Graduate School of Creative Science and Engineering Waseda University
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博 士 士 士 士 論 論 論 論 文 文 文 文 概 概 概 概 要 要 要 要
Doctoral Thesis Synopsis
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論 文 文 文 文 題 題 題 題 目 目 目 目
Thesis Theme
Gigatonne-scale reduction of CO 2 emissions via mineralization using iron and steel slags
Corey Adam MYERS
マイヤズ コーリ アダム
Department of Modern Mechanical Engineering, Research on Exergy Engineering
May, 2019
The large inertia of the Earth system means that climate change is already set to cause millions of deaths and untold suffering. However, no matter how far climate change progresses, it is a moral imperative to attempt to limit its impacts. Addressing this challenge, the Paris Agreement calls for, “a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century, on the basis of equity, and in the context of sustainable development and efforts to eradicate poverty”. Meeting this ambition requires immediate, deep, and rapid emissions reductions. Of the major emitters, ironmaking and steelmaking (ISM) stands out, not only as a necessary industry to supply materials for climate adaptation, but also as an industry without any clear way to rapidly reduce emissions. Proposals for new, low CO2 ISM techniques and equipment will likely require decades to develop and diffuse globally; in other words, too slowly to adequately address ISM’s emissions. Recently, some have suggested using biomass in place of fossil fuels in ISM. However, this narrow view fails to recognize that the loss of greenhouse gases from natural carbon stocks nullifies or exceeds the benefits from avoiding fossil fuel use. These conundrums have led to the growing interest in applying CO2 capture and storage (CCS) to the current generation of ISM facilities. However, the high costs of CCS combined with the global nature of the iron and steel market means that the absence of a global price on carbon makes CCS a non-starter for the ISM industry. A profitable method to reduce CO2 emissions that could be scaled-up rapidly would help ISM reduce emissions while new ISM methods and policies mature. This dissertation proposes that the solid waste product of ISM called ‘slag’ provides such an opportunity as a feedstock for stabilizing CO2 as a solid mineral (so-called: CO2 mineralization). This doctoral dissertation re-examines a method first proposed nearly three decades ago: simple, gas-solid CO2 mineralization. In contrast to previous studies, CO2 mineralization is achieved without chemical additives, takes place at ambient temperatures, and uses unaltered flue gas or ambient air. The critical design feature that allows for CO2
mineralization under such moderate conditions is the separation of the disparate minerals within slag. In two novel processes developed as part of this dissertation, the separation of minerals is achieved by control of the solidification of molten slag as it leaves the ironmaking and steelmaking process. In one process, molten slag is separated by centrifuge into high purity layers of (Ca,Mg)-oxide, (Ca,Mg)-silicate, and low oxidation state Fe. In a separate process called ‘MYNA’, molten slag is slowly solidified followed by quenching of the high-temperature, solid slag. The slow solidification of the MYNA process generates large mineral grains; the quenching process fractures and liberates the disparate minerals. To design these processes, the first ever application of deep neural networks (DNN) to molten slag property prediction was realized. These DNNs not only provide the best property estimates available in the literature, but also are able to predict hitherto intractable phenomenon. Finally, to quantify the rate of CO2 mineralization, the first ever comprehensive determination of the CO2 mineralization characteristics of common slag minerals under flue gas conditions was performed.
This doctoral dissertation consists of 9 chapters. Chapter 1 provides a background of the science of climate change, its causes, its potential impacts moving forward, and the social and technical solutions commonly advanced. Additionally, the economic and political structures that have failed to draw humanity’s efforts to solving climate change are examined. Design principles to help avoid such failures are distilled and used throughout the dissertation.
In Chapter 2, a background of the ISM process, the industry’s current makeup, and methods being explored to reduce CO2 emissions are discussed. Chapter 2 spends considerable time examining the physical and mineralogical aspects of ISM slag. Traditional and alternative reuse pathways for slag are discussed and the logic behind using slag as a CO2 mineralization feedstock is laid out. The history of attempts to use slag for CO2
mineralization is discussed along with the primary causes for the poor performance record.
Chapter 3 focusses on molten slag property estimation by DNN. The chapter begins by examining conventional molten slag property estimation methods and their shortcomings before discussing the theoretical framework of DNNs. The artificial intelligence community has done vanishingly little work on physical property estimation since the explosion of DNN capabilities, so a fair amount of space is taken up in Chapter 3 converting the methods of ‘traditional’ DNNs into methods that are optimal for the physical sciences. Chapter 3 discusses the training and skill of DNN for the prediction of molten density, viscosity, thermal conductivity, liquidus temperature, and the nucleation lag time. In particular, the prediction of nucleation lag time shows the potential of DNN as it is the first ever general-purpose prediction. To build such a prediction, a new concept of merging DNN with classical knowledge was developed. This method has broader implications as it may allow for an understanding of the inner workings of DNNs while concurrently improving classical theories.
Chapter 4 builds atop the molten property predictions from DNN to design the centrifuge process and the solidification portion of the MYNA process. The centrifuge is modeled using a numerical simulation and shown to separate molten slag within 5 minutes into distinct mineral layers. These layers solidify due to an increased liquidus temperature that accompanies the composition change. Solidification is avoided during the separation process due to the long nucleation lag time from the sudden changes in chemical composition. In the MYNA process, the slow solidification of molten slag is designed to generate large mineral grains. Calculation of grain size is done through classical theories of ion diffusion in a molten melt which requires DNN prediction of complex properties. The MYNA process is predicted to produce mineral grains that are ~100-1000 times larger than those from traditional slag treatment methods.
In Chapter 5, the solid-state quenching of the MYNA process is developed. The design of this thermal fracturing processes begins with the calculation of the mineral-specific grinding energy and fracture stresses.
From this information, the transient temperature distribution and thermal stress of quenched high-temperature solid slag in water is modeled. Quenching generates fractures which alter the heat transfer characteristics of the slag and thus the thermal stress. Accounting for these feedbacks shows that the larger grain sizes of MYNA enhance the fracturing and liberation that results from quenching, reducing grinding energy by ~40%. Chapter 5 also examines the energy of grinding minerals that will be reacted with CO2. Such grinding is necessary to enhance CO2 mineralization reactions but comes at the cost of energy usage and the associated CO2 emissions.
Chapter 5 also improves traditional grinding energy estimations by accounting for details such as the full particle size distribution and inherent surface roughness. Using this improved calculation, the degree of grinding beyond which a process is a net CO2 emitter is quantified - important information for all CO2 mineralization methods.
Chapter 6 primarily focusses on the empirical determination of CO2 mineralization rates for 35 compounds common to ISM slag. Such rates are captured by the diffusion coefficient of CO2 through the product layer
around reacting minerals. These empirical results highlight the extreme variation in the speed of CO2
mineralization as a function of the feedstock mineral. These results also provide guidance on the potential of other solid wastes or natural rocks for CO2 mineralization. In Chapter 6, a new quantitative theory to examine the reduction in CO2 mineralization extent that occurs when disparate minerals are left in a mixed state (termed:
‘mineral locking’) is developed. The phenomenon of mineral locking has been qualitatively proposed but never quantified. This new theory suggests that the historically poor performance of gas-solid CO2 mineralization is largely due to mineral locking effects.
In Chapter 7, the results and methods of the previous chapters are leveraged to calculate the speed and net CO2 mineralization rate of ISM slags. The analysis examines both extant slags and MYNA slags. A separate analysis looks at the net emissions reduction from the centrifuge process based on how the recovered materials are utilized. The MYNA process greatly improves the speed of CO2 mineralization and the net CO2
mineralization rate over traditional slag methods. However, the centrifuge process is even more effective at reducing emissions as it also recovers low oxidation state Fe which can be recycled to the ISM process as a portion of the feedstock. All processes benefit from application of renewable energy as process energy; this effect is especially strong for legacy slags due to the large amount of grinding energy required.
Chapter 8 examines the cost and scale-up potential of the centrifuge process, MYNA process, and direct CO2
mineralization of legacy slag. Capital expenses, operating expenses, and revenue from the sale or reuse of products are considered, but no carbon tax or credits are assumed. All processes are found to be profitable through the sale of slag as construction aggregate. The largest profit occurs in the centrifuge process due to recovery of high value flux and low oxidation state Fe. Estimated profits are on the order of $20-70 per tonne of CO2 for the centrifuge process, ~$30 per tonne of CO2 for the MYNA process, and ~$4 per tonne of CO2 for the legacy slag processes. Without the revenue sources, the centrifuge, MYNA, and legacy slag processes cost ~$5,
~$10, and ~$25 per tonne of net CO2 mineralized. The CO2 reduction potential, including conservative assumptions for technology scale-up and diffusion time, shows that the MYNA process supplemented with CO2
mineralization for legacy slag can reduce cumulative emissions by ~36-45 Gt-CO2 by 2100. The centrifuge process, supplemented with CO2 mineralization for legacy slags, can provide ~47-59 Gt-CO2 emissions reduction by 2100.
Chapter 9 summarizes the novel aspects of this doctoral dissertation and discusses the open issues of this work. Given the pace and severity of climate change, the major open issue is scaling these processes up as quickly as possible. Ironmaking and steelmaking are projected to emit ~100-400 Gt-CO2 by the end of the century, disproportionately consuming the remaining carbon budget to stay below 2 ˚C. As such, the 10’s of gigatonnes of CO2 mineralization using slag is an important lever for reducing the CO2 footprint of ISM.
Likewise, application of gas-solid CO2 mineralization to other solid wastes such as demolition waste and fly ash would provide an additional 10’s of gigatonnes of emissions reductions globally. Ultimately, the application of CO2 mineralization to natural rocks ground using renewable energy could provide net removal of CO2 from the atmosphere to pre-industrial levels and stabilize the Earth system.
No.1
早稲田大学 早稲田大学 早稲田大学
早稲田大学 博士（ 博士（ 博士（ 博士（工学 工学 工学 工学） ） ） ） 学位申請 学位申請 学位申請 学位申請 研究業績書 研究業績書 研究業績書 研究業績書
(List of research achievements for application of doctorate (Dr. of Engineering), Waseda University)
氏 名 (Corey Adam Myers) マイヤズ コーリ アダム 印 ( ) （As of July, 2019） 種 類 別
(By Type)
題名、発表・発行掲載誌名、発表・発行年月、連名者（申請者含む）
(theme, journal name, date & year of publication, name of authors inc. yourself) a. Journal
article
a. Journal article
a. Journal article
a. Journal article
a. Journal article
○
○
○
○
○
1. Quantification of the CO2 mineralization potential of ironmaking and steelmaking slags under direct gas-solid reactions in flue gas, International Journal of Greenhouse Gas Control Vol. 87C p.100-111 (2019), Corey A. Myers, Takao Nakagaki, and Kosei Akutsu.
2. Prediction of nucleation lag time from elemental composition and temperature for iron and steelmaking slags using deep neural networks, ISIJ International Vol. 59 No. 4 p.687-696 (2019), Corey Adam Myers and Takao Nakagaki.
3. Effect of Solidification and Cooling Methods on the Efficacy of Slag as a Feedstock for CO2 Mineralization, ISIJ International Vol. 58 No. 2 p.211-219 (2018), Corey Adam Myers and Takao Nakagaki.
4. Application of quenching to polycrystalline metallurgical slags to reduce comminution energy and increase mineral liberation, In Proceedings of the 16th International Heat Transfer Conference Beijing China, IHTC Digital Library, p. IHTC-22437 (2018), Corey A. Myers and Takao Nakagaki.
5. Enhanced recovery process of calcium oxide and metals from steelmaking slag with net carbon sequestration, Energy Procedia Vol. 114 p.6246-6255 (2017), Corey Myers, Takao Nakagaki, and Takuya Mitamura.
b. Review article
1. CCS、CCUS のレビューと技術展望 ～コスト、量的寄与、リスクの観点から
～. 日本機械学会誌、 第 122 巻 第1203 号 特集 二酸化炭素分離回収と貯 留・固定および利用技術 p.8-13 (2019), Takao Nakagaki and Corey Myers.
c. Reviewed international conference c. International conference
c. International conference
c. International conference
c. International conference
1. Application of quenching to polycrystalline metallurgical slags to reduce comminution energy and increase mineral liberation, In Proceedings of the 16th International Heat Transfer Conference, p. IHTC16-22437 (2018), Corey A. Myers and Takao Nakagaki.
2. Experimental determination of CO2 mineralization depth of slag minerals at CO2
concentrations available in iron and steelmaking flue gases, 14th International Conference on Greenhouse Gas Control Technologies Melbourne Australia (October 2018), Corey Myers and Takao Nakagaki.
3. Feasibility study of net CO2 sequestration using seawater desalination brine with profitable polyproduction of commodities, 14th International Conference on Greenhouse Gas Control Technologies Melbourne Australia (October 2018), Yohei Tsubuku, Corey Myers, and Takao Nakagaki.
4. Molten slag property estimation using deep neural networks for advanced material recycling, 1st International Conference on Energy and Material Efficiency and CO2
Reduction in the Steel Industry Kobe Japan (October 2017), Corey Myers and Takao Nakagaki.
5. Enhanced recovery process of calcium oxide and metals from steelmaking slag with net carbon sequestration, 13th International Conference on Greenhouse Gas Control Technologies Lausanne Switzerland (November 2016), Corey Myers and Takao Nakagaki.
No.2
早稲田大学 早稲田大学 早稲田大学
早稲田大学 博 博 博 博士（ 士（ 士（ 士（工学 工学 工学 工学） ） ） ） 学位申請 学位申請 学位申請 学位申請 研究業績書 研究業績書 研究業績書 研究業績書
(List of research achievements for application of doctorate (Dr. of Engineering), Waseda University) 種 類 別
By Type
題名、発表・発行掲載誌名、発表・発行年月、連名者（申請者含む）
(theme, journal name, date & year of publication, name of authors inc. yourself) c. Domestic
conference
c. Domestic conference
1. CO2 utilization via mineralization into construction aggregate using waste brine, In SCEJ 50th Fall Meeting Kagoshima (2018), Kohei Sato, Corey Myers, Yohei Tsubuku, and Takao Nakagaki.
2. Improvement of HCl recovery efficiency in brine-based CO2 mineralization using Mg. In SCEJ Regional Meeting Kanazawa (2017), Yohei Tsubuku, Corey Myers, Kei Shiraishi, and Takao Nakagaki.
c. Poster presentation c. Poster presentation
1. CCUS development supported by prediction via Deep Neural Networks, IEAGHG 2018 CCS Summer School Trondheim Norway (2018), Corey Myers.
2. ディープ・ニューラル・ネットワークを用いた複雑な組成の液体物性の効率 的な予測, 第2回WIRPワークショップ Tokyo Japan (2017), Corey Myers.
e. Official report
e. Official report
e. Patent (pending)
1. 実践的モデルを活用した CCS 全体システムのコスト計算成果報告書 (2019), Takao Nakagaki, Corey Myers, Yohei Tsubuku, Naoya Ogiyama, Hirotaka Isogai, Daisuke Hasegawa, Kohei Sato.
2. 地上設備を含めた CCS システム全体のコスト評価成果報告書 (2018), Takao Nakagaki, Corey Myers, Dabin Wang, Hyeongseok Park, Akira Ozeki, Yohei Tsubuku, Naoya Ogiyama, Daiichi Watanabe.
3. 特願 2019-0243．二酸化炭素固定化方法 （早稲田大学，出光興産，日揮の共
願）
No.3
早稲田大学 早稲田大学 早稲田大学
早稲田大学 博士（ 博士（ 博士（ 博士（工学 工学 工学 工学） ） ） ） 学位申請 学位申請 学位申請 学位申請 研究 研究 研究 研究業績書 業績書 業績書 業績書
(List of research achievements for application of doctorate (Dr. of Engineering), Waseda University)
種 類 別By Type
題名、発表・発行掲載誌名、発表・発行年月、連名者（申請者含む）
(theme, journal name, date & year of publication, name of authors inc. yourself) Award
Award
Award
1. “Most Outstanding Student”, IEAGHG, 2018 CCS Summer School.
2. “Best Essay Explaining Negative CO2 Emissions”, Carbon 180 (formerly: Center for Carbon Removal), Travel and attendance scholarship to 1st International Conference on Negative CO2 Emissions, Gothenburg, Sweden 2018.
3. “Best Presentation Award” for Master’s Thesis 2016, Waseda University Graduate School of Environment and Energy Engineering, “Reducing the Carbon Footprint of the Iron and Steel Making Industry -Separation and Conversion of Constituent Elements of Slag-”
