Effect of phosphorus-based additives on sodium release during Zhundong coal gasification in flat flame-assisted entrained flow reactor

Co-gasification of high-alkali coal and phosphorus-rich sludge sewage is an effective way to lower the release of alkali and alkaline earth metals and avoid ash-related problems, such as fouling, corrosion, and slagging. However, to date, the effect of phosphorus-rich sludge sewage on the sodium release of Zhundong coal (ZD) and its mechanism under entrained flow gasification is still unclear. In this work, we investigated the effect of phosphorus-based additives, NH4H2PO4 and Ca3(PO4)2, on sodium release and mineral evolution during ZD gasification in a flat flame-assisted entrained flow reactor. Results show that the carbon conversion of ZD decreases with the addition of NH4H2PO4 and Ca3(PO4)2 because they are flame retardants, reducing the gasification reactivity of the coal. At the initial stage of coal gasification, much more sodium is released by the additives for the formation of fine particulate matter NaxPOy. The ratio of sodium release is 34.69%, 37.49%, and 37.66%, respectively for ZD, ZD blended with NH4H2PO4 and Ca3(PO4)2 when the PO4 3 -/Na molar ratio is 1/1 at 1400 degrees C. As the coal is further gasified, fine par-ticulate matters collide, condense, and react with alkali and alkali earth metals to produce NaAlSi3O8 and Ca9MgNa(PO4)7. Much more sodium is found in the slag, and the ratio of sodium release decreases from 65.78% to 61.89% and 57.51% at 1400 degrees C, which demonstrates that the sodium release of ZD is lowered by the additives. Besides, Ca3(PO4)2 shows a better effect on the sodium release of Zhundong coal under entrained flow gasification. When the PO4 3 -/Na molar ratio is 1/1, the ratio of sodium release reaches the minimum value. (c) 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.