Modeling of approach processes for equal or unequal sized fluid particles

The approach of two unequal or equal sized fluid particles is modeled using a simple parallel film model, giving expressions for interaction time and maximum film area, disregarding all external forces. The interaction time is found independent of the initial approach velocity and it explains why the effective virtual mass coefficient changes with the radius ratio of particles in the model of Chesters and Hofman (1982). A more general parallel film model is also developed based on the balance of forces acting on the particles and shows how initial velocity, radius ratio and buoyancy affect the interaction time, approach velocity and film area. Both models are compared to the experimental data of Scheele and Leng (1971).     

Kinetics of the reaction of carbon dioxide with aqueous sodium and potassium carbonate solutions

Kinetics for CO₂ absorption into 5–30 wt-% sodium carbonate solutions and 5–50 wt-% potassium carbonate solutions up to 70 °C were studied in a string of discs apparatus under conditions, in which the reaction of CO₂ could be assumed pseudo-first-order. The experimental data were evaluated based on the use of activities in the reaction rate expressions. The second order kinetic constant for the CO₂ reaction CO₂+OH^??HCO₃^? at infinite dilution is discussed and an expression for it is obtained up to 70 °C.The difference between the activity and concentration based kinetic constants were found to be small at low concentrations, where the apparent Henry’s law constant is close to that at infinite dilution in water. However, at high concentrations (high apparent Henry’s law constants), the difference was bigger. Using the activity based approach, the second order kinetic constant was calculated, compared to the second order kinetic constant in infinite dilution and found to be independent of both carbonate concentration and the cation present in the solution.     

Vapor–liquid equilibrium in aqueous amine amino acid salt solution: 3-(methylamino)propylamine/sarcosine

Vapor–liquid equilibrium (VLE) measurements were conducted for both unloaded and CO₂ loaded aqueous amine amino acid salt (AAAS) solutions; 3-(methylamino)propylamine/sarcosine (SARMAPA). Vapor–liquid equilibrium for unloaded solutions for 1.0–5.0 M SARMAPA were measured using a Swietoslawski ebulliometer for temperatures 40–100 °C and for total pressures 4.08–99.1 kPa. CO₂ equilibrium was determined for loaded 5 M SARMAPA using low and high temperature VLE apparatuses from 40 to 120 °C. A thermodynamic model representing equilibrium in the H₂O–AAAS–CO₂ system was developed using the extended UNIQUAC thermodynamic framework. The developed model predicts simplified speciations in H₂O–SARMAPA–CO₂ system and adequately correlates the experimental total and partial pressure data with an average absolute deviation of 8.9%.     

Persistent organic pollutants and mercury in dead and dying glaucous gulls (Larus hyperboreus) at Bjørnøya (Svalbard)

Dead and dying glaucous gulls (Larus hyperboreus) were collected on Bjørnøya in the Barents Sea in 2003, 2004 and 2005. Autopsies of the seabirds only explained a clear cause of death for three (14%) of the 21 birds. A total of 71% of the birds were emaciated. Liver and brain samples were analysed for organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ether (PBDEs), hexabromocyclododecanes (HBCDs) and mercury (Hg). High levels of ΣOCPs, ΣPCBs, ΣPBDEs and α-HBCD were found in liver and brain. Compared to the dead and dying glaucous gulls found 1989, the congeners' composition tended to change toward more persistent compounds in the 2003–2005 samples. The brain levels of OCPs and PCBs did not differ between 1989 and 2003–2005, while the liver levels were significantly lower. The brain/liver ratio for PCB and PBDE significantly decreased with halogenations of the molecule, indicating a clear discrimination of highly halogenated PCBs and PBDEs entering the brain. There was further a clear negative correlation between contaminant concentrations and body condition. The brain levels were not as high as earlier published lethal levels of p,p′-DDE or PCB. However, more recent studies reported a range of sub-lethal OCP- and PCB-related effects in randomly sampled glaucous gulls. An additional elevation of pollutants due to emaciation may increase the stress of the already affected birds. The high brain levels of OCP, PCB and PBDE of present study might therefore have contributed to the death of weakened individuals of glaucous gull.     

Vapor–liquid equilibrium in amino acid salt system: Experiments and modeling

Vapor–liquid equilibrium (VLE) measurements were carried out for both unloaded and CO₂ loaded aqueous amino acid salt (AAS) solutions of the potassium salt of sarcosine (KSAR). Vapor–liquid equilibrium for unloaded solutions; 1.0–5.0 M KSAR was measured using a Swietoslawski ebulliometer for temperatures 40, 60, 80 and 100 °C and for total pressures 4.08–97.8 kPa while vapor–liquid equilibrium for CO₂ loaded solutions of 3.5 M KSAR was measured using both low and high temperature VLE apparatuses for 40, 60, 80, 100 and 120 °C and for CO₂ partial pressures ranging from 0.03 to 971 kPa. A thermodynamic model representing the AAS solvent system was developed using the extended UNIQUAC framework. The developed model accurately predicts the equilibrium speciation in loaded solutions from ¹³C NMR data and gives a very good representation of the solubility of CO₂ in the amino acid salt solution as well as the total pressure of the unloaded system at all measured temperatures, loadings and pressures.     

Solubility of CO2 in 15, 30, 45 and 60 mass% MEA from 40 to 120 °C and model representation using the extended UNIQUAC framework

New experimental data for vapor–liquid equilibrium of CO₂ in aqueous monoethanolamine solutions are presented for 15, 30, 45 and 60 mass% MEA and from 40 to 120 °C. CO₂ partial pressures over loaded MEA solutions were measured using a low temperature equilibrium apparatus while total pressures were measured with a high temperature equilibrium apparatus. Experimental data are given as CO₂ partial pressure as function of loading in solution for temperatures from 40 to 80 °C and as total pressures for temperatures from 60 to 120 °C for the different MEA concentrations. The extended UNIQUAC model framework was applied and model parameters were fitted to the new experimental VLE data and physical CO₂ solubility data from the literature. The model gives a good representation of the experimental VLE data for CO₂ partial pressures and total pressures for all MEA concentrations with an average absolute relative deviation (AARD) of 24.3% and 11.7%, respectively, while the physical solubility data were represented with an AARD of 2.7%. Further, the model predicts well literature data on freezing point depression, excess enthalpy and liquid phase speciation determined by NMR.     

Capital costs and energy considerations of different alternative stripper configurations for post combustion CO2 capture

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.     

A model for turbulent binary breakup of dispersed fluid particles

Accurate predictions of particle size distributions, and therefore of the underlying processes of fluid particle breakup and coalescence are of vital importance in process design, but reliable procedures are still lacking. The present paper aims at developing a modular formulation for the turbulent particle breakup process. The model is to be included in a population balance model which is formulated such as to facilitate the direct future implementation into a full multifluid CFD model.The breakup process is described without introducing adjustable parameters. The current model is a further development of an existing model by Luo and Svendsen (AIChE J. 42 (5) (1996) 1225), which has been expanded and refined, and where an inherent weakness regarding the breakup rate for small particles and small daughter particle fragments are removed. A new criterion regarding the kinetic energy density of the colliding turbulent eddy causing breakup has been introduced. This new criterion is a novel concept describing the breakup process. The details are thoroughly discussed together with possible further modifications. The results from the new model are encouraging because the breakup rate is greatly reduced when the dispersed fluid particles are reduced in size. Further, the response to changes in system variables is reasonable and the distribution of daughter sizes vary in a reasonable way for the different collision possibilities.     

Density and N2O solubility of sodium and potassium carbonate solutions in the temperature range 25 to 80 °C

To deduce kinetic parameters for the reactions of carbon dioxide (CO₂) in carbonate solutions the physical solubility of CO₂ into the reacting solution is needed. To measure the physical solubility directly with CO₂ is not possible, so the solubility of nitrous oxide (N₂O) is normally measured instead. The physical solubility of CO₂ can then be calculated based on the solubility of CO₂ and N₂O into water and the solubility of N₂O in the solution of interest invoking the so called N₂O analogy (Clarke, 1964; Laddha et al., 1981). To obtain good accuracy of the solubility measurements the accurate density of the solution is needed. In this study the densities were measured with pycnometers up to 353 K.In this paper the parameters in the model of Weisenberger and Schumpe (1996) were refitted specifically for the two carbonate systems using experimental data up to 353 K and up to 30 wt% (3.7 kmol/m³) aqueous sodium carbonate and up to 50 wt% (5.5 kmol/m³) aqueous potassium carbonate solutions.     

Experimental investigation of liquid holdup in structured packings

Liquid holdup is an important hydrodynamic parameter for characterizing the gas/liquid flow pattern in packed beds. In this paper, a study of liquid holdup in 3 different structured packings: Mellapak 2X from Sulzer, Koch-Glitsch Flexipac 2Y HC, and Montz-Pak B1-250M is presented, using air/water, air/water/sugar solutions with liquid viscosity up to 12 cP and air/30 wt% MEA in a 0.5 m ID absorption column with a packing height of 5 m. As expected, at a given liquid load, the liquid holdup was close to constant as a function of gas flow, with an increase at high gas velocities. In general, the Sulzer packing had a higher liquid holdup than observed in the two other packings. A possible explanation for this could be the lack of enhanced draining of liquid as seen with the modifications of the end-section of the Koch-Glitsch and Montz packings. Liquid holdup was found to increase with increasing liquid viscosity. The influence was higher at high liquid load than at low liquid load. Our results indicate a higher dependency at high liquid load and a lower at low liquid load. There was a reasonable agreement between our results and the data found in the literature.