Numerical Simulation Of Super Heater And Analysis Of Thermal Deviation In Supercharged Boiler

The nonuniformity of steam mass flowrate and the unevenness of heat load distribution in parallel tubes of boiler super-heater are two major factors that lead to difference in steam temperature and tube wall temperature, local overheating and even tube rupture. Numerical calculations in traditional super heater hydrodynamics and in available articles paid more attention to platen super heaters used in power plants, in which the header was simplified as one-dimensional cylinder with constant cross section. Super heater headers of marine boiler are commonly divided into multiple chambers with irregular shapes and small length to diameter ratios by internal baffles, and form complicated three-dimensional flow patterns, thus are inappropriate to be simplified as one-dimensional cylinder, nor to be approximately regarded as a basic structure with known static pressure distribution.In view of the complexity of super-heater structure for marine boiler, on the base of the basic theory of header, put forward the structural parameters factors which affect the distribution of flow. By using soft ware make three dimensional cold state numerical simulation of flow field including Z-type header prototype,Π-type header prototype and different structural parameters header, analyze, conclude and verify various structural factors which affect the distribution of flow. By using "PRO/E" establish the whole simplified three dimensional model of outside smoke of super heater and inside space of steam, choose reasonable boundary conditions. Take the basic equations of hydrodynamics and "k-ε" turbulence model as the mathematical model, make three dimensional hot state numerical simulation of simplified super heater flow and heat-transfer of the whole steam, directly get the distribution of steam mass flow , steam temperature and steam enthalpy value of each part, the highest temperature of pipe wall, thermal flow and heat transfer coefficient.From the simulation results: temperature of pipe wall becomes higher gradually along the flow direction of steam; The highest temperature and deviation is the main steam pipe near the middle part of the third process; At the position, the flow of steam is low, but the heat load is high, which makes the high deviation, the high temperature steam and pipe wall, so it is dangerous; As the heat load becomes big, the pipe temperature of different positions become high, the difference between each branch pipe becomes big; And the position of the highest temperature of pipe walls of the third process transfers back forward; The steam temperature of both sides is lower than the middle one in every pipes, which relates to flow distribution and smoke temperature; The heat deviation of third process is higher, the main reasons are the mode of steam in and out, structure arrangement, so it needs a further improvement from the design in order to make the heat load and flow match, reduce the heat deviation and the temperature of pipe wall.Starting from the basic theory, deduce and obtain simplification principle of super heater model. The whole three dimension calculation and analysis of super heater in marine supercharged boiler was realized first. By coupling calculation about steam, pipe wall, smoke, get the law of heat transfer and flow of super heater, establish the position of the highest temperature of pipe wall and the conditions of dangerous situations, conclude and get the law of thermodynamic performance parameters with the changing of load, which can supply some technical support for the designing and operating of supercharged boiler.