Studies Of The Flow And Combustion Characteristics Of Low-NO_x Pulverized Coal Swirl Burners Of Large Capacity Boilers

Coal is the dominant energy source of power generation in China, and about half of the coal consumed is combusted to generate electricity. The burner is the key equipment to realize pulverized-coal combustion, and a rational designed burner can not only guarantee the ignition and the reduction of energy consumption but also reduce the pollutant emissions. In the past decade, environmental pollutions brought about by pulverized-coal combustion greatly stifle the improvement of resident’s living standards. As a result, the government enacted a serious of standards to control pollutions. Many advanced low-NOx swirl burners abroad have been imported and utilized on supercritical furnaces in China. The characteristic of poor and varying coals quality utilized by utility boilers in our country leads to the high carbon content in fly ash, the sintering of particles around the outlet of burner and the high temperature corrosion of waterwalls. In order to solve above problems, it is very essential to design a swirl burner adaptive to the characteristics of coals in our country based on asorbing the low-NOx concept abroad.This dissertation begins with the measurement of the gas particle flow characteristics of a HT-NR3 swirl burner by a phase Doppler anemometer (PDA). The flow field of the swirl burner can be devided into the primary air, the annular recirlation zone and the secondary air. The enlargement of the cone angle of the outer secondary air can enhace the air staging and is beneficial to NOx reduction. However, when the cone angle is 60 degree, the secondary air flows along the wall. Then the DEM-CFD method was used to investigate the influences of the primary air pipe structure on the particle separation in primary air. Small particles can track the flow perfectly and the distribution of small particles is hardly affected by the primary air pipe structure. Large particles with St larger than 1 can be concentrated into a narrow band area by the primary air pipe, forming a fuel rich/lean flow field.A novel low-NOx swirl burner was designed and optimized. The shape, structure and NOx emission characteristics of the swirl burner were numerically investigated. Particles ejected from the novel swirl burner can penetrate into the recirculation zone possibility of washing lateral wall waters for the burner flame close to the lateral water walls. And besides,20% of the secondary air is used as the over fire air, which is ejected into the furnace above the main combustion zone and makes the flame oxygen deficient. This is beneficial to the formation of FeS. When the reducing flame wash the lateral water walls, the unburnt fuel and FeS will deposit on lateral water walls, resulting into the high temperature corrosion of lateral water walls. for a long distance, and then diffuse to the secondary air zone through the recirculation zone. This is beneficial to form a large reducing atmosphere, which contributes to NOx reduction. The novel swirl burner was arranged on a 600 MW utility boiler, and the NOx concentration at the outlet of the furnace was kept within 300 mg/Nm3(6%02). The expanding angle of the burner is about 60 degree, and the diameter of the flame increases firstly and then decrease from the outlet of burner downstream. The maximum diameter is about 1.25 m and the diameter reaches a minimum value about 1.6 m from the outlet. The flame of the burner is divided into the primary air zone, recirlation zone, high temperature zone and secondary air zone. The recirculation zone exists between the primary air and the high temperature zone, delaying the mixing of the primary air and the secondary air. This enhances the air staging of the burner and inhibites the NOx emission. The flame of the burner can represent the combustion condition of the burner, and the brightness and temperatue of burners in furnace increase firstly and then decrease and reach largest value at the third burner layer.A novel tiny-oil ignition cyclone burner was designed from the Foster Wheeler (FW) burner based on the concept of staged ignition. In the fuel rich nozzle of tiny-oil ignition cyclone burner, there are two combustion chambers. In the first combustion chamber, the concentrated pulverized coal is ignited by the heat of the oil combustion. The remaining pulverized coal is ignited by the heat of the oil and the concentrated pulverized coal combustion in the second combustion chamber. As a result, the majority of the coal particles are ignited in the swirl burner stage-by-stage, and the oil consumption is decreased largely. This burner has been employed for a 300 MW down-fired pulverized coal utility boiler in China, and the oil consumption reduces by 70% compared with the technology of FW Company.Finally, the high temperatue corrosion of a 600 MW utility boiler equipped with HT-NR3 swirl burners is investigated. The area of high temperature corrosion is located at the central zone of the lateral walls and the main corrosion production is iron sulfides. The HT-NR3 swirl burner adoptes the concept of in-flame NOx reduction and its flame is short and its expanding angle is large, which increases the...