Low NO{sub x} combustion of pulverized coal using the radially stratified flame core burner

Conference · Thu Jul 01 04:00:00 EDT 1999

OSTI ID:20006863

Barta, L E; Lewis, P F; Beer, J M

Results are presented of a theoretical-experimental study aimed at determining the characteristics of pulverized coal flames produced with the Low NO{sub x} Radially Stratified Flame Core (RSFC) Burner. Following earlier studies with this burner in which very low pollutant emissions were attained with natural gas and heavy fuel oil, the present investigation turned to the combustion of pulverized coal. In particular, the fulfillment of the conditions required for staged combustion, i.e., maintenance of a fuel-rich flame core at high temperature and for an extended period of time by the stratification of the flow, have been investigated. The criterion for radial stratification of the flow was theoretically developed from the equations of motion, by balancing the rate of generation of turbulence and the rate of turbulence damping; the latter being due to a combination of steep radial density gradients and swirling flow. The optimal radial stratification was obtained in forced vortex flow, when the radial profiles of the axial and tangential components of the air flow at the burner exit were adjusted to satisfy the condition along the flame front: 1 {partial{underscore}derivative}{bar {rho}}/{bar {rho}} {partial{underscore}derivative}r = P{sub T} ({alpha}/{beta}){sup 2} 1/r where {rho} is density, r is the radial distance of the flame front, P{sub T} is the turbulent Prandtl number, and {alpha} and {beta} are the first radial derivatives of the axial and the tangential velocity, respectively, evaluated at the radial distance r. A parametric combustion study carried out by burning a high volatile bituminous coal at a thermal input of 1.5 MW has shown that by setting a ratio {alpha}/{beta} = 0.76 at the burner, a stratified flame was created, and the NO{sub x} emission was reduced from an uncontrolled range of 700--900 ppm to 217 ppm. Further reduction to 70 ppm was achieved by external air staging. For this latter condition, however, the RSFC burner was operated to produce a well stirred, high temperature, fuel-rich flame with overfire air injected at some distance downstream of the burner. Both flame types were highly stable with 99.5% and 99.3% carbon conversion, respectively.

• Research Organization: Massachusetts Inst. of Tech., Cambridge, MA (US)
• OSTI ID: 20006863
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
AIR POLLUTION ABATEMENT
BITUMINOUS COAL
BURNERS
FLAMES
NITROGEN OXIDES
PERFORMANCE
PULVERIZED FUELS
STAGED COMBUSTION
STRATIFICATION