基于計(jì)算機(jī)的電廠鍋爐監(jiān)控系統(tǒng)外文翻譯、中英文翻譯、外文文獻(xiàn)翻譯,基于,計(jì)算機(jī),電廠,鍋爐,監(jiān)控,系統(tǒng),外文,翻譯,中英文,文獻(xiàn) Computer system for monitoring power boiler operationJ Taler1,B We glowski1,W Zima1*,P Duda1,S Gra dziel1,T Sobota1,A Cebula1,and D Taler21Institute of Process and Power Engineering,Cracow University of Technology,Krako w,Poland2AGH University of Science and Technology,Krako w,PolandThe manuscript was received on 2 February 2007 and was accepted after revision for publication on 24 October 2007.DOI:10.1243/09576509JPE419Abstract:The computer-based boiler performance monitoring system was developed to per-form thermal-hydraulic computations of the boiler working parameters in an on-line mode.Measurements of temperatures,heat flux,pressures,mass flowrates,and gas analysis datawere used to perform the heat transfer analysis in the evaporator,furnace,and convection pass.A new construction technique of heat flux tubes for determining heat flux absorbed bymembrane water-walls is also presented.Flux tubes mounted at different levels in the boilerwork at similar conditions as water-walls tubes.The current paper presents the results ofheat flux measurement in coal-fired steam boilers.During changes of the boiler load,the necessary natural water circulation cannot beexceeded.A rapid increase of pressure may cause fading of the boiling process in water-walltubes,whereas a rapid decrease of pressure leads to water boiling in all elements of the boilersevaporator water-wall tubes and downcomers.Both cases can cause flow stagnation in thewater circulation leading to pipe cracking.Two flowmeters were assembled on central downco-mers,and an investigation of natural water circulation in an OP-210 boiler(with steam capacityof 210?103kg/h)was carried out.On the basis of these measurements,the maximum rates ofpressure change in the boiler evaporator were determined.The on-line computation of the conditions in the combustion chamber allows for real-timedetermination of the heat flowrate transferred to the power boiler evaporator.Furthermore,with a quantitative indication of surface cleanliness,selective sootblowing can be directed atspecific problem areas.A boiler monitoring system is also incorporated to provide details ofchanges in boiler efficiency and operating conditions following sootblowing,so that the effectsof a particular sootblowing sequence can be analysed and optimized at a later stage.The current paper also presents an analysis of stresses occurring in the boiler drum and thedowncomer junction during-start up and shut-down of the boiler.Keywords:power boiler,heat flux measurement,evaporator,natural water circulation,performance and thermal stress monitoring1INTRODUCTIONPower boiler shut-down and start-up processes,aswell as boiler load changes,should be carried outsuch that no allowable stresses in the boiler areexceeded,while the essential natural circulation ismaintained at all times.A rapid increase of pressure may cause fading ofthe boiling process in water-wall tubes,whereas arapid decrease of pressure leads to water boiling inall elements of the boilers evaporator water-walltubes and downcomers.Both cases can cause flowstagnation in water circulation in the evaporatorthat leads to pipe cracking.Thus,the flowmeterswere assembled on two downcomers of the OP-210boiler(theboilercapacityis210?103kg/hoflive steam with 9.8 MPa pressure and 54052108Ctemperature).An investigation of natural water circu-lation was carried out and the maximum rates of*Corresponding author:Institute of Process and Power Engineer-ing,Cracow University of Technology,AL.Jana Pawla II 37,Krako w 31-864,Poland.email:zimamech.pk.edu.pl13JPE419#IMechE 2008Proc.IMechE Vol.222 Part A:J.Power and Energypressurechangeintheboilerevaporatorweredetermined.Stresses are mainly controlled by the so-called cri-terion elements that limit the rate of boiler loadchanges.One such elements is the boiler drum,andin particular its connection with the downcomers.The distribution of equivalent and circumferentialstresses for these connections depends,to a largeextent,on the boiler drums heating and coolingrates.The boiler manufacturers reserve the right torecommend the specific heating and cooling ratesfor boiler drums,that often could be larger.Byincreasing such rates the operation time of a boilerunder transient conditions can be shortened.The monitoring of an operating boiler also includesthe monitoring of a wide range of other parametersthat affect its efficiency and safety.The current paper presents a system that allowson-line monitoring of operating conditions for anevaporator.Its basic element is a set of original heatflux tubes used to determine the temperature andheat load distribution along the height of the boilerscombustion chamber.This heat distribution is veryimportant for the proper operation of the evaporatorand combustion chamber 14.The obtained resultscould also be used to monitor the circulation ofwatervapour mixture and the scale deposition onthe inner surfaces of waterwall tubes.The system issupplemented by measurements of water mass flowcirculating in the boilers evaporator from two centraldowncomers.The monitoring of thermal-flow conditions of aboiler in the on-line mode should also take intoaccount the variability of the excess air number,which directly influences the boiler efficiency.Itsvalue can be reduced by means of the appropriateair distribution(primary,secondary,and over-firedair(OFA)nozzles)while using the heat flux tubeslocated at different levels.Air distribution shouldensure the emission of NOxand the content of flam-mable elements in fly-ash below allowable levels.Thecorrect estimation of the degree of slagging in theboilers combustion chamber is also very important.Time changes of the chamber wall slagging coeffi-cient,along with changes of water mass flows toinjection attemperators,and the temperature of fluegas can be the basis for an automatic activation ofslag and ash blowers in the boiler.Comparing the computed and measured super-heated steam mass flowrate,the average slaggingdegree of a combustion chamber wall is determinedin the on-line mode.This allows for full automationof soot blowers operating in a combustion chamber,therefore reducing the medium usage in soot blowersand increasing the water-wall lifetime.Theon-linecomputationofthecombustionchamberallowsforreal-timeheatflowratedetermination,whichis transferred to the power boiler evaporator.Based onthe energy balance for the power boiler evaporator,the superheated steam mass flowrate is computed(takingintoaccountthewaterflowrateforattemperators).Several investigators have contributed to variousaspects of thermal performance and remnant lifemonitoring of power plants.The monitoring of thermal conditions in powerplants is considered in many papers 5,6.Afinite-element-basedfatiguemonitoringsystemdeveloped for on-line monitoring of fatigue degra-dation of components used in various plants isshown in reference 7.Paper 8 describes practicalexamples where component life monitoring hasbeen implemented on power plants.The results offull-scale investigations on fouling in convective bun-dles of coal-fired boilers are presented in paper 9.2HEAT LOAD MEASUREMENT OF THECOMBUSTION CHAMBER WALLSDue to the difficulties occurred while measuring thehigh temperature of flue gas,the measurement ofthe heat load of the boilers combustion chamberusing the thermometric inserts presented in Fig.1was proposed.The heat load is the density of theabsorbed heat flux,defined as the ratio of the heatflowrate absorbed by the wall to the projected wallsurface area,and was determined on the basis oftemperature measurement of the insert located onFig.1Heat load measuring insert:I,waterwall pipe;II,eccentric pipe;III,heat resistant metal sheetingcover;IV,pipe leading the thermoelementsoutside the boiler,and 15 location of thethermoelements14J Taler,B We glowski,W Zima,P Duda,S Gra dziel,T Sobota,A Cebula,and D TalerProc.IMechE Vol.222 Part A:J.Power and EnergyJPE419#IMechE 2008its front side(points I to IV in Fig.1).The insert wasmade of carbon steel,and the temperature wasmeasured using four Ni-NiCr thermocouples(outsidediameter of the sheath equalling 1 mm),placed inholes located parallel to the axis of the insert toavoid errors caused by heat conduction along theaxis of the thermoelement outputs.This distributionof the openings causes the temperature of the ther-moelement to remain constant,and assures thatheat flows neither in nor out of the point in whichthe temperature is measured.The thermoelementsare led out at the back of the tubes.A 20 mm widegroove,in which the thermoelements are located,iscovered by a 3 mm heat resistant metal sheet pre-venting burning of the thermoelements(Fig.1).The insert was made of 20G steel,for which thethermal conductivity k was determined by theexpressionkT 53:26?0:02376224?T W=mK1To check whether the insert was able to work safely,computations using the finite-element method wereperformed.The pressure of the medium was assumedto be p 11 MPa and the temperature of the systemwas assumed to be T 3708C.The results of thosecomputations,carried out with the use of theANSYS software,are presented in reference 10.Allowablestressequals118 MPa,whereasthemaximumstressattheassumedloadequals73 MPa.Thus,the maximum stress is lower than theallowable one.2.1Description of the heat load determinationmethodIn order to determine the waterwall heat load depen-dency q q(DT),temperatures T1,T2,T3,and T4measured at four points of the front insert were used(Fig.1).The heat distribution was computed using themethod of finite capacity from the CFD software 11.DT is the average temperature differenceDT T1 T22?T3 T422Due to the symmetry of the temperature field in theinsert,only half of the cross-section of the insert wasanalysed.Changes of the density of the heat flux onthe surface of the insert and of the neighbouringtubes depend on the slagging factorc,which changessignificantly with location.The dispersion of the heatflux density on the surface of the insert and in thetube on the side of the furnace has been approxi-mated using a step line.The back surface of theinsert and the tubes was completely insulated.Onthe inside surface of the tube,the boundary conditionof the third kind,requiring the knowledge of the heattransfer coefficientaand the temperature of themedium Tmwas assumed.The heat load can be expressed as a function of themeasured temperature differenceq a b?DT3where the temperature difference DT is expressed byequation(2).Temperatures T1,T2,T3,and T4were computedusing the CFD software 11 for various values ofthe heat load q and the heat transfer coefficienta.The temperature of the medium was assumed to beTm 3208C.This is the temperature of the watervapour mixture in the evaporator of the OP-210boiler.The results of the numerical calculations wereapproximated using the function(3)by means ofthe least squares method.Constants a and b,whichdepend on the heat transfer coefficientaon theinside surface of the insert,equala 8367:9549W=m2;b 5357:8165W=m2Kfora 5000W=m2Ka 6800:9790W=m2;b 5432:89W=m2Kfora 10000W=m2Ka 4899:67W=m2;b 5519:0615W=m2Kfora 50000W=m2KThe analysis of the changes of the heat load q infunction DT proved that the heat transfer coeffi-cientaon the inside surface of the pipe has aminor influence on the heat load value q 10.This slightly surprising result can be explained bythe fact that when the value ofadecreases,the cir-cumferential heat flow from the front of the insertto its back side increases,which causes a drop inthe temperature through the thickness of the wall.Simultaneously,the reduction of theacoefficientcauses an increase of the insert temperature onthe side of the furnace,which in turn causesreduction of the thermal conductivity k determinedby equation(1)and increasing of the temperaturedrop through the thickness of the wall.Those twoopposite phenomena make q practically indepen-dent froma.For the on-line computations the following depen-dencyq q(DT)fora 10 000 W/(m2K)wasassumedq 6800:979 5432:89?DT W=m24Computer system for monitoring power boiler operation15JPE419#IMechE 2008Proc.IMechE Vol.222 Part A:J.Power and EnergyEquation(4)was derived with the assumption,thatthe interior surface of the insert is clean,and there areno residues of a low thermal conductivity coefficient(boiler scale or iron oxides)on the surface.If theinterior surface of the insert is covered with scaledeposition,then the temperature of the front surfaceof the insert increases,in turn causing the increase ofthe circumferential heat flux in the insert.To provethe correctness of the heat load q measurement in asituation,when the scale deposition characterizedby a low thermal conductivity coefficient accumu-lated on the interior surface of the insert,compu-tations of the temperature distribution for the cleanand dirty interior surface of the insert were carriedout,using FLUENT.Temperatures measured on the insert located at15.4 m level on the front wall of the evaporator ofthe OP-210 boiler:T1 405.1 8C,T2 402.4 8C,T3366.8 8C,T4 364.1 8C were used for verification.Temperature T5 318.2 8C of the external back sur-face(w 1808)of the insert was also known fromthe measurement.The density of the heat flux q,calculated fromequation(4),equals toq 6800:979 5432:89405:1 402:42?366:8 364:12?214888:7W=m25Measured temperatures for the clean insert formeda basis for the determination of the specific values ofthe heat load q,heat transfer coefficientaon theinterior surface of the insert,and the temperature ofthe medium Tm.Those values were derived usingthe control volume method,and FLUENT.The computations were carried out using the leastsquares method,for whichX5i1Tci?Ti2!min6andfollowingvalueswereobtained:q 220 135.3 W/m2,Tm 318.28C,anda 37 105.47 W/(m2K).Applying those values as data for FLUENT,thetemperature distributions at the cross-section of theinsert devoid of any residue and with scale depositionof thicknessd 0.5 mm(with the thermal conduc-tivity k 0.5 W/(mK)on the inside surface werecomputed.Thecomputedtemperaturesatthecharacteristic points of the cross-section are pre-sented in Table 1.Table 1 also contains,for the pur-pose of comparison,the measured temperatures.An analysis of the results proved that the measuredtemperatures Timatch the calculated temperaturesTcifor the clean insert.Assuming the calculated temperatures Tcifor theinsert with scale deposition to be the measured temp-eratures,the density of the heat flux q was calculatedusing equation(4)q 6800:979 5432:89642 636:582?600:86 596:362?227810:9W/m27The obtained value of the heat load agreed verywell the value derived from condition(6)equalling:q 220 135.3 W/m2.Accumulation of deposit onthe inside surface of the insert does not adverselyaffect the precision of the heat load measurement.2.2Results of the heat load measurementsThe described sensors in form of measuring insertswere installed on the middle tube of the frontwaterwall of the combustion chamber of the OP-210boiler.The inserts were mounted at four differentelevations:12.6,15.4,19.2,and 23 m.Real-time calcu-lations of heat load q can be displayed on the monitor.The values of the heat load for the determined discretepoints were approximated using the continuous func-tion(Fig.2(a).An analysis of the figure proves thatthe maximum values of heat load occur just above theburners.Changes to this heatload are determined con-tinuously with time.A sample history of the heat load,for the most thermally affected insert,at the level of15.4 m,is presented in Fig.2(b).Maximum heat loadvalues,occurring at this level are typical for steam boi-lers fuelled with pulverized coal 1.Since the heat flux measurements are carried out inthe on-line mode,heat flux distribution along the fur-nace height is known at any time.Table 1Temperatures at the characteristic points of thecross-sectionTemperatureCalculatedtemperature(cleaninsert)Tic(8C)MeasuredtemperatureTi(8C)Calculatedtemperature(insert withscaledeposition)Tic(8C)T1404.43405.1642.00T2402.05402.4636.58T3365.59366.8600.86T4363.99364.1596.36T5318.2318.2344.6516J Taler,B We glowski,W Zima,P Duda,S Gra dziel,T Sobota,A Cebula,and D TalerProc.IMechE Vol.222 Part A:J.Power and EnergyJPE419#IMechE 20083MEASUREMENT OF THE WATERCIRCULATION RATIO IN BOILEREVAPORATORBoiler start-up and shut-down processes,as well asboiler load changes shall be carried out in such way,that no allowable stresses are exceeded,while theessential natural circulation is maintained at alltimes.A rapid increase of pressure may causefading of the boiling process in water-wall tubes,whereas a rapid decrease of pressure leads to waterboiling in all elements of the boilers evaporator water-wall tubes and downcomers.Both cases cancause flow stagnation in the water circulation in theevaporator that leads to pipe cracking.In orderto examine the actual natural circulation in the evap-orator of the OP-210 boiler,the rate of water flow ismeasured continuously on two(from the total often)downcomer tubes with an outer diameter of273 mm and wall thickness of 25 mm.The flow-meters were installed on the opposite sides of theboiler,at the height of 10.5 and 11.5 m.The flowmeterconsists of two main elements:a measuring devicemanufacturedbyTorbarTMandadifferentialpressure converter manufactured by YokogawaTM.Figure 3 shows the results from measurementstaken during a steady-state boiler operation(boilerefficiency fluctuated between 180210?103kg/h)and the computed circulation ratio.From the analysisof the diagram,the velocity in the downcomer tubesranges between 1.6 and 1.8 m/s,while the circulationratio is at about eight to nine.On the basis of themeasured water flowrate and its variability range,the maximum allowable pressure change rates havebeen determined for the dp/dt evaporator(in orderto avoid the stagnation of water circulation in theevaporator).For the measured water velocity in the downco-mers(w 1.61.8 m/s)andthepressurep 10.79 MPa(at the beginning of the shut-down pro-cess)the allowable pressure lowering rate shallrange from 0.023 to 0.027 MPa/s 12(Fig.4(a).The pressure lowering rate at the boiler drum,resulting from the manufacturers recommendations,is set at 2 K/min 10 and is lower than the allowableFig.2Selected measurement and calculation results:(a)measuredtemperaturehistoriesandcalculated heat load for the measuring insertlocated at the height of 15.4 m,and(b)heatloaddistributionalongthecombustionchamber:14 measurement inserts,I and II,two rows of burners located,respectively,atthe height of 10.4 and 12.6 mFig.3Measured water velocity histories in boilerdowncomers(a)and(b),and determinedcirculation multiplicity(c)Computer system for monitoring power boiler operation17JPE419#IMechE 2008Proc.IMechE Vol.222 Part A:J.Power and Energypressure lowering rate established with regard to thestability of the water circulation in the evaporator(Fig.4(b).The analysis proved that if the boiler drum heatingand cooling rates recommended by the manufacturerare not exceeded,there is no risk of instability ofwater circulation occurring in the evaporator.4MONITORING OF THERMAL-HYDRAULICOPERATING CONDITIONSIn the following the determination of boiler effi-ciency,fuel and live steam mass flows as well as fur-nace slagging factor will be discussed in details.When coal is burned,a relatively small portion ofthe ash will cause deposition problems.Due to thedifferences in deposition mechanisms involved,twotypes of high temperature ash deposition have beendefined as slagging and fouling.Slagging is the for-mation of molten,partially fused deposits on furnacewalls and other surfaces exposed to radiant heat.Fouling is defined as the formation of high tempera-ture bonded deposits on convection heat absorbingsurfaces,such as superheaters and reheaters,whichare not exposed to radiant heat 13,14.Slaggingand fouling conditions are critical factors influencingreliability and availability of a coal-fired utility boiler.However,boiler surface deposits have been,tra-ditionally,one of the most difficult operating vari-ables to