Two-stage numerical simulation for temperature profile in furnace of tangentially fired pulverized c

Vol. 12 No. 1. CENT. SOUTH UNIV. TECHNOIFeb.2005Article i:1005-9784(2005)01-0097-05Two-stage numerical simulation for temperature profilein furnace of tangentially fired pulverized coal boilerZHOU Nai-jun(周乃君), XU Qiong-hui(徐琼辉), ZHOU Ping(周萍)(School of Energy and Power Engineering, Central South University, Changsha 410083, China)Abstract: Considering the fact that the temperature distribution in furnace of a tangential fired pulverized coal boiler is difficult to be measured and monitored, two-stage numerical simulation method was put forward. First, multi-field coupling simulation in typical work conditions was carried out off-line with the software CFX-4. 3, and then theexpression of temperature profile varying with operating parameter was obtained. According to real-time operatingparameters, the temperature at arbitrary point of the furnace can be calculated by using this expression. Thus thetemperature profile can be shown on-line and monitoring for combustion state in the furnace is realized. The simulation model was checked by the parameters measured in an operating boiler, DG130-9.8/540, The maximum of relative error is less than 12% and the absolute error is less than 120 C, which shows that the proposed two-stage sim-ulation method is reliable and able to satisfy the requirement of industrial applicationKey words: pulverized coal boiler; combustion monitoring; temperature distribution; numerical simulationCLC number: TK223Document code, AINTRODUCTIONprofile, component distribution and releasing heatfield by combustion, was caEffective monitoring and diagnosing of com- cial software CFX-4.3. Then by analyzing the rebustion states in the boiler are important ways to sults of calculation, the influences of all parame-ensure the pulverized coal boilers to run safely and ters at every nozzle, such as air flux, air tempera-states in ture and pulverized coal flux on temperature atthe furnaces have almost been monitored and diagevery point were obtained and the expression ofnosed according to monitoring and measuring flamedirectlyl-. Moreover, the numerical simulationtemperature at every point in furnace varying withsingle parameter at every nozzle wasfor pulverized coal boiler was performed off-lineway, temperature at every point in the case of dif-and dynamic on-line numerical simulation of comustion states in boilers have not been devel-ferent parameters, ie air flux, air temperatureoped[5-12. Therefore, a novel method for monito- pulverized coal fluIx. was calculated according toring temperature profile in boiler, namely two- the above expressions and temperature profile onstage numerical simulation, was put forward inin the key section was displayed dynamically onthis paper, which can be used to realize dynamic screen of the computer in applied software. Thus itdisplay of temperature profile and provide founda- can realize transplant from off-line simulation retions for observation and adjustment of combustion sults to on-line temperature profile display. Obvistatesously, this process is two-stage simulation in essence. The direct simulation was not adopted bePRINCIPLE OF TWO-STAGE SIMULATIONcause of the limitation of computer hardware nowavailable, that is, if on-line multi-field couplingCombusting process of pulverized coal in the calculation in the boiler is carried out. it will befluence factors, such as structure of furnace, ar- cannot satisfy the requirement of real-time at al ofurnace is very complicated, and there are many income so complicated and take very much time atrange order of nozzles, property of fuel, flux andThe details of two-stage simulation for tendistribution of air and pulverized coal. The thermal perature profile of the furnace are as follows.characteristics of the furnace cannot be described in1) The work condition of each group burner issimple mathematical models. Therefore, in orderdedV凵中国煤化工 average of the meato realize dynamic display of combustion statesCNMHGd is defined as refer-first, off-line coupling simulation of multi-field in ence worK[lon.the furnace, ie velocity profile, temperature2)The temperature distribution T(i,i,k) ino Received date: 2004-03-10: Accepted date 2004-06-11Corresp点款据:0 U Nai, Professo:rd:+8673188: -mail: pizhou a mail. cs. HJournal csut Vol 12 No. 1 2005the reference work condition is calculated with between work condition and reference work condicommercial software CFX-43tion at corner 2, respectively3)The work condition of a group of burner4) The rules of the effect of every parameter(for example, corner 2) includes 11 main parame- on temperature distribution are transferred fromters. When every parameter is changed once or corner 2 to other corners based on the above coeffitwice, temperature distribution T2(i,j, k) of the cient matrixes.relative work condition is calculated with commer-5) The effect of all parameters at 4 corners oncial software CFX-4. 3, and the coefficient matrixes temperature at computational node is accumulatedwith influence of the operating parameter on tem- and temperature at every point on the displayedperature distribution in furnace are got, that Issection is obtainedKx(,/,)△T(i,j,k)(1)6) Temperature at any point on the displayedsection is interpolated according to temperature atwhere (i,j,k) is the space point in the furnace, computational node, and temperature distributionie computational grid node, Xm stands for the pa- on the displayed section is obtainedrameter in 1l work conditions at corner 2 and re-7) The result of temperature distribution isfers to Table 1 and Fig. 1. AXm2,AT2(i,j, k) refer displayed dynamically on the screen of computerto parameter difference and temperature difference with corresponding color.Table 1 Dynamic simulation parameters in changed operating parametersParameter nameUCorner 1Corner 2Corner 3Corner 4Pulverized coal flux in up-primary airPulverizedlux in down-primaryFlux of up-primary airFlux of down-primary airVFlux of middle-secondary airm/h ViFlux of down-secondary air13/hTemperature of down- primaryt2Temperature of secondary airHeat output of pulverized coalkJ/kgQ。4300Up-primary air and Cormer ICorner 448.33°Middel-secondary airBurnerDown-primary airandpulverized coald445Down-secondary airIl中国煤化工oner 3CNMHGFig. 1 Sketch of (a) furnace, burners and(b) imaginary tangential circle of boiler(DG.8/540)ZHOU Naijun, et al Twostage numerical simulation for temperature profile in furnace of tangentially fired pulverized coal boiler .99of the same construction there are s grids in both3 DYNAMICAL SIMULATION MODELdirections) and even distributed (or distributedsymmetrically). the effect of every parameter atTemperature distribution in the furnace is other corners on temperature at space point (i, jsupposed belowk) is described similarly by formula(5), and onlywhere(,y, z)stands for the space coordinate in spondingly. It can be derived easily as follows te.T=T(x,y,2, X(2) coefficient matrixes need to be transformed correthe furnace, and X refers to the set of all operatingThe coefficient matrix of effect of every paparameters.rameter at corner 1 on temperature distributionThis function is supposed to be continuously Kx (s+l-j,ik); the coefficient matrix of effecdifferentiable on X, then if X-Xo+AX, tempera- of every parameter of corner 3 on temperature disture at the fixed space point (x, y, z)can be ob- tribution is Kx ( s+l-i,k); and the coefficienttained by the following formula(approximation of matrix of effect of every parameter of corner 4 onthe first order being chosen)temperature distribution is Kx,(s+l-i, s+l-jI(a, y,2, X)=T(x, y, 2, Xo)+vXk). So the effect of every parameter at 4 corners ontemperature distribution can be given byz,X。)+aTaX△X(3)T(i,j,k,t)T(i,j,k, X(to))+where Xo refers to a group of operating parame-Kx(i,j,k)·△Xm]+ters in reference work conditionFor discrete temperature profile obtained byKx,(s+1-j,i,k)·△Xm]+off line numerical calculation. its space coordinate(x, y, z) is transformed into discrete grid node∑[Kx(j,+1-,k)·△X′m]+(i,j,k), and partial differential in the above formula is replaced approximately with finite difference-quotient, then∑[Kx(s+1-1,s+1-j,k)·△Xm](6)r(,k,1)≈T(kX)+∑∑(A△xn) re AX mI=xm-Xm,AXm=xm-xmT(i,),k,X)+∑∑(K△Xm)4 ON-LINE DISPLAY OF TEMPERATUREPROFILE(4)where Kx is the variation rate of temperature atAfter the theoretical models being estabspace point to variable Xom, subscript n eqn\d' lished, the following step is used to display the re2.3. 4. which stands for nozzle at 4 corners, result of formula(6), ie the calculated temperaturespectively; and subscript m equals 1. 2,3, 1I. distribution, on the specified zone of screen withwhich stands for ll operating parameters in Table different colors (interpolating when necessary )inorder to realize on-line displaying temperature disBy adopting off-line calculation, temperature tribution in furnace. In principal, any section indistribution T(i,j,k, Xo) in reference work condifurnace can be selected to display temperature pro-tion is got, and temperature variation rate matrixesKx (i,j,k) are obtained when 1l parametersfile, but in fact the selected section where temperature is more sensitive to the parameter change andAX,2 at corner 2 are changed relatively to referencehere the situation of flame brushing wall is obwork condition. When every parameter of corner 2 served easily, is more valuable for guiding operais changed (may be it is different from that in refertion. According to the analysis and comparison ofence work condition), temperature distribution is off-line numerical results. the cross section locagiven by the following formulating at the upper of up-primary air is selected toT2(i,j,k,t)≈T(i,j,k,X。)十display temperature distribution.[Kx(i,j,k)·△Xm2ber of the grids for off-liwhere△Xn2=Xn2(t)-Xn2(t),or△X'n2=andSiH中国煤化工s near wall are finerand even distributedCNMHGin configurationConsidering that the burners at 4 corners are ware is limited the grid on the displayed section isof the same strid are arranged symmet17×17(be of the coordinate difference bically, there are the same rules of every parameter tween computational grids and displayed grids, theat 4 corners on temperature distribution in fur- temperature at displayed grid point should be inter-naceIn磊右数据en grids in x and y directions are polated according to the simulation results ). SeJournal csut Vol 12 No. 1 2005the parameters in formula (6) are as follows:1-17,k=25( computationalgrid coordination in z direction locating at the upper of up-primary airIn this way, the expression of the secondstage of numerical simulation for temperature dis-1267.5分ibution in furnace of tangentially fired pulverized14D11250coal boiler is obtained5 MODEL CHECKIn order to check the reliability of on-line re-sult of temperature distribution, temperature distribution between the simulated in representationalmeasured work condition and the calculated in termof formula (6) was compared. The main resultFig 4 Temperature distribution by two-stagare shown in Figs. 2-5. Figs 2 and 3 are temperasimulation in measured work conditiondistributions by numerical simulation in thereference work condition and in the measured workcondition, respectively. Fig. 4 shows temperaturedistribution by two-stage simulation in the meas-ured work condition, and Fig. 5 is the difference oftemperature distribution between numerical simulation and two-stage simulation in the measuredork condition13125312.5155.0Fig. 5 Difference between off-lirsimulation and two-stage simulation in840.0measured work conditionThe figures show that the temperature distribution in two-stage simulation is completely consistent with that in off-line simulation the maxiFig 2 Temperature distribution by off-mum of relative error is less than 12%( the maxi-mum of absolute error is less than 120 C), and theline simulation in reference work conditionrequirement of engineering application can be satified basically. The results indicate that the methodfor transplanting off-line simulation result to on-line display system is practicable.When the mathematical model in this paper257.5employed and two-stage simulation is performed4001150according to results of off-line numerical calcula1257tion, there are mainly two aspects to cause errors830.0nation error resulting from the first-or972d中国煤化工 is substituting finite8300diffCNMHGI difference. So if theoperating parameters are lar from reference workcondition, the calculating error will be increasedFig 3 Temperature distribution by off-line6 CONCLUSIONSsin点教据 I work conditiZHOU Naijun, et al: Two-stage numemulation for temperature profile in furnace of tangentially fired pulverized coal boiler .1011)Considering that the temperature distribL4 WANG Fei, MA Zeng-yi, CEN Ke-fa, et al. 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Journal of Huazhongthan 120 C, which illustrates that two-stage simuUniversity of Science and Technology, 1996, 24(11)lation is reliable and the requirement of industrial107-109. (in Chinese)[7 DONG Peng. HONG Mei, QIN Yu-kun, et al. Aapplication can be satisfied basicallystudy of the combustion and heat transfer one-dimen-3)Two-stage simulation for combusting worksional mathematical model for a pulverized coal-firedcondition in furnace is applied in a boiler of DG13boiler furnace[J]. Journal of Engineering for Thermal9.8/540, and good results are obtained. As a kindEnergy, 1999, 14(6): 424-427(in Chinese)of economical and practical method for monitoring [8 QIAN Li-geng, FAN Jian-ren, SUN Ping, et al. Nucombusting condition, two-stage simulation af-merical simulation of flow and combustion processes infords not only a new means for real-time monitoa 600 MW tangentially fired furnace[J. 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