I. Introduction
The delayed coking technology can convert petroleum residue into more valuable cracked gas and light distillates. The petroleum coke as a by-product contains the majority of heavy metal and condensed aromatics of the residue which are difficult to be processed. The delayed coking technology can process various residues, including conventional AR, VR and all residues from other processing units in refinery. The delayed coking technology is the preferred technology for processing inferior residue.
II. Process description
The simplified typical PFD is shown as follows. After heat-exchanging with the side-draw products from the fractionator, the feedstock enters the bottom of the fractionator and blends with the recycle oil which is condensed in the fractionator. The blended residue is pumped to the heater and rapidly heated to the desired temperature, and then enters one of a pair of coke drums where the thermal cracking reaction takes place. When the height of the coke reaches to the upper limit, the blended residue is switched to the other coke drum for continuous operation. The cracked oil vapor enters the fractionator and is separated into coker gas, naphtha, LCGO and HCGO. The coker gas enters the gas recovering system. The coke deposited in the coke drum is removed by the hydraulic decoking system.
Key operating parameters are as following
(1)Heater outlet temperature: 485~515°C
(2) Coker drum overhead pressure: 0.10~0.25MPa(G)
(3) Recycle ratio (recycle oil/fresh feedstock): 0~1.0
III. Technology characteristics
1.The operation can be flexibly adjusted to meet market demands, including maximizing distillate yield, maximizing light oil yield, increasing LCGO yield, producing needle coke, etc.
2.The delayed coking technology can process various residues, including AR, VR, DOA, hydrocracking unconverted residue, visbroken residue, FCC slurry, steam cracking tar, etc.
The typical properties of feedstock are shown as follows:
| Items | Case 1 | Case 2 | Case 3 |
| Density (20°C)/(g/cm3) | 0.9945 | 1.0344 | 1.0539 |
| Kinematic Viscosity (100°C)/(mm2/S) | 1291 | >5000 | >5000 |
| Solidification Point/°C | 33 | 48 | >50 |
| w(Carbon Residue)/% | 16.8 | 24.3 | 23.7 |
| w(S)/% | 1.8 | 5.5 | 4.6 |
| w(N)/% | 1.00 | 0.34 | 0.87 |
| w(Asphaltenes)/% | 4.2 | 13.7 | 18.1 |
| w(Ni+V)/(μg/g) | 59.2 | 211 | 928 |
3.The heater with double fired, multi-point steam (or water) injection, online spalling, online steam-air decoking and other technologies can prolong the run length of the heater. The high severity coking technology reduces low valuable coke yield and increases high valuable liquid product yield.
4.The anti-foaming agent injection to the top of coke drum reduces coke fine carry-over into the fractionator. Applications of the upper circulation washing, the lower spraying washing and the high efficiency internals in the fractionator reduces asphaltenes and metal content in HCGO.
5.The energy consumption of 1.0 MMTA delayed coker unit (including gas recovering section) is about 26 kg Eo/t of feedstock.
6.The run length of delayed coker unit between main turnarounds is 3 years.
7.The typical product yields are shown as follows:
| Items | Yield/wt% |
| Coker Gas | 4~6 |
| Coker LPG | 3~4 |
| Coker Naphtha | 10~15 |
| LCGO | 25~35 |
| HCGO | 20~30 |
| Coke | 20~35 |
IV. Commercial Experience
By 2021, delayed coking technology has been licensed to 80 projects in China or overseas, including Sudan, Iran, Cuba, etc. The largest capacity of licensed delayed coker unit is up to 5.20 MMTA.