Cascaded thermoelectric generation and absorption refrigeration waste heat recovery

Thermoelectric generation (TEG) and absorption cooling have been identified as promising pathways for waste heat recovery (WHR). TEGs reject most of the high-source-temperature thermal energy they receive to the ambient, while converting only 5-10% of that energy. Absorption cycles can harness low-to-mid grade waste heat (70 - 200°C) to deliver refrigeration at COPs of 0.5 - 1.2+. These two technologies are well-suited for integration. If the heat rejection temperature of a TEG system is slightly elevated, its power generation capacity would only be somewhat reduced, and its unconverted input energy can activate an absorption system. This can be considered cascaded WHR, because waste heat cascades through processes that harness both high and low availability portions of input energy. In this study, a model is developed for cascaded TEG and absorption cooling WHR. Thermoeconomic performance is assessed for two potential applications. In a refrigerated transport truck, engine exhaust could be used to produce 770 W electricity and 12 kW cooling at -15°C. Payback periods could approach 3 years. Cascaded WHR from an industrial carburizing furnace (50 kW recovered) could deliver electricity (3.3 kWe) and chilled water (27 kWth). The cascaded system payback period (6.7 yrs) is projected to be higher than standalone TEG (5.4 yrs) but lower than absorption cooling (6.9 yrs). While further research is needed to refine these thermoeconomics projections, the integration and flexibility advantages of this concept may advance adoption of waste heat recovery.