BOILER WATER TREATMENT

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What is the purpose of boiler water treatment?

(a)     To prevent scale formation in the boiler

(b)     To give alkalinity and minimize corrosion

(c)      To condition sludge (by sodium aluminate).

(d)     To remove oxygen from water.

(e)     To reduce risk of caustic cracking.

(f)      To reduce risk of carry over of foam (by antifoam)

(g)      To minimize feed and condensate system from corrosion and filming amines

The principal objects of boiler feed water treatment should be:-

          (a)     Prevention of scale formation in the boiler and feed system by

                    (i)      Using distilled water or

                    (ii)     Precipitating all scale forming salts into the form of a non-         adherent sludge.

(b)     Prevention of corrosion in the boiler and feed system by maintaining the boiler water in and alkaline condition and free from dissolved gases.

(c)      Control of sludge formation and prevention of carry over with the system.

(d)     Prevention of entry into the boiler of foreign matter such as oil, waste, mill-scale, iron oxide, copper particles, sand weld spatter etc.  By careful use of coil heating arrangements, effective pre-commission cleaning and maintaining the steam & condensate system in a non-corrosive condition.       

Boiler water should be regularly tested and the treatment of the boiler water should be conducted according to the results obtained from the results.  For low pressure boilers salinometers and litmus paper s are still frequently used as testing equipment.  For accurate testing of the boiler water, above said tests are inadequate.  Refined tests are being practiced to ascertain the exact quantity of alkalinity and salinity concentrations.

TOTAL HARDNESS TEST

Apparatus                                                              Reagents

1-Burette, automatic, 10 ml                          16 oz, bottle Versenate solution

                                                                   Ethylenedimaine Tetraacetate

                                                                    (1ml equals 1 ml as CaCO₃)

1-Evaporating Dish                                        4 oz. bottle Drew Dry total

                                                                   Hardness Buffer Reagent with plastic

                                                                   scoop

1-Cylinder, graduated,100ml capacity            4 oz. bottle Drew Dry Total

                                                                   Hardness Indicator

1-Strirring Rod                                             

1-Brass measuring scoop                                                                    

Procedure

1.       Transfer 50 ml feedwater sample to the evaporating dish.

2.       Add one plastic scoop of Drew Dry Total Hardness indicator.  Stir until dissolved.

3.       Add one brass scoop of Drew Dry Total Hardness indicator.  Stir until dissolved.

4.       If a pure blue color develops, the hardness is zero.  Any reddish color indicates hardness is present.

5.       Titrate with standard versenate solution, adding the reagent drop by drop with continuous stirring as the red color fades.  The end point is a pure sky blue color without any reddish tinge.

Calculations:

          Total hardness (PPM as CaCO3) equals ml versenate solution X 20. If test result is in excess of _____________ add ____________ B according to dosing instructions and investigate source of contamination.

ALKALINITY TEST

Apparatus

10 ml automatic burette

White porcelain evaporating dish

100ml graduated cylinder

Stirring rod

Reagents

Sulfuring acid N/50 16 oz. bottle with burette

Phenolphthalein Indicator1 oz dropping bottle

Total Alkalinity Indiacator 1 oz. dropping bottle

Procedure

A.      PHENOLPHTHALEIN ALKALINITY TEST

1.    Fill burette to 0.0 mark with N/50 sulfuric acid\

2.    Using graduated cylinder, measure 50ml of boiler water to be tested.

3.    Add 4 drops of phenolphthalein Indicator.  Stir.

4.    If no pink or red color develops, record Zero phenolphthalein alkalinity.  Proceed to Part B (Total Alkalinity test)

5.    If, however, sample turns pink or red with Phenolphthalein, add N/50 sulfuric acid drop by drop while stirring continuously.  Continue until pink color disappears (sample is back to its original color.)                                           Do not discard sample  do not refill burette

6.    Calculations of results

(Ml of N/50 sulfuric acid) X 20 = (ppm phenolphthalein alkalinity).  For convenience, use the titration chart to get result.

7.    Record the Phenolphthalein Alkalinity in the daily log and proceed with Part B

B.       TOTAL ALKALINITY TEST

1.    Do not refill burette. Use the same sample that was used for the Phenolphthalein Alkalinity test and add exactly 4 drops of Total Alkalinity Indicator.  Sample will turn a green color.

2.    Add sulfuric acid, drop by drop, stirring continuously.  A purple color will soon begin to form where the drops fall into the sample.  When a permanent, pale purple color develops throughout the sample, the test is ended.  Color change will go from green to slate gray to purple.  The purple color is the end point.

3.    Calculation of result:

(Total ml of N/50 sulfuric acid – 0.6) X 20 = ppm Total Alkalinity.   For convenience use titration chart to get results.

4.     Record the total alkalinity in the daily log.  Discard sample.

CHLORIDE TEST

Apparatus

10 ml automatic burette

White porcelain evaporating dish

100ml graduated cylinder

Stirring rod

Reagents

Mixed Chloride Indicator – Make up fresh every 4 weeks.  Discard any indicator over 4                                               weeks old

Nitric Acid N/50 1 oz. dropping bottle

Mercuric Nitrate, 0.0141 N 16 0z.bottle with burette

Preparation of mixed chloride indicator

Apparatus

100 ml  graduated cylinder

4 oz. Amber glass dropping bottle

Reagents

1 capsule of mixed chloride indicator (Diphenyl Carbazone Indicator) Methyl alcohol

(anhydrous)

Procedure

1.  Empty capsule of indicator powder into 4 oz. amber glass dropping bottle.

2.  Measure 100ml alcohol and add to bottle.

3.  Cap bottle, Dissolve powder by swirling or shaking.

4.  Make up fresh every 4 weeks.  Discard any indicator that is 4 weeks old.

CAUTION!    METHYL ALCOHOL IS POISONOUS.  DO NOT SWALLOW.  AVOID CONTACT WITH EYES

Test procedure

1. Do not use th4e sample that was used for the Alkalinity tests.  Fill burette to 0.0 mark with 0.0141 N Mercuric Nitrate.
2. Using graduated cylinder, measure 50 ml of boiler water and transfer into the evaporating dish.
3. Add 10 drops of Mixed Chloride Indicator.  Stir.
4. Add N/5 Nitric Acid drop by drop, while stirring.  Continue until sample just turns yellow.  Then add another 5 drops of the acid.
5. Add 0.0141 N Mercuric Nitrate drop by drop while stirring until the sample shows the first permanent violet color.  Read the burette.
6. Calculation of results: 

(Ml of 0.0141 N Mercuric Nitrate) X 10 = ppm Chloride.  For convenience, use the titration chart to get results.  Compare test result with limit marked on the control chart.  If too high, start continuous blowdown and investigate source.  Repeat test in 30 minutes.

7. Place the comparator base slide in its slot the base.  Move the slide form side to side, while comparing the color of the sample with those of the standards in the slide.  Continue until the color of the sample color appears to be between two standards.  In the latter case, take the average of both readings.

NOTE that a comparison can be made only when one of the white lines on the slide is opposite the middle (sample) tube.

8. When a color match is obtained, read the test result in ppm phosphate from the numbers on the slide.  Compare phosphate readings with limit marked on the control chart.  Readings in excess of limits require blowdown.  Readings below recommended limits require proportionate dosing.  Refer to dosing instructions.

If the results of the phosphate test show a reading above the upper limit of 25 ppm, it will be necessary to repeat the testing using a diluted sample.

Procedure

(1)      Filter 5 ml of boiler water into the phosphate mixing tube.  Dilute to 10 ml with distilled or demineralized* water.  Proceed with steps 2 through 8 and, for results, double the ppm reading.  (for example if slide shows 15 ppm with diluted sample, the actual reading is 30 ppm).

_*       To make demineralized water, simply fill plastic bottle with distillate and squeeze though demineralizer cartridge.  The water discharged from the cartridge will be equivalent to distilled water.

          The cartridge is good until the demineralizer beads change color as indicated in the manufacturer’s instructions.   (In the “Deem” cartridge, the color change is from blue to brown.)  When this occurs, simply replace the cartridge.

Boiler water treatment using “BOILER WATER TEST KIT (FULL SERVICE) SPECTRAPAK 311

          This test kit is for phosphate, P&M alkalinity chloride and pH.  The hydrazine is an optional extra (Spectrapak 312).

Sampling

          A representative ware sample is required.  Always take water sample from the same place.  Allow the water to flow from the sample cock before taking the sample for testing to ensure the line is clear of sediment.

Phosphate PPM PO₄

·         Take the comparator with the 10 ml cells provided.

·         Slide the phosphate disc into the comparator.

·         Filter the water sample into both cells up to the 10ml mark.

·         Place one cell in the left hand compartment

·         To the other cell add one phosphate tablet, crush and mix until completely dissolved.

·         After 10 min place this cell into the right hand compartment of the comparator.

·         Hold the comparator towards a light.

·         Rotate the disc until a colour match is obtained.

·         Record the result obtained on the log sheet provided, against the date on which the test was taken.

P Alkalinity (PPM CaCO₃)

·         Take a 200ml  water sample in the stopped bottle.

·         Add one P alkalinity tablet and shake or rush to disintegrate.

·         If alkalinity is present the sample will turn blue.

·         Repeat the tablet addition, one at a time (giving time for the tablet to dissolve), until the blue colour turns to permanent yellow.

·         Count the number of tablets used and carry out the following calculations:-

P Alkalinity, ppm CaCO₃ = (Number of tablets x 20) – 10

e.g. 12 tablets = (12 x 20)-10 = 230 ppm CaCO₃

·         Record the result obtained on the log sheet provided, against the date on which the test was taken.

·         Retain the sample for the M Alkalinity test.

M Alkalinity (PPM CaCO₃)

·         To the P alkalinity sample add one M alkalinity tablet and shake or crush to disintegrate.

·         Repeat tablet addition, one at a time (giving time for the tablet to dissolve), until the sample turns to permanent red/pink.

·         Count the number of tablets used and carry out the following calculations:-

M Alkalinity, ppm CaCO₃ = (Number of P & M tablets x 20) – 10

e.g. 12 P, and 5M.  Alkalinity tablets are used

M alkalinity = [(12+5) x 20)]-10 = 330 ppm CaCO₃

·         Record the result obtained on the log sheet provided, against the date on which the test was taken.

Chloride (PPM) Cl

The range of chloride to be tested determines the size of water sample used.  The higher the chloride level the smaller the size of water sample used – this saves tablets.

 e.g. for low chloride levels use 100ml water sample

        for higher chloride levels use 50ml water sample

·         Take the water sample in the stoppered bottle provided.

·         Add one chloride tablet and shake to disintegrate.  Sample should turn yellow if chlorides are present.

·         Repeat the tablet addition, one at a time (giving time for the tablet to dissolve), until the yellow colour changes to permanent red/brown.

·         Count the number of tablets used and perform the following calculations:-

For 100ml water sample –

Chloride ppm = (Number of tablets x 10)-10

e.g. 4 tablets = (4 x 10) – 10 = 30 ppm

For 50ml water sample –

Chloride ppm = (Number of tablets x 20)-20

          e.g. 4 tablets = (4 x 20) – 20 = 60 ppm

          For smaller steps of ppm chloride use a larger sample.

          For larger steps of ppm chloride use a smaller sample.

·         Record the result obtained on the log sheet provided, against the date on which the test was taken.

pH Test        7.5 – 14.0 For boiler water

                   6.5 – 10.0 For condensate water

·         Take a 50ml sample of water to be tested in the plastic sample container provided.

·         Using the white 0.6grm scoop provided, add one measure of the pH reagent to the water sample, allow to dissolve.  Stir if required.

·         Select the correct range of pH test strip and dip it into the water sample for approximately 10 seconds.

·         Withdraw the strip from the sample and compare the colour obtained with the colour scale on the pH indicator strips container.

·         Record the pH value obtained on the log sheet provided, against the date at which the test was taken.

Hydrazine PPM Spectrapak 312

          This is an optional extra (order Spectrapak 312).  This test must be performed below 21⁰C.  A cooling coil should be fitted at the sampling point or the sample should be cooled immediately under cold running water.  Cloudy samples should be filtered before testing.

·         Take the comparator with the 10ml cells provided.

·         Slide the hydrazine disc into the comparator.

·         Add the water sample to both cells up to the 10 ml mark.

·         Place one cell in the left hand compartment of the comparator.

·         To the other cell add one measure of hydrazine powder (using the black 1grm scoop provided) and mix until completely dissolved.

·         Wait 2 minutes and place the cell in the right hand compartment of the comparator.

·         Hold up to the light and rotate the disc until a colour match is obtained.

·         Record the reading shown as ppm hydrazine.

Safety:  These reagents are for chemical testing only.  Not to be taken internally.  Wash hands after use.  Keep away from children.