Due to the different calcining facilities, technologies of calcining petroleum coke and qualities of calcined petroleum coke are also different. There are three main calcining facilities worldwide. Can-type calcining furnace, rotary kiln and electric calciner.
Can-type calcining furnace
Can-type calcining furnace is consisting of several calcining jars which are made of refractory bricks. The raw materials are heated by heat radiation in the calcining jar. There are two types of can-type calcining furnaces: co-current and counter-current. The following takes the process of co-current can-type calcining furnace as an example.
The direction of movement of the raw materials is the same as that of the hot gas. The raw materials are added to the furnace from the top of the furnace. Heat is transferred to the raw materials indirectly through the flame path. When the temperature reaches 1200~1300℃, the raw material enters the water jacket from the feeding system to cool down, and finally exits the furnace.
The feeding system and the flame path are the most important. Per four calcining jars are one group, and every calcining furnace is formed by three to six groups mostly, promptly include 12 to 24 calcining jars.
The green coke is fed from the kiln tail. Due to the tilt of the kiln body, the green coke slowly moves towards the kiln head as the cylinder rotates. Gas or heavy oil is sprayed from the nozzle of the kiln head and mixed with the air controlled by the kiln head to form a high-temperature calcination zone of 5-10 meters long. The temperature of the calcination zone is 1200~1350℃. The green cokes are calcined inside for 50-60 minutes. Then it is discharged from the kiln head to the cooling kiln.
In electric calcining process, screening 10-30mm particles is very important, because it keeps the resistance stably in the furnace. Due to the high resistance of green coke, it is necessary to add 1/3 of the calcined cokes at the bottom of the furnace. And then loading the raw materials from the top of the furnace, so that the electrode end is buried at a depth of 300-500mm of cokes. At the beginning, the voltage should be increased to allow the current to pass. As the temperature of the raw material rises, the resistance decreases and the current rises. Slowly adjust the voltage to the best value. Usually baked every 20 minutes.
Petroleum coke is also called green coke, which contains a lot of volatile matter and needs to be calcined before used. Graphite electrode requires high performance, including flexural strength, volume density, and physical and chemical indexes, so its raw materials must be calcined before they can be used.