Fuzzy modelling of a moving grate biomass furnace for simulation and control purposes

Takagi–Sugeno (TS) fuzzy models are developed for a moving grate biomass furnace for the purpose of simulating and predicting the main process output variables, which are heat output, oxygen concentration of flue gas, and temperature of flue gas. Numerous approaches to modelling biomass furnaces have been proposed in the literature. Usually their objective is to simulate the furnace as accurately as possible. Hence, very complex model architectures are utilized which are not suited for applications like model predictive control. TS fuzzy models are able to approximate the global non-linear behaviour of a moving grate biomass furnace by interpolating between local linear, time-invariant models. The fuzzy partitions of the individual TS fuzzy models are constructed by an axis-orthogonal, incremental partitioning scheme. Validation results with measured process data demonstrate the excellent performance of the developed fuzzy models.     

我国电解铝用阳极与阴极炭块市场需求预测

本文首先分析了最近几年我国电解铝行业的特点,并在此基础上应用统计学知识建立统计模型,对2007～2011五年间我国的电解铝的产量进行了预测;通过分析历年来实际生产中积累的数据,本文得到了电解铝生产过程中阳极和阴极炭块的用量与电解铝产量的比例的区间值;结合2007～2011电解铝产量的预测值,文中最后得到了今后几年我国铝用阳极和阴极炭块的需求量,并给出了在置信度为95%时的区间估计值.     

Mathematical modeling of industrial aluminum electrolysis

The problem of aluminum electrolysis is discussed. The mathematical model of an industrial electrolyzer presented in the paper is written under the assumption that the electrolyte and metal media are immiscible. At the basis of the mathematical statement is a three-dimensional, nonstationary, and nonlinear system of magnetic hydrodynamics equations which is written separately in the aluminum medium and in the electrolyte medium with a geometric account for wall accretion, skull, and arrangement of anodes. The proposed system allows one to model various forms of anodes, the number of anodes in a bath, and their sizes. Interfaces of media are connected by a viscous friction. Initial values of speeds and electromagnetic fields in the media and the medium interface are considered as set. On the skull, bottom, and anodes the attachment conditions are set. The speed of change of a magnetic field in the metal and electrolyte on the interface is considered zero. On the basis of a numerical method of solution of the system of equations, there is a well-proved method of division over physical processes. The analysis of results of the numerical experiment has shown that it is actually possible to allocate a ??middle?? layer for modeling of the electrolysis process. The proposed model allows one to investigate media behavior upon the occurrence of a long anode effect due to sharp reduction of the electric conductivity of the electrolyte and subsequent sharp growth of the electric-field strength.     

Assessment of the effect of high ash content in pulverized coal combustion

The existing literature on CFD-based coal combustion modelling is applicable mainly for coals of low ash content and the calculations are done on an ash-free basis. In Indian coals, the ash content may be significantly higher, up to 40% or more. Studies reported in the literature show that the mineral matter in the coal may have a number of effects on the combustion characteristics. In the present study, a sensitivity analysis is performed, using the CFD code CFX of AEA Technology, on the likely effect of ash content on the char reactivity, oxygen diffusion rate for char combustion and on the radiative heat transfer parameters. The results show that the effect of enhanced char reactivity is negligible whereas reduced oxygen diffusion rates due to a thicker ash layer may result in a significant reduction in char oxidation rates with a resultant decrease in the peak temperature in the furnace. The global parameters such as the peak temperature and the flue gas temperature remain relatively insensitive to the presence of high ash content. These results are consistent with the experimental observations of Kurose et al. [R. Kurose, M. Ikeda, H. Makino, Combustion characteristics of high ash coal in pulverized coal combustion, J. Fuel 80 (2001) 1447–1455].     

Large eddy simulation of non-premixed pulverized coal combustion in corner-fired furnace for various excess air ratios

Large-eddy simulations (LES) were carried out to study the effects of burning atmosphere on the coal combustion process in a corner-fired furnace. The LES for the turbulent gas was coupled with the discrete phase model (DPM) for coal particles trajectories and the non-premixed mixture fraction probability density function (MF-PDF) combustion model for pulverized coal combustion. The coal combustion processes, including the flame characteristics, burning coal behaviors and NO_x pollutant emissions, for different burning atmospheres are analyzed qualitatively and quantitatively. The heat and momentum transfer between burning coal and turbulent gas are greatly enhanced by the corner-fired flow. With a given particle size, the char particles present a similar distribution in the whole chamber. For a fuel-rich atmosphere, the concentration is obviously much higher and exhibits much higher spatial variability than the other two conditions. The coal combustion efficiency decreases in oxygen-rich and fuel-rich burning atmospheres, but the flame stability is more affected at the fuel-rich atmosphere by the lack of oxygen. NO pollutant is obviously reduced at the fuel-rich atmospheres, and the NO pollutant emissions are more affected by the reducing atmosphere than the low temperature. These findings may provide insight into strategies to design and monitor tangentially-fired pulverized coal boilers.     

CFD modelling of the flow and reactions in the Olympic Dam flash furnace smelter reaction shaft

The performance of flash furnace burners can be evaluated quickly and efficiently using CFD modelling. Gas flows are modelled using the conventional Eulerian approach, while Lagrangian particle tracking is used to model the flow of solid feed through the burner and into the reaction shaft. A composite particle model has been developed that considers the solid feed to be made up of single particles containing appropriate quantities of concentrate, flux and dust. Solid fuels (such as coal) can also be included in the composite particle. Reactions between the solids and gas are then modelled using standard heat and mass transfer relationships. Results from the modelling process are shown for BHP-Billiton’s Olympic Dam copper flash smelter with the burner that was used from 1998–2003. Flow patterns, temperature and gas composition distributions, particle dispersion and residence time, and overall extent of sulphur removal are predicted and used to evaluate furnace performance. However, results are sensitive to the assumed size of the composite particles, and plant measurements are required to determine the appropriate composite particle size to predict quantitative data.     

Mathematical modeling and process simulation of perlite grain expansion in a vertical electrical furnace

Expanded perlite is a lightweight material with remarkable thermal and acoustic insulation properties, rendering it widely useful in the construction and manufacturing industries. Currently applied perlite expansion technology suffers numerous technical disadvantages, which adversely affect product quality and limit the range of its applications. To overcome these established drawbacks, a new perlite expansion process has been designed on the basis of a vertical electrically heated expansion furnace. The novel furnace enables precise control of experimental conditions, in order to allow for efficient adjustment of particle residence time and internal temperature. The quality of expanded perlite strongly depends on raw material thermophysical properties as well as furnace operating conditions, and the experimental investigation of the isolated effect of each parameter on expanded product quality is technically cumbersome and extremely time-consuming and expensive.A mathematical model for perlite grain expansion has been developed in order to perform a detailed numerical investigation of process efficiency, toward the optimization of the expansion process in the novel pilot-scale furnace. The dynamic model consists of ordinary differential equations for both air and particle heat and momentum balances, as well as nonlinear algebraic equations for both air and perlite melt thermophysical and transport properties, probing the air temperature distribution within the vertical electrical furnace as well as the particle velocity, temperature and size along its trajectory inside the heating chamber. The effect of raw material physical properties (raw feed origin, initial particle size, effective water content) as well as operating parameters (air inlet temperature and flowrate, furnace wall temperature) on evolution of the particle state variables is presented and discussed. Model results indicate perlite expansion is strongly affected by raw ore feed origin, size and water content. Moreover, operating conditions affect expansion considerably, and furnace wall temperature has the strongest effect on the final particle expansion ratio attained. The new dynamic model is instrumental towards achieving a detailed comprehension of perlite expansion in the vertical electrical furnace towards multi-parametric sensitivity analysis, process optimization and efficient control.     

合成氨煤气炉DCS数据建模与统计分析

利用相关系数阵的条件数研究影响煤气炉上部温度的各影响因素之间的复共线性,利用对数回归方法建立煤气炉上部温度与各影响因素之间的线性回归模型。经检验回归方程与回归系数均具有良好的显著性.所建模型对改善炉况,保持生产过程持续稳定具有现实指导意义。     

Scheduling Production in a Heavily Constrained Plant – Anode Manufacture in an Aluminium Smelter

In this paper a mathematical model of an anode manufacturing plant is developed with the objective of assisting in the planning and scheduling of production for up to a month ahead. A model of the overall smelter already exists and is based on a monthly time frame. The anode plant is a part of this model but is a very heavily constrained area and it is necessary to have a daily planning model that will help to achieve the optimal level of operations as dictated by the overall model of the smelter. The anode area is responsible for the production of carbon blocks (called anodes) which are an integral part of the aluminium smelting process. The plant is also responsible for the delivery of all raw materials within the smelter. The model developed is a daily one replicated for up to a month ahead, interconnected by opening and closing stocks.     

数值模拟计算在1000MW塔式锅炉NO_x生成特性中的应用研究

在新建的大型燃煤电站锅炉设计时,通过对炉内燃烧过程的合理组织,以取得锅炉低NO_X排放的效果.采用计算流体力学(CFD)模拟的方法,进行了某电厂1000MW超超临界塔式锅炉的数值模拟计算分析,获得了该1000MW塔式锅炉炉内速度场、温度场、CO浓度场、O-2浓度场和NO_X浓度场分布.计算结果表明:该1000MW塔式锅炉炉膛主燃烧区域的中心形成了巨大还原区,并且在炉膛上部具有明显的还原区域,能实现低NO_X排放的预期目标.数值模拟计算研究结论可用于指导锅炉燃烧系统的优化运行和NO_X排放的控制.     

基于变工况运行超超临界锅炉NO_x排放的数值模拟研究

基于变工况运行,采用计算流体力学(CFD)模拟方法,对某电厂1000MW超超临界锅炉炉膛内CO、O_2、NO浓度场和温度场进行计算和分析.影响该锅炉NO_x排放浓度主要运行因素有燃用煤质、附加风量(AA风量)和过剩空气系数等.CFD数值模拟计算结果表明:锅炉通过合理组织炉内燃烧,实现了主燃烧区的较均匀的温度分布,主燃区的燃烧方式属于还原态燃烧方式;大量AA风的深度空气分级燃烧和锅炉低过量空气系数的有机结合及PM燃烧器的应用是该型锅炉NO_x排放浓度低的主要原因.     

Numerical simulation study on gas–solid two-phase flow in pre-calciner

A three-dimensional numerical simulation of DD (dual combustion and denitratior process) pre-calciner for cement production was conducted in this paper. In Euler coordinate system, the fluid phase is expressed with RNG k–ε two-equation model and the solid phase is expressed with particle stochastic trajectory model in Lagrange coordinate system. Four mixture fractions are deduced in this article to simulate the gas compositions. The results of numerical simulation predicted the burn-out ratio of coal and the decomposition ratio of limestone particles along with particle trajectories. It also supplied theoretical foundation for industrial analysis of the coupling relation between coal combustion and calcium carbonate decomposition.     

Analyses on 3-D gas flow and heat transfer in ladle furnace lid

In order to verify the reasonableness of off-gas pressure and wall temperature, a mathematical model for gas flow and heat transfer in ladle furnace (LF) lid is developed based on 3-D Navier–Stokes equations and k–ε two equation turbulent models as well as energy conservation equation. The gas velocity vector distribution of skirt clearance between the top edge of ladle and furnace lid and electrode gaps between three graphite electrodes and furnace lid, the gas flow line distribution, pressure and temperature distribution on the furnace lid wall are simulated. Simulation results show that appropriate off-gas pressures are 200 Pa, 200 Pa and 150 Pa when electric arc emerges from molten steel surface and alloy hole is unsealed, electric arc emerges from molten steel surface and alloy hole is closure, electric arc immerges into molten steel surface and alloy hole is closure, respectively. The maximum temperature presents in the middle of LF lid in all of heating conditions, and the temperature value are 563, 603 and 343 K. Finally, the relations between gas volume and off-gas pressure are analyzed in different width of skirt clearance, and some relevant mathematical expressions are obtained. By comparing both simulation results and practical data, the advice on reducing off-gas pressure is proposed, and the maximum temperatures of furnace lid wall have good agreement with actual data.     

Recent applications of CFD modelling in the power generation and combustion industries

Computational fluid dynamics (CFD) modelling is now widely applied as an industrial plant development and process optimisation tool. The steady increase in computer power over recent years has enabled process engineers to model reacting multi-phase flows in a realistic geometry with good mesh resolution. As a result, the number of applications of CFD to industrial processes is also growing rapidly and increasing in sophistication. This paper reviews some of the recent applications of the CFX-4 code [CFX-4.3: Solver Manual, AEA Technology Engineering Software, 1999] to the power generation and combustion industries. The aim is to illustrate what can be done and also to identify trends and those areas where further work is needed. Examples include coal-fired low-NO_x burner design, furnace optimisation, over-fire air, gas reburn, and laminar flames. It is argued that the trend is for CFD models to become more comprehensive and accessible by being coupled to other process models and embedded in automated information and process control systems.     

Coal blending models for optimum cokemaking and blast furnace operation

An important problem at an integrated steel-producing plant is the blending of different types of coals to make coke for the blast furnace operation. Historically, linear blending models were not appropriate because coal properties important for both optimum cokemaking and blast furnace operation do not combine linearly and are not completely understood. In this paper, a solution methodology is developed that utilizes two techniques: (1) a mixed integer linear programming model for blending the candidate coals to produce coke at a minimum cost and (2) binary decision tree analyses and results that are converted into model constraints to ensure the production of high-quality coke. Subsequently, the model results are used at the pilot-scale oven for testing and for validating the new, improved blend(s) that have been recommended by the model. This is an on-going need that is dictated by changing availabilities in both coal prices and sources. These steps reduce costs by both minimizing the number of blends to be tested at the pilot-scale facility and ensuring a minimum cost coal blend that is useable for the operating facilities. Hypothetical, but realistic, data are used to illustrate how the model performs.     

Multi-physical field coupling numerical investigation of alumina dissolution

Alumina dissolution, which is controlled by both heat and mass transfer mechanisms, is a key process in the aluminum electrolytic cell. A solution module for alumina dissolution coupling heat and mass transfer was established using the open source platform OpenFOAM, including particle shrinking, bubble driven flow and thermal response associated with dissolution. The dissolution process was modeled, and the critical diameter which can identify whether the dominant mechanism for dissolution is heat or mass transfer was proposed and computed. The calculated results show that the critical diameter of alumina dissolution is about 520 µm. Alumina particles with diameter less than 520 µm are controlled by the mass transfer mechanism, while particles with diameter larger than 520 µm are controlled by the heat transfer mechanism. Optimal feeding quantity was calculated by simulating and comparing different feeding quantities in a 300 kA aluminum electrolytic cell. The optimal feeding quantity is 1.2 kg based on the analysis of concentration fluctuation in the space-time domain and average dissolution rate. The models and methods can provide guidance for the design of feeding strategy for large aluminum electrolytic cells.     

Incorporating dust lift-off into a CFD model of a blast furnace gravity dust-catcher

A gravity dust-catcher separates a mixture of dusts from the spent top gas flow of a blast furnace. These dusts are predominantly made up of limestone, iron ore and coke/coal. As a result of the turbulent gas flow patterns within a dust-catcher, modelling of the flow pattern can be very complex, attributed to the turbulent vortices that can be formed within the main body of the structure. Using data from an experimental prototype test rig, a simple model to capture the lift-off characteristics of particle lift-off from dust pile surfaces is created and incorporated into a computational fluid dynamics (CFD) model of the dust-catcher.The variation of particle separation performance over a typical blast furnace (BF) operational cycle is analysed. An attempt is made to explain the observed phenomena in terms of particle–fluid interaction. It is found that particle separation efficiency is largely unaffected by dust lift-off at low dust-catcher hopper fullness levels, but is significant at higher levels. It is found that the topography of the dust surface is important when predicting particle lift-off trends. It is concluded that this is due to the exposure experienced by a given particle when subjected to a surface velocity.     

Numerical simulation of methane partial oxidation in the burner and combustion chamber of autothermal reformer

This study aims to model the methane partial oxidation process in the burner and combustion chamber of autothermal reactor. The numerical simulation based on this model offers a powerful tool that can assist in reactor design and optimization and scale up of the process saving expensive pilot work. The steady-state governing equations were solved using the SIMPLE algorithm and the effect of turbulence on the mean flow field was accounted for using the RNG k–ε model. A two-step reaction mechanism was used for the gas combustion with CO as the intermediate species. The reaction rates were modeled using an Eddy-Dissipation Model. In terms of the geometrical model, a 3D model for burner was developed while an axis-symmetric model for the combustion chamber was implemented to reduce the computational costs. The model formulated was validated against a currently operating autothermal reactor and then has been used to investigate different aspects of these reactors. Results show that effect of oxygen to methane ratio is more than that of feed temperature. It is demonstrated that a 60% increase in O₂/CH₄ ratio causes a 15.4% decrease and 42.7% increase in H₂/CO ratio and methane conversion, respectively. In contrast, a 60% increase in feed temperature does not have a significant effect on the process.     

Fuzzy predictive temperature control for a class of metallurgy lime kiln models

The combustion temperature and progress control problems are key factors to ensure the production quality of metallurgy lime kiln. The combustion process of lime kiln is a nonlinear and large time‐delay thermal process, so it is difficult to achieve satisfactory results by the traditional proportional integral derivative control, fuzzy control, or predictive control. This article analyses physics and chemistry mechanism of the combustion process and expounds the complex nonlinear, multivariable and large time‐delay characteristics, and the control target of the production system. Then, the mathematical model of combustion control system is deduced in view of the requirements of simulation. Based on these, the fuzzy predictive control scheme is employed. Through simulation, the control algorithm is verified to be effective. Finally, the industrial sleeve kiln as a practical example is used to demonstrate the effectiveness and feasibility of the control algorithm. © 2016 Wiley Periodicals, Inc. Complexity 21: 249–258, 2016     

Einfluss eines Verbrennungsvorganges auf den Wärme- und Stoffaustausch in einer laminaren Grenzschicht

Summary The influence of combustion on heat and mass transfer is investigated on the following model. A mixture of an inert with a combustible gas (air) flows in steady, laminar flow over a flat plate. A mass flux of gaseous fuel away from the plate surface is produced by some means. Combustion is assumed to occur with very fast reaction rate so that the process is purely controlled by diffusion and the equilibrium is assumed as very close to complete combustion. It is studied under which conditions the combustion occurs at the surface or when the flame is displaced into the boundary layer. The influence of combustion on the heat transfer from a hot gas to the plate surface is calculated, for the condition that combustion occurs at the surface.