The Structure of Coal Char: Part I—Pore Branching

Abstract

A semi-empirical model is developed to describe the structure of porous coal char. The pores are assumed to be cylindrical tubes of length l_p and radius r_p . The number of pores whose radius is between r_p and r_p + dr_p is denoted by a pore distribution function. A statistical theory and the available data suggest a r_p ⁻³ distribution of pore number density. The pore length is expressed as a collision integral over the distribution function and is shown to be proportional to the pore radius. Each pore that reaches the exterior surface of the char particle is depicted as the trunk of a tree. Each tree trunk of radius rt is associated with an internal structure whose surface area is proportional to rt³ . The theory suggests that the structure of this “pore tree” resembles that of an ordinary tree or river system.