| 摘要 |
Flue gas recirculation (FGR) provides low NOX combustion of natural gas in a compact steam boiler 2 having output steam delivery controlled by predetermined outlet steam pressure. The compact boiler employs a small high heat release combustor 30 discharging into a forced draft convective heat exchange section 5. The compact boiler is automatically self-operating, wherein the FGR is admitted into the burner combustion air through a valve 24 controlled by boiler flue gas NOX content. A bell mouthed flue gas scoop 22 is utilized in the boiler stack upstream of the NOX sensor (28, fig 1). in an alternative combustion chamber design, a cylindrical water wall coil 38 surrounds the combustion process, increasing boiler efficiency through the inherent large temperature difference between the coil and the combustion in process. along with reducing the combustion temperature and further reducing the NOX content of combustion products. A further variation in the combustion system utilizes a ceramic shield (56, 58, fig 4) surrounding a natural gas burner as it fires into the compact combustion chamber. Primary and secondary combustion air are admitted to the combustion chamber through first stage combustion inside the shell and second stage combustion occurring in the boiler combustion chamber. <IMAGE> |
