Gas / liquid mixer using dilution and division

Abstract

Device for mixing a gas in a liquid, implementing a screw structure in a pipe where the liquid is able to circulate, as well as means for injecting the gas at one or more points in the pipe, the screw being able to be of any type, such as an Archimedean screw or other screw with a central shaft and blades organized on this shaft, characterized in that: - two different action zones are implemented in the screw: in a first part of the screw, a mixing by dilution where the gas is gradually distributed in the liquid, followed by a second part of the screw carrying out a mixing by division; - in that the first zone seen by the liquid comprises a portion of screw within which the shaft is a pipe pierced with orifices, the liquid to be treated passing into the space internal to the pipe surrounding the shaft, while the gas is distributed inside the shaft and flows via the orifices into the liquid;- the second zone seen by the liquid located downstream of the first zone and being perfectly adjacent to it and in fluid communication is constituted by a portion of screw whose shaft is devoid of orifices.;

Description

[0001] The present invention relates to devices for mixing a gas in a liquid.

[0002] We know that such dissolution processes, enriching a liquid into a gas, are used in many industrial fields, particularly the aeration of wastewater, the preparation of carbonated drinks, or the dissolution of gases in chemical products.

[0003] We can cite here: Dissolving Chlorine in Water: Chlorine (Cl2) dissolves in water to form hypochlorous acid (HOCI) and hydrochloric acid (HCl), which is used in drinking water treatment and in swimming pools to disinfect water. Ammonia in Water: Ammonia (NH3) dissolves in water to form ammonium hydroxide (NH4OH), which is important in fertilizer production and in some chemical reactions. Sulfur Dioxide in Water: Sulfur dioxide (SO2) dissolves in water to form sulfurous acid (H2SO3), which can contribute to acid rain and other environmental problems.

[0004] And the question of injecting neutral gases for deoxygenation in chemical liquid products can be useful for several reasons: Stability: Removing dissolved oxygen reduces the risk of oxidation of sensitive components in the liquid, which can extend the product's shelf life. Reactivity: Some chemical processes require the absence of oxygen to proceed efficiently, so deoxygenation can promote these reactions by removing oxygen that could interfere. Corrosion prevention: In some cases, the presence of oxygen can promote corrosion of containers or equipment in contact with the chemical liquid. Deoxygenation can therefore help reduce this risk. Final product quality: Removing oxygen can also reduce the formation of unwanted by-products that could result from unwanted reactions with oxygen.

[0005] The operation and performance observed will depend on the design of the mixer used, which may use nozzles, agitators, or other mechanisms to efficiently mix the gas and liquid.

[0006] An example is the static mixer, which is a device for continuously mixing fluids that can adopt many geometries, including a tubular shape composed of a set of stationary elements placed end to end in a tube. Each element has a particular rigid geometric structure that divides the flow and recombines it. In general, contact between fluids takes place thanks to the radial movement generated in the mixers. The interfacial area generated depends directly on the energy dissipated in the form of pressure drop. The efficiency of the mixing operation in a static mixer depends greatly on the flow regime.

[0007] Different mixer geometries have thus been created to adapt in particular to laminar and turbulent flows.

[0008] Some of these mixers have more or less significant elongational flows. This is why they are particularly used for mixing polymers with high viscosity ratios as well as for the production of emulsions.

[0009] Other static mixers are based primarily on shear.

[0010] The use of static mixers is very well known, and is the subject of a very abundant literature, the disadvantages of these mixers are thus well known, among which we can cite: limitations regarding the achievable mixtures: in fact, static mixers are not suitable for all types of mixtures, particularly when very viscous or difficult-to-mix elements are involved. They can then present difficulties or even impossibilities in achieving perfect homogeneity. their size and bulk: static mixers can be bulky, which can be a disadvantage if the manufacturer has space constraints. They can also be difficult to integrate into certain global industrial process configurations (integration made difficult by the generated deltaP which reduces the flow rate or even requires more energy to maintain the flow rate). their cleaning: intrinsically, by their very design, very dense and "tortured", cleaning static mixers can be difficult and tedious due to their complex design with numerous fins and channels.This can lead to downtime in production. Initial cost: High-quality static mixers can be expensive to purchase, which can represent a high initial investment for some companies. Susceptibility to clogging: As discussed above, static mixers are susceptible to clogging by solid particles, which can affect their mixing efficiency over time. A need for constant pressure or flow rate: Some static mixers require a constant flow rate or pressure to operate properly, which can be restrictive in some applications and requires either the addition of a pump or the oversizing of the existing pump.

[0011] As will be seen in more detail below, the present invention seeks to propose a new mixing configuration characterized in that two different action zones are implemented in a screw: in a first part, mixing by dilution where the gas is gradually distributed in the liquid, followed by a second part carrying out mixing by division.

[0012] And as we will see, this mixer ensures high gas enrichment efficiency with minimal hydraulic loss, and it is capable of solubilizing many gases such as carbon dioxide (CO 2 ), oxygen (O 2 ) and ozone (O 3 ) in water, including at the saturation limit.

[0013] This technology is very effective in process waters where gas solubility is limited by operating conditions. Limiting operating conditions include: The distance available to have the necessary contact time for the gas to dissolve: we know that depending on the case, tens of meters are sometimes necessary, which represents a very penalizing space. Pressure: certain systems operate at high pressures (from the atmosphere to, for example, 200 bars): this system, entirely made of stainless steel, makes it possible to meet pressure resistance constraints. Temperature. The aggressiveness of certain liquids (soda, acid, etc.)

[0014] The mixer according to the invention can be integrated into the existing pipes on the site, or even configured in a bypass loop using a pump (for example in a recirculation loop of a basin to be oxygenated or pH regulated).

[0015] The high efficiency of this new system is based on the principle of progressive dilution of the gas in the liquid, resulting from a large gas-liquid interface. The gas-liquid transfer is then optimized thanks to a splitting function that generates little pressure loss. The system is also resistant to abrasion.

[0016] Let us explain the above better using the [ Figure 1 ] attached which provides a partial schematic view of an example of implementation in the sequence of these two zones (with a zoomed view in the right part of the figure and showing the direction of advancement of the fluid in the structure): We therefore visualize a first zone (first zone seen by the fluid to be treated), first zone which includes a portion of Archimedes screw within which the shaft is a pipe pierced with orifices, the liquid to be treated passes into the space internal to the pipe surrounding the shaft, while the gas passes inside the shaft and pours via the orifices into the liquid surrounding the shaft. As will be explained below, we can call this zone "dilution zone"). This first zone is followed by a second zone, zone which can be called "mixing zone" or "division zone", as constituted by the only sequence of blades of a screw (without gas inlet). Dilution in the first zone, and we can even say progressive dilution since at each turn of the water in the Archimedes screw the water encounters an orifice through which the gas escapes, the gas is therefore not injected at a single point but at a succession of points.The distribution of gas in the water is therefore progressive, to keep the gas bubbles separated. Division in the second zone: the idea is to divide the "liquid / gas" flow in two at each turn, at each turn it divides and rejoins to be divided in two again, allowing easy mixing.

[0017] And we can consider the example illustrated in [ Figure 2 ] annexed, of mixing zone (of “division”) counting in the example represented 15 turns, therefore 15 division operations, a given volume of water will be divided thus 15 times.

[0018] The number of orifices and the diameter of the pipe will be chosen according to the dissolution requirement. It is obvious to those skilled in the gas field that the more spaced holes there are and the smaller the hole diameter, the more small bubbles will be formed. The size of the bubbles at creation (entry into the liquid) will be at least identical or even partly already dissolved at the exit of the tube. It is therefore necessary to take care to produce small bubbles, and favor a high speed, preferably a turbulent regime, to obtain a good, forced mixing of the gas with the liquid (gas speed of typically 1 to 2 m / s, preferably around 2 m / s).

[0019] The invention then relates to a device for mixing a gas in a liquid, implementing a screw structure in a pipe where the liquid is able to circulate, as well as means for injecting the gas at one or more points in the pipe, the screw being able to be of any type, such as an Archimedes screw or a screw with a central shaft and blades organized on this shaft, characterized in that: two different action zones are implemented in the screw: in a first part a mixture by dilution where the gas is gradually distributed in the liquid, followed by a second part carrying out a mixture by division; the first zone seen by the liquid comprises a portion of screw within which the shaft is a pipe pierced with orifices, the liquid to be treated passing into the space internal to the pipe surrounding the shaft, while the gas is distributed inside the shaft and pours via the orifices into the liquid; the second zone located downstream of the first zone and being perfectly adjacent to it and in fluid communication is constituted by a portion of screw whose shaft is devoid of orifices.

[0020] As mentioned, the screw used can be of any type: Augers: Used for conveying bulk materials, such as grains, powders, or granules. Archimedean screws: Mainly used for pumping and moving liquids, such as water or viscous liquids. Metering screws: Designed to precisely meter bulk materials or liquids, often used in industrial processes. Pressure screws: Used to apply controlled pressure to the conveyed materials to compact or expel them.

Claims

1. Device for mixing a gas in a liquid, using a screw structure in a pipe where the liquid is able to circulate, as well as means for injecting the gas at one or more points in the pipe, the screw being able to be of any type, such as an Archimedes screw or other screw with a central shaft and blades organized on this shaft, characterized in that : - two different action zones are implemented in the screw: in a first part of the screw a mixture by dilution where the gas is gradually distributed in the liquid, followed by a second part of the screw carrying out a mixture by division; - in thatthe first zone seen by the liquid comprises a portion of screw within which the shaft is a pipe pierced with orifices, the liquid to be treated passing into the space internal to the pipe surrounding the shaft, while the gas is distributed inside the shaft and flows via the orifices into the liquid; - the second zone seen by the liquid located downstream of the first zone and being perfectly adjacent to it and in fluid communication is constituted by a portion of screw whose shaft is devoid of orifices.

2. Mixing device according to claim 1, characterized in that the device is suitable for integration into an existing pipeline of a global installation.

3. Mixing device according to claim 1, characterized in that the device is capable of being integrated into a bypass loop of a global installation using a pump, for example in a recirculation loop of a basin to be oxygenated or pH regulated.

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