In chemical plant production, distillation tower is the most common, typical separation equipment, anyone engaged in chemical production of distillation tower will not be unfamiliar, but the operation of the distillation tower common outstanding problems, such as: liquid flooding, flooding tower, rushing tower phenomena are not clear about the reasons.

　　However, the causes of common outstanding problems in the operation of the distillation tower, such as: liquid flooding, flooding tower, rushing tower phenomenon, are not very clear, the problem for the tower of parameter changes are not sensitive to the reaction, which often delays the resolution of the problem, affecting the production of the device.

　　01 liquid flooding phenomenon

　　1, what is liquid flooding?

　　In the distillation tower, due to a variety of reasons caused by the liquid phase buildup over the range of the space in which it is located, known as liquid flooding. Liquid flooding can be divided into drop tube liquid flooding, spray entrainment liquid flooding.

　　Liquid flooding of the drop tube refers to the liquid phase in the drop tube accumulates to the last layer of the tower plate. Foam entrainment liquid flooding refers to the gas phase flow rate in the open space on the tower plate reaches a certain speed, so that the liquid phase on the tower plate accompanied by the rising gas phase into the previous layer of the tower plate.

　　The operating condition at which the liquid flood is generated is called the liquid flood point. In the design of the distillation column, must control to maintain the liquid flood rate within a certain range to ensure the stable operation of the distillation column. At the beginning of liquid flooding, the pressure drop of the tower rises sharply and the efficiency drops sharply. Subsequently, the operation of the tower is destroyed.

　　2, the causes of liquid flooding phenomenon?

　　1) the liquid in the drop tube backflow back to the upper plate

　　As the tower plate on the rising gas flow resistance, the pressure above the lower plate than the pressure above the upper plate, the height of the foam in the drop tube is equivalent to the static pressure head to overcome this pressure difference, the liquid can flow down.

　　When the liquid flow rate is unchanged and the gas flow rate is increased, the pressure difference between the lower plate and the upper plate also increases, and the liquid level in the descending tube rises.

　　If the gas flow increases to make the liquid in the liquid drop tube rises to the top of the weir, the liquid in the tube will not only can not flow down, but began to flow back up to the upper plate, the plate will begin to accumulate liquid; to operate continuously from the liquid outside the tower into the final will be

　　Make the whole tower full of liquid. The formation of liquid flooding.

　　If the gas flow rate is certain and the liquid flow rate increase, the liquid through the drop tube resistance increases, as well as the liquid layer on the plate thickening, so that the pressure difference between the plate above and below increases, will make the drop tube liquid level rises, thus leading to liquid flooding.

　　2) Excessive liquid foam entrainment to the upper plate

　　Air entrainment to the last layer of liquid foam on the board, can make the board on the liquid layer thickening, the normal increase to a certain extent, the thickening of the liquid layer will be significant (the amount of liquid on the board to increase the number of bubbles to add more, increase). Airflow through the thickened layer of liquid brought out by the liquid foam and further increase.

　　Further increase. This excessive liquid foam entrainment so that the distance between the top of the foam layer and the bottom of the last layer of the plate is narrowed, the liquid foam entrainment continues unabated, large droplets are easy to spray directly to the last layer of the plate, the foam can be bubbled up to the last layer of the plate, and ultimately the whole tower is filled with liquid.

　　The whole tower is filled with liquid.

　　3、How many kinds of liquid flooding phenomenon?

　　1)The pressure difference between the bottom and the top of the tower increases; 2)The pressure difference between the bottom and the top of the tower increases; 3)The liquid flooding phenomenon has several kinds.

　　2) The temperature difference between the bottom and top of the tower decreases.

　　3) The liquid level in the return tank at the top of the tower decreases; 4) The product at the bottom of the tower decreases.

　　4) Decrease in product yield at the bottom of the tower.

　　5) The product quality at the top and bottom of the tower are unqualified.

　　4、What methods to deal with?

　　1) Rectify the gap at the bottom of the liquid drop plate; 2) Reduce the amount of rising steam.

　　2) reduce the amount of rising steam.

　　3) reduce the amount of feed.

　　4) Reduce the amount of steam, return flow.

　　Note: the above two contributing causes of liquid flooding, the more common is excessive liquid foam entrainment.

　　02 Flooded tower phenomenon

　　In the distillation process, from a plate up the liquid gradually accumulated to fill part of the tower section, so that the rising gas is blocked, gas, liquid and two-phase mass and heat transfer process can not be carried out normally, which is called flooding tower.

　　1, the phenomenon of tower flooding is: the top of the tower temperature drop; reflux tank level drop; the bottom of the tower liquid level and pressure increase.

　　2, leading to the flooding of the reasons for the occurrence of the tower

　　1) Settling tube blocked, reflux liquid can not flow down

　　Iron filings, welding slag and other debris at the start of normal production in the deposition of equipment corrosion, or the precipitation of solids in the liquid, the solution of self-polymerization, are prone to cause the descending liquid pipe blockage.

　　2) The amount of liquid is too large, so that the drop tube is overloaded

　　3, treatment methods are

　　1) Appropriately reduce the amount of feed and return flow.

　　2) If the equipment failure, then stop work to deal with.

　　03 Punch tower phenomenon

　　Distillation tower in normal operation, the gas and liquid phase load is relatively stable. When the gas-liquid phase load are too large, the gas pressure drop through the tower plate increases, will make the liquid level in the drop tube increases; liquid phase load increases, the liquid level on the exit weir increases. When the liquid

　　When the liquid filled with the entire drop tube, the upper and lower tower plate connected to a piece, the fractionation is completely destroyed, there will be a tower.

　　1, the reason for the tower is: all the formation of the tower gas-liquid phase load is too large a factor can cause the tower, such as the amount of crude oil handling, raw materials, raw material nature of too light, the water content of crude oil into the tower, the bottom of the tower blowing amount of steam, feed temperature is too high, reflux interruptions or uneven distribution, and so on.

　　2, the phenomenon: the occurrence of tower rushing, due to the tower fractionation effect becomes worse, destroying the normal mass and heat transfer, resulting in the tower temperature, pressure, side line distillation outlet temperature, reflux temperature are rising, the tower low level suddenly drop, distillate oil color becomes black.

　　3, the principle of treatment: is to reduce the steam-liquid load, that is, to reduce the return flow and the bottom of the tower heating steam, if because of the processing volume is too large, you can reduce the amount of feed. If necessary, you can interrupt the feed, shut down the bottom of the tower heating steam, to wait for the temperature of each layer of the tower plate back down to

　　After the temperature of each layer of the tower plate falls below the normal value, then re-heat and feed.

　　4, data analysis

　　By stabilizing the tower parameter changes can be seen:

　　1) the separation effect of the tower has deteriorated, the purity of the product at the bottom of the tower is reduced, resulting in increasing the amount of steam in the case of sensitive plate temperature is still lower than the normal production of the indicators.

　　2) the top of the tower pressure is unchanged, increase the return flow, reflux under the tower disk temperature is still higher than the normal index value, indicating that the top of the tower product purity is reduced, the separation effect has become worse;.

　　3) Sensitive plate (3rd layer tower plate) and the 21st layer of tower plate temperature difference is significantly smaller, indicating that the lower tower plate light component increase, the upper tower plate heavy component increase, while the bottom of the tower level can still be controlled normally, it can be judged that the tower appeared in a serious liquid flooding phenomenon. If the

　　Punching the tower will rapidly reduce the level at the bottom of the tower, which is the obvious difference between the punch tower and liquid flooding.

　　5, the cause

　　For has been designed and normal operation of the distillation tower, in the composition of raw materials does not change much in the case of the phenomenon of flushing or liquid flooding, should be analyzed mainly from the operation.

　　From the comparative data in the above chart when the stabilizer column is liquid flooded, it can be seen that the return flow rate of the stabilizer column and the amount of heated steam at the bottom of the column are higher than normal, which is the most common operation that leads to the occurrence of liquid flooding.

　　Operators are not experienced, do not have a deep understanding of the operation of the distillation tower, when the temperature of the sensitive plate is low, increase the amount of heating steam at the bottom of the tower, when the temperature at the top of the tower is high and increase the flow rate, and so on and so forth, resulting in heating steam and flow rate is too large, the gas

　　The load of the gas and liquid phases greatly exceeded the design load of the tower, resulting in liquid flooding, and the gas-liquid equilibrium in the tower was damaged.

　　After the liquid flooding phenomenon in this stabilizer tower, the return flow rate and the steam volume at the bottom of the tower were readjusted, but after 16 hours the tower still did not reach a normal equilibrium state. Finally, the measures of shutting down the heating steam, stopping the feed and lowering the temperature were taken, and the tower was put into operation again before adjusting normally.

　　The stabilizer was put back into operation and adjusted to normal.