Design and Simulation of a Hybrid Entrained-Flow and Fluidized Bed Mild Gasifier: Part 1—Design Considerations and Development of a Multiphase Model

2011 ◽  
Author(s):  
A. K. M. Monayem Mazumder ◽  
Ting Wang ◽  
Jobaidur R. Khan
Keyword(s):  
Power Plant ◽  
Computational Model ◽  
Fluidized Bed ◽  
Stokes Equations ◽  
High Energy ◽  
Multiphase Model ◽  
Entrained Flow ◽  
Design Considerations ◽  
Gasification Process ◽  
Coal Particles

A mild gasification process has been developed to provide an innovative form of clean coal technology, which can be utilized to build a new, highly efficient, and compact power plant or to retrofit an existing coal-fired power plant in order to achieve lower emissions and significantly improved thermal efficiency. The core technology of the mild gasification power plant lies on the design of a compact and effective mild gasifier that can produce synthesis gases with high energy volatiles through a hybrid system: utilizing the features of both entrained-flow and fluidized bed gasifiers. The objectives of this study are to (a) describe the features and design considerations of this mild gasifier and (b) develop a multiphase computational model to guide the design of the mild-gasifier by investigating the thermal-flow and gasification process inside a conceptual mild gasifier. Due to the involvement of a fluidized bed, the Eulerian-Eulerian method is employed to calculate both the primary phase (air) and the secondary phase (coal particles). Multiphase constitutive equations developed from kinetic theory are employed for calculating the effective shear viscosities, bulk viscosities, and effective thermal conductivities of granular flows to simulate the hydrodynamic and thermal interactions between the solid and gas phases. Multiphase Nativer-Stokes equations and seven global reaction equations with associated species transported equations are implementd to simulate the mild gasification process. Part 1 of this paper documents the design principle of the mild gasifier as well as the development of the computational model starting from single phase, then using multiple phases, and finally including all reactions in the multiphase flow.

Effect of Radiation Models on Coal Gasification Simulation

2012 ◽  
Author(s):  
Xijia Lu ◽  
Ting Wang
Keyword(s):  
Wall Temperature ◽  
Coal Gasification ◽  
Cfd Simulation ◽  
Stokes Equations ◽  
Heterogeneous Reactions ◽  
Coal Slurry ◽  
Radiation Model ◽  
Entrained Flow ◽  
Gasification Process ◽  
Coal Particles

Adequate modeling of radiation heat transfer is important in CFD simulation of coal gasification process. In an entrained-flow gasifer, the non-participating effect of coal particles, soot, ashes, and reactive gases could significantly affect the temperature distribution in the gasifier and hence affects the local reaction rate and life expectancy of wall materials. For slagging type gasifiers, radiation further affects the forming process of corrosive slag on the wall which can expedite degradation of the refractory lining in the gasifier. For these reasons, this paper focuses on investigating applications of five different radiation models to coal gasification process, including Discrete Transfer Radiation Model (DTRM), P-1 Radiation Model, Rosseland Radiation Model, Surface-to-Surface (S2S) Radiation Model, and Discrete Ordinates (DO) Radiation Model. The objective is to identify the pros and cons of each model’s applicability to the gasification process and determine which radiation model is most appropriate for simulating the process in entrained-flow gasifiers. The Eulerian-Lagrangian approach is applied to solve the Navier-Stokes equations, nine species transport equations, and seven global reactions consisting of three heterogeneous reactions and four homogeneous reactions. The coal particles are tracked with the Lagrangian method. Six cases are studied—one without the radiation model and the other five with different radiation models. The result reveals that the various radiation models yield uncomfortably large uncertainties in predicting syngas composition, syngas temperature, and wall temperature. The Rosseland model does not yield reasonable and realistic results for gasification process. The DTRM model predicts very high syngas and wall temperatures in the dry coal feed case. In the one-stage coal slurry case, DTRM result is close to the S2S result. The P1 method seems to behave stably and is robust in predicting the syngas temperature and composition; it yields the result most close to the mean, but it seems to underpredict the gasifier’s inner wall temperature.

Design and Simulation of a Hybrid Entrained-Flow and Fluidized Bed Mild Gasifier: Part 2—Case Study and Analysis

2011 ◽  
Author(s):  
A. K. M. Monayem Mazumder ◽  
Ting Wang ◽  
Jobaidur R. Khan
Keyword(s):  
Multiphase Flow ◽  
Fluidized Bed ◽  
Flow Behavior ◽  
Flame Temperature ◽  
Heterogeneous Reactions ◽  
Thermal Flow ◽  
Entrained Flow ◽  
Progressive Development ◽  
Gasification Process ◽  
Flow And Heat Transfer

To help design a mild-gasifier, a reactive multiphase flow computational model has been developed in Part 1 using Eulerian-Eulerian method to investigate the thermal-flow and gasification process inside a conceptual, hybrid entrained-flow and fluidized-bed mild-gasifier. In Part 2, the results of the verifications and the progressive development from simple conditions without particles and reactions to complicated conditions with full reactive multiphase flow are presented. Development of the model starts from simulating single-phase turbulent flow and heat transfer in order to understand the thermal-flow behavior, followed by introducing seven global, homogeneous gasification reactions progressively added one equation at a time. Finally, the particles are introduced, and heterogeneous reactions are added in a granular flow field. The mass-weighted, adiabatic flame temperature is validated through theoretical calculation and the minimum fluidization velocity is found to be close to Ergun’s correlation. Furthermore, the predicted exit species composition is consistent with the equilibrium values.

Review of Coal-to-Synthetic Natural Gas (SNG) Production Methods and Modeling of SNG Production in an Entrained-Flow Gasifer

2016 ◽  
Author(s):  
Xijia Lu ◽  
Ting Wang
Keyword(s):  
High Temperature ◽  
Computational Model ◽  
Catalytic Reaction ◽  
Reaction Rates ◽  
Sensitivity Study ◽  
Synthetic Natural Gas ◽  
Entrained Flow ◽  
Methanation Reaction ◽  
Gasification Process ◽  
Entrained Flow Gasifier

In this paper, the coal-to-synthetic natural gas (SNG) technologies have been reviewed. Steam-oxygen gasification, hydrogasification, and catalytic steam gasification are the three major gasification processes used in coal-to-SNG production. So far, only the steam-oxygen gasification process is commercially proven by installing a catalytic methanation reactor downstream of the gasification process after syngas is produced, cleaned, and shifted to achieve an appropriate H2/CO ratio for methanation reaction. This process is expensive, less efficient, and time consuming. Ideally, it will be more effective and economic if methanation could be completed in an once-through entrained-flow gasifier. Technically, this idea is challenging because an effective gasification process is typically operated in a high-pressure and high-temperature condition, which is not favorable for methanation reaction, which is exothermic. To investigate this idea, a computational model is established and a sensitivity study of methanation reactions with and without catalysts are conducted in this study. In modeling the methanation process in a gasifier, correct information of the reaction rates is extremely important. Most of known methanation reaction rates are tightly linked to the catalysts used. Since the non-catalytic reaction rates for methanation are not known in a gasifer and the issues are compounded by the fact that inherent minerals in coal ashes can also affect the methanation kinetics, modeling of methanation in an entrained-flow gasifier becomes very challenging. Considering these issues, instead of trying to obtain the correct methnation reaction rate, this study attempts to use computational model as a convenient tool to investigate the sensitivity of methane production under a wide range methanation reaction rates with and without catalysts. From this sensitivity study, it can be learned that the concept of implementing direct methanation in a once-through entrained-flow gasifier may not be attractive due to competitions of other reactions in a high-temperature environment. The production of SNG is limited to about 18% (vol) with catalytic reaction with a pre-exponential factor A in the order of 107. A further increase of the value of A to 1011 doesn’t result in more production of SNG. This SNG production limit could be caused by the high-temperature and short residence time (3–4 seconds) in the entraind-flow gasifier.

Prediction and Validation of Performance of an Entrained Flow Gasifier Model

2011 ◽  
Author(s):  
Arnab Roy ◽  
Srinath V. Ekkad ◽  
Uri Vandsburger
Keyword(s):  
Particle Deposition ◽  
Cfd Simulation ◽  
Particle Surface ◽  
Model Parameters ◽  
Discrete Phase Model ◽  
Improve Design ◽  
Entrained Flow ◽  
Gasification Process ◽  
Coal Particles ◽  
Entrained Flow Gasifier

Computational fluid dynamics (CFD) simulation of a single stage, dry-feed entrained flow gasifier is carried out to predict several physical and chemical processes within the gasifier. The model is developed using a commercial software package FLUENT. The CFD model is based on an Eulerian-Lagrangian framework, where the continuous fluid phase is modeled in Eulerian approach and the particle flow trajectory is simulated in Lagrangian frame. The two phases are coupled by appropriate source terms in the conservation equations. The gasification process can be divided into the following sub-processes, which are inert heating, moisture release, coal devolatilization, char gasification and gas phase reactions. Discrete Phase Model (DPM) is used to model the coal particles and coupled with heterogeneous particle surface reactions in Species Transport module. The interaction between reaction chemistry and turbulence is described by Finite-rate/Eddy dissipation model. The simulation provides detailed information of temperature field and species concentration profile inside the gasifier. The temperature distribution clearly indicates the three different reaction zones for devolatilization, gasification and reduction. Steady state model predictions are compared with benchmark experimental data from literature. The trend of the predicted species mole fraction distribution is in good agreement within error bound of the experiment. The model thus provides a validated set of model parameters along with an insight to the underlying flow physics and chemical reactions of gasification process that can be employed to improve design of experiments. This study also develops the basis to achieve further accuracy incorporating complex effects such as detailed reaction kinetic mechanisms, proper devolatilization models, effect of ash-slag transition and particle deposition.

Investigation of a dual cold-flow fluidized bed for calcium looping gasification process

2019 ◽  
Vol 353 ◽  
pp. 10-19 ◽  
Author(s):  
Yijun Liu ◽  
Shiyi Chen ◽  
Min Zhu ◽  
Ahsanullah Soomro ◽  
Wenguo Xiang
Keyword(s):  
Fluidized Bed ◽  
Cold Flow ◽  
Calcium Looping ◽  
Gasification Process

A Computational Analysis of Flow Field in Twin-Track Subway Tunnel to Improve Air Quality

2013 ◽  
Vol 319 ◽  
pp. 599-604
Author(s):  
Makhsuda Juraeva ◽  
Kyung Jin Ryu ◽  
Sang Hyun Jeong ◽  
Dong Joo Song
Keyword(s):  
Air Quality ◽  
Computational Model ◽  
Stokes Equations ◽  
Ventilation System ◽  
Three Dimensional ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Subway Tunnel ◽  
Air Supply ◽  
And Performance

A computational model of existing Seoul subway tunnelwas analyzed in this research. The computational model was comprised of one natural ventilationshaft, two mechanical ventilationshafts, one mechanical airsupply, a twin-track tunnel, and a train. Understanding the flow pattern of the train-induced airflow in the tunnel was necessary to improve ventilation performance. The research objective wasto improve the air quality in the tunnel by investigating train-induced airflow in the twin-track subway tunnel numerically. The numerical analysis characterized the aerodynamic behavior and performance of the ventilation system by solving three-dimensional turbulent Reynolds-averaged Navier-Stokes equations. ANSYS CFX software was used for the computations. The ventilation and aerodynamic characteristics in the tunnel were investigated by analyzing the mass flowrateat the exits of the ventilation mechanicalshafts. As the train passed the mechanical ventilation shafts, the amount of discharged-air in the ventilationshafts decreased rapidly. The air at the exits of the ventilation shafts was gradually recovered with time, after the train passed the ventilation shafts. The developed mechanical air-supply for discharging dusty air and supplying clean airwas investigated.The computational results showed that the developed mechanical air-supplycould improve the air quality in the tunnel.

Field Conversion of a Low-Firing Frame 7B Gas Turbine Power Plant to Ultra-Low Emission Combustion

2015 ◽  
Author(s):  
Nicolas Demougeot ◽  
Jeffrey A. Benoit
Keyword(s):  
Power Plant ◽  
Gas Turbine ◽  
Energy Demand ◽  
Water Injection ◽  
Cost Benefit ◽  
High Energy ◽  
Nox Emissions ◽  
Environmental Controls ◽  
Low Emission ◽  
Technical Discussion

The search for power plant sustainability options continues as regulating agencies exert more stringent industrial gas turbine emission requirements on operators. Purchasing power for resale, de-commissioning current capabilities altogether and repowering by replacing or converting existing equipment to comply with emissions standards are economic-driven options contemplated by many mature gas turbine operators. NRG’s Gilbert power plant based in Milford, NJ began commercial operation in 1974 and is fitted with four (4) natural gas fired GE’s 7B gas turbine generators with two each exhausting to HRSG’s feeding one (1) steam turbine generator. The gas turbine units, originally configured with diffusion flame combustion systems with water injection, were each emitting 35 ppm NOx with the New Jersey High Energy Demand Day (HEED) regulatory mandate to reduce NOx emissions to sub 10 ppm by May 1st, 2015. Studies were conducted by the operator to evaluate the economic viability & installation of environmental controls to reduce NOx emissions. It was determined that installation of post-combustion environmental controls at the facility was both cost prohibitive and technically challenging, and would require a fundamental reconfiguration of the facility. Based on this economic analysis, the ultra-low emission combustion system conversion package was selected as the best cost-benefit solution. This technical paper will focus on the ultra low emissions technology and key features employed to achieve these low emissions, a description of the design challenges and solution to those, a summary of the customer considerations in down selecting options and an overview of the conversion scope. Finally, a technical discussion of the low emissions operational flexibility will be provided including performance results of the converted units.

scholarly journals Numerical simulation of gas-solid flow in an interconnected fluidized bed

2015 ◽  
Vol 19 (1) ◽  
pp. 317-328 ◽  
Author(s):  
Giuseppe Canneto ◽  
Cesare Freda ◽  
Giacobbe Braccio
Keyword(s):  
Numerical Simulation ◽  
Fluidized Bed ◽  
Experimental Tests ◽  
Solid Particles ◽  
Multiphase Model ◽  
Cold Model ◽  
Conservation Equations ◽  
Solid Flow

The gas-particles flow in an interconnected bubbling fluidized cold model is simulated using a commercial CFD package by Ansys. Conservation equations of mass and momentum are solved using the Eulerian granular multiphase model. Bubbles formation and their paths are analyzed to investigate the behaviour of the bed at different gas velocities. Experimental tests, carried out by the cold model, are compared with simulation runs to study the fluidization quality and to estimate the circulation of solid particles in the bed.

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