Techno-economic assessment of a rotary kiln shell radiation waste heat recovery system

Abstract

Heat transfer from the rotary kiln surface was assessed through CFD simulations. • Influence of geometric parameters of the absorber was explored. • Incident heat flow to the absorber was used as input to a Recuperated ORC. • The waste heat recovery system is economically evaluated to determine its feasibility considering electricity prices. In this work, the feasibility of implementing a waste heat recovery system based on the capture of radiation emitted from the surface of a rotary kiln is evaluated by coupling CFD analysis and process modelling including mass, energy, and exergy balances. It is found a potential heat recovery of up to 4980 kW of heat with an annulus absorber panel which extends 30 m of the kiln length and reaches an average temperature of up to 240 °C. Such heat could be used to generate 864.25 kWe of electricity through a Recuperated ORC with a thermal efficiency ηth = 17.35% and an exergetic efficiency ηexg = 48.62% for a total saving of 16.6 MJe per tonne of clinker. An economic feasibility for this recovery alternative is highly dependent on the electricity price in the cement plant location. It is observed for markets with electricity prices exceeding 0.1 $/kWh, the return on investment could reach values of 5% corresponding to a NPV close to 0.06 MUSD.