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Coking Process of Graphite Electrode

Release time:2019-11-04 From: Zhengnai Industry in China

5 types of coking process

There are two kinds of coking processes for early production of petroleum coke:
  • 1. kettle coking,
  • 2. flat furnace coking.
At present, there are three commonly used production processes:
  • 1. delayed coking,
  • 2. fluid coking, and
  • 3. contact coking.
Kettle coking process
The coke type coking is intermittent production. After the raw materials are sent to the coking kettle, after the temperature rise, soaking, blowing, cooling, etc., the oil and gas components are fully volatilized and the coke remains. The kettle type coke generally has more cokes and less powder coke.


 

Delayed coking characteristics

The characteristic of delayed coking is that the residual oil passes through the furnace tube of the heating furnace at a high flow rate, and the residual oil is heated to about 500 ° C, and immediately enters a coking tower of several tens of meters high, and the residual oil is brought into the coking tower by itself. The heat is subjected to a coking reaction.
 

Definition of delayed coking unit

The delayed coking unit is a heating furnace equipped with two coking towers. The residual oil heated to a specified temperature enters one of the two coking towers. When coke is generated and accumulated in a coking tower to a certain height, the hot residue oil is switched to another In a coking tower.


 

Contact coking definition

Contact coking is a thin oil layer coking, and the contact coking heat carrier is coke, and the active surface of the coke is the center of the new coke layer.
 

Contact coking is divided into 2 categories

  • (1) The moving bed with a larger particle size is in contact with coking.
  • (2) Fluidized bed contact coking of powdered coke, referred to as fluid coking.
 

Characteristics of fluidized coking

Fluidized coking has greatly improved the heating conditions for coking. The main equipment for fluid coking is a fluidized bed reactor.


 

Powdered petroleum coke is not suitable for the carbon industry

The loosely structured powdered petroleum coke is not suitable for use in the charcoal industry. The fluidized coking liquid product has a high yield, but the coke yield is low and mostly powder coke.
 

Fluidized bed reactor use process

The fluidized bed reactor is filled with high temperature coke powder (heat carrier) in a fluidized state, and the oil and gas and water vapor cause the powder coke to be fluidized.

The role of two coking towers

In the delayed coking, the steam-liquid product recovery fractionation system outside the coking tower is continuously produced. For the two coking towers, only one is in the coking production state, and the other is in the coke or ready state.

Size of UHP Graphite electrode

Item Unit UHP
300-500mm 550-600mm 700-800mm
Electric resistivity Electrode μΩm 4.6-6.2 4.5-6.0 4.5-5.8
Nipple 3.5-5.0 3.4-4.5 3.3-4.3
Bending strength Electrode Mpa ≥10.5 ≥10.0 ≥10.0
Nipple ≥20.0 ≥22.0 ≥23.0
Elastic modulus Electrode Gpa ≤14.0 ≤14.0 ≤14.0
Nipple ≤20.0 ≤22.0 ≤22.0
Bulk density Electrode g/cm3 1.66-1.73 1.68-1.74
Nipple 1.75-1.82 1.78-1.85
CTE(100-600℃) Electrode 10-6/℃ 1.20-1.50 1.10-1.50
Nipple 1.10-1.40 1.00-1.30
Ash % ≤0.3

 

Petroleum coke quality is related to 5 operating parameters

  • Temperature inside the tower. As the temperature increases, the volatiles of the coke decrease and the strength of the coke increases.
  • Pressure inside the tower. The pressure in the coking tower is increased, and the volatile matter of the coke is lowered.
  • Coking time. Extending the coking time can reduce the volatile content of the coke and increase the mechanical strength, but will affect the yield of the device.
  • Speed of water injection and steam injection. The flow rate is too fast, the coking reaction is severe, part of the spherical coke is formed, the true density is lower after graphitization, and the linear expansion coefficient is relatively large, which is not suitable for the production of graphite electrodes.
  • Cycle ratio. The cycle ratio is increased, the coke yield is increased, the volatile content is decreased, and the mechanical strength of the coke is correspondingly increased.
Operational factors that contribute to needle coke generation
When producing needle coke, the coking tower should maintain a high pressure, generally delayed coking is 0.2~0.3 MPa, and the pressure in the coking drum producing needle coke needs to reach about 0.7 MPa. At the same time, a larger cycle ratio is required, such as a cycle ratio of 1.8~2.0 (generally delayed coking cycle ratio is only 0.3~0.4). These operational factors facilitate the generation of needle coke.

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