Slagging and element migration characteristics of Zhundong coal in horizontal liquid slag cyclone furnace
The clean and efficient conversion and resource utilization of high-alkali coal have significant strategic importance for achieving the"dual carbon"targets.Liquid slag boilers have considerable advantages in burning high-alkali coal,but there is still a lack of re-search on the ash deposition and elemental migration characteristics of coal that is entirely burned with high alkali.This study investigated the ash deposition and slagging characteristics and the elemental migration patterns of Zhundong coal during combustion in a 20 MW hori-zontal liquid slag boiler.Ash deposition probes 1 and 2 were set up before and after the slag trap to study the effect of ash deposition on the heat transfer surface on thermal efficiency.The results indicate that during the initial layer formation stage,the heat flux density across the probe surface rapidly decreases,and as the deposit grew,the heat flux density gradually decreases,and when the deposit growth becomes stable,the heat flux density will fluctuate within a certain range.The formation process of ash deposition can be divided into three stages according to the rate of change of heat flux density on the probe surface:a rapid decline phase,a slow decline phase,and a stable phase.The final stable relative heat flux densities of probes 1 and 2 are 0.75 and 0.83,respectively.In addition,by analyzing the appearance,mineral composition,and chemical composition of the ash and deposits at different positions in the furnace,the impact of ele-mental migration on ash deposition and slagging was explored.The micro-characterization of ash deposition shows that oxides such as Al2O3,Fe2O3,and SiO2 are enriched in the high-temperature slag samples,while CaO,MgO,Na2O,and SO3 are mainly found in the deposits of the low-temperature area.The formation of the initial layer on the heat transfer surface is closely related to the condensation of alkali metals and their sulfates,with the average mass fractions of Na2O in the high-and low-temperature area samples being 1.38％and 4.70％,respectively.The iron element is enriched in the slag and acts as a flux,forming a low-temperature eutectic with the silicon-cal-cium-magnesium-aluminum system,which leads to a reduction in the ash melting temperature.
liquid slaggingZhundong coalelement migrationash deposition and slaggingalkali metalcoal combustion
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