A Research On Enhancing Anti-Slagging Capacity For Pulverized-Coal-Fuel Boilers

In pulverized-fuel boiler, slag-bonding is one of the most noticeable matters that influence the boiler safety and economic run seriously. Some power plant boilers in our country have various degrees of slagging phenomenon. Slagging not only affect the normal operation, but would also easily result in devastating consequences when the boiler have to be stopped to clear the slag or adopt the directional explosion. Therefore, it is one of the most important problems how to prevent and relieve the slagging when the boiler is designing and running.The factors that influence the slagging include coal quality, designed parameters of a furnace, aerodynamic field in a furnace, load and atmosphere in a furnace, among which coal quality is most important since it is the fundamental cause that contribute to slagging. Theoretically, all burning coal could cause slagging, however, a suitable aerodynamic field in a furnace could make this risk reach a minimum level. Furthermore, the operation that deviates designed working conditions due to change of coal quality and load can also cause slagging on the water-wall in a furnace. This thesis deals with the slagging problem that happens in GZ power plant when it burn with Shenhua coal. First of all, we come to a conclusion that Shenhua coal is easy to get fire and burnout, but has a strong tendency of slagging, which is attained by using fire stability discriminance, fuel burnout discriminance, thermo-gravimetric analysis and slagging tendency discriminance. Second, we analyze the furnace original parameters, aerodynamic field in the furnace and the buff-body in the lowest primary air spout. Then a conclusion come that the existence of the buff-body, however, has aggravated the degree of slagging on the water-wall. Based on this fact, we suggest that GZ power plant use horizontal fuel rich-lean burner because it can stabilize the burning flame, reduce the NOx emission and adjust the atmosphere in the furnace to control slagging. For the sake of optimal design, we use CFD software FLUENT to simulate the gas-solid two phrase fluid inner the horizontal fuel rich-lean burner. It uses RNG k-εmodel based on Euler frame of reference for the computation of gas phase flow field and stochastic tracking model based on Lagrangian frame of reference for the computation of particle phase, which can reflect complex movement and collision of particle and wall. The computational results show that the separating effect of horizontal fuel rich-lean burner improves with baffle angleα, its height H and the distance L between baffle body and spout, but the effect of L is not so significant asα and H, and that commonly bigger particles are better than small ones when it comes to separating effect. Finally, the cold state and normal state test after reconstruction indicate that the severe slagging pressure in GZ power plant has been greatly alleviated. Meanwhile, this experience is also beneficial to people whose work is furnace designing and furnace operating.