Simultaneous HCl/SO₂ Capture by Calcined Limestone from Hot Gases

Abstract

Some confusion still exists in the literature regarding the simultaneous absorption of SO2 and HCl by calcined limestone in hot flue gases. Therefore, further efforts to understand and clarify the absorption behaviors of SO2 and HCl are presented in this study. Experiments were carried out under conditions that simulated combustion in a fixed-bed reactor coupled with an online Fourier transform infrared spectrometer. The fixed-bed reactor used was specially designed to be capable of handling high-temperature operations involving gas–solid reactions. This paper described and explained the phenomena of variations in the concentration profiles of SO2 and HCl during the simultaneous absorption process. This work suggested possible heterogeneous and homogeneous reactions that may occur under the conditions being studied. Particular emphasis is placed on elucidating why concurrent sulfation enhancement and chlorination suppression occurs; experimental evidence confirmed that these processes were caused because of the behavior of the sulfation process of chloride. In the present study, to continuously monitor SO2 and HCl discharged during reaction processes plays a crucial role in observing particular phenomena, providing important information regarding absorption characteristics. From the experimental results, it was observed that, upon increasing the temperature from 650 to 700 °C, chlorination was considerably suppressed because chloride started to vigorously react with SO2, leading to the indirect enhancement of sulfation and the re-release of HCl into the gas phase. It was also surprising to find that, at or above 700 °C, the overall uptake efficiency remained nearly unchanged despite the difference in reactivity of SO2 and HCl. Besides, the importance and impact of the gas atmosphere on the uptake efficiency was also analyzed and compared.

The Influence of SO2 and HCl Concentrations on the Consumption of Sodium Bicarbonate during Flue Gas Treatment

“…When limestone was used in a fluidized bed to decrease the emissions of SO 2 and HCl, it was also reported by Xie et al that the presence of HCl promotes the capture of SO 2 . However, the dependence of competition of HCl and SO 2 capture on temperature can be significant as was found when the simultaneous capture of HCl and SO 2 by CaO was studied by Lin et al…”

Effects of Sulfur and Calcium Compounds on Dioxin Reduction in a Fluidized Bed Combustor

“…When calcium and sulfur were added, desulfurization and dechlorination reactions occurred simultaneously. Lin and Chyang (2016) found that chlorination is significantly suppressed as chloride begins to vigorously react with SO 2 , leading to the indirect enhancement of sulfation and the re-release of HCl into the gas phase, as shown in Eq. (5).…”

“…Lawrence and Bu (2000) stated that the calcium oxide entrained into the freeboard at 650°C has a better hydrogen chloride removal efficiency. Kobyashi et al (2005) stated that Ca-based substances can be used to remove hydrogen chloride in a fluidized bed, even at temperatures exceeding 1000 K. The results of recent research indicate that the simultaneous desulfurization and dechlorination are possible at high temperatures in a furnace (Lin and Chyang, 2016). Hung et al (2018) indicated that total PCDD/Fs concentrations ranging from 45.5% to 73.8% were partitioned in the solid phase.…”

“…However, comprehensive studies are minimal. Calcium can simultaneously desulfurize and dechlorinate substances at high temperatures (Lin and Chyang, 2016), but experimental data regarding the effects of dioxin formation are still required. The purpose of this study is to investigate the relationship between sulfide, calcium, and the dioxin in fly ash.…”

Controllable growth of Na2CO3fibers for mesoporous activated alumina ball modification towards the high-efficiency adsorption of HCl gas at low temperature

“…At present, more studies have paid attention to the removal of acid gases from the hot ue gas (673-1073 K) of the coal industry. [4][5][6][7][8][9][10][11] The reaction mechanism mainly depends on the neutralization of acid and alkali to capture acid gas in the process of gas stream cleaning. Duo et al 5,12 reported that the higher HCl capacity of sorbents correspond to the higher temperature from 573 to 873 K. Na sorbents showed optimal HCl sorption performance in the temperature range of 673-773 K. Dou et al 13,14 found that Na 2 CO 3 , Ca(OH) 2 , or CaO were suitable to achieving the tolerance limit of 1 ppmv HCl from hot gas.…”