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BOILER WATER TREATMENT AND CLEANING

A boilerman must understand the methods, tests, and safety precautions involved in boiler water treatment and the procedures for cleaning boiler firesides and watersides. To ensure a boiler operates at peak efficiency, you must treat and clean it. Water testing, treatment. and cleaning go hand-in-hand. The reason for this is because the effect of the impurities in the water on interior surfaces determines the method and frequency of boiler cleaning. In this section, we will discuss the relationships between water testing. treatment. and cleaning and the procedures for each.

WATER IMPURITIES

All natural waters contain acid materials and scale-forming compounds of calcium and magnesium that attack ferrous metals. Some water sources contain more scale-forming compounds than others; therefore, some waters are more corrosive than others. Subsurface or well waters are generally more scale-forming, while surface waters are usually more corrosive. To prevent scale formation on the internal water-contacted surfaces of a boiler and to prevent destruction of the boiler metal by corrosion, chemically treat feedwater and boiler water. This chemical treatment prolongs the useful life of the boiler and results in appreciable savings in fuel, since maximum heat transfer is possible with no scale deposits.

SCALE

Crystal clear water, satisfactory for domestic use, may contain enough scale-forming elements to render it harmful and dangerous in boilers. Two such scale-forming elements are precipitates of hardness and silica.

Scale deposited on the metal surfaces of boilers and auxiliary water heat exchange equipment consists largely of precipitates of the hardness ingredients—calcium and magnesium and their compounds. Calcium sulfate scale is, next to silica, the most adherent and difficult to remove. Calcium and magnesium carbonates are the most common. Their removal requires tedious hand scraping and internal cleaning by power-driven wire brushes. When deposits are thick and hard, the more costly and hazardous method of inhibited acid cleaning must be used. Scale deposits are prevented by the following: removal of calcium and magnesium in the feedwater to the boiler (external treatment); chemical treatment of boiler water (phosphate, organic extracts, etc.); and changing scale-forming compounds to form soft nonadherent sludge instead of scale that can be easily removed from the boiler by blowdown (internal treatment).

Silica in boiler feedwater precipitates and forms a hard, glossy coating on the internal surfaces. In the feedwater of high-pressure boilers, such as those used in electric generating plants, a certain amount of silica vaporizes under the influence of high pressure and temperature. The vapor is carried over with steam and silica deposits on the intermediate and low-pressure blading of turbines. In boilers operating in the range of 10- to 125-psig pressure, the silica problem is not so troublesome. When the water is low in hardness, contains phosphate that prevents calcium silicate scale from forming, or has enough alkalinity to keep the silica soluble. no great difficulty is encountered. The amount of soluble silica can be limited by continuous or routine boiler blowdown to prevent buildup of excessive concentrations.

CORROSION

Corrosion control occurs with the problem of scale control. Boilers, feedwater heaters, and associated piping must be protected against corrosion. Corrosion results from water that is acidic (contains dissolved oxygen and carbon dioxide). Corrosion is prevented by removing these dissolved gases by deaeration of feedwater, by neutralizing traces of dissolved gases in effluent of the deaerating heater by use of suitable chemicals. and by neutralizing acidity in water with an alkali.

METHODS OF TREATMENT

The specific method of chemical treatment used varies with the type of boiler and the specific properties of the water from which the boiler feed is derived. In general, however, the chemical treatment of feedwater and boiler water is divided into two broad types or methods-external treatment and internal treatment of makeup water for alkalinity control and for removal of scale-forming materials and dissolved gases (oxygen and carbon dioxide) before the water enters the boiler. "Internal treatment" means that chemicals are put directly into the boiler feedwater or the boiler water inside the boiler. Frequently, both external and internal chemical treatments are used.

External treatment. frequently followed by some internal treatment, often provides better boiler water conditions than internal treatment alone. However, external treatment requires the use of considerable equipment, such as chemical tanks, softening tanks, filters, or beds of minerals, and the installation costs are high. Such treatment is therefore used only when the makeup water is so hard or so high in dissolved minerals or when internal treatment by itself does not maintain the desired boiler water conditions. What is the dividing line between the hardness and the concentration of dissolved matter in water? What factors other than the dividing line determine the need for external treatment? These factors are the physical makeup of the plant. the type and design of the boilers used, the percentage of makeup water being used, the amount of sludge the boiler can handle, the space available, and the adaptability of the operators. Many methods of internal treatment are in use. Most of these treatments use carefully controlled boiler water alkalinity, an alkaline phosphate, and organic material. One of the organic materials used is tannin. Tannin is a boiler water sludge dispersant; that is, it makes precipitates more fluid and prevents their jelling into masses that are difficult to remove by blowdown. Because of treatment costs and simplicity of chemical concentration control, the alkaline phosphate-tannin method of internal treatment is perhaps the most widely used. When properly applied and controlled, this treatment prevents formation of scale on internal boiler surfaces and prevents corrosion of the boiler tubes and shell.

BOILER WATER TESTING

As we have just seen. boiler water must be treated with chemicals to prevent the formation of scale on the internal surface of the boiler and to prevent deterioration of the boiler metal by corrosion. Boiler water must be tested to determine the sufficiency of chemical residuals to maintain clean boiler surfaces. As a boilerman, you should be able to make various boiler water tests. The procedures for a few types of tests that you may have to make is given here—tests for hardness. phosphate. tannin. caustic alkalinity (with and without tannin), sodium sulfite, and pH. A test kit is provided for the different tests. Each test kit contains the equipment and materials for the specified test. If a kit is not available, you have to use the laboratory equipment (fig. 1-28) provided in the boiler or water treatment plants.


Figure 1-28.—General laboratory equipment.

CAUTION Test for Hardness

The following caution applies to each test that is discussed: IF THE TESTING PROCEDURES OF THE EQUIPMENT AND/OR REAGENT SUPPLIER DIFFERS FROM THAT PRESCRIBED IN THIS TEXT, THE SUPPLIER’S PROCEDURE SHOULD BE USED.

Boilers operating at pressures of 15 psi and less are normally used for space heating and hot-water generation. Practically all the condensate is returned to the plant. Only a small amount of makeup is required, and secondary feedwater treatment usually is sufficient. When appreciable quantities of steam are used in process work and not returned as condensate to the plant, the problem of scaling and corrosion arises, and more complete treatment of feedwater must be considered. The ideal water for boilers does not form scale or deposits. does not pit feedwater systems and boiler surfaces, and does not generate appreciable CO2 in steam. However. such raw makeup water is impossible to get in the natural state from wells or surface sources. Does the advantage of treatment make up for the cost of treatment?

Feedwater of 20- to 25-ppm hardness as calcium carbonate (CaCO3) need not be treated externally to reduce hardness if enough alkalinity is present to precipitate the hardness in the boiler as CaCO3, or if hardness reducers, such as phosphates, are introduced to combine with and precipitate the hardness. Precipitation of this hardness in a low- or medium-pressure boiler generally does not cause wasteful blowdown. When the mixture ofcondensate and makeup in a medium-pressure steam plant has a hardness greater than 20 to 25 ppm as CaCO3, the hardness should be reduced to a level of 0 to 2 ppm as CaCO3.

Feedwater of a hardness in excess of 2 ppm as CaCO3 should be treated to bring it within the range of 0 to 2 ppm as CaCO3. This small remaining hardness can be precipitated in the boiler by secondary treatment and removed by continuous blowoff equipment.

The test for hardness, as presented here, uses the calorimetric titration method. This test is based on finding the total calcium and magnesium content of a sample by titration with a sequestering agent in the presence of an organic dye sensitive to calcium and magnesium ions. The end point is a color change from red to blue, which occurs when all the calcium and magnesium ions are separated.

The following equipment is used for the hardness test:

  • One 25-ml buret, automatic, complete
  • One 210-ml casserole, porcelain
  • One 50-ml cylinder, graduated
  • One stirring rod, glass

The reagents for the test are as follows:

  • Hardness indicator
  • Hardness buffer
  • Hardness titrating solution

The steps of the hardness test are as follows:

1. Measure 50 ml of the sample in the graduated cylinder and transfer it to the casserole.

2. With the calibrated dropper, add 0.5 ml of the hardness buffer reagent to the sample, and stir.

3. Add 4 to 6 drops of hardness indicator. If hardness is present, the sample will turn red.

4. Add the hardness titrating solution slowly from the burette, and stir continually. When approaching the end point, note that the sample begins to turn blue, although you can still see a definite reddish tinge. The end point is the final discharge of the reddish tinge. Adding more hardness titrate solution does not produce further color change.

In using this procedure, add the hardness titrating solution slowly because the end point is sharp and rapid. For routine hardness determination, measure 50 ml of the sample, but add only approximately 40 to 45 ml to the casserole at the start of the test. The hardness buffer reagent and the hardness indicator should then be added as directed and the mixture titrated rapidly to the end point. The remaining portion of the sample should then be added. The hardness in the remainder of the sample will turn the contents of the casserole red again. Titrating is continued slowly until the final end point is reached. A record should be kept of the total milliliters of hardness titrating solution used.

To calculate the results in ppm hardness, use the following equation:

    ppm hardness = ml titrating solution x 1,000 (CaCO3) (ml sample)

With a 50-ml sample, the hardness in ppm as CaCO3 is equal to the ml of titrating solution used, multiplied by 20.

Test for Phosphate

The calorimetric test for phosphate uses a decolorizing carbon to remove tannin. Carbon absorbs the tannin, and the carbon and tannin are then filtered out. When tannin is not present, carbon improves the test for residual phosphate by making the tricalcium phosphate sludge more filterable.

The equipment required for the phosphate test is as follows:

  • One phosphate color comparator block of two standards—30 ppm and 60 ppm of phosphate as PO4 . (The Taylor high-phosphate slide comparator may be used instead.)
  • Four combination comparator mixing tubes, each marked 5, 15, and 17.5 ml, with stoppers.
  • One filter funnel, 65-mm diameter.
  • One package of filter paper, 11 cm in diameter. One 20-ml bottle.
  • One 0.5-ml dropper.
  • One 1/4-tsp measuring spoon or spatula.
  • Two plain test tubes, 22 mm by 175 mm (about 50 ml).
  • Two rubber stoppers, No. 3 flask.
  • One 250-ml glass-stoppered bottle or flask, labeled comparator molybdate reagent.

The reagents you need are as follows:

  • One 32-oz comparator molybdate.
  • One 2-oz concentrated stannous chloride.
  • One 32-oz standard phosphate test solution (45 ppm of phosphate, PO4).
  • One pound decolorizing carbon. (This is a special grade of decolorizing carbon tested to make sure it does not affect the phosphate concentration in the sample.)

For test purposes, the stannous chloride is supplied in concentrated form. The reagent must be diluted and should be prepared from the concentrated stannous chloride on the day it is to be used, because the diluted solution deteriorates too rapidly for supply by a central laboratory. If not fresh, diluted stannous chloride gives low test results. Concentrated stannous chloride also deteriorates and should not be used if more than 2 months old.

The procedure for making diluted stannous chloride is as follows:

1. Fill the 1/2-ml dropper up to the mark with the concentrated stannous chloride.

2. Transfer it to a clean 20-ml bottle.

3. Add distilled water up to the shoulder of the bottle, then stopper and mix by shaking.

CAUTION

Any diluted stannous chloride not used the day it is made should be discarded.

The following procedure is used to make the test for phosphate:

1. Without disturbing any settled sludge, transfer enough of the sample to the test tube to till it about half full.

2. Add 1/4 tsp of decolorizing carbon. Stopper the tube and shake vigorously for about 1 minute. The carbon absorbs the tannin so it can be filtered out.

3. Fold a filter paper and place it in the filter funnel. Do not wet down the filter paper with water. Filter the shaken sample, using a combination mixing tube as a receiver. The carbon absorbs tannin, and the tannin and sludge present are filtered out more rapidly. Avoid jiggling the funnel, as unfiltered boiler water may overflow the edge of the filter paper into the tube. You have to support the funnel.

4. After 5 ml of the sample has filtered through, as indicated by the level in the tube, discard it. Continue filtering to bring the level in the test tube again up to the 5-ml mark. The sample should come through clear and free, or nearly free, of any color from the tannin. If not nearly free of tannin color. repeat the test, using 1/2 tsp of carbon. adding it in two 1/4-tsp portions, shaking it for 1 minute after each addition.

5. Add the comparator molybdate reagent to bring the level up to the second mark ( 15 ml). Stopper and mix by inverting the tube several times.

6. Add fresh diluted stannous chloride up to the third mark (17.5 ml). Stopper and mix by inverting. If phosphate is present, the solution in the mixing tube turns blue.

7. Place the tube in the comparator block. Compare the color of the solution in the tube with the standard colors of the phosphate color block. Colors between the two standard colors may be estimated. Take the reading within 1 minute after adding the stannous chloride, because the color fades quickly.

8. Record the results as LOW, if below 30 ppm; HIGH, if above 60 ppm, or OK, if between 30 and 60 ppm.

Test for Tannin

The purpose of the tannin test is to determine the amount of tannin in the boiler water. Tannin holds sludge in suspension. In treating boiler water with tannin, control the dosage by the depth of brown formed in the boiler water by the tannin. To estimate the depth of the color, which is necessary in adjusting tannin dosages, compare a sample of the boiler water with a series of brown color standards of successively increased depths of color. A tannin color comparator, which is used for the comparison, has five glass color standards:

No. 1, very light;
No. 2, light:
No. 3, medium;
No. 4, dark; and
No. 5, very dark.
The kit for the tannin test contains the following:
  • One tannin color comparator
  • Two square tubes, 13-mm viewing depth
  • One plain test tube, 22 mm by 175 mm
  • One filter funnel, 65 mm by 65 mm
  • One package of filter paper, 11 cm in diameter


Tannin test kit
(Photo courtesy Isopure Water)

Making this test, you first fill a plain test tube almost to the top with cool boiler water. Then place a square test tube in the slot of the comparator, and insert the filter funnel in it. Fold a filter paper and place it in the funnel without wetting it down. Filter water from the plain test tube into the square tube until the tube is neatly full. Remove the square tube from the comparator and hold it up to a good source of natural light. Note the appearance of the filtered boiler water. Is it free of suspended solids and sludge? If not, refilter the sample, using the same funnel and filter paper. Repeat, using a double filter paper if necessary, until the sample does come through free of suspended solids and sludge.

To complete the test, place the square tube of filtered sample in the middle slot of the comparator. Then compare the color of the sample with the five standards, viewing it against a good source of natural light. The color standard most closely matching the color of the filtered sample gives the tannin concentration of the boiler water. For a number of boiler water conditions, the tannin dosage is usually satisfactory if it maintains a medium (No. 3) tannin color. If the tannin color is too high, blow down; if too low, add tannin.

Test for Caustic Alkalinity (OH) without Tannin

The boiler water sample for this test is collected at a temperature of 70°F or below.

The equipment required is as follows:

  • Two 8-in. droppers with bulbs
  • Two 250-ml glass-stoppered bottles or flasks labeled causticity No. 1 and causticity No. 2
  • Four marked test tubes, 22 mm by 185 mm
  • Three plain test tubes, 22 mm by 175 mm Three rubber stoppers, No. 2
  • One 14-in. test-tube brush One test-tube clamp
  • Two 9-in. stirring rods
  • One 1-oz indicator dropping bottle for phenolphthalein
  • One test-tube rack

The following reagents also are required:

  • One 24-oz bottle or flask causticity reagent No. 1
  • One 24-oz bottle or flask causticity reagent No. 2
  • One 4-oz bottle phenolphthalein indicator

The following are the steps to follow in conducting a test for causticity when tannin is not used:

CAUTION

Avoid exposure of the sample to the air as much as possible to reduce absorption of the CO2.

1. Without disturbing the settled sludge, fill a marked test tube exactly to the first mark (25 ml) with some of the original boiler water sample.

2. Shake causticity reagent No. 1 (barium chloride solution saturated with phenolphthalein) thoroughly and add enough to the graduated tube to bring the level exactly to the second, or long, mark (30 ml).

3. Stir the solution with the 9-inch stirring rod, which must be kept clean and reserved for the causticity test only. When the mixture remains colorless or does not turn pink, the causticity in the boiler water is zero and the test is finished. When the mixture turns pink, causticity is present. (If the pink color is not deep, intensify it by adding two drops of phenolphthalein indicator to the mixture in the tube.) Add causticity reagent No. 2 (standard one-thirtieth normal acid), using the 8-inch dropper, thatch must be kept clean and reserved for the causticity test only. Causticity reagent No. 2 is sucked from the reagent bottle into the dropper by its rubber bulb and added, drop by drop, to the test tube. After each addition, stir the mixture with a stirring rod. After sufficient reagent has been added, the pink color disappears; the change point is usually sharp. As soon as the pink color just fades out, stop adding the reagent.

4. The amount of causticity reagent No. 2 required to make the pink color disappear shows the concentration of hydroxide (OH) or causticity in the boiler water. The amount of reagent used is shown by the marks on the test tube above the long mark (30 ml). The distance between any two marks on the test tube equals 5 ml, and readings less than 5 ml can be estimated. For example, when only three fifths of the distance between the long mark and the next mark above were filled, then 3 ml was added. When the distance filled was past one mark plus three fifths of the distance to the next, then 5 + 3 = 8 ml was used. To obtain the actual ppm of hydroxide or causticity shown by the test, multiply the number of ml by 23. This constant number, 23, represents the amount of sodium hydroxide in the boiler water by volume. Thus, for 8 ml of causticity reagent No. 2, there are 8 x 23 = 184 ppm hydroxide or causticity in the water.

5. Record the results of the test in a boiler log or chemical log and adjust the range to meet requirements. When causticity is too high, blow down; if too low, add sodium hydroxide (caustic soda).

Test for Caustic Alkalinity (OH) with Tannin

For this test, start with a warm sample of about 160°F. It may be reheated by placing the sample-collecting container in a stream of hot boiler water drawn through the boiler water cooler connection. In a test for causticity when tannin is used, make sure you observe the same precautions as carefully as when tannin is not used.

CAUTION

Avoid exposure of the sample to the air as much as possible to reduce absorption of the CO2.

The equipment and reagents required for this test are the same as those listed in the preceding section where tannin was not used.

  • Two 8-in. droppers with bulbs
  • Two 250-ml glass-stoppered bottles or flasks labeled causticity No. 1 and causticity No. 2
  • Four marked test tubes, 22 mm by 185 mm
  • Three plain test tubes, 22 mm by 175 mm Three rubber stoppers, No. 2
  • One 14-in. test-tube brush One test-tube clamp
  • Two 9-in. stirring rods
  • One 1-oz indicator dropping bottle for phenolphthalein
  • One test-tube rack

The procedure for conducting a test for causticity with tannin is as follows:

1. Fill two test tubes to the first mark (25 ml) with some of the original boiler water sample, taking care not to disturb the settled sludge in the container. (Transfer as little sludge as possible from the sample-collecting container to the test tubes.)

2. Shake causticity reagent No. 1 thoroughly and add enough to each of the two marked tubes to bring the levels up to the second, or long, mark (30 ml). Stir both with the stirring rod, which must be kept clean and reserved for the causticity test only.

3. Stopper both tubes and let them stand until any sludge formed has settled to the bottom. The sludge carries down with it much of the tannin or other colored matter in the solution; settling takes a few minutes if the sample is warm.

4. Without disturbing the sludge at the bottom, pour enough solution from the tubes into the third marked tube to fill it to the second, or long, mark. Discard the mixture left in the first two. When the sample in the third tube is still warm, cool it by letting cold water run on the outside of the tube. It is sometimes possible to intensify the pink color by adding two drops of phenolphthalein from the indicator-dropping bottle to the sample in the tube. Stir the solution. When it is not pink, the causticity in the boiler water is zero.

5. When the sample is not pink, the test is finished. But if the mixture turns pink, proceed in the same manner as directed in Steps 3, 4, and 5 when no tannin is used.

Here is a brief explanation of an alternate procedure for making the test for causticity when tannin is used. In this procedure any glass container, such as a large test tube or graduated cylinder, marked for 50 to 60 ml can be used instead of the two standard marked test tubes used in Steps 1 and 2 above. With the large test tube or graduated cylinder, the warm (160°F) sample is added up to the 50-ml mark and causticity reagent No. 1 up to the 60-ml mark. Stir the mixture and stopper the tube, or graduate. After the sludge settles, pour off enough of the solution into one of the standard marked test tubes to fill it to the long mark (30 ml). When the sample is warm, cool it by letting cold water run on the outside of the tube. Adding two drops of phenolphthalein may intensify the pink color. When the solution is not pink, the causticity in the boiler water is zero. But if it turns pink, proceed in the same manner as in Steps 3, 4, and 5 when no tannin is used.

Test for Sodium Sulfite

The sample for this test should be cooled to 70°F, or below, and exposed to the air as little as possible, because oxygen in the air combines with sodium sulfite in the sample and causes low readings. Collect a separate sample, using the boiler water sample cooler, with the line reading to the bottom of the sampling bottle. Allow the boiler water to run until a few bottlefuls overflow to waste.

The equipment necessary to make the sodium sulfite test is as follows:

  • Two marked test tubes Two plain test tubes
  • One stopper for plain test tube One stirring rod
  • One 8-in. dropper
  • One 1/4-measuring tsp One 50-ml beaker One 150-ml beaker
  • One 30-ml acid-dropping bottle, with dropper marked at 0.5 ml for hydrochloric acid 3N
  • One 30-ml starch-dropping bottle, with dropper marked at 0.5 ml for starch indicator

The reagents required are as follows:

  • One 2-oz bottle of potato, or arrowroot starch One 8-ml vial of thymol
  • One 24-oz bottle of hydrochloric acid 3N
  • One 1-pt amber bottle of standard potassium iodate-iodide reagent

The starch indicator for this test must be prepared locally. The procedure to adhere for good results is as follows:

1. Measure out a level one-fourth tsp of potato or arrowroot starch and transfer it to the 50-ml beaker.

2. Add a few milliliters of distilled water and stir the starch into a thick paste, using the end of the stirring rod.

3. Put 50 ml of distilled water into the 150-ml beaker. (It is convenient in this step to have the 150-ml beaker marked at the point where it holds 50 ml, or one of the marked test tubes can be used by filling it with distilled water to the fourth mark above the long mark.)

4. Bring the water in the 150-ml beaker to a boil by any convenient method.

5. Remove the source of heat and immediately pour the starch paste into the boiling water while stirring the solution.

6. Put a crystal of thymol into the starch solution and stir. After the solution has cooled, pour off any scum on the surface and transfer 30 ml to the indicator-dropping bottle.

7. The starch solution loses its sensitivity as an indicator after a time. Addition of the thymol preserves it for about 2 weeks. The starch should be dated when prepared.

In making the sodium sulfite test, proceed as follows:

1. Transfer 1 ml of hydrochloric acid 3N to a clean, marked test tube by measuring out 0.5-ml portions with the dropper of the acid-dropping bottle.

2. From the starch-dropping bottle, transfer 0.5 ml of starch to the marked test tube.

3. Without disturbing any settled sludge in the sample, pour enough of the sample into the marked test tube to bring the level up to the first mark (25-ml). Stir the mixture in the tube with the plunger end of the stirring rod.

4. To add the standard potassium iodate-iodide reagent to the mixture in the marked test tube, have the marked test tube supported and the stirring rod placed in the tube, so the reagent can be added with one hand while the mixture is stirred with the other. Fill the 8-inch dropper with standard potassium iodate-iodide reagent from the stock bottle by sucking it up with the rubber bulb. (The dropper must be kept clean and reserved for this test only.)

5. Add the reagent to the mixture in the marked test tube, one drop at a time, counting the number of drops and stirring after each is added until a permanent blue color, which is not removed by stirring, is obtained. The standard iodate-iodide reagent reacts with sodium sulfite in the mixture, and the formation of the permanent blue color from the action of excess reagent with the starch shows that the iodate-iodide reagent has consumed all the sodium sulfite in the mixture.

6. Each drop of iodate-iodide reagent used (except the last one) indicates 5 ppm of sodium sulfite in the boiler water sample. To figure the concentration of sodium sulfite in the boiler water, multiply the total number of drops of the standard iodate-iodide reagent used, less one, by 5. For example, when 5 drops were used, subtract 1 from 5 = 4, 5 x 4 = 20 ppm.

7. Record the results of the test as ppm.

Test for pH

The value of pH indicates the degree of acidity or alkalinity of a sample. A pH of 7.0 represents the neutral point; the lesser values denote acidity; the greater values denote alkalinity. The test is made as soon as possible after you take the sample. Avoid exposure to the air as much as possible to reduce absorption of CO2.

The following equipment is used in making the pH test of boiler water:

  • Two vials of indicator paper, hydrions pH 10 to 20
  • Two vials of indicator paper, hydrions C pH 11 to 12
  • One 50-ml beaker One 2-oz bottle

In conducting the test for pH of boiler water, remove a strip of pH 10 to 12 indicator paper from the vial and dip it into the sample in the beaker. Keep the paper immersed for 30 seconds; then remove it. When the sample does not change the color of the paper or colors it yellow or light orange, the pH of the sample is too low and the test is finished. When the paper turns orange or red, the pH is either satisfactory or too high.

In that case, remove a strip of paper of pH 11 to 12 from the vial and dip it into the sample in the beaker. Keep the paper immersed for 30 seconds; then remove it. When the sample does not change the color of the paper or colors it a light blue, the pH is satisfactory. When the paper turns deep blue, the pH is higher than necessary. Blow down or reduce the dosage of caustic soda (NaOH).

Test for pH of Treated Condensate

In making a test for pH of treated condensate, take the sample from a point in the return piping near which condensation takes place, such as after a trap, or preferably where the return-line corrosion is known to occur. The sample must represent water flowing in the return lines. Water taken from the return tank, especially of large installations, generally shows a higher pH. A sample should not be taken from a collecting tank if other water, such as makeup, is received in the tank.

The equipment required for this test is as follows:

  • One 4-oz brown bottle of condensate pH indicator
  • One 1-oz indicator bottle, with dropper marked at 0.5 ml
  • One 100-ml beaker, marked at 50 ml One 9-in. stirring rod, glass

In making a test for pH of treated condensate, proceed as follows:

1. Pour a freshly drawn sample into the testing beaker until it is filled to the 50-ml mark. You do not have to cool the sample.

2. Transfer 0.5 ml of indicator solution to the 50-ml testing beaker, using the marked dropper. Stir the solution in the beaker. If the color of the solution changes to light pink. the sample is NEUTRAL, or slightly alkaline; therefore, the condensate pH is satisfactory and the test is over.

3. Record in a log that the pH range is between 7 and 7.5.

4. When the color change is green, the sample is in the acid range and the boiler water must be treated with Amines. Treat the boiler water with Amines gradually (in small amounts at a time), and retest after each treatment. Amines are the only chemicals used to treat boiler water that will vaporize and leave with the steam and thereby protect the return system.

WARNING

Permission to treat with Amines must be obtained from your supervisor. Amines are volatile, poisonous, and in the alkaline range.

5. When the color change is red or purple, the sample is in an excessive alkaline (pH) range. In that case, reduce the Amines treatment gradually (in small amounts at a single time), and retest after each treatment. Remember, the condensate pH normal acceptable range is between 7 and 7.5.

Test for Total Dissolved Solids

The solu-bridge method is a simple and rapid way to determine the total dissolved solids (TDS) content. Ionizable solids in water make the solution conduct electricity. The higher the concentration of ionizable salts, the greater the conductance of the sample. Pure water, free from ionizable solids, has low conductance and thus high resistance. The solu-bridge instrument measures the total ionic concentration of a water sample, the value of which is then converted to parts per million. The solu-bridge test equipment and reagent are furnished by the supplier in a kit.

CAUTION

The model of the solu-bridge given below is not suitable for measuring solids in condensed steam samples or an effluent of the demineralizing process. A low-conductivity meter is necessary. because of the extremely low solids content of condensed steam and demineralized water.

The equipment and reagent are as follows:

  • One solu-bridge meter
  • One polystyrene dip cell
  • One thermometer, 0°F to 200°F.
  • One 0.1-g dipper for gallic acid.
  • One cylinder, marked at the 50-ml level. Gallic acid powder, 1 lb.
  • Calibration test solution. I qt.

The test is made as follows:

1. Without shaking, pour 50 ml of the sample into the cylinder. Add 2 dippers of gallic acid powder and mix thoroughly with a stirring rod.

2. Connect the dip-cell leads to the terminals of the solu-bridge. Turn the switch ON.

3. Clean the cell by moving it up and down several times in distilled water. Measure the temperature of the sample to be tested; then set the point of the solu-bridge temperature dial to correspond to the thermometer reading.

4. Place the cell in the cylinder containing the 50-ml sample. Move the cell up and down several times under the surface to remove air bubbles inside the cell shield. Immerse the cell until the air vents on the cell shield are submerged.

5. Turn the pointer of the solu-bridge upper dial until the dark segment of the tube reaches its widest opening.

6. Calculate the result in ppm by multiplying the dial reading either by 0.9 or by a factor recommended by local instructions. For example, when the dial reading is 4,000 micromhos and the factor used is 0.9, then 4,000 x 0.9 = 3,600 ppm.

7. Record the results of the test in ppm.


Q22. Scale deposited on metal surfaces of’ boilers consists largely of what scale-forming element?

Q23. What are the two broad types or methods of chemical treatment of‘ boiler water?

Q24.Results of a phosphate test would need to be between what lower and higher ppm to be at an acceptable level?

Q25. In a causticity test without tannin, when the mixture turns pink, what does this mean?

Q26.A sample of boiler water for a sodium sulfite test should be cooled to what temperature before conducting the test?

David L. Heiserman, Editor

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Revised: June 06, 2015