FI96581C - Process and apparatus for preparing mixtures - Google Patents

Description

96581

The present invention relates to a process according to the preamble of claim 1 for the preparation of liquid slurries and powder mixtures with a well-defined dry matter content.

The invention also relates to an apparatus for applying the invention.

The invention further relates to a method for determining the amount of dry matter to be mixed for a continuous mixing apparatus.

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Dosage solvents have generally been used for the preparation of liquid sludges with well-defined dry matter content, such as pigment dispersions for the ceramic and paint industries and pigment dispersions for coating pastes in the paper industry, as well as for the so-called pre-hydrated cementitious adhesives for the concrete industry. These slurries 1. Dispersing devices are typically tanks in which the ingredients required for one batch of slurry are dispensed at a time, which are then mixed with the mixing means in the tank to mix into a homogeneous slurry. Sludges are generally aqueous solutions and the dry matter contents of sludges for various purposes vary considerably. For example, the dry matter contents of the coating compositions 30 for paper coating range from a few percent to several tens of percent. The dry matter content of the sludges strongly affects their viscosity, and with some combinations of substances the viscosity increases very rapidly as the dry matter content increases, and in case of dosing error 35 the sludge quickly becomes too viscous and unusable or the dry matter content remains too low.

Disadvantages of batch solvents include e.g. the high investment costs due to the large size 5 and the uneven distribution of the mixing intensity, i.e. the shear force on the mass to be mixed, over the whole volume of the tank due to the high energy consumption and the inhomogeneous quality of the product.

10 In recent years, instead of batch solvents, devices have been developed to eliminate the above-mentioned disadvantages of batch mixing. These devices are usually continuous mixers in which a large amount of energy is quickly applied to a relatively small amount of material to be mixed, allowing the dry matter to be irrigated efficiently. Finnish patent publication 91602 describes a rotor mixer which is suitable for continuous slurry production. This device has two impellers, each with 20 spaced apart impellers, and the impellers are arranged opposite each other so that the impellers overlap. When the impellers are rotated in opposite directions, the substances fed to the center of the device are ejected radially to its outer circumference. Due to the opposite directions of movement of the impellers 25, the material to be mixed in this way is subjected to rapid changes of direction by high shear forces as the material moves from one impeller to another.

The continuous slurry works particularly advantageously compared to a batch-30 mixer when its operation is based on stretching and shearing a thin mixture film by centrifugal force, the so-called in rotor mixers, such as that described in Finnish patent 91602. In such a device, flocculation of the dispersion is prevented, the energy consumption 35 is small and the device can be relatively small compared to the amount of sludge required. Efficient slurrying with such a known rotor mixer requires that the device operate substantially empty of the mixture to be slurried, thereby forming a thin mixture film on the blades of the device, which is mixed vigorously by cutting, whereby the film 5 stretches and tears. In this case, the residence time of the mixture in the device is also typically very short, less than 0.1 s, and the amount of mixture in the device during the residence time is very small, even less than 2 liters.

The advantageously low operating content and short processing time of the rotary mixer have revealed new disadvantages which have made it difficult to use and generalize continuous solvents in processes in which the dry matter content of the product is precisely defined, with an accuracy of up to 0.01%. The first new drawback relates to the measurement and control accuracy of continuous dosing and the second to ensuring the homogeneity of the product. This problem is particularly difficult in installations with a high yield requirement, as they require up to tens of tons of mixing in 20 days.

The known dosing technology is based on the weighing of the components and / or the volume measurement of the flow, the control messages of which are used to control the feed rate of the dosing devices. With equipment operating on this principle; it is not possible to adjust the amount and concomitant dosing of the ingredients with sufficient accuracy and speed for the rotary blender. Since the residence time in the mixer is typically at most tenths of a second, the weighing speed 30 must be faster than this, because the weighing before mixing describes the situation that has already taken place. This leads to the need for even faster adjustment and it is clear that equipment handling large volumes of mass cannot be designed to operate in such a need for rapid adjustment.

Inadequate dosing accuracy and rapid simultaneous handling of a small amount of mixture 9 35 96581 4 mean that the slurry produced from the rotor-blender in the form of blade-sized film pieces is not uniform, but each said piece of film has a different composition according to the dosing variation. In practice, for example, when preparing a sludge with a dry matter content of 50.0% from calcined kaolin, dosing deviations from the setpoint that cannot be achieved within the control accuracy of the known dosing technology can result in the sludge producing momentarily dry powder and very thin skin.

Applicant's practical studies have shown that when the dispersing apparatus described in the above-mentioned patent publication has been used in such a way that the dosing equipment is known to weigh either the dosing conveyor flow or the storage silo lightening in the known manner, we have surprisingly found that would be up to ± 0.5% and a ha-20 stray frequency of 50 Hz, the instantaneous dosing error of the continuous solvent may even exceed ± 50%. This has been found to be due, on the one hand, to the insufficient time accuracy of the known weighing-based dosing method, as the residence time of the mixture in the solvent is only 25 less than 0.1 second and the current control mechatronics does not allow timing or control measures with this accuracy.

On the other hand, we have found that the inaccuracy is also caused by the amounts to be weighed in the dosing being too large in relation to the actual usable contents of the solvent when, for example, a belt scale moving at a speed of 0.3 m / s: · weighs 0.6 m. average information on the amount of dry matter fed to the solvent in two seconds, i.e. the minimum amount to be weighed is more than 20-35 times the usable content of the solvent. For this reason, for example, sudden fluctuations in density •

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96581 5 in the dry matter either go undetected from the measuring system or even cause incorrect control measures in time or quantity.

The object of the present invention is to provide a process for the preparation of slurries and powder mixtures, by means of which slurries and mixtures with well-defined mixing ratios can be produced continuously.

The invention is based on the fact that the mass flow fed to the continuous mixer is metered by standardizing the density of the solid to be fed and by dosing the constant density substance with a constant volume flow per unit time.

More specifically, the method according to the invention is characterized by what is set forth in the characterization of claim 1.

The apparatus according to the invention, in turn, is characterized by what is set forth in the characterizing part of claim 7.

Such an apparatus preferably comprises a dispersing device as described in Finnish patent publication 91602, supplemented by a dry matter dispensing device comprising a vibrating screen with a grinding roller, an encapsulated compartment belt conveyor and a belt scale, and a constant temperature, nozzle pressure and flow meter. In addition, it is advantageous for carrying out the process that the apparatus uses one or more post-mixers after the dispersing device, by means of which the final product is homogenized and, if necessary, the processing time required for the chemical reactions in the product is provided. 1

The dosing method according to the invention is in turn characterized by what is stated in the characterizing part of claim 12 96581 6.

The invention provides considerable advantages.

By means of the invention, the production of sludges of uniform quality with a well-defined dry matter content by means of a continuous dispersing device produces products of better quality than before with even lower investment, energy and operating costs. It is now possible to use equipment for dispensing dry matter into a continuous slurry in which the feed and dispensing device mechanically ensures that the density and volume flow of the dry matter fed to the slurry remain constant and in addition the density, temperature and volume flow of the liquid to be fed are constant. whereby the concentrations of the finished sludge are exactly correct. The method makes it possible to use as a continuous solvent an apparatus in which good dispersion is achieved at low operating power, for example based on the application of higher shear forces to a thin alloy film in a short time in a smaller amount of the mixture to be treated simultaneously. Most preferably, a rotor mixer is used as the dispersing device, in which the substantially plate-like impingement surfaces obtain a thin alloy film on their surface, to which a shear force due to the difference in speed and / or direction of rotation between successive impingement surfaces is applied. The mixture is homogeneous in that the dispersing device discharges the product into a tank mixer-type post-mixer, the volume and power consumption of which are determined by the characteristics of the dispersion to be produced and the production capacity of the equipment. The purpose of the post-mixer is to: · homogenize the dispersion prepared from the dispersing device in small batches (as films of the size of the impact surface) into a continuous slurry and, if necessary, also allow chemical reactions in the dispersion that require a longer processing time. The volume of the post-mixer is preferred

It: 96581 7 at least 20 times the minimum dosing volume. In the post-mixer, the mixing power transferred to the pulp is very small compared to the slurry mixer, and the actual dispersion here no longer takes place.

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In addition to the preparation of slurries, the invention can be applied to the preparation of dry material mixtures and to obtain mixtures with well-defined mixing ratios, in which the distribution of the ingredients is very evenly distributed.

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The invention is explained in more detail below with the aid of the accompanying drawings.

Figure 1 schematically shows one apparatus according to the invention used for carrying out the invention.

Figures 2 and 3 show an enlarged view of the solids dispensing part of the apparatus of Figure 1.

The apparatus used in the method according to the invention comprises a dry steel steel feed silo 1, a compartment belt conveyor 2 with a dust-tight housing integrated with a solvent feed hopper, a belt scale 3, a liquid dispenser with a solvent feed a tank-type after-mixer 6 equipped with a tank, to which the slurry leaving the rotor slurry is led by a pipe. 1 2 3 4 5 6 • ·

When using the equipment, the feed silo 1 is regularly filled with slurry dry matter 2 so that the amount of substance 3 in the silo remains between certain lower and upper limits.

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Mounted on the lower part of the feed silo 1 is a vibrating screen plane 7, described by the dotted line 5, through which the dry matter is sprinkled 6 to standardize the density in the compartments of the tray belt conveyor 2. In addition, the screen 7 prevents 96581 8 foreign particles larger than the permitted grain size from entering the process. The throughput of the screen 7 must, of course, be greater than the maximum amount of material to be dispensed in order to obtain sufficient material for the conveyor 2. When slurrying solids, such as spray-dried kaolin, which easily clump during transport and storage, a second screen level is installed in the feed silo 1 slightly above the screen level described above, against which the lumps are comminuted by grinding with rollers or rollers. The lumps present in the spray-dried kaolin can be ground finely with considerably less energy than when wet, in addition to the fact that it is important for the dosing density standardization that the particle size distribution of the dry matter to be spread on the tray belt is as small as possible.

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The adjusting plate 8 resting on the upper surface of the sides of the tray belt 2, shown in Figures 2 and 3 in two different adjustment positions, stabilizes the volume of dry matter conveyed by the belt 2 per unit length of belt and further adjusts it according to the refractive properties of the dry matter to be treated. , there are no greater than permitted variations in the density and volume of the dry matter on the dosing belt 2.

The belt scale 3 mounted on the conveyor section between the feed silo 1 and the unfolding end drum 9 of the tray belt conveyor 2 continuously weighs the dry matter flow and transmits the weighing information from the current running time of the equipment to the process control system, which uses weighing information e.g.

30 setpoint 8 and the set speed of the conveyor 2 for checking the recipe compliance, • monitoring and documenting the production quantity and recipe compliance, and in the event of disturbances as a basis for alarm and stop functions.

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The compartment belt conveyor 2 is completely encased in a dust cover

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96501 9 la, which is integrated into the so-called. To the feed hopper of a "Atrex" type root rotary mixer or similar continuous sludge 5. The purpose of the enclosures, in addition to preventing dust nuisances, is to minimize the passage of excess air to the dosing slurry on the dosing side. According to our experiments, the entry of excess air into the solvent causes a large amount of undesired foam formation in several slurries.

10 When the dry matter discharged by the turntable roller 9 of the conveyor belt conveyor 2 falls in the hopper towards the throat of the solvent 5, it comes into contact with the liquid medium, usually water or water / additive suspension, 15 Sufficient simultaneous and proportionate dosing in a continuous solvent 5.

The mixture dispensed in the rotor nozzle 5 is caused by centrifugal force 20 to flow as thin films from one agitator blade to another so that the film is continuously stretched and a shear force is applied to the film as it moves from successive blades to successive speed and / or rotation. . In the apparatus described in Finnish Patent Publication No. 91602, successive mixing surfaces are moved in opposite directions, but in our experiments we have surprisingly found that it is not advantageous to apply as high shear forces and shocks to all slurries as caused by successive mixing surfaces rotating in opposite directions. In order for the apparatus according to the present invention to be usable for as many slurry solids as possible, the slurry used should be adjustable so that successive impact surfaces can be set to move at the same or different speeds according to the requirements of the slurry. in the same or opposite direction to each other or so that only one of the successive impact surfaces moves while the other is stationary. In this case, the magnitude of the impact and shear forces applied to the slurry film can also be adjusted correctly when the recipe requires several treatments of the slurry with a rotor slurry (so-called circulating slurry).

With the discharge pipe of the continuous slurry 5, the slurry is discharged into the post-mixer 6. The post-mixer 6 has the effect of even small dosing inaccuracies in such a large amount of sludge to be treated at the same time that the correct control measures can be performed if necessary. In particular, the volume of the post-mixer limits the possibilities of increasing the dry matter content when operating at the extremes of sludge flow. It has been found that the post-mixer must be able to process at least the amount produced by the continuous casting in three minutes at a time. Another function of the post-mixer 20 is to enable chemical processes in the slurry in connection with the slurry that require longer treatment of the slurry. Prolonged reaction time comes into question, for example, in the production of so-called fast-setting high-strength concrete 25, prehydrated cementitious adhesive by slurrying fine binders and fillers in water before mixing with the aggregate. Among others, of the pigment slurries used by the paper industry, a high-shear post-blending is preferred, and for others, such as calcined kaolin, the so-called dissolver mixing. Therefore, when applying the method according to the invention to an apparatus intended for the production of pigment slurries in turn from several different raw materials, it is advantageous to equip the apparatus with two or more small post-mixers, each post-mixer having a different type of mixer element.

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11 The combination of P65P1 achieves the most suitable post-mixing for each sludge type.

When the post-mixer 6 is filled, the treated sludge 5 is continuously passed on to a storage silo or for transport to the end user. In some cases, it is sufficient to use a large storage silo with agitator members as the post-mixer.

10 In addition to the vibrating screen, other equipment can be used as the screening device, by which the solid to be dispensed can be divided into particles of sufficiently uniform size and sprinkled as a uniform density on the dispensing member. According to current experience, a conveyor belt conveyor is the most suitable conveyor, but the apparatus according to the invention can be implemented with many other conveyor solutions. As the conveyor, for example, a kola conveyor can be used, which has fixed or movable side walls which limit the constant volume required by the conveyor. The volume can also be limited by a curved flat belt, in which case the volume is limited, as in other embodiments, by a damper or other similar control member.

Of course, if the process according to the invention produces dry products by mixing powders together, the amount of solids dispensing devices operating simultaneously must, of course, be equal to the number of substances to be mixed at one time.

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Claims (17)

A process for preparing mixtures of at least one solid and at least one other solid or liquid, wherein - at least one solid and at least one other solid or liquid are fed in a metered manner to a continuous mixer (5), 10 - the metered substances are mixed in a continuous mixer (5) and the mixture is removed from the continuous mixer (5) to at least one storage mixer (6), 15 characterized in that - the amount of solids to be metered into the continuous mixer (5) is stabilized according to the desired mixture ratio 20 by - first stabilizing the solids density, and 1 2 3 4 5 6 35 II: - a specified volume flow is taken from the substance of standard density, which, determined by density 3 and volume flow, 4 corresponds to the mass flow required for the mixer (5) at the desired mixing ratio, and 6 - the volume flow from the continuous mixer (5) eats to a post-mixer (6) having a mixing volume substantially greater than the mixing volume of the continuous mixer (5). 13 96581 Process according to Claim 1, characterized in that at least one solid and water are mixed. Method according to Claim 1 or 2, characterized in that the density of the solid is stabilized by feeding it through a sieve (7). A method according to claim 1, 2 or 3, characterized in that the volume flow is conditioned by passing a solids flow of constant density through a limited cross-section. Process according to one of the preceding claims, characterized in that the residence time of the solid in the post-mixer (6) corresponds to a yield of 3 minutes for the continuous mixer (5). Method according to one of the preceding claims, characterized in that the volume flow of the substance to be mixed is conditioned by dropping it through a sieve (7) onto a conveyor (2) which partially restricts the constant volume and limits the amount of substance dropped to the conveyor (2). (8) the amount of material on the conveyor (2) to a constant volume determined by the conveyor (2) and the restrictor (8). Method according to Claim 6, characterized in that the amount of solids fed to the continuous mixer (5) is controlled by varying the speed of the conveyor (2). Apparatus for forming a mixture of at least one solid and at least one other solid or liquid, the apparatus comprising: 96581 14 - a continuous mixer (5), - a conveyor and dosing system (1, 2, 3, 7, 8, 9) with at least one to supply the solid and at least one other solid or liquid to the imaging mixer (5), and - at least one post-mixer (6) to which the mixture from the continuous mixer (5) can be fed, characterized in that - the conveyor and dosing system comprises : - a screening device (7) for stabilizing the density of the solids to be dispensed, - a conveyor (2) which partially determines the constant volume, and - a stop member (8) for limiting the constant volume partially defining the conveyor (2), 25 - the mixing volume of the post-mixer (6) is larger than the mixing volume of the continuous mixer (5). 1 2 3 4 5 6 I! Apparatus according to claim 8, characterized in that the dispensing system comprises a screen device 3 (7) extending above the conveyor (2) so that the screen (7) drops the density-conditioned substance 5 over a certain length of the conveyor (2). and the stop member (8) 6 is displaceable so as to be able to determine the distance over which the screening device (7) drops the solid directly on the conveyor (2) 96581 15. Apparatus according to Claim 8 or 9, characterized in that the screening power of the screening device (7) is greater than or equal to the volume flow transmitted by the conveyor (2). Apparatus according to claim 8, 9 or 10, characterized in that the continuous mixer (5) and the post-mixer (6) are dimensioned such that the residence time in the continuous mixer (5) corresponds to at least 3 minutes of output of the post-mixer (6). Apparatus according to claims 8-11, characterized in that the conveyor system comprises a scale (3) with which the amount of substance dispensed to the conveyor (2) can be checked. 12 96581 Apparatus according to one of Claims 8 to 13, characterized in that the conveyor system comprises a compartment belt conveyor (2) and a stop member which is a damper (8) which can be moved on top of the conveyor. 14. A method for accurately continuously dispensing a high solids volume flow, characterized in that - the density of the substance to be dispensed is stabilized, and a constant volume flow is taken from the constant density substance 30. < Method according to Claim 14, characterized in that the density of the substance to be dispensed is stabilized by sieving. 96581 16 A method according to claim 15, characterized in that a constant volume volume flow is taken from the screened material so that the material is screened on a conveyor (2) which partially limits the constant volume and the constant volume partially limited by the conveyor (2) is determined by a movable restrictor (8). Method according to Claim 16, characterized in that the constant volume is limited by a compartment conveyor (2) and a mechanical stop (8). Il 96581 17