Many authors have proposed a critical particle size, below
which gasification is performed in the chemical regime and the
gasification rate is constant. For instance, Van De Steene et al.
(2011) found that, for particle thickness below 2.5 mm, the char
steam gasification is chemically controlled at 900 C. Mermoud
et al. proposed 1 mm as the critical size, below which char steam
gasification is chemically controlled at 900 C