Distillation tower overhead pressure operation

Factors causing changes in the pressure at the top of the distillation tower: 1. Top pressure control or vacuum system failure, which can be manifested in unstable pressure, abnormal opening of the control valve, etc.; 2. Excessive heating of the column reboiler, excessive evaporation, which can also be manifested in abnormal tower temperature. 3. Overload operation of the distillation tower, causing liquid flooding, etc., manifested as abnormal tower pressure difference. 4. Sudden changes in the feed composition, such as an increase in light components, cause overloading of light components at the top of the tower.

There are many factors that cause changes in distillation tower pressure, generally including heat load, cooling capacity at the top of the tower, reflux volume, material composition, stability of tower operation, and accumulation of non-condensable gas. These will all affect changes in the pressure at the top of the distillation tower.

The explanation above is more comprehensive, and if the trays or packings are clogged or the ambient temperature difference is large (such as heavy rain in summer), the pressure will be affected.

What are the factors that cause changes in the pressure at the top of the distillation tower? There are the heat load at the bottom of the tower, the operating status of air cooling and water cooling at the top of the tower, the reflux ratio, the amount of light components in the feed, the salt formation on the tray, the operating status of the pressure control valve at the top of the tower, etc. Phenomena caused by changes in top pressure: ⒈Safety valve tripping ； ⒉The liquid level in the reflux tank fluctuates high and low ； ⒊The discharge volume at the bottom of the tower suddenly increases and sometimes decreases. etc.

The heat load at the bottom of the tower, the air cooling tray or packing at the top of the tower is blocked, and the control system fails.

1. First, eliminate the instrument cause. For example, if the pressure display has deviations and fluctuations, is there a problem with the regulating valve of the pressure control system? 2. Pressure control system equipment problems. If a water ring vacuum pump is used to draw negative pressure, check whether the vacuum pump is operating normally. If a high-pressure jet pump is used to pump negative pressure, check whether the pressure flow of the high-pressure gas fluctuates. 3. Problems with the overhead gas condensation system. Check whether the cooling water or chilled water flow and pressure of the tower top condenser fluctuate. 4. Whether the return flow fluctuates greatly. Increasing the coolant dosage and reflux ratio of the overhead condenser can reduce the overhead pressure. The above is summarized in my personal production. Below is the information: Tower pressure is one of the main control indicators for distillation operations. If the tower pressure fluctuates too much, it will destroy the material balance and gas-liquid balance of the entire tower and make the product quality unqualified. Therefore, the distillation operation must be stable. Methods for adjusting tower pressure include: (l) When the tower top condenser is a partial condenser, the tower pressure is generally adjusted by the amount of vapor phase product taken out of the tower top. Take it out and increase the pressure, and the tower pressure will drop. ； The withdrawal decreases and the tower pressure increases. (2) The reboiler steam consumption is too large, the reflux flow is large, and the tower pressure increases. At this time, the steam volume should be appropriately reduced to regulate the tower still pressure. The factors that affect changes in tower pressure include: ①Tower top temperature ② tower kettle temperature ② feed composition ④ feed amount ⑤ reflux flow ⑥ refrigerant amount and refrigerant pressure. In addition, instrument failure, freezing blockage of equipment and pipelines can also cause changes in tower pressure.