Limestone Dissolution in Flue Gas Scrubbing: Effect of Sulfite

Abstract

Batch limestone dissolution experiments were carried out in a pti stat apparatus at 55°C with CO 2 sparging and dissolved sulfite. Particle size distribution, utilization, sulfite in solution, limestone type, and the approach to calcite equilibrium were all found to contribute to the limestone reactivity. In the absence of sulfite, limestone dissolution was controlled solely by mass transfer. For a given stone under mass transfer control, film thickness was found to be independent of pH. The dissolution rate in the presence of sulfite was controlled by a combined surface kinetics/mass transfer regime. SEM micrographs supported this conclusion. A surface rate correlation was developed which accounted for observed inhibition by an inverse dependence on calcium sulfite concentration at the limestone surface. While the form of the rate expression was applicable to all stones, the surface rate constant was stone dependent. A computer code which accounted for mass transfer with surface kinetics was tested against experimental observations of four limestone types. Changes in pH and the concentrations of calcium, carbonate, sulfite, sulfate, and adipic acid were accurately modeled.

Equilibria in a Limestone Based FGD Process: A Pure System and with Chloride Addition

“…Experiments aimed at the measurement of the limestone dissolution rate are usually performed in simpler systems than the FGD one [3,4, 8±10]. In most cases, strong acids like sulfuric [3,8] or hydrochloric [9,10] acid are used instead of ªsulfurousº acid. Each experiment described is performed in a well-stirred batch reactor where the pH is kept at a constant value in the range 5.4±6 [3,8] and 4.8±5.3 [9,10].…”

“…The model of SO 2 absorption into single droplets is formulated [3] on the basis of these results. It is worth noting that acid replacement (or a lack of notice of some component (like CaSO 4 in [9,10]) in a system where weakly soluble salts are produced) can lead to significant errors in the measurement of the dissolution rate for the solid substrate.…”

“…It is significant that the reaction constant changes by almost two orders of magnitude when the concentration of the MeHSO 3 ion pair changes. The dependence of limestone dissolution rate in hydrochloric acid on calcium sulfite concentration in the bulk solution has a maximum [9,10]. The increase in calcium carbonate mass flux is caused by the conversion of calcium sulfite into calcium hydrogen sulfite at the limestone interface.…”

Liquid‐phase mass transfer in spray contactors

“…The chemical reactions in the limestone slurry have been studied extensively under well-characterized mass transfer conditions (Gage and Rochelle, 1992), and computer simulations have been employed to study the effect of different parameters on SO 2 removal. Examples include the work of Noblett et al (1995), Agarwal (1995, Brogren andKarlsson (1997), andDeVincentis (1998).…”

The effect of additives on lime dissolution rates. Final report, September 1, 1993--August 31, 1994

“…The dissolution rates of the limestone under different pH was obtained and compared to the reference (Gage and Rochelle, 1992). It can be seen in Table I that the measured dissolution rates are comparable.…”