AU615257B2

AU615257B2 - Equipment and process for dissolving gas in liquids

Info

Publication number: AU615257B2
Application number: AU29778/89A
Authority: AU
Inventors: Udo Schmitz
Original assignee: LAir Liquide GmbH; Air Liquide SA
Current assignee: Air Liquide Deutschland GmbH
Priority date: 1988-02-08
Filing date: 1989-02-08
Publication date: 1991-09-26
Anticipated expiration: 2009-02-08
Also published as: BR8900535A; DK50689A; DE3804179C2; JPH01293125A; EP0328444A3; AU2977889A; DK50689D0; PT89646A; EP0328444A2; DE3804179A1

Description

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AUSTRALIA

Patents Act 615257 ?0 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority *Related Art: APPLICANT'S REFERENCE: 3091 Name(s) of Applicant(s): a L'Air Liquide GMBH Address(es) of Applicant(s); Konrad-adenauer-Platz 11, 4000 Dusseldorf 1, Allemagne, FEDERAL REPUBLIC OF GERMANY.

Address for Service is: PHILLIPS ORMONDE FIT.~'1--RICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Complete Specification for the invention entitled: EQUIPMENT AND PROCESS FOR DISSOLVING GAS IN LIQUIDS Our Ref 122334 POF Code: 1290/96584 The folloving statement is a full desiription of this invention, including the best method of performing it known to applicant(s): 6003q/1

I

-3- 09.02.1988 Fl/Br 47317 L'AIR LIQUIDE GMBH Konrad-Adenauer-Platz 11 j Equipment and process for dissolving gas in liquids The present invention relates to equipment and to a process for dissolving gas in liquids.

The state of the art has disclosed various types i, 10 of equipment and processes for dissolving gas in liquids, :00000in particular for the neutralization of alkaline liquids 4 o by me'ans of carbon dioxide. Such units essentially o ~ooconsist, of a delivery pump, a CO 2 mixing system, a reac- 0 tion zone or a corresponding reaction vessel and a pH measuring point. Control is effected as a function of the rCO 2 rate. From German Patent Specification 2,638,428, a process for neutralizing alkaline effluent by admixture 0~ of a neutralizing gas is known, wherein the effluent and a gas are fed separately to a nozzic! of special design.

Moreover, German Patent Specification 2,627,880 rela~tes to a process for atomizing liquids by means of gases or for dividing gases into small bubbles by means of a liquid', the two phases being mixed with one another.

00 However, all the known processes for dissolving gases in liquids have disadvantages. Thus, these processes requiire expensive and large units and hence also high investment costs. A further point is that considerable expense on control is necessary, since high-value expensive control instruments must be used. There is also a risk of the gas not being completely dissolved, so that a disproportionately large part of the gas escapes.

Likewise, the processes are unsuitable f or elevated temperatures. Moreover, the known units can be used only f or batch operation and not continuously. Finally, theV units, must be tailored to the specific application, so that standardization is impossible. The neutralization units according to the state of the art have the L0 1.' ~1 p.

j I ft, ft.

ft.

additional disadvantage that sharp alkalinity peaks cannot be neutralized. As a consequence, the pH value in the outflow fluctuates widely. At low pH values, the CO 2 conversion is poor, with the consequence of operation at reduced load due to escape of CO 2 gas.

It was therefore an object of the present invention to provide equipment and a process for dissolving gas in liquids, which equipment overcomes at least some of the problems of the prior art.

According to the present invention there is provided equipment for dissolving gas in a liquid, said equipment comprising: an inflow line connectable to a source of liquid for receiving liquid from the source; .1 5. a delivery pump having a suction side connected to the inflow line; a reaction zone connected to an outlet from the pump; a gas feed line communicating with the reaction zone and connectable to a source of gas to be dissolved in the ~0 liquid; an outflow connected to the reaction zone for the discharge of liquid from the reaction zone; the inflow line, pump, reaction zone and outflow forming a throughf low line for the flow of liquid from the source for discharge from the outflow, the equipment further comprising: a measuring probe f itted in said throughf low line between said reaction zone and outflow so as to lbe operable to measure a required parameter of the liquid flow in said throughf low line which parameter is variable with dissolution in the liquid of gas supplied to the reaction zone through the gas feed line; a recycle line :for the recycling of liquid from a first location in the throughflow line which is downstream of the probe, to a second location in the throughf low line which is upstream of the suction side of the pump; and control means in the throughflow line which is S downstream of the first location and is operable in response to said parameter to open and close; A t 4.

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-4the recycle line being free of any element controlli.g the rate of recycled flow and defining a closed circuit with portion of the throughflow line between said first and second locations in which closed circuit a portion of liquid flow in said throughflow line is continuously recycled, said control means being operable in response to said probe to open for discharge of liquid from the outflow when said parameter attains a predetermined set value.

The present invention also provides a process for dissolving gas in a liquid in equipment according to the present invention, wherein said inflow line is connected to a source of the liquid for flow of the liquid along the throughflow line for discharge from said outflow and said gas feed line is connected to a source of gas to supply o" gas to the reaction zone for dissolution in the liquid, and wherein: *o a part of the liquid is caused to be recycled continuously in said closed circuit via the recycle line; Sb the parameter of the liquid is measured by the measuring probe; t'le control means is opened or closed in dependence on the parameter and a predetermined set value for the o. parameter; and a ratio of recycled flow to total flow through the 0. throughflow line is established to enable discharge from t. the outflow of liquid for which said parameter has S" attained said predetermined set value.

The measuring probe is preferably an instrument, by means of which the pH, p0 2 pCO 2 and rH value can be I determined. The reaction zone is one of the reactors usually according to the state of the art. For example, the nozzle shown in German Patent Specification 2,638,428 can be used. A buffer vessel with a device for controlling the liquid level and with an inflow can be %A 19X provided upstream of the feed line, Any type of control (w elements can be used in the outflow. However, motorized f control elements are particularly preferred.

-4ai/ t 5 jc a ccntinuously recycled v-ia a recycle line-te the liqui flow, a control variable is detected by means of a measuring e which is located between the reaction zone and the recycle lin da control element in the outflow is opened or closed as a fun -iaof the control variable and of a pred&termined--e~t-value--- For example, the pH, pOz, pCOz and/or rH values can be determined by means of the measuring probe. The gases used are especially carbon dioxide, oxygen and hydrogen.

The process according to the invention is partio* o cularly applicable to the neutralization of liquids by o means of carbon dioxide. The unit is very particularly o suitable for the neutralization of strongly alkaline 15 liquids. The pH value of the liquids fed in can be above o0 0 12. A particularly preferred range is a pH value between 0 12 and 14. The gas used for the neutralization is preferably carbon dioxide. As a result of the process according to the invention, it is possible to dispense with expeno 20 sive reaction zones in a neutralization. Consequently, space-intensive and cost-intensive post-reaction zones are no longer necessary. In fact, by means of the recycle 0 mechanism, the liquid can be circulated, and carbon dioxide can be added to it, until neutralization has taken place. The pH value is determined continuously by a measuring probe. When a certain pH value is reached, a valve in the outflow is opened by a control device, so that the neutralized liquid leaves the unit. The pH value of the liquid flowing out is between 6.5 and 9.0, preferably 8.

The process according to the invention and the equipment according to the invention substantially differ from the existing state of the art, in particular by the recycle of a part stream to the place of reaction and by the control depending on the flow rate. This is a novel process concept which avoids all the existing disadvantages of the state of the art. The result is a simple and ,rr- inexpensive alternative to the existiig state of the art.

/AL \The process can be universally employed wherever 1S ^v~y (-'viU -6gases of low solubility, such as H12 and 02, are to be dissolved in a liquid almost up to the saturation limit.

A Moreover, the process is suitable for accomplishing chemical liquid/gas reactions at an optimum with regard to m~aterials, engineering and economics. Finally, the process also allows gases to be stripped out of contaminated liquids.

Above all in the case of neutralization, the process according to the invention has considerable advantages over the existing state of the art. By means of the process, it is possible that in fact only neutralized effluent is discharged, in accordance with the a cond.!,tions imposed by the authorities. The neutralized water flowing out and the recycle water rate are automaticalll and dynamically adjusted in accordance with the 0 extent of neutralization at the time. Furthermore, ef fluents having a pH value at any high level can be neutralized. This means that even vnny high alkalinity values, which the existing state of the art was unable to 0 20 eliminate satisfactorily, are amenable to neutralization 0 0. 0 by means of the process according to the invention.

Moreover, the unit according to the invention can be used 0 ~a for both continuous operation and batch operation. The gas rate/effluent rate ratio is always adjusted to a constant value. The consequence is that the reaction system always runs at the optimum operating point with the maximum efficiency. Especially when the process according to the invention is used, the nozzle according to German Patent Specification 2,638,428 can reach a hitherto unknown efficiency. The recycle also has the advantage that it is possible to neutralize even at elevated temperatures, at which neutralization has hitherto involved difficulties. In this case, the neutralization does not require a special reaction vessel.

In the table which follows, the advantages of the process according to the invention are illustrated by I comparison with the state jf the art, which oparates without recycle: 7 Comparison between a process for neutralizing a liquid and the process according to the invention Criteria State of the art Process according to the invention process principle linear circulation complete neutrality not ensured ensured safety against not ensured ensured impermissible outflow 0 o 0 0 °4 effluent/feed 0o fluctuations 0 o rate sensitive insensitive 000 0 o 0i o u concentration sensitive insensitive rate and con- 0 '00 centration sensitive insensitive 0 0

CO

2 feed pH-dependent constant 0 0 o 0 outflow pH fluctuating constant o effect of effluent large small *o 0 temperature effective loop open closed pH-regulated pH-controlled

CO

2 conversion fluctuating optimum i gas/water ratio not optimizable optimizable mass transfer varying mass transfer varying optimum ITa 8 ble continued

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Criteria State of the art Process according to the invention suitability for poor good gases of low solubility suitability for poor good stripping precise control not possible readily possible o o, o o o 00 0 00 0 00 The present invention is explained in more detail below with reference to the figures.

In Figure 1, the basic principle of the equipment according to the invention is shown. In Figure 2, a particularly preferred embodiment is illustrated, which is preferentially suitable for the neutralization of strongly alkaline liquids by means of carbon dioxide.

In Figure 1, the liquid is fed to the unit via the inflow 1. Tho liquid is fed via the pump 2 to the reaction zone 3. The gas which is to be dissolved in the liquid is also fed to this reaction zone via a line 4.

The liquid/gas mixture is continuously monitored by the measuring probe 5. Depending on the gas fed or on the reaction, this can be a pH probe, P 0 2 probe, pCO 2 probe or rH probe. As a function of the values measured, the valve 8, which is actuated via the control device 9, in the outflow opens or closes. Depending on the position of the valve 8, a part stream of the reaction solution is recycled via the line 7 and re-introduced via the pump 2 into the reaction zone 3, where gas is added again via the line 4. The rate leaving the unit via the outflow 6 is the difference between feed and part stream. At the same time, the corresponding liquid rate again enters the unit via the inflow 1. A recycled part stream/outflow rate ratio is established automatically in accordance with the predetermined set value. The result of this is that liquid is discharged via the outflow 6 only in accordance with the predetermined set value. By a

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-9suitable choice of the recycle ratio, liquids can be enriched with gas up to almost their saturation limit.

In Figure 2, alkaline effluent 17 is first fed to a collecting tank 16. As soon as an upper level point has been reached, the pump 2 is put into operation via the level control 15, the switching point 10, the controller 11 and the motor 12. The pump delivers the effluent via the reaction zone 3 to the pH measuring point 5. As long as pH values above the set value, which preferably is in the region of pH 6.5 9, are indicated, the control valve 8 driven by the motor 13 remains closed. The carbon dioxide feed valve 14 is opened, so that the gas can flow a into the reaction zone via the lines 15 and 4. At the i °same time, the effluent is fed back to the reaction zone 3 via the recycle line 7. When the effluent then reaches S0 the set desired value at the measuring point 5, the control valve 8 opens and a part of the effluent passes into the outflow. At the same time, an equal part of untreated effluent passes into the inflow 1 and, mixed with the recycle stream 7, enters the reaction zone 3. In the latter, carbon dioxide gas 4 is once more added to the mixture. If the value now measured at the pH measuring point 5 deviates from the set value the controller 11, the control element 8 consistently corrects S 25 the outflow rate, and hence the inflow rate and the °recycle rate, so that only effluent which meets the measured set value can be discharged.

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Claims

1. Equipment for dissolving gas in a liquid, said equipment comprising: an inflow line connectable to a source of liquid for receiving liquid from the source; a delivery pump having a suction side connected to the inflow line; a reaction zone connected to an outlet from the pump; a gas feed line communicating with the reaction zone and connectable to a source of gas to be dissolved in the liquid; an outflow connected to the reaction zone for the discharge of liquid from the reaction zone; the inflow line, pump, reaction zone and outflow forming a throughflow line for the flow of liquid from the source S for discharge from the outflow, the equipment further comprising: a measuring probe fitted in said throughflow line between said reaction zone and outflow so as to be operable to measure a required parameter of the liquid flow in said throughflow line which parameter is variable with dissolution in the liquid of gas supplied to the reaction zone through the gas feed line; a recycle line for the recycling of liquid from a first location in the throughflow line which is downstream of the probe, to a second location in the throughflow line which is upstream of the suction side of the pump; and control means in the throughflow line which is downstream of the first location and is operable in response to said parameter to open and close; the recycle line being free of any element controlling the rate of recycled flow and defining a closed circuit with portion of the throughflow line between said first and second locations in which closed circuit a portion of liquid flow in said throughflow line is continuously recycled, said control means being operable in response to said probe to open for discharge of liqUid from thn J outflow when said parameter attains a predetermined set 2 Svalue.

2. Equipment according to claim 1, wherein the measuring probe is instrument means for determining at least one of pH, pO 2 pC0 2 and rH values.

3. Equipment according to claim 1 or claim 2, wherein a buffer vessel with a device for controlling the liquid level and with an inflow is located upstream of the feed line.

4. Equipment according to any one of claims 1 to 3, wherein the control means is a motorized control element.

5. A process for dissolving gas in a liquid in equipment according to claim 1, wherein said inflow line is connected to a source of the liquid for flow of the liquid along the throughflow line for discharge from said outflow and said gas feed line is connected to a source of i gas to supply gas to the reaction zone for dissolution in the liquid, and wherein: a part of the liquid is caused to be recycled continuously in said closed circuit via the recycle line; the parameter of the liquid is measured by the measuring probe; the control means is opened or closed in dependence O Io I on the parameter and a predetermined set value for the parameter; and a ratio of recycled flow to total flow through the throughflow line is established to enable discharge from the outflow of liquid for which said parameter haq attained said predetermined set value.

6. A process according to claim 5, where. 'he pi, po 2 ,0 pCO 2 and/or rH values are determined by means of the measuring probe,

7. A process according to claim S or claim 6, Wherein the recycle rate is controlled by the control means,

8. A proce.3s according tO any one of claims 5 to 7, wherein C02' 02 or H 2 is used as the gas.

9. A process according to any one of claims 5 to 8, wherein for neutralizing a liquid, Co 2 is fed and, at a pH value of between 6.5 and 90, the control means is y. At opened in order to allow outflow of neutralized liquid.

A process according to claim 9, wherein the p1 Ve ue -4 0 -11- zJB is 8.

11. A process according to claim 9 or claim 10, wherein alkaline liquids having a pH value between 10 and 14 are neutralized.

Equipment according to claim 1, substantially as herein described with reference to the accompanying drawings.

13. A process according to claim 5, substantially as herein described with reference to the accompanying drawings. DATED: 12 July, 1991 PHILIPS ORMONDE FITZPATRICK Attorneys For: L'AIR LTQLUDE GmbH A f ktW<A -4 *~r 1484Z -12-