CN114781188A - Dynamic modeling method for solid oxide electrolytic hydrogen production system for fluctuating electric energy consumption - Google Patents
Dynamic modeling method for solid oxide electrolytic hydrogen production system for fluctuating electric energy consumption Download PDFInfo
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Abstract
The invention discloses a dynamic modeling method of a solid oxide electrolysis hydrogen production system for fluctuating electric energy absorption, and relates to the field of hydrogen production and energy storage. The method comprises the following steps: s1: constructing a dynamic model of a high-temperature solid oxide electrolytic cell by taking fluctuating renewable energy power as a unique energy source based on electrochemistry and a heat transfer mechanism; s2: constructing a dynamic model of each auxiliary machine component of the high-temperature solid oxide electrolytic hydrogen production system and simulating the electrolytic hydrogen production process; s3: identifying a double-input double-output transfer function model of a mechanism model of the high-temperature solid oxide water electrolysis hydrogen production system; s4: and performing Model Predictive Control (MPC) design based on the established identification model. The invention provides a dynamic simulation model of a high-temperature solid oxide water electrolysis hydrogen production system for fluctuating electric energy consumption, and reaction raw materials meeting the reaction requirements are quantitatively supplied to the electrolysis system through system identification and control design, so that the accurate control of the reaction temperature is realized, and the stability of the hydrogen production system is improved.
Description
Technical Field
The invention relates to the technical field of hydrogen preparation and energy storage, in particular to a dynamic modeling method for a solid oxide electrolysis hydrogen production system for fluctuating electric energy consumption.
Background
With the gradual reduction of the power generation price of renewable energy sources, clean energy sources are expected to become important sources of power supply. In the comprehensive energy microgrid, hydrogen is produced by electrolyzing water, and the hydrogen storage module can play a role in stabilizing renewable energy power, inhibiting energy fluctuation, improving system operation stability, realizing diversified utilization of energy resources and the like, and particularly has obvious advantages compared with electrochemical energy storage in the power balance process of medium and long time scales.
At present, the water electrolysis hydrogen production technology mainly comprises three types: an alkaline water electrolysis hydrogen production (AWE) system, a proton exchange membrane water electrolysis hydrogen Production (PEMEC) system and a high-temperature solid oxide water electrolysis hydrogen production (SOEC) system. Where AWE has been used for hydrogen production in the fertilizer and chlorine industries, cell operation ranges from 10% minimum load to 110% maximum design capacity. Compared with other electrolytic cell technologies, alkaline water electrolysis avoids the cost burden caused by the use of precious materials. The method has the most extensive commercial application, but has the defects of low hydrogen production efficiency and low energy density of an electrolytic cell, and is difficult to realize high-density design. Due to the introduction of the proton exchange membrane, the PEMEC overcomes the defects of low energy density and low hydrogen production efficiency of AWE, and also has the defects of short service life of materials and high cost. Because of the high-temperature electrolytic environment, the SOEC has the highest theoretical hydrogen production efficiency.
The SOEC is commonly used in tubular and plate type designs, the plate type electrolytic cell has simple structure, easy processing, low processing cost and convenient high current density design, but has more exposed area, difficult encapsulation and large reaction thermal stress, especially when the fluctuating renewable energy is absorbed. At present, the efficiency of the solid oxide electrolytic cell is the highest among three electrolytic cells, the reaction waste heat can be utilized, and the total efficiency of the system can reach 90%. But the high temperature working conditions of 1000 ℃ make it more challenging in terms of materials, etc.
The new energy power technology has the characteristic of clean and low carbon, but the fluctuation and intermittency of the new energy power technology also bring challenges to the water electrolysis hydrogen production system, so for example, Chinese patent document CN111663150A discloses a fluctuation type power input water electrolysis hydrogen production method and a device thereof; chinese patent document CN113862696A discloses a hydrogen production method based on solid oxide electrolysis of water: both the above two documents are studying hydrogen production methods by water electrolysis, but for the solid oxide hydrogen production system facing the fluctuation type power input, the introduction of reasonable control design has important significance for improving the stability of the electrolytic cell operation, ensuring that the steam flow meets the reaction requirement, inhibiting the fluctuation of the reaction temperature along with the change of the electric energy input, improving the stability of hydrogen production and prolonging the material life.
Disclosure of Invention
In order to solve the control design problem in the face of the input of power of renewable energy sources with volatility, the invention provides a dynamic modeling method of a solid oxide electrolytic hydrogen production system facing the consumption of fluctuating electric energy, which can realize dynamic modeling and simulation analysis of the SOEC electrolytic water hydrogen production system and realize system control in response to the input of unstable electric energy.
In order to achieve the purpose, the invention is realized by the following technical scheme:
the invention relates to a dynamic modeling method of a solid oxide electrolysis hydrogen production system for fluctuating electric energy absorption, which comprises the following steps:
s1: constructing a dynamic model of a high-temperature solid oxide electrolytic cell by taking fluctuating renewable energy power as a unique energy source based on electrochemistry and a heat transfer mechanism;
s2: constructing a dynamic model of each auxiliary machine component of the high-temperature solid oxide electrolytic hydrogen production system and simulating the electrolytic hydrogen production process;
s3: identifying a mechanism model of the high-temperature solid oxide water electrolysis hydrogen production system by a double-input double-output transfer function model;
s4: and performing model prediction control based on the identified transfer function model.
The invention is further improved in that: the specific steps of S1 are:
s11, constructing an electrochemical dynamic response model of the high-temperature solid oxide electrolytic cell according to an electrochemical principle;
and S12, constructing a heat transfer dynamic response model of the high-temperature solid oxide electrolytic cell according to the electrolytic cell model structure.
The invention is further improved in that: the total electrolysis voltage in the electrochemical dynamic response model of S11 is obtained by adding reversible voltage, activation polarization voltage, ohmic polarization voltage and concentration polarization voltage, namely:
Vel＝E+Vel,act+Vel,ohm+Vel,conc
wherein, VelFor total electrolytic voltage, E is reversible voltage, Vel，actTo activate the polarization voltage, Vel，concIs a concentration polarization voltage, Vel，ohmOhmic polarization voltage;
the invention is further improved in that: the heat transfer dynamic response model in S12 is represented as:
wherein T is the reaction temperature, ρ is the density of the substance, cpConstant pressure heat capacity, phi heat flow, V mass volume, h convective heat transfer coefficient, AA、AC、AS、AIRespectively the heat exchange areas of the anode fluid, the cathode fluid, the solid structure and the connection structure, sigma is Stefan constant, epsiloneFor emissivity, subscripts a, C, S, I denote anode fluid, cathode fluid, solid structure, and connecting structure, respectively.
The invention is further improved in that: the model identification in S3 simulates the input/output characteristics of the system using a set of transfer functions including 2 poles and 1 zero, and the transfer function model is represented as follows:
in the formula: u. of1For heating the steam generator u2As air flow rate, y1To reflect the steam flow, y2Is the electrochemical reaction temperature.
The invention is further improved in that: in the step S4, MPC control is adopted for model prediction control, the characteristics of electrochemistry and flow response rapidness and the comprehensive influence of steam and air flow on reaction temperature are considered according to the analysis of multi-time scale of variable response of the electrolytic cell, the power of a steam generator can be dynamically adjusted to supply steam flow without overshoot through control design, the reverse characteristic of the air flow is weakened, and the operation stability of the electrolytic cell is facilitated.
Wherein, the variable response of the electrolytic cell has the following characteristics in multiple time scales: electrochemical reactions (milliseconds), gas flow (seconds), and heat transfer (minutes).
In the control design, for each working condition, constraint parameters are set, including: sampling period tau, modeling time domain N, prediction time domain P, control time domain M, and step response sequence of output quantity to control quantity and disturbance quantity in the modeling time domain.
The invention is further improved in that: under the control of the MPC, when the fluctuation electric energy is dealt with, the steam flow is as follows:
wherein N is the total number of the cells, I is the electrolytic current, etaFFor electrolytic efficiency, F is the Faraday constant, MH2OIs the molar mass of water and alpha is the steam surplus ratio.
The beneficial effects of the invention are: according to the invention, a dynamic model of the high-temperature solid oxide water electrolysis hydrogen production system is established, model identification and control design are carried out, the problem of dynamic response lack of the hydrogen production system model when renewable energy input fluctuates is solved, and meanwhile, the high-efficiency control of the dynamic system is completed, so that the service life of materials is prolonged, and the operation stability of the system is improved.
Drawings
FIG. 1 is a schematic diagram of the apparatus of the present invention;
FIG. 2 is a schematic diagram of an apparatus model according to the present invention;
FIG. 3(a) is a response curve of the reaction steam flow rate when the heating power of the steam generator is stepped;
FIG. 3(b) is a response curve of the electrochemical reaction temperature at the step of the heating power of the steam generator;
FIG. 3(c) is a response curve of the reaction steam flow at the air flow step;
FIG. 3(d) is a response curve of electrochemical reaction temperature at air flow step;
FIG. 4 is a control system layout of the present invention (dashed line- -representing energy flow; solid line- -representing material flow);
FIG. 5 is a step disturbance plot of the power input of the present invention;
FIG. 6(a) is a steam generator power graph;
FIG. 6(b) is a graph of air flow rate;
FIG. 7(a) steam flow response graph;
FIG. 7(b) is a graph showing the temperature response of the electrolytic reaction.
The system comprises a steam generator 1, a hydrogen side heat exchanger 2, a gas-water separator 3, a hydrogen compressor 4, a hydrogen storage tank 5, a hydrogen side electric heater 6, a hydrogen side connection structure 7, a cathode flow channel 8, renewable energy direct current power 9, an air pump 10, an air side heat exchanger 11, an air side electric heater 12, an electrolytic bath 13, a cathode 14, an electrolyte 15, an anode 16, an anode flow channel 17 and an air side connection structure 18.
Detailed Description
The following further describes a dynamic energy efficiency optimization control method of an air source heat pump under outdoor temperature fluctuation conditions, which is disclosed by the invention, with reference to the accompanying drawings and the detailed description.
As shown in FIG. 1, the device for producing hydrogen by electrolyzing solid oxide facing to the consumption of fluctuating electric energy comprises an electrolytic bath 13 and an auxiliary machine; the auxiliary machine comprises a steam generator 1, a heat exchanger, an electric heater, a hydrogen storage tank 5, a hydrogen compressor 4, an air pump 10 and the like. The heat exchanger is used for recovering heat of reaction products and heating reaction raw materials, and comprises a hydrogen side heat exchanger and an air side heat exchanger, the air side heat exchanger 11 is communicated with the air pump 10, and the air pump 10 pumps air into the air side heat exchanger 11 for heat exchange to obtain hot air. The electric heater comprises a hydrogen side electric heater 6 and an air side electric heater, and the system auxiliary machine flow design adopts a multi-stage heat return and electric auxiliary heating method, so that the efficiency of the system is improved under the condition of ensuring the reaction temperature requirement.
The electrolytic bath 13 is a high-temperature solid oxide electrolytic bath, and specifically comprises an electrolyte and a cathode flow channelAn anode flow channel and a cathode-supported plate-type electrolytic cell of the connecting structure. Wherein the connection structure includes a hydrogen side connection structure 7 and an air side connection structure 18. The water vapor as a reaction raw material is generated by deionized water through the steam generator 1 and subjected to heat regeneration and reheating, and finally reaches the inlet of the electrolytic bath 13. In this embodiment, the cathode flow channel 8 and the anode flow channel 17 are both used for gas circulation, the height is 1mm, the length is 100mm, and the total contact area of the cathode flow channel 8 and the solid structure of a single cell is 0.025m2. The thickness of the solid structure formed by the electrolyte and the electrode is 0.57mm, the thickness of the connecting structure is 0.5mm, the mass of the solid structure of a single battery is 33.6g, and the mass of the connecting structure is 40 g.
The electrolytic cell consumes direct current power 9 of renewable energy, and superheated steam heated in multiple stages is electrified in the electrolytic cell to generate electrolytic reaction to generate hydrogen and oxygen. The cathode flow path 8 of the electrolytic bath 13 communicates with the hydrogen-side electric heater 6 and the hydrogen-side heat exchanger 2, the anode flow path 17 communicates with the air-side electric heater 12 and the air-side heat exchanger 11, and the cathode 14, the anode 16, and the electrolyte 15 are located between the flow paths so that oxygen ions pass therethrough. Wherein, the superheated steam ensures at least 10% hydrogen content to prevent electrode oxidation, the superheated steam obtains electron synthesis hydrogen by diffusing in the cathode flow channel 8 to the cathode 14 of the porous medium, the mixed gas of hydrogen and unreacted steam is produced in the cathode flow channel 8; oxygen ions pass through the solid oxide electrolyte 15 to the porous medium anode 16, lose electrons to generate oxygen, and are mixed with high-temperature air in the anode flow channel 17 to generate oxygen. The anode flow channel 17 is filled with high-temperature air, and the purpose of the high-temperature air is two, firstly, the high-temperature air can timely sweep and take away oxygen generated by the reaction to prevent the oxygen from being too high in concentration so that the reaction resistance is large, secondly, the high-temperature air can provide certain heat for the electrolytic reaction, and the temperature difference of the two poles is reduced to prevent the service life of the electrolytic cell 13 from being reduced due to too large thermal stress.
The amount of steam consumed is equal to the amount of hydrogen produced, which depends on the electrolysis current and the number of electrolysis cells. The electrolysis of 1mol of steam produces 1mol of hydrogen and 0.5mol of oxygen. The hydrogen and oxygen production was calculated as follows:
wherein N is the total number of cells, I is the electrolytic current, etaFFor electrolytic efficiency, F is the Faraday constant.
The water decomposition reaction is an endothermic process, and additional heat needs to be supplied to the electrolysis device in addition to the electric energy to ensure the reaction. The total energy input into the electrolytic cell comprises the enthalpy of reaction raw materials and electrolytic electric energy, the energy output by the electrolytic cell comprises the enthalpy of hydrogen and oxygen and the heat value of the hydrogen, and work is done on the environment by neglecting gas expansion. The total energy change of electrolysis is as follows:
ΔH＝ΔG+TΔS (3)
wherein, Δ H is reaction enthalpy change, Δ G is Gibbs free energy, and Δ S is reaction entropy change.
The dynamic modeling method of the solid oxide electrolysis hydrogen production system facing fluctuating electric energy absorption comprises the following specific steps:
s1: constructing a dynamic model of a high-temperature solid oxide electrolytic cell by taking fluctuating renewable energy power as a unique energy source based on electrochemistry and a heat transfer mechanism; the internal state variable of the electrolytic cell dynamic model is constructed by a dynamic differential equation, and the multi-time scale characteristic of electrolytic cell variable response is considered: electrochemical reactions (milliseconds), gas flow (seconds), and heat transfer (minutes);
s2: constructing a dynamic model of each auxiliary machine component of the high-temperature solid oxide electrolytic hydrogen production system and simulating the electrolytic hydrogen production process; the auxiliary machine flow design adopts a method of combining multi-stage heat regeneration and electric auxiliary heating, and the efficiency of the system is improved under the condition of ensuring the reaction temperature requirement;
the method for combining the multistage backheating and the electric auxiliary heating specifically comprises the following steps: the anode reaction product is air backheating in the air side heat exchanger 11, the cathode reaction product is steam backheating in the hydrogen side heat exchanger 2, and the reaction product after heat exchange is continuously introduced into the steam generator 1 for secondary backheating to provide phase change heat for water; meanwhile, an electric heating device is arranged in the steam generator 1 and performs graded electric auxiliary heating with the electric heater, so that the inlet gas of the electrolytic cell 13 meets the requirements of flow and reaction temperature;
s3: identifying a mechanism model of the high-temperature solid oxide water electrolysis hydrogen production system by a double-input double-output transfer function model;
s4: performing model prediction control based on the identification model; the model prediction control method considers the characteristics of electrochemistry and quick flow response and the comprehensive influence of steam and air flow on reaction temperature according to the analysis of a multi-time scale of an electrolytic cell dynamic model, and dynamically adjusts the steam supply flow under the condition of no overshoot by controlling the design so as to weaken the reverse characteristic of the air flow and be beneficial to the operation stability of the electrolytic cell.
The construction of the dynamic model of the electrolytic cell in S1 specifically comprises the following steps:
s11: constructing an electrochemical model of the high-temperature solid oxide electrolytic cell according to an electrochemical principle;
s12: and constructing a heat transfer model of the high-temperature solid oxide electrolytic cell according to the electrolytic cell model structure.
In the step S11, in order to calculate the electrochemical characteristics and the electric energy consumption of the electrolytic cell, various voltages and energy consumption of the electrolytic cell are analyzed, and the method specifically comprises the following steps:
s111: calculating the reversible voltage of the electrolytic reaction:
the reversible voltage is related to the reaction temperature, and can be obtained by Gibbs free energy calculation:
E(V)＝1.29-0.000292(T-273) (4)
in the formula, T is electrochemical reaction temperature, and E is reversible voltage;
s112: calculating the voltage loss of the electrolytic reaction, and analyzing the ohmic polarization, concentration polarization and activation polarization voltage of the electrolytic reaction:
the activation loss is represented by an activation polarization voltage:
wherein R is an ideal gas constant, J is an electrolytic current density, J0To exchange current density.
The ohmic loss is expressed by ohmic polarization voltage:
Vohm＝JdLRohm (6)
in the formula (d)LIs the thickness of the electrolyte, RohmIs an ohmic resistance.
The concentration loss is represented by concentration polarization voltage:
in the formula dCThe thickness of the cathode is taken as the thickness of the cathode,
is the effective diffusion coefficient of the vapor and,
is the pressure of the steam, and is,
is the hydrogen pressure.
S113: calculating the total energy consumption of the electrolytic reaction;
the total electrolysis voltage is obtained by adding the reversible voltage, the activation polarization voltage, the ohmic polarization voltage and the concentration polarization voltage, namely:
Vel＝E+Vel,act+Vel,ohm+Vel,conc (8)
wherein, VelFor total electrolytic voltage, E is reversible voltage, Vel，actTo activate the polarization voltage, Vel，concIs a concentration polarization voltage, Vel，ohmIs the ohmic polarization voltage;
the total reaction energy consumption is obtained by multiplying the electrolysis energy consumption of a single cell by the total number of cells of the electrolytic cell stack, namely:
W＝N·VelI (9)
wherein, W is the total energy consumption of the electrolytic cell, N is the total number of the batteries, and I is the electrolytic current.
In S12, the cell heat transfer model considers convective heat transfer of the reactant materials with PEN (solid structure, including anode, electrolyte, and cathode), convective heat transfer of the reactant materials with the linking structure, and radiative heat transfer of PEN with the linking structure. The heat transfer differential equation for the cell dynamic model is shown below:
wherein T is the reaction temperature, rho is the material density, cpConstant pressure heat capacity, phi heat flow, V mass volume, h convective heat transfer coefficient, AA、AC、AS、AIRespectively the heat exchange areas of the anode fluid, the cathode fluid, the solid structure and the connection structure, sigma is Stefan constant, epsiloneFor emissivity, subscripts a, C, S, I denote anode fluid, cathode fluid, solid structure, and connecting structure, respectively.
The steam generator in the S2 comprises a heat recovery device and an electric heating device, wherein the heat recovery device is used for absorbing the waste heat of the reaction product, the electric heating device is used for complementing the latent heat of vaporization of the deionized water, so that the pressure head of the water vapor is enough to meet the required flow of the reaction raw material, and the flow of the water vapor is controlled by the power of an electric heater in the steam generator. The steam generator 1 consumes deionized water, generates steam slightly higher than normal pressure, generates steam with the output temperature of about 400K, passes through the hydrogen-side heat exchanger 2 and the hydrogen-side electric heater 6, raises the temperature to about 1000K, and is introduced into the electrolytic cell 13 for reaction. The hydrogen and the oxygen-enriched air as reaction products are produced by the reaction of the electrolytic cell 13, and have higher internal energy, and part of heat energy can be used for reheating the reaction raw materials through the hydrogen side heat exchanger 2 and the air side heat exchanger 11. After the heat regeneration process is finished, the gas temperature is about 400K, unreacted steam is contained in hydrogen at the moment, the cathode product needs to be condensed and subjected to steam-water separation without obtaining dry hydrogen, the separated hydrogen is compressed and stored through the hydrogen compressor 4 and the hydrogen storage tank 5, the power consumption of the hydrogen compressor 4 depends on the mass flow of the produced hydrogen, and the gas storage pressure is 3 MPa.
The multi-equipment high-temperature solid oxide water electrolysis hydrogen production system is composed of mass equations and energy equations of all the equipment, has complex dynamic characteristics, and a model established by adopting a differential equation has higher calculation complexity, so that the system is identified to obtain a transfer function of input and output data so as to simplify calculation in control design. Two input variables are considered in the recognition design of step S3: air flow and steam generator heating power, the input-output characteristics of the system were modeled using a set of transfer functions containing 2 poles and 1 zero. The transfer function model is as follows:
in the formula: u. u1For heating the steam generator u2As air flow rate, y1To reflect the steam flow, y2Is the electrochemical reaction temperature.
When identifying the step of the input variable in the model, the response curve of the output variable is shown in FIG. 3(a), FIG. 3(b), FIG. 3(c) and FIG. 3(d)Heating power (u) in the steam generator1) And air flow rate (u)2) In the case of a step change, the steam flow (y) can be simulated1) And reaction temperature (y)2) The response curve of (c). The manipulated variable u is shown in FIGS. 3(a) and 3(b)1When the speed is changed from 500W to 800W, the controlled variable y1And y2The response curve of (c). The graph illustrates that as the steam generator heating power increases, the steam flow increases and the reaction temperature decreases. The manipulated variable u is shown in FIGS. 3(c) and 3(d)2From 2X 10-4Step change of kg/s to 3X 10-4kg/s, controlled variable y1And y2The response curve of (c). The results show that an increase in air flow results in an increase in reaction temperature, while steam flow is not affected.
The heating power and the air mass flow of the steam generator are used as control input quantities, and the electrolysis reaction temperature and the steam flow are used as controlled variables. And carrying out open-loop step response tests under different steady-state working conditions to obtain the identification models of the controlled object under different working conditions. In the control design, constraint parameters are set for each working condition, and the constraint parameters comprise: sampling period tau, a modeling time domain N, a prediction time domain P, a control time domain M, and a step response sequence of an output quantity in the modeling time domain to a control quantity and a disturbance quantity; setting the constraint parameters comprises: control delta constraint Deltaumax、ΔuminControl quantity constraint umax、uminOutput quantity constraint ymax、ymin(ii) a Wherein, Δ umaxTo control the maximum value of the increment, Δ uminTo control the minimum value of the increment, umaxAs maximum value of the control quantity, uminAs minimum value of control quantity, ymaxAs maximum value of the output quantity, yminIs the minimum value of the output.
FIG. 4 is a model of a constructed dual input dual output MPC controller, in the case shown, with the steam reaction temperature in the electrolyzer set to 1073K and the steam flow set to 3X 10-4kg/s, when dealing with fluctuating electric energy, the steam flow is obtained by converting the flow of reaction products, and specifically comprises the following steps:
in the formula (I), the compound is shown in the specification,
alpha is the steam surplus rate, and the value of alpha is 10-20% generally.
The controller design is carried out based on a high-temperature solid oxide water electrolysis hydrogen production system. The controller adopts the heating power and the air flow of the steam generator as manipulated variables, and adopts the steam flow and the reaction temperature as controlled variables. The prediction and control ranges are set to be 20 seconds and 1 second respectively, and the ranges optimize the calculation time on the premise of ensuring smaller prediction error and convergence of the controlled object. The controller is designed to ensure that the actual flow of reaction raw materials reaches 1.25 times of the theoretical electrolysis requirement, and the reaction temperature is stabilized at 1073K, so that the stability of the hydrogen production process is maintained, and the service life of the materials is prolonged. The control variables of the control design are measured by a temperature sensor for recording the real-time temperature of the electrolysis reaction and a flow sensor for recording the mass flow of the gas generated by the steam generator.
FIGS. 6(a) and 6(b) show the respective amplitudes of the current densities at 0.7A/cm2， 0.8A/cm2，0.9A/cm2When the input electric energy is increased, the hydrogen production amount of the electrolysis reaction is correspondingly increased, and the flow of the anode fluid needs to be increased to provide heat for the electrolysis reaction. However, since the time scale of fluid flow and heat transfer is large, the thermoelectric loss due to the increase of current density is instantaneously increased at the initial stage of the increase of input electric energy, that is, at the stages of 500s-560s and 1000s-1060s, the reaction raw material is not replenished in time, the electrolytic heat loss is increased and the reaction heat demand is not significantly increased, so that the heat supply overflows and the reaction temperature rises, and the anode flow is temporarily reduced to reduce the reaction heat supply. And in the later period, along with the increase of the flow of the reaction raw materials and the increase of the demand of electrolysis heat, the flow of the anode fluid is gradually increased to provide heat for the reaction. As shown in the figure6(a) and 6(b), under the MPC control strategy, the steam generator power can dynamically adjust the steam supply flow rate under the condition of no overshoot, the reverse characteristic of the air flow rate is weakened, the flow rate fluctuation is small, and the stability of the air pump and the electrolytic cell is facilitated. The control result is shown in fig. 7(a) and 7(b), under the step disturbance of the electric energy input, the traditional two-way PI control is adopted, the maximum deviation of the reaction temperature is larger than 3K, the influence of the air flow and the steam flow on the reaction temperature is comprehensively considered by adopting an MPC control scheme, the fluctuation range of the reaction temperature is controlled within 1071.5K-1074K, the maximum deviation is smaller than 1.5K, the response time is about 300s, and the system response is fast and small.
According to the invention, through dynamic modeling of the solid oxide electrolytic hydrogen production system, system identification and MPC control design, in the face of inputting fluctuating renewable energy, reaction raw materials meeting the reaction requirements can be quantitatively supplied to the electrolytic system by adjusting the power and air flow of the steam generator, so that the accurate control of the reaction temperature is realized, the stability of the electrolytic hydrogen production process is facilitated, the thermal stress of an electrolyte material is reduced, and the service life is prolonged.
The technical means disclosed in the scheme of the invention are not limited to the technical means disclosed in the above embodiments, but also include the technical means formed by any combination of the above technical features. It should be noted that modifications and adaptations can be made by one of ordinary skill in the art without departing from the principles of the present invention. Such modifications and refinements are also considered to be within the scope of the present invention.
Claims (7)
1. A dynamic modeling method for a solid oxide electrolytic hydrogen production system facing fluctuating electric energy absorption is characterized by comprising the following steps: the method comprises the following steps:
s1: constructing a dynamic model of a high-temperature solid oxide electrolytic cell by taking fluctuating renewable energy power as a unique energy source based on electrochemistry and a heat transfer mechanism;
s2: constructing a dynamic model of each auxiliary machine component of the high-temperature solid oxide electrolytic hydrogen production system and simulating the electrolytic hydrogen production process;
s3: identifying a mechanism model of the high-temperature solid oxide water electrolysis hydrogen production system by a double-input double-output transfer function model;
s4: and performing model predictive control design based on the identified transfer function model.
2. The dynamic modeling method for the solid oxide electrolysis hydrogen production system facing fluctuating electric energy absorption as claimed in claim 1, is characterized in that: the specific steps of S1 are:
s11, constructing an electrochemical dynamic response model of the high-temperature solid oxide electrolytic cell according to an electrochemical principle;
and S12, constructing a heat transfer dynamic response model of the high-temperature solid oxide electrolytic cell according to the electrolytic cell model structure.
3. The dynamic modeling method for the solid oxide electrolysis hydrogen production system facing fluctuating electric energy absorption as claimed in claim 1, characterized in that: the internal state variable of the electrolytic cell (13) model is constructed by a dynamic differential equation, and the multi-time scale characteristic of electrolytic cell variable response is considered: electrochemical reactions on the order of milliseconds, gas flows on the order of seconds, and heat transfer on the order of minutes.
4. The dynamic modeling method for the solid oxide electrolysis hydrogen production system facing fluctuating electric energy absorption as claimed in claim 1, characterized in that: the heat transfer dynamic response model in S12 is expressed as:
wherein T is the reaction temperature, rho is the material density, cpConstant pressure heat capacity, phi heat flow, V mass volume, h convective heat transfer coefficient, AA、AC、AS、AIRespectively the heat exchange areas of the anode fluid, the cathode fluid, the solid structure and the connection structure, sigma is Stefan constant, epsiloneFor emissivity, subscripts a, C, S, I denote anode fluid, cathode fluid, solid structure, and connecting structure, respectively.
5. The dynamic modeling method for the solid oxide electrolysis hydrogen production system facing fluctuating electric energy absorption as claimed in claim 1, characterized in that: model identification in S3 simulates input/output characteristics of a system using a set of transfer function models including 2 poles and 1 zero, and the transfer function models are expressed as follows:
in the formula: u. u1For heating the steam generator u2Is the air flow rate, y1To reflect the steam flow, y2Is the electrochemical reaction temperature.
6. The dynamic modeling method for the solid oxide electrolysis hydrogen production system facing fluctuating electric energy absorption as claimed in claim 1, is characterized in that: the model predictive control in the step S4 is MPC control, air flow and steam generator heating power as manipulated variables, steam flow and reaction temperature as controlled variables, and prediction and control ranges are set to 20 seconds and 1 second, respectively.
7. The dynamic modeling method for the solid oxide electrolysis hydrogen production system facing fluctuating electric energy absorption as claimed in claim 6, characterized in that: under the control of the MPC, the steam flow during the wave electric energy is taken as a system state variable, and the value of the steam flow is related to the electrolytic current:
wherein N is the total number of the cells, I is the electrolytic current, etaFFor the electrolytic efficiency, F is the Faraday constant,
is the molar mass of water and alpha is the steam surplus ratio.
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| CN117153280B (en) * | 2023-08-31 | 2024-05-03 | 山东大学 | Simulation model building method, simulation method and simulation system of alkaline electrolysis hydrogen production system |
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| CN117153280B (en) * | 2023-08-31 | 2024-05-03 | 山东大学 | Simulation model building method, simulation method and simulation system of alkaline electrolysis hydrogen production system |
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