Abstract
Water inside coal particles could potentially enhance the interior char–steam reactions during pyrolysis and gasification. This study aims to examine the effects of water contents on the char conversion during the pyrolysis and gasification of Shengli lignite. The ex-situ reactivities of chars were further analyzed by a thermo gravimetric analyzer (TGA). Under the pyrolysis condition, the increase in water contents has monotonically decreased the char yields only when the coal particles were small (<75 µm). In contrast, the water in only large coal particles (0.9–2.0 mm) has clearly favored the increase in char conversion during the gasification condition where 50% steam in argon was used as external reaction atmosphere. The waved reactivity curves for the subsequent char–air reactions were resulted from the nature of heterogeneity of char structure. Compared to the large particles, the less interior char–steam reactions for the small particles have created more differential char structure which showed two different stages when reacting with air at the low temperature in TGA.
Highlights
IntroductionWith the continual diminishing of high-rank coal, lignite as a low-rank fuel is becoming an increasingly important resource for producing chemicals and generating energy [1,2,3,4]
With the continual diminishing of high-rank coal, lignite as a low-rank fuel is becoming an increasingly important resource for producing chemicals and generating energy [1,2,3,4].The high-water content which sometimes exceeds 50 wt % for some lignites greatly restricts its utilization
This study has indicated that the water content in lignite could affect the char conversions during the pyrolysis and gasification in steam, and impact the subsequent char–air reactions
Summary
With the continual diminishing of high-rank coal, lignite as a low-rank fuel is becoming an increasingly important resource for producing chemicals and generating energy [1,2,3,4]. The high-water content which sometimes exceeds 50 wt % for some lignites greatly restricts its utilization. Dewatering is the first and essential step in almost all lignite utilization processes. Dewatering coal on a large scale is always very energy-intensive, especially for those processes requiring a very deep extent of drying. It will greatly favor the economic feasibility if (partially dried) lignite containing a certain level of water could be used as feedstock
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