| The fundamental circumstance of being rich in coal and lack in oils and gasesdetermined China’s energy structure, such that coal played as the primary energy sourcein China and this will last for a long time in the future. The coal gangue, which is themain waste produced during the coal mining process, not only occupied large amountsof lands, but also caused harmful damages to the ecological environment and humanbeings. Besides, the coal gangue with a small calorific value can also be used as a kindof fuel, and its application on boilers has become the main reutilization method for thehuge waste as it was generated during the coal mining process. The CFB boilers withsuperior combustion and clean performances have become the most suitable combustionsystem for coal gangue in the common sense. However, with the development of coalpreparation technology nowadays, the calorific value of coal gangue becomes lower andlower year by year. Then the traditional CFB boilers designed for coal gangue usuallyuse the high-quality-coal/coal-gangue blended fuel for operation, which will result inreduced economical efficiencies of the overall units. In order to further improve theeconomic efficiency of the units, it is necessary to study and develop the CFBcombustion technologies suitable for the pure coal gangue with low calorific values. Atthe same time, the potential problems of combustion instability due to the decreasingcalorific values of coal gangue, and large abrasion of the heating surfaces, reducedcombustion efficiency, as well as difficulties during the controlling process of bedtemperature, which may be accompanied with its application on the traditional CFBboilers, should also be particularly concerned in this attempting activity.Consequently, the following work was conducted in the present study:①Employing the thermol gravimetric analyzer (TGA), the combustion characteristic oflow-calorific-value coal gangue with different particle sizes were studied.The combustion stability and burnout behavior of the coal gangue with differentparticle sizes are very crucial to its performance in the CFB boilers. However, thecombustion performances of the coal gangue in these fields were not studied asthoroughly by far. The combustion stability and burnout behavior of theNorthern-Sichuan low-calorific-value coal gangue with different particle sizes wereinvestigated presently, which will particular conductive to the design and operation ofthe CFB units fueled by it. ②Combustion characteristic of the Northern-Sichuan low-calorific-value coalgangue were experimentally investigated on a semi-industrial CFB combustion testapparatus.During the tests, the Northern-Sichuan low-calorific-value coal gangue wasapplied to a semi-industrial CFB combustion test apparatus. The ignition process of theCFB apparatus, as well as the effects of bed pressure drop and excess air coefficient oncarbon contents of the bottom and fly ash, was examined.③Finally, a cold model test was also conducted to study the exchangingcharacteristic between the coarse and fine materials at different bed-layers, which is akey technology for the patent “a type of CFB boiler designed for combustionlow-calorific-value coal gangue”. The results showed that the coarse and fine particleswere exchanged in different patterns. Besides, under different operational conditions,the majority of fine particles could be transferred into the fine bed and the coarseparticles still stayed in the thick bed, indicating that the present patent had goodsize-classification performance and could transfer the coarse and fine materials intotheir corresponding bed zones. There existed an optimum differential value between theheight of partition wall and that of the thick bed surface, at which the effect ofcoarse-fine particle exchange was the best. Furthermore, when the height of the fine bedwas increased above a critical value, the “backward transferring” phenomenon occurredaccordingly, which is rather helpful for the control of bed temperature in the practicaloperations. |
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