Process and device for dispersing gas in a liquid

Abstract

Process and device for dispersing gas in a downward flow of liquid, according to which the liquid is distributed along at least one jet (A) directed downwards, preferably along a plurality of jets; gas is distributed radially (F) towards the liquid jet or jets in order to be entrained by the liquid; and the liquid-gas mixture is channeled into a downflow vertical tube (P).

Claims

1. A device for injecting gas into a liquid comprising an inlet pipe (1) for the liquid to be treated, characterized in that the device comprises: in an upper part, an injection head (H) connected to the inlet pipe and comprising a liquid-jet mixing chamber (3), and in a lower part, a vertical tube (P) with two-phase flow, the injection head (H) comprises a compartment (B) with, in the lower part, a horizontal distribution plate (2) for the liquid perforated with orifices (2a), and an annular chamber (5) provided under the plate (2) over its periphery, and comprising at least one opening for distribution of the gas along a centripetal radial direction (F), the mixing chamber (3), located under the plate, being in the form of a convergent section for coupling to the vertical tube (P), wherein said device further comprising a radial inlet (4a) of the gas into the annular chamber (5), from a gas pipe (4) that extends to and beyond the radial inlet (4a) as to form a venting system (6) configured to vent to the atmosphere or inert gas, the venting system (6) comprising a vent valve disposed in the gas pipe beyond the radial inlet and a gas inlet valve disposed in the gas pipe that extends to the radial inlet.

2. The device as claimed in claim 1, wherein the diameter of the orifices of the plate is sufficient to prevent clogging due to particles contained in the liquid.

3. The device as claimed in claim 1, wherein the cross section of the vertical tube is at least equal to the total area of the orifices (2a) of the plate, and at most equal to 2 times this total area.

4. The device as claimed in claim 1, wherein the length of the vertical tube (P) is between 1 and 25 meters.

5. The device as claimed in claim 1, wherein the convergent section of the mixing chamber (3) is frustoconical, the angle of inclination of the generatrices of the frustum of the frustoconical section relative to a vertical axis being between 15 and 45.

6. The device of claim 1, wherein the vent valve is configured to introduce outside air or inert gas into the mixing chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention consists, apart from the arrangements set out above, of a certain number of other arrangements that will be mentioned more explicitly hereinbelow with respect to an exemplary embodiment described with reference to the appended drawing, but which is in no way limiting. In this drawing:

(2) FIG. 1 is a schematic perspective top view of the dispersion device according to the invention,

(3) FIG. 2 is a schematic perspective view along another viewing angle and with cutaway portions of the device from FIG. 1, and

(4) FIG. 3 is a perspective view of the underside of the device FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) With reference to the drawing, it can be seen that the dispersion device D comprises two assemblies: an injection head H and a jet dispersion tube P, forming a nozzle. The injection head H is the structure that connects the liquid and gas inlets, mixes these fluids and directs the resulting mixture into the down tube P.

(6) The injection head H is connected to the liquid inlet pipe 1 and comprises a compartment B with, in the lower part, a device for distributing the liquid, preferably a horizontal distribution plate 2 for the liquid, perforated with orifices 2a. The liquid flows vertically underneath the plate, following jets depicted by arrows A in FIG. 2.

(7) An inlet line 4 for the gas to be injected is connected, via a radial box 4a, to an annular chamber 5 located under the plate 2, of which it surrounds the lower periphery. A wall E inwardly radially limiting the chamber 5 comprises nozzles or openings O for distribution of the gas following centripetal radial directions represented by arrows F in FIG. 2.

(8) A mixing chamber 3 is located under the plate 2. The mixing chamber 3 is preferably of tulip or convergent frustoconical shape, but could be of cylindrical or parallelepipedal shape.

(9) In the case where the chamber 3 is in the form of a downward frustoconical convergent section, the inclination of the generatrices of the convergent section relative to the geometric axis is preferably between 15 and 45. The chamber 3 provides the coupling to the vertical down tube P, which is preferably coaxial and cylindrical.

(10) An atmosphere-venting system 6 for the start-up phase is provided at the end of the pipe 4 beyond the coupling with the annular chamber 5. A vent valve 7 is provided in the system 6, and also a gas inlet valve 8.

(11) The jet dispersion tube P is described hydraulically as a straight length of vertical pipe.

(12) The operation of the device is the following.

(13) The start-up sequence of the device, integrated in a surrounding contactor (not represented) makes it possible to better understand the general design of the device in its entirety. When the device or system is shut down, the water level inside the submerged tube P is equal to the water level outside. Above this level, the mixing chamber 3 and the tube P are filled with gas. The liquid supply is started according to a flow rate equal to a third of the desired operating flow rate. The liquid fills the supply line 1 of the system. The distribution plate 2 produces low-velocity liquid jets. The atmosphere-venting system 6 makes it possible to purge the gas initially contained in the injection head and the pockets of gas entrained at the start-up upstream in the top of the tube P. When the purge flow rate becomes zero, the vent valve 7 of the vent pipe of the atmosphere-venting system 6 gradually switches to gas supply via the pipe 4 and the system can begin production. The liquid flow rate is brought to its operating value. In steady state, the mixture of gas and water formed in the chamber 3 circulates toward the bottom of the tube.

(14) The sequence for shutting down the dispersion device is structured as follows: The first step consists in evacuating the gas contained in the device, by replacing it with outside air or an inert gas. For this, the vent valve 7 of the system 6 is gradually opened to the outside air or an inert gas, after which the gas inlet valve 8 of the system 6 is closed. The device continues to operate, all of the gas present is replaced. After a short period corresponding to the replacement with 5 times the total volume of the device, the device may be shut down under completely safe conditions, by gradually reducing the flow rate of water.

(15) Although the foregoing descriptions that relate to the start-up and shutdown of the device mention several times the gradual variation of the operating conditions in terms of gas and liquid flow rate, it should be noted that the device is capable of reacting correctly to sudden changes in conditions, resulting for example from a power failure or any other event capable of resulting in an unscheduled shutdown.

(16) This device makes it possible to provide a gaseous engagement that is eminently variable between 0.01 and 2 (if expressed as a ratio of the gas and liquid volume flow rates), at the best cost under the effect of the necessary pressure reduction, to produce a homogeneous dispersion of gas in the liquid suitable for providing the transfer of the required amounts of mass.

(17) Simultaneously, it offers the following advantages: the operating safety and stability; the speed of executing the steps of starting up and setting a regime; the potential operating time (corrosion, maintenance, . . . ).

(18) This device resolves the drawbacks of the systems described in the prior art and is furthermore capable of replacing all or some of the gas injection and diffusion systems of bubble column type contactors, of the gas injection and agitation systems of agitated contactors. The contactors that result therefrom are much more efficient both from a technical and economic point of view.