Cycle development and design for CO2 capture from flue gas by vacuum swing adsorption

Cooperative Research Centre for Greenhouse Gas Technologies, Department of Chemical Engineering, Monash University, Victoria 3800, Australia.
Environmental Science and Technology (Impact Factor: 5.48). 02/2008; 42(2):563-9. DOI: 10.1021/es0706854
Source: PubMed

ABSTRACT CO2 capture and storage is an important component in the development of clean power generation processes. One CO2 capture technology is gas-phase adsorption, specifically pressure (or vacuum) swing adsorption. The complexity of these processes makes evaluation and assessment of new adsorbents difficult and time-consuming. In this study, we have developed a simple model specifically targeted at CO2 capture by pressure swing adsorption and validated our model by comparison with data from a fully instrumented pilot-scale pressure swing adsorption process. The model captures nonisothermal effects as well as nonlinear adsorption and nitrogen coadsorption. Using the model and our apparatus, we have designed and studied a large number of cycles for CO2 capture. We demonstrate that by careful management of adsorption fronts and assembly of cycles based on understanding of the roles of individual steps, we are able to quickly assess the effect of adsorbents and process parameters on capture performance and identify optimal operating regimes and cycles. We recommend this approach in contrast to exhaustive parametric studies which tend to depend on specifics of the chosen cycle and adsorbent. We show that appropriate combinations of process steps can yield excellent process performance and demonstrate how the pressure drop, and heat loss, etc. affect process performance through their effect on adsorption fronts and profiles. Finally, cyclic temperature profiles along the adsorption column can be readily used to infer concentration profiles-this has proved to be a very useful tool in cyclic function definition. Our research reveals excellent promise for the application of pressure/vacuum swing adsorption technology in the arena of CO2 capture from flue gases.

  • [Show abstract] [Hide abstract]
    ABSTRACT: A large number of promising adsorbent materials for CO2 capture are reported almost daily. Unfortunately, the assessment of an adsorbent in a process is far more challenging. Statements on expected performance are usually confined to visual inspection of isotherms or calculations of pure component selectivities. These are poor indicators of performance in an actual capture process. We present here a new simplified pressure/vacuum swing adsorption model which can be used to quickly screen adsorbents for use in CO2 capture applications. The model strikes a balance between full adsorption simulation (which requires detailed knowledge of PSA operation and is time consuming) and simple visual inspection of isotherms and calculations of selectivities (which is incorrect and misleading in many cases). Our model has been validated against analytical PSA models, full adsorption numerical simulations, and experiments. Using post-combustion VSA as an example, we use the model to compare several types of adsorbents (zeolite 13X, Mg-MOF-74, Activated Carbon, PEI/MCF chemisorbent). Our analysis shows that 13X remains the best adsorbent in VSA applications (for dry flue gas of 12% composition) even though Mg-MOF-74 shows considerably higher CO2 capacity. We have also conducted a sensitivity study to determine which properties are most important to improving performance and we estimate the limits of PSA performance. Adsorbent selectivity and thermal effects have a more significant effect on the specific power consumption than does CO2 adsorption capacity. The optimal heat of adsorption of CO2 for PSA application is between 35 and 45 kJ/mol regardless of N-2 heat of adsorption. Furthermore, continual increase in surface area is not necessarily beneficial to overall performance, becoming more detrimental as the heat of adsorption of N-2 increases. As an estimate of an upper limit of material performance, a hypothetical material with the same surface area as MOF-177, no N-2 adsorption, and a CO2 heat of adsorption of 35 kJ yields a 68% increase in working capacity and an increase in purity from 78% to 94% when compared to 13X. (c) 2013 Elsevier Ltd. All rights reserved.
    International Journal of Greenhouse Gas Control 07/2013; 15:16-31. DOI:10.1016/j.ijggc.2013.01.009 · 3.82 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Due to climate change it is necessary to reduce anthropogenic climate gas emissions. The application of carbon capture and storage (CCS) technologies could be a suitable approach to lower the specific CO2 emissions from coal-fired power plants. One of these CCS technologies is the Oxyfuel process. In the Oxyfuel process the coal is burned in a mixed atmosphere of O2 and recycled flue gas. The flue gas thus generated has a high CO2 concentration, because of the missing air nitrogen. Still the dried flue gas consists of approximately 15 mol-% impurities (O2, N2, Ar, NOx and SOx). To increase the CO2-purity the flue gas is treated in a gas processing unit (GPU). Two promising technologies to perform the gas processing are partial condensation and distillation. Both are well known and available at industrial scale. Using these technologies about 90% of the CO2 can be separated. The remaining part of the CO2 leaves the GPU with the offgas.
    Energy Procedia 12/2013; 37:1301-1311. DOI:10.1016/j.egypro.2013.06.005
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract A dual-column temperature/vacuum swing adsorption (TVSA) with 3-aminopropyltriethoxysilane-loaded carbon nanotubes (CNT(APTS)) was built to study cyclic CO2 capture from gas streams. The working CO2 capacities and the characteristics of CNT(APTS) were preserved through 100 TVSA cycles under dry or wet conditions, displaying the multi-cycle stability of CO2 capture with CNT(APTS). The cyclic working CO2 capacity of CNT(APTS) was notably enhanced in the presence of saturated water vapor in the gas stream at 25 °C which gives relatively high desorbed CO2 concentrations (∼67%). These results suggest that a dual-column TVSA with solid CNT(APTS) has the possibility to be a promising CO2 capture technology, especially in the post-flue gas desulfurization in which saturated water vapor is present in the flue gas.
    Applied Energy 01/2014; 113:706 - 712. DOI:10.1016/j.apenergy.2013.08.001 · 5.26 Impact Factor