Study of process intensification for post-combustion carbon capture based on chemical absorption through modelling and simulation

Joel, Atuman Samaila

Abstract

There have been a lot of questions on impact of greenhouse gas on changes in climate conditions regarding expected future dangers if mitigation measures are not put in place. Carbon dioxide emission from power sector is a major contributor of greenhouse gases. As a result, the sector is key target for deploying carbon abatement technologies such as carbon capture. Post-combustion capture (PCC) based on chemical absorption technology is one of the major capture approaches and the most matured of them. However, it is beset by some challenges such as high capital and operating costs due to required large sizes of packed columns and high solvent re-circulating rate. Through process intensification (PI) technology, the columns could be downsized by an order of magnitude without compromising their processing capacity. However, there have been limited studies on the techno-economics of PI-based technologies.

In this study, steady state models for standalone intensified absorber and stripper based on rotating packed bed (RPB) technology were developed and validated with experimental data from Newcastle University UK and Tsing Hua University Taiwan respectively. The models were developed in Aspen Plus® and dynamically linked with visual Fortran subroutines. Therefore, this is same as newly developed RPB models (i.e. absorber and stripper). To obtain more insights into the design and operation of standalone intensified absorber, standalone intensified stripper and close loop intensified PCC process, process analysis was carried out. Process analysis in standalone intensified absorber indicates that: (a) CO₂ capture level increases with increase in rotating speed. (b) Higher lean MEA inlet temperature leads to higher CO₂ capture level. (c) Increase in lean MEA concentration results in increase in CO₂ capture level. (d) Temperature bulge is not present in intensified absorber. (e) With fixed RPB equipment size and fixed Lean MEA flow rate, CO₂ capture level decreases with increase in flue gas flow rate. (f) At higher flue gas temperature (from 30°C to 80°C), the CO₂ capture level of the intensified absorber can be maintained. For standalone intensified stripper, the impact of rotor speed on the regeneration efficiency and energy were studied, the impact of reboiler temperature on the rate of CO₂ stripping was established and the impact of rich-MEA flow rate on regeneration energy and efficiency was determined.

From comparative assessment of conventional packed bed and RPB, it was found that a volume reduction factor of 12 and 10 times is possible for the absorber and stripper respectively.

The two validated models, together with model for heat exchanger were then linked together to form a closed loop intensified PCC process. Steady state model of the closed loop intensified PCC process was then used to perform process analysis on (i) the impact of liquid to gas (L/G) ratio on regeneration energy and CO₂ capture level, (ii) the impact of lean-MEA loading on regeneration energy and capture level (iii) capital and operating cost estimation for intensified PCC process were done, which shows a reduction in an investment cost compared to conventional PCC process.

The findings in this study showed that capital and operating costs can be reduced owing to its smaller size compared to conventional PCC process. Also cooling cost for flue gas and inter-cooling in the absorber can be saved since the RPB absorber can be operated at slightly elevated temperature of up to 80°C without compromising the absorber performance and also since higher lean-MEA temperature and/or higher flue gas temperature shows little or no effect on the performance of the RPB. The newly proposed intensified PCC process PFD in the recommendation section of this thesis if successfully implemented can reduce operating and capital costs of PCC process. Finally, these insights can be useful for the design and operation of intensified PCC process.

Citation

Joel, A. S. Study of process intensification for post-combustion carbon capture based on chemical absorption through modelling and simulation. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4218249

• Thesis Type: Thesis
• Deposit Date: Jul 27, 2016
• Publicly Available Date: Feb 23, 2023
• Keywords: Engineering
• Public URL: https://hull-repository.worktribe.com/output/4218249
• Additional Information: School of Engineering, The University of Hull
• Award Date: Apr 1, 2016