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Four common problems in the operation of the distillation tower: Liquid flooding During the distillation operation, the liquid on the lower tray rushes to the upper tray. Flooding is the excessive accumulation of liquid in the tower, making it impossible for the liquid to flow from the top to the bottom of the tower, and the normal operation of the tower is damaged. This phenomenon is called flooding. 1. Jet entrainment. Flooding entrainment is caused by the jetting effect of liquid. If the steam velocity is too high, a large amount of mist will be entrained, and the liquid will accumulate on the upper tray instead of flowing down plate by plate. Generally, it occurs in the area where the liquid phase load is small, and the vapor-liquid contact is in a spray state. 2. Foam entrained liquid floods in the larger liquid phase load area, and the two phases are in a foam state when in contact. As the steam speed increases, the height of the foam layer on the board increases and the amount of entrainment increases. When the steam speed reaches a certain flooding speed, the foam level is close to the upper tray, and the entrainment increases sharply, causing liquid to accumulate on the upper tray and causing flooding. This kind of liquid flooding generally only occurs when the plate spacing is small (less than 375mm~450mm). When the plate spacing is large, it will transform into jet entrained liquid flooding. 3. The downcomer is overflowing due to the pressure drop caused by the vapor flow passing through the tray and the liquid layer on the plate, as well as the pressure drop of the liquid flowing through the downcomer, making the liquid level in the downcomer higher than the liquid level on the plate, and because the vapor-liquid mixture staying in the downcomer is a mixture of vapor and liquid, the liquid level rises higher. As the steam flow increases, the pressure drop also increases. ； As the liquid flow increases, the liquid layer on the plate thickens, increasing the luminous resistance, both of which cause the liquid level in the downcomer to rise. When the liquid level rises above the overflow weir height of the upper tray, the liquid no longer flows downward through the downcomer plate by plate, but flows backward, resulting in downcomer overflow. 4. Downdraft obstruction and liquid flooding. Measuring the pressure drop is the main means of judging liquid flooding. Measuring the pressure drop at each section of the vapor and liquid phase loads in the tower can more sensitively determine the occurrence and location of liquid flooding. Since liquid flooding causes liquid accumulation in the tower body, the pressure drop increases accordingly. To judge the liquid flooding phenomenon, the pressure drop is too large or rises sharply. Measuring the pressure drop is the main method to judge the liquid flooding. Measuring the pressure drop of each section of the vapor and liquid phase load in the tower can more sensitively judge the occurrence and location of the liquid flooding. Since the liquid flooding causes liquid accumulation in the tower body, the pressure drop increases accordingly. The liquid level at the bottom of the tower drops and fluctuates. Due to liquid flooding in a certain part of the tower, especially the part below the feed port, the liquid cannot overflow smoothly, and the reboiling vaporization continues, which will inevitably lead to a drop in the liquid level at the bottom of the tower. If the operating steam speed only slightly exceeds the liquid flooding speed, the control system will cause the steam speed to fluctuate up and down the flooding point. Then, liquid will sometimes accumulate in the tower, and sometimes liquid will drain out from the bottom of the tower. The liquid level at the bottom of the tower will also fluctuate accordingly. If the liquid flooding position is close to the bottom of the tower, the sign of liquid flooding will be more obvious. ； On the contrary, if it appears in the upper part of the tower and above the feed port, this sign is not obvious and there is a large lag. The amount of product at the bottom of the tower decreases or disappears. As the liquid level at the bottom of the tower drops, the control system will reduce the amount of product at the bottom of the tower by 2. When the liquid level drops seriously, the product will disappear. The disappearance of products at the bottom of the tower is a sign of flooding, but the products do not necessarily disappear when flooding occurs. As long as the flooding position is away from the bottom of the tower, especially at the upper part of the feed port, even if flooding occurs, the product at the bottom of the tower will not disappear but will only decrease. When the separation energy is significantly deteriorated and approaches flooding, the mist entrainment is already very serious. The agitation in the liquid accumulation section of the liquid flooding is violent, and the entrained foam in the liquid phase in the high-pressure tower also increases, resulting in a deterioration in her ability. This can be determined through product analysis, and increasing the reflux ratio does not improve the separation degree of the product. On the contrary, it becomes worse due to severe entrainment. Generally, significant deterioration in separation ability precedes the occurrence of flooding. On-site liquid flooding solution mist entrainment Mist entrainment refers to the liquid droplets brought by gas from the lower tray to the upper tray. During the mass transfer process, a large amount of mist entrainment will bring heavy components that should not go to the top of the tower into the product, thereby reducing the quality of the product. It will also reduce the concentration difference during the mass transfer process, but the tray efficiency will decrease. For a given tower, the maximum allowable entrainment of mist limits the rate of rise of the gas. There are many factors that affect the amount of mist entrainment, such as tray spacing, empty tower velocity, weir height, liquid flow velocity and physical and chemical properties of the material. It must also be pointed out: The amount of mist entrainment is also closely related to the structure of the collection device. Although there are many factors that affect the amount of mist entrainment, the most important factors are the empty column velocity and the gas-liquid separation space between the two trays. For a fixed tower, the amount of mist entrainment mainly increases with the increase of the empty tower velocity. However, if the distance between trays is increased and the separation space is enlarged, the superficial velocity will be increased accordingly. Liquid leakage is called liquid leakage, and the phenomenon that the liquid on the tray flows back from the ascending gas channel to the lower tray is called leakage. In the distillation operation, if the energy of the rising gas is not enough to pass through the liquid layer on the tray, or even lower than the potential energy of the liquid layer, then it will not be able to hold the liquid and leakage will occur. The lower the superficial velocity, the more severe the leakage. The result is that part of the liquid on the tray flows to the lower tray without contacting the rising gas, and the low-boiling-point components that should not remain in the liquid are not evaporated, resulting in a decrease in tray efficiency. Therefore, the minimum empty column velocity for suitable operation of the tray is limited by the amount of liquid leakage. Normal operation requires that the leakage amount of the tray should not be greater than 10% of the liquid volume on the tray. The size of the leakage is also one of the characteristics for evaluating the performance of the tray. The backmixing phenomenon occurs on a tray with a downcomer. The liquid crosses the tray and is in a cross-flow state with the gas. The concentration of volatile components in the liquid gradually decreases along the direction of flow. However, when the rising gas forms a vortex with the liquid on the tray, the liquid with high concentration and the liquid with low concentration are mixed together, destroying the concentration change of the liquid along the flow direction. This phenomenon is better known as backmixing. Backmixing can lead to a decrease in separation efficiency. The occurrence of backmixing is affected by many factors, such as residence time, liquid flow conditions, flow channel length, tray levelness, hydraulic gradient, etc.