Application Of Coriolis Mass Flowmeter In Urea Machine

Diesel vehicle exhaust purification treatment is an important part of urban pollution control system.At present,SCR(Selective Catalytic Reduction)technology with urea solution as reducing agent is the mainstream scheme of purifying diesel engine tail gas.The NOx in tail gas is reduced by adding urea solution in urea machine to generate pollution-free N2 and H2 O.At present,the measurement instrument commonly used in the urea machine on the market is the volumetric flowmeter.This flowmeter has higher measurement accuracy at room temperature and pressure.However,it is easy to change the density of urea solution in the area where the temperature and pressure are different,resulting in greater measurement error.Although the Coriolis mass flowmeter has some errors in the measurement of two-phase flow,it is very little affected by temperature and pressure in the measurement of single-phase flow,so it can not only directly measure the mass flow rate and density of the fluid,but also has a very high measurement accuracy.Therefore,this paper studied the application of Coriolis mass flowmeter in urea machine,solved the related technical problems,and developed a real-time measurement system.In order to study the characteristics of the sensor signal of micro-bend type of Coriolis mass flow meter in the process of urea machine filling,an experimental scheme was designed to collect the signal of Coriolis mass flow sensor in the process of urea machine filling,and the experiment was carried out to collect the experimental data of large,medium and small gear filling.Data were processed on Matlab,and the phase difference signal model of the sensor in the process of urea machine filling was established,which showed that the phase difference of the sensor signal changed rapidly and frequently in the process of urea machine filling,and the phase difference was very small at a small flow rate.Based on the characteristics of the phase difference signal model of the urea machine filling process,the zero-crossing detection algorithm and DTFT algorithm which have better practical effect in the industrial field are evaluated,and the conclusion is drawn that the zero-crossing detection algorithm is more suitable for the urea machine filling measurement.The zero-crossing detection algorithm is improved to improve the dynamic response speed and small flow measurement accuracy.The research selects the full digital driving method and the sinusoidal starting vibration method,which improves the starting speed of the flow tube and speeds up the tracking speed of the driving signal,so as to ensure the fast and steady vibration of the flow tube.Taking TMS320F28335 as the core,the hardware and software system of Coriolis mass flow transmitter suitable for urea machine filling are designed.In order to realize the networked measurement instrument,the RS-485 bus communication system based on Modbus protocol is developed.The developed transmitter was matched with the primary instrument of Coriolis mass flowmeter produced by E+H Company.The single-phase water flow calibration experiment was carried out in our laboratory.Within the range ratio of 12:1,the measurement error was less than 0.1% and the repeatability error was less than 0.05%.The filling experiment of urea machine was carried out in the industrial site.The measurement errors of the three scales were all less than 0.1%,and the repeatability errors were all less than 0.05%,which met the requirement of 0.1 level accuracy.Compared with the 0.02 level accuracy of the volumic-type flowmeter used in the traditional urea machine,the Coriolis mass flowmeter developed by us has higher measurement accuracy.