废气,除尘自控系统

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The dust removal system is mainly composed of a fan, an electric butterfly valve, a rotary valve, a dust collector, a dust conveying device, a pipe, a valve, etc. Under the attraction of the fan, the dust-containing gas will enter the bag dust collector after the flue gas temperature drops. The dust in the flue gas is removed with a cloth bag, and the purified gas is discharged into the atmosphere from the chimney. Along with the accumulation of dust, the pressure difference increases gradually. When the pressure difference increases to the set value, the dust removal bin will be dusted from bin to bin, and then the dust will be discharged one by one and transported regularly. 

The dust removal control system can realize the following functions: to realize high precision intelligent detection of temperature signal and pressure difference signal; to realize temperature control, ash cleaning control and ash unloading control; to have manual / automatic, pressure difference / compulsive control function; It has the functions of historical data storage, real-time data dynamic display, printing and alarm for all the control and detection analog quantity, and can realize parameter setting and remote control in the upper computer for all the controls. The process flow can be dynamically displayed on a computer screen. 

Structure and configuration of control system. 
According to the characteristics of dust removal control, the dust removal automatic control system is divided into three parts, which are field level (detection instrument, sensor and execution device), lower computer (PLC) and upper computer. The system uses PLC as slave computer to process analog and on-off signals directly, and industrial control computer as upper computer, and uses configuration software to establish a friendly real-time operation interface to communicate with the lower computer. The field instrument mainly detects the process parameters and the running state parameters of the equipment, PLC and distributed I / O through the data scanning to collect the signal and carry on the data processing, then sends the control signal to the spot execution equipment according to the control request to complete the control function. On the one hand, the host computer receives the input signal of PLC, on the other hand, according to the control requirements, it sends control instructions to PLC to monitor the process and realize the function of process data management. 

Ash cleaning control. 
Ash cleaning control can be achieved according to the needs of manual / automatic control, pressure / forced control. The PLC first judges the control mode of the system, that is to say, the system chooses the forced mode or the differential pressure mode, if the forced mode is chosen, then judges whether or not the ash is cleaned according to the forced cleaning signal; if the system chooses the pressure difference control, The dust-clearing signal is effective only when the differential pressure of the dust collector reaches the set value. If the automatic cleaning mode is selected, after the cleaning signal is effective, the control system will clear the ash in turn for each storehouse. The cleaning process includes two processes: reverse blowing and settling. The times of these two processes and the running time of each process can be set according to the technological requirements. 

Temperature control. 
For high-temperature flue gas purification systems such as furnaces and kilns, temperature control is related to the safety and life of the equipment. If the flue gas temperature entering the dust collector is too high, it will burn out the filter bag or shorten the filter bag life; if the flue gas temperature is too low, the phenomenon of condensation will occur, causing dust to harden on the filter bag, leading to difficulties in cleaning ash, and the resistance of the dust collector will continue to rise or even form a vicious circle. The system is paralyzed. In addition, when the flue gas temperature is too low, the fan load will increase, and the fan motor will be overloaded. Therefore, the temperature must be controlled. The system adjusts the mixing air volume by adjusting the opening of the electric butterfly valve, and realizes the adjustment of the temperature by controlling the air volume. The temperature control strategy is as follows: when the inlet temperature is greater than the fixed value, the electric butterfly valve should be opened immediately; if the temperature is on the high side, the valve should be opened if the temperature is too high and has a rising tendency; and the valve should be opened according to the inlet temperature value to adjust the opening degree of the air mixing valve. If the temperature is on the low side and has a downward trend, turn off the valve properly. The PID algorithm is adopted in the control system. The selection of the proportion, integral and differential constants of the controller is decided by the model of the controlled object and the required optimal objective function. 

Upper computer. 
The upper computer of the system is industrial control computer, which communicates with PLC through industrial Ethernet. The communication medium is optical fiber, which is composed of network card, switch, photoelectric conversion module and PLC communication module. At the same time, the system can be connected with other process control processes in the workshop to form a two-level network to realize the production management. The screen monitor is programmed by Siemens WINCC configuration software with friendly interface. The operator can monitor the whole production process through HMI, and has the alarm and print functions such as parameter setting, each control screen, curve, historical data, print management and so on. 

Single check and system debugging. 
Single check refers to the operation and debugging of a single device, which is the basis of system debugging. Including all the sensor components, detection instrument output, display is normal, parameter adjustment is correct, motor, hydraulic coupling, fans, valves and other executive devices, start, running state is normal. Monitor their running on the PLC program and HMI, solve the problems in time, prepare for the next step of system debugging. System debugging is the debugging of the entire control system after the end of the single debugging, under the normal operation conditions of all the equipment. Including all the system control, interlocking conditions of the debugging, HMI control procedures and debugging of the monitoring program. 

Trial operation. 
At the end of the system debugging, the system enters the trial operation phase. The trial operation is to complete the debugging of the automatic monitoring system under the working conditions with load. Including the adjustment of some important control parameters in the system. For example, under different operating conditions of electric furnaces, the air volume of the straight row system and the roof cover is different, and the theoretical value and the actual value are always somewhat different, so it is necessary to adjust the rotational speed of the supercharged fan and the main fan under the actual production conditions. It can not only meet the requirements of dust removal, but also save energy.

除尘系统主要由风机、电动蝶阀、旋转阀、除尘器、粉尘输送装置、管道、阀门等组成,含尘气体在风机的吸引下,使烟气温度下降后进入布袋除尘器,用布袋除去烟气中的粉尘,净化后的气体从烟囱排入大气。除尘器随着粉尘的积累,压差逐渐增大,当压差增至设定值时,除尘仓逐仓进行清灰,然后逐仓进行卸灰,定期运走。


除尘控制系统可实现如下功能:对温度信号、压差信号实现高精度智能检测;实现温度控制、清灰控制、卸灰控制;具有手动/自动、压差/强制控制功能;对所有控制和检测的模拟量具有历史数据存储、实时数据动态显示、打印和报警功能;对所有的控制均能在上位机实现参数设定和远程控制;工艺流程能在计算机屏幕上动态显示。


控制系统构成与配置

针对除尘控制的特点, 除尘自动控制系统共分三大部分,分别由现场级(检测仪表、传感器和执行装置),下位机(PLC)和上位机组成,系统采用PLC作为下位机直接处理模拟量和开关量信号,选用工控机作为上位机,利用组态软件建立友好的实时操作界面与下位机进行通信。现场仪表主要检测工艺过程参数和设备运行状态参数,PLC及分布式I/O通过数据扫描采集信号并进行数据处理,然后根据控制要求向现场执行装置发出控制信号完成控制功能。上位机一方面接收PLC的输入信号,另一方面根据控制要求向PLC发出控制指令,对工艺过程实现监控,同时实现过程数据管理功能。


清灰控制

清灰控制可根据需要实现手动/自动控制、压差/强制控制。PLC首先判断系统的控制方式,即判断系统选择强制方式或差压方式,若选择强制方式,则根据强制清灰信号判断是否清灰;若系统选择压差控制,仅当除尘器的差压达到设定值时,清灰信号才有效。如果清灰选择自动方式,清灰信号有效后,控制系统对各仓依次进行清灰。清灰过程包括反吹、沉降两个过程,这两个过程的次数以及各过程的运行时间可按工艺要求设定。


温度控制

对于炉窑等高温烟气净化系统,温度控制关系到设备的安全和寿命。进入除尘器的烟气温度过高会烧毁滤袋或使滤袋寿命缩短;烟气温度过低又会产生结露现象,引起粉尘在滤袋上板结,导致清灰困难,除尘器阻力不断上升甚至形成恶性循环,系统瘫痪。另外,烟气温度太低时,风机负荷加大,会出现风机电机超载。因此须对温度进行控制。系统利用调节电动蝶阀的开度调节混风量,通过对风量的控制实现温度的调节。温度控制策略为:当吸风口温度大于定值时立即将电动蝶阀全部打开;根据进口温度值调节混风阀开度,若温度偏高且有上升趋势则阀门开大;若温度偏低且有下降趋势则适当关小阀门。控制采用PID算法,控制器的比例、积分、微分常数的选择根据被控对象的模型和要求的最优目标函数决定。


上位机

系统上位机采用的是工控机,通过工业以太网与PLC进行远程通讯,通讯介质采用光纤,由网卡、交换机、光电转换模块、及PLC通讯模块组成。 同时,该系统可与车间内其它工艺控制过程联网,组成二级网络,实现生产管理。画面监控采用西门子WINCC组态软件编程,界面友好,操作人员通过HMI可 监控整个生产过程,并具参数设置、各控制画面、曲线、历史数据、打印理等报警和打印功能。


单体校检与系统调试

单体校验是指对单个设备的运行调试,是系统调试的基础。包括所有的传感器元件、检测仪表输出、显示是否正常,参数调整 是否正确,电机、液力偶合器、风机、阀门等执行装置,启动、运行状态是否正常。在PLC程序和HMI上监控它们的运行,出现问题及时排除,为下一步系统联 调做好准备。系统调试是在单体调试结束后,所有设备运行正常的条件下,对整个控制系统进行的调试。包括系统中所有控制、联锁条件的调试,PLC控制程序的 调试及HMI监控程序的调试等。


试运行

在系统调试结束后,进入试运行阶段,试运行是在带负荷的工况条件下,完成系统自动监控的调试。包括系统中一些重要的控制参数的调整。比如在不同 的电炉工况下,直排系统和屋顶罩的风量是不同的,理论值和实际值总会有些差异,这就需要在实际生产工况下调整增压风机和主风机的转速,使其既满足排尘的要求,又节省能源。