WO2019179594A1

WO2019179594A1 - A gas supply assembly

Info

Publication number: WO2019179594A1
Application number: PCT/EP2018/056858
Authority: WO
Inventors: Tomi PRITTINEN; Björn HATT; Jonatan BYGGMÄSTAR; Markus NORRGÅRD; Rasmus NYBO
Original assignee: Wärtsilä Finland Oy
Priority date: 2018-03-19
Filing date: 2018-03-19
Publication date: 2019-09-26
Also published as: KR20200135783A; EP3769004A1; JP7189962B2; JP2021516749A; EP3769004B1; CN111819390B; KR102269975B1; CN111819390A

Abstract

A gas supply assembly (10) comprising a tank configured to store liquefied gas in the tank (12) so as to have an gaseous phase section (12.1) and a liquid phase section (12.2), the assembly further comprising a first gas supply line (18), a second gas supply line (16), wherein the second gas supply line (16) comprises a second heat exchanger (20) configured to heat the gaseous gas in the second gas supply line (16) and the first gas supply line (18) comprises a first heat exchanger (24) configured to evaporate the liquefied gas in the first gas supply line (18), and a compressor (22) configured to increase the pressure of the gaseous gas in the first supply line (16) in which the compressor is provided with a third heat exchanger (28). The assembly (10) comprises a heat transfer circuit (30) to which the second heat exchanger (20), the first heat exchanger (24), the third heat exchanger (26) and a fourth heat exchanger (32) are connected. The second heat exchanger (20) and the third heat exchanger (28) are arranged in series with each other and that the first heat exchanger (24) is arranged in parallel with the second and the third heat exchanger (20, 28).

Description

A gas supply assembly

Technical field

[001] The present invention relates to a gas supply assembly according to the preamble of claim 1.

Background art

[002] The propulsion system of liquefied gas, such as LNG (Liquified Natural Gas) transport vessel is usually powered by making use of the cargo gas. Storing of the gas in the tanker is arranged by using heat insulated cargo tanks into which an ullage space section and a liquid phase section are formed. The pressure in the cargo tanks is approximately at atmospheric pressure level and the temper- ature of the liquefied gas is about minus 163 Celsius degrees. Although the insu- lation of the cargo tank is extremely good, gradually increasing of the liquefied gas temperature causes formation of so called natural boil-off gas. The boil-off gas must be removed from the tank in order to avoid extensive increasing of pressure in the cargo tanks. That is because the cargo tanks are very sensitive to pressure changes. The boil-off gas may be utilised in vessel’s gas consumers, like its propulsion system. However, the amount of natural boil-off gas is not suf- ficient for providing all propulsion energy required in all circumstances and there- fore the vessel must be provided with additional means for acquiring extra gas, so called forced boil-off gas.

[003] EP 1348620 A1 shows a gas supply apparatus in which the natural boil- off gas is led to a cryogenic compressor, which increase the pressure of the gas prior to feeding it to consumption via a feed line. Additionally, the apparatus also includes a forced boiling vaporiser in which the liquid gas previously pumped to the higher pressure is vaporised. In this arrangement the forced boiling gas por- tion is combined to the natural boil-off gas after the pressure of the natural boil- off gas has been increased. [004] EP1291576 discloses an apparatus for supplying natural gas fuel to heat the boilers of an ocean-going tanker for the transport of LNG. The apparatus comprises a forced LNG vaporiser having an inlet communicating with a liquid storage region of the said tank and an outlet communicating with a conduit lead- ing to fuel burners associated with the boilers. The apparatus also comprises a compressor having an inlet communicating with the ullage space of at least one LNG storage tank and an outlet communicating with a conduit leading from the compressor to fuel burners associated with the boilers. The pressure of the gas is raised by operation of the compressor. The compressor needs to withhold the cryogenic temperatures which is technically very demanding.

[005] An object of the invention is to provide a gas supply assembly arrange- ment in which the performance is considerably improved compared to the prior art solutions.

Disclosure of the Invention

[006] Objects of the invention can be met substantially as is disclosed in the independent claim and in the other claims describing more details of different embodiments of the invention.

[007] According to an embodiment of the invention a gas supply assembly com- prising a tank configured to store liquefied gas in the tank so as to have an gas- eous phase section and a liquid phase section, the assembly further comprising a first gas supply line configured to deliver the gas from the liquid phase section of the tank to one or more gas consumers, a second gas supply line configured to deliver the gas from the gaseous phase section of the tank to one or more gas consumers, wherein the second gas supply line comprises a second heat ex- changer configured to heat the gaseous gas in the second gas supply line and the first gas supply line comprises a first heat exchanger configured to evaporate the liquefied gas in the first gas supply line, the second gas supply line further comprising a compressor configured to increase the pressure of the gaseous gas in the first supply line in which the compressor is provided with a third heat ex- changer. The assembly comprises a heat transfer circuit which the second heat exchanger, the first heat exchanger, the third heat exchanger are connected to, and which heat transfer circuit comprises a fourth heat exchanger which is con- figured to transfer heat to heat transfer medium in the heat transfer circuit, and a pumping means configured to circulate the heat transfer medium in the heat transfer circuit, and that the second heat exchanger and the third heat exchanger are arranged in series with each other and that the first heat exchanger is ar- ranged in parallel with the second and the third heat exchanger.

[008] This way both the natural boil-off gas in the second gas supply line and the forced boil-off gas in the first gas supply line may be prepared for feeding to the gas consumer(s) making use of a single heat source and simple, shared heat transfer medium circuit.

[009] According to an embodiment of the invention the third heat exchanger configured to receive heat from the compressor and control the temperature of the compressor.

[0010] According to an embodiment of the invention a gas supply assembly corn- prising a tank configured to store liquefied gas in the tank so as to have an gas- eous phase section and a liquid phase section, the assembly further comprising a first gas supply line configured to deliver the gas from the liquid phase section of the tank to one or more gas consumers, a second gas supply line configured to deliver the gas from the gaseous phase section of the tank to one or more gas consumers, wherein the second gas supply line comprises a second heat ex- changer configured to heat the gaseous gas in the second gas supply line and the second gas supply line further comprising a compressor configured to in- crease the pressure of the gaseous gas in the first supply line in which the com- pressor is provided with a compressor cooling means. The assembly comprises a second temperature probe arranged to the second gas supply line downstream the compressor, and power of the compressor cooling means is arranged con- trollable based on temperature of the boil-off gas at a location downstream the compressor.

[001 1 ] According to an embodiment of the invention assembly comprises a sec- ond temperature probe arranged to the second gas supply line downstream the compressor, and heat transfer power of the third heat exchanger is arranged controllable based on temperature of the boil-off gas at a location downstream the compressor. This provides an effect and straightforward manner of controlling the temperature of the boil of gas leaving the second gas supply line.

[0012] According to an embodiment of the invention the heat transfer circuit com- prises two branch , and the circuit comprises an auxiliary circuit section which extends from a first branch point to a second branch point and a main circuit section which also extends from a first branch point to a second branch point, parallel to the auxiliary circuit section, and that the second heat exchanger and the third heat exchanger are arranged to an auxiliary circuit section between the branch points, and the first heat exchanger is arranged to the main circuit section between the branch points.

[0013] According to an embodiment of the invention the auxiliary circuit section comprises a first valve to control the portion of the heat transfer medium through the auxiliary circuit section. [0014] According to an embodiment of the invention the first branch point is at upstream side of the first heat exchanger and the second branch point is at down- stream side of the first heat exchanger.

[0015] This provides an effect of efficiently controlling the overall heat transfer in the assembly. [0016] According to an embodiment of the invention the assembly comprises a first temperature probe arranged to the auxiliary heat transfer circuit between the second heat exchanger and the third heat exchanger, based on which the first valve in the auxiliary circuit section is controlled.

[0017] According to an embodiment of the invention the compressor comprises an oil circuit which is arranged to flow through the third heat exchangerfor cooling the oil in the oil circuit.

[0018] According to an embodiment of the invention the third heat exchanger for cooling the compressor is provided with a by-pass conduit and a valve for con- trolling proportion the flow of heat transfer medium via the third heat exchanger and via the by-pass conduit and that the assembly comprises a second temper- ature probe arranged to the second gas supply line downstream the compressor, the valve being arranged to control the flow of heat transfer medium via the third heat exchanger and via the by-pass conduit based on temperature of the boil-off gas at a location downstream the compressor.

[0019] According to an embodiment of the invention the compressor comprises an oil circuit which is arranged to flow through the third heat exchangerfor cooling the oil in the circuit, and the third heat exchanger in the circuit is provided with a by-pass conduit and a three way valve for controlling proportion the flow of heat transfer medium via the third heat exchanger and via the by-pass conduit based on temperature of the oil in the oil circuit.

[0020] According to an embodiment of the invention the second branch point in the heat transfer circuit is at downstream side of the first heat exchanger and the fourth heat exchanger. In other words the second branch point is between an outlet of the fourth heat exchanger and an inlet of the first heat exchanger.

[0021] According to an embodiment of the invention the second branch point in the heat transfer circuit is downstream side of the first heat exchanger and up- stream side of the fourth heat exchanger. In other words the second branch point is between an outlet of the first heat exchanger and an inlet of the fourth heat exchanger.

[0022] According to an embodiment of the invention assembly comprises a third temperature probe arranged to the heat transfer circuit downstream the fourth heat exchanger and the second branch point by means of which the power of the fourth heat exchanger is arranged to controlled. [0023] The present invention relates gas utilizing arrangement in connection with liquefied gas storage tank adapted to store liquefied gas at cryogenic tempera- ture and substantially atmospheric pressure, at least at a pressure which is too low for using the gas in a gas consumer without raising the pressure of the gas outside the storage tank. [0024] By means of the invention is it also possible to combine the assembly into a single assembly which makes its assembly and installation into a marine vessel advantageous.

[0025] The exemplary embodiments of the invention presented in this patent ap- plication are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as charac- teristic of the invention are set forth in particular in the appended claims.

Brief Description of Drawings

[0026] In the following, the invention will be described with reference to the ac- companying exemplary, schematic drawings, in which Figure 1 illustrates a gas supply assembly according to an embodiment of the invention, and

Figure 2 illustrates a gas supply assembly according to another embodiment of the invention.

Detailed Description of Drawings

[0027] Figure 1 depicts schematically a gas supply assembly 10 which is config- ured to supply gaseous fuel to one or more gas consumers 14 connected thereto. The gas supply assembly comprises one or more tanks 12, only one of which is shown in the figure. The tank 12 is configured to store liquefied gas in the tank 12 so as have a gaseous phase section 12.1 and a liquid phase section 12.2 in the tank 12. The tank is such of its construction that it is capable of maintaining substantially atmospheric pressure and cryogenic temperature of the liquefied gas, which is about -163 Celsius degrees, so that the gas may remain mainly in the liquid phase. Since the tank is substantially at atmospheric pressure the gas supply system must be provided with means for increasing the gas pressure to a level required by gas consumer / consumers which it is connected to. The gas supply assembly is particularly advantageous for use in a marine vessel such that the gas is used as fuel in an internal combustion engine in the vessel. The tank may be a cargo tank or dedicate fuel storage for a gas consumer in the vessel. When the gas consumer is a gas operated internal combustion four stroke piston engine (a gas engine in the following) the fuel absolute pressure is typically 400 - 800 kPa at a gas supply to the engine. Naturally the actual pressure of the fuel is depending on the demands of the gas consumers and it may be even 1400 -1600 kPa.

[0028] The liquefied gas can be utilised in the gas engine 14 by means of a first gas supply line 18 arranged to the gas supply assembly 10. The first gas supply line 18 is configured to deliver the gas from the liquid phase section 12.2 of the tank 12 to the gas consumers 14. The first gas supply line opens at its first end (an inlet end) to the lower part of the tank 14 below the surface of the liquefied gas in the tank. The liquid phase section contains liquefied gas at temperature of substantially - 163 °C and at substantially atmospheric pressure. The first gas supply line 18 comprises a first heat exchanger 24 which is configured to evapo- rate the liquefied gas into gaseous gas in the first gas supply line 18. The first heat exchanger 24 can be therefore called also as a main gas evaporator. The first gas supply line 18 comprises also a cryogenic pump 26 in which the pressure of the liquefied gas is raised so that the gas pressure meet the demand of the gas consumers 14. The first heat exchanger 24 is positioned downstream to the cryogenic pump 26. The first heat exchanger 24 is configured to transfer heat from a heat transfer medium into the gas so as to evaporate the liquefied gas and increase the temperature of the gas from about - 163 °C to +40 to +50°C, typically +45°C, which is suitable temperature of the gas for the gas consumers. The first supply line 16 and the second supply line 18 may be connected with each other prior to i.e. upstream the connection to the engine(s) 14, in which case the mixing temperature of the natural and forced boil-off gases is between +40 to +70°C.

[0029] The boil-off gas can be utilised in the gas engine 14 by means of a second gas supply line 16 arranged to the gas supply assembly 10. The second gas supply line 16 is configured to deliver the gas from the gaseous phase section 12.1 of tank 12 to the gas engines 14. The second gas supply line 16 opens at its first end (an inlet end) to the upper part of the tank 14 such that it is always in connection with the gaseous phase section 12.1 above a surface of the liquefied gas in the tank 12. The second gas supply line 16 comprises a second heat ex- changer 20 which is configured to heat the gaseous gas in the second gas supply line 16 to desired temperature. The second gas supply line 16 comprises also a compressor 28 in which the pressure of the gas is raised so that the gas pressure is suitable of the gas engine 14. Advantageously the compressor 22 is a screw or rotary vane compressor. The second heat exchanger 20 is positioned up- stream to the compressor 22 so that the gas temperature can be raised to a level being suitable for a screw of a rotary vane compressor. The second heat ex- changer is configured to transfer heat from a heat transfer medium into the gas so as to increase the temperature of the gas from about - 163 °C to -50 to -20 °C, typically -25°C, which is the inlet temperature range of the gas entering the compressor 22. The temperature of the gas increases also in the compressor 22 advantageously to a temperature +40 - +70 °C, typically 60°C, which corre- sponds the temperature of the gas suitable for introduction to the engine 14.

[0030] The compressor 22 in the second supply line 16 is provided with a com- pressor cooling means 28, 29 for maintaining the temperature of the compressor 22 within desired limits. The compressor uses for example oil for lubrication and controlling the temperature of the compressor 22. The compressor 22 is provided with an oil flow circuit 29 which is arranged to direct an oil flow through the third heat exchanger and thus the third heat exchanger 28 which is configured to trans- fer heat from the compressor oil to the heat transfer medium in the heat transfer medium circuit 30, and that way control the temperature of the compressor 22 but also the temperature of the boil of gas in the second gas supply line 16. Even if not necessary, the oil flow circuit may be provided with a circulation pump. Normally the compressor creates its own differential pressure for the oil in which case the flow is provided without a separate pump. While the compressor is run- ning oil is fed into the compressor from the oil flow circuit. The oil is lubricating operational parts of the compressor and it also receives heat so that the temper- ature of the oil increases while flowing through the compressor. The compressor may be provided with an oil separator 22’ which separates oil from the corn- pressed gas. Oil which has been heated in the compressor is cooled by the third heat exchanger 28 and is recirculated back to the compressor 22. It is optionally also feasible to provide the compressor 22 with an indirect cooling system to which the third heat exchanger 28 is coupled. The compressor is provided with the third heat exchanger 28 such that it may be realized as being an integral part of the compressor or as only arranged in heat transfer communication with the compressor 22. Since the temperature of the compressor 22 has an effect on the temperature of the compressed gas this is advantageously utilized as a method of controlling the temperature of the boil-off gas. The method utilizes the com- pressor cooling means 28, 29 for maintaining the temperature of the boil-off gas within desired limits. When the compressor 22 is running, the temperature of the boil-off gas compressed by the compressor 22 is measured and the compressor cooling means 28, 29 is operated based on the temperature of the boil-off gas. Thus, in case the temperature of the boil-off gas is higher than a predetermined set value the cooling power of the compressor is increased and in case the tem- perature of the boil-off gas is lower than a predetermined set value the cooling power of the compressor is decreased.

[0031 ] The assembly comprises a heat transfer circuit 30 which is configured to control the temperature of the gas supplied via the first and the second gas sup- ply lines to the gas engines 14, as well as to control the temperature of the com- pressor 22 in the second gas supply line 16. The heat transfer circuit 30 corn- prises a fourth heat exchanger 32 which is configured to transfer heat to a heat transfer medium in the heat transfer circuit 30. The heat transfer medium can be water based solution containing one or more antifreeze additive(s). Also suitable thermal oil can be used. The second heat exchanger 20, the first heat exchanger 24, the third heat exchanger 28 and the fourth heat exchanger 32 are all con- nected to the heat transfer circuit 30. The heat transfer circuit is also provided with a pump 34, by means of which the heat transfer medium is arranged to flow and circulate in the circuit 30.

[0032] The fourth heat exchanger 32 is connected to a heat source 42, such as a steam system made available for the assembly 10 so as to bring heat to the heat transfer medium in the circuit 30 and increase its temperature in the fourth heat exchanger 32. The circuit 30 comprises a main circuit section 30’, in which the heat transfer medium flows through the pump 34, the fourth heat exchanger 32 and the first heat exchanger 24. This is, because a major portion of the heat transferred into the heat transfer medium in the fourth heat exchanger 32 is used for evaporating the liquefied gas in the first heat exchanger 24. The circuit 30 comprises two branch points 38, 40 which are arranged such that the first branch point 38 is at upstream side of the first heat exchanger 24 and the second branch point 40 is at downstream side of the first heat exchanger 24 and the fourth heat exchanger 32. The terms upstream and downstream is defined by the flow direc- tion of the heat transfer medium in the circuit section 30 in relation to the pump 34 in the circuit, which flow direction is illustrated by arrow heads in the lines of the circuit. The circuit 30 comprises an auxiliary circuit section 30” which extends from the first branch point 38 to the second branch point 40 parallel to the portion of the mail conduit 30’ between the first branch point 38 to the second branch point 40. The second heat exchanger 20 and the third heat exchanger 28 are connected in series to the auxiliary circuit section 30” such that the second heat exchanger 20 is arranged upstream to the third heat exchanger 28. This way the second heat exchanger 20 and the third heat exchanger 28 are arranged parallel to the first heat exchanger 24 and the heat obtained from the common heat source 42 via the fourth heat exchanger 32 is used as a heat source for heating the gaseous gas in the second heat exchanger 20, and for evaporating the liq uefied gas in the first heat exchanger 24. The auxiliary circuit section 30” is pro- vided with a first control valve 44 for controlling the portion of the flow of the heat transfer medium through the first and the third heat exchangers.

[0033] The third heat exchanger 28 which is configured to transfer heat from the compressor 22 and control the temperature thereof is arranged to the auxiliary circuit section 30” downstream the second heat exchanger 20. The third heat exchanger 28 is provided with a by-pass conduit 31 and a three-way valve 33 for controlling proportion the flow of heat transfer medium via the third heat ex- changer 28 and via the by-pass conduit 31 , and thus the cooling power of the third heat exchanger 28.

[0034] As an example of a certain operational state of the gas fuel supply as- sembly the assembly is operated in a following manner. The numerical values are only examples of a certain practical application of the invention and the val- ues may be different in different practical solutions of the invention. When the heat transfer medium is arranged to flow in the circuit 30 by operating the pump 34 its temperature is raised in the fourth heat exchanger 32 from 27°C to 47°C at which temperature the heat transfer medium enters the second heat ex- changer 20 and the first heat exchanger 24. The portion of the heat transfer me- dium directed to the auxiliary circuit section 30” is controlled by the first valve 44, based on the temperature of the heat transfer medium after the second heat ex- changer 20 but before the third heat exchanger 28. The temperature is measured by a first temperature probe 46 arranged between the second heat exchanger 20 and the third heat exchanger 28 in the auxiliary circuit section 30”. Typically the temperature of the heat transfer medium between the second heat exchanger 20 and the third heat exchanger 28 is 35°C. Next the heat transfer medium in the auxiliary circuit section 30” flows into the third heat exchanger 28 in which tem- perature of the heat transfer medium is increased because it is used for cooling the compressor 22. The three way valve 33 for controlling proportion the flow of heat transfer medium via the third heat exchanger 28 and via the by-pass conduit 31 , is controlled based on temperature of the boil-off gas at a location down- stream the compressor 22. The temperature of the boil-off gas at the location is measured by a second temperature probe 48 arranged to the second gas supply line 16 downstream the compressor 22. The heat transfer medium receives heat in the third heat exchanger 28 so that its temperature will typically raise to 50°C.

[0035] At the first branch point 38 the portion of the heat transfer medium which in not directed to the auxiliary circuit section 30” is directed to flow further in the main circuit section 30’ via the first heat exchanger 24. The heat transfer medium enters the first heat exchanger 24 at temperature of about 47°C in which it re- leases heat for evaporating and heating the liquefied gas in the first gas supply line 18. Typically the temperature of the heat transfer medium after the first heat exchanger 24 is 25°C. After the first heat exchanger 24 the heat transfer medium is arranged to flow back to the fourth heat exchanger 32 where the heat transfer medium receives heat from the common heat source 42. At the second branch point 40 the flows of heat transfer medium from the auxiliary circuit section 30” and the main circuit section 30’ are combined. The power of the fourth heat ex- changer is controlled based on temperature of the heat transfer medium at a location downstream the fourth heat exchanger 32 and the second branch point 40. There is a third temperature probe 50 arranged to the main circuit section 30’ downstream the fourth heat exchanger 32 and the second branch point 40 by means of which the temperature of the mixture of the heat transfer medium flows from the main circuit section 30’ and the auxiliary circuit section 30” is measured. This way the mixing temperature of the returning flows combined in the second branch point 40 is taken into account and used as a variable for controlling the power of the fourth heat exchanger. This is advantageous since the temperature of the heat transfer medium when it exits the third heat exchanger 28 is normally so high that it does not require heating before it can be fed to the first of the second heat exchanger. In the embodiment of the figure 1 the heat source 42 comprises a steam system arranged to bring heat to the fourth heat exchanger. The fourth heat exchanger 32 comprises a bypass conduit 35 which is provided with a three way valve 52 for controlling proportion the flow of heat transfer me- dium via the fourth heat exchanger 32 and via the by-pass conduit 35. The three way control valve 52 controls the heat power transferred in the fourth heat ex- changer to the heat transfer medium. The operation of the control valve 52 is controlled based on the measurement data of the third temperature probe 50. The heat source 42 may be any suitable and available heat source which advan- tageously is the engines 14, using heat originating from one or several of cylin- ders, block, oil, combustion air, or other cooling system, exhaust gas boiler, or other heat source in the engine, in which the heat may be transferred to suitable heat transfer medium such as steam, water based solution or heat transfer oil, made available for use in the gas supply assembly.

[0036] Figure 2 depicts schematically a gas supply assembly 10 according to another embodiment of the invention which is configured to supply gaseous fuel to one or more gas consumers 14 connected thereto. The gas supply assembly shown in the figure 2 provide substantially same operation with substantially same elements, where however following features differ from that shown in the figure 1 .

[0037] The fourth heat exchanger 32 is connected uses a cooling system of the engines 14 as a heat source 42 so as to bring heat to the heat transfer medium in the circuit 30 and increase its temperature in the fourth heat exchanger 32. The circuit 30 comprises two branch points 38, 40 which are arranged such that the first branch point 38 is at upstream side of the first heat exchanger 24 and the second branch point 40 is at downstream side of the first heat exchanger 24 but upstream the fourth heat exchanger 32. The terms upstream and down- stream is defined by the flow direction of the heat transfer medium in the circuit section 30, which is illustrated by arrowhead in the lines of the circuit.

[0038] The third heat exchanger 28 is provided with a by-pass conduit 31 and a three-way valve 33 for controlling proportion the flow of heat transfer medium via the third heat exchanger 28 and via the by-pass conduit 31 , and thus the cooling power of the third heat exchanger 28. The three way valve 33 for controlling pro- portion the flow of heat transfer medium via the third heat exchanger 28 and via the by-pass conduit 31 , is controlled based on temperature of compressor cool- ing oil at a location downstream the third heat exchanger 28. The temperature is measured by a second temperature probe 48 arranged to the compressor 22 cooling oil line downstream the third heat exchanger 28. The heat transfer me- dium receives heat in the third heat exchanger 28 so that its temperature will typically raise to 50°C.

[0039] Figure 2 also depicts an embodiment of the invention according to which the valve 44 in the auxiliary circuit section 30’ is not used for continuous control but is it a manual balancing valve to once set the flow through the auxiliary circuit section 30’. This feature is also applicable to the embodiment of the figure 1 .

[0040] At the first branch point 38 the portion of the heat transfer medium which is not directed to the auxiliary circuit section 30” is directed to flow further in the main circuit section 30’ via the first heat exchanger 24. The heat transfer medium enters the first heat exchanger 24 at temperature of about 47°C in which it re- leases heat for evaporating and heating the liquefied gas in the first gas supply line 18. Typically the temperature of the heat transfer medium after the first heat exchanger 24 is 25°C. At the second branch point 40 the flows of heat transfer medium from the auxiliary circuit section 30” and the main circuit section 30’ are combined to flow back to the fourth heat exchanger 32. The power of the fourth heat exchanger is controlled based on temperature of the heat transfer medium at a location downstream the fourth heat exchanger 32. There is a third temper- ature probe 50 arranged to the main circuit section 30’ downstream the fourth heat exchanger 32 by means of which the temperature of the heat transfer me- dium is measured. In the embodiment of the figure 2 the heat source 42 corn- prises a control valve 52 for controlling the power output of the third heat ex- changer 32. [0041] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred em- bodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the in- vention, as defined in the appended claims. The details mentioned in connection with any embodiment above may be used in connection with another embodi- ment when such combination is technically feasible.

Claims

1. A gas supply assembly (10) comprising a tank configured to store lique- tied gas in the tank (12) so as to have an gaseous phase section (12.1 ) and a liquid phase section (12.2), the assembly further comprising a first gas supply line (18) configured to deliver the gas from the liquid phase section (12.2) of the tank to one or more gas consumers (14), a second gas supply line (16) config- ured to deliver the gas from the gaseous phase section (12.1 ) of the tank to one or more gas consumers (14), wherein the second gas supply line (16) comprises a second heat exchanger (20) configured to heat the gaseous gas in the second gas supply line (16) and the first gas supply line (18) comprises a first heat ex- changer (24) configured to evaporate the liquefied gas in the first gas supply line (18), the second gas supply line (16) further comprising a compressor (22) con- figured to increase the pressure of the gaseous gas in the first supply line (16) in which the compressor is provided with a third heat exchanger (28), characterized in that the assembly (10) comprises a heat transfer circuit (30) which the first heat exchanger (24), the second heat exchanger (20), the third heat ex- changer (26) are connected to, and which heat transfer circuit (30) comprises a fourth heat exchanger (32) which is configured to transfer heat to heat transfer medium in the heat transfer circuit (30), and a pumping means (34) configured to circulate the heat transfer medium in the heat transfer circuit (30), and that the second heat exchanger (20) and the third heat exchanger (28) are arranged in series with each other and that the first heat exchanger (24) is arranged in parallel with the second and the third heat exchanger (20,28).

2. A gas supply assembly (10) according to claim 1 , characterized in that the assembly comprises a second temperature probe (48) arranged to the sec- ond gas supply line (16) downstream the compressor (22), and that heat transfer power of the third heat exchanger (28) is arranged controllable based on temper- ature of the boil-off gas at a location downstream the compressor (22).

3. A gas supply assembly (10) according to claim 1 , characterized in that the heat transfer circuit (30) comprises two branch points (38, 40), and that the circuit (30) comprises an auxiliary circuit section (30”) which extends from a first branch point (38) to a second branch point 40, and that the circuit (30) comprises a main circuit section (30’) which extends from the first branch point (38) to the second branch point 40 and that the second heat exchanger (20) and the third heat exchanger (28) are arranged to an auxiliary circuit section (30”) between the branch points (38,40), and that the first heat exchanger (24) is arranged to the main circuit section (30’) between the branch points (38,40).

4. A gas supply assembly (10) according to claim 3, characterized in that the auxiliary circuit section comprises a first valve (44) to control the portion of the heat transfer medium through the auxiliary circuit section (30”).

5. A gas supply assembly (10) according to claim 3, characterized in that the assembly comprises a first temperature probe (46) arranged to the heat trans- fer circuit (30) between the second heat exchanger (20) and the third heat ex- changer (28), based on which the first valve (44) is controlled.

6. A gas supply assembly (10) according to claim 1 , characterized in that the compressor comprises an oil circuit (29) which is arranged to flow through the third heat exchanger (28) for cooling the oil in the circuit.

7. A gas supply assembly (10) according to claim 1 , characterized in that the third heat exchanger (28) for cooling the compressor (22) is provided with a by-pass conduit (31 ) and a valve (33) for controlling proportion the flow of heat transfer medium via the third heat exchanger (28) and via the by-pass conduit (31 ), and that the assembly comprises a second temperature probe (48) ar- ranged to the second gas supply line (16) downstream the compressor (22), and that the valve (33) is arranged to control the flow of heat transfer medium via the third heat exchanger (28) and via the by-pass conduit (31 ) based on temperature of the boil-off gas at a location downstream the compressor (22).

8. A gas supply assembly (10) according to claim 1 , characterized in that the compressor comprises an oil circuit (29) which is arranged to flow through the third heat exchanger (28) for cooling the oil in the circuit, and the third heat exchanger (28) in the circuit (30) is provided with a by-pass conduit (31 ) and a three way valve (33) for controlling proportion the flow of heat transfer medium via the third heat exchanger (28) and via the by-pass conduit (31 ) and that the portions of the flow of heat transfer medium via the third heat exchanger (28) and via the by-pass conduit (31 ) is controlled based on temperature of the oil in the oil circuit (29).

9. A gas supply assembly (10) according to claim 3, characterized in that the second branch point (40) in the heat transfer circuit (30) is at downstream side of the first heat exchanger (24) and the fourth heat exchanger (32).

10. A gas supply assembly (10) according to claim 3, characterized in that the second branch point (40) in the heat transfer circuit (30) is downstream side of the first heat exchanger (24) and upstream side of the fourth heat exchanger (32).

1 1. A gas supply assembly (10) according to claim 9 or 10, characterized in that assembly comprises a third temperature probe (50) arranged to the heat transfer circuit (30) downstream the fourth heat exchanger (32) and the second branch point (40) by means of which the power of the fourth heat exchanger (32) is arranged to be controlled.