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TRAINING MANUAL FOR
STEAM AND WATER SAMPLING SYSTEM
EROOM TECHNOLOGY CO., LTD.
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CONTENTS
1. SWSS General
2. Basic Cycle Chemistry of Drum-type Units
2.1 Steam Generator (Boiler) Conditioning
2.2 Feedwater Cycle Condit ioning
3. Sample Points and Analysis Selection
3.1 Feedwater Pump Inlet (Sample #1, 8)
3.2 LP Drum Water (Sample #2, 9)
3.3 LP Superheated Steam (Sample #3, 10)
3.4 LP Saturated Steam (Sample #4,11)
3.5 HP Drum Water (Sample #5, 12)
3.6 HP Saturated Steam (Sample #6, 13)
3.7 HP Superheated Steam (Sample #7, 14)
3.8 Condensate extraction pump discharge (Sample #15)
3.9 Condensate pol isher outlet (Sample #16)
3.10 Aux. cooling water (Sample #17)
4. Sample Obtaining and Transport
4.1 Sample Obtaining
4.2 Sample Transport
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5. Sample Condit ioning
5.1 Pressure control
5.2 Flow control
5.3 Temperature control
5.4 Other sampling system components
5.5 Instrumentation and control
6. Sample Analysis
6.1 Precautions for grab sampling
6.2 Precautions for on-line analysis
6.3 Analysis definition, methods and applications
7. References
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1 SWSS General
1.1 Purpose of SWSS
To transport and condition samples without altering the constituents in the
samples.
To provide information on cycle chemistry to help assure the performance
determination of significant components and of the steam cycle in general.
1.2 Parameters to be controlled : Velocity (flow), temperature and pressure
1.3 Components constituting Sampling System :
pipes (tubes), Primary and secondary coolers, pressure reducing valves,
pressure and flow regulators, isolation valves, blowdown valves, resin
columns, control systems, analyzers and instruments.
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2 Basic Cycle Chemistry of Drum-type Units
2.1 Steam Generator (Boiler) Conditioning
2.1.1 Problems that could be caused by inappropriate steam generator
chemistry
(1) Deposition of solids on inside boiler tube walls.
- Corrosion products from condensate and feedwater systems,
and hardness constituents (Ca and Mg) in boiler water.
- form scales on high heat flux area of S/G
- reduces heat transfer and results in overheating and failure of
tubes.
(2) Corrosion of S/G material which causes
- material loss
- heat transfer resistance by resultant oxides resulting in tube
failure due to overheating and caustic attack
(3) Contamination of steam entering turbine beyond the steam purity
requirements of the turbine
- Steam could be contaminated by mechanical and vaporous
carryover of boiler water.
- mechanical carryover ; drum water entrainment in steam
- Vaporous carryover ; volatilization of impurities in drum water.
Silica presents most difficult problem due to its high solubility in
steam at intermediate S/G pressure.
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- Steam quality requirement for typical HRSG plant during
normal and constant operation
Parameter Target value Units
Cation conductivity < 0.2 /
Sodium, Na < 10 /
Silica, SiO2 < 20 /
Total Iron (Fe) < 20 /
Total Copper(Cu) < 3 /
2.1.2 Methods to minimize the problems
(1) Blowdown of S/G ; by continuously blowing down a portion of drum
water (less than 1% of feedwater flow rate) the impurities
concentrated in drum water can be removed.
(2) Corrosion within S/G can be minimized by maintaining pH of S/G
water at 9.0 or above, depending on the operating pressure. In
general, sodium phosphate (Na3PO4) is injected to drum water to
obtain desired pH level.
2.2 Feedwater Cycle Conditioning
Cycle conditioning is performed to minimize corrosion and subsequent
transport of corrosion products to downstream and to the S/G.
2.2.1 Conventional Treatment
(1) Elevates cycle pH in reducing environment by removing oxygen
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from feedwater at condenser and deaerator or by adding reducing
agent (Oxygen scavenger, N2H4).
(2) Reducing environment forms protective layer of magnetite (Fe3O4)
over steel material.
(3) To minimize the solubility of magnetite, pH should be kept around
9.5.
(4) If copper is present in cycle material, the copper solubility also has
to be minimized, which could be obtained at pH value of around 8.5.
(5) Compromised pH value of around 9.0 is used in case copper is
present in cycle.
(6) Ammonia typically is used as pH control agent.
2.2.2 Oxygenate Treatment (OT)
(1) Mostly for all-steel cycle of once-through boiler, oxygen or other
oxidizer is fed to the cycle to make oxidizing environment in the
feedwater.
(2) In the oxidizing environment, protective corrosion layer of ferric
hydrate oxide is formed over base layer of magnetite, with the
solubility of the former much lower than the latter, thus reducing
corrosion.
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3 Sample Points and Analysis Selection
Sample points and the analyses of each sample are selected based on the
criteria that they should give data for the decision whether steam and water
quality requirements of the cycle are met and the performances of important
equipment in the cycle are satisfactory.
In addition to the on-line analyses of each sample as selected, grab sampling
facility is furnished to enable further diversified analysis at laboratory environment.
In the following sections, each sample is discussed for the necessity of its
selection and types of analysis for a typical HRSG Cycle as shown in Fig.3.1.
3.1 Feedwater Pump Inlet (Sample #1, 8)
3.1.1 Purpose of analysis
To monitor the performance of deaerator
To check the effectiveness of oxygen scavenging and use the data
for dissolved oxygen control.
To determine compliance with the steam generator feeedwater
purity requirements.
3.1.2 Types of on-line Analysis and measuring ranges
Dissolved oxygen, 0~200 ppb
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Chem.
dosing
#1,8
Chem.dosing
Chem.
dosing
#6,1
3
#7,1
4
Chem.
dosing
#5,1
2
#2,9
#4,1
1
#3,1
0
Note:Thesecondsa
mplenumberinasetof
two
numbers
(#7,1
4forex.)
isfor
HRSG#2
#16
#15
Fig. 3. 1 Simplified d iagram of typical HRSG cycle
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Cation conductivity, 0~2 /
pH, 0~14 pH
3.2 LP Drum Water (Sample #2, 9)
3.2.1 Purpose of analysis
To monitor the purity of boiler water which is critical for the
performance and operational lifetime of boiler unit
To use the analysis results as the basis for blowdown control
3.2.2 Type of on-line analysis and measuring ranges
pH, 0~14 pH
Specific conductivity, 0~100 /
3.3 LP Superheated Steam (Sample #3, 10)
3.3.1 Purpose of analysis
To determine compliance with the turbine steam purity requirements
3.3.2 Type of on-line analysis and measuring ranges
pH, 0~14 pH
Cation conductivity, 0~2 /
3.4 LP Saturated Steam (Sample #4,11)
3.4.1 Purpose of analysis
To determine the quantity of moisture and chemical carryover from
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the boiler
3.4.2 Type of on-line analysis and measuring range
Cation conductivity, 0~2 /
3.5 HP Drum Water (Sample #5, 12)
3.5.1 Purpose of analysis
To monitor the purity of boiler water which is critical for the
performance and operational lifetime of boiler unit
To use the analysis results as the basis for blowdown control and
Na3PO4 dosing
3.5.2 Types of on-line analysis and measuring ranges
pH, 0~14 pH
Specific conductivity, 0~100 /
3.6 HP Saturated Steam (Sample #6, 13)
3.6.1 Purpose of analysis
To determine the quantity of moisture and chemical carryover from
the boiler
3.6.2 Types of on-line analysis and measuring range
Cation conductivity, 0~2 /
3.7 HP Superheated Steam (Sample #7, 14)
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3.7.1 Purpose of analysis
To check for the contamination of superheated steam due to
attemperation water impurities.
To determine compliance with the turbine steam purity requirements
3.7.2 Types of on-line analysis and measuring ranges
pH, 0~14 pH
Cation conductivity, 0~2 /
3.8 Condensate extraction pump discharge (Sample #15)
3.8.1 Purpose of analysis
To monitor for in-leakage of cooling water in condenser
To monitor for air in-leakage in condensate extraction pump
To check for proper functioning of air ejectors
3.8.2 Types of on-line analysis and measuring ranges
pH, 0~14 pH
Cation conductivity, 0~2 /
Dissolved oxygen, 0~200 ppb
Sodium, 0~50 ppb
3.9 Condensate polisher outlet (Sample #16)
3.9.1 Purpose of analysis
To check for proper function of condensate polisher
To obtain base data for determining the performance of deaerator
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3.9.2 Types of on-line analysis and measuring ranges
pH, 0~14 pH
Cation conductivity, 0~2 /
Specific conductivity, 0~100 /
Dissolved oxygen, 0~500 ppb
3.10 Aux. cooling water (Sample #17)
3.10.1 Purpose of analysis
To monitor for contamination of auxiliary cooling water of the plant.
Therefore, the sample is not taken from feedwater cycle but from
the cooling water supply line being introduced to Steam and Water
Sampling System.
3.10.2 Types of on-line analysis and measuring ranges
pH, 0~14 pH
Specific conductivity, 0~100 /
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4 Sample Obtaining and Transport
The most important criteria in deciding methods of obtaining and transporting
samples are whether they guarantee truly representative samples of fluids at
their respective sampling points.
4.1 Sample Obtaining
4.1.1 Water sampling
(1) Sampling nozzles
See Fig. 4. 1 for typical nozzle for water sampling
Sample taking from vertical pipe is preferable to avoid settling
resulting from low velocity
In case the water sample has to be taken from horizontal pipe,
the nozzle should not be installed on the bottom of the pipe.
(3) Location of sampling nozzle : on long vertical pipes to avoid
stratification of suspended solids and ensure that all water droplets
are carried in the flow stream.
(4) Nozzle insertion length : For single port nozzle, assuming fully
developed turbulent flow, the nozzle is normally inserted 0.2R of
the pipe from pipe inner surface, since this is the location where
actual and average velocities are equal.
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Multi-point nozzle can be used at locations where the velocity
profile across the pipe is known.
(5) Port size : is determined to maintain isokinetic sampling in the
nozzle port(s) at the desired sampling rate and design flow. But
port diameter should be larger than 1/8 inch to prevent plugging.
(6) Structure and material of nozzle: should be designed strong
enough to prevent failure due to vibration, thermal stress cycling
and other possible causes.
Nozzles normally are made of 316 stainless steel or other
austenitic stainless steel or alloy 600.
4.1.3 Superheated steam sampling
(1) Since superheated steam is usually regarded as single phase fluid,
isokinetic sampling requirement may not apply. However, the same
nozzle described for use with saturated steam can be used.
(2) High-pressure superheated steam can dissolve most contaminants
which, as steam pressure and temperature are reduced at nozzle
and sample line, can deposit on the surfaces causing biased
analytical results.
4.2 Sample Transport
Sample can be affected in many ways when they are transported from
nozzles to sample conditioning system.
Physical phenomena such as deposition and erosion, thermodynamic
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changes such as throttling and heat loss, and chemical and physical
changes such as reactions of oxygen scavengers, crystallization and
sorption are major causes that change the sample constituents.
Design of sample transport system should be focused on the ways to
minimize these changes and keep the samples unaffected as possible
during the transport.
4.2.1 Sample line construction
(1) Valves : Root valves should be installed at sample source. For high
pressure samples, double valves may be required depending on
safety considerations.
Valve and bore diameter should be selected so that velocity of
sample through the valve does not change much. Stainless steel
316 is preferred material for wet part of the valve.
(2) Sample line material selection; Wall thickness and material of the
tubes should be suitable for the temperature and pressure of the
sample source and should be of corrosion-resistant material. 316
Stainless Steel is preferred.
Tube inside diameter should be selected based on considerations
of sample velocity and pressure drop as discussed in section 4.3.
Fitting also should be selected based on their temperature and
pressure rating and made of materials compatible with the sample.
(3) Installation : Sample lines should be free of dead legs, particulate
traps(such as strainers), and low velocity zones. They should be as
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short as practical.
Adequate support to prevent fatigue failure from vibration should be
provided but free expansion and contraction with temperature
change should be allowed.
Sample lines normally should not be insulated.
(4) Fabrication : Weldings on the sample tubes on small diameter tube
(up to 3/8 inch) should be avoided as possible.
Tube bends are recommended instead of right angle fitting.
Burrs that could be produced after use of hacksaws and tube
cutters should be blown out with clean, oil free air or flushed prior
to installation.
4.2.2 Deposition
Results from chemical analysis can be biased either by the loss of
contaminants to the deposit on the tube wall or the gain of
contaminants from the deposits.
Mechanisms of deposition of contaminants are,
(1) Settling of particles: particles in the sample can stick to the wall
crossing the boundary layer by inertia, diffusion or gravity. Particles
so deposited can be eroded later by fluid drag force becoming re-
entrained in the fluid stream.
Steady state deposit weights are at the minimum when liquid
velocity is at 1.5 to 2.1 m/s. Minimum deposits is desirable because
of their shorter period of time for equilibrium and less susceptibility
to particulate bursts.
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All colloidal materials such as ion oxides and effluents from
demineralizers tends to form deposits also.
(2) Sorption of dissolved species: Deposits on tube walls are porous
and tend to sorb dissolved species by ion exchange, absorption,
adsorption or other mechanism.
(3) Crystallization: Most contaminants can be dissolved in superheated
steam. As the pressure and temperature of steam decrease, the
solubility of many contaminants is decreased and the contaminants
crystallize and deposit on the surfaces of dry wall tubes.
4.2.3 Saturated steam
(1) Typical behavior of saturated steam during transport.
Phase changes from saturated steam to two phase liquid of
vapor and liquid then to liquid as the sample temperature
decreases.
Sample velocity decrease from high speed of steam to lower
speed of liquid. As the desirable velocity of sample in the tube is
1.5 to 2.1m/s, which could be attained only in case of liquid
(condensate), the length of steam portion in the transport tube
should be short as possible.
When the steam velocity entering sample line is high, it will
cause pressure drop, increase the volume then further decrease
the pressure. In case of combined cycle plants, where steam of
pressure less than 35/ are produced, this pressure drop
temporarily causes the steam to enter the superheat region. The
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phase changes, from saturated steam to superheat steam then
to liquid water will result in abrupt flow speed changes, which
gives harmful effect to obtaining representative sample.
(2) Sample flow rate should be maintained constant as possible to
avoid condensing length changes, regional changes of phase and
resulting flow.
(3) Steam sample line sizing : For deciding sample line size and length,
calculations to determine heat loss and pressure drop for different
flow condition is required. Table 4.1 summarizes the calculations
for typical tube sizes at different pressure and flow condition. In the
table, following abbreviations are used.
Max. L : Maximum recommend length. N.R. indicates not
recommended for any length due to excessive
pressure drop.
Cond. L : Length where all steam is condensed. indicates that
the steam is not condensed within recommended length.
SteamVmax : Maximum velocity of steam at recommended length.
A bullet() indicates that the steam velocity is
increasing due to expansion. Where tube size is not
recommended for any length, required steam
velocity is given.
Cond. Vmin : Velocity of condensate at 500ft(154m). indicates
that the steam is not fully condensed in the
recommended length or within 500ft(154m).
*
*
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Table 4.1
Recommended Sample Tube Sizes
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The calculations for Table 4.1 are based upon straight tubing. In
case unusual number of bends is used in the sample transport line,
allowance for additional pressure drop has to be made.
4.2.4 Superheated steam
(1) To minimize deposit and loss of contaminants on the dry wall
portion of sample line where the temperature is higher than the
saturation temperature of the steam, it is recommended that
superheat be removed from steam sample as early as possible.
Where applicable, source cooling is recommended for this purpose.
(2) Once the sample lose all its superheat, it will behave in the same
manner as saturated steam. Table 4.1 includes recommendations
for superheated steam also.
4.2.5 Liquid samples
Liquid sample lines should be sizes for sample speed of 1.5 to 2.1 m/s.
This velocity range will result in minimum equilibrium deposit weight
reached in the minimum operation period of about 30 days.
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5 Sample Condit ioning
The objective of steam and water sample conditioning system is to modify and
control the temperature, pressure and flow rate of the samples from the sample
sources so that they are safe for grab sampling or are compatible with the
requirements of on-line analytical instruments.
5.1 Pressure control
Pressure control of a sample is performed by incorporating two control
methods, pressure reduction and back pressure control. Final target of
these controls is to establish a constant pressure zone so that analyzers
being fed from this zone get constant flows independent of actions taken in
other branch lines, while maintaining constant flow in the main sample line.
Normally, the pressure at the constant pressure zone is controlled at
0.5~1.5/.
5.1.1 Pressure reducer
(1) Pressure reducer is located down stream of primary sample cooler
so that the liquid is sub-cooled before pressure reduction.
(2) For samples greater than 35/, variable rod-in-tube type orifices
are recommended for they
provide varying pressure drop
are cleanable in place
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Fig. 5. 1 Typical arrangement of a sample conditioning system for a high-pressure
high-temperature sample.
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eliminate possible sample bias due to dissociation of water into
hydrogen and oxygen that can occur across throttling valves
when sampling at high pressures.
(3) For Samples less than 35/, needle valve is recommended for
pressure reduction.
5.1.2 Back pressure regulators.
(1) By maintaining upstream pressure at constant value (0.5~1.5/),
back pressure regulator performs two important functions, feeding
constant flows and pressure to analyzers and maintaining fixed
total sample flow.
(2) Back pressure regulator continuously discharges the flow
difference between total main sample flow and the sum of flows to
analyzers.
(3) Fore pressure regulator cannot provide constant sample line flow.
5.2 Flow control
Flow control is attained by adjusting flow meter control valve for each
analyzer in conjunction with pressure control of section 5. 1.
5.2.1 Total flow rate through a sample line is basically decided considering
optimum velocity requirement in the sample transport line
(1.5~2.1m/sec for water).
However, other factors such as pressure drop along the transport line,
total transport time etc. also have to be taken into account and
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compromise has to be made when required.
5.2.2 The total flow is obtained by adjusting the pressure reducer in flowing
condition.
Downstream pressure of the reducer is controlled by back pressure
regulator at 0.5~1.5/ as described in 5. 1. 2.
5.2.3 Once the pressure is established at constant pressure zone, flow to
each analyzer should be set at rate required by the analyzer by
adjusting control valve that is normally an integral part of flow meter.
5.2.4 Flow meters
(1) Flow meters for total flow and flow to each analyzer are
required.
(2) Flow meter for analyzer has manual flow adjust valve as an
integral part of the meter.
(3) Flow meters are normally rotameter types with visible indicator
(4) The rotameter shall be made of materials that are corrosion
resistant and not reactive with samples.
5.3 Temperature control
Temperature of all sample is reduced and controlled at 25 because most
on-line analyzers require samples to be standard temperature to ensure
repeatable and accurate results.
5.3.1 Primary cooler
Primary cooler is used to reduce the sample temperature to less than
2.8 of cooling water inlet temperature for water sample and 5.6
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of the cooling water inlet temperature for steam sample at
representative sample flow.
In general, for sample temperature greater than 80, primary cooler
can be used. But the decision should be based on the capability of
secondary cooler and chiller unit.
5.3.2 Secondary cooler
Secondary cooler should be capable of 0.5 approach to the chilled
water temperature.
5.3.3 Material and construction
Cooler are normally tube coils in a shell type. Cooler tube and shell
shall be made of stainless steel, preferably SS316 for tubes. For high
chlorides in the cooling water, however, Alloy 600 is recommended.
5.4 Other sampling system components
5.4.1 Blowdown valve
(1) Blowdown valves are used to purge sample lines that are not in
continuous service or where suspended solids deposition
affects the sample.
(2) The blowdown valves can be located either prior to primary
cooler or downstream of pressure reducer or at both.
(3) Blowdown valve prior to primary cooler may be operated on
initial startup of the system or after long period of shutdown of
the system to remove any foreign materials and deposits in the
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sample transport line.
(4) Blowdown valve downstream of pressure reducer is operated
every time before the sample line is put into operation to flush
the cooler and reducer in addition to sample transport line.
(5) Regulating type valve is used for blowdown valve prior to
primary cooler and ball valve for down stream of reducer.
5.4.2 Isolation valves.
For sample pressure higher than 48/ double isolation valves are
recommended.
Regulating type or ball valve rated for sample pressure and
temperature are used.
5.4.3 Sample relief valve
Each sample line should be provided with a pressure relieving device
to protect components from over-pressurization. Spring-loaded type
back pressure relief valve is commonly used located downstream of
pressure reducer.
5.4.4 Cooling water valves on sample coolers.
Each sample cooler should have an inlet isolation valve and outlet
throttling valve. Cooling water flow is adjusted by the outlet valve to
give optimum cooling water flow to the cooler and make balance
between cooling waters to different coolers from same cooling water
source.
5.4.5 Fitting
It is preferable to use bends rather than fittings to change direction of
sample tubing.
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Compression or socket weld fitting should be selected based on
application but compression fittings are preferable.
5.4.6 Sample filters may be installed in the line to trap particles and reduce
plugging on downstream components. But filters can affect sample
analytical results and are not recommended normally.
Filters made of stainless steel 316 with mesh size of about 100 is safe
enough if filters are to be used.
5.5 Instrumentation and control
5.5.1 In addition to monitoring flows by rotameters, pressures and
temperatures of final samples are monitored either by local indicators
or indications on control panel.
5.5.2 To protect components and analyzer sensors from abnormal high
temperatures due to failures on coolers, temperature switches may be
installed on final sample line which will trigger alarms and/or divert
sample flows to blowdown valves.
5.5.3 Control of sample and blowdown valves.
Control of sample valves and blowdown valves can be performed
either local-manually, remote-manually or remote automatically.
(1) Local manual method : Opening and closing of valves are done
at the valve locations by hand.
(2) Remote manual method : Pneumatic on-off valves are used
enabling manual operation of the valve from control panel.
(3) Automatic operation of valves: In automatic operation,
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blowndown and sample valves are operated in automatic
sequence with the blowndown duration is preset as required.
The automatic operation of sample lines can be performed
individually or in groups.
(4) Remote operation of valves can be initiated from control panel
of the sample conditioning system or from the main control
system (DCS) of the plant.
(5) PLC system is commonly used to realize remote and automatic
operation in sample conditioning system.
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6 Sample Analysis
Sample transported to and conditioned at sample conditioning system are either
grab sampled and analyzed at plant chemical laboratory or analyzed on-line by
analyzers on the sampling system control panel.
6.1 Precautions for grab sampling
(1) Samples should be taken from continuously flowing stream, not from
any dead leg in the sample conditioning system.
(2) If sample has not been flowing prior to grab sampling, blowdown of the
sample line has to be performed for enough time to flush and stabilize
the line.
Blowdown time to flush six times the total line volume is acceptable. But
when the system is being started initially or when new tubes or sample
coolers are installed, much longer period of time for flushing (preferably
several weeks) by continuous flow is required.
(3) The sample velocity in transport line during flushing and sample taking
should be maintained at 1.5~2.1 m/sec.
6.2 Precautions for on-line analysis
(1) Proper sample conditioning, particularly constant flow and temperature
has to be maintained.
(2) Manufactures requirements for sensor operation, flow rate range,
maximum pressure etc. have to be met.
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(3) Regular calibration of analyzers according to manufactures instructions
has to be performed.
(4) When the sensors, especially pH and Dissolved Oxygen, are out of
service or when the sample lines have to be left dry, special cares have
to be taken to avoid critical damages to the sensors. Instructions of
manufacturers manual has to be followed.
6.3 Analysis definition, methods and applications
In this section, brief explanations on the definitions, methods and
applications for the analyses being made in NEKA plant are given. Detailed
information on each analysis will be presented in separate class for each
analyzer.
6.3.1 Specific Conductivity
(1) A measurement of all ionic species which contributes to the electric
conductivity of a solution.
(2) Unit in normal use is micro Siemens per centimeter(/), which is
the reciprocal of the resistance in ohms measured between opposite
faces of a cubic centimeter of an aqueous solution referenced to
25.
(3) High-purity conductivity analyzer should adopt specialized
algorithms to account for the dramatic change in ionization of water
with temperature. The unique effects of ammonia, morpholine, etc.
present in the sample also has to be compensated for.
(4) Keeping the sample temperature at reference temperature of 25
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is very important for accurate measurement of conductivity because
the temperature compensation algorithm cannot count for all the
effect of varying constituents in the water and the temperature
sensor itself could produce erroneous signal.
(5) Specific conductivity tends to follow the concentration of pH
adjusting agents(usually ammonia).
(6) Electrical conductivity methods are widely used for monitoring
makeup water, feedwater and condenser leakage for its
comparatively little maintenance required, low cost and high
reliability.
6.3.2 Cation conductivity
(1) A measurement of anionic contamination rather than total ionic
species. Sample is passed through a hydrogen ion exchange
resin before conductivity measurement, where ammonia, amines
and other cationic contaminants are removed.
(2) Removing cation ions will greatly sharpen sensitivity to
contamination by removing the masking affects of ammonia,
amine and convert salts to the corresponding mineral acids,
which are a more conductive than the salts, thus further
increasing sensitivity.
(3) Non-ionized or weakly ionized substances (for ex. SiO2) and
hydroxide ions are not measured by this method.
(4) Is useful for detecting the leakage of cooling water into
condensate.
6.3.3 Dissolved oxygen
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(1) Oxygen dissolved/entrained in aqueous media.
(2) Measured by electrochemical method. Unit is in /L (ppb).
(3) Dissolved oxygen measurements is used to detect oxygen inleakage
at condensate pump discharge and also to monitor deaerator
performance and results of oxygen scavenger (N2H4) injection.
6.3.4 pH
(1) The negative logarithm of concentration or activity of hydrogen
ion (-log[H+]).
(2) Measured by electrometric instrumental probe method.
(3) pH measurements are made on most of the samples to monitor
whether the required pH level for minimizing corrosion of
steam/water cycle materials are maintained. The measurements
also provide data for the decision of pH control agent injection.
6.3.5 Sodium
(1) Alkali metal present in water as cation Na+.
(2) Measured by ion-selective electrode method. Unit is in
/L(ppb).
(3) Sodium measurement is made on samples from condenser
extraction pump discharge to detect condenser in-leakage and
breakthrough from condenser polisher dimineralizer.
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7 References
(1) Power Plant Engineering, by Chapman & Hall, 1966
(2) Steam and Water Sampling, Conditioning and Analysis in the Power Cycle,
ASME PTC 19.11-1997
(3) Standard Guide for Equipment for Sampling Water and Steam in Closed
Conduits, ASTM D1192-98
(4) Standard Practices for Sampling Water from Closed Conduits, ASTM D3370-
1999
(5) Standard practice for Sampling Steam, ASTM D1066-97