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Simulation of the Swelling of High-Volatile Bituminous Coal during Pyrolysis. Part 2: Influence of the Maximum Particle Temperature

Yang, He, Li, Sufen, Fletcher, Thomas H., Dong, Ming
Energy & Fuels 2015 v.29 no.6 pp. 3953-3962
bubbles, coal, macropores, models, plastics, pyrolysis, temperature
A model was established previously to predict the swelling ratio of high-volatile bituminous coal during pyrolysis based on the assumption that the structure of bubble distribution in the particle at the beginning of the plastic stage is a central bubble surrounded by many surrounding bubbles. The initial number and size of the bubbles when the particles become plastic are calculated by the pressure in the particle, and the chemical percolation devolatilization (CPD) model is used to describe pyrolysis. In this paper, to obtain accurate results at low pyrolysis temperatures, the previous model is improved and the following parts in the model are adjusted: (1) the method for estimating the volume of macropores in the particle at the beginning of swelling and (2) a correlation between the initial bubble number and the particle diameter. The swelling behavior of eight bituminous coals from the literature spanning a wide range of gas temperatures and gas pressures was simulated to test the suitability of the model. The influence of the maximum particle temperature during pyrolysis (Tₘₐₓ) on swelling is analyzed. The predicted particle swelling for a Pittsburgh #8 bituminous coal particle during pyrolysis increases with Tₘₐₓ up to about 950 K, decreases as Tₘₐₓ increases from 950 to 1100 K, and then changes little with further increases in Tₘₐₓ. The influence of Tₘₐₓ coupled with the heating rate makes the swelling ratio in experiments from the literature increase from 1.07 to 1.51 as Tₘₐₓ increases from 840 to 952 K and the heating rate increases from 1.38 × 10⁴ to 2.18 × 10⁴ K/s. Particle swelling decreases from 1.51 to 0.95 as Tₘₐₓ decreases from 952 to 1662 K and the heating rate increases from 2.18 × 10⁴ to 2.24 × 10⁵ K/s. At a constant heating rate of 1 × 10⁴ K/s, when Tₘₐₓ is larger than 950 K, the predicted particle swelling during pyrolysis increases and then decreases with increasing ambient pressure. However, when Tₘₐₓ is smaller than 950 K, the predicted particle swelling during pyrolysis decreases with increasing ambient pressure.