Research On Waste-heat Utilization System Based On Thermal And Air Leakage Calculation Of Quad-sectional Air Preheater

With the pressure of environment and resource protection keep growing,China put more and more attention on energy conservation and emission conduction of thermal power plant.In order to reduce the loss of exhaust gas at the end of boiler,a new waste-heat utilization system began to get application.The new system based on quad-section air preheater,at the meantime,a gas by-pass was set at the entrance of gas.2 low-temperature economizer was set in the gas by-pass to realize coupling utilization of high and low level waste-heat.Quad-section air preheater played a central role in the system and the structure was much more complex than traditional air preheater.But the research of quad-section air preheater was incomplete,many problems was waiting to be solved.This paper established a coupling model between thermal calculation and air leakage calculation of quad-section air preheater.Thermal calculation model based on heat convection and energy conservation equations,which considered the axial heat conduction of matrix.The equations was solved by finite difference method.Thermal calculation can provide thermal parameters of air preheater,such as temperature distribution,pressure distribution and velocity distribution.This paper established a model of air leakage distribution and the calculation based on energy and mass conservation equations.Calculation result can provide the mass and direction of air leakage.This paper wrote a calculation program on Matlab to solve the coupling calculation model conveniently.Through the thermal and air leakage analysis,we found that,the temperature of fluent and matrix was very similar,the heat transfer temperature difference was very small and mainly existed at the cold end.The lowest outlet temperature of gas was very close to the inlet temperature of air,which means vulnerable to low-temperature corrosion.The radial air leakage was the mainly air leakage pattern.This paper compared a quad-secotional and a tri-sectional air preheater with same heat transfer area,volume,seal gap and operation condition.The result showed that the air leakage rate of 2 type air preheater owned same change rule under different operation condition.,but the air leakage rate of quad-secional air preheater was always lower than tri-secontion air preheater.This paper carried out variable condition analysis of operation parameters,such as bypass primary air rate,primary air rate and rote speed,under fixed gas flow and fixed outlet gas temperature conditions.The result provided the change rules of outlet temperature,system efficiency,bypass gas flow rate and so on.Finally,this paper put up with the method of ε-NTU analysis of rotor air preheaters and provided the ε-NTU alignment chart.This method can efficiently block the influence of inlet temperature,rotor speed,flow rate,so we can get the air preheater efficiency form the alignment chart conveniently.