Lingyan Zeng

Effect of the Vane Angle for Outer Secondary Air on the Flow and Combustion Characteristics and NO x Emissions of the Low-NO x Axial-Swirl Coal Burner

We conducted a cold air experiment and numerical simulation to investigate flow and combustion characteristics and NO x emission of a low-NOx axial-swirl burner in a 600 MWe bituminous coal-burning boiler. Comparison of single-phase numerical simulation results and measurements made by a probe with hot-film sensors shows that the numerical model is a reasonable description. By changing the vane angle for outer secondary air, we obtain different results for the recirculation zone, the divergence angle, the distance that the recirculation zone extends into the burner, the mass of the flue gas that returns to the burner, the temperature of the furnace, and the concentration of NO x emission. The best vane angle for the outer secondary air is determined to be 15°.

Numerical Simulation of Flow, Combustion, and NO x Emission Characteristics in a 300 MW Down-Fired Boiler with Different OFA Ratios

A computational fluid dynamics model of a 300 MW down-fired furnace equipped with over-fire air (OFA) has been developed using Fluent 6.3. The validated CFD model is applied to investigate the effects of several operating conditions at full load with different OFA ratios. Simulation results indicate that as the OFA ratio rises from 0% to 40%, the NO x emission falls and the combustible material content in the fly ash increases. On the whole, n, the optimal OFA ratio for the studied down-fired boiler is 20%. This study provides a basis to assess in depth future operations of down-fired boilers.

Industrial Application of an Improved Multiple Injection and Multiple Staging Combustion Technology in a 600 MWe Supercritical Down-Fired Boiler

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/m(3) at 6% O2 and 6.18%, respectively, achieving NOx and carbon in fly ash significant reduction by 33% and 37%, respectively.

Numerical Simulations of Combustion Characteristics and NO x Emissions for Two Configurations of Swirl Coal Burners in a 300 MWe Wall-Fired Boiler

We studied both experimentally and numerically the pulverized-coal combustion process and NO x emissions in a 300 MWe wall-fired boiler burning bituminous coal. In simulations of an enhanced ignition-dual register (EI-DR) burner arrangement, results gave values of 6.39% and 861.43 mg/m3 at 6% O2 for combustible material content in the fly ash and NO x concentration at the furnace outlet, respectively. Meanwhile, simulations with a centrally fuel rich (CFR) swirl burner arrangement gave similar results of 3.63% and 695.36 mg/m3 at 6% O2. Comparing the two, the NO x concentration of the latter had decreased by 19.28%.

Effect of Stoichiometric Ratio of Fuel-Rich Flow on Combustion Characteristics in a Down-Fired Boiler

AbstractNumerical simulations and industrial experiments were conducted to study the effect of the stoichiometric ratio of the fuel-rich flow (0.46, 0.49, 0.51, 0.53, and 0.55) on the flow, combustion, and NOx emission characteristics in a 600-megawatt electric (MWe) supercritical down-fired boiler with multiple-injection and multiple-staging combustion technology. The simulation results indicate that as the stoichiometric ratio of the fuel-rich flow increases from 0.46 to 0.55, the flow fields all form a symmetric W-shaped pattern; this is identical to the symmetric temperature distributions obtained experimentally. The ability of downward coal/air flows to entrain high-temperature gases from the recirculation zone weakens, and the airflow declination angle in tertiary-air regions and the downward flame penetration depth decrease. Coal burnout is enhanced. The temperature in the lower furnace rises, the high-temperature (≥1,700  K) area gradually increases from 64 to 120  m2, the carbon in the fly ash at...

Experiment and numerical simulation investigations of the combustion and NOx emissions characteristics of an over-fire air system in a 600 MWe boiler

ABSTRACT Several numerical simulations are conducted to investigate the influence of pulverized-coal combustion characteristics and NOx emissions with different configurations of nozzle and arrangements of an over-fire air device for a 600 MWe boiler unit. It is found by a series of comparisons that the numerical simulation results are almost in agreement with the in-situ experimental results, including the flue gas temperature of the burner outlet, the flue gas temperature along the furnace height, the NOx concentration, and combustible content in the fly ash of the air preheater outlet, which indicates that the numerical model and the grid are reasonable. Numerical simulation results show that setting the over-fire device in which the inner is straight flow and the outer is swirl flow and the staggered arrangement of two layers of over-fire air (OFA) in the boiler are both conducive to the pulverized-coal combustion in the furnace and to the reduction of NOx emissions. The results also show the values of 241.64 mg/m3 @ 6% O2 for the lowest NOx concentration at the furnace outlet. Compared with the boiler without OFA, the NOx concentration decreased by 60.4%. Using the staggered arrangement of two layers of OFA in the practical 600 MW boiler unit, the gas temperature can reach 1100 K at the height of 100 mm away from the burner outlet, leading to coal particle ignition immediately; moreover, the NOx emission concentration reduced to 284 mg/m3 @ 6% O2 and heat loss due to unburned carbon in refuse of the air preheater outlet is 3.17%.