Reaction of Ca(OH)₂ with SO₂ at Low Temperature

Abstract

Lime is widely utilized as a sorbent in dry and semidry sulfur removal processes. In this study limestone was calcined at high temperature and lime was produced by water vapor steam treatment at low temperature. Experiments were performed at conditions that also cover those usually present in coal-fired power plants. The investigation of the reaction of lime with synthetic flue gas showed that the relative humidity of the gas has a major impact on the reactivity. Also the presence of oxygen and/or carbon dioxide does not show a significant influence on the sulfur dioxide removal reaction though some intermediate formation of calcium carbonate cannot be excluded. Mainly calcium sulfite hemihydrate was found to be the reaction product, but some calcium sulfate hemihydrate was also formed when oxygen was present. Four regions with different prevailing reaction mechanisms can be defined: In the beginning the formation of a monolayer is mainly determined by the SO 2 concentration and to some smaller extent also by the relative humidity. This period is followed by the formation of the consecutive product layers which can initially be determined by a dissolving process of SO 2 . Afterward this formation is only determined by the relative humidity and most likely by product layer diffusion. Above a conversion of around 9% reaction rate drops significantly which can be due to pore closure.

Modeling study on the impaction and humidification process in desulfurization activation reactor

“…In general, ionic reactions are instantaneous in aqueous phase, but extremely slow in the absence of water (Hill and Zank, 2000); the fundamentality of water are also observed by other researchers in the process of desulfuriztion (Yu et al, 2001;Krammer et al, 1997;Izquierdo et al, 1992;Garea et al, 2001). Therefore, the inertial impactions between high-CaO coal ash particles and atomization droplets is very important for the flue gas desulfurization (FGD) process, which could make the droplets contain large quantity of ash particles and make slow gas-solid reaction transform into instantaneous ionic reaction.…”

A realistic approach to modeling an in-duct desulfurization process based on an experimental pilot plant study

“…In order to show the SO 2 removal efficiencies for an induct desulfurization process using different kinetic models, five of them were selected: Klingspor et al [5,6], Ruiz-Alsop and Rochelle [7], Irabien et al [8], Khinast [2] and Krammer et al [9]. Then, the units of the reaction rate were unified as follows:…”

“…Likewise, he believed that pore closure or the loss of reacting surface could be responsible for the rapid decline in the reaction rate. Krammer et al [9] proposed that the conversion during the first stage of the reaction between Ca(OH) 2 and SO 2 can be described by a certain equation for a kinetically controlled adsorption process. Also, they were able to define four regions with different prevailing reaction mechanisms, indicating that, in the end, the reaction rate drops significantly possibly because of pore closure.…”

“…Furthermore, in this paper, different kinetic models have been adapted to the actual conditions of an in-duct desulfurization process, and the disagreement between predictions from these models and the experimental results obtained in a pilot plant, which are also published (i.e., [1,3]), is shown. Thus, a general kinetic model similar to the approaches of [9] and [10] has been adapted by minimizing the difference between the calculated and the experimental results from the pilot plant, using Matlab TM . The calculated values were obtained by simulation based on an in-duct desulfurization model together with a kinetic model.…”

AFM Observation of Ca(OH)2 (0001) Surfaces Reacted with SO2: Role of Water Vapour on Product Morphology

“…3 Moreover, the reaction product (CaSO 3 . (1/2)H 2 O (s) ) could also build up in a cluster-like form at high relative humidities (RH > 70%), 5 which might result in a better accessibility of SO 2 to the still unreacted Ca(OH) 2 surface.…”