HCl removal from cement bypass flue gas at medium-high temperatures using cement bypass dust: Performance, mechanism, and adsorption kinetics

Abstract

The use of alternative fuels is a growing trend in the cement industry, and it may lead to issues with HCl emissions. This study investigated the HCl removal performance of cement bypass dust (CBPD) at medium-high temperatures (500–700℃). This is not only of great significance for controlling HCl emissions from cement kilns but also alleviates the disposal pressure of this industrial solid waste. The results show that HCl adsorption capacity increased first and then decreased with increasing temperature, reaching a maximum of 676 mg/g at 600°C. The HCl concentrations significantly influenced the reaction rate, yet its impact on the uptake chlorine capacity is comparatively minimal. CBPD without size separation showed the best dechlorination performance and highest final chlorine capacity compared with CBPD of size 0–48 μm and 48–75 μm. Blending inert SiO2 particles into CBPD can greatly increase the breakthrough time. The longest breakthrough time is 7580 seconds, approximately 35 times that of CBPD without dispersion. CaO is the primary substance in CBPD to remove HCl, and the reaction produces CaCl2 and its hydrate. A shrinking core model was used to analyse the experimental data, suggesting a combination control of the chemical reaction and the product diffusion.