Patent Application
20250042729
The present invention relates to a method for starting up a reactor for producing a hydrogen containing gas, and the system for making such. The method and system are designed to decompose a substance to release hydrogen, which hydrogen can be used by for example a fuel cell to generate power.
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 H2 gas stream by converting the hydrogen carrier substance, wherein the H2 gas 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 H2 gas stream from the reaction chamber. In case of converting formic acid in the reaction chamber a H2 gas 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 H2 gas stream from the reaction chamber to the fuel cell.
In US-A-20180337416 a portable energy generation device is disclosed to convert formic acid into released hydrogen, alleviating the need for a hydrogen tank as a hydrogen source for fuel cell power. A disadvantage of the apparatus and method described is that it is an early stage design.
To bring the technology to the market, there are still some problems to be solved or systems to be improved. A disadvantage of the above described energy generation system is that the design makes it such that the gas quality that is being produces is less, resulting in poor applicability possibilities. Another disadvantage is that the efficiency requires improvement. A further disadvantage is that this system cannot be easily used for scale up for bigger applications.
Accordingly, there is a demand for a process and system to generate power that is flexible and portable, and ready to commercialize. There is furthermore a demand for a system that produces hydrogen containing gas with a higher purity.
It is an object of the present invention to provide a method for starting up a reactor for producing a hydrogen containing gas and subsequently maintaining the reactor at a working temperature. A fuel cell is fluidly connected to the reactor downstream thereof and to a catalytic afterburner upstream thereof. The method comprises the following steps:
By using the hydrogen that is stored in the system itself, it is not required to use an additional heat source for starting up the process. Furthermore, by converting hydrogen in for example a fuel cell to generate electricity has a lower efficiency than catalytically burning of the hydrogen. Thus starting the process with the catalytic afterburner instead of for example electric heaters improves the total efficiency of the system significantly. Once the working temperature of the reactor is reached, it can be maintained by leading the hydrogen containing gas from the reactor via the fuel cell to the catalytic afterburner. The fuel cell can produce electricity for an external load.
The present invention also relates to a system for starting up a reactor for producing a hydrogen containing gas. It is thus a further object of the present invention to provide a system for decomposing a fuel comprising: a vessel for storing a hydrogen containing gas; a reactor for producing a hydrogen containing gas; a catalytic afterburner for burning the hydrogen containing gas from the vessel and/or from the reactor intermixed with an oxygen containing gas, such as air, to create heat and an exhaust gas, the catalytic afterburner being in fluid communication with the reactor and with the vessel; means for supplying the oxygen containing gas, such as air, to the catalytic afterburner; and means for supplying heat from the catalytic afterburner to the reactor.
It is also an object of the present invention to provide a system for reforming a fuel comprising: a vessel for storing a hydrogen containing gas, wherein the vessel is a reactor for producing a hydrogen containing gas; a catalytic afterburner for burning the hydrogen containing gas from the vessel to create heat and an exhaust gas, the catalytic afterburner being in fluid communication with the vessel; means for supplying air to the catalytic burner; and means for supplying heat from the catalytic afterburner to the reactor.
The above systems in particular further comprise:
These systems enable a convenient implementation of the method according to the invention. Such implementation can be under manual control, partial automatic control or be fully automated.
The system may comprise a temperature sensor arranged with the reactor to detect the temperature of the reactor. The system may be configured to control the bypass valve based on the detected reactor temperature. Measurements of the temperature sensor may directly act upon the bypass valve or via a controller of the system. For example, a controller, e.g. processor or microchip, can be configured to receive the detected reactor temperature from the temperature sensor and on the basis of the received temperature control the bypass valve. The controller may control the bypass valve to switch from directly providing hydrogen containing gas to the catalytic afterburner to providing hydrogen containing gas from the reactor to the fuel cell, which in turn leads to the catalytic afterburning to maintain the working temperature in the reactor.
Alternatively or additionally, such controller can be configured to control a fuel inlet into the reactor, e.g. when a predetermined threshold temperature is reached at which the reactor can produce hydrogen containing gas. In this way, an automated start-up from cold, via the predetermined temperature and to the working temperature of the reactor can be implemented.
It is understood that the predetermined temperature and the working temperature can be selected based on the fuel reforming process performed in the reactor, including parameters such as type of fuel, type of catalyst, and pressure.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
The present invention is thus related to fuel cell technology. When for example a fuel cell system starts from cold to generate electricity, heat input is required for the generation of hydrogen. At start up the reactor is not sufficiently warm to produce hydrogen gas, thus for start-up hydrogen from a storage vessel is used. As storage vessel the reactor itself can be used or a separate vessel can be used. The hydrogen is preferably released slowly by using a pressure regulator or a valve. This hydrogen is then preferably mixed with the right amount of air by for example injecting the hydrogen in the air stream via a gas divider (e.g. tube(s) with multiple small holes). The formed mixed exhaust gas/air mixture is passed through the catalytic afterburner, where hydrogen and oxygen react to create mainly heat and water (vapor). The increased temperature of the catalytic afterburner will improve the efficiency of the catalyst so once it has started it keeps itself going for as long that there is fuel and oxygen present. The advantage of this method is that the reactor can be heated entirely from the catalytic afterburner, thus for example no electric heaters are required during the reformer start-up.
The main function of the catalytic afterburner is to produce heat for heating up and keeping the reformer at the optimal reaction temperature. This is done by burning the hydrogen containing exhaust gas from the fuel cell and converting it to heat. Depending on the stoichiometry of for example a fuel cell in the range of from 20% up to 40% of the hydrogen that is produced in the reformer will not be converted to electricity, this gas may be catalytically burned in the catalytic afterburner with the means of a catalyst, for example a metallic foam coated with a catalyst, such as for example a platinum-coated FeCr-alloy foam.
A catalytic afterburner can advantageously operate at higher temperatures (e.g. in the range 250° C. to 400° C.) and with hydrogen containing gas of lower purity than a fuel cell. A fuel cell typically operates at roughly 70° C., which may be insufficient to heat the reactor to desired working temperatures. Further, CO may be present in the hydrogen containing gas from the vessel and/or reactor which would quickly deteriorate the effectiveness of the fuel cell by spoiling its catalytic membrane. However, a catalytic afterburner is not degraded by CO, nor by humidity or even water droplets in the gasses supplied to it. Though a fuel cell generally required additional purging hydrogen gas for efficient operation, a catalytic afterburner can convert practically all hydrogen supplied to it by adjusting the infeed of oxygen.
In a catalytic afterburner, a gas stream of hydrogen containing gas is mixed with a stream of oxygen containing gas such as air, and the mixture is catalytically combusted to produce heat and exhaust gas. In contrast, gas streams are separate in a fuel cell: a hydrogen containing gas is supplied to one side of membrane while an oxygen containing gas is supplied to the other side of a membrane.
The step of reacting the released hydrogen containing gas intermixed with oxygen containing gas, preferably air, in a catalytic afterburner to create heat and a heated exhaust, may comprise intermixing the hydrogen containing gas with the oxygen containing gas and supplying the resulting mixture to the catalytic afterburner. This mixing may be performed as before the gas streams are introduced into the catalytic afterburner, though it is also envisioned to mix these inside the catalytic afterburner upon introduction therein.
Preferably, the catalytic afterburner is the single burner used in the method.
It is not required to heat the reformer to its optimal working temperature to be able to convert formic acid to hydrogen. At a lower temperature the fuel, for example formic acid, is already converted. Thus the amount of hydrogen required to be stored is such that it is sufficient to heat it up to a temperature at which it is able to convert sufficient fuel to maintain a steady hydrogen supply to the catalytic afterburner to further increase the temperature of the reformer. Thus the amount of hydrogen stored, and related thereto the size of the storage vessel, is not so big that it contains all hydrogen gas needed to completely heat up to reformer to its optimum working temperature.
The predetermined temperature may be equal to or be lower than the working temperature.
For example, the working temperature is in the range of 90° C. to 130° C., preferably 90° C. to 110° C., more preferably 100° C.
For example, the predetermined temperature is at least 50° C. and/or in the range of 40° C. to 90° C., preferably 50° C. to 80° C.
When the system is shut-down the hydrogen storage vessel is preferably refilled with hydrogen generated in the reformer which still functions due to its residual heat. This hydrogen is preferably hereafter used in the next start-up sequence.
The hydrogen containing gas is stored in a vessel. Preferably, the vessel is the reactor. Alternatively, the vessel is a separate vessel. This requires additional space, but is in some cases the preferred option.
Preferably, a fuel cell is fluidly connected to the reactor downstream thereof and to the catalytic afterburner upstream thereof. In the fuel cell, the chemical energy of a fuel (e.g. hydrogen) and an oxidizing agent (e.g. oxygen) is converted in an electrochemical cell that converts into electricity through a pair of redox reactions. Fuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.
There are many types of fuel cells, but they all consist of an anode, a cathode, and an electrolyte that allows ions, often positively charged hydrogen ions (protons), to move between the two sides of the fuel cell. At the anode a catalyst causes the fuel to undergo oxidation reactions that generate ions (often positively charged hydrogen ions) and electrons. The ions move from the anode to the cathode through the electrolyte. At the same time, electrons flow from the anode to the cathode through an external circuit, producing direct current electricity. At the cathode, another catalyst causes ions, electrons, and oxygen to react, forming water and possibly other products. Fuel cells are classified by the type of electrolyte they use and by the difference in startup time ranging from 1 second for proton-exchange membrane fuel cells (PEM fuel cells, or PEMFC) to 10 minutes for solid oxide fuel cells (SOFC). Individual fuel cells produce relatively small electrical potentials, about 0.7 volts, so cells are “stacked”, or placed in series, to create sufficient voltage to meet an application's requirements. In addition to electricity, fuel cells produce water, heat and, depending on the fuel source, very small amounts of nitrogen dioxide and other emissions. The energy efficiency of a fuel cell is generally between 40 and 60%.
The fuel cell that is preferably used is a proton-exchange membrane fuel cell (PEMFC), a phosphoric acid fuel cell (PAFC), a solid acid fuel cell (SAFC), an alkaline fuel cell (AFC), a high-temperature fuel cell, or an electric storage fuel cell, more preferably a proton-exchange membrane fuel cell (PEMFC), even more preferably a low temperature proton-exchange membrane fuel cell (PEMFC).
Advantageously, there is a bypass that fluidly and directly connects the reactor to the catalytic burner. Advantageously, the vessel wherein hydrogen is stored is a separate vessel and is located in the bypass.
The heat of the hotter exhaust gas from the catalytic burner is preferably transported to the colder liquid in the reactor. Advantageously, the heated exhaust gas is introduced in a heat exchanger to transfer heat to the reactor in order to heat the reactor to a predetermined temperature. More preferably, more heat exchangers are being used in order to heat the reactor to a predetermined temperature.
Advantageously, in the method of the present invention, during start-up hydrogen containing gas bypasses the fuel cell and subsequently when the reactor has reached a working temperature of at least 50° C. the hydrogen gas flows through the fuel cell prior to being introduced into the catalytic afterburner.
In some cases, it is preferred to also use an electric heater to partly heat up the reactor to a temperature at which it is able to convert fuel to a hydrogen containing gas. This might be useful the very first time the whole method and system is being started. Once it has been started for the first time, always some hydrogen is present to start op the reactor.
Preferably, the hydrogen containing gas is mixed with an excess amount of air, such that a mixture with less than 15% hydrogen is created prior to reaction in the catalytic afterburner, more preferably less than 10% hydrogen, even more preferably less than 4% hydrogen. The catalytic afterburner is most preferably operated by mixing the exhaust gas with an excess of air to create a mixture with less than 4% hydrogen to keep it below the LFL at ambient pressure. Preferably, the hot air that is created after the catalytic burning is passed through a radiator to heat up a heat transfer liquid. This liquid might then be used to keep the reformer at the right temperature.
Preferably, the method according to the present invention provides the fuel as a liquid fuel and the fuel is introduced into the reactor with a catalyst to provide a mixture of liquid fuel and catalyst inside the reactor. This has as advantage that separation of gas from the liquid is better, as the reaction has taken place earlier in the process.
In an alternative embodiment, the method of the present invention provides the mixture of liquid fuel and catalyst that is withdrawn from the reactor to be introduced to a second heat exchanger that is provided externally of the reactor and externally of the catalytic afterburner, the second heat exchanger being fluidly connected with the first heat exchanger by means of a closed water loop, whereby
In a further embodiments, the method of the present invention provides the possibilities that air is transported directly through the reactor, preferably via one or more pipes, by which the reaction mixture is heated, or that a heat exchanger is placed inside the reactor that heats the reaction mixture. More preferably, the pipes have a small diameter to create an extensive surface, where heat exchange may be performed faster. A further possibility is that a heat exchanger is outside the reactor, and that the reaction mixture is pumped through this heat exchanger, to be heated to the desired reaction temperature. In another alternative set-up a combination of heat exchangers is used, and a heat exchange transfer liquid, e.g. a water loop.
To feed the fuel cell with hydrogen, formic acid is preferably used as hydrogen source in the reactor, thus the fuel fed to the reactor is preferably formic acid. Formic acid is a relatively non-toxic chemical. It is one of the major products formed in biomass processing and can be a convenient hydrogen carrier for fuel cells designed for portable electricity generation and use. The decomposition of formic acid into hydrogen is a promising way to solve the difficulty of hydrogen gas storage, which has severely limited the hydrogen economy. A sustainable cycle can be envisioned using formic acid to supply hydrogen.
To store hydrogen, hydrogen and CO2 are added together to form formic acid. To release hydrogen, formic acid is decomposed into hydrogen and CO2 in the reactor. The hydrogen storage density of formic acid is relatively high. Because formic acid is low in cost, nonflammable, readily available as exhaust from fuel cells, and contains only water and CO2, an automobile or other electricity-requiring device or system constructed based on the formic acid technology can be environmentally-friendly. The system is unlikely to explode or ignite. The technology can be used independently or integrated with electrical automobiles in order to provide an instant power source so that the long battery charging time can be avoided.
The present invention furthermore relates to a system for reforming a fuel comprising: a vessel for storing a hydrogen containing gas; a reactor for producing a hydrogen containing gas; a catalytic afterburner for burning the hydrogen containing gas from the vessel and/or from the reactor to create heat and an exhaust gas, the catalytic afterburner being in fluid communication with the reactor and with the vessel; means for supplying air to the catalytic afterburner; and means for supplying heat from the catalytic afterburner to the reactor.
Alternatively, the present invention relates to a system for reforming a fuel comprising: a vessel for storing a hydrogen containing gas, wherein the vessel is a reactor for producing a hydrogen containing gas; a catalytic afterburner for burning the hydrogen containing gas from the vessel to create heat and an exhaust gas, the catalytic afterburner being in fluid communication with the vessel; means for supplying air to the catalytic burner; and means for supplying heat from the catalytic afterburner to the reactor.
In a preferred embodiment, a fuel cell is fluidly connected to the reactor downstream thereof and to the catalytic afterburner upstream thereof.
In another embodiment, the means for supplying heat from the catalytic afterburner to the reactor comprise a first heat exchanger for heating the reactor by transferring heat from the exhaust gas, the first heat exchanger being located externally and separately from the catalytic afterburner.
Preferably, a bypass fluidly and directly connects the reactor to the catalytic burner. It is then preferred that the vessel for storing the hydrogen is a separate vessel and is located in the bypass.
The system according to the present invention, further preferably comprises a bypass valve that allows to switching between directly and fluidly connecting the reactor to the catalytic afterburner and fluidly connecting the reactor to the fuel cell.
The system according to the present invention, further preferably comprises an electric heater for partly heating up the reactor to a temperature at which it is able to convert fuel to a hydrogen containing gas. This might be useful the very first time the whole method and system is being started. Once it has been started for the first time, always some hydrogen is present to start op the reactor.
Preferably, the system according to the present invention, further has the reactor comprising one or more inlets for introducing a liquid fuel and a catalyst, such that the reactor can be filled with a mixture of liquid fuel and a catalyst.
In a further preferred embodiment, the system further comprises:
Preferably, the heat transfer liquid is water, glycol or oil.
The following non-limiting figures show the present invention further.
In
In
The following, non-limiting examples are provided to illustrate the invention. Various system components can be coupled to a controller to allow automated implementation of the method of the invention, including the bypass valve (V1), the proportional valve (V2), the fuel feed (P1), and the heat transfer liquid pump (P2). For example, the system may comprise a temperature sensor coupled to the reactor and a controller configured to control the bypass valve based on a temperature signal received from the temperature sensor. The system may be configured to perform the method of the invention, even in an automated manner.
To test the working of the invention, a number of situations were computer modeled. In this first modulation, the assumed starting state was a reactor that is 10° C. and the pressure inside the reactor is 15 bar. At startup the bypass valve (V1) is switch from the fuel cell to the catalytic heater, so that the gas flow will not pass through the fuel cell. Then the catalytic heater blower is started and the catalytic block is preheated if necessary (maybe needed during the winter). The back pressure regulator (BPR) is slightly opened to the point that the H2 flow is sufficient to power on the catalytic heater to the point that the required H2 flow is achieved. The valve is gradually opened further to compensate for the pressure lowering in the reactor. The heat transfer liquid pump (P2) is started to transfer the heat from the catalytic afterburner to the reactor. When the reactor reaches its working temperature of 100° C. the bypass valve is switched back to the fuel cell and the proportional valve (or back pressure regulator) is closed. Now the formic acid feed is started (P1) and the reactor can start producing more H2 (and CO2). The generation of the gas will increase the pressure back up to its pre specified working point, in this case of 15 bar. When the reactor is back at its working pressure the back pressure regulator can open again and the gas can pass through the fuel cell.
To shut down the reactor no special shut down procedure was needed because the reactor was already at pressure and was big enough to store all the needed hydrogen to start-up again a next time.
In this modulation, the assumed starting state was a reactor that is 10° C. and the pressure inside the reactor is 15 bar, and there is 1000 nL of H2 stored in the storage vessel at a pressure of 15 bar.
At startup the bypass valve (V1) was switched from fuel cell to catalytic heater, to prevent that the gas flow will pass through the fuel cell. The catalytic heater blower was started. The proportional valve (V2) was slightly opened to the point that the required H2 flow was achieved. Optionally the back pressure regulator can be opened to use the H2 (and thus the pressure) from the reactor as well. The valve was gradually opened further to compensate for the pressure lowering in the storage vessel. Then the heat transfer liquid pump (P2) was started to transfer the heat from the catalytic afterburner to the reactor. When the reactor reached its working temperature of 100° C. the bypass valve was switched back to the fuel cell and the proportional valve was closed. Then the formic acid feed was started (P1) and the reactor started producing more H2 (and CO2). In case the H2 in the reactor was used, the generation of the gas increased the pressure back up to its working point of 15 bar, otherwise the gas was immediately transferred to the fuel cell, by opening the back pressure regulator.
To shut down the fuel cell, the bypass valve (V1) from the reactor was opened to the storage vessel. Formic acid was still added to the reactor to produce more H2 and CO2 with the residual heat that was left in the reactor. When the storage vessel reached the correct pressure the formic acid feed was stopped and the valve from the reactor to the storage vessel was closed.
We found that the advantage of using a separate storage vessel is that during shutdown the residual heat that is still left in the reactor is used to generate the H2 that is required for starting the reactor again. When the reactor itself is the storage vessel there will be downtime between the startup state and the working state to get the reactor back up to working pressure, as a result of depressurizing it to get the gas out. In order to return to the operating point, extra gas will have to be produced to build up pressure, which gas cannot be used in the fuel cell. Only when the pressure is high enough again, the extra gas produced is let through.
In this modulation the same conditions and procedure was used as in example 2, only now with a storage pressure that was higher than the working pressure. The storage volume was smaller proportional with the pressure as compared to example 2. This worked out very well, as long as the storage vessel itself and the equipment around the storage vessel (temperature sensors, pressure sensor, level sensor, valves etc) were compatible with the higher pressure. We calculated that the equipment downstream of the storage vessel could remain the same as in example 2.
During start up of the reactor it is possible to already start converting a small amount of formic acid at a reactor temperature which is lower than the normal working temperature of the reactor. The following procedure was tested:
At startup the bypass valve (V1) was switched from fuel cell to catalytic heater, to prevent that the gas flow will pass through the fuel cell. The catalytic heater blower was started. The proportional valve (V2) was slightly opened to the point that the required H2 flow was achieved. Optionally the back pressure regulator can be opened to use the H2 (and thus the pressure) from the reactor as well. The valve was gradually opened further to compensate for the pressure lowering in the storage vessel. Then the heat transfer liquid pump (P2) was started to transfer the heat from the catalytic afterburner to the reactor. When the reactor reached a predetermined threshold temperature of e.g. 80° C. a small amount of formic acid was added to the reactor and a small amount of H2 and CO2 was produced to slow down the consumption of the gas in the storage vessel. When the reactor was increased in temperature it was also possible to convert more formic acid, so the formic acid feed could gradually rise together with the reactor temperature. In other words, infeed of fuel into the reactor can be increased as the temperature of the reactor increases from the predetermined temperature to the normal working temperature. When the reactor reached its working temperature of 100° C. the bypass valve was switched back to the fuel cell and the proportional valve (or back pressure regulator) was closed. Now the reactor produced more H2 (and CO2). The generation of the gas increased the pressure back to its working pressure. With the reactor back at its working pressure the proportional valve (or back pressure regulator) was opened again and the gas was passed through the fuel cell.
The system was filled in the previous examples with hydrogen in the storage vessel during shutdown what means that for the very first startup there is no H2 available yet.
Different options were modelled to find the best solution for this situation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2030045 | Dec 2021 | NL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NL2022/050704 | 12/6/2022 | WO |
