A time-delay-based hydrogen production system and its temperature control method

Abstract

This invention discloses a time-delay-based hydrogen production system and its temperature control method. The time-delay-based hydrogen production system includes an electrolyzer and two gas-liquid separators connected in parallel to the electrolyzer. A radiator and cooling coil are configured around each gas-liquid separator, with the cooling coil connected to the radiator to form a coolant circuit. A water pump connects the gas-liquid separator and the electrolyzer to form an electrolyte circuit. The system also includes an externally mounted gas treatment system, water treatment system, electrolyzer system, voltage conversion system, auxiliary system, and AC / DC rectifier. This invention achieves rapid and stable temperature control of the hydrogen production system and exhibits good robustness to load and ambient temperature fluctuations, maintaining high electrolysis efficiency and improving hydrogen production efficiency.

Description

Technical Field

[0001] This invention relates to the field of hydrogen production, and more specifically to a time-delay-based hydrogen production system and its temperature control method. Background Technology

[0002] The use of fossil fuels releases high levels of greenhouse gases, exacerbating global warming and glacial melting. Decarbonization technologies, such as hydrogen production through water electrolysis using renewable energy sources, are crucial for meeting global energy needs and promoting sustainable development.

[0003] The water electrolysis equipment is the core of the entire hydrogen production system. It is essential to ensure the safe and efficient operation of the electrolyzer to guarantee a stable hydrogen output. When the stack temperature is below the rated temperature, the electrolysis reaction is hindered, and the system efficiency decreases. Conversely, when the internal temperature of the electrolyzer is too high, the corrosion resistance of the entire equipment decreases, adversely affecting the lifespan of the electrolyzer.

[0004] Due to the heat transfer delay in the electrolysis system, PID parameter tuning is very time-consuming and often fails to achieve satisfactory results, frequently leading to stack temperature oscillations and current fluctuations. Affected by temperature variations, the electrolyzer temperature setpoint usually deviates from the limiting temperature, sacrificing system efficiency. To predict and control the electrolyzer temperature, it is necessary to consider the system's time delay effect and establish a high-precision dynamic thermodynamic model of the water electrolysis hydrogen production system. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the proton exchange membrane water electrolysis hydrogen production system cannot reach the optimal operating temperature, resulting in a decrease in hydrogen production efficiency and failing to meet the application requirements of renewable power scenarios.

[0006] To address the aforementioned technical problems, the present invention provides a time-delay-based hydrogen production system, comprising an electrolyzer and a gas-liquid separator. Two gas-liquid separators are connected in parallel to the electrolyzer. A radiator and a cooling coil are configured around each gas-liquid separator. The cooling coil is connected to the radiator to form a coolant circuit. A water pump connects the gas-liquid separator to the electrolyzer to form an electrolyte circuit. The system also includes an externally mounted gas treatment system, water treatment system, electrolyzer system, voltage conversion system, auxiliary system, and AC / DC rectifier.

[0007] The above scheme also includes a solenoid valve switch, and the auxiliary system includes, but is not limited to, a flow sensor and a temperature sensor, which are connected in the electrolyte circuit.

[0008] In the above scheme, the two gas-liquid separators are respectively connected to the hydrogen cylinder group and the oxygen cylinder group.

[0009] In the above scheme, the radiator includes, but is not limited to, water-cooled radiators and air-cooled radiators.

[0010] The present invention also provides a temperature control method for the time-delay-based hydrogen production system, comprising the following steps:

[0011] A high-precision dynamic thermodynamic model of a water electrolysis hydrogen production system was established based on variable time delay, and the model was linearized and discretized.

[0012] Monitor the liquid flow rate before the inlet of the electrolytic cell, gas-liquid separator, cooling coil, and radiator;

[0013] Calculate the variable time-delay sequence in the current period prediction time domain;

[0014] Optimize the cost function by considering the case where the current control input takes effect after a time delay;

[0015] To reduce computational load, the first element of the optimized solution is applied to the system by defining a control time domain.

[0016] In the above scheme, variable delay includes the case of constant delay, and constant delay is a special case of variable delay.

[0017] In the above scheme, the control-oriented model is linearized and then discretized to obtain the prediction equation based on the state-space model.

[0018] In the above scheme, considering the case where the current control input takes effect after a time delay, we find the state variables after the variable time delay takes effect and optimize the cost function.

[0019] This invention, considering the impact of variable time delays, improves the accuracy of the dynamic thermodynamic model of a water electrolysis hydrogen production system. After linearizing the control-oriented model at the operating point, it is discretized to obtain a prediction equation based on a state-space model. This equation can predict the future dynamics of the system. The liquid flow rates at the inlets of the electrolyzer, gas-liquid separator, cooling coil, and radiator are monitored. The variable time delay sequence within the prediction time domain of the current period is calculated. Only the case where the current control input takes effect after the time delay is considered is considered. The state variables after the variable time delay are identified and substituted into the cost function for further optimization. Finally, the control time domain is determined to reduce computational load. The first element of the optimized solution is applied to the system, and this process is repeated once per sampling period. In other words, this invention achieves rapid and stable temperature control of the hydrogen production system, exhibits good robustness to load and ambient temperature fluctuations, maintains high electrolysis efficiency, and improves hydrogen production efficiency. Attached Figure Description

[0020] Figure 1 A simplified schematic diagram of a time-delay-based water electrolysis hydrogen production system is provided as an embodiment of the present invention.

[0021] Figure 2 A simplified heat transfer diagram of a time-delay-based water electrolysis hydrogen production system is provided for an embodiment of the present invention.

[0022] Figure 3 This is a partial flowchart of a time-delay-based water electrolysis hydrogen production system temperature control method provided in an embodiment of the present invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings.

[0024] This invention discloses a time-delay-based hydrogen production system and its temperature control method. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. Furthermore, those skilled in the art can clearly modify or appropriately alter and combine the content described herein without departing from the content, spirit, and scope of this invention to implement and apply the technology of this invention.

[0025] In this invention, unless otherwise stated, scientific and technical terms used herein have the meanings commonly understood by those skilled in the art.

[0026] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0027] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] It should be noted that in the description of this invention, the terms "first" and "second" are used only for convenience in describing different components and should not be construed as indicating or implying a sequential relationship, relative importance, or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" and "second" may explicitly or implicitly include at least one of those features.

[0029] like Figures 1 to 3 As shown, the present invention provides a time-delay-based hydrogen production system, including an electrolyzer 1 and a gas-liquid separator 2. Two gas-liquid separators 2 are connected in parallel to the electrolyzer 1. A radiator 3 and a cooling coil 5 are configured around the gas-liquid separator 2. The cooling coil 5 and the radiator 3 are connected to form a cooling liquid circuit. The gas-liquid separator 2 and the electrolyzer 1 are connected to form an electrolyte circuit through a water pump 4. The system also includes an external gas treatment system, a water treatment system, an electrolyzer system, a voltage conversion system, an auxiliary system, an AC / DC rectifier, and a solenoid valve switch. The auxiliary system includes, but is not limited to, a flow sensor 6 and a temperature sensor 7. The solenoid valve switch, the flow sensor 6, and the temperature sensor 7 are connected in the electrolyte circuit. The two gas-liquid separators 2 are respectively connected to a hydrogen cylinder group 8 and an oxygen cylinder group 9.

[0030] Among them, the AC / DC rectifier can rectify 380V AC power into DC power within a certain range, affecting the power of hydrogen production and heat production.

[0031] The water pump 4 can control the volumetric flow rate at the inlet of the electrolyzer 1 and the cooling coil 5, and use this as a control input to ensure that the temperature of the hydrogen production system is maintained at the set value.

[0032] The flow sensor can monitor the flow rate before the inlet of electrolytic cell 1, gas-liquid separator 2, cooling coil 5 and radiator 3, and the temperature detector can monitor the temperature after the inlet of electrolytic cell 1, gas-liquid separator 2, cooling coil 5 and radiator 3.

[0033] This invention also provides a temperature control method for a time-delay-based hydrogen production system, comprising the following steps:

[0034] A high-precision dynamic thermodynamic model of a water electrolysis hydrogen production system was established based on variable time delay, and the model was linearized and discretized.

[0035] Monitor the liquid flow rate before the inlet of the electrolytic cell, gas-liquid separator, cooling coil, and radiator;

[0036] Calculate the variable time-delay sequence in the current period prediction time domain;

[0037] Optimize the cost function by considering the case where the current control input takes effect after a time delay;

[0038] To reduce computational load, the first element of the optimized solution is applied to the system by defining a control time domain.

[0039] Variable time delay includes the case of constant time delay, with constant time delay being a special case of variable time delay. After linearizing and discretizing the control-oriented model, we obtain the prediction equations based on the state-space model. Considering the case where the current control input takes effect after a time delay, we find the state variables after the variable time delay takes effect and optimize the cost function.

[0040] The time-delay-based temperature control method for hydrogen production systems is as follows:

[0041] Inside the electrolyzer, a water electrolysis chemical reaction occurs, converting some electrical energy into chemical energy and the rest into heat energy, increasing the temperature of the fuel cell stack. The electrical input power P... ele Heat production Q ele The relationship is as follows:

[0042] P ele =U cell I cell N cell (1)

[0043] Q ele =(U cell -U th )I cell N cell (2)

[0044] Among them. U cell I is the voltage of the electrolytic cell. cell U is the current in the electrolytic cell. th For thermal neutral voltage, N cell This indicates the number of cells in the electrolytic cell that are in operation.

[0045] In existing commercial electrolysis systems, the electrolysis reaction releases a large amount of heat energy, requiring cooling devices such as heat exchangers. Controllers are used to regulate the flow of cooling water to suppress interference, maintain the temperature at the optimal operating point, and ensure the stable and efficient operation of the hydrogen production system.

[0046] When the temperature at the in-pile changes, the temperature at the out-of-pile will change after a certain period of time due to convection of the internal electrolyte. Similarly, time delays will also occur in the gas-liquid separator, cooling coils, and radiators.

[0047] The thermal balance of the fuel cell stack, gas-liquid separator, cooling coils, and radiators can be expressed as:

[0048]

[0049] The subscript t indicates the measurement time.

[0050] Formula (3-a) indicates the back-of-pile temperature T stack,t The change depends on the heat production power Q ele,tThe heat and power carried away by the electrolyte And the power loss to the environment (heat convection and heat radiation) Q dis,stack,t .

[0051] [C stack C sep C c C r ]、[T stack,t ,T sep,t ,T c,t ,T r,t ] and [v stack ,v sep ,v c ,v r [c] represents the heat capacity, outlet temperature, and inlet volumetric flow rate of the electrolytic cell, gas-liquid separator, cooling coil, and radiator, respectively. lye ,c c ] and [ρ lye ,ρ c [] indicates the specific heat capacity and density of the electrolyte and coolant.

[0052] Equations (3-b) and (3-c) illustrate the heat exchange process between the gas-liquid separator and the cooling coil. The 1 / 2 in the first term of equation (3-b) is because only the electrolyte flow rate on the hydrogen side is calculated, which is half of the total flow rate. The second term represents heat transfer through the heat transfer system k, the contact area A, and the average logarithmic temperature difference ΔT. t Calculate. In formula (3-d), Q dis,radiator,t This indicates the power of the radiator for heat dissipation.

[0053] The above parameters and units can be obtained through actual situations or empirical formulas in literature.

[0054] The state variables, control inputs, and control outputs are defined as follows:

[0055]

[0056] The liquid flow rate before the inlet of the electrolytic cell, gas-liquid separator, cooling coil, and radiator is monitored, and the discrete-time variable delay N is calculated. d sequence:

[0057] In each control cycle, solve the following optimization problem:

[0058]

[0059] where

[0060]

[0061] Where x(k+i|k) represents the predicted state variable based on the current period k at discrete time k+i, and q and α represent the weights of the state variable and the control input, respectively.

[0062] For a system with a time delay, the changes in the controlled variables become significant once the time delay has elapsed. Therefore, to find the optimal control sequence, the cost function needs to consider only the output prediction occurring after the time delay. This means the minimum prediction range should be equal to the time delay, i.e., N1 = N. d For a constant time-delay system, N1 is easily determined. Then, the maximum prediction range N2 can be set to an appropriate value to ensure the system's robustness; the distance between N1 and N2 is the prediction time domain N. p .

[0063] To reduce the computational cost per cycle and improve control performance, a control time-domain N is introduced. u In each cycle, the control sequence changes. In the prediction time domain, the input control quantity that exceeds the control range is set to the final calculated value and remains unchanged: u(k+j|k)=u(k+N) u -1), j=N u …N2-1. Negative feedback is achieved through rolling optimization, with only N… u The first element is applied to the controlled object, the remaining control inputs are discarded, and the entire process is repeated at the next sampling time.

[0064] Alternatively, solving the cost function directly without using the control time domain is also a special case of this example, and this patent should be protected.

[0065] In this invention, variable delay is a broad expression, including but not limited to variable time delay, variable delay, variable time delay, time-varying delay, time-varying time lag, changing transmission delay, changing time lag, etc., which represent a time lag that can be varied.

[0066] This invention considers the impact of variable time delays, improving the accuracy of the dynamic thermodynamic model of the water electrolysis hydrogen production system. After linearizing the control-oriented model at the operating point, it is discretized to obtain a prediction equation based on a state-space model, which can predict the future dynamics of the system. Liquid flow rates at the inlets of the electrolyzer, gas-liquid separator, cooling coil, and radiator are monitored. The variable time delay sequence within the prediction time domain of the current period is calculated, considering only the case where the current control input takes effect after the time delay. The state variables after the variable time delay are identified and substituted into the cost function for further optimization. Finally, a control time domain is determined to reduce computational load, and the first element of the optimized solution is applied to the system, executed once per sampling period. Thus, this invention achieves rapid and stable temperature control of the hydrogen production system, exhibits good robustness to load and ambient temperature fluctuations, maintains high electrolysis efficiency, and improves hydrogen production efficiency.

[0067] This invention is not limited to the preferred embodiments described above. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

Claims

1. A temperature control method for a time-delay-based hydrogen production system, characterized in that, Includes the following steps: A high-precision dynamic thermodynamic model of a water electrolysis hydrogen production system was established based on variable time delay, and the model was linearized and discretized. Monitor the liquid flow rate before the inlet of the electrolytic cell, gas-liquid separator, cooling coil, and radiator; Calculate the variable time-delay sequence in the current period prediction time domain; Optimize the cost function by considering the case where the current control input takes effect after a time delay; To reduce computational load, the first element of the optimized solution is applied to the system by defining a control time domain.

2. The temperature control method as described in claim 1, characterized in that, Variable delay includes the case of constant delay; constant delay is a special case of variable delay.

3. The temperature control method as described in claim 1, characterized in that, After linearizing the control-oriented model, it is discretized to obtain the prediction equation based on the state-space model.

4. The temperature control method as described in claim 1, characterized in that, Considering the case where the current control input takes effect after a time delay, find the state variables after the variable time delay takes effect and optimize the cost function.

Images