Water electrolysis system (SOEC) or fuel cell (SOFC) operating under pressure in a tight enclosure with improved regulation

Abstract

A system for regulating the pressure of a high-temperature electrolysis or co-electrolysis (HTE) reactor or a fuel cell (SOFC) operating under pressure. The operation of the system includes: regulating the DH wet gas flow upstream of one of the chambers so as to ensure the electrochemical stability of the predetermined operating point; regulating the DO gas flow upstream of the at least one second chamber so as to ensure gas scavenging in the at least one second chamber, and in the enclosure; regulating the flow of second gas circulating in the enclosure, downstream of the enclosure, so as to ensure the detection of leaks and safety in relation thereto and to prevent the formation of an explosive atmosphere; and controlling the pressure, by means of the regulation valves arranged downstream of the stack, on the gases, including the wet gas, which are also generally hot.

Claims

1. A system, comprising: at least one first chamber through which a first gas, which is a gas that is potentially wet, is able to flow; at least one first supply line that is able to supply an inlet of the first chamber with potentially wet gas up to a maximum operating pressure P.sub.max, the first supply line comprising a first flow-rate regulator that is able to regulate a flow rate D.sub.H of the first gas between a zero value and a maximum value D.sub.H,max; at least one second chamber through which a second gas is able to flow; a seal-tight enclosure in which the first and second chambers are housed, and through which the same second gas is able to flow, the enclosure being able to operate under a pressure of the second gas up to the maximum operating pressure P.sub.max; at least one second supply line that is able to supply the seal-tight enclosure and an inlet of the second chamber with the second gas, the second supply line comprising a second flow-rate regulator that is able to regulate a flow rate D.sub.O of the second gas between a zero value and a maximum value D.sub.O,max; at least one outlet line that is able to exhaust the second gas from inside the seal-tight enclosure, said outlet line comprising a third flow-rate regulator that is able to regulate a flow rate D.sub.purge, of the second gas between a zero value and a maximum value D.sub.purge,max; pressure sensors (P.sub.H, P.sub.O) that are able to measure a pressure in each of the first and second chambers, between atmospheric pressure and the value of the maximum pressure P.sub.max; at least two regulating valves (V.sub.H, V.sub.O) that are arranged outside the enclosure and on outlet lines of the one or more first chambers and of the one or more second chambers, respectively, each valve being able to operate each at a temperature above a condensation temperature of the wet gas at the maximum pressure P.sub.max in question, each valve being able to be open from 0% to 100% and having a capacity K.sub.v suitable for the maximum pressure P.sub.max and for an average flow rate of the gas in question in each of the two outlet lines; means for heating the lines containing the wet gas to a temperature above the condensation temperature of this wet gas at the maximum pressure P.sub.max in question; and commanding and automatically controlling means for commanding and automatically controlling the regulating valves (V.sub.H, V.sub.O) depending on differences in pressure values measured by the pressure sensors so as to obtain a minimum pressure difference between the one or more first chambers and the one or more second chambers.

2. The system as claimed in claim 1, comprising a condenser for condensing the wet gas, said condenser being arranged downstream of the regulating valve V.sub.H on the outlet line of the one or more first chambers.

3. The system as claimed in claim 1, the commanding and automatically controlling means furthermore being able to command and automatically control the regulators regulating the flow rate D.sub.O of the second gas depending on the state of openness of the valves V.sub.O for regulating the second gas, in order to prevent states of complete openness or closedness of the valves V.sub.O for the second gas.

4. The system as claimed in claim 1, comprising a high-temperature electrolysis or co-electrolysis (HTE) reactor comprising a stack of elementary solid-oxide (co-)electrolysis cells each comprising an anode, a cathode, and an electrolyte inserted between the anode and the cathode, the cells being electrically connected in series, the stack comprising two electrical terminals for a supply of current to the cells and defining flow chambers for, with respect to the first chambers, a flow of steam and hydrogen or of steam, hydrogen and carbon dioxide (CO.sub.2) over the cathodes and flow chambers for, with respect to the second chambers, a flow of air or nitrogen or oxygen or of a mixture of gases containing oxygen over the anodes.

5. The system as claimed in claim 1, comprising a high-temperature fuel-cell (SOFC) stack comprising a stack of elementary solid-oxide electrochemical cells each comprising an anode, a cathode, and an electrolyte inserted between the anode and the cathode, the cells being electrically connected in series, the stack comprising two electrical terminals for a collection of current from the cells and defining flow chambers for, with respect to the first chambers, a flow of dihydrogen or another fuel gas or of a mixture containing a fuel gas over the anodes and flow chambers for, with respect to the second chambers, a flow of air or nitrogen or oxygen or of a mixture of gases containing oxygen over the cathodes.

6. The system as claimed in claim 1, wherein the pressure sensors are at least two absolute pressure sensors (P.sub.H, P.sub.O) that are each able to measure an absolute pressure in each of the first chambers and in each of the second chambers, respectively.

7. The system as claimed in claim 1, wherein the one or more pressure sensors (P.sub.H) are one or more absolute pressure sensors P.sub.H that are each able to measure an absolute pressure in each of the first chambers, and comprising one or more differential pressure sensors that are able to measure a pressure difference P.sub.O=(P.sub.OP.sub.H) between the one or more second chambers and the one or more first chambers, respectively.

8. The system as claimed in claim 1, furthermore comprising bypass valves V.sub.H,bypass, V.sub.O,bypass that are each arranged in parallel with the regulating valves V.sub.H, V.sub.O, respectively.

9. A method for operating the system as claimed in claim 1, comprising: a/defining the following operating setpoints: a1/defining a flow rate D.sub.H that corresponds to an amount of potentially wet gas required for a preset electrochemical operating point; a2/defining a flow rate D.sub.O that corresponds to an amount of second gas required for the preset electrochemical operating point and to purge the seal-tight enclosure; a3/defining a flow rate D.sub.purge that corresponds to an amount of second gas required to ensure detection of and safety with respect to leaks and to avoid a formation of an explosive atmosphere in the enclosure; a4/defining a pressure P.sub.setpoint for the preset operating point; a5/defining a differential pressure P.sub.O,setpoint corresponding to a pressure difference between the pressure in the one or more second chambers and in the seal-tight enclosure, and the pressure in the one or more first chambers; b/ applying the following regulations: b1/actuating the regulator(s) for regulating the flow rate of the first wet gas, in order to regulate the flow rate D.sub.H of the first wet gas; b2/actuating the regulator(s) for regulating the flow rate of the second gas, in order to regulate the flow rate D.sub.O entering into the one or more second chambers and into the enclosure; b3/actuating the regulator(s) for regulating the flow rate of purge gas, in order to regulate the flow rate D.sub.purge of second gas exiting from the enclosure; b4/actuating the valve V.sub.H for regulating the first wet gas in order to regulate the actual pressure P.sub.H of the one or more first chambers to the setpoint value P.sub.setpoint; and b5/actuating the valve V.sub.O of the second gas so that the actual differential pressure P.sub.O=(P.sub.OP.sub.H) between, on the one hand, the one or more second chambers and in the enclosure and, on the other hand, the one or more first chambers, is regulated depending on a measured error (P.sub.O,setpointP.sub.O) with respect to the setpoint, so that the pressure P.sub.O of the second gas follows that P.sub.H of the one or more first chambers with the setpoint differential pressure P.sub.O,setpoint.

10. The operating method as claimed in claim 9, further comprising: increasing the flow rate D.sub.O of the second gas if the valve V.sub.O for regulating the second gas is close to a state of complete closedness.

11. The operating method as claimed in claim 9, further comprising: decreasing the flow rate D.sub.O of the second gas if the valve V.sub.O for regulating the second gas is close to a state of complete openness.

12. The system as claimed in claim 1, wherein the second gas is air.

Description

DETAILED DESCRIPTION

(1) Other advantages and features of the invention will become more clearly apparent on reading the detailed description of examples of implementation of the invention, given by way of non-limiting illustration with reference to the following figures, in which:

(2) FIG. 1 is a schematic view of an elementary electrochemical cell of an HTSE electrolyzer;

(3) FIG. 2 is a schematic view of a stack of cells according to FIG. 1;

(4) FIG. 3 is a schematic view of an electrochemical cell of an SOFC stack;

(5) FIG. 4 is a schematic view of a system according to the invention comprising an HTE electrolyzer, the figure showing the flow-rate regulators and sensors required to regulate pressure in the flow chambers for steam and hydrogen and for oxygen and in the pressurized seal-tight enclosure that houses the chambers;

(6) FIG. 5 is a schematic view of the flow-rate regulators and sensors with the automatic-control loops used to control the system according to FIG. 4 shown;

(7) FIG. 6 is a computational flowchart of the pressure regulations according to the embodiment of FIG. 4; and

(8) FIG. 7 is a computational flowchart of the regulation according to the invention of the flow rate D.sub.O of the oxygen-flow chambers depending on the percentage of openness of the valve V.sub.O in a high-temperature electrolysis module with a seal-tight enclosure.

(9) FIGS. 1 to 3, which relate to the prior art, have already been commented on in the preamble. They are therefore not described below.

(10) For the sake of clarity, the same elements of an HTE reactor according to the prior art and of an HTE reactor used as a component in a system according to the invention have been referenced with the same reference numbers.

(11) It will be noted here that throughout the present patent application, the terms bottom, top, above, below, inside, outside, internal and external are to be understood with reference to an interconnector according to the invention seen in transverse cross section along its axis of symmetry.

(12) It will also be noted that the terms upstream, downstream, inlet and outlet are to be considered with respect to the flow direction of the gases.

(13) It will also be noted that the electrolyzer or fuel-cell modules described are solid-oxide-electrolysis-cell (SOEC) electrolyzer modules or solid-oxide-fuel-cell (SOFC) modules that operate at high temperature.

(14) Thus, all the constituents (anode/electrolyte/cathode) of an electrolysis or fuel-cell-stack cell are ceramics. The high operating temperature of an electrolyzer (electrolysis reactor) or of a fuel-cell stack is typically between 600 C. and 950 C.

(15) Typically, the characteristics of an elementary SOEC suitable for the invention, of the cathode-supported type (CSC), may be those indicated as follows in the table below.

(16) TABLE-US-00001 TABLE Electrolysis cell Unit Value Cathode 2 Material from which it is Ni-YSZ made Thickness m 315 Thermal conductivity W m.sup.1 K.sup.1 13.1 Electrical conductivity .sup.1 m.sup.1 10.sup.5 Porosity 0.37 Permeability m.sup.2 10.sup.13 Tortuosity 4 Current density A .Math. m.sup.2 5300 Anode 4 Material from which it is LSM made Thickness m 20 Thermal conductivity W m.sup.1 K.sup.1 9.6 Electrical conductivity .sup.1 m.sup.1 1 10.sup.4 Porosity 0.37 Permeability m.sup.2 10.sup.13 Tortuosity 4 Current density A .Math. m.sup.2 2000 Electrolyte 3 Material from which it is YSZ made Thickness m Resistivity m 0.42

(17) With reference to FIG. 4, the pressure of the system according to the invention is regulated from atmospheric pressure to a chosen pressure of about 30 bars.

(18) The system firstly comprises a high-temperature co-electrolysis or electrolysis (HTE) reactor comprising a stack 20 of elementary solid-oxide (co-)electrolysis cells each comprising an anode, a cathode, and an electrolyte inserted between the anode and the cathode, the cells being electrically connected in series, the stack comprising two electrical terminals for the supply of current to the cells and defining flow chambers 21 for the flow of steam and hydrogen or of steam, hydrogen and carbon dioxide (CO.sub.2) over the cathodes and flow chambers 23 for the flow of air or nitrogen or oxygen or of a mixture of gases containing oxygen over the anodes.

(19) The system furthermore comprises: a supply line 22 that is able to supply the inlet of the chambers 21 with steam up to a maximum operating pressure P.sub.max, on which supply line a flow-rate regulator that is able to regulate the flow rate D.sub.H of steam and produced hydrogen between a zero value and a maximum value D.sub.H,max is arranged; an enclosure 40 in which the stack 20 with its chambers 21, 23 is housed, through which air, by way of purge gas, is able to flow, the enclosure being able to operate under pressure up to the maximum operating pressure P.sub.max; a supply line 25 that is able to supply the inlet of the chambers 23 and the pressurized seal-tight enclosure 40 with air, on which supply line a flow-rate regulator that is able to regulate the flow rate D.sub.O of air between a zero value and a maximum value D.sub.O,max is arranged; an outlet line 29 that is able to make a flow of purging air flow into the inside of the enclosure, on which supply line a flow-rate regulator that is able to regulate the flow rate D.sub.purge of air between a zero value and a maximum value D.sub.purge_max is arranged; pressure sensors P.sub.H, P.sub.O that are able to measure the pressure in the chambers 21, 23, between atmospheric pressure and the value of the maximum pressure P.sub.max; at least two regulating valves V.sub.H, V.sub.O that are arranged outside the enclosure 40 and on the outlet lines of the chambers 21 and of the chambers 23 respectively, each valve being able to operate at a temperature above the condensation temperature of the wet gas at the maximum pressure P.sub.max in question, each valve being able to be open from 0% to 100% and having a capacity K.sub.v suitable for the maximum pressure P.sub.max and for the average flow rate of the gas in question in each of the two outlet lines; at least two bypass valves V.sub.H,bypass, V.sub.O,bypass that are each arranged in parallel with the regulating valves V.sub.H, V.sub.O, respectively; means for heating the lines of the steam and produced hydrogen to a temperature above the condensation temperature of this wet gas at the maximum pressure P.sub.max in question; a condenser 50 that is arranged downstream of the regulating valve V.sub.H on the outlet line of the chambers 21; and commanding and automatically controlling means for commanding and automatically controlling the regulating valves (V.sub.H, V.sub.O) depending on differences in pressure values measured by the pressure sensors so as to obtain a minimum pressure difference between the chambers 21, 23.

(20) The commanding and automatically controlling means in particular comprise a microprocessor and proportional-integral-derivative (PID) regulators.

(21) The means for heating the various wet-gas lines are in particular temperature-regulated heating wires.

(22) Reference is now made to FIG. 5, which illustrates an example of regulating loops implemented automatically by a system according to the invention.

(23) Beforehand, an operator responsible for operating the system defines operating setpoints.

(24) The regulating loops according to the invention consist in succession in: regulating, upstream of the stack 20, the flow rate D.sub.H of gas consisting of a mixture of steam and hydrogen, which flow rate is defined by the operator so as to guarantee the stability of the operating point of the solid-oxide cells; regulating, upstream of the stack 20, the flow rate D.sub.O of air, which flow rate is defined by the operator so as to guarantee the stability of the operating point of the solid-oxide cells; regulating, downstream of the enclosure 40, the flow rate D.sub.purge of air, which flow rate is defined by the operator so as to guarantee the safety of the system; regulating to an operator setpoint P.sub.setpoint the pressure of the hydrogen chambers 21 by virtue of the regulating valve V.sub.O downstream of the stack 20; regulating to an operator setpoint P.sub.O,setpoint the pressure difference P.sub.O=(P.sub.OP.sub.H) between the oxygen chambers 23 and hydrogen chambers 21 by virtue of the regulating valve V.sub.O placed downstream of the stack 20; periodically adjusting, in steps of 10%, the oxygen flow rate D.sub.O if the valve V.sub.O closes to less than 5% or opens to more than 80%.

(25) By way of example, the setpoints defined by the operator may be the following: hydrogen/steam flow rate D.sub.H in the range from 0 to 10 l/h; air flow rate D.sub.O in the range from 0 to 100 l/h; air flow rate D.sub.purge in the range from 0 to 90 l/h; P.sub.setpoint in the range from atmospheric pressure to 30 bars; and P.sub.O,setpoint in the range from 100 to 100 mbar and preferably 50 mbar.

(26) FIG. 6 gives the order of and details on the regulations of the valves V.sub.O, V.sub.H implemented by the PID modules: the regulating valve V.sub.H is automatically controlled with respect to the difference (P.sub.setpointP.sub.H); the differential pressure P.sub.O=(P.sub.OP.sub.H) is calculated; and the regulating valve V.sub.O is automatically controlled with respect to the difference (P.sub.OP.sub.O,setpoint).

(27) FIG. 7 provides numerical values corresponding to the implementation of the invention in a seal-tight enclosure.

(28) More precisely, FIG. 7 gives details on the loop for regulating the oxygen flow rate D.sub.O depending on the state of openness of the regulating valve V.sub.O: if V.sub.O<5% for 5 seconds, then D.sub.O is increased by 10%; if V.sub.O<3% for 2 seconds, then D.sub.O is increased by 10%; if V.sub.O>80% for 5 seconds, then D.sub.O is decreased by 10%; if V.sub.O>90% for 2 seconds, then D.sub.O is decreased by 10%.

(29) Other variants and advantages of the invention may be applied without departing from the scope of the invention.

(30) The invention is not limited to the aforementioned examples; in particular, features of the illustrated examples may be combined in variants that have not been illustrated.

CITED REFERENCES

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