Abstract
This work evaluated the effects of inherent alkali and alkaline earth metals on nitrogen transformation during steam gasification of Shengli lignite at the temperature of 873–1173 K in a fluidized-bed/fixed-bed quartz reactor. The results indicated that the alkali metal Na and alkaline earth metals Ca, Mg in coal have different effects on inherent nitrogen transformation to NH3, HCN and char-N during the lignite steam gasification. Specifically during the steam gasification of Shengli lignite, Na and Ca, Mg not only catalyze the inherent nitrogen conversions to NH3, but also promote the secondary reactions of the nascent char-N as well as the generation of NH3 from the generated HCN, meanwhile they also inhibited the inherent nitrogen conversion to HCN and char-N. The presence of Na, Ca and Mg hindered the formation of oxidized nitrogen (N-X) functional groups, but enhanced pyridinic nitrogen (N-6) and quaternary nitrogen’s (N-Q) formation in char.
Highlights
Gasification is an important route for efficient and clean utilization of the coal resources
This work evaluated the effects of inherent alkali and alkaline earth metals on nitrogen transformation during steam gasification of Shengli lignite at the temperature of 873–1173 K in a fluidized-bed/fixed-bed quartz reactor
The results indicated that the alkali metal Na and alkaline earth metals Ca, Mg in coal have different effects on inherent nitrogen transformation to NH3, HCN and char-N during the lignite steam gasification
Summary
Gasification is an important route for efficient and clean utilization of the coal resources. It was pointed out that the alkali and alkaline earth metallic species in lignite tended to favour the release of coal-N as tar-N but limited char-N conversion during gasification. There are few studies about the effects of alkali and alkaline earth metals on the nitrogen transformation in coal gasification process. Further study is still in immediate need in order to unveil the effects of alkali and alkaline earth metals on nitrogen migration and transformation during coal gasification. Based on the previous researches and the knowledge that tar yield could be reduced by steam in gasification process (Wang et al 2014a, b, c, d), this study further investigated effects of inherent alkali and alkaline earth metals on the nitrogen transformation in the steam gasification of Shengli lignite. This study is focusing on the nitrogen transformations to gaseous products (e.g. NH3, HCN) as well as solid products (e.g. char-N), together with the effects on N-containing functional groups in char
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