Experimental Investigation of the Growth of Ash Deposits with and

Article pubs.acs.org/EF

Experimental Investigation of the Growth of Ash Deposits with and without Additives through a Digital Image Technique Hao Zhou,* Bin Zhou, Huige Qu, Aping Lin, and Kefa Cen State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China ABSTRACT: This paper presents experimental results on the growth of ash deposits of JinYang (JY) coal and blends (with additive) tested in a pilot-scale furnace. The additive used in the experiment was atacamite [Cu2Cl(OH)3]. The digital image technique was used to monitor the morphology of ash deposit growth and to determine the change in thickness of the deposits with time. Two type K thermocouples were installed in the oil-cooled deposition probe to measure the temperature of the inner and outer surfaces of the deposition probe. This work indicated that the process of ash deposit growth included four stages. For pure coal, the growth rates of deposits on the second probe were 0.079, 0.034, 0.045, and 0 mm/min, corresponding to stages 1, 2, 3, and 4, respectively. Growth rates of the additive blends were 0.056, 0.053, 0.017, and 0 mm/min for the four stages mentioned above. According to these results, the additive could slightly reduce the thickness of the ash deposits of JY coal and the stable thicknesses for pure coal and additive blends were 6.1−6.3 and 5.05−5.15 mm, respectively. It was demonstrated that this additive could result in augmentation of the coefficient of thermal conductivity of the ash deposit in high-temperature regions (T ≥ 1250 °C) while promoting the thermal resistance of the ash deposit in low-temperature regions (T ≤ 1200 °C). This may be a result of the production of deposit constituents other than those of the pure coal with the addition of the additive. The focus of our future work would be to investigate this mechanism further.

1. INTRODUCTION Because coal is the main fossil energy source in China, coalfired power plants will remain a major source of electrical power production for the foreseeable future. The constituents of coal influence the overall performance of the utility, including waste treatment, electricity power generation capacity, equipment breakdown, and effect of all of these on the environment.1 The most severe influence of coal is ash deposits on the heat-transfer surfaces of boilers. Ash deposits on heat-transfer surfaces not only lead to the reduction of their heat-exchange ability but also cause the corrosion of boiler tubes, which may result in reduced electricity generation capacity, unscheduled shutdowns, and subsequent decreases in the availability of the system and increases in the cost of the generated electricity.2−6 Ash deposition phenomena can be influenced by many physical and chemical processes, for instance, the chemical composition of ash, the distribution of mineral matter in the ash, the ash fusion temperature, the temperature of the furnace, the temperature of the ash particles, the surface temperature of the heat-exchanger tubes, the tube materials, the flow field in the furnace, and the ash transport mechanisms.7 Inorganic constituents of coal can be transported into fly ash during combustion. Subsequently, ash species are transported to the boiler tubes from the flue gas, mainly through diffusion, thermophoresis, and inertial impaction.8 According to Rushdi et al.,9 the transport process of large particles to the heattransfer surfaces is controlled by inertial impaction and turbulent diffusion, while that of fine particles is controlled by Brownian motion and thermophoretic forces. In recent years, much work has been carried out to investigate the characteristics of ash deposits. Some research work has focused on simulation of the growth of ash deposits, © 2012 American Chemical Society

while others were experimental studies. For theoretical studies on ash deposit growth, the selection of parameters, such as the critical viscosity, initial porosity of the slag, thermal conductivities of the solid and liquid, and sticking probability of the deposit surface was very important.10 Our previous studies10 had developed a model of ash deposition growth in the ash hopper of power station boilers. The model included a comprehensive combustion code, which could predict the characteristics of deposition growth. Galen et al.2 simulated the deposit thickness, heat flux along the reactor wall, and temperature at the surface of the deposit, varying with time. Erickson et al.11 investigated the variation of the deposit surface and the internal temperature profile with deposit growth through a numerical simulation method. Nevertheless, it was very difficult to simulate the ash deposit growth process accurately because of the numerous physical and chemical processes involved. Consequently, online precise monitoring of the growth of slagging through a charge-coupled device (CCD) was important. As for experimental studies, Su et al.12 applied the minimum heat flux ratio and the total heat flux ratio to rank slagging propensities; the results showed that the two indices were better in ranking the slagging propensities than the build-up rate (g/h) and the visual physical characteristics. Heinzel et al.13 used air-cooled probes to collect slags and compared the macroscopic characteristics, elemental composition, melting temperature, and amounts of the deposits for each case. Vuthaluru et al.14 quantified the ash deposits by measuring the Received: June 28, 2012 Revised: October 14, 2012 Published: October 24, 2012 6824

dx.doi.org/10.1021/ef301093j | Energy Fuels 2012, 26, 6824−6833

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Figure 1. Schematic diagram of the pulverized coal combustion furnace.

weight of deposits on an air-cooled probe at different furnace temperatures after the experiments were finished. Additionally, Akiyama et al.15 obtained the fraction of molten slag in ash by a chemical equilibrium calculation, and the results showed that it was consistent with the deposition fraction of ash obtained by experiments conducted in a refractory furnace using a watercooled tube. Moreover, Kupka et al.16 investigated the growth of ash deposits by an online weighing technique. Even so, limited studies could observe the morphology of the ash deposit growth online and quantify the deposits. This paper used a digital image technique to achieve this purpose. On the other hand, using additives to reduce slagging in pulverized coal-fired boilers was a potential candidate. Many researchers have focused on the subject of using an additive to alleviate boiler slagging; some were successful to a certain extent. In particular, there have been many investigations with respect to Victorian brown coal. Stella et al.17 reported that kaolinite, clays, and overburden appear to be potential additives to mitigate fouling associated with the combustion of Victorian brown coal in a furnace. According to Fraser et al.,18 a calcite additive could significantly increase the degree of sintering and decrease the porosity of the deposit during burning of Daw Mill coal in a combustion test facility (CTF). Even with these references, knowledge of the effect of additives on ash deposition of JY coal, which is extensively used in pulverized coal-fired plants in China, is scarce. More research is essential to elucidate the behavior of ash deposition of JY coal in furnaces. The aim of the present work is to investigate the growth of ash deposits in the boiler through a digital image technique and, additionally, to analyze the influence of the additive on ash deposition.

Figure 2. Deposition probe inserted into the furnace. mainly consisted of the vertical furnace, coal feeder, swirl burner, temperature measurement system, ash deposition sampling system, and image sampling system. The length and inner diameter of the vertical furnace were 3950 and 350 mm, respectively. Refractory material was installed in it to reduce heat loss. The coal feeder was used to provide a constant fuel flow rate to the combustion furnace. The feed rate can be adjusted within the range of 10−45 kg/h by changing the rotational speed of the electromotor. When the furnace reached a stable state, the coal was supplied at 40 kg/h. The pulverized coal was transported to the swirl burner through the coal feeder with preheated primary air at 47−50 °C. The temperature of the preheated secondary air, which was used to produce swirling flow to maintain a stable flame, was the same as that of the primary air. There were four ports with type S thermocouples to measure the temperature of different locations in the furnace. According to the location of the type S thermocouples (along the vertical direction downward), the furnace was divided into four stages: first, second,

2. EXPERIMENTAL SECTION 2.1. Combustion Facility. The schematic diagram of the experimental rig used for the slagging tests is shown in Figure 1. It 6825


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of stainless steel were inserted into the center of the furnace at distances of 1160, 1910, and 2660 mm from the burner nozzle exit (see Figure 1). Figure 2 shows the probe inserted into the combustion facility, opposite of the middle ash deposition probe located image sampling system to measure the growth of slag on line. At the outlet of the vertical furnace, the gas pre-processor and gas analyzer were used to measure the concentration of O2, CO2, CO, SO2, and NOx of the flue gas. A bag filter was used to remove the fine particles from the flue gas. To protect the flue gas duct from the high temperature of the flue gas, a direct quench system was installed to cool the flue gas to about 400 °C. 2.2. Deposit Sampling System. When the combustion furnace approached the steady-state operating condition, the temperature of every stage furnace was stable; for instance, the second stage was 1250 °C, the third stage was 1200 °C, and the fourth stage was 1050 °C. Moreover, the oxygen concentration in the flue gas was kept in the range of 4.5−5.5%), and three ash deposition probes were inserted into the furnace through three ports, which were located along the vertical axis, shown in Figure 1. A schematic diagram of the probe is shown in Figure 3a. It consisted of a deposit sampling section and an oil-cooling tube section, connected to each other through a thread. The deposit sampling part was a hollow cylinder (length, 76 mm; inner diameter, 27 mm; and outer diameter, 40 mm), internally cooled by heat-conducting oil. Figure 3b shows the details of the deposition probe. Two small holes were located on the end surface of the deposit sampling part (see Figure 3c). The inner diameter of these was 1.8 mm. A pair of type K thermocouples was installed in the small holes to measure the temperature of the inner and outer surfaces of the deposition probe. The oil cooling tube was annular. The heat-conducting oil circulating in the annular tube was used to ensure that the surface temperature of the deposition probe did not become too high (it fluctuated in the range of 340−500 °C along with the growth of deposits), which is at the same level of that of the water-wall tube in the utility boiler. At the inlet and outlet, cooling oil temperatures were 230 and 240 °C, respectively. The temperature was kept almost constant in the experiments by a 9 kWe oil-circulating temperature control unit. 2.3. Slagging Imaging System. A CCD monitoring system was used to monitor the growth of the slag. A schematic diagram of this system is shown in Figure 4a. Figure 4b illustrates the details of the monitoring system. It was located opposite of the second deposition probe at the same height (see Figure 1). The monitoring system mainly consisted of four parts, as follows: (1) A protection tube was used to protect the camera lens from damage in the furnace from high temperatures. The tube had two channels. The outer channel was water-cooled and was used to isolate the high temperature of the furnace. The inner channel was filled with pressurized air, which could produce a gas film in the forepart of the camera lens to prevent the fly ash from depositing on the front of the lens and influencing the quality of the image. (2) A CCD camera was used to generate the image. During monitoring, the frame rate of the CCD camera was 1 frame/ second (F/s), the resolution was 1280 × 1024, and the exposure time was 5 ms. (3) A camera protection system was used to protect the camera from being destroyed because of the severe environment around the furnace. (4) A camera lens was used to obtain the image of the slag and to send the signals to the sensor chip of the CCD camera. 2.4. Description of the Digital Image Technique. During the experiment, the recorded video was obtained through the CCD camera, which was used to monitor the growth of the deposits. Subsequently, the recorded video was post-processed into 24-bit images. In this work, the growth of deposits was represented by the thickness. The thickness of the deposits was denoted as h and was the maximum height of deposits on the deposition probe. During the experiment, the outer diameter of deposition probe D1 was constant. In the deposit images, the pixels along the diameter direction and the thickness direction were represented by PD and Ph, respectively. After post-processing, PD and Ph were both counted. Consequently, the following equation can be used to formulate the thickness of the deposits h:

Figure 3. (a) Schematic diagram of the deposition probe, (b) deposition probe detail, and (c) deposition sampling part detail.

Figure 4. (a) CCD monitoring system and (b) CCD monitoring system in detail.

Table 1. Proximate Analysis, Ultimate Analysis, Ash Fusion Temperature, and Calorific Value of Feed Coal JY coal

proximate analysis (wt %, ad)

ultimate analysis (wt %, db)

ash fusion temperature (°C) HV (MJ/kg)

moisture volatile matter ash fixed carbon carbon hydrogen nitrogen sulfur oxygen DT ST HT FT LHV

7.52 30.76 9.39 52.33 71.36 3.88 0.70 0.56 13.35 1150 1160 1170 1180 21.16

third, and fourth stages. All of the temperature signals were collected by a data acquisition system and sent to a personal computer (PC), which recorded and processed the data. Three deposition probes made 6826


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Table 2. Chemical Composition of Ash (wt %) Al2O3

CaO

13.95 SiO2

19.47 SO3

46.95

5.88

Fe2O3

K2O

MgO

MnO2

Na2O

NiO

P2O5

7.70

0.78

3.30

0.09

1.16

0.01

0.07

TiO2

V2O5

0.62

0.02

Figure 5. Size distribution of the JY coal.

Table 3. Physicochemical Properties of the Additive mineral

bulk density (kg/m3)

true density (kg/m3)

median particle size diameter (μm)

chemical formula

atacamite

1953

3760

13

Cu2Cl(OH)3

h = D1Ph /PD

(1)

2.5. Coal Sample. In all of the experiments, the feed fuel was JY coal. The proximate analysis, ultimate analysis, ash fusion temperature, and calorific value of JY coal are given in Table 1. Results for the ash chemical composition of the feed coal are shown in Table 2. The coal was pulverized with 74.9% in the mass fraction less than 74.9 μm, as measured by a Malvern particle size analyzer, as shown in Figure 5. 2.6. Experimental Conditions. Two cases were analyzed in this work. One was the pure JY coal, and the other was a blend (0.125% mass of the additive content). The additive was milled to a particle size less than 20 μm before mixing with the coal. The chemical composition of the additive was atacamite. The physicochemical analysis results of the additive are shown in Table 3 in detail. At the beginning, diesel oil was burned to start up. It would take 4−5 h for the furnace burning coal to achieve a steady state, corresponding to the temperature of the second stage of the furnace, approximately 1250 °C, after which the three ash deposition probes were inserted into the combustion chamber. The temperatures of every stage of the furnace were measured during the experiments by type S thermocouples, and the temperatures of case 1 (pure coal, with no additive) and case 2 (with 0.125 wt % additive) are shown in panels a and b of Figure 6, respectively. Because of slag deposits on the probes, the heat flux through the probes decreased with time. Consequently, the temperature of the furnace increased a little during the experiments. During both tests, the oxygen concentration in the flue gas at the furnace exit was kept in the range of 4.5−5.5% (by volume, on a dry basis). The exposure time of the deposition probe in the furnace was 3 h.

Figure 6. (a) Temperature of each stage furnace for pure coal and (b) temperature of each stage furnace for additive blends.

Figure 7, respectively. The order of deposits on the three deposition probes shown from left to right was probe 1, probe 2, and probe 3. Panels a and b of Figure 7 show that the color of the deposits on the third probe was lighter than that of the other two deposits. This may be because of more molten slag fraction in the ash deposits on the first probe and the second probe or the different content of some specific mineral matter in the surface of the deposits, which resulted from a higher temperature at the locations where the two probes were located than that of the third probe. Moreover, observation of the deposits for the two cases (panels a and b of Figure 7) indicated that the width and structure of the deposits did not change significantly when the additive was added to the JY coal. The cross-sections of the deposits on the second probe in the two cases are shown in panels a and b of Figure 8. As shown, the deposit on the second probe appeared as a clearly layered structure with different colors and porosity in both cases. Along the growth direction, the deposit could be divided into three

3. RESULTS AND DISCUSSION 3.1. Visual Inspection of the Ash Deposits. The photos of the ash deposits collected after an exposure time of 3 h for the pure coal and additive blends are shown in panels a and b of 6827


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Figure 7. (a) Ash deposits on the three probes for pure coal and (b) ash deposits on the three probes for additive blends.

layers: layer 1 (the initial layer), layer 2 (the sintered layer), and layer 3 (the slag layer).9 Yanqing et al.19 and Junying et al.20 reported similar results for deposits, with the depth of color for every layer following the order: slag layer > sintered layer > initial layer. This may result from the different content of the mineral matter in every layer. As shown in Figure 8a, the color of the initial layer indicated that it was relatively abundant in iron-bearing mineral.20 This appearance was consistent with the results analyzed by X-ray diffraction (XRD) spectrometry, as shown in Table 4. The initial layer contained significantly more hematite and maghemite than the slag layer. In addition, a significant amorphous phase was observed for the slag layer, while a much smaller amorphous content was seen in the initial layer. This may be because the slag layer was located in a hightemperature area near the flame, while the initial layer was located in a low-temperature area on the metal surface. When the contents of minerals in different layers of ash deposits were compared on the second probe for pure coal, it could be found that anorthite, diopside, and quartz were relatively enriched in the initial layer. This may be a result of these minerals changing into an amorphous phase at high temperatures. In addition, the initial layer was loose and easily removable, and the sintered layer consisted of a dense structure. Nevertheless, the slag layer was mainly composed of a porous structure (see panels a and b of Figure 8). 3.2. Deposit Growth. In this study, the growth of the deposit on the second probe was determined by measuring the

Figure 8. (a) Cross-section of the ash deposit on the second probe for pure coal and (b) cross-section of the ash deposit on the second probe for additive blends.

deposit thickness from the images. Because the frame rate of the CCD camera was 1 F/s, there were many images produced during the 3 h experiment. We extracted one image every 5 min from the video to calculate the thickness of the deposit. Figure 9 shows the slagging deposit images for pure coal as an example to show how the images were extracted from the video during the 3 h experiment. 6828


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Article A−B), stage 3 (stage B−C), and stage 4 (stable stage). At the stable stage, the thickness of the deposit did not increase any more but fluctuated around a certain stable value. This result was consistent with the observations reported in section 3.1 that the deposit on the second probe had three layers. As shown in panels a and b of Figure 10, during the 3 h experiments, the deposit grew almost linearly with time in stage 1. Stage 1 lasted 10 and 20 min for pure coal and additive blends, respectively. In this stage, the heat flux through the second probe decreased significantly, as shown in panels a and b of Figure 11. The ratio of heat flux versus deposit thickness rose to 453.0 and 345.1 kW m−2 mm−1 for pure coal and additive blends, respectively. This fact suggested that the thermal conductivity of the deposits produced in stage 1 was low. In addition, panels a and b of Figure 10 show that the thickness of the deposit increased with time in stages 2 and 3. However, the rates of increment in stages 2 and 3 were slightly less than in stage 1. The heat flux curves presented a rather moderate decrease in heat flux, suggesting a leveling off in stages 2 and 3 for pure coal and additive blends, as shown in

Table 4. Analysis Results of Amorphous and Crystalline Phases in the Ash Deposits on the Second Probe for Pure Coal (wt %) phase

layer 1 (initial layer)

layer 3 (slag layer)

amorphous anorthite (CaAl2Si2O8) diopside [CaMg(SiO3)2] hematite (Fe2O3) maghemite (Fe2O3) quartz, low (SiO2)

39.6 19.5 16.6 0.7 5.3 18.3

83.3 3.0

3.4 10.3

The thicknesses of the deposits on the second probe for pure coal and additive blends are shown in panels a and b of Figure 10, respectively. Moreover, panels a and b of Figure 11 show the heat flux through the second probe versus deposit thickness for pure coal and additive blends, respectively. It can be seen that both curves in panels a and b of Figure 10 consist of four segments with different slopes. Consequently, this indicates that the process of growth for the deposits could be divided into four stages, namely, stage 1 (stage O−A), stage 2 (stage

Figure 9. Image of ash deposits in the initial 40 min through CCD for pure coal. 6829


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Figure 11. (a) Heat flux through the second probe versus deposit thickness for pure coal and (b) heat flux through the second probe versus deposit thickness for additive blends.

Figure 10. (a) Deposit thickness as a function of time on the second probe for pure coal and (b) deposit thickness as a function of time on the second probe for additive blends.

peak point A″ in Figure 12c. The result was in accordance with the conclusion reported above. As shown in panels a and b of Figure 11, the difference between these was that there were some points aggregated in an ellipse in Figure 11a. These points represented some moments that the heat flux changed slightly; however, the deposit thickness changed significantly. This might be because the porosity structure was continuously generated and ruptured in the interior of the deposit at the stable stage of slagging. This result was not detected in Figure 11b, which might have resulted from the addition of the additive to the coal changing the viscosity of the deposit. The various parameters of the deposits on the second probe for pure coal and additive blends are given in Table 5. In conclusion, adding the additive into the coal could delay the time to achieve the stable stage of slagging and decrease the thickness of the deposits slightly. For instance, the times to achieve the stable state of the deposit for pure coal and additive blends were 135 and 160 min, respectively. The stable thickness fluctuated within the range of 6.1−6.3 mm for pure coal, while that for additive blends was in the range of 5.05−5.15 mm. Moreover, the additive could decrease the heat flux at the stable

panels a and b of Figure 11, respectively. This might result from the different contents of mineral matter in the deposits produced in different stages. Panels a and b of Figure 10 show that the deposits grew to a certain stable thickness and then the deposit achieved the “stable stage of slagging”.21 At stage 3, the temperature of the deposit surface became high enough to melt the deposit; therefore, the pattern of the deposit surface was fluid to some extent.9 The liquid flowed off the deposit surface, resulting in no more growth in the thickness. In Figure 10a, one point in an ellipse, corresponding to a thickness of 6.95 mm and a time of 130 min, deviated seriously from the curve. Nevertheless, at the next time of 135 min, the thickness of the deposit was 5.90 mm. Between the two cases, when the time was 132 min, the thickness of the deposit was 6.78 mm. This phenomenon could be explained by molten slag running off the deposit surface. CCD images of the three moments are shown in panels a−c of Figure 12. It was observed that the height of the peak point A in Figure 12a and the height of the peak point A′ in Figure 12b were both higher than the 6830


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Figure 12. (a) CCD image of the second probe for pure coal at 130 min, (b) CCD image of the second probe for pure coal at 132 min, and (c) CCD image of the second probe for pure coal at 135 min.

Table 5. Results of the Growth Rate of the Deposit on Probe 2 and Corresponding to the Heat Flux case pure coal

additive blends

time (min)

thickness (mm)

slope (mm/min)

rate of heat flux versus thickness (kW m−2 mm−1)

10 60 135 20 65 160

0.79 2.51 5.90 1.11 3.50 5.13

0.079 0.034 0.045 0.056 0.053 0.017

453.00 122.42 57.19 345.10 67.90 39.74

stable thickness (mm)

stable heat flux (kW/m2)

6.1−6.3

822.24

5.05−5.15

440.93

deposit growth achieved a stable state, the heat fluxes through the first probe (located at the second stage of the furnace, where the ambient temperature was approximately 1250 °C) for pure coal and additive blends were 509.56 and 607.48 kW/ m2, respectively (see panels a and b of Figure 13). For the second probe (located at the third stage of the furnace, where the ambient temperature was approximately 1200 °C), the heat flux values for pure coal and additive blends were 822.24 and 448.93 kW/m2, respectively. Finally, for the third probe (located at the fourth stage of the furnace, where the ambient temperature was approximately 1050 °C), the heat flux values for pure coal and additive blends were 592.65 and 438.19 kW/ m2, respectively. This indicated that the additive could promote the thermal conductivity of ash deposits in high-temperature regions (T ≥ 1250 °C). Nevertheless, it could also result in the reduction of heat transfer to the probe from ash deposits in

stage of slagging significantly. The stable heat flux for pure coal doubled the stable heat flux for additive blends. This might be because the addition of the additive to the coal, which resulted in generating some mineral matter, decreased the thermal conductivity of the deposits. 3.3. Results of Heat Transfer on the Three Probes. The heat flux values through the three probes for pure coal and additive blends are shown in panels a and b of Figure 13, respectively. It could be concluded that all of the heat flux values through each probe had a similar tendency. The heat flux reached the local maximum value in a very short time after the probe was inserted into the furnace (approximately 1 min), and subsequently, the heat flux decreased with time, until finally the value fluctuated around a certain value. The value of the heat flux when the stable state was reached depended upon the location of the probe in the furnace and the thermal load. When 6831


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Figure 13. (a) Heat flux through three probes for pure coal and (b) heat flux through three probes for additive blends.

low-temperature regions (T ≤ 1200 °C). This might result from different chemical reactions between the additive and the ash particles in different temperature regions. Consequently, the compounds in the deposits for pure coal and blends in different regions were different. Apparently, it could be concluded that spontaneous shedding took place around 45 min on probe 3 for additive blends, as shown in Figure 13b. This might be because the addition of the additive to the coal changed the viscosity of the ash deposits. Consequently, the ash deposits were easy to remove.

According to the results, the digital image technique could accurately measure the growth rate of the deposits. From analysis of the deposit growth process, it was found that the process of growth for JY coal ash deposits consisted of four stages. The stable thicknesses of the ash deposit on the second probe for pure coal and additive blends were 6.1−6.3 and 5.05−5.15 mm, respectively. These results indicated that the addition of the additive could decrease the thickness of the deposits. Additionally, the additive could change the structure and viscosity of the deposits, which resulted in spontaneous shedding taking place during the experiment. According to the results of heat flux through the probes, it was concluded that the additive could increase the coefficient of thermal conductivity of ash deposits in high-temperature regions (T ≥ 1250 °C). Nevertheless, it could also result in the reduction of heat transfer to the probe from ash deposits in low-temperature regions (T ≤ 1200 °C). This may result from

4. CONCLUSION A digital image technique was proposed to investigate the growth of deposits and to determine the effect of the additive on slagging propensity in the slagging furnace. A CCD was used to monitor the morphology of deposit growth. Three specially designed oil-cooled tubes were used to collect the ash deposits. 6832


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deposit collected during co-firing of coal with sewage sludge and sawdust. Energy Fuels 2009, 23, 3429−3436. (17) Kyi, S.; Chadwick, B. L. Screening of potential mineral for use as fouling preventatives in Victorian brown coal combustion. Fuel 1999, 78, 845−855. (18) Wigley, F.; Williamson, J.; Riley, G. The effect of mineral additives on coal deposition. Fuel Process. Technol. 2007, 88, 1010− 1016. (19) Niu, Y.; Tan, H.; Ma, L.; Pourkashanian, M.; Liu, Z.; Wang, X.; Liu, H.; Xu, T. Slagging characteristics on the superheaters of a 12 MW biomass-fired boiler. Energy Fuels 2010, 24, 5222−5227. (20) Zhang, J.; Zhao, Y.; Wei, C.; Yao, B.; Zheng, C. Mineralogy and microstructure of ash deposits from the Zhuzhou coal-fired power plant in China. Int. J. Coal Geol. 2010, 81, 309−319. (21) Kupka, T.; Mancini, M.; Irmer, M.; Weber, R. Investigation of ash deposit formation during co-firing of coal with sewage sludge, sawdust and refuse derived fuel. Fuel 2008, 87, 2824−2837.

different reactions between the additive and ash particles in different temperature regions.

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AUTHOR INFORMATION

Corresponding Author

*Telephone: +86-571-87952598; Fax: +86-571-87951616. Email: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Key Technologies Research and Development Program of China (2011BAA04B01) and the Zhejiang Provincial Natural Science Foundation of China (LZ12E06002).

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REFERENCES

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Experimental Investigation of the Growth of Ash Deposits with and

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