Application case 22: Alumina baking furnace control system
Introduction
It is a 1920t/d localization circulating roaster, which saves foreign investment and makes the production capacity more than import baking furnace in the premise of ensuring product quality. Similarly, the process control system is changed from the UNIX distributed control system original produced by HoneyWell to the 900 type of DCS control system produced by honeywellCompany, The configuration of the application software and the design, commissioning and installation of control are system independently completed by our company. Process of circulation baking furnace is that transport the wet aluminium hydroxide which is from the pre filter process to alumina storage bin, a screw feeder in the bunker exports add the wet material into the one-level Venturi dryer, here heat exchange with the hot flue gas from the preheating system, after dried by the hot air, the dried aluminium hydroxide get into the first-level mechanical dust collector, and then accept the Aluminium hydroxide of fine particles by the electrostatic precipitator. all the accepted aluminium hydroxide through screw conveyor, air chute conveyor, air hoist sent to spiral separator, after the separation the dried aluminium hydroxide get into the two-level stage Venturi preheater, removing part of crystal water, the aluminium hydroxide separated by the two-level cyclone separator get into the baking furnace, and then complete the baking cycle of the circulating baking system which consists of recycle separator, blank groove. After baking, the separate alumina get into one -level cooler and indirect heat exchange with the air, and then enter the two-level cooler indirect heat with cooling water, after cooling the alumina gets into the bin by discharge valve, the belt conveyor
1 system structure and function
1.1 system structure
The DCS system consists of 1 engineer station, 2 operator stations, 2 servers, 1 I/O stations and Ethernet, and the network is divided into two parts, namely system network (CTNET) and control network (CMNET), system structure shown in Figure, 14 HUB form 100MB, by engineer station and operator station to select and use the DELL, frequency PIV1.3GHz; RAM 128MB; hard disk 500GB, and is equipped with 3 type FB006 membrane touch special keyboards, a EPSONLQ1600K printer, and a HP1125C printer. the serve With the DELL, frequency PIV2.13GHz; RAM 128MB; hard disk 146GB; I/O station with the CMT-300, comprises of 2 mutual hot standby main control units, 12 power modules, 40 modules of AI, AO, DI, DO, 1 cold end compensation module, and 2 terminal matching devices. Considering the interference of the start of large current fan to AI signal, we selected 20 WS1562 type isolation terminals, installed in power supply cabinet of the main control room.
System network hub uses a DUNKDEF-908DX type, totally has 4.
1.2 functions
Engineer station mainly completes the system software configuration, compile and download, and executed on the system operation monitoring.
☆operator station:
(1) Through the running state of the equipment of the Chinese friendly interface and animation with all Chinese, real-time monitoring the running state of the system. The system provides more than 30 pieces pictures, such as 1 main picture, 7 sub system pictures, 8 screens, 2 data displays, 1 report display, and historical curve equipment log, operation log and so on.
(2) The complete alarm management functions. Process, equipment process alarm signal can sound alarm through the operator station, AI signal according to the process requirements set the upper alarm and the lower alarm, fault signal in the DI signal also provides alarm, to real-time remind the operator of the necessary processing. At the same time, the system provides alarm function of the network and the hardware fault on its own, and provides DCS system network, equipment state diagram.
(3) The accident retrospection function. The failure of process equipment operation can be real-time export history curves, operation log, and equipment log, to facilitate analysis.
(4) Print function. The system timing print class, daily, and any print all data, graphics, and curve in the screen, to provide the necessary basis for production planning, quality analysis and products, energy consumption assessment.
The Server mainly completes the control software download from engineer station to I/O station, the storages of real-time data, history data, operating records, log record, and the calculation of report data, and ensures the consistency of operation data.
☆I/O station mainly completes:
(1) Loop control, including the blower outlet temperature control, furnace pressure control, the two rotary valves’ single loop control and the optimization algorithm temperature control during adjusting PID with auxiliary fan and heavy oil valve by temperature in the control of the furnace roof.
(2) The logic control: through the ladder configuration, complete the control of the system, such as sequence control, the start- stop of interlocks / unlock motor and so on.
(3) Data acquisition. Through the DI, AI module accomplishes the data collection of open people, mode people needed by all control system.
(4) signal output. The instructions insured after 1/O station main control unit operation output to control field devices by means of DO, AO module.
(5) The electricity protection. Configuration software solidified in Semiconductor disk of the main control unit, real-time data storage in SRAM with power-off protection, which can meet the system requirements of reliability, safety, real-time. Reliability and openness of the system is high. The system uses hot standby double server, dual master control unit, double wire for each other, so that the reliability of the system is greatly improved. At the same time, because the system uses the opening WindowsNT operating system, can exchange data through connecting gateway with the network, and lay a solid foundation of joining company management network for the future.
2 Detection and control of the main process parameters
2.1 Detection of process parameters
The total of Pressure and differential pressure measuring points is 38, including the positive pressure system of baking furnace and the flue using instrument for reliable detection, overcomes the pressure blocking phenomenon. The total of Flow detection points is 31, according to the requirements of the process of baking furnace’s conveying wind system, detected by the Nubuck flowmeter with minimal pressure loss; the heavy oil with much more viscous is detected by the mass flowmeter naishide; the steam flow is detected by vortex flowmeter; and water metering is measured by electromagnetic flowmeter. In addition, position is detected by cable type radar level meter, the outlet oxygen content of two-level cyclone is detected by the import zirconia analysis instrument, the concentration analyzer of gas concentration, temperature is measured by thermocouple, thermal resistance, and the alumina product is measured by electronic belt scale, electronic drawing board scale. 3 sets of main burner to ignite and flame detect, two sets of auxiliary burner to ignite and flame detect etc.
2.2 The logic control
The field equipments are logic controlled by DCS, with start-stop control of 076 fan (transport and sealing groove air blower) for example, not only have to consider motor control principle, but also consider the power controlled device. Therefore, firstly we provide the capital to electrical design, make it add the contactor control circuit into the intermediate relay (which is controlled by the relay of DCS system I/O DO module), in order to meet the requirements of the relay of DO module (I<-8A). The configuration of Logic control uses ladder diagram mode, need to use "remote control", "fault", "run" signal in the applications, we lead these DI into DCS system through 1/O station. When the operator press the "start" button on the control panel, based on meet the Conditions of the "remote control" for 1, "the fault" (discussed later in this neglect, interlock condition) the system make the relay contact in the corresponding point of the DO module closure. Taking into account that the motor within the time specified does not start, we introduce "time relay" into the ladder diagram, when DO signal output and "run" signal does not feedback during the time constant, DCS will stop output.
2.3 adjustment function
Process control in DCS system is realized by configuration software function block. The complex of the system is the top temperature control, there are two kinds of control modes (see Figure 3, the switch mode), the basic principle of the one is that: set production load, control the feeding screw motor, through the algorithm comprised of frequency conversion fan 076 fan ladder diagram configuration and heavy oil control valve FV150 with top temperature control to regulate the loop control for the temperature at the top; another is based on the setting top temperature to control the feeding screw motor, through optimization algorithm comprised of frequency conversion fan 072 and heavy oil control valve FV150 and the production load to adjust the control for a given load. The key point of the two kinds of control is that based on the optimal air/fuel ratio coefficient FY150A value to calculate the best ratio by the optimization algorithm, adjust the 072 fan frequency and FV150 oil valve, make the whole system to achieve the maximum wind and the minimum oil, and make the system running at its best.
3 Comparison of two control systems
3.1 control system
The control system of imported furnace use UNIX distributed control system produced by Hone Will Company, is not conducive to connect with the local area network and especially Internet network, it is difficult to realize data sharing.
The control system of domestic furnace uses CMT-300 type DCS control system produced by Beijing CIMAC Company, due to the use of the WindosNT operating system, it is easy to connect with and the LAN and Internet network, data sharing.
3.2 interface
The operating system of imported furnace is pure English interface and only uses two colors to show the running state of equipment, so the higher requirement on the English level of operating personnel, more operation difficulty.
The operating system of Domestic furnace is pure Chinese interface and uses a variety of color and animation to show the running state of the equipment, the operating workers can master this operating system with friendly interface only need through a short-term training.
3.3 monitoring system
The Control system of domestic furnace installs monitors34 inch in the main control room, which can monitor the 12 key parts of production, more intuitive, convenient operate.
3.4 control range
The Control system of domestic furnace not only contains the main process control (the only control system of imported furnace), but also integrates the control of discharge system (belt to silo section) into the main process control system, reducing the field operation human resources.
3.5 The locking / unlocking
As the imported furnace without the device unlock function, debugging the original system of single machine become more difficulty, when the system is operating, the following equipment stop running caused by upper-class equipment failure, and hardly recovering, affecting production. The domestic system is set with soft unlock function, divide more than 40 interlocking blocks into groups, completes the soft unlock by the computer 12 keys (password), so that to reduce the difficulty of debugging the original system. When the system failure, can unlock the following equipment of the failure equipment, continue to run, keep low load, maintain production, providing precious time for equipment repair.
3.6 The anti-interference ability
The Wiring method of the imported furnace system is that, signal line according to the classification accesses into the 9 BC boxes (analog / digital conversion), and then the BC box communication line accesses into the cabinet CMT-3000 control of the main control room. Because the BC boxes are on the site, have long distance with the control cabinet and poor anti-interference ability of communication line, so the interference on the communication line caused by fan start often results in shutdown, the shutdown time is more than 20 days each year.
Due to the Control system of domestic furnace directly accesses the signal line into I/O station, part of the important signal use the method of that firstly accessing to WS1562 isolation terminal cabinet (in the main control room) and then accessing to I/O station, so as to avoid the interference on the communication line caused by fan start, can guarantee the reliability of controlling the system operation.