What is coke dry quenching?

Coke dry quenching refers to a coke quenching process that uses inert gas to cool down the red coke.

After coal is made into coke in the carbonization chamber, it should be pushed out of the carbonization chamber in time. The temperature of red coke when pushed out is about 1000°C. In order to avoid coke burning and make it suitable for transportation and storage, it cannot be sent directly to the blast furnace for ironmaking, and the temperature of red coke must be lowered.

 

Disadvantages of coke wet quenching

 

One coke quenching method is to use water spray to reduce the temperature of the red coke to below 300°C, which is commonly known as wet coke quenching. The advantages of traditional wet coke quenching are that the process is relatively simple, the device occupies a small area, there is less investment in infrastructure, and the production operation is more convenient. But the disadvantages of wet quenching are also very

(1) Wet quenching wastes a lot of sensible heat from red coke

(2) Rapid cooling of red coke during wet coke quenching will increase coke cracks, reduce coke quality, and cause large fluctuations in coke moisture, which is not conducive to blast furnace ironmaking production;

(3) The steam generated by wet coke entrains corrosive media such as phenol, cyanide, and sulfide remaining in the coke, corroding surrounding objects and causing large-scale air pollution in the surrounding area. As the number of coke-quenching water cycles increases, this erosion will and pollution will become more and more serious;

(4) The steam generated by wet quenching carries a large amount of dust, usually up to 200-400 g/t, which not only pollutes the environment but is also a waste.

The CDQ process mainly consists of a CDQ furnace, loading device, coke discharge device, elevator, electric locomotive and coke tank trolley, coke tank, primary dust collector, secondary dust collector, CDQ process boiler unit, and circulating fan, dust removal ground station, water treatment unit, automatic control part, power generation part, etc. Depending on the design, the main equipment included in the dry quenching process system is also different.

 

Coking Plant, coke dry quenching

 

What is the process of coke dry quenching?

 

During the dry quenching process, red coke is loaded from the top of the dry quenching furnace. Low-temperature inert gas is blown into the red coke layer in the cooling section of the dry quenching furnace by a circulating fan to absorb the sensible heat of the red coke. The cooled coke is discharged from the dry quenching furnace. It is discharged from the bottom. The high-temperature inert gas coming out of the annular flue of the dry quenching furnace flows through the dry coke quenching process boiler for heat exchange. The boiler generates steam. The cooled inert gas is blown back into the dry quenching furnace by the circulating fan. The inert gas is in the closed recycled within the system. The dry coke quenching process is superior to wet coke quenching in terms of energy saving, environmental protection and improving coke quality.

 

Advantages of coke dry quenching

 

Since the coke dry quenching process can improve coke strength and reduce coke reactivity, it is beneficial to blast furnace operations, especially for coke used in large blast furnaces with strict quality requirements. The main advantage of the dry coke quenching process is to avoid corrosion of surrounding equipment and pollution to the atmosphere. , the dust pollution when the coke comes out of the coke oven is easy to control, the red coke can be placed in the coke quenching chamber, and most of the heat can be recovered and reused.

1) Coke quality is significantly improved

The temperature of the coke pushed from the carbonization chamber is about 1000°C. During wet quenching, the red coke is rapidly cooled by water spray, which generates great thermal stress in the internal structure of the coke. There are many network cracks and the porosity is very high, so its The strength of the drum is low and it is easy to break into small pieces. During the dry coke quenching process, the coke is slowly cooled, which reduces internal thermal stress, reduces network cracks and has low porosity. Therefore, the strength of the drum is increased and the true density is also increased. big.

During the dry quenching process, when coke flows from top to bottom in the dry quenching furnace, the number of mutual friction and collisions between coke blocks increases. The cracks of large coke blocks crack in advance, and the coke blocks with lower strength fall off in advance. The edges and corners of the blocks are eroded in advance, which improves the mechanical stability of the metallurgical coke, and the large blocks of coke with a blockiness above 70 IDA’n are reduced, while the medium blocks of 25 to 75 mm are correspondingly increased, that is, the coke blockiness The uniformity of the coke is improved, which is also beneficial to the blast furnace. The former Soviet Union conducted another comparative test on the coke quality of the dry coke quenching process and the wet coke quenching process. The coke was subjected to the dry coke quenching process after shortening the coking time by 1 hour. The quality is slightly better than that of coke wet quenched according to the original coking time.

2) Utilization of red coke heat in coke dry quenching process

Overseas, processes such as hot water recovery and hot air recovery have been tested, as well as experiments on using dry coke quenching process heat to facilitate coal preheating, but these have not been widely used in industry. The technically mature method is to produce superheated steam and utilize it. This method enables the steam output of the dry coke quenching process to meet the self-use steam volume of the entire coking plant. As for whether to further utilize steam to generate electricity, it will mainly depend on its steam production scale and steam pressure.

Compared with wet coke quenching, the dry coke quenching process can recycle about 83% of the sensible heat of red coke, and the heat recovered per 1 ton of dry coke is about 1.35 GJ. There is no energy recovery in wet coke quenching. The coke dry quenching process of Wuhan Iron and Steel Coke Ovens No. 7 and No. 8 uses the method of guided air combustion to control the concentration of combustible components such as H2 and CO in the circulating gas. The circulating fan adopts variable frequency speed regulation and is designed with a water supply preheater to further absorb the dry quenching process. The heat of the furnace quenching circulating gas, the design level (steam pressure, temperature) of the dry coke quenching process boiler is 3.82MPa, 450℃. Each 1 ton of dry quenched coke can produce about 0.54 t of steam with a pressure of 3.82 MPa and a temperature of 450°C.

3) Reduce the emission of harmful substances and protect the environment

The coke dry quenching process uses inert circulating gas to cool the red coke in a closed dry quenching furnace, which can avoid corrosion of surrounding equipment and pollution to the atmosphere. In addition, due to the use of coke tank positioning to receive coke, dust pollution from coke output from the coke oven is easier to control. The dust generated by coke loading on the top of the dry quenching furnace and the bottom row of the furnace, coke transportation, the gas emitted after the circulating fan, and a small amount of gas emitted from the pre-storage section of the dry quenching furnace are purified by the dust removal ground station to reduce the dust content to less than 100 nag/l. emissions to the air.

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