Numerical Investigation of the Effects of Gas-release Rate and Viscosity under Various Heating Rates on Swelling Ratio of Coal in the Coke Production Process

The effect of heating rate on the swelling ratio of coke during heating of coal was investigated using numerical simulations. The mathematical model in our previous study was modified to observe the effect of the heating rate, and the equation for the reaction rate of coal pyrolysis and gas formation was changed to a first-order temperature-dependent equation. The original and viscosity-dependent classical bubble nucleation equations were compared, and the results showed that the swelling ratio in the numerical simulation results reduced with an increase in the mass transfer rate of gas from coal. At low mass transfer rate (1 × 10−13 m3/s), the dependence of the swelling ratio on the heating rate was not straightforward. The swelling ratio increased in the order of the following heating rates: 10, 30, and 3°C/min. At high mass transfer rate (1 × 10−12 m3/s), the swelling ratio increased with increasing heating rate. Experimental results of varying the heating rate agreed well with the results of the large mass transfer case. The numerical simulation results indicated two issues—the gas escaping from coal is a key factor affecting the swelling of coal during heating, and the swelling ratio increased with increasing heating rate because of the short gas release time.