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The air distribution system was one of the key devices that affects solid flow characteristics in circulating fluidized bed (CFB). Different air distribution systems have an influence on gas–solid flow uniformity, solids velocity, and concentration. In the conventional CFB, the air distribution system which composed of air chamber and distributor was placed on the bottom of the reactor. In this paper, an atmospheric circulating fluidized bed gasifier (AT-CFBG) was examined. The chamber and distributor of CFB was canceled and which was replaced by six nozzles with asymmetrical and symmetrical arrangement that mounted on the bottom of the furnace. A cold test was established at a scale of 1:15, the optical fiber was used to measure solids concentrations and velocities in the furnace under the asymmetrical and the symmetrical arrangement. The results showed that the asymmetrical arrangement has a better uniform velocity profile and has a higher solids concentration than those of the symmetrical arrangement. And it also has a stable solids circulation and a higher solids circulation rate (0.37 kg/h) than those of the symmetrical arrangement (0.34 kg/h). [ABSTRACT FROM AUTHOR]

To overcome the problem of high carbon content in the fly ash of down-fired utility boilers using low-volatility coals, the combustion system of a 660 MWe full-scale down-fired boiler was retrofitted, with the direction of the secondary air under the arch being changed from horizontal to an angle of declination of 20°. Industrial experiments were performed using the boiler before and after the retrofit to determine the reconstruction effect. Data are reported for the gas temperature distribution along the primary air and coal mixture flow, furnace temperature, gas compositions, such as O2, CO, CO2, and NOx, and gas temperatures in the near-wall region. Comparisons between the two cases were made, and the results show that with the angled secondary air under the arches, ignition of the primary air and pulverized coal mixture was brought forward in the boiler. Gas temperatures rose in the fuel-burning zone, and the residence time of pulverized coal in the fuel-burning zone was extended. Thus, the quantity of unburned carbon in fly ash and the gas temperature at the furnace outlet decreased, and the boiler efficiency increased. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) has been applied to evaluate two NOx reducing schemes in a 100 MWe per hour (p/h) boiler that uses double volute burners without over-fire-air (OFA). The new schemes involve: a) changing the double volute burners for centrally fuel rich (CFR) burners, and b) using the OFA system in conjunction with a). In analyzing the results of these two schemes, various conclusions were drawn: 1) gas temperatures and related rise rates in the central zone of burners were higher, O2 and NOx concentrations were lower; and 2) cross-sectional gas temperature distributions through the burner centers in scheme employing b) is higher than that of original furnace set-up, and lower than that of scheme employing a). Comparing the b) scheme with those of the a) scheme and the original set-up, which is 277 mg/m3 (at 6% O2) at the furnace outlet, the peak value of NOx concentration has decreased 571 mg/m3 (67.4%) and 436 mg/m3 (61.2%), respectively. [ABSTRACT FROM AUTHOR]