Dual fuel burner for a shortened flame and reduced pollutant emissions
View Patent ↗A dual fuel burner including an elongated supply pipe and a gas injector for a boiler furnace having a plurality of peripheral openings around a center opening. The peripheral openings are pitched radially away from the longitudinal axis of the gas injector and also pitched either clockwise or counter-clockwise, to impart a swirling motion to gaseous fuel exiting the injector through the openings. A first sleeve member is concentrically spaced about the supply pipe and the gas injector to form an inner annular passageway for conveying a mixture of primary air and pulverized coal to the furnace combustion zone. A second sleeve member is concentrically spaced about the first sleeve member to form an outer annular passageway for conveying secondary air to the furnace combustion zone, and a plurality of circumferentially spaced vanes mounted within the outer annular passageway for inducing a swirling motion to the secondary air discharging from the outer annular passageway into the furnace combustion zone.
1. In combination with the boundary wall of a boiler furnace, a combustion zone established within the furnace, at least one burner port formed in the boundary wall and fronting the combustion zone, a dual fuel burner facing the combustion zone through the burner port, and comprising:
an elongated supply pipe having an inlet end and an outlet end, and defining a conduit for conveying natural gas therethrough;
an injector connected to the outlet end of the supply pipe, the injector having a chamber communicating with the conduit, the chamber having a longitudinal axis and an end wall, wherein the diameter of the injector along the longitudinal axis prior to the end wall is substantially the same as the diameter of the elongated supply pipe;
a plurality of peripheral flow directing openings extending through the end wall in a circumferentially spaced array about the chamber axis, each opening having a longitudinal axis inclined at a first acute angle greater than zero with respect to the chamber axis, and each being further inclined, in a direction toward an adjacent peripheral opening, at a second acute angle greater than zero for inducing swirling motion to the natural gas being injected into the combustion zone;
a first sleeve member concentrically spaced about the supply pipe and the injector to form an inner annular passageway for conveying a mixture of primary air and pulverized coal separately from the natural gas and into the combustion zone;
a swirler connected to the outlet end of the supply pipe, the swirler having a plurality of vanes positioned upstream of the injector;
a second sleeve member concentrically spaced about the first sleeve member to form an outer annular passageway for conveying secondary air to the combustion zone; and
a plurality of circumferentially spaced vanes mounted within the outer annular passageway for inducing swirling motion to the secondary air discharging from the outer annular passageway into the combustion zone.
2. The combination according to claim 1 , further including a central opening extending through the end wall concentric with the chamber axis.
3. The combination according to claim 1 , wherein the peripheral openings induce the natural gas to swirl in a first rotational direction, and the vanes induce the secondary air to swirl in the same rotational direction as the natural gas.
4. The combination according to claim 1 , wherein the peripheral openings induce the natural gas to swirl in a first rotational direction, and the vanes induce the secondary air to swirl in a second rotational direction different from that of the natural gas.
5. The combination according to claim 1 , wherein the first acute angle is in the range of about 10° to 45°.
6. The combination according to claim 1 , wherein the second acute angle is in the range of about 10° to 30°.
7. The combination according to claim 1 , wherein the first acute angle is about 40°.
8. The combination according to claim 1 , wherein the second acute angle is about 15°.
9. A method for reducing flame length and CO and NO x emissions from the combustion of fuel, including a boundary wall defining a boiler furnace, a combustion zone established within the furnace, at least one burner port formed in the boundary wall and fronting the combustion zone, means for supplying primary air, secondary air, natural gas and pulverized coal to the combustion zone including a dual fuel burner facing the combustion zone through the burner port, the dual fuel burner having a supply pipe, an injector connected to the supply pipe wherein the diameter of the injector is substantially the same as the diameter of the supply pipe, the injector including openings for inducing swirling, means forming an inner annular passageway about the supply pipe and injector, swirling means connected to the supply pipe within the inner annular passageway, means forming an outer annular passageway about the inner annular passageway, and swirl vanes mounted within the outer passageway, and comprising the steps of:
conveying the natural gas through the supply pipe and the injector;
inducing swirling motion to the natural gas being injected into the combustion zone through the openings;
conveying a mixture of primary air and pulverized coal through the inner annular passageway separately from the natural gas and into the combustion zone;
conveying secondary air through the outer annular passageway and into the combustion zone; and
inducing swirling motion to the secondary air being conveyed into the combustion zone.
10. The method according to claim 9 , wherein the natural gas is induced to swirl in a first rotational direction, and the secondary air is induced to swirl in the same rotational direction as the natural gas.
11. The method according to claim 9 , wherein the natural gas is induced to swirl in a first rotational direction, and the secondary air is induced to swirl in a second rotational direction different from that of the natural gas.