57 research outputs found
Solubility of the Precombustion Gases CO2, CH4, CO, H2, N2, and H2S in the Ionic Liquid [bmim][Tf2N] from Monte Carlo Simulations
No full textFinancial support by ADEM, A green Deal in Energy Materials, a program of the Dutch Ministry of Economic Affairs (Mahinder Ramdin). This work was performed as a part of the CATO-2 program, the Dutch national R&D program on CO2 capture, transport and storage, funded by the Dutch Ministry of Economic Affairs (Sayee Prasaad Balaji). This work was also supported by NWO Exacte Wetenschappen (Physical Sciences) for the use of supercomputer facilities, with financial support from the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Netherlands Organization for Scientific Research, NWO) (Mahinder Ramdin and Sayee Prasaad
Balaji). The authors thank David Dubbeldam and Ariana Torres-Knoop for their support with the RASPA tool.Monte Carlo simulations were used to compute the solubility of the pure gases CO2, CH4, CO, H2, N2, and H2S in the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [bmim][Tf2N]. Simulations in the osmotic ensemble were performed to compute absorption isotherms at a temperature of 333.15 K using the versatile continuous fractional component Monte Carlo (CFCMC) method. The predicted gas solubilities and Henry constants are in good agreement with the experimental data. The Monte Carlo simulations correctly predict the observed solubility trend, which obeys the following order: H2S > CO2 > CH4 > CO > N2 > H2. Relevant separation selectivities for the precombustion process are calculated from the pure gas Henry constants and a comparisonwith experimental data is providedSistemas Físicos, Químicos y Naturale
Solving Vapor-Liquid Flash Problems Using Artificial Neural Networks
No full textVapor-liquid phase equilibrium (flash) calculations largely contribute to the total computation time of many process simulation models. As a result, process simulations, especially dynamic cases, are limited in the amount of detail that can be included due to time restrictions. In addition, under certain conditions flash calculations can fail to provide acceptable results. In this work, artificial neural networks were investigated as a potentially faster and more robust alternative to conventional flash calculation methods. Classification neural networks were used to determine the phase stability of a given mixture of fluids, while regression networks were used to make predictions of thermodynamic property values. In addition to conventional flash types such as the constant pressure, constant temperature (PT), and constant pressure, constant entropy (PS) flash, neural networks are used to develop two concept flash types: a constant entropy, constant volume (SV), and a constant enthalpy, constant volume (HV) flash. All neural networks were trained on, and compared to, data generated using the PT-flash algorithm from the Thermodynamics for Engineering Applications (TEA) property calculator. Data was generated for mixtures of water and methanol over a wide range of pressures and temperatures. The artificial neural networks showed speed improvements over TEA of up to 35 times for phase classification and 15 times for property predictions. Overall phase classification accuracy scores of around 97% were achieved. Average property value prediction errors range between 0.5% and 7% when compared to the spread in magnitude of the test data, and R2 scores were in the general order of 0.95 and higher, although classification and property prediction in the two-phase region showed markedly higher errors than properties in the pure liquid or vapor regions. Moreover, thermodynamic consistency and the stability of a system consisting of multiple neural network flash types both still require considerable improvement. Finally, this work shows that artificial neural networks can be used to create unconventional flash types such a the SV- and HV-flash
Phase Equilibria Predictions of Binary Mixtures of Light/Heavy Hydrocarbons by Monte Carlo Simulations
No full textFor the design and optimization of different processes and technologies in the chemical and petrochemical industry, the knowledge of the accurate vapor-liquid phase equilibrium of hydrocarbons and their binary mixtures is fundamental. The main focus of this thesis is the binary mixtures of methane with various n-alkanes and the binary mixture of methane and toluene, at temperatures ranging from 400 to 650 K and pressures ranging from 2 MPa to 50 MPa. Despite the currently increased importance of these asymmetric binary mixtures of methane and long n-alkanes due to Enhanced Oil Recovery technologies and depletion of old, easily accessible and highly profitable hydrocarbon reservoirs, the available vapor-liquid equilibrium (VLE) data from experiments are scarce or unknown.Currently, the most common practice for volumetric and phase behavior calculations in the industry is based on different cubic, such as Peng-Robinson, SRK or on higher order equations of state like PC-SAFT . However, the predicted data by equations of state are not accurate enough, due to the lack of experimental data. This is more pronounced for high temperature and pressure conditions or in the vicinity of the critical point. This thesis aims to produce vapor-liquid phase equilibrium data for binary mixtures of methane with various long n-alkanes by performing Monte Carlo molecular simulations in the Gibbs ensemble with TraPPE force field. The simulation results are used to validate the applied TraPPE force field by comparing its results to available experimental data. At extrapolated conditions, the new data are compared to PC-SAFT predictions in order to assess the performance of the CBMC technique and to highlight the deviations between the CBMC and PC-SAFT results. Additionally, this new data could be used to adjust the parameters of the applied PC-SAFT equation of state to achieve better predictions at extrapolated conditions
Mass Transport Limitations in Electrochemical Conversion of CO2 to Formic Acid at High Pressure
No full textMass transport of different species plays a crucial role in electrochemical conversion of CO (Formula presented.) due to the solubility limit of CO (Formula presented.) in aqueous electrolytes. In this study, we investigate the transport of CO (Formula presented.) and other ionic species through the electrolyte and the membrane, and its impact on the scale-up process of HCOO (Formula presented.) /HCOOH formation. The mass transport of ions to the electrode and the membrane is modelled at constant current density. The mass transport limitations of CO (Formula presented.) on the formation of HCOO (Formula presented.) /HCOOH is investigated at different pressures ranges from 5–40 bar. The maximum achievable partial current density of formate/formic acid is increased with increasing CO (Formula presented.) pressure. We use an ion exchange membrane model to understand the ion transport behaviour for both the monopolar and bipolar membranes. The cation exchange (CEM) and anion exchange membrane (AEM) model show that ion transport is limited by the electrolyte salt concentrations. For 0.1 M KHCO (Formula presented.), the AEM reaches the limiting current density more quickly than the CEM. For the BPM model, ion transport across the diffusion layer on either side of the BPM is also included to understand the concentration polarization across the BPM. The model revealed that the polarization losses across the bipolar membrane depend on the pH of the electrolyte used for the CO (Formula presented.) reduction reaction (CO 2RR). The polarization loss on the anolyte side decreases with an increasing pH, while, on the cathode side, it increases with increasing catholyte pH. With this combined model for the electrode reactions and the membrane transport, we are able to account for the various factors influencing the polarization losses in the CO (Formula presented.) electrolyzer. To complete the analysis, we simulated the full cell polarization curve and fitted with the experimental data. Engineering Thermodynamic
Process Chain Development of a ReSOC System with ammonia as fuel and steam electrolysis
No full textEnergy storage systems are an emerging field of interest for the future of electrical grids. With the rapid growth of renewable but intermittent sources of electricity, energy storage systems can help smooth the variations, making the grid more stable and reducing the need for maintaining an overcapacity of power production infrastructure. Among energy storage solutions, power-to-chemical storage is of particular interest due to the high energy density of chemicals and seasonal storage capabilities. Developments made in power-to-chemical technologies can also go a long way towards making the transportation and chemical industries sustainable. The chemical considered in this work is ammonia (NH3), which has advantages of being an easily liquefiable fuel, and has also been in industrial use for over a century. This thesis project aims towards the development of an efficient power-to-ammonia energy storage system using reversible solid oxide cells. The system designed in this thesis is based on direct ammonia utilisation in fuel cell mode, and steam electrolysis coupled with Haber-Bosch ammonia synthesis in the electrolysis mode. A steady state process model is designed in Aspen Plus. This is followed by extensive thermodynamic exergy analysis, used as the basis for the further design and optimisation of the system, with a goal to maximise the round trip efficiency. Exergy analysis is used to identify the sources with most scope for improvement. The final system can attain a maximum round trip efficiency of 61.20 %, improved from a basic system efficiency of 19.79 %. The maximum round trip efficiency is comparable to values reported in recent times for thermodynamically studied models from literature using other fuels, such as 56.72 % for methanol. The optimised system attains high efficiencies without the need for thermal energy storage or an afterburner. Further, it is demonstrated that the designed system is efficient enough that heat integration across modes with high temperature energy storage does not provide any significant benefit.Balance Projec
Direct Water Injection in Catholyte‐Free Zero‐Gap Carbon Dioxide Electrolyzers
No full textA zero-gap flow electrolyzer with a tin-coated gas diffusion electrode as the cathode was used to convert humidified gaseous CO2 to formate. The influence of humidification, flow pattern and the type of membrane on the faradaic efficiency (FE), product concentration, and salt precipitation were investigated. We demonstrated that water management in the gas diffusion electrode was crucial to avoid flooding and (bi)carbonate precipitation, to uphold a high FE and formate concentration. Direct water injection was validated as a novel approach for water management. At 100 mA/cm2, direct water injection in combination with an interdigitated flow channel resulted in a FE of 80 % and a formate concentration of 65.4+/−0.3 g/l without salt precipitation for a prolonged CO2 electrolysis of 1 h. The use of bipolar membranes in the zero-gap configuration mainly produced hydrogen. These results are important for the design of commercial scale CO2 electrolyzers.Accepted Author ManuscriptEngineering Thermodynamic
CO<sub>2</sub> stripping from ionic liquid at elevated pressures in gas-liquid membrane contactor
No full textIn this study, the gas-liquid membrane contactor was considered for regeneration of the room-temperature ionic liquids (RTIL) that can be used as physical solvents for carbon dioxide capture process at elevated pressures. Poly[1-(trimethylsilyl)-1-propyne] (PTMSP) was selected as a membrane material due to its high mass transport characteristics and good mechanical properties. Nine different RTILs, such as [Emim][DCA], [Emim][BF4], [Emim][DEP], [Bmim][BF4], [Bmim][Tf2N], [Hmim][TCB], [P66614][DCA], [P66614][Br] and [P66614][Phos], were used to evaluate the solvent-membrane compatibility. The long-term sorption tests (40+ days) revealed that the solvent-membrane interaction is mainly determined by the liquid surface tension regardless of viscosity and molecular size of RTILs. For instance, [Emim][BF4] and [Emim][DCA], having the surface tension of 60.3 and 54.0 mN/m, demonstrated a very low affinity to the bulk material of PTMSP (sorption as low as 0.02 g/g; no swelling); while for the next ionic liquid [Bmim][BF4] with surface tension of 44.4 mN/m, the sorption and swelling of PTMSP was 0.79 g/g and 21%, respectively. The long-term RTIL permeation test (Δp = 40 bar, T = 50°С t > 400 h) confirmed that there is no hydrodynamic flow through PTMSP for [Emim][DCA] and [Emim][BF4]. The concept of CO2 stripping from RTIL with the membrane contactor by the pressure (Δp = 10 bar) and temperature (ΔT = 20 °С) swing was proved by using dense PTMSP membrane and [Emim][BF4]. The overall mass transfer coefficient value was equal to (1.6 − 3.8) × 10−3 cm/s with respect to liquid flow rate. By using the resistance-in-series model, it was shown that the membrane resistance contribution to the gas transfer was estimated to be approximately 8%.Accepted Author ManuscriptEngineering Thermodynamic
Further Experiments on the Flow and Heat Transfer in a Heated Turbulent Air Jet
No full textMeasurements have been made of the mean total-head and temperature fields in a round turbulent jet with various initial temperatures. The results show that the jet spreads more rapidly as its density becomes lower than that of the receiving medium, even when the difference is not sufficiently great to cause measurable deviations from the constant-density, dimensionless, dynamic-pressure profile function. Rough analytical considerations have given the same relative spread. The effective "turbulent Prandtl number" for a section of the fully developed jet was found to be equal to the true (laminar) Prandtl number within the accuracy of measurement. (author
Spectrums and Diffusion in a Round Turbulent Jet
No full textIn a round turbulent jet at room temperature, measurement of the shear correlation coefficient as a function of frequency (through bandpass filters) has given a rather direct verification of Kolmogoroff's local-isotropy hypothesis. One-dimensional power spectrums of velocity and temperature fluctuations, measured in unheated and heated jets, respectively, have been contrasted. Under the same conditions, the two corresponding transverse correlation functions have been measured and compared. Finally, measurements have been made of the mean thermal wakes behind local (line) heat sources in the unheated turbulent jet, and the order of magnitude of the temperature fluctuations has been determined. (author
- …
