The mechanism of ramming coking

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Mechanism of rammed coking: In the rammed coking process, the coal is compacted in an iron box outside the coke oven, with dimensions similar to those of the carbonization chamber. The compacted coal cakes are then fed into the carbonization chamber through the open furnace door. After being compacted, the bulk density of the coal increases from 0.7–0.75 t/m3 for loose coal to 0.95–1.15 t/m3, which helps to improve the cohesion of the coal. As the bulk density of the coal increases, the contact between coal particles becomes tighter, reducing the gaps; consequently, the amount of colloid liquid phase products required to fill these gaps also decreases accordingly. In other words, the certain amount of colloid produced during the thermal decomposition of coal can fill the gaps between coal particles; fewer colloid liquid-phase products are needed to evenly cover the surfaces of these particles, thereby enabling stronger interfacial bonding between them during the coking process. Furthermore, during the coking process, the dry distillation gases generated from the compacted coal material do not easily escape; as a result, the expansion pressure of the coal particles increases. This forces the deformed coal particles to come closer together, increasing their contact area, which facilitates condensation reactions between the free radicals and unsaturated compounds produced by coal pyrolysis. At the same time, the increased resistance encountered by the gases produced by pyrolysis as they escape prolongs the residence time of these gases within the colloid. This gives the free atomic groups present in the gases, as well as the intermediate products of pyrolysis, more time to interact with each other, thereby enabling the formation of stable substances with an appropriate molecular weight. It also increases the amount of non-volatile liquid products within the colloid, so that the colloid not only increases in quantity but also becomes more stable. All these contribute to improving the cohesion of coal materials. Studies have shown that under the coking conditions of chamber-type coke ovens, as the density of the coal charge increases, the bonding between adjacent layers becomes stronger, which reduces the effect of shrinkage stress. As a result, cracks are more likely to form in the coke, leading to a decrease in its crush strength. By including an appropriate amount of coke dust or other reducing components in the compacted coal charge, it is possible to reduce shrinkage stress and increase the size of the coke pieces. Additionally, this approach helps to achieve an optimal ratio between the binding components and the reducing components in the coal charge, thereby enhancing the strength of the pore walls. The ramming coking process is most suitable for coking coal blends primarily composed of coal with high volatility and poor bonding properties. The purpose of adding a small amount of coking coal or fat coal, or using binders, is to adjust the proportion of binding components and compensate for the insufficient bonding properties of the blended coal mixture. Practice has shown that the crush resistance index of coke produced by ramming coking increases significantly when thinning agents such as coke dust and lean coal are appropriately added. Preheated ramming coking technology is a process that combines coal preheating with ramming and drying. In the preheating and ramming coking process, measures to improve coke quality are comprehensively applied, such as increasing the bulk density of the coal material, altering the heating rate before the coal softens, adding anti-cracking agents, and supplementing binders. During preheated rammed coking, although the heating rate and the thickness of the plastic layer are similar to those in the case of preheating coal in bulk form, the increased bulk density of the coal material due to ramming results in the resinous matter staying in the plastic layer for about 12% longer compared to when coal is preheated in bulk form ； Furthermore, since it takes less time for preheated coal to reach its softening temperature once it enters the furnace compared to wet coal, in preheated compacted coking, the residence time of the gelatinous substance in the plastic layer is increased by about 18% compared to wet coal compacted coking. As a result, in the preheated compacted coking process, the modifying effect of the binders added to the coal, as well as the effect of anti-cracking agents, are more effectively utilized.