Patent Application
20120051990
The present invention relates to an exhaust gas cleaning apparatus and a method for the cleaning of exhaust gas which originates from a combustion process. The exhaust gas cleaning apparatus and the related method is particularly suitable for removing unwanted combustion products like NOx, hydrocarbons and soot which is present in the exhaust gas. The present invention also relates to the use of a cold flame gas to remove NOx and particulate matter from an exhaust gas.
The cold flame is a phenomenon which has so far not received much attention. In a cold flame the fuel is partially oxidized in preheated air and the temperature is kept constant at about 450° C. The temperature is independent of air/fuel ratio and residence time. In the cold flame process, only 2-20% of the calorific value of the fuel is released, and this heat is used to evaporate the fuel, resulting in a homogenous gaseous fuel. Such a gaseous fuel is hereafter called a cold flame gas. A definition of a cold flame gas may then be a gas which is formed by partial oxidation of a hydrocarbon (fuel) in a mixture of air and hydrocarbon and wherein only a relatively small fraction of the air (5-10% of the air) is consumed in the oxidation.
A more complete description of the cold flame gas phenomenon can be found in the U.S. Pat. No. 6,793,693 B1.
During developmental work on the use of cold flame gas, carried out by the applicant, it was at first observed that the cold flame gas was able to remove carbon deposits from the reactor walls. As the applicant continued the work on applications utilizing the cold flame gas it was further discovered that the cold flame gas has oxidizing as well as reducing properties. The reason for this has not been firmly established yet, but is thought to be due to free radicals that are present in the cold flame gas, i.e. the partially oxidized, gaseous fuel.
Exhaust gas from combustion engines may contain impurities such as particulate matter (soot), NOx and incomplete combustion products, i.e. hydrocarbons (HC) and CO. The incomplete combustion products can be removed by an oxidation catalyst, while particulate matter can be removed from the exhaust gas with a particle filter. NOx can be removed catalytically from the exhaust gas if the exhaust gas is slightly reducing (as in an Otto engine) or otherwise by an NOx absorber (for instance for exhaust gas from a compression ignition engine).
For a complete treatment of the exhaust gas a particle filter, an NOx absorber and a oxidation catalyst are used today. After some time in use, the particle filter and the NOx absorber must be regenerated. Such a cleaning process requires two operations since the particle filter is regenerated under high temperature (about 600° C.) in an oxidizing environment while the NOx absorber is regenerated at lower temperatures in a reducing environment (about 500° C. with CO gas).
Hence, the objective of the present invention is therefore to provide a simplified apparatus and a simplified method for the treatment of exhaust gas from a combustion process.
More specifically, it is an objective of the present invention to provide a simplified apparatus and a simplified method to remove impurities like NOx, particulate matter and hydrocarbons from exhaust gas from a combustion process.
These objectives are achieved by the present invention as defined in the independent claims. Further embodiments of the present invention are defined in the dependent claims.
Impurities are in the description and in the claims defined to include soot particles, NOx (nitrogen oxides), hydrocarbons and other substances that can be removed (oxidized or reduced) by the cold flame gas.
There is provided an exhaust gas cleaning apparatus for cleaning of exhaust gas which originates from a combustion process in a combustion chamber where the exhaust gas cleaning apparatus comprises
The cold flame gas supply is further arranged in fluid communication with the exhaust gas flow path such that the cold flame gas can be injected into the exhaust gas flowing in the exhaust gas flow path and thereby, at least partly, remove impurities, like NOx and/or particulate matter (for example soot) and/or hydrocarbons, which are present in the exhaust gas.
The combustion chamber may be part of an internal combustion engine, for example a compression ignition engine (imprecisely called a diesel engine) or an Otto-engine. The exhaust gas is removed from the combustion chamber through an exhaust flow path like for example a conduit, a pipe, a tube or any other suitable means for conducting the exhaust gas. The combustion chamber may also be part of an incineration plant or a power plant based on a combustion process of for example coal or any other combustible material. Other areas of use of the present invention are also easily conceivable. The combustion chamber is the place wherein the combustion of the combustible material takes place producing the exhaust gas which needs cleaning. The combustion chamber may obviously take many different forms depending on the technical field of use, i.e. in an engine, an incineration plant, a power plant etc. If the combustible matter being combusted in the combustion chamber is not in liquid or gas form, which may be the case in an incineration plant or a power plant, the exhaust gas cleaning apparatus preferably includes feeding means (not shown in the figures) for feeding the combustible matter into the combustion chamber. In this case, the fuel tank preferably feeds hydrocarbon fuel to the cold flame gas generator only.
There is also provided a cold flame gas supply which can be connected to the exhaust flow path with a fluid line such that the cold flame gas may be injected into the exhaust gas flowing in the exhaust flow path. The fluid line is preferably provided with the necessary valve means such that injection of cold flame gas into the exhaust flow path can be regulated. The cold flame gas generator may be regulated by adjusting the amount of fuel and/or air which is fed to the cold flame gas generator. The valve means are preferably automatically controlled based on measurements of temperature and/or pressure and/or measurements related to the composition of the exhaust gas taken at one or several positions in the exhaust gas flow path.
The exhaust gas and the cold flame gas are mixed in a mixing chamber in the exhaust flow path. The mixing chamber can simply be a portion of the exhaust flow path itself as long as an efficient mixing of the exhaust gas and the cold flame gas is ensured. Alternatively, the exhaust gas flow path can be provided with a mixing chamber through which the exhaust gas flows and in which the cold flame gas and the exhaust gas is mixed. The mixing chamber can be configured as a conduit with an increased diameter or cross sectional area as compared to the same of the exhaust gas flow path. Alternatively, the mixing chamber can be configured as a larger container to which the exhaust gas flow path is connected. The cold flame gas is preferably injected into the exhaust flow path upstream the mixing chamber, or into an upstream end portion of the mixing chamber, relatively close to the point where the exhaust gas enters the mixing chamber.
In an embodiment of the invention there is provided mixing means in the mixing chamber, i.e. either in the exhaust flow path or in the mixing chamber, for enhanced mixing of the exhaust gas and the cold flame gas. Such mixing means can comprise a porous material through which the exhaust gas and the cold flame gas flow and are thereby getting mixed. The mixing means may also comprise blades or similar devices which are arranged in the mixing chamber and which are arranged such that the mixing means causes turbulence in the flow and thereby a more efficient mixing of the exhaust gas and the cold flame gas. A more even mix of exhaust gas and cold flame gas results in more efficient chemical reactions between components of the cold flame gas on one hand and the impurities in the exhaust gas on the other hand. The result is that a large part of the impurities can be removed from the exhaust gas by the cold flame gas.
The cold flame gas supply may simply comprise a cold flame gas generator which is arranged in fluid communication with the exhaust gas flow path. Cold flame generators will be known to a skilled person in the art and their construction are not explained any further here. The cold flame gas generator may be placed outside the exhaust gas flow path in which case there are separate supply fluid lines for air and hydrocarbon fuel to the cold flame gas generator. Alternatively, the cold flame gas generator is arranged within the exhaust gas flow path. A separate supply fluid line for hydrocarbon fuel is then provided. Oxygen for the cold flame gas generator is in this case preferably supplied through air in the exhaust gas, or alternatively through a separate supply fluid line for air providing air from outside the exhaust gas flow path. If the cold flame gas generator is arranged outside the exhaust gas flow path, the air supply may be preheated by using a heat exchanger which utilizes the heat energy contained in the exhaust gas to preheat the air.
The cold flame gas supply may also comprise a reservoir for cold flame gas where the reservoir can be arranged in fluid communication with the cold flame gas generator and the exhaust gas flow path through fluid lines. The reservoir itself may be configured as an inline conduit with a larger inner diameter than the fluid line connecting the cold flame gas generator and the exhaust gas flow path. The length of the reservoir conduit should be decided according to the desired storing capacity of the reservoir. Alternatively, the reservoir may be configured as a separate tank, which may be suitable when a larger quantity of cold flame gas needs to be stored. For both these alternatives, there is preferably provided a bypass fluid line such that the cold flame gas can flow directly from the cold flame gas generator to the exhaust gas flow path without passing through the reservoir. Preferably there is also provided valve means in the fluid lines, including any bypass fluid line, which regulates the flow of cold flame gas from the cold flame gas generator to the reservoir and/or to the exhaust gas flow path, and from the reservoir to the exhaust gas flow path. The exhaust gas flow path can therefore receive a controllable quantity of cold flame gas.
In an embodiment of the invention the reservoir comprises heating means such that the temperature of the cold flame gas which is stored in the reservoir is kept above the condensation point of the cold flame gas. The heating means may comprise a heat exchanger and fluid lines connecting the heat exchanger and the exhaust gas flow path such that the cold flame gas can be heated by the exhaust gas. Preferably there is also provided valve means in the fluid lines such that the temperature of the cold flame gas can be kept within a desired temperature interval, which is above the condensation point of the cold flame gas.
In a further embodiment of the invention the exhaust gas is used to heat the cold flame gas generator. This can be done in the same way as the cold flame gas reservoir is heated, as explained above.
Alternatively, it would be possible to heat the reservoir and the cold flame gas generator by other means, like for example one or more electric heaters.
In a further embodiment of the exhaust gas cleaning apparatus further comprises an exhaust gas return loop (EGR-loop) through which a part of the exhaust gas flowing in the exhaust flow path can be returned to the combustion chamber. The EGR-loop comprises a fluid line which preferably extends from the exhaust gas flow path downstream the mixing zone and to the combustion chamber. The fluid line is preferably provided with valve means such that the amount of exhaust gas which is returned to the combustion chamber can be regulated. Generally, up to 40% of the exhaust gas may be returned through the EGR-loop.
In a further embodiment of the invention the EGR-loop comprises a EGR-loop particle filter such that any particular matter like soot particles, which has not been oxidized by the cold flame gas, can be removed. In order to facilitate the regeneration of the EGR-loop particle filter, it is arranged in fluid communication with the cold flame gas supply. The fluid communication can be effected by fluid lines extending from the reservoir for cold flame gas or the cold flame gas generator to the EGR-loop particle filter. Preferably there is provided valve means in fluid line such that the flow of cold flame gas to EGR-loop particle filter can be controlled and regulated.
In a further embodiment of the invention the exhaust gas flow path is also provided with an exhaust gas flow path particle filter such that the exhaust gas flows through the exhaust gas flow path particle filter before the cold flame gas is injected into the exhaust gas flow path. At least a part of the particulate matter, like soot-particles, can then be removed from the exhaust gas before cold flame gas is injected into the exhaust gas. The exhaust gas flow path particle filter may further be arranged in fluid communication with the cold flame gas supply such that the exhaust gas flow path particle filter can be regenerated by the cold flame gas. The fluid communication can be effected by fluid lines extending from the reservoir for cold flame gas or the cold flame gas generator to the exhaust gas flow path particle filter. Preferably there is provided valve means in fluid line such that the flow of cold flame gas to exhaust gas flow path particle filter can be controlled and regulated.
For a more comprehensive explanation of how particle filters may be regenerated using cold flame gas, reference is made to the applicant's own international patent applications PCT/NO2008/000309 and PCT/NO2008/00310.
In a further embodiment of the invention an oxidation catalyst is provided in the exhaust gas flow path downstream the EGR-loop. The oxidation catalyst will remove the hydrocarbons and CO which were not oxidized by the cold flame gas. In order to regulate the temperature in the oxidation catalyst and to ensure that there is enough oxygen present for the oxidation process in the oxidation catalyst, the exhaust gas flow path may be provided with air supply means upstream the oxidation catalyst such that air is fed into the exhaust gas flow path before the exhaust gas enters the oxidation catalyst.
There is also provided a method for cleaning an exhaust gas which originates from a combustion process in a combustion chamber, where the exhaust gas is flowing in an exhaust gas flow path which is arranged in fluid communication with the combustion chamber. The method includes the steps of providing a cold flame gas, and injecting the cold flame gas into the exhaust gas flowing in the exhaust gas flow path. In this way are impurities, like NOx and/or particulate matter (for example soot) and/or hydrocarbons, at least partly, removed from the exhaust gas.
The combustion chamber may be part of an internal combustion engine, for example a compression ignition engine (imprecisely called a diesel engine) or an Otto-engine. The exhaust gas is removed from the combustion chamber through an exhaust flow path like for example a conduit, a pipe, a tube or any other suitable means for conducting the exhaust gas. The combustion chamber may also be part of an incineration plant or a power plant based on a combustion process of for example coal or any other combustible material. Other areas of use of the present invention are also easily conceivable. The combustion chamber is the place wherein the combustion of the combustible material takes place producing the exhaust gas which needs cleaning. The combustion chamber may obviously take many different forms depending on the technical field of use, i.e. in an engine, an incineration plant, a power plant etc.
In further embodiment of the invention the method may include the step of providing a mixing chamber through which the exhaust gas is flowing and injecting the cold flame gas such that the cold flame gas and the exhaust gas in the mixing chamber.
In an embodiment of the invention the method may include the step of providing mixing means for enhanced mixing of the exhaust gas and the cold flame gas. As explained above, such mixing means may include a porous material that the exhaust gas and the cold flame gas passes through in such a way that the two gases are mixed. Alternatively, blades or other types of mechanical mixing means may be provided in the mixing chamber such that there is created turbulence in the fluid flow which enhances the mixing of exhaust gas and cold flame gas.
In a further embodiment of the invention the method includes the step of producing cold flame gas in a cold flame gas generator. As explained above, cold flame generators are well known to the skilled person in the art.
In a further embodiment of the invention the method may include the step of storing the cold flame gas, which has been produced by the cold flame gas generator, in a reservoir. As explained above, the reservoir may be configured as an inline conduit with a larger diameter as compared to the fluid line connecting the cold flame gas generator and the exhaust gas flow path. Alternatively, the reservoir is configured as larger container. In both cases there may be provided a bypass fluid line such that the cold flame gas may flow directly from the cold flame gas generator to the exhaust gas flow path.
In a further embodiment of the invention the method may include the step of heating the cold flame gas which is stored in the reservoir such that the temperature of the cold flame gas is kept above the condensation point of the cold flame gas. As explained above, the heating may be carried out using a heat exchanger which is arranged in fluid communication with the exhaust gas flow path such that the heat energy contained in the exhaust gas can be used to heat the cold flame gas in the reservoir or to keep the cold flame gas at a steady temperature above the condensation point. An alternative for heating or keeping the cold flame gas in the reservoir at a temperature above the condensation point would be to use one or more regular electric heating elements. The cold flame gas generator may also be heated or kept warm in the same way by using heat energy in the exhaust gas or alternatively by using electric heating elements.
In a further embodiment of the invention the method may include the step of returning a part of the exhaust gas flowing in the exhaust gas flow path to the combustion chamber in an EGR-loop. As explained above, the EGR-loop comprises a fluid line connected to the exhaust gas flow path and the combustion chamber. Furthermore, the method includes the step of removing particles in the exhaust gas flowing in the EGR-loop by providing an EGR-loop particle filter in the EGR-loop.
In a further embodiment of the invention the method may include the step of arranging the EGR-loop particle filter in fluid communication with the cold flame gas supply such that the EGR-loop particle filter can be regenerated by the cold flame gas.
In a further embodiment of the invention the method may include the step of providing an exhaust gas flow path particle filter in the exhaust gas flow path.
As for the EGR-loop, the method may further include the step of arranging the exhaust gas flow path particle filter in fluid communication with the cold flame gas supply such that the exhaust gas flow path particle filter can be regenerated by the cold flame gas.
In a further embodiment of the invention the method may include the step of providing an oxidation catalyst in the exhaust flow path downstream the injection of the cold flame gas.
In a further embodiment of the invention the method may include the step of injecting air into the exhaust gas flow path upstream the oxidation catalyst such that the temperature in the oxidation catalyst can be regulated and enough oxygen for the oxidation process in the oxidation catalyst can be ensured.
There is also provided a use of a cold flame gas to remove impurities, like NOx and/or particulate matter (for example soot) and/or hydrocarbons, from an exhaust gas by injecting the cold flame gas into the exhaust gas, where the exhaust gas may originate from a combustion process in for example an internal combustion engine, an incineration plant, a power plant etc.
Below follows a detailed description of preferred embodiments of the invention with reference to the attached drawings where
A mixing chamber 14 is connected to the combustion chamber 12 via exhaust gas flow path 51. The mixing chamber can be a part of the exhaust gas fluid pipe itself, a fluid line section with increased diameter compared to that of the exhaust gas flow path or a container. The mixing chamber 14 may be provided with mixing means that enhances the mixing of the exhaust gas and the cold flame gas. After the mixing chamber 14, the exhaust gas leaves through exhaust gas flow path 52. Exhaust gas flow paths 51, 52 may be in the form of conduits, pipes, tubes or other suitable means for conducting the exhaust gas. The cold flame gas generator 16 is connected to the mixing chamber 14 via fluid line 55. Valve means 81 controls and regulates the flow of cold flame gas from the cold flame gas generator 16 to the mixing chamber 14.
The reservoir is connected to the mixing chamber 14 via fluid line 61. Valve means 80 controls and regulates the flow of fuel from the fuel tank 10 to the cold flame gas generator 16. Valve means 84 controls and regulates the flow of cold flame gas from the cold flame gas generator 16 to the reservoir 18, while valve means 85 controls and regulates the flow of cold flame gas from the reservoir 18 to the mixing chamber 14. As before, the cold flame gas generator is connected to an air supply 17 via fluid line 54 and the exhaust gas leaves the mixing chamber 14 through exhaust gas flow path 52 after being cleaned.
The cold flame gas generator 16 is connected to the mixing chamber 14 through fluid lines 65 and 66. Valve means 89 controls and regulates the flow of cold flame gas from the cold flame gas generator 16 to the mixing chamber 14. The EGR-loop, in its simplest form, includes a fluid line 68 which is connected to the exhaust gas flow path 52, as shown on the figure, or alternatively to exhaust gas flow path 51, and to the combustion chamber 12 (this is not shown on the figure) such that a portion of the exhaust gas can be returned to the combustion chamber 12. Valve means 91 controls and regulates the flow of exhaust gas through the EGR-loop. The EGR-loop shown on
All the embodiments of the invention shown in the figures include, although not shown on the figures, a control unit which registers temperature, pressure and other relevant measurements and controls the valve means and other functions of the exhaust gas cleaning apparatus 100 which are controllable, based on the measurements.
Furthermore, features which are not relevant for the invention as such are not shown on figures for the sake of clarity. A skilled person in the art will, however, immediately be able to add such features when applying the features of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0903447.1 | Feb 2009 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NO2010/000075 | 2/26/2010 | WO | 00 | 11/4/2011 |
