Marine boiler and method of operating a marine boiler

Abstract

A marine boiler and a method of operating the marine boiler are provided for transferring heat from exhaust gases EG1, EG2 to a medium in the form of boiler water to produce steam on board a ship. The marine boiler comprises a vessel, an exhaust gas inlet for receiving exhaust gases EG1 from a first exhaust gas source 4, a first exhaust gas outlet for discharging exhaust gases from the first exhaust gas source, and a means for conveying the exhaust gas to the first exhaust gas outlet. The marine boiler further comprises a medium inlet for receiving the medium, a steam space S inside the vessel for storing the medium after heating by the exhaust gas, a medium outlet for discharging the medium, and a means for conveying the medium from the medium inlet to the medium outlet. The marine boiler is characterized in that it further comprises an electric heater 44 for heating the medium by electricity supplied from a power source 52, the power source 52 being separate from the first exhaust gas source 4, and the steam space S being arranged to store the medium after heating by the electric heater 44.

Description

Technical Field

[0001] The present invention relates to a marine boiler for transferring heat from exhaust gas to a medium on board a ship, and to its design. The present invention also relates to a method of operating such a marine boiler.

Background Art

[0002] Boilers are well known and used in many different heat exchange applications. For example, a marine boiler may be placed on a ship behind an exhaust gas source in the form of one or more main engines for propelling the ship, and optionally one or more auxiliary engines, in order to recover heat from the exhaust gas generated by the engines. Such marine boilers are often referred to as heat recovery marine boilers. In such a marine boiler, a medium carried through the marine boiler, typically water, is heated by the heat from the engine exhaust gas carried through the marine boiler, thereby typically producing hot water and steam. The hot water and steam exiting the marine boiler are used for various purposes on board the ship.

[0003] In open seas where the ship may move at a relatively high speed and the main engine may be operated at a relatively high engine load, a sufficient amount of hot water and steam can be produced by the exhaust gas generated by the engine to meet the demand on board. When the ship is in a port or in an area that should be handled with care, and the ship may move at a relatively low speed or not move at all, the main engine is typically operated at a relatively low engine load or not operated at all. In that case, an insufficient amount of hot water and steam may be produced by the exhaust gas generated by the engine. Also, to ensure sufficient production of hot water and steam when the main engine is operated at a low or zero engine load, the marine boiler may be equipped with a burner configured to supply oil and / or gas and burn them to generate combustion gas for the production of hot water and steam. The problem is that the exhaust gas from the engine and the combustion gas from the burner usually contain pollutants. Pollutants are harmful to the environment and are particularly undesirable in ports and areas that should be handled with care.

[0004] Patent Document 1 discloses an exhaust heat recovery type ice system for removing ice on the deck of a ship operating in a cold environment.

[0005] Patent Document 2 discloses a marine system for optimal use of heat, and the marine system includes a heat generating unit and a heat consuming unit.

[0006] Patent Document 3 discloses a system for ship waste heat utilization.

[0007] Patent Document 4 discloses a device for reusing the condensate water and waste heat of a ship.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to provide a marine boiler and a method of operating a marine boiler that at least partially solves the above problems. The basic concept of the present invention is to provide external energy to a marine boiler for the production of hot water and steam. The marine boiler and the method for achieving the above object are defined in the appended claims and discussed below.

Means for Solving the Problems

[0010] The boiler for ships according to the present invention is configured to transfer heat from exhaust gas or flue gas or combustion gas to a medium in the form of boiler water in order to produce steam on board. The boiler for ships includes a container, an exhaust gas inlet for receiving exhaust gas from a first exhaust gas source into the container, a first exhaust gas outlet for discharging the exhaust gas from the first exhaust gas source from the container, and means for transporting the exhaust gas from the exhaust gas inlet to the first exhaust gas outlet to the first exhaust gas source. The boiler for ships further includes a medium inlet for receiving a medium into the container, a steam space inside the container for storing the medium heated by the exhaust gas, a medium outlet for discharging the medium from the container, and means for transporting the medium from the medium inlet to the medium outlet. Further, the boiler for ships includes a peripheral wall provided inside the container, and inside or within the peripheral wall, the exhaust gas from the first exhaust gas source and the medium are arranged to be transported. The boiler for ships is characterized by further comprising an electric heater for heating the medium by electricity supplied from a power source. The power source is separate from the first exhaust gas source. The steam space is arranged to store the medium heated by the electric heater.

[0011] Therefore, according to the present invention, a specific medium capacity is heated by the exhaust gas from the first exhaust gas source or the electric heater, or a combination thereof. Therefore, in the boiler for ships according to the present invention, the electric heater is integrated with the rest of the boiler so as not to require another feed water system, another safety valve, a main steam system, a water level control system, etc.

[0012] The medium to be heated is boiler water, that is, water containing a certain degree of impurities. The medium changes phase, that is, from a liquid phase to a gas phase, at least partially or completely through the boiler for ships. More specifically, the medium inlet is arranged to receive the medium at least partially in the liquid phase, that is, in the form of liquid water, and the medium outlet is arranged to discharge the medium at least partially in the gas phase, that is, in the form of steam.

[0013] The steam space is at least partially, typically mainly a gas phase, a volume typically within the upper part of a container, arranged to store heated boiler water. Instead of several separate steam spaces, one common steam space is arranged to receive the boiler water heated by the exhaust gas, an electric heater, or a combination thereof, so that the marine boiler can be made relatively small with a relatively small installation area.

[0014] As described above, in the marine boiler according to the present invention, a specific medium volume is heated by the exhaust gas from a first exhaust gas source or an electric heater, or a combination thereof. The medium is pushed through the marine boiler by natural circulation without the need for a circulation pump. In this specification, the expression "carry from the inlet to the outlet" and the like means "carry in the direction from the inlet to the outlet", and does not necessarily mean all from the inlet and all to the outlet. Thus, the means for carrying the exhaust gas and the means for carrying the medium may, but not necessarily, extend throughout between their respective inlets and outlets.

[0015] The peripheral wall can have any suitable shape, such as the shape of a tube with a cross-section like circular, elliptical, polygonal, rectangular, etc. The peripheral wall can further have any suitable design, such as solid or hollow, and / or can have a uniform or non-uniform thickness. By way of example, the peripheral wall can be a so-called panel wall comprising a number of parallel tubes connected by a solid wall portion. The cooling medium may be supplied through these tubes to cool the exhaust gas carried through the marine boiler.

[0016] The components of the marine boiler can be made of any suitable material, for example, carbon steel, stainless steel or aluminum.

[0017] The electric heater may have any suitable design. By way of example, the electric heater may be an electrode heater. The marine boiler may optionally comprise one or more additional electric heaters for heating the medium by electricity supplied from said power source.

[0018] The power source for supplying electricity to the electric heater may be of any suitable design. By way of example, the power source may be configured to supply electricity produced from any suitable fuel, solar power, wind power, hydropower, nuclear power, or any combination thereof.

[0019] In that the power source is separate from the first exhaust gas source, electricity may be supplied to the electric heater even when the first exhaust gas source is not operating so as to enable sufficient production of steam and hot water. The power source may typically be a “clean” power source such that operation of the electric heater produces little or no emissions, as may occur when the ship is in a harbor or other area where care should be taken.

[0020] The power source may be separate from any exhaust gas source, such as a main or auxiliary engine, mounted on the ship. Thus, the power source may not emit exhaust gases.

[0021] The power source for supplying electricity to the electric heater may be located on board the ship. However, according to one embodiment of the present invention, the power source is separate from the ship, for example on land. Such an embodiment makes it possible to minimize the pollution caused by operation of the electric heater near the middle of the ship.

[0022] The first exhaust gas source may be of any suitable type, such as an auxiliary engine, burner or turbine. However, according to one embodiment, the first exhaust gas source comprises an engine for propelling the ship, for example a diesel or dual fuel main engine. Such an embodiment may enable automatic generation of steam and hot water when the ship is being propelled.

[0023] The marine boiler may be configured such that the means for carrying the exhaust gas from the exhaust gas inlet to the first exhaust gas outlet comprises a first bundle of tubes, and the means for carrying the medium from the medium inlet to the medium outlet comprises the peripheral wall of the marine boiler surrounding the first bundle of tubes.

[0024] The tubes and the peripheral wall can be made of the same material so as to reach substantially the same temperature during the operation of the marine boiler, which may allow relatively low thermal stresses within the marine boiler.

[0025] The tubes may have any suitable design, such as straight, curved, or coiled or helical shapes, and may have circular, elliptical, or polygonal cross-sections, and the tubes may be the same or different from each other. The tubes may be provided with surface enlarging elements such as helical fins, plate fins, or fins of any other suitable design.

[0026] The number of tubes may be two or more, and they may extend along each other and, in some cases, additionally in parallel. The longitudinal central axis of the electric heater may extend parallel or perpendicular to the tubes.

[0027] According to this embodiment, the exhaust gas is supplied through the marine boiler into the tubes surrounded by the heated medium surrounded by the peripheral wall of the marine boiler, and the heat exchange between the exhaust gas and the medium occurs through the wall surfaces of the tubes. Such a marine boiler may be called a smoke tube marine boiler.

[0028] Instead of being designed as a smoke tube marine boiler, the marine boiler may be configured such that the means for carrying the medium from the medium inlet to the medium outlet comprises one or more tubes. Further, the means for carrying the exhaust gas from the exhaust gas inlet to the first exhaust gas outlet may comprise the peripheral wall of the marine boiler surrounding the one or more tubes.

[0029] In addition, one or more such tubes may have any suitable design, such as straight, curved, coiled or spiral shapes, may have a circular, elliptical or polygonal cross-section, and may extend along each other, either in the same or different ways, parallel to each other, and may be provided with surface enlargement elements of any suitable design. Here, too, the longitudinal central axis of the electric heater may extend parallel or perpendicular to the tube.

[0030] According to this embodiment, the medium to be heated is supplied through a marine boiler in a tube surrounded by exhaust gas from a first exhaust gas source, the exhaust gas is surrounded by the peripheral wall of the marine boiler, and heat exchange between the exhaust gas and the medium occurs through the wall surface of the tube. When the medium is water, such a marine boiler may be called a water-tube marine boiler.

[0031] The design of the marine boiler may be such that the electric heater is arranged inside the peripheral wall or surrounded by the peripheral wall. This design may enable a small and component-efficient marine boiler.

[0032] In another way, the design of the marine boiler may be such that the electric heater is arranged in a container arranged outside the peripheral wall. Further, the container may communicate with the means for carrying the medium from the medium inlet to the medium outlet in order to enable the movement of the medium between the container and the means for carrying the medium from the medium inlet to the medium outlet. By way of example, the container and the means for carrying the medium from the medium inlet to the medium outlet may communicate by means of one or more pipes extending between the container and the means for carrying the medium from the medium inlet to the medium outlet, for example, one pipe for supplying the medium from the means to the container and another pipe for supplying the medium from the container to the means. When the marine boiler is provided with two or more electric heaters, they may be arranged in a common container or in separate containers. Such a plurality of containers may be connected in parallel or in series.

[0033] As used herein, "communicating" and the like mean "communicating directly or indirectly".

[0034] A method of operating a marine boiler according to the present invention for transferring heat from exhaust gas to a medium in the form of boiler water to produce steam on board a ship includes receiving exhaust gas from a first exhaust gas source into a container through an exhaust gas inlet of the marine boiler, conveying the exhaust gas from the first exhaust gas source from the exhaust gas inlet to a first exhaust gas outlet of the marine boiler, discharging the exhaust gas from the first exhaust gas source from the container through the first exhaust gas outlet, and receiving a medium into the container through a medium inlet of the marine boiler. The method of the present invention further includes conveying the medium from the medium inlet to a medium outlet of the marine boiler through a steam space of the marine boiler, the steam space being arranged to store the medium after being heated by the exhaust gas. The marine boiler includes a peripheral wall provided in the container, and inside the peripheral wall, the exhaust gas and the medium from the first exhaust gas source are arranged to be conveyed. The method further includes supplying electricity from a power source separate from the first exhaust gas source to an electric heater, heating the medium by the electric heater, and receiving the medium heated by the electric heater in the steam space.

[0035] The electric heater may be supplied with electricity only when the first exhaust gas source is operating at a low load in some cases, or when the first exhaust gas source is idle, i.e., not operating.

[0036] The method may be such that the power source is provided separately from any exhaust gas source on board the ship.

[0037] The method may be such that the power source is separate from the ship and provided on land, for example.

[0038] The method may be such that an engine for propelling the ship is provided as the first exhaust gas source.

[0039] The electric heater may be provided inside the peripheral wall.

[0040] In another way, the electric heater may be provided in a container arranged outside the peripheral wall, and the container may be provided in communication with the means for carrying the medium from the medium inlet to the medium outlet.

[0041] The advantages discussed above for different embodiments of the boiler for ships according to the present invention can be naturally transferred to different embodiments of the method according to the present invention.

[0042] Further other objects, features, aspects and advantages of the present invention will be apparent from the following detailed description and the drawings.

[0043] The present invention will now be described in more detail with reference to the accompanying schematic drawings.

Brief Description of the Drawings

[0044]

Figure 1a

Figure 1b

Figure 2

Figure 3a

Figure 3b

Figure 4a

Figure 4b

Figure 5

Figure 6

Figure 7

MODE FOR CARRYING OUT THE INVENTION

[0045] In FIGS. 1a and 1b, a smoke tube type marine boiler 2 is illustrated. The marine boiler 2 is arranged on a ship (not shown) and is connected by a duct 6 to a first exhaust gas source 4 in the form of a diesel engine 4a of the ship, the engine 4a being configured to propel the ship. The exhaust gas EG1 generated by the diesel engine 4a is supplied through the duct 6 to the marine boiler 2 for exhaust gas heat recovery. The marine boiler 2 comprises a carbon steel vessel 8 which comprises a lower chamber or header 10, a housing 12 and an upper chamber or header 14 arranged in vertical longitudinal continuity. Both the lower chamber 10 and the housing 12 have a cylindrical shape and are integrally formed so as to have a similar cross-section and be arranged concentrically. The upper chamber 14 has a partially cylindrical shape and a smaller cross-section than the lower chamber 10 and the housing 12.

[0046] The marine boiler 2 further comprises exhaust gas conveying means 16 in the form of a first bundle of carbon steel tubes 18 extending inside the container 8 between the carbon steel lower tube plate 22 and the upper tube plate 24, the plates forming the lower and upper wall surfaces of the housing 12 separating the housing 12 from the lower and upper chambers 10, 14. The tubes 18 are basically straight, have a circular cross-section, and extend parallel to each other and to the longitudinal central axis c of the housing 12. The tubes 18 are arranged to carry the exhaust gas EG1 through the container 8, the exhaust gas EG1 being received by the marine boiler 2 through an exhaust gas inlet 26 extending into the lower chamber 10 and discharged by the marine boiler 2 through a first exhaust gas outlet 28 extending from the upper chamber 14. When the diesel engine 4a is operating, the exhaust gas EG1 is supplied through the exhaust gas inlet 26 into the lower chamber 10, through the tubes 18 into the upper chamber 14, and through the first exhaust gas outlet 28.

[0047] Furthermore, the marine boiler 2 comprises a furnace 30 arranged inside the container 8 and a second bundle of carbon steel tubes 34 extending inside the housing 12 between the furnace 30 and the upper tube plate 24 of the marine boiler. The tubes 34 are basically straight, have a circular cross-section, and extend parallel to each other and to the longitudinal central axis c of the housing 12. The tubes 34 are arranged to carry the exhaust gas EG2 from a second exhaust gas source in the form of an oil-fired burner (not shown) arranged inside the furnace 30 through the housing 12 before the exhaust gas EG2 exits the marine boiler 2 through a second exhaust gas outlet 36 arranged in the upper tube plate 24.

[0048] The housing 12 of the marine boiler 2 is filled with a medium, here boiler water (also simply called water herein), supplied into the housing 12 through a medium inlet 38. The boiler water may have different characteristics and may meet the following requirements according to the EN boiler standards.

[0049]

Table 1

[0050] The housing 12 is filled with boiler water up to level L, and a steam space S is formed above the water volume between level L and the upper wall surface of the housing 12. During the operation of the engine 4, the exhaust gas EG1 is supplied through the pipe 18. Further, when the burner using oil as fuel is operating, the exhaust gas EG2 is supplied through the pipe 34. The water surrounds the pipe 18, the pipe 34, and the furnace 30 and flows around them. Since the water is colder than the exhaust gases EG1 and EG2, heat is transferred from the exhaust gases through the pipe walls and the furnace to the water that is heated and converted into steam collected in the steam space S before exiting the marine boiler 2 through the medium outlet 40. Of course, due to the steam velocity, there is also a small amount of liquid water in the steam space S that exits the marine boiler 2 through the medium outlet 40, and the liquid water is mixed with the steam. Thus, the housing 12 including its peripheral wall 42 serves as means 32 for carrying the medium from the medium inlet 38 to the medium outlet 40. The housing 12, the pipe 18, and the pipe 34 are made of the same material and are all exposed to a common water volume, so their temperatures are relatively slightly different, resulting in relatively limited thermal stresses within the marine boiler.

[0051] The marine boiler 2 further comprises an electric heater 44 in the form of an electrode heater, a cylindrical container 46, an inlet pipe 48, and an outlet pipe 50. The pipes extend between the housing 12 and the container 46 and fluidly connect them. The electric heater 44 extends into the cylindrical container 46, and the longitudinal central axis of the electric heater 44 extends basically parallel to the longitudinal central axis c of the housing 12 and the longitudinal central axis of the container 46. The electric heater 44 is arranged to be connected to an external power supply 52 located on land, for example in a harbor, and is supplied with electricity when the ship is not moving and the engine 4a is not operating or is operating at a low load.

[0052] The cylindrical container 46 is filled with water, and the water is supplied from the housing 12 into the container 46 through the inlet pipe 48. During the operation of the electric heater 44, heat is transferred from the electric heater 44 to the water that is heated and supplied from the container 46 into the steam space S in the housing 12 in the form of a mixture of water and steam through the outlet pipe 50. The heated water exits the marine boiler 2 through the medium outlet 40. The water from the housing 12 is supplied through the container 46 by natural circulation.

[0053] When the ship is at sea, the engine 4a usually operates, and steam is generated by the exhaust gas EG1 from the engine 4a. If an insufficient amount of steam is generated from the engine 4a by the exhaust gas EG1, the oil-fired burner may also be operated for additional steam generation by the exhaust gas EG2 from the oil-fired burner. However, when the ship is idling, for example, in a harbor, since the propulsion of the ship does not occur, the engine 4a may not operate. Furthermore, the oil-fired burner may not be operated to minimize the release of harmful pollution in the harbor. Nevertheless, steam may be further required, and steam production may be further required on board. Thereafter, the electric heater 44 may be connected to an external power source 52 in order to produce the required steam with a minimum release of pollution in the harbor by the electric heater 44.

[0054] Therefore, in the marine boiler 2, hot water and steam can be generated by the exhaust gas from the diesel engine, the exhaust gas from the oil-fired burner, and the electric heater. The electric heater is integrated with the rest of the boiler so as not to require a separate feed water system, steam space, steam pipe or another safety valve. Since a separate steam space is not required for the electric heater, it can be made relatively small with a relatively small installation area. This enables a small and cost-effective marine boiler.

[0055] Figure 2 shows another marine boiler 54 of the smoke tube type. The marine boiler 54 is very similar to the marine boiler 2 of FIGS. 1a and 1b, and hereinafter, the focus will be on the characteristic mechanism of the marine boiler 54. The marine boiler 54 includes a plurality, here three, electric heaters 44 disposed within a cylindrical container 46. The electric heaters 44 extend within the cylindrical container 46, and the longitudinal central axis of each of the electric heaters 44 extends substantially perpendicular to the longitudinal central axis c of the housing 12 and substantially parallel to the longitudinal central axis of the container 46. The electric heaters 44 are configured to be connected to an external power source 52 disposed on land so that electricity is supplied thereto.

[0056] FIGS. 3a and 3b show another marine boiler 56 of the smoke tube type. The marine boiler 56 is very similar to the marine boiler 2 of FIGS. 1a and 1b, and hereinafter, the focus will be on the characteristic mechanism of the marine boiler 56. The marine boiler 56 includes a plurality, here two, electric heaters 44, but there is no cylindrical container 46, inlet pipe 48, and outlet pipe 50. Instead, the electric heaters 44 extend within the housing 12 so as to be surrounded by the peripheral wall 42, and the longitudinal central axis of the electric heaters 44 extends substantially parallel to the longitudinal central axis c of the housing 12. The electric heaters 44 are configured to be connected to an external power source 52 disposed on land so that electricity is supplied thereto. Thus, the electric heaters 44 are surrounded by the same water volume as the pipes 18 and 34, and heat is transferred to the water volume during operation of the electric heaters 44.

[0057] FIGS. 4a and 4b show another marine boiler 58 of the smoke tube type. The marine boiler 58 is very similar to the marine boiler 56 of FIGS. 3a and 3b, and hereinafter, the focus will be on the characteristic mechanism of the marine boiler 58. The electric heaters 44 extend within the housing 12, and the longitudinal central axis of each of the electric heaters 44 extends substantially perpendicular to the longitudinal central axis c of the housing 12.

[0058] Figure 5 shows another marine boiler 60 of the smoke tube type. The marine boiler 60 is very similar to the marine boiler 54 of Figure 2, and hereinafter, the focus will be on the characteristic mechanisms of the marine boiler 60. The marine boiler 60 includes a plurality, here two, of electric heaters 44 disposed in respective cylindrical containers 62 and 64 that are fluid-connected in series via intermediate pipes 66. The inlet pipe 48 fluid-connects the housing 12 and the container 62, and the outlet pipe 50 fluid-connects the container 64 and the housing 12. The electric heaters 44 extend through the respective cylindrical containers 62 and 64, and the longitudinal central axis of each electric heater 44 extends substantially perpendicular to the longitudinal central axis c of the housing 12 and substantially parallel to the longitudinal central axis of each of the containers 62 and 64, respectively.

[0059] Figure 6 shows another marine boiler 68 of the smoke tube type. The marine boiler 68 is very similar to the marine boiler 60 of Figure 5, and hereinafter, the focus will be on the characteristic mechanisms of the marine boiler 68. The marine boiler 68 includes a plurality, here two, of electric heaters 44 disposed in respective cylindrical containers 62 and 64 that are fluid-connected in parallel via an inlet pipe 70 and an outlet pipe 72 that branch to connect to both of the cylindrical containers 62 and 64. The inlet pipe 70 fluid-connects the housing 12 and the containers 62, 64, and the outlet pipe 72 fluid-connects the containers 62, 64 and the housing 12.

[0060] Figure 7 shows a water-tube type marine boiler 74. The marine boiler 74 is arranged on a ship (not shown) and is connected by a duct 76 to a first exhaust gas source in the form of a diesel engine 4a of the ship, and the engine 4a is configured to propel the ship. The exhaust gas EG1 generated by the diesel engine 4a is supplied to the marine boiler 74 through the duct 76 for exhaust gas heat recovery. The marine boiler 74 includes a carbon steel container 78, which comprises a lower chamber or header 80, a housing 82, and an upper chamber or header 84 arranged continuously in the vertical longitudinal direction. Here, the lower chamber 80, the housing 82, and the upper chamber 84, which also serve as a steam space S, all have a cylindrical shape, have a similar cross-section, and are integrally formed to be arranged concentrically.

[0061] The marine boiler 74 further includes a bundle of tubes 86 extending between a lower tube plate 88 and an upper tube plate 90, and the plates form the lower and upper wall surfaces of the housing 82 separating the housing 82 from the lower and upper chambers 80, 84. The tubes 86 form means 92 for carrying a medium, here water and steam, through the housing 82. Water is received by the marine boiler 74 through a medium inlet 94 extending into the lower chamber 80, and steam and hot water are collected in the steam space S before being discharged from the marine boiler 74 through a medium outlet 96 extending from the upper chamber 84.

[0062] The housing 82 is arranged to carry the exhaust gas EG1 through the marine boiler 74. The exhaust gas EG1 is received by the marine boiler 74 through an exhaust gas inlet 98 extending into the lower portion of the housing 82 and is discharged from the marine boiler 74 through an exhaust gas outlet 100 extending from the upper portion of the housing 82. The peripheral wall 102 of the housing 82 serves as means 104 for carrying the exhaust gas EG1 from the exhaust gas inlet 98 to the exhaust gas outlet 100.

[0063] During operation of the diesel engine 4a and the marine boiler 74, the exhaust gas EG1 is supplied through the housing 82. Inside the housing 82, the exhaust gas EG1 surrounds the pipe 86 and flows around it. Further, water is supplied from the medium inlet 94 into the pipe 86. Since the water is colder than the exhaust gas EG1, heat is transferred from the exhaust gas EG1 through the wall surface of the pipe 86 to the water in the pipe 86, which is heated and exits the marine boiler 74 in the form of steam or a mixture of water and steam through the medium outlet 96 via the steam space S.

[0064] The marine boiler 74 further comprises three electric heaters 44 in the form of electrode heaters, a cylindrical container 46, an inlet pipe 106 and an outlet pipe 108. The pipes extend between the housing 82 and the container 46 and fluidly connect them. The electric heaters 44 extend into the cylindrical container 46, and the longitudinal central axis of each of the electric heaters 44 extends substantially perpendicular to the longitudinal central axis c of the housing 82 and substantially parallel to the longitudinal central axis of the container 46. The electric heaters 44 are configured to be connected to an external power supply 52 arranged on land, for example in a harbor, and are supplied with electricity when the ship is not moving and the engine 4a is not operating or is operating at a low load.

[0065] The cylindrical container 46 is filled with water, and the water is supplied from the housing 82 into the container 46 through the inlet pipe 106. During operation of the electric heaters 44, heat is transferred from the electric heaters 44 to the water supplied from the container 46 to the housing 82 in the form of a mixture of water and steam through the outlet pipe 108. The heated water is collected in the steam space S before exiting the marine boiler 74 through the medium outlet 96. The water from the housing 82 is supplied through the container 46 by natural circulation.

[0066] When the ship is at sea, the engine 4a usually operates, and steam is generated by the exhaust gas EG1 from the engine 4a. However, when the ship is idling, for example, in a harbor, since the propulsion of the ship does not occur, the engine 4a may not operate. Nevertheless, steam may still be required, and steam production may still be necessary on board. Thereafter, the electric heater 44 may be connected to an external power source 52 to produce the required steam and hot water with minimal release of pollution in the harbor by the electric heater 44.

[0067] The above embodiments of the present invention should be regarded as illustrative only. It will be understood by those skilled in the art that the described embodiments can be modified and combined in numerous ways without departing from the concept of the present invention.

[0068] For example, the boiler according to the present invention can be provided with any number of electric heaters, that is, one, two, three or more. In the case of two or more electric heaters, the electric heaters may be of the same type or different types.

[0069] The electric heater of the boiler can be arranged inside the housing or outside the housing of the boiler, that is, inside an external container. In the case of a plurality of electric heaters, combinations are possible, that is, one or more of them can be arranged inside the housing and the rest outside the housing.

[0070] Furthermore, in the case of a plurality of electric heaters, all or some of them can be arranged inside a common external container or inside respective external containers.

[0071] In the case of a plurality of external containers, these can be fluid-connected in parallel, in series, or separately from the housing of the boiler. Any combination thereof is also possible.

[0072] The electric heater of the boiler can extend longitudinally in any suitable direction, for example, parallel or perpendicular to the longitudinal central axis c of the boiler housing. In the case of a plurality of electric heaters, combinations are also possible, that is, one or more of them can extend longitudinally parallel to the longitudinal central axis c of the housing, and the rest can extend longitudinally perpendicular to the longitudinal central axis c of the housing.

[0073] In the case of a boiler equipped with one or more external containers for storing one or more electric heaters, these one or more external containers can extend longitudinally in any suitable direction, and in the same or different directions such as parallel or perpendicular to the longitudinal central axis c of the boiler housing.

[0074] Furthermore, in the case of a boiler equipped with one or more external containers for storing one or more electric heaters, these one or more external containers can have any suitable design, and can have the same or different designs. Therefore, the external container does not have to be cylindrical, but can have any suitable cross-section such as a polygonal cross-section.

[0075] Naturally, other components of the boiler can also have alternative designs other than those shown in the drawings.

[0076] The components of the boiler do not have to be made of carbon steel, but can be made of other materials such as aluminum or stainless steel.

[0077] Combinations of the above design alternatives are possible.

[0078] The power source for supplying electricity to the electric heater does not have to be located in the harbor and can be located in another place regardless of whether it is on land or not. As an example, the power source can be a "clean" power source, such as a solar power source installed on a ship.

[0079] A smoke tube type marine boiler need not be provided with a tube extending from a furnace for carrying exhaust gas from a furnace and a burner disposed inside the furnace. Further, a smoke tube type marine boiler need not be arranged to receive exhaust gas from an engine. As an example, a marine boiler can be arranged to receive exhaust gas from a first exhaust gas source in the form of a burner, which can be disposed inside the furnace in some cases and then inside the container of the marine boiler. Referring to FIG. 1, such a marine boiler has no exhaust gas inlet 26, lower chamber 10, tube 18, upper chamber 14 and exhaust gas outlet 28.

[0080] Details not relevant to the present invention are omitted, and it should be emphasized that the figures are merely schematic and not drawn to scale. Also, some of the figures are said to be more simplified than others. Thus, although some components are shown in one figure, they may be omitted in another figure. Finally, as used herein, prefixes such as "first", "second", "upper", "bottom", "upper side", "lower side", "horizontal", "vertical", etc. are used only to distinguish different components and do not impose requirements regarding relative position or orientation.

Description of Reference Numerals

[0081] 2 Marine boiler 4 First exhaust gas source 4a Diesel engine 6 Duct 8 Carbon steel container 10 Lower chamber or header 12 Housing 14 Upper chamber or header 16 Exhaust gas conveying means 18 Carbon steel pipe 22 Lower tube plate 24 Upper tube plate 26 Exhaust gas inlet 28 First exhaust gas outlet 30 Furnace 34 Carbon steel pipe 36 Second exhaust gas outlet 38 Medium inlet 40 Medium outlet 42 Peripheral wall 44 Electric heater 46 Cylindrical container 48 Inlet pipe 50 Outlet pipe 52 External power supply 54 Marine boiler 56 Marine boiler 58 Marine boiler 60 Marine boiler 62 Cylindrical container 64 Cylindrical container 66 Intermediate pipe 68 Marine boiler 70 Inlet pipe 72 Outlet pipe 74 Marine boiler 76 Duct 78 Carbon steel container 80 Lower chamber or header 82 Housing 84 Upper chamber or head 86 Pipe 88 Lower pipe plate 90 Upper pipe plate 92 Means 94 Medium inlet 96 Medium outlet 98 Exhaust gas inlet 100 Exhaust gas outlet 102 Peripheral wall 104 Means 106 Inlet pipe 108 Outlet pipe EG1 Exhaust gas EG2 Exhaust gas S Steam space

Claims

1. A marine boiler (2, 54, 56, 58, 60, 68, 74) for transferring heat from exhaust gas (EG1, EG2) to a medium in the form of boiler water to produce steam on board a ship, wherein the marine boiler (2, 54, 56, 58, 60, 68, 74) comprises a container (8, 78), an exhaust gas inlet (26, 98) for receiving exhaust gas (EG1) from a first exhaust gas source (4) within the container (8, 78), a first exhaust gas outlet (28, 100) for discharging the exhaust gas (EG1) from the first exhaust gas source (4) from the container (8, 78), means (16, 104) for conveying the exhaust gas (EG1) from the first exhaust gas source (4) from the exhaust gas inlet (26, 98) to the first exhaust gas outlet (28, 100), a medium inlet (38, 94) for receiving the medium within the container (8, 78), a steam space (S) inside the container (8, 78) for storing the medium after heating by the exhaust gas (EG1, EG2), a medium outlet (40, 96) for discharging the medium from the container (8, 78), means (32, 92) for conveying the medium from the medium inlet (38, 94) to the medium outlet (40, 96), a peripheral wall (42, 102) provided within the container (8, 78), wherein inside the peripheral wall (42, 102), the exhaust gas (EG1) from the first exhaust gas source (4) and the medium are arranged to be conveyed, the peripheral wall (42, 102), and further comprising an electric heater (44) for heating the medium by electricity supplied from a power source (52), the power source (52) being separate from the first exhaust gas source (4), and the steam space (S) being arranged to store the medium after heating by the electric heater (44), wherein at least a part of the peripheral wall (42, 102) extends circumferentially along the peripheral wall of the container (8, 78) with a predetermined interval from the peripheral wall of the container (8, 78) such that the medium after heating by the electric heater (44) diffuses around the radially outer surface of the peripheral wall (42, 102), characterized in that it is a marine boiler.

2. The marine boiler (2, 54, 56, 58, 60, 68, 74) according to claim 1, wherein the power source (52) is separate from any exhaust gas source on board the ship.

3. The marine boiler (2, 54, 56, 58, 60, 68, 74) according to claim 1 or 2, wherein the power source (52) is separate from the ship.

4. The marine boiler (2, 54, 56, 58, 60, 68, 74) according to any one of claims 1 to 3, wherein the power source (52) is arranged on land.

5. The marine boiler (2, 54, 56, 58, 60, 68, 74) according to any one of claims 1 to 4, wherein the first exhaust gas source (4) includes an engine (4a) for propelling the ship.

6. The means (16) for carrying the exhaust gas (EG1) from the exhaust gas inlet (26) to the first exhaust gas outlet (28) includes a first bundle of tubes (18), and the means (32) for carrying the medium from the medium inlet (38) to the medium outlet (40) includes the peripheral wall (42) of the marine boiler (2, 54, 56, 58, 60, 68) surrounding the first bundle of tubes (18). The marine boiler (2, 54, 56, 58, 60, 68) according to any one of claims 1 to 5.

7. The means (92) for carrying the medium from the medium inlet (94) to the medium outlet (96) includes one or more tubes (86), and the means (104) for carrying the exhaust gas (EG1) from the exhaust gas inlet (98) to the first exhaust gas outlet (100) includes the peripheral wall (102) of the marine boiler (74) surrounding the one or more tubes (86). The marine boiler (74) according to any one of claims 1 to 5.

8. The electric heater (44) is arranged inside the peripheral wall (42). The marine boiler (56, 58) according to any one of claims 1 to 7.

9. The electric heater (44) is arranged in a container (46, 62, 64) arranged outside the peripheral wall (42, 102), and the container (46, 62, 64) communicates with the means (16, 104) for carrying the medium from the medium inlet (38, 94) to the medium outlet (40, 96). The marine boiler (2, 54, 60, 68, 74) according to any one of claims 1 to 7.

10. A method of operating a marine boiler (2, 54, 56, 58, 60, 68, 74) to transfer heat from exhaust gases (EG1, EG2) to a medium in the form of boiler water to produce steam on board. Receiving exhaust gas (EG1) from a first exhaust gas source (4) into a container (8, 78) through an exhaust gas inlet (26, 98) of the marine boiler (2, 54, 56, 58, 60, 68, 74); Carrying the exhaust gas (EG1) from the first exhaust gas source (4) from the exhaust gas inlet (26, 98) to a first exhaust gas outlet (28, 100) of the marine boiler (2, 54, 56, 58, 60, 68, 74); Discharging the exhaust gas (EG1) from the first exhaust gas source (4) from the container (8, 78) through the first exhaust gas outlet (28, 100); Receiving the medium into the container (8, 78) through a medium inlet (38, 94) of the marine boiler (2, 54, 56, 58, 60, 68, 74); Carrying the medium from the medium inlet (38, 94) to a medium outlet (40, 96) of the marine boiler (2, 54, 56, 58, 60, 68, 74) through a vapor space (S) of the marine boiler (2, 54, 56, 58, 60, 68, 74), wherein the vapor space (S) is arranged to store the medium after heating by the exhaust gas (EG1, EG2), the marine boiler (2, 54, 56, 58, 60, 68, 74) comprises a peripheral wall (42, 102) provided in the container (8, 78), and inside the peripheral wall (42, 102), the exhaust gas (EG1) from the first exhaust gas source (4) and the medium are arranged to be carried; A method comprising: Supplying electricity from a power source (52) separate from the first exhaust gas source (4) to an electric heater (44); heating the medium by the electric heater (44); and receiving the medium heated by the electric heater (44) into the vapor space (S); At least a part of the peripheral wall (42, 102) extends circumferentially along the peripheral wall of the container (8, 78) with a predetermined interval from the peripheral wall of the container (8, 78) such that the medium heated by the electric heater (44) diffuses around the radially outer surface of the peripheral wall (42, 102).

11. The method according to claim 10, comprising providing the power source (52) separately from any exhaust gas source on the ship.

12. The method according to claim 10 or 11, including the step of providing the power supply (52) on land.

13. The method according to any one of claims 10 to 12, including the step of providing an engine (4a) for propelling the ship as the first exhaust gas source (4).

14. The method according to any one of claims 10 to 13, including the step of providing the electric heater (44) inside the peripheral wall (42, 102).

15. The method according to any one of claims 10 to 13, including the step of providing the electric heater (44) in a container (46, 62, 64) arranged outside the peripheral wall (42, 102), and the step of providing the container (46, 62, 64) in communication with means (16, 104) for carrying the medium from the medium inlet (38, 94) to the medium outlet (40, 96).

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