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The influence of mass-flow-rate ratio of inner to outer secondary air on gas–particle flow characteristics was determined in the near-burner region of a centrally fuel-rich swirl coal combustion burner. Velocity and particle volume flux profiles and normalized particle number concentrations were obtained. Peaks in tangential mean velocity and three-dimensional root-mean-square fluctuation velocities were found to decrease as the mass-flow-rate ratio increased. Moreover, the peaks in the mean axial velocities and particle volume flux near the wall increased, whereas those near the chamber axis decreased. Simultaneously, both recirculation zone and swirl number decreased as the mass-flow-rate ratio increased.

Cold airflow experiments on a small-scale burner model, as well as in situ experiments on a centrally fuel-rich swirl coal combustion burner were conducted. Measurements were taken from within a 300 MW e wall-fired pulverized-coal utility boiler installed with eight of centrally fuel-rich swirl coal combustion burners in the bottom row of the furnace during experiments. Various primary air ratios, flow characteristics, gas temperature and gas species concentrations in the burner region were measured. The results of these analyses show that with decreasing primary air ratio, the swirl intensity of air, divergence angles and maximum length and diameter of the central recirculation zone all increased, and the turbulence intensity of the jet flow peaked but decayed quickly. In the burner nozzle region, gas temperature, temperature gradient and CO concentration increased with decreasing primary air ratio, while O 2 and NO x concentration decreased. Different primary air ratios, the gas temperatures and gas species concentrations in the side-wall region varied slightly.

Due to the limits of reserves and price for the high rank coal, the low rank coal has been employed as fuel for power generation in China and will be eventually employed in the world. To burn low rank coal, centrally fuel-rich swirl coal combustion burner has been studied in Harbin Institute of Technology. This paper reviews and analyzes the major research results. The work has included both experiments and numerical simulation. The experiments were conducted using small-scale single-phase experimental equipment, a gas/particle two-phase test facility and 200- and 300-MWe wall-fired utility boilers. For the burner, the primary air and glass beads partially penetrate the central recirculation zone and are then deflected radially. At the center of the central recirculation zone, there is high particle volume flux and large particle size. For the burners the local mean CO concentrations, gas temperatures and temperature gradient are higher, and the mean concentrations of O2 and NOx in the jet flow direction in the burner region are lower. Moreover, the mean O2 concentration is higher and the gas temperature and mean CO concentration are lower in the side wall region. Centrally fuel-rich burners have been successfully used in 200- and 300-MWe wall-fired pulverized coal utility boilers.

We measured various operational parameters of a 200-MW e , 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 O 2 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, O 2 and NO x concentrations decrease, but CO concentrations vary only slightly.

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, NOx 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, NOx 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 NOx 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 NOx emission at the air preheater exits for 190-MWe load increases from 589.5 mg/m3 (O2 = 6%) to 794.6 mg/m3 (O2 = 6%), and the boiler efficiency increases from 90.73% to 92.45%.

Turbulence intensities at the exit of a centrally fuel rich (CFR) burner were measured employing a probe with hot-film sensors. In addition, using glycol as a smog tracer, optical images of the highlighted primary airflow were taken with a CCD camera and contrast-enhanced by computer. Profiles of the interface between primary and secondary air were obtained from which fractal dimensions (FDs) of the primary air boundary were estimated. Results indicate that FDs of this air boundary are in the range of 1.10–1.30 depending on burner conditions. As the FD and mean turbulence intensities of the primary air boundary have uniform distributions, they can be used to analyze coal combustion and NOx formation characteristics of the burner. When either decreasing the outer secondary air vane angle or increasing either the inner secondary air vane angle or total mass flow rate of the secondary air, the burner swirl number increases which subsequently shows up as an increase in the FD and mean turbulence intensities of the primary air boundary. Increasing the ratio of the mass flow rate of inner to outer secondary air decreases the burner swirl number, but increases the FD and mean turbulence intensities of primary air boundary.

Measurements were taken for a 300 MWe wall-fired pulverized-coal utility boiler installed with eight centrally fuel rich swirl coal combustion burners in the bottom row of the furnace during experiments. For various outer secondary air vane angle settings, flow characteristics, gas temperature and gas species concentrations in the burner region were measured. The results show that with decreasing outer secondary air vane angle, the swirl intensity of air, divergence angles and maximum length and diameter of the central recirculation zone all increased; the turbulence intensity of the jet flow first increased and then quickly decreased. With decreasing outer secondary air vane angle, the rate of increase in the gas temperature in the early stage and the rate of decrease in the later stage increased along the jet flow direction. For outer secondary air vane angle of 25°, the O2 concentration along the jet flow direction in the burner region was low, and the CO concentration decreased with increasing outer s...

Experiments on a single-phase test facility were done to optimize primary air outlet cones of a centrally fuel rich swirl coal combustion burner. On the basis of optimized results from the single-phase test, a three-component particle-dynamics anemometer was used to measure, in the near-burner region, the characteristics of gas/particle two-phase flows for the burner with two primary air outlet cones, on a gas/particle two-phase test facility. Velocities, RMS velocities and particle volume flux profiles were obtained. According to the results, the primary air outlet cone structure of the centrally fuel rich burner was matching a 670 ton per hour boiler. The performance of the burner on a 670 ton per hour boiler was studied.

Measurements were performed on a 200 MWe, wall-fired, lignite utility boiler. For different overfire air (OFA) damper openings, the gas temperature, gas species concentration, coal burnout, release rates of components (C, H, and N), furnace temperature, and heat flux and boiler efficiency were measured. Cold air experiments for a single burner were conducted in the laboratory. The double-swirl flow pulverized-coal burner has two ring recirculation zones starting in the secondary air region in the burner. As the secondary air flow increases, the axial velocity of air flow increases, the maxima of radial velocity, tangential velocity and turbulence intensity all increase, and the swirl intensity of air flow and the size of recirculation zones increase slightly. In the central region of the burner, as the OFA damper opening widens, the gas temperature and CO concentration increase, while the O{sub 2} concentration, NOx concentration, coal burnout, and release rates of components (C, H, and N) decrease, and coal particles ignite earlier. In the secondary air region of the burner, the O{sub 2} concentration, NOx concentration, coal burnout, and release rates of components (C, H, and N) decrease, and the gas temperature and CO concentration vary slightly. In the sidewall region, the gasmore » temperature, O{sub 2} concentration, and NOx concentration decrease, while the CO concentration increases and the gas temperature varies slightly. The furnace temperature and heat flux in the main burning region decrease appreciably, but increase slightly in the burnout region. The NOx emission decreases from 1203.6 mg/m{sup 3} (6% O{sub 2}) for a damper opening of 0% to 511.7 mg/m{sup 3} (6% O{sub 2}) for a damper opening of 80% and the boiler efficiency decreases from 92.59 to 91.9%. 15 refs., 17 figs., 3 tabs.« less

A three-component particle-dynamics anemometer is used to measure, in the near-burner region, the characteristics of gas/particle two-phase flows with a centrally fuel rich swirl coal combustion burner and enhanced ignition–dual register burner, on a gas/particle two-phase test facility. Velocities, RMS velocities, particle mean diameters and particle volume flux profiles were obtained. For the centrally fuel rich burner, particles penetrate the central recirculation zone partially, and are then deflected radially. For the enhanced ignition–dual register burner, particles completely penetrate the central recirculation zone. Compared with the enhanced ignition–dual register burner, in the same cross-section, the particle volume flux peak value for the centrally fuel rich burner is much closer to the chamber axis and much larger near the chamber axis. In six cross-sections from x / d = 0.3 to 2.5, the particle volume flux in the central recirculation zone for the centrally fuel rich burner is much larger than that for the enhanced ignition–dual register burner. For the centrally fuel rich burner, most of bigger particles are resident in the region near the chamber axis and the residence time is prolonged. The influence of gas/particle flow characteristics on combustion has been analyzed.

Computational fluid dynamics (CFD) has been applied to evaluate two NO x 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 NO x 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 NO x concentration has decreased 571 mg/m3 (67.4%) and 436 mg/m3 (61.2%), respectively.

Experiments with a small-scale cyclone burner used for burner enrichment in a down-fired pulverized-coal 300 MWe utility have been conducted on an air/particle test facility. Particle separating efficiency was obtained with different positions of an adjustable vane. Industrial experiments were performed on a full-scale boiler. The gas temperature distribution along the primary air and coal mixture flow, gas temperature distribution of the furnace, and gas components such as O2, CO, CO2 and NOX in the near-wall region were measured for the first time. The influence of the adjustable vane position on coal combustion in the furnace was determined. With the adjustable vanes at the nozzle, ignition of the primary air and pulverized-coal mixture was delayed and the gas temperature peak was above the burner arch, with high NOX emission. Raising the vanes can bring forward the ignition point but results in the fuel-rich flow being up ahead of time, leading to a rise in carbon content in fly ash and NOX emission.

A three-component particle-dynamics anemometer is used to measure, in the near-burner region, the influence of the particle bias in the primary air duct on the gas/particle flow characteristics for a centrally fuel rich swirl coal combustion burner, in conjunction with a gas/particle two-phase test facility. Velocities, particle volume flux profiles and normalized particle number concentrations were obtained. Compared with a common burner (a centrally fuel rich burner without a particle concentrator), the degree of penetration for the centrally fuel rich burner is higher, the residence time of particles in the central recirculation zone is longer and the central recirculation zone is larger. The particle volume flux and normalized particle number concentration for the centrally fuel rich burner are much larger near the chamber axis. The influence of gas/particle flow characteristics on combustion has been analyzed.

A three-component particle-dynamics anemometer is used to measure the characteristics of two-phase gas/particle flows in the near-burner region for a centrally fuel rich swirl coal combustion burner using a gas/particle two-phase test facility. Velocities, mean particle diameters and particle-volume flux profiles were obtained. The primary air and glass beads partially penetrate the central recirculation zone and are then deflected radially. At the center of the central recirculation zone, the mean radial velocities and tangential velocities are low and a zone of high particle-volume flux and large particle size is formed. The influence of gas/particle flow characteristics on combustion is analyzed.

Measurements were performed in a 300-MWe wall-fired pulverized-coal utility boiler. Enhanced ignition-dual register (EI-DR) burners and centrally fuel rich (CFR) swirl coal combustion burners were installed in the bottom row of the furnace during experiments. Local mean concentrations of O2, CO, CO2 and NO x gas species, gas temperatures, and char burnout were determined in the region of the two types of burners. For centrally fuel rich swirl coal combustion burners, local mean CO concentrations, gas temperatures and the temperature gradient are higher and mean concentrations of O2 and NO x along the jet flow direction in the burner region are lower than for the enhanced ignition-dual register burners. Moreover, the mean O2 concentration is higher and the gas temperature and mean CO concentration are lower in the side wall region. For centrally fuel rich swirl coal combustion burners in the bottom row, the combustion efficiency of the boiler increases from 96.73% to 97.09%, and NO x emission decreases fro...

A three–component particle–dynamics anemometer is used to measure, in the near–burner region, the influence of the primary air ratio on the gas/particle two–phase characteristics for a centrally fuel rich swirl coal combustion burner, on a gas/particle two phase test facility. Velocities, particle volume flux profiles and particle relative number concentrations were obtained. With a low primary air ratio, the axial velocities for gas and particles on the chamber axis are always small and easily reach the negative, and the central recirculation zone is easily formed and much closer to the outlet of the burner. In each cross–section, in the radius range from R