The Study Of Quantitative Calculation Methods Of Fly Ash Wear Based On The UDF

The flue gas of pulverized coal boiler is rich in fly ash particles that collide with the heating surface and give rise to the abrasion when going through and transferring heat with the heating surface. The prolem of wear is the main reason for economizer tubes bursting. The heating surface wearing problem caused by the fly-ash has a long history and is a serious threat to the safe operation of the boiler. Comparing to the surfaces with higher temperature, the wearing condition is even worse because the flue gas temperature is lower and characterized by its high hardness. At the same time it is also more serious than the air heater inside which the smoke flows although at a lower temperature just on account of the cross abrasion in bundles by particles in economizer.The main influencing factors of economizer wear concludes particle hitting speed and shape(particles of edges or round particles),the chemical and physical properties of particles, the gathered degree(concentration of fly ash),the knocked material temperature, properties and the economizer structure and so on.In this paper, the discrete phase model in commercial computational fluid software Fluent is adopted to simulate the economizer wall wearing. The velcocity distribution rule between the bundles and the particle running trajectory can be got from the results by simulating the flow field of the simplified columns in line and stagger arrangement model. Then the flow field in symmetric separation region is initialized by the obtained velocity distribution. The wear simulating calculation is conducted using the software Fluent UDF and wear equations. The wear amount of economizer distribution regular along the wall caused by the fly ash can be got from the results.It is showed from the data obtained from the results that in the same geometrical model and operation conditions, the changing rule of wear is different between tubes in-line and staggered columns. The in-line tube wear along the economizer wall in different rows first increases and then decreases and may get the maximum wear in the middle row of the tubes. The wear amount along the wall of staggered bundle has a similar trend, but its wear magnitude is two orders of magnitude bigger than that of the in-line bundles. So it is obvious that the wear in the staggered bundle economizer is much more serious than that of the in-line bundle. When a single pipe is concerned, the abrasion amount that is in the circumferential direct of the wall along the in-line and staggered bundle first increases and then decreases with regularity and reaches the maximum value in the angle (the maximum abrasion position).The maximum wearing position in the in-line bundle is in the angle of50-60℃from the windward and that is in the angle of5～10℃in the staggered bundle of the economizer.When just changing the particle size (diameters) and ensuring the other influencing conditions are the same, the wearing amount of the in-line and staggered bundle also present different changing rule. With the increasing of the particle size, the abrasion wearing is reduced and the staggered bundle shows a rule of first increase and then decrease, reaching the maximum abrasion loss with the particle in size of70μm.In this paper, the real simulation of the bundles field and the wearing amount of the economizer tubes are conducted and the results are close to the physical fact fundamentally. It is of some reference value for the engineering application.