Alkaline electrolytic cell cold start method

Abstract

The invention discloses a cold start method for an alkaline electrolytic cell, which comprises the following steps: (1) gradually boosting to the maximum safety voltage, and keeping an alkaline liquor circulating pump closed in the process; (2) starting an alkali liquor circulating pump when the temperature of the alkali liquor in the electrolytic cell reaches a set temperature, so that the temperature of the alkali liquor in the system rises, and the temperature of the alkali liquor in the electrolytic cell drops; (3) closing the alkali liquor circulating pump, and continuously electrifying the electrolytic bath; (4) on the basis of the set temperature, starting the alkali liquor circulating pump every time the temperature of the alkali liquor in the electrolytic bath is increased by 5-10 DEG C, and returning to the step (3) when the temperature of the system alkali liquor and the temperature of the alkali liquor in the electrolytic bath are stable; and (5) repeating the steps (3) and (4) until the temperature of the system alkali liquor and the temperature of the alkali liquor in the electrolytic bath reach rated temperatures. The cold start time of the alkaline electrolytic cell can be further shortened.

Description

Technical Field

[0001] The invention relates to the technical field of electrolytic hydrogen production, and in particular to a cold start method for an alkaline electrolytic cell. Background Art

[0002] Using green electricity such as wind power and photovoltaic power to produce hydrogen through electrolysis is the core technology to promote the development of hydrogen energy storage. At present, electrolysis of hydrogen is mainly based on alkaline electrolyzers. Alkaline electrolyzers mainly include electrolyzers and BOP systems. The electrolyzers have electrodes and diaphragms, which are generally divided into dozens or even hundreds of electrolysis chambers. During the electrolysis process, the anode produces oxygen and the cathode produces hydrogen. The diaphragm is used to prevent the mixing of hydrogen and oxygen.

[0003] Due to the structure and working principle of the alkaline electrolyzer, its current density is relatively low and the cold start time is long. Taking a 1000 standard cubic meter alkaline electrolyzer as an example, its cold start usually takes 1 to 2 hours. This limits the utilization efficiency of green electricity to a certain extent. At the same time, the lower utilization efficiency of green electricity will also lead to an increase in hydrogen production costs. Therefore, shortening the cold start time of the alkaline electrolyzer has become a key direction to improve its adaptability and promote the efficient use of green energy.

[0004] At present, there are three main solutions to shorten the cold start time of alkaline electrolyzers:

[0005] 1) Use external heating equipment to heat the system. The rated operating temperature of the external heating equipment is about 90-95°C. Its high current will greatly increase the risk of electrical explosion in hydrogen-related places. Therefore, customers generally do not accept this solution.

[0006] 2) Precious metals are added to the electrodes to reduce electrochemical polarization and increase current and heat generation power. However, under green power conditions, daily starts and stops will cause the precious metals on the electrode surface to fall off quickly, and the performance cannot be sustained. In addition, the electrodes with added precious metals are expensive and have a low cost-performance ratio.

[0007] 3) Optimize the control strategy. Currently, the industry generally adopts the solution of gradually increasing the current under the maximum safe voltage. Although this shortens the cold start time to a certain extent, there is still considerable room for optimization. Summary of the invention

[0008] Purpose of the invention: The purpose of the present invention is to provide a method for further shortening the cold start time of an alkaline electrolytic cell without increasing the cost of equipment.

[0009] Technical solution: A cold start method for an alkaline electrolytic cell of the present invention comprises:

[0010] (1) Gradually increase the voltage to the maximum safe voltage, and the alkali solution circulation pump remains closed during this process;

[0011] (2) When the alkali solution temperature inside the electrolytic cell reaches the set temperature, the alkali solution circulation pump is started to increase the system alkali solution temperature and decrease the alkali solution temperature inside the electrolytic cell;

[0012] (3) Turn off the alkali solution circulation pump and keep the electrolytic cell powered;

[0013] (4) starting the alkali solution circulation pump every time the alkali solution temperature inside the electrolytic cell increases by 5 to 10° C. on the basis of the set temperature, and returning to step (3) when the alkali solution temperature of the system and the alkali solution temperature inside the electrolytic cell are stable;

[0014] (5) Repeat steps (3) and (4) until the system alkali solution temperature and the alkali solution temperature inside the electrolytic cell reach the rated temperature.

[0015] Furthermore, the temperature rise curve of the electrolytic cell is in a step shape.

[0016] Furthermore, the set temperature is 50-60°C.

[0017] Furthermore, the maximum safe voltage = number of electrolysis chambers * 2.0V.

[0018] Furthermore, the temperature of the alkaline solution inside the electrolytic cell is obtained by setting a temperature measuring point inside the electrolytic cell or at the outlet.

[0019] As an optional solution, a cold start method for an alkaline electrolytic cell comprises:

[0020] (1) Gradually increase the voltage to the maximum safe voltage, and the alkali solution circulation pump remains closed during this process;

[0021] (2) When the alkali solution temperature inside the electrolytic cell reaches the set temperature, the alkali solution circulation pump is started to increase the system alkali solution temperature and reduce the alkali solution temperature inside the electrolytic cell; the electrolytic cell is continuously powered on until the system alkali solution temperature and the alkali solution temperature inside the electrolytic cell reach the rated temperature.

[0022] Beneficial effect: Compared with the prior art, the present invention has the following significant advantages: in the startup phase, the alkali solution flow rate is effectively controlled by controlling the start and stop timing of the alkali solution circulation pump, which not only effectively utilizes the electrochemical characteristics that the higher the temperature, the lower the electrochemical polarization inside the electrolytic cell and the larger the current, but also reduces the heat dissipation between the electrolysis system and the external environment, thereby achieving the purpose of further shortening the cold start time, and can improve the green electricity utilization rate of the electrolytic hydrogen production equipment and reduce the comprehensive cost of green hydrogen preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the voltage-density curve at different temperatures;

[0024] Figure 2 It is the temperature rise curve of the electrolytic cell under the present invention and the traditional strategy. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings.

[0026] Example 1

[0027] A cold start method for an alkaline electrolytic cell comprises the following steps:

[0028] (1) Gradually increase the voltage to the maximum safe voltage, and the alkali solution circulation pump remains closed during this process;

[0029] Before boosting, necessary preparations need to be made, such as pipeline inspection, electrical connection inspection, cooling system inspection, hydrogen and oxygen pipeline safety inspection, etc. Boosting is performed after the alkali solution is introduced, and the voltage is gradually increased to the maximum safe voltage through low-voltage pre-charging. In this embodiment, the maximum safe voltage = number of electrolytic chambers * 2.0V.

[0030] (2) When the alkali solution temperature inside the electrolytic cell reaches the set temperature, the alkali solution circulation pump is started, so that the alkali solution temperature of the system is quickly raised and the alkali solution temperature inside the electrolytic cell decreases;

[0031] In this embodiment, the set temperature is 50-60°C, which is the inflection point temperature of electrochemical polarization of most electrodes. That is, below this inflection point temperature, the temperature is more sensitive to the electrochemical polarization of the electrode, and above this inflection point temperature, the sensitivity is significantly reduced.

[0032] The temperature of the alkali solution inside the electrolytic cell is obtained by setting a temperature measuring point inside the electrolytic cell or at the outlet.

[0033] (3) Turn off the alkali solution circulation pump, keep the electrolytic cell powered on, and the internal temperature of the electrolytic cell continues to rise;

[0034] When to turn off the alkali circulation pump: Since the electrolytic cell is a hot spot and there is a certain distance between the BOP system and the electrolytic cell, the system alkali temperature will be 2-5°C lower than the alkali temperature in the electrolytic cell. Therefore, when the system alkali temperature and the alkali temperature inside the electrolytic cell tend to be stable, the alkali circulation pump can be turned off.

[0035] (4) On the basis of the set temperature, the alkali solution temperature inside the electrolytic cell increases by 5 to 10° C., and the alkali solution circulation pump is started. When the system alkali solution temperature and the alkali solution temperature inside the electrolytic cell are stable (in this process, the system and the alkali solution temperature inside the electrolytic cell are neutralized again), return to step (3);

[0036] Starting the alkali solution circulation pump once every time the alkali solution temperature inside the electrolytic cell increases by 5 to 10°C can also prevent the local temperature of the electrolytic cell from being too high and burning the electrodes and diaphragms.

[0037] (5) Repeat steps (3) and (4) until the system alkali solution temperature and the alkali solution temperature inside the electrolytic cell reach the rated temperature.

[0038] The principle of shortening the cold start time according to the present invention is described below.

[0039] (I) Thermal analysis of electrolytic cell cold start

[0040] The total heat required for cold start can be expressed as:

[0041] Q 启动 =Q 加热 +Q 损失 +Q 欧姆热

[0042] Q 欧姆热 =(UU 中性 )*I*t

[0043] Among them, Q 加热 Indicates the heat required to heat the electrolyte and electrolytic cell components to the operating temperature; Q 损失 Indicates the heat lost during the heating process; Q 欧姆热 Indicates the ohmic heat generated by the electrolytic cell when it is powered; U 中性 The theoretical electrolytic voltage for maintaining the temperature of the electrolytic cell is 1.48V; t represents time. In order to accelerate the start-up of the electrolytic cell and shorten the start-up time, it is necessary to increase the ohmic heat as much as possible within a certain period of time. Because it is a constant voltage start-up, that is, U = constant (2.0V), so to determine the ohmic heat, it is necessary to determine the relationship between the voltage and the current I at a specific temperature.

[0044] The BV equation is an equation that describes the relationship between voltage and current in electrochemistry:

[0045]

[0046] Where i is the total current density, which represents the net current per unit area, A / m 2 ; i0 is the exchange current density, which indicates the current density when the reactants and products on the electrode surface are in dynamic equilibrium, A / m 2 ; α a is the electron transfer coefficient of the anode (oxidation) reaction, reflecting the symmetry of the reaction; α c is the electron transfer coefficient of the cathode (reduction) reaction, usually α a +α c =1; n is the number of electron transfers in the reaction; F is the Faraday constant, 96485C / mol; η is the overpotential, which represents the deviation between the actual electrode potential and the equilibrium potential, V; R is the gas constant, 8.314J / (mol·K); T is the absolute temperature, K.

[0047] The voltage-current density at different temperatures is plotted as a curve. Figure 1As shown, when the temperature rises, the current at a specific voltage will increase, and the ohmic heat will increase, which is conducive to rapid temperature rise.

[0048] (II) Analysis on shortening startup time

[0049] 1) During cold start, the alkali solution circulation pump is turned off, but the electrolytic hydrogen and oxygen production continues. The bubbles formed after the gas is generated will separate from the electrode and move upward under the action of gravity and buoyancy. The space after the bubbles separate from the electrode is filled with alkali solution at the bottom, that is, the electrolytic hydrogen production system can complete self-circulation and work normally without starting the alkali solution circulation pump. Therefore, the heat exchange between the electrolyzer and the BOP system is continuous. Turning off the alkali solution circulation pump only reduces the alkali solution circulation volume and reduces the heat exchange between the hydrogen production equipment and the environment, that is, reducing Q 损失 .

[0050] 2) Considering from the perspective of polarization principle: The polarization of the electrolytic cell refers to the phenomenon that the actual working voltage is higher than the theoretical decomposition voltage (equilibrium voltage) during the electrolysis process. Polarization will lead to a decrease in efficiency and increase in energy consumption. Polarization is usually caused by three main factors: activation polarization, ohmic polarization and concentration polarization.

[0051] Activation polarization is an overvoltage caused by the kinetic limitation of electrochemical reactions and is the additional voltage required for the electrode surface reaction. It mainly occurs during the electrochemical reaction at the anode and cathode. Temperature is the main factor affecting electrochemical polarization: high temperature can accelerate the reaction kinetics and reduce activation polarization.

[0052] Concentration polarization can only be manifested under high current density conditions. Under current technical conditions, the concentration polarization of alkaline electrolyzers is almost zero, so it can be ignored.

[0053] Ohmic polarization is the voltage loss caused by the resistance inside the electrolytic cell, including: the ionic resistance of the electrolyte, the resistance of the electrode material, and the ionic resistance of the membrane (for membrane-separated electrolytic cells). Temperature is the main influencing factor. The conductivity of the electrolyte is usually better at high temperatures, so high temperatures can effectively reduce ohmic polarization.

[0054] In summary, turning off the alkali circulation pump during cold start can cleverly prioritize heating of the electrolysis system. The electrolytic cell containing the electrodes has a higher priority. The electrodes are the site of electrochemical reactions. Not starting the alkali circulation pump in the early stage of cold start can make the temperature inside the electrolytic cell rise fastest. Higher temperatures will lead to lower electrochemical polarization, lower ohmic polarization, higher current, and higher ohmic heat input to the electrolysis system at a specific voltage, thereby effectively shortening the startup time.

[0055] Figure 2The temperature rise curves of the electrolyzer of the present invention and the traditional strategy are shown. It can be seen that the temperature rise curve of the electrolyzer of the present invention presents a step shape. At startup, the temperature in the electrolyzer rises rapidly. After reaching the set temperature, the alkali solution circulation pump is started, the temperature of the alkali solution in the electrolyzer is neutralized, and the temperature drops. Then the alkali solution circulation pump is turned off, and the alkali solution in the electrolyzer is rapidly heated again under the action of ohmic heat. When it reaches a certain temperature, the alkali solution circulation pump is started again. The above process is repeated many times until the electrolytic hydrogen production system reaches the rated temperature. The temperature rise curve of the electrolyzer under the traditional strategy is relatively smooth. During the cold start process, not only the heat exchange with the environment becomes larger, but also the temperature inside the electrolyzer is always lower than the temperature under the strategy of the present invention. The electrochemical polarization and ohmic polarization are large, resulting in a smaller electric density at a specific voltage and a slower overall temperature rise.

[0056] Example 2

[0057] A cold start method for an alkaline electrolytic cell comprises the following steps:

[0058] (1) Gradually increase the voltage to the maximum safe voltage, and the alkali solution circulation pump remains closed during this process;

[0059] (2) When the alkali solution temperature inside the electrolytic cell reaches the set temperature, the alkali solution circulation pump is started to increase the system alkali solution temperature and reduce the alkali solution temperature inside the electrolytic cell; the electrolytic cell is continuously powered on until the system alkali solution temperature and the alkali solution temperature inside the electrolytic cell reach the rated temperature.

[0060] The difference between Example 2 and Example 1 is that the number of cycles of starting and shutting down the alkali solution circulation pump in Example 1 is multiple, while it is once in Example 2. The advantage of multiple cycles is that it can ensure rapid temperature rise while preventing the internal temperature of the electrolytic cell from being too high and damaging the diaphragm and electrodes.

Claims

1. A cold start method for an alkaline electrolytic cell, characterized in that: include: (1) Gradually increase the voltage to the maximum safe voltage, and the alkali solution circulation pump remains closed during this process; (2) When the alkali solution temperature inside the electrolytic cell reaches the set temperature, the alkali solution circulation pump is started to increase the system alkali solution temperature and decrease the alkali solution temperature inside the electrolytic cell; (3) Turn off the alkali solution circulation pump and keep the electrolytic cell powered; (4) starting the alkali solution circulation pump every time the alkali solution temperature inside the electrolytic cell increases by 5 to 10° C. on the basis of the set temperature, and returning to step (3) when the alkali solution temperature of the system and the alkali solution temperature inside the electrolytic cell are stable; (5) Repeat steps (3) and (4) until the system alkali solution temperature and the alkali solution temperature inside the electrolytic cell reach the rated temperature.

2. The cold start method of the alkaline electrolytic cell according to claim 1, characterized in that: The temperature rise curve of the electrolytic cell is in a step shape.

3. The cold start method of the alkaline electrolytic cell according to claim 1, characterized in that: The set temperature is 50-60°C.

4. The cold start method of the alkaline electrolytic cell according to claim 1, characterized in that: Maximum safe voltage = number of electrolysis chambers * 2.0V.

5. The cold start method of the alkaline electrolytic cell according to claim 1, characterized in that: The temperature of the alkali solution inside the electrolytic cell is obtained by setting a temperature measuring point inside the electrolytic cell or at the outlet.

6. A cold start method for an alkaline electrolytic cell, characterized in that: include: (1) Gradually increase the voltage to the maximum safe voltage, and the alkali solution circulation pump remains closed during this process; (2) When the alkali solution temperature inside the electrolytic cell reaches the set temperature, the alkali solution circulation pump is started to increase the system alkali solution temperature and reduce the alkali solution temperature inside the electrolytic cell; the electrolytic cell is continuously powered on until the system alkali solution temperature and the alkali solution temperature inside the electrolytic cell reach the rated temperature.

7. The cold start method of the alkaline electrolytic cell according to claim 6, characterized in that: The temperature rise curve of the electrolytic cell is in a step shape.

8. The cold start method of the alkaline electrolytic cell according to claim 6, characterized in that: The set temperature is 50-60°C.

9. The cold start method of the alkaline electrolytic cell according to claim 6, characterized in that: Maximum safe voltage = number of electrolysis chambers * 2.0V.

10. The cold start method of the alkaline electrolytic cell according to claim 6, characterized in that: The temperature of the alkali solution inside the electrolytic cell is obtained by setting a temperature measuring point inside the electrolytic cell or at the outlet.

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