CA1133232A - Exhaust gas purification process for diesel engines - Google Patents

Abstract

Process for purifying the exhaust gases emitted by an internal combustion engine of the Diesel type, characterized in that it comprises: a) the deposition on an entanglement of metallic wires, of alumina trihydrate from a solution of alkaline aluminate; b) calcining said alumina in order to give it a specific surface of at least 120 m2 / gram; c) placing said tangle of metal wires covered with alumina in the exhaust circuit of said engine; and d) bringing the gases into contact. exhaust with said entanglement of metal wires covered with alumina for a duration at least equal to 0.3 seconds at a temperature of at least 250.degree.C. The invention makes it possible to carry out an almost total afterburning of the unburned hydrocarbons, and a retention of carbonaceous particles, responsible for the opacity of the exhaust fumes; it applies to all types of vehicles, to site compressors, diesel generator sets, with a view to eliminating the nuisance caused by exhaust gases.

Description

3 ~ 32 The present invention relates to a purification process exhaust fumes from internal combustion engines Diesel type.
We know that there is between the exhaust gases emitted by petrol and diesel engines differences important in nature and composition.
In the first case, in addition to nitrogen, carbon dioxide and water vapor from the cornbustion hydrocarbons, carbon monoxide (4 to 6%), oxides nitrogen (500 to 2000 ppm), unburnt hydrocarbons (500 to 2000 2000 ppm), oxidized sulfur derivatives, and lead, the latter from plornb tetraethyl added as an antiknock.
In the second case, we find in the exhaust gases besides nitrogen, carbon dioxide and water vapor also from the combustion of hydrocarbons, a very low proportion of carbon monoxide (500 to 800 ppm, i.e.
almost a hundred times less than in the first case), oxides nitrogen (from SOO to 2000 ppm), unburnt hydrocarbons (from 100 at 500 ppm), oxygen (7 to 15%) due to the fact that ~ always injects a very large amount into the combustion chambers excess air, and very fine nut particles, due to 40 to 70 mg approximately per liter of fuel injected into the engine who are responsible for the characteristic color and opa cited fumes emitted by the exhaust.
The exhaust fumes from diesel engines constitute for the environment a serious nuisance due to the nor ~ re considerable and rapidly increasing number of vehicles Diesel engines (transport of goods and passengers) and the frequent use of air compressors or groups generators driven by diesel engines, used in premises closed or underground galleries.
And, although due to their low oxide content 23 ~
carbon and ~ e the absence of lead, their toxicity is relativernent weak, their foul odor due, in particular, to hydes, the presence of polycyclic aromatic derivatives including some are suspected of being carcinogenic, and the presence of carbonaceous particles that quickly cloud the atmosphere when the exhaust is in a confined environment, make essential devices for purifying these exhaust gases is lying.
The Applicant has discovered that it is possible in certain conditions, to take advantage of the properties of alumina deposited on a metal substrate having a large area, to purify engine exhaust Diesel, eliminating most of the unburnt hydrocarbons and carbonaceous particles, which are the two most important constituents more annoying.
It is known that aqueous aluminate solutions alkaline can, under certain conditions, decompose into alumina, which precipitates in the form of trihydrate A1203, 3H20, and in alkali hydroxide, either spontaneously or by adding sprouts that serve as a primer for the decomposition reaction.
These reactions are carried out, for example, in the process Bayer, which makes it possible to obtain alumina from bauxite pure for the production of aluminum by electrolysis igneous.
It is also known that certain physical forms alumina have catalytic and adsorbent properties which are used in many industrial operations.
More recently, following work to reduce the level of pollution from engine exhaust we have found that certain forms of alumina can not only play a catalyst role, but also adsorb most of the lead entrained as compounds ~ 33 '~ 3' ~
in the exhaust gases, ledi-t lead from the decomposition, in the engine combustion chambers, ~ es tetra lead drifts ~ alkyls added to the amelio fuel ~
rer s s <octane number ~, ie its resistance capacity uto ~ detonation.
It was found, and this is the subject of patents ~ americans 3.227.659, 3.231.520, 3.495.950, 3.362.783, in the name of TEX ~ CO Inc., that the catalytic and adsorbent properties of alumina were particularly effective when it was deposited on a metal substrate ~ bordered by a tangle fine yarn, such as metallic wool or straw metallic ~, the texture of this tangle being such that it offers only a low resistance to the passage of exhaust gases-and that it only decreases insignificantly makes it engine.
In French Patent No. 2,335,616, the application-~ resse described an improvement to the aluminum deposition processes mine on a metallic substrate making it possible to obtain continuously, and with a simultaneous regeneration of the aluminate liquor, very adherent deposits with excellent properties adsorbent.
However, if one attempts to use such repositories to purify the exhaust gases from diesel engines, Tate that the e ~ efficiency of the purification is very weak and, in particular, that the unpleasant smell and the opacity of the ~ umées ~ largely remain.
The invention therefore relates to a process epu ~
ration of exhaust gases emitted by a combustion engine internal Diesel type characterized in that it includes:
3G a) deposition on a wire enc ~ encetrement metallic, alumina tri.h ~ dratee from a solution alkaline aluminate;
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b) calcining said alu ~ nine a ~ ir ~ of give it a specific surface area of at least 120 m2f ~ ram ~ e (me-sure by the classic method B. E. Nitrogen adsorption a low temperature according to French standard AFNOR X 11.621) i ~) the setting up ~ udit enchevetrement de metal wires covered with alumina in the exhaust system said motor, and d) .contacting the exhaust gases with said enc ~ ey ~ trement of metallic wires of alumina for a duration at least equal to 0.3 seconds at a temperature at least 250. ~ C.
When these conditions are met, we see that, on the one hand, the imbrQlées hydrocarbons which are mixtures of excess air always present in the exhaust gases undergo an almost complete post-combustion and, in in all cases, at a rate sufficient to remove any odor ~ noticeable and that, on the other hand, the carbonaceous particles, responsible for the opacity of the fumes are retained in a . proportion at least equal to 70 ~ and up to 80%.
It turns out that, quite surprisingly, this post-combustion takes place in the absence of any catalytic element metallic lyser, whereas in the previous processes, in particular ~ ment those which are the subject of French patents 1,047,802 and 1,400,504r and US Patents 3,231,520 and 3,495,950, it was necessary to introduce, into the alumina, elements metal catalysts, such as copper, vanadium, chromium, manganese, platinum or palladium, which lost progressively their efficiency by the phenomenon known as poisoning ~>, which limited its lifespan so economically unacceptable.
The temperature at least equal to 250 ~ C, which is necessary to produce post-combustion of hydrocarbons ~ ~ - 4 -.
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unburnt, is obtained without dif ~ iculté, d ~ starting engine temperature. of exhaust being noxmale-ment superior ~ 500 ~~, this ~ ui amane the exhaust has a temperature can reach ~ ~ 380 ~ C when the engine works at full load.
. In the event that ambient conditions could cause significant cooling of the purifying device, it is possible to provide thermal insulation by any means known. '' . . .
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The specific surface of the alumina which must be at less equal to 120 m3 / g is obtained in fa ~ con known by a choice suitable conditions for drying and calcining the trihydrate A1203, 3H20 which is deposited on a metal substrate from the alkaline aluminate solution.
A gradual rise in temperature, from the ambient at 530-550 ~ C, allows to obtain such a specific surface.
It is also essential that the contact time between the exhaust gases and the purification device either sufficient and, in any case, at least equal to 0.3 seconds so that the double retention process of carbonaceous particles and post-combustion of the unburned hydrocarbons, can unfold in full. In practice, this duration is obtained by giving the purification device a volume related to the volume of exhaust gas emitted per second.
The following examples illustrate the invention without however limit it.
Example 1 We made a gas cleaning device exhaust from a 6-cylinder 149 kW diesel engine (about 202 CV) mounted on a fixed test bench, consisting of a cylinder 350 mm in diameter and 880 mm long, in which was introduced 8,500 grams of stainless steel wool ferritic with 17% chromium, composed of elementary strands substantially rectangular section of 0.1 x 0.4 mm, on which was deposited, from an alkaline aluminate solution, known way, 17 00 grams of alumina presenting, after ~ s calcina-tion, a BET specific surface of approximately 140 m / gram.
This cylinder was closed at both ends by two elements expanded metal ~ large mesh, for the sole purpose of immobi-read the metallic wool, and has been plugged into the diesel engine exhaust system.

3 ~ 3i2 Different tests have been carried out, corresponding to different engine loads, under respective powers 42, 79 and 149 kw ~ The consumption of the engine was around 217 grams of fuel per kilowatt per hour. ~ u diet maximum of 149 kW, the exhaust gas flow rate was 530 Nm3 / hour, and the exhaust temperature was 380 ~ C
about.
The duration of gas passage in the purification device tion, calculated according to their flow rate and the volume of said provision sitive, was approximately 0.46 seconds.
The exhaust gases exiting the purification device, whatever the engine load, no longer had or odor, appreciable opacity. Analysis has shown that the content in unburned hydrocarbons had gone from 200 ppm upstream of the filtration device less than 20 ppm downstream and that 77%
carbonaceous particles had been retained.
The duration for which the purification device retains its effectiveness is of the order of several thousand of hours. At the end of this time, the pressure drop in the exhaust system, which is around 100 mm of water, for the case taken as an example, has not increased significantly.
Example 2 We made a gas cleaning device exhaust emitted by a 150 Kw diesel engine, mounted on a locomotive engine intended to circulate in underground galleries, made up of two 350 mm cylinders in series diameter and 920 mm in total length, in which we have introduces 8900 grams of ferritic stainless steel wool with 17% chromium, composed of elementary section strands substantially rectangular of 0.1 x 0, ~ rnrn, on which we have deposited, from an alkaline aluminate solution, so known, 17000 grarnmes of alumina present, after calcination, a speci ~ i ~ ue BET surface of about 140 m / gram.
this cylinder was closed to the two ex ~ emitted by two elements of expanded metal with large meshes, for the sole purpose to immobilize the metallic wool, and was plugged into the Diesel engine exhaust system, with a flared diffuser at the inlet, intended to limit pressure losses.
The duration of passage of the exhaust gases in this purifier was, on average, 0.6 seconds.
Under normal operating conditions of the loco-tractor, the exhaust gases were analyzed at the point and at the outlet of the purification device. The results were following:
(they are given in parts per million) _ Enter exit carbon monoxide 1 ~ 5,150 nitrogen oxides 400 270 aldehydes 20 3 to 4 opacity index measured on the device 3 to 4 ~ 0.5 BOSCH
There is a slight decrease in the content ~ n Co, due to a partial oxidation of CO2, the oxide content nitrogen, and an approximately 85% reduction in opacity, measured the BOSCH device, which corresponds to a reduction, in a identical proportion, of the content of carbonaceous particles opacifying.
The content of aldehydes, mainly responsible of the offensive odor of smoke has been reduced in a proportion 80 to 85%.

Claims (2)

The achievements of the invention, about which the exclusive right of property or privilege is resold defined, are defined as follows: 1. Exhaust gas cleaning process emitted by an internal combustion engine of the diesel type charac-terrified in that it includes:
a) deposition on a tangle of threads metal, aluminetrihydrate from aluminum solution alkaline minate;
b) calcining said alumina in order to give a specific surface of at least 120 m2 / gram;
c) the establishment of said entanglement of metallic wires covered with alumina in the exhaust system said motor; and d) bringing the exhaust gases into contact with said tangle of metallic wires covered with alumina for a duration at least equal to 0.3 seconds at a temperature at least 250 ° C. 2. Method according to claim 1, characterized in that the exhaust circuit of step c) is calori-run away so as to maintain the temperature at which the process at least equal to 250 ° C.