点击这里下载电力行业快讯第14期

Power Generation
Perspectives in Pure Water Analytics
14
News
THORNTON
Leading Pure Water Analytics
Chinese Research Agency
Choose Thornton Analyzer
When China’s Thermal Power Research Institute was developing a mobile
chemical instrument calibration device, they searched for the world’s
best conductivity analyzer. They found the 770MAX to be the most
accurate and reliable instrument.
Background
The Thermal Power Research Institute
(TPRI) in Xi’an, China is a research organization devoted mainly to developing
engineering technologies and equipment
for use in the country’s fossil-fired power
plants. The institute’s objectives are to
improve the safe running and economic
and reliable operation of plants, and to
reduce their pollutant output.
The TPRI’s Department of Chemical
Technology has developed an internationally leading mobile chemical instrument
calibration device by referring to the relevant standards both in China and abroad.
The aim of the device is to enhance the
stability and reliability of Chinese power
plant in-line chemical analyzer measurements and to improve the accuracy of
plant chemical supervision. The calibration device is of great significance to the
security, economic operation, energy efficiency and emission reduction in China’s
power plants.
Search for leading conductivity
analyzer
The TPRI identified conductivity as an
important parameter to test, and to choose
a conductivity analyzer for its calibration
device, performed rigorous tests on the
instrument systems provided by many
world-class manufacturers, based on relevant international standards and
regulations. Finally, Mettler-Toledo
Thornton’s 770MAX conductivity analysis
system was recognized by the institute for
its excellent performance, and was chosen
as the standard conductivity instrument
for the mobile instrument inspection device. The Thornton system comprises:
n770MAX multi-parameter transmitter
n58 031 003 conductivity Smart Sensor
(in titanium, with built-in temperature sensor)
Why Thornton were chosen
For pure and ultrapure water in-line
conductivity measuring systems, 75 % of
errors originate in sensor and temperature
compensation. For conductivity sensors,
accurate conductivity and maintaining
the correct calibration are very important,
and for temperature compensation, accurate temperature measurement is a
crucial prerequisite.
All Mettler-Toledo Thornton conductivity
sensors, and their built-in temperature
measuring elements, undergo particularly
rigorous calibration before leaving the
factory, with the conductivity and temperature calibration being traceable to
relevant ASTM and NIST standard criteria.
Also, the 770MAX transmitter can provide
a variety of optional temperature compensation modes according to the actual
measurement conditions. In addition,
Thornton’s unique sensor signal processing and transmission technology can
minimize the impact of the external environment during signal transmission.
Based on a series of rigorous tests, Director
Cao Jieyu from the Thermal Power
Research Institute, made the following
comments on Mettler-Toledo Thornton’s
770MAX conductivity measuring system:
nWide measurement range, reliable
measurement accuracy. Within the
tested 0.055 μS/cm – 200 μS/cm scope,
the error of the instrument is less
than 0.2 % FS.
Publisher / Production
Mettler-Toledo AG
Process Analytics
Im Hackacker 15
CH-8902 Urdorf
Switzerland
Illustrations
Mettler-Toledo AG
Kodym, Crashoran, Scaramushe,
Jerryd | Dreamstime.com
Subject to technical changes.
© Mettler-Toledo AG 12/09
Printed in Switzerland.
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METTLER TOLEDO
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nHighly accurate measurement, with
the measurement precision of
0.0001 μS/cm.
nExact temperature compensation, capable of automatically conducting
accurate non-linear temperature
compensation on ultrapure water, hydrogen exchange column flow, and
ammonia injecting feed water.
nOne multiple-purpose instrument
compatible with four different sensors
such as conductivity, pH and DO sensor, at the same time, equivalent to
simultaneous use of four separate instruments.
nExcellent price / performance ratio.
Exceptionally reliable
Currently in China’s power industry, nine
plants have adopted the mobile inspection
device configured with the 770MAX. After
over a year of use, all found the performance of the 770MAX analyzer system to
be extremely stable and reliable, and none
of the instruments has ever required
maintenance. The 770MAX was further
praised for its strong anti-interruption
capability and has never been interrupted
under the different power plants’ diverse
environments.
Discover more at:
www.mt.com/Cond
Transmitter 770MAX
Industry Support
ASTM International Committee
Mettler-Toledo Thornton Participation
Water Committee standards from ASTM are widely used in the industries
utilizing pure waters such as power, as well as the pure water treatment
industry itself. Mettler-Toledo Thornton contributes to this important
work, enabling customers to benefit from optimized measurements.
Globally respected body
ASTM International, originally known as
the American Society for Testing and
Materials (ASTM), was formed in 1898.
Today it continues to develop voluntary
consensus standards with input from expert producers, users, consumers,
government and academia. The concept
of consensus is effectively built into the
standards approval process. All committee
members have a voting interest and all
objections must be addressed fairly and
objectively by the group. As a result, the
ASTM plays a respected leadership role in
addressing the standardization needs of
the global marketplace.
Water Committee
Of special interest to Mettler-Toledo
Thornton and its customers is the ASTM
Committee D19 on Water. It was formed in
1932 and currently has approximately 340
members in nearly 30 countries, with
jurisdiction of over 300 standards documents. Key areas of committee interest are
the development of standard methods for
sampling, identification, and analysis of
water and materials dissolved or suspended in water. In addition, it develops
standards on the performance of water
treatment materials and the determination of the corrosivity or deposit-forming
properties of water.
Water Committee standards are widely
used in the industries utilizing pure waters
including power, pharmaceutical and
microelectronics, as well as the pure
water treatment industry itself. ASTM
Standards take the form of: Methods for
measurement, calibration and accuracy
determination; Specifications for the purity or other characteristics of water or
treatment materials; Practices that outline
accepted procedures; and Guides that describe a variety of approaches to
measurements.
Sharing expertise
These standards not only provide widely
accepted means for industry standardization, they also serve as important learning
tools to those new to particular measurement or testing technologies. For over 15
years, Mettler-Toledo Thornton has sponsored its personnel in participating in the
ASTM Water Committee with industry
colleagues, contributing in their areas of
expertise. These areas have included
continuous conductivity measurement
and temperature compensation in high
purity waters, total organic carbon determination, pH measurement (especially in
low conductivity waters), oxidation-reduction (redox) potential measurement,
dissolved oxygen measurement in ppb
ranges, ozone measurement, plus related
pure water treatment methods and materials. At the same time, their participation
keeps Thornton personnel up to date with
new treatment methods, user-developed
measurement techniques and industry
trends.
Thornton conductivity sensors for pure
water measurements are all manufactured, factory calibrated and certified in
accordance with ASTM standards D 1125
and D 5391 which define standard conductivity solutions and the techniques for
handling pure water measurements.
Thornton high purity pH and dissolved
oxygen sensors are designed and operate
in accordance with ASTM standards
D 5128 and D 5462 respectively.
Participants on the Committee have found
it to be a rewarding, on-going challenge
to articulate technology into clear and
concise standards and to keep them up to
date. In addition, the work has helped
enable Thornton and Thornton customers
to benefit from optimized measurement
techniques over the years.
www.mt.com/THORNTON
METTLER TOLEDO
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3
Sampling Practice
Good In-line Sampling
How to Meet the Challenge
High-quality measurements require that representative samples reach
the sensors. Effects of sample delay, continued reaction and air
contamination must be minimized to obtain dependable results.
Sample source
Mettler-Toledo Thornton instrumentation
has been optimized for accurate measurements of power plant samples. However,
they can only measure the samples presented to them. Here are some
recommendations to maintain sample
integrity.
Where two-phase flow (steam / water
droplet mixture) must be sampled, the
sample should contain the same ratio of
steam and water as the process line. A
sample nozzle should be located near the
center of the process pipe, facing into the
flow. The sample flow velocity should be
isokinetic – with the same velocity inside
the nozzle as in the surrounding process
pipe. This will prevent pulling in excessive
steam at too high a sample velocity or
accumulating too many water droplets at
too low a velocity.
Sample reaction
Where reducing agents such as hydrazine
or reducing amines are used, the sample
should be cooled as close to the sampling
point as possible to prevent continued reaction with dissolved oxygen along the
length of the hot sample line.
Sample deposits
Corrosion product particles that accumulate on sample tube walls create a large
active surface area along the length that
can adsorb and desorb materials in the
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Power News 14
sample. A sample line with a lot of deposits can act like an ion chromatograph and
delay the passage of ions through the line
much longer than a simple calculation
from flowrate, diameter and length would
predict. It has been found that a flow
velocity of 2 m/s produces the least accumulation of particles in horizontal sample
lines and is recommended wherever possible. This high velocity is only practical
using very small diameter tubing for the
long lengths of the sample line. The
sample is then divided for measurement
by multiple sensors, some of
which require much lower
flow rates.
Sample flow
The appropriate sample
flowrate at the sensor depends on the particular
measurement. For example,
cation (acid) conductivity
requires a high flowrate to
obtain good ion exchange.
ASTM standard D 6504
Cation Conductivity recommends a flow velocity
through the resin of at least
300 mm/min. Lower flow
tends to reduce turbulence
and allows channeling
through the resin, resulting
in incomplete exchange. On
the other hand, pH measurement in low conductivity
samples requires low flowrates to minimize electrostatic pickup and reference
junction potentials to yield a stable measurement.
Filtration
Placing a filter in the sample line upstream of optical analyzers can protect
them from particulate contaminants and
errors. However, the filter elements must
be changed frequently to prevent a thick
accumulation of sediment that slows the
response to real sample changes.
Portable in-line pure water
instrumentation
Moving away from optical analyzers,
electrochemical measurements such as
conductivity, pH, ORP and dissolved oxygen are not directly affected by particles.
Mettler-Toledo Thornton sensors for these
parameters have flow housings designed
with a very small volume that encourages
any particles to flow on through the housing and down the drain. In this way, the
delays and maintenance of filters and the
cleaning of bowl-shaped flow chambers
are eliminated and better overall measurements result.
Of course, during initial startups when
very high particulate concentrations are
expected, all sample lines should be diverted to drain. Pressure regulators and
flowmeters as well as sensors, with or
without filters, should not be subjected to
these heavy loads of corrosion products
which could clog tubing and fittings.
Air leaks
Dissolved oxygen samples at ppb levels are
especially vulnerable to air inleakage.
Although samples are pressurized and
flowing, it has been observed that a loose
rotameter, valve or compression fitting
seal that leaves a path through a thin film
of water can allow a trace amount of oxygen to diffuse into the sample. At ppb
levels no bubbles will be present but a
significant change in readings can occur.
A quick test for this is to increase the
sample flowrate. If the dissolved oxygen
reading goes lower, it is an indication
there is a leak and the higher flow is diluting it. The readings should be fairly
insensitive to flow.
Air can also pass through polymer sample
tubing and have the same effect as a leak.
Stainless steel should be used for all dissolved oxygen samples. But if flexible
tubing is needed, it should be as short as
possible and be made of PVDF or nylon
which have especially low gas permeability. The same precautions should also be
used for low conductivity measurements
where CO2 from the air can contaminate
a sample and raise the conductivity due to
increased bicarbonate and hydrogen ion
concentrations.
in a portable mode. Shown left is a twowheeled portable system using the
Thornton 770MAX that can be moved
around the plant to confirm measurements of conductivity, pH, dissolved
oxygen and TOC with the same capability
and quality as permanent in-line measurements.
Find out more at:
www.mt.com/THORNTON
Grab samples
Off-line samples are inevitably subject to
contamination from the air and the container. Whenever possible it is always
preferable to take a portable instrument
and sensor to the flowing sample rather
than taking a grab sample to the laboratory. However, there are virtually no
laboratory or portable instruments for
conductivity and pH that have temperature
compensation suitable for high purity
measurement. They do not take into account the changing dissociation of water
and ammonia or amines with temperature
which is a major factor at low concentrations. Much better results are obtained by
using in-line pure water instrumentation
METTLER TOLEDO
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5
Power Plant Upgrade
More Efficient Cycle Chemistry Monitoring
with a Multi-parameter Transmitter
Aging power plants can remain efficient if regular modifications are
implemented. Cycle chemistry monitoring equipment is no exception.
For one plant the compact size, functionality and accuracy of the 770MAX
multi-parameter transmitter turned a modification into a true upgrade.
US power station
One of our US customers has a plant with
three coal-fired 235 MW units that date
from the early 1960s. Despite its age the
generating equipment remains highly efficient, thanks to various modifications
that have been implemented over the
years. A recent change replaced a deteriorating sampling equipment and analytical
instrumentation monitoring panel for one
of the units.
Smart Sensors, clever transmitter
For this upgrade the plant chemist considered a number of solutions and selected
the Thornton 770MAX because of the
Smart Sensor technology, convenient
menu-driven operation and compact
four-channel design. The need to replace
equipment for conductivity, dissolved oxygen and pH was matched very well by the
capabilities of the 770MAX, which allowed
the measurements to be configured in the
most straight-forward combinations.
4 transmitters for 16 channels
A total of 4 dissolved oxygen, 2 pH and 10
conductivity measurements on 4 - 770MAX
instruments were designed into a very
compact panel that fitted into the available space. The sensors were designed
specifically for high purity measurements
on power plant samples. The high performance dissolved oxygen sensor can
withstand very hot samples in case a
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METTLER TOLEDO
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cooler should fail and uses a simple, low
cost, drop-in membrane cartridge that
minimizes maintenance time and expense. The compact pHure Sensor provides
accurate pH measurements in low conductivity samples without cumbersome
electrolyte reservoirs or other refilling
requirements. Conductivity sensors are
individually factory calibrated with NIST
traceability and are used with exceptionally accurate specific and cation
conductivity temperature compensation
algorithms in the 770MAX.
Reliability overcomes skepticism
Early in the project, plant chemical technicians were skeptical of having new,
Transmitter 770MAX
unfamiliar instrumentation specified for
the unit. However, after just a few weeks of
use, they began recognizing the ease of
operation and reliability of the 770MAX
measuring system, which is making the
job of obtaining consistent data on water
and steam quality significantly easier
than it had been previously. The data, in
turn, is helping the power plant to comply
with the high company standards for
monitoring and controlling cycle chemistry conditions.
Discover more at:
www.mt.com/770MAX
Reliable Standards from a Trusted Source
Conductivity Standards
Conveniently Available from Thornton
Thornton conductivity standard solutions provide a way to verify or calibrate
the conductivity sensor cell constant after the period of initial calibration has
expired. Similar to pH buffer solutions, conductivity standard solutions can be
used periodically to confirm the accuracy of readings.
Stability of cell constant
A conductivity cell constant is generally
quite stable. Thornton conductivity
sensors are factory calibrated with traceability to ASTM and NIST and are certified
for a period of one year from installation
under normal operating conditions. Longterm evaluations of our sensors in clean
makeup water systems have shown
changes of less than a percent over several
years of operation. However, in cycle
chemistry monitoring with temperature
excursions or corrosion product deposition
and the resulting cleaning can result in
changes.
Accuracy verification
The cell constant has direct impact on the
critical specific and cation conductivity
measurement accuracies. For this reason,
a 1 to 12 month verification period for
conductivity sensors is
commonly practiced,
depending on the application. For this
verification, there are
three options:
1.Return the sensor to
the factory for recalibration.
Thornton 1875 Portable Calibration System
2.Compare measurements with a
recently calibrated plant standard sys- The buffering capacity of pH standards
tem such as the Thornton 1885
tends to resist pH change and makes them
Portable Conductivity / Resistivity
much more forgiving of contamination.
Calibration System.
Conductivity standards on the other hand
3.Verify and / or calibrate in a conducare directly affected by dilution or contivity standard solution.
tamination and their values will change
readily, especially at low values.
Use of conductivity standards
Thornton conductivity standard solutions The wide rangeability and consistent linare provided for this third option with earity of Thornton measuring systems
values from 25 to 100,000 μS/cm. Although between 100 μS/cm and pure water has
many conductivity measurements are been shown to provide much better accumade below 25 μS/cm the use of very low racy in practice than is typically obtained
conductivity standards is not recom- using standards below 100 μS/cm.
mended. Low conductivity standards are
much more vulnerable than pH buffer
solutions to contamination by variable
amounts of CO2 from the air and from For more information, go to:
other sources.
www.mt.com/THORNTON
Thornton conductivity standards
METTLER TOLEDO
Power News 14
7
Comprehensive Website
The Information you Want
is at www.mt.com/pro
The METTLER TOLEDO Process Analytics website contains a vast amount of up-to-date
information on all our products and services.
A typical Product page: with Features
Content is localized for your country and tailored
to suit your selections.
and Benefits and quick access to relevant application information,
related products and downloads
Simple layout allows you to quickly find the information and features you are looking for.
nLearn
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ments
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certificates
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Application pages help guide you to the
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9
The THORNTON Solution
One Transmitter for Multi-Parameters
for TOC, pH, Conductivity, DO …
THORNTON solution
Wide range of instruments for your processes …
Mettler-Toledo Thornton is the market leader in critical ultrapure and
pure water analytics.
Our 770MAX instrument is a multiparameter meter with a broad range
of measurement sensor options.
The in-line 5000TOC rapidly detects
organic contamination in real time.
As well as TOC, THORNTON produces sensors for monitoring pH / ORP,
DO2 / DO3, conductivity, flow and
pressure.
Flow
Sm
■ 770MAX
multi-parameter
transmitter
ar t
■ 5000TOC
sensor for continuous Total Organic Carbon measurements
■ pH
for ultrapure water applications
■ 2-electrode,
4-electrode and
inductive conductivity sensors
pH / ORP
DO2 / DO3
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METTLER TOLEDO
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THORNTON benefits
■ All-in-one
supplier with sensors
for all your pure water analytics needs
■ Multi-parameter
transmitter
capabilities saves panel space
and lowers costs per parameter
■ 5000TOC
Pressure / Tank level
Transmitter 770MAX
allows a real-time TOC
measurement, in-line, all the
time
■ No
Sm
gases or reagents to handle,
store or replace for TOC sensor;
absence of moving parts minimizes routine maintenance
ar t
ar t
Sm
Sensor technology offers
“Plug and Measure” communication from sensor to transmitter
Sm
ar t
■ Smart
■ Sterilizable
sensors designed for
exceptionally long lifetime
Conductivity
TOC
METTLER TOLEDO
Power News 14
11
Get in-line with METTLER TOLEDO
Take Conductivity
to a Digital Level
With measurement technology built into each sensor, Intelligent Sensor
Management (ISM) conductivity sensors from Mettler-Toledo Thornton
have the ability to store unique sensor identity, measurement, configuration and calibration data, all within the sensor!
Installation and startup are effortless when utilizing pre-calibrated ISM
technology. Each sensor automatically communicates via an electronic “handshake” to the transmitter providing quick and consistent
installation for simple Plug and Measure performance.
Sensors send digital signals to the transmitter with less ambient noise
and interference, extending cable lengths and improving measurement
performance. When simplicity and installation speed are important,
think ISM conductivity sensors from Mettler-Toledo Thornton.
www.mt.com/cond
Mettler-Toledo S.p.A.
Via Vialba, 42
20096 Novate Milanese (MI)
Phone: +39 02 333 321
Fax: +39 02 356 29 73
E-Mail: customercare.italia@mt.com
Mettler-Toledo Ltd
64 Boston Road
Beaumont Leys
Leicester LE4 1AW
Tel: +44 (0)116 235 7070
Fax: +44 (0)116 236 5500
Email: enquire.mtuk@mt.com
www.mt.com/pro
Visit for more information
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