PELLEGRINO LUIGI (IT)
TENCI PIER LUIGI (IT)
| EP1123728A1 | 2001-08-16 | |||
| US4195063A | 1980-03-25 | |||
| US3956185A | 1976-05-11 | |||
| US5145825A | 1992-09-08 |
| 1. | A device for reducing atmospheric pollution from exhaust gases, comprising a casing (2) having an inlet section (3) and an outlet section (4), and a catalytic cartridge (6), which comprises silica fibres and is housed inside the casing (2) and is set between the inlet section (3) and the outlet section (4), said device being characterized in that said catalytic cartridge (6) comprises at least a first and a second layer (14,15) of silica fibres of different density. |
| 2. | The device according to Claim 1, characterized in that said at least first layer and second layer (14,15) are joined together. |
| 3. | The device according to any one of the preceding claims, characterized in that the ratio between the density of said second layer (15) and the density of said first layer (14) is between 2.7 and 10. |
| 4. | The device according to any one of the preceding claims, characterized in that said first layer (14) consists of silica fibres with an Si02 content of at least 99 wt%. |
| 5. | The device according to the Claim 4, characterized in that said first layer (14) consists of silica fibres with an Si02 content of at least 99.9 wt%. |
| 6. | The device according to any one of the preceding claims, characterized in that said first layer (14) has a density of between approximately 15 kg/m3 and approximately 30 kg/m3. |
| 7. | The device according to any one of the preceding claims, characterized in that said second layer (15) consists of silica fibres with an SiO2 content of between approximately 94 wt% and approximately 98 wt%. |
| 8. | The device according to any one of the preceding claims, characterized in that said second layer (15) has a density of between approximately 80 kg/m3 and approximately 150 kg/m3. |
| 9. | The device according to any one of the preceding claims, characterized in that said second layer (15) contains A1203 in an amount of between 2 wt% and 4 wt%. |
| 10. | The device according to any one of the preceding claims, characterized in that the silica fibres constituting said first layer (14) are coated with at least one metal chosen from the group consisting of platinum, palladium and rhodium. |
| 11. | The device according to any one of the preceding claims, characterized in that the silica fibres constituting said second layer (15) are coated with at least one metal chosen from the group consisting of platinum, palladium and rhodium. |
The invention finds, however, application in the treatment of exhaust gases of various types, for example in the field of industrial, commercial and domestic heating plants.
Various devices have already been proposed with the purpose of reducing the content of pollutants of exhaust gases, in particular the exhaust gas of diesel engines.
The document EP-A-1123728 describes a device according to the preamble of the main claim, which comprises a cylindrical casing having an inlet for the exhaust gases to be purified, an outlet for the purified exhaust gases, and a tubular cartridge, which is housed in the casing and is set between the inlet and the outlet. The cartridge comprises mineral fibres comprising at least 70 wt% of silica (Si02) and at least one of the following catalytic metals: platinum, rhodium and palladium.
Even though the solution described in the document EP-A-1123728 has enabled good results to be obtained as regards the percentages of abatement of pollutant substances of exhaust gases, such as unburnt
hydrocarbons, nitrogen oxides and carbon oxides, it has been found that the solution known from this document does not enable an equally effective abatement of carbon particulate to be obtained for an economically advantageous length of time, when a fuel with a high sulphur content, i. e. , over 10 ppm by weight, is used.
The main purpose of the present invention is to provide a device which will enable chemical conversion of the carbon particulate contained in the exhaust gases to be obtained and which will be able to operate even with gas-oil with high sulphur content. More precisely, the purpose of the present invention is to provide a solution which will enable reduction, through chemical conversion, of carbon particulate, operating also with gas-oil containing up to a 500 ppm by weight of sulphur, and which will be capable of converting carbon particulate for economically acceptable lengths of time. In addition, the purpose of the invention is to provide a device that will be able to operate with low pressure drops. According to the present invention, the aforesaid purposes are achieved by a device having the characteristics forming the subject of the main claim.
One of the main advantages of the device according to the present invention is the capacity for containing the emission of sulphur trioxide (S03) within minimum values.
In addition, with the same device, by treating the gas recirculated towards the engine, thanks to the absence of carbon particulate and unburnt hydrocarbons, it is possible to reduce the amount of nitrogen oxides introduced into the atmosphere, achieving and exceeding the limits envisaged by the EURO 5 standards.
The invention will now be described in detail, purely by way of non-limiting example, with reference to the annexed drawings, in which: - Figure 1 is a schematic axial cross-sectional representation of a device according to the present invention; - Figure 2 is a cross section taken according to the line II-II of the cartridge of catalytic material used in the device according to the present invention; and - Figure 3 is a cross section taken according to the arrow III of the cartridge of the present device.
With reference to Figure 1, the number 1 designates a device that can be applied to the exhaust system of vehicles with diesel engines, for example lorries or buses, but it may be appreciated that the shape and dimensions of the device according to the present invention can be modified to adapt it to vehicles of another type, such as for example motor vehicles, machines for earth removal, generator sets, steam rollers, lift trucks, or else to heating plants of an industrial, commercial or domestic type.
The device 1 comprises a casing 2, for example of cylindrical shape, having a section 3 for the intake of the gas to be purified and a section 4 for the outlet of the purified gas. The casing 2 may moreover comprise a layer of thermally insulating material (not illustrated).
A catalytic cartridge 6 is housed in the central body 7 of the casing 2. In the embodiment illustrated in Figures 1 and 2, the cartridge 6 has a tubular shape.
The internal part 8 of the cartridge 6 is connected to the inlet section for intake of the gas 3.
The cartridge 6 bears at its front end (on the left in
Figure 1) a plate 9, which is connected with a fixing stay-rod 10, which engages at its end (on the right in Figure 1) to the radial wall 11.
The outlet section 4 has a manifold chamber 12, which communicates via an annular chamber 13 surrounding the cartridge 6 and through which the purified gas that has traversed the catalytic cartridge flows. The manifold chamber 12 communicates with the outlet section 4.
The catalytic cartridge 6, represented schematically in Figure 2, is made up of at least two layers 14,15 of silica fibre of different density. A first layer 14 is made of silica fibre with an Si02 content of at least 99 wt%, preferably of at least 99.9 wt%, even more preferably of at least 99.99 wt%, with a density of between approximately 15 kg/m3 and approximately 30 kg/m3. The first layer 14 is in direct physical contact, without any spacing, with a second layer 15 of silica fibres with an Si02 content of between approximately 94 wt% and approximately 98 wt%, with a density of between approximately 80 kg/m3 and approximately 150 kg/m3.
The silica constituting the layer 15 may also contain alumina (Al203) in a quantity of between 2 wt% and 4 wt%.
The ratio between the density of the second layer 15 and the density of the first layer 14 is hence between 2.7 and 10.
The first layer 14 and the second layer 15, alternatively to or in combination with one another, are made of silica fibres coated with at least one metal chosen from the group consisting of palladium, platinum and rhodium as catalytic elements.
The double-density configuration of the layers 14 and 15 of the cartridge of the present device enables
the chemical conversion of the carbon particulate, which has already reached 95% in the first layer 14, to continue and to stabilize at 99% in the second high- density layer 15.
The device according to the present invention has originated from the realization of the fact that only silica fibre with a purity of at least 99%, which constitutes the first layer 14, is able to convert carbon particulate even in the presence of high amounts of sulphur oxides, such as for example SO2, and that the second layer 15 with an Si02 content of between 94 wt% and 98 wt%, used for completing the cycle of chemical conversion as high-density catalytic medium, may last in time only if it is located in direct contact with the high-purity silica fibres.
Thanks to the physical combination and to the chemical composition of the two layers 14 and 15 constituting the cartridge, the reactions that determine the chemical reduction/conversion of the carbon particulate with carbon dioxide are balanced in favour of oxidation of the carbon rather than oxidation of the SO2. In a preferred embodiment, the cartridge 6 is made up of three layers 14,15 and 16 of silica fibre of different densities; the layer 16 may have the same composition and the same density as the layer 14.
The geometrical location inside the cartridge of the layer 15 is such that the speed of passage of the gas respects the time limits required, so that there will be conversion of the carbon particulate without, however, this causing a formation of sulphur trioxide S03, which would jeopardize the reduction in weight of the total particulate.
In particular, the present device oxidizes the carbon, which is the principal constituent of the carbon particulate of diesel engines, in a single
physical unit, without producing sulphur trioxide (S03) in any considerable amount. The oxidation of the carbon occurs principally through the oxygen adsorbed in the catalytic cartridge 6, which becomes available in the layers of silica 14 and 15 even with very low values of nitrogen oxides emitted by the engine, enabling the EURO 5 limits at least to be met, without any further reducing process obtained via the use of urea or via the addition of hydrocarbons, such as for example the gas-oil deriving from a post-injection.
The process of oxidation of the carbon is triggered at low temperature, close to a 200°C, also thanks to the oxygen adsorbed in the layers 14 and 15, and proceeds even at high temperatures of up to 500°C and over, albeit in the presence of considerable amounts of sulphur and percentages of nitrogen dioxide even lower than 10% of the total nitrogen oxides.
The capacity demonstrated by the present device to oxidize carbon particulate even in the conditions referred to above renders the device usable even when it is employed for operation in a mine or in poorly ventilated environments; in fact, as is known, nitrogen dioxide is a strong irritant of the airways and eyes.
Finally, the double-density and double-chemical- composition cartridge, as described above, enables the pressure drop to be kept within particularly contained values, thanks to its high efficiency in reducing carbon particulate.
The catalytic cartridge 6 may be preceded by a device (not illustrated) consisting of bimetals that are able to keep by-pass holes open until the exhaust gas has reached the temperature of catalysis of the hydrocarbons in order to protect the cartridge from water condensation inside it at the first starting after a long period of inactivity of the vehicle.
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