Process Overview
Crude benzene is a complex mixture of many organic compounds. Its main components are benzene and its homologues such as toluene, xylene, and trimethylbenzene. The crude benzene purification process is a process in which unsaturated compounds, quinones, and the like in crude benzene are removed by chemical methods, and then the benzene products are separated by distillation.
In the process of continuous crude benzene refining, the most common process is a five-tower distillation process.
Crude benzene refining process flow diagram
Control plan
In the refining process of crude benzene, it is mainly to solve the operation problems of various towers. The common point of these towers is to conduct the material separation. The principle of its separation is: according to the relative volatility of various components in the mixed liquid, The light components in the liquid phase rise and the heavy components decrease, thereby achieving the effect of separating the substances.
Tower kettle temperature control block diagram
Tower temperature control is achieved by cascade control of the heating steam flow rate and the tower temperature. The main factor affecting the temperature of the tower reactor is the amount of heat taken by the material after it enters the reboiler, and the heat of the reboiler is entered by the tower. The steam from the kettle provides, therefore, the temperature of the kettle can be controlled by adjusting the flow of steam into the reboiler, and feed flow is introduced to feed forward control to achieve temperature control of the kettle, due to the steam The amount of addition has great influence on the other parameters of the tower such as the tower pressure. To ensure the safety of the tower, a condition judgment is added here. When the tower pressure is controlled within the safety range by steam flow and temperature cascade control, the tower pressure is used when the tower pressure is too high. The tower pressure control method reduces the tower pressure to ensure the safety of the tower equipment.
There are many factors affecting the temperature at the top of the tower, such as the flow rate of the material, the amount of steam heated by the reboiler, the amount of cooling water in the condenser, etc. Among them, the most influential one is the material return flow, so the tower can be controlled by return flow. The temperature at the top, due to the tower's feed and its composition is the main interference factor, because the five towers are connected in series before and after, the discharge of the previous tower is the feed of the latter tower, before and after correlation, the amount of feed is not controllable That's why feedforward is introduced here.
Tower temperature control block diagram
Five tower crude benzene refining flow chart
Distillation process control curve