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Application of DCS control system in a Cements Limited
Project Scope: To provide a complete DCS for the new dry process cement production line with a daily output of 2500 tons, to meet the needs of cement production, and to provide stability guarantee for the production of high quality cement. The overall goal of control system design is:
Provide reliable operation environment for producing high quality cement.
Improving the automation level of the entire cement production line.
To achieve high quality operation of units and improve operation economy;
To improve the working efficiency of the operators and meet the requirements of the crew running on duty.
Improve efficiency and reduce energy consumption.
2.The design idea of system design and application.
1) Functional design: embody the degree of automation after the completion of DCS, the ability to deal with accidents (alarm, analysis, guidance, treatment, etc.) and advanced control strategies, to maximize efficiency, reduce energy consumption as the design idea. The details are as follows:
The process of automation is coordinated by the DCS system to achieve energy balance.
Ensure the safe, reliable and efficient operation of the unit and start and stop
Improving technical and economic benefits of unit operation
The unit runs at the upper limit of the rated parameters, so that the unit is in the best operating condition.
To achieve high automation input rate, improve reliability, reduce misoperation and reduce accident rate.
Perfect operation guidance and accident analysis means.
The operating conditions of the unit can be reflected by many monitoring parameters. When abnormal operating conditions occur, on the one hand, the overspeed function and process restriction mechanism are implemented, on the other hand, relevant parameters, trends, charts and other efficient ways are provided to inform the operators to deal with in tim
Operation record printing, alarm printing, accident recall printing, periodic report forms and other functions are conducive to the daily management of the unit and accident analysis.
Efficient and convenient system online maintenance.
2) system design: it embodies the design idea of DCS's high reliability, advanced nature, easy maintenance and easy configuration. The details are as follows:
All components are standardized, universal and modular.
Control system should be stratified, decentralized and autonomous.
All I/O modules are designed intelligently with isolation measures and high common mode rejection ratio and differential mode rejection ratio. And have
Software digital filtering and elimination of accidental interference.
System self diagnosis to channel level.
Selecting modular functional configuration software to improve software transparency.
Adopt industrial Ethernet network structure, communication rate is 100 mpbs, backbone network is redundant ring network, each sub-station is connected to the backbone network through twisted pair cable, which has strong communication expansion ability.
Provide communication interfaces with other systems, such as industrial Ethernet, PROFIBUS DP or MODBUS.
Support international standard data interfaces, such as OPC, ODBC, OLE, DDE, SQL and so on.
Support SIS system to realize DCS data monitoring.
Three system configuration and function realization
According to the characteristics of cement production and the design and distribution of I/O points, the following design schemes are carried out. The basic functions of the design include: raw material mixing system, raw material grinding system, raw material homogenizing system, firing system, kiln head system, coal grinding system, power system, alarm system and trend chart. The system is designed according to the process flow. The following are the following:
1 raw material batching system
The control system mainly carries on the automatic control to the iron powder, sandstone and limestone level gauge, which is the raw material for cement production, and realizes the reasonable and high efficiency ratio of each raw material. The purpose of batching is to determine the consumption ratio of various raw materials and fuels and to produce cement clinker with high quality, high yield and low consumption. The principle is that the raw meal prepared is easy to grind and burn, the clinker produced is of high quality, the production process is easy to operate, control and management, and simplify the process.
2 raw meal grinding system
Grinding is the process of breaking small pieces of granular material into fine powder. Raw meal mill is a process for grinding raw materials into raw meal after grinding. It mainly includes raw meal mill, separator and dust recovery function. Reasonable raw meal grinding system is of great significance to ensure the quality and output of raw meal, improve the quality and output of clinker, and reduce the power consumption per unit product.
3 raw meal homogenization system
Raw meal homogenization is the use of air stirring and gravity under the effect of the "funnel effect", so that raw meal powder falling down when cutting as many layers of material surface as possible to be mixed. At the same time, under the action of different fluidized air, different sizes of fluidized expansion will occur along the parallel material surface in the reservoir. Some discharged materials in the reservoir area, and some fluidized in the reservoir area, so that the material surface in the reservoir will produce radial tilt and carry out radial mixing homogenization.
4 firing system
The firing system is the process of converting raw meal into clinker, which directly determines the output and quality of cement, the consumption of fuel and lining, and the safe operation of rotary kiln. The key technologies are suspension preheating, calciner and rotary kiln, which undertake the preheating, decomposition and firing of cement clinker respectively.
5 kiln header system
The function of grate cooler in kiln head system is to realize gas-solid heat transfer between clinker and cooling air efficiently and quickly. When the clinker is quench, there is also the heating and warming task of two times of entering the kiln and three times of entering the furnace.
6 cement grinding and packaging for the latter stage of construction, has not yet started.
7 power system
It is mainly for real-time monitoring of raw material power room high voltage cabinet and firing power high voltage cabinet.
8 network configuration
The control stations of cement production are very dispersed, and the safety of the system depends largely on the stability of the control network. The design and application of redundant optical fiber ring network technology make our process control.
From the hardware structure, the system can be divided into:
1. operator station (OS station) and engineer station (ES station)
The DCS system is equipped with four independent operator stations (OS stations), including remote batching, raw meal grinding, firing kiln tail kiln, kiln head and coal mill, one OS station, namely, four operator stations (each operating station with 24 inch LCD), and one ES station in the central control room. Each set of OS adopts a mature and reliable DELL commercial computer.
OS station provides graphics, lists, operations, historical data reproduction for the operator, and can be output on the printer. Run WINCC6.2 application software under Windows XP multitask network operating system. All OS stations are all-round duty configuration, image, operation, data consistency, to achieve on-site start-stop, monitoring, data storage operation.
The system is equipped with 1 sets of engineer stations (ES station) and a mature and reliable DELL commercial computer.
ES station mainly completes the generation and downloading of real-time database, control block, graphics, trends, reports and other system data, completes the detailed self-diagnosis of the system and the list and backup of system data. Run the STEP7v5.4 and WINCC6.2 application software under the Windows XP multitask network operating system.
The system can be configured and maintained by electrical professionals through the engineering station. Professional engineers can modify the system online or offline on the spot. At the same time, all operating conditions and control logic can be viewed on the engineer's station, which increases the degree of user's mastery of the system, as well as the transparency of system software and hardware. When no configuration is needed, the software that runs exactly the same as the operator station can be run.
The whole system is equipped with 2 network printers for recording printing and CRT image copies. Printer selects HP network printer.
2. remote I/O station
The system is composed of Siemens CPU and remote I/O station of Uygur UNIMAT. Each distributed I/O station adopts Uygur UNIMAT's UN 300 series module, and communicates with PROFIBUS-DP through 153 interface module and S7-400 central control station. Among them are UN 300 series UN 321-1BL00-0AA (32DI), UN 322-1BL00-0AA0 (32DO), UN 331-1KF01-0AB0 (8AI), UN 331-7KF02-0AB0 (8TC), UN 332-5HD01-0AB0 (4AO), which not only saves costs but also reduces energy consumption.
3. redundant communication network
CP443-1 as a standard industrial Ethernet connection device, in the physical layer using a high level of protection of communication cables, industrial Ethernet cards with CPU can handle communication signals independently. High-speed industrial Ethernet is based on the communication protocol of industrial Ethernet, which increases the communication rate to 100M/s. High-speed Ethernet in SIMATIC NET uses full-duplex parallel (FDX) communication mode, which allows stations to send and receive data at the same time, and the communication rate can be doubled. SIMATIC NET also uses switching technology on high-speed Ethernet. The whole network segment is divided into several subnets by using switching module. Each subnet can independently form a data communication network segment, which can greatly improve communication efficiency. Due to the existence of data communication congestion on the network segment, the actual communication technology on the network is only 40%. With full duplex parallel communication technology and switching technology, the communication capability of the network can be fully utilized.
Four, control points and Strategies of cement production
Cement production process equipment has large capacity per unit, continuous production, high speed and coordination. In order to improve the production efficiency and competitiveness of enterprises, the implementation of automatic control is very important. The combination of Siemens CPU and the remote I / O station of UNIMAT can satisfy the control requirements of cement industry, which is mainly based on switch quantity, supplemented by analog quantity and accompanied by a few adjusting circuits.
1. Limestone crushing and conveying system
The equipment of limestone crushing and conveying system has interlocking relationship. The equipment is controlled sequentially according to the principle of "starting up in reverse flow and stopping in downstream flow". The control difficulty of the limestone crushing and conveying system lies in the automatic control of the feeding quantity of the limestone crusher. The speed of the plate feeder can be adjusted automatically by the change of the power of the crusher so as to keep the speed within the required range of operation, so that the material in the limestone silo can not be unloaded because of the high speed of the plate feeder. The plate feeding machine plays a certain protective role for the equipment.
Flowchart of raw meal grinding (refer to raw material mill 1.bmp)
The technological process range of raw material preparation system: from the bottom of raw material dispensing station to the top of raw material homogenization storehouse, including raw material dispensing and transportation, including raw material grinding, raw material transportation into storehouse. The control points and strategies are as follows:
Raw meal quality control (QCS) system
QCS system (quality control system) is widely used in cement production. The raw meal quality control (QCS) system consists of an on-line calcium-iron fluorescence analyzer, a computer and a speed-regulating electronic belt scale. Intelligent on-line Ca-Fe fluorescence analyzer can automatically sample, sample preparation and continuous measurement, calculate the burden by QCS system, and adjust the proportion and control the composition of the material by DCS, so as to keep the three-rate value of raw meal fluctuated near the target value, thus greatly improving the qualified rate of raw meal ingredients. And quality stability.
Raw meal grinding load control system
The control difficulty of the raw meal grinding control system lies in the load control of the mill. When the feed moisture and hardness change, the system ensures that the mill is in the best grinding state with stable load by adjusting the feed material quantity to avoid blocking or air grinding. The usual adjusting methods for load automatic control system are: setting a constant of grinding input, and adding new feeding quantity to the grinding input of the separator under steady state is equal to it; secondly, adjusting the power of the elevator or the electric signal of the mill as the main control or monitoring signal in time; thirdly, adjusting the grinding return, lifting function and electricity of the separator. Mathematical models of ear and other signals are analyzed or controlled or extreme value controlled.
Most of the vertical mills are controlled by constant, while the ball mills are mostly controlled by electric ears or hoist power signals.
3. Raw meal homogenization storehouse control
Fig. 4 flow chart of raw meal homogenization storehouse (refer to raw meal homogenization system 1.bmp)
Raw meal pre homogenizing system
Raw meal pre homogenization is achieved by controlling the bottom discharging electric vibrator. Raw material pre-homogenization storehouse is usually a long bar storehouse. There are 26 electric vibrators at the bottom of the storehouse, which are divided into two groups. Each group has 13 electric vibrators, each of which can be controlled by time program separately. The two electric vibrators are controlled by a programmable controller (PLC) according to a certain time program, so as to achieve the pre-homogenization of different time feeding according to a certain proportion. Get into the mill.
Raw meal homogenization system
Homogenization of raw meal is based on air blowing with uniform pressure to homogenate raw meal. Usually an air-filling device is installed at the bottom of the reservoir, and the time sequence control strategy is adopted. According to the time sequence, the air-filling solenoid valve at the bottom of the reservoir is opened and stopped to make the material fluidized and agitated, and the raw material is mixed to achieve the goal of homogenization.
Automatic control system for measuring stock quantity
The opening of the electric flow valve on the side of the raw material warehouse can be adjusted automatically by the weight signal of the measuring silo, so that the material quantity of the weighing silo can be kept stable, so as to ensure the stability of the discharge quantity of the measuring silo.
Blanking control of raw meal homogenization storehouse
In the production process, the firing zone temperature is generally required to be controlled in a suitable range, because it is very important to the quality of clinker. The setting value of raw meal discharge is set by combining raw meal volume, fan air volume and firing zone temperature. The system can automatically adjust the opening of the electric flow valve under the measuring silo by using the feedback value of the solid flowmeter, so that the raw meal can be stabilized on the setting value, so that the raw meal into the kiln can be kept stable, and ultimately the kiln can be guaranteed. Stable operation of the system.
4. Pulverized coal preparation system
Flow chart of pulverized coal preparation (refer to "coal grinding system 1.bmp")
Automatic control of gas temperature in grinding mill
The temperature of grinding gas is directly related to the moisture and safety operation of the finished products. In order to ensure the production of qualified pulverized coal, and at the same time to ensure that the system temperature can not be too high, the control system set up the mill outlet gas temperature automatic control loop, by changing the mill inlet cold air valve opening to control the mill outlet gas temperature stability.
Automatic load control of mill
The change of pulverized coal quantity in the pulverized coal bin will affect the metering accuracy of the part of pulverized coal feeding. The amount of pulverized coal in the pulverized coal bin should be as constant as possible in normal production. At the same time, the normal and safe operation of the mill should be guaranteed to prevent "full grinding". An automatic control loop is adopted to automatically adjust the feed quantity of the grinding head quantitative feeder by the electric ear signal of the mill.
5. Firing system
Kiln end flow chart (refer to firing system 1.bmp)
Metering and automatic adjustment of coal feed in calciner
The temperature of calciner is an important control parameter to ensure the normal operation of rotary kiln. The mixing ratio of fuel and air must be properly controlled when the raw meal volume is constant. Therefore, the temperature of the decomposition furnace is measured in order to achieve optimal control. The temperature of the decomposition furnace is adjusted by automatically increasing and decreasing the amount of coal, so that it can be controlled at the desired set value. Not only can the calciner maintain the highest decomposition rate, but also can not cause the raw meal to bind because of the high temperature, which affects the normal operation of the kiln system.
Regulation of outlet pressure of preheater
The outlet pressure of the preheater is a main index of the air balance of the reaction system. The outlet pressure of the preheater is controlled by adjusting the valve opening of the high temperature fan.
Automatic purging device for preheater
In order to prevent the crust blockage from affecting the normal operation of the preheater system, the computer turns on the corresponding solenoid valve on the preheater in a certain time sequence regularly, opens the compressed air pipeline in turn, and purges the preheater step by step to prevent the crust blockage from affecting the normal operation of the preheater system.
Kiln head flow chart (refer to kiln head system 1.bmp)
Automatic control of kiln head negative pressure
The negative pressure of kiln head represents the balance between the ventilation in the kiln and the two air entering the kiln. According to the negative pressure of kiln head, the valve opening of the exhaust fan of electrostatic precipitator can be adjusted automatically to control the balance among the secondary air volume at kiln head, the third air volume at kiln tail and the waste gas volume at kiln head, so as to achieve a stable balance between calcination and cooling clinker.
Speed control of rotary kiln
The strategy adopted is to maintain the balanced and stable production of the whole kiln system by properly adjusting the rotary speed of the rotary kiln on the premise of stabilizing the raw material and fuel quantity.
Automatic adjustment of air volume in one or two chamber of grate cooler
Secondary air has a great influence on the combustion quality, stability and fuel consumption in kiln. The control aim of the system is to stabilize the fresh air flow into the kiln by stabilizing the air flow in the first and second chambers, so as to provide conditions for the stable operation of the kiln.
Automatic adjustment of material layer thickness of grate cooler
Controlling the bed thickness of grate cooler can stabilize the secondary air temperature to stabilize the normal operation of the kiln, and make the clinker achieve the best cooling. Because it is difficult to measure the thickness of grate cooler bed, the pressure under grate is used to adjust the grate speed in order to stabilize the thickness of grate cooler bed. For the two stage grate cooler, it also involves one or two stages of grate speed regulation.
6. Exhaust gas treatment system
The key of the waste gas treatment system is to control the spray quantity of the humidifier. The control strategy is to control the number of nozzles according to the outlet temperature of the humidifier, so as to improve the dust collection efficiency of the electrostatic precipitator by humidifying and cooling. The outlet temperature of the humidifier is generally controlled at about 130 degrees.
7. Cement grinding and conveying system
Feed quantity control
The feeding quantity is uniform and stable, and the feed quantity is adjusted by grinding the sound signal and the power of the hoist.
Automatic control of gas temperature in grinding mill
The gas temperature is controlled by adjusting the ventilation volume of the mill.
Adjustment and control of separator
Storage and transportation of clinker
There is a process interlocking relationship between conveyor and storage equipment. The equipment is controlled sequentially according to the principle of "start-up in reverse flow, stop-down in parallel flow".
8, power system
Four use effect analysis
The DCS system is composed of Siemens CPU and long-distance I/O station of Uygur UNIMAT. It has been running steadily and reliably since its completion. The control precision fully meets the design requirements. It not only saves the cost, but also reduces the energy consumption, improves the efficiency, and fully achieves the expected goal.