Waste Heat Utilization for the Energy Requirements of a Post Combustion CO 2 Capture Retrofit Study of a Cement Manufacturing Facility

This paper presents a preliminary investigation of utilizing waste heat available from a cement manufacturing facility for carbon dioxide (CO2) capture and compression processes. The cement manufacturing facility considered in this study emits 600,000 - 750,000 tonnes of CO2 annually while producing 800,000 – 1,000,000 tonnes of clinker. Determining an alternative energy source for amine regeneration will be a major deliverable and a challenging component of this study. Previously utilized methods from the power industry do not apply in this situation since cement plants do not normally produce steam. Cement manufacturing is an energy intensive process resulting in multiple high temperature exhaust gas streams. In this study, preliminary thermodynamic investigations of the utilization of thermal energy have been performed in two gas streams including kiln flue gas and clinker cooler air exhaust. The scenarios investigated in this study include (1) direct recovery of heat using heat recovery boilers and (2) employing of duct firing to increase the temperature of the flue gas prior to heat recovery. The recovered energy can be used for the amine regeneration process. The use of duct burning subsequently produced excess heat which exceeded the energy need for amine regeneration. However, this option can be utilized to produce medium pressure steam which can then be paired with the installation of a back pressure turbine to produce electricity. The results obtained in this study focused solely on the thermodynamic feasibility and efficiency. To justify whether the proposed strategies are practical or not, several factors including CAPEX and OPEX, requirements for modifications to the existing plant, impacts on the existing cement kiln process, and complexity and reliability of the proposed heat recovery system need to be further considered.