How does sorbent particle structure influence sulfur capture under PFBC conditions?
- Aabo Akademi Univ., Turku (Finland). Dept. of Chemical Engineering
The physical structure of a limestone or dolomite to be used in in-bed sulfur capture in fluidized bed boilers has great impact on the efficiency of sulfur capture and sorbent use. Therefore in process optimization and model calculations parameters describing the pore structure of these sorbents must be included. In this study an unreacted shrinking core model with variable effective diffusivity is applied to sulfation test data from a pressurized thermogravimetric apparatus (P-TGA) for various limestone and dolomite samples. The particle size was 250--300 {micro}m for all sorbents. The tests were done under typical conditions for a pressurized fluidized bed combustor, i.e. 850 C or 950 C, 15 bar, and were reported earlier at the 12th International Conference on Fluidized Bed Combustion. At these conditions the limestone remains uncalcined, while the dolomite is half-calcined. The sorbents were characterized by chemical composition analysis, particle density measurement, mercury porosimetry and BET internal surface measurement. A key parameter in this analysis is the conversion-dependent Thiele parameter. The shift in rate determining mechanism during the sorbents sulfation is clearly seen in the changing Thiele parameter. The extended model allows for evaluating the effect of particle structure on the reaction rate constant and the product layer diffusivity. Since test data from two temperatures are used, estimates for the apparent activation energy of the kinetics and the product layer diffusion can also be given.
- OSTI ID:
- 288001
- Report Number(s):
- CONF-950522--; ISBN 0-7918-1305-3
- Country of Publication:
- United States
- Language:
- English
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