CN115911469B - Control method of solid oxide fuel cell system for autothermal reforming of methanol - Google Patents

Abstract

The present invention discloses a control method for a solid oxide fuel cell system for methanol autothermal reforming. The method comprises the following steps: constructing a reforming temperature model, a reforming gas production model, a buffer tank pressure model, a stack power model, and a stack anode inlet flow model; a first controller selects the inlet flow _F3 of the cold end of the combustion heat exchanger as a control variable to realize feedback tracking of the set value T2 _{, ref} of the outlet gas temperature of the cold end of the reforming heat exchange chamber; a second controller selects the inlet flow _F1 of the cold end of the reforming heat exchange chamber as a control variable to realize feedback tracking of the set value F2 _{, ref} of the outlet flow of the cold end of the reforming heat exchange chamber; a third controller selects the output current I of the SOFC stack as a control variable to realize feedback tracking of the set value _{Ps, ref} of the stack power. The present invention overcomes the temperature control interference caused by the fluctuation of the reforming material while ensuring the balance of the system reforming gas production and the stack gas supply, and realizes the rapid and accurate tracking and control of the load power and the reforming temperature.

Description

A control method for a solid oxide fuel cell system for methanol autothermal reforming

Technical Field

The present invention relates to the technical field of fuel cell system control, and in particular to a control method for a methanol autothermal reforming solid oxide fuel cell system.

Background Art

The cheap production of hydrogen energy and its safe storage and transportation are important bottlenecks that restrict the large-scale development of fuel cells. Direct use of hydrogen as fuel has disadvantages such as poor safety, low storage efficiency, and strict requirements for hydrogen storage devices. It is currently only applicable to high value-added industries such as hydrogen fuel cell vehicles. In this context, fuel cell technology based on methanol reforming stands out. It uses methanol in liquid form to store hydrogen energy. When needed, hydrogen is prepared through methanol reforming reactions, and then introduced into fuel cells for electrochemical reactions to convert hydrogen energy into electrical energy. However, compared with the direct use of hydrogen for power generation, the process structure of the methanol reforming SOFC system is relatively complex, and it is difficult to achieve a balance between the temperature and logistics characteristics of slow reforming hydrogen production and the rapid electrochemical reaction of the fuel cell during operation.

At present, the research on the control of methanol reforming fuel cell system mainly focuses on the control requirements of reforming hydrogen production and fuel cells, such as hydrogen supply management, power distribution, reforming temperature control, etc., ignoring the material and temperature coupling balance problem when the fuel cell and reforming hydrogen production are linked. Especially when facing fast-changing load conditions, how to stabilize the fluctuation of key reaction temperature of the system while ensuring the balance of reforming gas production and stack gas supply needs further exploration. In addition, most of the research objects are concentrated in the PEMFC system, which is different from the methanol reforming SOFC system process, and the relevant research results are difficult to be directly applied to the SOFC technology route.

Summary of the invention

In order to solve the above technical problems, the present invention provides a control method for a solid oxide fuel cell system with methanol autothermal reforming, which not only ensures the balance of system reforming gas production and fuel cell stack gas supply, but also overcomes the temperature control interference caused by fluctuations in reforming materials, and realizes rapid and accurate tracking and control of load power and reforming temperature.

In order to solve the above problems, the present invention adopts the following technical solutions:

A control method for a methanol autothermal reforming solid oxide fuel cell system of the present invention, the solid oxide fuel cell system comprises a reforming combustion integrated machine, a buffer tank, an SOFC stack, a first controller, a second controller, and a third controller, the reforming combustion integrated machine comprises a reforming heat exchange chamber, a combustion heat exchanger, and a combustion chamber, comprising the following steps:

S1: Construct the reforming temperature model and reforming gas production model of the reforming combustion integrated machine, construct the buffer tank pressure model of the buffer tank, construct the stack power model and stack anode inlet flow model of the SOFC stack;

S2: The first controller selects the inlet flow _F3 of the cold end of the combustion heat exchanger as the control variable to realize feedback tracking of the set value T2 _{, ref} of the outlet gas temperature of the cold end of the reforming heat exchange chamber; the second controller selects the inlet flow _F1 of the cold end of the reforming heat exchange chamber as the control variable to realize feedback tracking of the set value F2 _{, ref} of the outlet flow of the cold end of the reforming heat exchange chamber; the third controller selects the output current I of the SOFC stack as the control variable to realize feedback tracking of the set value _{Ps, ref} of the stack power.

Preferably, the method for feedback tracking of the set value _T2,ref of the outlet gas temperature at the cold end of the reforming heat exchange chamber by the first controller in step S2 is as follows:

The first controller adjusts the inlet flow rate _F3 of the cold end of the combustion heat exchanger according to the difference between the outlet gas temperature _T2 of the cold end of the reforming heat exchange chamber and the set value T2 _,ref of the outlet gas temperature of the cold end of the reforming heat exchange chamber.

The first controller is an incremental PID controller, which adjusts the inlet flow _F3 of the cold end of the combustion heat exchanger according to the difference between the outlet gas temperature _T2 of the cold end of the reforming heat exchange chamber and the set value T2,ref, so that the outlet gas temperature _T2 of the cold end of the reforming heat exchange chamber approaches the set value _{T2, ref} , thereby realizing fast and accurate tracking and control of the reforming temperature.

Preferably, the method for feedback tracking of the set value _F2,ref of the outlet flow rate at the cold end of the reforming heat exchange chamber by the second controller in step S2 is as follows:

The second controller includes a second main controller module and a second sub-controller module. The second main controller module corrects the reforming heat exchange chamber cold end outlet flow set value _F2,ref according to the difference between the buffer tank pressure _Pt and the buffer tank pressure set value _Pt,ref. The second sub-controller module adjusts the reforming heat exchange chamber cold end inlet flow _F1 according to the difference between the reforming heat exchange chamber cold end outlet flow F2 and the corrected reforming heat exchange chamber cold end outlet flow set value _F2,ref .

The second main controller module and the second sub-controller module are both incremental PID controllers. The second main controller module adopts a PID control strategy with a dead zone to construct an outer-loop pressure control loop according to the difference between the buffer tank pressure _Pt and the set value _Pt,ref , so as to realize the real-time correction of the set value F2 _, ref of the outlet flow rate at the cold end of the reforming heat exchange chamber. The second sub-controller module adjusts the inlet flow rate _F1 at the cold end of the reforming heat exchange chamber according to the difference between the outlet flow rate F2 at the cold end of the reforming heat exchange chamber _and the corrected set value _F2,ref , so that the outlet flow rate _F2 at the cold end of the reforming heat exchange chamber approaches the set value F2 _,ref , thereby realizing the rapid and accurate tracking and control of the reforming gas production.

Preferably, the method for feedback tracking of the stack power setting value P _s,ref by the third controller in step s3 is as follows:

The third controller includes a third main controller module and a feedforward controller module. The third main controller module calculates the output current I that the SOFC stack should output according to the difference between the stack power _Ps and the stack power setting value Ps _,ref . The feedforward controller module calculates the value of the stack anode inlet flow _F9 according to the SOFC stack fuel utilization setting value _Uf,ref and the output current I, and adjusts the stack anode inlet flow _F9 accordingly to reach the calculated value.

The third main controller module is an incremental PID controller. The third main controller module calculates the output current I that the SOFC stack should output according to the difference between the stack power _Ps and the set value Ps, _ref . The feedforward controller module calculates the value that the stack anode inlet flow _F9 should reach for the SOFC stack to achieve the output current I according to the set value _Uf,ref of the SOFC stack fuel utilization and the output current I, and controls the stack anode inlet flow _F9 of the SOFC stack to reach the calculated value, thereby realizing rapid and accurate tracking and control of the stack power.

Preferably, the formula of the reforming temperature model is as follows:

Wherein, _Cr is the heat capacity of the cold end of the reforming heat exchange chamber, Kr is the heat capacity of the hot end of the reforming heat exchange chamber, _T2 is the outlet gas temperature of the cold end of the reforming heat exchange chamber, _T7 is the outlet gas temperature of the hot end of the reforming heat exchange chamber, _F1 is the inlet flow rate of the cold end of the reforming heat exchange chamber, _F2 is the outlet flow rate of the cold end of the reforming heat exchange chamber, C1 _,i is the mole fraction of the i reactant at the inlet of the cold end of the reforming heat exchange chamber, C2 _,i is the mole fraction of the i reactant at the outlet of the cold end of the reforming heat exchange chamber, h _i is the molar enthalpy change of the i reactant, _U1 is the heat transfer coefficient of the reforming heat exchange chamber, and _A1 is the heat exchange area of the reforming heat exchange chamber.

Preferably, the formula of the reforming gas production model is as follows:

Wherein, _F1 is the inlet flow rate of the cold end of the reforming heat exchange chamber, _F2 is the outlet flow rate of the cold end of the reforming heat exchange chamber, _vij is the stoichiometric coefficient of the i reactant in the j reaction, _Rj is the reaction rate of the j reaction, DE is the methanol decomposition reaction, SR is the methanol direct reforming reaction, and WGS represents the water steam shift reaction.

Preferably, the formula of the buffer tank pressure model is as follows:

Wherein, _Vt is the volume of the buffer tank, _Pt is the pressure of the buffer tank, R is the gas constant, T is the gas temperature in the buffer tank, _F2 ' is the gas inlet flow rate of the buffer tank, _F9 ' is the gas outlet flow rate of the buffer tank, is the mole fraction of CH ₃ OH at the buffer tank inlet, is the mole fraction of H ₂ O at the buffer tank inlet.

Preferably, the formula of the stack power model is as follows:

_Ps = VI,

Among them, _Ps is the stack power, V is the output voltage of the stack, and I is the output current of the stack.

Preferably, the formula of the stack anode inlet flow model is as follows:

Wherein, _Uf is the fuel utilization rate of the stack, N is the number of cells in the stack, I is the output current of the stack, F is the Faraday constant, _F9 is the anode inlet flow rate of the stack, is the mole fraction of _H2 at the anode inlet of the stack.

The beneficial effects of the present invention are: while ensuring the balance of system reforming gas production and fuel cell stack gas supply, it overcomes the temperature control interference caused by reforming material fluctuations and realizes rapid and accurate tracking and control of load power and reforming temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of the present embodiment;

FIG2 is a schematic diagram of the structure of a reforming and combustion integrated machine;

FIG3 is a diagram showing the control effect of the battery stack power;

FIG4 is a control effect diagram of the reforming temperature;

FIG. 5 is a diagram showing the control effect of the fuel utilization rate of the fuel cell stack.

In the figure: 1. Reforming and combustion integrated machine, 2. Buffer tank, 3. SOFC stack, 4. Reforming heat exchange chamber, 5. Combustion heat exchanger, 6. Combustion chamber, 7. First controller, 8. Second main controller module, 9. Second sub-controller module, 10. Third main controller module, 11. Feedforward controller module.

DETAILED DESCRIPTION

The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

Embodiment: A control method for a methanol autothermal reforming solid oxide fuel cell system of this embodiment, as shown in FIG1 and FIG2, the solid oxide fuel cell system includes a reforming combustion integrated machine 1, a buffer tank 2, an SOFC stack 3, a first controller 7, a second controller, and a third controller. The reforming combustion integrated machine 1 includes a reforming heat exchange chamber 4, a combustion heat exchanger 5, and a combustion chamber 6, and includes the following steps:

S1: Construct the reforming temperature model and reforming gas production model of the reforming combustion integrated machine, construct the buffer tank pressure model of the buffer tank, construct the stack power model and stack anode inlet flow model of the SOFC stack;

The formula for the reforming temperature model is as follows:

Wherein, _Cr is the heat capacity of the cold end of the reforming heat exchange chamber, _Kr is the heat capacity of the hot end of the reforming heat exchange chamber, _T2 is the outlet gas temperature of the cold end of the reforming heat exchange chamber, _T7 is the outlet gas temperature of the hot end of the reforming heat exchange chamber, _F1 is the inlet flow rate of the cold end of the reforming heat exchange chamber, _F2 is the outlet flow rate of the cold end of the reforming heat exchange chamber, _C1,i is the mole fraction of the i reactant at the inlet of the cold end of the reforming heat exchange chamber, C2 _,i is the mole fraction of the i reactant at the outlet of the cold end of the reforming heat exchange chamber, h _i is the molar enthalpy change of the i reactant, _U1 is the heat transfer coefficient of the reforming heat exchange chamber, and _A1 is the heat exchange area of the reforming heat exchange chamber;

The formula of the reforming gas production model is as follows:

Wherein, _F1 is the inlet flow rate of the cold end of the reforming heat exchange chamber, _F2 is the outlet flow rate of the cold end of the reforming heat exchange chamber, _vij is the stoichiometric coefficient of the i reactant in the j reaction, _Rj is the reaction rate of the j reaction, DE is the methanol decomposition reaction, and the chemical reaction formula of DE is CH ₃ OH(g)→CO+2H ₂ , SR is the direct reforming reaction of methanol, and the chemical reaction formula of SR is CH ₃ OH(g)+H ₂ O(g)→CO ₂ +3H ₂ , WGS represents the steam shift reaction, and the chemical reaction formula of WGS is CO+H ₂ O(g)→CO ₂ +H ₂ ;

The formula for the buffer tank pressure model is as follows:

Wherein, _Vt is the volume of the buffer tank, _Pt is the pressure of the buffer tank, R is the gas constant, T is the gas temperature in the buffer tank, _F2 ' is the gas inlet flow rate of the buffer tank, _F9 ' is the gas outlet flow rate of the buffer tank, is the mole fraction of CH ₃ OH at the buffer tank inlet, is the mole fraction of H ₂ O at the buffer tank inlet;

The formula of the stack power model is as follows:

_Ps = VI,

Wherein, _Ps is the stack power, V is the output voltage of the stack, and I is the output current of the stack;

The formula of the stack anode inlet flow model is as follows:

Wherein, _Uf is the fuel utilization rate of the stack, N is the number of cells in the stack, I is the output current of the stack, F is the Faraday constant, _F9 is the anode inlet flow rate of the stack, is the mole fraction of _H2 at the anode inlet of the stack;

S2: The first controller selects the inlet flow _F3 of the cold end of the combustion heat exchanger as the control variable to realize feedback tracking of the set value T2 _{, ref} of the outlet gas temperature of the cold end of the reforming heat exchange chamber; the second controller selects the inlet flow _F1 of the cold end of the reforming heat exchange chamber as the control variable to realize feedback tracking of the set value F2 _{, ref} of the outlet flow of the cold end of the reforming heat exchange chamber; the third controller selects the output current I of the SOFC stack as the control variable to realize feedback tracking of the set value _{Ps, ref} of the stack power.

In step S2, the method for the first controller to feedback and track the set value T2 _,ref of the gas temperature at the cold end outlet of the reforming heat exchange chamber is as follows:

The first controller adjusts the inlet flow rate _F3 of the cold end of the combustion heat exchanger according to the difference between the outlet gas temperature _T2 of the cold end of the reforming heat exchange chamber and the set value T2 _,ref of the outlet gas temperature of the cold end of the reforming heat exchange chamber.

In step S2, the feedback tracking method of the second controller for the set value _F2,ref of the outlet flow rate at the cold end of the reforming heat exchange chamber is as follows:

The second controller includes a second main controller module 8 and a second sub-controller module 9. The second main controller module corrects the outlet flow rate setting value F2, _ref of the cold end of the reforming heat exchange chamber according to the difference between the buffer tank pressure _Pt and the buffer tank pressure setting value Pt, _ref. The second sub-controller module adjusts the inlet flow rate _F1 of the cold end of the reforming heat exchange chamber according to the difference between the outlet flow rate _F2 of the cold end of the reforming heat exchange chamber and the corrected outlet flow rate setting value _F2,ref of the cold end of the reforming heat exchange chamber.

In step s3, the method for feedback tracking of the stack power setting value P _s,ref by the third controller is as follows:

The third controller includes a third main controller module 10 and a feedforward controller module 11. The third main controller module calculates the output current I that the SOFC stack should output according to the difference between the stack power _Ps and the stack power setting value _Ps,ref . The feedforward controller module calculates the value of the stack anode inlet flow _F9 according to the SOFC stack fuel utilization setting value _Uf,ref and the output current I, and adjusts the stack anode inlet flow _F9 accordingly to reach the calculated value.

In this solution, the first controller is an incremental PID controller, which adjusts the inlet flow _F3 of the cold end of the combustion heat exchanger according to the difference between the outlet gas temperature _T2 of the cold end of the reforming heat exchange chamber and the set value T2, _ref , so that the outlet gas temperature _T2 of the cold end of the reforming heat exchange chamber approaches the set value T2 _,ref , thereby realizing rapid and accurate tracking and control of the reforming temperature.

The second main controller module and the second sub-controller module are both incremental PID controllers. The second main controller module adopts a PID control strategy with a dead zone according to the difference between the buffer tank pressure _Pt and the set value _Pt,ref, and constructs an outer ring pressure control loop, thereby realizing real-time correction of the set value F2 _,ref of the outlet flow rate at the cold end of the reforming heat exchange chamber, and sends the corrected outlet flow rate set value F2 _,ref of the cold end of the reforming heat exchange chamber to the second sub-controller module. The second sub-controller module adjusts the inlet flow rate _F1 of the cold end of the reforming heat exchange chamber according to the difference between the outlet flow rate F2 of the cold _end of the reforming heat exchange chamber and the corrected set value _F2,ref , so that the outlet flow rate _F2 of the cold end of the reforming heat exchange chamber approaches the set value F2 _,ref , thereby realizing rapid and accurate tracking and control of the reforming gas production.

The third main controller module is an incremental PID controller. The third main controller module calculates the output current I that the SOFC stack should output according to the difference between the stack power _Ps and the set value Ps, _ref , and sends the calculated output current I to the feedforward controller module. The feedforward controller module calculates the value that the stack anode inlet flow F9 should reach for the SOFC stack to achieve the output current I according to the set value _Uf,ref of the SOFC stack fuel utilization rate and the output current _I , and controls the stack anode inlet flow _F9 of the SOFC stack to reach the calculated value, thereby realizing rapid and accurate tracking and control of the stack power.

The load power reference value is set to change randomly between 150W and 200W, with a change cycle of 600S and a duration of 6000S. The control effect diagram of the stack power of the solid oxide fuel cell system under the control method of this scheme is shown in Figure 3, the control effect diagram of the reforming temperature is shown in Figure 4, and the control effect diagram of the stack fuel utilization rate is shown in Figure 5. It can be seen from Figures 3, 4 and 5 that during the rapid step change of the load reference value, the stack output power and fuel utilization rate can quickly achieve error-free tracking of the target reference value, where the power tracking stabilization time is about 25S (the overshoot is constrained within ±1.5W), and the fuel utilization rate tracking stabilization time is about 30S. Although each load change will cause the fuel utilization rate control to overshoot, the related overshoot is always kept below 0.75, which effectively solves the fuel deficit problem caused by the sudden change of the load. The reforming temperature control stabilization time is relatively long (about 3000S), and under the influence of the material flow fluctuation, there is only a slight deviation (about 0.8℃) from the target value, which also achieves accurate tracking of the target value.

Claims (1)

1. A control method for a methanol autothermal reforming solid oxide fuel cell system, the solid oxide fuel cell system comprising a reforming combustion integrated machine, a buffer tank, an SOFC stack, a first controller, a second controller, and a third controller, the reforming combustion integrated machine comprising a reforming heat exchange chamber, a combustion heat exchanger, and a combustion chamber, characterized in that it comprises the following steps: S1: Construct the reforming temperature model and reforming gas production model of the reforming combustion integrated machine, construct the buffer tank pressure model of the buffer tank, construct the stack power model and stack anode inlet flow model of the SOFC stack; S2: The first controller selects the inlet flow rate _F3 of the cold end of the combustion heat exchanger as the control variable to realize the feedback tracking of the set value T2 _{, ref} of the outlet gas temperature of the cold end of the reforming heat exchange chamber; the second controller selects the inlet flow rate _F1 of the cold end of the reforming heat exchange chamber as the control variable to realize the feedback tracking of the set value F2 _{, ref} of the outlet flow rate of the cold end of the reforming heat exchange chamber; the third controller selects the output current I of the SOFC stack as the control variable to realize the feedback tracking of the set value _{Ps, ref} of the stack power; In step S2, the method for the first controller to feedback and track the set value T2 _,ref of the gas temperature at the cold end outlet of the reforming heat exchange chamber is as follows: The first controller adjusts the inlet flow rate F ₃ of the cold end of the combustion heat exchanger according to the difference between the outlet gas temperature T ₂ of the cold end of the reforming heat exchange chamber and the set value T _{2, ref} of the outlet gas temperature of the cold end of the reforming heat exchange chamber; The method for feedback tracking of the set value _F2,ref of the outlet flow rate at the cold end of the reforming heat exchange chamber by the second controller in step S2 is as follows: The second controller includes a second main controller module and a second sub-controller module. The second main controller module corrects the outlet flow rate setting value _{F2, ref} of the cold end of the reforming heat exchange chamber according to the difference between the buffer tank pressure _Pt and the buffer tank pressure setting value Pt,ref. The second sub-controller module adjusts the inlet flow rate _F1 of the cold end of the reforming heat exchange chamber according to the difference between the outlet flow rate F2 of the cold end of the reforming heat exchange chamber and the corrected outlet flow rate setting value _F2,ref of the cold end of the reforming heat exchange _chamber . The method of feedback tracking of the stack power setting value _Ps,ref by the third controller in step S2 is as follows: The third controller includes a third main controller module and a feedforward controller module. The third main controller module calculates the output current I that the SOFC stack should output according to the difference between the stack power _Ps and the stack power setting value Ps _,ref . The feedforward controller module calculates the value of the stack anode inlet flow _F9 according to the SOFC stack fuel utilization setting value _Uf,ref and the output current I, and adjusts the stack anode inlet flow _F9 accordingly to reach the calculated value. The formula of the reforming temperature model is as follows: i∈{CH ₃ OH, CO, H ₂ , CO ₂ , H ₂ O, O ₂ , H ₂ }, Wherein, _Cr is the heat capacity of the cold end of the reforming heat exchange chamber, _Kr is the heat capacity of the hot end of the reforming heat exchange chamber, _T2 is the outlet gas temperature of the cold end of the reforming heat exchange chamber, _T7 is the outlet gas temperature of the hot end of the reforming heat exchange chamber, _F1 is the inlet flow rate of the cold end of the reforming heat exchange chamber, _F2 is the outlet flow rate of the cold end of the reforming heat exchange chamber, _C1,i is the mole fraction of the i reactant at the inlet of the cold end of the reforming heat exchange chamber, C2 _,i is the mole fraction of the i reactant at the outlet of the cold end of the reforming heat exchange chamber, h _i is the molar enthalpy change of the i reactant, _U1 is the heat transfer coefficient of the reforming heat exchange chamber, and _A1 is the heat exchange area of the reforming heat exchange chamber; The formula of the reforming gas production model is as follows: i∈{CH ₃ OH, CO, H ₂ , CO ₂ , H ₂ O, O ₂ , N ₂ }, j∈{DE,SR,WGS}, Wherein, _F1 is the inlet flow rate of the cold end of the reforming heat exchange chamber, _F2 is the outlet flow rate of the cold end of the reforming heat exchange chamber, _Vij is the stoichiometric coefficient of the i reactant in the j reaction, _Rj is the reaction rate of the j reaction, DE is the methanol decomposition reaction, SR is the methanol direct reforming reaction, and WGS represents the steam shift reaction; The formula of the buffer tank pressure model is as follows: Where, _Vt is the volume of the buffer tank, _Pt is the pressure of the buffer tank, R is the gas constant, T is the gas temperature in the buffer tank, _F2 ' is the gas inlet flow rate of the buffer tank, _F'9 is the gas outlet flow rate of the buffer tank, is the mole fraction of CH ₃ OH at the buffer tank inlet, is the mole fraction of H ₂ O at the buffer tank inlet; The formula of the stack power model is as follows: _Ps = VI, Wherein, _Ps is the stack power, V is the output voltage of the stack, and I is the output current of the stack; the formula of the stack anode inlet flow model is as follows: Wherein, _Uf is the fuel utilization rate of the stack, N is the number of cells in the stack, I is the output current of the stack, F is the Faraday constant, _F9 is the anode inlet flow rate of the stack, is the mole fraction of _H2 at the anode inlet of the stack.