Optimal Design And Combustion Characteristics Study Of Partial Premixed Swirling Burners For Low Calorific Value Coal-bed Methane

The reserves of the unconventional natural gas resources, coal-bed methane (CBM),are very abundant. And their industrial application mainly focuses on the high calorificvalue part which can be used directly. But the composition of low calorific valuecoal-bed methane is very huge in the national coal-bed methane resources and the re-search and application of these resources as auxiliary fuel is relatively poor. Due to thelow methane concentration, its combustion as auxiliary fuel exhibits flame length getlonger, combustion stability characteristics get worse and so on. Therefore it is neces-sary to optimize the design of burner, and study combustion characteristics of the newburner.Firstly, using the methods of installation bluff bodies and numerical simulation onthe partial premixed swirling burners for low calorific value coal-bed methane, thestructure optimization of the burner is studied. It is showed that installed the buff bodyon the outside wall of fuel pipe can increase partial premixed effect; installed the buffbody on the outlet of support pipe can improve the jet rigidity, entrainment capacity andscope of recirculation zone; In the following experiment, the flow field characteristicsof the optimized burner is researched. It indicates: the pressure loss in the secondary airpipe is biggest, and in the primary air pipe is smallest among the fuel pipe, primary airpipe and secondary air pipe; And when the excess air coefficient is less than1.2, thepressure loss in the primary air descends with the excess air coefficient increasing; withthe flow rate of secondary air pipe inlet increasing, the average swirl intensity value willsignificantly improves, but excess air coefficient has little affection to the swirl intensityon full heat load condition, and to the axial velocity distribution along the axial andradial direction; in addition, when the primary/secondary air ratio increases, the scopeof reverse velocity gradient gets narrower, and the length of the recirculation zone be-comes shorter; in the cross-sections perpendicular to the axial direction, when the dis-tance between the section and the burner outlet was less than100mm, the reverse veloc-ity gradient along the radical direction exists, and disappears at the section200mm farfrom the nozzel；Meanwhile, with the distance between the section and the nozzle outletincreasing, the scope of reverse axial velocity gradient along the radial direction at eachcross-section and the width of recirculation zone decreases.Then the combustion characteristic is studied by the numerical method. The tem- perature outside the nozzle raises as the taper angle of the bluff body gets larger, and themost property value is30.96°. Installation of bluff body outside the support pipe canreduce the flame deflection and the non-uniform temperature field, improve the jet ri-gidity. When the methane concentration in the fuel gas fluctuates between20%and25%,the optimized burner can be operated normally. The bluff body on the fuel pipe wall candecrease the NOxconcentration in the flue gas, the bluff body near the nozzel, on thehand, will increase the NOxconcentration.By numerical simulation and experiment study, the optimized burner can be usedto low calorific value coal-bed methane of20%methane concentration with excellentcombustion stability. In addition, the burner can get preferable jet rigidity and auxiliarycombustion affection used for the coal-bed methane and coal gangue co-combusting inthe circulating fluidized bed.