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Title:
METHOD, APPARATUS AND SINGLET OXYGEN GENERATOR FOR CLEANING GASES
Document Type and Number:
WIPO Patent Application WO/2003/068369
Kind Code:
A1
Abstract:
The invention relates to a method and apparatus for cleaning gases. The invention relates also to a singlet oxygen generator, which finds a particular application in cleaning the gases of a waste disposal plant. At a first stage, a gas is subjected to the removal of particles by flowing the gas through a particle separator (1) capable of ionizing particles. At a second stage, the gas, which has been cleaned to a substantially particle−free state, is subjected to the removal of harmful gaseous substances by oxidation, such that the flow is supplied with singlet oxygen by means of a singlet oxygen generator (2).

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Inventors:
SUOMINEN HANNU L (FI)
Application Number:
PCT/FI2003/000108
Publication Date:
August 21, 2003
Filing Date:
February 12, 2003
Export Citation:
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Assignee:
BCDE GROUP WASTE MAN LTD OY (FI)
SUOMINEN HANNU L (FI)
International Classes:
B01D53/34; B03C3/019; B03C3/38; C01B13/02; (IPC1-7): B01D53/34; B03C3/00; C01B13/02
Domestic Patent References:
WO1998011982A11998-03-26
Foreign References:
EP0308505A11989-03-29
DE4425117A11996-01-25
Other References:
DATABASE WPI Week 200308, Derwent World Patents Index; Class D15, AN 1994-341691
Attorney, Agent or Firm:
LEITZINGER OY (Helsinki, FI)
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Claims:
Claims
1. A method for cleaning gases, characterized in that, at a first stage, a gas is subjected to the removal of particles by flowing the gas through a particle separator (1) capable of ionizing particles and, at a second stage, the gas is subjected to the removal of harmful gaseous substances by oxidation, such that the gas flow is supplied with singlet oxygen by means of a singlet oxygen generator (2).
2. A method as set forth in claim 1, characterized in that the gas flow is analyzed by means of a gas analyzer (21), having its sampling points (16, 17) upstream and downstream of a singlet oxygen supply point, and the singlet oxygen generator (2) is controlled on the basis of analytical data.
3. An apparatus for cleaning gases, characterized in that the apparatus comprises an ionizing particle separator (1) for ionizing particles in a gas to be cleaned and for collecting the same from a gas flow by means of an electric field, and a singlet oxygen generator (2) downstream of the particle separator (1) in the gas flowing direction, which is adapted to supply singlet oxygen into the gas flow to be cleaned, as well as a degassing unit (3,7) for removing harmful gaseous substances in an oxidized and odourless state.
4. A singlet oxygen generator for oxidizing gaseous substances, characterized in that the singlet oxygen generator (2) comprises a tube (13) of an electrically nonconducting material, an electrically conducting electrode (11) present inside the tube (13) and a spiral electrode (12) present outside the tube (13), a highfrequency highvoltage supply (10) present between first ends of the electrodes (11,12), a jacket tube (14), providing a flow channel which houses the spiral electrode (12), and a fan (8) for blowing air through the flow channel, whereby a corona effect developing around the spiral electrode (12) breaks up oxygen molecules of the flowing gas to singlet oxygen.
5. An apparatus as set forth in claim 3, which is provided with a singlet oxygen generator as set forth in claim 4.
6. An apparatus as set forth in claim 3 or 5, characterized in that the apparatus is used for cleaning gases from a waste disposal plant and that the apparatus includes a gas analyzer (21) for analyzing the composition of a gas to be cleaned upstream and downstream of a singlet oxygen supply point.
Description:
Method, apparatus and singlet oxygen generator for cleaning gases The invention relates to a method and apparatus for cleaning harmful gases.

A particular application for the method and apparatus is the cleaning of exhaust gases from a waste disposal plant or an incineration plant. The invention relates also to a singlet oxygen generator, which is capable of producing singlet oxygen in a gas flow for oxidizing harmful gaseous substances present therein. The singlet oxygen generator finds a particular application in a method and apparatus of the invention for cleaning the gases of a waste disposal plant or an incineration plant.

Waste disposal and incineration plants produce exhaust gases, which contain both particles and gaseous harmful substances. The particles can be e. g. microbial germs or other very small organic or inorganic particles. Harmful gaseous substances may include e. g. ammonia, methane, or hydrogen sulphide. The removal of both particles and harmful gases from a gas mixture to be cleaned is particularly problematic. Especially, the elimination of small particles (< 0, 3 um) from air is difficult with conventional air cleaners. Filters become blocked quickly, particularly in the process of cleaning moist air and the cleaning and replacement thereof requires a lot of work. It is prior known to clean gases by means of gas scrubbers, but, for example, methane, hydrogen sulphide, and ammonia are often present in such large amounts that powerful and expensive gas scrubbers are required, and a sufficient degree of cleaning is still not achieved.

It is an object of the invention to provide an improved method and apparatus, enabling an effective removal of both particles and harmful gases from gases to be cleaned.

This object of the invention is achieved by a method of the invention, the characterizing features of which are set forth in the appended claim 1. This

object is also achieved by means of an apparatus of the invention, the characterizing features of which are set forth in the appended claim 3.

A second object of the invention is to provide a singlet oxygen generator, which is suitable for the oxidation of gaseous substances and which finds a particular application in the method and apparatus of the invention for cleaning the gases of a waste disposal or incineration plant. The singlet oxygen generator has its characterizing features set forth in the appended claim 4.

The invention will now be described in more detail by way of exemplary embodiments with reference to the accompanying drawings, in which Fig. 1 shows schematically an apparatus of the invention for implementing a method of the invention; and Fig. 2 shows a singlet oxygen generator of the invention in a longitudinal section.

In reference to fig. 1, the gases of a waste disposal plant to be cleaned are first supplied to a particle separator 1, wherein the gas flows in a spirally whirling motion from bottom upwards. Inside the flow is a high-voltage electrode 5, the ion beams issuing from its tips charging particles present in the gas flow. The charged particles are collected by means of an electric field on energized collector surfaces 6, from which the particles are flushed with water sprayed from pipes 7 and the water is removed to receivers and/or further treatment processes, which do not constitute an object of this invention.

The gas flow, from which the particles have been eliminated, is delivered by a fan 4 along a duct to a gas cleaner 3,7, which in the present case

comprises a combination gas scrubber and particle separator, whose operation is otherwise similar to that of the particle separator 1 as described above, with the exception that the wash liquid sprayed from the pipes 7 can be provided with solvents and neutralizers needed for the scrubbing of gases to be removed in each particular application. However, a jet of water alone is often sufficient for the removal of oxidized gases from a flow of exhaust gas.

The harmful gases, and particularly foul-smelling gases to be removed, are more readily scrubbed from an exhaust gas flow by oxidizing the same according to the invention with a singlet oxygen generator 2. What is essential in the invention is that the oxygenation is not performed until the gas has been cleaned to a substantially particle-free state.

The singlet oxygen generator 2, shown schematically in fig. 1, will now be described more closely with reference to fig. 2. The generator 2 comprises a tube 13 of glass, inside which is an electrically conducting electrode 11, comprising e. g. a bar of acid-proof stainless steel. Outside the tube 13 is a spiral electrode 12. Between the tips of the electrodes 11,12 is coupled a high-voltage supply 10. Its potential is typically within the range of 1-10 kV.

Potential is preferably adjustable for controlling the production of singlet oxygen. Frequency is typically within the range of 10-100 kHz, and frequency can also be adjustable for optimizing the generator operation or controlling its output. A substantially larger-diameter jacket tube 14 provides a flow channel for housing the spiral electrode 12. A fan 8 can be used for blowing air through the flow channel constituted by the jacket tube 14. Consequently, a corona effect, created by the spiral electrode 12 around itself, breaks up oxygen molecules of a flowing gas to singlet oxygen 0'according to the following formula : °2 + E => O'+O' (wherein E represents the energy of an electric field associated with a corona discharge).

The optimal operation and output of the singlet oxygen generator 2 can also be adjusted by controlling the speed of the fan 8.

As shown in fig. 1, the flow channel for a gas to be cleaned is provided with a mixer 20 for providing a turbulent flow and with sampling sensors 16 and 17 for a gas analyzer 21 upstream and downstream of a singlet oxygen supply point, respectively. A control unit 15 controls the singlet oxygen generator's operation (voltage and/or frequency and/or air flow). Samples are picked up from the gas analyzer's 21 sampling points 16,17 for the comparison of analytical data. For example, methane is converted by means of singlet oxygen to carbon dioxide and water (CH4 + 40'=> CO, + 2H20), and hence, by analyzing the amount of methane upstream and downstream of a singlet oxygen supply point, the yield of singlet oxygen can be controlled in such a way that the proportional reduction of methane remains within a certain range. The same applies also e. g. to the conversion of hydrogen sulphide to gypsum and water by means of singlet oxygen: (H2S + 40 > H2504 ; H2SO4 + Ca (OH) 2 > CaSO4 + 2H2O) In fig. 1, the discharge pipes of the combination particle separator and gas scrubber 3 and the particle separator 1 are provided with a viewing glass 18 and a debris screen 19, which denies admission of larger pieces of debris into a gas scrubbing solution, as well as with an outlet gate 22 for removing large pieces of debris.

As for the operation of the ionizing particle separator 1, it is important that the electrodes 5 and 6 have therebetween an active direct-voltage field with no alternating-current component. The result of this is that the ion beams of the electrode 5 do not yet develop ozone at this stage, as the gas flow contains plenty of particles. Only at the next stage, as the particles have been removed, is the generator 2 used for controlled production of singlet oxygen, but no more than the amount needed for the oxidation of gaseous compounds, and thus, for deodorizing the same. Thus, the exhaust gas does not contain ozone, either.