Low nitrogen oxides emissions from carbonaceous fuel combustion using

Abstract

A method and apparatus for reducing NO.sub.x emissions from the combustion of carbonaceous fuels using three stages of oxidation. In the first stage, a partial oxidation combustor is used to partially combust the fuel in the presence of heated combustion air. The fuel gas produced in the partial oxidation process is passed to a second stage partial oxidation combustor while molten slag is removed and disposed of. A second preheated combustion air is introduced into the second stage combustor to produce a reducing flue gas. A third combustion air is mixed with the flue gas in a third stage combustor to substantially complete the combustion process. Preheated steam may be added at any or all of the combustion stages. The stochiometric ratios at each stage of combustion are controlled to minimize overall NO.sub.x emissions to acceptable levels. An excess air cyclone-fired furnace modified to operate in a three-stage combustor mode by adding a preheated air system, with air introduction into the furnace at the cyclone barrel re-entrant throat location followed by overfire air introduction in the upper part of the furnace can be utilized to provide the three stages of combustion.