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Ca(OH)2 superheating as a low - attrition steam reactivation method for CaO in calcium looping applications / Vlatko Materic in Industrial & engineering chemistry research, Vol. 49 N° 24 (Décembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 24 (Décembre 2010) . - pp.12429-12434 Titre : Ca(OH)2 superheating as a low - attrition steam reactivation method for CaO in calcium looping applications Type de document : texte imprimé Auteurs : Vlatko Materic, Auteur ; Susan Edwards, Auteur ; Stuart I. Smedley, Auteur Année de publication : 2011 Article en page(s) : pp.12429-12434 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Attrition  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 Résumé : Steam 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. DEWEY : 660 ISSN : 0888-5885 En ligne : http://www.irl.cri.nz/caoh2-superheating-low-attrition-steam-reactivation-method [...] [article] Ca(OH)2 superheating as a low - attrition steam reactivation method for CaO in calcium looping applications [texte imprimé] / Vlatko Materic, Auteur ; Susan Edwards, Auteur ; Stuart I. Smedley, Auteur . - 2011 . - pp.12429-12434. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 24 (Décembre 2010) . - pp.12429-12434 Mots-clés : Attrition  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 Résumé : Steam 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. DEWEY : 660 ISSN : 0888-5885 En ligne : http://www.irl.cri.nz/caoh2-superheating-low-attrition-steam-reactivation-method [...]

High temperature carbonation of Ca(OH)2 / Vlatko Materic in Industrial & engineering chemistry research, Vol. 50 N° 10 (Mai 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 10 (Mai 2011) . - pp. 5927-5932 Titre : High temperature carbonation of Ca(OH)2 Type de document : texte imprimé Auteurs : Vlatko Materic, Auteur ; Stuart I. Smedley, Auteur Année de publication : 2011 Article en page(s) : pp. 5927-5932 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Carbonation Résumé : Steam hydration is reported to be an effective method for reactivating spent sorbents in calcium looping applications; however, uncertainties remain regarding the optimal method of returning the hydrated sorbent to the CO2 capture loop. Carbonation conversions were found to be higher when Ca(OH)2 was directly carbonated at high temperatures compared to conversions reached when Ca(OH)2 was dehydrated prior to carbonation. This observation can lead to improved hydration based reactivation techniques for calcium looping applications. Upon heating in CO2, calcium hydroxide remained stable at temperatures >450 °C and the extent of carbonation was controlled by temperature only. The carbonation mechanism of Ca(OH)2 at high temperatures appears to be more complex than the expected simple mechanism comprising the dehydration reaction of Ca(OH)2 and the subsequent carbonation of the resulting CaO. An alternate mechanism was proposed, involving the formation of liquid like layers of water on the surface of Ca(OH)2. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24158889 [article] High temperature carbonation of Ca(OH)2 [texte imprimé] / Vlatko Materic, Auteur ; Stuart I. Smedley, Auteur . - 2011 . - pp. 5927-5932. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 10 (Mai 2011) . - pp. 5927-5932 Mots-clés : Carbonation Résumé : Steam hydration is reported to be an effective method for reactivating spent sorbents in calcium looping applications; however, uncertainties remain regarding the optimal method of returning the hydrated sorbent to the CO2 capture loop. Carbonation conversions were found to be higher when Ca(OH)2 was directly carbonated at high temperatures compared to conversions reached when Ca(OH)2 was dehydrated prior to carbonation. This observation can lead to improved hydration based reactivation techniques for calcium looping applications. Upon heating in CO2, calcium hydroxide remained stable at temperatures >450 °C and the extent of carbonation was controlled by temperature only. The carbonation mechanism of Ca(OH)2 at high temperatures appears to be more complex than the expected simple mechanism comprising the dehydration reaction of Ca(OH)2 and the subsequent carbonation of the resulting CaO. An alternate mechanism was proposed, involving the formation of liquid like layers of water on the surface of Ca(OH)2. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24158889