NOx encompasses thermal NOx, fast NOx, and fuel NOx. Thermal NOx is primarily produced by high temperatures (above 1500°C) during fuel combustion, oxidizing nitrogen in the air to NOx. Its emission levels are influenced by combustion temperature, oxygen concentration, and residence time. Fast NOx is formed when there is an excess of hydrocarbon fuel in the mixture, and is typically only a concern during low-temperature combustion of nitrogen-free hydrocarbon fuels. Fuel NOx is mainly generated by the oxidation of nitrogen in the fuel during combustion, with its formation closely related to the combustion atmosphere of the fuel. Fuel NOx is produced when the fuel's combustion temperature is around 700°C. For gas boilers, fuel NOx is significantly less than thermal NOx.
Due to the influence of combustion temperature, oxygen concentration, and residence time on the emission of thermal NOx: nearly undetectable NOx generation is observed when the combustion temperature is below 1500°C; when the combustion temperature exceeds 1500°C, the rate of NOx formation increases exponentially; higher oxygen concentration and combustion temperature lead to greater NOx generation; and the longer the combustion time, the more NOx is produced.
The low-NOx burner for this project employs staged combustion and rich-lean combustion technology: the combustion air enters through the burner's air inlet, where different combustion air channels are set at the nozzle. For the low calorific value anthracite flue gas, this type of low-NOx burner features a central combustion air zone (*** staged air), rich combustion swirl air (*** staged air), and nitrogen combustion swirl air (*** staged air) areas, which mix with corresponding gas zones to achieve rich-lean and staged combustion. This results in an even furnace temperature field and the reduction of thermal-type nitrogen oxides.
Each boiler is equipped with four burners, arranged in a double-layer configuration on the front wall with two burners on each level. The low nitrogen burners are based on the axial dynamics characteristics and the principle of segmented fuel supply, utilizing the combined effect of swirl and non-streamlined bodies to ensure uniform distribution of fuel and combustion air. This simultaneously achieves super-mixing of fuel and air, resulting in a uniform flame temperature and a reduction in the generation of thermal NOx.
In addition to the burner body and nozzle, the system also includes the combustion gas pipeline section, the combustion air section, and the control section.
The gas pipeline system consists of main and branch pipelines. The main pipeline section includes manual shut-off valves, pressure gauges, etc. The branch pipeline section is composed of manual valves, pressure gauges, etc. The combustion system's auxiliary combustion air must match the on-site conditions and features a damper actuator on the main air duct for automatic adjustment of the auxiliary air volume during load changes.
