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 | |
| EP | 400 | |
| Coke | |
|---|---|
| Apparent density (lb./cu.ft.) | 61–69 |
| Volatile combustible matter (wt%) | 7.5–9.5 |
Table 6.1.3.4 Variation of the carbon and hydrogen ratio in production steps of pitch coke.
| C (wt%) | H (wt%) | C/H (atomic ratio) | References | |
|---|---|---|---|---|
| Feed | 91.6 | 5.1 | 1.50 | [6] |
| Raw coke | 94.6 | 2.8 | 2.82 | [5] |
| Pitch coke | 98.68 | 0.34 | 24.19 | [4] |
