Effect of CO2 and H2O on lignite char structure and reactivity in a fluidized bed reactor

Lignite chars were produced in a fluidized bed (FB) reactor under 100%N2, 100%CO2 and 50%N2/50%H2O atmospheres, respectively. The physicochemical characteristics of the three kinds of chars were subsequently characterized, and the gasification reactivity of these chars were studied. The results indicated that the char produced under H2O and CO2 atmospheres have a rougher surface and a more developed pore structure than that produced under N2 atmosphere. The specific surface areas of different samples follow the trend: raw coal < N2 char < CO2 char < H2O char. Interestingly, it is found that the gasification of CO2 - char is beneficial for the development of 2–4 nm pores, while the gasification of H2O - char is beneficial for the development of 4–30 nm pores. The chemical groups existing on the three chars are similar, indicating that the impact of the pyrolysis atmosphere on the chemical groups of char is insignificant. It is also showed that the best reactivities of gasification are obtained on the chars produced under 50%CO2/50%N2 and 50%H2O/50%N2 atmospheres, which is largely affected by porosity of the chars.