Chemical Kinetic and High Fidelity Modeling of Transesterification

The modeling and simulation of transesterification require an understanding of the chemical reactions that take place inside the reactor. The development of reaction mechanism of the multiple step triglyceride, triglycerides and mono-glycerides and their reversal reaction is beyond the interest of chemical or mechanical engineers, whose main interests are to assess the conversion overall and to establish performance process metrics. This chapter undertakes the transesterification conversion by firstly establishing and formulating the overall process kinetics as far as the rate constant and activation energy. Secondly, use the obtained kinetic values to carry out high fidelity reactive flow of the multiple species which are co-present inside the reactor and otherwise complex to capture experimentally. Following these two steps, this work provides qualitative and quantitative information on the concentration of the reactants, intermediates and the overall yield. This two-step-approach can also be utilized as reactor design tool and gaining in-depth insight on reaction progress and species distribution. Experimental results, high-fidelity numerical results, and parametric sensitivity studies will be introduced and discussed

Numerical Simulation of Tower Rotor Interaction for Downwind Wind Turbine

Downwind wind turbines have lower upwind rotor misalignment, and thus lower turning moment and self-steered advantage over the upwind configuration. In this paper, numerical simulation to the downwind turbine is conducted to investigate the interaction between the tower and the blade during the intrinsic passage of the rotor in the wake of the tower. The moving rotor has been accounted for via ALE formulation of the incompressible, unsteady, turbulent Navier-Stokes equations. The localized CP, CL, and CD are computed and compared to undisturbed flow evaluated by Panel method. The time history of the CP, aerodynamic forces (CL and CD), as well as moments were evaluated for three cross-sectional tower; asymmetrical airfoil (NACA0012) having four times the rotor's chord length, and two circular cross-sections having four and two chords lengths of the rotor's chord. 5%, 17%, and 57% reductions of the aerodynamic lift forces during the blade passage in the wake of the symmetrical airfoil tower, small circular cross-section tower and large circular cross-section tower were observed, respectively. The pronounced reduction, however, is confined to a short time/distance of three rotor chords. A net forward impulsive force is also observed on the tower due to the high speed rotor motion

Hydrogen production from coal gasification using solar energy : Thermodynamic equilibrium modelling and exergy analysis

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.In this study the merits of hydrogen production using solar energy are discussed. The primary focus of the paper is to perform thermodynamics analysis of coal gasification via solar energy. Initially the chemical properties of coal are determined using proximate analysis, ultimate analysis and calorimeter. Using the coal properties a thermodynamics model bases on equilibrium constant approach is developed. The model is tested against the experimental data and further exergetic and cold gas efficiency is calculated. The effect of temperature and moisture contents is studied which shows that efficiency as high as 70% can be achieved with hydrogen yield of around 57% by volume. The model is further used to explore the potential of solar energy along with the partial combustion of coal. The result shows a sharp decline in the CO2 emission, while 43% increase in the yield of Hydrogen is calculated.dc201

A Unified Approach for Taxonomy-based Technology Forecasting

For decision makers and researchers working in a technical domain, understanding the state of their area of interest is of the highest importance. For this reason, we consider in this chapter, a novel framework for Web-based technology forecasting using bibliometrics (i.e. the analysis of information from trends and patterns of scientific publications). The proposed framework consists of a few conceptual stages based on a data acquisition process from bibliographic online repositories: extraction of domainrelevant keywords, the generation of taxonomy of the research field of interests and the development of early growth indicators which helps to find interesting technologies in their first phase of development. To provide a concrete application domain for developing and testing our tools, we conducted a case study in the field of renewable energy and in particular one of its subfields: Waste-to-Energy (W2E). The results on this particular research domain confirm the benefit of our approach

Techno-economic analysis of the co-gasification of sewage sludge and petroleum coke

In this study, the co-gasification of sewage sludge and petroleum coke is assessed with equilibrium and numerical modeling. The gasification process of these binary wastes provides a potential pathway for waste management and environmental sustainability. First, the thermodynamic equilibrium approach is used to calculate the maximum cold gasification efficiency (CGE) at different mixture ratios in an attempt to narrow down and focus on the appropriate composition of the two kinds of feedstock within the entrained flow gasifier. Furthermore, a parametric study is conducted to show the gasification metrics, i.e., CGE and feedstock conversion, and the syngas composition at different gasification conditions. The equilibrium model is based on eight unknowns in the gasification product, namely, H2, CO, CO2, H2O, CH4, O2, Csolid, and the temperature, under variable O2 and H2O molar ratios. Using three elemental mass balances, four equilibrium (Csolid) constant relations, and energy balance, the mathematical model is developed. The model incorporates the solid unburnt carbon in the product species. The temperature of gasification is determined through an iterative process. Using the result of the equilibrium model, a high-fidelity reactive flow model that accounts for the reactor geometry and the devolatilization kinetics is developed. This model accounts for an extended set of reactions covering the char combustion, water and gas shifts, Boudouard and devolatilization. Finally, economic analysis is carried out to assess the conditions when such a process can be deemed to be profitable. The result of the model shows that the maximum CGE is achieved when all the solid carbon is converted into carbon monoxide with nearly all hydrogen present in the feedstock converted into hydrogen gas. The maximum conversion was attained with sewage sludge and petroleum coke ratio of 1 at 1,200°C. The mole fraction of the syngas species obtained is XH2 = 0.4227 and XCO = 0.5774 and a small fraction of XCH4 = 0.0123. Moreover, the cold gasification efficiency (CGE) measures 87.02% for the H2 and CO syngas species and reached 91.11% for the three species, including CH4. The gasification of the sewage sludge and petroleum coke at 50:50 is economically viable at temperatures higher than 950°C. A peak net gain of 0.16 $/kg of fuel blend was achieved at 1,250°C. At temperatures lower than 950°C, net losses were realized. This could be associated with less product gas yield, which is not significant enough to counteract the input costs. For instance, the net losses were −0.03 and −0.17$/kg of feedstock at 950 and 800°C, respectively

Flow around an Oscillating Cylinder at Low Reynolds Number with Forced Convection: Effect of Corner Radius and Reynolds Number

This numerical study investigated the flow-induced vibration (FIV) on non-heated and heated cylinders with different normalized corner radii (r*) at different Reynolds numbers (Re). Four different values of r* were considered (i.e., 0 (square cylinder), 0.5, 0.75, and 1.0 (circular cylinder)) at three different Re: 100, 150, and 200 within the laminar regime. The cylinder constrained in the axial direction and oscillated transversally was considered for a fixed nondimensional cylinder mass (m*)  of 10 and a reduced velocity (Ur) of 4.92. The effect of r* and Re could be seen in the vibration modes of cylinders. The two-dimensional incompressible Navier–Stokes and energy equations were solved together with Newton’s Second Law governing the motion of the cylinder with the help of a computational solver. Four different modes were observed in this study: Mode-I characterized by exceptionally low amplitude; Mode-II characterized by fluctuating amplitude known as hysteresis (beating); Mode-III characterized by high amplitude due to synchronization or lock-in; and Mode-IV characterized by the monotonic oscillation of fixed amplitude. For r* = 1, synchronization phenomenon/lock-in was observed. For the heated cylinder cases, due to the change in the normalized corner radius, a notable change in nondimensional vibrational amplitude A/D and the average Nusselt number Nuavg was seen. It was observed that A/D was higher when lock-in occurred (at Re = 100 and r* = 1), leading to a rise in Nuavg by 47.9% compared to Re = 100 and r* = 0. Due to the change in r*, a shifting phenomenon was observed at Re = 150, r* = 0.75 and Re = 200, r* = 1. A major change in Nuavg was observed from the circular cylinder to square cylinder at different Re. The beating phenomenon was observed at Re = 100 for r* = 0.75, which was similar to that occurring at Re = 150 and r* = 0.5, and those at Re = 200 and r* = 0. Heat transfer and wake structure parameters were found to be dependent on r* and Re

Refinery processed water treatment via the low energy Direct Contact Membrane Distillation (DCMD)

The amount of refinery water discharged to the environment from oil industry has increased vigorously in current times. Recent research has been focusing on the use of membrane technology for the refinery processed water treatment. Membrane Distillation (MD) is an emerging technology that has been highly marked by its low-energy requirement and high desalination efficiency. However, conventional MD membranes (i.e. PVDF) are not feasible for oil-water separation processes. That is due to the oleo-philic property of the membrane and thus, causes membrane fouling and halts the production of mass flux. An anti-oil-fouling membrane is essential for a successful oil-water separation by MD. Underwater-oleophobic as well as omniphobic are two different approaches in fabricating such membranes. The former approach is based on the asymmetric surface wettability, whereas the latter is attributed to the surface structure that is characterized by having a very large contact angle for all liquids. However, such composite membranes are characterized by their lower porosity, smaller pore size, but with unique surface slippage, in comparable with the conventional PVDF membranes. As such, in this work, high fidelity numerical simulation of DCMD is performed using non-isothermal Computational Fluid Dynamics (CFD) validated model in order to assess the role of the anti-oil-fouling membrane properties on the performance of the DCMD. Results are presented in terms of temperature polarization coefficient, mass flux, latent heat flux, and thermal efficiency. Results show the compromising effect of membrane porosity to 45% reduces the mass flux and thermal efficiency respectively by 68% and 40%, and reduction of pore size to the half (i.e. 50 nm) can cause a reduction by 50.6% in mass flux and 24.18% in thermal efficiency compared to the baseline (i.e. 100 nm). On the other hand, the omniphobic slippage effect leads to a noticeable gain of 16% in DCMD mass flux with slight gain in thermal efficiency. This can maximize mass flux and thermal efficiency to be as much as 50.3 kg/m2 h and 69%, respectively