Estonian calcareous rocks as SO{sub 2} sorbents in AFBC and PFBC conditions
Sulfation of several chemically and physically different Estonian limestone and dolomite samples was studied by atmospheric and pressurized thermogravimetric analysis, accompanied by BET surface area, Hg-porosity and SEM measurements. Rate parameters were calculated for the sulfation reaction at atmospheric and pressurized conditions and an attempt was made to apply an unreacted shrinking core (USC) model with variable effective diffusivity to the CaO and CaCO{sub 3} sulfation data. The SO{sub 2} binding of the samples (particle size 125--160 {micro}m) was analyzed isothermally under conditions typical for fluidized bed combustion at 850 C and at 1 bar or 15 bar in a gas mixture of 4% O{sub 2}, 15% CO{sub 2}, 0.5% SO{sub 2} and N. Dilution of 50 mg of sample with 250 mg of SiO{sub 2} and a special sample holder was used to diminish the external mass transfer effects. It was found that the reaction of SO{sub 2} with calcined limestone and dolomite samples was initially remarkably rapid. The rate constants were in the range of 1--10 cm/s. At up to 25--44% of CaO conversion, the sulfation process proceeded evenly throughout the particles and no noticeable product layer diffusion limitation was found. The final values of conversion at atmospheric pressure were in the range of 30--60%, the amount of bound SO{sub 2} being 15.5--33.9 mg per 100 mg of initial sample. At pressurized conditions for uncalcined samples the switch from chemical kinetics control to product layer diffusion control took place at significantly lower conversion values, rate constants were in the range of 0.02--0.05 cm/s and the degree of CaCO{sub 3} conversion after 3 h of reaction time was 30--70%. Under atmospheric pressure a satisfactory fit of the extended USC model and sulfation data was achieved by splitting the overall process into two parts, the first of them kinetically controlled, the other controlled by diffusion. Under pressurized condition the model was successfully used in one step.
- Research Organization:
- Tallinn Technical Univ. (EE)
- OSTI ID:
- 20006724
- Report Number(s):
- CONF-990534-; TRN: IM200008%%331
- Resource Relation:
- Conference: 15th International Conference on Fluidized Bed Combustion, Savannah, GA (US), 05/16/1999--05/19/1999; Other Information: 1 CD-ROM. Operating system required: Windows 3.x; Windows 95/98/NT; Macintosh, Power Macintosh; UNIX. All systems need 2X CD-ROM drive.; PBD: 1999; Related Information: In: Proceedings of the 15th national conference on fluidized bed combustion, by Reuther, R.B. [ed.], [1800] pages.
- Country of Publication:
- United States
- Language:
- English
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