Explain to laypeople the fractionation system of a catalytic cracking unit
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Hello everyone, I have a question I’d like to ask. I study chemical engineering, and my teacher asked us to design systems involving oil pipelines; it’s sad because I don’t know much about oil. I am working on the design of the distillation system for a 30kt/a catalytic cracking unit. I have always been unsure as to what components and equipment are part of a distillation system, and what aspects should be considered when designing such a system And that 30kt/a – does it refer to the total mass of all the products obtained through distillation?
In simple terms, the equipment of a distillation system consists of a distillation tower, one or two diesel towers, a re-refining tank, a rich gas liquid separation tank, and an acidic water tank. The top of the tower is equipped with a cooling system, while the oil slurry system at the bottom includes pumps, heat exchangers, etc.; the middle and top sections of the tower also have similar components such as pumps and heat exchangers.
The fractionation system is the linking component of a catalytic cracking unit; its main equipment includes a fractionation tower, a diesel stripping tower, a re-refining tank, a top-of-tower cooling system (air cooling, water cooling), a reflux tank, three circulation circuits for the fractionation tower, heat exchangers, and mechanical pumps. Designing requires considering various factors (cooling load, vapor phase load, tray structure, pipe diameter, pump power, etc.)
Simply put, the distillation section mainly includes the distillation tower, re-refining tank, feed oil tank, side-line stripping tower, top circulation system, middle section, and overhead liquid separation tank. I’m not sure if your supervisor wants you to work on the stabilization section; if so, there will be even more components, including absorption towers and desorption towers. It’s likely that your supervisor only wants you to work on the distillation tower – otherwise, adding pumps such as bottom oil pumps and reflux pumps would result in too many components. Ask your supervisor carefully
In the fractionation section, the reaction oil and gas coming from the heavy oil settler enters the bottom of the fractionation tower, where it comes into countercurrent contact with the circulating slurry via herringbone baffles. This process washes away the catalyst from the reaction oil and gas and removes any excess heat, resulting in the oil and gas being in a saturated state as they proceed to the upper part of the tower for fractionation. The oil and gas at the top of the distillation tower is cooled to 40°C and then sent to the oil and gas separator at the tower’s top for gas-liquid separation. The crude gasoline resulting from this separation is pumped to the gasoline lift pipe, while the rich gas is fed into the compressor. The light diesel from the autonomous fractionation tower flows by gravity to the light diesel stripping tower. The stripped light diesel is pumped out by a light diesel pump, cooled to 60°C, and then divided into two streams: one stream is used as the product and exits the plant, while the other stream is cooled further to 40°C and sent to the reabsorption tower as an absorbent. The excess heat in the fractionation tower is removed respectively by the top circulation reflux, the middle section circulation reflux, and the slurry circulation reflux. The reaction oil and gas coming from the gasoline settler enters the bottom of the secondary distillation column, where it comes into countercurrent contact with the circulating oil slurry from the distillation column via circular baffles; this process washes away the catalyst from the reaction oil and gas and removes any excess heat, after which it proceeds to the upper part of the secondary distillation column for further distillation. The wash oil slurry at the bottom of the tower flows by gravity to the bottom of the main distillation column.
30kt/a refers to the processing capacity of the plant.
This isn’t something that can be understood just by talking about it! It’s best to visit an oil refinery to learn about it – that way you’ll understand everything completely! This is also beneficial for the design! It is also beneficial for calculating thermal equilibrium!
30kt/a refers to the annual processing capacity of the distillation tower.
A fractionation tower is a vessel equipped with trays, featuring side streams for extraction, heat exchangers, and a stripping tower