Method and apparatus for the purification of air, flue gases or the like

Abstract: Procedure and apparatus for the purifica­ tion of air, flue gases or equivalent, in which procedure the air, flue gases or equivalent are directed into a duct or equivalent, in which procedure the air, flue gases or equivalent are ionized, and in which procedure the charged impurity particles (7) present in the air, flue gases or equivalent are attracted by one or more collector surfaces (2) by virtue of a difference in the states of charge, causing the particles to settle on said surface. The air, flue gases or equiva­ lent are ionized by means of one or more ionizing electrodes (5) directed at a collector surface. The distance between the ionizing electrode or equivalent and the collector surface as well as the difference between the states of electric charge of the collector surface and the charged impurity particles are so ad­ justed that the impurity particles will be carried by an ion beam essentially di­ rectly towards the collector surface and settle on it.

Description: The present invention concerns a method and an apparatus for the purification of air, flue gases or the like, in which procedure the air, flue gases are directed into a duct, in which method the air, flue gases are ionized and charged impurity particles present in the air, flue gases are attracted by collector surfaces by virtue of a difference in the states of charge, causing the particles to settle on said surface(s), and in which method the air, flue gases is ionized by means of one or more ionizing electrodes directed towards the collector surface. GB-patent publication 1 238 438 proposes a method and an apparatus for the removal of dust particles from the air in a tunnel. In the method presented in the publication mentioned, the tunnel is provided with electrodes, to which a high voltage is applied. The electrodes charge the particles in the air in the tunnel by producing an electric field between the interior wall of the tunnel and the electrodes. Thus the charged dust particles are attracted to the interior walls of the tunnel. For the air to be sufficiently purified, it has to be very strongly ionized in order that all particles in the tunnel should be charged and settle when they encounter an interior surface of the tunnel. Moreover, several electrodes and a long tunnel are needed. SE-application publication 8501858-8 proposes a procedure for eliminating or reducing the emissions of SO x and NO x . DE-C-526.021 refers to a centrifugal electofilter which is a combination of a normal ionizing apparatus and a centrifugal device. Particles transported with the flow of air become ionized in the duct, whereupon the centrifugal force cause the particles to be displaced towards the outer duct wall. The particles are displaced only in the direction of the centrifugal force. The ionization gives the particles a retaining force, whereby the particles adhere to the duct wall, when they have already been moved there by the centrifugal force. This gives a much higher energy consumption and limits the applicability of the process and device. The object of the present invention is to eliminate the drawbacks of the previously known techniques. The method of the invention for the purification of air, flue gases or equivalent is characterized in that the voltage applied to the ionizing electrode (5) is in the order of 100 - 250 kV whereby a conical ion beam is produced and in that the distance between the ionizing electrode and the collector surface as well as the difference between the states of electric charge of the collector surface and the charged impurity particles are so adjusted that the impurity particles will be carried only by said conical ion beam essentially directly towards the collector surface and settle on it. The preferred embodiments of the invention are presented in the other claims. The invention provides the following advantages over current methods: Efficient purification even in a short duct. Considerable reduction in energy consumption as compared to current procedures. The need for maintenance is reduced as the collector surfaces can be washed simply with a water jet. Air can be purified regarding different particle sizes down to pure gases. The invention makes it possible to remove particles as small as 0.005 µm and even smaller. In the following, the invention is described in greater detail by the aid of examples with reference to the drawings attached, in which Fig. 1 illustrates air purification in a duct by the procedure of the invention. Fig. 2 also illustrates air purification in a corridor or duct by the procedure of the invention. Fig. 3 illustrates the cleaning of a wall acting as a collector surface. Fig. 4 shows a tube used for air purification. Fig. 5 shows an expanded tube used for air purification. Fig. 6 shows a spiral tube. Fig. 7 shows a voltage supply unit. Fig. 8 shows a structure for air intake and air outlet. Fig. 1 presents a duct which has side walls 1 and 2, a ceiling 3 and a floor 4. The fresh air supplied into a building or the air to be re-circulated is directed into the duct for removal of impurity particles. For purification, the air is ionized by means of an ionizing electrode 5 mounted on a bracket 6 and connected with a cable to a voltage supply unit, which will be described later. The ionizing electrode 5 is directed at the opposite side wall 2, which is earthed and acts as a particle-collecting surface. The voltage applied to the ionizing electrode 5, which is of the order of 100 - 250 kV, and the distance between the ionizing electrode and the side wall are so adjusted that a conical ion beam or ion jet as indicated by the broken lines is produced. With this arrangement, the (negatively) charged impurity particles 7 will move directly to the side wall 2 and settle on it due to the difference in electric charge between the particles and the wall. The ion jet can be felt near the wall as a cool ion current. The distance between the ionizing electrode and the collecting wall is typically 100 - 1000 mm. Fig. 2 shows a top view of a duct with earthed side walls 8 and 9 and two ionizing electrodes 10 and 11 mounted on brackets 12 and 13. This arrangement allows a more efficient purification of the air as the first electrode 10 produces a conical ion beam causing impurity particles 14 to move towards wall 8 and settle on it while the second electrode 11 produces an ion beam causing impurity particles 15 to move to the opposite wall 9, so that the air is efficiently purified over the whole sectional area of the duct. Fig. 3 illustrates the cleaning of the collector surface 2 using a water jet. The water is sprayed onto the surface through a nozzle 16, to which it is supplied via a hose 17 from a container 18. The duct floor 19 is V-shaped, so that the water is gathered in the middle of the floor, from where it can be directed further e.g. into a drain. Fig. 4 shows a tubular purification duct 20 with ionizing electrodes 21. The duct has a curved shape such that the cleaning water will flow out through an exit opening 22 as indicated by the arrows. Fig. 5 shows a tubular purification duct 22 provided with an expansion 23 to retard the flow of air through it, the walls of the expanded part acting as collecting surfaces. The expanded part is provided with ionizing electrodes 24 and 25 mounted on brackets 26 and 27 on opposite walls. The impurity particles 28 and 29 drift towards the collecting surfaces as explained above. Fig. 6 presents a spiral tube 30 with ionizing electrodes 31 and 32 mounted on brackets 33 and 34. The impurity particles settle on the earthed wall of the tube 30. The water used for cleaning the spiral tube exits through the lower end as indicated by the arrows. Fig. 7 shows a diagram of the power supply unit, which supplies a voltage to the ionizing electrodes. The unit comprises high-voltage and low-voltage units 37 and 38, which are fed by the mains voltage V in , e.g. 220 V. The high-voltage and low-voltage units control a pulse-width modulator 39. The output of the pulse-width modulator is connected to the primary side of a high-voltage transformer 40, and the transformer output is connected to a high-voltage cascade 41, whose output voltage V out is applied to the ionizing electrodes. The mains voltage also feeds the power supply 43 of a microprocessor 42. Connected to the microprocessor are sensors for the ionizing current, duct temperature and humidity and for a solenoid controlling the spraying of wash water through the nozzle. The sensors give an alarm in the form of a signal light in an alarm unit 44 and also an inhibit signal to the modulator, preventing the supply of voltage. The output voltage V out is adjusted by means of a regulating element 45. Fig. 8 presents a tubular duct 37a for intake air, provided with an ionizing electrode 38a in the manner described above. The purification duct 37a is surrounded by an exit air duct 39a, so that the action of the structure resembles that of a heat exchanger. It is obvious to a person skilled in the art that different embodiments of the invention are not restricted to the examples described above, but that they may instead be varied within the scope of the following claims. Instead of earthed collector surfaces, it is also possible to use collector surfaces having a charge of opposite sign in relation to the ions.

Claims: Method of purifying air, flue gas or the like, in which the air, flue gas or the like are directed through a duct (1-4), in which method the air, flue gas or the like are ionized and charged impurity particles (7, 14, 15, 28, 29,35,36) present in the air, flue gases or the like are attracted by the duct serving as collector surface (2, 8, 9, 20, 23, 30, 37) by virtue of the difference in the states of charges, causing the particles to settle on said surface, and in which method the air, flue gases or the like are ionized by means of ionizing electrodes (5, 10, 11, 21, 24, 25, 31, 32, 38) directed towards the collector surfaces, characterised in that the voltage applied to the ionizing electrodes (5) is in the order of 100 to 250 kV whereby a series of non-overlapping conical ion beams is produced, each conical ion beam being produced by one single discharge point ionizing electrode. Apparatus implementing the method of claim 1 of purifying air, flue gases or the like, comprising a duct (1-4) through which the air, flue gases or the like are directed, a series of ionizing electrodes (5) for the ionization of the air, flue gases or the like, the duct serving as collector surface (2, 8, 9, 20, 23, 30, 37) attracting charged impurity paticles (7, 14, 15, 28, 29, 35, 36) by virtue of a difference in the states of electric charge from the air, flue gases or the like so that the particles will settle on said surface, the ionizing electrodes (5) being directed towards the collector surface, characterised in that the voltage applied to the ionizing electrodes (5) is in the order of 100 to 250 kV where a series of non-overlapping ion beams is produced by individual single discharge point electrodes (5). Apparatus according to claim 2, characterised in that it is provided with cleaning equipment (16 - 18) for cleaning the collector surface. Apparatus according to claims 2 or 3, characterised in that the duct (20) is so constructed that the cleaning fluid, e.g. water, is allowed to flow out of the duct through an exit opening (22). Apparatus according to anyone of claims 2 to 4, characterised in that the duct is provided with an expansion (23) to retard the flow of air, flue gases or the like through it, the expanded part being provided with one or more ionizing electrodes. Apparatus according to claim 2, characterised in that the purification duct (37a) is placed inside an exit air duct (39a). Apparatus according to claims 1 to 6, characterised in that it comprises a supervision unit (42) for interrupting the supply of power when the humidity, temperature or the current of the ionizing electrode is outside a permitted range.

Inventors: ILMASTI VEIKKO, ILMASTI, VEIKKO
Applicants: ION BLAST OY
Application year: 1990
Main classification: B03C3
IPC codes: B03C3, B01D53