GB2432544A

GB2432544A - The use of reactive organo/inorgano clays for the treatment of volatile organic compounds in contaminated air streams

Info

Publication number: GB2432544A
Application number: GB0523889A
Authority: GB
Inventors: Robert Mcintyre Weir
Original assignee: ROWE TECHNOLOGY Ltd
Current assignee: ROWE TECHNOLOGY Ltd
Priority date: 2005-11-24
Filing date: 2005-11-24
Publication date: 2007-05-30
Also published as: WO2007060429A2; GB0523889D0; EP1954378A2; WO2007060429A3

Abstract

An apparatus and method for the treatment of contaminants in a contaminated fluid are described. The apparatus comprises a containment volume through which fluid to be treated can be passed in use; particulate organo/inorgano clay selected to provide a reactive medium for chemically binding with the contaminants; and fluidisation means to cause particulate organo/inorgano clays to form, in use, a fluidised dispersion within the volume in particular by forming a slurry dispersion of the clays and spraying into the volume. In particular, the apparatus may be used for removing volatile organic compounds from contaminated air streams.

Description

APPARATUS AND METHOD FOR THE TREATMENT OF

VOLATILE ORGANIC COMPOUNDS

The invention relates to an apparatus and method for environmental control, and in particular provides an apparatus and method for the treatment and removal of contaminant materials in contaminated fluids. The invention is particularly applicable to the removal of low! medium level volatile organic compounds from contaminated air streams, and examples of such use are described herein, but this should not be taken as excluding from the scope of the invention its applicability to the treatment and removal of other organic and inorganic compounds present as contaminant materials in contaminated fluids.

Various existing processes are known which are effective to varying degrees in the removal of organic and inorganic contaminants from fluid volumes, and in particular volatile organic compounds (VOCs) where they have contaminated air volumes.

For example, the volume may be passed through an absorbent material, various materials serving this purpose. Absorption methods can be of varying effectiveness depending on the materials involved, and absorbent capacities can be limited.

In the alternative, it is know to develop adsorption processes using activated carbon or the like. Such processes can be effective at adsorbing quite high volumes of VOCs, but are nevertheless inclined to be relatively expensive.

Achieving effective mass transfer is an issue, especially with air streams. The requirement this imposes to keep a pressure drop across the adsorbent material relatively low means that for a given volume large areas are required. The process can be expensive, in particular in relation to regeneration of the adsorbent material when contaminated.

In certain cases, bio-filters can be used. However, bio-filtration of necessity requires a relatively steady ambient load. It can not be suitable to a batch process, or to significantly varying or shock loads. Bio-filtering is really only suited to 24 hour operation, for example in relation to waste water treatment plants.

VOCs in industrial wastes, and in particular in contaminated industrial air streams, may be dealt with by wet scrubbing in which the air stream is passed through scrubbing materials such as gas oil, light spindle oil or the like to dissolve the VOCs. Such a process is particularly suited where there is a desire to recover high value VOCs. However, it raises problems of its own, since emissions from the scrubbing liquid can themselves raise environmental concerns.

It has been well established that modified organo/inorgano clays, such as those used for example in the treatment technology operated under the name Envirotreat (RTM), react with a very wide variety of organic and inorganic compounds which are found in contaminated land. These clays in particular chemically react with VOCs through a number of complex bonding processes.

Clays of the type, and operating in the manner described in greater detail in UK patent GB2302685 are particularly relevant in this regard. The various VOCs react in different ways depending upon their structural chemistry, but typically bond to the clays via bonding processes such as Lewis acid/base bonding, Van der Waals bonding, hydrogen bonding, transition metal ligand bonding, and adsorption due to hydrophobicity. VOCs can be removed from contaminated land in this way in that they are locked irreversibly into the structure of the clay.

By analogy, it was suggested in UK patent application number 9715863.8 that such clays could be used to remove VOCs from contaminated air or liquid streams. Clay of the type described is retained within a container, and the contaminated fluid passed there through. However, achieving adequate mass transfer is again a problem, and the technique is in practice of limited applicability for high volumes of fluid to be decontaminated, and in particular for decontamination of high volume, relatively low contaminate level air streams.

All of these prior art methods are limited in some respects, and in particular tend to be limited in relation to the removal of VOCs at relatively low concentration from high volume air flows. Examples of such a situation are provided by the general atmospheric levels of VOCs in a paint spray workshop, a printing plant or the like, where the VOCs might be present to a level of, say, 300 to 400 ppm, and a legislative requirement is imposed to reduce this, say, to below 100 ppm.

It is an object of the present invention to provide an alternative system and method for the treatment of VOC contamination that mitigates some or all of the above disadvantages.

It is a particular preferred object of the invention to provide a system and method which lends itself to the removal of VOCs from contaminated fluids, and in particular from contaminated air streams, where the contaminant is present at relatively low levels, and where high volumes need to be treated.

Thus, in accordance with the invention in a first aspect there is provided an apparatus for the treatment of contaminants, and in particular for the removal of volatile organic compounds (VOCs) from a contaminated fluid stream such as a contaminated air stream, the apparatus comprising containment means defining a volume through which fluid to be treated can be passed in use, and for example having an inlet there into and an outlet therefrom; particulate organo/inorgano clay selected to provide a reactive medium for chemically binding with the contaminants; means to cause particulate organo/inorgano clays to form, in use, a fluidised dispersion within the volume.

In accordance with the invention, the reactive clay is provided in fine particulate form, for example in powder or granulated form, within the volume. Further, the clay is fluidised within the volume. Fluidising gives an active surface area that maximises mass transfer rates, and is therefore capable of giving the necessary volume flow for practical decontamination processes.

in particular, the reactive clay can then be used at relatively low contamination levels and for high volume flow situations. Fluidising the reactive clay within the container makes use of the clay in a decontamination apparatus much more practical than it was in the apparatus described in UK patent application number 9715863.8.

The apparatus may be adapted to process fluid to be decontaminated either as a continuous or as a batch process.

A fluidised dispersion of reactive clays can be achieved in one of two general ways. In the first alternative, the dispersion is a fluidised solid, and for example makes use of fluidised bed technology. In the second alternative, particulate reactive clay is suspended in a liquid, for example in a slurry, which then dispersed, for example as a spray, mist or the like, to form the fluidised dispersion within the volume.

In the case of the former alternative, the apparatus comprises a fluidiser to cause solid particulate reactive clay to become a fluidised dispersion within the volume in use. The particulate clay is preferably provided in granular form, for example in that at least 80% of the particulates have a mean dimension between 0.5 mm and 5 mm.

In the latter alternative, the apparatus comprises a suspension of particulate reactive clay in a suitable suspension liquid, which may for example be water, and means to form, in use, a dispersed mist within the volume from the slurry.

Optionally, the apparatus may comprise a supply of the suspension liquid, a supply of the particulate reactive clay, and a mixing unit to mix these together within the apparatus to prepare the slurry. The particulates are preferably in powder form, for example in that 80% of the particulates have a mean dimension below 50 jim and for example between 2 jim to 20 jim.

In the preferred embodiment, the apparatus is adapted to be used with a slurry suspension of reactive clays within a suitable liquid, such as water, which is dispersed in use within the volume into which the fluid to be treated is introduced by being dispersed into the form of a mist or the like.

Conveniently, to effect this, the apparatus includes at least one spray nozzle to distribute spray into the contained volume and consequently to create the required fluidised dispersion of particulate clay therein. For example, the means to distribute the spray comprises a venturi apparatus. In a particular preferred embodiment, the apparatus is a low-energy venturi scrubber.

The fluid to be treated is introduced into the volume either on a batch or continuous basis. If the fluid to be treated is a contaminated liquid, the liquid to be treated is conveniently also dispersed therein as a spray. If the apparatus is being used to treat contaminated gas, such as a contaminated air flow, the gas is introduced directly into, and for example cause to pass through, the volume.

Thus, the invention provides an effective and relatively inexpensive way of treating VOCs both in industrial and domestic situations, and in particular of treating high volume air streams contaminated with low value VOCs.

The reactive clays used in accordance with the invention are organo/inorgano clays which are selected to be reactive with the VOCs to be removed from the fluids to be treated, and are selected in particular to provide an effective medium for an irreversible chemical bonding reaction with the VOCs in question.

The reactions which occur between the reactive clays and the VOCs are irreversible and the material created by the bonding process is usually stable and inert. The resultant material can thus be safely disposed of as routine waste. Because the clays being used are relatively inexpensive materials, and because the intended contaminants to be treated are likely to be low level and low value, there is no desire or requirement to recover the VOCs and/or to regenerate the absorbent material as would be the case for example with activated carbon systems.

Preferably, the reactive clays are organoclays, and/ or modified modified to have organophilic properties. In a particular preferred embodiment, the reactive clays and reactions are of the type set out in detail in GB2302685 incorporated herein by reference.

That is to say, the clay is preferably a modified organoclay having organophilic properties and treated by a pillaring agent and a salt of a transition metal in quantities corresponding to no more than 100% stoichiometric exchange of the exchangeable cations of the clay.

As described in the reference, the pillaring agent creates interlamellar spacing sufficient to provide access for larger molecules such as polychlorinated biphenyls and polyaromatic hydrocarbons. This is preferably at least 15A (15 x10' m).

The pillaring agent may comprises an aluminium or other metal hydroxide polymer, or transition metal clusters, or appropriate silicon or titanium oxides.

In particular the modified organoclay may be further provided with intercalation additives comprising one or more in combination of an aluminium hydroxide polymer, a quaternary ammonium salt and a salt of a transition metal, such as a ferric salt and for example ferric chloride.

The amount of clay to be used, and the absorption rate which is achievable by the apparatus, will be dependent in part upon the type of pollutants to be removed from the air streams, and on input and desired output contaminant levels. However, clays of the type described in GB2302685 are known to offer exceptionally high absorption rates in theory, for example as high as 1 to 20, and the fluidising apparatus of the present invention allows this theoretically high adsorption rate to be exploited in particularly effective manner.

In accordance with the invention in a further aspect there is provided a method of treatment of contaminated fluid to remove contaminants such as volatile organic compounds therefrom, which method comprises providing a fluidised dispersion of particulate clays selected to bind with the contaminant within a suitable containment volume; causing the fluid to be decontaminated to pass into the volume; removing the fluid with reduced contamination from the volume.

The process may be operated as a batch process, whereby a quantity of fluid to be treated is passed into the containment volume, and simultaneously or sequentially therewith the reactive clay therein is caused to pass into a fluidised state to remove VOCs from the fluid to be treated, and the decontaminated fluid is then removed from the volume. However, more preferably, the process is operated continuously or semi-continuously, in that the clay within the volume is caused to go into a fluidised state, and fluid to be decontaminated is passed on a continuous or semi-continuous basis into the volume by suitable inlet means, and extracted at a reduced contamination level via suitable outlet means.

The fluidised dispersion of reactive clays may be provided within the volume by providing a suitable particulate solid clay volume and causing the same to go into a fluidised state. Alternatively, the fluidised dispersion may be provided by first suspending the particulate clay within a suitable suspension fluid, such as water, to form a slurry and then dispersing the slurry as a spray, mist or the like within the volume.

In particular, the particulate clay is suspended in water and the resultant slurry is dispersed within the volume using a venturi system.

The invention will now be described by way of example only with reference to Figure 1 of the accompanying drawings which illustrates an apparatus embodying the principles of the invention.

Figure 1 is a low-energy venturi scrubber designed to operate using a slurry comprising approximately 300 litres of water and upto 50 kilograms of organo/inorgano clay.

The apparatus comprises a main body (1), a fan (6), a recirculation pump (3), and an additional recirculation pump (4) acting from the bottom of the main body to its top in order to recirculate the slurry as it tends to become solid when left immobile. The fan (6) operates via a mist eliminator (8).

Spray is introduced via the inlet (9) to the venturi (10) which creates the required spray dispersion for operation of the invention. Contaminated air flow is introduced to the system via the ductwork (12), and the spray dispersion of fine particulate clay binds to and effects removal of the volatile organic compounds from the air stream.

Claims

CLAIMS

1. An apparatus for the treatment of contaminants in a contaminated fluid, the apparatus comprising containment means defining a volume through which fluid to be treated can be passed in use; particulate organo/inorgano clay selected to provide a reactive medium for chemically binding with the contaminants; fluidisation means to cause particulate organo/inorgano clays to form, in use, a fluidised dispersion within the volume.

2. An apparatus in accordance with claim 1 wherein the apparatus comprises a fluidiser to cause solid particulate reactive clay to become a fluidised dispersion within the volume in use.

3. An apparatus in accordance with claim 2 wherein the particulate clay is provided in granular form with at least 80% of the particulates having a mean dimension between 0.5 mm and 5 mm 4. An apparatus in accordance with claim I comprising a suspension of particulate reactive clay in a suitable suspension liquid and means to form, in use, a dispersed mist within the volume from the suspension.

5. An apparatus in accordance with claim 4 comprising a supply of the suspension liquid, a supply of the particulate reactive clay, and a mixing unit to mix these together within the apparatus to prepare a slurry.

6. An apparatus in accordance with claim 4 or 5 wherein the particulate clay is provided in powder form with 80% of the particulates having a mean dimension below 50 jim and for example between 2 jim to 20 jim. ii

7. An apparatus in accordance with one of claims 4 to 6 wherein the means to form a dispersed mist comprises at least one spray nozzle to distribute spray into the contained volume and consequently to create the required fluidised dispersion of particulate clay therein.

8. An apparatus in accordance with claim 7 wherein the spray nozzle comprises a venturi apparatus.

9. An apparatus in accordance with claim 8 wherein the apparatus is a low-energy venturi scrubber.

10. An apparatus in accordance with any preceding claim wherein the reactive clays are organo/inorgano clays which are selected to be reactive with the VOCs to be removed from the fluids to be treated to provide an effective medium for an irreversible chemical bonding reaction with the VOCs in question.

11. An apparatus in accordance with claim 10 wherein the reactive clays comprise modified organoclays having organophilic properties and treated by a pillaring agent and a salt of a transition metal in quantities corresponding to no more than 100% stoichiometric exchange of the exchangeable cations of the clay.

12. An apparatus in accordance with claim 11 wherein the pillaring agent is such as to create interlamellar spacing of at least 15 xl 0 10m 13. An apparatus in accordance with claim 11 or 12 wherein the pillaring agent is selected from an aluminium or other metal hydroxide polymer, or transition metal clusters, or appropriate silicon or titanium oxides.

14. An apparatus in accordance with one of claims 11 to 13 wherein the modified organoclay is further provided with intercalation additives comprising one or more in combination of an aluminium hydroxide polymer, a quaternary ammonium salt and a salt of a transition metal, such as a ferric salt and for example ferric chloride.

15. A method of treatment of contaminated fluid to remove contaminants such as volatile organic compounds therefrom, which method comprises providing a fluidised dispersion of particulate clays selected to bind with the contaminant within a suitable containment volume; causing the fluid to be decontaminated to pass into the volume; removing the fluid with reduced contamination from the volume.

16. A method in accordance with claim 15 comprising providing a fluidised dispersion by providing a suitable particulate solid clay charge within the volume and causing the same to go into a fluidised state.

17. A method in accordance with claim 15 comprising providing a fluidised dispersion by first suspending the particulate clay within a suitable suspension fluid to form a slurry and then dispersing the slurry as a spray, mist or the like within the volume.

18. A method in accordance with claim 17 wherein the particulate clay is suspended in water and the resultant slurry is dispersed within the volume using a venturi system.