DD297345A5 - DEVICE FOR REMOVING PARTICULAR EXHAUST GASES AND SMOKE GASES - Google Patents

Abstract

The combustion of high-carbon substances causes a high emission of carbon particles (solids) due to lack of air in the burnt mixture or even due to poor mixing. According to the invention, solids are removed by means of a system of conductors between which there is a high potential difference. As the carbon particles move between these conductors, they cause a discharge that causes them to become white and they are burned. Fig. 3 {exhaust gas purification; Flue gas cleaning; Solids removal; Environmental Protection; Solids mission; Electrostatic precipitator; Diesel exhaust; Coal combustion; Automobile exhaust}

Description

For this 1 page drawings

Field of application of the invention

The invention relates to a device for removing solids from exhaust gases and flue gases, in particular a system for eliminating or at least substantially reducing the emission of solids in exhaust gases of diesel engines or in flue gases. These gases arise from alkn applications related to the combustion of diesel fuel or heavy oils, even mixtures with aromatic fraction fraction (heating systems, portable power supplies, large power plants, etc.) or coal.

Well-known technical solutions

The combustion of hydrocarbons, starting with molecules of about ten carbon atoms or simple aromatic molecules, not only produces the traditional combustion products, such as CO, CO ₂ and H ₂ O, but also products such as unburned organic compounds, carbon black and nitrogen oxides. The same applies to the combustion of coal, at least insofar as it concerns soot.

The composition of exhaust gas may vary widely depending on the amount of air used for combustion. However, for a good process yield (eg, to achieve sufficient performance), the air-fuel ratio is set close to certain values, making it difficult to avoid the emission of solids. The phenomenon is particularly evident to the observer in the case of automotive diesel engines, which as a result give the impression of causing severe environmental pollution and severely damaging human health.

By and large, these allegations are unfounded. In fact, compared to gasoline engines, diesel engines encounter four to six times less carbon monoxide (which is a potent poison because it inhibits oxygen exchange in the blood), about half the amount of unburned hydrocarbons (which are highly carcinogenic), and about half nitrogen oxides ( that belong to the compounds that are responsible for the acid rain). However, diesel engines encounter about forty times more carbon particles (which in the long run are bronchitis and other diseases of the

Respiratory systems) as well as sulfur oxides (which are also responsible for acid rain, but could be eliminated if the diesel fuel were desulfurized, as is the case with petrol).

It should also be noted that soot absorbs unburned hydrocarbons and thus acts as a vector for these carcinogens.

In conclusion, there can be no doubt that the soot developed by the combustion of diesel fuel, heating oil and the like is extremely unpleasant and therefore such emissions should be eliminated or at least substantially reduced.

Some reduction in the solids emission caused by the combustion of hydrocarbons can be achieved by ceasing combustion by electronic means. However, this setting only causes - .ne reduction of the amount of solids by about 20%, which is not sufficient for a wide range of applications. As a result and many efforts have been made to solve this problem.

Numerous patents (e.g., J 63-232817, EP 283240 and 114696, U.S. Patents 4,622,810,460,468 and 4,571,938, etc.) use ceramic filters of various descriptions which mechanically trap the solids and regularly, for example, by combustion using one special burners produced hot gases or a stream of preheated air, to be regenerated. The filter is also often impregnated with a catalyst - usually platinum - to facilitate combustion.

In this way the solid emission is substantially reduced. The complexity of the previously chosen solutions, the cost and fragility of the ceramic filters, as well as the cost and degradation of the effectiveness of the catalysts (for example by poisoning) have hitherto made the use of such filters, particularly in vehicles, uneconomical.

US Pat. No. 4,741,746 suggests the use of a corona discharge electrostatic precipitator for precipitating the carbon particles from diesel exhaust gases.

US Pat. No. 4,587,808, which also relates to diesel engines, contemplates the use of a molecular disassociation apparatus which, with a charge of up to 15OkV, causes the decomposition of the CO, CO ₂ and NO _x molecules and unburned hydrocarbons into the elemental chemical constituents and then eliminating the carbon particles thus produced and the carbon particles already contained in the exhaust gas with the aid of an electrostatic precipitator, an azo separator and a cyclone.

However, it was reported at the Congress "Transport-Induced Air Pollution" in Paris in 1987 that when incorporating systems adopted from the industry into motor vehicles, their effectiveness is dubious (as in the case of cyclones), they are too large or their complexity (electrostatic precipitators) is a hindrance (See Pollution Atmospherique, Special Edition, December 1987, pp. 268-285).

The above teachings show that the technical and economic problems associated with reducing the solids content of gases as a result of the combustion of hydrocarbons are still far from being solved in size-limiting applications (such as in automotive diesel engines, etc. or in home heating systems).

Object of the invention

The object of this invention is to eliminate the disadvantages inherent in existing solids disposal systems by providing a simple, inexpensive, compact apparatus for reducing solid emissions in gases produced by the combustion of hydrocarbons.

Essence of the invention

The invention has for its object to develop a & device for removing solids from exhaust gases or flue gases by means of electrically conductive internals.

According to the invention, the device consists of a two-pole high voltage generator, a plurality of alternately connected with di η one or the other pole conductors, which are installed in an exhaust pipe through which the combustion products of hydrocarbons flow, means for introducing air into the exhaust pipe above the conductors and means for Regulation of the air introduction means.

Each of said current conductors consists of a conductive metal grid in the interior of said tube, wherein the grid is inserted perpendicular to the general flow direction of said exhaust gases.

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

These values are due to the need to achieve a good balance between a non-excessive obstruction of the tube cross-section and the coverage of a sufficient area by the electrical discharge device.

As a further possibility, said current conductors may consist of grids and / or plates and / or wires which are arranged so as to form flat layers or tubes lying parallel to the general direction of flow of said exhaust gases.

In this case, the space occupied by said conductors may be less than 35% and greater than 4%, as defined above, while the grid and / or plates and / or wires exceed a length no greater than ten times the tube diameter, can run parallel to the axis of said tube. In these two variants, the current conductors mentioned can be provided with tips which protrude at right angles from their surface.

The supply of voltage to the conductors must be such as to produce an electric field whose intensity is between 50 and 98% of the strength of the field which would cause a discharge in the gas at the operating temperature and operating conditions.

The mentioned means for introducing air into said pipe comprise a valve pipe and a pipe.

The mentioned means for controlling the means for introducing air consist of a sensor which analyzes the exhaust gas and transfers the results to a microprocessor which controls the pump and the valve for introducing the desired amount of air into the pipe above said conductors.

The present invention will now be described in more detail with reference to the accompanying drawings, which illustrate them by way of example only, but in no way limit the objectives and scope of the invention:

- Fig.1 shows the general schematic arrangement

Fig.2 shows a sectional view of an embodiment in which the conductors are arranged parallel to the general gas flow direction

Fig. 3 is a perspective sectional view of an embodiment in which the conductors are arranged perpendicular to the general gas flow direction.

Referring to Fig. 1, a pipe 2 is inserted into an exhaust pipe 1. Said line is completely with conductors (not shown), which are connected via the cables 4 and 5 to the voltage generator 3. A microprocessor 9 processes the signals relating to the composition of the gas analyzed by the sensor 6 and controls the valve 8 in the pipe 7 connected to the pipe 2 to introduce into the pipe 2 the desired amount of air supplied via the pump 10.

During operation, the sensor 6 analyzes the gas, in particular with regard to its content of CO, CO ₂ and O ₂ . The signals are routed to the microprocessor 9, which determines the amount of unburned material and soot, and hence the amount of air required for their combustion, based on previously established programs and other specific fuel consumption data, thus controlling the pump 10 and valve 8 ,

At the same time, a high voltage is built up between the current conductors by the voltage generator 3.

As the gas flows between the electrodes, the soot contained therein lowers the dielectric constant of the system, creating a strong spark that discharges onto the carbon particles and causes them to glow so that they are burned.

The enrichment of the gas with air and the attained high temperature enable the combustion of most carbon particles, whereas the production of mainly carbon dioxide is ensured. In this way, for example, the very low carbon monoxide content of diesel engine exhaust is maintained and in some cases even lowered.

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

In Fig. 2, the current conductors in the form of flat plates 12,12 'and 13 are used parallel to the general flow direction of the gas from left to right; the cables 4 and 5 feed the plates 12,12 'and 13, the cable 5 is passed through the insulated section 11 through the wall of the pipe 2. To assist in the generation of electrical discharges between the carbon particles and the plates themselves, the plates may have protruding tips 14.

In Fig. 3, the current conductors in the form of circular grids 12,12 '. 13 and 13 'used perpendicular to the general flow direction of the gas, they are fed via the cables 4 and 5, while they are insulated from insulators 11, which also allow the passage of the cables 4 and 5 through the wall of the pipe 2.

Of course, other forms and arrangements of the current conductors 12 and 13 may be used without adversely affecting the protection provided by the invention.

The present invention has been tested on the exhaust system of a diesel generator unit having an engine with displacement 3860cm ³ and a generator with an output of 4OkW at 1500U / min. The engine was operated at a speed of 1400rpm during the tests.

The ladder, as in Fig.3 in the form of a grid, were used at intervals of 3cm. The diameter of the four conductor pairs was 20% smaller than the inside diameter of the exhaust pipe. The voltage between the conductors of a pair of conductors was between 50 and 65kV. The space occupied transversely of each grid, as defined above, was 22% of the cross-sectional area of the tube.

The engine was operated for one hour for each test, and the solids removal device operated for a fixed period of time. At the same time samples were taken from the exhaust gases and the sample was passed through a weighed filter. After passing one cubic meter of gas, the filter was weighed again with its charge of solids.

The average amount of solids contained in the exhaust gas not treated according to this invention was 17.2 mg / m ³ with a variation between -3 and +4 mg / m.

The successive insertion of the grid pairs resulted in a decrease in the solids content of the treated gas, which was between about 15% (for a 52kV voltage grid pair) and approximately 70% (four grid pair and 6OkV voltage).

Claims (8)

Device for removing solids from exhaust gases and flue gases from an exhaust pipe, characterized by the corresponding combination of the following parts: - a bipolar high voltage generator ~ a number of conductors alternately connected to one or the other of the poles - Means for introducing air into the tube above the conductors - means for regulating the means for introducing the air. 2. A device for reducing solids in exhaust gases according to claim 1, characterized in that each of the conductors consists of a conductive metal grid, which is arranged in the interior of the tube perpendicular to the general flow direction of said exhaust gases. A device for reducing solids according to claim 2, characterized in that the ratio between the cross-sectional area of each grid and the pipe cross-section is less than 50% and greater than 10%. 4. A device for reducing solids according to claim 3, characterized in that the ratio is less than 35%. 5. A device for reducing solids according to claim 1, characterized in that the conductors have the form of grids and / or plates and / or wires, which are arranged parallel to the general flow direction of the exhaust gases. 6. Apparatus for reducing solids according to claim 3, characterized in that the ratio between the total cross-sectional area of said conductors and the cross-section of the tube is between 35 and 4%, said conductors being of a length at most ten times the diameter of the pipe extend parallel to the axis of said tube. A solids reducing apparatus according to claim 1, characterized in that each of the electric conductors has a large number of protruding tips. A solids reducing device according to claim 1, characterized in that the high voltage generator feeds said current conductors to form an electrical field having a magnitude between 50 and 98% of the strength necessary to provide a discharge between them To cause electrical conductors under operating conditions.