GB2039762A - Apparatus for the gasification of liquids - Google Patents

Abstract

A hollow annular member (10) has a central liquid flow passageway (14) comprising a lower convergent portion (17), a throat (18) and an upper divergent portion (19). The throat has a circumferential row of apertures (20) communicating with said hollow (11) for emission of gas as bubbles into liquid induced thereby to flow up through said passageway. The divergent portion (19) has a further row (21, 22) of much smaller apertures to emit smaller diameter bubbles to supplement the gas transfer rate into solution. <IMAGE>

Description

SPECIFICATION Apparatus for the gasification of liquids This invention relates to apparatus for the treatment of liquid media by gasification. One application of such apparatus is to the gasification of liquid media which contain organic matter degradable by the action of gases theron, for example the aeration or oxygenation of sewage or other waste water.

British Patent No. 1,482,191 discloses a device for the gasification of liquids which comprises a hollow ring member having a gas inlet and an outer surface which bounds a central liquid passageway. A portion of the surface facing the passageway is apertured so that in operation the gas passes from the hollow into liquid in the passageway. The cross-section of the liquid passageway progressively increases away from the apertured area.

In operation that device is immersed in a liquid preferably such that the liquid passageway has its longitudinal axis substantially vertical. The gas forms bubbles on passing through the apertures into the liquid in the passagway, the bubbles rising through the liquid to induce a flow of liquid upwardly through the passageway. The induced liquid flow passing the apertures exerts a shearing effect on the gas bubbles as they leave the ring member thereby producing smaller gas bubbles than in prior art devices and in consequence increasing the overall gas/liquid interface area for a given volume of gas, and thus increasing the rate of gas-to-liquid transfer.

Such devices have been found to be highly effective in practical use, particularly for aeration of waste water containing aerobically degradable organic matter, for example sewage. Such devices achieve a high rate of gas transfer into solution with low energy requirements and are also highly effective insetting up and maintaining a strong circulation pattern in the body of liquid being treated. This latter is of importance when the liquid medium includes a substantial proportion of suspended solids prone to settle out in a potentially anaerobic mass in any region of the medium not subject to a good circulation current.

It has been found that the efficiency of gas transfer into the liquid phase is influenced by the number, size and positioning of the apertures in the surface of the device facing the liquid passageway.

According to the present invention there is provided a device for the gasification of liquids which comprises a hollow annular member having a gas inlet into said hollow and an outer surface which bounds a central liquid flow passageway extending between a lower inlet and an upper outlet, the passageway comprising a lower convergent portion, an intermediate throat portion, and an upper divergent portion, said convergent portion having no apertures therein communicating with said hollow, said throat portion having a row of first apertures extending around a generally horizontal circumference thereof, and said divergent portion having a row of second apertures extending around a generally horizontal circumference thereof, said second apertures being no more than half the diameter of said first apertures.

Said first apertures are preferably substantially similar to one another and are substantially regularly spaced. Likewise the second apertures are preferably substantially similar to one another and are substantially regularly spaced.

In one form there is provided a single row of first apertures and one or two vertically spaced rows of second apertures. it is possible to provide two or more vertically spaced rows of first apertures but this is at present not thought necessary. Experimental work has shown that in use the bubbles emitted from the first apertures rise almost precisely vertically in straight lines, and thus the individual apertures in the first row can be as close to one another as structural and fabrication considerations permit without any significant chance of the effective surface area of bubbles being reduced by coalescence of adjacent bubbled. For similar reasons it is not thought necessary or desirable to provide more than about two rows of second apertures.However, where more than one row of either the first or second apertures is provided, the apertures in each upper row should desirably be circumferentially offset from those in the row below.

The second apertures are preferably much smaller in -diameter than the first apertures, for example one-quarter the diameter or less. The gas flow rate therethrough is proportional to the aperture cross-sectional area and thus the mass flow rate through the second apertures would be one-tenth or less of the mass flow rate through the first apertures, the precise figure also being dependent on the vertical spacing between the rows of apertures which influences the effective pressure drop across the aperture from the pressurized hollow into the moving liquid flow.

The number of the much smaller second apertures may however be substantially larger than the number of first apertures.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1 and 2 are vertical cross-sections through two gasification devices according to the invention.

Referring to Figure 1 there is shown a gasification device comprising an annular member 10 conveniently moulded of plastics material. The member has a hollow 11 which, when the device is ready for installation, is partially filled with concrete or other dense material 12 to enable the device to remain in liquid. A gas inlet 13 communicates with the hollow and in use a gas supply hose is coupled thereto. The outer surface of the device bounds a central liquid flow passageway 14 extending between a lower inlet 15 and an upper outlet 16. In normal use the axis cf the passageway 14 is vertical and for convenience the device is described in that sense.

The passageway comprises a lower convergent portion 17, an intermediate throat portion 18, and an upper divergent portion #19. The throat portion 18 is itself preferably slightly convergent divergent, symmetrically about its central horizontal plane.

The convergent portion has no apertures therein communicating with the hollow, and it will be seen that the interior of the device adjacent portion 17 is normally largely filled with concrete 12. The throat portion 18 is substantially 15 cm.

in diameter and is provided with a single row of forty-four identical first apertures 20 of substantially 4mm. diameter. The divergent portion 19 has two vertically adjacent circumferential rows of fifty identical, regularly spaced, second apertures 21, 22 of substantially 1 mm. in diameter. In use the overall gass flow rate out from the hollow into the liquid to be gasified is thus only increased by a few percent by the addition of the second apertures 21, 22 to the first aperture 20, whereas the overall gas transfer rate to the liquid phase is increased by a usefully larger percentage in view of the fact that all the additional bubbles are necessarily of small diameter and thus of increased specific surface area.The presence of the second relatively much smaller apertures 21, 22 does not detract from the strong circulation pattern set up by the emmission of gas from the relatively large first apertures 20 in the central plane of the throat portion 18.

Fig. 2 is a vertical cross-section through a second embodiment of gasification device according to the invention, in which similar features are identified with the same reference numerals as used in Fig. 1. The Figure 2 device is provided with three integral legs 30 so that it can stand on the base of a liquid treatment vessel as disclosed in our copending British Patent Application No. 48512/77.

It will be appreciated that variations may be made in the shape of the illustrated devices and in the number and disposition of rows and apertures within the scope of the invention. For example in another form there may be a single row of first apertures of 6mm. diameter and a single row of second apertures of 3mm. diameter.

Claims (9)

1. A device for the gasification of liquids which comprises a hollow annular member having a gas inlet into said hollow and an outer surface which bounds a central liquid flow passageway extending between a lower inlet and an upper outlet, the passageway comprising a lower convergent portion, an intermediate throat portion, and an upper divergent portion, said convergent portion having no apertures therein communicating with said hollow, said throat portion having a row of first apertures extending around a generally horizontal circumference thereof, and said divergent portion having a row of second apertures extending around a generally horizontal circumference thereof, said second apertures being no more than half the diameter of said first apertures.

2. A device as claimed in claim 1 wherein said first apertures are substantailly similar to one another and are substantially regularly spaced.

3. A device as claimed in claim 1 or claim 2 wherein said second apertures are substantially similar to one another and are substantially regularly spaced.

4. A device as claimed in any one of claims 1 to 3 wherein there is a single row only of said first apertures.

5. A device as claimed in any one of claims 1 to 4 wherein there is a single row only of said second apertures.

6. A device as claimed in any one of claims 1 to 4 wherein there are two rows only of said second apertures, the second apertures in one said second row being circumferentially offset from those in the other said second row.

7. A device as claimed in any one of claims 1 to 6 wherein said second apertures are no more than one-quarter the diameter of said first apertures.

8. A device as claimed in any one of claims 1 to 7 wherein there is a substantially larger number of said second apertures than said first apertures.

9. A device for the gasification of liquid substantially as described herein with reference to Figure 1, or Figure 2, of the accompanying drawings.