Application of the hottest PLC in the large active

2022-07-23
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Application of PLC in large-scale active lime complete equipment

active lime is an essential raw material for steelmaking in large-scale iron and steel enterprises. Using it to replace ordinary metallurgical lime for steelmaking can achieve the purpose of energy saving, consumption reduction and steel quality improvement. In the 1980s, China spent millions of dollars to import two sets of activated lime equipment from Germany and Japan, which were installed at WISCO and Baosteel respectively. Our company has developed two sets of 600t/D active lime equipment. The first set was put into operation at Angang in 1987 and the second set was put into operation at WISCO in 1996. The main feature of this equipment is that it has a large number of devices, hundreds of monitoring points and complex control. The whole production line needs to invest tens of millions of yuan. Due to the advanced PLC control, the powerful application software is compiled, and the degree of automation has reached a high level

1 system composition and hardware selection

as the active lime equipment is an important equipment in the steel plant and has high requirements for the reliability of the control system, we selected the PLC of ABB and Siemens respectively according to the specific conditions of various enterprises at that time

19 for example, the coaxiality between the cylinder sleeve and the 10 head slideway can not meet the specified requirements, and the different shafts between the piston rod and the cylinder sleeve, ABB's master piece260 PLC and master view820 man-machine dialogue system were selected in Angang in 1986. Configure digital I/o528 points and analog i/o72 points. The monitoring scope includes the feeding system, hydraulic push rod system, stop wheel hydraulic station, analog panel signal system and heavy oil combustion system. The system configuration is shown in Figure 1

in 1995, Siemens S5-115U PLC and cp527 communication processor with color monitor were selected in WISCO. Configure digital I/o1120 points and analog I/O48 points. The monitoring scope includes raw material conveying system, feeding system, hydraulic pusher system, main reducer lubrication station, stop wheel hydraulic station, cooling system, process thermal parameter monitoring system and analog panel signal system. The system configuration is shown in Figure 2

2 system functions

(1) control function PLC can control all subsystems within the monitoring range. Two control modes are designed according to the process requirements: 1) automatic control in the central control room. This mode is the main operation mode. At this time, the whole production line is divided into several parts, and each part can start and stop according to the predetermined logical relationship. 2) Field manual control. This method is only used for equipment maintenance or single machine adjustment commissioning. The two control modes are interlocked with each other by a change-over switch. Press the emergency stop button in case of emergency failure, and all equipment will stop immediately

(2) the display function operator can not only understand the working condition of the equipment through the analog signal panel controlled by PLC, but also simulate and display the whole process flow and each link process flow on the color monitor

(3) the process recording system is equipped with a color printer, which can print the defined process flow, color graphics of all input and output change curves, and various process thermal parameter reports

(4) fault alarm in case of equipment failure or abnormal process parameters, the corresponding signal light on the analog signal panel controlled by PLC flashes quickly and starts the buzzer. After the operator presses the alarm elimination button, the signal light changes from fast flash to slow flash, and the buzzer is cut off at the same time. If the fault is still not eliminated within the specified time, the signal light will flash again and the buzzer will be started to urge the operators to eliminate the fault as soon as possible. When the equipment is normal, the alarm signal will be automatically eliminated

3 system design

3.1 raw material conveying system

the raw material conveying system of WISCO consists of 4 silos, electric vibrators and 3 belts. See Figure 3 for the sequence control diagram. When the 15m3 bin reaches the low level, the 17 #, 16 #, 15 # belts are started in sequence. The starting sequence of the electric vibrator is as follows: when the material level of 1 #~ 4 silo is higher than the low material level, the one with smaller number shall be started first. When the 15m3 silo reaches the high material level, power off the vibrator first, and then delay the shutdown of 15 #, 16 #, 17 # belts by classification. 4 and 5 electric vibrators start and stop at the same time. In case of equipment failure, one belt will be shut down, all equipment will be shut down along the reverse direction of material flow, and an alarm signal will be sent at the same time

3.2 feeding system

the feeding system requires that the block material be continuously added, because the specimen is always pulled into the preheater at the clamping position during stretching, as shown in Figure 4. The material can be artificially aged on the samples as required (the samples that need to be straightened should be artificially aged after straightening). The function of the system is realized by four gates and four vibrators working strictly in sequence. This can not only ensure the sealing of preheater, but also realize continuous feeding. After starting, PLC will automatically adjust various mechanical states, and then put into operation. After the shutdown command is issued, the PLC will automatically adjust to the shutdown status before shutdown. The feeding amount can be easily modified on the monitor at any time through the programmer or the monitoring keyboard

3.3 preheater system

the preheater system is located at the lower part of the feeding system. 12 hydraulic pushrods are distributed equidistantly around the preheater to push the preheated material into the rotary kiln. See Figure 5 for the control requirements of the hydraulic pushrod. This is a typical sequential control. If the program is designed according to the control requirements in Figure 5, the equipment is difficult to operate normally. This is mainly due to the frequent failure of the pusher system. See Figure 6 for the possible failure points. We adopted the fault-tolerant technology in the program design, that is, the PLC does not command the whole system to stop working after detecting the fault phenomenon, but suppresses its impact on the whole system through the program. For example, if a push rod is stuck during the operation of the push rod, the program will automatically separate it from the large cycle without affecting the normal operation of other push rods. At the same time, the corresponding signal lamp on the analog panel enters the flash state, and the buzzer alarms. After maintenance, the operator presses the reset button, and the separated push rod will automatically return to the large cycle. The feeding amount can be adjusted by adjusting the interval time of the push rod. This time parameter can be modified either through the programmer or on the monitor with the monitoring keyboard

3.4 the signal system of the analog panel has two working conditions: one is to monitor the working condition of the equipment, and the other is to monitor the over value alarm of the analog quantity. If the motor is normal

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