Effect of water-soluble sodium on combustion characteristics of Zhundong rapidly pyrolyzed coal char

The occurrence modes of sodium in Zhundong Wucaiwan bituminous coal were studied by the extraction with distilled water,ammonium acetate and hydrochloric acid step by step. Elements and anions in the extraction liq- uids were determined by inductively coupled plasma-atomic emission spectroscopy ( ICP-AES) and ion chromatogra- phy (IC) respectively. The results show that the predominant occurrence mode of sodium in Zhundong coal is water- soluble sodium,which is mainly in the chemical forms of NaCl,Na2 SO4 ,NaNO3 and NaHCO3 . Through adding different chemical forms of water-soluble sodium to the acid washed coal and then fast heating to generate char in Drop Tube Furnace (DTF),the authors studied the effect of single chemical form of sodium salt on char’s combustion character- istics in a thermogravimetric analyzer (TGA). Results demonstrate that,compared to the acid washed coal,the chars made from coals loaded with whichever form of water-soluble sodium have a lower initial reaction temperature,ignition temperature and burnout temperature of combustion. It indicates that water-soluble sodium promotes the combustion of high-sodium coals. Catalysis of different chemical forms of water-soluble sodium differs,among which Na2 CO3 shows most effective. Activation energy of char combustion was calculated by the method of Coats-Redfern. The loading of wa- ter-soluble sodium decreases the activation energy of char combustion,while the extent varies with the form of water- soluble sodium.