Modelling and simulation of coal gasification process in fluidised bed

The emission from FBC is very dependent on a number of operating conditions (temperature, staged air, fuel feed rate, excess air, etc.) and fuel properties. This paper describes the experimental results taken in a staged air fluidized bed combustion laboratory scale, using palm fiber and palm shell as fuels and silica sand as the inert bed material. In this experiment, a variation of excess air and secondary air were measured. Measurement of gas emissions of CO and CO2 concentrations, combustion efficiency and temperature, were taken along the combustor height as well as in flue gas. The experimental results show that the axial temperature profiles decrease successively along the FBC height. The CO emission obtained was lower for the staged- air condition than for the un-staged-air condition. The combustion efficiencies show satisfactory values.

Evaluation of the energy efficiency of the shell coal gasification process by coal type

Gasification is a clean and efficient technology with a long history dating up to the 19 th century. The possible application of this process ranges from gas production and chemical synthesis to the energy sector and therefore this technology holds noticeable potential for future applications. In order to advance it, a new efficient approaches for this complex process are necessary. Among possible methods, a process enhancing additives, such as alkali and alkaline earth metals seems to be a promising way of achieving such a goal, but in practice might turn to be a wasteful approach for metal economy, especially in large scale production. This paper shows alkali abundant waste material that are green liquor dregs as a viable substitute. Green liquor dregs is a waste material known for its low potential as a fuel, when used separately, due to its low organic content, but its high ash content that is also abundant in alkali and alkaline earth elements seems to make it a suitable candidate for application in coal gasification processes. The aim of this work is an evaluation of the suitability of green liquor waste to work as a potential process enhancing additive for coal steam gasification process. During the experiment, three blends of hard coal and green liquor dregs were selected, with consideration for low corrosive potential and possibly high catalytic activity. The mixtures were gasified in steam under four different temperatures. Their energies syngas yield, coal conversion degree and energies of activation were calculated with use of Random Pore Model (RPM) and Grain Model (GM) which allowed for their comparison.

The object of this work is to model and simulate a fluidized bed desulfurization reactor by coupling a reactor kinetic model with a fluidized bed model based on two –phase theory(bubbling-bed model) proposed by Kunni and Levenspiel(1968).This model is useful for analysis of a reaction involving gas and solid. It generates the conversion data with respect to reaction time of both reacting gas and solids in a continuous flow(for both gas and solids) in fluidized bed. The flue gas or stack gas from a combustor which normally contains sulfur dioxide mixed with excess air is used as the fluidizing gas with calcium oxide as the fluidized solids . Calcium oxide is quite capable of reacting with 2 SO to effect its removal from the gas phase according to the exothermic reaction :s  CaO + g  SO2 + 2 1g  O2 s  CaSO4 + HeatThe effects of the solid feed rate, SO2 concentration in the flue gas, bed height, bed diameter, particle size, fluidizing velocity and operating temperature on the extent of conversion of both gas and solid were investigated, for a fixed feed rate of flue gas and SO2concentration (50.000 cm3/sec ,3-5% by volume)at temperature range of (950-1000oC)and pressure 1 atm.

Hydrodynamic studies on three-phase fluidized bed using CFD analysis

Simulation of the layer inversion phenomenon in binary liquid--fluidized beds by DEM–CFD with a drag law for polydisperse systems

Knowledge of both dense bed expansion and freeboard solids inventory are required for the determination of bed height in fluidized beds of fine particles, e.g., Fluidized Catalytic Cracking (FCC) catalysts. A more accurate estimation of the solids inventory in the freeboard is achieved based on a modified model for the freeboard particle concentration profile. Using the experimentally determined dense bed expansion and the modified freeboard model, a more practical method with improved accuracy is provided to determine the bed height both in laboratory and industrial fluidized beds of FCC particles. The bed height in a fluidized bed can exhibit different trends as the superficial gas velocity increases, depending on the different characteristics of the dense bed expansion and solids entrainment in the freeboard. The factors that influence the bed height are discussed, showing the complexity of bed height and demonstrating that it is not realistic to determine the bed height by a generalized model that can accurately predict the dense bed expansion and freeboard solids inventory simultaneously. Moreover, a method to determine the bed height, based on axial pressure fluctuation profiles, is proposed in this study for laboratory fluidized beds, which provides improved accuracy compared to observation alone or determining the turning points in the axial pressure profiles, especially in high‐velocity fluidized beds.

The fluid dynamics presented in this paper for a fluidized bed gasifier consists of estimating the volume fraction fields of gas and solid phases, as well as the velocity fields of gas and solid phases and the pressure drop inside the fluidized bed. However, understanding of the flow characteristics has an important role in understanding of the operation of the gasifier. The analyzed system consists of the fundamental equations of mass balance for the gas and solid phases, as well as the equations of momentum balance for gas and solid phases and an equation for the pressure given by the sum of the momentum balance equations of the gas and solid phases. The sets of equations developed form a system of one-dimensional partial differential equations (PDEs). The PDEs system has been transformed in a coupled ordinary differential equation (ODEs) system. The ODEs system has been solved using an implementation of the Runge-Kutta Gill method. The objective of this work is to obtain the profiles of state variables such as volume fraction of gas (eg) and solid phases (es), the velocity profiles of gas (Vg) and solid phase (Vs) and pressure field (Dp). Key words: Fluid dynamics, gasifier, fluidized bed, gas-solid, biomass.

Influence of air bubble size on float–sink of spheres in a gas–solid fluidized bed

In order to understand the effect of coal type on coal gasification process at 15 atmospheric pressure of pressurized drop tube furnace (PDTF), a numerical study was conducted. Eulerian approach is used for the gas phase, whereas Lagrangian approach is used for the solid phase. Turbulence is modelled using the standard k–ε model. The turbulent gas-phase combustion model incorporates the eddy dissipation model. One-step two-reaction model is employed for the devolatilization. Effect of coal type on carbon conversion at the same coal feed rate and gas flow rate cannot be verified due to the variation of equivalence ratio according to coal composition. Therefore, the same equivalence ratio is chosen to evaluate the effect of coal type on gasification. It is found that the volatile release based on experimental results should be taken in computations to predict accurate carbon conversion, especially in coal gasification due to the low gasification reaction. Even at over 1500 K and 15 atmospheric pressure, at which reactions are primarily diffusion-controlled, the exit carbon conversion varies with the coal type. The temperature gradient in near-burner region becomes gentle with increasing proximate volatile and moisture contents, but the volatiles released can make the temperature gradient steep by means of the fast reaction with oxygen. Copyright © 2001 John Wiley & Sons, Ltd.

A novel multigrid technique for Lagrangian modeling of fuel mixing in fluidized beds

The emissions from FBC are very dependent on a number of operating conditions (temperature, staged air, excess air, fuel feed rate, etc.) and fuel properties. This paper described the experimental results taken in a staged air fluidized bed combustion laboratory scaled, using palm shell as fuel and silica sand as the inert bed material. The silica sand was used for ensuring sustainable fuel ignition and combustion in FBC. The variation of fuel feeding rate was taken in these experiments. Gaseous emissions of CO and CO2 concentrations and temperature along the combustor height as well as in flue gas were measured in the experimental tests. The experimental results showed that the axial temperature profiles decrease successively related along the FBC height. The CO and CO2 emission obtained results lower for staged air condition than for un-staged air condition. The palm shell gives significant contribution for reduction of pollution from combustion process.

Convective drying of particulate solids – Packed vs. fluid bed operation

The influence of NH 3 addition on the no emissions from a coal fired fluidised bed combustor

Fluidization is a well-established technique for processing particulate materials, characterized by intensive interactions between solid particles and the fluid flow. Among the various design parameters of fluidized bed dryers, bed height plays a critical role, directly influencing flow resistance, heat and mass transfer, and consequently, the system’s energy efficiency and overall performance. A thorough understanding of the mechanisms governing fluidized bed dynamics is therefore essential for process optimization. In this study, a three-dimensional gas-solid fluidized bed was simulated using a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) framework. This approach enables precise tracking of particle motion and distribution, allowing the temporal evolution of bed height to be quantified. Simultaneously, flow characteristics such as gas velocity, pressure, and particle distribution were analyzed under various operating conditions. Before performing a sensitive simulation study, the model was validated against data from previously published studies, showing strong agreement with established empirical correlations and confirming the reliability of the numerical framework. Building on this validation, a parametric study was conducted to examine the effects of key operating variables - namely, inlet gas velocity and bed height - on the hydrodynamic behavior of the system. The obtained results demonstrate that these parameters have a significant impact on flow uniformity and overall bed stability.