of the reactor. Typical bed temperatures are 510–540 °C. Vapor products from the conversion reactions in the bed go overhead through cyclone separators, which remove most of the entrained coke and return it to the reactor bed. The cyclone outlets discharge the vapor product directly into a scrubber (b) where heavy liquid is used to scrub out the remaining coke dust and condense unconverted high‐boiling fractions. The dust laden liquid is recycled as “slurry cycle” to the reactor with the feed. The scrubbed vapor is sent to the coker fractionator, where the stream is split into gas, naphtha, distillate, and heavy gas oil streams. Coke produced in the reactor is gasified by steam and air in the gasifier (d), which operates at a bed temperature of approximately 955 °C. The heater (c) serves as a surge vessel and transfers heat from the gasifier overhead gas to coke, which in turn supplies the heat of reaction in the reactor. The heater bed temperature is approximately 610 °C. Coke is continuously circulated between the three vessels to transfer heat and maintain vessel inventories. Heat for the endothermic cracking reactions in the reactor is supplied by coke combustion in the gasifier. In addition to the coke fines recovered from the heater overhead gas, product coke can be withdrawn from the heater bed. All liquid or gas streams require further treating [25]. The low net coke product is very fine and has very high metals content. It has been used as fuel coke with the resultant high vanadium ash suitable for metals recovery.
Figure 6.1.2.7 Flow sheet of flexicoking. (a) Reactor. (b) Scrubber. (c) Heater. (d) Gasifier. (e) Cyclones. (f) Airblower.
6.1.2.3.2 Calcination
About 27% of the petroleum coke derived from delayed coking processes is calcined for use in downstream aluminum and steel production. The amount of calcined petroleum coke produced worldwide was 28 × 106 t/a in 2013. Calcination includes the elimination, burning, and coking of water and higher‐boiling hydrocarbons contained in petroleum coke. Finally a carbon product remains that contains sulfur and nitrogen plus small amounts of vanadium, nickel, sodium, calcium, iron, and silicon.
Calcining was carried out at about 40 calciner sites in 2005 (see Table 6.1.2.4). While the calciners in North America are usually run by independent companies or attributed to aluminum production, the calciners in other regions are production units of the refineries.
At present 66% of the calcining capacity are controlled by merger (biggest: Rain C II Carbon and Oxbow Calcining), 25% by Aluminum works/Smelter (Aluminum Bahrain, Alcan Inc., JSC Bratsk), and 9% by Refineries (ConocoPhillips, BP).
Calcining is mostly carried out in rotary kiln and rotary hearth plants. While the rotary kiln largely predominates in America, some hearth plants are used in Europe. Generally the kiln type is the technology of choice. Shaft kilns are starting to be used mostly in China.
In both types of rotary calcining complexes, the water and VCM contents of green coke are eliminated by heating up to 1200–1350 °C. The heat required for calcining the green coke is primarily provided by burning the VCM released from the coke calcination process. Combustion air is admitted to the calciner. In normal operation only the quantity of air needed for the complete combustion of the VCM release from the coke is added; no free oxygen occurs in the off‐gas.
Table 6.1.2.4 Petroleum coke calciners [25].
| Owner | Location | State | Type | Production capacity (103 t/a) |
|---|---|---|---|---|
| North America | ||||
| Alcan | Arvida | Quebec | Kiln | 215 |
| Alcan | Kitimat | British Columbia | Kiln | 80 |
| Alcan/Intalco | Edmonton | Alberta | Kiln | 165 |
| Arco | Cherry point | Washington | Hearth | 675 |
| Arco | Los Angeles | California | Kiln | 315 |
| Calciner Industries | Chalmette | Louisiana | Kiln | 200 |
| Calciner Industries | Gramercy | Louisiana | Kiln | 230 |
| Calciner Industries | Norco | Louisiana | Kiln | 170 |
| Calciner Industries | Purvis | Mississippi | Kiln | 80 |
| Conoco | Lake Charles | Louisiana | Kiln | 260 |
| Great Lakes Carbon | Enid | Oklahoma | Kiln | 470 |
| Great Lakes Carbon | Port Arthur | Texas | Kiln | 635 |
| Kaiser Aluminum | Mead | Washington | Kiln | 80 |
| Landmark Petroleum | Fruita | Colorado | Kiln | 240 |
| Reynolds Metals | Baton Rouge | Louisiana | Kiln | 620 |
| Reynolds Metals | Lake Charles | Louisiana | Kiln | 200 |
| Union Chemicals | Rodeo | California | Kiln |
|
