Patent Application
20110258987
The invention relates to a vaporizer device which works together with an exhaust pipe carrying process exhaust gas, wherein an exhaust duct of the evaporator device opens into said exhaust pipe. The evaporator device has a burner comprising an injection device for fuel and air, a combustion chamber, and said exhaust duct. An exhaust gas aftertreatment device is inserted into the exhaust pipe downstream of the junction with the exhaust duct. The invention also relates to a method for the operation of such a vaporizer device.
Such a vaporizer device is known from DE 10 2004 048 336 A1. The vaporizer is inserted into the exhaust system of an internal combustion engine, wherein the internal combustion engine exhaust is discharged, and undesired emissions are reduced, by means of said exhaust system. In addition, a fuel feed device, an oxidative catalytic converter, and a particulate filter are arranged in the exhaust system. In order to improve the introduction of the fuel into the exhaust, a recirculation unit is provided which also functions as a vaporizer, which is connected to the exhaust system, and to which the fuel feed device is connected, such that the fuel is introduced into the exhaust via or through the recirculation unit. In this case, air can also be supplied to the recirculation device in addition to the fuel, and the resulting mixture in the recirculation device, which works as a burner, can be ignited and burned. Particularly, the amount of fuel can be adjusted for the purpose of regulating the power of the burner. The power of the burner must be determined in accordance with the working of the oxidative catalytic converter in such a manner that it is possible to carry out a regeneration of the particulate filter in all possible operating conditions.
In addition, vaporizers for an exhaust system of an internal combustion engine are known which directly obtain energy for the purposes of heating and vaporization from the process exhaust gas. Such vaporizers are not entirely functional in cases where process exhaust gas temperatures are low.
Finally, vaporizers for an exhaust system of an internal combustion engine are known which obtain energy for the purposes of heating and vaporization from electric heating devices. In many such cases, it is difficult or impossible, or is undesirable due to reasons of efficiency, to make the required amount of electrical energy available.
It is an object of the present invention to provide a vaporizer device and/or a method for the operation of such a vaporizer device which is expanded and/or improved with respect to the function thereof.
The present invention provides an introduction device for a vaporizable liquid is inserted into the exhaust duct of a burner. The corresponding method is characterized in that the burner provides sufficient thermal energy, wherein the lower limit thereof is prespecified by the provision of an amount of energy which is sufficient for the vaporization of an amount of vaporizable liquid which is larger than the amount of vaporizable liquid introduced into the exhaust duct.
The configuration according to the invention is characterized in that the vaporizer device can be used for any vaporizable liquid. As such, an incombustible liquid, such as an aqueous solution of urea for example, can be vaporized. In the event that the liquid is a flammable fuel, said fuel is preferably the same fuel which is injected by means of the supply device of the burner, for example diesel fuel.
However, in principle, it is also possible to use a gaseous fuel for the operation of the burner, for example natural gas. The separate introduction of the additional fuel via the introduction device offers the advantage that a partial volume of the total required fuel is supplied as a “secondary fuel volume” downstream from the burner. This is in contrast to the prior art, wherein an amount of fuel, for example required for a process, must be supplied in its entirety via the supply device of the burner. This secondary fuel volume is then ultimately prepared and/or burned in a completely controlled manner. The corresponding possible method variants are explained below together with the dependent method claims.
One implementation of the invention has an atomizer nozzle in the opening of the introduction device in the exhaust duct, particularly a pressure atomizer nozzle or an air atomizing nozzle. In the configuration having the pressure atomizer nozzle, the vaporizable liquid is atomized simply by means of the pressure of the vaporizable liquid. As an alternative, however, the introduction device can also be designed as an air atomizing nozzle. In this case, the air atomizing nozzle is operated in such a manner that a vaporizable liquid is introduced into the exhaust duct with a small amount of air. If the vaporizable liquid is fuel, in cases of normal operation of an air atomizing nozzle, 20 L air/min. and 2 cm3/min. of fuel would be supplied for the provision of a combustible mixture of fuel and air; however, up to 100 cm3/min of fuel would be supplied by the air atomizing nozzle operated according to the invention. Such a thick fuel-air mixture is not primarily combustible.
In a further embodiment, a venturi device is arranged in the exhaust duct near an opening of the introduction device. This effects a rapid mixing of the partial streams of exhaust gas and vaporizable liquid encountering each other.
In a further embodiment of the invention, the burner with the combustion chamber, the exhaust duct, and the introduction device are integrated into a housing, and the housing is adapted on the exhaust duct.
Consequently, a component is provided which can be installed on various different exhaust pipes. Here, the housing can be designed in an ideal case in such a manner that the same can be installed on the exhaust system, preferably near to the internal combustion engine in applications involving an internal combustion engine, for example directly behind the exhaust manifold or an exhaust turbo loader of the internal combustion engine.
In a further embodiment, the exhaust duct projects into the exhaust pipe with at least one port thereof. In this way, a good mixing of the converging streams of gas is ensured. For this purpose, the exhaust duct is preferably inserted concentrically into the exhaust pipe in such a manner that the port of the exhaust duct is arranged in the direction of the process exhaust gas stream, that is, for example, the internal combustion engine exhaust stream. This configuration achieves an increase in the velocity of flow of the process exhaust gas, which leads to a rapid mixing of the gas mixture, the same including the burner exhaust and the vapor (vaporized liquid), and the process exhaust. In this way, ignition of the gas mixture can be prevented if the process exhaust gas contains oxygen.
In order to further inhibit chemical reactions in the region of the inlet, appropriate auxiliary means can be provided which facilitate the same. Possible examples of such auxiliary means are, for example, a plate or a cone which is arranged before the port of the exhaust duct, wherein the tip of the cone is oriented facing the port of the exhaust duct. This configuration also provides a narrowing of the flow area in the region of the port, in addition or as an alternative to a further increase in the flow velocity, said narrowing being provided in the form of a venturi device or a venturi nozzle, for example. In other words, the configuration should quench a possible reaction between the process exhaust gas and the burner exhaust, the latter being prepared with vaporizable liquid.
In a further implementation of the invention, a gas feed device opens into the exhaust duct and carries a process exhaust. In this way, process exhaust gas is fed to the burner exhaust and the vaporizable liquid.
In this way, the burner exhaust is cooled down in a controlled manner (where the feed is configured upstream from the opening of the feed inlet device in the direction of flow), and in such a manner that sufficient energy is provided for the purpose of vaporizing the vaporizable liquid, although the combustion of the same is prevented (if the vaporizable liquid is fuel). However, the feed can also be configured in the region of the opening, or downstream from the opening in the direction of flow. A chemical reaction between the vaporizable liquid and the burner exhaust and/or the process exhaust gas can be either facilitated or inhibited depending on requirements by means of appropriately selecting the described auxiliary means. Particularly by means of influencing the temperature in the region of the feed inlet device, it is possible to generate substances in a targeted manner by means of reactions between the vaporizable liquid and the burner exhaust, wherein said substances facilitate desired reactions in the downstream catalytic converters.
In a further embodiment, the exhaust gas aftertreatment device has a catalytic converter which selectively catalytically reduces oxides of nitrogen, and/or has an NOx storage catalytic converter, and/or an oxidative catalytic converter, and/or at least one particulate filter. Each of the catalytic converters and/or the catalytic converter—particle filter systems can be operated with the vaporizer device according to the invention, either alone or in any possible combination thereof, as is explained in greater detail below in the context of the method for operation. In this case, the scope of the invention also includes a configuration wherein the oxidative catalytic converter is a multi-purpose catalytic converter particularly containing vanadium, the same also being suitable for catalytically facilitating the selective reduction of nitrogen oxides.
The constructive configurations described above are utilized in a reasonable manner for the purpose of implementing the further embodiment of the operating method according to the invention described below. As such, the burner is operated in a lambda range from 0.75 to 1.75, preferably at a lambda of 1. In addition, the burner is designed in such a manner that it can be operated in a power range up to 20 kW, preferably up to 15 kW, and most preferably up to 5 kW. It is one aim of the invention to operate the burner at the lower possible power, because particularly the air supply device required for the supply of (combustion-) air can then be designed with a relatively simple construction.
Furthermore, by means of the method according to the invention, and in general, vaporizable liquid (optionally along with the direct addition of a partial volume of the process exhaust gas) is vaporized by means of the burner exhaust gas, and is directed into the exhaust aftertreatment device together with the burner exhaust gas and the entire volume of the process exhaust gas, for the purpose of inciting the intended reactions at that point. For applications involving internal combustion engines which are operated with diesel fuel, NH3 which is generated from a vaporized solution of urea effects a chemical reaction in an SCR catalytic converter wherein the nitrogen oxide and the NH3 are converted to nitrogen and water vapor. In the event that, also for applications involving internal combustion engines which are operated with diesel fuel, the vaporizable liquid is a combustible fuel, the same is fed to an oxidative catalytic converter and a downstream particulate filter via the exhaust pipe together with the burner exhaust and the process exhaust, and is oxidized in the oxidative catalytic converter and/or in a catalyst-coated particulate filter. A particular advantage of this configuration is that the oxidation reaction therefore occurs only in the oxidative catalytic converter, and as a result, the temperatures required for the regeneration of the particulate filter are only generated at that point in the system. If the injected fuel were to be ignited at the point of introduction in the exhaust duct, as takes place in the system described in the prior art, this would be associated with a higher thermal load on the entire exhaust system, and significant heat loss would have to be compensated for by a higher quantity of fuel. A temperature of up to 650° C., for example, is generated by the oxidation of the vaporized fuel in the oxidative catalytic converter, and the same is required for the regeneration of particulate filters.
In a further embodiment of the invention, different vaporizable liquids, particularly fuel and aqueous urea solution, can be introduced into the exhaust duct via one or multiple introduction devices.
In cases where only one introduction device is included, the supply of vaporizable liquid is controlled in an alternating manner via a corresponding switching device, whereas no switching device is necessary in cases where two introduction devices are included. Such a case also normally includes the alternating supply of vaporizable liquid. This alternating supply can be used advantageously, for example, if the oxidative catalytic converter is a multi-purpose catalytic converter particularly containing vanadium, the same also being suitable for facilitating the catalytic reduction of NOx. In this case, the oxidative catalytic converter is alternatingly used for various different functions. However, it is also certainly possible to include an oxidative catalytic converter and a separate catalytic converter which effects a selective catalytic reduction of NOx.
In an further embodiment of the method, a partial volume of the total volume of combustible fuel, the same being introduced as the vaporizable liquid and then vaporized, is oxidized within the exhaust duct and/or in the place where the same is brought together with the process exhaust, releasing heat. In this way, the total thermal energy provision is increased, coincident with burner performance adjusted to a minimal setting, to such a degree that the startup of a catalytic converter is ensured. In order to initiate the activity thereof, that is, in order to start a catalytic reaction of the introduced, vaporized fuel, an oxidative catalytic converter must achieve a prespecified minimum temperature, for example 300° C. This temperature is achieved by means of the total sum of energy from the burner and the energy generated by the combusted partial volume.
In a further embodiment, the oxidized partial volume of the total volume of vaporized fuel is kept at least essentially constant, independent of the total volume of vaporized fuel. This embodiment also includes the discontinuation of the partial conversion of the fuel once a threshold volume of the partially converted fuel has been reached, at which point the total fuel volume is vaporized in its entirety. These differing effects are achieved by strict control of the combustion mixture ratio in the burner and/or by strict control, in a configuration utilizing an air atomizing nozzle, of the amount of atomizing air supplied to the air atomizing nozzle.
Additional influencing variables are the location of the attachment of the opening of the introduction device, and the feed of a partial volume of process exhaust gas (for the purpose of cooling the burner exhaust and consequently the vaporizable liquid), likewise with respect to the location of said feed.
Additional advantageous embodiments of the invention are described below with reference to the illustrations, which depict an embodiment, wherein:
For all embodiments, the vaporizer device has a housing 1, in which a burner 2, a combustion chamber 3, an exhaust duct 4, and an introduction device 5 for a vaporizable liquid are integrated. Here, the housing 1, likewise in all embodiments, is connected to an exhaust pipe 6 in such a manner that the exhaust duct 4, having a port 7, is inserted concentrically into the exhaust pipe 6, and the port 7 is arranged in the direction of the flow of the process exhaust gas flowing through the exhaust pipe 6.
The burner 2 has a supply device 8a for a gaseous or liquid combustible fuel, as well as a supply device 8b for air. The fuel and the air are mixed with each other in a suitable manner and introduced into the combustion chamber 3, for example via an air atomizing nozzle 9. The mixture is then combusted in the combustion chamber 3. For this purpose, the mixture in the burner 2 and/or the combustion chamber 3 is ignited in a suitable manner. In order to keep heat loss low, the combustion chamber 3 is inserted into the housing 1 and insulated as extensively as possible. The combustion chamber 3 has an exhaust opening 10 through which the burner exhaust enters into the exhaust duct 4, then flows along the exhaust duct 4 to the port 7. At this point, said burner exhaust mixes with the process exhaust gas flowing in the exhaust pipe 6, which in the embodiment is the exhaust of an internal combustion engine. The mixture of burner exhaust and air is adjusted in such a manner that the oxidation reaction is largely completed in the region of the exhaust opening 10 of the combustion chamber 3, and as a result, a heated stream of exhaust gas flows into the exhaust duct 4. The introduction device 5 opens with an opening 11 into the exhaust duct 4, preferably concentrically with respect to the exhaust duct 4. An atomizer nozzle 16 is arranged at the location of the opening 11, and vaporizable liquid supplied via the introduction device 5 is finely atomized by means of the same. The vaporizable liquid introduced in this manner is consequently heated and vaporized. A venturi device 12a is inserted into the exhaust duct 4 in the region of the opening 11. The venturi device 12a effects an additional mixing of the vaporizable liquid with the exhaust gas. A quenching device 13 is arranged in the region of the port 7, wherein said quenching device 13 is designed as a baffle plate in the embodiment and functions to mix the exhaust gases, the same flowing out of the port 7 and being mixed with the vaporized vaporizable liquid, with the process exhaust gas. At the same time, the quenching device 13 can be used to prevent ignition of the full mixture formed at this point. A venturi device 12b is installed in the exhaust pipe 6 in the region of the port 7 and/or the quenching device 13 for the purpose of increasing the flow velocity of the process exhaust gas.
The full mixture formed in the described manner is then fed to an exhaust gas aftertreatment device 17, shown schematically, which has a catalytic converter 18 which catalytically reduces nitrogen oxides, and/or has an NOx storage catalytic converter, and/or an oxidative catalytic converter, and has a particulate filter 19. A catalytic converter 20, shown schematically, can also be provided in exhaust duct 4.
The embodiment according to
The embodiment according to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 063 515.4 | Dec 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/008912 | 12/12/2009 | WO | 00 | 6/16/2011 |
