Development Of A Multi-component And Multi-parameter Laser Sensor For The Denitration Process Of Coal-fired Power Plants

In order to reduce the emission of nitrogen oxides(NOx),flue gases discharged from coal-fired power plants are usually denitrified by a selective catalytic reduction(SCR)device.The denitrification efficiency is decisively affected by the amount of ammonia sprayed,the temperature of the flue gas and the water content in the actual denitration process.Therefore,real-time monitoring of the flipped ammonia concentration,flue gas temperature and water vapor concentration in the flue gas is of great significance for effectively improving the denitration efficiency of coal-fired power plants and maximizing energy conservation and emission reduction.The dissertation addressed actual demands,and developed a portable laser sensor based on wavelength modulation spectroscopy(WMS)detection technology for simultaneous measurement of multi-component and multi-parameters in denitrification tail gas of coal-fired power plants.The main work is as follows.Firstly,the second harmonic of WMS detection normalized by the first harmonic(WMS-2f/1f)method for simultaneously calibration-free measurement of NH3 and H2O concentrations and temperatures was developed.With considering the signal amplitude and spectral line overlap,the NH3 and H2O absorption lines in the target spectrum segment(6611-6613cm-1)are respectively employed with different modulation amplitudes,namely variable modulation technique,to obtain the optimal WMS signals.A simulation algorithm of WMS signal was improved,and the algorithm was combined with Levenberg-Marquardt nonlinear least squares method to obtain the parameters of ammonia concentration,water vapor temperature and concentration by WMS-2/71/signal multi-line regression analysis.The method has the advantages of fast inversion and calibration-free detection.Secondly,a portable laser sensor for simultaneous measurement of the escaping NH3 concentration,temperature,H2O concentration and pressure was integrated.The laser sensor consists of a host instrument and a probe that can be inserted into the flue for sampling.In the beginning,the characteristics of the core module,namely a 1512nm distributed feedback laser,were tested and the modulation parameters were obtained.After that,the host instrument was integrated with the laser,a laser driving module,a lock-in amplification module,a control module and a display screen.In addition,the programs of data acquisition,processing,storage and display were written,and the design of the sensor main part was completed.Furthermore,based on the Herriott gas cell structure,the probe of the sensor was mechanically designed,including the extension rod,filter,plenum,and laser emitting and receiving coupling portions.The probe has the advantages of dustproof,anti-vibration,high temperature resistance and good air tightness.Finally,the performance of the laser sensor was evaluated and field experiments were conducted.The performance of the developed laser sensor was tested according to national standards under laboratory conditions.The results showed that the detection limit of ammonia gas can reach 0.5ppm with the integral time of 5s.The laser sensor system was field tested in a power plant in Shenhua Guoneng,China.The ammonia slip results were in good agreement with that measured by an on-line system,which indicated that the laser sensor can meet the detection requirements of the coal-fired power plant for the escape of denitration NH3 under severe conditions.