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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]

A membrane contactor process for pre-combustion CO 2 capture from shifted synthesis gas originated from IGCC power plant is assessed from the technical and economical point of views. The process is designed as pressure swing absorption and desorption in a closed loop. The design basis for process simulation were synthesis gas containing CO 2 and H 2 only, and the CO 2 capture efficiency was fixed to 90%. The CO 2 gas was absorbed in ionic liquid [bmim][TCM] inside a hydrophobic, porous hollow fibre membrane contactor. One-dimensional mathematical model of membrane contactor developed in MATLAB was integrated to the process simulation software (HYSYS) through Cape-Open simulation compiler. The energy evaluation of this process revealed that compressors are the most energy demanding process equipment. The specific energy requirement for this process is estimated 0.75 MJ/kg CO 2 . A parametric study was also performed to analyse the effect of CO 2 concentration in feed gas and liquid to gas ratio. The capital cost investment and total operating costs of CO 2 capture unit were also evaluated. The capital investment required for capturing 0.14 M ton CO 2 /year including CO 2 compression is 47.4 M $, and the operating cost per year is 9.04 M $. The membrane absorber contributed about 39% to total investment cost. The specific cost of this capture unit is calculated to be 87 $/ton CO 2 . [ABSTRACT FROM AUTHOR]

Aerosols are systems of droplets or wet particles suspended in gases. In post combustion CO 2 absorption systems aerosols can be formed by spontaneous phase transitions in supersaturated gas phases or by droplets or particles entering the absorber with the gas to be treated. Micron and sub-micron mist droplets and fog formed in these processes cannot be removed by conventional demisting devices and because amine may be absorbed in the droplets this may increase dramatically the amine emissions from absorption columns as reported previously ( Khakharia et al., 2015; Schaber et al., 2002 ). Thus, it is important to understand the mechanisms governing droplet growth and amine uptake through absorber as well as the effect large numbers of aerosol droplets can have on the bulk gas phase composition. A model developed and implemented in Matlab, predicts how the gas phase composition and temperature change along the absorber taking into account mass and heat transfer to and from both the bulk liquid and the droplet phase. The objective of this work, compared to earlier work, Majeed et al. (2017) , is to study the possible effect of gas phase component depletion on the droplet growth and droplet internal variable profiles and how this varies with initial droplet size and composition, droplet number concentration and amine volatility. For MEA, as a relatively volatile solvent it is seen that gas phase depletion already takes place at number concentrations above 10 5 droplets/cm 3 with an initial droplet radius of 1.5 μ and 5 M MEA initial concentration. For initial droplet radius 0.15 μ and 0.0001 M MEA initial concentration, which may be a more realistic case, hardly any depletion effect is seen up to 10 7 droplets/cm 3 . With change in amine volatility it is seen that the gas phase depletion effect is significantly stronger in the case of low volatility than for MEA at high droplet number concentrations. It is found that gas phase amine depletion has a strong effect on droplet growth. [ABSTRACT FROM AUTHOR]

In absorption processes aerosols are generated by spontaneous condensation or desublimation processes in supersaturated gas phases. Amine volatility is a vital screening parameter for amines to be used in CO 2 capture. Higher volatility will result in higher losses through the gas phase and may also result in undesired aerosol formation and thereby to higher amine emissions and environmental impact. These amine emissions are one of the challenges in the realization of full scale absorption based post combustion CO 2 capture plants. It is crucial to understand the mechanisms governing in particular the aerosol formation and development through a column as this is not well understood. Rigorous modelling of aerosol dynamics leads to a system of partial differential equations. In order to understand mechanics of a particle entering an absorber an implementation of a droplet model is created in Matlab. The model predicts the droplet size, the droplet internal variable profiles and the mass transfer fluxes as function of position in the absorber. The focus of this paper is to study the effect of amine volatility and how this influences the droplet composition, growth rate, final size and the resulting amine loss. [ABSTRACT FROM AUTHOR]

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]

Dynamic modeling of post-combustion CO 2 capture has gained increasing attention the recent years. One of the main motivations behind this drive is the current limited knowledge of the operational flexibility of carbon capture units integrated with power stations. The present work presents an evaluation of various flexible operating modes through dynamic simulations of the Brindisi CO 2 capture pilot plant using the K-Spice ® general simulation tool. The evaluated modes are; load following, exhaust gas venting, varying solvent regeneration and solvent storage. Solvent storage gives a large potential for flexible operation with the possibility of maintaining 90% instantaneous CO 2 capture rate over the whole 24 h simulated period. Two large solvent storage tanks are however required as part of the process configuration in order to realize flexible operation by solvent storage. Exhaust gas venting and varying solvent regeneration does not require any additional process installations or modification, but their potential is limited by the maximum CO 2 capture capacity during off-peak electricity price periods in order to reach a time average CO 2 capture rate of 90%. Exhaust gas venting seems to be the favorable option of the latter two. [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: In this work, a system of unit operations is modeled and implemented in MATLAB for dynamic simulation of the regeneration part of the CO2 capture process. The system consists of a stripper, a reboiler and a condenser, and it is solved by a simultaneous equation based method. The method proves to be suitable for solving the regeneration part of the CO2 capture process and it shows numerically stable behavior in general. Further, two dynamic simulation cases are carried out and compared to steady state simulation results from CO2SIM. The dynamic simulation results show reasonably good agreement with steady state simulations, even though a very simplified flash tank model is used for simulation of reboiler and condenser and a simplified thermodynamic model is applied compared to the more robust CO2SIM model. Due to lack of dynamic pilot data, validation of the dynamic regeneration model has been difficult at this point. However, this is necessary for a thorough validation of the model for transient conditions. [Copyright &y& Elsevier]

Abstract: This paper describes in detail the numerical solution of a dynamic process developed for post-combustion absorption based CO2 capture. The method used in this work is sequential modular integration. This means that each process unit is modeled and integrated individually while co-ordination algorithms are developed to synchronize process units in time and provide input between connecting units. A pressure-flow interaction algorithm (p-f network solver) is also developed to provide estimates of downstream pressures for each unit. This is required in order to calculate the outlet flow from the units. The complete process plant model is developed to enable simulation of the post-combustion CO2 capture process at power plant load variations. Two examples of load variations are presented in this paper. [Copyright &y& Elsevier]

Abstract: In this work, a dynamic model is developed in the CO2SIM framework for transient modelling of CO2 absorbers and desorbers. Validation of code towards pilot data is presented, and the applicability of the model is shown with two examples of usage. Emphasis has been on developing flexible coding architecture for further development into dynamics and for a sequential modular dynamic handling of information when incorporated into a dynamic network solver. The model compares well with the pilot plant measurements and is numerically robust. The methods developed for handling pilot plant data and updating events (as e.g. multiple changes in the feed flow-rate) minimize the manual work for the engineer.^p [Copyright &y& Elsevier]

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 effect of heat distribution or inter-heating on the total energy requirement for CO2 stripping is investigated. Here we look at retrofit design of an existing column. It means the height and diameter of the stripper is given. The results show that inter-heating can have both negative and positive effects on the total energy requirement. If only one heat source at constant temperature exist, the inter-heating will increase the total energy requirement. If there are other heat sources at different temperatures, inter-heating can be beneficial. It depends on the energy price of the different heat sources and the temperature profile of the column. If there are some hot streams available to utilize the heat in the inter-heater, the total energy requirement will decrease. As a case study utilizing heat from lean amine in the inter-heater is investigated. The simulation results show a saving up to 6.4 and 11.3 percent by one and two inter–heater respectively [Copyright &y& Elsevier]

Abstract: The Fischer–Tropsch reactor is sectioned into stages based on the systematic method given by . The design functions are optimized to maximize the concentration of C11+ at the end of reactor path. The decision variables are fluid mixing, hydrogen distribution, heat transfer area distribution, coolant temperature, and catalyst concentration. With the path temperature constrained by 250°C, staging of the reactor will increase the concentration of C11+. For a three-stage reactor, the concentration is increased by 2.50% compared to a single-stage reactor. The optimal mixing structure is plug flow to have the maximum possible conversion. A case study is conducted to separate and distribute hydrogen along the reactor path. This will reduce H2/CO at the beginning of the path and increase chain growth probability. The results show that for a three-stage reactor, the concentration of C11+ is increased by 15.93% compared to single-stage reactor. [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]

Abstract: The implementations of a penetration type of the heat and mass transfer model for CO2 absorption into MEA solution in MATLAB were performed and validated with the experimental data from a String of Discs Contactor (SDC). The numerical PDEs solution method and its implementation were key factors in obtaining a stable, robust and fast computation. The penetration model of heat and mass transfer was implemented for testing a variety of numerical methods. It was found that the finite differences (FDM), in general, was not a proper algorithm in the case of high reaction rates as we observed an excessive number of discretization points were needed. Both a non-uniform adaptive grid routine, and a method based on orthogonal collocation were accurate and robust, and gave relatively fast solution. However, of the two, orthogonal collocation was by far the fastest. Based on this numerical scheme, the combined heat and mass transfer model will be developed further in the next phase of this study. [Copyright &y& Elsevier]

Abstract: The aqueous absorption technology is one of the most feasible options for post combustion CO2 capture. High energy requirement is the main problem for this technology. Intercooling is possibly one of the strategies that can reduce the energy consumption in some cases. It is used in other industries like oil refineries and has a promising effect on energy use reduction. However, the effect may depend on the absorbent system used and the configuration of the process. In this study, the effect of intercooling is investigated for monoethanolamine (MEA) and diethanolamine (DEA). The results show that the best location for intercooling, based on minimizing energy requirement per kg of CO2 captured is about 1/4th to 1/5th of the height of the column from the bottom. The effect of different parameters like lean loading, amine concentration, cooling temperature, etc is investigated in this study. The results for MEA and DEA are compared to see the effect of solvent on intercooling performance. [Copyright &y& Elsevier]

Abstract: Considerable effort on research in CO2 capture technologies has been directed towards steady state systems while less seems to have been done for the same systems in transient state. This work presents a dynamic model for CO2 absorption using aqueous mono-ethanolamine (MEA). Validation against experimental results both obtained at steady state and dynamic conditions is included. A parametric sensitivity study of the underlying model equations is carried out based alternative parameter correlations for the reaction rate constant. It is concluded that validated results for one specific pilot plant don’t necessarily apply to other plants of different sizes under other operational conditions. Furthermore, a parametric sensitivity study for the other parameters as well as for the rest of the CO2 capture process is also warranted. [Copyright &y& Elsevier]

Abstract: The foundation and implementation of a method for systematic reactor design is described. The reactor path is sectioned into stages where each stage is designed so as to optimize an overall objective. This is a further development of a previously proposed method for designing chemical reactors (). Reactants pass through a series basic operations or functions to form the desired products. The basic operations are represented by design functions on the path volume. The design functions are fluid mixing (dispersion), distribution of extra feed points, distribution of heat transfer area and coolant temperature, catalyst dilution distribution and more. The conceptual reactor design problem is solved as an optimal control problem. A direct method is applied where both the design functions and the state variables are discretized. The realization of the optimization is a staged process string of multi-functional units. A kinetic model of the gas phase methanol synthesis is used as an example. By applying the method on the model, a staged reactor design with less heat transfer area and higher production is possible. [Copyright &y& Elsevier]

Abstract: A new method is proposed for systematic generation of conceptual design of reactor networks. Here, non-isothermal conditions are considered. Optimal distribution of heat transfer area, in addition to optimal mixing and distribution of feeds are targeted. Given temperature and composition of feed streams, the objective is to find the sequence and size of ideal reactors, the distribution of extra feed streams, the heat transfer distribution along the reactor path and the total reaction time that maximizes the space–time yield of the key product component. The method can be applied to solve problems of any number of components and reactions. The method is applied to industrially important processes such as the methanol synthesis and the steam methane reforming process. Interesting results are obtained with respect to the required heat exchange area. [Copyright &y& Elsevier]

Abstract: A new method is proposed for systematic generation of conceptual design of reactor networks. Given feed compositions and a kinetic model, the objective is to find the optimal mixing structure and feed distribution. The method aims at finding the optimal sequence and sizes of ideal reactors and the optimal addition of extra feed streams along the reactor path. The total reaction time is calculated so as to maximize the space time yield subject to a minimum yield of the key product component. The method does not have any limitations with respect to the number of components or reactions. A new model formulation is proposed that comprises both CSTR and PFR model equations and the design problem is formulated as an optimal control problem. In this paper, only isothermal conditions are considered. [Copyright &y& Elsevier]

[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]

Flexible thermal power plants integrated with CO 2 capture systems can balance the intermittent power generation of renewable energy sources with low-carbon electricity. Among these power systems, natural gas combined cycles will play a fundamental role because of their faster operation and higher efficiency. Optimisation-based control strategies can enhance the flexible power dispatch of these systems and improve their performance during transient operation. This work proposes a model predictive control (MPC) strategy to stabilise these power plants with post-combustion CO 2 capture based on temperature swing chemical absorption and provide offset-free reference tracking. A delta-input formulation with disturbance modelling is proposed, as it provides more efficient computation with offset-free control. Data-based models were developed to replicate the performance of the actual power and capture plants. Prediction of nonlinear behaviour was accomplished by creating a network of local linear models, which allowed the formulation of the dynamic optimisation program in the MPC strategy as a convex quadratic programming problem. A case study demonstrated the effectiveness of the proposed MPC to balance drastic changes on power demand and keep specified capture ratios. Furthermore, the reduced deviations achieved in the reboiler temperature suggest that the nominal value of this parameter could be increased to improve the desorption process without risks of reaching temperatures where the solvent would degradate. [ABSTRACT FROM AUTHOR]

Highlights • Gas-liquid mass transfer for the Fischer-Tropsch synthesis was studied. • Conversion varied in the range 45–90% depending on choice of mass transfer model. • Conversion decreased linearly with increased inlet Sauter-mean diameter. • Bubble size dependency of the mass transfer coefficient showed effect on conversion. Abstract At high catalyst volume fractions the Fischer-Tropsch synthesis (FTS) operated in a slurry bubble column (SBC) is driven into the mass transfer limited regime. This study utilized literature models for the gas-liquid mass transfer coefficients in a multifluid-population balance model in which the gas-phase composition was a function of bubble size. The results confirmed that mass transfer limitations occur and that the choice of mass transfer coefficient model is crucial, yielding final conversion results ranging from 45% to 92% depending on the choice of k L models. At smaller k L values the composition is highly dependent on bubble size, whilst for the largest k L values the composition is not a function of bubble size at all. The population balance modeling (PBM) allowed for explicitly keeping track of the bubble size distribution. Varying the inlet Sauter-mean diameter (SMD) resulted in a linear decrease in conversion as the inlet SMD was increased from 5 mm to 20 mm. Illustrative models for the bubble size dependency of k L were implemented, which provided additional information compared to traditional models which use (bubble size) averaged values for the liquid-phase mass transfer coefficient k L and/or the gas-liquid interfacial area a and composition. [ABSTRACT FROM AUTHOR]

Modeling of reactive dispersed flows with interfacial mass transfer limitations require an accurate description of the interfacial area, mass transfer coefficient and the driving force. The driving force is given by the difference in species composition between the continuous and dispersed phases and thus depends on bubble size. This paper shows the extension of the multifluid-PBE model to reactive and non-isothermal flows with novel transport equations for species mass and temperature which are continuous functions of bubble size. The model is demonstrated by simulating the Fischer-Tropsch synthesis operated in a slurry bubble column at industrial conditions. The simulation results show different composition and velocity for the smallest and largest bubbles. The temperature profile was independent of bubble size due to efficient heat exchange. The proposed model is particularly useful in investigating the effects of bubble size on strongly mass transfer limited processes operated in the heterogeneous flow regime. [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]

In order to do a good and realistic design of a Gas-to-Liquid (GTL) plant, it is necessary to have kinetic models that correctly capture major variations of reaction rates and selectivities subject to changes in process parameters. In this study, a review of published kinetic rate models is done and twelve of them are analyzed based on different criteria, such as their behaviour at high conversions, high water partial pressure, sensitivity to added water, selectivity to C 5+ products, etc. The rate models are implemented in a plug flow reactor model. Both fixed bed and microchannel reactors can quite accurately be represented by such a model. Here, the main purpose is to see the kinetic effects with changing composition along the reactor. In order to predict the product distribution, we have proposed our own chain growth model and fitted parameters to experimental data from Yang et al. (2016) . The chain growth model includes the effect of water and predicts the C 5+ and methane selectivities quite well. [ABSTRACT FROM AUTHOR]

Optimization of once-through three-stage Fischer-Tropsch (FT) synthesis using path optimization is performed in this study to identify optimal structure and strategies in multi-stage FT synthesis design. The study also compares three-stage designs against recycled single-stage and two-stage designs with identical residence time and outlines key differences between different plant configurations. The results showed that it is optimal to operate at the maximum possible CO conversion and as low H 2 /CO ratio as possible. The comparison of the once-through three-stage and recycled two-stage processes against recycled single-stage process showed that two-stage and three-stage processes can achieve 2.3 % and 2.7 % higher syncrude production and 2.8 % and 3.2 % higher net material value (objective function). With the possibility of recycling in all three designs, the multi-stage processes improve further: 4.2 % and 5.3 % better in terms of syncrude production and 4.2 % and 6 % better in terms of the net material value. • Systematic staging of a Fischer-Tropsch catalytic process. • Optimal process configurations and design characteristics for staged Fischer-Tropsch synthesis. • Approximately 5 % improvement in production and CO conversion with an increase in the number of stages from 1 to 3. [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]

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]

Carbon efficiency of a biomass to liquid process can be increased from ca. 30 to more than 90% by adding hydrogen generated from renewable power. The main reason is that in order to increase the H 2 /CO ratio after gasification to the value required for Fischer-Tropsch (FT) synthesis, the water gas shift reaction step can be avoided; instead a reversed water gas shift reactor is introduced to convert produced CO 2 to CO. Process simulations are done for a 46 t/h FT biofuel production unit. Previous results are confirmed, and it is shown how the process can be further improved. The effect of changing the H 2 /CO ratio to the Fischer-Tropsch synthesis reactors is studied with the use of three different kinetic models. Keeping the CO conversion in the reactors constant at 55%, the volume of the reactors decreases with increasing H 2 /CO ratio because the reaction rates increase with the partial pressure of hydrogen. Concurrently, the production of C 5+ products and the consumption of hydrogen increases. However, the power required per extra produced liter fuel also increases pointing at optimum conditions at a H 2 /CO feed ratio significantly lower than 2. The trends are the same for all three kinetic models, although one of the models is less sensitive to the hydrogen partial pressure. Finally, excess renewable energy can be transformed to FT syncrude with an efficiency of 0.8–0.88 on energy basis. • By adding power to the BtL process, the carbon efficiency can be inceased to more that 90%. • Lowering the H2/CO ratio to the FT reactors will reduce the power requirement. • The added power to the BtL process can be transformed to liquid fuel at an energy efficiency of more than 80%. [ABSTRACT FROM AUTHOR]

Biomethane, produced by biogas upgrading, has a great potential to replace part of the fossil fuel natural gas, and may be injected into a gas grid or used as compressed biomethane as vehicle fuel. The state-of-the-art technologies for biogas upgrading in the European region are water scrubbing, pressure swing adsorption and chemical absorption, however, high performance carbon membranes may also have a great potential in this application. In this work, cellulose-derived hollow fiber carbon membranes were tested for CO 2 /CH 4 separation at moderate pressures (5–20 bar), and a CO 2 /CH 4 permeance selectivity >60 was obtained. The developed membranes were evaluated for biogas upgrading in a 1000 m 3 (STP)/h biogas plant based on HYSYS simulation and cost estimation. The results indicated that carbon membranes can be a promising candidate for biogas upgrading with a low processing cost of 0.078 $/m 3 at the feed pressure of 8.5 bar. Increased membrane performance can further reduce the cost. Moreover, a carbon membrane system can be very cost-effective for upgrading of biogas in small-scale plants of around 350 m 3 (STP)/h. [ABSTRACT FROM AUTHOR]

In this work an industrial Biomass-To-Liquid (BTL) plant simulation and optimization are presented. Biomass is first gasified with oxygen and steam, and the produced syngas is fed to a multi-tubular fixed bed reactor for Fischer-Tropsch (FT) synthesis, obtaining a distribution of hydrocarbons with different molecular weight. A simplified model for the biomass gasification section is implemented in HYSYS ® V8.4, while the Fischer-Tropsch reactor is simulated using MATLAB ® R2013a. The kinetic parameters of the FT reaction have been determined by using a non-liner regression performed with the experimenta data obtained with a bench-scale FT-rig. The model developed for the Fischer-Tropsch reactor takes into account the catalytic pellet's effectiveness factor and the eventual formation of a liquid phase in each point along reactor’s axial coordinate. The whole BTL plant is simulated connecting MATLAB and HYSYS. Moreover, the staging of the Fischer-Tropsch reactor is studied performing a techno-economic analysis of three different plant configurations and evaluating the corresponding pay-back time. [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]

A novel process concept is proposed for converting natural gas to liquid Fischer–Tropsch products. An autothermal reformer with enriched air as oxidant is applied for synthesis gas (syngas) production, and because of the inert nitrogen a once-through Fischer–Tropsch synthesis is the preferred option. In order to maximize the syngas conversion and the production of heavy hydrocarbons, a staged reactor path with distributed hydrogen feed and product withdraw is proposed. The hydrogen is produced by steam methane reforming in a heat exchange reformer (gas heated reformer), heat integrated with the hot effluent stream from the autothermal reformer. Tail gas from the last Fischer–Tropsch stage is sent to a gas turbine for power production. The hot exhaust gas from the gas turbine is used for natural gas preheating. The process is autonomous in the sense that it is self sufficient with power and water, and therefore well suited for production in remote locations such as a floating production unit. The process concept is simple and inexpensive since cryogenic air separation and fired heaters are not required. For the Fisher–Tropsch synthesis, both the conventional shell and tube fixed bed reactors and microchannel reactors are considered and compared. [ABSTRACT FROM AUTHOR]

• Novel kinetic expression for cobalt Fischer-Tropsch synthesis has been formulated. • The basis is the water assisted vinylene mechanism. • The rate can respond positive or negative to water partial pressure. • Kinetic parameters were fitted for several catalysts with excellent precision. • Deactivation by sintering and oxidation were implemented in the modelling. The paper describes development of a mechanism and a consistent rate expression for Fischer-Tropsch (FT) synthesis over cobalt-based catalysts. The developed mechanism relies on a two-step hydrogen assisted activation of CO. The carbon atom of CO is first hydrogenated by surface hydrogen to formyl; followed by the rate-limiting step whereby the oxygen atom is hydrogenated by adsorbed water. The produced CH* monomer is incorporated into the growing chain giving vinylene intermediate. The vinylene intermediate is either terminated to an olefin by adding hydrogen to the α-carbon atom or propagates by adding hydrogen to the β-carbon position. The resulting expression for CO consumption, the Fischer-Tropsch rate, can respond positively or negatively to the partial pressure of water, in agreement with experimental observations. A special feature is that the chain propagation probability does not depend on the partial pressure of hydrogen. The resulting kinetic model is tested on several cobalt catalysts supported on alumina; spanning from γ-alumina with average pore sizes ranging from 6.1 to 18.3 nm to α-alumina with a wide pore structure; and with cobalt particle sizes from 8 to 19 nm. Water was added sequentially to the syngas feed, causing enhanced deactivation, for testing the water response on activity and selectivity. A deactivation model comprising sintering and cobalt oxidation, and the FT-kinetics, describe the observed CO conversions with great precision for all catalysts. Selectivities are also well described, but with slight deviations at least partly due the effect of deactivation. Trends in some of the kinetic parameters are rationalized in terms of cobalt crystallite and pore sizes. [Display omitted] [ABSTRACT FROM AUTHOR]

Subsea processing is getting increased interest in the oil and gas sector as it can provide broader exploration of the oil and gas with a lower environmental footprint. Dehydration of natural gas with the use of triethylene glycol (TEG) is one of the main processing step for natural gas treatment to avoid transportation problems caused by the presence of water. Distillation is a commonly used technology for topside regeneration of TEG. However, for subsea operation alternative technologies are required to avoid complexity and the large energy consumption. Membranes are evaluated as promising solutions as they fulfil the subsea design criteria of compact design, flexible operation, and high modularity. In this work, the use of thermopervaporation for regeneration of TEG has been assessed. A mathematical model of a plate-and-frame thermopervaporation membrane module has been developed, where two-dimensional flow are considered for the liquid phases and the air gap is treated as a stagnant phase. Experimental pervaporation data were provided for the tuning of the model and the development of a temperature dependent permeability correlation. In addition, the effects of operation conditions and membrane properties on the separation performance were investigated. From this evaluation, it is clearly shown that the air gap significantly affects the separation performance and is a key parameter in the design of the thermopervaporation module. • A mathematical model of thermopervaporation for regeneration of triethylene glycol is developed. • Experimental pervaporation data is provided for model validation. • A temperature dependent permeability correlation is developed based on experimental data. • Sensitivity study on membrane and operation properties were investigated. • The air gap significantly affects the separation performance and is a key parameter in module design. [ABSTRACT FROM AUTHOR]