Method and cleaning apparatus for removal of SOx and NOx from exhaust gas

Abstract

A method for removal of SO.sub.x and NO.sub.x from an exhaust gas that contains SO.sub.x, NO.sub.x, soot and water vapor, the exhaust gas originating from a combustion of a fuel where the combustion takes place in an internal combustion engine. The exhaust gas is passed through at least one catalytic reactor having an oxidation catalyst, in which catalytic reactor at least SO.sub.2 is converted to SO.sub.3 and NO is converted to NO.sub.2. Thereafter the exhaust gas is passed through a condenser and cooled to a temperature which is below the dew point temperature of the water in the condenser such that SO.sub.3, NO.sub.2 and water is condensed and SO.sub.3 and NO.sub.2 is dissolved into the condensed water and removed from the exhaust gas.

Claims

1. A method for removal of SO.sub.x and NO.sub.x from an exhaust gas comprising SO.sub.x, NO.sub.x, soot and water vapour, the exhaust gas originating from a combustion of a fuel where the combustion takes place in an internal combustion engine, wherein the exhaust gas is passed through at least one catalytic reactor comprising an oxidation catalyst, in which catalytic reactor at least SO.sub.2 is converted to SO.sub.3 and NO is converted to NO.sub.2, where after the exhaust gas is passed through a condenser and cooled to a temperature which is below the dew point temperature of the water in the condenser such that SO.sub.3, NO.sub.2 and water is condensed and SO.sub.3 and NO.sub.2 is dissolved into the condensed water and removed from the exhaust gas, wherein water is injected into the condenser.

2. Method according to claim 1, wherein the exhaust gas is passed through a particle filter for removal of particulate matter before the exhaust gas is passed through the at least one catalytic reactor.

3. Method according to claim 2, wherein at least some exhaust gas, taken out downstream the catalytic reactor and upstream the condenser, is fed back into the exhaust gas upstream the at least one particle filter.

4. Method according to claim 2, wherein at least some exhaust gas, taken out downstream the particle filter and upstream the catalytic reactor, is fed back into the internal combustion engine.

5. Method according to claim 2, wherein the particle filter is regenerated by passing a cold flame gas through the particle filter.

6. Method according to claim 2, wherein the catalyst in the at least one catalytic reactor is heated during up-start of the catalytic reactor by passing a cold flame gas through the catalytic reactor.

7. Method according to claim 1, wherein exhaust gas is cooled down to a temperature in the range 20 C.-70 C.

8. Method according to claim 1, wherein exhaust gas is cooled down to a temperature in the range 30 C.-50 C.

9. A cleaning apparatus for removal of SO.sub.x and NO.sub.x from an exhaust gas comprising SO.sub.x, NO.sub.x, soot and water vapor, the exhaust gas originating from a combustion of a fuel where the combustion takes place in an internal combustion engine, the apparatus comprising at least one catalytic reactor which is fluidly connected to the internal combustion engine, the catalytic reactor comprising an oxidizing catalyst which at least converts SO.sub.2 to SO.sub.3 and NO to NO.sub.2 when the exhaust gas is passed through the catalytic reactor, the apparatus further comprising a condenser which is fluidly connected to the catalytic reactor downstream the catalytic reactor, in which condenser the exhaust gas is cooled to a temperature which is below the dew point temperature of the water in the condenser such that the SO.sub.3, the NO.sub.2 and the water is condensed and the SO.sub.3 and the NO.sub.2 is dissolved into the condensed water and removed from the exhaust gas whereby SO.sub.x and NO.sub.x is removed from the exhaust gas, wherein the condenser is connected to a fluid flow path which is connected to a source of water such that water can be injected into the condenser.

10. A cleaning apparatus according to claim 9, wherein the apparatus further comprising a particle filter for removal of particulate matter in the exhaust gas before the exhaust gas flows through the at least one catalytic reactor, the particle filter being fluidly connected to the internal combustion engine and the catalytic reactor.

11. A cleaning apparatus according to claim 10, wherein the apparatus comprises a conduit for transferring at least some exhaust gas from downstream the catalytic reactor and upstream the condenser, back into the exhaust gas upstream the particle filter.

12. A cleaning apparatus according to claim 10, wherein the apparatus comprises a conduit for transferring at least some exhaust gas from downstream the particle filter and upstream the catalytic reactor, back into the internal combustion engine in an EGR-loop.

13. A cleaning apparatus according to claim 10, wherein the apparatus further comprises a cold flame generator in which a cold flame gas is produced, the cold flame generator being fluidly connected to the particle filter such that the cold flame gas can flow through the particle filter.

14. A cleaning apparatus according to claim 10, wherein the apparatus further comprises a cold flame generator in which a cold flame gas is produced, the cold flame generator being fluidly connected to the catalytic reactor such that the cold flame gas can flow through the catalytic reactor.

15. A vessel comprising an internal combustion engine and a cleaning apparatus for removing SO.sub.x, NO.sub.x and soot from an exhaust gas according to claim 9 wherein the cleaning apparatus is fluidly connected to the internal combustion engine such that exhaust gas from the internal combustion engine can flow through the cleaning apparatus.

Description

(1) In the following, several non-limiting embodiments of the claimed invention will be described in detail, with reference to the figures, where

(2) FIG. 1 schematically illustrates a first embodiment of the present invention.

(3) FIG. 2 schematically illustrates a second embodiment of the present invention wherein exhaust gas is returned from downstream the oxidation catalytic reactor to the exhaust gas upstream the particle filter.

(4) FIG. 3 schematically illustrates a third embodiment of the present invention which is similar to the embodiment in FIG. 2, but where there are two parallel flow paths.

(5) FIG. 4 schematically illustrates a fourth embodiment of the present invention wherein exhaust gas is returned from downstream the particle filter to the internal combustion engine.

(6) In all FIGS. 1-4 the same technical features are given the same reference numbers. It should also be noted that the figures show the main parts of the present invention while other standard parts such as valve devices have not all been included. Such devices would, however, be obvious for a person skilled in the art to include in the cleaning apparatus where and when that is necessary.

(7) In FIG. 1 there is shown a first embodiment of a cleaning apparatus 10 for removing SO.sub.x, NO.sub.x and soot/particulate matter from an exhaust gas. The exhaust gas is produced in an IC-engine 12, typically an IC-engine on a vessel, but may also be an IC-engine arranged on other types of equipment such as vehicles, electrical generators driven by an IC-engine and so on.

(8) Fuel is fed into the IC-engine 12 through a fluid flow path 13. Air is fed into the IC-engine through a fluid flow path 14. In the combustion chamber of the IC-engine (not shown in the figures) the fuel is combusted with the air and forms an exhaust gas. The fuel comprises a high content of sulphur which forms predominantly SO.sub.2 during the combustion process in the IC-engine. Due to restrictions on emissions in exhaust gas, SO.sub.2 must be removed from the exhaust gas, at least so much of it that the sulphur content in the exhaust gas released into the atmosphere is below the limits set by official standards and requirements. For example for marine vessel the limits for SO.sub.x and NO.sub.x in the exhaust gas is given in the IMO regulations (IMO=International Maritime Organization).

(9) The cleaning apparatus according to the present invention is connected to the IC-engine 12 with a fluid flow path 25 which fluidly connects a particle filter 16 to the IC-engine.

(10) Downstream the particle filter 16 a catalytic reactor 18 is arranged in fluid communication with the particle filter through a fluid flow path 26. The catalytic reactor 18 comprises at least one oxidizing catalyst such that SO.sub.x, typically SO.sub.2, is converted to SO.sub.3 and such that NO.sub.x, typically NO, is converted to NO.sub.2. The oxidizing catalyst may for example be a vanadium pentoxide catalyst or another suitable catalyst. The particle filter 16 removes soot and particles which are present in the exhaust gas and which may damage or reduce the efficiency of the oxidizing catalyst in the catalytic reactor 18.

(11) The cleaning apparatus 10 further comprises a condenser 20 which is fluidly connected to the catalytic reactor 18 downstream the catalytic reactor with a fluid flow path 27. The condenser 20 cools the exhaust gas below the dew point temperature of the water contained in the condenser 20, i.e. the exhaust gas is cooled down to a temperature in the range 20 C.-70 C., or more preferably, in the range 20 C.-50 C. The water will be part of the exhaust gas as a result of the combustion process in the IC-engine. The cleaning apparatus 10 may, however, be provided with a fluid flow path 21 connected to a source of water such that water can be injected into the condenser 20 if necessary. A valve device 22 controls the flow of water through the fluid flow path 21.

(12) When the exhaust gas is cooled below the dew point temperature of the water, the water is condensed, the SO.sub.3 in the exhaust gas is also condensed out such that sulphuric acid is formed and the NO.sub.2 in the exhaust gas is condensed out such that nitric acid is formed. A fluid flow path 23 is connected to a first outlet of the condenser 20 through which the mixture of sulphuric acid, nitric acid and water leaves the condenser. A fluid flow path 28 is connected to a second outlet of the condenser 20 through which the remaining exhaust gas leaves the condenser 20.

(13) The cleaning apparatus 10 shown in FIG. 1 is also provided with a cold flame generator 30 in which a cold flame gas is produced. Fuel is fed into the cold flame generator through a fluid flow path 31 while preheated air is fed into the cold flame generator through a fluid flow path 32. The fuel may be the same fuel that is fed into the IC-engine 10. In the cold flame generator, the fuel is partially oxidized to form a cold flame gas as explained above. A fluid flow path 33 is connected to the cold flame generator 30 and the fluid flow path 25 such that the cold flame gas produced in the cold flame generator 30 may flow from the cold flame generator 30 into the fluid flow path 25. The fluid flow path 33 is provided with a valve device 34 such that the flow of cold flame gas through the fluid flow path 33 may be controlled. The cold flame gas is used to regenerate the particle filter 16 when it has become partly or completely blocked by soot/particulate matter. To regenerate the particle filter 16 cold flame gas is transferred from the cold flame generator and through the particle filter 16. The cold flame gas will oxidize the soot and thereby regenerate the particle filter 16. The cold flame gas may also be used to heat up the oxidizing catalyst in the catalytic reactor 18 to its working temperature, which is between 300 C.-700 C., before exhaust gas from the IC-engine is passed through the catalytic reactor.

(14) With the first embodiment of the present invention, the resulting exhaust gas, after having been past through the cleaning apparatus 10, has a very low content of sulphur and soot/particulate matter.

(15) The embodiment of the present invention shown in FIG. 2 is very similar to the embodiment shown in FIG. 1. As mentioned above, the same technical features have the same reference numbers in all figures and will therefore not be repeated again.

(16) The embodiment in FIG. 2 differs from the embodiment shown in FIG. 1 in that the cleaning apparatus 10 further is provided with a fluid flow line 36 which in one end is connected to the fluid flow path 27, which fluidly connects the catalytic reactor 18 and the condenser 20, and to the fluid flow path 25, which fluidly connects the particle filter 16 and the IC-engine when the cleaning apparatus is operating. The fluid flow path 36 is preferably provided with a valve device 37 such that the flow of exhaust gas through the fluid flow path 36 may be controlled. The inclusion of the fluid flow path 36 means that exhaust gas downstream the catalytic reactor 18, which comprises NO.sub.2, can be returned to the exhaust gas upstream the particle filter 16. When the NO.sub.2 flows through the particle filter 16 soot will react with the NO.sub.2 and form N.sub.2 which contributes to reducing the content of NO.sub.x in the exhaust gas and at the same time removes soot from the particle filter 16.

(17) With the second embodiment of the present invention, the resulting exhaust gas, after having been past through the cleaning apparatus 10, has a very low content of sulphur and soot and a low content of NO.sub.x.

(18) The embodiment shown in FIG. 3 is similar to the embodiment shown in FIG. 2. The difference is that the cleaning apparatus 10 is provided with two particle filters 16a, 16b and two catalytic reactors 18a, 18b where the particle filter 16a and the catalytic reactor 18a is arranged in a first branch of two parallel fluid flow paths for the exhaust gas, while the particle filter 16b and the catalytic reactor 18b is provided in the second branch of the two parallel fluid flow paths.

(19) The fluid flow path 25 which is fluidly connected to the 1C-engine when the cleaning apparatus 10 is operating, is divided into two branches at a first fluid flow path connection 24, a first branch 44 and a second branch 45. The two branches 44, 45 are joined together again in a second fluid flow path connection 29 as shown in FIG. 3.

(20) The first branch 44 comprises a particle filter 16a which is fluidly connected to the fluid flow path connection 24 with a fluid flow path 25a. The particle filter 16a is fluidly connected to a catalytic reactor 18a which is arranged downstream the particle filter 16a. The catalytic reactor 18a is further fluidly connected to the second fluid flow path connection 29 which is downstream the catalytic reactor 18a, with a fluid flow path 27a. Similar to the embodiment shown in FIG. 2, there is also provided a fluid flow path 36a which is connected in one end to the fluid flow path 27a and in the other end to the fluid flow line 25a such that exhaust gas flowing in the fluid flow path 27a downstream the catalytic reactor 18a can be returned and fed into the exhaust gas flowing in the fluid flow path 25a. The fluid flow path 36a is preferably provided with a valve device 37a such that the flow of exhaust gas through the fluid flow path 36a can be controlled.

(21) The second branch 45 comprises a particle filter 16b which is fluidly connected to the fluid flow path connection 24 with a fluid flow path 25b. The particle filter 16b is fluidly connected to a catalytic reactor 18b which is arranged downstream the particle filter 16b. The catalytic reactor 18b is further fluidly connected to the second fluid flow path connection 29 which is downstream the catalytic reactor 18b, with a fluid flow path 27b. Similar to the embodiment shown in FIG. 2, there is also provided a fluid flow path 36b which is connected in one end to the fluid flow path 27b and in the other end to the fluid flow line 25b such that exhaust gas flowing in the fluid flow path 27b downstream the catalytic reactor 18b can be returned and fed into the exhaust gas flowing in the fluid flow path 25b. The fluid flow path 36b is preferably provided with a valve device 37b such that the flow of exhaust gas through the fluid flow path 36b can be controlled.

(22) An alternative for routing the fluid flow paths 36a, 36b is to connect one end of the fluid flow path 36a to the fluid path 27a and the other end of the fluid flow path 36a to the fluid flow path 25b such that exhaust gas can be flowed from downstream the catalytic reactor 18a to upstream the particle filter 16b. Similarly, one end of the fluid flow path 36b can be connected to the fluid path 27b while the other end of the fluid flow path 36b is connected to the fluid flow path 25a such that exhaust gas can be flowed from downstream the catalytic reactor 18b to upstream the particle filter 16a.

(23) With the third embodiment of the present invention, the resulting exhaust gas, after having been past through the cleaning apparatus 10, has a very low content of sulphur, NO.sub.x and soot.

(24) In FIG. 4 there is again shown an embodiment which is similar to the embodiment shown in FIGS. 1-2. The only difference between the embodiment in FIG. 4 and in FIG. 1 is that the embodiment in FIG. 4 is provided with an EGR-loop (exhaust gas return). The cleaning apparatus 10 is provided with a fluid flow path 39 which in one end is connected to the fluid flow path 26, which connects the particle filter 16 and the catalytic reactor 18, and in the other end is connected to the engine 10 when the cleaning apparatus is operating such that exhaust gas can be past from the fluid flow path 26 back to the combustion chamber in the IC-engine 10. The fluid flow path 39 may be provided with a cooler 40 such that the exhaust gas may be cooled before being returned back into the combustion chamber and a valve device 41 such that the flow of exhaust gas through the fluid flow path 39 can be controlled. When the exhaust gas is returned back into the combustion chamber, the result is that the content of NO.sub.x in the exhaust gas is lowered.

(25) With the fourth embodiment of the present invention the resulting exhaust gas after having been past through the cleaning apparatus 10, has a very low content of sulphur and soot and a low content of NO.sub.x.

(26) The fluid flow paths 13, 14, 21, 23, 25, 26, 26a, 26b, 27, 27a, 27b, 28, 31, 32, 31, 33, 33a, 33b, 36, 36a, 36b, 39 are typically fluid lines in the form of pipes, tubes, conduits or similar devices through which a fluid can flow.

(27) As can be seen from the description of the various embodiments of the present invention, after the exhaust gas has been passed through the cleaning apparatus 10, a substantial amount of SO.sub.x, NO.sub.x and soot/particulate matter have been removed from the exhaust gas originating from the combustion process in the IC-engine 10. The content of SOx and NOx is well below the requirement in the IMO regulations, and generally the exhaust gas is very clean.