steam and water analyzer

STEAM & WATER ANALYSERS

Conductivity

pH

Dissolved oxygen

hydrazine

Silica

sodium

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Any variety of analyzer will consist of these sections:

Sample acquisition and conditioning

Predetermined mixing with the reagents

Measurement (via electrochemical or optical method)

Processing of values (electronic unit-alarms, annunciations)

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BASIC ANALYZER

ELECTROCHEMICAL

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•The mobile ions in the sample tend to move towards the electrodes.

•The ions get reduced at the cathode by chemical reaction and the necessary electrodes are generated at the other end thus leading to flow of electrons (or current) which could then be measured and calibrated in terms of ionic concentration (related by Nernst equation).

the ionization of water changes only with temperature, not with dilute salt concentration.

EXPLANATION:nernst equation

E = E0 –(RT/nF) log aiwhere:

E = total potential (in millivolts) between two electrodes

E0 = standard potential of the ion

R = universal gas constant (in Joules/mol-Kelvin)

T = absolute temperature (in Kelvin)

n = charge of the ion

F = Faraday constant (in Coulombs/mol)

ai = activity of the ion

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CONDUCTIVITY

The measure of the ability of a solution to carry an electrical current.

Importance

Conductivity is just a rough estimate to get a quick know-how of the process (irrespective of the alkalinity or acidity), so that any harmful ingress can be detected at the early.

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FACTORS

The accuracy of conductivity measurements can be influenced by the following factors:

Polarisation Contamination Cable resistance Cable capacitance Temperature

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POLARIZATION

Applying an electrical current to electrodes in solution may cause an accumulation of ionic species near the electrode surfaces and chemical reactions at the surfaces.

Thus, a polarisation resistance arises on the electrode surface, which may lead to erroneous results as it is a parasitic component to the solution resistance.

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TEMPERATURE

Ct = C25[1+ a (t-25)]

Where Ct –conductivity at temperature t

a- temp coeff

t- process temp.

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CATION CONDUCTIVITY

Importance

Contamination of feed water or steam is rarely due to a single contaminant. When a condenser tube springs a leak, chloride, sulfate, carbonate, and many other anions contaminate condensate and feed water. The combined effect will significantly raise cation conductivity and provide the desired early warning even when the individual contamination

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EQPT SPECS. ---CONTD. - ANALYSERS

Common specification for analysers:

Field proven monitors/ analyzers based on microprocessors with LCD display and with necessary fault diagnostic features shall be employed.

CONDUCTIVITY ANALYSER:Type For Hotwell, Two removable

Type of Cells.For Others, Continuous Flow Through

Type Accuracy <= +/- 1 %Response Time <= 1 Sec (90 % of Full Scale)Range 0-1,0-10,0-100 micro-Mho/cm(freely

programmable)for Specific Conductivity.0-1 micro-mho/cm log scale for Cation

conductivityTemperature Comp. Automatic

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Corrosion is function of ph and oxygenAlkaline condition increases stability of magnetite in all

volatile treatment

Principle: ph is normally measured with a glass electrode and a reference electrode. Glass electrode reduces H+ ions and thus leads to en emf dependent on electrode used, type of reference electrode used, and temperature related by Nernst equation.(59.16 mv/25 deg.)-nernstian slope.

pH unit measures the degree of acidity or basicity of a solution. pH is the measurement of the hydrogen ion

concentration, [H+].

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pH Analyser

PH SENSOR

pH sensor uses a differential electrode technique which employs two pH glass measuring electrodes. One electrode is used as the active or measuring electrode, and the other is used as part of a reference assembly. The reference assembly consists of a pH glass measuring electrode immersed in a 7 pH buffer solution. which is mechanically isolated from the solution being measured by a double junction "salt bridge"

The reference junction is located at the measuring end of the reference electrode (or reference electrode assembly for a differential pH sensor). The reference junction is also referred to as a "salt bridge," liquid junction, or frit.

Its purpose is to interface physically and electrically with the internal electrolyte and the solution being measured. This reference junction completes the current path from the glass measuring electrode to the reference electrode.

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PH

At 25°C the slope of the pH electrode is 59.16 mV/pH unit.

At 0°C the slope value is approximately 54 mV/pH, and at 100°C the slope value is approximately 74

mV/pH.

The millivolt output of the glass pH electrode will change with temperature in accordance with the Nernst equation. As the temperature increases, so does the millivolt output. Specifically, the slope of the electrode

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pH ANALYSER:

Type Flow Through Type

Accuracy <= +/- 1 %

Range 0-14 pH freely programmable

Temperature Comp. Automatic

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Based on Clark cell principle.An oxygen permeable membrane, (no interference)Electrode charged from a constant voltage

source( cathode-gold, anode-silver).Electric current due to reduction of oxygen, current

proportional to the concentration.Rates of reaction and diffusion are temperature

dependent, so RTD installed in the cell.Features: range(0-2 ppm); calibration in air;

programmable alarm levels; o/p’s on relays; 4 mA-20 mA or 0 mA-20 mA; RS-485; alarms4; cell current display( micro/ nano amp.); hysteresis settings; timer operation of relays; average options over a user defined number of inputs.

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Dissolved oxygen

DISSOLVED OXYGEN

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Dissolved oxygen may lead to corrosion on coming in contact with metal surfaces

HYDRAZINE ANALYSER Hydrazine dozing is done for the removal of dissolved

oxygen from water. So, to check dosing of hydrazine, hydrazine conc. has to be monitored.

Cell premixed combination of electrolyte and sample is passed

through a sensing chamber having a exposed porous member.

porous member having a platinum wire electrode wound about the outside thereof and having a silver wire inserted into silver chloride salt (gel) on the inside thereof to form a reference half cell. the porous member and electrode upon being placed in the path of the fluid will cause a current to be developed between the electrodes which is proportional to the amount of chemical in said fluid

pH and temperature compensated

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EQPT SPECS. ---CONTD. - ANALYSERSHYDRAZINE ANALYSER:

Type Automatic Continuous Electrochemical Type

Accuracy <= +/- 5 %Response Time <= 3 Min. (90 % of Full Scale)Range 0-50, 0-100 ppb freely

programmable


Sample shut off solenoid valve to be provided.

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SENSOR

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PHOSPHATE ANALYSER:

Type ColourimetricAccuracy <= +/- 5 % of reading

Response Time <= 6 min (90 % of Full Scale)

Range 0-10 ppm freely programmable


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SILICA

Importance

Solubility of silica decreases with decrease in pressure of steam, so even a small quantity of silica can cause appreciable amount of damage to LP turbine blades by deposition. That may lead to damage to seals or surfacing of vibrations in the turbine

Method of analysis: Continuous Colorimetric

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SILICA

Reagents

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molybdate Citric acid Amino acidmolybdosilicic

and molybdophosph

oric acids

masks any molybdophosphoric

acids &prevents molybdate from producing an

interfering blue colored compound.

Light absorbance is measured to determine a sample blank reference absorbance. Color formed at this point provides a zero reference.The amount of color formed is directly proportional to the silica concentration of the sample. Light absorbance through the sample is measured at 810 nm. This is compared with the sample blank reference absorbance and silica conc. is calculated.

SILICAOperation of the HACH analyzer is semi continuous where

discrete portions of sample are captured and analyzed in a timed sequenced.

A constant flow of sample is directed through a two way valve to the sample cell.

sample flow - 2-8 psi Reagents are stored in containers pressurized at 8-16 psi.

Calibration

Standard sol. from the reagent bottle is added to the sample cell in place of normal sample. the standard sol. is analyzed and the result is used to calculate the slope of the calibration curve.

SiO2= slope x log(reference / sample)

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SILICA ANALYSER:Type Continuous Colorimetric

Type - Multi stream

Accuracy <= +/- 5 % of readingResponse Time <= 15 min( including sample (90 % of Full Scale) switching)

Range 0-50, 0-100 ,0-500 ppb freely programmable


Sample shut off solenoid valve to be provided.

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SODIUM

Principle:electrolytic-type.

Sodium sensitive glass electrode has been previously conditioned to a pH > 10.0 .sample conditioning is necessary because sodium glass electrodes are not perfectly specific sensors, but are subject to interference by other ions, specifically hydrogen ion .

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SODIUM ANALYSER:

Type Continuous Flow through Type – Multi stream

Accuracy <= +/- 10 % of readingResponse Time <= 4 Min(90 % of Full Scale)Range 0-1,0-10, 0-200 ppb

(freely programmable)Temperature Comp. Automatic/

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SEQUENCERVia the help of sequencer, a single channel device can

be made to switch between six different samples.

Sequence of samples being analyzed can be fed into the memory via software interface with the user.

Timings can be programmed.

Serial communication with the analyzing medium.

Flow adjustment via valves.

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CONDENSATE PUMP DISCHARGE

PARAMETERS TARGETVALUE

---------------------------------------------------------------------------1.SODIUM, PPB < 3

2.CATION CONDUCTIVITY < 0.2 S/CM

3.OXYGEN, PPB < 10

---------------------------------------------------------------------------

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FEED WATER

PARAMETERS SAMPLE AVT OTFREQUENCY

----------------------------------------------------------------------------------------------------------------------

1. CATION CONDUCTIVITY C < 0.15 <0.15 S/CM2.HYDRAZINE, PPB C 10-15 -----

3. pH C 9.0-9.5 7.0-8.5

4. DISSOLVED OXYGEN, PPB C < 5 30-150

5. TOTAL IRON, PPB S < 2 <2

6. SILICA, PPB S <5 <5

7.SODUIM, PPB S < 2 < 2

8.CHLORIDE, PPB S < 2 < 2

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INSTRUMENTATION FOR CORE PARAMETERS

LOCATION PARAMETERS RANGE ------------------------------------------------------1.MAKE UP WATER CONDUCTIVITY 0 - 1 S/CM

2.CEP DISCHARGE SP.CONDUCTIVITY 0 - 10 S/CMCATION CONDUCTIVITY 0 - 1 S/CM

SODIUM 0 -1,0 - 100 ppbD.O. 0 - 100 ppB

-------------------------------------------------------------------------------

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4.FEED WATER pH 6 - 11SILICA 0 -20 -ppbD.O. 0 - 10 PPb

HYDRAZINE 0 -50 -100PppbCAT.CONDUCTIVITY 0 -1 S/CM

SP.CONDUCTIVITY 0 -10 S/CM

5.BOILER DRUMpH 6 - 11 SILICA 0 -500 ppbSP.CONDUCTIVITY 0 - 10 -20 S/CMCAT.CONDUCTIVITY 0 -1 S/CM

6.STEAM SP.CONDUCTIVITY 0 - 10 S/CM CAT.CONDUCTIVITY 0 -1 S/CM SODIUM 0 -10 ppB

----------------------------------------------------------------------------

LOCATION PARAMETERS RANGE--------------------------------------------------------------------

MAIN MENUAlarmsAnalog output (I / v)CalibrationDiagnosticsDisplay modeInstallation- program measurement range and no of sample-

underrange (on/off).PrinterSerial interface(RS-232)Sequence- upto a maximum of 15 is possible“Service” optionTime settings RangeRemote alarm board option (to make sampling options LOCAL-

REMOTE).

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FLUE GAS ANALYSER

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OXYGEN ANALYSER

Principle of Measurement

zirconia oxygen analyzers determine oxygen concentration using the conductivity of a zirconia ceramic cell. Zirconia ceramic cells only allow oxygen ions to pass through at high temperatures. With reference gas on one side and sample gas on the other, oxygen ions move from the side with the highest concentration of oxygen to that with the lowest concentration. The movement of ions generates an EMF (Electro Motive Force) which can be measured to determine the oxygen content

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CO ANALYSER

The main components are an infrared source (lamp), a sample chamber or light tube, a wavelength filter, and the infrared detector. The gas is pumped into the sample chamber, and gas concentration is measured electro-optically by its absorption of a specific wavelength in the infrared (IR).

The IR light is directed through the sample chamber towards the detector. In parallel there is an other chamber with an enclosed reference gas, typically nitrogen. The detector has an optical filter in front of it that eliminates all light except the wavelength that the selected gas molecules can absorb. Ideally other gas molecules do not absorb light at this wavelength, and do not affect the amount of light reaching the detector.

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THANK YOU

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steam and water analyzer

Documents

feed water

nernst equation

electrical

analysers

solution

type

electrodes

kelvin