Numerical simulations of flow, combustion characteristics, and NOx emission for down-fired boiler with different arch-supplied over-fire air ratios

Abstract This paper presents research on a 660 MW e Foster Wheeler (FW) type down-fired boiler. The arch-supplied over-fire air (OFA) plan and high efficiency measures are proposed for the boiler. The influence of different OFA ratios on flow field, temperature distribution, and O 2 and NO x concentration distributions inside the furnace are investigated by numerical simulation using Fluent 6.3.26 software. Also, the average temperature, the carbon content in the fly ash, and the O 2 and NO x concentrations at the exit of the furnace are calculated. Three high-temperature zones are identified in the furnace: at the front and rear wall under the arch, and at the bottom of the upper furnace. As the OFA ratio increases, the gas temperature, the carbon content in the fly ash, and the O 2 concentration increase, but the NO x concentration decreases significantly at the exit of the furnace. In particular, when the OFA ratio increases from 20% to 25%, the amplitude of the decrease of the NO x emissions is smaller, but the combustible content in the fly ash increases more obviously. Considering the NO x emissions and the combustible content in the fly ash, an OFA ratio of 20% is advisable for the arch-supplied OFA program.

[1]  Zhengchun Lin,et al.  Impact of air staging along furnace height on NOx emissions from pulverized coal combustion , 2010 .

[2]  Zhichao Chen,et al.  Combustion and NOx emission characteristics of a retrofitted down-fired 660 MWe utility boiler at different loads , 2011 .

[3]  T. Shih,et al.  A New K-epsilon Eddy Viscosity Model for High Reynolds Number Turbulent Flows: Model Development and Validation , 1994 .

[4]  A. Gosman,et al.  Aspects of computer simulation of liquid-fuelled combustors , 1981 .

[5]  Lixing Zhou,et al.  Theory and numerical modeling of turbulent gas-particle flows and combustion , 1993 .

[6]  W. Fan,et al.  The effect of air staged combustion on NOx emissions in dried lignite combustion , 2012 .

[7]  Zhichao Chen,et al.  Influence of declivitous secondary air on combustion characteristics of a down-fired 300-MWe utility boiler , 2010 .

[8]  Likun Huang,et al.  Numerical study on the effect of the Over-Fire-Air to the air flow and coal combustion in a 670 t/h wall-fired boiler , 2006 .

[9]  Zhichao Chen,et al.  Influence of the adjustable vane position on the flow and combustion characteristics of a down-fired pulverized-coal 300 MWe utility boiler , 2008 .

[10]  Klaus R. G. Hein,et al.  Development of an air staging technology to reduce NOx emissions in grate fired boilers , 2005 .

[11]  P. Cheng.  Two-dimensional radiating gas flow by a moment method , 1964 .

[12]  Zhichao Chen,et al.  New over-fire air arrangement and its air ratio optimization determined by aerodynamic characteristics in a cold small-scale model for a down-fired 660-MWe utility boiler , 2013 .

[13]  Alessandro Franco,et al.  The future challenges for “clean coal technologies”: Joining efficiency increase and pollutant emission control , 2009 .

[14]  Zhichao Chen,et al.  Improved NOx emissions and combustion characteristics for a retrofitted down-fired 300-MWe utility boiler. , 2010, Environmental science & technology.

[15]  L. Douglas Smoot,et al.  Coal Combustion and Gasification , 1985 .

[16]  Zhichao Chen,et al.  Effect of the anthracite ratio of blended coals on the combustion and NOx emission characteristics of a retrofitted down-fired 660-MWe utility boiler , 2012 .

[17]  Zhengqi Li,et al.  Evaluation of overfire air behavior for a down-fired 350 MWe utility boiler with multiple injection and multiple staging , 2012 .

[18]  L. Mekasut,et al.  Emission of NOx and N2O from co-combustion of coal and biomasses in CFB combustor. , 2012 .

[19]  F. Johnsson,et al.  NOx reburning in oxy-fuel combustion: A comparison between solid and gaseous fuels , 2011 .

[20]  S. C. Hill,et al.  Modeling of nitrogen oxides formation and destruction in combustion systems , 2000 .

[21]  Chang Nyung Kim,et al.  Numerical investigation on the flow, combustion and NOx emission characteristics in a 500 MWe tangentially fired pulverized-coal boiler , 2009 .

[22]  Jie Zhang,et al.  Influence of vent air valve opening on combustion characteristics of a down-fired pulverized-coal 300 MWe utility boiler , 2007 .

[23]  T. Shih,et al.  A new k-ϵ eddy viscosity model for high reynolds number turbulent flows , 1995 .