Energy & Fuels, Vol.29, No.8, 5322-5333, 2015
Model for the Evolution of Pore Structure in a Lignite Particle during Pyrolysis
In this paper, on the basis of the chemical percolation devolatilization (CPD) model and using the coal polymer network parameters to calculate the surface area and porosity of the particle, a model for the evolution of pore structure in a lignite particle during pyrolysis is established. The model connects the polymer network structure and the pore structure, and it may extend the application range of network statistical devolatilization models. Model predictions agree with experimentally observed trends reported in the literature for porosity and internal surface area with increasing mass release. Particle porosity increases during pyrolysis because of mass release and the opening of closed pores. Surface area changes little with mass release up to about 30% and then increases by 200 m(2)/g with further increases in mass release; this tendency is determined by the quantity of the pores that can adsorb adsorbent in the particle during pyrolysis. During the pyrolysis of Zap lignite, with the mass release increasing up to 30%, the quantity of pores that can adsorb adsorbent increases from 0 to 0.2 per aromatic cluster, and with the mass release increasing from 30 to 67%, the quantity of pores that can adsorb adsorbent increases from 0.2 to 1.2 per aromatic cluster. With the maximum particle temperature increasing from 900 to 1200 K, it is observed that the predicted porosity of char formed from Zap lignite during pyrolysis increases from 40.1 to 55.3%, the N-2 surface area increases from 18 to 447 m2/g, and the CO, surface area increases from 261 to 909 m(2)/g. However, with further increase of the maximum particle temperature, the predicted porosity and area change little. The influence of heating rate and ambient pressure on the change of pore structure during pyrolysis is small. The initial coal polymer structure significantly influences the final pore structure of the char.