Low NO.sub.x short flame burner

A burner for the combustion of a pulverized coal fuel plug air mixture, comprising:

• an nozzle pipe (16) having an inlet (14) for receiving a pulverized coal fuel plus primary air mixture, an outlet (36) for discharging the pulverized coal fuel plus primary air mixture, and an inner surface which diverges along at least part of the length of said pipe between said inlet and said outlet and which includes cylindrical portions upstream and downstream of the diverging portion of said pipe;
• a plug extending axially in said nozzle pipe and defining an annular nozzle space in said pipe for the passage of the pulverized coal fuel plug primary air mixture, said plug having an outer surface which diverges along at least part of the length of said plug in said annular nozzle space and opposite the diverging portion of said pipe for diverting the pulverized coal fuel plus primary air mixture outwardly along said nozzle space and which includes cylindrical portions upstream and downstream of the diverging portion of said plug;
• drive means connected to said pipe and said plug for moving said pipe and plug axially with respect to each other to change the cross-sectional area of the nozzle space at the diverging portions of said pipe and plug so the pulverized coal fuel plus primary air mixture moves at a different velocity near the diverging portions of the pipe and plug;
• means for supplying ducted air from the outer surface of the plug and the inner surface of the pipe at the diverging portions thereof into the annular nozzle space to reduce NO.sub.x ;
• and
• secondary air means extending around said pipe for supplying secondary air in an annular stream around the pulverized coal fuel plus primary air mixture discharged from said nozzle outlet.

A burner for the combustion of a pulverized coal fuel plus air mixture, comprising:

• a nozzle pipe (16) having an inlet (14) for receiving a pulverized coal fuel plus primary air mixture, and outlet (36) for discharging the pulverized coal fuel plus primary air mixture, and an inner surface which diverges along at least part of the length of said pipe between said inlet and said outlet and which includes cylindrical portions upstream and downstream of the diverging portion of said pipe;
• a plug extending axially in said nozzle pipe and defining an annular nozzle space in said pipe for the passage of the pulverized coal fuel plug primary air mixture, said plug having an outer surface which diverges along at least part of the length of said plug in said annular nozzle space and opposite the diverging portion of said pipe for diverting the pulverized coal fuel plus primary air mixture outwardly along said nozzle space and which includes cylindrical portions upstream and downstream of the diverging portion of said plug;
• drive means connected to said pipe and said plug for moving said pipe and plug axially with respect to each other to change the cross-sectional area of the nozzle space at the diverging portions of said pipe and plug so the pulverized coal fuel plus primary air mixture moves at a different velocity near the diverging portions of the pipe and plug;
• means for supplying recirculated gas from the outer surface of the plug at the diverging portion thereof into the annular nozzle space to reduce NO.sub.x ;
• and
• secondary air means extending around said pipe for supplying secondary air in an annular stream around the pulverized coal fuel plus primary air mixture discharged from said nozzle outlet.

A burner for the combustion of a pulverized coal fuel plus air mixture, comprising:

• an nozzle pipe (16) having an inlet (14) for receiving a pulverized coal fuel plus primary air mixture, an outlet (36) for discharging the pulverized coal fuel plus primary air mixture, and an inner surface which diverges along at least part of the length of said pipe between said inlet and said outlet and which includes cylindrical portions upstream and downstream of the diverging portion of said pipe;
• a plug extending axially in said nozzle pipe and defining an annular nozzle space in said pipe for the passage of the pulverized coal fuel plug primary air mixture, said plug having an outer surface which diverges along at least part of the length of said plug in said annular nozzle space and opposite the diverging portion of said pipe for diverting the pulverized coal fuel plus primary air mixture outwardly along said nozzle space and which includes cylindrical portions upstream and downstream of the diverging portion of said plug;
• drive means connected to said pipe and said plug for moving said pipe and plug axially with respect to each other to change the cross-sectional area of the nozzle space at the diverging portions of said pipe and plug so the pulverized coal fuel plus primary air mixture moves at a different velocity near the diverging portions of the pipe and plug;
• means for supplying recirculated gas from the outer surface of the plug and the inner surface of the pipe at the diverging portions thereof into the annular nozzle space to reduce NO.sub.x ;
• and
• secondary air means extending around said pipe for supplying secondary air in an annular stream around the pulverized coal fuel plus primary air mixture discharged from said nozzle outlet.