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1. Thermal Management Systems and Waste Heat Recycling by Thermoelectric Generators—An Overview

   https://doi.org/10.3390/en14185646  

   Hooshmand Zaferani, Sadeq ; Jafarian, Mehdi ; Vashaee, Daryoosh ; Ghomashchi, Reza ( September 2021 , Energies)

   null (Ed.)

   With the fast evolution in greenhouse gas (GHG) emissions (e.g., CO2, N2O) caused by fossil fuel combustion and global warming, climate change has been identified as a critical threat to the sustainable development of human society, public health, and the environment. To reduce GHG emissions, besides minimizing waste heat production at the source, an integrated approach should be adopted for waste heat management, namely, waste heat collection and recycling. One solution to enable waste heat capture and conversion into useful energy forms (e.g., electricity) is employing solid-state energy converters, such as thermoelectric generators (TEGs). The simplicity of thermoelectric generators enables them to be applied in various industries, specifically those that generate heat as the primary waste product at a temperature of several hundred degrees. Nevertheless, thermoelectric generators can be used over a broad range of temperatures for various applications; for example, at low temperatures for human body heat harvesting, at mid-temperature for automobile exhaust recovery systems, and at high temperatures for cement industries, concentrated solar heat exchangers, or NASA exploration rovers. We present the trends in the development of thermoelectric devices used for thermal management and waste heat recovery. In addition, a brief account is presented on the scientific development of TE materials with the various approaches implemented to improve the conversion efficiency of thermoelectric compounds through manipulation of Figure of Merit, a unitless factor indicative of TE conversion efficiency. Finally, as a case study, work on waste heat recovery from rotary cement kiln reactors is evaluated and discussed. 

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2. Optimal design of combined cycle power plants with fixed‐bed chemical‐looping combustion reactors

   https://doi.org/10.1002/aic.16516  

   Chen, Chen ; Bollas, George M. ( January 2019 , AIChE Journal)

   Process intensification options are explored for near‐carbon‐neutral, natural‐gas‐fueled combined cycle (CC) power plants, wherein the conventional combustor is replaced by a series of chemical‐looping combustion (CLC) reactors. Dynamic modeling and optimization are deployed to design CLC‐CC power plants with optimal configuration and performance. The overall plant efficiency is improved by optimizing the CLC reactor design and operation, and modifying the CC plant configuration and design. The optimal CLC‐CC power plant has a time‐averaged efficiency of 52.52% and CO₂capture efficiency of 96%. The main factor that limits CLC‐CC power plant efficiency is the reactor temperature, which is constrained by the oxygen carrier material. CLC exhaust gas temperature during heat removal and gas compressor to gas turbine pressure ratio are the most important operating variables and if properly tuned, CLC‐CC power plants can reach high thermodynamic efficiencies. © 2018 American Institute of Chemical EngineersAIChE J, 65: e16516 2019

    

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3. Exergy-Based Sustainability Analysis for Tile Production From Waste Plastics in Uganda

   https://doi.org/10.1115/ES2019-3897  

   Balcom, Paige ; Carey, Van P. ( March 2019 , Proceedings of the ASME 2019 13th International Conference on Energy Sustainability collocated with the ASME 2019 Heat Transfer Summer Conference. ASME 2019 13th International Conference on Energy Sustainability)

   This paper presents an exergy-based sustainability analysis of manufacturing roof tiles from plastic waste in Uganda. Exergy analyses measure the sustainability of industrial processes. This work focuses specifically on the developing country context and on utilizing waste material. A summary of the current plastic waste situation in Uganda, the environmental and health issues associated with plastic waste, current means of recycling plastic waste into new products, and an analysis of the Ugandan roofing market are presented. The motivation for this study is to examine the resources utilized to improve overall exergy efficiency, reduce production costs, and reduce negative environmental impacts. The company, Resintile, is the only manufacturer of roof tiles from plastic waste in Uganda. Their tiles comprised mainly of sand and plastic waste are manufactured in an industrialized process involving drying, extrusion, and pressing. The exergy consumed at each stage including transportation is presented. The extruder consumes the majority of the exergy, but wrapping insulation around the barrel could save over 3 MJ, and a heat engine could provide over 7.5 MJ of usable exergy. The total exergy consumed to produce one batch of seventy-five tiles is over 122 MJ, the potentially recoverable exergy is over 5 MJ (4.3% of consumed exergy), and the realistic recoverable exergy is nearly 10.7 MJ (8.7% of consumed exergy). The realistic can be greater than the potential by adding a heat engine to the sand drying process to generate usable exergy rather than merely recover consumed exergy. Resintile’s plastic roof tiles save a net 86.3 kg of CO2 from entering the atmosphere per batch of tiles and adoption of the suggested improvements to the manufacturing process would save an additional 3.8 kg of CO2 per batch.

    

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4. Bismuth Telluride/Half‐Heusler Segmented Thermoelectric Unicouple Modules Provide 12% Conversion Efficiency

   https://doi.org/10.1002/aenm.202001924  

   Li, Wenjie ; Poudel, Bed ; Nozariasbmarz, Amin ; Sriramdas, Rammohan ; Zhu, Hangtian ; Kang, Han Byul ; Priya, Shashank ( August 2020 , Advanced Energy Materials)

   The rapid enhancement of the thermoelectric (TE) figure‐of‐merit (zT) in the past decade has opened opportunities for developing and transitioning solid state waste heat recovery systems. Here, a segmented TE device architecture is demonstrated in conjunction with heterogeneous material integration that results in high unicouple‐level conversion efficiency of 12% under a temperature difference of 584 K. This breakthrough is the result of success in fabricating bismuth telluride/half‐Heusler segmented TE unicouple modules using a “hot‐to‐cold” fabrication technique that provides significantly reduced electrical and thermal contact resistance. Extensive analytical and finite element modeling is conducted to provide an understanding of the nature of thermal transport and contributions arising from various thermal and physical parameters. Bismuth telluride/half‐Heusler based segmented thermoelectric generators (TEGs) can provide higher practical temperature difference with optimum averagezTacross the whole operating range. These results will have immediate impact on the design and development of TEGs and in the general design of devices based upon heterostructures that take advantage of gradients in the figure of merit.

    

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5. Thermodynamic Feasibility of Shipboard Conversion of Marine Plastics to Blue Diesel for Self-Powered Ocean Cleanup

   https://doi.org/10.1073/pnas.2107250118  

   E. Belden, N. Kazantzis ( May 2021 , Proceedings of the National Academy of Sciences of the United States of America)

   Collecting and removing ocean plastics can mitigate their environmental impacts; however, ocean cleanup will be a complex and energy-intensive operation that has not been fully evaluated. This work examines the thermodynamic feasibility and subsequent implications of hydrothermally converting this waste into a fuel to enable self-powered cleanup. A comprehensive probabilistic exergy analysis demonstrates that hydrothermal liquefaction has potential to generate sufficient energy to power both the process and the ship performing the cleanup. Self-powered cleanup reduces the number of roundtrips to port of a waste-laden ship, eliminating the need for fossil fuel use for most plastic concentrations. Several cleanup scenarios are modeled for the Great Pacific Garbage Patch (GPGP), corresponding to 230 t to 11,500 t of plastic removed yearly; the range corresponds to uncertainty in the surface concentration of plastics in the GPGP. Estimated cleanup times depends mainly on the number of booms that can be deployed in the GPGP without sacrificing collection efficiency. Self-powered cleanup may be a viable approach for removal of plastics from the ocean, and gaps in our understanding of GPGP characteristics should be addressed to reduce uncertainty. 

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