Industrial Application of an Improved Multiple Injection and Multiple

Article pubs.acs.org/est

Industrial Application of an Improved Multiple Injection and Multiple Staging Combustion Technology in a 600 MWe Supercritical DownFired Boiler Minhang Song,† Lingyan Zeng,*,†,‡ Zhichao Chen,† Zhengqi Li,† Qunyi Zhu,† and Min Kuang§ †

School of Energy Science and Engineering, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001, P.R. China School of Chemical Engineering & Technology, Harbin Institute of Technology, 92 West Dazhi Street, Harbin 150001, P.R. China § Faculty of Maritime and Transportation, Ningbo University, Ningbo 315211, P.R. China ‡

S Supporting Information *

ABSTRACT: To solve the water wall overheating in lower furnace, and further reduce NOx emissions and carbon in fly ash, continuous improvement of the previously proposed multiple injection and multiple staging combustion (MIMSC) technology lies on three aspects: (1) along the furnace arch breadth, changing the previously centralized 12 burner groups into a more uniform pattern with 24 burners; (2) increasing the mass ratio of pulverized coal in fuel-rich flow to that in fuel-lean flow from 6:4 to 9:1; (3) reducing the arch-air momentum by 23% and increasing the tertiary-air momentum by 24%. Industrial-size measurements (i.e., adjusting overfire air (OFA) damper opening of 20−70%) uncovered that, compared with the prior MIMSC technology, the ignition distance of fuel-rich coal/air flow shortened by around 1 m. The gas temperature in the lower furnace was symmetric and higher, the flame kernel moved upward and therefore made the temperature in near-wall region of furnace hopper decrease by about 400 °C, the water wall overheating disappeared completely. Under the optimal OFA damper opening (i.e, 55%), NOx emissions and carbon in fly ash attained levels of 589 mg/ m3 at 6% O2 and 6.18%, respectively, achieving NOx and carbon in fly ash significant reduction by 33% and 37%, respectively.

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INTRODUCTION Lean coal and anthracite are two types of low-volatile fuels that are widely used in generating units around the world. However, because of their poor reactivity and low volatile matter, these low-volatile fuels present difficulties in timely ignition, maintaining steady combustion, and keeping favorable burnout.1−3 Until now, the down-fired furnace with its advantages in burning hard-to-burn coal in China has occupied more than 80% of the total market share in the world,4 however, various problems appear in its operations, such as poor burnout,5 asymmetric combustion,6 heavy slagging,7 and fairly high NOx emissions (reaching up to 1600 mg/m3 at 6% O28,9) which is an extremely harmful matter to environment and human health. To solve these problems, researchers have done further studies and put forward many measures, such as changing burner operation models7 to mitigate slagging, retrofitting the combustion configuration10,11 to enhance burnout, adjusting air distribution12,13 to reduce NOx emissions and so on. Apparently, regulating air-staging combustion in down-fired boilers to simultaneously achieve significant reduction of NOx emissions and good burnout is difficult. While developing comprehensive methods to simultaneously deal with this difficult and the problems above is necessary to popularize © XXXX American Chemical Society

the further application of down-fired furnace. Li’s group thus developed the multiple injection and multiple staging combustion (MIMSC) technology14 and keeps on improving its performance for the past 6 years. Its first industrial application was on two 600 MWe supercritical down-fired boilers,15 wherein overfire air (OFA) was not equipped and secondary air and staging air (i.e., tertiary air in this article) ratios were about 72% and 11%, respectively. The industrialsize measurements revealed that symmetric combustion and weak slagging tendency appeared in the lower furnace, but higher NOx emissions leveled up to 1292 mg/m3 at 6% O2, meanwhile, superheat and reheat steam temperatures were about 20 and 40 °C below design values, respectively.15 By reducing the declination angle of staging air from 45° to 20°, aimed to elevate the flame kernel position to increase the combustion share in upper furnace, however, it failed to raise the superheat and reheat steam temperatures and simultaneously resulted in worse coal combustion. To solve these problems and improve the performance of MIMSC technolReceived: August 16, 2015 Revised: December 20, 2015 Accepted: January 11, 2016

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DOI: 10.1021/acs.est.5b03976 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

Article

Environmental Science & Technology ogy,14 applying OFA on arches, reducing the arch secondary air ratio to 39%, and increasing staging air ratio to 20%, industrial measurements showed that the combustion share in the upper furnace increased, superheat and reheat steam temperatures reached design values, NOx emissions were significantly lower than before, under the optimal operation setting, NOx emissions and carbon in fly ash at furnace exit were 878 mg/ m3 at 6% O2 and 9.81%, respectively.14 But the carbon in fly ash remained at a higher level. The main reason for this is attributed to the limitation that the fuel-lean coal/air flow still owns a relatively high pulverized-coal share but suffers from late ignition, resulting a short burning distance to generate high carbon in fly ash. Moreover, the downward coal/air flow has an excessively deep penetration depth and entrains lots of unburnt pulverized-coal that combusting in the hopper zone, thereby making high gas temperature in this zone. Under these circumstances, the hopper water-cooled wall was vulnerable to overheat in the long running and consequently, accidents of water wall tube blast happened sometimes. Thus, countermeasures should focus on reducing the unburnt pulverized-coal in the hopper zone and shortening the downward flame penetration depth to improve the technology. In this work, further improvement on the MIMSC technology was carried out. Subsequently, the improved technology was applied to the prior 600 MWe supercritical down-fired boiler (with furnace dimensions unchanged), and in situ industrial experiments were carried out at full load. This paper focuses on two aspects: (1) by comparing the experimental results before and after the improvement, evaluating the effect of improved MIMSC technology on the downward flame penetration depth, ignition distances of fuelrich and fuel-lean coal/air airflows, fuel gas temperature distributions in the lower furnace and the near-wall region of furnace hopper, NOx emissions and carbon in fly ash; and (2) by adjusting the OFA damper opening, evaluating the OFA effect on NOx emissions and coal burnout.

Figure 1. Combustion configuration of the down-fired 600 MWe supercritical boiler with improved MIMSC technology (mm).

lean coal/airflows and secondary air) and meanwhile increasing the tertiary air ratio from 20.29 to 22.74% so as to lower the arch-air velocity. As a result, the arch-air momentum drops from 17 640 to 13 643 kg·m/s, while that of tertiary air increases from 3647 to 4528 kg·m/s. The countermeasures for negative effects of late-ignition of fuel-lean coal/air flow refer to changing the louver concentrators into cyclone concentrators with a higher separation efficiency. Consequently, the ratio of pulverized coal in the fuel-rich flow to that in the fuel-lean flow increases from 6:4 to 9:1. A detailed comparison of main design parameters before and after these improvements is shown in Table 1. Full-Scale Measurements. At a full load of 600 MWe and with the damper openings of secondary air and tertiary air fixed at 95% and 70% (the ratio of secondary air ratio to tertiary air

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EXPERIMENTAL SECTION Utility Boiler. Figure 1 presents the combustion configuration and burner arrangement with the improved MIMSC technology. There are 24 burners evenly and symmetrically located on front and rear arches. Each burner connects to one cyclone separator dividing the primary air/fuel mixture into fuel-rich and fuel-lean coal/air flows used to organize the fuel rich/lean combustion. A total of 24 cyclone separators connect with six millers labeled from A to F (i.e., every miller has four primary air pulverized coal pipes). Twelve OFA groups are uniformly arranged on arches near the furnace throat. Twelve groups of tertiary air slots locate at the lower part of the front and rear walls with tertiary air oriented 45° downward. The improved arch burner is shown on the left side in Figure 1d, outer secondary air, fuel-lean coal/air flow, inner secondary air, and fuel-rich coal/air flow are arranged in order from the front/ rear wall to furnace center. A more detailed introduction about the MIMSC technology can be found in literature.14 The countermeasures for shortening the excessively large downward flame penetration depth includes two aspects (1) along the furnace arch breadth, changing the previously centralized 12 burner groups14 (each burner group uses a centralized layout pattern with two burners) into 24 burners uniformly located on arches (as shown in Figure 1d). The aim is to quicken the downward coal/air flow decay, (2) increasing the burner nozzle outlet area (including the fuel-rich and fuel-

Table 1. Comparison of Main Design Parameters before and after Improvement

B

quantity

before

after

number of arch burner pulverized coal concentrator coal feeding rate (t/h) mass ratio of pulverized coal in fuel-rich flow to pulverized coal in fuel-lean flow ratio of fuel-rich coal/air flow(%) velocity of fuel-rich coal/air flow (m/s) ratio of fuel-lean coal/air flow (%) velocity of fuel-lean coal/air flow (m/s) secondary air ratio (%) secondary air velocity (m/s) tertiary air ratio (%) tertiary air velocity (m/s) OFA ratio (%) OFA velocity (m/s) arch-air momentum (kg·m/s) tertiary air momentum (kg·m/s)

12 burner groups louver 269 6:4

24 burners cyclone 269 9:1

7.85 15.00 11.77 22.60 39.81 47.10 20.29 23.73 14.50 41.43 17640 3647

7.85 13.11 11.77 17.49 39.00 37.03 22.74 26.29 12.86 37.85 13643 4528


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Environmental Science & Technology

couples with different diameters to measure the flame temperature at the same point and calculated its true flame temperature. We made further calculations according to De’s data, and the result shows that the true flame temperatures are 1.35−11.35% higher than the measured temperatures, with exceeding values of 10−104 °C. In our experiment, a great number of refractory belts also existed in the furnace, and the temperature measurement range was basically the same as that in ref 16. Therefore, it can be concluded that our experiment is of the same measurement error of thermocouple as that of De’s. (2) Measuring gas temperature distribution in the lower furnace. We used a type of hand-held single-wavelength infrared thermometer with a measuring range from 300 to 3000 °C and an intrinsic measuring error of ±30 °C to measure fuel gas temperature through the inspection ports and manhole (Figure 2). The general emissivity of pulverized coal flame is 0.80, and the flame emissivity has small variation under different experiment conditions in the same furnace. In situations of setting the same emissivity in the infrared thermometer, we can get the average flame temperature of a large region in the furnace, this type of measurement can reflect the temperature variation under different conditions by comparing the measured temperatures. Since (1) the in-furnace flame is mixed with lots of pulverized-coal particles and gas compositions, which have a strong ability to absorb the infrared radiation energy; (2) the decay rate of infrared radiation energy is proportional to the square of the distance and there is a long distance between the infrared radiation of the opposite wall and the measuring positions (about 24 m), the opposite wall with colder temperatures has less impact on the measured temperatures. During the process of the experiment, as a result of the fluctuations of the coal and air supply rate, the flame temperatures in the measuring area fluctuate. In this experiment, we took a long lasting measuring time for 5 min on each measuring position, the infrared pyrometer automatically calculated and showed the average flame temperature in that period, thus making the measured temperatures more representative. (3) Measuring gas temperature in the near-wall region of furnace hopper. A K-type, 6 mm-diameter thermocouple was used. The measurement pipe was put at fins between the declined water-cooled wall tubes and located at three heights (Figure 2), respectively, there were total six measurement pipes evenly and symmetrically located at one height of the front and rear sides along the furnace width. The thermocouple was inserted into the furnace along horizontal direction with an inserting depth from 0 to 200 mm, and recorded temperature values every 50 mm. The following analysis will use the average value of three measuring temperatures at the same height and depth of one side to represent its near-wall temperatures. Its measuring error and matters needing attention were as mentioned above. (4) Measuring fuel gas species concentrations at furnace exit and carbon in fly ash. A Testo 350 flue gas analyzer was used to measure the flue gas composition at the horizontal outlet of economizer. They were measured once every 10 min to calculate mean values during each

ratio is close to design value), respectively, the OFA damper opening was adjusted in turn to establish a OFA opening series of 20, 35, 55, and 70%. Before industrial-size measurements, all data-acquiring apparatuses, including thermometer, thermocouple device, and fuel gas analyzer were calibrated to ensure the accuracy of measurements. During the measurements, great efforts were made for maintaining the coal characteristics (as listed in Table 2, it is close to the coal used in literature,14 Table 2. Coal Characteristics proximate analysis, wt % (as received) volatile matter 7.36

ash

moisture

fixed carbon

net heating value (MJ/ kg)

29.79 7.4 55.45 ultimate analysis, wt % (as received)

20.98

carbon

hydrogen

nitrogen

oxygen

sulfur

56.23

2.08

0.72

1.07

2.71

indicating the measuring results before and after the improvement are comparable) stable and avoiding any interferential operation, such as soot blowing and pollution discharge. The main operation parameters under different OFA damper openings are given in the Supporting Information (SI). Methods in industrial-size data acquiring are as follows: (1) Measuring ignition distances of fuel-rich and fuel-lean coal/air flows. The thermocouple device (K-type, 6 mm diameter, 8m length) was vertically inserted into the furnace along the measuring pipes (Figure 2) on the fuel-

Figure 2. Measuring locations.

rich and fuel-lean coal/air flow nozzles of A4 burner to obtain gas temperature under arch burner. As the thermocouple was long, for protecting it and keeping its rigidity and stability when inserted into the furnace, placed it inside a 20 mm-diameter stainless steel pipe. However, it was unavoidable. The thermocouple swung violently caused by the flowing fuel gas inside furnace when inserted too long, which made the readings fluctuate greatly, thereby the inserted depth was kept within a 4.4 m distance to burner nozzles to get stable readings. In order to make the measurements more accurate, recording the average temperature of each measuring point in 1 min. To avoid measuring error due to soot or ash deposition on the thermocouple, while taking measurements, the thermocouple was frequently pulled out and examined, any depositions found were removed. In an experimental furnace whose inside surface was refractory-lined, De16 used three thermoC


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Figure 3. Heating process of fuel-rich and fuel-lean coal/air flows.

Figure 4. Gas temperature distributions in lower furnace (unit of gas temperature: °C).

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0.66−1.05 m to its nozzles, which is a moderate ignition distance. In comparison to the prior heating process of fuel-rich coal/air flow17 (ignited at 1.80−2.02 m) shown in Figure 3a, the improved ignition distance is shortened by around 1 m. This change occurs because: (1) the velocity of fuel-rich coal/ air flow decreases, and thus prolongs the pulverized-coal residence times under arches; this is favorable to absorb heat from the high-temperature gas entrained into the recirculating zones below furnace arches and therefore enhances ignition; (2) after applying cyclone concentrators, the pulverized-coal concentration in the fuel-rich coal/air flow increases significantly. The lower velocity and higher pulverized-coal concentration of the fuel-rich coal/air flow below the arches becomes, the less ignition heat needed to advance the ignition point. As shown in Figure 3b, the improved fuel-lean coal/air flow is not ignited within a 4.4 m distance to its nozzles. This means that its heating rate is significantly smaller than that of the fuel-rich coal/air flow. This occurs because: (i) the fuel-lean coal/air flow has a much lower pulverized-coal concentration; and (ii) the fuel-lean coal/air flow locates between inner and

experimental run. The measuring errors were 1% for O2, 5% for CO, and 50 ppm for NOx. An isokinetic sampling device was used to extract samples of fly ash at the horizontal outlet of the air preheater.

RESULTS AND DISCUSSION

Ignition Distances of Fuel-Rich and Fuel-Lean Coal/ Air Flows. As the used coal belongs to lean coal, this paper takes 900 °C as its ignition temperature. For down-fired boilers, a too early pulverized-coal ignition means a short distance between the flame and burners, which always results in burnout loss (a short flame penetration depth) or burner nozzle slagging. On the contrary, a too late ignition usually causes poor flame stability and burnout (short burning times in the hightemperature lower furnace), which is also unfavorable to economic operation of the boiler. Figure 3a shows the heating process of fuel-rich and fuel-lean coal/air flows before17 and after the present improvements. The improved fuel-rich coal/ air flow under different conditions is ignited at a distance of D


Article


Figure 5. Gas temperature distributions in the front near-wall region of furnace hopper.

fuel-rich coal/air flow ignites late, thus making the total heat release less. Apparently, the above observations mean that the high-temperature region in the lower furnace moves upward after these improvements. The detailed explanation will be introduced in the next subsection. As seen in panel b of Figure 4, the overall gas temperature in the lower furnace decreases gradually with the OFA damper opening. This is because opening OFA enhances the oxygenlean atmosphere in the lower furnace to cause negative effect on coal combustion. Meanwhile, a secondary-air velocity decrease weakens its carrying effect on the coal/air flow, thereby reducing the downward flow penetration depth and simultaneously dropping the pulverized-coal share into the hopper zone. Accordingly, the heat released in furnace hopper gradually reduces. Gas Temperature Distributions in Near-wall Region of Furnace Hopper. As seen in Figure 5a, prior to these improvements, the near-wall region in the hopper zone has high temperatures of 1100−1250 °C. This is the direct cause of the water wall overheating problem. The parts of the reasons have been presented previously in the Experimental Section and more detailed causes of such high temperatures are as follows: (1) the prior fuel-rich coal/air flow has a late ignition to release less heat in the upper part of the lower furnace; (2) the prior fuel-lean coal/air flow has more pulverized-coal (about 40% of the total coal supply) and a long ignition distance, which makes its combustion mainly concentrate in the tertiary air zone and the upper part of the hopper; (3) the prior downward coal/airflow has a larger momentum flow ratio (17 640 kg·m/s) and the 12 burner groups use a centralized layout pattern (see the right side of Figure 1d); these slow the downward airflow decay to allow it to penetrate rigidly into the hopper zone, still with a relatively high combustion share. In contrast, The improved temperatures under the same conditions (i.e., at the 3.3 m height under an OFA damper opening of 55%) are 690−870 °C, reducing by about 400 °C compared with the prior temperature levels. This change trend is attributed to three aspects: (i) The ignition of the fuel-rich and fuel-lean coal flows advances, increasing the heat release in the upper part of the lower furnace; (ii) 24 burners uniformly locate on arches to quicken the downward coal/air flow decay, thereby reducing the downward flame penetration depth; and (iii) in comparison to the prior jet momentum flow ratios, the improved downward coal/airflow momentum flow ratio reduces by 23% via an increase in the burner nozzle outlet

outer secondary air to allow itself quickly mixing with the lowtemperature secondary air, which further reduces its pulverizedcoal concentration and causes later ignition. As depicted in panels a and b of Figure 3, the heating-up rates of the fuel-rich and fuel-lean coal/air flows gradually increase with the OFA damper opening. The ignition distance of the fuel-rich coal/air flow reduces from 1.05 to 0.66 m. This is because the secondary air flux reduces with increasing OFA. The resulted secondary-air velocity decrease weakens the secondary-air carrying effect on the fuel-rich and fuel-lean coal/air flows, that prolonging the pulverized-coal residence times below arches to enhance heat absorption and coal combustion. Gas Temperature Distributions in the Lower Furnace. As shown in Figure 4, panels a14 and b are gas temperature distributions in the lower furnace before and after these improvements. All conditions show the same law: a relatively symmetric gas temperature distribution pattern forms (temperature differences between the front and rear sides are below 100 °C), therefore only the temperature distribution near the front side is described below. Temperatures of ports 1 and 6 are obviously lower than those of other ports. The temperature of port 2 (located right under fuel-rich coal/air flow nozzles) is over 1000 °C, showing the pulverized-coal begins to ignite. The temperature of port 3 (in the region closer to the furnace center) is higher than that of port 2. As the ignited coal/airflow proceeds, the continuous coal combustion and heat release generates gas temperatures increase in ports 4 and 5. The temperatures of ports 7 and 8 (near tertiary air slots) and port 9 (located at the upper part of the furnace hopper) also remain at high levels, because of tertiary air supplying additional oxygen for further coal combustion. Lower temperatures in the near wall zone are due to the cooling effect of outer secondary air and tertiary air. As seen from the comparison between panels a and b of Figure 4, before these improvements, higher temperatures of 1152−1279 °C appear in the 2nd−4th floor ports (i.e., ports 5, 8, and 9). After these improvements, higher temperatures of 1328−1467 °C (increasing by about 200 °C, as compared with the aforementioned levels) move upward in the 1st and 2nd floor ports (ports 3, 4, and 5). This is because: (i) the fuel-rich coal/ air flow shortens its ignition distance by around 1 m; and (ii) the fuel-lean coal/air flow has a longer ignition distance but with lower pulverized-coal share. On the contrary, the prior fuel-lean coal/air flow contains more pulverized-coal and the E


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Figure 6. Experimental results under different OFA damper openings after improvements.

In comparison to the prior carbon in fly ash of 7.84−15.1%,14 the improved carbon in fly ash of 5.65−6.4% gets a significant reduction. Reasons include two aspects: (1) the advanced fuelrich coal/air flow ignition facilitates to achieve coal burnout; and (2) the newly fuel-lean coal/air flow has much less pulverized-coal to weaken greatly its negative effect of late ignition on the overall burnout rate. As shown in Figure 6b, with the OFA damper opening increasing, the temperature at steam separator outlet reduces slightly from 397.5 to 395 °C, exhaust gas temperature at the air preheater outlet increases from 126.5 to 129 °C, and boiler efficiency reduces from 90.1 to 89.7%. As the steam separator connects with the water-cooled wall tubes in the furnace, its temperature indirectly reflects the working fluid temperature in water-cooled wall tubes. When opening the OFA damper, the flame kernel position moves upward to decrease the flame fullness degree in the lower furnace. Accordingly, this change reduces the water-cooled wall heat absorption capacity and thus lowers the steam separator outlet temperature. Meanwhile, the elevated flame kernel location increases the combustion share in the upper furnace, while the heat absorption capacity of heating surfaces in the upper furnace is limited. Consequently, the high-temperature fuel gas cannot be cooled sufficiently in the upper furnace and tail duct, resulting in the exhaust gas temperature increasing. The simultaneous increases in heat loss and carbon in fly ash reduce the boiler efficiency, while the positive effect of the improved coal combustion is higher, finally generating a boiler efficiency increase compared with the levels (83.97−89.0414) before these improvements. Taking economy and environmental protection for consideration, The optimal damper opening of 55%, 95%, and 70% for OFA, secondary air, and tertiary air damper openings, respectively, is recommended for the boiler with the improved MIMSC technology, at which NOx emissions and carbon in fly ash attain levels of 589 mg/m3 at 6% O2 and 6.18%, respectively. This achieves NOx and carbon in fly ash reduction by 33% and 37%, respectively, compared with the prior MIMSC technology in the same boiler. Meanwhile, the gas temperature in the near-wall region of the hopper markedly decreases, and the accident of water-cooled wall tube blast does not happen again, which indicates the improved MIMSC technology can completely solve the problem of water wall overheating in the lower furnace and guarantee the long-period and safe running of the boiler with MIMSC technology.

area, and the tertiary air flow ratio increases by 24%. These changes enhance the elevating effect on the downward flame and thus further reduce the downward flame penetration depth. Therefore, bringing down the near-wall temperature of the furnace hopper. This also explains why the high-temperature zone in the lower furnace moves upward after applying the improved MIMSC technology (Figure 4). Figure 5 shows the gas temperature distribution in the nearwall region under the same conditions as used for Figure 4. It can be seen that higher temperatures of 660−1020 °C appear at the 3.3 m height. As the furnace height increases, the gas temperature reduces and reaches 590−820 °C at the 9.1 m height near tertiary air slots; this reduce trend reflects the apparent tertiary-air cooling effect (about 322 °C) in the furnace hopper zone. As the OFA damper opening increases from 20 to 70%, the overall gas temperature distribution shows a decrease tendency; this also reflects the high-temperature zone moving upward and a temperature reduce in the near-wall region of the furnace hopper. Flue Gas Species Concentration, Carbon in Fly Ash, and Boiler Efficiency. As seen in Figure 6a, with the OFA damper opening increasing, CO emission concentration decreases from 245 to 54 ppm, carbon in fly ash increases from 5.65 to 6.4 %, and NOx emissions reduce from 702 to 575 mg/m3 at 6% O2. The results show that, when opening OFA damper, the air-staging combustion effect enhances to reduce NOx emissions but increase slightly carbon in fly ash. In comparison to conventional down-fired furnaces (NO x emissions of about 1600 mg/m3 at 6% O27−9) and the downfired boiler with the prior MIMSC technology (NOx emissions of about 800−1100 mg/m3 at 6%O214), the improved MIMSC technology attains further lower NOx emissions. The further NOx reduction is attributed to three aspects: (1) After these improvements, the enhanced fuel bias combustion makes the pulverized-coal combust in a stronger oxygen-lean atmosphere in its early combustion stage, and thus further restrains the generation of fuel NO; (2) the improved fuel-lean coal/flow has less fine pulverized-coal combust in the tertiaryair zone and hopper region both with an oxygen-rich atmosphere, thereby reducing thermal NO production; and (3) the high-temperature zone moves upward to elevate the flame kernel location, allowing shorter pulverized-coal residence times in the high-temperature lower furnace zone, this contributes another thermal NO reduction effect. F


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(12) Cañadas, L.; Cortés, V.; Rodríguez, F.; Otero, P.; González, J. F. NOx reduction in arch-fired boilers by parametric tuning of operating conditions. Proceedings of the Electric Power Research Institute (EPRI)/ Environmental Protection Agency (EPA) Megasymposium, Washington, DC, 1997. (13) Fan, J. R.; Liang, X. H.; Chen, L. H.; Cen, K. F. Modeling of NOx emissions from a W-shaped boiler furnace under different operating conditions. Energy 1998, 23 (12), 1051−1055. (14) Kuang, M.; Li, Z. Q.; Liu, C. L.; Zhu, Q. Y. Overall evaluation of combustion and NO x emissions for a down-fired 600 MW e supercritical boiler with multiple injection and multiple staging. Environ. Sci. Technol. 2013, 47 (9), 4850−4858. (15) Kuang, M.; Li, Z. Q.; Ling, Z. Q.; Chen, Z. F.; Yuan, D. Y. Characterization of coal combustion and steam temperature with respect to staged-air angle in a 600 MWe down-fired boiler. Energy Fuels 2014, 28 (6), 4199−4205. (16) De, D. S. Measurement of flame temperature with a multielement thermocouple. Journal of the Institute of Energy 1981, 54, 113− 116. (17) Kuang, M.; Li, Z. Q.; Jing, X. J.; Zeng, X. Y.; Zhao, L. F.; Ling, Z. Q. Characterization of combustion and NOx emissions with respect to over fire air damper opening in a down-fired pulverized-coal furnace. Energy Fuels 2013, 27, 5518−5526.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.5b03976. The main operation parameters under different OFA damper openings (Table S1) (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 451 8641 8854; fax: +86 451 8641 2528; e-mail: [email protected] (L.Z.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51406043), National Natural Science Foundation of China (Grant Nos. 51576055 and 51306167), Hei-longjiang Postdoctoral Fund (Grant No. LBH-Z12133), the Fundamental Research Funds for the Central Universities (Grant No. HIT.NSRIF. 20120735081), and the Zhejiang Provincial Natural Science Foundation of China (Grant No. LY15E060004).

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REFERENCES

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Industrial Application of an Improved Multiple Injection and Multiple

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