Patent Description:
In different situations, combustion of a fluid, such as gas or a mixture of gas and liquid, may be required. For example, gas combustion units are typically installed onboard LNG carriers, i.e. tank ships arranged to transport liquefied natural gas, LNG. The LNG, which has a vaporization temperature of -<NUM> degrees Celsius at atmospheric pressure, is contained in tanks. Even if these tanks are insulated, some evaporation of the LNG will inevitably take place and form so-called boil-off gas. This boil-off gas increases the pressure in the tanks and must be discharged from the tanks for the sake of safety. The boil-off gas removed from the tanks may be re-liquefied and returned to the tanks, used as fuel onboard the LNG carriers, or combusted by means of the gas combustion units.

A gas combustion unit may typically comprise a gas burner head extending into a combustion chamber. The gas to be combusted is fed, via the gas burner head, to the combustion chamber where it is ignited and burned. A known gas burner head comprises a perforated tube with an end closed by a cap. The gas is conveyed through the tube and, through the perforations of the tube, into the combustion chamber where the combustion takes place in a flame. When the gas pressure is relatively high, the gas will be fed through the perforations at a high velocity which will result in a flame at some distance from the gas burner head. Further, the gas flow inside the tube will cool the gas burner head. As a result, the temperature of the gas burner head will be kept low enough so as to avoid damages thereto. However, when the gas pressure is relatively low, the gas will be fed through the perforations at a low velocity which will result in a flame closer to the gas burner head. Further, the cooling of the gas burner head by the gas flow inside the tube will be reduced. This may result in very high temperatures in, and damages to, the gas burner head, typically in areas close to the closed end of the tube. <CIT> discloses a fluid burner head having the features of the preamble of claim <NUM>.

An object of the present invention is to provide a fluid burner head and a use of a fluid burner head that at least partly solves the problem above. The basic concept of the invention is to provide the fluid burner head with means for forcing the fluid to be combusted, and thus the combustion flame, further away from the fluid burner head. The fluid burner head, and the use of a fluid burner head, for achieving the object above is defined in the appended claims and discussed below.

A fluid burner head for a fluid combustion unit according to the invention comprises a body. The body comprises a hollow tube or pipe for conveying a fluid to be combusted into a combustion chamber and a cap which at least partly closes an upper end of the tube. The tube further comprises a lower end for receiving the fluid in the tube, i.e. in an interior of the tube. A wall of the tube comprises a plurality of rows of holes, which rows extend around a longitudinal center axis of the fluid burner head. The holes permit a flow of the fluid to be combusted from the interior to an exterior of the tube, i.e. through the wall of the tube. The fluid burner head is characterized in that it further comprises an annular first projection or protrusion extending around the longitudinal center axis of the fluid burner head. The first projection is projecting obliquely from an outer surface of the body and in a direction away from the lower end of the tube, i.e. upwards, above an uppermost row of holes of the tube, with an angle α relative to the longitudinal center axis of the fluid burner head, wherein <NUM> < α < <NUM> degrees. The uppermost row of holes is the row of holes being arranged closest to the cap.

The first projection may comprise opposing first and second edges. The first and second edges may be annular and extend along each other. The first projection may engage, directly or indirectly, with the body at and along the first edge and the second edge may be free.

Herein, "combust" and "burn" and variants thereof are used and intended to have the same meaning.

The fluid may be a gas or a mixture of a gas and a liquid. As an example, the fluid may be boil-off gas from a LNG tank, such as methane or a mixture of methane and nitrogen.

The tube could comprise a mesh formed into a cylinder.

The tube could be a perforated tube and the openings could be perforations of the tube.

The tube may be elongate, have any suitable wall thickness and have any suitable cross section, such as circular, oval or polygonal.

The tube may be made of any suitable material such as a metal, for example carbon steel, stainless steel or aluminum.

The longitudinal center axis of the fluid burner head may coincide with a longitudinal center axis of the tube.

By plurality of rows is here meant two or more rows.

The holes, openings, apertures or perforations of the tube may or may not all have the same size and/or shape, and they may have any suitable size and shape, such as circular, oval or polygonal. Further, the holes may or may not be equidistantly arranged.

"Annular" need not mean a circular longitudinal extension but could mean any closed longitudinal extension, such as an oval or polygonal extension.

Herein, "upper", "uppermost", "lower", "lowermost", "above", "below" etc. are references made to the fluid burner head when this is orientated for its normal state of use. Further, by "uppermost"/"lowermost" is meant arranged furthest from/closest to the ground or a surface on which a fluid combustion unit comprising the fluid burner head is arranged.

As said above, the cap closes the upper end of the tube at least partly. Here, an only partly closed upper end may for example mean that it is possible for gas to pass from within the tube to an outside thereof through an opening in the cap or between the tube and the cap.

The first projection may or may not have a uniform cross section, for example a constant width and/or thickness, along its longitudinal extension. As an example, the first projection could be formed as a skirt or flange. If the width and thickness is zero along one or more portions of the longitudinal extension, the first projection may be considered discontinuous.

The first projection is arranged to force the fluid to be combusted away from the fluid burner head to reduce the temperature of the fluid burner head and, thereby, the risk of damages to the fluid burner head, also when the fluid is fed through the holes of the tube at a relatively low velocity.

The tube and the cap may be integrally formed. However, according to one embodiment of the invention, the tube and the cap are separately formed. Thereby, the tube and the cap can be replaced independent of each other if needed.

The tube and the cap may be made of the same material. However, according to one embodiment of the invention, the cap and the tube are made of different materials. This may enable a more flexible construction of the fluid burner head. The cap may be made of any suitable material, such as refractory concrete or a metal, for example carbon steel, stainless steel or aluminum.

The first projection may be arranged anywhere between the uppermost row of holes of the tube and an upper end of the fluid burner head. However, according to one embodiment of the invention, the first projection projects from the outer surface of the body at a border between the tube and the cap. Without the first projection in place, the temperature locally at the border between the tube and the cap tends to be relatively high. Thus, by arranging the first projection at the tube-cap border, the risk of damages to the fluid burner head may be minimized.

The fluid burner head may be so constructed that the tube and the first projection are separately formed. Thereby, when the first projection is worn out it can be replaced with a new one without having to discard the tube and possibly the cap.

The tube may have a varying cross section along its longitudinal center axis. However, according to one embodiment of the invention, an upper portion of the tube comprising the holes has an essentially uniform cross section along the longitudinal center axis of the fluid burner head. This may facilitate production of the fluid burner head.

The fluid burner head may further comprise an annular support extending around the longitudinal center axis of the fluid burner head. The support may be connected to the first projection and engage with the body of the fluid burner head to fix the first projection to the body. Such a design may facilitate the arrangement of the first projection on the body. Just like the first projection, the support may or may not have a uniform cross section along its longitudinal extension, and be continuous or discontinuous.

The fluid burner head may further comprise an annular second projection extending around the longitudinal center axis of the fluid burner head. The second projection may project from the outer surface of the body between the uppermost row of holes of the tube and the first projection. The first projection may or may not project beyond the second projection. The second projection may aid in forcing the fluid to be combusted away from the fluid burner head to further reduce the temperature of the fluid burner head and, thereby, the risk of damages to the fluid burner head, also when the fluid is fed through the holes of the tube at a relatively low velocity.

The second projection may project from an outer surface of the tube to shield the tube locally in an area where the temperature of the tube otherwise tends to be relatively high. The risk of damages to the tube may thereby be minimized.

As said above, the fluid burner head may comprise an annular support extending around the longitudinal center axis of the fluid burner head. The support may be connected to both the first projection and the second projection and engage with the body of the fluid burner head to fix the first and second projections to the body.

Irrespective of if the support is connected to only the first projection or also to the second projection, it may engage in different ways with the body. As an example, it may be threaded onto the body with a tight fit so as to stay in place by friction. However, according to one embodiment of the invention, the support is clamped between the cap and the tube. Thereby, a precise location of the first projection and possibly also the second projection may be enabled, together with a reliable engagement between the support and the body of the fluid burner head.

The cap may be designed in many different ways. According to one embodiment of the invention it comprises an upper portion and a bottom portion, wherein the bottom portion projects into the tube. Thereby, a safe and precise engagement between the cap and the tube may be enabled.

The bottom portion of the cap may comprise a part which is tapering in a direction away from the upper portion of the cap. For example, the bottom portion may be conical, and possibly truncated conical. This may result in a flow area inside the tube, perpendicular to the longitudinal center axis of the tube, which is decreasing in a direction towards the cap, i.e. towards the upper end of the tube. In turn, this may result in a fluid flow velocity inside the tube which is increasing in a direction towards the cap, i.e. towards the upper end of the tube. Consequently, this design may enable forcing of the fluid fed through upper holes of the tube, and thus the combustion flame, further away from the fluid burner head. Thereby, further lowering of the temperature of the fluid burner head, and the risk of damages to the fluid burner head, may be enabled, especially when the fluid is fed through the tube at a relatively low pressure.

The fluid burner head may be so designed that an outer circumference of the upper portion of the cap is larger than an inner circumference of the tube. Thereby, the upper portion of the cap is prevented from being received in the tube which may enable a precise and safe engagement between the cap and the tube.

A fluid burner head according to the present invention may be used in a fluid combustion unit for burning boil-off gas from a fuel tank onboard a ship.

The above discussed advantages of the different embodiments of the fluid burner head according to the invention are naturally transferable to different embodiments of the use according to the invention.

The invention will now be described in more detail with reference to the appended schematic drawings, in which.

In <FIG> a fluid combustion unit <NUM>, more particularly a gas combustion unit, is illustrated. The fluid or gas combustion unit <NUM> is arranged onboard a ship (not illustrated), more particularly an LNG carrier, for burning boil-off gas from one or more LNG tanks of the ship. The fluid combustion unit <NUM> comprises a fluid burner system <NUM>, an air supply system (not illustrated), a combustion chamber <NUM> and a stack <NUM>. Boil-off gas from the LNG tank(s) is fed to the fluid burner system <NUM> and further into the combustion chamber <NUM> wherein it is ignited and combusted. The combustion products leave the combustion chamber <NUM> to be mixed with cool air in the stack <NUM> before leaving the fluid combustion unit <NUM>. The construction and function of fluid combustion units are well-known within the art and will not be described in further detail herein.

The fluid burner system <NUM> comprises a fluid burner head <NUM>, more particularly a gas burner head, which is illustrated in further detail in <FIG>. The fluid burner head <NUM> comprises a body <NUM>, which in turn comprises a hollow, elongate stainless steel tube <NUM> and a solid cap <NUM> of refractory concrete. The tube <NUM> and the cap <NUM> are discrete separable elements having a circular outer periphery as seen along a longitudinal center axis C of the fluid burner head <NUM>.

The tube <NUM> has a wall <NUM> of uniform thickness along and around the longitudinal center axis C of the fluid burner head <NUM>. With reference to <FIG> it comprises a lower end <NUM>, a lower portion <NUM>, an upper portion <NUM> and an upper end <NUM> arranged in succession along the longitudinal center axis C. The upper portion <NUM> of the tube <NUM> comprises a great number of circular holes <NUM> extending through the wall <NUM> of the tube <NUM>. The holes <NUM> are equidistantly arranged in rows <NUM>. The rows <NUM> of the holes <NUM> are parallel to each other and extend equidistantly around the longitudinal center axis C of the fluid burner head <NUM>.

With reference to <FIG>, the cap <NUM> comprises an upper portion <NUM> and a bottom portion <NUM> which are concentrically arranged with reference to the longitudinal center axis C of the fluid burner head <NUM>. The border between the upper and bottom portions <NUM> and <NUM> of the cap <NUM> is illustrated with a broken line. The upper portion <NUM> has the essential shape of a circular plate with a constant cross section along the longitudinal center axis C. The bottom portion has the essential shape of a truncated cone with a circular cross section which is decreasing along the longitudinal center axis C in a direction away from the upper portion <NUM> of the cap <NUM>. The largest cross section of the bottom portion <NUM> is smaller than the cross section of the upper portion <NUM>.

As is clear from the drawings, and especially <FIG>, the cap <NUM> closes the upper end <NUM> of the tube <NUM>. The bottom portion <NUM> of the cap <NUM> has a largest circumference which is smaller than an inner circumference of the tube <NUM> and it is accommodated inside the tube <NUM>. The upper portion <NUM> of the cap <NUM> has a circumference which is essentially equal to an outer circumference of the tube <NUM> and larger than the inner circumference of the tube <NUM>. The upper portion <NUM> of the cap <NUM> is arranged outside the tube <NUM> and abuts an annular edge thereof defining the upper end <NUM> of the tube <NUM>. Due to the above specified relative dimensions of the tube <NUM> and the cap <NUM>, an annular groove <NUM> is formed between the bottom portion <NUM> of the cap <NUM> and the tube <NUM>.

With reference to <FIG>, the fluid burner head <NUM> further comprises an annular support <NUM> in the form of a flat circular ring of stainless steel, an annular first projection <NUM> in the form of a circularly extending skirt of stainless steel, and an annular second projection <NUM> in the form of a very short tube with circular cross section and of stainless steel. The support <NUM>, the first projection <NUM> and the second projection <NUM> are concentrically arranged with reference to the longitudinal center axis C of the fluid burner head <NUM>. The first projection <NUM> projects upwards and outwards from an outer edge of the support <NUM> while the second projection projects downwards from the outer edge of the support <NUM>. The support <NUM>, the first projection <NUM> and the second projection <NUM> are integrally formed into an arrangement designed to cooperate with the body <NUM> of the fluid burner head <NUM>. More particularly, the support <NUM> is positioned and clamped between the tube <NUM> and the cap <NUM> with the first and second projections <NUM> and <NUM> projecting from an outer surface <NUM> of the body <NUM> (<FIG>). The first projection <NUM> has annular longitudinal first and second edges 39a and 39b extending along each other (<FIG>). The first projection <NUM> engages with the body <NUM> indirectly, more particularly via the support <NUM>, at and along the first edge 39a while the second edge 39b is free. The second projection <NUM> has annular longitudinal first and second edges 41a and 41b extending along each other (<FIG>). The second projection <NUM> encircles the body <NUM> and an inside thereof contacts the outer surface <NUM> of the body <NUM> between the first and second edges 41a and 41b. The tube <NUM> and the cap <NUM> are connected by means of elements not illustrated in the drawings. Thereby, the support <NUM> and the first and second projections <NUM> and <NUM> extend around the longitudinal center axis C of the fluid burner head <NUM> at a border <NUM> between the tube <NUM> and the cap <NUM> (<FIG>), i.e. above an uppermost row 29a of the rows <NUM> of holes <NUM> (<FIG>). Further, with special reference to <FIG>, the support <NUM> is clamped between the tube <NUM> and the cap <NUM> such that the first projection <NUM> projects obliquely upwards with an angle α = <NUM> degrees in relation to the longitudinal center axis C of the fluid burner head <NUM>, while the second projection <NUM> projects downwards and from an outer surface <NUM> of the tube <NUM> so as to enclose an uppermost portion of the tube <NUM>.

The fluid burner head <NUM> is arranged to convey the boil-off gas to be combusted into the combustion chamber <NUM> of the fluid combustion unit <NUM> (<FIG>). More particularly, with reference to <FIG>, the boil-off gas is arranged to be fed into an interior <NUM> of the tube <NUM> of the fluid burner head <NUM> via the lower end <NUM> of the tube <NUM>, then upwards through the lower portion <NUM> of the tube <NUM>, and then into the upper portion <NUM> of the tube <NUM> and further through the holes <NUM> of the tube wall <NUM> to an exterior <NUM> of the tube <NUM> and thus into the combustion chamber <NUM> (<FIG>). Inside the combustion chamber <NUM>, the boil-off gas is ignited and combusted in a flame, as previously discussed. The first and second projections <NUM> and <NUM> are arranged to force the boil-off gas, and consequently the combustion frame, away from the body <NUM> of the fluid burner head such that its temperature is kept low enough to avoid melting damages to the tube <NUM> and cracking damages to the cap <NUM>, even when the boil-off gas pressure and the boil-off gas velocity through the holes <NUM> are relatively low. The frustoconical shape of the bottom portion <NUM> of the cap <NUM> is arranged to speed up the boil-off gas velocity through the holes <NUM> close to the upper end <NUM> of the tube <NUM> to aid in the lowering of the temperature of the body <NUM> and, thus, the minimization of damages to the body <NUM>. The first and second projections <NUM> and <NUM> will protect and shield the body <NUM> of the fluid burner head <NUM> and will be subjected to an harsh environment. If and when the first and second projections <NUM> and <NUM> are damaged, the arrangement composed of the support <NUM> and he first and second projections <NUM> and <NUM> may be replaced with a new one while the tube <NUM> and cap <NUM> may be further used.

The above described embodiment of the present invention should only be seen as an example. A person skilled in the art realizes that the embodiment discussed can be varied in a number of ways without deviating from the inventive conception.

As an example, the fluid burner head need not comprise the second projection but could comprise the first projection only.

As another example, the fluid burner head need not comprise the support for fixing the first projection, and possibly the second projection, to the body of the fluid burner head. Instead, the first projection, and possibly the second projection, could be directly fixed to the body of the fluid burner head.

As yet another example, the support need not be fastened to the body of the fluid burner head by being clamped between the tube and the cap. In an alternative embodiment of the invention, the support could be arranged on the outside of the tube and/or the cap, with a tight fit so as to stay in place by friction. Accordingly, the first and second projections need not be arranged at the border between the tube and the cap.

The first and second projections need not be formed separate from the tube and the cap but could be formed integrally with the tube and/or the cap. Such a design may destroy the possibility of replacing only the first and second projections, and the support if present, if these are damaged.

The angle α between the first projection and the longitudinal center axis of the fluid burner head need not have the above value but may be larger or smaller.

The tube and the cap need not be separately formed and made of different materials but could instead be integrally formed and/or made of the same material.

Claim 1:
A fluid burner head (<NUM>) for a fluid combustion unit (<NUM>) comprising a body (<NUM>) which in turn comprises a hollow tube (<NUM>) for conveying a fluid to be combusted into a combustion chamber (<NUM>) and a cap (<NUM>) which at least partly closes an upper end (<NUM>) of the tube (<NUM>), the tube (<NUM>) further comprising a lower end (<NUM>) for receiving the fluid in the tube (<NUM>), a wall (<NUM>) of the tube (<NUM>) comprising a plurality of rows (<NUM>) of holes (<NUM>), which rows (<NUM>) extend around a longitudinal center axis (C) of the fluid burner head (<NUM>), an uppermost row (29a) of holes (<NUM>) being the row of holes (<NUM>) arranged closest to the cap (<NUM>), wherein the holes (<NUM>) permit a flow of the fluid to be combusted from an interior (<NUM>) to an exterior (<NUM>) of the tube (<NUM>), the fluid burner head (<NUM>) being characterized in that it further comprises an annular first projection (<NUM>) extending around the longitudinal center axis (C) of the fluid burner head (<NUM>) and projecting obliquely from an outer surface (<NUM>) of the body (<NUM>) and away from the lower end (<NUM>) of the tube (<NUM>), above the uppermost row (29a) of holes (<NUM>) of the tube (<NUM>), with an angle α relative to the longitudinal center axis (C) of the fluid burner head (<NUM>), wherein <NUM> < α < <NUM> degrees.