转炉炼钢原理.ppt

1、CHAPTER 9 Oxygen Steelmaking Processes,9.1 Introduction In 1952, the first LD steelmaking plant in the world was put into operation at Vereinigte terreichische Eisen- und Stahlwerke (VST) in Linz. A half year later the second LD plant went into operation at terreichisch-Alpine Montangesellschaft (MG

2、) in Donawitz.,Linde-Frkl process was discovered in 1928 for the large-scale production of oxygen; In his first attempt to refine hot metal with air, Henry Bessemer melted pig iron in an externally heated fire-clay crucible, deeply submerged a fire-clay blowpipe from above and blew air into the meta

3、l bath. This idea was suggested in his patent letter in 1855.,Development of LD Processing,These characteristics essentially form the basis for large-scale industrial application: 1. High reaction speeds allow high production rates. 2. The refractory lining and oxygen nozzle are at a sufficient dist

4、ance from the hot spot and are thus not damaged. 3. The refining processes with pure oxygen ensure the high quality of the steel. 4. The simplicity in the process and systems results in low investment and operation costs.,Fifty years later, the development of the LD process and its immediate large-s

5、cale industrial implementation are still recognized as great and unique achievements.,The fast-paced victory march of the LD process is explained by the high potential of further development and optimization that are inherent in this method of steelmaking. Another important aspect is that the invent

6、ion was made at just the right time. Many a good idea is not crowned with success because it comes either too soon or too late. The development of the LD process was evolutionary; however, its implementation and impact on the entire steelmaking industry was revolutionary.,Fig. 9.1 Schematic of opera

7、tional steps in oxygen steelmaking process (BOF).,9.2 Process Description and Events,Table 9.1 Basic Oxygen Steelmaking Event Times,9.2.1 Types of Oxygen Steelmaking Processes,Fig. 9.2 Methods of introducing oxygen and other gases into the steelmaking converter.,Evolution of the size and shape of th

8、e BOF vessel,Fig. 9.3 Plan view of 275 ton BOF shop,9.2.2 Sequence of OperationsTop Blown Plant Layout,Fig. 9.4 Elevation of 275 ton BOF shop-looking west,Fig. 9.5 Elevation of 275 ton BOF shop-looking north,9.3 Raw Materials,1. Hot metal: 4.0 4.5% carbon, 0.31.5% silicon, 0.252.2% manganese, 0.040.

9、20% phosphorus and 0.030.08% sulfur (before hot metal desulfurization) .,Determination of Carbon and Temperature,It is important to know the temperature and the carbon content of hot metal at the time it is poured into the BOF for steelmaking process control.,2. Scrap,3. High Metallic Alternative Fe

10、eds,DRI typically contains about 8894% total iron (about 8595% metallization), 0.53%C, 15% SiO2, 38% FeO and small amounts of CaO, MgO and Al2O3. DRI may contain P in the range of 0.005 to 0.09%, S in the range 0.001 to 0.03% and low concentrations of N (usually less than 20 ppm).,4. Fluxes,4.1. Bur

11、nt Lime The calcining reaction is given below: CaCO3 + Heat CaO + CO2 burnt lime containing about 96 wt.% CaO, 1 wt.% MgO, and 1 wt.% SiO2 . The sulfur content ranges from 0.03 to 0.1 wt.%. Most shops require less than 0.04 wt.% S in the lime to produce low sulfur steels. In basic oxygen steelmaking

12、, burnt lime consumption ranges from 40 to 100 lb. per net ton of steel.,4.2. Dolomitic lime,Dolomitic lime is charged with the burnt lime to saturate the slag with MgO, and reduce the dissolution of dolomite furnace refractories into the slag. Typically dolomitic lime contains about 3642 wt.% MgO a

13、nd 5559 wt.% CaO. The dolomitic lime charge into the BOF ranges from 30 to 80 lb. per net ton of steel.,Another flux addition sometimes used in high carbon heats is fluorspar (CaF2 , or spar). This mineral is charged to dissolve the lime and to reduce the viscosity of the slag. . It is used for maki

14、ng high carbon heats, (0.30%C at the end of blow) because the iron oxide concentrations are low on these heats.,4.3. Fluorspar,4.4. Limestone and dolomitic stone,In most BOF shops limestone (CaCO3 ) or dolomitic stone, (CaCO3 MgCO3 ) is frequently used as a coolant rather than as a flux.,5. Oxygen,t

15、he oxygen for steelmaking must be at least 99.5% pure, and ideally 99.7 to 99.8% pure. The remaining parts are 0.005 to 0.01% nitrogen and the rest is argon. In top-blown converters, the oxygen is jetted at supersonic velocities (Mach1) with convergent- divergent nozzles at the tip of the water-cool

16、ed lance.,Fig. 9.6 Convergent-divergent nozzles.,Fig. 10.43 Various types of BOF lance tips.,双流氧枪是20世纪80年代开发应用的新型氧枪，它具有主、副两层氧气喷孔，主流道氧气射流供给熔池完成炼钢任务副流道喷出的氧气将炉膛内的CO气体进一步燃烧，同时也将渣中的铁粒氧化。因此，双流通统枪可促使转炉炉膛内CO燃烧和加速化渣，是一种良好的节能设备。,9.4 Physical and Chemistry Phenomena in LD,9.4.1 Interaction of oxygen Stream and

17、 Molten Metal Bath,A. Character of Oxygen Stream,从氧枪喷头射出的氧气射流均是马赫数远大于1的超音速流股。根据实验研究的结果，氧气射流到达池面时都具有超音速或音速的流速。,氧气射流向熔池运动过程中，将从周围环境抽吸烟尘、渣粒和金属液滴等密度较大的质点，使射流速度降低，扩展角减小。,在转炉炉膛内，氧气射流会遇到熔池排出的以CO气体 为主的反向气流的混合与作用，它阻碍了氧气射流的运动，使射程减小。 在吹炼中期碳氧剧烈反应，CO排出量大且流速快，因而对氧气射流的阻碍作用影响最大；而在吹炼初期和末期，碳氧反应较少，对氧气射流的影响也较小。,氧气射流进入炉

18、膛时，其温度比周围介质温度低，而密度高(pO1.429kgm3, PcoPN21.25kgm3，pco21.963kgm3)，因此，氧气射流与炉内介质混合后温度升高，密度略有降低。气体密度降低和受热膨胀，有利于射流的射程和扩张角增加。,B. Status of Jet Stream-for Single jetting nozzle lance,Core length of jet stream with constant speed: 射流的等速核心区长度是确定氧枪操作高度的依据之一，在生产中希望到达铁水表面的氧气流股具有超音速或音速的射流，以便使其具有一定的冲击动能。射流在各个半径方向的速

19、度分布接近高斯分布。当氧气进口压力大于0.7MPa时，等速核心区长度可按下式计算： 式中 y-等速核心区长度 D-喷头出口直径 R=喷口处氧气密度与周围介质的密度比。,Expanding of radius of jet stream：射流直径的扩散，就是氧气流股对铁水液面冲击面积的表现。,Core speed of jet stream,射流中心速度随轴线距离的变化 Vcore/Vc=射流中心速度、射流出口速度；x/De=下游距离/喷嘴出口直径,For multi-jetting nozzle lance,多孔喷头的设计思想是增大流量，分散射流，增加流股与熔的接触面积，使气体逸出更均匀，吹炼

20、更平稳。然而，多孔喷头与单孔喷头的射流流动状态有重要差别，在总的喷出量相同的情况下，多孔喷头射流的速度衰减要快些，射程要短些，几股射流之间还存在相互影响。,B. PHYSICAL IMPACTING OF JET STREAM ON MOLTEN METAL BATH,(1) Impacting depth 氧射流到达液面后的冲击深度又叫穿透深度，它是指从水平液面到凹坑最低点的距离。冲击深度是凹坑的重要标志，也是确定转妒操作工艺的重要依据。,(cm),Po=供氧压力，Pa；Do喉口直径，H氧枪高度,For multi-jetting nozzle lance 计算公式可用因次分析求得，公式中的

21、系数由试验转炉的数据决定：,（2）Surface area of impacted pit：在冶炼过程中，一般把氧气射流与静止熔池接触时的流股截面积称为冲击面积，但这个冲击而积并不是气射流与金属液真正接触的面积能较好代表氧射流与金届液接触面积的应是凹坑表面积。 鞭岩等推导出的凹坑表面积公式为：,L-冲击深度，H氧枪高度，(P0/0.404)2,炉气温度对凹坑形状的影响 Po=0.8MPa; H=1.6m, Do=5cm, CO=85%,CO2=10%, N2=5%,(3)Temperature of impacted pit: 氧气射流作用下的金属熔池冲击区即凹坑区，是熔池中温度最高区，其温度

22、可达2200-2600。,(4）Stirring of molten metal bath: 由于氧射流的直接和间接作用，造成了熔池的强烈运动，其能量，一部分是射流的动能直接传输给熔池，另一部分是在氧射流作用下发生碳氧反应生成的CO气泡提供的浮力，另外还有温度差和浓度差引起的少量对流运动。,(5) Flow of molten metal bath,For soft blowing：,L/L00.2,L/L00.7,For hard blowing,(6) Emulsion of molten pool and jet stream,转炉吹炼中，由于氧气射流和CO气体共同作用，引起氧气射流与金

23、属液和炉渣之间的相互破碎，形成液滴和气泡，产生金属炉渣气泡的乳化液。它们之间的接触面积剧烈增大。,乳化造成的渣铁间接触面积可达0.61.5 m2/kg。,The factors of improving emulsification and stability of metal and slag: 增大炉渣粘度，使金属液滴在炉渣中的沉降速度大为减小，因而使乳化的稳定性提高； 固体质点附着在金属液滴和气泡表面时，可以阻碍乳化液的破坏； FeO、SiO2、P2O5等表面活性物质的增加，可使金一渣间界面张力降低，有利于金属液和炉渣间互相掺混和弥散，实现乳化液的形成和稳定。,9.4.2 Process

24、 Reactions,The commercial success of oxygen steelmaking is mainly due to two important characteristics： First, the process is autogenous meaning that no external heat sources are required. Second, the process is capable of refining steel at high production rates.,Fig. 9.7 Physical state of the BOF i

25、n the middle of the blow.,9.4.2.1 Composition Change of metal And Slag In LD steelmaking,During LD steelmaking processes, the oxidization sequence of components in hot metal are as follows: 1. below 1400， Si, V, Mn, C, P, Fe 2. 1400-1530，Si, C, V, Mn, P, Fe 3. above 1530，C, Si, V, Mn, P, Fe,1Premier

26、 stage of blowing: 由于铁水温度不高，Si, Mn的氧化速度比C快，开吹24min时，Si、Mn已基本上被氧化。同时，铁也被氧化形成FeO进入渣中，石灰逐渐熔解，使P也氧化进入炉渣中。Si、Mn、P、Fe的氧化放出大量热，使熔池迅速升温。吹炼前期的任务是化好渣、早化渣，以利磷和硫的去除；同时也要注意造渣，以减少炉渣对炉衬材料的侵蚀。,2Main stage of blowing: 铁水中Si、Mn氧化后，熔池温度升高，炉渣也基本化好，C的氧化速度加快。 吹炼中期是碳氧反应剧烈时期，使脱碳速度达到最大。由于碳氧剧烈反应，使炉温升高，渣中FeO含量降低，磷和锰在渣一金间的分配发生

27、变化，产生回磷和回锰现象。由于高温、低FeO、高CaO存在，使脱硫反应得以大量进行。吹炼中期的任务是脱碳和去硫，因此应控制好供氧和底气搅拌。防止炉渣返干和喷溅的发生。,3Final stage of blowing: 铁水中碳含量低，脱碳速度减小。这时吹入熔池中的氧气使部分铁氧化，使渣中(FeO)和铁水中O含量增加。同时，温度达到出钢要求，钢水中磷、硫得以去除。吹炼后期要做好终点控制，保证温度、C、P、S含量合乎出钢要求。此外还要根据所炼钢种要求，控制好炉渣氧化性对于复吹转炉，则应增大底吹供气流量，以均匀成分、温度、出除夹杂。若终点控制失误，则要补加渣料和补吹。,A) Importance o

28、f decarburization during oxygen steelmaking 1. The main task of steelmaking; 2. Supplying the main energy required for steelmaking meaning the process is autogenous;. 3. Improving emulsion and increasing reaction contacting area. 4. The process is capable of refining steel with high quality.,9.4.2.2

29、 Decarburization in Oxygen Steelmaking Processes,B) Thermodynamics Consideration of Decarburization,Mechanism of carbon oxidation When oxygen first contacts a liquid iron-carbon alloy it initially reacts with iron, even though thermodynamically it favors its reaction with carbon. Carbon in the liqui

30、d metal then diffuses to the interface reducing the FeO. Fe + 1/2 O2 = FeO FeO + C = CO + Fe C + 1/2O2 = CO When C 0.1%, the following reaction will take place, C+ O2=CO2,Thermodynamics data of Decarburization,C+O=CO 9.4.1 O+CO=CO2 9.4.2,In most case of steelmaking, CO content is more than 99%; CO2%

31、 decrease with increasing of C and Temperature. KCO will not be changed greatly during overall oxygen steelmaking processes.,Thermodynamical factors of affecting decarburization reaction,Decarburization will be favored with the increasing of fC; Of cause, high O% and large fO will improve decarburiz

32、ation; The reduced CO partial pressure will be helpful to decrease carbon in hot metal.,Fig.9.4.1 Effect of PCO on equilibrium C and O,Oxygen-Carbon Relation,The O is always more than Oeq: OeqOreal(O)slag,Fig. 9.4.2 Variation of product ppm O%C with carbon content of steel at first turndown.,For car

33、bon contents above 0.15% the product ppm O %C is essentially constant at about 30 2, which is near the equilibrium value for an average gas (CO) bubble pressure of about 1.5 atmosphere in the steel bath.,The non-equilibrium states of the carbon-oxygen reaction at low carbon contents in BOF and OBM(Q

34、-BOP) are represented by the following empirical relations.,Because the hydrogen content of gas bubbles in OBM is greater than the argon content of gas bubbles in BOF.,C. Kinetic Consideration of Decarburization,Fig.9.4.3 Decarburization rate change with refining time,Fig. 9.4.4 Change in melt compo

35、sition during the blow,熔池中碳氧反应是一个复杂的多相反应，其反应机理至少可以分为以下三个环节： (1)气相中的氧通过炉渣和金属向反应区域扩散； (2)反应区域碳氧进行化学反应。 (3)反应产物CO气泡新相的萌芽及排除。,The decarburization is divided into three stages:,In first stage: because of low temperature and Sis oxidation, De-C rate can be defined as:,The critical temperature and composit

36、ion for carbon oxidation is 1380, and (Si+0.25Mn1),the oxidization sequence of components in hot metal are as follows: 1. below 1400， Si, V, Mn, C, P, Fe 2. 1400-1530，Si, C, V, Mn, P, Fe 3. above 1530，C, Si, V, Mn, P, Fe,(SiO2)+2C=2CO+Si G013110073.8T J,In second stage: At high carbon contents the r

37、ate of mass transfer is high such that most of the FeO formed is reduced and the rate of decarburization is controlled by the rate of oxygen supply:,Fig. 9. 4.5 Effect of oxygen supply on De-C,or,In the third stage:,Below a critical carbon content the rate of mass transfer is insufficient to react w

38、ith all the injected oxygen. In this case the rate of decarburization is given by,or,Usually, the critical carbon is when k3%C=k2NO2 and is typically about 0.3% C.,9.4.2.3 Oxidation of Silicon,The Si dissolved in the hot metal (0.251.3 wt.%) is oxidized to very low levels (0.005 wt.%) in the first t

39、hree to five minutes of the blow. The oxidation of Si to silica (SiO2) is exothermic producing significant amounts of heat which raises the temperature of the bath. It also forms a silicate slag that reacts with the added lime (CaO) and dolomitic lime (MgO) to form the basic steelmaking slag. The am

40、ount of Si in the hot metal is very important since its oxidation is a major heat source to the process and it strongly affects the amount of scrap that can be melted. It also determines the slag volume and consequently affects the iron yield and dephosphorization of the metal.,9.4.2.4 Phosphorus Ox

41、idation,Dephosphorization is favored by the oxidizing conditions in the furnace. Phosphorus removal is favored by low temperatures, high slag basicity (high CaO/SiO2 ratio), high slag FeO, high slag fluidity, and good stirring.,Fig.9.4.6 composition change in LD,9.4.2.5 Sulfur Reaction The BOF is no

42、t very effective for sulfur removal due to its highly oxidizing conditions. Sulfur distribution ratios in the BOF (% S slag /% S metal 48) are much lower than the ratios in the steel ladle (% S slag /% S metal 300500) during secondary ladle practices. In the BOF, about 10 to 20% of sulfur in the met

43、al reacts directly with oxygen to form gaseous SO2. The rest of the sulfur is removed by the following slag-metal reaction S + (CaO) + Fe = (CaS) + (FeO) Sulfur removal by the slag is favored by high slag basicities (high CaO/SiO2 ratio), and low FeO contents.,9.5 Slagging System,9.5.1 Determination

44、 of type of slagging Single slagging: is used in most plant for high quality of hot metal or steel with low quality requirement. Double slagging: suitable for refining of hot metal with high P or S; the critical operation is how to determine the de-slag time, usually, for top-blowing (combination bl

45、owing)the de-slag time is at the 25% (30%)of overall blowing.,9.5.2 Determination of Lime and Basicity of Slag,9.5.2.1 Basicity: basicity is dominated by S and P content of hot metal; Usually, B=2.8-3.2 for low S and P B=3.2-3.5 for middle S and P B=3.5-4.0 for high S and P,9.5.2.2 Added amount of l

46、ime: 1). For P0.3% in hot metal,2). For P0.3% in hot metal,9.5.3 Control of slagging speed:,The following ways can be used to speed up slagging: 1) 使用高活性软烧石灰: 一是提高化渣速度，缩短冶炼时间。活性石灰晶粒细小、晶格不稳定、反应面积大，加入铁水后能迅速与其他化合物熔解成渣。在相同的操作条件下，石灰的活性越大，反应能力越强。 二是提高炼钢热效率，废钢比增加。因活性石灰中活性CaO含量高，在冶炼反应中能被充分利用，从而使炼钢的石灰消耗量比普通石

47、灰下降20至30。 三是提高脱硫、脱磷效果，改进钢的质量。由于活性石灰有效CaO含量高、气孔率高、比表面积大，CaO分子性能活泼，在冶炼中具有较好的脱硫、脱磷效果，去磷率比普通石灰高10。,2)向渣中加入铁矿石、氧化铁皮和萤石等熔剂，Fe2O3、A12O3、CaF2等物质能降低2CaO.SiO2的熔点，并有可能改变其形态，使之由致密的整体变成分散的聚集体； 3)使用白云石质石灰，降低共熔点，并可得到超软烧石灰； 4)使用化学成分接近炉渣成分的合成渣； 5)使用预热的废钢并提高铁水温度，使开吹后熔池温度迅速上升至1580-1600，加入散状材料后，温度也能保持在这个水平上。,9.5.4 Oxid

48、ation of Slag,在吹炼前期和中期，为了促进石灰的溶解和加快脱磷反应，要求炉渣具有较高的氧化能力；但在吹炼后期，终点氧化铁含量过高，钢水含氧量也会增加，从而使脱氧剂的消耗过多和钢质量下降。特别是吹炼低碳钢种时，应控制好炉渣的氧化性，以防止钢液过氧化。,9.6 Charging System,There are three charging models used in oxygen steelmaking plant: 1. fixed quantity charging 2. fixed depth of bath charging 3. variable quantity cha

49、rging at different stage of campaign,9.7 Oxygen supplying system,Pressure of oxygen: 0.6-1.3Mpa Oxygen flow rate: 2-3.5Nm3/min.T,Table 9.2 Example of Oxygen Batches in a BOF,Lance height change during a heat,lance height of slagging : lance height of main blowing : lance height of catching carbon :

50、A example from Baosteel: 1. 2.2 -2.3m 2. 2.0m 3. 1.8m,攀钢转炉冶炼主要特点,Determination of Oxygen Requirements,The volume of oxygen gas blown into the converter must be sufficient to oxidize the C, Si, Mn, and P during the blow, and it is computed from an oxygen balance as shown below. For the present exampl

51、e the oxygen required during the blow is about 52.8 Nm3 per metric ton of steel produced.,9.8 Process Control Strategies,Process control is an important part of the oxygen steelmaking operation as the heat production times are affected by it. Process control schemes can be broadly divided into two c

52、ategories: static and dynamic.,Static Models,The static charge model uses initial and final information about the heat to calculate the amount of charge and the amount of oxygen required. The static charge model calculation is performed at the beginning of the heat. The output from the model determi

53、nes the amount of oxygen to be blown and the amount of fluxes to be added to attain the desired (aim) carbon and temperature for that heat.,Fundamentals of the Static Charge Model,它的主要理论依据是冶金热力学与数学统计学。静态控制的基本功能与流程。,Static Charge mathematics Model,静态控制数学模型是静态控制的核心，其精度直接影响终点C与温度命中率的高低。从目前发展的状况看，静态控制数学

54、模型可分为: 理论型、统计型和经验型三类。,Static Charge Mathematics Model Based on Theory Calculation,理论型静态控制数学模型是以物料平衡与热平衡为出发点，并加进一些可认为是较合理的假定和实验值参数而建立的模型。 由于所作假定与所采用的实验值不尽一致，所推导出的理论型模型的具体形式也有所区别。它包括二个主要方程：耗氧方程和矿石用量方程。,理论型氧耗量方程,理论型氧耗量方程是通过冶炼一炉钢的氧气的物料平衡计算而建立的。氧气转炉炼钢中，氧的主要来源是吹入熔池的氧气，其次是加入的矿石与氧化铁皮等氧化剂。氧主要消耗于C、Si、Mn、和Fe等元

55、素的氧化及CO在炉膛内的部分完全燃烧。经过中间计算与简化处理后，得出理论型氧耗量方程, 如下为氧耗量方程的例子: VO2(1/) 铁（9.33铁+8.0Si铁+2.04n铁9.03铁2.0） ( 钢废钢）(9.73钢2.04钢 +9.03钢） 一矿（2.1e23矿1.55Fe矿）L,理论型矿石量方法,理论型矿石量方程是通过热平衡计算的，这种热平衡计算是一个十分复杂的问题，一般为简化计算特作如下假设： 1) 将所有参加反应的物质均冷却至常温（），并在此常温下发生反应，然后将反应产物加热至吹炼终点温度。由于可以直接运用已知的反应热效应。 2)热支出项中只有3个加热物质：钢液、炉渣、炉气。由此可以不

56、进行废钢、石灰、萤石等的熔化与加热计算。,W矿=W铁14 800+210t铁+27 530C铁+73 820 Si铁+15 700Mn铁+41 680P铁 +10 290Fe-3.27C铁(t铁+t钢)-W钢(1 100+208t钢) -(W钢-W废）27 530C钢+15 770Mn钢+41 680P钢 -3.27C 钢(t铁+t钢)-0.21L(t铁+t钢)-W渣(500t渣-33 000)+5 020L-Q损/(12 300Fe2O3矿+8 940FeO矿）,统计型静态控制数学模型,统计型数学模型是依据黑箱原理，不考虑过程中的物理化学规律，只考虑系统输出与输人量间的实际关系，在收集大量试

57、验数据的基础上，进行统计分析所编制的。,采用数理统计方法（回归分析），获得适应各具体条件的氧耗量方程与矿石量方程。 据称按此模型控制炼钢过程，目标终点钢水温度的命中率（土10）可由人工控制的40提高到64.2。 这类模型由于只考虑输出量与输入量间的统计关系，可以对随机偏差进行分析，消除随机因素的影响，因而能保证一定的精度，且结构比较简单。但这类模型有较强的条件性和针对性，要求统计大量的实际生产数据，建模前期工作量较大。,经验型静态控制数学模型,经验型静态控制数学模型是根据前一炉的吹炼结果和历史数据的统计，对下一炉的作业条件的影响进行修正，来算出该炉所需要的氧气量与冷却剂量的公式。 它们常以增量

58、形式出现，且结构比较简单。与自动控制中数字PID控制方法有类似之处。当前各国钢厂所使用的此类模型大致与其类似。,Advantage or Disadvantage,理论型、统计型和经验型这三种数学模型各有优缺点，在实际使用中，三种模型之间没有截然不同的界线，结合实际生产工程，可以灵活地综合地应用三种模型，以达到较好的预期目标。 就目前应用情况而言，增量模型(经验模型)由于考虑的时序性(前后若干炉次的数据关联)，其预报精度和模型的稳定性要略好于统计型。而理论模型的部分机理未明并且假定了部分条件，因而其使用效果欠佳。虽然其适用性较好，但仍有待发展。,Statistical and Neural Network Models,国内外将神经网络的BP网络模型应用到转炉计算机静态控制取得了一定的成绩。BP网络即多层前馈神经网络，BP网络