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The realistic numerical simulation of chemical processes, such as those occurring in catalytic reactors, is a complex undertaking, requiring knowledge of chemical thermodynamics, multi-component activated rate equations, coupled flows of material and heat, etc. A standard approach is to make use of a process simulation program package. However for a basic understanding, it may be advantageous to sacrifice some realism and to independently reproduce, in essence, the package computations. Here, we set up and numerically solve the basic equations governing the functioning of plug-flow reactors (PFR) and continuously stirred tank reactors (CSTR), and we demonstrate the procedure with simplified cases of the catalytic hydrogenation of carbon dioxide to form the synthetic fuels methanol and methane, each of which involves five chemical species undergoing three coupled chemical reactions. We show how to predict final product concentrations as a function of the catalyst system, reactor parameters, initial reactant concentrations, temperature, and pressure. Further, we use the numerical solutions to verify the "thermodynamic limit" of a PFR and a CSTR, and, for a PFR, to demonstrate the enhanced efficiency obtainable by "looping" and "sorption-enhancement". [ABSTRACT FROM AUTHOR]

Highlights • Droplet size distribution development predicted for absorption columns. • Outlet size distribution becomes narrower than the inlet distribution. • Outlet size distribution width increases with droplet number concentration. • Higher CO 2 content leads to larger droplets and narrower distributions. Abstract There are two main mechanisms for amine emissions from absorption columns. The first is connected to the volatility of amine, determining the gaseous concentration. The second mechanism is via aerosol droplets containing amine. Recently, aerosol based emissions in g/Nm3 were identified from typical PCCC plants (Khakharia et al., 2013). Mechanisms for aerosol formation, aerosol growth, emissions related to aerosol formation and in particular the development and testing of aerosol emission reducing systems for amine based post-combustion, are presently under study. However, there is still limited information available in the open literature. In some recent studies, the effect of water wash and demisting equipment was studied and results indicate that aerosol droplets still pass through these equipment sections. On the other hand, water wash systems help in increasing the droplet size as well as reducing both gas phase and aerosol based emission. However, this does not completely solve the problem (da Silva et al., 2013). Recently, modeling studies for mono-disperse droplet swarms are published (Majeed et al., 2017a, 2017b; Majeed and Svendsen, 2018a, 2018b). However, results for multi-sized droplet swarms and for droplet size distributions are missing. Droplets can be described by their size, temperature and composition. All droplet populations will have a size distribution, being just as important as any other parameter. Performing a distribution analysis is the best way to determine the sizes of droplets in a particular stream at any point in an absorber. In this work, both a multi-droplet size model and a size distribution model are implemented. The multi-droplet size model is used for validation and results are in line with findings from the mono-disperse model by (Majeed et al., 2017b; Majeed and Svendsen, 2018a). Droplet distribution model results are compared with experimental data from Toshiba (Fujita, 2017) and reasonable agreement is found. The development of inlet droplet distributions through an absorber and water-wash system is modelled for several flue gas sources. It is found that the outlet distribution mean size increases with inlet gas CO 2 concentration. Similarly, the outlet mean droplet size decreases and the size distribution width increases with incoming droplet number concentration. [ABSTRACT FROM AUTHOR]

Commercial methanol catalysts based on Cu/ZnO/Al 2 O 3 are less effective applied to direct hydrogenation of CO 2 to methanol. The main reason is that the catalyst deactivation increases with the water pressure and temperature, and from stoichiometry, water formation is equal to the CO 2 consumption. Here, the focus is on how the process can be designed to reduce this problem. Multi-stage reactor designs with inter-condensation of water and methanol will reduce the water pressure. Several optimal designs are generated with the use of a path optimization method to maximize the methanol production per pass with the use of the least possible reaction volume and hydrogen. Based on a published kinetic model, the optimal volume stage distribution, coolant temperature, and fluid mixing are found. Two configurations of the tail gas treatment are investigated, a once-though and a recycle configuration. A three-stage reactor design with recycling of the tail gas is found to be the better configuration. High CO 2 -conversion per pass and a low recycle ratio are obtained. Rigorous process simulations of the most promising designs are made to verify that the pressure drop, temperature peaks, and water pressure are good. The maximum water pressure is low. A shell and tube boiling water type reactor design is selected. For a 10 t h− 1 plant, all tubes of all three stages can be located in the same shell. • Systematic staging of hydrogenation of CO 2 to methanol. Objective to maximize the methanol production with use of least possible reaction volume and hydrogen. • Reduced sintering effect with a commercial catalyst. • Intensified process with three stages in one reactor shell. [ABSTRACT FROM AUTHOR]

With 40 mol% CO 2 , the energy content of biogas is too low to be used as motor fuel. Motor-grade compressed bio-methane can be produced by direct methanation of biogas with the use of hydrogen. A direct methanation process is considered here as the pre-processing step of separating the biogas is avoided. A systematic staging method is applied to design the process to upgrade biogas to motor-grade bio-methane by maximizing the production of methane with the use of the least possible reaction volume and subject to a quality specification. Here, a once-through process is the target so as to avoid the post-processing separation of the product and recycling. The most promising design is a three-stage configuration with water condensation after each stage. Shell and tube reactors are considered to be less expensive than micro-channel reactors. All three stages are placed in a single shell with boiling water on the shell side. The proposed design is verified by rigorous simulation. The method makes process intensification of chemical reaction systems possible, which is here demonstrated for direct methanation of biogas. • Systematic staging of direct methanation of biogas. • Maximizing the methane production with use of least possible reaction volume. • Once-through conversion of biogas to motor-grade fuel. • Intensified process with three stages in one reactor shell. [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]

The inevitable nexus between energy use and CO2 emission necessitates the development of sustainable energy systems. The conversion of CO2 to CH4 using green H2 in power-to-gas applications in such energy systems has attracted much interest. In this context, the present study provides a thermodynamic insight into the effect of water removal on CO2 conversion and irreversibility within a CO2 methanation reactor. A fixed-bed reactor with one intermediate water removal point, representing two reactors in series, was modeled by a one-dimensional pseudo-homogeneous model. Pure CO2 or a mixture of CO2 and methane, representing a typical biogas mixture, were used as feed. For short reactors, both the maximum conversion and the largest irreversibilities were observed when the water removal point was located in the middle of the reactor. However, as the length of the reactor increased, the water removal point with the highest conversion was shifted towards the end of the reactor, accompanied by a smaller thermodynamic penalty. The largest irreversibilities in long reactors were obtained when water removal took place closer to the inlet of the reactor. The study discusses the potential benefit of partial water removal and reactant feeding for energy-efficient reactor design. [ABSTRACT FROM AUTHOR]

[Display omitted] • Integrated biogas methanation for increased carbon conversion. • Direct methanation more efficient than indirect methanation. • Exergy efficiency comparable to conventional biomethane production if utilizing heat. • Economic feasibility dependent upon reduced hydrogen cost. Conventional liquefied biomethane (LBM) production plants consist of upgrading and liquefaction processes. Commonly, the captured CO 2 during biogas upgrading is emitted into the atmosphere. One alternative, to produce more LBM, is to combine the conventional LBM production plant with the Power-to-Gas concept. Within this context, green H 2 produced from renewable electricity can react with the CO 2 in the biogas mixture, producing additional CH 4. The present study evaluated the feasibility of integrating methanation with conventional LBM production plants. The performance of the proposed process designs was assessed through exergy and cost analysis considering detailed models. The results illustrated that integrated direct biogas methanation was superior to methanation of captured CO 2. The integrated scheme with direct biogas methanation increased the LBM production by 52.2 % compared to the conventional LBM production plant but with lower exergy efficiency. It was indicated the feasibility of the integrated scheme through direct biogas methanation was highly dependent on the price of H 2. A H 2 price of 1.27 USD/kg H 2 was required to produce LBM at a similar price as the conventional LBM production plant. [ABSTRACT FROM AUTHOR]

The evaluation of the Fischer-Tropsch experiment with H 2 /CO = 2.13 at 210 °C with changes in CO conversion and water addition. [Display omitted] • Co-based catalyst developed WGS activity at low H 2 /CO ratio. • Water has a positive effect on C 5+ selectivity for all H 2 /CO ratios. • Re-oxidation of cobalt is proposed as the main deactivation mechanism caused by water. Fischer-Tropsch synthesis has been investigated over a commercial type cobalt-based catalyst (20 %Co/0.5 %Re/γ-Al 2 O 3) by varying the H 2 /CO ratio (2.55–1.12), CO conversion (15–75 %), reaction temperature (210 °C, 230 °C), and by adding water to the syngas. The experiments were conducted in a fixed bed reactor with the main purpose of obtaining experimental data to be used in the development and fitting of a mechanistic model. A positive effect of water on the catalyst activity was found for experiments with a H 2 /CO ratio higher than 1.7. Water was found to always increase the C 5+ selectivity regardless of the H 2 /CO ratio. Increasing conversion led to increased C 5+ selectivity. The selectivity to CO 2 was significantly enhanced at higher conversions (high water partial pressure), particularly with the lowest H 2 /CO = 1.12, interpreted as the emergence of water-gas shift activity. Re-oxidation of cobalt, probably limited to small cobalt particles, is proposed as the main deactivation mechanism caused by water while a steeper deactivation curve was found for higher temperature, indicating that sintering also may play a role. [ABSTRACT FROM AUTHOR]

Process concepts for making synthesis gas by solar thermochemical cycling have been screened. The produced gas is delivered at 70 °C, 5 bar pressure and with a H 2 /CO ratio of 2.0 which, with moderate adjustments, fit specifications of Fischer–Tropsch synthesis using a cobalt-based catalyst. The cobalt ferrite/alumina assisted hercynite cycle run adiabatically between 1350 and 1330 °C was selected for the study. HYSYS process simulations comprise six process combinations; quenching of hydrogen with CO 2 ; separate solar splitting of water and CO 2 ; vacuum depletion of oxygen in cobalt ferrite; flushing out oxygen with nitrogen produced cryogenically; and flushing with nitrogen from high temperature dense membranes. Calculated energy demand eliminates cryogenic concepts whereas the dense membranes require further study. Most promising is the water-only splitting pathway in combination with CO 2 quench and vacuum oxygen depletion. The alternative with separate H 2 O and CO 2 solar splitting benefits from half the amount of inert CO 2 in the produced syngas and 7% reduction in heliostat size, but suffers from technical challenges with high temperature heat exchangers and severe coking probability; and calculated 7% higher installed cost. The novel chemical quench method limits the use of high temperature heat exchangers to just one for the depleted oxygen. [ABSTRACT FROM AUTHOR]