With the increasing global pursuit of clean energy and sustainable development, hydrogen energy, as an efficient and clean energy carrier, is gradually entering people’s vision. As a key link in the hydrogen energy industry chain, hydrogen purification technology not only concerns the safety and reliability of hydrogen energy, but also directly affects the application scope and economic benefits of hydrogen energy.
1.Requirements for product hydrogen
Hydrogen, as a chemical raw material and energy carrier, has different requirements for purity and impurity content in different application scenarios. In the production of synthetic ammonia, methanol and other chemical products, in order to prevent catalyst poisoning and ensure product quality, sulfides and other toxic substances in the feed gas must be removed in advance to reduce the impurity content to meet the requirements. In industrial fields such as metallurgy, ceramics, glass, and semiconductors, hydrogen gas comes into direct contact with products, and the requirements for purity and impurity content are more stringent. For example, in the semiconductor industry, hydrogen is used for processes such as crystal and substrate preparation, oxidation, annealing, etc., which have extremely high limitations on impurities such as oxygen, water, heavy hydrocarbons, hydrogen sulfide, etc. in hydrogen
2.The working principle of deoxygenation
Under the action of a catalyst, a small amount of oxygen in hydrogen can react with hydrogen to produce water, achieving the purpose of deoxygenation. The reaction is an exothermic reaction, and the reaction equation is as follows:
2H ₂+O ₂ (catalyst) -2H ₂ O+Q
Because the composition, chemical properties, and quality of the catalyst itself do not change before and after the reaction, the catalyst can be used continuously without regeneration.
The deoxidizer has an inner and outer cylinder structure, with the catalyst loaded between the outer and inner cylinders. The explosion-proof electric heating component is installed inside the inner cylinder, and two temperature sensors are located at the top and bottom of the catalyst packing to detect and control the reaction temperature. The outer cylinder is wrapped with insulation layer to prevent heat loss and avoid burns. The raw hydrogen enters the inner cylinder from the upper inlet of the deoxidizer, is heated by an electric heating element, and flows through the catalyst bed from bottom to top. The oxygen in the raw hydrogen reacts with the hydrogen under the action of the catalyst to produce water. The oxygen content in the hydrogen flowing out from the lower outlet can be reduced to below 1ppm. The water generated by the combination flows out of the deoxidizer in gaseous form with the hydrogen gas, condenses in the subsequent hydrogen cooler, filters in the air-water separator, and is discharged from the system.
3.Working principle of dryness
The drying of hydrogen gas adopts adsorption method, using molecular sieves as adsorbents. After drying, the dew point of hydrogen gas can reach below -70 ℃. Molecular sieve is a type of aluminosilicate compound with a cubic lattice, which forms many cavities of the same size inside after dehydration and has a very large surface area. Molecular sieves are called molecular sieves because they can separate molecules with different shapes, diameters, polarities, boiling points, and saturation levels.
Water is a highly polar molecule, and molecular sieves have a strong affinity for water. The adsorption of molecular sieves is physical adsorption, and when the adsorption is saturated, it takes a period of time to heat and regenerate before it can be adsorbed again. Therefore, at least two dryers are included in a purification device, with one working while the other regenerates, to ensure continuous production of dew point stable hydrogen gas.
The dryer has an inner and outer cylinder structure, with the adsorbent loaded between the outer and inner cylinders. The explosion-proof electric heating component is installed inside the inner cylinder, and two temperature sensors are located at the top and bottom of the molecular sieve packing to detect and control the reaction temperature. The outer cylinder is wrapped with insulation layer to prevent heat loss and avoid burns. The airflow in the adsorption state (including the primary and secondary working states) and the regeneration state is reversed. In the adsorption state, the upper end pipe is the gas outlet and the lower end pipe is the gas inlet. In the regeneration state, the upper end pipe is the gas inlet and the lower end pipe is the gas outlet. The drying system can be divided into two tower dryers and three tower dryers according to the number of dryers.
4.Two tower process
Two dryers are installed in the device, which alternate and regenerate within one cycle (48 hours) to achieve continuous operation of the entire device. After drying, the dew point of hydrogen can reach below -60 ℃. During a working cycle (48 hours), dryers A and B undergo working and regenerating states, respectively.
In one switching cycle, the dryer experiences two states: working state and regeneration state.
·Regeneration state: The processing gas volume is full gas volume. The regeneration state includes heating stage and blowing cooling stage;
1) Heating stage – the heater inside the dryer works, and automatically stops heating when the upper temperature reaches the set value or the heating time reaches the set value;
2) Cooling stage – After the dryer stops heating, the airflow continues to flow through the dryer in the original path to cool it down until the dryer switches to working mode.
·Working status: The processing air volume is at full capacity, and the heater inside the dryer is not working.
5.Three tower workflow
Currently, the three tower process is widely used. Three dryers are installed in the device, which contain desiccants (molecular sieves) with large adsorption capacity and good temperature resistance. Three dryers alternate between operation, regeneration, and adsorption to achieve continuous operation of the entire device. After drying, the dew point of hydrogen gas can reach below -70 ℃.
During a switching cycle, the dryer goes through three states: working, adsorption, and regeneration. For each state, the first dryer in which the raw hydrogen gas enters after deoxygenation, cooling, and water filtration is located:
1) Working status: The processing gas volume is at full capacity, the heater inside the dryer is not working, and the medium is raw hydrogen gas that has not been dehydrated;
The second dryer entering is located at:
2) Regeneration state: 20% gas volume: Regeneration state includes heating stage and blowing cooling stage;
Heating stage – the heater inside the dryer works, and automatically stops heating when the upper temperature reaches the set value or the heating time reaches the set value;
Cooling stage – After the dryer stops heating, the airflow continues to flow through the dryer in the original path to cool it down until the dryer switches to working mode; When the dryer is in the regeneration stage, the medium is dehydrated dry hydrogen gas;
The third dryer entering is located at:
3)Adsorption state: Processing gas volume is 20%, the heater in the dryer is not working, and the medium is hydrogen gas for regeneration.
Post time: Dec-19-2024
