428 / 2018-12-27 16:52:34

Study on the Effect of Particle Flow State on the Stability of LIBS Carbon Content Detection Signal

Rice husk ash; Laser-induced breakdown spectroscopy; Particle flow state; Signal stability

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ABSTRACT: Rice husk, a type of biomass fuel, is rich in amorphous silica. Laser-induced breakdown spectroscopy (LIBS) is a fast-responding non-contact detection method which can realize on-line detection of rice ash components and provide reference for boiler combustion control. This paper explores the optimum working conditions of LIBS technology through experiments, and extends the compatibility of LIBS technology with particle flow conditions through studies simultaneously.
In the industrial application of on-line detection of rice husk ash components, a vertically flowing sample state may occur in the ash discharge of a biomass boiler. After that, the ash is concentrated on the conveyor belt to be sent to the storage area, at which time the particles move horizontally with the conveyor belt. The paper uses the sample motion state simulation system to simulate the ash slag in the two motion states, so that the particles can be laser-induced breakdown during the vertical drop and horizontal motion for component detection, and then the effect of particle flow state on the stability of the LIBS detection signal can be determined.
According to the LIBS technology principle, a short pulse width laser can generate a stronger laser energy focusing in a short time under the same laser energy, while a long pulse width laser can continuously output energy for a longer period of time. The generated plasma temperature of a long pulse width laser is higher, and the secondary excitation ability is stronger with a larger expansion range of plasma plume. Therefore, this paper compares the effects of two laser pulse widths on the stability of LIBS detection signal by using a 1 ns pulse width laser and a 6 ns pulse width laser to further improve the detection error.
Experimental studies have found that long pulse width laser provides better stability of spectrum, and the relative standard deviation (RSD) of the detection result is smaller than that of short pulse width laser, and the RSD of the detection result is smaller in the state of horizontally transmitting samples. In addition, the LIBS detection in the state of horizontally transferring samples can obtain the spectral signal with stronger line intensity, and sample in conveyor, by contrast, leads to more stable signals. In summary, the use of long pulse width laser and LIBS detection in the state of transferring samples horizontally are effective means to improve the accuracy of multiple repeated detections of LIBS.