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Coking is an effective way for an integrated refinery to process the residues of crude oil. Coking processes are normally carried out to minimize coke and maximize liquid products. Production of liquid products drives economics except for specialty cokers (like needle coke). The first atmospheric coking processes were started in 1928. Coking, in general, has become more important over the years because traditional heavy fuel oil demand has declined and the demand for lighter products has increased. This has made it more attractive to convert the heavy fuel oil components into better marketable light, clean components. The present major source of production of marketable coke is the delayed coking process developed by Standard Oil. Conventional delayed coking is shown in the flow diagram in Figure 6.1.2.2. A delayed coke complex is depicted in Figure 6.1.2.3.

The refinery residues are heated in a furnace (b) up to about 485–500 °C. After passing a fractionator tower where middle distillates are topped off, they are fed into one of the coking chambers. The energy gained in the furnace passages is sufficient to release the cracking reaction in the filling time of the coking chamber (delayed coking). The reaction zone is also called mesophase, because the transition from liquid residue molecules to solid crystalline coke structure occurs here. The pressure in the coking chamber can be varied between 2 bar and 6 bar. In the furnace, steam is dosed to the residue to inhibit the formation of coke. The vapors in the coking chamber – gases, naphtha, middle distillates, and heavy coker gas oil – are routed to the fractionator for separation, then fractionated, and forwarded for downstream units for posttreatment. The heavy coker gas oil is recycled as coker feed or is used in other refinery processes such as hydrocracker or gas oil hydrotreater or as feed to fluid catalytic cracking unit [11].

Table 6.1.2.1 Refineries with petroleum coke production 2005.

Refinery	Estimated production Mta 2005	Typical analysis % S	Current FOB price	US$
North America
East Coast
Motiva, Delaware City	0.70	5.6	34	15–18
Valero Energy, Paulsboro	0.50	5.0	100	No export
West Coast
Tesoro	0.30	6.5–7.0	50	35–
BP, Cherry Point	1.00	3.5	45	Anode grade
Chevron, El Segundo	1.10–1.20	4.0–4.5	65–70	49–51
Bakersfield	0.25	0.9	30
Shell, Martinez	0.42–0.45	1.1–1.5	40	50–55
Shell, Wilmington	0.630	2.6	53–55	55–
ExxonMobil, Torrance	1.10	1.1–1.5	50	60–
ConocoPhillips, Santa Mariaa)	0.35	4.8	65	—
ConocoPhillips, Carson		2.6–3.0	40–42	48–50
ConocoPhillips, Rodeo	0.40	0.9	85	Anode grade
Tesoro Golden Eagle	0.43	2.5	28	37–40
Valero, Wilmington	0.60	4.2–4.5	60–65	49–51
Valero Benicia	0.40	3.5	30–35	30–
US Gulf
Marathon Galveston Bay refinery	0.90	5.0–5.5	80	28–29
Chevron, Pascagoula	2.50	6.3	35	25–26
CITGO, Corpus Christi	0.90	3.9–4.1	46–47	29–30
CITGO, Lake Charles	1.40	3.7	60–65	29–30
LyondellBasell	2.00	4.0–4.3	45–48	29–30
ConocoPhillips, Lake Charles	1.30	6.0–6.2	40–42	26–27
Valero, Corpus Christi	0.40	5.8–6.2	77–80	25–26
ExxonMobil, Baton Rouge	1.30	4.5–5.0	50	28–29
ExxonMobil, Chalmette	0.65	4.5	55–60	29–30
ExxonMobil, Beaumont	1.10	5.8	65–67	27–28
ExxonMobil, Baytown	1.00	6.2–6.3	47–50	24–25
Koch Petroleum, Corpus Christi	0.40	3.0–4.0	90	40–
Marathon, Garyville	0.90	5.8	42–44	24–25
Motiva, Port Arthur	0.90–1.0	6.7–6.9	57–62	26–27
Valero, St. Charles	1.40	4.0–4.5	42–	28–29
Valero, Texas City	1.00	6.5	40	24–25
ConocoPhillips, Sweeny	1.40	4.2	44–45	29–30
Valero, Port Arthur	1.40	5.8–6.3	38–39	25–26
Shell, Deer Park	2.00	5.8	42–50	25–26
Inland
BP, Toledo (US)	0.55	4.5	30–35	15–30
BP, Whiting	0.55	5.0–5.5	80	l5–30
CITGO, Lemont	0.40	4.0–5.0	80
ConocoPhillips, Billings	0.35	5.7	38–45
El Dorado’	0.40	2.1	50
ExxonMobil, Billings	0.20	6.0	30
ExxonMobil, Joliet	1.10	5.0–5.5	50	15–30
Koch Petroleum, Pine Bend	1.80	5.1	50	28–30
ConocoPhillips, Wood River	0.35	5.0	35–40	15–30
Central America
Pemex‐Refinación Madeira	0.80	7.0	40
Pemex‐Refinación Cadereyta J.	1.00	8.0	40
South America
PDVSA, Lagoven	0.65	4.3	60–65	29–30
PDVSA, Maraven	1.20	4.2	38–42	28–29
Petrozuata	1.20	4.1	70–75	29–30
Sincor	2.30	4.2–4.6	52–60	29–30
PDVSA Cerro Negro	0.85	4.2	65–70	29–30
Hovensa	1.20	4.0	37–39	27–28
Hamaca	1.30	4.0–4.3	60–65	29–30
Asia and Europe
Agip, Gela	0.70	4.5	60
Midor	0.30	5.5	55	50–
Malaysia Refining Co Sdn Bhd	0.35	5.0	45	40–
MiRO, Karlsruhe	0.29	3.0	60	50–
MOL	0.20	3.5	70
Reliance Oil	2.50	6.1–6.3	43–50	60–
Repsol. La Coruña	0.45	4.8	80	45–
Repsol, Puertollano	0.45	4.5	55	a) a)
BP, Gelsenkirchen	0.26	3.0	60	50–
BP, Lingen	0.15	1.5	65	60–
OMV, Burghausen	0.15	1.5	65	60–
Conoco, Immingham	2.1	0.2	—	Needle coke

^a S = Sulfur; HGI = Hardgrove.

While one coking chamber is being filled in the cycle time, the other chamber is emptied. Typical volume of a modern coke drum is about 1000 m³ with size range in diameter from 5 to 9 m and in height from 20 to 45 m. After steaming and cooling of the coke chambers, the coke is removed by drilling and cutting with high‐pressure water (up to 340 bar pressure). The green coke obtained is conveyed to its application after the draining step: either as fuel or feed for calcining. Table 6.1.2.2 shows the different green coke qualities in relation to use.

The following components can be used as feed to the delayed coking units [12]:

1 1. Crude residues (atmospheric or vacuum).

2 2. Crack components (visbroken tar, cycle oil, decant oil, or thermal crack tar).

3 3. Deasphalted residues (pitch).

4 4. Coal oils.

5 5. Used plastic materials (recycling).

The products of delayed coking processes are (basis: vacuum residue or crack components):

1 1. Gas/LPG (approximately 13 wt%).

2 2. Naphtha (approximately 11 wt%).

3 3. Middle distillates (approximately 45 wt%) – typical light and heavy coker gas oils.

4 4. “Green petroleum coke” (approximately 31 wt%).

Figure 6.1.2.1 Area petroleum coke production 2013 and production increase plans up to 2015.

Delayed coking is carried out in order to free refinery from the “heavy fuel oil” product that is not easily marketable. In terms of investment delayed coking is a much cheaper technology compared with flexicoking or hydrocracking (factor 3–5). A further argument in favor of delayed coking can be the revalorization potential for the carbon products “regular calcinate” or “needle coke.” Moreover, delayed coking shows good product results, which like all thermal conversions have “middle distillates” as main product.

Figure 6.1.2.2 Flow sheet of delayed coking. (a) Fractionator. (b) Furnace. (c) Coke drum. (d) Crusher. (e) Coke dewatering bin. (f) Water tank. (g) Coke–water pit.

Figure 6.1.2.3 Photograph of a refining delayed coker complex: furnace, coke drums, fractionator, and dewatering bins.

Figure 6.1.2.4 shows the product yields for the North Sea crude “Brent.” All thermal conversion processes reduce the coke make and increase yield of middle distillates, especially the delayed coker unit. The goal of nearly all delayed coker units is to minimize coke yield and maximize distillate fractions as possible. However, when the objective is to produce green coke that shall serve as raw material for higher‐quality coke products (regular calcinate and needle coke), a specific feed optimum must found that, which may not result in a minimum coke yield.

Table 6.1.2.2 Green coke qualities in relation to use.

	Heating medium	Regular calcinate feed	Needle coke feed
Sulfur content (wt%)	>2	1.0–3.0	0.1–0.8
V/Ni content (mg/kg)	200–500	50–200	<50
Ca/Na content (mg/kg)	50–300	20–100	<50
VCM (wt%)	9–14	7–9	5–7

Figure 6.1.2.4 Product yields with thermal conversion processes.

The distillate yields and thus the capacities of delayed coking can be increased by [12–14]:

1 1. Pre‐conversion of feed components [11].

2 2. Addition of light middle distillate to the feed stream.

3 3. High coke drum outlet temperature /high coker furnace outlet temperature (COT).

4 4. Low operating pressure.

5 5. Maximizing fresh feed rate by minimum recycle ratio.

6 6. Addition of coil steam.

Some quantitative effects are shown in Figure 6.1.2.5.

The following technical improvements have been achieved for the production of petroleum coke in modern delayed coking plants. They result in increased plant reliability, improved work safety, and better coke quality as well as increased production capacity [16–19]:

1 1. On‐stream spalling and/or pigging (allows spalling/pigging of one or two of the four furnace coils while the other are in operation).

2 2. Homogeneous petroleum coke quality (requires temperature and recycle ratio ramps over the cycle time to adjust continuous coking conditions).

3 3. Optimum coke chamber filling (requires mass balance of feed and products and measurement of the coke chamber level) and addition of antifoam medium (silicon oil).

4 4. Batch computerization (allows automatic checking and starting of operation steps without losing time).

5 5. Automatic coke cutting with vibration alarms at coke drum wall (coke cutting with no personnel).

6 6. Automatic hydraulic coke drum bottom head.

7 7. Combination tool for drilling and cutting.

8 8. Hydraulic feed line moving.

9 9. Hydraulic coke drum bottom head closing.

10 10. Use of slide valves for bottom and top drum unheading.

Figure 6.1.2.5 Relationship between plant operating conditions and plant yield. Parameters: (a) coke drum pressure = 2.5 bar; (b) feed/recycle ratio = 1 : 1.3; (c) coke drum outlet temperature = 440 °C [15].

With these technical advancements the cycle time for delayed coking can be reduced from about 24 to 12 hours [20–23]. The time required for different steps in typical 12 hours and 24 hours coking cycles is listed in Table 6.1.2.3.