Patent Description:
Invention relates to a field of storing liquefied gas at cold conditions in a pressure proof tank. Liquefied gas as a fuel of prime movers in marine vessels and other mobile power plants has increasingly become of interest while the importance of environmental issues of particularly the exhaust emissions have increased. Fuel which is in gaseous form at normal atmospheric conditions is typically stored in a tank or tanks in liquefied phase at low temperature. Typically, the tank is filled so that there is always gas in liquid phase and gaseous phase, the liquid substance being below the gas in gaseous phase, which reserves a space in the upper part of the tank. Even if the tanks are insulated as such the heat losses cause natural evaporation of the gas increasing the pressure in the tank. This can be handled by removing the excessive vapour and delivering it to e.g., an engine as fuel or another type of oxidizer, or optionally install refrigeration unit(s) in connection with a tank to prevent excessive increase of pressure.

<CIT> discloses a tanker for transporting liquefied petroleum gases including a plurality of insulated cargo tanks having the same or different liquefied cargoes therein. In order to control tank conditions, a refrigerating unit is provided with cooling coils extending from the unit to the tops or trunks of each tank so as to cool cargo liquids and to cool and condense cargo vapours within the tank so that condensate is returned to the tank interior. The refrigerating unit and coils are used to extract heat from the cargo liquid and during purging and tank cooldown processes in order to cool the cargo vapours and return the condensed vapours back to the bottom of the tank.

<CIT> disclose a thermoelectric power generation technologybased LNG (Liquefied Natural Gas) engine energy recovery device, which comprises a thermoelectric generator. An exhaust port of an LNG gas tank is connected to the thermoelectric generator through an LNG inlet pipe. The LNG fuel supply system uses a thermoelectric generator to replace the original vaporizer, so that it can complete the LNG gasification function while also using thermoelectric power generation technology for energy recovery installation.

Document <CIT> discloses an LPG fuel injection system of an internal combustion engine. A fuel tank stores the LPG fuel. Fuel is supplied to a cylinder in engine from the fuel supply pipe in connection with the fuel tank. The fuel remaining which is not injected to the cylinder in the engine is returned back to the fuel tank. A thermoelectric element absorbs heat from the fuel in the return pipe and the fuel is cooled prior to its entry into the tank. Accordingly, the inner pressure of the fuel tank is not risen.

<CIT> discloses a fuel tank cooler based on thermoelectric cells. The cooler is formed by two arrangements: a first arrangement comprises one or more Peltier thermoelectric cells, arranged throughout the peripheral layer of the tank, wherein the cooling side of the thermoelectric cells is in thermal contact with the surface of the fuel tank; and a second arrangement comprises a condensation passage located outside the tank and comprises one or more Peltier thermoelectric cells, wherein the cooling side of the thermoelectric cells is in thermal contact with the surface of the condensation passage.

<CIT> discloses a gas processing system including an arrangement for managing temperature of liquefied gas fuel in a fuel tank of a marine vessel, the arrangement comprising.

An object of the invention is to provide arrangement for managing temperature of liquefied gas fuel in a fuel tank of a marine vessel, in which the performance is considerably improved compared to the prior art solutions.

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.

According to an embodiment, an arrangement for managing temperature of liquefied gas fuel in a fuel tank of a marine vessel comprises.

By means of the invention t it is possible to cool down the gas in the tank making use of the gas as heat carrier in both of the first and the second heat exchange fluid flow paths of the first thermoelectric heat exchanger.

According to an embodiment, an arrangement for managing temperature of liquefied gas fuel in a fuel tank of a marine vessel a second fuel line is coupled to the second heat exchange fluid flow path, the second fuel line being arranged to lead liquefied gas from the tank to the tank via the first thermoelectric heat exchanger.

By means of this embodiment it is possible to cool down the liquefied gas in the tank making use of the liquefied gas as heat carrier in both of the first and the second heat exchange fluid flow paths of the first thermoelectric heat exchanger.

According to the invention the second fuel line is a branch line, which branches from the main fuel feed line at a location downstream the fuel transfer pump and which branch line is arranged in flow connection with the tank via the thermo electric heat exchanger such that the second heat exchange fluid flow path is coupled to the branch line. By means of this embodiment it is possible to cool down the liquefied gas in the tank making use of the liquefied gas as heat carrier in both of the first and the second heat exchange fluid flow paths of the first thermoelectric heat exchanger driven by the same pump which is also the fuel transfer pump.

According to an embodiment the arrangement comprises an electric power management system connected to the thermo electric generator cells of the first thermoelectric heat exchanger and a polarity control unit of the thermo electric generator cells of the first thermoelectric heat exchanger, which polarity control unit is configured to selectably change the polarity of connection of the thermo electric generator cells of first thermoelectric heat exchanger to the electric power management system. This way the arrangement may be controlled as desired to provide effects of the invention.

According to an embodiment the branch line branches from the fuel feed line at a location upstream the thermo electric heat exchanger, wherein the temperature level of the liquefied gas to be cooled for tank temperature management is initially as low as possible decreasing the required energy for cooling the liquefied gas.

According to an embodiment arrangement comprises a computer control unit adapted to:.

According to an embodiment the branch line branches from the fuel feed line at a location downstream the thermo electric heat exchanger.

According to an embodiment the arrangement comprises a second thermoelectric heat exchanger, which comprises a first heat exchange fluid flow path and a second heat exchange fluid flow path, and a number of thermo electric generator cells arranged in heat transfer communication with both the first heat exchange fluid flow path and the second heat exchanger fluid flow path, in which the first heat exchange fluid flow path is coupled to the main fuel feed line downstream the first thermoelectric heat exchanger.

According to an embodiment the second heat exchanger fluid flow path is arranged in heat transfer communication with a heat transfer medium flow circuit of the marine vessel.

According to an embodiment the second heat exchanger fluid flow path is arranged in heat transfer communication with a cooling system of a prime mover of the marine vessel.

According to an embodiment the arrangement comprises an electric power management system connected to the thermo electric generator cells of the first thermoelectric heat exchanger and to the thermo electric generator cells of the second thermoelectric heat exchanger, and the second thermoelectric heat exchanger is configured to produce electric power by its thermo electric generator cells and the electric power management system is configured to supply the electric power to the thermo electric generator cells of the first thermoelectric heat exchanger, so as to cool down the liquefied gas flowing through the second heat exchange fluid flow path of the first thermoelectric heat exchanger to the tank.

This way the tanks temperature and pressure levels can be maintained at desired level making use of high temperature waste heat available in the marine vessel. More specifically the electric power which is fed to the first thermoelectric heat exchanger is obtained from the second thermoelectric heat exchanger using high temperature waste heat.

According to an embodiment the arrangement comprises a first thermoelectric heat exchanger comprising a first heat exchange fluid flow path and a second heat exchange fluid flow path, and a number of thermo electric generator cells arranged in heat transfer communication with both the first heat exchange fluid flow path and the second heat exchanger fluid flow path, and a second thermoelectric heat exchanger comprising a first heat exchange fluid flow path and a second heat exchange fluid flow path, and a number of thermo electric generator cells arranged in heat transfer communication with both the first heat exchange fluid flow path and the second heat exchanger fluid flow path, and a computer control unit adapted to:.

According to an embodiment the second fuel line extends from upper part of the tank via the second heat exchange fluid flow path of the first thermo-electric heat exchanger to the tank. This provides an effect by means of which it is possible effect on the temperature of the liquefied gas in the tank and thus avoid undesired increase of pressure in the tank.

By the term liquefied gas fuel, it is meant fuel which is in gaseous form at normal atmospheric conditions and stored in a tank in liquefied state.

The invention has several benefits. In general, the invention provides effective way of preventing excessive heating of liquified gas fuel stored in a tank.

The thermoelectric effect refers to phenomena by which either a temperature difference creates an electric potential or an electric potential creates a temperature difference. These phenomena are known more specifically as the Seebeck effect (creating a voltage from temperature difference), Peltier effect (driving heat flow with an electric current), and Thomson effect (reversible heating or cooling within a conductor when there is both an electric current and a temperature gradient). Thermoelectric materials are used in the arrangement for cooling or heating, and to regenerate electricity from temperature difference between the gas flows at different temperatures.

A thermoelectric module is a circuit containing thermoelectric materials which generate electricity from heat directly. A thermoelectric module consists of two dissimilar thermoelectric materials joined at their ends: an n-type (with negative charge carriers), and a p-type (with positive charge carriers) semiconductor. Direct electric current will flow in the circuit when there is a temperature difference between the ends of the materials. Generally, the current magnitude is directly proportional to the temperature difference.

A thermoelectric heat exchanger is a unit comprising flow channels in both lower temperature and higher temperature sides in heat transfer communication with several thermoelectric modules such that medium flowing in the lower and higher temperature flow channels provide desired temperature difference over the thermoelectric modules. In other words, there is a first heat exchange fluid flow path and a second heat exchange fluid flow path, and a number of thermo electric generator cells arranged in heat transfer communication with both the first heat exchange fluid flow path and the second heat exchanger fluid flow path.

The exemplary embodiments of the invention presented in this patent application 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.

<FIG> depicts schematically an arrangement <NUM> for managing temperature of liquefied gas fuel in a fuel tank <NUM> of a marine vessel <NUM>. The arrangement <NUM> comprises a fuel tank <NUM> which is configured to store fuel for use of a gas consumer in the vessel <NUM>. The marine vessel <NUM> may have several (only one shown here) gas consumers <NUM>, at least its prime movers, such as main engines which are consuming gas as their fuel. In order to feed the fuel to the gas consumers <NUM> the arrangement comprises a main fuel feed line <NUM>. The main fuel feed line <NUM> begins from a bottom area <NUM>' of the fuel tank <NUM> and extends to the gas consumer <NUM>. The main fuel feed line <NUM> may be provided with various auxiliary components, such as valves, measuring instruments, evaporator, which are all denoted commonly by the block <NUM>. The block <NUM> may also include a booster pump or pumps for further increasing feed pressure to the gas consumers <NUM>. Naturally, the auxiliary component may be positioned at various locations in the main fuel feed line <NUM>. The main fuel feed line <NUM> is provided with a fuel transfer pump <NUM>. The fuel transfer pump <NUM> is shown here inside the tank <NUM>, but it can be positioned also outside the tank.

The arrangement <NUM> comprises further a first thermoelectric heat exchanger <NUM>. The thermoelectric heat exchanger comprises a first heat exchanger <NUM> and a second heat exchanger <NUM> and a number of thermo electric generator cells <NUM> between the heat exchangers <NUM>, <NUM>. The first heat exchanger <NUM> and the second heat exchanger <NUM> comprise a first heat exchange fluid flow path <NUM>' and a second heat exchange fluid flow path <NUM>' which act as flow channels of the heat exchanger. The thermo electric generator cells <NUM> are arranged in heat transfer communication with both the first heat exchange fluid flow path <NUM>' and the second heat exchanger fluid flow path <NUM>', by means of which a temperature difference over the thermo electric generator cells <NUM> can be maintained, and heat can be transferred between the thermo electric generator cells <NUM> and the first heat exchanger <NUM> and the second heat exchanger <NUM>. As is becomes clear the first heat exchange fluid flow path <NUM>' and the second heat exchange fluid flow path <NUM>' are not in direct heat exchange communication with each other.

In the first thermoelectric heat exchanger <NUM> the first heat exchange fluid flow path <NUM>' is coupled with the main fuel feed line <NUM>, at a location downstream the fuel transfer pump <NUM>. This way the first thermoelectric heat exchanger <NUM> is at the pressure side of the pump <NUM>.

There is a second fuel line <NUM>' which is arranged to lead fuel back to the tank <NUM> via the first thermoelectric heat exchanger <NUM>. The second fuel line <NUM>' is coupled to the second heat exchange fluid flow path <NUM>'. This way it is possible effect on the temperature of the liquefied gas in the tank <NUM> and thus avoid undesired increase of pressure in the tank. The amount, i.e., flow rate of the liquefied gas fuel led back to the tank <NUM>, is arranged controllable by providing a flow control valve <NUM> to the second fuel line <NUM>'. Even if the control valve in the second fuel line is shown to be upstream the first thermoelectric heat exchanger <NUM> it may also be at the downstream side thereof. Also, the temperature of the liquefied gas fuel led back to the tank <NUM> is arranged controllable by means of the thermo electric generator cells <NUM>.

The second fuel line <NUM>' which is coupled to the second heat exchange fluid flow path <NUM>' is a branch line from the main fuel feed line <NUM>, and it branches from the main fuel feed line <NUM> at a location downstream the fuel transfer pump <NUM>. In the embodiment of the <FIG> the branch line <NUM>' branches from the fuel feed line at a location upstream the thermo electric heat exchanger <NUM>. The inlet temperature of the gas entering both the first heat exchange fluid flow path <NUM>' and the second heat exchange fluid flow path <NUM>' is the same. Supplying electric power to the thermo electric generator cells <NUM> having their polarity set correctly cools down the gas flowing in the second heat exchange fluid flow path <NUM>' and heats the gas flowing in the first heat exchange fluid flow path <NUM>'.

The operation can be described such that the thermoelectric heat exchanger <NUM> receives liquefied gas fuel (such as LPG, Ammonia or LNG) from the tank <NUM> driven by the pump <NUM>. A small portion of the liquefied gas fuel delivered by pump <NUM> is recycled back to the tank under control of the valve <NUM> and enters the thermoelectric heat exchanger <NUM> where it is cooled to a desired lower temperature than what the current temperature in the fuel tank is. The larger portion of the liquefied gas flow is heated the thermoelectric heat exchanger <NUM> whilst the smaller portion of the flow is cooled. The process requires electric power input to drive the process. Tank temperature regulation is advantageously controlled by controlling the amount of electric power fed to the thermoelectric heat exchanger <NUM> and polarity applied thereto. Maintaining the control valve <NUM> open and controlling the temperature by the thermoelectric heat exchanger <NUM> gives the advantage that in case of a sudden shut down - such as an emergency shutdown - of the main fuel feed line <NUM> at least partially open control valve <NUM> mitigates the pressure shock in the line. The power input to the thermo electric generator cells <NUM> is controllable from zero to maximum - depending on cooling needs.

Cooling power to the gas flowing in second fuel line <NUM>' may be controlled such that the outlet temperature in gas stream <NUM>' is kept substantially constant and varying its flow rate, or optionally, the gas flow rated is substantially constant and the outlet temperature of the gas flowing from the thermoelectric heat exchanger <NUM> is the control variable.

The control may be realized also such that the temperature of the gas in the line <NUM>' reaches a desired minimum temperature, while also the flow rate of the gas is variably controlled.

If it is desired to heat up the liquefied gas in the tank <NUM> i.e. increasing the tank pressure, the polarity of the thermo electric generator cells <NUM> can be changed and the recycled liquefied gas flow can be heated instead of cooled.

The arrangement comprises an electric power management system <NUM> connected to the thermo electric generator cells <NUM> of the first thermoelectric heat exchanger <NUM>. The electric power management system <NUM> is configured to either supply or receive electric current to the thermo electric generator cells <NUM> and manipulate electricity to cope with the demands of power distribution network <NUM> to which it is connected to, and with the demands of the thermo electric generator cells <NUM>. The electric power management system <NUM> is in data and energy transfer communication <NUM> with the electric power management system <NUM>. For operation in a mode of cooling the gas by supplying electric power to the thermoelectric heat exchanger <NUM> the electric power management system comprises a power converter which is connected to a source of electric power. The power converted is configured to feed DC power controllably, and with controllable polarity to the thermoelectric heat exchanger. The response of the control to the gas temperature is detected by suitably positioned one or more temperature sensors. Measure temperature is made available to a controller which is configured to control the power converter. In the figures the temperature sensor is shown to measure the temperature of the gaseous phase in the tank, but there may be one or more sensors arranged to the main fuel feed line <NUM> and/or the second fuel line <NUM>', downstream the thermoelectric heat exchanger <NUM>.

There is also a polarity control unit <NUM> of the thermo electric generator cells <NUM> arranged in data transfer communication <NUM> with the thermo electric generator cells <NUM>. The polarity control unit <NUM> is configured to selectably change the polarity of connection of the thermo electric generator cells <NUM> for setting the direction of the heat transfer provided by the thermo electric generator cells <NUM>. Supplying electric power to the thermo electric generator cells <NUM> having their polarity set correctly cools down the gas flowing in the second heat exchange fluid flow path <NUM>' and heats the gas flowing in the first heat exchange fluid flow path <NUM>'.

The arrangement comprises a computer control unit <NUM>. The computer control unit <NUM> is data transfer communication with at least the electric power management system <NUM>, the polarity control unit <NUM> and the flow control valve <NUM>. There is also at least one temperature sensor <NUM> arranged in connection with the tank <NUM> which is data transfer communication with the computer control unit <NUM>.

The computer control unit <NUM> is adapted to control the operation of the arrangement <NUM> according to desired result to be achieved. Temperature of the liquefied gas fuel in the tank <NUM> can be controlled in efficient manner. The computer control unit <NUM> is adapted to determine temperature of the liquefied gas in the tank, and.

In the <FIG> there is shown an embodiment of the invention. The arrangement <NUM> for managing temperature of liquefied gas fuel shown in the <FIG> is otherwise similar to that shown and described in the <FIG>, except that here the branch line <NUM>' branches from the fuel feed line <NUM> at a location downstream the thermo electric heat exchanger <NUM>. The inlet temperature of the gas entering the first heat exchange fluid flow path <NUM>' equals to the exit temperature of the gas flowing from the second heat exchange fluid flow path <NUM>'. In order to facilitate cooling of the tank, the exit temperature of the gas from the first heat exchange fluid flow path <NUM>' is cooled to lower temperature than the temperature of the liquefied gas in the tank <NUM>.

In the <FIG> there is shown another embodiment of the invention. The arrangement for managing temperature of liquefied gas fuel in a fuel tank of a marine vessel arrangement comprises all the elements and functionalities of that shown in the <FIG> but in the <FIG> the arrangement comprises further a second thermoelectric heat exchanger <NUM>. The second thermoelectric heat exchanger <NUM> can also be used in connection with the embodiments illustrated in the <FIG>. The second thermoelectric heat exchanger <NUM> is substantially similar to the first thermoelectric heat exchanger <NUM>, and it comprises a first heat exchange fluid flow path <NUM>' and a second heat exchange fluid flow path <NUM>', as well as a plurality of thermo electric generator cells <NUM> arranged in heat transfer communication with both the first heat exchange fluid flow path <NUM>' and the second heat exchanger fluid flow path <NUM>'. The thermo electric generator cells <NUM> are arranged in heat transfer communication with both the first heat exchange fluid flow path <NUM>' and the second heat exchanger fluid flow path <NUM>', by means of which a temperature difference over the thermo electric generator cells <NUM> can be maintained, and heat can be transferred between the thermo electric generator cells <NUM> and the first heat exchanger <NUM> and the second heat exchanger <NUM>. As is becomes clear the first heat exchange fluid flow path <NUM>' and the second heat exchange fluid flow path <NUM>' are not in direct heat exchange communication with each other.

The first thermoelectric heat exchanger <NUM>, i.e. the first heat exchange fluid flow path <NUM>' is coupled with the main fuel feed line <NUM>. Also, the first heat exchange fluid flow path <NUM>' of the second thermoelectric heat exchanger <NUM> is coupled to the main fuel feed line <NUM> downstream the first thermoelectric heat exchanger <NUM>, those being this way connected in series. The first thermoelectric heat exchanger <NUM> is first in the flow direction of the liquefied gas and this way the initial temperature of the gas to be cooled in the first thermoelectric heat exchanger as low as possible, which minimizes the required energy for cooling the liquefied gas returned back to the tank <NUM>, as is explained also in the <FIG>.

In the second thermoelectric heat exchanger <NUM> the second heat exchanger fluid flow path <NUM>' is arranged in heat transfer communication with a heat transfer medium flow circuit <NUM> of the marine vessel, which is here a cooling system of a prime mover <NUM> of the marine vessel <NUM>. Also the arrangement <NUM> in the <FIG> comprises an electric power management system <NUM> connected to the thermo electric generator cells <NUM> of the first thermoelectric heat exchanger <NUM> and to the thermo electric generator cells <NUM> of the second thermoelectric heat exchanger <NUM>.

The second thermoelectric heat exchanger is configured to produce electric power by its thermo electric generator cells and the second heat exchanger fluid flow path <NUM>' is configured to transfer heat to the thermo electric generator cells <NUM> so as to produce electric power, as is depicted by the arrow in the line <NUM>.

The electric power management system <NUM> is configured to supply the electric power to the thermo electric generator cells <NUM> of the first thermoelectric heat exchanger <NUM>, so as to cool down the liquefied gas flowing through the second heat exchange fluid flow path <NUM>' of the first thermoelectric heat exchanger <NUM> to the tank <NUM>.

The electric power obtained making use of waste heat produced by the prime mover is fed to the first thermoelectric heat exchanger <NUM> for use in cooling the liquefied gas flowing through the second heat exchanger fluid flow path <NUM>' of the first thermoelectric heat exchanger <NUM>. Any surplus electric power is fed to the electric network <NUM>. In both of the thermoelectric heat exchangers the fluid in the first heat exchanger fluid flow path <NUM>' is heated and the fluid in the second heat exchanger fluid flow path <NUM>' is cooled. The liquefied gas which flows through the first heat exchanger fluid flow paths <NUM>', <NUM>' may even be partially or totally evaporated.

<FIG> discloses a still another embodiment of the invention. This feature is applicable for any liquefied gases. The pump <NUM> pumps liquefied gas through the thermoelectric heat exchanger <NUM>. The second fuel line <NUM>' extends from upper part <NUM>" of the tank <NUM> via the second heat exchange fluid flow path <NUM>' of the first thermo-electric heat exchanger <NUM> back to the tank. Boil off gas is generated from the liquefied gas in the tank by heat ingress, which boil off gas flows freely to the thermoelectric heat exchanger <NUM> in gaseous form. In the thermoelectric heat exchanger 24it is cooled by applying electric power to the thermo electric generator cells <NUM> and therefore advantageously condensed by cooling in the second heat exchanger fluid flow path <NUM>'. The second fuel line <NUM>' does not need a control valve, but switching off the power supply to the thermoelectric heat exchanger <NUM> stops the flow and there is no need to close off the line. Condensed gas flows further back to the tank and prevents excessive pressure increase in the tank. Also in this embodiment electric power is fed to the thermoelectric heat exchanger <NUM> for operation as described in preceding embodiments.

Claim 1:
An arrangement (<NUM>) for managing temperature of liquefied gas fuel in a fuel tank of a marine vessel (<NUM>), the arrangement (<NUM>) comprising
- a fuel tank (<NUM>),
- a main fuel feed line (<NUM>) extending from bottom area (<NUM>') of the fuel tank (<NUM>) to a gas consumer (<NUM>),
- a fuel transfer pump (<NUM>) arranged to the main fuel feed line (<NUM>),
- a first thermoelectric heat exchanger (<NUM>) comprising a first heat exchange fluid flow path (<NUM>') and a second heat exchange fluid flow path (<NUM>'), and a number of thermo electric generator cells (<NUM>) arranged in heat transfer communication with both the first heat exchange fluid flow path (<NUM>') and the second heat exchanger fluid flow path (<NUM>'), wherein
- the first heat exchange fluid flow path (<NUM>') being coupled to the main fuel feed line (<NUM>) downstream the fuel transfer pump (<NUM>),
- a second fuel line (<NUM>') being coupled to the second heat exchange fluid flow path (<NUM>'), the second fuel line (<NUM>') being arranged to lead fuel to the tank (<NUM>) via the first thermoelectric heat exchanger (<NUM>), characterized in that the second fuel line (<NUM>') is a branch line, which branches from the main fuel feed line (<NUM>) at a location downstream the fuel transfer pump (<NUM>) and which branch line (<NUM>') is arranged in flow connection with the tank (<NUM>) via the thermo electric heat exchanger (<NUM>) such that the second heat exchange fluid flow path (<NUM>') is coupled to the branch line (<NUM>').