Figure 6.1.3.2 illustrates a flow chart of the delayed coker and calciner (hereinafter abbreviated to as delayer coker) process. Delayed coker is similar to the delayer coker and calciner process for manufacturing petroleum coke and is provided with a coke drum (hereinafter abbreviated to as a drum) and a rotary kiln as major equipment.
Figure 6.1.3.2 Process flow of delayed coking/calcining process. (a) delayed coking process. (b) calcining process.
6.1.3 Delayed Coking
Delayed coking is operated as follows. SOP (softening point: 20–40 °C) as a raw material is fed into the bottom of the fractional tower and discharged (thermal cracking product) into the bottom of the drum after combining with the heavy fraction separated from the drum, followed by heating it in a heating tubular furnace at the temperature in a range of approximately 450–500 °C to charge into the drum under pressure [5, p. 318 and 2, 3]. At this time, high‐pressure steam is injected into the tubular furnace in order to prevent buildup of coke on the furnace tube. The heavy component in the thermal cracking product charged is carbonized in the drum to form raw coke, and a generated gas and steam are distilled off from the top of the drum together with the oily component not cracked to return to the fractional tower. Fractional distillates are separated as needed in the fractional tower for recovery, and light oil, gases, and water are recovered from the top of the fractional tower. There is a plurality of drums, and as the drum is filled with the solidified raw coke, the thermal cracking product is switched to the second drum. Steam is injected into the drum filled with solidified raw coke to eject the unreacted oily component with steam followed by charging water to cool. After, the top and bottom heads of the full coke drum cooled are removed, and then the solid raw coke is cut from the coke drum with a jet stream of high‐pressure water and transferred into a tank for dewatering.
A typical example of the material balance in coking and the physical properties of coke, oil, and gas is shown in Table 6.1.3.3 [1, 7, p. 79]. PC generally differs from petroleum coke as follows:
A yield of the coke relative to the raw material supplied is larger [1, 7, p. 76].
The content of ash and sulfur in raw coke is less and the content of nitrogen is higher [1, 7, p. 76].
Since the aromaticity of the raw material supplied is higher but its reactivity is lower [8, 9, p. 159], coking is performed at higher temperature [1, 7, p. 76].
The aromaticity of oil as a by‐product is high and the content of hydrogen and methane in the gas formed is high [1, 7, p. 76].
The variation of the carbon and hydrogen ratio in different production processes is given in Table 6.1.3.4 and Figure 6.1.3.3, respectively. In the case of PC, the C/H ratio indicates that the raw material comprises on average four aromatic rings as in chrysene, but coking of the raw coke increases the number of aromatic rings to exceed 10 as in ovalene, and after calcination the carbon content is almost 99%. The carbon content in the raw material is higher in the case of PC, but the carbon content of raw coke after coking and that in a product after calcination are similar.
As compared with the chamber coking process, the delayed coking process is substantially improved as follows:
Environmental pollution
Table 6.1.3.3 Production of PC by the delayed coking process.
| Material balance and properties of products. | |
|---|---|
| Typical delayed coking yield | wt% of charge |
| Product gas | 3.0 |
| Light oil | 10.7 |
| Heavy oil | 25.4 |
| Coke | 60.9 |
| Total | 100.0 |
| Average properties of products | |
|---|---|
| Product gas | |
| vol% | |
| H2 | 48.2 |
| N2 | Trace |
| CO | 1.0 |
| CO2 | Trace |
| CH4 | 44.9 |
| C2H4 | Trace |
| C2H6 | 5.9 |
| Light oil | ||
|---|---|---|
| Specific gravity | 1.018 | |
| Naphthalene content (wt%) | 32.5 | |
| Distillation (°C) | IBP | 180 |
| 10 | 205 | |
| 50 | 235 | |
| 70 | 247 | |
| 90 | 275 | |
| EP | 310 | |
| Heavy oil | ||
|---|---|---|
| Specific gravity | 1.085 | |
| Conradson carbon (wt%) | 0.30 | |
| Distillation (°C) | IBP | 256 |
| 10 | 293 | |
| 50 | 324 | |
| 70 | 338 | |
| 90 | 367 | |