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

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

Modelling and simulation of intensified absorber for post-combustion CO₂ capture using different mass transfer correlations

This paper studied mass transfer in rotating packed bed (RPB) which has the potential to significantly reduce capital and operating costs in post-combustion CO₂capture. To model intensified absorber, mass transfer correlations were implemented in visual FORTRAN and then were dynamically linked with Aspen Plus® rate-based model. Therefore, this represents a newly developed model for intensified absorber using RPB. 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 was 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 °C to 80 °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 rotating packed bed (RPB) improves mass transfer significantly. (2) Cooling duty cost can be saved since higher lean MEA temperature and/or higher flue gas temperature shows little or no effect on the performance of the RPB

Process analysis of intensified absorber for post-combustion CO₂ capture through modelling and simulation

Process intensification (PI) has the potential to significantly reduce capital and operating costs in postcombustion CO₂ capture using monoethanolamine (MEA) solvent for power plants. The intensified absorber using rotating packed bed (RPB) was modelled based on Aspen Plus® rate-based model, but some build-in correlations in Aspen Plus® rate-based model were replaced with new correlations suitable for RPB. These correlations reflect centrifugal acceleration which is present in RPB. The new correlations were implemented in visual FORTRAN as sub-routines and were dynamically linked to Aspen Plus® rate based model. The model for intensified absorber was validated using experimental data and showed good agreement. Process analysis carried out indicates: (a) CO₂ capture level increases with 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. Compared with conventional absorber using packed columns, the insights obtained from this study are (1) intensified absorber using RPB improves mass transfer significantly. (2) Higher flue gas temperature or lean MEA temperature will not be detrimental to the reactive separation as such cooling duty for flue gas can be saved. (3) Inter-cooling cost will not be incurred since there is no temperature bulge. A detail comparison between conventional absorber and intensified absorber using RPB was carried out and absorber volume reduction factor of 12 times was found. These insights can be useful for design and operation of intensified absorber for CO₂ capture

Preliminary Performance Assessment of Intensified Stripper in Post-combustion Carbon Capture through Modelling and Simulation

Intensified stripper used in chemical absorption process based on rotating packed bed (RPB) technology was studied through modelling and simulation in this paper. The model was developed by dynamically linking Aspen Plus® ratebased model with visual Fortran. Suitable correlations for RPB were implemented in Fortran to replace the default correlations in Aspen Plus® rate-based model. The standalone stripper model was validated with experimental data. The paper compared standalone intensified stripper with conventional stripper using MEA solvent. The result shows 9.69 times size reduction. Therefore PI has great potential for use in carbon capture application

Financial impact of sheeppox and goatpox and estimated profitability of vaccination for subsistence farmers in selected northern states of Nigeria

Sheeppox and goatpox (SGP) are important transboundary diseases, endemic in Nigeria, causing severe clinical manifestations, impacting production, and resulting in economic losses. Vaccination is an effective control measure against SGP in endemic countries but is not currently implemented in Nigeria. This study aimed to estimate SGP financial impact and assess economic viability of SGP vaccination at the herd and regional level under different scenarios in Northern Nigeria. Integrated stochastic production and economic herd models were developed for transhumance and sedentary herds. Models were run for two disease scenarios (severely and slightly affected) and with and without vaccination, with data parameterisation from literature estimates, field survey and authors’ experience. Herd-level net financial impact of the disease and its vaccination was assessed using gross margin (GM) and partial budget analyses. These were then used to assess regional financial impact of disease and profitability of a 3-year vaccination programme using a cost-benefit analysis. The regional-analysis was performed under 0 %, 50 % and 100 % government subsidy scenarios; as a standalone programme or in combination with other existing vaccination programmes; and for risk-based and non-risk-based intervention. Median SGP losses per reproductive female were £27 (90 % CI: £31-£22), and £5 (90 % CI: £7-£3), in sedentary, and £30 (90 % CI: £41-21), and £7 (90 % CI: £10-£3), in transhumance herds, for severely and slightly affected scenarios respectively. Selling animals at a reduced price, selling fewer young animals, and reduced value of affected animals remaining in the herd were the greatest contributors to farmer’s SGP costs. SGP-affected herds realised a GM reduction of up to 121 % in sedentary and 138 % in transhumance. Median estimated regional SGP cost exceeded £24 million. Herd-level median benefits of vaccination per reproductive female were £23.76 (90 % CI: £19.28-£28.61), and £4.01 (90 % CI: £2.36-£6.31), in sedentary, and £26.85 (90 % CI: £17.99-£37.02) and £7.45 (90 % CI: £3.47-£15.14) in transhumance herds, in severely and slightly affected scenarios, respectively. Median benefit: cost ratio (BCR) for severely affected herds at 50% subsidies was 6.62 (90% CI: 5.30-8.90) for sedentary, and 5.14 (90% CI: 3.31-13.81) for transhumance herds. The regional SGP vaccination standalone programme BCR: 7–27, regional SGP vaccination with existing vaccination programme BCR: 7–228 and vaccinating high-risk areas BCR: 19–439 were found to be economically viable for all subsidy levels explored. Vaccinating low-risk areas only realised benefits with 100 % of government subsidies. This study further increases understanding of SGP’s impact within Northern Nigeria and demonstrates vaccination is an economically viable control strategy at the herd-level and also regionally, depending on the strategy and government subsidy levels considered

Process intensification for post combustion CO₂ capture with chemical absorption: a critical review

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

Wide circulation of peste des petits ruminants virus in sheep and goats across Nigeria

Peste des petits ruminants (PPR) is a highly contagious viral disease that mainly affects goats and sheep in Asia, Africa and the Middle East, and threatens Europe [R.E.1]. The disease is endemic on the African continent, particularly in West Africa, and is a major factor driving food insecurity in low-income populations. The aim of this research study was to carry out surveillance, genetic characterisation and isolation of recently circulating PPR viruses (PPRV) in sheep and goats from the six agro-ecological zones of Nigeria. A total of 268 post-mortem tissue samples of lung and mesenteric ganglia were collected from clinically suspected sheep and goats in 18 different states, of which five never previously sampled. The presence of PPRV was confirmed using a reverse-transcription coupled with a polymerase chain reaction (RT-PCR) assay. A total of 72 samples, 17 sheep (6%) and 55 goats (21%), were found to be PPR positive. Positive samples were distributed in almost all states, except Kano, where PPR was detected in previous studies. The PPRV-positive samples were further confirmed by sequencing or virus isolation in areas where the infection had never previously been detected. These results confirm the active circulation of PPRV across all six agro-ecological zones of Nigeria, and consequently, the need for introducing strict measures for the control and prevention of the disease in the country