Key Points for Steady Operation of Distillation Columns (Practical Guide for Operators)

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The distillation tower is the core of a vacuum and atmospheric pressure unit; the stability of its operation directly determines the product quality, the energy consumption of the unit, and safe production. To ensure that the distillation tower operates stably over the long term with minimal fluctuations, on-site operations must focus on three key aspects: material balance, heat balance, and gas-liquid balance. Specifically, the following measures should be taken: 1. Stabilize the feed rate and the flow rates of material drawn from various lines; strictly control the amount of crude oil fed in, avoiding large changes in these amounts. Adjustments to the draw rates at the bottom of the tower and along the various side lines should be made in small amounts and slowly, with precise adjustments based on product quality and yield. It is strictly prohibited to make large fluctuations in these rates, in order to prevent severe variations in the load inside the tower. 2. Strictly control the temperature at various points to maintain thermal equilibrium throughout the tower. The feed temperature, furnace outlet temperature, tower top temperature, side stream distillation temperature, and reflux temperature all need to be kept under stable control. When there are slight fluctuations in temperature, make timely fine adjustments and take preemptive action to prevent large swings in temperature from disrupting the distillation process throughout the tower. 3. Coordinate the series operation of the three towers, taking into account both the front and back stages. The initial distillation tower, the atmospheric pressure tower, and the vacuum distillation tower are connected in sequence; instability in the earlier towers will inevitably affect those downstream. During operation, it is necessary to consider trends in a sequential manner. When the properties of crude oil change, adjustments should be made in the order of the initial distillation tower → atmospheric distillation tower → vacuum distillation tower, to avoid system imbalance caused by simultaneous adjustments at multiple points. 4. Stabilize the liquid level at the bottom of the tower and the amount of stripping steam. The liquid level at the bottom of the tower is crucial for the material balance throughout the tower; it must be controlled steadily to prevent vacuum conditions or an excessive level that could cause problems in the tower operation. At the same time, maintain stable levels of steam supplied to the bottom of the tower and for side-line stripping. Fluctuations in the amount of steam supplied can directly cause significant variations in the pressure and temperature at the top of the tower. 5. Maintain stable pressure and adjust the extraction temperature promptly; the pressure at the top of the tower and the vacuum level in the vacuum distillation column should be kept stable. When there are changes in pressure or vacuum level, the distillation temperatures of each side stream will shift accordingly; adjustments must be made promptly to ensure clear fractionation and satisfactory product quality. 6. Closely monitor crude oil water content and take preemptive action against fluctuations. Changes in the water content of crude oil have a significant impact on the operation of the initial distillation tower and atmospheric distillation tower; the presence of water can lead to sudden increases in pressure, sharp drops in temperature, and other issues related to tower malfunction. When significant fluctuations in water content are detected, it is necessary to adjust the load, steam injection, and return flow promptly to prevent loss of control over the operation. In one sentence: With stable feed, temperature, pressure, liquid level, and steam levels, as well as gradual adjustments and consideration for both stages of the three towers, the distillation tower can operate stably over long periods of time.