Off-grid electrolysis control method and device thereof independent of grid

The subject application is a continuation of PCT/CN2021/000042 filed on Mar. 15, 2021, which claims priority on Chinese Application No. CN202010287807.3 filed on Apr. 13, 2020 in China. The contents and subject matter of the PCT international application and the Chinese priority application are incorporated herein by reference.

The present invention relates to electrolysis techniques in the electrochemical field.

Hydrogen and oxygen are both important industrial raw materials. But the hydrogen is a completely clean energy source, and it has the characteristics of high fuel value

In addition to the reforming, decomposition, and photolysis of fossil fuels, the existing hydrogen production methods include water electrolysis for hydrogen production. So far, water electrolysis hydrogen production accounts for around 4% to 5% of the world's hydrogen production and more than 95% hydrogen is obtained through the reforming of fossil fuels, and the production process will inevitably emit CO 2 . The water electrolysis technology independently utilizes clean energy that can achieve zero CO 2 emissions. Hydrogen production by water electrolysis is to dissociate water molecules into hydrogen and oxygen through an electrochemical process under the action of stable direct current, which are separated out at the cathode and anode respectively. According to the different diaphragms, it can be divided into alkaline water electrolysis, proton exchange membrane water electrolysis, and solid oxide water electrolysis. However, since water electrolysis to produce hydrogen requires a large amount of electricity with stable power (voltage, current), grid power has been used as the energy source for hydrogen production.

Using fixed power supply water hydrogen production technology, several groups of electrode plates are arranged in parallel and upright in the electrolyzer, the electrolyzer is divided into several electrolytic chambers connected in series, the number of series electrodes is set according to the DC voltage value of the power supply, and then according to the power set the size of the electrolyzer, the total voltage of the electrolyzer is the sum of the voltages of each electrolytic chambers, and the total current is the same as that of each electrolytic chamber.

Although renewable energy (such as wind and solar energy) have been used for hydrogen and oxygen production in recent years, the stability of power supply is very high due to water electrolysis for hydrogen production and oxygen production, while wind and solar energy are both have the characteristics of large fluctuation, and not only the power fluctuation range is very large, but also the voltage fluctuation range is very large. The difference between minimum and maximum voltage of the source electrical energy could be as many as ten times larger. Therefore, the existing methods and technologies for hydrogen production by electrolysis of water using wind energy and solar energy still need to rely on the grid as the main power source, while wind energy or solar energy is considered to be the source electricity. As an auxiliary power source only, even in areas with better wind resources, such as areas where annual power generation reaches 1,500 hours, the availability of wind energy is around 17.1%, and the annual available sufficient sunlight is around 1,500 hours. Basically, most of the nominal hydrogen production and oxygen production schemes using new energy still rely on the grid as the main power source, which limits the way to use clean energy to produce hydrogen.

Chinese Patent Application No. 201720255416.7 outlines a single electrolyzer and multiple electrodes in parallel, and controls the number of parallel electrodes connected by a contact switch to solve the power supply fluctuation of the electrolyzer. However, the design does not consider the power characteristics of renewable energy such as wind energy and solar energy. The first reason for the change of wind and solar power is the change of voltage. Its output voltage changes rapidly, the current then changes rapidly accordingly when the wind speed or sunlight changes. The large-scale changes, the power tracking characteristics in the wind and solar energy industries are current (power) changes based on voltage changes, and different voltages correspond to different power outputs (current changes). The present invention adopts the method of automatically controlling the number of electrodes to be connected or cut out in parallel through a very large change from the input source power. The electrolytic cell can only carry a DC power supply of about 2 volts, which can only be used when the voltage fluctuation range is small (within the allowable range of the electrode voltage), and when the size of the electrolytic cell is fixed, the range of the electrolytic cell to adapt to current changes is also very limited, such as from 0.25-0.3 amp/cm 2 , it is not suitable for renewable energy with very large power fluctuations, meanwhile the large change of the voltage and current from the source power will damage the electrolyzer. The electric power characteristics of both wind and solar energy vary with the environment they are set up in, and the changes between the high and low voltage could be as much as ten times, which is far greater than the electrode reference voltage of 2 volts (0.6-1.1). So does the current.

To resolve the above problems, the present invention is proposing the control method and design structure for the electrolysis, which uses a very large fluctuation range of energy as a power source, such as wind or solar energy, so it is truly independent of the grid power, while the craft of the electrolysis is the same with traditional electrolysis.

In order to achieve the designing object, the present invention adopts the following technical solutions:

Under current technology, the conventional design of the existing electrolytic cell is that the size of the electrolytic cell is based on the current of 0.25 amp/cm 2 to 0.3 amp/cm 2 . Within this current range, the performance is the best. Referred to as the reference current in the present invention, that is, the preferred reference current (Ib) is between 0.25 amp/cm 2 to 0.3 amp/cm 2 , 0.3 amps per cm 2 is referred to as the maximum reference current in the present invention, and each electrical level is 2 volts Based on the DC voltage (the allowable variation range is 0.6-1.1 times of 2 volts), in the present invention, this voltage is called the reference voltage of the electrode.

Using renewable energy as a power source, such as wind and solar energy, the electrical power from the source varies due to the environment they are in. Usually, the voltage at the minimum available power is called the cut-in voltage, and the corresponding current is called the cut-in current (Ii). The core of the present invention is setting a certain number of basic series electrodes through the lowest cut-in voltage value of wind or solar energy at first, then setting the size of the electrode according to the ratio of the minimum cut-in current value corresponding to the minimum cut-in voltage value of wind or solar energy to the reference current value. When the power of wind or solar energy increases, the voltage of the power increases and the current of the power also increases. When the voltage increases, a certain number of electrodes will be connected in series to maintain the reference voltage of about 2 volts per electrode. On the contrary, when the voltage decreases, a certain number of series electrodes will be cut out; At the maximum reference current of the cell, an electrolyzer with the same number of electrodes in series (called parallel electrolyzer) will be connected in parallel to achieve the use of renewable energy water electrolysis (hydrogen production, Oxygen production) purpose.

FIG. 1 . is a schematic diagram of the arrangement structure of the electrolyzer. The electrodes of the electrolyzer are composed of basic electrodes and a different number of series electrodes. The series electrodes are arranged on one or both sides of the basic electrodes. The electrolyzer is composed of several electrolysis chambers. The basic composition of each electrolysis chamber is the same as that of the conventional electrolysis chamber. It consists of positive and negative electrodes. Different types of diaphragms can be used in the middle of the electrodes. The DC output power of wind or solar energy is used as the total power supply of the electrolyzer.

In FIG. 1 , the double contacts switch (or single-contact switch) is controlled by a controller composed of PLC or other control chips. The controller connects or cuts out a certain number of series electrodes according to the changing rule of the power supply voltage. When the power supply is initially connected, the electrode voltage has not risen high enough, the switch is at the a1/b1 position, the power supply is connected to the initial number of electrode, and the series electrodes are not connected at this time. When the voltage continues to rise, the reference voltage of each electrode reaches a higher level value (such as DC 2.2 volts), the switch is automatically connected to the a2/b2 position through the controller, the additional series electrodes will be connected, and the reference voltage of each electrode will drop; the same, when the controller detects that the reference voltage is lower than a certain level of value (for example, it is set to 1.6 volts), the connected series electrodes will be cut out of several groups, to maintain the reference voltage of each electrode at a designed voltage state, such as between 1.6-2.2 volts. The newly cutting in or cutting out series electrodes can be connected in several groups or in one by one according to the power changing value. When the power continues to increase and the electrodes connected in series can no longer consume the continuously increasing input power, the current of the electrodes will reach or exceed the maximum reference current Imax (such as 0.3 amps or 0.35 amps), then connect one or more in parallel electrolyzers with the same number of electrodes in series as the basic electrolyzer is referred to in the present invention as parallel electrolyzer; also as the power continues to decrease, the current in the electrolyzer is reduced to less than the setting reference current (such as 0.2 amp/cm 2 or 0.1 amp/cm 2 ), the electrolyzers connected in parallel will be automatically cut out one by one. That is, the voltage increases or decreases, the number of electrodes is connected in series or cut out first, and the current increases or decreases by connecting or cutting out the parallel electrolytic cell. When the negative electrode of the electrode is the common terminal, the negative electrode may not be set to be always in the ON state. The following will specifically illustrate how the series electrodes and the parallel electrolytic cells are connected or cut out through different embodiments.

The present invention provides a device for electrolysis comprising a power supply for supplying power to electrolysis, wherein the power supply is a fluctuating power supply with a power fluctuation in a range from a minimum power to a maximum power, and the maximum power is greater than 2 times of the minimum power, and in a range from a minimum cut-in current to a maximum current, and the maximum current is greater than 3 times of the minimum cut-in current.

In the present invention, the device may further comprise an electrolyzer system, wherein the electrolyzer system comprises a basic electrolyzer comprising a plurality of groups of basic electrodes connected in series with each other and a plurality of groups of controllable series electrodes, and a plurality of controllable parallel electrolyzers, wherein a number of the basic electrodes in the basic electrolyzer is set according to a minimum cut-in voltage value of the fluctuating power supply.

In the present invention, the reference voltage of each of the basic electrodes and the controllable series electrodes may be set to be between 1 to 2 Vdc.

In the present invention, the parallel electrolyzer may comprise the same number of the plurality of groups of basic electrodes connected in series with each other and the same number of the plurality of groups of controllable series electrodes as in the basic electrolyzer.

In the present invention, the size of the electrolyzer may be set according to the ratio of Ii/Ib, Ii is the minimum cut-in current corresponding to the minimum cut-in voltage of the fluctuating power supply, Ib is a reference current corresponding to the reference voltage, and the ratio Ii/Ib may be in a range of from 0.003 to 10.

In the present invention, the reference current Ib may be in a range of from 0.01 to 0.35 amp per square centimeter.

In the present invention, the number of the controllable parallel electrolyzers in the device may be 0 to 5, and the controllable parallel electrolyzer may be connected or cut out in parallel according to the power fluctuation.

In the present invention, the number of the controllable series electrodes may be connected or cut out in series according to the positive and negative voltage fluctuation of 20% or more, respectively.

In the present invention, the device may further comprise a controller, wherein the controller detects voltage, current, and the fluctuating power, connects with and controls that controllable series electrodes being connected in cutting in or cutting out in series and the controllable parallel electrolyzers being connected in cutting in or cutting out in parallel, and the controller comprises a negative terminal and a positive terminal, the negative terminal is a control terminal of the controller, and the positive terminal is a common terminal.

Further, the present invention provides a method for supplying and maintaining power supply for electrolysis, comprising providing a power supply for supplying power to electrolysis, wherein the power supply is a fluctuating power supply with a power fluctuation in a range from a minimum power to a maximum power, and the maximum power is greater than 2 times of the minimum power, and in a range from a minimum cut-in current to a maximum current, and the maximum current is greater than 3 times of the minimum cut-in current; providing an electrolyzer system, wherein the electrolyzer system comprises a basic electrolyzer comprising a plurality of groups of basic electrodes connected in series with each other and a plurality of groups of controllable series electrodes, and a plurality of controllable parallel electrolyzers; setting a number of the basic electrodes in the basic electrolyzer according to a minimum cut-in voltage value of the fluctuating power supply; setting a size of the basic electrolyzer and the controllable parallel electrolyzers according to a ratio of Ii/Ib, Ii is the minimum cut-in current corresponding to the minimum cut-in voltage of the fluctuating power supply, Ib is a reference current corresponding to the reference voltage, and the ratio Ii/Ib is in a range of from 0.003 to 10, and connecting in or cutting out the number of the controllable parallel electrolyzers in the device according to the power fluctuation.

In the method of the present invention, the reference voltage of each of the basic electrodes and the controllable series electrodes may be set to be between 1 to 2 Vdc.

In the method of the present invention, the parallel electrolyzer may comprise the same number of the plurality of groups of basic electrodes connected in series with each other and the same number of the plurality of groups of controllable series electrodes as in the basic electrolyzer.

In the method of the present invention, the reference current Ib may be in a range of from 0.01 to 0.35 amp/cm 2 .

In the method of the present invention, the number of the controllable parallel electrolyzers in the device may be 0 to 5.

The method of the present invention may further comprise the steps of connecting in the controllable series electrodes according to a positive voltage fluctuation of 20% or more, and cutting out the controllable series electrodes according to a negative voltage fluctuation of 20% or more.

In the method of the present invention, the device may further comprise a controller, wherein the controller detects voltage, current, and the fluctuating power, connects with and controls that controllable series electrodes being connected in cutting in or cutting out in series and the controllable parallel electrolyzers being connected in cutting in or cutting out in parallel, and the controller comprises a negative terminal and a positive terminal, the negative terminal is the control terminal of the controller, and the positive terminal is the common terminal.

FIG. 1 shows the basic structure of the electrolyzer of the present invention.

FIG. 2 shows the control method of the basic electrolytic cell and the parallel electrolytic cell in the present invention.

Due to the characteristics of renewable energy and customized power generation scales, the implementation of the present invention will be described in detail below with referenced examples. Defining the number of basic electrodes (electrolysis chambers) will be described in detail including the criteria of cutting-in and cutting-out of electrodes and electrolyzers. So do how to resize the electrode, and the approaches to the electrolyzers cutting in and out.

However, this should not limit the scope of protection of the present invention. It is understood that the professionals in the area can easily subdivide the number of electrodes and the number of electrolyzers in these embodiments without violating the scope of these claims. Changes and combinations, especially re-setting new reference current, reference voltage, or re-setting the minimum cut-in voltage, cut-in current, or re-setting the ratio of the minimum cut-in current and the reference current, so as to obtain a new specific implementation method, These new specific implementations obtained by changing the reference current, the reference voltage, the minimum cut-in voltage and the minimum cut-in current, the ratio setting of the minimum cut-in current and the reference current, the change of the number of electrodes, and the combination are also included in the protection scope of the present invention.