Study On The Release Behavior And Mechanism Of Sodium-based Flux During Gasification With High Ash And High Ash Fusion Temperature Coal In Shanxi

During clean utilization of the Shanxi high ash and high ash fusion temperature coal with abundant reserves by entrained-flow bed gasification,the slag has high viscosity and critical viscosity temperature due to the chemical properties of ash.Therefore,it is necessary to regulate the ash chemical properties of coal.The addition of sodium-based flux has the advantages of low cost and less additive amount to same fluxing effect for other flux.In this paper,the Na release behavior,mechanism and ash fusion characteristic in coal of adding different kinds and amounts of sodium-based flux were studied under coal gasification,and the theoretical model of sodium release was constructed.These provided theoretical basis for the application of high ash and high ash fusion temperature coal in Shanxi.In this study,the Na₂SO₄ and Na₂CO₃ flux were selected as research object,and the influence of different temperature and addition amount in the coal gasification of adding two kinds of sodium-based flux on Na release behavior was studied.The experiments found that the Na release rate decreased with the increase of sodium-based flux proportion due to the effect of catalytic gasification and reaction.The two kinds of sodium-based flux had different effects on Na release rate at different gasification temperatures.The Na release rate of adding Na₂SO₄ flux was higher when the full gasification temperature was not reached,and the Na release rate of adding Na₂CO₃ flux was higher when the full gasification temperature was reached.Then the theoretical model of sodium release was established,and the kinetic parameters in the model were solved by distributed activation energy model method.The research showed that the Na release content was only related to the content of sodium in coal and the release rate constant of sodium.The activation energy decreased after adding sodium-based flux,and the activation energy of adding Na₂SO₄ flux was lower than that of Na₂CO₃ flux at same conversion rate.In addition,the Na transformation mechanism during coal gasification was explained based on the analysis of residence time experiments at different gasification temperatures.Finally,the density functional theory was used to calculate the adsorption between sodium-based flux and typical minerals in coal,and XRD,SEM-EDX and ash fusion temperature were used to investigate the influence of sodium-based flux on ash fusion characteristics.The calculation showed that the adsorption between sodium-based flux and typical minerals in coal was chemical interaction,thereby resulting in the generation of low melting silicate aluminate mineral of sodium during coal gasification after adding sodium-based flux.The low melting mineral composition of ash increased with the increase of sodium-based flux amount,and the content of sodium in ash increased and the ash fusion temperature decrease.