A Hydrogen Generation Electricity System for Producing Electricity from Hydrogen Using a Hydrogen Carrier Substance and a Method for Operating the Hydrogen Generation Electricity System

A hydrogen generation electricity system for producing electricity from hydrogen using a hydrogen carrier substance, comprising: a reaction chamber arranged for generating a H2 gas stream by converting the hydrogen carrier substance; wherein the reaction chamber comprises an inlet arranged for receiving the hydrogen carrier substance; an output conduit for exiting the H2 gas stream; a fuel cell arranged for producing electric energy by converting hydrogen; the output conduit is arranged for supplying the H2 gas stream from the reaction chamber to the fuel cell; the system further comprising: a humidity determining unit arranged for determining a humidity level of the H2 gas stream; a water providing means for providing H2O to the reaction chamber; and a water vapour control means arranged for controlling the water vapour level in the reaction chamber, in response to the determined humidity level, wherein the generated H2 gas stream comprises hydrogen and water vapour.

FIELD OF INVENTION

The field of the invention relates to a hydrogen generation electricity system for producing electricity from hydrogen using a hydrogen carrier substance. The field of the invention further relates to a method for operating the hydrogen generation electricity system according to the invention.

BACKGROUND

A hydrogen generation electricity system for producing hydrogen using a hydrogen carrier substance is generally known. The hydrogen carrier substance may be a liquid hydrogen carrier substance, such as methanol and formic acid. The hydrogen generation system comprises a carrier reservoir for storing the hydrogen carrier substance, a reaction chamber arranged for generating a H2gas stream by converting the hydrogen carrier substance, wherein the H2gas stream comprises hydrogen. The reaction chamber comprises an inlet arranged for receiving the hydrogen carrier substance from the carrier reservoir. The system further comprises an output conduit for exiting the H2gas stream from the reaction chamber. In case of converting formic acid in the reaction chamber a H2gas stream is produced, which contains hydrogen gas and carbon dioxide gas.

Optionally, the output conduit of the hydrogen generation system may be directly coupled to a fuel cell. The fuel cell is arranged to produce electric energy by converting hydrogen. The output conduit supplies the H2gas stream from the reaction chamber to the fuel cell.

In general, a fuel cell demands a certain desired humidity level inside for operating effectively. The fuel cell produces electricity while forming water by converting the hydrogen gas and additional oxygen gas inside the fuel cell according to the reaction scheme H2+2O2->2 H2O. The output (gas) stream of the fuel cell contains water in a vapour phase, which output gas stream is (at least partly) used and transported back to the inlet of the fuel cell to maintain the humidity level inside the fuel cell at the desired humidity level. The output gas stream in general additionally contains remaining hydrogen and/or oxygen, which were not converted inside the fuel cell. The vapour content from the output gas stream needs to be separated from any remaining hydrogen and/or oxygen in the output gas stream before the vapour can be introduced into the fuel cell. In order to separate the vapour a NAFION membrane is used, which is a relatively expensive element. Additionally, a control on the vapour transport flow rate via the NAFION membrane to the fuel cell is limited.

Moreover, a desire exists to provide a system for producing electricity from hydrogen using a hydrogen carrier substance, which system enables an easy control of both a hydrogen content and a water (or vapour) level of a gas stream.

SUMMARY

According to a first aspect of the invention there is provided a hydrogen generation electricity system for producing electricity from hydrogen using a hydrogen carrier substance, the system comprising:

a reaction chamber arranged for generating a H2gas stream by converting the hydrogen carrier substance;

wherein the reaction chamber comprises an inlet arranged for receiving the hydrogen carrier substance;

an output conduit for exiting the H2gas stream from the reaction chamber;

a fuel cell arranged for producing electric energy by converting hydrogen;

and the output conduit is arranged for supplying the H2gas stream from the reaction chamber to the fuel cell;

the system further comprising

a humidity determining unit arranged for determining a humidity level of the H2gas stream;

a water providing means for providing H2O to the reaction chamber; and

water vapour control means arranged for controlling the water vapour level in the reaction chamber, in response to the determined humidity level, and

wherein the generated H2gas stream comprises hydrogen and water vapour.

According to another aspect of the invention there is provided a method for operating a hydrogen generation electricity system according to the invention, the method comprising the steps:

receiving in a reaction chamber a hydrogen carrier substance;

receiving water in the reaction chamber;

the reaction chamber generating a H2gas stream by converting the hydrogen carrier substance,

wherein the H2gas stream comprises hydrogen and water vapour;

a humidity determining unit determining a humidity level of the H2gas stream;

a water vapour control means controlling, in response to the determined humidity level, the water vapour level inside the reaction chamber;

a fuel cell producing electric energy by converting hydrogen, which is supplied by the H2gas stream to the fuel cell.

The hydrogen generation electricity system of the invention has the advantage that a H2gas stream may be produced by the system containing hydrogen and a suitably controlled water vapour concentration for a fuel cell. The water vapour concentration may be suitably controlled by the hydrogen generation system to be within a target vapour concentration range. The hydrogen generation system controls the formation of hydrogen by converting the hydrogen carrier substance and thereby may control the hydrogen concentration of the H2gas stream. Water is provided inside the reaction chamber by the water providing means. The water vapour control means is arranged for controlling the water vapour level in the reaction chamber, in response to the determined humidity level. The water vapour level in the reaction chamber determines the humidity level of the H2gas stream.

In embodiments, the water vapour control means controls the water vapour concentration of the H2gas stream by suitably controlling at least one of an internal gas pressure of the reaction chamber and a reaction temperature of the reaction chamber. The internal gas pressure of the reaction chamber and a reaction temperature of the reaction chamber affect an evaporation process of the water inside the reaction chamber, thereby controlling the water vapour concentration of the H2gas stream, which exits the reaction chamber. The reaction temperature is the temperature inside the reaction chamber where the hydrogen gas is formed.

In an embodiment, the water vapour control means is arranged for controlling the humidity level of the H2stream to be within a target vapour concentration range. In a preferred embodiment, the target vapour concentration range is selected for a fuel cell.

In an embodiment, the hydrogen carrier substance is liquid at room temperature.

In a particular embodiment, the hydrogen carrier substance is selected from formic acid and methanol and mixtures thereof. In a preferred embodiment, the hydrogen carrier substance is formic acid.

In an embodiment, the hydrogen generation system further comprises a fuel cell arranged for producing electric energy by converting hydrogen; and the output conduit is arranged for supplying the H2gas stream from the reaction chamber to the fuel cell.

In an embodiment, the water vapour control means comprises at least one of:

a pressure control unit for controlling the internal gas pressure of the reaction chamber; and

a temperature control unit for controlling the reaction temperature of the reaction chamber.

In an embodiment, the water vapour control means comprises a central control unit to control said at least one of a pressure control unit and a temperature control unit.

In an embodiment, the pressure control unit comprises a pressure valve arranged at the output conduit of the H2gas stream to control the internal gas pressure of the reaction chamber.

In an embodiment, the water providing means comprises at least one of:

a gas supply unit arranged for providing a gas stream comprising water vapour to the reaction chamber;

a water supply unit arranged for providing a liquid stream comprising water to the reaction chamber; and

wherein the system comprises a carrier reservoir for storing a hydrogen carrier composition comprising the hydrogen carrier substance and water, wherein the inlet of the reaction chamber is arranged for receiving the hydrogen carrier composition including water from the carrier reservoir. In a particular embodiment, as water providing means a combination is used of at least two of the gas supply unit, the water supply unit and a hydrogen carrier composition arranged inside the carrier reservoir which comprises an amount of water in addition to the hydrogen carrier substance.

In an embodiment, wherein the hydrogen carrier substance is liquid at room temperature, the water vapour control means is arranged for controlling a surface level of the reaction mixture inside the reaction chamber. In particular, the water vapour control means controls the surface level of the reaction mixture to maintain the surface level within a predetermined height range. In this way, an overflowing of the reaction chamber may be prevented. The water vapour control means may select at least one of the internal gas pressure of the reaction chamber and the reaction temperature of the reaction chamber to maintain the surface level within a predetermined height range.

In an embodiment, the H2gas stream comprises hydrogen and water vapour. The H2gas stream may additionally contain other reaction products. In an example, when formic acid is converted additionally carbon dioxide is formed, which exits the reaction chamber in the H2gas stream.

In an embodiment, the humidity determining unit comprises at least one of:

a sensor arranged at the output conduit of the H2stream; and

a level sensor unit arranged for sensing a surface level of a liquid reaction mixture comprising the hydrogen carrier substance inside the reaction chamber, wherein the humidity determining unit is arranged to calculate the humidity level based on the measured surface level.

The liquid reaction mixture contains the hydrogen carrier substance and water. In a specific example, the liquid reaction mixture may further contain a catalyst for catalyzing the conversion reaction of the hydrogen carrier substance.

In an example, the humidity determining unit may determine the humidity level based on a known supply of liquid hydrogen carrier substance and water to the reaction chamber, while the surface level is substantially held constant.

In another example, the humidity determining unit may determine the humidity level based on a known outflow rate of H2gas stream having hydrogen gas including water vapour from the reaction chamber, while the surface level is substantially held constant.

In an embodiment, the humidity determining unit is arranged to provide a signal for indicating the humidity level to the water vapour control means.

In an embodiment, the system comprises a carrier reservoir for storing the hydrogen carrier substance, wherein the inlet of the reaction chamber is arranged for receiving the hydrogen carrier substance from the carrier reservoir.

In an embodiment, the hydrogen carrier substance has a freezing temperature between 0 and 20 degrees Celsius. Preferably the hydrogen carrier substance is formic acid.

In a particular embodiment, the hydrogen generation system further comprises a freezing control unit for controlling a water supply to the carrier reservoir in response to a measured ambient temperature.

In an embodiment, the hydrogen generation system further comprises a conduit for delivering the water supply to the carrier reservoir.

In an embodiment, the hydrogen generation system further comprises a temperature sensor arranged for measuring the ambient temperature.

In an embodiment, the hydrogen generation system further comprises a water concentration determining unit for determining a water concentration of a hydrogen carrier composition containing the hydrogen carrier substance and an amount of water in the carrier reservoir.

In an embodiment, the water concentration determining unit may be a sensor for sensing the water concentration of the hydrogen carrier composition, and may be an input device for receiving a signal indicating the water concentration of the hydrogen carrier composition, such as by an input signal provided by an operator of the system.

In an embodiment, the water vapour controlling step comprises controlling at least one of an internal gas pressure of the reaction chamber and a reaction temperature of the reaction chamber in order to control the humidity level of the H2gas stream.

In an embodiment, the water vapour control means controls the humidity level of the H2gas stream to be within a target vapour concentration range.

In an embodiment, the target vapour concentration range is a dew point range from −70 degrees Celsius to 100 degrees Celsius at 1 bar. Preferably, the target vapour concentration range is a dew point range from 0 degrees Celsius to 80 degrees Celsius at 1 bar, more preferably from 30 degrees Celsius to 60 degrees Celsius at 1 bar.

In an embodiment, the hydrogen generation system further comprises a fuel cell, the method further comprising the step of the fuel cell producing electric energy by converting hydrogen, which is supplied by the H2gas stream to the fuel cell.

In an embodiment, wherein, in case a humidity level of the H2gas stream is lower than the target vapour concentration range, an internal gas pressure is decreased and/or a reaction temperature is increased, and wherein, in case a humidity level of the H2stream is higher than the target vapour concentration range, the internal gas pressure is increased and/or the reaction temperature is decreased.

In an embodiment, the temperature of the H2gas stream supplied to a fuel cell is maintained above the Dew point level of the H2gas stream during transport to the fuel cell. This prevents any loss of water vapour during the transport to the fuel cell.

In an embodiment, said reaction mixture is an aqueous solution comprising a formate salt.

In an embodiment, the reaction mixture additionally comprises a catalyst.

In a particular embodiment, said catalyst comprises a complex of the formula:

in which,

M is a metal selected from Ru, Rh, Ir, Pt, Pd, and Os, preferably Ru;

n is in the range of 1-4;

L is a carbene, or a ligand comprising at least one phosphorus atom, said phosphor atom being bound by a complex bond to said metal, the phosphorus ligand further comprising at least an aromatic group and a hydrophilic group, wherein,

if n>1, each L may be different from another L;

wherein the complex of formula (I) optionally comprises other ligands and is provided in the form of a salt or is neutral.

In embodiments a reaction temperature range of the reaction chamber is 20-200 degrees Celsius and/or the internal pressure in said reaction chamber is in the range of 1-1200 bar. Preferably, said reaction temperature range is 40-150 degrees Celsius.

Preferably, a partial pressure of said hydrogen is in the range of 0.5-600 bar.

Optionally, a partial pressure of carbon dioxide is in the range of 0.5-600 bar.

Preferably, a total internal gas pressure of the reaction chamber is in the range of 0.1-16 bar.

In another aspect of the invention a hydrogen generation system is provided for producing hydrogen using a hydrogen carrier substance, the system comprising:

a reaction chamber arranged for generating a H2gas stream by converting the hydrogen carrier substance;

wherein the reaction chamber comprises an inlet arranged for receiving the hydrogen carrier substance;

an output conduit for exiting the H2gas stream from the reaction chamber;

the system further comprising

a humidity determining unit arranged for determining a humidity level of the H2gas stream;

a water providing means for providing H2O to the reaction chamber; and

a water vapour control means arranged for controlling, in response to the determined humidity level, the water vapour level inside the reaction chamber,

wherein the generated H2gas stream comprises hydrogen and water vapour and

wherein the H2gas stream is suitable for fueling a fuel cell.

In another aspect of the invention a method is provided for operating an hydrogen generation system according to the invention, the method comprising the steps:

receiving in a reaction chamber a hydrogen carrier substance;

receiving water in the reaction chamber;

the reaction chamber generating a H2gas stream by converting the hydrogen carrier substance,

wherein the H2gas stream comprises hydrogen and water vapour;

a humidity determining unit determining a humidity level of the H2gas stream;

a water vapour control means controlling, in response to the determined humidity level, the water vapour level inside the reaction chamber,

wherein the H2gas stream is suitable for fueling a fuel cell.

In another aspect of the disclosure a hydrogen generation system is provided for producing hydrogen using a hydrogen carrier substance, the system comprising:

a carrier reservoir for storing the hydrogen carrier substance;

a reaction chamber arranged for generating a H2gas stream by converting the hydrogen carrier substance, wherein the H2gas stream comprises hydrogen, wherein the reaction chamber comprises an inlet arranged for receiving the hydrogen carrier substance from the carrier reservoir;

an output conduit for exiting the H2gas stream from the reaction chamber;

the system further comprising:

a water supplying means for supplying H2O to the carrier reservoir; and

a freezing control unit arranged for controlling the supply of water by the water supplying means to the carrier reservoir in response to a measured ambient temperature.

The freezing control unit controls the supply of water by the water supplying means to the carrier reservoir in order to prevent or limit a freezing of the hydrogen carrier substance inside the carrier reservoir. In case a measured ambient temperature decreases, such as below a predetermined threshold, the freezing control unit may control the supply of water by the water supplying means to the carrier reservoir in order to increase a water concentration of a hydrogen carrier composition containing the hydrogen carrier substance and water. Preferably, the hydrogen carrier substance and water form a homogeneous mixture.

In embodiments, the hydrogen carrier substance has a freezing temperature between 0 and 20 degrees Celsius. Preferably the hydrogen carrier substance is formic acid.

In a particular embodiment, the hydrogen generation system further comprises a freezing control unit for controlling a water supply to the carrier reservoir in response to a measured ambient temperature.

In an embodiment, the hydrogen generation system further comprises a conduit for delivering the water supply to the carrier reservoir.

In an embodiment, the hydrogen generation system further comprises a temperature sensor arranged for measuring the ambient temperature.

In an embodiment, the hydrogen generation system further comprises a water concentration determining unit for determining a water concentration of a hydrogen carrier composition containing the hydrogen carrier substance and an amount of water in the carrier reservoir.

In an embodiment, the water concentration determining unit may be a sensor for sensing the water concentration of the hydrogen carrier composition, and may be an input device for receiving a signal indicating the water concentration of the hydrogen carrier composition, such as by an input signal provided by an operator of the system.

DESCRIPTION OF EMBODIMENTS

System1is arranged for producing hydrogen by dehydrogenation of formic acid. The system1comprises a reactor vessel3, an inflow conduit13, a pump15and a temperature control arrangement17. The reactor vessel3comprises a reaction chamber5that is bound by a reactor wall7. The reactor wall7comprises a lower side wall27and an upper side wall23. The upper side wall23is provided with a gas outflow opening25for allowing hydrogen originating from a reaction mixture, comprising formic acid and a catalyst, to exit the reaction chamber5via the gas outflow opening25. Exiting of the hydrogen from the reaction chamber5may be restricted by a pressure valve arrangement31. The pressure valve arrangement31is arranged for controlling the internal pressure of the reaction chamber5by controllingly allowing the hydrogen gas stream originating from the reaction chamber5to pass the pressure valve arrangement31. The lower side wall27comprises a mixture outflow opening11that is provided in a centre part of a bottom side of the reactor vessel3.

The reactor vessel3is arranged for holding a reaction mixture of the catalyst, the formic acid and water in the reaction chamber5. The reactor vessel3comprises a mixture inflow opening9for allowing the reaction mixture to enter the reaction chamber5via the mixture inflow opening9. In the reaction chamber5a stationary flow organ29is provided at or near the reactor wall7. The flow organ29extends along substantially the complete height of the reaction chamber5. In an embodiment of the system1it is conceivable that the flow organ extends only along a lower half of the height of the reaction chamber5.

The reactor vessel3is provided with a further inflow opening21that is arranged for introducing the formic acid, from a carrier reservoir35, in the reactor vessel3for forming the reaction mixture. The carrier reservoir35is coupled for fluid flow to the reaction chamber5via a further pump37. The further pump37is arranged for pumping the formic acid from the carrier reservoir35into the reaction chamber5.

The reactor wall7comprises a plastic that is coated on a side of the plastic facing the reaction chamber5with polytetrafluoroethylene for thermally insulating the reactor vessel13and shielding the reaction mixture from the plastic of the reactor wall7that may otherwise degrade the catalyst present in the reaction chamber5. The reactor wall7further comprises a replaceable wall element33. The replaceable wall element33comprises a metal for locally reinforcing the reactor wall7. The replaceable wall element33is coated on a side of the replaceable wall element33facing the reaction chamber5with polytetrafluoroethylene for thermally insulating the reactor vessel13and shielding the reaction mixture from the metal of the replaceable wall element33that may otherwise degrade the catalyst present in the reaction chamber5. In an embodiment of the system1it is conceivable that the reactor wall is locally reinforced by a fixed wall element in addition to, or as an alternative of, the replaceable wall element33.

The inflow conduit13is communicatively coupled for fluid flow, via said mixture inflow opening9, to said reaction chamber5. The inflow conduit13is arranged such that said reaction mixture, in use, is introduced in said reaction chamber5, via said mixture inflow opening9, in a predetermined direction having a tangential component T for stirring39, in use, said reaction mixture in said reaction chamber5. In other words, the reaction mixture is introduced in a direction along the reactor wall7, wherein said direction of introduction has the tangential component T.

The pump15is communicatively coupled for fluid flow, via the mixture inflow opening9and the mixture outflow opening11, to the reaction chamber5. The pump15is arranged for withdrawing, via the mixture outlet opening11, the mixture from the reaction chamber5and introducing, via the inflow conduit13and the inflow opening9, the mixture into the reaction chamber5.

The temperature control arrangement17is communicatively coupled for fluid flow to said pump15and arranged for heating and/or cooling the reaction mixture withdrawn from the reaction chamber5. The temperature control arrangement17is further arranged for cooling and/or heating a part of the reaction mixture present in the temperature control arrangement17to be cooled and/or heated to a predetermined temperature in the range of 70 to 150 degrees Celsius before introducing, via the inflow conduit13, the part of the reaction mixture into said reaction chamber5.

The system1comprises a control unit41, a measurement unit43and a humidity determining unit45. The control unit41is communicatively coupled to said temperature control arrangement17, the pump15and the measurement unit43. The control unit41is arranged for controlling the temperature control arrangement17and the pump15in dependence of a temperature of the reaction mixture, in use present in the reaction chamber5and/or the temperature control arrangement17, measured by the measurement unit43.

The system1further comprises a water providing means for providing H2O to the reaction chamber5. The water providing means may be embodied as a gas supply unit arranged for providing a gas stream comprising water vapour to the reaction chamber5. The water providing means may be embodied as a water supply unit arranged for providing a liquid stream comprising water to the reaction chamber5. The control unit41is arranged to control said gas supply unit and/or said water supply unit to controllably supply water to the reaction chamber5. Alternatively or additionally, the system1the carrier reservoir35stores a formic acid composition comprising the formic acid and water at a certain concentration. The supply of the formic acid composition including water to the reaction chamber5is used as water providing means. Thus, by controlling the pump37the supply of formic acid and the supply of water to the reaction chamber is controlled.

The system1further comprises a water vapour control means arranged for controlling the water vapour level in the reaction chamber, in response to the determined humidity level. The water vapour control means may comprise the pressure valve arrangement31for controlling the internal gas pressure of the reaction chamber and the temperature control arrangement17for controlling the reaction temperature of the reaction chamber. In particular, the water vapour control means further comprises the control unit41to control said pressure valve arrangement31and temperature control arrangement17to control the water vapour level in the reaction chamber.

Method101is arranged for hydrogen production by converting a hydrogen carrier substance, such as by dehydrogenation of formic acid. The method101comprises the step of providing said formic acid103into said reaction chamber5. Additionally, the method101comprises the step of providing water105into said reaction chamber5.

In an embodiment of the method101, said providing of said water105and said formic acid103may be executed in one step104when the formic acid stream is a formic acid mixture, which contains formic acid and a predetermine concentration water. In an alternative or additional embodiment of the method101, said providing of said water may be executed in step105independently of the step of providing said formic acid103into said reaction chamber5. In other words the formic acid and the water may be provided in said reaction chamber during different steps, to allow said formic acid103and said water105to be stored separately and to be supplied independently to the reaction chamber5.

The step of providing of said water step105may be embodied by a gas supply unit, which supplies a gas stream comprising water vapour to the reaction chamber; and may be embodied by a water supply unit which supplies a liquid stream comprising water to the reaction chamber. In specific embodiment, both gas supply unit and water supply unit may be used to supply water to the reaction chamber5.

In another embodiment, a step of providing of said water step105may be combined with a step of providing water in the formic acid stream104.

The method101further comprises a step107of converting the hydrogen carrier substance, such as by dehydrogenation of formic acid, thereby forming a gas stream comprising hydrogen. The H2gas stream exits the reaction space5via the gas outflow opening25to the output conduit26.

The method101further comprises a step109of determining a humidity level of the H2gas stream by humidity determining unit45. In an example, a humidity sensor is coupled to the output conduit26for measuring the humidity level of the H2gas stream. The humidity sensor sends a signal to the control unit41indicating the humidity level of the H2gas stream.

In another example, a surface level sensor is provided at the reaction chamber5and is arranged to measure the liquid surface level of the reaction mixture in the reaction chamber5. The humidity determining unit45determines the humidity level of the H2gas stream based on the measured surface level (height). The operation of the surface level sensor is further explained below in the examples section.

The method101further comprises a step111of controlling, in response to a signal of the humidity determining unit45provided to the control unit41, at least one of an internal gas pressure of the reaction chamber and a reaction temperature of the reaction chamber in order to control the humidity level of the H2gas stream. Thus, step111may comprise a step of controlling the internal gas pressure of the reaction chamber111aand may comprise a step of controlling the reaction temperature of the reaction chamber111b, or may comprise a combination of step111aand step111b. The control unit41may decide which of the steps111a,111bis used in any combination. Specifically, the control unit41may select the steps111aand111bdepending on other desired attributes of the H2gas stream, such as hydrogen production flow rate, and on attributes of the reaction chamber and reaction mixture, such as operating temperatures of the reaction chamber.

In example, the internal gas pressure of the reaction chamber is controlled by the pressure valve arrangement31. The pressure valve arrangement31is controlled by the control unit41to control, if needed to adjust, the actual internal gas pressure to be a target internal gas pressure. The target internal gas pressure of the reaction chamber is determined by the control unit41and is selected to control the humidity level of the H2gas stream.

Alternatively, the internal gas pressure of the reaction chamber may be controlled in any other suitable way to control the humidity level of the H2gas stream.

In an example, the reaction temperature of the reaction mixture in the reaction chamber5is controlled by the temperature control arrangement17as indicated above. The temperature control arrangement17is controlled by the control unit41to control, if needed to adjust, the reaction temperature to be a target reaction temperature. The target reaction temperature of the reaction chamber is determined by the control unit41and is selected to control the humidity level of the H2gas stream.

In this example, step111bmay comprises a step205of withdrawing, by said pump15, said provided catalyst and said formic acid from said reaction chamber5. Subsequently, said reaction mixture, withdrawn during said step205, is heated and/or cooled, during a step207of heating and/or cooling, by said temperature control arrangement17, to said target reaction temperature. As said, said target reaction temperature is determined by the control unit and is selected to control the humidity level of the H2gas stream.

After said heating and/or cooling during said step207, said heated and/or cooled mixture is introduced, during a step209of introducing, via said inlet opening9, into said reaction chamber5. During the step209of introducing, the mixture is introduced into the reaction chamber5in the predetermined direction having the tangential component T for stirring39, in use, said mixture in said reaction chamber5. In other words, the mixture is introduced in a direction along the reactor wall7, wherein said direction of introduction has the tangential component T.

Alternatively, the reaction temperature of the reaction mixture may be controlled in any other suitable way to control the humidity level of the H2gas stream.

In a specific example, the reaction mixture inside the reaction chamber5comprises a catalyst comprising a complex of the formula

in which,

M is a metal selected from Ru, Rh, Ir, Pt, Pd, and Os, preferably Ru;

n is in the range of 1-4;

L is a carbene, or a ligand comprising at least one phosphorus atom, said phosphor atom being bound by a complex bond to said metal, the phosphorus ligand further comprising at least an aromatic group and a hydrophilic group, wherein, if n>1, each L may be different from another L;

wherein the complex of formula (I) optionally comprises other ligands and is provided in the form of a salt or is neutral.

InFIG.5another system100is disclosed. The system100is based on system1and comprises the same components as system1shown inFIG.1. The system100may in embodiments be with or without the humidity determining unit45, the water providing means and the water vapour control means as described in relation to system1.

The system100additionally comprises a freezing control unit55and a water supplying means51for supplying H2O to the carrier reservoir. The water supplying means51may be a water reservoir and a valve for controllably supplying water from the water reservoir to the carrier reservoir35. The freezing control unit55is arranged for controlling the supply of water by the water supplying means51to the carrier reservoir in response to a measured ambient temperature.

The system100may further comprise an ambient temperature sensor for measuring the ambient temperature. In an example, in case the ambient temperature decreases below a threshold temperature, the freezing control unit55may select an amount of water to supply by the water supplying means51to the carrier reservoir.

The freezing control unit55may calculate, e.g. based on a determined volume of the formic acid mixture inside the carrier reservoir35, how much water needs to be added to the carrier reservoir35, to form a formic acid mixture having sufficient water concentration to prevent a freezing of the stored formic acid mixture. The freezing temperature of a formic acid mixture comprising water is generally known to a skilled person.

In embodiments, the freezing control unit55may be part of the control unit41.

In embodiments, the system100further comprises a water concentration determining unit for determining a water concentration of a hydrogen carrier composition, containing the hydrogen carrier substance and an amount of water, inside the carrier reservoir5.

In each of the embodiments disclosed inFIGS.1-5, the system1,100may additionally comprise a fuel cell arranged for producing electric energy by converting hydrogen, and wherein the output conduit26is arranged for supplying the H2gas stream from the reaction chamber5to the fuel cell. The H2gas stream is maintained at a temperature above a dew point of the H2gas stream between the reaction chamber5and the fuel cell in order to prevent a loss of water vapour from the H2gas stream.

The following, non-limiting examples are provided to illustrate the invention.

Example

As an example of the present invention of operating the system1, formic acid is supplied from the carrier reservoir35to the reaction chamber5at a flow rate of 0.73 l/minute. The reactor chamber5has a reaction temperature of 95 degrees Celsius and an internal pressure of 12 bar. The reaction temperature of 95 degrees Celsius and the internal pressure of 12 bar determine the water vapour level of the gas above the liquid reaction mixture inside the reaction chamber5. At the same time the flow of water vapour exiting the reaction chamber is 2.03 kg/hr (at a water vapour level being a dew point of 95 degrees Celsius at 12 bars or a dew point of 39.17 degrees Celsius at 1 bar).

In case the reaction chamber5contains too much water, such as 2 liter water excess, then for a certain period, the reaction temperature is held 100 degrees Celsius and the internal pressure at 10 bar to provide a flow of water vapour exiting the reaction chamber of 2.88 kg/hr (at a water vapour level or dew point of 100 degrees Celsius at 10 bars or 46.14 degrees Celsius at 1 bar). The water vapour level is determined by the reaction temperature and the internal pressure under the condition that sufficient water is present in the reaction mixture to form the water vapour inside the reaction chamber at said conditions.

After a little more than 2 hours the 2 liter water excess has been removed from the reaction chamber.

This estimation is based on calculations of the vapour pressure in gas mixtures containing hydrogen gas and carbon dioxide gas (each 50 weight-%).

Stabilized Conditions

Relevant is the surface level of the reaction mixture inside the reaction chamber. This means that if the surface level increases, the amount of water entering the reaction chamber is higher then the amount of water that exits the reaction chamber. By increasing the reaction temperature or decreasing the internal pressure the surface level can be dropped.

The stabilized conditions presume that the supply flow of formic acid into the reaction chamber is equal to the conversion rate of the formic acid at said reaction conditions.

Output Values

For a system which converts formic acid and delivers the H2gas stream to a fuel cell, typical output values of the system are:

The dew point level of the H2gas stream is determined by the reaction temperature and the internal pressure of the reaction chamber.

Dynamic Processes

The first target is to achieve a constant surface level (meaning a constant water amount) in the reaction chamber. During a start-up condition, the reaction temperature is relatively low. Assumed is a constant supply of water using a formic acid composition having 99 weight-% formic acid and 1 weight-% of water. As such, the internal pressure needs to be kept low to prevent that the surface level in the reaction chamber raises during start-up condition above a certain threshold and/or a flow rate of supply of the formic acid composition is kept low during the start-up condition.

When the reaction chamber achieves operational temperatures (>60 degrees Celsius) then the control unit selects settings to achieve stabilized conditions.

The surface level (level height in the reactor) is monitored over time. If it changes over time, for example the surface level decreases, the reaction temperature should be lowered and the internal pressure should be increased. The operation window is in between 90-110 degrees Celsius and in between 5 and 16 barg internal pressure. This allows the system to achieve a Dew point level in between 40 and 90 degrees (at 1 bar). The temperature of the H2gas stream to a fuel cell is maintained above the Dew point level of the H2gas stream during transport to a fuel cell, to prevent any loss of water vapour during the transport to the fuel cell. Preferably, the H2gas stream has to be kept on at least 50 degrees Celsius on operational status to prevent any loss of water vapour.

The time it takes to reach stabilized conditions is depending on how much the surface level deviates from a desired surface level. Usually it may take from minutes up to some hours, depending of the volume of the reaction chamber and the start-up conditions (T, p) of the reaction chamber.

Water Concentration Determination of H2Gas Stream

This could be achieved by a humidity measurement in the H2gas stream before for example a fuel cell. Humidity sensors are commercial available. Another way of determining the humidity level is by measuring the temperature of the H2gas stream. This usually gives a good representation of the maximum dew point of the gas. If the output is thermally isolated from the reaction chamber, the dew point of the H2gas stream could be monitored with a simple temperature sensor.

A preferred way to determine the water concentration of H2gas stream is by using a surface level determining of the reaction mixture inside the reaction chamber. To determine a height of the surface level a floating element is used. Alternatively, a radar system may be used to determine the surface level in the reactor. Another option is to use temperature sensors in order to measure the surface level. At the interface between the gas and the fluid a temperature difference is present. This allows to place multiple temperature sensors in the wall of the reaction chamber and based on the temperature distribution in the reaction chamber it is possible to measure the height of the surface level.

If the surface level stays stable one can calculate based on the reaction temperature and the internal pressure how much water exits the reaction chamber and thus how much enters the reaction chamber.

Freezing Point Formic Acid Composition

The freezing point fp, of a formic acid composition containing formic acid and an amount of water is shown in the Table below:

Depending on the measured ambient temperature a molar fraction of water inside the formic acid composition containing formic acid and water may be adjusted to prevent freezing of the formic acid composition at said ambient temperature.

It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative units or modules embodying the principles of the invention.

Whilst the principles of the invention have been set out above in connection with specific embodiments, it is to be understood that this description is merely made by way of example and not as a limitation of the scope of protection which is determined by the appended claims.