锅炉自动给水外文翻译PLC在蒸汽锅炉汽包液位PID控制系统的应用分析

1、 蚌埠学院毕业论文（设计）外 文 翻 译题 目: 锅炉自动给水系统设计 姓 名: 学 号: 系 别: 机械与电子工程系 专 业: 电子信息工程 年 级: 2009级 指导老师: 高伟霞 2012年12月10日附件1：外文资料翻译译文plc在蒸汽锅炉汽包液位pid控制系统的应用分析1 引言 工业蒸汽锅炉汽包水位控制的任务是控制给水流量使其与蒸发量保持动态平衡，维持汽包水位在工艺允许的范围内，是保证锅炉安全生产运行的必要条件，也是锅炉正常生产运行的主要指标之一。若水位过高,影响汽水分离的效果,使用气设备发生故障;而水位过低则会破坏汽水循环,严重时导致锅炉爆炸，所以锅炉汽包水位必须严加控制。为了确保

2、锅炉生产的稳定、可靠和经济运行，我们设计采用了性能先进的永宏fbs-plc、变频调速器、计算机应用等自动化设备组成的锅炉pid自动控制系统。该控制系统通过检测水汽压力、温度，汽包液位等运行物理量，在运行过程中全自动调节，保证了工业锅炉的安全稳定高效运行。2 工业锅炉相关工艺介绍 蒸汽锅炉是厂矿重要的动力设备，其任务是供给合格稳定的蒸汽，以满足负荷的需要。为此，锅炉生产过程的各个主要参数都必须严格控制。而利用余热气体作为热交换介质的余热锅炉在全国占有很大的比例，其节能降耗效果尤为明显。某化工厂硫酸余热锅炉就是利用沸腾炉出来的炉气(主要是so2)温度过高，将其作为热交换对象，通过余热锅炉副产中压蒸

3、汽供各生产分厂使用，既保证了生产需要，也达到了节能降耗的目的。锅炉是一个较为复杂的调节对象，为保证提供合格的蒸汽以适应负荷的需要，与其配套设计的控制系统必须满足各主要工艺参数的需要。余热锅炉工艺流程如图1所示。图1 余热锅炉工艺流程图3 控制难点分析 锅炉计算机控制是近年来开发的一项新技术。它是微型计算机软、硬件、自动控制、锅炉节能等几项技术紧密结合的产物，作为锅炉控制装置，其主要任务是保证锅炉的安全、稳定、经济运行，减轻操作人员的劳动强度。采用微计算机控制，能对锅炉进行过程的自动检测、自动控制等多项功能。它的被调量是汽包水位，而调节量则是给水流量，通过对给水流量的调节，使汽包内部的物料达到动

4、态平衡，变化在允许范围之内，虽然锅炉汽包水位对蒸气流量和给水流量变化的响应呈积极特性，但是在负荷(蒸气流量)急剧增加时，表现却类似逆响应特性，即所谓的虚假水位。造成这一原因是由于负荷增加时，导致汽包压力下降，使汽包内水的沸点温度下降，水的沸腾突然加剧，形成大量汽泡，而使水位抬高。汽包水位控制系统，实质上是维持锅炉进出水量平衡的系统。它是以水位作为水量平衡与否的控制指标，通过调整进水量的多少来达到进出平衡，将汽包水位维持在汽水分离界面最大的汽包中位线附近，以提高锅炉的蒸发效率，保证生产安全。由于锅炉水位系统是一个设有自平衡能力的被控对象，运行中存在虚假水位现象，实际应用中可根据情况采用水位单冲量

5、、水位蒸汽量双冲量和水位、蒸汽量、给水量三冲量的控制系统。所谓三冲量调节系统就是把给水流量w，汽包水位h，蒸汽流量d三个变量通过运算后调节给水阀的调节系统。具体调节过程方框图如图2所示。图2 三冲量调节方框图先通过蒸汽流量变送器和给水流量变送器取得各自的信号乘以相应的比例系数，通过比例系数可以调节蒸汽流量或给水流量对调节系统的影响力度。通过差压变送器取得水位信号作为主调节信号h。如果水位设定值为g，那么在平衡条件下应有d×dk-w×wk+h-g=0的关系式存在。其中dk为蒸汽流量系数 wk为给水流量系数。如果再设定时，保证在稳态下d×dk=w×wk那么就

6、可以得到h=g。此时调节器的输出就与符合对应，给水阀停在某一位置上。若有一个或多个信号发生变化，平衡状态被破坏，pi调节模块的输出必将发生变化。当水位升高了，则调节模块的输出信号就减小，使得给水调节阀关小。反之，当水位降低时，调节模块的输出值增大，使给水阀开大。实践证明三冲量给水单极自动调节系统能保持水位稳定，且给水调节阀动作平稳。锅炉给水系统中还有一个比较重要的控制回路是给水压力回路，因为汽包内压力较高，要给锅炉补水必须提供更高的压力，给水压力回路的作用是提高水压，使水能够正常注入汽包。但在蒸汽流量未达到满负荷时，对给水流量的要求也不高。在老式的锅炉系统中一般采用给水泵一直以工频方式运转，用

7、回流阀降低水压防止爆管，现在一般采用通过变频器恒压供水的方式控制水压。锅炉给水量通过汽包液位调节。汽包液位测量选用浮筒液位计。为有效利用转换废热，降低消耗，减低劳动强度，有利于整体工艺稳定，要求汽包液位自动控制，正常生产时波动应小于±5。pid调节蒸汽出口阀可以很好的控制汽包压力。开车正常后波动范围不大，可以不考虑。转化负荷波动、出预热器锅炉给水温度变化、锅炉负荷波动、排污量变化这几个因素对汽包液位的影响必须考虑。以汽包液位为主调参数、以给水流量为副调参数、以蒸汽流量为前馈，但调节效果很差。引起汽包液位的大起大落。考虑到该废热锅炉控制参数耦合小，流程简单，产汽量也较稳定，我们从操作人

8、员的操作中得到启发，认为减少给水量的波动从而稳定给水温度成为该废热锅炉液位控制的要点。因此我们选用“以汽定水液位前馈”比值控制方案，方案框图如图3所示。图3 汽定水液位前馈比值控制方案框图其中系数k为汽水损失率(给水流量与蒸汽流量的比值)，范围为1.11.2。pid参数为p300、i0.4、d0。这组pid参数可以使阀位波动幅度不大而回路有较快的跟踪效果。液位前馈系数与锅炉额定负荷密切相关，一般是额定负荷越大前馈系数也越大。本项目废热锅炉的额定负荷为35th。前馈系数按表一给定，见附表图4实时液位记录曲线投运时首先投运给水流量单回路，调节平稳后，再切换为蒸汽流量比值控制，液位前馈同时起作用。以

9、汽定水液位前馈比值控制方案调试投运简单方便，投运后经负荷扰动(产汽量变化)、液位扰动(排污量变化)实验，抗扰动性能良好，投运以来运行平稳，达到工艺要求。图4为2.5h实时液位记录曲线，其中记录了负荷扰动情况。液位波动范围±3。附表 前馈系数表液位范围（%） <45 4546 4647 4748 48 49流量系数（t/h） 1.0 0.8 0.6 0.4 0.2液位范围（%）4951 5152 5253 5354 5455 >55流量系数（t/h）0 -0.2 -0.4 -0.6 -0.8 -1.04 永宏plc pid控制系统分析4.1 带pid控制功能的fatek可编

10、程控制器 pid控制及其控制器或智能pid控制器(仪表)已经很多，产品已在工程实际中得到了广泛的应用，有各种各样的pid控制器产品，作为国产plc企业，永宏电机股份公司一直致力于plc的研究开发工作，带pid控制功能的fatek可编程控制器(plc)就是利用其闭环控制模块来实现锅炉汽包液位的pid控制，在异常情况下，如液位偏离正常值较大时，通过plc控制系统控制，可以快速恢复水位，保证锅炉的安全稳定运行。当水位控制和主蒸汽温度控制发生矛盾时，可根据矛盾的主要方面进行两者的协调控制。它包含给水流量控制回路和汽包水位控制回路两个控制回路，实质上是蒸汽流量前馈与水位流量串级系统组成的复合控制系统。当

11、蒸汽流量变化时，锅炉汽包水位控制系统中的给水流量控制回路可迅速改变进水量以完成粗调，然后再由汽包水位调节器完成水位的细调。4.2 汽包水位pid控制设计优点 (1) 减少干扰对主回路的影响，可由副回路控制器予以校正。 (2) 由于副回路的存在减少了相位滞后，从而改善了主回路的响应速度。 (3) 对控制阀特性的变化具有较好的鲁棒性。 (4) 副回路可以按照主回路的需求对对象实施精确控制。 实际plc的控制程序采用主副回路进行串级控制，即主回路的输出作为副回路的设定值，经副回路输出作用于被控对象。也可以不用副回路只用主回路形成单回路调解，或手动操作完成。一般常见的过程控制应用， 开环回路控制就可以

12、满足大部份的应用要求，但随着使用时间、组件特性变化或受控负载或外界工作环境的变化，开环回路控制因为没有真实将受控程序的实际量反馈到控制器，因此控制结果可能与实际期望的结果会有些落差，闭环回路pid过程控制是用来克服并解决上述缺点的极佳选择。fbs-plc提供软件数字化的pid数学表达式，对于一般反应的闭环回路过程控制就可应付，但对于工业锅炉这样的需要有快速反应的闭环回路控制要使用本功能需要事先评估是否可行。典型的闭环回路程控示意图如图5示。图5典型闭环回路程控示意图根据应用要求，用户将pid 控制器设定成比例+积分+微分控制器，其控制器的数字化数学表达式如下:mn:“n”时的控制输出量d400

13、5:增益常数，默认值为1000;可设定范围为1 5000pb:比例带(范围:15000，单位为0.1%; kc(增益)=d4005/pb) en:“n”时的误差=设定值(sp)-“n”时的过程变数值(pvn) ki:积分常数( 范围:09999，相当于0.0099.99 repeats/minute) td:微积分时间常数(范围:09999，相当于0.0099.99minute) pvn:“n”时的过程变数值pvn-1:“n”时的上一次过程变数值ts:pid运算的间隔时间(范围:13000，单位:0.01s) bias:偏置输出量(范围:016383)加上微分项的控制器，目的在于消除程控系统的

14、过度反应，进而使程控系统能够平稳缓和达到稳定。虽然微分项有上述优点，但因其对输出量的贡献相当灵敏，大部分的应用不必使用微分项而将td设定为0。pid控制器的参数整定是控制系统设计的核心内容。它是根据被控过程的特性确定pid控制器的比例系数、积分时间和微分时间的大小。pid控制器参数整定的方法很多，概括起来有两大类:一是理论计算整定法。它主要是依据系统的数学模型，经过理论计算确定控制器参数。这种方法所得到的计算数据未必可以直接用，还必须通过工程实际进行调整和修改。二是工程整定方法，它主要依赖工程经验，直接在控制系统的试验中进行，且方法简单、易于掌握，在工程实际中被广泛采用。pid控制器参数的工程

15、整定方法，主要有临界比例法、反应曲线法和衰减法。三种方法各有其特点，其共同点都是通过试验，然后按照工程经验公式对控制器参数进行整定。但无论采用哪一种方法所得到的控制器参数，都需要在实际运行中进行最后调整与完善。现在一般采用的是临界比例法。利用该方法进行pid控制器参数的整定步骤如下: (1) 首先预选择一个足够短的采样周期让系统工作; (2) 仅加入比例控制环节，直到系统对输入的阶跃响应出现临界振荡，记下这时的比例放大系数和临界振荡周期; (3) 在一定的控制度下通过公式计算得到pid控制器的参数。除此以外为保证锅炉运行的安全，在进行自动化控制系统设计时，对锅炉水位、锅炉汽包压力等重要参数应设

16、置常规仪表及报警装置，以保证水位和汽包压力有双重甚至三重报警装置，这是必不可少的，以免锅炉发生重大事故。5 结束语 由于采用了plc进行控制，系统功能完善，结构先进合理，能耗小，扩展灵活，便于维护，并且可靠性高，而且还极大地提高了企业的生产效率和经济效益。该系统自动化程度较高，大大降低了操作者劳动强度，降低了成本，经过近2年的运行，用户给予了很高评价，认为利用国产永宏plc开发的控制系统功能完善，综合性强，人机界面友好，实用性好。随着国产优秀可编程控制器和高速计算元件的快速发展，锅炉控制系统将会更加完善。附件2：外文原文plc in steam boiler steam drum fluid

17、position pid control system applied analysis 1 introduction the industry steam boiler steam drum water monitor duty is the control causes it for the water current capacity with the transpiration rate maintenance dynamical equilibrium, maintains the steam drum water level in the craft permission scop

18、e, is guarantees the boiler safety in production movement the essential condition, also is one of boiler regular production movement major targets or quotas. if the water level excessively is high, affects the soft drink separation the effect, the use was mad the equipment breaks down; but the water

19、 level excessively low can destroy the soft drink circulation, is serious when causes the explosion of a boiler, therefore the boiler steam drum water level must strictly control. in order to guarantee the boiler to produce stable, reliable and the economical movement, we designed use the performanc

20、e to be advanced the boiler pid automatic control system which forever great automatic equipment and so on fbs-plc, frequency conversion velometer, computer application will compose. this control system through examination water vapor pressure, temperature, movement physical quantity and so on steam

21、 drum fluid position, in movement process entire automatic control, has guaranteed the industry boiler security stable highly effective movement. 2 industries boilers related craft introduction the steam boiler is the factories and mines important power equipment, its duty is the supplies qualified

22、stable steam, satisfies the load the need. therefore, boiler production process each main parameter all must strictly control. but holds the very great proportion using the afterheat gas as the heat change medium afterheat boiler in the nation, its energy conservation falls consumes the effect espec

23、ially to be obvious. some chemical plant sulfuric acid afterheat boiler is the furnace gas which comes out using the ebullition stove (mainly is so2) the hyperpyrexia, takes it as the heat change object, through afterheat boiler vice- mid-production pressure steam for each production branch factory

24、use, also has guaranteed the production need, also had achieved the energy conservation falls the goal which consumes. the boiler is a more complex controlled member, provides the qualified steam for the guarantee to meet the load need, if the necessary design control system must satisfy each main c

25、raft parameter the need. afterheat boiler technical process like chart 1 shows:chart 1 afterheat boiler flow chart3 controls difficulties analysis the boiler computer control is a new technology which the recent years developed. it is the microcomputer soft, the hardware, the automatic control, the

26、boiler energy conservation and so on several technical in close integration with product, as the boiler control device, its primary mission is guaranteed the boiler the security, is stable, the economical movement, reduces operator's labor intensity. uses the micro computer control, can carry on

27、 the process to the boiler the automatic detection, the automatic control and so on many functions. it is adjusted the quantity is the steam drum water level, but adjusts the quantity is for the water current capacity, through to gives the water current capacity the adjustment, enables the steam dru

28、m interior the material to achieve the dynamical equilibrium, changes in the permission scope, although the boiler steam drum water level assumes the positive characteristic to the vapor current capacity and for the fluent quantity change response, but when load (vapor current capacity) sharp growth

29、, performance actually similar counter response characteristic, namely so-called false water level. creates this reason is because time load increase, causes the dome pressure to drop, causes the steam drum boiling temperature to drop, the water ebullition suddenly intensifies, forms the massive ste

30、am bubbles, but makes the water level to raise. the steam drum water monitor system, in the essence is maintains the boiler turnover water volume balance the system. it is by the water level took the water volume balance or not control target, through adjusts the water volume how many to achieve the

31、 turnover balance, maintains the steam drum water level in the soft drink separation contact surface biggest steam drum nearby the position line, enhances the boiler the vaporization efficiency, the guarantee production safety. because the boiler water level system is equipped with the balance of th

32、e ability to control the object, in the movement has the false water level phenomenon, in the practical application may use the water level single impulse, the water level steam quantity double impulse and the water level, the steam quantity according to the situation, gives the water volume three i

33、mpulses the control systems. the so-called three impulses governing system is gives water current capacity w, steam drum water level h, the steam current capacity d three variables adjusts after the operation gives the water valve the governing system. concrete adjustment process block diagram like

34、chart 2 showschart 2 impulse adjustment block diagram first and obtains respective signal through vapor stream quantitative change delivering for fluent quantitative change delivering while by the corresponding scale-up factor, may adjust the steam current capacity through the scale-up factor or giv

35、e the water current capacity to the governing system influence dynamics. changes delivering through the difference pressure to obtain the water level signal to take host adjustment signal h. if the water level supposes the definite value is g, then should have under the equilibrium condition d×

36、dk-w×wk+h-g=0 relational type existence. dk is steam discharge coefficient wk gives the water discharge coefficient. if again establishes time, guaranteed d×dk=w×wk that may obtain h=g under the stable state. this time the regulator output on with conforms to the correspondence, stops

37、 to the water valve in some position. if has or many signals changes, the state of equilibrium is destroyed, the pi adjustment module output will certainly to change. when the water level elevated, then the adjustment module output signal reduces, causes to close slightly for the water regulating va

38、lve. otherwise, when the water level reduces, the adjustment module output value increases, causes to open in a big way to the water valve. the practice proved three impulses can maintain the water level for the water single pole regulator system stably, also gives the water regulating valve movemen

39、t to be steady. the boiler also has a quite important control loop for the aqueous system in is for the hydraulic pressure return route, because the steam drum internal pressure is higher, must make up the water to the boiler to have to provide a higher pressure, enhances the hydraulic pressure for

40、the hydraulic pressure return route function, enables the water normally to pour into the steam drum. but in the steam current capacity had not achieved when full load, to gives the water current capacity the request not to be high. generally uses the feed pump in the old style boiler system continu

41、ously by the labor frequency way revolution, reduces the hydraulic pressure with the return valve to prevent the cartridge igniter, now generally uses through the frequency changer constant pressure water supply way control hydraulic pressure. boiler to water volume through steam drum fluid position

42、 adjustment. the steam drum fluid position survey selects floats the tube liquidometer. for the effective use transformation waste heat, reduces the consumption, decreases the labor intensity, is advantageous is stable to the overall craft, requests the steam drum fluid position automatic control, w

43、hen regular production the undulation should be smaller than ±5%. the pid adjustment steam outlet valve may the very good control dome pressure. after drives normally undulates the scope not to be big, may not consider. the transformed load undulation, the pre-heater boiler for the water temper

44、ature change, the boiler load undulation, dumps pollutants the quantitative change these factors to have to consider to the steam drum fluid position influence. take the steam drum fluid position as the main tuning parameter, take gives the water current capacity as the vice- accent parameter, take

45、the steam current capacity as a forward feed, but the adjustment effect is very bad. causes the steam drum fluid position major rises and falls. considered this waste heat boiler controlled variable coupling small, flow simple, produces the steam quantity to be also stabler, we are inspired from in

46、operator's operation, thinks the reduction thus to stabilize to the water volume undulation to the water temperature becomes this waste heat boiler fluid position control the main point. therefore we select "to the steam decide the water + fluid position forward feed" the ratio control

47、 plan, plan diagram like chart 3 shows.chart 3 the steam decides the water + fluid position forward feed ratio control plan diagram coefficient k is the soft drink loss factor (gives water current capacity and steam current capacity ratio), the scope is 1.1 1.2. the pid parameter is p = 300%, i = 0.

48、4, d = 0. this group of pid parameter may enable the valve position margin of fluctuation not greatly but the return route to have the quicker track effect. the fluid position forward feed coefficient and the boiler fixed load close correlation, generally are the fixed load bigger forward feed coeff

49、icient is also bigger. this project waste heat boiler fixed load is 35t/h. the forward feed coefficient as soon as assigns according to the table, sees the attached list:the attached list forward feed is a mathematical tablethe scope of level（%） <45 4546 4647 4748 48 49flowcoefficien（t/h） 1.0 0.8

50、 0.6 0.4 0.2the scope of level（%）4951 5152 5253 5354 5455 >55flowcoefficien（t/h）0 -0.2 -0.4 -0.6 -0.8 -1.0throws transports when first throws transports for the water current capacity single return route, after the adjustment is steady, then cuts for the steam current capacity ratio control, at t

51、he same time the fluid position forward feed the function. to the steam decides the water + fluid position forward feed ratio control plan to move transports simply convenient, after throws transports (produces steam quantitative change) after the load perturbation, the fluid position perturbation (

52、dumps pollutants quantitative change) to test, since the anti- perturbation performance has been good, throws transports moves steadily, achieves the technological requirement. chart 4 was the 2.5h real-time fluid position record curve, in which has recorded the load perturbation situation. fluid po

53、sition undulation scope < ±3%.chart 4 real-time fluids positions record curve4 forever great plc pid control system analysis4.1 brings pid the control function the fatek programmable controller pid control and its controller or intelligent pid controller (measuring appliance) already very ma

54、ny, the product actual center obtained the widespread application in the project, has various pid controller product, took the domestically produced plc enterprise, forever the great electrical machinery joint-stock company continuously will devote to the plc research development work, will bring pi

55、d the control function the fatek programmable controller (plc) will be uses its closed-loop control module to realize the boiler steam drum fluid position pid control, in unusual situation, when the fluid position deviation normal value will be bigger, through the plc control system control, will be

56、 allowed fast to restore the water level, will guarantee the boiler the security stable movement. when the water monitor and the host vapor temperature control has the contradiction, may act according to the contradictory principal aspect to carry on two coordination controls. it contains for the wa

57、ter flow control return route and the steam drum water monitor return route two control loops, in the essence is the steam current capacity forward feed and the water level - current capacity cascade system composition compound control system. when steam current capacity change, in the boiler steam

58、drum water monitor system may rapidly change the water volume for the water flow control return route to complete the coarse adjustment, then completes the water level again by the steam drum water level regulator the thin accent. 4.2 steam drums waters level pid control design merit (1) reduces the disturbance to the host return route influence, may adjust by the vice- return route controller. (2) because the vice- return route existence reduced