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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]

Abstract: A new over-fire air (OFA) program, which called arch-supplied OFA, is proposed for Foster Wheeler (FW) type down-fired boiler in this paper. The OFA nozzles are setting on arches near the furnace center and emitting OFA flow into the furnace at an inclined angle. Cold airflow experiments were conducted to determine the effect of the OFA ratio on the aerodynamic field in a small-scale furnace modeled for a 660-MWe down-fired boiler. As the OFA ratio increases, the penetration depth of the OFA flow increases in the level direction and the turning point from downward to upward of the OFA flow moves to the furnace center. At the same time, the velocity of the F-tier airflow decreases and its ability to bring the arch-injected airflow to deeper positions weakens and the turning point from downward to upward of the F-tier airflow moves to the wall. When the OFA ratio is 20%, the OFA flow could penetrate to the furnace center in the level direction and mix with the upflowing gas completely, while the arch-injected airflow have sufficient travel distance and enough residence time in the lower furnace. Thus, considering the penetration depth of arch-injected flow in the vertical direction and the OFA flow in the level direction, an OFA ratio of 20% is recommended for the new OFA arrangement according to the present work. [Copyright &y& Elsevier]

Abstract: Industrial experiments were performed for a retrofitted 660-MWe full-scale arch-fired boiler. The ignition position of the primary air/fuel mixture flow, furnace temperature and flue gas component after the air heater were measured with different anthracite ratios at loads of 660- and 380-MWe. As the ratio of anthracite increased, the gas temperature decreased in the fuel-burning zones of the C4 and C6 burners, indicating a farther ignition position of the primary fuel/air flow under the arches, the gas temperature of the lower furnace decreased while that of the upper furnace increased, NO x emissions decreased while both the exhaust gas temperature and carbon content in fly ash increased, and the boiler efficiency decreased. At the rated load, an anthracite ratio of 35% was optimal for economical efficiency. At low load, the negative gas pressure fluctuated remarkably, which led to unstable combustion in the furnace. To ensure safe and stable operation of the boiler, a mass ratio of anthracite of 25% is advisable. [Copyright &y& Elsevier]

Abstract: Industrial experiments were performed for a retrofitted 660MWe full-scale down-fired boiler. Measurements of ignition of the primary air/fuel mixture flow, the gas temperature distribution of the furnace and the gas components in the furnace were conducted at loads of 660, 550 and 330MWe. With decreasing load, the gas temperature decreases and the ignition position of the primary coal/air flow becomes farther along the axis of the fuel-rich pipe in the burner region under the arches. The furnace temperature also decreases with decreasing load, as does the difference between the temperatures in the burning region and the lower position of the burnout region. With decreasing load, the exhaust gas temperature decreases from 129.8°C to 114.3°C, while NO x emissions decrease from 2448 to 1610mg/m3. All three loads result in low carbon content in fly ash and great boiler thermal efficiency higher than 92%. Compared with the case of 660MWe before retrofit, the exhaust gas temperature decreased from 136 to 129.8°C, the carbon content in the fly ash decreased from 9.55% to 2.43% and the boiler efficiency increased from 84.54% to 93.66%. [Copyright &y& Elsevier]

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]

Abstract: Air-surrounding-fuel is a well-known concept used within tangential and wall-fired boilers. Here, we report for the first time on industrial experiments performed to study the effects of this concept on a 660 MWe full-scale down-fired boiler. Data are reported for the gas temperature distributions along the primary air and coal-mixed flows, furnace temperatures, gas compositions, for example O2, CO and NO x , and gas temperatures in the near-wall region. The influence of concentration control valve (CCV) opening on combustion and NO x emission in the furnace were determined. The results show that the flame stability, temperature distribution, unburnt carbon are influenced by both concentration ratios and fuel-rich flow velocities. As CCV opening increases, NO x emissions decrease from 2594 mg/m3 to 1895 mg/m3. Considering altogether economic benefits and environmental protection issues, 30% is the optimal value for the CCV opening. [ABSTRACT FROM AUTHOR]

Abstract: We measured various operational parameters of a 200-MWe, wall-fired, lignite utility boiler under different loads. The parameters measured were gas temperature, gas species concentration, char burnout, component release rates (C, H and N), furnace temperature, heat flux, and boiler efficiency. Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has two ring recirculation zones that start in the secondary air region of the burner. With increasing secondary air flow, the air flow axial velocity increases, the maximum values for the radial velocity, tangential velocity, and turbulence intensity all increase, and there are slight increases in the air flow swirl intensity and the recirculation zone size. With increasing load gas, the temperature and CO concentration in the central region of burner decrease, while O2 concentration, NO x concentration, char burnout, and component release rates of C, H, and N increase. Pulverized-coal ignites farther into the burner, in the secondary air region. Gas temperature, O2 concentration, NO x concentration, char burnout and component release rates of C, H, and N all increase. Furthermore, CO concentration varies slightly and pulverized-coal ignites closer. In the side wall region, gas temperature, O2 concentration, and NO x concentration all increase, but CO concentration varies only slightly. In the bottom row burner region the furnace temperature and heat flux increase appreciably, but the increase become more obvious in the middle and top row burner regions and in the burnout region. Compared with a 120-MWe load, the mean NO x emission at the air preheater exits for 190-MWe load increases from 589.5mg/m3 (O2 =6%) to 794.6mg/m3 (O2 =6%), and the boiler efficiency increases from 90.73% to 92.45%. [Copyright &y& Elsevier]

Abstract: We measured various operational parameters of a 200-MWe, wall-fired, lignite utility boiler under various outer secondary air vane angles. The parameters measured were gas temperature, gas species concentrations, char burnout, and component release rates (C, H and N). Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has a single ring recirculation zone that forms in the secondary air region in the burner. By decreasing vane angles, maximum values of radial velocity, tangential velocity and turbulence intensity all increase. Moreover, swirl intensity of air flow and recirculation zone size increase. Concomitantly, in the central region of the burner, decreasing the vane angles of outer secondary air increases gas temperatures, CO concentrations, char burnout and component release rates of C, H, and N, while O2 and NO x concentrations decrease, and an early ignition of pulverized-coal occurs. Meanwhile, in the secondary air region of the burner, conditions are similar except that NO x mean concentrations are reversed showing instead an increase. In the side wall region, gas temperatures increase, O2 and NO x concentrations decrease, but CO concentrations vary only slightly. [Copyright &y& Elsevier]

Abstract: Industrial experiments were performed on a down-fired pulverized-coal 300MWe utility boiler with swirl burners. Gas temperature, concentrations of gas components (O2, CO, CO2 and NO x ) in the burning region and carbon content in the fly ash were measured with outer secondary-air vane angles of 25°, 32.5° and 50°. Results indicate that with increasing vane angle, NO x emission and boiler efficiency decrease. Overall evaluation boiler efficiency and NO x emission, the vane angle of 32.5° is optimum. Using an IFA300 constant-temperature anemometer system, cold air experiments on a quarter-scaled burner model were also carried out to investigate the influence of various outer secondary-air vane angles on the flow characteristics in the burner nozzle region. No central recirculation zone appeared for vane angles of 25° and 32.5°. Most of the pulverized-coal was ignited in the external recirculation zone. For vane angles of 45° and 55°, a central recirculation zone could be observed, and air flow rigidity and axial velocities decreased rapidly. [Copyright &y& Elsevier]