Ultra-repeatability measurement of coal calorific value by XRF assisted LIBS

The calorific value of coal mainly depends on the content of combustible organic elements and ash, which is a comprehensive indicator of coal quality. It is of great significance to quickly obtain the calorific value of coal into the boiler for the optimal control of coal blending and combustion in thermal power generation. However, the measurement repeatability of LIBS for coal calorific value has not yet met the requirement of standard deviation (SD) less than 120 J/g in Chinese national standard. This paper innovatively proposes an analysis method of XRF-assisted LIBS, which can not only analyze the combustible organic light elements by LIBS, but also can analyze the inorganic ash-forming elements by XRF with high stability, thus greatly improving the measurement repeatability of coal calorific value. According to the stability of intensity, the elemental emission lines in LIBS and XRF spectra are selected reasonably, and the prediction model is established through principal component analysis and multiple regression. Experimental results show that the SD of coal calorific values predicted is 72 J/g, which is one order of magnitude lower than 700 J/g of traditional LIBS, and fully meets the requirement of national standard. It is found that the measurement instability of calorific value mainly comes from the contribution of C line, and the SD of calorific value can be further reduced by means of spectra screening. This XRF-assisted LIBS technology with ultra-repeatability is expected to be applied in power plants, coal chemical industries and other industrial fields that need to pay close attention to coal quality.