Summary of operational experience with two distillation columns in KK process benzene hydrogenation

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I have some experience in operating benzene hydrogenation distillation, and I would like to share it with everyone. However, my experience in this area is not extensive, so I hope any mistakes in what I say can be pointed out! For now, I will only share information on the pre-distillation tower and the benzene purification tower; these two towers are connected to each other, making them relatively difficult to operate, so I have summarized the relevant points here. During the first start-up of T501 (pre-tower) and T504 (benzene pure tower), feed is introduced into the bottom of the towers; when the liquid level is at 30, it is possible to adjust the feed amount as needed. Steam is then added gradually to raise the temperature. Once the reflux tank reaches a low liquid level, the reflux pump is activated to ensure full reflux, and both the top and bottom of the towers continue to heat up. The reflux rate is controlled appropriately in order to regulate the rate at which the top temperature rises. When the top temperature exceeds 135 degrees, it is time to notify the laboratory to begin analysis and sample preparation. If it is not possible to control the liquid level in the reflux tank, material can be discharged from V501 (pre-tower feed level tank) to keep the liquid level in V502 (pre-tower reflux tank) at a low level (around 20% is appropriate). After the analysis shows satisfactory results, the product can be separated. Remember to note down the operating parameters at this stage, such as the reflux rate, top temperature, and top pressure. Due to issues with the flow meter, no strict requirements are imposed on the reflux ratio; the product specifications prevail. At the beginning of the temperature increase in T501, PV5102 (the pre-tower pressure control valve, through which the material flows to the reflux tank after condensation) is used to regulate the pressure in T501. Once the pressure reaches 300 kPa, FV5501 can be fully opened; this valve is controlled by the regulator of the T504 reboiler E513, and its function is to regulate the amount of heat supplied from the distillate at the top of T501 to E513, thereby allowing all gaseous substances in the pipes and equipment to be discharged into V502. As the temperature in T501 and the pressure in V502 increase (but not above 300 kPa), the opening degree of FV5501 is gradually reduced until the flow rate measured before FV5501 becomes stable and free of fluctuations; at that point, closing FV5501 can be stopped. Afterwards, by reducing the opening degree of PV5102, the heat from the distillate at the top of T501 can be transferred to E513, thereby increasing the temperature of T504. The ideal situation is that the PV5102 opening is at zero and the pressure of T501 remains constant; however, it still needs to be opened if pressure increase is required. Heating E513 is possible only if T504 already contains some material. During the heating process, it is necessary to wait until there is liquid level in the reflux tank before enabling full reflux at low liquid levels; then, the degree of reflux should be gradually reduced to keep the temperature at the top of the tower within a controllable range. Sampling and analysis begin when the temperature of TE5503 reaches 75 degrees. Based on the results of these analyses, a decision is made as to whether to extract the product. If toluene is present in the product, it must be sent to V607 to maintain a low liquid level in V504, thereby facilitating rapid replacement with qualified material. Once the tests show that the material is qualified, the product can be extracted. Stable operation goes without saying; just maintaining a few balances is sufficient. In particular, one should be aware of the specific values of temperature, pressure, and liquid level during normal operation; as for flow rate, it is sufficient to simply monitor its trend.