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Continuous Solar-Driven Calcination of Borates Assisted with a Novel Combined Sensible-Heat/Thermochemical Storage

Titel Englisch Continuous Solar-Driven Calcination of Borates Assisted with a Novel Combined Sensible-Heat/Thermochemical Storage
Gesuchsteller/in Steinfeld Aldo
Nummer 173438
Förderungsinstrument Argentina (AJRP)
Forschungseinrichtung Institut für Energietechnik ETH Zürich
Hochschule ETH Zürich - ETHZ
Hauptdisziplin Chemische Verfahrenstechnik
Beginn/Ende 01.09.2017 - 31.08.2020
Bewilligter Betrag 250'000.00
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Alle Disziplinen (2)

Disziplin
Chemische Verfahrenstechnik
Maschineningenieurwesen

Keywords (8)

renewable energy; borates; mineral processing; thermal energy storage; concentrated solar radiation; solar energy; industrial process heat; calcination

Lay Summary (Deutsch)

Lead
Das Ziel dieses Projekts ist die Entwicklung eines kontinuierlichen Mineral Kalzinationsprozesses, welcher mithilfe von heisser Luft als Wärmeträgermedium und konzentrierter Sonnenenergie als einzige Quelle von Prozesswärme betrieben wird.
Lay summary

Das Ziel dieses Projekts ist die Entwicklung eines kontinuierlichen Borat-Mineral Kalzinationsprozesses, welcher mithilfe von heisser Luft als Wärmeträgermedium und konzentrierter Sonnenenergie als einzige Quelle von Prozesswärme betrieben wird. Die Luft wird mittels konzentrierter Sonnenenergie entweder direkt in einem Solarturm oder indirekt über einen thermischen Speicher erhitzt und dann dem Kalzinator zugeführt. Der thermische Speicher basiert auf einem neuartigen Konzept bestehend aus einem Festbett aus Steinen, welches als sensibler Wärmespeicher dient, und einem thermochemischen Speicher in welchem thermische Energie mithilfe der Reaktionsenthalpie einer reversiblen endothermen/exothermen Reaktion gespeichert/freigelassen wird. Im thermochemischen Speicher werden die chemischen Reaktanden räumlich vom Wärmeträgermedium getrennt, so dass der Reaktionsdruck unabhängig variiert werden kann. Durch diese Druckregulierung kann gesteuert werden wieviel thermische Energie freigegeben werden soll, um so die gewünschte Austrittstemperatur des Wärmeträgermedium zu erzielen. Die Möglichkeit, die Austrittstemperatur der Luft bei über 600°C und einem konstanten Massenstrom aktiv zu steuern, macht diesen Speicher nicht nur einzigartig sondern ist essenziell um einen Kalzinator kontinuierlich in stationärem Zustand zu betreiben. Die erfolgreiche Realisierung dieses Projekts wäre ein signifikanter Schritt in Richtung der Implementierung von Solarenergie in einem Industriebereich welcher für Argentinien von grosser Bedeutung ist. Zudem würde das Projekt dazu beitragen, die Entwicklung thermischer Energiespeicher für die ununterbrochene Elektrizitätserzeugung basierend auf der Technologie der konzentrierten Solarenergie voranzutreiben.

Direktlink auf Lay Summary Letzte Aktualisierung: 24.05.2017

Lay Summary (Englisch)

Lead
The objective of this project is to develop a continuous mineral calcination process driven by hot air as the heat-transfer fluid (HTF) using concentrated solar energy as the only source of process heat.
Lay summary

The objective of this project is to develop a continuous borate-calcination process driven by hot air as the heat-transfer fluid (HTF) using concentrated solar energy as the only source of process heat. The air will be heated by concentrated solar radiation either directly in a solar tower or indirectly via a thermal energy storage (TES) before being delivered to the calciner. The TES is represented by a novel concept that combines a packed bed of rocks serving as a sensible heat storage with a thermochemical storage (TCS) section that enables storing/releasing thermal energy via the enthalpy of the reaction of a reversible endothermic-exothermic reaction. The reactants in the TCS section are physically separated from the HTF so that the reaction pressure van be varied independently. This regulation of the reaction pressure allows the heat release to be adjusted to maintain the desired HTF outflow temperature. The ability to actively control the HTF temperature beyond 600°C at a constant HTF flow rate does not only make this TES unique but is also essential to operate a calcinator at constant capacity in a steady state. The successful realization of this project would be a significant step towards exploitation of solar energy in the industry of a great importance for Argentina. In addition, the project would contribute to advancement of thermal energy storage for continuous electricity production based on concentrated solar power technology.

Direktlink auf Lay Summary Letzte Aktualisierung: 24.05.2017

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Abstract

Puna, the region in the North West Argentina (NOA), has the world’s third largest borate mineral reserves, after USA and Turkey [ ]. These minerals are commercialized as concentrates, refined or calcined products, and frits. Colemanite (2CaO 3B2O3 5H2O), kernite (Na2B4O7.4H2O), tincal (Na2B4O7.10H2O), and ulexite (Na2O.2CaO.5B2O3.16H2O), make up 90% of the borate minerals used by industry worldwide in more than 300 applications, mainly in the production of ceramics, detergents, fertilizers, and glass [ ]. The US imports of refined borax increased each year between 2011 through 2015, including an 8% estimated increase between 2014 and 2015. The consumption of borates is expected to continue increasing in the foreseeable future, spurred by demand in the agricultural, ceramic, and glass markets in Asia and South America [2].The borate deposits in the Puna region can be found as (a) tertiary deposits (hard borates) and (b) quaternary deposits (soft borates). Tertiary deposits located in Tincalayu, Sijes, and Loma Blanca have been estimated to 60 million tons of B2O3 [ ]. The borates that are found in these salars are: tincal, colemanite, hydroboracite (CaO.MgO.3B2O3.6H2O), inyoite (2CaO.3B2O3.13H2O), and ulexite. Of the quaternary deposits, the main borate that is exploited is ulexite with the total B2O3 reserves in 15 salars estimated to 40 million tons [3]. Argentinian income resulting from the exports of borates and its refined products during the 2013 - 2015 period amounted to U$S 34,546,492.9 (FOB) [3]. In the same period of time, the exports of hydroboracite (CaO.MgO.3B2O3.6H2O) and colemanite earned U$S 6,526,126.73 and U$S 1,483,579.75, respectively [3]. As borates are priced based on their boric oxide (B2O3) content, there is a strong commercial incentive to increase B2O3 concentration by thermal dehydration, i.e., calcination. For example, the price of raw colemanite containing 14-30% B2O3 is around 100-200 U$S / ton B2O3 but once it is calcined to 40-65 % B2O3 it may be sold for 300-450 U$S / ton B2O3 [3]. Similarly, the price of hydroboracite increases from 100-200 U$S / ton B2O3 for 10-30% B2O3 content to 300-450 U$S / ton B2O3 for 40-50.54% B2O3 content [3].The main obstacle to increasing the value of the Puna’s borate resources by calcination is the accessibility to energy sources. Namely, the calcination is an energy-intensive process requiring operating temperatures in the range of 400-600°C. However, the electricity and gas networks in the Puna region are essentially nonexistent. For this reason, ULEX S.A., the only company that exploits colemanite, inyoite and hydroboracite in the Salar de los Pastos Grandes (3,500 m.o.s.l) relies on a dedicated 300 kW/h gas/oil generator to provide the required process energy. At the same time, Puna’s environmental conditions are optimal for exploiting the solar radiation as the solar irradiance is estimated to 6-7.5 and 3.5-5 kWh/m2/day for months of January and June, respectively [ ].Powering an industrial-scale chemical process with concentrated solar energy is a rather challenging task. To assist a continuous industrial operation, the inherent intermittent availability of solar energy imposes either (i) consideration of exotic reactor configurations that could be operated in a hybrid mode via exploiting an alternative energy source of process heat in the absence of sufficient solar irradiation, or (ii) storing solar energy in a thermal energy storage from which the heat can be recovered during periods of insufficient solar irradiation. The scarcity of the conventional energy sources in the Puna region leaves the latter concept as the only option.The objective of this project is to develop a continuous borate-calcination process powered by hot air as the heat-transfer fluid (HTF) using concentrated solar energy as the only source of high-temperature process heat. The hot air will be delivered to a rotary kiln or a fluidized bed calciner, depending on the particle size distribution of the raw borate mineral and morphological/size changes it undergoes during the reaction. The process air is heated by concentrated solar radiation either directly in a receiver of a solar tower during periods of sufficient insolation or indirectly via solar energy stored in a thermal energy storage (TES) during periods of insufficient insolation. The TES is represented by a novel concept that combines (i) a packed bed of rocks serving as a sensible heat storage with (ii) a thermochemical storage (TCS) section housing a reversible endothermic-exothermic reaction that enables storing/releasing solar energy as the enthalpy of the reaction. The TCS section is physically separated from the sensible heat storage so it can be operated at variable pressure. By decoupling the reaction pressure from the HTF pressure, the reaction pressure during discharging the storage can be varied independently to obtain the heat release required for a specified HTF outflow temperature. As such, this is the only TES concept allowing for active control of the HTF temperature beyond 600°C at a constant HTF flow rate. This feature is essential to operating calcination or any other industrial reactor at constant capacity in a steady state. The project would be executed in 36 months through the synergetic partnership between the Professorship of the Renewable Energy Carriers (PREC) of ETH-Zurich (the Swiss partner) and the Minerals Beneficiation Institute (INBEMI) of the National University of Salta (the Argentinian partner). The two partners have strong and complementary expertise in the areas of thermal energy storage (PREC) and borate calcination processes (INBEMI). PREC would be responsible for developing, designing, and testing the combined thermal storage concept through the following steps: (1) selection and kinetic characterization of a suitable TCS material; (2) development and experimental validation of a strategy to control the HTF outflow temperature from the combined sensible heat/TCS TES; (3) energy and exergy analyses of the integrated plant comprising solar field, TES, borate calciner, and heat exchangers/recuperators to determine optimal HTF outflow temperature from the TES; (4) preliminary design of a 50 kWth combined TES. INBEMI would be responsible for evaluating reaction engineering aspects of calcination based on exploiting hot air as the HTF by accomplishing the following: (5) physicochemical and thermal characterization of selected borates and their dehydration reactions, (6) carrying out calcination tests on lab, bench, and pilot scales with feedstocks varying in borate composition and particle size, and (7) identifying optimal calciner configuration based on the energy efficiency of the integrated plant.Successful realization of this project would be a significant step towards exploitation of solar energy in the industry of a great importance for Argentina. In addition, it would contribute to advancement of thermal energy storage for 24/7 electricity production based on concentrated solar power that is readily available in Argentina and other parts of the world. The physico-chemical properties of valuable borate minerals such as colemanite, inyoite, and hydroboracite that are abundant in northwestern Argentina would be determined and documented. Finally, the value-adding increase in concentration of B2O3 by calcining those minerals would be explored leading to development of industrial applications.
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