Air lubrication systems for ships

Abstract

An air lubrication system for a ship is disclosed herein. The air lubrication system includes: a speed governor connected to a main propulsion shaft connected to a main engine of the ship, the speed governor changing the RPM of the main propulsion shaft and outputting the changed RPM; at least one air compressor connected to the speed governor and rotating at the RPM output from the speed governor to supply compressed air through compression of air; an air ejector disposed on the bow of the ship and discharging the compressed air supplied from the at least one air compressor to the outside of the ship; and an air delivery pipe, the compressed air supplied from the at least one air compressor being delivered to the air ejector via the air delivery pipe.

Description

Technical Field

[0001] The present invention relates to an air lubrication system for a ship, and more particularly, to an air lubrication system for a ship that can achieve high energy efficiency when compared with a typical air lubrication system driven by a power generation engine. Background Art

[0002] During the navigation of a ship, the hull of the ship is subjected to wave resistance, viscous resistance and air resistance. In order to reduce such resistances, most ships are streamlined.

[0003] Wave drag is caused by regular waves generated by the bow of a ship passing through the water during ship propulsion, and acts perpendicularly to the entire area of ​​the hull, causing energy loss to the ship. Viscous drag is caused by the viscosity of water and is generally classified into friction drag and form drag. Among them, friction drag refers to the traction that hinders the progress of a ship, which is caused by the viscous adhesion of seawater to the wetted surface of the hull.

[0004] In order to reduce frictional resistance, various solutions have been proposed, such as the design of hydrofoils adapted to minimize the contact area between the seawater and the hull, the design of air-lubricated ships adapted to improve the conditions of the wetted surface and bottom of the hull, and the design of supercavitating underwater vehicles.

[0005] As another solution to reduce frictional resistance, an air lubrication system has been proposed, which can reduce energy loss due to the viscosity of seawater by forming an air layer on the hull surface to prevent the hull surface from contacting the seawater.

[0006] A general air lubrication system reduces frictional resistance by creating air cavities on the surface of the hull to reduce the wetted surface area of ​​the ship, and is thus extremely environmentally friendly and easy to apply to actual ships.

[0007] Figure 1 Figure 1 is a diagram of a typical air lubrication system.

[0008] refer to Figure 1 The air lubrication system includes: an air ejector 11, which is arranged at the bow of the hull 20; two air compressors 13, 14, which are arranged adjacent to the air ejector 11; and two motors 15, 16, which are arranged adjacent to the air ejector 11 to drive the air compressors 13, 14. In addition, the air lubrication system may include a switchboard 17 to drive the motors 15, 16. In addition, the air lubrication system includes an air delivery pipe AP connected between the air ejector 11 and the air compressors 13, 14.

[0009] The generator engine GE is placed at the stern of the ship. The switchboard 17 receives power from the generator engine GE and distributes the received power to the motors 15, 16. In addition, the main engine ME may be placed at the stern of the ship.

[0010] The power generation engine GE may include a plurality of power generation engines. Here, a switchboard SB may be provided to manage the power generated by the power generation engine GE. That is, the switchboard SB may be electrically connected to the switchboard 17.

[0011] Although not shown, the air lubrication system may further include means for adjusting the amount of air discharged from the air injector 11 as required.

[0012] <Related Literature>

[0013] <Patent Documents>

[0014] (Patent Document 1) Korean Patent Publication No. 10-2020-0063398 (2020.06.05.) Summary of the invention

[0015] An object of the present invention is to provide an air lubrication system for a marine vessel that achieves high energy efficiency when compared to a typical air lubrication system driven by a power generation engine.

[0016] According to one aspect of the present invention, an air lubrication system includes: a speed governor connected to a main propulsion shaft connected to a main engine of a ship, the speed governor changing the revolutions per minute of the main propulsion shaft and outputting the changed revolutions per minute; at least one air compressor connected to the speed governor and rotating at the revolutions per minute output from the speed governor to supply compressed air through compression of the air; an air ejector disposed on the bow of the ship and discharging the compressed air supplied from the at least one air compressor to the outside of the ship; and an air delivery pipe through which the compressed air supplied from the at least one air compressor is delivered to the air ejector.

[0017] The speed governor may comprise at least one gear train adapted to vary the revolutions per minute of the main propulsion shaft.

[0018] The speed regulator may further include a clutch adapted to prevent the output of the varied RPM.

[0019] The air lubrication system may further include: at least one control valve disposed on the at least one air compressor and regulating the air supply pressure of the at least one air compressor.

[0020] The air lubrication system may further include: a temperature regulator disposed on the air delivery pipe and regulating the temperature of the compressed air supplied from the at least one air compressor.

[0021] According to another aspect of the present invention, an air lubrication system includes: a speed governor connected to a main propulsion shaft connected to a main engine of a ship, the speed governor changing the rotational speed per minute of the main propulsion shaft and outputting the changed rotational speed per minute; at least one rotary compressor connected to the speed governor and rotating at the rotational speed per minute output from the speed governor to supply compressed air through compression of air; at least one electrically driven compressor driven by electricity supplied from a power generation engine of the ship to supply compressed air; an air ejector disposed on the bow of the ship and discharging compressed air supplied from at least one rotary compressor and at least one electrically driven compressor to the outside of the ship; and an air delivery pipe, through which the compressed air supplied from at least one rotary compressor and at least one electrically driven compressor is delivered to the air ejector.

[0022] The air delivery duct may allow compressed air supplied from the at least one rotary compressor to merge with compressed air supplied from the at least one electrically driven compressor before the compressed air is delivered to the air ejector.

[0023] The at least one electrically driven compressor may include a third air compressor and a fourth air compressor disposed at the stern of the hull, wherein the air lubrication system may further include: a starter controlling current or voltage supplied to the third air compressor and the fourth air compressor.

[0024] According to the present invention, the air lubrication system is connected to the main propulsion shaft via a speed governor so as to be operated without electric power generated by a power generation engine as in the prior art, thereby achieving reduced fuel consumption.

[0025] Additionally, the air lubrication system allows the air compressor to be operated without a separate electrical panel.

[0026] In addition, when compared to a typical air lubrication system, the air lubrication system can better utilize the internal space of the vessel and reduce shipbuilding costs by using engines with relatively lower output power, and can significantly reduce shipbuilding costs by reducing the cost of auxiliary equipment (such as fresh water coolant pumps, seawater coolant pumps, coolers and fuel oil pumps, and engine room blowers).

[0027] Furthermore, the air lubrication system may reduce the weight of the vessel and sufficient cargo space by using an engine with relatively lower output power when compared to a typical air lubrication system.

[0028] Furthermore, the air lubrication system may achieve fuel savings at lower vessel speeds as well as at higher vessel speeds. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other aspects, features and advantages of the present invention will become apparent from the following detailed description of embodiments in conjunction with the accompanying drawings:

[0030] Figure 1 Figure 1 is a diagram of a typical air lubrication system.

[0031] Figure 2 FIG. 1 is a diagram of an air lubrication system for a ship according to an embodiment of the present invention.

[0032] Figure 3 is a diagram of an air lubrication system for a ship according to an embodiment of the present invention, which shows the connection between an air compressor and an air ejector via an air delivery pipe.

[0033] Figure 4 It is an enlarged view of a part of an air lubrication system for a ship according to an embodiment of the present invention.

[0034] Figure 5 FIG. 4 is a diagram of an air lubrication system for a ship according to another example of the present invention.

[0035] Figure 6 is a diagram of an air lubrication system for a ship according to another embodiment of the present invention, which shows the connection between the air compressor and the air ejector via the air delivery pipe.

[0036] Figure 7 The invention is an enlarged view of a part of an air lubrication system for a ship according to another example of the present invention.

[0037] Description of Figure Numbers

[0038] 11, 110: air ejector;

[0039] 13, 14: air compressor;

[0040] 15, 16: electric motor;

[0041] 17: Distribution board;

[0042] 20, 200: Hull;

[0043] 100, 100a: air lubrication system;

[0044] 120: speed regulator;

[0045] 122: Clutch;

[0046] 124: gear train;

[0047] 130: first air compressor;

[0048] 140: second air compressor;

[0049] 150: Temperature regulator;

[0050] 160: control valve;

[0051] 170: Emergency stop valve;

[0052] 180: the third air compressor;

[0053] 182: first driving motor;

[0054] 190: fourth air compressor;

[0055] 192: second driving motor;

[0056] AP: air delivery tube;

[0057] GE: Power generation engines;

[0058] MA: main propulsion shaft;

[0059] ME: main engine;

[0060] STT: starter;

[0061] SB: Switchboard. DETAILED DESCRIPTION

[0062] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0063] Descriptions of known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

[0064] In addition, when a component is referred to as being "on another component," "connected to another component," "supported by another component," or "coupled to another component," the component may be directly formed on, connected to, supported by, or coupled to the other component, or an intervening component may be "inserted" therebetween. Furthermore, when a fluid is referred to as being "supplied to" or "delivered to" a component, the fluid may be directly supplied to or delivered to the component, or may be supplied to or delivered to the component via an intervening component.

[0065] Although specific terms are employed herein, they are used and interpreted in a descriptive sense only and not for purposes of limitation. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0066] In addition, spatially relative terms such as “under,” “below,” “above,” “upper,” “right,” “left,” etc. are based on the depictions in the drawings and may be expressed in different ways when the orientation of the corresponding object is changed. For the same reason, some components are exaggerated, omitted, or schematically shown in the drawings, and the depicted size of each component may not necessarily reflect its actual size.

[0067] It should be understood that although the terms "first", "second", etc. may be used herein to describe various components, these components should not be limited by these terms. These terms are only used to distinguish one component from another element.

[0068] In addition, as used herein, the terms “comprises / comprising” and / or “includes / including” specify the presence of stated features, regions, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements and / or components.

[0069] Figure 2 A diagram of an air lubrication system for a ship according to an embodiment of the present invention; Figure 3 is a diagram of an air lubrication system for a ship according to an embodiment of the present invention, which shows the connection between the air compressor and the air ejector via an air delivery pipe; and Figure 4 It is an enlarged view of a part of an air lubrication system for a ship according to an embodiment of the present invention.

[0070] The air lubrication system 100 for a ship according to this embodiment discharges air generated by the air compressors 130 and 140 to the outside of the hull 200 via the air ejector 110 .

[0071] although Figures 2 to 4 The air lubrication system 100 according to this embodiment shown in FIG. 1 includes two air compressors 130 and 140 , but it should be understood that the present invention is not limited thereto, and the number of air compressors may vary as needed.

[0072] For convenience of description, the two air compressors will be referred to as a first air compressor 130 and a second air compressor 140 , respectively.

[0073] refer to Figure 2 According to this embodiment, the air lubrication system 100 includes an air injector 110, a speed regulator 120, a first air compressor 130, a second air compressor 140, and an air delivery pipe AP.

[0074] The air injector 110 discharges the air generated by the first air compressor 130 and the second air compressor 140 to the outside of the hull 200. The air injector 110 may be disposed at the bow of the hull 200. The air injector 110 may be provided with a device for adjusting the amount of air injected therethrough.

[0075] Here, the air ejector 110 may be provided with an emergency stop valve 170 to stop supplying air to the air ejector 110 in an emergency. The emergency stop valve 170 may prevent the air from being discharged to the outside of the hull 200 when the air ejector 110 fails to eject air normally due to, for example, abnormal pressure of air delivered through the air delivery pipe AP.

[0076] The speed governor 120 is connected to the main propulsion shaft MA, which is connected to the main engine ME. Figure 4 As shown in .

[0077] The speed governor 120 changes the RPM of the main propulsion shaft MA rotated by the main engine ME to the required RPM of the first air compressor 130 and the second air compressor 140. To this end, the speed governor 120 may include a clutch 122 and a gear train 124.

[0078] When the first air compressor 130 and the second air compressor 140 are not operating, the clutch 122 is used to cut off power transmission.

[0079] The gear train 124 changes the RPM of the main propulsion shaft MA to the desired RPM of the first air compressor 130 and the second air compressor 140. The gear train 124 may include a plurality of gears to change the RPM. The gear ratio of the gear train 124 may be varied as desired.

[0080] In this embodiment, the present invention is described with reference to an example in which the speed governor 120 includes a total of four gear trains 124, a pair of gear trains 124 for each of the first air compressor 130 and the second air compressor 140. Here, the corresponding pair of gear trains 124 changes the RPM of the main propulsion shaft MA to a desired RPM of the first air compressor 130 or the second air compressor 140 according to the gear ratio of each gear train 124.

[0081] In this embodiment, assuming that the main propulsion shaft MA rotates at about 100 rpm, the speed governor 120 may allow the first air compressor 130 and the second air compressor 140 to rotate at about 1,000 rpm to 3,000 rpm.

[0082] The gear train 124 may have a continuously variable gear ratio, or may have two or three gear ratios as desired. Alternatively, the gear train 124 may have a single fixed gear ratio as desired.

[0083] Each of the first air compressor 130 and the second air compressor 140 is disposed at an output side of the speed regulator 120 , and rotates at a rotational speed per minute output from the speed regulator 120 to supply compressed air to the air delivery pipe AP via the compressed air.

[0084] In this embodiment, each of the first air compressor 130 and the second air compressor 140 may be provided in the form of a centrifugal compressor, a screw compressor, or a positive displacement compressor.

[0085] In addition, each of the first air compressor 130 and the second air compressor 140 may be provided at its inlet and outlet sides with a cross-sectional area adjusting device (not shown), such as a guide vane, which changes the inlet and outlet cross-sectional areas of the air compressor.

[0086] Alternatively, each of the first air compressor 130 and the second air compressor 140 may be provided with a device adapted to adjust its internal RPM.

[0087] Although the clutch 122 is disposed in the speed regulator 120 in this embodiment, it should be understood that the present invention is not limited thereto. The clutch 122 may be disposed in each of the first air compressor 130 and the second air compressor 140 as needed.

[0088] The air lubrication system 100 may further include a temperature regulator 150 to adjust the temperature of the air supplied from the first air compressor 130 and the second air compressor 140. The temperature regulator 150 may reduce a change depending on the temperature by controlling the temperature of the air supplied from the first air compressor 130 and the second air compressor 140.

[0089] Each of the first air compressor 130 and the second air compressor 140 may be provided with a control valve 160 to control the air supply pressure of the first air compressor 130 or the second air compressor 140. For example, the control valve 160 may be connected in parallel to the first air compressor 130, such as Figure 3 As shown in .

[0090] The air delivery pipe AP is adapted to deliver air generated by the first air compressor 130 and the second air compressor 140 to the air injector 110. To this end, the air delivery pipe AP may include a section connected to the air injector 110 and two sections branched from the section and connected to the first air compressor 130 and the second air compressor 140, respectively.

[0091] In this embodiment, since the first air compressor 130 and the second air compressor 140 are disposed at the stern of the hull 200 and the air ejector 110 is disposed at the bow of the hull 200 , the air delivery pipe AP may extend from the stern of the hull 200 to the bow of the hull 200 .

[0092] The air lubrication system 100 according to this embodiment can inject air at an air injection rate according to the speed of the ship. To this end, the pressure of the air compressed by the first air compressor 130 and the second air compressor 140 can be determined according to the required air injection rate.

[0093] Therefore, the pressure of the air compressed by the first air compressor 130 and the second air compressor 140 may be controlled by adjusting the RPM output from the speed governor 120 connected to the main propulsion shaft MA.

[0094] In addition, the air supply pressures of the first air compressor 130 and the second air compressor 140 may be adjusted by a cross-sectional area adjusting device that changes the inlet and outlet cross-sectional areas of the first air compressor 130 and the second air compressor 140 .

[0095] That is, the air lubrication system 100 according to this embodiment may further include a controller that can change the gear stage of the gear train 124 of the speed regulator 120 to control the RPM output from the speed regulator 120 .

[0096] In addition, the controller may control a cross-sectional area adjusting device provided to each of the first air compressor 130 and the second air compressor 140 to change the inlet and outlet cross-sectional areas.

[0097] In addition, the controller may control the control valve 160. That is, the controller may control the air supply pressures of the first air compressor 130 and the second air compressor 140 by controlling the control valve 160.

[0098] The controller may control the emergency stop valve 170. Therefore, after abnormal air pressure occurs in the air delivery pipe AP, the controller may stop ejecting air through the air ejector 110 by controlling the emergency stop valve 170.

[0099] The controller may be implemented by a computing device including a microprocessor, a memory, etc. Since the method of implementing such a controller is well known to those skilled in the art, a detailed description thereof will be omitted.

[0100] Next, a method of operating an air lubrication system for a ship according to an embodiment of the present invention will be briefly described, wherein the air lubrication system further includes a control unit storing information about an optimal air injection rate according to a ship speed. The method includes: determining a required air injection rate according to the ship speed based on the information stored in the control unit; determining an operating pressure of an air compressor according to the required air injection rate; determining the rpm of the air compressor or the output rpm of a speed governor mounted on a main propulsion shaft; and adjusting the pressure of air to be injected outside the ship.

[0101] Here, the step of adjusting the pressure of air to be injected outside the ship may be performed by controlling guide vanes disposed at both inlet and outlet sides of the air compressor and a control valve disposed on a pipe connected between the inlet and outlet of the air compressor.

[0102] Thus, an air lubrication system according to the present invention may operate at high efficiency, thereby providing improved fuel savings when compared to a typical air lubrication system driven by a power generation engine.

[0103] Fuel consumption comparison

[0104] The inventors of the present invention verified the reduction in fuel consumption of the ship due to the use of the air lubrication system 100 according to this embodiment by calculating the fuel efficiency after applying the air lubrication system 100 according to this embodiment to an LNG carrier having a MEGI engine operating in the gas mode.

[0105] The following is a comparison between the fuel consumption of a ship employing a typical air lubrication system driven by a power generation engine (comparative example) and the fuel consumption of a ship employing the air lubrication system 100 according to this embodiment (example).

[0106] Here, the fuel efficiency is calculated for a ship speed of 18.5 knots.

[0107] In addition, calculations on fuel consumption of a ship adopting a typical air lubrication system were performed before operating the air lubrication system (Comparative Example 1) and after operating the air lubrication system (Comparative Example 2), and the results are shown in Table 1.

[0108] Table 1

[0109] Comparative Example 1 Comparative Example 2 Example 1 Fuel consumption (tons / day) 68.0 64.7 64.5 Fuel consumption reduction rate -- 4.853％ 5.147％

[0110] In Comparative Example 1, the fuel consumption of the vessel before the operation of the typical air lubrication system is calculated for a vessel speed of 18.5 knots. The shaft power of the main engine (ME) before the operation of the typical air lubrication system is calculated to be 16,950 kW (ME load: 67%). The specific fuel gas consumption (SGC) of the main engine calculated for the 67% ME load is 129.0 g / kWh.

[0111] Therefore, the daily fuel consumption of the main engines is calculated to be 52.5 tons / day. In addition, the power generation engines are calculated to consume 15.5 tons of fuel per day, and thus the total daily fuel consumption of the vessel is calculated to be 68.0 tons / day.

[0112] In Comparative Example 2, the fuel consumption of the ship after operating the typical air lubrication system driven by the power generation engine was calculated at the same ship speed as in Comparative Example 1. The shaft power of the main engine was calculated to be 15,187.4 kW (ME load: 60.3%). That is, when compared with before operating the air lubrication system, a power saving of about 10.4% was recorded.

[0113] The SGC of the main engine calculated for 60.3% ME load is 129.2 g / kWh. Therefore, the daily fuel consumption of the main engine is calculated to be 47.1 tonnes / day.

[0114] In addition, in Comparative Example 2, due to the operation of the air lubrication system, the load of each power generation engine is increased compared with Comparative Example 1. The additional gas consumption of the power generation engine is calculated based on the increase.

[0115] There are 2 groups of generator engines in operation. The SGC of each generator engine for load before / after operation of the ALS is obtained. The obtained SGC values ​​are multiplied by the horsepower of each generator engine, and then subtracted from each other. Therefore, the additional fuel consumption of the generator engine is calculated to be 2.1 tons / day. Therefore, the total fuel consumption of the ship after operating the typical air lubrication system is calculated to be 64.7 tons / day (47.1 tons / day + 15.5 tons / day + 2.1 tons / day).

[0116] In Example 1, the fuel consumption of the ship after applying the air lubrication system according to an embodiment of the present invention is calculated. In the operation of the air lubrication system according to the embodiment, 705 (698 / 0.99) kW of electricity is added to drive the air compressor connected to the speed governor. For a given ship speed, the shaft power of the main engine is calculated to be 15,892.3 kW (15,187.3 kW + 705 kW).

[0117] This value corresponds to an ME loading of 63%. The SGC of the main engine calculated for an ME loading of 63% is 128.6 g / kWh.

[0118] Therefore, the daily fuel consumption of the main engine is calculated to be 49.0 tons / day. Since there is no difference in the fuel consumption of the power generation engine between Example 1 and the comparative example, the daily fuel consumption of the power generation engine is calculated to be 15.5 tons / day. Therefore, the total daily fuel consumption of the ship is calculated to be 64.5 tons / day (49.0 tons / day + 15.5 tons / day).

[0119] As shown in Table 1, it can be seen that the fuel consumption of the ship adopting the typical air lubrication system is reduced by 4.853% after operating the typical air lubrication system (Comparative Example 2) when compared with before operating the air lubrication system (Comparative Example 1).

[0120] In addition, it can be seen that the use of the air lubrication system according to the embodiment (Example 1) can achieve a reduction in fuel consumption because the air lubrication system is connected to the main propulsion shaft via the governor to operate without using electricity generated by the power generation engine.

[0121] Furthermore, it can be seen that the fuel consumption is reduced by 0.3% after using the air lubrication system according to the embodiment (Example 1) when compared with after using the typical air lubrication system (Comparative Example 2).

[0122] That is, the use of the air lubrication system according to an embodiment of the present invention in a ship can eliminate the need to increase the generator capacity of the compressor for operating the air lubrication system and the need for a separate starter as in the prior art. In addition, since the air lubrication system according to an embodiment allows air drawn from the engine room to be supplied to the air compressor, unlike a typical air lubrication system in which the air compressor is placed at the bow of the hull, the existing engine room fan (ER FAN) can be used to supply air to the air compressor, thereby allowing the number of required equipment to be reduced and thus better utilization of the space inside the ship.

[0123] Figure 5 A diagram of an air lubrication system for a ship according to another embodiment of the present invention; Figure 6 is a diagram of an air lubrication system for a ship according to this embodiment, which shows the connection between the air compressor and the air ejector via an air delivery pipe; and Figure 7 is an enlarged view of a portion of an air lubrication system for a ship according to this embodiment.

[0124] In the description of the air lubrication system 100a for a ship according to this embodiment, the same components will be denoted by the same reference numerals.

[0125] refer to Figures 5 to 7Similar to the air lubrication system according to the above-mentioned embodiment, the air lubrication system 100a for a ship according to this embodiment includes an air ejector 110, a speed regulator 120, a first air compressor 130, a second air compressor 140 and an air delivery pipe AP.

[0126] Each of the first air compressor 130 and the second air compressor 140 may be a rotary compressor disposed at an output side of the speed regulator 120 and rotates at RPM output from the speed regulator 120 to supply compressed air to the air delivery pipe AP through compression of air, as described above.

[0127] The air lubrication system 100a according to this embodiment may further include at least one electric-driven compressor 180, 190 driven by electric power supplied from the power generation engine GE.

[0128] Although the air lubrication system will be described as including two electrically driven compressors, it should be understood that the present invention is not limited thereto and the number of electrically driven compressors may vary as desired.

[0129] For convenience of description, the two electrically driven compressors will be referred to as a third air compressor 180 and a fourth air compressor 190 , respectively.

[0130] The third air compressor 180 and the fourth air compressor 190 are driven by the first driving motor 182 and the second driving motor 192, respectively. The compressed air generated by the third air compressor 180 and the fourth air compressor 190 may be supplied to the air delivery pipe AP.

[0131] In this embodiment, the third air compressor 180 and the fourth air compressor 190 may be connected to the air delivery pipe AP connected to the first air compressor 130 such that compressed air generated by the third air compressor 180 and the fourth air compressor 190 is supplied to the air delivery pipe AP.

[0132] The first drive motor 182 and the second drive motor 192 are driven by the electric power generated by the power generation engine GE. The first drive motor 182 drives the third air compressor 180 , and the second drive motor 192 drives the fourth air compressor 190 .

[0133] To this end, the air lubrication system according to this embodiment further includes a starter STT that controls the voltage or current supplied to the first drive motor 182 and the second drive motor 192. The starter STT may be electrically connected to the switchboard SB of the power generation engine GE.

[0134] In this embodiment, the third air compressor 180 and the fourth air compressor 190 may be disposed at the stern of the hull 200, similar to the first air compressor 130. Therefore, in the air lubrication system according to this embodiment, the starter STT may be located at a relatively short distance from the switchboard SB of the power generation engine GE disposed at the stern of the hull 200 when compared to a typical air lubrication system.

[0135] When compared with the air lubrication system according to the above-mentioned embodiment, the air lubrication system for a ship according to this embodiment can achieve a significant reduction in shipbuilding costs by using an engine with relatively lower output power and reducing the cost of auxiliary equipment (such as fresh water coolant pumps, seawater coolant pumps, coolers and fuel oil pumps, and engine room blowers).

[0136] In addition, the air lubrication system for a ship according to this embodiment can provide a reduction in the weight of the ship, and can ensure sufficient cargo space by better utilizing the internal space of the ship.

[0137] Furthermore, the air lubrication system for a ship according to this embodiment can achieve fuel saving at low ship speeds as well as high ship speeds.

[0138] Next, a method of operating the air lubrication system for a ship according to this embodiment will be briefly described, wherein the air lubrication system further includes a control unit storing information about an optimal air injection rate according to a ship speed. The method includes the following steps: determining a required air injection rate according to a ship speed based on the information stored in the control unit; determining an operating pressure of an air compressor according to the required air injection rate; selecting at least one air compressor among the air compressors according to the ship speed and operating the selected air compressor; adjusting the rpm of the air compressor or the output rpm of a speed governor mounted on a main propulsion shaft; and adjusting the pressure of air to be discharged to the bottom of the ship.

[0139] For example, the step of adjusting the pressure of air to be injected to the bottom of the ship may be performed by controlling guide vanes at both the inlet and outlet sides of the air compressor and a control valve disposed on a pipe connected between the inlet and outlet of the air compressor.

[0140] In the step of selecting at least one air compressor and driving the selected air compressor, when the ship is traveling at a speed exceeding a predetermined value, the third air compressor 180 and the fourth air compressor 190 can be driven by electricity generated by the onboard power generation engine GE (that is, the electric power drives the compressor); and when the ship is traveling at a speed less than or equal to a predetermined value, the first air compressor 130 and the second air compressor 140 connected to the speed governor 120 can be driven.

[0141] Comparison of energy saving efficiency

[0142] Table 2 shows the comparison results of fuel consumption and energy saving efficiency of a container ship equipped with a 66,200 kW 11-cylinder main engine before operating a typical air lubrication system (ALS) (Comparative Example 3) and after operating the ALS (Comparative Example 4).

[0143] Table 2

[0144]

[0145] Referring to Table 2, it can be seen that at a ship speed at or above a certain value (18 knots), the ship records energy savings of approximately 0.3% to 3.6%, while at a ship speed of 17 knots or less, the ship records negative energy savings, that is, the typical air lubrication system fails to provide energy saving benefits.

[0146] Table 3 shows the results of comparing the fuel consumption between the case where the air lubrication system according to the embodiment is used (Example 2) and the case where a typical air lubrication system is used (Comparative Example 4) on the same ship.

[0147] Table 3

[0148]

[0149] Referring to Table 3, it can be seen that when compared with Comparative Example 4 in which a typical air lubrication system driven by electricity generated by a power generation engine is used, the air lubrication system according to the embodiment can achieve similar or significantly improved energy savings with reduced engine output power.

[0150] Specifically, whereas a typical air lubrication system results in negative energy savings at a ship speed at or below a certain value, an air lubrication system according to an embodiment achieves positive energy savings even at low ship speeds, thereby providing a reduction in fuel consumption when compared to a typical air lubrication system.

[0151] Although some embodiments have been described herein, it should be understood that the foregoing embodiments are provided for illustrative purposes only and should not be construed in any way to limit the present invention. Therefore, the scope of the present invention should be defined by the appended claims and their equivalents.

Claims

1. An air lubrication system, comprising: a speed governor connected to a main propulsion shaft connected to a main engine of the vessel, the speed governor varying the rpm of the main propulsion shaft and outputting the varied rpm; at least one air compressor connected to the speed regulator and rotating at the RPM output from the speed regulator to supply compressed air via compression of air; an air ejector disposed on the bow of the vessel and discharging the compressed air supplied from the at least one air compressor to the outside of the vessel; as well as an air delivery pipe, through which the compressed air supplied from the at least one air compressor is delivered to the air ejector, The air ejector is provided with an emergency stop valve for stopping the supply of air to the air ejector in an emergency.

2. The air lubrication system of claim 1, wherein the speed governor comprises at least one gear train adapted to vary the RPM of the main propulsion shaft.

3. The air lubrication system of claim 2, wherein the speed governor further comprises a clutch adapted to prevent output of the changed RPM.

4. The air lubrication system according to claim 1, further comprising: At least one control valve is disposed on the at least one air compressor and regulates the air supply pressure of the at least one air compressor.

5. The air lubrication system of claim 1 , further comprising: A temperature regulator is disposed on the air delivery pipe and regulates the temperature of the compressed air supplied from the at least one air compressor.

6. An air lubrication system comprising: a speed governor connected to a main propulsion shaft connected to a main engine of the vessel, the speed governor varying the rpm of the main propulsion shaft and outputting the varied rpm; at least one rotary compressor connected to the speed regulator and rotating at the RPM output from the speed regulator to supply compressed air via compression of air; at least one electrically driven compressor driven by electricity supplied from a power generating engine of the vessel to supply compressed air; an air ejector disposed on the bow of the vessel and discharging compressed air supplied from the at least one rotary compressor and the at least one electrically driven compressor to the exterior of the vessel; as well as an air delivery pipe through which the compressed air supplied from the at least one rotary compressor and the at least one electrically driven compressor is delivered to the air ejector, The air ejector is provided with an emergency stop valve for stopping the supply of air to the air ejector in an emergency.

7. The air lubrication system of claim 6, wherein the air delivery pipe allows compressed air supplied from the at least one rotary compressor to merge with compressed air supplied from the at least one electrically driven compressor before the compressed air is delivered to the air ejector.

8. The air lubrication system of claim 6, further comprising: A starter controls current or voltage supplied to the at least one electrically driven compressor.

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