JP2015025448A - Exhaust after-treatment method of internal combustion engine, and internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new exhaust after-treatment method of an internal combustion engine, and to provide a new internal combustion engine.SOLUTION: In an exhaust after-treatment method of an internal combustion engine (10), in particular, an internal combustion engine having at least one stage of exhaust turbo supercharge through at least one exhaust turbocharger (13), and exhaust emission control through a SCR catalyst (14), and being operated with a heavy oil, the SCR catalyst (14) is disposed on the exhaust turbocharger (13) or at an upstream side of each exhaust turbocharger (13) in the exhaust flowing direction, sulfur dioxide is oxidized to sulfur trioxide at a downstream side of the SCR catalyst (14) and on the exhaust turbocharger (13) or at the upstream side of each exhaust turbocharger (13) in the exhaust flowing direction, and sulfur trioxide is condensed to sulfuric acid to be removed from the exhaust as sulfuric acid at the exhaust turbocharger (13) or at a downstream side of each exhaust turbocharger in the exhaust flowing direction.

Description

  The invention relates to an exhaust aftertreatment of an internal combustion engine as described in claim 1. The invention also relates to an internal combustion engine as described in claim 8.

  From Patent Document 1, an internal combustion engine is known that performs one-stage or two-stage exhaust supercharging and exhaust purification via an SCR catalyst. In this prior art, in one stage of supercharging, the SCR catalyst is arranged either downstream of the turbine of the exhaust turbocharger or upstream of the turbine of the exhaust turbocharger. In this prior art, in a two-stage exhaust supercharging with two exhaust turbochargers, the SCR catalyst is arranged between the two turbines of the two exhaust turbochargers. From this prior art it is already possible to bypass the SCR catalyst via a bypass line and guide the exhaust in the direction towards the turbine of the exhaust turbocharger arranged downstream of the SCR catalyst without passing through the SCR catalyst. Are known. The exhaust flow through the bypass line can be adjusted by a regulating device.

By using an SCR catalyst, it is already possible to reduce nitrogen oxides in the exhaust, in particular nitrogen monoxide and nitrogen dioxide, as defined, but in particular for internal combustion engines operated with heavy oil, additional SO ₂ There is a need to reduce emissions.

German Patent No. 102004027593

  An object of the present invention is to provide a novel exhaust aftertreatment method for an internal combustion engine and a novel internal combustion engine.

  This problem is solved by the method according to claim 1. According to the present invention, a catalyst for oxidizing sulfur dioxide is provided in the exhaust of an internal combustion engine that performs exhaust turbocharging upstream of the exhaust turbocharger, and the exhaust turbocharger or each exhaust in the exhaust flow direction. Downstream of the turbocharger, sulfur trioxide is condensed into sulfuric acid and removed from the exhaust as sulfuric acid and / or sulfate.

In accordance with the present invention, two means are particularly useful for reducing SO ₂ emissions in internal combustion engines operated with heavy oil: oxidation of sulfur oxides to sulfur trioxide upstream of exhaust supercharging and exhaust supercharging. Condensation of sulfur trioxide into sulfuric acid downstream is used in combination. Oxidation of sulfur dioxide to sulfur trioxide is performed using an SO ₂ oxidation catalyst. At this time, since oxidation in the oxidation catalyst is performed upstream of the exhaust gas supercharging, sulfur dioxide is converted to sulfur trioxide. In the oxidation, the exhaust has a high temperature and a high pressure, so that the SO ₂ oxidation proceeds quickly under optimum operating conditions, and there is no need to preheat the exhaust with a corresponding preheating device. Furthermore, the condensation of sulfur trioxide to sulfuric acid occurs downstream of the exhaust supercharging, where the condensation of sulfur trioxide to sulfuric acid is caused by the enthalpy drop by the turbine or each turbine of the exhaust supercharging, resulting in nitrogen oxides. Condensation of sulfur trioxide into sulfuric acid downstream of exhaust supercharging also takes place at optimal operating conditions and can therefore be done efficiently because it occurs at a temperature significantly lower than oxidation to nitrogen dioxide.

Toko of the process according to the invention can be combined with the SCR catalyst in the form of placing a SCR catalyst upstream of SO ₂ oxidation catalyst.

  Desirably, ammonia and / or an ammonia precursor that is converted to ammonia in the exhaust is supplied upstream of the SCR catalyst. By supplying ammonia and / or an ammonia precursor into the exhaust gas upstream of the SCR catalyst, conversion of nitrogen oxides in the SCR catalyst is efficiently performed.

According to a preferred first development of the invention, ammonia and / or an ammonia precursor are fed into the exhaust such that the feed ratio is NH ₃ / NO _X > 1, thereby entering the exhaust downstream of the SCR catalyst. Ammonia is present and is used to neutralize the sulfuric acid. According to a preferred second development of the invention, the exhaust partial stream branches off upstream of the SCR catalyst and downstream of the position where ammonia and / or ammonia precursor is fed into the exhaust, via the exhaust partial stream. Ammonia used for sulfuric acid neutralization can be supplied to sulfuric acid downstream of sulfuric acid condensation or to exhaust gas upstream of sulfuric acid condensation. Two preferred developments make it possible to neutralize the sulfuric acid produced by condensation, and the ammonia used is anyway required in the SCR catalyst. Thus, no separate basic component is required to neutralize the sulfuric acid produced by condensation.

Desirably, the exhaust partial stream exhaust is guided through additional SCR and / or hydrolysis catalysts. This, in part, ensures quantitative decomposition of the NH ₃ precursor in the hydrolysis catalyst, but also releases nitrogen oxides through the exhaust path containing NH ₃ necessary for neutralization of sulfuric acid. Is done.

  The internal combustion engine of the present invention is defined in claim 12.

  Preferred developments of the invention can be seen from the dependent claims and the following description. Embodiments of the present invention will be described in detail with reference to the drawings, but are not limited thereto.

1 is a diagram of a supercharged internal combustion engine according to a first embodiment of the present invention. It is a figure of the supercharged internal combustion engine of the 2nd Example of this invention. It is a figure of the supercharged internal combustion engine of the 3rd Example of this invention. It is a figure of the supercharged internal combustion engine of the 4th Example of this invention.

  The present invention relates to an internal combustion engine, in particular a marine diesel internal combustion engine operated with heavy oil. The invention also relates to an exhaust aftertreatment method for such an internal combustion engine.

An internal combustion engine operated with heavy oil has a special situation in which the fuel used by the internal combustion engine, that is, the sulfur content of heavy oil is high. As exhaust emission regulations become more stringent, it is necessary to further reduce sulfur oxide emissions. The present invention proposes a means or features that can be efficiently reduced SO ₂ emissions in an internal combustion engine which is operated at heavy oil.

  A first internal combustion engine 10 of the present invention shown in FIG. 1 has an engine 11 having a plurality of cylinders 12, exhaust supercharging via an exhaust turbocharger 13, and exhaust purification via an SCR catalyst 14. Yes.

  Exhaust gas generated in the cylinder 12 of the engine 11 due to combustion of fuel, particularly heavy oil, first passes through the SCR catalyst 14 for exhaust purification, and then is guided through the turbine 15 of the exhaust turbocharger 13 to obtain energy. At this time, by using the energy obtained by the exhaust gas expanding in the turbine 15 of the exhaust turbocharger 13, the supply air necessary for the cylinder 12 for fuel combustion becomes the region of the compressor 16 of the exhaust turbocharger 13. Is compressed.

  Ammonia and / or an ammonia precursor is supplied into the exhaust gas upstream of the SCR catalyst 14, and this ammonia precursor can be, for example, an aqueous urea solution. Such an ammonia precursor is converted into ammonia in the exhaust, and the SCR catalyst 14 requires this ammonia as a reducing agent in nitrogen oxide conversion.

  FIG. 1 shows an ammonia generator 17 that generates ammonia. In FIG. 1, ammonia is supplied into the exhaust discharged from the cylinder 12 of the engine 11 upstream of the SCR catalyst 14.

In the present invention, the exhaust sulfur dioxide is oxidized to nitrogen dioxide downstream of the SCR catalyst 14 and upstream of the turbine 15 of the exhaust turbocharger 13 in the direction of exhaust flow, that is, according to FIG. This is performed using an SO ₂ oxidation catalyst 18 disposed downstream of the SCR catalyst 14 and upstream of the turbine 15 of the exhaust turbocharger 13 in the flow direction. By disposing the SO ₂ oxidation catalyst in this way, SO ₂ oxidation is performed at high temperature and high pressure, that is, efficiently, and exhaust preheating is not required upstream of the SO ₂ oxidation catalyst 18.

Further according to the invention, condensation of sulfur trioxide to sulfuric acid takes place downstream of the exhaust turbocharger 13 in the direction of the exhaust flow, ie downstream of the turbine 15 of the exhaust turbocharger 13, and for that reason, in FIG. An H ₂ SO ₄ condenser 19 is disposed downstream of the turbocharger 13, that is, downstream of the turbine 15 of the exhaust turbocharger 13. The H ₂ SO ₄ condenser 19 is supplied with the exhaust gas from the turbine 15 of the exhaust turbocharger 13, and the H ₂ SO ₄ condenser emits exhaust gas on one side and sulfuric acid on the other side. _This is generated by the condensation of sulfur trioxide in the ₂ SO ₄ condenser 19 and collected in the container 20.

Due to the enthalpy drop due to passing through the turbine 15, the condensation in the H ₂ SO ₄ condenser 19 takes place at a significantly lower temperature than the oxidation in the SO ₂ oxidation catalyst. Therefore, the oxidation in the SO ₂ oxidation catalyst 18 and the condensation in the H ₂ SO ₄ catalyst 19 are performed under optimum process conditions.

Here, vanadium V and / or potassium K and / or sodium Na and / or cesium Cs and / or iron Fe and / or cerium Ce and possibly oxidation of these elements in the region of the SO ₂ oxidation catalyst 18 It is pointed out that things can be used.

  The proportion of vanadium is higher than 5%, preferably higher than 7%, most preferably higher than 9%.

  According to one preferred development of the invention, it is proposed to neutralize the sulfuric acid produced by condensation to form a salt of sulfuric acid.

Therefore, in the embodiment of FIG. 1, ammonia and / or an ammonia precursor can be supplied into the exhaust gas so that the supply ratio is NH ₃ / NO _X > 1, whereby the SCR catalyst 14 Ammonia is present in the exhaust downstream and can be used to neutralize the sulfuric acid produced in the region of the H ₂ SO ₄ condenser 19.

In contrast to this, the neutralization of sulfuric acid is carried out by using a bypass 21 as a partial exhaust stream upstream of the SCR catalyst 14 and downstream of the position where the ammonia generated in the ammonia generator 17 is supplied into the exhaust as shown in FIG. It is also possible to branch off and bypass the SCR catalyst 14, the SO ₂ oxidation catalyst 18 and the turbine 15 of the exhaust turbocharger 13 and mix the exhaust partial stream with the exhaust upstream of the H ₂ SO ₄ condenser 19. is there. At this time, ammonia that can be used for neutralization of sulfuric acid is present in the exhaust partial stream. In this connection, it is possible to guide the exhaust of the partial exhaust stream guided via the bypass 21 through the additional SCR catalyst 22.

Also in the modification of the present invention illustrated in FIG. 3, the exhaust of the partial exhaust gas is exhausted by the bypass 21 upstream of the SCR catalyst 14 and downstream of the position where ammonia generated in the ammonia generator 17 is supplied into the exhaust. 3 is used to neutralize the sulfuric acid produced in the region of the H ₂ SO ₄ condenser 19, but in FIG. 3, unlike FIG. 2, the exhaust partial stream is fed to sulfuric acid or a sulfuric acid circulation. Thus, it is not mixed with the exhaust stream leaving the turbine 15 upstream of the H ₂ SO ₄ condenser 19. In the variant of FIG. 3 also, a separate SCR catalyst 22 can optionally be assigned to the bypass 21 in order to guide the exhaust of the exhaust partial stream through the SCR catalyst.

  In the variant of the invention illustrated in FIG. 4, ammonia precursor rather than ammonia is supplied downstream of the engine 11 into the exhaust, which is converted into ammonia in the exhaust. The ammonia precursor can be, for example, an aqueous urea solution that is converted into ammonia, carbon dioxide, and water vapor in the exhaust.

  In the modification of FIG. 4, as in the modification of FIG. 3, the exhaust partial flow is branched by the bypass 21 upstream of the SCR catalyst 14 and downstream of the position where the ammonia precursor is supplied into the exhaust. 4 this exhaust partial stream is guided through the hydrolysis catalyst 23 to speed up or improve the conversion of the ammonia precursor to ammonia.

A controllable or adjustable throttle valve 24 can be used to adjust the exhaust partial flow guided through the bypass 21. Controllable or adjustable using a throttle valve 25 and 26, how much by subsequent bypass 21 the amount, SCR catalyst 14, SO ₂ oxidation catalyst 18, and an exhaust turbocharger partial flow which is guided through the hydrolysis catalyst 23 It is possible to control whether to bypass 13 and supply to the sulfuric acid circulation or how much of the exhaust partial stream is returned to the main stream upstream of the SCR catalyst 14.

Common to all the illustrated embodiments, the supercharged internal combustion engine 10 which is operated at heavy oil, upstream S0 ₂ oxidation catalyst 18 of the turbine 15 downstream and exhaust turbocharger 13 is provided in the SCR catalyst 14 By using this, it is possible to speed up SO ₂ oxidation at high temperature and high pressure.

Furthermore, in all the embodiments, an H ₂ SO ₄ condenser is provided downstream of the turbine 15 of the exhaust turbocharger 13 to condense sulfur trioxide as sulfuric acid and discharge it in the form of sulfuric acid.

  Desirably, the resulting sulfuric acid is neutralized, that is, neutralized with the ammonia required as a reducing agent in the region of the SCR catalyst 14.

As described above, ammonia used for neutralization of sulfuric acid is mixed with exhaust gas upstream of the H ₂ SO ₄ condenser 19 and downstream of the turbine 15, or mixed with sulfuric acid downstream of the H ₂ SO ₄ condenser 19. The

At this time, ammonia is prepared so that a sufficient amount of ammonia for neutralizing sulfuric acid is prepared in the exhaust gas without requiring a bypass line downstream of the SCR catalyst 14 and upstream of the H ₂ SO ₄ condenser 19. Can be prepared with a supply ratio> 1.

  On the other hand, the exhaust partial stream containing ammonia and / or an ammonia precursor is branched from the exhaust main stream upstream of the SCR catalyst 14 using the bypass line 21, thereby preparing ammonia used for neutralization of sulfuric acid. You can also.

In a particularly preferred embodiment (see FIGS. 2 to 4), the exhaust partial flow bypassing the SCR catalyst 14, the SO ₂ oxidation catalyst 18 and the turbine 15 by the bypass line 21 is in the region of the bypass line 21 and the SCR catalyst 22 and Guided through the hydrolysis catalyst 23. Ammonia generation in the exhaust can be supported via the hydrolysis catalyst 23. Nitrogen oxides in the exhaust partial stream can be reduced via a separate SCR catalyst 22 in the bypass 21.

When the SCR catalyst 22 is provided in the bypass line 21, sufficient ammonia NH ₃ is prepared downstream of the SCR catalyst 22 to neutralize the sulfuric acid H ₂ SO ₄ to ammonium sulfate (NH ₄ ) ₂ SO _4. Thus, for the exhaust partial flow, it is also true that the supply ratio in the exhaust partial flow is> 1.

10 internal combustion engine 11 engine 12 cylinder 13 exhaust turbocharger 14 SCR catalyst 15 turbine 16 compressor 17 ammonia generating apparatus 18 SO ₂ oxidation catalyst 19 H ₂ SO ₄ condenser 20 container 21 bypass 22 SCR catalyst 23 hydrolysis catalyst 24 throttle valve 25 throttle Valve 26 Throttle valve

Claims (17)

  In an exhaust aftertreatment method for an internal combustion engine, in particular an internal combustion engine operated with heavy oil, having at least one exhaust turbocharger via at least one exhaust turbocharger and an exhaust desulfurizer, sulfur dioxide upstream of the exhaust turbocharger In the direction of the exhaust flow, sulfur trioxide is condensed into sulfuric acid downstream of the exhaust turbocharger or each exhaust turbocharger and removed from the exhaust as sulfuric acid and / or sulfate. A method characterized by that.   The process according to claim 1, wherein a catalyst for selective catalytic reduction is provided upstream of the catalyst for the oxidation of sulfur dioxide.   The method according to claim 1, wherein ammonia and / or an ammonia precursor that is converted into ammonia in the exhaust gas are supplied upstream of the SCR catalyst in the exhaust gas. Since the ammonia and / or the ammonia precursor is supplied into the exhaust gas so that the supply ratio is NH ₃ / NO _X > 1, ammonia is present in the exhaust gas downstream of the SCR catalyst, which is sulfuric acid. The method according to claim 3, wherein the method is used for neutralization.   The exhaust partial stream is branched upstream of the SCR catalyst, and ammonia can be supplied to the sulfuric acid downstream of the sulfuric acid condensation via the exhaust partial stream, and this ammonia is used for neutralization of sulfuric acid. The method according to claim 3.   The exhaust partial flow is branched upstream of the SCR catalyst, and ammonia can be supplied to the exhaust upstream of the sulfuric acid condensation via the exhaust partial flow, and the ammonia is used for neutralization of sulfuric acid. The method according to claim 3.   The method according to claim 5 or 6, characterized in that the exhaust partial stream exhaust is guided through a further SCR catalyst.   8. A process according to any one of claims 5 to 7, wherein the exhaust partial stream exhaust is guided through a hydrolysis catalyst to hydrolyze the ammonia precursor. As active elements in the SO ₂ oxidation catalyst, vanadium, sodium, potassium, cerium, iron, claim 1 in which at least one element or oxide thereof selected from the group of cesium, characterized in that it is used 8 The method according to any one of the above.   10. A method according to any one of the preceding claims, characterized in that the proportion of vanadium is higher than 5%, preferably higher than 7%, most preferably higher than 9%. In order to carry out the method according to any one of claims 1 to 10, an internal combustion engine comprising at least one exhaust turbocharger via at least one exhaust turbocharger (13) and an exhaust desulfurization device. In an internal combustion engine having a supply, a catalyst (18) for oxidizing sulfur dioxide is provided upstream of an exhaust turbocharger (13), and the exhaust turbocharger or downstream of each exhaust turbocharger in the direction of exhaust flow. An internal combustion engine characterized in that an H ₂ SO ₄ condenser (19) is arranged in the exhaust gas so that sulfur trioxide is condensed in the form of sulfuric acid and removed from the exhaust.   The internal combustion engine according to claim 11, wherein a catalyst for performing selective catalytic reduction is provided upstream of the catalyst to oxidize sulfur dioxide.   13. The internal combustion engine according to claim 12, wherein ammonia or ammonia precursor that can be converted into ammonia in the exhaust gas can be supplied upstream of the SCR catalyst (14). Branches before the SCR catalyst (14) opened into the exhaust stream downstream of the exhaust turbocharger (13) or each exhaust turbocharger (13) and upstream of the H ₂ SO ₄ condenser (19). 14. Internal combustion engine according to claim 12 or 13, characterized by a bypass line (21). The internal combustion engine according to claim 12 or 13, characterized by a bypass line (21) branched into the sulfuric acid downstream of the H ₂ SO ₄ condenser (19) and branched before the SCR catalyst (14).   The internal combustion engine according to claim 14 or 15, characterized in that a further SCR catalyst (22) is arranged in the bypass line (21).   16. Internal combustion engine according to claim 14 or 15, characterized in that a hydrolysis catalyst (23) is arranged in the bypass line (21).

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