Application characteristics of finned tube in hot water boiler
The thermal calculation of boiler is an important part of boiler performance design. The accuracy of thermal calculation, namely the number of heating surfaces, is the fundamental to ensure the output, parameters, thermal efficiency and cost of HRSG.
Different types of spiral finned tubes, such as spiral fins, H-shaped or disc fins, etc. have been widely used in conventional power station boilers, circulating fluidized bed boilers and residual heat boilers in metallurgy, chemical industry, building materials and other industries. However, in the process of design, the standard calculation method introduced abroad or the former Soviet Union was mainly adopted, and the long-term design experience of designers or the results of the model test for a certain structure of finned tube bundle were used. At present, there are no mature and standardized standard calculation methods for fin tube bundles in China.
The heat transfer calculation of spiral fin tube of combined cycle waste heat boiler is also the same. Although there are some calculation methods of heat transfer and resistance of spiral fin tube bundle in the standard calculation methods introduced abroad or in the former Soviet Union, there are limitations in the specific application. On the one hand, it is the structural parameters, such as the spacing of tube bundle and the specification of fins. On the other hand, it is not fully reflected the influence of the pollution characteristics of the exhaust gas turbine on the heat transfer calculation.
In addition, the heat transfer characteristics of spiral finned tube are still related to the welding method and welding rate of fins, but there are some differences in the welding process of fin tubes at home and abroad. The above factors limit the further optimization of the structure and layout of finned tubes and heating surfaces and the localization of fin tube bundles in the design of finned tube heating surface of combined cycle HRSG and other HRSG in boiler manufacturer, and the finned tube has affected the performance and cost of HRSG to a certain extent.
In addition, when the exhaust gas turbine is transferred to the steam in the pipe through spiral finned tube, although the spiral fin tube strengthens the heat transfer capacity of the heating surface, it also makes the outer fin work in the harsh high temperature environment, which makes the temperature of the spiral fins outside the pipe often higher, which may exceed the temperature tolerance allowed by the material, which may cause the fins to be burned. For HRSG, the heating surface of high pressure superheater and reheater is high because of the flue gas outside the pipe and the working medium temperature inside the pipe. If the fin height is unreasonable in design, the temperature at the outer end of spiral fin, usually referred to as the temperature at the wing end, may exceed the allowable temperature of the fin material, which will cause the fins to burn out due to over temperature, which will affect the operation reliability of the HRSG. In conclusion, the heat transfer and resistance characteristics of different structures of finned tubes and finned tubes, temperature distribution of spiral fins must be studied, so as to provide design and calculation methods for the structural optimization of finned tubes and the optimization design of heating surfaces of finned tubes.
