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TECHNOLOGY

Production Technology of Coal Needle Coke

Needle coke is an excellent carbon material, it is named for its slender needle shape after pulverization. The needle coke has a metallic luster and a layered structure inside. It has good orientation, good electrical and thermal conductivity, therefore, it is the main raw material for ultra-high-power electrodes for steelmaking. Using ultra-high-power electrodes and high-power electric furnace to produce steel, which is 10%~20% power energy less than the use of ordinary power electrode, and the smelting time is shortened by 20%, in a word, he unit cost is save above 10% than ordinary electrode.

There are two types of needle coke, oil needle coke and coal needle coke. Oil needle coke is produced from petroleum heavy oil, oil residue. Coal needle coke is produced from coal tar distillate or tar asphalt. The production processes are different for oil needle coke and coal needle coke, but the uses are basically the same. Here we are going to introduce coal based needle coke process.

Product quality index

Needle coke

 Needle Coke Quality Index

Binder asphalt

Binder asphalt Quality Index

Anthracene oil 

Quality Index of anthracene oil

Coking light-phase oil

Coking light-phase oil quality Index

Coking Heavy-phase Oil and Circulating Oil

Coking gas

Quality Index of Coking gas

      Main raw materials

The raw materials for the production of coal-based needle coke in China generally use soft asphalt produced by the coal tar deep processing.

If coal tar is directly used as raw material, the material should be high temperature dry distillation coal tar (coal tar is a liquid product obtained in coal distillation process, and tar obtained by high temperature distillation (ie coking) is called high temperature dry distillation coal tar). And a set of equipment is needed to separate the soft asphalt from the coal tar.

The requirements for coal tar and soft asphalt are as follows:

     Coal tar

Coal Tar Index Requirements

Soft asphalt quality index

Washing oil

Table 2-9 Washing oil quality index

      Process description

The needle coke manufacturing process is mainly composed of three main processes: refined coal tar soft asphalt process, delayed coking process and coke calcination process.

   1.Refined soft asphalt

Figure 1.Process flow chart of asphalt refining

The high temperature dry distillation coal tar is distilled to obtain soft asphalt, and then the soft asphalt is refined by solvent extraction and sedimentation method. Solvent extraction and sedimentation method is to extract coal tar soft asphalt by using two solvents with BMCI (aromatic index value) of 5 to 70. In this case, the primary QI is easy to form flocs, and then separated by static sedimentation. The light phase portion from which the QI has been removed is distilled, and the solvent is recovered to obtain a refined soft pitch. The technical key of this method is to control the reasonable recovery rate of refined asphalt, and at the same time make the heavy phase asphalt have good fluidity and ensure the smoothness of the process.

(2) Delayed coking process

Figure 2 Schematic diagram of the process flow of the delayed coking unit

The process of delayed coking for producing coal-based needle coke is shown in Figure 3. The refined soft asphalt obtained from the raw material pretreatment process enters the raw material buffer tank, is pumped out by the raw material pump, exchanges heat with the high-temperature coking heavy oil, enters the bottom of the fractionation tower, and contacts the high-temperature coking oil and gas at the bottom of the fractionation tower and the top of the coking tower. Heat causes some of the heavy components to condense, and the uncondensed components rise along the fractionation column, and the coking gas, coking light oil, and coking heavy oil are fractionated. The coking oil at the bottom of the fractionation tower is sent to the heating furnace through the feed pump of the heating furnace, heated to 505 ° C and sent to the coking tower. Continuously feeding in the coking tower for 24h (or 36h), the coking oil in the tower continuously undergoes thermal decomposition and thermal polycondensation reaction, gradually solidifies to generate raw coke, and the generated coking oil and gas escapes from the top of the coking tower into the fractionation tower. After the end of one column feed, another column feed is introduced. The coke is cooled down by blowing oil and water. The coke is discharged from the coke tower by high pressure water coking.

(3) Green coke calcination process

Figure 3 Schematic diagram of the calcining unit process

The calcining unit for producing needle coke is usually using a rotary kiln process. The raw delayed coke produced by the delayed coking unit (hereinafter referred to as coke) is transported by a belt conveyor to a dewatering tank of the calcining unit. After the coke is dehydrated in the dehydration tank, the water is reduced from about 20% to less than 10%, and the dehydrated water is returned to the coke pool. Then it is transported by the belt conveyor to the tooth roller crusher, and the large green coke is crushed to below 60mm. It is sent to the screening machine for screening by belt conveyor and bucket elevator. The large pellets and fine materials enter 2 respectively Pre-calcined raw silo storage. The green coke vibrating feeder is fed into the rotary kiln by the electromagnetic vibrating feeder at the bottom of the raw material bin at a set discharge speed. The rotary kiln is supported by coking coal gas, and the raw coke is calcined at a temperature of 1400-1500 ° C in the kiln to produce qualified needle coke. A secondary air device is arranged on the rotary kiln body, and combustion air is sent into the kiln body, so that the volatiles which are released during the heating process of the coke in the kiln are relatively fully burned, thereby improving the calcination effect.

The calcined coke is discharged from the rotary kiln and into a rotary chiller, and an appropriate amount of water that can be fully evaporated is sprayed into the cooler to accelerate the cooling of the calcined coke, thereby reducing the contact time of the calcined coke with the air and increasing the yield of the calcined coke.The calcined coke discharged from the cooler (the temperature is not higher than l00 ° C), sent to the calcined coke finished silo through the bucket elevator and the belt conveyor, and then put into the warehouse for sale.