FR2523865A1 - METHOD AND DEVICE FOR MIXING TWO LIQUIDS, IN PARTICULAR TO NEUTRALIZE WASTE WATER CONTAINING SULFURIC ACID - Google Patents

Abstract

METHOD AND DEVICE FOR MIXING TWO LIQUIDS. ONE OF THE LIQUIDS IS ADDED TO THE OTHER BY FORMING AN INITIAL F3 MIXTURE, WHICH IS INTRODUCED IN A MIXER 3, AND A CERTAIN QUANTITY OF THIS MIXTURE IS TAKEN, THEN RETURNED AFTER HAVING A PHASE SHIFT. THE MIXER 3 INCLUDES AN ANNULAR DUCT 13A, 13B TO WHICH ARE CONNECTED A DUCT 11 FOR INITIAL MIXTURE SUPPLY F3 AND A DUCT 12, DIAMETRALLY OPPOSED, FOR DRAINING THE HIGHER MIXTURE F5 OBTAINED. APPLICATION TO A CHEMICAL REACTION BETWEEN LIQUIDS, IN PARTICULAR TO THE NEUTRALIZATION OF WATER CONTAINING SULFURIC ACID.

Description

The present invention relates to a method and an installation

  intended to mix two liquids, in particular for the purpose of neutralizing waste water, by adding one of the liquids to the other with formation of a first mixture or initial mixture. In order to chemically react liquids, they must be mixed very intensively or intimately. The chemical reaction between ions may not last much less than a millionth of a second, but it is essential that the mixture be allowed to occur. The mixing operation is generally the step which determines the reaction rate. This mixing is generally done either in a closed reaction vessel or in larger open vessels for the purpose of distributing the two components of the reaction mixture. as homogeneous as possible However, because of the large volume, it is possible to obtain an intimate mixture only by consuming a lot of energy. Moreover, the mixture is slowly operated and is therefore only completed after a long time interval, giving the desired intimate mixture The second component of the mixture is

  added usually by pulses and very slowly.

  The mixing of two liquids is practically carried out on a large scale to neutralize waste water

  operation in which it is necessary to respect

  With the known method of pulse addition of the neutralizing agent, these requirements are difficult to satisfy, because, even if these pulses follow each other rapidly, there are alternating alkaline and acidic zones which must be harmonized. in order to arrive

  to the value of the desired p H when the intimate mixture is complete.

  If the state of the waste water, such as its pollution load or its temperature, varies, it is difficult to adapt to it. It is therefore advisable to carry out the addition continuously, provided that the be done quickly

  and that the duration of the downtime is short.

  In view of this state of the art, the invention

  The invention relates to a process for mixing two liquids with which dead time is of short duration, this method being

  simple and ensuring a more intimate mixture The invention

  also a facility for implementation

of this process.

  The process according to the invention is characterized in that a certain quantity of the initial mixture is taken or diverted and reintroduced into it after having subjected it to a certain shift or phase shift. The basic idea of the invention is therefore to mix the two components first to obtain an initial mixture, to take or immediately divert a certain amount of this mixture and to reintroduce it into it after having shifted it in time and / or in space It is possible to do this continuously, the sampling and the staggered reintroduction of

  the quantity taken from the initial mixture being advantageously

  In an advantageous embodiment of the invention, it is also possible to carry out the shift of

  phase ep differing the moment of the reintroduction of the quantity

  In this way, downtime is very

  short and an intimate blend is obtained quickly.

  Another variant of the process according to the invention consists in reintroducing with a reduced flow rate, advantageously reduced by about 50%, the quantity which has

been taken.

  Furthermore, according to another advantageous characteristic of the invention, after having carried out the main mixing, a complementary mixture is carried out by removing or again diverting a certain quantity of this mixture.

  and reintroducing it with a phase shift.

  This additional mixing operation is used in particular in the neutralization of waste water, to obtain a better equalization and in particular to precipitate and develop the solids flakes which were dissolved, but which are deposited during the neutralization During the execution of this complementary mixture, the formed flakes are mixed and can agglomerate and form flakes

  bigger ones which are then deposited more easily.

  The installation for the implementation of the method

  according to the invention, a mixture of two liquids is

  characterized in that it comprises an annular mixer composed of a system of closed or annular conduits, to which are connected at different places a supply line and a discharge line, which preferably have a smaller section than that of this

  These supply and discharge lines

  are advantageously opposed and are connected tangen-

  tally to the said annular conduct It has proved

  It is advantageous to give feed and

  a section for each between the fifth and half of that of the annular pipe In an annular mixer shaped in this way, we obtain very

  simply the desired phase shift of the amount detour-

  from the initial mixture Depending on the specific use cases, it is possible to vary the duration of the

  downtime by changing the section of the fuel line

  or evacuation pipe It is also possible

  to modify the mixing limits in this way.

  According to a feature of the invention, it may be advantageous to arrange on top of one another a plurality of annular pipe systems and to combine them by means of connecting lines to obtain in addition to the forced circular flow with offset of phase in each plane, a spiral flow in the vertical direction The flow pulses which are superimposed in this way give an even better mixture faster. To prepare the initial mixture which is then sent to an annular mixer of the kind described, it has proved advantageous, according to another characteristic of the invention to use a pressure line for one of the liquids and, for the second fluid , an injection line connected to the first, in order to give

  this initial mixture has a relatively high homogeneity.

  High speed injection can be made by pulse

  The pressure line is connected to a reservoir of liquid, in particular wastewater via a pump, upstream or downstream of which

  the injection pipe of the second liquid, which is particularly

  The pump is advantageously centrifugal For metering the second liquid, a metering valve or a dosing pump is mounted in the injection line.

  dosage, the exhaust pipe includes downstream of the

  a pH measuring device, whose signals are sent to a computer intended to exploit the information

  received and controlling the flow of the second liquid through the

  the valve or dosing pump.

  In addition, a complementary reaction vessel -

  (14, FIG. 4) can be arranged downstream of the annular mixer.

  Advantageously, this vessel is another annular mixer comprising a closed circuit system, to which feed lines are connected and

  evacuation mounted at a distance from each other.

  This downstream mixer is advantageously adjusted to operate with flow speeds that differ.

those of the first mixer.

  Other peculiarities, characteristics and advantages

  of the invention will emerge from the description

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE PREFERRED EMBODIMENTS OF THE INVENTION FIG. 1 is a diagrammatic representation of the process steps.

  FIG. 2 schematically represents an installation

  neutralization of residual water; Figure 3 is a schematic plan view of an annular mixer, or in a closed circuit; FIG. 4 represents an alternative embodiment of the neutralization installation of FIG. 2; and FIG. 5 is a graph of the concentration (ordinates) - as a function of time (abscissa) at the exit

of the mixer of FIG.

  Figure 1 depicts, independently of the installation

  for its implementation, a method for mixing two liquids by adding one Fl to another F 2 so as to form an initial mixture F 3, a certain amount F 4 is diverted and reintroduced after a certain shift This shift in the reintroduction of this diverted quantity F 4 is obtained on the diagram shown / transport upstream in the mixing stream (see arrow F 4). After an extremely short time interval, the mixture

  F 5 of the liquids is substantially homogeneous.

  example, refers to the implementation of

  continuation of the process in all stages of mixing

  also achieves good results by introducing

  mittence the liquid Fl in the liquid F 2, by means of pulses

  The introduction of the liquid F1 can also, or alternatively, be carried out fairly close to the location of the reintroduction of the derived current (this

  which is shown in phantom in Figure 1).

  The installation for carrying out this process is shown in FIG. 2 in the case, given by way of example, of the neutralization of a waste water. This installation comprises a tank 1 of sulfuric waste water, a tank 4 neutralization agent in the present case a caustic soda lye an annular mixer 3 and a complementary reaction vessel 7 The waste water tank 1 is connected to the mixer 3 by a pressure line 8 in which is inserted a centrifugal pump

  2 On the suction side of this pump 2, an injection pipe

  9, which is connected to the pipe 8, allows to deliver by means of a metering valve 5 the metered quantity of sodium lye coming from the tank 4 A device 6 for measuring the p H of the liquid mixture coming out of the mixer 3 , mounted downstream of this mixer, allows to control the valve

metering device 5.

  In the installation described, the centrifugal pump

  2 sends the wastewater into the pressure line 8.

  Upstream of this pump, the sodium liquor coming from the tank 4, and constituting the second liquid component, is mixed in a metered manner with this first component.

  of the great intensity of the centrifugal force, these two components

  are intimately mixed together forming an initial mixture

  F 3 The metered dose is continuously regulated according to

  the value of the p H, measured in the device 6, the values recorded being introduced into a computer 10 which constantly regulates the flow of the liquid leaving the valve

metering device 5.

  The initial mixture is sent to the annu-

  3, shown schematically in FIG.

  includes a closed loop system of pipes -

  forming an oval in the figure to which are connected a supply line 11 and a discharge pipe 12

  diametrically opposite The section of these supply lines

  11 and discharge 12 is between the fifth and the half approximately that of the annular pipe 13 The liquid is injected and taken tangentially, as indicated by the arrows The operation of this mixer 3 is described above. in the case where the section of the supply and bypass ducts is half that of

the annular pipe 13.

  The initial mixture F 3, which enters through the supply line 11, circulates at a certain speed, which is

  identical to the flow velocity in the evacuation

  This speed remains virtually the same in the

  annular conduct 13 A There is only a negligible slowdown

  However, since the section of the annular pipe 13 is twice that of the pipes 11 and 12, there is rotation in this pipe 13 B approximately once again

  the same volume of liquid In the embodiment

  the segment between the exhaust pipe 12 and the supply pipe 11 (lower half-arc B) has

  the same length as the segment that goes from this food conduit

  11 to this bypass duct 12 (upper half-arc A). Therefore, the flow velocity in the lower arc 13 B is reduced to about half of the flow velocity in the upper arc 13 A so that the time required to traverse this segment B is twice that required for

  change from the supply line 11 to the evaluation line

  cuation 12 There is therefore a time difference between the main current and that of the circuit which causes the mixture of the liquids of the two segments, A and B, to be mixed in the system. The tests were carried out with a mixer

  ring of the kind described for the purpose of determining, inde-

  while forming an initial mixture, the

  mixing properties of this mixer FIG.

  the variation, noted in this way, of the concentration

  in the case where the first liquid is pure at the beginning of the test and 100 g of a second component per unit of volume are suddenly added thereto. shows that, in this case the concentration does not increase suddenly, but that it varies for about 3 to 4 seconds, a value equal to 64% of the final concentration of component 2 being observed after a second already This demonstrates the quality and the rapidity

of the mixture.

  It goes without saying that it is possible, without departing from the scope of the invention, to make various modifications to the process and the mixing plant of two liquids.

described and represented.

Claims (18)

  A process for mixing two liquids, in particular for neutralizing waste water, by adding one of these liquids to the other to obtain an initial mixture, characterized in that a certain amount is withdrawn or diverts ( F 4) of this initial mixture (F 3) and is reintroduced after having subjected a certain offset or phase shift.   Process according to Claim 1, characterized in that the initial mixture (F 3) is constantly prepared and is withdrawn and reintroduced constantly thereafter.   phase shift, a certain amount (F 4).   3 -Procédé according to one-claims 1 and 2, characterized   in that the shift or phase shift is carried out, either by delaying the reintroduction of the sampled quantity (F 4), or by reintroducing it upstream, or by delaying   reintroduction of the sampled quantity and reintroduction upstream.   Process according to any one of the claims   in that the quantity (F 4) is reintroduced with a lower flow rate. which had been taken.   Process according to Claim 4, characterized in that the reduction of the flow velocity is 50%.   Process according to any one of the claims   previous arrangements, characterized in that   annular circuit the quantity (F 4) which had been taken.   Process according to any one of the claims   characterized in that, after the main mixing is carried out, a complementary mixture is carried out by withdrawing or diverting again a certain quantity of this mixture (F 5) and reintroducing it after having undergo a phase shift.   8 Installation for the implementation of the process   according to any one of the preceding claims,   characterized in that it comprises an annular mixer (3) composed of a substantially circular system of pipes to which are connected, at a distance from each other, a supply line (11) and a pipe exhaust (12).   9 Installation according to claim 8, characterized   in that the supply (11) and   (12) each have a smaller section than that of the annular pipe (13).   Installation according to claim 9, characterized   in that the supply lines (11) and   (12) are opposed and are connected tangentially   to the annular pipe (13).   11 Installation according to any one of the   8 to 10, characterized in that the supply (11) and discharge (12) lines have a section which is in each case between one fifth and one   about half that of the annular pipe (13).   12 Installation according to any one of the   8 to 11, characterized in that it comprises a number of annular pipe systems arranged   one above the other and combined by means of linkages.   13 Installation according to any of the   Claims 8 to 12, characterized in that a mixer   preliminary arrangement, arranged upstream of the annular mixer (3) comprises a pressure line (8) for one of the liquids and an injection line (9), connected to this   pressure pipe, for the second liquid.   14 Apparatus according to claim 13, characterized   characterized in that the pressure line (8) is connected to a tank (1), in particular a waste water tank, via a pump (2), upstream or downstream of which is disposed the connection of the injection line   (9) of the second liquid, especially a neutralizing agent.   Installation according to one of the claims   13 and 14, characterized in that the pump (2) is a centrifugal pump.   16 Installation according to any one of the   13 to 15, characterized in that a metering device, which is advantageously a metering valve (5), is mounted in the injection line (9).   Installation according to any one of claims 13 to 16, characterized in that it comprises a control and adjustment unit comprising a device (6) for measuring the value of p H and a computer (10) which   connects this device (6) to the metering device (5).   18 Installation according to any of the   Claims 8 to 17, characterized in that it comprises   a further reaction vessel (7) arranged downstream annular mixer (3).   19 Apparatus according to claim 18, characterized   characterized in that the further reaction vessel (7) is a further mixer having an annular pipeline system to which are connected, at a distance from each other, a feed line and a evacuation pipe.