0372 0375 vol a1 t02 water chemistry

7/31/2019 0372 0375 Vol a1 t02 Water Chemistry

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WATER CHEMISTRY

GUIDELINES FOR

HIGH PRESSURE BOILERS

PUB.NO. 2003


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CONTENTS

1.0 GENERAL

1.1 MAKE - UP WATER TREATMENT

1.2 INTERNAL CORROSION

1.3 EFFECT OF pH

1.4 EFFECT OF OXYGEN

1.5 BOILER WATER TREATMENT

1.6 CONDENSER LEAKAGE

FIG.1 RELATIVE CORROSION RATE OF CARBON STEEL VS pH

FIG.2 SILICA VS DRUM PRESSURE

FIG. 3 SILICA IN BOILER WATER VS DRUM PRESSURE

FIG. 4 OPERATION BETWEEN 70 - 125 kg/cm2




RECOMMENDED FEED WATER LIMITS

BOILER WATER LIMITS

GUIDELINES FOR EMERGENCY OPERATIONS

HOT WELL CONDITIONS FOR ALL VOLATILE TREATMENT


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WATER TREATMENT

1.0 GENERAL

High pressure boiler (operating above 60 kg/cm2 ) design needs a close look at the limiting

conditions like heat transfer, heat exchanger metal temperature,circulation etc., The entire

exercise of Water Treatment (both internal and external treatments) is aimed at (1) corrosion

control and (2) steam quality. The cost of corrosion and deposition to electric utilities is veryhigh due to repairs and loss of production (shutdowns).Poor steam quality leads to deposition

on turbine blades causing efficiency loss and failures .Thus the successful operation of high

pressure boilers and turbine units require a strict vigil on the Water Treatment practices and

controls, particularly for high pressure drum type and once through boilers.

1.1 MAKE - UP WATER TREATMENT

Trouble free continuous operations of high pressure boilers call for very stringent feed water

quality. Total solids and silica, other than corrosion products,being the main constituents are

responsible for carry-over and deposition reducing the units efficiency. Make up water isrequired to becontrolled and maintained at low levels. Silica in particular, is CARRIEDOVER

in the form of VAPOUR at high pressures, needs to be controlled at low levels.Feed water is

used for de-superheating spray and any contamination of feed water (either from steam

condensate or from make up water) directly enters the superheated steam . IMPURE FEED

WATER increases BLOW DOWN making the operation un-economical.Hence feed water is

required to be very pure for high pressure boilers. This inturn necessitates high purity

make up water, other than polishing the steam condensate, wherever applicable. Modern

demineralisation plants with different combinations of ion-exchangers, are capable of producing

the requiredquality of make up water with specific electrical conductivity less than 0.2 micro

mhos/cm and silica 0.02/0.01 ppm.

1.2 INTERNAL CORROSION

Corrosion is a common phenomenon in high pressure boilers. Corrosion in boiler circuits as

well as in pre-boiler circuits can cause tube failures followed by force shut down of boilers.

The causes of corrosion are,

i. pH ( acidity or high alkalinity )ii. Oxygen

iii. Excessive ammonia (on copper base alloys )

iv. Concentration of alkalising agents due to localised over heating

v. Poor quality of passivating layer or breaking of passivating layer due to thermal

shocks

vi. Decomposition of organics into corrosive products.


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1.3 EFFECT OF pH

The reaction of feed water on steel is spontaneous and rapid at high temperatures. The only

reason that boiler steel can survive normal operating conditions is that the passivated layer of

magnetite ( Fe3O

4) / hydrated iron oxide (FeOOH) forms a protective layer on the steel surface,

preventing corrosion. The whole exerciseof maintaining alkalinity control is to maintain an

environment in which the oxide film is stable and protective. One of the objectives of Water

Treatment in boilers is to protect this film against the aggressive action of impurities introducedinto the boiler with the feed water.

The work of Bell and Van Track has been used to relate the relative corrosion of steel over a

range of pH values. It was found that the protective layer is getting dissolved at pH values

below 5.0 and above 13.0 Minimum corrosion is indicated at pH of 9.0 to 11.0 (Fig. 1)

Although corrosion is low over a wide band of pH values, unfortunately, corrosion occurs by

localised concentration of alkaline chemicals on tube metal due to starvation, localised over

heating etc. Rather than the concentrations existing in the bulk boiler water. Local concentration

changes the pH drastically and corrosion takes place. Due to limitations of chemicals used, an

optimum pH of 8.8 to 9.2 is recommended for feed water, which can be achieved by use of notmore than 0.5 pprn of ammonia. Any excess presence of ammonia (indicated by higher pH

values) will cause copper corrosion in the pre-boiler system.

Another parameter which affects corrosion rate is the temperature inside the reaction vessel.

Hence different temperature ranges or the pressure ranges call for different pH values to be

maintained in order to minimize corrosion.

Accordingly boiler water pH requirements are higher than the feed water limits and different

for different pressure ranges. Boiler water pH is elevated to the recommended levels using

Trisodium phosphate. The use of caustic soda is not recommended for this purpose as it hasthe danger of concentration and destruction of protective oxide film to cause corrosion.

1.4 EFFECT OF OXYGEN

The exclusion of oxygen in feed water is essential to avoid corrosion. Small quantities of

dissolved oxygen are capable of causing severe corrosion pitting in boiler tubes. A combination

of poor oxygen control and chlorides in boiler water can result in serious hydrogen damage

type corrosion of water wall tubes. Power plants employee tight cycles to prevent oxygen

infiltration and condenser leakage are generally free from corrosion problems. Continuous

monitoring of oxygen is required in high pressure system.

Too often, oxygen enters the system undetected during periods of operation which are poorly

monitored. Poor start-up procedures are also responsible for oxygen ingress. A most common

error is the use of undeaerated water. Feed water at a temperature less than 100 deg. C contains

excessive quantities of dissolved oxygen and hence feed water should never be allowed into

the boiler at any time below this temperature.Deaerator is the main equipment to control

oxygen within 0.01 - 0.02 ppm.


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The best deaeration is obtained in units which operate above atmospheric pressure at all load

conditions. A normal contamination of feed water occurs, when the deaerator pressure varies

with a turbine bleed stage from above atmospheric to vacuum at low loads. Heater drips from

low pressure system contain varied quantities of oxygen. A significant oxygen increase occurs

in the heater drips as a heater drops below atmospheric pressure at low loads. A major problem

of oxygen leakage occurs at low loads when heater drips are pumped directly to the condensate

system. It is preferable to exhaust the drains to the deaerating section of the condenser.

The most serious corrosion occurs in boilers which shut-down and start-up frequently withoutincorporation of technique to minimise oxygen in the feed water. Much of the problems can

be reduced by pressurising the deaerator with steam at about 0.5 kg/cm2 (g) to exclude oxygen

from the water during any short outage. For long outages, the vapour and water contacted

surfaces of the feed water system should be pressurised with steam or nitrogen.

With the main oxygen removal by deaeration, residual oxygen in small quantities can be

reduced further by reducing agents such as sodium sulphite or hydrazine.Hydrazine being a

volatile chemical, should only be used for high pressure boilers. Hydrazine reacts with oxygen

to form nitrogen and water. This reaction is very low at temperatures below 175o C. Above

230o C, Hydrazine is decomposed rapidly to nitrogen, hydrogen and ammonia. Hence hydrazine

dozing alone cannot control oxygen without effective deaeration. Since hydrazine has also

the property of passivating the metal surfaces of the pre-boiler cycle by reducing the oxidised

form of iron and copper, it is advantageous to add hydrazine to the cycle at the outlet of the

condensate pump.

1.5 BOILER WATER TREATMENT

It is recommended to use co-ordinated phosphate - pH treatment ( Sodium to phosphate

ratio = 3) method for high treatment excludes free caustic from the boiler water. Caustic

present in boiler results in a ductile-gouging type corrosion. Even if bulk boiler water does

not contain large amount of free caustic, there is great potential for caustic to concentrate andcause corrosion. Internal metal oxide deposits provide sites for concentration. As steam is

produced, dissolved solids concentrate in the thin film between tube wall and bulk fluid. Low

sloped tubes permit concentration. It has been well established that phosphate even concentrated

under hide-out conditions is not aggressive to the tube metal.

Congruent phosphate program (Sodium to phosphate ratio = 2.6) takes care of both caustic

and acid corrosion but control of sodium to phosphate ratio is difficult, calling for continuous

feed and blow down.

Figs. 4 to 7 provide guidelines to use either of the programmes, subject to the operators

convenience.

Volatile treatment is another method of treatment but it is primarily to control corrosion of

heater surfaces in the pre - boiler circuit. Chemicals such as ammonia, cyclohexylamine and

morpholine are volatile at high pressure boiler water temperatures. As a result there is no

significant buffering of boiler water pH due to these chemicals. Any ingress of condenser

leakage contaminants requires the immediate addition of phosphate to prevent the depression

of pH and the incidence of hydrogen damage. The main attraction of volatile treatment is that

it assures good steam purity .


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Impurities due to vaporization of salts and mechanical carry-over are at a minimum.But it is

necessary to employ condensate polishing and have reliable instrumentation for detecting

immediately any condenser leak to safety operate with volatile treatment.

1.6 CONDENSER LEAKAGE

Condenser leakage, as mentioned earlier, is a major source for corrosion. The type of cooling

water and its interaction with boiler water determines whether b oiler water pH will become

more acidic or alkaline during a period of condenser leakage. It is very important to preventcondenser leakage of sea water as it results in acidic boiler water. The hardness chloride salts

present abundantly in sea water generate hydrochloric acids at boiler water temperatures.

Uncontrolled large leakages of sea water can cause within hours extensive corrosion (hydrogen

damage) of water wall tubes. There should be no hesitation to shutdown and save the unit if

boiler water specifications,as recommended cannot be maintained during the condenser leakage.

Any unit should have an on-line instrument with a cation column at the outlet of condenser to

monitor conductivity continuously and detect immediately any condenser leakage.

FIG.1 RELATIVE CORROSION RATE OF CARBON STEEL VS pH

FIG.2 SILICA VS DRUM PRESSURE


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FIG. 3 SILICA IN BOILER WATER VS DRUM PRESSURE



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RECOMMENDED FEED WATER LIMITS

DRUM OPERATING PRESSURE

Kg/cm2 (g)

61-100 100 and above

ONCE

THROUGH

BOILERS

TREATMENT TYPE P04 P04 AVT AVT

1. Hardness ppm (max) NIL NIL NIL NIL

2. pH at 250C 8.8-9.2 8.8-9.2 8.8-9.2 8.8-9.2

3. Sp. electrical conductivity after 0.50 0.30 0.20 0.20

cation in H+ form at 250C micromho s/cm (max)

4. Dissolved oxygen ppb (max) 5.0 5.0 5.0 5.0

5. Silica as SiO2 ppb (max) 20.0 20/10* 10 10

6. Iron as Fe ppb (max) 10 5 10 10

7. Copper as Cu ppb (max) 10 5/3* 3 3

8. Residual Hydrazene ppb 10-20. 10-20 10-20 10-20

* Should match with the corresponding values to be maintained in super heated steam


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BOILER WATER LIMITS

(FOR DRUM TYPE BOILERS NORMAL OPERATION)

DRUM OPERATINGPRESSURES Kg/cm2 (g)

61 90 91 125 125 165 165 180 181 & above

TREATMENT TYPE PO4 PO4 PO4 PO4 AVT PO4 AVT

1. Total Dissolved solids

ppm (max )

100 100 50 15

(Note)

2.0 10

(Note)

1.0

2. Sp. Electrical conductivitymicro. mhos/ cm (max)

200 200 100 30(Note)

4.0 20 2.0

3. Silica as Sio2 ppm (max) 4.0 To becontrolled as

per fig .2&3

0.20 0.10 0.10 0.10 0.10

4. Chlorides ppm (max) - - - 0.6 0.02 0.50 0.01

5. pH at 25o C 9.0-- 9.0-- 9.1-- 9.1-- 9.3-- 9.1-- 9.3--

10.0 10.0 9.8 9.7 9.5 9.7 9.5

6 . Phosphate , res idual ppm 5 20 5 20 5 20 2 6 N/A 2 6 N/A

* NOTE : Total solids 15 & 10 ppm correspond to 10 ppb sodium steam


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S I . N o

.

P r e s s u r e

r a n g e

k g / s q -

c . m ( g )

H o t w e l l s o l i d s

p p m

O p e r a t i o n a l

L i m i t a t i o n s

C o n t r o l

L i m i t s

B o i l e r

W a t e r

C o n t r o l

0 1 6 1 -1 2 5 0 . 5 - . 2 . 0

( A B N O R M A L )

> 2 . 0( E X C E S S I V E )

L i m i t e d

o p e r a t i o nN o t e . 1

E m e r g e n c yo pe r a t i o n -

N o t e . 3

T D S < 2 0 0

p p r np H 9 . 1 - 1 0 . 1

P 0 4 5 -4 0 p p m

- D O -

N O T E 2

N O T E 4

0 2 . 1 2 6 -1 6 5 0 . 5 -2 . 0

( A B N O R M A L )

> 2 . 0

( E X C E S S I V E )

L i m i t e d

o p e r a t i o n

N o t e . I

E m e r g e n c y

o pe r a t i o n -

N o t e . 3

T D S < 1 0 0 p p m

p H 9 . 1 - 1 0 . 1

P 0 4 5 - 2 0 p p r n

- D O -

N O T E 2

N O T E 4

0 3 . 1 6 6 -1 8 0 0 . 2 5 -1 . 0

( A B N O R M A L )

> 1 . 0( E X C E S S i V E )

L i m i t e d

o p e r a t i o nN o t e . 1

E m e r g e n c yo p e r a t i o n

N o t e . 3

T D S < 5 0 p p m

p H 9 . 1 - 1 0 . 1P 0 4 5 - 2 0 0 ' pr n

- D O -

N O T E 2

N O T E 4

0 4 . 1 8 1 -2 0 3 0 . 1 -1 . 0

( A B N O R M A L )

> 1 . 0

( E X C E S S I V E )

L i m i t e d

O p e r a t i o n -

N o t e 1

E m e r g e n c y

o pe r a t i o n -N o t e . 3

T D S < 5 0 p p m

p H 9 . 1 - 1 0 . 1

P 0 4 5 - 2 0P P M

- D O -

N O T E 2

N O T E 4

GUIDELINES FOR EMERGENCY OPERATIONS

(DRUM TYPE - PHOSPHATE TREATMENT)

NOTE 1: Schedule Inspection and repair of condenser as soon as possible

NOTE 2: Immediately start chemical injection to achieve higher phosphate and pH condition

not continue operation if pH cannot be maintained above 8 total solids below specified

limits. Avoid use of desuper heating spray.

NOTE 3: Immediately reduce load to permit isolation of damaged condenser and prepare for

orderly shutdown if hot well TDS cannot be re duced quickly below specified limits.

NOTE 4: Prepare for wet lay up of the boiler

NOTE 5: Control silica in boiler water in accordance with graph provided.


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GENERAL INSTRUCTIONS

1 . All Feed water measurements shall be made at high pressure heater outlet or economiser inlet

.

2. Oxygen can also be additinrially measured at deaerator outlet to determine the quantity of

N2H

4dozing .

3. The recommended pH in feed water can be obtained by dozing ammonia, morpholine or any

volatile amine. The concentration of volatile chemical in the feed water should not exceed

0.5 ppm.(expressed as Ammonia)

4. The phosphate and pH are recommended in accordance with co-ordinated phosphate curves

(Figs. 4 to 7) to prevent presence of free hydroxide in boiler water.

5. Water levels in drum should be maintained within limits during all operational modes, start-up,

load fluctuation and normal operation.

6. The allignment of drum internals should be checked and ensured to be in order atleast once

every year

7. It is needless to emphasize that correct sampling, accurate measurements with the use of

reliable instruments at adequate intervals and proper logging of readings go a long way in

ensuring trouble free operation.

HOT WELL SOLIDS (PPM)PRESSURE RANGE

(Kg/sq.cm) NORMAL

OPERATION

EMERGENCY

OPERATION

126-165 < 0.05 < 0.1 PPM

Above 166 < 0.05 < 0.25 PPM

Note: Switch over to phosphate treatment when hot well solids exceed emergency operation

levels.

HOT WELL CONDITIONS FOR ALL VOLATILE TREATMENT

(FOR DRUM TYPE BOILERS)

Go To Pub Index


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METHODS OF WATER

ANALYSIS


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CONTENTS

1. GENERAL INSTRUCTIONS ON SAMPLE COLLECTION AND USE OF

INSTRUMENTS

2. DETERMINATION OF TOTAL HARDNESS

3. DETERMINATION OF CARBON-DI-OXIDE

4. DETERMINATION OF P&M ALKALINITY

5. DETERMINATION OF FREE ALKALINITY IN BOILER WATER

(STRONTIUM CHLORIDE METHOD)

6. DETERMINATION OF SULPHITE

FIG.1 METHOD OF COLLECTING SAMPLE FOR OXYGEN

FIG.2 WINKLER FLASK FOR DISSOLVED OXYGEN DETERMINATION

7. DETERMINATION OF DISSOLVED OXYGEN (MORE THAN 0.10 PPM)

8. DETERMINATION OF PERMANGANATE NUMBER (DETERMINING

ORGANIC SUBSTANCES : POTASSIUM PERMANGANATE CONSUMPTION)

9. DETERMINATION OF EVAPORATION (T.D.S) IGNITION RESIDUES AND

VOLATILE MATTER

10. DETERMINATION OF OIL (FLUOROCARBON MATTERS)

11. DETERMINATION OF pH-VALUE

12. DETERMINATION OF CONDUCTIVITY (CONDUCTO BRIDGE METHOD)


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FIG.3 HYDROGEN ION EXCHANGER OF PLASTIC FOR MEASURING

CONDUCTIVITY

13. DETERMINATION OF DISSOLVED OXYGEN

14. DETERMINATION OF SOLUBLE SILICA

15. DETERMINATION OF TOTAL SILICA

16. DETERMINATION OF ORTHOPHOSPHATE

17. DETERMINATION OF IRON - BATHO PENANTHROLINE METHOD

18. DETERMINATION OF COPPER NEOCUPROINE METHOD

19. DETERMINATION OF AMMONIA

20. DETERMINATION OF HYDRAZINE

21. DETERMINATION OF CHLORIDE (COLORIMETRIC METHOD)

22. DETERMINATION OF MORPHOLINE

23. DETERMINATION OF CYCLOHEXYLAMINE

24. DETERMINATION OF SODIUM (FLAME PHOTOMETER)

25. DETERMINATION OF SODIUM-LOW LEVEL (ONLINE METHOD)


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INTRODUCTION

The operation of modem steam generating plant necessitates constant supervision of water and steam

conditions. For effective supervision, examination of water and steam samples is essential to provide

suitable data for those responsible for operating water treatment plant and steam generating units to

enable them to form a picture of the general operational state.These data should also help to give timelywarning of any changes to enable corrective measures to be taken before trouble or damage ensues.

Collection of representative sample and use of correct method of measurement are vital to obtain

accurate results. The frequency of sampling and analysis depends on the maximum time during which

lack of knowledge of the concentration of contaminants or additives, is acceptable. Local conditions

such as plant design, condenser leakage, blow down and startup will often dictate the sampling frequency.

In order to that the measurement of a contaminant or additive can be capable of detecting the smallest

significant deviation from a set standard, the precision of analytical results must not exceed given values.

Therefore, analyst must make regular checks to ensure that the precision remains satisfactory; a statistical

assessment of results is necessary.

Auto - analysers are of benefit, as they give a better overall picture and reveal trends towards change.

All automatic analytical instrumentations should be maintained in an operational and calibrated status.

If chemical auto-analysers are not operational, greater emphasis must be placed on laboratory analyses.

In general, major operational decision will be made on the results of these measurements to achieve

optimum plant operation; in other words, the longest possible service life for the plant with minimum

operational losses and consumption of chemicals.


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1. GENERAL INSTRUCTIONS ON SAMPLE COLLECTION AND USE

OF INSTRUMENTS

1.1. SAMPLE COLLECTION - PRECAUTIONS

In the conditioning of industrial water it is necessary that analyses be made to govern the treatment

processes. If the results obtain from a analysis are to be of any value, it is necessary to get a

sample that if freely representative of the condition of the water at the point at which the sample

has been collected.

Sampling lines are to be kept continuously flowing. Sampling and cooling water line should be

free from choking and sampling lines to be purged for about 30 minutes every day as a routine

and whenever choking is suspected. To avoid contamination of cooled samples they are to be

collected in dust-free atmosphere. Cooling water contamination of samples is to be prevented.

The sampling rate should be not less than 450 ml / min and sample temperature shall not exceed

about 40 degree C. The container used for collecting samples should be made of polythene with

innercap. Before collecting samples, rinse the container atleast 3 times. After collecting the samples,

rinse the stopper and tightly close the container.

1.2 USE OF INSTRUMENTS - GENERAL INSTRUCTIONS

i) Spectrophotometer :

The following instructions shall be followed to ensure the accuracy of Spectrophotometric determinations.

a) The Spectrophotometer used for colorimetric determinations is to be calibrated atleast once in

six months.

b) The temperatures of both sample solution and calibration solution shall be nearly equal preferablyabout 25 degree C.

c) Optically matched cells are to be used for calibration and measurement.

d) For the determinations of the various parameters, individual graphs are to be prepared with

standard solutions. The graphs are to be checked or redrawn if required during calibration checks.

e) The straight line portion of the curve which represents linearity only is to be used.

f) Solutions of higher concentrations are to be diluted suitably so that the concentration can bemeasured within the linear portion of the graph.

g) Suppliers operating instructions shall also be followed.

ii) Other Instruments :

The general operating instructions supplied along with instruments shall be followed.


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2. DETERMINATION OF TOTAL HARDNESS

2.1 INTRODUCTION

i) Total Hardness

Calcium and magnesium ions in water are sequestered by the addition of sodium ethylene

diamine tetra acetate. The end point of the reaction is detected by means of an indicator,

chrome-black T, at an optimum pH of 10.0-10.4 which has wine red colour in the presenceof calcium and magnesium, and a blue colour when they are sequestered.

ii) Calcium Hardness

Calcium ions in water are sequestered by the addition of EDTA. The end point of the

reaction is detected by means of an indicator, murexide which is dark purple in the

absence of calcium but with which calcium forms a light salmon red complex. The optimum

pH range is about 10.4

2.2 REAGENTS

i) Standard Calcium Chloride Solution

(1 ml equals 1 mg CaCO3)

Dissolve 1.0000 g of reagent grade calcium carbonate containing less than 0.04% Mg

(dry at 1100C for one hour) in 10 ml 1: 1 hydrochloric acid without spattering, dilute

exactly to one litre and transfer to a clean dry glass stoppered bottle for storage (or use a

commercially prepared standard.)

ii) Buffer Solution

350ml Ammonium hydroxide(conc.) + 54gms ammonium chloride + 20ml magnesium

complex solution are mixed and made upto one litre with distilled water.(Magnesium solution

is prepared as follows. 4.1 gm of MgO (analar) is mixed with 37.2 gms of EDTA and

dissolved in 410 ml of warmed distilled water.)

iii) Calcium indicator

Grind 0.2 gm of Ammonium purpurate(Murexide) with 100gms of Sodium chloride to

40 to 50 mesh size.

iv) Chrome Black T indicator

Grind 0.2gms of chrome black T powder with 80gms of powdered NaCl and store in a

dark coloured bottle.


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V) Standard EDTA Solution

Di-sodium dihydrogenethylene- diaminetetra-acetate of analytical reagent quality is dried

at 800C. Weigh 4.0 gm of the substance and dissolve it in 800 ml of demineralised water.

Adjust the pH to 10.5 with 5% NaOH solution. Pipette 25 ml of the standard Calcium

chloride solution (prepared above) into an Erlenmeyer flask (125 ml) . Add 1:4

Ammonia of Chrome-black T indicator.Titrate with the EDTA solution as per the procedure

given below (2.4). Let V be the volume of the standard EDTA solution required for thetitration.

Volume of EDTA to be taken up for dilution = V/25 x 1000.

The volume of EDTA solution as calculated above is taken in a 1000 ml. volumetric

standard flask. Dernineralised water is used to make up to the mark in the volumetric

flask. This EDTA solution corresponds to a value of 0.02N.

The solution is stored in polythene bottles and restandardised monthly.

Sodium hydroxide solution(4%)

Dissolve 4.0 gms of NaOH in water and dilute to 100ml.

2.3 GLASSWARES

Burette (0. 1 ml accuracy)

50ml measuring cylinder-1No.

White porcelain casserole with a glass stiffer.

2.4 PROCEDURE

i) Total Hardness

Pipette 50m l of the sample into a white porcelain casserole. If necessary adjust to

pH 7-10 by using ammonium hydroxide or HCL

Add 0.5ml of buffer solution and mix by stirring. (The pl-I of this solution should be

between 10- 10.2). Add approximately 0.2gms of dry chromeblack T indicator to produce

the required depth of colour. The titration with EDTA should proceed immediately uponaddition of the chrome blackT.

If hardness is present the solution will turn red. Standard EDTA solution is added slowly

with continuous stirring until the end point is reached which is pure blue colour with no

reddish tinge remaining. Further addition of EDTA will produce nofurther colour change.


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ii) Calcium Hardness

Pipette 50ml of the sample into a white porcelain casserole.

Add 2 ml of 4% NaOH solution and stir.(The pH of this solution should be above 10.4)

Add approximately 0.2gm of calcium(Murexide) indicator.

Add standard EDTA solution slowly with continuous stirring until the colour changes from

salmon pink to orchid purple.

iii) Calculation

Total Hardness (as ppm CaC03) = ml std EDTA soln x 20

Calcium hardness (as ppm CaC03) = ml std EDTA soln x 20

Magnesium hardness(as pprn CaC03) = Total hardness (as ppm CaC03) minus

calcium hardness (as ppm CaC03)

3. DETERMINATION OF CARBON -DI-OXIDE

3.1 INTRODUCTION

The carbon di-oxide content is the sole contributor to the acidity of the water. On this account,

the CO2 determination bears a close resemblance to the acidity titration. The differences reside

in the concentrations of the titrants and the fact tha t the titration is conducted in a manner thatminimizes the escape of the volatile CO2 gas.

3.2 REAGENTS

i) Boiled distilled water-This should be used in the preparation of all solutions.

ii) Phenolphthalein indicator solution.

iii) 0.02 N sodium carbonate solution.

(Prepare 0.1 N Na2CO

3solution by dissolving 5.3 g anhydrous Na

2CO

3in one litre of boiled

distilled water. This solution should be diluted suitably to get 0.02 N Na2CO3 solution)

3.3 EQUIPMENT

Glass flask with 100 cc and 200cc marks.

Burette-50cc capacity with 0. 1 ml marking


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3.4 ANALYSIS PROCEDURE

The water is run slowly for a long time through a hose reaching down to the bottom of the test

flask. After pouring-off excess water down to the 100 ml mark or 200 ml mark, the content of

free CO2 is determined at once on the spot. Add to the water I cc of phenolphthale in solution

and titrate with 0.02 N Na2CO3 Solution. After each fresh addition of Na2CO3 solution, the

flask is closed and turned upside down (Not shaken) before continuing. Titration is completedwhen the colour of the water stays weak pink for 5 minutes. In a second test the full quantity of

sodium carbonate solution needed is added at once, and if necessary a little more, until the pink

colour is retained for 5 minutes.

3.5 CALCULATION

CO2

milli-grams per litre = A x N x 22000 / ml.sample taken

Where A = milliliters of titrant used

N = normality of titrant

4. DETERMINATION OF P AND M ALKALINITY

4.1 THEORY OF TEST

This test is based on the determination of the alkaline content of a sample by titration with a

standard acid solution. In this measurement, the end-points are taken as points of change in the

colour of organic indicators; phenolophthalein (apporx.pH 8.3) and methyl orange(approx. pH

represent definite points to which the alkalinity of the sample has been reduced by the addition ofthe standard acid solution.

4.2 REAGENTS

i) Sulphuric acid, N/50

ii) Phenolphthalein Indicator

iii) Methyl orange indicator

iv) Methyl purple indicator

4.3 APPARATUS REQUIRED

1 Burette, 25ml or

1 Casserole, porcelain, 250ml

1 Cylinder, graduated, 50ml.

1 Stirring rod, glass.


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4.4 PROCEDURE FOR TEST

Measure a clear 50 ml sample of water in the graduate and transfer to the casserole. Add 4 or 5

drops of phenolphthalein indicator. If the sample is an alkaline water, such as usually is the case

with the boiler water, it will turn red. If the sample is a raw or natural water, it usually will remain

coloureless. Add the standard N/50 sulphuric acid from the burette drop by drop to the sample

in the casserole, stirring constantly until the point is reached where one drop removes t he last

trace of red colour and the sample becomes colourless. Stop and record the total number of mlto this point as the P reading.

Add 4 drops of methyl orange indicator (if no red colour develops on the addition of the

phenolphthalein indicator to the original sample, the titration may be started with the methyl

orange indicator at this point). Continue adding the acid drop by drop until one drop changes the

colour from a yellow to a salmon-pink., Record the final burette reading as the M reading. This

is a more difficult point and some practice may be required. The general tendency is to add too

much acid. If too much acid is added, the sample will change from a salmon-pink to a definite

red.Record the titration to the P point and the total titration to the M point as the P and M

readings respectively. (Note that the M Reading will always be greater than the P reading in as

much as the P reading is included in the M reading).

If the water sample is coloured, such as one containing chromate, methyl purple indicatormay be

substituted for methyl orange indicator to provide a more definite end-point. The color change

with methyl purple is from green to gray to purple. The end-point is taken as the first change to a

definite purple.

4.5 CALCULATION OF RESULTS

Formula:

ppm alkalinity as CaCO3 = ml N / 50 sulphuric acid x 1000 / ml.Sample

4.6 LIMITATIONS OF TEST

It is preferable to expresses the results of the alkalinity determination in terms of P and M

alkalinity as above.However, results are sometimes calculated in terms of bicarbonate, carbonate

and hydrate on the assumption that titration to the P end-point is equivalent to all the hydrate and

one half the carbonate alkalinity and that the titration to M is equivalent to the total alkalinity.

Many factors such as the presence of phosphate silica, organic and other buffers affect this

titration and the calculation of the form of alkalinity present may be in error. Under normal

circumstances in plant control, expression of results as P and M alkanity is entirely satisfactoryand is to be preferred from the standpoint of simplicity.


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4.7 ALKALINITY RELATIONSHIP

The following table summarises the relationship between P and M values and the concentration

of hydroxide, carbonate and bicarbonate.

5. DETERMINATION OF FREE ALKALINITY IN BOILER

WATER (STRONTIUM CHLORIDE METHOD)

5.1 INTRODUCTION

This method is based on the titration of the hydroxide ion with a standard acid to the

Phenolphthalein end-point after the carbonate and phosphate ions have been precipitated

with strontium chloride.

5.2 REAGENTS

i) Standard HCI solution 0.02 N

ii) Phenolphthalein indicator dissolve 0.5g of phenolphthalein in 100ml of 50% solutionof ethyl alcohol in water

iii) Strontium chloride solution = Dissolve 4.5g of strontium chloride in water

and dilute to a litre.


50 ml - measuring cylinder

250 ml - Erlenmeyer flask with stopper

50 ml - burette-readability 0.1ml

ppm as CaCO3

Condition (OH) (OH - ) (CO3)(CO3-) (HCO3) (HCO3

-)

P=O O O M

2PM 2P-M 2(M-P) O

P=M M O O


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5.4 PROCEDURE

Pipette 50 ml of sample into 250 ml. Erlenmeyer Flask.

Add 25 ml of stroniurn chloride solution

Keep loosely the stopper of the flask and heat to boiling.

Remove flask and immediately push stopper tightly into flask.

Allow to cool and add 5 drops of phenolphthalein solution. The absence of colour indicates no

free hydroxide alkalinity.

If pink colour is present, titrate with 0.02 N hydrochloric acid to a colourless end-point.

5.5 CALCULATION

Free alkalinity = (N) x (V) x 17,000 / ml sample

as ppm (OH)

Where, V = ml of HCI and N = Normality of HCl

5.6 INTERFERENCES

Chromates and Silicates

Method takes care of phosphates, carbonates and most ammonia.

6. DETERMINATION OF SULPHITE

6.1 INTRODUCTION

This method is designed primarily for the routine control of boiler feed waters subjects to sulphate

treatment. Reductants like sulphide and certain heavy metal ions react similarly to sulphite. Copper

catalyzes the oxidation of sulphite on exposure to air, especially at high temperatures.

6.2 REAGENTS

i) Standard Potassium Iodate

ii) Dissolve 0.566 g KI03, dried at 1200C, and 0.5 g NaHC03 in distilled water, and dilute

to 1000 ml. The equivalence of this titrant is 1.0 mg Na2SO

3per 1.00 ml.


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iii) Potassium Iodide Solution, (50 g per litre)-Dissolve 50 g of iodate-free KI and 0.5g of

sodium bi-carbonate (NaHC03) in freshly boiled and cooled water and dilute to one litre.

iv) Starch indicator.

v) Hydrochloric Acid, 1 +1


250 c.c erlemneyer flask

10 c.c pipette ( for 1:1 HCl )

100 ml pipette (for the sample to be measured)

5 ml pipette ( for the sample to be measured )

1 ml burette ( for KIO3

titrant)

6.4 PROCEDURE

Place 10 ml 1 + 1 HCl in a 250 ml flask. Rapidly add 100 ml. sample, submerging the pipette

tip below the acid surface to minimize air exposure. After adding I ml. starch indicator solution

and 5 ml KI solution, titrate ivith standard KI03 titrant to the first appearance of a persitent blue

colour. Determine the blank titration by carrying 100 ml. distilled water through the complete

procedure.

SO3

milligrams per litre = (A-B) x 6.35

Na2SO

3milligrams per litre = (A-B) x 10

Where A = millilitres of titration for sample.

B = millilitres of titration for blank.


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FIG.2 WINKLER FLASK FOR DISSOLVED OXYGEN

DETERMINATION

FIG.1 METHOD OF COLLECTING SAMPLE FOR OXYGEN

DETERMINATION ON HOT FEED WATER


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7. DETERMINATION OF DISSOLVED OXYGEN (MORE THAN

0.10 PPM)

7.1 SAMPLING

It is important to use air-tight connections in all apparatus used for sampling and testing. When

sampling hot water, a water cooled coil should be introduced into the sampling line. A convenient

arrangement for sampling for feed water is shown in the figure. The sample itself should be taken

in a 500 ml. Winkler flask, containing a few glass beads, as shown in figure and water should

flow through for atleast 10 minutes before taking the actual sample so as to displace all traces

of air. Care must be taken to see that air bubbles do not form around the stopper of the Winkler

flask while sampling.

7.2 REAGENTS REQUIRED

i) Manganous chloride

Dissolve 400gms of Manganous chloride(AR) in one litre of DM water.

ii) Alkaline iodide

Dissolve 600 gm of potassiumhydroxide and 140gm of potassium iodide in 1litre of water.

iii) N / 100 Sodium thiosulphate

Dissolve 2.482gm of AR Sodium thiosulphate(Na2S2O25H2O) in water and make up to

one litre. Add about I gm of AR Sodium carbonate to preserve the solution. Standardise

against standard potassium dichromate.

iv) Sulphuric Acid 1:1

Add 250ml of conc.sulphuric acid to 250 ml of water. Cool and store.

7.3 GLASSWARES

Winklers flask arrangement as shown in the figure.

2ml pipette

Burette 50 ml - 1 No.

7.4 PROCEDURE

By means of the funnel fitted to the Winklers flask, add 2 ml of the manganous chloride solution

and then add 2 ml of the alkaline Iodide soldtion. Mix, allow to stand for 10 minutes and then add

2 ml of 1:1 H2 SO4. Take 250 ml of the sample and titrate the liberated iodine with N/100

Thiosulphate solution using starch as indicator.


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ML of Oxygen / Litre = ML of N/100 Thio used x 0.224

1 ML of Oxygen / Litre = 1.430 Mg / Litre

8. DETERMINATION OF PERMANGANATE NUMBER (Determining

organic substances : Potassium Permanganate Consumption)

8.1 OXYGEN CONSUMED FROM PERMANGANATE

Two versions of the oxygen consumed from permanganate method are in the use for estimating

the strength of organic pollution in streams. One modification hastens the oxidative reaction by

elevating the sample temperature over a shorter time. The other determination is conducted near

room temperature for an extended period. Since both procedures are empirical, experimental

conditions must be uniform for the results to have significance. Clean glassware is mandatory.

8.2 REAGENTS

i) Standard potassium permanganate solution, 0.0125 N-Filter the supernatant from an

aged solution of 0. 1 N KMnO4 through sintered glass crucible, and dilute 12.5 ml to

100 ml withdistilled water. Standardize the solution daily. The equivalence of 0.0125 N

KMnO4 is 0.100 mg oxygen consumed per 1.00 ml.

Sulphuric acid solution,1 + 3 - Add 0.0125 N KMnO4 solution until a very faint colour

persists after 4 hours.

Sodium sulphide dechlorinating solution, 0.025 N 1.575 g per 100 ml.

ii) Reagents for Half-hour method

Standard Ammonium oxalate titrant, 0.0125 N Dissolve 0.8882 g. (NH4)2 C2O4. H2O,

dried at 105o C and dilute to 1000 ml with distilled water.

iii) Reagents for pour hour method

Standard sodium thiosulphate titrant, 0.0125 N. In a 1 litre volumetric flask place 0.6 g

NaHCO3 and dilute 12.5 ml 0.1 N Na2S2O3 with distilled water, Prepare daily and

standardize.

Starch Indicator.

Potassium Iodide.


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8.3 PROCEDURE

When the residual chlorine exceeds 0.5 mg per litre, dechlorinate the sample with a minute

amount of 0.025 N Na2SO3 solution to the 0.65 mg per litre level. Do not dechlorinate

completely.

i) Half hour method

Pipette 100 ml well-mixed sample and 100 ml distilled water into separate 250 ml flasks,

and treat both the sample and blank alike throughout the procedure. Add 10 ml (1+3)

H2SO

4and 10.00 ml standard 9.0125 N KMnO

4. Immerse the flask in a boiling water

bath for exactly 30 min. making certain that the liquid level in the flask is completely

submerged in the boiling water throughout- the entire period. If the KMnO4colour in the

sample grows faint or disappears, take a smaller volume and dilute to 100 ml standard

0.0125 N (NH4)

2C

2O

4solution, and while still hot, titrate with standard 0.0125 N

KMnO4

to a faint pink end-point.

Oxygen consumed from KMnO4

milligrams per litre = (A-B) x N x 8000 / millilitres of

sample

Where A = Millilitres of titration for sample

B = Millilitres of titration for distilled water blank, and

N = Normality of KMnO4

titrant.

(ii) Pour- hour method

Measure 250 ml well mixed sample and 250 ml distilled water into separate 400 ml glassstoppered bottles, and bring to 27C. Treat both the sample and blank alike throughout

the procedure. Add 10 ml (1+3) H2SO4 with a volumetric pipette introduce an appropriate

volume of standard 0.0125 N KMn04- Select a KMnO4

volume in sufficient excess to

require a back-titration of 5 to 15 ml at the end of 4 hour and in any case, use no less than

10.0 ml KMnO4. Gently rotate the bottle to mix the contents, and place in a water bath or

incubator at 27C for exactly 4 hours. Several times during the incubation, mix, by gentle

rotation, any sample that contains appreciable suspended matter. Cool to room temperature

and a few small crystals KI,mix, and titrate the contents of the bottles with standard 0.0125N

Na2S2O3 titrant.

Add 1.0 ml starch indicator when the colour turns pale straw, and complete the titration tothe first disappearance of the blue colour.


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9. DETERMINATION OF EVAPORATION (T.D.S.) IGNITION

RESIDUES AND VOLATILE MATTER

9.1 EVAPORATION RESIDUES AT 105C

i) Apparatus required

200 c.c Capacity platinum evaporation dish

100 c.c & 200 c.c Pipettes to measure water to be tested

Water bath

Drying oven

Desiccator

Ignition furnace

ii) Procedure

100 c.c or possible a greater quantity of water to be tested (filter if suspended solids are

present - estimate separately suspended solids content) is evaporated in a platinum dishon a water bath until it is dry, after which it is dried down, to constant weight in a drying

oven at 105C. It is weighed after cooling in the desiccator.

9.2 DETERMINING THE IGNITION RESIDUES

The evaporation residue determined at 105C as described above is ignited in an ignition furnace

at 600 + 25C until constant weight. Cool in the desiccator and weigh. Constant weight shall be

considered as attained when the change in weight of the dish plus residue shall not be > 0.5 mg

between two successive operations involving heating, cooling in a desiccator and weighing.

9.3 DETERMINING THE VOLATILE MATTER

Record the loss in weight in the previous determination as weight of volatile dissolved matter.

9.4 CALCULATIONS

Total dissolved solids ppm A/W x 1000

Ignition residue ppm B/W x 1000

Volatile matter ppm (A-B) / W x 1000

Where A = gms of dissolved matter

B = gms of ignition residue

(A-B) = gms of volatile matter

W = ml / weight of sample used


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10. DETERMINATION OF OIL (Fluorocarbon matters)

10.1 INTRODUCTION

In the determination of oil, an absolute quantity of a specific substance is not measured.

Rather,group of substances with similar, physical characteristics are determine quantitatively

on the basis of common solubility, in specified solvent. The constituent analysed may

therefore be said to include hydrocarbons, fatty acids, soaps, fats, waxes, oil and any

other material that is extracted by the solvent form an acidified sample.

10.2 REAGENTS

Acetone

Hydrochloric acid

Sodium bisulphate. (NaHSO4

H20)

Sodium chloride

Sodium sulphate (Na2SO

4)

Sulphuric acid

Fluorocarbon solvent (1,1,2-Trichloro-1,2,2-Trifluoro ethane)

10.3 APPARATUS

Drying oven

Evaporating flask

Separatory funnel

Steam bath

Desiccator

10.4 PROCEDURE

Dry a boiling flask in an oven at 105oC for lhr and cool in a desiccator. Weigh accurately,

(W1g).

Collect the sample in a glass container. Note the volume. Add HCl (1:9) dropwise and

adjust the pH to 3.0 & 4.0 pour the acidified sample into a separatory funnel.Add 60 ml.

of fluorocarbon solvent to the glass container in which the sample is collected. Cap and

shake the bottle well. Pour the solvent into the separatory funnel. Extract the sample by

shaking vigorously for 2 minutes. Invert the separatory funnel and vent with stopcock to

relieve pressure built up during the extraction. Allow the layers to separate. Drain the

solvent layer through filter paper (whatman) held by a small funnel- into the tared boilingflask. (if emulsion problems are anticipated, add 1 to 2g of sodium sulphate to the filter

paper cone and slowly drain t he solvent through the crystals, If a clear solvent is not

obtained, add about 100g of sodium chloride to the separatory funnel. Frequently this will

break the emulsion).


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Repeat the bottle rinse and extraction with two additional 60ml portion of the solvent.

combine all the solvents in the same boiling flask.Rinse the filter with 20ml of the solvent

into the same flask.Evaporate (in a fume hood) the solvent from the boiling flasks in a

steam bath. When the contents have been evaporated to dryness, (without any solvent

vapour or residual water), carefully wipe the exterior of the flask with a lint free cloth and

a small amount of acetone to remove any water adhering to the flask. Place in a desiccator

for 1 hr and weigh (W2

g)

10.5 CALCULATION

Extractable residue (mg/litre) = (W2-WI) x 1000 / ml.sample

11. DETERMINATION OF pH-VALUE

11.1 INTRODUCTION

As a yard stick for the concentration of hydrogen ions, the pH value gives an indication of

the percentage reaction (alkalinity or acidity) of the water and hence its aggressive nature.

The pH value is the negative logarithm to the base 10 of the hydrogen ion concentration,

expressed as gram-ions per litre.

The pH value of a given solution depends on the temperature and as a rule it is quoted for

250 C. Water with pH = 7 has a neutral reaction, while there is an acidic reaction at pH7.


pH meter with Associated glass and reference electrodes.

Buffer tablets of known pH.

11.3 ELECTROMETRIC DETERMINATION OF PH VALUE

With the electrometric method, the pH value is determined from the potential difference

between the measuring electrodes immersed in the liquid under test and a reference electrode

of known potential. For testing water, electrode assemblies comprising a glass electrode

and a calomel reference electrode are suited.

pH meter is to be operated in accordance with the instruction supplied with it, by its

manufacturer.

Where water is very pure, and the pH value and electrical conductivity are being determined

simultaneously, make sure that the pH electrodes are inserted. After the conductivity

electrodes if the measuring points are connected in series.


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11.4 ELECTRODE TREATMENT

New glass electrodes and those that has been stored dry shall be conditioned and maintained

as recommended by the manufacturer. If the assembly is in intermittent use, keep the

immersed ends of the electrodes, in water between measurements. For prolonged storage,

glass electrodes may be allowed to become dry, but the junction and filling openings of

reference electrodes should be capped to reduce evaporation.

11.5 STANDARDISATION OF ASSEMBLY

Turn on the instruments, allow it to warm up and bring it to electrical balance in accordance

with the manufacturers instructions. Wash the glass and reference electrodes and the

sample cap by means of a flowing stream of distilled water from a wash bottle. Note the

temperature of the test solution and adjust the temperature dial of the meter to correspond.

Select the two reference buffer solutions, near the pH of the test solution. (Buffer solutions

can be prepared from the buffer tablets following manufacturers instructions). Warm or

cool these reference solutions as necessary to match within 20 C the temperature of the

unknown.

Fill the sample cup with the first reference buffer solution, and immerse the electrodes.Engage

the operating button, turn the range switch if present to the proper position, and rotate the

assymmetry potential knob until the reading of the dial corresponds to the known pH of

the reference buffer solution. Repeat the above procedure until two successive instrument

readings are obtained, without changing the setting of the asymmetry potential knob. Care

should be taken to see that the level of the KCIsolution in the referencce electrode must

always be kept more than that of the measured solution. To reduce the effects of thermal

and electrical hysteresis, the temperature of electrodes reference buffer solutions and wash

water should be kept as close to that of the unknown sample as possible.

Wash the electrodes and sample cup three times with water. Place the second reference

buffer solutions in the sample cup, and measure pH. Do not change the setting of assymmetry

potential knob.

The assembly shall be judged to be operated satisfactorily if the pH reading obtained for

the second reference buffer solution agrees with its assigned pH value within 0.05 unit.In

long series of measurements, supplement initial and final standardisations by interim checks.

Wash the electrodes by means of a flowing stream from a wash bottle. Place the water

sample in a clean glass beaker. Measure the temperature. Insert the electrode and measure

pH as before.

11.6 INSTRUCTIONS

pH meter should be checked Periodically for its performance using buffer.


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12. DETERMINATION OF CONDUCTIVITY (Conducto Bridge Method)

12.1 CONDUCTANCE (SPECIFIC)

The specific conductance of water is a measure of the ability of the water to conduct an

electrical current. This property is of no consequence in itself with respect to water treatment.

However, from a control stand point, the conductivity test is important as a direct measure

of the total ionizable solids in the water. The conductivity test provides quick measurement

of steam purity as well as a simple control for boiler water solids. Conductivity also may

be used for blowdown control in recirculating cooling water systems.

Specific conductance is inversely proportional to electrical resistance. Pure water is highly

resistant to the passage of an electric current and therefore has a low specific conductance.

However, if the water contains ions, the water becomes a better conductor of electricity

and the specific conductance is increased. Inorganic compounds such as sodium chloride

and sodium sulphate dissociate into positive and negative ions, which will conduct electricity

in proportion to the amount of ions present. The conductivity test, therefore, is not specific

for any one ion, but rather a measure of the total ionic concentration.

The basic unit of electrical resistance is the ohm. since electrical conductivity is the reciprocal

of resistance, the unique term mho (ohm spelled backwards) was chosen as the basic

unit of conductivity. In the conductivity test, small amounts of electrical conductance are

measured and the instrument is usually calibrated in micromhos (a micromho is a millionth

of a mho). To calibrate a conductivity instrument to read directly in parts per million of

dissolved solids (or some specific ion or compound) is not recommended since such a

calibration introduces an error into the instrument reading itself. The conversion factor

from micromhos of specific conductance to parts per million will vary slightly with different

waters. To include a constant conversion factor in the instrument calibration is to introduce

an unnecessary source of error.

The conductivity test provides an accurate and simple method of blowdown control.

However, certain limitations must be considered. While the conductivity test measures the

total ionic concentration, the hydroxide ion has a much higher conductance than the other

ions present.Thus for accurate results the sample must be neutralised before the conductivity

test is made.

Conductivity is an exceedingly sensitive test and is accurate down to the level of

approximately 0.5 - 1.0 ppm ionizable solids. Until development of the flame

Spectrophotometer method for determining low sodium concentrations, conductivity was

the most accurate method of determining steam purity.


1-Conducto Bridge (0-5 to 0-5000 micro mho/cm with selector switch)

1-Dip cell

1-Cylinder, rimmed glass, not graduated

1-Thermometer, dial type (0- 100C)

1-Measuring cup , brass


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12.3 CONDUCTANCE OF BOILER WATER

Theory of test: The ionizable solids in boiler water have the ability to conduct an electric

current through a solution. This property of electrical conductance of solids makes it possible

to accurately measure the quantity of solids in solution by suitable conductance equipment.

12.4 CHEMICAL REQUIRED.

Gallic Acid

12.5 PROCEDURE FOR TEST

Pour approximately 50 ml of distilled water or steam condensate into the rimmed glass

cylinder and insert the conductivity cell. Move cell up and down several times to wash off

any solids present on the cell. Discard the water in the cylinder.

Pour approximately 50 in of boiler water into the cylinder (use a settled or filtered sample),

Add two dippers of gallic acid (approx. 0.2 g) to the sample. (Note: if a small amount of

the gallic acid remains undissolved, the conductivity test will not be adversely affected).

Measure temp of the sample and adjust the temperature correction dial on the conducto

Bridge to the proper temperature. Insert conductivity cell and move up and down several

times to insure equilibrium. Measure the specific conductance on the Conducto Bridge by

turning the conductivity dial until the electric or magic eyes is at its widest black angle.

Note: Two dippers of gallic acid will neutralize approximately 130 ppm of P alkalinity.

On some highly alkaline boiler waters, additional gallic acid may be required. A desirable

precaution is to add approximately four drops phenolphothalein indicator to the sample

and delay taking the conductivity reading until the pink colour has been completely

discharged by the addition of gallic acid.

12.6 CALCULATION OF RESULTS

The specific conductance in micromhos is read directly from the calibrated scale as indicated

by the pointer on the conductivity knob, when the eye is at its widest black angle.

The relationship between specific conductance and the dissolved solids content of a boiler

water depends on the characteristics of each individual boiler water and therefore may be

slightly different for each plant. Using the gallic acid neutralization method, an average

value determined over a wide range of operating conditions is that one micromho is equivalent

to 0.9 pprn dissolved solids. This value is sufficiently accurate for the average industrialplant.

The exact relationship between micromhos and solids can be individually established for

each plant by determining both the conductance and solids content of a series of

approximately ten sample taken over a two week period.


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12.7 LIMITATIONS OF TEST

The conductance method affords a rapid means of checking the dissolved solids content

of a sample. The effect of hydroxide in causing high conductivity is minimized by the gallic

acid neutralisation, thereby securing a consistent relationship between solids and

conductance. The conductance method does not measure non-electrolytic solids such as

organic matter, and in order to express results in terms of parts per million of boiler water

solids it is necessary to use a conversion factor.

12.8 CONDUCTANCE OF STEAM CONDENSATE AND FEEDWATER

i) Theory of test

The ionizable solids and gases in condensed steam and feed water have the ability to

conduct an electric current through a solution. In evaluating the conductance of condensed

steam and feed water samples, it is necessary to check for the presence of dissolved gases

such as ammonia and carbon dioxide which impart conductance. The effect of ammonia is

predominant and hence the sample is allowed to pass through a cation resin column (in H

+

form). An arrangement of resin column is shown figure 1. Ammonia is removed by this

method and. the conductivity measured will indicate the dissolved solids present.

The solids are converted to their corresponding acids by passing the sample through the

cation column and the approximate conductance of acids to ppb relationship can be as

follows:

Weak acids (H2CO

3,HAC =0.004 mmho/ppb (as CaCO

3)

Strong acids (HCl, H2SO

4, HNO

3) =0.007 mmho/ppb (as CaCO

3)

Cation conductivity measuring less than 0.3 micromho/cm will mean total solids in the

sample less than 50 ppb.

ii) Procedure for the test

Collect approximately 50 ml of the condensed sample after passing through the cation

column (in the H+

form). The effluent sample is measured for its conductivity.

For measuring conductivity above 10 micromho/cm, either a flow type or dip type cell

may be used. For samples with conductivity below 10 micromho/cm flow type conductivity

cell tube used. Adjust the sample stream to proper flow rate and temperature.(250 C).

Read the conductance by continuous (on-line) measurement.


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iii) Regeneration procedure for cation column

The cation resin in the H+ form when exhausted should be regenerated as per the procedure

described below:

iv) Backwards flushing

To remove contaminations, first shake the cation exchange thoroughly by hand then allow

condensate to flow through from the bottom upwards for about 5 minutes until the discharge

rinsing water is clear and colourless. Watch that no resin is flushed out.

v) Regenerating

For regenerating the exchanger resin allow 6 litres of technical hydrochloric acid 1:4 diluted

with condensate per I litre of resin to flow through the apparatus from the top downwards

for at least 30 minutes. (Flow rate approximately 8- 10 litres/hr.) There must be no air

bubbles on the bottom of the sieve, since these inhibit the flow and affect the regeneration.

The discharge is strongly acidic and must only be emptied into an acidresistant drain.

vi) Flushing-out

For 30 to 40 minutes in any case until the Cl-reaction (check with AgNO3) has disappeared

flush-out the remaining acid in the apparatus with condensate from the top downwards.

Flow rate 20- 30 litres/hr.

vii) Start-up

Before starting up again check once more to see whether there is any air bubbles on the

bottom of the sieve: otherwise, the cation exchanger will operate irregularly and inefficiently.

viii) Remarks

If the exchanger resin is considerably contaminated with iron oxides or other deposits, the

regenerating acid may be heated to 500 C and left for about half an hour in the resin before

flushing. ( Temperature resistance of the resin: Max.1000 C ). Following this backwards

flushing will have to be carried out again, if necessary, to remove any released particles

from the resin.

Resin contaminated with oil can be cleaned with. a detergent.


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FIG.3 HYDROGEN ION EXCHANGER OF PLASTIC FOR

MEASURING CONDUCTIVITY

13. DETERMINATION OF DISSOLVED OXYGEN

Colorimetric determination of low concentration of dissolved oxygen in water less than 0.10 ppm.

13.1 INTRODUCTION

This method uses the dissolved oxygen in the sample to oxidise a reduced solution of

indigo carmine. As the reduced solution of indigo carmine is oxidised, it changes colour

progressively from yellow to orange to pink to red to purple to green.

13.2 REAGENTS

i) Reagent solution

About 30 minutes before testing, add 20 ml of indigo carmine solution and 5 ml of

potassium hydroxide solution to a small beaker. Stir gently and pour into a 50 mlburette.

ii) Indigo carmine solution

Dissolve 0.018 gm of indigo carmine and 0.2 gm of dextrose in 5 ml. of boiled

eionized water. Add 75 ml of glycerol and stir well. This reagent should be used

within two weeks.


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iii) Potassium hydroxide solution

Dissolve 100 gms of potassium hydroxide in 200 ml of boiled deionized water.

13.3 GLASSWARES

BOD bottle 300 ml capacity with grounded neck

and stopper - I No.

Burette (50 ml capacity) - 1 No.

White porcelain tile - 1 No.

The colours produced by mixing the coloured solutions given below can be used as reference

for determining the dissolved oxygen content by indigo carmine test.

i) Colour standards

Stock solutions

a. Red colour standard (CS-A)

Dissolve 59.29 g of cobaltous chloride hexahydrate (COCl2.6H2O) in

sufficient HCl (1 : 99) to make one litre.

b. Yellow colour standard (CS-B)

Dissolve 45.05 g of Ferric chloride hexahydrate (FeCl3 6H2O) insufficient HCl (1:99) to make one litre.

c. Blue colour standard (CS-C)

Dissolve 62.45 g of cupric sulphate pentahydrate (CUSO4 5H2O) in

sufficient HCl (1:99) to make one litre.

ii) Store all stock solutions in dark-coloured bottles to prevent fading.


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iii) Preparation of colour standards

Prepare a series of colour standards as listed in the following table:

Disolved Oxygen Milliliters of colour standard

ppm CS-A CS-B CS-C

0.000 0.75 35.0 ---

0.005 5.00 20.0 ---

0.010 6.25 12.5 ---

0.015 9.40 10.0 ---

0.025 14.4 3.8 ---

0.050 18.3 1.7 ---

Place the amounts of stock solutions in the table in 300 ml borosilicate glass stoppered reagent

bottles. Add 2.3 ml of HCl (sp.gr.1.19) to each and dilute to the neck of the bottle with water.

Stopper the bottle and mix by inversion. Store in a dark place to minimise fading of colours.

13.4 PROCEDURE

i) Attach a minimum length of rubber tubing tipped with about a 4" piece of glass

tubing to the sample point.

ii) Insert the glass tubing to the bottom of the BOD bottle of 300 ml.capacity, having

a raised lip around the neck and glass stoppers ground to a conical lower tip. Permit

the sample to fill and overflow the bottle an equivalent of at least 10 times. The

sample should be at room temperature or below.

iii) Remove the glass tipped rubber tubing slowly.

iv) Insert tip of the burette containing the reagent, below the neck of the bottle and add

4 ml of the reagent.

V) Remove the burette, carefully stopper the bottle and shake well.

vi) Determine the colour immediately by placing the bottle in a white surface and view,

looking into the bottle at 450 angle.


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ppm Color

0.000 Yellow

0.005 Orange

0.010 Orange pink

0.015 Pink

0.025 Pink red

0.050 Red purple

14. DETERMINATION OF SOLUBLE SILICA

14.1 SUMMARY OF METHOD

This colorimetric method depends on forming molybdi-silicic acid by reacting the silica

and ammonium molybdate in acid solution. I-amino-2 napthol-4 sulfonic acid is then added

to reduce the molybdi-silicic complex. The method is designed to determine soluble silica

with high accuracy in the range of 5 to 1000 g/ litre [1g/litre =1 ppb.]

14.2 REAGENTS

i) Amino - naptho l- sulfonic acid solution - Dissolve 0.5 g of 1-amino-2napthol

4- sulfonic acid in 50 ml of a solution containing 1 g sodium sulphite (Na3 SO3).After is solving, add the solution to 100 ml of a solution containing 30 g of sodium

hydrogen sulphite (NaHSO3). Make up to 200 ml and store in a dark, plastic

bottle. Prepare a fresh solution every 2 weeks.

ii) Ammonium molybdat e solution - (100 g/litre) Dissolve 10 grams of ammonium

molybdate tetrahydrate in 100 ml of deionized water. Filter this solution each day

before using.

iii) Hydrochloric Acid (1 + 1) - Dilute 1 volume of concentrated hydrochloric acid

(HCl, sp. gr. 1.19) with I volume of deionized water.

iv) Oxalic Acid Solution - (100 g/litre) - Dissolve10 grams of oxalic acid dihydrate

(H2C

2O

42H

2O) in 100ml. of deionized water.

v) Silica, Standard solution (1 ml =1mg. Si02) - Dissolve 4.732 g of sodium

metasilicate (Na2SiO

39H

2O) in water and dilute to 1 litre. Check the concentration

of this solution in accordance with Reference Method A. (ASTM 859). Silica

standards may be purchased from several chemical supply houses.


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i) 50 ml - pipette

ii) 250 ml - polyethylene container

iii) 1 ml pipette (for 1: 1 HCl)

iv) 2ml pipette (for ammonium molybdate solution)

v) 2ml pipette (for oxalic acid solution)

vi) 2ml pipette (for ANS solution)

vii) Spectrophotometer

14.4 PROCEDURE

i) Pipette 50 ml of clear sample into a 250 ml polyethylene container

ii) Add I ml of 1 + 1 HCI solution

iii) Add 2 ml of ammonium molybdate solution

iv) Wait 5 minutes. The sample should be swirled during this period.

v) Add 2.0 ml of oxalic acid solution. Swirl to mix wait for 2 min.

vi) Add 2.0 ml of I-amino-2-napthol-4 sulfonic acid solution and swirl.

vii) Wait 5 minutes. Read on spectrophotometer at 815 nm. Transmittance of the reagentblank versus deionized water should not be less than 98.8%

14.5 CALIBRATION

Prepare a series of atleast 4 standards by proper dilution of the standard silica solution.Treat

50 ml aliquots of the standards in accordance with steps given under the procedure. (14.4)

Prepare a blank using a 50.0 ml aliquot of DM water that has been similarly treated. Read

the absorbance values from the spectrophotometer at 815 nm (A separate calibration

curve in the wave length range of 640 to 700 nm can also be prepared but with less

sensitivity)

14.6 CALCULATION

Silica concentration of the unknown solution can be read directly form the calibration

curve.

15. DETERMINATION OF TOTAL SILICA

15.1 INTRODUCTION

Some boiler stations using ion exchange columns for preboiler water purification, have

noticed silica concentrations building up in the units and at the same time a soluble silica

analysis onwater coming from the ion exchange column showed no silica. Analysis for

colloidal silica on these same samples showed the -silica was present as colloidal particle.

This technique has been developed as an analytical procedure to accurately determine

trace concentrations of silica where all or a part is present in colloidal form. Total silica is

determined spectrophotometrically after solubilization by the pressurized bomb method.

(Paar Oxygen Bomb).


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-25 ml , 50 ml, 10 ml - pipette for suitable aliquot sample

-Platinum cup with cover

-Oxygen bom

-1 ml pipette

-10 ml -Pipette (for deionized water)

-Nitrogen cylinder with pressure regulator, opener etc.-AIROVEN to be capable of giving a temperature 1900C. for 12 hours continuously

- Spectrophotometer.

15.3 PROCEDURE

i) Accurately measure 50 ml or a suitable aliquot of the sample into a platinum cup.

ii) Add I ml of 0.2 N NaOH and close the cup with a platinum cover

iii) Place the closed cup in a Paar oxygen bomb containing 10 ml of deionized water

and completely assemble the bomb.

iv) Nitrogen is added to obtain 30 pounds pressure and let out five times to completely

flush out oxygen in the bomb to prevent bomb corrosion.

v) Pressurize the bomb with nitrogen to 45 psig (maintained for specified period) and

place in an oven at 190o C for 8 hours. The oven should be placed in a hood since

all gaskets in the bomb are made of Teflon.

vi) Remove the bomb from the oven, cool, and remove the sample from the platinum

cup silica is determined spectrophotmetrically

15. 4 CALCULATION

i) See silica curve for the spectrophotometer used.

ii) Colloidal silica (ppm) = Total silica (ppm) -Soluble silica (ppm).

16. DETERMINATION OF ORTHOPHOSPHATE

16.1 INTRODUCTION

This method is applicable to the routine determination of orthophosphate in the 2 to 25

ppm PO4 range in industrial water and is based on the photometric measurement of the

yellow colour of the molybdo vanadophosphoric acid produced. The colour intensity is

proportional to the orthophosphate concentration in the sample. Highly coloured water

such as tannin treated boiler water and high concentration of ferric iron interfere thus

requiring preliminary treatment to remove these materials.


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16.2 REAGENTS

i) Ammonium vanadomolybdate solution - Dissolve 40 grams of ammoniummolybdate

tetrahydrate (NH4) MO

7O

24, 4H

20) in 400 ml of water. Dissolve1.0 gram of

ammonium metavanadate in 300 ml of water and add 200 ml concentrated nitric

acid (Sp. Gr. 1.42). Add the first solution to the second solution, mix well, and

dilute to one litre with water.

ii) Phosphate standard solution (1 ml= 1 mg PO4) -Dissolve 1.433 grams of oven-dried

(4 hours at 1050 c). Potassium dihydrogen phosphate (KH3PO

4) in water and

dilute volumetrically to one litre.


i) 125 ml Erlenmeyer flask

ii) 50 ml , 25 ml , 10 ml pipette for suitable aliquot sample

iii) Filter stand with funnel, whatman No.42 filter paper etc.

iv) 25 ml graduate (for Ammonium vanadomolybdate solution)

v) Spectrophotometer

16.4 PROCEDURE

i) To a 125 ml Erlemneyer flask, add 50 ml of the clear sample or aliquot there of

diluted to 50 ml with deionized water.

ii) Add, using a graduate, 25 ml of ammonium vanadomolybdate solution and mix well

by swirling.

iii) Allow 10 minutes for colour development and read within 30 minutes on the

spectrophotometer at 400 nm.

iv) Reagent blank and atleast two phosphate standards should be run along with samples.

16.5 CALIBRATION AND STANDARDIZATION

Prepare a series of standards to cover the range of 25 mg / litre (ppm) and preparecalibration curve.


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17. DETERMINATION OF IRON - BATHO PENANTHROLINE METHOD

17.1 INTRODUCTION

This method covers the determination of total iron in the range of 0-200 ppb. This method

is based upon the red ferrous complex produced by the bathophenanthroline and reduced

iron. The addition of hydroxylamine hydrochloride reduces ferric to ferrous with the pH

adjusted between 3.3 and 3.7 before extracting the complex with n-hexylalcohol.

17.2 SAMPLING

Although samples may be taken in polyethylene bottles, it is recommended that meticulously

clean 500 ml glass bottles with plastic caps be used. Prepare bottles by soaking in hot HCl

(l +1) for several hours prior to use. Drain and flush several times with iron-free water.

Add 1 ml of concentrated HCl to each 500 ml bottle and cap until used. When taking

sample, be sure, sample point has been continuously running for atleast four hours. Do not

overflow the acidified sample bottle during sample collection.

17.3 STANDARDS

Prepare a series of iron standards in 250 ml. separatory funnels to cover the range expected.

Use the iron std. solution (I ml=0.001 mg Fe). include a zero blank and follow procedure.

17.4 REAGENTS

i) Alcohol - lsopropyl

ii) Alcohol - n-hexyl

iii) Ammonium hydroxide (1 + 1)

iv) Hydrochloric acid concentrated and HCI (1+9)

V) Bathophenanthroline solution (0.835 g/litre). Dissolve 0.0835 of 4,7 dipheny

1-1, 10-phenanthroline in 100 ml of ethyl alcohol (95%)

vi) Hydroxylamine hydrochloride solution (100 g/litre). Dissolve 10 g of NH2OH HCl

in water and dilute to 100ml. Purify as follows: Adjust pH to 3.5 using a pH meter

by dropwise additions of NH2OH(1+1) and HCl (1+9). Transfer to a separatory

funnel. Add 6ml.of bathophenanthroline solution and shake. Let Stand for 1 minute.

Add 20 ml of n-hexyl alcohol and shake for I minute. Let separate, remove aqueous

layer and discard alcoholic layer. Repeat extraction by again adding 3 ml of

bathophenanthroline solution and 20 ml of alcohol with mixing. If no further extractions

are indicated, make an extraction with alcohol alone and let settle a long enough

time to remove all of the alcohol layer. Discard the alcohol layer.

vii) Iron, standard solution (1 ml =0.1 mg Fe). Dissolve 0. 1000 g of pure iron in 10 ml

of HCl (1+1) and 12 ml of bromine water. Boil until excess bromine is removed.


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Add 200 ml of HCI (1+1) cool and dilute to I litre in a volumetric flask with water.

Iron, standard solution (1 ml=0.001 mg Fe) Pipette 10 ml of standard solution

(1ml=0.1mg Fe) into a I litre flask, add 12 ml of HCl (1+1) and dilute to1 litre with

iron-free water. Prepare the dilute solution fresh before use.

viii) Thioglycollic acid - reagent grade.

17.5 GLASS WARE

All glasswares must be cleaned in HCl before making an iron extraction. Drain and

rinse with isoprophyl alcohol.


- 500 ml polyethylene bottles with sample extraction hose.

- 250 ml separatory funnel

- 2 ml pipette (for conc. HCl)

- 2 ml pipette(for NH2OH HCl)

- 2 ml pipette (for bathophenanthroline)

- 2 ml pipette (for thiogly collic acid)

- 25 ml pipette (for n-hexyl alcohol)

- 10 ml pipette (for iso-propyl alcohol)

- Spectrophotometer

- 5.0 cm cell - 0-5 ppb

- 2.0 cm cell - 50-200 ppb

- waterbath suitable for heating (thermostat)

17.7 APPLICATION RANGE OF APPARATUS

Set spectrophotometer at 533 nm

5.0 cm cell 0-50 ppb

2.0 cm cell 50-200 ppb

17.8 PROCEDURE

i) Place acidified sample bottle (with top off) in hot water bath for one hour after

adding 2 ml of conc. HCl, 2ml of NH2OH HCI, and 2 ml of thioglycollic acid (see

Note).

ii) Cool to room temperature and transfer 200 ml of the samples to a 250 ml separatory

funnel.


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NOTE:

The pH of a 500 ml feed water sample which has been acidified with 1 ml of

concentrated HCl is approximately 1.5. At this low pH nearly all the iron oxide

(Fe2O

3+Fe

3O

4) in the feed water will generally go into solution over a short period of time.

However, the above digestion step in the water bath gives some assurance of complete

solubility. Nevertheless an occasional sample will require prolonged heating and

concentration. A magnet drawn across the bottom of the sample bottle that has beenstanding several hours will usually attract insoluble magnetite

iii) Add 1ml of NH2OH HCl and then 2 ml. of bathophenanthroline. (Shake for 30seconds).

(Add 3 ml. for over 50 ppb Fe).

iv) Adjust pH with NH2OH (1+1) or HCl (1+9) to pH 3.3 to 3.7. (This can be done with a

single pH elecctrode hung down in the separatory funnel). Rinse electrode with distilled

water before going to next sample.

V) Add 25 ml. of n-hexyl alcohol and shake for 1 minute. Allow 5 minutes for separation and

drain aqueous phase.

vi) Add 10ml. of isoprophyl alcohol to the funel and swirl to clear solution.

vii) Read colour.in the appropriate cell.

NOTE:

Isoamyl alcohol can also be used in place of Isopropyl alcohol.

18. DETERMINATION OF COPPER-NEOCUPROINE METHOD

18.1 INTRODUCTION

This method covers the determination of total copper in the 2 to 2000 ppb range. This

method is based upon the yellow colour produced by the neocuproine cuprous complex.

A buffer solution maintains the pH between 4.0 to 6.0, but full colour development takes

place over the range of 2.3 to 9.0. The hydroxylarnine hydrochloride reduces the copper

to the cuprous state.

18.2 SAMPLING

Although samples may be taken in polyethylene bottles, meticulously clean 500 ml glass

bottles with plastic caps are preferred. Prepare bottles by soaking in HNO3 (1+9) for

several hours prior to use. Then rinse bottles with distilled water and drain before sampling.

Take the sample from the sample point, which has been continuously running for at least

four hours. Do not overflow or rinse bottle. Do not touch valve or jar line.


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18.3 STANDARDS

Prepare a series of copper standards in 250 ml separatory funnels using the standard

copper solution (1 ml =4 mg Cu). Add 1.0 ml of 1+1 HCL Dilute each to 200 ml include

a blank and gtreat similarly.

Application Range of Apparatus

Set spectrophotometer at 454 nm1.0 cm cell 20 to 1000 ppb.

10.0 cm cell 2 to 100 ppb.

18.4 REAGENTS

i) Copper, Standard Solution (1 ml =0.02 mg Cu) weigh 0.200 g of electrolytic

copper. Place it in a 250 ml beaker under a hood, add 3 ml of water and 3 ml of

HNO3(Sp.gr.1.42), and cover the beaker with a watch glass. After the metal

hascompletely dissolved add 1ml of H2SO4 (Sp.gr.1.84) and heat on a hot plate

just short of complete dryness. Do not bake the residue. Cool the residue, wash

down the sides of the beaker and the bottom of the watch glass, and again evaporate

the solution nearly to dryness to expel the HN03- Cool the residue, dissolve it in

water, and dilute the solution to 1 litre. Make the standard as needed by diluting

100ml. of the prepared solution to I litre with water. One millilitre of the standard

contains 0.02 mg Cu or when diluted to 50 ml. with water it represents a

0.4 mg/litre (ppm) Cu solution.

ii) Copper, Standard Solution (1 ml = 4 mg Cu ) dilute 200 ml of copper solution

(1ml=0.02 mg Cu) to I litre with water. One millilitre of this standard solution contains

4 mg of copper or, when diluted to 200 ml with water, it contains 20mg /litre(ppb).

Concentrated hydrochloric acid (HCl).

iii) Hydroxylamine hydrochloride Solution (200 g/litre). Remove traces of copper from

the solution prepared by treating in a separatory funnel with neocuproine solution

and isoamyl Alcohol solvent in accordance with procedure. Discard the organic

extract.

iv) Isoamyl Alcohol.

v) Isopropyl Alcohol.

vi) Neocuproine solution (1g/litre)-Dissolve 0.1 9 of neocuproine (2,9 dimethy 1 -1,10 - phenanthroline) in 50 ml. of isopropyl alcohol.Dilute the solution to 100 ml with

water.

vii) Sodium acetate Solution (275 g/litre-Dissolve 55 g of sodium accetate trihydrate,

(CH3

COONa 3H2O) in water and dilute to 200 ml. Remove traces of copper

from the solution by treating in a separatory funnel with NH2

OH. HCl, neocuproine,

and isoamyl alcohol solvent solutions in accordance procedure. Discard the organic

extract.


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* NOTE : Copper analysis should be run prior to iron. The copper in boiler feedwater

is generally in the form of the soluble copper - ammonium complex and the acidified

sample (approximately pH 1.5) will prevent plating out of elemental copper. The preliminary

digestion step in the above procedure will generally assume complete solubility of low

concentrations of copper (less than 50 ppb.)

18.5. APPARATUS REQUIRED

- 500 ml glass bottles with plastic caps with sample extraction hose.

- 250 ml - separating funnels

- 1 ml pipette (for 1:1 HCI)

- 1 ml pipette (for NH2

OH. HCl)

- 10 ml pipette (CH3

COONa solution)

- 2 ml and 4 ml pipettes (for neocuproine)

- 25 ml graduate (for isomyl alcohol)

- 10 ml graduate (for isoprophyl alcohol)

- Spectrophotometer

1.0 cm cell 20 to 1000 ppb

10.0 cm cell 2 to 100 ppb

- Waterbath suitable for heating (Thermostat).

18.6 PROCEDURE

i) Place acidified sample bottle (with top off) in a hot water bath at 900o C for one

hour (See Note)

ii) Cool to room temperature and transfer 200 ml of the sample to a 250ml separatory

funnel.

iii) Add 1 ml of NH2

OH.HCl solution and mix by shaking.

iv) Add 10 ml of CH3

COONa solution and mix again.

V) Then add 2 ml of neocuproine solution (4 ml for greater than 100g of Cu in

sample). Mix by shaking. Allow to stand for about 3 min.

vi) Add 25 ml of isoamyl alcohol and shake for one minute. Allow to stand five minutes

and permit aqueous phase to separate from alcohol phase. Alcohol phase will be at

top and aqueous phase can be drained off.

vii) Collect alcohol layer and add 10 ml of isopropyl alcohol to clear solution. Swirl to

mix thoroughly.

viii) Read in the appropriate cell at 454 nm.


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19. DETERMINATION OF AMMONIA

19.1 SUMMARY OF METHOD

A sample aliquot is Nesslerised directly and ammonia content determined colorimetrically.

Turbid samples may be clarified with ZnSO4 and NaOH. The precipitated Zn (OH)2 is

filtered or centrifuged off and the ammonia is determined on clear aliquot by direct

Nesslerization.

19.2 REAGENTS

i) Ammonium Chloride - Standard Solution A

Dissolve 3.819 g of anhydrous ammonium chloride NH4

Cl, dried at 105o C and

diluted to 1000 ml. (1.0 ml.=1.00 mg N = 1.22 mg NH3).

ii) Standard Solution B

Take 10 ml of solution A and dilute to 1000 ml.

(1.0 ml.= 10.0 mg N = 12.2 mg NH3)

iii) Nessler Reagent

Dissolve 100 g of anhydrous HgI2

and 70 g of anhydrous KI in a small volume of

water, and add this mixture slowly, with stirring, to acooled solution of 160 g of

NaOH in 500 ml of water. Dilute the mixture to1 litre. If this reagent is stored in a

chemically resistant bottle out of direct sunlight, it will remain stable up to a period

of 1 year.

iv) Sodium Hydroxide Solution - 250 g per litre

Dissolve 250 g of NaOH in water, and dilute to 1 litre.

v) Sodium Potassium Tartrate Solution 500 g per litre

Dissolve 500 g of sodium potassium tartrate tetrahydrate in 1 litre of water. Boil

until ammonia-free, and dilute to 1litre.

vi) Zinc Sulphate Solution (100 g per litre)

Dissolve 100 g of ZnSO4

0372 0375 vol a1 t02 water chemistry

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