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TitleCa(OH)2 superheating as a low-attrition steam reactivation method for CaO in calcium looping applications
Publication TypeJournal Article
Year of Publication2010
AuthorsMaterić, V., Edwards S., Smedley S.I., and Holt R.
JournalIndustrial and Engineering Chemistry Research
Pagination12429 - 12434
Date Published2010
ISSN08885885 (ISSN)
KeywordsAttrition rate, Calcium, Carbonation/calcination cycle, Dehydration, Dehydration reactions, Dewatering, Fluid-beds, Fluidization, Free lime, Heat storage, Hydration, Initiation temperature, Lime, Non equilibrium, Reactivation process, Sorption, Steam, Steam hydration, Superheated state, Temperature, Thermodynamic equilibria, Water vapor
AbstractSteam hydration of lime is an effective method for restoring CO2 capture activity but gives rise to high particle attrition rates in a fluid bed reactor. This paper describes the phenomenon of Ca(OH)2 superheating, also referred to as superheated dehydration (SD). The potential of an attrition-free lime reactivation process using this phenomenon is also investigated. Attrition rates of the sorbent are measured when a reactivation step using steam hydration is implemented every three carbonation/calcination cycles. It has been shown that the presence of CO2 during the dehydration step reduces attrition during subsequent cycles. Experiments performed in a small fluid bed reactor show that the presence of 40-100% CO 2 during the dehydration step increases the initiation temperature of the decomposition of Ca(OH)2 from 445 to 618 °C. The thermodynamic equilibrium water vapor pressure for the dehydration reaction at 618 °C is 516 kPa, whereas no water vapor was detected in the reactor during the dehydration step before the temperature reached 618 °C. Under these circumstances it is proposed that the Ca(OH)2 is in a nonequilibrium "superheated state". A CO2 capture cycling experiment, with a reactivation step every three carbonation/calcination cycles, maintained an average activity of 60%, creating only 3.25% of fines < 150 μm after 28 carbonations. The reactivation step consisted of hydrating the sorbent at a temperature of 270 °C and dehydrating it in 100% CO2 with a 23 min hold at 520 °C. It is proposed that the SD phenomenon may be a key step in the development of an industrially feasible method of lime reactivation for use in CO2 capture and in thermal energy storage applications. © 2010 American Chemical Society.

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