| As a kind of high quality ironmaking raw material,iron ore pellet is increasing in the structure proportion of blast furnace charge.The pellet produced by grate-rotary kiln-ring cooler process has high compressive strength,uniform quality,low energy consumption and obvious scale benefit.The grate is the main equipment in pellet production to realize pellet drying and preheating.In the process of pellet drying and preheating,with the complex changes of water evaporation,convection heat transfer and chemical reaction,it was found in production practice that the instability of pellet grate temperature field will lead to crack or burst of pellets in the drying stage,resulting in powder particles affecting pellet output and polluting the environment.In the preheating stage,the pellet oxidation is not sufficient,which affects the strength of the pellet.The temperature field of pellet grate changes dynamically in time domain and space domain,which is a very complex spatio-temporal coupling system.To realize the cooperative and stable control of pellet grate temperature field is a major problem that must be faced and urgently solved to improve pellet production quality and output,effectively reduce energy consumption and transform to low carbonBased on the pelletizing chain grate machine temperature field in time and space coupling complex system as the research object,and around the ball chain grate machine multi-scale modeling of the temperature field analysis,numerical simulation and control system design and test research,established the pellets chain grate machine multi-scale model of temperature field,reveals the pellets chain grate machine coupling temperature field in time and space distribution and change rule,The thermal parameters of pellet drying and preheating were optimized,the way and method to improve the efficiency of heat energy and strengthen the effect of pellet drying and preheating were proposed,the fuzzy cooperative controller of pellet grate temperature field was designed,and the cooperative experimental system of pellet grate temperature field was constructed.The main research contents and conclusions are as follows:(1)Spatio-temporal coupling multi-scale modeling of temperature field of pellet chain grate.A macro-scale modeling method based on CFD(computational fluid dynamics)and DEM(discrete element method)coupling for temperature field of pellet grate is proposed.The information of flow field and pellet can be obtained by using this method.Based on DFT(density functional theory)and the MD(molecular dynamics theory)pellet preheating oxidation process of micro scale model is established,from the atomic scale pellet was studied and the mechanism of adsorption and diffusion of oxygen interface,for pellets chain grate machine temperature field modeling provides the accurate rate of pellet preheating oxidation,oxidation kinetics parameters,such as diffusion rate.(2)Multi-scale analysis of pellet drying process and preheating oxidation mechanism of grate.The drying process of pellet of grate was analyzed based on Fluent-EDEM macro-simulation.The results showed that the temperature gradient of pellet layer in the direction of grate bed movement was 145K/m,and the maximum drying rate of pellet layer was 0.42Kg/(m3·s).Based on DFT and MD microscopic studies,the preheating oxidation mechanism of pellets was analyzed.The results showed that electrons were transferred by bonding between O2 molecule and Fe3O4(11 11)surface,and O2 could be adsorbed stably on the surface of Fe3O4(11 11).The diffusion rate of O2 could be improved by increasing oxygen concentration in hot air flow field.Strengthening the oxidation effect of magnetite pellets.The compressive strength,oxidation degree,X-ray photoelectron spectroscopy(XPS)and microscopic morphology of the preheated oxidized pellets were tested and analyzed,and the compressive strength of the pellets was 600 N,the maximum oxidation degree of the pellets was 65%,and the phenomenon of "shrinking core" was obvious.(3)Numerical simulation and thermal energy matching of pellet grate temperature field.Based on FLUENT,the temperature coupling distribution and its changing law of pellet grate were numerically simulated.The results showed that the temperature gradient of each section of pellet grate was obvious,the drying rate of pellet layer increased first and then decreased,and the oxidation rate distribution of pellet layer was positively correlated with the temperature gradient.The thermal parameters of pellet drying preheating were optimized by orthogonal test with double indexes of dryness and effective heat utilization rate,and the effective heat utilization rate increased by 8.89%.A method of pellet chain grate heat matching based on double indexes optimization was proposed.(4)Cooperative control strategy and system simulation of pellet grate temperature field.The pellets of temperature control of chain grate machine simplified into four segments(drum wind drying,preheating,convulsions,dry paragraphs Ⅰ and preheating Ⅱ four sections)five source(fan,exhaust fan fan 1,2,1,2,and regenerative five control heat source)of the source control system,this paper proposes a fusion of spatial information pellets chain grate machine 3 d temperature field of fuzzy coordinated control strategy,Based on the traditional fuzzy set(variable domain,membership domain),the spatial dimension was added to express the spatial information,and the 3D fuzzy set(variable domain,membership domain,space domain)was formed.The 3D fuzzy cooperative controller architecture of pellet grate temperature field was designed.Through Simulink simulation analysis,the results show that the temperature fields of the blast and blast drying sections and the preheating ⅰ and ⅱ sections reach stability after 5s,8s,15 s and 24 s after disturbance at10 K,20K,50 K and 100 K,respectively.The temperature overshoot does not exceed2.0%,and the steady-state error is controlled within the range of [-10,10]K.(5)Cooperative control experiment and analysis of pellet grate temperature field.Based on the multi-physical field measurement and control experiment device,a3 D fuzzy cooperative control experiment system of pellet grate temperature field was constructed.The experimental results show that the spatial temperature data collected by thermocouple is consistent with the temperature field distribution characteristics of pellet grate.The average error between the temperature of the collection point and the CFD model is 8.1%.The maximum temperature control error is 13.8K and the maximum relative error is 1.76%.After the disturbance of 100 K,the temperature fields of blast drying section,blast drying section,preheating ⅰ and preheating ⅱsection returned to the stable state after about 8s,16 s,14s and 30 s respectively.The maximum overshoot was 3.25% and the steady-state error was ±12K.The 3D fuzzy cooperative control of pellet grate temperature field has strong stability.The above research work has carried out beneficial exploration in strengthening the pellet drying preheating effect and realizing the stable control of the temperature field of the grate.The research conclusions have important reference value for modern pelletizing enterprises to improve pelletizing production quality,energy saving and emission reduction,and achieve the national strategy of "dual carbon target". |
