• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
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  • 优先权
    • 专利摘要:
    A system for both steam production and disposal of boil-off gasses from cargo tanks on Liquid gas carriers is provided. The system comprises an electric steam boiler and a steam dump condenser. This equipment together takes up much less room capacity, ensures sufficient steam provision and imply zero risk of fire on-board and is economical efficient to operate at the same time.
    公开号:DK201770391A1
    申请号:DKP201770391
    申请日:2017-05-29
    公开日:2018-06-14
    发明作者:Tonni Bækgaard Kristensen
    申请人:Matonel Holding Ivs；
    IPC主号:
    专利说明:

    Description
    The present invention relates to a system for disposal of boil-off gases onboard liquefied gas carrying ships and a method for controlling the system.
    The area of the technology is introduced by describing the disposal of boil-off gases on-board a conventional liquid gas carrying ship, see Fig. 1. The engine room comprises a gas combustion unit, GCU, 1, for disposal of excess Boil-off gas, a waste heat recovery unit, WHR, 2, for recovering energy from exhaust gas from other equipment, a dual fuel boiler, DFB, 3, for producing steam, an inert gas generator, IGG, 4, and a Dual Fuel Diesel Electric, DFDE, engine, 5, which is a diesel/gas engine combined with an electric generator. A set of DFDEs burns gas from the head space of liquid natural gas tanks, LNG tanks, 7, but any liquefied gas may be carried, and each is connected to an electric generator, GENSET. The GENSETs produce electricity for the ship including the propulsion electric motors, PEMs, 6. The PEMs runs the propellerfor propulsion of the ship.
    When a combustible gas with a low boiling point is carried on liquid gas carriers, heat influx, Q, from the outside causes boil-off evaporation from the liquid gas which results in a pressure rise if the gasses are not consumed in the same rate as they evaporate. E.g. Liquid Natural Gas, methane, ethane, propane, and butane. Therefore, it is a technical requirement to have means available for the continuous disposal of these boil-offgasses to maintain a stable pressure below the Maximum Allowable Relief Valve Setting (MARVS) of the LNG tank, 7. During voyage, the ship's DFDE engine, 5, would typically consume the full amount of boil-off gas for propulsion. On ships with an electric propulsion system (Dual Fuel Diesel Electric), the main engines will run on the boil-off gas and convert it into electric energy through a generator. This electricity powers the Propulsion Electric Motor, PEM, 6. During harbour operations, the Propulsion Electric
    Motors are not available and it is not possible to consume the full amount of electricity produced at the Natural Boil-off Rate, NBOR. Therefore, a Gas Combustion Unit, GCU, 1, is installed to burn the excess boil-off gas that cannot be disposed of via the DFDE engine, 5.
    Heat influx from ocean, Q, causes boil-off from LNG tanks, 7. The safety relief valves, 8, on deck will only open when the LNG tank pressure exceeds MARVS. Releasing methane on deck is not allowed unless it is an emergency situation as methane is a highly flammable greenhouse gas. For this reason, the GCU, 1, will start to burn NBOG before reaching MARVS pressure.
    As said above, because NBOG must be disposed of to avoid a rise in pressure in the LNG tanks, 7, a GCU, 1, has been installed to burn the excess boil-off gas. Starting of the GCU, 1, only occurs when the consumption of gas by the DFDEs, 5, is lower than the Natural Boil-off Rate, such as laying in harbour or at anchor. During periods where the NBOR is larger than the gas fuel consumption, the pressure in the LNG tanks will gradually rise until reaching a level where the GCU is started. The GCU is a relatively large equipment with a combustion chamber where a considerable amount of gas is burned. Fig. 2 shows a sketch of a Gas Combustion Unit, 1.
    The only function of the GCU is to lower the gas pressure of the LNG tanks, 7, and the heat from the combustion is not utilized. The hot exhaust gas from the GCU combustion process in the combustion chamber, 9, is heavily diluted with air from the combustion/dilution air fans, 10. The cooling of the exhaust gasses is mandatory since strict limits for maximum allowable exhaust gas temperatures are given by the safety regulations of the Class societies. A limit for exhaust gas temperature at the outlet from exhaust gas stack, 11, is prescribed because of the potential risk of being an ignition source in case of a major gas leakage on the deck. Therefore, all exhaust gas temperatures must be controlled.
    On gas carrying ships with DFDE, the steam used on-board is produced by a steam boiler plant, which is sometimes possible to operate on both gas and oil. This allows the ship owner to choose the fuel based on both fuel prices and requirements for emissions. An example is a Dual Fuel Boiler, DFB, 3. It is similar to an oil-fired boiler, except from a specially designed burner that can work on both oil and gas. An oil-fired steam boiler may also be employed instead.
    Waste heat from exhaust gas from the engines is recovered in a Waste heat recovery boiler, WFIR, 2. This boiler converts waste heat into steam to recover the energy of the hot exhaust gasses from the DFDE engines, 5.
    The conventional LNG carriers have the GCU, 1, and DFB, 3, on-board to burn excess NBOG respectively to provide steam for the steam consumers on-board.
    The disadvantages of the Gas Combustion Unit, GCU, 1, are:
    The exhaust gas temperature at outlet must never exceed 535 °C. If the combustion is not in balance, there is a risk of unstable combustion and flames/sparks on the deck. Self-ignition temperature of methane is only 595 °C and the exhaust gas from a GCU is typically about 480 °C. This leaves little room for errors. If a major leakage of LNG happens on the deck, it only takes one single spark to initiate a catastrophic fire or explosion.
    In extremely cold areas where the ambient temperature is down to -60 °C (-76 °F) there is a significant risk that combustion/dilution air that is not preheated before entering the combustion chamber, 9, will drastically cool the flame and make it become unstable. KR20160044329 discloses a solution on how to avoid the risks of selfignition on board. The GCU is simply removed and any surplus of electricity is dissipated in a resistance portion. It is, however, not disclosed how this resistance portion should be installed except for that it should be on the medium voltage level.
    Thus, the objective problem is to provide a system for safe disposal of NBOG, having no burning or explosion risks while it is still possible to provide sufficient steam for the consumers on-board but in a cheaper and more effective way providing no or less pollution superior to applying a resistance portion and a fired boiler for providing steam on-board.
    Summary of the invention.
    The above problem has surprisingly been solved by providing an electric steam boiler and means for disposal of excess steam such as a steam dump condenser, which are sized to secure that the engines can always consume the full amount of NBOG from the tanks on-board as claimed in claim 1.
    An anticipated embodiment of the invention as in claim 2 is where the electric steam boiler, 12, is an electrode steam boiler comprising an inner vessel with electrodes immersed therein and an outer vessel for pressurization and to serve as a reservoir for feeding water to the inner vessel. A system wherein said electric boiler having one or more of a steam trap at the periphery of the tank at maximum water level position of its outer vessel or alternatively blow down lines for removal of condensate from heating with steam, is anticipated in claim 3. A system for disposal of boil-off gases wherein the electric steam boiler has at least six electrodes which are connected pairwise two and two, each pair to one electric phase, arranged symmetrically on a diagonal along the water surface within an insulated inner vessel connected to zero is anticipated in claim 4.
    Further, a system with an electric steam boiler and a waste heat recovery boiler, which share a common header for produced steam and share a water supply line via pipe connections, is also anticipated as in claim 5.
    Another anticipated embodiment is a system where the steam dump condenser via fluid connections shares a seawater cooling circuit together with an inert gas generator as claimed in claim 6. A system for disposal of boil-off gasses wherein the power supply is redundant and connected to two independent sets of cables and medium voltage switchgear is anticipated in claim 7. A method of controlling a system of the invention, as anticipated in claim 8, is to control the boil-off gas pressure in head spaces of said tanks, so that the pressure does not exceed a pre-set value by increasing the amount of electricity dissipated in the electric boiler by increasing the water level of the inner vessel of said electric boiler causing the gas consumption of said DFDE electric generators to be increased.
    Other features of the method of claim 8 are anticipated as disclosed in claim 9 and 10.
    Another embodiment of the invention is where the method of control of a liquefied gas carrier is equipped with a system according to any of the claims 1 to 7 where the method for control of the boiler is implemented in the Integrated Automation System, IAS, for control of the ship.
    Yet another embodiment of the invention is where the carrier is for carrying any liquefied gas that is used to fuel an electric propulsion plant. Some examples are Liquid Natural Gas, LNG carrier, Liquid Ethane Gas, LEG carrier, or Liquid Petroleum Gas, LPG carrier.
    In order that the invention may be well understood, some non-limiting examples will now be described in which:
    Fig. 3 A shows an Engine room comparison, Conventional
    Fig. 3 B shows an Engine room comparison, Invention.
    Fig. 4A shows an Electrode boiler (Immersion type).
    Fig. 4B shows an illustrative presentation of the roll and pitch mode of a ship in water on the left, and the resulting roll/pitch angle of a cylinder tank inside the ship as of an ESDU on the right.
    Fig. 5A shows a drawing of a GCU in its casing.
    Fig. 5B shows a drawing of an EDSU in its casing. If compared Fig. 5A and Fig. 5B show the difference in installation footprint.
    Fig. 6 shows a flow diagram of a conventional system for disposal of Natural Boil-Off Gas, NBOG, and supply of feed water and steam.
    Fig. 7 shows the system of the invention for disposal of NBOG, and supply of feed water and steam.
    Fig. 8 shows the conventional system of an electric propulsion plant with a GCU and a fired steam boiler.
    Fig. 9 shows the system of an electric propulsion plant according to the invention with an electric steam boiler.
    Fig. 10 shows a diagram where the steam dump condenser shares a cooling circuit with the Inert Gas Generator.
    Fig. 3 A shows an engine room having installed a system of the conventional type comprising a GCU, 1, a Waste Heat Recovery boiler, WHR, 2, a Dual Fuel Boiler, DFB, 3, an IGG, 4, DFDEs, 5, and PEMs, 6. The drawbacks of the system for disposal of a surplus of NBOG is discussed in the introduction above.
    Fig. 3 B shows an engine room having installed a system for disposal of a surplus of NBOG according to the invention comprising an electric steam boiler, 12, which because of its function is named an Electric Surplus Disposal Unit, ESDU, 12, and means for disposal of excess steam, which in this example is a steam dump condenser, CND 13, which may be placed in the lower part of the engine room. In an anticipated embodiment of the invention the system for disposal of electric surplus may be configured together with a Waste Heat Recovery boiler, WHR, 2, as the WHR may be operated in a beneficial way together with the ESDU, 12. The engine room does in this example further include DFDEs, 5, and PEMs, 6. The WHR, 2, is installed to provide the basic steam supply and to recover the energy of the hot exhaust gas from the DFDEs, 5. An inert gas generator, IGG, 4, is installed for supplying inert gas for emptying tanks, 7, upon service inspection. A steam dump condenser, 13, is a heat exchanger for condensing steam using a cooling media, such as sea water. A steam dump condenser is used for removing energy from steam in case there is not sufficient demand for the steam that has already been produced.
    The electric steam boiler may be powered directly from the ships GENSET, at medium voltage without the use of a transformer.
    The nominal capacity of the electric steam boiler and the steam dump condenser may be based on the GENSET electrical power conversion of Boil-off Gas equivalent to the nominal Natural Boil-off Rate, i.e. amount of electricity produced by the GENSETs from a given number kg/hr boil-off gas. Instead of disposal of NBOG by means of combustion in a Gas Combustion Unit, the gas is converted into electrical power through the DFDEs and GENSETs and the electricity is used to produce steam in an electric boiler. Thereafter, any steam not used is condensed in a steam dump condenser. The seawater cooling circuit can be shared with the ship’s Inert Gas Generator, 4.
    The system replaces both the Gas Combustion Unit and any fired Boiler onboard gas carrying ships such as Liquid Natural Gas Carriers and Floating Storage and Regasification Units, FSRUs.
    Another embodiment of the invention is where the electric steam boiler is of the immersion type shown in Fig. 4A. The electric boiler has redundant power supply, 14, providing power for the electrodes, 15. The inner vessel is equipped with a level sensor, 16, based on a differential pressure measurement of the water column, giving the water level. The outer vessel comprises in double a temperature transmitter, TT, 17, a pressure transmitter, PT, 18, a steam trap, 19, a circulation pump, 20, and outer level sensor, 21.
    Fig. 4A shows an electric steam boiler of the Immersion Type. The Electrode Steam Boiler is a well proven concept based on using electrodes with a medium voltage in water. Relative to size, the electrode boiler transfers more energy to the boiler water compared to a fired boiler based on combustion. The electrode boiler uses a medium voltage over the boiler water, which functions as a conductor/resistor. The alternating current flow between electrodes through the water, which has resistance, generates dense heating directly in the water. Immersion type means that the electrodes are immersed in water and the water level in the inner vessel is controlled to generate steam from a surplus of electricity. The higher the water level is on the electrodes the more heat is generated and more steam is produced. The system has many advantages, such as very few major mechanical parts and no sensitivity to low water level like a fired boiler.
    It is important that the consumed electric load between phases is stable and in balance. On ships at the sea, all liquid surfaces follow the roll and pitch of the ship. See Fig. 4 B. Thus, an electric boiler must supply steam from electricity without disturbing the voltage output and frequency of the GENSETs. An example of a suitable electric boiler which is capable of this is described in patent EP2401549 B1. A workable embodiment comprises a number of these sufficient to provide the needed capacity.
    Fig. 5 A shows a conventional system for disposal of NBOG, a GCU, in its casing. Each deck is approximately 5 meters in height. Both length and width of each floor is about 10-12 meters. The total height of the GCU is typically 21 meters and takes up much space in the casing that is designed to accommodate the GCU.
    Fig. 5 B shows, when comparing with Fig. 5 A, how much of the ship's casing that can be saved, when there is no need for a GCU as with the solution of using an electric steam boiler. The fired boiler as of a conventional system requires roughly the same space as the steam dump condenser, so no space savings are anticipated for removal of the fired boilers.
    Fig. 6 shows a block diagram of a conventional system for disposal of a surplus of NBOG comprising a GCU, 1, a WHR, 2, DFB, 3, one or more DFDEs, 5, a storage for feed water, a hot well, 22, equipment on ship using steam, so called steam consumers, 23, and equipment for water treatment, 24, where sea water is desalinated and supplied as make-up water to the hot well, and the pipe connections between the process equipment on a liquid gas carrier.
    Fig. 7 shows a block diagram of a system according to the invention comprising one or more ESDUs, 12, a steam dump condenser, 13, and a WHR, 2, together with one or more DFDEs, 5, on a liquid gas carrier, and the pipe connection between the process equipment. It is anticipated that for the system of the invention for disposal of surplus of boil-off gas to be energy efficient as a replacement for any fired steam boilers, the resulting greater amount of exhaust gas of the DFDE must be utilized in a Waste Heat Recovery boiler, WHR, 2. The WHR can only function as a base load boiler, so the WHR, 2, and the ESDU, 12, could be sharing a common feedwater supply and steam header.
    The hot exhaust gas from DFDE GENSETs, 5 and 25, is further utilized in the WHR boiler, 2. Both WHR boiler, 2, and ESDU, 12, produce steam to the ships steam consumers, 23. Condensate is returned to the Hot well, 22. Make up water is transferred from the water treatment unit, 24, to compensate for loss of condensate/steam.
    Fig. 8 shows a block diagram of a conventional liquid gas carrying ships with electric propulsion system based on the Dual Fuel Diesel Electric GENSETs, 5 and 25. DFDE GENSETs can run on NBOG, MDO or perhaps HFO. The choice of fuel depends on availability and price. This gives the ship-owner more flexibility to adapt to changes in fuel prices to lower his operational expenses.
    During harbour operation, it is not possible to consume the full amount of NBOG, which evaporates from the liquefied gas tanks, 7. Therefore, a GCU, 1, is required, to be able to dispose of the NBOG safely. There could also be a reliquefaction plant, RELIQ, installed on board. A RELIQ plant is able to perform reliquefaction of the boil-offgas, converting the gas to liquid, that can be transferred back to the LNG tanks, 7. However, due to installation costs and complexity, RELIQ plants are rarely sized for 100% of the NBOR and do not offer full redundancy. More often a RELIQ is only sized 50% of the NBOR as this would cover most operating scenarios. Therefore, a single fault on a RELIQ can prevent it from functioning and a secondary means for gas disposal must still be available.
    The GENSETs, 25, produce electricity for the electric consumers. The biggest consumers are the propulsion electric motors, PEM, 6. During voyage the NBOR can be consumed by the DFDEs, 5, when producing power for the PEMs, 6. During harbour operations, the PEMs, 6, are not available and the consumers on the Low voltage distribution boards, 26, TRAFO, cannot consume electricity equivalent to the NBOR. This causes an increment of the cargo tank pressure as the liquid gas continues to boil. When the pressure becomes too high, the GCU, 1, will burn the excess NBOG to lower the pressure.
    As shown in the example; switch gear, power supply, DFDE, 5, GENSET, 25, and PEM, 6, are redundant to meet the requirements for redundancy. The GCU, 1, is simple process equipment and only the most vital parts hereof are redundant/duplicated.
    Fig. 9 is a block diagram of a liquid gas carrying ship with electric propulsion. GENSETs, 5 and 25. DFDE GENSETs, 5 and 25, can run on NBOG, MDO or perhaps HFO as the system of the ship with a conventional setup in Fig. 8.
    The block diagram shows, in addition, a system for disposal of NBOG according to the invention.
    In a system according to the invention, a GCU, 1, and a fired boiler, 3, is replaced with an ESDU, 12, and a steam dump condenser, 13.
    In case the steam pressure drops below a given lower value the ESDU, 12, will also start to increase the steam pressure to its normal value (set point).
    As seen in the example in Fig. 9, the power produced on the GENSETs, 25, can always be disposed of, including during harbour operations. Even though there is only one ESDU body, 12, there are two power lines available, as the medium voltage switch gear must be redundant to fulfil requirements for redundancy, like the rules and regulations applicable for the GCU. The ESDU may consume electric power at medium voltage directly from the DFDE, 5, generator sets.
    The electric boiler disposes of electric surplus from the GENSETs, 25, during harbour operations as well as produces steam when required. This new method is based on only electrical steam production rather than burning excess boil-off gas in a Gas Combustion Unit or gas fired boiler, thus the gas is burned in the DFDE, 5, to produce the extra electricity for steam production.
    The electric steam boiler installation fulfils the same high redundancy requirements as required for Gas Combustion Unit, GCU, 1. As a result, the Control system and all other essential components are also redundant to secure continued operation in case of a single failure.
    When the electrode steam boiler, 12, is inactive, is in Standby-mode, it shall be kept warm and ready for operation by condensation of steam from the WHR boiler, 2. Excess condensation may continuously be removed by a steam trap, 19, connected to the outer vessel at maximum water level position. A still further advantage of this invention is that during increased ESDU steam production, the WHR, 2, will also start to produce more steam because more exhaust gas is produced by the DFDEs, 5.
    The WHR, 2, and ESDU, 12, may produce steam to a common header. The WHR, 2, produces basic steam demand while the ESDU, 12, will supply more steam whenever required. When the ESDU produces steam, it increases the load on the DFDEs, 5. This increases the energy in the exhaust gas from the engines, which again increases steam production in the WHR until equilibrium is met between WHR, 2, and ESDU steam production. The use of the WHR, 2, ensures an overall satisfactory energy efficiency for steam production on the ESDU, 12.
    Another advantage of this invention is that the combined overall footprint and installation costs for the entire equipment needed to fulfil the purpose can be reduced.
    The ESDU system may be controlled as follows:
    During voyage, the steam dump condenser will most likely not be used, as all NBOG can be used for propulsion and steam purposes as well as general electric consumers. For ships with RELIQ installed, the dumping of steam would not be required unless there is a malfunction to the RELIQ. In both scenarios, the steam dump condenser would be in standby.
    When the ESDU, 12, is in standby and sufficient steam can be produced by the WHR boiler, 2, the ESDU is kept hot, i.e. ready for operation within short time, by internal condensation of steam supplied by the WHR. The condensate will accumulate within the outer vessel of the electrode boiler and must be removed by means of either bottom blowdown or by drain with a steam trap placed in the periphery of the outer vessel maximum water level.
    Alternatively, an electric heating element can maintain the standby temperature of the ESDU, 12. In case the steam trap, 19, fails, the blow down lines after opening the valve can be used as alternative means of disposal of condensate.
    An automation system ensures that electric steam production is triggered directly by a rise of pressure in the liquid gas tanks, 7, above a given threshold, which, then, is the set point for control of the ESDU, 12, and by the steam pressure below a given threshold, which, then, is the set point for control of the ESDU. Both functions can run simultaneously and each function contributes / adds to the value of the set point of the ESDU, 12. a. BOG disposal: Electrode boiler, 12, starts up or increase the production of steam when pressure in LNG tank, 7, is high. When steam pressure rises over a given set point above e.g. 7bar(g), a steam dump condenser, 13, will dump the excess steam to maintain steam pressure. b. Steam production: When steam pressure drops below its set point the electric boiler, 12, will start up or increase the production of steam to compensate for the loss of steam pressure in the system. The water level of the electric steam boiler’s inner vessel is the control variable of the capacity of the electric steam boiler.
    The implementation of an electric boiler for disposal of NBOG on gas carrying ships with an electric propulsion plant comprises a control system for the ship which provides interconnection between the ESDU, 12, and ship’s Integrated Automation System, IAS, to control the cargo tank pressure. Thus, IAS provides an output which is part of the control loop for the ESDU.
    The electrode boiler is running on same voltage as the DFDE output without the use of a transformer directly by the GENSET, 25, medium voltage.
    The rated steam capacity of the electrode boiler, 12, and the dump condenser, 13, is based on the electrical power conversion through the DFDE, 5, of the Natural Gas Boil-off Rate (NBOR [kg/hr]). Therefore, steam capacity will be higher than if it was sized for actual on-board steam demand. Means of condensing the excess steam will be present, such as a large steam dump condenser, 13.
    The present invention provides an economical installation. The further advantages are:
    Its operation is simple and requires minimal maintenance due to fewer moving parts and subsystems.
    There is no combustion control systems, burners and heating surfaces, no thermal stress induced to the pressure part by high differential temperatures, no part of the electrode boiler is hotter than the water. If scaling occurs it would electrically insulate the conductors and reduce the current flow and steam output, but no damage would be caused to the boiler.
    Electrodes in the ESDU have long lifespan (about 10 yrs.) and are simple to replace.
    The system can be placed in the engine room with no ATEX requirements for equipment.
    It has no possible damage from low water levels as there is no heat transfer surfaces as in the fired boiler type.
    Its performance is high in an extreme cold temperature environment as the entire ESDU system is placed inside the engine room. Outside ambient air temperature is irrelevant to the ESDU proper function.
    The ESDU generates no exhaust gas emissions. Further, it generates very low noise levels in the engine room, as there is no noise from either combustion or mechanical parts/fans etc.
    It has high efficiency (about 99.9% for electrode boiler), high turn down ratio (1 to 100%). It is safer as no risk of sparks or hot temperatures occur on the deck. The ESDU has no combustion or stack to the deck, and, thus, no risk that the ESDU could be ignition source to any gas present on the deck.
    Another anticipated embodiment of the invention is shown in Fig. 10. LNG carriers may, in addition, comprise an Inert Gas Generator, IGG, 4, for production of inert gas to displace the natural gas, prior to internal inspection of the cargo tanks. The IGG, 4, in Fig. 10 uses a large amount of seawater for cooling. Its seawater capacity alone is enough to supply the steam dump condenser, 13, for the ESDU system.
    The numbers and abbreviations used in the figures are as follows:
    1 GCU
    Gas Combustion Unit (Gas burning equipment used to directly dispose of natural boil-off gas)
    2 WHR
    Waste Heat Recovery boiler (A boiler powered by hot exhaust gasses to increase efficiency of engine)
    3 DFB
    Dual Fuel Boiler (A steam producing boiler equipped with a diesel/gas burner)
    4 IGG
    Inert Gas Generator (A plant for producing inert gas for inerting of LNG tanks)
    5 DFDE
    Dual Fuel Diesel Electric (Diesel/gas engine combined with an electric generator)
    6 PEM
    Propulsion Electric Motor (Large electric motorfor propulsion) 7 LNG tanks
    Cargo tanks for Liquid Natural Gas (Liquid Natural Gas is a fuel gas containing various alkanes) 8 LNG Tank Safety Relief Valve 9 GCU combustion/dilution air fans 10 GCU combustion chamber 11 GCU exhaust gas stack
    12 ESDU
    Electric Surplus Disposal Unit (Electric boiler used for both steam production and indirect disposal of boil-off gas)
    13CND
    Steam dump condenser for condensation of excess steam 14 Redundant Power Supply 15 Electrodes 16 Level control, inner vessel
    17 Temperature transmitter, TT
    18 Pressure transmitter, PT 19 Steam trap 20 Circulation pump 21 Level control, outer vessel 22 Feed water tank / Hot well 23 Steam Consumers 24 Water treatment plant
    25 GENSET
    Generator Set (A set comprising an engine and a generator) 26 Low Voltage electric distribution board 30 Pressure Safety Valve A boiler pressure part safety valve that opens to atmosphere, when the internal pressure exceeds the boiler design pressure. 31 Throttle Valve A valve that drains water from the inner vessel of an electrode boiler to the outer vessel, thus reducing the inner vessel water level and steam output.
    The other abbreviations used in the text are as follows:
    ATEX EU directive describing requirements in environment with explosive atmosphere (gas, dust etc.)
    FSRU
    Floating Storage and Regasification Unit (A LNG Carrier used for storage and regasification of liquid gas)
    FIFO
    Fleavy Fuel Oil (A tar-like fuel oil that is used primarily due to its low cost) IAS
    Integrated Automation System (Automation system for monitoring and control of equipment) LNG carrier
    Liquid Natural Gas Carrier (A ship that carries liquid natural gas as cargo) LEG carrier
    Liquid Ethane Gas Carrier (A ship that carries liquid gas comprising mostly ethane) LPG carrier
    Liquid Petroleum Gas Carrier (A ship that carries liquid gas comprising mostly propane or butane or mostly a mixture of these two gases)
    MARVS
    Maximum Allowable Relief Valve Setting (The set point for opening of the LNG tank relief valve)
    MDO
    Marine Diesel Oil (A diesel fuel oil with much lower sulphur content but more expensive than FIFO)
    Medium Voltage
    Medium voltage is defined by the Institution of Electrical and Electronic Engineers (IEEE) as a voltage range between 1 kV to 100 kV. Typically, the voltage on a DFDE GENSET is 6.6 kV.
    NBOG
    Natural Boil-off Gas (The specific gas coming from natural evaporation of the liquid gas cargo)
    NBOR
    Natural Boil-off Rate (The rate of natural evaporation of a liquid gas due to surrounding heat influx)
    RELIQ
    Reliquefaction Plant (A nitrogen cooling plant, that is able to cool and reliquefy boil-offgas)
    权利要求:
    Claims (10)
    [1] 1. A system for disposal of boil-off gases from tanks, 7, on-board liquid gas carrying ships with an electric propulsion plant based on engines, 5, able to run on boil-off gas and combined with generators, 25, for production of electricity characterised in that it comprises at least one electric steam boiler, 12, which run on electricity produced by said electric generator(s), 25, driven by said engine(s), 5, being fed by boil-off gas, and which electric steam boilers have a capacity for conversion of electricity into steam large enough to convert any surplus of electricity produced at said generator(s) run by said engine(s) thereby converting all boil-offgas, and at least one means for disposal of excess steam such as a steam dump condenser, 13.
    [2] 2. A system for disposal of boil-off gases according to claim 1 wherein the electric steam boiler, 12, comprises an inner vessel with clean water or other suitable liquid and electrodes, 15, immersed therein and an outer vessel with the first vessel placed therein.
    [3] 3. A system for disposal of boil-off gases according to claim 2 wherein the electric steam boiler, 12, further comprising one or more of a steam trap, 19, at the periphery of the tank at maximum water level position, or bottom/surface blow down lines for removal of condensate.
    [4] 4. A system for disposal of boil-off gases according to claim 2 or 3 wherein the electric steam boiler, 12, has at least six electrodes, 15, which are connected pairwise two and two each pair to one electric phase arranged symmetrically on a diagonal along the water surface within an insulated vessel to be insensitive to pitch and roll of the ship causing a pitch and roll of the water surface and thus how much each electrode is covered by water from time to time to be constant for a given amount of water in the inner vessel as the same total area of a pair of electrodes is covered all the time.
    [5] 5. A system for disposal of boil-off gasses according to any of the claims 1 to 4 wherein the electric steam boiler, 12, and a waste heat recovery boiler, 2, produce steam to a common header via pipe connections, and share a feed water supply line.
    [6] 6. A system for disposal of boil-off gasses according to any of the claims 1 to 5 wherein said steam dump condenser, 13, shares a seawater cooling circuit together with an inert gas generator, 4.
    [7] 7. A system for disposal of boil-off gasses according to any of the claims 1 to 6 wherein the electric boiler is equipped with a redundant power supply such as with the electrodes connected to two independent sets of cables each set to a separate medium voltage switchgear.
    [8] 8. A method of controlling the system of any of the claims 2 to 7 characterised in that the ship’s Integrated Automation System, maintains a pre-set boil-off gas pressure in head spaces of said tanks, 7, by controlling the water level of said inner vessel of said electric boiler, 12, increasing the water level when the boil-offgas pressure increases above the pre-set value, and decreasing the water level when the pressure drops again.
    [9] 9. A method of claim 8 wherein the electric boiler is running directly at medium voltage without the use of a transformer.
    [10] 10. A method of any of the claims 8 to 10 wherein the waste heat recovery boiler, 2, functions as a base load boiler.
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    同族专利:
    公开号 | 公开日
    DK179420B1|2018-06-18|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    KR20160044329A|2014-10-15|2016-04-25|대우조선해양 주식회사|Liquefied natural gas carrier and apparatus for treatment bog of a liquefied natural gas carrier|
    KR20160095442A|2015-02-03|2016-08-11|대우조선해양 주식회사|The Dual Fuel Engine fitted Breaking Resistor Operating Method and System on Gas Carrier Ship|
    JP2017061929A|2015-09-22|2017-03-30|ゼネラル・エレクトリック・カンパニイ|Method and system for electric and steam supply system|
    法律状态:
    2019-12-14| PBP| Patent lapsed|Effective date: 20190529 |
    优先权:
    申请号 | 申请日 | 专利标题
    DKPA201670950|2016-11-30|PCT/DK2017/050349| WO2018099526A1|2016-11-30|2017-10-25|System for disposal of boil-off gases on-board liquid gas carrying ships|
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