Waste Heat to Power: Full‐Cycle Analysis of a Thermally Regenerative Flow Battery

Abstract

To achieve the climate goals of the Paris Agreement, efficient use of energy is critical. Still, approximately 30% (31.9 EJ) of the energy input to global industry is lost as waste heat, with 28% as so-called low-temperature waste heat between 60 and 120 °C. [1] Therefore, using low-temperature waste heat offers an opportunity to develop the potential of waste heat and thereby reduce global greenhouse gas emissions.Technologies to utilize low-temperature waste heat can be divided into three categories: 1) passive heat recovery (e.g., heat exchangers); 2) heat transformation (e.g., heat pumps); and 3) power production (e.g., organic Rankine cycles (ORCs)). [2] Among these technologies, power-production technologies have the advantage that electrical power has a higher energy quality than heat. Thus, power production from lowtemperature waste heat is a promising target.For power production from low-temperature waste heat, the ORC can be considered as state-of-the-art technology. [3] The advantages of ORCs include the use of standard components, often known from the well-researched Rankine cycle, and the possibility of using working fluids perfectly tailored for a specific application. [4] Despite the advantages, today's ORCs are often unprofitable for converting low-temperature heat due to their system complexity and low thermal efficiencies. [4,5] Rahimi et al. [6] have recently reviewed three alternative technologies for power production from low-temperature waste heat: 1) thermo-osmotic energy conversion (TOEC); 2) thermally regenerative electrochemical cycle (TREC); and 3) thermally regenerative battery (TRB).TOEC are turbine-based systems that exploit a static pressure difference between a high-pressure reservoir at ambient temperature and a low-pressure reservoir at heat source temperature. [6] TOEC directly integrates heat by vaporizing water through a vapor-permeable membrane from the low-pressure to the high-pressure reservoir. [7] The TREC is an electrochemical cell that exploits a temperaturedependent redox couple. [6] The temperature dependence allows

Simulating Discharge Curves of an All-Aqueous TRAB to Identify Pathways for Improving System Performance

“…where T H is the hot side temperature (100 °C), 16,17,25,26 T L is the cold side temperature (25 °C), ΔT HE is the heat exchanger temperature difference (5 °C), 3,4 and ΔT * is the temperature difference across a single process of a multi-effect and heat recovery scheme (MEHRS) (75 °C). 3,4 Polarization curves were simulated to validate that the model cell resistance was the same as that of the experimental cell resistance and therefore matched previous experimental data.…”

“…14,15 A full cycle analysis was conducted on the metallic-copper TRAB to investigate trade-offs between power density and efficiency to identify the operating conditions to maximize each simultaneously. 16 Recently, a numerical sensitivity analysis was completed on the Cu aq -TRAB which showed that ohmic losses were previously the main contributor to poor battery performance. 17 This led to an experimental investigation of different membranes in the Cu aq -TRAB resulting in very high power and energy densities relative to the previous membrane choices.…”