Combustion system for reduction of nitrogen oxides

A burner for low NO.sub.x -emission burning of fuels, comprising:

• a chamber with an insertion region, said insertion region including:
• a low divergence fuel nozzle arranged on an axis for providing a flow of a combustible fuel, and
• a concentrically arranged first nozzle for providing a first concentric component flow about said combustible fuel flow,
• a concentrically arranged second nozzle, for providing a second concentric component flow about said first component flow,
• a concentrically arranged third nozzle for providing a third concentric component flow about said second component flow,
• said nozzles arranged to introduce said fuel and first, second and third component flows to said chamber at substantially the same axial location,
• a controller for stratifying to limit mixing of oxidant gases with said fuel flow to maintain a high-temperature fuel rich core zone near said insertion region and to induce mixing with oxidant gases in a lower temperature recirculation zone spaced from said insertion region,
• said controller including a flow controller for controlling the amount of flow through said first, second and third nozzles, said flow controller set such that said first concentric flow comprises a fraction of about 0.2 or less of the total concentric flow,
• said controller further including a swirl controller for controlling the swirl of said first, second and third concentric component flows, said swirl controller being set such that the swirl velocity of said first flow is higher than the swirl velocity of the second and third flows,
• said concentric component flows, in combination with a radial density gradient from a low density high temperature in said core to higher density, lower temperature spaced radially from said core, effective to bring about a condition of stratification, whereby mixing of ambient gas with said combustible fuel flow is limited to maintain a high temperature fuel rich core zone near said insertion region and to induce mixing in a lower temperature recirculation zone spaced from the insertion region, and
• an ignitor for initiating burning of said combustible fuel flow.

A method for low NO.sub.x -emission burning of a fuel, comprising the steps:

• providing a fuel flow along an axis and a concentric flow, including oxidant gases, disposed about said fuel flow, said fuel flow and concentric flow being introduced into a chamber at substantially the same axial location at an insertion region,
• stratifying said fuel flow and concentric flow to limit mixing of oxidant gases with said fuel flow to maintain a high temperature fuel rich core zone near said insertion region and induce mixing with oxidant gases in a lower temperature recirculation zone spaced from said insertion region,
• said stratifying being achieved by providing the combination of a radial density gradient from low density, high temperature in said core zone close to said axis to higher density, lower temperature spaced radially from said core zone and swirling said concentric flow;
• controlling said stratifying to limit mixing such that said fuel is substantially confined within a region about the core where the modified Richardson number of said concentric flow is about 0.04 or greater;
• pyrolizing said fuel in the core in a high-temperature zone near said insertion region, where the mixing of ambient gases with said fuel in said core flow is limited, thereby limiting NO.sub.x in said high temperature zone;
• and
• combusting the product of said high temperature zone in a lower-temperature recirculation zone spaced from said insertion region, where mixing of oxidant gases and said fuel mixture is induced, and low-temperature combustion results in limited formation of NO.sub.x.

A method for low NO.sub.x -emission burning of a fuel, comprising the steps:

• providing a fuel flow along an axis and a stratifying flow, including oxidant gases, formed by multiple component flows concentrically disposed about said fuel flow,
• stratifying to limit mixing of oxidant gases with said fuel flow to maintain a high temperature fuel rich core zone near said insertion region and induce mixing in a lower temperature zone spaced from said insertion region,
• said stratifying being achieved by providing the combination of a radial density gradient from low density, high temperature in said core zone close to said axis to higher density, lower temperature spaced radially from said core zone and swirling said stratifying flow;
• determining the degree of stratification by determining the modified Richardson number;
• controlling the stratification to effect low NOx emission.