Analysis of a cascading power cycle without electric pumps for recovering waste heat from vanadium slag

Abstract

In this article, a novel cascading power cycle (CPC) driven by waste heat in a wide temperature range is proposed for promoting the energy grade, heat source recovery rate and cycle performance, which is consisted of a pumpless absorption power cycle and a pumpless organic Rankine cycle, taking ammonia-water and R245fa as working fluids, respectively. Based on an 800 t/d rotary kiln, the air of 300 C to 350 C from the solid-gas heat exchanger is recovered for power generation and the calcining process. Gravity-assisted thermally driven "pump" (GTP) substitutes the conventional electric driven pump to realize "pumpless." The two sub-cycles are analyzed with the T-s diagram. Moreover, multi-objective optimization is adopted to obtain an optimal decision by comprehensively considering system efficiency and net work. The optimization results of the CPC-GTP are concluded as 47.52% exergy efficiency, 130.90 kW total net work, 16.53% thermal efficiency and 82.58% heat recovery rate, with the evaluation index value of 97.01%.