How is the process controlled?

1.1.1 Principles for adjusting the operating parameters of the distillation column: The operation of the distillation column must ensure that all light components in the reactant, those below naphtha, are vaporized and removed from the top of the column. The adjustment of the operating parameters should be determined based on the analysis results of samples taken from the bottom of the column (to check for the presence of light components) as well as the analysis results of samples from the top product (crude gasoline, dry gas). To avoid operational confusion, do not change the assigned value of “PIC” rapidly. The normal tower pressure should not be changed; the stability of tower operation is controlled by temperature adjustment. The operator can control the feed and bottom temperature from the hydrogen sulfide stripping tower, which are heated by F-201. They can also monitor the temperatures of the overhead gas and the overhead condensate outlet, as well as the temperatures of the liquid stream and the liquid at the bottom of the distillation tower; these temperatures reflect the quality of the product and the degree of evaporation. The feed temperature to the tower is at an optimal value; if it is too high, a large amount of the feed will evaporate, and the separation efficiency of the tower will be reduced due to the improper separation of various components on the trays in the stripping section. When the feed temperature is too low and the degree of fractionation is insufficient, the stripping steam should be increased to raise the bottom temperature of the tower, as the bottom temperature is the determining factor for the efficiency of distillation. The level of the bottom temperature plays a significant role in determining the concentration of light components in the liquid at the tower bottom. If the bottom temperature is too high, it is necessary to increase the reflux flow at the top of the tower, reduce the amount of liquid discharged from the top, or adjust the amount of steam used for stripping at the bottom. The top temperature is the key indicator of the concentration of heavy components in the product at the tower top; if the top temperature is too high, it is necessary to increase the reflux rate or reduce the amount of liquid discharged from the tower top. 1.1.2 Operating principles of the distillation tower 1.1.2.1 Temperature control of the tower: The temperature of the tower is a very important parameter. The temperature level has a direct impact on the quality of the product and the stable operation of the tower. Under normal operation, the temperature distribution in the tower corresponds to a certain product distribution at different heights. The top temperature of the tower, the bottom temperature, the feed temperature, and the reflux temperature must be kept stable. Careful operation is required when making adjustments to avoid disrupting the proper functioning of the tower and to prevent the production of defective products. The top of the tower temperature is controlled by the reflux flow at the tower top. The tower top temperature is high and the product is heavy; therefore, the reflux flow rate should be increased. However, the backflow rate must not be too high to prevent overloading of the upper trays and the tower top. The bottom temperature of the tower is the main factor determining the amount of evaporation of the material in that tower. The temperature at the bottom of the tower is high, resulting in large evaporation rates ； Excessively high temperatures can even lead to carrying over, resulting in a higher dry point and a darker color for the product ； However, when the temperature at the bottom of the tower is low, the appropriate components cannot evaporate; the product components become lighter, which also increases the load on the equipment at the bottom of the tower. The bottom pump is prone to cavitation, which damages the seal. The temperatures at various points in the distillation column are primarily determined by the properties of the feed; in other words, the temperatures at these points decrease as the degree of cracking of the feed increases. Therefore, during normal operation, it is necessary to adjust the temperatures at various points in a timely manner according to the properties of the feed, especially the temperature at the bottom of the tower, and to adjust the other parameters accordingly based on this temperature. 1.1.2.2 Tower pressure The set value of the tower pressure must not be changed arbitrarily to avoid significant fluctuations, tower overpressure, or leakage and fire. When adjusting the tower pressure, it is necessary to first identify the main factors affecting the fluctuations in the outlet pressure. When it is necessary to open the tower top vent valve to adjust the tower pressure, the control valve should be opened slowly: open it a little at first, wait for a while while monitoring pressure changes, and then make further adjustments until the pressure is within the normal range. Tower pressure has a direct impact on the boiling points of the components in the entire distillation column; as the tower pressure increases, the boiling points of the product oils also rise, thereby making it more difficult to separate the components. If the column pressure decreases and the column temperature drops, the pressure of the fluid being transported to the downstream equipment will decrease, the flow rate of the exhaust gas will increase, and the load on the tray columns will also increase. Therefore, attention should be paid to the travel of the control valves in the product line or the product specifications. To avoid confusion or accidents, do not change the assigned value of the “PIC” rapidly. The normal tower pressure should not be changed; the stability of tower operation is controlled by temperature adjustment. 1.1.2.3 Level control: The stability of level control is a key factor among the various operating parameters in a tower’s automatic control system, as it directly affects the yield of the product. Excessively high liquid levels can easily lead to foam entrainment, and even tower flooding ； An excessively low liquid level can easily cause the bottom pump to experience vacuum conditions, leading to equipment damage. The liquid level must be monitored carefully, and adjustments should be made with precision to avoid large fluctuations in the liquid level. When adjusting various parameters, it is essential to take them into account together in order to determine which ones are the primary factors and which ones are the secondary ones ； Under normal circumstances, it is necessary to avoid making large adjustments to the control parameters to prevent fluctuations in the normal operation of the system.

Thank you for the reply from above; I’ve learned a lot. But how does the branch circuit controller carry out its functions? Especially in terms of pumps – is it necessary to set up branch circuit control based on the requirements of the medium being transported?

The branch line is auxiliary; in the case of a pump, adjustments need to be made based on the liquid level and subsequent continuous operation. Make every effort to ensure the smooth operation of the equipment.

The main aspects to pay attention to in the operation of a distillation tower are: 1. Tower temperature (the temperatures at the top and bottom of the tower should be within the normal operational range). 2. The amount of feed, its temperature, location, and concentration. 3. Reflux temperature and the volume of reflux. 4. Operating pressure and the cooling efficiency of the top cooler. 5. The heating efficiency of the reboiler, as well as whether the steam pressure and temperature remain stable