Speed control solution for AFC
This speed control solution (Figure 5)
is not aimed at raising production; it
is a designed mechanism to obtain
higher efficiency of the drive. The
basic idea is simple: adjust the speed
according to the coal volume.
There are four occasions when
adjusting the speed may be
necessary:
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Condition 1:
When the shearer
is found in either terminal of the
AFC. This takes up to 20% of the
working time.
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Condition 2:
When the shearer is
cutting coal in a single direction
only. In this model, the shearer
is only working when walking
from the AFC tail to the head.
So the AFC is empty when the
shearer moves from the head to
the tail. This takes up to 10% of
the working time.
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Condition 3
: When there is an
incident that stops downstream
equipment, such as the belt
conveyor, the AFC usually keeps
running even if there is no coal
on it.
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Condition 4:
When the load
from the shearer is unstable. It
will be desirable to slow down
the AFC when the coal flow is
small and speed it up when the
flow increases.
How to adjust the speed? Speed
adjustment is based on the
information of the mining process
and condition of the working faces.
Different speed models are
pre‑calculated. Shearer speed,
shearer position, torque and coal
production feedback from coal
volume detector, etc. are all
necessary inputs for speed
adjustment.
The AFC drive and control
system in Meihuajing coal
mine
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Mine name: Meihuajing coal mine,
Yinchuan, China.
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AFC type: SGZ1000/2 x 1000.
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Nominal capability: 2200 tph.
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Length: 300 m.
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Total power: 2 x 1000 kW.
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Nominal chain speed: 1.35 m/sec.
Control method 1
Constant speed control (normal control
before system optimisation). The AFC
speed was 1.35m/sec., regardless of the
load difference during production. The
total energy cost per day was
30 564 kWh and the total chain mileage
per day was 103 712 m.
Control method 2
Variable speed control according to
coal load. The following speeds were
applied:
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0.54 m/sec. (40% of full speed),
when the load is between 0 – 30%.
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0.81 m/sec. (60% of full speed),
when the load is between
40 – 50%.
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1.08 m/sec. (80% of full speed),
when the load is between
60 – 70%.
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1.35 m/sec. (full speed), when the
load is larger than 80%.
The total energy cost per day is
27 263 kWh and the total chain mileage
per day is 76 973 m.
The second control method is the
optimised control method for AFC
control. By comparing the data, it is
straightforward to conclude the
benefits of using variable speed
control. The energy cost is reduced to
89.2% and the chain mileage is
reduced to 74.2%. In other words, it is
more energy saving and less
equipment wearing.
With the rapid development of
underground mining and with the
challenging market situation, ABB
believes that this VFD solution will
help more and more AFCs greatly
reduce operational costs and increase
economic benefits for mines.
Figure 5. AFC Speed Control Model.
Figure 4. Reduce wear in tail area.
66
|
World Coal
|
August 2015
