Coke (referred to as coking) is a deep thermal cracking process and one of the means of treating residual oil. It is the only process that can produce petroleum coke, which cannot be replaced by any other process. In particular, the special demand for high-quality petroleum coke in some industries has caused the coking process to occupy an important position in the refining industry.

Raw material

Delayed coking and catalytic cracking similar to the decarburization process to change the hydrocarbon’s hydrocarbon ratio, the delayed coking feedstock can be heavy oil, residual oil or even asphalt, the quality requirements of raw materials are relatively low. The main conversion processes for residual oils are delayed coking and hydrocracking.

2. Product

The main products are wax oil, diesel oil, coke, crude gasoline and some gases. The respective proportions are: wax oil accounts for 23-33%, diesel oil 22-29%, coke 15-25%, crude gasoline 8-16%. Gas is 7-10%, and external eucalyptus oil is 1-3%.

3. Basic concepts

Coking is a deep thermal cracking reaction at a high temperature (400 to 500 ° C) using a heavy hydrogen-depleted residual oil (such as vacuum residue, cracked residue, and asphalt) as a raw material. A portion of the residue is converted to gaseous hydrocarbons and light oils by a cleavage reaction; another portion of the residue is converted to coke due to the condensation reaction. On the one hand, due to the heavy raw materials, a considerable amount of aromatic hydrocarbons are contained, and on the other hand, the reaction conditions for coking are more severe, so the condensation reaction accounts for a large proportion and generates more coke.

4. Production process

The production process of the delayed coking unit is divided into two parts: coking and decoking, coking is continuous operation, and decoking is a gap operation. Since industrial plants typically have two or four coke drums, the entire production process is still continuous.

1. The crude oil is preheated, and the coking raw material (vacuum residue) first enters the raw material buffer tank, and then is pumped into the heating furnace to raise the convection section to about 340~350 °C.

1. The preheated crude oil enters the bottom of the fractionation column and exchanges heat with the oil produced by the coke drum in the fractionation column (the bottom temperature does not exceed 400 ° C.

1. The feedstock oil and the circulating oil are taken out from the bottom of the fractionation tower, and the hot oil pump is used to drive into the radiant section of the heating furnace, heated to the temperature required for the coking reaction (about 500 °C), and then enters the coke drum from the lower part through a four-way valve to carry out the coking reaction. .

1. The raw materials are reacted in the coke drum to form coke, which is accumulated in the coke drum. The oil and gas flows from the top of the coke drum to the fractionation tower, and after heat exchange with the feedstock oil, the gas, gasoline, diesel oil and wax oil are obtained by fractional distillation. The bottom circulation oil and the raw materials are further subjected to a coking reaction.

5. Production equipment

1. Coke tower

The coke drum is an empty cylinder made of thick boiler steel plate and is a place for coking reaction.

1. Hydraulic decoking equipment

The coke drum is used in rotation, that is, when the coke in one tower is coalesced to a certain height, the raw material is switched to another coke tower through a four-way valve. The coke drum that coalesces coke is first cooled with steam and then hydraulically defocused.

1. Flameless burner

The coking furnace is the core equipment of the device, and its function is to heat the rapidly flowing residue in the furnace to a high temperature of about 500 °C. Therefore, it is required to have a high heat transfer rate in the furnace to ensure that sufficient heat is supplied to the oil in a short time, and at the same time, it is required to provide a uniform heat field to prevent coking of the furnace tube due to local overheating. For this reason, delayed coking usually employs a flameless furnace.