Simulation Study on the Demercuration Performance of Wet Flue Gas Desulfurization System
Wet flue gas desulphurization (WFGD) technology is the most mature and widely applied desulphurization technique in the world at present. As divalent mercury (Hg2+) is easily dissolved in aqueous solution, the effect of WFGD on mercury transformation and
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Abstract
Wet flue gas desulphurization (WFGD) technology is the most mature and widely applied desulphurization technique in the world at present. As divalent mercury (Hg2+) is easily dissolved in aqueous solution, the effect of WFGD on mercury transformation and removal efficiency has become a hot subject in the research of how to control mercury contamination with low cost. In this paper, the demercuration property of limestone– gypsum WFGD process is simulation studied by Aspen plus software, assessing the effect of different process parameters on demercuration efficiency. Results show that conventional WFGD system has a high removal efficiency for Hg2+ (>90 %) but ineffective at removing Hg0, and even Hg0 slightly increases due to reduction in Hg2+ by SO2 or SO32−. Mercury removal efficiency is negatively influenced by the increase in the temperature of flue gas, but can be enhanced by increasing the pH of slurry solution and the concentration of SO2 in flue gas. In addition, presence of chloride can lead to the formation of HgCl2 and ClHgSO3−, which inhibits the re-emission of mercury. Keywords
Remove mercury
1
WFGD
Introduction
Mercury is one of the most toxic heavy metals having a severe impact on the public health and environment [1]. According to the United Nations Environment Programme (UNEP) chemical branch in the 11th International Conference on Mercury as a Global Pollutant in July 2013, the total anthropogenic emission of mercury to the atmosphere in 2010 was estimated at 1960 tons. Mercury is present in trace amounts in coal, waste, and other materials and is released as a gas when these materials are burned. Coal burning is a major source of mercury emission, responsible for 475 tons of mercury emission into the air [2]. The growing concern over mercury emissions and effects is reflected by the move H. Kunkun (&) C. Guozhen N. Jianjun ShangHai Boiler Works, LTD, Huaning Road no. 250, Shanghai 200245, China e-mail: [email protected]
Simulation study
Aspen plus
toward establishing emission limits for sources such as coal combustion. Mercury in the flue gas occurs primarily in three forms: elemental (Hg0), oxidized mercury (Hg2+), and particle bound mercury (Hgp) [3]. Hg compounds can be controlled by existing air pollution control devices (APCDs) installed to control particulate, NOx and SOx, as a co-benefit control, which is a low-cost method. For example, Hgp can be easily captured by particulate matter control devices (PMCDs), such as electrostatic precipitators (ESP), bag filters [4]. Part of Hg2+ can be adsorbed onto fly ash and is subsequently collected along with ash in PM control devices. Wet flue gas desulfurization (WFGD) can remove most of Hg2+ due to its water-soluble property [5–7]. However, parts of Hg2+ would be reduced to Hg0 by sulfite in desulfurization process, increasing the re-emission of mercury, which decrease the removing mercury efficiency of WFGD [8]. Aspen Plus software has a powerful database, including various physical parameters of inorganic, organ
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