Influence of water-soluble sodium on the pyrolysis and thermal nitrogen transformation of high alkali coal

Zhundong coalfield has a huge coal resource,some of which is called high alkali coal because the alkali metal content exceeds 0. 4% . In the process of thermal utilization,Na acts as a catalyst to affect the thermal reaction process and NOx emissions by changing the activity of the coal reaction process. In order to study the effect of watersoluble Na on the pyrolysis and nitrogen transformation of high alkali coal,Zhundong coal was selected as a typical high alkali coal. Different content of NaCl was added into Zhundong coal after washing by hydrochloric acid solution to represent water-soluble sodium. Pyrolysis experiments were carried out by thermogravimetry and differential scanning calorimetry,Fourier transform infrared spectroscopy,and mass spectrometry (TG-DSC-FTIR-MS). The Coats-Redfern integration method was used to analyze the kinetics of coal pyrolysis reaction. The results show that a small amount of sodium promotes the degassing reaction at low temperature of 40-295 ℃ ,excessive sodium exhibits a promoting effect at high temperature of greater than 800 ℃ ,and the effect of sodium on the main pyrolysis stage is not obvious. The kinetic analysis shows that the apparent activation energy decreases when the amount of added Na is less than 0. 6% ,indicating that Na has a catalytic effect on the pyrolysis characteristics of high alkali coal. The comprehensive analysis of infrared and mass spectrometry found that HCN is the main gaseous precursor of NOx during coal combustion process under slow heating conditions,and its production is much larger than NH3. The addition of Na can significantly promote the formation of NH3 during coal pyrolysis,which can be increased by 61% at the Na content of 0. 7% . The amount of HCN produced increases when the amount of Na is less than 0. 6% ,but the addition of Na inhibits the formation of HCN when its content is more than 0. 6% . The generation of NOx precursor is reduced at the Na content above 0. 6% . Therefore,the pyrolysis utilization of high alkali coal is beneficial at the Na content of 0. 6% ,which promotes coal pyrolysis and reduces the formation of NOx precursors.