Ammonia is a gas that is easily soluble in water. There are various common detection methods, but ammonia is toxic and corrosive. Currently, measurement is mainly carried out using the TDLAS direct measurement method. TDLAS is essentially a spectral absorption analysis technology. It utilizes the selective absorption characteristics of gas molecules to specific wavelength lasers, and obtains the gas concentration by analyzing the changes in laser absorption intensity. The TDLAS spectral absorption method can directly measure the concentration of ammonia gas and can achieve measurements from % to PPm.
TDLAS technology is a high-resolution spectral absorption technology. The attenuation of light intensity as the laser passes through the measured gas can be expressed by the Lambert-Beer Law. In the formula, IV, 0, IV represent the laser with frequency V, the incident and the laser passing through the gas with pressure P, concentration X, and optical path L; S(T) represents the intensity of the absorption line; the linear function g(v-v0) represents the shape of the absorption line. The gas absorption is generally small, and these relationships indicate that the higher the gas concentration, the greater the light attenuation. Therefore, the concentration of the gas can be measured by measuring the attenuation of the laser by the gas.
The principle of the laser gas analyzer is based on the principles of laser spectroscopy and optical absorption. Its working process can be divided into the following key steps:
Laser source: The laser gas analyzer uses a monochromatic coherent laser beam as the light source. The attenuation of the light intensity of the laser beam passing through the measured gas can be expressed by the Lambert-Beer Law. In the formula, IV, 0, IV represent the laser with frequency V, the incident and the laser passing through the gas with pressure P, concentration X, and optical path L; S(T) represents the intensity of the absorption line; the linear function g(v-v0) represents the shape of the absorption line. The gas absorption is generally small, and these relationships indicate that the higher the gas concentration, the greater the light attenuation. Therefore, the concentration of the gas can be determined by measuring the attenuation of the laser by the gas.
Laser gas analyzer data processing: The analyzer calculates the ratio of absorbed light intensity to unabsorbed light intensity to determine the concentration of the target molecule.
In industries such as metallurgy, coking, power, and cement that use biomass as fuel, the removal of nitrogen oxides from combustion flue gas and the prevention of environmental pollution have been keenly recognized by people, and it is also a challenging issue. The removal of nitrogen oxides (denitrification) is mainly divided into two mainstream processes: SCR and SNCR. The required drugs for operating SCR and SNCR are ammonia and urea (the main reason for using urea is that it can be stored and used when needed, and urea still decomposes into ammonia for use). When monitoring the efficiency of SCR and SNCR operations, an ammonia gas online analysis system must be adopted to control the consumption of ammonia water through the ammonia gas analysis system.
Monitoring the ammonia escape from the SCR outlet is of great significance. During the denitrification process, the consumption of ammonia is in a chemical stoichiometric ratio of 0.8 to 1.2 with the total amount of NOx. Therefore, controlling the injection amount of ammonia will be very important; the injection amount of ammonia should both have enough NH3 to react with NOx to reduce the emission of NOx and meet the emission requirements of the pollution source; and avoid injecting excessive NH3 into the flue gas, which not only increases corrosion, shortens the lifespan of the SCR catalyst, but also pollutes the smoke dust and increases the deposition of ammonia salts in the air preheater, and increases the emission of NH3 to the atmosphere.
Denitrification process ammonia escape NH3 detection flue gas denitrification refers to the reduction of NOX to N2 to remove NOX from the flue gas. The mainstream processes for denitrification are: SCR denitrification and SNCR denitrification. SCR denitrification technology is a selective catalytic reduction method. In the presence of a catalyst (SNCR denitrification technology is a selective non-catalytic reduction method, without a catalyst and high temperature), ammonia gas derived from the decomposition of liquid ammonia or urea is used as the reducing agent to reduce nitrogen oxides and water in the flue gas. During the reduction process, ammonia escape caused by residual reducing agents is inevitable. The escaped ammonia easily forms ammonium bisulfate with SO3 in the flue gas, such as ammonium bisulfate, which has strong adhesion, corrosiveness, tar-like solids, causing corrosion, blockage, and dust accumulation in the air preheater, affecting the dust removal effect. It may even damage the downstream dust removal equipment; at the same time, it means an increase in the consumption of liquid ammonia/urea, reducing the economic benefits of the denitrification device; the remaining ammonia gas is discharged into the atmosphere, causing secondary pollution of the atmosphere.
Therefore, the detection of escaped ammonia during the reverse nitrification process is of great significance for optimizing ammonia injection control and reducing pollutant emissions.
In industries that use biomass as fuel, such as metallurgy, coking, power generation, and cement, the importance of removing nitrogen oxides from combustion flue gases and preventing environmental pollution has been keenly recognized. It is also a challenging problem. The most mainstream processes for removing nitrogen oxides (denitrification) are SCR and SNCR. To operate SCR and SNCR, the reagents required are ammonia and urea (urea is mainly used because it is readily available, and when used, it still decomposes into ammonia for use). To monitor the efficiency of SCR and SNCR, an ammonia online analysis system must be used to control the consumption of ammonia water.
Monitoring the ammonia slip at the SCR outlet is of great significance. During the denitrification process, the stoichiometric ratio of ammonia consumption to the total amount of NOx should be between 0.8 and 1.2. Therefore, controlling the amount of ammonia injected is very important. The amount of ammonia injected must be sufficient to react with NOx to reduce NOx emissions and meet pollution source emission requirements. At the same time, it is necessary to avoid injecting excessive amounts of NH3 into the flue gas. Excessive ammonia injection not only increases corrosion, shortens the lifespan of the SCR catalyst, but also contaminates the flue dust, increases ammonia salt deposition in the air preheater, and increases NH3 emissions into the atmosphere.
Ammonia slip detection in the denitrification process Flue gas denitrification refers to the reduction of generated NOx to N2, thereby removing NOx from the flue gas. The most mainstream processes are SCR denitrification and SNCR denitrification. SCR denitrification technology is a selective catalytic reduction method. In the presence of a catalyst (SNCR denitrification technology is a selective non-catalytic reduction method, which occurs without a catalyst and at high temperatures), ammonia decomposed from liquid ammonia or urea is used as a reducing agent to reduce nitrogen oxides in the flue gas to nitrogen and water. During the reduction process, ammonia slip caused by residual reducing agents is inevitable. The escaped ammonia easily forms ammonium bisulfate with SO3 in the flue gas. Ammonium bisulfate is a highly adhesive, corrosive, tar-like solid that causes corrosion, blockage, and dust accumulation in the air preheater, affecting dust removal efficiency. It can even damage downstream dust removal equipment. At the same time, it means an increase in the consumption of liquid ammonia/urea, reducing the economic efficiency of the denitrification unit. The remaining ammonia is discharged into the atmosphere, causing secondary air pollution.
Therefore, the detection of ammonia slip during denitrification is of great significance for optimizing ammonia injection control and reducing pollutant emissions.
