| OCR Text |
Show Figure 1. CONCEPTUAL FLOW PATTERN IN A CYCLONIC COMBUSTOR relatively high velocity, creating intensive cyclonic motion. Because the swirl intensity is usually much higher than that achieved by other types of swirlers (for example, axial or radial swirlers), intensive turbulent mixing and substantial internal combustion products recirculation (ICPR) that enhance flame stabilization as well as combustion completion are obtained. The intensive swirl and the ICPR can also improve the uniformity of temperature and gas composition in the chamber. As a result, high peak flame temperatures and localized pockets of high O2 availability are minimized, thereby reducing NOx formation. The swirl flow and ICPR are further enhanced by plaCing an orifice of appropriate size at a specific distance from the nozzles. Moreover, by appropriately positioning the tangential nozzles and contrOlling the velocities of nozzle injection, the flame established from each nozzle can be enhanced by each other. It is possible, therefore, to operate a premixed cyclonic combustor beyond the lean limit of flammability with sufficient intenSity of combustion reaction to minimize the formation of all combustion pollutants. Different types of cyclonic combustors based on this similar concept have been developed. For example, Syred's cyclone combustor has 14 tangential inlets arranged in two rows of seven for flame stabilization.9 As low as 1-vppm NOx emissions were demonstrated from this multi-inlet cyclonic combustor. The cyclonic combustor developed at IGT has only two to four tangential nozzles. Earlier tests at IGT had shown that NOx emissions as low as 1 to 2 vppm were achieved in a single-stage cyclonic combustor.8 Further reduction of NOx formation requires higher excess air operation. A flame stabilizer, as the first-stage combustor, was adopted to enhance flame stability of the higher lean premixed flame in the main combustor. Figure 2 shows a conceptual design of the twostage cyclonic combustor. Both combustors are operated In a lean premixed combustion mode, while a less lean operation is desired in the flame stabilizer in order to provide "hotter' combustion gases for enhancing flame stability in the main combustor, which is operated at leaner conditions. A 350-kW firing capacity test combustor was designed, fabricated, and tested. The combustor consists of a smaller cyclonic chamber as the flame stabilizer and a larger chamber as the main combustor. The combustion chambers are tully lined with refractory to provide a near-adiabatic environment for flame stabilization at very lean conditions. An orifice is installed 4 |
