What are the pathways by which nitrogen oxides are generated in coal-fired boilers during combustion?
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The nitrogen oxides produced during the combustion of coal are mainly nitric oxide and nitrogen dioxide. Nitric oxide is unstable in the natural environment, and under certain conditions it oxidizes with oxygen in the air to form nitrogen dioxide. What are the pathways by which nitrogen oxides are generated in coal-fired boilers during combustion?
There are two ways by which nitrogen oxides are generated in coal-fired boilers during the combustion process: one is the oxidation of nitrogen in the air by oxygen at high temperatures, resulting in the formation of nitrogen oxides; the other is the oxidation of elemental nitrogen present in the coal by oxygen at high temperatures, also leading to the formation of nitrogen oxides. Ways to reduce the formation of nitrogen oxides include: combustion at low temperatures, thereby lowering the flame temperature ； Low-oxygen combustion to reduce the excess air coefficient at the furnace outlet ； Staged combustion is achieved primarily through burner design and staged air supply.
There are three pathways by which nitrogen oxides are generated in coal-fired boilers during combustion: (1) Thermal type: Nitrogen in the air is oxidized at high temperatures to form nitrogen oxides； (2) Rapid type: Nitrogen oxides generated by the reaction of nitrogen in the air with hydrocarbon ion groups (-HC) in the fuel, etc ； (3) Fuel-type: The nitrogen compounds contained in the fuel undergo thermal decomposition during combustion, followed by oxidation to produce nitrogen oxides. In coal-fired boilers, nitrogen oxides are primarily of the fuel-type, followed by the thermal-type, with the rapid-type being the least common.
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