几种
李文蛟1，邱建荣1，李琳琅2，岑可法3，郑楚光1
(1.华中科技大学，湖北武汉,430074;2.西安交通大学，陕西，西安710049;3.浙江大学，浙江杭州310027)
[摘 要] 浅析了3种形式的无油直接点火煤粉燃烧器的点火机理，提出了无油点火过程中火炬的扩张理论，这一理论较明晰地反映了着火进程。影响火炬扩张的因素有：初始火炬能量强度β、火炬卷吸扩张因子a1,(x)、扩散引起的扩张因子a2,(x)。煤粉火炬在扩张过程中，随时间、空间、空气动力场等的变化，火炬扩张的形式不同。3种形式的无油直接点火煤粉燃烧器性能各异，应根据燃煤特性等因素确立适当的直接点火形式。 [关键词] 电站锅炉；燃烧器；无油直接点火；煤粉；火炬扩张
[中图分类号]TQ534 [文献标识码]A [文章编号]10023364(2003)02006203
煤粉燃烧器无油直接点火技术主要分为以下3种:(1)低温等离子体无油直接点火技术(简称I AB);(2
)感应式无油直接点火技术(简称E AB);
G AB)，这些易燃气体包括乙炔、甲烷等。本文将以无油直接点火技术为重点，剖析其点火机理。
1 低温等离子体无油直接点火技术
低温等离子炬发生装置示意见图1，将该装置用于电站煤粉锅炉无油直接点火示意见图2。阴极与阳极
之间的高压电场，将流过其间的工作气体电离，形成温度达4000K以上的低温等离子体流。描述等离子炬在炉膛引燃煤粉气流，须定义几个参数:
等离子炬能量强度:
β=E
plasma
/Q ig,coal(1)式中,E plasma为等离子炬能量;Q ig,coal为所要引燃的煤粉气流的着火热。
等离子炬在喷入炉膛后，卷吸周边的煤粉气流，卷入的煤粉颗粒迅即燃烧，焦炭等残余物即刻升华，其燃
1—阴极碳棒2—阳极3—等离子炬4—工作气体
图1 低温等离子结构示意
烧热使得火炬能量发生增值；在大量煤粉颗粒急剧升温的同时，由于颗粒中存在挥发分及水分，煤粉颗粒发生炸裂。这些高温碎片穿越火炬，进入周围的气流中。火炬随即与周界发生质的交换，高温火
炬通过对流、辐射耦合作用的方式，向周界进行热传递。火炬在前延过程中，直径增大，范围扩张。定义以点火器出口为原点，其中心轴向为x轴，并简化认为火炬是对称发展的，则火炬直径D(x)可定义为:
D(x)=D0+∫
x
tg(a x)・d x(2) D0为等离子体炬初始直径;a(x)为火焰炬表面在x处
问题讨论
62 热力发电・2003(2)
图2 等离子炬在炉膛内引燃煤粉气流
切向与x轴夹角，为当地时均值。显然，火焰炬要扩张，参数a(x)尤为重要。由图2可见，影响a x的因素有：火炬卷吸周界煤粉气流(m pc)，煤粉颗粒迅即燃烧、焦炭等残余物即刻升华、体积膨胀而引起火炬向外扩张因子a1,(x)；火炬中的挥发分、煤粉颗粒高温碎片进入周界气流m va，高温火炬通过对流、辐射耦合作用的方式，向周界进行热传递(Q ra,co)，并由此引发周界煤粉气流挥发乃至着火，引发火炬向外扩张的因子a2,(x)。这样，即可以认为:
a(x)=f(β,a1,(x),a2,(x))(3) a(x)可正可负，正值意味着火炬在此处为扩张，负值意味着火炬在此处收缩。β值在初始已经确立，其对火炬扩张的影响亦显而易见。
实际上，对a1,(x)起主要影响的是炉膛内空气动力场、煤粉气流的布置等可控因素。煤粉卷入离子炬，可对其在时间的先后、空间的不同位置以及卷入的量上加以控制。对于难燃的无烟煤，可通过适当的安排，让部分浓度较高的煤粉气流较早地卷入离子炬，这时这部分煤粉气流的着火，已基本上同其挥发分等构成没多大关系。当然，在常规着火中，这些因素的影响至关重要。由于无烟煤含碳量较高，其燃烧后释放的热量比较可观，这样，火焰炬的能量增值很快，从而使总的煤粉气流顺利着火。
对a2,(x)起作用的影响因素较多，但主要取决于煤粉气流的一些特征，比如颗粒中挥发分含量、煤粉浓度、颗粒尺寸等。对于挥发分高的煤粉气流，如烟煤、贫煤,a2,(x)起到决定性的影响。
简单地讲，低温等离子体无油直接点火技术，以具有极高能量密度的等离子体炬为核心激发能量，来点燃大量的煤粉气流。因此，其技术关键在于如何恰好地运用这部分能量，在引燃煤粉气流的同时，又使火炬的能量得到最大的增值。
2 感应式无油直接点火技术
作者等人在1997年秋，开始提出了感应式无油直接点火这一概念。在全面总结世界各国在无油直接点火技术、煤粉点火与稳燃技术之后，研制出新型的感应式无油直接点火燃烧器(图3)
。
1—煤粉气流2—环流调节风3—水冷感应线圈4—耐火保温层5—
耐高温合金管(点火室内壁)6—点火室
图3 感应式加热无油直接点火燃烧器
感应式加热无油直接点火燃烧器的点火室内壁面为耐高温合金，外侧为耐火保温层。水冷感应线圈敷设于耐火保温层之外。煤粉气流从点火室的入口端喷入点火室；环流调节风由一次风管与点火室内壁面组成的环状通道送入。其工作原理是，给水冷感应线圈中通入中频电流，在高温合金管及点火室的整个区域，产生强的交变电磁场。在交变电磁场的作用下，耐高温合金管中产生电涡流，高温合金管被加热并迅即升温。在高温合金管，即点火室内壁温度合适时，送入一次风粉气流。煤粉气流迅即点燃，在点火室出口形成强烈燃烧的煤粉火炬，喷入锅炉炉膛。由此而实现煤粉锅炉的无油直接点火。显然，第一级煤粉气流在点火室中，是在高温壁面与强交变电磁场的协同作用下，直接着火，形成火炬，并在喷入炉膛后，进一步引燃第二级煤粉气流。
煤粉火炬与等离子炬相比，前者能量密度远不如后者；但是，在相对小的功率输入下，感应式加热无油直接点火燃烧器可以形成一个初始直径较大的火炬。进入炉膛后，引燃周界煤粉气流的方式也大不相同。煤粉火炬温度相对较低，主要靠常规的化学反应方式进行；等离子炬则靠极高的能量密度，特别是在初始阶段，与煤粉气流发生非常规的物理化学反应。
感应式加热无油直接点火燃烧器比较适合于点燃
问题讨论
热力发电・2003(2)63
挥发分较高的烟煤、贫煤。如果采取诸如增大回流区等强化着火措施，无烟煤也可以引燃。
3 以易燃气体燃烧热作为煤粉气流着
火热的点火技术
图4为以易燃气体燃烧热作为煤粉气流着火热的
直接点火燃烧器，其点火机制比较简单：甲烷、乙炔或其它易燃气体，从燃烧器的中心引入，被点火引燃，燃烧气体喷入炉膛，火焰迅速扩散至周界煤粉气流，煤粉气流在燃烧气体的火炬中进行热解、挥发分乃至碳的燃烧。由于气体燃料的强扩散能力，使火炬的扩张能力也很强。这种机制，同电站锅炉中应用极广的小油点火基本一致，但问题的关键是如何供给易燃气体。电站一般设在城市的远郊，对于一些没有城市煤气系统的地方，还要在电站附近设立易燃气体供给系统。这一点无疑削弱了该点火技术同其它技术竞争的优势
。
图4 以易燃气体燃烧热作为煤粉气流着火热的点火技术示意
但是，利用烃基燃料再燃技术，可以将氧化性气氛
中生成的NO x 降解。如果将该直接点火技术同燃气再燃脱硝技术结合起来，将有很好的发展前景。
4 结 论
(1)本文提出了无油直接点火燃烧器引燃煤粉气
流的扩张理论，清晰地表述了无油点火过程;
(2)在点火过程中影响火炬扩张的直接因素有3个：等离子炬能量强度β；火炬卷吸扩张a 1,(x )；火炬扩散引起的扩张a 2,(x );
(3)煤粉火炬在扩张过程中，随时间、空间、空气动力场等的变化，其扩张的形式不同。强化煤粉着火能力，就在于善于运用各扩张形式;
(4)所列3种形式的无油直接点火燃烧器，性能上各有特征，应根据电站位置、燃用煤种等确立适当的
直接点火形式。
[参 考 文 献]
[1] 李文蛟.感应式加热煤粉锅炉无油直接点火燃烧器的基
础和试验研究[D ].浙江大学博士论文,2000.
[2] Bartok ,williamed.Fossil fuel combustion :a source book
[M ].New Y ork :Wiley ,1991.
[3] [美]L.D.斯穆特，等.煤的燃烧与气化[M ].科学出版
社,1992.
[4] XiangyangDu ,Chengappalli ,G opalakrishnan and K alyan
Annamalai.Ignition and combustion of coal particle stream [J ].Fuel ,vol.74:487494.[5] Dong
ke Zhang and Terry F.Wall.Brief Communication :
an analysis of the ignition of coal dust clouds[J ].Combus 2tion and flame ,1993,92:475480.
[6] 翁卫国，等.北京国华热电厂410t/h 低NO x 燃烧系统机
理及试验分析[J ].电站系统工程,2001,17(2).
(上接第47页)
(5)汽泵的小端盖及Q G400/300型前置泵的大端盖上使用的O 型密封圈易老化变脆而失去密封性能，建议制造厂改进泵盖密封结构。
4 结 语
利用引进技术生产的KSB 给水泵在首阳山电厂
已运行了6年多的时间，性能良好。其所发生的故障，如推力瓦磨损和平衡装置问题，只要进行适当改进是可以得到解决的。
[参 考 文 献]
[1] 郭立君.泵与风机[M ].水力电力出版社,1986.[2] 80CHTA/4型给水泵说明书[Z].沈阳水泵厂.
问题讨论
64 热力发电・
2003(2)
APPL ICATION OF TECHN OLOG Y T O PUT OI L -GUN LEVE LS RAPIDLY INT O OPERATION FOR STABI L IZING COMBUSTION IN THE FURNACE TAO R ONG (41)
………………………………………………………………………………………………………………………………………Through cause analysis of the combustion system faults leading to actu ation of MFT for boiler shutdow n ,a scheme of putting oil -gun levels rapidly into operation has been put forw ard,and the process of implementation ,as w ell as problems needed to pay attention in the course of application are also presented.
RETR OFITTING HEAT RECOVER Y SURFACE OF B OI LER N O.3AT KAIFENG POWER PLANT ZHANG Yi et al(43)
…………The successful retrof itting experiences of heat recovery surface of boiler N o.3at K aifeng Pow er Plant have been presented,the influence of changing some parts of a boiler upon the entire p
erform ance of it being discussed,hence ,the perform ance of entire boiler must be checked when the heat recover y surface of it is to be retrof itted,and corres ponding improved measures should be taken.The butterfl y type f ined tube economizer which w as used in the retrof it enables more heatin g surface can be arranged into a limited space ,and being effective for low ering the exhaust gas temperature of the said boiler.
APPL ICATION AN D IMPR OVEMENT OF K SB FEE D -WATER PUMPS IN SH OU YANG SHAN POWER PLANT YANG Yun -qian et al(46)
………………………
…………………………………………………………………………………………………………………………………………………K SB feed -w ater pumps m anufactured by using imported technology has been put into operation in shouyangshan Pow er Plant for more than six years ,having good perform ance ,but some troubles ,such as w ater leakage from end cover of steam -driven pumps ,oil leakage from bearing pad of the free end,abrasive w ear of thrust bearin g shoes ,and serious w orn out of tungsten alloy of bearing shoes etc.,having also occurred.After adopting appropriate measures ,all trouble problems have been solved,m aking the said pumps can be reliabe in long -term operation.
AN APPR OACH T O RETR OFTTING SCHEME OF HIGH PRESSURE 50MW TURBINE WITH ADJUSTING STEAM EXTRACTION
ZHANG De -hu a et al(48)
…………………………………………………………………………………………………………………………………………………The current situ ation ,existing problems and the necessity of retrof itting high pressure turbines with ad justing steam extraction have been analysed,and the new technology usable for said retrof itting presented.Some views on key problems in the retrof itting ,such as (1)whether the m ax.output under condensing operation condition to be elevated;(2)where are the key points in retrof itting to enhance the eff iciency;(3)how to carry out the acceptance after enhancing eff iciency;(4)measures for low ering the thrust bearing shoe etc.,have been put forw ard.The retrof it of turbine N o.5in Therm al Pow er Plant under Yangzi Petrochemical Works has been com pleted according to the suggested scheme ,m aking the cylinder eff iciency to be enhanced 5.329%.
ADJUSTMENT OF FR ONT BEARING B OX AN D R OT OR ’S UPL IFT DEGREE FOR STEAM TURBINE N O.4AT THERMA L POWER PLANT UN DER QI L U PETR OCHEMICA L INC LONG Zhen -bo et al(53)
…
………………………………………………………………………………Due to found ation subsidence of the front bearin g box is not consistent with that of the rear c yninder of title steam turbine ,great deviation occurred betw een u plift degree of frond bearing box and that of the rotor at bearing pad N o.1,affecting safe operation of said unit.Throu gh supporting the cylinder ,dra wing off the front bearing box ,and grinding the tableplate of found ation etc.,the ad justment of uplift degree for the front bearing box and the rotor has been com pleted,m aking the concentricity of them both to be consis 2tent with each other.After m ajor repair ,the unit has successfully started up on its f irst run.
A STU DY ON DETECTION TECHNIQUE REG AR DING TRACE AMOUNT OF SODIUM IONS IN HIGH LY PURE WATER TIAN Li et al(56)
…………
………………………………………………………………………………………………………………………………………………………………For trace amount of sodium ions below densit y of 5
μg/L ,detection can be carried out b y using second derivative flame spectroscopic method.This method is fast ,being simple and easy to use ,and having high accuracy.It is hopeful to spread and popularize this method b y cooperating with utilization of home -m ade intelligent analysers having b
etter perform ance/cost ratio.
H ORIZINTA L F LOCCU LATION AN D SE DIMENTATION BASIN USE D FOR PURIFICATION OF CIRCU LAT OR Y COOL ING WA 2TER IN POWER PLANT ZHANG Cui -hong et al(58)
………………………………………………………………………………………………………………I n view of the problems concerning high content of silt and suspended m atters in circulatory cooling w ater in Shengli Pow er Plant ,a horizontal flocculation and sadimend ation b asin has been constructed in the w ater -pool of cooling tow er ,After putting the said b asin into operation ,the turbity of circulatory cooling w ater has been low ered about 68%,the w ater qu ality obviously improved,so that the level of safe and economic o peration of the unit can be enhanced.
AN APPR OACH T O THE FEE DBACK MODE OF DEN VA L VE POSITION ZHANG lu(60)
……………………………………………The retrof it of DEN control s ystem for unit N o.1at H u aneng Dezhou Pow er Plant has been described,the feed -b ack defects existing in double channel high -selected position of linear variable differential transformer (L V DT )in DEN s ystem having been pointed out.C ause analysis is m ade ,and measures of im provement are given.
E LEMENTAR Y ANA LYSIS O
F MECHANISM
G OVERNING SEVERA L COA L -POWDER BURNERS USE D FOR OI LLESS DIRECT IGNITION L I Wen -ju ao et al(62)
…………………………………………………………………………………………………………An elementary analysis of ignition mechanism governing three types of coal -pow der burners used for oilless direct i gnition has been m ade ,and a torch expanding theory in the process of oilless direct ignition being suggested.The said theory can distinctly reflect the process of catching f ire.The factors influencing upon torch expanding are :the energy intensity B of initial torch;expanding factor (α)1,(x)due to torch ’s rolling suction ;and expanding factor (α)2,(x)caused by diffusion.I n the expanding process ,the coal pow der torch ’s expanding form is varying with the change of time ,space ,and air flow f ield.The perform ance of coal -pow der burners for three said types is different ,an ap 2propriate direct ignition style should be determined on the b asis of fuel coal properties etc..
FAI L URE ANA LYSIS OF STEAM TURBINE ’S BEARING PAD DAMAGE GUAN Fu -an(65)
………………………………………Vibration under overload condition had occurred due to thegoverning valve doesn ’t w ork smoothly on a 3000K W unit in Jiaozuo G eneral Chemical Plant ,
H enan Province ,leadin g to typical failure of bearing pad d am age caused by rolling compaction while the lubrication s ystem of b ack -up bearing pad w as in norm al condition.The course of failure and status of equipment d am age are presented,and countermeasures for preventing such failures are given.
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