Numerical Simulation Of Combustor Optimization In Submersion Combustion Natural Gas Heating Device

The immersion combustion natural gas heating device is an original type of heating device for natural gas heatingused in natural gas pressure regulating gate station.It was put into use for the first time in 2017,the heat exchange effect of natural gas reaches reaches the goals established as designed.However,the initial design of the combustion chamber is still based on the traditional empirical design.Considering the compactness of the structure of the device,this paper optimizes the design for the combustion chamber of the device through theoretical analysis and numerical simulation experiment research,combined with the actual operation of the device,on the premise of ensuring the stable and complete combustion.In order to meet the requirement of the compact structure of the whole submerged combustion natural gas heating device,both of the NO_xemission and the size and weight of the combustion chamber are needed to be reduced,while the combustion intensity is considered to be improved as much as possible.Finally,the recommended value range of the important parameter in the design of this type of combustor,that is,the velocity of the flue gas outlet flow section,is given,which provides a reference for the subsequent design of domestic submerged combustion natural gas heating device.Firstly,according to the actual situation of the device,the calculation model of flame height and flow velocity of flue gas outlet section is established.Aiming at the key parameter laminar flame propagation velocity in the flame height calculation model,a one-dimensional laminar premixed flame propagation velocity model is established.By solving the basic data of the flame propagation velocity model,and using the chemical dynamics software CHEMKIN to figure out the laminar flame propagation velocity under specific actual working conditions,the corresponding flame height was finally calculated.Secondly,the three-dimensional numerical simulation of the in-service structure combustor under cold condition is carried out.The results show that the pressure distribution in the combustor is uniform and the combustor is at positive pressure under cold conditions,and the gas velocity distribution on the surface of metal fiber is uniform.On the basis of reasonable cold simulation results,the model is further simplified and two-dimensional hot simulation is carried out.The flow field temperature and component distribution of in-service structure combustor under rated design power and different excess air coefficient were analyzed and compared.The results show that the combustion condition of in-service structure combustor is good and the temperature distribution is uniform.The optimal excess air coefficient of the device is 1.4,which is consistent with the actual optimal operating conditions;under different excess air coefficients,the combustion can achieve complete combustion in the position close to the metal fiber,and the radial combustion space can be further reduced and optimized.Then,four kinds of combustors with different structures are designed under rated design power,and the optimization simulation is carried out under four different excess coefficients.The temperature distribution of combustors with 20 kinds of different flue gas outlet flow cross-section velocities,including in-service combustors,are analyzed and compared,as well as the variation rules of outlet average temperature,NO_xand CO concentration.The results show that for the design of this kind of submerged combustion cylindrical metal fiber burner,reducing the combustion chamber diameter is beneficial to reduce NO_xemission;considering the influence of excess air coefficient on combustion chamber design and NO_xemission,it is suggested that the excess air coefficient should be 1.4;the structure with stable combustion,Co emission standard and lowest NO_xemission should be taken as the optimal combustion chamber structure Finally,it is concluded that under different flame heights,the design velocity of flue gas outlet section corresponding to the optimal combustion chamber structure is about 5m/s.Therefore,for the design of this type of combustion chamber,it is suggested that the velocity of flue gas outlet section should not be greater than 5m/s.Finally,the variable power simulation analysis of the in-service device is carried out under the optimal combustion chamber structure and excess air coefficient,and the combustion load adaptability is verified.The results show that the combustion of the in-service device is stable and the NO_xemission meets the emission standard within the load regulation range,and the load adaptability is strong.At the same time,the rationality of the optimized combustion chamber structure is also confirmed.