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Accident phenomenon: The liquid level in the stripping tower was at zero. Cause of the accident: As confirmed by personnel on site, LICA-39 could be opened fully, but it encountered varying degrees of sticking during the process of closing it; sometimes it got stuck at 50% or 70% of its full opening. Handling of the accident: 1. When the liquid level was at zero, communication was used with the personnel on site to ask them to gradually reduce the opening of the upstream valve of LICA-39, thereby allowing liquid to accumulate slowly until the liquid level started to rise. 2. When the liquid level is full, use the walkie-talkie to coordinate with the personnel on site and instruct them to open the upstream valve of LICA-39 until the liquid level begins to drop. 3. The control principle is that LICA-39 should neither be under liquid level nor empty. Hazards of the accident: 1. When LICA-39 is full, it is easy for the stripping tower to carry liquid with it, which can lead to water entering the pre-conversion furnace. This results in a decrease in the temperature of the process gas at the inlet of the pre-conversion furnace, and the pre-conversion catalyst gets soaked in water, causing severe damage to it and a reduction in its activity. 2. When LICA-39 is empty, it is easy for steam to enter C66401, which can lead to damage to the packing in the stripping tower or to the heat exchangers. Thoughts on the accident: There are frequent failures of LICA-39, especially during startup; it is therefore necessary to pay close attention to controlling the liquid level in the stripping tower. To prevent or eliminate the occurrence of accidents, when LICA-39 gets stuck or clogged, it is quite difficult to deal with the situation. Based on past experience, it is necessary to contact a safety inspection company to disassemble the valve; this requires the personnel on duty to isolate this valve. It is very challenging to do so when the entire process system is functioning normally, as bypass control becomes difficult in such cases.