The concentration of CO2 in the atmosphere is increasing rapidly. CO2 emissions may have an impact on global climate change. Effective CO2 emission abatement strategies such as carbon capture and storage (CCS) are required to combat this trend. Compared with pre-combustion carbon capture and oxy-fuel carbon capture approaches, post-combustion CO2 capture (PCC) using solvent process is one of the most mature carbon capture technologies. There are two main barriers for the PCC process using solvent to be commercially deployed: (a) high capital cost; (b) high thermal efficiency penalty due to solvent regeneration. Applying Process intensification (PI) technology into PCC with solvent process has the potential to significantly reduce capital costs compared with conventional technology using packed columns. This paper intends to evaluate different PI technologies for their suitability in PCC process. The study shows that rotating packed bed (RPB) absorber/stripper has attracted much interest due to its high mass transfer capability.Currently experimental studies on CO2 capture using RPB are based on standalone absorber or stripper. Therefore a schematic process flow diagram of intensified PCC process is proposed so as to motivate other researches for possible optimal design, operation and control. To intensify heat transfer in reboiler, spinning disc technology is recommended. To replace cross heat exchanger in conventional PCC (with packed column) process, printed circuit heat exchanger will be preferred. Solvent selection for conventional PCC process has been studied extensively. However, it needs more studies for solvent selection in intensified PCC process. The authors also predicted research challenges in intensified PCC process and potential new breakthrough from different aspects.
Solvent-based carbon capture is the most commercially-ready technology for economically and sustainably reaching carbon emission reduction targets in the power sector. Globally, the technology has been deployed to deal with flue gases from large scale power plants and different carbon-intensive industries. The success of the technology is due to significant R&D activities on the process development and decades of industrial experience on acid gas removal processes from gaseous mixtures. In this paper, current status of PCC based on chemical absorption-commercial deployment and demonstration projects, analysis of different solvents and process configurations-is reviewed. Although some successes have been recorded in developing this technology, its commercialization has been generally slow as evidenced in the cancellation of high profile projects across the world. This is partly due to the huge cost burden of the technology and unpredictable government policies. Different research directions, namely new process development involving process intensification, new solvent development and a combination of both, are discussed in this paper as possible pathways for reducing the huge cost of the technology.
Intensified regenerator/stripper using rotating packed bed (RPB) for regeneration of rich-MEA solvent in post-combustion CO2 capture with chemical absorption process was studied through modelling and simulation in this paper. This is the first systematic study of RPB regenerator through modelling as there is no such publication in the open literature. Correlations for liquid and gas mass transfer coefficients, heat transfer coefficient, liquid holdup , interfacial area and pressure drop which are suitable for RPB regenerator were written in visual FORTRAN as subroutines and then dynamically linked with Aspen Plus ® rate-based model to replace the default mass and heat transfer correlations in the Aspen Plus ®. The model now represents intensified regenerator/stripper. Model validation shows good agreement between model predictions and experimental data from literature. Process analyses were performed to investigate the effect of rotor speed on the regeneration efficiency and regeneration energy (including motor power). The rotor speed was varied from 200 to 1200 rpm, which was selected to cover the validation range of rotor speed. Impact of reboiler temperature on the rate of CO2 stripping was also investigated. Effect of rich-MEA flow rate on regeneration energy and regeneration efficiency was studied. All the process analyses were done for wide range of MEA concentration (32.6 wt%, 50 wt% and 60 wt%). Comparative study between regenerator using packed column and intensified regenerator using RPB was performed and the study shows a size reduction of 9.691 times. This study indicates that RPB process has great potential in thermal regeneration application.
This paper studied mass transfer in rotating packed bed (RPB) which has the potential to significantly reduce capital and operating costs in post-combustion CO2 capture. To model intensified absorber, mass transfer correlations were implemented in visual FORTRAN and then were dynamically linked with Aspen Plus ® rate-based model. Two sets of mass transfer correlations were studied and compared through model validations. The second set of correlations performed better at the MEA concentrations tested as compared with the first set of correlations. For insights into the design and operation of intensified absorber, process analysis were carried out, which indicates: (a) With fixed RPB equipment size and fixed lean MEA flow rate, CO2 capture level decreases with increase in flue gas flow rate; (b) Higher lean MEA inlet temperature leads to higher CO2 capture level. (c) At higher flue gas temperature (from 30 o C to 80 o C), the CO2 capture level of the intensified absorber can be maintained. Compared with conventional absorber using packed columns, the insights obtained from this study are (1) Intensified absorber using RPB improves mass transfer significantly. (2) Cooling duty cost can be saved since higher lean MEA temperature can improve the performance of RPB and high flue gas temperature shows little or no effect on the performance of the RPB.
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