SE505437C2 - Apparatus for reducing the amount of particulate matter in an exhaust pipe - Google Patents

Abstract

The particulate removal device comprises a two-pole high-voltage generator and a number of conductors alternately connected to one or other of the poles. The conductors each consist of a conductive metal grid arranged inside the pipe perpendicular to the general direction of flow of the exhaust gases. The ratio between the cross-sectional area of each grid and that of the pipe cross-section is pref. less than 50% and more than 10% and pref. less than 35% to provide a good balance between not unduly obstructing the cross-section of the pipe while having an adequate area covered by the electric discharge. Alternatively, the conductors can consist of grids and/or plates and/or wires, e.g. arranged to form flats or tubes, set parallel to the general direction of flow of the exhaust gases. The conductors may have points protruding at right angles from their surface. The voltage supply to the conductors is preferably such as to provide an electric field between 50 and 98% of that which would cause a discharge in the gas at the operating temperature and under the relevant working conditions. A valved conduit or line and a pipe introduces air into the pipe and is controlled using a probe which analyses the exhaust gas and transmits the results to a microprocessor which controls a pump and a valve for introducing the desired quantity of air into the pipe upstream of the conductors.

Description

505 437 -fuel ratio fixed to around certain values, which 2 makes it difficult to avoid the emission of particulate matter.

The phenomenon is particularly obvious to observers in the case of vehicle diesel engines, which are accused of causing severe environmental pollution and seriously damaging public health.

Generally speaking, these accusations are unfounded. Compared to gasoline engines, diesel engines actually emit from four to six times less carbon monoxide (which is a powerful poison because it blocks blood oxygen exchange), about half the amount of unburned hydrocarbons (which are highly carcinogenic) and about half the amount of nitrogen oxides. (belonging to substances responsible for acid rain). However, diesel engines emit about forty times more carbon particles (which in the long run can cause bronchitis and other chest or lung problems) as well as sulfur oxides (which are also responsible for acid rain but which could be eliminated if the diesel fuel was desulfurized, as is done with petrol).

It should also be noted that soot adsorbs unburned hydrocarbons and thus acts as a carrier for these carcinogenic substances.

In summary, there is no doubt that soot emitted during the combustion of gas oil, fuel oil and the like is extremely unpleasant and that such emissions should therefore be eliminated or at least greatly reduced.

Some reduction in the particulate matter caused by the combustion of hydrocarbons can be achieved by adjusting the combustion by electronic means. However, this adjustment will only reduce the amount of particulate matter by about 20%, which is not sufficient for a large variety of applications. Many attempts have thus been made to solve this problem.

BNSDOCID: BNSOXIDE 3 505 437 A variety of patents (eg J63-232817, EP 283240 and 114696, US 4622810, 4604868 and 4571938, etc.) utilize ceramic filters of various designs, which mechanically capture the particulate materials and periodically regenerated, for example by combustion using hot gases produced by a special burner or with a stream of preheated air. The filter is also often impregnated with a catalyst, usually platinum, to facilitate combustion.

In this way, the amount of particulate matter is greatly reduced. The complexity of the solutions used so far, the cost and fragility of the ceramic filters and the cost and destruction of the catalysts (due to poisoning, for example) have so far made the use of such filters uneconomical, especially for vehicles.

U.S. Patent 4,741,1746 proposes the use of an electrostatic precipitating device with corona power for separating carbon particles from diesel exhaust gases.

U.S. Patent 4,587,808, which also relates to diesel engines, relates to the use of a molecular dissociator which, with a charge of up to 150 kV, causes dissociation of CO, CO 2 and NOx molecules and unburned hydrocarbons into the constituent chemical elements and subsequent removal of the carbon particles thus formed, as well as those already present in the exhaust gas, by means of an electrostatic separator and a cyclone.

However, at the 1987 Paris Meeting on Air Pollution Caused by Transport, it was reported that when systems developed for industry are installed in cars, their efficiency is questionable (as in the case of cyclones) or their size is too large and their complexity an obstacle (electrostatic separators ). (See Pollution Atmospherigue, Special Number, December 1987, pp. 268-285).

From the foregoing, it is apparent that in use of limited size (such as diesel engines for automobiles, etc., or home heating systems), the technical and economic problems associated with reducing the particulate matter content in gases resulting from the combustion of hydrocarbons far from dissolved. The object of this invention is to eliminate the inconveniences associated with existing systems for removing particulate matter by providing a simple, inexpensive and compact device for reducing the emission of particulate matter in gases resulting from the combustion of hydrocarbons.

According to this invention, in an exhaust pipe, through which the combustion products of hydrocarbons flow, a device for removing particulate matter is introduced, which is characterized by the following parts: - Two-pole high-voltage generator - A plurality of conductors connected alternately to one or the other of the poles - Means for insertion of air in the pipe upstream of the conductors - Means for regulating the means for introducing air.

These conductors each consist of a conductive metal grid inside the tube arranged perpendicular to the general or main flow direction of the exhaust gases.

The size of the grid (or the percentage ratio of the total cross-sectional area of the wires or strands forming the grid to the cross-section of the tube) must be less than 50% and preferably less than 35% but more than 10%.

These values are determined by the need for a good balance between the requirement not to disturb too much or clog the cross section of the pipe, while maintaining a sufficient area covered by the electrical discharge.

BNsDoc | D: BNSÛCCID 505 437 Alternatively, the conductors may be grids and / or plates and / or wires, arranged to form flat disks or pipes parallel to the general flow direction of the exhaust gases.

In this case, the space occupied by these conductors, as defined above, may be less than 35% and more than 4%, while the grid and / or plates and / or wires may extend parallel to the axis of the tube along a length of up to ten times the pipe diameter. In both of these embodiments, the conductors may have points or tips projecting at right angles from their surface.

The voltage supply to the conductors must be such that it provides an electric field of between 50 and 98% of that which would cause a discharge in the gas at the operating temperature and under the relevant operating conditions.

The means for introducing air into the pipe consist of a valve fitted with a valve and a pipe.

The means for regulating the means for introducing air consist of a probe, which analyzes the exhaust gas and transmits the results to a microprocessor, which regulates the pump and the valve for introducing the desired amount of air into the pipe upstream in relation to the conductors.

The invention will be described in more detail below with reference to the accompanying drawing, which illustrates the invention only as an example and in no way limits the object and scope of the invention: Fig. 1 shows a general schematic plant design.

Fig. 2 shows a cross section through an embodiment, according to which the conductors are arranged parallel to the general direction of the gas flow.

Fig. 3 is a perspective view in section of an embodiment, in which the conductors are arranged perpendicular to the main direction of the gas flow. 5Û5K37C2 I: »505 437 6 As shown in Fig. 1, a duct 2 is arranged in a pipe 1 which conducts exhaust gas. This channel is complete with conductors (not shown) connected via cables 4 and 5 to a voltage generator 3. A microprocessor 9 processes the signals regarding the composition of the gas analyzed with the probe 6 and regulates the valve 8 in the line 7, which is connected to the channel 2, for supplying to the latter the desired amount of air supplied by a pump 10.

During operation, the probe 6 analyzes the gas, in particular as regards the content of CO, CO2 and 02. The signals are sent to the microprocessor 9, which - on the basis of predetermined programs and other information regarding specific fuel consumption - determines the amounts of unburned material and soot and thus the amount of air required to burn them and, as a result, regulates the pump 10 and the valve 8.

At the same time, a high voltage is created between the conductors with the voltage generator 3.

When the gas flows between the electrodes, soot present therein lowers the dielectric constant of the system and causes a strong spark to be discharged into the carbon particles, making them glowing, so that they are burned.

Enrichment of the gas with air and the high temperature achieved enables the majority of the carbon particles to be combusted, ensuring that substantially carbon dioxide is formed. In this way, for example, the very low carbon monoxide content of diesel engine exhaust gases can be maintained and in some cases even reduced.

Two embodiments of the invention are illustrated in Figures 2 and 3.

According to Fig. 2, the conductors, in the form of flat plates 12, 12 'and 13, are arranged parallel to the general flow direction of the gas, from left to right; cables 4 resp. 5 feeds the plates l2, _2 '' and 13, the cable 5 extends through the wall BNSDOCID: BNSDOCIÛ 7 505 437 of the conductor 2 via an insulated section ll. The plates may have projecting tips 14 to facilitate the formation of electrical discharges between the carbon particles and the plates themselves.

According to Fig. 3, the conductors, in the form of circular grids 12, 12 ', 13 and 13', are arranged perpendicular to the general flow direction of the gas and are supplied via cables 4 and 5 while being insulated with insulators 11, which also allows the passage of cables 4 and 5 through the wall of the duct 2.

Of course, other arrangements and shapes of the conductors 12 and 13 can also be used without any loss of protection for the invention.

The present invention has been tested on an exhaust system for a diesel-electric plant with a 3860 cm: engine and a generator with a rated power of 40 kW at 1500 rpm. The engine was run at 1400 rpm during the trials.

The conductors, in the form of a grid, as in Fig. 3, were arranged at a mutual distance of 3 cm. The diameter of the four pairs of conductors was 20% smaller than the inside diameter of the exhaust pipe.

The voltage between the conductors in a pair of conductors ranged from 50 to 65 kW. The size of the space occupied in the transverse direction of each grid, as defined above, amounted to 22% of the cross-sectional area of the pipe.

The engine was operated for one hour during each test and the particulate removal device was operated for specified periods of time. At the same time, samples were taken of the exhaust gas and the sample was passed through a weighed filter. After the passage of one cubic meter of gas, the filter was weighed again with its loading of particulate matter.

The average amount of particulate matter present in the exhaust gas which was not treated according to the invention was 17.2 mg / m 3, with a variation between -3 and +4 mg / m 3. 505437C2 I> 505 437 8 The introduction of the pairs of grids one by one led to a reduction of the content of particulate matter in the treated gases, ranging from about 15% (in the case of a pair of grids with a voltage of 52 kV) to about 70% (with four pairs of grilles and a voltage of 60 kV).

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Claims (8)

BNSDOCIÛ -zSE 9 505 437 PATENTKRAV 1. A device for reducing the amount of particulate matter in exhaust gas in an exhaust pipe, characterized by a combination of the following parts: - a two-pole high-voltage generator - a plurality of conductors alternately connected to one or the other of these poles - means for the introduction of air into the pipe upstream of the conductors - means for regulating the means for introducing air. Device according to claim 1, characterized in that the conductors each consist of a conductive metal grid arranged inside the pipe perpendicular to the general flow direction of the exhaust gas. Device according to claim 1 or 2, characterized in that the ratio between the cross-sectional area of each grid and the cross-sectional area of the pipe is less than 50% and more than 10%. Device according to claim 3, characterized in that the ratio is less than 35%. Device according to claim 1, characterized in that the conductors are present in the form of grids and / or plates and / or wires arranged parallel to the general flow direction of the exhaust gases. Device according to claim 3, characterized in that the ratio between the total cross-sectional area of the conductors and the cross-sectional area of the pipe is between 35 and 4%, the conductors extending parallel to the axis of the pipe along a length of up to ten times the diameter of the pipe . Device according to any one of claims 1-6, characterized in - 5Ü5437C2! > 505 437 m n e t e c k n a d that the conductors have a large number of protruding points or tips. Device according to any one of claims 1 to 7, characterized in that the high voltage generator supplies the conductors to provide an electric field between 50 and 98% of what is required to cause discharge between the conductors under the operating conditions. BNSDOCIDI