Fuel Processing Technology 142 (2016) 6–12

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Fuel Processing Technology

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Effect of fly ash composition on the retention of mercury incoal-combustion flue gas

Ping He a,b, Xianbing Zhang b, Xiaolong Peng b, Jiang Wu b,⁎, Xiuming Jiang a,⁎a School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, Chinab School of Energy and Environmental Engineering, Shanghai University of Electric Power, Shanghai 200090, China

⁎ Corresponding authors.E-mail addresses: wjhg2000@126.com (J. Wu), xmjian

http://dx.doi.org/10.1016/j.fuproc.2015.09.0230378-3820/© 2015 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 17 May 2015Received in revised form 7 September 2015Accepted 19 September 2015Available online xxxx

Keywords:Mercury retentionFly ashesDecomposition temperatureCarbonInorganic components

Fly ash from coal-fired power plant has been reported to be a promising sorbent for mercury capture. However,the nature of the Hg–fly ash interaction is still unknown. In this work, the thermal decompositionmethod is usedto evaluate the effect of the fly ash composition on the retention ofmercury in coal-combustion flue gas. Eight flyash samples were collected from the electrostatic precipitators of eight full-scale pulverized coal-fired powerplants. The high-temperature treatment is performed to gradually decompose the carbon and mercury speciesin the fly ashes, and each fly ash are divided into four groups. The content of the carbon and mercury presentin all the examined samples was measured. The results show that the most mercury species are decomposedfrom the fly ash at 300 °C. The quantity of carbon in the fly ash alone does not determine the amount of mercuryretained at any temperature. The decomposed mercury content is related to the mercury content of the fly ash.The carbon particle with ultra-strong mercury capture capacity cannot be found in the fly ash. Furthermore,X-ray fluorescence spectrometry (XRF) is used to identify the elemental composition of inorganic componentsof all the native fly ashes. Multivariate linear regression method is used to assess the dominated componentsthat determine the mercury retention capacity of these fly ashes. The results indicate that the carbon, silicon,iron, sulfur, andmagnesium infly ash all play amajor role inmercury retention. Hence, both carbon and inorgan-ic components influence the retention of mercury in the fly ash.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction

Currently, mercury has become a leading concern among the air toxicmetals because of its high toxicity, volatility, bioaccumulation in the envi-ronment, and severe health effects [1]. Coal-fired power plants are nowclassified as the largest single anthropogenic source of mercury air emis-sions [2]. Combustion can gasify mercury in coal, allowing the vaporizedmercury to enter the combustion gas exhaust stream [3]. Previous studieshave reported that fly ash, as the by-product of coal combustion, mightcatalyze the oxidation of mercury and contribute to its capture [4,5].

Fly ash mainly consists of unburned carbon (UBC) particles and alu-minosilicate particles. Various methods are used to explore the interac-tion between mercury and fly ash [6–16]. Among them, many authorshave focused on the characterization of native fly ash and their proper-ties of mercury retention [8–12]. They have found that the carbon in flyash shows a remarkable retention capacity for retaining the mercury influe gas [9]. At the same time, some scholars have studied the adsorp-tion capacity of fly ash for mercury by laboratory-scale experiments[13–16]. The results have also shown that themercury adsorption is de-termined by the carbonaceousmaterials in fly ash [13,17]. However, not

gsh@126.com (X. Jiang).

all carbon in fly ash is equal in ability to capturemercury in flue gas [10].The quantity of carbon in fly ash alone does not determine the amountof Hg captured [8]. The mercury retention depends on the characteris-tics offly ash and the process conditions [18]. Since fly ash is a very com-plicated mixture, the variables that influence the retention of mercuryin fly ash are still unknown. Hence, further studies should be put toidentifying the fly ash composition responsible for mercury retention.

Temperature also considerably affects the capture capacity of fly ashfor mercury [8,19–21]. Recently, the temperature-programmed decom-position desorption (TPDD) technique has been proposed, with whichthe molecular structure of mercury species in fly ash can be identified[20–23]. The results show that HgClx (including HgCl2) can bedecomposedwhen temperature reaches 300 °C [23], andmercury sulfatecontaining chlorine (HgSxOyClz) desorbs from fly ash at about 500 °C[22]. Lopez-Anton et al. [21,24] have further studied the properties ofmercury species in fly ash. They first obtained the database of thermaldecomposition profiles (TDP) of many mercury species. Thereafter,they measured the TDP of the gaseous mercury evaporated fromthe fly ash by TPDD technique. As compared with the database, theyhave found that there are four mercury species (HgS, HgO, HgCl2, andHgSO4) in fly ash. However, the mercury–fly ash interaction, as well asthe role of inorganic components, is still unknown and needs to be stud-ied more thoroughly. To the best of our knowledge, a limited number of

Table 2Pore volume, pore size and BET surface area of every sample.

Flyash

Pore volume (cm3/g) Pore size(nm) BET surface (m2/g)

20 °C 300 °C 20 °C 300 °C 20 °C 300 °C

FA1 0.0009 0.0008 55.77 33.82 0.1193 0.2190FA2 0.0006 0.0004 n/a n/a 0.0310 0.0488FA3 0.0011 0.0009 n/a n/a 0.0094 0.0038FA4 0.0009 0.0007 66.46 37.31 0.0588 0.0998FA5 0.0009 0.0008 n/a 9.12 0.1312 0.0683FA6 0.0017 0.0009 4.78 94.70 3.6441 0.0600FA7 0.0010 0.0010 n/a n/a 0.0341 0.0478FA8 0.0013 0.0010 6.11 7.02 0.8294 0.5454

Table 3Elemental composition of the inorganic components of the native fly ashes (wt.%).

FA1 FA2 FA3 FA4 FA5 FA6 FA7 FA8

Na2O 0.91 0.00 0.60 0.70 0.80 0.85 0.83 0.58

7P. He et al. / Fuel Processing Technology 142 (2016) 6–12

experiments have been performed to investigate how the fly ash compo-sition, including carbon and inorganic components, affects the amount ofmercury species.

In this work, eight fly ash samples collected from full-scale pulverizedcoal-fired power plants were tested to explore the interaction betweenmercury and fly ash composition. Four different temperatures are usedto decompose the carbon and mercury species in the fly ashes. The con-tent of the carbon and the mercury species were measured by the losson ignition (LOI) and automatic mercury emission analyzer (Lumex RA-915 M), respectively. The X-ray fluorescence (XRF) is also used todetermine the elemental composition of the inorganic components ofthe nativefly ashes. Finally, the effect of thefly ash composition, includingcarbon and inorganic components, on the mercury retention wereevaluated by multivariate linear regression method.

2. Experimental method

2.1. Fly ash samples

In general, there is no comparability for two fly ashes since their el-emental composition is different and depends on the combusting condi-tion and the quality of coal feed. However, since all the fly ash includetheUBCand inorganic components. Theirmain composition is very sim-ilar relatively. Hence, the uniform tendency of Hg–fly ash interactionsstill can be obtained by statistical analysis when the number of samplesis enough large. In this way, some individual characteristics of one flyash, such as its coal feed with high content of mercury, would bring aslight influence on the terminal results.

In this work, eight fly ash samples were collected from the electro-static precipitators of eight fully-scale pulverized coal-fired powerplants in the East of China. They are denoted as FA1-FA8. Therein, theFA1 sample comes from the burning of coal blend of bituminous andsubbituminous coal, and the others are obtained from the burning ofthe mixtures of bituminous and lignite coal. Their power capacities are350 MW, 325 MW, 125 MW, 660 MW, 300 MW, 135 MW, 600 MWand 300 MW, respectively.

2.2. Experiments

From the above discussion, mercury retention may strongly associ-ate with the carbon in fly ash. It is well known that the carbon in flyash is a complex material with various different carbon structures.One question about retention of mercury in fly ash presented here iswhether retention capacity is mainly determined by a certain type ofcarbon material. We cannot give a direct answer because separatingeach carbon material in fly ash is almost impossible via current experi-mental tests. However, some groups of carbonmaterials can be separat-ed for the carbon in fly ash by physical or chemical methods [10,14].

In general, differentmaterials have different decomposition temper-atures. For a mixture consisting of many types of carbon materials, suchas the carbon in fly ash, some carbon materials can be separated bydecomposing the others when the temperature is more than theirdecomposition temperatures. Therefore, if we suitably adjust decomposi-tion temperature of carbon, the carbon infly ash can be divided into somegroups. Note that high temperature is also capable of decomposing themercury in fly ash. Considering the fact that mercury retention is closelyrelated to the carbon infly ash, the decomposedmercury and carbonmay

Table 1Unburned carbon (UBC) percentage of every sample.

Temperature (°C) FA1 FA2 FA3 FA4 FA5 FA6 FA7 FA8

300 0.219 0.148 0.119 0.262 0.066 0.175 0.007 0.192450 0.471 0.419 0.348 0.516 0.244 2.037 0.290 0.819600 0.593 0.627 1.358 2.429 0.314 4.255 0.668 2.053750 1.958 1.459 1.885 3.164 0.781 5.034 0.780 2.076

imply some information of the interaction between mercury and fly ash.According to this research, the amounts of decomposed carbon andmer-cury species in these fly ashes are measured in this work to evaluate theeffect of the carbon on mercury retention.

Here, four temperatures, i.e. 300 °C, 450 °C, 600 °C, and 750 °C, areset to change the decomposition temperatures for dividing each flyash into four groups. All the samples undergo this four-temperaturetreatment for 1 h of each time to fully decompose the carbon particlesby muffle furnace. The carbon content of each sample is estimated asloss on ignition (LOI) and determined by combustion of the carbon at815 °C for 0.5 h. An automatic mercury emission analyzer (LumexRA-915 M), using an adsorption spectrometer, is adopted to determinethe mercury content of solid directly.

The porous texture of each fly ash is performed using amicrometricsAccelerated Surface Area and Porosimetry (ASAP) 2020 system. It ischaracterized by the Brunauer–Emmett–Teller (BET) surface area,pore volume and pore size analysis. Prior to the experimental measure-ments, every samples are heated to 110 °C at least 6 h to remove themoisture, and then degassed for 12 h under vacuum.

Chlorine is measured to estimate the interaction with mercury re-tention. For Cl content, the solution is prepared for fly ash to injectinto a Dionex DX 500 ion chromatograph (Dionex Co., CA).

This work also focuses on the influence of the inorganic componentsof the fly ash on mercury retention. Thus, the elemental composition ofthe inorganic components is analyzed from fused-glass disks of high-temperature ash by X-ray fluorescence (XRF). Prior to XRF analysis,thefly ashes are preheated to oxidize all carbonaceousmaterials andde-compose minerals containing carbonates, sulfides, and hydroxides inthe atmosphere [11]. The fused-glass disks are prepared to be used forthe XRF analysis following ASTMmethods D-3682 and D4326.

3. Results and discussion

3.1. LOI, porous texture, and XRF analysis

Table 1 shows the LOI values of all the examined samples. The car-bon content of all the fly ashes is very low, which is regarded as a clas-sical characteristic of fly ash. Only a small number of carbon materials

MgO 0.86 1.01 0.95 0.83 1.07 1.30 1.59 0.55Al2O3 37.50 31.40 43.20 35.90 36.80 28.70 34.90 40.20SiO2 42.50 43.30 44.80 49.50 49.30 52.30 47.80 52.50P2O5 0.34 0.00 0.33 0.16 0.18 0.00 0.20 0.00SO3 0.94 0.72 0.59 0.52 0.53 0.67 0.45 0.37K2O 0.96 1.02 0.89 1.53 1.13 1.80 1.49 0.28CaO 9.70 10.20 3.19 3.55 4.63 6.66 6.52 1.33TiO2 1.16 1.55 1.41 1.24 1.29 0.95 0.91 1.21MnO2 0.11 0.17 0.03 0.05 0.05 0.09 0.08 0.00Fe2O3 4.82 9.81 3.90 5.88 4.07 6.45 5.08 2.86

Fig. 1. Curves of the mercury content of the fly ashes as a function of temperature.

8 P. He et al. / Fuel Processing Technology 142 (2016) 6–12

are decomposed from the fly ashes at 300 °C. As the temperature in-creases, the LOI value of each sample gradually increases. A large in-crease in the LOI values can be found at 600 to 750 °C, indicating thatthe decomposition temperatures of most carbon materials in the flyashes are at above 600 °C.

Table 2 lists the pore volume, pore size, BET surface of every sampleat 20 and 300 °C. The measured data are very lower than those of coals[11], indicating that fly ash cannot be regarded as porous material. It isnoted that FA6 sample has the largest pore volume, pore size, BET sur-face. This may result from its high UBC percentage (5.034%) becausethe carbon is characteristic of porous textures. FA5 sample has the largerBET surface than FA4 sample, while the former has the smaller UBC per-centage than the later. Hence, the UBC shows a complicated influence

Fig. 2. Evolution of the mercury content with the decomposed carbon content at the

on the porous textures of fly ash. Not all the UBC particles are benefitfor improving the porous textures, and some inorganic componentsalso affects BET surface of the fly ash. It is also found that temperaturecannot provide the obvious tendency for porous textures.

Table 3 lists XRF data to obtain the elemental composition of the in-organic components of all the native fly ashes calculated as percentageof oxides. It has been observed that the inorganic components mainlymake up of aluminosilicates at different stages of transformation andcontain a small proportion of the other elemental composition.

3.2. Carbon content and mercury retention

For all the samples, mercury content is measured to evaluate the ef-fect of the composition of these fly ashes on mercury retention. Fig. 1shows the curves of themercury content of all the fly ashes as a functionof temperature. As the temperature increases, the mercury would begradually decomposed from the fly ash. All the samples exhibit a re-markable decrease inmercury content at 300 °C. This behavior suggeststhatmostmercury in thefly ash is stable at ambient temperature.Whenthe temperature reaches up to 450 °C, mercury content of all the sam-ples retains at the low level. The results indicate that at the high temper-ature of 600 °C, all the samples almost have nomercury species. Due tothe very lowmercury content of the fly ashes at 600 °C, the analysis forthe fly ashes at 750 °C is not carried out in this work.

The LOI values indicate that the carbon in the fly ashes can also bedecomposed as the temperature increases. As mentioned above, therole of carbon is not clear in mercury retention. Then we investigatewhether the decomposed mercury content depends upon thedecomposed carbon content or not. Fig. 2 shows the evolution of thedecomposed mercury content with the decomposed carbon content atthe different temperatures. For eight native fly ashes at the temperature

temperatures of (a) 20 °C, (b) 20–300 °C, (c) 300–450 °C, and (d) 450–600 °C.

Fig. 3. Evolution of the residual mercury content with the carbon content at the tempera-tures of (a) 300 °C, (b) 450 °C, and (c) 600 °C.

9P. He et al. / Fuel Processing Technology 142 (2016) 6–12

of 20 °C, although FA6has the highest carbon content, itsmercury contentis lower than that of FA8, FA4, FA3, and FA1 (see Fig. 2a). This may resultfrom the mercury content in coal or the UBC quality. The low mercurycontent in the coal leads to capturing little mercury on FA6. In this analy-sis, this sample would bemore efficient to retain higher amounts of mer-cury when exposed to higher mercury concentrations in the flue-gas dueto its higher andmore porous unburned carbon content. Then, themercu-ry contents in some coals used in power stations 4, 5, and 6 aremeasuredto verify the above hypothesis. The results show that the ranking of themercury content in coals follows the trend FA4 (96.9 ng g−1) N FA6(84.3 ng g−1) N FA5 (72.4 ng g−1), which is the same as that in fly ash(see Fig. 2a), rather than the carbon content in fly ash (see Table 1).This suggests that UBC is not a major factor in determining the mercuryretention in fly ash. Some UBC show theweak chemical strength to inter-act with the mercury specials. At the temperature of 300 °C, FA4 has thehighest content of decomposed carbon and mercury. FA1 has the higherdecomposed carbon content than FA3 and FA8, but it has the lowerdecomposed mercury content than FA3 and FA8 (see Fig. 2b). At thetemperatures of 450 °C, FA3 has the highest decomposed mercurycontent, but its decomposed carbon content is not highest among theeight fly ashes (see Fig. 2b). Similarly, at the temperature of 600 °C, FA8also shows the same tendency as FA3 at the temperature of 450 °C(see Fig. 2c). Hence, the conclusion can be found that the carbon contentcannot determine the amount of mercury retained at any temperature,since all the data manifest the nonlinear variation between carbon con-tent and mercury content. This is in agreement with previous studies [8].

On the other hand, the original mercury content of the fly ash mightaffect the amount of the decomposed mercury. Fig. 3 shows the evolu-tion of the residual mercury content with the carbon content in the flyashes at the different temperatures. No correlation between the residualmercury content and the carbon content is observed. This is similarto the behavior of the decomposed carbon and mercury. For all thenative fly ashes, the ranking of the mercury content follows the trendFA4 N FA8 N FA3 N FA1 N FA6 N FA7 N FA5 N FA2 (see Fig. 2a). Whenthe temperature reaches 300 °C, the decomposed mercury contentalso retains this ranking (see Fig. 2b). Fig. 3a shows that there is a slightchange in the ranking of the residual mercury content of the fly ashes at300 °C, i.e. FA3 N FA8N FA4 N FA1N FA6 N FA7N FA5 N FA2. This is same asthe ranking of the decomposed mercury content at the temperature of450 °C (see Fig. 2c). Similarly, at the temperature of 650 °C, the amountof the decomposedmercury of each sample also depends on the residu-al mercury content of the fly ashes at 450 °C (see Figs. 3b and 2d).Hence, it is observed that the quantity of mercury in these fly ashes de-termines the amount of decomposed mercury.

In addition, the interaction between mercury retention and poroustexture cannot be found after an analysis of the measured data, asshown in Table 2, Figs. 2a and 3. FA4 sample at 20 °C has the highest re-sidual mercury content, but its porous texture, excluding pore size, isnot the best among all the examined samples. In this way, when poresize is used as a main parameter to characterize the mercury retentioncapacity, the same evolution cannot be observed for the othersamples.FA3 sample with the second highest pore size (55.77 nm) provides alower residual mercury content than FA8 sample with 6.11 nm poresize. Hence, the mercury retention is not closely associated to the po-rous textures of fly ash. Such phenomena also occur at a temperatureof 300 °C. FA3 sample with the highest residual carbon content doesnot provide the special porous textures as compared with the others.

Fig. 4 gives the possible interaction betweenmercury and carbon inflyash. Two retention modes are labeled as Model A and Model B to modelthe terminal structures of mercury species in fly ash. It is well knownthat fly ash has many types of mercury species. Model A represents thateach type of carbon material only adsorbs a type of mercury species.That is to say, when one carbon is decomposed due to high temperature,the mercury adsorbed on this decomposed carbon would be spontane-ously removed from fly ash. But the above data suggests that Model Acannot occur in fly ash, since there is no correlation between the

decomposed carbon and the mercury. Thus, the carbon loss is not theonly factor for the highest decomposed mercury content present in thefly ashes at 300 °C. The carbon particle with ultra-strongmercury capturecapacity cannot be found in fly ash. In this analysis, Model B might beclose to the practical model of mercury species present in fly ash. Whenthe temperature increases, some mercury species are desorbed from theresidual carbon.Hence, both thedecomposed carbon and themercury de-sorption form the total amount of decomposed mercury of fly ash. Forthese fly ashes at 300 °C, the obvious confusion between the highestdecomposed mercury content and the lowest decomposed carbon con-tent also suggests that most of the mercury would be desorbed fromthe residual carbon. As the temperature increases, the mercury speciescontinues to escape from the residual carbon. Terminally, at the tempera-ture of 600 °C, the residual mercury contents of the fly ashes are verysmall. This is the result of the lower decomposed mercury contentalthough the residual carbon content is relatively high.

Fig. 4. Schematic of decomposed mercury from fly ash. Hg-X denotes the mercury species in fly ash.

10 P. He et al. / Fuel Processing Technology 142 (2016) 6–12

3.3. Chlorine content and mercury retention

Fig. 5 shows the evolution between residualmercury and Cl contentsat the temperature of 20 °C. The Cl contents of all the examined fly ashesare less than 100 ppm. It can be seen that the Cl contents in fly ashesshow a nonlinear correlation with the residual mercury content. Thisis consistent with the previous experimental and theoretical results[11,25]. Other characteristics of fly ash may affect the mercuryretention.

3.4. Inorganic components and mercury retention

Since the carbon content cannot alone determine the retention ofmercury in fly ash, the inorganic components might affect mercury

retention. As listed in Table 2, the inorganic components are a complexmixture with many chemical elements. Obviously, knowing the domi-nant components determining retention capacity is very important toevaluate the mechanism of mercury retention by fly ash. In this work,multivariate linear regressionmethod [26] is used to estimate the dom-inant components. First, the corresponding equations need to be built.For these fly ashes, all the equations used in this calculation should re-late to the fly ash composition, including the decomposed carbon andthe elemental composition of inorganic components. Herein, their con-tent is set as the independent variable (x), and thedecomposedmercurycontent is classified as the dependent variable (y). Then the basic modelfor linear regression is.

yi ¼ β0 þ β1xi1 þ β2xi2 þ…þ βmxim þ εi: ð1Þ

Fig. 5. Evolution of residualmercury contentwith the Cl content at the temperature of 20 °C.

11P. He et al. / Fuel Processing Technology 142 (2016) 6–12

For Eq. (1), the system has n observations of one dependent variableand m independent variables. Thus, yi is the ith observation of the de-pendent variable, i=1, 2,…, n. xij is ith observation of the jth indepen-dent variable, j = 1, 2, …, m. The value βj denotes parameters to beestimated, and εi is the ith independent identically distributed normalerror. The t-test is performed to obtain the least residual error of regres-sion by adjusting the coefficient of determination [26]. The forwardstepwise regression algorithm is used to assess the dominated indepen-dent variables [27]. Here, the former six fly ashes are selected as thetraining samples, and FA7 and FA8 samples are used as the testing sam-ples for verified the accuracy of our calculatedmodel. The calculated re-sults show that the decomposed mercury content in these fly ashes at300 °C is mainly determined by the content of carbon, SiO2, Fe2O3,SO3, and MgO. All the coefficients of Eq. (1) are carried out. The expres-sions are described as follows.

yi ¼ 1114:873þ 2117:705xc−19:615xSiO2−31:513xFe2O3−720:148xSO3

þ 247:122xMgO: ð2Þ

Fig. 6 plots the absolute and relative errors of all the training andtesting data. Their values are very small, suggesting our calculatedmodel is suitable for predicting the properties of mercury retention infly ashes by an analysis of the components of fly ash. In Eq. (2), the co-efficient of carbon content is the largest value, suggesting the carbon isan important variable that influences the mercury retention. Since thecarbon content (xC) is very low, the second item in the right-hand ex-pression of Eq. (2) is a not large value. Although the coefficients ofSiO2, Fe2O3, SO3, and MgO are smaller than that of carbon, the valuesof SiO2, Fe2O3, SO3, and MgO are considerably larger than xi1. Hence,

Fig. 6. Absolute and relative errors between the measured and calculated data.

the sum of the last four product terms in the right-hand expression ofEq. (2) still significantly affects themagnitude of yi. That is to say, silicon,iron, sulfur, and magnesium in fly ash also partially determine the re-tention of mercury. This is the result of no linear correlation betweenthe decomposed carbon and mercury as described above.

4. Conclusions

Eight fly ash samples collected from full-scale pulverized coal-firedpower plants are evaluated to study the mechanism of mercury reten-tion. In order to find themost effective carbon that determines retentioncapacity of fly ash for mercury, separating carbon was performed for allthe samples by adjusting the decomposition temperature of carbon.Here the temperatures are set as 300 °C, 450 °C, 600 °C, and 750 °C.The LOI values reveal the very low decomposed carbon content of thefly ashes at 300 °C. The decomposition temperatures of most carbon inthe fly ashes are more than 600 °C. But most mercury in the fly ashescan be decomposed at the temperature of 300 °C, and there is a verylow mercury content of the fly ashes when the temperature reaches600 °C. No correlation between carbon and mercury is found for thesefly ashes at any temperature. The quantity of carbon in the fly ashesdoes not affect the amount of mercury captured at any temperature.The decomposed mercury content depends on the residual mercurycontent. Meanwhile, linear correlation is not found between residualmercury and Cl contents.

The elemental composition of the inorganic components is furthercarried out by XRF to evaluatemercury retention.Multivariate linear re-gression analysis is applied in an attempt to evaluate the influence of flyash composition on themercury retention. A mathematic equation wasbuilt, in which the dependent variable represents the decomposedmer-cury content, and the independent variables were set as the content ofthe decomposed carbon and elemental composition of inorganic com-ponents. The least residual error of regression are carried out usingthe t-test theory, and the forward stepwise regression algorithm givesthe dominated components determining the retention of mercury inthe fly ashes. From these calculations, the decomposedmercury contentdepends on the amount of decomposed carbon, silicon, iron, sulfur, andmagnesium. Hence, both carbon and inorganic components determinethe mercury retention in fly ash.

Acknowledgements

This work is partially supported by the National Natural ScienceFoundation of China (21237003, 50806041), Shanghai Science andTechnologyDevelopment (11dz1203402), and the fund of Shanghai En-gineeringResearchCenter of PowerGeneration Environment Protection(11dz2281700),

References

[1] F. Zahir, S.J. Rizwi, S.K. Haq, R.H. Khan, Environ. Toxicol. Pharmacol. 20 (2005)351–360.

[2] Y.J. Wang, Y.F. Duan, L.G. Yang, C.S. Zhao, X.L. Shen, M.Y. Zhang, Y.Q. Zhu, C.H. Chen,Fuel Process. Technol. 90 (2009) 643–651.

[3] A. Kolker, C.L. Senior, J.C. Quick, Appl. Geochem. 21 (2006) 1821–1836.[4] G.E. Dunham, R.A. DeWall, C.L. Senior, Fuel Process. Technol. 82 (2003) 197–213.[5] T. Sakulpitakphon, J.C. Hower, A.S. Trimble, W.H. Schram, G.A. Thomas, Energy Fuel

14 (2000) 727–733.[6] M.A. Lopez-Anton, M. Diaz-Somoano, P. Abad-Valle, M.R. Martinez-Tarazona, Fuel

86 (2007) 2064–2070.[7] M.A. Lopez-Anton, M. Diaz-Somoano, M.R. Martinez-Tarazona, Ind. Eng. Chem. Res.

46 (2007) 927–931.[8] F. Goodarzi, J.C. Hower, Fuel 87 (2008) 1949–1957.[9] F. Goodarzi, J. Reyes, J. Schulz, D. Hollman, D. Rose, Int. J. Coal Geol. 65 (2006) 26–34.

[10] J.C. Hower, M.M. Maroto-Valer, D.N. Taulbee, T. Sakulpitakphon, Energy Fuel 14(2000) 224–226.

[11] S. Li, C.M. Cheng, B. Chen, Y. Cao, J. Vervynckt, A. Adebambo, W.P. Pan, Energy Fuel21 (2007) 3292–3299.

[12] I. Kostova, C. Vassileva, S. Dai, J.C. Hower, D. Apostolova, Int. J. Coal Geol. 116 (2013)227–235.

12 P. He et al. / Fuel Processing Technology 142 (2016) 6–12

[13] A. Fuente-Cuesta, M.A. Lopez-Anton, M. Diaz-Somoano, M.R. Martinez-Tarazona,Chem. Eng. J. 213 (2012) 16–21.

[14] J.R. Li, M.M. Maroto-Valer, Carbon 50 (2012) 1913–1924.[15] M.A. Lopez-Anton, M. Diaz-Somoano, M.R. Martinez-Tarazona, Energy Fuel 21

(2007) 99–103.[16] L.L. Xing, Y.L. Xu, Q. Zhong, Energy Fuel 26 (2012) 4903–4909.[17] P. Abad-Valle, M.A. Lopez-Anton, M. Diaz-Somoano, M.R. Martinez-Tarazona, Chem.

Eng. J. 174 (2011) 86–92.[18] M.A. Lopez-Anton, P. Abad-Valle, M. Diaz-Somoano, I. Suarez-Ruiz, M.R. Martinez-

Tarazona, Fuel 88 (2009) 1194–1200.[19] J.C. Hower, C.L. Senior, E.M. Suuberg, R.H. Hurt, J.L. Wilcox, E.S. Olson, Prog. Energy

Combust. Sci. 36 (2010) 510–529.[20] H. Biester, G. Nehrke, Fresenius J. Anal. Chem. 358 (1997) 446–452.

[21] M.A. Lopez-Anton, R. Perry, P. Abad-Valle, M. Diaz-Somoano, M.R. Martinez-Tarazona, M.M. Maroto-Valer, Fuel Process. Technol. 92 (2011) 707–711.

[22] A. Murakami, M.A. Uddin, R. Ochiai, E. Sasaoka, S.J. Wu, Energy Fuel 24 (2010)4241–4249.

[23] M.A. Uddin, M. Ozaki, E. Sasaoka, S.J. Wu, Energy Fuel 23 (2009) 4710–4716.[24] M.A. Lopez-Anton, Y. Yuan, R. Perry, M.M. Maroto-Valer, Fuel 89 (2010) 629–634.[25] P. He, X. Zhang, X. Peng, X. Jiang, J. Wu, N. Chen, J. Hazard. Mater. 300 (2015)

289–297.[26] K.V. Mardia, J.T. Kent, J.M. Bibby, Multivariate Analysis, Academic Press, New York,

1979.[27] N. Draper, H. Smith, Applied Regression Analysis, JohnWiley & Sons, Inc., New York,

1981.