Technical field

[001] The present invention relates to method of inerting a fuel delivery system in a marine vessel according to the preamble of claim 1 .

[002] The present invention relates to inerting system for inerting a fuel delivery system in a marine vessel.

Background art

[003] Due to its toxic and explosive nature releasing ammonia to the atmosphere is not desirable or is restricted. When ammonia is used as a fuel as such or as a source of hydrogen, for example in marine vessels escaping of ammonia into the atmosphere should be prevented. Purging the piping with an inert gas is called inerting. There are a number of operation scenarios where the fuel piping will have to be emptied and inerted. That is why all equipment for handling and regulating gas fuel is subjected to stringent safety regulations. There may occur operational releases, such as escape of ammonia from fuel bunker system during purging operations, handling of small liquid releases from relief valves and handling of ammonia vapour in the event of an engine shut down including gas purge from engines, which need to be handled in appropriate manner. These fuel supply systems may be especially long in case of marine vessels, where the fuel supply pipeline can be tens or even hundreds of meters. In case of ammonia this inerting may be done with nitrogen.

[004] An object of the invention is to provide method of inerting a fuel delivery system in a marine vessel which is more environmentally friendly than prior art solutions. Disclosure of the Invention

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

[006] According to an embodiment of the invention in method of inerting a fuel delivery system in a marine vessel, the fuel delivery system having an internal fuel space, inert gas is admitted to the internal fuel space of the fuel delivery system at a first location of the fuel delivery system and fuel is replaced with the inert gas and is led out from the internal fuel space of the fuel delivery system at a second location of the fuel delivery system wherein fuel is replaced or diluted by the inert gas. Fuel is led from the second location as an inlet stream to a buffer vessel, from which buffer vessel fuel, or mixture of fuel and inert gas, is removed as an outlet stream to a fuel processing vessel such that the outlet stream flow is in asynchrony with the inlet stream flow, and that the fuel is oxidized in the processing vessel.

[007] This way it is possible to utilize the processing vessel and run the oxidation more efficiently and more indecently from the inerting.

[008] According to an embodiment of the invention the fuel is gaseous ammonia in which method inert gas is admitted to the internal fuel space of the fuel delivery system at a first location of the fuel delivery system and ammonia is replaced with the inert gas and is led out from the internal fuel space of the fuel delivery system at a second location of the fuel delivery system, wherein ammonia is led from the second location as an inlet stream to a buffer vessel, from which buffer vessel ammonia removed as an outlet stream and led to a processing vessel such that the outlet stream is in asynchrony with the inlet stream, and the ammonia is cracked and oxidized in the processing vessel.

[009] According to an embodiment of the invention method comprises: a first stage during which flow rate of the inlet stream into to the buffer vessel is greater than flow rate of the outlet stream from the buffer vessel to the processing vessel, and a second stage during which flow rate of the inlet stream into to the buffer vessel is smaller than flow rate of the outlet stream from the buffer vessel to the processing vessel.

[0010] According to an embodiment of the invention method comprises: a first stage during which fuel is stored into, but not discharged from the buffer vessel, and a second stage during which stored fuel is discharged from the buffer vessel to the processing vessel where the fuel is first at least partially cracked and thereafter oxidized.

[0011] According to an embodiment of the invention fuel is led from several locations as an inlet stream to one buffer vessel, from which fuel is led to the fuel processing vessel.

[0012] According to an embodiment of the invention fuel is led from several locations as an inlet stream to more than one buffer vessel, from which fuel is led to the fuel processing vessel.

[0013] According to an embodiment of the invention the fuel delivery system comprises a fuel feed channel having a first portion and a second portion, and a valve arranged to separate the first portion and the second portion when closed, wherein the method comprises closing the valve and inerting the second portion of the fuel delivery pipeline by feeding inert gas into the second portion of the fuel feed channel.

[0014] According to an embodiment of the invention fuel from the first portion of fuel feed channel is fed to the processing vessel and combusted in the vessel, and heat produced by the combustion is utilized for oxidizing fuel fed from the second portion of the fuel feed channel to the processing vessel.

[0015] Inerting system for inerting a fuel delivery system in a marine vessel, in which the fuel delivery system having an internal fuel space, comprising a. source of inert gas connected by a first inert gas valve to the fuel delivery system at a first location of the fuel delivery system, b. a buffer vessel connected by a vent valve to the internal fuel space at a second location of the fuel delivery system, and c. a fuel processing vessel for oxidizing the fuel, connected by a control valve to the buffer vessel such that an outlet stream flow from the buffer vessel to the fuel processing vessel is controllable to be in asynchrony with an inlet stream flow to the buffer vessel by means of the vent valve and the control valve.

[0016] According to an embodiment of the invention the inerting system comprises at least two buffer vessels connected to different locations in the fuel delivery system and one fuel processing vessel to which the at least two buffer vessels are connected.

[0017] According to an embodiment of the invention fuel pro-cessing vessel comprises a reaction part and an oxidizer part, and that the reaction part comprises a. a burner which comprises a first inlet for fuel and oxygen containing gas, and b. a cracking part comprising a third inlet which is in connection with the buffer vessel, wherein the burner is configured to burn fuel obtained from the fuel delivery system for producing heat for the cracking part and the cracking part is configured to crack the fuel obtained from the buffer vessel, and the oxidizer part comprises a. a constriction connecting the oxidizer part to the reaction part for receiving gas from the reaction part b. an inlet for oxygen containing gas for combusting the gas from the reaction part in the oxidizer part

[0018] According to an embodiment of the invention the fuel de-livery system comprises a fuel feed channel having a first portion and a second portion, and a valve arranged to separate the first portion and the second portion when closed, wherein the source of inert gas is connected by the valve to sec-ond portion of the fuel delivery pipeline.

[0019] According to an embodiment of the invention the reaction part comprises a. a burner is in connection with the first portion of the fuel feed channel, and with a source of oxygen containing gas, b. a cracking part comprising a inlet which is in connection with the buffer vessel. [0020] According to an embodiment of the invention the system comprises a control unit comprising executable instructions which, when executed by the control unit, cause the control unit to carry out a method of any one of the claims 1 to 8.

[0021] This provides an effect by means of which handling of toxic or flammable venting gas is considerably improved.

[0022] Typical operations where the GCU will be in operation are:

- purging or draining operations of fuel pipes

- bleeding operations from double block and bleed arrangements on the fuel piping systems

- releases from opening of pressure relief valves on the fuel piping system

- any other releases of ammonia occurring from normal operation of the system

[0023] 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

[0024] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates a fuel delivery system provided with an inerting system according to an embodiment of the invention,

Figure 2 illustrates a fuel delivery system provided with an inerting system according to another embodiment of the invention, Figure 3 illustrates a fuel cracking arrangement according to an embodiment of the invention,

Figure 4 illustrates schematically a side view of a marine vessel having an inerting system according to an embodiment of the invention, and

Figure 5 illustrates a fuel delivery system provided with an inerting system according to another embodiment of the invention.

Detailed Description of Drawings

[0025] Figure 1 depicts schematically a fuel delivery system 200 configured to feed fuel to a fuel consumer 210, such as an internal combustion piston engine, a fuel cell or alike. The fuel delivery system comprises fuel feed channel 212 which leads from a tank 201 to the gas consumer 210. The invention relates particularly fuel delivery systems intended to be used with fuel which are substantially volatile in normal atmospheric conditions, such as ammonia, hydrogen or alcohols. The fuel feed channel 212 may be provided with a transfer pump 213 when necessary, arranged for example at a bottom region of the tank 201 . In the figure 1 the tank is configured to store fuel in liquid phase. The fuel delivery system comprises additionally necessary auxiliaries, such as a gas valve unit 214 provided with internal gas handling instruments 214’ depicted only generally and a fuel preheater and/or evaporator 216, which is optional depending on the practical application, and a high-pressure pump 218, which is also optional feature. The fuel delivery system 200 has an internal fuel space in the fuel feed channel 121 and its auxiliaries configured to transfer, and when necessary, process, the fuel for utilizing it in the fuel consumer 210, which is in the following referred to as a gas consumer. The internal fuel space has a volume which is depends on pipe sizes, pipe lengths, pressure, temperature, equipment location etc.

[0026] The fuel delivery system 200 comprises an inerting system 220 which configured to inert the internal fuel space of the fuel delivery system when necessary. The actual need or manner of triggering the inerting of the fuel system may vary. [0027] The inerting system 220 comprises a source of inert gas 222, which is preferably a source of nitrogen N ₂ and therefore the gas used for inerting the fuel delivery system is nitrogen. The source of nitrogen 222 is connected by a first inert gas valve 224 to the fuel feed channel 212 of the fuel delivery system 200 at a first location L1 of the fuel delivery system. As a preferable embodiment, the inert gas valve is also referred to as a nitrogen inlet valve. Respectively there is a first vent valve 226 arranged at a second location L2.1 of the fuel delivery system 200. Particularly in the embodiment of the invention the second location is in the gas valve unit 214. In the embodiment of the figure 1 there is also a second vent valve 228 arranged to the fuel delivery system 200 at a third location L2.2 thereof, illustrating that fuel delivery system can have several vent valves for purging fuel away from the internal fuel space. The third location is a fuel introduction system 210’ of the gas consumer 210. Normally the vent valves 226, 228 are closed but during inerting process the valve are opened so as to purge fuel away from the fuel space in the fuel delivery system 200 by means of replacement with nitrogen. The fuel feed channel 212 is provided with at least one closing valve 230 which is positioned to a location between the tank 211 and the location where the first nitrogen valve 224 is connected to the fuel feed channel 212, i..e. the first location L1. This way the internal fuel space of the fuel feed channel 212 is possible to be isolated between the first nitrogen inlet valve 224 and the first and the second vent valves 226, 228, or a valve-isolated fuel space is formed into the fuel delivery system by the closing valve 230.

[0028] The inerting system 220 comprises at least one buffer vessel 232, 234 connected to the internal fuel space of the fuel delivery system by a vent channel 236 through the vent valve 226,228, that is in the embodiment of the figure 1 through the first and the second vent valves 226, 228. As it can be seen there are two buffer vessels 232,234 in the embodiment shown in the figure 1 arranged such that a first buffer vessel 232 is connected to the internal gas space of the fuel feed channel 212 within the gas valve unit 214 and the second buffer vessel 234 is connected to internal gas space of the fuel delivery system in the fuel introduction system 210’ of the fuel consumer 210. Generally, there may be several buffer vessels each connected to separate valve-isolated fuel spaces. [0029] Further the inerting system 220 comprises a fuel processing vessel 10 for oxidizing the fuel. The processing vessel 10 is in flow connection with each one of the buffer vessels 232. As it can be seen in the figure 1 as a general, but not essential, feature of the invention, the inerting system comprises at least two buffer vessels 232, 234 connected to one fuel processing vessel 10. The buffer vessels 232,234 are connected to the processing vessel 10 through control valves 238,239 such that an outlet stream flow from the buffer vessels 232,234 to the processing vessel is controllable to be in asynchrony with an inlet stream flow to the buffer vessel 232,234 by means of the vent valves 226,228.

[0030] The fuel delivery system comprises a fuel delivery pipeline having a first portion in a first region R1 and a second portion in a second region R1 , and the closing valve 230 is arranged to separate the first portion and the second portion when closed. Closing the valve 230 and inerting the second portion of the fuel delivery pipeline by feeding inert gas into the second portion of the fuel delivery pipeline makes it possible to inert only a desired part of the fuel delivery system.

[0031] The fuel delivery system 200 comprises a gas tight outer enclosure 240, which encloses the fuel feed channel 212 in a first region R1 , while in a second region R1 the fuel feed channel 212 is of a single wall type. The first and the second regions R1 , R2 may be defined by applicable safety regulations relating to the fuel which is used in a particular practical application of the invention. This way the region can be referred to as a safety region as well. For example the first safety region R1 may be a region in a marine vessel below its main or weather deck and the second safety region R2 may be above the weather deck. The separate valve-isolated fuel space mentioned above may extend within the first safety region R1 .

[0032] The fuel processing vessel 10 is provided with a burner 14 which is in connection with ambient air as a source of oxygen containing gas 22. As the closing valve 230 separates the portion of the fuel delivery system 200 which is to be inerted from other portion of the fuel delivery system 200, particularly from the upstream portion of the fuel feeding channel 212 extending between the tank 211 and the closing valve 230, the upstream portion is maintained filled with fuel and maintained operable for delivering the fuel. The fuel feed channel 212 is provided with a branch fuel line 242, which extends from the fuel feed channel 212 to the burner 14 of the fuel processing vessel 10 to be used as fuel therein. The branch fuel line is provided with a valve 246 for controlling the flow of fuel from the tank to the burner 14.

[0033] The inerting system operates such that fuel pressure is decreased and all practically recoverable fuel in the fuel delivery system is led to a section of the fuel delivery system that will not be inerted, like returned to the tank 221. When inerting of the fuel delivery system 200 is desired, a section of the fuel delivery system 200 is isolated by closing the closing valve 230. Also, the fuel processing vessel 10 is activated such that its burner 14 is started in a pilot mode. Burner combusts the fuel obtained from the fuel feeding channel 212 upstream the closing valve 230. Advantageously the burner is heated to suitable temperature within a few minutes, preferably in less than 5 minutes, after which the fuel processing vessel is ready to receive fuel from the portion of the fuel delivery system 200 which is to be inerted.

[0034] Preferably the burner 14 and the fuel processing vessel are configured such that flow rate of the fuel to be inerted (fed under control of the valves 238,239) is 3 to 4 times the flow rate of the fuel fed to the burner 14. Thus, for example by using 5 kg/h fuel in the burner the fuel processing vessel 10 can process about 20 kg/h fuel from the interted portion of the fuel delivery system 200, fed controllably from the buffer vessels 232,234 to the fuel processing vessel 10.

[0035] Inert gas, preferably nitrogen, is admitted from the source of inert gas 222 to the internal fuel space of the fuel delivery system 200 at a first location L1 of the fuel delivery system 200 by opening the first inert gas valve 224. Flow of nitrogen (or generally inert gas) at least replaces the fuel in the internal fuel space. Within the internal fuel space fuel is pushed by the flow of inert gas gradually towards the second location L2 where the vent valve 226 is open and finally through the vent valve 226, 228 as an inlet stream to the buffer vessel 232,234. Admission of inert gas into the internal fuel space and transferring fuel into the buffer vessel 232,234 is advantageously started substantially simultaneously to starting the burner 14 in the pilot mode described above. Buffer vessel receives and temporarily stores the fuel at least until the fuel processing vessel is at desired temperature to process the fuel. At a desired stage the fuel, or mixture of fuel and inert gas is removed as an outlet stream from the buffer vessel 232,234 to the fuel processing vessel 10 such that the outlet stream flow is in asynchrony with the inlet stream flow. Finally, the fuel is oxidized in the processing vessel 10. After the desired section of the fuel delivery system 200 fully inerted, it can be depressurized by venting the inert gas to the atmosphere.

[0036] The control valves 238,239 between buffer vessels 232,234 may be closed or open, depending on if the fuel is desired to be oxidized concurrently or temporarily stored in the buffer vessel 232,234. It is also possible to oxidize a portion of the fuel concurrently and store a portion of the fuel in the buffer vessel until its oxidized at later stage.

[0037] The buffer vessel 232,234 has a volume depends on total gas volume and pressure which is purged from the valve-isolated fuel space. The buffer vessel 232,234 is capable of receiving the fuel contained in the valve-isolated fuel space to which the buffer vessel is dedicated. It should be noted that the volume of the buffer vessel need not to be equal the volume of the fuel space, but is smaller, because the feed of the inert gas increases the pressure of the fuel fed into the buffer vessel and the fuel processing vessel 10 can be used simultaneously to feeding gas way from the buffer vessel while also filling the buffer vessel. In other words there may be a concurrent outlet stream flow from the buffer vessels 232,234 to the processing vessel and inlet stream flow to the buffer vessel 232,234 through the vent valves 226,228.

[0038] The buffer vessels 232,234, control valves 238,239 and the vent valves 224,226 provides versatile operation of the system. According to an embodiment of the invention the system can be operated such that there is a first stage during which flow rate of the inlet stream into to the buffer vessel 232,234 is greater than flow rate of the outlet stream from the buffer vessel 232,234 to the processing vessel 10, and a second stage during which flow rate of the inlet stream into to the buffer vessel 232,234 is smaller than flow rate of the outlet stream from the buffer vessel 232,234 to the fuel processing vessel 10.

[0039] According to another embodiment of the invention the system can be operated such that there is a first stage during which fuel is stored into, but not discharged from the buffer vessel 232,234, and a second stage during which stored fuel is discharged from the buffer vessel 232,234 to the fuel processing vessel 10 where the fuel is first at least partially cracked and thereafter oxidized.

[0040] Combustion of fuel fed from tank 211 in the burner supports and ensures proper oxidation of the fuel fed from the buffer vessel 232,234 to the fuel processing vessel 10. This way the fuel feed channel 212 has a first portion in a first region R1 and a second portion in a second region R1 , and the closing valve 230 is arranged to separate the first portion and the second portion when closed. Closing the valve 230 and inerting the second portion of the fuel feed channel by feeding inert gas makes it possible to inert only a desired part of the fuel delivery system. Fuel, which is of normal tank quality from the first portion of fuel feed channel is fed to the processing vessel 10 and combusted in the vessel, and heat produced by the combustion is utilized for oxidizing fuel fed from the second portion of the fuel feed channel to the processing vessel 10.

[0041] As is shown in the figure 1 the system comprises a control unit 250 comprising executable instructions which, when executed by the control unit, cause the control unit to carry out a method according to the invention.

[0042] Figure 2 discloses an embodiment of the invention otherwise similar to that shown in the figure 1 , but where only one buffer vessel fuel arranged and fuel is led from several locations L2.1 , L2.2 as an inlet stream to one buffer vessel 234, from which fuel is led to the processing vessel 234 is arranged. Thus, the number of buffer vessels may vary depending on the practical application.

[0043] The inerting system is particularly advantageous for use when the fuel is gaseous ammonia. An embodiment of the fuel processing vessel 10 for oxidizing the fuel is described in more detailed manner in the figure 3. For ammonia as a fuel the fuel processing vessel 10 is called in the following as a cracking arrangement 10 which is configured to first crack the ammonia and the oxide the product gas.

[0044] Figure 3 depicts schematically a cracking arrangement 10 for cracking ammonia according to an embodiment of the invention. The cracking arrangement comprises a reaction part and an oxidizer part which are explained in more detailed manner in the following. The arrangement comprises a cracking vessel 12. The cracking vessel 12 is advantageously rotationally symmetrical, such as cylindrical, vessel having a longitudinal centre axis 16. When the vessel is cylindrical the length of inner reaction space 100 of the vessel is greater than diameter of the vessel. There is a burner 14 arranged at the first end 12.1 of the rection space 100 of the vessel 12 for combustion of fuel. The cracking vessel 12 is provided with an outlet 18 for product gas in the second end 12.2 of the reaction space 100 of the vessel 12, opposite to the burner 14. The outlet 18 is not necessarily arranged to the centre axis 16 even if that is shown in the figure 3.

[0045] The burner 14 is, however, arranged to the centre axis 16 of the vessel such that its flame is directed coaxially to the centre axis 16 inside the vessel 12. The burner 14 comprises a first inlet 20 which is connected to a source of ammonia 22 for feeding ammonia as fuel into the burner 14. The source of ammonia 22 is in this connection the fuel tank 211 and the branch fuel line 242 provided with the valve 246 connects the tank 211 to the burner 14. The first inlet 20 is also connected to a source of gas containing oxygen 26 for feeding gas containing oxygen into the burner 14, thus serving as a second inlet for oxygen as well. It is also conceivable feed gas containing oxygen and the fuel as separate streams to the burner (not shown). The first inlet 20 functions as introduction of gases needed for production of heat for cracking ammonia in the vessel 12.

[0046] The cracking vessel 12 further comprising a number of third inlets 28 for feeding ammonia into cracking vessel 12 arranged to a side wall 30 in the vessel. The third inlets 28 are connected to the buffer vessels 232,234 and they function as introduction of ammonia purged from the valve-isolated fuel space of the fuel delivery system 200 into the cracking vessel 12 for cracking the ammonia by means of the heat produced by combustion of ammonia fed from tank 211 with the burner 14.

[0047] The reaction space 100 inside the cracking vessel 12 is an open space 100, in which a combustion part 101 adjacent to the burner 14 is formed when the burner 14 is in operation and a cracking part 102 in the portion of the space 100 at the second end 12.2 of the space 100 of the vessel 12. The combustion part 101 can be considered to be a flame area where oxidation of ammonia from the tank 211 takes place in a presence of oxygen. Since the vessel is intended to operate at considerably high temperatures, its walls are preferably provided with a heat insulation and/or with a cooling system, like a fluid jacket.

[0048] Advantageously there are several third inlets 28 arranged at a side wall 30 of the vessel at a distance from the end wall 32 at the first end 12.1 of the space 100 of the vessels 12. Alternatively, the third inlets 28 are in a form on continuous annular slot. The third inlets 28 are positioned such that ammonia which is introduced via the third inlets 28 is heated by the combustion of ammonia in the burner in the space 100. The cracking part 102 outside the combustion part 101 is practically non-oxidizing part. There may be control valves 34 arranged in connection with each one of the inlets and/inlet channels suitable balancing the gas flows.

[0049] In the embodiment shown in the Figure 3 the space 100 is empty. When the space 100 is empty the cracking reaction is non-catalytic thermal cracking, therefore the cracking part 102 in the embodiment of figure 3 can be called non- catalytic cracking part 102. Alternatively, an inner wall bordering the space 100 may be provided with a catalyst coat on its surface wherein the catalyst will promote cracking reactions in the vessel 12.

[0050] Method of cracking ammonia is practised in the cracking vessel according to figure 3 in a following manner. Ammonia is fed from the source of ammonia 22, that is from the tank 211 into the burner 14 and additionally gas containing oxygen is fed also to the burner 14. Since the fuel in the fuel feed channel 212 is also ammonia, the first portion of ammonia originating from the tank 211 is combusted in the burner 14 wherein heat is produced into the vessel 12 and the combustion part 101 is formed in the cracking vessel 12.

[0051] Combustion of ammonia follows generally the following reaction:

4NH ₃ + 3O ₂ -> 2N ₂ + 6H ₂ O

Combustion of ammonia is exothermic reaction producing heat and consuming oxygen in the vessel. Therefore, combustion of the first portion ammonia forms outside the combustion part in the vessel is substantially oxygen free, that is the non-oxidizing part 102. [0052] Second portion of ammonia, which is fed from the buffer vessels 232,234 is fed via the third inlets 28 into the cracking part 102 of the cracking vessel 12 outside the combustion part 101 , wherein the second portion of ammonia is cracked thermally by utilizing the heat produced by the combustion of the first portion of ammonia.

[0053] Cracking of ammonia follows generally the following reaction:

2NH ₃ -> 3H ₂ + N ₂ so the produced product gas produced from the second portion of ammonia comprises hydrogen and nitrogen.

[0054] Also, the cracking vessel 12 is provided with an oxidizer part 104 after the cracking part 120 in the flow direction of the gas when in use. Furthermore, the vessel 12 has at least part of its walls cooled. The vessel 12 comprises a fluid jacket 44 which is arranged for cooling the vessel by circulating a cooling fluid, such as water therein. For that purpose, the fluid jacket 44 is provided with a fluid inlet 46 and a fluid outlet 48. The second portion of ammonia originates from inerted section of the fuel feed channel 212 which may have composition different from that from the fuel tank 211 , fed to the burner 14. This way in this embodiment the combustion gas used in the burner 14 may have different composition compared to the ammonia containing gas cracked in cracking part 102 of the vessel. In the cracking vessel 12 the cracking part 102 is provided with an outlet 18’ which forms a constriction to the cross-sectional area of the cracking part 102. As it is shown, the constriction is preferable conical at both sides of the constriction smoothly separating the cracking part and the oxidizer part 104. The oxidizer part 104 is provided with one or more oxidizer inlets 50 connected to the source of gas containing oxygen 26 via flow channels 52. The flow channels open into an annular slot 54 which is arranged radially outside to the sleeve 29. The annular slot 54 is formed between an inner wall of the vessel 12 and a second sleeve 56. The second sleeve 56 extends from the end wall 32 to the outlet 18’ such that the slot 54 has substantially constant radial width. The slot and the second sleeve 56, which extend axially farther than the sleeve 29 from the end wall 32 is arranged in direct heat transfer communication with the cracking part 102 preheating the gas, due to heat transfer from the gas and/or flame in the space 100. The flow channels 52 are preferably arranged not to be in direct heat transfer connection with the fluid jacket 44, or cooled wall of the vessel 12. The source of gas containing oxygen 26 is connected to the flow channel 52. As is shown in the figure the source of gas containing oxygen 26 which is connected to the flow channel 52 may be different from the source of gas containing oxygen connected to the burner 14 for improving controllability of the burner 14. The oxidizer inlet 50 opens into a space in the oxidizer part 104 at proximity to the outlet 18’ of the cracking part.

[0055] The burner 14 combusts the ammonia and provides heat for cracking, and ammonia is cracked in the cracking part 102 as is described in the other embodiments. The product gas from the cracking part 102 is fed into the oxidizer part 104 is auto ignited in the presence of oxygen due to the gas temperature being higher than its autoignition temperature.

[0056] Ammonia 22 and combustion air 26 is premixed and swirled in the burner inlet 14, ignited and making a rich i.e. excess fuel flame 101. This flame will provide heat for ammonia cracking 102. Vent gas from inerting procedure of the fuel line with nitrogen (a second source of ammonia 22’), preferably a mixture of ammonia and nitrogen (vent composition will vary), is injected in the annular space between the side wall 30 and the inner shield 29 and heated as it flows towards the cracking part 102. There, the heat from combustion will decompose ammonia into nitrogen and hydrogen. As the combustion is rich, there is no air available to burn the hydrogen. The exhaust, consisting of N ₂ , NO, NO ₂ and H ₂ , will leave the cracking part 102 stage through the outlet 18’, where air is supplied through the inlets 50, mixing with the hydrogen and being ignited by the hot surface. The outlet area is made of high temperature resistant material, being not cooled by cooling fluid and the mixture will burn in the oxidizer part 104. The downstream exhaust will consist of N ₂ , H ₂ O and small traces of NO and NO ₂ (in the 10-15 ppm range).

[0057] Preferably the burner 14 and the fuel processing vessel are configured such that flow rate of the ammonia to be inerted (fed under control of the valves 238,239) is 3 to 4 times the flow rate of the ammonia fed to the burner 14. Thus, for example by using 5 kg/h ammonia in the burner the fuel processing vessel 10 can process about 20 kg/h ammonia from the interted portion of the fuel delivery system 200, fed controllably from the buffer vessels 232,234 to the fuel processing vessel 10.

[0058] Figure 4 shows an embodiment of a practical application of the inerting system 200 in a marine vessel 1 . In this embodiment the fuel tank 211 is on the weather deck of the vessel while the gas valve unit 214 and the gas consumer 210 are inside the vessel. As is depicted by the dashed lined the fuel tank 211 may be also inside the vessel.

[0059] The embodiment shown in the figures 1 and 2 are most suitable for use with fuel that is utilized in gaseous form in the gas consumer. In case the fuel is utilized by the gas consumer in liquid phase, like the case could be for example using methanol or other alcohol, the inerting system 200 may require additional liquid separating vessels 248 arranged to the vent channel 236 upstream the buffer vessel. This embodiment is schematically shown in the figure 5. This way when inerting fuel channel which contains liquid fuel, the liquid phase is separated in the liquid separating vessel 248 and returned for use and only gaseous phase is fed to the buffer vessel 232,234 and further to the fuel processing vessel 10 for oxidation. In some practical application there may be a need for arranging a pressure reduction valve 252 between the liquid separating vessel 248 and the buffer vessel 232,234.

[0060] 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.

Part list a fuel processing vessel 10 a cracking vessel 12 a first end 12.1 of the space in the vessel a second end 12.2 of the space in the vessel a burner 14 a centre axis of the cracking vessel 16 an outlet 18 a first inlet 20 a source of ammonia 22 a gas mixture feed line 25 a source of gas containing oxygen 26 a third inlet 28 a sleeve 29 a side wall 30 an end wall 32 valve 34 a fluid jacket 44 a fluid inlet 46 a fluid outlet 48 oxidizer inlet 50 oxidizer flow channel 52 an annular slot 54 inner space of the vessel 100 a combustion part 101 a cracking part 102 an oxidizer part 104 a fuel delivery system 200 a fuel consumer 210 a fuel introduction system 210’ a tank 211 fuel feed channel 212 a transfer pump 213 a gas valve unit 214 gas handling instruments 214’ a preheater and/or evaporator 216 a high-pressure pump 218 an inerting system 220 a source of inert gas 222 a first inert gas valve 224 a first vent valve 226 a second vent valve 228 a closing valve 230 a first buffer vessel 232 a second buffer vessel 234 a vent channel 236 a control valve 238, 239 outer enclosure 240 branch fuel line 242 a valve 246 a liquid separating vessel 248 a control unit 250 a pressure reduction valve 252 a first location L1 a second location L2.1 a third location L2.2