Impact of changes in crude oil properties on distillation units and practical adjustment strategies

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Changes in crude oil properties are the most common type of operational fluctuations in atmospheric and vacuum distillation units. These changes mainly fall into two categories: lighter crude oil and heavier crude oil, and they often occur when there is a change in the crude oil storage tanks, adjustments to the blending ratios, or fluctuations in the composition of the incoming crude oil. A change in properties can directly disrupt the thermal equilibrium, material balance, and gas-liquid equilibrium of the unit; if adjustments are not made in a timely manner, this may result in substandard product quality at best, or it can lead to production accidents such as excessively high tower pressure, tower flooding, overload of the heating furnace, or an empty liquid level at the bottom of the tower. Based on actual on-site operations, the influence patterns and key handling points are summarized as follows. I. Operational impacts when the properties of crude oil become lighter
1. The pressure at the top of the primary distillation tower/atmospheric tower rises rapidly; the production of non-condensable gases increases significantly. Consequently, the cooling load at the tower top becomes greater, and the temperature after cooling remains relatively high. 2. The gasoline yield at the top of the tower increases, the dry point is lower, and there is more light fraction. 3. The gasification rate in the tower increases significantly, the liquid level at the bottom of the tower drops, and in severe cases it can easily become empty. 4. Pressure rises in the crude oil heat exchange system, furnace tubes, and oil transfer lines. 5. An increase in the gas-phase load in the tower leads to increased internal reflux and a rise in the side-stream distillation temperature, which can result in heavier side-stream fractions and greater overlap. 6. The actual thermal load requirement of the heating furnace increases. Corresponding adjustment measures: 1. Slightly increase the tower top temperature to compensate for the increased vapor pressure of oil and gas, ensuring that the dry point of gasoline meets the specifications. 2. Increase the number of burners in the heating furnace and raise the heat supply to meet the increased gasification demand ； Increase the furnace outlet temperature appropriately if necessary. 3. Appropriately increase the extraction volume of side-stream products to avoid excessive internal reflux, which could lead to an overly high load on the trays. 4. Increase the proportion of heat recovery from the middle section, reduce the load at the tower top, and stabilize the temperature distribution throughout the tower. 5. Appropriately reduce the steam supply at the bottom of the tower to alleviate the gas-phase load inside the tower ； The side-line stripping steam remains unchanged to ensure the product flash point meets the specifications. 6. If the pressure rises too rapidly or the cooling load is insufficient, the processing volume can be reduced appropriately to prevent overpressure, tower flooding, and excessive temperatures after cooling. 7. Strengthen monitoring of tower top pressure, liquid level, and temperature after cooling, and adjust the reflux flow rate in a timely manner. II. Effects of increased crude oil properties on operations 1. The pressure at the top of the initial distillation tower/atmospheric distillation tower decreases, the amount of non-condensable gas reduces, and the temperature after cooling drops. 2. Gasoline yield decreases, dry point is high, and there is a shortage of light components. 3. The gasification rate in the tower decreases, and the liquid level at the bottom of the tower rises significantly. 4. The side-stream distillation temperature decreases, resulting in a lighter product and a reduced yield. 5. The load requirement of the heating furnace decreases, making it easy for the furnace temperature to be low. 6. The distillation efficiency deteriorates, and the precision of product separation decreases. Corresponding adjustment measures: 1. Slightly reduce the tower top temperature to counteract the effect of the decrease in oil vapor partial pressure and stabilize the dry point of gasoline. 2. The heating furnace should reduce the number of burners or lower the gas supply accordingly, to prevent overheating of the furnace chamber and avoid fuel waste. 3. Appropriately reduce the side-stream draw-off rate to ensure that the distillation range of the side-stream product meets specifications and to prevent it from being too light. 4. The steam injection at the bottom of the tower can be increased moderately to improve the vaporization and distillation of the oil at that location. 5. Appropriately reduce heat extraction from the middle section of the reflux to increase the temperature at the upper part of the tower, thereby stabilizing the distillation conditions. 6. Strengthen monitoring of the liquid level at the bottom of the tower to prevent excessive liquid levels from causing unstable feeding to the heater or allowing heavier components to rise upward. 7. If there is an excessive amount of Reconstituted components and distillation becomes difficult, the processing volume can be reduced slightly to ensure product quality and stable operation of the plant. III. General operating principles 1. Before changing the tank for crude oil, contact the dispatch team and the tank farm in advance to anticipate any changes in its properties, and make slight adjustments in advance to avoid significant fluctuations. 2. Adjustments should follow the principle of \"small increments and frequent adjustments\"; large-scale adjustments at once are strictly prohibited to prevent repeated disruption of balance. 3. Prioritize stabilizing the three key balances: material balance (liquid level), heat balance (temperature), and gas-liquid balance (pressure). 4. With product quality as the core, ensure safety and stability first, then optimize the yield; prevent any loss of operational control caused by the pursuit of higher output.