Catalytic cracking

Generally, only 10-40% of light oil such as gasoline, kerosene and diesel oil can be obtained from crude oil after atmospheric and vacuum distillation, and the rest are heavy distillate oil and residual oil. If more light oil products are to be obtained, secondary processing of heavy distillates and residual oils is necessary. Catalytic cracking is the most commonly used production process for gasoline and diesel, and gasoline and diesel are mainly produced through this process. This is also the most important production link for general petroleum refining and chemical enterprises.

1. Feedstocks:

Residual oil and wax oil are about 70%. Catalytic cracking generally uses vacuum distillate oil and coking wax oil as raw materials. However, with the increasing crude oil and the increasing demand for light oil, most petrochemical enterprises have begun to Add vacuum residual oil to the raw material, or even directly use atmospheric residual oil as raw material for refining.

2. Products:

Gasoline, diesel oil, oil slurry (heavy distillate oil), liquid propylene, and liquefied gas; each accounted for 42% of gasoline, 21.5% of diesel, 5.8% of propylene, 8% of liquefied gas, and 12% of oil slurry.

3. Basic concepts:

Catalytic cracking is the main process of processing heavy oil (such as residual oil) into light oil (gasoline, kerosene, diesel) in the presence of catalyst, and is the main secondary processing method in the refining process. It is a chemical processing process.

4. Production process:

The normal residue and wax oil enter the riser, settler and regenerator through the raw material oil buffer tank to form oil and gas, and enter the fractionation tower.

Part of the oil and gas enters the crude gasoline tower, absorption tower, and air compressor into the condensed oil tank, and passes through the reabsorption tower, stabilization tower, and finally gasoline refining to produce gasoline.

A part of the oil and gas enters the diesel stripping tower through the fractionation tower, and then the diesel oil is refined to produce diesel oil. Part of the oil and gas enters the oil slurry circulation through the fractionation tower, and finally produces the oil slurry.

Part of the oil and gas enters the liquid hydrocarbon buffer tank through the fractionation tower, passes through the desulfurization adsorption tank, the sand filter tower, the water washing tank, the desulfurized alcohol extraction tower, the pre-alkali washing tank, the amine liquid recoverer, the desulfurization extraction tower, and the buffer tower, and finally enters the liquid state. Hydrocarbon tank to form liquefied gas.

Part of the oil and gas passes through the liquid hydrocarbon buffer tank and enters the depropanizer, reflux tower, deethanizer, refined propylene tower, reflux tank, and finally enters the spherical tank in the propylene area to form liquid propylene. The liquid propylene is further processed in the polypropylene workshop to produce polypropylene.

5. Production equipment:

a. Regenerator

The main function of the regenerator is to burn off the coke on the coked catalyst to restore the activity of the catalyst, and also to provide the heat required for cracking. The regenerator consists of a shell, a cyclone separator, an air distributor, an auxiliary combustion chamber and a heat collector

b. Riser reactor

Straight pipe type: mostly used in high and low parallel reverse regeneration system, which is characterized by direct insertion from the bottom of the settler, simple structure and low pressure drop.

Folding type: mostly used for coaxial type anti-regeneration system.

c. Settler

The function of the settler is to separate the reaction oil and catalyst from the riser. The oil and gas are separated from the entrained catalyst by the cyclone separator and then passed through the gas collecting chamber to the fractionation system; the catalyst from the rapid separator settles down in the settler by gravity. , falls into the gas segment.

d. Three machines

Main fan: supply air for regenerator scorch.

Compressor: used to boost the pressure of the rich gas from the fractionation system, and then send it to the absorption stabilization system.

Booster: supply the dense phase riser of the IV type reaction regeneration device to adjust the catalyst circulation.

e. Three valve

Single-acting slide valve: In type IV catalytic cracking unit, it is fully opened in normal operation, and closed in emergency to cut off the connection between the two devices to prevent the catalyst from flowing backward; in the riser catalytic cracking device, adjust the catalyst circulation amount of the two devices.

Double-acting slide valve: Installed between the outlet of the regenerator and the venting chimney to adjust the pressure of the regenerator and keep the pressure of the two devices in balance.

Plug valve: Adjust the circulation amount of the catalyst in the coaxial catalytic cracking unit.