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Deregulation in the electricity markets and increasing demand for
improved power-generating plant efficiency and availability
whilst maintaining and even reducing operating and maintenance
costs have led to the development of sophisticated
instrumentation and control (I&C) systems.
There are over 1600 pulverised coal-fired power plants in the world
(>4000 units) with a total capacity greater than 1000 GWe
currently in operation, accounting for almost 40% of total
electricity production. As plants age they tend to become less
reliable. Their performance and efficiency decline, and
operating and maintenance costs increase. In December 2001, IEA
Coal Research, the Clean Coal Centre, will be publishing a
review of traditional
and modern I&C in conventional, pulverised coal- firing power plant.
A modern, advanced I&C system plays a major role in the
profitable operation of a plant by achieving maximum
availability, reliability, flexibility, maintainability and
efficiency. These advanced systems can also assist in
maintaining emissions compliance.
In order to highlight how efficiency improvements can impact the
profitability of a power station, an example of main boiler
efficiency losses in a UK 500 MWe coal-fired unit are given as:
Breakdown
of major boiler efficiency losses for a UK 500 MWe coal-fired
unit
(AEA Technology Environment, 2000)
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Efficiency
loss
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%
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Dry flue gas loss
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5.04
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Sensible heat loss
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0.33
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Carbon in ash loss
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1.36
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Unburnt gas loss
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0.09
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Radiation and unaccounted losses
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1.36
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|
|
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Total boiler efficiency losses
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8.18
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|
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Boiler efficiency
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91.82
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Turbine cycle efficiency
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43.4
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Overall, gross-on net cycle efficiency
(based on net calorific value basis)
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39.85
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In this case, carbon in ash loss is a large contributor due mainly to
the retrofit of low NOx burners. Overall cycle efficiency
combines boiler efficiency and the steam cycle efficiency.
Assuming a plant load factor of 90% and a fuel net calorific
value of 25 MJ/kg, this equates to a fuel burn of 1,424,000
tonnes per year. Supposing an efficiency improvement programme
is carried out or a combustion process optimisation is applied
that increases efficiency by 1% with no net impact on auxiliary
power requirements, annual fuel consumption would be reduced by
over 14,000 t/y. At UK domestic fuel prices of the year 2000 the
savings are over £415,000 in fuel costs alone. Fuel accounts
for ~45-55% of the cost of electricity generated and 60-80% of
the operating cost in pulverised coal power plant. Reduction of
1% in total annual fuel cost was also achieved in power stations
retrofitting vintage I&C with modern systems in the USA. The
reduction in fuel would significantly benefit other areas such
as fuel transportation, auxiliary power consumption, particulate
control system performance and ash handling and disposal
Advanced, digital I&C systems are being installed from new and
retrofitted in existing coal-fired power plants throughout the
world. These systems enable:
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faster plant startup and shutdown by programming plant
control sequences,
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higher availability by detecting and indicating the
causes of impending malfunctions,
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greater thermal efficiency by moving variable set points
closer to the operating limits,
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reduced emissions by controlling the combustion process
and downstream emission control technologies,
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lower maintenance costs by replacing pneumatic,
electromechanical or electronic/analogue devices, and
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decrease operational costs by reducing staff
requirements.
There
are several further developments that are currently being
investigated which can accelerate the uptake of advanced I&C
systems in coal-fired power plant. For example development of
smaller and more robust I&C products that can reduce
installation and maintenance costs and introduction of advanced
software to extract and manage information from the I&C
system. Also, developing predictive or anticipatory diagnostic
software to detect malfunctions and recommend actions to reduce
unplanned plant outages.
References:
AEA Technology Environment (2000)
A guide to improving the
efficiency of coal-fired power plant in India. Harwell, UK,
AEA Technology Environment, 97 pp (2000)
Nalbandian H (2001)
Instrumentation and control in coal-fired power plant. IEACR,
London, UK, IEA Coal Research - The Clean Coal Centre, vp (in
preparation – available Dec 2001)
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