Method and apparatus for operating a fuel cell in combination with an electrochemical cell to produce a chemical product

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METHOD AND APPARATUS FOR OPERATING A

causing the fuel cell to require a larger amount of fuel for a given amount of power.

FUEL CELL IN COMBINATION WITH AN As shown in FIG. 2, fuel cells typically produce ELECTROCHEMICAL CELL TO PRODUCE A electrical energy with a voltage characteristic that de CHEMICAL PRODUCT creases as current increases. This graphical representa

CROSS-REFERENCES TO RELATED

tion of voltage and current is often referred to as the voltage characteristic of the fuel cell. The voltage drops

APPLICATIONS with increasing current because of ohmic and polariza This is a continuation of application Ser. No. 501,239, O tion losses. In addition, there is a voltage loss with time filed June 3, 1983 which is now abandoned. due to the slow deterioration of catalysts used at the anode and cathode of the fuel cell.

TECHNICAL FIELD This decreasing voltage characteristic of fuel cells This invention relates to a method for operating a fuel causes difficulties in directly coupling the fuel cell to an cell which produces electrical energy in combination 15 electrochemical cell to perform an electrochemical with an electrochemical cell which uses electrical en process. Examples of electrochemical cells that use ergy. More particularly, this invention is directed to a electrical energy to produce a chemical product such as method and apparatus for permitting the fuel cell and chlorine or caustic alkalis are shown in U.S. Pat. No. electrochemical cell to operate at voltages which are 4,031,000 issued to Nakamura et al. entitled "Dia independent of each other. This invention has applica 20 phragm. For Electrolytic Production Of Caustic Al tion to all types of fuel cells including acid, base, solid kali', in U.S. Pat. No. 4,272,337 issued to Darlington electrolyte and molten carbonate fuel cells and to all entitled "Solid Polymer Electrolyte Chlor-Alkali Elec types of electrochemical cells including cells that pro trolysis Cell' and in U.S. Pat. No. 4,273,626 entitled "Electrolyte Series Flow. In Electrolytic Chlor-Alkali duce a reactant for the fuel cell and cells that do not Cells', the information in which is incorporated herein produce a reactant for the fuel cell. 25 by reference.

BACKGROUND ART These electrochemical processes typically employ an A fuel cell is an electrochemical cell which consumes electrochemical cell having a voltage characteristic fuel and an oxidant on a continuous basis to generate of which is opposite in nature to the voltage characteristic the fuel cell. In these cells, the production of the electrical energy. The fuel is consumed at an anode and 30 saleable the oxidant at a cathode. The anode and cathode are product is directly proportional to the flow of placed in electrochemical communication by an electro current through the cells. As shown in FIG. 2, increas lyte. One typical fuel cell employs a phosphoric acid ing voltages are required as the flow of electrical cur electrolyte. The phosphoric acid fuel cell uses air to rent is increased through the electrochemical cell to provide oxygen as an oxidant to the cathode and uses a 35 produce more product. The increasing voltages are needed to overcome ohmic and polarization losses in hydrogen rich stream to provide hydrogen as a fuel to the electrochemical cell and other losses which are the anode. After passing through the cell, the depleted similar air and fuel streams are vented from the system on a currenttoandthepower losses occuring in a fuel cell. Thus, as the consumption is increased in the elec continuous basis.

A typical fuel cell power plant comprises one or more trochemical cell to produce more chemical product at an efficient operating point, the voltage increases. As stacks of fuel cells, the cells within each stack being the power supplied by the fuel cell increases to meet this connected electrically in series to raise the voltage po demand, tential of the stack. A stack may be connected in parallel decreased.the operating voltage of the individual cells is with other stacks to increase the current generating Accordingly, scientists and engineers are seeking a capability of the power plant. Depending upon the size 45 way to match the performance of a fuel cell to an elec of the power plant, a stack of fuel cells may comprise a trochemical half dozen cells or less, or as many as several hundred yet to allowcell to combine the two cells in a cycle and the fuel cell to operate at a voltage most cells. Air and fuel are usually fed to the cells by one or beneficial more manifolds per stack. Examples of typical fuel cell operate at toa voltage the fuel cell and the electrochemical cell to most beneficial to the electrochemi power plants are shown in U.S. Pat. No. 3,585,078 is 50 cal cell.

sued to Sederquist et al. entitled "Method Of Reformer

Fuel Flow Control', U.S. Pat. No. 3,976,507 issued to DISCLOSURE OF INVENTION Bloomfield entitled "Pressurized Fuel Cell Power Plant

With Single Reacting Gas Stream'; and U.S. Pat. No. calAccording cell using to the present invention, an electrochemi electrical power at a first voltage to pro 4,202,933 issued to Riser, et al. entitled "Method For 55 duce a chemical product and a fuel cell using fuel to Reducing Fuel Cell Output Voltage To Permit Low produce electrical power at a second voltage are linked Power Operation'. The information contained in these by a device allowing the fuel cell to operate at the sec patents is incorporated herein by reference. ond voltage and the electrochemical cell to operate at Fuel cell components are designed to operate within the first voltage.

a band of predetermined voltages. Voltages above the In accordance with one embodiment of the invention, predetermined maximum are avoided in acid cells be the electrochemical cell produces fuel which in con cause excessive voltages may damage internal equip sumed in the fuel cell.

ment and cause excessively fast corrosion of compo In accordance with the present invention, an electro nents such as the cathode. In all fuel cells, such high chemical cell is operated at a first current and a first voltages result in low power densities and uneconomi 65 voltage to produce a chemical product and a fuel cell is cal operation of the power plant. Voltages below a operated at a second voltage and a second current to predetermined minimum are avoided because such low produce power for the electrochemical cell by convert voltages adversely affect the efficiency of the fuel cell ing the power output of the fuel cell to a current and

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output voltage which matches the voltage of the elec BEST MODE FOR CARRYING OUT THE trochemical cell. INVENTION

A primary feature of the present invention is a elec trochemical cell which uses power to produce a chemi FIG. 1 is a schematic representation of an embodi cal product efficiently at a first voltage. Another feature 5 ment of the present invention showing an apparatus 10 is a fuel cell which utilizes a fuel and an oxidant to for carrying out an electrochemical process to produce produce electrical power efficiently at a second volt a chemical product. The apparatus employs a chlor age. Another feature is a device for regulating the elec alkali electrochemical electrolysis cell 12 and an elec trical power received from the fuel cell. The device is trochemical fuel cell 14 to produce chlorine and sodium connected to the fuel cell and electrochemical cell. In 10 hydroxide. The term fuel cell includes a single fuel cell, one embodiment the electrochemical cell is a chlor a fuel cell stack formed of a plurality of fuel cells, and a alkali cell. In another embodiment the device for regu fuel cell power plant formed of one or more fuel cell lating electrical power includes a direct current con stacks. Similarly the term electrochemical cell or elec verter having a duty cycle to provide for the intermit 15 trolysis cell includes a single electrochemical cell, an tent flow of current through the direct current con electrochemical cell stack formed of a plurality of elec verter. The converter may be responsible to voltage, trochemical cells, and an electrochemical plant formed (i.e., a voltage regulator) or responsive to current (i.e., a of one or more electrochemical stacks. current regulator). Regulator means for regulating the power received from

A primary advantage of the present invention is the said power the fuel cell 14 to adjust the voltage and current of efficiency which results from carrying out an electro 20 ysis and for supplying the power to the electrol chemical process by combining a fuel cell with an elec trolysis cell. connected cell are to the fuel cell and to the elec

An example of such a means is a direct trochemical cell and allowing the fuel cell and the elec current regulator 15 having a direct current converter trochemical cell to operate at preferred voltages and 16 and a control means 17. The direct current converter currents independent of each other. In one embodiment, 25 is connected to both the an advantage is the efficient utilization of a by-product cell. A high voltage, ACfuel cell and the electrolysis rectifier 18 is in electrical of the electrochemical process as fuel in the fuel cell. In communication with a source of purchased electric one embodiment, an advantage is the reduction in the power. The rectifier is capable of supplying direct cur average cost of electrical power by supplementing elec rent power to the electrolysis cell under selected oper trical power supplied from an outside source with 30 ating conditions. Under such operating conditions the power provided by the fuel cell. fuel cell supplies at least a portion of the power required The foregoing features and advantages of the present by the electrochemical cell.

invention will become more apparent in the light of the The fuel cell 14 shown in FIG. 1 is formed of at least following detailed description of the best mode for carrying out the invention and in the accompanying 35 one which individual fuel cell and in fact is a power plant includes pluralities of fuel cells stacked in series drawing. to form fuel cell stacks 20. The fuel cell stacks are con BRIEF DESCRIPTION OF ORAWINGS nected electrically in parallel to form the power plant. The fuel cell includes a manifold 22 and a manifold 24

FIG. 1 is a diagrammatic representation of an appara for supplying reactant gases to the fuel cell. A flow path tus for carrying out an electrochemical process, the 26 for oxidant rich gas. stream, such as air, extends apparatus including an electrochemical cell and a fuel through the manifold 22 and a flow path 28 for fuel rich cell. gases, such as a hydrogen rich gas stream, extends FIG. 2 is a graphical representation of the voltage through the stacks to provide the cathode of each cell characteristic of a typical fuel cell and the voltage char with an oxidant and the anode of each cell with fuel. acteristic of a typical electrochemical cell. 45 Under normal operating conditions the fuel cell will not FIG. 3 is a diagrammatic representation of the rela consume all of the oxidant in the oxidant stream nor will tionship between the fuel cell, the electrochemical cell the fuel cell consume all of the fuel in the fuel stream. and regulator means connected to the fuel cell and the The electrolysis cell 12 has an anode side 30 and a electrochemical cell. cathode side 32. A brine mixer 34 is connected to the FIG. 4 is a schematic illustration of one embodiment 50 anode side via conduit 36. The brine mixer receives of a direct current converter used in regulating electri sodium chloride via conduit 38 and hot water via con cal power between the fuel cell and the electrochemical duit 40 to form brine. A plurality of chlorine washers 42 cell. are connected to the anode side by conduit 44. The FIG. 5 is a schematic illustration of a second embodi chlorine washers receive water via conduit 46 and dis ment of a direct current converter used in regulating 55 charge product chlorine via conduit 48. A stripper 50 electrical power between the fuel cell and the electro for the chlorine wash water is connected to the chlorine chemical cell. washers by conduit 52. The stripper discharges clean FIG. 6 is an alternate embodiment of the device water for recycling or dumping via conduit 54. An shown in FIG. 4. on-site steam boiler 56 is in flow communication with FIG. 7 is an alternate embodiment of the device 60 the stripper via conduit 58. The stripper also receives shown in FIG. 5. steam from the fuel cell via conduit 60. Alternatively, FIG. 8 is a graphical representation illustrative of the conduit 60 might be connected to other components wave forms used to explain the operation of the direct requiring steam, such as the brine mixer 34 or other current converter shown in FIG. 4 and FIG. 6 components requiring heat.

FIG. 9 is a graphical representation illustrative of 65 The on-site steam boiler 56 receives fuel via conduit wave forms used to explain the operation of the direct 62 and feed water via conduit 64. A vacuum evaporator current converter shown in FIG. 5 and FIG. 6, with 66 for processing sodium hydroxide received from the reference to the wave forms shown in FIG. 8. cathode side of the electrolysis cell via conduit 68 also

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receives high pressure steam from the boiler via conduit is a voltage variation with time for each cell during 70. The temperature of the steam is greater than 300 F. operation because of the natural degeneration of the The vacuum evaporator discharges fifty percent by cells.

weight sodium hydroxide via conduit 72. A hydrogen FIG. 3 is a diagrammatic representation showing the washer 74 receives hydrogen gas from the cathode side relationship between the electrolysis cell 12, the fuel of the electrolysis cell via conduit 76. The hydrogen cell 14 and the direct current regulator 5 which is re discharges water via conduit 78 and supplies the fuel ponsive to the output power of the fuel cell. The direct cell 14 with a hydrogen rich fuel stream via conduit 80. current regulator

The conduit 80 is connected to the hydrogen manifold 6 and the control includes means the direct current converter 17. An example of a control 24 of the fuel cell. 10 means is a microcomputer having analog to digital sig Other electrochemical cells might be used in combi nation with the fuel cell 14. One example is a chlorate nal converters which develops a duty cycle response of electrolysis cell which uses input electrical power to two preselected parameters. The control means devel produce a chlorate product and hydrogen. As with the ops a duty cycle signal for the converter. For example, chlor-alkali process, hydrogen is produced at the cath 15 the duty cycle may be set as a result of a difference ode and the chlorate product is produced as a result of between the actual current I3 flowing from the regula the electrochemical process at the anode. The product tor in comparison with a desired current or might be set is sent to a reactor for further processing. The hydrogen as a function of the voltage of the electrochemical cell is preferably processed through a hydrogen washer and the actual voltage of the fuel cell. As shown in FIG. before being sent to the fuel cell. The chemical reac 20 8 and FIG. 9, the duty cycle signal may be sent to the tions are summarized as follows: regulator in the form of a plurality of energizing gate ELECTROLYSIS CELL signals to gated swith means. In addition, the control means has the capability of energizing components in the direct current converter during start up operations.

NaCl-Na-Cl FIG. 4 is a schematic illustration of one embodiment

Clt-Cl2--e. Anode of the direct current converter 16. This particular direct current converter is a bucking regulator which de

Cl2--HO-le-CIO + H2. Cathode creases the voltage through the regulator. The bucking regulator has a first circuit 90 and a second circuit 92.

Na+ClO NaOCl 30 The second circuit is enclosed is broken lines. The first REACTOR circuit has a first leg 94 extending between the fuel cell and the electrolysis cell and a second leg 96 extending between the fuel cell and electrolysis cell. The first leg

NaOCl-NaClO3--NaCl includes a first gated switch, such as a first thyristor 98 35 responsive to a gate signal Q1 from the control means

This electrochemical process was discussed in a paper 17. The first leg includes an inductor 100 which is con presented at the International Chlorine Symposium nected to the cathode of the first thyristor and which is 1982 on June 3, 1982 in London, England entitled "En in series with the first thyristor between the first thy ergy Saving In Chlorate Production With The Use Of ristor and the electrolysis cell. The first leg has a point The Fuel Cell' by I. H. Warren. The paper is available 4. A between the first thyristor and the inductor 100. The from the Chemetics International Company, a division first leg includes a means to enable the flow of current of C-I-Inc, 1818 Cornwall Ave., Vancouver, B.C., to the electrolysis cell through the inductor 100 during Canda, the material in which is hereby incorporated by the period of time said first gated switch is in the non reference.

Another electrochemical cell having a useful by-pro 45 conducting flow of position and to oppose the divergence of the current from the electrolysis cell to ground duct is an electrolysis cell used in the production of through point A between the first thyristor 98 and the adiponitrile. This electrochemical process was dis inductor 100. In the embodiment shown, the means is cussed in an article entitled "Adiponitrile' contributed the diode 102; the diode is connected by the Asahi Chemical Industry Co., Ltd. and appear tween the first thyristor and the inductoratinpoint Abe the first leg ing in the November 1977 issue of Hydrocarbon Pro 50 such that the cathode of the diode is joined to the cath cessing published by the Gulf Publishing Co., U.S.A., ode of the first thryristor 98. The anode of the diode 102 the material in which is herein incorporated by refer is connected to the second leg.

ence. This cell produces oxygen, a by-product. The oxygen in a combined cycle is sent to the fuel cell for The second circuit 92 includes a first leg 106, a sec consumption in the cathode of the fuel cell. Preferably 55 ond leg 108 and a third leg 110. The first leg has a paral the oxygen will pass through an oxygen washer. In lel diode 112 extending in parallel across the first thy other cells, chlorine may be sent to a fuel cell which ristor 98 of the first circuit 90. The anode of the parallel uses chlorine as an oxidant. The by-product of genera diode is connected to the cathode of the first thyristor. tion of such a fuel is hydrogen chloride. A pulse means 114 for creating a current is formed by FIG. 2 is a graphical representation characterizing in the second leg and the third leg. The second leg extends general the voltage characteristic of a typical fuel cell in parallel across the first thyristor. The second leg has and the voltage characteristic of a typical electrochemi a second gated switch means, such as the second thy cal process employing an electrolysis cell. As shown, a ristor 116 and a diode 118. The second thyristor 116 is fuel cell has a decreasing voltage characteristic with responsive to a gate signal Q2 from the control means current. An electrochemical cell has an increasing volt 17. The diode 118 has a cathode connected to the cath age characteristic with current. As discussed earlier, 65 ode of the first thyristor 98. The diode has an anode these voltage characteristics are not compatible if varia connected to the second thyristor 116. The second thy tions in the operating characteristics of either cell ristor 116 has an anode connected to the anode of the changes, as they most certainly will. For example, there first thyristor 98. The third leg is connected in parallel

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from the anode side of the first thyristor 98 to the cath tor has one side connected to the anode side of the first ode side of the second thyristor 116. The third leg in thyristor 298 and a second side connected to the induc cludes a capacitor 120 for storing charge and an induc tor 322. The second side is also connected through the tor 122. The capacitor has one side connected to the inductor to the cathode side of the second thyristor. anode side of the first thyristor 98 and a second side 5 FIG. 7 is an alternate embodiment of the boosting connected to the inductor 122 and connected through regulator shown in FIG. 6 with two modifications to the inductor to the cathode side of the second thyristor the second circuit 292. The first modification is the 116. substitution of a third gated switch means, such as the FIG. 5 is an alternate embodiment of the bucking third thyristor 328, for the diode 318. The third thy regulator shown in FIG. 4 with two modifications to 10 ristor is responsive to a gate signal Q3 from the control the second circuit 92. The first modification is the sub means 17. The second modification is the addition of a stitution of a third gated switch means, such as the third resistor 330 which extends from a point between the thyristor 128, for the diode 118. The third thyristor 128 capacitor 320 and the inductor 322 in the third leg of the is responsive to a gate signal Q3 from the control means second circuit to the second leg of the first circuit 396. 17. The second modification is the addition of a resistor 15 Operation of these different embodiments of the regu 130 which extends from a point between the capacitor lator is illustrated 120 and the inductor 122 in the third leg to the second and FIG. 9. These by the wave forms shown in FIG. 8 wave forms are a simplified represen leg of the first circuit 96. tation for clarity of the complex wave forms that occur FIG. 6 is a schematic illustration of another embodi during operation. They are simplified for purposes of ment of the direct current converter 16. This particular 20 explanation.

direct current converter is a boosting regulator which These wave forms include the Q1 wave form which is increases the voltage through the regulator. The boost a control wave form generated by the control means. ing regulator has a first circuit 390 and a second circuit The Q1 wave form is applied to the gate of thyristor 98. 292. The second circuit is enclosed in broken lines. The

If the voltage at the anode is positive with respect to the first circuit has a first leg 394 extending between the fuel cathode, the thyristor

cell and the electrolysis cell and a second leg 396 ex voltage Q1 conducts when the positive tending between the fuel cell and electrolysis cell. The form is the voltage changetoacross

Q1 is applied gate cathode. The second wave thyristor 98 from the first leg includes a first gated switch, such as a first anode to the cathode. The third wave thyristor 298 responsive to a gate signal Q1 from the age with respect to ground EA at point form A in is the volt the circuit.

control means 17. The first thyristor has an anode con 30 nected to the first leg and a cathode connected to the The fourth wave form is the current I98 through the first second leg. The first leg includes an inductor 300 which thyristor 98. The wave form I100 is the current through is connected to the anode of the first thyristor. The first the inductor 100 and is a measure of the curent supplied leg has a point Abetween the first thyristor 298 and the to the electrochemical cell. The wave form I102 is the inductor 300. The inductor 300 is between point A and 35 current through the diode 102. The wave form Q2 is a control wave form from the microcomputer and is ap the fuel cell. The first leg includes a means to enable the plied as a positive pulse to the gate of thyristor Q2. At flow of current to the electrolysis cell through the in ductor 300 during the period of time said first gated the time of application, Q2 is a measure of the voltage switch is in the nonconducting position and to oppose from gate to cathode of the thyristor. The wave form the divergence of the flow of current from the electrol I116 is the current flowing through the second thyristor ysis cell to ground through point A between the first 116. The voltage V120 is the voltage relative at point C thyristor 298 and the inductor 300. In the embodiment at the side of the capacitor 120 joined to the anode of shown, the means to enable and to oppose is a diode 302 the the first thyristor and to a measure of the voltage across having an anode connected at point A between the first capacitor 120. The wave form I118 is the current thyristor and the inductor in the first leg having a cath 45 through diode 18. Superimosed on I 118 is a line showing ode connected directly to the electrolysis cell by the the current I100 flowing at the same point in time first leg. Thus, the diode 302 is between point A and the through the inductor 100. The current I112 is the current electrolysis cell. through the diode D112.

The second circuit 292 includes a first leg 306, a sec During operation of the apparatus 10, brine is fed ond leg 308 and a third leg 310. The first leg has a paral 50 from the brine mixer via conduit 36 to the anode side of lel diode 312 extending in parallel across the first thy the electrolysis cell. The chlorine, present as chloride ristor 298 of the first circuit 390. The anode of the paral ion in the solution, forms chlorine according to the lel diode 312 is connected to the cathode of the first reaction: 2Cl-)-Cl2-2e. The alkali metal ion and its thyristor. A pulse means 314 for creating a current is water of hydration pass through a permionic membrane formed by the second leg and the third leg. The second 55 to the cathode side 32 of the electrochemical cell. The leg extends in parallel across the first thyristor. The water may be fed both externally into the cathode side second leg has a second gated switch means, such as the or fed as water of hydration passing to the cathode side. second thyristor 316, and a diode 318. The second thy The cathodic reaction is H2O--et-OH -- H2. The ristor 316 is responsive to a gate signal Q2 from the chlorine gas evolved is sent to a chlorine washer via control means 17. The diode 318 has a cathode con 60 conduit 44 where the chlorine gas is mixed with water nected to the cathode of the first thyristor 298. The to remove contaminants. Wash water discharged from diode 318 has an anode connected to the cathode of the the chlorine washer 52 is flowed to the stripper 50 for second thyristor 316. The second thyristor 316 has an chlorine where the water is mixed with low pressure anode connected to the anode of the first thyristor 298. steam. The overall requirement for fuel for the process The third leg is connected in parallel from the anode 65 is reduced if low pressure steam is recirculated from the side of the first thyristor 298 to cathode side of the fuel cell to transfer heat from the fuel cell to the electri second thyristor 316. The third leg includes a capacitor cal chemical process. After processing the water dis 320 for storing charge and an inductor 322. The capaci charged from the chlorine washer through the stripper,

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the cleaned water is discharged from the process. The by the current I3 resulting in the disconnection of the water may be recycled to the process or dumped. AC power supply from the circuit. In those cases the The on-site steam boiler 56 provides high pressure current I3 will equal I. Under operating conditions in steam to the vacuum evaporator where sodium hydrox which the electrical power is also provided by the recti ide solution from the cathode is treated by evaporation. fier, the current I will be the summation of the current The resultant solution is approximately fifty percent I3 and I4.

(50%) by weight sodium hydroxide. The hydrogen gas As shown in FIG. 3, the direct current converter 16 evolved at the cathode is sent to a hydrogen washer is designed to intermittently pass electrical current. The which removes containments from the hydrogen gas. amplitude of the output current is the weighted average The water is discharged from the hydrogen washer and 10 of the current intermittently flowing through the direct the product hydrogen is sent via conduit 80 to the fuel current converter. This amplitude is a function of the cell 14 for consumption of at least a portion of the hy duration of time during which current is allowed to pass drogen in the fuel cell. through the direct current converter during any given In an alternate embodiment, conventional fuel may be period of time. The period of time current flows as a treated by a fuel processor 82 to provide additional 15 percentage of the given period of time is called the duty hydrogen to the fuel cell. If enough hydrogen is pro cycle. Thus a fifty percent duty cycle results in the vided to the fuel cell the process can dispense with the passage of current for fifty percent of any period of use of additional DC power. It is expected that the most time. As discussed earlier, the duty cycle is established efficient operation of the fuel cell of the overall process in response to input signals which establish an error will result in the maximum possible consumption of the 20 signal. The control means 17 uses these signals to deter product hydrogen in the fuel cell to provide electrical mine the length of time between a pulse Q1 turning on energy to the electrolysis cell and to decrease the reli the direct current converter to allow the direct current ance of the process on purchased AC electric power converter to pass current and a pulse Q2 turns off the from an outside source. direct current converter. The length of time from the The electrochemical cell uses electrical power at a 25 first pulse to the subsequent Q which turns on the cur predetermined voltage and a predetermined current to rent converter is the period of time used to calculate the produce the chemical product. Depending on the num duty cycle. If the current converter is acting as a volt ber of electrochemical cells which are grouped together age regulator, the input signals will be the output volt and the configuration of the individual cells, this prede age of the current converter and the desired voltage termined voltage and current results in a requirement of 30 which may be sent by an operator or automatically a first voltage V1 and a first current I for the electro which may be automatically established by the system. chemical cell stack. As a result of the error signal. A duty cycle is estab Each fuel cell utilizes fuel and oxidant to supply elec lished and the current converter is operated to provide trical power at a second current and a second voltage. a variable resistance by intermittently passing current These voltages V1 and V2 and currents I1 and I2 are 35 through the regulator. Finally, a duty cycle will be selected to optimize the performance of the overall reached which results in a zero error.

process. Normally the fuel cell will be operated within Alternatively, and most preferably, the direct current a band of voltages which represent the optimum condi converter acts as a current regulator sensing the output tions for the individual fuel cell in terms of life, effi current on the regulator and establishing an error signal ciency and economics. For acid fuel cells this band has in response to a desired current. The control means been found to lies between a lower limit of fifty percent determines the error between the desired current and (50%) of the open circuit voltage and an upper limit the actual current establishing a new duty cycle for the which is equal to sixty-five percent (65%) of the open current converter and adjusting the duty cycle of the circuit voltage of the individual fuel cell. Similar ranges current converter until the correct current as an output have been established for aklaline and molten carbonate 45 is established. The desired current may be set, for exam fuel cells. Preliminary estimates have established the ple, to consume all of the hydrogen which is being following ranges: for molten carbonate fuel cells fifty percent (50%) to sixty-five percent (65%) of the open produced by the electrochemical cell in which case the microcomputer may sense the hydrogen input to the circuit voltage; for alkaline fuel cells the range is equal fuel cell (e.g., signal F) and use a lookup table to deter to seventy percent (70%) to eighty percent of the open 50 mine the output current of the fuel cell. Then, using the circuit voltage. In some situations it may be desirable voltage available from the electrochemical cell the mi for reasons not connected with efficiency or with dura crocomputer will determine the current which must be bility of the fuel cell to operate the fuel cell at voltages delivered by the converter. Any increase in hydrogen which are different from the band of predetermined output is accompanied by an increase in the amount of values for the fuel cell or for the band balues for the fuel 55 current that can be delivered and the concomitant de cell which results in the most efficient operation of the crease in the electrical power purchased until the total process. power going to the electrolysis cell satisfies the operat Placing the individual cells in series to form a stack ing requirements of electrolysis cell. In ine embodiment and placing the stacks in parallel to provide additional additional hydrogen is produced by processing fuel current results in a utilization of fuel and oxidant which through a fuel processor such that the maximum current produces electrical power at a second voltage V2 and a available from the fuel cell to the electrolysis cell satis second current 2. After regulating the direct current fies the electrolysis cell so that no additional electrical power by passing the power through the direct current power need be purchased.

converter, a current I3 is supplied to the electrochemi During operation of the buck regulator, the anode cal cell at voltage V3 which matches the voltage V1. 65 side of thyristor 981 has a voltage which is equal to the Purchased electrical power supplied by the rectifier at a voltage supplied by the fuel cell Efe. As shown in FIG. current I4 is supplemented by the current I3 and, under 8, during the time thyristor 98 is in the off position, the certain operating conditions, may be replaced entirely anode is positive with respect to the cathode as is shown

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by the waveform V98. The waveform Q1 describes the I118 is generated. I118 is the commutation current is pulses which are placed on the gate of thyristor 98 and generated.

the gate to cathode voltage of thyristor 98. At time As the pulse of current I118 comes out of the capacitor equal zero, the Q waveform or control waveform is a through diode 118 and moves toward point A, the cur. pulse which is a step function having a width of some rent I98 goes to zero. One way describing the commuta microseconds. The pulse is applied gate to cathode and tion is the current flowing from the fuel cell to the first causes the thyristor 98 to conduct. The voltage V.98 thyristor 98 seeks to go to point C which is no at across the thyristor goes to zero because once the thy -Ef-c and does not flow to point A which is at a ristor is in conduction, the voltage drop across the thy voltage equal to E?--c. Thus, the current I98 is shunted ristor is essentially zero. By placing the positive pulse O and replaced by a portion of the current I118. Alterna on the gate of the thyristor, a positive voltage from gate tively, the process may be described as the production to cathode results and the thyristor becomes conducting of a pulse of current through diode 118 which may go because the voltge from the anode to the cathode was through diode 112 or towards point A. The current I100 positive. is still building up, and, as the large pulse of current I118 At point C on the positive side of the capacitor, the 15 approaches point A, the inductor prevents an instanta capacitor is charged up with some positive voltage neous increase in the current. As a result, the current Ef-c which is greater than the voltage Efe (Ef-cEf). I98 no longer flows, the current I100 is replaced by a The summation of the current I98 through the first thy portion of the current I102 and the remainder is passed ristor and the current It02 through the diode 102 of the through diode 112 as 12. As can be seen, I112 is a very first circuit is equal to the current I100 supplied through small pulse of current that returns to charge the capaci the inductor 100 to the load which is the electrolysis tor 120 at a voltage Ef-c. As the pulse of current I118 cell. Before the thyristor 98 is turned on by the pulse Q1 moves through point A and through diode 112 (with the at time equal to zero, the current through the thyristor thyristor Q1 in a nonconducting position), the diode the Q1 is equal to zero (198=0, TC0). The current I100 25 first circuit beings to pass a current I102 to supply the through the load is decreasing from some high valve. current I100 to the electrolysis cell. The magnitudes of The current I102 is equal to the current I100. As the I102 and I100 are equal and the current I98, which was thyristor 98 is turned on, the load current I100 starts to building up at this point in time, now returns to zero. increase, the thyristor current rapidly increases to a The voltage Eagoes back to zero and the voltage across value equal to the current through I102 and the current 30 the thyristor goes back to positive. As a result, a nega through I102 goes back to zero. In effect, as thyristor 98 tive voltage exists across the inductor and is equal to is turned on, the current fed to the electrolysis cell is minus V load which is the voltage dropped across the transferred from being fed from the diode 102 to being electrolysis cell.

fed from the thyristor Q1. The inductor 100 ensures that In summary, as a current passes through diode 112 the current I100 does not change instantaneously but 35 during the time current I118 is greater than I100. The rather acts to retard the instantaneous increase in cur interval when diode 112 conducts and Ig8 L is zero is the rent and acts as a means to resist changes in current to commutation time for thyristor 98. As I 118 drops to the value of the electrochemical cell. The slopes of the changing I100, diode 112 no longer conducts. Current now flows currents in the thyristor and the diode are not instanta from fuel cell through the inductor 122, capacitor 120, neous but are nearly so. The curves as drawn to approx diode 118 and the filter reactor to the load. imate a perfect switch having instantaneous response, FIG. 9 summarizes several of the voltages and cur but as will be realized, there is some small slope which rents in the first conduit for the buck and boost regula has been eliminated for clarity. tors. The cycle for the buck regulator T (T=Tcycle) Once the thyristor 98 begins conducting, the thyristor includes a period Ton during which the thyristor 98 98 will conduct until the thyristor is made nonconduct 45 (switch) is in the "on' position and conducting and a ing. For the thyristor 98 to conduct current intermit period of time Toirduring which the thyristor 98 is not tently, the thyristor must stop carrying current. Ac conducting. Because the cycle time T is very great cordingly, a second circuit 92 is provided to turn off the compared to the pulse time it takes for the thyristor to thyristor. This process is referred to as commutation. turn off when the pulse Q2 arrives at thyristor 116, the Commutation is begun by sending a control waveform 50 pulses Q1 and Q2 are shown as spikes coinciding with Q2 to the gate of thyristor 116 and causing a positive the on and off period for the thyristor 98. When the voltage to exist between the gate and the cathode. The thyristor 98 is on, point A has a voltage EA which is voltage across the capacitor through the thyristor 116 is equal to the voltage Ef neglecting any small circuit positive and as a result of the control waveform Q2, a losses that might exist. When the thyristor switch 98 is pulse of current 116 begins to flow as shown in FIG.8. 55 off, point A has a voltage EA which is equal to zero The time sclae for these waveforms is very expanded (EA=0). The current I100 is increasing during the period to show the approximate shape of the waveform. In of time the switch is on and is decreasing during the actual operation these waveforms appear almost as period of time the switch98 is off. The current Ilois the pulses. As the current I116 flows to the capacitor 120 the summation of the current 98 through the thyristor voltage V120 at point C decreases rapidly from the posi 60 switch and the current I102. The current I102 is zero tive voltage Ef-c to a negative voltage -E?--c. The during the period of time that the thyristor switch 98 is components in the second circuit such as the diode 118 on and is decreasing from some preselected value dur and the inductor 122 are sized such that the capacitor ing the period of time when the switch is off. The cur will fully charge in a reverse polarity from the polarity rent I98 through the thyristor switch 98 is increasing that existed at a time just before Q2. Thus, the circuit 65 during the on period and is decreasing from its maxi rings around upon itself, fully charging the capacitor mum value during the off period. As can be seen, the before the capacitor 120 begins to discharge through pattern for the current I100 is one of developing a triang the diode 118. As the capacitor discharges, a current ular current where the rising portion is being carried by

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the switch 98 and the falling portion is being carried by The second commutation circuit in the boost regula the diode 102.

tor and the buck regulator work

The voltage V 100 across the inductor is equal to the cuits. In both circuits you gate the the same in both cir inductance multiplied by the first derivative of the cur ristor 116,316 by producing a pulse ofcommutation current Q2 thy from rent with respect to time (V100=Ind-di/dt). The voltage drop is positive during the period of time when the microcomputer. As a result of the discharge of the ca pacitor 120,320 and the rerecharging of the capacitor switch is on. The voltage drop is equal to the voltage at with reserve polarity, a buck current flows and forces point A minus the voltage across the load. As can be the current through the switch thyristor 98, 298 to zero seen, the positive voltage is less than the voltagge sup with the excess current flowing back into the capacitor plied by the fuel cell. The voltage drop V100 across the 10 and the rest going to replace the output current of the inductor 100 is negative during the period of time when thyristor. Thus, the commutation circuits are the same the switch is off being equal to the negative of the load in both the buck regulator and the boost regulator. voltage.

In summary we have a switch means which is the regulator FIG. 5 and 7 shows an improved design of the buck thyristor 98, a means to resist changes in current 15 provements and the boost regulator includes the two im through the primary circuit which is the inductor 100 a resistor for mentioned earlier. The first improvement is and a means to maintain the current flowing in the the current to charge the capacitor means to resist changes in current which is the diode cient120,320. This enables an operator to be sure that suffi 102. The second circuit 92 is a means to turn off the charge exists on the capacitor for the capacitor to switch means by generating a current pulse that is 20 provide a source of current for commutation. In cases greater than the current flowing through the means to where the resistor is not employed as is shown in the resist changes in current, inductor 100. basic design of the buck regulator in FIG. 4, the mi The boost regulator works in a similar fashion to the crocomputer might be programmed to supply an initial buck regulator but, instead of the voltage being lower charge to the capacitor to ensure that a sufficient charge than the source (the fuel cell voltage), the voltage is 25 on the capacitor exists during start-up operation. As higher as a result of the orientation of the components. will be realized, the conern for the intial charge on the The commutation or second circuit 292 for the boost capacitor is a concern during start-up operations but is regulator works in the same fashion as the commutation not once either regulator is running. circuit described above for the buck regulator. The second improvement to both the buck regulator As with the buck regulator, the pulse signals Q1 and 30 and the boost regulator is replacing the diode 118,318 in Q2 to the first thyristor switch 298 and the second thy the commutation circuit with a thyristor 118,318. In ristor switch 318 determine the period during which the both the buck regulator and the boost regulator shown thyristor 298 conducts and the period during which the in FIG. 5 and FIG. 7, the control signal Q2 causes the thyristor switch98 does not conduct. The voltage Ea at capacitor to ring and charge before it can discharge into point A is pulled to ground (Eas-0) during the period of 35 the diode. Thus, before you actually turn the current off time the thyristor switch 298 is “on” or conducting. The through the switch thyristor 98,298, you must wait for thyristor 298 acts as a short cicuit. The voltage E. at the capacitor to charge. By replacing the diode with a point A is equal to the voltage Efe of the fuel cell source second thyristor 128,328 in you can initial the charging plus the voltage across the inductor V300 (i.e., Eas-Ef action earlier, in fact right after the signal Q1, have the --Ind-di/dt). Although the voltage across the inductor capacitor already charged so that it waits for a gate 300 is negative during the period when the switch is in signal Q3 to the third thyristor. As soon as the gate the on position, the voltages EA at point A is zero when signal Q3 reaches the thyristor Q3, the thyristor dis you turn the switch on. Thus the voltage across V300 is charges the capacitor and it enables you to save, for as shown, staring negative when the switch is on and example, a hundred microseconds resulting in a finer going positive when the switch is off. The current I300 45 control of the current through the direct current con through the inductor 300 increases during the period of verter. If only a diode D2 is in the circuit, than as soon time when the switch is on and decreases during the as the capacitor reverses its polarity and reaches a full period of time the switch off. The voltage V302 across charge the capacitor will discharge through the diode. the diode in the first circuit is negative and is equal to As will be realized the direct current converter may the voltage of the electrochemical cell Vload because the 50 consist of a plurality of boost regulators or buck regula diode 302 is blocking the flow of current through the tors extending in parallel with each other between the electrochemical cell. Thus, the current is being shunted fuel cell and the electrochemical cells. This will result in through the first thyristor switch 298 with the result reduced probability for AC ripple in the electochemical that the currrent 1302 flowing through the diode is equal cell when using a boost regulator. As will be appreci to the current Iload through the electrochemical cell is 55 ated, AC ripple is to be avoided if possible in electro discontinuous. Thus, the inductor 300 in the boost regu chemical cells.

lator acts as an intermediate storage of electrical energy Although the invention has been shown and de because the output voltage is greater than the input scribed with respect to detailed embodiments thereof, it voltage. In the buck regulator the inductor 100 acts as a should be understood by those skilled in the the art that filler to provide a continuous source of current to the various changes inform and detail thereof may be made electrochemical cell. In summary, the buck regulator without departing from the spirit and the scope of the has a discontinuous source of current resulting in a claimed invention.

continuous output of current and in the boost regulator We claim:

the source of current is continuous and the output cur 1. A method for operating a first electrochemical fuel rent is discontinuous. This continuous current may be a 65 cell in combination with a second electrochemical cell source of AC ripple in the electrolysis cell by placing a plurality of boost regulators in parallel, this effect will which employs a direct current converter, the fuel cell consuming a fuel and an oxidant to produce electrical be decreased.

power, the second electrochemical cell producing a

Page 16

chemical product and an oxidant as a result of the con having a duty cycle to provide for the intermittent flow sumption of electrical power, which comprises: of current through the direct current converter is used operating the electrochemical cell at a first current to convert the power output of the fuel cell at the sec and at a first voltage to produce a chemical product ond current and at the second voltage to a third current and an oxidant; and an output voltage, wherein the method includes the supplying the oxidant to the fuel cell for consumption step of flowing current intermittently between the fuel of at least a portion of the oxidant in the fuel cell; cell and the electrochemical cell through the direct operating the fuel cell to consume fuel and at least a current converter during the duty cycle of the con portion of the oxidant to produce direct current veter.

electrical power at a second current and at a sec- 10 9. The method of operating the combined cells of ond voltage which is independent of the voltage of claim 8 wherein the method further includes the steps of the electrochemical cell; sensing the first voltage of the electrochemical cell, converting the power output of the fuel cell which is establishing a desired voltage for the electrochemical at the second current and the second voltage to a cell and establishing a voltage change across the direct third current and an output voltage which matches 15 current converter which is equal to the difference be the first voltage of the electrochemical cell by tween the first voltage and the second voltage by ad flowing current intermittently through a direct justing the duty cycle of the direct current converter. current converter responsive to the power output 10. The method of operating the combined cells of of the fuel cell and the fuel available to the fuel cell; claim 8 wherein the step of intermittently flowing cur and, 20 rent between the fuel cell and the electrochemical cell supplying the third current to the electrolysis cell to includes the steps of sensing the actual third current provide at least a portion of the power required to delivered by the direct current converter, establishing a produce the chemical product and the oxidant at desired amplitude for the third current and adjusting the the first current and the first voltage. duty cycle of the direct current converter to provide for 2. The method as claimed in claim 1 wherein the 25 the third current and to establish a voltage change electrochemical cell further includes components in across the direct current converter which is equal to the flow communication with the electrochemical cell for difference between the second voltage and the first producing the chemical product, wherein the electro voltage.

chemical cell is a component for producing the chemi 11. The method of operating the combined cells as cal product, and wherein the method further includes 30 claimed in claim 7 wherein the fuel cell emmploys an the step of producing heat with the fuel cell and trans acid electrolyte and wherein the step of establishing an ferring the heat from the fuel cell to at least one of said upper limit and a lower limit on the value of the voltage components for producing the chemical product. of the fuel cell includes the step of establishing a lower 3. The method as claimed in claim 2 wherein the step limit on the voltage of the fuel cell at fifty percent of transferring heat from the fuel cell to at least one of 35 (50%) of the open circuit voltage of the fuel cell and the the components for producing the chemical product step of establishing an upper limit on the voltage of the includes the step of transferring heat from the fuel cell fuel cell at sixty-five percent (65%) of the open circuit to water to make steam and flowing the steam to the voltage of the fuel cell.

component for producing the chemical product. 12. The method of operating the combined cells as 4. The method as claimed in claim 1 wherein the 40 claimed in claim 7 wherein the fuel cell employs molten electrochemical cell is a first source of the oxidant and carbonate as the electrolyte and wherein the step of the oxidant flowed from the electrochemical cell is establishing an upper limit on the value of the voltage flowed to the fuel cell and wherein a second source of and a lower limit on the value of the voltage of the fuel an oxidant is in flow communication with the fuel cell, cell includes the step of establishing a lower limit on the wherein the method includes the step of providing the 45 voltage of the fuel cell at fifty percent (50%) of the open oxidant from the second source to the fuel cell to supply circuit voltage of the fuel cell and the step of establish the fuel cell with an additional amount of oxidant. ing an upper limit on voltage of the fuel cell at sixty-five 5. The method as claimed in claim 1 wherein the fuel percent (65%) of the open circuit voltage of the fuel cell is capable of supplying a portion of the power to the cell.

electrochemical cell and wherein a means for supplying 50 13. The method of operating the combined cells of additional power to the electrochemical cell is in paral claim 7 wherein the fuel cell employs a base as the lel with the fuel cell, wherein the method includes the electrolyte for the fuel cell and wherein the step of further step of supplying additional power to the elec setting an upper limit and a lower limit on the voltage of trochemical cell from another source. the fuel cell further includes the step of setting the 6. The method as claimed in claim 2 wherein the fuel 55 lower limit on the voltage of the fuel cell equal to sev cell is capable of supplying a portion of the power to the enty percent (70%) of the open circuit voltage of the electrochemical cell and wherein a means for supplying fuel cell and the step of setting the upper limit on the additional power to the electrochemical cell is in paral voltage of the fuel cell equal to eighty percent (80%) of lel with the fuel cell, wherein the method includes the the open circuit voltage.

further step of supplying additional power to the elec 60 14. An apparatus for carrying out an electrochemical trochemical cell from another source. process which comprises:

7. The method as claimed in claims 4, 5 or 6 which an electrochemical cell which uses electrical power includes the steps of establishing an upper limit and a at a first voltage to produce a chemical product and lower limit on the voltage of the fuel cell and adjusting an oxidant;

the power output from the fuel cell to maintain the 65 means for supplying the oxidant to the fuel cell; voltage between the upper limit and the lower limit. at least one fuel cell which utilizes a fuel and at least 8. The method of operating the combined cells of a portion of the oxidant supplied to the cell to claims 1, 4 or 5 wherein a direct current converter produce electrical power at a second voltage

Page 17

which is independent of the voltage of the electro cludes a means for supplying additional power to the chemical cell and a second current; and electrochemical cell.

means for the intermittent flow of current through a 18. The apparatus as claimed in claim 16 or 17 direct current converter responsive to the power wherein produced by the fuel cell and the fuel available to voltages the and fuel cell has a schedule of desired operating wherein the fuel cell includes means for the fuel cell which is connected to the fuel cell and the electrochemical cell for receiving power from the fuel cell liesfuel controlling the cell voltage such that the voltage of within said schedule of desired operat the fuel cell, for regulating the electrical power ing voltages.

received from the fuel cell to adjust the current and 19. The apparatus as claimed in claim 16 or 17 voltage supplied by the fuel cell so that the voltage 10 wherein said oxidant for the fuel cell is oxygen. change across said means is equal to the difference 20. The apparatus as claimed in claim 19 wherein said between the first voltage and the second voltage electrochemical cell is an adiponitrile cell. and for supplying at said first voltage power re 21. The apparatus as claimed in claim 15, 16 or 17 ceived from the fuel cell to the electrochemical cell to provide at least a portion of the power used by 15 wherein the means for regulating the electrical power the electrochemical cell; includes a direct current converter having a duty cycle wherein the means for regulating electrical power per the to provide for the intermittent flow of current through mits the fuel cell to operate at a second voltage which is direct current converter. different from the first voltage of the electrochemical 22. The apparatus as claimed in claim 21 wherein the cell to enable the fuel cell to operate at a desirable volt 20 direct current converter has a variable duty cycle re age for the fuel cell and to enable the electrochemical sponsive to a duty cycle signal and wherein the means cell to operate at a desirable voltage and current for the for regulating electrical power includes a second means electrochemical cell. for establishing the duty cycle of the direct current 15. The apparatus as claimed in claim 14 wherein the converter and for sending a duty cycle signal to the apparatus further includes components in flow commu 25 direct current converter in response to a first signal nication with the electrochemical cell for producing the indicative of the desired amplitude of the first voltage of chemical product, wherein the electrochemical cell is a the electrochemical cell and a second signal indicative component for producing the chemical product, of the actual first voltage of the electrochemical cell. wherein the fuel cell produces heat and wherein the 23. The apparatus as claimed in claim 22 wherein the apparatus further includes means for transferring heat 30 direct current converter has a variable duty cycle re from the fuel cell to at least one of said components for sponsive to a duty cycle signal to establish an output producing the chemical product. third current and wherein the means for regulating 16. The apparatus as claimed in claim 14 wherein the electrical power includes a second means for establish electrochemical cell is a first source of fuel and wherein ing the duty cycle of the direct current converter and the apparatus includes a second source of fuel for sup 35 for sending a duty cycle signal to the direct current plying additional fuel to the fuel cell. converter in response to a first signal indicative of a 17. The apparatus as claimed in claim 14 wherein the desired amplitude for the third current and a second fuel cell supplies a portion of the power to the electro signal indicative of the actual third current. chemical cell and wherein the apparatus further in sk it k k