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1. Factors affecting distillation operations. Apart from equipment issues, the main factors affecting the distillation process include the following: the temperature and pressure of the tower (including the top, bottom of the tower, and certain trays of special significance) ； Feeding status ； Feed rate ； Feed composition ； Feed temperature ； Steam rise velocity in the tower and heating capacity of the evaporation kettle ； Backflow volume ； Top condenser cooling capacity ； Top draw rate and bottom draw rate. The operation of the tower involves adjusting these influencing factors in accordance with the composition requirements of the products at the top and bottom of the tower. 2. Effect of changes in feed composition on distillation operations. Changes in the feed composition have a direct impact on distillation operations; as the concentration of heavy components in the feed increases, the load on the distillation section rises. For a tower with a fixed number of rectification section plates, this will result in the heavier components being carried to the top of the tower, causing the quality of the product at the top to be substandard. If the concentration of the light components in the feed increases, the load on the stripping section increases. For a column with a fixed number of trays in the stripping section, this will result in incomplete evaporation of the light components in that section, leading to an increased loss of light components in the bottom liquid. At the same time, changes in the feed composition will also cause changes in the material balance of the entire tower and the process conditions. As the composition becomes lighter, the overhead distillate increases while the amount of liquid discharged from the reactor decreases. At the same time, the temperature of the entire tower decreases while the tower pressure increases. The component becomes heavier; the situation is the opposite. When the feed composition changes, the following measures can be taken. (1) Improve the feed port. When the component becomes heavier, adjust the feed inlet downward ； When the component becomes lighter, move the feed inlet upward. (2) Change the reflux ratio. Increase the reflux ratio when the component weight increases ； When the component becomes lighter, reduce the reflux ratio. (3) Adjust the refrigerant and heat dosage. Based on changes in the composition, the amount of refrigerant at the top of the tower and the heat input at the bottom of the tower are adjusted accordingly to maintain constant product quality at both the top and the bottom. 3. What are the different feeding conditions, and what impact do they have on distillation operations? 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, changing to a cold feed means that the liquid enters the tower and comes into contact with the vapor rising from the stripping section on the feeding tray, 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 to restore the reflux rate of the column to its original level. 4. What is the impact of the feed rate on distillation operations? There are two scenarios: (l) when the range of feed flow variations does not exceed the load ranges of the top condenser and the heating vessel, proper adjustment will result in no significant changes in the top temperature and vessel temperature; instead, it only affects the velocity of the steam rising within the tower. (2) When the range of feed rate variations exceeds the load range of the top condenser and heating device, 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 amount 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. 5. What is the effect of changes in feed temperature on distillation operations? Changes in feed temperature have a significant impact on distillation operations. A low feed temperature increases the heat load on the heating tank 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? The amount of coolant at the top of the tower causes changes in the reflux flow 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 amount taken from the tower top on distillation operations? The amount of material taken out from the top of the tower is closely related to the feed rate: as the feed rate increases or decreases, the amount of material taken out also increases or decreases accordingly, so as to maintain a constant reflux ratio within the tower and ensure its proper operation. If the feed remains unchanged and the amount taken from the top of the tower is increased, this will lead to a decrease in the reflux ratio and a drop in operating pressure, causing the heavier components to reach the top of the tower and resulting in substandard product. Reducing the draw rate leads to an increase in the reflux ratio, more material remaining in the tower, an increased velocity of the rising steam, and a greater pressure difference between the top and bottom of the tower. Over time, this can result in flooding, thereby causing the product at the bottom of the tower to be of substandard quality. 8. What is the impact of the bottom product yield on distillation operations? 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 amount of liquid that circulates through the reboiler. This leads to poor heat transfer, preventing the light components from evaporating, and as a result, both the products at the top and bottom of the tower are of substandard quality. If the amount of product removed from 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 drop in the temperature of the liquid in the tower, 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. 9. What is forced reflux? What is natural backflow? What are their respective advantages and disadvantages? Reflux is introduced into the tower using a pump; a reflux system in which a 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 reflux 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 reflux can be used when the tower is 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 move 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 turns slowly when production is abnormal, and the plant requires a frame structure. 10. How is the pressure in the tower adjusted during distillation operations? What are the factors that affect tower pressure? 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 product quality that does not meet standards; therefore, distillation operations must be kept 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 expansion element, 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. Additionally, instrument failures and freezing of equipment and pipelines can also cause changes in tower pressure. 11. How to adjust the reactor temperature in distillation operations? What are the factors that cause fluctuations in the kettle temperature? Usually, the temperature of the kettle is adjusted by changing the amount of steam supplied to it. Increase the steam volume, and the temperature of the kettle rises ； Reducing the steam volume causes the temperature of the kettle 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 bottom to the heating reactor – all of these can lead to fluctuations in the reactor temperature. 12. How is the pressure difference in a distillation column adjusted during its operation? 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 streams in the distillation process are in balance. With a balanced feed and discharge and a constant reflux ratio, the pressure difference across the tower 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 changing the amount taken from the top of the tower while keeping the feed constant, the pressure difference can be altered. Low differential pressure when removed ； If less is taken out, the pressure difference in the tower will become greater and greater. (2) When the draw rate remains constant, use feed to adjust the pressure difference ； As the feed rate increases, the tower pressure difference rises; conversely, it falls. (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. 13. What are the purposes and methods of reboiler preheating? Purpose of preheating the reboiler: (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 starts to spray from the vent valves. 14. What are the means for controlling the liquid level in the tower bottom? The liquid level in the tower bottom is controlled by adjusting the amount of liquid taken out from the tower bottom; as the liquid level rises, the discharge volume increases, and as the liquid level drops, the discharge volume decreases. There is also a method of controlling the liquid level in the reactor using the heat input of the heating vessel; as the liquid level rises, the heat input increases. Only when the liquid level in the bottom of the tower is stable can heat transfer at the bottom of the tower be maintained stable, which in turn ensures stability in aspects such as the temperature at the bottom of the tower, the flow rate of steam rising within the tower, and the composition of the liquid at the bottom of the tower; this is essential to ensure the proper operation of the tower. 15. What are the factors that affect changes in the level of liquid in the reactor? The main reasons are as follows: (1) Changes in the composition of the reactor liquid. By reducing the reactor temperature while keeping the pressure constant, the gas-liquid equilibrium composition at the bottom of the tower is altered, resulting in an increase in the amount of reactor liquid and in the concentration of light components within it. With the extraction of the kettle liquid remaining unchanged, it will cause the level of the kettle liquid to rise. When this phenomenon occurs, the normal kettle temperature should be restored first; otherwise, a large amount of light components will be lost. (2) Changes in feed composition: When the content of heavy components in the feed increases, according to material balance, the volume of liquid in the reactor will increase. In such cases, the discharge rate of this liquid from the reactor must be increased accordingly; otherwise, the liquid level in the reactor will rise. If the normal discharge rate of the reactor liquid is maintained while raising the reactor temperature to keep the liquid level at a normal level, this will cause the heavier components to reach the top of the tower, resulting in a decline in the quality of the product at the tower top. (3) Change in feed rate: As the feed rate increases, the discharge volume of the reactor liquid should increase accordingly; otherwise, the level of the reactor liquid will rise. (4) Failure of the adjustment mechanism: When the adjustment mechanism fails, it should automatically switch to manual adjustment, and maintenance personnel should be contacted at the same time. (5) At the beginning of operation, due to the small amount of liquid on the trays, proper gas-liquid contact has not yet been established; as a result, a large amount of light components easily enter the bottom of the tower. The amount of these components that can be vaporized in the bottom of the tower is not sufficient to meet the heat requirements inside the tower at that time. Therefore, for a tower that has just been put into use, the heating vessel should be preheated appropriately before feeding begins. Once a liquid level is visible in the vessel, an appropriate amount of heat should be supplied; otherwise, it will be difficult to raise the temperature of the vessel, the liquid level inside it will rise too high, and the volume of liquid discharged from the vessel will increase, resulting in greater loss of the light components in the liquid. What impact does the installation of the tower have on distillation operations? If the tower body, tray plates, overflow ports, etc., are not installed in accordance with the requirements, it is possible for this to affect the distillation process. (1) Tower body: The tower body must be vertical; the allowable inclination is generally no more than one in a thousand. Otherwise, dead zones will form on the tray surfaces. In the case of distillation towers with small diameters, if the trays are installed in sections first and then assembled, any deviation in the verticality of the tower body will directly affect the levelness of all the trays in the tower, thereby reducing its efficiency. (2) The trays must be level; the levelness, as measured with a level, shall not exceed ±2 millimeters. (3) Distance between the overflow port and the lower tray: This is determined based on the production capacity and the height of the overflow weir of the lower tray; however, it is necessary that the overflow port be submerged in the liquid within the liquid receiving tray in order to seal off the rising steam. If the overflow port is too close to the lower tray, it may prevent the reflux from the upper trays from flowing properly into the lower trays. This leads to an increase in the liquid level in the upper trays and an increase in pressure in the lower trays; in severe cases, this can result in flooding. If the overflow port is too high, exceeding the height of the overflow weir, the rising steam takes a shortcut, rising directly from the overflow pipe to the upper tray levels, failing to serve as a liquid seal and thus affecting the efficiency of the trays. During installation, various specific types of trays have different requirements; failing to follow these requirements may result in a **17% decrease in the tower’s production efficiency. How should the position of the feed inlet be adjusted in distillation operations? A distillation tower usually has three feed inlets, installed at different heights within the tower. As implied by the concept of the optimal feed plate position, for a distillation column fed at or near the bubble point, the selection of the feed inlet is determined based on ensuring that the composition of the feed matches that of the feed plate. Generally speaking, when the proportion of volatile components in the mixture to be separated increases, a feed inlet located at a higher position should be used; the feed inlet should also be adjusted accordingly when the feeding conditions change. When the feed temperature decreases, a feed inlet at a higher position should be utilized ； Conversely, a lower feed port 18 is used. For a distillation column that employs forced reflux, what causes the sudden interruption of the reflux? How to deal with it? The reason for the sudden interruption of the reflux flow could be a motor trip in the reflux pump ； The material in the reflux liquid tank was evacuated ； The reflux liquid pump cannot deliver fluid ； For low-boiling reflux liquids, due to excessively high temperatures or insufficient pump output, the material vaporizes inside the pump and fails to flow upward.