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

Clean Energy Systems and Experiences

This book reports the latest developments and trends in "clean energy systems and experiences". The contributors to each chapter are energy scientists and engineers with strong expertise in their respective fields. This book offers a forum for exchanging state of the art scientific information and knowledge. As a whole, the studies presented here reveal important new directions toward the realization of a sustainable society

Study of closed-cycle gas turbine for application to small modular reactors (SMRs) and coal-fired power generation through modelling and simulation

Closed-cycle GT has the potential for improved efficiency of electricity generation, compact and simple design, and reduced CO2 emissions and therefore could complement conventional power conversion systems (PCSs). However, power generation from closed-cycle GT needs to be demonstrated to establish the integrity, operation and performance of the plant before commercial deployment can be realised. This thesis provides an understanding, through modelling and simulation, of the thermodynamic performance and component design parameters, and the dynamic behaviours, operation and control of closed-cycle GTs for the purpose of assessing their feasibility for near-term demonstration. A systematic, full-scope study was performed for nitrogen closed-cycle GT coupled to small modular sodium-cooled fast reactor (SM-SFR) and supercritical carbon dioxide (s-CO2) closed-cycle GT coupled to small modular pressurised water reactor (SM-PWR). The study included selection between alternative plant designs, steady state performance analysis, preliminary design of components, dynamic model development and simulation of plant transients, and design of control systems. Additionally, performance evaluation was performed for s-CO2 closed-cycle GT for application to coal-fired power generation integrated with solvent based PCC. Intercooled closed-cycle GT using nitrogen as working fluid and with a single shaft configuration has been one common PCS option for possible near-term demonstration of SFR. In this work, a new nitrogen cycle configuration was proposed to further simplify the design of the turbomachinery and reduce turbomachinery size without compromising the cycle efficiency. Mathematical models in Matlab were developed for steady state thermodynamic analysis of the cycles and for preliminary design of the heat exchangers, turbines and compressors. The study indicated that the new configuration has the potential to simplify the design of turbomachinery, reduce the size of turbomachinery and provide opportunity for improving the efficiency of the turbomachinery. Dynamic model of the new nitrogen cycle power plant was developed in Matlab/Simulink. Control schemes, which enables the plant to satisfy the operational requirements under load-following and loss-of-load conditions, were implemented. Inventory control is unable to keep the generator speed within the specified ±30 rpm of the synchronous speed during normal load-following operation. However, bypass valve control is able to maintain the generator speed within ±17 rpm of the synchronous speed. Maximum generator shaft overspeed is below 105% during sudden loss-of-load condition, which is below the 120% maximum limit. Hence, stable and controllable operation of the nitrogen GT power plant is possible. Matlab models were developed for thermodynamic performance analysis and preliminary design of components for s-CO2 closed-cycle GTs coupled to SM-PWR. Recompression s-CO2 layout is the most common configuration for s-CO2 cycle power plant. However, the performance assessment of the recompression s-CO2 cycle for application to PWR shows that temperature of the turbine exhaust is too low to allow any meaningful recuperation in the high temperature recuperator. Hence, a new layout is suggested. The efficiency of the new layout is comparable to that of the recompression cycle and higher than that of the simple recuperated cycle layout. Investigation of the impact of heat exchanger design on plant performance showed that the recompression cycles have higher pressure losses than the simple recuperated cycle. Therefore, if the heat exchanger design and pressure loss is considered in performance evaluation, the recompression cycles might not be that superior to the simple cycle. However, parametric analysis indicated that the new layout is the most promising for application to PWR. Dynamic modelling, simulation and control system design was also carried out for the new s-CO2 layout coupled to SM-PWR. Inventory/pressure control is not considered to avoid issues associated with the rapid variation of CO2 properties around the critical point. To effectively control the plant, flow split control and throttle valve were added to the normal control systems (bypass valve, control rod, coolant pump and cooling water control). The change in shaft speed during load-following operation is about ±27 rpm while shaft overspeed during loss-of-load is about 107% of the synchronous speed. These are all within the allowable shaft speed limit. Aspen Plus simulation was performed to evaluate the thermodynamic performance of cascaded s-CO2 cycles coupled to coal-fired furnace and integrated with 90% post-combustion CO2 capture. Three bottoming s-CO2 cycles were investigated: simple recuperated cycle, partial heating cycle and the newly proposed s-CO2 cycle. Results for a 290 bar and 593 0C power cycle without CO2 capture showed that the configuration with the new cycle as bottoming cycle has the highest plant net efficiency of 42.96% (HHV), followed by the simple recuperated, 42.46% and the partial heating, 42.44%. Integration of CO2 capture reduced the efficiencies of the new cycle, the simple recuperated and the partial heating configurations to 31.76%, 31.22% and 31.13% respectively. Without CO2 capture, the efficiencies of the coal-fired supercritical CO2 cycle plants were about 3.34-3.86% point higher than the reference steam cycle plant and about 0.68-1.31% point higher with CO2 capture. The findings so far underscored the promising potential of cascaded s-CO2 power cycles for coal-fired power plant application

Study on ash deposition under oxyfuel combustion of coal/biomass blends

Combustion in an O₂/CO₂mixture (oxyfuel) has been recognized as a promising technology for CO₂capture as it produces a high CO₂concentration flue gas. Furthermore, biofuels in general contribute to CO₂reduction in comparison with fossil fuels as they are considered CO₂neutral. Ash formation and deposition (surface fouling) behavior of coal/biomass blends under O₂/CO₂combustion conditions is still not extensively studied. Aim of this work is the comparative study of ash formation and deposition of selected coal/biomass blends under oxyfuel and air conditions in a lab scale pulverized coal combustor (drop tube). The fuels used were Russian and South African coals and their blends with Shea meal (cocoa). A horizontal deposition probe, equipped with thermocouples and heat transfer sensors for on line data acquisition, was placed at a fixed distance from the burner in order to simulate the ash deposition on heat transfer surfaces (e.g. water or steam tubes). Furthermore, a cascade impactor (staged filter) was used to obtain size distributed ash samples including the submicron range at the reactor exit. The deposition ratio and propensity measured for the various experimental conditions were higher in all oxyfuel cases. The SEM/EDS and ICP analyses of the deposit and cascade impactor ash samples indicate K interactions with the alumina silicates and to a smaller extend with Cl, which was all released in the gas phase, in both the oxyfuel and air combustion samples. Sulfur was depleted in both the air or oxyfuel ash deposits. S and K enrichment was detected in the fine ash stages, slightly increased under air combustion conditions. Chemical equilibrium calculations were carried out to facilitate the interpretation of the measured data; the results indicate that temperature dependence and fuels/blends ash composition are the major factors affecting gaseous compounds and ash composition rather than the combustion environment, which seems to affect the fine ash (submicron) ash composition, and the ash deposition mechanismsThe research work reported in this paper was partly carried out with the financial support from the RFCS contract number RFCRCT- 2006-00010. The very fine work done by Peter Heere in carrying out the experiments is highly acknowledgedPublicad