Wear Mechanism And Protection Of Waterwall In A CFB Boiler

Wear on water walls in a circulating fluidized bed (CFB) furnace is a major problem and affects the security and stability of CFB boilers, which detracts from the overall benefits of these boilers. Anti-wear beams installed on water walls of CFB boilers are one of the most effective ways to protect against water wall wear. Currently, CFB boiler technology is advancing toward supercritical and ultra-supercritical units. Larger area of suspended heating surfaces will be required in these furnaces. However, Increasing the number and length of the traditional wing walls may not be sufficient to meet this requirement. Based on these two background, gas-solid hydrodynamics and wear characteristics on water walls with and without anti-wear beams were investigated using experimental methods and numerical model simulations in this work. Besides, the gas-solid hydrodynamics over two novel suspended heating surfaces were also studied in this paper.In this work, investigations of the gas-solid hydrodynamics and wear distribution characteristics on water walls around an anti-wear beam were conducted in a 2D CFB test rig. Secondly, experimental investigations of the gas-solid hydrodynamics over the two novel suspended heating surfaces were performed. Thirdly, an innovative water wall wear model was established based on the gas-solid hydrodynamics on water walls in CFB boilers. Finally, the gas-solid hydrodynamics in 330MW and 600MW CFB boilers with and without anti-wear beams were studied numerically. And based on the numerical results of the gas-solid hydrodynamics on the water walls, the wear distribution characteristics on water walls of the 330MW and 600MW CFB boilers with and without anti-wear beams were calculated and studied using the water wall wear model.Experimental results show that the downward solids flow of the wall layer is partially disrupted by the beam and the velocity of the falling solids of the wall layer around the beam decreases. Below the beam, some upward-moving solids are observed along the wall. And at the upper surface of the beam, some solids accumulate dynamically. An anti-wear beam installed on a water wall reduces the wear rate of the water wall below it, especially for the water wall close to the bottom surface of the beam, the wear rate is almost zero. However, the wear on the water wall just above the beam is serious. From the perspective of the overall wear on the water wall around the beam, and for a downward solids flow of the wall layer with a specific thickness, there is an optimum beam width that, when combined with the smallest beam height, results in less wear.The solid volume fraction inside a U-wall and a □-wall have a U-shaped profile in the middle and lower sections and an approximate straight-line shape profile in the upper section. The solids vertical velocity inside the U-wall and the □-wall have an inverted-U-shaped profile, and there are downward and upward flows of solids coexisted at the suspended walls. In a CFB furnace, there is an optimal width for the U-wall and the □-wall respectively.In terms of the numerical study on the gas-solid hydrodynamics in 330MW and 600MW CFB boilers with and without anti-wear beams, the three dimensional distributions of the gas-solid hydrodynamics on water walls and in furnaces are obtained. It is observed that the average vertical velocity of the falling solids on the water walls decrease to 2m/s and the maximum solids volume fraction at the upper surface of the beam is almost 0.3～0.4.In terms of the numerical model study on the wear of water walls in 330MW and 600MW CFB boilers with and without anti-wear beams, the three dimensional distributions of the wear rates of water walls are calculated. For different water wall regions around the anti-wear beam, the mechanism that the beam affects the water wall wear is found to be different. Overall, the mian wear style of the water walls transfers from abrasive wear of particle clusters to impact wear of dispersed phase particles. In addition, the numerical model results of the wear rates of water walls agree with the field data. Finally, some advices for the design and arrangement of anti-wear beams in CFB boilers are proposed based on the research work in this paper.