time-dependent curve of a dry matter concentration c(t) with saturation character (Fig. 6), as it can be described by the equation (2) indicated above, (c(t) « k2 ° _λ ), a further configuration of the method provides that this curve is

Pmw defined by a variable duration-time interval-ratio V between the duration of the metering pulse Δί1 and the assigned time interval between adjacent metering pulses Δί2 (V = Δί1/Δί2 Ψ 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 lo(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 lo(t) by more than the specified tolerance downward, the duration-time interval ratio V is enlarged.

The respective 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 mp which is constantly metered in pulses, viewed over the entire duration t of the mixing process, is indeed preferably constant (rhp = constant), the duration of the metering pulse Δί1, however, steadily decreases and, consequently, a steadily decreasing quantity of pulverulent material mpis metered. The mass flow of pulverulent material rhp 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 Pm 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 c_E.

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 = ιτίρΔΐΙ 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 lo(t) at the end of the time interval between adjacent metering pulses Δί2 or respectively is to the greatest possible extent congruent therewith. A curve in this respect describes a successful mixing process 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 require any control-engineering measures in the sense explained above. Only if deviations from the permissible overcurrent or undercurrent ΔΙ1, ΔΙ2 occur, do the control mechanisms 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 Δί1 with an invariable time interval between adjacent metering pulses Δί2 or, if the duration of the metering pulse Δί1 does not vary, to lengthen or to shorten the time interval between adjacent metering pulses Δί2 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 Δί1 and the time interval between adjacent metering pulses Δί2 are selected such that at the respective end of the time interval between adjacent metering pulses Δί2, the power consumption l(t) for stirring and/or shearing and homogenizing the temporarily available mixing product M*, which power consumption is ascertained depending on the time, approaches the time-dependent curve of a reference power consumption lo(t), which is required 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 apparatus

First drive motor

Second drive motor

Valve housing

2a Valve seat

2b Seat opening

2c Pipe connection

Lantern-type housing

Drive housing

Valve closure member

8a Valve disk

8b Valve rod

Seat seal

Return spring

Control head housing

Signal pick-up

Supply line

Signal line

Stirring apparatus

Shearing and homogenizing apparatus

D Default data

F Liquid

Io Initial value of a reference power consumption (for the homogenized mixing product M; lo(t =0) = Io) lo(t) Time-dependent curve of a reference power consumption l(t) Time-dependent power consumption (for the temporarily available mixing product M*) l*(t) Time-dependent upwardly deviating power consumption l**(t) Time-dependent downwardly deviating power consumption ΔΙ1 Permissible overcurrent

ΔΙ2 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 interval ratio (V = Δί1/Δί2)

Vm Volume of the mixing product

Pm Density of the mixing product c Dry matter concentration c(t) Time-dependent curve of a dry matter concentration c_E Specified final value (of the time-dependent curve) h Height of the liquid column i Metering pulse k1 First proportionality constant (kl = k2 Second proportionality constant (k2 = mF Quantity of liquid mp Quantity of pulverulent material rhp Mass flow of pulverulent material rhp(t) Time-dependent 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

At1 Duration of the metering pulse

At2 Time interval between adjacent metering pulses

Claims

Claims

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 discontinuous manner in such a way that o a quantity of liquid (m_F) 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 constantly stirred and/or mixed to form a mixing product (M) and the mixing product (M) is homogenized, and o the pulverulent material (P) is supplied until such time as a timedependent 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), characterized 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 (c_E) 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 material (rhp), a duration of the metering pulse (At1) and a time interval between adjacent metering pulses (At2), • the time-dependent curve of a dry matter concentration (c(t)) ending in the specified final value (c_E) 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 available mixing product (M*), • a time-dependent curve of a reference power consumption (lo(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 concentration (c(t)), and • at the end of the time interval between adjacent metering pulses (Δΐ2) 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(t)) by more than a specified tolerance, either upwards or downwards, the duration of the metering pulse (Δί1) 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 concentration (c(t)) without saturation character are defined by a fixed duration-time interval ratio (V) between the duration of the metering pulse (Δΐ1) and the assigned time interval between adjacent metering pulses (Δΐ2) (V = Δί1/Δί2 = constant).
3. The method according to Claim 1, characterized in that time-dependent curves of a dry matter concentration (c(t)) with saturation character are defined by a variable duration-time interval ratio (V) between the duration of the metering pulse (Δΐ1) and the assigned time interval between adjacent metering pulses (Δΐ2) (V = Δί1/Δί2), 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 (lo(t)) by more than the specified tolerance upwards, the durationtime 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 (lo(t)) by more than the specified tolerance downwards, the duration-time interval ratio (V) is enlarged.
4. The method according to any one of the preceding claims, characterized in that the mass flow of the pulverulent material (rhp) is constant over the duration of the metering pulse (At1).
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 (At1) is effected if a current corridor determined in each case by a permissible overcurrent (ΔΙ1) or a permissible undercurrent (ΔΙ2) is left by an upwardly deviating power consumption (l*(t)) or a downwardly deviating power consumption (l**(t)), wherein the permissible overcurrent and the permissible undercurrent (ΔΙ1, ΔΙ2) are each determined by a percentage proportion of the assigned time-dependent curve of a reference power consumption (lo(t)).
6. The method according to any one of the preceding claims, characterized in that the degree of the shortening or the lengthening of the duration of the metering pulse (Δί1) is determined as a function of the degree of the deviation of the time-dependent power consumption (l(t), l*(t), l**(t)) from the assigned time-dependent curve of a reference power consumption (lo(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 rotation (n1, n2) of apparatuses for stirring and/or shearing and homogenizing, and • a permissible overcurrent (ΔΙ1) dependent on the assigned curve of a reference power consumption (lo(t)) and a permissible undercurrent (ΔΙ2).
8. The method according to any one of the preceding claims, characterized in that the expedient formulation-dependent control parameters (S) obtained in the course of controlling the introduction of the pulverulent material (P) into the at least one liquid (F), namely • the duration of the metering pulse (Δί1) and • the time interval between adjacent metering pulses (Δί2), 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 completely closed (closed position) or completely 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 closure member (8) can be moved into the closed or into the open position, characterized in that • the control apparatus (30) provides formulation-dependent default data (D) and formulation-dependent control parameters (S) in the form of the duration of the metering pulse (Δί1) and the time interval between adjacent metering pulses (Δί2), • 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 relation to the default 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.