Device for continuous mixing of materials

[57] ABSTRACT

A method and a device for the continuous mixing of at least two materials of which one can be pumped and providing a tank for the mixing process in which the material to be mixed is caused to circulate by means of a feed pump.

Claims, 1 Drawing Figure

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PATENTEDMAY 9 1972

3,661,364

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Mi/εκτο/ζ, J//ME F. //6/

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/Τ/Ο/7Λ/Ε/6

3,661,364

DEVICE FOR CONTINUOUS MIXING OF MATERIALS

This invention relates to a device for the continuous mixing of at least two materials of which at least one can be pumped, a tank being used for the mixing process in which the material to be mixed is caused to circulate by means of a feed pump.

In one known mixing device part of the materials to be mixed are withdrawn from the surface at one comer or section of the tank and reintroduced centrally in the vicinity of the tank bottom. The circulation of the mixture due to part of the material being returned to the tank in the form of three streams, is not controlled, the mixing effect is not uniform, and there is no certainty that the entire material particupates in the circulatory movement.

In another mixing device also part of the tank contents are withdrawn laterally and are reintroduced centrally in the vicinity of the tank bottom, but with this device measures are taken to insure that the stream of material which is discharged has a uniform and predetermined circulatory movement with very long flow paths. Only a small part of the fresh material which has to be mixed and reaches the tank travels only once 20 along the flow path because a part of the mixture is constantly being discharged and passed again back into the tank. By far the greater part of the material travels several times around the flow path. In this way a much more intensive mixing is achieved, but this of course requires a correspondingly larger 25 power input for the necessary pumping capacity.

Mixing processes are known, such as introducing gases into liquids, where a very high degree of miscibility is required but only a short flow path in the mixing tank is adequate. The object of the present invention is to produce an expedient device 30 for such processes whereby the pumping power required per unit throughout can be considerably reduced when compared with that required with conventional devices. According to the invention this problem is solved in that at least a part of the fresh material which flows to the mixing device is continuously 35 passed into the mixing tank by way of a central supply pipe, the outlet of which is constructed in the form of a pressure nozzle that is located only slightly above the bottom of the mixing tank which uniformally diverts the flow which is discharged from the nozzle radially in all directions.

A constructional example of the invention is shown diagrammatically in the accompanying drawing which is a vertical cross-section of the apparatus.

The fresh materials that are to be mixed flow under pressure in the direction indicated by the arrow 1 through a supply pipe 11 towards the mixing device and by means of a supply device 2, hereafter briefly referred to as a pump, are conveyed through a feed pipe 5 into the mixing tank 4. The outlet of supply pipe 5 is constructed in the form of a pressure nozzle 6 with a restricted discharge section and is located slightly above the bottom of the mixing tank 4. The jet from the nozzle impinges against the bottom of the tank where it is diverted radially in all directions in a uniform manner. The material in the tank is thus subjected to a rotationally symmetrical circulatory movement with a return flow to the starting point along closed flow paths which are indicated by the arrows 8. The mixed material emerges from the tank by way of a discharge pipe 7. Due to the influence of the lateral discharge the circulatory movement is transformed into a spiral movement, the axis of the spiral being arcuate. The individual particles of the fresh material which is supplied to the tank by way of the pipe 5, travel not more than once along the entire spiral flow path, that is in the drawing from the right side of the tank to the discharge pipe 7 on the left hand side, this depending upon the direction in which the particles are diverted after they emerge from the nozzle. As a result of the impact of the jet of material on the tank bottom as it is discharged from the pressure nozzle and the rotating circulatory movement of the mixture, a very intense mixing effect is achieved, when the conveying power is suitably selected.

The throughput or travel of the material can be controlled in a suitable manner. For example, a device can be provided to vary the amount of material passing through the supply pipe 11 to the mixing tank or by varying the speed of the feed pump 2.

In the case of materials which can easily be mixed, it is not necessary that the entire quantity of fresh material should pass through the supply pipe 5 into the mixing tank and due to the impact on the tank bottom undergo a primary mixing and also the circulating movement in the mixing tank can be less turbulent, so that it is' then an advantage to provide a connecting pipe 3 between the supply pipe 11 and the mixing tank 4. When the amount of material passing to the mixing device exceeds the capacity of the pump, part of the material then 10 bypasses the pump and flows through the connecting pipe 3 directly into the mixing tank 4. Due to the circulating movement in the tank the part of the material which passes through a bypass is also carried along and mixes with the material in the tank. It is thus possible to reduce the power required by the pump per throughput unit, to a value which is in keeping with the surplus amount of material supplied to the pump when compared with the pumping capacity of the latter.

By means of the connection pipe 3 it is possible to influence the mixing intensity of the device in a very simple manner. If the output of the pump is kept constant, it is only necessary to vary the amount of fresh material that is supplied to the mixing device. If this amount exceeds the output of the pump very considerably, then a large part of the material will pass through the connection pipe 3 into the tank and the throughput or capacity of the device is increased but the mixing intensity is diminished. As the supply of material decreases, the part of the material which is directly bypassed into the tank decreases and is finally zero when the amount of material supplied to the tank exactly corresponds to the output capacity of the pump. The mixing intensity has then increased and no more material flows through the connection pipe even when the throttle valve 10, located in pipe 3, is open.

In order to intensify the mixing process still more it is possible to reduce the supply of fresh material even further. As soon as it is less than the output capacity of the pump, which can still be maintained constant, the pump will suck the missing quantity of material through the connection pipe 3 from the tank and convey this material together with the fresh material back into the tank. The smaller the amount of fresh material, the better will be the mixing effect achieved in the tank and the smaller the throughput or flow, the greater will be the pumping power per throughput unit.

The possibility of allowing the material to pass through the connection pipe 3 in either direction is indicated in the drawing by the double arrow 9. The throttle valve 10 enables an additional individual adjustment to be obtained in order to accommodate various operating requirements so that very flexible hydraulic conditions can be achieved.

The described device serves primarily for materials that can easily be mixed, and it is characterized by its high efficiency, because depending on the materials it is desired to mix and the required mixing intensity an optimum adjustment can be obtained whereby only a minimum amount of power per unit throughput is required.