Design And Research Of On-line Measurement And Control Of Heavy Medium Density In Coal Preparation Plant

The dense medium coal separation technology has advantages of high separation efficiency,wide applicability and easy to be automatic.It is the most widely used coal preparation technology in China.This technology utilizes the difference in density between coal and gangue to achieve separation,and its separation efficiency is directly affected by the density of the dense medium suspension.At present,most small and medium-sized coal preparation plants in China still rely on manual measurement and control of heavy medium density.Only a few new and transformed large coal preparation plants have used automatic measurement and control technology of heavy medium density,which still faces issues such as low accuracy and poor stability.Based on an test bench for on-line measurement and control of heavy medium density,this thesis conducts design and research of on-line measurement and control of heavy medium density in coal preparation plant.Taking lump coal separation process in coal preparation plant as the object,the basic process of heavy medium coal separation process was studied,and the influence of heavy medium density on separation efficiency and the reasons for the change of heavy medium density were analyzed.By introducing Bernoulli equation,the influence factors and defects of differential pressure densitometer under dynamic measurement conditions are pointed out,and the basic principle and design process of PID control and Fuzzy-PID control are studied,so as to guide the design and research on on-line measurement and control of heavy medium density in coal preparation plant.The CFD software is used to numerically simulate the solid-liquid two-phase flow in the installation pipeline of the differential pressure densitometer.By analyzing the distribution characteristics of the flow field,the causes of fluctuation and error in the measurement of heavy medium density by the differential pressure densitometer are revealed,and the influence of the variation of heavy medium flow and density on the measurement of the densitometer is studied in depth.Based on PLC,the differential pressure heavy medium on-line densitometer is designed for measuring the heavy medium density in test bench.In order to solve the problem of fluctuation and error in the densitometer measurement,software filtering and flow compensation are used to optimize,filtering and compensation are realized by writing PLC subprogram.After measurement experiments,the output curve of the densitometer was found to be smooth,and it has good stability and measurement accuracy.Based on the heavy medium coal preparation process,a test bench for on-line measurement and control of heavy medium density is established,and simulation on automatic control of heavy medium density with different control strategies is conducted by establishing the mathematical model of density control for test bench.By designing and writing the automatic control program of heavy medium density,PID control and Fuzzy-PID control are applied to control the heavy medium density of test bench.The control effects of Fuzzy-PID control are proved to be better than PID control through the experimental research.Based on the configuration software WINCC,the operation interface for on-line measurement and control of heavy medium density is designed,which has functions such as online monitoring,graphic display,system control and hardware status monitoring and alarm.This thesis has 65 pictures,27 tables and 108 references.