Coke is produced from residues of crude oil distillation. The crude oil is first water-washed in a de-salter to remove solids and salts. The desalted crude oil is preheated, and then vaporized in a fired heater. The vaporized oil is fed to a distillation tower, where it cools and condenses as it flows up the tower. The crude oil remaining at the bottom of the distillation tower, knows as "bottoms" or reduced "crude" is routed to another unit. In this unit the bottom oil is reheated and subjected to vacuum in another distillation tower. The vacuum causes the oil to boil at a lower temperature and allows distillation of additional intermediates, without thermally decomposing the still valuable reduced crude to carbon (or coke).
Once the bottoms from the vacuum distillation operation cannot be further distilled, the "vacuum residuum" is routed to the next unit in the process, the Coker.
The calcining process takes anode grade green coke from the oil refining process and converts it to almost pure carbon, with a defined structure. This is essentially a time-temperature function with the most important control variables being heating rate. To obtain the calcined coke properties required by the industries, the coke must be subjected to temperatures of 1200-1350 Deg C or higher to refine its crystalline structure. This is usually done using a rotary kiln. When the hot calcined coke leaves the kiln, it is transferred to a rotary cooler. In the cooler, the hot coke is quenched by water, sprayed from a number of nozzles. The exit temperature is controlled at approximately 150 degrees C to assure a moisture-free product.