Wavelength modulation spectrum technology-based denitrified ammonia escape rate measurement device and method

Abstract

The invention relates to a wavelength modulation spectrum technology-based denitrified ammonia escape rate measurement device and method, belonging to the technical field of tunable diode laser absorption spectroscopy. The method is characterized in that laser is split through an optical beam splitter on the basis of quadruple sub-harmonic in the wavelength modulation spectrum technology, a part of laser permeates a high-concentration reference cell to be used for locking a central wavelength and monitoring the zero point of an instrument constantly, and the other part of laser permeates a smoke measurement cavity to be used for obtaining the concentration of an ammonia gas. In an in-situ sampling mode, a sampling rod and the measurement cavity are both arranged in a flue of a denitrified air preheater. The method has the characteristics that with adoption of a low-pressure measurement method, the pressure of the measurement cavity is kept at 0.1atm, a strong absorption spectrum line can be selected and the interference from other gas spectrum lines can be avoided, the sensitivity of the instrument can be improved, and the lower limit of measurement can be lowered. Through the method, a series of problems, caused during application of an existing ammonia escape rate instrument, such as the incapability of laser to permeate dust with high concentration, the deflection of laser resulted from mechanical deformation of a flue wall, the incapability of marking, and blocking of a filtering permeation probe, can be solved.

Description

technical field [0001] The invention relates to an online measuring device and method for denitrification ammonia escape rate, in particular to an online measuring device and method for denitrification ammonia escape rate in a low pressure environment based on the fourth harmonic method in wavelength modulation spectroscopy technology. Background technique [0002] In recent years, the problem of environmental pollution has attracted more and more attention. In the "Twelfth Five-Year Plan for Energy Conservation and Emission Reduction", there are clear requirements for emission reduction in the power industry, and denitrification has become the top priority. At present, domestic power plants generally adopt selective catalytic reduction technology (SCR) for denitrification. The principle of SCR technology is: under the action of a catalyst, ammonia is injected into the flue gas to reduce NO x reduced to N 2 and H 2 O. The injected ammonia can be directly as NH 3 In the ...

AI Technical Summary

Problems solved by technology

[0013] First of all, in terms of instrument structure, the LasIR of Canada's Winner Optical Instrument, the GM700 of Germany's Sick, the Servomex's Servomex Laser of the United Kingdom, and the Norway's NEO's LaserGas II adopt the in-situ installation method, and the laser transmitter and receiver are installed in the flue. On both sides, the structure of the product is simple, but due to the high dust content of domestic coal-fired power plants, the laser cannot pass through. In addition, due to the high temperature environment and the deformation of the flue wall caused by the vibration of the flue wall will cause the laser to shift, the receiving end cannot The laser is received, and since this measurement method is an open measurement, it is impossible to inject a known concentration of ammonia gas to verify the accuracy of the measurement, that is, it cannot be calibrated

The LDS6 of Siemens in Germany adopts in-situ diagonal installation. Although the optical path is short, there are still problems of laser offset caused by lens pollution and flue wall deformation, and the representativeness of diagonal installation is poor.

The GM700 of SICK in Germany adopts a single-side installation reflective measurement method, and uses a gas permeable membrane measuring probe to filter the dust in the flue. However, because this product uses a permeable form to enter the flue gas into the measurement chamber, the response time is long and the gas update is slow. , filter hole blockage, measurement lag and other problems, lost the real-time monitoring effect

Concentrating Technology LGA-4500 adopts the sampling method, installing a sampling probe in the flue, and then equipped with a flue gas treatment device (heating to 150-200°C), but when the temperature is lower than 300°C, NH 4 HSO 4 It has already begun to form, and the heat tracing is difficult to be uniform, and there is also the problem of ammonia adsorption, which leads to the change of the ammonia content during the sampling process, resulting in distortion of the measurement results

Secondly, in terms of measurement principle, other products use the second harmonic in TDLAS wavelength modulation technology. Although the second harmonic has a large amplitude and high sensitivity, the background signal of the second harmonic method also fluctuates greatly. In the way of background, the background signal fluctuation is still on the order of 1-3ppm, which will bring large errors to the measurement

Images