Comparative assessment of processes for the transportation of thermal energy over long distances

Abstract

This papers deals with the transportation of thermal energy over long distances that could allow the recovery of waste heat from industrial sites. Processes involving thermochemical transformations can be relevant for such purpose as they involve the transportation of a reactive fluid at ambient temperature, and thus allow large distances between source and users. This paper aims to evaluate the performances of a thermochemical system designed for the transportation of thermal energy, and to compare it to classical processes devoted to the same purpose (involving electricity, coolant, slurry). A general method has been developed to assess the performances of all the paths of energy transportation. This paper is focused on the application of this methodology to cold utilities on the user site. The aim is to analyze the relevance of each process on the same basis. The exergy destruction in each part of these systems is analyzed and the exergy efficiencies are compared.Keywords: Thermochemical process; heat transportation over long distance; exergy. IntroductionIndustrial waste heat represents a huge amount of thermal energy, which is usually released several tens of kilometers away from potential users. The most obvious application is the recovery of this low temperature waste heat for distant heat and/or cold needs such as district heating, food-processing industry, etc. Therefore, the transportation of heat over long distances (over 10 km) represents a real scientific and technical challenge for a better and sustainable management of the energy resources.Several research projects are focused on this research area (Kugeler et al., 1975;Hoehlein et al., 1981;Zeng et al., 1992;Bach et al., 1998, Nasako et al., 1998Hasegawa et al., 1998;Liu et al., 2002;Stitou et al., 2002;Martin et al., 2006;Berthiaud et al., 2006;Le Pierrès et al., 2009; IEA-ECES-annex 18, 2010).A lot of them propose to implement a thermochemical process between the source and user sites, in order to replace the transportation of thermal energy by the transportation of an active fluid (a reactive gas for example). As the fluid is transported at ambient temperature, the thermal losses are low, and transportation over long distances can be considered.

Heat recovery opportunities in UK industry

“…Approximately 25% of potential can be recovered in the 100-500°C temperature band, steambased transportation systems may be viable here. Above this temperature band alternative technologies may be required, these include reversible chemical reactions, phase change thermal storage, absorption and adsorption techniques [27,42,43]. According to the current analysis this higher temperature demand represents only a small proportion of the total potential.…”