WO1994004266A1 - Separation of aqueous and organic components - Google Patents

Separation of aqueous and organic components Download PDF

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Publication number
WO1994004266A1
WO1994004266A1 PCT/GB1993/001756 GB9301756W WO9404266A1 WO 1994004266 A1 WO1994004266 A1 WO 1994004266A1 GB 9301756 W GB9301756 W GB 9301756W WO 9404266 A1 WO9404266 A1 WO 9404266A1
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WO
WIPO (PCT)
Prior art keywords
aqueous
stteam
chamber
gas
removal
Prior art date
Application number
PCT/GB1993/001756
Other languages
French (fr)
Inventor
Colin Ramshaw
Colin Howarth
Raymond Fowler
Simon Davies
Original Assignee
University Of Newcastle Upon Tyne
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University Of Newcastle Upon Tyne filed Critical University Of Newcastle Upon Tyne
Priority to AU49668/93A priority Critical patent/AU4966893A/en
Publication of WO1994004266A1 publication Critical patent/WO1994004266A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/18—Stationary reactors having moving elements inside
    • B01J19/1806—Stationary reactors having moving elements inside resulting in a turbulent flow of the reactants, such as in centrifugal-type reactors, or having a high Reynolds-number
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/38—Treatment of water, waste water, or sewage by centrifugal separation
    • C02F1/385—Treatment of water, waste water, or sewage by centrifugal separation by centrifuging suspensions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J2219/00049—Controlling or regulating processes
    • B01J2219/00164—Controlling or regulating processes controlling the flow

Definitions

  • the invention relates to an apparatus and method for use in the removal of organic components from an aqueous stream and particularly the removal of dispersed and dissolved organic components.
  • the invention is most useful in producing an aqueous stream which is substantially free from organic components or in which the organic content is significantly reduced.
  • the invention may be worked when the organic components are present as a dispersed liquid phase or when both dispersed and dissolved organic components are present.
  • processes such as steam distillation or steam cracking produce steam/hydrocarbon mixtures which on condensation give rise to ⁇ an aqueous stream containing both dispersed and dissolved hydrocarbon, or organic, components.
  • aqueous dilute acid streams are produced which contain suspended organic droplets, which droplets need to be removed prior to electrowinning or other forms of metal recovery.
  • Water treatment and also gas treatment, for example, the treating of natural gas, are two major industrial applications of the invention.
  • Froth floatation in which gas bubbles are used to capture dispersed phase components at their surface and aid coalescence and/or rapid disengagement.
  • Centrifugal field separators Principle examples of these are the centrifuge and hydrocyclone in both of which the centrifugal force produced by rotation of the fluids aids the more rapid disengagement of dispersed phase material.
  • the separator consists of a rotating element containing packing that is a reticulated material which provides both a large surface area per unit volume and a very high voidage. Typically the specific surface area is around 2,500 m 2 /m 3 and the voidage is greater than 90% .
  • the rotating element is provided in a stationery outer casing. Gas or vapour enters the casing, via vapour feed, and is forced through the rotating packing. There it comes into intimate contact with liquid, entering via liquid feed, which is forced outwardly through the packing by the centrifugal force.
  • the gas or vapour leaves from the centre of the apparatus, while the liquid impinges on the innermost side of the casing walls and is drained from the casing via the liquid outlet.
  • the centrifugal force intensifies mass transfer of the dissolved organic component into the gas.
  • an apparatus for removing dispersed and dissolved organic components from an aqueous stream comprising: a hollow Removal chamber in which there is provided a porous medium, the chamber having; an inner aqueous stream inlet and an outer aqueous stream outlet for removal of the cleansed aqueous stream; and also an outer gas inlet and an inner gas outlet for removal of gaseous stream carrying the dissolved organic component; wherein said chamber is adapted so that said aqueous stream and said gas within said chamber are rotated and thus subjected to a centrifugal force whereby said stream is forced outwardly towards the sides of the chamber and said gas moves inwardly towards the innermost part of the chamber characterised in that; there is further provided an inner organic film or stream outlet whereby the organic film or stream representing the dispersed organic component can be removed.
  • the present invention differs from all the foregoing prior art in that it uses simultaneously a centrifugal field to enhance separation, a porous medium to aid coalescence, and gas injection to effect a type of floatation which aids both coalescence and rapid transport of the dispersed phase. Further, the gas injection is also effective in stripping volatile components so that both dispersed and dissolved components are reduced.
  • an apparatus for removing dispersed and dissolved organic components from an aqueous stream comprising: a hollow Removal chamber in which there is provided a porous medium, the chamber having; an inner aqueous stream inlet and an outer aqueous stream outlet; and also an outer gas inlet and an inner gas outlet; wherein said chamber is adapted so that said aqueous stream and said gas within said chamber are rotated and thus subjected to a centrifugal force whereby said stream is forced outwardly towards the sides of the chamber and said gas moves inwardly towards the innermost part of the chamber characterised in that; said at least one further such Removal chamber is provided downstream of the first chamber, and said outer aqueous stream outlet is adapted to terminate near to the axis of rotation of said chambers so as to reduce the kinetic energy of said aqueous stream leaving the first chamber and so optimise power consumption of the apparatus.
  • an apparatus for removing dispersed and dissolved organic components from an aqueous stream comprising: a hollow Removal chamber in which there is provided a porous medium, the chamber having; an inner aqueous stream inlet and an outer aqueous stream outlet; and also an outer gas inlet and an inner gas outlet; wherein said chamber is adapted so that said aqueous stream and said gas within said chamber are rotated and thus subjected to a centrifugal force whereby said stream is forced outwardly towards the sides of the chamber and said gas moves inwardly towards the innermost part of the chamber characterised in that; there is provided a control means whereby the relative flow rates of said aqueous stream and said gas can be varied thereby controlling the selective removal of dispersed and/or dissolved organic components.
  • conduit means may be provided for the re- circulation of said stream through said Removal chamber and the ratio of flow of the aqueous stream in the gas may be varied for each cycle through said Removal chamber.
  • a relatively small gas flow may be used in the first stage to aid coalescence and separation of dispersed organic material while an increased gas flow may be used in a subsequent stage to primarily strip out volatile dissolved organic components.
  • gas injection tubes are provided at the site of the gas inlet so as to ensure that bubbles of gas pass through the packing medium. Further, ideally, weirs are provided towards the innermost part of the chamber for the removal of essentially organic froth or fluid.
  • the Removal chamber is provided within a hollow outer casing which is provided with a central aqueous stream outlet whereby aqueous fluid leaving the Removal chamber via the outer aqueous stream outlet travels inwardly towards the central aqueous stream outlet provided in the outer case.
  • the kinetic energy of the aqueous stream is significantly reduced and therefore this arrangement is ideally suited to an apparatus including a plurality of said Removal chambers arranged in series and the sequential passage of an aqueous sample stream therethrough. Alternatively, this arrangement is also ideally suited to an apparatus where cycling of the aqueous stream repeatedly through the Removal chamber takes place. It will be apparent to those skilled in the art that a lowering of the kinetic energy of the aqueous stream leaving each Removal chamber optimises power consumption of the apparatus.
  • a method for removing dissolved and dispersed organic components from an aqueous stream comprising; arranging for counter flow of an aqueous stream and a gas stream through a porous medium and; controlling the relative rates of flow of said aqueous stteam and said gas stteam so as to selectively conttol the removal of dispersed and dissolved organic components from said aqueous stream.
  • Figure 2 shows a centrifugal apparatus for removing dissolved and dispersed organic components from an aqueous stteam flowing through the apparatus in a direction indicated by arrows A.
  • Arrows B indicate the direction of flow of a gas stream through the apparatus.
  • the apparatus comprises a hollow shaft 1 sealingly divided by partition 2 into aqueous channel 1A and gaseous channel IB. Attached to the outermost side of shaft 1 is a cylindrical drum 3 which is divided into two compartments, an inner compartment comprising Removal chamber 4 and an outer compartment comprising return conduit 5. A dividing wall 6 is provided between the two compartments. Wall 6 is hollow and in fluid connection with hollow shaft IB such that gas flowing through shaft IB flows between dividing wall 6 and into injection tubes 7. From injection tubes 7 gas enters Removal chamber 4 and specifically, enters as relatively small bubbles.
  • Removal chamber 4 is packed with a porous medium 8 which aids both the coupling of fluid rotation and the coalescence of the dispersed organic phase.
  • Weirs 9 are provided towards the innermost part of Removal chamber 4 so as to facilitate removal of organic froth or fluid from chamber 4.
  • Fluid entering Removal chamber 4 passes into such chamber below the surface of the gas/liquid interface.
  • An aqueous stream outlet 10 is provided in drum 3 and outlet 10 is located adjacent shaft 1.
  • Drum 3 is rotated about the central axis of hollow shaft 1 using conventional rotation means.
  • This rotation means has been omitted from Figure 2 for the purpose of clarity.
  • aqueous fluid containing both dispersed and dissolved organic components enter the apparatus via hollow shaft 1A and pass through distribution tubes 11 into Removal chamber 4.
  • the fluid passes through the porous packing medium 8 and droplets of organic components tend to coalesce on the surface of the medium eventually forming an inner organic film or stream. This occurs because the centrifugal acceleration encourages the dispersed organic components to migrate inwardly and so increases the settling velocity.
  • gas passes from hollow shaft IB through hollow divider wall 6 and enters Removal chamber 4 via gas injection tubes 7.
  • Gas enters as bubbles near the periphery of the Removal chamber 4.
  • These bubbles due to their buoyancy in the centrifugal field produced by the rotation of the apparatus move relatively rapidly through the packing medium towards the central axis of rotation of the machine. In doing so they provide additional surface area, forcing the liquid to pass through the bubble cloud and so aid coalescence.
  • the organic components tend to concentrate around the surface of the bubbles and so are rapidly transported, in counter flow to the bulk of the aqueous stteam, towards the centte of the apparatus where they form the said inner organic film or stream such as a continuous organic layer or a froth rich in organic components.
  • the organic layer or froth is allowed to overflow weirs 9 and leave the apparatus as a stteam rich in the organic component of the mixture.
  • the aqueous phase, now cleansed of dispersed components leaves Removal chamber 4 at the periphery of chamber 4 and enters cavity 5 provided in drum 3. In this cavity the aqueous stteam flows towards outlet 10 provided near the innermost part of the drum and so leaves the apparatus.
  • the gas bubbles in the Removal chamber 4 are used to strip out these volatile organic components. This occurs via mass transfer.
  • the stripping can be controlled by controlling the relative flow rate of the aqueous stteam with respect to the gas stteam. A large proportion of the dissolved volatile organic components then leave the apparatus as a vapour at the site of the gas outlet.
  • Flow through the drum outlet 10 is controlled to ensure that all the organic components leave via weirs 9 in the Removal chamber 4.
  • Outlet 10 enables the aqueous stteam to be discharged near to the axis of rotation of drum 3 and so minimises the overall prior requirement for machine rotation.
  • centrifugal acceleration at the weir in the active chamber should be at least 100 M/sec ⁇ at the periphery of the machine it may be as high as 12000
  • gas injection rates may be as low as l/20th the volume rate of the flow of the heavy phase.
  • the stripping gas may be any suitable and available gas, such as nitrogen, inert gas, natural gas or even air when this does not give rise to any explosive or flammability hazard.
  • rotation of the contents of the Removal chamber 4 may be affected by providing a suitably designed baffled rotor. In this instance, chamber 4 will be stationary.
  • a plurality of Removal chambers are provided in series so that an aqueous stteam may be subject to more than one stage of organic removal by directing the outflow from outlet 10 into at least one subsequent Removal chamber.
  • the gas flow in each removal chamber need not be the same.

Abstract

The invention relates to an apparatus and a method for use in the removal of organic components from an aqueous stream and especially the removal of both dispersed and dissolved organic components. The invention uses the counter flow of an aqueous stream and a gaseous stream to effect the removal of organic components from the aqueous stream. Specifically the invention concerns the provision of a porous medium through which the aqueous stream and the gaseous stream flow. The medium is provided to facilitate the coupling of fluid rotation in a centrifugal system and the coalescence of dispersed organic components. The invention also concerns the control of the relative flow of said aqueous stream and said gaseous stream so as to selectively control the removal of dispersed and dissolved organic components. Further, the invention provides for recycling of an aqueous stream through a single apparatus, or alternatively, the sequential transfer of an aqueous stream through a plurality of apparatus in accordance with the invention. At each stage of operation the apparatus may be adjusted so as to selectively remove a given type of organic component.

Description

SEPARATION OF AQUEOUS AND ORGANIC COMPONENTS
The invention relates to an apparatus and method for use in the removal of organic components from an aqueous stream and particularly the removal of dispersed and dissolved organic components. The invention is most useful in producing an aqueous stream which is substantially free from organic components or in which the organic content is significantly reduced.
As mentioned, the invention may be worked when the organic components are present as a dispersed liquid phase or when both dispersed and dissolved organic components are present.
Many industrial processors produce aqueous streams which become contaminated with organic components. For example, in the production of crude oil, the oil itself is often mixed with what is called "produced water". Even after primary separation, the "produced water" is contaminated with dispersed and dissolved organic components and needs to be treated to remove these components before it can be discharged.
Further, in many refinery operations, processes such as steam distillation or steam cracking produce steam/hydrocarbon mixtures which on condensation give rise to^an aqueous stream containing both dispersed and dissolved hydrocarbon, or organic, components.
Similarly, in solvent extraction processes, as for example in the hydrometallurgical recovery of copper or uranium, aqueous dilute acid streams are produced which contain suspended organic droplets, which droplets need to be removed prior to electrowinning or other forms of metal recovery. Water treatment and also gas treatment, for example, the treating of natural gas, are two major industrial applications of the invention.
Hitherto, four principle methods of treating aqueous/organic streams to remove dispersed phase organics only, have been used. These are:
1. Gravity separation in which an aqueous stream is held at very low velocity in an apparatus, such as a settling tank, so allowing natural gravity to separate the organic and aqueous phases.
2. Coalescence and gravity separation, in which the aqueous stream is passed through a porous medium of high surface area, upon which the dispersed phase is gathered. This produces large droplets of dispersed phase component which will then separate more easily.
3. Froth floatation, in which gas bubbles are used to capture dispersed phase components at their surface and aid coalescence and/or rapid disengagement.
4. Centrifugal field separators. Principle examples of these are the centrifuge and hydrocyclone in both of which the centrifugal force produced by rotation of the fluids aids the more rapid disengagement of dispersed phase material.
The main disadvantage of all these prior art methods for removing organic components from an aqueous stream lies in the fact that both dispersed and dissolved components cannot be removed. Typically, such dissolved components are currently removed by either distillation or gas stripping, usually carried out in a packed column.
An example of a prior art apparatus for removing dissolved organic components is shown in Figure 1. The separator consists of a rotating element containing packing that is a reticulated material which provides both a large surface area per unit volume and a very high voidage. Typically the specific surface area is around 2,500 m2/m3 and the voidage is greater than 90% . The rotating element is provided in a stationery outer casing. Gas or vapour enters the casing, via vapour feed, and is forced through the rotating packing. There it comes into intimate contact with liquid, entering via liquid feed, which is forced outwardly through the packing by the centrifugal force. The gas or vapour leaves from the centre of the apparatus, while the liquid impinges on the innermost side of the casing walls and is drained from the casing via the liquid outlet. The centrifugal force intensifies mass transfer of the dissolved organic component into the gas.
This apparatus has been available for over a decade. The need to provide a single apparatus that can remove both types of organic components has existed for longer.
There is therefore a need to provide an apparatus for removing both dispersed and dissolved organic components from an aqueous stream. Further, there is a need to provide a method whereby dissolved and dispersed organic components can be removed from an aqueous stream.
It is therefore an object of the invention to provide such an apparatus and method.
According to a first aspect of the invention there is therefore provided an apparatus for removing dispersed and dissolved organic components from an aqueous stream comprising: a hollow Removal chamber in which there is provided a porous medium, the chamber having; an inner aqueous stream inlet and an outer aqueous stream outlet for removal of the cleansed aqueous stream; and also an outer gas inlet and an inner gas outlet for removal of gaseous stream carrying the dissolved organic component; wherein said chamber is adapted so that said aqueous stream and said gas within said chamber are rotated and thus subjected to a centrifugal force whereby said stream is forced outwardly towards the sides of the chamber and said gas moves inwardly towards the innermost part of the chamber characterised in that; there is further provided an inner organic film or stream outlet whereby the organic film or stream representing the dispersed organic component can be removed. The present invention differs from all the foregoing prior art in that it uses simultaneously a centrifugal field to enhance separation, a porous medium to aid coalescence, and gas injection to effect a type of floatation which aids both coalescence and rapid transport of the dispersed phase. Further, the gas injection is also effective in stripping volatile components so that both dispersed and dissolved components are reduced.
According to a second aspect of the invention there is provided an apparatus for removing dispersed and dissolved organic components from an aqueous stream comprising: a hollow Removal chamber in which there is provided a porous medium, the chamber having; an inner aqueous stream inlet and an outer aqueous stream outlet; and also an outer gas inlet and an inner gas outlet; wherein said chamber is adapted so that said aqueous stream and said gas within said chamber are rotated and thus subjected to a centrifugal force whereby said stream is forced outwardly towards the sides of the chamber and said gas moves inwardly towards the innermost part of the chamber characterised in that; said at least one further such Removal chamber is provided downstream of the first chamber, and said outer aqueous stream outlet is adapted to terminate near to the axis of rotation of said chambers so as to reduce the kinetic energy of said aqueous stream leaving the first chamber and so optimise power consumption of the apparatus.
According to a third aspect of the invention there is provided an apparatus for removing dispersed and dissolved organic components from an aqueous stream comprising: a hollow Removal chamber in which there is provided a porous medium, the chamber having; an inner aqueous stream inlet and an outer aqueous stream outlet; and also an outer gas inlet and an inner gas outlet; wherein said chamber is adapted so that said aqueous stream and said gas within said chamber are rotated and thus subjected to a centrifugal force whereby said stream is forced outwardly towards the sides of the chamber and said gas moves inwardly towards the innermost part of the chamber characterised in that; there is provided a control means whereby the relative flow rates of said aqueous stream and said gas can be varied thereby controlling the selective removal of dispersed and/or dissolved organic components.
In this latter aspect of the invention it may be desirable to subject an aqueous stream to more than one stage of separation and therefore conduit means may be provided for the re- circulation of said stream through said Removal chamber and the ratio of flow of the aqueous stream in the gas may be varied for each cycle through said Removal chamber. In particular, for example, a relatively small gas flow may be used in the first stage to aid coalescence and separation of dispersed organic material while an increased gas flow may be used in a subsequent stage to primarily strip out volatile dissolved organic components.
In preferred embodiments of the invention gas injection tubes are provided at the site of the gas inlet so as to ensure that bubbles of gas pass through the packing medium. Further, ideally, weirs are provided towards the innermost part of the chamber for the removal of essentially organic froth or fluid.
In yet a further preferred embodiment of the invention the Removal chamber is provided within a hollow outer casing which is provided with a central aqueous stream outlet whereby aqueous fluid leaving the Removal chamber via the outer aqueous stream outlet travels inwardly towards the central aqueous stream outlet provided in the outer case. In this embodiment, the kinetic energy of the aqueous stream is significantly reduced and therefore this arrangement is ideally suited to an apparatus including a plurality of said Removal chambers arranged in series and the sequential passage of an aqueous sample stream therethrough. Alternatively, this arrangement is also ideally suited to an apparatus where cycling of the aqueous stream repeatedly through the Removal chamber takes place. It will be apparent to those skilled in the art that a lowering of the kinetic energy of the aqueous stream leaving each Removal chamber optimises power consumption of the apparatus.
According to a yet further aspect of the invention there is provided a method for removing dissolved and dispersed organic components from an aqueous stream comprising; arranging for counter flow of an aqueous stream and a gas stream through a porous medium and; controlling the relative rates of flow of said aqueous stteam and said gas stteam so as to selectively conttol the removal of dispersed and dissolved organic components from said aqueous stream.
An embodiment of the invention will now be described by way of example only with reference to Figure 2 which is a schematic illustration of an apparatus in accordance with the invention.
Figure 2 shows a centrifugal apparatus for removing dissolved and dispersed organic components from an aqueous stteam flowing through the apparatus in a direction indicated by arrows A. Arrows B indicate the direction of flow of a gas stream through the apparatus.
The apparatus comprises a hollow shaft 1 sealingly divided by partition 2 into aqueous channel 1A and gaseous channel IB. Attached to the outermost side of shaft 1 is a cylindrical drum 3 which is divided into two compartments, an inner compartment comprising Removal chamber 4 and an outer compartment comprising return conduit 5. A dividing wall 6 is provided between the two compartments. Wall 6 is hollow and in fluid connection with hollow shaft IB such that gas flowing through shaft IB flows between dividing wall 6 and into injection tubes 7. From injection tubes 7 gas enters Removal chamber 4 and specifically, enters as relatively small bubbles.
Removal chamber 4 is packed with a porous medium 8 which aids both the coupling of fluid rotation and the coalescence of the dispersed organic phase.
Weirs 9 are provided towards the innermost part of Removal chamber 4 so as to facilitate removal of organic froth or fluid from chamber 4.
Fluid enters Removal chamber 4 from hollow shaft 1A via fluid distribution tubes 11. Thus fluid entering Removal chamber 4 passes into such chamber below the surface of the gas/liquid interface. An aqueous stream outlet 10 is provided in drum 3 and outlet 10 is located adjacent shaft 1.
Drum 3 is rotated about the central axis of hollow shaft 1 using conventional rotation means. This rotation means has been omitted from Figure 2 for the purpose of clarity.
In use, aqueous fluid containing both dispersed and dissolved organic components enter the apparatus via hollow shaft 1A and pass through distribution tubes 11 into Removal chamber 4. In chamber 4, the fluid passes through the porous packing medium 8 and droplets of organic components tend to coalesce on the surface of the medium eventually forming an inner organic film or stream. This occurs because the centrifugal acceleration encourages the dispersed organic components to migrate inwardly and so increases the settling velocity.
In contrast, gas passes from hollow shaft IB through hollow divider wall 6 and enters Removal chamber 4 via gas injection tubes 7. Gas enters as bubbles near the periphery of the Removal chamber 4. These bubbles due to their buoyancy in the centrifugal field produced by the rotation of the apparatus move relatively rapidly through the packing medium towards the central axis of rotation of the machine. In doing so they provide additional surface area, forcing the liquid to pass through the bubble cloud and so aid coalescence. In addition, the organic components tend to concentrate around the surface of the bubbles and so are rapidly transported, in counter flow to the bulk of the aqueous stteam, towards the centte of the apparatus where they form the said inner organic film or stream such as a continuous organic layer or a froth rich in organic components. The organic layer or froth is allowed to overflow weirs 9 and leave the apparatus as a stteam rich in the organic component of the mixture.
The aqueous phase, now cleansed of dispersed components leaves Removal chamber 4 at the periphery of chamber 4 and enters cavity 5 provided in drum 3. In this cavity the aqueous stteam flows towards outlet 10 provided near the innermost part of the drum and so leaves the apparatus.
In circumstances where the aqueous stteam contains dissolved volatile organic components which it is desired to remove, the gas bubbles in the Removal chamber 4 are used to strip out these volatile organic components. This occurs via mass transfer. The stripping can be controlled by controlling the relative flow rate of the aqueous stteam with respect to the gas stteam. A large proportion of the dissolved volatile organic components then leave the apparatus as a vapour at the site of the gas outlet.
Flow through the drum outlet 10 is controlled to ensure that all the organic components leave via weirs 9 in the Removal chamber 4. Outlet 10 enables the aqueous stteam to be discharged near to the axis of rotation of drum 3 and so minimises the overall prior requirement for machine rotation.
The centrifugal force at any point is given by w\r where:
w = speed of rotation in radians/sec r = distance from the axis of rotation.
In the practice of this invention the centrifugal acceleration at the weir in the active chamber should be at least 100 M/sec\ at the periphery of the machine it may be as high as 12000
M/sec2.
In cases when the primary interest is in removing dispersed phase material gas injection rates may be as low as l/20th the volume rate of the flow of the heavy phase.
In cases when it is desired in addition to remove dissolved volatile components the gas injection rate will very much depend upon the nature and composition of the components to be stripped. In general however it will be desirable to maintain the stripping factor (S defined below) greater than 1.2, where stripping factor S = m.G/L where m = slope of the equilibrium line g = Molar gas flow rate
L = Molar liquid flow rate.
The stripping gas may be any suitable and available gas, such as nitrogen, inert gas, natural gas or even air when this does not give rise to any explosive or flammability hazard.
In an alternative embodiment of the apparatus rotation of the contents of the Removal chamber 4 may be affected by providing a suitably designed baffled rotor. In this instance, chamber 4 will be stationary.
5 In alternative embodiments of the apparatus a plurality of Removal chambers are provided in series so that an aqueous stteam may be subject to more than one stage of organic removal by directing the outflow from outlet 10 into at least one subsequent Removal chamber. In this instance, the gas flow in each removal chamber need not be the same. In fact, there may be advantages in using a relatively small gas flow in the first stage for dispersed phase removal
- and a higher gas flow in a subsequent stage so as to remove dissolved volatile organic components.
The apparatus of the invention has a number of advantages over the prior art these include the following:
1. Because of the action of the centrifugal field of rotation the phases separate rapidly 5 and the apparatus is more compact, more efficient and less costly than gravity separators or coalescence devices.
2. Because both the porous packing medium and the bubble surfaces act to coalesce small droplets the device is more efficient and compact than other devices such as hydrocy clones or centrifuges which rely on centrifugal action alone.
0 3. Additionally other centrifugal devices rely upon the relatively small density between the light and heavy phase fluids to effect the separation. In the practice of this invention there is a very large density difference between the gas phase bubbles which carry the light phase with them and the heavy phase aqueous stteam. This again results in rapid separation and more compact equipment. 4. The practice of the invention affords the opportunity to strip out dissolved volatile components from the aqueous stteam in addition to separating dispersed phase material.

Claims

1. An apparatus for removing dispersed and dissolved organic components from an aqueous stteam comprising: a hollow Removal chamber in which there is provided a porous medium, the chamber having; an inner aqueous stteam inlet
- and an outer aqueous stteam outlet for removal of the cleansed aqueous stteam; and also an outer gas inlet and an inner gas outlet for removal of a gaseous stteam carrying the dissolved organic component; wherein said chamber is adapted so that said aqueous stream and said gas within said chamber are rotated and thus subjected to a centrifugal force whereby said 0 stteam is forced outwardly towards the sides of the chamber and said gas moves inwardly towards the innermost part of the chamber characterised in that; there is further provided an inner organic film or stteam outlet whereby the organic film or stream carrying the dispersed organic component can be 5 removed.
2. An apparatus for removing dispersed and dissolved organic components from an aqueous stteam according to Claim 1 wherein; said at least one further such Removal chamber is provided downstream of the first chamber and said outer aqueous stteam outlet is adapted to terminate near to the axis of rotation of 0 said chambers so as to reduce the kinetic energy of said aqueous stteam leaving the first chamber and so optimise power consumption of the apparatus.
An apparatus for removing dispersed and dissolved organic components from an aqueous stream according to Claim 1 or 2 wherein; there is further provided a control means for selectively controlling the 5 relative flow rates of said aqueous stream and said gas stteam so as to control the selective removal of dispersed and/or dissolved organic components.
4. An apparatus according to any preceding Claim wherein a plurality of gas injection tubes are provided at the site of the gas inlet so as to ensure that bubbles of gas enter Removal chamber 4.
5. An apparatus according to any preceding Claim wherein said inner organic film or stteam outlet comprises at least one weir for the removal of essentially organic waste.
6. An apparatus according to Claims 1 or 3 to 5 wherein conduit means is provided for the purpose of recycling an aqueous stteam emerging from the apparatus whereby a plurality of separation stages can be performed.
7. An apparatus according to any preceding Claim wherein said chamber is adapted so that said aqueous stteam and said gas within said chamber are rotated by the provision of at least one baffle rotor.
8. A method for removing dispersed and dissolved organic components from an aqueous stteam comprising; arranging for counter flow of an aqueous stteam and a gas stteam through a porous medium and; controlling the relative rates of flow of said aqueous stteam and said gas stream so as to selectively control the removal of dispersed and dissolved organic components from said aqueous stream.
PCT/GB1993/001756 1992-08-20 1993-08-18 Separation of aqueous and organic components WO1994004266A1 (en)

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