Study On Sodium Release Behavior Of Zhundong Coal And Its Ash Melting Mechanism Of Blending Coal

As the main fuel resource,coal will play an important role in China’s energy structure in long time.Zhundong area of Xinjiang province is rich of their coal resource.Due to high cost of transportation of limited geographical location and"Xinjiang power delivery"national strategy,it is crucial to use this coal to generate electricity rationally and reasonably.Whether it is pulverized coal furnace,or fluidized bed boiler,the heat transfer surface are serious contaminated,fouled and deposited,which damages operation of the boiler.As a result,it is of great significance to study and optimize these problems.First,Zhundong coal,Xinqiao coal and Binxian coal were prepared for elements/industry/ash analysis and TGA-DSC were conducted for combustion reaction kinetics analysis.Experiments results show that Zhundong coal have high sodium（6.43%）and calcium（41.78%）,of which acid/alkali ratio is 9.2 and it belongs to serious slagging coal.The coal have earlier ignition point（385℃）and narrow and strong DTG/DSC single reaction peak,which combined the volatile and fixed carbon peak and caused wonderful combustion characteristics.And kinetics results show that the activation energy of TGA and DSC are 88.02 kJ/mol and 97.41 kJ/mol,respectively,which are better than Binxian and Xinqiao coal and the reason are high volatiles and high alkali metal/alkaline earth metal contents.Secondly,the sodium in Zhundong coal was regarded as object and a series of heat behavior were conducted.Through three extraction experiments,the sodium content was3.406mg/g and organic sodium,water soluble sodium and insoluble sodium were about25.38%,54.21%and 20.42%,respectively.Through evaporation experiments,organic sodium began to evaporate at 200-300℃and the fastest period is 400-700℃and it come to the end at 800℃.Meanwhile,the thermodynamic equilibrium system of Zhundong coal sodium migration and transformation was simulated by Gibbs minimum energy principle.The mutual transformation between gas phase and coagulation phase of NaCl,Na₂SO₄,NaOH and Na₂O·SiO₂ were focused on discussing.Then,the sodium condensation experiments were conducted.The sodium compound had the best cooling temperature period of 670±20℃.And condensation was easy to occur on the scattered roughened surface.Besides,the formation of the"inner layer"and corrosiveness were also proved by the flowability of the sodium compound observed through SEM.Finally,the ash of Zhundong coal and its blending coal were prepared.TGA-DSC,which were used to determine the phase transition temperature,XRF,which analyzed elements,XRD,which analyzed the mineral transformation mechanism,and FSEM-EDS,which were used to observe the micro-morphology,together were explained ash fusion mechanism.The decomposition products of CaO,free SiO₂ and melt Fe-S-O of Zhundong coal ash promoted the low temperature eutectic reaction.High calcium ash samples formed1um square block particles after 900℃.With the increase of temperature,the particles embedded into the molten substrate and fully melted at last,which could be observed visible flow traces.Meanwhile,high aluminum and silicon coal samples were sintered to irregular particles at high temperature and the large pieces of slag became into smooth and dense vitreous matters,but small amounts of pores could be observed.