Technologies and fundamentals of waste heat recovery from high-temperature solid granular materials

Large amounts of high-temperature solid granular (HTSG) materials are produced throughout the world in metallurgy and building materials industries whose activities are energy intensive, and therefore the implementation of waste heat recovery technologies would reduce primary energy consumption and greenhouse gas emission in the longer term. This paper aims at reviewing the natures of solid granular materials, the progress on available technologies and key fundamentals of waste heat recovery from HTSG materials, as well as the future issues and research needs in this field. Prior to the review of current technologies and key fundamentals on waste heat recovery, the examples, properties and classification of solid granular materials in natural, technical and industrial fields are described. Subsequently, available technologies including packed bed, moving bed, and fluidized bed are critiqued. The above-mentioned technologies, are comprehensively summarized in terms of heat transfer manner, main characteristics, particle size and HTSG examples. Moreover, typical applications of waste heat recovery from HTSG materials are introduced and critical considerations are discussed when a certain technology is selected in a given case. Additionally, key fundamentals with respect to fluid flow, particles flow, tubes arrangement, Nusselt number correlations and heat transfer enhancement are addressed. The key findings of this review provide avenues to promote the development of waste heat recovery technology. At the end, future issues and research needs which satisfy the new requirements for maximizing the energy efficiency, minimizing the negative impacts, and recovering the waste heat from HTSG with the wide range of particle diameter and productivity are discussed.