Effect of characteristics of calcium-based sorbents on the sulfation kinetics

2013

Cerâmica

ResumoCalcários são muito utilizados na captura das emissões gasosas sulfurosas emitidas durante a queima do carvão na geração de energia, por meio de sua injeção em caldeiras e fornalhas. A caracterização técnica deste material torna-se necessária à correta seleção e utilização de uma rocha calcária. Neste trabalho, foi realizada a análise técnica e microestrutural dessa matéria-prima, incluindo-se a caracterização dos parâmetros físico-químicos, texturais e microestruturais do calcário in natura, calcinado e sulfatado. Um calcário dolomítico foi avaliado quanto às propriedades físico-químicas, distribuição de tamanhos de partículas, área específica, volume de poros e análise em microscópio eletrônico de varredura. Por apresentar origem metamórfica, o calcário apresentou-se compacto e pouco poroso, porém após a calcinação a textura muda drasticamente, com a diminuição da densidade, aumento da superfície reativa e desenvolvimento de porosidade aberta. Estes são parâmetros fundamentais a um bom sorvente de óxido de enxofre. A fratura de partículas é gerada pela pressão interna durante a conversão dos carbonatos em óxido de cálcio e liberação do CO 2 durante a calcinação. O óxido de cálcio nascente reage com óxido de enxofre, formando uma camada compacta de sulfato de cálcio, a qual reduz a área específica pelo bloqueio dos poros, causando o aumento de granulometria média e relativa, na etapa de sulfatação. A caracterização tecnológica realizada mostrou aspectos relevantes quanto à microestrutura dos calcários calcinados e sulfatados. A pressão gerada pelo CO 2 durante a sulfatação, resultado da calcinação incompleta do calcário, é capaz de romper a fina camada de CaSO 4 , deixando poros arredondados. Palavras-chave: calcário, caracterização tecnológica, calcinação, sulfatação. Abstract Limestones are widely used to capture sulfur gas emissions emitted during the burning of coal in power generation through its injection in boilers and furnaces. The technical characterization of this material becomes necessary to correct selection and use of a limestone rock. In this work, the technical and microstructural analysis of this raw material, including the characterization of

Section: Caracterização Tecnológica De Um Calcário Dolomítico In Naturaunclassified

Caracterização tecnológica de um calcário dolomítico in natura, calcinado e sulfatado como meio dessulfurante

Souza

2013

Cerâmica

“…It is well understood that the large molar volume of CaSO 4 is an obstacle to a higher SO 2 retention: the molar volume of CaSO 4 is large compared to the molar volume of calcium carbonate and therefore complete conversion of the limestone particle is impossible. Therefore, the MgO acts as an inert component and may help in CaSO 4 formation, since there is no MgSO 4 formation as reported in many studies (Bramer in: Valk, 1995;Han et al, 2005;Laursen et al, 2005), and also in the analysis of the sulfated ashes in a study realized before (Sebag et al, 2001). Besides, the number of sorbent particles in the reactor is higher for dolomites, considering the same Ca/S, which would probably lead to a better mixing.…”

Section: Chemical Composition Of Limestonementioning

confidence: 88%

“…Recently, studies showed the importance of limestone attrition (Chen et al, 2008;Scala et al, 2008), and reactivation of limestone sorbents by water hydration (Anthony et al, 2007;Montagnaro et al, 2004). The presence of alkali metal salts showed influence in sulfation process and kinetics of the limestones (Han et al, 2005). Those studies showed that the choice of the kind of sorbent utilized in FBC is a very complex task.…”

Section: Introductionmentioning

confidence: 99%

FBC desulfurization process using coal with low sulfur content, high oxidizing conditions and metamorphic limestones

Castellan

2009

Braz. J. Chem. Eng.

-A metamorphic limestone and a dolomite were employed as SO 2 sorbents in the desulfurization of gas from coal combustion. The tests were performed in a fluidized bed reactor on a bench and pilot scale. Several parameters such as bed temperature, sorbent type, and sorbent particle size at different Ca/S molar ratios were analyzed. These parameters were evaluated for the combustion of coal with low-sulfur/high-ash content, experimental conditions of high air excess and high O 2 level in fluidization air. Under these conditions, typical of furnaces, few published data can be found. In this work, a medium level of desulfurization efficiency (~60%) for Ca/S = 2 was obtained.

“… The formation of eutectic compounds reduces the melting temperature, increasing the reactivity of the limestone, by forming a liquid phase, which causes an expansion and increased intraparticle pore diffusion (Han, 2005).…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Limestone Impurities in the Desulfurization Process of Coal Combustion Gas

Souza

2017

Braz. J. Chem. Eng.

-Limestones have been used to capture SO2 emitted during the combustion of coal for decades. However, due to the complexities of the variables involved in this process, many issues are still being studied. Some tests were performed in a fluidized bed reactor, which was used to evaluate the performance of the limestones in the bed for flue gas desulfurization, burning low sulfur coal. Metamorphic dolomitic limestones of low cost were evaluated considering the impurity level and need for beneficiation. They were characterized chemically, physically and microstructurally (X-ray fluorescence, X-ray diffraction, laser particle size analyzer, scanning electronic microscope). The data obtained were compared to a calcitic limestone of elevated purity and higher market value. The results showed little effect of the major impurities present in the dolomitic limestones in the calcination and desulfurization processes. Microcrystalline impurities showed a marked effect promoting grain sintering in calcination conditions of TGA/DTA tests in different atmospheres, as shown in SEM images. Dolomitic limestones generate more solid waste and capture less SO2 per kcal (a slightly decrease in the thermal efficiency of the reactor) compared to calcitic limestones. However, due to the lower cost, they were considered to be attractive for the FBC process (2 mg SO2/kcal at Ca/S=3).