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Guodian, China

Xu L.,Tianjin University | Liu J.,Tianjin University | Kang Y.,Tianjin University | Miao Y.,Guodian Fuel Co. | And 2 more authors.
Energy and Fuels | Year: 2014

Efficient utilization of the low-rank coal has been a headachy problem, especially when firing the high alkali-containing coal in a typical pulverized fuel boiler, where severe slagging and fouling originating from the alkali metal vapors may occur. The additives injection technology has been proved to be a promising method in combating these problems. In this study, the alkali capture mechanism of kaolin was investigated by burning a kind of high-sodium lignite in a laboratory-scale drop tube furnace. The effects of kaolin content, reaction temperature, and particle sizes of both kaolin and fuel on the sodium capture efficiency of kaolin were also investigated. It was found that kaolin could chemically adsorb NaCl, the primary sodium species proved in the flue gas, to form high-melting sodium aluminosilicates such as nepheline and albite, and the nepheline-forming reaction dominated the sorption mechanism. More kaolin addition led to more sodium fixed into the ash. However, the promotion was not that pronounced in high kaolin dosages. The sodium capture efficiency decreased as temperature was increased or larger kaolin particles were injected. Effect of the coal size on the sodium capture efficiency could be neglected in the tested size range. The sodium retention with 6 wt % kaolin addition of the fuel at 1200°C could attain 70% of the total sodium in the combusted coal, which can considerably reduce the ash-related problems and facilitate the safe firing of high alkali coal in boilers. © 2014 American Chemical Society.

Xu L.,Tianjin University | Kang Y.,Tianjin University | Zhang G.,Tianjin University | Wang T.,Guodian Fuel Co. | Wu T.,Guodian Fuel Co.
Combustion Science and Technology | Year: 2015

In this study, the sodium emission and control with firing a high-alkali coal was investigated in a high-temperature muffle furnace. Kaolin was chosen as an additive tested to clarify its sodium capture mechanism and assess its capture performance. The influence of some firing-related factors, such as kaolin dosage, temperature, and particle sizes, of both kaolin and coal on sodium release and sodium capture performance of kaolin was also studied. It was found that more sodium was released when the combustion temperature rose or fine fuel particles were combusted. Kaolin could efficiently capture sodium species to form high-melting sodium aluminosilicates, primarily nepheline or carnegieite. Increasing kaolin dosage led to the promoted sodium retention. However, the promotion was not that pronounced in high kaolin dosages. High temperature had a negative effect on sodium capture by kaolin, which could be ascribed to the increasing sodium emission with temperature. Fine kaolin particles exhibited a good sodium capture performance. Coal particle size had little impact on the interactions between kaolin and sodium species. More than 80% of the total sodium was retained in ash by kaolin when firing coal (30 m) with 3 m kaolin addition in the dosage of 6 wt% at 1100°C. Copyright © Taylor & Francis Group, LLC.

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