Habib I. Shaban

Steady-state analysis of multi-stage flash desalination process

The multi-stage flash (MSF) water desalination process plays a vital role in the provision of fresh water in many areas of the world, particularly in the Arab Gulf countries. This paper describes a steady-state mathematical model developed to analyze the MSF water desalination process. Relationships between parameters controlling the product water cost (e.g., thermal performance ratio, specific heat transfer surface area, and specific flow rate of cooling water and recirculated brine) to other operating and design variables are established. These relationships can be used to design new plants or to analyze already existing units. The model assumes the practical case of constant heat transfer surface area per stage in each section. It considered the variation of the physical properties of water with temperature and salt concentration, the effect of fouling factors and presence of non-condensable gases on the overall heat transfer coefficients, and variations in stage flash down and thermodynamic loss from stage to stage. The model also takes into consideration the heat transfer losses from the stages to the surroundings and through rejection of the noncondensable gases. The results obtained from the model developed are compared with data from six different MSF plants. Good agreement is obtained between data of these plants and model predictions.

Improving cubic equations of state for heavy reservoir fluids and critical region

Abstract It is shown that by considering the “b” parameter in a cubic equation of state (EOS) as acentric factor/temperature-dependent, liquid densities especially for heavy compounds and the region near the critical point can be estimated more accurately. The proposed equation can also be used for accurate estimation of critical compressibility factors of different compounds, Although the method is applied to Peng-Robinson equation of state (PR-EOS), it can be used for any other cubic equation of state. The proposed method is particularly useful for phase equilibrium calculations of reservoir fluids. The proposed equation requires critical temperature, critical pressure and acentric factor as the input parameters. The proposed equation of stale estimates properties of liquids, vapor-pressure and critical compressibility factors with greater accuracy for pure compounds and mixtures as well as light and heavy compounds found in reservoir fluids.

Simulation of an atmospheric residue desulfurization unit by quasi-steady state modeling

The current trend in petroleum refining is to maximize the conversion of the bottom of the barrel to improve the profitability of the refinery. Atmospheric residue desulfurization (ARDS) plays a key role in this, especially, when processing crudes with moderate to high sulfur contents. A deterministic quasi-steady state model has been developed to simulate the long term behavior of the reaction section of an atmospheric residue desulfurization (ARDS) unit, consisting of four co-current catalytic trickle bed reactors in series. The model uses the properties of the feedstock and the catalyst and is capable of simulating profiles of sulfur, coke, and metal depositions and the temperature along the reactors, taking into account also catalyst deactivation. Hydrogen quenching has also been simulated and simulation results predict all the essentials of the long term behavior of both experimental and industrial scale ARDS reactors satisfactorily. Comparing the simulation results with actual commercial data, the model predicted perfectly the middle part of the run. The model is unable to simulate the End-of-Run conditions due to pore mouth plugging phenomenon.

Experimental Investigation of the Performance of Two-Stage Evaporative Coolers

Experiments have been conducted to investigate the thermal effectiveness and the air-side pressure drop of single- and two-stage evaporative coolers. Two different configurations of the two-stage evaporative cooler have been tested. The first one uses an external cooling tower to cool the water required to precool the air in the indirect water-to-air precooler. In the second design the cooled water in the direct-contact evaporative cooler is used as the cooling medium in the air precooler. Tlie variables considered are packing thickness, mass flow rate of water to the precooler, and mass flux of water irrigating the packing. The data obtained indicate that the thermal effectiveness of the two-stage evaporative cooler with a cooling tower is high compared to that of the system without a cooling tower, which in turn is superior to that of the single-stage, direct-contact evaporative cooler. Increasing the mass flow rate of water to the air precooler improves the effectiveness of the two-stage evaporative co...

A study of foaming and carry-over problems in oil and gas separators

In oil fields, separators are used to separate oil and gas contained in the crude oil pumped from the wells before processing. Although there are many factors influencing the performance of these separators, one of the crucial problems is the formation of foam due to the impurities present in the crude. Another operating problem is carry-over, which occurs when free liquid escapes with the gas phase. Of the several methods used to control foam, chemical control by use of antifoam agents is very important. In this work, the main objective is to study the poor separation of oil and gas due to foaming and the carry-over problem in separators observed in one of the oil fields in Kuwait. Studies were also conducted on the effect of a silicone antifoam agent used to control foaming in order to increase the separation efficiency and thereby increase the production capacity.

Crude oil dissolution in saline water

The solubilities and diffusion coefficients of crude oils having API° ranging from 11 to 28 have been measured in distilled and saline water of 44 g L−1 NaCl at temperatures 25, 35, and 45 °C. A linear relationship was observed between the maximum oil solubilities in distilled water and those in saline water for all the crudes over the range of temperature studied. The Setschenow salting-out parameter was found to be 0.125 independent of temperature and API°. Such a parameter is valuable in estimating the crude oil solubilities in waters of different salinity. An analytical solution for unsteady-state diffusion was done using Fourier series. A linear relationship was found between the diffusion coefficients of oils in distilled water and those in saline water. Observed data for diffusion coefficients of the oils have been correlated in terms of API°, temperature and ionic strength with an average absolute deviation of 2%.

Decolorization by ozone of direct dyes in presence of some catalysts

Abstract Decolorization of two direct dyes by ozone in aqueous medium was studied in absence and in presence of some salts at room temperature. It was found that zinc sulfate catalyses the process of decolorization. Equations to describe the process and to allow prediction of ozone requirement were developed. The new findings of this study would have an impact on wastewater treatment techniques using ozone.

Thermal, Mechanical and Rheological Properties of Polypropylene/Poly(ethylene-co-methyl acrylate) Blends

Isotactic polypropylene (PP) has been blended with poly(ethylene-co-methyl acrylate) (EMA) (75/25 wt/wt%) in a single-screw extruder. The compatibilizing effect of polypropylene grafted with maleic anhydride (PP-g-MAH) has been examined. The nonisothermal crystallization of the developed blends has been investigated using differential scanning calorimetry (DSC) and analyzed using Avrami, Tobin and Liu models. The thermal stability of the blends was assessed through thermogravimetric analysis (TGA). The tensile and impact properties, as well as the melt viscosity, have also been determined. The presence of rubber accelerates the crystallization of PP. The thermal stabilities of the blends are intermediate between those of their constituents. Tensile strength and modulus are reduced upon incorporation of EMA into PP, but ultimate elongation and impact strength are improved. The melt viscosity variation with shear rate for all the systems was typical of shear-thinning behavior. The compatibilizing agent has a pronounced effect on enhancing the thermal and mechanical properties of the blend.

Pervaporation separation of water from organic mixtures

Preliminary work on the pervaporation separation of water from organic mixtures using a simple technique is discussed. The experiments were conducted at 75°C. The separation of water from aqueous organic mixtures was carried out using a standard poly(vinyl alcohol) (PVA) membrane. The initial feed composition was 10 wt.% water (A), 25 wt.% ethanol (B), 20 wt.% n-propanol (C), 10 wt.% acetic acid (D), 15 wt.% ethyl acetate (E) and 20 wt.% n-butanol (F). The composition of all the constituents in the feed reservoir decreased with time. Separation factors ranging between 15 and 215 were obtained for acetic acid, propanol and butanol. The permeation rates of individual components followed the order αAC>αAB>αAB>αAE>αAF at 75°C. The influence of reaction temperature and molecular size on the permeation rate and separation factor is discussed. The role of water as a plasticizing agent and the effect of the interaction between different permeates on the rate of permeation of the individual components is also discussed. Diffusion coefficients for water, ethanol, propanol, ethyl acetate, acetic acid and butanol have been evaluated. The values range between 1 and 7 m2 h−1.

A qualitative investigation on the importance of boundary layer in pervaporation separation of an aqueous organic reaction

The importance of boundary layer was investigated for the hydrolysis of ethyl acetate using a dense standard poly(vinyl alcohol) (PVA) membrane. A resistance in a series model approach was used to study the effect of a boundary layer for the permeation of aqueous organic mixtures involved in the study. The initial feed mixture consisted of 10% water (H2O), 40% ethyl acetate (EA), 50% acetic acid (AA), and 0% ethanol (E) (all weight percentage basis). The experiments were conducted at 65°C. The amount of all species in the feed reservoir was found to decrease with time. Selectivity calculations based on a resistance in the series model approach indicates that the boundary layer contributes to selective permeation of aqueous organic compounds.