The electrolytic hydrogen production unit includes a complete set of water electrolysis hydrogen production equipment, with the main equipment including:
1. Electrolytic cell
2. Gas liquid separation device
3. Drying and purification system
4. The electrical part includes: transformer, rectifier cabinet, PLC control cabinet, instrument cabinet, distribution cabinet, upper computer, etc
5. The auxiliary system mainly includes: alkali solution tank, raw material water tank, make-up water pump, nitrogen cylinder/busbar, etc/ 6. The overall auxiliary system of the equipment includes: pure water machine, chiller tower, chiller, air compressor, etc
hydrogen and oxygen coolers, and the water is collected by a drip trap before being sent out under the control of the control system; The electrolyte passes through hydrogen and oxygen alkali filters, hydrogen and oxygen alkali coolers respectively under the action of the circulation pump, and then returns to the electrolytic cell for further electrolysis.
The pressure of the system is regulated by the pressure control system and differential pressure control system to meet the requirements of downstream processes and storage.
The hydrogen produced by water electrolysis has the advantages of high purity and low impurities. Usually, the impurities in the hydrogen gas produced by water electrolysis are only oxygen and water, with no other components (which can avoid poisoning of certain catalysts). This provides convenience for producing high-purity hydrogen gas, and the purified gas can meet the standards of electronic grade industrial gases.
The hydrogen produced by the hydrogen production unit passes through a buffer tank to stabilize the system’s working pressure and further remove free water from the hydrogen.
After entering the hydrogen purification device, the hydrogen produced by water electrolysis is further purified, using the principles of catalytic reaction and molecular sieve adsorption to remove oxygen, water, and other impurities from the hydrogen.
The equipment can set up an automatic hydrogen production adjustment system according to the actual situation. Changes in gas load will cause fluctuations in the pressure of the hydrogen storage tank. The pressure transmitter installed on the storage tank will output a 4-20mA signal to the PLC for comparison with the original set value, and after inverse transformation and PID calculation, output a 20-4mA signal to the rectifier cabinet to adjust the size of the electrolysis current, thereby achieving the purpose of automatic adjustment of hydrogen production according to changes in hydrogen load.
The only reaction in the process of hydrogen production by water electrolysis is water (H2O), which needs to be continuously supplied with raw water through a water replenishment pump. The replenishment position is located on the hydrogen or oxygen separator. In addition, hydrogen and oxygen need to take away a small amount of water when leaving the system. Equipment with low water consumption can consume 1L/Nm ³ H2, while larger equipment can reduce it to 0.9L/Nm ³ H2. The system continuously replenishes raw water, which can maintain the stability of the alkaline liquid level and concentration. It can also replenish the reacted water in a timely manner to maintain the concentration of the alkaline solution.
- Transformer rectifier system
This system mainly consists of two devices, a transformer and a rectifier cabinet. Its main function is to convert the 10/35KV AC power provided by the front-end owner into the DC power required by the electrolytic cell, and supply DC power to the electrolytic cell. Part of the supplied power is used to directly decompose water molecules into hydrogen and oxygen, and the other part generates heat, which is carried out by the alkali cooler through cooling water.
Most of the transformers are oil type. If placed indoors or inside a container, dry-type transformers can be used. The transformers used for electrolytic water hydrogen production equipment are special transformers that need to be matched according to the data of each electrolytic cell, so they are customized equipment.
Currently, the most commonly used rectifier cabinet is the thyristor type, which is supported by equipment manufacturers due to its long usage time, high stability, and low price. However, due to the need to adapt large-scale equipment to front-end renewable energy, the conversion efficiency of thyristor rectifier cabinets is relatively low. Currently, various rectifier cabinet manufacturers are striving to adopt new IGBT rectifier cabinets. IGBT is already very common in other industries such as wind power, and it is believed that IGBT rectifier cabinets will have significant development in the future.
- Distribution cabinet system
The distribution cabinet is mainly used to supply power to various components with motors in the hydrogen oxygen separation and purification system behind the electrolytic water hydrogen production equipment, including 400V or commonly referred to as 380V equipment. The equipment includes the alkali circulation pump in the hydrogen oxygen separation framework and the make-up water pump in the auxiliary system; The power supply for the heating wires in the drying and purification system, as well as the auxiliary systems required for the entire system such as pure water machines, chillers, air compressors, cooling towers, and back-end hydrogen compressors, hydrogenation machines, etc., also includes the power supply for the lighting, monitoring, and other systems of the entire station.
- Control system
The control system implements PLC automatic control. The PLC generally adopts Siemens 1200 or 1500, and is equipped with a human-machine interaction interface touch screen. The operation and parameter display of each system of the equipment as well as the display of control logic are realized on the touch screen.
5. Alkali solution circulation system
This system mainly includes the following main equipment:
Hydrogen oxygen separator – Alkali solution circulation pump – Valve – Alkali solution filter – Electrolytic cell
The main process is as follows: the alkaline solution mixed with hydrogen and oxygen in the hydrogen oxygen separator is separated by the gas-liquid separator and refluxed to the alkaline solution circulation pump. The hydrogen separator and oxygen separator are connected here, and the alkaline solution circulation pump circulates the refluxed alkaline solution to the valve and alkaline solution filter at the back end. After the filter filters out large impurities, the alkaline solution is circulated to the inside of the electrolytic cell.
6.Hydrogen system
Hydrogen gas is generated from the cathode electrode side and reaches the separator along with the alkaline solution circulation system. Inside the separator, hydrogen gas is relatively light and naturally separated from the alkaline solution, reaching the upper part of the separator. Then, it passes through pipelines for further separation, cooled by cooling water, and collected by a drip catcher to achieve a purity of about 99% before reaching the back-end drying and purification system.
Evacuation: The evacuation of hydrogen gas is mainly used during start-up and shutdown periods, abnormal operations, or when purity does not meet standards, as well as for troubleshooting.
7. Oxygen system
The pathway of oxygen is similar to that of hydrogen, except that it is carried out in different separators.
Emptying: Currently, most projects use the method of emptying oxygen.
Utilization: The utilization value of oxygen is only meaningful in special projects, such as applications that can use both hydrogen and high-purity oxygen, such as fiber optic manufacturers. There are also some large projects that have reserved space for the utilization of oxygen. The backend application scenarios are for the production of liquid oxygen after drying and purification, or for medical oxygen through dispersion systems. However, the precision of these utilization scenarios still needs further confirmation.
8. Cooling water system
The electrolysis process of water is an endothermic reaction, and the hydrogen production process must be supplied with electrical energy. However, the electrical energy consumed in the water electrolysis process exceeds the theoretical heat absorption of the water electrolysis reaction. In other words, a portion of the electricity used in the electrolysis cell is converted into heat, which is mainly used to heat the alkaline solution circulation system at the beginning, raising the temperature of the alkaline solution to the required temperature range of 90 ± 5 ℃ for the equipment. If the electrolysis cell continues to operate after reaching the rated temperature, the generated heat needs to be carried out by cooling water to maintain the normal temperature of the electrolysis reaction zone. The high temperature in the electrolysis reaction zone can reduce energy consumption, but if the temperature is too high, the diaphragm of the electrolysis chamber will be damaged, which will also be detrimental to the long-term operation of the equipment.
The optimal operating temperature for this device is required to be maintained at no more than 95 ℃. In addition, the generated hydrogen and oxygen also need to be cooled and dehumidified, and the water-cooled thyristor rectifier device is also equipped with necessary cooling pipelines.
The pump body of large equipment also requires the participation of cooling water.
- Nitrogen filling and nitrogen purging system
Before debugging and operating the device, a nitrogen tightness test should be conducted on the system. Before normal startup, it is also required to purge the gas phase of the system with nitrogen to ensure that the gas in the gas phase space on both sides of the hydrogen and oxygen is far away from the flammable and explosive range.
After the equipment is shut down, the control system will automatically maintain pressure and retain a certain amount of hydrogen and oxygen inside the system. If the pressure is still present during startup, there is no need to perform a purging action. However, if the pressure is completely relieved, a nitrogen purging action needs to be performed again.
- Hydrogen drying (purification) system (optional)
The hydrogen gas prepared from water electrolysis is dehumidified by a parallel dryer, and finally purified by a sintered nickel tube filter to obtain dry hydrogen gas. According to the user’s requirements for product hydrogen, the system may add a purification device, which uses palladium platinum bimetallic catalytic deoxygenation for purification.
The hydrogen produced by the water electrolysis hydrogen production unit is sent to the hydrogen purification unit through a buffer tank.
The hydrogen gas first passes through a deoxygenation tower, and under the action of a catalyst, the oxygen in the hydrogen gas reacts with the hydrogen gas to produce water.
Reaction formula: 2H2+O2 2H2O.
Then, the hydrogen gas passes through a hydrogen condenser (which cools the gas to condense water vapor into water, which is automatically discharged outside the system through a collector) and enters the adsorption tower.
Post time: Dec-03-2024
