Technical field

[001 ] The present invention relates to a dual fuel burner according to the pre- amble of claim 1.

Background art

[002] Liquefied gas as a fuel of prime movers in marine vessels and other mobile, and immobile, power plants has increasingly become of interest while the importance of environmental issues of particularly the exhaust emissions have increased.

[003] Liquefied gas, such as liquefied natural gas, is typically stored at extremely low temperature and due to e.g. heat transfer from surrounding a part of the gas is evaporated as so called boil off gas. Admitting the boil off gas to the atmosphere is not desired. It is known as such to burn excess gas to convert it into composition significantly less harmful to the environment.

[004] Such liquefied gas tanks and a fuel handling system requires also inerting of the spaces related to the tanks, pipes and so on for example for maintenance work. It is known as such to burn the gas present in the tanks and their auxiliaries to convert it into composition of non-reactive gas i.e. inert gas.

[005] KR 20150096540 discloses a method of combusting and providing inert gas for filling a storage tank by the inert gas.

[006] As an examples of boil off gas flaring arrangements it is referred to publications WO 00/47463 A1 and DE 202005009890 U1 . [007] As the critical component in such combined, or independent system, for providing inert gas or burning excess gas, is the burner itself, it has been found a need to develop a burner which provides better performance than known burners. [008] An object of the invention is to provide a burner suitable for inerting a gas tank in a marine vessel with minimised pressure drop and adjustable operation.

Disclosure of the Invention [009] Objects of the invention can be met substantially as is disclosed in the independent claim and in the other claims describing more details of different embodiments of the invention.

[0010] According to an embodiment of the invention a dual fuel burner comprises:

an air duct part configured to introduce combustion air having a longitudinal center axis, wherein the air duct part comprises an inlet section and an outlet sections having their longitudinal center axes at an angle in respect to each other, a liquid fuel nozzle arranged to the outlet section,

a gaseous fuel nozzle arranged to the outlet section, and

a throat part and a diffusor part arranged successively in the outlet section of the air duct part.

[001 1 ] The liquid fuel nozzle and the gaseous fuel nozzle are symmetrically arranged in respect to the longitudinal center axis of the outlet section, and the gaseous fuel nozzle is arranged in coaxial relation with the liquid fuel nozzle. [0012] Position of the liquid fuel nozzle is adjustable in the direction of the longitudinal center axis at the outlet section and a position of the gaseous fuel nozzle is adjustable in the direction of the longitudinal center axis at the outlet section of the air duct part.

[0013] According to an embodiment of the invention the inlet section and the outlet section of the air duct part are arranged at substantially right angle in respect to each other.

[0014] According to an embodiment of the invention the position of the liquid fuel nozzle and the position of the gaseous fuel nozzle are independently adjustable. [0015] According to an embodiment of the invention the outlet section is of cylindrical cross section having a first diameter, and wherein the throat part having a second diameter less than the first diameter.

[0016] According to an embodiment of the invention the diameter of the throat part and the diffusor part is adjustable.

[0017] According to an embodiment of the invention the diffusor part is conical.

[0018] According to an embodiment of the invention the liquid fuel nozzle comprises a first pipe, at the end of which a nozzle head is arranged, and the first pipe is arranged inside a second pipe, wherein there is a gap arranged between the first pipe and the second pipe which gap is configured to deliver fuel to the gaseous fuel nozzle.

[0019] According to an embodiment of the invention the gaseous fuel nozzle is arranged to an annular opening of the gap between the first pipe and the second pipe. [0020] According to an embodiment of the invention the first pipe and the second pipe are arranged to extend in the outlet section of the air duct, in the longitudinal center axis thereof, from the vicinity of the throat part to a transition part between the inlet section and the outlet sections, and further through a wall of the air duct; the inlet section and the outlet sections having their longitudinal center axes at an angle in respect to each other.

[0021 ] According to an embodiment of the invention a means to adjust the position of the liquid fuel nozzle and the position of the gaseous fuel nozzle are arranged outside the air duct.

[0022] The dual fuel burner according to the invention is specifically configured for use in connection with a gaseous fuel storage and feeding system for internal combustion engines. In connection with such system a so called Inert Gas Generator (IGG) or a Gas Combustion Unit (GCU) or a combined Inert Gas Generator and Gas Combustion Unit (IGG/GCU) is used for either inert gas generation i.e. creating a non-reactive gas with mainly nitrogen and Carbon Dioxide or burning excess natural gas (methane, CH4) to convert methane (CH4) into carbon dioxide (CO2), a gas significantly less harmful to the environment or acting as a combined unit to both creating inert gas and converting CH4 to CO2, simultaneously or in- dependency.

[0023] The burner can be advantageously used for inerting a gas tank in a marine vessel, and in a process of preparing a liquefied gas tank in a marine vessel for bunkering service and/or fuel change, and in an arrangement for inerting a gas tank in a marine vessel, as is described in an International patent application number PCT/EP2016/061544, where a gas treatment unit corresponds to the dual fuel burner, the contents of which is incorporated by reference.

[0024] 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 depending 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

[0025] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates a dual fuel burner according to an embodiment of the invention, and Figure 2 illustrates a detail of a dual fuel burner according to an embodiment of the invention. Detailed Description of Drawings

[0026] Figure 1 depicts schematically a dual fuel burner 10 according to an embodiment of the invention which is configured to combust liquid fuel, such as a light fuel oil, and gaseous fuel, such as LNG, LPG, etc. In the following the dual fuel burner 10 is referred to as a burner 10 for sake of simplicity.

[0027] The burner 10 comprises an air duct part 12 via which the air needed for combustion of fuel is introduced into a combustion section 16 of the burner 10. The air duct part 12 is generally of circular cross section having a longitudinal center axis 14. The air duct part 12 comprises an inlet section 12.1 and an outlet section 12.2. The longitudinal center axis 14 has a first section 14.1 at the inlet section 12.1 and a second section 14.2 the outlet section 12.2 which sections 14. ,14.2 are at an angle in respect with each other, substantially at right angle. This way the dimension of the burner 10 in the direction of the second section of the longitudinal axis 14.2 is minimized. The air duct part 12 comprises a transition part 18 by means of which the change of the angle between the inlet section 12.1 and the outlet section 12.2 is accomplished i.e. the change of direction of the sections. The angle need not to be exactly a right angle to provide a fuel nozzle assembly 26 lead through into the air duct part, but the angle of more than 45 degrees would suffice. In the figure 1 the transition part 18 comprises a set of guide vanes 20 which facilitates smooth change of flow direction of the air. The guide vanes 20 has their leading edge in the direction of the first section 14.1 of the longitudinal center axis 14 and their trailing edge in the direction of the second section 14.2 of the longitudinal center axis 14. The set of guide vanes 20 forms a grid which covers the whole face area of the air duct part. By using the guide vanes the inlet section 12.1 and the outlet section 12.2 can be arranged to meet even at a right angle with each other, as is shown in the figure 1.

[0028] The burner 10 comprises a throat part 22 and a diffusor part 24 arranged at the end of the outlet section 12.2 of the air duct part 12. The throat part 22 and the diffusor part 24 are arranged as an extension of the outlet section 12.2 successively in the direction of the second section 14.2 of the longitudinal axis 14. The outlet section 12.2 has a first diameter D1 and the throat part 22 has a second diameter D2 which is less than the first diameter. The diffusor part begins from the throat part 22 and has its diameter gradually extending from its first end to its second end. [0029] The burner 10 is provided with a fuel nozzle assembly 26 into which a liquid fuel nozzle 28 and a gaseous fuel nozzle 30 are arranged. The liquid fuel nozzle 28 is arranged symmetrically in respect to the longitudinal center axis 14 of the outlet section 12.2. Respectively, the gaseous fuel nozzle 20 is also arranged symmetrically in respect to the longitudinal center axis 14 of the outlet section 12.2. Additionally the gaseous fuel nozzle 20 is arranged in coaxial relation with the liquid fuel nozzle 28.

[0030] The fuel nozzle assembly 26 comprises an elongated body 32 which is provided with a cylindrical inner space. The body is advantageously, but not necessarily, formed of a tube such that also the outer surface of the body is generally cylindrical. The body 32 is attached to the air duct part 12 of the burner 10 such that it extends in the direction of, and along with the second section 14.2 of the longitudinal center axis 14 through a wall of the inlet section 12.1 of the air duct part 12. Inlets of the gaseous fuel and liquid fuel are arranged into a first end of the fuel nozzle assemble 26 and fuel nozzles to its second end. [0031 ] The second end of the body 32 which is extending into the air duct part 12 is supported to the outlet section 12.2 of the air duct part 12 by a support member 34. The support member 34 is also provided with a swirl plate or blades 36, as is shown in the figure 1 , for providing rotational movement of the air around the center axis 14 to the air flowing through the swirl blades 36. The liquid fuel nozzle 28 and the gaseous fuel nozzle 30 are arranged downstream from the swirl blades 36 in the flow direction of the air, when the burner is in use. This way the transition of the flow direction creates only minimal pressure drop.

[0032] The fuel nozzle assembly 26 comprises a first pipe 38 and a second pipe 40 which are arranged coaxially slidable with each other, such that the first pipe 38 is arranged to extend inside the second pipe 40. The first pipe 38 and the second pipe 40 are arranged inside the body 32. The first pipe 38 extends through an end of the second pipe 40 inside the burner. The inner diameter of the second pipe 40 is greater than the outer diameter of the first pipe 38 such that there is an annular gap 42 formed between the pipes. The gap 42 serves as a flow channel for the gaseous fuel. There is a sealing 43 arranged into the gap 42 for preventing the leakage of the gaseous fuel. The first pipe 38 is arranged adjustably into the body 32 such the position of the first pipe 38 can be changed independently in respect to the body 32 and the second pipe 40.

[0033] The longitudinal position of the second pipe 40 can be changed in respect to the body 32 and the first pipe 38. The gaseous fuel nozzle is arranged at the opening end of the annular gap 42 and therefore also the position of the gaseous fuel nozzle is adjustable in the direction of the second section 14.2 of the longitudinal center axis 14. Respectively the second pipe 40 is arranged independently adjustably into the body 32. Also the longitudinal position of the first pipe 38 can be changed in respect to the body 32 and the second pipe 40. The liquid fuel nozzle is therefore also adjustable in the direction of the second section 14.2 of the longitudinal center axis 14. The second pipe 40 is provided with a nozzle head 44 at the end thereof so that a desired fuel jet can be provided. Thus, both the first pipe 38 and the second pipe 40 are independently adjustable in relation to the body 32 of the burner 10 and each other.

[0034] The body 32 of the fuel nozzle assembly 26 is provided with an opening 46 at a section outside the air duct part 12 in the side of the body. There is a gas feed pipe 48 arranged to extend through the opening 46 inside the body 32. The gas feed pipe 48 is coupled with the second pipe 40 such that they are in flow communication with each other for introducing gaseous fuel into the second pipe 40, more particularly into the gap 42. The sealing 43 in the gap 42 is arranged at the opposite end to the gaseous fuel nozzle i.e. at the first end thereof. Thus, the gas feed pipe 48 is arranged to the region between the sealing 43 and the gaseous fuel nozzle. The opening 46 is oblong i.e. longer in the direction of the second section 14.2 of the longitudinal center axis 14 than in transverse direction i.e. along the perimeter of the body 32. Since the oblong opening 46 allows the change of position of the gas feed pipe 48 in respect to the body 32, this therefore makes it possible to change the position of the second pipe 40 in respect to the body 32 also. [0035] At the first end of the fuel nozzle assembly opposite to the end where the actual fuel nozzles are located, there is a means 50 to adjust the position of the liquid fuel nozzle 28 and the position of the gaseous fuel nozzle 30. The means to adjust the position of the nozzle is configured to move the first and the second pipes 38, 40 in their longitudinal direction, independently from each other in respect to the body 32. This is realized according to an embodiment of the invention by means of a worm gears 52, linear motors or alike coupled between the body and both the first and the second pipe. The body 32 is provided with a fixing points 54 where the worm gears are fixed rotatable. At least one of the worm gears is coupled with the second pipe 40 and at least one of the worm gears is coupled with the first pipe 38 such that when the worm gear is activated the position of the first pipe and/or the second pipe is changed in respect to the body 32.

[0036] Figure 2 there is shown a perspective view of the throat part 22 and the diffusor part 24 according to another embodiment of the invention. The throat part 22 and the diffusor part are formed of rotatable segments 21 arranged on a perimeter of the outlet section 12.2 of the air duct part 12 (not shown in the figure 2). This way the part 22 and the diffusor part 24 are configured to be adjustable. More particularly, in the embodiment shown in the figure 2 the throat part 22 and the diffusor part 24 are formed into a common segment plate 21 so that the ratio of the diameter of the throat part to the diffusor part remains substantially equal.

[0037] Each segment 21 is pivotably attached e.g. by a pivot pin 56 in a body flange 60 to a hole 58 in the segment 21. The segments are provided with a guide groove 62 into which a control stem 64 is arranged. The control stems 64 are coupled to a control flange 66. The control stems 64, the control flange 66 (shown schematically as a circle line), the guide groove 62, the pivot pin 56 and the hole 58 and such arranged that the rotational movement (arrow 68) is transformed into expansion or extraction of the adjustable throat part 22 and diffusor part 24. When the adjustable throat part 22 - diffusor part 24 is used it replaces the throat part 22 and the diffusor part 24 in the figure 1 by assembling it in connection with the outlet section 12.2 of the air duct part 12.

[0038] It should be noted that the cross sectional shapes of inner wall of the body of the burner and the outer wall of the second pipe, and respectively the inner wall of the second pipe and the outer wall of the first pipe are not necessarily circular, as far as the operation described herein is achievable. Thus, the cross section may be also for example rectangular.

[0039] 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 to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.