Boiler Water analysis and it’s importance

Water analysis

The process of determining how much of various substances (impurities) are present in given sample of water is known as Water Analysis. Boiler water analysis is very important things in any power plant industries because of maintaining life of boiler or its equipment’s

Need for Boiler Water Analysis

Water analysis is essential for the following reasons:

1. a) Raw water source selection.
2. b) Analysis of raw water determines the type of treatment and unit size.
3. c) Treated water analysis indicates the efficiencies of various units of water treatment.
4. d) Designing of most economical water treatment plant.

To design a water treatment plant knowing the impurities present in the water to be treated is needed. Complete analysis helps in determining the degree of pre-treatment required in Ion Exchange and other process like reverse osmosis etc. Minor constituent like silica is very important since it may have influence on the regeneration technique used and can effect the capacities that can be obtained. Analysis of Iron and chlorine is important for reverse osmosis design.

*INTRODUCTION AND WORKING PRINCIPAL OF REVERSE OSMOSIS

Treams used in water analysis:-

pH:

It is common practice to express hydrogen ion concentration in terms of pH. By definition the pH is the negative logarithm of hydrogen ion concentration to the base of l0.

pH = – log10 (H+) = log (1/H+)

Ionic product of water Kw has a value of 1 x 10 – 14 and in neutral water H + concentration is equal to OH – concentration.

Kw = H + x OH- = 1 x 10- 14 —————– (1)

For neutral water = (H+) = (OH-) = 1×10 – 7

The equilibrium represented by equation (1) occurs universally in aqueous solution regardless of the equilibrium or the solutes present. Hence equation (1) should always be satisfied. Thus the terms pH expresses the acidity or basicity of water. Neutral water has a pH of 7. pH lower than 7 indicates acidity and greater than 7 is alkaline.

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Alkalinity:

As mentioned earlier alkalinity in water is due to presence of HCO-3. CO- 3 and OH- ions. In raw water alkalinity is mostly due to HCO-3, but in some cases CO- 3 ions also may be present. It is important to note that out of the three ions only two ions can exist in any system. That is HCO-3, CO- 3 or OH- can exist alone or in combination with one more ion. Any water analysis reporting the presence of all three ions should be discarded. Alkalinity of water is determined by titration with phenolpthalein and methyl orange indicator. The result of titration with methyl orange indicator is called Total Alkalinity or M-Alkalinity.

1. Alk. = Total Alk = HCO- 3 + CO- 3 + OH-.

The result of titration with phenolpthalein indicator is called P-Alkalinity.

3. Alk = OH + 1/2 CO3.

Hardness

Calcium and Magnesium salts impart hardness to water. Hard water is defined as a water which does not lather or foam with soap easily. The salts of calcium and magnesium which causes hardness is divided in two parts.

1. Temporary hardness or carbonate hardness.
2. Permanent hardness or non-carbonate hardness.

The sum of temporary and permanent hardness is called Total Hardness.

Total Hardness = Carbonate hardness + Non Carbonate hardness

Carbonate Hardness

It is mainly due to presence of bicarbonates of Calcium and Magnesium. Alkalinity in raw water is normally due to bicarbonate ions. Therefore, carbonate hardness (Alkalinity) plus Non Carbonate hardness is equal to total hardness.

1) Carbonate hardness = Alkalinity, when alkalinity is less than total

hardness.

2) Carbonate hardness = Total hardness, when alkalinity is greater or equal

to total hardness.

Conductivity:

The conductivity of water is dependent on the ionic content of water, specifically on the ability of ionic impurities in the water to conduct electricity. Ionic impurities have the ability to conduct electric current and thus there is direct linear relationship between ionic impurities and conductivity which help in determining the ionic impurities in water. Conductivity is also related to TDS empirically.

Conductivity x 0.65 = TDS.

Total Dissolved Solids

This represents all the soluble inorganic solids in water expressed in ppm.

Total Solids

Total solid is defined as SUM of soluble and insoluble solids.

Electrolytes

This is total ionizable dissolved solids in water. Total electrolyte is numerically equal to total cation or total anions (not sum of both). Total electrolyte does not include CO2 and silica.

Total Cations

Sum of calcium, magnesium, sodium and potassium all measured in the same unit.

Total Anions

Sum of alkalinity (HCO-3 + CO-3+ OH-) + Cl + SO4 + NO3 all measured in the same unit.

Total Cation = Total Anion = Total Electrolyte

Equivalent Mineral Acidity (EMA)

The equivalent mineral acidity, EMA is equal to the sum of equivalent concentration of sulphate, chloride and nitrate. It is also called sometimes as Total Mineral Acidity.

Free Mineral Acidity (FMA)

Free mineral acidity is equal to (EMA – Sodium leakage).

EMA – Sodium leakage = FMA

EMA – FMA = Sodium leakage.

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Hi, all power engineers. I am Joginder Chauhan(B.Tech(Mech.Engg.)BOE/E.M.) I am the founder of the website www.askpowerplant.com. I am also a power plant engineer with over 12+ years of experience in the power sector. I learned about power technologies like AFBC, CFBC, TRAVELLING GRATE, PULSATING GREAT, PF BOILER, WHRS, and many more during this period. My motive for this site is to share my power sector knowledge with every person who belongs to this field; on this website, I share information related to boiler operation, boiler maintenance, turbine operation & maintenance, boiler & turbine question answers, D.M plant, and all topic related to power plant sector please join this website for latest updation regarding power plant ………..thanks ( JOGINDER CHAUHAN )

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