Comparative analysis of the effects of dry and wet quenching on coke strength

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Comparative Analysis of the Effects of Dry and Wet Quenching on Coke Strength Wei Yuling, Xu Wensheng, Hu Jianjun (Technical Supervision Department, Jinan Iron and Steel Group Corporation, Jinan 250101, Shandong, China) Abstract: By measuring coke strength and moisture content, a comparative analysis was conducted on the impact of dry quenching and wet quenching on coke quality. The results show that quenched coke improved maturity, reduced the formation of microcracks, and enhanced the internal structure; its crush strength M40 was 6% higher than that of wet-quenched coke, while the moisture content of the coke decreased by 5%. Keywords: dry quenching of coke ； Wet quenching of coke ； Crush resistance ； Moisture Content in Coke Chinese Library Classification Number: TQ522.16 Document Code: B Article Number: 1004-4620(2002)05-0029-02 Comparative Analysis of the Effects of Dry Quenching and Water Quenching of Coke on Coke Strength WEI Yu-ling, XU Wen-sheng, HU Jian-jun (Technical Supervision Department of Jinan Iron and Steel Group, Jinan 250101, China) Abstract: The effects of dry quenching and water quenching on coke strength were compared and analyzed by measuring coke strength and moisture content. The results showed that dry-quenched coke has improved maturity, reduced crack initiation, and a better internal structure; its breaking strength M40 was 6% higher than that of coke quenched with water, while the moisture content in the coke was reduced by 5%. Keywords: dry quenching of coke; water quenching of coke; breaking strength; moisture content in coke 1 Introduction Dry quenching of coke means that after the coke is removed from the carbonization chamber, it is not extinguished using water, but rather by blowing inert gases or non-flammable gases. 　? The main process in the coke system is: coke oven – coke tanker – elevator – coke feeding device – dry quenching furnace – coke discharging device – conveyor belt – intermediate coke bin. Wet quenching involves quickly transporting the coke that has just been discharged from the carbonization chamber to the bottom of the quenching tower, where it is sprayed with water for 80–120 seconds; the water supply is then controlled for 1 minute, after which the coke is unloaded onto the coke bed. 　Since adopting dry quenching in March 1999, Jinan Iron and Steel Group Corporation (abbreviated as Jigang) has played a positive role in reducing quenching dust, recovering the residual heat from red coke, and improving the atmospheric environment. The mechanical strength of the coke has been significantly enhanced, providing high-quality raw material for blast furnace iron production. 2. What is the impact of dry quenching on coke moisture? Coke moisture is an important physical property indicator of metallurgical coke, and its level and stability play a significant role in the operation of blast furnaces. The results of moisture measurement for wet coke and dry coke are shown in Tables 1 and 2. Table 1: Moisture content of coke before dry quenching, in % 12345678910; average fluctuation range: 5.1, 4.3, 5.0, 4.3, 4.4, 5.1, 5.2, 4.7, 4.7, 4.3; 4.5, 6.5, 2.8, 5.5, 5.4, 5.3, 4.2, 4.4, 4.2, 5.8, 4.7, 2.8–5.8, 4.8, 5.0, 3.9, 4.6, 4.6, 4.6, 4.4, 4.2, 4.6, 5.3. Table 2: Moisture content of coke after normal operation of dry quenching, in % 12345678910; average fluctuation range: 0, 0, 0.2, 0, 0.2, 0.2, 0.2, 0.17, 0.2–0.8, 0, 0.2, 0.2, 0.2, 0.2, 0.2, 0.2, 0.2, 0.2. As can be seen from Table 1, the moisture content of coke when using wet quenching is around 2.8%–5.8%; wet quenching tends to cause fluctuations in moisture levels. When calculating the amount of coke used in blast furnaces on a weight basis, this can lead to variations in the feed rate and thus cause instability in furnace operation. As can be seen from Table 2, with dry quenching, the moisture content of coke ranges between 0.2% and 0.8%, with very little variation, which is conducive to stabilizing blast furnace operation. 3. What is the effect of dry quenching on the mechanical strength of coke? The mechanical strength of coke refers to its resistance to crushing (M40) and its wear resistance (M10). 　?The strength test results for wet quenched coke and dry quenched coke are shown in Tables 3 and 4 respectively. Table 3: Percentage of coke mechanical strength before dry quenching
Items: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
Average:
Fluctuation range:
M40: 78, 76.6, 76.8, 77.0, 78.6, 77.2, 77.8, 77.2, 78.6, 76.8
M40
M40
M10: 7.2, 7.4, 7.2, 7.2, 7.6, 7.4, 7.6, 7.6, 7.0, 7.0
Average: 77.3
Fluctuation range: 75.2–81.4
M40: 76.4, 76.2, 76.2, 78.2, 81.4, 77.2, 76.8, 76.2, 76.0, 76.8
M10
M10
M40: 77.2, 78, 78, 77.8, 78.6, 78.0, 77.0, 76.0, 77.8, 75.2
Fluctuation range: 66.6–80.0
M10: 7.6, 7.6, 7.6, 7.4, 7.6, 7.4, 6.6, 7.2, 7.6, 7.6

Table 4: Percentage of dry-quenched coke strength during normal operation
Items: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
Average:
Fluctuation range:
M40: 80.4, 81.6, 79.8, 81.0, 80.8, 80.8, 80.6, 81.4, 80.2, 81.2
M40
M40
M10: 6.6, 6.4, 6.2, 6.4, 6.8, 6.4, 6.6, 6.8, 7.0, 6.4
Average: 80.84
Fluctuation range: 79.8–81.8
M40: 81.4, 80.8, 80.8, 80.4, 80.8, 81.8, 81.6, 80.4, 81.0, 81.0
M10
M10
M40: 80.4, 81.2, 80.2, 81.2, 80.2, 80.2, 80.2, 81.6, 80.8, 80.8
Fluctuation range: 76.5–87.0
M10: 6.0, 6.8, 6.4, 6.6, 6.0, 6.0, 6.6, 7.4, 6.8, 6.2
M10
M10

As can be seen from Table 3, the strength of coke produced by wet quenching is relatively low and unstable; it tends to break under the pressure and friction encountered in blast furnaces. At the same time, due to the rapid temperature drop, the internal stresses generated within the lump coke can also cause it to break apart. Broken coke and coke dust affect the flow and uniform distribution of air in the blast furnace, leading to an increase in the coke ratio and fluctuations in furnace temperature. In severe cases, this can cause problems such as material accumulation, collapse of the furnace structure, nodulation, and damage to the tuyeres, thereby disrupting the normal operation of the blast furnace. As can be seen from Table 4, the dry quenching strength **has increased and remains relatively stable**. The analysis suggests that: (1) In the dry quenching furnace, red coke is subjected to impact; the cokes collide and rub against each other, resulting in thorough mechanical \"grinding\" of the coke. The ability of coke to resist impact forces and to break into smaller pieces along cracks or defects in its structure is enhanced, thereby improving M40 ； Friction on the red coke causes the coke to resist the formation of a thin layer of separation on its surface, enhancing its ability to break down into fragments and powder, thereby reducing M10. (2) Dry quenching of coke reduces the dust attached to it, further lowering the M10 value of the coke. (3) Coke cooled slowly during the dry quenching process, which overcomes the increase in internal stress in the coke that occurs during wet quenching, prevents the formation of microcracks, and improves its structure. Moreover, within the dry quenching equipment, the red-hot coke is subjected to a \"soaking\" period in the pre-storage chamber, which enhances its maturity and results in more uniform and stable coke quality. 4 Are there any issues? (1) Due to limitations in production conditions, the advantages of dry quenching of coke have not been fully utilized; only the coke from coke ovens No. 3 and No. 4 is quenched using dry methods. The coke from Coke Oven No. 5 cannot yet be quenched dry ； Currently, both dry-quenched and wet-quenched coke are used in iron production, which can lead to fluctuations in moisture content and strength, thereby having an adverse effect on blast furnace ironmaking processes. (2) It is recommended to use a single type of coke for each blast furnace. 5 Conclusion? Dry quenching of coke is beneficial for improving coke quality, with particularly significant effects on enhancing coke strength and reducing moisture content. Dry quenching of coke improves its maturity, reduces the formation of microcracks, and enhances its internal structure. The crushing strength M40 increases by about 6%, while the wear resistance strength M10 decreases by about 4%. The moisture content of the coke is reduced by about 5%. As the quality of coke improves, it provides a solid guarantee for blast furnace operation, contributes to an increase in the blast furnace utilization rate, reduces the coke consumption per unit of output, and decreases operational accidents, thereby creating conditions for optimizing the operating environment of blast furnaces.