An innovative strategy for improvement of energy efficiency in cement production by means of stratified thermal energy storage integration

Abstract

The cement industry represents a heavy emission source due to its large heat demands in its high-temperature processes, as well as a substantial source of CO2 emissions due to the ongoing chemical reactions. The primary air going into the combustion chambers could be pre-heated using available waste heat from the raw mill. However, batch operation imposes a challenge in supplying a continuous heat flow. Therefore, medium-to-high-temperature thermal energy storage technologies could be assessed using pinch analysis to design and determine the operating parameters of a heat network with storage, aiming to facilitate the use of waste heat. Using a European cement plant as a reference, an assessment of a heat recovery system with storage is presented based on primary air preheating. The system is assessed considering thermal energy storage technologies that commonly present thermal stratification in order to reduce costs by working with a single storage tank. Air and thermal oil are evaluated as heat transfer fluids, and different filler materials for storage are considered for thermocline thermal energy storage systems. Results show that low-cost media such as copper slags could recover the system’s investment in less than a year, providing savings in the plant heat demand of up to 1.04%.