OPTIMISATION OF A DEEA–MAPA PHASE CHANGE SOLVENT FOR CO₂ CAPTURE FROM CEMENT KILN FLUE GAS
Cement manufacture contributes about 8% of global anthropogenic CO2 emissions, and roughly 60% of that burden is process-intrinsic calcination CO2 that no fuel switch can remove. Conventional MEA scrubbing imposes regeneration duties above 3.6 GJ per tonne CO2, making low-energy solvents essential for cement decarbonisation. This study aims to optimise a 5 M DEEA + 2 M MAPA phase-change solvent for CO2 capture from the Ashaka Cement Plant, Gombe State, Nigeria (304,996 kg h-1, 22.4 mol% CO2), and to demonstrate that lean loading and stripper pressure must be optimised jointly rather than sequentially. A rate-based Aspen Plus V14 model was developed using electrolyte NRTL-RK thermodynamics with DEEA, MAPA, H2O, CO2 and ionic species, Bravo et al. mass-transfer correlations, and Mellapak 250Y / Flexipac 250Y packing. A twenty-equation reduced-order surrogate calibrated against rigorous runs mapped the lean-loading (0.12-0.30 mol mol-1) and stripper pressure (2.0-4.5 bar) design space, with total equivalent work as objective. At base case, the decanter delivers 65 vol% DEEA-rich light phase at 0.12 mol mol-1 and 35 vol% MAPA-rich heavy phase at 0.82 mol mol-1, with 96.8% of absorbed CO2 in the heavy phase. Solvent circulation for 90% capture is 420 t h-1 vs 680 t h-1 for 30 wt% MEA (cyclic capacity 0.55 vs 0.30). Joint optimisation reduces specific reboiler duty to 2.133 GJ per tonne CO2 at 4.0 bar, 0.17 mol mol-1 lean loading, versus 2.65 GJ at 1.5 bar – 25.4% below AMP/PZ (2.86), 40.9% below 30 wt% MEA (3.61) and 47.5% below 40 wt% cement MEA (4.06). Equivalent work optimum is 0.7419 GJ per tonne at 4.5 bar, limited by 130 °C thermal degradation at 4.22 bar. It is recommended that Ashaka adopt the DEEA-MAPA blend at 3.8 bar, 0.17 mol mol-1 lean loading with 0.3-0.5 bar margin, tighten cross-exchanger ΔTmin to 5-7 K, and integrate waste heat from clinker cooler (200-300 °C) which can supply up to 48% of reboiler duty, offering a route below 2.0 GJ per tonne.
Authors : Abubakar, H., Luka, Y., Mustapha, A.B. and Pariya, A.B.
Category : Open Access Volume (Issue) : 12(1) Date Uploaded : 9th October 2026