Low NOx, high efficiency, high temperature, staged recirculating burner and radiant tube combustion system
Embodiments of the present invention include high-temperature staged recirculating burners and radiant tube burner assemblies that provide high efficiency, low NOx and CO emissions, and uniform temperature characteristics. One such staged recirculating burner includes a combustion tube having inside and outside helical fins forming opposing spiral pathways for combustion gases and products of combustion, a combustion nozzle coupled to the combustion tube, a gas tube running axially into the combustion tube, and a staging gas nozzle coupled to the gas tube, where the staging gas nozzle includes radial exit holes into the combustion tube and an axial gas staging tube extending into the combustion nozzle to stage combustion.
1. A staged recirculating burner, comprising:
a combustion tube including inside and outside helical fins forming opposing spiral pathways for combustion gases and products of combustion;
a combustion nozzle coupled to the combustion tube;
a gas tube running axially into the combustion tube;
a heat exchanger coupled to the combustion tube to heat the combustion gases provided to the combustion tube using the products of combustion from the combustion tube; and
wherein the gas tube runs axially through a central bore of the heat exchanger and into the combustion tube.
2. The staged recirculating burner of claim 1 , wherein the heat exchanger is connected to the combustion tube via a ceramic thread.
3. The staged recirculating burner of claim 2 , wherein the ceramic thread comprises SiC.
4. The staged recirculating burner of claim 1 , wherein the direction of flow of the combustion gases and the direction of flow of the products of combustion are opposite, and the combustion tube includes a ceramic wall separating the flow of the combustion gases and the flow of the products of combustion.
5. The staged recirculating burner as in claim 1 , wherein the combustion gas nozzle is conically shaped combustion nozzle.
6. The staged recirculating burner as in claim 1 , comprising a staging gas nozzle coupled to the gas tube, the staging gas nozzle including radial exit holes into the combustion tube and an axial gas staging tube extending into the combustion nozzle to stage.
7. The staged recirculating burner as in claim 6 , wherein the staging gas nozzle is configured to inject only a portion of the gas through the radial holes to create a gas mixture that is substantially lean to suppress a temperature of products of combustion, and is configured to inject the remainder of the gas through the axial gas staging tube.
8. The staged recirculating burner as in claim 1 , wherein the heat exchanger comprises a plurality of helical combustion air channels defining a plurality of helical flow paths configured to heat the combustion gas, wherein preheated combustion gas coming from the plurality of helical flow paths combines in a transition between the heat exchanger and the combustion tube before entering the combustion tube.
9. The staged recirculating burner as in claim 1 , wherein the combustion tube is made of silicon carbide.
10. The staged recirculating burner as in claim 1 , wherein a staging gas nozzle is configured to inject gas radially into a spiral flow of preheated air flowing through the combustion tube.
11. The staged recirculating burner of claim 1 , wherein the heat exchanger comprises a plurality of helical combustion air channels extending around the central bore in a length direction of the heat exchanger.
12. The staged recirculating burner of claim 11 , wherein each helical combustion air channel defines a helical flow pathway for combustion air to flow through the helical combustion air channel.
13. The staged recirculating burner of claim 11 , further comprising a preheat flow reducer disposed at a downstream end of the heat exchanger and configured to combine preheated combustion air from the plurality of helical combustion air channels into a single flow into a combustion tube.
14. The staged recirculating burner of claim 11 , wherein the heat exchanger is adapted so that the combustion air flowing through the plurality of combustion air channels is preheated to a temperature greater than 400° C. by energy from the combustion product passing through the surrounding fluid path when the combustion air exits the helical combustion air channels.
15. The staged recirculating burner of claim 11 , wherein the heat exchanger comprises an introductory port section having an individual port for each of the plurality of helical combustion air channels.
16. A radiant tube burner system, comprising:
the staged recirculating burner of claim 1 ;
an outer radiant tube coupled to the burner;
an inner recirculating tube located concentrically inside the outer radiant tube, the outer radiant tube and the inner recirculating tube forming an annulus therebetween; and
a turning vane spacer located inside the outer radiant tube and positioned between the distal end of the inner recirculating tube and the distal end of the outer radiant tube to cause products of combustion to flow through the annulus between the outer radiant tube and the inner recirculating tube.
17. The radiant tube burner system of claim 16 , wherein the outer radiant tube and the inner recirculating tube comprise a ceramic material.