Automated system in cement plant Holcim Serbia
As the specialists say, the Cement will be the main building material during the whole XXI Century. It is the reason, that the Cement Plants need a lot of reconstructions, automation and innovations for all processes and departments. The Cement plants are separated into highly independent sub-processes (departments) and it reflects in the design and layout of the process control system. In the same way, automation system of cement plants are divided to separate control systems for each department. At last 3 years SAT Ltd. company has completed a number of process automation systems for all departments at the Cement Plant HOLCIM (Srbija) –Popovac, Republic of Serbia and Montenegro.
The main supplied and commissioned systems for this plant are:
• Complete automated system for Raw Mill Department;
• Complete automated system for Coal Grinding Plant;
• Complete automated system for Kiln Department;
• Complete automated system for Cement Mill Department;
• Complete automated system for Packing Plant and Palletizing Plant;
• Complete automated system for Bulk Cement Loading Department.
A completely new Automated system for Coal Grinding Plant was supplied, installed and commissioned for HOLCIM (Srbija) in March 2005 by SAT Ltd. Sofia, Bulgaria. The Coal Grinding Plant was made on a “green meadow” by European producers of the equipment for cement industry like - Loesche Germany, KHD (MVT) Germany and FLSmidth Denmark - for mechanical suppliers; SAT Ltd. (Systems. Automation. Technologies) Sofia, Bulgaria - for electrical and process automated control system. The realization of the Project started in October 2003 and was realized in period of 6 month. The electrical engineering, design, production of the equipment and programming was made in period of 3 month in the end of 2003. The erection, installation, testing and commissioning was realized in period of 3 month also, during the planned winter stoppage of the plant in 2004.
Structure and specifics of the system
The uniform structure of the process control system, which is applied for each process department, indicates the principles of the concept for automation.
The process control is organized in the following levels:
• The I/O Level: using I/O devices to connect sensors, valves and for motor control.
• The BUS Level: using standard field bus (Profibus DP) for the communication of the I/O level to the Process Stations.
• The Controller Level: using the Process Station (PS) with it’s software, assuring the operation of machines and process and provide all required communication interfaces to other control levels.
• The Operator Level: using the Operator Stations (OS), assuring a simple and efficient human machine interface (HMI) for the remote automatic operation of the Plant.
• The Supervisory Level: using high-level specific tools to supervise the whole plant.
The process control system comprises all necessary hardware and software for motor and process control and for interface with products for high level automation. It includes all Equipment required for Safe, Local, Remote, Manual and Automatic operation of the Coal Grinding Plant. Process control system comprises also all necessary equipment for power supply, machine control, data exchange, visualization and Human-machine interface.
Automation System for CGP is made as following separate functional groups with specific functions & parameters:
• L11 - unloading and transportation of the raw coal and petcoke from Unloading Station to the main Storages;
• L21 - unloading and transportation of the raw coal and petcoke from main Storages to the two Raw Silos;
• L61 – dosing, mixing, grinding and extracting of coal and petcoke;
• L91 – extracting and transportation of fine material to the two Fine Coal Silos;
• 481 – dosing, transportation and firing of the fine coal to the Kiln Burner. Automated system (motor and process control) for this Project is based on the new DMC Concept of SAT Company.
Separate Distributed Motor Control Centers (DMC’s) for each motor are installed in the field close to the machines. In each DMC are included distributed modules of main PLC Process Station and all necessary low voltage equipment for this motor (circuit breakers, contactors, relays, fuses, terminals and start/stop push buttons).
For power supply of the DMC’s are used Low Voltage Distributed (LVD) Power Boards. Several DMC’s are connected to one power feeder using “chain” concept for power cables. For LVD equipment was used components of Schnieder Electric. All other process signals were connected to distribute modules of main Process Station into Distributed Input Output Boxes (DIO’s), installed at site close to the Field Devices and Sensors. All DMC’s and DIO’s are connected to the main Process Station (PS) using Profibus DP communication.
Process Stations are based at Siemens Simatic S7 400 PLC system. For the distributed boxes were used Siemens Simatic ET200 S modules.
This DMC Concept assure easy complete maintenance and comfort adjusting of the equipment, decrease quantity of the cables, installation materials and installation works and totally go down the price of the automated system more 15%. Control functions for machine control are realized using Siemens system software Step 7. The application software is based on special PLC Standard Modules of SAT Ltd. Bulgaria (SAT SM04/ST7/WinCC6 Ver.4.0). For visualization of the processes and Human-machine interface were used PC based Operator Station (OS) with WinCC 6.x system software of Siemens. Application software for Operator Stations was based on the same Standard Modules of SAT Ltd. Bulgaria. The communication between main PS and OS is Profibus DP. For Middle Voltage Distributed System (MVD) was used equipment from Schnieder Electric for upgrading of the existing 6 kV panels. For each department of the Plant is used separate Process and Operator Stations. The communication between Departments is made using Industrial Ethernet.
Scope of supply and services for CGP
The scope of supply for this Project included:
• Upgrade of 2 Outgoing MV Feeders (6 kV) and 2 Dry (6 kV) Transformers;
• New Low Voltage Distribution (LVD) Power Panels (400V), incl. PLC I/Ocomponents and Power Factor Compensation - 7 pcs.;
• VSD control - frequency converters of ABB – 8 pcs.;
• Distributed Motor Control boxes (DMC’s), incl. PLC I/O-components – 48 pcs.;
• Field devices and sensors;
• Operator Station, incl. Standard and Application Software of SAT Ltd. and System software of Siemens;
• Process Station (PLC Simatic S7 416 CPU), incl. Standard and Application Software of SAT Ltd. and System software of Siemens;
• Distributed Input / Output boxes (DIO’s), incl. PLC I/O-components – 13 pcs.;
• Installation material (cable traces and accessories);
• Power, control and communication cables;
• Grounding, Lightning and Earth protection systems;
• Lighting System for new plant section. The Project for CGP, realized by SAT, included the following services:
• Electrical Design and Engineering;
• Producing and supplying of the electrical equipment;
• Erection and installation of all electrical equipment, cable traces and cables;
• Signal, Rotation and Sequence Tests;
• Training of the maintenance and production personnel.
Main function of the system
The main functions realized with automated system for Coal Grinding Plant are - Fully automated process control; Deserted department operation; Optimization of the processes that ensures high efficiency and productivity of the Coal Mill; Friendly Human-machine interface; Diagnostic of the equipment and self diagnostic of the system; Alarm, Warning and Status messages (text and sound) for all parameters and equipment; Visualization and animation of all process parameters, signals and status of the equipment; “Automatic”, “Remote Manual Free” and “Local Free” modes for each consumers; Historical Trends and digital records for main parameters; Reports – automatically creating of daily, monthly and shift reports; Records of the operator’s actions; Password protected 4 level system; Monitors (password protected) for adjustment of motors, parameters and loops without knowledge of programming; Creating of database for systems of higher level;
Coal grinding plant
• GROUP L11 – Unloading of the coal/petcoke
Group L11 transports coal or petcoke from the unloading station to the two different storages. The material can be chosen either from the operator’s station or from the local panel that is mounted at the unloading station. The material is extracted from the source hopper by the four Chain Conveyors to the several Belt Conveyors. The Metal Separator is mounted above the belt to prevent metal pieces going to the storage. The Stacker is using for unloading the coal into the storage. The Stacker has its own PLC Simatic S7 300 based Sub-Control System that controls reclaiming processes. The Belt Scale measures the total quantity of material fed to the storages. It measures also current weight on the measuring point and current flow. The Sub-control system of the Belt scale was supplied by SAT and is based on the PLC Simatic S7 200 of Siemens also. The speeds of the belt and chain conveyors are controlled using variable speed drives of ABB to keep constant weight on the Belt Scale.
• GROUP L21 – Feeding the raw material silos
This group extracts raw material from the storages and transports it to the raw silos. It transports either coal that is extracted by the Re-claimer or petcoke that is loaded by human operated digger. The transport at the silos inlet is dedusted by the Bag Filter equipped with separate Sub-control System. The Metal Detector detects metal pieces in the material that have incidentally passed the Metal Separator and caused automatically redirection of the material containing a metal piece out of the silos. The system measures the weight of the silos and control automatically silos refill. The coal automatically extracts from the storage by Reclaimer. A separate Subcontrol system (based on PLC S7 300), connected to the main automation system, controls the Reclaimer.
• GROUP L61 – Coal mill grinding
The coal grinding is the main group of the department for Coal Roller Mill, produced by Loesche. It uses hot kiln gas for drying the ground material and fine coal transport. Several automatic control loops keep the technological parameters such as temperatures, gas flow and pressure. The Gas Analyzer measures constantly the CO and the O2 at the gas way and detects dangerous conditions. The equipment is protected against explosion by the Inertisation System. When a danger arises, the Inertisation System automatically injects CO2 at the system and prevents from explosion.
The main systems of this group are:
- The Lubrication System of the mill main drive and gearbox. It is essential for keeping the oil flow, pressure and temperatures in their technological parameters and to protect the equipment.
- The Hydraulic System - raises and lowers the mill rollers automatically using two discrete control loops.
- The Dynamic Separator - separates the fine coal ground by the Roller Mill. It is mounted on the top of the Mill and is driven by frequency converter.
- The main Bag Filter - separates the fine coal from the mixed air and coal flow. The system has to control: the inlet max temperature to protect the cleaning bags; the max level signals - the filter is jammed; the differential pressure max limit - the mill fan is stopped.
- The Inertisation System - consists of a gas CO2 tank, tank-monitoring system and a system of pipes and valves to protect the equipment when dangerous conditions arise.
- The Gas Analyzer for CO and O2 with a lot of measuring points.
- The Water Injection Cooling System - for injecting cooling water in the mill and to maintain the mill outlet temperature by PID-controller.
- The Mill Vibrations and Seal Fan - the purpose of the fan is to blow at the mill shelf and to maintain the pressure higher outside than inside.
- Mill feed - the materials dozen using VSD control of the Chain Conveyorskeeping all interlocks with temperature and differential pressure.
• GROUP L91 – Fine coal transport.
This group transports finely ground coal to the two Fine Coal Silos and work automatically according to the levels of the silos. A special Sampler makes trials of finely ground coal.
• GROUP 481 – Kiln firing.
This group transports and doses finely ground coal from the silos to the Kiln Burner. Group 481 consists of a main and secondary Fans, two Blowers - for coal transport and Pfister Dosing System to dose the finely ground coal to the burner.
- The sub-control system of Pfister - controls the prehoppers weight, dosing and supply constant quantities of fine ground coal to the kiln burner.
- The Burner - controlled by a subcontrol system of FLS, based on Simatic S7 300 Siemens and communicated with main control system.
- Silo Aeration - a system for maintenance of fast emptying of powdered materials from silos.
- The Bowers - to provide fine ground coals to the burner from Phister Dosing System.
• Startup signalization.
Fully automatic operation needs of separate sirens and flash lamps assigned to the each of the devices of the CGP for startup signalization.
Control loops of the Automation System
The Coal Grinding Plant in Popovac has six main control loops (PID controllers) that support more important parameters.
• Mill inlet pressure. In this coal grinding plant the mill inlet pressure influences the supply of gas from the kiln and the recirculation duct and it must be maintained constant. The regulating unit for the mill inlet pressure is the control damper in the recirculation duct.
• Mill outlet temperature. The mill outlet temperature is decisive for drying the material to be groundand must be held constant. The regulating unit is the speed of the booster fan that supplies hot gas from the kiln.
• Mill differential pressure. The mill differential pressure depends on the corresponding mill air volume flow rate, the quality and quantity of material being fed to the mill and should be held constant by means of controlling the material feed to the mill.
• Mill air volume flow. The volume rate of gas flow through a mill per unit time influences the grinding, classifying and de-dusting process in a grinding plant and for this reason must be held constant. The regulating unit is the speed of the mill fan.
• Mill water flow. This PID-controller gives assistance to mill outlet temperature PID-controller.
• Prehopper coal dosing. This PID controls the motor speed in order to maintain the prehopper weight constant before coal dosing system to the burner.
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