Sustainable urea production via CO2 capture from cement plants: A techno-economic analysis with focus on process heat integration and electrification

Abstract

Urea, a key derivative of ammonia, is widely used in agriculture and has a significant impact on food security. This study evaluates a sustainable urea production pathway that utilizes hydrogen generated from water electrolysis for green ammonia synthesis and CO₂ captured from a cement plant using an MEA-based process. This study employed Aspen Plus V12.1 and MATLAB to develop rigorous system-level models of all subsystems involved in the sustainable urea production process. These subsystems include a cryogenic air separation unit (CASU), a modular system of alkaline electrolysers (AEL), a green Haber-Bosch (HB) process, an MEA-based CO₂ capture system, and the Stamicarbon process. To enhance the energy efficiency and cost-effectiveness of urea production, waste heat generated during green ammonia synthesis in the HB process was integrated into the stripper column of the MEA-based CO₂ capture system for solvent regeneration. A detailed economic analysis was conducted to assess the impact of this heat integration (HI) on reducing the CO₂ capture costs and, consequently, the overall urea production costs. Additionally, several heat supply scenarios were evaluated to meet the heat demand of the CO₂ stripper column in the Stamicarbon process. These included natural gas combustion, a cascade heat pump (HP), and natural gas combustion integrated with a cryogenic CO₂ capture (CCC) system. The results indicated that HI significantly decreases both the energy penalty and costs of the MEA-based CO₂ capture process, reducing the CO₂ capture costs by 41.27 % in 2024 and lowering the energy penalty by 50.40 %. Among the scenarios investigated, the cascade HP with HI proved to be the most cost-effective option for urea production. Additionally, electricity costs for operating the modular alkaline electrolyzers (AEL) dominate the sustainable urea production expenses, with 88.07 %–91.26 % of electricity costs allocated to AEL, depending on the selected production scenario. The modular AEL also represents the largest share of initial investment costs, accounting for 90.62 % of total capital expenditures in the urea production process.