Study On Flame Stability And Application For Petal Swirl Burner

There are abundant low volatile coal stores, such as anthracites and semi-anthracites coal in China. These fuels have the characteristics of difficulties in ignition, flame stability and carbon conversion due to contain lower volatile matter (VM). How to successfully burn low volatile coals has been becoming one of the key issues in power plant boiler. Most of low volatile coal units in China have adopted corner firing technology. Boilers with tangentially-fired burner are easy to form slagging and great temperature deviation of flue gas at the exit of boiler furnace, which will be more serious with the increase in capacity of the power units, and impact the operation of large boiler seriously. While swirl combustion has obvious advantages in reduction of slagging and temperature deviation, large-scale units in the western countries are often use the wall opposed firing swirl burner. But swirl burners are considered to be suitable for burning high grade bituminous coal. The stable combustion as the primary issue for the reliable operation of low volatile coal with wall opposed firing swirl burner, has not been solved yet. It is anxious to develop a new type of swirl burner with great stable combustion performance and suitable for the situation of our country.Based on the reasons of common swirl burners could not stable combustion of low volatile coal, this paper introduces the invention of a new type of stabilizer– Petal Flame Stabilizer(PFS). The new type of swirl burner with PFS -Petal Swirl Burner(PSB) and the good flame stability and low NOx emission are discussed. By means of numerical simulation theory analysis in combination with industry experimentation in power plant, studies on the stable combustion performance of petal flame stabilizer and petal swirl burner are performed in detail.This paper sets up a three-dimensional(360˙) coal combustion mathematics model to simulate the flow field, temperature filed and the combustion species's concentration distributions(CO2,O2,NOx) for Petal Swirl Burner. The dimension of the recirculation zone, recalculating flux and mixed coefficient are analyzed to research the combustion stability of PSB. The Petal Swirl burner's designs take the mixture of the primary air- pulverized coal flow and the recirculation flue gas into consideration carefully. The air-pulverized coal flow leaving the burner rapidly moves into the recirculation zone, the pulverized coal particles don't diffuse into the secondary air zone as the older swirl burner designs do. The mass and heat transfer between the pulverized coal and the flue gas depend on not only the fluctuation of microscopic turbulence at the edge of the recirculation zone which are the main drive force in the older swirl burner, but also the great-intensity macroscopic convection transfer. The flow field in the near burner flame consists of many kinds of stable recirculation zones such as radial and axial recirculation behind the flame stabilizer. And the flame always on duty behind every petal can steadily heat up the pulverized coal flow from two sides. This kind of flow pattern is profitable for part of pulverized coal being moved into recirculation zone and for the reliable ignition and burnout of low volatile pulverized coal, and for turndown capabilities meanwhile for lower NOx emission.PSB has applied in a 210MW power plant for a long time, and shown to possess enhancing ignition, flame stabilization and different coal flexibility. It can be observed from the inspection neol of center pipe that the pulverized coal particles run through the valley of PFS and circulate in the recirculation zone. Different from common burner's stable principles, Petal Swirl Burner has the character that a great of pulverized coal particles can be moved into circulation zone, and rapidly ignited, and then burnt. The result of industry experimentation indicate that the Petal Swirl Burner can stably combust semi- anthracites coal with Vdaf=12~18% in 55~100% boiler load. The comparison of flame temperature between the simulation value and the test results at the exit of PSB shows a good agreement.The invention of PFS and PSB are aimed to solve the issue of low grade coal stable combustion in China, which has the great theoretic significance and practicality value. The concept of"mixed coefficient"put forward in this paper for evaluating the mixed speed and intensification between the pulverized coal-air flow and the recirculation high temperature gas, seems to develop the theory of stable combustion, which is important to deepen the investigation in stable combustion and flow field for swirl burner.