GB1565571A

GB1565571A - Apparatus for the aeration of liquids

Info

Publication number: GB1565571A
Application number: GB3170/77A
Authority: GB
Original assignee: Sulzer AG; Gebrueder Sulzer AG
Current assignee: Sulzer AG
Priority date: 1976-01-27
Filing date: 1977-01-26
Publication date: 1980-04-23
Also published as: FR2339431A1; FR2339431B1; DE2603798B1; CH607934A5; DE2603798C2; IT1085056B

Abstract

The gas admixture appliance is mainly used for introducing gases into waste waters. A reactor vessel (2), a gas admixture element (3) equipped with static mixing elements (19), and a forced-circulation delivery appliance (8) are combined into a closed gas admixture circuit. A gas infeed appliance (20) is located in the circuit between the reactor vessel (2) and the inlet of the gas admixture element (3). The gas-laden medium enters into the bottom region of the reactor vessel (2). <IMAGE>

Description

(54) APPARATUS FOR THE AERATION OF LIQUIDS (71) We, SULZER BROTHERS LIMITED, a Company organized under the laws of Switzerland, of Winterthur, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a device for aerating a medium consisting of liquid or a mixture of liquid and solid using an aeration element equipped with static mixing elements. The term "aeration" and like terms are used herein in their broad sense to include gases other than air.

In order to bring about reactions between a gas and a liquid or a gas and a solid in a liquid, it is frequently necessary to aerate the liquid or liquid-solid mixture; the gas has to be thoroughly mixed with the treated substances and the gas must be introduced with high efficiency, i.e. with minimum losses of gas which does not contribute to the desired reactions and therefore escapes without being used (a particularly important factor when relatively expensive gases are used). The effective work is done by that portion of the introduced gas in which mass transfer occurs through the phase interface.

Accordingly, it is desirable to obtain a very large continuously renewed phase interface, in addition to a maximum number of collisions between the reactants i.e. thorough mixing). The gas is efficiently used if the thorough mixing is intensive and the gas is introduced in an efficient manner.

As a result of the flotation effect of the rising bubbles of introduced gaa the aeration of the treated mixture is accompanied by degassing, particularly if the mixture contains highly volatile components or if such components are produced during the reactions. This degassing effect, which increases in proportion to the amount of gas introduced, is undesirable in many cases, e.g. in the biological treatment of waste water containing highly volatile solvents. Such treatment is carried out more particularly in the chemical industry. During waste-water processing it is undesirable to operate with large quantities of gas, since otherwise the waste gas, usually air, contains considerable amounts of harmful solvent vapour, which has to be removed in an additional scrubbing stage.

Accordingly it is an object of the invention to produce thorough mixing of the gases with the liquid or liquid-solid mixture and to introduce gas in a very efficient manner, using relatively small quantities of gas.

It has been proposed to use aeration elements equipped with static mixing elements for the aforementioned aeration and mixing operations (see e.g. Water & Sewage Works, Feb. 75, page 34 et seq). Hitherto, the aeration elements have been disposed inside the liquid to be treated, the flow of liquid through the element and the circulation of the liquid being brought about by natural circulation, assisted by gas introduced under pressure at the bottom of the element. This arrangement is not wholly satisfactory.

According to the present invention, apparatus, for aerating a medium comprising liquid or a mixture of liquid and solid, comprises an aeration element including static mixing elements, a reactor vessel in which the gas-charged medium remains for a given time' and a forced-circulation device forming an aeration circuit; and a gas-supply device in the circuit upstream of the aeration element; an inlet to the reactor vessel for the medium charged with gas leaving the aeration element being located adjacent the bottom of the reaction vessel.

In apparatus according to the invention, the gas is used only for its own properties, e.g. as a reactant in a chemical and/or chemical and biological process; it need not also be used for maintaining the flow of medium through the aeration element. Consequently, the apparatus is very efficient.

In addition, the forced-circulation device, e.g. a pump, provides the energy required for circulation and mixing the gas-charged mixture in the reaction vessel, with the re sult that this energy also is not taken from the gas flow. This also ensures particularly intensive mixing of the contents of the vessel. Also, the aeration element can be small and therefore requires relatively low investment.

If there is a risk that the aeration element will become clogged up by the medium to be aerated, the aeration element is advantageously placed outside the vessel, so that it is more accessible for cleaning.

Preferably, in order to suck foam from the surface of the liquid in the reactor vessel, the apparatus includes a connecting line which leads from the outlet of the aeration element, enters the reactor vessel from above and leads to the inlet to the reactor vessel, an ejector being provided in the connecting line adjacent the normal surface level of liquid in the reactor vessel. The reactor vessel can be constructed as a bubble column, so that it is high relative to its crosssection and generally tubular, and thus the gas remains a relatively long time in the vessel as it rises through the mixture to be treated.

There are various possible methods of cleaning the aeration element. The degree of contamination of the element can be determined by means for measuring the pressure drop therein, without interrupting operation.

In one method of cleaning, which is relatively simple and inexpensive, a closable bypass line is provided round the aeration element, in which case the gas supply and the degree of mixing can be somewhat reduced during the relatively short cleaning time, when the aeration element is out of operation. If even a short change in aeration quality is unacceptable two aeration elements can be provided and connected alternately into the aeration circuit.

If large amounts of medium have to be aerated a number of aeration elements in a forced circuit can be located in a common reaction vessel and operated in parallel.

The invention may be carried into practice in various ways but one form of apparatus embodying the invention will now be described by way of example with reference to the accompanying drawing the single figure of which shows the apparatus diagrammatically.

A medium which is to be treated in the apparatus (i.e. a liquid or a liquid containing solids) by being subjected to a gas/fluid or gas/solid reaction flows through a supply line 1 to a reactor vessel 2 which, in the example, is a bubble column, the ratio of its diameter to its effective height being 1: 8.

The effective height is the distance travelled in the vessel by the gases and treated substances from the point where the aerated mixture flows into the vessel 2 out of an aeration element 3, to the point where it leaves through a discharge line 4. The size of the vessel relative to the flow speed of the medium is determined by the residence time required for the aforementioned reactions.

In order to prevent direct short-circuit flow, the place where line 7 is connected to the vessel 2 is shielded by a wall 5 from the end of a line 6 which connects the element 3 to the vessel 2 and through which the aerated medium flows into the vessel 2; in order to form a forced aeration circuit, the line 7 leads to the bottom end of the element 3 and contains a pump 8 acting as a forced-circulation delivery device. Line 7 also has a gas or air-supply device 20 which in the simplest case can be T-member. A gas line 9 supplying gas for introduction into the medium leads from a compressedgas source (not shown), e.g. a blower or gas cylinder, and terminates in the device 20. Of course, a different gas supply device 20, e.g.

an ejecetor, can be used. Line 9 can also contain a gas measuring device.

Line 7 also has a shut-off means 10 downstream of a bypass 11 around the element 3, the bypass also having a shut-off means 12. Line 7 also has a terminal 13 to which a pressure-gauge for measuring and monitoring the pressure drop in element 3 can be connected, a second terminal 14 being provided in line 6.

The aeration circuit is completed by the line 6, which extends from the outlet end of the element 3 via a shut-off means 15 -into the vessel 2.

The line 6, which ends near the bottom of the vessel 2 in a distributor 16, can contain an ejector 17 at the surface of the liquid in the vessel 2, the level of which is determined by the discharge line 4. Foam accumulating on the liquid in vessel 2 is then sucked by the ejector into the flow of medium in the line 6.

The distributor 16, which can be mounted on a bearing member 18 in the bottom of the vessel 2, can be constructed like a rotating lawn sprinkler. A distributor of this contruction causes the gas bubbles to travel in a spiral track as they rise through the vessel, so that they remain therein for a longer time. Alternatively, of course, the line 6 can simply be an open tube ending adjacent, anr facing the bottom of the vessel 2, so that the stream coming out of it rebounds on the bottom and is distributed through the cross-section of the vessel 2.

The aeration element 3 is made up of six static mixing elements 19 between which there are rings 22 acting as spacers and bearing elements and being connected by bars 21.

The pump 8 sucks some of the contents of the vessel 2 through the line 7 and conveys it through the gas feed device 20 to the aera tion element 3. In the element 3, which is highly efficient, the introduced gas is reduced into fine bubbles and intimately mixed with the stream of material sucked though the pump 8, so that the gas is very uniformly distributed in the mixture to be treated. The gas-charged mixture is conveyed through the line 6 into the distributor 16 via the ejector 17 which sucks away any foam. When the mixture leaves the distributor 16, its distribution and energy on entering the vessel 2 are such that the contents of the vessel in the neighbourhood of the distributor 16 is made turbulent and thoroughly mixed over the entire cross-section, the necessary energy being supplied by the pump 8. This prevents dead spaces in the vessel 2 and increases the amount of circulation in vessel 2 and the probability of collisions between reactive particles of gas and liquid or solid.

As previously mentioned, the pressure drop is measured. This is in order to monitor the degree of contamination of element 3, so that if a given pressure drop is exceeded, the element 3 can be cleaned after closing the shut-off members 10 and 15 so as to remove the element 3 from the circuit, which is maintained during the short cleaning time by the bypass line 11, which is opened by opening the member 12.

The flow in forced circulation through the element 3 is relatively fast, e.g. at more than 105 m/h. Consequently a transit through the aeration circuit takes a few seconds, whereas the average residence time in the vessel 2 is, for example, several hours.

In a modified apparatus, not shown, a second aeration element is arranged in parallel with the element 3 shut-off elements being provided so that the aeration elements may be connected into the aeration circuit alternately.

WHAT WE CLAIM IS:- 1. Apparatus, for aerating a medium comprising liquid or a mixture of liquid and solid, comprising: an aeration element including static mixing elements, a reactor vessel in which the gas-charged medium remains for a given time, and a forced-circulation device forming an aeration circuit; and a gas-supply device in the circuit upstream of the aeration element; an inlet to the reactor vessel for the medium charged with gas leaving the aeration element being located adjacent the bottom of the reaction vessel.

2. Apparatus as claimed in Claim 1 in which the aeration element is located outside the vessel.

3. Apparatus as claimed in Claim 1 or Claim 2 which includes a connecting line which leads from an outlet of the aeration element, enters the reactor vessel from above and leads to the said inlet.

4. Apparatus as claimed in Claim 3 which includes an ejector in the connecting line at the normal surface level of liquid in the reactor vessel.

5. Apparatus as claimed in any of the preceding Claims which includes means for measuring the pressure drop in the aeration element.

6. Apparatus as claimed in any of the preceding Claims which includes a closable bypass line around the aeration element.

7. Apparatus as claimed in any of the preceding Claims which includes a second aeration element arranged so that the two aeration elements may be connected alternately into the aeration circuit 8. Apparatus for aerating a medium consisting of liquid or a mixture of liquid and solid, the apparatus being substantially as described herein with reference to the ac companying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tion element 3. In the element 3, which is highly efficient, the introduced gas is reduced into fine bubbles and intimately mixed with the stream of material sucked though the pump 8, so that the gas is very uniformly distributed in the mixture to be treated. The gas-charged mixture is conveyed through the line 6 into the distributor 16 via the ejector 17 which sucks away any foam. When the mixture leaves the distributor 16, its distribution and energy on entering the vessel 2 are such that the contents of the vessel in the neighbourhood of the distributor 16 is made turbulent and thoroughly mixed over the entire cross-section, the necessary energy being supplied by the pump 8. This prevents dead spaces in the vessel 2 and increases the amount of circulation in vessel 2 and the probability of collisions between reactive particles of gas and liquid or solid. As previously mentioned, the pressure drop is measured. This is in order to monitor the degree of contamination of element 3, so that if a given pressure drop is exceeded, the element 3 can be cleaned after closing the shut-off members 10 and 15 so as to remove the element 3 from the circuit, which is maintained during the short cleaning time by the bypass line 11, which is opened by opening the member 12. The flow in forced circulation through the element 3 is relatively fast, e.g. at more than 105 m/h. Consequently a transit through the aeration circuit takes a few seconds, whereas the average residence time in the vessel 2 is, for example, several hours. In a modified apparatus, not shown, a second aeration element is arranged in parallel with the element 3 shut-off elements being provided so that the aeration elements may be connected into the aeration circuit alternately. WHAT WE CLAIM IS:-

1. Apparatus, for aerating a medium comprising liquid or a mixture of liquid and solid, comprising: an aeration element including static mixing elements, a reactor vessel in which the gas-charged medium remains for a given time, and a forced-circulation device forming an aeration circuit; and a gas-supply device in the circuit upstream of the aeration element; an inlet to the reactor vessel for the medium charged with gas leaving the aeration element being located adjacent the bottom of the reaction vessel.

7. Apparatus as claimed in any of the preceding Claims which includes a second aeration element arranged so that the two aeration elements may be connected alternately into the aeration circuit

8. Apparatus for aerating a medium consisting of liquid or a mixture of liquid and solid, the apparatus being substantially as described herein with reference to the ac companying drawing.