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At 6:00 a.m. on March 23, 2009, the ammonia synthesis plant was brought online at reduced capacity in preparation for a planned shutdown for maintenance work. The main tasks of this maintenance were the replacement of catalysts in reactor 109-D and reactor 106-D, as well as sealing leaks in unit 123-C1. Our shift is the night shift; we take over at 4:00 p.m., by which time the plant has already been shut down safely and steadily, and system replacement is underway. Below is a summary of this replacement process. The system replacement in the conversion unit is mainly divided into the feed gas system and the fuel gas system, while the steam system and the demineralized water system are relatively simpler. 1. Fuel gas system: When the ammonia synthesis plant is shut down, the fuel gas system needs to be purged. The replacement of the fuel gas system refers to the areas from PIC-1602 to 101-B, 103-B, and 101-BU at the gas distribution station. ① First, it is necessary to confirm that the fuel gas blind valve at the gas distribution station causes a \"blocked\" state, while the blind valve on the N5 pipeline results in an \"unblocked\" state; the N5 gas has already been supplied into the boundary area. Start N5 pressure charging and replacement. PCV-34 is on. ② Open the fuel gas valve MCV-9 of the burner in row 9 of Unit 101-B, and activate the drain to purge the furnace chamber of Section 1. If the purging time is short, more rows can be used; in that case, one burner cock and the upstream valve for each row can also be opened to increase the flow rate of N5 and thus reduce the purging time. ③ For 103-B, one cock and one front valve are provided for each row of burners; meanwhile, the control room verifies that 103-B has been reset, the fuel gas solenoid valves for each row of burners are activated, and the vent valves are opened. ④ Decide whether to open the burner cock of the auxiliary boiler as needed. ⑤ Conduct sampling and analysis based on the displacement situation. 2. Raw gas system 2.1 From the gas distribution station to the 108-DA outlet: ① First, it is necessary to confirm that the blind flange at the gas distribution station causes a \"blocked\" condition, while the blind flange on the N5 pipeline results in an \"unblocked\" condition; the N5 gas has already been delivered into the boundary area. Start N5 pressure charging and replacement. The control center confirms that SP-2 is on. (If it is not turned on, contact the control room to force it to be turned on.) ② Inform the site to open the vent valve at outlet 108-DA. ③ Verify that the flow is unobstructed; depending on the situation, contact Sinochem for sampling and analysis. 2.2 From 109-D to MCV-26 (high-pressure converter): ① Confirm that N80 has been introduced into the process area. ② Open the hydrogenation valve at 109-D to feed N80 in. ③ The control room should activate MCV-26 for venting. ④ Take samples for analysis based on the results of the displacement process. 2.3 Displacement of 104-DB and 108-DB (low-pressure converters): ① Open the outlet vent valves to relieve pressure, bringing it to a slightly positive level. ② Turn on the drain valves (as the pressure drops, steam in the process gas condenses). ③ Open the inlet valve N120 at 104-DB to introduce pressure. ④ Open the inlet valve N5 at 108-DB to introduce pressure. ⑤ The control room should monitor the temperatures of the catalyst beds in both high- and low-pressure converters; if these temperatures rise significantly, the site should be notified immediately to increase the nitrogen supply. 3. Steam system: ① After stopping 103-J, withdraw S100 in a timely manner, depending on the situation. ② Continue to supply water to 101-F and 122-F to cool them down. ③ When the pressure in 101-F drops to 6.7 MPa, open V1007. ④ Combine the steam from 122-F with that from S38. ⑤ When the wall temperatures of the pressure vessels drop to around 50°C and the pressure falls to 0.04 MPa, open the 2-inch vent valve at the top of the pressure vessels. ⑥ Stop supplying water. 4. Desalinated water system: ① Once water supply to the pressure vessels is stopped, inform the site to stop the pumps. ② Instruct the site to close the valves before and after LCV-23. ③ If unit 4# has not stopped operating, ensure that water continues to be supplied to it. ④ If no water is being supplied to unit 4#, directly close the water supply valves for 106-C and 134-C. ⑤ If unit 4# has not stopped operating, make sure that the bypass valve leading to it is open