Fluidized Research Articles

Effect of Operating Parameters, Reaction Kinetics and Comparative Assessment of Fluidized-Bed Fenton Oxidation of 4-Nitrophenol

The oxidation of 4-Nitrophenol (4-NP) has been studied using recirculating fluidized-bed Fenton process. The effect of various parameters such as pH, the concentration of hydrogen peroxide, the concentration of ferrous ions, various types of carriers, and dosage of the carrier were investigated on the oxidation of 4-NP. Al2O3 and SiO2 were used as two different carriers for the oxidation of 4-NP. The experimental results are reported in terms of degradation percentage of 4-NP, Chemical Oxygen Demand (COD), and Total Organic Carbon (TOC). The results showed that the degradation and COD removal of 4-NP in the presence of Al2O3 carrier was higher as compared to SiO2 carrier. The degradation of 96% was achieved under the optimal operating conditions of pH 3, 0.2 mM Fe2+, 4 mM H2O2, and 5g/L of Al2O3 as a carrier. The TOC and COD removals were 70% and 55%, respectively after 1 h of reaction time. The presence of Fe-O bond onto Al2O3 carrier after the reaction was confirmed by the FT-IR studies. The total iron remained in the solution after reaction using fluidized-bed Fenton process was lower (8.5%) than homogeneous Fenton process (17%). The fluidized bed Fenton process also showed higher TOC and COD removal as compared to the homogeneous Fenton process.

Modeling and optimization of energy consumption and performance characteristics of a solar assisted fluidized bed dryer

The major problem regarding conventional rice mills is the use of fixed-bed drying systems, which is accompanied by high energy consumption. In this study, a novel solar-assisted fluidized-bed system for drying paddy grains was used. The system included a solar water heater, an infrared lamp powered by photovoltaic panels, along with a gas water heater, which were used together to provide the required thermal energy. The working factors were drying air temperature (35, 45, and 55 °C), drying air velocity (7, 8, and 9 m/s), and the angle of the desiccant wheel regeneration gate (0, 45, and 90 degrees). The performance characteristics of the drying system were measured in terms of drying rate, total energy consumption, solar fraction and energy efficiency. Several mathematical models were also applied to fit the moisture ratio curves. In order to analyze the results and obtain the optimized working conditions of the drying system, Response Surface Methodology (RSM) based on the Box–Behnken technique was used. In all of the evaluated conditions, the model entitled “Approximation of diffusion” had the best results for fitting the moisture ratio curves with a correlation coefficient value of at least 0.9729. The selected optimum point included drying air velocity of 7 m/s, drying air temperature of 52.77 oC and regeneration gate angle of 0. Under the mentioned working conditions, the drying time of 75.99 min, the total energy consumption of 0.297 kWh, solar energy fraction of 0.540 and energy efficiency of 47.67% could be obtained with a desirability value of 0.970.

An experimental study of fluidization post impinging fluid in granular bed for breaking sedimentation

Ударная жидкость может быть использована для предотвращения седиментации в потоке трубы и в процессе смешивания. Седиментация является проблемой, которая часто возникает при транспортировке жидкости и псевдоожижении. Поведение зернистого материала при соударении − это явление, которое редко изучается. Данное состояние трудно поддается наблюдению из-за положения сложных движений жидкости в слое. В исследовании предпринимается попытка определить поведение псевдоожижения при различных размерах зерен. В ходе экспериментальных исследований наблюдался эффект ударения в зернистый слой. В качестве инструмента для процесса наблюдения используется ячейка Хеле-Шоу. Средой для псевдоожижения служит стеклянный песок. Высокоскоростную жидкость за короткое время впрыскивают в зернистый слой. Зернистый материал движется благодаря давлению соударения при псевдоожижении. Движение зернистого материала наблюдают с помощью камеры для определения поведения зернистого материала. Основным результатом настоящего исследования является выявление двух весьма разных режимов. Существует два типа постударного псевдоожижения. Первым типом является жидкостная полость и псевдоожижение. Это состояние начинается с расширения полости жидкости с последующим процессом псевдоожижения. Полость жидкости возникает когда ударное давление жидкости толкает зернистый материал вверх. Зернистые связи удерживают связь частиц и образуют полость. Псевдоожижение после расширения полости − это оседающее движение, на которое влияет сила тяжести, плавучесть, сопротивление и зернистые связи. Другой тип − это локальное псевдоожиженное состояние. Предел возникновения жидкостной полости и псевдоожижения наблюдается при числе Рейнольдса соударения. Число Рейнольдса соударения рассчитывают по скорости проникновения ударной жидкости в зернистый материал и умноженному размеру частиц, деленному на вязкость. Последующее соударение полости жидкости происходит при числе Рейнольдса процесса соударения менее 4000 (область ламинарного и переходного течения). Локальное псевдоожиженное состояние имеет Re соударения более 4000, а псевдоожижение следует за потоком и немедленно исчезает. Это состояние приводит к тому, что связь зерен не может поддерживать агломерацию зерен

대기압 이하에서 운전하는 유동층 반응기의 유동 특성

최근 대기압이하 진공 압력 상태에서 운전되는 유동층 반응기는 진공건조 공정이나 플라즈마 화학증착과 같이 감압 유동화가 요구되기에 관심이 증대되어 왔다. 그러나 대기압 이하에서 운전되는 유동층의 수력학적 특성 연구는 많이 연구되지 않았다. 본 연구에서는 대기압 이하에서 운전하는 유동층의 압력강하를 층내 압력을 1.33 에서 101.3kPa 까지 변화시키며 측정하였다. 유동층의 운전 압력이 진공인 상태에서는 최소유동화속도가 압력이 감소함에 따라 증가하며, 이는 기체 밀도와 평균 자유경로 변화와 같은 slip 흐름에 의한 변화이다. 또한 기존의 상압 상태에서 운전되는 유동층의 최소유동화속도 상관식과 비교함으로써 압력 감소에 따른 slip 흐름의 영향 뚜렷하게 나타남을 가리키는 임계 Knudsen 수를 결정하였다. 이로부터 slip 흐름이 주도하기 시작하는 임계 압력을 실험적으로 결정하였다.

Experimental Study on Sugarcane Bagasse Pyrolysis in a Hermochemical Processes Pilot Plant

This paper investigates the sugarcane bagasse pyrolysis for bio-oil and biochar production in a pilot plant that was designed to perform the gasification process. After some modifications of changing the temperature of fluidized bed reactor and the catalytic reforming reactor, the fast pyrolysis process was performed at 500–600 °C using a fluidized bed reactor (air flow rate: 20–70 L.min-1) under atmospheric pressure, with sugarcane bagasse feeding (2–3.5 kg.h-1) with particles size less than 1.18 mm. Fluidization tests were performed with air feed (oxidative pyrolysis), to guarantee the fluidization is occurring, finding that the minimum fluidization rate was 22 L.min-1 (minimum velocity of gas: 6.3 cm.s-1). The residence time was 7 seconds (ratio between empty reactor volume by fluidizing gas flow). The highest bio-oil yield of 7.43 wt. % was obtained at 500 °C, with a bagasse flow rate of 3.5 kg.h-1 and 25.93 L.min-1 of air flow rate, and this low yield can be explained by the inefficient heat exchanger used. On the other hand, biochar yield achieved 35.88 wt. % using a temperature of 570 °C, 3.1 kg.h-1 of bagasse flow rate, and 28.26 L.min-1 of air flow rate. Considering this pilot plant has never operated in a pyrolysis mode, these results demonstrate that pyrolysis can be applied to this pilot plant, being versatile for different types of processes with a great potential for biochar and bio-oil production besides the high gas production.

Determination of a Complete Conversion Model for Gasification of Lignite Char

The conversion of solid fuels via gasification is a viable method to produce valuable fuels and chemicals or electricity while also offering the option of carbon capture. Fluidized bed gasifiers are most suitable for abundantly available low-rank coal. The design of these gasifiers requires well-developed kinetic models of gasification. Numerous studies deal with single aspects of char gasification, like influence of gas compositions or pre-treatment. Nevertheless, no unified theory for the gasification mechanisms exists that is able to explain the reaction rate over the full range of possible temperatures, gas compositions, carbon conversion, etc. This study aims to demonstrate a rigorous methodology to provide a complete char gasification model for all conditions in a fluidized bed gasifier for one specific fuel. The non-isothermal thermogravimetric method was applied to steam and CO2 gasification from 500 °C to 1100 °C. The inhibiting effect of product gases H2 and CO was taken into account. All measurements were evaluated for their accuracy with the Allan variance. Two reaction models (i.e., Arrhenius and Langmuir–Hinshelwood) and four conversion models (i.e., volumetric model, grain model, random pore model and Johnson model) were fitted to the measurement results and assessed depending on their coefficient of determination. The results for the chosen char show that the Langmuir–Hinshelwood reaction model together with the Johnson conversion model is most suitable to describe the char conversion for both steam and CO2 gasification of the tested lignite. The coefficient of determination is 98% and 95%, respectively.

Fluidized Electrocatalysis

Fluidized Electrocatalysis

Fluidized Electrocatalysis

Fluidized Electrocatalysis

Production of Syngas Suitable to be Used in Fermentation to Obtain Biochemical Added-Value Compounds

Lignin-rich residues are a side stream in advanced ethanol biorefineries and they are usually used for heat and power production. However, an alternative is the lignin valorisation by thermochemical and biochemical processes that might be economically more suitable. In this work lignin-rich residues were firstly thermochemical converted to syngas in a fluidised bed gasifier, using steam and oxygen as gasifying agents. The obtained results so far showed that the rise of steam/lignin-rich residues ratio favoured the release of H2 and CO2 and led to a decrease in CO and hydrocarbons content, as steam reforming reactions were favoured. On the other hand, the rise of the equivalent ratio clearly favoured partial oxidation reactions and thus the release of CO and CO2, while H2 and hydrocarbons contents were reduced, due to their partial combustion. The increase of temperature favoured the formation of H2, at the expenses of hydrocarbons and tar release, as both decreased. However, it is fundamental to control gasification temperature to prevent ash melting and consequent bed agglomeration, due to the high ash content in lignin-rich residues, generally with high content of silica and alkali metals. The results led to the selection of gasification conditions (800 °C, equivalent ratio of about 0.13 and steam/lignin ratio of around 0.4) that headed to the following gas ratio CO/CO2/H2=1:0.7:0.7, which was tested for further bacterial fermentation. Fermentation tests with Butyribacterium methylotrophicum showed that the above syngas composition strongly influenced the production levels of acetic and butyric acids. Marked differences in the CO, H2 and CO2 consumption rates were also observed and were correlated with cell growth and metabolites production.

Optimization of Gravity-Driven Granular Flow Around the Tube for Heat Transfer Enhancement

Nowadays, moving bed heat exchanger (MBHE) has been gradually adopted in the field of heat recovery from the granular flow. Compared with fluidized bed, the moving bed cost less. However, it usually brings with relatively poor heat transfer performance. The current study aims to optimize the heat transfer in gravity-driven granular flow through tube vibration, which is helpful to the efficient design of MBHE in the future. The vertical granular flow is numerically simulated with discrete element method, where careful discussion about vibration tube effect is developed. The model has been carefully validated. To focus on the mechanism of heat transfer enhancement, the geometry model is simplified as a single tube. The results show that, tube vibration in different directions could improve heat transfer performance, where the effect of horizontal vibrating direction is more remarkable. It’s also found that a slight sinusoidal vibration is able to accelerate particles update above the tube and drive some particles contact the bottom zone of tube. Therefore, it mitigates the negative effect of stagnation zone and void zone in cases of static tube. Then the heat transfer coefficients would increase. What’s more, tube vibration would rebound particles around the wall, where additional mass diffusion is beneficial to heat transfer at sides of tube at some extent. However, it should be noted that vibration would increase wear rate between tube and particles significantly at the same time. The industrial application relies on the development of wear-resistant technology.

Effect of the solids inventory and fluidization gas velocity on the hydrodynamics of a circulating fluidized bed

The hydrodynamics behavior of a bench-scale circulating fluidized bed (CFB) system has been analyzed in terms of the axial pressure profile and solids circulation rate. Experimental runs were carried out at room conditions using beds of quartz sand and air as the fluid phase in order to know the effect of the overall solids inventory and the superficial gas velocity used in the riser. Static pressure signals obtained from the gas-particle flow were registered at several positions along the CFB loop and the solids circulation rate was measured by using a diverter valve installed at the standpipe section. A statistical analysis applied on the experimental data show that the solids inventory and the superficial gas velocity in the range here studied lead to significant changes on the hydrodynamics of the circulating fluidized bed system.Keywords: Circulating fluidized bed riser, gas-particle hydrodynamics, static pressure signals, solids circulation rate.

Analysis of Particle Growth Kinetic of Pea Protein Isolate in Fluidized Bed by In-line Monitoring of Particle Size

Nowadays, there is a demand for products with good nutritional, technological and sensory characteristics. In this context, vegetable protein isolates, as pea protein, has been studied as a substitute to the soy protein, since it has higher levels of essential amino acids and vitamins. These powders are obtained commonly by spray drying that can modify the protein structure and that produces fine particles. So, to improve physicochemical properties, other processes, as agglomeration in fluidizing bed, could be used. The aim of this work was to study the influence of binder solutions characteristics on particle growth kinetics using an in-line particle size monitoring by spatial filter velocimetry. Two different acacia gum solutions (0.7 and 20.0 % w/w) were used as liquid binder. The operating conditions used were drying air temperature of 75 °C and binder flow rate of 3.0 mL/min. Atomization air pressure and atomization nozzle height were kept constant at 7.0 psi and 0.3 m, respectively. Fluid bed agglomeration was a useful method to produce instant pea protein concentrate powder under the operating conditions studied. This process produced larger particles, free-flow improved and shorter wetting time. The binder solution with higher concentration and more viscous provided a more pronounced particle growth and higher process yield. The in-line particle size monitoring was useful to observe the particle growth kinetics and the operating conditions influence on the growth kinetics and particle growth rate in fluidized bed agglomeration. It also was possible to observe that the particle growth rate oscillated during the process showing that the particle size growth results from a positive balance between agglomeration and break.

Agglomeration Phenomena During Fluidized Bed Combustion/gasification of Biomass Fuels

The objective of this research is to investigate the occurrence of agglomeration phenomena during fluidized bed processing of biomass fuels. These are to be ascribed to the alkali content in biomass materials that gives rise to low melting compounds in combination with SiO2, normally present in bed materials. The results obtained in a lab scale facility under operating conditions of gasification highlight that other materials may be adopted (e.g. olivine and chromite), despite they have higher density with respect to silica sand, affecting the bed fluid-dynamics. As alternative the addition of metakaolin is effective in order to delay the occurrence of bed agglomeration, as demonstrated by experiments carried out in alumina crucible at 900 °C and complemented by electronic scanning microscopy (SEM) and x-ray diffraction (XRD) analyses. The results are reported and discussed in the article, with the sake of providing further insights for contrasting the undesired agglomeration behavior in practical applications.

Modelling of the Aromatic Aldehyde Production by Catalytic Oxidation of Lignin in a Three-phase Fluidized Bed Reactor

Lignin derivatives are obtained in low levels of production by using catalytic processes in batch operations. Considering the availability of vegetable biomass with high lignin content it is processing to be economically feasible, should be conducted through continuous processes. In this way, the objective of this paper is to provide predictions for the aromatic aldehyde production from the aqueous alkaline lignin processed by wet oxidation in a three-phase fluidized bed reactor. A heterogeneous steady-state model was formulated to describe the continuous, isothermal operations of lignin oxidation associating hydrodynamic phenomena, mass transfer, and chemical reaction. The reactor operation was simulated considering a feed with 0.21 mmol/L of oxygen and 0.30 g/L of lignin at 393K and 20bar, presenting stationary profiles of the reagents and products. The mathematical model studied represented a stationary behavior and was solved by the finite difference methods in a code in FORTRAN 95.

H2 production over Pt-Ni/CeO2-SiO2 via ethanol reforming in a fluidized bed

The aim of the present work is to study the application of a fluidized bed reactor for oxidative steam reforming of ethanol (OESR) over a bimetallic 3wt% Pt-10wt% Ni/CeO2-SiO2 catalyst. In particular, the effect of cerium salt precursor (nitrate (N), ammonium nitrate (AN) and acetylacetonate (AC)) on catalyst activity and stability was investigated. Three catalysts were synthetized. In all cases, the support was composed of a CeO2-SiO2 mixed oxide and the ceria content for all the catalysts was fixed to 30 wt%. The tests were carried out at a steam to ethanol ratio (f.r.) of 4 and oxygen to ethanol ratio (o.r.) of 0.5; temperature was fixed to 500°C and the weigh hourly space velocity (WHSV) to 12.3 h-1. All the samples displayed a partial deactivation with time-on-stream and ethanol was completely converted only for few hours. The initial H2 yield was very close to the predicted thermodynamic value (41.5%) and a gradual yield lowering was observed over the three catalysts. However, after 80 h of test, all the samples reached a plateau condition, with no more variation in selectivity. It is worthwhile noting that, for the sample AC, the final conversion was attested to 75%, while the other two catalysts displayed a similar behaviour with plateau conversion of almost 60%. In addition, a higher H2 yield (20%) was recorded after 100 h of test for the sample AC and the carbon formation rate measured after the test on the latter catalyst was almost 1 half of the values found for the catalysts N and AN: in the case of acetylacetonate, the organic group of the salt probably assures a templanting effect, which protects ceria molecules, improving their dispersion and increasing catalyst activity towards both reforming and carbon gasification reactions.

Influence of initial density of granular stack on transient regime of homogeneous fluidization

This study complements a series of preliminary experimental studies of the destabilization of a granular stack immersed by fluidization, the particular case being the transient regime of homogeneous fluidization. The significant influence of the initial density (initial volume fraction) of the granular stack on the transient homogeneous fluidization regime is highlighted. An initially loose stack fluidizes turbulently and chaotically in a few seconds, from the injection zone to the top of the granular layer. Conversely, for the same material in an initially dense state, there is a mass takeoff of the stack, which is added to the propagation of porosity wave instability from the bottom to the top of the stack with fast kinetics that decompacts the medium. The results also showed that the velocity of this porosity wave seems almost constant regardless of the fluidization velocity.

Hypercholesterolemia antagonized heart adaptation and functional remodeling of the mitochondria observed in acute diabetes mellitus subjected to ischemia/reperfusion injury.

Intrinsic cardioprotective mechanisms become activated in the early diabetes mellitus (DM) and this may protect the heart from ischemia/reperfusion (I/R) similarly as in case of ischemic preconditioning. However, this protection may by blunted in the presence of cardiovascular risk factors. Assuming that hypercholesterolemia (HCH) frequently accompanies DM, this study extends findings from separate models of DM and HCH by investigation the impact of HCH on DM-induced changes, including those of compensatory nature, in rat heart and its mitochondria. We used a factorial design with all combinations of treatment factors DM and HCH: control rats (C) and streptozotocin-treated rats (DM), both on standard chow (C and DM) and fed fat-cholesterol diet (HCH and DM-HCH). Isolated, Langendorff perfused hearts were subjected to 30 min global ischemia followed by reperfusion. Significantly increased levels of cholesterol in DM-HCH after I/R injury abrogated compensatory fluidization characteristic of DM mitochondria membranes. Concomitantly, the mitochondrial Mg2+-ATPase activity in DM-HCH was depressed. In comparison with DM, which showed significantly reduced size of myocardial infarction with simultaneously improved recovery of contractile function due to conditioning, DM-HCH hearts exhibited attenuated resistance to I/R injury. Taken together, cholesterol-enriched diet was associated with inflicting damage and has been implicated in the mechanisms leading to suppression of cardiac protection presented in diabetic group. Apparently, DM and HCH are factors which are not additive in their effects, therefore, caution should be exercised, when interpreting findings from studies considering these factors in isolation. Our findings suggest that this complex condition could accelerate the development of late diabetic complications.

Application of Mathematical Modeling in Optimization of Synthesis Process Parameters of Methylchlorosilane

Methylchlorosilane is an important chemical raw material. It has been matured since the direct synthesis technology has been applied for many years. However, due to the characteristics of gas-solid two-phase catalytic reaction, it still faces many problems in industrial production. The use of systems engineering methods to solve production problems has become an important task for organic chlorosilane monomer manufacturers. This paper introduces the application of mathematical modeling in the optimization of methylchlorosilane synthesis process parameters as an example to illustrate the important role of system engineering ideas in the production practice process, to achieve digitization of the fluidized bed reactor control process, parameter optimization. Through the research and analysis of the production control process, the mathematical model of superficial gas velocity and catalyst feed coefficient control was established to optimize the methylchlorosilane synthesis process. The results show that the apparent gas velocity should be controlled in stages during the direct synthesis of methylchlorosilane. The induction period is 0.10~0.12 m/s, and the stable period is 0.25~0.28 m/s. After the catalyst is added to the reactor, it will undergo three stages of induction period, stable period and aging period. After the catalyst reaction performance, the catalyst will gradually lose its catalytic ability due to various physical and chemical factors. Catalyst stability and life-span in industrial production are related to its own performance and mixing ratio, the ternary copper catalyst life-span is generally 50-60 hours, the suitable mixing ratio is 2.0-2.5%.

Study on the Heat and Fluid in a Pressurized Fluidized Bed calculated by DEM

Study on the Heat and Fluid in a Pressurized Fluidized Bed calculated by DEM

Integration of Biomass Gasification and Hot Gas Cleaning Processes

In the near future, most of the world population will live in the developing countries, and it is plausible that biomass will be one of the main renewable energy sources of the future. Fluidized bed reactors should be the best solution to transform biomasses having different physical properties in energy and chemical vectors through gasification, due to its possibility to operate continuously, at high temperatures, and to utilize catalysts into the reactor and downstream of it, in order to reduce tar, NH3 etc. in the product gas.Catalytic filter candles are an innovative solution for hot gas cleaning & conditioning. It has been demonstrated that catalytic ceramic filters inserted in the freeboard of a fluidized bed gasifier, allow the complete removal of particulate by means of their anisotropic porous filtering structure, and furthermore act as catalyst to remove tar and ammonia, thanks to the Ni based catalyst contained into the filter itself (Rapagna, Gallucci and Foscolo, 2017).To by-pass the preparation of the catalytic ceramic filters and to render the overall process more feasible in practice, ceramic filters filled with commercial steam reforming catalyst pellets have been located in the freeboard of a 0.1 m ID fluidized bed reactor, where olivine particles act as bed inventory.Experimental tests were carried out to check the values of the gas pressure drop through the plain filter and through the filter containing catalyst pellets, at different temperatures and gas filtration velocities. It has been found that at the highest temperature and filtration velocity (T 800°C and v 140 m/h) the pressure drops are around 48 mbar, while at the operating conditions (T 800°C and v 100 m/h) the total pressure drops are only 35 mbar. Furthermore it was observed that there is an almost negligible difference between the pressure drops in the case of empty and filled candle; it was thus deduced that the catalyst pellets do not cause relevant additional losses compared to the empty filter. The trends of pressure drops were fitted with the empirical Darcy-Forchheimer relation and with the Ergun equation, and it was found that the major contribution is given by the viscous term of the relation. Furthermore an additional contribution of concentrated pressure drops was identified and ascribed to the outer Al2O3 membrane of the candle characterized by very fine pores.