Frequency inverter for dusting fan

In recent years, an Alum Extracting Steel Refining Plant built 2 sets of converters and dusting systems. It has a high requirement for fan operation. So we adopt technology of high voltage frequency inverters. They are mainly used to control SA fan of 6#, 7# converter, and PA fan of 4#, 5# converter.

Bypass circuit
Bypass cabinet is used to switch motor to direct on line when frequency inverter is broken to ensure production continuity. The steel plant adopts modes of "one drive one" and auto bypass cabinet.



Comparison between Gozuk frequency inverter and current source frequency inverter

Gozuk frequency inverter	Current source frequency inverter
High power factor	Low power factor, with power factor compensator
Without pollution for grid	There is pollution for grid, harmonic suppresser is needed
Applicable to common motor	Not applicable to common motor
Non-stop when control power faults	Stop immediately when control power faults
"one drive several" is available	"one drive several" is unavailable
Can not operate in four quadrant	Can operate in four quadrant, applicable to brake state
Cell-cascade, high reliability	With problem of components in series average voltage, low reliability
Interface is easy-operation and stable	Interface is easy-operation but unstable
Software is broken sometimes and can be solved easily	Hardware is broken sometimes and can not be solved easily
Solution of fault can be mastered easily for maintenance personnel	Solution is not mastered easily

Advantages of frequency inverter
1. Energy saving
Take 4# and 5# converters as example: converter capacity is 120t, average iron water input is 120t, max iron input is 140t, max gas flow is 60000Nm3/h, blowing time is 10min, refining period is 20min, dust in gas is 80g/Nm3--120g/Nm3, fan pressure is 19000Pa, rated speed of fan is 1480rpm, motor voltage is 6kV, motor power is 1400kW. In converter refining technics drawing, we can see:

A~B: add waste iron, 2min
B~C: fan acceleration, 1min
C~D: blowing&refining, 10min
D: fan begins to decelerate
D~E: measure temperature and sample, 1min
E~F: output iron, 5min
F~G: discharge draff, 1min

The refining period is 20min. Frequency inverter runs in high speed 35Hz in C~D, and runs in low speed 18Hz in other time ranges. In original operation, fan run in 50Hz all the time during refining period. For 4# and 5# converter, monthly power consumption of PA fan is 1680000kW·h. This value is reduced to 1050000 kW·h by frequency inverter. Power price is 0.55yuan/kW.h, monthly cost saved is 346000yuan (USD 50882).


2. Benefits
After using frequency inverter, fan runs in low frequency and small current according to refining technics. In addition, soft start avoids big current impact on grid and motor, reduces wear and tear on bearing and impeller, reduces times of changing rotor. There is excessive 5 hours for refining every month. Each furnace steel:120t; refining period: 20 min; steel profit: 200yuan/t

Additional steel produced every month:
5×60÷20=15 (furnace)
120×15=1800t
1800×200=360000yuan (USD52941)

Conclusion
The frequency inverters have been running stably for several months in steel plant. They save lots of energy and heighten work ability of dusting fan, improve environment, heighten efficiency and make contribution for safety and environmental protection. So the frequency inverter is indispensable in dusting system and it is worthy to promote in the field.