Ind. Eng. Chem. Res. 1994,33, 448
448
CORRESPONDENCE Comments on “Thermal Dehydration of Calcium Hydroxide. 1. Kinetic Model and Parameters” Miloslav Hartman. and Otakar Trnka Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, 165 02 Prague 6, Suchdol, The Czech Republic Sir: The article by Irabien et al. (1990) presents new results on the thermal decompositionof calciumhydroxide. This study is of great practical interest because such data are needed in the design of flue gas desulfurization processes operated at medium temperatures. However, on examining the authors’ data we find that the proposed rate equation cannot describe somewhat sigmoid behavior of the experimental, conversion-time curves. In order to take into account this fact, we have attempted to develop an alternative correlation for the rate of reaction. Having treated the data unbiased with transport phenomena, we propose the following formula for predicting the rate of thermal decomposition of calcium hydroxide
dX = [ ~ -( Xi) D+ BX(I - X)DI ~ ~ ~ [ - c / ( R T ) I dt where A = 2.9319 X lo5s-l, B = 3.1508 X lo6s-l, C = 1.1359 X l o 5 J mol-l, D = 0.768 72, R = 8.3144 J mol-’ K-l, X E (0,0.95), and T E (603, 723 K). The symbols X and t are the same as in the original article. The proposed correlation predicts the conversion of Ca(0H)Z to CaO (X)as a function of time (t) and temperature (13with an accuracy better than 107%.
Literature Cited Irabien, A.; Viguri, J. R.; Ortiz, I. Thermal Dehydrationof Calcium Hydroxide. 1. Kinetic Model and Parameters. Znd. Eng. Chern. Res. 1990,29, 1599-1606.
Response to Comments on “Thermal Dehydration of Calcium Hydroxide. 1. Kinetic Model and Parameters” J. Angel Irabien Departamento de Qulmica, E.P.S.I., Universidad de Cantabria, CISevilla, 6, 39001 Santander, Spain
After a careful review of the papers “Thermal Dehydration of Calcium Hydroxide. 1. Kinetic Model and Parameters” and “Thermal Dehydration of Calcium Hydroxide. 2. Surface Area Evolution” (Ind.Eng. Chern. Res. 1990,29, 1599-16111, I suggest the following minor corrections: Page 1599. In the abstract, the value should be AH = 138.5 kJOmol-l instead of -AH = 138.5 kJ-mol-’. Page 1605. The Nomenclature section should read kso: preexponential factor of the surface reaction, cms-l,
0888-588519412633-0448$Q4.50/0
instead of KSO:preexponential parameter of the surface reaction, cm-s-l. The units for SOshould be cm2*mol-l instead of mz.gl. Page 1611. The Nomenclature section should include KSO:preexponential factor, eq 6, mol cm-2atm-l s-l. The definition for p w should read pw: water vapor pressure, atm, instead of pw: water vapor pressure at equilibrium, atm. I acknowledge Dr. M. Hartman for pointing out the corrections.
0 1994 American Chemical Society
