| Thermal power generation is a dominant part of power generation structure in China, in which, coal-fired thermal power generation is definitely the most common one, especially the coal powder burning thermal power generation. At present, energy saving and reduction of power consumption is more demanding with increasingly short energy resources. Finding out combustion characteristics of pulverized coal particles, especially the effect of coal powder fineness to combustion characteristics is theoretically and practically important to conventional coal powder burning technology, newly developed burning technology as well as in-furnace burning technology which is aiming at reducing emission of pollutant NOx. In this thesis, a series of exploring research is carried out to find out how coal powder fineness to influence the coal powder combustion characteristics.This thesis starts with analyzing coal powder burning effect. By analyzing characteristics of combustibles in fly ash with different size, the thesis discusses the influence of coal particle size on burning performance. The research finds out that relationship between combustibles in fly ash and diameter of coal particles is not completely conform with the linear relation we have made out that combustibles in fly ash is decreasing with fly ash fineness decreasing. As the research finds out that in certain circumstances, there is an inflection point and the typical changing tendency is as follows: with diameter of coal particles decreasing, combustibles in fly ash decreases first and then increases, especially to fly ash below 20μm , there is a tend for combustibles to increase.By applying TGA researching method, this thesis has analyzed combustion property of coal powder samples in different diameter. On the basis of analysis in ignition and burnout of coal powder, the thesis moves on to carry out the thermal-gravimetry study of effect of coal particles diameter on pyrolysis of pulverized coal and combustion of coke coal. Then the thesis uses parameters of coal powder burning characteristic such as ignition temperature, burnout temperature, ignition stability index, combustible index, combustion stability judging index, average combustion speed and comprehensive combustion property, etc to prove the study. The study shows that with coal particles diameter decreasing, soft coal, lean coal and blind coal takes on increasing trend in burning behavior; while to superfine pulverized coal powder, especially coal powder below 20μm , change of diameter of coal particles has little influence on coal powder combustion property; compared with lean coal and blind coal, the ignition and burnout characteristic, especially the burnout characteristic of soft coal is more easily influenced by diameter of coal particles; with coal particles diameter decreasing, release of volatile matters is speeded up and large amount of volatile matters in soft coal is released in s short time. Thermal-gravimetry study in coke coal burning shows that coke coal burning is more easily influenced by coal powder size.By using image processing and fractal theory, the thesis studies the effect of coal particle diameter on coal powder shape features and fractal characteristics. The preliminary result shows that coal particle diameter has little effect on coal powder shape features and fractal characteristics. The result also shows that the fineness of coal powder has little effect on the difference between the results of either industrial analysis or element analysis, the difference variation of results provided by industrial analysis and by element analysis is ranged with 10%. The test of apparent activation energy shows that in low temperature part, with diameter of coal particles increasing, apparent activation energy of coal powder is increasing gradually, i.e. combustion characteristics of fine coal powder is better than that of coarse coal powder; in high temperature part, with diameter of coal particles increasing, apparent activation energy of lean coal and blind coal increases, while apparent activation energy of soft coal is decreasing with increasing in diameter of coal particles. The above study result shows that type of coal powder has more obvious influence on corresponding apparent activation energy.By making use of CFD software FLUENT, the thesis has made numerical simulation study to combustion process of coal powder with different fineness in furnace. The result shows that with diameter of coal particles increasing, resident time for coal powder in furnace extends, and resident time variation extent can be up to and even more than 30%. In addition to that, resident time varies for coal powder injected from different highness. Finer coal powder burns quickly in a comparatively shorter time inside furnace, then the remained char burns out slowly; while the combustion rate of coarse coal powder changes more slowly. By applying CBK model to simulate coke coal burning, the study finds out that with diameter of coal powder increasing, burn-out rate of coke coal increases too, while to superfine coal powder especially the ones whose diameter is below 10μm, with diameter decreasing, burn-out degree of coke coal increases on the contrary.The thesis has also studied technological by-product of fly ash treated by acid and brought forward technical plan of processing step-by-step and utilizing level by level, i.e. using fluidized drying technology to remove crystal water, then by carrying out ammonolysis and thiolysis to the residue to get ammonium sulfate and sulphuric acid to get back to technological circulation of acid treatment, finally the residue aluminium oxide will be used as metallurgy material. Processing step-by-step and utilizing level by level has greatly reduced energy consumption, increased reclamation rate of ammonium sulfate and sulphuric acid. Through experimental study of technological plan, the result shows that reclamation rate of sulphuric acid is above 90% and ammonium sulfate is above 70%. 0.21t ammonium sulfate, 0.1t sulphuric acid and 0.114t Al2O3 can be reclaimed from 1 ton aluminum ammonium sulfate by pyrogenation.The thesis has carried out systematic study on combustion characteristics of wide sized distribution coal particles, which provided large amounts of basic statistics for new combustion technology and in-furnace pollutant controlling technology research and development, which can also be reference and informative to relevant technology development and project application. Circulation utilization technology of aluminum ammonium sulfate can be important to technology of treating fly ash by acid to extract vanadium and aluminium so as to reduce consumption of sulphuric acid and ammonium sulfate and effectively avoid producing new pollutants.
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