Finite Element Analysis of Reaction Front Tracking in Lime Calcination

Calcination process is carried out in shaft kilns or rotary kilns for producing the lime. In the present work, the decomposition rates of the limestone in shaft kiln are experimentally measured in laboratory scale equipment. Mathematical model has been developed by using Finite element technique to track the reaction front movement from the surface to the core. The results obtained from the experiments are compared and validated with that of the model. Influences of parameters such as ambient temperature and the particle size are studied. The variation of reaction zone thickness during the process of decomposition has been studied and analyzed. Temperature profiles inside the lime particle are calculated and the influence of the reaction front position on these temperature profiles has been analyzed.

Container Substrate-pH Response to Differing Limestone Type and Particle Size

The objective of this study was to develop reactivity indices to describe the pH response for liming materials incorporated into container substrates. Three reactivity indices [particle size efficiency (PSE), fineness factor (FF), and effective calcium carbonate equivalence (ECC)] were developed based on lime particle size distribution and lime neutralizing value (NV) in CaCO3 equivalent. Six lime particle size fractions (2000 to 850, 850 to 250, 250 to 150, 150 to 75, 75 to 45, and <45 μm) separated from each of three calcitic limes and seven dolomitic limes were used to calibrate PSE, and were based on the increase in substrate pH (ΔpH) incited by the particle size fraction relative to reagent grade CaCO3 when mixed in a sphagnum peat substrate at 5 g CaCO3 equivalents per liter of peat. PSE for calcitic carbonate limes at day 7 (short-term pH response) were 0.13, 0.40, 0.78, 0.97, 1.00, and 1.00 for 2000 to 850, 850 to 250, 250 to 150, 150 to 75, 75 to 45, and <45 μm particle fractions, respectively. Other PSE values were described for dolomitic carbonate limestones and for long-term pH response, and PSE was modeled with a function over time. FF was calculated for a liming material by summing the percentages by weight in each of the six size fractions multiplied by the appropriate PSE. ECC rating of a limestone was the product of its NV and FF. ECC multiplied by the applied lime incorporation rate could be used to predict substrate-pH response. Estimated PSE values were validated in two experiments that compared expected and observed substrate pH using 29 unscreened carbonate and hydrated lime sources blended with peat. Validation trials resulted in a close correlation and no bias between expected and observed pH values. Revised PSE values are useful to evaluate the reactivity of different limestone sources for container substrates given the fine particle size, short crop duration, and pH sensitivity of many container-grown crops.

(66) Modeling Lime Reaction in Horticultural Substrates

Limestone is incorporated into horticultural substrates to neutralize substrate acidity, increase pH buffering capacity, and provide calcium and magnesium. Limestones differ in their rate of pH change, equilibrium pH, and proportion of unreacted “residual”? lime. In horticulture, lime reactivity is currently measured empirically in batch tests, whereby limestone is incorporated into a batch of substrate and pH change is measured over time. Our objective was to develop a quantitative model to describe reaction of lime over time. The lime reaction model predicts the substrate-pH based on lime acid neutralizing capacity, lime type (calcitic, dolomitic, or hydrated), lime particle size distribution, application concentration, and the non-limed pH and neutralizing requirement (buffering) of the substrate. Residual lime is calculated as the proportion of lime remaining following gradual neutralization of the substrate acidity (by subtraction of reacted lime from total applied lime).

(70) Improved Reactivity Indices for Horticultural Limes

The objective was to develop indices to describe reactivity of different lime particle size fractions with respect to pH change in horticultural substrates. Particle size efficiency (PSE) was calibrated from pH responses for separated six lime particle size fractions (>850, 850 to 250, 250 to 150, 150 to 75, 75 to 45, and <45 μm) from three calcitic limes, and seven dolomitic limes, based on their increase in substrate pH relative to reagent grade CaCO3 when mixed in a sphagnum peat substrate at 5 g CaCO3 equivalents per liter of peat. The fineness factor (FF) was calculated for a liming material by summing the percentages by weight in each of the six size fractions multiplied by the appropriate PSE. The effective calcium carbonate equivalence (ECC) of a limestone was the product of the FF and the acid neutralizing value (NV) in CaCO3 equivalents. Reliability of the parameters for FF and ECC were then validated in two experiments, using 29 unscreened carbonate and hydrated lime sources, including the 10 calibration limes. In one experiment, 1 L of peat was blended at 5 g of lime (i.e., not corrected for differences in NV between limes). In the second experiment, 5 g CaCO3 equivalents for each lime, corrected for NV, were blended with 1 L of peat (a different peat source), using the same 29 lime sources. Both FF and ECC were positively correlated with the corresponding substrate-pH changes, with P < 0.001 and r2 from 0.87 to 0.93. This calibration of PSE, FF, and ECC can improve limestone selection and application rate for the short term response and fine limestone sources used in horticulture.

Dolomite lime’s reaction applied on the surface of a sandy soil of the Northwest Paraná, Brazil

Low Ca and Mg are serious limitations to crop production in sandy soils of the northwest Paraná, Brazil. Thus soil samples of an Oxisol collected in this region were packed into 30cm long columns. Dolomite lime (2.0, 0.84, 0.30, and < 0.30 mm screen) was added on soil surface, then leached with deionized water. Thereafter, the columns were dismantled and the soil cut into 5cm segments for chemical analysis. Dolomite lime increased pHCaCl2,, KCl-exchangeable Ca and Mg and residual CO3 mostly in the top surface layers. Surface dolomite lime had no effect on pH, Ca, Mg, and CO3 in the leachate, independent on the lime particle size. These results indicated that surface dolomite lime application had no effect on subsoil composition and mostly of the calcium and magnesium carbonates are still unreacted on the soil surface.