The Study On Mechanism Of Ice-pellet Penetrating The Molten Slag At High Temperature

Slagging is one of the most common and the most difficult problems during the operating process of the coal-fired boilers in thermal power plants. It not only increases the thermal resistance and reduces the boilers efficiency, but also is hidden trouble of many safety accidents. The use of soot blowers is the main way to the problem of boiler slagging, whereas there are still a lot of deficiencies during using these traditional soot blowers, for instance the heating surface damage, much consumption of soot blowing media and disability of working online. Ice-pellet soot blowing is a new-developed technology which mainly destroys the slag’s structure through the powerful thermal stress gained from the large temperature grads between the ice pellet and slag. Ice-pellet soot blowing owns many advantages which the traditional ones don’t have. At first, it minimizes possible damages to the heating surfaces. Secondly, the resource of soot blowing media-ice pellet is sufficient and inexpensive. Third, it is achievable to blowing the slag online. overall, Ice-pellet soot blowing is a new technology of safety, economy and potential in the future.During cleaning the heating surface, the ice-pellet firstly penetrates the melt layer of slag, then penetrates the solidified layer of slag, at last stops in this layer due to large drag force. Non-Newtonian flow characteristics of the melt layer make the motion of ice-pellet coupled with heat transfer characteristics. In order to ensure the ice-pellet flow through the melt layer successfully, it is necessary to study this coupled process. Remaining situation of Ice-pellet in the melt layer is also a thermal-structural coupled process. The thermal stress damage results from great temperature grads between ice-pellet and melt layer which influences the soot blowing efficiency. Combining experiment method with numerical simulation, this thesis did some preliminary and exploratory researches about mechanisms of the two processes. The main work is illustrated as follows:(1) In order to verify the feasibility of VB simulation program, the Xanthan gun solution of2g/L was selected as experimental subject whose rheological characteristics were tested with rheometer; through the experiment of ice-pellet penetrating Xanthan gun solution, the ice-pellet’s motion curve was obtained with PIV technology. Based on the rheological characteristics of Xanthan gun solution, the ice-pellet’s experimental motion curve was calculated by VB simulation program. The numerical and experimental results are compared and analyzed to verify the accuracy and credibility of VB simulation program. (2) Via VB simulation program, the thermal-structural coupled process of ice-pellet penetrating the melt layer of slag was simulated to obtain the motion curve of ice-pellet at different initial penetration velocity. The result shows that ice-pellet could flow through the melt layer as long as the initial velocity exceeds160m/s.(3) The ANSYS thermal-structural coupled module was applied to calculate the thermal stress field of melt layer when ice-pellet was stuck in melt layer. The analysis result indicated that there was great thermal stress of at least50MPa which can damage the melt layer near the contact between ice-pellet and ice-pellet.