GB2117261A

GB2117261A - Method and device for mixing two liquids

Info

Publication number: GB2117261A
Application number: GB08307254A
Authority: GB
Inventors: Friedrich Heinemann
Original assignee: Zoellner & Sohn & Co GmbH; Accumulatorenwerk Hoppecke Carl Zoellner and Sohn KG
Current assignee: Zoellner & Sohn & Co GmbH; Accumulatorenwerk Hoppecke Carl Zoellner and Sohn KG
Priority date: 1982-03-29
Filing date: 1983-03-16
Publication date: 1983-10-12
Also published as: FR2523865A1; GB8307254D0

Abstract

The two liquids to be mixed (F1, F2) are brought together to form a premixed stream (F3) after which definitive intermixing is produced by withdrawing or branching off a fraction from the stream and re- feeding thereto phase-displaced in terms of time and/or position. A device for performing the method includes a circular mixer (Fig. 3) consisting of a closed circular pipe system with a feed connector (11) and a discharge connector (12) separated therefrom. The method is particularly useful in the treatment of effluent water and Fig. 2 discloses a plant layout, embodying the invention for the controlled neutralisation of sulphuric acid effluent. <IMAGE>

Description

SPECIFICATION Method and device for mixing two liquids together The invention relates to a method and device for mixing two liquids together, in particular for neutralising effluent waters, by feeding one of the liquids to the other in order to produce a premixed stream.

When chemically reacting liquids, it is necessary to mix them together very intensively.

The chemical ionic reaction itself occurs in times of less then one millionth of a second, however, it is important that the reaction is made possible by the mixing operation. The mixing operation is generally the step which determines the rate.

Generally, the mixing operation is carried out in a closed reaction vessel or in large open tanks, with the object of attaining the most possibly uniform distribution of the two components. Because of the large volume, intensive intermixing is however, only possible with high energy expenditure.

Moreover, the mixing operation is slow, and therefore terminates only after lengthy periods on attaining the required intermixing. The second component of the mix is generally fed in pulses and very slowly.

The mixing together of two liquids widely occurs in practice in the neutralisation of effluent waters, for which very exact tolerances must be set. With the known pulse-type feed of the neutralisation medium, the requirements can only be fulfilled difficultly, because even when the feed of the neutralisation medium is in the form of pulses which follow each other rapidly, alkaline and acid zones alternate with other and must be so coordinated that after the complete intermixing they have attained the required pH value. With varying effluent conditions, such as the effluent loading or temperature, coordination is hardly possible. Continuous feed is therefore recommended, but this presupposes rapid control and short idle times.

In consideration of this state of the art, the object of the invention is to develop a method for mixing two liquids together which operates with short idle times, is simple, and ensures rapid intermixing with improved results. A further object of the invention is to provide a device for carrying out the method.

The object is attained according to the invention in the case of the initially stated method in that a fraction of the premixed stream is withdrawn or branched off, and is again fed displaced in phase. The basic idea of the invention is therefore to firstly mix the two components which have to be mixed together, in order to produce a premixed stream, then to withdraw or branch off a fraction of the premixed stream and to again feed this to the premixed stream displaced in phase with respect to time and/or position. This can be carried out continuously, in which case the withdrawal and phase-displaced refeeding of the fraction to the premixed stream is preferably likewise effected continuously.

According to a desirable embodiment of the invention, the phase-displacement is preferably effected by the delayed re-feeding of the mixed fraction. By this means, very short idle times together with intensive and rapid intermixing are attained.

According to a further embodiment of the method of the invention, the withdrawn fraction is fed back at a reduced flow velocity, preferably of about 50%.

According to a desirable embodiment of the invention, after the main mixing operation an after-mixing operation is carried out by again withdrawing or branching off a fraction from the main mixed stream and again feeding it displaced in phase. In particular, the after-mixing operation in the neutralisation of effluent waters serves for further equalisation, in particular for the precipitation and growth of flakes of materials which were present in solution, but had precipitated on neutralisation. The formed flakes are mixed in the after-mixing operation, and can unite into larger flakes which later deposit more easily.

According to the invention, the device for carrying out the method for mixing two liquids together is characterised by a circular mixer, consisting of a closed circular pipe system with a feed connector and, separated therefrom, a discharge connector, these preferably having a smaller cross-sectional area than the circular pipe.

Preferably, the feed connector and discharge connector are disposed opposite each other and are connected tangentially to the circular pipe where they enter it. It has proved advantageous to choose cross-sectional areas of the feed and discharge connectors at between 1/5 and 1/2 of the circular pipe cross-sectional area. In a circular mixer formed in this manner, the required phasedisplaced return of a branched fraction of the premixed stream is attained in an easy manner in terms of apparatus. Depending upon the specific applications, a variation in the idle time can be attained by varying the cross-sectional areas of the feed connector and discharge connector. The mixing limits can also be varied in this manner.

According to a desirable embodiment of the invention, it can be advantageous to dispose several circular pipe systems one above the other and to combine them by means of connection pieces, in order to produce spiral flow in a vertical direction, in addition to the circular flow with phase displacement produced in each plane. The flow pulses which are superposed in this manner produce a further improved more rapid intermixing.

In order to produce the premixed stream which is then fed to a circular mixer of the described type, it has proved advantageous according to a desirable embodiment of the invention to provide a pressure feed pipe for one of the liquids and an injection pipe for the second liquid connected to the pressure feed pipe, in order to already attain in this manner a relatively good intermixing in the premixing operation. The high velocity injection can thus be of pulse-type or continuous. In terms of apparatus, the pressure feed pipe is connected to a liquid storage container, in particular an effluent water storage container, by way of a pump, on the upstream of downstream side of which there is disposed the connector for the injection pipe for the second liquid, in particular a neutralisation medium. The pump is preferably a centrifugal pump.In order to meter the second liquid, in particular the neutralisation medium, a metering valve or metering pump is disposed in the injection pipe. In order to control the metering device, there is disposed downstream of the circular mixer in the pipe from the discharge connector a device for measuring the pH value, of which the signals are fed, for evaluating the result of the measurement, to a connector computer which controls the flow rate of the second liquid by way of the metering valve or metering pump.

In addition, an after-reaction vessel (Figure 4) can be provided in the flow direction downstream of the circular mixer. The after-reaction vessel is preferably a second circular mixer, consisting of a closed circular pipe system with a feed connector and a discharge connector disposed separated from this latter. In this case the after-connected circular mixer is advantageously coordinated such that it operates with different flow velocities than the first circular mixer.

Further details, characteristics and advantages of the subject matter of the invention will be apparent from the description given hereinafter of the accompanying drawing, in which various embodiments of a mixing device according to the invention are illustrated, and in which: Figure 1 is a process flow diagram, Figure 2 is a diagrammatic illustration of an effluent water neutralisation plant, Figure 3 is a diagrammatic plan view of a circular mixer, Figure 4 is a further embodiment of the neutralisation plant of Figure 2, Figure 5 shows the variation in the concentration at the outlet of the circular mixer of Figure 3 as a function of time.

Figure 1 of the drawing shows, independently of the apparatus concerned, a method for mixing two liquids together by feeding one liquid F1 to the other F2 to produce a premixed stream F3 from which a liquid fraction F4 is branched and again fed displaced in phase. The phase-displaced refeeding of the branched fraction F4 takes place on the illustrated flow diagram by a return to the circulating stream (see arrow). The substantially homogeneous mixed liquid stream F5 is produced after an exceptionally short time. The illustrated flow diagram example relates to continuous operation in all mixing stages. Good results are however also obtained with intermittent feed of the liquid F1 to the liquid F2 either with constant pulse periods or with random pulses.

The implementation of this method in terms of the plant is shown in Figure 2 of the drawing, which represents an example of effluent water neutralisation. The plant consists of an effluent water storage container 1 for sulphuric acid effluent, a tank 4 for storing a neutralisation medium - in the present case caustic soda solution~, a circular mixer 3 and an afterreaction vessel 7. The connection between the effluent water storage container 1 and the circular mixer 3 consists of a pressure feed pipe 8 comprising a centrifugal pump 2. An injection pipe 9 is connected to the pressure feed pipe 8 on the suction side of the centrifugal pump 2, to allow the metered feed of caustic soda solution from the tank 4 by way of a metering valve 5.A device 6 which measures the pH value of the mixed liquid stream leaving the circular mixer 3 is provided downstream of the circular mixer 3 in the flow direction for controlling the metering valve 5.

In the described plant, the centrifugal pump 2 conveys the effluent water through the pressure feed pipe 8. This first liquid component is mixed upstream of the pump with the caustic soda solution metered from the tank 4, and forming the second liquid component. Due to the strong centrifugal effect, intensive intermixing of the two components takes place to produce a premixed stream F3. The metering is effected by continuous control on the basis of the pH measurement in the device 6, the signals of which are fed to a computer 10 which continuously controls the flow rates leaving the metering valve 5.

The premixed stream is fed to the circular mixer 3, which is shown diagrammatically in greater detail in Figure 3 of the drawing. It consists of a closed circular pipe system - here in an oval arrangement - with a feed connector 1 1 and a discharge connector 12 disposed diametrically opposite each other. The feed and discharge connectors 11. 12 have a cross-sectional area which is between about 1/5 and 1/2 of the crosssectional area of the circular pipe 13. The feed and discharge of the medium takes place tangentially in accordance with the illustrated arrows. A description is given hereinafter of the operation of the circular mixer 3, in which the feed and discharge connectors have one half the crosssectional area of the circular pipe 13.

The premixed stream F3 which enters through the feed connector 1 1 has a determined flow velocity which is the same as that in the discharge connector 12. This flow velocity is practically maintained in the circular pipe 13. There is only a slight reduction in velocity. Because of the fact that the cross-sectional area of the circular pipe 13 is twice the cross-sectional area of the feed connector 1 1 and discharge connector 12, there is an additional flow circulating through the circular pipe 13 of approximately the same liquid flow. In the embodiment of the example, the portion of the circle extending from the discharge connector 12 to the feed connector 11 (lower half arc) has the same length as the circle portion extending from the feed connector 11 to the discharge connector 12 (upper circular arc). The flow velocity in the lower half arc is therefore reduced to approximately one half of the flow velocity in the upper circular arc, so that the time required for traversing this segment is double the time for the segment between the feed connector 1 1 and discharge connector 12. Consequently, a phase displacement occurs in terms of time between the main stream and the circular stream, leading to a mixing of the various segments in the system.

Tests have been carried out with a circular mixer of the described type in order to determine the mixing properties of this device, independently of the production of a premixed stream. Figure 5 of the drawing shows the variation in the concentration determined in this manner at the discharge connector of the circular mixer, where a pure liquid is present at the beginning of the test, and 100 g of a second component per volume unit is suddenly fed to it. The illustration shows that in this case, there is no sudden jump in the concentraion, but instead the concentration varies over a time of about 3 to 4 seconds, during which a value of 64% of the initial value of component 3 has already been attained after one second. This shows the good and rapid intermixing effect.

Claims

1. A method of mixing two liquids together, in particular for neutralising effluent water, by feeding one of the liquids to the other in order to produce a premixed stream, characterised in that a fraction (F4) is drawn or branched off from the premixed stream (F3) and is again fed displaced in phase.

2. A mixing method as claimed in claim 1, characterised in that the premixed stream (F3) is continuously produced, and the withdrawal and phase-displaced re-feeding of a fraction (F4) to the premixed stream (F3) is likewise effected continuously.

3. A mixing method as claimed in claim 1 and 2, characterised in that the phase displacement is effected by the delayed re-feeding of the mixed fraction (F4) and/or by returning.

4. A mixing method as claimed in one of claims 1 to 3, characterised in that the withdrawn fraction (F4) is returned at a reduced flow velocity.

5. A mixing method as claimed in claim 4, characterised in that the reduction in the flow velocity is 50%.

6. A mixing method as claimed in one of claims 1 to 5, characterised in that the fraction (F4) is conveyed in cyclic flow.

7. A mixing method as claimed in one of claims 1 to 6, characterised in that after the main mixing operation, an after-mixing operation is carried out by again withdrawing or branching off a fraction from the main mixed stream (F5) and again feeding it displaced in phase.

8. A device for carrying out the mixing method as claimed in one of claims 1 to 7, characterised by a circular mixer (3), consisting of a closed substantially circular pipe system with a feed connector (11) and, separated therefrom, a discharge connector (12).

9. A device as claimed in claim 8, characterised in that the feed connector and discharge connector (11, 12) have a smaller cross-sectional area than the circular pipe (13).

10. A device as claimed in claim 8 and 9, characterised in that the feed connector (11) and discharge connector (12) are disposed opposite each other and are connected tangentially to the circular pipe (13) where they enter it.

11. A device as claimed in one of claims 8 to 10, characterised in that the cross-sectional areas of the feed connector and discharge connector are chosen such that they are each between 1/5 and 1/2 of the cross-sectional area of the circular pipe (13).

12. A device as claimed in one of claims 8 to 11, characterised in that several circular pipe systems are disposed one above the other and are combined with each other by means of connection pieces.

13. A device as claimed in one of claims 8 to 12, characterised in that upstream of the circular mixer (3) there is disposed a premixer comprising a pressure feed pipe (8) for one of the liquids and an injection pipe (9) for the second liquid connected to the pressure feed pipe (8).

14. A device as claimed in claim 13, characterised in that the pressure feed pipe (8) is connected to a liquid storage container, in particular an effluent water storage container (1), by way of a pump (2), on the upstream side of which there is disposed the connector for the injection pipe (9) for the second liquid, in particular a neutralisation medium.

15. A device as claimed in claims 13 and 14, characterised in that the pump (2) is a centrifugal pump.

1 6. A device as claimed in one of claims 13 to 1 5, characterised in that a metering device, preferably a metering valve (5), is disposed in the injection pipe (9).

17. A device as claimed in one of claims 13 to 16, characterised by a control and regulating unit comprising a device for measuring the pH value of the mixed liquid stream (F5) and a computer (10) which produces the connection to the metering device.

18. A device as claimed in one of claims 1 to 17, characterised in that an after-reaction vessel (7) is provided in the flow direction downstream of the circular mixer (3).

19. A device as claimed in claim 18, characterised in that the after-reaction vessel (7) is a further circular mixer (14), consisting of a closed circular pipe system with a feed connector and a discharge connector disposed separated from this latter.

20. Apparatus for mixing two liquids comprising means for feeding the liquids into a common flow pipe, two pipe portions each having an end connected to the output end of said flow pipe and having their other ends connected to a further common flow pipe, said pipe portions being arranged such that liquid flowing through one pipe portion takes a longer time than liquid flowing through the other so as to ensure a thoroughly mixed fluid flow in said further common flow pipe.

21. A method of mixing two liquids together substantially as hereindescribed with reference to the accompanying drawings.

22. A device for mixing two liquids substantially as herein described with reference to Figures 2 and 3 or Figure 4.