FIELD OF THE INVENTION The invention relates to the equipment and method defined in the independent claims 1 and 1 1 for purifying a process solution.

BACKGROUND OF THE INVENTION Generally, agitation reactors are cylindrical and they have standard diameters. Typically, they are provided with flow resistances, which are attached to the walls of the reactor and the purpose of which is to eliminate the central turbulence, which is considered harmful and which absorbs gas from the surface. Solid-solution processes normally require mixing, wherein both strong turbulences and sufficient circulation occur. One important process is, e.g., the removal of cadmium by cementation. Cadmium is one of the harmful substances in the electrolytic processing of zinc.

The feeding into the agitation reactor mostly takes place by feeding both the solid matter and the solution into the reaction space from above. Generally, in a continuous reactor, it is desirable that both the solid matter and the solution escape approximately at the slurry density of the reaction space. Thus, it is not desirable for the heaviest or coarsest particles to remain in the reactor. In that case, it is natural that the outlet of the slurry flow can preferably be mounted on the reactor wall to mainly take place as an overflow.

In the method according to US patent 3,954,452, the solution rises from a fluidization part through a conical extension into a clarification part, from where there is a discharge outlet of the solution on the wall of the clarification part. The process disclosed comprises the cementation of cadmium solution and zinc powder. In this cementation reaction, cadmium powder is formed, which due to its porosity is lighter and, at the same time, also finer. One object is to prevent the exit of solid particles, which are formed as reaction products, out of the reactor along with the solution. A difficulty in this case is also the adherence of hook-like particles to each other, e.g., agglomeration. Gradually, the agglomerates grow so large that the motion in the fluidized bed weakens and, finally, stops completely. Therefore, a flocculation solution that prevents the agglomeration of particles is fed into the fluidization space. As the prevention, in practice, is not quite perfect, a mixing member that crushes the agglomerates is placed in the lower part and, correspondingly, fairly small flow resistances that receive the impact forces and prevent turbulences are placed on the walls. The solution flows as directly as possible along the shortest route towards the exhaust unit, whereby the flow field is rendered the form of a reducing curved cone. This, again, means that the speed of the solution flow that carries possible particles increases and the particles have no chance of detaching from the flow.

One problem with the equipment described above is that the bed material that prevents the exit of solid matter should be quite coarse. However, with the reactions advancing, the grain size of the solid matter in the bed decreases, whereby the amount of solid matter drifting along with the solution increases.

Present reactors face the disadvantage that the flow permeates through the fluidized bed once in each reactor. This has a significant effect on the purification of the solution and the number of circulation phases. Additionally, the present fluidized-bed reactors have no adjustment, but their properties are determined according to the feed of the process flow and the particle size. Naturally, this causes problems when these magnitudes vary according to the status of the process. Furthermore, the reactors are of the batch type and it is not easy to take into account the flexibility brought by the capacities. In the present fluidized-bed reactor system, the pressure losses are controlled by the liquid bed accumulating on top of the exhaust units. As the potential energy should cover the pressure loss caused by the fluidized bed of each reactor, the transfer of solution through the series of reactors then requires a large liquid bed.

OBJECT OF THE INVENTION

The object of the present invention is to eliminate the disadvantages occurring in the prior art described above. According to the invention, a novel, more effective method and equipment for purifying solid matter from the process solution by means of the fluidized bed are thus presented. By means of the invention, the separation of solid matter is enhanced by circulating the solution in the fluidized bed and the flexibility required by the process changes is increased by controlling the amount of solution to be circulated in the fluidized bed.

SUMMARY OF THE INVENTION

The invention relates to a reactor for purifying solid matter from the process solution in the fluidized bed, whereby the reactor comprises a means of feeding and removing the process solution, the reactor being formed from at least three parts, the lowermost of which is an essentially cylindrical reaction part for forming the fluidized bed; a conically upwards-widening calming part is attached to the upper part of the reaction part and a cylindrical clarification part is connected to the upper part of this, its diameter being the same as the upper part of the calming part, whereby a mixing member is placed in the reactor to circulate at least part of the process solution back to the fluidized bed and to control the amount of circulating solution in the fluidized bed. By the solution according to the invention, the removal of solid matter is enhanced by gaining a better purification result by circulating the solution in the fluidized bed. When the process conditions change, the solution according to the invention can respond to the changes without causing breaks in the process.

According to an embodiment of the invention, the mixing member is placed in the centre of the reactor to produce an axial flow in the solution in the reactor. Consequently, the most advantageous flow conditions are reached in the reactor. According to the invention, the mixing member comprises a pipe element, the lower par of which extends below the fluidized bed. Consequently, the flow can be directed to flow through the fluidized bed. According to an application of the invention, the mixing member is a tunnel propeller. According to an example of the invention, the lower part of the reaction part of the reactor has a rounded shape. In that case, the flow that is fed from the pipe element of the mixing member into the lower part can most preferably and evenly be directed to the fluidized bed.

According to an embodiment of the invention, the feeder pipe of the process solution is placed above the mixing member, whereby the solution to be purified can be guided directly to the pipe element through the mixing member.

According to the invention, the upper part of the reactor comprises an overflow tank for removing the clarified solution from the reactor. According to the invention, the reactor comprises a means, such as a pump arrangement, for transferring the solid matter out of the fluidized bed. According to an embodiment of the invention, the amount of solution circulating in the fluidized bed is larger than the amount of solution fed into the reactor, enhancing the purification of the solution that is fed. According to the example, the solid matter that is removed from the solution to be purified is cadmium.

The invention also relates to the method of purifying solid matter from the process solution in the fluidized bed in the reactor, into which the process solution is fed to form the fluidized bed in the essentially cylindrical reaction part that is the lowermost part in the reactor, from which bed the flow further moves to the calming part that widens conically upwards into the upper part of the reactor part and, further, to the cylindrical clarification part that is connected to the upper part of the same, the diameter of the clarification part being the same as the upper part of the calming part, whereby at least part of the solution that is fed into the reactor is circulated to the fluidized bed more than once, and that the amount of circulating solution is controlled in the fluidized bed by means of the mixing member placed in the reactor.

According to an embodiment of the invention, the mixing member produces an axial flow in the process solution in the reactor, extending the flow below the fluidized bed. According to the invention, at least part of the solution that permeates the fluidized bed moves back to the pipe element that is connected to the mixing member, from where the solution circulates back to the fluidized bed.

According to an embodiment of the invention, solid matter is removed from the fluidized bed at desired intervals without stopping the process and emptying the reactor. The amount of solution flowing in the fluidized bed is adjusted by the rotation speed of the mixing member. In that case, the rotation speed of the mixing member is decreased, when the amount of solution that is fed increases, whereas the rotation speed of the mixing member is increased when the amount of solution that is fed decreases. According to the invention, the energy needed to fluidize the particles in the fluidized bed is produced by the mixing member.

According to the invention, the operation of the fluidized bed can be adjusted, whereby any variations in the process flow and particle size do not cause problems to the process. The changes caused by the variation in capacity can preferably be implemented without having to stop the process. The density of the fluidized bed and the solid matter content of the overflow can always be reactor-specifically optimized to suit the process status, respectively. The dimensioning of a new reactor model can be made for a wide feeding range and, in practice; the capacity of the system can be controlled by the number of reactors. In the model according to the invention, the mixing member that circulates the solution produces the energy needed for the fluidization.

The essential features of the invention are disclosed in the appended claims.

LIST OF FIGURES

The equipment according to the invention is described in detail with reference to the appended drawings, in which

Fig. 1 a shows a vertical section of the reactor according to the invention;

Fig. 1 b shows the reactor according to the invention as viewed in the direction A.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 a shows the reactor 1 according to the invention, wherein a liquid process solution 2 and solid matter are treated, so that the powdery solid matter forms a fluidized bed 3 with the liquid and, at the same time, reacts with the process solution 2 to be purified, which is fed into the reactor. In the fluidized bed 3, the flow fluidizes the solid matter that reacts with the solution. According to the example, the cementation reaction in question is to remove cadmium from the zinc-bearing solution, where the aqueous solution, i.e., Cd-bearing solution of the substance to be cemented flows through the bed of zinc powder. Now, a reaction takes place, according to which zinc dissolves in the solution and cadmium is removed from the solution. In the lower part of the reactor, i.e., the cylindrical reaction part 4, the fluidized bed 3 is formed. From the lower part, a conically upwards-widening calming part 5 and, further, a cylindrical clarification part 6 rise up for raising upwards the solution 9 that is mainly free of solid matter to be further removed to the overflow tank 1 1 in the upper part 10 of the reactor and to be further treated. Generally, we talk about purifying the solution, whereby chemical components, such as cadmium, are removed from the solution. At the next process stage, cadmium can further be removed from the solution 16 that is to be removed. The lower part 7 of the reaction part 4 of the reactor has a rounded shape, which furthers the flow of solution 8 back to the fluidized bed 3.

According to the invention, the energy needed for the fluidization of the fluidized bed is produced by a separate rotary mixing member 12, which is placed in the reactor. The mixing member, i.e., a propeller, preferably a tunnel propeller, is placed below the fluid level in the reactor and it is protected by blades to prevent the absorption of air into the propeller. Naturally, the mixing member 12 is attached, e.g., to the upper structures of the reactor 1 and it is controlled by a control unit 13 outside the reactor. The mixing member can be controlled automatically according to the solid matter content of the feeding flow or the overflow. In the reactor, the propeller produces an axial flow in the process solution 2 that is fed along the feeder pipe 15 above the same, enabling the circulation of the solution through the fluidized bed 3 more than once. Circulation in the fluidized bed 3 further enhances the separation of solid matter. The solution 2 that is fed into the reactor moves to the pipe element 14 of the mixing member, such as a circulating tube, and from there to below the fluidized bed, from where it further flows through the bed 3, whereby the chemical component to be purified reacts with the solid matter of the bed. When moving upwards from the reaction part to the calming part in the reactor, the cross-sectional area of the reactor increases and when the flow velocity decreases, the particles floating in the bed are separated from the solution. Thereafter, part of the solution exits as an overflow and part moves back to the pipe element by means of the tunnel propeller to further flow through the fluidized bed. The properties of the fluidized bed are controlled by the rotation speed of the pumping mixing member, and conforming to the changes in capacity takes place by adjusting the same. If the amount of solution fed into the reactor is increased, the rotation speed of the pumping mixing member is correspondingly decelerated; therefore, the fluidized bed remains stable. Correspondingly, the procedure is reversed, when the amount to be fed decreases. According to the invention, the solid matter used for purification is removed upstream from the fluidized bed by means of a piping and pump arrangement 18, which is separate with respect to the flowing solution. The removal of solid matter 17 is implemented by a suitable pump, such as an airlift pump, into the upper part 10 of the reactor and from there to be further treated.

EXAMPLE

The invention is illustrated by means of the following example. According to the example, a present well-known reactor for removing cadmium is compared with the reactor according to the invention. Table 1 shows measurement results in both cases mentioned above. 440 m ³ /h of process solution to be purified were fed into the reactor, whereby the flow velocity that floats the solid matter particles in the fluidized bed is 0.039 m/s. According to the example, by using the reactor according to the invention, the diameter of the fluidized bed can be increased to 3600 millimetres, the diameter of the present reactor remaining at 2000 millimetres. The solution to be purified is subjected to axial flow under the effect of the rotational power of the propeller placed in the reactor, whereby under the effect of the flow, the solution is pushed into the pipe element of the propeller, i.e., the circulating tube, at a velocity of 1 .2 m/s. The diameter of the pipe element of the propeller, by which an advantageous stability of the fluidized bed is achieved, is 550 millimetres in the solution according to the invention. The rate of flow required in conventional fluidization is always determined according to the amount of solution to be fed, but according to the example that applies the invention, the rate of flow can be increased to as much as 1023 cubic metres an hour. According to the invention, the solution can be circulated according to changing conditions by adjusting the amount of circulating flow in the fluidized bed by a separate tunnel propeller. The amount of circulating flow needed for the fluidization is controlled by the rotation speed of the tunnel propeller. According to the example, the control range of the circulating flow is 1000-1500 m ³ /h, whereby the flow rate of the solution fed into the reactor can be adjusted within a range of 0-900 m ³ /h. According to the invention, the same reactor can thus conform to the changes in the process conditions. According to the example, the volume of the fluidized bed in the reactor can be increased to 15 m ³ . Furthermore, for fluidizing the same flow rate, only one reactor is needed in the solution according to the invention compared with a case, where conventionally a series of many reactors is used.

Table 1 .

It is obvious to those skilled in the art that with the technology improving, the basic idea of the invention can be implemented in various ways. Thus, the invention and its embodiments are not limited to the examples described above but they may vary within the claims.