Method and apparatus for purifying exhaust gases

A method for purifying exhaust gases, the gases comprising combustible and NOx containing exhaust-gas constituents, from a lean-burn internal combustion engine, in an exhaust-gas converter (1), having a heat exchanger (12) with catalysts (15, 33) arranged in at least one inflow passage (6) and at least one outflow passage (7), in which incoming exhaust gas (2) flowing in is heated by heat exchange with exhaust gas flowing out of the heat exchanger, and the heat being supplied to the incoming exhaust gas, the method comprising the steps of:

• allowing the incoming exhaust gas (2) to enter an inlet region (3) through a plurality of parallel inflow passages (6) of the heat exchanger (12) without encountering any diversion or flow obstacle which is susceptible to blockage, and the incoming exhaust gas (2) flowing through the plurality of parallel inflow passages into a diversion region (9), the diversion region (9) being located opposite the inlet region (3), the incoming exhaust gas (2) being deflected in the diversion region (9) into a plurality of parallel outflow passages (7), each of which is situated between two inflow passages (6), the incoming exhaust gas (2) flows in the plurality of outflow passages (7) in an opposite direction to a flow direction of the incoming exhaust gas in the plurality of inflow passages (6), whereby heat exchange between the incoming exhaust gas in the plurality of inflow passages (6) and the incoming exhaust gas in the plurality of outflow passages (7) is promoted, the incoming exhaust gas (2) exiting the plurality of outflow passages (7) via an outlet region (4) located adjacent the inlet region (3), and the inlet region (3) and the outlet region (4) being sealed with respect to one another;
• feeding heat in a form of burner exhaust gas to the incoming exhaust gas by a burner (19) which is arranged in the diversion region (9), the burner (19) is electrically heated and is provided with at least one oxidation catalyst (31, 32), the burner (19) being operated with fuel and one or more of air and engine exhaust gas in such a way that the burner (19) supplies either an oxidizing or a reducing (substantially CO- and H2-containing) exhaust gas, the burner (19) being operated in one of a lean burn mode and a rich burn mode with one of air and portion of the lean engine exhaust gas as an oxidizing agent, the burner exhaust gas being fed into the diversion region (9), and during operation in the rich burn mode, the burner exhaust gas being used to at least one of oxidized at the oxidation catalyst to create additional heat and enhance NOx reduction at a NOx conversion catalyst (33),
• admixing the burner exhaust gas with the incoming exhaust gas which emerges from the plurality of inflow passages (6) and enters the plurality of outflow passages (7) together with the burner exhaust gas, and nitrogen oxides are removed from the incoming exhaust gas by at least one deNOxing catalyst (33) which is present in the plurality of outflow passages (7),
• setting the gas and fuel throughput of the burner exhaust gas by a control unit (52) in such a way that,
• during a cold start the catalyst (15, 33) is quickly heated to an optimum operating temperature and is held at the optimum operating temperature, and
• a reducing burner exhaust gas is generated at regular intervals to regenerate the deNOxing catalyst (33).

An apparatus for purifying exhaust gases having one of combustible and NOx containing exhaust gas constituents, from lean-burn internal combustion engines, the apparatus comprising:

• a parallel passage arrangement (16) formed from a monolith of a plurality of passages consisting of ceramic or metallic material with a rectangular passage cross section, every second row of the passages being used as an inflow passage (6) and every other row of the passages being used as outflow passage (7), the outflow passages (7) being closed off at an end side facing an inlet region (3) and being laterally open toward an outlet region (4) through continuous slots;
• a housing (5) with a hood (8) and openings for incoming and outgoing exhaust gas surrounding the monolith, the inlet region (3) being sealed off with respect to the outlet region (4) by a sealing device (17) between the monolith and the housing (8), and the arrangement of a purification component (15, 33, 34, 35) required for the conversion, being effected by coating passage walls, the monolith, which is used for the parallel passage arrangement (16), over the entire length or at least in the filter region (40), being made from a porous filter ceramic or a porous metal suitable for the particulate filtering, one or more of the inflow and outflow passages of the monolith, starting at the inlet region (3), being at least substantially gas tight or being made gas tight by one of a glaze or corresponding coating, over a length of heat exchange and catalyst regions (41, 42), the inflow passages (6) being closed off at an end face which is directed toward the hood (8), so that in the filter region (40) the exhaust gas passes from the inflow passages (6) into the outflow passages (7) and being filtered in the process, and the particulates which have been deposited on the filter being burnt off by an electrical heater which is integrated in the filter in a region of one of the hood (8) or by the hot fuel gas fed into the hood (8) from one of a thermal or catalytic burner (19).

An apparatus for purifying exhaust gases having exhaust-gas constituents which are one or more of combustible, contain NOx and are in particulate or soot form, the exhaust gases coming from lean-burn internal combustion engines, the apparatus comprising:

• an exhaust-gas heat exchanger (12), which includes a housing (5) and a plurality of inflow passages (6), arranged next to one another in the housing (5), and outflow passages (7) located between the inflow passages (6), one of the inflow passages (6) or the outflow passages (7) being closed on all sides at lateral surfaces (10, 11) and, together with the housing (5), forming the outflow passages (7) or inflow passages (6) located between them, the inflow passages (6) and the outflow passages (7) together forming a parallel-passage arrangement (16), and to achieve a constant distance between adjacent inflow passages (6) or outflow passages (7), either spacer elements (14) are arranged therein, or the side walls (10) of the inflow passages (6) are supported against one another on account of being profiled, and the housing (5) forms a diversion region (9) at a transition from the inflow passages (60) into the outflow passages (7),
• a catalytic burner (19), which is arranged in one of the diversion region (9) or a filter admission space (37) of the exhaust-gas heat exchanger (12),
• components (15, 33, 34, 35) for purifying one of the conversion, separation or storage of the exhaust-gas constituents which are one or more of combustible, contain NOx and are in particulate or soot form, the purifying components are arranged within the exhaust-gas heat exchanger (12),
• an inlet region (3) and an outlet region (4), which are formed by the housing (5),
• one or more of the inflow passages (6) and the outflow passages (76), at the filter admission space (37), being connected to the respectively adjacent passages (7, 6) and the housing (5) and sealed with respect to one another by one or more of welding, soldering, folding and a sealing device (17) in such a way that no leakage flow or only a negligible leakage flow occurs between the inlet region (3) and the outlet region (4).