Alfred A. Susu

Liquid pipeline leak detection system: model development and numerical simulation

Abstract A new model to detect leaks optimally in liquid pipelines is presented. The model uses the concept based on the Liapunov stability criteria to evolve a criterion for pipeline leak detection. A flow model was derived for a typical pipeline flow system, and the inclusion of leak factor kL in the flow model gives an indication of the relative degree of deviation from equilibrium or no leak situation. The numerical solution by the implicit finite difference scheme was used to solve the transient second-order partial differential equations describing the flow process. A set of parametric velocity and pressure profiles were generated and validated using industry data. A stability matrix, useful for determining the eigenvalues (λ’s), evolves from the deviation model of velocity and pressure. A leak is detected whenever any of the eigenvalues is less than −1, whereas a surge in the pipeline is detected whenever any of the eigenvalues is greater than 1. The simulation profiles of eigenvalues of a crude oil transporting pipeline segment, of a pipeline network of an operating oil company in the Niger Delta region of Nigeria, show that pressure deviations are more sensitive parameter for leak detection than volume deviations. Volume deviations appear to be good indicators for larger leak systems. Single leak situation as well as double leak situations in a pipeline system were analyzed and discussed.

Mathematical modelling of fixed bed adsorption of aromatics and sulphur compounds in kerosene deodorisation

Abstract A mathematical model that adequately predicts the effluent concentration and breakthrough profiles of aromatic and sulphur compounds in kerosene deodorisation has been developed. The contributions of radial transport (pore and surface diffusion) were incorporated in the mathematical formulations. Thus, the final model took into account the overall effect of both the solid and liquid phase mass transfer resistances. The resulting model expressions were coupled partial differential equations which were resolved into first order ordinary differential equations using the orthogonal collocation technique. The roots of the Jacobi orthogonal polynomials (PNα,β) with N=8 and α=β=0 were taken as the interior collocation points while the exterior points were ζ=1, z=0 and z=1. The fourth-order Runge Kutta method was then used to integrate the 4N differential equations and the resulting functions were solved simultaneously to obtain the effluent and breakthrough profiles. Theoretical predictions from the model were compared with column adsorption data to ascertain the authenticity of the model. The agreement was good for both cases of aromatics and sulphur breakthroughs. The experimental breakthrough time of 8 h was predicted by the model. The breakthrough profiles also confirmed the formation of multiple adsorption layers.

Platinum—rhenium/alumina catalyst III. Mechanism of C6-ring hydrogenation/dehydrogenation reactions

Abstract Results of the hydrogenation/dehydrogenation reactions of cyclohexane, cyclohexene and benzene in hydrogen carrier at 4 atm and temperatures between 47 and 375°C in continuous flow experiments are presented. The orders of reaction were 0.9, 0 and 0 for cyclohexane dehydrogenation to benzene, cyclohexene hydrogenation to cyclohexane and benzene hydrogenation to cyclohexane, respectively. Activation energies for these three reactions are 24 kcal/mol, 100 kJ/mol (315–375°C), 6 kcal/mol, 25 kJ/mol (47–203°C) and 8 kcal/mol, 33 kJ/mol (107–203°C), respectively. Rate equations were developed using the dehydrogenation model of Ruiz-Viscaya et al. (J. Catal., 51 (1978) 108) modified for hydrogenation/dehydrogenation reactions of the three C 6 -ring hydrocarbons, and their validity with respect to the experimental data is discussed.

Nickel-catalyzed hydrogenation of soybean oil: I. Kinetic, equilibrium and mass transfer determinations

The kinetic and equilibrium constants were determined for the hydrogenation of soybean oil on a commercial nickel catalyst in a 300-ml Parr batch reactor. These constants were used to calculate the hydrogen gas absorption coefficients by coupling mass transfer with reaction rate based on a Langmuir Hinshelwood model. The activation energy for the rate-determining step was 23 kcal/g mol whereas the adsorption energy for hydrogen was −12.5 kcal/g mol. The gas absorption coefficients varied between 0.3 to 0.7 min−1 as the temperature ranged between 140–180 C.

Kinetics, mass transfer and scale-up in nickel-catalyzed oil hydrogenators

Abstract The kinetics of the hydrogenation of refined groundnut oil are described by a Langmuir-Hinshelwood model. The activation energy of the rate determining step was found to be 24 kcal mol −1 and the heat of adsorption for hydrogen on a commercial nickel catalyst was found to be 32 kcal mol −1 . These constants (kinetic and thermodynamic) were then utilized in calculating the gas bubble mass transfer coefficients for hydrogenation runs carried out under mass transfer using a general expression relating mass transfer to chemical reaction. The calculated mass transfer coefficients were correlated with P/V, the power input by the impeller per unit volume. The following correlation was found good for the two reactor scales (0.31 and 3.81) used in this investioation: k b a b = 0.027 (P/V) 0.34 min −1 .

Adsorption and Desorption Kinetics of Naphthalene, Anthracene, and Pyrene in Soil Matrix

Abstract The adsorption and desorption kinetics of naphthalene, anthracene, and pyrene in a soil slurry reactor at ambient conditions have been investigated to ascertain the mechanisms controlling the retention and release rates of these compounds in the soil matrix. A stirred-flow method was employed to perform the experiments. The extent of partitioning for the polycyclic aromatic hydrocarbons (PAHs) tested was found to be dependent on their solubility and diffusivity in the aqueous phase. Apparent adsorption and desorption rate coefficients were determined using the Langmuir and Freundlich isotherm models. Equilibrium adsorption and desorption at the external surface and in the internal pore of the soil particle obeyed the Freundlich isotherm equation. The pseudo-equilibrium condition established at the minimum contact time suggests that equilibrium adsorption attained for the contaminant PAHs was not instantaneous but rather time dependent.

Ethylbenzene isomerization on bifunctional platinum/alumina product yields and pseudo mass action kinetics

Abstract Ethylbenzene isomerization on bifunctional Pt/Al 2 O 3 catalyst was investigated in the gas phase using a micro-catalytic reactor. Product yields were determined as functions of temperature for ethylbenzene, o-, m-, and p-xylene in the temperature range 513 – 673 K and 181.8 kPa. At temperatures ≦ 553 K, p-xylene was the sole product of the isomerization reaction. o-Xylene became significant from 563 K and went through a maximum at 539 K where p-xylene went through a maximum: m-xylene was produced at the higher temperatures. The Wei-Prater method was used in the calculation of absolute rate constants for the twelve single reactions of the network. Estimated activation energies appear to account for the high yield of ortho from meta-xylene.

Gas Condensate Reservoir Modeling, Part I: From Deterministics To Stochastics

Abstract For gas condensates, black oil models and at best modified black oil models are limited and inadequate due to their deterministic nature. Gas condensate models, which will match the required adequacy and serve in the development of techniques that can ensure optimal recovery, need to be stochastic in nature. In the near future, this will become increasingly important as gas gradually becomes more prominent in the worlds petroleum energy generation platform.

Mechanistic Kinetic Models for n-Heptane Reforming on Platinum/Alumina Catalyst

Abstract The kinetics of the reforming of n-heptane on a platinum/alumina catalyst has been studied in a pulse microcatalytic reactor at a total pressure of 391.8 kPa over a relatively wide temperature range of 420°C–500°C. The differential and integral methods were used for the kinetic analyses of the reforming reaction. Twenty-nine reaction rate equations of the Langmuir-Hinselwood-Hougen-Watson type, based on molecular and atomic adsorption of hydrogen, were developed. Parameter estimates for the n-heptane reforming reactions were obtained by application of the Nelder-Mead simplex optimization technique to the predicted and observed conversion/production rates of the reaction components. Discrimination among rival kinetic models was based upon physicochemical criteria, analysis of the residuals, and statistical and thermodynamic tests. The rate-determining step was found to be the surface reaction of adsorbed iso-heptane to adsorbed methylcyclohexane with dissociative adsorption of hydrogen on the catalyst surface during dehydrocyclization of iso-heptane to methylcyclohexane. Hence, the surface reaction on the metallic function is rate-determining for the n-heptane reforming on the Pt/Al2O3 catalyst.

High temperature thermal stability investigation of paraffinic oil

Abstract The physical and thermal properties of paraffinic oil were investigated at 250–360°C to determine its suitability for use as a heat-transfer fluid. Thermal stability test was conducted at 360°C for a period of 480 hr in a stainless steel high-pressure autoclave. The paraffinic oil offered sufficient thermal stability for a period of about 300 hr and then became unstable resulting in thermal break down or cracking of the oil. Degradation of the oil led to the formation of gases, liquid components, and solid coke of about 5 wt.% of the starting material. The distillation test performed on the liquid components showed that the composition varied from light naphtha to heavy bituminous material. The paraffinic oil compared favorably with synthetic organic fluids and the typical properties revealed its suitability as a heating fluid in a system with maximum usage temperature of 310°C as indicated by the thermal stability test. Comparative evaluation of the general properties of the tested paraffinic oil with other paraffinic and mineral oils of different product formulations showed excellent agreement. From these results, it is concluded that the paraffin oil sample produced by the local refinery is suitable for use as a potential thermal fluid at temperatures below 315°C, which is quite adequate for many industrial applications.