Sulphation of limestones in a fluidized bed combustor: The relationship between particle attrition and microstructure

Abstract

Sulphation of two limestones in a fluidized bed combustor has been investigated. One limestone (coarse-grained) was characterized by a significant population of relatively large pores after calcination; the other (fine-grained) presented a finer and fairly unimodal pore size distribution. Differences in the microstructure were reflected by different thickness of the sulphate shell formed upon sulphation and ultimate calcium conversion degree. Particle attrition/fragmentation were fairly small under moderately bubbling fluidization conditions. Fragmentation upon impact was significant. The fine-grained limestone, characterized by a thinner sulphate shell, was more susceptible to fragmentation than the other. Particle fragmentation discloses unreacted CaO enabling secondary sulphation of exhausted particles.On aétudié la sulfatation de deux calcaires dans un combusteurà lit fluidisé. Un calcaire (à grainsépais) aété caractérisé par une population significative de pores relativement larges après calcination; l'autre (à grains fins) présente une distribution de tailles de pores plus fine et assez unimodale. Les différences de microstructure se reflètent par l'épaisseur différente de la coque de sulphate formée par sulfatation et le degré ultime de conversion du calcium. L'attrition et/ou fragmentation des particules sont relativement faibles dans des conditions de fluidisation par bullage modéré. La fragmentation lors de l'impact est significative. Le calcaireà grains fins, caractérisé par une coque de sulphate plus fine, est davantage sujetà la fragmentation que l'autre. La fragmentation des particules révèle du CaO non réagi permettant la sulfatation secondaire des particules traitées.

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

“…It is clear that the process is governed by the core/shell pattern of sulfation, because the longer residence time of the 47 mm fraction did not contribute to higher desulfurization efficiency. A significant contribution of attrition of the sorbent is not expected, as pointed out in other works (Chen et al, 2008;Scala et al, 2008). The sorbents here are metamorphic limestones, what means a hard rock and low attrition rate.…”

“…Limestones of different ages may show different behavior, and also those that suffer high attrition rate, exposing new unreacted surface, as cited before (Anthony et al, 2001, Shimizu et al, 2003, Chen et al, 2008Scala et al, 2008). Fig.…”

“…The mechanisms of the sulfation reaction are still not properly understood, and there is dispute over the explanation of the well-known temperature maximum for optimum sulfur capture found in FBC boilers (Anthony et al, 2001). 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).…”

The calcium looping cycle for CO2 capture from power generation, cement manufacture and hydrogen production

“…This pore blockage then prevents access of CO 2 to the centre of a particle. There has been a large volume of research published on the attrition characteristics of limestone for SO 2 capture (Anthony and Granatstein, 2001;Smith, 2007;Chen et al, 2008;Saastamoinen et al, 2008;Scala et al, 2008;Blamey et al, 2010). However, there is less research regarding limestone for CO 2 capture.…”

Limestone Attrition under Simulated Oxyfiring Fluidized‐Bed Combustion Conditions

“…Limestone attrition during the air-blown fluidized-bed (FB) combustion of sulfur-bearing fuels has been thoroughly characterized over the last decade [1][2][3][4][5][6][7]. Key phenomenological features and mechanistic pathways of sorbent attrition have been determined with the aid of a comprehensive test protocol consisting of different and mutually complementary test procedures [1,3,8].…”