作者简介:　李学明(1965),襄樊发电有限责任公司高级工程师,华北电力大学(北京)在读博士研究生。

过热蒸汽温度控制系统优化李学明1,刘吉臻1,李志军1,朱广华2,李　军2(11华北电力大学,北京　102206;21襄樊发电有限责任公司,湖北襄樊　441141)[摘　要]　针对300MW 火电机组锅炉过热汽温系统二级减温器后两侧温度的差异情况,确定了过热汽温控制系统的优化方案:增加1个副调节器,使每个二级喷水阀单独由1个串级回路的副调节器输出进行控制。

优化后的系统可以对温度高的一侧增加喷水量,对温度低的一侧减少喷水量,保证二级喷水总量不变。

该方案经仿真实验后应用于实际,取得了明显效果。

该优化方案适用于采用分散控制系统且有分隔屏过热器的锅炉。

[关键词]　火电机组;过热蒸汽;温度控制;控制系统优化;调节[中图分类号]T K323 [文献标识码]A [文章编号]10023364(2004)05004203 目前,世界各国制造的大容量高参数锅炉过热蒸汽温度多数控制在540℃以上。

为保证汽轮机的安全经济运行,在规定负荷下,对过热蒸汽温度提出了较高的要求,即要将其控制在额定值的+5℃～-10℃范围内。

但过热蒸汽系统是一个有迟延、有惯性的复杂热力系统,实际运行中经常出现超温和温度过低的情况。

本文介绍襄樊电厂在3号锅炉上对过热蒸汽温度控制系统所做的试验、分析及优化工作。

1　过热汽温热力系统结构襄樊电厂3号炉是上海锅炉厂生产的SG 1025/17.53M842亚临界自然循环汽包炉,过热蒸汽压力和温度分别是17.53MPa 和540℃。

过热汽温热力系统结构如图1所示,从锅炉汽包的汽水分离器分离出来的蒸汽经低温过热器加热后,由一级减温器减温后,分别进入左右(A 、B )侧分隔屏过热器加热。

二级减温器控制分隔屏过热器出口过热蒸汽温度。

过热蒸汽经二级减温器后进入联箱中混合,再进入高温过热器,在高温过热器中加热后,经过热蒸汽管道进入汽轮机高压缸。

图1　过热汽温热力系统结构2　过热蒸汽温度控制过热蒸汽温度设计采用喷水减温,即通过改变减温水阀门开度来改变减温水量,控制蒸汽温度。

一级喷水阀控制采用典型的串级控制系统,系统中有主副2个调节器,分隔屏过热器出口温度测量值作为主信号,一级喷水阀出口温度信号是导前信号,主调节器输出作为副调节器的定值。

汽机第一级压力信号经函数修正后作为主调节器的定值。

二级喷水阀控制与一级喷水阀控制相似,不同之处在于导前信号取的是二级喷水阀后温度的平均值。

图2是二级喷水阀串级控制技术交流　42　热力发电・2004(05)系统简图。

机组的控制系统由WDPF Ⅱ型分散控制系统构成。

图2　二级喷水阀串级控制系统3　过热蒸汽温度控制现状及存在的问题过热蒸汽温度控制的任务是维持高温过热器出口温度在允许范围之内,并保护过热器,使其管壁温度不超过允许的工作温度。

引起过热蒸汽温度变化的扰动因素归纳起来主要有蒸汽流量、烟气传热量和减温水量,,控制对象的动态特性都是有迟延、有惯性且有自平衡能力的。

过热蒸汽温度采用传统的串级控制系统借助两级喷水阀进行控制。

从过热蒸汽系统的结构可以看出,蒸汽经一级喷水后,分两路进入分隔屏过热器,因此,不可能用一级喷水阀控制两侧蒸汽温度达到同一设定值。

现场试验发现,分隔屏过热器两侧出口温度偏差较大。

在蒸汽流量和烟气传热量基本不变的情况下,一级喷水阀门开度增加10%,流量增加约10t/h ,二级减温器前A 侧的温度比B 侧高15℃。

因流过A 、B 两侧分隔屏过热器的蒸汽流量基本相等,二级喷水流量也相同,混合后的蒸汽温度波动较大,致使过热蒸汽温度经常偏高或偏低。

一级喷水控制只起粗调作用,是二级控制的基础,主要靠二级喷水控制过热蒸汽温度。

因两侧喷水阀对蒸汽温度影响的动态特性不相同,但系统设计中,分隔屏过热器后A 、B 两侧喷水阀门采用的串级控制系统副调节器输出的却是同一个指令,所以无法消除A 、B 两侧分隔屏出口蒸汽温度的偏差,从而造成过热蒸汽温度波动很大,经常超出允许偏差,影响机组安全经济运行。

4　过热汽温控制试验及控制优化4.1　一级喷水试验及控制优化通过对3号锅炉进行试验,得到了一级喷水扰动下低温过热器系统的动态特性曲线(图3)。

实际上,因为一级喷水控制是二级喷水控制的基础,只起粗调作用,所以对一级喷水控制系统不作改动,只是考虑到蒸汽流量、燃料量指令等外部扰动对主蒸汽温度的影响,添加了它们扰动的前馈信号,以提早补偿扰动对系统的影响。

图3　一级喷水扰动下汽温响应特性4.2　二级喷水试验及控制优化图4是二级喷水扰动下动态特性曲线(襄樊电厂3号机组,负荷210MW ),图中上面两幅曲线是分隔屏过热器A 、B 两侧减温水的流量,中间两幅曲线是过热器A 、B 两侧喷水阀后的温度,下边左侧曲线是主蒸汽温度,右侧曲线是燃料量指令曲线。

图4　二级喷水扰动对象的动态特性根据现场试验得到的数据,确定A 、B 两侧分隔屏喷水阀后蒸汽温度的偏差,是造成混合后的过热蒸汽温度有很大波动的直接原因。

因此对原来的串级控制系统结构进行了优化,具体方案是:将原来2个二级喷水阀由串级控制回路的1个副PID 调节器的输出进行控制,改为增加1个副调节器,使每个二级喷水阀单独由1个串级回路的副调节器输出进行控制。

优化后的系统可以对温度高的一侧增加喷水量,对温度低的一侧减少喷水量,保证二级喷水总量基本不变。

这样A 、B 两侧二级喷水阀后的过热蒸汽温度基本相等,使混技术交流热力发电・2004(05)43合后的过热蒸汽温度波动较小。

二级喷水控制优化原理见图5。

图5　二级喷水控制方案优化原理5　过热蒸汽温度控制效果及应用前景借助WDPF 分散控制系统上述控制方案在襄樊电厂3号机组上得以实现。

图6是2002年12月12日在襄樊电厂3号机组上主蒸汽温度定值扰动下系统的响应曲线。

现场运行表明,优化后的控制系统在控制性能方面有较大的提高,在正常运行工况下,机组没有出现温度偏高或偏低现象,保证了机组的安全性和经济性。

由于该方案无需改造锅炉系统及分散控制系统的硬件设备,只需对分散控制系统的软件组态做少量修改,就能达到较好的控制效果,所以,对于采用分散控制系统且有分隔屏过热器的锅炉,该方案具有较好的应用前景。

图6　主蒸汽温度定值扰动下系统的响应曲线6　结　论在目前运行的300MW 机组上,应用本文研究的方案,对分散控制系统组态只需做少量修改,即可明显改善过热蒸汽温度的控制品质,提高锅炉运行的安全性和经济性,值得有关单位借鉴。

[参　考　文　献][1]　能源部西安热工研究所.热工技术手册[M ].水利电力出版社,1992.[2]　李遵基.热工自动控制系统[M ].中国电力出版社,1997.[3]　黄忠霖.控制系统MA TLAB 计算及仿真[M ].国防工业出版社,2001.(上接第39页)改变。

直径越小,速度越高,雾化平均粒径越细。

采用音速设计可以获得较好的雾化效果。

(2)气流射入角越大,气液比越大,雾化粒径越细,但是当射入角过大时,气耗量增加,轴向动量损失大,不利于二次雾化。

(3)油液沿中心柱形成的液膜厚度对雾化粒径的大小影响很大。

液膜厚度越小,雾化效果越好,但在实际应用中要注意避免液体通道的堵塞。

[参　考　文　献][1]　A.H.Lefebvre.Atomization and sprays[M ].1989.[2]　王娇娜,赵忠祥,李育民,等.预膜气流式雾化器的结构尺寸对雾化结果的影响[J ].化学工业与工程,1998,(15):3438.[3]　I.S.Carvalho ,M.V.Heitor.Liquid Film Breakup in aModel of a Prefilming Airblast Nozzle [J ].Experiments inFluids.1998,(24):408415.[4]　高家锐.动量、热量、质量传输原理[M ].重庆大学出版社,1987.技术交流　44　FEATURES AN D METH ODS OF HEAT RECOVER Y STEAM GENERAT OR ASME PTC 4.4ZHAO Yong jian ,L IU Zhen qi(32)…………………………………………………………………………………………………Abstract :Test items ,test technology ,and test method in the gas turbine heat recovery steam generators (HRSG )performance test code ASME PTC4.4have been presented ,the HRSG efficiency test technology and the heat loss method used for efficiency calculation being emphatically described.K ey w ords :heat recovery boiler ;performance test code ;efficiency test ;heat loss methodSTU DY ON ABN ORMAL VIBRATION OF GENERAT OR ’S REAR BEARING FOR H OME MADE 125MW (135MW)UNITS HU Jian xin(35)……………………………………………………………………………………Abstract :Directing against the problem of abnormal vibration of generator ’s rear bearing for home made 125MW (135MW )units ,analysis of the said problem has been carried out in detail based on vast amount of field test data obtained from thorough tests and study ,and on making full use of re 2search achievements regarding rotor dynamics ,and combining with work experience of many years in the field ,suggesting ways for remedying and re 2solving the said problem.Practice shows that the analysis and remedial method for the vibration problem to be effective.K ey w ords :125MW unit ;turbine ;generator ;bearing vibration ;rotor dynamicsINF L UENCE OF STRUCTURAL DIMENSIONS UPON THE AT OMIZING PERFORMANCE OF A PREFI LMING SPRAY N OZZ L E ZH OU Chun li ,CHENG Chong ming ,L I Ding kai et al(38)………………………………Abstract :Through changing the key parameters of a prefilming airblast spray nozzle ,such as air injecting angle ,diameter of the air passage ,and the thickness of the ring form liquid film etc.,the influence of structural parameters upon atomizing performance of the spray nozzle has been studied ,obtaining the regularity of atomizing particles variation ,providing basis for optimal design of the atomizing spray nozzles.K ey w ords :prefilming airblast spray nozzle ;regularity of atomizing particles variation ;optimal designPARTIC L E SIZE DETERMINATION OF L IQUID D R OPL ETS IN G AS F LOW B Y USING IMPACT DI 2APHRAG M METH OD L I Shen ,YU Juan li ,HUI shi en et al(40)………………………………………………Abstract :The working principle and measuring method of particle size determination for liquid droplets carried in gas flow by using impact diaphragm method have been presented ,and the operation steps for applying magnesium oxide film or vaseline film on the carrier glass being given.The said method has low cost ,being easy to operate ,and suitable for measuring liquid droplets or fog droplets in outlet or inlet of mist remover in flue gas cooling facility and wet desulphurization system of boilers.K ey w ords :liquid droplets ,fog droplets ,particlel size measurement ;carrier glass ;impact diaphragmOPTIMIZATION OF CONTR OL SYSTEM FOR SUPERHEATE D STEAM TEMPERATURE L I Xue ming ,L IU Ji zhen ,L I Zhi jun et al(42)…………………………………………………………………………………Abstract :In view of temperature difference on two sides after secondary stage desuperheater in the superheated steam system of boiler for 300MW thermal power unit ,an optimization scheme of control system for superheated steam temperature has been determined.i.e.a secondary regulator has to be added ,making each secondary stage water spraying valve to be separately controlled by the output of secondary regulater in a cascade circuit.The optimized system can increase the spraying water quantity for the high temperature side ,and decrease the spraying water quantity for the low tem 2perature side ,ensuring the total secondary stage spraying water quantity to maintain constant.After simulation test ,the said scheme has already been used in practice ,obtaining obvious effectiveness.The said scheme is suitable for using to boilers with distributed control system and with separative platen superheater.K ey w ords :thermal power unit ;superheated steam ,temperature control ;optimization of control schemeMU LTI SENSOR INFORMATION MERGING TECHN OLOG Y AN D IT ’S APPL ICATION IN VIBRITION FAU LT DIAGN OSIS OF R OTAR Y MACHINES JIN Feng hua ,L I Lu ping(45)………………………………Abstract :A brief description of the multi sensor information merging technology has been bining with the requirements and properties of vibration fault diagnosis system for rotary machines ,an approach of the basic hierarchic structure of the diagnotic system by using the information merging technology has been carried out ;and making the hierarchy of information merging to correspond with the functions of fault diagnosis ,a model of information merging for vibration fault diagnosis of rotary machines has been put forward ,and the realizing method of information merging on dif 2ferent hierarchy of the vibration fault diagnosis system for rotary machines being discussed.K ey w ords :information merging ;multi sonser ;fault diagnosis ;rotary machine ;rotor vibrationOPERATION DIAGN OSIS SYSTEM BASE D ON NEURAL NETWORK FOR THERMAL POWER UNIT GE Xin ,GE Yan ,H e Xin et al(49)………………………………………………………………………………………Abstract :An operation diagnosis expert system for thermal power unit has been designed by fusing the neural network and the pattern recognition tech 2nology on TPRI SIS platform.Trough failure simulation test in detail ,a practical diagnosis example on 660MW unit has been analysed by using the said system ,obtaining good results of failure recognition.K ey w ords :thermal power plant ;operation diagnosis ;SIS ;expert system ;neural network ;pattern recognitionREAL IZATION OF INTEGRATE D WDPF T YPE DCS CONTR OL FOR HEAT SUPPLYING POWER GENER 2ATING UNIT WITH F L UIDIZE D BE D QIAO Zheng yu ,CHEN Xiu ping(53)…………………………………Abstract :In view of the situation concerning installation of several circulating fluidized bed (CFB )coal fired boilers and so many small steam turbines in Daliuta Thermal Power Plant ,Combining with the requirements from production practice for the system ,during the time of retrofitting WDPE type DCS control system for adding capacity ,the electriy control has been included in the said retrofitting ,to make an integrated system of DCS ,SCS ,MCS and electric control system.Thus ,the problem of insufficient I/O capacity in WDPE system has been resolved ,having improved the situation of inadequate space in the operators ’station and of monitoring in a tense at mosphere ,realized display of the remote operation and the state of the electric control ,made the system to be even more safe and reliable.K ey w ords :heat supplying unit ;control system ;DCS ;WDPF ;electric control ;adding capacityTEST METH OD OF INTEGRAL PERFORMANCE AUT OMATIC CAL IBRATION SYSTEM FOR THERMO 2E L ECTRIC COUPL ES SHANG Li ping(55)…………………………………………………………………………Abstract :Based on experiences obtained from practical inspections ,a test method of integral performance automatic calibration system for thermo electric couples has been summarized out.The said method can be used for the acceptance of calibration system ,for establshment of standard ,for recheck authentification ,and for inspection in application ,as well as for affirmation of system performance after upgrading the software edition of the system.At the sametime ,the problems occurred in tests and elimination of them have also been presented.K ey w ords :temperature measurement ;high temperature measuring value ;automatic calibration system of therma electric couple ;system acceptanceAPPL ICATION OF WAVE L ET TRANSFORM FOR N OISE E L IMINATING FR OM CHR OMAT OGRAPHIC SIG 2NALS AN D SOFTWARE DESIGN THEREOF ZHAO Xiao dan ,YANG W an sheng(59)………………………Abstract :A processing method of eliminating noises from chromatographic signals based on wavelet transform has been put forward.Through process 2ing of concrete data ,it shows that the said method can successfully eliminate noises from chromatographic signals ,creating conditions for carrying out accurately chromatographic analysis.At the same time ,software design for realizing noise elimination technology based on wavelet transform has been made ,using three kinds of software ,i.e.VB ,Componet Works ,and Matlab ,for hybrid programming ,making the programme to be simple ,and in 2terface to be friendly.。