Establishment And Application Of Water Prediction And Control Model For Continuous Corn Dryer

Grain drying is an effective means of post-harvest quality assurance.It can significantly shorten the time from high-moisture to safe moisture after grain is harvested,and effectively avoid the mildew loss of grain due to the long storage period of high-moisture grains.In addition,northeast of China is an important producing area for maize and rice,since the food harvesting period in this region is in the cold autumn and winter,dry precipitation of grain cannot be realized by means of natural drying,and mechanical drying has become an indispensable means.At present,the level of automation of grain drying machinery in China is still low.Although online moisture detection has been achieved and applied to the control system of grain drying machinery,there are still many problems.On the one hand,on-line detection of grain moisture is susceptible to the environment and the temperature of grain itself,the detection accuracy and stability still need to be improved.On the other hand,due to the mechanized drying of grain is a big lag process,it is still unable to solve the large lag problem by detecting the moisture content at the outlet of the dryer through the on-line grain moisture analyzer and making the control judgment.The control system based on the mathematical model is an important branch of the intelligent control system.Because of the well predictability of the mathematical model,it is very suitable for the process control with large hysteresis.Therefore,the establishment of the relevant mathematic model of the dryer can solve the problem of large hysteresis and improve the control accuracy of the dryer control system.Aiming at the existing problems of grain drying control and taking into account the excellent characteristics of mathematical models,the paper studied the drying process of continuous corn drier,and the aim is to establish a predictive control model for the moisture.On the one hand,the theory of accumulated temperature in agronomy was applied to the drying process of corn,the equivalent accumulated temperature model of the drying process of continuous corn drier was established,and the coarse adjustment of dry moisture of corn is realized by the equivalent accumulated temperature model.On the other hand,took the thin layer drying of corn as a starting point,on the basis of improving the thin layer drying model of corn,the moisture prediction model of continuous corn drier was established.The moisture prediction model is used to realize the fine adjustment of corn moisture.This paper mainly carried out the following research work:(1)Aimed at the common problem that the influence of hot air relative humidity on thin layer drying process is neglected at present,the influencing factors of thin layer drying of corn were comprehensively analyzed.Selected five variables as experimental variables,it's including hot air temperature,relative humidity of hot air,initial moisture of corn(w.b.),hot air flow rate and the ratio of tempering time to drying time.The experimental scheme was designed and tested by the multivariate quadratic orthogonal rotation combined experimental design method,Chosed the Decision coefficient,Chi-square test value and the Root mean square error as the evaluation criteria.Used the experimental data of thin layer drying to compared and optimized 14 commonly used thin layer drying equations,and the Weibull?equation was finally selected as the thin layer drying equation.A multivariate quadratic regression analysis was performed on the four drying coefficients of the Weibull?equation and the regression model for each drying constant with respect to the hot air temperature,relative humidity of hot air,initial moisture of corn(w.b.),hot air flow rate,and the ratio of tempering time to drying time was obtained.The results showed that the model was significant.Besides,three sets of confirmatory experiments were done and the results showed that the Weibull?equation had a good fitting effect on the thin dry precipitation curve of corn,which met the precision requirements of practical application;(2)According to the theory of accumulated temperature in agronomy,put forward the concept of accumulated temperature suitable for grain drying,On the basis of analyzing the drying process of corn thin layer,the model of accumulated temperature of corn drying was established.The accumulated temperature graph was established by using the accumulated temperature model.The graph is mainly used for manual inspection.During the actual drying process,the accumulated temperature value required for the drying process of corn could be quickly determined,provided the basis for setting the initial parameters of the drying control system;(3)The common forms of grain drying were analyzed.Took the study of downstream flow deep-bed drying as a research object,the precipitation model of downstream flow deep-bed drying of corn was established and simulated by MATLAB.(4)Based on the analysis of internal structure and drying process of continuous corn drier,the drying precipitation model and equivalent accumulated temperature model of continuous corn drier were established.Among them,the equivalent accumulated temperature model can be used to coarse-tune the moisture content of the corn at the outlet,dry precipitation model is used to fine-tune the moisture content of the corn at the outlet,provided models to support the establishment of the control system.(5)The experiment of corn drying with continuous corn drier showed that the control system with equivalent accumulated temperature model and dry precipitation model could achieve better control of the moisture content of corn at the outlet and the percentage of the moisture error within ±0.5% is 81.9%,the control accuracy had been greatly improved.