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Formation of aerosols can cause serious complications in industrial exhaust gas cleaning processes. Small mist droplets and fog formed can normally not be removed in conventional demisting equipment because their submicron size allows the particles or droplets to follow the gas flow (Schaber et al., 2002). As a consequence of this aerosol based emissions in the order of grams per Nm 3 have been identified from PCCC plants ( Khakharia et al., 2015 ). In absorption processes aerosols can be created by spontaneous condensation or desublimation processes in supersaturated gas phases or as a result of droplets or particles entering with the exhaust gas. Undesired aerosol formation may lead to amine emissions many times larger than what would be encountered in a mist free gas phase in PCCC development. It is thus of crucial importance to understand the formation and build-up of these aerosols in order to mitigate the problem. This paper presents a rigorous model of aerosol dynamics leading to a system of partial differential equations. In order to understand the changes taking place with a particle entering an absorber an implementation of the model is created in Matlab. The model predicts the development in droplet size, droplet internal variable profiles and the mass transfer fluxes as function of position in the absorber, and thus also at the outlet. The Matlab model is based on a subclass method of weighted residuals for boundary value problems named, the orthogonal collocation method. The model comprises a set of mass transfer equations for transferring components and the necessary diffusion reaction equations to describe the droplet internal profiles for all relevant constituents. Also included is heat transfer across the interface and inside the droplet. This paper presents results describing the basic simulation tool for the characterization of aerosols formed in CO 2 absorption columns and gives examples as to how various entering droplets grow or shrink through an absorber and how their composition changes with respect to position. [ABSTRACT FROM AUTHOR]

A general dynamic process model of the post-combustion carbon dioxide (CO 2 ) absorption process based on aqueous monoethanolamine (MEA) is developed and implemented in MATLAB. The overall process model contains several unit models developed from first principle conservation laws for mass and energy, each representing individual process equipment. An equation based numerical integration method is used to solve the overall equation system simultaneously in MATLAB. Pilot plant data from specifically designed dynamic experiments with 30 wt% MEA is collected from a pilot plant at NTNU and SINTEF laboratories. This includes steady state data for eight different conditions along with six dynamic data sets with relevant step changes in lean solvent flow rate and reboiler duty. The pilot plant data show a very good steady state mass balance which indicates that the generated data sets are reliable. Two of the dynamic data sets are used for model validation and the results shows adequate agreement between model and pilot plant data. An average of 0.3% and −2.8% deviation in absorbed CO 2 is seen for the two simulated cases compared to pilot plant results and it is concluded that the model is able to capture the main dynamics of the experiments. The main cause of deviation is believed to concern uncertainties in mass transfer and effective mass transfer area correlations. [ABSTRACT FROM AUTHOR]

Abstract: The recent years have seen growing attention towards the study of dynamic behavior in post-combustion CO2 capture plants using amines, albeit, apparently contesting yet without comparison or critique. This paper reviews what has been reported in literature concerning issues pertinent to transient behavior of CO2 capture including interaction with power plants. Details of models used, their validation and modeling tools as well as an attempt to piece-out convergent points from the various conclusions are given. Knowledge gaps and areas that still need more attention are emphasized. [Copyright &y& Elsevier]

Abstract: The dynamic behavior of three process configurations proposed for CO2 capture from flue gas is investigated. In the previous paper () the different configurations were investigated with respect to energy requirement and capital costs and the best configurations were defined based on CO2 avoided cost and total capture cost. In addition to the economy, the dynamic behavior is important when operation of the plant is considered. In this study the transient behavior of the vapor recompression and the split-stream configurations are investigated when different disturbances happen, and the results are compared with the conventional configuration as a benchmark. All process configurations are operationally feasible with the proposed control configuration. The results show that the conventional configuration is the most inherently resilient to disturbances, and that the vapor recompression configuration can handle disturbances better than split-stream configuration. The same relative reduction in reboiler duty has more negative effect (more reduction in capture ratio) for split-stream configuration than two other configurations. The control structure generated is able to control the plant for all configurations except the situation where the reboiler duty is an active constraint. In this situation the energy loss will increase and it is better to find another control variable to pair with reboiler duty. This will be done in future studies. [Copyright &y& Elsevier]

Capturing and storing the greenhouse gas carbon dioxide produced by power plants and chemical production plants before it is emitted to the atmosphere will play a major role in mitigation climate change. Among the different technologies, aqueous amine absorption/stripping is a promising one. In this study, five different configurations for aqueous absorption/stripping have been compared with regards to capital investment and energy consumption. The process simulations are made with the use of Unisim Design and ProTreat, while for the cost calculations, data from Turton et al. (2009) and Sinnott and Towler (2009) are used. We cannot identify one single configuration to be the optimum always for all situations, as it depends on many parameters like energy and material costs, interest rate, plant complexity, etc. With the assumption and estimated parameters in this study we find that vapor recompression configuration is the best configuration because it has the lowest total capture cost and CO2 avoided cost. In addition, the plant complexity does not increase very much compared to the benchmark. The split-stream configuration with cooling of semi-lean amine is the second best. However, this configuration increases the investment cost and plant complexity significantly. The effect of heat integration between the compression section and the stripper is also considered. We can reduce heat requirement by heat integration, but since the inlet temperature to the compressors become higher, the compression efficiency will decrease and compression work will increase. In addition, the capital cost and the complexity of the plant will increase. Because of the higher inlet temperature the water content of produced CO2 is higher and consequently the corrosion problems is more serious in pipes and equipment for compression and injection section. [ABSTRACT FROM AUTHOR]

Mass transfer and mathematical modelling of CO 2 absorption in a tubular membrane contactor using 1-Butyl-3-methylimidazolium Tricyanomethanide ([Bmim][TCM]) for pre-combustion CO 2 capture has been studied in this work. A 1D-model was developed based on resistance in series model and CO 2 material balance. The developed model was validated with the experimental data, and good agreement was observed between the simulated and experimental results. A new mass transfer resistance term is added to reflect the non-flat concentration profile in the liquid phase. Simulation results indicate that the liquid phase resistance contributes 67% and 44% to the total mass transfer resistance for non-wetted and wetted modes of membrane respectively. The resistance that occurred due to considering transport in liquid phase contributes 31 and 20% for non-wetted and wetted modes of membrane contactor respectively. CO 2 flux along the axial length of membrane contactor was modeled, giving the maxima at the gas outlet. The influences of operational constraints including liquid/gas flow rates, operation pressure/temperature, length of membrane contactor, and CO 2 concentration in feed gas were also inspected. [ABSTRACT FROM AUTHOR]

A dynamic model of the post-combustion CO 2 capture process based on chemical absorption is used to investigate the transient behavior and dynamic responses of the process and to detect stabilization time when various disturbances are introduced. Plant dimensions and parameter settings are based on the SINTEF CO 2 capture pilot plant at Tiller in Norway, and the overall process model is validated using two sets of steady state pilot plant data. A deviation between model and pilot plant results of −0.8% and −4.5% in absorbed CO 2 and 2.6% and 1.2% in desorbed CO 2 is seen for the two cases used in validation, respectively, which is within the observed pilot plant CO 2 mass balance error of ±6%. The simulated absorber and desorber temperature profiles show also adequate agreement to the pilot plant measurements. The process model is further used to simulate set-point changes in flue gas flow rate, reboiler duty and solvent flow rate in order to investigate typical stabilization times at various locations in the process. As expected, mixing models such as the absorber sump and reboiler will introduce time constants that affect the dynamic response profiles, while plug flow models such as the cross heat exchanger and lean cooler causes pure transport delays and no additional settling time. Mass transfer and chemical reaction rates causes some process inertia, but it is relatively small compared to the inertia of larger mixing vessels such as the absorber sump, reboiler and buffer tank and transport delay caused by plug flow. Changes to the solvent flow rate are also seen as a larger disturbance to the process compared to changes in flue gas flow rate and reboiler duty, reflected by longer process stabilization time to reach new steady state conditions. The estimated 90% settling times for the response in CO 2 capture rate in the Tiller pilot plant are less than 1 h, 3.5–6 h and 3.5–4 h for step changes in flue gas flow rate, solvent flow rate and reboiler duty, respectively. [ABSTRACT FROM AUTHOR]

Amino acid ionic liquids are green solvents with low toxicities and properties suitable for precombustion CO2 capture, such as high CO2 absorption, good thermal stability, and negligible vapor pressure. However, their high viscosities and relatively high costs have hampered their industrial applications. In this work, we systematically studied the amino acid ionic liquid tetrabutylphosphonium glycinate ([P4444][Gly]) and its blends with the low-cost and less viscous cosolvent poly(ethylene glycol) (PEG400). The concentration of the blend solvent was optimized with respect to CO2 solubility, regeneration efficiency, and cyclic capacity. The solubilities of CO2 in [P4444][Gly], PEG400, and their blends of four different concentrations were measured experimentally in the temperature range of 60-140 °C and up to a pressure of 17 bar. The results showed that the CO2 solubility increased with increasing ionic liquid concentration in the blend and decreased with increasing temperature. The optimum CO2 absorption was determined to occur at 30 wt % of [P4444][Gly] in the blend. The regeneration study of the 30 wt % [P4444][Gly]-70 wt % PEG400 blend for three cycles verified its reusability in the process and confirmed that the reaction between [P4444][Gly] and CO2 can be reversed at 140 °C. The CO2 absorption capacity of the blend absorbent was found to be up to a loading of 1.23 mol of CO2/mol of absorbent. The parameter fitting of the experimental data using empirical correlations was evaluated, and these correlations were developed in particular to predict the blend solvent of an amino acid ionic liquid-PEG400 system based on the ionic liquid concentration and temperature. [ABSTRACT FROM AUTHOR]