Boiler Air Preheater Air Leakage Research And Reconstruction

Rotary air preheater, in which the heat of flue gas is recovered to reduce the exhaust gas temperature, is one of the main auxiliary equipment in the power plant. It works in the tail heating surface in boiler region with the lowest flue gas temperature.Due to its construction, there are always some problems during operation in rotary air preheater. One of the most serious is leakage. The rotary air preheater leakage rate is about 6% within a year and about 8 percent a year later. With the increase of the running time, the leakage will be more and more serious, and may reach 20%. To reduce air leakage is the impendency desired of the fossil-fuel power plants. All kinds of malfunction of rotary air preheater is expounded from its structural. Including secondary combustion, leakage, ash deposit, fouling, abrasion and low temperature corrosion etc. The leakage issues were discussed in detail from the preheater structure itself. And the cause and location of air leakage is also described.Through the above analysis and the actual situation of Dalian Ganjingzi thermal power plant, the necessity of the air preheater transformation is proposed. For the actual situation of rotary air preheater leakage, the flexible sealing device of transformation is used. Re-fixed sector plate and axial seal curved plate. Primary sealing structure is transformed into double seal. The automatic tracking system is canceled. All the heated element is also replaced. And the fan heater has been transformed. The leakage significant declined After the transformation of rotary air preheater. The "leakage triangle area" caused by "mushroom strain", center tube leakage, and mutual abrasion between the static and dynamic element is solved.The calculation method of trisector heat transfer evolved form "boiler unit standard thermodynamic calculation method" is used in the heat transfer calculation. The primary and secondary air is merged to computing. Resistance calculation is divided into resistance along the way, scaling local resistance in the fluid passage section and the expansion flow resistance of the fluid passages. The comparison of heat transfer and resistance calculations before and after the air preheater transformation shows that the air leakage is reduced, exhaust gas temperature is lower, and the preheater outlet temperature is increased after the transformation.The entire project cost is evaluated in the end. The air preheater seal system equipment is stable after put into operation. The entire reconstruction project is analyzed technically and economically. The payback period of entire project with significant benefits is about a year.