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Abstract
Two kinds of high alkali and alkaline earth metal (AAEM) lignite (TTc and ZDc) were used as fuels, and three atmospheres of CO2, CO/CO2, and H2O (g) were used in the horizontal tube furnace experiments to simulate the gasification conditions in different parts of the boilers. The relevant thermodynamic calculations on the atmospheres and ash compositions were conducted in FactSage 7.2. The results show that both two coals have a high risk of slagging. Decreasing the relative content of SiO2 or increasing the relative content of Al2O3 can increase the ash fusion temperatures (AFTs) of TTc; increasing the relative content of CaO can increase the AFTs of ZDc. Besides, it is not recommended to adjust the relative content of Fe2O3. The proportion of the liquid phase of ZDc ash in CO/CO2 atmosphere is much higher than that of CO2 and H2O (g) in a typical circulating fluidized bed (CFB) gasification temperature interval, while the generation of liquid phase of TTc ash is less affected by atmospheres. The bottom of boilers is the most severe slagging zone, and purging with H2O (g) is a good way to alleviate the low-temperature slagging of the return feeder.
Highlights
Low-rank lignite is widely distributed in China, the United States, Australia, Indonesia, and Germany, and it plays an integral role in primary energy production and consumption [1]
3.1 Influence of typical mineral components on ash fusion temperatures (AFTs) The calculated ternary and pseudo ternary phase diagrams are shown in Fig. 2 and Fig. 3
TTc ash located in the primary crystallization region of Nepheline that closes to the region of Albite, indicating that a large number of low-temperature eutectic systems could be generated at a relatively low temperature
Summary
Low-rank lignite is widely distributed in China, the United States, Australia, Indonesia, and Germany, and it plays an integral role in primary energy production and consumption [1]. AAEMs (mainly referring to Na, K, Ca, and Mg) in low-rank lignite can act as good catalysts during coal gasification, while, the different migration and transformation characteristics of AAEM elements and complex reactions between AAEMs and other minerals such as Al, Si, and Fe, will low the AFTs and lead to slagging [1-5]. The CFB gasification technology is extensively applied in the coal chemical process and power generation for their high gas production and low environmental pollution. Coal particles will experience different atmospheric conditions, in which the bottom of the boiler can be approximately regarded as a high concentration CO2 atmosphere, the upper of the boiler as a reducing atmosphere (CO/CO2), and the segment of feeder mainly as H2O (g) atmosphere. Some studies have been conducted on the impact of the equivalence ratio on slagging and fouling characteristics of high-AAEM lignite, there is still lacking a systematic study to explore the influence of gasification agent types in different segments of boilers on slagging and ash fusion characteristics of lignite
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