Numerical Simulation Of Combustion Process In A 200MW Tangential Fired Boiler With Anthracite

Because of the high ignition temperature, the main problem of the anthracite with low volatile is how to achieve the goal of prompt ignition and stable combustion. The #2 boiler in Jiaozuo Power Plant is 670 ton per hour (tph) tangential firing boiler. While being operated, it has the problems of unstable combustion under the condition of low load and severe slagging. To solve the problems above, the boiler was retrofitted. A kind of horizontal bias pulverized coal burner was used instead of the original burner. The problem of slagging did not arise after the boiler was retrofitted. The minimum load without assist of oil firing can reach 50 percent of the rated load.This paper established the calculation model for the retrofitted #2 boiler and used the software of Fluent to simulate the combustion characteristics in the furnace. The results were analyzed and compared with the data collected from full-scale boiler experiments.From the results both from calculation and full-scale boiler experiments shows that the flows mix well in the furnace. The flame occupies the furnace fully. In the zones near water-cooled wall, the oxygen concentration is high, which can restrain the high temperature corrosion effectively. After adopting the horizontal bias pulverized coal burner, in the zones near the wall, the pulverized coal concentration and the temperature is lowered. This is advantageous for solving the problems of slagging.In the cross section where the burners lie, the temperature grad is large, and so is the heat transfer power, which is advantageous for prompt ignition and stable combustion.As the problems of environment protection become serious, the emission of contamination is regarded more and more. So the #2 boiler in Jiaozuo power plant was retrofitted for the second time. OFA was equipped on the upside of the burner. The method of staged combustion was adopted to lower the NOx emission. The results can be concluded as flows from simulation and full-scale experiments:After air staging, when the pulverized coal is fed into the furnace, it is burned in reductive atmosphere and a great deal of CO is produced, which can restrain the production of NOx effectively.From analysis of the results of simulation and full-scale boiler experiment, it shows that to lower the NOx emission, the secondary air velocity at several ports should be slowed down. In view of the condition of economic operation, at the precondition of stable combustion, the velocity of nether secondary air is suggested 40m/s, that of middle secondary air 25 m/s and that of upper should be set as slow as possible.The analysis of the simulation results shows that the influences of OFA on economic operation and NOx emission of the boiler are great. Increasing the ratio of OFA can lower the NOx emission effectively. Because when the ratio of OFA is increased, the combustion is under lean-oxygen atmosphere, so the temperature is low, which can lower the emission of fuel NOx and thermal NOx. At the same time, because the anthracite have difficulty in burning out, the velocity of OFA should increased to strengthen the final mixing, which is advantageous to lower the carbon content in fly ash.