Jamal Naser

Computational Fluid Dynamic Modeling of Zinc Slag Fuming Process in Top-Submerged Lance Smelting Furnace

Slag fuming is a reductive treatment process for molten zinciferous slags for extracting zinc in the form of metal vapor by injecting or adding a reductant source such as pulverized coal or lump coal and natural gas. A computational fluid dynamic (CFD) model was developed to study the zinc slag fuming process from imperial smelting furnace (ISF) slag in a top-submerged lance furnace and to investigate the details of fluid flow, reaction kinetics, and heat transfer in the furnace. The model integrates combustion phenomena and chemical reactions with the heat, mass, and momentum interfacial interaction between the phases present in the system. A commercial CFD package AVL Fire 2009.2 (AVL, Graz, Austria) coupled with a number of user-defined subroutines in FORTRAN programming language were used to develop the model. The model is based on three-dimensional (3-D) Eulerian multiphase flow approach, and it predicts the velocity and temperature field of the molten slag bath, generated turbulence, and vortex and plume shape at the lance tip. The model also predicts the mass fractions of slag and gaseous components inside the furnace. The model predicted that the percent of ZnO in the slag bath decreases linearly with time and is consistent broadly with the experimental data. The zinc fuming rate from the slag bath predicted by the model was validated through macrostep validation process against the experimental study of Waladan et al. The model results predicted that the rate of ZnO reduction is controlled by the mass transfer of ZnO from the bulk slag to slag–gas interface and rate of gas-carbon reaction for the specified simulation time studied. Although the model is based on zinc slag fuming, the basic approach could be expanded or applied for the CFD analysis of analogous systems.

Numerical simulation of froth formation in aerated slurry coupled with population balance modelling

ABSTRACT A computational fluid dynamic (CFD) model has been developed to incorporate pulp and froth zones into one model. In the present research, froth was considered as a separate phase comprised of a mixture of gas, liquid and solids. Considering the froth phase as a separate phase, allowed the incorporation of pulp and froth zones into one model by tracking the formation and destruction of the froth phase due to mass exchange between the pulp and froth. Bubble break-up and coalescence were taken into account in the pulp zone, by employing user functions, written using FORTRAN. The effect of bubble coalescence process due to film rupture was considered in the froth phase. The variation in the concentration of attached particles due to attachment and detachment processes were also taken into account. The CFD model predicted the height of froth layer, the concentration of different bubble sizes in both pulp and froth zones, and finally the multiphase flow phenomena in the slurry column. Froth height was found to increase with the increase of gas flow rate while increasing solid concentration decreased froth height.

Modeling of Solid and Bio-Fuel Combustion Technologies

Inefficient process in the thermal power station leads to greenhouse gas emission. Reductions in emissions are largely dependent on the improvement of efficiency, with lower fuel consumption as a 1% improvement in power station efficiency delivering an almost 3% reduction in CO2 emissions. Maximum CO2 reduction is also possible through the use of alternative fuels and CO2 capture. Therefore, there is a need for energy-efficient technology to improve power plants that are able to utilize alternative fuels and CO2 capture. Coal is a major source of fuel, while biomass fuels, such as energy crops, waste wood, and agricultural residues are supplementary. The design, operation, and maintenance of combustion equipment require detailed understanding of the combustion process inside the furnace. In order to explore the major challenges, experimental methods are important but often inadequate to analyze the detailed phenomena inside the boiler, especially for industrial furnaces. A computational technique provides the opportunity to investigate in detail, the combustion phenomena and contaminant development inside the furnace. In order to understand combustion-related issues and problems for direct firing or packed bed combustion, modeling and analysis are required. This chapter will briefly report the recent advances in the combustion technologies, different carbon capturing and storage systems, modeling methodology for coal combustion, biomass co-combustion, packed bed combustion, and slag formation modeling. Also, examples of coal/biomass combustion will be illustrated to investigate, in detail, the combustion phenomena and related issues in the furnace.

Analysis of steelmaking kinetics from IMPHOS pilot plant data

It is widely accepted that understanding the kinetics of steelmaking is a complex task, and reliable and validated kinetics models are required for developing successful steelmaking process models. Therefore, as an initial attempt, this paper analyses the applicability of first order kinetics to explain the steelmaking reaction kinetics using the published data in the IMproving Phosphorus Refining research report. The process data for 20 heats in a 6 tonne pilot plant were analysed for the removal of carbon, silicon, manganese and phosphorus using first order kinetics with static and dynamic equilibrium conditions. It was observed that the removal behaviour of silicon closely followed a first order kinetics relationship, while that of carbon only approximately followed a first order kinetics relationship. The removal of manganese did not show a good degree of fit with first order kinetics using static equilibrium condition, but a clear improvement was observed when calculated using dynamic equilibrium condition. In contrast, the kinetics of phosphorus oxidation did not follow any first order relationship.

A CFD model for biomass combustion in a packed bed furnace

Climate change has now become an important issue which is affecting environment and people around the world. Global warming is the main reason of climate change which is increasing day by day due to the growing demand of energy in developed countries. Use of renewable energy is now an established technique to decrease the adverse effect of global warming. Biomass is a widely accessible renewable energy source which reduces CO2 emissions for producing thermal energy or electricity. But the combustion of biomass is complex due its large variations and physical structures. Packed bed or fixed bed combustion is the most common method for the energy conversion of biomass. Experimental investigation of packed bed biomass combustion is difficult as the data collection inside the bed is challenging. CFD simulation of these combustion systems can be helpful to investigate different operational conditions and to evaluate the local values inside the investigation area. Available CFD codes can model the gas phase combustion but it can’t model the solid phase of biomass conversion. In this work, a complete three-dimensional CFD model is presented for numerical investigation of packed bed biomass combustion. The model describes the solid phase along with the interface between solid and gas phase. It also includes the bed shrinkage due to the continuous movement of the bed during solid fuel combustion. Several variables are employed to represent different parameters of solid mass. Packed bed is considered as a porous bed and User Defined Functions (UDFs) platform is used to introduce solid phase user defined variables in the CFD. Modified standard discrete transfer radiation method (DTRM) is applied to model the radiation heat transfer. Preliminary results of gas phase velocity and pressure drop over packed bed have been shown. The model can be useful for investigation of movement of the packed bed during solid fuel combustion.

Bubbly flow with particle attachment and detachment – A multi-phase CFD study

ABSTRACT The available computational fluid dynamics (CFD) models for multi-phase bubble column ignore the effects of attached particles on the dynamics of the bubbles. Bubbles become heavier with the attachment of solid particles which has significant impact on their buoyancy, and hence their flow dynamics. The present paper endeavours to simulate multi-phase slurry bubble column accounting for the effect of bubble–particle aggregate density on the flow dynamics in a multi-phase slurry bubble column. A CFD model was developed and validated against air–paraffin oil data at ambient conditions to understand the hydrodynamics of a three-phase slurry bubble column.

A Modified Eulerian-Lagrangian Approach Applied to a Compact Down-Hole Sub-Sea Gas-Liquid Separator

This article presents a modified Eulerian-Lagrangian approach for solving multi-phase flow applied to a laboratory-scale gas-liquid separator designed for high gas content. The separator consists of two concentric pipes with a swirl tube in the annular space between the pipes. The gas-liquid mixture comes from a tangential side inlet and the system works with a combination of gravity and centrifugal forces to achieve a high-efficient gas-liquid separation. In the modified Eulerian-Lagrangian method, gas flow is coupled with the spray and wall film models. The spray model involves multi-phase flow phenomena and requires the numerical solution of conservation equations for the gas and the liquid phase simultaneously. With respect to the liquids phase, the discrete-droplet method (DDM) is used. The droplet-gas momentum exchange, droplet coalesces and breaks-up, and the droplet-wall interaction with wall-film generation and entrainment of the water droplet back into the gas stream are taken into account in this investigation. To be consistent with the experiments the experimental air water mixture on the liquid carry over (LCO) curve is used for the numerical investigation. The standard k-ϵ turbulence model is used for turbulence closure. The predicted results from the modified Eulerian-Lagrangian multi-phase model explain the complex flow behavior inside the separator and are in good agreement when compared with experiments.

Numerical modelling of flow through foam's node

In this work, for the first time, a three-dimensional model to describe the dynamics of flow through geometric Plateau border and node components of foam is presented. The model involves a microscopic-scale structure of one interior node and four Plateau borders with an angle of 109.5 from each other. The majority of the surfaces in the model make a liquid-gas interface where the boundary condition of stress balance between the surface and bulk is applied. The three-dimensional Navier-Stoke equation, along with continuity equation, is solved using the finite volume approach. The numerical results are validated against the available experimental results for the flow velocity and resistance in the interior nodes and Plateau borders. A qualitative illustration of flow in a node in different orientations is shown. The scaled resistance against the flow for different liquid-gas interface mobility is studied and the geometrical characteristics of the node and Plateau border components of the system are compared to investigate the Plateau border and node dominated flow regimes numerically. The findings show the values of the resistance in each component, in addition to the exact point where the flow regimes switch. Furthermore, a more accurate effect of the liquid-gas interface on the foam flow, particularly in the presence of a node in the foam network is obtained. The comparison of the available numerical results with our numerical results shows that the velocity of the node-PB system is lower than the velocity of single PB system for mobile interfaces. That is owing to the fact that despite the more relaxed geometrical structure of the node, constraining effect of merging and mixing of flow and increased viscous damping in the node component result in the node-dominated regime. Moreover, we obtain an accurate updated correlation for the dependence of the scaled average velocity of the node-Plateau border system on the liquid-gas interface mobility described by Boussinesq number.

Numerical modelling of biomass combustion: Solid conversion processes in a fixed bed furnace

Increasing demand for energy and rising concerns over global warming has urged the use of renewable energy sources to carry a sustainable development of the world. Bio mass is a renewable energy which has become an important fuel to produce thermal energy or electricity. It is an eco-friendly source of energy as it reduces carbon dioxide emissions. Combustion of solid biomass is a complex phenomenon due to its large varieties and physical structures. Among various systems, fixed bed combustion is the most commonly used technique for thermal conversion of solid biomass. But inadequate knowledge on complex solid conversion processes has limited the development of such combustion system. Numerical modelling of this combustion system has some advantages over experimental analysis. Many important system parameters (e.g. temperature, density, solid fraction) can be estimated inside the entire domain under different working conditions. In this work, a complete numerical model is used for solid conversion process...

Oxy–Fuel Combustion in the Lab–Scale and Large–Scale Fuel– Fired Furnaces for Thermal Power Generations

Recently, the environmental and health threat from anthropogenic emissions of greenhouse gases (GHG) of power plants has been considered as one of the main reasons for global climate change [1]. The undesirable increase in global temperature is very likely because of increase the concentrations of these syngas in the atmosphere. The most important resource of these anthropogenic GHG emissions in the atmosphere is carbon dioxide emissions. At present, fossil fuels provide approximately 85% of the world’s demand of electric energy [2]. Many modern technologies in the electricity generation sector have been developed as sources of new and renewable energies. These new technologies include solar energy, wind energy, geothermal energy, and hydro energy. While these sources of renewable energy are often seen as having zero greenhouse gas emissions, the use of such technologies can be problematic. Firstly, sources of renewable energy are often still under development. Therefore, there can be a higher cost involved in their installation and in other related technical requirements. Secondly, the sudden switching of these energy sources (zero emission) has caused serious problems with the infrastructure of energy supply and global economy [3]. In order to reduce the problem and obey the new environmental and political legislation against global warming, it is necessary to find an appropriate solution to cut pollution which is with cost-effective, from the energy sources. The most effective technique, which can achieve a high level of reduction in GHG emission to atmospheric zone, is to capture carbon dioxide from the conventional power generations. At present, several organizations, energy research centres, companies, and universities, particularly in developed countries, are working to develop these conventional power plants in order to make them more environmentally friendly, with near-zero emissions sources. This chapter continues on different CO2 capture technologies such as pre-combustion capture, post-combustion capture, and oxy-fuel combustion capture. The developments on