The Impact of Cement Plant Air Ingress on Membrane-Based CO2 Capture Retrofit Cost

Abstract

The industrial sector is responsible for a significant portion of global CO2 emissions. Since some industrial CO2 emissions cannot be avoided, carbon capture and storage has a critical role to play in industrial decarbonization. The objective of this study is to highlight the impact of false air ingress—a standard cement production process occurrence that dilutes kiln CO2 emissions—on utilizing membrane-based capture for cement plant decarbonization. Correlations for ideal countercurrent membrane separation and a compression and purification unit (CPU) model are integrated to estimate the performance of a two-stage membrane system with CPU; membrane parameters are varied, with permeance ranging from 1,000 to 10,000 GPU and CO2:N2 selectivity ranging from 25 to 200. The range of permeance and selectivity values evaluated in this study reflects current commercially available membranes through future stretch performance of yet to be developed membranes. By evaluating this large range of material performance, this study can be used by material developers to inform which performance parameters offer the greatest potential for overall cost reductions based on the study assumptions. The capital and operating costs and the resulting cost of CO2 captured (COC) are estimated. A conventional solvent-based capture system with costs derived on a similar basis is presented for comparison. The results indicate that for the two-stage configuration presented, (1) increasing CO2:N2 selectivity from 25 to 60 can significantly reduce cost, but further improving selectivity, or increasing permeance beyond 1,000 GPU, has only incremental impact; (2) the COC for membrane-based capture systems can be comparable to solvent-based capture systems when the impact of false air ingress into the emissions stream is neglected; and (3) when false air ingress is included, while the COC for solvent-based systems is incrementally affected, the COC for membrane-based capture systems is significantly impacted, rising by 64–111%. Cement plants have typically been characterized with flue gas CO2 concentrations higher than those of coal- or natural gas-fired power plants, which in idealized scenarios provides a higher driving force for membrane separation; however, the substantial false air ingress typically diluting kiln emissions reverses this advantage, leading to higher-than-expected costs. It is recommended that future research and development and techno-economic analyses of membrane-based capture from cement plants address the impact of false air ingress on system design.

Keywords

• Post-combustion carbon capture
• Cement plant emissions
• Techno-economic assessment
• Membrane gas separation