Application And Study On Thermal Analysis And Control Of Alumina Rotary Kiln

The calcination of stuff in rotary kiln is a key process of aluminaproduction by sintering, which may directly influence the yield andquality of alumina. Along with raised production in our country in recentyears, higher demands are required on alumina quality. For improving thealumina yield and quality, reducing the intensity of labor, decreasingenergy consumption as well as promoting the technical progress ofalumina industry, it is important both in theories and practices to deeplyunderstand influence factors in stuff calcination and to realize automaticcontrol of the rotary kiln production.The process in rotary kiln is characterized with large inertia, longtime delay, nonlinearity, time-dependent and multi-disturbance and thekiln body keeps rotating during the production. It is very difficult toperform temperature on-line measurement, and parameters monitoring isseverely delayed. Furthermore, the distributed control system applied incurrent rotary kiln production of alumina can only fulfill regularmonitoring and some simple control, and the information are not fullyused. All these problems severely harm the process optimization andintelligent control of rotary kiln. But some advanced process controltechnologies such as on-line simulation, image processing, fuzzy control,soft-sensing technique can be used with unique superiority in solving theabove problems.Based on analyzing the heat balance and heat transfer process ofrotary kiln, through studying the transient heat transfer of cylindrical wall,material flow and heat transfer process, this paper proves that the heattransfer process of cylindrical wall can be assumpted as steady state in aenergy storage or energy releasing period, and the temperature of materialon a certain cross section can be treated as the same. It provides thetheory basis for developing an one-dimensional mathematical model forheat transfer of rotary kiln.This research puts forward calculation formula of material naturalangle in rotary kiln, and builds physical-mathematical model of heat conduction between material and covered furnace wall, and gets the heatconduction overall coefficient. It deduces calculation formula of radiationheat transfer and temperature expression of multilayer cylindrical wallwhich possesses temperature dependent thermal conductivity. Combinedwith pulverized coal combustion, material pyrogenation, cooling offurnace wall finally, and heat transfer and mass transfer, this paper buildscombined heat transfer mathematical model of rotary kiln.Combined with the real production process of the rotary kiln, a flowrate meter measuring end gas and an arc cirque temperature measuringinstrument have been developed for realizing the on-line monitoring ofend gas flow rate and temperature in the kiln. According to thecharacteristics of the shape of inner liner and kiln crust, an infrared raytemperature measuring instrument was adopted to collect the temperatureon the surface. A kiln condition monitoring system was developed byintegrating digital filter compensating method. The system improves theoperation of kiln effectively and enhances the efficient of facilities.The on-line simulation and optimization model and software weredeveloped by applying synthetically the principles of kiln thermalengineering and reaction kinetics. This system can realize real-timecalculation of the section lengths and temperature distribution in the kiln,which can be displayed real-time on the computer and recorded ashistorical curves. It offers a tool for in-site examination and management.This information combined with technical characteristics of rotary kilnand experiences of engineer and specialized worker, a rotary kilndiagnosis system was developed for realizing the function of data input,auto alarm and malfunction display etc. This system offers on-lineguidelines for the operation of the rotary kiln.Based on the theory of connectivity and relativity of image,combined with the neighborhood averaging method, this paper presentsan improved gradient inverse weight smoothing algorithm which makesimage pretreatment better. The application of C means, fuzzy C meansand approximate fuzzy C means clustering methods in rotary kiln flameimage dividing was compared and researched throughly. Based on filtering pretreatment, the characteristic values such as the height ofmaterial, the temperature of flame and material can be obtained bydividing rotary kiln image with approximate fuzzy C means clusteringmethod. These values can reflect the thermal condition in the kilnquantitatively and provide reliable data for the operation optimization andautomatic control.By improving basic devices of related hardware and communication,and combining on-line simulation, condition forecasting, imageprocessing and optimization control of rotary kiln, the fuzzy controlsystem of alumina rotary kiln was developed. With the flame temperature,material height, and tail temperature of rotary kiln as input parameters,and the pulverized coal feed and door opening size of smoke exhauster asoutput parameters, the system firstly realized the united adjustment ofpulverized coal quantity and air volume which achieved good economicbenefit.Thermal analysis and intelligent control system for aluminaproduction in rotary kiln has been applied successfully for more than ayear, which realizes technical parameters optimization and automaticcontrol, reduces the intensity of labor, enhances the efficient of facilitiesand achieves the goals of the production increasing and energyconsumption decreasing. According to the in-site statistic data, theconsumption of pulverized coal can save above 1.5 kg per ton stuff andthe production of stuff can improve above 2t per hour after realizing autocontrol of the rotary kiln. The aim to increase production and decreasecost has been achieved.