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1. What are the factors that affect the operation of a distillation tower? Answer: The factors that affect distillation operations are as follows: (1) The influence of the reflux ratio ； (2) Influence of feed condition ； (3) Influence of feed rate size ； (4) Effect of changes in feed composition ； (5) Effect of feed temperature variations ； (6) Influence of the amount of cooling agent at the tower top ； (7) Influence of the top extraction volume ； (8) Influence of the bottom of tower production volume. 2. What are the different feeding conditions, and what impact do they have on distillation operations? Answer: There are five feeding states: (1) Cold feeding ； (2) Saturated liquid ； (3) Gas-liquid mixture ； (4) Saturated gas ； (5) Superheated gas. For a column with a fixed feed, changes in the feed condition will affect product quality and losses. For example: if a tower is fed with saturated liquid, switching to a cold feed causes the liquid to encounter the vapor rising from the stripping section on the feeding tray upon entering the tower, where it is heated to the saturation temperature. At the same time, part of the rising vapor condenses. An excessive number of trays in the distillation section and an insufficient number of trays in the stripping section result in increased losses in the bottom liquid. At this point, in terms of operation, the reboiler steam should be adjusted appropriately so that the reflux flow rate to the tower returns to its original level. 3. What is the impact of the feed rate on distillation operations? Answer: There are two scenarios: (1) When the fluctuation range of the feed rate remains within the load capacity of the top condenser and the heating vessel, proper adjustment will not result in significant changes in the top temperature or the vessel temperature; it will only affect the velocity of the steam rising inside the tower. (2) When the range of feed flow variation exceeds the load range of the top condenser and heaters, it not only affects the change in the upward steam velocity within the tower but also alters the temperatures at the top and bottom of the tower, thereby changing the gas-liquid equilibrium composition on the tray columns. This directly impacts the quality of the product at the top of the tower as well as the losses at the bottom of the tower. In short, excessive fluctuations in the feed rate will disrupt the normal material balance and process conditions within the tower, resulting in a series of fluctuations. Therefore, the feed should be balanced and adjusted carefully. 4. What is the impact of changes in feed composition on distillation operations? Answer: Changes in the composition of the feed directly affect distillation operations. When the proportion of heavy components in the feed increases, the load on the distillation section rises, which can lead to those heavy components reaching the top of the tower and resulting in substandard product at the top. If the proportion of light components in the feed increases, the load on the stripping section increases as well, potentially leading to greater losses of light components in the bottom liquid. Changes in the feed composition also lead to changes in material balance and process conditions. 5. What is the impact of changes in feed temperature on distillation operations? Answer: Changes in feed temperature have a significant impact on distillation operations. A low feed temperature increases the heat load on the heating vessel and reduces the cooling load on the top condenser. The same is true in reverse. When the feed temperature changes significantly, it usually affects the temperature of the entire tower, thereby altering the vapor-liquid equilibrium. Furthermore, changes in the feed temperature lead to changes in the feed conditions, which in turn affect the load on the distillation section and the stripping section; this results in changes in product quality as well as in material balance. Therefore, the feed temperature is one of the important factors affecting distillation operations. 6. What is the impact of the amount of coolant at the top of the tower on distillation operations? Answer: The amount of coolant at the top of the tower affects the reflux rate and reflux temperature. As the cold dose increases, the reflux flow also increases, and the top temperature of the tower drops ； A decrease in the cooling capacity leads to a reduction in the reflux flow, which in turn causes the top temperature to rise; therefore, the cooling capacity at the tower top must be appropriate. 7. What is the impact of the bottom product flow rate on distillation operations? Answer: In distillation operations, the liquid level in the tower bottom must remain stable, and the amount of product taken from the bottom of the tower can cause changes in this liquid level. When too much liquid from the bottom of the tower is discharged, it causes the liquid level in the tank to drop or even become empty, reducing the circulation volume of the liquid through the reboiler. This leads to poor heat transfer, preventing the light components from evaporating, and as a result, both the product at the top of the tower and that at the bottom are of substandard quality. If the draw rate at the bottom of the tower is too low, it will cause the liquid level in the tower bottom to rise excessively; in severe cases, it may even exceed the vaporization pipe. This increases the resistance to the circulation of the liquid in the tower, leading to poor heat transfer, a decrease in the tower temperature, and difficulties in operation. The level of the liquid in the kettle is too low; once it is emptied, the pump will be unable to draw fluid, which can damage the equipment and lead to accidents. 8. What is pressure distillation? Answer: A distillation process that operates at a pressure higher than atmospheric pressure is called pressurized distillation. Pressure distillation is often used when the boiling points of the mixtures to be separated are low. If, under normal temperature and pressure, the mixture is in a gaseous state, pressurized distillation is used. Because, in terms of the distillation process, achieving a higher pressure ratio compared to a lower one is more economical in terms of equipment and energy consumption. 9. What is vacuum distillation? Answer: The distillation process in which the pressure at the top of the tower is lower than atmospheric pressure is called vacuum distillation. Vacuum distillation is commonly used to separate mixtures with high boiling points or those that tend to polymerize at high temperatures. Vacuum separation is used for the separation of substances such as ethylbenzene and styrene, as well as for the separation of diethylbenzene, triethylbenzene, tetraethylbenzene, and other components with higher boiling points. 10. What is a sensitive plate? Why use a sensitive plate to control the reactor temperature? Answer: In the plate-by-plate calculation of a distillation column, it is often found that the composition of a certain plate differs significantly from that of the adjacent plates, resulting in large temperature changes as well. When operating conditions change, this plate experiences the most significant temperature changes; hence, it is called a sensitive plate. The advantage of using a sensitive plate for control is: (1) high sensitivity and accurate adjustment. (2) It is possible to anticipate the trend in changes of the material in the bottom of the tower and make adjustments in advance, thereby preventing light components from entering the liquid in the tank. 11. What is the distillation section? What is a stripping section? What is the basis for changing the feed inlet in distillation operations? Answer: Taking the feed inlet as a reference, the area above the feed inlet is called the distillation section, while the area below the feed inlet is called the stripping section. Changing the feed inlet in distillation operations should be considered based on changes in feed composition, as well as the purity of the top product and the losses at the bottom of the tower. When the component becomes heavier, move the feed inlet downward ； When the component becomes lighter, move the feed inlet upward. Use the intermediate feed port when the composition is normal. Additionally, when the quality of the product at the top of the tower declines, the feed inlet is moved downward ； When the reboiler bottom loss increases, move the feed inlet upward. 12. What is forced reflux? What is natural backflow? What are their respective advantages and disadvantages? Answer: Reflux is introduced into the tower using a pump; a reflux system in which the reflux condenser does not need to be installed at the top of the tower is called forced reflux. The reflux condenser is installed at the top of the tower; the method in which the reflux liquid returns to the tower under the force of gravity is known as natural reflux. The amount of forced backflow is stable and easy to adjust; it can be adjusted quickly in case of production abnormalities. The factory building does not need to have a high-frame structure, and forced backflow can be used when the tower is very tall, making installation convenient. However, forced reflux requires a reflux pump, which consumes a lot of energy; especially materials with low boiling points can make it difficult for the pump to transport the fluid. Natural reflux is simple to operate; no reflux pump is required, saving energy. However, the reflux flow changes with tower pressure; the reflux ratio is not precise, it takes time to respond when production is abnormal, and the plant requires a frame structure. 13. How is the pressure in the tower adjusted during distillation operations? What are the factors that affect tower pressure? Answer: Tower pressure is one of the main control parameters in distillation operations. Excessive fluctuations in tower pressure can disrupt the material balance and gas-liquid equilibrium throughout the tower, resulting in substandard product quality; therefore, the operation of the distillation unit must be stable. Methods for adjusting tower pressure include: (1) When the top condenser is a fractional condenser, the tower pressure is generally adjusted based on the amount of vapor product taken from the top of the tower. Remove the increase, and the tower pressure drops ； The drawdown decreases, and the tower pressure rises. (2) If the steam consumption in the reboiler is too high and the reflux volume is large, the tower pressure increases; in such cases, the steam supply should be reduced appropriately to regulate the pressure at the bottom of the tower. The factors that affect the variation in column pressure are: ① top temperature of the column, ② bottom temperature of the column, ③ feed composition, ④ feed rate, ⑤ reflux rate, ⑥ refrigerant amount and refrigerant pressure. Furthermore, instrument failures and freezing of equipment and pipelines can also cause changes in tower pressure. 14. How to adjust the kettle temperature in distillation operations? What are the factors that cause fluctuations in the kettle temperature? Answer: Usually, the temperature of the reactor is adjusted by changing the amount of steam supplied to the heating vessel. Increase the steam supply, and the temperature of the kettle rises ； Reducing the steam volume causes the reactor temperature to drop. There are also methods that involve adjusting the temperature of the heating tank by changing the level of the liquid in the tank; by increasing the discharge rate and lowering the liquid level, the tank temperature rises ； Emissions are reduced, the liquid level rises, and the reactor temperature drops. Factors that cause fluctuations in the temperature of the reactor include: sudden increases and decreases in tower pressure, fluctuations in the liquid level at the bottom of the tower, fluctuations in the pressure of the heating steam, malfunctioning control valves, malfunctioning traps that result in an excess of condensate inside the heating reactor, polymerization within the heating reactor, and blockages in the pipes connecting the tower and the heating reactor – all of these can lead to fluctuations in the reactor temperature. 15. How is the pressure difference in a distillation column adjusted during its operation? Answer: The tower pressure difference is a key factor in determining the gas load within the tower, and it is also one of the important indicators for judging whether the feed and product flows in the distillation operation are balanced. With a balanced feed and discharge and a constant reflux ratio, the tower pressure difference remains essentially unchanged. When the tower pressure difference changes, corresponding adjustments should be made based on the cause of that change. There are three common methods: (1) By keeping the feed constant, changing the amount taken from the top of the tower can alter the pressure difference. Low differential pressure when removed ； If less is taken out, the pressure difference in the tower will become greater and greater. (2) When the extraction rate remains constant, use feed to adjust the pressure difference ； When the feed rate is high, the tower pressure difference increases; otherwise, it decreases. (3) Within the allowable range of process parameters, the pressure difference is adjusted by changing the reactor temperature ； Increasing the kettle temperature raises the pressure difference ； Lowering the kettle temperature results in a decrease in pressure difference. 16. What are the purposes and methods of reboiler preheating? Answer: The purpose of preheating the reboiler is: (1) to remove non-condensable gases from within the reboiler, so as to avoid affecting the heat transfer area ； (2) When metal is suddenly exposed to high temperatures, its internal crystal structure can easily be disrupted, which affects its mechanical properties and leads to creep; in severe cases, this can cause the metal to break. Therefore, the reboiler needs to be preheated to prevent deformation or cracking that could disrupt normal production. Reboiler preheating method: Open the vent valves of the reboiler and the level tank, and slowly preheat it using steam bypass until liquid begins to spray from the vent valves. 17. What are the means for controlling the liquid level in the tower bottom? Answer: The bottom liquid level of the tower is controlled by adjusting the amount taken out from the tower bottom.