http://hdl.handle.net/2282/290 Search the Channel search http://teora.hit.no/dspace/simple-search http://hdl.handle.net/2282/1316 Title: Degradation of Aqueous 2-Amino-2-methyl-1-propanol for Carbon Dioxide Capture <br/> <br/>Authors: Wang, Tielin <br/> <br/>Abstract: Absorption-stripping with aqueous 2-amino-2-methyl-1-propanol (AMP), and especially AMP blends with other amines, such as monoethanolamine (MEA) and piperazine (PZ), presents an attractive option for carbon dioxide (CO2) capture from flue gas in coal-fired power plants. Alkanolamine based solvents degrade in this service. The purpose of this work was to investigate AMP solvent degradation under thermal and oxidizing conditions, to measure rates of degradation for comparison with other solvents, to identify the degradation products and to identify possible degradation pathways. 5 mol/kg AMP without CO2 loading was thermally stable up to 140°C under a blanket gas of N2, exhibiting very low loss rates. However, with an initial CO2 loading of 0.15 and 0.3mol CO2/mol AMP at 135°C, AMP lost 3.8(mol)% and 5.5 (mol)% after 5 weeks, respectively. The steric hindrance in AMP molecule slows down CO2 induced degradation of AMP as compared to MEA, but it does not prevent oxazolidinone formation and oxazolidinone ring-opening into further degradation products. The rate of oxidative degradation of AMP was investigated over a range of temperature, CO2 loading, and AMP concentration. At 100 to 140 °C, degradation was found to be O2 mass transfer limited in the employed batch reactors, however, the degradation rate increased with CO2 loading. No significant effect of pH value was observed on the AMP degradation rate. Acetone, 2,4-lutidine, 4,4-dimethyl-2-oxazolidinone and formate were the main identified degradation products. Oxidative degradation of AMP likely proceeds through a Habstraction step followed by production of a peroxyl radical. The peroxyl radical is proposed to decompose to primary products by intramolecular H-abstraction via a six-membered cyclic transition sate. The reactions of AMP and the primary degradation products lead to the final degradation products. Acetone oxime and 4,4-dimethyl-1,3-oxazolidine were minor products at 100-140°C, but they were major products at 80°C. Temperature significantly affects the distribution of the ultimate degradation products. UV radiation with a medium mercury lamp can dramatically accelerate the oxidation of AMP at 55°C. It seems that UV radiation does not change the primary degradation mechanism of AMP. The degradation products of UV accelerated oxidation are different from those of thermally accelerated oxidation of AMP, probably due to the impact of temperature on the secondary reactions of the primary products. AMP oxidation is proposed to be initiated by a radical mechanism, but the reaction is not a chain reaction. The degradation rate of 1.5 mol/kg PZ is 1.2 mmol/(kg·h) within 19 days, which is approximate half of that of 5 mol/kg AMP under 250 kPa O2 and at 100°C. A possible degradation pathway of PZ is proposed based on the identified products. The degradation rate of AMP in AMP/PZ blends is close to that in a single AMP system, however, PZ degraded faster in the blends than it degraded individually at identical degradation conditions. As compared to degradation of single MEA and AMP solvents, no new product was found in the degraded AMP/MEA mixture without CO2 loading. Increasing the initial MEA concentration in the mixture, the amount of AMP loss decreased indicating that MEA protects AMP from oxidation. This inhibition effect of MEA on AMP degradation could be due to the fact that MEA degrades faster than AMP in the blends. <br/> <br/>Description: Papers I-IV (p. 176-210) not available in TEORA due to publisher restrictions http://hdl.handle.net/2282/1314 Title: Mass Transfer Kinetics of Carbon Dioxide into Concentrated Aqueous Solutions of Monoethanolamine <br/> <br/>Authors: Ying, Jiru <br/> <br/>Abstract: Global warming arguments have gained more and more attention due to the new regulations of carbon dioxide (CO2) emission in the world. Monoethanolamine (MEA) has been employed as an important industrial absorbent for CO2 capture since the 1930s because of its high reaction rate, relatively low cost, and thermal stability. The concentration of MEA in aqueous solution is generally increased to 30 mass % in the CO2 capture process. The energy consumption is high in the present MEA process because of the high reaction heat of MEA with CO2, and a large number of liquid transportation. To reduce the energy consumption and improve the efficiency of CO2 capture in the present MEA process, further increase in solution concentration of MEA is a potential solution. Basic research on the properties and reaction kinetics with CO2 of concentrated aqueous MEA solution is necessary to perform engineering calculations and important for the dimensioning of pipes, pumps and heat exchangers etc. In this work, a novel solubility apparatus and technique was designed and built for the measurement of physical solubility of a gas in liquid. The technique employs a scaled spiral glass tube with a small drop of mercury inside as a eudiometer as an alternative to a three–branch U–tube setup to keep the system pressure constant, and measure the volume drop of absorbed gas at constant temperature. A “vacuum gas saturation” method is proposed for gas saturation operation in the measurement. The physical solubilities of N2O in pure water over the temperature range from 298.15 to 323.15 K and in aqueous salt MEA solutions at 313.15 K were measured under a constant ambient pressure to validate the new technique. The new solubility apparatus and technique possesses some advantages including easy operation, lower mercury inventory, higher sensitivity and greater accurate. The physical mass transfer coefficients of N2O in aqueous MEA solutions were performed using the new apparatus as well. The physical solubilities of N2O in aqueous MEA solutions over the full concentrations range were measured by the novel solubility apparatus over a temperature range from 298.15 to 323.15 K under a constant ambient pressure. The physical solubilities of CO2 in aqueous MEA solutions were estimated using “N2O analogy” method. The results of the solubility measurements of N2O and CO2 in water and N2O in aqueous MEA solutions agree with literature. A semiempirical model to solubility proposed by Wang et al. was used to correlate the solubilities of N2O and CO2 in aqueous MEA solutions, and the correlation results are in agreement with experiment data. The results show that the solubilities of both N2O and CO2 in aqueous MEA solutions showed negative deviation behaviors from the linear additive principle. The viscosities of aqueous MEA solutions over the full concentration range were measured using a rheometer with a double–gap measuring system at a temperature range from 298.15 to 353.15 K. The measured viscosity data are in good agreement with the literature values. An exponent model proposed by DiGuilio et al. was used to correlate the data and the results are very satisfied for the regression of the viscosities of pure MEA from 298.15 to 353.15 K. The polynomial model proposed by Teng et al. with five parameters is satisfied the aqueous MEA solution. The relationship between the viscosity and mole fraction of MEA shows both positive and negative deviation behavior and the critical mole fraction of MEA was found is 0.2. The molecular diffusivities of N2O in aqueous MEA solutions up to 12 M were studied from 298.15 to 333.15 K using a laminar liquid jet absorber, and the diffusivities of CO2 in aqueous MEA solutions were calculated by the N2O analogy method. A modified construction of the temperature control for the laminar liquid jet was proposed. The relationship between the diffusivity and the viscosity of the solution is roughly in agreement with the modified Stokes–Einstein equations. On the other hand, an exponent mathematical model was used to correlate N2O diffusivities in aqueous MEA solutions satisfactorily for calculation of the diffusivities of CO2 in aqueous MEA solutions. Based on the measured physical properties in this work, the chemical reaction kinetics of CO2 with aqueous MEA solutions over a wide concentration range from 0.5 to 12 M were investigated using a stirred cell absorber with a plane gas–liquid interface over a temperature range from 298.15 to 323.15 K. To satisfy the criterion of pseudo-first-order reaction, low CO2 partial pressure (3 – 4 kPa) was employed. The rates of CO2 absorption in the solutions were determined from the fall in pressure, and the reaction rate constants were determinate by two treatment methods on the same experimental data, viz. a “differential” and an “integral” method, which are derived from the mass balance principle and Henry’s law. The reaction between MEA and CO2 is based on “zwitterion” mechanism in this work. The gas-phase resistance was investigated systematically in the stirred cell. To reduce the gas phase resistances in the measurements of CO2 absorption in the solutions, speeding up the gas phase fans and employing very low inert gas pressures of N2 and solution vapor were suggested. The chemical reaction kinetics of CO2 in aqueous MEA solutions were measured over the concentration range from 0.5 to 12 M by a stirred cell absorber with batchwise operation for both gas and liquid. As same as the dilute solution, the reaction of concentrated aqueous IV MEA solution with CO2 is also first order with respect to MEA and the reaction is in the fast reaction regime. The reaction activation energy (Ea) of aqueous MEA + CO2 is calculated based on the experimental data. The enhanced mass transfer coefficient in liquid phase, kLE, increases with the concentration of MEA solutions but decreases when the molarity of MEA is higher than 8 M. Last, some recommendations are given to the future work. CO2–loaded MEA solution is suggested to focus on in the next–step work, the properties and gas absorption of the system can be measured and discussion by the same experimental method mentioned in this thesis. The gas absorption and desorption from the CO2–loaded aqueous MEA solutions should be performed as well. The issue of heat transfer should be taken into account and investigated when the concentrated aqueous MEA solution is employed in the CO2 capture process. The stirred cell or laminar liquid jet can be employed in these studies under a suitable pressure. However, to obtain more accurate experimental data, some modifications on the construction of both the laminar liquid jet and stirred cell should be made. For example, the absorption cell of the liquid laminar jet can be smaller, and the nozzle or receiver should be adjustable etc. Regarding the modification on the temperature control of these equipments, the main idea is to immerse all the gas and liquid pipes in to the same water bath or its hose. Some suggestions of these modifications are proposed in the appendix of this thesis. http://hdl.handle.net/2282/1241 Title: Empirical modeling, state estimation, and process control with real-life applications to the Czochralski crystallization process <br/> <br/>Authors: Komperød, Magnus <br/> <br/>Abstract: This PhD thesis presents research work within the field of systems and control engineering, with emphasis on applications to real-life processes, the Czochralski (CZ) crystallization process in particular. During the PhD study, two journal articles and five conference papers have been published. All seven publications are based on logged data from real-life processes or include examples based on such data. For four of the publications, logged process data are essential. The seven publications are referred to as Paper A through Paper G. The publications focus on data preprocessing, empirical modeling, process control, and state estimation for the purpose of noise filtering. The Czochralski (CZ) crystallization process is a batch process that converts multicrystalline materials into monocrystalline materials, i.e. materials that have homogeneous crystal structures. Among the most important applications of the CZ process is production of monocrystalline silicon. This is the only application of the CZ process that has been considered during this PhD study. Monocrystalline silicon is used in solar cell wafers and in computers and electronics. Solar cells based on monocrystalline silicon have higher efficiency than those based on multicrystalline silicon. During the CZ batch process, multicrystalline silicon is melted in a crucible. The silicon is then solidified on a monocrystalline seed crystal, thereby growing a crystal. The grown crystal is monocrystalline and is referred to as an ingot. There are several challenges associated with modeling and control of the CZ process: (i) The process dynamics is challenging to model using mechanistic (first principle) modeling. (ii) The process has multivariable character. (iii) The process is timevariant due to its batch nature. (iv) There are several difficulties regarding sensor technologies. In particular the ingot diameter is difficult to measure online. The candidate’s literature search indicates that most published research works considering modeling and control of the CZ process are simulation studies, which are not validated against real-life processes. Only one publication was found that documents that a suggested control strategy works on real-life CZ processes. During the PhD study, the candidate had access to a real-life CZ process at SINTEF Materials and Chemistry in Trondheim, Norway. As published research results that are validated on real-life CZ processes seem to be rather sparse, the candidate focused his research on experiments at this plant. Unfortunately, issues regarding sensor technologies forced the candidate to focus on other parts of the CZ process than initially planned. However, these issues have also given useful experiences and provided ideas for further research. The work of this PhD study has focused on the heating element power and the temperature of the molten silicon. The ingot diameter has not been considered, partly because of unreliable diameter sensor, partly because the diameter depends on the silicon temperature. Hence, it is reasonable not to consider the ingot diameter until the heating element power and the silicon temperature are properly measured, modeled, and controlled. Logged process data from the SINTEF CZ plant are used extensively during this PhD study. Paper D and Paper E consider empirical modeling of the heating element power, Paper F suggests a cascade control strategy for improving temperature control of the molten silicon, and Paper G presents state estimation for the purpose of measurement noise filtering. Also, logged process data from the SINTEF CZ plant are used as an example in Paper C. Paper A and Paper B include work on logged process data from the copper refining process at Xstrata Nikkelverk in Kristiansand, Norway. These data were made available from the process by Dr. Tor Anders Hauge. Paper A presents work on data preprocessing, using the Xstrata data as real-life examples. Paper B considers system identification and compares two system identification algorithms using process data from Xstrata. System identification is the science of developing dynamic, empirical models based on process inputs and the corresponding process outputs. http://hdl.handle.net/2282/1224 Title: Removal of CO2 from exhaust gas <br/> <br/>Authors: Øi, Lars Erik <br/> <br/>Abstract: Removal of CO2 from exhaust gas (CO2 capture) has become a very important topic the last years. There is international agreement to limit the emissions of greenhouse gases to reduce the global warming problem, and CO2 is regarded to be the most important greenhouse gas. One of the possible ways to reduce CO2 emissions to the atmosphere is to perform large scale CO2 capture and storage. There are several suggested methods for removal or capture of CO2. The most mature method is to absorb CO2 in an aqueous amine solution followed by desorption. Many calculation models for CO2 removal by absorption have been developed. These models differ in accuracy, efficiency and robustness. In the case of absorption column calculations combined with flowsheet calculations, there will often be a question whether a detailed and complex model is better than a simple and robust model. In this work, calculation methods for CO2 removal from atmospheric exhaust have been developed. To improve and validate these methods, some experimental work has also been included. Emphasis has been on calculation methods for an absorption and desorption process using MEA (monoethanolamine). One aim of the work has been to calculate cost optimum parameters in the process. Most of the calculations have been performed in combination with the process simulation tool Aspen HYSYS. Measured viscosities and densities in CO2 loaded solutions of MEA and water up to 80 ºC have been correlated. The new viscosity data of CO2 loaded MEA solutions at higher temperatures have reduced the uncertainty in the viscosity at typical absorption conditions. Pressure drop, liquid distribution and effective mass transfer area have been measured in a 0.5 m diameter column in collaboration with NTNU/SINTEF. The experiments validate the performance of structured packing in columns at typical process conditions. Murphree efficiencies have been estimated for typical CO2 absorption conditions in MEA solutions. According to calculations of absorption rates based on concentration profiles in the liquid film and approximation calculations, the deviation from pseudo first order conditions is less than 10 % for typical operation conditions below 50 ºC. Murphree efficiencies as a function of temperature for typical conditions at column top and column bottom have been calculated. These efficiencies are convenient to implement in stage to stage column calculation models. On the assumptions that pseudo first order conditions are met and the temperature at a stage is approximately constant, the accuracy in calculating overall CO2 removal efficiency using Murphree efficiencies is the same as for more rigorous calculations. A CO2 removal process from exhaust gas from a natural gas based power plant has been calculated in Aspen HYSYS. Total CO2 removal grade and heat consumption have been calculated as a function of circulation rate, absorber temperature and other parameters. Simulations of the absorber have also been performed with Aspen Plus using both constant Murphree efficiencies and rate-based simulation and all the simulations give similar trends as a function of the varying parameters. Aspen HYSYS calculations using varying Murphree efficiencies give similar temperature profiles compared to Aspen Plus rate-based calculations. The process simulation calculations have also included split-stream configurations. A splitstream process using MEA with a heat consumption of only 3.0 GJ/ton CO2 removed has been calculated in Aspen HYSYS compared to approximately 4.0 GJ/ton CO2 for a standard process. However, cost estimation calculations show that it is uncertain whether a splitstream process is more economical than a standard process. Equipment dimensioning and cost estimation have also been included in the calculations. From a series of calculations, a cost optimum can be calculated. Optimum gas inlet temperature to the absorber has been calculated to values between 33 and 35 ºC which is lower than traditionally assumed values. Optimum minimum temperature difference in the main amine/amine heat exchanger has been calculated to values between 12 and 19 ºC which is higher than traditionally assumed. This optimum is very dependent on the ratio between investment and energy cost. Optimum rich loading has been calculated to 0.47 mol CO2/mol MEA which is similar to earlier optimization calculations. Automatic calculation of these optimums is possible when using e.g. Aspen HYSYS with specified Murphree efficiencies.