EP4788910A1

EP4788910A1 - An apparatus for abating exhaust gas methane emissions and method of operating an apparatus for abating exhaust gas methane emissions

Info

Publication number: EP4788910A1
Application number: EP23783806.5A
Authority: EP
Inventors: Jan Torrkulla; Pekka Kinnari; Robert Peltonen
Original assignee: Wartsila Finland Oy
Current assignee: Wartsila Finland Oy
Priority date: 2023-10-02
Filing date: 2023-10-02
Publication date: 2026-08-12
Also published as: CN121969822A; WO2025073344A1; KR20260065930A

Abstract

Invention relates to an apparatus (10) for abating exhaust gas methane emis- sions from internal combustion piston engines, comprising - a housing (12) having an exhaust gas inlet (14) and an exhaust gas outlet (16) defining a normal flow direction of exhaust gas from the inlet to the outlet when in use, and - a methane oxidation catalyst (18) for decreasing methane concentra- tion in the exhaust gas, arranged in the housing (12) and a sulphur guard bed (20) for removing methane oxidation catalyst poi- sons from the exhaust gas, the sulphur guard bed (20) being arranged upstream to the methane oxidation catalyst (18) in the normal flow direction of the exhaust gas in the housing (12), - a second gas outlet (22) between the sulphur guard bed (20) and the me-thane oxidation catalyst (18), the second gas outlet (22) being in connection with an outlet conduit (23) provided with a first valve (24), and - a guard gas inlet (26) between the methane oxidation catalyst (18) and the exhaust gas outlet (16), and - a second valve (28) arranged between the guard gas inlet (26) and the outlet (16). Invention relates also to a respective method of operating the apparatus.

Description

An apparatus for abating exhaust gas methane emissions and method of operating an apparatus for abating exhaust gas methane emissions

Technical field

[001] The present invention relates to an apparatus for abating exhaust gas methane emissions according to the preamble of claim 1.

[002] The present invention relates to method of operating an apparatus for abating exhaust gas methane emissions according to the preamble of the second independent claim.

Background art

[003] Natural gas is an abundant and economical alternative to oil-derived fuels such as gasoline, kerosene and diesel. Natural gas contains between approximately 70% to approximately 95% of methane (CFL). Natural gas, in the form of compressed natural gas (CNG) and/or liquified natural gas (LNG), is more and more utilized as a fuel in place of or in parallel with oil- derived fuels (e.g., gasoline, coal, etc.) for engines in stationary (power, drilling etc.) and transport (marine, railroad, and other on road) applications. For example, an internal combustion engine may combust natural gas (e.g., CNG and LNG) to produce a combustion gas that contains energy that is extracted by the engine components (e.g., pistons, turbines, etc.) to provide power to the system. The combustion gas may contain unburned methane, oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NO_X), water (H₂O), nitrogen (N₂) and other gases that exit the system as exhaust gas. The combustion gas from the natural gas engine also contains small levels of sulphur dioxide (SO2). The SO2 in the combustion gas results from small levels (between approximately 0.1 to approximately 8 parts per million (ppm)) of sulphur (S) present in the natural gas as well as that present in the diesel pilot (e.g., for dual fuel engines) and in the lubrication oil. For example, for spark ignited natural gas engines, the level of SO2 in the combustion gas is dependent on the level of S in the natural gas fuel and the S level in the oil as well as on the fuel and oil consumption rates.

[004] However, under certain operating conditions, natural gas fueled engines may not completely burn CH₄. Accordingly, the unburned CH₄ may slip into the exhaust gas and be released from the system. For example, natural gas engines operating under lean fuel (e.g., an oxygen-rich fuel) regime, may generate exhaust gas having between approximately 200 parts per million volume (ppmv) to approximately 3000 ppmv CH₄. It has been recognized that CH₄ is a more potent greenhouse gas compared to CO₂ (e.g., 1 mol of CH₄ > 25 CO2 mol equivalents). Therefore, it is desirable to develop and deploy an exhaust gas emissions abatement system that may remove or decrease the amount of CH₄ slip in such a way so that the CH₄ level in the exhaust gas is at or below regulated emission levels.

[005] One technique for CH₄ abatement includes oxidation of methane in the presence of a methane oxidation catalyst.

[006] WO2021262219A1 discloses a method of and apparatus for abating methane emissions from natural gas fuelled engines. Publication discloses a dual bed methane emissions abatement system having a guard bed for converting, capturing, or otherwise removing methane oxidation catalyst poisons from exhaust gas generated from natural gas fuel engines and a methane oxidation catalyst bed for converting and abating the methane emissions in the exhaust gas. The proposed solution has a problem that at certain operational conditions the guard bed may not be at an adequate temperature to remove methane oxidation catalyst poison from the exhaust gas.

[007] An object of the invention is to provide an apparatus for abating exhaust gas methane emissions from internal combustion engines in which the operation circumstances of the methane oxidation catalyst performance is considerably improved compared to the prior art. Disclosure of the Invention

[008] Objects of the invention can be met substantially as disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

[009] According to an embodiment of the invention an apparatus for abating exhaust gas methane emissions from internal combustion piston engines, comprising a housing having an exhaust gas inlet and an exhaust gas outlet defining a normal flow direction of exhaust gas from the inlet to the outlet when in use, and a methane oxidation catalyst for decreasing methane concentration in the exhaust gas, arranged in the housing and a sulphur guard bed for removing methane oxidation catalyst poisons, particularly sulphur, from the exhaust gas, the sulphur guard bed being arranged upstream to the methane oxidation catalyst in the normal flow direction of the exhaust gas in the housing, a second gas outlet between the sulphur guard bed and the methane oxidation catalyst, the second gas outlet being in connection with an outlet conduit provided with a first valve, a guard gas inlet between the methane oxidation catalyst and the exhaust gas outlet, and a second valve arranged between the guard gas inlet and the outlet.

[0010] This makes it possible to heat the sulphur guard bed with heat contained in the exhaust gas and bypass the methane oxidation catalyst. The sulphur guard bed needs to be at its normal operating temperature in order it to be capable of removing substances harmful the methane oxidation catalyst and if not, methane oxidation catalyst will be poisoned. Therefore, this makes it possible to heat up the sulphur guard bed without poisoning the methane oxidation catalyst.

[0011] According to an aspect of the invention the methane oxidation catalyst and sulphur guard bed are arranged at a distance from each other forming a space therebetween, to which space the second gas outlet opens. [0012] The space between the methane oxidation catalyst and sulphur guard bed facilitates guiding of the exhaust gas to the second gas outlet without negatively effecting the methane oxidation catalyst.

[0013] According to an aspect of the invention the second outlet is in flow connection with a first bypass conduit which extends between upstream side of the methane oxidation catalyst and upstream side of the exhaust gas outlet in the housing.

[0014] This way the bypass of the methane oxidation catalyst can be arranged in the apparatus in advantageous manner, making the solution compact.

[0015] Sulphur compounds are particularly harmful to the methane oxidation catalyst, and this effectively prevents poisoning of the methane oxidation catalyst.

[0016] According to an aspect of the invention the sulphur guard bed comprises a sulphur removing bed of solid material.

[0017] Forming the sulphur guard bed as a bed of solid material provides large surface area of the solid material and substantially low pressure losses to the flowing exhaust gas. Construction is also straightforward.

[0018] According to an aspect of the invention the sulphur guard bed comprises a lateral flow reactor.

[0019] In the lateral flow reactor exhaust gas is arranged to flow partly also in a direction deviating sideways from the normal flow direction of the exhaust gas. This provides compact and efficient exhaust gas treatment in the sulphur guard bed.

[0020] According to an aspect of the invention the guard gas inlet is controllably connected to a source of pressurized air. Using air as the guard gas is efficient because the air is not harmful to the catalyst, and it is readily available.

[0021] According to an aspect of the invention the guard gas inlet is controllably connected to the exhaust gas inlet of the apparatus via a dedicated flow channel, and the apparatus is provided with a second sulphur guard bed in the flow channel between the guard gas inlet and the exhaust gas inlet of the apparatus. [0022] According to an aspect of the invention apparatus comprises a second bypass conduit extending between the exhaust gas inlet and one of the following: exhaust gas outlet and the first bypass conduit.

[0023] This provides a full bypass of the methane oxidation catalyst and the sulphur guard bed, which is needed for situations of irregular operation of the apparatus or if the engine would be operated using fuel resulting exhaust gas components which are incompatible with the methane oxidation catalyst or the sulphur guard bed.

[0024] Method of operating an apparatus according to the invention connected to an internal combustion engine, wherein in the method the engine is running by combusting methane containing fuel and its exhaust gas is led via the exhaust gas inlet to the apparatus, temperature of the sulphur guard bed is monitored, and a target normal operating temperature is set for temperature of the sulphur guard bed, and in an event that monitored actual temperature of the sulphur guard bed is less than the set target normal operating temperature, the first valve is opened, the second valve is closed, and exhaust gas is passed through the sulphur guard bed while the methane oxidation catalyst is bypassed by leading the exhaust gas to the outlet conduit through the second gas outlet, and in an event that monitored actual temperature of the sulphur guard bed is equal to or more than the target normal operating temperature the first valve is closed, the second valve is opened, and exhaust gas is passed through the sulphur guard bed and the oxidation catalyst methane oxidation catalyst.

[0025] This way the sulphur guard bed is heated to desired temperature with heat contained in the exhaust gas without poisoning the methane oxidation catalyst. [0026] According to an aspect of the invention further in the event that monitored actual temperature of the sulphur guard bed is less than the set target normal operating temperature, guard gas is led to the apparatus via the guard gas inlet.

[0027] The guard gas effectively minimizes the exhaust gas from entering the methane oxidation catalyst, and this way the guard gas guards the methane oxidation catalyst from poisoning.

[0028] According to a preferred aspect of the invention the guard gas is air. Using air as the guard gas is efficient because the air is not harmful to the catalyst, and it is readily available.

[0029] According to a preferred aspect of the invention the guard gas is exhaust gas of the engine from which methane oxidation catalyst poisons have been removed. Using the exhaust gas as the guard gas is efficient because it is readily available.

[0030] According to an aspect of the invention flow rate of the air led through the guard gas inlet is controlled such that methane oxidation catalyst is guarded from exposure to the methane oxidation catalyst poisons, particularly sulphur in the exhaust gas such that air flows through the methane oxidation catalyst against the normal flow direction of the exhaust gas in the housing. The guard gas effectively prevents the exhaust gas from entering the methane oxidation catalyst, and this way the guard gas guards the methane oxidation catalyst from poisoning.

[0031] According to an aspect of the invention flow rate of the air is controlled using one or more of the following variables as a feedback signal: exhaust gas pressure at the inlet of the apparatus, exhaust gas velocity at the inlet of the apparatus, exhaust gas mass flow, engine load, a modelled set value provided by an engine control, e.g. derived from cylinder pressure and/or charge air pressure.

[0032] According to an aspect the target normal operating temperature of the sulphur guard bed is a modelled set value derived e.g. from cylinder pressure and/or charge air pressure. [0033] According to an aspect of the invention further in the event that monitored actual temperature of the sulphur guard bed is less than the set target normal operating temperature, operation of the engine is controlled to increase temperature of the exhaust gas. This way the sulphur guard bed can be heated to it normal operating temperature faster, and the methane oxidation catalyst can be harnessed to use sooner.

[0034] According to an aspect of the invention further in the event that monitored actual temperature of the sulphur guard bed is less than the set target normal operating temperature, exhaust gas of the engine is heated by bringing heat to the exhaust gas from an auxiliary heater. This way the sulphur guard bed can be heated to it normal operating temperature faster.

[0035] Word “substantially” means variation in values due to normal manufacturing tolerances and process operation fluctuations which still results in the same technical effect.

[0036] The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims.

Brief Description of Drawings

[0037] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates schematically an apparatus for abating exhaust gas methane emissions according to an embodiment of the invention,

Figure 2 illustrates schematically an apparatus for abating exhaust gas methane emissions according to another embodiment of the invention, and

Figure 3 illustrates schematically an apparatus for abating exhaust gas methane emissions according to still another embodiment of the invention, Figure 4 illustrates schematically the apparatus shown in the figure 2 in connection with an internal combustion piston engine.

Detailed Description of Drawings

[0038] Figure 1 depicts schematically an apparatus 10 for abating exhaust gas methane emissions. A practical application of the apparatus is reducing a so- called methane slip (unburned methane) which may be produced by an internal combustion piston engine which is operated by making use of methane containing gas, such as natural gas, as its fuel. The apparatus 10 comprises a housing 12, which is provided with an exhaust gas inlet 14 and an exhaust gas outlet 16 defining a normal flow direction of exhaust gas in the housing 12 from the inlet to the outlet when in use. The apparatus 10 comprises a methane oxidation catalyst, hereinafter MOC 18, arranged in the housing 12 for decreasing methane concentration in the exhaust gas. The methane oxidation catalyst comprises preferably a so-called honeycomb support structure having suitable catalyst material arranged on its surface which will be in contact with the flowing gas. Methane oxidation catalyst in presence of oxygen converts CF into CO2 and H2O when temperature is suitable for the selected catalyst. Exhaust gas from a lean burn gas engine contains required amount of oxygen. The MOC 18 is preferably a so called high cpsi catalyst. The catalyst suitable for use in connection with the invention has cells 100 - 600 cpsi (cells per square inch), preferably 300-500 cpsi.

[0039] There is also provided a sulphur guard bed 20, hereinafter SGB 20, for removing MOC poisons from the exhaust gas prior to feeding to MOC 18. Removing comprise converting MOC poisons from the exhaust gas. A MOC poison is a substance or composition which reduces the effectiveness of, or partially or totally deactivates a catalyst used in reduction reaction. Particular poisons of a MOC are sulphur compounds, such as SO2 in the exhaust gas. The SGB 20 is arranged upstream to the MOC 18 in the housing, that is nearer to the inlet 14 than the MOC 18, seen in the normal flow direction of exhaust gas in the housing 12. In the SGB 20 sulphur compounds, and generally MOC poisons (such as, SO2, Zn, P, Ca, Si, ash) are substantially removed thereby generating exhaust gas suitable for the MOC 18. [0040] The apparatus is provided with a second gas outlet 22 which is located in the housing 12 such that exhaust gas coming from the sulphur guard bed 20 can be guided not to enter the MOC 18 when so desired, and instead the exhaust gas is guided out before effecting on the MOC. In other words, the exhaust gas can be guided instead of MOC 18 to the second gas outlet 22. The second gas outlet 22 is in connection with an outlet conduit 23, which is provided with a first valve 24 for controlling exhaust gas flow in the apparatus 10. The apparatus 10 is further provided with a guard gas inlet 26 which is positioned between the MOC 18 and the exhaust gas outlet 16 and a second valve 28 arranged between the guard gas inlet 26 and the outlet 16.

[0041] The apparatus 10 operates such that when an engine to which the apparatus 10 is connected, is started and running by combusting methane containing fuel and its exhaust gas is led via the exhaust gas inlet 14 to the apparatus 10, and the apparatus, or more precisely the SGB 20, is at a temperature which lower than its target normal operational temperature, where its capability of reducing MOC poisons is reduced. In such circumstances the first valve 24 is open to admit exhaust gas into the apparatus 10 and the second valve 28 is closed which practically prevents gas flow in a direction from the MOC 18 to the outlet 16. Instead, exhaust gas is passed through the SGB 20 while the methane oxidation catalyst MOC 18 is bypassed by leading the exhaust gas to the outlet conduit 23 through the second gas outlet 22, and open first valve 24. This operation may be called as heating stage.

[0042] In order to guard the MOC 18 from MOC poisons during the heating stage the guard gas inlet 26 can be opened which causes guard gas flow into the apparatus 10 between the MOC 18 and the exhaust gas outlet 16. Guard gas flow though the guard gas inlet 26 may be controlled by a third valve 27 arranged in connection to the guard gas inlet 26. The guard gas inlet 26 is preferably connected to a source of pressurized air 32, which may be implemented by a blower or a compressor and any auxiliaries relating to viable operation of the blower. The source of pressurized air may be provided with a heater or alike, which may be used for keeping temperature of the air fed to the apparatus at desired level. It may be feasible to maintain the air at such a temperature possible disadvantages of heat expansion are avoided. The third valve 27 being open and the source of pressurized air 32 being operating, indicates that the guard gas inlet is also active, and respectively when at least the third valve 27 is closed the guard gas inlet is inactive. The second outlet 22 is in flow connection with a first bypass conduit 30 which extends between upstream side of the MOC and upstream side of the exhaust gas outlet 16 in the housing, and downstream side of the second valve 28. This may be called as an internal bypass arranged to the apparatus 10.

[0043] During the heating stage, the exhaust gas heats up the SGB 20, and when it is at its target normal operational temperature, the second valve can be opened and the first valve 24 can be closed, after which the heating stage ends and the exhaust gas flows successively through the SGB 20 and the MOC 18, which belongs to normal operation of the apparatus 10.

[0044] As a summary the following table shows statuses of the relevant parts in the apparatus at different operation stages.

[0045] As it becomes clear from the figure 1 the MOC 18 and SGB 20 are arranged at a distance from each other forming a space 21 therebetween, to which space the second gas outlet 22 opens. The space between the MOC 18 and SGB 20 helps bring about flow of exhaust gas from the SGB 20 to the second gas outlet 22 without effecting the MOC 18, during the heating stage. The space 21 , the MOC 18 and the SGB 20 have a cross section, or a face area, of substantially equal size and form, and thus the space 21 does not constrict the gas flow area between the SGB 20 and the MOC 18.

[0046] The sulphur guard bed 20 comprises a sulphur removing bed of solid, granular material, such as pellets. The granular material comprises mostly MnO2 and being arranged as a bed, and a flow channel is formed between individual granulates or pellets. The sulphur guard bed 20 comprises a lateral flow reactor containing sulphur removing material. In the lateral flow reactor gas is arranged to flow partly also in a direction deviating sideways from the normal flow direction of the exhaust gas. In practise this means that when the lateral flow reactor has an inlet face and an outlet face and a direct distance therebetween, the gas flow path in the lateral flow reactor is longer than the direct distance. Exhaust gas is arranged to flow in lateral direction (sideways) considerably longer route than size of the granular or pellet in use. The lateral flow reactor may comprise internal flow guides, such as baffles, to enhance lateral flow through the bed.

[0047] Figure 2 discloses a preferred embodiment of the apparatus 10 for abating exhaust gas methane emissions from internal combustion engines, which is otherwise similar to and operates in a similar manner to the embodiment shown in the figure 1 , but as a difference the apparatus 10 comprises a second bypass conduit 34 which extends between the exhaust gas inlet 14 and the exhaust gas outlet 16. The second bypass conduit 34 preferably forms a flow path between the between the exhaust gas inlet 14 and the exhaust gas outlet 16 partly via the first bypass conduit 30. However, in some practical application the second bypass conduit 34 and the first bypass conduit may be separate flow channels (not shown in the figure. Thus, it can be said that second bypass conduit 34 extends between the exhaust gas inlet 14 and one of following: the exhaust gas outlet 16 and the first bypass conduit 30. The second bypass conduit 34 is provided with fourth valve 36 for controlling gas flow through the second bypass conduit 34. The second bypass conduit 34 (either alone when connected directly upstream and next to the exhaust gas outlet 16, or together with the first bypass conduit 30) makes it possible for the exhaust gas flow to bypass both the SGB 20 and the MOC 18, i.e. a full bypass. This is an optional operation manner for certain exceptional circumstances. The full bypass is provided particularly for when running the engine (temporarily, depending on the available fuel) with fuels, like diesel oil not suitable for the apparatus or when abnormal combustion, like misfiring, takes place in the engine.

[0048] Figure 3 discloses an embodiment of the invention the guard gas inlet 26 is connected to the exhaust gas inlet 14 of the apparatus 10 or alternatively to an exhaust gas duct of engine to which the apparatus 10 is connected. The exhaust gas of the engine can be used as the guard gas when any MOC poisons are removed from the exhaust gas prior to feeding to the apparatus 10. The flow channel 46 connecting the exhaust gas inlet 14 and the guard gas inlet 26 comprises a second sulphur guard bed 20’ which is considerably smaller that the SGB 20 for the main exhaust gas flow. There is a heater 42 for heating the second SGB 20’ arranged to the flow channel 46. Because the second SGB 20’ is substantially small it can be heated to normal operational temperature very quickly so that in practical conditions sulphur is removed efficiently from the start of activation of the guard gas inlet 26. Optionally the flow channel 46 may be provided with a booster blower if needed. The heater 42 may be an electric heater. The heater 42 may be integrated to the second SGB 20’. The exhaust gas as guard gas minimizes the main flow of exhaust gas in the space 21 from entering the methane oxidation catalyst, and this way the guard gas guards the methane oxidation catalyst from poisoning. The guard gas is used here in similar manner as in other embodiments.

[0049] Figure 4 discloses schematically the apparatus 10 shown in the figure 2 in connection with an internal combustion piston engine 100. The engine is connected to a source of fuel containing methane, such as an LNG or LPG tank, thus it is running by combusting methane containing fuel. When in operation, the engine produces exhaust gas which is led to the apparatus 10 via an exhaust duct 104. The exhaust duct 104 is connected to the inlet 14 of the apparatus 10. The apparatus is provided with a control system 250 which comprises a control computer in which one or more computer programs controlling operation of the apparatus may be executed. The apparatus 10 is provided with a temperature sensor 251 configured to monitor temperature of the SGB 20. Temperature value obtained this way is transmitted to the control system 250 as an input variable for the control. The first valve 24, the second valve 28, the third valve 27 and the fourth valve 36 are provided with actuators which are in control communication c1 ,c2,c3,c4 with the control system, which control communication comprises transmitting actuation command from the control system to the valves and optionally transmitting actual position information from the valves to the control system. In operation, a target normal operating temperature of the SGB 20 is set, and temperature of the SGB 20 is monitored. In an event that monitored actual temperature of the SGB 20 is less than the set target normal operating temperature, the first valve 24 is open or opened, the second valve 28 is closed, and exhaust gas is passed through the SGB 20 while the methane oxidation catalyst MOC 18 is bypassed by leading the exhaust gas to the outlet conduit 23 through the second gas outlet 22. In an event that monitored actual temperature of the SGB 20 is equal to or more than the target normal operating temperature the first valve 24 is closed, the second valve 28 is opened, and exhaust gas is passed through the SGB 20 and the oxidation catalyst MOC 18. The computer program in the control system 250, when executed by the control computer, cause the computer to carry out the method.

[0050] Preferably the method comprises further step that in the event that monitored actual temperature of the SGB 20 is less than the set target normal operating temperature, guard gas is led to the apparatus via the guard gas inlet 26 by activating the source of compressed air 32 and/or opening the third valve 27.

[0051] Flow rate of the air led through the guard gas inlet 26 is controlled such that MOC 18 is guarded from exposure to the MOC poisons, particularly sulphur in the exhaust gas such that air flows through the MOC 18 against the normal flow direction of the exhaust gas in the housing 12.

[0052] Flow rate of the guard air may be controlled using one or more of the following variables as a feedback signal: exhaust gas pressure at the inlet of the apparatus 10, exhaust gas velocity at the inlet of the apparatus, exhaust gas mass flow, engine load. For using these variables required measurement sensors are arranged to the apparatus 10 and/or the engine 100, which are also arranged in data transfer communication with the control system 250 (not shown in the figures).

[0053] Sealing air requirement is not significant since the backpressure over the MOC layer is higher, due to being a high cpsi element, than that for the porous sulphur guard bed, and therefore the simplest way of implementing the invention in this respect is to use a fixed air flow rate setting in the source of pressurized air 32 and control the flow by opening and closing the third valve 27.

[0054] As a further development of the invention the control system 250 of the apparatus is in data transfer communication with the engine’s control system 101 , and the method comprises a step that in the event that monitored actual temperature of the SGB 20 is less than the set target normal operating temperature, operation of the engine 100 is controlled to increase temperature of the exhaust gas. An option to increase exhaust gas temperature in a gas operated engine is making use of pilot injection system and perform a post injection of the pilot fuel after the pilot injection and ignition of the gaseous fuel.

[0055] As a further development of the invention the apparatus 10 comprises an auxiliary exhaust gas heater 40, which is arranged to the exhaust gas duct 104, and the method comprises a step that in the event that monitored actual temperature of the sulphur guard bed 20 is less than the set target normal operating temperature, exhaust gas of the engine 100 is heated by bringing heat to the exhaust gas from an auxiliary heater 40. Such an auxiliary heater may be for example a gas burner. The auxiliary heater (of any desired type) may also be arranged to the apparatus 10 upstream position to the SGB 20, as is indicated by reference numeral 40’.

[0056] The features explained in connection with the figure 4 are technically usable also in combination with the embodiments shown in the figures 1 or 3.

[0057] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is obvious to the skilled person that, along with the technical progress, the basic idea of the invention can be implemented in many ways. The invention and its embodiments are thus not limited to the examples and samples described above but they may vary within the contents of patent claims and their legal equivalents. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.

Claims

1. An apparatus (10) for abating exhaust gas methane emissions from internal combustion piston engines, comprising

- a housing (12) having an exhaust gas inlet (14) and an exhaust gas outlet (16) defining a normal flow direction of exhaust gas from the inlet to the outlet when in use, and

- a methane oxidation catalyst (18) for decreasing methane concentration in the exhaust gas, arranged in the housing (12) and

- a sulphur guard bed (20) for removing methane oxidation catalyst poisons from the exhaust gas, the sulphur guard bed (20) being arranged upstream to the methane oxidation catalyst (18) in the normal flow direction of the exhaust gas in the housing (12), characterized in that the apparatus is provided with

- a second gas outlet (22) between the sulphur guard bed (20) and the methane oxidation catalyst (18), the second gas outlet (22) being in connection with an outlet conduit (23) provided with a first valve (24), and

- a guard gas inlet (26) between the methane oxidation catalyst (18) and the exhaust gas outlet (16), and

- a second valve (28) arranged between the guard gas inlet (26) and the outlet (16).

2. An apparatus (10) according to claim 1 , characterized in that the methane oxidation catalyst and sulphur guard bed (20) are arranged at a distance from each other forming a space (21) therebetween, to which space the second gas outlet (22) opens.

3. An apparatus (10) according to claim 1 or 2, characterized in that the second outlet (22) is in flow connection with a first bypass conduit (30) which extends between upstream side of the methane oxidation catalyst and upstream side of the exhaust gas outlet in the housing.

4. An apparatus (10) according to claim 1 , characterized in that the sulphur guard bed (20) comprises a sulphur removing bed of solid material.

5. An apparatus (10) according to claim 4, characterized in that the sulphur guard bed (20) comprises a lateral flow reactor.

6. An apparatus (10) according to claim 1 , characterized in that the guard gas inlet (26) is controllably connected to a source of pressurized air (32).

7. An apparatus (10) according to anyone of the preceding claims, characterized in that the apparatus (10) comprises a second bypass conduit (34) extending between the exhaust gas inlet (14) and one of the following: exhaust gas outlet (16) and the first bypass conduit (30).

8. Method of operating an apparatus (10) according to anyone of the preceding claims connected to an internal combustion piston engine (100), wherein in the method the engine (100) is running by combusting methane containing fuel and its exhaust gas is led via the exhaust gas inlet (14) to the apparatus (10), temperature of the sulphur guard bed (20) is monitored, and a target normal operating temperature is set for temperature of the sulphur guard bed (20), and in an event that monitored actual temperature of the sulphur guard bed is less than the set target normal operating temperature, the first valve (24) is opened, the second valve (28) is closed, and exhaust gas is passed through the sulphur guard bed (20) while the methane oxidation catalyst (18) is bypassed by leading the exhaust gas to the outlet conduit (23) through the second gas outlet (22), and in an event that monitored actual temperature of the sulphur guard bed is equal to or more than the target normal operating temperature the first valve (24) is closed, the second valve (28) is opened, and exhaust gas is passed through the sulphur guard bed (20) and the oxidation catalyst (18).

9. Method according to claim 8, wherein further in the event that monitored actual temperature of the sulphur guard bed is less than the set target normal operating temperature, guard gas is led to the apparatus via the guard gas inlet

10. Method according to claim 9, wherein the guard gas is air.

11. Method according to claim 9 and 10, wherein flow rate of the air led through the guard gas inlet (26) is controlled such that methane oxidation catalyst (18) is guarded from exposure to the methane oxidation catalyst poisons, particularly sulphur in the exhaust gas such that air flows through the methane oxidation catalyst (18) against the normal flow direction of the exhaust gas in the housing (12).

12. Method according to claim 11 , wherein flow rate and/or temperature of the air is controlled using one or more of the following variables as a feedback signal: exhaust gas pressure at the inlet of the apparatus, exhaust gas velocity at the inlet of the apparatus, exhaust gas mass flow, engine load, a modelled feed set value provided by an engine control, e.g. derived from cylinder pressure and/or charge air pressure.

13. Method according to anyone of the claims 8 - 12, wherein further in the event that monitored actual temperature of the sulphur guard bed (20) is less than the set target normal operating temperature, operation of the engine (100) is controlled to increase temperature of the exhaust gas.

14. Method according to anyone of the claims 8 - 12, wherein further in the event that monitored actual temperature of the sulphur guard bed (20) is less than the set target normal operating temperature, exhaust gas of the engine (100) is heated by bringing heat to the exhaust gas from an auxiliary heater (40,40’).

15. Method according to claim 9, wherein the guard gas is exhaust gas of the engine (100) from which methane oxidation catalyst poisons have been removed.