Detailed steps for the normal shutdown of a dry gas hydrogen production unit

For a normal shutdown, the main steps are as follows: 1. Reduce the flow rate and temperature. 2. After switching all the fuel gas to high-pressure gas, shut down the PSA unit; direct the medium-pressure gas to vent. 3. Lower the pressure in the system. 4. Gradually stop the supply of dry gas, and introduce nitrogen at the compressor inlet. 5. Establish a circulation within the plant to continue cooling. 6. Cut off the gas supply. 7. Continue cooling. 8. Turn off the burners, stop the fans, and cease circulation

Normal shutdown: the main steps are as follows: 1. Report to the dispatcher； 2. Remove the hydrogenation reactor and establish a large-scale circulation in the plant ； 3. Reduce volume and lower temperature ； 4. Gradually reduce the dry gas feed, supply nitrogen at the compressor inlet, disconnect the system from the PSA unit, and shut down the PSA unit in accordance with the operating procedures ； 5. System voltage reduction ； 6. Continue to cool down; stop using all fuel gas and analysis gas, and shut down the large burners ； 7. Stop steam supply 8. Close the boundary gas valve ； 9. Turn off the burner, stop the blower fan, and halt circulation.

Normal shutdown and reduction in throughput: 1. Reduce the feed rate to 40%–50% of the value specified in the plant’s feed schedule, as required. 2. Once the feed is stopped, switch to a large-cycle operation mode. 3. Reduce the throughput to zero over a period of 0.5–1 hour. 1. Maintain normal conversion rates, while adhering to the specifications for medium-voltage operations. 2. When reducing the throughput, first reduce the feed volume and then reduce the steam supply. 3. During this reduction process, introduce N2 or hydrogen at the conversion inlet to ensure that the catalyst operates under reduced conditions during shutdown. 1. Normal operation. 2. Excess steam drainage pipeline. 1. Reduce the plant’s capacity by 40%–50% and stop feeding material. 2. Follow the shutdown procedure: reduce temperature. 1. After stopping the feed of raw gas, cool the hydrogenation reactor at a rate of 30–50°C per hour. 1. After stopping the feed, if the CH4 content at the outlet is 0, continue cooling at 30–50°C per hour. 2. Cool the medium-pressure transformation reactor at 30–50°C per hour until the outlet temperature reaches 1580–200°C. 3. Reduce the amount of gas fed to the transformation unit to 2 T/h; use steam produced internally and disconnect it from the transformation unit. 1. Before cutting off the steam supply to the transformation unit, isolate the circulation process in the system. 2. Displace the system with N2. 3. Stop the circulation when the bed temperature reaches 100°C, and shut down the raw material furnace. 4. Install blind flanges on all reactors to maintain nitrogen pressure. 1. Stop supplying steam to the medium-pressure transformation unit when the outlet temperature reaches 180–200°C. 2. Cool the transformation unit at a rate of 50°C per hour. 1. As the temperature of the furnace drops, the cooling rate of the steam produced internally in the steam drum is 0.5–1 MPa per hour; shut down the transformation furnace and stop the circulation. Protect the hydrogenation reactor with nitrogen. 1. Shut down the transformation furnace and stop the circulation when the temperature at the inlet of the transformation unit reaches 200°C. 2. Stop the blower and exhaust fan when the furnace temperature falls below 100°C. 3. Maintain pressure in the medium-pressure transformation reactor using nitrogen. 4. Follow the normal shutdown procedure for displacing the gas system. 1. Exhaust system. 2. Maintain pressure with nitrogen. Operating procedures and key points for emergency shutdown: Regardless of the cause of the emergency shutdown, the shift supervisor must take decisive action to address it. While identifying the cause, it is also necessary to inform the dispatch team so that external coordination can be handled accordingly. (1) Internally shut off the feed gas; stop the output of product hydrogen, and cease fuel supply to F4001 and F4002. For outdoor operations, the upstream and downstream valves as well as the bypass valves mentioned above shall be closed; if there is a main valve, it shall also be closed. (2) After the PSA unit is shut down, pressure retention measures should be taken. Check whether the feed valve, product hydrogen valve, and the valve leading exhaust gas to F4002 are properly closed. (3) After stopping the feed to the conversion unit, close the main valve at the desulfurization outlet to depressurize the desulfurization system so that its pressure is 0.1~0.2 MPa lower than that of the conversion unit. Operate manually to establish the flow path for the oil and gas to go to E4006 and V4010; after depressurization, arrange for N2 to be supplied to purge and displace the desulfurization system separately. If C4001 is shut down, check whether the inlet and outlet valves of the unit are closed. (4) After the converter is shut down, the two fans, C4002 and C4003, can be stopped, and the flue dampers of the converter should be closed to allow for a gradual cooling process. At the same time, the steam generation system can slowly reduce the pressure via the PIC4601 (usually to between 0.2 and 0.6 MPa). (5) During the cooling and pressure reduction process of the steam generation system, close attention must be paid to the temperature of the conversion bed layer and the parameters of the steam drum. When both the pressure and flow rate of the generated steam are insufficient, the conversion process can stop using the generated steam and promptly arrange for external steam to be supplied, controlling the steam flow rate at around 5 t/h. The steam produced internally can be discharged through a silencer; by shutting off the drain from the steam drum, the water supply volume can be reduced accordingly. (6) Maintain normal levels of all liquid surfaces to prevent cross-contamination between high and low pressures. After the conversion process is halted and steam is introduced, the water present in each liquid separation tank and in the acidic water stripping tower can be drained into the drain. The liquid level in T4001 must be adjusted by draining it through the DN40 valve at the bottom of the tower, in order to maintain a proper liquid level. Measure the pH value before discharge to prevent stress on the wastewater treatment plant. (7) After the above treatments, if the conversion system permits, an N2 circulation should also be established, and the process should continue following the normal shutdown procedures

I have reviewed everyone’s suggestions; due to the differences in their respective devices, the shutdown procedures vary greatly

To prevent back conversion during shutdown, attention must also be paid to the gas holder. The rest depends on the purpose of the shutdown – things like catalyst replacement or coking, for example

Shutting down simply means reducing production volume and load; for shut-down reactors, blind flanges are installed and the pipelines are purged with nitrogen: D