Method for producing hydrogen by adjusting the power of a compressor

Abstract

The present invention relates to a method for producing hydrogen by adjusting the power of a compressor according to the generation rate of an electrolytic cell. The method includes: a) an electrolysis step using an electrolytic cell that produces hydrogen at an output pressure of 1 to 50 bar and a flow rate of 0.5 to 5 Nm3 / h; b) a step of compressing hydrogen using an electrochemical compressor. The method further includes a step of correcting the power supply current of the electrochemical compressor with respect to a target pressure value.

Description

Technical Field

[0001] The present invention relates to a method for adjusting the power of a compressor to produce hydrogen. In particular, it is applied in the fields of hydrogen production, compression and storage facilities, and the maximum daily output is 10 kg / day.

[0002] These facilities can be used for various applications, such as autonomous distribution stations for mobility or systems for houses that can be self-sufficient in energy using hydrogen as an energy vector. With this developed innovation, hydrogen compression can be carried out quite easily.

Background Art

[0003] In hydrogen production and compression facilities for small-scale equipment, reciprocating mechanical compressors (piston or diaphragm compressors) are used, reaching pressures of 150 to 1,000 bar. It is suggested that these have several limitations as summarized below.

[0004] Startup flow rate: At startup, the electrolyzer requires time to reach its set flow rate. Therefore, this flow rate changes almost linearly between 0 and its set flow rate. Next, the mechanical compressor operates at a specific speed determined by the operating constraints of the motor. The electrolyzer can produce hydrogen at a variable flow rate depending on the application. Therefore, it is necessary to throttle the electrolyzer to operate at a specific speed that matches the speed of the compressor.

[0005] Limitations of the compression ratio: An essential characteristic of a mechanical compressor is its compression ratio. This is the ratio of the discharge pressure to the suction pressure. This ratio is determined by the suction temperature, the nature of the gas and its heating capacity during compression, especially the type of compressor whether it is cooled or not, and the mechanical state of the compressor. In the most desirable case, with an integrated cooling system, a compression ratio of 10 can be reached. For example, starting from a suction pressure of 30 bar, it reaches 300 bar. If the discharge pressure is higher than 300 bar, it can be reached in a second compression stage. This second stage further complicates the management of the flow rates of the two compressors and requires additional cost for purchasing the second compressor.

[0006] Synchronization of Flow Rate with Buffer Volume: Standard hydrogen mechanical compressors generally have a rated suction flow rate higher than the generation rate of small-scale electrolyzers (i.e., 0.5 - 5 Nm3 / h). For this reason, a buffer volume is placed between these two devices (electrolyzer and compressor). This fills the flow rate difference and maintains sufficient pressure to hold an acceptable compression ratio. To hold an acceptable compression ratio, the suction pressure of the compressor is set higher than 30 bar to maintain a compression ratio of less than 10 so as to reach 300 bar at discharge. The maximum pressure that the electrolyzer can reach is generally 35 bar, and the difference between these operating values is close. Therefore, it is necessary to increase the buffer volume to limit the startup frequency of the compressor. Generally, a buffer volume of at least 150 L is required for a generation rate of 500 Nl / h.

[0007] Flow synchronization by mechanical adjustment: Some mechanical compressors can operate at the same flow rate as the rated flow rate of the electrolyzer, for example, 500 NL / h. However, regardless of the technology, the electrolyzer requires a speed-up time before reaching the rated flow rate. This time varies from a few minutes for PEM or AEM electrolyzers to several hours for alkaline technology. As described, the motor of the mechanical compressor can generally only operate at specific limited speeds by operating a motor with four speeds, which only allows for a first rough adjustment of the flow rate. However, there are techniques to more precisely adapt the flow rate of the mechanical compressor. These techniques induce degradation of the compressor's operation and are corrected either during design or by adding adjustment elements. In either case, excessive hardware costs and a significant development time are required. First, the suction pressure can be reduced. In each operation, the piston compresses less gas, reducing the flow rate. As a result, the compression ratio increases, leading to efficiency losses. A bypass can also be used to recycle the compressed gas. The bypass connects the outlet and inlet of the compressor together with an expansion valve, thereby artificially increasing the flow rate at the inlet. Since hydrogen is a gas that gets hot during the compression and expansion stages, there is significant overheating. Due to the need for further cooling and the need to compress a large amount of gas, the efficiency is greatly reduced. Although it significantly increases the complexity and cost of the machine, other methods used for high-power machines can also be mentioned, which are to place a valve under vacuum or to reduce the suction capacity by using a servo motor to delay the closing of the suction valve. These techniques can be arranged simultaneously to improve the accuracy of flow control, but complex research and development are required to limit the overall efficiency losses.

[0008] Starting power: Since high energy is required to start the moving parts in each start-up, it is important to limit the start-up frequency of the compressor. In order to prevent the motor power from being too large, generally, the compression and the start-up of the machine cannot be reliably carried out simultaneously. For this reason, reciprocating compressors almost always start in a vacuum. A bypass is used to reduce the discharge pressure to a value close to the suction pressure. The pressure reduction causes an efficiency loss. Increasing the firing frequency also consumes the hardware and reduces the service life of the compressor.

[0009] European Patent Application Publication No. 3550056, US Patent Application Publication No. 2022025529, and US Patent Application Publication No. 2004040862 are examples of hydrogen compressors. Still, the optimization of the operation is not sufficient.

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention aims to overcome these drawbacks by a completely innovative approach.

[0011] Another compression technology, electrochemical compression, solves many of the problems described above.

Means for Solving the Problems

[0012] Electrochemical compression is a compression technology using PEM (Proton Exchange Membrane) technology and is also used in fuel cells or electrolyzers. Its basic principle is to pass hydrogen through a membrane, and a high-pressure storage tank is located behind the membrane. The passage of hydrogen is strictly determined by the application of an electric current. The obtained compression ratio is mainly determined by the resistance of the membrane to the upstream / downstream pressure difference.

[0013] More specifically, the object of the present invention is to provide a compression technology that combines many advantages.

[0014] Since electrochemical compression operates without a mechanical mechanism, it is quiet and vibration-free. It does not require any sound insulation and vibration prevention like mechanical compression.

[0015] The compression flow rate can be finely and continuously adjusted.

[0016] Different from a mechanical compressor that undergoes isentropic compression, it is carried out under isothermal conditions. In the case of a mechanical compressor, the heat generated by the increase in the compression ratio rises. Under actual conditions, in the case of an electrochemical compressor with a compression ratio exceeding 10, this influence is significantly less. This is difficult to achieve using a mechanical compressor.

[0017] The rated flow rate is limited by the dimensions and number of the membranes. The size of the compressor can be selected to adapt to the manufacturing capacity. For a mechanical compressor, it may be necessary to re - examine the overall structure of the compressor (selection of the motor size, piston size, etc.).

[0018] These objects, as well as other objects that will become apparent below, are achieved according to a first aspect by utilizing a method for producing hydrogen by adjusting the power of a compressor according to the generation rate of an electrolytic cell. The method comprises the following · a) an electrolysis step using an electrolytic cell that produces hydrogen at an output pressure of 1 - 50 bar and a flow rate of 0.5 - 5 Nm3 / h; · b) a step of using an electrochemical compressor to compress the hydrogen obtained from step a); and It should be noted that it further includes a step of correcting the power supply current of the electrochemical compressor with respect to a target pressure value; the correction step is a sub - step of changing the target pressure value: · Immediately when the output pressure of the electrolytic cell exceeds the target pressure reference value, increasing the value of the power supply current of the electrochemical compressor; · Immediately when the output pressure of the electrolytic cell is less than the output pressure reference value of the electrolytic cell, decreasing the value of the power supply current of the electrochemical compressor.

[0019] As a result of these arrangements, the present invention is technically simple and inexpensive and is purchased and used for compressing hydrogen at a ratio of more than 10 and a flow rate of less than 5 Nm3 / h. The buffer between the hydrogen production and compression processes is significantly reduced. Therefore, the space occupied by this system is also substantially saved. This is made possible as a result of the dynamic management of the flow rate of the electrochemical compressor and the humidity management of the gas being fully integrated with the requirements of the compressor and the application of small hydrogen production and compression equipment.

[0020] The present invention varies the power of the compressor according to the production rate of the electrolyzer. Therefore, the electrolyzer and the compressor can be automatically operated simultaneously at the same flow rate. As a result, the buffer volume is reduced by 500 times. For this purpose, a program is implemented on the control panel. By means of this control panel, the current setting is changed according to the pressure between the electrolyzer and the compressor. Since the compressor can reach its rated flow rate after a few seconds, it can follow the production of the electrolyzer during these start-up and shutdown phases.

[0021] The value of the power supply current of the electrochemical compressor changes in proportion to the difference between the measured pressure and the target pressure. The greater the pressure difference, the higher the current setting rises to reach the target pressure.

[0022] The value of the power supply current of the electrochemical compressor changes in proportion to the pressure difference between the latter and the target value. The greater the pressure difference, the lower the current setting drops until the compressor comes to a complete stop.

[0023] Advantageously, the present invention is implemented according to the embodiments and variations disclosed below, which should be considered individually or in any technically feasible combination.

[0024] In one embodiment, the method further includes a step of humidifying the hydrogen with a humidifier so that the hydrogen produced in step a) contains a relative humidity of 80% to 99%.

[0025] Using an electrochemical compressor implies that the input hydrogen is quasi-saturated with water (80 - 99% RH) and that proper operation of the compressor is ensured. This condition is not met if the hydrogen is obtained directly from an electrolyzer rather than from a standard storage tank.

[0026] Relative humidity represents the saturation rate of a gas with water. This humidity is liable to vary according to pressure and temperature.

[0027] In one embodiment, during the correction step, the target pressure value is adjusted by a proportional-integral or proportional-integral-derivative regulator.

[0028] In one embodiment, during the correction step, the target pressure value uses data from at least one of a pressure sensor and a temperature sensor.

[0029] In one embodiment, during the correction step, the pressure sensor is located in the humidifier between the electrolyzer and the electrochemical compressor. Thus, the sensor can be located upstream, inside, or downstream of the humidifier.

[0030] In one embodiment, during the humidification step, the buffer volume of the humidifier is less than 500 ml.

[0031] The buffer volume is within the humidifier. It is located between the electrolyzer and the compressor. Therefore, the buffer volume has two functions: humidification and buffering.

[0032] This has the advantage that by using the tank of the humidifier, there is no need to install an additional tank.

[0033] Other advantages, objects, and features of the present invention will become apparent from the following description, which is shown for illustrative and non-limiting purposes with reference to the accompanying drawings.

Brief Description of the Drawings

[0034]

Figure 1

Figure 2

DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention relates to equipment for controlling the humidity of a gas and operating at a pressure higher than 10 bar.

[0036] Previous systems could accurately control the humidity level of the gas, were very expensive, and were not suitable for the needs of small equipment.

[0037] A humidity control system consisting of standard elements can be used, which is fully adapted to the operation of this type of application.

[0038] Input gas: The humidifier is maintained at a temperature close to the temperature of the input gas so that the relative humidity of the input gas reaches 80 - 100% at the inlet.

[0039] At the same temperature, 100% relative humidity is reached.

[0040] Therefore, the humidifier is maintained at a temperature a few degrees lower than the temperature of the input gas to maintain the relative humidity level within the required range (80% ≤ RH ≤ 99%).

[0041] If the temperature of the humidifier is higher than the temperature of the input gas, condensation will begin to appear and may affect the overall operation.

[0042] To achieve this, the input gas is temperature - controlled by a temperature regulator. A finned tube and a fan are used to perform temperature control in the humidifier.

[0043] The solution is to incorporate the humidifier and the input gas into the same temperature - controlled circuit. This avoids the electrical consumption for maintaining the temperature (heating the resistor and the cable). The humidifier and the coaxial tube containing the input gas are involved in heat dissipation when the system produces an exothermic reaction that requires cooling.

[0044] As a result, the temperature regulator is selected to be slightly smaller in size than the initial configuration required for the same amount of input gas.

[0045] The object of the present invention is to ensure the saturation of the gas by humidity regardless of the operating temperature.

[0046] In one embodiment, the present invention is integrated with a method for regulating the humidity of a gas.

[0047] The method for regulating the humidity of a gas includes the following steps. · The first step is to regulate the humidity of the gas entering the humidifier at a flow rate of 500 NL / h to 50,000 NL / h, and the humidifier includes the following elements. · A humidifier tank including an inlet and an outlet, · A temperature regulation tank surrounding the humidifier tank, · A large amount of temperature regulation water contained in the temperature regulation tank, · A temperature regulation water circulation pump; · The humidifier tank includes a first porous matrix located at the bottom of the humidifier tank closest to the inlet. The gas entering the humidifier through the inlet of the humidifier tank passes through the first porous matrix, thereby generating gas microbubbles and enabling more absorption of humidity. This matrix is located in a large amount of water contained in the humidifier tank, and the humidified gas exits from the outlet of the humidifier tank and circulates to the compressor; a large amount of temperature regulation water circulates in a closed circuit flowing through the temperature regulation tank, the circulation pump, and the compressor. · The second step is to dry the gas obtained from the first step. The gas exiting the compressor passes through a T-shaped pipe including one inlet and two outlets, one of the outlets being vertical, and the liquid phase of the gas flows due to the gravity effect to generate condensate. The other outlet is connected to the bottom of the desiccant tank; at the outlet of the desiccant tank, the dried gas is stored in the tank and the humidity is lower than a predetermined reference value.

[0048] As a result of these arrangements, the gas entering the compressor is saturated with humidity, i.e., 80% ≤ HR ≤ 99%, optimizing its operation. After the drying process, the water concentration of the exhaust gas is less than 5 ppm, and hydrogen can be used for various applications.

[0049] There is another advantage that there is less need for cooling compared to another method where the conditions of the exhaust gas are ensured and the criteria are met.

[0050] Furthermore, the internal volume of the humidifier is used as a damper for the pressure fluctuations of the inlet gas, thereby simplifying the management of the compressor.

[0051] The humidifier uses an automatic purge and filling system to maintain the optimal water level.

[0052] A single thermostat installed around the humidifier sets the temperature of the humidifier and the connected compressor.

[0053] By separating the condensate upstream of the gas dryer, the gas loss when purging this condensate is minimized.

[0054] In one embodiment, during the first step, the temperature of the temperature-controlled water is ensured by a temperature control element.

[0055] In one embodiment, the temperature control element of the first step includes fins arranged around a temperature control tank.

[0056] In one embodiment, the temperature control element of the first step includes a fan in contact with the fins and configured to ensure air circulation.

[0057] In one embodiment, during the first step, the second porous matrix is located at the upper part of the humidifier tank closest to the outlet of the humidifier tank, and the humidified gas passes through the second porous matrix before exiting the humidifier tank. It is used as a security element to prevent the passage of liquid water.

[0058] In one embodiment, during the first step, the relative humidity of the input gas in the compressor is 80 - 99%, preferably 95 - 99%.

[0059] In one embodiment, the method includes a third stop step of purging a large amount of water contained in the humidifier tank and then filling it with a new large amount of water.

[0060] The water storage tank of the humidifier is used as a buffer volume. Thereby, an additional water storage tank is not required, and space can be saved and costs can be reduced.

[0061] In one embodiment, during the third stop step, the condensate contained in one of the outlets of the T - tube is purged.

[0062] In one embodiment, when the humidity level of the gas is higher than a predetermined reference value, preferably when it exceeds the reference value of 5 ppm, the method includes a visual or auditory warning step, or a warning step using a terminal indicating the need to replace the desiccant.

[0063] This humidity control method ensures a humidity close to 99% regardless of the pressure and temperature conditions of the compressor.

[0064] Generally, the electrolyzer operates at a pressure of 10 - 50 bar. The use of the humidifier shown above enables operation within these pressure ranges. Therefore, there is no need to expand the gas at a low pressure for humidification. Since the pressure difference between the inlet and outlet of the compressor becomes lower, this method can have optimized efficiency.

[0065] Due to another element, it becomes difficult to integrate electrochemical compression in the case of small equipment. Compressed hydrogen is stored in the tank at a low humidity level (<5 ppm). Therefore, it is necessary to dry the compressed gas.

[0066] Commercially available products cannot dry hydrogen in these flow rate ranges, at pressures of 500 - 1,000 bar, and at similarly low humidity levels. Thus, it is necessary to use specific materials that have been certified for operation at high pressures. Systems that are possible at low pressure are expensive compared to the generation rate.

[0067] Also, these uses cause significant gas losses in each operating cycle.

[0068] The use of the dryer shown above provides a drying strategy based on standard components such as high-pressure tanks, enabling significant cost reduction, simplified maintenance, and excellent modularity. Since mechanical compressors require dry hydrogen to operate, the drying process is essential in both cases. However, drying is carried out upstream of compression. The simple drying strategy can achieve cost reduction by more than 10 times compared to the drying strategy upstream of compression or the existing drying strategy downstream of compression. Certainly, the pressure increase condenses most of the gaseous water present in the gas. Therefore, the amount of water extracted from the gas is less after compression, allowing the use of technologies that are affordable and easy to implement.

[0069] Figure 1 shows a block diagram of the implementation steps in the method of the present invention.

[0070] The steps are an electrolyzer, a humidifier, a compressor, a dryer, a tank, and a fuel cell (for possible applications).

[0071] Figure 2 shows the steps more specifically between the electrolyzer and the dryer.

[0072] This method uses a PID (Proportional Integral Derivative) controller. The program installed in the control panel of the compressor dynamically changes the current setting of the compressor according to the pressure measured by the pressure sensor between the electrolyzer and the compressor. The purpose is to maintain a fixed pressure between the two devices.

[0073] Therefore, the pressure sensor measures the pressure between the two devices and delivers information to the control panel. The control panel has the function of adjusting the power current of the compressor and maintains the pressure constant at, for example, 30 bar. The humidifier and the dryer are humidity control elements that are simpler and less expensive than existing solutions. They address the need for small-scale equipment and make hydrogen production and compression more affordable.

[0074] At the same time, new humidification, dynamic flow control measures for compressors, compression technology, and drying can provide products that are significantly less expensive than those currently available on the market. Simplification of assembly and management reduces maintenance time and costs and extends the service life of the set.

[0075] Consideration of the embodiment: This system operates at a rated speed. Therefore, the electrolyzer and the compressor operate at the same flow rate. We change the flow rate setting of the electrolyzer to decrease it from 100% to 90%. At this time, since the compressor still has a 100% production setting, a pressure drop occurs between the two devices due to the decrease in the generation rate of the electrolyzer. The PID detects the pressure drop and sends a decrease in the power current setting to the compressor. This decrease reduces the flow rate of the compressor, stabilizes the intermediate pressure, and causes it to reach 30 bar again. The response speed and stabilization speed of the PID are determined by 1) the function of the compressor that implements the speed change and 2) the buffer volume. This inference may be the same during startup, stop, and speed change phases. Therefore, the specific purpose of the compressor is to automatically maintain a constant pressure.

[0076] This solution has the advantage that the arrangement is very simple and does not require any additional equipment or changes to the initial design of the compressor. However, a suitable humidification system is still required.

[0077] Electrochemical compression is modular, and an increase in the number of cells increases the rated flow rate of the compressor. Each cell consists of a PEM membrane and two electrodes, and the assembly is a so-called MEA (membrane electrode assembly). The surface area is 150 cm 2A standard cell, for example, generally corresponds to a flow rate of 20 NL / h. Therefore, in the manufacture of a compressor, the rated flow rate, and thus the number of cells, can be selected according to the application and the size of the electrolyzer. Flexibility is possible with a mechanical compressor, but it is necessary to fully adapt the mechanical structure of the mechanical compressor (motor size, piston diameter, etc.).

[0078] When this system is in operation, the humidifier contains two volumes. The first volume contains a large amount of liquid water, where the gas moves and is humidified as it passes through. The second volume contains the humid gas. This volume is approximately 300 ml for a system that produces 0.5 - 5 Nm3 of hydrogen per hour. This volume is sufficient to be used as a buffer in this solution, and no additional tank is required.

[0079] Through more advanced support for the compressor by PID optimization and the electrolyzer during startup, the volume is reduced. However, this is useful for humidification and optimizes the separation of the liquid phase from the gas phase. In comparison, the current solution requires a minimum buffer volume of 150 L, i.e., a volume 500 times larger, in these operating ranges.

[0080] The present invention is suitable for facilities that produce less than 10 kg of hydrogen per day. Furthermore, it can also be applied to facilities with larger capacities.

[0081] Since the buffer volume can be significantly reduced, the present invention can save a considerable amount of space. By using a very simple calculation program, the complexity of implementation can also be reduced. Also, there is no need to change any hardware of the compressor. This is particularly useful for manufacturers of hydrogen production and distribution stations for small mobility or industrial applications of hydrogen, as it reduces the size of the equipment and cuts costs.

[0082] The present invention can also be used in any other system that requires hydrogen production and compression. For example, it can be used in a residential environment to generate green hydrogen and enable energy autonomy by using it as a vector. In this case of use, the present invention can save a non-negligible amount of space for a residence where the available space is limited. Also, by integrating quiet compression, it is suitable for a residential environment.

[0083] Therefore, the present invention addresses many of the current limitations in hydrogen production and compression systems. These limitations are obstacles in leveraging these solutions for different applications.

[0084] PID servo control: The compression function is ensured by current control. When the compression of the compressor is increased, the pressure between the compressor and the electrolyzer decreases. Conversely, when the compression of the compressor is decreased, the pressure between the compressor and the electrolyzer increases.

[0085] Therefore, the pressure regulation function between the electrolyzer and the compressor is possible by servo control of the current with respect to the measured pressure.

[0086] The desired pressure represents the PID set value.

[0087] PID servo control is a third-order regulation: · Proportional regulation → reaching the set pressure quickly; · Integral regulation → static error between the set pressure and the measured pressure; · Derivative regulation → reducing pressure fluctuations centered around the set pressure characterized by.

[0088] These three orders correspond to coefficients Kp, Ki, and Kd, respectively.

[0089] According to one example, this method implements the following type of PID.

[0090] TIFF2025520283000002.tif14170

[0091] Output = current; e = set value - input

[0092] The adaptation of the number of electrolytic cells and the compression power, and thus the hydrogen production according to the pressure regulation, is possible as a result of the dynamic evolution of the PID coefficients Kp, Ki, Kd.

Claims

1. A method for producing hydrogen by adjusting the power of a compressor according to the generation rate of an electrolytic cell, comprising the following a) an electrolysis step using an electrolytic cell that produces hydrogen at an output pressure of 1 to 50 bar and a flow rate of 0.5 to 5 Nm3 / h; b) a compression step using an electrochemical compressor to compress the hydrogen obtained from step a); including further comprising a correction step of correcting the power supply current of the electrochemical compressor with respect to a target pressure value, wherein the correction step is a sub-step of changing the target pressure value: - a step of increasing the value of the power supply current of the electrochemical compressor as soon as the output pressure of the electrolytic cell exceeds a target pressure reference value; - a step of decreasing the value of the power supply current of the electrochemical compressor as soon as the output pressure of the electrolytic cell is less than the output pressure reference value of the electrolytic cell.

2. The method according to claim 1, further comprising a humidification step of humidifying the hydrogen with a humidifier such that the hydrogen produced in step a) contains a relative humidity of 80% to 99%.

3. The method according to claim 1, wherein in the correction step, the target pressure value is adjusted by a proportional-integral or proportional-integral-derivative controller.

4. The method according to claim 1, wherein in the correction step, the target pressure value uses data from at least one of a pressure sensor and a temperature sensor.

5. The method according to claim 4, wherein in the correction step, the pressure sensor is located in the humidifier between the electrolytic cell and the electrochemical compressor.

6. The method according to claim 2, wherein in the humidification step, the buffer volume of the humidifier is less than 500 ml.

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