Research On Continuous Emissions Monitoring System Of Velocity Of Flue Gas With Ultrasonic Flow Meter

The requirements of environmental protection become more and more strict. Thermalpower plants are major sewage enterprises, and the requirements of environmentalprotection department for CEMS (Continuous Emission Monitoring System) are verystrict. The flue gas flow rate is an important parameter for environmental protectiondepartments’ detection. Because of the characteristic of turbulence flow in the duct, themeasurement precise of flue gas flow can not meet the requirements of criterion.Based on advanced ultrasonic flow measurement technology, and combined withultrasonic transit-time measurement principle, a feasible and practical measurementmethod of flue gas flow is proposed in this paper. As the core of the high-precisionmeasurement system for ultrasonic flow meter, Altera’s high performance FPGA(Field-Programmable Gate Array) and Texas Instruments MSP430series of ultralowpower microcontroller (MCU) are used to complete the study for the system. The studymakes the system realize the accurate measurements of ultrasonic reverse travel time, thestore of them, and the display of the instantaneous flow/velocity and cumulative flow. Themain work for this paper:(1) This paper studies the principle of transit-time ultrasonic flow meter, and presentsthe design of overall system;(2) MSP430is designed as the core of the serial communication, LCD displaymodule and SD card storage module circuit;(3) Based on FPGA DDS pulse signal generator, pulse train driving ultrasonictransducer using adjustable amplitude of pulse sequence is put forward, which isconducive to emit more energetic ultrasonic signal;(4) Based on FPGA Boxcar integrator, sampling module using weak signal detectiontechnology is proposed, which improves the signal-to-noise ratio of signal and enhancesthe accuracy of measurement;(5) The overall performance of the system is verified by the scene test, and the mainfactors of measurement error are analyzed. Analyze experiment data and improve the structures and properties of instrument, in order to make ultrasonic flow meter havecertain accuracy and good stability. The system can continuously monitor stationarysources, and configure with other monitoring equipments to constitute CEMS system.