Introduction
With the development of science and technology in recent years and the importance of industrial energy conservation and emission reduction, the requirements for flue gas purification and emission of thermal power plants are also getting higher and higher. Burning coal in thermal power plants will emit a large amount of sulfur dioxide, which is the most serious atmospheric pollutant to the environment detected worldwide. Therefore, it is urgent to solve environmental problems. Now the mainstream desulfurization method in thermal power plants is limestone/gypsum wet desulfurization. How improve the efficiency of the system and reducing energy consumption is the key to energy conservation and emission reduction. There are many kinds of flowmeters on the market now. Compared with various traditional flowmeters, ultrasonic flowmeters have the characteristics of non-contact measurement, no flow pressure loss, wide working range, good portability, and are suitable for large pipe diameters and large flow measurement occasions.Measurement principle
The pipe flow measurement system of the slurry circulating pump introduced in this paper is based on the ultrasonic Doppler method. There are many ultrasonic measurement methods, among which the Doppler method has many advantages: (1) The detection element can be placed outside the pipe wall without direct contact with the measured fluid, without damaging the flow field of the fluid body and without pressure loss; (2) The installation and maintenance of the external clip ultrasonic Doppler flowmeter will not affect the normal operation of the pipeline system and equipment; (3) The accuracy of ultrasonic Doppler flow measurement is less affected by fluid temperature, pressure, viscosity, density, and other parameters.
In the process of flow measurement by the ultrasonic flowmeter, ultrasonic probe T sends an ultrasonic emission signal with the frequency of Tf. The emission signal is reflected by the fluid and impurities in the fluid (usually solid particles or small bubbles), and ultrasonic probe R receives the ultrasonic wave transmitted from the pipeline. Since the fluid and its internal impurities have a certain relative velocity with the sensor T and sensor R installed on the pipe wall, according to the Doppler effect, the frequency of the reflected signal received by the transmitting signal through the fluid impurities becomes f, while the frequency of the transmitted signal reflected by the impurity particles received by the receiving sensor R is Rf.System design
In this paper, according to the principle of Doppler measurement, a flow measurement device for a slurry circulating pump is designed, including hardware design, software design, and experimental environment construction.Hardware design
The Doppler flow measurement system designed in this paper takes the new DSC chip as the core, which is mainly responsible for the system control and signal processing functions. The circuit is divided into a digital board and an analog board.
The analog signal transmitting, receiving, and processing part is located on the analog board, and the AD signal sampling, transmission, display, and other modules are located on the digital board. The system process is: DSC sends trigger signals to DDS, and DDS generates sine wave signals of fixed frequency, amplitude, and phase, which are transmitted by the transmitting probe after power amplification and harmonic amplification.
After receiving the echo signal, it goes through the LNA amplifier circuit and the band-pass filter to perform frequency mixing and demodulation. After the demodulated signal passes through the low-pass filter, it is sampled by the AD module of DSC itself, and further processed the signal to calculate the frequency difference, and finally, the flow data is obtained; The measured data can be stored through FLASH, displayed in real-time through the OLED display screen or transmitted to the remote monitoring center through GPRS wireless.
Experimental test
First, we need to build an experimental environment and platform. The experimental platform is composed of a water pump, pipeline, liquid storage tank, solid containing acidic liquid, and experimental instruments. Pour the solid containing acidic liquid into the liquid storage tank and stir it evenly. Turn on the water pump to make the solid-liquid mixture flow in the pipeline. When the flow rate is stable, use the flow measuring device designed in this paper to measure the flow.