Conceptual design and life-cycle environmental and economic assessment of low-carbon cement manufacturing processes

Abstract

Cement manufacturing, a fundamental process industry characterized by high CO2 emissions, sees over 58% of its emissions stemming from the limestone calcination process. However, this significant source of CO2 has not yet been adequately addressed by most existing cement decarbonization processes. As such, systematic environmental and economic comparisons between different cement processes are essential. This paper proposes a new cement process (NCP) that uses natural gas to react with limestone to reduce CO2 emissions and simultaneously produce high-value-added chemical products (methanol). To explore strategies for further improving the performance of the CO2 emission reduction, two processes are developed, integrating the organic Rankine cycle (ORC) and carbon capture and storage (CCS) units with the traditional cement process (TCP) and the NCP, namely TCP-ORC-CCS and NCP-ORC-CCS respectively. Life cycle assessment (LCA) and economic analysis were performed on the TCP, NCP, TCP-ORC-CCS, and NCP-ORC-CCS processes, revealing their advantages and limitations in different scenarios. LCA adopts the "cradle to gate" system boundary, which includes the whole cement process from ore mining to clinker generation and other processes used for carbon reduction. The LCA results show that four cement processes exhibit different environmental performances when choosing different allocation methods. Under economic allocation, the global warming potential (GWP) of TCP, NCP, TCP-ORC-CCS, and NCP-ORC-CCS are 933, 300, 432, and 194 kgCO2eq/ton·clinker, respectively. The comprehensive analysis indicates that NCP has the best comprehensive economic and environmental performance when natural gas and methanol prices are 332 and 319 $/ton, respectively. The price fluctuation of natural gas and methanol is found to greatly impact the levelized cost of clinker (LCOC) of NCP through sensitivity analysis. NCP is economically preferred over TCP when the price of methanol (MeOH) is at least $76 above approximately two-thirds of the price of methane (CH4). Similarly, NCP-ORC-CCS is more advantageous than TCP-ORC-CCS when the price of MeOH is at least $87 above nearly two-thirds of the price of CH4. This study provides a comprehensive analysis for low-carbon cement process design to achieve CO2 emissions reduction.