DE2129210A1 - Purification of exhaust gases - by catalytic reduction of nitrogen oxides,adsorption of hydrocarbon and catalytic oxidation - Google Patents

Abstract

The exhaust gases are (I) indirectly cooled to 150-600 degrees C (2) passed through a ceramic carrier for noble metal catalysts to reduce nitrogen oxides by the hydrocarbons or CO present, (3) indirectly cooled, opt. with cold fresh air, to a temp. above the dew pt. of water, (4) passed through a layer of granular active carbon to adsorb the hydrocarbons, and (5) passed through a catalyst layer to oxidise CO.

Description

Process for cleaning exhaust gases from internal combustion engines The invention relates to a method for cleaning the exhaust gases of internal combustion engines from nitrogen oxides, Residual hydrocarbons and carbon monoxide.

When burning hydrocarbons in internal combustion engines, Especially for driving motor vehicles, exhaust gases are generated which, in addition to carbon dioxide, Steam and nitrogen residues of unburned hydrocarbons, partially oxidized Contain hydrocarbons, e.g. aldehydes, as well as carbon monoxide and nitrogen oxides. Among the burned hydrocarbons are those of a carcinogenic nature, which, like carbon monoxide and nitrogen oxides, are extraordinarily physiological Are harmful.

The increase in internal combustion engines, especially the increasing density of motor vehicles in the densely populated industrial countries, the cleaning of the metor exhaust gases closes an indispensable necessity. For this purpose, there are purely different in the last 1 January Working methods developed and suggestions made. In practice it has happened so far none have been implemented because they all still have considerable shortcomings.

Most of the proposals consist in the catalytic implementation of the Residual hydrocarbons and carbon monoxide together with the residual oxygen of the Engine exhaust fumes on a catalyst mass at elevated temperature caused by the Waste heat the hot engine exhaust is maintained.

Carrier-free heavy metal oxides are usually used as catalytic masses, such as Cr2 03, Fe2O3, V205, MnO2 or the like, or these oxides or precious metals, such as Pt or Pd, used on ceramic substrates.

With such catalyst masses a complete one has hitherto been achieved Conversion of hydrocarbons and carbon monoxide to carbon dioxide achieved, the nitrogen oxides, however, were hardly converted and therefore remained in the engine exhaust gases. In addition to this disadvantage, these catalysts did not prove to be in the long run sufficiently thermally resistant. In addition, they only work in certain temperature ranges, which are not always effective in operation, especially by Qtto notors. This is especially true if the vehicles have only started a short time or have started at all can only be operated and stopped over short distances.

Despite these shortcomings, the principle described is still in place in the practice of engine exhaust gas cleaning and continued to work on its improvement been. So recently there has been a development of two-step working methods the catalytic engine exhaust gas purification endeavored. In part, their goal is a first Catalyst stage the nitrogen oxides through the reducing ones still contained in the engine exhaust To reduce residual hydrocarbons and carbon monoxide to elemental nitrogen and in the second catalyst stage the still verbil level residual hydrocarbons through Addition of secondary fresh air to oxidize completely to CO2 and H2O (German Offenlegungsschrift 15 94 699) But here, too, compliance @ makes itself certain for success temperature ranges necessary for catalytic conversions disadvantageous noticeable. For example, according to Report No: RL-49 M-70 of Esso Research andEngineering Co. of 4/4/1970 when using metallic catalysts a temperature range of 750 - 900 ° C must be maintained if the conversion of the nitrogen oxide succeeds and the catalyst should not be destroyed. Such a temperature is in the start-up state des, engine only reached after a certain time, while it is easy in continuous operation can be exceeded, whereby the catalyst is destroyed. The same applies also for the mode of operation of the catalyst of the post-combustion stage, which is a J \ nspring temperature of 200 - 300 ° C is required, while in continuous operation it is slightly destructive to the catalytic converter Temperatures of over 800 0C can occur.

The invention avoids these disadvantages.

In particular, compliance with such a discrete, in particular Temperature ranges that are difficult to achieve in the practice of Otto engine operation, be waived. The invention has a method that is gentle on the catalytic converter Operating state of the internal combustion engine is largely independent of the content and allows the economy of the operation of internal combustion engines through recovery increase in unburned hydrocarbons.

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After reaching the maximum load of activated carbon in hydrocarbons the engine exhaust gas flow is switched over and the activated carbon is regenerated. The regeneration the loaded activated carbon takes place with fresh air. The fresh air is expedient used, which are sucked in by the engine to the end of the combustion process anyway and loaded with fuel before or during Eintntt in the internal combustion engine got to. To increase the regenerative effect of the fresh air, this is preferred preheated to a temperature in the range of 100-3000C, preferably 150-200 ° C, what can be done in the simplest way 'by engine waste heat.

At the beginning of the regeneration of the loaded activated carbon adsorber the exhaust gas flow is switched to a second activated carbon layer, which regenerates beforehand had been.

Both layers alternate in the cleaning process switched to loading and regeneration. The change can be made by the company the internal combustion engine vorzugswese due to a certain number of engine revolutions or can be controlled by fuel consumption.

After passing through the activated carbon layer, the engine exhaust occurs, which is still Contains carbon monoxide residues, mixed with air if necessary, in a catalyst layer, preferably consisting of hopcalite mass, one in which the carbon monoxide becomes carbon dioxide is oxidized. The catalyst can be activated depending on the carbon monoxide content of the The gas considerably, possibly even by a few 100 ° C. The heat can for heating the fresh air required for the regeneration of the loaded activated carbon or useful for reoxidation of the oxidation catalyst for carbon monoxide be recycled. The one free of nitrogen oxide, hydrocarbons and carbon monoxide Engine exhaust can then be discharged into the atmosphere.

With the help of the invention it is possible to control the exhaust gases from internal combustion engines practically completely free of physiologically damaging components.

In addition, the process is extremely cost-effective, since the next age and setting of the internal combustion engine a better utilization of the fuel of 5 - 20%, on average 10%, takes place. The in preferred The embodiment or the invention used alternating two activated carbon layers can be designed small with frequent changes, so that one especially for Motor vehicles practically no significant spatial and weight-wise load arises.

The invention is illustrated using the attached scheme, for example explained in more detail.

The exhaust gas withdrawn from the internal combustion engine 1 through line 2 is achieved by indirect air or water cooling to temperatures of approx. 150 - 600 ° C cooled and enters the catalyst layer 4, where on a ceramic Carrier precipitated noble metal catalyst the nitrogen oxides by the residual hydrocarbons and the carbon monoxide of the exhaust gas are reduced to elemental nitrogen. On that the gas passes a heat exchange device 5, in which the cooling occurs approx. 50 - 700C takes place. From there it occurs via line 6 'via the appropriately placed Throttle valve 7 'in the AR.tivRohleadsorher 8', where the residual hydrocarbons adsorbed on activated carbon. In the next layer of -Hopcalite 9 ' the carbon monoxide still present in the exhaust gas is converted into carbon dioxide. The gas leaves this layer practically free of oxide, hydrocarbon and carbon monoxide and passes through the throttle valve 10 'set to passage via line 11 into the Free.

During the adsorption in the activated carbon adsorber 8 ', that of the Brendiraftmaschine 1 fresh air sucked in through line 12 after preheating by a heat exchange device 5 to a temperature of around 150 - 200 ° C through the throttle valve set to open 10 @@ for the purpose of regenerating the activated carbon adsorber loaded with residual hydrocarbons 8 "is inserted into the hot hopcalite layer 9", from which it is inserted into the activated carbon layer 8s' crosses. Due to the hot air, those in the previous switching phase The hydrocarbons absorbed by the activated carbon are desorbed and carried along with it the hot air through the put on passage throttle 7 ″ and line 13 via the fuel carburetor 14 into the internal combustion engine 1. Claims

Claims (8)

P a t e n t a n s p r ü c h e 1) Process for cleaning the exhaust gases of internal combustion engines, of nitrogen oxides, residual hydrocarbons and carbon monoxide, characterized in that 1) the exhaust gases initially indirectly to a temperature cooled in the range between 150 - 600 ° C, 2) for the purpose of reducing nitrogen oxides due to the residual hydrocarbons or carbon monoxide contained in the exhaust gases by a layer of a deposited on a ceramic substrate Noble metal catalyst are steered, 3) after further indirect cooling - if necessary through cold fresh air - to a temperature above the water vapor dew point brought, 4) to adsorb the residual hydrocarbons in a layer / granular Activated carbon and 5r introduced into a catalyst layer to oxidize the carbon monoxide will. 2) Method according to claim 1, characterized in that the Activated carbon layer adsorbed residual hydrocarbons through the combustion air desorbed urLrt are fed back into the internal combustion engine. 3) Method according to claim 2, characterized in that the combustion air is preheated before the desorption of the residual hydrocarbons. 4) Method according to claim 3, characterized in that the preheating is made by exhaust gas heat. 5) Method according to claim 1, characterized in? that after Loading of the activated carbon layer with residual hydrocarbons the exhaust gas flow into a second activated carbon layer is introduced. 6) Method according to claim 5, characterized in that during the loading of the second activated carbon layer regenerates the first activated carbon layer will. 7) Method according to claim 5 or 6, characterized in that the dan alternating loading and regeneration of the activated carbon layers by the company of the motor is controlled. 8) Method according to claim 7, characterized in that «iiz control takes place by the speed or the fuel consumption of the internal combustion engine.