MX2008010510A - Method and mixer apparatus for mixing gas into slurry in a closed reactor - Google Patents

Abstract

A mixer apparatus accordant with the invention includes a closed reactor (20);two mixers at different heights (28, 29), which are on the same shaft (27), a gas feed pipe (30) below the lower mixer and baffles. The blades of the mixers are mostly rectangular in shape and a minimum of six in number. The angle of inclination of the blades of the lower mixer is around 50-70°and that of the upper mixer around 25-35°. The number of baffles (23) is at least six and their range around 20%of the reactor diameter. The invention also concerns a corresponding method.

Description

METHOD AND MIXING APPARATUS FOR MIXING GAS IN A GROUND IN A CLOSED REACTOR.

Field of the Invention The invention presented herein relates to a mixing apparatus and a method for mixing gas in a slurry found in a closed reactor, which uses gas as a chemical process with high efficiency and in which it is high the solids content in solution. The mixing apparatus according to the present invention comprises a closed reactor, at least two mixers at different heights, which are on the same axis, a gas supply pipe below the lower mixer and screens located in the wall area. The blades of the mixer are mostly rectangular in shape and consist of a minimum of six in number. In the method according to the invention, the gas fed into the lower section of the reactor is dispersed in a slurry formed by a liquid and solids by means of the lower mixer, so that the slurry flow is discharged onto the wall of the space of the reactor, a part of which flow is returned under the mixer and another part is made to rise within the space between the screens and the reactor wall in the upper section of the reactor space. The flow of slurry in the upper section of the reactor is diverted with the help of the upper mixer to direct it to the center of the reaction space, simultaneously causing horizontal and vertical flows to be formed that transport gas bubbles. The grout flow is also diverted by means of the upper mixer to discharge it downwards as a uniform flow to the lower mixer.

BACKGROUND OF THE INVENTION Conventionally, a closed vertical reactor consists of a vertical cylindrical section and a closed bottom part and a cover section. The cover section has an opening in it, which is generally slightly larger than the diameter of the mixer. The large gas vortex that is caused by mixing in the reactor is mainly avoided by four standard screens. In a typical case, the width of the screens is 0.05 to 0.10 times the diameter of the reactor, and the opening between the screens and the wall is 0.017 times the diameter of the reactor. A common four blade mixer is attached to the lower end of the arrow, where the angle of the blade can be adjusted separately. It is usually 45 °. In cases where a suction surface is desired, the mixer can be raised so that it is close to the surface of the solution. In those cases, the conical formations of gas made by the mixer, vortexes, are dispersed in bubbles by the mixer and are pushed down in some way, however, not directly to the bottom, because the flow achieved by the mixer in the direction of the well is not yet powerful enough for the suspension of the solids in the lower part to take place properly. If the effective volume of the reactor is such that the depth of the liquid to be mixed is approximately the same as the diameter of the reactor, in normal cases a mixer member at the lower end of the shaft is sufficient. The direction and strength of the force effect of the mixing member depends on its type (shape). The processes normally require mixing, which forms both strong turbulence and sufficient circulation. If the effective volume is so large that the depth of the solution is 1.5 to 2 times or more than the diameter of the reactor, often several mixing members are required on top of each other at a suitable distance between them. In this case the types (shapes) of mixer on the same axis may be different between them. Gas supply usually occurs by feeding oxygen (oxidation) or hydrogen (reduction) within the impact zone of the dispersion mixing member with sufficient force. Often in closed reactors one wants to get the gas from above the surface of the grout circulation back into the solution. If air is used, this does not seem prudent, because then the amount of nitrogen only increases in the circulation, but both with pure oxygen and with hydrogen the final gas can be recovered for later use by its suction from above the surface. In order to suck the gas from above the surface and further disperse it in the slurry, transverse self-suction pipes are known in the prior art, in which the gas space at the lower end of the hollow shaft normally branches in an open tube with four points. The rotating transverse pipe causes a low pressure in the gas space, due to which the gas is discharged into bubbles in the solution space of the reactor. It should be noted that as the temperature of the solution increases, the vapor pressure rises simultaneously, whereby the effect of the low pressure weakens. This type of cross-pipe structure is not able, however, to disperse the gas further into the solution, much less keep the thick suspension of moving solids. A method for sucking gas from the surface in what is termed as the principle of the downstream is also known. U.S. Patent Publication No. 4,454,077 discloses an apparatus, in which a dual-head screw-type mixing member is used to pump the gas down through a central tube, and additionally the apparatus includes upper and lower screens. U.S. Patent Publication No. 4,328,175 discloses the same type of device, but the upper end of the central tube is conical in configuration. In this way, it is known that the gas travels towards the mixer by means of the intensification of the powerful central vortex created by the mixer shaft. This strong and often voluminous gas vortex transports gas from the surface into the liquid or slurry to be mixed sometimes very effectively, but at a certain volume of gas the operation of the mixer member weakens as the mixer rotates "in a big gas bubble. " Then, because the power increases with greater weakness, the vortex weakens and the gas entry from the surface into the solution is reduced. The vortex generated in the manner described above however is uncontrolled and as it reaches the mixing member it causes violent variations of power and therefore damage to the equipment, etc. The worst of all is that the mixer can no longer perform the mixing of the powdery solids due to its inefficiency, particularly with a high density of suspension of the powdery solids. In the article "Onset of gas induction, power, gas holdup and mass transfer in a new gas-induced reactor," Hsu, Y-C-, Peng, R.Y. and Huang, C-J., Chem. Eng. Sci., 52, 3883 (1997), a method is presented in which the gas is sucked from the surface by means of a swirl generated at the base of a long arrow. The method uses two mixers attached to the same arrow and located in a cylindrical current tube, which cause the vortex effect in question by means of the low pressure they create. There are no bulkheads in the reactor to prevent swirling. The upper mixer thus causes a deep swirl at the base of the arrow, and the gas is sucked into the liquid from the bottom of the vortex. Probably the suction of the gas inside the mixer occurs in gusts and places a tension on the mixer member. The lower mixer receives both sucked gas and gas fed into it and disperses it in the liquid. The gas-liquid that runs from the bottom of the suction pipe is discharged to the lower section of the reactor, deflecting it along the sides upwards towards the surface. The gas is discharged above the surface. The disadvantage of the method consists in the fact that the gas no longer circulates in the liquid down from the top, that is, there is no real circulation of the gas, instead of this it is discharged directly above the surface, where the gas is released from the liquid due to the centrifugal effect. This gas discharge still intensifies the large and powerful vortex from the upper section and the gas penetrates through the vortex in an irregular manner and therefore causes damage to the mixer (cavitation, etc.). From U.S. Patent No. 5,549,854 a method is known for suctioning gas from above a liquid surface by means of adjustable and special screens using a rotary mixer member as an energy source. With this method controlled suction vortices can be achieved, which do not necessarily transport the gas as far as the mixer member itself. There is no approach in this patent regarding the capture of air bubbles that move upward in the return flow, so as to prevent them from rising above the surface of the slurry. From EP Patent No. 1,309,394 a gas suction method is also known from above the surface of a solution in a closed reactor with two special mixers on the same shaft. In that method, the gas is both dispersed and spread down with the top mixer and simultaneously towards the edge of the reactor. There is no attempt to prevent the gas moving up from the edge of the reactor from leaving the slurry space and sucking it back into the lower mixer.

Obtaining a sufficient quantity of gas within a suspension of solids and solution in closed oxidation and reduction reactors, particularly when the solids content is high, ie, around 30%, usually requires that the gas be directed into the Solution space in the lower part of the reactor, mainly under the mixer member. Frequently this gas is fed down through the surface of the solution by means of a pipe, which is from its lower part directed towards the arrow of the central reactor and is caused to turn under the mixer. This ensures that the gas is transported to the lower section of the reactor and is dispersed with the mixer. If the process requires a large amount of power (kW / m3), there is a reason to use a mixer that requires / provides a large amount of energy. It is known how to increase the power provided by a mixer by increasing the speed of revolutions, but it should be noted that at the same time the peripheral speed of the mixer increases and when it increases significantly (> 6 m / s), the mixer begins to wear noticeably.

OBJECTIVES AND SUMMARY OF THE INVENTION The invention presented herein refers to a mixing apparatus and a method for mixing gas in a closed mixing reactor, which uses gas as a chemical process with a high efficiency and in which the concentration of solids powdery in solution is high, that is, it may be in the region of above 40%. The purpose of the invention is to present a mixing apparatus and a method by means of which the disadvantages of the devices mentioned above are avoided. With the method and apparatus according to the invention, one can effectively mix a gas in a slurry formed of a liquid and solids and circulate gas bubbles containing unreacted gas with the slurry so that the majority of the bubbles of gas travel with the grout flow and allow the reactions between the gas and the grout. Only a small number of gas bubbles are discharged above the surface of the slurry and even that amount can be brought back into the slurry circulation in the desired amount by means of vertical vortices formed at the top of the slurry. .

The mixing apparatus according to the invention is intended to mix gas in a slurry formed of a liquid and solids. The mixing apparatus comprises a closed reactor, with an effective slurry depth that is 1.5 to 2 times the diameter of the reactor, two mixers located at different depths, which are in the same arrow, screens directed inwards from the wall area of the reactor. reactor and a gas supply pipe. The reactor is typically a cylindrical vertical reactor, which is provided with a base and a cover. The upper mixer is equipped with at least six, preferably eight, blades directed towards the side and inclined from the horizontal. The angle of inclination is small, approximately 25-35 degrees. The lower mixer is similar to the upper mixer in structure. The angle of inclination of the mixing blades of the lower mixer is approximately 50-70 degrees and the height of the mixer is preferably 1.5 times that of the upper mixer. The number of screens is at least 6 and preferably 8. The range of the screens is approximately 1/5 of the diameter of the reactor. The gas supply pipe is located in the lower section of the reactor below the lower mixer. The invention also relates to a method for dispersing gas fed into the lower section of a closed reactor in a slurry formed of liquid and solids by means of a desirable and controlled flow field, which in turn is formed in the space of reaction by means of screens and a mixer member located in the reaction space. The effective profanity of the grout of the reaction space is 1.5 to 2 times the diameter of the reaction space and the mixing member consists of two mixers located on the same axis. The gas is fed below the lower mixer into the grout flow, which is directed with said mixer into the lower section of the wall of the reaction space and is discharged there in two separate streams. A current is caused to be diverted through the wall towards the center of the lower part of the reaction space and the second is to rise in the area formed by the wall of the reaction space and the screens up towards the surface. In the vicinity of the surface, the flow is diverted by means of the upper mixer towards the center of the reaction space so that horizontal and vertical vortices carrying gas bubbles are formed simultaneously in the flow. The surface current is so fast that the surface breaks and the air is also mixed directly in the current in question. The direction of the slurry stream in the middle part of the reaction space is diverted by means of the upper mixer so that it flows downwards as a uniform flow similar to a tube towards the lower mixer. This arrangement allows the elimination of the disadvantages of the known methods and the achievement of effective horizontal vortices in the vicinity of the liquid surface, which are directed from the edge of the reaction space towards the center and small vertical vortices that suck gas inside. of the liquid. The horizontal and vertical vortices formed in the upper part of the reactor are mainly achieved with the help of the upper mixer. In addition to the gas vortices in question, the fairly small gas bubbles uniformly distributed within the slurry formed of liquid and solids are pressed downward with the vast flux of slurry surrounding the arrow towards the lower mixer. The lower mixer takes considerably more energy than the upper mixer. This energy is used to disperse the gas bubbles sucked down from the top of the slurry suspension into even smaller bubbles. In this way the contact surface between the gas and the liquid is increased, so that the reactions occur much more quickly and completely than in the conventional methods. The residual energy of the lower mixer is used to mix solid particles in high slurry densities and disperse them throughout the reaction space, and to mix the gas fed from below the lower mixer into the slurry. It is characteristic of the mixing of the mixing apparatus and the method that the power taken by the lower mixer is at least three times, more preferably about five times, than that of the power requirement of the upper mixer. The essential features of the invention will be clearer in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS The apparatus according to the invention is further described with reference to the accompanying drawings, in which: Figure 1 presents a vertical section of a reaction space of the prior art with its flow field. Figure 2 shows a vertical section of an embodiment of the invention with its flow field. Figure 3A shows a vertical section of an upper mixer of a mixing member according to the present invention and Figure 3B shows how the mixer is viewed from above. Figure 4A shows a vertical section of a lower mixer of a mixer member according to the present invention and Figure 4B shows the mixer as seen from above, and Figure 5 shows a cross section of a bulkhead according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION According to a preferred embodiment of the invention, unreacted gas that is in the reaction space rising from below and along the edge is prevented from reaching the surface of the liquid. of the reaction space, by means of the upper mixer. Instead, the direction of the slurry-gas flow is diverted in the upper part of the reaction space to be directed from the edges towards the center and downwards in the central part. It is also part of the embodiment that the upper mixer is configured so that it also sucks the small amount of gas, which has however been released out of the slurry and above the liquid surface, into the flow which is directed in a manner falling. The mixing apparatus according to the present invention includes a reactor in a vertical position, with an effective profiling of slurry of 1.5 to 2 times that of the diameter of reactor T. The solids content of the slurry is typically high, in the region of 500 g / 1. The reactor typically has a curved bottom (known as a shallow bottom of a pressure vessel) and a gas tight cover in order to achieve a confined space. The background can also be straight. Reactors can be used under both pressure and atmospheric pressure conditions.

The mixing apparatus according to the present invention typically includes a mixer member, where there are two mixers located at different heights on the same axis. The diameter of both mixers is the same and these are large, that is, the ratio of the diameter D of the mixer to the diameter T of the reactor is between above 0.4, but at a maximum of 0.5. The number of mixer blades is a minimum of six, preferably eight. The blades are mainly rectangular in shape and are inclined from the horizontal. The angle of inclination of the blades of the upper mixer is 25-35 °, preferably 30 °. The angle of inclination of the blades of the lower mixer is greater, in the region of 50-70 °, preferably 62 °. The height of the lower mixer is preferably 1.5 times that of the upper mixer. The rotation speed of the mixers is adjusted so that the peripheral speed does not rise higher than 5 m / s. If the peripheral velocity rises higher, particularly hard and angular materials such as pyrite, quartz and chromite wear the blades to a damaging degree. The distance of the lower mixer from the bottom is preferably about the diameter of the mixer. When the effective grout height is in the range described above, that is, 1.5 to 2 times the diameter of the reactor, and the grout density is high, the response in conventional solutions generally consists of a third mixer, but in the solution of In accordance with the present invention, effective mixing with two mixers is achieved. The distance between the mixers depends on the height of the reactor. When the effective height of the slurry is in the range of 1.5 times the diameter of the reactor, the distance between the mixers is approximately 50-60% of the effective grout height. When the effective height of the slurry is in the range of 2 times the diameter of the reactor, the distance between the mixers is approximately 60-70% of the effective slurry height. According to a preferred embodiment of the invention, the upper mixer is designed in such a way that it achieves a vast flow oriented downwards in the middle part of the reactor, by means of which the flow behaves precisely as if there were a tube around it ( "downstream"). The diameter of the cross section of this flow is approximately the same or larger than the diameter of the mixers. In the correct speed range, due to its lightness, the gas bubbles try to resist the downward flow, whereby they end with an oscillating movement and in this way the bubbles increase the reactions between the gas and the slurry. According to a preferred embodiment, an important task of the lower mixer in addition to the dispersion is to achieve a flow field such that the gas, liquid and solid particles are in a circular motion in the lower section of the reactor, by means of which substances fed into the process have time to react between them. The flow field formed with the aid of the mixers according to the present invention can be described as follows: the lower mixer receives the vast flow coming from the upper mixer and scatters it obliquely down towards the wall of the lower section of the reactor. Here the flow is divided in two. Part of the directed flow in the lower section of the reactor is diverted less than 90 degrees and veers through the wall towards the center of the reactor bottom and continues below the lower mixer, where new reactive gas is fed into the flow at through the gas pipeline to be dispersed. The purpose of an excellent and controlled mixing is to get the solution, solids and gas to react between them. In this form in a well-mixed suspension the desired components are leached from the solids and at the same time the desired parts of the gas, such as the oxygen in the air, dissolve in the liquid. The second part of the flow directed in the wall of the reactor is diverted so that it flows upwards. This means that the directed flow upward first makes a strong and rapid 90 degree turn, which sweeps the solid particles that are close to the wall upwards towards the upper section of the reactor. The upward flow typically takes place in the space between the inner edge of the screens and the wall, which is sized to be 1/5 of the diameter of the reactor. Another strong change of direction occurs in the slurry flow near the surface of the slurry, this time in the direction from the center of the reactor to the upper mixer. This means that the extra support of the screens allows the formation of horizontal vortices that transport gas bubbles with them, which powerfully prevents the unreacted gas from leaving the slurry.

In most known reactors the gas in the grout in large volumes is only partially dispersed, thus reducing the potential removal of the mixer. The mixing equipment arrangement according to the present invention also includes large screens, of which there are at least six, but preferably eight. The range of the screens from the wall to the center is about one fifth of the reactor diameter ( T / 5), in other words the distance from the inner edge of the screen from the reactor wall is approximately 20% of the diameter of the reactor and the width of the screen is 12-15% of the diameter of the reactor. The vertical opening that remains between the screen and the wall is also larger than usual, that is, 6 - 8% of the diameter of the reactor. Screens can be used in other ways than forming the desired flows. It is known that an increase in the flow velocity in the vicinity of heat transfer pipes improves the transfer of heat considerably. The heat transfer is particularly effective when the heat transfer pipes are located in the screens, that is, the screens act as heat transfer members. In this way the screen is formed from a module of tubes used to transfer heat. Normally there is always an opening between the tubes in a tube module of at least the size of the tube, by means of which a medium flows around each tube, with the intention of transferring or recovering its heat. The tube modules with openings between them can not be used in the solution according to the invention, because the openings weaken the formation of the desired flow field. Instead of this, a solution according to the invention consists in using what have been called fin tubes, where vertical tubes are connected to each other by means of plate-like components. In this way a structure is formed that is equivalent to a normal screen in relation to the flow of slurry according to the invention. In this way the screens used in the mixer apparatus and method according to the present invention work both to form the desired desired fluxes as well as a means of heat transfer. Figure 1 shows that reactor 1 is a closed reactor such as for example an autoclave. A mixer 2 according to the prior art consists of a lower mixer 3 and an upper mixer 4, which are suspended from an arrow 5. This type of mixers is described, for example, in EP 1,309,394. The mixers are approximately the size of the opening 6 of the cover, that is, a mixer / diameter ratio of the D / T reactor < 0.4. The numerous gas formations 8, small and conical, of the upper mixer 4 obtained on the surface of the solution 7 are dispersed by means of the inner and vertical vanes 9 of the upper mixer in considerably smaller bubbles. The outer vanes 1 1 of the upper mixer 4 spread and push the bubbles formed there towards the mixer 3, but due to the "smallness" of the upper mixer and the dispersion caused by the mixer, more energy is required to press the bubbles down that in the case of the invention now presented. As the flow chart shows, three (I-III) zones are formed in the reactor flow field according to the prior art; an upper zone I of dispersion and surface suction, in the middle part a zone II of collision of the flow of the mixer, which is the reason why additional energy is required to press the gas bubbles downwards, and the lowermost zone III of dispersion and of the reaction itself. This zone additionally receives and disperses the bubbles of gas in extremely small bubbles 12 by means of the vertical shaped vanes 13 of the lower mixer 3. The same vanes that provide a powerful flow disperse these small bubbles in the surrounding solution and at the same time make a suspension of solid particles. The gas required in the reactions is fed into the upper section of the reactor, its gas space, through a gas connection 14. The screens 15 used according to the publication are standard flow screens. As Figure 1 shows and the description of the patent in question makes it clear, the apparatus and particularly the upper mixer have been developed to suck gas from above the liquid surface. In practice it has been found that a collision zone is formed between the first and third zones, resulting in the fact that the mixer solution is not especially effective, at least not when working at a high density of slurry. Figure 2 presents a diagram of a reaction space according to the invention and the flow fields formed therein. In the solution according to the invention attention is paid specifically to the properties required in the leaching, such as the effective and uniform mixing of solids and prevention means to prevent the unreacted gas from escaping the suspension. In the solution according to the invention, attention is also paid to the manner in which the gas is sucked from the layer of the rising edge region back into the downwardly directed circulation occurring around the central arrow. According to the solution. The gas that has risen above the liquid surface is also sucked together within the circulation. In Figure 2 the reactor 20 in vertical position is filled according to our invention with a solids-solution mixture, that is, a slurry up to the height Z (effective height of the slurry), which is preferably 1.5-2. times the diameter T of the reactor. The solids content of the slurry is typically high, approximately 500 g / 1. The reactor has a curved bottom 21 (known as shallow bottom of pressure vessel) and a gas-tight cover 22 to achieve a closed space. The reactor includes essentially wide flow screens 23, of which there are at least six, but preferably eight. The range of the screens from the wall to the center is approximately one fifth of the diameter of the reactor (T / 5), that is, the distance of the inner edge 24 of the screen from the wall 25 of the reactor is approximately 20% of the diameter of the reactor. Naturally there remains a vertical opening between the screen and the wall, which is also larger than the standard, that is, approximately 6-8% of the diameter of the reactor. The energy required for the reactions between liquid, solids and gas is mainly achieved with the help of the mixing member 26 according to the invention. The mixing member consists of two mixers fixed one above the other on the same axis 27, namely, an upper mixer 28 and a lower mixer 29. The mixers in this case are in some way of the same type, that is, what is called step propeller models. The process gas, such as oxygen, nitrogen or some other "pure" gas, is fed into the lower section of the reactor below the lower mixer 29 through a gas line 30. The lower mixer 29 does the actual work, that is, it takes approximately 75-85% of the power released into the slurry. The mixer forms a flow field in the lower section of the reactor in such a way that the slurry flow is discharged from the tips of the mixer blades obliquely down towards the bottom of the reactor wall 31 so that the "point of impact" is in fact on the vertical wall and not in the background. This means that the flow near the wall is divided in two. The current that is obliquely biased downwards 32 continues in turn towards the center of the lower part of the reactor and continues from the center to within the coverage area of the lower mixer. The current diverted downwards from the point of impact of the reactor wall forms a toroidal circulation in the area of the reactor wall 31 and the curved bottom. The powerful circulation 32 that is generated improves contact between solids, solution and gas. In this way the driving power is obtained for the desired reactions between the solution, solids and gas. In some cases some of the reaction products try to accumulate on the surface of the solid particles and in this way the reactions are slow, but it has been found that the accumulation of these types of reaction products is minimal thanks to the powerful lower mixer . One such reaction product is the elemental sulfur that is formed in sulfur leaching, which tries to accumulate on the surfaces of the sulfur still undissolved, causing them to become passive. The second part 33 of the flow formed by the lower mixer rises in an extremely steep curve guided by the screens 23 in the vicinity of the wall 25 upwards towards the surface. The purpose of the lower mixer is thus to form a flow field in the lower section of the reactor. In addition, the lower mixer is configured in such a way that it disperses the gas fed under the mixer and the circulation gas that comes from above in small bubbles in order to achieve the largest possible contact surface for the reactions. In addition, the mixer is configured in such a way that it causes the solid particles in the reaction space to move and keeps them moving and further ensures that the solids content is uniform throughout the entire reaction space. The profile of the lower mixer also makes possible a large difference in speed or turbulence between the particles and the other phases in order to promote the reactions. Advantageously, the large angle of the blades of the lower mixer generates vortices, which facilitate the advance of chemical reactions.

The power taken by the upper mixer is smaller, that is, approximately 15-25%. The upper mixer is configured such that it forms a flow field in the upper section of the reactor such that the flow of slurry containing gas and rising to the surface in the vicinity of the wall makes an extremely pronounced turn before the surface towards the center of the reactor. This means that the bulkheads help form strong horizontal vortices 34 in the horizontally flowing field, which push the gas that is in the flow that rises with them at least as far as the area of the upper mixer 28. The second task of the upper mixer consists in achieving such puddles of powerful suction mainly above the mixer, that the gas that is above the surface is sucked through them and mixed in this same horizontal flow and moved further towards the upper mixer. From here the upper mixer 28 presses the gas-slurry suspension in question as a flow with the cross section 36 as wide as possible downwards towards the lower mixer 29. The large diameter size of the mixers is precisely the reason why the principle described above works, so that one could still talk about the formation of an invisible tube of downward current in the center of the reactor. The formation of the change flows described above has also been proven in practice. The large cross-sectional area of the downwardly directed flow forces the cross-sectional area of the slurry flow rising onto the reactor wall to be small, and thus the upwardly moving flow has a great velocity. Typically the rate of the upward flow is in the region of 0.5 to 1.5 m / s, preferably between 0.8 and 1.2 m / s. If the reactor size is in the region of 300-500 m, this means that the entire content of the reactor passes through the lower mixer at intervals of 15-40 seconds. Mixing reactors are often used, for example, in the leaching of ore or concentrate. In this case, the leaching step usually includes several reactors and for example in the apparatus included in the scope of this invention the slurry is transferred from one reactor to another as an overflow, so that it is not shown in detail in the diagram.

In the now developed mixing apparatus and method, a large cross-sectional area of the downwardly directed flow and the gas bubbles oscillating therein are characteristic. The horizontal vortices 34 on the surface of the grout layer directed from the edges towards the center take a significant part of the gas bubbles towards the upper mixer 28, which presses the bubbles in a new circulation towards the lower mixer. A small amount of gas is however capable of being discharged into the gas space of the reactor, but is sucked back into the slurry through the vertical vortices 35 formed by the upper mixer and the surface is broken by the rapid flow of water. return surface towards the suction zone of the upper mixer. It has been found in tests that the efficiency of gas use is in the region of 90-100%, frequently above 95%. The residual drive power for chemical reactions comes from the gas that dissolves from the bubbles that flow downwards about ten times more than the bubbles that flow upwards. The flow with downward direction takes place precisely in the space between the mixers, so that it is advantageous that the mixers are at a distance from one another according to our invention. Correspondingly, it is characteristic of our method that the cross-sectional area of the flow with downward direction be much bigger than the conventional. The flow with downward direction preferably extends from the axis 27 of the mixer outwards just up towards the inside edge of the screens. The flow with downward direction represents approximately 30-40% of the cross section of the entire reactor. On the other hand, the flow velocity of the large upward flow has the effect that the flow deviations in both the upper section and the lower section of the reactor are abrupt, by means of which both the flow of upwardly moving solids 33 and the horizontal vortices 34 that suck gas are reinforced. The velocity of the downstream slurry flow 36 that occurs in the center can be regulated precisely by sizing the upper mixer in such a way that the gas bubbles that flow with it begin to oscillate, thereby increasing the reactions between the gas and the grout. The combined effect of the mixers gives rise to macro fluxes, one of which circulates through the lower part and the other through the surface area back to the lower mixer. In addition, a toroidal circular flow is generated against the bottom, which also increases the chemical performance values. The combination of mixers according to the invention works ideally, because by their great dimension both mixers deliver considerably more mixing energy than normal both for gas dispersion and for the production of a solids suspension. At the same time the mixers lose their power very slowly as the amount of gas sucked increases, which is precisely due to the effective dispersion and the method of mixing the dispersion of the bubbles. Figure 3A shows an upper mixer 28 according to the invention in greater detail from the side and Figure 3B shows it from above. The upper mixer has at least six, preferably eight rectangular and plate-like blades or blades 37, which are installed on the arrow 27. The blades of the upper mixer 28 are inclined from the horizontal at an angle of at 25 ° -35 ° , preferably 30a, and the height of the mixer 38 itself is in the region of one sixth of the diameter of the mixer Di (hi / Di = l / 6). The purpose of the mixer sheets is to cause such a stable flow field near the surface of the slurry in the reactor that the horizontal 34 and vertical 35 vortices are formed from the surface and the flow rises from the edge area of the reactor , which sucks gas inside them. The sheets 37 of the mixer mix the gas in the slurry and push it as a uniform flow 36 down from the center of the reactor towards the lower mixer 29. Figure 4A represents a lower mixer 29 according to the invention, seen from the side and Figure 4B shows the mixer seen from above. The lower mixer 29 has at least six, preferably eight rectangular, plate-like mixer blades 39. Each blade is at a certain angle with respect to the horizontal, which in the case of the lower mixer is between 50 and 70 °, but preferably 62 °. The blades are wider than normal so that viewed from the side the height of the mixer 40 is a quarter of the diameter of the mixer D2 (h2 / D2 = l / 4).

The purpose of the lower mixer 29 is to receive the gas-slurry flow 36 pushed down by the upper mixer 28 from the center of the reactor, to disperse the gas smaller and more uniform bubbles and also to push the suspension that is formed towards the lower cylindrical section of the vertical wall 31 of the reactor. The shock on the wall occurs near the bottom of the reactor, but nevertheless, above it. At this point the flow is divided into two parts: the first sub-stream 32 that transports gas bubbles with it, bends down gently towards the center of the reactor bottom and continues from the center upwards towards the middle part of the lower mixer , flow within which the reaction gas is fed, and the second sub-stream 33 abruptly bends along the wall in a small radius, taking with it solid particles and gas bubbles thanks to its force. Both mixers 28 and 29 are larger in diameter than normal, that is, between above 0.4 times, but a maximum of 0.5 times the diameter of the reactor. Both mixers have their own important task, according to which the mixers are specified. The height 40 of the lower mixer is approximately 1.5 times the height 38 of the upper mixer. Figure 5 presents a cross section of a flow screen 23 according to the invention, which is composed of heating / cooling tubes 42 joined together by means of fin-like projections 41. The invention is described in more detail with the help of the appended examples.

Example 1 In one study, a comparison was made of the effect of three mixers of normal construction with different diameters (D) in the vertical vortex generation mechanism. The mixers were therefore four-bladed "propeller" type mixers, where the angle of inclination of the blades was 45 ° and the ratio of the height h of the mixer to the diameter D of the mixer was also that used in the mixer. most conventional solutions, that is, h / D = 1/6. In all the tests the distance of the mixer from the surface of the slurry by diameter of the mixer was the same. In the measurements provided in Table 1, the rotational velocity Ncr¡t at which the vertical vortices began to form was determined. Using this measured rotational speed, the dimensionless number KcV was determined and it was shown to be constant. The closest inspection of the constant shows that it is a valid function: Frcv = Kcv * (D / T) 2 where: Frcv = Froude number = N D / g N = rotational speed of the mixer D = mixer diameter T = reactor diameter g = gravitational acceleration This type of test series showed that the behavior of vertical vortices is highly dependent on the number of Froude and therefore according to the theories presented in the literature.

Table 1 Limit rotational speed Ncv for the generation of vertical vortices Test D / T Ncrit wcri «Kcv Kcv av. No. - rps m / s 1 Ncrit2D3 / gT2 Ncrit2D3 / gT2 1 0.381 4.00 4.79 0.690 - 2 0.483 2.83 4.30 0.706 - 3 0.525 2.42 3.96 0.657 0.684 Example 2 At the same time, the effect of the mixer on the horizontal vortex behavior mechanism was studied by comparing the same three mixers with different diameters. The mixers were therefore again four-blade "propeller" type mixers, as in the previous example. In all tests the distance of the mixer from the surface of the slurry per mixer diameter was the same here as well. In the measurements provided in Table 2, the rotational speed Ncrit at which the horizontal vortices were formed in an acceptable manner was determined. Using this measured rotational speed, the dimensionless number Kcv was determined, which proved to be a constant. The closest inspection of the constant shows that it is a valid function: where: Recv - Reynolds number = ND2 / v N = rotational speed of the mixer D = mixer diameter v = kinematic viscosity This series of short tests on its part showed that the behavior of the horizontal vortices does not depend on the number of Froude, but in its place it is actually "controlled" by the Reynolds number. This in turn means that according to the rules of the rheology which influencing factor is in fact the correct flow field, which is known to remain the same, as long as the turbulent zone is sufficient, this is Re > 10,000.

Table 2 Limit rotational speed Ncri for the formation of horizontal vortices Test D / T Ncrit Wcnt ch Kch av. No. - Rps m / s Ncri, D2 / v I NcritD2 / v 1 0.381 6.00 7.19 872000 - 2 0.483 3.83 5.82 896000 - 3 0.525 3.00 4.95 826000 865000 Example 3 The effect of the size of the upper mixer and the lower mixer on the behavior of both the horizontal vortex and the vertical vortex was studied. It was found that with a small ratio D / T of mixer / reactor diameter of below 0.4 a deep vortex formed on the surface of the slurry at the base of the arrow, which deepened as the rotational speed increased as much as below the lower mixer. In conclusion one could say that if several constant and effective vortices of the type according to this invention are desirable, the D / T size of the mixer diameter should be above 0.4.

Example 4 The effect of the size and number of screens on the flow field behavior in a cylindrical mixing reactor with a mixer member according to the invention was studied in the example. Eight screens were used as screens according to the invention with a width of 12.4% of the diameter of the reactor and an inner edge extending to a distance of 18.2% of the diameter of the reactor. Standard screens were used as reference screens, of which there were four, with a width of 8.3% and a range of 10% of the diameter of the reactor. A very clear difference was found in the comparison in the behavior of the flow. When ordinary flow screens were used, indeterminate fluctuations in the grout flow appeared. However, when screens were used according to our invention indeterminate fluctuations in the grout flow were stabilized and were in accordance with the description of the method. In conclusion, it was found that the mixing member according to the invention is not sufficient only to achieve the desired and stable flow field but a characteristic part of the mixing apparatus according to the invention consists of the bulkheads described in the text, in relation to both its number and its size.

Example 5 In this example, we studied the distribution of slurry concentration in a cylindrical mixing reactor, which was a mixing apparatus according to the invention. The solids used were pyrite ore, which was ground to a fineness of 95% below 1 10 micrometers. The solids content was 500 g 1, that is, a slurry density of 1,400 kg / m3. Air was fed from below the mixer below 2.4 m3 / h / m3. The rotational speed of the mixers corresponded to a peripheral speed of 2.8 m / s. Samples of solids were taken from three depths, whereby each represented one third of the total slurry density. The following results were obtained: Table 3 Concentration of slurry in a reactor according to the invention The results in the taba show that the mixing has been extremely capable of lifting these lightly weighed particles well (particle density 5000 kg / m3) towards the surface layer of the reactor and in addition to distributing the particles very uniformly in the whole of the complete reaction space (1350 kg / m3 ± 1.3%).

Claims (21)

1. Claims 1. A mixing apparatus for mixing gas in a slurry formed of a liquid and solids, wherein the apparatus consists of a closed and cylindrical vertical reactor, provided with a bottom and a cover, with an effective grout height of approximately 1.5 - 2 times the diameter of the reactor, a mixing member located inside the reactor and consisting of two mixers joined one above the other on the same axis, at least six, preferably eight flow screens directed inwards with a reach from the wall of the reactor which is about 1/5 of the diameter of the reactor and a gas supply pipe located in the lower section of the reactor, characterized in that: the reactor is equipped with a mixing member, which consists of a top mixer and a mixer lower, by means of which the upper radial blade mixer is equipped with at least six, preferably eight, blades, which are in clinados from the horizontal to an angle of 25 - 35 °, and the lower mixer with radial blades is equipped with at least six, preferably eight, blades, which are tilted from the horizontal to an angle of 60 - 70.
2. 2. A mixing apparatus according to claim 1, characterized in that the power taken by the lower mixer is at least three times, preferably at least five times, that taken by the upper mixer.
3. 3. A mixing apparatus according to claim 1, characterized in that the blades of the upper mixer are inclined from the horizontal at an angle of 30 °.
4. 4. A mixing apparatus according to claim 1, characterized in that the blades of the lower mixer are inclined from the horizontal at an angle of 62 °.
5. 5. A mixing apparatus according to claim 1, characterized in that the height of the lower mixer is in the region of ¼ of the diameter of the mixer.
6. 6. A mixing apparatus according to claim 1, characterized in that the height of the lower mixer is in the region of 1/6 of the diameter of the mixer.
7. 7. A mixing apparatus according to claim 1, characterized in that the height of the lower mixer is in the region of 1.5 times the height of the upper mixer.
8. 8. A mixing apparatus according to claim 1, characterized in that the diameter of the mixers is about 0.4, but a maximum of 0.5 times the diameter of the reactor.
9. 9. A mixing apparatus according to claim 1, characterized in that the distance between the mixers, one of the other, is in the region of 50-70% of the effective height of the reactor slurry.
10. 10. A mixing apparatus according to claim 1, characterized in that the distance of the lower mixer from the bottom of the reactor is in the region of the mixer diameter.
11. 11. A mixing apparatus according to claim 1, characterized in that the width of the screens is 12-15% of the diameter of the reactor.
12. 12. A mixing apparatus according to claim 1, characterized in that the distance between the screens and the wall of the reactor is in the region of 6-8% of the diameter of the reactor.
13. 13. A mixing apparatus according to claim 1, characterized in that the screen forms a heat transfer member.
14. 14. A mixing apparatus according to claim 13, characterized in that the screen consists of tubes joined together by means of plate-like components.
15. 15. A mixing apparatus according to claim 1, characterized in that the bottom of the reactor is curved.
16. 16. A method for dispersing gas fed into the bottom section of a closed reaction space in a slurry formed of a liquid and solids by means of flow screens and a mixing member located in the reaction space, by means of which The effective grout height of the reaction space is in the region of 1.5 - 2 times the diameter of the reaction space, the mixing member consisting of two mixers located on the same shaft, by means of which the gas is fed below the lower mixer into the slurry flow, characterized in that the slurry flow by means of said mixer is directed towards the lower part of the wall of the reaction space and it is made to discharge there in two separate streams, one of which is made to turn through the wall towards the center of the bottom of the reaction space in the form of a toroidal flow and the other it rises in the zone formed by the wall of the reaction space and the bulkheads up towards the surface, where the flow is diverted by means of the upper mixer towards the center of the reaction space and is made to form at the same time horizontal and vertical vortices that they transport gas bubbles; the direction of the slurry flow in the center of the reaction space is diverted by means of the upper mixer so that it flows downwards as a uniform tubular flow towards the lower mixer.
17. 17. A method according to claim 16, characterized in that the solids content of the slurry is in the region of 500 g / 1.
18. 18. A method according to claim 16, characterized in that the flow velocity of the updraft in the area of the wall of the reaction space and screens is 0.5-1.5 m / s, preferably 0.8-1.2 m / s.
19. 19. A method according to claim 16, characterized in that the cross-sectional area of the slurry flow directed downwardly in the center of the reaction space is in the region of 30-40% of the cross-sectional area of the reactor.
20. 20. A method according to claim 16, characterized in that the gas bubbles in the slurry flow directed downwards in the center of the reaction space are set in an oscillating motion.
21. 21. A method according to claim 16, characterized in that the feeding of slurry into the reaction space and its removal from there occurs as a spill.