“…One more phenomenon to be noted in Figure b is that the samples under all four conditions were calcined completely at 300 s. This is different from the findings on Massicci limestone in the work of Wang et al, where they found that the samples which experienced 90 min of reaction still contained 3%–5% mass fraction of undecomposed CaCO 3 . The reason may be that the sulfation reactivity of the limestone used in the present work is lower than for Massicci limestone, as has been pointed out elsewhere …”
Section: Resultscontrasting
confidence: 75%
“…But it should be noted that in the simultaneous calcination/sulfation reaction, the minimum mass point occurs when the mass loss rate caused by the calcination reaction equals the mass gain rate caused by the sulfation reaction, not the end of the calcination reaction or the beginning of the sulfation reaction like that in the calcination‐then‐sulfation reaction. This means that both calcination and sulfation reactions occur in both stages in the simultaneous calcination/sulfation reaction . The mass‐growth stage can also be divided into two stages according to the sulfation rate, namely the fast‐sulfation stage (from the minimum mass point to 40 min) and the slow‐sulfation stage (beyond 40 min).…”
Section: Resultsmentioning
confidence: 99%
“…The actual process proceeds as follows: after limestone reaches hot flue gases containing SO 2 , the calcination and sulfation reactions occur simultaneously, and the two reactions affect each other. We call this process the “simultaneous calcination/sulfation of limestone” and have carried out preliminary investigations on it . Some important phenomena were demonstrated in our earlier work, in particular, the decomposition rate of limestone particles was impeded by SO 2 , and some of the CaCO 3 did not decompose completely even after 90‐min reaction in the presence of 0.38% SO 2 .…”
Section: Introductionmentioning
confidence: 98%
“…It is worth noting that the issue of reaction product interfering with limestone calcination is not only limited to SO 2 capture in CFBs, but is also important for other processes like CO 2 capture by calcium looping . Therefore, in our previous work, the characteristics of the simultaneous calcination/sulfation reaction were investigated by thermogravimetric analysis (TGA).…”
“…One more phenomenon to be noted in Figure b is that the samples under all four conditions were calcined completely at 300 s. This is different from the findings on Massicci limestone in the work of Wang et al, where they found that the samples which experienced 90 min of reaction still contained 3%–5% mass fraction of undecomposed CaCO 3 . The reason may be that the sulfation reactivity of the limestone used in the present work is lower than for Massicci limestone, as has been pointed out elsewhere …”
Section: Resultscontrasting
confidence: 75%
“…But it should be noted that in the simultaneous calcination/sulfation reaction, the minimum mass point occurs when the mass loss rate caused by the calcination reaction equals the mass gain rate caused by the sulfation reaction, not the end of the calcination reaction or the beginning of the sulfation reaction like that in the calcination‐then‐sulfation reaction. This means that both calcination and sulfation reactions occur in both stages in the simultaneous calcination/sulfation reaction . The mass‐growth stage can also be divided into two stages according to the sulfation rate, namely the fast‐sulfation stage (from the minimum mass point to 40 min) and the slow‐sulfation stage (beyond 40 min).…”
Section: Resultsmentioning
confidence: 99%
“…The actual process proceeds as follows: after limestone reaches hot flue gases containing SO 2 , the calcination and sulfation reactions occur simultaneously, and the two reactions affect each other. We call this process the “simultaneous calcination/sulfation of limestone” and have carried out preliminary investigations on it . Some important phenomena were demonstrated in our earlier work, in particular, the decomposition rate of limestone particles was impeded by SO 2 , and some of the CaCO 3 did not decompose completely even after 90‐min reaction in the presence of 0.38% SO 2 .…”
Section: Introductionmentioning
confidence: 98%
“…It is worth noting that the issue of reaction product interfering with limestone calcination is not only limited to SO 2 capture in CFBs, but is also important for other processes like CO 2 capture by calcium looping . Therefore, in our previous work, the characteristics of the simultaneous calcination/sulfation reaction were investigated by thermogravimetric analysis (TGA).…”
“…In our preliminary previous work [30,31], the simultaneous calcination and sulfation of limestone in CFBs was investigated and from this work some important observations were made. First, the weight loss rate was slower for limestone calcined with SO2; and second, some CaCO3 was still undecomposed after 90 min of reaction [31]. However, two questions still remained: how the SO2 influenced the calcination rate of limestone; and by what mechanism this influence occurs.…”
The interaction of calcination and sulfation in the simultaneous calcination/sulfation of limestone sorbent under circulating fluidized bed boiler conditions was studied. A specially designed constant-temperature reactor which can stop the reaction at a given time was employed. When limestone entered the furnace of mixed gases of CO2, O2, SO2, etc., its weight went down first, then up, so there was a minimum weight point. The whole reaction period could be divided into two stages by this minimum weight point, named the weight-loss stage and the weight-growth stage, which were dominated by the calcination reaction and by the sulfation reaction, respectively. In the weight-loss stage, the sulfation reaction took place and CaSO4 formed simultaneously together with limestone calcination as long as SO2 was present. In the weight-growth stage, the sulfation ratio at 60 min in simultaneous calcination/sulfation is 30.7% higher than that in the sequential calcination then sulfation process. The weight loss rate of limestone calcined in the presence of SO2 was lower than that without SO2 present but the final weight was higher. The calcination of limestone was slowed by the presence of SO2; a probable mechanism was proposed, namely that the CaSO4 formed may fill or plug the pores in the CaO layer, and impede the transfer of CO2 and, therefore, retard the calcination reaction. This mechanism was supported by the observation that the effective diffusion coefficient of CO2 in CaO produced in the presence of SO2 was reduced. The impeding effect increased with increasing SO2 concentration (0-3000 ppm), while, when the particle size decreased from 0.4-0.45 mm to 0.2-0.25 mm, the calcination rate of limestone was higher, no matter whether there was SO2 present or not. The impeding effect was less pronounced at 880°C than at 850°C. The reason for this appears to be the fact that there was less CaSO4 formed at 880°C and, therefore, fewer pores of the particle were filled or plugged.
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