WO1989006711A1

WO1989006711A1 - Fully automated current-controlled electrolytic cell assembly for the production of gases

Info

Publication number: WO1989006711A1
Application number: PCT/AU1988/000166
Authority: WO
Inventors: George Racz
Original assignee: Hydra-Gas Pty. Ltd.
Priority date: 1988-01-21
Filing date: 1988-06-01
Publication date: 1989-07-27

Abstract

A fully automated current-controlled electrolytic cell assembly for the production of gases consists of a number of cell units, each cell unit comprising a cathode (1), constructed from a number of spaced parallel walls (2), forming a honeycomb-like structure, with apertures (3) of rectangular cross section. The structure may be extended from metal, fabricated from interlocking plates welded together or square section tubing cut to length and welded along the upper and lower exposed ends. The metal normally used is stainless steel. Metal rod-like conductor members (4) are welded to adjacent faces (5, 5a) of the cathode structure (1). An anode assembly (6) consists of an anode plate (7) having rod-like electrode members (8) spaced over the upper surface of the anode, so that when assembled with its cathode counterpart, the anode members (8) are positioned longitudinally within respective cathode apertures (3). Electrical conductor members (9) are attached underside of anode plate (7) for connection to the power supply. The electrode conductor members (4, 9) have apertures (10, 11) bored into their respective free ends. These apertures (10, 11) are internally threaded and aligned radially to the electrode assembly. In practice the electrolytic cell is housed within an apparatus for the production of electrolytic gas consisting of a housing having an internal chamber accommodating the cell, a gas chamber communicating with the internal chamber, a gas outlet port communicating with the gas chamber, a fluid inlet port communicating with the internal chamber for the resupply of 16 % NaOH/20 % KOH and power supply.

Description

FULLY AUTOMATED CURRENT-CONTROLLED ELECTROLYTIC CELL ASSEMBLY FOR THE PRODUCTION OF GASES . THI S INVENTION relate s to a proc e s s f or the electrolytic production of a combustible gas, and an electrolytic cell for the production of such gas. BACKGROUND ART

Electrolytic decomposition of water into its gaseous components, hydrogen and oxygen, is a well known process but hitherto has had little commercial application. Known fuel cells which rely upon an exothermic recombination of hydrogen and oxygen gases produced at the electrodes of an electrolytic cell are not considered to be energy efficient. Possibly the only commercial application of an electrolytic cell to produce hydrogen and oxygen is employed in the production of hydrogen peroxide for rocket fuels and as an oxidant in certain chemical processes.

Early attempts to utilize as a fuel electrolytic gas, a mixture comprised essentially of hydrogen and oxygen gases produced by the electrolytic decomposition of water, have not been commercially successful. (However, it has been recognized that the combination of monatomic hydrogen with oxygen to form water releases much more heat energy than the combination of molecular hydrogen with oxygen to form the same amount of water.) The lack of commercial success has been attributed to inefficient production of the gas due largely to poor cell design. Other problems include the safe storage of the gas so produced. Although pure hydrogen and oxygen gases present in the ratio 2:1 respectively would not normally spontaneously recombine at ambient temperatures, the presence of various ionized species or free radicals in the gas and/or catalytic reactions with the surface of the storage vessel may give rise to a chain reaction with potentially disastrous results.

For these reasons little cognisance haa been given to water as a source of a fuel gas comprising hydrogen and oxygen gases liberated in an electrolytic cell, despite the fact that such "electrolytic" gas is self-maintaining in combustion, non-polluting and can be ionized to increase its calorific value in combustion. It is an aim of the present invention to overcome or alleviate the problems of prior art electrolytic cells by providing a more efficient method and apparatus for producing electrolytic gas. It is a further aim of the invention to provide a safer process and apparatus for the economic production of a combustible electrolytic gas.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided an electrolytic cell comprising a plurality of cell units, each cell unit consisting of a first electrode having a generally tubular configuration with open ends, and a second electrode of rod-like configuration located substantially coaxially within said first electrode to define a substantially annular space therebetween.

Preferably, the first electrode is the cathode of the cell unit while the second electrode is the anode.

Advantageously, the ratio of the operative internal surface area of the first electrode to the operative external surface of the second electrode is within the range 1.8:1 to 2.2:1, and preferably 2:1.

Suitably, the tubular first electrodes of the cell unit are parallel, and integrally formed or connected together to form a honeycomb-like structure. The rod-like second electrodes are also parallel and spaced apart on a base member, so as to be each located coaxially within a respective tubular first electrode.

The cross-sectional shape of the tubular first electrodes may be of any suitable configuration, such as circular, triangular, rectangular or polygonal. Preferably the tubular first electrodes are square in cross-sectional shape, and the second electrodes are of complimentary cross- sectional shape.

The rod-like second electrodes may be of solid form, or hollow rods open at opposite ends.

According to a further aspect of the invention, there is provided apparatus for the production of electrolytic gas, comprising: a housing having an internal chamber and an electrolytic cell as described above disposed within said chamber, said housing further having a gas chamber therein communicating with said internal chamber for accumulating gas generated by the electrolytic cell, a gas outlet port in said housing communicating with said gas chamber, a fluid inlet port in said housing communicating with said internal chamber, and power supply means for applying electrical energy to the electrodes of said electrolytic cell.

Preferably, the housing consists of a plurality of interconnected modular segments, each segment having an internal chamber and an electrolytic cell disposed therein. The internal chambers of the modular segments are in fluid communication to allow electrolyte to circulate therebetween. The upper part of each chamber is also in fluid communication with the gas chamber so that gas produced by each cell accumulates in the gas chamber from where it can be drawn off via the gas outlet port.

Advantageously, the power supply means includes a current control circuit which applies pulsed DC current to the electrodes of the cell(s). The current control circuit typically comprising a pulse with modulated high current regulator which applies 25 kHz DC current pulses to the electrodes.

Suitably, the apparatus also includes pressure sensing means responsive to the pressure within said gas chamber for selectively controlling the operation of the power supply means. For example, if the pressure exceeds the preset high limit, the power supply means is shut down to thereby stop further gas production.

The apparatus also suitably comprises an infrared light transducer which is responsive to the level of electrolyte in the housing. If the electrolyte level drops, below a preset level, further liquid is introduced into the electrolytic cell(s) via the fluid inlet port. The liquid (water) is derived from a water reservoir. A mercury-glass float switch is preferably in the reservoir to detect when the water level drops below a preset minimum level. In that event, a solenoid valve is open to allow the reservoir to receive more water, e.g. from a mains supply or main tank.

Preferably, the apparatus includes energy conservation features such as means for storing the back EMF generated in the electrolytic cells during the pulse current OFF time, and utilizing that stored back EMF during the pulse current ON time.

Preferably, the power supply means also comprises means for gradually increasing the initial current supplied to the electrolytic cell(s) thereby providing a "soft start" characteristic.

To assist in identifying the presence of the gas and its flame, an additive is typically added to the gas. Such additive may comprise menthol or camphor.

In order that the invention may be more clearly understood and put into practice, a preferred embodiment will now be described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a plan view of an electrode assembly according to the preferred embodiment; Fig. 2 shows a side elevation of the assembly of

Fig. 1;

Fig. 3 shows a cross-sectional elevational view of an electrolytic cell assembly using two electrode assemblies of Fig. 1; Fig. 4 shows a side elevational view of the electrolytic cell assembly of Fig. 3;

Fig. 5 is a schematic block diagram of the apparatus for production of electrolytic gas;

Fig. 6 is an electrical circuit diagram for the apparatus of Fig. 5;

Fig. 7 is a schematic diagram of the configuration of the light transducer of the electrolyte level sensor of Fig. 5; Fig. 8 is a sectional view of the water level monitor of Fig. 5; and

Fig. 9 is a circuit diagram of the gas production switch and system pressure interlocks. DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in plan view in Fig. 1 the cathode 1 of the electrode assembly comprises a plurality of spaced parallel walls 2 forming a honeycomb-like structure with apertures 3 of rectangular cross section. The tubular apertures 3 are open at the top and bottom. The cathode structure 1 may be extended from metal or otherwise fabricated from interlocking plates welded together. Conveniently the honeycomb or grid¬ like structure is fabricated from square section stainless steel tube cut to appropriate lengths and welded along abutting upper and lower exposed ends of the tubing lengths to form a mechanically and electrically integral structure.

Metal rod-like conductor members 4 are welded to adjacent faces 5, 5a of the cathode structure 1 for connection to a source of electrical energy for the cathode 1.

An anode assembly 6 is also shown in Figs. 1 and 2 and comprises an anode plate 7 having extending from one face thereof a plurality f rod-like electrode members 8 spaced over the upper surface of the anode plate such that when the anode and cathode assemblies are assembled, the anode electrode members 8 are positioned longitudinally within respective cathode apertures 3. Attached to the underside of anode plate 7 are electrical conductor members 9 for connection to a power supply for the anode assembly 6. As shown more clearly in Fig. 2, the electrode conductor members 4, 9 have apertures 10' 11 bored into their respective free ends. The apertures 10, '11 are internally threaded and aligned radially with respect to the electrode assembly, the purpose of which will be described hereinafter. The lower edge of the cathode assembly 1 is spaced above the anode plate 7.

Fig. 3 illustrates a cross-sectional view of an electrolytic cell assembly 12 embodying two electrode assemblies 13, 14 of the type illustrated in Figs. 1 and 2.

The cell assembly 12 comprises a generally cylindrical hollow housing 15 comprising a base 20, a lower electrode housing 16, an intermediate electrode housing 17 and an upper compartment 18. The upper compartment 18, and electrode housings 16, 17 each generally comprise a cap portion and a cylindrical skirt portion depending downwardly therefrom, the bottom edge of the skirt portions being received in a groove formed on the top face of the cap immediately below. The bottom edge of the skirt portion of bottom electrode housing 16 is received in a groove formed in the top of base 20.

It will be apparent therefore, that the housing 15 is of modular construction and can be assembled with as many electrode housings as may be required. The modular housing sections are preferably formed of an electrically insulating material such as a plastics material; for example thermoplastics material such as nylon, polypropylene, rigid PVC, polybutylene, with or without partiσulate or fibrous reinforcing material. Other suitable plastics materials may include thermosetting plastics such as polyester resins, epoxy resins and the like or combinations of any of the above. Conveniently the modular housing components are fabricated from rigid PVC. The electrode assemblies 13, 14 are mounted respectively on base 20 and the cap of electrode housing 16, with the downwardly depending electrical conductors 4, 9 being embedded in base 20 and the housing cap 16 in a fluid- tight manner. Electrode housing 17 includes a tubular member 25 having a bore 24 therethrough. A groove or bore 23 in the cap of housing 16 communicates via the tubular passage 24 with the interior of upper compartment 18. In this manner, the upper part of the interior of housing 16 is vented to the interior of compartment 18. The interior of housing 17 is vented to the interior of compartment 18 via a bore 26 in the cap of housing 17.

The interior chamber of compartment 18 is divided into an outer annular chamber 29 and a central chamber 30. The outer annular chamber 29 is packed with polystyrene foam balls to form a protective cushion in the event of an explosion within the compartment 18. The gas chamber 30 includes a stainless steel wool filter at the entry end thereof and communicates with a threaded outlet port 36. Annular chamber 29 communicates with another threaded port 35 through which a electrolyte solution for the cell assembly may be introduced. Each housing 16, 17 also includes interconnecting tubular members 31 with communicating bores 32. The bores 32 extend through the caps of each housing 16, 17, the upper opening of the bore 32 of housing 17 being below the electrolyte level 22. The lower end of bore 32 of housing 16 communicates with a radially bored and internally threaded liquid outlet port 34 in the base 20. Each tubular member 31 has an opening 33 communicating with the lower region of a respective electrode assembly 13, 14. The operation of the electrolytic cell assembly will now be described.

A suitable electrolyte, such as an aqueous solution of 20% potassium hydroxide KOH or 16% sodium hydroxide NaOH, is introduced into the cell via liquid inlet port 35 until a level shown generally at 22 is achieved. When electrolyte is introduced into the annular space 29, it flows down through tubular members 31 and fills the hollow interior of housings 16 and 17 by expelling air therefrom via bore 23 and tubular passageway 24 and bore 26, respectively, into the interior of compartment 18, through gas chamber 30 and finally out through gas outlet port 36. The liquid outlet port 34 is closed during filling and operation of the cell 12. Port 34 may be used for drainage of electrolyte from the cell or if a number of cells are to be employed simultaneously, respective ports 34 may be connected in parallel.

When the electrolyte has filled the housings 16, 17 and reached the desired level 22 in upper compartment 18, port 35 is closed and port 36 is connected to a conduit for conveyance of gas produced in the cell .

A source of low voltage high current DC power is then connected to the electrodes in housings 16 , 17 whereupon electrolytic decomposition of the electrolyte occurs at the surfaces of the anode and cathode. Electrolytic gas produced at the electrodes rises to the upper chamber of housings 16 and 17 from where it is vented to the interior of compartment 18 via bores 23 and 24, and 26 , respectively. The stainless steel filter 21 acts as a liquid entrainment separator to remove entrained moisture particles and water vapour from the gas before it fills chamber 30 from which it may be drawn off via port 36.

Electrolytic cells of the abovede scribed type may be operated at a variety of electroltye temperatures although temperatures in the range of 60 to 100 degrees Celsius are preferred to maximi se cell ef fi ciency . At elevated electrolyte temperatures a condenser may be employed in addition to the moisture entrainment device 21 to remove excess undecomposed water vapour from the gas produced. The condensor may be located within chamber 30 or it may be associated with the conduit connected to outlet port 36.

Electrolyte s which may be util ized with the invention are preferably inexpens ive , thermally and chemically stable and non-agressive towards the materials from which the cell housing and electrodes are manuf ctured. Pref erred electrolyte s are alkaline earth oxides and hydroxides including potassium hydroxide and sodium hydroxide in a concentration range of from 2-30% w/w, preferably 11- 18% . With such electrolytes the risk of producing dangerous gas eous by-products such as chlorine or the like are alleviated.

The anode material i s pre f erably chemi c ally re s i s.tant t o the op er ating environment within the electrolytic cell . Metals such as nickel plated copper or stainless steel (preferably 304 grade ) are particularly suitable for electrode materials .

The configuration of the cell is important in achieving maximum cell efficiency (and thus cost effective gas production) . First, in order to obtain the right stoichiometric ratio of hydrogen and oxygen gases produced at cathode and anode respectively, the ratio of surface area of cathode to anode is preferably 2:1. Secondly, and more importantly, the spatial separation of the anode and cathode surfaces should be set correctly. Hitherto, the failure to achieve the high operating efficiency of cells according to this invention is believed to have been a result of poor cell design. Parallel plate or grid-like electrodes when spaced too closely result in rapid consumption of anode material due to plate out on the cathode. When spaced further apart anode consumption is reduced but internal cell resistance is increased with consequent thermal runaway in the cell at high current densities. The electrolytic cells made in accordance with the present invention achieve their high efficiency due to the coaxial relationship between the anode and cathode. With such coaxial relationship, laminar flow is established between the anode and cathode surfaces with a laminar layer of gas bubbles adjacent the electrode surfaces and separated by a thin layer of electrolyte. This three layer laminar flow is believed to prevent migration of metal ions from the anode to the cathode. The laminar flow provides a smooth convection current in the electrolyte in the cell without turbulence in the region between the anode and cathode surfaces. Cells according to the invention have been operated for extended periods with no visible deterioration to the electrodes.

The gas produced by the apparatus according to the invention comprises predominantly hydrogen and oxygen present in a ratio of approximately 2:1 with possibly some ozone 0_ and a small amount of H*, OH^~ and H_0"*" ions and possibly some H* and OH* free radicals. This hypothesis is based on the fact that flame temperatures of up to 3000 degrees Celsius have been reached upon combustion of the electrolytic gas.

Fig. 4 shows the external electrical connections between the anode and cathode assemblies in housings 16 and 17 of the cell 12. Surrounding the outer cylindrical surface of housing 16 are heavy copper bus-bars 40, 41 and 42, each spaced from the other and, if required, covered in a protective electrically insulating material (not shown) .

Bus-bar 41 is electrically connected by connecting members 43 to the four anode terminals 9 of each anode assembly located in housings 16 and 17. Electrical connection is achieved by copper or copper alloy bolts 44 extending through radial apertures in base 20 and the cap of housing 16 to locate in the radially oriented threaded bored apertures 11 in anode conductor members 9 shown in Fig. 2.

Similarly, bus-bars 40, 42 are electrically connected by connecting members 45 to the four cathode terminals or conductor members 4 of each cathode assembly. Bolts 46 extending through the base 20 and the cap of housing 16 locate in the radially oriented threaded apertures 10 in cathode conductor members 4. The electrolytic cells 13, 14 are connected in series, but could of course be connected in parallel.

A schematic block diagram of apparatus for producing electrolytic gas is illustrated in Fig. 5, the apparatus utilizing four cells of the type shown in Figs. 3 and 4. The apparatus can be powered either by A.C. mains supply or directly by a DC supply.

A pulse width modulator is used to supply a pulsed, rather than a constant, DC voltage to the electrodes in the electrolytic cells 12. It has been found that a pulsed DC supply has several advantages over a continuous DC voltage supply, including the ability to harness back e.m.f. generated in the electrolytic cells. The operation of the electrical circuit will be described in more detail later.

Production of electrolytic gas is controlled by a variety of interconnected means with overriding safety control mechanisms. The apparatus is designed to provide combustible gas only as required rather than continuously, thereby obviating the need for dangerous and generally inconvenient pressurized storage vessels.

For example, the gas chamber 30 or a conduit connected to outlet port 36 is provided with a pressure sensing means comprising a three-level pressure switch 67, 68, 69 operative to selectively control the DC power supply connected to the electrolytic assemblies. With the mains power supply switched on, a reduction in gas pressure in compartment 30 below a predetermined limit (caused by consumption of gas for example) causes the pressure sensor to connect the DC power supply to the electrolytic cells. When the gas pressure within the compartment 30 reaches a predetermined (higher) pressure value (such as when gas consumption ceases) , the pressure sensor then operates to disconnect the DC power supply from the cells and gas production ceases.

A number of other safety and sensing devices are suitably employed with the apparatus. For example, as gas production through decomposition of water causes the electrolyte level to drop, an electrolyte level sensor 51 (and/or a pH meter) can be employed to automatically replenish via inlet port 35 water consumed during gas production. Other safety devices include a pressure relief valve

52 and a flame arrestor 53 in the event of "flash-back". As the flame velocity of electrolytic gas is relatively high, very sensitive and quick acting flash-back arrestors are preferred. A circuit diagram for the electrical circuit of Fig.

5 is shown in Fig. 6. The electrical circuit includes the following sub-circuits:

1. an electrical power distribution circuit

2. an on-board voltage regulator 3. an adjustable pulse width modulated high current regulator

4. an electrolyte level monitor having a solid state infrared light trnasducer

5. a water level sensor having a mercury-glass float switch.

As shown in Fig. 6, AC mains power supply applied to input 60 is connected to the power transformer TI via a series connection of fuse 61 (FS1), Relay 63 (RL1), key switch 62 (KSW) and high pressure switch 69 (HPS1). The high pressure switch HPS1 is normally closed, (and is opened upon detection of electrolytic gas pressure above a predetermined level to thereby disable power supply to the circuit) . The key operated closure of switch KSW closes the contacts of the relay RL1. Preferably, capacitors C24 are provided to protect the contacts of relay RL1 against arcing during the switching of key switch KSW. When power is supplied to the circuit, the capacitors C24 also provide power factor correction across the primary winding of the transformer TI. The secondary winding of transformer TI is centre- tapped and connected to rectifier diodes D6, D7 to provide full-wave rectification. An isolation diode D8 is also provided to isolate the DC supply input from the rectifier circuit.

Advantageously, the diodes D6, D7, D8, and other heat generating electronic components are mounted directly onto the heat exchanger of the gas generator so as- to be cooled by the generated gas. The heat absorbed from these components by the gas assists the gas to absorb an identifying substance (e.g. camphor) as described hereinafter. A cooling fan Fl is also provided to cool the electronic components.

The integrated circuit IC3 provides an on-board voltage regulator circuit for the control logic of the gas generator. The voltage regulator IC3 is typically a TO220 package and is mounted on the "E" copper bus bar with mica thermal insulation. Supply to voltage regulator IC3 is isolated from the main DC supply by diode D4 and capacitor C15 to limit interference from the main load. The output of the voltage regulator circuit is filtered by capacitors C19 and C17 and is used to provide a stable voltage supply to all monitor, logic and control circuits.

In the illustrated embodiment, a pulse width modulated high current regulator is used to provide pulses of DC current at a frequency of 25 KHz to the electrolytic cells. Experimental results have shown greater occurrence of electronic interactions between the ions and the electrodes when high frequency pulsed direct current is used to supply the electrolytic cells, rather than constant DC.

Furthermore, the pulse width modulated (P.W.M.) switched mode current regulator used in the preferred embodiment has been found to be more efficient than conventional direct current regulators. It also occupies less volume and weighs less than linear regulators.

This adjustable P.W.M. regulator is designed to operate from a 24 volt uncontrolled DC source to supply efficiently eight series connected electrolytic cells with 0 to 70 Amp current, at up to- 1.2 kW continuous power level. The output is matched to clamp the back E.M.F. generated by the electrolytic cells during off cycle and pump it into reservoirs (capacitors) for use during the on cycle, thus making the system very efficient.

The P.W.M. current regulator comprises a regulating pulse width modulator integrated circuit IC2. This integrated circuit includes a 5 volt regulator, a control amplifier, an oscillator, a pulse width modulator, a phase splitting flip-flop, dual alternating output switch, current limiting and shutdown circuitry.

The voltage regulator in IC2 provides a supply for all internal circuits and is used as a reference in this system, a reference for the current feed-back at R30, R31, Cll and CT1 junction, and also at R32, pin 1 on IC2, CIO, R33 and R34 junction. This regulator is the supply for the thermal feed-back at R19, the soft start circuit at C8 and R21, the shutdown circuit at R23 and is also the reference for the current control adjustment VR2 from R24. The voltage regulator output of IC2 is at pin 16 and is filtered by C7 capacitor.

The IC2 integrated circuit provides a stable in¬ built oscillator whose frequency is set to 50 KHz by an external resistor R23 at pin 6 and capacitor C13 at pin 7. This oscillator generates signals for triggering an internal flip-flop which clocks the P.W.M. information to the output by dividing the oscillator frequency by 2 to 25 KHz, and a blanking pulse to turn off both outputs during transitions to ensure that cross conduction does not occur. The oscillator output can be monitored at pin 3.

The control amplifier in IC2 is a differential input (pins 1 and 2) error amplifier. As the current limit amplifier is not used in this system, its input pins 4 and 5 are grounded. The inputs of the error amplifier at pins 1 and 2 are connected by CIO to filter out high frequency noise. The non-inverting input pin 2 is adjusted by the output of current control potentiometer VR2 which is part of the R24, R25 voltage divider network, to set a reference voltage representing the output over current limit. Pin 2 is also shunted by capacitor C9 to the OV rail of this circuit. The inverting input pin 1 is referenced by R32 and R33 and is supplied by current feedback from current transformer CTl via R34 and D16, while C14 acts as a filter condenser and R35 is a shunt for the secondary of CTl which monitors the high current output. The gain of this control amplifier, which is set by its output loading at pin 9 by R27 and R28, and also the total value of R27 and R28, sets the maximum duty cycle of the output switches. The minimum duty cycle is set by R26 bias resistor for D13 and D14 diodes and by D12 hold up diode. C12 provides compensation at pin 9 to avoid self oscillation. The output (pin 9) of this error amplifier also controlled by transistor TR3. The base of TR3 is supplied with current via diode D9 from (negative temperature coefficient) resistor NTC1 which is used to monitor the output heat exchanger temperature and is part of the R19 and R20 voltage divider network. C5 and C6 are by-pass capacitors. When the heat exchanger temperature is above the normal limit, the TR3 transistor limits the duty cycle of IC2 at pin 9 accordingly, thus reducing the output power (current) of the high current regulator to avoid damage.

The base of transistor TR3 is also supplied by current from the RC network R21 and C8 at every turn on. When C8 is in discharge condition, TR3 turns on and pulls the output duty cycle of IC2 to zero at pin 9. As C8 is charged by R21 the base current to TR3 gradually reduces and the collector emitter reactance of transistor TR3 alters the condition of the error amplifier output at pin 9. Thus, the output duty-cycle of IC2 and the high current switches gradually increase the pre-set value (by RV2) , thereby providing a soft start (current ramp up) at 'power on' or 'gas on' functions. The diodes D10 and Dll form a first discharge clamp for capacitor C8; D10 functions when the whole supply is off while Dll functions at shutdown to discharge C8 via R23.

The output switches of IC2 are NPN transistors. These transistors are driven 180 degrees out of phase from each other and have their collectors connected in common at pin 12 and 13 and also to pin 15 which is the V+ supply input to IC2. The emitter outputs are also connected in common at pins 11 and 14 of IC2, and current drained by R36 before being coupled by D15 to the common bases of transistors TR4 and TR5. Diode D15 is current drained by R37. The transistors TR4 (NPN) and TR5 (PNP) provide a low output impedance buffer for IC2. Their emitters are connected together and current drained by R38 resistor. The output of IC2 via the TR4 and TR5 complementary pair buffer drive stage is ac/dc coupled: by C18 and R39 to the gate of the MOS power transistor TR6, by C19 and R40 to the TR7 gate, and by C20 and R41 to the TR8 gate. All of these components are doubled up in the circuit, e.g. there are two of capacitors C18, C19, C20; resistors R39, R40, R41; and MOS power transistors TR6, TR7, TR8, the second set not being shown on the circuit diagram. The outputs of IC2 and TR4, TR5 are in digital (pulse) mode, either 'ON' V+ level or 'OFF* at OV level. The on pulse width (duty cycle) is controlled by the current feedback from CTl and depends upon the VR2 output current setting set by the operator and upon the condition of TR3, at pin 9. The repetition rate is set by the oscillator circuit (25KHz) and is fixed.

The high current output switching stage is preferably constructed of power MOSFETS with their drains connected in common and their sources also connected in common to form one very high current switching transistor with low power loss. The commoned sources of TR6, TR7, TR8 are connected to the negative side (D) of the DC supply, while the commoned drains of TR6, TR7, TR8 are connected to the end cathode (G) of the series connected electrolytic cells. The collective drains are also connected to an over- voltage protection zener diode (ZD2), to back EMF clamp diodes D5, D18, and to a toroid transformer back EMF clamp coil T2.

The end anode (H) of the series connected electrolytic cells is connected to the DC power supply positive side (E) via the primary coil of the toroid transformer T2 to limit the initial current when the power MOSFETs TR6, TR7, TR8 turn 'ON'. Current trasnformer CTl provides negative feedback for IC2 at its secondary coil via diode D16 for the set current regulation during the pulse 'ON' time. During the pulse 'OFF' time diode D17, which is connected in series with the secondary winding of the T2 transformer, goes into conduction and dumps the energy of transformer T2 generated by its own back EMF into the electrolytic cells. Furthermore, during the output current pulse 'OFF' time, the back EMF generated by the electrolytic cells is clamped by diodes D5 and D18 and stored in reservoir capacitors C21, C23, C25. This stored energy is utilized

.during the next current pulse 'ON' time. The zener diode ZD2 connected across the power MOSFETs acts as a very fast over- voltage protector before the diodes D5, D18 and D17 go into conduction during the current pulse ±OFF' time.

The output current pulse shutdown (turn off) input at IC2 (pin 10) is pulled up by R23 to +5 volt and is shunted by capacitor C26 at the J and I terminals. This is a current loop input which must be shorted to function (output ON) . However the output only turns ON in the soft start mode (current ramp up) because the R23 pull up resistor discharges the capacitor C8 via diode Dll when the shutdown inputs (J and I) are open circuit. .When the shutdown inputs (J and I) .are shorted to enable an output current pulse to be generated, the IC2 pin 9 is held down by transistor TR3 which is controlled by the charging up time of C8 via R21. The output duty cycle at IC2 pin 11 and pin 14 only builds up gradually to avoid high peak currents at the mains supply.

The electrical circuit also includes a solid state infrared light transducer for sensing electrolyte level, and an associated monitoring circuit. The infrared light transducer comprises an infrared light emitting diode (ILED1) and a photo transistor (PHTl). The configuration of the light transducer is shown schematically in Fig. 7 and operates on the principle of light reflection and refraction. That is, the photo transistor PHI receives reflected light from the inside of the dome lens of ILED1 when the transducer is located in the air. If the transducer is placed in liquid however, refraction occurs at the dome of ILEDl and• the reflected light to PHTl is significantly reduced. This variation in reflected light is detected by the photo transistor PHTl. The transducer (sensor) is located at the desired minimum electrolyte level, typically at the bottom of the interior chamber of upper compartment 18.

Referring now to Fig. 6, the infrared light transducer circuit produces its own ambient light level at ILEDl by receiving DC current via Rl and R3. ^' Part of this ambient light is received by photo transistor PHTl, whose collector receives current via R4. The junction of C2, R4 and the collector of PHTl is connected to the base of TR1, which is in emitter follower mode (voltage follower), supplying additional DC current to ILEDl via resistors R2 and R3, thus creating a negative feedback to keep the transducer at ambient light and temperature.

The actual signal current to ILEDl is produced by a pulse generator TR2 and is also sent via resistor R3. TR2 is a programmable unijunction transistor (PUT) having its anode connected to a timing network (R7 and Cl) and its gate G biased by the voltage divider R5 and R6. When the anode voltage of TR2 passes the gate voltage level as capacitor C is charged via R7, TR2 will trigger and discharge Cl via its cathode (C), R3 and ILEDl, thus producing a pulse of additional infrared light at the ILEDl. (This sequence is automatically repeated to create a series of IR pulses) . The pulsed light will be received by photo transistor PHTl only when the ILEDl is functioning in the reflective mode (i.e. out of the liquid) , and produces negative going pulses at the collector of PHTl accordingly. The negative going pulses from the collector of PHTl (Z) are AC coupled by C2 to the trigger input pin 2 of integrated circuit IC1 which is biased by the voltage divider formed by R8 and R9. IC1 is a. monostable multivibrator integrated circuit, with an adjustable offset circuit (VR1, R12) and a by-pass capacitor (C4) at its control voltage input (pin 5), to adjust the trigger level to not trigger in the reflective mode (when ILEDl is in liquid) .

A monostable timing (RC) network is formed by RIO and C22. Rll is a discharge limiting resistor from the discharge output (pin 7) to the threshold input (pin 6) of IC1. The reset input (pin 4) is disabled by connecting it to pin 8 to which is the V+ supply input, the OV supply being connected to pin 1. The timing pulse duration is designed to be much longer than the pulse generator TR2 repetition rate so that when the pin 2 of IC1 is triggered from C2, the output pin 3 changes to a high state (V+) for the time set by the RIO and C22 network (approx one sec). During this time the trigger input pin 2 may or may not receive many trigger pulses from PHTl, depending on the level variations of the liquid monitored by it. The one second time delay eliminates false detection which may be caused by the waving liquid (electroltye) .

When IC1 is triggered, the output (pin 3) turns ON both power MOSFETs TR9 and TRIO via R13, R14 and R15. (Capacitor C3 is provided to delay the off time) . TR9 turns on the water pump PI. Diode D3 clamps the back EMF during the off time of the pump PI. TRIO turns on the water solenoid valve SV2, which is clamped for back EMF by diode D2. Solenoid valve SV2 functions as a gate valve when many converter units are interconnected (masters and slaves) and also functions as an isolation valve between the cells and the water tank to prevent the electrolytic gas from the cells leaking into the water filter (in the tank) and thereby escaping through it. The infrared light transducer is both robust and accurate, being able to differentiate between liquid levels to within 3 mm under harsh environmental conditions.

The circuit also includes a mercury-glass float switch and associated monitoring circuit for detecting low water level in the water supply tank for the electrolytic cells. As shown in Fig. 8, the mercury float switch comprises a glass envelope mercury switch 81, typically 2.5 cm long and 1 cm diameter. The glass envelope 81 is encapsulated in flotation material, typically a polystyrene foam package 80. The package 80 containing the mercury switch 81 floats in a horizontal orientation on the surface of the water within the water tank. The mercury switch 81 is connected by flexible wires to terminals P, Q of its associated monitoring circuit on the printed circuit board.

When the water level in the tank is below a predetermined height, the glass envelope of the mercury switch 81 will be vertical or inclined so that the mercury makes contact between the terminals within the glass envelope. This in turn makes contact between the P and Q terminals of the monitoring ciruit, thereby supplying V+ voltage to the gate of power MOSFET TRl via voltage divider network R17 and R18, and R16. A zener diode ZD1 protects the gate of TR11 from unwanted transient high voltages which may occur in the wire cable loom. The TR11 turns on and supplies current to solenoid valve SV1 which opens the water supply to the water tank.

As the water level in the tank increases, the angle of the mercury switch glass envelope increases towards the horizontal. When the water level reaches a predetermined height, the angle of the glass envelope will be so shallow as to cause the mercury within the envelope to break contact between the terminals therein. This in turn creates an open circuit between terminals P, Q of the monitoring circuit, thereby turning TR11 and SV1 off. The diode Dl is provided to clamp the generated back EMF by the solenoid valve coil SV1.

Like the infrared transducer, the mercury float switch is of the non-contact type, and is very sensitive, being able to differentiate between water levels to within 4 nuns.

Electrolytic gas production can be controlled both locally (by a local gas output solenoid valve 56) and remotely (by gas output solenoid valve 57) . The control circuits for the gas output solenoid valves are shown in Fig. 9. Typically, the local switch (GSW1) is on the front panel of the apparatus, while the remote switch (GSW2) is located on the hand piece of the welder, or the burner.

The switch control circuit also incorporates pressure interlocks for safety. In the illustrated embodiment, three pressure interlocks are used, namely a low pressure switch (LPSW) 67, a medium pressure switch (MPSW) 68 and a high pressure switch (HPSW) 69. Key switch KSW1 is also connected into the gas production circuit to shut down gas production. The actual gas flow is opened or closed internally by solenoid valve SV3, and externally by solenoid valve SV4, to avoid flashback from the burner, or the hand piece.

The gas production control circuit is supplied from the main DC supply terminals D, E. Resistor R42 is inserted on the positive side to reduce the electrical power to the solenoid coils, the negative side being supplied via LPSW which interlocks the system by closing its contact only if the gas back up pressure is above the minimum required level to be burned. With LPSW closed, current is supplied via the silicon controlled rectifier (SCR1) latch circuit whose gate is triggered by the gas output switch (GSWl) in the ±OFF¹ position. The gate of SCR1 is shunted to its cathode by R44 (to provide noise immunity) and the anode is supplied with hold-on current via resistor R43. When the gas output switches GSWl and GSW2 are in the 'ON' position (closed contacts) and if the plug PL1 is plugged into SKI socket, the solenoid valves SV3 and SV4 will open the gas flow.

With the key switch (KSW1) contacts closed, the MPSW, HPSW contacts (normally) closed, the GSWl and GSW2 switches on (contacts are closed) and PL1 plugged into SKI, the IC2 current control circuit is activated to control the cells' supply current and thereby the conversion of water to electrolytic gas. The gas output flow is indicated by a green light emitter diode LED2 which is supplied by current via R45 resistor.

If the initial gas conversion is too low and the back up gas pressure drops below normal (or if the burner orifice is too large for the system, or if the system develops a gas leak), LPSW turns 'OFF' thereby interrupting the supply current to the solenoid valves SV3, SV4 which close off the gas line. (The solenoid coil SV3 is clamped by diode D19 while SV4 is clamped by diode D20 for back EMF generation during the OFF time.) The cessation of current flow through LPSW resets the SCR1 latch circuit and there will be no current flow to the solenoid valves SV3 and SV4 when the pressure builds up against the LPSW turns ON. The system output will not deliver gas, but at the same time the supply current control circuits are functioning and the cells are producing gas. When the internal gas pressure reaches the preset medium pressure level, the medium pressure switch MPSW will open its contacts and the PWM current regulator turns OFF the power supply tp the electrolytic cells to thereby cause gas production. In the event of failure of the latter, the internal pressure would build up to the preset high limit and the HPSW would open its contacts to shutdown the current regulator and the mains supply, thereby preventing the whole system from producing or discharging electrolytic gas.

To reset the SCR1 latch circuit, the GSWl gas ON/OFF switch on the front panel of the converter must be turned OFF and ON once (to activate the gas output) . It cannot be done from the burner or the hand piece gas ON/OFF switch GSW2, thereby ensuring that the operator goes back to the converter unit and inspects the system. Under normal operating conditions the gas output flow is controlled by the setting of the gas flow control knob by the operator and the gas back pressure is regulated internally by MPSW, without interrupting any of the operational functions.

If the PL1 is unplugged from SKI socket, or if the gas line is accidentally severed, or if the remote cable is cut or shorted, or if the internal gas pressure builds up above the HPSW level, the system will cease functioning.

Advantageously, the state of the more important functions and operations of the system are displayed by light emitting diodes at the front panel for visual inspection. For example, the light emitting diodes can be wired to indicate the provision of mains or DC power, the provision of current regulated pulsed DC power to the electrolytic cells, sufficient electrolyte solution in the cells, the operation of the water pump and sufficient water in the water tank. The flow of output gas can also be indicated by an appropriately coloured LED.

Preferably, the EMF of the cells is also monitored, and the current flow into and from the electrolytic cells is indicated by different coloured LEDs.

As the electrolytic gas is odourless and has an almost colourless flame, it is advantageous to add an additive to the electrolytic gas. The additive should be non-pollutant and should not adversely affect the properties of the electrolytic gas. Suitable additives include, camphor or menthol. Such additives can be added to the gas by passing the gas through the additive in powdered or crystalline form.

It is also advantageous to add carbon to the electrolytic gas to provide flux which is necessary to welding applications because the high power densities of the flame in the higher frequency region will cause photoionization of the material.

Electrolytic gas produced by the apparatus according to the invention is particularly suitable for heating applications or as a source of fuel due to the non-toxic and non-polluting nature of the combustion product - water.

Suitable applications may include domestic heating and cooking, industrial welding and flame cutting, fuel for internal combustion engines and even heat treatment of steel due to its non-oxidizing nature. In other applications the gas may be used in plasma heating and cutting operations as well as other aplications utilizing a gaseous plasma.

The foregoing describes only one embodiment of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention as defined in the following claims.

Claims

1. An electrolytic cell comprising a plurality of cell units, each cell unit consisting of a first electrode having a generally tubular configuration with open ends, and a second electrode of rod-like configuration located substantially coaxially within said first electrode to define a substantially annular space therebetween.

2. An electrolytic cell as claimed in Claim 1, wherein the ratio of the operative internal surface area of said first electrode to the operative external surface area of said second electrode is within the range of 1.8:1 to 2.2:1.

3. Apparatus for the production of electrolytic gas, comprising: a housing having an internal chamber and an electrolytic cell as described above disposed within said chamber, said housing further having a gas chamber therein communicating with said internal chamber for accumulating gas generated by the electrolytic cell, a gas outlet port in said housing communicating with said gas chamber, a fluid inlet port in said housing communicating with said internal chamber, and power supply means for applying electrical energy to the electrodes of said electrolytic cell.

4. Apparatus as claimed in Claim 3, wherein said housing comprises a plurality of modular segments, each segment having a said internal chamber and a said electrolytic cell disposed therein.

5. Apparatus as claimed in Claim 4, wherein said power supply means comprises a current control circuit for applying pulsed DC current to said electrodes.

6. Apparatus as claimed in Claim 5, wherein said current control circuit comprises a pulse width modulated high current regulator.

7. Apparatus as claimed in Claim 5, wherein said power supply means includes means for storing back EMF generated in said electrolytic cell(s) during the pulsed current OFF time and utilizing said back EMF during the pulsed current ON time.

8. Apparatus as claimed in Claim 5, wherein said power supply means includes means for gradually increasing initial current supply to said electrolytic cell(s).

9. Apparatus as claimed in Claim 3, further comprising pressure sensing means responsive to the pressure within said gas chamber for selectively controlling the operation of said power supply means.

10. Apparatus as claimed in Claim 3, further comprising infrared light transducer means responsive to the level of electrolyte in said housing.

11. Apparatus as claimed in Claim 3, further comprising a water reservoir in fluid communication with said fluid inlet valve, and a mercury-glass float switch responsive to the water level in said reservoir.

12. Apparatus as claimed in Claim 3, further comprising means for adding an additive to said electrolytic gas produced by the electrolytic cells.

13. Apparatus as claimed in Claim 12, wherein said additive is menthol or camphor.