Numerical Simulation On Slagging Characteristics In A Pulverized-Coal Boiler Gurnace Of600MW Supercritical Units

Slagging is a common and difficult problem in boiler operation, which affects the safety and economy of boiler operation. So it is important to predict the furnace slagging in order to provide a strong guarantee for the safe operation of the boiler.A tangentially-fired boiler of600MW supercritical unit was taken as the object. Against serious slagging on the burner region, numerical simulation was carried to the combustion process with FLUENT. By analyzing velocity field, temperature field, concentration field and gas distribution components, the author predicted the furnace slagging position. Based on the combustion simulation, the slagging process was simulated and the measures were proposed to reduce the slagging.The author used PDF combustion model to simulate full load operating conditions of the furnace. The results show that the velocity field inside the furnace is well organized. Low oxygen content and higher temperature than the ash softening temperature locate in the position of the burner along the stream direction, so the slagging position may be close to the corners of the burner along the stream direction.On the basis of the convergence of the combustion simulation, we developed a method based on sticking model to count the number of particle sticking to the waterwall and to judge the degree of the slagging. Based on the properties of fly ash injections and the division of the grid, the total number of the fly ash particles was192000. the simulation results show that the particle adhesion number is3207, which a very small proportion (1.67%). The number of particles adhered to the burner region is2900and accounts for90.4%of the total adhesion number, which verifies the burner area is the serious slagging area. The number of particles in the burner corners accounts for79%of the total adhesion number, where the area is small and complex. The burner corners should be the slagging position, which is consistent with the prediction.According to the causes of slagging, this thesis proposed several measurements to reduce the slagging in furnace, such as increasing perimeter air, changing the vertical shade separation burner to the horizontal shade separation burner and burning the coal which has the higher ash softening temperature. FLUENT waas used to simulate the conditions after taking three measurements.When the perimeter air velocity was increased to60m/s, the layers of cross section oxygen content at the slagging position increases and the flue gas temperature is lower than the ash softening temperature. In this case, the number of particles adhered to the burner region falls to607.After changing the vertical shade separation burner to the horizontal shade separation burner, the oxygen content at the slagging position increases. Except the burner at bottom, the flue gas temperature is over the ash softening temperature. The number of particles adhered to the burner region falls to2453.After burning coal with higher softening temperature, the flue gas temperature is lower than the ash softening temperature at the slagging positions of the cross sections. The number of particles adhered to the burner region falls to532. The slagging may be improved by using the coal with the ash softening temperature.