In this study, the transformation characteristics of sodium in Zhundong coal were investigated during oxygen-rich gasification in a circulating fluidized bed (CFB) reactor. The reactor, with a fuel treatment rate of 0.4 t/d, was specially made for experiments on thermochemical conversion of high alkali coal. The equilibrium distribution of sodium in an oxygen-rich atmosphere with water steam was predicted by thermodynamic equilibrium calculations. Sodium in the ash increased with the injection of water steam and the increase in O₂ concentration in the gasification agent; accordingly, less sodium was released in the gaseous phase. Sodium existed mainly as NaAlSiO₄ in the bottom ash, and as NaCl and NaAlSiO4 in the fly ash. With the injection of water steam and the increased O₂ concentration, the NaAlSiO₄ content increased markedly. No slag phase of sodium was found in either the experimental study or the equilibrium calculation. It is beneficial to inhibit slagging and fouling in the CFB reactor during the oxygen-rich gasification with water steam.

Conclusions

In this work, the transformation mechanism of sodium during the oxygen-rich gasification with water steam of Zhundong coal in a CFB reactor was investigated, and the equilibrium distribution of sodium under an oxygen-rich gasification atmosphere was analyzed. The main conclusions are as follows:

(1) Sodium in the ash increases with the injection of steam and the increase in O₂ concentration. Accordingly, less sodium is released into the gaseous phase, which could mitigate the severe fouling and depositing problems.

(2) Sodium exists mainly as NaAlSiO₄ in the bottom ash during the oxygen-rich gasification with water steam in the CFB reactor, and mainly as NaCl and in the fly ash. With the injection of steam and the increase in O₂ concentration, the amount of sodium existing as NaAlSiO₄ increases. The formation of NaAlSiO₄ increases the melting temperature of the bottom ash. The experimental study and equilibrium calculation arrived at the same conclusion.

(3) Fewer fine particles were produced with the injection of steam and the increase in O₂ concentration during CFB gasification, which is helpful to inhibit the slagging and fouling problems.

(4) No slag phase of sodium was found in either the experimental study or the equilibrium calculation. It is helpful to inhibit the slagging and fouling problems in the CFB reactor under the oxygen-rich gasification with water steam.

The results have been published on Fuel 182 (2016) 660–667.