Study On High Temperature Corrosion Prevention Of 600MW Wall Type Opposed Firing Boiler

With the increasingly prominent environmental problems,the standard of NO_x emission from boilers is stricter,and the low nitrogen combustion technology is applied in boilers all over the country.However,after the implementation of low nitrogen combustion technology,the high-temperature corrosion phenomenon of water wall becomes more and more common,and the resulting economic and safety problems cannot be underestimated,so it is of positive significance to study the high-temperature corrosion solutions.Aiming at the high temperature corrosion problem of a 600 MW opposed firing boiler in a power plant,this paper analyzes the cause of high temperature corrosion by measuring the operation data in the field industrial test,and studies the solution through single-phase cold state test and hot state numerical simulation.The industrial test results in this paper show that when the boiler burns low sulfur coal,the received total sulfur is 0.36%,and the furnace temperature is within the normal range,but the furnace temperature increases with the increase of load.The atmosphere near the water wall has strong reducibility,the concentration range of O2 is 0-0.18%,the concentration range of CO is 4.18%-12.9%.The pulverized coal has been ignited in the premixed section of the burner,and the ignition point is at the distance from the primary air injection At 300-400 mm of the port,the pulverized coal diffuses to both sides along with the swirling air flow,which is easy to wash the side wall.According to the analysis of the results,the high temperature corrosion of the boiler is mainly due to the unreasonable structure of the pulverized coal of the swirl pulverized coal burner,the concentration outside the pulverized coal and the distribution inside the pulverized coal.A large number of pulverized coal are burned in the swirl area of the burner,and the unburned pulverized coal is easily thrown into the water-cooled wall and reacts with the oxygen near the wall to generate carbon monoxide.According to the causes of high temperature corrosion of the boiler,and combined with the research of domestic and foreign scholars on high temperature corrosion prevention measures,this paper proposes to solve the problem from the burner structure optimization and the introduction of wall wind.According to the modeling principle of the cold test-bed,a single burner cold test-bed is designed and built according to the ratio of 1:4.The swirl strength is changed by changing the position of the inner and outer secondary air swirl blades.By extending the length of each air nozzle and changing the length of the premixed section,the backflow area and the expansion angle of the burners with different structures are studied.The test results show that the burner is in the lowest swirl strength and the premixed section is in the lowest swirl strength The mixing section is changed from the primary air nozzle and the internal and external secondary air nozzles with a certain distance to the shortest premixed section,that is,when the central air,primary air and internal secondary air nozzles are flush with the burner flaring,the return area is the smallest,the flaring angle is small,the jet rigidity is strong,and the scour on the side wall is reduced.In this paper,the thermal numerical simulation is carried out for the boiler installed with horizontal rectangle,square rectangle and vertical rectangle with height width ratio of 0.61,1 and 1.64 respectively,and the diameter of the boiler is 260 mm.The simulation results show that the horizontal rectangle with height width ratio of 0.61 has a better effect of high temperature corrosion protection,and the atmosphere oxidation in the area covered by the wall wind is obviously improved,and the oxygen range is increased from 0.0005% to 3%~7% The range of carbon oxide is reduced from 5%~10% to less than 1%,and the average temperature of the side wall of the water wall is reduced from 1380 k to 1100 k.Therefore,the final transformation plan of this paper is to optimize the burner of the boiler with the front and rear walls close to the water walls on both sides.Six horizontal rectangular wall mounted air devices with height of 180 mm,width of 295 mm and height width ratio of 0.61 are installed at the positions with the front and rear walls close to the walls on both sides.In this paper,the thermal numerical simulation of the boiler with burner optimization structure and different wall wind structure is carried out.The simulation results show that,compared with the whole oxygen concentration near the water wall on both sides of the original boiler,the carbon monoxide concentration and the average temperature of the side wall are significantly reduced.Therefore,this paper predicts that the high temperature corrosion problem of the boiler can be greatly alleviated after adopting the recommended transformation scheme.