【Daily Question】12.27 Short-answer question: Reasons for changes in the dry point of gasoline

Circulation volume, top temperature, top pressure, stripping steam, bottom gas volume, amount of contaminated oil recycled

The dry point of gasoline is affected by factors such as the pressure and temperature at the top of the tower, the temperature of the feed material, changes in the composition of the feed entering the tower, changes in the flow rate of the mid-stage reflux, changes in the flow rate of the side products, as well as the pressure and flow rate of the gas blown at the bottom of the tower. If the flow rate of reflux at the top of the tower is too low, there is insufficient internal reflux, which results in a poorer distillation effect and thus changes in the dry point of gasoline

Reasons for changes in the dry point of gasoline: The reasons for changes in the dry point of gasoline are as follows: (1) Changes in the temperature and pressure at the top of the distillation tower； (2) Amount of water injected, amount of stripping gas, or amount of steam supplied to the vapor seal in the coke tower ； (3) Backflow of water or interruption ； (4) Reflux flow and temperature changes at each stage of the distillation column ； (5) Failure of the tower top temperature control instrument ； (6) Poor distillation efficiency of the tray ； (7) Fault inside the tower or excessive load.

The dry point of gasoline is influenced by the temperature and pressure at the top of the tower, the temperature of the feed entering the tower, changes in the density of the feed, variations in the flow rate and temperature of the reflux at intermediate stages, changes in the flow rate of side products, the pressure and flow rate of steam supplied to the bottom of the tower, whether the reflux oil from the top of the tower contains water, and any salt deposition or blockages in the tower trays. Too little reflux at the top of the tower, insufficient internal reflux, and poor distillation efficiency can cause changes in the dry point of gasoline.

(1) Changes in the temperature and pressure at the top of the distillation column； (2) Amount of water injected, amount of stripping gas, or amount of steam supplied to the vapor seal in the coke tower ； (3) Backflow of water or interruption ； (4) Reflux flow and temperature changes at each stage of the distillation column ； (5) Failure of the tower top temperature control instrument ； (6) Poor distillation efficiency of the tray ； (7) Fault inside the tower or excessive load.

Reasons for changes in the dry point of gasoline: The dry point of gasoline is influenced by the temperature and pressure at the top of the tower, the temperature of the feed material entering the tower, changes in the density of the feed material, changes in the flow rate and temperature of the reflow from the middle section of the tower, changes in the flow rate of the side products, the pressure and flow rate of the steam supplied to the bottom of the tower, whether the reflow oil from the top of the tower contains water, and any salt deposition or blockages in the tower trays. Too little reflux at the top of the tower, insufficient internal reflux, and poor distillation efficiency can cause changes in the dry point of gasoline. The tower top temperature is the main means of adjusting the dry point of gasoline; when the tower top pressure decreases, the tower top temperature should be reduced appropriately, and when the pressure increases, it should be increased appropriately. When the feed to the tower becomes lighter, the dry point of gasoline decreases, and the top temperature of the tower should be increased. A sudden drop in the reflux flow rate in the middle section, along with an increase in the temperature of the reflux oil, causes heat to move upward in that part of the tower, resulting in an increase in the dry point of gasoline; it is therefore necessary to stabilize the reflux flow rate in the middle section. When the distillate volume from the first column is too high, the amount of oil returning to the column decreases, resulting in poor fractionation; this can lead to an increase in the dry point of gasoline. It is therefore necessary to stabilize the distillate volume from the first column. High steam injection pressure at the bottom of the tower, large opening of the steam injection valves, high volume of steam injected, high steam velocity, and high liquid level at the tower bottom – all these factors cause steam to carry heavier components, resulting in heavier products in the various side streams, as well as a higher dry point for the gasoline at the top of the tower. Water in the reflux oil can cause an increase in the dry point of the gasoline at the top of the tower; it is essential to properly dehydrate the reflux oil tank. An increase in tray pressure drop leads to salt scaling; this scaling should be removed to improve the distillation efficiency. Insufficient reflux at the tower top and inadequate internal reflux can cause the dry point of the gasoline at the tower top to increase. It is necessary to appropriately reduce the reflux flow at the middle stages 1 and 2, and increase the top reflux or top circulation reflux flow, in order to improve the distillation efficiency at the tower top and ensure that the dry point of the gasoline there is within acceptable limits. When the water content in the crude oil fed into the initial distillation tower increases, although the pressure at the top of the tower rises, the presence of large amounts of water vapor reduces the vapor pressure of the oil and gas, which in turn raises the dry point of the gasoline at the tower top. It is therefore essential to carry out effective electrodialysis desalination and dehydration processes.

Answer: The dry point of gasoline is affected by the temperature and pressure at the top of the tower, the temperature of the feed material entering the tower, changes in the composition of that feed material, changes in the amount of material recycled from the middle section of the tower, changes in the flow rate of side products, as well as the pressure and flow rate of steam supplied to the bottom of the tower. If the amount of material recycled from the top of the tower is too low, there is insufficient internal recirculation, which results in a poorer distillation effect and thus changes in the dry point of gasoline.

1) Fluctuations in top temperature: Strengthen control of the tower top temperature and adjust the reflux rate to ensure good gasoline quality； 2) Adjust the top temperature appropriately at the stable operating point, in response to changes in top pressure, furnace temperature, and steam injection rate ； 3) Return water to the system, enhance the oil-water separator, control the oil-water interface, and adjust the top temperature of the tower ； 4) Changes in the properties of the raw materials: Adjust the top temperature based on changes in the dry point of gasoline ； 5) Overload, reduce load.

Reasons for changes in the dry point of gasoline: The dry point of gasoline is influenced by the temperature and pressure at the top of the tower, the temperature of the feed material entering the tower, changes in the density of the feed material, changes in the flow rate and temperature of the reflow from the middle section of the tower, changes in the flow rate of the side products, the pressure and flow rate of the steam supplied to the bottom of the tower, whether the reflow oil from the top of the tower contains water, and any salt deposition or blockages in the tower trays. Too little reflux at the top of the tower, insufficient internal reflux, and poor distillation efficiency can cause changes in the dry point of gasoline.

(1) Changes in the temperature and pressure at the top of the distillation column； (2) Amount of water injected, amount of stripping gas, or amount of steam supplied to the vapor seal in the coke tower ； (3) Backflow of water or interruption ； (4) Reflux flow and temperature changes at each stage of the distillation column ； (5) Failure of the tower top temperature control instrument ； (6) Poor distillation efficiency of the tray ； (7) Fault inside the tower or excessive load.