Product for the depollution of exhaust gases, especially from an internal combustion engine, and method for the depollution of exhaust gases using said product

Abstract

A product for depollution of exhaust gas includes a mixture of an additive for treating particles and a reductant for eliminating nitrogen oxides (NOx). The reductant can contain ammonia or a compound generating ammonia by decomposition, or a hydrocarbon from a hydrocarbon-containing substance, oxygenated or not. The addictive for treating particles can be an additive for catalyzing particle oxidation.

Claims

1. A method for depollution of exhaust gas circulating in an exhaust line using a product for depollution of exhaust gas, the exhaust line comprising a catalysis means for selective nitrogen oxides (NOx) catalytic reduction, a particle elimination means and means for feeding the product into the exhaust line, the method comprising: determining the exhaust gas temperature, and feeding the product into the exhaust line when the exhaust gas temperature reaches a threshold allowing treatment of the nitrogen oxides by the catalysis means, wherein the product comprises a mixture of an additive for treating particles and a reductant for eliminating nitrogen oxides (NOx), wherein the reductant comprises ammonia, or a compound generating ammonia by decomposition, or a hydrocarbon from a hydrocarbon-containing substance, oxygenated or not, and the additive comprises an additive for catalysing particle oxidation.

2. The method as claimed in claim 1, wherein the product comprises at least one metallic compound.

3. The exhaust gas depollution method as claimed in claim 2, wherein the metallic compound is an organometallic compound.

4. The exhaust gas depollution method as claimed in claim 2, wherein the metallic compound is a metal selected from among the following elements: sodium, potassium, magnesium, calcium, barium, strontium, titanium, cerium, chromium, molybdenum, manganese, iron, rubidium, cobalt, rhodium, nickel, palladium, platinum, copper, silver, or a mixture of at least two of these elements.

5. The exhaust gas depollution method as claimed in claim 3, wherein the organometallic compound comprises ferrocene.

6. The exhaust gas depollution method as claimed in claim 2, wherein the metallic compound is an inorganic metallic compound.

7. The exhaust gas depollution method as claimed in claim 6, wherein the inorganic metallic compound is a compound selected from among: fluorides, chlorides, bromides, iodides, oxides, nitrates, sulfates, phosphates, hydrides, carbonates, nitrides, or a mixture of at least two of these compounds.

8. The exhaust gas depollution method as claimed in claim 1, further comprising feeding the product into the exhaust line on a regular basis.

9. The exhaust gas depollution method as claimed in claim 1, wherein feeding the product into the exhaust gas line comprises injecting the product into the exhaust gas line, and the method further comprises controlling the injected product flow rate as a function of the amount of NOx.

10. The exhaust gas depollution method as claimed in claim 1, further comprising combining, in a single element, the catalysis means for selective nitrogen oxides catalytic reduction and the particle elimination means in an SCR catalysed filter.

11. The exhaust gas depollution method as claimed in claim 1, further comprising positioning the catalysis means for selective nitrogen oxides catalytic reduction before the particle elimination means.

12. The exhaust gas depollution method as claimed in claim 1, further comprising positioning the particle elimination means before the catalysis means for selective nitrogen oxides catalytic reduction.

13. The exhaust gas depollution method as claimed in claim 1, further comprising arranging at least one additional catalyst in the exhaust line.

14. The exhaust gas depollution method as claimed in claim 1, wherein the exhaust line is of an internal combustion engine.

15. The exhaust gas depollution method as claimed in claim 1, wherein a selective catalytic reduction filter comprises the catalysis means for selective nitrogen oxides catalytic reduction and the particle elimination means.

16. The exhaust gas depollution method as claimed in claim 1, wherein the catalysis means for selective nitrogen oxides catalytic reduction and the particle elimination means are arranged in series.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other features and advantages of the invention will be clear from reading the description given hereafter by way of non limitative example, with reference to the accompanying figures wherein:

(2) FIG. 1 shows a plant using the product and the method according to the invention,

(3) FIG. 2 illustrates a first variant of FIG. 1, and

(4) FIG. 3 is another variant of FIG. 1.

DETAILED DESCRIPTION

(5) This exhaust gas depollution treating plant comprises an exhaust line 10 carrying exhaust gas from an internal-combustion engine 12, of a motor vehicle for example.

(6) The internal-combustion engine is understood to be a Diesel engine, but this does not rule out by any means all the other internal-combustion engines such as engines running on gasoline or gas.

(7) As can be better seen in FIG. 1, exhaust line 10 comprises, in the direction of circulation of the exhaust gas from inlet 14 near to exhaust manifold 16 of the engine to outlet 18 where it vents to open air, at least one means for capture and elimination of the particles present in the exhaust gas, as well as a means for reduction of the NOx also contained in this gas.

(8) Advantageously, but not necessarily, these means are combined in a single element better known as SCR catalysed filter or SCRF filter 20.

(9) Preferably, this SCRF filter 20 is arranged downstream from an oxidation catalyst 22 whose purpose is to treat the unburnt hydrocarbons and the carbon monoxide contained in the exhaust gas before the latter passes through the SCRF filter.

(10) This oxidation catalyst 22 is also intended to partly convert the nitrogen monoxide to nitrogen dioxide, the ideal case being an equimolar distribution among nitrogen monoxide and nitrogen dioxide at the SCRF filter inlet so as to maximize the efficiency thereof.

(11) The exhaust line comprises a means, preferably an injector 24, for feeding a mixture of an additive for particle regeneration and of a reductant for NOx elimination.

(12) This injector is arranged upstream from the SCRF filter and near to its inlet 26 so that this mixture can combine as homogeneously as possible with the exhaust gas before they are fed to the SCRF filter.

(13) As is generally well known, the line comprises a means 28 for determining the differential pressure between SCRF filter inlet 26 and its outlet 30.

(14) By way of example, this means comprises an upstream pressure detector 32 at SCRF filter inlet 26 which measures the exhaust gas pressure at this inlet, another detector 34, referred to as downstream detector, arranged at SCRF filter outlet 30, which measures the exhaust gas pressure at this outlet, and a calculation unit 36 for determining the pressure difference between the SCRF filter inlet and outlet. This allows the SCRF filter clogging rate due to the particles to be known.

(15) In a manner known per se, the exhaust line carries a temperature detector (not shown) arranged on the exhaust line, more particularly at the SCRF filter inlet, which allows to know at any time the temperature of the exhaust gas circulating in this line.

(16) Alternatively, logic and/or computer means can be provided, which allow to estimate at any time the temperature of the exhaust gas circulating in the line.

(17) This line can also comprise an NOx detector (not shown) arranged at the outlet of SCRF filter 20 which allows to know at any time the amount of NOx flowing from the SCRF filter.

(18) Similarly, logic and/or computer means can be provided, which allow to estimate at any time this amount of NOx.

(19) The mixture fed into the exhaust line by injector 24 is carried through a pipe 38 connecting this injector to a tank 40 containing this mixture. The mixture is circulated between the tank and the injector under the effect of a pumping means such as a metering pump 42.

(20) The mixture contained in the tank comprises an NOx reductant, which can be ammonia or a compound generating ammonia by decomposition, such as urea, or which can be a hydrocarbon from a hydrocarbon-containing substance, oxygenated or not, and a catalytic type additive for treating particles, more particularly an additive for catalysing the oxidation of these particles.

(21) The catalytic type additive for particle treatment can be a metallic compound.

(22) This metallic compound can be an organometallic compound, such as ferrocene for example. The metal of this organometallic compound can be sodium, potassium, magnesium, calcium, barium, strontium, titanium, cerium, chromium, molybdenum, manganese, iron, rubidium, cobalt, rhodium, nickel, palladium, platinum, copper, silver, or a mixture of at least two of these elements.

(23) This metallic compound can be an inorganic metallic compound, such as nickel chloride for example. More generally, this inorganic metallic compound can belong to the family of fluorides, chlorides, bromides, iodides, oxides, nitrates, sulfates, phosphates, hydrides, carbonates, nitrides, or a mixture of these compounds.

(24) For operation, the ECU that any engine is usually provided with knows at any time the exhaust gas temperature and the amount of NOx at the SCRF filter outlet.

(25) As soon as the exhaust gas temperature has reached a threshold allowing the NOx treatment by SCRF filter 20 to start, the mixture contained in tank 30 is fed on a regular basis to the exhaust line by injector 24 upstream from the SCRF filter.

(26) Advantageously, the amount of mixture injected into the exhaust line is substantially proportional to the formation of NOx and it is determined by the ECU.

(27) Injection of this mixture upstream from the SCRF filter throughout the particle filter loading phase allows intimate mixing of the catalytic regeneration additive and the particles within the SCRF filter. The combination of the catalytic activity of the additive and the intimate contact between the particles and this catalytic additive allows to lower the temperature at which combustion of the particles starts, so as to make it compatible with the temperatures usually encountered at the exhaust of engines, if need be after addition of a post-injection that oxidizes on oxidation catalyst 22 and generates a heat release at inlet 26 of the SCRF filter.

(28) The variant of FIG. 2 differs from FIG. 1 in that the SCRF filter of FIG. 1, which is made of a single element, is replaced by at least two exhaust gas treating means.

(29) One of the means is a SCR type catalyst 44 followed by another means which is a particle filter 46.

(30) In this configuration, injector 24 is arranged upstream from the SCR catalyst.

(31) On the other hand, as illustrated in the variant of FIG. 3, one of the means is a particle filter 46 followed by another means such as a SCR type catalyst 44.

(32) In this other configuration, injector 24 is upstream from particle filter 46.

(33) The exhaust line comprises, for the variant of FIG. 2 as well as the variant of FIG. 3, an injector 24 for the mixture described above which comprises an additive for regenerating the particles of the particle filter and a reductant for NOx elimination by SCR catalyst 44.

(34) This injector is arranged upstream from the exhaust gas treating means (SCR catalyst 44 or particle filter 46) that is the closer to oxidation catalyst 22.

(35) Of course, without departing from the scope of the invention, the exhaust line comprising SCRF filter 20 or the exhaust line comprising an SCR catalyst 44 and a particle filter 46 can comprise additional catalysts, for example an SCR catalyst in addition to the SCRF filter, and/or a clean-up catalyst, etc.