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A16 ORCHIDEE:
Efficiency Optimisation of Coal Ash
Collection
in Electrostatic Precipitators
Véronique
Arrondel, Jean Salvi
Ivo
Gallimberti, Gianluca Bacchiega
Abstract
In a coal thermal power
plant, one of the industrial solutions for collecting the fly ashes produced
during the
combustion process,
is the
electrostatic precipitation.
However, electrostatic
precipitation is a process affected by many parameters, in
particular the physical and chemical nature of
the ash,
the flow
rate and
composition of
the flue
gas. In
addition, the
operation and
the maintenance of an
electrostatic precipitator may prove to be difficult on account of
the great number of physical
processes concerned.
To satisfy current
regulations, the efficiency of the electrostatic precipitator must
always be greater
than 99.5%. To sustain these high performances requires good control
of the impact of various malfunctions on the level of emissions. For that, two distinct
approaches can be described. The first, influenced by the problems
the ESP manufacturers, describes the process as a whole and requires
a substantial experimental
database. The second, influenced by research in universities,
accurately describes the physical phenomena.
With the ORCHIDEE software, an intermediate approach is proposed, based on physical modelling of
the collection
process. This
approach enables
to estimate
the efficiency
of an
electrostatic precipitator
without using
an experimental
database, and
to be
independent on
manufacturer's empirical data. The operator is then able to have a
better real time understanding of
the problems, and to react efficiently. By
introducing properly all input data, ORCHIDEE makes it possible:
¾
to evaluate
the impact
of combustion
parameters on
dust emission
rapidly
(too much
air
inleakages,
flue gas temperature too high in the electrostatic precipitator).
¾
to test the hypotheses of blending types of coal to avoid
back-corona.
¾
to evaluate the impact of unfavourable distribution of the
flue gas in the electrostatic precipitator. ¾
to simulate electrical malfunctions: a field or section out
of service.
The Maintenance Department
can optimise its actions. The Technical Department can make a better
assessment of
slow drift
in operation.
The Engineering
Department can
better appreciate
actions for renovation, as the ORCHIDEE physical model makes
possible to verify the effect of changes in internal
components (height, plate-to-plate distance, and type of wires),
changes in the electrical power supplies, the addition of a new
field, for both existing units to be retrofitted, and for new units
that to be designed.
ORCHIDEE is a tool to assist operation and
maintenance of electrostatic filters, that is unique for
its high scientific content and its user-friendly interface: it has
shown to fulfil the expectations of its users.
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A17
Improvements
of An European Type Electrostatic Precipitator With Chinese Design
Experiences
Huang
Mei
Abstract
In
the beginning of
1980’s, China imported precipitator technology from a
European country. Several hundreds of such type precipitators have
been manufactured and
operated in
Chinese cement and other industries. Some drawbacks of detailed
design lead
to abnormal
operations.
Improvements
by using
of Chinese
experiences
are described.
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A18 PRACTICAL
EXPERIENCE AND RESULTS OF ESP
OPERATION
COLLECTING HIGH RESISTIVITY FLY ASH
WITH
HIGH DUST LOAD.
Abduazim
A. Rustambayev, Alexander Koptev and Kjell Porle
Abstract
The article describes results gained during
an ESP replacement programme at Aksu power plant in Kazakhstan, carried
by the power plant and under the pressure from the State, in order
to improve environmental situation in the region.
The task was to both meet reduced emission requirements when
collecting a high resistivity fly ash
from Ekibastus
coal in
combination with
the use
of the
same foundation
and support structures.
The coal has low sulphur (<0.6%) and high ash content (> 40%)
resulting in an ESP inlet load of
60 g/Nm3
and higher. Intensive back-corona was expected to develop inside the
ESP.
The fly
ash is
highly abrasive.
The combination
of these
factors required
special precautions during project implementation.
Combination of modern ESP technology with the
use of spiral discharge electrodes and state-of-
the-art
microprocessor controllers resulted in successful project
implementation with much lower than
required emission level.
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A19
How
to Eliminate ESP Insulator
Thermal
Break Down and Insulation Aging
Long
Tao, Xu Jian, Zhou Baoshan
Abstract
High voltage electric field combining with high temperature may
lead to ESP insulator failure. Particulates having a relatively
lower breakdown voltage strength stick on
the
insulator surface
can induce
corona discharge
and local
temperature rise
thereby speed
insulator aging.
Select insulator
material with
higher Te (the
temperature when the resistivity lowers to 1MΩ·cm) and
optimize design to even the
field around insulator can effectively protect insulator from heat
breakdown and aging.
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A20 ESP
emission reductions with advanced electrode rapping together with
novel energising methods
Christer Mauritzson,
Martin Kirsten, Hans Jacobsson,
Anders Karlsson
Abstract
To help keep the collecting plates clean,
Power Down Rapping (PDR) and Power Off Rapping (POR) have
been used for many years.
In
this paper it is shown, that the simple TR interaction available
with PDR and POR can be made in more elaborate ways, and that this
greatly reduces the ESP emission compared to the old
strategies.Increased rapping losses that may cause major emission
peaks when conventional PDR or POR is used can, in many cases, be
managed with the more advanced rapping regimes discussed in this paper.
For the ESP entry fields, excessive dust
build-up on the collecting plates may increase the voltage that is
required to start the corona. The increased voltage increases the
risk for spark-over limitation at a
[too] low current.
This and other disturbances have been
successfully addressed with more intricate novel rapping strategies
combined with new ways of using PDR, what we call Power Control
Rapping (PCR).
Compared
with ESPs that use conventional rapping the novel methods have in
several ESP plants
reduced the emission with 30 % for low to medium resistivity dusts.
For dusts characterised by a high resistivity this novel method is
even more successful, and emission reductions of more than 50 % have been obtained at
several plants.
Combining advanced rapping and a more smooth
HVDC supply - also referred to as Switched Mode Power Supply (SMPS)
technology - even higher emission reductions have been obtained in a
number of ESPs, especially when operating with low to medium
resistivity dust.
It seems possible that the above mentioned
emission reductions can be obtained for all ESPs, provided the dust
is, for whatever reason, difficult to dislodge from the collecting
plates.
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