SK113994A3 - Dosing process and device for its realization - Google Patents

Abstract

A process is disclosed for dosing and in particular for mixing substances, in particular for mixing at least one granulated or powdery solid with a liquid. A first substance, in particular the granulated or powdery solid, is fluidized with a continuously or intermittently supplied gas and then this homogenized gas-substance mixture is brought together and mixed in time-constant doses with a second substance. In order to dose the homogenized gas-substance mixture, gas is additionally supplied thereto before it is mixed with the second substance. Said gas is supplied so as to flow parallel to and surround the stream of gas-solids that flows into the mixing device.

Description

Method of dosing and apparatus for its implementation

Technical field

The invention relates to a method of dispensing substances, in particular for mixing at least one particulate or powdered solid with a liquid and an apparatus for carrying out the method.

BACKGROUND OF THE INVENTION. In many cases, as with mixing, it is important that the exact amount of the substance or the exact ratio of the mixing of the substances to each other is kept as far as possible. This problem can be solved in many cases by volumetric dosing in which volume units of a predetermined size are fed to the mixing device. However, this volumetric dosing is not accurate if the bulk density of the mixed solids is significantly different.

In this case, it is also possible to envisage weight dosing. However, it is assumed that the mass is available as a whole as a whole, which again makes it difficult to mix, especially for substances which tend to form deposits, such as fly ash, when adding liquid. The use of continuous weighing is also contemplated, but it is known that the accuracy of such weighing is very limited, especially since the instantaneous mass flow at its output may be subject to unexpected fluctuations, for example due to a change in bulk density. Careful dosing is also necessary for weighing, as the corresponding substance can generally be added but can no longer be removed. Changing the bulk density of the solid may also cause unexpected fluctuations in the instantaneous output mass flow.

The use of a fluidized bed for dosing is known per se. In such an embodiment, the solid is kept moving away from the top layer of the fluidized bed. However, the time-constant dosing is not yet carried out, as gas bubbles are generally formed inside the fluidized bed and partly even the rigid bodies perform uncontrollable movements.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a precise dosing method and apparatus for carrying out it. In particular, a mixing system should be provided for admixing at least one liquid to at least one solid, in which they are brought into contact in a predetermined ratio and internally mixed. Therefore, according to the invention of the method of the initially mentioned type, the features of claim 1 are proposed.

Indeed, it has been found that the aforementioned irregularities in the fluidized bed, which adversely affect the time-constant dosing, do not occur over the entire height of the fluidized bed and do not occur to a large extent in the bottom region.

A particularly important use and arrangement of the method according to the invention results from the features of claim 2. Indeed, the mixing is particularly homogeneous when all parts of the surface area of each particle are loosened by fluidized bed fluidization. Particularly homogeneous mixtures are also formed with the liquid, even if the solid is difficult to mix and if it tends to settle or adhere. This creates particularly favorable conditions for mixing hardly miscible substances with other substances, as is particularly the case for mixtures with liquids. In the context of the invention, the metering device according to the invention can be adapted for all the components of the mixture upstream of the mixing device.

According to a particularly preferred embodiment, it is proposed that the liquid be injected into the fluidising substance. It has been shown that this mixing operation provides optimal mixing with the fluidized substance.

For an economical and efficient dosing, according to a further embodiment of the invention, it is proposed that for the dosing of the homogenized gas-substance mixture before the mixing with the second substance a gas is additionally introduced into the gas mixture, this gas being introduced around the mixing device flowing the gas and solids flow. in the direction of its flow. Optionally changing this additional gas supply provides a more or less large dilution of the biphasic fluid bed mixture.

According to a further preferred embodiment of the invention, particularly effective and thus accurate dosing is achieved when the speed of the additionally introduced feed is the same as the flow rate of the gas-substance mixture.

In the apparatus according to the invention for carrying out the method, it is proposed to provide a fluidized bed device for fluidizing a first, in particular granular or powdered substance having an inlet for the first material, one or more inlet openings, preferably at the bottom of the fluidized bed for gas and a discharge for a fluidized gas-solid mixture which is arranged such that the discharge is provided at the outlet to a mixing device into which the second substance is also supplied, in particular as a liquid, preferably by means of spray nozzles or the like. This device according to the invention makes it possible to carry out the individual steps of the process according to the invention economically with low construction costs and creates a precondition for mixing hardly miscible substances.

The dosing according to a preferred embodiment of the invention can be carried out particularly efficiently in that a nozzle device is preferably designed as a hollow body as a dosing device, especially for the mixing process, which has channels for supplying additional gas through the fluidized bed outlet or in the region of the discharge pipe. a porous wall, a nozzle and the like of a hollow body into or optionally a homogeneous mixture of gas and substance.

If, in the context of some process, mixing and dosing is required to be self-regulating, for this purpose, according to a preferred embodiment of the invention, it is proposed that the fluidized bed and nozzle device be equipped, if necessary, spaced pressure measuring points, preferably electrical or electronic pressure measuring devices, or level sensors, whose output signals are fed, for example, to a memory programmable electronic control, whose output signals are preferably fed to control valves, in particular distribution valves and / or valves for reducing the pressure and preferably from a conveying device for supplying the first substance to the fluidized bed device for controlling it.

The described dispensing device is sufficient to effect a small deviation correction by gassing, and in order to effect a larger deviation correction it is proposed according to a further preferred embodiment of the invention that the fluidized bed device be controlled in particular by a preselectable memory pressure by a control valve.

Drawing overview *

The device according to the invention is schematically shown in the attached figure.

Further details of the invention will be apparent from the following description of an exemplary embodiment, which is illustrated in a single drawing of the drawing.

DETAILED DESCRIPTION OF THE INVENTION

As shown, a particulate solid, such as fly ash or other granular or powdered material, which tends to form deposits, is fed to the fluidized bed device 1 from the upstream part 20 of the device via a conveyor device 21, such as a screw or pneumatic conveyor. and is fed into the fluidised bed device 1. For example, the upstream part 20 of the device may be constituted by a storage vessel or a separating and conveying system, as described roughly in EP-A-0 168 614. A release device (not shown) is provided in the reservoir of the device part 20 as usual. also ensures the flow of solid particles at different filling heights of the container of the device part 20. In order to achieve transport with as little particulate abrasion as possible, the conveying device 21 can preferably be a pneumatic dense conveyor as proposed in accordance with EP-A-0 168 614. The point of entry 21a of the particulate matter is expediently selected so that it was possible to neglect the impulse forces of the solids particles coming from the conveying device 21 into the fluidized bed 2.

Through the bottom 11 of the fluidized bed device 1, which is permeable to gas or also to steam and is therefore generally provided with inlet openings 11a. flowing in the direction of the arrow G, fluidizing gas flows from the pipe 19 upwards and expands the interposed solids particles to form the fluidized bed 2. This fluidizing bottom 11 may be formed as a perforated bottom or a bottom of porous material may also be usable. In the case of the mixtures considered, the gas may also consist of the steam supplied to the liquid, but in any case only to achieve pre-wetting. As the inlet gas flow rate increases, the layer is released more and more so that the solid particles in this two-phase system make smaller and larger changes in location. From a certain inlet flow rate at which the bulk layer passes into the fluidized bed, i.e. above the so-called release point, the pressure drop across the layer is roughly constant, which, as will be described, can be used to better control dosing.

Theoretically, the region of the fluidized bed extends from a lower cutoff rate, i.e., a release rate, to an upper cutoff rate, which can be characterized such that the layer is already released so that each individual particle is suspended in the fluid stream without being affected by the adjacent particle.

If the fluidized solid is to be withdrawn from the fluidized bed 2 over time constant and dosed, this can be effected only from an as homogeneous fluidized bed as possible. It has been shown that this condition can be met better than hitherto by arranging the outlet 3 in the area of the bottom XI, and to achieve a substantial improvement by introducing a gas flow in the direction of arrow G with the gas velocities usual for such fluidized beds. Only then will the particles of solid matter remain very evenly distributed throughout the fluidized bed volume. Ideally, no bonding forces are generated between the individual particles.

The gas / solid mixture of the fluidized bed 2 behaves to a large extent as a liquid. By means of the outlet 3 at the bottom 11 of the fluidized bed device 1, the homogenized gas-solid mixture 17 can flow into the discharge pipe into the fluidized bed 2.

If, to a large extent, a homogeneous gas-solid mixture 17 is present, the individual particles of which always have the same mutual distance in the environment, it has been found that this creates particularly advantageous conditions for mixing hardly miscible substances with other substances, especially liquids. As mentioned above, the pressure drop across the fluidized bed 2 is constant, which makes it possible to use pressure differences as a measure of the amount of solids present in the fluidized bed 2. This not only allows quantitative accurate determination of the amount of solids available but also to obtain a homogeneity of the gas and solid stream and even increase it, i.e. to fulfill a quality condition which provides an optimal solution for the problem.

The entire amount of gas that is fed to the fluidised bed device 1 exits it through the exhaust duct 34. into which a valve for adjusting the pressure in the fluidized bed device 1 can be integrated. Optionally, a pre-cleaning or exhaust air purification device can also be installed in the fluidized bed device 1, which can be designed, in particular, as a centrifugal separator 36 or as a return separator, whereby the separated solid is returned to the fluidized bed by means of an extended pressure tube. second

To control the solids content of the fluidized bed 2, a pressure difference measurement is preferably provided between the pressure measuring point 12 just above the fluidizing bottom 11 and another pressure measuring point 12e above the fluidized bed 2. Optionally, it is also possible to determine the amount of solids in the fluidized bed 2 make use of the pressure difference between the sensors at 12f and 12f and / or 12 of the pressure measurement. While these methods are designed to utilize particular fluid bed ratios, the invention is not limited to this type of solids content measurement. It can also be detected otherwise, for example by means of weighing cells on which the entire fluidized bed device 1 is mounted.

In order to be able to remove the mass flow, which is a gas-solid mixture and which, in itself, is subject to very slight uncontrollable fluctuations or fluctuations from the fluidized bed device X in short periods of time, at least one expediently provided in its bottom 11 is provided. a centrally arranged nozzle device 28 at the outlet 3. · Each nozzle of the nozzle device 28 is associated with an inlet pipe 4, which may have a shut-off member 4. By supplying additional gas, the density of the solids stream in the biphasic mixture is influenced and thus allows accurate dosing. In this case, the velocity through the nozzle 28 of the feed gas, which may be other than in the fluidized bed 2, for example the already mentioned steam of the mixed liquid, is expediently substantially equal to the velocity through the outlet 3 of the gas and solids passing therethrough.

Since, as already described above, the quality of dosing of the effluent solid is very much determined also by the homogeneity of the effluent gas and solid stream, it is desired to eliminate possible sources of instability by appropriate measures already in the fluidized bed. For example, if high porous sintered bottoms with a mean pore diameter of 25 μm and a bottom thickness of about 20 mm are selected, fluid flows finely divided into fluidized bed 2. Vibration capable of fluidized bed bottoms 11 which they can be vibrated by a pulsating sensor, for example, they support this process. The use of stirrers is also possible in the same way. The fluidizing gas or steam, which flows in the fluidized bed 1 so that, in addition to the described inwardly, through the bottom 11, it also emulsifies, also improves, by measures, the homogenization of the fluidized bed 2.

The trouble-free outlet diameter D of the inlet zone is determined by the ratio a of the height H and / or the bottom area of the fluidized bed 2, at a consistently maintained flux rate.

It has proved expedient to establish a ratio as a minimum requirement

D: H 1: 2. The greater the height H of the fluidized bed and thus the solids content relative to the diameter D of the outlet 3, the better the homogeneity of the fluidized bed 2 and thus the pre-homogenization of the effluent gas stream and solid matter. In addition, the greater height H of the fluidized bed 2 acts to dampen the oscillations which can be formed, for example, when filling solid particles into the fluidized bed 2 by means of, for example, a conveying device 21.

Furthermore, one or more fluidizing nozzles 6 can be arranged symmetrically with respect to the outlet 3, by means of which a fluidising fluidising means 2 is supplied to the fluidized bed 2 by means of a pneumatic channel 10 additional to the gas flow in the direction of arrow G which flows through gas. The fluidizing nozzle 6 is here formed in the form of an annular channel with a porous insert which allows additional fluidization of the outlet 3 concentrically. This creates the possibility to counteract, to a certain extent, the creation of instabilities that are characteristic of the entry zone. It has also been shown that in this way the drawing of bubbles into the discharge pipe 4 can be limited. Therefore, the velocity through the fluidising nozzle 6 of the additional gas should preferably be lower than the velocity of the gas flowing through the bottom 11 of the fluidized bed device 1. The solid bridges that like to be formed in the area of the outlet 3 can thus be broken and released.

The mass flow rate of the effluent solid is essentially determined by the mass of the solid present in the fluidized bed 2 and the pressure difference between the point above the fluidized bed 2 and the point in the part of the apparatus immediately adjacent to the discharge conduit 4. can be affected as described below.

The approximate pre-setting of the solid mass flow is effected by means of the solids content in the fluidized bed 2 and / or by increasing or decreasing the pressure over the fluidized bed 2. The solids content is determined as described above and is controlled by control or a control means 34 which acts to supply the solid to the fluidized bed by means of a conveying device 21.

It is particularly advantageous for the pressure to be determined via the pressure measuring point 12e in the space above the fluidized bed and controlled by, for example, a memory-programmed control 34 or by controlling the valve 35 in the exhaust duct 34 of the fluidized bed device X and / or via a valve 33 in duct 31 by controlled addition at a higher pressure level of the supplied gas, which gas may coincide with the fluidizing gas or be a different gas.

Instead of the pressure at the sensor at the pressure measuring point 12e, the pressure difference between the pressure sensor at the pressure measuring point 12e and the pressure measuring point 12g provided in the following part of the device, such as the mixing device 18, can be used. if the pressure in this part of the apparatus or in the mixing apparatus 18 is subject to conditions and changes that are subject to operation.

If it is provided, preferably in the immediate vicinity of the outlet 3, the aforementioned gas supply, which is formed by the hollow body 5 and the gassing channel 8, can be influenced by the mass transfer of the solid during extremely small reaction times. This can in principle be realized by means of individual nozzles arranged on the discharge pipe 4, for example in the form of a rim, with the advantageous arrangement being a cylindrical gas-permeable hollow body 5, for example of ceramics, surrounded by an annular gassing channel 8. This is via a gas line 10. which can be connected to the duct 10 to the fluidizing nozzles 6, also filled with fluidizing gas, whereby the valves 13 can be provided. optionally also distribution valves and / or pressure limiting valves.

For measuring the outgoing gas and solid stream, a pressure measuring point 12 can be arranged in the porous wall 7 of the hollow body 5, preferably near the outlet 3, by means of which a pressure measuring point 12 is arranged together with the pressure measuring point 12 near the bottom 11 of the fluidized bed device 1. the pressure difference between the fluidized bed 2 near the bottom 11 and between the discharge line 4 near the outlet 3, for which a piezoresistive pressure sensor or a pressure difference, or two separate piezoresistive pressure sensors can optionally be provided for this. By positioning the pressure measuring points 12, 12, the dead time between the entry of the solid into the outlet 3 and the measurement of the mass flow of the solid through the pressure measuring points 12, 12 is reduced to a minimum.

Of course, this measurement could also be carried out by another method of measurement, for example based on the Coriolis principle, but this would undesirably affect the mass flow of the solid in terms of transition and homogeneity.

The measured data available through the differential pressure measurement can be fed to the aforementioned controller 34 with a built-in regulator which again controls the fluidization or gassing of the effluent stream and solids via the gassing channel 8 and / or controls the fluidization nozzle 6 or fluidization nozzles. 6 and thus allows the flow of gas and solid to be regulated.

The addition of the additional fluidizing gas, which is necessary to influence the solid mass transfer, constitutes only a fraction of the total amount of fluidizing gas, thus allowing very fast control and control times of less than 100 milliseconds.

The provision of additional pressure measurement sites 12a to 12e allows, on the one hand, the control of the porosity and homogeneity of the fluidized bed 2 by measuring the pressure difference within the fluidized bed 2, which is carried out at the pressure measuring points 12a and 12b. However, pressure losses above and just below the bottom 11 of the fluidized bed device X can also be used to measure the pressure drop over the bottom 11, which makes it possible to detect possible plugs of the porous bottom 11 in time.

In order to prevent fine particulate matter from the fluidized bed 2 from depositing on the measuring membranes of the pressure transducers, small, fine, porous plastic filters are preferably provided, or particulate matter is prevented from being purged by purging the pressure line with the gas.

The measured homogeneity measurement data in the fluidized bed 2 can serve as a regulator both by additionally adjusting the fluidizing gas inlet velocity and also by supplying the additional fluidizing gas by means of the fluidizing nozzles 6, the fluidizing bottom 11 and in particular through the gas supply through the hollow body 5. the gassing channel 8, thereby ensuring, on the one hand, the homogenization of the fluidized bed 2 and, on the other hand, an effluent gas and solid stream.

As a result, a greater number of control or control mechanisms are created in order to achieve the desired accuracy and dosing speed, whose combinations or separate applications provide a large control area and perfect control characteristics.

This fulfills two good preconditions for dosing accurately mixing hard-to-mix solids with a liquid, namely that the amount of solid can be accurately determined and, on the other hand, this amount is available for mixing under particularly favorable conditions. Therefore, as a third prerequisite for solving the problem according to the invention, a mixing device 18, which is shown only symbolically and in principle can be constructed in different ways, is provided following the fluidized bed device 1, which is a fluidizing and dosing device. For example, the fluidized bed device 1 can be filled up to a height H, as determined by the sensors in the manner described, and can be dosed emptied into the mixing device 18, which operates in a metering operation.

The admixed liquid or fluids are introduced into the system via line 40 at least one location. In particular, it is also possible to add the same liquid at several points simultaneously. In this case, the liquid can be injected into the fluidized solid by means of spray nozzles, for example also through the hollow shaft 27 of the mixing device 18 and / or also in liquid or vapor form directly into the fluidized bed 2 and / or the nozzle device 28.

In the fluid line 40, in which two alternative or cumulatively used variants are shown, corresponding devices for targeted changes in the passage are provided, for example a control valve 41 and / or a pump, as well as a measuring device 42 for measuring the additional amount of liquid, , for example in the form of a magnetically inductive transit meter, an ultrasonic meter or the like. It is also possible to operate these transit meters only temporarily to regulate the basic setting. By means of the measured liquid-solid passage, the quantity of liquid is also controlled according to the requirements of the operation, for example by acting on the control valve 41.

As already mentioned, the mixing device 18 can be constructed in a variety of ways. The use of batch operation is advantageous in fly ash because the fly ash is in practice discharged in very different amounts over time.

Although the invention has been described on the basis of a mixing device 18, which in itself can be made differently, it can be used without difficulty in other dependencies, for example for additional weighing. Numerous modifications are also possible in the apparatus shown. For example, to control the pressure difference between the point above the fluidized bed 2 and the mixing device 18, a valve 33 can be integrated into the duct 31 of the fluidized bed device 1, which is controlled depending on the pressure difference between the pressure measuring point 12f and 12g.

Claims (10)

A method for dispensing granular or powdered materials using a fluidized bed metering, characterized in that the granular or powdered materials are withdrawn from the bottom region of the fluidized bed. Method according to claim 1, characterized in that the grained or powdered solid which is drawn off from the bottom region of the fluidized bed is then passed together as a homogenized mixture of gas and substance and mixed with at least one second substance, in particular a liquid, injected into the fluid. Method according to one of the preceding claims, characterized in that for the metering of the homogenised gas-substance mixture, a gas is additionally introduced into it before mixing with the second substance, the gas being introduced around, for example to a mixing device flowing the gas and solids flow. and optionally parallel to its direction of flow, and the speed of the additionally supplied gas-to-gas mixture flow is preferably as high as the gas-to-substance gas flow rate. Apparatus for carrying out the method according to one of the preceding claims with at least one inlet and at least one outlet equipped with a gas permeable fluidizing bottom, for example a perforated bottom equipped with a fluidized bed device for forming a biphasic mixture of granular or powdered solids with fluid supplied through the fluidizing bottom characterized in that the at least one outlet (3) of the fluidized bed device (1) is connected to and terminates in the fluidized bed (11). Apparatus according to claim 4, characterized in that it is provided with a measuring device for measuring the solids content of the biphasic mixture, in particular in the fluidized bed device (1). Apparatus according to claim 4, characterized in that a discharge device (18) is provided on the outflow line (4) which opens out or 5, marked (3), into which the second substance, in particular as a liquid, is fed. preferably via spray nozzles or the like. Apparatus according to one of Claims 4 to 6, characterized in that a nozzle device, preferably designed as a hollow body (5), is provided on the outlet (3) of the fluidized bed device (1) or in the region of the discharge pipe (4). (28) as a metering device, in particular for the mixing process, having channels (10) for supplying additional gas through the porous wall (7), nozzle and the like hollow body (5) to or optionally a homogeneous mixture of gas and substance. Device according to one of Claims 4 to 7, characterized in that the fluidized bed device (1) and the nozzle device (28) are provided with spaced points (12a to 12), possibly spaced apart, for measuring the substance content in the fluidized gas-substance mixture. 12f) measuring the pressure with preferably electrical or electronic pressure measuring devices or level sensors, the output signals of which are fed to, for example, a memory programmable electronic control (34), whose output signals are fed preferably to the valves (13, 13), in particular distribution valves and / or pressure limiting valves, and preferably from a conveying device (21) for supplying at least one substance to the fluidized bed device (1) and / or the mixing device (18). Device according to one of Claims 4 to 8, characterized in that the fluidized bed device (1) is operable in particular by a preselected gas pressure - 17 by means of a valve (35) controlled by a control (34). Device according to one of Claims 4 to 9, characterized in that it has a liquid control circuit (34, 40, 41) provided, which is preferably controllable by a control or control circuit (34) connected to a corresponding pressure gauge at a location (12-12f) measuring the pressure on the fluidized bed apparatus (1).