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The main purpose of coking coal pretreatment: The strength of coke depends to a large extent on the caking property of the raw coal, and low-quality coal has poor caking properties, so it cannot be used directly as raw coal； Pre-treatment of low-quality coal (including processes such as pre-drying, rapid preheating, and granulation) has proven to be an effective method for improving the properties (cohesiveness) of low-quality coal ； Thereby achieving: clean charging of the furnace ； Use more low-cohesion coal to reduce coal blending costs (the main benefit, accounting for 2/3 of the total benefits) ； Increase coke oven production (secondary benefit; (primary benefit, accounting for 1/3 of total benefits)) ； Energy savings (more gas production) and environmental protection (reduced wastewater treatment needs) ； The main approach to improving the bindability of weak-cohesive coal: increasing the bulk density of coking coal fed into the furnace (the main method) ； Quick preheating of the coke coal fed into the furnace ； Add binders such as petroleum asphalt/tar ； Increase the bulk density of coking coal fed into the furnace ； Mechanism of improving the bulk density of coking coal fed into the furnace to enhance the bindability of weakly cohesive coal ； The increased bulk density of the coking coal fed into the furnace results in a smaller distance between the coal particles, thereby enhancing the bonding force between them ； The increased bulk density of coking coal when it enters the furnace not only enhances the cohesion of the coal itself but also strengthens its bonding with surrounding coal particles, thereby improving the cohesion of coals with low adhesiveness ； The increased bulk density of the coking coal fed into the furnace reduces the distance between particles, thereby increasing particle-to-particle contact ； The increased bulk density of the coking coal fed into the furnace allows the gas between the particles to be expelled, thereby preventing an increase in pressure inside the coke during the coking process ； Mechanical compression of the raw coal can be used to increase the bulk density of the coking coal fed into the furnace, thereby improving the bindability of weakly cohesive coal ； Application example: Tamping coke process ； Blended coal production process ； This method cannot reduce the moisture content of the coking coal fed into the furnace (it may even increase it) ； Pre-drying the raw coal can also achieve the goal of increasing the bulk density of the coking coal fed into the furnace, thereby improving the bindability of weakly caking coal ； Application example: CMC process ； DAPS process ； SCOPE 21 process ； Precarbon process ； It can simultaneously reduce the moisture content of the coking coal fed into the furnace (to 0% is possible) ； The mechanism by which pre-drying of coking coal can increase the bulk density of coking coal fed into the furnace ； As the moisture content of coking coal decreases, the water film on the surface of the particles is reduced, and the surface tension resulting from moisture between the coal particles also decreases. As a result, the resistance to relative movement between the coal particles is reduced; this enables smooth material flow during loading, and the coal can settle evenly and compactly once it is in the furnace. The packing density is significantly higher compared to when wet coal is used for loading ； Experiment: Fill a bucket with wet coking coal/coal blend, place it in an oven for drying, and after drying, put everything back into the bucket. It can be observed that the volume of the dried coking coal decreases significantly, and its fluidity improves markedly after drying ； The fluidity of coal (including coking coal) increases as moisture content decreases ； The figure below shows the experimental results regarding moisture and the fluidity of coal powder ； https://pic2.zhimg.com/80/v2-2ade8f77edfefaf1477174c036995805_1440w.jpg The relationship between coking coal moisture and bulk density is shown in the figure below ； There is not always a linear relationship between coking coal bulk density and its moisture content ； Within the range of 0–4% to 5%, there is a linear relationship between the moisture content and bulk density of coking coal; above 4% to 5%, the relationship between moisture content and bulk density is nonlinear ； https://pic2.zhimg.com/80/v2-c10de37d85b02865c402a44957084141_1440w.jpg The effect of the temperature of coking coal entering the furnace on its bulk density is achieved through the moisture content of the coking coal ； The relationship between coking coal temperature and coking coal moisture is shown in the figure below ； https://pic1.zhimg.com/80/v2-2d4b49390eedce3d1a978495ec659934_1440w.jpg There is not always a linear relationship between coking coal temperature and its moisture content ； Within the range of 20–120°C, there is a linear relationship between the temperature of coking coal and its moisture content: when the temperature of the coking coal reaches 120°C, its moisture content has been reduced to 0% ； Thereafter, even as the temperature of the coking coal continued to rise, its moisture content remained at 0% ； The moisture content of coking coal not only affects its bulk density but also has an adverse effect on the coking process (based on existing research findings) ； The impact of moisture in coking coal fed into the furnace on coke quality ； The higher the moisture content of the coking coal fed into the furnace, the greater the porosity of the coke produced after coking, and the worse the thermal conductivity of the coke. As a result, more time is required for the coking coal to reach the desired temperature ； The image below shows the pores of coke produced by the conventional wet coal process ； The image at https://pic2.zhimg.com/80/v2-d8241b8a2a8015e3be1d4fb73190a3d5_1440w.jpg shows the pores in coke produced using the Precarbon process (the moisture content of the coal used in the furnace is 0%, and no coal powder granulation is involved) ； https://pic1.zhimg.com/80/v2-05759c120f3a57fd611e101e6dfb8694_1440w.jpg The effect of moisture in coking coal on the volume of the coke formed ； https://pic3.zhimg.com/80/v2-9de60bfe40ac55a4d4062ce722736e8a_1440w.jpg The maximum volume contraction occurs when the moisture content of the coking coal fed into the furnace is 6% ； The volume contraction is minimal when the moisture content of the coking coal fed into the furnace is 1% ； Effect of moisture in coking coal fed into the furnace on the coking volume ； https://pic3.zhimg.com/80/v2-9de60bfe40ac55a4d4062ce722736e8a_1440w.jpg The maximum volume contraction occurs when the moisture content of the coking coal fed into the furnace is 6% ； The volume contraction is minimal when the moisture content of the coking coal fed into the furnace is 1% ； Effect of moisture in coking coal fed into the furnace on the morphology of the coke formed ； https://pic1.zhimg.com/80/v2-9a00b4934a7072f2c73b265a58786944_1440w.jpg When dry coal with 1% moisture is coked, the coke produced is dense, with the fewest air pores in its center and minimal amount of foamy coke ； After coking, wet coal with 6% moisture content yields coke of a looser structure, with more central bubble coke ； When wet coal with 12% moisture is coked, the coke produced is loose, with numerous central pores and many bubble cocks ； Effect of moisture in coking coal fed into the furnace on the morphology of the coke formed ； The pressure generated by the expansion of water as it vaporizes when heated causes the water vapor to escape through the gaps between the coal particles, which in turn increases those gaps and makes the coke structure looser ； The lower the moisture content of the coal fed into the furnace, the denser the coke formed; there are fewer gas bubbles in the center of the coke, its thermal reactivity is lower, its strength increases after reaction, and the quality of the coke is better ； The impact of moisture in coking coal fed into the furnace on coke quality ； The figure below shows the relationship between the moisture content of coking coal fed into the furnace and CSR ； https://pic2.zhimg.com/80/v2-136ce99c1c94a8726f8bb273efe75d09_1440w.jpg To increase the bulk density of coking coal and improve the quality of coke, the moisture content of the coal fed into the furnace should be reduced to 0% ； To this end, the temperature of coking coal should be no less than 120°C ； By pre-drying the raw coal while granulating the separated coal powder, the bulk density of the coking coal fed into the furnace can be further increased ； Mechanism by which coal powder granulation increases the bulk density of coking coal fed into the furnace: The bulk density of coal powder is relatively low, at only 0.47–0.55 or less ； The bulk density of coal powder after granulation can be increased to over 0.8 ； Bulk density of coal powder with different particle size distributions (Delta Company test data) ； https://pic2.zhimg.com/80/v2-dbffefe4bf0e7a105fb24bb1d02494b5_1440w.jpg has a mechanism similar to that of the ramming coke process ； Test: The dried coking coal was screened to obtain ultra-fine coal powder with a particle size of 140 mesh/0.1 mm, which was then placed in a bucket. When the hand was inserted into this ultra-fine coal powder, it was possible to easily move the hand up, down, left, and right within it ； Effect of coal powder granulation ratio on the bulk density of coking coal fed into the furnace: The figure below shows the relationship between the coal powder granulation ratio and the bulk density of coking coal ； https://pic4.zhimg.com/80/v2-7f52de864ef8e16b7386c4765b3bc247_1440w.jpg There is a nonlinear relationship between the bulk density of coking coal and the proportion of coal powder used for granulation: there is an optimal proportion of coal powder granulation that allows for the highest bulk density to be achieved ； Both excessively high or low granulation ratios will reduce the bulk density of coking coal; the optimal granulation ratio is 10-20% (depending on the type of coal) ； The figure below shows the relationship between the coal powder granulation ratio and the bulk density of the coking coal fed into the furnace ； https://pic3.zhimg.com/80/v2-62ead147d0eec504622be1f1813777e6_1440w.jpg Mechanism of the influence of coal powder granulation ratio on the bulk density of coking coal fed into the furnace ； Its mechanism is similar to that of crushing ； The gaps between briquettes need to be filled with a certain amount of coal powder in order to achieve the highest density when fed into the furnace ； When the proportion of pulverized coal used for granulation is too high (i.e., excessive granulation), there is not enough pulverized coal to fill the gaps between the briquettes, which in turn results in a lower density of the material fed into the furnace ； Excessive granulation of coal powder not only reduces the density of the material fed into the furnace, but also leads to increased investment and operating costs ； Both the DAPS and SCOPE processes suffer from excessive coal powder granulation ； The DELTA process avoids the problem of excessive granulation of coal powder ； Analysis and comparison of mechanical extrusion and drying methods for improving bulk density ； To simplify the analysis process, the representative process using mechanical extrusion is the rammed coke process ； The representative process that uses drying is the DELTA process ； https://pic2.zhimg.com/80/v2-623361d74bfd9f2c46bba912ab1e456d_1440w.jpgDELTA process parameters: The moisture content of the coking coal fed into the furnace is 0% (it can be adjusted between 0 and 3%) ； The temperature of coking coal entering the furnace is 120°C (adjustable between 80-200°C) ； Coal powder granulation ratio and particle size: 15-20%/0-0.2mm ； The coal powder granulation process involves extrusion granulation using a water-soluble binder ； The DELTA process can be regarded as the DPAS process with 0% moisture content in the coking coal fed into the furnace ； Analysis and comparison of mechanical extrusion methods and drying methods for improving bulk density ； The table below shows the dimensions of the tamped coke chamber and coal cake ； https://pic1.zhimg.com/80/v2-fd2bec1727b14cbd2ee6cf89e8bc47e4_1440w.jpg The image below shows the bulk density of dry coal when it is loaded into the furnace for different coking processes, as well as the volume of steam generated by the moisture contained in each unit volume of coked coal ； https://pic1.zhimg.com/80/v2-6bf3af987acee21f0f4991ce579876c0_1440w.jpg For the ramming coke process, after the coal briquettes are added to the carbonization chamber and crushed, their bulk density decreases from 1.1 to 0.91 ； After further deducting its water content, the dry-basis stacking density in the rammed coke process is similar to that of the DELTA process ； Due to the large amount of moisture retained within the coal briquettes of compacted coke, this moisture generates a significant amount of water vapor during the coking process ； The steam generation per unit volume in the rammed coke process is 1.5 times that of the wet coal process ； With the DELTA process, since the moisture is dried to 0%, there is no residual moisture at all ； The water vapor generated by the residual moisture in coking coal can have an adverse effect on the quality of coke, reducing the proportion of weakly caking coal used ； If the ramming coke process and the DELTA process use the same coal blend, the CSR of the DELTA process (top-loading furnace) should be (significantly higher? ）Higher than the rammed coke process ； It can be inferred that the proportion of weakly cohesive coal used in the consolidation coking process should be lower than that in the DELTA process; the DELTA process is likely the preferred method for top-loading furnaces when binders such as asphalt or petroleum are used ； Application example: SCOPE21 process ； Blended coal production process ； Mechanism: The added binder, asphalt/oil, is directly converted into colloids during the coking process, and these colloids can enhance the cohesion of coals with weak bonding properties ； Suitable operating conditions: It can only be considered when the price of asphalt/oil is close to that of high-quality coking coal (this is perhaps the main reason why the briquette-making process and the SCOPE process have not been widely adopted) ； The expert panel organized by Japan’s Ministry of Economy, Trade and Industry issued a disappointing assessment regarding the use of asphalt as a binder in the SCOPE21 process ； https://pic2.zhimg.com/80/v2-7c798d2bf3b8295a7bc0c70cc3dda2fd_1440w.png Rapid preheating of coking coal ； Application example: SCOPE 21 mechanism (directly confirmed in MRI images): Rapid preheating reduces non-covalent interactions such as hydrogen bonding and π-π interactions between molecules in coking coal ； Rapid preheating relaxes the aggregated structures in coking coal, thereby improving the cohesive components and the cohesion of the coal; the minimum preheating rate must be > 1000°C/minute, with the preheating temperature ranging from 350–400°C. Appropriate application scenarios: This approach can be considered only when there is a need to significantly increase the capacity of coke ovens, or in the case of new coking projects ；