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Cofiring of coal slime in existing utility boilers is a promising approach to the disposal of coal slime. However, reports about cofiring coal slime with anthracite in the down-fired utility boiler are still few. This work presents a comprehensive study on the combustion characteristics, slagging potential, and NOx emissions of cofiring coal slime and anthracite through lab-scale experiments, numerical simulations, and full-scale industrial measurements in a 600MW down-fired utility boiler. The lab-scale experiments show combustion interactions between anthracite and coal slime, which have both a promotive effect on the ignition of anthracite and inhibitive effect on the combustion and burnout of anthracite. Especially, the inhibitive effect is greater than the promotive effect when the blending ratio of coal slime is above 5%. The addition of coal slime can effectively improve the ash fusion temperature of blended samples. In addition, simulations and full-scale industrial measurements of anthracite cofiring with coal slime are performed in a down-fired utility boiler. The results show that as the blending ratio of coal slime increases, the carbon content in fly ash increases and the boiler efficiency and NOx emissions decrease. A 5% ratio is validated to be a reasonable cofiring ratio of coal slime in the actual operation without no slagging phenomenon. These results provide more insights into the cofiring behavior of coal slime and anthracite and guide the application of blending coal slime in a down-fired boiler. [ABSTRACT FROM AUTHOR]

• Effects of SOFA angles on combustion, NO x and steam parameters are evaluated. • A SOFA angle of 30° is advisable for the novel combustion system. • Significant NO x reduction are achieved while limiting the carbon in the fly ash. A novel combustion system, consisting of moving fuel-lean nozzles from the arches to the front/rear walls, rearranging staged air, and introducing separated over-fire air (SOFA), has been proposed and successfully applied in a 600 MW e Foster Wheeler down-fired boilers to reduce high NO x emissions while limiting the carbon content in the fly ash. This study comprehensively evaluates the effect of SOFA angles on flow, combustion characteristics and NO x emissions for the novel combustion system by numerical simulation and in-situ experiment. The numerical simulation shows in acceptable consistence with the in-situ experiment. The simulated results show that significant NO x reduction is obtained for all five SOFA angles compared to the original combustion system. O 2 and CO concentrations at the furnace outlet, as well as the carbon content in the fly ash decrease significantly with increasing SOFA angle from 0° to 40°. NO x emissions increase slightly and the average temperature at the re-heater entrance changes slightly with the increase of SOFA angle from 0° to 30°. However, with further increasing SOFA angle from 30° to 40°, NO x emissions increase substantially due to the smaller reducing region below the SOFA and the average temperature at the re-heater entrance falls significantly. Taking combustion, NO x and steam parameters into account, a SOFA angle of 30° is advisable. The actual industrial measurements also show that the steam can achieve the designed values when the SOFA angle is set at 30° instead of 40°. Significant NO x reduction (over 50 %) and good performance are attained after adopting the novel combustion technology of 30 °SOFA angle. [ABSTRACT FROM AUTHOR]

A novel combustion system has been applied to a 600 MW e down-fired boiler to reduce NO x emissions without producing an obvious increase in the carbon content of fly ash. The system mainly includes moving fuel-lean nozzles from the arches to the front/rear walls, and re-arranging the staged air, as well as introducing separated-over-fire air (SOFA). This paper evaluates the effects of the SOFA locations (on the arches, on the throat, and on the upper furnace) on the combustion and NO x emissions characteristics using simulations. The numerical results are in good agreement with the measured results. Compared to the original combustion system, significant NO x reduction (approximately 50%) is found for all three SOFA location settings. Taking economic efficiency and NO x emissions into account, the SOFA on the upper furnace is adopted in the actual modification, and no negative effects are observed. [ABSTRACT FROM AUTHOR]

Coal combustion is the major contributor to global toxic selenium (Se) emissions. Inorganic elements in coals significantly affect Se partitioning during combustion. This work confirmed that the calcium (Ca) in ash had a stronger relationship with Se retention at 1300 °C than other major elements. Ca oxide chemically reacted with gaseous Se, and its sintering densification slightly affected Se adsorption capacities (44.45 −1840.71→35.17 −1540.15 mg/kg) at 300 − 1300 °C. Therefore, Ca in coals was identified as having potential for hindering gaseous Se emissions, and coals with increased Ca contents (2.74→5.19 wt%) were used in a 350 MW unit. The decreased Se mass distribution (3.54%→2.63%) in flue gas at air preheater inlet (320 −362 °C) confirmed the effectiveness of increased Ca content on gaseous Se emission reduction. More gaseous Se further condensed and was chemically adsorbed by fly ash when passed through an electrostatic precipitator, resulting in a significant increase in the Se content of fly ash. Additionally, the corresponding Se leaching ratio decreased from 4.88 − 35.74% to 1.87 − 26.31%, indicating enhanced stability of Se enriched in fly ash. This research confirmed the feasibility and environmental safety of sequestration of gaseous Se from flue gas to fly ash by increasing the Ca content in coals. [Display omitted] ● Se retention at 1300 °C is associated with Ca content in ash. ● Ca oxide removes more gaseous Se via chemical reaction during flue gas cooling. ● Coals with higher Ca contents will release less gaseous Se into flue gas. ● A higher Ca content in fly ash can enhance the stability of Se within. ● Electrostatic precipitator induces Se emission reduction with increased Ca content. [ABSTRACT FROM AUTHOR]

Coal combustion is one of the major pathways by which lead (Pb) enters the ecological environment. An effective method to control Pb emissions in a furnace is to transform the Pb from vapors to particles using Si-Al-based sorbents. However, the high price, poor thermal stability, and difficult molding of sorbents limits their application. Fly ash cenospheres (FACs) prepared from the waste of coal-fired power plants, which are mainly composed of SiO 2 and Al 2 O 3 , are ideal materials for Pb sorbents because of their high strength, light weight and low price. In this study, the adsorption and reaction mechanisms of FACs and several Si-Al-based sorbents for Pb vapors were investigated in a two-stage fixed-bed reaction system, and the thermal stability and regeneration characteristics of FACs were tested. The results indicate that the adsorption capacity for Pb vapors is FAC > kaolin > SiO 2 > γ-Al 2 O 3. The acidic sites, such as Si-O and Al-O bonds in FACs, were the main reaction sites for Pb adsorption and captured Pb in the form of stable Pb compounds (Pb2+). As the temperature increased from 700 to 1200 °C, the Pb adsorbed by FACs increased, and 55.21% of the Pb in the simulated flue gas was removed at 1200 °C. Kaolin is an excellent sorbent for Pb vapors. The adsorption capacity of kaolin for Pb first increases and then decreases with increasing temperature, and the maximum removal rate occurs at 1000 °C, reaching 33.46%. In addition, FACs are thermally stable and reusable. Therefore, the high-temperature application of FACs to remove Pb vapors has good prospects. [ABSTRACT FROM AUTHOR]