Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CA 02487683 2004-11-17
Electrodeless Ultraviolet Discharge Fluid Remediation
Technical Field
This invention relates to remediation of fluids in a finite space by
means of ultraviolet radiation from electrodeless ultraviolet discharge
devices, induding the excitation of photocatalytic surfaces to promote
chemical reactions.
Background Art
Typical air purifiers use electrode discharge ultraviolet lamps; in
some cases, the ultraviolet light is relied upon to wholly or partially
destroy microorganisms; in other cases, the ultraviolet light activates a
photocatalyst on the surface of a packed bed of pellets or of a structure
which is permeable by the air flowing therethrough. Similar apparatus
is may be used in chemical processes in which photocatalytic oxidation of
air or water streams is performed either to remediate (i.e., sterilize) or
otherwise condition the stream.
Because of the short lamp life, air-purifier designs must be made
suitable .for lamp changeover. Such designs are unnecessariiy large in
volume, require a large number of ultraviolet lamps and photocatalyst
elements (when used). The efFiciency of electrode ultraviolet lamps
(such as mercury lamps) is less than 30%; that is, less than 30% of the
electrical input is converted to ultraviolet radiation. Lamps of this sort
are utilized in U.S. Patent 6,280,686 and patents referred to therein.
Consider, as an example, current, standard practice employed in
commercial photocatalytic treatment of process streams, such as air-
purification of contaminated air in occupied space of buildings. An
effective design requires the bringing together, in space and time, of the
ultraviolet photon, the photocatalyst surface element, and the process
stream (e,g., the contaminants in the air in the air-purification example).
Present design practice fixes the photocatalyst in space and places the
ultraviolet irradiating source extemally to the photocatalyst.
Consequently, photocatalyst surface elements are rendered non-
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uniformly irradiated, dimly irradiated, and non-irradiated. This prac6ce
necessarily imposes a limit on the degrees of freedom available to the
design.
As an illustrative application example, present commercial
photocatalytic air purifiers all use electrode discharge ultraviolet lamps
and a photocatalyst element that is configured as a packed bed of
photocatalyst pellets or as a porous monolith support (i.e., honeycomb,
reticulate foam, screen, woven or unwoven fiber, etc.) having a
photocatalyst coating. The primary deficiendes of this design are
70 twofold: First, because the source of ultraviolet radiation is external to
the
photocatalyst support and photocatalyst surface, that is, the source of
ultraviolet radiation and the photocatalyst surface are necessarily
separate in space, the illumination is inherently non-uniform, which
results in dimly irradiated or non-irradiated surface elements, and
consequently poor contaminant destruction. Because of this inherent
deficiency, the design objective of delivery of the ultraviolet photons to
the photocatalyst, while simultaneously achieving delivery of the
contaminant (process stream) to a suitably activated photocatalyst,
creates a difficult design problem. Second, fluid processing apparatus
has heretofore been limited by the use of ultraviolet lamps which rely on
an electric discharge between electrodes in order to sustain the creation
of ultraviolet radiation. These devices suffer from the deposit of
impurilaes resulting from heat concentration at the electrodes, which in
tum inhibits electron emission and, therefore, UV photo emission. Lamp
irradiation diminishes with time as the lamp ages and results In a useful
lamp life that is less than about 8,000 hours; an inherent characteristic of
electrode based ultraviolet lamps. These deficiencies result in air-purifier
designs that are large in volume, require a large number of ultraviolet
lamps and photocatalyst elements, and consume a large amount of
electricai power. Although the air-pucification example is used to
illustrate shortcomings of external irradiation, those same deficiencies
are inherent in all applications that have the ultraviolet radiation sources
external to the photocatalyst.
CA 02487683 2005-03-14
2a
There is described in WO-A-0109924 an ultraviolet light source comprising an
ultraviolet bulb(s), a microwave energy source for exciting the UV bulb(s),
and an
enclosure for enclosing the UV bulb(s), the enclosure being an optically
transparent
waveguide. The disclosed UV light source may be used in the promotion of
photochemical, reactions and of molecular dissociation in liquids flowing past
the
enclosure.
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Disclosure of Invention
As used herein, "remediation" encompasses photocatalytic and
photochemical processes, and indudes (' )"decontamination" which
means (a) (i) to wholly or (ii) partially (b) (i) destroy, (ii) kill or (iii)
vaporize
any microorganism, and (2) "decomposition", which means oxidation or
reduction of compounds.
Objects of the invention indude: fluid remediation utiiizing
ultraviolet radiation having lamp life exceeding ten years; ultraviolet fluid
remediation having highly efficient utilization of electricai input energy,
such as on the order of 80% efficiency; fluid remediation which can be
performed in relatfvely compact space; highly efficient photocatalytic fluid
remediation; photocatalytic fluid remediation which is easily implemented
in an energy efficient manner, and improved uftraviolet and
photocatalytic fluid remediation.
Acoording to the present invention, electrodeless ultraviolet
lamps are used in a fluid remediation zone. The ultraviolet lamps may
be used alone or in conjunction with ultraviolet-activated photocatalyst
surfaces in the space. The lamps may be activated by microwaves
provided by a magnetron, in groups, or individually. The lamps may be
activated by inductiveiy coupled radio frequency power. Photocatalytic
surfaces may be on the lamps, or on partides of photocatalyst or non-
photocatalyst elements. The lamps may be spheres or cylinders. The
fluid being treated may be air, water or other fluids.
Furthermore, this invention relates to photocatalytic and
photochemical processing for processing oxidation or redudion
reacfaons. Possible appiications for this invention are varied, for
example, air-purification of occupied spaces (e.g., residential and
comrnerciai buildings, transportation vehicles, etc.), ethylene control in
transportation of horticultural commodities, remediation of contaminated
soil and water, and generally for any contaminated air or water stream,
for chemical synthesis, and for microbial sterilization. The key feature of
this aspect of the invention is the intimate integration of UV light and
photocatelyst surfaces, which allows increased freedom to independently
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control UV intensity and fluid phase mass transport processes. The
present invention provides a long-lived source of ultraviolet emission as
well as compact and highly efficient photc :atalytic reactors for air
purification and other applications. The present invention brings the
ultraviolet source and the photocatalyst surface into intimate proximity,
thereby achieving nearly uniform irradiation of ail photocatalytic surface
elements. This intimate integration of ultraviolet irradiating source and
photocatalytic surface greatly improves the freedom to independenfiy
control ultraviolet intensity and transport processes, that is, transport of
chemical reactants in the process stream to the photocatalyst surface.
The invention provides fluid remediation having ultraviolet lamps
with lives exceeding ten years, thereby simplifying the apparatus and
reducing the cost of maintenance significantly. The invention provides
ultraviolet efficiency on the order of 80%, induding power transfer losses
by the radio or microwave generators and cavities.
Other objects, features and advantages of the present invention
will become more apparent in the light of the following detailed
description of exemplary embodiments thereof, as illustrated in the
accompanying drawings.
Brief Description of the Drawings
Fig. I is a simplified, stylized side schematic view of a duct
having spheres induding electrodeless ultraviolet lamps in a magnetron-
activated microwave cavity.
Fig. 2 is a parti:ally broken away, simplified schematic
perspective view of cylindrical electrodeless ultraviolet lamps disposed in
a magnetron-activated microwave cavity within a duct.
Fig. 3 is a partially broken away, stylized schematic perspective
view of cylindrical electrodeless ultraviolet lamps disposed between
photocatalytic-coated fluid-permeable substrates.
Fig. 4 is a simplified, schematic perspective view of a cylindrical
electrodeless ultravioiet lamp being inductiveiy excited by radio
frequency power.
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CA 02487683 2004-11-17
Fig. 5 is a simplified, schematic perspective view of a tubular
electrodeless ultraviolet lamp disposed within a magnetron-energized
microwave cavity.
Fig. 6 is a simplified, schematic side eievation view of a tubular
5 electrodeless ultraviolet lamp having starter electrodes and power
supply.
Mode(s) for Carrying Out the Invention
In Fig. 1, a fluid remediation zone 13 is formed within a duct 14
1o which comprises microwave reflecting material. At each end of a finite
space 17, microwave reflectors 18, 19, which are permeable to the fluid
in the duct 14, form a resonant microwave cavity. A magnetron 22
provides microwave electromagnetic radiation into the cavity. Within the
cavity are spheres 23, 24. The spheres 23, 24 may all comprise
spherical electrodeless microwave lamps, in which case the fluid
remediation zone of Fig. 1 operates to wholly or partially destroy
microorganisms by means of ultraviolet radiation alone. On the other
hand, in accordance vvith the invention, the spheres 23 may comprise
spherical electrodeless ultraviolet lamps and the spheres 24 may be non-
lamp spheres having an ultraviolet-activated photocatalyst surfaces, in
which case the fluid remediation zone of Fig. I utilizes photocatalyst
reaction with the fluid to remediate the fluid in some fashion, such as to
oxidize or reduce organic compounds within the fluid. The spheres 23,
24 may instead comprise spherical electrodeless ultraviolet lamps having
a photocataiytic coating thereon, the coating being sufficiently thin to be
substantially transparent to microwave electromagnetic radiation, so the
radiation can penetrate to the substance within the sphere thereby to
maintain the ultraviolet radiation which activates the photocatalyst on the
surface of the spheres 23, 24. The thickness of the coating can be
determined from U.S. Patent 5,865,959. In this case, there is a
photocatalytic reaction with material in the fluid. ln Fig. 1, instead of
spheres 24, the spherical electrodeless ultraviolet lamps 23 may have
particles interspersed therewith, the particies either being of a
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photocatalyst material, or being of a non-photocatalyst materiaf but
having a photocatalyst coating thereon. In Fig. 1, if desired, the
microwave reflectors 18, 19 may be coa 3d with a photocatalyst so as to
enhance the interaction with the fluid.
In Fig. 2, a fluid remediation zone 26 includes the duct 14, the
microwave reflective surfaces 18, 19 and the magnetron 22, but Instead
of spheres, it contains cylindrical electrodeless ultraviolet lamps 27. The
lamps 27 are disposed with their axes of symmetry parallel to the long
dimension of the duct so that fluid can flow within the interstices
therebetween, but any possible angle between the cylinder axis and the
duct flow is acceptable. The lamps 27 may be coated with an
appropriately thin layer of ultraviolet-activated photocatalyst In Fig. 2,
the cylindrical electrodeless ultraviolet lamps 27 may have partides (e.g.,
spheres, cylinders, or any geometry) interspersed therewith, the particles
i5 either being of a photocatalyst material, or being of a non-photocatalyst
material but having a photocatalyst coating thereon.
In Fig. 3, a remediation zone 30 comprises the duct 14 and
magnetron 22, with a plurality of permeable substrates 31-33 with
cylindrical electrodeless ultraviolet lamps disposed therebetween. At
least the end substrates 33 (the other not shown) must be microwave-
reflecting material so as to form a microwave cavity within the duct 14.
All of the substrates 31-33 are provided with a photocatalytic surface
which, when activated by radiation from the lamps 36, wiil cause
chemical reactions with material (typically hydrocarbons) in the fluid, to
oxidize or reduce such materials in order to affect them in a desired way,
such as to render them harmless.
Instead of being energized through cavity resonance as In Figs.
1-3, the tubes 36 may be activated as in Fig. 4 by radio frequency (RF)
electromagnetic radiation inductively coupled from an RF power supply
39 by coils 40. The power supply 39 may have coils 40 for each of the
tubes, or each tube may have its own power supply, as suits any
implementation of the present invention. On the other hand, each of the
tubes 36 may be disposed as in Fig. 5 within its own microwave cavity
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which is formed, with a magnetron 22, by suitable microwave neilective,
permeable material 43 as shown In Fig. 5. The permeable substrates
31-33 and 43 may be any sort of iabyrin i, mesh, net, screen or other
perforated material which can both serve as an micrnwave nirror and
allow adequate fluid to pass therethrough.
As used herein, the term "eiectrodeiess ultraviolet iamp" means
an ultraviolet lamp which can sustain uitraviolet radiation, without
exc,itation by electrodes within the lamp, due to microwave or RF
excitation, but indudes lamps in which electrodes are provided in order
to assist in commencement of the uitraviolet discharge. as Illustrated by
the electrodeless lamp 44 In Fig. 6. Therein, the lamp 44 has bms 45
in addition to the gas fiiied cylinder 46, there being electrodes 47
extending from each base into the cyfinder 46. Ducing ignilon, a start-up
power supply 48 temporarily provides eiedric power to the eiec,trodes 47
is so as to enhance the ultraviolet discharge within the cyiinder46, as the
cylinder is irradiated with electromagnetic radiation, as descxibed
hereinbefore. However, eiectric power to the electrodes is shut off oncso
ultraviolet radiation has been obtajned, and the ultraviolet radiation Is
sustained solely by the electromagnetic radiation. In this way, the iong-
2o term heat effects, induding generating deposits In the lamp, are avoided.
Emission of ultraviolet radiation is described In Boulos, M.I. et al,
T ermai Plasma: Fund~als and Aapiications, Vol. 1, Pienum Press,
N.Y., 1944. Microwave driven electrodeless ultraviolet lamps are
available from Fusion UV Systems, Inc. Inductively driven electrodeless
25 ultraviolet lamps are available from Sylvania and from Phillips.
