Two-phase Reactor Research Articles

Comparative simulation study of gas-phase propylene polymerization in fluidized bed reactors using aspen polymers and two phase models

A comparative study describing gas-phase propylene polymerization in fluidized-bed reactors using Ziegler-Natta catalyst is presented. The reactor behavior was explained using a two-phase model (which is based on principles of fluidization) as well as simulation using the Aspen Polymers process simulator. The two-phase reactor model accounts for the emulsion and bubble phases which contain different portions of catalysts with the polymerization occurring in both phases. Both models predict production rate, molecular weight, polydispersity index (PDI) and melt flow index (MFI) of the polymer. We used both models to investigate the effect of important polymerization parameters, namely catalyst feed rate and hydrogen concentration, on the product polypropylene properties, such as production rate, molecular weight, PDI and MFI. Both the two-phase model and Aspen Polymers simulator showed good agreement in terms of production rate. However, the models differed in their predictions for weight-average molecular weight, PDI and MFI. Based on these results, we propose incorporating the missing hydrodynamic effects into Aspen Polymers to provide a more realistic understanding of the phenomena encountered in fluidized bed reactors for polyolefin production.

A novel approach for simultaneous hydrodynamic characterization of gas–liquid and gas–solid systems

An attempt was made to find an analogy between hydrodynamic structures in fluidized beds and bubble columns in the frequency domain. This approach provides a better picture of hydrodynamic similarities between these two-phase reactors. The experiments were carried out in an air–water bubble column and an air-FCC fluidized bed. Pressure fluctuations were recorded for both systems at various gas velocities, aspect ratios and probe positions and were analyzed in frequency and time-frequency domains. Frequency spectrum of fluidized bed and bubble column revealed differences and similarities which can be related to properties of liquid and solid. Hydrodynamic phenomena were classified into three structures applicable to both bubble column and fluidized bed: macro (0–3.125Hz), meso (3.125–12.5Hz) and micro (12.5–25Hz) structures. It was found that the macro and meso structures exhibit a similar behavior in both systems. The plot of dimensionless standard deviation of pressure fluctuations in bubble column and fluidized bed against dimensionless velocity showed the similar qualitative and quantitative behavior for both systems. The analogous phenomena found for each structure can be used as a criterion for better understanding of both systems.

Study on Cultivation and Morphology of Granular Sludge in Improved Methanogenic UASB

Based on the mesophilic two-phase anaerobic reactor for maize ethanol wastewater treatment, the start-up, cultivation and the morphology of mature granular sludge in improved methanogenic UASB were studied. The reactor was initiated at a low loading rate. By means of increasing volume loading rate gradually and regulating internal circulation, the improved methanogenic UASB was operated under an optimal condition. After more than two months of operation, the size for the 63% of total granular sludge was more than 1.3mm, the biogas production rate and COD removal rate achieved 539L/d and 90%, respectively. Start-up of improved methanogenic UASB was accomplished successfully. Improved UASB, served as methanogenic phase of two phase anaerobic process, can adjust pH value of influent automatically. The manual regulation of pH value during start-up could be stopped when the granular sludge in improved methanogenic UASB went into maturity stage. The microfloras of mature methanogenic granular sludge are mainly brevibacterium and filamentous bacteria. Methanothrix soehngenii is the dominant consortium after the long-term operation under low-strength.

Fiber-Optical Sensors: Basics and Applications in Multiphase Reactors

This work presents a brief introduction on the basics of fiber-optical sensors and an overview focused on the applications to measurements in multiphase reactors. The most commonly principle utilized is laser back scattering, which is also the foundation for almost all current probes used in multiphase reactors. The fiber-optical probe techniques in two-phase reactors are more developed than those in three-phase reactors. There are many studies on the measurement of gas holdup using fiber-optical probes in three-phase fluidized beds, but negative interference of particles on probe function was less studied. The interactions between solids and probe tips were less studied because glass beads etc. were always used as the solid phase. The vision probes may be the most promising for simultaneous measurements of gas dispersion and solids suspension in three-phase reactors. Thus, the following techniques of the fiber-optical probes in multiphase reactors should be developed further: (1) online measuring techniques under nearly industrial operating conditions; (2) corresponding signal data processing techniques; (3) joint application with other measuring techniques.

Temperature increases from 55 to 75 °C in a two-phase biogas reactor result in fundamental alterations within the bacterial and archaeal community structure

Agricultural biogas plants were operated in most cases below their optimal performance. An increase in the fermentation temperature and a spatial separation of hydrolysis/acetogenesis and methanogenesis are known strategies in improving and stabilizing biogas production. In this study, the dynamic variability of the bacterial and archaeal community was monitored within a two-phase leach bed biogas reactor supplied with rye silage and straw during a stepwise temperature increase from 55 to 75°C within the leach bed reactor (LBR), using TRFLP analyses. To identify the terminal restriction fragments that were obtained, bacterial and archaeal 16S rRNA gene libraries were constructed. Above 65°C, the bacterial community structure changed from being Clostridiales-dominated toward being dominated by members of the Bacteroidales, Clostridiales, and Thermotogales orders. Simultaneously, several changes occurred, including a decrease in the total cell count, degradation rate, and biogas yield along with alterations in the intermediate production. A bioaugmentation with compost at 70°C led to slight improvements in the reactor performance; these did not persist at 75°C. However, the archaeal community within the downstream anaerobic filter reactor (AF), operated constantly at 55°C, altered by the temperature increase in the LBR. At an LBR temperature of 55°C, members of the Methanobacteriales order were prevalent in the AF, whereas at higher LBR temperatures Methanosarcinales prevailed. Altogether, the best performance of this two-phase reactor was achieved at an LBR temperature of below 65°C, which indicates that this temperature range has a favorable effect on the microbial community responsible for the production of biogas.

Degradation of high energetic and insensitive munitions compounds by Fe/Cu bimetal reduction

A reductive technology based on a completely mixed two-phase reactor (bimetallic particles and aqueous stream) was developed for the treatment of aqueous effluents contaminated with nitramines and nitro-substituted energetic materials. Experimental degradation studies were performed using solutions of three high energetics (RDX, HMX, TNT) and three insensitive-munitions components (NTO, NQ, DNAN). The study shows that, on laboratory scale, these energetic compounds are easily degraded in solution by suspensions of bimetallic particles (Fe/Ni and Fe/Cu) prepared by electro-less deposition. The type of bimetal pair (Fe/Cu or Fe/Ni) does not appear to affect the degradation kinetics of RDX, HMX, and TNT. The degradation of all components followed apparent first-order kinetics. The half-lives of all compounds except NTO were under 10min. Additional parameters affecting the degradation processes were solids loading and initial pH.

Multidimensional analysis of fission gas transport following fuel element failure in sodium fast reactor

Abstract Significant progress in several areas will have to be made to achieve the required technological and safety standards for future Gen. IV reactors, including both novel experimental methods (starting with separate-effect, then followed by integral experiments) and high performance computational models characterized by the necessary level of modeling detail and high accuracy of predictions. Furthermore, it is important that the experimental and theoretical/computational research complement each other, so that the results of measurements could be directly used for model validation purposes, whereas the results of simulations should provide input to identify modeling uncertainties and provide guidelines for prioritizing future experiments. The purpose of this paper is to present the modeling concept for mechanistic computer simulations of the injection of a jet of gaseous fission products into a partially blocked SFR coolant channel following localized cladding overheat and breach. A three-dimensional model of gas/liquid-sodium interaction has been developed based on a multifield modeling framework implemented in the NPHASE-CMFD code. The boundary conditions used as input to NPHASE-CMFD have been obtained by averaging the results of direct numerical simulations (DNS) performed using the PHASTA code. The novel aspects of the results discussed in the paper include the demonstration of advantages of using a multiscale approach to model local phenomena governing gas/liquid-sodium two-phase flow inside reactor coolant channels following cladding breach, as well as the observations about areas where future experiments are needed to improve the predictive capabilities of two-phase flow models.

豚舎排水の２槽UASBと接触酸化槽の組合せシステムによる処理

排水中の有機物を脱窒に優先利用するように，２相式UASB反応槽に脱窒槽を組合せ，さらにアンモニアを部分硝化する接触酸化槽を組合せて脱窒オリエンテッドシステム（著者らが命名）とし，パイロット装置により豚舎排水の高度処理が検討された．アンモニアは部分硝化（硝化率68％でNO2－－N/NO3－－N比は１：１），第１UASB槽のBOD残留率64.2％，BOD/N比２～３，硝化液の脱窒槽への循環比９～10とし，BOD除去率98.5％，TN除去率76.5％，CODCr除去率91％が得られた．

Experimental Study on Chinese Pharmacy Wastewater Treated by Two-Phase Anaerobic

The performance of two-phase anaerobic in a laboratory-scale operating on traditional Chinese pharmaceutical industry wastewater at various hydraulic retention times was investigated. The wastewater with high pollutant concentration in reactor designed based on two-phase anaerobic principles was analyzed with GC-MS. The effect of controlling the pH of the methanogonic phase of traditional Chinese pharmaceutical industry wastewater digestion on the biogas production rate and pollution potential reduction was also investigated. The reactor was designed to act as a liquid-solid separator, in order to maximize the microbial mass in it, and was operated at different hydraulic retention times. It operated as a two-phase reactor when the pH of the wastewater was controlled in the methanogenic phase. The results of experiment indicate that acidifier discomposes compounds composed of big molecule were degraded into small acid molecule which is more subject to biochemical treatment, and after the final treatment of reactor producing methane, species and contents of compound contained in treated wastewater are obviously reduced.

Energy optimisation from co-digested waste using a two-phase process to generate hydrogen and methane

The total energy produced from co-digested food waste and sewage sludge was compared for single phase mesophilic anaerobic digestion producing methane and two-phase hydrogen production followed by methane production. Both single and two-phase reactors were operated at close to optimum conditions. The single phase methaniser had a methane yield of 0.48 m 3 methane/kg VS destroyed. The two-phase system had a hydrogen yield of 0.13 m 3 hydrogen/kg VS destroyed, and a methane yield of 0.67 m 3 methane/kg VS destroyed. Introduction of a hydrogen producing, pre-treatment phase increased the overall VS destruction 69–89%, however the total energy yield decreased by 13.4% due to the low hydrogen yield obtained in the first stage. The release of ammonia in the hydrogeniser was low and so with less alkalinity available, pH control was necessary. It was much higher in the methaniser and adequate to buffer any pH change. This also ensures more nitrogen in the digestate to enhance its value for recycling. The two-stage process is an attractive option where solids destruction is an important consideration but further optimisation of the hydrogen production stage is still required.

Process Characteristics Study of Organic Wastewater Treated by Two-Phase Anaerobic Biotechnology

The performance of two-phase anaerobic in a laboratory-scale operating on traditional Chinese pharmaceutical industry wastewater at various hydraulic retention times was investigated. The wastewater with high pollutant concentration in reactor designed based on two-phase anaerobic principles was analyzed with GC-MS. The effect of controlling the pH of the methanogonic phase of traditional Chinese pharmaceutical industry wastewater digestion on the biogas production rate and pollution potential reduction was also investigated. The reactor was designed to act as a liquid-solid separator, in order to maximize the microbial mass in it, and was operated at different hydraulic retention times. It operated as a two-phase reactor when the pH of the wastewater was controlled in the methanogenic phase. The results of experiment indicate that acidifier discomposes compounds composed of big molecule were degraded into small acid molecule which is more subject to biochemical treatment, and after the final treatment of reactor producing methane, species and contents of compound contained in treated wastewater are obviously reduced.

Toward A Truly Multiscale Computational Strategy For Simulating Turbulent Two-Phase Flow Processes

In chemical reactor engineering, simple concepts are used for describing the flow in a reactor. Turbulent two-phase flow processes, however, are characterized by a broad range of time and length scales. Two-phase reactors operated in the turbulent regime therefore qualify for multiscale modeling. Multiscale models are being developed in such diverging fields as chemical reaction engineering (among which are packed bed reactors, fluidized beds, and risers), chemical vapor deposition reactor modeling, turbulent single-phase and two-phase flow simulations (among which is combustion), and materials science. The common aspects of these multiscale models are highlighted: they all comprise a coarse-grained simulation for the macroscale and some type of fully resolved microscale simulation. Different simulation techniques are used however. Processes involving single-phase flow may require one of three computational fluid dynamics (CFD) techniques: direct numerical simulations (DNSs), large eddy simulations (LESs), and Reynolds averaged Navier−Stokes (RANS)-based simulations. For two-phase flows, two CFD options are open: Euler−Lagrangian (or particle tracking) and Euler−Euler (or two-fluid). The characteristics of all these approaches are discussed. One of the more interesting options in dealing with turbulent two-phase, i.e., multiscale, flow reactors is to run a DNS for the local small-scale processes. Such a DNS is carried out in a periodic box, a dedicated forcing technique being used to impose the turbulent-flow conditions pertinent to a specific position in the macro domain. Several such successful DNSs are reviewed, which all exploit lattice Boltzmann (LB) techniques. Some new and promising results from LB simulations for gas−liquid flow systems are presented. Finally, a truly multiscale simulation strategy is presented for turbulent two-phase flow reactors, which combines a coarse-grained simulation for the macro domain concurrently run with several DNSs for properly chosen positions in the domain. LB techniques are recommended. The crucial step of this strategy—feeding the results of the local DNS frequently back into the coarse-grained simulations until convergence is reached—is described but has not been implemented yet.

Two-phase reactors applied to the removal of substituted phenols: comparison between liquid-liquid and liquid-solid systems

In this paper, a comparison is provided between liquid-liquid and liquid-solid partitioning systems applied to the removal of high concentrations of 4-nitrophenol. The target compound is a typical representative of substituted phenols found in many industrial effluents while the biomass was a mixed culture operating as a conventional Sequencing Batch Reactor and acclimatized to 4-nitrophenol as the sole carbon source. Both two-phase systems showed enhanced performance relative to the conventional single phase bioreactor and may be suitable for industrial application. The best results were obtained with the polymer Hytrel which is characterized by higher partition capability in comparison to the immiscible liquid solvent (2-undecanone) and to the polymer Tone™. A model of the two systems was formulated and applied to evaluate the relative magnitudes of the reaction, mass transfer and diffusion characteristic times. Kinetic parameters for the Haldane equation, diffusivity and mass transfer coefficients have been evaluated by data fitting of batch tests for liquid-liquid and liquid-solid two phase systems. Finally, preliminary results showed the feasibility of polymer regeneration to facilitate polymer reuse by an extended contact time with the biomass.

Textile Dye Removal in Single-Phase and Two-Phase Anaerobic Biotreatment Systems

This research compares performances of an anaerobic two-phase reactor system and a conventional single-phase reactor system in treatment of a synthetic dye wastewater. The two-phase reactor setup used four anaerobic reactors based on upflow anaerobic sludge blanket technology as acid reactors and an expanded granular sludge bed (EGSB) reactor as a methane reactor. An anaerobic reactor based on EGSB technology constituted the single-phase reactor setup. The reactors were operated at different hydraulic retention times (HRTs). The acid reactors removed up to 67% of the influent chemical-oxygen demand (COD) and 77% of the influent dye or color. An average of 10–25% acidification was achieved, and acetic acid, propionic acid, and butyric acid were the major volatile fatty acids produced in the acid reactors. The organic loading or the influent dye concentration did not have any significant effect on acid production or its speciation. The two-phase system could be operated at a HRT as low as 7.5 h with at leas...

The observer with linearized structure for uncertain objects with delay

The problem of designing a stabilizing robust control for non-stationary uncertain systems with delay presence in object structure is considered. An observer based on linear model, approximating the initial object model, is constructed. The results of simulation and evaluation of norm deviation for the problem of control synthesis for two-phase chemical reactor stabilization are presented.

Synthesis of monoacylglycerols by enzymatic methods

Monoacylglycerols are non-ionic surfactants widely used in the food industry. They are also important in cosmetic and pharmaceutical industries as drug carriers and for the consistency improvements in creams and lotions. Current process for their production is based on the glycerolysis of natural fats and oils in the presence of inorganic catalysts at temperatures higher than 220 oC. The major drawbacks of this process include high-energy consumption, low yield, and poor product quality. The use of lipases for the monoacylglycerols production offers environmental advantages and a reduction in energy consumption. Besides, the same surfactants prepared by the enzymatic synthesis may be labeled as ?natural?. Recent progress in the application of highly-stable lipases in the organic solvents offers the possibility of employing various methods to the enzyme-catalyzed synthesis of monoacylglycerols, such as selective hydrolysis of fats and oils using 1,3-regiospecific lipases, the esterification of glycerol with fatty acids and the glycerolysis of fats or oils. In this review, different reaction systems such as aqueous-organic two-phase systems, microemulsions and reverse micelles systems, anhydrous organic solvents, solvent-free systems with free or immobilized lipases, as well as the use of two-phase membrane reactor systems are presented. We discuss some of the key factors, such as the control of water content, removing of the products from reaction system, and the effects of solvent on the lipase activity and selectivity, that must be addressed in order to obtain an efficient reaction system with high yields of monoacylglycerols. Engineering of the enzymatic monoacylglycerols synthesis processes requires also optimization of other factors as: molar ratio of substrates, temperature, type of lipase immobilization and supports (if any), reactor design and operating regime.

Heat transfer metrology issues in two-phase bubble column reactors

The metrology and the impact of various parameters and operating conditions on the bulk-to-tube heat transfer coefficients in two-phase bubble columns are investigated on a small-scale mock-up. It is shown that (1) quasi-adiabatic conditions can be reached in the column; (2) the bulk-to-tube heat transfer coefficients for each U-tube downward and upward sections may or may not differ significantly, depending on the way uncertainty of the measurements is estimated; (3) using the different measurements and uncertainty estimates for given conditions, a mean heat transfer coefficient over all tubes is estimated within ±5%. The consequences for bulk-to-tube heat transfer coefficient prediction in a larger column are discussed.

A Two-Phase Reactor Model for the Hydrocracking of Fischer−Tropsch-Derived Wax

A two-phase reactor model that describes the hydrocracking of Fischer−Tropsch-derived wax (≤C80) has been developed that combines elementary hydrocracking kinetics and vapor−liquid equilibrium (VLE) with the design equations for an ideal fixed-bed reactor. The kinetics of the reaction considers each carbon number as an independent species in which all structural isomers and (de)hydrogenation steps are in chemical equilibrium. β-Scission cracking is rate-controlling for each carbon number; thus, an increase in reaction rate with increasing carbon number is observed. The VLE is described by a Peng−Robinson equation of state, and phase equilibrium is maintained at all locations down the reactor by simultaneous solution of the VLE within the reactor design equations. The model has only one adjustable rate constant: the β-scission rate constant, which controls the conversion. Meanwhile, the selectivity has no adjustable parameters and is controlled completely by the kinetic model and VLE. Results show that the...

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling, optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.

Transient behavior of the methane partial oxidation in a short contact time reactor: Modeling on the base of catalyst detailed chemistry

Abstract The objective of the paper is a numerical study of the partial oxidation of methane to synthesis gas in a monolith reactor with Pt/Ce-Zr-La catalyst. A dynamic one-dimensional two-phase reactor model of the processes with accounting for both transport limitations in the boundary layer of a fluid near the catalyst surface and detailed molecular unsteady-state kinetic model for surface reactions have been developed and verified with the transient experiments data. The mathematical model was used to explain a transient behavior of the process in the monolith reactor during start-up (ignition). Also studied is the influence on the process dynamics such parameters as linear velocity, equivalent diameter of triangular channel and effective thermal conductivity of the monolith. It was found that higher linear velocity and equivalent channel diameter as well as the worse axial conductivity of solid phase favor decreasing a time delay in syngas production in the Pt/Ce-Zr-La/α-Al2O3 honeycomb monolith with a triangular shape channels.