Problems with the methanol distillation feed inlet
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The design of distillation towers involves determining appropriate feed inlets based on the specific processes and production volumes. But what happens if there are significant deviations from the designed values during actual operation? How do we adjust the feed based on the actual process conditions? Can a feed inlet be added during the renovation?
Changes in the feed composition directly affect distillation operations; as the concentration of heavier components in the feed increases, the load on the distillation section rises. For a column with a fixed number of plates in the rectification section, this will result in the heavier components being carried to the top of the column, causing the quality of the product at the top to be substandard. If the concentration of the light components in the feed increases, the load on the stripping section increases at that time. For a column with a fixed number of plates in the stripping section, this will result in incomplete evaporation of the light components in the stripping section, leading to increased loss of light components in the bottom liquid. At the same time, changes in the feed composition will also cause changes in the material balance of the entire tower and the process conditions. As the component becomes lighter, the overhead distillate increases while the amount of liquid discharged from the reactor decreases. At this point, the temperature of the entire tower drops while the tower pressure increases. The component becomes heavier; the situation is the opposite. When the composition of the feed changes, the following measures can be taken: (1) Improve the feed inlet; when the composition becomes heavier, move the feed inlet downward ； When the component becomes lighter, move the feed inlet upward. (2) Changing the reflux ratio: When the components become heavier, increase the reflux ratio ； When the component becomes lighter, reduce the reflux ratio. (3) Adjusting the refrigerant and heat input: Based on changes in the composition, the refrigerant used in the top condenser and the heat input at the bottom of the tower are adjusted accordingly to maintain constant product quality at both the top and bottom of the tower. I wonder if it helps?
Thank you for your support; it’s very helpful! The basic phenomena and solutions have been outlined. Of course, these are directional guidelines; for plate towers, is it easier to change the feed inlet? What about packed towers? As for whether the feed inlet needs to be adjusted according to the distribution of the packing, if significant deviations from the original design are observed during actual production, changing the feed may require altering the packing distribution within the tower; this would involve substantial engineering work. In many cases, it is necessary to compromise by increasing energy consumption, raising the reflux rate, or adjusting the cooling capacity in order to meet the quality requirements.
The position of the feed inlet on the tower is closely related to the composition of the feed; if there are changes in the composition of the feed, it can still be controlled by adjusting the feed temperature. Typical energy-saving methods involve designing the feed to be at a temperature slightly below the bubble point. If the proportion of heavier components in the feed increases, it is possible to adjust this by raising the feed temperature; if the proportion of lighter components increases, the feed temperature can be reduced. The appropriate number of tower plates ensures effective separation, though the components will simply shift upward or downward. In fact, under different loads, the components of the same tray are different. If a separation result cannot still be achieved, the adjustment can only be made by increasing the reflux ratio to boost the heating power of the reboiler at the bottom of the tower.
Depends on the same composition of the feed liquid and the liquid on the tray
Please explain it more clearly upstairs. How can this be controlled intuitively to identify this problem?
Adjust the load of the distillation section and the stripping section based on the inlet temperature and composition
The feed inlet is related to the feed concentration; consult the manufacturer’s design data for the tower internals, and adjust the operating conditions of the distillation section and the retraction section according to the concentration or composition of your installation. Generally, a 20% margin is included in the design
Changes in the feed composition directly affect distillation operations; as the concentration of heavier components in the feed increases, the load on the distillation section rises. For a column with a fixed number of plates in the rectification section, this will result in the heavier components being carried to the top of the column, causing the quality of the product at the top to be substandard. If the concentration of the light components in the feed increases, the load on the stripping section increases at that time. For a column with a fixed number of plates in the stripping section, this will result in incomplete evaporation of the light components in the stripping section, leading to increased loss of light components in the bottom liquid. At the same time, changes in the feed composition will also cause changes in the material balance of the entire tower and the process conditions. As the component becomes lighter, the overhead distillate increases while the amount of liquid discharged from the reactor decreases. At this point, the temperature of the entire tower drops while the tower pressure increases. The component becomes heavier; the situation is the opposite. When the composition of the feed changes, the following measures can be taken: (1) Improve the feed inlet; when the composition becomes heavier, move the feed inlet downward ； When the component becomes lighter, move the feed inlet upward. (2) Changing the reflux ratio: When the components become heavier, increase the reflux ratio ； When the component becomes lighter, reduce the reflux ratio. (3) Adjusting the refrigerant and heat input: Based on changes in the composition, the refrigerant used in the top condenser and the heat input at the bottom of the tower are adjusted accordingly to maintain constant product quality at both the top and bottom of the tower. It’s quite comprehensive. In operation, both the pre-tower and the atmospheric tower typically have four or five feed inlets; these inlets can also be adjusted depending on the requirements regarding water removal and the efficiency of removing light components.
How many feed inlets does each tower typically have in the three-tower distillation designed by the Second Chemical Engineering Institute? Thank you all!
Changes in the feed composition will also lead to changes in the material balance throughout the tower as well as in the process conditions. The feed inlet is related to the feed concentration; accordingly, the conditions in the distillation section and the retraction section need to be adjusted based on the concentration or composition of your plant.
Our pre-tower and pressure tower share one feed inlet, while the atmospheric tower has three. I wonder if this design can handle problems similar to those encountered by the original poster
The feed inlet of a plate tower is usually located above the sensitive plates, and there are formulas available for calculating its position. Typically, 3–4 feed inlets are provided in the upper part to facilitate adjustments during production