Shrinkage kinetics of large-sized briquettes during pyrolysis and its application in tamped coal cakes from large-scale chambers

• The shrink of large size briquette was studied by self-developed mass and volume integrated measuring device.
• The large size briquette shrinkage kinetic model during the pyrolysis process was established.
• The volume shrink calculation method of industrial tamped coal cake was obtained.

Aiming at the general problem that both for the production of foundry coke made by anthracite pulverized coal and furnace coke made by tamped coke in the coke oven, namely the shrinkage problem for large-size briquette and tamped coke in the pyrolysis process, a mass and volume integrated measuring device was used to study the shrinkage process of large-sized briquettes (volume equals 103 cm3) under constant temperature (450 °C, 550 °C, 650 °C and 850 °C). The briquette shrinkage kinetic model was also established according to the regulation of mass loss and volume shrinkage, where the volume shrink calculation method of tamped coal cakes (13,280 mm × 500 mm × 4300 mm) was also obtained. Three conclusions were drawn in this study: 1. In the process of the carbonization, the dehydration and degassing reaction before 450 °C as well as polycondensation reaction at 650 °C were the main reason causing the briquette shrinkage, the decomposition reaction at 550 °C came second, while the hydrogen evolution reaction after 850 °C has the least effect on briquette volume shrinkage. There were three main reasons causing the shrinkage of large-size briquette: the decrease of coal volume caused by the volatilization of moisture and volatiles, the decrease of coal volume caused by the pyrolysis reaction and the density increase of briquette caused by the decrease of coal volume. 2. The briquette shrinkage kinetic model was represented as follows: dVt/dt = V0[(1 − x)dβ/dt − A0e−E/RT(1 − x)nβ]; There was a positive correlation between the volume changing parameter β and the density of briquette, and the volume changing parameter increased with the reaction; the shrinkage reaction was divided into three stages; with the reaction went on, the reaction order and reaction rate constant decreased, the pre-exponential factor increased and the activation energy decreased firstly and increased then. 3. The shrinkage of the tamped coal cakes from the large-scale chamber was counted in the calculated unit whose thickness was 100 mm. The shrinkage velocity of the tamped coal cakes in carbonization chamber was obtained by weighted calculating the shrinkage parameters of each volume unit at different temperatures. The shrink regulations of the tamped coal cakes in the carbonization chambers, which were in agreement with industrial production, were approximately the same as those of the large-sized briquettes. However, the shrinkage rate curve of the tamped coal cake in the carbonization chamber was gentler than that of the large-sized briquette, as a result of the large temperature gradient of different coal in carbonization chamber.