Combustion Characteristics And Sulfur Migration Mechanism Of Ningdong Coal Chemical Chain

Chemical looping combustion（CLC）technology is a new type of flameless combustion technology,which relies on the reduction and oxidation reaction of oxygen carrier（OC）between fuel reactor（FR）and air reactor（AR）to transfer lattice oxygen and heat required by the reaction.OC with excellent performance is an important condition to ensure CLC has high efficiency and stable operation.The artificial preparation of OC has the problems of high cost and easy deactivation,so in this work,the easy to obtain and highly active natural manganese ore is selected as OC to explore its performance in the CLC of Ningdong coal.So far,there are few studies on the transformation mechanism of sulfur in the process of CLC.In this work,molecular dynamics simulation method is used to explore the migration mechanism of sulfur in the process of CLC.Thermogravimetric analysis（TGA）results show that the selected manganese ore OC have good oxygen carrying capacity and reactivity,and the maximum weight loss rate in reducing atmosphere is about 9.03%.The Mn based oxides and Fe based oxides have reactivity at 600℃ and 700℃ respectively.At 900℃,the CLC effect of manganese ore OC and Ningdong coal is good.About 80%of carbon in coal is converted into CO₂,the reaction time of coal gasification is shortened by 48%,and the generation of SO₂is reduced by 72%,which indicates that manganese ore can catalyze coal gasification and has a certain capacity of sulfur fixation.In the multi cycle experiment,slight sintering occurred on the surface of manganese ore OC,and the BET surface area decreased from 0.64 m²/g to 0.40 m²/g,resulting in the gradual decrease of reaction activity.After 30 cycles,the wear rate of manganese ore is about9.9%,the estimated service life is about 150 h.In addition,the capacity of sulfur fixation will gradually decrease with the consume of alkali metals.Manganese ore has no obvious inhibitory effect on NO_xemission in experiments.The composition structure of Ningdong coal was analyzed by XPS,¹³C–NMR and other means,and the chemical structure of low rank Ningdong coal was constructed.After density optimization and structure optimization,Ningdong coal pyrolysis model was established.Molecular dynamics simulation of the pyrolysis process of Ningdong coal in the early stage of CLC,the calculation tool is Lammps software package.The results show that in the simulated temperature range of1000–3000 k,with the increase of heating rate,the heavy tar products increase and the gas products decrease,the overall pyrolysis effect decreases.However,different heating rates have little effect on the final product form of sulfur in Ningdong coal,and sulfur will be transferred to H₂S or sulfur-containing organic gas.There are many kinds of pyrolysis products in Ningdong coal model under constant temperature（2500K）,and secondary reaction will occur.In the process of constant temperature pyrolysis,sulfur is easy to migrate to small molecular weight fragments,which will eventually form hydrogen sulfide and combine with H radical to form H₂S,and then participate in the subsequent combustion reaction.