In the actual operation of 130t/h boiler in a power plant, due to the unstable coal quality, there are some problems such as serious clinker formation in the water-cooling wall area of furnace, boiler ignition and poor combustion stability. The $\mathrm{k}-\Omega$ turbulence model is used for numerical simulation of the horizontal thick-thin burners. The ratio of the concentration of thick and thin pulverized coal is about 1.5, and the flow direction of the coal powder can be controlled by the horizontal thick-thin burner technology, which can improve the combustion in the furnace. The combustion conditions in the furnace before and after the renovation of the four-corner tangential combustion boiler are simulated by using the $\mathrm{k}-\varepsilon$ two-phase model. The results show that the overall temperature level in the furnace is reduced, and the cross-section temperature of the burner is reduced, which can make the ash particles not easy to melt and the probability of clinker on the furnace wall is reduced. The boiler was reformed by installing horizontal thick-thin burner system and removing a certain area of refractory belt. After the renovation, the boiler can burn stably at 80 t/h, the degree of clinker formation in the furnace is reduced, and the boiler parameters are stable.

In the operation of a 3100t/h ultra-supercritical boiler, there are some problems such as high combustible content of slag, low reheat steam temperature, poor combustion stability and uneven distribution of primary air at four corners of the furnace. The combustion conditions in the furnace before and after the transformation of the four-corner tangential combustion boiler are numerically simulated by numerical calculation. The calculation results show that the amount of pulverized coal falling into the cold ash hopper is reduced from 0.065kg/m 3 before the transformation to 0.052kg/m3 after the transformation, which is reduced by about 20%. The centralized arrangement of secondary air at the bottom layer enhances the lifting ability of pulverized coal. In the direction of the burner section, the low temperature zone in the center of the furnace is reduced, the annular high temperature zone around the furnace is increased, and the heat load of the furnace section is increased. Along the height direction of the furnace, the average temperature of the section of the burner area at the bottom of the furnace is increased by about 50°C~80°C, which is conducive to the ignition and combustion of the pulverized coal gas. The average cross section temperature of the main combustion zone in the upper part of the furnace is increased by about 20°C~30°C, which is conducive to improving the temperature of reheated steam. The conversion rate of pulverized coal carbon in the four corners of the bottom burner nozzle is increased from 92.2% before the transformation to 93.1% after the transformation. The reconstruction of the primary and secondary air nozzles at the bottom, the installation of backburner belt in the lower group of burners, and the installation of adjustable shrinkage holes in the primary air pipeline are proposed. After the transformation is completed, the boiler can be stable combustion at 500MW low load without oil injection, the combustible content of slag is reduced to 2.5%~5.5%, the temperature of reheated steam is improved to a certain extent, the boiler is in good running condition, and the boiler efficiency is increased by about 0.3 percentage points.

The collector-rings' fire accident resulted from bad contact between carbon brushes and collector-rings on the generator and burnt process on main shaft of the generator have been analysed.It is believed that the local sparks resulting from bad contact between carbon brushes and collector-rings make the temperature of collector-rings to be risen,the non-uniform distribution of excitation current among carbon brushes leads further to fire accident on collector-rings,thereby,preventive measures for occurrence of fire accident on collector-rings have been presented.

Severe defects existing on stator winding bars had been discovered in operation of generator no.2 in one power,after retrofits,such as replacement of stator winding bars,and improvement of their fixed mode etc.,the defects still hadn't effectively eliminated.Based on summation and analysis of defects existing in the generator and causes of ineffective retrofit,three measures for defect-eliminating and capacity-increasing retrofit have been put forward,and the feasibility of said three methods being compared in detail,to determine the retrofit scheme.