Issues related to separators in hydrogenation units. . .
Thread Content
I’ve been working on my graduation project recently, and the topic involves the process design of a hydrorefining unit for coker gasoline. There are some aspects I don’t understand during this work – I’m not sure how to choose between hot high fraction, cold high fraction, hot low fraction, and cold low fraction. I hope everyone can help me solve these issues. Thank you!
I think ordinary hydroprocessed gasoline and diesel refining only uses cold heavy fractions and cold light fractions. Hot high fraction and hot low fraction are used in the paraffin oil hydrogenation unit. There are relevant posts on the forum; please refer to: http://bbs.hcbbs.com/viewthread.php?tid=399315&highlight=%C8%C8%B8%DF%B7%D6
Hydrogenation at low temperatures is more commonly used for diesel and gasoline, while hydrogenation at high temperatures is more often used for wax oil and residue. The key issue in choosing between the cold high-pressure and hot high-pressure processes is how to conduct an economic comparison of the two. The advantage of the hot high-pressure process is that it reduces the energy consumption of the plant and decreases the area required for heat exchange. In cold regions, it helps to prevent freezing in air coolers, and for full-circulation processes, it helps to avoid the accumulation of polycyclic aromatic hydrocarbons that could clog the high-pressure air coolers. However, its disadvantages include the need for a more complex high-temperature oil-gas separation system and higher oxygen losses. The concentration of circulating oxygen is also slightly lower in this process, resulting in a slight increase in the pressure throughout the reaction system. A prerequisite for using the hot high-pressure process is that the hydrogen contained in the low-pressure gas must be effectively recovered
All the various separators you listed are present in the unit I operate. After the oil undergoes hydrogenation and exits the reactor, it first enters the hot high-pressure fractionator through heat exchange; the material coming out of the bottom of this fractionator goes directly into the hot low-pressure fractionator. The light hydrocarbons at the top of the hot low-pressure fractionator are sent to the cold low-pressure fractionator after cooling. The material from the bottom of the hot low-pressure fractionator goes directly into the atmospheric distillation column for fractional separation. The material from the top of the hot high-pressure fractionator is cooled before being sent to the cold high-pressure fractionator, and the heavy hydrocarbons at the bottom of the cold high-pressure fractionator end up in the cold low-pressure fractionator!
Higher temperature high-pressure units require higher purity of circulating hydrogen, while lower temperature high-pressure units can tolerate lower purity.
Depending on the volume of processing, for small-scale operations, a cold high-pressure plus cold low-pressure setup is sufficient. For larger-scale operations, heat recovery needs to be taken into account, which requires a high-temperature high-pressure process; however, this process results in significant hydrogen losses, so recovery devices must be considered, such as a small PSA unit
Oils with a high raw material weight have high thermal viscosity and are not suitable for emulsification; diesel and gasoline use oils with low thermal viscosity