The hydrogen production plant is shut down; where should the pressure be released from the adsorption towers in the PSA section?

When the hydrogen production plant is shut down normally, especially when the PSA (Pressure Swing Adsorption) unit stops operating, it is necessary to depressurize the adsorption towers and then fill them with nitrogen as a protective measure. This process is aimed at protecting the equipment and ensuring the safety of the system. 1. **Pressure relief**: The pressure in the absorption tower is usually released through specific pressure relief pipes. These pressure relief pipes may be connected to the system’s safety valves or a dedicated pressure relief system. It is not necessarily through the gas discharge pipeline that pressure is released. The specific procedures depend on the design of the equipment and its operating protocols. In some cases, if the design permits, pressure can indeed be relieved by manually opening the programmable valve for the purge gas. 2. **Nitrogen purging**: Nitrogen is introduced to replace the gas in the adsorption tower, creating an inert environment to prevent oxidation and other chemical reactions. Nitrogen filling is usually done through the air inlet of the adsorption tower or a specific interface, which requires opening the corresponding program-controlled valve. Nitrogen filling is not done by opening all the programmable valves; instead, specific paths and valves are used, which allows for more effective control of the nitrogen flow and ensures that the gas inside the adsorption tower is fully replaced. In practical operation, it is necessary to follow the device’s operation manual or safety procedures, as different devices may have varying designs and operating procedures. For beginners, it is recommended to operate under the guidance of experienced operators or technicians to ensure safety and accuracy. .

When releasing pressure from the adsorption tower, it is essential to do so from the bottom of the tower to prevent impurities in the adsorbent from penetrating. In normal design, a flare line is provided at the bottom of the absorption tower, allowing for manual pressure relief when the pressure becomes too high. When the pressure is low, it is also possible to vent directly through the desorption gas tank, but attention must be paid to the pressure in the adsorption tower. If the programmable valve is fully open, the high pressure from the adsorption tower can reach the desorption gas tank, potentially causing the overpressure safety valve to activate. . . If nitrogen flushing is used, all the adsorption towers can be connected together for flushing

Is it necessary to purge with nitrogen for parking and protection, the PSA unit, the gas-liquid separation tank, the 5 adsorption towers, and the sequential discharge tank? Do all pipes also need to be filled with nitrogen? Or does it just require filling the 5 adsorption towers with nitrogen?

When releasing pressure from the PSA adsorption tower during shutdown: manually open the inlet valve of the adsorption tower in sequence, as well as the flare vent valve on the inlet pipeline. Release the pressure inside the adsorption tower to the flare; it is strictly prohibited to release pressure from the outlet of the adsorption tower, as this can cause the adsorbed impurities to penetrate the adsorption bed, resulting in substandard hydrogen quality during the next operation. Nitrogen flushing generally requires filling the adsorption tower with nitrogen from the outlet valve of the self-adsorption tower, and then opening the inlet valve at a certain pressure to carry out flushing; this process of pressurization and depressurization is repeated until the desired conditions are achieved.

Stopping the PSA is very simple: close the main PSA inlet valve, close the PSA product outlet valve, and open the local vent valve as well as the valve for sending off the desorbed gas. Just keep running the PSA; the pressure in each adsorption tower is reduced by allowing the regeneration gas to flow out from the desorption outlet during the flushing process. The system pressure will gradually decrease. At the same time, when the feed gas supply is stopped, the impurity gases trapped in the adsorption towers that need to be regenerated are desorbed. Once the system pressure drops, almost all of the gas in the towers will be hydrogen. It facilitates operation with refeeding. In the case of a vacuum desorption system, when shutting down the operation, simply stop the vacuum pump and vent the desorbed gas through the bypass.

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