Enhancement of citric acid on low-grade limestone wet desulfurization performance coupled with spray and partial bubble technology

Abstract

Developing low-grade limestone as absorbents has been recognized as a prerequisite for industrial application of wet flue gas desulfurization (WFGD) due to the serious depletion of high-grade limestone for SO2 capture. In this research, citric acid was utilized as additive in order to improve the SO2 removal efficiency of low-grade limestone. The enhancement of citric acid on desulfurization performance and the effects of citric acid concentration were investigated based on the spray and partial bubble technology. The results show that the addition of citric acid into low-grade limestone slurry can significantly improve the desulfurization efficiency and the optimal blending ratio between citric acid and low-grade limestone was 1:5. The spent absorbents and reacted liquid phase products were analyzed by X-Ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ion chromatography (IC) and inductively coupled plasma luminescence spectrometry (ICP-OES). These characterizations illustrated that the oxidation of SO32− into SO42− ions along with formation of gypsum was inhibited in the presence of citric acid because of its strong reducibility, whereas the reaction between SO2 and SO32− was greatly promoted, leading to the high SO2 removal efficiency. Furthermore, molecular dynamics (MD) calculation was conducted to provide the microscopic information including the self-diffusion and hydration behavior of SO2 and the gas-liquid interface microstructure. These investigations are of significant importance in providing enhancement mechanism of citric acid on low-grade limestone WFGD process.