Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-07-16
2002-08-13
Valentine, Donald R. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S266000, C204S278000, C123S00100A
Reexamination Certificate
active
06432283
ABSTRACT:
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, pre
Dong Charlie
Fairlie Matthew J.
Stewart William J.
Stuart Andrew T.B.
Thorpe Steven J.
Manelli Denison & Selter
Stemberger Edward J.
Stuart Energy Systems Corporation
Valentine Donald R.
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