Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1997-10-06
2000-10-17
Griffin, Steven P.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
55318, 55321, 55342, 95 47, 95 54, 95130, 96 7, 96 8, 96 9, 96134, 96136, 96141, 96143, 96144, 423212, C01B 2100, B01D 5912, B01D 5926, B01D 4700, B01D 5000, B01D 900, B01D 5322, B01D 5302
Patent
active
061326933
DESCRIPTION:
BRIEF SUMMARY
This Application is the National Stage of PCT/DE 96/00643, filed Apr. 6, 1996.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for reducing pollutants, particularly nitrogen oxides, in combustion exhaust gases and a device for reducing pollutants.
2. Description of the Related Art
State of the Technology
Processes and devices for reducing pollutants in combustion exhaust gases in a combustion process that takes place with the supply of oxygen are known. For example, in internal combustion engines in motor vehicles, which use a fuel-air mixture that is ignited with the aid of an ignition means, the nitrogen is removed from the oxygen-nitrogen-air mixture (atmosphere) prior to supply into the internal combustion engine, as disclosed in DE-PS 44 04 681. For this purpose, the oxygen-nitrogen-air mixture is guided across a barrier that is impermeable to nitrogen. Consequently, combustion can continue with the supply of atmospheric oxygen removed from the atmospheric air, while the atmospheric nitrogen present in the atmospheric air is not supplied to the combustion process. The formation of nitrogen oxides during the combustion process is prevented, or at least drastically reduced.
Moreover, ceramic components are known that have a membrane comprising an oxygen ion-conducting material. Components of this type are used, for example, as so-called lambda sensors to determine the oxygen content in exhaust gases of combustion processes. It is known that these oxygen ion-conducting membranes have differing oxygen-conducting capabilities at different temperatures and under different pressure conditions.
So-called zeolites are further known from physical chemistry. They are distinguished by a structure having large, internal hollow spaces that are connected to one another by pores of defined size. These pores of defined size can be set in a range of a few tenths of an Angstrom by, for example, interspersed cations that move freely within the crystal grid and can be exchanged in solution. If such zeolites are acted upon by an oxygen-nitrogen-air mixture, due to the steric effect only the molecules whose diameters are smaller than the width of the pore opening reach the interior of the crystal structure. Thus, a sieving effect occurs. In the kinetic effect, certain molecules diffuse in and through the crystal structure faster than others, likewise causing a separating effect. If the oxygen-nitrogen-air mixture is fragmented, the separation of nitrogen and oxygen is based on the equilibrium effect. In this instance, different absorption forces are responsible for the stronger bonding of one component, for example nitrogen, than another component, such as oxygen.
SUMMARY OF THE INVENTION
The present invention provides a process of reducing pollutants, particularly nitrogen oxides, in combustion exhaust gases in a combustion process that takes place with the supply of oxygen, with the oxygen being removed from an oxygen-nitrogen-air mixture in a two-step process, characterized in that, in at least one step, the oxygen-depleted oxygen-nitrogen-air mixture is carried off via an outlet device provided with means that cause the outlet device to be more permeable to nitrogen than oxygen.
The process of the invention, offers the advantage that relatively little energy can be used to remove the oxygen from the oxygen-nitrogen-air mixture. In accordance with the invention, a fortification of oxygen is effected in the oxygen-nitrogen-air mixture in a first step (fortification step). In a subsequent, second step, the oxygen is removed, in pure or virtually pure form, from the oxygen-fortified oxygen-nitrogen-air mixture (removal or separation step). A result of the oxygen fortification in the first step is a lower energy consumption for heating the oxygen-nitrogen-air mixture during the second step, because no unnecessarily large quantity of nitrogen need be heated with the mixture. In addition, because of the oxygen fortification in the first step, the oxygen partial pressure of the oxy
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Dieterich Klaus
Franke Steffen
Gruenwald Werner
Griffin Steven P.
Medina Maribel
Robert & Bosch GmbH
Spencer George H.
Wells Ashley J.
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