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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
	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]

Figure 6.1.3.3 Variation of the carbon and hydrogen ratio in production steps of pitch coke.

Potential factors of causing environmental pollution such as foaming of a raw material charged and leaking of pitch from the space between the furnace body and the furnace lid in the chamber coking process can be eliminated.

 Occupational health

Such a dangerous work is not required as a repair work under dangerous and hot condition frequently required for the oven wall of the carbonization chamber that is likely to be frequently damaged and a raking work under dangerous and hot condition work when plugged during discharge of coke.

 Productivity

A work of unloading coke that requires a large amount of manpower becomes unnecessary, thereby improving the occupational safety and health and the productivity.

 Diversity of products

The chamber coke process can produce mostly only single coke product, but the delayed coking process can produce various coke products with different properties.

Honda et al. reported that the quinolone‐insoluble (QI) components contained in coal‐tar pitch interfere in the production process of pitch needle coke (see [6]). Various methods such as elimination by hot filtration (see [10]), after dissolving in a solvent separation by filtration, centrifugation, and precipitation (see [11]), improvement of quality of a mid‐cut fraction by distillation (see [7, 12]), separation by supercritical fluid extraction (see [9]), and the like are proposed, but a method that is scaled up to industrial application is only the method in which an antisolvent is added to separate QI (see [2–4]). In this method a properly selected solvent is added to dissolve coal‐tar pitch from which QI can be easily separated. A detail of this method is described only in the patent described above. At present development activity directed to the pitch needle coke process is high in China, and many patents are applied (see [13–17]).