Implementation of Blast Furnace Gas Water Spray Cooling Cont(2)

another control way once serious warning occurs, and we can

also manually start the lance.

Figure2. Working principle of the system.

PLC program consists of the main program, the extended module check, frequency converter check, pressure release, reducing temperature scanning, start, alarm, analog quantity processing, PID control and AD conversion. The main program flowchart is shown in figure 3.

2.3 Principle of Temperature Measurement

Classify the situation of time interval and time variation at first according to the time process of the craft: When start the machine, the smoke capacity is unstable and the smoke temperature is also unstable, so the outlet temperature will fluctuate, and at this time PLC will analyze and process the temperature collection. There are some phases (figure 4): (1) When the outlet gas temperature reaches between upper and lower temperature limits, the frequency converter works between the defined upper and lower frequency, and the running frequency is regulated by PID loop. (2) If the temperature reaches above the upper limit, the system regulates the running frequency range of the frequency converter, and adds 1 to it. The frequency converter works at the new frequency plus 3Hz, and the system begins to timing. If the temperature keeps on a rise, repeat the steps before, and while the temperature stops to increase, stop regulating frequency. (3) When the outlet gas temperature decreases between upper and lower temperature limits, the frequency converter works between the new upper and lower frequency, and the running frequency is regulated by PID loop. (4) If the temperature is lower than the lower limit, the system regulates the running frequency range of the frequency converter, and minus 1. The frequency converter works at the new frequency minus 3Hz. If the temperature continues to decrease, repeat the steps before, and while the temperature stops to decrease, stop regulating frequency, and a regulating period finishes.

The allowable deviation of the target temperature is 0.2 , and PID loop does not work during the range (dashed in figure 4). The sampling period of the temperature is set between 15 to 20 seconds according to experiment.

Figure3. Main program flowchart.