Benchmarking study of demolition wastes with different waste materials as sensible thermal energy storage

Highlights

• For industrial applications abundance, cost and durability of sensible thermal energy storage materials are important.

• Waste materials have a great potential as sustainable and cheap sensible thermal energy storage material.

• Valorization of waste material is a sustainable way of creating cost effective thermal energy storage systems.

• Demolition waste is a good option as sensible thermal energy storage material in packed beds up to 750 °C.

Abstract

Waste materials have a great potential as sustainable and cheap sensible thermal energy storage material (STESM). There are a number of previous studies on the use of wastes as STESM such as Cofalit, coal fly ash and electric arc furnace slags, by-products of the ilmenite mining industry and by-products of the potash production, municipal waste glass and by-products generated in steel industry. The aim of this study is to assess demolition wastes (DW) from urban regenerations in Turkey as a STESM and compare relevant properties with other waste and by-product storage materials. Results show that DW developed here has better or similar storage performance compared to other STESM from wastes. DW is found to be durable up to 750 °C and can be used for high temperature thermal energy storage applications in packed beds.

Introduction

Industrial development and rapid population growth increase total energy consumption in the world. Energy systems are generally based on the use of fossil fuels. In addition to increase in energy prices, use of fossil fuels affect the environment adversely by increasing CO₂ concentration in the atmosphere. Solar energy being the major renewable source is the main alternative to fossil fuels. Waste heat from industrial processes is also considered as a renewable energy resource to decrease fossil fuel-based energy consumption. Thermal energy storage (TES) systems are necessary to cover the mismatch between supply and demand of such fluctuating resources. Among the TES methods, sensible thermal energy storage (STES) systems can provide sustainable, cheap and eco-friendly energy to the users. More efficient and economical exploitation of alternative resources can be realized through integration of STES in the energy system. For industrial scale applications abundance, cost and durability of STES materials (STESM) are especially important.

Any solid material can be considered as STESM. Fernandez et al. [1] used CES selector software to determine which of these vast materials the best alternatives for sensible storage are. Based on this work, Khare et al. [2] gave the following expected properties for appropriate STESMs:

• Thermophysical properties: High energy density, heat capacity and conductivity and long-term thermal cycling stability.

• Chemical properties: Chemical stability, non-toxic, non-explosive, low potential reactivity with the heat transfer fluid (HTF) and the container material.

• Mechanical properties: Good mechanical stability, low coefficient of thermal expansion, high fracture toughness and high compressive strength.

• Economic properties: Cheap and abundant materials with low cost of manufacturing into suitable shapes.

Water is the cheapest medium with the highest energy density. On the other hand, water in liquid form can only be used for low temperature storage applications up to 100 °C. In literature there are a lot of studies on STESM from natural sources. Natural materials such as river rocks, gneiss rocks, desert sands, quartzite-rocks are good candidates for high temperature TES systems. Even if, these natural materials have high density up to 3200 kgm⁻³, their specific heat capacities are limited between 700 and 1100 J kg⁻¹K⁻¹ depending on rock structure [[3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]]. Basalt is suggested as an alternative storage material with its stable, non-explosive and high energy density properties [11,[14], [15], [16], [17]].

Main advantages of using natural materials are: a) abundance and low-cost, b) suitability for high temperature applications, c) mechanical and thermal stability, d) no reaction with HTF in direct use [18]. Alumina is another alternative storage material, which can be used directly as aluminum beads or as composite material [2,[19], [20], [21]]. Compared with rocks, alumina has higher thermal conductivity, this brings shorter charge and discharge time. On the other hand, high cost and low specific heat capacity make the system using alumina more expensive [22].

Molten salt commonly used for high temperature applications is the general name used for inorganic salts in their liquid phase. Among these, solar salt mixture (60% NaNO₃-40% KNO₃) is used in several commercial concentrated solar power plants (CSP). Operation temperature range for solar salt is limited between 220 and 565 °C. It is relatively cheap, but it freezes below 220 °C and is very corrosive. This may require expensive anti-freeze solutions and continuous heat supply. In addition, thermal conductivity values are too low, approximately 0.5 W m⁻¹K⁻¹. The most mature storage technology is 2-tank storage system filled with molten salt. But the main drawback is the necessity of complex and expensive heat exchanger devices [[23], [24], [25]].

Thousand tons of storage material may be needed for especially industrial scale applications to store high amount of thermal energy. This increases investment cost and will affect the environment [26]. Researchers are now focusing on thermocline and packed-bed storage systems more, because single tank storage systems offer advantages by using low cost filler materials [27].

Waste materials have a great potential as STESM. Reducing and recycling of waste materials towards a circular economy is included in sustainability agenda of governments and industries. Advantage of using by-products and waste materials is to reduce the consumption of new/natural materials, to create low cost alternative storage materials and ultimately decrease use of fossil fuels [28]. Using inertized products derived from waste materials of different sources in STES is a sustainable way of valorization. These materials were first considered as fillers in direct molten salt storage applications. Motte et al. [29] investigated usability of wastes from different sources such as asbestos containing (Cofalit), coal fired power plants (CFA), electric arc furnaces (EAF) and blast furnaces (BFA) as fillers. As a result, Cofalit, CFA and BFA were recommended as alternative filler materials in direct solar molten salt systems. On the other hand, due to the high iron content, EAF was not suitable. Calvet et al. [30] filled thermocline tank with Cofalit in ceramic form, which was produced by applying high temperature plasma at 1500 °C to asbestos containing wastes. Cofalit in this form was stable up to 500 °C in direct contact with nitrate salt and recommended as a low-cost filler material.

According to Naimi et al. [31], wastes from metal industries have a great potential with their low-cost, abundant, chemical and thermal stable properties. In addition to EAF slag, ladle furnace (LF) slag, aluminum pot skimming (APS) and aluminum white dross (AWD) can be used up to 1000 °C in TES applications.

Navarro et al. [32] investigated by-products derived from the pyrometallurgical refining process of copper (Slag P), steelmaking process in electric arc furnace (WDF), the potash production process (IB) and ilmenite mining process (WrutF) as solid STESM. These materials were defined as low cost STESM with maximum unit cost of 0.15 €/kg.

Most of the wastes investigated as STESM are slags from different types of furnaces in metallurgical industry. Wang et al. [33] presented thermal and microstructure properties of EAF slag samples from steelmaking industry to prove the feasibility as heat storage material. Grosu et al. [34] evaluated a by-product from steel industry that is formed during the solidification of the steel in basic oxygen furnace (BOF). BOF slag was used as a filler material for a pre-industrial 20MWhth thermocline packed bed TES system with a storage efficiency of 76%. Fernandez et al. [35] investigated two other slags from electric arc furnace of steel making process. One (EAF Slag 1) was obtained by fast cooling with water, while the other one (EAF Slag 2) was produced by low slow cooling with open-air. Both materials were found to be stable up to 1100 °C and have potential to be used in CSPs at temperatures above 600 °C. Agalit et al. [36] investigated induction furnace slag (IFS) and recommended it as a candidate STESM up to 1000 °C with a volumetric heat capacity of 1850&#xA0Jm⁻³K⁻¹.

Asbestos containing wastes (ACW) is another group that has been researched as potential STESMs. Py et al. [37] investigated cycled industrial ceramics made by vitrification of ACW. This material was suggested as a potential TES material up to 1200 °C with high energy density and low cost. Faik et al. [38] analyzed ACW and fly ashes (FA) from municipal solid waste incineration to evaluate their thermal properties. Physical and chemical characteristics of ACF and FA proved that these inertized materials could be candidates for STESM.

Miro et al. [39] studied by-products from potash industry in STES system from 100 °C to 200 °C applications. Granulated by-product with 1–2 mm particle size was mainly composed of NaCl. By-product was analyzed both as directly in molten form (Salt A) and as solid form with low porosity after water treatment (Salt B). After water treatment, sample thermal conductivity and density increased. Cycling performance was determined as 63% for Salt A and 88% for Salt B.

Demolition waste (DW) is the most voluminous and substantial waste material. In Europe, over 800 million tons of waste is generated from partial or total demolition of residential, commercial and municipal buildings, roads or civil infrastructures [40]. According to EU Construction and Demolition Waste Management Protocol [41], demolition waste accounts for 33% of all wastes and it includes building components such as gypsum, plywood, chip wood, sawdust, brick, concrete, rock, metal, plastic and cardboard. Waste Framework Directive (2008/98/EC) [42] commits that minimum of 70% (by weight) of non-hazardous demolition wastes will be recycled by 2020. Therefore, valorization of DW is an important issue.

The aim of the present work is characterization of DW from urban regeneration projects in Turkey and comparison with other waste/by-product STESMs found in literature.