DE102008001161A1 - Device for accommodating e.g. ammonium carbonate, in generator in diesel engine of diesel fuel operated vehicle, has line guiding gas to catalyst and is tempered and/or heated, and container that is provided with two chambers - Google Patents

Abstract

The device has a catalyst (2) to which gases discharged from a generator is supplied. Parts heated with help of heating energy to an operating temperature are in direct contact with solid reducing agent. The generator has parts which come in contact with the gas. A line (35) guiding the gas to the catalyst is tempered and/or heated. The generator has a container (1) i.e. pressure container, with two chambers, where one of the chambers serves as a storage chamber for accommodating the agent and a heater i.e. heating plate. Other chamber accommodates the gas formed from the agent.

Description

State of the art

The Legislative and ever lower exhaust emission limits for diesel engines require very powerful Catalysts.

When using accumulator injection systems, diesel engines can be used to optimize fuel consumption through virtually unlimited choice of the determination of the injection time, injection profile, injection length and injection pressure, although very high NO _x values are formed. To counteract the increased NO _x emission, NO _x exhaust aftertreatment systems are used. The device according to the invention is designed for an SCR (Selective Catalytic Reduction) catalyst, which previously worked with a 32.5% urea water solution (Ad Blue).

The Use of a urea water solution as a reducing agent in An SCR catalytic converter requires elaborate reducing agent treatment or a longer one Treatment section. A urea water solution can only be used from a temperature> 180 ° C become. In case of incomplete urea decomposition By-products occur and form in the catalyst as well damaging in the dosing system Deposits. Furthermore have to in the vehicle constantly size Tanks are carried to receive the reducing agent and the driver is also forced, often to refill the reducing agent.

Disclosure of the invention

Under consideration the aforementioned problems it is advantageous to use alternative reducing agents with a higher storage density use. Ammonia gas is a cost-effective alternative can but not readily used due to environmental regulations become. For this reason, the use of reducing agent supplying substances in solid form more advantageous.

Can be used Ammonium carbonate, ammonium carbamate, urea, ammonium bicarbonate and other ammonia-supplying substances, since they have a high ammonia storage density and therefore opposite a urea water solution are more advantageous as a reducing agent.

The Use of this solid reductant makes a power supply in a closed container required in which the reducing agent is absorbed and in ammonia gas and corresponding additional Components are decomposed.

It is important to control the sublimation rate, avoid the insulating gas or particle layer in the individual components of a treatment plant or a generator and the consideration of the thermophoresis in the design of the corresponding system for forming the gas, in particular the NH ₃ gas.

at Use of a solid reducing agent is with the help of Principle of thermophoresis the sub and Resublimierung of the reducing agent in solved in an advantageous manner.

According to the teaching of thermophoresis, first the dust particles of the initially solid reducing agent contained in the gas, for example NH ₃ gas, impinge uniformly on all sides on a hot object, ie on the gas molecules. This process leads to Brownian motion. However, this movement is undirected. If the particle is in a temperature gradient, faster molecules will be found on the hot side than on the cold side. The particle thus experiences a net impulse in the direction of the cold side. The movement is still undirected, but over a long time the particle moves towards "cold". Thermophoresis is responsible for a phenomenon of deposition of small particles, especially on cold objects.

So far used generator systems with solid reducing agents have worked too long start-up times and the reducing agents used a low evaporation rate. These disadvantages arise through the poorly formed heat input, by the formation of a particle and / or gas insulating layer between the heater used and the reducing agent bulk material used.

Disclosure of the invention

According to the invention, it is proposed for this purpose that the parts heated with the aid of the heating energy to an operating temperature have direct contact with the solid reducing agent and / or at least the parts of the generator which have contact with the gas and / or a line leading the gas to the catalyst Help additional heat energy tempered or can be heated. As a result, the insulation layer and the associated poor heat coupling between the heater and reducing agent is avoided or greatly reduced. It is also advantageous that the dust particles formed in the sublimation of the reducing agent, which tend to deposit in the container or in the generator and on the heating medium or on the heater, are dissipated quickly. At least the parts of the generator which are in contact with gas and / or which conduct the gas to the catalyst NEN be warmed up so far, especially with the help of additional heat energy that the temperature of these parts is slightly greater than the process temperature in the generator. Since this cold zones in the generator can be avoided, deposits in the generator and the associated line to remove the gas are avoided.

Advantageous it is that the generator comprises a container with at least two chambers is equipped, with the first chamber as a storeroom for receiving the solid reducing agent and a heater and the second chamber for receiving the from the reducing agent formed gas, wherein in the upper region of the container at least the line is connected, with the help of which the gas to the catalyst guided becomes. Since the solid reducing agent rests directly on the heater, prevents the gases between heating surface and the bulk material the mentioned Insulating layer and thus form a thermal bridge, the heat input reduced from the heater to the reducing agent bulk material.

A additional possibility is according to a development the invention that the container as a pressure vessel is formed, which is equipped with the first and second chambers is, wherein the components within the first chamber a lower mass weight have as within the second chamber and / or that the components of the generator are cooled more slowly within the second chamber as the heater and / or the components of the generator in the range the heater. Because the parts of the generator, further away from the heater are, a bigger mass have as the heating or the parts in the heating, cool These parts are slower than the heater, so it is to this distant parts can not form deposits. The in the area of heating during the cooling process Deposits formed quickly when the generator is restarted dismantled again.

Advantageous It is also that the heating provided in the first chamber is designed as a heating element or as a heating plate and at least the heating plate many with the same or different distance from each other having arranged openings, being at least in one opening a riser is included above which directs the gas into the exhaust system and / or into the catalyst becomes. The openings provided in the heating plate also serve to that is between the surface of the Heating and the solid reducing agent can not form a gas buffer that would be insulating.

Advantageous it is also that at least the heating associated with the first chamber the opening has, over the gas formed in the first chamber into the second chamber and then led into the catalyst of the exhaust system. The direct connection the line in the field of heating and thus very fast removal the gases from the generator leads to prevent buildup of deposits on the walls of the generator. As the line for the removal of the gas in the immediate vicinity of the heater are the temperature differences between heating and the attached components, in particular the cable for removal of the gas, approximately equal. Thus, a few cold spots are formed, in which can deposit an insulating particle and / or gas layer. Further Is it possible, to heat the pipe.

According to one preferred embodiment of inventive solution after all provided that the heating or the heating plate in such a way Inner wall of the container adjoins and / or is connected to this, that they have a floor for the first Chamber or the storage space for receiving the solid reducing agent forms, delimits them to one side and that by far to the bottom or the heating of the first chamber, a second plate is provided, which limits the first chamber to the other side.

From special meaning is for the present invention that the first chamber after a Side limiting plate as a pressure plate for the solid reducing agent is formed and on the riser against the action of a force such Spring is adjusted. With the help of the adjustable plate, which as Pressure plate is formed, the solid reducing agent pressed firmly against the heater, so that the sublimation efficiency improves and at the heating surface can not form an insulating separation layer.

in the Connection with the construction and arrangement according to the invention It is advantageous that in the lower part of the container End element and / or brackets are provided for receiving of the container and serve at least one further heating element, by means of which at least the lower part of the container and / or the connecting element preheated or heated up. When commissioning the generator is his warming up shortened and the associated ones container parts heated very quickly to the process temperature of the generator. All the main components of the generator where the gas passes or passes are bigger, so Slowly cool them when the heater is switched off. This will cause deposits locked out. The deposits formed on the heater are not disturbing, because they are broken down very quickly when restarting the generator.

Further It is advantageous that below the heater one after the container below limiting end plate is provided with the bracket and / or the end element is connected and one in the final element provided cavity, wherein the end element to the Heating elements can be connected.

Besides that is it is advantageous that the container cylindrical or funnel-shaped is formed and with a gas metering valve, a pressure sensor and / or a thermosensor cooperates such that the gas metering valve upon reaching a certain pressure level or the critical Pressure ratio opens and the gas in the catalyst of the exhaust system leads. With the help of the gas metering valve the gas is metered or cycled into the catalyst. Is the container funnel-shaped formed, so the granules or the solid reductant while the sublimation phase very well to the heater and make sure that there is good contact with the heater.

Advantageous is also that the container and / or at least parts thereof and / or the line to the catalyst system at least partially from a coolant or warm-up room and / or an insulating means are surrounded. This will all important parts that come in contact with the gas at the start of the start of the generator so far heated that no insulating deposits can form. Only after the generator or container the desired operating temperature has, begins the conversion or sublimation phase of the solid reducing agent in a gaseous Status.

By the advantageous use of the coolant or warm-up room and / or insulating cool the parts that are not near the heating, after switching off of the generator so fast, so the deposits here be avoided and occur only in the heating area. The heating system can be made predominantly of aluminum and thus stores less heat, so that the heating cools faster in the resublimation phase than z. B the wall parts of the container.

The the cooling jacket supplied Cooling or warming agent has a temperature that is equal to or only slightly greater as the process temperature. Has the cooling or heating z. For example, not the desired process temperature, so is the corresponding facility with the help of a control device only switched on when the temperature is above the process temperature of the Generator is located. This as a cooling jacket described device part has a fluid which, depending on the process phase, z. B. in the starting phase, the generator thermal energy or supplies in the shutdown phase of the generator ensures that heat energy dissipated becomes.

The power supply to the generator can z. B. from the coolant of the coolant system be taken from the motor vehicle or other system. The Temperature of the coolant the coolant system of the motor vehicle is higher as the process temperature of the generator. It can also be from the warmer fuel or from the area of the exhaust system of the vehicle energy for the generator be derived to the essential parts of the generator, the be lapped by the gas, so far to heat up or in the shutdown phase of the generator yet a short time warmed up too let that be during of the sublimation and Resublimation process do not deposit particles on these parts can.

Based In the drawings, the invention will be described in more detail below.

embodiments

It shows:

1 a container for receiving and processing a reducing agent connected to a catalyst;

2 a partial perspective view of the generator with a container for receiving a solid reducing agent in longitudinal section;

3 a partial perspective view of the container in longitudinal section according to 2 with provided in the container heating and storage space for receiving the solid reducing agent;

4 a further variant of the integrated in a spare tire trough generator according to 2 , where for the sake of simplicity, only the container of the generator and the heater are shown here;

5 various parameters on the relationship between internal pressure of the container and the outflowing NH ₃ mass flow, taking into account the critical pressure ratio.

In the illustration according to 1 is a generator below also as a container 1 referred to an SCR catalyst 2 connected. The container 1 serves to receive a solid reducing agent such as ammonium carbonate NH ₂ CO ₂ NH ₄ .

When fueled with diesel fuel vehicle due to the emissions legislation in Europe and USA, among others the pollutant NO _x must be significantly reduced. A method for the Application is the selective catalytic reduction (SCR) process, in which the pollutant NO _{x is} reduced to N ₂ and H ₂ O with the aid of a reducing agent on a catalyst. The chemical reaction of the reduction is selective, which means that not all exhaust gas components are reduced, only the nitrogen oxides (NO, NO ₂ ). The reaction requires ammonia (NH ₃ ), which is added to the exhaust gas. The products of the reaction are water (H ₂ O) and nitrogen (N ₂ ).

The to the catalyst 2 connected generator has the container 1 in that for the catalyst 2 require reducing agents, as explained in more detail below, prepared and via a line 35 in the catalyst 2 is fed.

The container 1 is according to 1 and 2 cylindrically shaped and at its upper end with a flange 22 with an opening 38 ( 2 ) and at its lower end with a flange 27 with an opening 38.1 ( 3 ) provided for connecting each of a thermosensor, not shown in the drawing.

The container 1 has in its lower region adapted to its inner diameter circular end plate 31 on, the one above it pantry 14 for receiving the reducing agent downwards divides.

In a final element 30 can have additional heating elements 33 be provided, which can accelerate the heating process at the start phase of the generator.

The container 1 is formed double-walled approximately over its entire length and thereby has a heat storage space or coolant space 34 for receiving a coolant. The coolant space 34 is connected via lines not shown in the drawing with a coolant system of the motor vehicle or a separate cooling system in connection. With the help of the coolant, the container 1 set very quickly to a specific operating temperature at startup and end of the generator. At system cold start of the generator 1 this is independent of one in the container 1 arranged heating 4 through the separately connected additional heating 33 preheated, which is designed as a glow plug. The heating elements 33 can heat the generator so that when the generator is switched off, the heat in the generator remains stored for the longest time.

In the flange 22 is next to the thermosensor a gas metering valve 36 and a pressure sensor 37 provided, which cooperate in such a way that the gas metering valve 36 upon reaching a certain pressure level or the critical pressure ratio opens and the gas in the catalyst 2 an exhaust system 2.2 leads. Furthermore, also the gas metering valve 36 be heated to protect it against deposits.

The generator with the tank 1 is with at least two chambers 11 . 14 equipped, the first chamber 14 , as already mentioned, as a storage space for receiving the solid reducing agent and the heating 4 and the second chamber 11 serves to receive the gas formed from the reducing agent.

Above the end plate 31 is the circular hot plate 4 provided on the entire surface of a plurality of spaced apart openings 4.1 are admitted. The heating plate 4 is by far the end plate 31 arranged and forms the lower boundary of the first chamber 14 or the storage space for receiving the solid reducing agent. Below the end plate 31 is a cavity ( 32 ), which serves to reduce the masses in this area.

The heating plate 4 is attached to a bracket 29 firmly connected and has a concentrically arranged opening 4.2 in which is an upright riser 3 is attached. In the area of the upper end is on the riser 3 a trained as a biasing device circular plate or pressure plate 15 slidably mounted. The plate or pressure plate 15 forms with the heating plate the first chamber 14 or the storage space for receiving the solid reducing agent.

The on the riser 3 slidably arranged plate 15 is against the action of a force or a biasing mechanism according to the example according to 2 against the action of a spring 3.1 in the direction of the arrow 6 postponed. The feather 3.1 lies with its one end against the surface of the plate 15 and with its other end against a flange 3.2 of the riser 3 at.

The one in the first chamber 14 provided heating 4 , which is designed as a heating element or as a heating plate, has numerous with the same or different distances from each other arranged openings 4.1 . 4.2 on, at least in one opening 4.2 the riser 3 is added, about which the gas is the catalyst 2 the exhaust system 2.2 is supplied.

The container 1 is at the flange 27 firmly attached, at least partially in the container 1 extending end element 30 includes.

In the upper part of the container 1 is at least the lead 35 connected, with the help of which the gas to the catalyst 2 to be led. The cable is with a heating jacket or with an insulating agent 35.1 jacketed.

The heating system 4 or the heating plate is adjacent to an inner wall 28 of the container 1 or is connected to it so that it has a floor for the first chamber 14 or forms the reservoir for receiving the solid reducing agent. The heating system 4 borders the chamber 14 off to one side. The second plate 15 is at a distance to the ground or to the heating 4 provided and adjacent to the first chamber 14 to the other side or upwards.

In order to ensure a constant and metered mass flow of the reducing agent NH ₃ in the generator system and in the exhaust gas tract, it is advantageous that other framework conditions for the working process of the generator 1 be improved. This includes optimum heat transfer between engine cooling water in the coolant or warm-up room 34 and the generator so that the medium can be quickly adjusted to the required operating temperature. Advantageously, the existing heat energy in the vehicle can be used and thereby the overall efficiency of the motor vehicle can be improved.

The critical pressure ratio for sublimation of the medium is defined by the quantities P _a / P _m . P _a refers to that in the container 2 existing pressure P _mi and the pressure outside the container. The critical pressure can be determined by the formula P _crit = P _a / P _mi .

Here the dimensionless value of 0.55 applies.

Assuming the maximum possible exhaust gas back pressure or external pressure, the P _a value is 1.6 bar absolute and a tank internal pressure of P _mi is 2.93. The critical pressure ratio is then 0.55. If the pressure P _mi in the gas buffer chamber rises to a value above 3 bar absolute, then there is a critical pressure ratio and the sublimation process can take place. Furthermore, it is now possible with the help of the metering valve 36 the mass flow of NH ₃ to the catalyst 2 control and the required amount of the reducing agent NH ₃ in the catalyst 2 initiate.

The inclusion of the critical pressure ratio is very important, since only then the required amount of NH ₃ gas can be introduced metered into the exhaust tract, when the container internal pressure P _{mi is} equal to or greater than 3 bar. If the container internal pressure P _mi rises above a value of 3 bar, then according to 4 even with fully opened metering valve 36 the mass flow of NH _{3 are} no longer increased. Therefore, it is important for an energy-saving process flow that the container internal pressure P _mi does not fall below the value of 3 bar and does not exceed too much.

With the help of the container 1 connected thermosensor and the pressure sensor 37 the parameters of the process flow are detected and set the container internal pressure P _mi accordingly to the desired value of 3 bar. The tank internal pressure can be regulated by the heat energy supply. If the tank internal pressure rises above the value of 3 bar, the heat energy supply is throttled and, to this end, the heating energy of the heating plate 4 lowered and / or shut down the coolant circuit.

5 shows the influence of the pressure level up to 5 bar P _mi at variable throttle opening factors and the resulting NH ₃ mass flow. The three upper curves for the pressures 3, 4 and 5 bar also show that the NH ₃ mass flow can not be increased if the value 3 bar P _{mi is} exceeded.

Claims (11)

Apparatus for receiving a solid reducing agent such as ammonium carbonate or Ammoniakcarbamat, in a generator, which is supplied with the aid of heating energy for sublimation of the solid reducing agent energy, wherein in the sublimation of the solid reducing agent within the generator gases are produced, which removed from the generator and a catalyst ( 2 ), characterized in that the heated by means of the heating energy to an operating temperature parts have direct contact with the solid reducing agent and / or at least the parts of the generator which have contact with the gas and / or a gas to the catalyst ( 2 ) leading line ( 35 ) are tempered or heated. Device according to claim 1, characterized in that the generator comprises a container ( 1 ) containing at least two chambers ( 11 . 14 ), the first chamber ( 14 ) as a storage space for receiving the solid reducing agent and a heater ( 4 ) and the second chamber ( 11 ) is used to receive the gas formed from the reducing agent, wherein in the upper region of the container ( 1 ) at least the line ( 35 ), by means of which the gas to the catalyst ( 2 ) to be led. Device according to claim 1 or 2, characterized in that the container ( 1 ) is formed as a pressure vessel which is connected to the first and second chambers ( 11 . 14 ), wherein the components within the first chamber ( 14 ) a small one res mass weight than within the second chamber ( 11 ) and / or that the components of the generator within the second chamber ( 11 ) are cooled more slowly than the heater and / or the components of the generator in the heating ( 4 ). Device according to one of the preceding claims, characterized in that in the first chamber ( 14 ) provided heating ( 4 ) is designed as a heating rod or as a heating plate and at least the heating plate numerous with the same or different distance from each other arranged openings ( 4.1 . 4.2 ), wherein at least in one opening ( 4.2 ) a riser ( 3 ), via which the gas in the exhaust system ( 2.2 ) and / or in the catalyst ( 2 ). Device according to one of the preceding claims, characterized in that at least that of the first chamber ( 14 ) associated heating ( 4 ) the opening ( 4.2 ), over which in the first chamber ( 14 ) formed gas in the second chamber ( 11 ) and then into the catalyst ( 2 ) of the exhaust system ( 2.2 ) to be led. Device according to one of the preceding claims, characterized in that the heating ( 4 ) or the heating plate in such a way to an inner wall ( 28 ) of the container ( 1 ) and / or is connected to it, that it has a bottom for the first chamber ( 14 ) or the storage space for receiving the solid reducing agent, this delimits to one side and that at a distance from the ground or the heating ( 4 ) of the first chamber ( 14 ) a second plate ( 15 ), which is the first chamber ( 14 ) is limited to the other side. Device according to one of the preceding claims, characterized in that the first chamber ( 14 ) to one side limiting plate ( 15 ) is formed as a pressure plate for the solid reducing agent and on the riser ( 3 ) against the action of a force (spring 15.1 ) is adjusted. Device according to one of the preceding claims, characterized in that in the lower region of the container ( 1 ) a conclusion element ( 30 ) and / or mounts ( 29 ) are provided for receiving the container ( 1 ) and at least one further heating element ( 33 ), by means of which at least the lower part of the container ( 1 ) and / or the connecting element ( 30 ) is preheated or heated. Device according to one of the preceding claims, characterized in that below the heater ( 4 ) one the container ( 1 ) downwardly limiting end plate ( 31 ) provided with the holder ( 29 ) and / or the conclusion element ( 30 ) and one in the final element ( 30 ) provided cavity ( 32 ), wherein the end element ( 30 ) the heating elements ( 33 ) can be connected. Device according to one of the preceding claims, characterized in that the container ( 1 ) is cylindrical or funnel-shaped and with a gas metering valve ( 36 ), a pressure sensor ( 37 ) and / or a thermal sensor ( 38 ) cooperates such that the gas metering valve ( 36 ) on reaching a certain pressure level or the critical pressure ratio opens and the gas in the catalyst ( 2 ) of the exhaust system ( 2.2 ) leads. Device according to one of the preceding claims, characterized in that the container ( 1 ) and / or at least parts thereof and / or the line ( 35 ) to the catalyst system ( 2 ) at least partially from a coolant or warm-up room ( 34 ) and / or an insulating agent ( 35.1 ) are surrounded.