Analysis of sCO2 Waste Heat Recovery System for Application in a Cement Plant

Abstract

The industrial sector contributes approximately 28% of global CO2 emissions. CO2 emissions from energy-intensive industries can be reduced by converting waste heat into electricity. This represents a low-cost, zero-emissions power generation option with near-term deployment opportunities. One energy-intensive industry is cement production. Two cement plant heat sources are flue gas streams from preheater and clinker cooler, with temperatures of 250–450 °C. Potential energy conversion systems include Organic Rankine (ORC), steam Rankine (SRC), and supercritical CO2 (sCO2) power cycles. ORC/SRCs have been commercially deployed in cement plants. However, sCO2 power cycles offer benefits such as high thermal stability of CO2, higher cycle efficiencies, and compact power generation equipment. The paper is focused on multi-objective optimization of four sCO2 cycle layouts (Recuperated, Re-compression, Partial recuperative, and cascade) and comparison with ORCs/SRCs. The optimization considers waste heat temperatures of > 300°C. The results show that sCO2 power cycles can reach cycle efficiencies up to 30 %, which is higher than corresponding ORCs and almost similar to SRCs. However, cycle efficiency is not the only parameter to evaluate waste heat utilization. More meaningful parameters are the net power and capital costs. Results show higher power outputs from the sCO2 cycle compared to ORCs and SRC.