Surface textural changes during reaction of CaCO3 crystals with SO2 and O2 (air). 2. Large crystal faces, 670–1070 K

To understand the contribution of lime to the abatement of N2O emission from fluidized coal combustor, the catalytic activity of the lime for the decomposition of N2O under coal combustion conditions was studied. Lime was active for the catalytic decomposition of N2O, and its activity was stable in the simulated coal combustion flue gas in the absence of SO2 at 800 °C. The catalytic activity of lime was depressed by the presence of CO2, H2O, and SO2. The affect of the presence of SO2 seemed to be most important: the catalytic activity of the lime gradually decreased as the degree of sulfation increased, and the specific surface area decreased with the progression of sulfation. From N2O pretreatment and temperature-programmed desorption studies on the used lime, it was found that two oxygen species and one species of NO desorbed. A surface character change due to sulfation is expected from these gas desorptions. From the relation of the activity to the surface area or the desorption of the gases or both, it was concluded that a decrease in the surface area contributed to the decay of the activity more effectively than the surface character change caused by the sulfation.

Section: Resultsmentioning

confidence: 99%

“…However, the catalytic activity of lime in the presence of SO 2 is not well-known. ,− In particular, the effect of the sulfation of lime on its activity for N 2 O decomposition has not been clarified. This work focuses on the understanding of the characteristics of partially sulfated lime as a catalyst for N 2 O decomposition.…”

Section: Introductionmentioning

confidence: 99%

Catalytic Activity of Lime for N₂O Decomposition under Coal Combustion Conditions

and¹,

Sada²,

Hara³

et al. 1999

“…In a coal combustor at atmospheric pressure, limestone usually decomposes into CaO and CO 2 , and then CaO reacts with SO 2 to form CaSO 4 , as is shown in the following reactions: …”

Section: Introductionmentioning

confidence: 99%

Effect of the Pore-Size Distribution of Lime on the Reactivity for the Removal of SO₂ in the Presence of High-Concentration CO₂ at High Temperature

Uddin

et al. 2002

To develop a SO 2 sorbent that is highly reactive in the presence of high concentrations of CO 2 at high temperature, the effect of the pore-size distribution on the reactivity was investigated at 800°C using a natural limestone, natural lime, modified macroporous lime, and limestone. The modified lime samples were prepared from a kind of natural lime by water-acetic acid swelling and water swelling methods. The modified limestone was prepared from the modified lime by carbonation. Pores smaller than ca. 200 nm in the modified lime and natural lime virtually disappeared, and pores larger than ca. 200 nm also considerably decreased in pore size after carbonization. The reactivity of the modified limestone depended on the degree of development of pores larger than 200 nm, because the macropores provided a diffusion route for SO 2 in the sorbent during sulfation.

“…In coal combustors, limestone usually decomposes into CaO and CO 2 and then reacts with SO 2 : CaO formed from limestone is converted to CaSO 3 and then CaSO 4 − Therefore, sulfidation reactions of CaO and/or that of CaCO 3 have to be considered.…”

Section: Introductionmentioning

confidence: 99%

“…Hartman et al and Zevenhoven et al reported pore plugging due to the molar volume change on conversion of CaO to CaSO 4 (the molar volume ratio CaSO 4 /CaO: ca. 2.7). , Anderson et al reported that the CaSO 4 from CaO constituted an adhering barrier that limited the extent of the reaction . Efthimiadis and Sotirchos reported that the sulfidation rate of lime was affected by the connectivity of the intraparticle pores (molar volume ratio CaS/CaO: ca.…”

Section: Introductionmentioning

confidence: 99%

Preparation of Macroporous Lime from Natural Lime by Swelling Method with Acetic Acid for High-Temperature Desulfurization

Sasaoka

Sada

Uddin

1998

To develop a highly active calcium oxide high-temperature desulfurization sorbent, a method of preparation of macroporous calcium oxides from lime was studied. This method is composed of two steps: swelling of the lime and calcination of the swelled sample. Swelling occurred when lime was exposed to the vapor of acetic acid. The swelling resulted from calcium acetate formation in the sample. The swelling rate was at a maximum in the presence of acetic acid and depressed by the presence of water vapor. The swelled sample was converted to macroporous calcium oxide by heating to 850 °C. The reactivity of the macroporous calcium oxide for the removal of SO2 or H2S in the presence of H2O vapor was higher than that of the calcined raw limestone. In particular, its SO2 removal capacity and the oxidative character of CaS to CaSO4 and CaO were greatly improved by this swelling method. These characteristics were also compared with those of a sample prepared from limestone by this swelling method.