Abstract:
A hydrogen replenishment system for providing hydrogen to a hydrogen-receiving apparatus, the system comprising 
     (i) an electrolytic cell for providing source hydrogen; 
     (ii) a compressor means for providing outlet hydrogen at an outlet pressure; 
     (iii) means for feeding the source hydrogen to the compressor means; 
     (iv) means for feeding the outlet hydrogen to the hydrogen-receiving apparatus; 
     (v) central processing unit means for controlling the cell and the compressor; and 
     (vi) user activation means for operably activating the central processing unit means. 
     The invention provides a practical user interface in the treatment of data provided, computed, measured and stored, to offer a convenient, essentially self-contained, hydrogen fuel replenishment system for vehicles based on water electrolysis. The apparatus has virtually no stored hydrogen and provides pressurized hydrogen on the demand of a user. The system is preferably operative at times of off-peak electrical supply, with electricity and water being substantially the only feedstock.

Description:
FIELD OF THE INVENTION 
     This invention relates to the electrolytic production of hydrogen for use, particularly as a fuel for vehicles; and particularly to a system comprising an electrolytic cell for said production and a data network comprising data gathering, control and, optionally, storage. 
     BACKGROUND TO THE INVENTION 
     Electrosynthesis is a method for production of chemical reaction(s) that is electrically driven by passage of an electric current, typically a direct current (DC), through an electrolyte between an anode electrode and a cathode electrode. An electrochemical cell is used for electrochemical reactions and comprises anode and cathode electrodes immersed in an electrolyte with the current passed between the electrodes from an external power source. The rate of production is proportional to the current flow in the absence of parasitic reactions. For example, in a liquid alkaline water electrolysis cell, the DC current is passed between the two electrodes in an aqueous electrolyte to split water, the reactant, into component product gases, namely, hydrogen and oxygen where the product gases evolve at the surfaces of the respective electrodes. 
     Water electrolysers have typically relied on pressure control systems to control the pressure between the two halves of an electrolysis cell to insure that the two gases, namely, oxygen and hydrogen produced in the electrolytic reaction are kept separate and do not mix. 
     One such pressure control system provides a water seal to equalize pressure in the two halves of the cell. This is the approach most often followed in “home made” electrolysers. Typically the water seal is a couple of inches deep and so the cell operates at a couple of inches of WC pressure above atmospheric. 
     An alternative system provides a membrane separator which can sustain a pressure difference between the two halves of the cell without gas mixing. The PEM (polymer electrolyte membrane) cell is the best example of this type of system. The PEM cell can sustain up to a 2500 psi pressure difference without a significant loss of gas purity. 
     A third is an active control system which senses pressure and controls the outflow of gases from the two cells. Control can be achieved in one of two ways: 
     by a mechanical system which relies on pressure regulators, such as a dome-loaded flow regulator to control pressure between the two cells which, for example, might employ the oxygen pressure as a reference pressure to regulate the pressure in the hydrogen half of the cell; and 
     by an electronic system which relies on measurement of the difference in gas pressure between the two cell to control the rates of gas outflow from the two sides of the cell so as to maintain a desired pressure difference of usually zero or with the hydrogen side slightly higher. 
     Typically, however, for very small commercial hydrogen generators (0.1 Nm 3 /h) PEM type electrolysis cells are favoured. Although the cost of the cell is far higher than for conventional alkaline electrolysers, these costs are more than offset by the controls needed for the conventional alkaline systems using mechanical or electronic actuators, and by the need for higher pressures and, hence, compression in electrolysers using a water seal pressure control system. 
     A hydrogen fuel replenishment system is operative in at least one North American city, wherein a fleet of public vehicles, namely, transit buses are refueled on a timely i.e. generally daily, basis from a storage tank(s) in a bus depot. 
     The hydrogen fuel tank on the bus is attached solely to the storage tank and the quantity of hydrogen to be furnished is calculated from the initial pressure and desired resultant pressure as read from pressure gauges on the bus or on the ground storage tank. 
     At the depot, hydrogen is provided to the storage tank(s) from on-site electrolyser(s) which maintain hydrogen pressure at a pre-determined value in the tank(s). Replenishment time is, generally, about 20-30 minutes. 
     However, the aforesaid hydrogen fuel replenishment system suffers from a significant number of disadvantages, as follows. 
     1. Modulation of the electrolyser cell bank is only by manual operation. 
     2. The cell bank is not easy to modulate, and accordingly, if the demand for hydrogen to be stored and for refueling vehicles in real time is lower than the cell supply rate, it is necessary to vent the hydrogen, generally to atmosphere. 
     3. The cell bank in real time cannot be modulated to optimize electricity usage at times of favourable, reduced electricity costs rates. 
     4. Each vehicle is filled by only manual operation. 
     5. Each vehicle is filled independently of other vehicles in the depot. 
     6. The nature of the filling operation is steady state with respect to the rate of filling from the cell bank. In filling a vehicle tank with hydrogen, the expansion and compression within the tank causes the gas temperature to rise and, hence, to yield a false value of a high pressure (full tank) if the rate of filling is too rapid. Upon subsequent cooling, the tank pressure falls and the tank requires a refill (top up) to achieve a truer desired pressure. 
     7. The use of storage tank(s) expands the necessary green space and foot print required for a filling station. 
     8. The use of storage tank(s) provides a potential safety risk requiring proper management. 
     There is, therefore, a need for a hydrogen fuel replenishment system which does not suffer from the aforesaid disadvantages. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a system for the in situ generation, on demand, of hydrogen gas for use particularly as a fuel for vehicles, requiring negligible on-site hydrogen storage. 
     It is a further object to provide a hydrogen fuel replenishment system which provides a practical user friendly control and activation interface. 
     It is a further object of the present invention to provide efficacious methods and apparatus for producing hydrogen at a minimum desired pressure. 
     Accordingly, in one aspect, the invention provides a hydrogen replenishment system for providing hydrogen to a hydrogen-receiving apparatus, said system comprising 
     (i) an electrolytic cell for providing source hydrogen; 
     (ii) a compressor means for providing outlet hydrogen at an outlet pressure; 
     (iii) means for feeding said source hydrogen to said compressor means; 
     (iv) means for feeding said outlet hydrogen to said hydrogen-receiving apparatus; 
     (v) central processing unit means for controlling said cell and said compressor; and 
     (vi) user activation means for operably activating said central processing unit means. 
     As used herein the term “cell”, “electrochemical cell” or “electrolyser” refers to a structure comprising at least one pair of electrodes including an anode and a cathode with each being suitably supported within an enclosure through which electrolyte is circulated and product is disengaged. The cell includes a separator assembly having appropriate means for sealing and mechanically supporting the separator within the enclosure. Multiple cells may be connected either in series or in parallel to form a cell stack and there is no limit on how may cells may be used to form a stack. In a stack the cells are connected in a similar manner, either in parallel or in series. A cell block is a unit which comprises one or more cell stacks and multiple cell blocks are connected together by an external bus bar. A functional electrolyser comprises one or more cells which are connected together either in parallel, in series, or a combination of both. 
     The electrolytic cell may comprise the compression means within its structure in that in one embodiment, hydrogen pressure is built up within the cell to the resultant desired user pressure and wherein the outlet hydrogen comprises source hydrogen. 
     The system and method according to the invention are of particular value for replenishing hydrogen fuel for a vehicle, such as a personal vehicle, truck, bus and the like. 
     Thus, the invention provides in a preferred aspect the system as hereinabove defined wherein said means (iv) comprises apparatus, preferably, vehicle attachment means attachable to the apparatus (vehicle) to provide the outlet hydrogen as fuel to the apparatus (vehicle). Accordingly, there is provided a system as hereinabove defined wherein means (iv) for feeding the outlet hydrogen to the hydrogen-receiving apparatus comprises conduit means and fitting engagement means adapted to be received in sealing engagement by said apparatus. 
     In an alternative embodiment, a system as hereinabove defined is provided wherein the conduit means and fitting engagement means comprises a plurality of conduits and fitting engagement members adapted to receive a plurality of the hydrogen-receiving apparatus. 
     The source hydrogen is preferably pumped through a conduit to the compressor. 
     The CPU comprises a system as hereinabove defined wherein the central processing unit comprises cell control means for activating the cell to provide the hydrogen source when the outlet pressure falls to a pre-selected value. The CPU preferably comprises the user activation means having data receiving means adapted to receive data from or by transfer means selected from the group consisting of an electronic data card, voice activation means, manually-operable selection and control means, radiated wavelength and electronic or electrical transfer. The CPU preferably comprises means for receiving and treating physical parameter data selected from the group consisting of temperature, pressures anolyte and catholyte liquid levels, bus continuity, KOH concentration, gas purities and process valves positions of the cell; and modulating and controlling the cell in consequence of said treatment of the cell data. It further comprises means for receiving and treating physical parameter data selected from the group consisting of temperature, inlet and outlet hydrogen pressures and valve status of the compressor means; and modulating and controlling the compressor means in consequence of the treatment of the compression means data. The CPU preferably comprises means for receiving and treating data selected from the group consisting of hydrogen demand of the hydrogen-receiving apparatus; and means for determining the amount, rate of delivery and duration of delivery of hydrogen to the apparatus in consequence of the hydrogen demand data. The CPU preferably comprises storage means for storing data selected from the hydrogen demand data, dates, times of day and night, and numbers of hydrogen-receiving apparatus. 
     Most preferably the CPU is in direct electrical or electronic communication with each of the cell, compressor and user activation means by means of electrical wires. 
     Thus, the control means and activation means provide for a practical user interface. 
     The system as hereinabove defined has also preferred utility wherein the conduit means and fitting engagement means comprises a plurality of conduits and fitting engagement members adapted to receive a plurality of the hydrogen-receiving apparatus, for example, a plurality of vehicles at a commercial, industrial or like outlet. 
     The introduction of the user activation means in combination with the CPU allows the advantageous exchange of data flow between the cell(s), compressor, vehicles(s) and sundry process control valves and conduits. This user interface allows for 
     1. defined demand, in real time, of the hydrogen needs for all vehicles, single or a plurality thereof, connected to the cell bank; 
     2. defined time to fill each vehicle(s) connected to the cell bank; 
     3. modulation of the cell bank to ensure the exact supply of hydrogen required by all vehicles over time; 
     4. modulation of the compressor in conjunction with the cell bank to ensure adequate supply of hydrogen to all vehicles in the absence of any storage tank(s), which reduces safety concerns; 
     5. modulation of the rate of filling of each vehicle via dynamic control of filling to provide a variable rate of filling to stabilize the temperature of the gas within the vehicle(s) and to ensure a correct real time value of pressure so as to assess a level of filling of the tank (i.e. half full, full, etc.) and a successful completion of the filling operation; 
     6. the achievement of aforesaid (1) to (5) with no manual user intervention; 
     7. the completion of data history of the operation of the cell bank and compressor is stored/recorded in run time hours to permit schedule maintenance, and 
     8. a complete data history of the storage of each vehicle to be stored/recorded. 
     The invention is of particular value in one embodiment when the apparatus comprises a cell to provide hydrogen at a desired minimum pressure; comprising an anolyte solution having an anolyte liquid level; 
     a catholyte solution having a catholyte liquid level; 
     oxygen generation means for generating oxygen at an oxygen pressure above said anolyte; 
     hydrogen generation means for generating hydrogen at a hydrogen pressure above said catholyte; 
     generated hydrogen outlet means; 
     and comprising pressure means for raising the oxygen pressure above the anolyte to effect a positive liquid level pressure differential between said catholyte liquid level and said anolyte liquid level to a pre-selected value to effect closure of said hydrogen outlet means and an increase in the hydrogen pressure to a value to effect opening of said hydrogen outlet means to provide hydrogen at said desired minimum pressure through said outlet means. 
     This preferred aspect of the invention as hereinabove defined relies on creating a liquid level pressure differential between the catholyte liquid and the anolyte liquid levels by causing oxygen pressure build-up above the anolyte and fall in anolyte liquid level and a commensurate rise in catholyte level, while hydrogen is free to leave the cell until either (a) the anolyte level drops to a pre-selected level to trigger a control valve to prevent hydrogen release from the cell or (b) the catholyte level rises to similarly trigger the control value to similarly prevent hydrogen release from the cell. Subsequent build-up of hydrogen pressure above the catholyte reverses the respective liquid levels to effect opening of the control valves to provide hydrogen at the desired minimum pressure. Hydrogen pressure builds up under the closed release valve situation because two moles of hydrogen are produced for each mole of oxygen in the electrolytic process. 
     Accordingly in a further aspect, the invention provides a process for providing hydrogen at a desired minimum pressure from an electrolyser comprising 
     an anolyte solution having an anolyte liquid level; 
     a catholyte solution having a catholyte liquid level; 
     oxygen generated at an oxygen pressure above said anolyte; 
     hydrogen generated at a hydrogen pressure above said catholyte for passage through hydrogen outlet means; the process comprising raising the oxygen pressure above the anolyte to effect a liquid levels pressure differential between said catholyte liquid level and said anolyte liquid level to a pre-selected value to effect closure of said hydrogen outlet means and an increase in the hydrogen pressure to a value to effect opening of said hydrogen outlet means to provide hydrogen at said desired minimum pressure. 
     In a further aspect, the invention provides an electrolyser for providing hydrogen at a desired minimum pressure comprising 
     an anolyte solution having an anolyte liquid level; 
     a catholyte solution having a catholyte liquid level; 
     oxygen generation means for generating oxygen at an oxygen pressure above said anolyte; 
     hydrogen generation means for generating hydrogen at a hydrogen pressure above said catholyte; 
     generated hydrogen outlet means; and comprising pressure means for raising the oxygen pressure above the anolyte to effect a liquid level pressure differential between said catholyte liquid level and said anolyte liquid level to a pre-selected value to effect closure of said hydrogen outlet means and an increase in the hydrogen pressure to a value to effect opening of said hydrogen outlet means to provide hydrogen at said desired minimum pressure through said outlet means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be better understood preferred embodiments will now be described by way of example only, with reference to the accompanying drawings wherein 
     FIG. 1 is a block diagram showing the major features of a hydrogen fuel supply system according to the invention; 
     FIG. 2 is a logic block diagram of the control program of one embodiment of the system according to the invention; 
     FIG. 3 is a logic block diagram of a cell block control loop of the control program of FIG. 2; 
     FIG. 4 is a block diagram of an electrolyser according to the invention; 
     FIG. 5 is an alternative embodiment of an electrolyser according to the invention; and wherein the same numerals denote like parts. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to FIG. 1, this shows a system according to the invention shown generally as  100  having an electrolyser cell  112  which produces source hydrogen at a desired pressure P 1  fed to compressor  114  through conduit  116 . Compressor  114  feeds compressed outlet hydrogen through conduit  118  to apparatus  120  at pressure P 2 , exemplified as a vehicle attached by a fitting  122 . Cell  112 , compressor  114  and user  124  are linked to a computer processor unit control means  126  which provides both data acquisition and process control. 
     In more detail, user  124  defines a demand to fill vehicle  120 . User  124  may transmit its demand by means of use of (i) a credit card; (ii) a smart card; (iii) a voice activation system; (iv) manual activation via front panel control, and by transmission by, for example, wire or infrared or other suitable radiation from vehicle  120 , itself. 
     Upon receipt of the demand, CPU  126  determines the status of electrochemical cell  112 , which initial status check includes monitoring of the process parameters for starting cell  112  and, in particular, temperature, pressure, anolyte liquid level, catholyte liquid level, bus continuity, KOH concentration, and process valve status. Further, upon receipt of the demand, CPU  126  determines the initial status of compressor  114 . Such initial checks include monitoring of the temperature, inlet and outlet pressure in one or more stages. 
     After CPU  126  determines the initial status of cell  112  and compressor  114 , CPU  126  analyses the needs of user  124  in terms of the quantity of hydrogen to be delivered, the rate of delivery, and duration of the time of delivery to vehicle  120 . CPU  126  then initiates the starting sequence for cell  112  to ensure the demands of user  124 . Power is applied to cell  112  and the process parameters of temperature, pressure, anolyte liquid level, catholyte liquid level, KOH concentration and process valve status are monitored and controlled in such a fashion as permit safe operation of cell  112  in the generation of hydrogen and oxygen gases of some minimum purities. An incorrect status in any of the operational parameters noted above or in the quality/purity of the product gases causes CPU  126  to alter or interrupt the operation of cell  112  until an appropriate status has been reached. 
     Upon successful operation of cell  112 , CPU  126  then monitors the pressure, P 1 , in the conduit between cell  112  and compressor  114  via a pressure sensor installed in line  116 . Upon reaching a minimum pressure, P * , in conduit  116 , CPU  126  having previously recognized an appropriate status for compressor  114 , turns compressor  114  on and begins to discharge gas into conduit  118  at some pressure, P 2 . CPU  126  then monitors the pressure in conduit  118  via a pressure sensor (not shown) to ensure that the pressure, P 2 , reaches some minimum pressure, P 2   * , for suitable discharge into vehicle  120  as demanded by user  124 . 
     The operations of cell  112  and compressor  114  are suitably modulated and controlled by CPU  126  through appropriate process valves so as to provide the minimum quantity of hydrogen at the minimum rate of delivery over the minimum amount of time as specified by user  124  such that the requirements of vehicle  120  are met. Upon receiving notification from vehicle  120  that the requirements have been successfully met, CPU  126  instructs cell  112  and compressor  114  to cease operation and to ensure discharge of any remaining pressure to some minimum acceptable value, P 2   ** , in conduit  118  such that user  124  can facilitate the disconnection of vehicle  120  from conduit  118  and complete the filling operation. 
     With reference to FIG. 2 this shows the logic control steps effective in the operation of the system as a whole, and in FIG. 3 the specific cell control loop, sub-unit wherein a logical block diagram of the control program of one embodiment of the system according to the invention; wherein 
     P MS —Compressor start pressure; 
     P L —Compressor stop pressure; 
     P LL —Inlet low pressure; 
     P MO —Tank full pressure; 
     ΔP—Pressure switch dead band; 
     P MM —Maximum allowable cell pressure; 
     L L —Minimum allowable cell liquid level; 
     P HO —Cell output pressure on the hydrogen side; and 
     P C —Compressor outlet pressure. 
     In more detail, FIG. 2 shows the logic flow diagram of the control program for the operation. Upon plant start-up, cell  112  generates hydrogen gas at some output pressure, P HO . The magnitude of such pressure, P HO , is used to modulate the operation of compressor  114 . If P HO  is less than some minimum pressure related to the liquid level in  112 , P LL , a low pressure alarm is generated and a plant shutdown sequence is followed. If the output pressure, P HO , is greater than P LL , then a further comparison is made. If the output pressure, P HO , is greater than P MS , the minimum input pressure to start compressor  114 , the latter begins a start sequence. If the output pressure is less than some minimum value, P L , then compressor  114  remains at idle (stopped) until such time as the magnitude of P HO  exceeds P MS  to begin compressor operation. 
     Upon starting compressor  114 , the hydrogen gas is compressed in one or more stages to reach an output pressure, P C , from the exit of compressor  114 . If the output pressure, P C , exceeds a safety threshold, P MO , then operation of compressor  114  is terminated. If the output, P C , is less than some desired minimum, P MO −ΔP, compressor  114  runs to supply and discharge hydrogen. 
     FIG. 3 comprises a block diagram of the hydrogen fuel replenishment apparatus shown generally as  200  used to supply hydrogen and/or oxygen gas at a minimum desired pressure. Apparatus  200  includes a rectifier  210  to convert an a.c. signal input to a desired d.c. signal output, a bus bar  212 , electrolytic cell(s)  112 , means of measuring oxygen  214  and hydrogen  216  pressure in conduits  218  and  220 , respectively, valve means for controlling the flow of oxygen  222  and hydrogen  224 , respectively, and a process/instrument controller  226  to ensure desired operation of electrolytic cell(s)  112  with suitable plant shutdown alarms  228 . 
     FIG. 3 also comprises a process flow diagram for the cell block of FIG.  2 . Upon plant start-up, rectifier  210  establishes a safe condition by examining the status of plant alarm  228  with respect to pressure and level controls. If the alarm indicates a safe status, current and voltage (power) are transmitted along cell bus bar  212  from rectifier  210  to electrolytic cell  112 . With the application of a suitable current/voltage source, electrolysis takes place within electrolytic cell(s)  112  with the resultant decomposition of water into the products of hydrogen gas and oxygen gas. The oxygen gas is transported along conduit  218  in which oxygen pressure means  214  monitors oxygen pressure, P O , at any time, and to control oxygen pressure via modulation of valve  222 . Similarly, the hydrogen gas is transported along conduit  220  in which means  216  monitors hydrogen pressure, P H , at any time, and to control hydrogen pressure via control valve  224 . In the operation of electrolytic cell(s)  112 , the anolyte level of the cell on the oxygen side, L O , and the catholyte level on the hydrogen side, L L , are detected via P/I controller  226  to provide a control signal to valve  224  to facilitate the supply of hydrogen and/or oxygen gas at some desired pressure. 
     With reference to FIG. 4, this shows generally as  10  an electrolyser having an oxygen gas product chamber  11  above anolyte  12 , a hydrogen gas product chamber  13  above catholyte  14 , cell membrane  15 , electrical connections  16  to a solar energy power source  18 , oxygen and hydrogen pressure release vents  20  and  22 , respectively. Oxygen product line  24  has a regulator check valve  26  set at a desired pre-selected value. While hydrogen product line  28  has an outlet  30  to receive a bobber or float ball  32  on the catholyte surface in sealing engagement therewith as explained hereinbelow. 
     Hydrogen outlet product line  28  leads, in the embodiment shown, to a metal hydride chamber  34 , through a disconnect fitting  36 . Anolyte cell half  38  has a safety low liquid level electrical switch  40  connected through electrical conduit  42  to power source  18 . 
     In operation, oxygen gas builds up in chamber  11 , since oxygen release is controlled by regulator  26 , set at a desired pressure, typically up to 100 psi and preferably about 60 psi. Hydrogen produced escapes chamber  13  through open outlet  30  while the oxygen pressure in chamber  11  builds up to cause liquid anolyte level to fall from its initial start-up level P 1  to lower operating level P 2  with a concomitant rise in catholyte level from start-up Q 1  to sealing level Q 2 , whereby float  32  seals outlet  30 . However, since hydrogen gas is produced twice as fast by volume than oxygen gas in cell  10 , hydrogen pressure builds up to a value which forces a lowering of catholyte level to a degree which causes bobber  32  to partially disengage outlet  30  and release of hydrogen at that value pre-determined by regulator  26 . 
     Accordingly, a steady state supply of hydrogen at the desired minimum pressure is provided to metal hydride production unit  34 , or elsewhere as desired. 
     Oxygen product may be taken-off at pressure through valve  26  or vent  20 . 
     Pressure release features are provided by bellows system  42 , vents  20 ,  22  and low level switch  40  which cuts off power to cell  10  if oxygen pressure build up in chamber  11  is excessive. 
     Thus, notwithstanding the ability of cell  10  according to the invention to provide hydrogen and oxygen at desired minimum pressures, the pressure differential across cell membrane  15  is low. 
     With reference now to alternative embodiment shown in FIG. 5 this shows, basically cell  10  having hydrogen production line  28  under a valve control not by floating bobber means  32  but by actual anolyte level sensing and associated control means. 
     In more detail, in this embodiment cell  10  has a pair  50 ,  52  of hydrogen product line  28 . Anolyte level sensors  50 ,  52  operably connected through control means  54  to activate a solenoid value  56  so positioned that upper sensor  50  maintains valve  56  open, until oxygen pressure build up in chamber  11  forces the anolyte level to drop to a desired pre-selected level where it activates sensor  52  and control  54  which overrides sensor  50  to close valve  56 . Build up of hydrogen pressure causes sensor  52  to be inactivated by a rise in anolyte level and defer to sensor  50 , which causes valve  56  to open and release product hydrogen at the desired minimum value. A steady state of activation and deactivation may ensure if liquid level pressure differentials fluctuate otherwise hydrogen gas is continuously provided at the requisite minimum pressure set by oxygen regulator  26 . 
     Although this disclosure has described and illustrated certain embodiments of the invention, it is to be understood that the inventions is not restricted to those particular embodiments. Rather, the invention includes all embodiments which are functional or mechanical equivalence of the specific embodiments and features that have been described and illustrated.