Numerical Simulation On Hydrogen Leakage And Diffusion In Hydrogen Cooling System Of Power Plant

Turbine generators generate a large amount of heat during high-speed operation,and they need to be cooled by hydrogen in a hydrogen cooling system to reduce the temperature of the generator and ensure the safe operation of the generator in power plant.However,the hydrogen cooling system of power plant generally has a hydrogen leakage phenomenon.When it leaks in a confined space,it will form an explosive mixture with air.If it encounters an ignition source,it will cause combustion and explosion accidents.Therefore,it is necessary to study the hydrogen leakage diffusion process of the hydrogen cooling system in power plants.This paper uses CFD to numerically simulate the leakage and diffusion of hydrogen in hydrogen production stations and turbo-generator buildings.The main research contents are as follows:(1)This paper takes a power plant in Dalian as an example.Based on understanding the process flow and production equipment in the hydrogen production station and the turbo-generator building,the hydrogen leakage points and ignition sources in the process are identified and analyzed.(2)According to the characteristics of production equipment and technological process,combined with the characteristics of each numerical method of FLUENT,the numerical methods used in the numerical simulation of gas diffusion are described.The k-εturbulence model is used for the turbulence of air in space.The diffusion process is used for hydrogen diffusion and the SIMPLEC algorithm is used to numerically calculate the flow field.Based on this,FLUENT software was used to carry out numerical simulations of experimental research done by J.M.Lacome.The results of numerical simulation were compared with experimental data to confirm the correctness of the mathematical model.(3)This paper establishes a simplified geometric model of the hydrogen production station,and uses the mathematical model and numerical method selected above to numerically simulate the hydrogen leakage diffusion in different operating conditions.It is found that there is the following relationship between T1、T2 and the hydrogen leakage mass flow Q(Where T1 is the ultimate hydrogen leakage time when the molar fraction of hydrogen in the vicinity of the leak is within the explosive limit range,and T2 is the hydrogen leakage time when the molar fraction of hydrogen in the entire space reaches the explosive limit range):T1=0.69337×Q-1.03362;T2=0.69262×Q-1.15307.(4)Under different operating conditions,the molar fractions of hydrogen at the four detection points at the top corner of the hydrogen production station at the same time are almost the same.It is impossible to infer the leakage position from the changes in the molar fractions of hydrogen at these four points.In this paper,by monitoring the hydrogen mole fraction at point F,it is found that the mole fraction at this point varies greatly under different operating conditions.Therefore,it is recommended to install a hydrogen concentration detector at point F.(5)This paper establishes a simplified geometric model of the turbo-generator building,and uses the mathematical model and numerical method selected previously to perform numerical simulations of hydrogen leakage and diffusion under different operating conditions.Studies have shown that when the leak hole diameter a≤2mm,the buoyancy of hydrogen in the plant will have a significant effect on the diffusion process of hydrogen.When the leak hole diameter a>2mm,the buoyancy of hydrogen in the factory building will have very little effect on the diffusion process of hydrogen.(6)In the turbo-generator building,when the hydrogen leaks in the X direction for 60 minutes,this is the following relationship between leakage hole diameter a and the farthest distance L(between leak hole and the point at which the molar fraction of the hydrogen in the X direction is within the explosion limit range):L=0.15757×a+0.02081.The research in this paper can provide guidance for the emergency response of hydrogen leakage and diffusion of hydrogen cooling system in power plants,and provide reference for the installation location of hydrogen concentration detector.