Measurements of mercury speciation and fine particle size distribution on combustion of China coal seams Lei Zhang a , Michael Daukoru b , Sarah Torkamani b , Shuxiao Wang a,⇑ , Jiming Hao a , Pratim Biswas b,⇑ a School of Environment, State Key Joint Laboratory of Environment Simulation and Pollution Control, Tsinghua University, Beijing 100084, China b Aerosol and Air Quality Research Laboratory, Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USA highlights " Quantified effect of Hg and Cl concentration on mercury speciation in flue gas. " Isokinetic model with multiple linear regression and iterative methods. " Evaluation of effect of mineral composition of coal on fine particle formation. article info Article history: Received 5 January 2012 Received in revised form 13 June 2012 Accepted 14 June 2012 Available online 27 June 2012 Keywords: Bench-scale measurements Mercury speciation Fine particle formation Oxy-coal combustion abstract The percentage of mercury that is removed in currently used air pollution control devices (APCDs) depends on the speciation in the flue gas exhausting from the coal combustor. Bench-scale measure- ments were carried out in the flue gas from combustion of different types of coal in a drop-tube furnace set-up to better understand the formation process of three mercury species, i.e. Hg 0 , Hg 2+ and Hg p , in gas- eous phase and fine particles. It was observed that due to chemical reaction kinetics limitations, higher mercury concentrations in flue gas lead to lower Hg 2+ proportions. The concentration of chlorine has the opposite effect, not as significantly as that of mercury though. With the chlorine concentration increasing, the proportion of Hg 2+ increases. Combusting finer sized coal powders results in the formation of more Hg 2+ . Mineral composition of coal and feed coal particle size has a great impact on fine particle formation. Increased Al in coal results in more finer particle formation, while Fe in coal increases concentration of larger particles. The coexistence of Al and Si can enhance the particle coagulation process. This process is also enhanced at higher coal feed rates, and when feed coal particle sizes are smaller. Results from oxy-coal and conventional air combustion were compared. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Coal combustors for electricity production are one of the largest sources of global anthropogenic mercury emissions [1]. Mercury is initially released from the coal in the elemental form. The mercury speciation during coal combustion consists of two processes, homogeneous mercury oxidation in the gaseous phase and hetero- geneous mercury adsorption onto the particles. A large fraction of the mercury remains in the gaseous phase [2–10]. Electrostatic precipitators (ESPs) can remove over 99% of the particulate mer- cury (Hg p ), and wet flue gas desulfurization (WFGD) systems, if present, can retain 67–98% of the gaseous oxidized mercury (Hg 2+ ) [10]. It is therefore important to understand the mercury oxidation mechanisms in the flue gas. Chlorine related species are known to be important oxidizing agents for mercury [11]. Other flue gas constituents such as SO 2 , NO, H 2 O; are reported to have secondary effects on the rate of the mercury oxidation [12,13]. To determine the mercury oxidation mechanism, kinetic and thermodynamic data were either calculated or obtained from sim- plified chamber experiments [12–15]. The assumption of gas- phase equilibrium for the mercury oxidation process in exhaust gases from coal combustors is not valid at temperatures below approximately 800 K [11]. The reaction mechanism begins with the kinetic framework proposed by Widmer et al. [16]. In the flue gas, conversion of HCl to Cl 2 is kinetically limited. At temperatures similar to those in the inlet to the APCD, equilibrium estimations indicate that half of the chlorine will be in the form of Cl 2 , but ki- netic calculations show that less than 1% of the chlorine is con- verted to Cl 2 [11]. The oxidizers such as Cl, Cl 2 and HOCl are all generated from HCl. 0016-2361/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2012.06.069 ⇑ Corresponding authors. Tel.: +86 10 62771466 (S. Wang), +1 314 935 5482 (P. Biswas). E-mail addresses: shxwang@mail.tsinghua.edu.cn (S. Wang), pbiswas@wustl. edu (P. Biswas). Fuel 104 (2013) 732–738 Contents lists available at SciVerse ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel