Two Englishmen Thompson and Way, first recognized the process of ion exchange in 1850. They reported that when a fertilizer solution poured over a column of soil, ammonia in the fertilizer solution was replaced by calcium from the soil.
Ion exchange was not used for any industrial application until 1905.
At that time a German chemist Gans, used a synthetic sodium aluminosilicate cation exchange material called zeolite in water softeners.
Gans’ water softeners exchanged sodium ions in the zeolite for both the calcium and magnesium ions in the water. softening water through the process of removing these hardness ions.
A naturally occurring zeolite called greensand later replaced synthetic aluminosilicate for use in softeners. Greensand has greater physical strength than aluminosilicate because It was more suitable for industrial applications.
In 1944, strong acid cation (SAC) exchange resin was produced by co-polymerization of styrene and divinylbenzene.
The styrene-divinylbenzene (S-DVB) copolymer is very stable and has more capacity for ion exchange than greensand.
A styrene-divinylbenzene strong base anion (SBA) exchange resin was developed in 1948. It was capable of removing all anions including silica and carbon dioxide in water.
Many modifications have been made to the copolymer structure of the original SAC and SBA styrene-divinylbenzene ion exchange resins since 1948.
These modifications have been made in an attempt to meet specific industrial needs and to provide increased resin life.
Application of Ion Exchange Resin:
Ion exchange resins are selected to treat specific process water with a specific treatment objective, such as demineralization (deionization), softening, dealkalization or organic scavenging (organic matter removal)
Demineralization or deionization is the complete removal of ions from the process water. Only pure water remains after treatment.
Demineralization requires Strong Acid Cation (SAC) and Strong Base Anion (SBA) resins because Weak Acid Cation (WAC) resin does not remove all cations and Weak Base Anion (WBA) resin does not remove weak acids i.e. carbonic acid and silicic acid.
Water Softening process uses Strong Acid Cation(SAC) resin in Sodium(Na+) form.Softening process only removes calcium and magnesium ions from water.
Alkalinity means acid neutralization capacity of water. When we add acid in water (adding H+ ions) water absorbs H+ ions without showing significant change in pH mainly it is due to carbonate, bicarbonate & hydroxide ion present in water or the mixture of two ions present in water. The possibility of OH– and HCO3– ions together is not possible since they combine together to form CO3-2 ions.
OH- + HCO3- ⇒ CO3-2 + H2O
Two types of Alkalinity present in water,
P-Alkalinity also called Phenolphthalein Alkalinity because Phenolphthalein indicator used for analysis
M-Alkalinity also called Methyl orange Alkalinity because Methyl orange indicator used for analysis
In alkalinity analysis different ions can be estimated separately by titration against standard acid solution, using selective indicators like phenolphthalein and methyl orange.
Below reaction occurs during analysis:
OH- + H+ ⇒ H2O
CO3-2 + H+ ⇒ HCO3-
HCO3- + H+ ⇒ H2O + CO2
The neutralization reaction up to phenolphthalein end point shows the completion of reactions (1) and (2) only.
The amount of acid used thus corresponds to complete neutralization of OH– plus half neutralization of CO32–.
The titration of water sample using methyl orange indicator marks the completion of the reactions (1), (2) and (3).
Based on above three reaction,
P-Alkalinity = Total Hydroxide + 1/2 Carbonate M-Alkalinity = (Total Hydroxide + 1/2 Carbonate) +1/2 Carbonate + Total Bicarbonate
Alkalinity Summary Table
P = 0
P = 1/2M
P > 1/2M
P < 1/2M
P = M
1.Phenolphthalein alkalinity (P) = 0; that means the volume of acid used till the completion of reaction (1) and (2) is 0. This can only happen when both OH– and CO32– ions are not present in water. Alkalinity is present due to HCO3– ion only which can be determined using methyl orange indicator and called methyl orange alkalinity (M).
2. P = ½ M; indicates that only CO32– ions are present. Using phenolphthalein indicator neutralization reaches upto HCO3– but using methyl orange indicator the complete neutralization of HCO3– takes place.
3.P > ½M; implies OH– ions are also present along with CO32– ions. Upto phenolphthalein alkalinity OH– ions will be neutralized completely whereas CO32– will be neutralized upto HCO3– ion. But using methyl orange indicator HCO3– will be completely neutralized along with OH– and CO32–.
4.P < ½ M; indicates that beside CO32– ions HCO3– ions are also present. The volume of acid required for the neutralization upto phenolphthalein end point correspond half neutralization of CO32– (equation 2). Neutralization using methyl orange indicator corresponds to HCO3– obtained from CO32– and HCO3– originally present in the water sample
5.P = M; indicates only OH– ions are present.
Alkalinity of water is very important parameter in boiler water treatment program. Based on alkalinity analysis we can predict the presence of free caustic as mentioned in above table. Free caustic is responsible for caustic corrosion in boiler system.
Simple defination of hardness is the amount of calcium & magnesium ions present in water. It is divided in two parts carbonate or temporary hardness and non-carbonate or permanent hardness.
It is a major source of scale in water systems i.e.boiler water & cooling water systems. Softening is proven method for removal of hardness from water.
Let us discuss both the types of hardness in detail:
#1. Carbonate or Temporary Hardness
Carbonate and bicarbonate ions are responsible for this type of water hardness.It is also known as temporary hardness because it removes from water when we boil the water.
When we boil the water carbonate & bicarbonates ions present in water decomposes & insoluble carbonate is reformed.Boiling the water causes the precipitation of calcium and magnesium carbonate so that, calcium and magnesium ions are remove from water.
Example: CaCO3, MgCO3, Ca(HCO3)2, Mg(HCO3)2
#2. Non-Carbonate or Permanent Hardness
Chloride and Sulfate (non-carbonate) ions are responsible for this type of water hardness.It is also known as permanent hardness because it isn’t remove from water by boiling it.
It is only remove from water either by softening or demineralization process.
Example: CaCl2, MgCl2, CaSO4, MgSO4
Water Hardness Scale:
As a general rule for classification of hardness, Water having hardness below 60 ppm is considered as soft water,61 ppm to 120 ppm as moderately hard; 121 ppm to 180 ppm as hard & above 181 ppm as very hard.
Total Hardness ppm as CaCO3
Grains per gallon
Water Hardness Measurement:
Water harness analysis divided in three parts namely total hardness,calcium hardness & magnesium hardness.
Total hardness is a sum of calcium & magnesium hardness.
Total hardness = Calcium Hardness + Magnesium Hardness
To determine total hardness ammonia buffer solution is added to the sample to maintain the pH of around 11. Then Eriochrome Black T indicator is added so the wine red color is developed in the sample.
After that sample is titrated against EDTA solution and sample color will change from wine red to blue. This is the end point of total hardness titration.
Determine the calcium hardness by titration sodium hydroxide solution is added to the sample to maintain pH & then murexide indicator is added. Sample color turns into pink & titrate the sample against EDTA solution this time sample color will change from pink to purple. This is the end point of calcium hardness test.
Magnesium hardness is the difference of total hardness & calcium harness value. It is determined by subtracting calcium hardness value from total hardness value.
Magnesium Hardness = Total Hardness – Calcium Hardness
Water Hardness Conversion:
Grains per gallon
In Conclusion, Water hardness is a major source of scale in water treatment system. It is very essential to remove it from water by selecting proper water treatment program.
Molarity Calculator For Concentrated Liquid Chemical
Molarity Calculator is very handy tool for science student to make reagents for analysis. You can easily calculate molarity of any concentrated acid or base liquid solution. All you need to do is only enter the three values which is mentioned on label of reagent bottle.
Hope, This article will clear your concept about molarity formula & its calculations.
Types of water circulation in industrial steam water tube boilers:
Water circulation in boiler can be classified in three different types of systems.
#1.Natural Circulation In Boiler:
Boiler feed water which is pumped with high pressure boiler feed water pumps first reaches at economizer. Here temperature of the boiler feed water is around the saturation temperature corresponding to its pressure. Saturation temperature means the temperature at which water vaporization is starts for a given pressure. It is also called the boiling point of water. Feed water flows through economizer gets further heated by flue gas and enters into the steam drum. Steam drum acts as a pressure vessel and separates steam and water from steam water mixture.
Normally steam drum water level is maintained around 50%.It means steam drum is half filled with water & remaining 50% above the water level contains steam. Water inside the drum flows down through down comer pipes and distributed by bottom header to water walls. Down comer pipes are outside the boiler furnace while water walls are inside the furnace. Water rises through water wall tubes are exposed to furnace heat. When water rises upside in tubes, a portion of the water is converted into steam and continue to rise upwards as a mixture of steam and water. Heat absorbed in water wall is latent heat of vaporization creating a mixture of steam and water.
The ratio of the weight of water to the weight of steam in the mixture leaving the heat absorption surface is called circulation ratio. This mixture is continuously rises till it reaches back to the steam drum. Separated steam from steam drum is sent to the turbine.
The value of circulation ratio varies from 6 to 30 in industrial boilers. Circulation ratio for utility high pressure boilers is between 6 to 9.Circulation ratio is higher side as the density difference between steam & water is high. Medium pressure industrial boilers adopted higher circulation ratio. These boilers have to respond quick load changes.
The circulation, in this case, takes place on the basis of thermo-siphon principle. The Down comer contains relatively cold water, whereas the riser tubes contain a steam & water mixture, whose density is comparatively less. This density difference is the driving force, for the mixture. Circulation takes place at such a rate that the driving force and frictional resistance are balanced.
As the pressure increases, the difference in density between water and steam decreases. (See Fig. 3). Thus the hydrostatic head available will not be able to overcome the frictional resistance for a flow corresponding to the minimum requirement of cooling of water wall tubes. Therefore natural circulation is limited to boiler with drum operating pressure around 175 kg/cm2.
#2.Controlled Circulation In Boiler:
If the Operating pressure of boiler is between 180 kg/cm2 to 200 kg/cm2 then circulation in boiler is to be assisted with mechanical pumps, to overcome frictional losses. To regulate the flow through various tubes, orifice plates are used.
#3.Combined Circulation In Boiler:
This circulation in boiler is applicable to the boilers which are operating at critical pressure. In this system phase transformation is absent means water is directly converted into the steam at these pressure and temperature. Generally, operating pressure of this system is 260 Kg/cm2
This term is generally applicable in boiler water treatment.The concept is same as Strong Acid Cation(SAC) column works in DM Plant. To measure cation conductivity water sample is passing through cation column filled with cation resin in the hydrogen (H+) form. It is also known as acid conductivity.
Why It is Important:
Cation resin removes positively charged ions (cations) & replaces with H+ ions. In a high purity water cation present in ppb levels very small amount. For instance,If NaCl is present in this case when we passing sample through cation column Na+ ion is removed & Cl– ion react with H+ ion produces HCl (hydrochloric acid) that have a higher conductivity.
Please keep in mind that particular cation or anion is separately not present in water. Always they are present in combination with each other. e.g. NaCl,MgCl2 etc.
As name suggest it is a measurement of the conductivity after removing cations from water sample. it is indirect measurement of anions present in water, mainly chloride & sulphate present in steam samples.
In other words cation conductivity magnifies the anion present in water & indicates steam purity. Most steam turbine manufacturer recommends cation conductivity limit of <0.3 µs/cm.
High conductivity observed in water sample due to below points:
Exhausted cation column
Overfeed of amine & oxygen scavenger chemicals
Total organic carbon or organic decomposition products(acetate, formate) present in high level
High level of anion contamination present in water.
In practice, well controlled & maintained feed water chemistry can consistently maintain cation conductivity below 0.5 µs/cm when using organic amine and organic oxygen scavenger.
Degassed Cation Conductivity:
The degassed cation conductivity measurement uses the same ion exchange strategy as the cation conductivity measurement. The degassed measurement incorporates a reboiler to remove volatile compounds (like ammonia, amine, volatile organics, and CO2) from the steam to provide a more accurate indication of sulfate and chloride levels.
In the degassed measurement, the sample passes through a reboiler. Volatile organic compounds and CO2 are vented to atmosphere. Non-volatile inorganic compounds (like sulfate and chloride) remain behind. Thus, the degassed cation conductivity measurement provides the most accurate indication of inorganic anion levels (salts) in the steam.
Most steam turbine manufacturers recommend cation conductivity limits of 0.2-0.3 uS/cm. As stated earlier, the steam turbine manufacturer limits are not realistic unless ammonia and hydrazine are the only products used for feedwater treatment. In practice, well-controlled feedwater chemistry can consistently maintain cation conductivities in the 0.4-0.8 uS/cm range when using organic amine or organic passivators.