Abdullah A. Shaikh

DEVELOPMENT EXPERIMENTAL VALIDATION AND DYNAMIC ANALYSIS OF A GENERAL TRANSIENT BIOFILTER MODEL

In this study, a general transient biofiltration model, which incorporates general mixing phenomena, oxygen limitation effects, adsorption phenomena and general biodegradation reaction kinetics, is developed. Solutions are presented with and without the assumption of pseudo-steady state for the biofilm leading to approximate and general models, respectively. Solutions of the model are presented and validated with experimental transient data of benzene and toluene. Significant improvement in the model prediction is observed in comparison to earlier simplified models. However, the general model predictions seem to be better and it is superior to the approximate model as it does not require any correlations for film thickness or effectiveness factors. Dynamic analysis of the model is performed and compared with experimental data from the literature. Transient behavior during shut-down and restart-up are also well predicted by the model and the transient period does not seem to be long. Model predictions show that the biofilter is able to withstand extreme practical conditions such as random variations in the inlet concentration and gas flow rate. Theoretical analysis shows that the assumption of excess oxygen availability is not a good one, specially at high inlet concentration levels. Sensitivity studies show that mixing in the gas phase is an important phenomenon which should not be neglected and that some parameters need to be accurately estimated.

Solids suspension in stirred tanks with pitched blade turbines

Abstract In view of developing a universal correlation for critical speed of suspension, extensive suspension experiments were conducted with tank scales in the range of 15– 121 cm , D / T from 0.083 to 0.625, using four different sizes of spherical glass beads and employing Pitched Blade Turbines with four and six blades as the impellers. The periphery of the tank bottom was modified to include a permanent fillet in order to eliminate the effect of induced recirculation loop, which account for the formation of peripheral fillets of unsuspended solids. The critical speed of suspension N c and power P c were observed to vary independently both with D and T to give two correlations for each of the variables, N c and P c ; one for the close proximity impeller operation where both N c and P c remained invariant with off-bottom impeller clearance and the second for the region where N c and P c were affected significantly by the impeller position. The effects of the physical characteristics of the solids were also included in the four correlations so proposed. It was clearly noticed that the correlations were valid up to a critical value of D / T beyond which the trapped particles in the stagnant zone below the impeller needed extra energy to be raked out and suspended, thus breaking the log-linear relationship between N c (or P c ) and D / T hitherto maintained. Comparisons of the suspension speed and power have been made with open literature. More importantly, the reasons why the earlier studies differed with each other in N c -predictions have been identified.

Axial dispersion in biofilters

Abstract Biological destruction of toluene vapor from air streams was studied in a laboratory scale biofilter. The packing material (peat) used in the reactor was immobilized with acclimatized bacterial suspension. The original microbial consortium was obtained as an activated sludge suspension from a local waste water treatment plant. The use of porous packing materials in biofilters may lead to considerable mixing of the gas phase. Since the performance of a reactor greatly depends on the mixing characteristics, a detailed analysis of the residence time distribution (RTD) was performed under abiotic conditions. The RTD results show that there is a significant amount of dispersion in the biofilter. An axial dispersion model has been developed and solved numerically using dispersion numbers obtained from RTD studies along with other model parameters. The predicted concentration profiles were in very good agreement with the experimental data.

Biofiltration of volatile organic compound (VOC) mixtures under transient conditions

Abstract In this study, a transient biofilter model for binary volatile organic compound (VOC) mixture is developed. In the model, general mixing, oxygen limitation aspects, multi-component adsorption phenomena, Monod- and Andrews-type kinetics with interference between the components are considered. Multicomponent adsorption isotherms are developed and used in the solution of the model. The model has been solved by two approaches, (approximate and general) and validated with biofiltration of benzene-toluene mixture data of previous work. The approximate model is based on the quasi-steady-state approximation in the biofilm, but the general model is solved as it is without any simplifications. The results show that the predictions by the general model are closer to the actual experimental results. It was also found that inlet oxygen composition plays an important role in the biofiltration of mixed VOC removal, specially at high inlet concentrations.

KINETICS OF CATALYTIC OXIDATION OF AQUEOUS SODIUM SULFITE

A gas-lift bubble column was used to investigate the kinetics of the reaction between oxygen and aqueous solutions of sodium sulfite in the presence of cobalt sulfate catalyst. Reaction orders have been determined for the sulfite, catalyst, and oxygen under high and low oxygen partial-pressure conditions.

Introduction of the arc-length continuation technique in the chemical engineering graduate program at KFUPM

The present paper describes the arc‐length continuation method; a mathematical technique that can solve a wide variety of chemical engineering problems. Several case studies involving distillation, reaction engineering, and thermodynamics are treated with the help of this method. The approach is powerful enough to elucidate situations when several turning points occur. Finally, the authors conclude with their experience teaching this technique. Indeed, this methodology was introduced to the graduate students of the nonlinear dynamics course at King Fahd University of Petroleum & Minerals (KFUPM).

Chebyshev orthogonal collocation technique to solve transport phenomena problems with Matlab® and Mathematica

We present in this pedagogical paper an alternative numerical method for the resolution of transport phenomena problems encountered in the teaching of the required course on transport phenomena in the graduate chemical engineering curricula. Based on the Chebyshev orthogonal collocation technique implemented in Matlab® and Mathematica©, we show how different rather complicated transport phenomena problems involving partial differential equations and split boundary value problems can now readily be mastered. A description of several sample problems and the resolution methodology is discussed in this paper. The objective of the incorporation of this approach is to develop the numerical skills of the graduate students at King Fahd University of Petroleum & Minerals (KFUPM) and to broaden the extent of transport‐phenomena problems that can be addressed in the course. We noted with satisfaction that the students successfully adopted this numerical technique for the resolution of problems assigned as term projects.

A modelling analysis of non-isothermal bubble column reactors

A generalized mathematical model has been developed to simulate the non-isothermal performance of bubble column reactors. Steady-state reactor behavior is rigorously described without limitations on the extent of macro-mixing, flow configuration, absorption-reaction regime, and nature of reactive species. A parametric sensitivity analysis shows that the idealized lumped-distributed models do not offer a realistic portrait of the non-isothermal behavior of bubble column reactors. Implications on the possible occurrence of static bifurcations are discussed.

Modeling and Parametric-Sensitivity Analysis of Nonisothermal Reactive Absorption

We address the uniqueness and multiplicity of the equilibrium solutions in a specific class of chemically reactive system involving nonisothermal reactive gas absorption. A film model that is not restricted to a particular reaction regime is developed for (m,n)th-order irreversible reactions. Lower and upper bounds for the interfacial temperature rise are proposed, and tested by application to real systems, including the chlorination of n-decane, chlorination of toluene, and sulfonation of dodecylbenzene (DDB). We further develop a categorization of the possible bifurcation parameters, and propose lower and upper bounds for each of the new parameters in the generalized model. A parametric-sensitivity analysis in the kinetic- and reactor-parameter spaces is presented. It is shown that the steady-state multiplicity behavior of the system is more sensitive to the kinetic parameters, whereas a few of the new reactor parameters are of significant impact.