The Study Of Effects Of Metal Oxides And Salts Additives On Sulfur Fixation During Coal Pyrolysis And Char Conmbustion

In this thesis,the effects of different metal oxides（CaO,CuO）,salts（ZnCl₂,Na₂CO₃）and the mixtures of CaO and other additives on the release of sulfur-containing gases（H₂S,COS and SO₂）and their sulfur-fixed ratios were investigated during pyrolysis and char combustion ofOrdos（ED）and Yangquan（YQ）coals.The influence of different additives on the change of sulfur forms during pyrolysis was analyzed by XPS technology.The main conclusions are drawn as following:（1）ZnCl₂ and CuO can effectively inhibit the release of sulfur-containing gases and improve the sulfur-fixed ratios during pyrolysis of ED and YQ coals.By XPS analysis,the pyrolysis sulfur-fixed products of ZnCl₂ and CuO in the chars were mainly Zn S and Cu₂S,respectively.The inhibition effect of CaO on the release of sulfur-containing gases in the pyrolysis process is lower than that of ZnCl₂ and CuO.The sulfur-fixed products of CaO are stable Ca S and Ca SO₄.The inhibitory effect of Na₂CO₃is weak on the release of sulfur-containing gases during pyrolysis of ED coal with high pyrite content,while significantly strong for YQ coal with high organic sulfur contents.Thus,Na₂CO₃ has little sulfur-fixed effect on ED coal,while it appears strong sulfur-fixed effect on YQ coal.The sulfur-fixed products of Na₂CO₃ are stable Na₂SO₄ and a small amount of Na₂S.Four kinds of additives all can strongly promote the decomposition of pyrite sulfur,meanwhile,ZnCl₂ and CaO can also promote the decomposition of thiophene sulfurs.During combustion,because Zn S and Cu₂S are easy to be oxidized,so a large amount of SO₂ was released,so that the combustion sulfur-sulfur ratios is very low.Ca S is oxidized to stable Ca SO₄,and Na₂SO₄ also has good stability,so the char obtained by adding CaO or Na₂CO₃ has good combustion sulfur-fixed performance.（2）Calcium-based sulfur-fixed agents are mainly CaO,mixing with a certain proportion of ZnCl₂,CuO and Na₂CO₃,respectively.Compared with these single additives,the calcium-based sulfur-fixed agents all appear comparatively higher comprehensive sulfur-fixed during coal pyrolysis and its char combustion,as they can effectively reduce H₂S and COS release during coal pyrolysis,and capture released SO₂ during char combustion and improve pyrolysis and combustion sulfur-fixed ratios.（3）To verify whether the sulfur-fixed reaction during coal pyrolysis and char combustion is gas-solid reaction,the absorption reactions of these additives on sulfur-containing gases were further investigated.It is found that the sulfur-fixed reaction of metal oxides and salts is solid-solid reaction.ZnCl₂ has better absorption of H₂S and COS,CuO is inferior to ZnCl₂,CaO and Na₂CO₃ have weaker absorption capacity,and no synergistic effect was observed in the direct absorption of sulfur-containing gases by composite sulfur-fixed agents.This is not consistent with the sulfur-fixed effect of these additives on coal pyrolysis and char combustion process.