1. Introduction

2. Electric arc-furnace energy demand

3. Demand-side management techniques

4. Ampacity

5. Quality of service

6. Optimization

7. Results

8. Conclusions

Acknowledgments

References

Abstract

An electric arc-furnace is a complex industry which demands high levels of electrical energy in order to heat iron materials and other additives needed for the production of cast iron and/or steelmaking. The cost of the electrical energy demanded by the factory during the production can be greater than 20% of the overall cost. This kind of arc-furnace allows the production of steel with levels of scrap metal feedstock up to 100%. From an electrical point of view, the factory size in terms of its maximum apparent power demanded from the grid is designed to make use of the static capacity of the transmission line that supplies the energy. In that case, it is not possible to increase the power of the factory above the static rating by adding new facilites without installing new transmission infrastructures. This paper presents a methodology that allows an increase in net power of an arc-furnace factory without installing new transmission lines. The novelty of the proposed solution is based on a mix strategy that combines Demand-Side Management (DSM) methodologies and the use of ampacity techniques according IEEE 738 and CIGRE TB601.

The application of DSM methodologies provides an improvement in the sustainability of not only the industrial customer but also in the overall grid. As a secondary effect, it reduces operational costs and the greenhouse gas emissions.

Introduction

An electric arc furnace (EAF) is a furnace that heats charged material by using an electric arc. They are usually devoted to the production of cast iron and/or steelmaking. From an energy point of view, it is a load that it is intensive in terms of its power demanded from the grid [1].

As the electrical energy consumption in an EAF based steel factory is typically greater than 20% of the overall production cost, most of the modeling effort has been devoted to the analysis of energy comsuption considering cost minimization [2] as the main target [3]. From the point of view of predicting the electrical energy consumption of Electric Arc Furnaces using statistical Modeling it is possible to find several approaches using both linear and non-linear models. Table 1 summarizes several contributions in the field of EAF modeling.

Recent studies have demonstrated how Electric Arc Furnace (EAF) concrete represents a sustainable alternative to ordinary concretes, and that it could be satisfactorily employed to realize reinforced concrete (RC) elements. However, a comprehensive study about the effects of its use in RC structural systems, both in terms of structural safety under static and dynamic loads, and environmental impacts along the whole life cycle, has not been investigated yet. This work analyzes the seismic reliability of standard residential buildings (cast in place RC frames), considering three different configurations (3-, 6- and 9- story building type) designed considering ordinary concretes made with natural aggregates (NA) according to the novel Italian seismic code, which is similar to the Eurocode 8 approach. Non-linear time history analyses have been carried out to investigate the seismic response of the analyzed cases comparing results obtained from the benchmark structures (i.e. the NA ones) with those coming from the same made with EAF mixes, in order to verify the suitability in using sustainable EAF concrete mixes in seismic areas. Lastly, a seismic reliability analysis has been carried out for comparative purposes, demonstrating how EAF concrete overstrength compensates for the extra efforts that the analyzed RC frames may undergo during seismic events.

Introduction

Among the Sustainable Development Goals (SDG) that have been adopted by the Agenda 2030 of the United Nations [1], one of the main global challenges that the construction market has to face, together with the society, is to substantially reduce waste generation through prevention, reduction, recycling and reuse policies. In this field, the reduction of waste disposal through the promotion of recycling opportunities as construction materials has been largely a matter of study and research within the scientific world. Specifically, an extensive research has been devoted to safely use various type of waste in the construction industry, and due to the great amount of natural aggregates (NAs) consumption, this represents an important part of the market that has been explored. As indicative numbers, the European aggregates demand alone is 2.7 billion tonnes per year [2]; additionally, also for structural concrete production it is worth recalling that aggregates represent 70% in volume of a concrete mixture, in average. The most well-known case of recycling is that of Construction and Demolition Waste (C&DW), which can be used to produce Recycled Aggregates (RAs); their use is currently allowed and regulated in most of the building codes and standards around the world [3–5]. More recently, the suitability of using other kind of waste and by-products to produce so-called industrial aggregates has been object of a dynamic research, which for instance analyzed the applicability of plastic waste [6,7], recycled waste glass [8,9], recycled tires [10,11], and many other by-products, particularly from steelmaking industry [12–15].

This study investigated the shrinkage properties of concretes using blast furnace slag cement and frostresistant accelerator as a construction technology in environmental-load-reducing cold weather concretes. The investigation results showed that as the frost-resistant accelerator was added to both Ordinary Portland Cement (OPC) and Blast Furnace Slag Cement (BB), the effect on the properties of fresh concrete was reduced and the compressive strength was increased from an early age. In addition, the free shrinkage strain and cracking potential at the same age tended to increase and the study result verified that the crack generation was also fast in the restrained condition. Meanwhile, the study results verified that the length of both of OPC and BB tended to increase upon adding the frost-resistant accelerator. Pore volume <30 nm diameter, in particular, 20–30 nm pore volume, and ink-bottle pore volume decreased such that the shrinkage volume increased, and the change in pore volume in this range was regarded as having a large effect on the shrinkage properties.

Introduction

The use of blast furnace slag cements has been expanded to reduce environmental load or employ industrial wastes efficiently. More recently, low heat and shrinkage-reduced blast furnace cement, which has a high content ratio of blast furnace slag, and Energy CO2 Minimum (ECM) cements that achieve the Class C slag content ratio have been studied, but their use has been limited practically [1–3]. Although blast furnace slag cements have many advantages such as low heat, increased long-term strength, flame interruption performance, and suppression of the alkali–aggregate reaction, they also have drawbacks such as delayed early strength development and early frost damage during winter construction due to high temperature dependence, which is why much care must be taken when using blast furnace slag [4]. When concretes are used in winter, it is important that the concretes do not freeze until sufficient strength has been developed to prevent early frost damage due to the delayed strength development or freezing, and heat curing via temporary enclosure and use of a heater is typical [5–8]. However, the use of a temporary enclosure for concrete curing may cause CO2 emissions due to the heater or warm curing in a space with extremely bad heat efficiency, which is why the use of a frost-resistant accelerator has increased to prevent early frost damage [9–14].

The integrated utilization of wastes in a cement kiln has become an international megatrend. Various hazardous compounds containing in wastes might be enriched in the particulate matter (PM) emitted during the waste disposal and cause adverse environmental consequences. In order to evaluate the potential environmental issues caused by the PM emission from the cement kiln for co-processing wastes, the chemical characteristics and formation mechanism of the PM was investigated for the first time by using a laboratory-scale tube furnace to simulate this process. PM was collected to analyze the major components (heavy metals, inorganic and organic components) and morphologies. The results reveal that volatile heavy metals in municipal sewage sludge (MSS) can be enriched in PM. The process can elevate the levels of sulfate and the organic contents in PM, and the existence of organic moieties such as CNþ and CHNþ suggest that the co-processing of MSS can affect the PM organic compositions. Single particle imaging analyses indicate that PM can be classified into nine types based on their elemental compositions. Further analysis reveals that most particles usually mix with other types of particles and those mixed particles may cause a more serious impact on the environment. Based on the TEM observation, a two-step formation mechanism of PM is proposed. Our findings point out the potential environmental adverse effects and call attentions to a full environment assessment of this new type of cement production process, and also indicates stringent measures should be taken to reduce PM emissions during this process.

Introduction

Municipal sewage sludge (MSS) is a common waste worldwide, and its production has reached 30 Mt/y with an annual increasing rate of 8e10% (Xiao et al., 2017). The accumulation of MSS has become a serious environmental concern. Landfill and incineration are the two most common routes for MSS disposal in China (Zhou et al., 2014). Such methods have their own bottlenecks. For example, the reduction of land resource and undesired emissions (e.g., leachate and landfill gas) to ambient water, soil and air restricts the implementation of landfills (Jin et al., 2017). Incineration can also aggravate emissions of hazardous substances such as heavy metals and some organic species into the environment. The methods of gasification, pyrolysis and digestion have been proposed for the disposal of MSS, but the associated intensive energy consumption, complex operation, etc., may also limit further development of those methods. The integrated utilization of wastes such as MSS in cement kiln has become a promising method and attracts public interests due to its multiple advantages. For example, the MSS contains Ca, Si and Al, which are similar to the raw materials for cement production and the co-processing of MSS in a cement kiln can save natural resources. Dried MSS also contains significant calorific values, which could save energy at the same time. The silicate in the cement clinker such as tricalcium silicate and dicalcium silicate can help stabilize the heavy metals during the high temperature calcination process. Hazardous organic substances might also be decomposed due to the high temperature and long residence time in a cement kiln. The co-processing of wastes in cement kiln can also receive subsidies from the government. Despite aforementioned advantages, this disposal method may pose some environmental problems, such as the emission of particulate matter (PM) into the air.

Ground granulated blastfurnace slag (GGBFS), obtained as a by-product in the production of metallic iron, is granulated, rapidly cooled, and therefore predominantly glassy, basic slag. The slag contains the same oxides (SiO2, Al2O3, CaO) that make up Portland cement but in different proportions. According to the European cements standard EN 197-1, at least two16 thirds of the slag by mass must be glass and the mass ratio (CaO+MgO)/SiO2 must also be greater than 1.0 [1]. The latent hydraulic properties of slag are activated in the presence of cement clinker, sulphates or calcium hydroxide (but other alkaline substances are also effective). With all activators, the calcium silicate hydrate or C−S−H phase is produced as the hydration product which governs the hardening. Clinker activation is used in the manufacture of Portland slag cements and blastfurnace cement, and sulphate activation in the manufacture of super sulphate cement. Generally, the rate of hardening of slag cement is somewhat slower than that of ordinary Portland cement (OPC) during the first 28 days, but increases thereafter so that at 12 months the strength becomes close to or even exceeds that of OPC [2]. GGBFS can be used as a direct replacement for OPC on one-to-one basis by mass. Replacement rates for GGBFS vary from 30 mass % to up to 85 mass %. In general, up to 50 mass % GGBFS is used in most applications. However, higher replacement rates up to 85 mass % GGBFS are used in special applications either to improve the durability of concrete in aggressive environments or to reduce heat of hydration in massive concrete structures [3]. Nowadays the GGBFS is most widely used as the main constituent to produce high-performance Portland cement blends that are more economical and environmentally friendly. The EN 197-1  differentiates some main categories of cements containing different proportions of GGBFS, i.e., Portland slag cement (CEM II), Blastfurnace cement (CEM III) and Composite cement (CEM V). The Portland slag cement type (CEM II) exists in two classes designated as CEM II/A–S and CEM II/B–S in which the maximum content of GGBFS is and 35 mass %, 12 respectively. There are two classes of Composite cements CEM V designated as CEM V/A and CEM V/B in which, in addition to cement clinker and pozzolana, the maximum content of GGBFS is 30 and 50 mass %, respectively. Blastfurnace cements CEM III (where CEM III is the designation for three types of blastfurnace cements A, B and C), in addition to Portland cement clinker, contain between 36 and 95 mass % of GGBFS with subdivisions at 66−80 mass % of GGBFS [1]. Table 1 shows the composition of three types of blastfurnace cements (BFSC).

در مطالعه قبلی یک سیستم جدید قاب با بادبند کمانش ناپذیر برای قاب‌های بتن مسلح پیشنهاد شد که ویژگی‌اش استفاده از آرایش زیگزاگی بادبندهای کمانش ناپذیر جهت سهولت اتصال فولاد به بتن بود. آزمایش‌های آزمایشگاهی به منظور ساخت مدل‌های عددی واقعی اتصالات بادبندی در سیستم پیشنهادی انجام شدند. با این مدل‌های عددی، یک تحلیل غیرخطی برای نمونه اصلی ساختمان انجام شد تا رفتار لرزه‌ای سیستم قاب بادبندی جدید بررسی شود. نتایج نشان دادند که بادبندهای کمانش‌ناپذیر در این سیستم جدید در کاهش پاسخ ساختمان، حتی اگر غیرخطی بودن اتصال بادبند لحاظ شود، کارآمدند. علاوه بر این، مقاومت موردنیاز اتصالات بادبند حساسیت زیادی به مودهای بالای سیستم پس از تسلیم بادبندها دارد.