ENGINEERING A NEW MATERIAL FOR HOT GAS CLEANUP
The overall purpose of this project was to develop a superior, regenerable, calcium-based sorbent for desulfurizing hot coal gas with the sorbent being in the form of small pellets made with a layered structure such that each pellet consists of a highly reactive lime core enclosed within a porous protective shell of strong but relatively inert material. The sorbent can be very useful for hot gas cleanup in advanced power generation systems where problems have been encountered with presently available materials. An economical method of preparing the desired material was demonstrated with a laboratory-scale revolving drum pelletizer. Core-in-shell pellets were produced by first pelletizing powdered limestone or other calcium-bearing material to make the pellet cores, and then the cores were coated with a mixture of powdered alumina and limestone to make the shells. The core-in-shell pellets were subsequently calcined at 1373 K (1100 C) to sinter the shell material and convert CaCO{sub 3} to CaO. The resulting product was shown to be highly reactive and a very good sorbent for H{sub 2}S at temperatures in the range of 1113 to 1193 K (840 to 920 C) which corresponds well with the outlet temperatures of some coal gasifiers. The product was also shown to be both strong and attrition resistant, and that it can be regenerated by a cyclic oxidation and reduction process. A preliminary evaluation of the material showed that while it was capable of withstanding repeated sulfidation and regeneration, the reactivity of the sorbent tended to decline with usage due to CaO sintering. Also it was found that the compressive strength of the shell material depends on the relative proportions of alumina and limestone as well as their particle size distributions. Therefore, an extensive study of formulation and preparation conditions was conducted to improve the performance of both the core and shell materials. It was subsequently determined that MgO tends to stabilize the high-temperature reactivity of CaO. Therefore, a sorbent prepared from dolomite withstands the effects of repeated sulfidation and regeneration better than one prepared from limestone. It was also determined that both the compressive strength and attrition resistance of core-in-shell pellets depend on shell thickness and that the compressive strength can be improved by reducing both the particle size and amount of limestone in the shell preparation mixture. A semiempirical model was also found which seems to adequately represent the absorption process. This model can be used for analyzing and predicting sorbent performance, and, therefore, it can provide guidance for any additional development which may be required. In conclusion, the overall objective of developing an economical, reusable, and practical material was largely achieved. The material appears suitable for removing CO{sub 2} from fuel combustion products as well as for desulfurizing hot coal gas.
- Research Organization:
- Iowa State University (US)
- Sponsoring Organization:
- (US)
- DOE Contract Number:
- FG26-99FT40587
- OSTI ID:
- 827445
- Resource Relation:
- Other Information: PBD: 1 Sep 2003
- Country of Publication:
- United States
- Language:
- English
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