1. Define pH and how it is measured and controlled.PH Test

Solutions of which water forms a part, contain hydrogen ions and hydroxyl ions, when this are present in equal amounts the solution is said to neutral. When there is an excess of hydrogen ions it is acid, and when an excess of hydroxyl ions it is alkaline. Keeping the water in slightly alkaline condition reduces corrosion. The level of acidity or alkalinity is usually express in terms of pH Value. This is basically a measure of the hydrogen ion concentration in the solution; for convenience the very small values involved are express in terms of the logarithms of their reciprocals.

PH = Logarithm of the reciprocal of the Hydrogen Ion in the solution

It should be noted that as the reciprocal is being use, the pH value increases as the actual hydrogen ion concentration decreases.

PH Value (Reciprocal or Hydrogen Ion) Test7.5 – 14.0 for Boiler Water6.5 – 10.0 for Condensate Water

Purpose:

1. To give warning on acidity or alkalinity of boiler water sample.2. Result help to establish the dosage of boiler compound to fight against corrosion.

Procedures:1.Take a 50 ml sample of the water to be tested in the plastic sample container provided.2.Using the white 0.6 gram. Scoop provided, add one measure of the pH reagent to the water sample, allow dissolving – stirring if required.3.Select the correct range of pH test strip and dip it into the water sample for one minute.4.Withdraw the strip from the sample and compare the color obtained with the color scale on the pH indicator strips container.5.Record the pH value obtained on the log sheet provided, against the date on which the test was taken.

2.Evaluate the test used in the control up Boiler and Feedwater Treatment.

a. Removing impurities from boiler feedwaterFeedwater is filtered to remove suspended matter and if the

suspended solids are very fine, a flocculation step may be needed to enable effective filtration. The water is then subjected to other treatments to make it suitable for the boiler. b. Filtration

Filtration is the essential first step before the chemical treatment and conditioning of the boiler feedwater. Filtration removes or minimizes all types of suspended solid impurities. If rust, sand (silica) etc. are not filtered out, they lead to severe scale formation, which is difficult to clean and reduce boiler efficiency. Even the condensate feedwater must be filtered before returning to the boiler. c. Coagulation and flocculation

The suspended particles in water are so fine that even cartridge filters are unable to remove them. In such a situation, before cartridge filtration, the water is first treated with coagulants. Coagulation is charge neutralization of finely divided and colloidal impurities in water into masses that can be filtered.d. Chemical precipitation

Chemical precipitation is a process in which chemical added reacts with dissolved minerals in the water to produce a relatively insoluble reaction product. Precipitation methods are used in reducing dissolved hardness, alkalinity, and silica. e. Reaction of lime and soda in softening process

Calcium hydroxide (hydrated lime) reacts with soluble calcium and magnesium carbonates to form insoluble precipitates. They form a sludge that can be removed by settling and filtration. Lime, therefore, can be used to reduce hardness present in the bicarbonate form (temporary hardness) as well as decrease the amount of bicarbonate alkalinity in water. Lime

reacts with magnesium sulfate and chloride and precipitates magnesium hydroxide, but in this process soluble calcium sulfate and chlorides are formed. The calcium carbonate formed by the reaction precipitates as sludge and can be filtered out. The resulting sodium sulfate and chloride are highly soluble and non-scale forming.f. Ion Exchange

Minerals dissolved in water form electrically charged particles called ions. Calcium carbonate, for example, forms a calcium ion with positive charges (a cation) and a bicarbonate ion with negative charges (an anion). Some synthetic and natural materials have the ability to remove mineral ions from water in exchange for others.

g. Deaeration of waterDissolved oxygen in water is a major cause of boiler system

corrosion. It should be removed before the water is put in the boiler. Feedwater deaeration removes oxygen by heating the water with steam in a deaerating heater. Part of the steam is vented, carrying with it the bulk of the dissolved oxygen.h. Combination of ion exchange and lime process

A common combination treatment is the hot lime-zeolite process. This involves pretreatment of the water with lime to reduce hardness, alkalinity, silica, and subsequent filtration and a cation exchange softening. This combination accomplishes several functions like softening, alkalinity and silica reduction, some oxygen reduction, and removal of suspended matter and turbidity.i. Reverse osmosis

Reverse osmosis overcomes the osmotic pressure with a higher artificial pressure to reverse the process and concentrate the dissolved solids on one side of the membrane. Operating pressures of about 300 to 900 psi are required to achieve this. Reverse osmosis reduces the dissolved solids of the raw water, making the final affluent ready for further treatment. This process

is suitable for any type of raw water, but sometimes the installation and operation cost may not be economical.j. Internal treatment of boiler feedwater

Internal treatment of water inside the boiler is essential whether or not the feedwater has been pretreated. Internal treatment compliments external treatment and is required regardless of whether the impurities entering the boiler with the feedwater are large or small in quantity. k. Blowdown

Blowdown is the discharge of boiler water containing concentrated suspended and dissolved feedwater solids. As the blowdown water is replaced with lower solids feedwater, the boiler water is diluted The amount of blowdown needed depends on how much feedwater impurities a given boiler can tolerate.

l. Corrosion in steam condensate systemCorrosion in steam condensate system is caused by carbon

dioxide and oxygen carried into the system by steam. Dissolved carbon dioxide in condensed steam forms corrosive carbonic acid. If oxygen is present with carbon dioxide, the corrosion rate is much higher, and is likely to produce localized pitting. Ammonia, in combination with oxygen, attacks copper alloys.m. Care of out-of-service boilers

Much of the corrosion damage to boilers and condensate equipment results during idle periods due to corrosion caused by the exposure of wet metal to oxygen in the air. Wet boiler lay-up method is of storing boilers full of water. Material, such as hydrated lime or silica gel, which absorb moisture, is placed in trays inside the boiler. The boiler is then sealed to prevent air from entering. Periodic replacement of the drying chemical is required during long storage periods.