Jolius Gimbun

A CFD Study on the Prediction of Cyclone Collection Efficiency

This work presents a Computational Fluid Dynamics calculation to predict and to evaluate the effects of temperature, operating pressure and inlet velocity on the collection efficiency of gas cyclones. The numerical solutions were carried out using spreadsheet and commercial CFD code FLUENT 6.0. This paper also reviews four empirical models for the prediction of cyclone collection efficiency, namely Lapple [1], Koch and Licht [2], Li and Wang [3], and Iozia and Leith [4]. All the predictions proved to be satisfactory when compared with the presented experimental data. The CFD simulations predict the cyclone cut-off size for all operating conditions with a deviation of 3.7% from the experimental data. Specifically, results obtained from the computer modelling exercise have demonstrated that CFD model is the best method of modelling the cyclones collection efficiency.

A Study of Particle Histories during Spray Drying Using Computational Fluid Dynamic Simulations

Computational fluid dynamics (CFD) models for short-form and tall-form spray dryers have been developed, assuming constant rate drying and including particle tracking using the source-in-cell method. The predictions from these models have been validated against published experimental data and other simulations. This study differs from previous work in that particle time histories for velocity, temperature, and residence time and their impact positions on walls during spray drying have been extracted from the simulations. Due to wet-bulb protection effects, particle temperatures are often substantially different from gas temperatures, which is important, because the particle temperature–time history has the most direct impact on product quality. The CFD simulation of an existing tall-form spray dryer indicated that more than 60% of the particles impacted on the cylindrical wall and this may adversely affect product quality, because solids may adhere to the wall for appreciable times, dry out, and lose their wet-bulb protection. The model also predicts differences between the particle primary residence time distributions (RTD) and the gas phase RTD. This study indicates that a short-form dryer with a bottom outlet is more suitable for drying of heat-sensitive products, such as proteins, due to the low amounts of recirculated gas and hence shorter residence time of the particles.

Characterization of La-promoted Ni/Al2O3 catalysts for hydrogen production from glycerol dry reforming

In the current paper, dry (CO2)-reforming of glycerol, a new reforming route, was carried out over alumina (Al2O3)-supported, non-promoted and lanthanum-promoted nickel (Ni) catalysts. Both sets of catalysts were synthesized via a wet co-impregnation procedure. Physicochemical characterization of the catalysts showed that the promoted catalyst possessed smaller metal crystallite size, hence higher metal dispersion compared to the virgin Ni/Al2O3 catalyst. This was also corroborated by the surface images captured by the FESEM analysis. From temperature-programmed calcination analysis, the derivative weight profiles revealed two peaks, which represent a water elimination peak at a temperature range of 373 to 473 K followed by nickel nitrate decomposition from 473 to 573 K. In addition, BET surface area measurements gave 85.0 m2·g−1 for the non-promoted Ni catalyst, whilst the promoted catalysts showed an average of 1% to 6% improvement depending on the La loadings. Significantly, reaction studies at 873 K showed that glycerol dry reforming successfully produced H2. The 2%La-Ni/Al2O3 catalyst, which possessed the largest BET surface area, gave an optimum H2 generation (9.70%) at a glycerol conversion of 24.5%.

CO2 reforming of glycerol over La-Ni/Al2O3 catalyst: A longevity evaluative study

This paper reports on the longevity of glycerol-dry (CO2) reforming over the lanthanum (La) promoted Ni/Al2O3 catalysts. The XRD results showed that the Ni particle was well-dispersed in the presence of La promoter. In addition, via the NH3-TPD analysis, it was found that the La promoter has reduced the acidity of Ni catalyst which may have explained the mitigation of carbon laydown. It was determined that the 3.0 wt% La-promoted Ni/Al2O3 catalyst possessed the largest BET specific surface area of 97 m2·g−1. Consequently, it yielded the best catalytic longevity performance with conversion attained more than 90%, even after 72 h of reaction duration. Significantly, it can be confirmed that the presence of CO2 during the glycerol dry reforming was essential in reducing carbon deposition, most likely via gasification pathway. This has ensured a stability of catalytic activity for a long reaction period (72 h).

Application of Computational Fluid Dynamics (CFD) Simulations to Spray-Freezing Operations

A 3D computational fluid dynamics (CFD) simulation for spray-freezing in a cold gas has been developed and used to identify design improvements. This model includes an approximate method to model the latent heat of fusion and is able to track particle trajectories. The simulation predictions agreed reasonably well with experimentally measured gas temperatures and droplet velocities. The results suggest that a hollow-cone spray is more effective in cooling the particles uniformly. The CFD simulation suggested that buildup of an icy layer on the cone walls observed experimentally was due to incomplete freezing of larger particles (>100 µm). Collection efficiencies could be raised (from 20 to 57%) by increasing the diameter of the chamber outlet.

Catalytic Performance of Cement Clinker Supported Nickel Catalyst in Glycerol Dry Reforming

The paper reports the development of cement clinker-supported nickel (with metal loadings of 5 wt%, 10 wt%, 15 wt% and 20 wt%) catalysts for glycerol dry (CO2) reforming reaction. XRF results showed that CaO constituted 62.0% of cement clinker. The physicochemical characterization of the catalysts revealed 32-folds increment of BET surface area (SBET) with the addition of nickel metal into the cement clinker, which was also corroborated by FESEM images. Significantly, XRD results suggested different types of Ni oxides formation with Ni loading, whilst Ca3SiO5 and Ca2Al0.67Mn0.33FeO5 were the main crystallite species for pure cement clinker. Temperature-programmed reduction analysis yielded three domains of H2 reduction peaks, viz. centered at approximately 750 K referred to as type-I peaks, another peaks at 820 K denoted as type-II peaks and the highest reduction peaks, type-III recorded at above 1000 K. 20 wt% Ni was found to be the best loading with the highest XG and H2 yield, whilst the lowest methanation activity. Syngas with lower H2/CO ratios (0.6 to 1.5) were readily produced from glycerol dry reforming at CO2-to-Glycerol feed ratio (COR) of unity. Nonetheless, carbon deposit comprised of whisker type (Cv) and graphitic-like type (Cc) species were found to be in majority on 20 wt%Ni/CC catalysts.

Comment on: “Performance of Different Analytical Methods in Evaluating Grade Efficiency of Centrifugal Separators” by Ray M.B., Hoffmann A.C. and Postma R.S. (2000): J. Aerosol Sci., 31(5), pp. 563–581

Recently Ray, Hoffmann, and Postma (2000) have performed detailed experimental studies on a Stairmand high-efficiency cyclone, with a diameter of Full-size image (<1 K) and height of Full-size image (<1 K). The test dust was chalked (Snowcalk 40 from Blue Circle Industries) with a particle density of approximately Full-size image (<1 K) and a size range of 0.3–Full-size image (<1 K). The test dust was charged to the cyclone through a sandblasting nozzle with an air supply to the nozzle at an overpressure of Full-size image (<1 K). The inlet velocity was Full-size image (<1 K) and the dust load was Full-size image (<1 K) air, respectively. They evaluated a few analytical models, namely Barth (1956), Dietz (1981), Mothes and Loffler (1985), Leith and Licht corrected by Clift, Ghadiri, and Hoffman (1991) and Barth modified by Dirgo and Leith (1985). All these models were able to simulate correctly the trend of Rays experimental data. However, the quantitative agreement is not satisfactory.

Three-way coupling simulation of a gas-liquid stirred tank using a multi-compartment population balance model

Abstract Modelling of gas-liquid stirred tanks is very challenging due to the presence of strong bubble-liquid interactions. Depending upon the needs and desired accuracy, the simulation may be performed by considering one-way, two-way, three-way or four-way coupling between the primary and secondary phase. Accuracy of the prediction on the two-phase flow generally increases as the details of phase interactions increase but at the expense of higher computational cost. This study deals with two-way and three-way coupling of gas-liquid flow in stirred tanks which were then compared with results via four-way coupling. Population balance model (PBM) based on quadrature method of moments (QMOM) was implemented in a multi-compartment model of an aerated stirred tank to predict local bubble size. The multi-compartment model is regarded as three-way coupling because the local turbulent dissipation rates and flow rates were obtained from a two-way computational fluid dynamics (CFD) simulation. The predicted two-phase flows and local bubble size showed good agreement with experimental data.

Successive optimisation of waste cooking oil transesterification in a continuous microwave assisted reactor

This paper presents an optimization study of waste cooking oil (WCO) transesterification in a continuous microwave assisted reactor (CMAR). The custom-built CMAR employed an integrated proportional-integral-derivative controller for accurate control of temperature and reactant flowrate. The fatty acid methyl ester contents in the sample were determined using gas chromatography mass spectrometry (GC-MS). The results from two-level factorial design showed that the methanol to oil molar ratio, amount of NaOCH3 catalyst and reaction time influenced markedly the biodiesel conversion, with the significance of 45.99%, 6.76% and 3.21%, respectively. Further analysis using a successive optimization method generated by the Box–Behnken design predicted an optimum biodiesel conversion of circa 97.13% at 0.68 wt% of catalyst loading, 11.62 : 1 of methanol to oil molar ratio and 4.47 min of reaction time. Experimental validation of the optimum conditions showed an excellent agreement, with a minimum deviation of 0.18% from three replicates. The biodiesel produced in this work also met the specification of ASTM D6751.

Optimization of Ultrasonic-Assisted Extraction of Polyphenolic and Flavonoids from Labisia pumila

This work presents an optimization study of polyphenol extraction from L. pumila with aid of sonication. The polyphenol content was evaluated using Singleton’s method and aluminium chloride colorimetric assay. The two level factorial design [2LF] was used to screen the significance of the extraction parameters. The results proposed that the polyphenols extraction are mainly affected by the total solid ratio [TSR] and residence time. The highest flavonoid content of 31.79 mg QE/ g DW and phenolic content of 19.65 mg GA/g DW was obtained from 80% and 10% aqueous ethanol [EtOH], respectively via 2LF design. Three most important parameters [TSR, residence time and amplitude] were then further optimized thru central composite design. The highest simultaneous flavonoid [21.77 mg QE/ g DW] and phenolic [21.86 mg GA/g DW] extraction yield were attained from the probe sonicator extraction with desirability of 0.998 at 10% aqueous EtOH with TSR 0.01, residence time of 13 min and amplitude of 55%.