WO2011088830A1 - Dual fuel supply system, methods for switching between different fuel types and method for retro-fitting a heavy fuel system - Google Patents

Dual fuel supply system, methods for switching between different fuel types and method for retro-fitting a heavy fuel system Download PDF

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Publication number
WO2011088830A1
WO2011088830A1 PCT/DK2010/000012 DK2010000012W WO2011088830A1 WO 2011088830 A1 WO2011088830 A1 WO 2011088830A1 DK 2010000012 W DK2010000012 W DK 2010000012W WO 2011088830 A1 WO2011088830 A1 WO 2011088830A1
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WO
WIPO (PCT)
Prior art keywords
fuel
light
storage tank
combustion unit
heavy
Prior art date
Application number
PCT/DK2010/000012
Other languages
French (fr)
Inventor
Jens Hvas Olesen
Original Assignee
York Industries International Hk. Ltd
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Application filed by York Industries International Hk. Ltd filed Critical York Industries International Hk. Ltd
Priority to PCT/DK2010/000012 priority Critical patent/WO2011088830A1/en
Publication of WO2011088830A1 publication Critical patent/WO2011088830A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0626—Measuring or estimating parameters related to the fuel supply system
    • F02D19/0628—Determining the fuel pressure, temperature or flow, the fuel tank fill level or a valve position
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0602—Control of components of the fuel supply system
    • F02D19/0605—Control of components of the fuel supply system to adjust the fuel pressure or temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0639—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed characterised by the type of fuels
    • F02D19/0649—Liquid fuels having different boiling temperatures, volatilities, densities, viscosities, cetane or octane numbers
    • F02D19/0657—Heavy or light fuel oils; Fuels characterised by their impurities such as sulfur content or differences in grade, e.g. for ships
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0663—Details on the fuel supply system, e.g. tanks, valves, pipes, pumps, rails, injectors or mixers
    • F02D19/0665—Tanks, e.g. multiple tanks
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0663—Details on the fuel supply system, e.g. tanks, valves, pipes, pumps, rails, injectors or mixers
    • F02D19/0668—Treating or cleaning means; Fuel filters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0663—Details on the fuel supply system, e.g. tanks, valves, pipes, pumps, rails, injectors or mixers
    • F02D19/0684—High pressure fuel injection systems; Details on pumps, rails or the arrangement of valves in the fuel supply and return systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/08—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed simultaneously using pluralities of fuels
    • F02D19/081—Adjusting the fuel composition or mixing ratio; Transitioning from one fuel to the other
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M31/00—Apparatus for thermally treating combustion-air, fuel, or fuel-air mixture
    • F02M31/20—Apparatus for thermally treating combustion-air, fuel, or fuel-air mixture for cooling
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M37/00—Apparatus or systems for feeding liquid fuel from storage containers to carburettors or fuel-injection apparatus; Arrangements for purifying liquid fuel specially adapted for, or arranged on, internal-combustion engines
    • F02M37/0047—Layout or arrangement of systems for feeding fuel
    • F02M37/0052—Details on the fuel return circuit; Arrangement of pressure regulators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M37/00—Apparatus or systems for feeding liquid fuel from storage containers to carburettors or fuel-injection apparatus; Arrangements for purifying liquid fuel specially adapted for, or arranged on, internal-combustion engines
    • F02M37/0047—Layout or arrangement of systems for feeding fuel
    • F02M37/007—Layout or arrangement of systems for feeding fuel characterised by its use in vehicles, in stationary plants or in small engines, e.g. hand held tools
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
    • F02D19/0626—Measuring or estimating parameters related to the fuel supply system
    • F02D19/0634—Determining a density, viscosity, composition or concentration
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/30—Use of alternative fuels, e.g. biofuels

Definitions

  • the present invention relates to a dual fuel supply system for a combustion unit (2) able to be operated on different fuel types, to methods for switching from heavy fuel operation to light fuel operation and vice versa, and to a method for retro-fitting an existing heavy fuel system for updating it to a dual fuel system.
  • HFO Heavy Fuel Oil
  • the burner and fuel supply systems of such machinery must be constructed to or at least be modified to be able to run on lighter types of fuel, such as Marine Diesel Oil (MDO) and Marine Gas Oil (MGO) as well as on HFO, which is the most economic and, therefore, the preferred fuel type for open sea operation.
  • lighter types of fuel such as Marine Diesel Oil (MDO) and Marine Gas Oil (MGO) as well as on HFO, which is the most economic and, therefore, the preferred fuel type for open sea operation.
  • the HFO storage tank In order for the HFO to be in a liquid state, the HFO storage tank must be heated. Furthermore, the HFO is heated even more to a temperature of more than 100 °C in the fuel supply system in order to obtain a viscosity of the HFO supplied to the burner system that is low enough to be suitable for the nozzles thereof. On the other hand, MDO and MGO need to be cooled in order to get a viscosity high enough to be suitable for the nozzles of the burner system. Furthermore, the use of MDO or MHO under the heated conditions of the fuel supply system suitable for HFO operation may result in fuel pump trouble and/or vapour lock due to vaporization of these highly volatile fuel types in the heated fuel supply system.
  • the flash point of MDO/MGO is found at a relatively low temperature, meaning that these light fuel types should be secured from being exposed to temperatures above approximately 60 °C. This means that care should be taken when placing the MDO/MGO fuel storage tank to avoid excessive heating of the tank, e.g. from heat radiation from the HFO fuel storage tank.
  • a dual fuel supply system with possibility for cooling the fuel has been disclosed in German patent application DE 198 28 772 A 1 (MAN B & W Diesel A/S). The disclosed system, however, requires for retrofitting modification of the existing heating means in the core part of the fuel supply system and does not deal with the problems of placement of the MDO/MGO fuel storage tank.
  • the present invention relates to such dual fuel supply system for supplying a heavy fuel oil, a light fuel, such as Marine Gas Oil or Marine Diesel Oil, or a mixture of heavy fuel and light fuel to a combustion unit
  • the system comprising a heavy fuel storage tank for storing heavy fuel, a light fuel storage tank for storing light fuel, a combustion unit supply connection for supplying fuel to the combustion unit, such as the main engine, auxiliary engines and/or boilers, a main return conduit for leading excess fuel from the combustion unit back towards the combustion unit supply connection, at least one circulation pump arranged in the combustion unit supply connection for driving fuel through the combustion unit supply unit and the main return conduit, a heavy fuel supply conduit for supplying heavy fuel from the heavy fuel storage tank to the combustion unit supply connection, and a light fuel supply conduit for supplying light fuel from the light fuel storage tank to the combustion unit supply connection, where the system further comprises cooling means arranged for cooling contents of the light fuel storage tank.
  • the light fuel storage tank By cooling the light fuel storage tank, it is made redundant to build in a new fuel cooler before the combustion unit so that the parts of the combustion unit, such as pumps and nozzles, that require a certain viscosity level to function properly will operate with the light fuel or the mixture of the light fuel and heavy fuel.
  • Such fuel cooler may as seen in the prior art be build into an existing heating means for heating the heavy fuel to an operational temperature, or it may be a separate unit. It is also obtained by cooling the light fuel storage tank that the risk of reaching the flash point of the light fuel in the tank may be removed and the light fuel storage tank may be arranged e.g. next to the heavy fuel storage tank.
  • the pumps for pumping the light fuel from the storage tank may be the same as the ones applied to pump the heavy fuel from the heavy fuel storage tank as the viscosity of the cold light fuel does not deviate much from the viscosity of the heated heavy oil.
  • the cooling means includes circulation means for circulating refrigerant, preferably fresh water, in a heat exchanger arranged in the light fuel storage tank, and a refrigeration unit, preferably a vapour-compression refrigeration unit, for cooling said refrigerant.
  • a refrigeration unit preferably a vapour-compression refrigeration unit
  • the control unit of the cooling means mat be arranged for, during a second mode of operation of the system, i.e. when the combustion unit is operating on heavy fuel, to maintain a temperature of the light fuel stored in the light fuel storage tank in the range of 25 °C to 45 °C, such as in the range of 30 °C to 40 °C.
  • the system may further comprise a first return way valve, preferably an electrically operated 3-way valve controlled by control means, in the main return conduit for controlling whether excess fuel from the combustion unit is directed towards the combustion unit supply connection or towards a fuel storage tank, a circulation return conduit for leading excess fuel from the first return way valve back to the combustion unit supply connection, and a storage return conduit for leading excess fuel from the first return way valve towards a fuel storage tank.
  • a first return way valve preferably an electrically operated 3-way valve controlled by control means, in the main return conduit for controlling whether excess fuel from the combustion unit is directed towards the combustion unit supply connection or towards a fuel storage tank
  • a circulation return conduit for leading excess fuel from the first return way valve back to the combustion unit supply connection
  • a storage return conduit for leading excess fuel from the first return way valve towards a fuel storage tank.
  • the system may also comprise a second return way valve in the storage return conduit, preferably an electrically operated 3-way valve controlled by control means, for controlling whether excess fuel from the main return conduit is directed towards the heavy fuel storage tank or towards the light fuel storage tank, a heavy fuel return conduit connecting the second return way valve with the heavy fuel storage tank, and a light fuel return conduit connecting the second return way valve with the light fuel storage tank.
  • a second return way valve in the storage return conduit preferably an electrically operated 3-way valve controlled by control means, for controlling whether excess fuel from the main return conduit is directed towards the heavy fuel storage tank or towards the light fuel storage tank
  • a heavy fuel return conduit connecting the second return way valve with the heavy fuel storage tank
  • a light fuel return conduit connecting the second return way valve with the light fuel storage tank.
  • the mixture of heavy fuel and light fuel may at a certain point in the which-over be directed to the heavy fuel storage tank instead of being recirculated so that all heavy fuel can be removed fast from the system and a full switch-over may be accomplished where the excess fuel from the combustion unit may be returned to the light fuel storage tank for cooling without the risk of sending an amount of heavy fuel to the light fuel storage tank.
  • the system may comprise a mixed fuel supply conduit through which both the heavy fuel from the heavy fuel supply conduit and the light fuel from the light fuel supply conduit may reach the combustion unit supply connection.
  • the system may be equipped with a fuel mixing valve arranged so that the heavy fuel from the heavy fuel supply conduit and the light fuel from the light fuel supply conduit are mixed in the fuel mixing valve before reaching the mixed fuel supply conduit.
  • the combustion unit supply connection (6) may comprises temperature sensing means (18) for measuring the temperature of the fuel supplied to the combustion unit (2) and/or viscosity sensing means (19) for measuring the viscosity of the fuel supplied to the combustion unit (2) so as to control the mixing and switch-over process. Additionally, a temperature sensing means may be positioned near to and upstream from the circulation pump.
  • the system may further comprise a circulation tank, such as a degassing and/or mixing tank, arranged connecting the main return conduit and the combustion unit supply connection.
  • a circulation tank such as a degassing and/or mixing tank, arranged connecting the main return conduit and the combustion unit supply connection.
  • the heavy fuel from the heavy fuel supply conduit and the light fuel from the light fuel supply conduit may enter the combustion unit supply connection by means of the circulation tank, which in that case will ensure a complete mixing of the two types of fuel and the fuel returned from the combustion unit during a switch-over before the fuel is delivered to the combustion unit.
  • the present invention further relates to a method for switching from heavy fuel operation to light fuel operation of a combustion unit comprising the steps of:
  • the light fuel being supplied from the light fuel storage tank is being kept at a substantially constant temperature in the range of 5 °C to 30 °C, preferably in the range of 10 °C to 25 °C by cooling the light fuel storage tank.
  • the viscosity may be measured and used for control of the switching process to ensure that the viscosity is suitable for the nozzles of the combustion unit.
  • the method may prior to the step of mixing the fuel, comprise the steps of
  • the method may further comprise the steps of: changing the return path of excess fuel from the combustion unit so that, when the decreasing temperature of the fuel in the circulation unit reaches a previously defined threshold temperature, the excess fuel is no longer returned to the circulation circuit but is instead returned to the heavy fuel storage tank, and
  • Said threshold temperature is preferably selected in the range of 40 °C to 60 °C, such as within the range of 45 °C to 55 °C.
  • Said predefined time period is preferably selected within the range of 5-60 minutes, preferably within the range of 10 to 30 minutes, such as about 15 minutes.
  • the fuel in the light fuel tank is advantageously being held at a constant temperature selected in the range of 25 °C to 45 °C, such as in the range of 30 °C to 40 °C during the operation of the combustion unit on heavy fuel and cooled down to said substantially constant temperature of the fuel in the light fuel storage tank before start of the switching procedure.
  • the present invention relates in yet an aspect to a method for switching from light fuel operation to heavy fuel operation of a combustion unit comprising the steps of: operating the combustion unit on light fuel being supplied to the combustion unit from a light fuel storage tank, the excess fuel from the combustion unit being lead back to the light fuel storage tank, changing the return path of excess fuel from the combustion unit so that, the excess fuel is no longer returned to the light fuel storage tank but is instead returned to the combustion unit through a circulation circuit,
  • the proportion of heavy fuel in the fuel supplied to the circulation circuit gradually until only heavy fuel is supplied to the circulation circuit while continuously measuring and controlling the temperature of the fuel in the circulation circuit, the proportion of heavy fuel being increased in such a way that, at any given time, it is ensured that the temperature of the mixed fuel does not increase by more than 2 °C per minute, wherein throughout the switching procedure, the light fuel being supplied from the light fuel storage tank is being kept at a substantially constant temperature in the range of 5 °C to 30 °C , preferably in the range of 10 °C to 25 °C by cooling the light fuel storage tank (4).
  • This method may further comprise the step of changing the return path of excess fuel is done in two steps, so that from the beginning of the switching over from light fuel supply to heavy fuel supply, the excess fuel is instead returned to the heavy fuel storage tank, and then, when the increasing temperature of the fuel supplied to the combustion unit reaches a previously defined threshold temperature, the excess fuel is no longer returned to the heavy fuel storage tank but is instead returned to the combustion unit through a circulation circuit including a circulation tank.
  • Said threshold temperature may preferably be selected in the range of 40 °C to 60 °C, such as within the range of 45 °C to 55 °C.
  • the method may further comprise the step of switching on heating means for heating the fuel in the circulation circuit to an operational temperature.
  • the method may include to hold the light fuel tank at a constant temperature selected in the range of 25 °C to 45 °C, such as in the range of 30 °C to 40 °C, after completion of the switching procedure.
  • the present invention furthermore relates to a method for retro-fitting an existing fuel supply system for updating it to a dual fuel supply system as described above.
  • fig. 1 is a schematic view of an embodiment of a non-pressurised dual fuel supply system according to the invention
  • fig. 2 is a schematic view of an embodiment of a pressurised dual fuel supply system according to the invention.
  • Fig. 1 discloses schematically an embodiment of a non-pressurised dual fuel system 1 according to the invention.
  • the fuel system 1 comprises a heavy fuel storage tank 3 and a light fuel storage tank 4 and provides heavy fuel, light fuel or a mixture thereof to be combusted by a combustion unit 2.
  • the light fuel may be Marine Diesel Oil (MDO) or Marine Gas Oil (MGO), while the heavy fuel typically will be the type of Heavy Fuel Oil (HFO) that is well-known for operation of marine combustion units 2, such as the main engine, auxiliary engines and/or boilers.
  • MDO Marine Diesel Oil
  • MGO Marine Gas Oil
  • HFO Heavy Fuel Oil
  • the light fuel storage tank 4 is provided with cooling means 12 comprising a refrigeration unit 27 and circulation means 26 for circulating a cooling fluid, which may be fresh water.
  • the cooling means 12 must be sufficiently efficient to cool down the light fuel in the light fuel storage tank 4 to a temperature of 15 °C or less.
  • Heavy fuel can be drawn off from the heavy fuel storage tank 3 through a heavy fuel supply conduit 10 and, similarly, light fuel can be drawn off from the light fuel storage tank 4 through a light fuel supply conduit 1 1.
  • the heavy fuel from the heavy fuel supply conduit 10 and the light fuel from the light fuel supply conduit 1 1 are mixed together in a fuel mixing valve 16, from which the mixed fuel continues its flow towards the combustion unit 2 through a mixed fuel supply conduit 13.
  • the fuel mixing valve 16 in the shown embodiment is an electrically operated 3-way valve controlled by control means 17 in response to signals from temperature sensing means 18 and viscosity sensing means 19 in the fuel supply system 1.
  • the mixed fuel supply conduit 13 lead the mixed fuel to a circulation circuit comprising a combustion unit supply conduit 6, the combustion unit 2, a main return conduit 7, a circulation return conduit 21 and a circulation tank 5, such as a degassing and/or mixing tank.
  • the combustion unit supply conduit 6 leads from the circulation tank 5 to the combustion unit 2 and is provided with two circulation pumps 8 arranged in parallel to allow continued operation of one of the circulation pumps 8, while the other may be out of function due to maintenance work or for other reasons.
  • a temperature sensing means 18 is arranged in connection with the combustion unit supply conduit 6 in order to measure the temperature of the fuel flowing towards the combustion unit 2.
  • This temperature sensing means 18 is connected to the control means 17, which may comprise a Programmable Logic Controller (PLC) or any other device suitable for controlling the operation of the fuel supply system 1.
  • PLC Programmable Logic Controller
  • heating means 9 are arranged in connection with the combustion unit supply conduit 6 for heating of the fuel flowing towards the combustion unit 2 when necessary.
  • Two heating means valves 28 and a heating means bypass valve 29 are arranged so that, when the heating means valves 28 are open and the heating means bypass valve 29 is closed, the fuel flowing towards the combustion unit 2 will pass through the heating means 9, whereas, when the heating means valves 28 are closed and the heating means bypass valve 29 is open, the fuel will bypass the heating means 9.
  • a viscosity sensing means 19 is arranged in connection with the combustion unit supply conduit 6 in order to measure the viscosity of the fuel flowing towards the nozzles of the combustion unit 2. Like the temperature sensing means 18, this viscosity sensing means 19 is connected to the control means 17.
  • Excess fuel is lead from the combustion unit 2 through the main return conduit 7 to a first return way valve 20, which in the shown embodiment is an electrically operated 3-way valve controlled by the control means 17 in response to signals from the temperature sensing means 18.
  • the excess fuel from the combustion unit 2 may continue in the circulation circuit 2, 5, 6, 7, 8, 9, 20, 21 , 28 through the circulation return conduit 21 and the circulation tank 5 and back into the combustion unit supply conduit 6, or it may continue through a storage return conduit 22 towards a second return way valve 23, which in the shown embodiment is also an electrically operated 3 -way valve controlled by the control means 17 in (delayed) response to signals from the temperature sensing means 18.
  • the circulation tank 5 works as a degassing tank when the combustion unit 2 is operated on heavy fuel, and a degassing tank closing valve 14 is placed in the combustion unit supply conduit 6 near the outlet from the circulation tank 5.
  • the excess fuel from the combustion unit 2 may continue through a heavy fuel return conduit 24 to the heavy fuel storage tank 3, or it may continue through a light fuel return conduit 25 towards the light fuel storage tank 4.
  • the degassing tank closing valve 14 is open and the heating means valves 28 and the heating means bypass valve 29 are set up to lead the fuel through the heating means 9 to be heated before reaching the combustion unit 2.
  • the first return way valve 20 is set up by the control means 17 to close the inlet to the storage return conduit 22 and open the inlet to the circulation return conduit 21 so that the heavy fuel circulates in the circulation circuit 2, 5, 6, 7, 8, 9, 20, 21 , 28, which is defined above, passing the combustion unit 2 and being degassed in the circulation tank 5.
  • the cooling means 12 is controlled so that, during operation of the combustion unit 2 on heavy fuel, the temperature of the light fuel in the light fuel storage tank 4 is kept at about 35 °C.
  • the degassing tank closing valve 14 is closed and the heating means valves 28 and the heating means bypass valve 29 are set up to let the fuel bypass the heating means 9.
  • the first return way valve 20 is set up by the control means 17 to open the inlet to the storage return conduit 22 and close the inlet to the circulation return conduit 21
  • the second return way valve 23 is set up by the control means 17 to close the inlet to the heavy fuel return conduit 24 and open the inlet to the light fuel return conduit 25.
  • the cooling means 12 is controlled so that, during operation of the combustion unit 2 on light fuel, the temperature of the light fuel in the light fuel storage tank 4 is kept at about 15 °C.
  • the procedure of switching over from heavy fuel operation to light fuel operation begins approximately 24 hours before arriving to an area where light fuel operation is required by starting to cool down the light fuel in the light fuel storage tank 4 from about 35 °C to about 15 °C.
  • the next step of the procedure is to close the heating means valves 28 and to open the heating means bypass valve 29 so that the heavy fuel circulating in the circulation circuit 2, 5, 6, 7, 8, 20, 21 , 29 will bypass the heating means 9 and the temperature of the circulating heavy fuel will start decreasing.
  • the control means 17 changes the position of the fuel mixing valve 16 in order to add light fuel (having a temperature of about 15 °C) from the light fuel storage tank 3 to the fuel circulating in the circulation circuit 2, 5, 6, 7, 8, 20, 21, 29. This is done in a controlled way so that the temperature of the mixed fuel circulating in the fuel supply system 1 decreases at rate of change not exceeding 2 °C/minute in order to avoid thermal shock of any parts of the fuel supply system 1.
  • the first return way valve 20 is set up by the control means 17 to open the inlet to the storage return conduit 22 and close the inlet to the circulation return conduit 21
  • the second return way valve 23 is set up by the control means 17 to open the inlet to the heavy fuel return conduit 24 and close the inlet to the light fuel return conduit 25.
  • the first return way valve 20 is set up by the control means 17 to close the inlet to the storage return conduit 22 and open the inlet to the circulation return conduit 21.
  • control means 17 changes the position of the fuel mixing valve 16 in order to add heavy fuel (having a substantially higher temperature than 15 °C) from the heavy fuel storage tank 4 to the fuel circulating in the circulation circuit 2, 5, 6, 7, 8, 20, 21 , 29. This is done in a controlled way so that the temperature of the mixed fuel circulating in the fuel supply system 1 increases at rate of change not exceeding 2 °C/minute in order to avoid thermal shock of any parts of the fuel supply system 1.
  • Fig. 2 discloses schematically an embodiment of a pressurised dual fuel system 1 according to the invention.
  • the circulation tank 5 is not used as a degassing tank but rather as a pressure tank being a part of the pressurised circulation circuit 2, 5, 6, 7, 8, 9, 20, 21, 29.
  • the mixed fuel supply conduit 13 leads from the fuel mixing valve 16 to the circulation tank 5 and is provided with two booster pumps 15 arranged in parallel to allow continued operation of one of the booster pumps 15, while the other may be out of function due to maintenance work or for other reasons.
  • the booster pumps 15 drive the mixed fuel from the heavy fuel storage tank 3 and the light fuel storage tank 4 into the circulation tank 5 at a pressure of about 5.5 bars, and the circulation pumps 8 drive the fuel in the combustion unit supply conduit 6 towards the combustion unit 2 at a pressure of about 6.5 bars.
  • Control means

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Abstract

A dual fuel supply system for supplying a heavy fuel oil, a light fuel, such as Marine Gas Oil or Marine Diesel Oil, or a mixture of heavy fuel and light fuel to a combustion unit is disclosed, comprising cooling means arranged for cooling the contents of the light fuel storage tank. Furthermore, methods for switching from heavy fuel operation to light fuel operation and back are also disclosed. By cooling the light fuel storage tank, it is made redundant to build in a fuel cooler before the combustion unit so that the parts of the combustion unit, such as pumps and nozzles, that require a certain viscosity level to function properly will operate with the light fuel or the mixture of the light fuel and heavy fuel.

Description

DUAL FUEL SUPPLY SYSTEM, METHODS FOR SWITCHING BETWEEN DIFFERENT FUEL TYPES AND METHOD FOR RETRO-FITTING A HEAVY FUEL SYSTEM
Field of the invention
The present invention relates to a dual fuel supply system for a combustion unit (2) able to be operated on different fuel types, to methods for switching from heavy fuel operation to light fuel operation and vice versa, and to a method for retro-fitting an existing heavy fuel system for updating it to a dual fuel system.
Background of the invention
For the sake of the environment, an increasing number of regulations and legislations put restrictions on the emissions from main and auxiliary machinery of maritime vessels. As a result of some of these regulations, the combustion of Heavy Fuel Oil (HFO) is not permitted during port stay and in specific, mostly inshore, areas at sea.
Therefore, the burner and fuel supply systems of such machinery must be constructed to or at least be modified to be able to run on lighter types of fuel, such as Marine Diesel Oil (MDO) and Marine Gas Oil (MGO) as well as on HFO, which is the most economic and, therefore, the preferred fuel type for open sea operation.
While most burner systems, although designed to burn HFO, will have no problems with temporary change-over to MDO or MGO, the switch-over procedure requires monitoring and modifications to the fuel supply system as compared to a fuel supply system for HFO operation only.
In order for the HFO to be in a liquid state, the HFO storage tank must be heated. Furthermore, the HFO is heated even more to a temperature of more than 100 °C in the fuel supply system in order to obtain a viscosity of the HFO supplied to the burner system that is low enough to be suitable for the nozzles thereof. On the other hand, MDO and MGO need to be cooled in order to get a viscosity high enough to be suitable for the nozzles of the burner system. Furthermore, the use of MDO or MHO under the heated conditions of the fuel supply system suitable for HFO operation may result in fuel pump trouble and/or vapour lock due to vaporization of these highly volatile fuel types in the heated fuel supply system.
Taking also into account that the thermal change rate of the piping and other parts of the fuel supply system should not exceed 2 °C/minute in order to avoid thermal shock, it is clear from the above that the viscosity and temperature of the fuel in the fuel supply system should be monitored carefully during switch-over from HFO to MDO/MGO and vice versa.
Even further, the flash point of MDO/MGO is found at a relatively low temperature, meaning that these light fuel types should be secured from being exposed to temperatures above approximately 60 °C. This means that care should be taken when placing the MDO/MGO fuel storage tank to avoid excessive heating of the tank, e.g. from heat radiation from the HFO fuel storage tank. A dual fuel supply system with possibility for cooling the fuel has been disclosed in German patent application DE 198 28 772 A 1 (MAN B & W Diesel A/S). The disclosed system, however, requires for retrofitting modification of the existing heating means in the core part of the fuel supply system and does not deal with the problems of placement of the MDO/MGO fuel storage tank.
Different procedures for switching over between operation on heavy fuel and light fuel have been proposed, for instance in international patent application WO 2009/065397 Al (Thomas Porep - Bernd Memarow Gbr.), in "Changing from HFO to MDO or MGO", Aalborg Solutions No. 12, January 2009, Aalborg Industries and in "Technical Considerations of Fuel Switching Practices", API Technical Issues Workgroup, June 3, 2009. It is an object of the present invention to provide an improved dual fuel supply system for supplying a heavy fuel, a light fuel or a mixture thereof to a combustion unit which in particular is more suited for retrofitting into an existing fuel supply system.
Brief description of the invention
Thus, the present invention relates to such dual fuel supply system for supplying a heavy fuel oil, a light fuel, such as Marine Gas Oil or Marine Diesel Oil, or a mixture of heavy fuel and light fuel to a combustion unit, the system comprising a heavy fuel storage tank for storing heavy fuel, a light fuel storage tank for storing light fuel, a combustion unit supply connection for supplying fuel to the combustion unit, such as the main engine, auxiliary engines and/or boilers, a main return conduit for leading excess fuel from the combustion unit back towards the combustion unit supply connection, at least one circulation pump arranged in the combustion unit supply connection for driving fuel through the combustion unit supply unit and the main return conduit, a heavy fuel supply conduit for supplying heavy fuel from the heavy fuel storage tank to the combustion unit supply connection, and a light fuel supply conduit for supplying light fuel from the light fuel storage tank to the combustion unit supply connection, where the system further comprises cooling means arranged for cooling contents of the light fuel storage tank.
By cooling the light fuel storage tank, it is made redundant to build in a new fuel cooler before the combustion unit so that the parts of the combustion unit, such as pumps and nozzles, that require a certain viscosity level to function properly will operate with the light fuel or the mixture of the light fuel and heavy fuel. Such fuel cooler may as seen in the prior art be build into an existing heating means for heating the heavy fuel to an operational temperature, or it may be a separate unit. It is also obtained by cooling the light fuel storage tank that the risk of reaching the flash point of the light fuel in the tank may be removed and the light fuel storage tank may be arranged e.g. next to the heavy fuel storage tank. The pumps for pumping the light fuel from the storage tank may be the same as the ones applied to pump the heavy fuel from the heavy fuel storage tank as the viscosity of the cold light fuel does not deviate much from the viscosity of the heated heavy oil.
In a particularly preferred embodiment, the cooling means includes circulation means for circulating refrigerant, preferably fresh water, in a heat exchanger arranged in the light fuel storage tank, and a refrigeration unit, preferably a vapour-compression refrigeration unit, for cooling said refrigerant. In this way it is possible in all operational situations to reach lower temperatures, such as about 15 °C of the light fuel that by cooling with seawater. The cooling means may comprise a control unit for maintaining a temperature of the light fuel stored in the light fuel storage tank during a first mode of operation of the system, i.e. when the light fuel is fed to the combustion unit or the system is about to be switched over to use light fuel, below a temperature of 25 °C, such as below 20 °C and preferably a temperature selected in the range of 10 °C to 18 °C. Furthermore, the control unit of the cooling means mat be arranged for, during a second mode of operation of the system, i.e. when the combustion unit is operating on heavy fuel, to maintain a temperature of the light fuel stored in the light fuel storage tank in the range of 25 °C to 45 °C, such as in the range of 30 °C to 40 °C.
The system may further comprise a first return way valve, preferably an electrically operated 3-way valve controlled by control means, in the main return conduit for controlling whether excess fuel from the combustion unit is directed towards the combustion unit supply connection or towards a fuel storage tank, a circulation return conduit for leading excess fuel from the first return way valve back to the combustion unit supply connection, and a storage return conduit for leading excess fuel from the first return way valve towards a fuel storage tank. The system may also comprise a second return way valve in the storage return conduit, preferably an electrically operated 3-way valve controlled by control means, for controlling whether excess fuel from the main return conduit is directed towards the heavy fuel storage tank or towards the light fuel storage tank, a heavy fuel return conduit connecting the second return way valve with the heavy fuel storage tank, and a light fuel return conduit connecting the second return way valve with the light fuel storage tank.
By means of there 3 -way valves, the mixture of heavy fuel and light fuel may at a certain point in the which-over be directed to the heavy fuel storage tank instead of being recirculated so that all heavy fuel can be removed fast from the system and a full switch-over may be accomplished where the excess fuel from the combustion unit may be returned to the light fuel storage tank for cooling without the risk of sending an amount of heavy fuel to the light fuel storage tank.
Further, the system may comprise a mixed fuel supply conduit through which both the heavy fuel from the heavy fuel supply conduit and the light fuel from the light fuel supply conduit may reach the combustion unit supply connection. Also, the system may be equipped with a fuel mixing valve arranged so that the heavy fuel from the heavy fuel supply conduit and the light fuel from the light fuel supply conduit are mixed in the fuel mixing valve before reaching the mixed fuel supply conduit.
The combustion unit supply connection (6) may comprises temperature sensing means (18) for measuring the temperature of the fuel supplied to the combustion unit (2) and/or viscosity sensing means (19) for measuring the viscosity of the fuel supplied to the combustion unit (2) so as to control the mixing and switch-over process. Additionally, a temperature sensing means may be positioned near to and upstream from the circulation pump.
The system may further comprise a circulation tank, such as a degassing and/or mixing tank, arranged connecting the main return conduit and the combustion unit supply connection. The heavy fuel from the heavy fuel supply conduit and the light fuel from the light fuel supply conduit may enter the combustion unit supply connection by means of the circulation tank, which in that case will ensure a complete mixing of the two types of fuel and the fuel returned from the combustion unit during a switch-over before the fuel is delivered to the combustion unit.
The present invention further relates to a method for switching from heavy fuel operation to light fuel operation of a combustion unit comprising the steps of:
operating the combustion unit on heated heavy fuel being supplied to the combustion unit from a heavy fuel storage tank, the excess fuel from the combustion unit being returned to the combustion unit through a circulation circuit,
mixing the heavy fuel supplied to the circulation circuit with light fuel from a light fuel storage tank, and
increasing the proportion of light fuel in the fuel supplied to the circulation circuit gradually until only light fuel is supplied to the circulation circuit while continuously measuring and controlling the temperature of the fuel in the circulation circuit, the proportion of light fuel being increased in such a way that, at any given time, it is ensured that the temperature of the mixed fuel does not decrease by more than 2 °C per minute,
wherein throughout the switching procedure, the light fuel being supplied from the light fuel storage tank is being kept at a substantially constant temperature in the range of 5 °C to 30 °C, preferably in the range of 10 °C to 25 °C by cooling the light fuel storage tank.
Furthermore, the viscosity may be measured and used for control of the switching process to ensure that the viscosity is suitable for the nozzles of the combustion unit.
The method may prior to the step of mixing the fuel, comprise the steps of
switching off heating means arranged in the circulation circuit and heating heavy fuel to an operational temperature, and waiting until the temperature of the heavy fuel in the circulation circuit is substantially the same as the temperature of the heavy fuel in the heavy fuel storage tank before said mixing step is initiated. The method may further comprise the steps of: changing the return path of excess fuel from the combustion unit so that, when the decreasing temperature of the fuel in the circulation unit reaches a previously defined threshold temperature, the excess fuel is no longer returned to the circulation circuit but is instead returned to the heavy fuel storage tank, and
changing again the return path of excess fluid from the combustion unit so that, a previously defined time period after the decreasing temperature of the fuel in the circulation unit reaches said substantially constant temperature of the fuel in the light fuel storage tank, indicating that the switching over from heavy fuel supply to light fuel supply has been completed, the excess fuel is no longer returned to the heavy fuel storage tank but is instead returned to the light fuel storage tank. Said threshold temperature is preferably selected in the range of 40 °C to 60 °C, such as within the range of 45 °C to 55 °C. Said predefined time period is preferably selected within the range of 5-60 minutes, preferably within the range of 10 to 30 minutes, such as about 15 minutes. The fuel in the light fuel tank is advantageously being held at a constant temperature selected in the range of 25 °C to 45 °C, such as in the range of 30 °C to 40 °C during the operation of the combustion unit on heavy fuel and cooled down to said substantially constant temperature of the fuel in the light fuel storage tank before start of the switching procedure. The present invention relates in yet an aspect to a method for switching from light fuel operation to heavy fuel operation of a combustion unit comprising the steps of: operating the combustion unit on light fuel being supplied to the combustion unit from a light fuel storage tank, the excess fuel from the combustion unit being lead back to the light fuel storage tank, changing the return path of excess fuel from the combustion unit so that, the excess fuel is no longer returned to the light fuel storage tank but is instead returned to the combustion unit through a circulation circuit,
mixing the light fuel supplied to the circulation circuit with heavy fuel from a heavy fuel storage tank, and
increasing the proportion of heavy fuel in the fuel supplied to the circulation circuit gradually until only heavy fuel is supplied to the circulation circuit while continuously measuring and controlling the temperature of the fuel in the circulation circuit, the proportion of heavy fuel being increased in such a way that, at any given time, it is ensured that the temperature of the mixed fuel does not increase by more than 2 °C per minute, wherein throughout the switching procedure, the light fuel being supplied from the light fuel storage tank is being kept at a substantially constant temperature in the range of 5 °C to 30 °C , preferably in the range of 10 °C to 25 °C by cooling the light fuel storage tank (4).
This method may further comprise the step of changing the return path of excess fuel is done in two steps, so that from the beginning of the switching over from light fuel supply to heavy fuel supply, the excess fuel is instead returned to the heavy fuel storage tank, and then, when the increasing temperature of the fuel supplied to the combustion unit reaches a previously defined threshold temperature, the excess fuel is no longer returned to the heavy fuel storage tank but is instead returned to the combustion unit through a circulation circuit including a circulation tank. Said threshold temperature may preferably be selected in the range of 40 °C to 60 °C, such as within the range of 45 °C to 55 °C.
The method may further comprise the step of switching on heating means for heating the fuel in the circulation circuit to an operational temperature.
The method may include to hold the light fuel tank at a constant temperature selected in the range of 25 °C to 45 °C, such as in the range of 30 °C to 40 °C, after completion of the switching procedure.
The present invention furthermore relates to a method for retro-fitting an existing fuel supply system for updating it to a dual fuel supply system as described above.
The drawings
In the following, a few exemplary embodiments of the invention are described and explained in more detail with reference to the drawings, wherein fig. 1 is a schematic view of an embodiment of a non-pressurised dual fuel supply system according to the invention, and fig. 2 is a schematic view of an embodiment of a pressurised dual fuel supply system according to the invention. Detailed description
Fig. 1 discloses schematically an embodiment of a non-pressurised dual fuel system 1 according to the invention. The fuel system 1 comprises a heavy fuel storage tank 3 and a light fuel storage tank 4 and provides heavy fuel, light fuel or a mixture thereof to be combusted by a combustion unit 2. The light fuel may be Marine Diesel Oil (MDO) or Marine Gas Oil (MGO), while the heavy fuel typically will be the type of Heavy Fuel Oil (HFO) that is well-known for operation of marine combustion units 2, such as the main engine, auxiliary engines and/or boilers.
The light fuel storage tank 4 is provided with cooling means 12 comprising a refrigeration unit 27 and circulation means 26 for circulating a cooling fluid, which may be fresh water. The cooling means 12 must be sufficiently efficient to cool down the light fuel in the light fuel storage tank 4 to a temperature of 15 °C or less.
Heavy fuel can be drawn off from the heavy fuel storage tank 3 through a heavy fuel supply conduit 10 and, similarly, light fuel can be drawn off from the light fuel storage tank 4 through a light fuel supply conduit 1 1. The heavy fuel from the heavy fuel supply conduit 10 and the light fuel from the light fuel supply conduit 1 1 are mixed together in a fuel mixing valve 16, from which the mixed fuel continues its flow towards the combustion unit 2 through a mixed fuel supply conduit 13.
The fuel mixing valve 16 in the shown embodiment is an electrically operated 3-way valve controlled by control means 17 in response to signals from temperature sensing means 18 and viscosity sensing means 19 in the fuel supply system 1.
The mixed fuel supply conduit 13 lead the mixed fuel to a circulation circuit comprising a combustion unit supply conduit 6, the combustion unit 2, a main return conduit 7, a circulation return conduit 21 and a circulation tank 5, such as a degassing and/or mixing tank.
The combustion unit supply conduit 6 leads from the circulation tank 5 to the combustion unit 2 and is provided with two circulation pumps 8 arranged in parallel to allow continued operation of one of the circulation pumps 8, while the other may be out of function due to maintenance work or for other reasons. Immediately before the circulation pumps 8, a temperature sensing means 18 is arranged in connection with the combustion unit supply conduit 6 in order to measure the temperature of the fuel flowing towards the combustion unit 2. This temperature sensing means 18 is connected to the control means 17, which may comprise a Programmable Logic Controller (PLC) or any other device suitable for controlling the operation of the fuel supply system 1.
Between the circulation pumps 8 and the combustion unit 2, heating means 9 are arranged in connection with the combustion unit supply conduit 6 for heating of the fuel flowing towards the combustion unit 2 when necessary. Two heating means valves 28 and a heating means bypass valve 29 are arranged so that, when the heating means valves 28 are open and the heating means bypass valve 29 is closed, the fuel flowing towards the combustion unit 2 will pass through the heating means 9, whereas, when the heating means valves 28 are closed and the heating means bypass valve 29 is open, the fuel will bypass the heating means 9.
Immediately before the combustion unit 2, a viscosity sensing means 19 is arranged in connection with the combustion unit supply conduit 6 in order to measure the viscosity of the fuel flowing towards the nozzles of the combustion unit 2. Like the temperature sensing means 18, this viscosity sensing means 19 is connected to the control means 17.
Excess fuel is lead from the combustion unit 2 through the main return conduit 7 to a first return way valve 20, which in the shown embodiment is an electrically operated 3-way valve controlled by the control means 17 in response to signals from the temperature sensing means 18.
From the first return way valve 20, the excess fuel from the combustion unit 2 may continue in the circulation circuit 2, 5, 6, 7, 8, 9, 20, 21 , 28 through the circulation return conduit 21 and the circulation tank 5 and back into the combustion unit supply conduit 6, or it may continue through a storage return conduit 22 towards a second return way valve 23, which in the shown embodiment is also an electrically operated 3 -way valve controlled by the control means 17 in (delayed) response to signals from the temperature sensing means 18. In the shown embodiment, the circulation tank 5 works as a degassing tank when the combustion unit 2 is operated on heavy fuel, and a degassing tank closing valve 14 is placed in the combustion unit supply conduit 6 near the outlet from the circulation tank 5. From the second return way valve 23, the excess fuel from the combustion unit 2 may continue through a heavy fuel return conduit 24 to the heavy fuel storage tank 3, or it may continue through a light fuel return conduit 25 towards the light fuel storage tank 4. When operating the combustion unit 2 on heavy fuel, the degassing tank closing valve 14 is open and the heating means valves 28 and the heating means bypass valve 29 are set up to lead the fuel through the heating means 9 to be heated before reaching the combustion unit 2. The first return way valve 20 is set up by the control means 17 to close the inlet to the storage return conduit 22 and open the inlet to the circulation return conduit 21 so that the heavy fuel circulates in the circulation circuit 2, 5, 6, 7, 8, 9, 20, 21 , 28, which is defined above, passing the combustion unit 2 and being degassed in the circulation tank 5.
As heavy fuel is combusted by the combustion unit 2, additional heavy fuel is added to the circulation circuit 2, 5, 6, 7, 8, 9, 20, 21 , 28 from the heavy fuel storage tank 3 through the heavy fuel supply conduit 10, the fuel mixing valve 16 and the mixed fuel supply conduit 13. The cooling means 12 is controlled so that, during operation of the combustion unit 2 on heavy fuel, the temperature of the light fuel in the light fuel storage tank 4 is kept at about 35 °C. When operating the combustion unit 2 on light fuel, no degassing is necessary. The degassing tank closing valve 14 is closed and the heating means valves 28 and the heating means bypass valve 29 are set up to let the fuel bypass the heating means 9. The first return way valve 20 is set up by the control means 17 to open the inlet to the storage return conduit 22 and close the inlet to the circulation return conduit 21 , and the second return way valve 23 is set up by the control means 17 to close the inlet to the heavy fuel return conduit 24 and open the inlet to the light fuel return conduit 25.
This means that light fuel is supplied to the combustion unit 2 from the light fuel storage tank 4 through the light fuel supply conduit 1 1, the fuel mixing valve 16 and the combustion unit supply conduit 6, and that excess fuel from the combustion unit 2 is returned to the light fuel storage tank 4 through the main return conduit 7, the first return way valve 20, the storage return conduit 22, the second return way valve 23 and the light fuel return conduit 25. The cooling means 12 is controlled so that, during operation of the combustion unit 2 on light fuel, the temperature of the light fuel in the light fuel storage tank 4 is kept at about 15 °C.
The procedure of switching over from heavy fuel operation to light fuel operation begins approximately 24 hours before arriving to an area where light fuel operation is required by starting to cool down the light fuel in the light fuel storage tank 4 from about 35 °C to about 15 °C.
The next step of the procedure is to close the heating means valves 28 and to open the heating means bypass valve 29 so that the heavy fuel circulating in the circulation circuit 2, 5, 6, 7, 8, 20, 21 , 29 will bypass the heating means 9 and the temperature of the circulating heavy fuel will start decreasing.
When the decreasing temperature of the heavy fuel circulating in the circulation circuit 2, 5, 6, 7, 8, 20, 21, 29 has reached the temperature of the heavy fuel in the heavy fuel storage tank 3, the control means 17 changes the position of the fuel mixing valve 16 in order to add light fuel (having a temperature of about 15 °C) from the light fuel storage tank 3 to the fuel circulating in the circulation circuit 2, 5, 6, 7, 8, 20, 21, 29. This is done in a controlled way so that the temperature of the mixed fuel circulating in the fuel supply system 1 decreases at rate of change not exceeding 2 °C/minute in order to avoid thermal shock of any parts of the fuel supply system 1.
At the stage over the switching-over procedure where the decreasing temperature of the mixed fuel circulating in the fuel supply system 1 no longer exceeds about 50 °C, degassing is not necessary. The first return way valve 20 is set up by the control means 17 to open the inlet to the storage return conduit 22 and close the inlet to the circulation return conduit 21 , and the second return way valve 23 is set up by the control means 17 to open the inlet to the heavy fuel return conduit 24 and close the inlet to the light fuel return conduit 25.
This means that mixed fuel is supplied to the combustion unit 2 from both of the fuel storage tanks 3, 4 through the fuel mixing valve 16, the mixed fuel supply conduit 13 and the combustion supply conduit 6, and that the excess fuel from the combustion unit 2 is returned to the heavy fuel storage tank 3 through the main return conduit 7, the first return way valve 20, the storage return conduit 22, the second return way valve 23 and the heavy fuel return conduit 24.
When the temperature of the fuel in the combustion unit supply conduit 6 has decreased to about 15 °C, which is the same as the temperature of the light fuel in the light fuel storage tank 4, indicating that now only light fuel is being supplied to the combustion unit 2, a timer in the control means 17 is started. During the next 15 minutes, the operation continues like before with the excess oil being returned to the heavy fuel storage tank 3, whereupon the control means 17 changes the set-up of the second return way valve 23 so that the excess fuel is instead returned to the light fuel storage tank 4. The reason for the 15 minutes delay is that it is important to avoid that heavy fuel enters and contaminates the light fuel storage tank 4. The procedure of switching over from light fuel operation to heavy fuel operation is basically a similar procedure, only executed in a reversed order.
First, the first return way valve 20 is set up by the control means 17 to close the inlet to the storage return conduit 22 and open the inlet to the circulation return conduit 21.
This means that the excess fuel from the combustion unit 2 is no longer returned to the light fuel storage tank 4 but is instead lead through the circulation return conduit 21 to the circulation tank 5 and back to the combustion unit 2 through the combustion unit supply conduit 6.
Next, the control means 17 changes the position of the fuel mixing valve 16 in order to add heavy fuel (having a substantially higher temperature than 15 °C) from the heavy fuel storage tank 4 to the fuel circulating in the circulation circuit 2, 5, 6, 7, 8, 20, 21 , 29. This is done in a controlled way so that the temperature of the mixed fuel circulating in the fuel supply system 1 increases at rate of change not exceeding 2 °C/minute in order to avoid thermal shock of any parts of the fuel supply system 1. When the increasing temperature of the heavy fuel circulating in the circulation circuit 2, 5, 6, 7, 8, 20, 21 , 29 has reached the temperature of the heavy fuel in the heavy fuel storage tank 3, indicating that now only heavy fuel is being supplied to the combustion unit 2, the heating means valves 28 are opened and the heating means bypass valve 29 is closed so that the heavy fuel circulating in the circulation circuit 2, 5, 6, 7, 8, 9, 20, 21 , 28 is lead through the heating means 9 and the temperature of the circulating heavy fuel will keep increasing until an appropriate operational temperature has been reached.
Finally, the cooling means 12 are controlled so that the temperature of the light fuel in the light fuel storage tank 4 is allowed to rise slowly from about 15 °C to about 35 °C. Fig. 2 discloses schematically an embodiment of a pressurised dual fuel system 1 according to the invention.
Only a few structural features distinguish the shown pressurised fuel supply system 1 from the non-pressurised fuel supply system 1 shown in Fig. 1.
First, in the pressurised fuel supply system 1 , the circulation tank 5 is not used as a degassing tank but rather as a pressure tank being a part of the pressurised circulation circuit 2, 5, 6, 7, 8, 9, 20, 21, 29.
Second, the mixed fuel supply conduit 13 leads from the fuel mixing valve 16 to the circulation tank 5 and is provided with two booster pumps 15 arranged in parallel to allow continued operation of one of the booster pumps 15, while the other may be out of function due to maintenance work or for other reasons.
In order to keep up an appropriate pressure in the circulation circuit 2, 5, 6, 7, 8, 9, 20, 21 , 29, the booster pumps 15 drive the mixed fuel from the heavy fuel storage tank 3 and the light fuel storage tank 4 into the circulation tank 5 at a pressure of about 5.5 bars, and the circulation pumps 8 drive the fuel in the combustion unit supply conduit 6 towards the combustion unit 2 at a pressure of about 6.5 bars.
The operational and switching-over procedures of the fuel supply system 1 shown in Fig. 2 are similar to the ones of the fuel supply system 1 shown in Fig. 1.
List of reference numbers
1. Dual fuel supply system
2. Combustion unit
3. Heavy fuel storage tank
4. Light fuel storage tank
5. Circulation tank
6. Combustion unit supply conduit
7. Main return conduit
8. Circulation pump
9. Heating means
10. Heavy fuel supply conduit
1 1. Light fuel supply conduit
12. Cooling means
13. Mixed fuel supply conduit
14. Degassing tank closing valve
15. Booster pump
16. Fuel mixing valve
17. Control means
18. Temperature sensing means
19. Viscosity sensing means
20. First return way valve
21. Circulation return conduit
22. Storage return conduit
23. Second return way valve
24. Heavy fuel return conduit
25. Light fuel return conduit
26. Circulation means of the cooling means
27. Refrigeration unit
28. Heating means valve
29. Heating means bypass valve

Claims

Claims
1. A dual fuel supply system (1) for supplying a heavy fuel, a light fuel or a mixture thereof to a combustion unit (2), the system (1) comprising
a heavy fuel storage tank (3) for storing heavy fuel,
a light fuel storage (4) tank for storing light fuel,
a combustion unit supply connection (6) for supplying fuel to the combustion unit (2),
a main return conduit (7) for leading excess fuel from the combustion unit (2) back towards the combustion unit supply connection (6), at least one circulation pump (8) arranged in the combustion unit supply connection (6) for driving fuel through the combustion unit supply unit (6) and the main return conduit (7),
a heavy fuel supply conduit (10) for supplying heavy fuel from the heavy fuel storage tank (3) to the combustion unit supply connection (6), and a light fuel supply conduit (1 1) for supplying light fuel from the light fuel storage tank (4) to the combustion unit supply connection (6), characterised in that the system (1) further comprises cooling means (12) arranged for cooling contents of the light fuel storage tank (4).
2. A system (1) according to claim 1, wherein the cooling means (12) includes circulation means (26) for circulating a refrigerant in a heat exchanger arranged in the light fuel storage tank (4), and a refrigeration unit (27) for cooling said refrigerant.
3. A system (1 ) according to claim 2, wherein the refrigerant is fresh water.
A system according to any of claims 1-3, wherein the cooling means (12) comprises a control unit for maintaining a temperature of the light fuel stored in the light fuel storage tank (4) during a first mode of operation of the system (1) below a temperature of 25 °C, such as below 20 °C and preferably a temperature selected in the range of 10 °C to 18 °C.
A system according to claim 4, wherein the control unit of the cooling means (12) is arranged for, during a second mode of operation of the system (1) to maintain a temperature of the light fuel stored in the light fuel storage tank (4) in the range of 25 °C to 45 °C, such as in the range of 30 °C to 40 °C.
A system (1) according to any of the preceding claims further comprising
a first return way valve (20) in the main return conduit (7) for controlling whether excess fuel from the combustion unit (2) is directed towards the combustion unit supply connection (6) or towards a fuel storage tank (3, 4),
a circulation return conduit (21) for leading excess fuel from the first return way valve (20) back to the combustion unit supply connection (6), and
a storage return conduit (22) for leading excess fuel from the first return way valve (20) towards a fuel storage tank (3, 4).
A system (1) according to claim 6, wherein the first return way valve (20) is an electrically operated 3-way valve controlled by control means (17).
A system (1) according to claim 6 or 7 further comprising
a second return way valve (23) in the storage return conduit (22) for controlling whether excess fuel from the main return conduit (7) is directed towards the heavy fuel storage tank (3) or towards the light fuel storage tank (4), a heavy fuel return conduit (24) connecting the second return way valve (23) with the heavy fuel storage tank (3), and
a light fuel return conduit (25) connecting the second return way valve (23) with the light fuel storage tank (4).
9. A system (1) according to claim 8, wherein the second return way valve (23) is an electrically operated 3-way valve controlled by control means (17).
10. A system (1) according to any of the preceding claims further comprising a mixed fuel supply conduit (13)
through which both the heavy fuel from the heavy fuel supply conduit (10) and the light fuel from the light fuel supply conduit (1 1) may reach the combustion unit supply connection (6).
1 1. A system (1) according to claim 10, further comprising
a fuel mixing valve (16)
arranged so that the heavy fuel from the heavy fuel supply conduit (10) and the light fuel from the light fuel supply conduit (1 1) are mixed in the fuel mixing valve (16) before reaching the mixed fuel supply conduit (13).
12. A system (1) according to claim 1 1 , wherein the fuel mixing valve (16) is an electrically operated 3-way valve controlled by control means (17).
13. A system (1) according to any of the preceding claims, wherein the combustion unit supply connection (6) further comprises temperature sensing means (18) for measuring the temperature of the fuel supplied to the combustion unit (2).
14. A system (1) according to any of the preceding claims, wherein the combustion unit supply connection (6) further comprises viscosity sensing means (19) for measuring the viscosity of the fuel supplied to the combustion unit (2).
15. A system (1) according to any of the preceding claims further comprising a circulation tank (5) arranged connecting the main return conduit (7) and the combustion unit supply connection (6).
16. A system (1) according to claim 15, wherein the heavy fuel from the heavy fuel supply conduit (10) and the light fuel from the light fuel supply conduit (1 1) enters the combustion unit supply connection (6) by means of the circulation tank (5).
17. A system (1) according to any of the preceding claims, wherein a temperature sensing means (18) is positioned near to and upstream from the circulation pump (8).
18. A method for switching from heavy fuel operation to light fuel operation of a combustion unit (2) comprising the steps of:
o operating the combustion unit (2) on heated heavy fuel being supplied to the combustion unit (2) from a heavy fuel storage tank (3), the excess fuel from the combustion unit (2) being returned to the combustion unit (2) through a circulation circuit (5, 6, 7, 8, 9, 20, 21),
o mixing the heavy fuel supplied to the circulation circuit with light fuel from a light fuel storage tank (4), and
o increasing the proportion of light fuel in the fuel supplied to the circulation circuit gradually until only light fuel is supplied to the circulation circuit while continuously measuring and controlling the temperature of the fuel in the circulation circuit, the proportion of light fuel being increased in such a way that, at any given time, it is ensured that the temperature of the mixed fuel does not decrease by more than 2 °C per minute, the method being characterised in that throughout the switching procedure, the light fuel being supplied from the light fuel storage tank (4) is being kept at a substantially constant temperature in the range of 5 °C to 30 °C, preferably in the range of 10 °C to 25 °C by cooling the light fuel storage tank (4).
19. A method according to claim 18 further comprising, before the step of mixing the fuel, the steps of
o switching off heating means (9) arranged in the circulation circuit and heating the heavy fuel to an operational temperature, and
o waiting until the temperature of the heavy fuel in the circulation circuit is substantially the same as the temperature of the heavy fuel in the heavy fuel storage tank (3) before said mixing step is initiated.
20. A method according to claim 18 or 19 further comprising the steps of: o changing the return path of excess fuel from the combustion unit (2) so that, when the decreasing temperature of the fuel in the circulation unit reaches a previously defined threshold temperature, the excess fuel is no longer returned to the circulation circuit but is instead returned to the heavy fuel storage tank (3), and changing again the return path of excess fluid from the combustion unit (2) so that, a previously defined time period after the decreasing temperature of the fuel in the circulation unit reaches said substantially constant temperature of the fuel in the light fuel storage tank (4), indicating that the switching over from heavy fuel supply to light fuel supply has been completed, the excess fuel is no longer returned to the heavy fuel storage tank (3) but is instead returned to the light fuel storage tank (4).
21. A method according claim 20, wherein said threshold temperature is selected in the range of 40 °C to 60 °C, such as within the range of 45 °C to 55 °C.
22. A method according to claim 20 or 21, wherein said predefined time period is selected within the range of 5-60 minutes, preferably within the range of 10 to 30 minutes, such as about 15 minutes.
23. A method according to any of claims 18-22, wherein the fuel in the light fuel tank is being held at a constant temperature selected in the range of 25 °C to 45 °C, such as in the range of 30 °C to 40 °C during the operation of the combustion unit (2) on heavy fuel and cooled down to said substantially constant temperature of the fuel in the light fuel storage tank (4) before start of the switching procedure.
24. A method according to any of claims 18-23, wherein the light fuel is Marine Gas Oil or Marine Diesel Oil.
25. A method for switching from light fuel operation to heavy fuel operation of a combustion unit (2) comprising the steps of:
o operating the combustion unit (2) on light fuel being supplied to the combustion unit (2) from a light fuel storage tank (4), the excess fuel from the combustion unit (2) being lead back to the light fuel storage tank (4), o changing the return path of excess fuel from the combustion unit (2) so that, the excess fuel is no longer returned to the light fuel storage tank (4) but is instead returned to the combustion unit (2) through a circulation circuit (5, 6, 7, 8, 9, 20, 21),
o mixing the light fuel supplied to the circulation circuit with heavy fuel from a heavy fuel storage tank (3), and
o increasing the proportion of heavy fuel in the fuel supplied to the circulation circuit gradually until only heavy fuel is supplied to the circulation circuit while continuously measuring and controlling the temperature of the fuel in the circulation circuit, the proportion of heavy fuel being increased in such a way that, at any given time, it is ensured that the temperature of the mixed fuel does not increase by more than 2 °C per minute, the method being characterised in that throughout the switching procedure, the light fuel being supplied from the light fuel storage tank (4) is being kept at a substantially constant temperature in the range of 5 °C to 30 °C , preferably in the range of 10 °C to 25 °C by cooling the light fuel storage tank (4).
26. A method according to claim 25, wherein the step of changing the return path of excess fuel is done in two steps, so that from the beginning of the switching over from light fuel supply to heavy fuel supply, the excess fuel is instead returned to the heavy fuel storage tank (3), and then, when the increasing temperature of the fuel supplied to the combustion unit (2) reaches a previously defined threshold temperature, the excess fuel is no longer returned to the heavy fuel storage tank (3) but is instead returned to the combustion unit (2) through a circulation circuit including a circulation tank (5).
27. A method according claim 26, wherein said threshold temperature is selected in the range of 40 °C to 60 °C, such as within the range of 45 °C to 55 °C.
28. A method according to any of claims 25 to 27 further comprising the step of switching on heating means (9) for heating the fuel in the circulation circuit to an operational temperature.
29. A method according to any of claims 25-28, wherein the light fuel tank is being held at a constant temperature selected in the range of 25 °C to 45 °C, such as in the range of 30 °C to 40 °C, after completion of the switching procedure.
30. A method according to any of claims 25-29, wherein the light fuel is Marine Gas Oil or Marine Diesel Oil.
31. A method for retro-fitting an existing fuel supply system for updating it to a dual fuel supply system (1) according to any of claims 1-17, the method comprising the step of:
o adding to the system at least
a light fuel storage tank (4) for storing light fuel,
a light fuel supply conduit (1 1) for supplying light fuel from the light fuel storage tank (4) to a circulation circuit, and
cooling means (12) for cooling the light fuel storage tank (4).
PCT/DK2010/000012 2010-01-25 2010-01-25 Dual fuel supply system, methods for switching between different fuel types and method for retro-fitting a heavy fuel system WO2011088830A1 (en)

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