In Situ Heating Stage Analysis of Fusion and Catalytic Effects of a Na2CO3 Additive on Coal Char Particle Gasification

Catalytic gasification characteristics of coal using Na2CO3 as a catalyst were studied in thermogravimetric analyzer­(TGA) and in situ heating stage, respectively. The effects of gasification temperature (650–900°C) and catalyst loading amounts (10,15 wt %) on the associated gasification process were investigated. Interactions of Na2CO3 with carbon at gasification phases were observed by an in situ heating stage microscope. The results show that the interactions of Na2CO3 with coal at gasification phase varied with reaction temperature and the morphology structure of carbonaceous materials. Two different gasification reaction forms were observed for Shenfu (SF) and Zunyi (ZY) acid-washed char samples mixed with Na2CO3. For the SF-acid-0.15Na-800P sample, the Na2CO3 liquid film might flow and enter the inner space of SF-acid-0.15Na-800P at or above the melting point of Na2CO3, while with the consumption of carbon continuously, the internal Na2CO3 liquid film gradually exposed and spread outward. While ZY-acid-0.15Na-800P had a denser surface structure than SF-acid-0.15Na-800P, and most of Na2CO3 particles were mainly distributed on the outside surface of the ZY coal/char sample, when the temperature was higher than the melting point of Na2CO3, Na2CO3 began to melt, flow on the surface of ZY-acid-0.15Na-800P, and spread outward continuously. The specific reactivity was introduced as the quantitative index system of catalytic effects. The specific reactivity of all the SF samples increased with the temperature from 700 to 800 °C, while 800 °C was a turning point as the specific reactivity significantly decreased with the further increase of temperature. While the turning point did not appear for ZY acid-washed coal mixed with Na2CO3, the specific reactivity of ZY samples generally increased with increasing temperature. Two catalytic gasification reaction mechanisms were proposed, which were associated with the interactions of Na2CO3 with coal char observed during the in situ heating stage.