NEWS
JOURNAL
N° 81 /
Dossier on Water Chemistry
Corrosion prevention adapted to new CCPP
design
EIGHTH
MARCH
YEAR
2007
Innovation in power plant water
chemistry
The water chemistry of power plants is a
domain that is constantly evolving. Innovation
enables us to anticipate new environmental
standards and meet the requirements of
new types of coal- and gas-fired power
plants. The Laborelec Chemistry team
develops and assesses new techniques in its
continuous search for the most cost-effective
solutions for pre-treatment of process water,
wastewater purification, and prevention of
corrosion and fouling.
Feed water treatment with concentrated ammonia
The new generation of combined cycle power plants (CCPP) requires
a water-steam cycle corrosion control treatment that differs from that
of a conventional CCPP. Laborelec compared different techniques and
identified the most efficient and economic one.
Conventional CCPP configurations
include a feed water tank that collects
the condensed water. This water is
then moved on to different drums at
different pressures. Increasing the pH
value of the water by adding ammonia
to the water protects the cycle from
corrosion. But because ammonia is very
volatile at lower pressures, the low and
sometimes the intermediate pressure
systems receive additional treatment with
phosphates.
Lower costs, better performance
In the new CCPP design, the condensate
is directly pumped from the condenser
to the steam generator. It offers better
performances and reduces system cost
since a feed water tank is not included.
It is not compatible however with the
use of phosphates in the low pressure
drum since the phosphates would
contaminate the higher pressure steam.
Electrabel asked Laborelec to investigate
how to prevent corrosion without using
phosphates.
Complicated steam quality control
We first investigated the alternative
proposed by several constructors: using a
mixture of organic amines. This treatment
resulted in acceptable corrosion control.
But the amines influenced the cation
conductivity of the water, one of the
most important parameters used by
power plants to assess steam quality
and to detect cooling water in-leakage.
This could lead to serious operational
problems. Moreover amines are easily
ten times more costly than ammonia.
Meeting new CCPP needs
We then suggested treating the water
with high concentrations of ammonia –
24% - instead of using diluted ammonia
solutions. We tested this treatment in a
power plant with an air-cooled condenser
and in a power plant with a water-cooled
condenser. The results are satisfactory.
We will now recommend this treatment
for new CCPPs with similar water-steam
cycle design.
[email protected]
The technical Competence Centre
in energy processes and energy use.
From innovation to operational assistance.
CONTENTS
Innovation in power plant water
chemistry
p. 1
Corrosion prevention adapted to
new CCPP design
p. 1
Lower maintenance costs for
ultra super critical boilers
p. 2
Oxygenated treatment for
ultra super critical boilers
p. 2
Efficient removal of nitrogen
compounds in wastewater
p. 3
Cost-benefits of fouling release
coatings
p. 3
Improved treatment of DeSOx
wastewater
p. 3
Reliable oxygen measurement in
cooling water
p. 4
New surface water pre-treatment
process for Amercœur
p. 4
Lower maintenance costs for ultra super critical boilers
Comeback for condensate polishing treatment
Electrabel intends to enlarge its coal-fired production park with state of the art ultra super critical boilers.
These however require an in-depth purification of the water steam cycle. Tractebel asked Laborelec to
investigate how to remove any impurities from the water entering these boilers.
Purification treatment necessary
An additional purification treatment of
the water is crucial before it enters ultra
super critical boilers. This water inevitably
contains a certain amount of impurities
that can mount up in the water steam
cycle. This, among other things, increases
corrosion risk, especially in combination
with the higher temperature and pressure
characteristics of this type of boiler.
Laborelec advised the reimplementation
of the well-proven condensate polishing
technology. From our experience we
know that this is a highly efficient method
of removing various kinds of impurities:
a battery of top-filters blocks suspended
particles such as iron oxide, while an ion
exchange treatment with small cation and
anion resin beads removes ions.
Lower maintenance cost
The installation of a polisher between
condenser and boiler will enable
power plants to cut down on boiler
maintenance costs. In the event of a
raw water ingress, it will also prevent the
distribution of impurities into the entire
cycle and guarantee a safe shutdown.
[email protected]
Oxygenated treatment for ultra super critical boilers
Corrosion degradation of key components in fossil-fueled power plants must be avoided. Electrabel asked
Laborelec to search for the best chemistry treatment to protect its ultra super critical boilers from corrosion.
Lower cost, more efficient
Laborelec investigated the efficiency of the
‘oxygenated treatment’ on the water-steam
cycle. This method injects both ammonia
and oxygen in the water to increase its pH
value and protect the water-steam cycle
from corrosion. The oxygen injection can
only be used with ultra pure water and for
boilers without copper alloys, such as ultra
super critical boilers and certain conventional
once-through boilers. Within these design
specifications, this treatment is more efficient
and less expensive than the all volatile
treatments (AVT) which are currently used at
power plants and inject only ammonia.
impact of our treatment on the cycle
and even remove certain boiler parts for
further examination. We discovered that
Tested at Monceau
We began testing such an oxygenated
treatment at the Belgian Monceau power
plant in spring 2006. In autumn 2006
Monceau was completely shut down, which
enabled us to extensively investigate the
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JOURNAL EIGHTH YEAR - N° 81 / MARCH 2007 - Dossier on Water Chemistry
the concentration of corrosive products in
the water had decreased to 1 microgram
per kilo with the oxygenated treatment,
while it stood at 3 micrograms with AVT.
Ammonia consumption was also reduced
by 50%.
We recommend applying this approach
to all new ultra super critical boilers
and are investigating the application
possibilities for some once-through
boilers currently in use at Electrabel.
[email protected]
Efficient removal of nitrogen
compounds in wastewater
Improved treatment
of DeSOx wastewater
Promising results from the ELONITA pilot
Ammonium ions and nitrates must be removed from industrial
wastewater before release into the environment. In large amounts,
these can be harmful to nature. Laborelec has developed a new
technique for removing such compounds: ELONITA. Compared to
other methods, ELONITA reacts more quickly to variations in impurity
concentrations and avoids the cost of extra sludge treatment.
More flexibility, less effluents
ELONITA is an innovative technique that
simultaneously removes ammonium ions
and nitrates from wastewater by electrodegradation. Compared to conventional
purification techniques, ELONITA has
a much faster reaction time, which
makes it possible to adapt the treatment
precisely to the ever fluctuating impurity
concentration. It also has the added
advantage that the N-compounds are
removed without creating sludge, further
reducing effluent treatment costs.
Laborelec has been studying ELONITA
at a pilot power plant for the past year.
The system had already shown promising
results during laboratory and small-scale
tests.
On the other hand, the tests revealed
some limitations with the process.
We observed that ELONITA is less
efficient when the wastewater has a low
conductivity. The performance of the
process also falls when the amount of
organic matter in the wastewater is high.
In such cases, Laborelec recommends
thorough wastewater analysis to decide
which purification process is best suited.
In the coming months, more tests will
be conducted to find ways to further
reduce ammonium ions concentrations
in wastewater. Commercialization of
the process should then be further
examined.
[email protected]
Low operational costs
The pilot tests have proven ELONITA to
be efficient at an industrial scale. They
demonstrated that ELONITA effectively
removes ammonium ions and nitrates
from wastewater, bringing concentrations
below legal limits (~15 mg N/l). They
also showed that implementation costs
can be similar or even lower than that of
conventional purification techniques in
some cases.
Cost-benefits of fouling release coatings
Are environmentally friendly fouling
release coatings a cost-effective
way of preventing macro fouling in
a cooling circuit? The answer highly
depends on plant-specific conditions.
Based on literature and experience,
Laborelec can estimate the total
cost of the different techniques,
taking into account investment cost
and labour costs for operations and
maintenance. We can also estimate
the impact on plant efficiency.
Recently, we compared different
coatings with more common
anti-fouling techniques such as
biocides and thermal shock on an
economical and technical basis. Local
circumstances such as legislation and
water type (seawater or freshwater)
play an important role. This study
showed that each decision about
whether or not to apply coatings
should be based on a thorough costbenefit analysis of the plant involved
and its site-specific characteristics.
[email protected]
[email protected]
Power plant operators are
seeking additional wastewater
treatment techniques in
anticipation of new, more
stringent European standards.
Laborelec carries out fullscale investigations into the
performance of such new
techniques and provides advice
to help plant operators avoid
ineffectual investments.
Modern coal-fired power plants are
equipped with a flue gas desulphurization
(DeSOx) unit. This unit produces two byproducts: gypsum, a useful raw material
for the building industry and wastewater.
Whenever wastewater is discharged into
a river, legislation imposes strict standards
regarding its quality. With the EU Water
Framework Directive, the European Union
will most probably require additional
efforts from all industries.
Laborelec advises power plants and
industries on choosing more efficient
and cost-effective purification techniques.
We conduct full-scale tests on the
performance of new methods, under real
process conditions. Laboratory results
from suppliers and scientific literature
indeed often fall short of expectations
when put in place on a full-scale. The
thorough insight of our experts into
plant’s wastewater composition and its
treatment processes also significantly
strengthens the plant’s position during
emission permit negotiations.
We have recently focused on the
removal of nitrogen compounds. Our
future studies are aimed at verifying if
available biological treatment techniques
are able to remove additional nitrogen
compounds, organic compounds, and
highly oxidized metals.
[email protected]
JOURNAL EIGHTH YEAR - N° 81 / MARCH 2007 - Dossier on Water Chemistry
3
Reliable oxygen
measurement in
cooling water
New surface water
pre-treatment process for
Amercœur
Assistance from feasibility study to implementation
To comply with environmental
legislation, power plants monitor
the oxygen concentration in their
cooling water before discharging
it into surface water. Laborelec
investigated which technique
guarantees the best availability
and accuracy of measurements.
Electrabel’s data management system
ECODATA indicated that there was a high
unavailability of oxygen measurement
results at various power plants. Electrabel
asked Laborelec to evaluate the different
measurement techniques.
Our experts examined electrochemical
and optical methods, both of which
are currently used at power plants
to measure the dissolved oxygen
concentration in cooling water. We carried
out a literature study to identify the
advantages and disadvantages of both
methods and concluded that the optical
technique utilizing the luminescent
dissolved oxygen (LDO) method
appeared to best fulfill the requirements
of the power plant staff.
The practical experiences of the different
power plants confirmed these results. The
optical probes clearly demonstrated better
reliability. They also require less follow up.
For instance, they don’t need frequent
cleaning, calibration, or electrolyte
replacement.
To promote a uniform approach, we
advised to use new probes based on the
LDO method. We drew up a list of “Best
Practices” to enable power plants to use
their probes more efficiently.
[email protected]
[email protected]
Because it contains many impurities, surface water must be carefully pretreated before being used as process water in power plants. Laborelec
assists power plants with the implementation of pre-treatment systems,
from feasibility study to parameter optimization and assistance during
implementation. The example of the Amercoeur power plant is given
below.
In the framework of the Amercœur 1
repowering, Laborelec was called in to
replace the entire water pre-treatment
system, going from a coagulation
system to one using ultra-filtration
and reverse osmosis. The latter,
unlike the coagulation system, can
be fully automated and requires little
surveillance. It also provides a filtrate
with more constant quality, produces
much less sludge, and enables to
decrease the salt discharge of about
35 %.
Pilot confirms project viability
Laborelec suggested implementing
the installation in a pilot project first.
Amercoeur uses surface water from a
nearby river to produce its process water.
A pilot project was necessary to check
water filterability by ultra-filtration and to
verify system cost-effectiveness.
During the pilot tests, which ran from
August 2006 to February 2007, we
confirmed the technical and economic
viability of the system. We studied,
among other things, variations in surface
water composition throughout the
seasons and their impact on filtered
water quality, as well as the impact of
system effluents on plant discharges.
We also used the pilot installation to
determine some crucial parameters of
the future Amercoeur pre-treatment
system. We identified, for instance, ideal
water flow through the ultra-filtration
membranes and the optimal membrane
cleaning frequency as a function of the
period of the year.
Assisting the call for tenders
Laborelec is now preparing for
implementation of the system at
industrial-scale. In coming months,
we will help Amercoeur write system
specifications for the call for tenders.
We will then analyze the offers from
suppliers and help identify the most
cost-effective one. Finally, we will
supervise the suppliers during actual
system implementation and assist in
the final fine-tuning of the pre-treatment
parameters.
[email protected]
Responsible editor: André Even
Rodestraat 125
B-1630 Linkebeek
Belgium
Tel: + 32 (0)2 382 02 11
Fax: + 32 (0)2 382 02 41
www.laborelec.com
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JOURNAL EIGHTH YEAR - N° 81 / MARCH 2007 - Dossier on Water Chemistry