Alumina Bed Research Articles

Thermal regulation for buildings using evaporative cooling technique: Experimental study

Global warming and increased air-conditioning demand drive up energy use. A passive cooling system for the building's roofs is one solution to this problem. The current study intends to provide a unique evaporative cooling concept for cooling building roofs that use significantly less water than prior approaches. To reduce room temperature, saturated-activated alumina beds with 2, 4, and 6 cm thicknesses were put over the roof. Pure and 35 PPT saline water were utilised to evaluate system performance and sustainability. The device successfully reduced rooftop temperatures by 84 % and 70.9 % after 24 h of testing (6 h during daytime and 18 h at night) under heat loads of 800 and 1000 W/m2. The findings show that salt water is a feasible alternative to freshwater that does not sacrifice cooling efficiency. From an environmental standpoint, compared to a bare roof, a 6-cm layer of saturated activated alumina tables can reduce annual carbon dioxide emissions by 71.3 tCO2/m2 and 92 tCO2/m2 for roof areas subjected to daily solar radiation of 6000 W h/day and 4800 W h/day, respectively.

Influence of bed material density on fluidized bed flotation performance: A study on the flotation performance of quartz and alumina beds in the HydroFloat

This work investigated the influence of bed material density on fluidized bed flotation performance. Experiments were carried out in a HydroFloat cell to investigate the influence of bed material density on required bed masses and bed behaviour at a bed level of 15 cm and water rate of 1.19 cm/s. Bubble size image analysis was carried out under four different fluidization conditions: water only, water and frother (1 ppm), water, frother (1 ppm) and quartz, and water, frother (1 ppm) and aluminium oxide. Flotation experiments were undertaken to investigate the influence of the resulting bed density and characteristics on concentrate recovery and grade performance. The results confirm that there is an upper particle size limit on fluidization. Apparent bed density was higher for the denser bed material (aluminium oxide) even though bed behaviour remained identical with both being highly permeable. The product Cu grades for the quartz bed were lower (8.42 % and 15.82 %) compared to the alumina bed (23.81 % and 21.86 %). This was due to the elutriation of quartz into the concentrate with Si concentrations of 25.85 % and 15.69 % compared to 2.4 % in the feed. In contrast, Al concentrations were 2.44 % and 1.09 % in the concentrates compared to the 0.38 % in the feed. However, recovery performances for both bed materials were identical (39.72 % and 40.88 % at low collector concentrations and 98.93 % and 97.95 % after ethylenediaminetetraacetic acid (EDTA) cleaning and increased collector concentration for the quartz and aluminium oxide beds respectively). This indicates that apparent bed density may have only a slight influence on flotation recovery compared to other direct control variables such as fluidization water rate and bed height.

Removal of chlorine, microparticles and water from high-viscosity liquids by a sand filter coupling hydrocyclone

Separation energy consumption in industrial production accounts for 10–15 % of global energy consumption. Nonthermal separation represented by sand filtration can open a new door to separation energy savings. Traditional sand filters cannot be regenerated completely, which limits their efficiency. A sand filter coupling hydrocyclone (SFCH) was proposed to enhance regeneration. The performance of SFCHs with different separation particle sizes was systematically analyzed, as indicated by turbidity, water, and chlorine in a pilot-scale experiment. The larger the sand particle size of the SFCH was, the longer it took to reach saturation. The efficiency and cycle were balanced by combining SFCHs with particle sizes of 1–2 mm and 0.5–1 mm. The average turbidity, water and chlorine decreased from 793 NTU, 1439 mg/L, and 126 mg/L to 155 NTU, 389 mg/L, and 88 mg/L, respectively, with a cycle of 88 h. Under the same conditions, the effluent turbidity of the SFCH was half of that of the original disc centrifuge, which indicates that the life of the downstream alumina bed was doubled. Almost 260 t/year alumina consumption can be reduced in a 200,000 tons/year-capacity petroleum resin plant, saving 600,000 USD/year, mainly due to the extension of the service life of the alumina bed.

Mitigating bed agglomeration in a fluidized bed gasifier operating on rice straw

Fluidized bed gasifier is a promising technology with respect to converting biomass to useful energy. Bed agglomeration is an operational challenge that arises during fluidized bed gasification with rice straw as raw materials. Rice straw contains high amounts of potassium and other components that may lower the melting point of ash, causing bed agglomeration. Using alternative bed materials such as alumina, in the place of silica, can mitigate this problem. In Thailand, rice straw is an agricultural by-product of the rice milling processes, produced in large quantities every year. Usually, rice straw management comprises open field burning, which releases greenhouse gases, particulate matter, and other pollutants. In this paper, the behaviors of bed agglomeration and defluidization were investigated during the fluidized bed gasification of rice straw, using silica and alumina as bed materials. The effect of the percentage ratio of silica and alumina (0:100; 25:75; 50:50; 75:25; 100:0) was examined. The operating parameters were as follows: rice straw particle size of 425–850μm, reaction temperature of 700–900 °C, and equivalence ratios (ER) of 0.2 and 0.4. The results showed that the percentage ratio of silica and alumina, 0:100 at 700 °C, had extended the defluidization time of 60 min. The effect of equivalence ratio on bed agglomeration was found to be apparently heightened at a high temperature. The result of SEM/EDX analysis showed that the major elements at the linkage point of the agglomerated particle were Si, K, and Ca, with regard to any proportion of the alumina bed and temperature. In conclusion, low temperature agglomerate formation can be explained by a K2O-CaO-Si2O phase diagram. The results from this investigation can be applied to biomass-fluidized bed gasification, where bed agglomeration entails a plant shutdown and is expensive in terms of maintenance.

Arsenic Mitigation Technologies from Ground Water: A Brief Review

Contamination of drinking water due to the presence of as has become a global environmental and socio-economic threat. The appearance of high Arsenic (As) in drinking water causes a serious health issue around the world. Many countries in different parts of the world have reported high arsenic concentrations. Among all groundwater arsenic contamination affected countries, the position of Bangladesh is the worst. Therefore, it is very important to develop affordable and efficient techniques to remove As from drinking water to protect human health. The most used methods are oxidation, coagulation, adsorption, ion exchange, and membrane technologies. Oxidation is usually used as pretreatment for most of the methods. Coagulation is the most common arsenic mitigation technology in Bangladesh. This technique is effective from pH 6-8. Ion exchange resins can only remove arsenate. Activated alumina beds work best in slightly acidic waters and usually have much longer run times than ion exchange resins. A cost-effective method for mitigation of As from drinking water is the use of low-cost adsorbent. Membrane methods which are more costly than other arsenic mitigation techniques but very effective where very low arsenic levels are required. Providing a safe water source may not possible in some of the arsenic affected regions or sometimes this process becomes very expensive. Mitigation of As from drinking water may be more appropriate in these situations. This paper presents a review of the conventional methods used for mitigation of As from contaminated drinking water.

Potentiality of “orujillo” (olive oil solid waste) to produce hydrogen by means of pyrolysis

The extraction of olive oil generates great amounts of solid waste and wastewater. The objective of this work is to evaluate the potentiality of slow pyrolysis of the solid oil waste, known as “orujillo”, to produce hydrogen rich gases. The effect of temperature and of different treatments of pyrolysis vapors on the yield and composition of the gases has been experimentally studied. “Orujillo” was pyrolyzed at 500 °C and 700 °C, and the pyrolysis vapors produced were directly fed to a second reactor where they were treated at 800 °C in different ways: just thermally, thermally treated through a refractory alumina bed and thermo-catalytically treated through a three layer bed (alumina + SiC mixed with Ni catalyst + alumina). The catalyst used was a commercial prereduced nickel-catalyst which contains 44 wt% Ni over calcium aluminate support (CaO/Al2O3). Concerning the effect of temperature, it has been proved that the raise in temperature leads to a decrease in the liquid yields and an increase in the gas yields, as well as to an increase in H2 and a decrease in CO2 content of the gases. With respect to the vapors treatments it has been observed that as a general rule any of the treatments reduces liquid and increases gas yields, and concerning gas composition, H2 content increases, CO slightly increases and CO2 decreases. These effects are more pronounced when the Ni-catalyst is used. With the Ni-catalyst about 50 wt% gas yield is obtained, with ≈ 50 vol% H2 both at 500 and at 700 °C.

Comparison of porous and nonporous alumina bed materials for PAHs formation during plastic waste fluidized-bed incineration

In order to understand adsorption effect of porous materials on PAHs generation during waste fluidized-bed incineration, comparison of porous and nonporous alumina bed materials for PAHs formation was experimentally investigated in a plastic waste fluidized-bed incinerator. Meanwhile, the distributions and contents of gaseous PAHs, particulate associated PAHs, PAHs precursors (monocyclic aromatic hydrocarbons and light hydrocarbon) in the dense region, freeboard region and outlet of the incinerator were also measured. The results indicated that ethylene (C2H4), ethyne (C2H2), propene (C3H6), benzene (C6H6), and styrene (C8H8) were the main precursors for PAHs formation. The 3-ring and 4-ring PAHs were dominant, and the particulate associated PAHs was the main components in flue gas. Meanwhile, the gaseous PAHs and particulate associated PAHs were respectively reduced by 49.20% and 39.41% when the non-porous alumina was replaced by the porous alumina bed materials. Based on the PAHs formation routes, the suppression mechanism for PAHs formation was proposed that the porous alumina adsorbed more PAHs precursors in the dense region due to its higher adsorption capacity, simulateously reduced the evolution rate of the PAHs precursors and prolonged the residence time of PAHs precursors in the freeboard region of the incinerator.

Effect of bed particle size and temperature variation on the minimum fluidisation velocity: A comparison with minimum fluidisation velocity correlations for bubbling fluidised bed designs

This work presents hydrodynamic studies on the effect of temperature and bed particle variation on minimum fluidisation velocity. A lab-scale bubbling fluidised bed made of stainless steel, with column height of 1 m and internal diameter of 0.15 m was used. Five Geldart-B-type alumina bed materials of mean particle sizes 75, 177, 250, 320 and 500 µm were used and the bed temperature was varied between 50 ℃ and 600 ℃. The hydrodynamic results showed that minimum fluidisation velocity varied directly with mean particle size and inversely with temperature. The pressure drop was found to increase with bed temperature for all the sizes of bed particles. The minimum fluidisation velocity is a key parameter in the design of fluidised bed systems and as such its prediction lies with good choice of correlation. The experimental values were compared with predicted minimum fluidisation velocity from six correlations, with the overall objective of verifying the most suitable correlation. Of the correlations used, the Hartman et al. correlation showed very good fitting with experimental data for beds of 75 and 177 µm particles, and the Mohanta et al. correlation showed good fitting with 250–500 µm bed particles. The models exhibited very good coefficient of multiple determination ( R2), very low fitting errors and low geometric standard deviations across the range of particle sizes and temperature variation. However, the lack of understanding of the parameters such as voidage, particle sphericity, density and viscosity would need more attention, particularly in view of the sensitivity of the minimum fluidisation velocity predictions to these parameters. Further studies are therefore recommended for the verification of the correlations in this regard.

Reducing polycyclic aromatic hydrocarbon and its mechanism by porous alumina bed material during medical waste incineration

In this paper, porous alumina was used as an alternative bed material to reduce polycyclic aromatic hydrocarbon (PAH) and monocyclic aromatic hydrocarbons (MAH) emission during medical waste incineration in a fluidized bed combustor (FBC). In order to understand the reduction mechanisms of MAH and PAH, porous alumina, nonporous alumina, and silica sand (180–250 μm and 250–320 μm) were used as the bed materials. In comparison to the silica sand (180–250 μm) bed material, the reduction efficiencies of ∑MAH, ∑PAH and ∑PAH toxic equivalent (TEQ) by porous alumina bed material were in sequence as 91.57%, 58.90% and 73.23% during medical waste incineration under 800 °C. There were three mechanisms for the reduction of PAH under porous alumina bed materials. Firstly, the evolution rate of hydrocarbon was reduced by porous alumina due to its low heat transfer coefficient. Secondly, porous alumina bed materials could absorb more gaseous hydrocarbon and prolong the residence time of hydrocarbon in the diluted zone of FBC due to its higher BET. Lastly, the oxidization of the gaseous hydrocarbon was accelerated by porous alumina due to its catalytic effect. Thus, less light hydrocarbon, MAH and PAH were formed during medical waste incineration. The experimental results also indicated that the heat transmission, catalytic effect, and adsorption effect of porous alumina bed materials respectively accounted for 22.8%, 29.2% and 20.9% of the ∑PAH reduction.

Stable flame limits for optimal radiant performance of porous media reactors for thermophotovoltaic applications using packed beds of alumina

Porous media combustion (PMC) is characterized by intense heat exchange from the combustion gases to the solid media, enabling higher temperatures at the outer surface of the solid matrix. This paper, for the first time, experimentally investigates how to control combustion inside a porous media matrix to take advantage of its hot outer surface for active emission to a thermophotovoltaic (TPV) system. This ‘coupled porous media combustion-based thermophotovoltaic (PMC-TPV) system’ requires a stable flame over (only) the narrow height where the photovoltaic cells are mounted. Thus, this study reports a systematic flame stability analysis for lean Air/methane mixtures to optimize the radiant performance of three different porous media combustor designs for thermophotovoltaic applications. In this study, the equivalence ratio was set at 0.7 and the firing rates were varied in order to find the stable and unstable regimes of each reactor. Results indicate that the use of a radiant reflector shifts the stable flame regimes and increases the radiant efficiency to 63% at an operating temperature of 1356 °C. Superadiabatic conditions were also found to be possible in this system, with a maximum temperature of 1538 °C, which improves the radiant emission spectrum for the photovoltaic (PV) cells. These fundamental combustion findings will help to define the operating parameters and improve the electrical conversion efficiency in future PMC-TPV systems.

Benzene Conversion in a Packed Alumina Bed Continuously Fed with Woody Char Particles

This Article investigates the decomposition of benzene (as a model tar) over finely dispersed char particles continuously distributed into a packed bed. Fragmented char particles and benzene plus a ...

Kinetic study of the thermal decomposition of octamethylcyclotetrasiloxane on activated gamma alumina

Biogas produced at wastewater treatment plants and landfills is contaminated with siloxanes that impedes its use as fuel. Before being safe to use in solid oxide fuel cells or engines, siloxane contamination must be reduced to below 0.01 and 9.1ppm (vol/vol) Si equivalent respectively. The literature has identified thermal decomposition in a packed bed of heated gamma alumina as a method that can remove siloxanes to the requisite levels Finocchio (2008) & Urban (2009). Missing from the literature is a kinetic study of the decomposition reaction where a theoretical model is fitted to experimental breakthrough curves so that breakthrough times can be predicted. The present work is this kinetic study.Experiments with synthetic biogas (0 to 100% methane and carbon dioxide mixtures) contaminated with octamethylcyclotetrasiloxane (D4) at concentrations between 32.3 and 72.7ppm (vol/vol) Si equivalent were conducted. Beds of alumina were exposed to the gas at temperatures between 307 and 384°C for contact times between 5.0 and 8.0ms. The effluent D4 concentration was measured by GC-FID.The breakthrough curves obtained were fitted with a kinetic model that assumed a first order surface reaction, shrinking core particle kinetics, and plug flow in the reactor. For temperatures between 333 and 384°C, the model fit the data well, most especially near the breakthrough point. Experimental conditions had no effect on quality of fit. At 307°C, the model was inadequate; possibly due to D4 physisorption or shrinking core kinetics assumptions not holding true anymore.

Experimental analysis of hybrid and conventional air conditioning systems working in hot-humid climate

This paper reports the experimental performance characteristics of a hybrid air conditioning system consists of a conventional (vapor compression) system integrated with thin-multilayer activated alumina bed with single, double and triple-layers. The performance characteristics of both systems are investigated under hot very humid climate with fresh air mixing ratio from 40 to 100% that is replicated at various process air temperature (28–36°C) and relative humidity (50–80%). The performance characteristics of hybrid and conventional evaporators and systems are compared under different conditions. Also, effect of desiccant cycle duration on hybrid system performance is investigated. The obtained results revealed that thin-multilayer alumina bed has substantial effect on hybrid system characteristics. Using the right desiccant layers, hybrid systems achieve better characteristics (smaller evaporator size system and compressor power with higher COP) than conventional system for all the mixing ratios. In the case of pure fresh air, the degree of superheat, pressure ratio and compressor power are lower than those for conventional system by 14.5, 2.0 and 2.7% with higher COP of hybrid system by 12.4%. Short cycle duration has higher sensible heat factor and lower evaporator size while long cycle duration has lower compressor power and higher COP.

Performance characteristics of thin-multilayer activated alumina bed

This paper reports the experimental mass transfer characteristics of thin-multilayer activated alumina bed that is used in desiccant-cooling systems working in humid and very humid climates, during adsorption and regeneration processes. These characteristics include transient response, adsorption and desorption rates, mass transfer coefficients and latent COP. Effects of dry bulb temperature and humidity of ambient air on single, double or triple-layers bed are experimentally investigated. In addition, effects of cycle duration on latent COP and adsorption process are considered. The experimental results proved that long cycle duration achieves high latent COP but with large moisture content of exit air while short cycle duration accomplishes uniform moisture content of exit air but with lower latent COP. The mass transfer characteristics of activated alumina beds are superior for hot very humid climates (high ambient temperature and relative humidity) with more uniform relative humidity of exit air being achieved by triple-layers bed. The comparison between activated alumina and silica gel, under the same conditions, revealed that activated alumina achieves higher COP, particularly for short cycle duration.

Effect of Ca addition on interface formation in Al(Ca)/Al2O3 composites prepared by gas pressure assisted infiltration

The aim of the work is to study interface formation between Al2O3 particles and Al(Ca) matrix in dependence of Ca content. Aluminium matrix composites (AMC) subjected to investigation were prepared by gas pressure assisted infiltration of alumina beds with aluminium-calcium alloys. It is shown that alumina particles in the AMC are covered with a monocalcium aluminates layer whose coherence increases with increasing amounts of Ca in the aluminium-calcium alloys. Moreover, Al4Ca intermetallic phases are formed with increasing Ca content and interconnect alumina particles. XRD confirms the presence of both CaAl2O4 and CaAl4O7 ternary phases. However, HRTEM analysis confirmed CaAl2O4 with a rather complex structure containing a high density of stacking faults. It appeared that annealing at 735°C does improve consistency of interface for Al 2wt.%Ca/Al2O3 AMC, but do not affect the thickness of the interface in dependence on annealing time.

Particle–particle heat transfer coefficient in a binary packed bed of alumina and zirconia-ceria particles

Solar thermochemical processes for fuel production require the incorporation of heat recovery systems for substantial efficiency gains.A heat recovery concept for processes using a particulate redox material proposed by the authors utilizes a second particulate material as a solid heat transfer medium. This work is about the experimental investigation of the heat transfer between these two particle species in a binary packed bed. Experiments were performed at temperatures up to 250 °C regarding the influencing factors of contact time, mass ratio, average temperature, temperature difference and particle diameters. Design of experiments helped as a method to plan and analyze these experiments. In addition, the temperature dependent specific heat capacity, the density and the size of the investigated particles were experimentally analyzed.In order to consider heat losses to the experimental setup, a correction measurement campaign was undertaken.The results are in the form of a polynomial which predicts the heat transfer coefficient depending on its influencing factors. This polynomial was obtained by a stepwise linear regression method. Values between 90 and 260 W/m2 K are predicted for the given temperature range.In an alternative approach we characterized the heat transfer in terms of the temperature difference of one particle species.

Reduction of Polycyclic Aromatic Hydrocarbon Emission by Porous Alumina Bed Material during Sewage Sludge Incineration

In this paper, porous alumina was used as an alternative bed material to reduce polycyclic aromatic hydrocarbon (PAH) emission and improve the combustion efficiency during sewage sludge combustion in a fluidized bed combustor (FBC). To discover the reduction mechanism, the Brunauer–Emmett–Teller (BET) surface area, critical fluidized velocity, and heat-transfer coefficient of three bed materials (silica sand, alumina sand, and porous alumina sand) were characterized. In comparison to the conventional silica bed material, the reduction efficiencies of PAH emission and PAH total toxic equivalent (TEQ) by porous alumina bed material under 850 °C were 52.0 and 97.7%, respectively. Porous alumina bed material had more BET surface area than that of the conventional silica sand, which could adsorb gaseous hydrocarbon and prolong the residence time of hydrocarbon in the diluted zone of the FBC. At the same time, it was well-known that gaseous hydrocarbons were a precursor of PAHs. Thus, PAH formation was suppress...

The Effect of using Different Bed Powder in PZT Synthesis

In this study, different bedswhich are alumina and PZT powder were used, and their effect on Pb(Zr0.52Ti0.48)O3, (PZT)based ceramics sample was investigated. The mixed powder was pressed by using a hand press at 200MPa, followed by sintering at 1150°C for 1 hour. The sintered sample was then characterized by using X-ray diffraction, Field Emission Scanning Electron Microscope, Energy Dispersive X-Ray Analysisand impedance analyzer in order to determine the phase of the element, microstructure and dielectric properties, respectively. The observed microstructure showed that when the alumina was used as the bed powder, the surface of sintered sample that was in contact with alumina powder contained flake structure which represented the alumina element. However, the sample that was sintered with PZT as a bed powder only showed the present of PZT element. From the Archimedes method, the density obtained from the sample that used PZT as bed powder is higher (8.06g/cm3) compared to the sample that used alumina bed powder (7.9g/cm3). The dielectric constant measured at 1kHz is high (2890)and the loss factor islower (0.0852) for the sample used PZT bed powder compared to the sample that used alumina bed powder shows the lower dielectric constant (2715) and high loss factor (0.875). The results showed that PZT powder as the bedpowder wasbeneficialin improvingthe dielectric properties of PZT sample.

Enhanced combustion efficiency and reduced pollutant emission in a fluidized bed combustor by using porous alumina bed materials

Experimental comparisons of polypropylene combustion in porous and nonporous alumina bed materials were conducted in a semi-pilot scale fluidized bed combustor (FBC). The results indicate that polypropylene can be effectively used as a fuel in both bed materials. The combustion efficiencies of polypropylene in porous alumina (PA) and nonporous alumina (NA) are above 99.3%, and CO concentrations in flue gas are below 343 ppm. During polypropylene combustion, no obvious flame is observed in PA, which implies the combustion temperature is low. Hence, NO formation can be suppressed. Further, PA has the capacitance effect, which can capture or absorb some combustible hydrocarbons or melted polypropylene in the micropore of PA and causes lower CO emission and high temperatures in PA. Thus, the temperature of the freeboard zone is significantly decreased in PA. In the case of NA, the temperature in the freeboard zone seems to be independent of the height. The influence of temperature on polypropylene combustion in PA is also investigated, the experimental results demonstrate that the combustion efficiency is above 99.9% when the temperature is above 750 °C.

Combustion of an oil palm residue with elevated potassium content in a fluidized-bed combustor using alternative bed materials for preventing bed agglomeration

Palm kernel shell (PKS) was burned at 45kg/s and excess air of 20–80% in a fluidized-bed combustor using alumina, dolomite, and limestone as the bed material. Temperature and gas concentrations were recorded along the reactor centerline as well as at stack. A SEM–EDS analysis was performed to investigate morphology and elemental composition of bed particles. An X-ray fluorescence method was used to determine the composition of used/reused bed materials and PM emitted from the combustor at different operating times. Excess air of 40% seems to be most appropriate for burning PKS in this combustor with an alumina bed, whereas 60% excess air is more suitable when using dolomite and limestone, as ensuring high (98.6–98.9%) combustion efficiency and acceptable CO and NO emissions. By using the selected bed materials, bed agglomeration can be prevented in this combustor. However, the bed materials exhibit substantial time-domain changes in physical and chemical properties.