| As China’s fossil resources are characterized by relatively rich in coal,lack of oil and gas,coal is of vital importance in the energy structure of China.Data from the National Bureau of Statistics show that in 2021,China’s raw coal production reached 4.13 billion tons,up 5.7% year-on-year;total energy consumption increased by 5.2% year-on-year,of which coal consumption reached 2.934 billion tons of standard coal,accounting for 56%of total energy consumption.At the same time,the national power generation reached8,534.25 billion kilowatt-hours,up 9.7% year-on-year;among them,thermal power generation was 580.57 billion kilowatt-hours,up 8.9% year-on-year,accounting for 68%of the total power generation.This shows that,even in the longer period in the future,coal will still play the most basic role to ensure national energy security.In recent years,with the continuous implementation of China’s energy conservation and emission reduction,low-carbon environmental protection and energy transformation policies,improving the clean and efficient use of coal has become the most urgent task.In this task,the clean and efficient use of coal has become the core of precise efforts.In practice,it is necessary to realize the clean and efficient utilization of coal through important ways such as quantity and quality of coal purchase,price according to quality and optimization of combustion.However,there are many types of coal in China,and the coal quality varies greatly,so the actual supply coal quality in thermal power generation often cannot match the boiler design coal quality,resulting in low combustion efficiency and high power generation cost.In order to optimize coal distribution and combustion control in thermal power generation,it is necessary to achieve rapid testing of incoming or incoming coal quality.However,at present,power plants still widely use the traditional national standard method of manual testing,which requires separate equipment for different industrial indicators.This method is inefficient and does not allow for truckload analysis of incoming coal or online testing of incoming coal,thus preventing accurate coal allocation and optimal combustion control.Although there are developed robotic assay systems to replace manual operations,the core coal analysis principle remains unchanged and therefore remains time-consuming,expensive and bulky.In addition,neutron activation online testing equipment is not widely used due to radioactive contamination.Therefore,conducting research on new coal quality analysis technologies that are low-cost,safe,and fast is a key issue that needs to be urgently addressed in thermal power production.Laser-induced breakdown spectroscopy(LIBS)uses strong laser pulses to focus on the sample surface to generate plasma and predict the sample components by analyzing its fluorescence spectrum,which has the advantages of safe,rapid,real-time and simultaneous analysis of all elements,and has attracted much attention in the field of coal quality analysis.However,due to the limitations of Rayleigh-Taylor instability,pulse energy fluctuation,small focus point and poor representativeness,and plasma susceptibility to external interference,the measurement repeatability of LIBS for coal quality index is still difficult to meet the requirements specified in national standards.Therefore,how to break through the bottleneck of measurement repeatability of coal quality index by LIBS technology becomes the key to its real application in coal combustion industry.X-ray fluorescence spectroscopy(XRF)uses X-rays to excite the atoms in the substance to be measured to produce the characteristic X-fluorescence of the elements contained,and the characteristic X-fluorescence intensity is recorded by a detector to perform qualitative and quantitative analysis of the elements in the sample.The current XRF performs well in coal ash analysis,and can measure the content of ash-forming elements such as Si,Al,Fe,Ca,Mg,Na,K and Ti in coal,and the repeatability has been better than the national standard.However,due to the low fluorescence generation rate and poor sensitivity of XRF for light elements,it can usually only analyze elements with atomic number greater than 11,but not light elements such as C and H in coal,so it cannot analyze the heat content and volatile fraction of coal.In conclusion,based on the advantages of LIBS total elemental analysis and the characteristics of XRF highly stable analysis,this paper proposes a LIBS-XRF dual-spectrum method for coal quality analysis by combining both LIBS and XRF.The two techniques can be used together to complement each other,which can not only measure organic light elements closely related to heat and volatile matter in coal,but also detect inorganic ash-forming elements related to ash in coal with high stability,and then compensate for the deficiency of the current LIBS stability,and realize the high stability analysis of coal industry indexes.This thesis revolves around the issue of how to improve the reproducibility of LIBS coal analysis,focusing on the following research:1,LIBS-XRF high stability quantitative analysis technology research.Based on the quantitative analysis principles of LIBS and XRF,the complementarity of the two techniques in combination was explored.LIBS-XRF quantitative analysis experiment set-up was built.conducted research on the experimental and spectral analysis modeling methods of LIBS-XRF coal quality analysis.The reproducibility of the measurement of coal elements and industrial analysis indexes was evaluated.The feasibility of applying LIBS-XRF technology to coal quality analysis was verified.2.Research on modeling method of LIBS-XRF dual-spectrum coupled analysis.A LIBS-XRF coal precision analysis algorithm integrating spectrum pre-processing,principal component analysis(PCA)and partial least squares regression(PLS)was developed,and the spectrum data of coal samples were analyzed and modeled.3.Theoretical research on LIBS self-absorption characterization.Firstly,the principles and theories of quantitative analysis of LIBS in local thermal equilibrium are introduced,and the generation,evolution and spectral line characteristics of laser-induced plasma are described;Then the LIBS self-absorption mechanism is described,the relationship between self-absorption and spectral lines and plasma properties is analyzed in detail,and the self-absorption is evaluated and characterized.Further,the LIBS experiment set-up is constructed and introduced from both hardware and software aspects,and the stability design of the set-up is also explained.After that,based on the self-absorption related theory,the self-absorption correction analysis of C-element spectral lines in LIBS spectra was performed,and finally,the coal heat generation was characterized.4.The development,industrial testing and performance evaluation of LIBS-XRF dual-spectrum coupled coal analyzer.The overall design scheme of the instrument,details of each module,operation flow,sample pretreatment process,model quantitative analysis method and industrial test results are introduced,and the analytical performance of the set of LIBS-XRF coal analysis technology and instrument is evaluated.The innovations of this thesis are:1.The highly stability LIBS-XRF coal analysis technology has been developed.It can analyze not only the content of organic light elements such as C and H in coal,but also the content of inorganic ash-forming elements in coal with high stability by excitation of inner and outer atomic electrons by X-ray and laser respectively,which has greatly improved the repeatability of coal quality analysis.The repeatability(SD)of the measurement of heat,volatile matter and ash of coal reaches 0.11 MJ/kg,0.17% and 0.41% respectively,which meets the requirements of national standards.2.Developed a LIBS-XRF coal precision analysis algorithm incorporating spectral preprocessing,principal component analysis(PCA)and partial least squares(PLS).The self-absorption characterization theory and correction method based on the plasma ionization degree and radiation particle surface density under thermal equilibrium conditions were proposed,and the root mean square error(RMSE)of coal calorific value,ash,volatile fraction,sulfur and elements reached 0.53 MJ/kg,0.89%,0.96%,0.15% and2%,respectively.3.With integrated LIBS-XRF dual-spectrum coal quality analyzer and complete set of control and analysis programs,the opto-electro-mechanical device can simultaneously test coal calorific value,ash,volatile matter and sulfur content,with a single measurement time of 2.5 minutes,and has completed industrial application in Shanxi Sunshine Power Plant.The field test results show that the equipment is reliable,easy to operate,accurate in measurement and can be controlled remotely,which can meet the needs of industrial applications and play a guiding role in coal blending and optimization of combustion in power plants. |
PDF Full Text Request