Exhaust gas after treatment device

Abstract

Embodiments relate to an exhaust gas after-treatment device with an exhaust line having an inlet for discharging the exhaust gas and a thermal reactor, which is arranged in the exhaust line and has a first, thermal reaction zone for the exhaust gas flow, where a mixing device is provided for admixing a reducing agent to the exhaust gas flow in the exhaust line, which is arranged between the inlet and the thermal reactor and where the thermal reactor has at least one second reaction zone for a catalytic reaction in the exhaust gas flow with the involvement of the reducing agent.

Claims

1. An exhaust gas after-treatment device, comprising: an exhaust line having an exhaust inlet for discharging an exhaust gas flow; a thermal reactor arranged in the exhaust line, the thermal reactor comprising: a first thermal reaction zone for a catalytic reaction in the exhaust gas flow; a second thermal reaction zone for a catalytic reaction in the exhaust gas flow; and a third reaction zone for a catalytic reaction in the exhaust gas flow, wherein the third reaction zone is between the first thermal reaction zone and the second thermal reaction zone; a mixing device arranged between the exhaust inlet and the thermal reactor, and connected to a control and/or regulation unit for admixing a reducing agent into the exhaust gas flow in the exhaust line; and at least one bypass line with a shutoff valve arranged therein, the at least one bypass line connected by a first end to the exhaust line downstream of a switching valve and by a second end to the thermal reactor between the first thermal reaction zone and the second thermal reaction zone.

2. The exhaust gas after-treatment device according to claim 1, wherein nitrogen oxides in the exhaust gas flow can be reduced by the catalytic reaction in the first thermal reaction zone and the second thermal reaction zone.

3. The exhaust gas after-treatment device according to claim 1, wherein the reducing agent includes urea and/or ammonia and/or a hydrocarbon.

4. The exhaust gas after-treatment device according to claim 1, wherein the first thermal reaction zone and the second thermal reaction zone comprise a surface structure with a coating.

5. The exhaust gas after-treatment device according to claim 1, wherein the thermal reactor has two openings and the openings are used alternately as an inlet opening or as an outlet opening for the exhaust gas flow depending on a switching status of the switching valve.

6. The exhaust gas after-treatment device according to claim 5, wherein the thermal reactor comprises a heater between the first thermal reaction zone and the second thermal reaction zone.

7. The exhaust gas after-treatment device according to claim 5, wherein the first thermal reaction zone comprises a first heat accumulator and the second thermal reaction zone comprises a second heat accumulator.

8. The exhaust gas after-treatment device according to claim 1, wherein the at least one bypass line is configured so that the first thermal reaction zone or the second thermal reaction zone can be bypassed by the exhaust gas flow.

9. The exhaust gas after-treatment device according to claim 1, wherein the shutoff valve is configured to shut off the at least one bypass line.

10. The exhaust gas after-treatment device according to claim 1, wherein the third reaction zone comprises a surface structure with a coating.

11. The exhaust gas after-treatment device according to claim 1, wherein the third reaction zone is heated.

12. The exhaust gas after-treatment device according to claim 11, wherein the third reaction zone is heated by an electrical heater.

13. The exhaust gas after-treatment device according to claim 1, further comprising a feeding device configured to introduce a fuel into the third reaction zone.

14. The exhaust gas after-treatment device according to claim 1, further comprising at least one temperature sensor arranged upstream and/or downstream of the third reaction zone.

15. The exhaust gas after-treatment device according to claim 1, wherein the control and/or regulation unit is configured to control and/or regulate at least one of: the mixing device, the switching valve, the shutoff valve, or a heating device.

16. The exhaust gas after-treatment device according to claim 15, wherein an at least one temperature sensor is connected with the control and/or regulation unit, and at least one of the following elements can be controlled and/or regulated based on an at least one measured temperature: the mixing device, the switching valve, the shutoff valve, or the heating device.

17. The exhaust gas after-treatment device according to claim 1, further comprising a fourth catalytic reaction zone between the first thermal reaction zone and the second thermal reaction zone.

18. A system comprising: a combustion engine; an exhaust gas after-treatment device coupled to the combustion engine, the exhaust gas after-treatment device comprising: an exhaust line having an exhaust inlet for discharging an exhaust gas flow; a thermal reactor arranged in the exhaust line, the thermal reactor comprising: a first thermal reaction zone for a catalytic reaction in the exhaust gas flow; a second thermal reaction zone for a catalytic reaction in the exhaust gas flow; and a third reaction zone for a catalytic reaction in the exhaust gas flow, wherein the third reaction zone is between the first thermal reaction zone and the second thermal reaction zone; a mixing device arranged between the exhaust inlet and the thermal reactor, and connected to a control and/or regulation unit for admixing a reducing agent into the exhaust gas flow in the exhaust line; and at least one bypass line with a shutoff valve arranged therein, the at least one bypass line connected by a first end to the exhaust line downstream of a switching valve and by a second end to the first thermal reaction zone of the thermal reactor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and features of the invention are illustrated with the help of the figures as well as the descriptions corresponding to them. Please refer to the Figures:

(2) FIG. 1 is a schematic representation of a first embodiment of an inventive exhaust gas after-treatment device together with a combustion engine; and

(3) FIG. 2 is a schematic representation of a second embodiment of an inventive exhaust gas after-treatment device together with a combustion engine.

DETAILED DESCRIPTION

(4) FIGS. 1 and 2 respectively present a combustion engine 10 purely schematically. The exhaust gas enters the exhaust line 3 through the inlet 2, where four different sections of the exhaust line 3 have been given the reference numbers 3a, 3b, 3c and 3d. The section 3a extends from the inlet 2 up to switching valve 9. The sections 3b and 3c each extend from the switching valve 9 to a separate opening 8 in the thermal reactor 4. (Only one of the openings 8 has been shown with a reference number for the overview.) The section 3d of the exhaust line 3 extends from the switching valve to a chimney or a similar provision (not shown), allowing the exhaust gas to flow into the opening.

(5) The thermal reactor 4 is essentially divided symmetrically into two parts. This makes it possible to let the thermal reactor 4 get flow in two directions, in which essentially similar flow conditions prevail.

(6) The switching valve 9 has at least two different switching positions. In a first switching position, the exhaust gas flow entering the switching valve 9 through from inlet 2 over the section 3a of exhaust line 3 is led into the thermal reactor through the branch 3b. The exhaust gas comes out of the thermal reactor and returns back to the switching valve 9 through the line 3c. The switching valve 9 allows the exhaust gas flow from 3c further to section 3d of the line through which the exhaust gas flows into the open. In the second switch position of the switching valve 9, the thermal reactor 4 flow is in the opposite direction. The flow in the exhaust line 3 will be in the sequence 3a, 3c, 3b, 3d.

(7) The switching valve 9 may have one or more intermediate positions, and both the openings 8 of the thermal reactor 4 can be actuated proportionately. If an intermediate position is designed to approximately 50% of the total flow, then the exhaust gas flow can practically bypass the thermal reactor 4, which may be beneficial if the entire thermal reactor 4 or its parts are about to be overheated or have already been overheated, because during the exhaust gas flow, the thermal reactor 4 is bypassed and thus no heat/energy is supplied to it any longer, and the thermal reactor 4 can cool off.

(8) The thermal reactor is arranged in an enclosure 11. The reaction chamber 5 arranged in the upper part of the thermal reactor 4 as shown in the figures forms the first thermal reaction zone.

(9) It is to be noted that the thermal reactor 4 need not be oriented as shown in the figure. For example, it can also be horizontally oriented. Also, the schematically represented design of the enclosure 11 with two parts is not absolutely necessary. The thermal reactor 4 can be arranged, for example, in a nearly tube-shaped enclosure 11 with a partition or such.

(10) Heat accumulators 12 are arranged symmetrically around the reaction chamber 5, which preheat the exhaust gas or store the heat arising in the reaction chamber 5, depending on the switching status of the switching valve 9. If, for example, the heat accumulator 12 on the right as shown in the figures is so much heated that the exhaust gas flow is not able to increase the temperature of the heat accumulator 12 further, then the switching state of the switching valve 9 can be changed. The heated heat accumulator 12 can then transfer heat to the exhaust gas flow, in order to preheat this for the reaction in the reaction chamber 5.

(11) At the same time, the other heat accumulator 12, which had served to heat the fuel exhaust gas flow in the previous switching state, is recharged, i.e. heated.

(12) In addition to the heating of the exhaust gas flow through the heat accumulator 12, feeding devices 17 are provided in both embodiments for the introduction of fuel into the reaction chamber 5. The fuel F required for this can be typically the same fuel F, which is used for the operation of the combustion engine. The type of the reservoir from which the fuel F is obtained is not important for the invention (example: Tank).

(13) In the embodiment according to FIG. 1, an additional electrical heating device 16 is provided.

(14) In addition, the thermal reactor 4 has two second reaction zones 7. For the catalytic reaction to be produced in the thermal reactor, a mixing device 6 is provided in the line section 3a of the exhaust line 3, through which a reduction agent is admixed to the exhaust gas. The reducing agent is an aqueous urea solution in these embodiments.

(15) In this embodiment, the mixing device 6 is designed as the mixing tube with an injector. Mixing setups can also be provided, which produce swirls downstream of the injector for causing a thorough mixing. Such mixing facilities can include vanes and louvers.

(16) Until the exhaust gas flow (with admixed reduction agent) enters the first of the two second reaction zones 7, the urea is dissociated to ammonia. In the second reaction zone through which the flow took place first, a catalytic reaction takes place, in which the nitrogen oxides in the exhaust gas flow react together with the ammonia to form molecular nitrogen and water.

(17) Thereby, the quantity of admixed reducing agent should be so regulated or controlled so that no more ammonia will be present when leaving the second reaction zone 7 through which the flow took place first. Otherwise, nitrogen oxides are produced again in the thermal, first reaction zone 5. It is to be noted that the selective catalytic reduction takes place with the involvement of the reducing agent almost exclusively in the second reaction zone 7 through which the flow took place first, because, as mentioned above, no more ammonia is present when the exhaust gas flows through the other second reaction zone 7.

(18) This procedure results in an optimal thermal situation both for the selective catalytic reduction as well as for the regenerative thermal oxidation. Immediately after through-flow in the second reaction zone 7, the exhaust gas flow is heated in one of the heat accumulators 12 so that the temperature of the exhaust gas flow has the higher temperature that is necessary for the regenerative thermal oxidation in the first reaction zone 5. As mentioned above, this can be achieved by means of a heating device 16 and the injection of fuel by means of the feeding device 17.

(19) The second reaction zones 7 are characterized by a honeycomb structure construction with an appropriate coating for the described reaction.

(20) Both embodiments show additionally at least one third reaction zone 15, which concerns catalytic oxidation zones. These are also characterized by a honeycomb structure or such with appropriate coating.

(21) The heat accumulator 12 can be constructed, for example, out of a metallic honeycomb structure or ceramic bulk material.

(22) In the embodiment according to FIG. 1, the third reaction zone 15 is arranged inside the reaction chamber 5. In order to bypass that second reaction zone 7, through which the exhaust gas flows first, a bypass line 13 is provided. This connects the chambers in the enclosure 11, which are arranged between the reaction chamber 5 and the heat accumulators 12, with the section 3d of the exhaust line 3 leading into the open. Also, a shutoff valve 14 is provided in the bypass line 13. If it is detected that the temperature in one of the second reaction zones 7 is too high, the switching valve 9 can be switched, such that the gas flows through overheated second reaction zone 7 secondly and the shutoff valve 14 can be opened. By this, the exhaust gas flow bypasses the overheated second reaction zone 7, causing it to cool down. It is to be noted that efficiency of a catalyst for the selective catalytic reduction may be adversely affected by overheating.

(23) FIG. 2 shows an embodiment with an alternative arrangement of the third reaction zones 15 for the catalytic oxidation and a corresponding alternative arrangement of the bypass line 13.

(24) In both embodiments, a control and/or regulation device is provided, which performs the described operation of the thermal reactor 4 and other elements. For that, the control and/or regulation device 19 is connected with temperature sensors18, which measure the temperature of the exhaust gas flow at various points of the thermal reactor 4. It is to be noted that the figures show only one temperature sensor 18, so as not to affect the clarity of the figures. Identical temperature sensors 18 are provided at appropriate places of the other branch of the thermal reactor 4.

(25) The same applies to the feeding device 17. Even though this is indicated only once for the sake of clarity, it should be present at least in pairs, so that fuel F can be injected in each direction of through-flow into the reaction chamber 5.

(26) It should also be noted that various elements, which are present symmetrically in pairs in the thermal reactor 4, have been identified with a reference number only on one side of the thermal reactor 4. This is also the case for the sake of clarity in the figures.

(27) The control and/or regulation unit 19 is connected, apart from with the temperature sensors 18, even with the combustion engine 10, the mixing device 6, the switching valve 9, the shutoff valve 14 and the feeding device 17, and controls and/or regulates these elements accordingly. Again, for the sake of clarity, not all the connections have been shown.

(28) It is to be noted that the so-called ammonia slip in the embodiments presented is compensated in a natural way, since the provided catalytic oxidation zones 15 reduce excess ammonia.

(29) The invention is not limited to the embodiments presented here. For example, second reaction zones can be used, which allow ammonia slip specifically. This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.