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Impact of Improved Sorbents on the Performance of the Carbonate Looping Process

Schüppel, Ben (2012)
Impact of Improved Sorbents on the Performance of the Carbonate Looping Process.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung

Kurzbeschreibung (Abstract)

This thesis was considered with the Carbonate Looping (CL) process and in particular the impact of improved sorbents on the process performance. A broad overview about solid state chemistry was given. Crystal systems of CaCO3, CaO, Ca(OH)2 and CaSO4 have been presented. It was shown that CaO has the most dense package of all substances. However, CaO has the highest melting point in the group which indicates that sintering phenomena like loss of specific surface area and irreversible pore mouth blockage are much more likely to happen during the re-carbonation than during the calcination step. Impurities of the coal appear to become a challenge for the operation of the CL process: On the one hand impurities might get enriched in the loop causing high circulating mass flows and on the other hand melting phases are very likely to occur. Special emphasis should be put on the usage of a fuel containing very low amounts of alkali metals. As well, reducing conditions should be avoided in the calciner to avoid any undesired effects resulting of the system CaSO4-CaSO3-CaO. Theoretical investigations of the CaCO3 decomposition showed that the majority of sorbent particles should be calcined within seconds in the calciner. Low residential times and rather low mass loadings in the calciner seem to be achievable. The literature review on CL sorbents revealed a critical response of the CO2 capture ability of sorbents on changed TGA test conditions. In this perspective a lot of promising approaches, like special thermal pre-treatments became less promising. It was speculated that the good reported outcomes on these materials, was only an effect of randomly beneficial chosen TGA test conditions. Own experiments under harsh TGA test conditions with improved and synthetic products did not indicate any benefits for the CL process in terms of CO2 capture ability. Mechanical and chemical reactivation routes were presented. The only process discussed within literature offering both reactivations at the same time is the SD process. Increased mechanical stability and refreshed CO2 capture ability were reported by [86]. However, this process would have to be repeated after each third cycle leading to huge additional efforts for the sorbent reactivation. The sophisticated CL process model showed that optimisations could be done with a variety of targets. Optimising the economics, for example, would only require large utilities that should be operated with a sorbent as hard as possible. In contrast, an optimal efficiency could only be reached with special sorbents offering an optimal compromise between CO2 capture ability and hardness. Minimal CO2 capture costs were calculated to 20 €/t (including the compression of the CO2 produced by the power plant and the CL process). The calculations indicate that the handling of the huge amount of make-up and bleed might become a problem. Sorbent research was categorised into basic, advanced and synthetic materials. Basic materials are common, now available limestones, advanced materials are thermally treated oxides and synthetic products are tailor-made lab samples. Based on TGA experiments it turned out that neither advanced nor synthetic materials had any long term advantages under harsh TGA conditions compared to good performing natural sorbents. Hardness investigations with different experimental setups created a confusing picture in that no real correlations between the measurements of the individual test were achieved. Basically, two reasons were identified for this observation: First, depending on experimental conditions attrition by surface wear or impact stress was dominant. According to the nature of the products, the reaction on surface wear and impact might be completely different. Second, the cyclic change of sorbent properties that change from a carbonate shell to a soft CaO shell to a sintered particle. Additionally, the duration of the appearance of the different Ca-forms depends strongly on process conditions.

Typ des Eintrags: Dissertation
Erschienen: 2012
Autor(en): Schüppel, Ben
Art des Eintrags: Erstveröffentlichung
Titel: Impact of Improved Sorbents on the Performance of the Carbonate Looping Process
Sprache: Englisch
Referenten: Epple, Prof. Dr.- Bernd ; Vogel, Prof. Dr.- Herbert
Publikationsjahr: 1 Oktober 2012
Ort: Dissertation
Datum der mündlichen Prüfung: 11 Juli 2012
URL / URN: urn:nbn:de:tuda-tuprints-31194
Kurzbeschreibung (Abstract):

This thesis was considered with the Carbonate Looping (CL) process and in particular the impact of improved sorbents on the process performance. A broad overview about solid state chemistry was given. Crystal systems of CaCO3, CaO, Ca(OH)2 and CaSO4 have been presented. It was shown that CaO has the most dense package of all substances. However, CaO has the highest melting point in the group which indicates that sintering phenomena like loss of specific surface area and irreversible pore mouth blockage are much more likely to happen during the re-carbonation than during the calcination step. Impurities of the coal appear to become a challenge for the operation of the CL process: On the one hand impurities might get enriched in the loop causing high circulating mass flows and on the other hand melting phases are very likely to occur. Special emphasis should be put on the usage of a fuel containing very low amounts of alkali metals. As well, reducing conditions should be avoided in the calciner to avoid any undesired effects resulting of the system CaSO4-CaSO3-CaO. Theoretical investigations of the CaCO3 decomposition showed that the majority of sorbent particles should be calcined within seconds in the calciner. Low residential times and rather low mass loadings in the calciner seem to be achievable. The literature review on CL sorbents revealed a critical response of the CO2 capture ability of sorbents on changed TGA test conditions. In this perspective a lot of promising approaches, like special thermal pre-treatments became less promising. It was speculated that the good reported outcomes on these materials, was only an effect of randomly beneficial chosen TGA test conditions. Own experiments under harsh TGA test conditions with improved and synthetic products did not indicate any benefits for the CL process in terms of CO2 capture ability. Mechanical and chemical reactivation routes were presented. The only process discussed within literature offering both reactivations at the same time is the SD process. Increased mechanical stability and refreshed CO2 capture ability were reported by [86]. However, this process would have to be repeated after each third cycle leading to huge additional efforts for the sorbent reactivation. The sophisticated CL process model showed that optimisations could be done with a variety of targets. Optimising the economics, for example, would only require large utilities that should be operated with a sorbent as hard as possible. In contrast, an optimal efficiency could only be reached with special sorbents offering an optimal compromise between CO2 capture ability and hardness. Minimal CO2 capture costs were calculated to 20 €/t (including the compression of the CO2 produced by the power plant and the CL process). The calculations indicate that the handling of the huge amount of make-up and bleed might become a problem. Sorbent research was categorised into basic, advanced and synthetic materials. Basic materials are common, now available limestones, advanced materials are thermally treated oxides and synthetic products are tailor-made lab samples. Based on TGA experiments it turned out that neither advanced nor synthetic materials had any long term advantages under harsh TGA conditions compared to good performing natural sorbents. Hardness investigations with different experimental setups created a confusing picture in that no real correlations between the measurements of the individual test were achieved. Basically, two reasons were identified for this observation: First, depending on experimental conditions attrition by surface wear or impact stress was dominant. According to the nature of the products, the reaction on surface wear and impact might be completely different. Second, the cyclic change of sorbent properties that change from a carbonate shell to a soft CaO shell to a sintered particle. Additionally, the duration of the appearance of the different Ca-forms depends strongly on process conditions.

Alternatives oder übersetztes Abstract:
Alternatives AbstractSprache

Der Carbonate Looping (CL) Prozess ist eine CO2 Abscheide Technologie der zweiten Generation. Dieser Prozess, welcher im 1 MWth Pilotmaßstab an der TU Darmstadt untersucht wird, hat als zentrale, chemische Reaktion das zyklische Be- und Entladung von CaO mit CO2. CaO, sowie CaCO3 (beladenes CaO) sind Feststoffe, welche bzgl. ihrer Korngröße und Morphologie besondere Eigenschaften aufweisen müssen, damit sie im CL Prozess eingesetzt werden können: Die Sorbenspartikel sollten idealerweise eine Korngröße zwischen 100 und 500 µm, sowie eine möglichst hohe mechanische Stabilität aufweisen. Ebenfalls, bezogen auf einen effizienten Prozess, ist eine hohe CO2 Aufnahmefähigkeit über viele Be- und Entladezyklen hinweg, wünschenswert. In der vorliegenden Dissertation waren folgende Fragen von hoher Bedeutung: 1. Welche Sorbenseigenschaften sind wünschenswert bezogen auf verschiedene Optimierungsziele (wie z.B.: Wirkungsgrad oder spezifische Abscheidekosten)? 2. Wie können die Sorbenseigenschaften am besten im Labor bestimmt werden? 3. Welche Möglichkeiten der Sorbensverbesserungen gibt es? Um diese Fragestellungen möglichst gut zu beantworten, wurde ein ausgedehnte Literaturrecherche über die Eigenschaften der im Prozess zu erwartenden Spezies (CaO, CaCO3, CaSO4, Ca(OH)2) angestellt. Eine Diskussion, wie diese Stoffe mit Verunreinigungen (SiO2, Al2O3, Fe2O3, usw.), die über den Brennstoff in das System eingetragen werden, wechselwirken können, wurde angestellt. Ein Schwerpunkt der Arbeit wurde bei der CaCO3 Dissoziation und der CaO Recarbonatation gelegt, um zu verstehen, welche grundlegenden Prozesse zum Verlust der CO2 Aufnahmefähigkeit der Sorbenspartikel nach nur wenigen Zyklen führen. Es zeigte sich, dass nicht die Calcinationsbedingungen sondern vielmehr die Recarbonatationbedingungen für den Verlust der chemischen Reaktivität verantwortlich sind; je nach CO2 Partialdruck und Dauer der Recarbonatation zeigten sich unterschiedliche Abklingkurven der CO2 Aufnahmefähigkeit. Anhand eines komplexen Prozessmodelles, welches den Prozess durch die Sorbenseigenschaften beschreibt, wurden verschiedene optimale Sorbenseigenschaften abgeleitet: Soll der Prozess, z.B. so günstig wie möglich CO2 Abscheiden, so sollte das Sorbens einfach nur Preiswert sein. Soll der Prozess hingegen so effizient wie möglich CO2 Abscheiden, so ist eine mittlere Partikelhärte und eine sehr hohe CO2 Aufnahmefähigkeit erforderlich. Ausgedehnte Laboruntersuchungen zeigten zum einen, dass die Definition eines vernünftigen Wertes für Partikelhärte mit großen Unwägbarkeiten verbunden ist, und zum anderen, dass gemessene CO2 Aufnahmekurven über viele Zyklen hinweg im hohen Maße von den Testbedingungen und weniger von den Partikeleigenschaften abhängen. Der erste Fakt lässt sich dadurch verstehen, dass im CL Prozess eine permanente Änderung der Partikelmorphologie erfolgt (z.B. von dichtem CaCO3 zu porösem CaO). Der zweite Fakt ist dem Umstand geschuldet, dass der Verlust der CO2 Aufnahmefähigkeit vor allem durch die Recarbonatation verursacht wird.

Deutsch
Schlagworte:
Einzelne SchlagworteSprache
carbonate looping, ca-looping, ca looping, co2 sorbent,Englisch
Sachgruppe der Dewey Dezimalklassifikatin (DDC): 500 Naturwissenschaften und Mathematik > 540 Chemie
600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau
Fachbereich(e)/-gebiet(e): 16 Fachbereich Maschinenbau
16 Fachbereich Maschinenbau > Institut für Energiesysteme und Energietechnik (EST)
07 Fachbereich Chemie
07 Fachbereich Chemie > Eduard Zintl-Institut > Fachgebiet Anorganische Chemie
07 Fachbereich Chemie > Ernst-Berl-Institut > Fachgebiet Technische Chemie
Hinterlegungsdatum: 29 Okt 2012 11:05
Letzte Änderung: 05 Mär 2013 10:03
PPN:
Referenten: Epple, Prof. Dr.- Bernd ; Vogel, Prof. Dr.- Herbert
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: 11 Juli 2012
Schlagworte:
Einzelne SchlagworteSprache
carbonate looping, ca-looping, ca looping, co2 sorbent,Englisch
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