One Question per Day in Applied Chemistry (9-8)
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Leveraging knowledge related to applied chemistry, including (analytical chemistry, physical chemistry, and principles of chemical engineering), we are launching the \"One Question per Day\" campaign; simply reply to get the question. To encourage ongoing participation from everyone! You get 3 wealth rewards just for participating! Answering 1 category correctly earns an additional wealth reward. I hope everyone will participate actively, learn together, and make progress together! ! ! What are the factors that control the generation of thermally induced NOx in exhaust gas treatment? (1 point = 4 wealth points) @juniger
The two main factors affecting the concentration of thermally generated NOx are high temperature and the residence time in the high-temperature zone. As can be seen from the thermally generated NOx curve, the concentration of thermally generated nitrogen oxides is very low at temperatures below 1500 K; once the temperature exceeds 1500 K, this concentration increases rapidly in an exponential manner. The main factors affecting thermally generated NOx are temperature and oxygen content
Temperature, excess air coefficient, residence time, fuel type
Temperature, excess air coefficient, residence time, fuel type
Mechanism of NOx formation: During the combustion process, there are three pathways by which NOx is generated: 1. It is produced by the oxidation of nitrogen in the air at high temperatures, known as thermally generated NOx； 2. It is due to the CH radicals generated by the high-temperature decomposition of hydrocarbons in fuel vapors reacting with nitrogen in the air to produce HCN and N, which then further react with oxygen to generate Nox at an extremely fast rate; this is known as rapid-type Nox ； 3. It is Nox generated by the oxidation of nitrogen-containing compounds in the fuel during combustion, known as fuel-type NOx. The formation mechanism of thermal NOx is the oxidation of N2 in air at high temperatures to form NO ； Its main formation rate is closely related to the combustion temperature; when the combustion temperature is below 1400°C, the formation rate of thermal NOx is slow, while the reaction accelerates significantly when the temperature exceeds 1400°C. According to Arrhenius’ law, the reaction rate increases exponentially. This shows that, when the actual temperature within the furnace is uneven, a large amount of NOx is generated in the areas with higher temperatures ； It will also have a decisive impact on the total amount of NOx generated throughout the furnace. The amount of thermally generated NOx is highly dependent on the air excess factor; as the oxygen concentration increases, so does the amount of NOx generated. The NOx generation reaches its maximum when there is a 15% excess air: when the excess air exceeds 15%. As NOx is diluted and the combustion temperature drops, it actually leads to a reduction in NOx formation. The formation of thermal NOx is also related to the residence time of the flue gas in the high-temperature area; the longer the residence time, the more NOx is generated.
1. The volatile matter content, nitrogen content, fuel ratio (fixed carbon/volatile matter), and carbon/hydrogen ratio in coal all affect the amount of NOx generated; 2. The opening degree of the burnout air damper has an impact on nitrogen oxides in the flue gas; 3. When the unit reduces its load rapidly, it can also lead to a rapid increase in oxygen levels in the boiler, thereby increasing the nitrogen oxide content in the flue gas; 4. The oxygen level in the boiler affects nitrogen oxides in the flue gas; 5. The combustion method used in the boiler also influences nitrogen oxides in the flue gas.
Reduce the combustion temperature in the boiler furnace and avoid the formation of local hot spots, thereby reducing the generation of thermally induced NOX.
The influencing factors include: (1) Temperature； (2) Excess air coefficient ； (3) Residence time ； (4) Fuel type.
What are the factors that control the generation of thermally induced NOx in exhaust gas treatment? 1. Reduce the combustion temperature. 2. Decrease the residence time of gases in the high-temperature zone. 3. Lower the excess air ratio
The amount of NOx generated depends primarily on temperature: 1. Under identical conditions, the generation of NOx increases as the temperature rises; when the temperature is below 1,350°C, almost no thermal NOx is produced. 2. It is proportional to the residence time of the medium in the furnace and to the square root of the oxygen concentration. 3. As the O2 concentration and the air preheating temperature increase, there is a maximum value for the amount of NOx generated. When the O2 concentration is too high, the excess oxygen has a cooling effect on the flame, resulting in a decrease in NOx levels