大学精品课件：燃气燃烧第6章.ppt

1、2023-3-112023-3-1201012023-3-132023-3-14Burner for industrial&commercial applications can be broadly classified under 5 headings,based on the means adopted for mixing gas&air:1.Diffusion-flame,post-aerated,neat gas,non-aerated,luminous burnerGas issuing from the burner or pipe is neat,no premixing o

2、f air and gas takes place.The necessary air for combustion arrives at the reaction zone from the surrounding atmosphere by diffusion or entrainment after burner nozzle.Laminar flow,turbulent flow2.Atmospheric burner,Natural-draught,Gas Blast BurnerGas entrains a%of the air for combustion before ente

3、ring the burner.This is achieved by an atmospheric injector,where the gas under pressure entrains atmospheric air.Flame:short&intense.Gas pressure 10-20mbar,air injected less than stoichiometric,secondary,LP Gas pressure increase,air injected=stoichiometric,no 2nd air,HP2023-3-153.Air-blast,All or p

4、art of the air required is supplied at pressure above atmospheric by fan or compressor.Air entrains gas.Another premix system4.Nozzle-mix burnersno prior mixing of the gas and air until the burner nozzle.Gas and air proportioned separately by linked valves or other techniques and fed independently t

5、o burner nozzle.The air and gas enter separate manifolds prior to burner nozzle where their flow patterns are controlled.Mixing by this method is very positive,intense rates of combustion are developed for high temperature work5.Other burner systemPulsating combustor,catalytic combustor,radiant tube

6、s,immersion tube burner etc.2023-3-162023-3-172023-3-18Neat gas supplied to burner head and mixes with surrounding atmospheric airLaminar diffusion/posted aerated flames:mixes by molecular diffusionTurbulent post-aerated flame:Eddy diffusionMixing+combustionLuminous appearance:unburnt gas being crac

7、ked by heat developed by the outer flameHistorically in the era of manufactured gas,diffusion flame burners dominated the design of most domestic,commercial and low temperature industrial heating plant2023-3-192023-3-110节流圈节流圈或阀门或阀门燃气燃气2023-3-1112023-3-112集气管集气管涡卷形管子涡卷形管子2023-3-1132023-3-1142023-3-1

8、152023-3-1162023-3-117Laminar Post-aerated Burner for Natural Gas2023-3-118Laminar Post-aerated Burner for Natural Gas2023-3-119Turbulent Post-aerated Burner for Natural Gas2023-3-1202023-3-1212023-3-1222023-3-1232023-3-124四，管式扩散燃烧器的计算四，管式扩散燃烧器的计算2023-3-125五，炉床式扩散燃烧器的计算五，炉床式扩散燃烧器的计算2023-3-126tunnel

9、mixing burners,or package burners,Air supply at pressure,discharged through an annulus or annuli at the burner head or face.Gas ports,which again may be of many forms,admit gas into the air stream Combustion takes place either totally or partially in a burner tunnel or at the burner face.Air/gas mix

10、ing and combustion takes place simultaneously at the burner nozzle,usually in a refractory tunnel or quarl.The tunnel acts as a means of flame retention:1.heat stored in the refractory walls serves to stabilise the flame,2.recirculation of flame gases keeps the root of the flame at temperatures enco

11、uraging ignition.This enables satisfactory operation at quite low throughputs,both in stoichiometric conditions and with a large excess of air.Light-back is unlikely to occur,since combustion and mixing are co-current.2023-3-1272023-3-1282023-3-129British Gas Self Proportioning Tunnel Mixing BurnerL

12、arge area for mixing,a series of air jets is used surrounding the central gas pipe,all discharging axially into a refractory tunnel,or quarl.Air jets provide a recirculation stabilising system.Multi-tube versions of this burner are used for large loadings,in excess of 300 kw2023-3-130Stordy-Hauck NM

13、G BurnerThis type of burner provides low velocity gas entry,whilst air enters in three ways:1.Tangentially in a plane at 90 to the flow axis,through a series of holes in the gas pipe.2.Axially through a ring of small holes situated in a stepped collar surrounding the gas pipe.3.Axially,through an ou

14、ter annulus formed by the stepped collar of the gas pipe and the burner quarl Tunnel mixing burner with parallel flow discharge and stabilisation by hot refractory surface2023-3-131Urquhart NM BurnerTunnel mixing burner with opposing gas and air swirls to assist mixingAir is supplied through a serie

15、s of air jets inclined to burner axis,Gas entering through a central orifice.Mixing surface area is increased by using a series of air orifices rather than an annulus.The air jets constitute a means for forming stabilising eddies2023-3-1322023-3-1332023-3-134燃气喷嘴燃气喷嘴2023-3-135Tunnel mixing burner wi

16、th swirling flow discharge and stabilisationOpposed gyrations in the two streams,setting up high relative velocities.Overall flow from the burner is largely axial,since the gyration of the air stream is relatively low speed.Combustion is stabilised within a divergent refractory quarl,material and he

17、at transfer in the swirl system encourage ignition at the entry to the quarl.2023-3-1362023-3-137由由2张平行钢板卷制而成，具有张平行钢板卷制而成，具有2个螺旋通道。个螺旋通道。燃气和空气燃气和空气分别从偏心切向进入各自通道，边旋转边向前流动，在燃分别从偏心切向进入各自通道，边旋转边向前流动，在燃烧器出口开始混合。烧器出口开始混合。特点：燃气与空气接触面积大，混合特点：燃气与空气接触面积大，混合均匀，燃烧器调节范围大。均匀，燃烧器调节范围大。2023-3-138空气切向进入空气切向进入,燃气轴向进入

18、燃气轴向进入,在高速旋转的空气在高速旋转的空气带动下带动下,燃气也随之旋转燃气也随之旋转,并进行混合燃烧。火焰并进行混合燃烧。火焰呈圆筒型。空气在圆筒形火焰与燃烧室壁中间旋呈圆筒型。空气在圆筒形火焰与燃烧室壁中间旋转流动。转流动。2023-3-1392023-3-1402023-3-1412023-3-1422023-3-1432023-3-144已知：已知：燃气热值，燃气热值，密度，密度，理论空气需要量，理论空气需要量，燃气压力，燃气压力，空气压力，空气压力，燃气用量燃气用量（热负荷），（热负荷），燃气温度，燃气温度，空气预热温度，空气预热温度，过剩空气系数过剩空气系数选取：选取：喷管中燃气

19、流速，燃气空气混合物速度喷管中燃气流速，燃气空气混合物速度计算：计算：燃烧器尺寸燃烧器尺寸2023-3-1451.0,1.5(6 10ag图的结构时）1.计算出口截面燃气和空气的流速计算出口截面燃气和空气的流速2000000,(,22ogoaTTPTTPTT 状态方程）或阻力系数阻力系数 P燃烧器前燃气或空气的表压（燃烧器前燃气或空气的表压（Pa）2023-3-14636004gggggLFFd236004aaaagoutaLFFdd2244agoutaddF2023-3-1470gogTT0aoaTT2023-3-14836004mmmLdmagLLLVm混合物出口流速m/s2030m/s选取 2023-3-149例题63：燃气流量 300Nm3H例题64：天然气流量40Nm3H