Effect of precursor, ambient pressure, and temperature on the morphology, crystallinity, and decomposition of powders prepared by spray pyrolysis and drying

The effect of reactor pressure and temperature on the morphology, crystallinity, and decomposition behavior of various powders produced by spray pyrolysis or drying is investigated. Zirconia, magnesium sulphate, and sodium chloride powders are produced at the reactor pressures of 760, 400, 250, and 120 Torr, and at the reactor temperatures of 100 °C, 200 °C, and 400 °C. Zirconia and magnesium sulphate powders are spherical, whereas the sodium chloride powders are cubic. Regardless of the pressure, the powders produced at 100 °C and 200 °C appear solid, and powders produced at 400 °C are hollow and disrupted. The experimental data and the calculations indicate that the evaporation rate, which is a function of pressure and temperature, controls the solute distribution within the droplet and as such determines the morphology of the powders. In addition, the shape and morphology of the powders are strong functions of the precursor type. The decomposition and crystallinity of the powders are determined using XEDS and XRD analyses, respectively. The crystallinity and decomposition of the powders are weak functions of pressure and strong functions of temperature.     

Effect of temperature and type of sand on the magnesium sulphate attack in sulphate resisting Portland cement mortars

External Sulphate Attack on sulphate-resisting Portland cement concretes is a well-researched field. However, the effect of temperature on the performance of sulphate attack requires further attention. For this purpose, cubic mortars were made with sulphate resisting Portland cement (low C₃A) and two types of sand, silica and limestone, which were then immersed in a 5% MgSO₄ solution at different temperatures: 5, 20 and 50 °C, for 24 months. The deterioration of mortars due to magnesium sulphate attack was evaluated by measuring changes in mass, compressive strength, porosity and sorptivity. The X-ray diffraction was also used to determine the different mineral phases, and the pH of the conservation solutions was monitored. No damage was observed on the samples exposed at 50 °C. However, serious damage was noted on mortars made with silica sand exposed at 5 °C. Results show that high temperature improved some physical and mechanical properties and do not necessarily accelerate the degradation due to magnesium sulphate attack. Sulphate-resisting Portland cements with limited C₃A content was found to be susceptible to Thaumasite Sulphate Attack. The type of sand has a remarkable effect on the performance of mortars at low temperature compared to high temperature. The samples with limestone sand showed better resistance against magnesium sulphate attacks.     

Soda Ash Production from Trona in a Spray Dryer

Production of soda ash from Trona solution was achieved in a spray dryer reactor. Fractional conversion of NaHCO₃ reached to values close to unity in this unit within a residence time of less than a second. Results indicated that above 140°C, heat transfer limitations played a significant role on the calcination process taking place in the spray dryer. Equilibrium limitations may become important only at very low temperatures and at high CO₂ and H₂O partial pressures. Results obtained in the spray dryer and from the thermal gravimetric analysis of Trona crystals agreed well. It was also shown that the predictions of the unreacted core model are in good agreement with the kinetic data. © 1997 SCI.     

Analysis of the Solid Combustion Products of a Mg‐Based Fuel‐Rich Propellant used for Water Ramjet Engines

A high‐pressure combustor and a metal/steam reactor were used to simulate the two‐stage combustion of a fuel‐rich propellant used for water ramjet engines. The solid combustion products from the two stages were collected and characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD). In addition, the thermal properties of the solid products of the primary combustion were characterized by differential thermal analysis (DTA) and simultaneous thermogravimetry (TG). The burning rates at different pressures were measured and the secondary combustion process in hot steam was monitored by high‐speed cinematography. The results showed that the propellant has a good combustion performance and a high burning rate. After primary combustion, the solid product mainly contained magnesium, magnesia, magnesium chloride, and carbon. During the secondary combustion, the ignition temperature was approximately 720 °C, and two burning stages were observed. The rest of magnesium hasn’t completely reacted with hot steam until the temperature reached a value higher than 800 °C for 30 min.     

Survival,oxidative stability,and surface characteristics of spray dried co-microcapsules containing omega-3 fatty acids and probiotic bacteria

The objective of the study was to determine optimum inlet and outlet air temperatures of spray process for producing co-microcapsules containing omega-3 rich tuna oil and probiotic bacteria L. casei. These co-microcapsules were produced using whey protein isolate and gum Arabic complex coacervates as shell materials. Improved bacterial viability and oxidative stability of omega-3 oil were used as two main criteria of this study. Three sets of inlet (130°C, 150°C, and 170°C) and outlet (55°C, 65°C, and 75°C) air temperatures were used in nine combinations to produce powdered co-microcapsule. The viability of L. casei, oxidative stability of omega-3 oil, surface oil, oil microencapsulation efficiency, moisture content, surface elemental composition and morphology of the powdered samples were measured. There is no statistical difference in oxidative stability at two lower inlet air temperatures (130°C and 150°C). However, there was a significant decrease in oxidative stability when higher inlet temperature (170°C) was used. The viability of L. casei decreased with the increase in the inlet and outlet air temperatures. There was no difference in the surface elemental compositions and surface morphology of powdered co-microcapsules produced under these nine inlet/outlet temperature combinations. Of the range of conditions tested the co-microcapsules produced at inlet-outlet temperature 130–65°C showed the highest bacterial viability and oxidative stability of omega-3 and having the moisture content of 4.93?±?0.05% (w/w). This research shows that powdered co-microcapsules of probiotic bacteria and omega-3 fatty acids with high survival of the former and high stability against oxidation can be produced through spray drying.     

Kinetics of the calcination of calcium sulphate dihydrate

The kinetics of calcination of calcium sulphate dihydrate were studied at 100° at air pressures from 760 to less than 10^?5 mm Hg. Any reduction in air pressure below atmospheric caused an increase in reaction rate. Water vapour removal initially facilitated the dehydration at higher pressures, but began to impede the reaction at low pressures.     

Pro-oxidative effects of spray drying orange oil in a bench top dryer

The influence of potential heat exposure during spray drying on the oxidative stability of spray dried orange oil was studied. The design of some of the table top spray driers expose dried product to dryer exit air temperatures in the powder collection chamber or on the walls of the dryer if there is an accumulation of material on the drying chamber walls. This heat exposure may accelerate oxidation of the product in subsequent storage. To determine the potential for heat damage to affect oxidation of the powders produced, an orange oil infeed emulsion (carrier material - modified starch) was prepared and spray dried using the sample collection chamber supplied by the manufacturer as standard equipment. The spray dryer was then modified to extend the collection chamber inlet such that the product remained cooler than in the standard collection chamber. In this study, the spray dryer was operated for 1?h (inlet air temperature; 180°C and an exit air temperature; 100°C). Thus, the spray dry product could have been exposed to as much as 1?h of heating in the collection chamber (potentially at temperatures as high as the exit air temperature). In the case of spray drying with a collection chamber extension, the collected product was maintained at ca. room temperature. This would approximately mimic the heat exposure powders receive in an industrial spray dryer. Powders produced using both equipment designs were taken from both the collection and drying chambers, adjusted in water activity (0.33) under a nitrogen environment, and then put into storage in an incubator maintained at 35°C for 4 weeks (exposed to air). The ratio of limonene oxide to limonene was used to monitor oxidation using gas chromatography. This study showed a substantial increase in rate of oxidation of the spray dried powder from the table top spray dryer with the standard commercial collection chamber and much less in case of an extended collection chamber. The powder from the respective drying chamber also showed a higher rate of oxidation in comparison to its collection chamber. Thus, we urge researchers studying heat damage (e.g., oxidation) of powders produced on the table top dryers to be conscious of overestimating heat damage during drying.     

Effects of hydrogen pressure on hydrogasification of Taiheiyo (Japan) coal

The non-isothermal hydrogasification of Taiheiyo coal is studied at hydrogen pressures up to 5 MPa and temperatures of 900 °C using a high-pressure thermobalance and tubular reactor. Gaseous products are analysed and liquid products obtained from the mass balance. Rates of formation of methane increased with temperature to two maxima, at 550 °C and at 750 °C. Corrections to rate are necessary because of appreciable weight losses. In the temperature range 650–800 °C the activation energy of methane formation is ≈ 115 kJ mol^?1. Below 55 °C, the pressure dependence of reaction is 0.3, becoming first order at higher temperatures. Rates of formation of methane and ethane indicate a similar mechanism of formation. Rates of formation of liquid hydrocarbons maximize at ≈ 450 °C and increase with hydrogen pressure.     

Physical and chemical properties of powder produced from spray drying of inulin component extracted from Jerusalem artichoke tuber powder

In this study, inulin was extracted from Jerusalem artichoke tuber (JAT) powder and then concentrated before spray drying. The aims of this study were to (1) determine the drying condition that provided high powder yield together with superior qualities of JAT inulin powder and (2) investigate the chemical and physical properties of inulin powder. The inulin extracts at different concentrations of 10, 20, and 30 °Brix were spray-dried and then compared. The spray drying experiments were conducted at the inlet/outlet air temperatures of 150/90, 170/90, and 190/90?°C for the chosen concentration of inulin extract. It appeared that spray drying of the 30 °Brix extract at the inlet/outlet drying air temperatures of 190/90?°C resulted in the highest value of powder recovery, bulk density, water solubility and the lowest moisture content and hygroscopicity in comparison with its counterparts. SEM micrographs showed that the powder produced by this condition was more stable and less sticky than others. The sugars, total fructo-oligosaccharides (1-kestose, nystose, and 1^F-β-fructofuranosyl nystose) and inulin-type fructans contents of powder were 12.88, 11.12, and 64.36?g/100?g of powder, respectively. The moisture sorption data and models developed in this work could be used for determining the suitable condition of surrounding air for inulin powder storage.     

倾斜喷射时喷雾冷却无沸腾区换热特性

采用雾化角60°的半实心旋流式机械雾化喷嘴,以水为冷却介质,对流量4.44～7.05 L•h^-1,倾斜角在0°～49°之间变化时无沸腾区换热进行实验研究,并且给出了反映喷雾换热特性的量纲1换热准则公式。结果表明,倾斜角固定不变时,当喷射底面椭圆长轴与换热面相切时所对应的喷嘴高度为最佳高度,换热效果最好,冷却效率最高,其次分别是喷射底面椭圆长轴和换热面内接、外接的情况;对比不同倾斜角度、最佳高度下的换热,发现倾斜角度越大换热效果越佳,冷却效率越好。     

Droplet size distribution and evaporation characteristics of fuel spray by a swirl type atomizer

Spray atomization and evaporation play extremely important roles in mixture formation and combustion processes of direct injection (DI) gasoline engines. In this study, the fundamental characteristics of a swirl spray injected into a constant volume vessel are investigated by means of several laser diagnostic techniques including the laser diffraction-based method for droplet size distribution, the laser induced fluorescence-particle image velocimetry for velocity distributions of droplets and spray-induced ambient air flow, and the two-wavelength laser absorption-scattering technique for concentration distributions of liquid and vapor phases in the spray. The results show that the droplets at outer zone of the spray exhibit larger diameter than those at inner zone under both ambient pressures 0.1 and 0.4 MPa. While this can be partially attributed to the effect of spray-induced ambient air flow, the strength of ambient air flow become small when increasing the ambient pressure from 0.1 to 0.4 MPa, indicating the strong influence of spray dynamics on the droplet size distribution. In the evaporating spray, there are higher vapor concentrations near the spray axis than at peripheral zones. At 4.0 ms after start of injection, spray droplets almost completely evaporate under ambient temperature 500 K and pressure 1.0 MPa, but there are significantly amount of fuels with equivalence ratio below 0.5 in the spray. Reduction in ambient pressure promotes the air entrainment and droplet evaporation, but lowered ambient pressure results in more fuel vapor of equivalence ratio above 1.3 along the spray axis.     

The Effect of Dryer Inlet and Outlet Air Temperatures and Protectant Solids on the Survival of Lactococcus lactis during Spray Drying

The influence of spray-drying conditions, inlet air temperature (130°C to 200°C), outlet air temperature (38°C to 65°C), drying medium (air and nitrogen) and milk-derived protectants (10%, 15%, and 25% lactose; 5% and 10% sodium caseinate; 10%, 25%, and 35% lactose:sodium caseinate (Lac:NaCas, 3:1)) on the survival of Lactococcus lactis ssp. cremoris was studied using a laboratory-scale spray dryer. An inlet air temperature of 130°C and 65°C as the outlet air temperature maintained high survival of the bacteria without sacrificing low moisture content. Inlet air temperature, previously considered to have no significant effect, was shown to play an important role in the survival of bacteria during spray drying. A mixture of Lac:NaCas (3:1) showed a better protective effect on the survival of bacteria than lactose and sodium caseinate individually, and this effect increased with increasing amount of protectant. The results were generalized by substituting whey protein isolate for sodium caseinate. Finally, the positive effect of elimination of oxygen was demonstrated both by replacing air with nitrogen and adding ascorbic acid as an oxygen scavenger to improve survival of the bacteria. Adding an oxygen scavenger would be a better candidate for industrial application considering the potential high cost of manufacturing if nitrogen was used as the atomization and/or drying medium.     

PROTOTYPE HIGH TEMPERATURE/HIGH PRESSURE KILN FOR THE EVALUATION OF WOOD DRYING SCHEDULES

ABSTRACT

A new laboratory kiln was developed and built to perform over a very wide range of drying conditions. For example, the dry bulb temperature can vary from 30°C to 150°C and the dew point can be adjusted between 20°C and 130°C. Obviously, with such a high level of dew point, pressures over atmospheric pressure may be induced inside the chamber. For this reason, the kiln has been designed to withstand pressure of up to 3 bars. This kiln can also perform vacuum drying.

A programmable controller allows the temperature levels to be maintained within ± 0.2°C. Because the whole kiln can be heated only through the agitated water present at the bottom of the kiln, the load temperature can be increased up to 130°C in saturated conditions, without any change of moisture content.

The kiln has various sensors attached and is capable of withstanding severe conditions (high temperature, saturated vapour and elevated pressures). At present, air and water temperatures as well as temperature at different locations within the board can be collected during the drying process. A load cell and pressure gauges are also available. The first tests performed using this equipment are presented at the end of the paper.     

Energy requirements and production cost of the spray drying process of cheese whey

The influence of spray drying conditions on the energy required, production cost, and physicochemical characteristics of cheese whey was researched. The factors investigated were the inlet air temperature (180–220°C), outlet air temperature (80–100°C), and silica and maltodextrin (DE-10) as additives at 2 and 5% (w/w), respectively. Analysis of variance revealed that the inlet and outlet air temperatures, and the addition of additives had significant effects (p?T_inlet of 180°C, T_outlet of 80°C, and the addition of 5% additive material. Under these conditions, 0.2165?kg/h of dried product was obtained, with a moisture content of 2.08% and water activity of 0.125, and the product cost was $17.06?kg with an energy consumption of 2.0490?kW?·?h/kg of dry product.     

Spray-combustion synthesis of indium tin oxide nanopowder

Nanocrystalline indium tin oxide (ITO) powders were prepared by a novel spray combustion method. Using single-drop study equipment, we studied the thermodynamics of the combustion reaction. The reaction can be ignited at air temperature as lower as 171.3°C when using urea and glucose as composite fuel. Once the reaction is ignited, the combustion temperature can surge to above 500°C, generating nanocrystalline ITO powders with grain size about 40 nm. Footages from high-speed camera demonstrated that the reaction is in three-step: moderate beginning, violent middle, and decaying end. It is also noticed that the ignition is very sensitive to the air temperature, even 0.2°C minus deviation may fail the combustion. The combustion reaction is self-sustainable, which saves the energy supply. And the low ignition temperature means the combustion reaction can be carried out in a conventional spray dryer. Our results provide a feasible way to mass production of nanocrystalline ITO powders, which as a methodology, may be extended to the production of other oxide nanopowders.     

Numerical Simulation of the Two‐Phase Fluid Field in a Gas‐Around‐Liquid Spray Nozzle

A new gas‐around‐liquid spray nozzle (GLSN) was designed, and the two‐phase flow fluid field in this nozzle was simulated numerically. Flow characteristics under different structural parameters were obtained by changing the L/D ratio of the premixing chamber, incident angle, and inlet pressures. Increasing the L/D ratio and incident angle improved flow characteristics such as atomization flow, outlet velocity, and turbulence intensity. The nozzle performed optimally at an L/D ratio of 0.5 and incident angle of 60°. The atomization flow decreased with higher gas pressure and increased with higher liquid pressure. The outlet velocity mainly depended on the inlet gas pressure, not on the inlet liquid pressure. These results provide an indication for optimum structures and parameters of the GLSN.     

Microstructural evaluation and thermal oxidation behaviors of YSZ/NiCoCrAlYTa coatings deposited by different thermal techniques

In this paper, two coating techniques, the high velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques, were used to deposit a bond coat of NiCoCrAlYTa on the Inconel 625 substrate, followed by applying a topcoat of yttria-stabilized zirconia (YSZ). The samples were preoxidized in an argon-controlled furnace at a temperature of 1000 °C for 12 and 24 h to characterize the microstructure of a thermally grown oxide (TGO) using the two coating techniques. The most suitable preoxidized samples were further tested for isothermal oxidation at 1000 °C for up to 120 h, and a hot corrosion test was performed at 1000 °C for up to 52 h or until spalling occurred. As-sprayed and oxidized samples prepared with different coating techniques were evaluated in terms of their microstructure using different characterization methods, such as field emission scanning electron microscopy (FESEM), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) equipped with energy dispersive X-ray and X-ray diffraction (XRD) analyses. In addition, the mechanical properties of these samples were evaluated using adhesion tests. The results show that the YSZ/NiCoCrAlYTa coating applied with the HVOF technique forms a more thin and continuous layer of TGO than that obtained when applying a YSZ/NiCoCrAlYTa coating using the APS technique, indicating that a severe brittle oxidation interface exists between the two layers. The results also indicate that the mechanical strength obtained from the adhesion test of the coated samples is observably affected by the oxidation behaviors obtained with the different deposition techniques chosen.     

Catalytic activity of coal minerals in hydrogasification of coal

Hydrogasification of six bituminous coals was studied in a fixed-ped flow reactor at pressures up to 2 MPa and temperatures from 790 to 960 °C. Ranges of distinct methane formation are found with all coals between 500 and 600 °C, 750 to 800 °C and >850 °C. The reactions in the first two ranges are determined by the molecular structure of coal and are not affected by catalytic activities of constituents of coal minerals. In the third range, >850 °C, iron as a constituent of mineral matter of coal can accelerate methane formation significantly if the pressure is sufficiently high. Thermodynamic calculations indicate, and were verified by thermogravimetric studies, that iron disulphides in original coals can be desulphurized during gasification. Alkali and alkali earth oxides and carbonates can act as sulphur scavengers via an exchange reaction and thus accelerate the desulphurization of iron sulphides.     

Wet air oxidation of soluble components in waste water

Wet Air Oxidation (WAO) can be used to remove combustible materials from wastewater. This process takes place in the liquid phase at 200 to 300°C and up to 2500 psi (17.3 MPa) with air present. In this work, the WAO of phenol, which is soluble and volatile, and nitrilotriacetic acid (NTA) which is soluble and non-volatile were studied. The process was carried out on a continuous basis in an unmixed 1 liter, bubbling reactor with conditions up to 250°C and 2200 psi (15.3 MPa) and liquid residence times from 15 minutes to two hours. A model which describes the effect of pressure, temperature and liquid residence time on the reaction was developed and used to compare the results for phenol and NTA oxidations.     

Process technology for recovery of magnesia from brines

Laboratory tests for the utilization of natural trona mineral for the recovery of magnesium from high sulphate brines, in the form of basic magnesium carbonate, were conducted at a fixed temperature of 60 °C. The role of the precipitation pH on the chemical constitution of the precipitated magnesium was investigated. The prepared precipitates were examined by X-ray, DTA, chemical analysis, loss on ignition at 1000 °C and spectrographic analysis of the minor impurities which may influence the refractory properties of the magnesia produced. When the basic magnesium carbonate, obtained under optimum conditions of pH = 10 and at a temperature of 60 °C, was calcined at 1100 °C pure magnesium oxide assaying 99.4% MgO was obtained.