Inlet Mixture Research Articles

Experimental and numerical study of a falling film heat exchanger used in a vapour absorption refrigeration system

Falling film evaporators have found applications in a wide range of industries, varying from chemical industries, petroleum refinery, desalination and food process industries. These heat exchangers are preferred mainly because of high heat exchange rates with low temperature difference between the heat exchange fluids at low film fluid flow rates with low evaporation temperature. This study is focused on numerical and experimental investigation of vapour generator (falling film heat exchanger) of a vapour absorption refrigeration (VAR) system. The influence of key operating parameters like mass flow rate of fluid, inlet temperature and the concentration of the thermic fluid as well as the coolant, are experimentally studied and are compared with the numerical results. The deviation between the experimental and numerical results was found to be 8.72%, with a lesser deviation at lower temperatures. The minimum percentage error is 2.15%, for a thermic fluid temperature at 50 °C. There is a stronger agreement in the results for lower values of the glycol water mixture inlet temperature, than at high temperatures. A maximum of 1000 W/m2 heat is transferred to the aqua-ammonia with ammonia concentration of 0.6 by volume is observed for thermic fluid inlet temperatures of 80 °C. The effect of various operating parameters were numerically studied and interpreted. The results obtained were in correlation with the concepts of heat transfer.

CFD Simulations of Microreactors for the Hydrolysis of Cellobiose to Glucose by β-Glucosidase Enzyme.

The enzymatic hydrolysis of lignocellulosic biomass-derived compounds represents a valid strategy to reduce the dependence on fossil fuels, with geopolitical and environmental benefits. In particular, β-glucosidase (BG) enzyme is the bottleneck in the degradation of cellulose because it catalyzes the hydrolysis of cellobiose, a known inhibitor of the other cellulolytic enzymes. However, free enzymes are unstable, expensive and difficult to recover. For this reason, the immobilization of BG on a suitable support is crucial to improve its catalytic performance. In this paper, computational fluid dynamics (CFD) simulations were performed to test the hydrolysis reaction in a monolith channel coated by BG adsorbed on a wrinkled silica nanoparticles (WSNs) washcoat. We initially defined the physical properties of the mixture, the parameters related to kinetics and mass transfers and the initial and boundary conditions thanks to our preliminary experimental tests. Numerical simulation results have shown great similarity with the experimental ones, demonstrating the validity of this model. Following this, it was possible to explore in real time the behavior of the system, varying other specified parameters (i.e., the mixture inlet velocity or the enzymatic load on the reactor surface) without carrying out other experimental analyses.

Investigation of the Gas-Liquid Two-Phase Flow and Separation Behaviors at Inclined T-Junction Pipelines.

The T-junction is a novel type of separator used in the petroleum and gas industry. It is used to achieve the gas–liquid or liquid–liquid two-phase separation. To obtain an applicative T-junction separator, in the present study, the gas–liquid two-phase separation characteristics in multiple inclined T-junctions were investigated through a series of numerical simulations and field experiments. Two representative multiphase modes, namely, the Euler model and the mixture model, were chosen for this study. Comparisons of the field experiments were made to obtain a highly accurate simulation model. The mixture model was chosen to be better suited for this study. It is used to investigate the gas–liquid two-phase flow and the separation behaviors, which include the effect of inlet flow velocity, inlet bubble diameter, and the split ratio of two outlets. The results indicate that the best flow split ratio exists when the two-phase separation reaches the best consequence, and the best flow split ratio changes when the separation demands of gas or liquid are different. Furthermore, the separation efficiency keeps decreasing as the inlet velocity is increased. Hence, the inlet mixture velocity should be reduced to improve the gas–liquid two-phase separation. More specifically, to obtain a better separation for the same throughput, the size of the T-junction should be increased. Moreover, the separation efficiency increases as the inlet bubble diameter increases. Consequently, the results can be used to design the T-junction as an industrial separator, which can then be directly used in petroleum and gas production.

Performance enhancement of axial concurrent liquid\u2013liquid hydrocyclone separator through optimization of the swirler vane angle

Vane angle configuration is considerably affecting the internal flow behavior and separation performance of a concurrent axial inlet liquid–liquid hydrocyclone. This study was carried out to improve the design of the swirl generator by optimizing the vane’s deflection angle in an oil/water axial inlet hydrocyclone separator. Angles ranging from 37° to 75° were examined at various operational conditions, including mixture temperature, mixture flow rate, and water-to-oil ratio. Two analysis techniques have been coupled to achieve the aim. First, design of experiment by the response surface method was utilized to generate a combination of run/boundary conditions of swirler vane angles, inlet mixture temperatures, flow rates, and concentrations. The obtained 15 run/boundary conditions were adopted as cases for computational fluid dynamics simulation to determine the separation efficiency, tangential velocity and pressure drop of each case using ANSYS Fluent software. The optimization results show that the swirl generator with a 45° deflection angle generated slightly higher tangential velocity compared with higher and lower vane deflection angles. The separation efficiency obtained by using the 45° swirl generator was higher than other angles, in spite that the turbulence intensity is slightly higher at 45° compared to other vane angles.

Improvement hydrocyclone separation of biodiesel impurities prepared from waste cooking oil using CFD simulation

ABSTRACT Raw biodiesel usually contains a considerable amount of impurities that need to be separated. In this work, a 10-mm diameter Dorr-Oliver hydrocyclone was used to investigate the separate behavior of impurities from biodiesel prepared from waste cooking oil under different operational conditions. The experimental results showed a maximum impurity separation of 82.2% (v/v). The operational conditions including inlet mixture temperature, pressure drop across the hydrocyclone, and the percentage of inlet impurities were optimized using Taguchi method. Then, the hydrocyclone was modeled using CFD to optimize its dimensions. The experiments performed by the optimized hydrocyclone indicated an impurities separation of 90.76%.

Kinetics of non-oxidative propane dehydrogenation on Cr2O3 and the nature of catalyst deactivation from first-principles simulations

As the global demand for propene (propylene) is increasing, classic commercial production processes are becoming unable to keep up. Non-oxidative dehydrogenation, although hitherto underutilised industrially, has been put forward as a viable and green alternative, which is already used in a few commercial processes. In this work, we present detailed first-principles calculations of this reaction over a chromium oxide catalyst, which is the cornerstone of the Catofin® process. A complete reaction pathway for the dehydrogenation of propane to propene and ultimately to propyne (methylacetylene) was considered. Cracking, which can yield C1 and C2 hydrocarbons, and the deactivation of the catalyst because of coking were also included and modelled. We used density functional theory calculations with the Hubbard model to study the structure of the involved intermediates, their adsorption and their interconversion to explain how chromium oxide catalysts facilitate this reaction and which processes cause their deactivation. We showed that the interaction of the hydrocarbons and molecular hydrogen with the catalytic surface is rather weak, resulting in low surface coverages, but increasing with multiple bonds present in hydrocarbons. Having constructed the potential energy surface with all the intermediates and the transition states linking them, we proposed a kinetic model for the reaction. Kinetic Monte Carlo simulations were performed at experimentally relevant temperatures (700–1000 °C), pressures (up to 10 bar) and inlet mixture compositions to study the kinetics of the reaction and discover the rate determining steps. As the reaction is highly endothermic, considerable conversions only occur at high temperatures. The accumulation of propene and propyne in the reaction mixture adversely affects the reaction rate and selectivity. Higher pressures increase the reaction rate but also increase the rate of coke formation, which poisons the catalyst. Deactivation of the catalyst has a strong temperature dependence and is caused by the accumulation of C∗ and CH3CC∗ on the surface, which are hard to remove even with hydrogen.

Numerical analysis of membrane–absorption separation for supercritical carbon dioxide and water mixture of plume geothermal power generation systems

A plume geothermal system provides a viable option for simultaneously storing carbon dioxide and producing supercritical working fluid with geothermal energy. Its water content, however, may cause problems, such as water hammer and corrosion, when the geothermal energy is utilized. A membrane–absorption separation method is employed to remove water from the supercritical carbon dioxide–water mixture. A numerical solution procedure is thereafter employed to evaluate the separation performance with different design parameters. If it is assumed that each membrane is repeatable and independent, then it can be divided into regular hexagon structures. The results show that a lower mixture inlet velocity and a higher lithium bromide solution concentration lead to a better separation performance. Moreover, the membrane remains practically unchanged even when the mixture inlet temperature varies. A multi-objective genetic algorithm optimization is implemented with an optimal solution search method. For a 65% concentration lithium bromide solution, the optimization results indicate that the best separation efficiency can reach 93.53%, and the total mass transfer area is 1093.5 m2. The findings suggest that membrane–absorption separation is efficient and commercially viable for separating supercritical carbon dioxide–water mixtures. This separation technology can provide purified working fluids for power generation systems.

Extraction of hydrogen from a lean mixture with methane by metal hydride

Hydrogen/methane mixtures draw attention due to the idea of the injection of hydrogen into natural gas networks and biological production of biohythane by one- and two-step anaerobic fermentation/digestion methods. It is hard to extract hydrogen from dilute mixtures with methane by traditional separation processes, since hydrogen is the minor component with low partial pressure. Metal hydrides selectively absorb hydrogen and offer an opportunity to overcome the limitations of traditional separation methods. In the present paper, we present experimental results on the separation of a dilute mixture of hydrogen (10%) with methane in a flow-through metal hydride reactor with inlet mixture pressure of 0.95 MPa by the LaNi4.8Mn0.3Fe0.1 intermetallic compound. Hydrogen was separated in one step with roundtrip (absorption/desorption) recovery of 74%. An exergetic analysis of the metal hydride separation of a binary mixture containing hydrogen was implemented and equations for hydrogen recovery and exergy efficiency of separation are obtained. Thermodynamic analysis shows that the exergy efficiency of the metal hydride purification has a clear maximum at hydrogen concentrations around 5–20%. The advantage of metal hydride purification is the absorption of the minor fraction from the feed, thus it is preferable for dilute mixtures and could be feasible for practical applications. With the use of low potential or waste heat to drive the reaction, it is possible to increase the efficiency of hydrogen purification by metal hydrides. The maximum exergy efficiency is 61% for 0.8 MPa outlet pressure, taking into account the quality of involved heat flows.

Natural Gas-Oxygen Combustion in a Super-Critical Carbon Dioxide Gas Turbine Combustor

The paper presents results for chemical kinetics of combustion process in the combustor of oxy-fuel cycle super-critical carbon dioxide gas turbine based on the Allam thermodynamic cycle. The work shows deviation of the normal flame propagation velocity for the case of transition from the traditional natural gas combustion in the N2 diluent environment to the combustion at super-high pressure up to 300 bar in CO2 diluent. The chemical kinetics parametric study involved the Chemkin code with the GRI-Mesh 3.0 kinetic mechanism. This mechanism provides good correspondence between calculation results and test data. The CO2 and N2 diluents temperature, pressure and contents influence the flame propagation velocity and the chemical kinetics parameters in the two gas turbine types. It is demonstrated that the CO2 diluent slows down chemical reactions stronger than the N2 one. The flame propagation velocity in carbon dioxide is four time smaller than in the N2 one. In the oxy-fuel cycle combustor a pressure increase reduces the flame propagation velocity. Increase of the CO2 content from 60 to 79% reduces the flame propagation velocity for 65% at atmospheric pressure and for 94% at super-critical pressure. An increase of the combustor inlet mixture temperature from 300 to 1100 K at super-critical pressure causes the flame propagation velocity increase for 94%. The flame propagation velocities compatible with the traditional gas turbines may be reached at the CO2 diluent content of the O2 + CO2 mixture in the active combustion zone must be below 50%.

Design and Test of Wind Plate-type Residual Membrane Hybrid Separator

In order to realize the effective separation of the residual membrane mixture, this paper designs the wind plate-type membrane hybrid separation device, which is composed of square air box, residual film discharge, conveyor belt, wind plate, soil and orange stalks shredded final row outlet, drive shaft, residual membrane mixture inlet, drive belt wheel and driven belt wheel, through analysis to determine the drain-outlet shape, number of wind plates and wind plate materials. Experiments showed that the membrane hybrid separation rate of membrane hybrid separation device is 91.5%, which meets the requirements of agronomy and realizes the effective separation of residual membrane mixture.

Oxidation and pyrolysis of ammonia mixtures in model reactors

The present work was devoted to an experimental characterization of NH3 oxidation and pyrolysis processes in model reactors. The oxidation tests were performed in a Jet Stirred Flow Reactor (JSFR) for stoichiometric ammonia/oxygen/argon and ammonia/oxygen/argon/water mixtures, as a function of mixture inlet temperature (Tin), at fixed pressure and residence time. Following, the behavior of ammonia/oxygen/argon mixture was analyzed in two tubular laminar flow reactors (LFRs) made of different materials (quartz and alumina), to evaluate potential surface heterogeneous effects.Pyrolysis tests were performed in both the reference model reactors, by substituting oxygen with argon.Experimental results realized in the JSFR allowed to identify three different kinetics regimes in ammonia oxidation: low (Tin < 1130 K), intermediate (1130 < Tin < 1250 K) and high temperatures (Tin > 1250 K). Surface heterogeneous reactions seemed to be negligible on ammonia reactivity and hydrogen profiles, but some effect could be observed on NOx concentration in the low-intermediate temperature range. Experiments realized in presence of water suggested that such species may passivate the surface, minimizing heterogeneous effects.Experimental tests realized in the LFRs confirmed these results, as hydrogen and oxygen profiles were independent of the reactor material, while NOx concentrations exhibited significant changes. Experimental results suggested that heterogeneous reactions were more relevant under pyrolytic conditions.Numerical simulations were performed with different kinetic mechanisms available in literature to value their capability to describe ammonia chemistry. None of them could accurately reproduce the experimental data for ammonia oxidation process, while they completely failed to predict ammonia pyrolysis features.

Phase split of oil-water two phase flow at double-layer T-junctions pipes

Offshore oil and gas production systems are in urgent need of a more compact, high-efficient oil-water separator. T-junction pipes are a potential solution to the need. Combining dynamic separation principle of T-junctions pipes with shallow pond theory, this paper presents a novel design of double-layer T-junctions pipes to realize high-efficient oil-water separation. The separation system consisted of upper and lower double-layer pipes that are connected by two vertical pipes. There exists an axially floating oil pipe along the top of the upper outer pipe. This design makes the Reynolds number decrease, which is beneficial to the formation of oil-water stratified flow. The slender seam at the bottom of inner pipe reduces the turbulence intensity, thus avoiding remixing oil with water. The influence of mixture velocity, oil content, water superficial velocity, oil superficial velocity, and inlet flow pattern on the phase split of oil-water two phase flow at double-layer T-junctions pipes has been investigated. Experimental results showed that the separation performance was less affected by the inlet oil content than by the inlet mixture velocity. Additionally, the phase split in the separation system was very sensitive to the inlet flow pattern. For separated flow pattern, oil-water can be well separated. But for dispersed flow pattern, the oil-water separation efficiency was low. Besides, the using of floating oil pipe can increase the system separation efficiency.

On the turbulent flow and pollutant emission characteristics of disk stabilized propane-air flames, under inlet mixture stratification and preheat

The reacting, time averaged and fluctuating flow field characteristics of bluff-body stabilized, stratified, propane-air flames have been systematically investigated for a range of conditions, under a combination of inlet mixture stratification and preheat. The burner consists of three concentric disks that form two premixing cavities. Fuel is injected in the first cavity and is partially premixed with air flowing through this cavity system, resulting in a radially stratified equivalence ratio profile at the inlet of the stabilization region. Investigations have been carried out at four levels of preheat temperatures, of the incoming reactants, ranging from 300 to 743 K, for lean and ultra-lean mixtures. The burner set up is capable of anchoring flames of sub-limit mixtures, down to global equivalence ratio values of about 0.13 at 743 K. The time averaged and fluctuating reacting velocity fields, developing in the downstream near wake, have been evaluated with Particle Image Velocimetry (PIV) analysis, indicating a proportionate decrease of the recirculation zone length with increasing fuel levels. OH∗ chemiluminescence emissions revealed a progressive alignment of the reacting front with the flame axis at weaker mixtures, while exhaust gas measurements have been obtained to evaluate the impact of preheat on emissions performance and combustion efficiency.

Characterization of Coal Fly Ash Based Adsorbent for CO2 Removal

The study of CO2 removal from air-CO2 mixture using coal fly ash (CFA) based adsorbent has been conducted. The sieved CFA was calcined at various temperature (200, 300 and 400 °C) for 4 hours. The calcined adsorbent pellets were characterized before utilizing in CO2 removal. Result suggested that calcination temperature slightly affected the yield of adsorbents. Increasing calcination temperature decreased the density and bulk density; but increased the percentage of adsorbed moisture of the adsorbents. SEM micrograph revealed various shape and size of the adsorbent and matched the result of XRD pattern and EDS analysis. The characterized adsorbents then were utilized to remove CO2 in an adsorption column. The inlet mixture contained 35%-vol of CO2 with flow rate of mixed gas of 200 ml/min. The highest removal was accomplished by using CFA based adsorbent pellet with particle size of 140 mesh, calcination temperature 300 °C for 4 hours. The CO2 removal efficiency was 71.43% with adsorbent capacity of 8.027 mg CO2/g adsorbent.

Experimental investigation of isothermal scalar mixing fields downstream of axisymmetric baffles under fully premixed or stratified inlet mixture conditions

The work discusses the characteristics of isothermal flow and scalar mixing fields, downstream of a variety of axisymmetric baffles in a double-cavity premixer/disk burner configuration. The scope of the work is to enhance knowledge regarding the impact of fully premixed or stratified, inlet fuel-air mixture conditions on the mixing disposition and fuel-air placement in the recirculating wake of a range of practical flame stabilizers. PIV and FTIR instrumentation are employed to obtain measurements of the mean and turbulent velocity fields and of the fuel concentration topologies throughout the near wake development.The measurements are obtained over a range of inlet conditions and geometric parameters, such as inlet fuel-air mixture profiles, blockage ratios and after- and fore-body stabilizer geometry characteristics. The results help to delineate differences and similarities in the cold flow mixing performance and fuel-air entrainment properties in the near wake of the examined baffles with implications for the flame anchoring and disposition in counterpart reacting configurations. The findings can be suitably exploited for the regulation of inlet mixture profile variations for realizing potential benefits in the optimization of operational stability and the minimization of emissions in the development of combustors.

Experimental investigation of the separation performance of oil/water mixture by compact conical axial hydrocyclone

Petroleum has long been the main fuel for power generation and transportation. However, mature oil wells are experiencing high water cut production with the crude oil resulting in high production and processing costs, as well as environmental impacts. Co-current hydrocyclonic technique has been adopted to solve oil/water separation in the downhole, but this process has some limitations. This paper introduces a compact axial inlet conical hydrocyclone to resolve the high water cut problem in mature fields. Experimental investigation results are presented to evaluate the separation of the newly introduced hydrocyclone. An experimental test loop was designed and fabricated. The flow loop was calibrated to manipulate and control various operational variables, namely, the oil/water mixture flow rate (1.5–4.0 m3/h), mixture temperature (50 and 80 °C), and water-to-oil ratio (70/30, 80/20, and 90/10). A gear pump is used to circulate the mixture. The droplets were measured and found to be within 35–38 µm with a mean droplets size of 37 µm. The results showed that mixture inlet flow rate, water cut, and temperature were influencing the separation efficiency and the pressure drop. The pressure drop of the water part was larger than the pressure drop of the oil part. Optimal separation efficiency was observed when the inlet flow rate is 4 m3/h with 80:20 water cut at 80 °C. A general trend of increase in separation efficiency with increased temperature was also observed.

Performance Evaluation of a Liquid-Liquid Cylindrical Cyclone (LLCC) for Oil-Water Separation

In this experimental study, the type of Hydrocyclone Separators that used is Liquid-Liquid Cylindrical Cyclone (LLCC). The objective of this experimental study is to understand the influences of operating and design parameters such as inlet velocity, split-ratio, and vortex finder diameter towards the result of separation process (LLCC’s performance). The separation performance of LLCC is determined by measuring the watercut that goes through the lower output called as underflow. The examined inlet mixture velocity in this experimental study are 1 m/s and 1.2 m/s with split-ratio variation of 5%, 15%, 30%, 45%, 60%, 75%, and 90%. The diameters of vortex finder that used in this experimental study are 18 mm, 22 mm, and 27 mm. All variables are tested under a constant inlet oil volume fraction 25%. From the experiment with those various variables, LLCC can achieve 99% of watercut with different Optimum Split Ratio (OSR) for each inlet mixture velocity and vortex finder diameter.

Cation influence in adsorptive propane/propylene separation in ZIF-8 (SOD) topology

Separation of propylene/propane is one of the most challenging and energy consuming processes in the chemical industry. Propylene demand is increasing and a 99.5% purity is required for industrial purposes. Adsorption based solutions are the most promising alternatives to improve the economical/energetic efficiency of the process. Zeolitic Imidazolate Frameworks (ZIFs) combine the desired characteristics from both MOFs and zeolites: tunability and flexibility from metal organic frameworks, and exceptional thermal and chemical stability from zeolites. In order to enlighten the role of the cation in the sodalite ZIF-8 framework for propane/propylene separation, dynamic breakthrough measurements have been performed over ZIF-8(Zn), ZIF-67 (i.e. ZIF-8(Co)) and MUV-3 (i.e. ZIF-8(Fe)), all isostructural materials based on the same linker (2-methylimidazole). Cation substitution has a remarkable influence in the framework flexibility, and, consequently, in SOD-ZIF selectivity for light hydrocarbons. The differences between the crystallographic pore sizes of the material and the molecular dimensions of propane and propylene are so small, that the slightest change in the framework causes notable advantages/disadvantages in the final application. While cobalt is known to promote a more rigid framework resulting in an adsorption selectivity towards propane, iron presents the inverse effect yielding selectivity to propylene. Zinc has an intermediate effect. A threshold pressure in the isotherm is observed for propylene uptake by ZIF-67 at 273 and 298 K, and only at the lower temperature for ZIF-8. Inlet mixture composition does not highly influence the adsorptive selectivity, although it clearly affects the pure hydrocarbon recovery. Over ZIF-67 breakthrough experiments at 298 K yield a temporary pure propylene flow representing 10–15% of the amount fed. ZIF-67 is a promising candidate for propylene/propane adsorptive separation.

Experimental investigation of synthesis gas production by methane reforming with flue gas over a NiO-Al2O3 catalyst: Reforming characteristics and pressure drop

An experimental investigation of methane reforming with flue gases obtained by combustion of methane with the ratio of air to methane of 1 is carried out over NiO-Al2O3 catalyst. The set of experiments was conducted to understand the effects of operational parameters such as temperature, pressure, residence time and inlet gas composition on the conversion of the reactants and the yields of products. It is found that at the residence time above 4 kgcat s/mol the methane conversion has a value close to equilibrium. A change in pressure from 1 to 5 bar has a negligible effect on methane conversion, not more than 1–2% for various operating parameters. The steam addition to the inlet reaction gas mixture increases the methane conversion considerably; especially at the temperature range from 500 to 800 °C. The steam addition to the inlet mixture has a notable on synthesis gas composition, especially at the temperature range below 700°C. Moreover, the experiments have been carried out to determine the pressure drop and the loss factor in a packed-fixed bed of a methane reformer. A characteristic quadratic dependence of the pressure loss versus velocity ΔP=f(v2) is observed for all experiments.

Fuel and thermal load flexibility of a MILD burner

The strategy to stabilize distributed combustion regimes adopting cyclonic flow fields has been proven to be challenging. In fact, the establishment of a toroidal flow field within a combustion chamber may ensure the recirculation of mass and sensible enthalpy required to simultaneously dilute the fresh reactants and increase the temperature above the autoignition one. The combination of reactants dilution and preheating may greatly increase system energy efficiency and lower pollutants production producing very peculiar combustion regime (named MILD Combustion). At the same time this strategy can be compromised if the sensible enthalpy is not high enough to promote the auto-ignition process of diluted mixtures. This may happen either because of an inefficient recirculation system or due to a too low calorific fuel. The paper aims at exploiting the performance of a small-size cyclonic burner for a conventional fuel (CH4) and a low calorific fuel (synthetic biogas) through the characterization of the process stabilization and pollutant emissions as a function of the mixture equivalence ratio and the nominal thermal power of the inlet mixture (from 2 to 10 kW), with the aim of identifying the optimal operating condition of the system. Results suggest that the system has to be exercised with mixtures with compositions slightly under the stoichiometric conditions and in a well identified temperature range to minimize both NOx and CO emission. The burner can be easily exercised also with low calorific fuels for higher thermal powers according to the low LHV. However, it results that an efficient recirculation of the exhausts produces a robust MILD combustion condition also when low calorific fuels are used.