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.

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.

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 (4.5m in diameter, 90m 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.

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.

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.

Enhanced recovery of zinc and lead by slag composition optimization in rotary kiln

High-efficiency recovery of Zn and Pb from silicon-rich zinc leaching residues is realized in a rotary kiln.Characterizations by means of XRD,SEM,EDS and ICP reveal that the leaching residue contains 12.4 wt.%SiO_(2),16.1 wt.%Zn,and 7.4 wt.%Pb.Thermodynamic analysis shows that metallic vapor of Zn and Pb can be easily generated from the zinc leaching residue at 1150-1250°C inside the rotary kiln.Viscosities and melting points of 13 slag compositions were analyzed and three slag compositions(47wt.%SiO_(2)-23wt.%CaO-30wt.%FeO,40wt.%SiO_(2)-28wt.%CaO-32wt.%FeO,and 40wt.%SiO_(2)-30wt.%CaO-30wt.%FeO)possessed the desirable physical properties,with the melting point and viscosity in the range of 1150-1280°C and 0.2-0.5 Pa·s,respectively.The industrial tests show that adopting the optimized slag composition can contribute to very high recovery rates of Zn and Pb(97.3%for Zn and 94.5%for Pb),corresponding to slags with very low average contents of Zn and Pb(0.51 wt.%Zn and 0.45 wt.%Pb).The National-Standard leaching tests of the water-quenched slags result in 1.82 mg/L Zn,~0.01 mg/L Cu,0.0004 mg/L As,~0.01 mg/L Cd,0.08 mg/L Pb,and~0.02 mg/L Hg in the leachate,verifying the detoxification of the zinc leaching residue at the same time.

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.

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 the axial distribution of process variables along the length of the reactor has been developed in present work.The model is established based on the principle of mass and heat balance in the system under a steady state with the 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 good agreement between the predicted results and the measured data has been obtained.

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.

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 prepar- ing measures of hercynite are analyzed.

Application of coal-water slurry on the rotary calcining kiln of pedgion magnesium reduction process

Energy saving has been an important concept in modern industry especially to the countries and regions with energy shortage such as China and Japan. Utilization of Coal-Water Slurry （CWS） can improve the burning efficiency of coal and reduce the pollutions of soot, sulfide and the nitride by burning lump coal directly. The CWS is a promising energy saving technique and the effectual substitute of oil. The study on the preparation and application of the CWS has made progresses in many aspects. The present paper studied the basal problems for applying the CWS on the rotary kilns during the calcining-dolomite process in the magnesium factory, summarized the key points for the application process of the CWS and gave the corresponding solutions.

Modeling and optimization of rotary kiln treating EAF dust

Electric arc furnace （EAF） dust from steel industries is listed by the United Sates EPA as a hazardous waste under the regulations of the Resource Conservation and Recovery Act due to the presence of lead, cadmium and chlorine. The disposal of the approximately 650000 t of EAF dust per year in the U.S. and Canada is an expensive and unresolved problem for the majority of steel companies. The Waelz process has been considered as the best process for treating the EAF dust. A process model, combined thermodynamic modeling with heat transfer calculations, has been developed to simulate the chemical reactions, mass and heat trans- fer and heat balance in the kiln. The injection of air into the slag and the temperature profile along the kiln have been modeled. The effect of （CaO＋MgO）/SiO2 on the solidus temperature of slag has also been predicted and discussed. Some optimized results have been presented.

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.

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 re- act 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 spaUing 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 spaUing resistant high alumina bricks and anti-coating SiC castables, and preheating equipment should adopt high strength alkali-resistant bricks and castables.

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 muUite 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 configura- tion 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.

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.

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.

Numerical study of particle behaviours and heat transfer in a complex rotary kiln

Rotary kiln is widely used for thermal disposal of solid waste due to its effectiveness and high efficiency in recent years.To further improve the processing efficiency,a newly designed rotary kiln with three-section structure is proposed,and the behaviours of particle motion and heat transfer are investigated.Firstly,a lab-scale rotary kiln is manufactured,and experiments are carried out.Verified by experimental data,a CFD-DEM numerical model is developed to analyze the particle motion and heat transfer characteristics with the effects of inlet flue gas temperature,feeding rate and rotating speed.The results show that the outlet temperature increases linearly with the flue gas temperature,while it is negatively correlated with the feeding rate and rotating speed.In addition,the volumetric heat transfer coefficient in this complex rotary kiln is analyzed,the overall heat transfer coefficient is between 200 and 700 W/(m^(3)K).

Plant Test of Industrial Waste Disposal in a Cement Kiln

Destruction of industrial waste in cement rotary kilns (CRKs) is an alternative technology for the treatment of certain types of industrial waste (IW). In this paper, three typical types of industrial wastes were co-incinerated in the CRK at Beijing Cement Plant to determine the effects of waste disposal (especially solid waste disposal) on the quality of clinker and the concentration of pollutants in air emission. Experimental results show that (1) waste disposal does not affect the quality of clinker and fly ash, and fly ash after the IW disposal can still be used in the cement production, (2) heavy metals from IW are immobilized and stabilized in the clinker and cement, and (3) concentration of pollutants in air emission is far below than the permitted values in the China National Standard-Air Pollutants Emission Standard (GB 16297-1996).