Effect of H2O on the volatilization characteristics of arsenic during isothermal O2/CO2 combustion

Abstract

The effect of H 2 O on the volatilization behavior of arsenic in coal was studied under O 2 /CO 2 combustion conditions at 800-1300 ºC, which covers the effective range of coal combustion temperatures appropriate for conventional coal combustion technologies. By controlling the combustion time of coal, the volatilization percentage and rate of As versus time were obtained. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were used to study the evolution of minerals with and without H 2 O under O 2 /CO 2 combustion conditions. The effect of CO 2 on As volatilization was first investigated and it was found that increasing CO 2 concentrations inhibits the volatilization of As, with this effect decreasing with increasing temperature. When a fraction of the CO 2 was replaced with H 2 O, the volatilization of As increased, but the positive effect of H 2 O also decreased with increasing temperature. The volatilization percentage of As with 30% H 2 O was 6.1% higher than that without H 2 O at 800 ºC, while it was only 2.7% higher at 1300 ºC. When the concentration of H 2 O increased from 0 to 30%, the peak value of the As volatilization rate increased and the time needed to reach the peak value decreased. The volatilization characteristics of As for three coals were very similar, which demonstrates that the effect of H 2 O was not limited to only one specific coal. IntroductionCoal combustion accounts for about 70% of Chinese power generation and this situation is unlikely to change in the near future [1]. Pollutants from coal combustion are responsible for numerous environmental problems [2,3]. Given its nature as a semi-volatile toxic metal, most of the arsenic (As) in coal will volatilize during combustion and be found in fly ash, bottom ash and the gas phase as the flue gas cools down, and some of it will finally be emitted into the atmosphere [4,5]. The release of As is attracting increasing attention because it not only affects several human organs, but also interferes with the immune system [6].The volatilization and partitioning behavior of As is influenced by several factors, including the combustion temperature and combustion atmosphere [7][8][9][10][11]. In O 2 /CO 2 combustion, the CO 2 concentration in the furnace can reach 60%~80% or more [12][13][14][15], which is significantly higher than that in air fired combustion. Zhuang and Pavlish [16] studied the fate of As in a pilot-scale furnace during O 2 /CO 2 combustion, and found that the concentration of As in fly ash was lower than that in O 2 /N 2 combustion. While for a bench-scale fluidized bed study, Roy et al. [17] found that there was little difference in the volatilization of As between O 2 /CO 2 combustion and O 2 /N 2 combustion at 21% oxygen. However, Liu et al. [8] conducted combustion experiments in a customized isothermal thermogravimetric system, and concluded that high concentrations of CO 2 in oxy-fuel atmosphere inhibited the volatilization of As as compared to air at a low temperature, but that the volatilization r...

The effect of H2O on formation mechanism of arsenic oxide during arsenopyrite oxidation: Experimental and theoretical analysis

“…The solid samples (raw coal and residue after sequential chemical extraction) must be digested before measurement to obtain the concentration of arsenic. More details on the digestion procedures can be found elsewhere [17,26].…”

“…S1 in Supporting Information. The description of the combustion system and experimental procedure are described in our previous work [17].…”

“…In recent years, several studies have focused on the release characteristics of arsenic [14][15][16]. In the research of Zou et al [17], combustion experiments were conducted to investigate the volatilization of arsenic, and the results showed that arsenic release is mainly dependent on oxidative decomposition of sulfide-bound arsenic. Liu et al [18] conducted combustion experiments to investigate the simultaneous release behavior of sulfur and arsenic in an isothermal thermogravimetric reactor, and found that the content of sulfide-bound arsenic in coal has a positive influence on the arsenic release.…”

The Influence of NH3 on Coal Combustion Kinetics during Coal/NH3 Cocombustion: Experiments and ReaxFF MD Simulations

“…Each coal sample utilized weighed approximately 0.08 g with a precision of ±0.0001 g. The total gas flow rate was 2.67 L/min. Our prior research demonstrated that the gas flow rate of 2.67 L/min can mitigate the impact of external diffusion on experimental outcomes. − At least three experiments per group were conducted to reduce experimental errors. Table shows the detailed experimental conditions.…”