Intrinsic reaction selectivity between gaseous HCl and SO2 over ethanol-hydrated CaO adsorbent in coal-fired flue gas dechlorination

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The conversion of divalent mercury to elemental mercury using a solid reductant is the advanced technology of the mercury continuous emission monitoring system (Hg-CEMS). This work proposed new iron-and nickelbased reductants. In the fixed-bed experiments, the reductant carriers were screened and the effects of temperature, preparation parameters, and flue gas components on the efficiency of HgCl 2 reduction were investigated. The results show that SiO 2 has no effect on Hg 0 and does not adsorb Hg 2+ , which satisfies the requirements of the reductant carrier. The reduction efficiency of both Fe/ SiO 2 and Ni/SiO 2 exceeds 90% at 400 °C, and their reduction efficiency increases to almost 95% under the optimum parameters of active component to carrier molar ratio of 2 and particle size of 8−20 mesh. Nevertheless, HCl, O 2 , and NO in the flue gas have some negative impacts on the reduction efficiency of Fe/SiO 2 and Ni/SiO 2 because they react with the active components Fe and Ni and inhibit the conversion of Hg 2+ to Hg 0 . However, SO 2 and CO 2 basically have no effect on the Hg 2+ reduction performance of the two reductants.

Section: Introductionmentioning

confidence: 99%

Reduction of Divalent Mercury to Elemental Mercury by Fe- and Ni-Based Reductants

Li,

Shang

et al. 2024

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“…Coal-fired power generation is anticipated to remain the primary source of electricity for a longer period in China, despite the rapid advancements in alternative energy sources . However, coal combustion power plants emit various atmospheric contaminants, including NO x and mercury, which are harmful to human health and the ecological environment.…”

Section: Introductionmentioning

confidence: 99%

Study on SO₂ Poisoning and Regeneration of the Low-Temperature Fe–Sn–Mn/TiO₂ Catalyst for Simultaneous Removal of NO_x and Mercury

Li,

Huang,

Zhou

et al. 2024

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A catalyst of Fe−Sn−Mn/TiO 2 was synthesized by the impregnation method employed for selective catalytic reduction (SCR) to remove NOx and mercury at a low temperature. The effects of SO 2 on the performance and poisoning of the catalyst Fe−Sn−Mn/TiO 2 and the regeneration of water washing, acid washing, and thermal reduction on the activity restoration of the deactivated catalyst were investigated. The sulfur poisoning and regeneration mechanisms were determined through a comprehensive array of characterization methods. The findings show that SO 2 causes irreversible deactivation of the Fe−Sn−Mn/TiO 2 catalyst. The consumption of metal active components and deposition of metal sulfates/sulfites, as well as ammonium sulfates/sulfites on the catalyst surface, are proven to be the primary cause to the deactivation. Stirring water washing and sulfur acid washing effectively remove ammonium sulfates/sulfites and metal sulfates/ sulfites adhered to the catalyst surface so that the poisoned catalyst is recovered to its original activity as effectively as the fresh one. The thermal reduction regeneration exhibits effectiveness in eliminating ammonium sulfates/sulfites yet falls short of completely removing metal sulfates/sulfites, and the acid sites are consumed under NH 3 atmosphere, leading to 80% recovery of the activity compared with the fresh catalyst.

“…10 As a result, it produces a lot of extra HCl/Cl 2 in the resultant HgCl 2 calibration gas, which is not allowed for the Hg-CEMS calibration gas because a tiny quantity of HCl/ Cl 2 can easily oxidize Hg 0 , resulting in much bigger errors in the calibration procedure. 11,12 That is why the HgCl 2 calibration gas must be HCl/Cl 2 -free. It reported that metal chlorides, such as MnCl 2 , FeCl 3 , and CuCl 2 , can potentially catalyze and oxidize Hg 0 .…”

Section: Introductionmentioning

confidence: 99%

“…Given the constraints of gas-phase reaction kinetics, the dosage of HCl/Cl 2 is often several hundred times that of Hg 0 to speed up the reaction rate of Hg 0 oxidation . As a result, it produces a lot of extra HCl/Cl 2 in the resultant HgCl 2 calibration gas, which is not allowed for the Hg-CEMS calibration gas because a tiny quantity of HCl/Cl 2 can easily oxidize Hg 0 , resulting in much bigger errors in the calibration procedure. , That is why the HgCl 2 calibration gas must be HCl/Cl 2 -free.…”

Section: Introductionmentioning

confidence: 99%

HgCl₂ Calibration Gas Generated by a Solid Oxidant

Zhou,

Li,

et al. 2024

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The generation of gaseous, chlorine-free, and pure HgCl 2 calibration gas is a vital technology for the mercury continuous emission monitoring system (Hg-CEMS). Presently, the conventional approaches involve gaseous chlorine sources (Cl 2 /HCl) to oxidize Hg 0 or liquid HgCl 2 to be evaporated. However, the former inevitably engenders the excessive chlorine species that detrimentally affects the purity of HgCl 2 , and the latter does not achieve a steady flow rate of HgCl 2 . In this paper, a new technology was invented that uses the metal chlorides as the chlorine source to oxidize Hg 0 to produce highly pure and precise gaseous HgCl 2 calibration gas that can be entirely applied in the Hg-CEMS. The impacts of metal chlorides, carrier materials, agent dosages, and reaction temperatures on the HgCl 2 generation efficiency were investigated. The findings demonstrate that the optimal oxidant is CuCl 2 as the active component, which is supported by MCM-41 as the carrier with a dosage of 10% in mass. The active component manifests a highly dispersed amorphous state and a crystalline state upon the carrier that are characterized in different activation temperatures. Amorphous state Cu and Cl efficiently oxidize Hg 0 to HgCl 2 at 60 °C, while crystalline CuCl 2 requires a higher activation temperature of 180 °C, suggesting a reaction temperature of 180 °C that optimally allows the active components to be fully utilized and avoids HgCl 2 condensation at a low temperature to ensure the efficiency of the oxidation reaction. HgCl is verified as an intermediate species to form ultimate HgCl 2 . HgCl is formed by Hg 0 and active chlorine in CuCl 2 through the fast chemical reaction, which subsequently produces the resultant HgCl 2 by exchanging the electrons with Cu 2+ through the Cl atoms.