In kraft pulp mills, lime is used to convert sodium carbonate to sodium hydroxide (Ca(OH)2). The causticizing reaction precipitates lime mud which is washed, dewatered, and calcined in a lime kiln to generate lime for reuse. Clean, dry, and more stable lime mud helps reducing the energy usage of the kiln, improving burner flame stability, minimizing ring formation, and alleviating emissions of reduced sulphur gases from the kiln stack. The dewatering efficiency of lime mud is greatly affected by the mud and liquor properties, and the equipment design and operation. The properties of the mud vary continuously due to changes in the liquor strength, lime quality and dosage, which is known as the “liming ratio”. Many studies have been carried out to relate lime mud properties to dewatering and filtration behaviours, the mechanisms by which lime mud becomes difficult to settle and filter are not well understood. A systematic study was therefore conducted to examine the effect of the liming ratio on the settling rate and filterability of lime mud. The results show that the mud settling rate and filterability decreased with an increase in liming ratio. The effect was more noticeable as the liming ratio exceeded a critical level leading to an overliming condition. The results also show that the particle size of the resulting lime mud did not appreciably change with liming ratio. Therefore, the decrease in settling rate and filterability cannot be attributed to the smaller particle size of Ca(OH)2 compared to that of lime mud as commonly believed. Rather, it was caused by a change in zeta potential of Ca(OH)2-containing mud particles.This study also shows that the zeta potential of the mud slurry increases proportionally to the free lime content in the lime mud. This suggests that the zeta potential can be used to indicate the extent of overliming in the causticizing plant. The correlation between zeta potential and free lime content can be used to develop an on-line overliming monitoring system to help regulate theamount of lime addition to the system to achieve optimum operating conditions for the mud settling and filtering equipment.

In kraft pulp mills, lime is used to convert sodium carbonate to sodium hydroxide (Ca(OH)2). The causticizing reaction precipitates lime mud which is washed, dewatered, and calcined in a lime kiln to generate lime for reuse. Clean, dry, and more stable lime mud helps reducing the energy usage of the kiln, improving burner flame stability, minimizing ring formation, and alleviating emissions of reduced sulphur gases from the kiln stack. The dewatering efficiency of lime mud is greatly affected by the mud and liquor properties, and the equipment design and operation. The properties of the mud vary continuously due to changes in the liquor strength, lime quality and dosage, which is known as the “liming ratio”. Many studies have been carried out to relate lime mud properties to dewatering and filtration behaviours, the mechanisms by which lime mud becomes difficult to settle and filter are not well understood. A systematic study was therefore conducted to examine the effect of the liming ratio on the settling rate and filterability of lime mud. The results show that the mud settling rate and filterability decreased with an increase in liming ratio. The effect was more noticeable as the liming ratio exceeded a critical level leading to an overliming condition. The results also show that the particle size of the resulting lime mud did not appreciably change with liming ratio. Therefore, the decrease in settling rate and filterability cannot be attributed to the smaller particle size of Ca(OH)2 compared to that of lime mud as commonly believed. Rather, it was caused by a change in zeta potential of Ca(OH)2-containing mud particles.This study also shows that the zeta potential of the mud slurry increases proportionally to the free lime content in the lime mud. This suggests that the zeta potential can be used to indicate the extent of overliming in the causticizing plant. The correlation between zeta potential and free lime content can be used to develop an on-line overliming monitoring system to help regulate theamount of lime addition to the system to achieve optimum operating conditions for the mud settling and filtering equipment.

No description available.

A rotating disk technique was used to determine the dissolution rate and diffusivity of CaO and MgO in slags. The dissolution rate was deduced from the measured changes in concentration of oxides in slag with respect to reaction time. The experimental set- up was initially tested with dissolution of magnesia in the CaO ??? 55 wt% Al2O3 slag at 1430 ??C and a measured rate of 2.7 ??10 -5 g/cm2.s was obtained. The dissolution rate was increased by slag chemistry and ranged from 6.5??10-5 to 2.1??10-4 g/cm2.s. The dissolution rate of CaO was measured in CaO ??? 42 wt% Al2O3 ??? 8% SiO2 based slag. The measured dissolution rates were found to be strongly dependent on the slag chemistry and temperature and ranged from 5.03??10 -5 to 3.3??10 -4 g/cm2.s. The dissolution rates were strongly dependent on the rotation speed and results indicate mass transfer in the slag phase to be rate- limiting step. The diffusivity of MgO / CaO was calculated from the dissolution rate and solubility data, using known mass transfer correlations. The diffusivity of MgO in the calcium aluminate slag at 1430 ??C was found to be about 1.1??10-5 cm2/s. Additions of 5 and 10 wt% Fe2O3 increased the diffusivity by a factor ~ 1.5 to 3, respectively. However, with introduction of (CaF2 5 wt% + Fe2O3 5 wt%) and (CaF2 5 wt% + Fe2O3 10 wt%) in the slag, the diffusivity increased considerably by a factor of about 29 and 11, respectively. The diffusivity of CaO in calcium aluminosilicate was measured to be in the order of 10-6 to 10-5 over a temperature range of 1430 ??? 1600 ??C. CaF2 increased the diffusivity by a factor of 3 to 5 while MnOx and FeOx, ilmenite and TiO 2 increased the diffusivity substantially and SiO2 had an opposite effect. The measured diffusivities are in accord with published data on comparable systems and are discussed with reference to Eyring theory. It was concluded that MnOx, FeOx and ilmenite in the slag increase the dissolution rate and diffusivity of lime, showing comparable results with respect to CaF2.

A rotating disk technique was used to determine the dissolution rate and diffusivity of CaO and MgO in slags. The dissolution rate was deduced from the measured changes in concentration of oxides in slag with respect to reaction time. The experimental set- up was initially tested with dissolution of magnesia in the CaO ??? 55 wt% Al2O3 slag at 1430 ??C and a measured rate of 2.7 ??10 -5 g/cm2.s was obtained. The dissolution rate was increased by slag chemistry and ranged from 6.5??10-5 to 2.1??10-4 g/cm2.s. The dissolution rate of CaO was measured in CaO ??? 42 wt% Al2O3 ??? 8% SiO2 based slag. The measured dissolution rates were found to be strongly dependent on the slag chemistry and temperature and ranged from 5.03??10 -5 to 3.3??10 -4 g/cm2.s. The dissolution rates were strongly dependent on the rotation speed and results indicate mass transfer in the slag phase to be rate- limiting step. The diffusivity of MgO / CaO was calculated from the dissolution rate and solubility data, using known mass transfer correlations. The diffusivity of MgO in the calcium aluminate slag at 1430 ??C was found to be about 1.1??10-5 cm2/s. Additions of 5 and 10 wt% Fe2O3 increased the diffusivity by a factor ~ 1.5 to 3, respectively. However, with introduction of (CaF2 5 wt% + Fe2O3 5 wt%) and (CaF2 5 wt% + Fe2O3 10 wt%) in the slag, the diffusivity increased considerably by a factor of about 29 and 11, respectively. The diffusivity of CaO in calcium aluminosilicate was measured to be in the order of 10-6 to 10-5 over a temperature range of 1430 ??? 1600 ??C. CaF2 increased the diffusivity by a factor of 3 to 5 while MnOx and FeOx, ilmenite and TiO 2 increased the diffusivity substantially and SiO2 had an opposite effect. The measured diffusivities are in accord with published data on comparable systems and are discussed with reference to Eyring theory. It was concluded that MnOx, FeOx and ilmenite in the slag increase the dissolution rate and diffusivity of lime, showing comparable results with respect to CaF2.

A rotating disk technique was used to determine the dissolution rate and diffusivity of CaO and MgO in slags. The dissolution rate was deduced from the measured changes in concentration of oxides in slag with respect to reaction time. The experimental set- up was initially tested with dissolution of magnesia in the CaO ??? 55 wt% Al2O3 slag at 1430 ??C and a measured rate of 2.7 ??10 -5 g/cm2.s was obtained. The dissolution rate was increased by slag chemistry and ranged from 6.5??10-5 to 2.1??10-4 g/cm2.s. The dissolution rate of CaO was measured in CaO ??? 42 wt% Al2O3 ??? 8% SiO2 based slag. The measured dissolution rates were found to be strongly dependent on the slag chemistry and temperature and ranged from 5.03??10 -5 to 3.3??10 -4 g/cm2.s. The dissolution rates were strongly dependent on the rotation speed and results indicate mass transfer in the slag phase to be rate- limiting step. The diffusivity of MgO / CaO was calculated from the dissolution rate and solubility data, using known mass transfer correlations. The diffusivity of MgO in the calcium aluminate slag at 1430 ??C was found to be about 1.1??10-5 cm2/s. Additions of 5 and 10 wt% Fe2O3 increased the diffusivity by a factor ~ 1.5 to 3, respectively. However, with introduction of (CaF2 5 wt% + Fe2O3 5 wt%) and (CaF2 5 wt% + Fe2O3 10 wt%) in the slag, the diffusivity increased considerably by a factor of about 29 and 11, respectively. The diffusivity of CaO in calcium aluminosilicate was measured to be in the order of 10-6 to 10-5 over a temperature range of 1430 ??? 1600 ??C. CaF2 increased the diffusivity by a factor of 3 to 5 while MnOx and FeOx, ilmenite and TiO 2 increased the diffusivity substantially and SiO2 had an opposite effect. The measured diffusivities are in accord with published data on comparable systems and are discussed with reference to Eyring theory. It was concluded that MnOx, FeOx and ilmenite in the slag increase the dissolution rate and diffusivity of lime, showing comparable results with respect to CaF2.

A rotating disk technique was used to determine the dissolution rate and diffusivity of CaO and MgO in slags. The dissolution rate was deduced from the measured changes in concentration of oxides in slag with respect to reaction time. The experimental set- up was initially tested with dissolution of magnesia in the CaO ??? 55 wt% Al2O3 slag at 1430 ??C and a measured rate of 2.7 ??10 -5 g/cm2.s was obtained. The dissolution rate was increased by slag chemistry and ranged from 6.5??10-5 to 2.1??10-4 g/cm2.s. The dissolution rate of CaO was measured in CaO ??? 42 wt% Al2O3 ??? 8% SiO2 based slag. The measured dissolution rates were found to be strongly dependent on the slag chemistry and temperature and ranged from 5.03??10 -5 to 3.3??10 -4 g/cm2.s. The dissolution rates were strongly dependent on the rotation speed and results indicate mass transfer in the slag phase to be rate- limiting step. The diffusivity of MgO / CaO was calculated from the dissolution rate and solubility data, using known mass transfer correlations. The diffusivity of MgO in the calcium aluminate slag at 1430 ??C was found to be about 1.1??10-5 cm2/s. Additions of 5 and 10 wt% Fe2O3 increased the diffusivity by a factor ~ 1.5 to 3, respectively. However, with introduction of (CaF2 5 wt% + Fe2O3 5 wt%) and (CaF2 5 wt% + Fe2O3 10 wt%) in the slag, the diffusivity increased considerably by a factor of about 29 and 11, respectively. The diffusivity of CaO in calcium aluminosilicate was measured to be in the order of 10-6 to 10-5 over a temperature range of 1430 ??? 1600 ??C. CaF2 increased the diffusivity by a factor of 3 to 5 while MnOx and FeOx, ilmenite and TiO 2 increased the diffusivity substantially and SiO2 had an opposite effect. The measured diffusivities are in accord with published data on comparable systems and are discussed with reference to Eyring theory. It was concluded that MnOx, FeOx and ilmenite in the slag increase the dissolution rate and diffusivity of lime, showing comparable results with respect to CaF2.

Thesis (M.S.)--University of Pennsylvania, 2006. / Title from PDF title page (viewed on Aug. 11, 2008). Includes bibliographical references (p. (71-85) and index.

Thèse--Université de Toulouse. / At head of title: ... H. Margulis ... "Bibliographie": p. [115]-116.

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 159-168.