Multi-Objective Adaptive Optimization Model Predictive Control:Decreasing Carbon Emissions from a Zinc Oxide Rotary Kiln

The zinc oxide rotary kiln,as an essential piece of equipment in the zinc smelting industrial process,is presenting new challenges in process control.China’s strategy of achieving a carbon peak and carbon neutrality is putting new demands on the industry,including green production and the use of fewer resources;thus,traditional stability control is no longer suitable for multi-objective control tasks.Although researchers have revealed the principle of the rotary kiln and set up computational fluid dynamics(CFD)simulation models to study its dynamics,these models cannot be directly applied to process control due to their high computational complexity.To address these issues,this paper proposes a multi-objective adaptive optimization model predictive control(MAO-MPC)method based on sparse identification.More specifically,with a large amount of data collected from a CFD model,a sparse regression problem is first formulated and solved to obtain a reduction model.Then,a two-layered control framework including real-time optimization(RTO)and model predictive control(MPC)is designed.In the RTO layer,an optimization problem with the goal of achieving optimal operation performance and the lowest possible resource consumption is set up.By solving the optimization problem in real time,a suitable setting value is sent to the MPC layer to ensure that the zinc oxide rotary kiln always functions in an optimal state.Our experiments show the strength and reliability of the proposed method,which reduces the usage of coal while maintaining high profits.

Modeling of Rotary Kiln in Cement Industry

Cement production is a highly energy-intensive process, and the rotary kiln is the most important part of the process. Having a comprehensive model of the kiln in order to reduce manufacturing costs, better performance can be created. In this paper, the influence processes in a simulated cement rotary kiln and operating parameters on the output of the study were to develop and validate the systems using the same batch. The followings were examined: solid phase, gas and coating temperature change in a rotary kiln.

Simulation research of a counter‑fow rotary kiln hazardous waste incineration system

As industrialization accelerates and the amount of hazardous waste generated gradually increases,the means of disposal of hazardous waste is of increasing concern.In this paper,a 40 t/d counter-fow rotary kiln incineration system owned by a Jiangsu environmental protection company was researched.The software Aspen Plus was used to build the mixed pyrolysis model and the software Fluent was used to build the computational fuid dynamics model of the incineration system.The infuence of the calorifc value of the hazardous waste,the operating temperature and the air supply on the operational efectiveness of the incineration system were analyzed by varying the simulation conditions.The results show that the SO_(x)and NO_(x)content of the product is lower when the operating temperature is above 800℃.The incineration system could only operate above 800℃when the calorifc value of the hazardous waste is not less than 1500 kcal/kg.The incineration system operated best at a primary air velocity of 1.5 m/s.The simulation results in this paper serve as a guide for the operation of counter-fow rotary kiln incineration systems.

Typical Refractories Design of Rotary Kiln Hazardous Waste Incineration System

This paper summarizes the current situation of China’s industrial hazardous waste treatment,the disposal technology and the characteristics of rotary kiln incineration system,analyzes the refractory lining design of rotary kiln incineration system in China,and puts forward optimization suggestions according to the process characteristics.

Damage Mechanism of Silicon Carbidemullite Bricks for Transition Zone of Cement Rotary Kilns

In order to improve the service performance and explore the damage mechanism of silicon carbide-mullite bricks for the transition zone of cement rotary kilns,the phase composition and the microstructure of a used brick in the transition zone of a cement rotary kiln were analyzed by XRD,SEM and EDS.The results show that the liquid and alkali vapor phases generated by the reaction between cement materials and the silicon carbide-mullite brick mostly enter the silicon carbide-mullite brick through the pores;meanwhile,Ca+and K+in the cement penetrate through the liquid maintaining a high chemical potential energy to dissolve Al2O3 and SiO2 at the top of the liquid phase thus enhancing the phase penetration;with the decreasing temperature,crystals such as gehlenite,potassium feldspar and potassium chloride are precipitated,which destroy the original structure and increase the difference of thermal expansion coefficient between the high temperature dense end and the metamorphic layer thus resulting in cracks,spalling,and rupture.

An Innovative Process for Direct Reduction of Cold bound Pellets from Iron Concentrate with a Coal-based Rotary Kiln

Successfully developed an innovative process of direct reduction of cold bound pellets from iron ore concentrate with a coal based rotary kiln, in comparison with the traditional direct reduction of fired oxide pellets in coal based rotary kilns , possesses such advantages as: shorter flowsheet, lower capital investment, greater economic profit, good quality of direct reduced iron. The key technologies , such as the composite binder and corresponding feasible techniques were employed in practice. A mill utilizing this process and with an annual capacity of 50 thousand ton DRI has been put into operation.

Mathematical Model for the Rotary Kiln Process and Its Application

A mathematical model to predict the operation behaviours of the rotary kiln process and to describe theaxial distribution of process variables along the length of the reactor has been developed in present work.Themodel is established based on the principle of mass and heat balance in the system under a steady state withthe consideration of kinetic characteristics of the processes.Four examples of the simulation processes in a pi-lot kiln and 3 commercial kilns by using the present mathematical model are given in this paper.The goodagreement between the predicted results and the measured data has been obtained.

Mathematic simulation of heat transfer and operating optimization in alumina rotary kiln

Based on the analysis of material motion in the axial direction, heat transfer and mass transport processes in a rotary kiln, and combining with pulverized coal combustion, material pyrogenation, cooling of furnace wall finally, and heat transfer and mass transport equations, the combined heat transfer mathematical model for alumina rotary kiln was built up. According to the in-site real operation parameters, the heat transfer mathematical model was solved numerically for an alumina rotary kiln to predict the temperature profiles of gas and material in the axial direction. The results show that as the excess air coefficient reduces from 1.38 to 1.20, the temperature of the sintering zone increases and the length decreases. However, as the excess air coefficient reduces from 1.20 to 1.10, the temperature of the sintering zone decreases and the length increases. When the mixed coal amount at the end of kiln is reduced from 68.6 kg/t to 62.0 kg/t and the burned coal amount at the head of kiln correspondingly increases from 155.3 kg/t to 161.9 kg/t, the sintering zone temperature increases and the length reduces. The suitable excess air coefficient and mixed coal amount at the end of kiln are recommended for the rotary kiln operation optimization.

Flame image recognition of alumina rotary kiln by artificial neural network and support vector machine methods

Based on the Fourier transform, a new shape descriptor was proposed to represent the flame image. By employing the shape descriptor as the input, the flame image recognition was studied by the methods of the artificial neural network(ANN) and the support vector machine(SVM) respectively. And the recognition experiments were carried out by using flame image data sampled from an alumina rotary kiln to evaluate their effectiveness. The results show that the two recognition methods can achieve good results, which verify the effectiveness of the shape descriptor. The highest recognition rate is 88.83% for SVM and 87.38% for ANN, which means that the performance of the SVM is better than that of the ANN.

Mathematical models and expert system for grate-kiln process of iron ore oxide pellet production.Part Ⅱ:Rotary kiln process control

Rotary kiln process for iron ore oxide pellet production is hard to detect and control.Construction of one-dimensional model of temperature field in rotary kiln was described.And the results lay a solid foundation for online control.Establishment of kiln process control expert system was presented,with maximum temperature of pellet and gas temperature at the feed end as control cores,and interval estimate as control strategy.Software was developed and put into application in a pellet plant.The results show that control guidance of this system is accurate and effective.After production application for nearly one year,the compressive strength and first grade rate of pellet are increased by 86 N and 2.54%,respectively,while FeO content is 0.05% lowered.This system can reveal detailed information of real time kiln process,and provide a powerful tool for online control of pellet production.

CFD prediction of physical field for multi-air channel pulverized coal burner in rotary kiln

A 3-D numerical simulation with CFX software on physical field of multi-air channel coal burner in rotary kiln was carried out. The effects of various operational and structural parameters on flame feature and temperature distribution were investigated. A thermal measurement was conducted on a rotary kiln (4.5m in diameter, 90m in length) with four-air channel coal burner to determine the boundary conditions and to verify the simulation results. The calculation result shows that the distribution of velocity near burner exit is saddle-like; recirculation zones near nozzle and wall are useful for mixture primary air with coal and high temperature fume. A little central airflow can avoid coal backing up and cool nozzle. Adjusting the ratio of internal airflow to outer airflow is an effective and major means to regulate flame and temperature distribution in sintering region. Large whirlcone angle can intensify disturbution range at flame root to accelerate ignition and mixture. Large coal size can reduce high temperature region and result in coal combusting insufficiently. Too much combustion air will lengthen flame and increase heat loss.

Numerical analysis of behavior of active layer in rotary kilns by discrete element method

The behavior of the active layer of material bed within rotary kilns plays a key role in industrial applications.To obtain its influences on industrial process,different regimes of particle motion have been simulated by discrete element method(DEM) in three dimensions under variant rotation speeds,filling degree,based on the background of induration process of iron ore pellets.The influences of the mentioned factors on the maximum thickness of the active layer and the average velocity of particles have been investigated.The average velocity of particles increases with Froude number following the power function over a wide range,and the maximum thickness rises with increasing rotation speed in a way of logarithm.The influence of the filling degree f on the maximum thickness exhibits a good linearity under two classic regimes,but the increasing of the average velocity of the active layer is limited at f=0.4.This basic research highlights the impact of the active layer within rotary kilns,and lays a good foundation for the further investigation in mixing and heat transfer within the particle bed inside rotary kilns.

Chrome-free Basic Refractories for Burning Zone of Cement Rotary Kiln

Based on the relevant phase diagrams of ternary system in MgO-CaO-ZrO2-SiO2 quarternary systems,the phase diagram of Fe-O system and the condensed phase stability area diagram of iron oxides,the corrosion resistance of MgO-CaO-ZrO2 refractories to silicate cement,and the forming conditions and preparing measures of hercynite are analyzed.

Key Points of Monolithic Lining Engineering of Rotary Kilns

There are many factors affecting the monolithic lining engineering of rotary kilns,resulting in the difficult quality control. In this paper,the key points of the whole lining engineering were discussed from the aspects of lining structure design,personnel preparation,site construction management,maintenance and baking.

LSSVM Predictive Control for Calcination Zone Temperature in Rotary Kiln with IHS Algorithm

The calcination zone temperature control is an important problem in rotary kiln production process. In order to solve this problem,a predictive control method based on improved harmony search algorithm( IHS)and least square support vector machine( LSSVM) is proposed. LSSVM is utilized to bulid the nonlinear predictive model of calcination zone temperature in rotary kiln. The calcination zone temperature can be predicted through input control variable,the error and error correction of output feedback. The performance index function is established by deviation and control variable. An IHS algorithm with better fitness and faster convergence speed is proposed. The optimal control variable can be obtained by rolling optimization through this IHS algorithm. The stability of this predictive control method is proved to be feasible. The simulation and actual experiment results show that the proposed predictive control method has good control performance.

Improving Municipal Solid Waste Land Filling Disposal Process: Experiments with a Laboratory Scale Rotary Kiln

Developing countries often face the challenge of managing continuously growing quantity of municipal waste. Waste is often disposed of by stockpiling and land filling because these have been found the cheapest waste disposal methods in the world. Unfortunately, these waste disposal methods are often source of visual pollution, water contamination and greenhouse effect gas emissions. Waste disposal by incineration has been found effective and now is one of the mostly used waste disposal method in several developed countries. Nevertheless, setting up appropriate waste incinerator requires a good of the combustion process. Unfortunately, direct studies on industrial facilities are not easily feasible because of technical issues and financial limitations. Studies and throughout testing frequently need to be carried out at laboratory scale. Work herein reported first overviewed operation conditions of the landfill facility in the town of Ouagadougou. In the second time for incineration simulation, batch experiments are carried out with a rotary kiln furnace to study the effects of the residence time on emissions of NO, NO2, CO, CO2 and SO2 in the atmosphere. For each rotation speed, emissions of NO, NO2, CO, CO2 and SO2 from the incineration of a household combustible fraction model waste consisting of wood (53%), cardboard (25%) and plastics (22%) have been recorded. The lifespan of the land filling facility with incineration has been estimated. Our work show that it may be improved up to roughly three times that of simple land filling. Visual pollution maybe drastically reduced and atmospheric pollution reduced.

Temperature Calculation of Pellet Rotary Kiln Based on Texture

In order to improve the quality of clinker produced by pellet rotary kiln, flame temperature that it is a very important factor of affecting on the quality of clinker is studied. The flame images collected from pellet rotary kiln are decomposed into three gray images by the method of RGB, so we can get more information of flame. Taking advantage of gray level co-occurrence matrix, the monitoring model for flame temperature based on image texture is established with RGB channels. In order to test the universality of the algorithm, candle flame temperature is detected by this method. The maximum error of the model is less than 3%.

A Short Communication on Refractories as Kiln Lining along Various Thermal Zones in Pre-calcining Cement Rotary Kiln

Modern cement rotary kiln is often large in size while rotating in high speed. Thermal condition within a rotary kiln is rather complex,exerting severe thermal and chemical attack on refractory of its kiln lining. In the present paper,the cause that leads to refractory failure was analyzed; requirements for refractory to overcome such failure was discussed. Composites and properties of different refractories most often used as kiln lining were assessed,including magnesia-chrome bricks,magnesia spinel bricks, dolomite bricks, silicon carbide mullite bricks and castables etc. Recommendation was made for refractories with suitable composites and properties to be used as kiln lining in each specific zone to best counteract the severe thermal conditions. A cost-effective configuration was presented to assemble kiln lining for rotary kiln's different zones in line with the regulation at JC/T 2196-2013 "Specifications of refractory for cement rotary kiln". Chromite-free refractories with property of high endurance to thermal attack and corrosion are required to be used in modern Pre-calcining cement rotary kilns.

Corrosion of Disposing Urban Domestic Wastes on Refractories for Cement Rotary Kilns

Corrosion of burning urban domestic wastes to alkali-resistant bricks and spalling-resistant high alumina bricks was researched by static crucible method and SEM in order to choose refractories for cement rotary kilns for collaboratively disposing wastes. The result indicates that the main corrosion mechanism is slag permeation and corrosion; the emitted high temperature gases containing alkali,sulfur and chlorine during burning the wastes react with refractories forming low melting point sulfate,chloride and compound salts,which metamorphose the refractories,and the loose metamorphic layer is easy to spall under thermal stress. So,corrosion resistance and spalling resistance shall be taken into account when choosing refractories for cement rotary kilns for collaboratively disposing wastes. It is suggested that decomposition furnaces should adopt spalling resistant high alumina bricks and anti-coating Si C castables,and preheating equipment should adopt high strength alkali-resistant bricks and castables.

The Liner Formulas between the Supporting Force and Axis Warp of Large-scale Rotary Kiln with Multi-support

Kilns are the key equipment in the metallurgy,architectural and chemistry industry. It is the statically indeterminate system with over load, large torque and multi-support. The kiln move axis warp resulting in that the load distribution is asymmetry, cause many mechanical failure and safe accidents and the interruption of the produce, which bring a great losses. Treating the distribution of the kiln load and the complexity of the stiffness change, the all-purpose model and matrix, used to solve the variable-stiffness beam upon complex load, are established in this paper. The resultant force of kiln in vertical and horizontal direction is calculated. Accordingly, the liner formulas for calculating the supporting force of the support wheels are obtained, and the wheel supporting force also can be easily obtained based on each shell warp. This will provide theory conference for safety management and rational maintenance.