US3888750A

US3888750A - Electrolytic decomposition of water

Info

Publication number: US3888750A
Application number: US437571A
Authority: US
Inventors: Lee E Brecher; Christopher K Wu
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp; Day International Inc
Priority date: 1974-01-29
Filing date: 1974-01-29
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10
Also published as: JPS589042B2; GB1488084A; DE2501726A1; AU7761975A; JPS50114395A

Abstract

Electrolysis and catalytic thermochemistry are combined to decompose water while minimizing the energy demanded to accomplish the decomposition. The electrolyte is H2SO3 produced by supplying SO2 and the water to be decomposed to the electrolyzer. The H2SO3 is ionized and oxidized in the electrolyzer into SO4 and H ions and electrons. Hydrogen is derived from the negative electrode of the electrolyzer. The SO4 is combined with H to form H2SO4. The H2SO4 is removed from the electrolyzer to the thermochemical unit, concentrated and decomposed predominately into H2O, SO2 and O2. The SO2 is liquefied and thus separated from the O2 which is derived from the thermochemical apparatus. The liquid SO2 is vaporized and returned to the electrolyzer.

Description

United States Patent Brecher et al.

ELECTROLYTIC DECOMPOSITION OF WATER Inventors: Lee E. Brecher, North Huntingdon;

Christopher K. Wu, Turtle Creek, both of Pa.

Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Filed: Jan. 29, 1974 Appl. No.: 437,571

[52] US. Cl. 204/129; 423/539; 423/579; 423/580 [51] Int. Cl.. C01b 13/04; C01b 13/02; COlb 17/50 [58] Field of Search 204/129, 104; 423/522, 423/526, 539, 579, 648, 644, 580

[56] References Cited UNITED STATES PATENTS 704,831 7/1902 Jacobs 204/104 OTHER PUBLICATIONS Hydrogen Sought via Thermochemical Methods C and EN, Sept. 3, 1973 pages 32-33.

Primary ExaminerR. L. Andrews Attorney, Agent, or FirmZ. L. Dermer [57] ABSTRACT Electrolysis and catalytic thermochemistry are combined to decompose water while minimizing the energy demanded to accomplish the decomposition. The electrolyte is H 50 produced by supplying S0 and the water to be decomposed to the electrolyzer. The H 80 is ionized and oxidized in the electrolyzer into SO, and H ions and electrons. Hydrogen is derived from the negative electrode of the electrolyzer. The SO, is combined with H to form H 50 The H 30 is removed from the electrolyzer to the thermochemical unit, concentrated and decomposed predominately into H O, S0 and 0 The S0 is liquefied and thus separated from the 0 which is derived from the thermochemical apparatus. The liquid S0 is vaporized and returned to the electrolyzer.

6 Claims, 10 Drawing Figures ELECTROLYTIC HEAT ll3.8kcal CELL UNIT 0 550 EXCHIANGERJ HEAT MAKEUP 2 M EXCHANGE D, 0. 2 I300K GENERATOR 223 Kcul DECOMPOSITION REAcmR-2 Q=275Kcul 300m GAS I [6000K 900m ACID TURBNE 78.3 SULFURIC ACID Q00: DECOMPOSITION 35m see-Pr:

V RI R CO 4 i O=45,0Kcol STEAM GENERATOR 53K Q= 37.5 Km! o5oq 5 5m (l500psl,700Fl s0 (uoum) m zoom I R 59W 544% 273.4

OXYGEN,20utm ,2oo'=K STEAM 200' K FEED WA 'I E a 3 8? i I PREHEATER '20 lb .100 SEPARATION I 2 2. o 9 i213 6.95 3oo| K |OOF 589k 307K Km! 4 [20mm o=o.4| 390% F l "y COOLER CONDENSER |59|68l in .2 1 0-435 Kcol coouue WATER 0-455 Kccl s02 COLLECTOR Q=0JK00| was SULFURIC ACID I L VAPOR LIQUID SEPARATION PATENTEDJuHm m5 I 3.888750 SHEET 1 i E I7 l5 |3-' l9! I 3 4 H so T0 ACID PREHEAT I s0 FROM 2 VAPOR LIQUID RECEIVED SEPARATOR UNIT CONDENSER EVAPORATOR FIG. 4

PIC-3.5

SHEET PATENTED JUN 10 I975 PATENTEDJUH ms 3.888.750

1000- REACTION GAS DECOMPOSITION FROM HX4lb REACTOR 339 LSULFURIC ACID H368 VAPORIZATION 400 I I I I l l I 1 10 so 90 I00 no I I I Kcol 1000- A l l K 800 STEA FIG 1 .6C 600 P l l I so I00 no Kcol I I l l l 1 0 so 70 so 9'0 IOO no ELECTROLYTIC DECOMPOSITION OF WATER REFERENCE TO RELATED APPLICATIONS This application relates to an application Ser. No. 437,575 for Conversion Of Coal Into Hydrocarbons filed concurrently herewith to Andrew R. Jones (herein called Jones application) and assigned to Westinghouse Electric Corporation.

BACKGROUND OF THE INVENTION This invention relates to the chemical art and has particular relationship to the decomposition of water into hydrogen and oxygen. Jones application discloses the conversion of coal into hydrocarbons by reacting the coal with hydrogen. Hydrogen is readily obtained by decomposing water. It is an object of this invention to produce hydrogen for coal conversion into hydrocarbons, and for other purposes, by decomposition of water at a minimum cost in energy. It is a specific object of this invention to decompose the water at tem- 2.4 volts. In the practice of this invention the oxygen, instead of being drawn off, oxidizes the electrolyte. Typically, the electrolye is H SO produced by supplying water and to the electrolyzer. By oxidation 80., ions are produced. The $0., is converted into H SO which is drawn off and decomposed thermochemically to produce the oxygen. In a typical cell in which the concentration of the electrolyte is one molar, the drop is only 0.17 volts theoretically or about 0.34 volts actually. In accordance with this invention, energy is applied directly to decompose the sulfuric acid and derive the oxygen rather than indirectly, in the form of electrical energy, as the prior art teaches.

In accordance with this invention, electrolysis and catalytic thermochemistry are combined to decompose water; the hydrogen being derived from the electrolytic means, which consists of electrolytic cells and an electrical power supply, and the oxygen from the thermochemical means. The reactions are presented in the following Table I:

peratures no higher than l,200K. This temperature is AH is the energy and G the work supplied in kilocalothe maximum temperature for water decomposition made available by the gas from the gas-cooled nuclear reactor which, as disclosed by Jones application, supplies the energy for the coal conversion.

In accordance with the teachings of the prior art, hydrogen is obtained by decomposing water by electrolysis. The electrolytic process has relatively low thermal efficiency and its energy demands to produce hydrogen in the quantities required for coal conversion is excessive. Hydrogen is also obtained by treatment of fossil fuels but this practice has the disadvantage that it demands substantial quantities of the fossil fuel. Thermochemical processes for producing hydrogen have also been proposed. Typical of these processes is the Marchetti Mark I process which is described briefly in Jones application and is presently under study. This process demands substantial quantities of mercury which presents problems due to toxicity, environmental hazards and cost.

It is an object of this invention to overcome the above-described disadvantages of the prior art and to provide a method and apparatus for producing hydrogen efficiently by decomposing water and which shall not require substantial quantities of fossil fuel or such objectionable and costly chemicals as mercury. It is also an object of this invention to provide such apparatus and method which shall operate throughout at ternperatures not exceeding 1,200K.

SUMMARY OF THE INVENTION This invention arises from the realization that in prior art electrolytic cells where both the hydrogen and oxygen are drawn off, the voltage required by the cell is high. Theoretically, for a typical cell in which the concentration of the electrolyte is one molar, this voltage is about 1.43 volts; in actual practice it rises to 2.2 to

ries per mole in an endothermic reaction (positive) or derived in an exothermic reaction (negative), T is the absolute temperature and AS the change in entropy. Reaction (1) takes place in the electrolytic means and reactions (2) and (3) in the thermochemical means. S0 and water are supplied to the electrolyic means to form H 50 The reactions in each cell of the electrolytic means are presented in the following Table II:

TABLE II (6) H O H 50 H H 50 (Overall) Overall the e is an electron.

The hydrogen is drawn off. The H SO is drawn off, concentrated (reaction 2), and decomposed (reaction 3) into H O, S0 and 0 The S0 is liquefied and returned to the electrolytic means. The O is drawn off.

The energy for the decomposition of the water is in the usual practice of this invention derived from gascooled nuclear reactors through heat exchangers as taught by Jones application. The electrolytic cells are supplied from a generator whose primary source is typically a nuclear reactor. The primary source for the generator may be wholly or partly the waste energy from the decomposition reactor. Typically, the cells are connected in series in banks with a number of banks in parallel. The number of cells in series depends on the voltage available. If 220 volts are available at the terminals of the supply and each cell absorbs 0.34 volt, about 60 cells are connected in series. If each bank draws 100 amperes and the capacity of the supply is 1,000 amperes, 10 banks are connected in parallel.

In principle, the thermodynamic efficiency of the chemical cycle according to this invention for decomposing water should approach Plant layouts confirm the essential attractiveness of this cycle, showing thermal efficiencies of 50-53% being possible with unoptimized plants.

It is advantageous that the electrolytic cells be pressurized. Pressurized cells not only supply hydrogen under pressure, but also improve the practical and thermodynamic efficiencies of the cycle. Similarly, removal of water from the gas stream fed the decomposition reactors dramatically reduces the waste heat dumped to cooling water at the condensers.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of this invention, both as to its organization and as to its operation, together with additional objects and advantages thereof, reference is made to the following description, taken in connection with the accompanying drawings, in which:

FIG. 1 is a diagram showing an electrolytic cell typically used in the practice of this invention;

FIG. 2 is a block diagram of apparatus according to, and for practicing, this invention;

FIGS. 3A and 3B are flow schematics of apparatus in accordance with this invention and for practicing this invention;

FIG. 4 is a diagram which serves to illustrate the operation of the apparatus shown in FIGS. 2 and 3;

FIG. 5 is a diagram which also serves to illustrate the operation of the apparatus shown in FIGS. 2 and 3;

FIG. 6A, B, C and D are graphs showing the relationship between the heat or energy input to the various components of FIGS. 2 and 3 the temperatures at which these components operate derived by evaluating the heat demands and the heat rejection of decomposition of water carried out in the practice of this invention; and

FIG. 7 is a flow schematic similar to FIG. 3 both showing heat flow and other parameters.

The apparatus shown in FIG. 1 is a cell 11, one of the many cells used in the practice of this invention. The cell includes a container 13 which is, with the other cells, in a pressure-tight enclosure (not shown). The cell 11 includes positive electrode 15 and negative electrode 17 across which an appropriate DC potential is impressed from a DC generator 325 (FIG. 3). The

electrodes

15 and 17 are hollow and are provided with spargers 18. In the practice of this invention, the potential between the electrodes is a few tenths of a volt. A membrane 19 separates the

electrodes

15 and 17. The membrane 19 is a diffusion barrier which passes I-I ions and electrons but not S0 or 80., ions. The cell 11 contains an aqueous electrolytic solution-21, H SO Water from a suitable source is continually renewed in the cell 11. In addition, S0 is circulated to the cell from the vapor-liquid separator unit (FIG. 3). There are losses of S0 in the process and these losses are replenished by supply of $0 from an external source (not shown). Sulfuric acid is supplied from the portion of the cell 11 on the side of the membrane 19 which contains the positive electrode 15. Hydrogen is derived from the cell 11 and transmitted to the conversion process or to a collector (not shown).

The apparatus shown in FIGS. 2 and 3 includes intermediate heat exchangers 41a and 41b, an electrolyzer or electrolysis means 300, an acid preheater 311, an acid vaporizer 313, an acid decomposer 305, a wasteheat recovery unit 358 and a vapor liquid separator unit 307.

The heat exchangers 41a and 41b are supplied from a nuclear heat source 31 (FIG. 2). Jones application states that in a typical situation about 10,000 megawatts would be demanded from the source 31 and three nuclear reactors may be required. The heat exchangers 41a and 41b may be supplied directly from the source 31 or through interposed intermediate heat exchangers.

The electrolyzer 300 includes the electrolytic cell unit 301 and the DC generator 325. The generator 325 supplies electrical energy to the electrolytic cell unit 301. The electrolytic cell unit 301 includes a large number of cells 11 (FIG. 1) in series-parallel, the network connection of the cells depending on the voltage and current available from the generator 325.

In the electrolytic cell unit 301, reaction (1) Table I of the process is carried out producing hydrogen and H SO The hydrogen is transmitted for use. The H SO is transmitted to the vaporizer 303 to carry out reaction (2) Table I of the process and also to vaporize the H This vaporizer 303 includes an acid preheater 311 and an acid vaporizer 303. The energy for operating this vaporizer 303 is derived from the secondary path 315 of intermediate heat exchanger 41a. The gas from this secondary path is compressed by a compressor 317; the compressed gas is passed through path 315 and expanded in a gas turbine 319 which drives the compressor 317. From the turbine 319 the gas flows through

primary paths

321 and 323 of the acid vaporizer 313 and acid preheater 311 back to the compressor 317. The gas turbine 319 also drives the electric generator 325 which supplies energy to the electrolytic cell unit 301. The temperatures at which this gas enters and leaves the components in the gas circuit are shown in degrees Kelvin in FIG. 3.

The acid decomposer 305 includes

decomposition reactors

337 and 339. Typically, the catalyst which is used in carrying out the decomposition is vanadium. The waste-heat recovery unit 358 includes

turbines

363, 364, 366 and their associated steam generator 357, feedwater preheater 343, and condenser 365. The vapor-liquid separator unit 307 includes vapor-

liquid separators

349, 379, 395 and 401, the heat exchanger 373, the cooler 377, the cooler 385, and the

compressors

383, 391 and 397.

The dehydrated and vaporized H SO from the vaporizer 303 is transmitted from the secondary path 331 of the acid vaporizer 313 through the

secondary paths

333 and 335 of the

successive decomposition reactors

337 and 339, where reaction (3) of the process, Table I, is carried out. The resulting product, including water, S0 and O is passed through the primary path 340 of the decomposition reactor 337, the primary path 341 of the feedwater preheater 343, and the primary path 345 of the cooler 347 into the vapor-liquid separator 349 of the vapor-liquid separator unit 307 where a weak sulfuric acid stream is drawn off and returned to the electrolytic cells.

Energy is supplied to the acid decomposer 305 from the intermediate heat exchanger 41b. The gas (I-Ie) from the secondary path 351 of this heat exchanger flows through the primary path 353 of decomposition reactor 339, the primary path 355 of a steam generator 357 of the waste-heat recovery unit 358 to the primary path 351.

The secondary path 361 of the steam generator 357 supplies the

turbines

363, 364 and 366, the exhaust from these turbines flowing through a condenser 365 Output in kilocaloriespe r gram mole and the secondary path 367 of the feedwater preheater aig f jg hlg g? fig 343. The turbines drive AC generators (not shown) Losses: P I which supply electrical power where needed. h Unit 301 I L? The liquid phase of the vapor-liquid separator 349 5 822 ;2 5:353 N I 73.: includes water and small quantities of S0 forming Total 1788 weak H SO which is returned to the electrolytic cell unit301 The $02 and the 02 f the vapor hquid As presented n Table II, the reactions in each elecarator 349 flows through the primary path 371 of a heat trolytle Cell 11 as follows! exchanger 373, and a secondary path 375 of a cooler H2808 2 4H 4 26 377 into another vapor-liquid separator 379. The pri- 3 2e 2 mary path 381 of the cooler 377 is supplied with a cool- The voltage 6 absorbed by the reaction(4) is theoretiing gas from a compressor 383 through a cooler 385 cally 0.l7 volts; and by reaction (5) 0.00 volts. The where the compressed gas is cooled with water. The 15 t t l v ltage 6 across a cell is given by compressed gas is expanded in the primary path 381. 3. 6 6 (0059/2 1 (aso=) p /p The S0 and 0 of liquid separator 379 is compressed h i a by compressor 391 and passed through a secondary total energy b b d path 393 of cooler 377 into a vapor-liquid separator a i it f H+ i 395. The gas from separator 395 is compressed by a asm=activity f so =i compressor 397 and passed through another secondary p partial pressure f H2 path 399 of cooler 377 into vapor-liquid separator 401. p partial pressure of 502 The S0 is liquefied in vapor-

liquid separators

379, 395 Equation (8) becomes and 401 and transmitted to collector 403 whence it is 9 e 1.5) (.059) 10g (Pu, IP80) n so returned to the electrolytic cell 301 through a secon- 1() a so 7 H so m so i dary path 405 of heat exchanger 373. where t z z FIG. 7 shows heat quantities and parameters. The 'Y actvitycoefficient of H SO. heat quantities are in kilocalories per gram mole of mHzso mole concentration of H SO water decomposed; the Qs presented are the heat duty The following Table III shows the ratios of the partial cycles'per mole of water decomposed. The concentrapressures of H to S0 for various mole quantities of tion of the sulfuric acid is in weight percent, w/o. FIG. H 80 TABLE III u so u so 11,80 8" H2 504 PH: m PM: (11 PS0 2 0.147 0.294 O.532 0.l23 0.0345 3 0.166 0.498 O.302 0. 143 0.0547 4 0.203 0.812 0.090 0.l62 0.0735 5 0.242 1.210 +0.083 0.l774 0.0889 10 0.660 6.60 +0820 0.2426 0.l54l 15 1.260 18.9 +1.276 0.2830 0.l945 20 2.22 44.4 +1.646 0.3 159 0.2274

3 does not show the pumps and other components The requirement of work, AG, per cell depends on e which are included in the flow circuits. and 6 depends on the concentration of the H SO 1n the apparatus shown in FIG. 3, the sulfur dioxide For 64.3 weight percent 6 70.316V is separated from the oxygen by liquefying the sulfur For 100 weight percent 6 0.453V dioxide. Other separation processes may be used. For For 78,3 weight rcent 6 38()V assumed example, the separation may be effected chemically by For l.72 mole feed acid 6 0. 123V assumed reacting the mixture with a reactant which reacts either The above data presents the theoretical magnitudes for with the oxygen or the sulfur dioxide, collecting the une. reacted compound of the S0 or 0 and subsequently Th diff between -,38()V d 123V treating the compound resulting from the reaction to -(),257\/ hi h i equivalent to release the reacting compound of the $0 or 0 AG 1 L8 kilocalories.

In Summary, the Overall electrolytic reaction is This work is supplied by the generator 325. For this op- 1 21420) Sow) Hm) HQSOMQ) (see Table I) eration it is necessary that heat exchanger 41a supply and the catalytic thermochemical reaction is 24 kilocalories to the generator 325 and22.8 kilocalo- 7 H 30 H O 0 O2 ries to the electrolytic cell unit 301. A mixture f 0 50 0 and 0 leaves the acid A reaction which is important to the practice of this composer'305. H 0 and 80;; are removed by condens- 6O invention 151 ing a weak acid solution, 80 and 0 are separated by 3 Q 2 V2 2 successive compression at about 200 K h h b 1 It is desirable to consider the equilibrium constant K ance summary is as follows: for this YBaCtiOIII Input in kilocalories per gram mole From heat exchanger 41a 1 13.8 From heat exchanger 41b 65.0 Total 178.8

where any of the partial pressures, designated Pi is given by:

13. Pi Yi 1r I where Yi mole fraction corresponding to Pi 1r total pressure. The relationship between absolute temperature, K, and AH for the reaction is presented in the following Table IV:

The heat demands in the successive steps of the decomposition of sulfuric acid with the apparatus shown in FIG. 3 will now be determined, assuming sulfuric acid of 78.3 w/o, feed from the electrolyzer to the thermochemical unit.

TABLE IV T, K log K, K, AH Kcal o 1200 0527 336 22.023 The starting pomt 1s a batch of SllIfLlI'lC acid at 70 F 1100 0.161 1.45 22.309 cons1st1ng of 108.78 grams or 1.1 1 moles of H SO 1n 1000 -0.268 0.540 22.577

900 837 01458 228,9 10 30 grams or 1.656 moles of H wh1ch produces l 800 293x104 23,035 mole of hydrogen. The following Table VII shows the 700 169007 23-224 various endothermic process steps and the energy de- 600 3.649

mand at each step.

TABLE VII Energy Step Process Demand No. Preheating Kcal 1 70F to 436 K 10.8 2 1.1 lH SO +l .656H O 1.1 lI'I SO +l .656Hz0 m0l0 43.465

vaporization 3 1.1 m so u 1.1 1H 0 +1 .1 150 8 41.412

Sensible Reactions 4 1.1 ISO Q -l.1 lSO 1.929 5 2.77 H O ,o 2.77 H O o 2.440 6 0.05SO .05SO .025 Ommpm l. l6l 7 1.06 SO o l.06 50 1.933 8 0.05 s0 0.05 50 0.062 9 0.025 O o, 0.025 0 0.020 10 2.77 H O o, 2.77 H O o 2.52l l l 0.13 SQ- r' 0.l3 SO o -l-0065 O o 2.995 12 0.93 so,.,..,.,s,.,+ 0.93 SO o L760 l3 0.l8 S0 a 0.18 80 0.228 14 0.09 o o 0.09 O o 0.073 15 2.77 HzOmoom-f" 2.77 Hzowoom) 2.604 16 0.25 sO o e 0. SO +0.l25 0 0 5.705 17 0.68 Sq -10.68 SO L325 18 0.43 SO, 0.43 80 0.556 19 0.215 0 ,-"0.2l5 0 0.l78 20 2.77 H O 2.77 H O 2.684 21 0.29 so 0.29 so ,+0.14s 0 6.547 22 0.39 SO 0.39 80 0.780 23 0.72 SO 0.72 SO 0.944 24 0.36 C 036 0 0.302 25 2.77 H O 2.77 H O 2.773 26 0.19 SO 0.19 SO 0.095 0 4.239 27 0.20 SO 0.20 503 12001 0.408 28 0.91 SO 0.9l 80 L207 29 0.455 O 0.455 0 0.386 30 2.77 H O r 2.77 H 0 2.853 3] 0.09 SO -v 0.09 SO ,+0.045 1.982

AH, is the reaction heat in kilocalories. Here feed is assumed to be 78.3 w/o acid at 1 atmosphere.

For illustration purposes assume the data presented in Table V below to represent a typical situation:

TABLE V Chemical Component Moles H 0 2.77 S0 1.1 l-x SO; x

Total 3.88 k x Then 14.K,, (.X/I.l l-x) (x/7.76 x) /2 Table VI below gives the magnitude of x, the moles of S0 decomposed at different temperatures T in degrees Kelvin:

TABLE VI As presented in steps 6, ll, 16, 21, 26 and 3] the S0 is progressively decomposed into S0 b 0 as the temperature is increased from 600K to l,200l(. The total S0 from the decomposition is 1 mole but 0.0135 moles is carried away in the oxygen stream.

The exothermic heat or energy which is given up in It is next desirable to consider the acid condensation. Consider a batch which when fully diluted has 10.78 grams or 0.1 1 moles H in 48 grams H O. This is a dilute solution 18.3 w/o H 80 having a boiling point of 218F. To form 0.ll H S0 the following reaction takes place:

i Hzom ooo I 803015000X) l-l SO s Energyl.141Kcal 9 The heat exchange involved in acid condensation is The properties of the mixture (approximately 97% 0 presented in the following Table IX: are assumed to approximate those of oxygen. Two

TABLE IX G1 ams Grams mir vap z an 0) atbul) T(2 K) w/oAcid I-IQSO4 H2O cal/g cal/g Kcal Kcal Kcal Kcal 450 72 10.78 4.19 8.3 675 2.l30 -1.008 400 52 10.78 9.95 2.8 652 3.954 0.875 l.443 375 18 10.78 48 55.5 640 -2l.604 0 0.120

In Table VIII H is the enthalpy of the mixture and stags of adiatgatic Compression are used h l Hum is the enthalpy f the vapor which is taken as an cooling to 200 K. The first stage of compresslon is to average f water 1 5 atm. and the second is to atm.

The following is a sample computation: 16. 10.78 H SO (l,600K)+0.94 H O(g, The theoretical work of compression (per mole of 600K) 11 2 gm of 92W/0 2504 at 550K O is shown in Table XI below:

TABLE XI Stage No. 1 Stage No. 2

H(3I7K,S=25.66)=3363 cal/mole H(20 atm,S=22.36)=3260 cal/mole I-I(200K,S=25.66)=2565 1-1(5 atm,S=22.36)=2547 AH=W=0.798 Kcal/mole AH=W=0.713 Kcal/mole In Table XI S is the entropy. Intereooling Requirements (per mole of 0 Stage No. 1 I Stage N0. 2 3363 cal/mole 3260 cal/mole 2547 2479 0.816 Kcal/mole 0.78l cal/mole Moles of S02 entering first compressor 0.01350 Moles of S02 removed at 5 atm. and 200K 0.01085 Moles of S02 removed at 20 atm. and 200K 0.00200 Moles of S02 remaining in oxygen 0.00065 Oxygen purity 99.8+%

1= Since work of compressing S0 was neglected, as-

: 0943-0703- 315 K681 sume all recovered S0 is combined as liquid at 200K 1.075 Kcal and 1 atm. Neglect small S0 losses in heat up calcula- AH 47.06 724-748 1.12 Kcal tion. The reactions are:

AH 1 mole S0 (2043-3237) l.144 Kcal 0.5 mole O (l.455-2.210)==0.378 Total 1.522 Kcal 0 S AH, Kcal v ft 6 h (21) o (1,200K)- s0 (1,300K) 1.410

. following able X is a Summary 0 f er 22 0.5 O (g,200l(,20a:m.)- 0.5 O (g,300K,20atm.) 0.367

mic reaction while the product cools to 375 K. Total 1.777

TABLE X The refrigeration requirements will now be consid- AH, K 1

Temperature Range K ca ered w1th reference to FIG. 5 wh1ch represents the 1200 600 27.239 See Table VII vaporliquid separator unit symbolically disclosing a 600 550 -7.l06 fl .d l 5 550 q 500 2942 u1 circuit inc u mg an evaporator 01, a compressor 500 450 3.85? 503, a condenser 505 and an expansion valve 507. It is 238 3 9 5 assumed that the refrigerant is ethane and that its temperature is 100F at the evaporator and 61F at the condenser. The energy, q imprpessed on the evapora- Co in t 300I results in the followin additional en- 0 l g o g tor 501 is 87.5 BTU/lb and the work, Wev, performed ergy:

SO 375K) SO 3QOK) 973 Kca] by the compressor 503 is 74.9 BTU/lb. The vapor re- 3751() HA). O2(g, 00K) 0.260 Kcal frigerant which flows from the evaporator 501 to the Specific heat of H SO 0.86 compressor 503 is at a temperature of l00F and 58.78 grams (75C)(0.86 ca1/gC) 3.792 Kcal pressure 31.32 psi and has an enthalpy, H, of 386.8 BT. Overall total exothermic (to 300K) 73.446 Kcal Out of the compressor 503 the refrigerant has a tem- The heat energy given up in separating the oxygen perature of about 147F and an enthalpy H of 461.7 from the sulfur dioxide will now be considered. BTU/1b (386.8 74.9). The energy, q delivered by The reactions are: the condenser 505 is 164.4 BTU/lb and the resulting AH, Keel i 8 5 2,20g? i 825 so 1,2001 j id (19) 0.5 O2(g,300K)- 0.5 O (g,200K) 0.348

The total reaction is: e (20) SO (g,300K) 0.5 O (g,300l() 0.0135 SO2(g.2OO K) 0.9865 SO (l,200K) 0.5 O (g,200K) 7.8l69 total Second refrigeration 0.408 Kcal Third refrigeration 0.390 Kcal Total 6.89 Kcal FIG. 5 represents diagrammatically the gas turbine cycle which serves as a primary source for the DC generator 325. As indicated the input heat (from heat exchanger 4la) q and the output heat is q,,. The gas turbine 319 is assigned a mechanical efficiency 17 0.90 and the compressor 317 an efficiency 11 0.85. The

water preheat 30.0 Kcal mole vaporization and superheat 37.5 Kcal per mole work 24.0 Kcal per mole The following data is developed: Common to all cycles 25. H 0 (1500 psia,100F) H O(1,500 psia, satd liq.) AH=54O BTU/lb 26. H O (1,500 psia, satd) H O(l,500 psia, satd vap.) AH=556 BTU/lb 27. H O (1,500 psia, satd vap.) H O (1,500 psia,

700F) AH=119 BTU/lb Total AH=1,215 BTU/lb To provide 1,200 psia steam 28. 11 0 (1,500 psia, 700F) H O(1,200 psia,

628F) AH 36 BTU/lb To provide 600 psia steam 29. H O (1,500 psia, 700F) H O(600 psia,

493F) AH 77.7 BTU/lb To provide power 30. 11 0 (1,500 psia, 700F) H O(1 psia, 101F) AH 433 BTU/lb Mass and Energy Balance lnputs 1,767,661 lbs BFW/hr Outputs 1,591,681 lbs/hr condensate 55,880 lbs/hr 1200 psia steam 120,100 lbs/hr 600 lpsia steam 1,767,661 lbs/hr Tota Prep. BFW By Product Work 4.16 MM BTU/hr Enthalpy H of Exit Steam 202.47 MM BTU/hr Preheater 954.82 Work (205,197 kw) 700.54

vaporization & Superheat 1 193.20 Waste heat to condenser 1249.17

Total 2152.18 MM BTU/hr Total 2152.18 MM BTU/hr temperature T, of the gas flowing into the compressor 317 is 760R and the temperature T of the gas flowing into the turbine is 2,310R. The overall efficiency 1;, is given by:

24. '1 (3.32 x x 2.32/2.73 x x assuming s 1.74, P 4.0, 1;, 0.24, k 1.4 T 848K 17, for different magnitudes of X is presented in the folowing Table XII:

TABLE Xll With reference to the waste-heat recovery unit 358, which includes the

steam turbines

363, 364, 366, it is assumed that:

w(work) 433 BTU/lb Graphs A through D of FIG. 6 summarize the data developed above. In each graph energy or heat in kilocalories (Kcal) is plotted horizontally and temperature in degrees Kelvin vertically. The graphs are labeled to indicate the parts and the functions of the apparatus shown in FIG. 3 to which they correspond. The distance between the ordinates of

curves

521 and 523 of graph 6A measures the temperature difference for preheating the sulfuric acid, the difference between the ordinates of curves 521 nd 525, the temperature difference in vaporizing the sulfuric acid. The distance between the ordinates of

crubes

527 and 529 of graph B measures the temperature difference for the decomposition reactor 337 and the distance between the ordinates of

curves

531 and 533 the driving force for decomposition reactor 339, and so forth.

While a preferred embodidment of this invention is disclosed herein, many modifications thereof are feasible. This invention is not to be restricted except insofar as is necessitated by the spirit of the prior art.

What is claimed is:

l. The method of decomposing water into hydrogen and oxygen with apparatus including electrolytic means having positive and negative electrodes and thermochemical means, the said method comprising supplying water to said electrolytic means, supplying sulfur dioxide to said electrolytic means to form with the water an ionized electrolytic solution including sulfurous acid and 11* ions, impressing a potential between said positive and negative electrodes to suply energy to form hydrogen gas at said negative electrode and to oxidize sulfurous acid to sulfuric acid at the positive electrode of said negative electrode, deriving said hydrogen gas from said electrolytic means, transferring said sulfuric acid from said electrolytic means to said thermochemical means, decompsing said sulfuric acid in said thermochemical means into water, sulfur dioxide and oxygen, deriving said last-named oxygen from said thermochemical means, and transferring said last-named formed sulfur dioxide to said electrolytic means.

2. The method of claim 1 wherein the sulfuric acid derived from the electrolytic means is concentrated by the thermochemical means prior to being decomposed.

3. The method of claim 1 wherein the sulfur dioxide is separated from the oxygen by liquefying the sulfur dioxide while the oxygen remains in gaseous phase.

4. The method of claim 1 wherein energy is supplied to the thermochemical means to decompose the sulfuric acid and the residual energy left from the decomposition is supplied to generate electrical energy.

5. The method of claim 4 wherein energy derived by cooling the products of the decomposition of the sulfuric acid is also supplied to generate electrical energy.

6. The method of claim 4 wherein the electrical energy is generated by turbine means and the feed fluid for said turbine means absorbs heat from the products of the decomposition of the sulfuric acid to cool said sulfuric acid.

Claims

1. The method of decomposing water into hydrogen and oxygen with apparatus including electrolytic means having positive and negative electrodes and thermochemical means, the said method comprising supplying water to said electrolytic means, supplying sulfur dioxide to said electrolytic means to form with the water an ionized electrolytic solution including sulfurous acid and H ions, impressing a potential between said positive and negative electrodes to suply energy to form hydrogen gas at said negative electrode and to oxidize sulfurous acid to sulfuric acid at the positive electrode of said negative electrode, deriving said hydrogen gas from said electrolytic means, transferring said sulfuric acid from said electrolytic means to said thermochemical means, decompsing said sulfuric acid in said thermochemical means into water, sulfur dioxide and oxygen, deriving said last-named oxygen from said thermochemical means, and transferring said last-named formed sulfur dioxide to said electrolytic means.

2. THE METHOD OF CLAIM 1 WHEREIN THE SULFURIC ACID DERIVED FROM THE ELECTROLYTIC MENS IS CONCENTRATED BY THE THERMOCHEMICAL MEANS PRIOR TO BEING DECOMPOSED.