Briefly describe the normal shutdown steps for double-column distillation?

Upon receiving the shutdown command, stop feeding material to the tower immediately; product extraction can continue. When it is determined that the product is of poor quality, cease both extraction and reflux, and divert the product to a tank designated for defective products. Once the liquid level at the bottom of the tower has evaporated, stop the heat source used to reboil the mixture. After the reflux tank is emptied, shut down the reflux pump and the condenser. Perform pressure relief, first at high pressure and then at low pressure, doing so slowly to prevent the equipment materials from becoming brittle due to low temperatures. When the pressure drops to zero, open the vent valve, and finally carry out purging and replacement.

Normal shutdown of double-column distillation. 1) Notify the control room and relevant departments to stop the supply of residual liquid and steam condensate. 2) Stop the refined methanol pump in the warehouse, close the inlet and outlet valves, close the alkali addition valve and the extraction condensate addition valve, stop the steam supply, and close the remote control valve for the condensate. 3) Stop the extraction of fusel oil, extract crude methanol, and feed it to the main tower. Stop the feed pump at the main tower, and turn off the power and air supply for the instruments. 4) Residual liquid discharge valve. 5) Methanol recovery valve. 6) Main steam valve, and steam inlet valves for each cycle evaporator. Close the condensate discharge valve of the circulating evaporator, and slightly open the steam line drain valve. 7) Stop the reflux pumps of the pre-tower and main tower when the liquid levels in their collection tanks are drained. Close the inlet and outlet valves of the pre-cooling and main reflux pumps. 8) Inlet valves for the pre-cooler, main tower condenser, pure methanol cooler, and fusel oil cooler (can be slightly opened in winter to prevent freezing)