Research On Grain Continuous Drying Model And System On Mass Flow Methods

Drying is an important processing link after the harvest of grain,and it has a great influence on the quality of grain.It is an important means to maintain and improve the quality of grain by rationally arranging drying process and parameters through intelligent monitoring and control technology.In this paper,aiming at the existing problem of continuous drying measurement and control technology,the strategy that process problem was solved in the process was adopted.The new online moisture detection and control models,algorithms and system were proposed and realized by the method of combining online precise measurement of the mass flow and intelligent prediction model for the first time,and thus achieved good detection accuracy and stability.The research project was supported by "Research on grain drying speed control model and intelligent system",which is based on the public welfare industry of food industry(NO: 201313001-07).The main contents are as follows:(1)A new moisture measurement and control method of grain drying process based on mass flow method and model is proposed for the first timeThe dynamic and accurate on-line measurement of the mass and flow rate in the continuous grain drying process is realized by adjusting the duty cycle of the intermittent feeding and discharging.Combined with the prediction model and the algorithm of grain drying process(MPC),3 kinds of new methods and models for moisture online detection was invented,that is mass and volume weight average moisture model prediction method(MVW),mass and flow linear equal proportion method(MFL)and mass and flow nonlinear model rolling prediction method(MFNL).In mass and volume weight average moisture model prediction method,grain total weight and height were detected in real time during the drying process,and average moisture content of grain in drier was predicted by means of the relationship between moisture and volume weigh.According to the problem that the deviation of prediction moisture which was caused by grain height and volume measurement errors and outlet moisture calculation errors,MFL and MFNL were proposed.In mass and flow linear equal proportion method and mass and flow nonlinear model rolling prediction method,grain import and export apparatus ofgrain dryer were controlled automatically,alternating grain feed,grain discharging and quality inspection was realized,online monitoring of the feed flow rate,discharge rate and the total amount of grain in the machine were achieved,and continuous detection of the outlet moisture and average moisture was achieved.(2)An intelligent control method and model for grain drying process based on mass flow method was proposedAccording to the characteristics of grain drying is a multivariable and large time delay process,3 kinds of continuous drying process intelligent control method were proposed,that is mass and volume weight average moisture model rolling prediction method(MVW),mass and flow linear equal proportion method(MFL)and mass and flow nonlinear model rolling prediction method(MFNL)which were based on the multiple parameter data fusion and prediction,through the method of establishment of forward and reverse process model and the optimization of model parameters.The combined control mode of drying process control,inverse process control,parameter optimization control and feedback control was adopted in mass and volume weight average moisture model rolling prediction method(MVW).Grain discharging rate was optimized by the inverse model,model parameters were rectified by the moisture difference between the actual and ideal discharged grain.According to the problem that the deviation of prediction moisture which was caused by grain height and volume measurement errors and outlet moisture calculation errors,MFL and MFNL were proposed.The interval time between grain import and export(i.e.time grain remains in dryer)was adjusted by mass and flow linear equal proportion method(MFL)and mass and flow nonlinear rolling model prediction method(MFNL)by comparing moisture of actual and ideal discharged grain.(3)Based on mass and flow linear method grain continuous drying process was simulated and analyzed.The moisture on-line detection process and moisture control process based on mass and flow method were simulated and analyzed.The calculation error of mass flow method grain moisture measurement was simulated and analyzed.The eysteresis effects of open loop parameter variations were simulated and analyzed.And closed loop grain automatic regulation process based on empty occupation ratio was simulated and analyzed.(4)The automatic precision measurement and control system of grain continuous drying process was studied.A set of automatic and precise measurement and control system for grain continuous drying process was developed combined with mass and volume weight average moisture model rolling prediction method,mass and flow linear equal proportion method and mass and flow nonlinear rolling model prediction method.By the analysis of the function of the measurement and control system,the overall design of the measurement and control system was determined.The hardware of control system for continuous drying process of grain is designed or improved and the software of control system was developed by using virtual instrument technology.The data acquisition function,data processing function,data storage function and control function of the software were analyzed.Experimental study on the operation condition of the grain continuous drying process measurement and control system was carried out.During the test,the mass of grain feeding and discharging was obtained by the weighing sensors those were installed in the bottom of the dryer.The grain discharging moisture of thousands of times grain feeding and discharging and all accumulation grain feeding and discharging was obtained by mass and flow quantity linear equal proportion method.And thus compared with determination of moisture of the GB/T5497-1985 "Moisture Determination and Inspection Method of Grain and Oilseeds".The test results showed that the error of moisture between prediction and determination of GB was-0.522%~0.281% by the 3-sigma error analysis method that the calculating of grain discharging moisture of thousands of times grain feeding and discharging was used.The average unit energy consumption is 4850.06 k J/kg in the process of test determination,and thus the energy saving effect reached 39.37% which was compared with GB / T 16714-2007 "continuous grain dryer" on unit energy consumption of corn drying less than 8000 k J / kg.And thus meets the requirements of actual production application.Through the work of the thesis,2 SCI papers were published,4 invention patents were applied(3 authorized),4 utility model patents were obtained.In the second and third chapter,the technical method is embodied in the invention patent ZL201510741411.0 In the fifth chapter,the technical method is embodied in the invention patent ZL201610522631.9.And the third authority of product identifycation of 2 products was obtained by cooperated with the enterprise.Meanwhile grain moisture meter online intelligent algorithm and circulation drying measurement and control technology were studied.Because of the limitation of space and the relation of research topic,these contents were presented in the appendix.