Improvement Of Char Combustion Model Based On Ash Inhibition Effect In FLUENT And A New Method Of Grid Treatment

As the most abundant fossil energy,coal occupies an absolute dominant position in the structure of energy production in China.With the rapid growth of China's economy,the domestic thermal power industry has developed rapidly.In the new situation,the computer software is used to simulate the combustion status and pollutant generation process of power station,which has become an effective research means.Because the combustion process is a complicated physical and chemical process in large thermal power plant,the accurate description of the process needs to be improved.This paper introduces the calculation model of the numerical simulation of the furnace combustion.In view of the whole process numerical simulation of pulverized coal fired boiler in large power plant,the following two aspects are improved in theory and technique.Firstly,the char combustion model of CFD software default is analyzed.The current mainstream commercial software CFD model of pulverized coal combustion in char FLUENT default rough comparison,due to ignoring the ash layer on the reaction inhibition led to the prediction of the char combustion rate too fast.This paper reestablished the char combustion model,considering the resistance when gas through ash during combustion process.According to the theoretical derivation,the combustion rate of char based on the ash content was deduced,and the char combustion model was modified in FLUENT.A 110 MW super high pressure natural circulation boiler is studied,and the thermal state of the furnace is calculated by using the two models before and after the improvement.Results: considering the inhibitory effect of ash layer have improved model of the pulverized coal combustion process the more uniform and lasting,the carbon content of fly ash and furnace temperature is closer to the actual.Secondly,it is aimed at the technology optimization of the numerical simulation grid processing method for swirl burner.Because of the large difference between the burner and the whole furnace,so the burner structure is usually simplified.There are two methods to realize the numerical simulation of combustion swirl opposed boiler at present.Traditional method one is simplified burner as a short cylindrical,given a swirl intensity artificially;Traditional method two is that all burners and furnace as a whole was simulated.Advantages and disadvantages of the two methods was summarized in this paper,and a new method of "subsection modeling and non difference transition" was put forward.A representative of the burner is simulated,simulation results will adjust the entrance conditions as the whole furnace simulation.The no difference transition between the two objects by custom editing the "boundary profile" in ANSYS FLUENT software,solving the three main difficult problems from a single burner to whole furnace,which is transition of velocity,the transition of left and right rotation and the transition of concentration of pulverized coal.And a 600 MW supercritical boiler as an example,using the traditional method and new method for the simulation calculation of the furnace,the numerical results show that the new method can not only ensure the details of the burner without loss,but also greatly reduce the number of the furnace grid,so that the accuracy of the calculation is ensured.