Evaluation of Coal Thermoplastic and Dilatation Behavior with Coke Pore Structure Analysis

Abstract

The strength of coke largely depends on the thermoplastic and dilatation behavior of its coal constituents. Therefore, understanding the behaviors that ensure high-strength coke is important. In this study, the combination of blended coal was varied and (in a separate experiment) asphalt pitch (ASP) was added to the blended coal. The resulting changes in coke pore structure were investigated by image analysis of a cross-section of coke. The main findings are summarized below.
(1) When the thermoplastic temperature of low- and high-rank coal was very different, the proportion of low-circularity pores increased in the textures of both the grades of coal. It was concluded that when the particles of high-rank coal did not dilate, those of the low-rank coal freely expanded. Meanwhile, the dilatation of high-rank coal decreased the extent of dilatation in the neighboring low-rank coal. Consequently, high-rank coal not adjacent to low-rank coal achieved free expansion, and its texture became characterized by increased low-circularity pore areas.
(2) The addition of ASP to blended coal decreased the number of low-circularity pores in the texture of high-rank coal. ASP appears to lower the softening temperature of high-rank coal, enabling it to fill the voids between coal particles before the low-rank coal solidifies.
The abovementioned investigation of coke pore structure assists our understanding of the thermoplastic and dilatation behavior of coal.