Exploration of effective bed material for use as slagging/agglomeration preventatives in circulating fluidized bed gasification of high-sodium lignite. (1st April 2018)

• Record Type: Journal Article
• Authors: Qi, Xiaobin; Song, Guoliang; Yang, Shaobo; Yang, Zhao; Lyu, Qinggang
• Is Part Of: Fuel. Volume 217(2018)
• Page Start: 577
• Page End: 586
• Publication Date: 2018-04-01
• Subjects: Bed material -- Slagging -- Agglomeration -- Circulating fluidized bed -- High-sodium lignite; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2017.12.126
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: The feasibility of three minerals as bed material was studied via experiment and calculation. SiO2 and Al2 O3 could retain sodium within the residual ash via chemical reactions. CaO could enhance the release of sodium via competing reactions. The SiO2 -based mineral is not suggested as the bed material. Boiler ash is a potentially effective and low-cost bed material for high-sodium lignite. Abstract: An effective bed material is crucial to remit slagging/agglomeration for high-sodium lignite during circulating fluidized bed (CFB) gasification. In this study, the exploration of effective bed material for use as slagging/agglomeration preventatives of high-sodium lignite mined from Zhundong district was conducted in a 0.4 T/D CFB test system. Three mineral materials, SiO2 -based quartz sand, Al2 O3 -based corundum and CaO/Fe2 O3 -rich boiler ash collected from bottom ash of a CFB industrial boiler, were selected as the potential bed material. Their impacts on the de-fluidization tendency, transformation and migration of alkali metals, priority of reactions involving sodium-based species, formation of liquid slags and ash fusibility were investigated through the characterization of ash samples and thermodynamic equilibrium calculation by Factsage 6.1. The particle-size analysis results presented the improvement of three bed materials in the growth of ash particles followed the order of quartz sand > corundum > boiler ash. This order was ascribed to their reaction priority with sodium-based compounds in coal and the chemical property (mainly referring to ash fusibility) of corresponding products. Generally, reactions between sodium-based species and minerals (Al2 O3 and SiO2 ) were the main way of sodium retention within the ash in gasifier. As boiler ash was used, however, Al2 O3 and SiO2 preferentially reacted with the CaO enriched in boiler ash rather than sodium-based species in coal, resulting in very low sodium retention. Under such circumstances, computing results suggested the ash in gasifier could withstand higher gasification temperature, consistent with the measured results of ash fusibility. Additionally, the gasification temperature operating range could be largely widened by simply increasing CaO/Fe2 O3 content in gasified ash. Therefore, boiler ash is an effective and low-cost bed material for use as the slagging/agglomeration preventative of high-sodium lignite during CFB gasification.