Study And Application Of Mixed Burning Indonesian Coal In Large Scale Coal-fired Boiler

The power generation in China relies very much on coal-fired thermal power generation. Due to the heterogeneous distribution and shortage of coal resources, as well as the current transportation situation in China, it is difficult for boiler to use the designed coal continuously. Operation problems were caused because of the variety of combustion coal, such as the low combustion efficiency, slagging and the excess emissions. These problems can be solved by using blended coals. However, based on fully understanding of the coal combustion characteristics, the appropriate combustion method and optimization of the operation condition are needed to achieve safe, efficient and clean combustion. Therefore, the study of the combustion characteristics of blended coals is important. In this thesis, the combustion characteristics, microstructure, pollutant emissions of the blended coals, and simulation as well as combustion optimization of boiler were investigated.Two coals including lignite from Indonesia and Shanxi-youhun bituminous were selected as parent coals and studied via thermogravimetric experiments. The results show that Indonesian coal has good ignition and burnout characteristics compared to that of bituminous, the ignition temperature can be improved by the co-combustion of the blends. However, the burnout temperature cannot be improved. X-ray diffraction was adopted to analyze the main mineral matter of the parent coals. The uniform design was used to study the effect of main mineral matter on coal combustion characteristics. The results show that the interactions between the minerals affect the combustion of parent coals significantly, morever, mSiO2/mFeS2 and mSiO2/mFe2O3 of different mass ratio respectively affect the combustion of demineralized coal from the parent coals. In addition, coal quality was an important Influence Factors for the combustion characteristics of parent coals.Char of blended coals was made in a horizontal tube furnace. The combustion reactivity, microstructure and crystallite configuration of blended coals were measured by thermogravimetric analyzer, N2 adsorption isothermal and Laser Raman spectroscopic analyzer separately. The effects of temperature on the combustion reactivity and micro-physical chemistry of blended coals were studied. The correlations of BET-surface and ignition temperature, fractal dimension and burnout temperature, crystallite configuration and combustion reactivity were found. These findings disclose the internal reason for blended coals'combustion characteristics deviate from those of parent coals.The pollutant emissions of blended coals were investigated in a horizontal tube furnace using an infrared gaseous analyzer under different combustion medium. The effects of O2 concentration on the emission of NO and SO2 were investigated. The results show that both the emission of NO and SO2, in low temperature region, are detected in high O2 concentration atmosphere. This is because the high O2 concentration atmosphere is favorable for the emission of SO2, but the high O2 concentration has double effects on the emission of NO. The emission of NO and SO2 decrease in high CO2 concentration atmosphere compared to that in O2 atmosphere. This is because the concentration of CO is higher in CO2 atmosphere, results in the reduction of NO and formation of other sulfurous phases in flue gas.In addition, the pollutant emissions of blended coals were influenced by the interaction of parent coals, the emission time of NO and SO2 advanced with the increase of Indonesian coal content, the interaction of parent coals could lead to the emission of NO lower than calculated value obtained by the weight of parent coals.The numerical simulation of the combustion of blended coals was conducted in a 660MW tangentially coal-fired boiler. The effect of operation mode and boiler load on the combustion and pollutant emissions were investigated. The results show that mixed burning and uniform distribution of air are favorable to improve the combustion and control the pollutant emissions, the high content of overfire air can reduce the emission of NO, but the use of the lowest layer of primary air go against burnout. The reasonable operational parameters were obtained by the means of simulation.The combustion optimization adjusting tests were applied to analyze the reasons of slagging and the solutions were proposed. The effect of operating mode on NO emission was studied. The results indicate that the upmost layer of auxiliary air can be applied to reduce NO emission. To achieve the safe, efficient, economic and clean operating, an econometric oxygen model was presented, which integrates the effects of operating parameters, such as combustion efficiency, pollutant emissions, coal consumption rate and unburned carbon in fly ash.