WO2004076723A2

WO2004076723A2 - Conversion circuit, system and method of executing an electrochemical process

Info

Publication number: WO2004076723A2
Application number: PCT/NL2004/000142
Authority: WO
Inventors: Taco Wijnand Neeb
Original assignee: Tendris Solutions B.V.
Priority date: 2003-02-26
Filing date: 2004-02-25
Publication date: 2004-09-10
Also published as: CA2515442A1; WO2004076723A3; NL1022786C2; EP1597815A2; AU2004215028A1; CN1754300A; US20060076240A1

Abstract

A conversion circuit for converting an alternating current into a feed current for an electrochemical process is provided with at least one supply terminal for supplying an alternating feed current, a rectifier circuit for rectifying a supplied alternating feed current; and an output stage for supplying the rectified current to a device in which the electrochemical process is taking place. The conversion circuit is further provided with an input stage connected between the supply terminals and rectifier circuit, which input stage, in use, confers upon the conversion circuit a substantially reactive input impedance.

Description

Conversion circuit, system for and method of executing an electrochemical process.

The invention relates to a conversion circuit for converting an alternating current into a feed current for an electrochemical process, which conversion circuit is provided with at least one supply terminal for supplying an alternating feed current; a rectifier circuit for rectifying a supplied alternating feed current ; and an output stage for supplying the rectified current to a device in which the electrochemical process is taking place. The invention also relates to a system for carrying out an electrochemical process, suitable for placing a device in which an electrochemical process is running and comprising such a conversion circuit .

The invention also relates to a method of carrying out an electrochemical process using such a conversion circuit .

Examples of a conversion circuit, system and method as described above are known from GB 2 197 551. In said publication a battery charger is described. This battery charger may be used for charging miniature batteries. When powered by the mains , the input impedance of the known battery charger is substantially resistive in nature. The known battery charger has an input stage having a capacitor connected in series between the rectifier circuit and the power supply terminals. In the known battery charger, the capacitor serves to bring about a voltage drop, in order that the voltage across the terminals of the battery doesn't become too high.

A disadvantage of the known apparatus is that the performance of the electrochemical process that takes place when charging the battery takes a relatively long time. It is an object of the invention to provide a conversion circuit, system for carrying out an electrochemical process and method of carrying out an electrochemical process that can accelerate that process and show a relatively high level of efficiency.

This object is achieved by the conversion circuit of the type mentioned in the opening paragraph, wherein the conversion circuit is further provided with an input stage connected between the supply terminals and rectifier circuit, which input stage, in use, confers upon the conversion circuit a substantially reactive input impedance.

The conversion circuit, in use, thus has an input impedance of which the reactive component is higher than the resistive component. By using the input stage it is possible to supply more power to the electrochemical process, without the apparent power uptake increasing appreciably. By using a reactive input impedance in combination with power supply from an alternating feed current, a pulsating power is supplied to the electrochemical process, because the electrical and magnetic component of the electromagnetic waves propagating through conductors in the conversion circuit are out of phase. The invention is based on the idea that by thus separating the two components, the charge carriers which are involved in the electrochemical process acquire a higher mobility. In this way, the efficiency of the electrochemical process, and thus its speed, increases.

Preferably, the input stage comprises at least one capacitor connected in series between the supply terminals and the rectifier circuit, and more particularly, the input stage is comprised of a capacitor bank, which comprises one or more capacitors connected in parallel .

In this manner an almost purely reactive input impedance may be obtained, as a result of which the advantageous effects of the conversion circuit according to the invention manifest themselves in an enhanced manner.

The supply terminals are suitable for connection of the conversion circuit to the mains network, amongst others. If the conversion circuit is connected directly to the mains network, it is simple to use in many places. Therefore, no separate alternating current power source is needed. According to another aspect of the invention, there is provided a system for carrying out an electrochemical process, suitable for placing a device in which an electrochemical process is running and comprising a conversion circuit according to any one of the claims .

This system has the same advantageous effects as the conversion circuit

Preferably, the system is suitable for use of a device in which the electrochemical process is taking place that comprises a container for an electrolyte solution, wherein the system is provided with means for generating pressure waves in the electrolyte solution present in the container of a device placed in the system.

The pressure waves improve the transport of the charge carriers that are involved in the electrochemical process. Additionally, they ensure a rapid removal of gasses released in the electrochemical process, so that the concentration thereof in the electrolyte solution is lower. This enhances the operation of the conversion circuit according to the invention, so that the electrochemical process executes even faster. An additional effect is that any crystallised electrolyte dissolves again more rapidly. Thus, a regenerative effect is obtained that is particularly advantageous if the electrochemical process is taking place in a relatively cold environment or has previously run in the opposite direction, because crystallisation of the electrolyte occurs most often in those cases.

In a preferred embodiment, the system comprises a fluid bath, in which the container can be placed and is provided with means for generating pressure waves in the fluid bath when filled with fluid.

This is a highly effective manner of transmitting pressure waves, as the impedance of the fluid and electrolyte solution are in the same range, so that more power is transmitted. Furthermore, the system is usable in combination with various containers, which may thus be adapted to the type of electrochemical process without detracting from their suitability for use in the system according to the invention. According to yet another aspect the invention provides a method of carrying out an electrochemical process, wherein us is made of a conversion circuit according to the invention. This method has the advantage of being of relatively short duration.

In a preferred embodiment, the method comprises having the electrochemical process take place in a container filled with an electrolyte solution, and generating pressure waves in the electrolyte solution present in the container.

The pressure waves improve the transport of the charge carriers involved in the electrochemical process. This enhances the operation of the conversion circuit according to the invention, so that the electrochemical process runs even faster.

Preferably, the method comprises generating pressure waves having a frequency in the range of 20 kHz and higher.

It has been determined experimentally that the effect of the pressure waves is highest in the frequency range between 20 kHZ and 50 kHz. When using an electrolyte solution with water as a component, the range of 38-46 kHz and, within that range, 41-43 kHz in particular, is best. This is connected with the fact that the resonance frequency of water molecules lies at approximately 42 kHz.

The invention will now be explained in further detail with reference to the accompanying drawings, wherein: in Fig. 1A and IB schematic top and side plan views are shown respectively of an example of a system according to the invention; and in Fig. 2 a circuit diagram of an embodiment of the conversion circuit according to the invention is shown.

The system according to the invention, of which Fig. 1A and IB schematically show an example, comprises a conversion circuit and a vessel 2 filled with water 1 forming a fluid bath. In the fluid bath, an electrolysis device 3 has been placed. The electrolysis device 3 comprises a fluid container 4, with a duality of electrodes 5 therein, which are immersed in an electrolyte solution 6. The electrodes 5 are connected to positive and negative poles 7,8 of the electrolysis device 3.

The invention is generally suitable for any type of electrochemical process. The example that is detailed herein concerns electrolysis, for example of a sodium chloride solution to win chlorine. In a special embodiment of the invention, a system according to the invention forms part of the drive train of a vehicle. This drive train further comprises a power source for driving the vehicle, which power source uses the product of the electrolysis as a source of energy. The power source may for instance consist of an internal combustion engine or a Stirling-motor running on hydrogen, but also of a combination of fuel cells and one or more electric motors. A generator supplying the alternating supply current to the conversion circuit according to the invention may consist of a dynamo and optionally be used to recoup energy when slowing down the vehicle. The system comprised of the generator for generating alternating current, the conversion circuit according to the invention, the electrochemical cell in which an electrochemical process is taking place and a power source using the product of the electrochemical process, provides an especially efficient and rapidly responding system for vehicle propulsion. The invention is, however, also suitable for charging batteries and accumulators. The invention is even suitable for charging batteries of types that cannot be recharged with conventional charging apparatus, such as carbon batteries. The invention is particularly suitable for recharging lead sulphate batteries, such as are used in cars and lorries, for instance. There, the problem occurs that through repeated overcharging and deep discharging (in combination with low temperatures) , sulphate is deposited on the electrode plates, as a result of which the capacity of the accumulator decreases over its lifetime. By means of the system according to the invention this effect can be reversed and prevented. In use, the electrolysis device 3 is placed on a pedestal 9 in the vessel 2 filled with water 1, wherein the fluid level is set such that the poles 7,8 just surface above the water 3. The poles 7,8 are connected to leads 10,11, for example by means of alligator clips (not shown) or other suitable connection means. The electronics of the conversion circuit according to the invention, of which a generalised example is shown schematically in Fig. 2, are accommodated in a housing 12. Thus, the system according to the invention in this example is comprised of the conversion circuit, the housing 12 with the electronics accommodated therein, and the fluid bath, of which the function will be described in more detail further on.

The conversion circuit according to the invention is preferably powered from the mains, although another source of alternating current could be used in principle, which in the context of the invention should also be taken to mean sources of polyphase current (three-phase current) , such as a power current network. An example of a suitable source is an alternating current generator such as a car dynamo or an emergency backup power generator. It would also be possible to use a source of direct current coupled to a converter for converting the direct current into an alternating current. In principle, the conversion circuit according to the invention is usable separately from the fluid bath, for example in a vehicle, to charge the accumulator whilst driving. Such an application is not limited to cars, but also extends to other vehicles, such as electric trains, trams, wheelchairs, boats or aeroplanes, for instance. Returning to the example of Fig. 2, the depicted conversion circuit is provided with plugs 13,14, which constitute a supply terminal for supplying the alternating current from the socket. The supplied alternating current is first passed through an input stage, which in this example is comprised of a capacitor bank 15. The capacitor bank 15 comprises three capacitors 16 connected in parallel . In a variant (not shown) of the shown circuit the capacity of the capacitor bank 15 as a whole is adjustable by means of switches placed before the capacitors 15. By using the capacitor bank 15 with capacitors 16 of suitable capacity, no separate transformer is needed, and conferment of an almost completely reactive input impedance by the input stage upon the conversion circuit, when supplied from the mains (that is to say with alternating current having frequency in the range between 40 and 60 Hz) , is also attained. Thus, current and voltage are almost 90° out of phase, as a result of which the apparent power consumed is almost equal to zero. The capacitor bank 15 makes the use of a separate transformer superfluous .

In other applications the input impedance is always adjusted to the frequency of the power supply. For power current or current from a car dynamo, the frequency will be much higher, for example around 600 Hz. The input impedance of the conversion circuit according to the invention is then again substantially reactive, through an appropriate choice of capacitors 16. The input stage is thus always adapted to the properties of the alternating feed current (which should also be taken to mean polyphase current) , such that the input stage confers upon the circuit a substantially reactive input impedance in use .

After the input stage the current is only rectified by a bridge circuit 17 connected to the input stage. The rectified current is supplied to the electrolysis device 3 through connector clamps 18,19, attached to the positive and negative poles 7,8 of the electrolysis device 3. Because the conversion circuit is essentially comprised of the input stage with an almost purely reactive input impedance and the bridge circuit 17, a pulsating power is supplied to the electrolysis device 3.

It is observed that other rectifier circuits than the bridge circuit 17 shown in Fig. 2 are possible within the scope of the invention. In principle a half-wave rectifier circuit is possible, but it is preferable, with a view to having the electrochemical process run faster and more efficiently, to use a full-wave rectifier circuit. The choice of rectifier circuit, in addition to the nature of the electrochemical process, determines whether and which harmonics of the alternating current frequency are passed. In an electrochemical process, only even harmonics are involved. This is an additional advantageous effect of the circuit according to the invention, as odd harmonics are undesirable. The presence of the electrochemical process causes those components, usually responsible amongst others for problems such as overheating, to be eliminated. The harmonic components enhance the accelerating effect on the electrochemical process.

Returning to Figs. 1A and IB, the function of the fluid bath will now be described. Although vibrations in the electrolysis device can also be generated by other means, for example by means of a vibratory pad in the pedestal 9, pressure waves are preferably generated in the water 1, by means of an actuator 20 attached to the vessel 2. The actuator 20 could be a piezo actuator, but specially adapted loudspeakers driven by means of a magnet and solenoid are equally possible. Preferably, ultrasonic pressure waves are generated, preferably with a frequency of 20 kHz or more. The range above 25 kHz has proved to be particularly advantageous. It has been established experimentally that the effect of the pressure waves is largest between 20 kHz and 50 kHz. When using an electrolyte solution with water as component, the range of 38-46 kHz, and within that range

41-43 kHz in particular, is best. This is connected with the fact that the resonance frequency of water molecules lies at about 42 kHz.

The actuator generates a pressure wave with a plane wave front 30 propagating in a direction A towards the fluid container 4. The pressure wave impinges perpendicularly on a wall of the fluid container. This wall starts to vibrate and thus transmits the pressure wave to the electrolyte solution 6. The electrodes 5 also start to vibrate. Through simultaneous driving of the actuator 29 and feed current through the conversion circuit according to the invention, it is ensured that the electrolysis process in the electrolysis device 3 takes place quickly. The ion transport in the electrolyte solution 6 is accelerated, whilst outgassing of electrolysis products is accelerated by the pressure waves. By these means, the concentration of electrolysis product in solution is decreased, as a result of which the reaction in the electrolyte solution is accomplished more rapidly.

The invention is not confined to the embodiments described herein, which may be varied within the scope of the accompanying claims. In particular, the system according to the invention is not limited to the electrochemical processes mentioned. A galvanisation process for example, takes place more rapidly and more efficiently when use is made of the conversion circuit according to the invention.

Claims

1. Conversion circuit for converting an alternating current into a feed current for an electrochemical process, which conversion circuit is provided with at least one supply terminal (13,14) for supplying an alternating feed current; a rectifier circuit (17) for rectifying a supplied alternating feed current; and an output stage for supplying the rectified current to a device (3) in which the electrochemical process is taking place, wherein the conversion circuit is further provided with an input stage (15) connected between the supply terminals (13,14) and rectifier circuit (17), which input stage (15) , in use, confers upon the conversion circuit a substantially reactive input impedance.

2. Conversion circuit according to claim 1, wherein the input stage (15) comprises at least one capacitor (16) connected in series between the supply terminals (13,14) and the rectifier circuit (17).

3. Conversion circuit according to claim 2 , wherein the input stage (15) is comprised of a capacitor bank, which comprises one or more capacitors (16) connected in parallel .

4. Conversion circuit according to any one of the preceding claims, wherein the supply terminals (13,14) are suitable for connection of the conversion circuit to the mains network.

5. Conversion circuit according to any one of the preceding claims, wherein the rectifier circuit (17) comprises a full-wave rectifier circuit.

6. System for carrying out an electrochemical process, suitable for placing a device (3) in which an electrochemical process is running and comprising a conversion circuit according to any one of claim 1-5.

7. System according to claim 6 , suitable for use of a device (3) in which the electrochemical process is taking place that comprises a container (4) for an electrolyte solution (6) , wherein the system is provided with means (20) for generating pressure waves in the electrolyte solution (6) present in the container (4) of a device (3) placed in the system.

8. System according to claim 7, comprising a fluid bath (1,2) , in which the container (4) can be placed and provided with means (29) for generating pressure waves in the fluid bath (1,2) when filled with fluid (1) .

9. Method of carrying out an electrochemical process, wherein use is made of a conversion circuit according to any one of claims 1-5.

10. Method according to claim 9, comprising having the electrochemical process take place in a container (4) filled with an electrolyte solution (6) , and generating pressure waves in the electrolyte solution (6) present in the container (4) .

11. Method according to claim 10, comprising generating pressure waves having a frequency in the range of 20 kHz and higher .