enexal: novel technologies for enhanced energy and exergy ... d10_2.pdf · consortium of the...

ENEXAL: Novel technologies for enhanced energy and exergy efficiencies in primary aluminium production

industry

EC Grant Agreement No ENER/FP7EN/249710/ENEXAL

Deliverable D10.2

Report on the results of the dissemination activities

Deliverable Nature: Report

Dissemination Level: PU

Work Package: WP10

WP Lead Beneficiary: ALSA

Due date of deliverable: Month 12

ENEXAL WP10 Deliverable D10.2

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Contents

1 Introduction ................................................................................................................................................. 3

2 ENEXAL Project Web Site ............................................................................................................................. 3

3 Scientific Publications / Conference presentations ..................................................................................... 6


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1 Introduction The present report constitutes ENEXAL’s deliverable “D10.2: Report on the results of the dissemination activities ”, of WP10 as described in ENEXAL’s ECGA – ANNNEX I.

This activity falls within the OTHER activities of the ENEXAL Project, ECGA 249710 and was carried out by ALSA, NTUA, RWTH-Aachen, ETHZ, WEIZMANN, TMF-Serbia and LINDBERGH.

2 ENEXAL Project Web Site As described in the WP10 Task 10.1 a specific Internet Web has been designed and maintained by Partners 1 and 2 in order to promote the project’s RTD results. This web site is installed onto the web server of Partner 2 at the address

http://www.labmet.ntua.gr/ENEXAL/

and was launched on the 15/07/2010.

Figure 1: Screenshot of the ENEXAL site - Home page

The ENEXAL site contains information about the objectives of the project, details about the consortium of the partners involved in the project, a constantly updated calendar of project activities, links to other relevant sites and of course a section dedicated to presenting the results of the project. This latter section will be used as the “open access” repository for all project publications and public reports. It is expected that this web site will comprise an open and public medium for providing knowledge exchange and rising social awareness for the efforts and advances made towards a “green” primary aluminium industry.


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Figure 2: Screenshot of the ENEXAL site - About page

Figure 3: Screenshot of the ENEXAL site - Objectives page


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Figure 4: Screenshot of the ENEXAL site - Calendar page

Figure 5: Screenshot of the ENEXAL site - Publications page


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3 Scientific Publications / Conference presentations

Some preliminary results of RTD efforts made in WP2, WP3 and WP4 have been already sent for publication in referee journals or presentation in international scientific conferences. However as these publications reflect results from the end of first semester, the relevant papers have not been published yet and some are still under consideration. Conference presentations have been accepted but in all cases the conferences will take place after the end of first period of ENEXAL. Therefore in this report for the dissemination activities of the first ENEXAL period, only a list with a brief description (abstracts) of these publications/ conference presentations is given, as technically all of them will belong to the second period of ENEXAL.

1. E.Balomenos, D. Panias, I. Paspaliaris, B. Friedrich, B. Jaroni, A. Steinfeld, E. Guglielmini, M. Halmann, M. Epstein, I. Vishnevsky: Carbothermic Reduction of Alumina : A Review of developed processes and novel concepts, Accepted at EMC 2011 (Germany, June 2011) The Hall-Héroult process for the electrolytic reduction of alumina was developed at the end of the 19th century and is still currently the only industrial process for the production of aluminium. Today this process is ranked among the most energy and CO2 intensive industrial processes, consuming about 1% of the globally produced electric energy and producing 2.5% of the world’s anthropogenetic GHG emissions. The direct carbothermic reduction of alumina has been proposed as an alternative process which can substantially improve the sustainability of primary aluminium production. Processes developed so far suffered from critical design issues, which resulted in low aluminium yields, primarily due to aluminium carbide and -oxycarbide formation and aluminium vaporization. Novel concepts currently being developed under the ENEXAL collaborative research project have the potential to overcome such problems by applying fundamental thermodynamic principles and innovative reactor designs. Thermochemical calculations predict that by carrying out the carbothermic reduction under vacuum, not only will the required reaction temperature be considerably lowered, but also the formation of gaseous Al should occur without the accompanying formation of Al2O, Al4C3, and of Al-oxycarbides. Alternatively, liquid Al can be produced by a combination of high temperatures and high excess of carbon thereby again avoiding carbide and sub-oxide formation. The implementation of such carbothermic reduction processes in aluminium production could lead to energy savings of up to 21%, GHG emissions reductions of up to 52% and exergy efficiency increase of up to 10 percentile points. Additionally, the prospect of utilizing concentrated solar energy to provide process heat can render the primary aluminium production truly sustainable. This paper presents a thermodynamic study of the Al-C-O system, a short review on the alumina carbothermic processes developed so far and two novel carbothermic reductions concepts along with preliminary experimental results. Partners involved: NTUA,RWTH,ETHZ,WIS Relevant WP: 2,3

2. E. Balomenos, I. Gianopoulou, D. Panias, I. Paspaliaris, K. Perry, D. Boufounos: Efficient and complete exploitation of the bauxite residue (red mud) produced in the Bayer process, Accepted at EMC 2011 (Germany, June 2011)

The Bayer process for the production of alumina from Bauxite ore is characterized by low exergy efficiency and it results in the production of significant amounts of dust-like, high alkalinity bauxite residues known as red mud. Currently red mud is produced almost at 1 to 1 mass ratio to metallurgical alumina and is disposed into sealed or unsealed artificial impoundments (landfills), leading to important environmental issues. A patent-pending energy and exergy efficient process has been recently developed by the Advanced Mineral Recovery Technologies (AMRT, Ltd.) and NTUA’s Laboratory of Metallurgy, for the direct transformation of red mud into valuable


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products, such as pig –iron and mineral wool. The novel process utilizes an innovative electric arc furnace (EAF) technology to achieve the carbothermic reduction of the red mud waste without any pre-treatment, producing pig iron and viscous slag suitable for direct mineral wool production. Thus, the environmental footprint of the Bayer process is reduced substantially, as the initial bauxite ore is exploited in full and no solid wastes are produced. The overall exergy efficiency of the new bauxite exploitation schema increases from 3% in the conventional Bayer Process to 6% -9% depending on the method used to produce the electricity needed to power the Electric Arc Furnace. Additionally, as the novel process enables the single step co-production of two highly valuable by-products (pig iron and mineral wool), it has the potential to significantly increase the versatility and profit margin of the alumina producing industry. In this paper a thermodynamic study and preliminary experimental results of the red mud treatment process are presented, along with an overall energy, exergy and economic analysis of the new bauxite exploitation schema. Partners involved: ALSA,NTUA,LINDBERGH Relevant WP: 4

3. E. Balomenos, D. Panias, I. Paspaliaris: Exergy Analysis of Extractive Vacuum Metallurgy-Sustainability prospects, Accepted at ELCAS2 (Greece, June 2011) Based on the fundamental Le Chatellier principle, gas producing reactions can be pushed at lower temperatures if an appropriate vacuum is applied. A basic thermodynamic analysis is used to predict the effect of pressure decrease on the temperature and exergy cost of a reaction with gaseous products. The energy analysis of 11 different metal producing carbothermic reductions revealed that the pumping work substitutes relatively the same amount of heat in all 11 reactions, despite the fact that the volume of gases evolved in each case differs significantly. The exergy analysis for conducting these reactions with non-renewable resources showed that due to the high exergy cost of fossil fuel generated electricity the application of vacuum would increase the overall exergy cost of these reductions. If the heat needed for the reactions could be produced through renewable resources, such as concentrated solar radiation, then the use of vacuum would have a positive effect in the cases of high temperature reductions of Al2O3, MgO and CaO, where a significant decrease in reaction temperature is observed as more exergy is spent in pumping work. Partners involved: NTUA Relevant WP: 2,3

4. D. Gerogiorgis, D. Panias, I. Paspaliaris: Molten slag jet free surface flow and breakup in mineral wool fiberization, Accepted at 8th European Congress of Chemical Engineering, (Germany, September 2011)

Red mud fiberization has remarkable industrial potential, alleviating environmental pressure by transforming this major by-product of aluminium production into marketable mineral wool products. The most widespread mineral wool production process is molten rock (molten red mud) fiberization, either via fast rotating spinning wheels, or via an impinging air jet; the latter is a promising method which avoids mechanical wear as well as rotating parts, but has not been elucidated. The molten slag which remains after pig iron casting enters a heated homogenization reservoir via a siphon neck, flows out of a heated ladle orifice at a high temperature (1400 °C) and adjustable flowrate, and forms a free-falling jet. This paper focuses on high-fidelity CFD modeling of the molten jet free surface flow with external cooling. The CFD model encompasses all interrelated physicochemical phenomena (melt laminar flow, radiative cooling) and considers temperature-dependent transport properties (density, viscosity, surface tension) for the molten slag, to understand how the foregoing geometric degrees of freedom (manipulated process variables) affect the shape and temperature of the resulting flow field until the fiberization zone. Multiphase flow phenomena can then be modeled separately in the zone of droplet and fiber generation. Sensitivity analyses with respect to key variables provide further insight and operational guidelines in order to use the validated CFD model for optimization and control studies towards optimal operation.


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Partners involved: NTUA Relevant WP: 4

5. D. Gerogiorgis, D. Panias, I. Paspaliaris: CFD Modeling of a Molten Slag Jet Free Surface Flow During Mineral Wool Fiberization, Accepted at American Institute of Chemical Engineers (AIChE) Annual Meeting, (USA, October 2011) Red mud fiberization is a process with remarkable industrial importance, alleviating environmental pressure by ensuring the transformation of this major by-product of aluminium production into useful mineral wool products. The most widespread mineral wool production process is molten rock (in this case, molten red mud) fiberization, either by means of fast rotating spinning wheels (Sirok et al., 2008), or via an impinging air jet; the latter is a promising method which avoids mechanical wear as well as rotating parts, but has not been adequately elucidated. The molten slag which remains after pig iron casting enters via a siphon neck into a heated homogenization reservoir, flows out of a heated ladle orifice at high temperature (1400 °C) and adjustable flowrate, and forms a free-falling vertical jet which visibly radiates its excessive heat: at a given distance, a high-velocity impinging air jet meets the vertical melt jet perpendicularly (or at an angle), inducing intensive droplet generation and breakup. Melt droplets (briefly connected by surface tension and viscous forces to each other) emerge at a high velocity, and nascent fibers are rapidly ejected away from the vertical melt jet, experience rapid cooling along their trajectory and then accumulate in a fiber collection chamber, to undergo further processing towards mineral wool. Molten red mud fiberization is a free-boundary problem which can be tackled via advanced CFD methods. Typically, a free-boundary problem consists of a set of elliptic partial differential equations (PDE) which must be satisfied within a bounded domain, together with the necessary momentum and heat flux boundary conditions. The actual axisymmetric flow field is not known, but is assumed to be well within a cylindrical bounded domain. A rigorous mathematical formulation has been derived and published by Epikhin et. al. (1981), while other studies focus on multiphase phenomena during jet breakup (Silaev, 1967; Kuan, 2009) and fiber formation (Kulago, 1985). Thermophysical and transport properties of the molten melt have been studied extensively; however, it is unclear how both geometric characteristics (reservoir/ladle/orifice dimensions, melt jet height, impingement angle) as well as operational parameters (reservoir/ladle/ambient temperature, ambient relative humidity, melt flowrate and composition, air jet velocity) affect both the performance and robustness of this novel process, as well as the quality characteristics of the product (fiber size distribution, mass and size distribution of unfiberized droplets). This paper focuses on high-fidelity CFD modeling of the molten jet free surface flow under external cooling. The CFD model encompasses all interrelated physicochemical phenomena (melt laminar flow, radiative cooling) and considers temperature-dependent transport properties (density, viscosity, surface tension) for the molten slag, in order to understand how the foregoing geometric degrees of freedom (manipulated process variables) affect the shape and temperature of the resulting flow field until the fiberization zone, where it meets the impinging air jet. Sensitivity analyses with respect to the key geometric variables provide further insight and operational guidelines. Experimental validation is also anticipated via data from a novel NTUA pilot plant which is under construction. The validated CFD model will be used for optimization and control studies towards achieving optimal operation. Partners involved: NTUA Relevant WP: 4

6. Halmann, M,. Epstein, M., Steinfeld: A. Bauxite Components Vacuum

Carbothermic Reduction: A Thermodynamic Study. Minerals Processing & Extractive Metallurgy Review, in press. The possibility of direct vacuum carbothermic reduction of bauxite minerals to metallic aluminum at a temperature of 1400-1500 K and a pressure of 10-7 bar is examined by thermochemical equilibrium calculations on AlO(OH) (boehmite and diaspore) and Al(OH)3 (gibbsite) in the absence and presence of SiO2, TiO2, and FeO(OH). Carbon monoxide and hydrogen co-produced


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by the reaction may be used as combustion fuel or further processed to liquid hydrocarbons. The vacuum carbothermic reduction of iron-rich calcined bauxite was studied for Al2O3 – Fe2O3 – C mixtures at 10-4, 10-5, and 10-6 bar, indicating narrow temperature ranges at which the equilibrium for the release of gaseous Al is favored relative to gaseous Fe. Alternatively, for iron-rich bauxite, a preliminary step of iron-removal would be necessary. The proposed process could potentially decrease energy consumption and greenhouse gas emissions, and avoid the production of “red mud”. Partners involved: WIS, ETHZ Relevant WP: 3, 4

7. E.Balomenos, D. Panias, I. Paspaliaris: Theoretical investigation of the volatilization phenomena occurring in the carbothermic reduction of alumina , Metallurgical And Materials Transactions B (under consideration) The carbothermic reduction of alumina has long been recognized as an attractive alternative to the energy intensive Hall-Héroult process used in primary aluminium production. Its implementation however in a viable industrial process has yet to be established due to extensive aluminium volatilization phenomena occurring at the high temperatures needed to achieve the complete reduction of alumina. Such phenomena have been so far attributed primarily to kinetic reasons, such as CO(g) bubbling through the produced liquid aluminium melt. In the present work a theoretical thermodynamic study identifies a mechanism, which can explain aluminium vaporization and alumina incomplete reduction as a result of interactions among aluminium species at different oxidation states. Partners involved: NTUA Relevant WP: 2, 3

8. Halmann, M., Epstein, M., Steinfeld, A.: Carbothermic Reduction of Alumina by Natural Gas to Aluminum and Syngas: A Thermodynamic Study. Minerals Processing & Extractive Metallurgy Review (under consideration)

The carbothermic reduction of alumina to aluminum by methane is analyzed by thermochemical equilibrium calculations in order to determine its thermodynamic constraints. Calculations predict that in the temperature range 2300-2500oC at 1 bar pressure, the reaction Al2O3 + 3CH4 = 2Al + 6H2 + 3CO should occur without significant interference by the formation of unwanted by-products such as Al2O, Al4C3, and Al-oxycarbides, and with higher yields than by using solid carbonaceous compounds as reducing agent. The reaction was examined for several initial Al2O3/CH4 molar ratios. The proposed process may be carried out in a fluidized bed reactor, using concentrated solar energy, induction furnaces, or electric discharges as sources of high-temperature process heat. An important advantage of such a process would be the co-production of syngas, with the molar ratio H2/CO = 2, suitable for the synthesis of liquid hydrocarbon fuels and polymeric materials.

Partners involved: WIS, ETHZ Relevant WP: 3

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