Influences of In-Furnace Kaolin Addition on the Formation and

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Influences of in-furnace kaolin addition on the formation and emission characteristics of PM2.5 in a 1000 MW coal-fired power station Yishu Xu, Xiaowei Liu, Hao Wang, Xianpeng Zeng, Yufeng Zhang, Jinke Han, Minghou Xu, and Siwei Pan Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b02251 • Publication Date (Web): 02 Jul 2018 Downloaded from http://pubs.acs.org on July 9, 2018

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Environmental Science & Technology

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Title Page

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Influences of in-furnace kaolin addition on the formation

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and emission characteristics of PM2.5 in a 1000 MW

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coal-fired power station

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Yishu Xu a, Xiaowei Liu a, *, Hao Wang a, Xianpeng Zeng a, Yufeng Zhang a, Jinke Han a, Minghou Xu a, *,

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Siwei Pan b

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a

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State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Luoyu Road 1037, Wuhan 430074, China.

b

Electric Power Research Institute of Guangdong Power Grid Corporation, Guangzhou 510080, China

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*Corresponding Author.

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E-mail: [email protected]; Tel: +86-27-87542417; Fax: +86-27-87545526

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E-mail: [email protected]; Tel: +86-27-87546631; Fax: +86-27-87545526

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** Submitted to “Environmental Science & Technology” *** A file as Supporting Information is attached to this manuscript. 1 ACS Paragon Plus Environment


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Abstract Art (TOC)

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ABSTRACT: The impacts of in-furnace kaolin addition on the formation and emission characteristics

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of PM2.5 from a 1000 MW coal-fired utility boiler equipped with electrostatic precipitators (ESPs) are

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investigated for the first time ever in this contribution. Detailed characterization of the chemical

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composition, micromorphology, melting characteristics of the fine PM, total fly ash and/or bottom ash

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samples were carried out using the X-ray fluorescence probe, the field emission scanning electron

30

microscope coupled with an energy dispersive X-ray detector, the ash fusion analyser and the dust

31

specific resistivity analyzer. The results showed that the formation of fine PM was reduced when kaolin

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was added, and the mass concentrations of the particulate matter with the aerodynamic diameters of ≤0.3

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and 2.5 µm (PM0.3 and PM2.5) were reduced by 55.97% and 5.48% respectively. As expected, kaolin

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reacted with the volatile mineral vapors (e.g., Ca, Na) and inhibited their partitioning into ultrafine PM.

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It was interesting to find that the added kaolin modified the ash melting behaviour, and promoted the

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capture of the ultrafine PM onto the coarse particles. What is more, the added kaolin reduced the

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specific resistivity of the fly ash and improved their capture efficiency in the ESPs. Finally, the above

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combined effects brought about the emission reductions of 41.27% and 36.72% for PM0.3 and PM2.5

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after the ESPs. These results provided a direct confirmation on the feasibility of in-furnace kaolin

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addition on the PM reduction in the realistic combustion conditions.

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KEYWORDS: Particulate matter; Coal combustion; Kaolin; de-PM additive; Electrostatic precipitator. 2 ACS Paragon Plus Environment

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1. Introduction

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PM2.5 (particulate matter with the aerodynamic diameters of ≤2.5 µm), which is enriched in

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hazardous components and harmful to human beings, has become one of the most concerned air

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pollutants

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primary PM emission sources

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electrostatic precipitators (ESPs) are equipped downstream of the boilers to dedust the flue gas

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However, these dust collectors cannot effectively remove the fine and ultrafine PM

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troublesome PM, various methods improving the performance of dust collectors have been tried, yet

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they are generally costly

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additive(s) has been proposed and rapidly developed 11-21. The “de-PM” additives are designed to reduce

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the formation of fine/ultrafine PM during the combustion process and thereby make up for the

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deficiencies of the dust collectors. In this way, this technique could targetedly strengthen the emission

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control of the fine PM, and help the power stations meet emission requirements at lower costs.

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1-3

. China is suffering a severe PM2.5 pollution and coal-fired power stations are one of the

8-10

4,5

. Currently, various PM removal devices/technologies such as

5-8

3,5

.

. To handle these

. In recent years, a novel in-furnace PM reduction technology based on

Existed studies in this area are mainly carried out on the bench/pilot scale reactors and focused on 15,16,20

14,18-21

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the screening of additives

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combustion conditions (e.g., temperature, atmosphere, fuel properties, etc.)

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regarded as the most practically feasible one in the future industrial application. As reported by Chen et

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al. 19 and Si et al. 18, adding 5% kaolin into coal could reduce the emission of PM1 and PM2.5 by 33~58%

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and 35% during the combustion. It is generally recognized that fine PM is reduced via two pathways. On

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one hand, the added kaolin would react with the gaseous PM precursors (e.g., Na-contained mineral

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vapor, etc.) and inhibit their partitioning into the fine PM 14,16,19,21. On the other hand, some products of

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kaolin would melt during the high-temperature combustion process and form liquidus substance, which

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captures the PM via collision and aggregation 18,20. The performance of kaolin on reducing the formation

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of fine PM is of the highest level of all the reported additives; however, it would change with the

, their PM capture mechanism

and performance under different 17-19

. Clay mineral kaolin is

3 ACS Paragon Plus Environment


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specific work conditions. It is reported that its PM capture efficiency would significantly decrease when

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the temperature exceeds 1373 K because of the melting/sintering phenomenon, indicating a high

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sensitivity to temperature

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more complicated. Studies of Chen et al.

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better performance in the O2/CO2 atmosphere. Nevertheless, studies of Si et al. 18 at a temperature (1773

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K) higher than Chen et al. showed some contrary results. The above disparities seem to be resulted from

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the different formation behaviors of the liquidus substance on the additive/products at the different

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experimental conditions. What is more, our latest study showed that the combustion-derived species

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such as H2O and HCl would also affect the PM capture characteristics of kaolin 17. To sum up, the PM

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reduction performance and process of kaolin are strongly related to the combustion conditions, which

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makes its performance and feasibility in the realistic industrial applications of great uncertainty and

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concerns.

14,19

. The effects of combustion atmosphere on the performance of kaolin are 19

at temperature of ≤1573 K showed that kaolin exhibited a

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In the full-scale boiler’s furnace, there are much more complicated temperature/atmosphere

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profiles and turbulent flow conditions compared with the simplified ones in the lab, which may lead to

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different behaviors and performances of kaolin. However, there are still no reports on the PM reduction

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performance of kaolin in those real furnaces. So, the PM reduction efficiency of kaolin, its controlling

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mechanism as well as the possible disparities with that in the lab studies are still unknown. What is more,

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to evaluate the feasibility of the de-PM additive in the large scale power plants, the potential effects of

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additives addition on the whole unit system should also be considered. In-furnace kaolin addition might

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also change the physical/chemical properties of the fly ash (e.g., composition, resistivity, etc.) out of the

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furnace besides of the concentration, which might affect their capture characteristics in the downstream

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dust collectors, especially the ESPs. Therefore, the impacts of kaolin addition on the PM capture

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efficiency of ESPs and the final PM emission are also required to be clarified.


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To address these gaps, kaolin was mixed into the coal at a 1000 MW utility boiler and burned

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together with the pulverized coal in the furnace. Systemic field samplings and measurements were

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performed at the inlets and outlets of the ESPs, and the ash/slag hoppers below the furnace. Systematic

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information on the mass yield, size distribution, composition and morphology, melting and specific

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resistivity characteristics of the PM, total fly ash and/or bottom ash/slag was obtained. Finally,

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comprehensive discussions on the influence of kaolin on the formation of PM in the furnace, the PM

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removal performance of ESPs and the emission of PM after the ESPs were performed. This is the first

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ever study clarifying the influences of in-furnace kaolin addition on the formation and emission

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characteristics of PM2.5 on the full scale coal-fired power stations world widely, which is desired to

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complement the lab studies and makes great contributions to the development of the de-PM additive

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based in-furnace PM reduction technique.

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2. Experimental methods

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2.1. Material

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The field study was carried out on a 1000 MW ultra-supercritical coal-fired power station unit

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located in Guangdong province in China (sketched in Fig. 1). Briefly, the unit is equipped with a dry-

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bottom-furnace boiler, two ammonia-spraying SCR DeNOx reactors, two three-chamber four-electric-

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field ESPs and a limestone-gypsum WFGD reactor. The boiler has six groups of swirling burners (i.e.,

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B/F, C/E and D/A) located oppositely on the front and back walls in the furnace. Coal is prepared in a

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direct-fired pulverizing system equipped with six HP type medium-speed mills. Bottom ash/slag from

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the furnace is treated in a dry-type slag extractor and then stored in the hopper. Detailed information on

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this unit is provided in Table S1 in the Supporting Information.



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Fig. 1. Sketch of the 1000 MW power station unit with the kaolin adding system and the distribution of

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sampling sites.

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Blends of a lignite and a bituminous coal (denoted as YN and SH respectively) were burned and

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their properties are listed in Tables S2 and S3. As can be seen, the feed coal has relatively high contents

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of Ca, S and Na. Natural kaolin powder was selected as the de-PM additive. Its chemical composition,

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size distribution and mineral composition are presented in Table S4 and Fig. S1. Most importantly, the

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kaolin is mainly composed of kaolinite with a little content of quartz. The volume-moment mean

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diameter D[4, 3] of the kaolin is ~30.77 µm, which indicates that most of the kaolin are coarse particles.

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2.2. Kaolin adding strategy

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During the measurements, kaolin was added into coal at a constant ratio of 2.5 g-kaolin/100 g-coal.

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The coal/kaolin blends were loaded into coal bunkers corresponding to the bottom and middle burners

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(i.e., burner groups B/F and C/E in Fig. 1) to provide kaolin a sufficient residence time in the furnace.

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Particularly, a kaolin adding system was designed and embedded into the coal conveying system. As

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shown in Fig. 1, the adding system was positioned at the inlets of the standby coal feeder in the coal

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yard, and consisted of additive storage silos, feeders and speed controllers. When loading the coal

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bunkers, kaolin and coal fell onto the conveyer belt at the set ratio, preliminarily mixed in the coal


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crushers and then stored in the bunkers. Then, the crushed coal and kaolin were further mixed during the

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coal grinding.

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The actual work performance of the kaolin adding strategy was verified by the composition of the

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total fly ash collected at the ESPs’ inlets, and the detailed results were provided in Fig. S2. What is more,

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the power load, coal feeding rate and O2 content in the flue gas during the measurements were

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monitored and exhibited in Fig. S3. As can be seen, the boiler load was stabilized at ~90% of its full

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load and the other key operating parameters were also stable, which facilitated the study to focus on the

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influences of kaolin addition.

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2.3. PM sampling and analysis

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PM samplings were performed at the inlets and outlets of the ESPs (see Fig. 1) with two DLPI 22-24

137

sampling systems, following the procedures described elsewhere

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system consists of a cyclone (SAC-10, Dekati), a Dekati low pressure impactor (DLPI), a pressure

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gauge and a vacuum pump. During the sampling, a stream of flue gas (10 L/min) was isokinetically

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extracted from the center of the flue duct via a probe and introduced into the cyclone to separate the

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particles with the aerodynamic diameters of >10 µm (PM>10). Then, the flue gas passed through the

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DLPI in which the left particles ≤10 µm (PM10) were separated and collected into 13 stages according to

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the particle size. All the sampling probe, cyclone, DLPI and the tubes connecting them were heated to

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408 K, which is above the condensing temperature of SO3 (~383K) in the flue gas, to avoid the

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condensation of acidic gases 10, 22, 23. Each PM sampling at the inlets and outlets of the ESPs lasted for

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1.5 minutes and 90 minutes respectively to collect suitable amount of PM sample. Moreover, PM

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samplings at the ESPs’ inlets and outlets at each experimental condition were repeated for 4 times and 3

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times respectively, with the averages and error bars presented in the results.

. Briefly, the DLPI sampling

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Aluminum foils and polycarbonate membranes were used in the DLPI. Aluminum foils, before and

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after each sampling, were weighed on a microbalance (MSA6.6S-0CE-DM, Sartorius Co., accuracy of 7 ACS Paragon Plus Environment


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0.001 mg) to obtain the mass yield of PM. A high temperature grease (Apiezon-H) was coated on the

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aluminum foils used. Meanwhile, PM samples collected on the polycarbonate membranes were analyzed

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via an X-ray fluorescence probe (XRF, EAGLE III, EDAX Inc.) and a field emission scanning electron

154

microscope coupled with energy dispersive X-ray analyzer (FESEM-EDX, Sirion 200, FEI Inc.) to

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characterize their micromorphology and chemical composition characteristics. Prior to the observation

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under FESEM, a thin layer of platinum (Pt) was coated onto the samples to improve their conductivity 16.

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To ensure the reproducibility of the data, three parallel runs were conducted under each condition, with

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the average values and error bars being reported.

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2.4. Total fly ash and bottom ash/slag

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Samples of the total fly ash in the flue gas into the ESPs were also collected via a commercial dust 22

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collector (Laoying 3012H smoke/gas analyzer), following the procedures described elsewhere

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gas was extracted out of the flue duct via a probe and the entrained ash particles were collected in the

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glass fiber filter cartridge embedded in it. The chemical composition and specific resistivity of the ash

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samples were determined via the XRF and a dust specific resistivity analyzer (DR-3, North China

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Electric Power University). Unfortunately, due to the malfunction of the dust collector, the mass

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concentrations of the total fly ash were not successfully obtained in the experiments. However, the

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measured chemical composition (see Fig. S2) agreed well with the calculated one with the factor “R

168

adding ratio”

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fly ash, which would lead to the increase of the total fly ash emitted out of the furnace.

. Flue

being set as 2.5%. This suggested that most of the added kaolin powder migrated into the total

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The bottom ash/slag samples were collected from the slag extractor below the furnace. Ash/slag

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samples were put into a mortar grinder (RM200, Retsch) and grinded with identical settings (e.g., speed,

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pressure and time). The ash/slag powders were sieved into 6 size fractions (0.3 µm

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contents via XRF) revealed that the ultrafine PM had high contents of the volatile inorganic species such

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as Ca, S and Na. Consistent with the previous studies

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the volatile mineral matter in coal via the vaporization-nucleation process. It is interesting that the

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ultrafine PM had a high Ca content, possibly due to two reasons. First, Ca in the lignite/bituminous

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blends primarily occurred as organic-bound and/or included minerals, which underwent higher

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combustion temperature and stronger reducing atmosphere 28,29. Thereby it vaporized and migrated into

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the ultrafine PM at a great extent. Second, coal and mineral particles experienced a much higher

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temperature and more violent fragmentation in the real furnace than in the bench/pilot scale reactors,

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which would also promote the vaporization of mineral matter. Refractory elements such as Si and Al

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were also observed in the ultrafine PM, which was resulted from the reduction-vaporization-nucleation

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mechanism 3,30.

25

. Results in Figs. 2(a) and S4 (detailed results on elemental

3,26,27

, the ultrafine PM was mainly derived from



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Fig. 2. (a) PSDs of the PM at the ESPs’ inlets, with inserted figure giving composition of the PM0.08-0.15

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(particles collected on the 3rd stage of DLPI); (b) PM reduction efficiency of kaolin.

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For investigating the impacts of kaolin addition on the formation of PM2.5, the size-fractionated PM

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reduction efficiencies of kaolin were further calculated according to Eq. (1), with the results being

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presented in Fig. 2(b). Moreover, the mass concentrations of PM0.3, PM1 (particulate matter with the

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aerodynamic diameters of ≤ 1 µm) and PM2.5 were calculated and listed in Table 1. The contents of

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some typical components (e.g. Na, Ca), micromorphology and composition of PM, and the composition

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of the bottom ash/slag were also provided in Figs. 3~5 respectively. At least three important findings

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can be made from these data.

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η, , , / , 100%

(1)

204 205


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Table 1 Mass concentrations of PM0.3, PM1, and PM2.5 without

with

Efficiency

kaolin

kaolin

of kaolin, %

PM concentration, mg/Nm3 ESP inlet PM0.3

17.56±2.21

7.73±0.89

55.97±9.56

PM1

45.88±2.65

32.86±1.61

28.38±2.15

PM2.5 307.39±22.35 290.53±25.93

5.48±0.63

ESP outlet PM0.3

0.63±0.05

0.37±0.05

41.27±5.88

PM1

2.04±0.09

1.32±0.11

35.29±3.24

PM2.5

9.15±0.19

5.79±0.37

36.72±2.44

Efficiency of ESP, % PM0.3

96.41±13.87

95.21±16.14

–

PM1

95.55±6.91

95.58±9.07

–

PM2.5

97.02±7.33

98.01±10.71

–

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First, the generated PM was still of bimodal distribution after kaolin was added. However, as

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expected, the addition of kaolin significantly reduced the yield of the ultrafine PM. As listed in Table 1,

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the mass concentration of PM0.3 reduced from 17.56 mg/Nm3 to 7.73 mg/Nm3 under the experimental

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conditions, corresponding to a reduction efficiency of 55.97%. Comparatively, the influence of kaolin

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on the yield of coarse PM was not so significant. As can be seen, the concentrations of PM1 and PM2.5



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were reduced from 45.88 and 307.39 mg/Nm3 to 32.86 and 290.53 mg/Nm3 when kaolin was added,

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corresponding to reduction efficiencies of 28.38% and 5.48%.

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Second, the formation of the ultrafine PM appeared to be reduced by kaolin via two pathways. On

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one hand, as shown in Fig. 3, contents of Na and Ca in the ultrafine PM were remarkably reduced after

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kaolin was added. These phenomena indicated that kaolin and the derived meta-kaolin reacted with the

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Na-/Ca-contained vapors and fixed them onto the additive particles, inhibiting their nucleation into

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nuclei and thereby reducing the formation of ultrafine PM 14,17.

219 220 221

Fig. 3. Na2O and CaO contents in PM0.08-0.15, PM1.04-1.77 and PM2.65-4.45 (particles collected on stages 3, 8 and 10 of DLPI).

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On the other hand, as shown in Figs. 4(a-d), much more ultrafine and fine particles were adhered

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on the surface of coarse particles after kaolin was added. Further composition characterization of the

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aggregates [shown in Figs. 4(b1-b2)] confirmed that the aggregates were exactly the clusters of the

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above Ca-enriched ultrafine PM [Fig. 2(a)]. These direct morphology observations verified that adding

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kaolin promoted the liquidus-substance capture of the ultrafine PM by the melting coarse PM. It’s worth

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noting that the high content of Ca in the coal and the generated PM in this study contributed to the

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ultrafine PM reduction in the above liquidus capture mechanism

18,20,31

. As clarified by Ninomiya et al. 12

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20

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addition ratios. These results explained the above morphology results, and further confirmed that the

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added kaolin promoted the formation of liquidus substance (i.e., alkali silicates, alkali aluminosilicate,

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etc.), finally enhancing the capture of the formed ultrafine PM by collision and aggregation.

and Wei et al.

32

, kaolin would react with Ca and facilitate the formation of melt phase at certain

233 234

Fig. 4. (a-d) Micromorphology of the PM1.04-1.77 and PM1.77-2.65 (particles collected on the 8th and 9th

235

stages of DLPI) observed under FESEM and (b1-b2) the chemical composition of the representative

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particles.

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Third, as shown in Fig. 2(b), the reduction efficiency of the coarse PM by kaolin was lower than

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that of the ultrafine PM. The coarse PM was mainly captured by the collision and aggregation with other

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PM and/or kaolin particles, finally migrating into those large particles and/or the bottom ash/slag. The

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variation of the chemical composition of the bottom ash/slag testified this to some extent. As can been

241

seen in Fig. 5, higher contents of Al2O3 and CaO were observed in the bottom ash when kaolin was

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added, indicating that some added kaolin and ultrafine-PM-forming species (e.g., Ca) were migrated into

243

the bottom ash/slag. Yet, as the number concentration of the coarse PM was much lower than the



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ultrafine PM, the solid-solid collision/aggregation process between the coarse PM underwent at a lower

245

extent and thereby the coarse PM was reduced at lower efficiency than the ultrafine PM.

246 247 248

Fig. 5. Chemical composition of the pulverized bottom ash/slag. 3.2. Impacts of kaolin on the PM removal performance of ESPs

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Figs. 6(a-b) present the PSDs of the PM at the outlets of the ESPs before and after kaolin addition,

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coupling with the size-fractionated PM removal efficiencies of the ESPs. Interestingly, the emissions of

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both ultrafine and coarse PM at the outlets of the ESPs were significantly reduced when kaolin was

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added. As listed in Table 1, when no kaolin was used, the concentrations of PM0.3 and PM2.5 were

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reduced from 17.56 and 307.39 mg/Nm3 to 0.63 and 9.15 mg/Nm3 after passing the ESPs, corresponding

254

to the PM removal efficiencies of 96.41% and 97.02% respectively. In comparison, when kaolin was

255

added, concentrations of PM0.3 and PM2.5 at the outlets of the ESPs were further reduced to 0.37 and

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5.79 mg/Nm3, which meant that the final PM0.3 and PM2.5 emissions at ESPs’ outlets were reduced by

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41.27% and 36.72% respectively.


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Fig. 6. (a) PSDs of the PM at ESPs’ outlets and (b) fractionated PM removal efficiency of the ESPs with

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the resistivity of the total fly ash.

261

The size-fractionated PM removal efficiencies of the ESPs in Fig. 6(b) further confirmed the above

262

results. The promoting effects of kaolin addition on the capture behaviour of PM in the ESPs can be

263

attributed to two reasons. On one hand, as expected, the concentration of the hard-captured ultrafine/fine

264

PM at the inlets of the ESPs was reduced (Table 1), therefore less PM would penetrate the ESPs. On the

265

other hand, the specific resistivity of the ash particles into the ESPs was changed. As shown in the

266

inserted figure in Fig. 6(b), the resistivity of the total fly ash into the ESPs was reduced by one order of

267

magnitude. The effects of added kaolin on the resistivity of the fly ash were consistent well with the

268

reduced Ca and increased Si/Al contents (Figs. 3 and S4) in it, which finally enhanced the charging and

269

capture of the PM in the ESPs

270

studies, which gave an important enlightenment that the impacts on the equipment after boiler should

271

also be evaluated when screening suitable in-furnace de-PM additives.

33,34

. Above phenomena has never been observed or realized in previous

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3.3. Further discussion on the controlling mechanism of ultrafine PM reduction by kaolin

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The ultrafine PM reduction efficiency (~56%) of the kaolin in this field study is in the range

275

(22~77%) of those reported in the lab studies 16,18,19,35. However, the controlling mechanism of ultrafine

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PM reduction by kaolin appears to be different to a certain degree.

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As previously mentioned, kaolin could reduce the formation of the ultrafine PM via two pathways

278

– the vapor capture and the liquidus capture. In the real furnace, there are much more turbulent flow

279

conditions than the bench/pilot scale reactors. Besides, there are higher concentrations of PM in the

280

furnace than that in lab studies, because large air/fuel ratios are normally used in the lab studies to

281

ensure the burnout, which inevitably dilutes the concentration of PM. Both of the distinctive flow

282

conditions and PM concentrations facilitate the collision between the ash particles, which is usually

283

suppressed in the moderate flow/temperature conditions in the lab scale reactors. What is more, the

284

combustion temperature in the coal-fired furnace is reported to be ~2000 K, higher than that in the

285

simulated conditions (1173~1773 K) in the lab studies

286

promote the melting behaviour of the ash/additive particles and therefore more ultrafine PM could be

287

captured by the melting surface when collided together (see Fig. 4). So, under the combustion

288

conditions in the real furnace, the capture of ultrafine PM via the liquidus mechanism is promoted. On

289

the other hand, the enhanced melting behaviour of the kaolin particles would hinder their reactions

290

with those gaseous PM precursors (e.g., Na-contained mineral vapor, etc.), thereby inhibiting the

291

capture of ultrafine PM via the vapor capture mechanism. In the end, the liquidus capture process plays

292

a much more important role in the reduction of ultrafine PM than that in the lab studies.

16,18,19,36

. The increased temperature would

293


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Supporting Information

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A file as supporting information is attached to this manuscript. Tables S1−S4 and Figures S1−S4.

296

Disclosures

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The authors declare no competing financial interest.

298

Acknowledgements

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The authors acknowledge the financial support of the National Natural Science Foundation of China

300

(51476064), the National Postdoctoral Program for Innovative Talents (BX201700085) and the Project

301

funded by China Postdoctoral Science Foundation (2017M622438). The authors also thank the support

302

of the Analytical and Testing Center at the Huazhong University of Science and Technology and the

303

contributions of co-workers Jiang Cui, Penghui Zhang, Junzhe Guo, Zhiqiang Liao, Ming Mao, Yang

304

Peng, Jingkun Han and Ge Yu in the field sampling. The authors also appreciate the help of Wenqiang

305

Liu in revising the manuscript.

306 307

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Page 22 of 24

403

List of Figures

404

Fig. 1.

405

Sketch of the 1000 MW power station unit with the kaolin adding system and the distribution of

406

sampling sites.

407

Fig. 2.

408

(a) PSDs of the PM at the ESPs’ inlets, with inserted figure giving composition of the PM0.08-0.15

409

(particles collected on the 3rd stage of DLPI); (b) PM reduction efficiency of kaolin.

410

Fig. 3.

411

Na2O and CaO contents in PM0.08-0.15, PM1.04-1.77 and PM2.65-4.45 (particles collected on stages 3, 8 and 10

412

of DLPI).

413

Fig. 4.

414

(a-d) Micromorphology of the PM1.04-1.77 and PM1.77-2.65 (particles collected on the 8th and 9th stages of

415

DLPI) observed under FESEM and (b1-b2) the chemical composition of the representative particles.

416

Fig. 5.

417

Chemical composition of the pulverized bottom ash/slag.

418

Fig. 6.

419

(a) PSDs of the PM at ESPs’ outlets and (b) fractionated PM removal efficiency of the ESPs with the

420

resistivity of the total fly ash.

421


Page 23 of 24


422

List of Supporting Information

423

Tables

424

Table S1.

425

Key parameters of the tested 1000 kW power station unit.

426 427

Table S2.

428

Proximate and ultimate analysis of the feed coal.

429 430

Table S3

431

Ash analysis of the feed coal.

432 433

Table S4

434

Chemical composition and size analysis of the kaolin used.

435



436

Figures

437

Fig. S1.

438

XRD pattern of the kaolin powder.

Page 24 of 24

439 440

Fig. S2.

441

Comparison of the measured chemical compositions of total fly ash with/without kaolin addition and the

442

calculated ones.

443 444

Fig. S3.

445

Load, coal feeding rate and the O2 content in the flue gas during the experiments.

446 447

Fig. S4.

448

Chemical compositions of the PM0.08-0.15, PM1.04-1.77 and PM2.65-4.45 (stages 3, 8 and 10 of DLPI

449

respectively) with/without kaolin addition, determined by XRF.


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