• Energy Research

This study aims to analyse some of the most relevant issues that the energy intensive industry needs to face in order to improve its energy and environmental performance based on innovative retrofitting strategies. To this end, a case study based on the aluminium industry, as one of the most relevant within the European energy intensive industry has been thoroughly discussed. In particular, great efforts must be addressed to reduce its environmental impact; specifically focusing on the main stages concerning the manufacturing of an aluminium billet, namely alloy production, heating, extrusion and finishing. Hence, an innovative DC (direct current) induction technology with an expected 50% energy efficiency increase is used for retrofitting conventional techniques traditionally based on natural gas and AC (alternating current) induction. A life cycle assessment was applied to analyse three different scenarios within four representative European electricity mixes. The results reported reductions up to 8% of Green House Gases emissions in every country. France presented the best-case scenario applying only DC induction; unlike Greece, which showed around 150% increment. However, the suitability of the new DC induction technology depends on the electricity mix, the technological scenario and the environmental impact indicators. Finally, environmental external costs were assessed with comparison purposes to evaluate the increase of energy and environmental efficiency in existing preheating and melting industrial furnaces currently fed with natural gas.

Abstract Until now, a small number of studies have analysed the carbon footprint (CO2 eq. emissions) of the application of Phase Change Materials (PCMs) in conventional Thermal Energy Storage (TES) systems considering different conventional fossil fuels as the source of heat. In those scarce studies, the different environmental impact categories were estimated using, on the one hand, diverse environmental methodologies and, on the other hand, different environmental evaluation methods (the midpoint and endpoint approaches). Despite the fact that several researchers have used the Life Cycle Assessment (LCA) methodology as a tool to estimate the environmental impact of TES systems, there is no unanimity in the scientific community on the environmental evaluation method to be used. As a consequence, research results cannot be easily compared. This article evaluates the introduction of a TES system (using different PCMs) to recover the waste thermal energy released in industrial processes, which can be used in other applications, thereby avoiding fossil fuel consumption by the associated equipment to produce thermal energy. Five different fossil fuels have been considered to generate the 20 case studies that were analysed using the same methodology (LCA) and evaluation method (Global Warming Potential, GWP100, a midpoint approach). The results were used to identify the best cases, considering the environmental benefits that they generate. Additionally, this research indicates that the benefits can be achieved since, in general, the amount of conventional fuels saved is sufficiently large to balance the environmental impact associated with the inclusion of PCMs in conventional TES. Nevertheless, the selection of a PCM can increase or eliminate the environmental benefits obtained.

In Europe, science and innovation are boosting the agri-food sector and, in parallel, are helping to decrease greenhouse gas emissions (GHG) and European dependency on non-renewable resources. Currently, it is well-known that this sector contributes to the consumption of energy and material resources, causing significant environmental impacts that require a complex and comprehensive environmental evaluation in order to manage them effectively. This becomes even more complicated when new technologies are reaching the level of technological maturity needed to be installed in the production lines. To address this scientific challenge, the life cycle assessment (LCA) has been used in this paper to evaluate the potential of pulsed electric fields (PEF) technology at an industrial scale to facilitate the steam peeling of tomato fruits. Considering the thermo-physical peeling stage, the LCA has shown that PEF technology is environmentally friendly, because when PEF technology is applied, all the considered environmental indicators improve between 17% and 20%.

Abstract This work addresses the potential environmental effects of thermal energy storage using the life cycle assessment to perform an optimal system framework. The study assesses the recovery of waste thermal energy at medium temperatures through the application of phase change materials and the recovered heat use in other industrial processes avoiding the heat production from fossil fuel. To this end, twenty different situations were analysed in terms of energy and environmentally combining four thermal energy storage systems varying the type of phase change material incorporated (potassium nitrate, potassium hydroxide, potassium carbonate/sodium carbonate/lithium carbonate and lithium hydroxide/potassium hydroxide) which were defined as cases and five scenarios were the heat can be released based on the type of fossil fuel consumed (coal, heavy fuel, light fuel, lignite and natural gas). Moreover, a net zero environmental metric time parameter was calculated to assess the time period in which the environmental impacts associated to the thermal energy system were equal to the avoided impacts by the use of the heat recovered. Values that were lower than the thermal energy system lifetime were obtained in more than 40% of the total study situations. Finally, an additional analysis was performed to identify the most significant parameters for the further development of a mathematical model to predict the net zero environmental metric time.

The energy considered as waste heat in industrial furnaces owing to inefficiencies represents a substantial opportunity for recovery by means of thermal energy storage (TES) implementation. Although conventional systems based on sensible heat are used extensively, these systems involve technical limitations. Latent heat storage based on phase change materials (PCMs) results in a promising alternative for storing and recovering waste heat. Within this scope, the proposed PCM-TES allows for demonstrating its implementation feasibility in energy-intensive industries at high temperature range. The stored energy is meant to preheat the air temperature entering the furnace by using a PCM whose melting point is 885 °C. In this sense, a heat transfer model simulation is established to determine an appropriate design based on mass and energy conservation equations. The thermal performance is analysed for the melting and solidification processes, the phase transition and its influence on heat transference. Moreover, the temperature profile is illustrated for the PCM and combustion air stream. The obtained results prove the achievability of very high temperature levels (from 700 to 865 °C) in the combustion air preheating in a ceramic furnace; so corroborating an energy and environmental efficiency enhancement, compared to the initial condition presenting an air outlet at 650 °C.

Reductions in energy consumption, carbon footprint, equipment size, and cost are key objectives for the forthcoming energy-intensive industries roadmaps. In this sense, solutions such as waste heat recovery, which can be replicated into different sectors (e.g., ceramics, concrete, glass, steel, aluminium, pulp, and paper) are highly promoted. In this line, latent heat thermal energy storage (TES) contributes as an innovative technology solution to improve the overall system efficiency by recovering and storing industrial waste heat. To this end, phase-change material (PCM) selection is assisted through a decision-support system (DSS). A simplified tool based on the MATLAB® model, based on correlations among the most relevant system parameters, was developed to prove the feasibility of a cross-sectorial approach. The research work conducted a parametric analysis to assess the techno-economic performance of the PCM-TES solution under different working conditions and sectors. Additionally, a multicriteria assessment was performed comparing the tool outputs from metal alloys and inorganic hydrated PCM salts. Overall, the inorganic PCMs presented higher net economic and energy savings (up to 25,000 €/yr; 480 MWh/yr), while metal alloys involved promising results, shorter cycles, and competitive economic ratios; its commercial development is still limited.