Investigation of Potential Benefits of Using Bricks of High Thermal Capacity and Conductivity in a Rotating Calcining Kiln

Petroleum coke is processed into calcined coke in a rotary kiln, where the temperature profiles of flue gas and coke bed are highly nonuniform due to different flow and combustion mechanisms. Motivated by saving energy costs, the effect of refractory brick’s thermal properties on potential energy savings is investigated. This study focuses on investigating potential energy savings by replacing inner one-third of existing bricks with higher thermal capacity $(Cp)$ and/or higher thermal-conductivity $(k)$ bricks. This paper investigates the postulation: the bricks with higher thermal capacity could store more thermal energy during the period in contact with the hot gas and would release more heat to the cock bed when the bricks rotate to the position in contact with the coke bed. A rotational transient marching conduction numerical simulation is conducted using the commercial software FLUENT. The impact of brick heat capacity and thermal conductivity on transporting thermal energy to the coke bed is analyzed. The results show the following: (a) Increasing the heat capacity of brick layer reduces brick temperature, which helps increase the heat transfer between the hot gas and brick. In other words, it does help brick to store more heat from the hot gas, but heat transfer between brick and coke is reduced, which is opposite to the original postulation. (b) Higher brick thermal conductivity decreases brick temperature, thus increases heat transfer between hot gas and the brick layer. The heat transfer from brick to coke bed is also increased but not significantly. (c) Since usually a brick with a higher $Cp$ value also has a higher $k$-value, simulation of a brick layer with both four times higher $Cp$ and $k$-values actually shows a reduction in the brick temperature, and hence a degradation of the heat transfer between the brick and coke bed. Therefore, replacing the existing brick layer with a high $Cp$- and/or high $k$-value brick is not recommended.