EP4122587A1

EP4122587A1 - Improved mixing system for the introduction of chemical substances in a fluid to be treated

Info

Publication number: EP4122587A1
Application number: EP21182715.9A
Authority: EP
Inventors: René Pich; Julien Bonnier
Original assignee: SPCM SA
Current assignee: SNF Group
Priority date: 2021-06-30
Filing date: 2021-06-30
Publication date: 2023-01-25

Abstract

The present invention concerns an improved mixing system (10) for the introduction of chemical substances in a fluid to be treated, comprising: a container (11) comprising an external wall (12), an internal wall (13), a bottom (14) and a cover (15); at least two concentric mixing chambers in communication with each other, a first central chamber (16) defined within the internal wall (13) and a second chamber (17) defined outside the internal wall (13); an inlet duct (19) for a fluid to be treated, configured for the introduction of the fluid in the cone (14); an outlet duct (20) for the treated fluid, configured for the outflow of the fluid from the second chamber (17) to the outside of the container (11); the inlet duct (19), the first chamber (16), the second chamber (17) and the outlet duct (20) defining a labyrinthine mixing path (30); stirring blades (18) positioned inside the first chamber (16); at least one injection passage (22), characterized in that the bottom has the form of a cone (14) extending from the external wall (12), said cone (14) being extended by a tube (23) whose the end forms the inlet duct (19) for the fluid to be treated , the cone (14) has an internal angle alpha comprised between 10° and 60°, and the at least one injection passage (22) is positioned on the cone (14), or on the tube extending from the cone (14),

Description

The invention concerns an improved mixing system designed to introduce chemical substances in a fluid to be treated.
Nowadays clean water is considered a valuable resource which must be preserved and used only in the cases where its consumption is absolutely necessary. For example, the paper industry has always used huge quantities of fresh water, meaning new water, in order to be able to obtain high quality products.
However, in the last few years environmental regulations and a greater environmental awareness at a global level have been increasingly leading people to reduce water consumption. Today, for example, paper sludge is becoming increasingly important and is increasingly used for producing other paper, in the tile and cement industry, in environmental restoration projects, for covering dumps and in building mixes.
Some steps of a process for the treatment of the waste water of a paper mill include the use of a polyelectrolyte, for example a cationic flocculant powder, or even, for example, a cationic polyacrylamide, suited to be applied in the clariflocculation of water containing organic substances, in sludge thickening treatments, in sludge dehydration processes and also in other processes carried out in paper mills, such as froth flotation.
Other industries such as water treatment or enhanced oil and gas recovery use water-soluble polymers to flocculate wastewater or to thicken water-based composition.
During these process steps it is necessary to maximize the yield of the polymer in order to improve the polymer performances such as the flocculation or quality of the dry residue in the case of sludge or to improve froth flotation in the case of a froth flotation step.
In order to be activated, these polymers need premixing with water at a preestablished concentration. Nowadays, said premixing step is carried out in static mixing tanks, in which the polymer is introduced after being taken from a small storage container; said polymers are normally diluted in solutions between 0.2% and 1%, therefore they are very demanding in terms of water usage.
In the static mixing tank mixing is obtained from the simple turbulence of water. Successively, a booster pump introduces the water with the polymer into a pipe leading to a tank or a channel for the treatment of waste sludge.
Thus, as already mentioned, these systems using a flocculant, even if widely used and appreciated, require the use of considerable quantities of water and of specific mixing equipment, together with the corresponding ducts for preparation for use and for introduction in a sludge treatment line.
Another limitation of the sludge treatment systems currently known lies in that the polyelectrolytes are culture media for bacteria, therefore a polymer that remains in a storage tank for long is very likely to foster the proliferation of bacteria.
The patent document US5314076 describes a system for mixing two fluid phases, more specifically for mixing a treatment fluid with a fluid to be treated; said system comprises two concentric chambers that communicate with each other at least with their ends, the central chamber being provided with two turbines whose rotation axis is equal to the axis of symmetry of the installation.
In this technical solution known in the art, the fluid to be treated flows in from the top, flows out from the bottom and the turbines are interposed between the inlet and the outlet.
The patent document US2012/0199524 describes a clarifier silo comprising a closed container with an internal mixer surrounded by a diffuser with a cylindrical tube. The diffuser and the mixer define three internal chambers that are superimposed in vertical direction, an upper chamber, a central chamber and a lower chamber, as well as an external annular region. Each of the three internal chambers is in fluid communication with the annular region.
Even in this technical solution known in the art, the fluid to be treated flows in from the top, flows out from the bottom and the turbines are interposed between the inlet and the outlet.
Even in the mixer described in patent document US3392963 , the fluid to be treated flows in from the top, flows out from the bottom and the turbines are interposed between the inlet and the outlet.
The patent documents US2577856 and US3737288 , instead, describe mixing equipment in which the fluid to be treated flows in from the bottom and flows out from the top, and a propeller is interposed between the inlet and the outlet.
The mixers and the equipment described in the above-mentioned patent documents are not able to overcome the drawbacks and the limitations illustrated above.
The patent document EP3626336 describes a mixing system for the introduction of chemical substances in a fluid to be treated comprising two chambers. Despite great improvement of the performances, there is still a demand to enhance these performances.
It is the task of the present invention to provide an improved mixing system for the introduction of chemical substances in a fluid to be treated, which can overcome the above-mentioned drawbacks and limitations of the known art.
More specifically, it is an object of the invention to provide an improved mixing system that makes it possible to drastically reduce the use of water for the preparation of a polyelectrolyte suited to be introduced in the flow of waste fluid to be treated.
It is another object of the invention to provide an improved mixing system that favours the reduction of energy consumption in wastewater treatment processes.
It is a further object of the invention to provide an improved mixing system that improves water retention from sludge, thus increasing the quantity of dry product obtainable from sludge.
It is another object of the invention to provide an improved mixing system that can reduce the waiting times for the beginning of the action of the polymer in solution on the fluid to be treated, consequently improving the effectiveness of the polymer itself.
It is another object of the invention to provide an improved mixing system that is compact and can be easily set up also in already existing wastewater purification or treatment plants or sludge drying plants.
It is another object of the invention to provide an improved mixing system that limits the proliferation of bacteria on the same polyelectrolytes.
The task and the objects illustrated above are fulfilled by a mixing system for the introduction of chemical substances in a fluid to be treated according to claim 1.
Further characteristics of the mixing system according to claim 1 are described in the dependent claims.
The mixing system of the invention is characterized by a combination of three different characteristics compared to the prior art.
The first characteristic is that the bottom of said system has the form of a cone extending from the external wall, said cone being extended by a tube, and said cone having an internal angle alpha comprised between 10° and 60°, preferably between 15 and 50°, more preferably between 20 and 40°. In other words, the bottom of the system has the form of a funnel, respectively a cone continued by a tube.
The second characteristic is that end of the tube forms the inlet duct for a fluid to be treated.
The third characteristic is that the injection passage of the chemical additives, especially the polymer is positioned on wall of the tube extending from the cone or on the wall of the cone.
These new characteristics allow a significant improvement of the performances of the mixing device of the invention compared to the mixing device of the prior art.
The internal angle alpha is the angle between the wall of the cone and a plane, said plane being orthogonal to the revolution axis of the cone.
The task and the objects illustrated above, together with the advantages described below, are highlighted in the description of two embodiments of the invention, which are provided by way of non-limiting example with reference to the attached drawings, wherein:

Figure 1 shows a schematic side sectional view of an embodiment of a mixing system according to the invention.

With reference to Figure 1, in the context of a first embodiment, a mixing system according to the invention is indicated by the numeral 10.
Said mixing system 10 comprises:

a container 11 comprising an external wall 12, an internal wall 13, a bottom 14 and a cover 15,
two concentric mixing chambers, a first central chamber 16 defined within the internal wall 13 and a second chamber 17 defined outside the internal wall 13, the first chamber 16 and the second chamber 17 being in communication with each other,
an inlet duct 19 for a fluid to be treated, configured to introduce said fluid from the outside into the bottom 14,
an outlet duct 20 for the treated fluid, said outlet duct 20 being configured to allow the outflow of said fluid from said second chamber 17 to the outside of said container 11,
said inlet duct 19, first chamber 16, second chamber 17 and outlet duct 20 being configured to define a labyrinthine mixing path 30,
stirring blades 18 positioned inside the first chamber 16, operated by drive means through a rotation shaft 21,
at least one injection passage 22 for the introduction of a chemical additive,

the bottom 14 has the form of a cone 14 extending from the external wall 12, said cone being extended by a tube 23 whose the end forms the inlet duct 19 for the fluid to be treated,
the cone 14 has an internal angle alpha comprised between 10° and 60°, preferably between 15 and 50°, more preferably between 20 and 40°,
the at least one injection passage 22 is positioned on the wall of the cone 14, or on the wall of the tube 23 prolonging the cone 14.

In the present example of embodiment, the second chamber 17 is to be understood as ringshaped.
The labyrinthine mixing path 30 is indicated by arrows that schematically show the possible paths of the fluid being treated between the inlet duct 19 and the outlet duct 20.
The drive means comprise, for example and not exclusively, a motor 35 configured to set the rotation shaft 21 rotating.
Said rotation shaft 21 carries the stirring blades 18.
The rotation axis of the rotation shaft 21 is parallel to the direction of extension of the internal wall 13.
More specifically, in the present non-limiting example of embodiment of the invention, the external wall 12 has a cylindrical shape.
In the present non-limiting example of embodiment of the invention, also the internal wall 13 has a cylindrical shape.
More specifically, the second chamber 17 surrounds the first chamber 16.
More specifically, the second chamber 17 is concentric and coaxial with the first chamber 16.
In said example of embodiment, the inlet duct 19 is positioned at the end of the tube prolonging the cone 14.
In said example of embodiment, the stirring blades 18 comprise a first group of blades 18a positioned at the lower end of the rotation shaft 21.
More specifically, said first group of blades 18a is positioned below the outlet duct 20, and potentially below a second group of blades 18b, when two groups of blades are used.
Said first group of blades 18a is to be understood as capable of being arranged also in another position along the rotation shaft 21.
It is to be understood that the stirring blades 18 can be constituted by a single group of blades 18a.
In said example of embodiment, the stirring blades 18 comprise also a second group of blades 18b positioned in a central area of the rotation shaft 21.
More specifically, said second group of blades 18b is positioned below the outlet duct 20, and potentially above the first group of blades 18a.
The first chamber 16 and the second chamber 17 are in communication with each other through at least one passage opening 37 defined at the level of one end of the internal wall 13.
More specifically, but not exclusively, in said example of embodiment a first passage opening 37 is defined by a conical recirculation space between a lower end 13a of the internal wall 13 and the bottom cone 14.
The at least one injection passage 22 for the introduction of a chemical additive is placed on the wall of cone 14 or, preferably on the wall of the tube 23.
According to the invention, the bottom part of cone 14A is extended by a vertical and cylindrical tube 23, also called the pre-entry of the cone. The at least one injection passage 22 is preferably placed on said tube 23, preferably perpendicularly to the horizontal axe of said tube 23.
In a preferred embodiment, the mixing system comprises at least two feet 40 to allow the mixing system to stand in equilibrium. The mixing system can be supported by any other technical means.
According to its first embodiment illustrated in Figure 1, the mixing system 10 operates in such a way that the fluid to be treated, for example sludge, flows into the bottom of the cone 14 through the inlet duct 19 and, thanks to the action of the stirring blades 18 and downstreams in the first chamber 16, flows upwards, towards the passage opening 37, in which it is deviated upwards into the second chamber 17; while flowing upwards along the second chamber 17 the treated fluid meets the outlet duct 20 and is conveyed into it.
A chemical additive, for example cationic or anionic polyacrylamide, is injected in the fluid to be treated during its passage through the cone 14 or the pre-entry of the cone 23.
It has practically been shown that the mixing system 10 according to the invention fulfils its task and achieves the set objects.
In fact, the invention provides a mixing system thanks to which the fluid to be treated and the chemical additive are mixed with no need for the chemical additive to be prepared, meaning diluted, in advance in costly and bulky water tanks, thus drastically reducing water consumption.
The chemical additive, for example a cationic or an anionic flocculant polymer, is activated when it comes in direct contact with a fluid to be treated.
Furthermore, the invention provides a mixing system which, thanks to the stirring effect produced by the stirring blades, thanks to the turbulent effect produced in the conical part, and thanks to the introduction of the chemical additive at the bottom of the mixing system, improves the effectiveness and the efficiency of the chemical additive; for example, in the case of organic sludge, in which the sludge has an apolar surface membrane, the strong stirring action favours the breakage of said membrane and makes anionic sites available; the introduction of and the mixing with a cationic polyelectrolyte make the anionic sites react with the cationic polyelectrolyte releasing water molecules, which favours a greater separation of the solid fraction of the fluid being treated from the liquid fraction.
Therefore, the invention provides an improved mixing system that makes it possible to drastically reduce the use of water when preparing a polyelectrolyte intended to be introduced in a flow of waste fluid to be treated.
In addition to the above, the invention provides an improved mixing system that favours the reduction of energy consumption in waste water treatment processes, since it is no more necessary to manage a mixing and storage tank and the efficiency in terms of separation of the dry fraction from the liquid fraction is improved compared to the known treatment systems.
In fact, the invention provides an improved mixing system that improves water retention from sludge, thus increasing the quantity of dry product obtainable.
Moreover, the invention provides an improved mixing system that is capable of reducing waiting times before the beginning of the action of the polymer in solution on the fluid to be treated, consequently improving the effectiveness of the polymer itself; this has been obtained by introducing the chemical additive directly in the fluid to be treated and subjecting both of them to a mixing action produced by the stirring blades.
Furthermore, the invention provides an improved compact mixing system that can be easily set up also in existing wastewater purification or treatment systems or sludge drying systems.
Furthermore, the invention provides an improved mixing system that limits the proliferation of bacteria on the same polyelectrolytes, thanks to the direct introduction of the same polyelectrolytes directly in the fluid to be treated, without providing for a storage period before use.
The invention conceived in this way can be subjected to several modifications and variants, all falling within the inventive concept disclosed herein; furthermore, all the details can be replaced by other technically equivalent elements.
In practice, any components and any materials can be used, provided that they are compatible with the intended use, and any shape and size can be selected, according to the needs and the state of the art.
Where the characteristics and techniques mentioned in any of the claims are followed by reference signs, it must be understood that these reference signs are used only for the purpose of making the claims easier to understand, and consequently these reference signs do not have any limiting effect on the interpretation of each element identified by way of example by the same reference signs.

Claims

Mixing system (10) for the introduction of chemical substances in a fluid to be treated, comprising:
- a container (11) comprising an external wall (12), an internal wall (13), a bottom (14) and a cover (15),

- at least two concentric mixing chambers, a first central chamber (16) defined within said internal wall (13) and a second chamber (17) defined outside said internal wall (13), said first chamber (16) and second chamber (17) being in communication with each other,

- an inlet duct (19) for a fluid to be treated, configured for the introduction of said fluid from the outside into the bottom 14,

- an outlet duct (20) for said treated fluid, configured for the outflow of said fluid from said second chamber (17) to the outside of said container (11), said inlet duct (19), first chamber (16), second chamber (17) and outlet duct (20) being configured to define a labyrinthine mixing path (30),

- stirring blades (18) positioned inside said first chamber (16), operated by drive means through a rotation shaft (21),

- at least one injection passage (22) for the introduction of a chemical additive

- said stirring blades (18) comprising at least one first group of blades (18a),
characterized in that
- the bottom has the form of a cone (14) extending from the external wall (12), said cone (14) being extended by a tube (23) whose the end forms the inlet duct (19) for the fluid to be treated ,

- the cone (14) has an internal angle alpha comprised between 10° and 60°, and

- the at least one injection passage (22) is positioned on the cone (14), or on the tube extending from the cone (14).
Mixing system according to claim 1, characterized in that angle alpha is comprised between 15° and 50°.
Mixing system according to claim 1 or 2, characterized in that said drive means comprise a motor (35) configured to set said rotation shaft (21) rotating, wherein said rotation shaft (21) carries said stirring blades (18).
Mixing system according to one or more of the preceding claims, characterized in that said first chamber (16) and second chamber (17) are in communication with each other through at least one passage opening (37) defined by a conical recirculation space between a lower end (13a) of the internal wall (13) and the bottom cone (14).
Mixing system according to one or more of the preceding claims, characterized in that said at least one injection passage (22) is directly connected to said bottom cone (14).
Mixing system according to one or more of the preceding claims, characterized in that the at least one injection passage (22) for the introduction of a chemical additive is placed below the entry of the cone (14a).
Mixing system according to one or more of the preceding claims, characterized in that, the bottom part of cone (14) is extended by a vertical and cylindrical part (23).
Mixing system according to one or more of the preceding claims, characterized in that the at least one injection passage (22) is placed on said part (23), preferably perpendicularly to the horizontal axe of said part (23).
Mixing system according to one or more of the preceding claims, characterized in that the mixing system comprises at least two feet (40) to allow the mixing system to stand in equilibrium.