DE102007022858A1 - Catalytic nitrogen oxide-reduction selecting device for use in internal combustion engine, has larger ammonia storage medium connected with smaller ammonia storage medium by reloading valve - Google Patents

Abstract

The device (1) has a reduction catalyser utilizing ammonia gas supplied by a storage medium. Two different size ammonia gas sources include a fixed ammonia storage medium (9) and a heater (10). The heater of a smaller ammonia gas source (16) is presented in the form of an electrical heater (13). The heater of a larger ammonia gas source (15) is presented in the form of a waste heat heater (14). The larger ammonia storage medium is connected with the smaller ammonia storage medium by a reloading valve (19). An independent claim is also included for a method for selective catalytic nitrogen oxide reduction in oxygen-containing exhaust gases of an internal combustion engine.

Description

The invention relates to a device for selective catalytic NO _x reduction according to the preamble of claim 1. The invention further relates to a method directed thereto.

State of the art

Ammonia is known as a selective and efficient reducing agent for the catalytic reduction of nitrogen oxides in oxygen-containing exhaust gases, for example of internal combustion engines. Because of its toxicity, as well as the safety issues posed by the storage of gaseous ammonia, processes have been developed whereby ammonia is only produced at the site of its use as a reducing agent by the hydrolysis of urea. However, the apparatuses aimed at were very extensive and complicated to control. To avoid their disadvantages, the EP 0 932 440 B1 Prior to storing ammonia by means of a solid ammonia storage substance in the vehicle, for which a sufficiently large-sized storage medium is provided in a special tank. The release of ammonia from the storage medium is done by heating or temperature increase of the storage medium. However, the amount of energy required to heat the storage medium is considerable, so that in particular in cold, stationary vehicles and in particular during cold start problems with the provision of the required heating energy can exist. In particular, the voltage stability of electrical motor vehicle electrical systems when using electric heaters is critical here, which can lead to undesirable effects in modern vehicles, which are controlled by a variety of electronic systems.

Disclosure of the invention

task The invention is an ammonia storage and a method for To provide release of ammonia, the disadvantages mentioned avoids.

For this purpose, a device for selective catalytic NO _x reduction in oxygen-containing exhaust gases of an internal combustion engine is proposed, with a reduction catalyst and using ammonia gas, which is provided by storage medium heating. It is provided that at least two different sized ammonia gas sources are provided, each having a solid ammonia storage medium and each having a heater. As a storage medium solid ammonia storage substances are used, from which ammonia is released by means of temperature increase. Suitable storage substances here are, for example, salts, in particular chlorides and / or sulfates, of one or more alkaline earth elements, for example MgCl ₂ , CaCl ₂ and / or one or more 3d sub-group elements, such as manganese, iron, cobalt, nickel, copper and / or zinc. The storage media are in this case formed in different sized memories, each forming an independent ammonia gas source. Here, the one ammonia gas source is significantly larger than the other formed. In cold start mode, that is, when the storage medium is cold and no or very little gaseous ammonia is present, the smaller source of ammonia gas is used, which can be heated using a smaller amount of energy to the desired and / or required temperature level. In this way, the required amount of ammonia gas is achieved in a relatively short time and with relatively little expenditure of energy, so that the catalytic NO _x reduction can be effective quickly.

In In another embodiment, the heater is the smaller one Ammonia gas source an electric heater. Electric heaters, As known from the prior art, are via the vehicle electrical system, optionally using reinforced batteries, easily realizable. Because the electric heater (initially) is only in operation for the smaller ammonia gas source, is the load of the electrical system compared to embodiments, as known from the prior art, low. To this Way can quickly and with little energy required Amount of ammonia gas are released.

In A further embodiment provides that the Heating the larger ammonia gas source an electric and / or a waste heat heating. Of course can also be the heating of the larger ammonia gas source, in particular only delayed in time after the smaller source of ammonia gas is switched on, be an electric heater, in particular, if their supply already has the three-phase generator of the vehicle and not solely from accumulators. Prefers but is a combination or an exclusive Use of a waste heat heating provided, so one such as those in internal combustion engines to a large extent produced waste heat uses, for example, over Heat exchangers, which are integrated into the cooling system are, or in other ways the waste heat of the internal combustion engine use.

In a preferred embodiment, the waste heat heater is a combustion exhaust gas heater. For heating the larger source of ammonia gas, the hot exhaust gas of the internal combustion engine is used in this embodiment, which has a suitable, appropriately sized exhaust gas heat exchanger and / or a heat exchanger circuit using a medium such as water or oil, the heating of the larger ammonia gas source is supplied. In this case, the electrical system is not charged.

In a further preferred embodiment, the larger ammonia storage medium is connected to the smaller ammonia storage medium via at least one reload valve. The process of thermally induced ammonia gas evolution from a solid ammonia storage medium is reversible in most solid ammonia storage media, especially salts. The system for reloading must be carried out according to the required operating conditions for reloading, depending on the storage medium used. In the event that NH ₃ is stored in MgCl ₂ in the form of Mg (NH ₃ ) ₆ Cl ₂ , the reloading, ie the absorption of NH ₃ by MgCl _2, for example, at a temperature of 25 ° C and a pressure of 4 bar. This pressure build-up to the required pressure level via the at least one reload from the larger ammonia storage medium towards the smaller ammonia storage medium and an admission of smaller ammonia storage medium with ammonia from the larger ammonia storage medium, which is available during its operation. This supply takes place in particular in times when the ammonia requirement in the exhaust gas system for NO _x reduction is low. For Mg (NH ₃ ) ₆ Cl ₂ desorption can be carried out at 5 bar and 200 ° C. Alternatively, the reloading of the smaller ammonia storage medium may be done even after the engine is turned off as long as the temperature in the larger ammonia storage medium is high enough. Of course, all embodiments are conceivable here, which can be realized in a technically meaningful manner and based on the ammonia storage media used.

Further, a method for selective catalytic NO _x reduction in oxygen-containing exhaust gases of an internal combustion engine is proposed, with a reduction catalyst and using ammonia gas provided by storage medium heating. It is envisaged that two different sized ammonia gas sources will be used, with the smaller ammonia gas source providing ammonia gas by heating during a start-up of the engine. During the starting process of the internal combustion engine, the ammonia gas is recovered by heating the ammonia storage medium of the smaller ammonia gas source, wherein the energy requirement is much lower than when heating the larger ammonia gas source. In particular, it is provided in this case that the smaller source of ammonia gas is chosen to be substantially smaller than the larger source of ammonia gas, for example in such a way that it provides just the amount of ammonia gas required in the starting process (or slightly more), after reaching a required operating temperature the internal combustion engine and the larger ammonia gas source is switched to those.

Further advantageous embodiments will become apparent from the dependent claims and combinations thereof.

Brief description of the drawings

The Invention will be described below with reference to an embodiment and explained in more detail by figures.

It demonstrate

1 a schematic representation of an embodiment (without reloading the smaller ammonia storage medium);

2 an embodiment with reloading of the smaller ammonia storage medium and

3 the system off 2 with an ammonia gas buffer tank.

Embodiment (s) of the invention

1 shows a device 1 for the selective catalytic NO _x reduction in oxygen-containing exhaust gases of an internal combustion engine 2 which an exhaust tract 3 with a reduction catalyst 4 downstream of flow. Downstream of the internal combustion engine 2 and upstream of the reduction catalyst 4 flows through a Ammoniakdosierstelle 5 an ammonia feed 6 for providing ammonia gas at the ammonia dosing station 5 for further treatment of exhaust gas of the internal combustion engine 2 in the reduction catalyst 4 , Upstream of the ammonia dosing point 5 is an ammonia metering valve 7 arranged, which is the influx of the required ammonia gas to Ammoniakdosierstelle 5 regulates, in particular via a not shown here, preferably electronic control unit. Upstream of the ammonia metering valve 7 are two ammonia gas sources 8th arranged, which provide the ammonia gas. These are two independently operable ammonia gas sources 8th that have different sizes. Both ammonia gas sources 8th each have an ammonia storage medium 9 and in each case one of these each heating heating 10 on. The ammonia gas sources 8th are here as a large Ammoniakgashauptquelle 11 one on the one hand and as a much smaller ammonia gas type source 12 educated. The ammonia gas type source 12 differs from the ammonia gas source 11 in that your ammonia storage medium 9 is much smaller than the ammonia storage medium 9 the ammonia gas main source 11 , The ammonia gas storage medium 9 the ammonia gas main source 11 is designed to be in normal operation of the internal combustion engine 2 provide required volume flow of ammonia gas and at the Ammoniakdosierstelle 5 for exhaust gas treatment in the reduction catalyst 4 applied. For this reason, it has a large ammonia storage medium 9 on top of that, by a powerful heater 10 acting as electric heater 13 , but preferably as waste heat 14 is formed, is heated. When heating the ammonia storage medium 9 ammonia gas is released. On the required volume flow of ammonia gas for normal operation of the internal combustion engine 2 and the reduction catalyst 4 is just this ammonia storage medium 9 and accordingly the heating 10 the exhaust main source 11 designed. The main ammonia gas source is thus a larger source of ammonia gas 15 while the ammonia gas type source 12 a smaller source of ammonia gas 16 is. The smaller ammonia gas source 16 serves to provide ammonia gas, in particular during the starting process of the internal combustion engine 2 and in the period after the startup process, in which the larger source of ammonia gas 15 their normal operation due to their slower heating (due to the volume and mass of their ammonia storage medium 9 relative to their heating 10 ) has not reached yet. For this purpose, the smaller source of ammonia gas 16 also a heater 10 namely an electric heater 13 which is designed to hold the relatively small volume of ammonia storage medium 9 heats up quickly, in particular much faster than the slower, larger ammonia gas source 15 the case is. In this way, ammonia gas can be provided very quickly, so that already directly in or shortly after the starting process of the internal combustion engine 2 an effective NO _x reduction can take place. The smaller ammonia gas source 16 is this via a control valve 17 downstream of the larger source of ammonia gas 15 and upstream of the ammonia metering valve 7 into the ammonia line 6 involved. In principle, here is a refilling by reversing the thermally induced release of ammonia gas from the solid ammonia storage medium 9 the smaller ammonia gas source 16 possible; The supply of ammonia gas then takes place from the larger source of ammonia gas 15 via the ammonia line 6 and now in the reverse direction operated regulating valve 17 , The smaller ammonia gas source as Ammoniakgasstartquelle is thus refillable, this refilling preferably takes place in those operating conditions in which the demand for ammonia gas for NO _x reduction is low.

The heating system 10 the larger source of ammonia gas 15 is preferred as waste heat heating 14 formed, wherein the waste heat via a heat exchanger 18 is fed and obtained for example from hot exhaust gas of the internal combustion engine via an exhaust gas heat exchanger, not shown here.

2 shows the same device 1 , in contrast to the in 1 described embodiment, the smaller exhaust gas source 16 on the one hand via the regulating valve 17 to the ammonia line 6 for supplying ammonia gas via the ammonia metering valve 7 to the ammonia dosing point 5 in the exhaust system 3 between internal combustion engine 2 and reduction catalyst 4 integrated and on the other hand via a reloading valve 19 with the larger source of ammonia gas 15 connected is. Again, all metering and regulating valves are preferably operated again via a not shown, preferably electronic control / regulating device. In this embodiment with a separate reloading valve 19 is it possible to use the regulating valve 17 To operate unidirectionally, ie such that ammonia gas is always from the smaller ammonia gas source downstream via the regulating valve 17 into the ammonia line 6 flows, but not the other way around. Refilling the smaller ammonia gas source 16 from the larger ammonia gas source 15 takes place via the reload valve 19 This reloading can also take place when both ammonia gas sources 8th are in operation.

3 shows the device 1 out 2 , where between the regulating valve 17 containing the ammonia gas stream of the smaller ammonia gas source 16 in the ammonia gas line 6 regulated, and the ammonia metering valve 7 containing the total at the ammonia dosing point 5 in the exhaust system 3 between internal combustion engine 2 and reduction catalyst 4 regulates the amount of ammonia gas provided for NO _x reduction, an ammonia gas buffer 20 is arranged. The exhaust buffer storage 20 becomes in normal operation of the larger ammonia gas source 15 from this via a storage loading valve 21 filled while its storage discharge valve 22 closed is. In this way, a certain amount of ammonia gas in the ammonia gas buffer 20 be kept (in gaseous state, while in the ammonia storage media 9 the ammonia gas sources 8th the ammonia gas is present until heated as described above). In this way, it is possible, ready in the startup process, so even before fully effective operation of the smaller source of ammonia gas 16 or supporting to this ammonia gas at the Ammoniakdosierstelle 5 to To provide NO _x reduction. The ammonia gas storage tank 20 can also be involved in another, technically meaningful position.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• EP 0932440 B1 [0002]

Claims (7)

Device for the selective catalytic NO _x reduction in oxygen-containing exhaust gases of an internal combustion engine, with a reduction catalyst and using ammonia gas which is provided by storage medium heating , characterized in that at least two different sized ammonia gas sources ( 8th ) are provided, each a solid ammonia storage medium ( 9 ) and one heating ( 10 ) exhibit. Device according to claim 1, characterized in that the heating ( 10 ) of the smaller ammonia gas source ( 16 ) an electric heater ( 13 ). Device according to one of the preceding claims, characterized in that the heating ( 10 ) of the larger ammonia gas source ( 15 ) an electric heater ( 13 ) and / or a waste heat heating ( 14 ). Device according to one of the preceding claims, characterized in that the waste heat heating ( 14 ) is a combustion exhaust gas heating. Device according to one of the preceding claims, characterized in that the larger ammonia storage medium with the smaller ammonia storage medium via at least one reloading valve ( 19 ) connected is. Device according to one of the preceding claims, characterized by at least one ammonia gas buffer memory ( 20 ). A method for selective catalytic NO _x reduction in oxygen-containing exhaust gases of an internal combustion engine, comprising a reduction catalyst and ammonia gas provided by storage medium heating, characterized in that two different sized ammonia gas sources are used, wherein the smaller source of ammonia gas during a startup of the Internal combustion engine provides ammonia gas by heating.