- Aud Nina Wærnes
- Senior Business Developer
- 930 59 428
- Metal Production and Processing
- SINTEF AS
The overall goals are to:
- Integrate the components, cycles and concepts developed in other RAs into specifi c industry settings to generate more energyeffi cient processes and improved heat capture and utilisation concepts
- Recovery of surplus heat with a focus on high utilisation of significant industrial sources
- Develop further the potential of green industry clusters and local thermal grids
Recycling off-gas from silicon furnaces
An important activity has been the recycling of off-gas from silicon/ferrosilicon-furnaces, to increase the CO₂ content of the off -gas and make CO₂ capture easier. A highlight of this activity in 2021 has been the PhD work of Vegar Andersen and the 80-hour long pilot experiment he organised and ran in a collaboration between HighEFF and several other projects at NTNU/SINTEF.
Off-gas recycling also influences the gas- phase chemistry in other ways such as PAH emission. Controlling PAH-emissions is important for the industry, so it is necessary to establish how any new process or process modifi cation influences PAH formation and oxidation SINTEF Industry developed kinetic methods for PAH-formation and PAH-oxidation based on a chemical reactor network (CRN) approach to be used in post-processing of CFD-models to model the formation, oxidation and distribution of PAH during gas recycling.
Gas-recycling may also indirectly influence the conditions below the charge surface of the furnace. Changes in SiO-gas condensation will mean a change in how much SiO-gas leaves the charge surface (influencing Si-yield), and the concentration of SiO-gas that enters the combustion zone (influencing amount and possibly also quality of micro silica produced). SINTEF Industry are looking at how this influences the conditions for SiO-gas condensation, by modelling the kinetics of relevant reactions.
An important motivation for the recycling of off -gas is the potential to capture and store/utilise the CO₂. As part of the HighEFF New Emerging Concepts (NEC) project INTERCUR, "A mixed integer linear model for optimising material and energy flows in industrial clusters" was developed. The INTERCUR-model represents a general framework for decision support in the design of industrial clusters, but also presents some potential for application to a single plant. The possibility of using the INTERCUR-model to optimise energy use in a ferroalloys plant incorporating CCS has been briefly outlined in WP4 1.
Ferromanganese: status update
Variations in energy efficiency in Mn-furnaces occur due to variations in the prereduction zone. Ferromanganese prereduction mechanisms have been studied previously in HighEFF by PhD-candidate Trine Larssen Large amounts of experimental data have been produced over the years, as well as several models. This data and models are being evaluated for consistency and general applicability of results Gaps are being identified that need to be filled with further models or experimental data It is expected that experimental work will start within this task in 2022
Recovering excess heat from aluminium production
The Norwegian industry produces approximately 20 TWh of excess heat every year, where the aluminium industry is the largest producer of low temperature excess heat (below 250°C). The off-gas from aluminium electrolysis is a significant source of surplus heat that is currently unused. In order to possible utilise this surplus heat, the industry requires cost- and space-eﬃcient heat exchangers that can withstand the challenging conditions in the off-gas channels. In HighEFF, we have explored a modified plate-type heat exchanger concept without fins on the gas-side for this purpose. New developments in the in-house heat exchanger modelling software at SINTEF Energy Research have made it possible to study any type of heat exchanger geometry. This improved model was used in 2021 to design a prototype for a heat exchanger to be tested for aluminium electrolysis off-gas. This was based on the plate-no-fin concept developed at HighEFF, and the goal is to eventually validate its proposed resistance to scale formation. The proposed test site and the accompanying constraints were taken into consideration in the development of the design of the prototype.
Model predictive control
High-EFF PhD student Mandar Thombre defended his PhD in 2021. His PhD work was titled “Novel Approaches in Robust Multistage Nonlinear Model Predictive Control”. The work focuses on developing data-based methods for scenario selection, and on sensitivity-based methods for faster solution of large-scale optimisation problems that arise in model predictive control. Industrial data from our HighEFF partner Mo industry park was used to develop a realistic case study on energy storage.
The off-gas from the silicon furnace has a very low concentration of CO2, which makes its capture difficult and expensive. By recycling parts of the off-gas back into the furnace, it is possible to raise the CO2- concentrations to higher levels. HighEFF has explored this from a theoretical point of view, and the work has continued in 2020. Models show that NOx formation is suppressed under conditions of flue-gas recycle. PhD-student Vegar Andersen started in 2020 and will perform experiments investigating the effect of flue-gas recycle on microsilica-formation. Theoretical work from HighEFF has been instrumental in the design of a pilot-scale experiment that will be run in 2021 in a collaboration between several projects.
There are several different technologies available for CO2 capture, which have different advantages and disadvantages relating to working concentrations of CO2, energy demands and others. A review of existing technologies has been performed to answer the request from industry to look at an evaluation of capture and utilisation of energy from metallurgical furnaces in a system where one of the energy outputs is towards CO2 capture (e.g. amine regeneration), and the ultimate goal is an optimisation of the use of the recovered energy between electricity generation, CO2-capture, district heating, etc.
Another highlight of the year is the dissemination of PhD candidate Trine A Larssen, on the topic of "Prereduction of Comilog- and Nchwaning ore".
The off-gas from aluminium electrolysis is a significant source of surplus heat that is currently unused. Increased energy efficiency in this industry can be an important contribution to reducing the environmental footprint of the aluminium product. In order to make such investments, the industry requires cost- and space-efficient heat exchangers that can withstand the challenging conditions in the off-gas channels. In HighEFF, we have explored a modified plate-type heat exchanger concept without fins on the gasside for this purpose. Previous simulations showed that this concept can be competitive both in terms of installation cost and compactness, which led to a conference paper and presentation at the Rankine 2020 Conference.
New developments in the in-house heat exchanger modelling software at SINTEF Energy Research have made it possible to study any type of heat exchanger geometry. This improved model was in 2020 used to further investigate the "plate-no-fin" concept for aluminium smelter off-gas. We explored two different unconventional, non-constant geometries and showed that the heat exchanger weight can be further reduced at the expense of increased pressure drop. This trade-off between installation and operational cost will be further explored next year.
Visualisation of energy and material flows in an industry cluster
An interactive tool for visualising energy and material flows in an industrial cluster was created by a summer intern, NTNU-student Cosmin Aron. The work was supervised by researchers from the three SINTEF institutes Industry, Energy and Helgeland. The tool can be used for in-depth analysis of current synergies and by-product utilisation in an industrial cluster, as well as for improvements and integration of new actors. It can also be useful for communication and promoting sustainability and good practices. It combines the simplicity of a diagram with more layers of information added through interactivity.
The model was designed in Microsoft Visio and exported as an interactive webpage, with all the displayed data being imported from an external source (an Excel-file). The tool was applied for visualising the energy and material flows at Mo Industripark (MIP), as shown below.
The primary focus is on process improvements within ferroalloys. Recovery of surplus heat has a focus on high utilisation of significant industrial sources. With an existing industry park as a scenario, the potential of "green" industry clusters and local thermal grids on a Nordic scale are developed.
Work on efficient energy recovery from flue gases from smelters has been continued, and concepts for energy cascading were developed in 2019. These concepts have been presented to the industry and show potential for energy integration across industries.
The potential includes combined electricity recovery by Combined Heat & Power (CHP)-systems, biocarbon and biochemical production, integration towards carbon capture and storage (CCS) and at the lowest temperature ranges fish nurseries and green houses. The conceptual integration potential is large, the obstacles are more on the organizational level.
Modelling of the Submerged Arc Furnace (SAF) process has been studied for several decades. However, few of these models are integrated and show/represent the entire "picture" of the furnace. Initially a review of the work performed within The Norwegian Ferroalloy Producers Research Association (FFF)-companies has been performed to systematize the information available and start work to develop an understanding of the gaps. Two workshops with strong industrial involvement have been arranged. The results are compiled to form a basis for a Roadmap which shows the needs for further development of models. The models shall be used to improve the understanding of the mechanisms inside a furnace and how to influence/control it to minimize energy and carbon consumption, which in turn leads to cost savings.
Surplus heat recovery
Investigation of a novel heat exchanger concept for aluminium smelter off-gas was a key activity in 2019. By drawing inspiration from clean gas heat exchangers, a modified plate-type concept without fins on the gas side was developed. We hypothesize that such a concept can efficiently recover energy from the off-gas while simultaneously being able to avoid problems with scale formation, which will be important in order to avoid increased operational costs. Detailed heat exchanger simulations were performed, and results were compared to a clean gas reference exchanger. Results indicate that the developed concept can be competitive both in terms of weight and compactness compared to the reference case. Reduced weight will give lower capital costs and compactness is important because available space is often limited at aluminium plants. Increasing energy efficiency in the industry will be a key step towards reaching our climate ambitions. We will continue developing the plate-type concept in 2020.
Transferring knowledge to industry and sharing knowledge between academic and industrial partners is key for HighEFF to maximise its impact. In collaboration with the work package on energy-to-power conversion, a seminar entitled "Practical vs. Academic approach to Energy Recovery" was held within the Energy Recovery reference group. The seminar was well attended by both research and industry partners from HighEFF. Elkem and Finnfjord shared their practical experiences with operating industrial ferroalloy furnace off-gas energy recovery systems, and researchers from NTNU and SINTEF presented on improvement potentials, alternative technologies, novel ideas and concepts. In addition, Alcoa, Alfa Laval, Equinor, Eramet, GE Power, Hydro and KTH were present at the meeting. The workshop facilitated good disussions between researchers and industry and new potential topics for collaboration were identified.
Industry clusters and technology integration
A methodology for optimal Thermal Energy Storage (TES) tank dimensioning as well as an operation strategy for improved utilization of waste heat for district heating have been developed, in close collaboration with Mo Industripark/Mo Fjernvarme. The objective of the study has been to find an optimal TES size that minimizes investment costs while maximizing savings of peak heating costs, taking into account the actual dynamics of the heat central and impact of optimal control of the TES at the time of investment decision. The proposed methodology enables MFV to evaluate the potential economic, environmental and energy savings of TES relative to the investment costs.
Energy consumption and potential energy savings in power intensive industries such as ferro-alloy industries where the prime energy consumer is the submerged arc furnace (SAF) and potential reduction and/or use of energy recovered were the main activities in 2018. A literature review on auxiliary systems in ferro-alloy production processes with respect to reduced energy consumption, covers e.g. the utilization of the energy streams exiting the SAF through the furnace off-gases. Concepts for a cascading utilization of the energy in the temperature range from 800°C to approximately 150°C have been presented.
Starting from the energy cascading concept, a new task has been initiated to simultaneously reduce overall energy consumption, NOx-reduction and potentially facilitate CO2-capture from ferro-silicon furnaces. Currently, furnaces utilize fresh air for temperature control in the furnace hood, during the initial study a concept is developed where cleaned flue gas after energy recovery is recycled to the furnace, the study consist of (i) a CFD-model to evaluate the influence on the temperature profile in the furnace hood and thus NOx-formation and (ii) an evaluation of the potential energy savings and energy recovery through an improved temperature control which allows for higher temperatures into the energy recovery system.
In total three reports/papers on the technical and economical feasibility of simultaneously energy recovery and emission reduction have been presented linking activities within EnergiX-project "SCORE" to HighEFF. Two papers at Infacon considering the design and experimental verification of the SCORE concept; followed up by a technical and economical evaluation at SPIS/Flogen 2018.
Surplus heat recovery
The energy flow database was completed for Alcoa, Eramet, Hydro and Wacker's plants in Norway. The data provided by the industry partners was validated through mass and energy balances both on plant and sub-process level, revealing significant variations in the data quality. Exergy calculations were performed for some plants for additional validation. Process flow diagrams giving an overview of mass and energy flows as well as data validation have been completed for a selection of the plants. The diagrams and the database itself are available on the HighEFF eRoom.
A possible path for improving Al smelter off-gas heat exchanger design was explored. It was investigated whether changing tube geometry into a wavy cross-section would improve heat exchanger performance. Results were compared against the current state-of-the-art, showing both advantages and disadvantages.
Industry Clusters and Technology Integration
A methodology for modelling and optimization of energy exchange in industrial clusters and dynamic mathematical models for simultaneous exchange of energy and materials were developed. The description of barriers, whether they are physical, conceptual, technical or cultural, and understanding how thesecan be overcome are crucial in order to identify and implement future cross-industrial synergies and current activities will thus be extended to 2019.
A comprehensive literature review has been made on finalized and on-going projects within The Norwegian Ferroalloy Producers Research Association (FFF) with respect to energy recovery. Processes with high potential for energy recovery (in terms of energy quality and quantity) are identified and selected for further analysis together with the industry. Recycling of flue gas into ferroalloy furnaces is the first activity.
A report/paper on the technical and economical feasibility of simultaneously energy recovery and emission reduction has been made by linking activities within EnergiX-project "SCORE" to HighEFF. Two papers are prepared: 1) Experimental verification and operation presented at Infacon 2018, 2) a technical and economical evaluation submitted to SPIS/Flogen 2018.
Surplus heat recovery:
The framework for the database of thermodynamic potential in surplus heat sources has been developed, with extended scope compared to the initial idea. Work on data acquisition has begun for the metals and materials sector. So far, data from Alcoa, Hydro, Wacker Chemical, Eramet, and Elkem have been received.
The initial activity on "surplus heat database" has been tentatively extended to "Energy flow database", to also include energy and material input streams for each subprocess in the industry plants. This should enable the database to be useful for various activities in many RA's and WP's in HighEFF. Completed entries for individual plants in the "Energy flow database" has been presented as process flow diagrams showing energy and materials flows. Several site visits were arranged to observe authentic plant scenarios and conditions, and scrutinize the energy flow data on-site.
Industry Clusters and Technology Integration:
A Modelica-based modelling and optimization framework for coordinated exchange of surplus heat in industry clusters has been developed. Preliminary results have illustrated both advantages and challenges of using optimization-based control and intermediate storage as a means of leveraging varying surplus-heat streams and demands to improve utilization of surplus heat in industry clusters.