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 MARIETTA, GA – 06/2010
Typical fuel costs in a coal fired power plant will
account for over 75% of the total production cost of electricity. Because fuel
cost is such a large portion of the cost to produce electricity, it is important to
tightly control those costs. Equally important, fines and settlements for
excessive emissions can cost a power generation company millions of dollars.
The cost of coal is determined by the grade of the coal. Some grades of coal
are less expensive because they have a lower heat content, or because they
have a higher sulfur content. Coal with lower heat content produces less
electricity per ton and coal with higher sulfur content produces more sulfur
dioxide when burned. Sulfur dioxide emissions are regulated and a company can be fined for excessive sulfur
dioxide emissions.
 A large power generation plant in the eastern United States blends various
grades of coal to produce a coal with the optimum heat content and a sulfur
content low enough to meet emissions requirements. If too much high grade
coal is used, fuel costs are increased. If not enough high grade coal is used, the
coal may not burn efficiently. Similarly, if not enough high sulfur coal is used, it
may not burn with enough efficiency. If too much high sulfur coal is used, the
plant may not meet emissions requirements.
By using its existing scales, this coal-fired power plant was not accurately measuring coal in a continuous
blending process to tightly control the blend of different grades of coal. The scale must operate continuously
in the harsh environment of a coal fired power plant with little maintenance. The scale must also be reliable
and easy to calibrate so it is easily kept operating at peak performance.
The Siemens Solution:
Milltronics BW500 Integrator and MMI Weigh Bridge
This coal-fired power plant chose to update its existing scales because of the competitor’s poor service, and
to reduce maintenance costs at the facility. At this coal-fired power plant, two MMI weigh bridges were used to
measure two different grades of coal. The BW500 integrator with MMI weigh bridges are used to measure
different grades of coal as they are blended together. The feed rate onto the conveyor is controlled to produce
the correct blend of coal.
Siemens unique cascading design allows for a high accuracy scale (0.25%) by adding a second weighbridge.
The design provides a high accuracy scale without the need for a large multi-idler weigh frame. This design
also eliminates the need for pivots and check rods which require maintenance. The customer is impressed
with the ease of installation and reduced maintenance that has resulted by using the BW500 integrator with MMI weigh bridges.
The coal-fired plant chose Siemens because of the following benefits:
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Installation cost savings: The MMI, Siemens weigh bridge, uses loadcells that eliminate the need
for pivots and check rods, reducing the weight of the weigh bridge to less than 150 lbs. This makes it
manageable for two people to set into the conveyor and helps reduce installation costs. On the other
hand, many competitive units use pivots, which require a large weigh frame that can weigh hundreds
of pounds. They require the use of a crane to lift them into place, ultimately, raising installation costs.
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Two button calibration for ease of use: Since all belt scales require two points of calibration,
Siemens has implemented two buttons to help ease calibration. The two buttons automatically make
the calculations and adjustments for customers, eliminating several steps.
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Unique product features: Parallelogram loadcells used in the Siemens belt scale provide easier
installation and less maintenance.
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Excellent customer service
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