CH656673A5 - PROCEDURES FOR THE PROTECTION OF CATALYST IN GAS POWER OF GASOLINE ENGINES ON POISONING by deposited POLLUTANT PARTICLE. - Google Patents

Description

656 673

2nd

PATENT CLAIMS

1. A method for protecting catalysts in the exhaust gas flow from gasoline engines from poisoning by deposited pollutant particles by means of electrostatic separation, characterized in that the electrostatic separation is carried out only at those temperatures of the exhaust gas flow at which the pollutant particles have a damaging effect on the catalyst.

2. The method according to claim I, characterized in that outside the harmful temperature range, the separated pollutant particles are removed by system reversal of the separating electrode.

3. The method according to claim 1 or 2, characterized in that no electrostatic deposition is carried out below a temperature of 200 ° C.

To reduce the content of harmful constituents in the exhaust gas from gasoline engines, it is known to subject the exhaust gas stream to catalytic afterburning on exhaust gas catalysts or to regulate the composition of the fuel-air mixture supplied to the engine by means of sensors, so-called>. Probes, which are fitted in the exhaust gas stream, which also have a catalytically active zone and react to the content of oxygen and unburned hydrocarbons.

When using fuels containing lead, however, these catalysts are inactivated within a short time by the pollutant particles in the exhaust gas, in particular lead, but also sulfur or soot particles. It has therefore already been proposed to remove these particles from the exhaust gas stream by electrostatic deposition (DE-AS 10 17 147 or DE-OS 21 39 775 and DE-OS 17 51 135).

The separation of the lead particles from the exhaust gas flow by means of electrostatic filters has not yet led to the desired success. Even in the case of filters which are very effective per se, particles which have already separated out are separated again from the filter surface at high exhaust gas speeds and with a heavy filter load, which particles then damage the catalyst. Regular removal and cleaning of the filter are therefore necessary.

The object of the present invention is therefore to find a method which works with an electrostatic filter and with which the catalysts located in the exhaust gas stream can be protected against poisoning by pollutant particles.

This object is achieved by the method described in independent claim 1.

It was found that the pollutant particles damage the catalyst only within a certain temperature range, outside this temperature range there is no or only very little damage. Because of this temperature dependence, the pollutant particles are only separated within the harmful temperature range. No separation takes place outside the harmful temperature range and the already separated pollutant particles are removed from the separating electrode by the exhaust gas flow and the shaking movements of the vehicle. The removal is particularly thorough if the deposition system is reversed and the deposited particles are repelled by the deposition electrode. These measures ensure that the filter surface is always regenerated, that there is no overloading of the filter and that a filter with a fresh surface is always present during the separation.

The pollutant particles are charged in the electrostatic field of a charge path upstream of the catalyst by means of a high-voltage source, as is customary in electrostatic particle separation with direct current and e.g. in Perry. Chemical Engineers Handbook, McGraw-Hill 1973, pages 20-103 to 20-115. The generation of the ionizing electric field advantageously takes place between a wire electrode which is concentrically arranged in the exhaust pipe and the exhaust pipe which acts as a counter electrode (separating electrode). The wire electrode can also be provided with bristles, spikes and the like to increase the effectiveness. With larger exhaust pipe diameters, several wire electrodes can also be used. The high voltage applied to the wire electrode is about 10 to 40 kV. The effect is too low below 10 kV, above 40 kV the risk of sparking increases significantly. The exhaust pipe serves as the counter electrode on which the pollutant particles are separated. The length of the separation section depends on the gas velocity, the applied potential, the exhaust pipe diameter and the particle mobility of the pollutant particles and can be calculated using the known formulas (e.g. Perry, loc.cit.).

Since the electrostatic charging of particles is temperature-dependent, the charging section is expediently arranged at a point in the exhaust line where the temperature of the exhaust gases does not exceed 800 ° C. and the exhaust gases are also hot enough to be connected to the exhaust gas catalytic converter or to the / “- Probe respond. The particles are preferably charged negatively, since higher potentials can be achieved with a negative charge. Any ozone formation that occurs has an additional positive influence on the smell and the composition of the exhaust gases.

The catalytic converter is arranged behind the separation section in the course of the exhaust line. The catalyst can optionally be charged electrostatically in the same direction with the pollutant particles in order to repel pollutant particles that have not been separated off from its surface.

Platinum, rhodium or palladium-based catalysts are usually used as catalysts. The temperature range in which the pollutant particles contained in the exhaust gas have a detrimental effect on the catalytic converter depends on the nature of the catalytic converter and must be determined on a case-by-case basis by trials, but this does not pose any difficulties for a person skilled in the art. In the case of conventional platinum-based exhaust gas catalysts, there is practically no further damage to the catalyst below an exhaust gas temperature of approximately 200.degree. Above this lower temperature limit, the deposition device can always be in operation. At very high temperatures, the deposition effectiveness drops sharply, but there is no further damage to the catalyst, so that it can be advantageous to avoid electrical flashovers to put the deposition device out of operation.

example

An exhaust gas stream from an internal combustion engine, in which gasoline with a lead content of 0.4 g / l was consumed, was passed through an exhaust pipe with an inner diameter of 9 cm. The exhaust gas flow had a volume of 900 mVh, which corresponded to a driving speed of about 60 km / h for a medium-sized car. In the exhaust pipe, a wire with a diameter of 0.2 cm was attached from a 90 cm long wire centered to the exhaust pipe. A DC voltage of - 13 kV was applied to the wire, the exhaust pipe had the potential OV. The length of the exhaust pipe from the start of the charge5

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stretch to the catalyst was 90 cm. The catalytic converter consisted of a platinum-based catalytically active layer and was attached to a honeycomb-shaped steel support.

The electrostatic separation of the pollutant particles was only carried out when the temperature of the exhaust gases was between 300 and 600 ° C. No separation was carried out outside of these exhaust gas temperatures, which were determined by a thermal sensor immediately upstream of the catalytic converter. Cyclic operation with standstill, idle, acceleration and driving phases was simulated (according to DIN 70 030 Part 1 to determine city consumption), as is also common in the practical operation of a motor vehicle.

When using the process according to the invention, practically no deterioration in the catalyst activity could be found even after 50 hours.

Without electrostatic deposition, the catalyst was badly damaged after only 10 hours.

If the electrostatic filter is switched on continuously, as is known from the prior art, the effectiveness of the filter is greatly reduced after about 15 hours due to overloading of the separating surfaces, which has been noticed by a significant deterioration in the catalyst performance.

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